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Using couplings to cut vibration and torque amplification

08 September 2015

Table rollers in steel mills critical to production as failure to any part of this conveying system would result in the loss of ability to move product around the mill and could bring production to a halt.

Shock loading, vibration and torque amplification are common operating conditions on table rollers and the driveline must be designed to withstand this. When a shock load occurs, such as when a billet of steel hits the rolls the impact passes down the drive train transmitting the torque to the driving motor.

A key factor in peak torques and torque amplification is backlash, which acts like a hammer blow to the system as the torque from the shock load accelerates over the backlash gaps and then abruptly decelerates to the operating speed transmitting dynamic torque along the driveline.

Fitting rubber-in-compression couplings cures this problem as there is no metal-to-metal contact and the drive is through pre-compressed rubber elements that damp vibration, eliminate backlash, and ensure that the natural frequency of the drive train does not coincide with the running speed.

Rubber-in-compression type flexible couplings are comprised of two round, metal sections fitting one inside the other with what looks a bit like paddles projecting inwards from the outer section and outwards from the inner.

Rubber blocks are placed in the spaces in-between the paddles, and, as the outer section is turned by the motor, it drives the inner section through the rubber blocks. As this happens the rubber is compressed, and hence the term rubber-in-compression.

Renold Hi-Tec is a supplier of this type of coupling and the company's engineers are able to use a novel software application to measure and determine true torque loads and vibration frequencies in a system. Once these have been determined, the couplings can then be tuned with different types of rubber blocks to change the natural frequency of the system and avoid damaging resonant frequencies.

Rubber-in-compression couplings are maintenance free and the rubber blocks will provide at least 10 years of service before replacement. As well as being the perfect solution on table roller drives, rubber-in-compression couplings are also used on other applications in steel mills, including the main rolling mill drives, ladle cranes, hoists, pilgar mills, pickling lines and edger drives.

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