U.S. patent application number 11/358362 was filed with the patent office on 2007-02-01 for low profile plastic pallet.
Invention is credited to Ronald P. Brochu, Roy E. JR. Moore, Daniel J. Swistak.
Application Number | 20070022919 11/358362 |
Document ID | / |
Family ID | 36917174 |
Filed Date | 2007-02-01 |
United States Patent
Application |
20070022919 |
Kind Code |
A1 |
Moore; Roy E. JR. ; et
al. |
February 1, 2007 |
Low profile plastic pallet
Abstract
A predominately thermoplastic pallet, for use with a fork lift
device, is provided and includes a rectangular base including rails
having metal reinforcing beams, eight spaced apart outer columns
extending upwardly from the outer rails and one center column
extending upwardly from the center of the base. The pallet also
includes a top including a rectangular thermoplastic frame and a
corrugated sheet metal deck, wherein the frame is attached, to the
tops of the outer columns and wherein the deck is inset from the
outer edge of the frame and wherein the pallet has dimensions and
properties which include outside dimensions of about 40 inches by
about 48 inches, two forklift device openings on each side of the
pallet, each of which are at least 3.1 inches high and 12 inches
wide and a pallet height or 5.56 inches or less.
Inventors: |
Moore; Roy E. JR.;
(Killingworth, CT) ; Brochu; Ronald P.; (Richmond,
KY) ; Swistak; Daniel J.; (New Market, NH) |
Correspondence
Address: |
THE LAW OFFICES OF STEVEN MCHUGH, LLC
46 WASHINGTON STREET
MIDDLETOWN
CT
06457
US
|
Family ID: |
36917174 |
Appl. No.: |
11/358362 |
Filed: |
February 21, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60654760 |
Feb 18, 2005 |
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60654761 |
Feb 18, 2005 |
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60654765 |
Feb 18, 2005 |
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60654768 |
Feb 18, 2005 |
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Current U.S.
Class: |
108/57.25 |
Current CPC
Class: |
B65D 2519/00129
20130101; B65D 2519/00417 20130101; B65D 2519/00288 20130101; B65D
2519/0086 20130101; B65D 2519/00104 20130101; B65D 19/0063
20130101; B65D 2519/00557 20130101; B65D 2519/00437 20130101; B65D
2519/00447 20130101; B65D 2519/00293 20130101; B65D 2519/00069
20130101; B65D 2519/00442 20130101; B65D 2519/00373 20130101; B65D
2519/00825 20130101; B65D 2519/00572 20130101; B65D 2519/00333
20130101; B65D 2519/00393 20130101; B65D 2519/00273 20130101; B65D
19/0081 20130101; B65D 2519/00318 20130101; B65D 2519/00323
20130101; B65D 2519/00363 20130101; B65D 2519/00388 20130101; B65D
2519/00407 20130101; B65D 2519/00562 20130101; B65D 2519/00034
20130101; B65D 19/0059 20130101; B65D 2519/00024 20130101; B65D
2519/00044 20130101 |
Class at
Publication: |
108/057.25 |
International
Class: |
B65D 19/38 20060101
B65D019/38 |
Claims
1. A predominately thermoplastic pallet, for use with a fork lift
device, which comprises: a rectangular base comprised of rails
having metal reinforcing beams; eight spaced apart outer columns
extending upwardly from the outer rails and one center column
extending upwardly from the center of the base; a top comprised of
a rectangular thermoplastic frame and a corrugated sheet metal
deck; wherein the frame is attached to the tops of the outer
columns; wherein the deck is inset from the outer edge of the
frame; wherein the pallet has dimensions and properties which
include (a) outside dimensions of about 40 inches (1020 mm) by
about 48 inches (1220 mm), (b) two forklift device openings on each
side of the pallet, each of which are at least 3.1 inches (79 mm)
high and 12 inches (305 mm) wide; (c) a pallet height of 5.56
inches (141 mm) or less; (d) a weight of less than 55 pounds (25
kg) or less; and, (e) a racking creep strength such that, when the
pallet deck is subjected to a uniform load of 2800 pounds (1270 kg)
for a period of 720 hours at a temperature of 115.degree. F.
(46.degree. C.), while the pallet is supported along opposing 48
inch (1220 mm) sides by rack beams which are spaced apart 45 inches
(1145 mm), the center of the pallet deflects 0.8 inches (2 mm) or
less.
2. The pallet of claim 1 wherein the pallet height is about 5.4
inches (13.7 mm) or less.
3. The pallet of claim 2 wherein the pallet height is about 4.9
inches (12.4 mm) or less.
4. The pallet of claim 1 having a stacked pallet density property
which is greater than 2.2 pallets per vertical foot (7.2 pallets
per meter).
5. The pallet of claim 1 having a stacked pallet density property
which is greater than 2.3 pallets per vertical foot (7.54 pallets
per meter).
6. The pallet of claim 1 wherein the top deck is comprised of
corrugated aluminum sheet metal, and the base is comprised of steel
beams.
7. The pallet of claim 4 wherein the top deck is comprised of
corrugated aluminum sheet metal, and the base is comprised of steel
beams.
8. The pallet of claim 5 wherein the pallet is comprised of 30 to
45 percent metal by weight.
9. The pallet of claim 1 wherein the pallet has a fire test
property which meets Underwriters Laboratories fire test standard
UL 2335.
10. The pallet of claim 1 wherein the height of each entry opening
is at least 60 percent of the height of the pallet.
11. The pallet of claim 2, wherein the top is less than 15 percent
of the height of the pallet.
12. The pallet of claim 1, wherein said two openings are at least
12.5 inches wide.
13. The pallet of claim 1, wherein the weight of the pallet is less
than 51 pounds.
