U.S. patent application number 14/735779 was filed with the patent office on 2015-12-17 for pallet and method of manufacture and use.
The applicant listed for this patent is Eovations, LLC. Invention is credited to Brett M. Birchmeier, Andrew T. Graham, Richard McBride, Kevin L. Nichols.
Application Number | 20150360809 14/735779 |
Document ID | / |
Family ID | 54834244 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150360809 |
Kind Code |
A1 |
McBride; Richard ; et
al. |
December 17, 2015 |
PALLET AND METHOD OF MANUFACTURE AND USE
Abstract
A pallet has a top deck coupled with a bottom deck through a
plurality of spacer members. The bottom deck is provided as a
sub-assembly comprising at least two lead bottom deck boards and at
least one intermediate bottom deck board, each bottom deck board
coupled with at least one other bottom deck board by a bottom deck
joint, and wherein each board of the bottom deck sub-assembly is
further coupled with at least one of the plurality of spacer
members to couple the bottom deck sub-assembly with the top deck.
At least one of the bottom deck lead boards are made from a fiber
filled thermoplastic or oriented plastic composite material.
Inventors: |
McBride; Richard; (New
Carlisle, MI) ; Nichols; Kevin L.; (Freeland, MI)
; Birchmeier; Brett M.; (Midland, MI) ; Graham;
Andrew T.; (Midland, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Eovations, LLC |
Grand Rapids |
MI |
US |
|
|
Family ID: |
54834244 |
Appl. No.: |
14/735779 |
Filed: |
June 10, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62010607 |
Jun 11, 2014 |
|
|
|
Current U.S.
Class: |
108/57.19 ;
108/57.17 |
Current CPC
Class: |
B65D 2519/00039
20130101; B65D 2519/00034 20130101; B65D 2519/00069 20130101; B65D
2519/00044 20130101; B65D 2519/00114 20130101; B65D 2519/00099
20130101; B65D 2519/00064 20130101; B65D 2519/00562 20130101; B65D
2519/00029 20130101; B65D 2519/00333 20130101; B65D 2519/00079
20130101; B65D 2519/00323 20130101; B65D 19/0095 20130101; B65D
2519/00298 20130101; B65D 2519/00373 20130101; B65D 2519/00273
20130101; B65D 2519/00293 20130101; B65D 2519/00109 20130101; B65D
2519/00442 20130101; B65D 2519/00074 20130101; B65D 2519/00104
20130101; B65D 2519/00129 20130101; B65D 2519/00572 20130101 |
International
Class: |
B65D 19/00 20060101
B65D019/00 |
Claims
1. A pallet having a top deck comprising a first top deck lead
board at a first end of the top deck and a second top deck lead
board at a second end of the top deck, opposite the first, at least
one intermediate board positioned between the first and second top
deck lead boards, and a plurality of spacer members coupled with
the top deck, the pallet comprising: a bottom deck sub-assembly
comprising: a first bottom deck lead board at a first end of the
bottom deck sub-assembly and a second bottom deck lead board at a
second end of the bottom deck sub-assembly, opposite the first; and
at least one intermediate board extending between the first and
second bottom deck lead boards and fastened to an adjacent first
and second bottom deck lead board to form a joint between the at
least one intermediate board and the adjacent first and second
bottom deck lead boards; wherein the joint between the at least one
intermediate board and the adjacent first and second bottom deck
lead board has a joint strength in tension of 450 Newtons or
greater; wherein the bottom deck sub-assembly is coupled with the
top deck through the plurality of spacer members to form the
pallet; and wherein the first bottom deck lead board or the second
bottom deck lead board comprises an oriented plastic composite or
fiber filled thermoplastic material.
2. The pallet of claim 1 wherein a constrained impact strength of
the first bottom deck lead board, the second bottom deck lead
board, or both is greater than 95 Joules.
3. The pallet of claim 2 wherein a constrained impact strength of
the first bottom deck lead board, the second bottom deck lead
board, or both is greater than 235 Joules.
4. The pallet of claim 1 wherein the pallet further comprises at
least two longitudinally extending stringers coupled with at least
a portion of the plurality of spacer members and wherein the top
deck is coupled with the spacer members through the stringers.
5. The pallet of claim 1 wherein at least the first and second top
deck lead boards of the top deck comprise an oriented plastic
composite or fiber filled thermoplastic material.
6. The pallet of claim 1 wherein at least a portion of the top
deck, plurality of spacer members, bottom deck sub-assembly, or
combinations thereof comprise a natural wood material and a portion
of the top deck, plurality of spacer members, bottom deck
sub-assembly, or combinations thereof comprise an oriented plastic
composite or fiber filled thermoplastic material.
7. The pallet of claim 1 wherein the joint between the at least one
intermediate board and the adjacent first and second bottom deck
lead boards has a joint strength in tension of at least 1200
Newtons.
8. The pallet of claim 7 wherein the joint between the at least one
intermediate board and the adjacent first and second bottom deck
lead boards has a joint strength in tension of at least 5000
Newtons.
9. The pallet of claim 1 wherein the at least one intermediate
board is fastened to the adjacent first and second bottom deck lead
boards by at least one mechanical fastener.
10. The pallet of claim 9 wherein the at least one mechanical
fastener comprises a gang nail, a nail, a screw, a truss plate, a
connector plate, a corrugated fastener, or combinations
thereof.
11. The pallet of claim 1 wherein the at least one intermediate
board is fastened to the adjacent first and second bottom deck lead
boards by at least one non-mechanical fastener.
12. The pallet of claim 11 wherein the at least one non-mechanical
fastener comprises solvent welding, solvent based adhesives,
thermal welding, or combinations thereof.
13. The pallet of claim 1 wherein the joint between the at least
one intermediate board and the adjacent first and second bottom
deck lead boards comprises a shiplap joint.
14. The pallet of claim 13 wherein the joint further comprises at
least one mechanical or non-mechanical fastener.
15. The pallet of claim 1 wherein the first bottom deck lead board,
the second bottom deck lead board, or both have a flexural modulus
of at least 2.75 GPa.
16. The pallet of claim 1 wherein the first bottom deck lead board
and the second bottom deck lead board comprises an oriented plastic
composite or fiber filled thermoplastic material.
17. The pallet of claim 16 wherein the at least one intermediate
board also comprises an oriented plastic composite or fiber filled
thermoplastic material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 62/010,607, filed Jun. 11, 2014, which is
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] This invention relates generally to pallets and more
particularly to four-way entry pallets with improved resistance to
damage.
BACKGROUND
[0003] Wood pallets are in widespread use for shipping products
between manufacturers, distributors, and retailers. The vast
majority of pallets in current use are constructed with a top deck
formed of solid wood boards coupled with a bottom deck formed of
solid wood boards. The top and bottom deck boards can be coupled
together in a variety of ways to form the assembled pallet. Two-way
entry pallets typically employ long stringers as spacer members for
coupling the top deck boards and bottom deck boards, while four-way
entry pallets (which are becoming more popular because of the
greater ease of use that four-way entry allows) typically employ
horizontal stringers to aid in holding and strengthening the top
deck boards together and wood blocks as spacer members to couple
the bottom deck boards to the top deck boards through the
stringers. Wood pallets are typically of simple design and can be
repaired when damaged in use. The Uniform Standard for Wood
Pallets", Copyright 2012, National Wooden Pallet and Container
Association (referred to herein as the "NWPCA bulletin"),
Alexandria, Va. 22314-2805, describes several types of conventional
pallets.
[0004] The pool pallet system was developed as a means of
controlling overall pallet usage cost and to limit destruction of
timberlands used to provide wood for pallet construction. In the
pool pallet system, a provider operates service centers to supply
pallets and to receive returned pallets. When a pallet is returned
to the service center, the pallet owner performs any needed repairs
before returning the pallet to service. This process can continue
as long as the pallet can, at a reasonable cost, be satisfactorily
repaired and returned to service. Commonly used pool pallets have
the advantage of being fabricated and repaired using common
woodworking and fastening techniques that help make the pallet pool
system cost-effective. This means the parts needing to be repaired
can be readily deconstructed from the pallet. One particularly
useful type of pallet used in the "pool" system is a 4-way entry
block pallet with a full perimeter bottom deck.
[0005] Four-way entry pallets include a top deck, a bottom deck and
spacer members. The top deck includes a pair of end members and a
plurality of intermediate load supporting members. The bottom deck
is provided with openings to accommodate the wheels of a hand
transport. The top and bottom decks are separated by means of
spacer members including longitudinally extending stringers on
which are mounted spacer blocks, often of plywood or a composite
material. The deck members, stringers and spacer blocks are
typically mechanically fastened with, for example, nails or screws.
Typically, nine blocks are installed at the corners of the pallet
and intermediately of the end and side members to provide access to
the pallet by the forks of a forklift or hand transport (pallet
jack). In certain instances, the forks of a forklift truck can make
contact with the lead boards of the decks and/or block members
during alignment. If the force is significant, the lead boards
and/or block members can be damaged. Many common types of pallet
damage, and the requirement for their repair can be found in
"Uniform Standard for Wood Pallets", Copyright 2012 by the National
Wooden Pallet and Container Association, Alexandria, Va.
22314-2805.
[0006] A number of suggestions have been made to reduce damage to
lead boards for upper decks, including end-caps or protective parts
for the access end of the pallet, multi-ply laminated boards (e.g.
U.S. Publication No. 2011/0005435 to Renck et al.), pultruded
boards (e.g. U.S. Publication No. 2006/0081158 to Ingham), and
energy absorbing structures for the lead boards. However, because
the added cost of these materials cannot typically be recovered,
and because of the relative ease of repairing wood pool pallets,
these improvements are not used widely in pool pallet systems of
major North American pool pallet providers.
[0007] Another mode of damage is possible when a pallet jack is
used to transport a pallet. A pallet jack, unlike a forklift, has
forks that also serve as a base and includes wheels. In order to
lift a pallet with a pallet jack, the fork is wheeled into the
inner space of the pallet and then lifted, typically hydraulically.
Hitting or running into the lower lead board can damage that board
in the same manner as the lead board on the top deck of the pallet.
Damage can also occur on the bottom deck of the pallet when a
pallet jack is inserted into the pallet incorrectly so that the
wheels of the pallet jack reside on a board of the bottom deck,
rather than in the space designed for them. In this situation, the
action of the forks of the pallet jack can force the top and bottom
sections apart and can cause splitting or cracking of the boards of
the bottom deck and can also lead to loss of an entire board if the
mechanical fasteners fastening the board to the block spacer are
pulled out.
[0008] When a pallet is entirely constructed of relatively cheap
materials, these defects can be cost effectively managed by simply
replacing the damaged board with another board of the same
relatively cheap material. However, when pallets are constructed of
combinations of material, for example, wood planks or boards and a
relatively expensive energy attenuating lead board, such as a
multi-ply laminated or a pultruded lead board, replacement of the
lead board after damage and/or loss can become excessively costly.
Thus these energy attenuating lead board materials are often
undesirable even though they can reduce damage at the lead board
position on a pallet deck and allow such a hybrid pallet a longer
useful life.
SUMMARY
[0009] According to an embodiment of the invention, a pallet having
a top deck comprising a first top deck lead board at a first end of
the top deck and a second top deck lead board at a second end of
the top deck, opposite the first, at least one intermediate board
positioned between the first and second top deck lead boards, and a
plurality of spacer members coupled with the top deck, the pallet
comprises a bottom deck sub-assembly comprising: a first bottom
deck lead board at a first end of the bottom deck sub-assembly and
a second bottom deck lead board at a second end of the bottom deck
sub-assembly, opposite the first, and at least one intermediate
board extending between the first and second bottom deck lead
boards and fastened to an adjacent first and second bottom deck
lead board to form a joint between the at least one intermediate
board and the adjacent first and second bottom deck lead boards.
