Report No. PL-00-01
TABLE
OF CONTENTS
Page
1.0
Introduction
1
2.0
Materials
2
3.0
Test Methods
3
4.0
Results and Conclusions
7 1.0 INTRODUCTION
The
All Service All Packaging (ASAP) company of Green Acres, Washington
(www.asappallets.com),
manufactures skids, which are used as a platform for storing and shipping
very heavy loads. Specifically,
this 48”x48”, one-sided skid is used as a platform to transport and
store metal coils, flat sheet and plates.
The skid serves the same purpose as the conventional pallet
but for much heavier loads; typical pallets only support about 1,000
pounds. The typical load weight stored or transported on one skid ranges
from 10,000 to 30,000 pounds. The
skid is manufactured from a proprietary formulation of recycled high-density
polyethylene (HDPE); the primary feedstock being flaked HDPE recovered
from recycled, unpigmented beverage containers typical of milk or
water jugs.
The
purpose of this project was to test the strength and durability performance
characteristics of this recycled-content skid for use in the “heavy
capacity” skid market. ASAP
contracted the William H. Sardo Pallet & Container Research Laboratory
at Virginia Tech to conduct the evaluation.
The test objectives included:
· Determination of the joint compression strength for load capacity; · Determination of the leading deck edge impact resistance; and · Determination of the drop resistance at the corners of the skids. This
testing was conducted according to the American Society for Testing
and Materials standard ASTM D1185.
Testing follows a 1997 project titled “Performance Evaluation
of 48x48 Coil Pallets Made From 100% Recycled Plastic”, funded by
CWC, and primarily written by the authors of this report in partnership
with Keith Adkins of ASAP and John Dacquisto of Dacquisto Engineering
and Administrative Services. The original report was published September
1997 and can be found at this web address: http://cwc.org/PET-HDPEPubs.htm. The purpose of this set of tests was to acquire
independent verification of ASAP’s in-house evaluation and testing
of their skids.
2.0
MATERIALS
Figure 1: Typical 48x48 Skid for Metal Storage and Handling
3.0
TEST METHODS
3.1 Joint Compression Tests of Skid Stringer and Deckboard Joints
The joint compression test determines load capacity of the coil skids. During testing for the original skid design, in 1997, ASAP supplied Virginia Tech with 48” diameter simulated metal coils weighing 10,000 pounds each to simulate typical loads. The steel coils were not available for this test, so an alternate test method was used.
The test method described in American Society for Testing and Materials (ASTM) standard ASTM D1185. Specifically, ASTM D1185-98A section 8.3.2.2, “Standard Test Method for Pallets and Related Structures Employed in Materials Handling and Shipping” was used, with a loading rate from ASTM D695-91 section 9, “Standard Test Method for Compressive Properties of Rigid Plastics.” The loading rate of 5/100” per minute was chosen because the loading rate of the ASTM D1185-98A was too fast and high loads accumulated in just a few seconds. A servo-hydraulic testing machine was used to compress the joints at a rate of 5/100” per minute. Figure 2 depicts the joint compression test setup. Load and deflection were measured during each test.
The skids
were cut into stringer/deckboard joint sections.
Fifteen of these sections were tested in compression past the
load at the proportional limit, but not to failure.
Figure
2: Joint Compression Test
Setup
3.2
Leading Deck Edge Inclined Impact Tests
The purpose of this test is to determine the durability of the leader board under simulated industrial incidence of fork-tine impact from forklifts. The top deck leading edge impact test was performed according to ASTM D-1185-94, section 9.4. The skids were conditioned to -13° F prior to testing. The skid was positioned so that the leading edge deckboards would be impacted on the center span of each deckboard between stringers.
A 700 pound cargo load
was applied throughout the test.
The impact distance began at 12” and progressed through 24”,
48”, 72”, 96”, and 120”. Ten
(10) impacts were performed at each energy level.
The tests are normally terminated when a deckboard is removed
or broken from the stringer. The test was stopped when machine capacity
was reached.
