Whether it's a pallet load or a refrigerator, storing and staging large parts can be a challenge. Not only do they require significant cubic space, but large parts are often cumbersome to putaway and retrieve. Fortunately, there are several manual and automated options available to meet specific space, throughput, accessibility and related operational requirements.

On the manual side of the equation, for instance, single-deep pallet racks maximize accessibility but carry a penalty in terms of floor space required. Drive-in racks flip-flop that proposition. Meanwhile, automated storage and retrieval systems trim labor requirements without sacrificing accessibility yet cost considerably more than manual systems.

In the end, finding the most suitable large parts storage and staging system is a process of matching your needs to the options available. Making the right choice will directly impact your operation's efficiency and cost effectiveness.

Non-automated unit load storage and staging equipment comes in several different configurations. Depending on the design, loads are stored one or several deep with lift trucks typically used to store and retrieve. Unit load rack, which accounts for the vast majority of manual storage and staging systems, can rise 40 feet or more to maximize use of the cube and minimize floor space requirements. How-ever, most stand just 12-18 feet tall.

Single-deep pallet racks are the most common type of manual pallet rack. Loads are stored one pallet deep in a single bay, allowing maximum accessibility to each load. Because this design requires far more aisles to store the same number of pallets as other types, it also has the lowest storage density.

One pallet load is stored behind another in a double-deep rack structure. While storage density is doubled, the front bay must be open to access a load in the rear bay. As a result, double handling of loads occurs unless loads are stored in a last-in/first-out routine.

Drive-in racks are an extension of double-deep racks. Rather than stopping at just two pallets per bay, drive-in racks store loads three, four or more deep, creating extremely high-density storage. Lift trucks drive into the front of the bay and place the load in the most forward open position. A last-in/first-out routine eliminates double handling. Additionally, access to pallets at higher levels is limited by how far the lift truck can drive into the bay and by truck design. Drive-through racks, a variation on the same theme, allow lift trucks to drive into the bay from either end of the rack.

Gravity flow racks store and stage either pallets or individual cartons utilizing gravity to move the load into position. Loading occurs at the back end of the lane. The load then travels down the slightly inclined lane either on skatewheel or roller conveyor. It stops either at the front of the lane or behind a load already in place. Unloading is a first-in/first-out routine.

Another variation on gravity flow racks, pushback-racks, is generally used only with pallet loads. Rather than have lift trucks drive into or through rack for high storage density, pushback achieves the same end by placing loads on individual carts in a lane. The first load is placed on a cart. When the next load is delivered, the driver pushes back the first pallet and places the next on a second cart that has come into position. Push-back racks are two to five pallets deep.

Manual storage and staging of long tubes, bars, rods and similarly shaped items usually falls to cantilever racks. This design takes two uprights, places them at a distance half of the load's typical length, and hangs short horizontal members off both uprights at equal intervals to support the load. Loading and unloading is from the front of the rack.

Falling between manual and automated systems are high-density dynamic storage systems (HDDS) that are powered by gravity or electrical/mechanical means. HDDS are a more highly engineered version of gravity flow rack for palletized products. Pallets are loaded from the back and travel to the front of the incline rack lane. Some designs rely on gravity to move the load. Others use a pneumatic system that actually lifts the load and moves it forward.

Movable racks are mounted on carriages. At any given time, all racks but two rest alongside each other. An access aisle separates the other two banks of rack. To reposition the aisle, the carriages, which can be powered, are moved until the aisle appears in front of the rack and storage locations that must be accessed. While multiple rack banks typically must be moved to access inventory, this design minimizes floor space requirements.

When labor is tight, throughput requirements high and computerized inventory control essential, automated storage and staging is preferred over manual systems. The three primary types of automated systems are automated storage and retrieval systems (AS/RS), carousels and vertical lift modules (VLM).

While AS/RS come in three sizes, only the unit load type is suitable for large parts. In this configuration, two rows of standard rack face each other with a narrow aisle between them. Down the center of the aisle is a raised metal rail that a mast travels along. A putaway/retrieval mechanism travels up and down the mast (collectively called a storage/retrieval machine) to the height of the selected storage location to putaway or retrieve the load. All movements are under computer control.

Loads typically enter and exit an AS/RS at an end-of-aisle pickup/deposit station. Depending on the design, lift trucks or conveyors either deliver or takeaway loads.

The number of aisles in an AS/RS can vary. Similarly, rack height varies with some systems over 100 feet tall. Typically, the storage/retrieval (S/R) machine is dedicated to an individual aisle. How-ever, there are lower throughput systems that move the S/R machine on a transfer car between aisles as needed.

A cousin of AS/RS is a system that uses a powered lifting and handling device to store and retrieve pallets in an aisle of racks. The operator-directed handling device hangs in the middle of the aisle suspended from a crossbeam that runs along tracks mounted on top of both sets of racks. It handles loads to 4,000 pounds using a fork lift type attachment.

While vertical carousels store parts only as large as cases, horizontal carousels handle much larger parts including pallet loads. Both designs manage the inventory and movement of the carousel with dedicated software that may or may not interface with other information systems such as warehouse management software.

A hybrid design that combines features of AS/RS and vertical carousel technologies is the vertical lift module (VLM). The outside of the unit looks much the same as a vertical carousel. Inside, loads are stored on trays located on both sides of a column. An inserter/ extractor mechanism rides up and down a mast in the center of the column, accessing storage locations as needed.

Putaway and retrieval operations are under the control of either a push button or a PC-based inventory management software package. While typically associated with small parts storage, there are VLM designs that accommodate cases and pallets as well as large finished goods. The modularity of VLMs makes it very easy to change the unit's height, creating a storage bank tailored to specific storage requirements.

In the end, there are many options for managing the storage and staging of large parts, making possible a good match between requirements and equipment.

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