The German company ESW Röhrenwerke manufactures seamless steel pipes that are used worldwide as structural tubes in machinery, steel constructions, in the automotive industry, as boiler tubes and as pipelines and supply lines for combustible liquids, gases and oil worldwide. 70.000 tonnes of steel pipes are produced each year in the three-roller planetary rolling mill process. This high-reduction technology at the world’s unique planetary rolling mill has made ESW one of the leading producers of seamless hot rolled steel pipes in particularly high qualities. The steel pipes are available in outer diameters of 70 mm to 244.5 mm and with a wall thickness of between 7.1 mm and 60 mm. Depending on the application and customer requirements, grades ranging from plain carbon steel to high alloy steel are processed.
To manufacture the pipes, up to 2 m long steel billets are heated up to rolling temperature in a rotary hearth furnace. After an initial hot rolling stage in the hollow block cross rolling mill, the hollow blocks are transported to the three-roller planetary rolling mill for the second stage of the forming process. Three rollers form the hollow block into a tube using a mandrel bar. While each roller rotates around its own axis, all three rollers also circulate around the rolled steel like planets. In the third stage of forming, the steel is then rolled out into finished pipes. The subsequent manufacturing steps are slow cooling, the subdivision into cooling bed lengths and adjustment of the pipes to ensure they are straight.
An essential component for the three-roller planetary rolling mill process is a large bearing that acts as the front support for the rolling head assembly. As ESW Röhrenwerke owns only one rolling mill, failure of the bearing presents a particularly high risk. Therefore a regular replacement of the bearing is required. When it became necessary to replace the bearing recently, ESW Röhrenwerke opted for a special bearing from NKE. The special cylindrical roller bearing with a solid steel cage has an outer diameter of 3.3 m and weighs 2.2 tonnes. The large bearing will be loaded with a supporting force of 76.3 tonnes and operates at a speed of 125 rpm; the supported rotating mass is around 200 tonnes. The oil lubrication is very low at 10 l/min. The special bearing has a service life of between six and eight years.
ESW Röhrenwerke already had very good experience in the past with NKE in terms of product quality. The critical factor in the decision to go with NKE was the fast availability of the large-size bearing. “NKE is a competent and reliable partner in bearing technology. The short lead times in the production of large-size bearings for our planetary inclined rolling mill was a major factor behind our decision on this project,” explains Lothar Schmitz, Head of Maintenance and Engineering at ESW.
Alongside large bearings for the rolling mill industry, NKE also develops customised special bearings for other high end applications. Examples include bearings for use in tidal current power stations, wind turbines and mining machinery.