U.S. patent application number 11/366959 was filed with the patent office on 2006-09-14 for thermoplastic pallet for transporting food goods.
Invention is credited to Ronald P. Brochu, Kurt J. Kruger, Roy E. JR. Moore.
Application Number | 20060201402 11/366959 |
Document ID | / |
Family ID | 36941819 |
Filed Date | 2006-09-14 |
United States Patent
Application |
20060201402 |
Kind Code |
A1 |
Moore; Roy E. JR. ; et
al. |
September 14, 2006 |
Thermoplastic pallet for transporting food goods
Abstract
A plastic pallet, for use with fork lift devices and which meets
requirements associated with food handling, has a thermoplastic
deck made of two sheets which are spaced part by rigid plastic
foam. There are steel beams running in an x-pattern within the foam
of the deck. The deck sheets each have a multiplicity of relatively
large truncated conical depressions. Holes in the centers of the
depressions provide water and air passageways through the deck. The
deck sheets are welded together at the locations of the depressions
and at their outer edges. The base rails are reinforced by steel
beams which are sealed within.
Inventors: |
Moore; Roy E. JR.;
(Killingworth, CT) ; Brochu; Ronald P.; (Richmond,
KY) ; Kruger; Kurt J.; (Hamden, CT) |
Correspondence
Address: |
THE LAW OFFICES OF STEVEN MCHUGH, LLC
46 WASHINGTON STREET
MIDDLETOWN
CT
06457
US
|
Family ID: |
36941819 |
Appl. No.: |
11/366959 |
Filed: |
March 1, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60657379 |
Mar 1, 2005 |
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Current U.S.
Class: |
108/57.25 |
Current CPC
Class: |
B65D 2519/00139
20130101; B65D 2519/00318 20130101; B65D 2519/00442 20130101; B65D
2519/00104 20130101; B65D 2519/00149 20130101; B65D 2519/00373
20130101; B65D 2519/00557 20130101; B65D 19/0038 20130101; B65D
2519/00363 20130101; B65D 2519/008 20130101; B65D 2519/00129
20130101; B65D 2519/00308 20130101; B65D 2519/00069 20130101; B65D
2519/00437 20130101; B65D 2519/00273 20130101; B65D 2519/00467
20130101; B65D 2519/00562 20130101; B65D 2519/00447 20130101; B65D
2519/00288 20130101; B65D 2519/00034 20130101; B65D 19/0012
20130101; B65D 2519/00293 20130101; B65D 2519/00333 20130101 |
Class at
Publication: |
108/057.25 |
International
Class: |
B65D 19/38 20060101
B65D019/38 |
Claims
1. In a pallet for transporting goods, of the type having a base, a
multiplicity of spaced apart columns extending upwardly from the
base, and a top mounted on the columns which top comprises a
rectangular deck, the improvement which comprises: a deck
comprising a top sheet having a substantially planar upper surface,
for receiving goods placed on the deck; a bottom sheet, spaced
apart from and substantially parallel to the first sheet; and,
rigid plastic foam with the space between the sheets; wherein, at
least one of said sheets has a multiplicity of spaced apart
truncated conical depressions; wherein the sheets are attached to
each other at their edges and at the locations of said truncated
conical depressions.
2. The pallet of claim 1 wherein both the top and bottom sheets
have a multiplicity of spaced apart truncated conical depressions
arranged mating patterns; and, wherein the bottoms of the top sheet
depressions are attached to the bottoms of the bottom sheet
depressions.
3. The pallet of claim 1 wherein each depression has a flat
bottom.
4. The pallet of claim 2 wherein each depression has a flat
bottom.
5. The pallet of claim 3 wherein the deck has a multiplicity of
holes located in the bottoms of said depressions, for passage of
water or air through the deck.
6. The pallet of claim 1 further comprising at least two metal
beams positioned within said rigid plastic foam, each beam running
from a corner of the deck to a diagonally opposed corner, wherein
the beams form an x-pattern in the plane of the deck.
7. The pallet of claim 6 wherein the depressions are arranged in
four equilateral triangle shape arrays, with the base of each
triangle running parallel to, and centered along, one of the edges
of pallet.
8. The pallet of claim 1 wherein the top of the pallet comprises a
plastic frame which forms the periphery of the top; and wherein the
outer edge of the deck is attached to the frame and inset from the
outer edge of the top.
9. The pallet of claim 6 which further comprises: metal beams
within the base.
10. The pallet of claim 1 wherein the top comprises an injection
molded frame which forms the periphery of the top; wherein said
sheets are comprised of two thermoformed sheets welded to each
other and to the frame.
