Upgraded backstop clutch improves bucket elevator reliability

Bucket elevators provide a simple but effective means of hauling and lifting flowable or semi-flowable bulk materials, including grain, fertiliser, foods, wastes and minerals, often into storage silos. Their versatility means they can be easily tailored for use with challenging products, including fragile or abrasive materials. But, in all cases, safety is a prime concern, and the main shaft that drives the belt will always be fitted with a backstop clutch. This enables driving of the bucket in one direction but ensures there is no backwards slippage in the event of a drive problem.

The inherent weight of the bulk material, combined with their often abrasive nature and the fact that the bucket elevators typically operate outdoors, combine to create a harsh operating environment. The high levels of torque, plus the inherent dust, debris, rain, sleet, snow and temperature extremes, all take their toll on the drive train. For one leading manufacturer of bucket elevators, the backstop clutch in particular was causing reliability problems. High running temperatures were leading to early failure of the product and, while safety was never compromised, it was certainly leading to increased maintenance requirements and regular clutch replacements.

Trapped roller versus sprag

Looking for a solution to this problem, the company called in Tsubaki's engineers, who analysed the problem and recommended that the trapped-roller backstop clutch be replaced by a Tsubaki BSEU sprag-style clutch. Designed specifically for use on the low-speed shaft of inclined and bucket conveyors, the BSEU backstop cam clutch provides very safe reverse rotation prevention.

Trapped-roller clutches feature an inner race with ramps and individually sprung rollers. The rollers rotate during freewheeling in the drive direction but, in the reverse direction, the rollers lock against the outer race and inner race ramps to ensure near-instantaneous backstopping. The sprag clutch features an alternative design in which cam-shaped sprags separate the inner and outer races. The angle of the sprags allows movement in the forward direction but provides near-instant backstopping in the other.

The Tsubaki BSEU clutch features an increased number of sprags, which enables greater torque transmission in relation to the clutch's size and weight when compared with a trapped-roller clutch, resulting in extended fatigue life. Furthermore, overheating when the motor is idling is lower, which helps maintain lubrication by means of grease instead of oil and so improves the clutch's wear life and ensures less maintenance.

A further feature of the BSEU is its sealing arrangement. V-ring seals are fitted as standard to offer a high level of protection against dust. Even higher specification sealing is available for applications where protection is needed from more extreme environmental conditions, such as fly ash, coal dust, splash water and others.

Being dimensionally similar to other styles of backstop clutch, the BSEU offered the elevator manufacturer an easy upgrade path over its existing clutch. Fitted to the latest models of bucket elevators, the BSEU clutches are delivering safe operation, higher torque capacity, faster operating speeds, less maintenance and longer life.

Follow the link for more information about Tsubaki BSEU sprag-style clutches.