14. A GMA type pallet for use with a fork lift device which
comprises: a rectangular base comprised of outer rails arranged in
a rectangular pattern and cross rails connecting the opposing side
midpoints of the outer rails, the rails having steel reinforcing
beams; eight spaced apart outer columns extending upwardly from the
outer rails and one center column extending upwardly from the
center of the base; a 40 inch by 48 inch top, attached to the outer
columns; the top comprised of a thermoplastic rectangular frame, a
subframe and a corrugated sheet metal deck; wherein, the deck made
of aluminum alloy sheet and has a circumscribing flange and at
least three continuous corrugations running from one corner of the
deck to a diagonally opposed corner of the deck; wherein, the frame
forms the periphery of the top and comprises bridges which span the
spaces between the columns; wherein each bridge comprises a
multiplicity of vertical ribs which bound closed cells within the
bridge; wherein the deck flange is attached to the subframe;
wherein the edges of the deck are spaced apart at least 4 inches
from the exterior edges of the frame; wherein the pallet is
predominately comprised of a molded polyolefin selected from
polyurethane and polypropylene and combinations thereof; wherein
the metal parts weigh less than 40 percent of the weight of the
whole pallet; and wherein the pallet has (a) two forklift device
openings on each side of the pallet, bounded by the bridges and the
outer rails and adjacent outer columns, each opening having a
height of at least about 3.1 inches (79 mm) and a width of 12
inches (305 mm); (b) a height less not exceeding 5.5 inches (141
mm); and (c) a stacked pallet density property which is greater
than 2.2 pallets per vertical foot (7.2 pallets per meter).
15. The pallet of claim 14, having further properties which
comprise: (d) a racking creep strength such that, when the pallet
deck is subjected to a uniform load of 2800 pounds (1270 kg) for a
period of 720 hours at a temperature of 115.degree. F. (46.degree.
C.), while the pallet is supported along opposing 48 inch (1220 mm)
sides by rack beams which are spaced apart 45 inches (1145 mm), the
center of the pallet deflects 0.8 inches (2 mm) or less; and, (e) a
fire test performance which meets Underwriters Laboratories fire
test standard UL 2335.
16. The method of making a GMA type thermoplastic pallet, wherein
the pallet has a top mounted on columns extending upwardly from the
base, wherein the pallet has properties which include (a) a racking
creep strength such that, when the pallet deck is subjected to a
uniform load of 2800 pounds (1270 kg) for a period of 720 hours at
a temperature of 115.degree. F. (46.degree. C.), while the pallet
is supported along opposing 48 inch (1220 mm) sides by rack beams
which are spaced apart 45 inches (1145 mm), the center of the
pallet deflects 0.8 inches (2 mm) or less; and (b) a fire test
performance which meets Underwriters Laboratories fire test
standard UL 2335, which comprises: providing the pallet base with
steel reinforcing beams; providing the pallet with a top comprised
of a plastic frame and a corrugated sheet metal deck which is inset
from the outer edges of the frame and which has an area which is at
least 75 percent of the area of the top of the pallet; wherein the
corrugations of the deck comprise at least three of the
corrugations which run diagonally from comer to comer of the deck;
to thereby reduce the thermoplastic content of the deck to less
than 70 percent of the weight of the pallet.
Description
[0001] This application claims benefit of provisional patent
applications Ser. Nos. 60/654,760, 60/654,761, 60/654,765, and
60/654,768, all filed Feb. 18, 2005.
TECHNICAL FIELD
[0002] The present invention relates to plastic pallets,
particularly those used for transporting miscellaneous industrial
and commercial goods by means of forklift devices and the like.
BACKGROUND
[0003] Rectangular wood pallets have been long used with forklift
devices for transporting and storing common goods. They have been
attractive because of simplicity and low cost. However, wood
pallets are prone to damage during use, and constantly must be
replaced or discarded. They also are difficult to keep clean. In
recent years plastic pallets have been commercially available. They
would seem to offer a number of potential advantages over wood
pallets, including better durability, moisture resistance, and
other known advantages of a polymer material, compared to wood.
Plastic pallets have most often been made of familiar polyolefin
thermoplastics; some other polymers have been used, particularly
for fire-resistance. However, plastic pallets have not gained wide
acceptance, for a number or reasons, which can be stated briefly as
relating to a failure to satisfactorily meet all of a variety of
criteria, including mechanical performance, weight, cost, and fire
resistance.
[0004] A plastic pallet, which can be made in the present
invention, is often referred in the U.S. to as a GMA pallet. It has
a rectangular base, eight columns running up from the periphery of
the base, and a rectangular deck. The pallet is in the shape of a
40 inch.times.48 inch rectangle. A comparable European pallet is a
1000 mm by 1200 mm pallet, sometimes called a CP-1 pallet. For such
pallets to become accepted for widespread use in commerce, they
must meet various technical and performance standards. 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, the characteristics for a
GMA pallet which are required for acceptance by large commercial
users in the U.S. include the following: The height must be less
about 5.56 inches or less. The pallet must allow four-way entry by
forks, and each side must have two openings which are at least 3.1
to 3.8 inches high and 12 to 12.5 inches wide. The pallet should
weigh less than 55 pounds. The pallet has to be "rackable." By that
is meant, among other things, that the pallet must be capable of
being held on open beam warehouse racks without failing or
exceeding a specified amount of creep deformation when loaded.
[0005] "Recommended Test Protocol for Plastic Pallet, Version 3"
(1998) published by Virginia Tech, Blacksburg, Va., 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. Pallets must also
meet other standards. UL Standard 2335 specifies fire tests and
performance for warehouse pallets made of plastic. To meet such
fire test standard, pallets must not exceed a certain rate of heat
release rate during a simulated warehouse fire. ANSI/NSF 2-1996,
published by NSF and approved by American National Standards
Institute, at Section 7, sets standards for pallets used in food
service. Commercial purchasers have their own standards which are
often somewhat more demanding.
