The CST drive incorporates an infinitely variable multi-disc clutch system that is located on the output shaft side of the gearbox, allowing the motor to be started under no-load conditions. The clutch system comprises a set of rotating friction plates and opposing stationary plates, an oil pressure activated piston for engagement, and a spring mechanism for clutch release. Oil is circulated between the plates by a closed-circuit pump and cooled through a heat exchanger.  When hydraulic oil pressure is applied to the piston, the clutch plates engage, causing the output shaft to rotate and gradually accelerate to driving speed in a predetermined controlled time.

The CST delivers a range of benefits not available from electronic soft-start motor control alone.

CST delivers excellent motor load sharing within ± 2% to minimize the loads and stresses on all conveyor components. Maximum motor power is available throughout the controlled speed profile, and the clutch unit absorbs shock loads, protects the motor, gearbox, bearings, chains, sprockets, flight bars, line pan and drive ends. The CST control system delivers an S-curve acceleration ramp which further enhances safety, reliability and component protection. An additional advantage is a reduction in peak motor torque demand.

The CST control system executes synchronized soft start and load sharing control of up to four CST drives, and can be interfaced with mine remote supervisory systems, interlocks, and safety equipment via hard-wiring or over a data-network. The CST controller can be located up to 100m away from the drive.

While the unique clutch design of the CST gearbox delivers the smooth speed and load control during start-up and shut-down, the precision engineered planetary gear train converts the highspeed, low-torque input from the AC motor to a low-speed, high-torque output efficiently and safely.

As soon as the motor is up to speed, full torque is available to the clutch. Additional torque is then applied to overcome the inertia requirements of the loaded conveyor system, as well as the torque needed to accelerate the system to the final running speed. This minimizes system transient forces and delivers all the power and torque required to drive the load, irrespective of loading conditions.

Many CST drives installed in the last 35 years are still in full operation around the world. This is testament to the performance, strength, simplicity, reliability and serviceability of the material, components, and the design. CST clutch life has been proven over-and-over-again to be more than 7 to 10 years and gear life to be over 25 years when operated within specifications. Longwall mining customers like the simplicity of the design resulting in high reliability and the ease of serviceability. HBT CST drives have a proven track record of average availability >98% and a very low total life cost.