The function of adjustable pallet racking is to store goods on pallets. The weight of the load is transmitted through the pallet into the structure of the racking, so the pallet’s shape and design directly influence the design of the rack.
Pallets permit goods to be moved mechanically – by fork lift trucks, stacker cranes or conveyor systems. A pallet will have a deck on which goods are placed, and a space into which the forks of the handling equipment can enter. Also, usually it will have a bottom deck, although this is not compulsory. The gap in the pallet for forks is usually 100mm.
When used with racking, pallets normally rest on the rack’s beams. Consequently the underside of the pallet, the inter-face between the pallet and the beam, is most important. The spacing of the rack beams, their load bearing capacity and their length can all be affected by the underside of the pallet.
TWO-WAY OR FOUR-WAY?
Pallets are frequently described as two-way or four-way entry. Two-way entry only permit the entry of forks from two sides. Four-way pallets permit the entry of forks from all four sides.
The construction of the pallet dictates whether it is two or four-way entry. A two-way pallet has solid bearers that prevent access from the sides of the pallet. A four-way pallet has bearers, or blocks, in each corner that enables access from either end or the sides of the pallet. The sides of a four-way , through which the load of the pallet truck can pass without leaving the ground, are known as “free entry sides”, the other sides where the trucks wheels have to pass over the pallets bottom slats are termed “restricted entry sides”.
A pallet is made-up of different components. The most often referred to are:
- Bearers: Members under the deck that separate the top and bottom decks of the pallet and provide the space for entry of the forks.
- Deck: The top or bottom flat surface. This may be solid or open boarded.
Stringer: A horizontal member containing the bearers and supporting the deck.
- Entry: Space permitting the entry of forks or fingers in a particular direction.
- Wings: Those parts of the deck that project beyond the bearers.
- Chamfer: A rebated angle in the edges of the bottom deck to aid the passage of the load wheels of a pallet truck.
The most common pallet sizes used in the UK are:
- 800 x 1200mm
- 1000 x 1200mm
These sizes take into account the majority of transport vehicles and are designed to give the best load density, provided the pallets themselves are loaded to capacity.
The most common pallet types are:
Two-way entry, single decked:
A pallet with only a top deck. Suitable for items that can withstand the concentrated loads imposed by the bearers during stacking, e.g, wooden boxes and drums. Also used where little stacking is required and for storing unit loads in pallet racking when the bearers are supported by the rack framework.
Four-way entry, cruciform perimeter base:
The cruciform design of the bottom slats adds to the strength of the pallet and improves load distribution when stacked. This is the most widely used type of four-way entry pallet. Other pallet designs are available to improve load distribution or work better with specialised handling equipment such as stacker cranes and pallet trucks. However, the majority of the pallets in use in the UK will conform to one of the two previous definitions.
85% of the pallets in use in the UK are 1200 x 1000mm. Many of these are stored in rack. 75% of the pallets stored in racking are stored with the 1000mm dimension front to back, or “1000 deep” as it is popularly known. SEMA regulations stipulate that when using a two-way pallet 1000 deep the frame depth should be 750mm. A 900mm frame depth is stipulated when using a four-way entry pallet.
So, when you are considering your storage system one of the first decisions you have to make is about pallets. What type are you going to be putting into the racking system? The answer to this question will dictate many of the features of your rack lay-out. In a future article we will look at clearances – how you create the right amount of space to move your pallets around your storage system without wasting space.
This article is an extract from our booklet “The Principles of Pallet Storage”. If you would like a copy please call Tina in our sales office.