The joint between the at least one intermediate board and the
adjacent first and second bottom deck lead board has a joint
strength in tension of 450 Newtons or greater and the bottom deck
sub-assembly is coupled with the top deck through the plurality of
spacer members to form the pallet. The first bottom deck lead board
or the second bottom deck lead board can comprise an oriented
plastic composite or fiber filled thermoplastic material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] These and other features and advantages of the present
invention will become better understood to those of ordinary skill
in the art when considered in connection with the following
description and drawings:
[0011] FIG. 1 is a perspective view from a top deck side of a
conventional four-way entry block pallet.
[0012] FIG. 2 is a perspective view from a bottom deck side of a
conventional four-way entry block pallet.
[0013] FIG. 3 is a vertical sectional view longitudinally taken
along the line A-A of the pallet of FIG. 1 showing the position of
a forklift of the low lift or pallet jack type inserted
longitudinally into the pallet of FIG. 1 with the pallet jack
wheels correctly aligned in the open space between bottom deck lead
boards.
[0014] FIG. 4 is a vertical sectional view longitudinally taken
along the line A-A of the pallet of FIG. 1 showing the position of
a forklift of the low lift or pallet jack type inserted
longitudinally into the pallet of FIG. 1 so that the pallet jack
wheels are misplaced onto the lead board of the bottom deck of the
pallet.
[0015] FIG. 5 illustrates a bottom deck sub-assembly according to
an embodiment of the invention.
[0016] FIG. 6 is a partially exploded hybrid pallet having a bottom
deck sub-assembly according to an embodiment of the invention.
[0017] FIG. 7A illustrates a bottom deck sub-assembly according to
an embodiment of the invention.
[0018] FIG. 7B is an exploded view of the bottom deck sub-assembly
of FIG. 7A according to an embodiment of the invention.
[0019] FIG. 8 is a partially exploded hybrid pallet having a bottom
deck sub-assembly according to an embodiment of the invention.
[0020] FIG. 9 is a photograph illustrating pallet failure mode 1
for a conventional bottom deck structure having a test board made
from an OPC material in which the test board is coupled with a
spacer block by a plurality of nails. In FIG. 9, the heads of
several of the nails coupling the test board to the spacer block
have been pulled through the test board.
[0021] FIG. 10 is a photograph illustrating pallet failure modes 2
and 6 for a conventional bottom deck structure having a test board
made from an OPC material in which the test board is coupled with a
spacer block by a plurality of nails. In FIG. 10, several of the
nails coupling the test board to the spacer block have been pulled
out of the spacer blocks such that the test board can be removed by
hand.
[0022] FIG. 11 is a photograph illustrating pallet failure mode 3
for a conventional bottom deck structure having a test board made
from wood in which the test board is coupled with a spacer block by
a plurality of nails. In FIG. 11, the test board has split along
its length, with the grain.
[0023] FIG. 12 is a photograph illustrating pallet failure mode 4
for a conventional bottom deck structure having a test board made
from a wood plastic composite material in which the test board is
coupled with a spacer block by a plurality of nails. In FIG. 12,
the test board has split along its width.
[0024] FIG. 13 is a photograph illustrating pallet failure mode 5
for a conventional bottom deck structure having a test board made
from OPC material in which the test board is coupled with a spacer
block by a plurality of nails. In FIG. 13, a top deck of the pallet
has separated from the spacer blocks.
[0025] FIG. 14 is a photograph illustrating pallet failure mode 2
for a bottom deck sub-assembly using a welded shiplap joint and
having a test board made from an OPC material in which the test
board is coupled with a spacer block by a plurality of nails. In
FIG. 14, several of the nails coupling the test board to the spacer
block have been pulled out of the spacer blocks, but the shiplap
joint between the bottom deck boards is of sufficient strength to
inhibit removal of the test board from the pallet by hand or with
the use of hand tools.
[0026] FIG. 15 is a photograph illustrating pallet failure mode 2
for a bottom deck sub-assembly using a mechanical joint and having
a test board made from an OPC material in which the test board is
coupled with a spacer block by a plurality of nails. In FIG. 15,
several of the nails coupling the test board to the spacer block
have been pulled out of the spacer blocks, but the mechanical joint
between the bottom deck boards is of sufficient strength to inhibit
removal of the test board from the pallet by hand or with the use
of hand tools.
DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION
Terms
[0027] "Solid state" refers to a polymer (or polymer composition)
that is below the softening temperature of the polymer (or polymer
composition). Hence, "solid state drawing" refers to drawing a
polymer or polymer composition that is below the softening
temperature of the polymer (or polymer composition). "Solid state
die drawing" refers to drawing a polymer or polymer composition
that is below its softening temperature through a shaping die.
[0028] "Polymer composition" comprises at least one polymer
component and can contain non-polymeric components. A "filled"
polymer composition includes discontinuous additives, such as
inorganic or organic fillers.
[0029] An "orientable polymer" is a polymer that can undergo
induced molecular orientation by solid state deformation (for
example, solid state drawing). An orientable polymer can be
amorphous or semi-crystalline (semi-crystalline polymers have a
melt temperature (Tm) and include those polymers known as
"crystalline"). Desirable orientable polymers include
semi-crystalline polymers, and in particular, linear polymers
(polymers in which chain branching occurs in less than 1 of 1,000
polymer units). Semi-crystalline polymers can be particularly
desirable because they can result in greater increase in strength
and flexural modulus than amorphous polymer compositions.
Semi-crystalline polymer compositions can result in 4-10 times
greater increase in strength and flexural modulus upon orientation
over amorphous polymer compositions.
[0030] An "orientable polymer phase" is a polymer phase that can
undergo induced molecular orientation by solid state deformation
(for example, solid state drawing). Typically, 75 wt % or more,
even 90 wt % or more or 95 wt % or more of the polymers in the
orientable polymer phase are orientable polymers based on total
orientable polymer phase weight. All of the polymers in an
orientable polymer phase can be orientable polymers. An orientable
polymer phase may comprise one or more than one type of polymer and
one or more than one type of orientable polymer.
[0031] "Oriented polymer composition article", "OPC" and "oriented
polymer composition" are interchangeable and refer to an article
made by orienting the polymers of a polymer composition. An
oriented polymer composition comprises polymer molecules that have
a higher degree of molecular orientation than that of a polymer
composition extruded from a mixer.
[0032] "Weight-percent" and "wt %" are interchangeable and are
relative to total polymer weight unless otherwise stated.
[0033] "Softening temperature" (Ts) for a polymer or polymer
composition having as polymer components only one or more than one
semi-crystalline polymer is the melting temperature for the
continuous phase polymer in the polymer composition.
[0034] "Melting temperature" (Tm) for a semi-crystalline polymer is
the temperature half-way through a crystalline-to-melt phase change
as determined by differential scanning calorimetry (DSC) upon
heating a crystallized polymer at a specific heating rate. Tm for a
semi-crystalline polymer can be determined according to the DSC
procedure in ASTM method E794-06. Tm for a combination of polymers,
and for a filled polymer composition, can also be determined by DSC
using the same test conditions in ASTM method E794-06. If the
combination of polymers or filled polymer composition only contains
miscible polymers and only one crystalline-to-melt phase change is
evident in the a DSC curve, then Tm for the polymer combination or
filled polymer composition is the temperature half-way through the
phase change. If multiple crystalline-to-melt phase changes are
evident in a DSC curve due to the presence of immiscible polymers,
then Tm for the polymer combination or filled polymer composition
is the Tm of the continuous phase polymer. If more than one polymer
is continuous and they are not miscible, then the Tm for the
polymer combination or filled polymer composition is the highest Tm
of the continuous phase polymers.
[0035] "Softening temperature" (Ts) for a polymer or polymer
composition having as polymer components only one or more than one
amorphous polymer is the glass transition temperature for the
continuous phase of the polymer composition.
[0036] If the semi-crystalline and amorphous polymer phases are
co-continuous, then the softening temperature of the combination is
the lower softening temperature of the two phases. If the polymer
composition contains a combination of semi-crystalline and
amorphous polymers, the softening temperature of the polymer
composition is the softening temperature of the continuous phase
polymer of the polymer composition.
[0037] "Glass transition temperature" (Tg) for a polymer or polymer
composition is the temperature half-way through a glass transition
phase change as determined by DSC according to the procedure in
ASTM method D3418-03. Tg for a combination of polymers and for a
filled polymer composition can also be determined by DSC under the
same test conditions in D3418-03. If the combination of polymer or
filled polymer composition only contains miscible polymers and only
one glass transition phase change is evident in the DSC curve, then
Tg of the polymer combination or filled polymer composition is the
temperature half-way through the phase change. If multiple glass
transition phase changes are evident in a DSC curve due to the
presence of immiscible amorphous polymers, then Tg for the polymer
combination or filled polymer composition is the Tg of the
continuous phase polymer. If more than one amorphous polymer is
continuous and they are not miscible, then the Tg for the polymer
composition or filled polymer composition is the highest Tg of the
continuous phase polymers.
[0038] If the polymer composition contains a combination of
semi-crystalline and amorphous polymers, the softening temperature
of the polymer composition is the softening temperature of the
continuous phase polymer or polymer composition.
[0039] "Drawing temperature" refers to the temperature of the
polymer composition as it begins to undergo drawing in a solid
state drawing die.
[0040] "Linear Draw Ratio" is a measure of how much a polymer
composition elongates in a drawing direction (direction the
composition is drawn) during a drawing process. Linear draw ratio
can be determined while processing by marking two points on a
polymer composition spaced apart by a pre-orientated composition
spacing and measuring how far apart those two points are after
drawing to get an oriented composition spacing. The ratio of final
spacing to initial spacing identifies the linear draw ratio.
[0041] "Nominal draw ratio" is the cross sectional surface area of
a polymer composition as it enters a drawing die divided by the
polymer cross sectional area as it exits the drawing die.
[0042] An OPC is "similar" to another OPC if its composition is
substantially the same as the other OPC in all respects except
those noted in the context where the similar OPC is referenced.
Compositions are substantially the same if they are the same within
reasonable ranges of process reproducibility.
[0043] "ASTM" refers to ASTM International, formerly American
Society for Testing and Materials; the year of the method is either
designated by a hyphenated suffix in the method number or, in the
absence of such a designation, is the most current year prior to
the filing date of this application.
[0044] "Multiple" means at least two.
[0045] "And/or" means "and, or as an alternative."
[0046] Ranges include endpoints unless otherwise stated.
[0047] Temperatures are given in degrees Celsius, abbreviated as
"C" unless otherwise stated.
[0048] Flexural modulus (modulus of elasticity (MOE)) and flexural
strength (modulus of rupture (MOR)) are measured according to ASTM
method ASTM D-6109-05, "Standard Test Methods for Flexural
Properties of Unreinforced and Reinforced Plastic Lumber and
Related Products." Per ASTM D-6109-05, a force versus displacement
under a four point bending load is measured. The force versus
displacement curve is converted to a stress versus strain curve and
the MOE and MOR are subsequently determined from the curve
according to the methods set forth in ASTM D-6109-05.
[0049] Density is measured according to ASTM method ASTM
D-792-00.
[0050] "Block", "spacer", and "spacer block" are used herein
interchangeably. A block is a rectangular, square, multisided, or
cylindrical deck spacer, often identified by its location within
the pallet as corner block, end block, edge block, inner block, or
center or middle block.
[0051] A "deck board" is a pallet element or component of a pallet
top or bottom, perpendicular to stringers or stringer boards.
[0052] "Stringer and "stringer board" are used interchangeably
herein. A stringer is a continuous, longitudinal, solid, built up,
or notched beam component of a pallet, supporting and spacing deck
components, often identified by its location as edge (side) or
interior (center) stringer.
