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PERFORMANCE OF 24X20-INCH CORRUGATED QUARTER PALLETS FROM PACKAGING UNLIMITED by John W. Clarke Marshall S. White Ralph L. Rupert Center for Unit Load Design Virginia Tech Blacksburg, Virginia June 5, 2001 PERFORMANCE OF 24X20-INCH CORRUGATED QUARTER PALLETS FROM PACKAGING UNLIMITED by John W. Clarke Marshall S. White Ralph L. Rupert Center for Unit Load Design Virginia Tech Blacksburg, Virginia June 5, 2001 1. Introduction Packaging
Unlimited of Louisville, Kentucky has patented a corrugated/hardboard stringer
for use in corrugated pallets. The Virginia Tech Center for Unit Load Design
was contracted to determine the strength and material handling functionality of
a 24x20-inch, 2 stringer, 2-way, single-wing, non-reversible quarter pallet
design. 2. Objectives á
To determine the rated load during floor stacked storage according to
the procedures in ASTM D1185. á
To determine the rated load during forklift handling according to the
procedures in ASTM D1185. á
To determine the functionality of the design on typical material
handling equipment. 3. Materials Packaging
Unlimited of Louisville, Kentucky provided 10 24x20-inch quarter pallets. A
description of the design is given in Table 1. Table 1: Description of the 24x20-inch Corrugated Quarter Pallets from
Packaging Unlimited
A photograph of the pallet design is given in Figure 1. The average pallet weight was 6.4 pounds. Stringers were glued layers of double wall corrugated (flutes vertical) and hardboard. Stringers were layered as follows: 2 layers DW, 1 strand HB, 4 layers DW, 1 strand HB, 2 layers DW. The pallet was a single wing design with 4.25-inch wings (stringers 11.5-inches outside to outside). Top decks were AAC triple wall corrugated with flutes oriented perpendicular to the stringer direction. Bottom decks were CB double wall with flutes oriented perpendicular to the stringer direction. Adhesives joined the decks to the stringers. All assembly and gluing was performed by Packaging Unlimited.
Figure 1. Overview
of the 24x20-inch Quarter Pallet from Packaging Unlimited 4. Test
Methods 4.1 Stacking
Strength and Stiffness These
tests were conducted according to ASTM D1185-98[1],
Section 8.5. This test simulates bending stresses on the pallet deck during
unit-load block stack storage. Prior to testing, all pallets were conditioned
at 70oF (20oC) and 90% RH, or approximately 18-20% EMC
according to the procedures outlined in ASTM D1185 for paper-based pallets.
Test pallets were supported on a flat 1.5-inch thick plywood sheet that
simulated a warehouse floor. The test load was 1 layer of boxed sheet paper, 50
pounds per box, with 2 boxes per layer. An inflatable air bag above the layer
of boxes provided the remainder of the test load. The performance criteria was 0.25 inches maximum deck deflection and a safety factor of at least 2.0. Many loads will experience damage when decks deflect more than 0.25 inches between the stringers. In addition, pallet jacks require 3¼Ó tall openings between decks. The stringers on these pallets averaged 3.5 inches in height, and therefore, if decks deflected more than ¼Ó, there would be an expected loss of functionality with pallet jacks. Initially, 1 pallet was tested to failure to estimate the rated load. Then, pallets were tested for 2 hours at the estimated rated load to determine long term deck deflection (creep). Following the ASTM 2-hour load test and 1-hour recovery, the pallets were tested to failure to determine the ultimate load. The rated load was the lesser of: á
the load at which the 2-hour top deck creep deflection exceeded 0.25
inches, á
or the average load causing failure divided by a safety factor of 2. 4.2
Fork tine Support Strength and Stiffness These
tests were conducted according to ASTM D1185-98[2],
Section 8.5. This test simulates bending stresses on the pallet deck during
forklift handling. Prior to testing, all pallets were conditioned at 70oF
(20oC) and 90% RH, or approximately 18-20% EMC according to the
procedures outlined in ASTM D1185 for paper-based pallets. Test pallets were
supported on two simulated forktines measuring 4Ó wide and 40 inches in length.
Tines were placed outside the stringers with a 12-inch inside to inside
spacing. The test load was 1 layer of boxed sheet paper, 50 pounds per box,
with 2 boxes per layer. An inflatable air bag above the layer of boxes provided
the remainder of the test load. Pallets were tested to failure on these simulated tines. The rated load was the lesser of: á
the load at which the top deck deflection exceeded 0.25 inches, á
or the average load causing failure divided by a safety factor of 2. 4.3 Functionality
on Material Handling Equipment The
quarter pallets were evaluated with typical material handling equipment
including the following: electric and LP forklifts, electric and manual pallet
jacks, and roller conveyors (3Ó and 6Ó roller spacings). The LP forklift had
tines that measured 5Ó in width, 1.5 inches in depth, and 40 inches in length.
