Storage equipment used for holding or buffering materials over a period of time. The major types of storage equipment are:
The most common reason for storing a product allows the other elements of production to operate more efficiently on a per-unit basis because the fixed costs associated with utilizing the element can be spread over more products; e.g., storing up to a truckload of product in a facility reduces the per-unit costs of shipping; and buffering or storage of WIP enables batch production which reduces the per-unit setup costs.
Other potential reasons for storage include: time bridging—allows product to be available when it is needed (e.g., storing spare machine parts at the facility); processing—for some products (e.g., wine), storage can be considered as a processing operation because the product undergoes a required change during storage; and securing—e.g., nuclear waste storage.
1. Block Stacking (No Equipment)
Bulk storage using block stacking can result in the minimum cost of storage since cube utilization is high and no storage medium is required, but material accessibility is low since only the top of the front stack is accessible and loads at bottom of a stack must not require support
Storage racks are used when support and/or material accessibility is required
2. Selective Pallet Rack
Most popular type of storage rackPallets are supported between load-supporting beams
Special attachments and decking can be used to make the racks capable of supporting other types of unit loads besides pallets (e.g., coils, drums, skids)
Selective racks can be used for the following types of storage:
Standard—single-deep storage using a counterbalanced lift truck
Narrow-Aisle—storage using a narrow-aisle lift truck
Deep-Reach—greater than single-deep storage (typically double-deep storage)
3. Drive-Through Rack
Loads are supported by rails attached to the upright beamsLift trucks are driven between the uprights beams
Requires similar-width loads
Open at both ends, allowing access from both ends (FIFO)
4. Drive-In Rack
Same as drive-through rack, except closed at one end, allowing entry from only one end (LIFO)5. Flow-Through Rack
Loads are supported on an incline to enable gravity-based movement of the loads within the rack (via, e.g., a gravity roller conveyor)Loaded at the higher end and unloaded at the lower end (FIFO)
6. Push-Back Rack
Same as push-back rack, except loaded and unloaded at the lower end and closed at the higher end (LIFO)7. Sliding Rack
Only one mobile aisle is used to access several rows of racksLocation of the aisle is changed by sliding the rows of racks along guide rails in the floor
Typically found in library stacks
8. Cantilever Rack
Loads are supported by cantilever "arms"Used to store long loads (e.g., bar stock, pipes, lumber)
Similar to pallet racks, except the front upright beams and the front supporting beams are eliminated
9. Stacking Frame
Interlocking units that enable stacking of a load so that crushing does not occurCan be disassembled and stored compactly when not in used
Pallet frames can be used to enable multilevel block stacking
10. Shelves/Bins/Drawers
11. Storage Carousel
Carousel consists of a set of vertically or horizontally revolving storage baskets or binsMaterials (and the storage medium) move to the operator, "part-to-man," for end-of-aisle picking
Each level of the carousel can rotate independently in a clockwise or counter-clockwise direction
Control ranges from manually activated push buttons to automated computer controlled systems
Provides an alternative to typical "man-to-part" AS/RS, where the S/R machine moves to the part
Similar to a trolley conveyor with storage baskets
12. Automatic Storage/Retrieval Systems (AS/RS)
Consists of an integrated computer-controlled system that combines the storage medium, transport mechanism, and controls with various levels of automation for fast and accurate random storage of products and materials
Storage/retrieval (S/R) machine in an AS/RS operates in narrow aisle, serving rack slots on both sides of aisle; can travel in horizontal (along the aisle) and vertical (up and down a rack) directions at same time
Advantages: fewer material handlers, better material control (including security), and more efficient use of storage space
Disadvantages: high capital and maintenance costs, and difficult to modify
12(a) Unit Load AS/RS
Used to store/retrieve loads that are palletized or unitized and weigh over 500 lbs.Stacking heights up to 130 ft. high, with most ranging from 60 to 85 ft. high; 5 to 6 ft. wide aisles; single- or double-deep storage racks
12(b) Miniload AS/RS
Used to store/retrieve small parts and tools that can be stored in a storage bin or drawerEnd-of-aisle order picking and replenishment
Stacking heights range from 12 to 20 ft.; bin capacities range from 200 to 750 lbs.
Termed a "microload AS/RS" when used in assembly, kitting, and testing operations to deliver small containers of parts to individual workstations, where workstations are typically located on the sides of a pair of racks and the S/R machine operates between the racks to move containers to openings in the racks (storage lanes) located next to each station
12(c) Man-On-Board AS/RS
Used for in-aisle picking; operator picks from shelves, bins, or drawers within the storage structureManual or automatic control
S/R machine is similar to an order picker or turret truck and can sometimes operate as an industrial truck when outside an aisle, except the S/R is guided along a rail when operating in an aisle
12(d) Deep-Lane AS/RS
Similar to unit load AS/RS, except loads can be stored to greater depths in the storage rackA rack-entry vehicle is used to carry loads into the racks from the S/R machine, and is controlled by the S/R machine
Termed an "automated item retrieval system" when used to automatically retrieve individual items or cases, with replenishment (storage) taking place manually from the rear of a flow-through storage lane and items are pushed forward with a rear-mounted pusher bar for automatic picking from the front of the storage lane
13. Split-Case Order Picking System
Unlike an AS/RS, a split-case order picking system enables fully automated picking of individual itemsTwo general categories of split-case order picking system are robotic based systems and magazine/dispenser based systems
Robotic based systems are similar in construction to robotic pick and place palletizers
Magazine/dispenser based systems are similar to vending machines, but larger in scale
"A-Frame" dispenser system (pictured) is popular within pharmaceutical distribution centers; items are dispensed onto a belt conveyor that carries them into a container
14. Mezzanine
Inexpensive means of providing additional storage or office spaceMakes use of clear space over activities not requiring much headroom (e.g., restrooms, block storage, etc.)
At least 14 ft. of clear space is needed for a mezzanine
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