Introduction to Storage Systems

Storage Systems, simply refers to the system in which the cargoes are being stored in the warehouse.

A well-designed storage system should:

• Make good use of building volume, by choice of appropriate storage system, careful layout, minimising aisle widths and using headroom;
• Provide good access to stored goods, minimise travel distance and facilitate throughput of goods;
• Incorporate systems such as stock records and locations, and stock movement control and replenishment;
• Provide security against fire, damage and theft; and
• Provide an environment to prevent deterioration or contamination of stock.

In addition, the choice of storage medium for a particular application will depend on:

• Physical characteristics of goods stocked, such as weight, shape, size, strength, package, unit load weight, height, etc.;
• Hazard factor, such as fire, noxious gases;
• Value of the goods;
• Stocks and throughput levels;
• Contamination risks, regarding odours;
• Characteristics of the available storage methods and equipments;
• Number of line items;
• Capital availability; and
• Deterioration factors, considering product life.

Palletised Storage: Block Stacking

In Block Stacking, loaded pallets are placed directly onto the floor and built up in stacks, in rows. Ideally, any one row of pallets should only contain pallets of the same products to avoid double handling and to simplify stock location records.

The block stacking technique is used with plain palletised loads, pallet converters and similar load protection devices that are used if the load itself is not strong enough or flat enough to permit safe stacking.

When setting out simple block stacking, clearances should incorporate to facilitate fork truck movement. It is good practice to empty a row completely before putting any more stock into that row, and it is important to maintain stock location records to ensure stock discipline.

The technique is suitable where there is limited number of product lines, each of which has a comparatively high stock level.

The advantages of Block Stacking are:

• Lower capital costs;
• No storage equipment needed;
• Good use of area though not necessarily of height;
• Simple to control; and
• Suitable for high throughputs.

The disadvantages of Block Stacking are:

• Limits on stack height which can restrict the use of building height;
• Honeycombing which reduces storage capacity;
• No strict FIFO;
• Free access is only to pallets at the top of each row; and
• Fire risk.

Palletised Storage: Adjustable Pallet Racking (APR)

Adjustable Pallet Racking (APR) is the most widely used storage system for all palletised and non-palletised loads. Racking construction consists of end frames and horizontal beams, and the height of the beams can be adjusted to suit the height of pallet loads to be stored.

Single or double-sided runs of racking are separated by aisles that can be sized to suit the customer’s forklift trucks. The basic design of APR is for flat pallets, but accessories are available for storing particular unit loads, such as drum stoppers, decking, and channel supports.

The advantages of APR are:

• High accessibility to all pallets;
• Designed to suit all load sizes and available space;
• Use of standard forklift trucks;
• Easily installed and repositioned;
• High occupancy rates; and
• Cost-effective.

The disadvantages of APR are:

• Fork truck aisle gives access to only two rows of racking, hence, the building space utilisation is low; and
• For racking heights above 8 m, a chemically treated flat floor is needed to stabilise the racking with the load.

Palletised Storage: Double Deep Pallet Racking

The Double Deep Pallet Racking is constructed to store 2 pallets deep or 4 pallets deep in double entry rack, used ideally when multiple pallet quantities of each product are stored.

A derivative to the selective pallet racking, the double deep system requires the use of a specialist reach truck or an attachment fitted to reach truck. Whilst achieving increases in capacity of up to 30% above the former, only 50% of the pallets are immediately accessible.

This system, however, provides an excellent method of increasing warehouse capacity or when alternative systems, such as the Drive-in Racking, which require high numbers of homogenous pallet types, are not possible.

The advantages of Double Deep Pallet Racking are:

• Increased storage density; and
• Highly spaced-efficient storage system.

The disadvantages of Double Deep Pallet Racking are:

• Requires specialised forklifts like the double reach trucks;
• Speed of access to all of the pallet positions is restricted;
• Loss of absolute FIFO; and
• Poor visibility for the truck drivers when accessing the rear locations.

Palletised Storage: Drive-in and Drive-through Racking

Drive-in and Drive-through Racking is used for high-density storage in a given area to increase capacity by some 60-80% over conventional ‘aisle’ racking.

It is frequently used in facilities with a low number of product lines. This racking has veritical support frames, ties at the top, with cantilever pallet support beams at different heights. Pallets are stored in a block system with a reduced number of aisles.

Forklifts drive into the racking to load or retrieve pallets, which are stored on cantilevered rails running throughout the system. If the access into the racking is from one end, the term “drive-in” is used. Racking assessed from either end is called “drive-through”. Racking heights are up to 10 m, allowing the full height and floor area of the building to be used to provide maximum cubic storage space.

The advantages of Drive-in and Drive-through Racking are:

• High-density storage allowing a greater number of pallets to be stored per cubic metre than other storage systems;
• Ideal for batches of pallets;
• Suitable for seasonal goods and fluctuating stock demand;
• Ideal for cold and chill storage and bulk storage applications;
• Suitable for fragile loads, which cannot be block stacked;
• Low capital cost and no special handling equipment required; and
• Continuous racking up to 10 m high without aisles.