11. The pallet of claim 1 wherein the top comprises an injection
molded frame which forms the periphery of the top; wherein said
bottom sheet is injection molded and integral with the frame; and
wherein said top sheet is a thermoformed sheet.
12. The pallet of claim 1 wherein said truncated conical
depressions are have circular cross sections.
13. The pallet of claim 5 wherein a portion of said depressions
have oblong shapes, for enabling manual grasping of the pallet.
14. The pallet of claim 1 wherein the top, columns and base are is
predominately made of a high density polyethylene or polypropylene;
and, wherein said rigid foam is polyurethane.
15. A pallet for transporting goods, comprising: a base, comprised
of outer rails running in a rectangular pattern and cross rails
connecting the centers of opposing side outer rails; metal beams
within the rails of the base; eight peripheral columns and one
center column extending upwardly from the base; a rectangular top
mounted on the peripheral columns, for receiving goods, the top
comprising a frame and a rectangular deck, wherein the periphery of
the deck is attached to the frame, and the center of the deck is
attached to said center column; wherein the deck comprises: a top
sheet having a substantially planar upper surface, for receiving
goods placed on the pallet, and a multiplicity of spaced apart
truncated conical depressions; a bottom sheet, spaced apart from
and substantially parallel to the first sheet; and, rigid plastic
foam with the space between the sheets; wherein the sheets are
joined together along their outer edges and at the locations of
each of said truncated conical depressions; and, wherein the deck
has a multiplicity of holes located within the bottoms of said top
sheet depressions, for passage of water or air through the
deck.
16. The pallet of claim 15 wherein the bottom sheet has a
multiplicity of spaced apart depressions; wherein said depressions
of each sheet have flat bottoms with center holes; and wherein the
depressions are connected to each other at their flat bottoms.
17. The pallet of claim 14 wherein a portion of said depressions
have oblong shapes, for enabling manual grasping of the pallet,
said oblong depressions located proximate the corners and center of
the pallet
18. The pallet of claim 15 having the configuration of a GMA pallet
with a top which is 40 inches by 48 inches in rectangular
dimension; and wherein there is at least one depression for every
25 square inches of deck surface.
19. The pallet of claim 15 having the configuration of a GMA pallet
with a top which is 40 inches by 48 inches in rectangular
dimension, wherein the diameter of each depression at the top
surface of the upper sheet is greater than three percent of the
dimension of any side of the pallet.
20. The method of making a pallet for transporting goods, wherein
the pallet comprises a base, a multiplicity of spaced apart columns
extending upwardly from the base, and a top mounted on the columns
which top comprises a frame and a rectangular deck attached to the
frame; wherein the deck comprises a top sheet having a
substantially planar upper surface, for receiving goods placed on
the deck; a bottom sheet, spaced apart from and substantially
parallel to the first sheet; and, rigid plastic structural foam
with the space between the sheets, connecting sheets; wherein, both
sheets have a multiplicity of spaced apart truncated conical
depressions; and, wherein the sheets are attached to each other at
their edges and at the locations of said truncated conical
depressions; which method comprises: a) injection molding plastic
to form a body which comprises said frame, said bottom sheet of
said deck with said multiplicity of depressions according to a
first pattern; b) thermoforming plastic sheet to form a top sheet
of the deck, the deck having a multiplicity of spaced part
truncated conical depressions in a pattern which mirrors said first
pattern; c) welding the top sheet to the body, so the periphery of
the frame is attached to the frame and so the bottoms of the
depressions are attached to the bottoms of the depressions of the
bottom sheet; wherein the sheets are spaced apart from each other
except where they are welded; and, d) injecting plastic material
into the space between the sheets to form a rigid foam their, where
the form is bonded to the sheet surfaces.
21. The method of claim 20 which further comprises the steps of
placing metal beams upon the first sheet before carrying out step
(c), so the beams are included within the foam which is formed.
Description
[0001] This application claims benefit of provisional patent
application Ser. No. 10/657,379, filed on Mar. 1, 2005.
TECHNICAL FIELD
[0002] The present invention relates to molded plastic pallets, of
the type used with forklift devices for transporting goods.
