Thanks Lyle. ■

Hi Q3..

I have never needed to measue the torque on a holdback torque arm.

Why not just calculate what it will be... it wil save you time, effort and money!

Cheers

LSL Tekpro ■

I'm looking at a job now where by using a "load link" the torque on a headshaft can be measured and used to validate theoretical calculations for absorbed power.

(There's always removing the drive unit, wrapping a rope around the drive shaft and pulling with a spring balance ) ■

Latest technology resorts to magnetising the element under torsion and measuring the rotation of the magnetic field. It sounds about right so long as the material is magnetically susceptible. ■

Conveyor Dynamics, Inc. (CDI) have designed and installed many multiple driven pulleys with load sharing holdbacks. We typically analyzed the conveyor dynamics, and refine our typical beville-washer spring system to achieve load sharing within less than 20% error, and in some cases closer to 10% drive shaft torque deviation between drives. This highly depends on the drive sizes, belt modulus, belt speeds, drive analysis conditions (normal stop, aborted stop, et al), drive inertias, take-up system, locations of drives, brakes, and take-up and soft starting devices. ■

As Graham might know, we installed our first multiple holdback load-sharing system on the Palabora incline in 1988. We gave the spring design to PWH who had the supply responsibility for the drive station.

The holdback specification stated they had to load share within +/-15% (by memory). We fitted each of 3 x 3150 kW drives with load cells under the holdback arms and did achieve the desired load sharing. The holdbacks were rated at 720,000 ft-lbs/ each. The peak momentary torque could exceed the motor rating by > 25%. The Marland holdbacks were test rated well beyond their nameplate rating in 1987-1988. They operated from 1988 to about 2005 when the mine went underground.

We have systems in Australia, Brazil, USA... Often modern systems use a combination of flywheels, special types of shockwave controls, and holdback load-sharing devices.

We have studied systems that do not load share and cause holdback failures. ■