3.3
Corner Drop Tests
The purpose of this test was to determine the resistance of the outer corners of the skid to deformation and breakage. Corner drop tests were performed according to ASTM method described in ASTM D-1185. Unloaded skids were dropped on the corner from a height of 1 meter and 2 meters. Skids were dropped 10 times from each height, starting at 1 meter, until failure affecting safety or functionality was compromised. Figure 3 shows the corner drop test. Figure 3:
Corner Drop Test
4.0 RESULTS AND CONCLUSIONS
This testing is significant for ASAP Packaging, as it validates the quality, performance, and durability, and one area for improvement of their product. These test results are significant information for gaining additional markets.
In two of the three tests, joint compression strength and impact resistance, results proved that the skid is strong and durable, can bear up under rough handling with forklifts and forktine impacts incurred during shipping, and has a service life of 200 times longer than wood skids used in the same capacity. The drop resistance at the outer corners of the skid, showed good joint strength and fastener durability, however, the deck board corners tended to fracture past certain threshold loads and drop heights.
4.1 Joint Compression Tests of Stringer and Deckboard Joints
Typically, skids used in the metals handling, storage, and transport industry, hold between 5,000 and 30,000 pounds each. Often the skids are stacked two-high for storage. The test results for joint compression strength indicates the skid can support a rigid load of over 100,000 pounds. Since industry practice is to double stack loaded skids for storage and the upper end of the load weight is 30,000 pounds, the bottom skid can easily support double stacking. The impact resistance testing was terminated after the skids surpassed the height and weight capacity of the testing machine, without breakage.
The load causing failure was higher than the 20,000 pound capacity of the machine. Table 1 presents the summarized results from the ASTM D 1185-98A stringer/joint compression tests. The average proportional limit of the joints tested is a conservative estimate of joint compression strength, and is measured at the point when the compression of the sample begins to occur at a faster rate when equal load increments are applied. No visible damage to the skid joint was observed at this level of deformation.
The average compressive areas of the skid have been calculated and the top deck/stringer joint has the lowest compressive area with a 48” diameter metal coil load (198.5 in2). Using the proportional limit stress and multiplying that by the compressive area, the safe load per skid is calculated. The safe load per skid with a rigid coil load is 102,194 lbs. This load is very large and is certainly many times greater than the actual loads placed on the skids.
4.2 Leading Deck
Edge Inclined Impact Tests
This test indicated that the durability of the leader board, under simulated industrial incidence of fork-tine impact from forklifts, was very high. Testing was terminated after the skids surpassed the height and weight capacity of the testing machine, without breakage.
The impact force subjected to the new skids was 21,250 pounds per skid, over three times the average impact force per skid as tested on the September 1997 skid design. The force of each impact was calculated by the following formula:
Force = ½ (skid + load weight) x (velocity) 2
= ½ (skid + cargo load weight) x (velocity) 2
Table 2 contains a summary and comparison of results from the inclined impact tests.
* The skids did not fail after 10 impacts
at the 120” distance; the capacity of the test device.
Although no failures occurred, the leading edge deckboard was forced back ¼” on the center stringer. This is a result of the lag bolts bending from repeated impacts at high energy levels. The fasteners (lag bolts) holding the decks and stringer boards together, did not fail or withdraw from the boards. Slight bolt bending at the center stringer was measured. This performance indicates good durability of the skid through rough handling.
4.3 Corner Drop
Test
The purpose of this test was to determine the resistance of the outer corners, or wings, of the skid to deformation and breakage, and the joint strength when dropped or impacted. Table 3 contains the results from the corner drop tests. These results confirm that the joint is stiff, durable, and the fasteners maintained joint integrity through all tests.
Drop resistance testing at the outer corners of the skid showed that the deck board corners tended to fracture past certain threshold loads and drop heights. The failure mode of the skid from dropping on corner was a fractured corner of the drop edge wing as shown in Figure 4. The wing of this skid is more susceptible to damage than a flush design, because the wing is absorbing most of the impact. As such, ASAP is currently enhancing the material formulation to increase the flexural modulus of the molded material, which would increase the flex at the corners and minimize deck board breaking. Additional testing will be conducted on skids manufactured with the new material formulation. Figure
4: Typical Fractured Wing on Impact Corner (From Corner Drop Tests)
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