[0006] In the past, plastic pallets of the size and type described
have not been able to simultaneously meet all of the performance
criteria for an acceptable cost and weight. Thus, they have not
substantially replaced widely used wood pallets. It is an aim of
the invention to do better.
[0007] In the plastic pallets which have been commercially offered
or described in patent literature, decks appear to have been mostly
made from sheet or injection molded plastic. Typically, decks are
permanently attached to the other parts of the pallet, although
sometimes they have been mechanically and detachably assembled.
Often the decks have many openings and ribs for lightness and
drainage, which present large surface areas and adversely affect
fire test performance.
[0008] In order to have sufficient GMA strengths, the tops of
pallets have had to be thick or have had to make use of metal
beams, as described in various patents, including U.S. Pat. Nos.
5,868,080, 6,705,237, and 6,955,128. Beams, especially when they
are encapsulated in plastic for protection, tend to increase the
thickness, height and weight. Having a low pallet height, or low
profile, is of interest for the following reason. Economics and
current environmental concerns dictate that empty plastic pallets
be exchanged, or returned to a source of goods for reuse Shippers
want to pack as many empty pallets as possible on a truck or other
transport vehicle, to reduce the shipping cost per pallet. Thus, it
follows that the bigger the profile, the higher the cost of
transporting a pallet.
[0009] Despite the best efforts of engineers and designers, plastic
pallets which seek to meet the GMA standards--with or without using
beams, have tended to be at or beyond the user-specified maximum
5.56 inch height. Small height changes can have a powerful effect
on pallet strength, since section modulus and therefore stiffness
of any structure is a cubic function of section height.
[0010] It has also been difficult for plastic pallet designers to
meet the fire resisting requirements. The high energy content of
thermoplastics, combined with the high surface area of plastic
decks and other parts, have meant that the rate of heat evolution
during a fire is much greater than allowed by the UL 2335 standard.
While fire retardants have been included within the plastics to
address the issue, it has been difficult for plastic pallet makers
to meet the standard while meeting the other requirements. The fire
retarding additives can compromise mechanical properties, increase
cost and weight, and introduce environmental problems.
[0011] Thus, there is a need for further improvements in the design
and construction of plastic pallets, to meet the difficult goals
mentioned above.
SUMMARY
[0012] An object of the invention is to provide a plastic pallet
which has a desirable combination of properties that meet industry
requirements which include racking creep strength, maximum weight,
minimum size of openings for fork lift devices, and fire test
performance. A further object of the invention is to reduce the
cost of shipping empty pallets by reducing the height of pallets
below that which is required by the industry standards.
[0013] In accord with the invention, a 40 inch by 48 inch
rectangular thermoplastic pallet comprises a base having
beam-reinforced thermoplastic outer rails, cross rails which
connect the outer rails, hollow plastic columns, including a center
column, running upwardly from the base, a thermoplastic frame
attached to the tops of the outer columns, and a corrugated metal
deck which is fastened to the frame or a subframe which is within
the frame. The deck is inset from the outer edge of the top and
preferably the frame comprises impact absorbers and metal
stays.
[0014] The pallet has eight openings which are at least 3.2 inches
high and 12.5 inches wide, to provide four-way entry for fork
lifting devices. The reinforcing beams are preferably steel. The
deck is preferably a corrugated aluminum alloy sheet, with at least
three corrugations running substantially parallel to a line
connecting diagonally opposed comers of the deck. In an embodiment
of pallet, the deck area is at least 75 percent of the total area
of the pallet top. The pallet weighs less than 55 pounds and is
comprised of 30-45 percent metal by weight. When subjected to a
uniform load of 2800 pounds for a period of 30 days at a
temperature of 115.degree. F., while being supported along the
opposing 48 inch sides across a span of 45 inches, the center of
the pallet deflects less than 0.8 inches, thus meeting an industry
requirement for a so-called GMA pallet.
[0015] The use of the metal deck and avoidance of metal beams in
the top of the pallet, enables the deck to be made unusually thin
compared to the prior art. The deck is less than about 15 percent
of the height of the pallet. The metal deck also enables reduction
in the height of the beams, and thus of the rails, in the base.
Thus, the height of the fork openings is more than 60 percent of
the height of the pallet.
[0016] In further accord with the invention, the unique combination
of elements provides a pallet with a height which is significantly
less than the maximum 5.56 inches industry requirement, while still
meeting the multiplicity of other criteria necessary for commercial
acceptance as a GMA pallet, including weight, configuration,
structural strength and fire test performance. Pallets of the
invention have heights less than 5.4 inches, as low as 4.9 inches.
The pallets have a density property of stacked pallets, wherein the
stacking density is greater than 2.2, preferably less than 2.3
pallets per vertical foot. The number of pallets which can be
contained within a stack of a given height can be increased by
twenty percent or more, as can the number of pallets carried on a
standard size truck, so the shipping cost for each empty pallet can
be significantly reduced.
[0017] 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
[0018] FIG. 1 is an isometric view of a quarter section of a
pallet.
[0019] FIG. 2 is a vertical cross section through the outer edge
and part of the deck of the pallet of FIG. 1.
[0020] FIG. 3 is like FIG. 2, showing another embodiment pallet
deck attachment.
[0021] FIG. 4 shows in vertical section part of the top outer edge
of a pallet, where the deck is attached by means of plastic
nubs.
[0022] FIG. 5 is a vertical cross section of the top outer edge of
a pallet, where the deck is attached by means of a rail having
integral pins.
[0023] FIG. 6 shows in vertical section part of the top outer edge
of a pallet, where the deck is encapsulated with thermoplastic.
[0024] FIG. 7 is an isometric view of a quarter of a rectangular
pallet having diagonal corrugations.
[0025] FIG. 8 is a top view of the pallet, showing continuous
corrugations which run parallel to a line L connecting diagonally
opposing comers of the pallet.
[0026] FIG. 9 is a vertical cross section through a portion of a
corrugated deck showing the shape of the corrugations.
