Unit Load Formation Equipment

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Unit load formation equipment is used to restrict materials so that they maintain their integrity when handled a single load during transport and for storage. If materials are self-restraining (e.g., a single part or interlocking parts), then they can be formed into a unit load with no equipment.


1. Self-restraining (no equipment)

  • One or more items that can maintain their integrity when handled as a single item (e.g., a single part or interlocking parts)



2. Pallets

  • Platform with enough clearance beneath its top surface (or face) to enable the insertion of forks for subsequent lifting purposes.
  • Materials: Wood (most common), paper, plastic, rubber, and metal.
  • Size of pallet is specified by its depth (i.e., length of its stringers or stringer boards) and its width (i.e., length its deckboards)—pallet height (typically 5 in.) is usually not specified.
  • Orientation of stringers relative to deckboards of pallet is specified by always listing its depth first and width last: Depth (stringer length) × Width (deckboard length)
  • 48 × 40 in. pallet is most popular in the US (27% of all pallets—no other size over 5%) because its compatibility with railcar and truck trailer dimensions; e.g., the GMA (Grocery Manufacturers of America) pallet is four-way and made of hardwood
  • 1200 × 800 mm “Euro-Pallet” is the standard pallet in Europe
  • Single-face pallets are sometimes referred to as “skids”



3. Skids

  • Platform (typically metal) with enough clearance beneath its top surface to enable a platform truck to move underneath for subsequent lifting purposes
  • Forks can also be used to handle skids since the clearance of a skid is greater than that of a pallet
  • Compared to a pallet, a skid is usually used for heavier loads and when stacking is not required
  • A metal skid can lift heavier loads than an equal-weight metal pallet because it enables a platform truck to be used for the lifting, with the platform providing a greater lifting surface to support the skid as compared to the forks used to support the pallet



4. Slipsheets

  • Thick piece of paper, corrugated fiber, or plastic upon which a load is placed
  • Handling method: tabs on the sheet are grabbed by a special push/pull lift truck attachment
  • Advantage: usually used in place of a pallet for long-distance shipping because their cost is 10–30% of pallet costs and their weight and volume is 1–5% of a pallet
  • Disadvantage: slower handling as compared to pallets; greater load damage within the facility; special lift truck attachment reduces the vehicle’s load capacity



5. Tote Pans

  • Reusable container used to unitize and protect loose discrete items
  • Typically used for in-process handling
  • Returnable totes provide alternative to cartons for distribution
  • Can be nested for compact storage when not in use



6. Pallet Boxes / Skid Boxes

  • Reusable containers used to unitize and protect loose items for fork/platform truck handling
  • Pallet box sometimes referred to as a “bin pallet”



7. Bins / Baskets / Racks



    8. Cartons

    • Disposable container used to unitize and protect loose discrete items
    • Typically used for distribution
    • Dimensions always specified as sequence: Length × Width × Depth, where length is the larger, and width is the smaller, of the two dimension of the open face of the carton, and depth is the distance perpendicular to the length and width
    • Large quantities of finished carton blanks or knocked-down cartons can be stored on pallets until needed



    9. Bags

    • Disposable container used to unitize and protect bulk materials
    • Typically used for distribution
    • Polymerized plastic (“poly”) bags available from light weight (1 mil.) to heavy weight (6 mil.) in flat and gusseted styles
    • Dimensions of bag specified as: Width × Length, for flat bags, and Width × Depth (half gusset) × Length, for gusseted bags



    10. Bulk Load Containers

    • Reusable container used to unitize and protect bulk materials
    • Includes barrels, cylinders, etc.
    • Used for both distribution and in-process handling



    11. Crates

    • Disposable container used to protect discrete items
    • Typically used for distribution



    12. Intermodal Containers

    • Reusable container used to unitize and protect loose discrete items
    • Enables a load to be handled as a single unit when it is transferred between road, rail, and sea modes of transport; e.g., the container can be unloaded from a cargo ship and loaded onto a truck as a single unit
    • It is not as common to use intermodal containers for airfreight transport because of aircraft shape and weight restrictions
    • Standard outside dimensions of intermodal containers are: 20 or 40 ft. in length; 8 ft. in width; and 8, 8.5, or 9.5 ft. in height; less 8 in. of length, 5 in. of width, and 9.5 in. of height to determine the inside dimensions
    • Typical sea transport costs per 40-ft. container are: $3000–4000 from Japan to the US west coast, $4000–5000 from Singapore to the US west coast, and $2500–3500 from Europe to the US east coast; transport costs for a 20-ft. container is 70% of the costs of a 40-ft. container7



    13. Strapping / Tape / Glue

    • Used for load stabilization
    • Straps are either steel or plastic
    • Plastic strapping that shrinks is used to keep loads from becoming loose during shipment



    14. Shrink-wrap / Stretch-wrap

    • Used for load stabilization
    • Allows irregular loads to be stabilized
    • In shrink-wrapping, a film or bag is placed over the load and then heat is applied to shrink the film or bag; manual or automatic; most shrink-wrap applications are being replaced by stretch-wrapping
    • In stretch-wrapping, a film is wound around the load while the film is stretched; as compared to shrink-wrapping, stretch-wrapping has lower material, labor, and energy costs



    15. Palletizers

    • Used for load formation
    • Three general methods of building (or “palletizing”) unit loads

    (a) Manual Palletizing
  • Operators arrange items into the desired pattern used to form the unit load
  • Since the ergonomics of loading and unloading are important (e.g., vertically, the prime working zone is between the knees and the chest; horizontally, reaches of more than 24 in. with a load should be avoided), lift and turn tables are often used
  • Semi-mechanized palletizers use operators to arrange items into the desired pattern for each layer of the unit load and a powered device is used to transfer layers onto a pallet and then lower the load for the next layer
  • (b) Robotic Pick and Place Palletizers
  • Fully automated device to build unit loads
  • Used when flexibility is required (e.g., the “Distributor’s Pallet Loading Problem”)
  • Greatest limitation is capacity, typically 6 cycles per minute; capacity is determined by the number of items handled with each pick operation
  • (c) Conventional Stripper Plate Palletizers
  • Fully automated device to build unit loads
  • Used when high throughput of identical loads is required (e.g., the “Manufacturer’s Pallet Loading Problem”)
  • Capacity is typically greater (30–180 items per minute) than pick and place because an entire layer is placed on the load at one time; not as flexible as pick and place
  • Preformed layer of items (cases) are indexed onto the stripper plate (or apron); when properly positioned over the pallet, the apron is pulled out from underneath the layer to deposit the layer onto the pallet
  • “Right angle” pattern formation—very flexible patterns are possible; can handle a wide variety of case sizes and types; limited capacity (up to 80 items per minute); compact design
  • “In-line” pattern formation—flexible patterns are not possible; ideal for high speed operation (up to 180 items per minute); takes up more room (larger machine) than right angle