Blacksburg, Virginia—This spring I had the privilege of attending the three day “Unit Load Design Short Course” at Virginia Tech. Many readers are familiar with the Sardo Pallet Laboratory at Virginia Tech and Dr. Mark White, an industry expert who is known for his leadership in pallet design. For years, the Pallet Lab and more recently the Center for Unit Load Design have taught short courses and seminars that have been become one of the premiere management educational opportunities in not only the pallet world but also the materials handling world. This article will provide some insights into the course and the benefits that readers might receive by taking advantage of the unit load course series offered at Virginia Tech.
For most of my years of working with the pallet industry, Dr. White has been recognized as both an outstanding speaker and a renowned expert in wooden pallet design. After attending the Unit Load Design Short Course, I realize that the expertise of Mark and his staff goes way beyond pallets. The wooden pallet is not an island; it is an integral part of the unit load concept which includes packaging, pallets, and materials handling machinery. The last few years, Mark has promoted “The Big Idea,” which combines the three elements above into a management science concept of designing unit load material handling systems as a system, not as individual components. It is natural that the Unit Load Design course includes a complete coverage of these three elements. Any professional in the pallet industry will appreciate the integration perspective this course provides.
Dr. Mark White, director of the Virginia Tech pallet staff, Ralph Rupert, a packaging engineer on the staff, and John Clarke, the technical sales director with the Nelson Company and past member of the VPI staff, team taught the course. Two overriding things stood out to me. First, I was impressed by the overall materials handling and unit load knowledge of both Mark and his staff. They know pallets, but their understanding just begins there. Second, Mark and his team are carrying the Big Idea concept to its implementation stage. It is not just a theoretical idea. The team put some meat on the Big Idea structure to show how professionals can work with customers to truly improve their unit load handling systems.
Unit Load Storage
While parcel shipment is concerned more with shocks and blows, unitizing products into unit loads protects them more for compression and stabilization. Corrugated containers still dominate the container market. When pallets and corrugated boxes are combined, they mak eup the largest wood fiber market in the U.S., more than the paper market, new residential construction market, or repair and remodeling market (Table 1).
While the unit load has three components (distribution packaging with product, pallet, and material handling equipment), people have typically made materials handling decisions on individual components instead of on the whole unit load system. Dr. White pointed out that an unsafe workplace is one of the consequences of a component based design of the logistics system. Twenty-five percent of all occupational injuries are during materials handling practices; over half of those are related to packaging failure. In 2000, 566 fatalities and 155,000 serious injuries occurred during unit load warehousing and shipping. Packaging costs are large by any standard. In 2000, U.S. retail sales of $3.9 trillion included $30 to $50 billion in packaging costs (over 1%).
The annual operating expense of the U.S. logistics system is close to a trillion dollars or 9.5% of gross domestic product. Mark believes that 12-15% of this can be eliminated by using system design instead of the existing component design.
As an example of how a change in one unit load system component can impact the other components, Mark suggested that system savings could be brought about by reducing the profile height of pallet truck forktines by 0.75 inches, which would reduce the profile height of a pallet by 0.75 inches. Today typical forktines are 3.25” high. A nominal 5” high pallet would then become an actual 4” high pallet. A pallet would weigh 4 to 5 pounds less, contain 1.25 fewer board feet of lumber, and cost about $.50 less than a pallet does today. Something this conceptually simple could reduce the global wood consumption for pallets by an average of 6.7% and reduce the mass of packaging by 3.2 million tons annually. It would reduce the weight of pallets and the space that they take, but it would require a systems wide approach.
The Virginia Tech Unit Load Center is the logical place to father the Big Idea unit load concept because Tech has been the center of pallet design, and pallets are the central component of the three elements involved in unit load systems. System component interactions that are being studied at the Center include distribution vibration and unit load resonance, load bridging and unit load deformation, equipment spans and unit load deflections, interfacial friction and load stability, compression stress redistribution and product protection, and vertical stabilization versus horizontal stability (Table 2). During the course, participants learn 1) packaging, pallet, and handling equipment terminology, 2) design principles of each component in the system, 3) how these components interact, 4) how these interactions constrain system design, and 5) how to conduct a comprehensive material handling (palletization) audit.
The Palletization Audit
This audit concept is a new wrinkle that directs unit load system designers as to how to study materials handling systems as a system. Mark stated, “A palletization audit is an organized procedure that helps a system designer determine the location of one or more system constraints. The most common constraint is often the location in the system of the highest mechanical stress level. This will often dictate system and component cost. The approach is to redesign or modify the system to reduce these stresses.”
He continued, “All mechanical stress interactions pass through the pallet interface between packaging and handling equipment. The palletization audit is a documentation of all of the loading (packaging) and support (equipment) of the pallet interface.”
The basic concept in a palletization audit is to document the elements involved in a specific materials handling situation. Study and document the characteristics that need to be analyzed. These include load conditions, support conditions, shipping systems, and the pallet itself.
When studying load conditions, a researcher should document the product’s description, its mass, its shock fragility, and its compression strength. The primary package needs to be described, its external dimensions measured, and both its fill pattern and compression strength specified. A secondary package needs to be studied as well, specifying such items as package description, package size, stacking pattern on a pallet, and compression strength.
Other load condition items that must be analyzed include the maximum load weight per pallet and what kinds of unit load stabilizers are being used.
