Around 25 Starrag machine tools, which thyssenkrupp rothe erde® has bought since 1980 and which are still in use, play an important role in the machinery park. These now include six Dörries CONTUMAT vertical turning-grinding machines, which are primarily responsible for finishing the bearings for wind turbines. “We supply blade, tower and rotor bearings for wind turbines in dimensions of up to six metres in diameter”, explains Dr-Ing. Mattias Töfke, Production Manager at thyssenkrupp rothe erde®. The bearings are produced in an extremely high production depth on he very extensive machinery. “We take on the complete machining, thermal processing, surface treatment and assembly”, says Dipl.-Ing. Jürgen Lange, Head of Plant Maintenance and Planning, “only a few components such as screws or seals are sourced externally”.

Production starts at the ring-rolling mill in Dortmund, where high-strength steel special alloys are used to produce rolled rothe erde® rings. In Lippstadt, these rings are then used to manufacture slewing bearings which must meet the most exacting demands. For example, during the mechanical machining, thyssenkrupp rothe erde® relies on the electronically controlled coolant supply of the CONTUMAT centres to compensate for temperature fluctuations and ensure constant machining conditions. A larger oil circulation volume with temperature-controlled oil in the base also ensures controlled table growth.

Strict regulations of the wind power industry

This attention to detail is essential for thyssenkrupp rothe erde® to meet the demanding specifications of its customers, for example from the energy sector, which correspond to those of the aerospace industry. “We have had to develop new processes for these requirements over the years”, reports Lange. “In particular, we have optimised the hardening and finishing process using grinding”. Before rothe erde® slewing bearings enter series production, prototypes are produced that must pass endurance tests on test rigs. Töfke: “Prototypes undergo an endurance test for six months, in which we simulate typical load cycles, which correspond to more than 25 years of use”.  

Two powerful, water-cooled 89-kW drives move the rotary table with a torque of 461,900 Nm and a speed of 75 rpm. In this new, sixth Dörries CONTUMAT too, a rothe erde® slewing bearing ensures smooth, even running with extremely heavy components. The turning, drilling and milling movements are carried out by the right support. For grinding, a 60-kW spindle is used in the left support, which operates in the speed range of 1,500 to 3,500 rpm. Accord-ing to the Production Manager, the raw performance for finishing rothe erde® slewing bearings could theoretically also be fulfilled by other machines with regard to rigidity and accuracy. However, the subsequent quality of a bearing largely depends on the finishing. Key for Starrag here is that as the manufacturer, they not only supply the hardware, but also the software. Together with Starrag, grinding cycles have been developed and continuously optimised over the decades. But how does Starrag’s promise of "Engineering precisely what you value” meet the demands of regular customer thyssenkrupp rothe erde® for finishing?  The great benefit is the programming and the ease of use”, says the Production Manager. “Particularly in the area of grinding finishing operations, we have been able to build up shared expertise in recent years upon which we are happy to rely”.  Thanks to these good experiences, thyssenkrupp rothe erde® has ordered a further Dörries CONTUMAT, which will soon be used in Lippstadt to provide the rothe erde® slewing bearings with the finishing touch.