Light fantastic24 October 2019
Light lifting systems may seem simple but, as Julian Champkin finds, they are every bit as useful as heavier lifting equipment and repay consideration and good design.
Less can be more. Light cranes and lifting machinery, even when manually-powered, have advantages over heavier machines. Or perhaps we should say, especially when manually powered. Power to the people is well worth considering.
“An advantage of manually-operated light cranes is that they work at the speed of the operators,” says Maria Forti, spokeswoman for Greek manufacturers Niko Helm Hellas. If the operator is pushing or pulling the load rather than following along behind it, it goes at exactly the speed that they walk, and is ready at exactly the same time as the operator is ready. “That reduces waiting time, and provides more controlled accuracy.”
Another advantage of man over machine, says Forti, is that man-power is green. “Manual solutions are more environmentally friendly and can reduce the carbon footprint of a production line or factory.” It is not always possible of course; obstacles or safety considerations may preclude it. “However it is also possible to power light cranes for situations where the load cannot be pushed by the operator, or needs to travel over an obstruction.”
You can add the ability of lightweight cranes to function in ultra-low headroom situations: “Due to the compact nature of the profile tracks, light cranes can fit into spaces where conventional overhead travelling cranes cannot. This maximises lifting height and enables taller items to be lifted in rooms with low ceilings.” By positioning the hoist suspension point up between the bridge girders rather than below them, Niko’s hoists can be mounted with as little as 50mm below the lowest obstruction point.
An ideal application, says Forti, is in light vans, lorries and shipping containers. “Light hoists are suspended overhead, and therefore do not compromise floor space. Unlike tail lifts on a vehicle they can load, lift and position the cargo in a single-lift operation. They are a perfect solution for handling stone, barrels, pallets and specialist roadside equipment, up to 500kg per lift.”
Half a tonne is by no means the capacity limit of light crane systems. “About 5t is our sweet spot, up and down from there,” says Scott Goforth, product marketing manager of Gorbel, who specialise in them. Gorbel distinguish between bridge cranes, which cover rectangular work areas, and monorails, which are linear. Track can be steel or aluminium: the aluminium track weighs as much as 44% less. Enclosed track rather than I-beam is another advantage of light systems: the trolley runs protected inside it.
“Companies are increasingly seeing the benefits of enclosed profiles for cranes,” says Susanna Raty of Kito Erikkila. “We quite often supply cranes for companies to replace their old I-bean systems with our Prosystem light cranes.
“A significant advantage of enclosed profiles is that the running surface of the crane is protected from the dust or debris that is common in small machine shops. This increases the lifetime of the crane wheels. Another advantage is being able to install conductor rails inside the profile. This removes the risk of power cables getting stuck on something and maximises the useable work area. Enclosed profiles are much easier and faster to install than I-beams as well.”
Profiles, or cross-sections, of such track differ between manufacturers, some of whom offer more than one profile and several different sizes of track. In Gorbel’s case their box-shape cross-section, with a slit along the lower surface for the chain or rope to hang through, gives more strength for its weight than an I-beam profile, as well as keeping out dust and foreign bodies. The lower, running, flanges of the box, on which the trolley wheels run, are angled downwards, at 2°, which help keep the trolley centred and prevents debris settling on the rolling surface. “Enclosed track systems are up to three times easier to move than opentrack ones,” says Goforth; lower rolling resistance on the dust-free surfaces is one reason. Friction is of course more critical in lightweight systems, which are more disrupted by small obstacles that a heavyweight system would simply run over. Gorbel claim a low profile for their track, making it suitable for restricted headrooms. Spans, if of steel track strengthened with trusses, can be up to 30ft (10m) between supports. Fewer support columns of course give more uninterrupted work spaces.
Whether your lifting system should be free-standing on columns on the floor, or mounted suspended from the ceiling, is another decision for purchasers. Installation of free-standing is generally more straightforward, says Gorbel—all you need is six inches of reinforced concrete flooring to stand it on. Roof mounting may require stress analysis of the building itself. Free-standing workstation cranes are also easier to move at a future date. The supporting columns may, however, be an obstacle to free movement on the ground; ceiling-mounted give an uninterrupted workspace.
“Light lifting is a very mature industry in terms of what the product can do,” says Goforth. “But there is a change in that end users are getting more and more in tune with not asking their employees to lift weights.
“It used to be around the 50–70lb (20–30kg) mark that employers would start thinking of as a limit. Now 35lb (15kg) is considered heavy and requiring a crane or lifting gear; it is less than that if you are asking someone to hold out a load with their arms extended; even 30lb for that is asking a lot now. So we need hoists for lighter weights than before. Our main sellers for hoists are around 1t and under; we sell a lot of lower-capacity hoists and product lines.”
Raty at Erikkila agrees: “Over the years we have seen an increase in demand for cranes for smaller and smaller loads. Nowadays companies want to eliminate all manual lifting by workers by supplying all workstations with cranes. This is of course improving the efficiency of the workers as well as preserving their health.”
The Erikkila range includes standard and raised configurations, hoist tracks and different types of jib cranes. Telescoping track, switches, turntables and lifting stations are available. The systems can be motorised or manually operated. “For manual operation, reducing friction is of course important,” she says, “but more important is the rolling resistance of the wheels. To ensure smooth rolling, the wheels must have very tight tolerances. For this reason, we have strict tolerances and quality requirements for our wheels. Having the correct wheel material is also important, and this is something we are always working on. Having high quality maintenance-free bearings is also an important part of our system.