[0053] "Spacer member" refers to the pallet member which directly
or indirectly couples the top deck boards to the bottom deck
boards. In some cases, the spacer member may be in the form of a
stringer board which couples the top deck boards together and
through which the bottom deck boards are coupled with the top deck
to form the assembled pallet. The stringer boards may also
reinforce the pallet structure. A stringer pallet is an example of
such a configuration. Alternatively, the spacer member may be in
the form of blocks which are used to couple the top deck and the
bottom deck together. An example of this type of configuration is a
block pallet. It is also within the scope of the invention for a
combination of stringer boards and blocks to be used to form the
pallet. An example of this type of configuration is also sometimes
referred to as a block pallet in which one or more stringer boards
are used to couple the top deck boards together and a plurality of
blocks are coupled with the stringer boards and the bottom deck
boards to form the assembled pallet. The spacer members can also
provide space between a top deck and a bottom deck of a pallet to
allow entry of the forks of a forklift to lift and move the
pallet.
[0054] "Gang nail", "gang nail plate", "gang nail connector plate",
"mending plate" and "truss plate" are used interchangeably and
refer to a sheet of galvanized steel, with pointed prongs that are
cut and bent perpendicular to a plate face of the gang nail,
allowing it to be hammered or pressed into a number of surfaces
simultaneously. The prongs are often of triangular shape and the
gang nail typically has several prongs or teeth per square inch of
plate.
[0055] A "corrugated fastener" is a thin strip of sheet metal that
has a pattern of alternating grooves and is typically made from 18
to 22 gauge sheets of stainless or cold-rolled steel. Typically,
increased joint strength is observed as the number of corrugated
fasteners used to fasten a joint is increased. Also, typically, if
two or more corrugated fasteners are used in a given joint,
improved joint strength is observed when they are placed so that
they are not parallel to one another.
[0056] "Readily deconstructed" in the context of a pallet assembly
means that a worker using his hands and/or unpowered hand tools,
e.g., a claw hammer, can remove a pallet board that has been
damaged in less than 5 minutes, and still continue to use the
pallet assembly without the damaged, removed portion. Damage can
include damage to the board itself or damage to the connection
between the board and one or more parts of the pallet assembly,
such as damage to one or more fasteners, pull through of a
fastener, and/or pull out of a fastener. Removal of the damaged
portion of the pallet assembly may include removal of adjacent
portions that were not damaged.
[0057] A wood pallet can be any of those described as wood pallets
in Uniform Standard for Wood Pallets", Copyright 2012, National
Wooden Pallet and Container Association (referred to herein as the
"NWPCA bulletin"), Alexandria, Va. 22314-2805, but is not limited
to these pallet designs, especially when pallets are designed for
geographies other than North America. A top deck of a pallet can
consist of one or more than one deck board transverse to the length
direction of the pallet. A bottom deck can be a single board with
wheel openings or, preferably, can have 3 or more often up to 5
boards, while still leaving space for a pallet jack to enter and
lift a pallet. Between the top deck and the bottom deck are spacers
that may be stringers, as is common in two-way entry pallets, or
spacer blocks as is typical in four way entry pallets, or a
combination of stringers and spacer blocks. A non-limiting list of
suitable natural wood species can be found in Annex B, Wood Species
Classes, "Uniform Standard for Wood Pallets", Copyright 2012,
NWPCA.
[0058] Four-way entry pallets include a top deck, a bottom deck and
spacer members. The top deck of a pallet, in some instances may be
constructed of a single deck board, but more typically consists of
two or three or more deck boards and in some cases can consist of
as many as nine or more deck boards. The top deck typically
includes a pair of end boards (also referred to as lead boards) and
a plurality of intermediate load supporting deck boards. The bottom
deck is provided with a relatively large surface area, but with
openings to accommodate the wheels of a transport apparatus (e.g.
pallet jack).
[0059] In a conventional block pallet, the top and bottom decks are
separated by means of spacer members which can include
longitudinally extending stringers and/or mounted spacer blocks,
often of wood, laminated wood layers (plywood) or a wood composite
material. The spacer blocks can be square in horizontal
cross-section, but are more typically rectangular so that the
bottom perimeter deck board can be attached to the blocks.
Typically, nine blocks are installed at the corners of the pallet
and intermediately of the end and side members to provide access to
all four sides of the pallet by the forks of a forklift or hand
transport (pallet jack). The spacer bocks need not be all of the
same size, although the blocks are usually the full width of the
members that overlay them.
[0060] FIGS. 1-2 illustrate the construction of a conventional
four-way entry pallet 10. The block pallet 10 includes a top deck
12 which is adapted to support the articles which are placed on the
pallet 10 and a bottom deck 14. The top deck 12 includes a
plurality of deck boards 20a-g supported by a plurality of stringer
boards 18, which are supported by a plurality of spacer members in
the form of end blocks 16 and intermediate blocks 17. The block
pallet 10 has a length 21 and a width 22 which may be the same or
different. Preferably the stringer boards 18 have a width 23 that
is the same as a width 24 of the blocks 16, with the stringer
boards 18 extending across the full width 22 of the pallet 10. The
end blocks 16 and the intermediate blocks 17 can have the same or
different dimensions. In the pallet 10 of FIG. 1, the end blocks 16
and intermediate blocks 17 are illustrated as having the same width
24 with the end blocks 16 having a length 25 that is greater than
the width 24. The length 26 of the intermediate blocks 17 can be
the same as the width 24 or any other suitable length smaller or
greater than the width 24.
[0061] The deck boards 20a-g are provided at right angles to the
stringer boards 18 and extend for the full length 21 of the pallet
10. The two deck boards 20a and 20g located at the outside opposite
edges of the pallet 10 are commonly referred to as lead boards or
end boards. The top deck 12 can include any number of deck boards
20a-g that are all the same width or of different widths. As
illustrated in FIG. 1, a center deck board 20d can have the same or
a different width than the lead boards 20a and 20g. The center deck
board 20d may correspond to the deck board provided in the middle
of an equal number of deck boards on either side and/or may
correspond to the deck board which is aligned with the intermediate
blocks 17. The intermediate deck boards 20b-c and 20e-f can be of
the same or different widths and the number and width of the deck
boards 20a-g can be selected so as to provide a desired gap or
space 27, or lack thereof, between adjacent deck boards 20a-g. As
illustrated in FIG. 1, in some cases the deck boards 20b, 20f
adjacent to the lead boards 20a, 20g typically abut the lead boards
20a, 20g such that little to no space is provided between deck
boards 20b, 20f and lead boards 20a, 20g, respectively.
[0062] The pallet 10 can be constructed manually or can be
constructed using machines built for that purpose. In one
illustrative method of constructing a pallet, the top deck 12 of
FIG. 1 can be assembled by laying out the nine blocks 16 and 17 so
that the length dimension 25 is aligned lengthwise with the
stringer boards 18. Then the stringer boards 18 are placed on the
blocks 16, 17 at the correct positions followed by deck boards
20a-g in the arrangement shown in FIG. 1. The lead boards 20a, 20g
can be attached to the corner end blocks 16 with fasteners 32
through the stringer boards 18. Next, the center deck board 20d is
attached to the three intermediate blocks 17 with fasteners 32
through the stringer boards 18 to provide a top deck 12 and spacer
pallet assembly 33. The top deck 12 includes the lead boards 20a,
20g, the center deck board 20d, and the intermediate boards 20b-c,
e-f, while the spacer pallet assembly 33 includes the end blocks
16, the intermediate blocks 17, and the stringer boards 18. The
fasteners 32 used to fasten the top deck boards 20a-g to the blocks
16, 17 are typically longer than those used to fasten the top deck
boards 20a-g at positions at which there are no spacer blocks 16,
17. The most common prior art block pallets constructed for use as
returnable pallets comprise wooden boards and all wood or
wood-composite blocks and use nails or screws as fasteners. Typical
fasteners are nails of the types described in the NWPCA bulletin
and include nails and wire staples. However, screws can be used to
give added strength. Nails are typically driven using a nail gun of
any of the types known in the art. A portion or all of the assembly
process can be automated to facilitate uniform placement of the
fasteners and to reduce labor costs. The type and number of
fasteners used can affect the strength of the pallet assembly.
However, using more fasteners can also make the pallet more costly
for little additional benefit in use.
[0063] FIG. 2 illustrates the bottom deck 14 of the conventional
wooden block pallet 10 of FIG. 1. The bottom deck 14 comprises a
pair of bottom deck edge boards 34 which extend along the width 22
of the pallet 10, and are typically of the same width as the width
24 of the end blocks 16, and a pair of bottom deck lead boards 29.
The bottom deck lead boards 29 typically have a width 30 that is
less than the length dimension 25 of the end blocks 16 to provide
enough surface on the end block 16 to also fasten the bottom deck
edge boards 34 to the end block 16 adjacent the bottom deck lead
boards 29. The bottom deck 14 also includes a bottom center deck
board 31 which is typically of the same width as the intermediate
block 17 and is parallel to the bottom deck edge boards 34 and
spans a gap between the bottom deck lead boards 29. In some pallet
constructions, an additional board (not shown in the figure) can be
fastened to the intermediate blocks 17 between the bottom deck edge
boards 34 and midway between the bottom deck lead boards 29.
[0064] In one illustrative method of fastening the bottom deck 14
to the top deck 12 and spacer pallet assembly 33, the top deck 12
and spacer pallet assembly 33 are positioned so that the top deck
12 is facing toward a floor or work table surface with the spacer
pallet assembly 33 facing upward. The bottom deck boards 34, 29, 31
are laid out on the top deck 12 and spacer pallet assembly 33 with
the bottom deck lead boards 29 positioned above the top deck lead
boards 20a, 20g and the edge boards 34 and bottom center deck board
31 positioned above the stringer boards 18. The bottom deck boards
34, 29, 31 can be fastened using fasteners 42 to the top deck 12
and spacer assembly 33. In this construction, a thickness of the
bottom deck 14 is typically as thick as a single bottom deck board
34, 29, 31.
[0065] A source of damage to pallets can arise when, in certain
instances, the forks of a forklift truck or pallet jack make
contact with the lead boards 20a, 20g or 29 of the top deck 12 or
bottom deck 14, respectively, and/or block members 16 or 17 during
insertion of the forklift into the pallet 10 for lifting. If the
force is significant, the lead boards 20a, 20g, 29 and/or block
members 16, 17 can be damaged. A number of suggestions have been
made to reduce damage to lead boards for upper decks, including
end-caps or protective parts for the access end of the pallet,
multi-ply laminated boards (e.g. U.S. Publication No. 2011/0005435
to Renck et al.), pultruded boards (e.g. U.S. Publication No.
2006/0081158 to Ingham), and energy absorbing structures for the
lead boards (U.S. Pat. No. 8,261,673 to Ingham).
[0066] Because a pallet jack operates differently than does a
forklift, a pallet jack, unlike a forklift, has forks that serve as
a base and also includes wheels. Thus, an additional opportunity
for pallet damage is possible when a pallet jack is used to
transport a pallet. In order to lift a pallet with a pallet jack
the fork is wheeled into the inner space of the pallet and then
lifted, typically, hydraulically. FIG. 3 illustrates the correct
positioning of a pallet jack 50 with wheels 51 aligned in the
spaces of the bottom deck 14 between the edge boards 34 and the
bottom center deck board 31. Hitting or running into the bottom
deck lead boards 29 can damage the bottom deck lead boards 29 in a
manner similar to that described above for the top deck lead boards
20a, 20g of the pallet 10.
[0067] Referring now to FIG. 4, damage can also occur on the bottom
deck 14 of the pallet 10 when the pallet jack 50 is inserted into
the pallet 10 incorrectly. If the wheels 51 of the pallet jack 50
are sitting on one of the bottom deck lead boards 29 when the
pallet jack 50 is activated to raise the forks 52 against the top
deck lead board 20a, the action of the hydraulic pallet jack 50 can
force the top deck lead board 20a away from the bottom deck lead
board 29, potentially pulling the top deck lead board 20a away from
the blocks 16, 17. Alternatively, this action of the pallet jack 50
can result in splitting or cracking of the bottom deck lead boards
29 and/or the top deck lead boards 20a, 20g. Both of these damage
mechanisms can lead to loss of the entire bottom deck lead board 29
and/or the top deck lead boards 20a, 20g.
