Field trials of a new Walkersele Ultraglide rotary lip seal on a hot steel mill show that it protects bearings for well over 18 months with no obvious signs of wear or damage. The traditional nitrile rubber (NBR) seals usually survive for only three months on the intermediate stand at a Corus plant in the UK.
The Ultraglide is based on a hydrogenated nitrile (HNBR) elastomer that was specially developed by James Walker for lip seals that run for long periods under hot abrasive conditions.
The new grade of material can work at temperatures in excess of 150Β°C without hardening and cracking, instead of the 100Β°C maximum for traditional nitrile. It also has three times the wear resistance of nitrile, and twice that of the fluoroelastomer (FKM) compounds often used for rotary sealing duties.
In trials reported by David Edwin-Scott, James Walker's head of technology, a D Walkersele Ultraglide was installed on a 241.3 mm rolling mill shaft to retain lubricant within a bearing. In this environment it also has to exclude water, steam, scale and rolling fluid.
After 18 months in operation at speeds of 70-120 rev/min, the roll chocks were removed and the seals inspected in situ. The seal was found to be in 'as new' condition, so the chocks were refitted without removing the seals and the trial continued. The success of the seals is attributed to a low coefficient of dynamic friction, at 0.25. This in turn generates less heat at the sealing lip than conventional nitriles and fluoroelastomers, which have a coefficient of around 0.40.
The new material also has 40% higher thermal conductivity than the other materials, so heat is dispersed more efficiently and the lip retains its flexibility. Chemical compatibility is a further strong point for the HNBR, as it has a wider range of chemical resistance than conventional nitrile materials.
The seal being used in the trial is a Walkersele D6 type that has a fully molded-in spring. Problems had previously occurred in this application with retention of the spring. The design used makes the seal easier to fit, as well as