Pallets are an integral part of the supply chain for all types of products all over the world, as they allow products to be shipped in bulk and transported in standardized containers. Many different shapes of products are placed onto pallets, including corrugated boxes, bags, barrels, and pails (Image 1). These products each distribute their load onto the pallet slightly differently, which affects the bending of the pallet and potentially its strength as well. Building cost-efficient pallets means building those that are designed to deal specifically with these differently shaped loads.

In order to learn more about how pails affect the deflection of pallets, the National Wooden Pallet and Container Association (NWPCA) sponsored an undergraduate research project. Meredith Brooks, a junior pursuing a degree in packaging systems and design (Image 2), and Michael Phelps, a senior pursuing a degree in sustainable biomaterials (Image 3), were selected for this project. Both of these students were taking part in the Distribution Packaging Internship Program through CPULD and had been working as laboratory technicians in the pallet testing lab prior to being selected.

Image 2: Meredith Brooks, a junior, studying packaging systems and design.
Image 3: Michael Phelps, a senior, studying sustainable biomaterials.

This research project focused on investigating the load bridging effect of unit loads of pails on the deflection of a wooden pallet. Seven pail designs varying in volume, material, and closure mechanisms were investigated. The study simulated the behavior of a 40” x 48” stringer class, two-way, reversible, flush pallet supported across its 48” width on a warehouse rack system. The experiment utilized a scaled down pallet section with 20” x 48” dimensions. A pressure sensor mat was placed between the pails and the pallet’s top deck to measure the distribution of pressure on the top of the pallet. Two different deckboard gap scenarios were investigated during this study: a 2” gap and a 3.5” gap. In addition, the deflection of the pallet was also measured during the experiment.

The results revealed that the pails only interact with the pallet along their bottom rim, which causes the pressure to be distributed in a circular pattern (Image 4). It was also found that the pressure distribution from the pails on the pallets was not continuous for two reasons. First, pallets have gaps between their deckboards, so there is no pressure distribution in those areas. Second, the pails are too rigid to follow the deformation of the pallet and, therefore, do not tilt during pallet bending. This phenomenon causes the inside rims of the pails located on the edges of the pallets to lift off from the pallet during pallet deflection, creating a discontinuation of pressure. (Image 5)

Image 4: Pressure distribution observed on the top of the pallet during the warehouse racking test.
Image 5: Plastic pails lifting from pallet during deflection under the warehouse racking test.

In order to evaluate the effect of pails on the deflection of the pallet, a statistical analysis was conducted using an Analysis of Variance (ANOVA) test. The analysis found that the pail size had a significant effect on the deflection of the pallet. When the pail size increased, a statistically significant decrease was observed in the deflection of the pallet. The decrease was between 3% and 27% depending on the pail design and material. The highest reduction was observed with metal pails.

The same trends were observed for the deckboard gap scenarios with both the 2” gap and the 3.5” gap. It was observed that the pallets bend more when there is a larger deckboard gap, but it was only significant for the metal pails. These results are in line with previous research done on corrugated boxes interacting with pallet deflection that was conducted by former CPULD graduate students Jonghun Park, Page Clayton, and Steven Morrissette.

This study revealed that pail size has a significant effect on pallet deflection, while the pail material does not make as significant a difference. Future studies will focus on the investigation of pail stacking patterns on pallet deflection in order to gain more understanding about how pails can affect pallet performance.