Company
Bronto Skylift is a world leading manufacturer of truck mounted hydraulic platforms, which produces booms rising skywards up to heights beyond 110 m.
The requirements for the modern boom are to be at the same time light and strong in structure, which can be resolved using steels that are stronger than ever.
Bronto Skylift and Ruukki started working together in 1992. Today, the steel parts for Bronto Skylift’s aerial lift booms are made from Ruukki’s steel.
Customer’s profile:
Company: Bronto Skylift, Finland
Employees: 329 in Finland
Leading aerial lift manufacturer, 95% of production exported. Over 6000 deliveries globally.
Challenge
Conflicting requirements of lightness and strength
The weight of aerial lifts easily increases to the point where road durability becomes a problem when transporting them. Including the 7 axle chassis, the largest 112-metre lift weighs more than 77 tonnes. We’re balancing the conflicting requirements of lightness and strength the whole time. The higher the reach, the lighter the structure must be otherwise the device won’t stay on its chassis.
Solution
One hundred metres of better steel
Bronto Skylift uses Ruukki’s high strength steels, Optim® 650 MC and Optim® 900 QC, to manufacture booms. The high-strength steel grades enable smaller total weight and longer reach for the boom.
“Ruukki has been involved in development and has supplied increasingly stronger steels to enable us to reach a height of over a hundred metres. The steel in the topmost sections of the 100-metre telescopic boom is just 3mm thick. At the bottom, the thickest telescopic sections are 8mm thick,” reveals Mr. Marko Lepomäki, who is responsible for subcontractor purchases at Bronto Skylift.
Strong welded joints by planning
Booms must endure high static loads. The load experienced by the welded joint can be minimized with structural design and correct positioning of the joints. This optimizes the resistance of the welded joints.
According to Mr. Pertti Huuhka, supervisor at the company’s factory in Pori, Finland, “Flexibility of welded joints is important in the welding process of booms using high-strength steels. The flexible joint obtained with suitable choice of welding wires is very strong and it is more important as boom height increases.”
Mr. Marko Lepomäki says that the company uses plasma welding for long seams and Mig-welding for additional equipment. “In plasma welding, heat is brought to a very small area, which results in minimal steel distortion.” Also for lifting booms, design optimizes positioning of welded joints at an early stage.
Strict tolerance criteria
The tolerance criteria of the steel parts of the telescopic boom are very strict. In between the telescopic sections, which are inside each other, there is a space of just 5-6mm, inside which the long boom has to be able to be raised. A telescopic boom is usually raised using a cylinder inside the boom and connected multiplicative steel cables. “Rolling and form rolling the steel parts has gone really well and dimensional accuracy has been kept to,” Mr. Lepomäki notes.
Discerning customer adds to Ruukki’s expertise
Bronto Skylift’s design managers have been working together with Ruukki’s product development engineers to improve the quality of the Optim® 900 grade and are also involved in the development of new grades.
“Our demands are high, but we’re satisfied. Development is ongoing and we’ve been able to solve even the most difficult problems,” Marko Lepomäki sums up the customer experience.