[0068] When the pallet 10 is entirely constructed of relatively
cheap materials, for example, boards from wood species such as pine
or oak, damage can be cost effectively managed by deconstructing
the damaged portion of the pallet 10 and replacing the damaged or
lost board with another board of the same relatively cheap
material. However, when pallets 10 are constructed of more
expensive materials, deconstructing the damaged portion of the
pallet 10 and replacing the damaged or lost board with another
board of the same, more expensive material, may not be cost
effective. For example, in order to mitigate lead board damage,
more expensive materials, such as a laminated board or a pultruded
composite board, can be used to form the lead board. However, when
this more expensive lead board does get damaged and needs
replacement or becomes lost, the replacement costs compared to more
economic wood boards of oak or pine can become economically
unfeasible and thus can make these more expensive materials
undesirable for use, even though the more expensive materials can
make the lead board more resistant to damage.
[0069] The embodiments of the invention described herein provide a
bottom deck sub-assembly in which each bottom deck board is coupled
to an adjacent bottom deck board and wherein at least the bottom
deck lead boards are made from a fiber filled thermoplastic or
oriented plastic composite material. The fiber filled thermoplastic
or oriented plastic composite provides an increase in impact
strength of the deck boards as determined by the constrained impact
test described herein compared to conventional deck board materials
made of wood or wood plastic composite materials. The deck boards
of the sub-assembly can also be coupled with one another to provide
a predetermined joint strength to inhibit separation of a bottom
deck board from the sub-assembly. The joint strength can be
selected such that a joint strength of the bottom deck board joints
is greater than a joint strength between the bottom deck
sub-assembly and the spacer members. Alternatively, or
additionally, the bottom deck board joint strength can be selected
to prevent or minimize the likelihood that a damaged bottom deck
board is readily deconstructed and separated from the adjacent
bottom deck boards by hand and/or using unpowered hand tools, or
even using some predetermined powered tools. The bottom deck
sub-assembly described herein can minimize problems associated with
bottom deck lead board damage, subsequent loss of that board, and
the need to replace the expensive lead board when damaged, as
described above for the conventional pallet 10. The bottom deck
sub-assembly can also, with some types of pallet manufacturing
equipment, simplify the overall pallet assembly process.
[0070] As used herein, the bottom deck sub-assembly refers to a
pair of bottom deck lead boards coupled to one another through at
least one additional board. In an exemplary embodiment, the bottom
deck sub-assembly includes a pair of bottom deck lead boards
coupled with a pair of bottom deck edge boards and/or a center
board. It is also within the scope of the invention for the
sub-assembly to optionally include additional boards coupled with
the lead boards and/or the edge or center boards. It is also within
the scope of the invention for the bottom deck sub-assembly to be
provided as a unitary sub-assembly in which each bottom deck board
is coupled with the adjacent bottom deck board independent of the
coupling of the bottom deck with the top deck. When provided as a
unitary sub-assembly, the bottom deck sub-assembly can be
pre-assembled and then coupled to a top deck of a pallet as a
single unit. While the bottom deck sub-assembly is described in the
context of the conventional pallet 10 having a top deck 12 and
spacer blocks 16, 17, the bottom deck sub-assembly described herein
can be used with any type of pallet having a top deck and spacer
members in the form of blocks and/or stringers, or any other type
of spacer member, and may be configured for use with any type of
pallet, non-limiting examples of which include two-way, four-way,
or euro pallets. While the four-way entry pallet 10 is illustrated
as a block pallet in which the spacer members include a combination
of stringers and spacer blocks, it is also within the scope of the
invention for the four-way entry pallet 10 to be in the form of a
stringer pallet in which the spacer members are in the form of
stringers and which may also include openings for side entry of a
pallet transportation device. It is also within the scope of the
invention for the pallet 10 to be a two-way block or two-way
stringer pallet.
[0071] Referring now to FIG. 5, a bottom deck sub-assembly 100
includes a pair of bottom deck lead boards 102 coupled with a pair
of bottom deck edge boards 104 and a bottom deck intermediate board
106, in this case a single center board, by fasteners 108. The
bottom deck sub-assembly 100 may optionally include additional
intermediate deck boards (not shown) positioned between the bottom
deck edge boards 104 and spanning the distance between the bottom
deck lead boards 102, depending on the intended use of the bottom
deck sub-assembly 100.
[0072] The fastener 108 may be any type of mechanical fastener,
non-limiting examples of which include corrugated fasteners, truss
plates, connector plates, particularly truss plates of the gang
nail type, or any other type of fastening or fasteners know in the
art to give strength to a joint between two adjacent boards. The
fasteners 108 may be applied in any orientation with respect to the
direction of orientation, grain or fiber direction of the deck
boards 102, 104, and 106. A desired joint strength may be
engineered by using gang nails and by choosing the number of prongs
per unit area, the total area of the gang nail, the type of metal
used, and the size of the prong. These fasteners 108 provide great
joint strength and are not readily removed so that the bottom deck
sub-assembly 100 cannot be readily deconstructed when gang
nail-type fasteners are used. As illustrated in FIG. 5, the
fasteners 108 can be in the form of truss plates, preferably made
from galvanized steel, which bridge the joint between the bottom
deck edge boards 104 and the bottom deck center board 106 at each
end with the bottom deck lead boards 102. The fastener 108 can be
applied to the joint between deck boards on a bottom face of the
deck board, i.e. the face adjacent the surface upon which the
assembled pallet 100 rests, and/or on an upper face of the deck
board, opposite the bottom face, which is adjacent an interior of
the assembled pallet.
[0073] The dimensions of the bottom deck sub-assembly 100 can be
selected based on the dimensions of the top deck to which the
bottom deck sub-assembly 100 is to be coupled. For example, as
illustrated in FIG. 6, the dimensions of the bottom deck
sub-assembly 100 can be configured to correspond to the top deck 12
and spacer blocks 16, 17 of the conventional pallet 10 of FIG. 1.
The bottom deck sub-assembly 100 can be secured to the top deck 12
through the spacer blocks 16, 17 using any suitable fastening
system, such as screws or nails, to form a hybrid pallet 110.
[0074] The bottom deck sub-assembly 100 can be used with any type
of pallet, such as a two-way or four-way block pallet (see for
example block pallet 10 of FIG. 1) or stringer pallet. The bottom
deck sub-assembly 100 can be coupled with top deck boards through a
spacer member, such as one or more blocks and/or stringers to form
the assembled hybrid pallet. The spacer members can be made of any
material known in the pallet art, including wood composite
materials, plywood and wood of various species. Preferred spacer
members comprise wood, particularly pine or oak, for pallets in
which the bottom deck sub-assembly 100 is mechanically fastened to
the spacer members using nails or screws. The material and
dimensions for the spacer members and the size, type, and number of
fasteners can be selected to provide the desired joint strength
between the bottom deck sub-assembly 100 and the spacer
members.
[0075] The top deck boards of the hybrid pallet 110 which may be
used with the bottom deck sub-assembly 100 may be any known in the
art, such as the top deck boards 20a-g of the block pallet 10 of
FIG. 1, and can include one or more boards spanning the area of the
top deck. Where multiple boards span the top deck, it is preferred
that the lead board be of a damage resistant construction. A
particularly preferred lead board is a fiber filled thermoplastic
or OPC lead board, similar to that used for the bottom deck
sub-assembly 100, as is described in more detail below. The
remaining boards of the top deck may be any known in the art,
especially any species of wood or wood plastic composite suitable
for pallets.
[0076] FIGS. 7A-7B illustrate a second embodiment of the invention
comprising a bottom deck sub-assembly 200 that is similar to the
bottom deck sub-assembly 100, except for the manner in which the
sub-assembly 200 is assembled. Therefore, elements in the bottom
deck sub-assembly 200 similar to those of the bottom deck
sub-assembly 100 are numbered with the prefix 200. As illustrated
in FIG. 7A, the bottom deck edge boards 204 and the bottom deck
center board 206 are coupled at each end with the bottom deck lead
boards 102 through a shiplap joint 220, also sometimes referred to
as a rabbet joint.
[0077] Referring now to FIG. 7B, the shiplap joints 220 are formed
by machining a surface of the bottom deck lead boards 202 to form
lead board joint portions 222 in which a thickness of the bottom
deck lead boards 202 is reduced. Corresponding joint portions 224
can be machined into the bottom deck edge boards 204 and the bottom
deck center board 206 and the lead board joint portions 222 can be
overlapped with the joint portions 224 to form the shiplap joints
220. In a preferred embodiment the joint portions 222 and 224 are
machined into the respective boards 202, 204, and 206, to decrease
a thickness of the boards 202, 204, and 206 by one-half. In this
manner a total thickness of the shiplap joints 220 is the same as a
thickness of the adjacent deck boards 202, 204, and 206 forming the
shiplap joint 220. Alternatively, rather than reducing a thickness
of each of the deck boards 202, 204, and 206 forming the shiplap
joint 220 equally, the deck boards 202, 204, and 206 forming each
shiplap joint 220 can be reduced in thickness unequally. For
example, the thickness of the bottom deck lead board 202 can be
reduced by one-third to form the lead board joint portion 222 while
the thickness of the bottom deck edge boards 204 and the bottom
deck center board 206 can be reduced by two-thirds to form the
corresponding joint portions 224. The thus formed shiplap joint 220
will still have a total thickness equal to the thickness of the
adjacent deck boards 202, 204, and 206 forming the shiplap joint
220.
[0078] The bottom deck lead board 202 can be coupled with the
bottom deck edge boards 204 and the bottom deck center board 206 at
the shiplap joint 220 by causing the joint portions 222 and 224 to
adhere to one another using any suitable non-mechanical fastener.
Non-limiting examples of non-mechanical fastener joining include
solvent welding, solvent based adhesives and thermal welding. A
particularly preferred adhesive joint is an overlapping joint of
the shiplap type where the overlapping faces are thermally welded.
For example, the joint portion 222 and/or the joint portion 224 can
be heated to melt the surface of the joint portion 222 and/or the
joint portion 224 and the joint portions 222 and 224 can be
overlapped and pressure applied to form the joint 220. In another
example, the joint portion 222 and/or the joint portion 224 can be
provided with an adhesive, such as a solvent-based adhesive, to
adhere the joint portion 222 to the joint portion 224. In yet
another example, the joint portions 222 and 224 can be adhered
using an ultrasonic weld.
[0079] It is also within the scope of the invention for the bottom
deck lead board 202 to be coupled with the bottom deck edge boards
204 and the bottom deck center board 206 by a butt weld, which can
include solvent welding, solvent based adhesives, or thermal
welding, for example.
[0080] Similar to the bottom deck sub-assembly 100, the dimensions
of the bottom deck sub-assembly 200 can be selected based on the
dimensions of the top deck to which the bottom deck sub-assembly
200 is to be coupled with. For example, as illustrated in FIG. 8,
the dimensions of the bottom deck sub-assembly 200 can be
configured to correspond to the top deck 12 and spacer blocks 16,
17 of the conventional pallet 10 of FIG. 1. The bottom deck
sub-assembly 200 can be secured to the top deck 12 through the
spacer blocks 16, 17 using any suitable fastening system, such as
screws or nails, to form a hybrid pallet 210. Alternatively, as
described above with respect to the bottom deck sub-assembly 100,
the bottom deck sub-assembly 200 can be used with any suitable top
deck and spacer members, such as blocks and/or stringers, to form a
hybrid pallet 210.
