Achieving Effective Pallet Stack Unitization in Intermodal Shipping

Tests demonstrate how to achieve maximum load stability

In April 1998, the Packaging Technology & Engineering journal, published results of independent research on achieving effective pallet stack unitization in intermodal shipping. Those results, along with findings from other field tests, are summarized here to help us understand the most effective means of pallet stabilization.

The tests published in Packaging Technology & Engineering were conducted by Dr. Per G. Reinhall, Professor of Mechanical Engineering at the University of Washington, who determined that most pallet failure during shipping occurs from lateral vibrations, which are greatest with intermodal transport. He, therefore, focused his research and discussion on lateral strength.

Dr. Reinhall tested Lock n’ Pop alone, stretch wrap alone and Lock n’ Pop in combination with stretch wrap. Both interlocked stacking and column stacking were compared using each of these three pallet support systems, for two types of products packaged in two types of boxes.

The results were clear. The greatest stability was achieved by using:

• A combination of Lock n’ Pop and stretch wrap
• Column stacking

This is seen plainly in the following charts, which show results from the test on 1.5 liter bottles of water packed in 200# b-flute, side RSC, 11" x 10.5" x 12" boxes, in pallet stacks five high.

2. Top Wrap refers to wrapping just the top outer perimeter of a pallet.
3. Stretch Wrap refers to one complete single wrap layer.

Dr. Reinhall conducted a related two-year field test at a household goods plant where damage was significantly reduced with the introduction of Lock n’ Pop. This test involved a variety of products using both column and interlocked stacking.

Period Steps taken to reduce damage Results

Tests conducted by major Lock n’ Pop clients also produced similar results, with a large household products manufacturer finding that Lock n’ Pop, with two kraft liner tie sheets near the top and bottom of a column stacked load, performed equal to or better than stretch wrap in 11 separate tests of 1,000-mile truck shipments. In all these tests, the old notion was upset that interlocked stacking is stronger. The old assumption that vertical forces were the greater issue, was found invalid, opening the door to lighter weight boxes and higher stacking. While Lock n’ Pop can be used alone in many situations, especially where intermodal shipping is not being used, we see that it is most effective when combined with either a top wrap or full single layer of stretch wrap.

For those companies currently using stretch wrap, the addition of Lock n’ Pop can still represent a significant labor, cost and waste savings. Lock n’ Pop reduces the amount of stretch wrap and/or dunnage needed and reduces shipping damage with its related costs.