The world’s first topless luffing jib crane left Jost Cranes’ factory in Arneburg, Germany on a misty morning late last year. Although it is only just off the drawing board, the company has already sold about 10 units of the so-called JTL 108.6, with moving ballast designed by Franc Jost.
Alexander Jost, marketing director of Jost Cranes GmbH, believes that this crane type is destined to become the backbone of his company’s product line.
At first glance, the crane looks similar to a saddle jib topless crane in the 100tm capacity class. However, the secret of its design lies in the hydraulic ram, via which the jib can be raised up 85 degrees. In order to reduce the overturning moment, the counter jib with the swinging counterweight basket moves down when the jib moves up.
As well as 2.09m square sized tower systems for up to 42.07m free standing height, the well balanced upper crane can use compact 1.3m by 1.3m wide city tower systems, providing up to 30.2m free standing tower height. This is a special advantage when the crane has
to be installed into lift shafts.
Modularity simplifies erection
Although the use of luffing rams in tower cranes is not new, the Jost JTL 108.6 offers simpler erection because of its topless and modular design features.
The upper crane can be installed in just two lifts made up of the:
• ï„·Central turntable section with cabin platform, hoist unit hydraulic cylinder, and tower top weighting 9.2t.
• ï„·Complete pre-rigged jib (for a maximum jib length of 45m), and counterweight unit weighting 7.7t. If only limited access crane capacity is available, the weight can be reduced to less than 5t.
To increase safety, hoisting rope reeving at the jib is carried out on the ground. Thanks to the hydraulic ram, no luffing rope reeving or A-frame are necessary, speeding up erection and increasing the safety of the luffing mechanism.
Unconventionally, the hoisting winch is located in front of the turntable section, and can therefore be easily watched by the crane driver during operation, further increasing safety. On top of this, thanks to the topless design, the under hook height of the service crane during rigging operation is reduced in comparison to
a conventional luffing jib cranes.
Like all new Jost cranes, the JTL 108.6 is equipped with an own designed cabin platform, access to which is provided by a side door. In the back of the unit, an air conditioned walk-in electric cabinet separated by a door from the cabin houses the frequency regulated control systems. Thanks to the sophisticated frequency inverter, regulated drive power consumption is restricted to 30kW.
At the cabin side next to the turning platform, pre-installed plug connections speed up crane erection. Easy access to the counterweight basket is provided by a platform on the counterjib. Depending on the jib length, a maximum of only three concrete blocks have to be lowered into the basket.
The ability to store the jib at 75 degrees, or even 85 degrees in out of service operation mode with closed brakes of the slewing drive, make the crane especially suitable for cramped city sites.
In older hydraulic operated luffers, there is a danger that overnight falling pressure in the hydraulic system can let the jib boom down, sometimes causing serious safety problems. Although modern hydraulic systems are reliable, Jost increases the safety factor further
by connecting the counterjib with the towerhead section through two bolts controlled by a sensor when the crane
is in the steep-angled, out of service condition. In the horizontal position, the jib simply rests on the towerhead, as on conventional topless cranes.
Maximum lifting capacity in four-fall operation mode is restricted to 6t up to 21.4m when operated with a 30m jib. At 45m, a tip load of 1.6t is achieved with the jib in the horizontal position.
On the drawing board are bigger models following the same design principle. As a modified version, the JTL 158.6, for example, offers 50m maximum outreach where 2.4t can be lifted.
The JTL 108.6 has found a ready market in the UK, providing an alternative to the smaller capacity luffers built in conventional style like the Jaso J80PA, the Potain MR 90B, Peiner SN 86, Liebherr 112 HC-L, and the popular Wolff 100B. London Tower Crane Hire and Sales Ltd will take delivery of six Jost units in the next couple of weeks.
Besides the topless luffing crane, a more conventional JL 316.16 luffer was presented in Arneburg following the movable counterweight design principle developed by Franc Jost in 1997. In the UK, four of the smaller JL 216.16 are already serving high-rise projects. For many construction projects, the well-established Comedil CTL 400 is seen as too large, and rental companies are looking for less expensive models to fill the gap between 200 and 400tm.
Hence, Jost presented the JL 316.16 in iron ready for shipment. One crane has so far been ordered for the UK, and one for Korea. To satisfy the Korean market, where tower crane hiring rates are related to the maximum capacity, 16t can be lifted up to 22.1m radius while the impressive tip load is 4t at 60m radius.
When the JL 316.16 is using the same standard 2.24 by 2.24 square sized tower system as the JL 216.16, maximum free standing height is reduced from 60.2m to 42.2m. However, with a 2.42 by 2.42m sized tower, up to 53.4m free standing height can be achieved.
Depending on the customers’ fleet, other tower systems than the original Jost system can be used. For example, Falcon Crane Hire is already operating the JL 216.6 on third party towers.
Short, lightweight counterjib
Thanks to the frequency regulated drive of the luffing and hoisting winch, in comparison to the traditional Comedil CTL400, a short, lightweight counterjib can be used where only luffing and hoisting winches are located, fixed on separate frames, which can be installed as individual crane elements for assembly and dismantling under difficult conditions.
Electrical cabinet and drivers cabin form one spacious, side-mounted unit bolted to the turntable.
Some small details are added with easy and speedy erection in mind. For example, a tower top mounted derrick helps to install the boom retaining rope holding the jib during the rigging process. The pulley block is lowered from the tower top upper together with the first pendant section, adding weight for smooth luffing rope spoiling and simplifying the connection of the jib guy pendant line. The ballast basket of the Jost patented movable ballast system beneath the counter jib is kept above the tower line, in contrast to the former BKT system, so that maximum usage of the freestanding tower height is guaranteed. The centre of gravity of the filled in ballast lies under the mechanical link of the ballast basket with the jib. This means that no shock absorbers, common to the early BKT luffers, are required.
According to Alexander Jost, the worldwide best selling crane class is the 300tm capacity range. That is why Jost Cranes GmbH is concentrating on this market segment in its topless crane range. Shown in Arneburg was the JT352.12, an upgraded version of the BT312.12 displayed at Bauma in 2004. Again ready for delivery to the UK, the upper crane was fixed on the 2.24 by 2.24m square sized Jost tower system.
This crane showed up the newly designed compact cabin unit called CACON, housing all necessary electronic equipment and the crane driver cockpit. Thanks to the modular design of the
Jost topless cranes, the JT352.12 was developed in just four weeks. A weight of 12t can be lifted up to 30.5m radius, while at 75m outreach 2.7t can be handled. Again, tower systems other than Jost’s own can be used.
After manufacturing in China and Slovenia in the early years of the company’s history, Jost has now
returned the fabrication to Arneburg.
Company run as a network
The company is run as a kind of network as chairman Franc Jost calls it, in
order to respond quickly to customer requirements with easy to assemble and affordable modular cranes. All steelwork is carried out at the AMS manufacturing plant. Design is carried out in at the company’s Munich headquarters.
To ensure the highest quality for its CE certificated cranes, the company says it uses only reputable crane component suppliers. For example, Rothe Erde is delivering the slewing rings, while drive units are supplied by SEW.
So far, about 20 units of the new Jost crane generation have been built. While the UK and Asian markets are key at the moment, Alexander Jost is confident about expansion into other markets in the near future.