[0081] It is also within the scope of the invention for the bottom
deck sub-assembly to be assembled using a combination of the
fastener 108 of the bottom deck sub-assembly 100 of FIG. 5 and the
shiplap type joint 220 of the bottom deck sub-assembly 200 of FIG.
7A to provide the desired joint strength between the boards of the
bottom deck sub-assembly.
[0082] The bottom deck sub-assembly 100, 200 consists of fiber
filled thermoplastic or oriented plastic composite boards in at
least the lead board position 102, 202 and is assembled with
mechanical fasteners (bottom deck sub-assembly 100) or adhesive
fastening (bottom deck sub-assembly 200) to provide the bottom deck
subassembly 100, 200. The bottom deck edge boards 104, 204 and
bottom deck center board 106, 206 can be made of the same or
different material than the bottom deck lead boards 102, 202. In
one example, the bottom deck edge boards 104, 204 and/or the center
board 106, 206 can also be made from a fiber filled thermoplastic
or oriented plastic composite material to provide these boards with
protection against damage from a forklift or pallet jack.
Alternatively, the bottom deck edge boards 104, 204 and/or the
center board 106, 206 can be of wood of any suitable species, such
as pine or oak, or a wood composite material.
[0083] The bottom deck sub-assembly 100, 200 can be entirely or
partially made from fiber filled thermoplastic boards or OPC
boards. The fibrous filler in the fiber filled thermoplastic is
believed to improve the impact resistance and break strength of
such boards making them suitable in the lead board position. Any
fiber filler known in the art is useful, including but not limited
to naturally occurring fibers, such as flax or bamboo, glass fiber,
carbon fiber, polyester fiber, aramid fiber and the like. In
general, longer fibers provide a greater impact resistance than
shorter fibers.
[0084] OPC refers to an article made by orienting the polymers of a
polymer composition and comprises polymer molecules that have a
higher degree of orientation than that of a polymer composition
extruded from a mixer. OPC boards are OPC articles in the shape of
boards with a length, a thickness, and a width wherein the
cross-sectional shape is substantially rectangular. OPC boards can
be produced using a solid state die drawing process which elements
are described in U.S. Pat. No. 8,142,697 to Nichols et al. and in
U.S. Pat. No. 8,871,130 to Nichols et al., the contents of which
are incorporated herein by reference in their entirety. For use in
pallets, the length, width and thickness can be any dimensions
suitable for the desired pallet design. Standard pallets dimensions
depend on the geography, and industry of use. For example, the
length can vary from 600 mm to 1200 mm and the width can vary from
400 mm to 1200 mm. European pallets typically require deck boards
of 1000 mm length, but may be as short as 600 mm.
[0085] Suitable oriented plastic composite (OPC) boards may be made
by the following process. Selected plastics materials and additives
are introduced to an extruder and, after processing in the
extruder, are extruded through a die and calibrator to produce a
hot billet (extrudate) of the extruded material which is moved by a
puller to a temperature conditioning stage, where the material is
cooled below its softening temperature Ts. The cooled extrudate is
then drawn, using a puller, in a solid state die draw stage through
a solid state drawing die at a drawing temperature that aligns the
long chains of the polymer in the lengthwise direction of drawing
and then cooled with a cooling tank to a cutting temperature to
form a continuous OPC drawn piece. The OPC drawn piece is
subsequently fed using pullers or other means to a saw, to cut the
OPC drawn piece to a desired length to produce an OPC board. The
OPC board may be later cut to a shorter length if desired.
[0086] As described above, an orientable polymer is a polymer that
can undergo polymer alignment. Orientable polymers can be amorphous
or semi-crystalline. Herein, "semi-crystalline" and "crystalline"
polymers interchangeably refer to polymers having a melt
temperature (Tm). While not meaning to be limited by any theory,
polyolefins are believed to undergo cavitation in combination with
filler particles, because polyolefins are relatively non-polar and
as such adhere poorly to filler particles. Linear polymers (that
is, polymers in which chain branching occurs in less than 1 of
1,000 monomer units such as linear low density polyethylene) are
even more desirable.
[0087] Non limiting examples of suitable orientable polymers
include polymers and copolymers based on polystyrene,
polycarbonate, polypropylene, polyethylene (for example, high
density, very high density and ultra-high density polyethylene),
polyvinyl chloride, polymethylpentane, polyamides, polyesters (for
example, polyethylene terephthalate) and polyester-based polymers,
polycarbonates, polyethylene oxide, polyoxymethylene, and
combinations thereof. A first polymer is "based on" a second
polymer if the first polymer comprises the second polymer. For
example, a block copolymer is based on the polymers comprising the
blocks. Preferred orientable polymers include polymers based on
polyethylene and polypropylene, examples of which include linear
polyethylene having a weight average (Mw) or number average (Mn)
from 50,000 to 3,000,000 g/mol; preferably from 100,000 to
1,500,000 g/mol; more preferably from 750,000 to 1,500,000
g/mol.
[0088] Polypropylene (PP)-based polymers (that is, polymers based
on PP) are one example of a particularly preferred orientable
polymer for use in the present invention. PP-based polymers
generally have a lower density than other orientable polyolefin
polymers and, therefore, facilitate lighter articles than other
orientable polyolefin polymers. PP-based polymers also offer
greater thermal stability than other orientable polyolefin
polymers. Therefore, PP-based polymers, made by any of the means
known in the art may also form oriented articles having higher
thermal stability than oriented articles of other polyolefin
polymers. Suitable PP-based polymers include PP homopolymer; PP
random copolymer (with ethylene or other alpha-olefin present from
0.1 to 15 percent by weight of monomers); or PP impact copolymers.
It is preferred to use a PP-based polymer that has a melt flow rate
of greater than 0.3 g/10 min., preferably greater than 1 g/10 min.,
more preferably greater than 1.5 g/10 min., and even more
preferably greater than 2 g/10 min., while at the same time having
a melt flow rate of less than 8 g/10 min., preferably less then 6
g/10 min., more preferably less than 4 g/10 min., and even more
preferably less than 3 g/10 min. It is also preferred to use a
PP-based polymer that has 55% to 70%, preferably 55% to 65%
crystallinity.
[0089] PP obtained from either industrial or commercial recycle
streams, including filled or reinforced recycled PP, may be used.
The recycled PP may range from 0 to 100% of the orientable polymer
used in the orientable polymer composition.
[0090] PP can be ultra-violet (UV) stabilized, and desirably can
also be impact modified. Particularly desirable PP can be
stabilized with organic stabilizers. The PP can comprise titanium
dioxide or be free of titanium dioxide pigment.
[0091] The oriented polymer composition can further comprise
fillers, including organic fillers and inorganic fillers. OPC
articles can have filler levels from 10 wt % up to 60 wt %. Organic
fillers, because they are less dense than inorganic fillers can
often be as low as 10 wt % and as high as 35 wt %, 40 wt % or even
higher. Organic fillers can be cellulosic or synthetic polymers.
Cellulosic fillers include cellulosic materials such as wood fiber,
wood powder and wood flour and are susceptible, even within a
polymer composition, to decomposition, mold and mildew when exposed
to humidity. Furthermore, cellulosic fillers can harbor pests that
can be problematic for use of a pallet in international use.
[0092] Fillers are preferably, inert inorganic fillers. Inorganic
materials do not suffer from some of the challenges of organic
fillers. Inorganic fillers are either reactive or inert. Inert
fillers can be more preferred than reactive fillers in order to
achieve a stable polymer composition density. However, inorganic
fillers are generally denser than organic fillers. For example,
inert inorganic fillers for use in the present invention typically
have a density of at least two grams per cubic centimeter.
Therefore, polymer compositions comprising inorganic fillers
typically can contain more void volume than a polymer composition
comprising the same volume of organic fillers in order to reach the
same polymer composition density.
[0093] Non-limiting examples of inert inorganic fillers include
talc, clay (for example, kaolin), magnesium hydroxides, aluminum
hydroxides, dolomite, titanium dioxide, glass beads, silica, mica,
metal fillers, feldspar, Wollastonite, glass fibers, metal fibers,
boron fibers, carbon black, nano-fillers, calcium carbonate, and
fly ash. Particularly desirable inert inorganic fillers include
talc, calcium carbonate, magnesium hydroxide, or clay. The
inorganic filler can comprise one, or a combination of more than
one inorganic filler. More particularly, the inert inorganic filler
can be any one inert inorganic filler or any combination of more
than one inert inorganic filler. Embodiments of the invention can
have 20 wt % or more, 25 wt %, 35 wt %, 45 wt %, 50 wt %, 55 wt %
or more, or even 60 wt % filler. Embodiments in which the inorganic
filler level is between about 40 wt % and 55 wt % are preferred
because cavitation can increase and density decrease (void volume
increases) as filler level increases in this range.
[0094] Solid state die drawing is different from extrusion, in
which the material is pushed through a die in a hot, flowable state
above the glass transition temperature Tg of the material, and
pultrusion, where the material is both pushed and pulled. Solid
state die drawing involves pulling the material having a softening
temperature Ts at a temperature below its melt temperature Tm
through a drawing die using drive rollers or drive tracks or belts
(caterpillars) so that the material is under a state of tension and
the die drawing occurs at a drawing temperature Td below the
polymer composition softening temperature Ts. The drawing
temperature Td is ten or more degrees below the polymer softening
temperature, including, 15, 20, or even 30 degrees below Ts.
Generally, the drawing temperature Td range is 40.degree. C. or
less below the polymer composition's Ts in order to achieve a
linear draw ratio using economically reasonable draw rates. (Higher
rates are preferred on economic grounds.) It is preferred to
maintain the temperature of the polymer composition at a
temperature within a range between the polymer composition's Ts and
50.degree. C. below Ts inclusive of endpoints, while the polymer
composition is drawn. Preferably, the polymer composition is cooled
after exiting the drawing die prior to cutting to length.
Subsequently, the board can be treated to provide a length
dimension stable board.
[0095] Drawing causes the long polymer chains of the material to
elongate (or straighten) and generally align in the direction of
drawing. The individual polymer chains or groups of polymer chains
can be somewhat entangled and also mechanically bonded to one
another, giving the material great strength and toughness that can
be greater than that of typical un-oriented plastic material or
even some types of woods used to fabricate wood articles.
[0096] Fillers and additives can be incorporated with the
orientable polymer to make an orientable polymer composition. Such
fillers function as impediments to polymer chain alignment during
solid state drawing and have the effect of introducing cavitation
into the material as the polymer chains are forced to slide past
and detach from the particles during their elongation. Such
cavitation reduces the density of the composite polymer material.
The filler particles can vary in size, shape and selection
(blends). Other additives may include pigments, fire retardants,
and other additives known in the art. Some of these fillers, such
as fire retardants, may comprise hard particles and may have a
beneficial dual purpose as both a fire retardant and as a portion
of, or all, the filler constituent of the polymer composition if
cavitation of the material is desired.
[0097] Generally, the extent of cavitation (that is, amount of void
volume introduced due to cavity formation during orientation) is
directly proportional to filler concentration. Increasing the
concentration of inorganic filler, since it is typically of higher
density than the matrix thermoplastic, increases the density of a
polymer composition, but also tends to increase the amount of void
volume resulting from cavitation in the oriented polymer
composition. Particularly desirable embodiments of the present
filled oriented polymer composition article have 25 volume-percent
(vol %) or more, preferably 35 vol % or more, more preferably 45
vol % or more void volume and even 55 vol % or more based on total
polymer composition volume.
[0098] Additional void volume may be created by the use of foaming
agents, either exothermic or endothermic. Herein, "foaming agent"
includes chemical blowing agents and decomposition products
therefrom. Foaming agents include, but are not limited to moisture
introduced as part of a filler, for example wood flour or clay, or
by chemicals that decompose under the heating conditions of the
billet extrusion process, Chemical blowing agents include the
so-called "azo" expanding agents, certain hydrazide,
semi-carbazide, and nitroso compounds, sodium hydrogen carbonate,
sodium carbonate, ammonium hydrogen carbonate and ammonium
carbonate, as well as mixtures of one or more of these with citric
acid or a similar acid or acid derivative. Another suitable type of
expanding agent is encapsulated within a polymeric shell. Blowing
agent may be used up to at least 1.5 wt % blowing agent to achieve
density reductions compared to an un-foamed billet of up to 20% or
even more. Measure weight percent blowing agent relative to total
oriented polymer composition weight.