BACKGROUND
[0003] Commercial plastic pallets for use with fork lift devices
have often been made of familiar thermoplastics, which would appear
to provide them with a number of potential advantages over wood
pallets, including better durability and moisture resistance. A
common plastic pallet, which can be made in the present invention,
is often referred to in the U.S. as a GMA pallet. It has a 40
inch.times.48 inch rectangular base, eight columns running up from
the periphery of the base, and a rectangular deck. A comparable
European pallet is a 1000 mm by 1200 mm pallet. The Grocery
Manufacturers of America (GMA), Washington, D.C., U.S., in
conjunction with other organizations, has published a document
entitled "Recommendations on the Grocery Industry Pallet System"
(1992). From that and other references, for a GMA pallet to gain
acceptance by large commercial users in the U.S. it must have
certain dimensions and meet strength and durability requirements.
"Recommended Test Protocol for Plastic Pallet, Version 3" (1998)
published by Virginia Tech, Blacksburg, Virginia, U.S., sets forth
mechanical performance and test requirements for pallets including
a warehouse racking test. ISO 8611:1991 and proposed Underwriters
Laboratories (UL) Standard 2417 specify similar mechanical
performance and testing standards. UL Standard 2335 specifies fire
tests and performance for warehouse pallets made of plastic. The
disclosures of the foregoing documents are hereby incorporated by
reference. Commercial purchasers may have their own standards which
can be somewhat more demanding.
[0004] When pallets are uses in connection with food goods, they
often must meet the requirements of the U.S. Food and Drug
Administration, such as those at Section 7 of American National
Standard/NSF International Standard No. 2 (ANSI/NSF 2-1996),
hereafter called NSF requirements or NSF standards. Among the
requirements are that a pallet ought not to have small cavities or
crevices which could harbor microorganisms and insects, or which
are hard to clean. There are also limitations on the kinds of
exposed metals which can be used. Pallets for transporting food
goods also often have to sustain frequent sharp temperature
changes.
[0005] In pallets not specifically intended for use with food
goods, it is quite common to have ribbed and perforated decks,
since that helps minimize the weight and cost of plastic in the
pallet. However, although the decks embody good plastic structural
design, they are not helpful in meeting NSF requirements. On the
other hand, if the deck is a smooth continuous surface, then the
resultant lack of means for draining and air circulation is
disadvantageous. So, there are conflicting aims which the present
invention seeks to resolve.
[0006] Another barrier to the success of many plastic pallets has
been an inability to also meet the demanding mechanical strength
requirements of GMA pallets. One way of achieving strength has been
to incorporated steel beams within the tops and bases of plastic
pallets, See U.S. Pat. No. 6,705,237 of Moore et al., No. 6,955,128
of Apps et al., and No. 5,868,080 of Wyler et al. However, if such
beams are exposed, or if there are narrow crevices in their
vicinity, then the NSF requirements may not be met. Other problems
associated with the use of steel beams can be thermal fatigue which
arises from differential thermal expansion, and unacceptable
increases in pallet cost or weight.
[0007] Thus, there is a need for continuing improvements in pallets
used for carrying food goods, to meet the various technical
requirements. Any improved pallet must also be economic to
manufacture and low in weight.
SUMMARY
[0008] An object of the invention is to provide a pallet with
features which meet both the GMA and NSF requirements, and which
are economic to make. A further object is to provide a plastic
pallet for use in food service, which pallet is strong and light
and which is free of a multiplicity of recesses and crevices,
especially with respect to the deck.
[0009] In accord with the invention, a pallet has a rectangular top
which comprises a deck made of two spaced part sheets, at least one
of which has a multiplicity of spaced apart truncated conical
depressions. The sheets are attached to each other at the locations
of the depressions and at their edges. The space between the sheets
is filled with rigid plastic structural foam. The foam enables the
top sheet to resist impact loads, and provides bending strength to
the deck and pallet as a whole. Preferably, metal beams run
diagonally from corner to corner in an x-pattern between the sheets
and within the foam material of the deck. The pallet preferably has
a frame which forms the periphery of the top and the deck attached
to the frame, so it is inset from the outer edge of the top.
[0010] In an embodiment of the invention, mating flat bottom
circular conical depressions are present in both the top sheet and
the bottom sheet. The flat bottoms of the mating depressions are
welded to each other at the approximate center plane of the deck;
and there is a hole for passage of water or air through the deck at
the bottom of each depression. In alternative embodiments, the
depressions may be present in one sheet only and the other sheet
may be flat; and, some of the depressions have an oblong shape so
they are suited for manual grasping of the pallet. The depressions
are large, compared to features of decks in the past. The
depressions are arranged in four spaced apart arrays having the
approximate shape of equilateral triangles; thus, there are regions
between the arrays where the x-pattern beams run.
