|Higher Density Storage|
by Alan Moule
As we were all made aware from Nina’s paper, the most efficient way of storing a lot of product in a small space s almost certainly simple block stacking.
However, other issues intrude . . .
A large variety of different products require choice of retrieval – in other words selectivity . . .
Perishable products usually have a limited shelf life and need FIFO flow – that is stock rotation . . .
Many products, especially with today’s light-weight packaging, cannot support being stacked one on top of the other.
It is these three considerations - selectivity, rotation, and crushability - that give rise to the need for racking.
As we have seen from Ken Brazier’s erudite address, conventional beam racking – usually referred to as APR – is most often the adopted option, since it fulfils all the above criteria, and at an economical cost.
There are however many situations where the absolute need for space utilisation outweighs other considerations and thus dictates the solution.
Growth requiring increased capacity within an existing facility which cannot be easily expanded;
New buildings where land availability and/or costs limits size; and of course temperature controlled stores (chillers, freezers, etc) where every volume of air costs money to chill or freeze on an on-going and escalating basis – whether occupied by product or not!
We are deliberately omitting discussion about automated systems, but these also are invariably hi-density for both cost and control considerations.
It is these circumstances that create a need for so-called hi-density systems – and there are many.
While the specific topic of this section is Drive-in racking, it must be emphasised that there is no intent to convince you that this system is the answer to all your problems – only to present the concept.
All hi-density systems have their own particular advantages and disadvantages – and it has to be understood that ALL are a compromise in some way or other. (if any one system was perfect, there would be no others!)
There is always a delicate balance between the factors of space utilisation, selectivity, rotation, speed of throughput, flexibility, and (not least) capital costs!
The analysis of these factors is vital, and should be tailored for each particular customer. Very seldom is one customer’s criteria identical to another’s.
Indeed, for any given situation, often a combination of systems is the optimum solution.
Conventional APR is build around frames and beams.
Drive-in rack is based on frames and rails.
While APR supports it’s pallets loads on horizontal beams running left to right, and "face-approached" by the FLT from an aisle, Drive-in supports the pallets on rails running from front to back in a corridor normally called a "lane". The FLT actually drives into this lane (hence the name!) to deposit or retrieve pallets - there are no horizontal left-to-right members to impede it’s progress.
The racks are then arranged in blocks separated by access aisles.
The normal "aisle per pallet face" is thus eliminated, giving drive-in racking it’s space efficiency advantages.
Uniformity of Pallet size and quality are vital considerations.
The interface between handling machines and rack is an even more essential consideration than usual.
For a commonly-used ISO pallet 1200mm wide, the most-often specified aisle width is only 1350mm – providing no more than 75mm clearance each side of the pallet!
The clear distance (width) between the inside of the rails is normally only 850mm!
It can be clearly seen that the dimensions of the FLT are absolutely crucial:
A comprehensive guide-rail – or even better, plinth – system is strongly recommended and nearly always used – but this is as much to protect the racks from FLT damage as to actually guide the truck!
As far as usage is concerned, since Drive-in is one of the simplest and least expensive of the hi-density systems, it has proved very popular – especially in the types of situations mentioned above.
Costs of Drive-in racks typically vary between approx R300
up to R500 per pallet position, depending on load specifications, height, additional complexities, etc.
It has been used extensively in applications where large numbers of same or similar products are stored – especially where these are in a "holding-only" type situation. In other words where the product is stored away in a large quantity for a limited period only, and then shipped out again in large quantities.
This frequently applies to industries such as export fruit, and this business has been one of the largest users of Drive-in racking in the W Cape in recent years.
One recently popular and often-used applications in this industry is for forced, or pressure cooling of fruit prior to containerisation for export. Lanes are closed of by canvas curtains to form tunnels, and air cooled to the required temp is forced thru the fruit, in its packaging, to bring it down to temp more rapidly than would be otherwise possible. This is not a new concept, having been used in principle for years.
The difference is that Drive-in racking enables it to be carried out on multiple levels – often 3 high – instead of a single layer on the ground.
Other cold and chill stores have also taken advantage of the systems space efficiencies for products including meat, fish, poultry, vegetables, dairy products, and fruit juices.
In ambient storage, Drive-in has proved suitable for a large range of goods where shelf life & rotation are secondary to space-saving; such as for toilet tissue, packaging, feeds & grains, dried goods, canned dog-food, and baby foods.
There are several disadvantages to Drive-in racking:
Accordingly, adequate operator training is essential – ideally by a professional training body with specific experience with Drive-in racks.
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