Five Potential Benefits of Reusable Pallets & Containers
| Presented to Returnable Pallet & Container Coalition
Annual Meeting |
| |
| by John W. Clarke | September 22, 1999 |
Introduction
How do we justify reusable pallets or containers in an existing single-use system? There are many benefits of reusables, but 2 benefits that stand out are the theme of your meeting, Saving Dollars and Saving the Environment. In most cases, reusables are a more efficient use of our natural resources. That is, a durable plastic container that is used 20 times will use fewer resources than 20 disposable (but recyclable) plastic containers. For most pallet and container users, however, saving dollars takes priority over saving the environment. Therefore, manufacturers of reusable products must justify their products on a cost basis. This is typically measured in cost per trip, or all the costs associated with using the pallet or container. Many of these costs are obvious, such as purchase price, return logistics, washing, repair, etc. Other less obvious costs, such as reduced product damage, increased functionality, etc. are not easily quantified. This presentation will identify 5 potential benefits of reusable pallets and containers. These are not easily quantified, and do not apply in all cases, but could help make the sale when reusables compete with single use competitors. Each of the benefits is explained below.
1. We know that Shipping Vibrations Can Cause Product Damage for Some Products
We measure shipping vibration frequency in Hertz (Hz), or cycles per second.
Trucks and rail cars typically vibrate in the 2-15 Hz range. Every loaded pallet has a resonant frequency, or the frequency at which the load experiences the greatest movement. Low stiffness pallets may resonate below 15 Hertz. Increasing the pallet stiffness tends to increase the resonant frequency. Reusable pallets tend to have stiffer decks.
Potential Benefit #1
Reusable pallets tend to have stiffer decks, and will transmit fewer shipping vibrations to the product than Single use pallets with less stiff decks.
2. We Know that Stress Concentrations can Cause Product Damage
In a pallet, decks will bend when loaded, but stringers and blocks are rigid.
Flexible, low stiffness, decks will transfer a greater percentage of product weight to the rigid pallet stringers and blocks. More stiff decks distribute product weight over more of the pallet footprint, and away from the rigid stringers and blocks.
One of our clients was experiencing product damage with unit loads of industrial light fixtures. This damage occurred at the fixtures adjacent to the pallet. Previous protective packaging, such as corrugated pads and corner posts, had reduced some of the damage, but at a significant cost. Damage levels were still greater than acceptable. We felt that stress concentrations developed above the 3 stringers as developed as the ½" thick deckboards deflected under load. We tested 5 pallet designs representing different deck stiffness levels:
- Control pallet (current design) - 1/2" thick decks and 3 stringers
- Same design with 5/8" thick decks
- Same design with 3/4" thick decks
- 4 stringer pallet with 1/2" thick decks
- reoriented pallet with 1/2" thick decks (i.e. 40 × 48" rather than 48 × 40" pallet)
In the end, it was determined that the best solution was a 3 stringer pallet with ¾" thick deckboards. This cost more than the previous ½" deck pallet. Fortunately, however, the stiffer deck lowered stresses to the point that less protective packaging was needed. In the end, the client realized a net 20% overall savings in unit load packaging and pallet costs.
Potential Benefit #2
Reusable pallets tend to have stiffer decks, and will distribute product weight more evenly than Single-use pallets with less stiff decks.
3. Under heavy loads, any pallet deck will bend.
With such loads, the sum of the stringer or block area under the deck determines product stress concentrations.
This can be illustrated by comparing the Chep Mark III stringer pallet and a typical "GMA" pallet. The Mark III pallet has 9 top deckboards, 4 at 5.5" wide and 5 at 3.5" wide. Mark III stringers are 2.5" wide. Therefore, the area over the stringers covered by top deckboards is 296 square inches. A typical GMA has 7 top boards, 2 at 5.5" wide and 5 at 3.5" wide. Stringers are about 1.38" wide, and the top deck to stringer overlap is only 118 square inches. This is the area that will not bend under load. The rigid area of the Chep Mark III pallet is 2.5 times greater than that of the GMA pallet. In other words, if we have 2800 pounds per pallet, stacked 4 high, the pressure on the product directly over the Chep stringers is 38 psi. The pressure over the GMA stringers is 95 psi.
Potential Benefit #3
Reusable pallets tend to have more deck coverage, and larger blocks and stringers. These larger components transfer heavier product weights over a greater rigid bearing area.
4. Different products and packaging methods exhibit different levels of load bridging, or interlocking within the stack.
Listed below are the average deflections of a racked pallet with 5 different loads representing different levels of load bridging. All loads weighed 1500 pounds. All pallets were racked in the same span. The only difference was the load configuration. The inflatable test air bag represents the control with no load bridging.
| Load Configuration | Pallet Deflection in Rack |
| Control (Air bag load) | 0.77 inches |
| Bags | 0.70 inches |
| Small Boxes | 0.57 inches |
| Medium Boxes | 0.50 inches |
| Large Boxes | 0.33 inches |
These tests indicated that we could reduce pallet deflection with a 1500 pound load by up to 57% by changing the package! How does the load bridging of plastic Returnable Produce Containers (RPC's) proposed for the produce industry compare with the current corrugated boxes. A different level of load bridging will require a different strength and stiffness pallet.
Potential Benefit #4
If RPC's represent a greater level of load bridging than corrugated boxes, lower stiffness (lower priced) pallets may be acceptable. Conversely, if RPC's offer less load bridging than corrugated boxes, higher stiffness (probably reusable pallets) may be more economical.
5. Automated Material Handling Systems require high quality, consistent pallets.
The Center for Unit Load Design has documented pallet quality required for automated systems in "Performance Specifications for Pallets to be used in Automated Unit Load Material Handling Equipment." These specifications outline such things as size tolerances, squareness, and flatness. Higher quality pallets and containers that meet these specifications will cost more money. This extra money is more easily justified in reusable products where that cost is distributed over multiple trips.
Potential Benefit #5
It costs money to manufacture pallets that meet the performance requirements of automated systems. With reusable pallets, this cost is distributed over multiple trips.
In Summary, Reusable Pallets and Containers must be cost competitive to replace Single use systems. The potential benefits of Reusables, such as
- Reduced shipping vibrations
- More even product weight distribution
- Larger rigid bearing components
- Greater levels of Load Bridging
- More economical compatibility with automation
will help increase the cost competitiveness of Reusable Pallets and Containers.
