Conveyor News

HANDLING PROBLEMS PUT TO BED

Less than half of UK cold stores have automated systems for handling palleted loads, and those that do normally rely on powered or gravity roller conveyors. At Yearsley Group’s new Heywood cold store, a system believed to be unique to the industry is doing the job faster and more efficiently.

When the company commissioned the new store, its ideal solution would have been to automate the entire pallet handling process, as managing director Harry Yearsley explains.

“This is the route favoured today by companies dedicated to storing a single product on standardised pallets, but it was impractical for us as a third party storage company,” he says. “We have more than a hundred customers and handling flexibility is vital, because we have to accommodate pallets, often in less than perfect condition, that can vary in dimensions, height of load and many other respects.”

The alternative of partial automation using powered roller conveyors had already been tried at the company’s Midlands store in Coleshill, but with mixed results.

Counterbalanced fork lifts instead of electric pallet trucks had to be used to lift the pallets onto the conveyors, virtually doubling truck leasing and running costs, and there were frequent line jams when damaged pallets became trapped in the spaces between rollers.

In some cases damage was caused by the stresses imposed on the pallets as they passed from one roller to the next, which also took its toll on the roller bearings and increased maintenance costs.

“It was clear that roller conveyors wouldn’t be right for Heywood, but abandoning automation altogether and using forklifts at all stages of handling would have been a backward step,” says Harry Yearsley.

A possible solution came from Yearsley’s project managers R&D Engineering, who put forward the idea of using flat bed slat conveyors – a method whose advantages had been outlined to them by Sheffield-based handling specialist Geo Robson & Co.

Essentially a heavy duty version of the ‘moving pavements’ encountered at airports, the flat bed conveyor provides a travelling surface flush with the floor consisting of box-section steel slats connected at both ends to continuous chains that transfer the motive power.

The flat bed principle is by no means new, and Robson has designed and built variations on the theme for handling all kinds of materials and products - from stainless steel coils, limestone and metal swarf to springs in quenching tanks, and even vending machines on a moving assembly line.

The version developed for Yearsley is based on a reversible line of five conveyors, with the longest in the centre and progressively shorter sections on each side. The line runs from the loading dock to the central distribution aisle where pallets are picked up by high-reach trucks.

Four pallets can be accommodated on the three central conveyors, with two on the first and last – a configuration determined by computer modelling of typical traffic in and out of the store.

The infeed sequence, which is fully automated by means of a PLC system using bespoke software developed by Robson, starts when the first pallet is placed onto the conveyor outside the access door into the cold store. When the automatic door opens, the pallet passes immediately through all five sections to the unloading point.

As more pallets are added, their presence is detected by photo-electric sensors that relay signals to the PLC system, which builds up and then breaks down the appropriate groupings on each conveyor.

Removing pallets from the store is a mirror image of the infeed sequence. In both cases the line operates at a fixed 300mm per second, and can handle pallets up to 1 metre by 1.2 metres carrying loads as high as 2.1 metres.

To ensure trouble-free operation in the store’s -25ºC, Robson selected low-temperature grades for all materials and lubricants, and sensors are equipped with heated lenses to prevent frosting.

Any doubts about the practicality of flat bed conveying under cold store conditions were dispelled by the performance of the three lines in the first phase of Heywood, which opened in 1999.

“Although it took a while to get the system running at its best, we soon found out that it could handle almost anything we threw at it,” says Harry Yearsley. “It is tolerant of all types of pallets, regardless of their condition.

“Having a system that’s loaded at floor level means we can use standard electric pallet trucks, and the close spacing of the slats gives the underside of each pallet ample support – so jams are far less frequent than with rollers.”

To ensure maximum load-bearing capacity, Robson’s design includes support rails underneath each slat, so that trucks can drive onto the conveyors if they are out of action – to retrieve pallets, for example, or even to deliver them to the high reach pick-up point.

Under normal circumstances there is no reason for the loading bay forklifts to go into the store. That means the trucks make shorter journeys, and the access doors - which are smaller than the conventional type, are opened just once to admit each pallet, rather than twice to allow the truck to enter and then leave. Both these features help to reduce running costs.

The performance of the first flat bed lines meant that the technology was the natural choice for subsequent expansions. A fourth line was added in 2000, and a further two a year later when Yearsley completed the doubling of Heywood’s initial capacity to 28,000 mobile pallet sites. The system was also introduced into the company’s new Southern sales and distribution centre in Gillingham.

“Investing in the latest technology is essential for survival in today’s increasingly competitive cold storage sector,” says Harry Yearsley.

“Innovations such as mobile racking and inventory management systems that give customers real-time on-line information about their stocks have been essential to our success – and the introduction of flat bed pallet handling is another part of the process.”

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