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Mobile racking in South African fruit stores

By James Cunningham of Barpro Racking

How has racking in South African fruit stores changed over the years, and what are the advantages of mobile racking?

Traditionally, pallets of packed fruit were stored by securing steel corner posts to each pallet and then storing another level of pallets on top of it. While doubling store capacity, this form of block storage effectively prevented stock rotation, increased stock damage and, in some situations, prevented adequate cooling. As fruit packaging became further differentiated, accessing stock quickly for an order became practically impossible.

Pallet racking was introduced into existing fruit stores to solve these problems. ‘Drive in’ racking made better theoretical use of the chilled space and reduced product damage. However, the accessibility problem was not solved, leading to ‘drive in’ lanes being only partially used for immediate access to individual product lines. The alternative was to use fixed selective racking, giving immediate access to every pallet, but greatly reducing storage capacity.

Mobile racking was first used in 1997 in a fruit store outside Grabouw in the Western Cape. The mobile bases were 30 pallets long and stacked four pallets high, with a top beam level of 8 251mm. Designed to take a combination of 2 200mm and 2 400mm pallets with a maximum weight of 1 000kg, the pallets were stored with the 1 000mm side facing and the 1 200mm side in the depth of the racks.

What is mobile racking?

Mobile racking consists of special rails that are laid in the floor during construction.

Rails can also be retrofitted in existing rooms, provided the floor is suitable, by levelling the rails on the existing surface and pouring a 150mm reinforced slab. A low ramp is needed at the entrance. The mobile bases run on the rails and support pallet racking that is specially designed for use in a mobile application. The bases are motorised and energy efficient. Maximum tonnage per base varies, but should not exceed 360 tons. In larger stores, mobiles are arranged in banks of up to 10 bases, each with its own moving aisle. The bases are controlled either by push buttons, remote control, or by an interface with the warehouse management system. An access aisle is created at the push of a button.

Safety measures include photoelectric beams down the length of each base and across the front of each mobile bank, with additional emergency stops. To move one or multiple bases takes approximately one minute and 20 seconds. Mobiles are designed to give lighting signals so that the lights come on only in open aisles. This results in energy savings, as each light produces heat that must be removed by the refrigeration system.

The first installation

The first phase of the Grabouw facility stores 2 504 pallets on a floor footprint of 40.3m × 33.8m, or 1.84 pallets per square metre. The possibility of pallets breaking was removed by using a pallet support or saddle beams in the middle of each pallet slot. These were painted yellow to assist with pallet placement, especially on higher levels, and to increase rack strength.

Another challenge arose when packed fruit stores remained in use for extended periods. Improved ventilation in the mobiles allowed packed fruit to be chilled and store temperatures were reduced to around 0°C. Frost heave — caused by moisture freezing under the floor — is not good for mobiles, and recent installations have underfloor insulation and heater mats to make sure this doesn’t happen.

Mobile racking today

Sixteen years after the Grabouw installation, the advantages of using mobiles in fruit stores have become apparent. More expensive than ‘fixed selective’ or ‘drive in’, mobiles can increase the practical capacity of a store by up to 75% or 80% while still giving immediate access to every pallet. If the total cost of a proposed fruit store is divided by the practical pallet capacity, the mobile option can be surprisingly competitive.

Recently, mobiles have been installed in smaller stores, two and three pallets in the height with capacities of less than 450 pallets. Moving aisles have been widened to allow for the use of counterbalanced trucks and pallet bays extended, allowing the placement of three pallets on the longer 1 200mm side. Maximum pallet weights have increased to in excess of 1 300kg and storing five pallets in the height is now possible.

Pallet heights have increased with the standard now set at 2 450mm for a high cube pallet, making the top beam height for four pallets 8 479mm.

 

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Home REFRIGERATION Warehousing and Storage Mobile racking in South African fruit stores

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