The European factor

Chinese manufacturers want their customers to buy cranes incorporating local designed and built components. But is this realistic? Perhaps not, say manufacturers.

According to Christof Lautwein, co-managing director of German couplings manufacturer M.A.T. Malmedie Antriebstechnik GmbH, port commercial departments initially reacted positively to the all-Chinese crane, because of the cost savings involved. Nevertheless, more technical colleagues have taken a completely different view.

“Over the past two to three years, there has been a slight shift, involving some commercial decision makers asking for a particular crane specification that encompasses highly developed and high quality components. This is because cheaper components have invariably resulted in increased crane down times and higher life cycle costs,” Mr Lautwein says.

European drive components, in contrast, have a much better track record, but have been the victim of commercial pressures over recent years that have forced crane manufacturers to come up with ever cheaper catalogue prices for their products. Terminals have become obsessed with making upfront savings, which means buying the cheapest possible cranes.

But, “by ignoring lifecyle costs, many operators will end up paying more for their cranes in the longer term”, says Mr Lautwein.

As to whether cheaper Asian-produced drive motors can technically compete with those from European manufacturers, Klaus Sprekelmeyer, sales manager of Franz Wölfer Elektromaschinenfabrik Osnabrück GmbH, remains dubious, pointing out that many terminal operators nowadays insist on branded electrical components, since these have demonstrated much higher reliability over time.

The experience at Parker SSD Drives is similar.

Andrew Parker-Bates, the company’s marketing communications manager, notes that terminal operators really aren’t happy about operating cheaper cranes, incorporating non-branded, locally built drive motors. Operators, he says, are looking for drive systems that are reliable, readily available on a global basis, and with both local support and documentation available in the local language. Savings in capital cost of cranes can soon be wiped out if these are unavailable when they are most needed.

However, to stay in the market, European manufacturers have invested heavily in improvements that have given them a technological advantage, which has been crucial at a time when terminal operators have discovered a preference for AC drives in newer cranes rather than more traditional DC drives.

In part, this is because AC crane drives are not affected by high peaking start up torque. This benefits the whole drive train, since it makes the crane lifting sequence much smoother and reduces the need to incorporate torsional elastic couplings between the motor and the reducer. These latter devices required frequent replacement, implying a need for a substantial inventory, with concomitant expensive down times. By using torsional rigid couplings – such as gear-couplings or all steel disc couplings – there is much less wear and tear on the parts involved, resulting in cheaper overall maintenance costs.

Wölfer’s reaction to the new emphasis on AC motors – and also to potentially cheaper products coming from Asia – has been to both improve its baseline engineering and also offer clients a wholly bespoke service.

Mr Sprekelmeyer notes, for example, that if Wölfer is asked to position a motor’s terminal box at an angle of 45 degrees rather than 90 degrees, it can be done. The company’s AC drives can also be delivered with the same mounting dimensions as existing DC motors, so replacing these on cranes means that the machinery housing does not have to be modified.

“If Wölfer receives an inquiry for a retrofit that includes drawings of the old motor, we can offer a motor with the same dimensions,” he says.
Wölfer technology continues to develop, too.

Its motors, for example, work with all AC drives up to 690 volts. By having a higher pull-out torque, they can be driven smoothly over a higher range of speeds, which, coupled with their lower inertia, gives a much shorter acceleration time and lower energy demand. This in turn gives the crane operator a more comfortable environment to work in.
Traditional motors have tended to rely on cooling fins to reduce heat, while Wölfer has developed an inner-cooled motor, blowing air directly where the heat is generated. This means its motors can be mounted in a machinery housing, which results in the same power output generated, but from a smaller unit, thereby reducing the energy required for acceleration, as inertia is much lower. Because such motors require a lower starting current, smaller sizes of frequency inverters and cables can be used. The space required is also less as is the weight of the motors themselves.

“All these parameters enable manufacturers that we work with to reduce the size and weight of the machinery housings on their cranes, which, at the same time, can handle a higher number of containers,” Mr Sprekelmeyer says. “As a result, we calculate that operators can make energy savings of 2%-8% per hoist.”

At Parker SSD Drives, the switchover from DC to AC has also gone smoothly.

“The overall control philosophy between Parker’s AC and DC products is similar and means that special adaptations have not been required,” says Mr Parker-Bates .
On the whole, he maintains, AC and DC drive systems are matched in terms of performance, although warns that this needs to be judged on an application-by-application basis. When upgrading existing DC cranes, the decision to switch to AC is frequently dictated by the condition of the existing motors.

“DC motors can be significantly more expensive than AC motors to replace and therefore AC is more often used for new installations,” he says.