Life is full of compromises. Pallet storage is no different.

In fact, successful pallet storage is a trade-off between maximizing space, optimizing throughput, taking advantage of other materials handling equipment, and generating a return on investment.

'Selecting the right storage system can reduce a company's overall investment in building and equipment while keeping costs low,' says Geoffrey Sisko, senior vice president, Gross & Associates (732-636-2666, www.grossassociates.com). He's also author of A Complete Guide To Pallet Storage Systems, a detailed look at the costs and benefits of pallet handling and storage methods. (Visit November's click on section at www.mmh.com for more on this resource).

The options range from simply storing pallets on the floor to a variety of rack systems and fully automated storage systems, including automated storage and retrieval systems (AS/RS) and horizontal pallet carousels.

Most facilities are likely to include more than one storage system, depending on the space limitations in a given area, the product being stored, and the velocity of that product.

A number of considerations will drive the design of a pallet rack solution.

The first is the load itself. 'Unless you're talking to a company that only makes one product, loads vary by weight and height,' says Vinnie DePaola, manager of retail sales, Interlake Material Handling, Inc. (630-245-8800, www.interlake.com). 'Some are stackable and some are not. Some products are perishable and have to be stored on a first in/first out basis.'

The second is density versus selectivity. 'Most people want to maximize their storage area,' explains Michael Demetry, national sales manager, Ridg-U-Rak, Inc. (866-479-7225, www.ridgurak.com). 'They also want to maximize throughput. If you need 100% selectivity so that every load is accessible from the aisle, you're going to give up storage density.'

A third is the velocity of product movement. 'You don't store fast movers the same as you store slow movers,' says Carlos Oliver, president, Frazier Industrial Co. (908-876-3001, www.frazier.com). 'A well-designed facility should have different types of pallet racking or even automated storage systems to blend with the product mix.'

Other factors, like pallet handling equipment and ceiling heights, also come into play.

Selective, or single-deep rack, is the most common method of rack storage because every pallet can be readily accessed. But single-deep rack also consumes the most space. 'A lot of operations begin with selective rack and then look at alternatives when they run out of space,' says DePaola.

Double-deep rack stores pallets two deep. 'Double-deep rack is cost-effective any time you have two or more pallets of the same product,' says Frazier Industrial's Oliver. 'You get the benefits of denser storage at a price that's comparable to single-deep rack.'

Drive-in rack allows a lift truck driver to drive into the rack system to put away pallets. That allows for very deep storage, generally from three to 12 pallets deep. That means the last pallet in is the first pallet out.

'Drive-in is a slow process,' says Demetry. 'You want to use it for things that you don't need to access often and that you can put away all at one time.' Drive-in rack is also often used to stage a truckload of product prior to pick up.

Drive-through rack is a close cousin of drive-in. Storing loads several pallets deep, drive-through rack allows the lift truck to enter from either end, rather than just one end as with drive-in. This allows increased accessibility of pallets in the rack.

Push-back rack is usually used to store a single SKU up to five pallets deep. Pallets are stored on a cart or platform that is pushed back by the next pallet loaded into the system. Since the last pallet in is the first pallet out, push-back rack is used for product that doesn't have to be rotated.

Users who need first-in/first-out cap-abilities may use pallet flow rack, which can store loads eight to 10 pallets deep. Pallets are loaded at one end of the slightly angled rack. Gravity then transports pallets to the other end.

Automated storage and retrieval systems (AS/RS) make economic sense when space is at a premium, especially in high throughput operations. An AS/RS usually combines: a conveyor system for automatically delivering and taking pallets away from the system; a storage/retrieval machine to automatically put away and retrieve pallets; and a rack system for storage.

'With an AS/RS, you can go up to 100 feet high,' says Victor Hoerst, manager of business development, Witron Integrated Logistics (847-385-6000, www.witron.com).

You gain even more space, Hoerst adds, because the requirements for lane space for a storage/retrieval machine are less than what's required for a pallet truck.

Some companies turn to an AS/RS to expand the space in an existing facility rather than build a new one. 'We have had a number of customers who took advantage of the vertical height of a building in a metropolitan area because it was too expensive to relocate their facility to the suburbs,' says Paul Moore, director of system sales for FKI Logistex (877-935-4564, www.fkilogistex.com).

But it's not just space savings that justify an AS/RS. Because these systems are computer-controlled, they bring discipline, repeatability and enhanced inventory control to an operation. And since the systems are automated, they minimize product damage and pilfering.

'We justified an AS/RS at Chrysler just on the savings in lost inventory,' says Fintan Mulligan, deputy general manager for the logistics and automation division of Murata Machinery USA (704-394-6900, www.muratec-usa.com).

AS/RS is also ideal for operator unfriendly environments. 'If you're storing ice cream in a freezer, order pickers are going to be less productive than an AS/RS,' says Mike Kotecki, senior vice president, HK Systems (800-457-9783, www.hksystems.com).

Finally, says Kotecki, an AS/RS is often justified when compared to the cost of maintaining lift trucks, batteries and operators in high-throughput facilities.

There is a catch, however. Because they are static, manual solutions, like rack systems, are forgiving and accommodate unstable loads and marginal pallets.

'In any automated pallet storage system, your load should be stretch-wrapped or glued, and you need consistent, top quality pallets or permanent slave pallets,' says Larry Strayhorn, president, Diamond Phoenix (207-784-1381, www.diamondphoenix.com).

While AS/RS systems are used for permanent, dense pallet storage, horizontal pallet carousels are used for automated storage in picking or buffer areas. 'Horizontal carousels are terrific when you're doing batch or split-case picking from pallets to build other pallets,' says Ed Romaine, marketing director, Remstar International (800-639-5805, www.remstar.com).

As with carousels designed for cases, pallets are stored on carriers that rotate horizontally around a track. The operator keys in the pallet needed next, and the carousel delivers it to a picking station. Throughput can be increased by using multiple carousels.

Several hybrid solutions are available for facilities where traditional rack isn't enough, but full automation is too expensive.

HK Systems, for instance, has created a pallet runner machine with rotating forks that travels along a track in the floor. The system works with traditional selective rack or drive-through rack systems, but saves space with a very narrow aisle.

Stack systems combine a selective rack system and a semi-automated mast with pallet forks. 'The ideal application is a storage area directly across from a workstation in a manufacturing plant,' says Chris Helmstetter, product line manager, Stanley Vidmar (800-523-9462, www.stanleyvidmar.com).

'The operator can quickly retrieve a pallet needed for an operation without waiting for a lift truck driver.'

High-density dynamic storage with pneumatic flow rack is a solution that fits somewhere between gravity-enabled flow rack and an AS/RS. Like traditional flow rack, the system allows a user to store loads deeply. Movement of the loads, however, is driven by air, which allows a user to move loads forward or backward and to handle a wide variety of loads in the same lane. For that reason, these solutions are often used to stage a truckload of pallets at a loading dock.

No one pallet storage solution is likely to answer every problem. But used together, they can balance the trade-off between storage space and throughput.

Click on the icon to read how Rittal optimized pallet storage with an AS/RS.
(Retrofit for manufacturing success - May 2003)