[0027] FIG. 10 is like FIG. 9 and shows different contour
corrugations.
[0028] FIG. 11 is a graph comparing the mechanical behavior of
decks having different corrugation patterns.
[0029] FIG. 12 is like FIG. 2, showing a vertical cross section
portion of a pallet having metal beams, for describing pallet
vertical dimensions.
[0030] FIG. 13 is an isometric view of a quadrant of a pallet
having a deck mounted on a suspension system which comprises a
subframe.
[0031] FIG. 14 is an exploded view of the pallet of FIG. 13.
[0032] FIG. 15 is a graph of pallet stacking density as a function
of pallet height.
DESCRIPTION
[0033] The invention is mostly described in terms of a preferred
embodiment pallet, having the dimensions of a GMA pallet. The
invention will be useful in non-GMA pallets. As detailed further
below, the present invention is aimed at meeting particular
mechanical requirements, along with the fire test requirements of
UL Standard 2335, while minimizing the use of fire retardants.
[0034] In one aspect of the invention, a predominately
thermoplastic pallet has a combination of metal beams in the base
and a textured, preferably a metal, deck. A metal deck enables
avoiding the use of reinforcing beams in the top. That aspect is
described first. There is an advantage to having corrugations which
having specified orientations and dimensions. That is described
next. By using the special combination of features a GMA pallet has
the property of uniquely high stacking density. That is described
last.
[0035] A pallet of the present invention pallet may be molded-in
components and subassemblies, preferably by injection molding using
gas assistance. See U.S. Pat. No. 5,401,459. The several parts or
subassemblies 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 or other polyolefin. Other plastics,
including thermosets and engineered plastics, may be used for the
parts of the pallet.
[0036] FIG. 1 is an isometric view of a quadrant portion of pallet
20 which has a rectangular base 30. It is useful and illustrates
many principles of the invention. The pallet 320, described below,
is more complex and more preferred. There are nine columns which
run upwardly from the rectangular base. Frame 24 is supported by
the eight columns 28 which are at the rectangular periphery of the
pallet. There are four comer columns and four columns at the
midpoint of each side of the pallet. A frame is by definition a
rectangular structure with an interior opening; and the interior
opening is spanned by the deck. Formed aluminum sheet metal deck 22
is attached to frame 24. Base 30 is comprised of four outside rails
31 which form a rectangle that corresponds with the shape of frame
24. Two cross rails 33 connect the opposing centers of the outside
rails; they cross each other at the center of the pallet. Center
column 29 is at the cross rail intersection and deck 22 is fastened
to the top of the center column. The openings 34, between adjacent
columns 28 have a width and height which enables "four-way" fork
entry for lifting and transport and which meet industry dimensional
requirements.
[0037] Metal beams 74 are embedded within the rails 31, 33 of base
30. See also the vertical cross section of FIG. 2. The metal beams
provide strength and stiffness to the base of the pallet, so that
the pallet can be stored in a rack which has spaced apart rack
supports, and so the pallet can endure other specified loads. Beams
are incorporated within the frame in accord with the teachings of
U.S. Pat. Nos. 6,705,237 of Moore et al., 6,955,128 of Apps et al.,
and 5,868,080 of Wyler et al., the disclosures of which are hereby
incorporated by reference. The beams are preferably configured so
that during a fire the embedded beams, and the pallet, collapse
when the burning thermoplastic softens. See the related application
entitled "Fire collapsible beamed pallet," bearing Atty. No.
EPC-2443 filed on even date herewith by R. Moore et al., the
disclosure of which is hereby incorporated by reference.
[0038] The construction of the deck and its attachment to the
thermoplastic parts of the pallet are features of the invention.
The deck has texturing which provides the sheet material with
strength sufficient to both carry a load of goods and to impart
strength to the pallet as a whole. When meeting fire test
performance is the main criterion, and diminished strength can be
accepted, a variety of ways for imparting stiffness to the deck
sheet material may be used. For instance, Rigidized.TM. metal sheet
may be used. For instance, the sheet may have a waffle pattern.
Preferably, the deck has a multiplicity of corrugations, and it is
also made of metal, as described below.
[0039] With reference to FIG. 1 and FIG. 2, deck 22 of pallet 20
has corrugations running in several different directions, in accord
with the corrugation pattern shown as Type B in FIG. 11. The deck
is made of 0.060 inch thick Type 5052 aluminum alloy sheet. The
periphery of deck 22 comprises a flange 49, as shown in FIGS. 1 and
4, which is plain or un-textured and which and facilitates
attachment to the frame.
[0040] The deck may be attached to the frame 24 in various ways, to
act as a structural element for racking strength and the like. FIG.
3 through 6 show in vertical cross section some alternative deck
attachments. FIG. 3 shows how deck 22 is pinned to the frame by
screw or driven pin fasteners 36. FIG. 4 shows a multiplicity of
vertically extending projections or nubs, which are molded into the
plastic frame when it is fabricated. After a deck with mating holes
is placed on the frame, the nubs are headed, or flattened over, as
indicated by the arrows and phantom in FIG. 4. In another
embodiment, shown in FIG. 5, the deck and frame have holes, to
receive the stakes of a metal or plastic rail 40, which is pressed
down onto the frame to capture the flange of the deck.
[0041] In still another embodiment of deck attachment, illustrated
by FIG. 6, deck 22 is first encapsulated in whole or part by a
layer 340 of thermoplastic, using commercial processes. Then, the
layer is plastic-welded to the frame, for instance by ultrasonic,
vibratory or hot plate welding. This embodiment can provide a good
seal between the deck and the frame. See a related application
entitled "Plastic pallet with sealed deck to frame joint", bearing
Atty. No. EPC-2442, filed on even date herewith by R. Moore et al.,
the disclosure of which is hereby incorporated by reference. In
another embodiment, not shown, the outer edge of the deck may be
mechanically captured within the frame during the molding of the
frame.