[0011] In an embodiment of the invention, the pallet is shaped like
a GMA 40.times.48 pallet. The pallet has a base, columns extending
upwardly from the base, and a top mounted on the columns, for
receiving goods. The base is comprised of rails arranged in a
rectangular pattern; and the deck has aforesaid x-pattern of beams.
The diameter of each depression is at least 3 percent of the length
or width of the deck, and there is at least one depression for
every 25 square inches of deck area. The pallet is preferably made
of thermoplastic, such as high density polyethylene or
polypropylene, the rigid foam is made of polyurethane and the beams
are made of steel.
[0012] In one mode of constructing the pallet, the deck is
fabricated separately from the rest of the pallet by making and
joining together two thermoformed sheets. When joined together,
with placement of the metal beams, if desired, foam plastic is
formed between the sheets. Then the deck is welded to an injection
molded top or frame of the pallet. In another mode of constructing
the pallet, a pallet body is made by injection molded of plastic;
the bottom sheet has depressions and is formed as an integral part
of the frame of the body, which provides various advantages
including more uniform thickness sheet and fewer potential
crevices. The top sheet is thermoformed and attached to the bottom
sheet edges and depressions, after placement of the beams. In both
embodiments, the rigid foam is formed by injection of material into
the space.
[0013] The metal parts are sealed within the plastic of the pallet
and thus are protected from contact with food goods and corrosion.
The combination of a two-sheet deck having rigid plastic foam,
metal beams within the deck interior, and metal beams in base,
provides good strength to a pallet. The large depressions in the
surfaces of the deck are easily cleanable; and the simplicity of
design means there is an absence of hard to clean crevices,
cavities and passageways. The holes through the deck at the
locations of the depressions provide good drainage and air
circulation.
[0014] The foregoing and other objects, features and advantages of
the present invention will become more apparent from the following
description of preferred embodiments and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is an isometric view of a GMA pallet with a plastic
deck which has a multiplicity of shallow depressions and hand
holes.
[0016] FIG. 2 shows a corner of the pallet of FIG. 1.
[0017] FIG. 3 is a vertical cross section through the outer part of
the pallet of FIG. 1 and FIG. 2, showing how the deck is comprised
of two thermoformed sheets and structural foam.
[0018] FIG. 4 is an exploded view of the pallet shown in FIG.
1.
[0019] FIG. 5A-5D are fragmentary vertical cross sections of pallet
decks, to show alternative embodiments of conical depressions.
[0020] FIG. 6 is an exploded view of an alternative embodiment of
pallet, where the deck bottom sheet is integral with an injection
molded body.
[0021] FIG. 7 is like FIG. 3, showing a partial vertical cross
section through the assembled pallet of FIG. 6.
[0022] FIG. 8 is similar to FIG. 2, showing an alternative
embodiment of pallet body.
DESCRIPTION
[0023] The invention is mostly described in terms of a pallet
having the dimensions of a 40 inch by 48 inch by 5 to 6 inch high
GMA pallet. The essential design of the pallet, except for the top,
is in accord with the pallet described in U.S. Pat. No. 6,705,237
of Moore, the disclosure of which is hereby incorporated by
reference. The invention will be useful with other pallets which
have different kinds of bases and different shapes. Parts of the
pallet are injection molded, and may be made with gas assistance.
See U.S. Pat. No. 5,401,459. The several parts or subassemblies of
the pallet may be joined as an assembly by known thermoplastic
fabrication methods, for example, by mechanical means, by hot plate
welding, vibratory welding, or ultrasonic welding. See, for
instance, U.S. Pat. Nos. 6,250,234 and 6,283,044. The thermoplastic
parts of the pallet may be made of commercial grade polypropylene,
high density polyethylene (HDPE) or other polyolefin. The examples
herein are described in terms of HDPE. Other plastics, including
thermoset plastics and engineered plastics, may. Since the pallets
and parts comprise metal reinforcing beams they may be
characterized as predominately plastic.
[0024] Pallet 20 is shown in FIGS. 1, 2 and 3 and in the exploded
view of FIG. 4. Pallet 20 comprises a base 30, a top 90, and
columns 28, 29 which extend upwardly from the base to support the
top. Top 90 comprises deck 22 and frame 24. The deck comprises two
thermoformed HDPE plastic sheets 44, 46 which are attached to each
other, to the frame. The space between the deck sheets is filled
with rigid polyurethane foam 36. The manner in which the parts of
the pallet are manufactured is essential to pallet function. In
particular, the elements are made variously, e.g., by injection
molding, thermoforming, and foaming in place: and, they are
structurally interconnected, as will be described.