Examples
[0099] The following examples illustrate embodiments of the present
invention and not necessarily the full scope of the present
invention. While the exemplary embodiments are described in the
context of OPC materials, it will be understood that the scope of
the invention is not limited to such materials, but may also
include fiber filled thermoplastics. Fiber filled thermoplastics,
particularly those that include longer fibers, such as long glass
fibers, generally have high impact performance.
Description of Pallet Construction
[0100] Pallets were constructed similar to the conventional pallet
10 of FIGS. 1 and 2 and compared below with the hybrid pallets 110
and 210 constructed using the bottom deck sub-assembly 100 and 200
of FIGS. 5 and 7A, respectively, as described in more detail below.
The exemplary hybrid pallets 110 and 210 described below include
the bottom deck sub-assembly 100 and 200, respectively, coupled
with the top deck 12 and spacer pallet assembly 33 of the
conventional pallet 10 of FIGS. 1 and 2.
[0101] Test Top Deck Construction
[0102] The top deck 12 used in the comparisons was similar to that
shown in FIGS. 1 and 2 except that five intermediate oak boards of
thickness 0.688 inch (17.48 mm), width 3.5 inch (89 mm) and length
40 inch (1016 mm) were used between the lead boards, and four oak
boards of thickness 0.688 inch (17.48 mm), width 5.5 inch (140 mm)
and length 40 inch (1016 mm) oak boards were provided at the lead
board positions 20a, 20g and adjacent to the lead board positions
20b, 20f. Three oak stringer boards 18 of thickness 0.688 inch
(17.48 mm) width 5.5 inch (140 mm) and length 48 inch (1219 mm)
were also used. At each corner and at the midpoint between the
corners along the length 21 of the pallet were six spacer blocks 16
of height 3.5 inch (89 mm) width 5.5 inch (140 mm) and length 7.5
inch (190.5 mm) of either oak or treated pine as indicated in Table
3. At the midpoint between the blocks described above, in the width
direction 22 of the pallet, are three spacer blocks 17 of height
3.5 inch (89 nm) width 5.5 inch (140 mm) and length 3.75 inch
(95.25 mm) of either oak or treated pine as indicated in Table
3.
[0103] The top deck is assembled by laying the nine blocks 16, 17
on a fabrication surface so that the length dimension 25 of the
larger blocks 16 lies in the direction of the width dimension 22 of
the pallet. Then the stringer boards 18 are placed on the blocks
16, 17 at the correct positions followed by the lead boards 20a,
20g and the intermediate deck boards.
[0104] The top deck lead boards 20a, 20g are attached (fasteners
32) to each of the end blocks 16 with six 3 inch (75 mm) long,
0.120 inch (3.05 mm) diameter Grip Rite brand ring shank nails from
Prime Source Building Products Inc. installed with a Hitachi NR90AE
3.5 inch strip nailer. The top deck center board 20d is attached to
each of the three interior smaller blocks 17 with three of these
same type of nails. Two of these nails are also used wherever
intermediate deck boards 20b, 20f overlapped the spacer blocks 16.
The remaining nails 32 in the intermediate deck boards are 1.25
inch (31.8 mm) long, 0.090 inch (2.29 mm) diameter hot dipped
galvanized ring nails purchased from CLS Metal Fasteners, Grand
Rapids Mich., and were installed with a Bostich Model N66
Industrial siding nailer.
[0105] The conventional comparative bottom deck and the exemplary
bottom deck sub-assemblies were created from several different
materials and using several different assembly methods and coupled
with the above described test top deck 12 through the stringer
boards 18 and spacer members 16, 17 for comparison as described
below.
Determination of Joint Strength of Mechanical Fasteners
[0106] Table 1 illustrates the joint strength in tension for
exemplary fastening methods for the bottom deck sub-assemblies 100,
200. To determine the joint strength in tension, two OPC boards
were joined using the mechanical fasteners as noted in Table 1. The
boards were then placed in a mechanical testing device of the
constant-rate-of-crosshead-movement type with one fixed member
carrying a grip and one movable member carrying a second grip in a
position such that the joint could be tested in tension. The grip
area is 4.9 inches (12.45 cm) in length and the full width of the
board being tested and has four beads of approximate height 0.0625
inches (1.58) running across the board in the board width
direction. Each end of the boards making up the joint to be tested
are secured in the grips by tightening eight bolts on each of the
top and bottom grips, four on each of the grip plate edges. The
boards were then pulled in tension at a rate of 1 inch/minute (2.54
cm/min.). The joint break force is determined at failure of the
fastener, including pull-out or breakage of the fastener and is
reported in Newtons. The results of that testing are shown in Table
1. When more than one joint of the same type is tested, the results
are an average of the strength of the joints tested.
TABLE-US-00001 TABLE 1 Methods for fastening bottom deck
sub-assembly boards to one another Strength of Joint Method Short
Form in Tension No. Description Description (Newtons) 1 No
attachment of one bottom deck board to another. Nailed only -- 2
Attachment by truss plate* on the bottom face of the bottom Gang
nail 11,180 deck (as illustrated in FIG. 5) of the pallet at each
joint bottom between bottom deck boards. 3 Same as Method No. 2,
except the side on which the truss Gang nail 11,180 plates were
attached differed in orientation with respect to the top top deck.
The truss plates were facing the pallet interior. 3a Same as Method
No. 3, except the truss plates were smaller at Gang nail 3240 each
joint of the bottom deck sub-assembly.** top (A) 4 Attachment by
truss plates on both the top face and bottom face Gang nail 19460
of the bottom deck boards of the pallet at each joint between Both
bottom deck boards. 5 Corrugated fasteners, 2 per joint, driven
between the bottom Corrugated 600 deck boards and aligned with the
direction of orientation of the fastener bottom deck boards edge
and center boards. The corrugated fasteners were 5/8 inch high 20
gauge corrugated steel. 6 Lead, edge, and center deck boards of the
bottom deck were Welded Not routed so as to provide an overlap for
the full width of each determined board at the joint between the
lead board and the bottom deck edge and center boards. The routed
area on each board was heated to melt the polymer surface, and then
the routed areas were pressed together to provide a welded joint.
The joint area so welded was nominally 140 mm by 140 mm. *20 gauge
galvanized steel truss plates produced by Mitek Building Products
were used as follows: connecting the lead boards to the center
board are 2 inch (5 cm) by 5 inch (12.5 cm) plates and connecting
the lead boards to the edge boards are 3 inch (7.5 cm) by 4 inch
(10 cm) plates; the truss plates were placed so that plate slots
were aligned with the direction of orientation of the bottom deck
edge and center boards. **20 gauge galvanized steel truss plates
one inch (2.5 cm) by four inch (10 cm) at each joint.
[0107] The bottom deck lead boards for the conventional,
comparative pallets, and the exemplary bottom deck sub-assembly
were the same dimensions as the top deck lead boards and for each
of the examples and the comparative examples was as indicated in
Table 3. The bottom deck edge and center boards were of the
material indicated in Table 3 of thickness 0.688 inch (17.48 mm)
and width 5.5 inch (140 mm) and length 37 inch (940 mm). For the
exemplary bottom deck sub-assemblies, the boards of the bottom deck
were joined into a sub-assembly as described in Table 1, depending
on the type of joint specified in Table 1.
[0108] The exemplary bottom deck sub-assembly was attached with
fasteners to the top deck 12 through the spacer blocks 16, 17 with
the Grip Rite 3 inch (76.2 mm) long, 0.120 inch (3.05 mm) diameter
ring shank nails using the nail pattern shown in FIG. 2 for
fasteners 42 to form the exemplary hybrid pallets. Specifically,
the bottom deck lead boards had four nails in a square pattern in
to each of the corner and mid-point larger spacer blocks 16. The
bottom edge and center boards had four nails in a linear pattern in
the larger end blocks 16 and three nails in a triangular pattern in
to the smaller middle blocks 17 as shown in FIG. 2. The bottom deck
lead boards for the conventional, comparative pallets were fastened
to the spacer blocks 16, 17 using the same pattern illustrated in
FIG. 2 to form the conventional, comparative pallets.
[0109] The conventional, comparative pallets and the exemplary
hybrid pallets were tested using the pallet jack test procedure
described below. Because each pallet consists of two bottom deck
lead boards, two tests were performed on each pallet, one on each
of the two bottom lead deck boards. The pallet jack was positioned
and the hydraulic system was used to lift the top deck upward and
away from the bottom deck. The pressure gauge on the pallet jack
was monitored and the gauge reading was noted when failures
occurred. During and after the test, the pallets were examined to
determine which of the failure modes of Table 2 had occurred during
the test. Results were recorded and are compiled in Table 3.
Pallet Jack Lift Test
[0110] The pallet jack lift test was performed on the comparative
and exemplary hybrid pallets of Table 3 as follows. Place a pallet
on the warehouse floor so that a pallet jack can be inserted in the
entry position beneath one set of top and bottom deck lead boards.
Place a second pallet, upon which a 1200 pound (545 kilogram)
weight is loaded, on the top deck of the test pallet so that a
front edge of the weighted pallet is aligned vertically with a
front edge of the test pallet (i.e. the front edges of the lead
boards of the weighted pallet are aligned with the front edge of
the lead board to be tested). A pallet lift jack, equipped with a
pressure gauge capable of measuring the pressure of the hydraulic
system of the pallet jack is inserted into the test pallet so that
the lead wheels of the pallet jack are centered on the bottom deck
lead board to be tested, similar to the scenario illustrated in
FIG. 4. When the forks are raised by the hydraulic system, the
forks are aligned so that the top deck of the test pallet may be
lifted away from the bottom deck of the test pallet. The forks are
raised and the pressure gauge monitored until a bottom face of the
center spacer block of the test pallet at the lead board test
position is from 8 to 11.7 cm (3.2 to 4.7 inches off the floor).
During the raising of the forks of the pallet jack, the pressure
gauge reading is noted and the type of failure mode is recorded
when any failure of the pallet is observed. During the test, as
pallet failure occurs, the spacer blocks are lifted away from the
floor and any portions of the top deck attached to the spacer
blocks are also lifted from the floor. Because the wheels are
resting on the lead board, as the forks lift the top dock, the lead
board may flex and/or separate from the spacer blocks and
eventually break or splinter in some cases. The break force is
recorded as the breakage pressure based on the pressure gauge
reading as shown in Equation 1:
Breakage Pressure (psi)=1072*Gauge reading (psi)-229.4 (Equation
1)
Equation 1 was determined by applying known weights to a pallet
deck and recording the gauge reading required to lift the loaded
pallet, fitting the resulting graph of actual load weight versus
gauge reading to a straight line equation using a linear regression
software program. The breakage pressure, i.e. the break force, can
be converted from pounds per square inch (psi) to megapascals
(Mpa).
[0111] Subsequent to the test, the bottom deck lead board which was
tested was examined and the observations were recorded in Tables 3A
and 3B according to the failure modes described in Table 2.