[0042] FIG. 3 shows a corrugated deck 22 which has no flange and
which is not inset from the outer edge of the frame; the deck
covers the entire top of the pallet. Preferably, the edges of a
metal deck are inset from, or inwardly spaced apart from, the
outside edge of the frame by a distance D, as shown in FIGS. 1 and
2. With the inset of the deck edge, a peripheral portion of the top
of the frame is exposed. With the inset deck design, the edges of
the deck are less prone to being damaged when objects horizontally
impact the frame of the pallet. Distance D will be a design choice,
according to the character of the exposed part the frame and
anticipated impacts. In a FIG. 1 pallet embodiment, D is preferably
the same for all edges, at about 1-3 inches for a GMA size pallet.
D may be different at different sides of the pallet. In the pallet
120 embodiment discussed below, D is preferably about 4-5 inches.
Thus for a 40.times.48 GMA pallet the deck area will be at least
about 75 percent of total area of the top of the pallet. When the
deck is metal, fire test performance is much improved due to the
lessening of the quantity and surface area of combustible plastic
in the pallet.
[0043] In the generality of the invention, the frame may be
constructed in a manner which is familiar to those making ordinary
injection molded structural beams. For example it may be shaped
like a C-channel; it may have lightening pockets and ribs, etc.
Preferably, the bridge parts 25 of the frame 24 are less
conventionally constructed, and they have one or more lengthwise
compliant zones which comprise an impact absorber. 26. A bridge is
that portion of a frame which spans the space between adjacent
columns 28. One type of impact absorber 26 is shown in FIG. 1 and
FIG. 2; another is shown in FIG. 7. In FIG. 1, the impact absorber
comprises two parallel rows of open cells bounded by lengthwise and
transverse ribs near the outer edge 27 of bridge 25. The bridge
comprises a third lengthwise zone, namely, the innermost portion of
the bridge, where deck 22 is attached. See FIG. 6. That portion is
not designed for impact absorption and is of conventional
structural plastic design. Thus, when horizontally impacted, the
outer portion of the bridge 25 is more complaint, or less stiff and
therefore more deformable, than is the innermost part of the
bridge. The outer portions absorb the force of a horizontal impact
and the inner portion does not appreciably move. Impact absorber
construction is described more particularly in the related
application entitled "Plastic pallet with sealed deck to frame
joint," bearing Atty. No. EPC-2442, filed on even date herewith by
R. Moore et al., the disclosure of which is hereby incorporated by
reference.
[0044] Rectangular cross section beams 74 in the rails 31, 33 of
the base 30 are made of sheet metal. For example, 0.059 inch thick
AISI 1040 steel, having yield strength of at least 80,000 pounds
per square inch, may be used. For example, 0.090 inch thick cold
rolled AISI 1018 steel having a Rockwell B hardness of 60-65 may be
used. Preferably, the vertical height (or depth) of the beams is
about 0.7 inch, when a metal deck is used.
[0045] If pallet weight is not critical, then the deck could be
flat plate. However, it is preferred to use lighter gage sheet
material and to texture the sheet, so it has good stiffness and
section modulus. Some types of deck texturing are much preferred.
FIG. 11 illustrates some of the texturing patterns which are now
discussed. FIG. 7 shows in isometric view, similar to the view of
FIG. 1, a portion of pallet 120 having a preferred corrugated deck.
Pallet 120 has an essential construction and dimensions like those
of pallet 20. Numbers having two digits preceded by the digit 1, 2,
3, etc., here and below, denote elements which correspond with
two-digit numbered elements above. The texturing of deck 122 of
pallet 120 comprises parallel corrugations 45 which run at an angle
to the edges of the deck and pallet. While a GMA pallet 120
preferably has an aluminum alloy sheet metal deck, as described
above, the corrugation pattern invention may be employed other
pallets having non-metal decks. Flange 149 of deck 122 is attached
to the frame 124 of the pallet by means of screw or stake
fasteners, or in other ways mentioned above. The center of the deck
is fastened to the top of center column 129.
[0046] Deck 122 has a multiplicity of corrugations 45 which, when
viewed in a vertical cross section, comprise valleys 41 and peaks
47. Some exemplary corrugation cross section patterns are shown in
the vertical cross section decks of FIG. 9 and FIG. 10. In the
pattern shown in FIG. 9 the tops of peaks 47 and the bottoms of
valleys 41 of deck 122 are substantially flat and parallel to the
top of the frame; and, the peaks and valleys are connected by webs
running at a nominal 45 degree angle to the horizontal. The pitch,
P, or center to center spacing, of the corrugations is about 2
inches. Depth DP is the effective depth of the deck; and is
nominally the depth of the valleys. All valleys are preferably of
uniform depth and provide the deck with an effective depth of about
0.5 inches.
[0047] FIG. 10 shows the corrugation cross section of alternate
embodiment deck 122A which has peaks 45A and valleys 47A running
along a nominally sinusoidal path. Other dimension corrugations may
be used, including those in which the corrugations vary in width or
pitch. Depth DP may vary from valley to valley and along the length
of any valley. The bottoms of the valleys preferably have
spaced-apart drain holes, visible in FIG. 1 and FIG. 13, to make
fire sprinkler water drop onto the underlying cross rails, for
helping performance in fire tests. See related application entitled
"Fire sprinkler-friendly pallet," bearing Atty. No. EPC-2440, filed
on even date herewith by R. Moore et al., the disclosure of which
is hereby incorporated by reference. When made of metal, decks are
formed from flat sheet using conventional metalworking techniques,
including cold forming, press forming, drawing, etc. Especially
when there is a flat flange, the deck may be conceived as a flat
sheet into which valleys 41 have been pressed. Thus, in the
following discussion a reference to a corrugation may be considered
interchangeably to refer to a valley.