[0025] Frame 24 forms the periphery of the top of the pallet. By
definition the frame is an open rectangle. Deck 22 spans the
interior opening of the frame, and it and whatever portion of the
frame is exposed comprise the pallet surface which receives goods
for transporting. Deck 22 is comprised of two thermoformed plastic
sheets 44, 46, which are joined to each other by welding of the
sheets and by adhesion of rigid thermoset foam. Deck 22 has a
multiplicity of truncated circular conical depressions 42 in its
essentially planar horizontal surface; and preferably, it also has
a multiplicity of elongated slot openings 74 proximate the corners
and center of the pallet, to enable a worker to manually grasp the
pallet.
[0026] First, the non-deck elements are described in detail. The
base is comprised of outer rails 31 which form a rectangle. The
opposing side centers of the outer rails are connected by cross
rails 33. Eight columns 28 extend upwardly from the base; and top
90 is mounted on the columns. There are two openings 34 on each
side of the pallet for fork entry; they are nominally 3.2 inches
high and 12 inches or more wide. Center column 29 extends upwardly
from the intersection of the two cross rails 33. Deck 22 is
attached to both the frame 24 of the top and to the center
column.
[0027] Rectangular cross section steel beams 50 run within the HDPE
outer rails 31 of the base. Similar steel beams 45 run within the
thermoplastic cross rails 33. The beams provide reinforcement to
the base and pallet as a whole, in cooperation with the structural
parts of the top. The combination of features makes the pallet
suited for use in storing goods on open beam warehouse racks and in
meeting certain other GMA pallet strength requirements. Beams are
preferably shaped and incorporated within the base in accord with
the teachings of U.S. Pat. No. 6,705,237 of Moore et al. See also
the teachings of U.S. Pat. No. 6,955,128 of Apps et al. and U.S.
Pat. No. 5,868,080 of Wyler et al. The disclosures of the foregoing
patents are hereby incorporated by reference. The beams preferably
are light steel box beams having a multiplicity of lightening
perforations along their vertical edges. They are formed and shaped
generally as described in U.S. Pat. No. 6,705,237. At final
assembly, spaces within the rails which are in proximity of the
beams, and the interiors of the beams themselves, are preferably
filled with rigid foam so the beams are well captured within the
molded plastic parts. See the Moore patent.
[0028] Beams 50, 45 are not attached, as by welding, to each other
at their intersections, although they may be in other embodiments.
Preferably, the beams are constructed and positioned so that when
the plastic of the rails softens as a result of the heat from a
fire, the beams will be released their attachments, thus enabling
the pallet to collapse due to the weight of itself and goods, which
can help mitigate the rate of heat release. See the commonly
assigned U.S. patent application entitled "Fire collapsible beamed
pallet," bearing Atty. No. EPC-2443 filed on Feb. 21, 2006 herewith
by R. Moore et al., the disclosure of which is hereby incorporated
by reference.
[0029] Pallet 20 is preferably constructed by injection molding the
body 70 so it comprises the frame, the hollow columns and major
portions of the base rails. When the pallet is assembled, metal
beams are inserted into lengthwise open cavities that are provided
on the underside of the molded base rails of body. Then, cover
plate 54 is the welded to the bottom of the body, to seal the
cavities and the beams within the pallet, protecting them from
contact with the external environment. See FIG. 3 and FIG. 4.
[0030] With further reference to FIGS. 3 and 4, deck 22 is
comprised of two sheets 46, 48, each having spaced apart conical
depressions. The sheets are attached to each other by welding at
the depression locations and at their peripheries. They are also
structurally attached to each other by the rigid foam which fills
the interior space of the deck. Depressions are created in the deck
sheets prior to assembly by thermoforming of flat sheet of about
0.06 inch thick HDPE. That is, the sheets are heat softened and
shaped within the molds of a dual wall thermoforming machine.
Alternative known means of forming flat sheet may be used.
[0031] In the invention, at least one of the deck sheets has a
multiplicity of spaced apart conical depressions. As shown in FIG.
2, preferably both the top sheet 46 and bottom sheet 48 have
depressions, respectively depressions 42 and depressions 44. The
preferred depressions are truncated cones which have flat bottoms
77, 79. To assemble pallet 20, deck 22 is first fabricated by
placing formed bottom sheet 48 onto a fixture. Then, metal beams 53
are placed on the sheet, so that each beam from the vicinity of
diagonally opposed corners. The beams have slight bends at their
center points to enable crossing each other. Then the top sheet is
placed over the first sheet and welded to it, to fuse the mated
flat bottoms of the depressions 42, 44 and the outer edges. Then,
rigid polyurethane foam 36 is formed by chemical reaction within
the space between the sheets. The foam, described in more detail
below, provides support to the sheets, so the top sheet especially
has good resistance to concentrated downward impact loads. The foam
also provides a structural load-bearing connection between the
sheets.
