On Racking and Shelving

Jun 20, 2007 9:34 PM  By

Don’t know your racking from your shelving? Here’s a primer:

Pallet racks
Pallet rack comes in many different capacities, bay widths, and depths. The most common sized is 99 in. or 101 in. wide bays and 42 in. deep. Pallet racks can be decked or left with only the beams to support a pallet. There are hundreds of rack manufacturers, so only a few major suppliers are shown below. Unless your project is very large, it is likely that you will purchase your pallet racks from a local dealer or distributor. You may also want to contact a used equipment supplier for rack at a reduced price. In addition to pallet rack, there are several variations: double deep rack, push back rack, cantilever rack, pallet flow rack, drive in rack, drive-through rack. Pallet rack can be used to support a multi-level pick module. It is even possible to have a rack-supported building.

Flow Rack
Case or carton flow rack can create a very dense picking environment, while at the same time, permitting storage of a substantial amount of reserve stock. Flow rack stores stock in lanes front to back so that only one case is presented at the forward pick location at one time. When the case is emptied, it is removed, and all of the cases behind it flow forward. This insures FIFO (first in, first out) consumption of product. Flow racks are replenished from one side (the back) and picked from the other side (the front). The original flow rack consisted of roller wheels making up lanes with dividers between them. Newer rack uses small rollers that resemble conveyor rollers, but are only about ¾ in. in diameter and 9 to 12 in. long. Boxes track perfectly on the rollers and the rollers can accommodate a wide variety of box sizes without having to reset tracks and lane dividers. Flow rack creates an extremely dense and efficient picking environment, but it does take up a fair amount of space–two aisles and the deep storage for each and every SKU, whether you need it or not.

Shelving / cabinets / drawers /lockers
Shelving is another commodity item available from a variety of manufacturers and distributors. In addition to traditional bin shelving, it is also possible to purchase heavier duty shelving with stronger uprights. In fact, pallet-rack uprights can be used to create heavy duty shelving. Narrower depth pallet-rack frames can be combined with close horizontal beam spacing and either wire decking or solid wood or metal decks to create this heavy capacity product. In addition to shelving, there are cabinets, compartmentalized drawers, and movable aisle products.

Movable aisle shelving
Movable aisle shelving is shelving that moves on wheels, selectively opening only a single (or limited) number of aisles at one time. By limiting aisles, the amount of storage is dramatically increased, and space savings of up to 90% are possible. You should use this product only for low access materials where you don’t expect multiple pickers to be working at the same time.

Pallet flow
Pallet flow lanes can be set on the floor or into existing pallet rack. Pallet flow relies on gravity to more a loaded pallet into position when the pallet in front is removed. In a picking operation, the pallet may have eaches on it. In a bulk operation, the pallet may be taken out of any rack storage location, enabling the pallet behind to index forward. Pallet flow can be economical, but it gets more expensive the deeper and heavier the product to be stored. If pallet flow is used at higher levels, it is important that it be equipped with dampening mechanisms to prevent gravity from causing the pallet or the load stored on the pallet from falling forward when it hits the front stop. Pallet flow can be quite deep, if proper dampening mechanisms are used. Pallet flow can be automated using AS/RS mechanisms. Pallet flow is FIFO so it insures stock rotation. Another form of deep storage is called push back rack, and here, the storage system is LIFO (last in first out). With push back rack, the pallets sit on carriers that nest forward and push back up to five deep.

Sam Flanders is president of Durham, NH-based operations consultancy Warehouse Management Consultants. He can be reached at www.2wmc.com.