[0048] It has been discovered that particular corrugation
dispositions or arrangements are surprisingly advantageous. FIG. 8
is a top view of pallet 120 and illustrates the lay of the
lengthwise axes 53 of the corrugations. In FIG. 8, all the
corrugations of deck 120 run parallel to L, the line running
between the intersects of the edges at two diagonally opposed
comers. When the deck is congruent with the frame exterior, as is
ordinarily the case, L will also be the diagonal of the frame and
pallet as a whole. Line L of the deck will not be coincident with
the corresponding diagonal of the frame or pallet when the
rectangle of the deck is not congruent with the rectangle of the
pallet. For the exemplary 40.times.48 pallet, the line L lies at an
angle B of about 40 degrees to the longer edge of the frame 124.
The axes 53 of all the corrugations of deck 120, and of certain
corrugations in other embodiments, lie within plus or minus angle A
of parallelism with line L. Angle A is about 10 degrees, preferably
3 degrees. If a deck is deviant from a perfect rectangle shape, L
will be the diagonal of a best fit rectangle. The invention will be
useful with patents which are square. When it is said corrugations
are parallel, that means they are substantially parallel, and there
may be small deviations from exact parallelism between adjacent
corrugations.
[0049] FIG. 11 graphically illustrates the surprising advantage in
performance for certain deck corrugation patterns, as revealed by
finite element analysis (FEA) of decks which were subject to the
same uniform loads. In the analysis, decks were assumed to be made
of 0.050 inch Type 5052 aluminum alloy sheet. All corrugations had
the same width, depth and the cross section shape which is shown in
FIG. 9. Thus, only the orientations of the corrugations were
changed, from one type deck to another, in the analysis. The icons
in FIG. 11 are simplified top view sketches of pallet decks, to
show the different deck corrugation patterns of the analysis.
[0050] The decks in the FEA were analyzed when supported in two
different ways. First, the pallet was supported at the opposing 48
inch length sides, or in the so-called "long direction" (the data
for which is represented by circle symbols). Second, the pallet was
supported at the opposing 40 inch length sides, or in the so-called
"short direction" (the data for which is represented by circle
symbols). In FIG. 11, those two different support modes are
indicated by stating the span between the supports, e.g., a span of
40 inches means the deck was supported along the 49 inch sides. The
comparative FEA deformations of different configurations of decks
were determined. Those data are represented in the graph by the
open symbols. Maximum elastic stress in the deck was calculated
according to Von Mises theory and criteria. The Von Mises analysis
data are represented by solid symbols. A deck having better
strength will have lower deflection and lower Von Mises values,
when performance in both directions of support is considered. The
comparative deflection performance of some of the patterns was
confirmed in testing of prototype decks and pallets.
[0051] Decks of type INV and type I have surprising advantage over
the other patterns, and they are preferred embodiments of the
present invention. In type INV all the corrugations run parallel to
L, the diagonal. The associated data set is marked by the box 80.
Deck of type I, with which is associated data set 90, is only
somewhat inferior to the most preferred embodiment type INV. A deck
of type B provides inferior performance, compared to what artisan
intuition about its symmetry might suggest. In fact, such pattern
was used on early prototypes. The long direction corrugations which
characterize type III deck give the deck excellent results in one
span-support direction and quite inferior results in the other
span-support direction. The type II deck has similar but somewhat
lesser inadequacy.
[0052] The superior type I and type INV decks are characterized by
at least three corrugations running continuously and parallel to
the diagonal line of the deck. Type I deck has a second set of
three corrugations, namely those running along the other diagonal
of the pallet. The corrugations of the second set are discontinuous
where their path crosses the first set of corrugations. Type I has
in addition 4 to 6 valleys which run parallel to the each of the
rectangular edges of the deck. In another embodiment, type IA, not
shown, the configuration is like type I: A first set of at least 3
corrugations is parallel to a first diagonal line of the deck; and,
all the other corrugations on the deck are parallel to the second
diagonal.
[0053] When decks are made of sheet metal, fabricating a deck of
type I is much more difficult than fabricating a type INV deck.
There is more of tendency for thinning of the deck material during
forming, and the thinning can be difficult to predict or eliminate.
Thus, a type I deck is less preferred than a type INV deck, but
both are substantially superior to other types of texturing. Thus,
in a preferred embodiment of the invention there are at least three
parallel continuous corrugations running from one comer to the
diagonally opposite comer. The permissible range of alignment of
corrugations is as described above in connection with FIG. 8.
[0054] Variation is possible within the scope of the corrugation
orientation invention. In preferred embodiment deck, one
corrugation valley is centered on line L, and there are two or more
parallel valleys on either side of the primary valley. The two
adjacent the primary valley have only a little shorter than the
primary valley length. There need not be a primary valley along L;
that is, two equal length valleys of any set of three or more may
straddle L. The term "corner" as applied to this aspect of the
invention is to be interpreted as embracing a region of the deck,
rather than a point. When corrugations are said to run from one
corner of the deck to the other corner, that means the corrugations
run substantially to the portion of the deck which is in proximity
to the right angle intersection of two edges of the deck. Thus,
when the deck has a preferred flange, the three corrugations
nearest line L run to the corners, even though the outer portion of
the corner near the edge intersect is an un-textured flange. While
the analysis simulated a metal deck, the invention will be useful
with decks which are made of non-metals. Logic suggests that two,
or even one, continuous diagonal corrugations would suffice,
although providing less strength but that has not yet been
proved.
[0055] There is a benefit of having a deck with a flange in
combination with corrugations. Stated simplistically, the oblong or
cupped end of each corrugation provides strength to the edge of the
deck, and helps inhibits bending of the deck about the length axis
of the corrugation at the deck edge.
[0056] The combination of features of the invention provides
another unexpected advantage, namely, a heretofore unattainable low
profile, or total height, for a pallet which meets the many
requirements which have been mentioned above for a GMA pallet. When
invention pallets are stacked on top of each other, more pallets
can be contained within a stack of a given height, than heretofore;
i.e., the stacking density is significantly higher than heretofore.
