Coupling Helps Worms Turn Longer



Renold Hi-Tec Couplings, of Halifax, have solved a problem for a Korean company experiencing excessive wear to a gearbox fitted on a copper pipe drawing and coiling machine at Poongsan Metal in Changwon. The worm wheel reduction gearbox was connected, via a gear coupling and cardan shaft, to a rotating drum that coils the copper pipe. The high levels of vibration were damaging the worm gears to such an extent that they had to be replaced every 12 months as part of a planned maintenance regime. So severe was the problem that new worms were showing signs of wear after only two months.

Engineers at Poongsan contacted Renold Hi-Tec after it was decided that rubber-in-sheer couplings would not be suitable. Rubber-in-sheer couplings can fail catastrophically from just a small tear to the rubber block, whereas rubber-in-compression couplings are intrinsically failsafe. Renold Hi-Tec's engineers analysed the dynamics of the system using their own software and fitted a PM18 rubber-in-compression coupling with cardan shaft. A specially selected grade of rubber for the rubber blocks was chosen by Hi-Tec's engineers to dampen vibration, eliminate backlash and protect against torque amplification. Since installation the gearboxes are running smoothly and the worms are showing no sign of wear after six months operation.

Poongsan Metal is the world's third largest producer of copper products. It supplies 60% of the blanks for the world's copper coins and employs 4,500 people worldwide.