TABLE-US-00002 TABLE 2 Pallet failure types - description of
failure. Pallet Failure Mode Description 1 Fastener head pulled
through bottom deck board. In this failure mode at least one of the
fasteners used to couple the lead board to the spacer blocks is at
least partially pulled into or through the lead board. An example
of this type of failure mode is illustrated in FIG. 9. 2 Pull out
of bottom deck board nails from the spacer blocks. In this failure
mode at least one of the fasteners used to couple the lead board to
the spacer blocks is fully or partially pulled out of the spacer
block through the lead board. An example of this type of failure
mode is illustrated in FIG. 10. 3 Failure of deck board by breakage
in the direction of the board length. If the board is made of wood
or OPC, this corresponds to the wood or OPC grain direction; WPC
does not have a grain. An example of this type of failure mode is
illustrated in FIG. 11. 4 Failure of deck board by breakage in the
direction of board width. If the board is made of wood or OPC, this
corresponds to the wood or OPC cross grain direction; WPC does not
have a grain. An example of this type of failure mode is
illustrated in FIG. 12. 5 Failure of top deck board fastening. This
failure mode is not a failure mode of the test lead board but of
the top deck of the pallet. An example of this type of failure mode
is illustrated in FIG. 13. 6 This failure mode corresponds to the
test lead board being damaged or loosened such that the test board
separates from the spacer blocks or partially separates from the
spacer blocks such that the test board is readily deconstructed
(i.e. removed from the pallet by hand and/or unpowered hand tools).
Test boards which failed according to failure modes 3 and 4 in
which the integrity of the test board itself was damaged to such an
extent that the test board would have to be removed in order to
have an operable pallet are also considered to have failed
according to failure mode 6.
[0112] Tables 3A and 3B illustrate the lift jack test breakage
pressure and pallet failure mode results for pallets having a
conventional or non-bottom deck sub-assembly structure and pallets
having a bottom deck sub-assembly structure, respectively.
TABLE-US-00003 TABLE 3A Results of pallet jack lift test for
conventional/non- bottom deck sub-assembly Assembly Lift Jack Exam-
Spacer Bottom Method - Test Breakage Pallet ple block lead Short
Pressure Failure No. material boards form* (MPa) Modes Wood
Pine.sup.1 Pine.sup.1 Nailed only 16.9 3, 6 Exam- ple 1 WPC
Oak.sup.2 WPC1.sup.3 Nailed only 22.8 4, 6 Exa- mple 1 WPC
Pine.sup.1 WPC1.sup.3 Nailed only 22.5 4, 6 Exam- ple 2 WPC
Oak.sup.2 WPC2.sup.4 Nailed only 23.6 4, 6 Exam- ple 3 OPC
Oak.sup.2 OPC1.sup.5 Nailed only 35.4 2, 6 Exam- ple 1 OPC
Oak.sup.2 OPC1.sup.5 Nailed only 35.4 6 Exam- ple 2 OPC Oak.sup.2
OPC1.sup.5 Nailed only 35.4 1, 2, 6 Exam- ple 3
TABLE-US-00004 TABLE 3B Results of pallet jack lift test for
exemplary bottom deck sub-assembly structure Assembly Lift Jack
Exam- Spacer Bottom deck Method - Test Breakage Pallet ple block
sub-assembly Short Pressure Failure No. material boards form* (MPa)
Modes WPC Oak.sup.2 WPC1.sup.3 Gang nail 28 2, 4, 6 Exam- both ple
4 WPC Oak.sup.2 WPC2.sup.4 Gang nail 22.5/31.7 4, 6 Exam- both ple
5 WPC Pine.sup.1 WPC2.sup.4 Gang nail 22.5 4, 6 Exam- both ple 6
Hybrid Pine.sup.1 OPC2.sup.5 Gang nail 28.0 2 Exam- bottom ple 1
Hybrid Pine.sup.1 OPC2.sup.5 Gang nail 28.0 2 Exam- both ple 2
Hybrid Pine.sup.1 OPC2.sup.5 Gang nail 28.0 2 Exam- top ple 3
Hybrid Pine.sup.1 OPC1.sup.5 Welded 34.3 1 Exam- ple 4 Hybrid
Oak.sup.2 OPC1.sup.5 Welded 38 2 Exam- ple 5 Hybrid Oak.sup.2
OPC1.sup.5 Welded 28.7 2 Exam- ple 6 Hybrid Oak.sup.2 OPC2.sup.5
Gang nail 35.4 1 Exam- top (A) ple 7 Hybrid Pine2 OPC2.sup.5 Gang
nail 28.0 2 Exam- top (A) ple 8 .sup.1Yellow pine is No 2 pine
board, nominal 1 inch by 6 inch, purchased from Sequin Lumber, Bay
City MI, and machined to the required dimensions for use in
pallets. .sup.2Oak is pallet grade oak purchased from Hugo Brothers
Pallet Manufacturing, Kawkawlin, MI .sup.3WPC1 is Veranda brand
decking, a wood plastic composite manufactured by Fiberon from Home
Depot. It was planed to a thickness of 0.688 inch (17.48 mm)
specified for pallet boards and used at the purchased width of
5.375 inches (13.65 cm). .sup.4WPC2 is Azek brand decking, a
cellular PVC/wood composite produced by Azek Building Products, a
Division of CPG International, Scranton PA, USA. It was planed to a
thickness of 0.688 inch (17.48 mm) specified for pallet boards and
used at the purchased width of 5.375 inches (13.65 cm). .sup.5OPC1
and OPC2 are oriented plastic composite boards and are produced at
the required thickness and width. The orientable composition base
polymer is polypropylene Inspire 404 from Braskem, Philadelphia, PA
and is filled with 48 wt % calcium carbonate No. 10 white. *Short
form assembly method is defined in Table 1.
[0113] Table 3A compares the effect of different bottom deck board
materials on the lift jack test breakage pressure and the pallet
failure modes for conventional/non-bottom deck structures. Pallets
having a conventional bottom deck structure made from wood or a
wood plastic composite (WPC) material exhibited lower lift jack
test breakage pressures than similar pallets made using an oriented
polymer composition (OPC) material. As can be seen in Table 3A, all
of the pallets having a conventional bottom deck structure in which
the bottom decks boards are nailed to the spacer blocks and are not
coupled with adjacent deck boards exhibited failure mode 6. In some
cases, bottom decks boards can be damaged to such an extent, such
as by breakage of the board itself, that the board needs to be
removed and/or replaced in order for the pallet to remain
operable.
[0114] In some failure modes, a board can be separated or loosened
from the pallet, but the board itself is still usable. In these
cases, and particularly when the boards are made of more expensive
materials, it is more cost effective to reuse the separated or
loosened board. In a pool pallet system, when a board becomes
separated from the pallet or is damaged such that separation can be
achieved without special tools (e.g. a hammer or crowbar) and/or by
hand with little effort, the damaged board is removed and typically
discarded or lost, even when it is feasible to reuse the same
board. When the damaged board is made of a relatively inexpensive
material, such as wood, removal of the board can be cost
effectively addressed by replacing the missing board. However, when
more expensive materials, such as the WPC and OPC materials of WPC
Examples 1-3 and OPC Examples 1-3, replacement of the damaged board
can become cost prohibitive, especially in a large pool pallet
system where boards may be damaged over and over again. Table 3A
demonstrates that while exhibiting some increase in robustness
compared to wood, the WPC Examples 1-3 and OPC Examples 1-3 all
still exhibited failure mode 6, requiring replacement of the
damaged or discarded board(s) and are thus not a cost effective
solution for maintaining pallets.
[0115] Table 3B compares the effect of different bottom deck board
materials on the lift jack test breakage pressure and the pallet
failure modes for pallets assembled using the bottom deck
sub-assembly. Table 3B demonstrates that the exemplary bottom deck
sub-assembly structure described herein in combination with the use
of OPC material for forming the deck boards addresses the problem
of failure mode 6 in which the damaged lead board is discarded or
lost. Decreasing the likelihood that the expensive lead board is
discarded or lost can provide substantial cost savings in
maintaining pallets. The bottom deck sub-assembly structure couples
the lead board with the other boards of the sub-assembly and thus,
even when the lead board is damaged and becomes separated or
partially separated from the spacer blocks, the damaged lead board
is still connected with the remaining sub-assembly boards and thus
cannot be readily deconstructed. This can facilitate maintaining
the damaged lead board with the sub-assembly, such as for example
by re-fastening or fixing damaged fastening, rather than removing
the damaged lead board
[0116] WPC Examples 4-6 of Table 3B, exhibited failure modes, such
as failure mode 4 in which the lead board breaks in the direction
of board width, which would result in a need for the damaged board
to be removed and replaced. While WPC Examples 4-6 were not readily
deconstructed as a result of the joint strength between the bottom
deck boards of the sub-assembly, because the damaged board is
connected with the other boards in the sub-assembly, removal of the
damaged board can become time consuming and may require special
tools. In some cases, the entire sub-assembly may need to be
removed to replace the damaged board and/or the replace the entire
sub-assembly. Thus, even the combination of the more expensive WPC
material and the bottom deck sub-assembly may not provide the
desired cost effective solution for maintaining pallets.
[0117] In contrast, when OPC materials are used to form the bottom
deck sub-assembly and assembled with a top deck to form a hybrid
pallet (Hybrid Examples 1-8), none of the hybrid pallets
demonstrate failure modes 3 or 4, which would require removal and
replacement of the broken board, and further, none of the hybrid
pallets demonstrated pallet failure mode 6. FIG. 14 illustrates
pallet failure mode 2 for a bottom deck sub-assembly using a welded
shiplap joint similar to Hybrid Examples 4-6 in which several of
the nails coupling the test board to the spacer block have been
pulled out of the spacer blocks, but the shiplap joint between the
bottom deck boards is of sufficient strength to inhibit removal of
the test board from the pallet by hand or with the use of hand
tools. FIG. 15 illustrates pallet failure mode 2 for a bottom deck
sub-assembly using a mechanical joint similar to Hybrid Examples
1-3 in which several of the nails coupling the test board to the
spacer block have been pulled out of the spacer block, but the
mechanical joint between the bottom deck boards is of sufficient
strength to inhibit removal of the test board from the pallet by
hand or with the use of hand tools. Hybrid Examples 1-8 also
demonstrate a bottom deck sub-assembly in which the joint strength
between the bottom deck boards is stronger than the joint strength
between the bottom deck boards and the spacer members, and thus the
connection between the bottom deck boards and the spacer members is
lost or weakened before the connection between the bottom deck
boards is lost.
[0118] Tables 3A and 3B further illustrate examples that used OPC
boards (OPC Examples 1-5 and Hybrid Examples 1-8) and demonstrate
that OPC boards did not split or crack when acted upon by a pallet
jack in this test procedure. As demonstrated in Table 3B, the only
failure modes for the Hybrid Examples 1-8 related to the fastener
coupling the test board to the spacers. This type of damage can be
easily repaired by simply re-fastening the lead board to the spacer
blocks, either with the existing fasteners or with new fasteners.
Thus, it is preferred that the materials and the structure of the
bottom deck sub-assembly be selected such that the boards of the
sub-assembly do not break, split, or crack before the connection
between the spacer members and the bottom deck boards is broken or
weakened.
[0119] When the OPC deck boards are joined together using gang
nails or by thermal welding (Hybrid Examples 1-8), while the joint
between the bottom deck boards and the spacer members may be broken
or weakened, the bottom deck boards are still joined with the
adjacent bottom deck boards, decreasing the likelihood that a
damaged bottom deck board is removed and discarded or lost. Tables
3A and 3B demonstrate that it is the combination of the OPC
materials and the bottom deck sub-assembly structure that provides
a bottom deck structure that is sufficiently robust to resist board
breakage during the pallet jack lift test and which further
inhibits removal of a damaged or loosened bottom deck board and in
this manner the hybrid pallet can provide a solution for pallet
management having an increase in cost effectiveness.
