All-electric straddle carriers remain a pipe-dream for operators fed up with leaky hydraulic components. Alex Hughes reports
Straddle carriers are notoriously maintenance needy, due to the heavy use they make of hydraulic components and while manufacturers are increasingly experimenting with replacement technology, industry experts still believe we are at least five to ten years away from producing a viable, all-electric alternative.
Consequently, terminal operators working stacking yards with straddle carriers have had to learn to live with oil spillages. Hydraulic components do inevitably fail and, when they do, the consequences are not pleasant. Oil has to be mopped up and repairs undertaken, consuming valuable time and resources. The need to reduce the amount of oil used is therefore a must, according to Jost Dämmgen, Konecranes sale manager for port cranes.
The logical solution would be the development of an all-electric straddle carrier, which he says is what most of his container terminal clients want. But the simplest solution is often the most elusive.
“Straddle carrier steering and braking systems are similar in many ways to those of trucks. So, it will only be once proven all-electric systems are introduced by the haulage industry that straddle carriers will adopt them, too,” says Mr Dämmgen.
Paul Bolger, technical sales engineer at Liebherr Container Cranes, is similarly realistic. “An all-electric straddle carrier is still some way off,” he says, while adding that this doesn't mean that straddle carrier development isn't progressing; indeed nothing could be further from the truth as electric components are replacing incumbent hydraulics all the time.
“Shorter term, improvements could be made to the size of the engine used and also to more cost efficient energy storage solutions,” he says.
Manufacturers are also doing a lot of work with the spreader, where electric alternatives to the hydraulic spreader are already available, although not yet adopted by all terminals. Mr Bolger thinks he knows why. Although yard cranes have used electric spreaders successfully for some time, applying similar technology to ship-to-shore gantries and straddle carriers has not yet proven itself sufficiently to make a mainstream breakthrough, he says.
“Their durability when used with straddle carriers is open to question, although it's probably only a matter of time before they are sufficiently refined to function in what is a much tougher environment.”
However, while Mr Dämmgen remains confident that an all-electric spreader can be expected to be introduced across the entire industry within one to three years, he is a lot less bullish in respect to an all-electric straddle carrier, one without any on board hydraulic systems at all. This, he believes, will not be a reality for perhaps five to ten years.
“The straddle carrier market is a conservative one. New technology needs to come in, but understandingly nobody wants to be the guinea pig,” he says.
But there might well be competitive advantages for those terminals prepared to grasp the nettle: an all-electric straddle carrier might well have cheaper capital costs and, crucially, lower life-cycle costs.
“Hydraulic components need a lot of servicing. There are a lot of leaks, requiring hoses to be changed, along with things such as fluids and filters, all of which gets swept away when you go all-electric. Total cost of ownership can therefore only benefit from going all-electric, since fewer spares will have to be held and less maintenance needed,” he says.
He is also optimistic in respect of a cheaper cost price, pointing out that, in other sectors where electronics have replaced hydraulics, there has been little or no associated price increase. This is because electric motors and frequency drives are relatively cheap in comparison to hydraulic pumps and motors.
Logically, he argues, return on investment will be faster when going all-electric, although not dramatically so.
Mr Bolger also believes that an all-electric unit would have cheaper life-cycle costs. Return on investment should therefore be faster.
In the meantime, LCC and Konecranes customers are already benefiting from the adoption of several innovative electronic packages that are helping to produce a more maintenance-friendly machine.
The existing LCC design, for example, incorporates an electric hoist and an electric disc brake. It also makes use of drive-by-wire technology for steering and braking.
“Effectively, there are no hydraulics in the cabin or on the machinery platform, whereas other manufacturers use a hydraulic brake for the hoist and have engine driven hydraulics. We have no hydraulics at all on the upper level of the platform,” says Mr Bolger.
At Konecranes, straddle carrier controls are essentially “drive-by-wire” in design. There is a single sensor in the steering wheel, braking pedal and throttle, obviating the need for there to be any mechanical connection between any of the control devices.
“We transmit the steering signal electronically,” says Mr Dämmgen, although once again notes that this ultimately inter-acts with hydraulic components, which it is hoped will eventually be eliminated.
Mr Bolger adds that straddle carriers need a high dynamic steering response. LCC, he emphasises, has already gone a long way to achieving this by also incorporating drive-by-wire technology in its units.
In addition, he says, “all our hydraulics are concentrated at ground level. This means that steering is more reactive to driver input and gives a more consistent feel when compared to alternative systems where the hydraulics are located in the upper level and are linked to engine speed. With these, the feel of the steering controls can change relative to the engine speed.”
In respect of going to an all-electric steering system, Mr Bolger says that, while the products available on the market may indeed be rugged enough for use in straddle carriers, they nevertheless so far lack the necessary dynamic response that is a must.
A substantial portion of new straddle carriers on the market now also have electric hoist winches, he notes.
As for braking systems, LCC differs from some rivals is that it uses an electric disc brake rather than a traditional hydraulic brake. So maintenance is lower and reliability higher.
However, adopting an all-electric braking system also presents a particular problem: how to provide the necessary brake force and dissipate heat. Straddle carriers mostly incorporate regenerative technology for the first part of the braking cycle. In the LCC straddle carriers, explains Mr Bolger, regenerated travel brake power is used by the hoist and vice versa, thereby improving energy efficiency while reducing fuel consumption. But not all excess energy is taken up and some has to be burnt off.
For this reason, some operators have fitted capacitors to their straddle carriers to store this excess energy. However, despite claims to the contrary, Mr Bolger believes these high energy storage devices have yet to demonstrate that real savings can be made.
“The cost of the technology associated with energy storage remains quite high. Nevertheless, alternative storage technologies are under development and may become available in the near future, therefore making it worth while revisiting this topic,” he says.
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