A significant economic benefit results from higher stacking
density, since more GMA pallets can be carried on a standard
transport truck.
[0057] FIG. 12 is used to illustrate dimensions associated with
pallets. FIG. 12 is analogous to FIG. 2 and shows a vertical cross
section of a simplified prior art pallet 220 having metal beams
275, 274, respectively in the top and base. To meet the
aforementioned standards, the fork opening 234 (also sometimes
called the window) must have a height FO of at least 3.1 inches and
a width WO of at least 12.5 inches wide. As an example of a
difficulty associated with a prior art plastic deck pallet, in the
pallet of the Moore U.S. Pat No. 6,705,237 patent, the hollow
square AISI 1018 steel beams 275, 274 have a vertical height of
about 0.875 inches. That produces a base rail height DB of about
1.1 inches. The top frame has a similar beams and similar height
DT. The resultant total height of the pallet is near the maximum
5.56 inch height allowed.
[0058] The present invention which comprises a corrugated metal
deck, in particular an aluminum deck, having the corrugations of
Type INV or Type I, enables both omitting metal beams in the top
and reducing the height of the beams in the base, while meeting the
dimensional, load bearing and weight requirements attending a GMA
pallet. Leaving the beam out of the top means the top can be made
thinner than heretofore has been possible. In the invention, a top
frame height DT of about 0.7 inches is achieved. As mentioned, the
effective height of the deck is 0.5 inches, and that fits easily
within the frame profile. The corrugated deck is sufficiently stiff
and supported at the center column. Thus, when it deflects under a
load of goods, it does not deflect below the elevation of the
bottom of the frame.
[0059] The strong metal deck and thermoplastic elements of the top
cooperate with the base to provide good racking strength. The
pallet construction enables a reduction in the size of the beams
used in the base. For example, the vertical height (also called
"depth") of the steel beams in the base of a preferred embodiment
pallet is about 0.5 inches, which is about 60% of the previously
required beam height of 0.875 inches. Thus, in the present
invention, the thicknesses of both the top and both parts of the
pallet are thinner than was heretofore possible. The use of the
corrugated metal deck enables a surprising and significant
reduction in height and associated stacking density, compared to
what could be done in the past.
[0060] Exemplary pallets of the invention have heights of less than
5.4 inches. In a preferred embodiment a pallet is 4.7 to 4.9 inches
high. As a fraction of the height of the pallet, the required
minimum 3.1 inch fork opening height is more than about 60 percent;
the 0.7 inch top height is less than about 15 percent; and the 0.9
inch base height is less than about 20 percent. Those percentages
are a measure of the efficiency and uniqueness of the design.
[0061] A quadrant of an exemplary pallet 320 which has features of
the present invention is shown in FIG. 13. The exploded view of
FIG. 14 shows how it is constructed. With reference to FIG. 13,
pallet 320 has most elements like those previously described. The
corrugated deck is of the type INV and all the corrugations are
parallel to the deck diagonal. Pallet 320 is different from other
embodiments described up to this point in the following way: The
deck 322 is attached to a subframe 66 which is supported within the
frame by attachment to cantilever brackets 68, 78. The deck is also
fastened to center column 329 which preferably has vertical fins on
top rather than a mirror-fit corrugation contour pattern. The
subframe 66 and attached deck are spaced apart from the inner edge
72 of the frame. Preferably, the subframe, brackets and frame are
integrally molded. Each bridge 325 has impact absorber construction
across its whole width. Since the edge of the deck is spaced apart
from the inner edge of the bridge, the bridge can deform
compliantly and inwardly under horizontal impact loads without
damaging the deck. The construction of the pallet of FIG. 13 is
further described in a patent application entitled "Plastic pallet
having impact resisting top", bearing Atty. No. EPC-2437, and an
application entitled "Plastic pallet having deck suspension
system", bearing Atty. No. EPC-2439, both filed on even date
herewith by R. Moore et al., the disclosures of which is hereby
incorporated by reference.
[0062] A pallet of the present invention like that shown in FIG.
13, when made of polypropylene or comparable density plastic, and
when having corrugated aluminum alloy deck and steel beams only in
the base, is by weight about 30-45 percent metal, balance
thermoplastic. In a preferred embodiment pallet, the metal is about
32-40 weight percent. On a volume percent basis the preferred
embodiment pallet is approximately 90 percent plastic. Therefore,
on both bases, the invention pallet is characterized as
predominately plastic. In an exemplary a pallet, the total weight
is about less than 55 pounds, preferably about 51 pounds, according
to the particular height. The aluminum deck weighs about 6 lb. and
the steel reinforcing beams weigh about 12.5 lb., which are
respectively about 11-12% and 23-25% of the total pallet weight.
Such pallet is 34-37% percent metal by weight. Some or all of the
metal parts may be replaced by non-metal parts, such as with
engineered plastics or ceramics which provide comparable section
moduli and strengths to the metal parts.
[0063] In the present invention, the new technology makes possible
the construction of GMA-load rated pallets which are predominately
plastic, but at the same time they have a total height which is
10-15% less than GMA-rated pallets in the prior art. For example, a
pallet which has a 4.7 inch height has about 15% less height than a
5.56 inch high prior art pallet. That means that about 20% more
pallets can be carried within the volume of a typical large truck
or other vehicle, which is explained now.
[0064] A typical stack of pallets for carrying within a familiar
U.S. over-the-road enclosed semi-trailer cannot exceed about 109
inch. Obviously, if the remaining space above an uppermost pallet
is less than the height of a full pallet, that space must remain
empty. In the invention, a stack of 23 most preferred embodiment
4.7 inch high pallets will be about 108 inches high. A stack of 19
prior art 5.56 inch pallets will be about 106 inches high.
