Minis get big ideas

Traditionally, tower cranes have been used for the installation of glazing units and curtain wall panels. However, this task occupies a great deal of time of the tower crane, which may well have other priorities on that site or could be dismantled and moved on to its next site.

There is another method, through which the panels can be fixed from inside the building. A mini crane moving around the concrete floor-slab can do the job. It is cheaper to operate than a tower crane.

Wim Le Roy, sales manager France at Kranlyft, the major distributor for Maeda cranes in the EMEA area, says there has been a change of attitude towards the use of tower cranes for these jobs.

“High winds can stop tower cranes working. At a site they come under the main contractor and may not be available to the subcontractor who is installing the glazing or cladding. In any event he will have to wait on the contractor’s convenience for times when he can use it and he will be charged for it by the hour.

So for the smaller contractor or a subcontractor it makes absolute sense to have your own mini crane or spider crane to do the job. It makes you autonomous. You are no longer waiting for the convenience of others.”

“The modern construction site’s needs have evolved,” says Jekko’s sales manager Alberto Franceschini. “The demand is for compact, easy-to-use machines to save on manpower. 600kg is the lifting capacity that seems most wanted. Mini cranes allow reduction of the installation team by one or two fitters and brings the concept of ‘one operator, one machine’. That increases efficiency in terms of time, cost and quality.”

Hird are specialist mini crane operators and hirers of Valla, Maeda and Unic cranes. They are also distributors for Manitex Valla cranes and Winlet vacuum robots. 

Carl Cooper is their sales manager. “Glass and curtain walling used to be carried out by brute force, and more recently by rail systems, special installing rigs or the on-site tower crane,” he says.

“But due to the demands on the tower crane being needed for other contractors, and the need to close in the building as quickly as possible, glazing and curtain wall installers needed to be more independent. So came the emergence of the mini crane working on the concrete flooringslab of the building, sometimes many storeys up, to install both internal and external glazing and walling.

“Several major curtain walling contractors worked with mini crane manufacturers to develop mini cranes for that purpose.”

“Before the big crash in 2007 the curtain wall sector was split: the large contractors would work only on multimillion dollar, the +40 storeys/3 year + builds type contracts. They were able to work with architects to design more complex builds and increased weights more and more. So the small 2t pedestrian controlled electric pick and carry crane was used to carry and install curtain wall panels of 800kg and up, for both internal and external installing.

“Those small pedestrian controlled wheeled or track mounted pick and carry cranes were able to work on any floor, and using their winch with up to 60m of rope they could lift panels to several different floors below it. Being mobile, minis can close a complete floor very quickly as they don’t have the restriction of outriggers and can be quickly moved around the floor.”

A standard use now is to have the mini crane, or the spider crane, high on the building and use it to lift panels or glazing units that are stacked on the ground up to the right storey.

“Before mini cranes existed, most cladding was put on from the outside, from a tower crane or a ground crane,” says Tony Inman of Maeda USA. “For a decade now that task has been done from the inside. It is faster, it is safer, it uses smaller equipment sized to the lifting so it is cheaper, and crews work independently of the tower crane, and at their own pace. The mini crane is the tool that lets them work independently, and therefore much more efficiently. It is small and affordable, and you can have several on the job at once, speeding it up.”

Hoeflon make mini cranes with capacities up to 9t and hoisting heights up to 22m. “Our C1 crane, which is our smallest, lifts up to 600kg, is small enough to fit in a passenger lift, and is doing very well lately in the glazing industry,” says export manager David Fokker.

“The C1 has a good slewing radius, which is something that glazing robots lack.” And mini cranes, he says, are not limited to concrete floor-slabs inside buildings. “For rough outdoor construction sites the tracks of the C1 make it work really well.”

“Our C6 and C10 minis are used a lot for glazing also—some customers use them entirely for that. They use the jib to manoeuvre the glass sideways then pull it back and do the installation from inside. With remote-controlled vacuum lifters attached this has become a very easy job.” The C6 is claimed by Hoeflon to be the only compact crane that can lift more than its own weight. “This makes it possible for one crane to lower another into an underground space.”

Window of Opportunity

For small, easy-to-reach applications, mini cranes do, however, have a rival, in the glazing robot. The glazing robot is also small and light, moves independently, and does at least one of the jobs that mini-cranes are frequently used for. “In Europe, glazing is a major application for mini cranes,” says Kranlyft’s Le Roy: “Double glazing and even triple glazing panels are becoming the norm. Their loads are getting heavier, so the challenges for the glaziers are getting bigger.”

“Glazing robots are being used more and more and with bigger lifting capacities, over 1,000kg,” says Cooper of Hird. “They are reflecting what the 2t pick-andcarry cranes can do, and they are battery powered which reduces emissions and noise pollution on the site. A Winlet 1000 glazing robot weighs 1.8t all-up, not too far off the gross weight of a Valla 22E mini-crane. So, although the vacuum robot may not fully compete with the versatility of the mini and spider crane, the evolution of lifting practises means they are a valuable and required lifting solution.”

