MATERIALS HANDLING: Wider, Longer Factories Questioned
Recent Western Cape Business News
THE tendency to manage a need for additional factory space by extending the existing structure is being paralleled by a trend towards the construction of ever-wider factories to cater for future expansion.
The logic of both these schools of thought should be carefully questioned. This is the opinion of Marc Kleiner, general manager of Condra Cranes, who reports a steady increase in the spans of the overhead cranes on order.
“Two things are happening. First, we are manufacturing a greater number of overhead cranes with spans of between 25 and 30 metres, whereas before the norm was 17 or 18 metres.”
“We still manufacture many cranes with the shorter span, but the trend toward wider spans is there, and it’s growing,” he says.
“Second, we are seeing an increase in orders for twin, that is duplicated, cranes, to be installed in tandem with the original crane in cases where factories are being extended.”
“So, buildings are becoming wider, and they are also becoming longer, but the question needs to be asked whether the productivity and efficiency increases assumed to flow from these bigger factories are in fact being achieved.”
According to Kleiner, the economy of building wider factories is debatable, because as the span of the service crane increases to match factory width, so too does the cost of the factory structure needed to support the load of the overhead crane.
“The dead load that results from the wider span also makes the crane itself more expensive. For example, the 3-ton girder needed for a 17-metre span increases in weight to 12 tons when the span becomes 25 metres,” Kleiner explains.
Additional power is also needed to move this dead weight, further compounding the problem of increased costs.
“The other thinking that is emerging is that you put up the first building, which is, say, a two-bay layout, and incorporate planning to extend it, and to install a second crane to service bays Three and Four when required.”
“But this thinking may also be flawed, because operating two cranes in tandem often leads to production logjams. An example would be when goods in Bay One cannot be moved to Bay Three because of the second crane working in Bay Two.”
Kleiner says he has seen buildings measuring 26 metres by 28 metres, served by a single crane. “The logic of this confounds me. It seems to me to be a case of throwing money away.”
“Perhaps a better solution would be to build two 15-metre bays in the original factory, and then extend the factory in both directions along with the bays when the need arises. That way, the flow of work through the factory will not be interrupted by the use of the cranes.”
Kleiner says he would welcome an explanation to this conundrum, so that Condra could give useful advice to companies enquiring about overhead cranes with very large spans.
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