July-August 2015

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he damage resistance of a pallet is particularly important because a damaged or broken pallet cannot safely support or protect the customer's product within the unit load handling environment. The Pallet Design System™ (PDS) offers a solution with its "durability" (damage resistance) analysis of the pallet within the customer's specified unit load handling environment as part of the entire suite of PDS pallet performance evaluations. One of the most common questions the NWPCA PDS team receives regarding the Durability Analysis pertains to Handling Cycles, and what constitutes a cycle. The PDS User's Guide describes a cycle as follows: Each Handling Cycle assumes an average of 15 pallet handlings, with a handling defined as a single lifting, movement, and set-down of a pallet. Components at the periphery of the pallet, particularly the top deck leadboards, are the most frequently damaged during handling of pallets in service, and the PDS Durability Analysis reflects this phenomena. One technique that the pallet designer can use to increase damage resistance is to specify backup boards butted against the leadboards. As an example, for a typical GMA style pallet, the durability improves markedly when the backup boards are butted. The "Cycles to First Repair" improves from three to five cycles, and the "Cycles to First Replacement" improves from five to nine. As a result, the top lead deckboards are no longer the components that limit the service life. The PDS software's Durability Analysis simulates a series of forces and impacts applied to the pallet during each handling cycle. This analysis was developed based on both warehouse and laboratory analysis of the impact forces between pallets, forklifts and other handling equipment. It is partially based on the FasTrack Handling Cycle at Virginia Tech's Center for Packaging and Unit Load Design. The PDS Durability Analysis estimates the number of pallet cycles between repairs for the average pallet. The resistance to damage and the damage level requiring component repair or replacement are based on engineering analysis, laboratory testing and NWPCA's Uniform Standard for Wood Pallets. The PDS user can select either a Service Life Analysis or a Damage Rate Analysis. • The Service Life Analysis predicts the frequency of repairs or replacements for each component over the entire predicted lifespan of the pallet. • The Damage Rate Analysis assumes no repair information and simply estimates the fractional number of handling cycles before a pallet component requires repair or replacement. This analysis can be particularly useful for comparing competing designs with relatively minor changes in specification. To include the Durability Analysis, the user needs to specify in the "Service Environment" which type of analysis (Service Life or Damage Rate) is desired. The Durability Analysis requires additional information for the simulation, including the "Handling Environment Severity" and "Intended Service Duty." Handling Environment Severity reflects the general handling and treatment of pallets in their service environment. If workers are highly skilled and take care in handling pallets, then a "good" handling treatment may be specified, with a "rough" handling specification if the opposite is the case. Intended Service Duty reflects the approximate unit load weight and determines the weight to be used in the simulation. Many design factors affect the durability of a pallet, including: • Lumber species, grade, and moisture content • Fastener specifications, and thus damage resistance of connections • Pallet component dimensions and locations. To learn more about the Durability Analysis, you can consult the PDS User's Guide, or contact NWPCA Technical and PDS Manager, Brad Gething, at 22 PalletCentral • July-August 2015 T PDS Did You Know? Pallet Durability Analysis

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