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Virginia Tech: How to Design Around a Unit Load
Any pallet supplier can give a customer a price, but smart companies can become an extension of their customer’s packaging procurement operation by showing them how to cut costs and improve product protection.

By Peter Hamner, Marshall White
Date Posted: 11/1/2005

Pallet manufacturers and recyclers are always looking for ways to differentiate themselves. One way to stand out from the crowd is to give your client more than just a price.

Any pallet supplier can give a customer a price, but smart companies can become an extension of their customer’s packaging procurement operation by showing them how to cut costs and improve product protection.

Consider giving key customers a free consultation and complete packaging audit as part of a guaranteed order. Or you could offer a basic packaging audit — which would help them see their need for your service without giving them the answers they need unless they do business with you. This keeps them from taking your information and shopping it around for a lower price.

This article covers the basics of unit load design and some key points you need to learn to conduct a successful packaging audit.

Unit Load 101

Products, which because of their form cannot be shipped or stored in bulk, are consolidated or unitized for storage and transport. A unit load is a single item, a number of items, or a bulk material that is arranged and restrained so that the load can be stored, picked up, and moved between two locations as a single mass.

A typical unit load consists of corrugated containers stacked on a pallet and stabilized with stretch wrap or other materials. It is estimated that more than 2 billion unit loads are in continual daily use throughout the U.S.

Taken as a whole, the collective decisions of packaging and logistics professionals have a significant impact on the cost, safety, and environmental impacts of existing supply chain logistics systems. Yet, the primary goal of this group of professionals is supply chain cost reduction. That is, reducing the cost of activities associated with the movement of products and materials between seller (manufacturer) and buyer (consumer or customer).

Consumer product and industrial product move through slightly different supply chains. However, a common characteristic of both will be various dynamic and static mechanical stresses on the unit load.

Supply chains are predominately unit load based material handling systems consisting of three primary components, exclusive of the products being stored or shipped. These components are packaging, pallets, and unit load handling equipment.

Associated with each component of this system is a community of designers; each charged with reducing the cost of the component in the system for which they are responsible. Raw materials represent the largest cost of each of the three logistics systems components, and therefore cost reductions are typically associated with reducing raw material requirements by redesign of the package, pallet, or handling equipment.

Fundamentally, the three components of the supply chain system mechanically and physically interact during product storage and shipping. These interactions are both dynamic and static. Dynamic vibration and shock can lead to load shifting, product damage or packaging damage. Static compression force can lead to warehouse stacking instability or product damage.

The redesign of one component of the system will potentially affect the performance of one or both of the other components and ultimately impact the performance of the entire system.

For example, to reduce the cost of roll conveyor systems, conveyor designers may chose to increase spacing between rollers in the unit load transport within a distribution center. This will effectively change the load distribution on the pallet in the unit load moving across the conveyor. The consequence of this design change, if no other changes are made in the unit load, will be altering the direction of movement, the velocity of the unit load, or the shape of the unit load in the form of load instability.

Correspondingly, a packaging designer may reduce container cost by reducing liner weight or medium weight in a corrugated paperboard container. Doing this without corresponding changes in the pallet or handling equipment will alter the forces being applied to the contents of the container. This can result in product damage and it can also result in lowering the stiffness in the unit load. The subsequent increased deflections can alter the movement and storage efficiency of the unit load.

Systems-Based Engineering

A ‘systems-based’ approach to unit load design that encourages supply chain component designers to work together in an effort to streamline the efficiency of the entire system would be most practical in terms of reducing costs, improving workplace safety, reducing waste, and protecting the environment.

Unfortunately, this is seldom the case. Instead, we continue to design each component separate from the others. Subsequently, the design process ultimately continues in a manner that targets ‘component’ cost reduction instead of system cost reduction.

The avoidable costs of component-focused design are huge. In some cases these costs may not be as visible as the price tag of the packaging, but they are still there. These costs can be substantial compared to the few extra cents here and there for packaging tailored to the unique needs of each unit load. Regardless of the type of pallet or material used, systems-based design elevates the importance of the pallet and packaging provider while helping the customer save on overall systems cost.

Understanding how the components interact is necessary for proper systems design. Various component designers must work together, and the pallet provider can be the key link to combine the design components into one, easy-to-understand solution for the customer.

The first step toward streamlining an existing unit load materials handling system is to conduct a comprehensive palletization audit — an organized procedure that helps a system designer determine the location of one or more system constraints. System constraints often dictate pallet, packaging, and material handling equipment and component costs because they force system design requirements to — at a minimum — overcome the stress caused by the constraint.

What are system constraints? More often than not, the most common system constraint is the location of the greatest mechanical stress level. All mechanical stress interactions pass through the pallet interface between the packaging (load) and the handling equipment. The palletization audit documents the load condition on top of the pallet and the support conditions under the pallet such that all mechanical stress constraints can be identified.

Once the system constraint is identified, one can select from among several standard test procedures to determine the most economical way to reduce the stress on or within the unit load. The final step is implementation of the design change. Information necessary to conduct a complete palletization audit includes load and support conditions, shipping conditions, and detailed pallet characteristics.

For example, take a supply chain system failure whereby fragile countertops are packaged into cumbersome wooden crates, palletized into a unit load, and shipped by truck to retail outlets. Consequently, the countertops often arrive with significant damage incurred during truck transport.

After performing a palletization audit, it is discovered the source of greatest stress, the ‘system constraint,’ occurs during shipping and as a result of vertical shock and vibration as the trailer bounces down the road. The limiting interaction is shock and vibration during shipment. The over-designed crate provides no vertical stability while little lateral support is actually needed.

Using information from the American Society of Testing and Materials (ASTM) and the appropriate testing according to ASTM 4169, it was determined that by fitting a corrugated sleeve over the stacked countertops, and banding the counter tops directly to a pallet, the expensive crate could be eliminated. More importantly, this reduced, improved, and lower cost unit load design mitigates the product damage initially caused by the accelerated vertical vibration forces within the load.

In summary, the procedure for implementing system-based design for improving supply chain efficiency includes the design of the most efficient unit load. The first step is to document all existing pallet, load, and support conditions. Second, identify the locations of the high mechanical stress. Third, use one or more laboratory and field test procedures to determine the most economical approach to reduce the system constraint. The final step will be implementation. For more information, contact Virginia Tech’s Center for Unit Load Design (www.unitload.vt.edu).

Several computer programs are available that can assist with the design and implementation of unit loads into the logistics supply chain. Of these, the Pallet Design System (PDS®) is especially unique. PDS® was developed by Virginia Tech in cooperation with the National Wood Pallet and Container Association (www.palletcenral.com), and is the only computer aided structural design program for wood pallets. It takes into account the effect of packaging design, package or container stacking pattern, and load stabilizers used. Other programs, including TOPS® (www.topseng.com) and CAPE PACK® (www.capesystems.com), model the geometric configurations of various types of packages, pallets, and trailers. 

Other tests available to unit load designers are various unit load (pallet and packaging) test procedures, as well as specifications for strapping, shrink-wraps, and other load stabilizers. These are published by ASTM (www.astm.org), and the International Safe Transit Association (ISTA) (www.ista.org).

For more thorough training on unit load design, consider taking the Unit Load Short Course offered by Virginia Tech. The next one will be in the spring of 2006.

The global economy of this century will begin with a shift of export growth among non-industrialized countries, where materials handling systems development is in its infancy. The timing is ideal for a shift to more systems-based design with the materials handling expertise of Europe and North America leading the way.








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