“When working on skyscrapers, mini cranes are more versatile than glazing robots,” says Jekko’s Franceschini. “The crane can be stabilised and work from higher floors for easy and quick installation of facades on lower floors, even by retrieving the panels from the ground floor with a long-rope winch. The operator is able to work via radio remote control on the lower levels, which gives safety. And once the crane is stabilised, thanks to its greater boom and rotation, it can cover a wider area than a glass robot.”

“They can handle bigger glass panes and when greater outreach and maximum working height are needed mini cranes can reach even the second floor from the ground.”

“Glazing robots are more limited in what they can do,” says Maeda USA’s Inman. “They have limited reach and height, and are most effective installing glass right in front of themselves. They are not effective placing glass below floor grade or at extended height or reach. Generally they only work with a vacuum device.

“A mini- or spider-design in contrast can reach further, much higher and work with the load at levels below the machine; you see that often. The reach together with a slewing boom means that it can do multiple lifts from one spot without having to reposition. It can do most of what the robots can do, and more. And you can equip it in many ways, with rigging hooks to lift a panel, or hanging and fixed vacuum devices to hold glass; you can put on different tools for different jobs.”

What then of the spider crane? “The pick and carry mini crane has the advantage that it can move the units around the slab independently, whereas the spider crane tends to need the cladding unit being brought to them,” says Cooper.

“The spider is very popular with installers as it is small and compact and usually has a longer jib than the mini pick and carry. Being on outriggers it can service two or three installs before repositioning. Because of the outriggers the spider crane is usually lighter, helping to reduce ground pressure with better spread being possible using outrigger mats and the footprint of the tracks.

The disadvantages are that pick and carry duties are either very low or on the smaller models not possible at all. Moving around the slab you need to reposition the crane each time and adjust outriggers and place mats, all of which is time consuming. They are in the main either diesel or petrol powered for moving and driving, and mains electric for lifting, which gives the worst of both worlds, trailing cables as well as emitting fumes and noise. There are some all-electric cable models coming through but they are not as independent as the DC battery electric pick and carry type.”

Power is an issue, says Tony Inman of Maeda. “These cranes work in open air as well as inside. For inside use the power source can be mains electricity or battery; in North America propane is more common because of its ubiquity also in forklifts and man-lifts. In Europe, propane is less used. Maeda offer all three power sources.”

“Jekko is actively working on the green technology of the lithium battery supply, for example with the recent SPX532 and the upcoming SPX650,” says Franceschini.

Ease of moving into and around the building is another design criterion for mini cranes. “The most common model for glass is 75cm wide, which means they can get through single doorways. They can get high into a building on their own power via the elevator hoist, or be lifted by the tower crane, which takes just one single use of the crane rather than occupying it for days,” says Inman. “Or you can use a ground crane, such as a mobile. There are multiple ways.”

You can even do it with a helicopter: “It may be necessary to remove some parts or accessories of the mini crane to ease the transport, for instance in elevators or with a helicopter,” says Franceschini. “For this reason Jekko has developed modular machines, that can be broken down and reassembled very easily.”

Beside façade work, renovation is another good application for mini cranes, says Le Roy. “Indoor areas that are already finished are a constraint for traditional cranes, which cannot get in there. For fitting-out work inside almost-completed shopping malls and the like, mini cranes can be fitted with non-marking white tracks instead of the traditional black rubber. Delicate floors like churches, chapels, mosques can be worked on with suitable protection; but, curiously, in many modern buildings ground-pressure can be a problem even with lightweight minis. New buildings sometimes have very narrow ground-bearing tolerances, 400kg/sqm can be typical. Some of our mini cranes are only 75cm wide, which lets them fit through every single doorway; weights are less than 2t, but even that is sometimes the most that a floor can bear without load-spreading panels. But if our machines cannot do it, no machine can do it.”

Minis, as we have said, are not limited to high-rise work. “There are many places where a mini or a spider crane can get to that other cranes just cannot reach,” he continues. “One recent application was a wooden facade in Paris, just a few stories high. A good customer of ours used three mini cranes: the larger one lifted the panels and deposited them near the erection-point. Each panel was too heavy for one of the smaller cranes to lift alone, so they worked in tandem to lift and fit them.

“And our Turkish dealer has just completed a major project in Baku, in Azerbaijan, on three iconic high rises, the tallest in the country.

The architect has designed them in the shape of flames to symbolise the city’s history, and the facade consists of several hectares of glazing panels. But Baku, on the Caspian sea, is one of the windiest cities in the world—the word ‘baku’ means ‘wind-blown’—and 90km/hr winds are common. The tower crane was frequently out of action but a spider crane high on an upper floor was able to lift glazing panels from floors below and install them from inside the buildings even in gale-force winds.”

“Architects and building designers are using more and more glass. It is convenient, and inexpensive, and aesthetically pleasing,” says Inman.

So the demand for mini cranes for these applications is expected to increase further. And since they are equally useful on small buildings as on large ones it would seem that as far as cranes are concerned, less is more.