Thursday, 19 December 2013

Poor racking choice harms warehouse economics

It has been said that it is the supply chain that competes, not companies, and while that is a truncated version of the truth it stresses the pivotal role of logistics. Within the supply chain it is also true to say that the warehouse role is paramount, far more so than global transport costs, and therefore the racking/shelving function should receive the respect it deserves.

No longer a static, boring part of warehouses on which goods are stored and retrieved, today's racking comes in many dynamic forms with varying levels of 'intelligence' to deliver accurate throughput rates unheard of 40 years ago. But with so many choices comes complexity and therefore higher risks of making the wrong choice of racking equipment and layouts.

Fortunately, many leading racking and forklift companies have software packages to help prospective clients examine various storage scenarios under all operating conditions. Their 'what if' facility will quickly test specification changes and so hasten the decision process and highlight potential bottlenecks but they are only as good as the information fed into them. But while simulation packages should be seriously considered for large, complex warehouse layouts, a word of caution. Some 'what if' software packages have limited scope. They may not deal with floor factors, for example, which are so important for very narrow aisle (VNA) high bay stores. If a package is offered by a forklift company there is also the temptation to promote their own product range, even though they know that there is a more suitable product on the market outside their own portfolio. Warehouse operators, therefore, need to be aware of all the various truck types on offer or they could be foisted with aisles that are too wide and with too many forklifts. Reach trucks, for example, need aisles at least 2.6 mt wide but there are now articulating forklifts which can work in aisles only 1.6 mt wide and so store 30% more pallets in the same cube. For these reasons it is probably wiser to consult an independent, pure simulation software house with a long service record like Cirrus Logistics.*

Success depends on research

To ensure a successful installation, operators must adequately research the product dynamics of their stored goods. This will look at volume flows by stock keeping unit (SKU), sizes, weights, time sensitivity, seasonal demand variations and packaging (particularly crucial for automated stores). Hazardous goods will also affect racking arrangements. The choice of racking will set the permanent warehouse running costs, which can vary widely depending on the nature of the stored goods' dynamics. Where fast-moving pallet loads need 100% instant accessibility then adjustable pallet racking (APR) will be the usual choice. It is the most commonly used racking form, one of the cheapest and gives good stock rotation. It is, however, space hungry. A variation of APR is double-deep storage accessed by forklifts with pantographs or telescopic forks for loads two pallets deep. This improves storage density by 40% but at the expense of 100% instant selectivity.

Cheaper still than APR is block stacking, based on post or cage pallets. These can be stacked four or five pallet loads high, albeit in a relatively tricky operation, and the storage medium can be hired. Suited to homogeneous loads, this method offers one of the highest storage densities but the poorest, instant stock selectivity.

If 100% instant selectivity is not essential then drive-in and drive-through racking might be the answer. This is where a forklift can drive right down a racking lane because pallets are supported only on rails at the side of the lane. There are no obstructing beams. Cold stores favour them because of the high storage density achievable in what is a high energy cost environment, where energy can account for 20-30% of total warehouse running costs. Instant stock selectivity, however, is only about 30%, which means poor picking rates and stock rotation. This racking type is also notorious for damage from forklift collisions.

Why interface costs matter

A safer racking choice for cold stores is mobile racking, also valued for its high storage density. Unlike drive-in, it allows 100% instant selectivity, albeit at a slower rate than APR because time is spent while selected racking aisles are being powered open. Even so, surprisingly high pallet handling rates of 35 an hour are achievable. On the downside, mobile racking costs about three times as much as APR and is unsuitable for fast-moving goods. As with any equipment buying decision for warehouses, however, it should be the interface costs that matter most of all. Mobile racking, for example, achieves 50% more storage capacity than APR which not only cuts energy costs but also high construction costs when considering a new-build project. Bolted racking rather than welded should be preferred in cold stores because the latter is subject to weld failures.

Racking also becomes dynamic, in part, when live or dynamic storage is chosen. Various live storage forms use gravity or powered systems to index loads forward to the picking faces. Pallets or totes are fed in at the back and roll forwards on wheels or full-width rollers. Storage density is high and stock rotation good because it is a FIFO system. A variation of gravity-based live racking is push-back racking, which has storage lanes four or five pallets deep. Unlike conventional live storage, which is fed from the rear, replenishment and picking are at the same place and so it saves space at the racking's rear end.

The last 10 years have seen many advances in dynamic racking through the application of robotics from companies like Swisslog,* SSI Schaefer,* Knapp* and Redirack.* Their purpose is to maximise storage density while dispensing with slower and more inaccurate methods using labour. A good example is Redirack's recent, automated pallet storage, retrieval and sequencing solution. Unlike any other system, it combines pallet buffer and sequencing system with automated storage and retrieval system (ASRS) technology which can increase the storage density of existing warehouses by 80% when compared with very narrow aisle APR. Pallet throughput is much higher because the system delivers the retrieved pallets to the operator in the order they are required to floor level. One buyer of the system, Fredericks Dairies in north-west England, achieved a 30% cut in the total construction costs for its cold store against creating a building to house a conventional racking system, to say nothing of high energy running costs. Fredericks Dairies confirmed that they achieved 13,500 pallet storage slots with the Redirack solution compared with only 9,500 pallets from its nearest competitor.

There can be no doubt that time compression techniques will come to dominate many warehouse operations as they adjust to multi-channel routes to consumers galvanised by on-line shopping that threatens swathes of high street shops. A key weapon in the adjustment is the right mix of dynamic 'intelligent' racking. To be quick is better than to be dead.

*SSI Schaefer:


  1. Warehouse safety training is vital for any person working in a warehouse, and should be carried out by a qualified safety expert. It's advisable to have a test after the training course to determine whether any workers need to be retrained and tested.
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  2. I absolutely agree that good warehouse safety training is crucial. Perhaps a case could also be made when considering a new warehouse to bring in a racking safety expert to apprise the warehouse operator of the various risks associated with different types of racking.

  3. Informative blog....These days racks are coming in various types like Adjustable Pallet Racking, pigeon hole racking, pallets racks. Dynamic racking become more popular.

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