Steel mill runs smoothly on new couplings

Manchestrer, UK - A hot strip mill in the US has cut cut torque amplification -  a measure of the peak torque in a driveline compared to the steady working torque - by 23% through the installation of rubber-in-compression couplings. The installation was part of a refurbishment of the plant to protect the drivelines.

The couplings, from Renold Hi-Tec, were specified for two reversing roughing stands and one finishing stand. In all torsional applications the components in the driveline, including the gearbox, motor, shafts and pinions must withstand peak torques to prevent premature failure of the system.

A common causes of torque amplification is backlash across gears and couplings. Renold's coupling design is backlash-free due to the use of precompressed rubber blocks, which not only eliminate clearance but incorporate hysteretsis damping as the rubber deflects.

Renold's engineers used in-house software to analyse the dynamics of the system and select the correct type of coupling and rubber blocks to change the natural frequency of the system and avoid resonant frequencies. Three rubber-in-compression couplings were specified delivering up to 8 mega watts of power each - over ten million horse power, and operating at speeds of up to 725rpm.

The new couplings increased the life of the plant and cut the ongoing cost of ownership as rubber-in compression couplings are also maintenance free. Capital investment was also reduced as the plant did not have to be over engineered to accommodate much higher shock loads.

Another advantage for the reversing roughing stands was the benefit of no lost motion while reversing. A major contributor to wear and fatigue are the torque spikes which occur during reversal and this is cut significantly by the backlash-free nature of the new couplings.