Normalizing those numbers, a stack of 5.56 inch pallets has a
vertical density of 2.15 pallets per foot. In the invention, the
most preferred embodiment 4.7 inch high pallet has a stack density
of 2.55 pallets per foot. Table 1 shows data for different models,
or embodiments of the invention. The pallet height and density data
of Table 1 are plotted in FIG. 15. When certain cost considerations
are weighed, the design Model A, having a 4.9 inch height, is most
preferred at the present time; and a substantial advantage is
obtained.
[0065] Of course, increased stacking density is only of interest
when the pallet also meets the diverse other requirements which
have been stated. Creep test performance is a demanding and
critical parameter and it is used here as a measure of successful
design. The creep test behavior of 40.times.48 pallets having the
construction described in connection with FIG. 13 was found to have
the required creep properties, as well as meeting other
requirements. A uniformly distributed load of 2800 pounds was
applied to the deck for a period of 720 hours at a temperature of
115.degree. F. The pallet was simply supported by its opposing base
edges on open beam warehouse rack fixture. The span between the
rail supports of the fixture was 4 inches less than the length of
the pallet side which spanned the space between the support. In
passing the test, a 4.9 inch high pallet did not deform downwardly
more than 0.8 inches. Reference should be made to the Background
here and the Virginia Tech Test Protocol for Plastic Pallet and
proposed UL 2417 standard, the disclosures of which are hereby
incorporated by reference. See especially "Bending Tests," Section
1.2 of the Virginia Tech document, and the comparable Section 5.5
of the proposed UL 2417 standard. A pallet which passes the
aforementioned 30 day creep test is said here to be GMA
creep-rated. The exemplary pallet was capable of passing the other
structural tests which are required for commercial usage and is
thus said here to be GMA structurally rated. TABLE-US-00001 TABLE 1
Dimensional and stacking properties of pallets Stacking Pallet
Pallet height Maximum Stack Density Embodiment inches quantity
height(inches) units/foot D 4.7 23 108 2.55 A 4.9 22 108 2.44 B
5.15 21 108 2.33 C 5.45 20 109 2.2 Prior Art 5.56 19 106 2.15
[0066] Prototype GMA pallets which had the features of most
preferred embodiments of the invention passed the test of UL 2335.
The pallets were made of polypropylene containing fire retardants
and had a corrugated aluminum deck with drain holes over the base
rails, collapsible steel beams in the base rails, and thermoset
foam within the hollows of the columns.
[0067] While the above described combinations of aluminum and steel
and polypropylene materials are presently preferred, other
materials can be used. For example, while the aforementioned 5000
series aluminum alloy is the preferred metal deck material, other
wrought metals can be equivalently used within the scope of
invention. The 5052 aluminum alloy has an elastic modulus in
tension of 10.3.times.10.sup.6 psi (7.1.times.10.sup.4 MPa) and a
specific stiffness of about 105.times.10.sup.6 inch
(26.times.10.sup.5 m). In an alternate embodiment, AISI 300 series
stainless steel may be used. Such steel alloy has about three times
the density of the aluminum alloy, but it also has an elastic
modulus which is about three times that of the aluminum alloy. The
two classes of metals have about the same specific stiffness. Thus,
in a GMA creep rated pallet, the steel deck could be about
one-third of the thickness of an aluminum deck. Thus a deck may
alternately be made of any of a number of steels which have
mechanical properties comparable to the 300 series stainless
steels. Alternately, a deck may be made of alloys of magnesium or
titanium, although they have poor fire test characteristics. Sheet
of fiber reinforced thermoset plastic may be used. Pallets may be
alternately constructed using beams which are not metal, such as
those made of graphite or glass or metal fibers. The rails of bases
may be constructed wholly of engineered plastics.
[0068] As will be understood from the foregoing and as is
understood in the art, when a pallet is termed "plastic" or
"thermoplastic," unless qualified, the term does not exclude the
presence of other materials such as metal reinforcing members,
fillers, fibers, fire retardants, and the like; and it means that
the pallet is mostly or predominately plastic or thermoplastic, as
applies. A thermoplastic pallet or member may also be comprised of
lesser fraction thermoset and or elastomer materials. Such
terminology compares to a reference to a wholly or purely plastic
or thermoplastic pallet or article. In the invention, commercially
available fire retardants are ordinarily included with
thermoplastics, to help meet the UL 2335 requirements, as is known
in the art. See a related application entitled "Thermoplastic
pallet having portions with different fire resistances", bearing
Atty. No.EPC-2514, filed on even date herewith by R. Moore et al.,
and U.S. Pat. No. 6,807,910, the disclosures of which are hereby
incorporated by reference.
[0069] While the invention is described and in some respects
claimed in terms of a 40 inch.times.48 inch U.S. GMA pallet, those
dimensions may vary within a several percent; and thus, the
dimensions will comprehend a 1000 mm.times.1200 mm European pallet.
The features of the invention can be applied to pallets which have
other dimensions, different numbers of columns, and which meet
other performance specifications. For example, the base of a pallet
may have cross rails which run in a different pattern from that
described. For instance, the cross rails may run between diagonally
opposed corners. For instance, there may only be one cross rail.
The cross rails may be wholly metal. Likewise, the columns might be
wholly or part metal. For another example, a corrugated deck of the
invention can be used with pallets which have no reinforcing beams
in the base, or with pallets which have no base rails, but which
are supported by resting the lower ends of the columns on a flat
surface, in which case the columns might more accurately be called
feet.
[0070] The inventions will be useful as improvements for pallets
which are not GMA dimensioned or structurally rated. The deck
corrugation patterns can be used in other pallets having sheet
material decks, including where the deck material is any kind of
plastic, including engineered plastics, such as those reinforced
with graphite fibers and fiberglass. The invention may be applied
to wholly plastic pallets and pallets having wood bases.
[0071] 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.
* * * * *