ONE of the toughest tests for industrial gearboxes is stop-start operation in dusty and grimy environments. Such conditions - regularly encountered in heavy manufacturing and mineral processing applications - impose huge loads on bearings, belts, shafts and control components.
So when Saeco Bearings and Transmissions designed a new cement and aggregate mixing drive for Firth Industries East Tamaki plant in Auckland, New Zealand, they turned to a new range of Bonfiglioli planetary gearboxes designed to be remarkable for the amount of torque they can produce out of a compact installation.
"Firth was running an average of 80 batches a day of cement and aggregate for grey masonry and retaining walls," Saeco national sales manager Christopher Smith said.
"With loads of about 1.2 tonnes each, cycling through every 15 minutes, you can imagine the stresses imposed on the mixing equipment.
"The previous arrangement - using a belt motor driving through a half shaft to split pinions at the other end of the mixer - was inefficient, noisy and prone to breakdown."
Mr Smith worked with Firth production manager Ken Gotts to design an installation up to the standard of the international Fletcher Concrete and Infrasturcture organisaiton of which Firth is part.
The new installation, designed from the outset to be radically simpler and quieter, incorporated a Trasmital 313L2 gearbox with a gearbox ratio of 40.5 and output speed of 23.704rpm.
The installation - undertaken by T.P. Engineering - produces design output torque and maximum output torque of 19,334Nm and 22,723Nm respectively, driven by a 55kW Teco four-pole motor with a TD2 soft start.
Designed to function with typical ambient temperatures of 30°C and with an intermittent duty factor of 100 per cent, Mr Gotts says the new installation is much more compact and quieter than the old unit it replaces.
"It is totally enclosed so no dust can get in, and there are far fewer moving parts and none of the big efficiency losses of the old arrangement, which used a 50hp motor driving through a pulley to the half shaft driving split gear pinions at the far end of the mixer.
"The old installation clanked around and lost power because it was so complicated. The new installation locates the motor and compact gearbox at the same end of the mixer, connected by pulleys and driving through a direct coupling to minimise bearing loads. The soft start also minimises mechanical shock.”