Determination of Lead Board Constrained Impact Strength
[0120] The lead board constrained impact strength test was
performed on boards made of traditional wood or wood plastic
composite materials and exemplary OPC materials. Place a pallet
upside down on the warehouse floor so that a section of the bottom
deck lead board nailed to a spacer block is centered so that a dart
can be dropped on the bottom deck lead board. The dart has a weight
of 6.29 kg (13.85 pounds) and the dart face which impacts the
bottom deck lead board is a short section of standard nominal 2
inch.times.4 inch lumber (3.8 cm by 8.9 cm) affixed to weights to
provide the dart weight. The dart is raised sequentially from the
lowest test height for the test apparatus to the lowest test height
at which bottom deck lead board failure is observed. Failure is
defined as splitting according to any one of the definitions of
pallet damage set forth in sections 7.1.3 through 7.1.5 or missing
board as set forth in sections 7.1.6 through 7.1.12 of the NWPCA
bulletin. The impact strength is reported in units of energy
(Joules) and is the dart mass multiplied by the drop height and the
acceleration of gravity.
TABLE-US-00005 TABLE 4 Deck board materials and test results*
Constrained Impact Strength Avg. Highest Pass Density/
Energy/Lowest Board MOE MOR Ranges Fail Energy Material (GPa) (MPa)
(g/cc) (Joules) Oak 9.8 64 0.48 131/187 Yellow 13.2 80 0.47 94/113
Pine WPC1 4.47 20 1.1 47/56 WPC2** 1.46 Bent, did 0.58 56/66 not
break OPC1*** 3.55 .+-. 10% Bent, did 0.77/0.75-0.78 >263/did
not notbreak fail under test conditions OPC2*** 4.45 .+-. 10% Bent,
did 0.76 Test not run not break *Results for MOE, MOR and density
are the average of three measurements. The MOR was obtained using a
span of 21 inches instead of the normal test conditions for MOR of
16 inch span. **Technical Data Sheet for Azek Deck Board shows MOR
of 3600 psi.
http://www.azek.com/files/files/technical-center/techincal-docs/Deck,Porc-
h/AZEK%20Deck%20Tech%20Data%20Arbor%20Terra.pdf ***MOE, MOR and
Density data was obtained on multiple samples during the production
of the boards actually used in the testing.
[0121] One common source of damage to lead boards is from the
forklift or pallet jack running into the lead boards during
alignment of the forks. A preferred material will be tough enough
to withstand contact with the forklift or pallet jack without
suffering damage that requires the board to be replaced. As
described above, replacement of a damaged board forming part of the
bottom deck sub-assembly can decrease the cost effectiveness of the
hybrid pallet and thus should be minimized. The constrained impact
strength in Joules is determined as described for the Determination
of Lead Board Constrained Impact Strength and is representative of
the toughness of the board, i.e. the ability of the board to
withstand damage from contact with the forklift or pallet jack. As
demonstrated in Table 4, oak is tougher than pine, which are both
tougher than WPC1 and WPC2, as illustrated by the constrained
impact test. OPC1 is significantly tougher than both the wood
species, oak and pine, and the WPC materials, as demonstrated by
the constrained impact test. In order for the hybrid pallet to be
cost effective, the lead board needs to be at least as tough as the
wood species to withstand impact from the forklift or pallet jack
and minimize the number of times the bottom deck boards of the
sub-assembly need to be replaced. The OPC 1 material has
significantly higher constrained impact strength and did not fail
under the test conditions, which indicates that the OPC lead board
is more resistant to impact damage than the wood species or the WPC
material, and thus less likely to require replacement due to impact
forces. In a preferred embodiment, the constrained impact strength
of the material used in the lead boards of the bottom deck
sub-assembly is at least comparable to that of the wood species
typically used in pallets and thus the preferred constrained impact
strength of the bottom deck lead boards is not less than 95 Joules,
preferably not less than 113 Joules, more preferably not less than
131 Joules, and still more preferably not less than 190 Joules.
[0122] As discussed above, one of the challenges of using more
robust, and thus typically more expensive materials to form the
pallets, is that when pallet boards are damaged in a way such that
they could be re-used, they are typically discarded or lost, rather
than re-used, which can significantly increase the overall cost of
maintaining the pallet. This can negatively impact the benefits of
using a material that is more resistant to damage, such as an OPC
material. In order to address this challenge, Applicants have found
that when the bottom deck is made from OPC boards, it is desirable
to provide the bottom deck as a sub-assembly in which the bottom
deck boards are connected to adjacent bottom deck boards to inhibit
removal of a damaged or loosened bottom deck board from the pallet.
In one embodiment, the joint strength between adjacent bottom deck
boards is greater than a joint strength between the bottom deck
boards and the spacer members. In this manner, when a bottom deck
board is damaged such that it is loosened or disconnected from the
spacer members, the damaged bottom deck board is still connected
with at least one adjacent bottom deck board, thus minimizing the
likelihood that the damaged board will be separated from the pallet
and lost or discarded. Alternatively, or additionally, the joint
strength between adjacent bottom deck boards can be selected such
that if the bottom deck board is damaged it is not readily
deconstructed from the remainder of the sub-assembly.
[0123] The joint strength may be provided by a number of methods of
adhering the side boards to the lead boards, including but not
limited to nailing or gang-nailing, corrugated fasteners, thermal
welding or solvent based welding or adhesives, or a combination of
one or more of these methods. In one example, the number and type
of fasteners joining the boards of the bottom deck sub-assembly can
be selected to provide the desired joint strength based on the
desired decrease in the incidence of discarded or lost boards. In
an exemplary embodiment, any joints between the edge and lead
boards have a joint strength greater than that of the pull out
strength of the fasteners joining the bottom deck sub-assembly to
the spacer blocks so that the joints between the bottom deck boards
remains relatively undamaged in the pallet jack lift test.
Therefore, according to one embodiment of the invention, it is
desirable that the joint strength be two times, three times or even
more than the strength of the joint between the spacer blocks and
the bottom deck sub-assembly to minimize the damage during the
pallet jack lift test.
[0124] One challenge in pallet management, particularly in pallet
pool systems, is the incidence of discarded or lost boards as a
result of users removing damaged boards rather than repairing them.
Typically, users will remove damaged boards using their hands or
unpowered tools, such as a hammer or crowbar, which may be
available on site. As has been discussed, replacement of the
discarded or lost boards can become cost prohibitive as the cost of
the board increases and thus decreasing the incidence of discarded
or lost boards that could otherwise be re-used can provide
significant cost savings. The number and type of fasteners joining
the boards of the bottom deck sub-assembly can be selected to
provide the desired joint strength based on the desired decrease in
the incidence of discarded or lost boards. Thus, the joint strength
can be selected to resist separation of a board from the
sub-assembly by hand, such as a joint strength when pulled in
tension of at least 450 Newtons. In another example, the joint
strength can be selected to be higher to resist both separation by
hand and separation by unpowered hand tools, such as a claw tooth
hammer, such as a joint strength when pulled in tension of at least
1200 Newtons and preferably at least 5000 Newtons. The joint
strength can further be selected to resist separation by certain
powered tools to further decrease the rate of incidence of
discarded or lost boards, depending on the particular pallet
management system. It will be understood that a joint strength that
resists separation can vary depending on the strength of an
individual and the type of tools available to the individual, the
joint strength can be selected to provide the desired decrease in
the incidence of discarded or lost boards. As demonstrated by
methods 2, 3, and 4 in Table 1, several exemplary bottom deck
sub-assemblies have a joint strength of greater than 10,000
Newtons, making it extremely difficult for a user to separate a
board from the sub-assembly and thus decreasing the likelihood that
a damaged board is discarded or lost. The joint strength can be
selected based on the desired resistance to removal as well as
taking into consideration additional factors related to the
sub-assembly and hybrid pallet, such as manufacturing costs, type
of materials, assembly method, intended use, etc. and can be at
least 450 Newtons, preferably at least 1200 Newtons, more
preferably at least 5000 Newtons, and even 10,000 Newtons or
greater.
[0125] In warehouse storage racks, loaded pallets are typically
only supported by the edges of the pallet. Thus, pallets,
particularly the bottom deck of a pallet, must resist excessive
deflection when loaded pallets are stored in a rack. The materials
used to form the pallet bottom deck boards are selected to provide
the resistance to deflection based on the intended use of the
pallet. In the exemplary embodiment shown in Table 4 the OPC
material has a flexural modulus of at least 3.55.+-.10% GPa. The
boards may be selected to provide a lower or higher flexural
modulus and may be selected to have a flexural modulus greater than
2.75 GPa (400M psi), more preferably greater than 3.25 GPa, even
more preferably greater than 3.75 GPa, still more preferably
greater than 4.25 GPa and even still more preferably greater than
4.75 GPa, for example, depending on the intended use of the pallet.
OPC boards are particularly desirable because they do not fail in a
flexural modulus test and can be bent a full 180 degrees, while
having a significant elastic modulus.
[0126] The embodiments of the invention provide for a pallet having
a bottom deck sub-assembly in which at least the bottom deck lead
boards are made from a material that is resistant to impact damage
and damage as a result of an improperly aligned pallet jack or
forklift and further provides a bottom deck sub-assembly which
inhibits separation of a damaged, but re-usable board from the
pallet, thus decreasing the likelihood that a damaged or loose lead
board is discarded rather than repaired.
[0127] Additional non-limiting embodiments contemplated by the
present invention include:
[0128] A method of forming a pallet comprising the following steps:
coupling a plurality of top deck boards comprising at least a first
and second top deck lead board and at least one intermediate board
positioned between the first and second top deck lead boards, with
a plurality of spacer members; forming a bottom deck sub-assembly
by coupling a first bottom deck lead board at a first end of the
bottom deck sub-assembly and a second bottom deck lead board at a
second end of the bottom deck sub-assembly, opposite the first,
with at least one intermediate board extending between the first
and second bottom deck lead boards to form a joint between the at
least one intermediate board and the adjacent first and second
bottom deck lead boards, wherein the joint between the at least one
intermediate board and the adjacent first and second bottom deck
lead board has a joint strength in tension of 450 Newtons or
greater; and coupling the bottom deck sub-assembly with the top
deck through the plurality of spacer members to form the pallet,
wherein the first bottom deck lead board or the second bottom deck
lead board comprises an oriented plastic composite or fiber filled
thermoplastic material.
[0129] According to one embodiment, a pallet has a top deck coupled
with a bottom deck through a plurality of spacer members. A
plurality of fasteners join the top and bottom decks with the
spacer members to couple the top deck, bottom deck, and spacer
members into an assembled pallet. The bottom deck is provided as a
sub-assembly comprising at least two lead bottom deck boards and at
least one additional bottom deck board, each bottom deck board
coupled with at least one other bottom deck board by a bottom deck
joint, and wherein each board of the bottom deck sub-assembly is
further coupled with at least one of the plurality of spacer
members to couple the bottom deck sub-assembly with the top deck.
The bottom deck joints can be configured to have a predetermined
joint strength. In one embodiment, the predetermined joint strength
corresponds to a strength such that the bottom deck boards of the
bottom deck assembly are not readily deconstructed by hand and/or
with unpowered hand tools. Alternatively, or additionally, the deck
boards of the bottom deck assembly are configured such that the
predetermined joint strength of the bottom deck joint is greater
than a joint strength between the bottom deck sub-assembly and the
spacer members.
[0130] To the extent not already described, the different features
and structures of the various embodiments of the invention may be
used in combination with each other as desired. For example, one or
more of the features illustrated and/or described with respect to
one of the bottom deck sub-assemblies 100 or 200 can be used with
or combined with one or more features illustrated and/or described
with respect to the other of the bottom deck sub-assemblies 100 or
200. That one feature may not be illustrated in all of the
embodiments is not meant to be construed that it cannot be, but is
done for brevity of description. Thus, the various features of the
different embodiments may be mixed and matched as desired to form
new embodiments, whether or not the new embodiments are expressly
described.
[0131] While the invention has been specifically described in
connection with certain specific embodiments thereof, it is to be
understood that this is by way of illustration and not of
limitation. Reasonable variation and modification are possible
within the scope of the forgoing disclosure and drawings without
departing from the spirit of the invention defined in the appended
claims.
* * * * *
References