[0032] After the deck assembly has been made, the flange 49 of the
deck assembly is welded to ledge 80 of frame 24. The portion of the
frame which defines ledge 80 preferably comprises a multiplicity of
open cavities, bounded by transverse ribs. See FIG. 4. When the
deck flange is welded to the ledge of the frame, the cavities are
converted into closed cells. As needed, sealant may be applied to
the joints between the flange and the frame, both around the
periphery of the deck, and at the joint 57, shown in FIG. 3, which
is between the underside of the deck and the frame inner edge.
Known sealants of surface weld material may be used. See also the
commonly owned related U.S. patent application, entitled "Plastic
pallet with sealed deck to frame joint," bearing Atty. No. 2442,
filed on Feb. 21, 2006 by R. Moore, the disclosure of which is
hereby incorporated by reference. In an alternate mode of
fabrication, the bottom sheet may be placed within the frame of the
pallet, rather than in a fixture, before placement of the beams,
adding the top sheet, etc.
[0033] Beams 53 of the deck 22 run in an x-pattern as shown in FIG.
2 and FIG. 4. The x-pattern deck beams cooperate with the other
parts of the deck, with the frame 24, with the columns and with the
rectangular pattern of rails and beams of the base, to provide good
strength to the overall pallet, particularly with respect to
racking. Optionally, additional beams may be added to the top of
the pallet, to run around the periphery of the deck or within the
frame. The deck beams generally have the same kind of construction
as the beams of the base rails.
[0034] While the deck is preferably set within the frame that forms
the periphery of the top of the pallet, in an alternate embodiment,
the deck may extend to the outer edge of the top or frame.
Conversely, it may be desirable to inset the deck from the edge by
a greater amount than shown in the Figures, Lengthwise impact
absorbers may be placed in proximity to the outer edges of the
frame, particularly within the bridge parts of the frame which span
the fork lift openings 34 of the pallet. The object of such
alternative is to reduce the adverse effect on the deck of
horizontal impact blows on the top of the pallet. See the commonly
owned patent application entitled "Plastic pallet having impact
resisting plastic top" bearing Atty. No. EPC-2437 and filed on Feb.
21, 2006 by D. Swistak et al., the disclosure of which is hereby
incorporated by reference.
[0035] The top surface of deck 22 has a multiplicity of
spaced-apart truncated conical depressions 42. They are large
compared to the deck perforations which characterize the prior art.
For example, the diameter of the preferred embodiment 1.8 inch
diameter circular depression is greater than 3 percent of the
length or width of the top. The two sheets of the deck are welded
together at each depression location. As shown in FIG. 2, each
depression preferably has a flat bottom 77, 79. The depth of each
depression is sufficient to extend approximately half way across
the space between the parallel substantially planar surfaces of the
two sheets. In the assembled deck the bottom of each depression
preferably has an associated hole 55, so that in the assembled deck
there is means for draining of liquid and circulation of air
through the deck. Holes 55 may be made in the deck sheets before or
after they are joined together, by punching, drilling, and the
like. Alternatively, decks may be made with no through holes.
[0036] In an exemplary 40 inch.times.48 inch GMA pallet like that
shown in FIGS. 1 and 2 the edges of the rectangular deck are inset
about 2 inches from the frame outer edges. Thus the deck is about
36 inches.times.44 inches in dimension. An exemplary deck comprises
nominally 0.06 inch thick HDPE sheet and is about one inch in total
thickness. The rectangular cross section hollow metal beams 53 of
the deck are made of 0.035 inch thick cold rolled AISI 1018 steel,
with a height of about 0.88 inches high and a width of about 1.3
inches.
[0037] In the exemplary GMA pallet configuration, adjacent
depressions 42 are spaced apart center-to-center by nominally 3.5
inches and have the following nominal dimensions and features: The
major or base diameter (at the deck surface) is about 1.8 inches;
the minor or apex diameter (at the bottom of the depression and
center plane of the deck) is about 1.3 inches. The depth of each
depression is nominally 0.5 inches. The sidewalls slope at about 25
degrees to the vertical axis of the conical shape. The diameter of
each hole 55 is about 0.75 inches. In an exemplary GMA pallet there
are a total of 72 depressions, counting the hand-holes. Thus, there
is one depression for each 20-25 square inches of deck area.