“Aluminium has been gaining popularity in recent years. It is especially popular for assembly lines where the crane has to be constantly moved. Having less dead load, the crane is easier to move and less fatiguing for the user. Kito Erikkila philosophy is to deliver the optimal crane using aluminium and steel combinations.”
On installation decisions, Gorbel’s advice is ‘Less is more.’ Keep capacities to a minimum, says Goforth, to the maximum load you will need to carry; buy what you need, not more. “‘Overbuying’ capacity is a common temptation, since the systems are not expensive; but means that the operator will be moving a larger and therefore heavier bridge and trolley dead weight than is necessary, which is not good ergonomic practice,” he says.
Similarly, if you are going for a bridge crane, keep the bridge length to a minimum. “The less dead weight the operator has to move, the better.” Short bridge lengths are better for higher-cycle production areas; longer bridges are acceptable for lower production cycles or for maintenance areas. And keeping bridge heights to a minimum reduces swaying and makes it easier to control the load.
One might expect that a motorised system would be faster than a manual one. In fact, this seems not necessarily the case. Both Gorbel and Niko say that manual workstation cranes can do many jobs faster than motorised ones, with fewer delays. If the operator has to walk with the load the hoist will always be where the operator is, so there will be no waiting time delays while he or she summons it from the other end of the track. And motorisation may merely be adding an unnecessary level of complexity. Motorisation will be necessary for safety if the load has to travel to a pit, a vat or some other inaccessible area where the operator cannot accompany it; but otherwise a manual system may well be the better solution.
SWF Krantechnik presumably also see a great future for light lifting. In 2018 they launched their new light crane system for up to 2t loads, the ProfileMaster PLUS. It is available with aluminium or with steel profiles, and takes manual or electric chain hoists.
The aluminium system offers six aluminium profiles in four sizes.
“Since its own weight is extremely low, the system is ideal for installing in buildings that can only handle low static loads,” says Andreas Knopf, SWF product manager for light cranes. Two of the profiles come equipped with an internal power-conductor line. The system takes full advantage of the flexibility that light systems can offer. It is modular, with a selection of suspensions; it can be assembled in single and double girder arrangements. Precision-fit bolt-together joint connections allow, they say, ideal suspension distances and spans. It can be used with manual or motorised trolleys and SWF electric chain hoists.
Specially-designed, high-performance running wheels give, says Knopf, gentle load handling, smooth movements and easy travelling. The steel version offers seven profiles in five sizes; all are coldformed and powder-coated, which makes them very rigid.
Demag can claim to have invented the concept of the flexible, modular light crane system more than 50 years ago, when they introduced their KBK system back in 1968. It has evolved since then; today the KBK system is modular enough and flexible enough, with a range of components extensive enough, to assemble into single- and doublegirder suspension cranes, overhung and extending cranes, monorails, and pillar- and wall-mounted slewing jibs as well as stacker cranes and freestanding workstation cranes.
The aluminium-tracked KBK Aluline is designed to deliver high performance at a minimum weight, with the associated ergonomic benefits as loads can be moved and stopped quickly with minimum effort. Despite the low weight of the system, it offers high rigidity, and very smooth operation, which again gives ergonomic gains, and capacities of up to 2t. It comes in six different aluminium profile sections in four sizes, gives low noise levels, and, says Demag, is virtually maintenance-free.
Expansion in demand for light lifting is evident in the Far East. Kito are bringing new products to that market.
“We opened sales of our PRO light crane system to the Japanese market on August 1st this year, and the product was released to China and some other Asian markets as well,” says Tsuyoshi Oshita of their marketing department.
“It is designed to be light-weight and compact, which makes the system a perfect match for the manufacturing floor in Japan, where building areas and workspaces are often limited.
“Demand has been strong since the release, and we have received positive feedback from customers.”
One particular focus is the food industry: “Customers in that sector have chosen the PRO system with aluminium rails because it resists corrosion and meets the required strict standards of food hygiene control. A soup factory is using our electric chain hoists combined with light rail systems to move soup from the pot at the production line.”
Kito have worked on smooth movement as a design priority. “Adopting suspended profiles instead of heavyduty rails means that the crane can transfer loads along smooth, threedimensional paths. The system requires only light force to operate it, so it can easily be handled by women and older staff. Re-design of the cross-section has made it 10% lighter than the average aluminium rail in its class.”
And Oshita of Kito, like Goforth of Gorbel, points out that low mass reduces workloads in installation, and in relocating the cranes when production systems are altered.
All manufacturers stress versatility in this market. It is clearly advantageous if a lifting system can be easily adjusted to changes in production layout, and light systems are open to quick and easy realignments and re-routings.
“Modularity and ease of assembly are both a big thing for us at Kito Erikkila,” says Raty. “All of our products are designed with those things in mind. For example our very popular internal conductor rail was designed to work for both steel and aluminium profiles with many shared components. This has been very well received by our customers.”
“By ‘versatile’ we mean that customers’ needs are handled with bespoke solutions according to their requirements,” says Forti at Niko Helm Hellas.
“Their requirements vary depending on the working load, the mounting specifications, the working environment— whether it is a clean room of one with high humidity or a corrosive atmosphere. There may be restrictions on the installation area, such as ceiling height restrictions. All of these can be accommodated.”