http://www.han-tek.com/han-tek/news_hoistmag.html
Glass producers are increasingly demanding larger and larger refractories for their furnaces. Refractories are the linings for the furnaces, made of a material such as alumina, zirconia and silica to withstand high temperatures. One such producer, Vesuvius Monofrax, based in New York, USA, needed a new crane to work with its own furnace. Refractory producers use furnaces as well as supply them, to melt down the raw materials. The molten refractory material is then poured into moulds to create bricks that are used for the furnace lining.
The existing 7.5 US ton SWL single girder stacker crane was nearing the end of its useful life and required excessive maintenance. More importantly, it was no longer big enough for the size of refractory being demanded by its customers. A double girder stacker crane is the standard solution to the problem, but such a design would have proved too big for the existing facility, and building redesign would have been too expensive.
Instead, HAN-TEK engineered and installed a single girder stacker crane with an SWL of 15 US ton (13.5t) to work around the clock. "This crane and the furnaces it supports are the backbone of Vesuvius Monofrax's business," says a HAN- TEK spokesman. Existing runway girders and columns had to be reinforced to bear the increased wheel loads imposed by the larger crane. AceWorld Companies of Texas designed and built the crane and carried out runway reinforcements.
The new crane allows the operator to use the forks on the mast to reach into an area and pick up a silica mould standing up to 3m (l0ft) high. The crane then moves along a 30m ( I00ft) runway system to one of two furnaces. The furnace pivots to pour molten refractory- heated to 2,750°C - into the mould. The crane then backs out, deposits the filled mould, picks up an empty mould in sequence and moves back to the furnace, accomplishing several pours every half hour. Forklift truck operators move the moulds into and out of the staging area.
HAN-TEK claims that its crane system delivers greater operator control and more precise positioning. The controls are programmed to deliver full torque to the hoist braking system, checking for proper adjustment a split second prior to every brake release. If any slippage is detected, the brake will not be released. The crane also has a slack-cable detection system that eliminates the potential for operator error when lowering the carriage, HAN-TEK says. Variable-frequency drives are used on all motions to give soft starts, torque proving and load float and thus reducing wear and tear on the brakes and other mechanical components. The drives are housed in a separate, air-conditioned enclosure. Maintenance requirements consist primarily of regularly lubricating the moving parts and checking the wire rope and bearings for wear, says HAN-TEK. The less downtime there is on the stacker crane, the more refractory bricks can be produced.
The operator can control the crane either from a festooned pendant station or at one of two pedestal-mounted control stations at the furnaces. Fibreoptic cables connect hoist encoder to the crane's drives.
Project planning took three years, but installation took just three weeks. The cost of the project was $950,000.
HAN-TEK is an automation and integrated materials handling systems provider specializing in cranes, conveyors, robotics and controls. They are celebrating their 50th anniversary in 2011.
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