The electric forklift tines were 4Ó in width, 1.5 inches deep, and 40 inches in
length. The manual pallet jack had tines that were 14.5 inches (inside opening)
and 27 inches (outside span) with a lowered height of 3.25 inches. The electric
pallet jack had tines that were 12.5 inches (inside opening) and 27 inches
(outside span) with a lowered height of 3.25 inches. The roller conveyor was a
Pentek belt driven system. Rollers were 2.5 inches diameter, and spaced on
either 3-inch or 6-inch centers. Pallets
were tested on these systems under load and while empty. These are the primary
systems that quarter pallets are likely to encounter. 5. Test Results 5.1. Stacking Strength and Stiffness
Supporting Boxed Loads The
results of the static stacking tests are summarized in Table 2. The test setup
is illustrated in Figure 2. A
preliminary rated load of 750 pounds was selected based on the test to failure
of replicate #1. The test load was actually 862 pounds (1.15 times 750) per
ASTM guidelines. Two replicate pallets were tested for 2 hours under this load.
The average top deck deflection exceeded the 0.25 inch performance criteria,
primarily due to the top deck wings (sides) bending. It is expected that, with
this load, the design would pass all performance criteria at a rated load of
500 pounds, although there were not enough replicate pallets for confirmation.
The average load at which the top deck flutes crushed was 1612 pounds, and
ranged from 1400 to 1735 pounds. At a rated load of 500 pounds, this gives us
an average safety factor of 3.2. No stringer hardboard crushing was observed at
these load levels, just top deck crushing. Note
that the boxed paper was not stretch wrapped or otherwise restrained.
Restrained loads or rigid loads that will not bend the top deck of this winged
design may result in greater acceptable rated loads. For rigid loads, there may
be cost savings in using a lighter construction top deck and allowing the
stringers to bear the weight. Pallets used in less humid environments may
result in greater acceptable loads. Loads that are more flexible or
concentrated than boxed paper, however, may result in lower rated loads. Users
should verify the performance of this design in field trials with the actual
loads before implementation.
1 The
test load was 1.15 times the rated load per ASTM guidelines.
Figure 2: Test
setup for the warehouse stacking support mode.
Figure 3: Test
setup for the forklift tine support mode. 5.4.
Dynamic Strength and Stiffness with Forklift Tine Support The
results of the dynamic forktine strength and stiffness tests are given in Table
3. Figure 3 is a photograph of the test setup with tines parallel to the
24-inch pallet direction (parallel to and outside the two stringers). The
average load at which flute crushing was observed in the top decks directly
above the forktines was at 1200 pounds. We divide this by 2.0 to get a rated
load of 600 pounds. The stringers
and hardboard did not contribute to the performance in this support mode. In
general, pallets used in less humid environments may result in greater
acceptable loads. Even though the top deck flutes begin to crush at 1200
pounds, some residual strength remains. The boxed paper spans the 2 forktines,
and loads that are more flexible or concentrated than boxed paper may result in
lower rated loads. Users should verify the performance of this design in field
trials with the actual loads before implementation.
1 Rated load
determined by dividing load causing top deck failure by two (safety factor of
2). 5.3 Material
Handling Functionality Pallets
were tested both empty and loaded on typical material handling equipment. The load was 4 layers of boxed sheet
paper, 2 boxes per layer, for a total of 400 pounds. In material handling tests
on forklifts, pallet jacks, and roller conveyors, the following observations
were made:
Users of these pallets should ensure that potential warehouses and
distribution systems are audited to determine if other material handling
systems will be encountered. 6.
Conclusions A 24x20-inch Quarter Pallet manufactured by Packaging Unlimited was evaluated for floor stacking strength, forktine support strength, and functionality with material handling equipment. The load tested was boxed sheet paper. At 18% EMC, the safe rated load when floor stacked was 500 pounds. The safe rated load when handled with forktines was 600 pounds. The pallet functioned well with typical industry material handling equipment including forklifts, pallet jacks, and roller conveyors. The performance and functionality of this design will vary depending on
load rigidity and equipment interfaces. Users should field test samples of this
pallet design before full scale implementation. Table 4:
Summary of the ASTM D1185 Rated Loads for the Packaging
Unlimited 24x20-inch Quarter Pallets (18% EMC).
*24x20Ó,
Single wing, 2 stringer, 2 way, 2 strands of hardboard, TW top, DW bottom [1] ASTM D1185. 1998. Standard Test Methods for Pallets and Related Structures Employed in Materials Handling and Shipping. American Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103. [2] ASTM D1185. 1998. Standard Test Methods for Pallets and Related Structures Employed in Materials Handling and Shipping. American Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103. |
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