Unit load formation equipment used to restrict materials so that they maintain their integrity when handled a single load during transport and for storage. The major types of unit load formation equipment are ([+] = more info):
Advantages of unit loads:
- More items can be handled at the same time, thereby reducing the number of trips required and, potentially, reducing handling costs, loading and unloading times, and product damage.
- Enables the use of standardized material handling equipment.
Disadvantages of unit loads:
- Time spent forming and breaking down the unit load.
- Cost of containers/pallets and other load restraining materials used in the unit load
- Empty containers/pallets may need to be returned to their point of origin.
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 purposesMaterials: 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) x Width (deckboard length)
48 x 40 in. pallet is most popular in US (27% of all pallets—no other size over 5%) because its compatibility with railcar and truck trailer dimensions
1200 x 800 mm "Euro-Pallet" is the standard pallet in Europe
3. Skids
Platform (typically metal) with enough clearance beneath its top surface to enable a platform truck to move underneath for subsequent lifting purposesForks 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 placedHandling method: tabs on the sheet are grabbed by a special push/pull lift truck attachment
Advantages: 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
Disadvantages: 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 itemsTypically used for in-process handling
Returnable totes provide alternative to cartons for distribution
6. Pallet Boxes/Skid Boxes
Reusable container used to unitize and protect loose items for fork/platform truck handling7. Bins/Baskets/Racks
Storage equipment that also can be used to unitize and protect loose discrete items
8. Cartons
Disposable container used to unitize and protect loose discrete itemsTypically used for distribution
Dimensions always specified as sequence: Length x Width x 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 materialsTypically 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 x Length, for flat bags, and Width x Depth (half gusset) x Length, for gusseted bags
10. Bulk Load Containers
Reusable container used to unitize and protect bulk materialsIncludes drums, cylinders, etc.
Used for both distribution and in-process handling
11. Crates
Disposable container used to protect discrete itemsTypically used for distribution
12. Intermodal Containers
Reusable container used to unitize and protect loose discrete itemsEnables 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
The 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. container [15]
13. Strapping/Tape/Glue
Used for load stabilizationStraps 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 stabilizationIn shrink-wrapping, a film or bag is placed over the load and then heat is applied to shrink the film or bag; allows irregular loads to be stabilized; 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; allows irregular loads to be stabilized; manual or automatic; 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:
15(a) Manual Palletizing
Operators arrange items into the desired pattern used to form the unit loadSince 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
15(b) Robotic Pick and Place Palletizers
Fully automated device to build unit loadsUsed 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
Operators 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
15(c) Conventional Stripper Plate Palletizers
Fully automated device to build unit loadsUsed 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
"In-line" pattern formation (top picture)—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
"Right angle" pattern formation (bottom picture)—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
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