ISTA Views

MAY | 2018

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Freight in the truckload category is typically distributed on pallets in a unitized form to maintain stability and provide product protection during transit. Unitization of a load can also increase packaging and handling efficiency during distribution [5]. There are multiple ways of unitizing a load including stretch wrap, stretch hood, stretch net, and strapping or banding [6]. A few recent studies have investigated the specifications for the stretch wrapping operation as related to load stability [7-12]. As related to stretch wrapping and its effect on a unit load's stability, it is critical to understand how packaging, pallets and handling equipment interact. The interface between the pallet and unit load handling equipment during shipping and handling operations include vibration interactions, transfer of shocks and impact forces, compressive forces and load shifting [13]. Stretch wrap is applied to a unitized load to increase load containment and hence establish unit load stability. Load containment allows a load to be securely held in place so it can arrive undamaged at its desired destination. Proper stretch film application increases load containment [7]. Stretch film is properly applied when the film is stretched, applied under tension, and elastic recovery conforms the film to the load [14]. Additional wraps, heavier gauge film, and increased post-stretch can increase load containment. To obtain the maximum load containment, three factors must be considered. These factors are the unitized load type, wrapping configuration, and distribution environment [7]. The type of unitized load primarily refers to the items that are being shipped. The type of product and the orientation in which the product is unitized affect the ability of the load to be contained. Unitized loads that are uniform in shape and have no protrusions or puncture hazards are considered "A-Profile Loads"; loads with puncture hazards lesser than 7.62 cm (3 in) are considered "B-Profile Loads" and loads with puncture hazards over 7.62 cm (3 in) are considered "C-Profile Loads" [15]. There are many variables which affect the ability of stretch wrap to contain the load and they can be altered when stretch wrapping a pallet load. These variables include: wrap patterns which refers to the location that the stretch film is applied; film force to load which is the tension created due to the stretch film's attempt to return to its original state after having been stretched; number of layers; turntable and carriage speed; pre-stretch which is the process of stretching film before it is applied to the load; and the film type [7]. The distribution environment refers to the dynamic and static stresses that a unit load endures during the typical shipping and handling events. These events frequently cause unit load failure and are a critical factor when selecting the load type and wrapping configuration. Unitized loads in less than truckload (LTL) shipments are subjected to a harsher environment than truckload shipments (TL) [16]. While TL carriers move full containers or trailers of typically one product from one customer, LTL carriers consolidate multiple customers' orders on the same trailer [17]. TL shipments commonly have one destination while LTL shipments experience multiple exchanges and handling which potentially result in higher abuse and hence increased load failures. Initiatives to lightweight and reduce packaging materials to achieve sustainability goals have created unit load stability challenges in the transportation and handling of palletized packaged goods. Alternatives to standard rectangular corrugated fiberboard shippers, such as shrink-wrapped bundles, retail ready display cases, blister packs and clam shells, perform distinctively when exposed to typical distribution hazard elements such as horizontal impacts [18]. Such impacts may occur during distribution related transport and handling events such as railcar coupling, pallet marshalling and transport vehicle motions. Consequently, an increased focus is being placed on evaluating how current pre-shipment performance tests evaluate load stability. Numerous load stability evaluation test methods already exist and include rotary vibration, rotational drop testing, horizontal or inclined impact testing, fork lift handling courses, tilt testing, road courses, and programmable acceleration/deceleration sled testing [18]. The International Safe Transit Association (ISTA) is an organization focused on the specific issues of transport packaging. ISTA is the leading industry developer of testing protocols and design standards that define how packages should perform to ensure protection of their contents during the ever-changing hazards of the global distribution environment [19]. ISTA's mandate is to enhance the effectiveness of 14 ista views • May 2018 • www.ista.org Evaluation of Stability of Unit Loads for Tilt and Shock Events During Distribution > CONTINUED FROM FRONT COVER Figure 1: Weight & Value of Shipments by Truck as a Percentage of Total: 2007, 2012, and 2040

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