Then analysis must turn to support conditions. What types of warehouse racks are used, and what are the rack spans? How are pallets supported in racks, across length or across width (RAL or RAW)? Other important support characteristics include the maximum number of unit loads in a stack, the pallet dispenser mode of support, the pallet dispenser span, the palletizer mode of support (RAL or RAW), and palletizer span.
Conveyors need to be analyzed. Chain conveyor descriptions include the support mode (RAW or RAL), chain width and chain span. Other support conditions include roll conveyor types, the span between strands in a skate wheel conveyor, width of skate wheels, roll diameter and spacing, direction of pallet rolls relative to pallet length.
Fork lifts have to be analyzed, including lift description, fork tine size, and spacing between the forks. Pallet truck specifications include fork size, wheel location from the heel, and fork spacing.
Third, analysis turns toward shipping systems. What kind of shipping container is used, rail car, trailer, container, etc.? What are the dimensions of the shipping container? How are unit loads positioned in the container? What kinds of dunnage and stabilizers are used?
Of course, we must consider the pallet. What are its footprint and specification, including board and spacing dimensions? What are the strength and stiffness for each load and support condition in the audit?
While none of the ideas here may seem that difficult, many factors have to be considered in an audit. Talking about a systems approach doesn’t have many teeth in it until an audit concept is put in perspective. Simply put, analyze the unit load problem’s details. Document them, analyze them, and look at them from a sensitivity analysis perspective (i.e. what if this changes, or what if that changes, how do they impact the system’s performance?).
Principles of Packaging
Ralph Rupert, a packaging engineer on the Virginia Tech staff with a background in plastics and containerboard, presented a broad perspective on packaging materials. Packaging includes corrugated, metal pails and drums, plastic pails, bags, and wood (Table 3). As Table 3 indicates, corrugated dominates the list of packaging materials. Corrugated has three basic elements, linerboard, medium, and adhesives. Single wall, double wall, and triple wall corrugated provides alternatives with various physical characteristics. Different flute types, different medium grades (weights), different liner grades (weights), and different corrugated designs all affect package strength.
Various test protocols (ISTA, ASTM 4169, and DOT testing on hazardous material packaging) use three basic tests (drop test, vibration test, and stacking test) on corrugated packaging. A package is considered to have passed a test when no damage is seen on the products. Compression for stacked loads is an important characteristic that is studied. Degradation factors include humidity (moisture), storage time, and handling damage. While most degradation due to time occurs fairly quickly, it continues to a lesser degree almost indefinitely. Information on corrugated containers is widely documented for designers who desire information.
Pails usually hold less than six gallons and come with a handle. Pail characteristics include type (metal or plastic), wall thickness, shape, height and volume, diameters (top and bottom). Application areas include paint and chemicals. Metal drums come in the classic sizes of 55 and 32 gallons, but paperboard and plastic drums are used as well.
Various methods are used to maintain unit load integrity during transport. Stretc hwrap, netting stretchwrap, metal and plastic strapping, load adhesives, tie sheets, and corner posts help stabilize unit loads.
Pallet Design and Performance
John Clarke presented the basics of wooden pallets. Much of what he said may be known by many readers; I present here a few items that may interest readers. Within the U.S., it is estimated that some 450 million new pallets are manufactured each year, 1.9 billion pallets are thought to be in use at any one time, and at least 300 million pallets are recovered by recyclers each year. While the flexibility of making a wooden pallet is one of its assets, somewhere around 30% of the pallets made each year are 48x40s.
There are six accepted international pallet sizes (Table 4). The 1200×1000 and 1200×800 are both European standards, the 48×40 is a North American standard, the 1140×1140 is found in Australia, and the 1100×1100 is a common Asian size. The 42×42 is a common size for chemicals and telecommunications.
Some of the advantages and disadvantages of wooden pallets are presented in Table 5. While wooden pallet production in the U.S. is estimated to be close to 500 million units a year, plastic pallet production has grown over the past ten years from about 3.5 million units to 8.25 million units per year. Plastic pallets are made from high density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PV) and engineered thermoplastics. Table 6 lists many of the advantages and disadvantages of plastic pallets.
Composite wood pallets include plywood, oriented strand board, particle board, laminated veneer lumber, and wood/plastic composites. Paper-based pallets have enjoyed a little stronger market because of international phyto sanitary solid wood packaging standards but they continue to be a very small percentage of the market. Paper-based pallets include corrugated, honeycomb, solid fiberboard, and molded pulp. Corrugated is the most common container material in the U.S., transporting 90 to 95% of all goods, while wooden pallets make up a similar portion of the pallet market.
Unit Load Handling Equipment
The course would not be complete without addressing the unit load materials handling equipment, the third element in the equation. Unit load transport equipment includes conveyors, fork lifts and pallet trucks, automatic guided vehicles, stacker cranes, shuttle carts, and elevators. Unit load storage equipment includes static load beam racks, dynamic flow racks, portables racks, drive-in and drive-through racks, and push-back or glide-in racks. Unit load shipping systems include trailers, rail cars, freight containers (both air and sea), and air cargo pallets.
More information on this important topic will be presented in a future article. For more understanding of the kinds of material presented here, readers should consider attending some of the educational courses offered by Virginia Tech. The courses and their dates scheduled for later this year appear in Table 7. Call Bonnie McCubbin at 540/231-5370 for more information or to register. All subscribers to the Pallet Profile Weekly or Recycle Record receive registration discounts.
