CRAWLING FORWARDS

Any consideration of the design of crawler cranes needs first to recognise that this is not a discrete market segment. The larger, heavy-lifting machines are completely different from the sub-100t duty-cycle or bridge cranes. And lattice boom crawlers, which account for the vast majority, face issues different from those facing telescopic boom crawlers. In fact, many issues facing the conventional lattice crawler are also relevant to lattice boom truck cranes, for much of the technology is in the boom.

That said, it is generally reckoned that the single biggest issue for crawler crane manufacturers is to make their products easy to assemble/disassemble and transport. Lattice booms generally, whether crawler or truck mounted, are widely considered more cumbersome than telescopic booms – slower to prepare for lift, and slower to strip down. This is not necessarily the case, however, particularly at higher lifting capacities.

One of the earliest self-assembly crawlers, if not the very first, was Link-Belt’s LS-108B in the 1960s. With a little manoeuvring, this crane could be rocked onto a trailer. But it was not until early 1992, with the appearance of Manitowoc’s 250t-capacity M250, that the problem of economical and efficient self-assembly was really cracked, with hydraulic jacks used to raise the body of the crane during assembly/disassembly.

Manitowoc patented its design under the name of FACT – fast aligning connection technology. Putting hydraulic power onto such a big crane revitalised the large lattice boom crane market as previously they were seen as too big to mobilise for short-term rental. What used to take a crew of six and an assist crane three days to erect could now be assembled by a crew of just three in less than four hours with no assist crane.

Other manufacturers have addressed the assembly/disassembly issue in their own ways. Link-Belt’s new 80 US ton LS-138H II has a hydraulic counterweight removal system with hand-held remote control to lower counterweight to the ground.

Liebherr developed its Self Erection System (LSE-System) for the 250t-capacity LR 1250. Without the use of an auxiliary crane the LR 1250 can disassemble itself into small units and load them for transportation. The heaviest unit, consisting of the superstructure and the centre part of the undercarriage, weighs only about 40t and can be easily transported on a low-loader. The boom extensions are designed to fit in standard containers and the boom extensions for the luffing jib can be placed inside the boom extensions of the main boom, thus saving space and so reducing the number of transport vehicles as well as cost.

When developing the LSE-System, the aim was not only to aid transportation but also assembly at the jobsite. Thus all parts to be assembled are equipped with guides, and all heavy bolts are hydraulically operated, thus keeping assembly fast and easy, according to Liebherr. Moreover, assembly is guided by corresponding messages in the operator’s cabin.

Placing boom sections inside each other is a way of reducing the number of trucks needed for transportation. Link-Belt went even further with this concept in the 1970s and produced a telescoping lattice boom. This proved expensive to produce, however, and so was dropped. Maybe Link-Belt was ahead of its time and this idea could be resurrected in the future.

Another way to speed assembly would be to find faster ways to connect booms. Perhaps hydraulics could be used to eliminate the pennant work on attaching luffing jibs. Luffing jibs are becoming increasingly popular and their development would surely accelerate if they became easier and quicker to attach.

Many of the innovations in crawler crane technology have been led by the USA. But when it comes to making seriously big machines transportable, it is the Dutch that have shown the way in the past year or so. And, interestingly, it is a couple of end-users, the fierce rivals Mammoet and Van Seumeren, that have been trail-blazing here, rather than the established manufacturers.

First onto site, last year, was the Mammoet Sliding Gantry (MSG) concept, designed by Stotra. The MSG has capacities of up to 10,000t, depending on how it is configured.

This year saw the launch of Van Seumeren’s – arguably more versatile – 2,000t capacity Platform Twinring Containerised crane (PTC).

Neither of these machines could accurately be called crawler cranes, as both are ring-mounted and, being specially designed for super-heavy-lifting, have little in common with the duty-cycle rigs more commonly seen on construction sites.

However, the significant feature shared by the Mammoet and Van Seumeren innovations is that both are designed to be packed away into standard sized containers for easier shipping. (Features in this magazine in the June 1998 and March 1999 issues explored these machines in fuller detail.) Manitowoc general manager Ron Schad has observed the development of the two containerised machines with great interest. He suggests that the concept is particularly attractive to European owners because they are more dependent on shipping by sea to reach jobsites. But Manitowoc will not miss any lessons that can be learned.

“We will look at it [the containerisation concept] in future designs and see what components can be containerised,” Schad says, though he adds that each case would be taken on its merits.

Van Seumeren itself is committed to developing an entire fleet of five PTCs, likely to be built by the neighbouring fabricator Huisman-Itrec, which made the first unit. Thus the containerised concept seems well set to figure large in the future of heavy lifting crawler- and ring-mounted units.

Van Seumeren is conspicuous by its absence from Manitowoc’s client list. Manitowoc has a close relationship with Van Seumeren’s arch rival Mammoet, and is keen to work with Van Seumeren too. Schad has explored avenues recently, but Van Seumeren remains to be persuaded what added value the USA’s leading crawler manufacturer can bring.

International end-users, such as Van Seumeren and Lampson, being less dependent on manufacturers and developing their own special equipment could be another strong trend for the future. If this trend does develop, it must be regarded as an indictment of the manufacturers’ ability to serve their major clients.

Another major issue is manufacturability. To keep manufacturing costs down, cranes are increasingly being designed on a modular basis, so that standard components can be used for a whole range of product. A good example of this is Manitowoc’s latest design, the 21000, whose carbody and upper shares components with other Manitowoc cranes. Not only does this help keep Manitowoc’s costs down, it reassures buyers that proven technology is being used and that parts are likely to be more readily available than would otherwise be the case.

So much crane technology is dependent on other industries, such as automotive engineering and materials technologies. This industry is simply not big enough to support significant research and development programmes on its own. Developments in materials have seen higher strength steels and there is probably scope for at least a further 10% increase in yield strengths, according to the engineering director of one major manufacturer.

However, the problem, he says, is that the higher the strength, the greater the care needed in welding and cooling it, thus manufacturability is a constraint to significantly higher strength steels and other new materials.

Another suggestion put forward during the research for this article was that cranes may become more dependent on their supporting structure. What can be done to the base to increase capacities? Mounting them on rings to spread ground pressure and increase stability is well established technology. Perhaps there are applications where temporary ground anchoring can be used instead of additional counterweight.

Increased versatility will also add to the appeal of future products. Manufacturers can offer an extra drum, extra fall line and luffing jibs even on smaller cranes. Already some machines can be converted at the flick of a switch from duty-cycle use to quick lifting, though this is generally considered too expensive an option to be offered as standard.

Legislation is also a major factor in the development of all construction machinery. Cleaner and quieter engines, more ergonomic or environmentally-controlled cabs, more sophisticated operator assistance devices and highway weight restrictions will all promote development. It is likely to involve additional cost to the end-user and the type of sophisticated equipment that results may not last as long in the field as the old mechanical warhorses of yesteryear and thus may not hold their value as well.

In the final analysis, however, aside from the subject of legislation, the future of crawler cranes depends largely on what end-users primarily want – high performance, maximum reliability, or lowest cost. Basically, say the manufactures, their customers can have whatever they want, as long as they are prepared to pay for it. But it seems likely that today’s option is tomorrow’s standard feature.