Steel mill runs smoothly on new couplings
A hot strip mill in the USA has benefited from the installation of rubber-in-compression couplings, from Renold Hi-Tec, that have cut torque amplification by a staggering 23 percent. The couplings were specified during the refurbishment of the plant to protect the drivelines of two reversing roughing stands and one finishing stand.
Torque amplification is a measure of the peak torque in a driveline compared to the steady working torque. In all torsional applications the components in the driveline, including the gearbox, motor, shafts and pinions have to be designed to withstand peak torques or premature failure of the system will occur. In effect the driveline has to be over engineered to compensate, but if torque amplification can be reduced then so too can the size of the components in the driveline, and that can result in huge savings in capital investment.
One of the main causes of torque amplification is backlash across gears and couplings. The Renold Hi-Tec coupling is backlash free by virtue of the precompressed rubber blocks which not only eliminate clearance but incorporate hysteretsis damping as the rubber deflects. Renold's engineers were able to use in-house software to analyse the dynamics of the system and carefully 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, that's over ten million horse power, and operating at speeds of up to 725rpm. The new couplings dramatically 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 shock loads some 23% greater.
An added 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 rubber-in-compression couplings.