Improvement in Maintenance Practices for Enhancing the Reliability of SMS Mould Oscillators

摘要

In the continuous casting of steel, the continuously cast strand withdrawn from the mould consists of a thin outer shell surrounding a molten core (because only a thin layer of steel adjacent to the walls of the mould undergoes a solidification process). There is friction between the shell and the mould where the shell has a tendency to stick to the mould. The shell is relatively weak because it is very thin and at very high temperature. Utmost care is required to limit the stress which is applied to the shell in order to withdraw the strand from the mould. Excessive stress will cause the shell to rupture. Rupture of the shell inside the mould is bad for the surface quality of the strand while rupture outside of the mould will result in a breakout, i.e. an escape of the molten core. Therefore, mould oscillators are provided to prevent the sticking and reduce the friction-resistant force between the solidified shell and the mould castings. These oscillators are very critical for continuous casting of steel. Generally, an oscillator comprises of a motor drive which is coupled to a reducing gearbox where the gear output shaft is coupled to an eccentric rotating shaft for oscillation of the mould. This eccentric rotating shaft is simply supported on two bearings. Problem in oscillator directly affects the production and quality of the steel. The SMS maintenance team of JSPL was facing chronic problems in all of its six mould oscillators. The common problem was the abnormal sound from the gearbox. More often, the coupling bolts of gearbox and mould oscillators were getting sheared off. Sometimes, the oscillator bearings were getting damaged. In addition to it, the vibration level on DE side of motor was high. Due to poor reliability of mould oscillators, the steel's productivity and quality were getting affected. But a small change in the maintenance strategy of mould oscillators minimized their vibration levels and reduced the noise intensity from their gearboxes. Since last eight months, the reliability of mould oscillators has improved a lot and all are running without any breakdowns.