[0038] In an exemplary pallet deck which includes x-pattern beams,
the depressions are arranged in four essentially equilateral
triangular shape arrays. Each array has a triangle base running
along and centered on an edge, as the pallet is viewed looking
downwardly. See FIG. 1. The triangular groups are separated from
each other by areas which lack depressions, to thereby provide
locations in the deck where beams 53 run.
[0039] FIG. 5A through 5D are fragmentary views of decks, to show
alternative embodiments of depressions. In these other Figures,
elements which are analogous to those previously discussed have the
same number with a suffix. In FIG. 5A, depressions 42B are only
present in top sheet 46B; the bottom sheet 48B is flat. The bottom
of each depression 42B comprises a flat 77B, which facilitates
welding of sheet 46B to sheet 48B. FIG. 5B shows a deck having
sheets with opposing depressions 42D and 44D, which had been formed
as open ended truncated cones without any flat bottoms. When the
sheets 46D, 48D were welded, the open conical ends of the
depressions mated and formed welded joint 76. In FIG. 5C,
depression 42E of sheet 46E is also made as an open truncated cone.
Upon assembly, the small end of the cone passed through a
previously made hole in bottom sheet 48E. The end of the cone was
then swaged over, or headed, to form lip 78. The lip is then welded
to the bottom sheet, to avoid any crevice. FIG. 5D shows a deck
where the bottom sheet 48F only has depressions 44F. The
depressions 44F extend to the elevation flat top sheet 46F. When
the sheets 46F, 48F were welded a joint 52 was formed where the end
of the depression 44F touches the underside of the top sheet. The
construction shown in FIG. 5D is preferably used to form the hand
holes 74. An exemplary hand hole is at least about one inch wide
and at least 4 to 5 inches long, sufficient in dimension for a
worker's fingers or hand to be inserted.
[0040] Other than when the depressions form hand holes, the
depressions shown in FIG. 3 are preferred, because the array of
mating flat bottoms along the center plane of the deck and the
stubbiness of each depression provide better strength and easier
fabricability. Thus, a preferred embodiment comprises the hand
holes having the configuration of FIG. 5D and other depressions
having the configuration of FIG. 3.
[0041] While the depressions have been described in terms of
equilateral circular cones, in the generality of the invention the
horizontal cross section of the depressions may be other than
round, for instance, it may be rectangular or non-round. And the
depressions may be asymmetric with respect to a vertical axis
running through a hole or the center of the depression. When a
reference is made herein to a diameter associated with a
depression, for any non-circular depression that shall mean the
diameter of a circular depression having the same area. The sheets
of the deck may have other texturing in addition to any
depressions, for instance, corrugations; and, the upper surface of
the top sheet may have an anti-slip or other surface finish
treatment.
[0042] Obviously, when the depressions in one sheet are intended
for mating with depressions in the other sheet, then the pattern or
arrangement of depressions on one sheet has to mirror the pattern
or arrangement on the other sheet. The depression pattern, which
encompasses the number, sizing, locations, spacing of the
depressions, may be varied within the invention. There are several
considerations in the choice of depression parameters. They
include: The depressions and associated holes ought to be
sufficiently large, so that they do not become easily plugged, and
so that they can be readily cleaned should debris accumulate
within. A multiplicity of depressions is desirable because they
strengthen the sheets of the deck as does any texturing. But if the
depressions are either too large or too many in number, the result
may be insufficient planar surface for supporting certain kinds of
goods; and, there may be an unacceptable diminution in section
modulus and resultant rigidity and strength of the deck. If there
are too few depressions, then the desired draining or venting can
suffer. Engineering analysis and design choice can be used to trade
off the different parameters relating to depressions, according to
the particular needs of the pallet user.
[0043] Preferably, within the limitations of the foregoing factors,
when depressions have through holes, some will be preferentially
located so that any fire sprinkler water which falls onto the deck
can fall onto the rails 33, 31 of the base, to help suppress
burning there. See related U.S. patent application entitled
"Sprinkler friendly pallet" of R. Brochu, bearing Atty. No.
EPC-2440, filed on Feb. 21, 2006, the disclosure of which is hereby
incorporated by reference.
[0044] Particular structural foams are desirable for filling the
spaces between the sheets of the deck. A preferred material is a
polyurethane foam having a density of 2 to 4 pounds per cubic foot;
for example, such as Elastopor polyurethane Product No. P12570R
available from BASF Corporation, Wyandotte, Mich., U.S. The foam is
a two-component system consisting of an isoncyanate component and a
polyol blend component and is formed in place by chemical reaction.
