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Tech Briefs
Conveying
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Perkins Engines, the British power unit manufacturer, faced a problem with its end-of-line engine block process. The blocks exit a washer and are subject to "plugging" before being tested. Perkins wanted this part of the process to be automated. The blocks are discharged from a high pressure washing machine to be manually pushed around a gravity conveyor system to operating positions where various plugging operations would take place. Major difficulties were that the process was slow, manually demanding and susceptible to damage. Perkins decided the solution would be to use a driven roller conveyor, which would allow an accumulation of discharged blocks but demand a minimal amount of floor space prior to the operating station. The process duty cycle is continuous over 24 hours and production peaks may reach 45 blocks an hour.
"It became clear that we could design a conveyor system with a series of bends to optimize the available space and form a queue of blocks accumulating up to the first operating stop," explained Project Engineer, John Craythorne. "The blocks are precision engineered and weigh up to 113 kg (248 lb), so we initially specified rollers of case-hardened steel to protect the blocks from any damage caused by the rollers becoming marked or imbedded with swarf."
Chain-driven systems were considered but Perkins opted for Power Moller motorized rollers produced by Itoh Denki Europe SA. The blocks needed to be driven at slow speed to reduce the risk of damage when they accumulated on the line. Load separation was not needed for the blocks, so low pressure line accumulation was achieved via high impedance motorized rollers that can operate for an unlimited period in a stalled state without overheating as the loads build up against a stop. Rather than case-hardened steel rollers, polyurethane lagged rollers were selected. Polyurethane has a very positive rolling co-efficient and is durable, with a Shore value of 90ShA, said Craythorne: "By using a combination of tapered and straight polyurethane lagged Power Moller accumulation motorized rollers, interspersed with our standard gravity rollers, an economical solution was designed and manufactured by Mobility Engineering (Cheshire). The system includes a series of 90° – 180° bends and straight sections."
Stuart Birch
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