As known in the art, the interior surfaces of the top and bottom
sheets, which are in contact with the foam, are preferably
pre-treated by flame or electric charge devices, so there is a good
bond between the sheet and the foam.
[0045] At final assembly, the same rigid foam is also placed within
the hollows 72 of the columns and in any spaces in the base rails,
including the interiors of the beams. When the thermoset
polyurethane structural foam is so placed, it can provide the
pallet with additional strength and can have a favorable effect on
fire test performance, such as that measured by UL 2335. The foam
material constituents may be deposited into the diverse cavities of
the pallet by means of access ports not shown in the Figures. After
filling, the ports are preferably sealed with plugs or sealant, or
by means or spin-welded plastic nubs, as described in a related
U.S. patent application entitled "Pallets having multi-purpose
nubs" of D. Swistak et al., bearing Atty. No. EPC-2444, filed on
Feb. 21, 2006. The disclosures of both the foregoing patents are
hereby incorporated by reference.
[0046] The preferred rigid foam by design has relatively low shear
strength compared to the other plastic parts of the pallet. Thus,
during cool down after fabrication, and during thermal cycling in
use, a beam may differentially thermally expand lengthwise relative
to the foam and rest of the pallet, by shearing the foam which
unavoidably passes through the beam perforations. See the related
U.S. patent application entitled "Thermoplastic pallet having
thermoset foam-filled or foam-coated structural parts" of R. Moore,
bearing Atty. No. EPC-2140, filed on even date herewith.
[0047] The HDPE or thermoplastic material of the pallet may
comprise known commercial flame retardant, depending on
requirements related need to be met, such as the fire test
requirements of Underwriters Laboratories (UL) Standard 2335.
Likewise, the foam may incorporate a flame retardant.
[0048] FIG. 6 and FIG. 7 show an alternate embodiment pallet 20A.
The pallet has a deck 22A and other features which are essentially
like those which have been described in connection with pallet 20.
The primary difference between pallet 20A and pallet 20 is in the
way deck is constructed. In pallet 20A only the top sheet is
thermoformed and the bottom sheet 44A is injection molded as an
integral part of pallet body 70A. This provides certain advantages.
Among them is the elimination of the joint 57 where the underside
of the deck and frame meet. See FIG. 2. Another is that the sheet
can be made more uniform, compared to the localized thinning which
characterizes thermoformed sheets. Further, the bottom sheet may be
provided with more pronounced and detailed surface features, for
instance, for locating the beams. Normally, injection molding is
not a very practical way of fabricating plastic sheets, owing to
feeding difficulties. However, in pallet 20A, the frame and
multiplicity of columns 28A, 29A which are part of the body
facilitate feeding of the bottom sheet. Bottom sheet 44A comprises
the both circular depressions 44A and oblong depressions 79A which
provide the hand holes. When pallet 20A is assembled, beams 53A are
put in place on the sheet 46A and the thermoformed top sheet 46A is
welded to the ledge 80A of frame 24A and at any location where
there is a depression.
[0049] FIG. 8 is like FIG. 7 and shows a portion of pallet 20C.
Pallet 20C illustrates an alternative injection molded body
construction. Body 70C comprises open top columns 28C and base 30C.
The top 90C comprises the injection molded frame 24C. The top is
welded to the open tops of the outer columns 28C. The deck is not
shown in the Figure, but will be attached to the ledge 80C.
Alternately, the bottom sheet of the deck may be as described in
connection with pallet 20A, that is integral with the frame
24C.
[0050] While the invention has been described in terms of a pallet
with a base, the invention may be used with pallets which have
downwardly extending columns only, and on base connection the
bottoms of the columns, which in such instance may be called feet.
While it is preferred to have the above-described reinforcing beam
patterns, e.g., the x-pattern in the deck and rectangular pattern
in the base, alternative beam patterns may be used. A pallet may
have fewer or no beams, although strength will be probably be
inadequate for GMA pallet purposes. Fusion welding is the only
presently known economic way of continuously joining mating parts.
However, the term welding as used herein shall encompass the use of
adhesives and chemical bonding, should strong and economic products
become commercially available.
[0051] The advantages of the invention have been described in the
Summary and above. Although this invention has been shown and
described with respect to a preferred embodiment, it will be
understood by those skilled in this art that various changes in
form and detail thereof may be made without departing from the
spirit and scope of the claimed invention.
* * * * *