Shane,

The physics is the same above or below ground. The trick is to not allow either excessive belt sag or excessive high tensions, during starting and stopping, that depart from the respective steady-state forces. Also, dynamic instability (shock wave oscillation between drives) can occur as presented on our website.

THere are quite a number of successful and not so successful booster systems throughout the world both under and above ground.

With the advent of transient elastic dynamic analysis we are able to understand how it is achieved. I offer the sucessful 16km ZISCO (Zimbabwe, 1995-1996) overland which is accelerated by the tail drive, on an S curve, and boosted by the 3 head drives via a load cell. THe load cell has a PID loop linking both head and tail. The motor manufacturer made many attempt to regulate the drives and failed. CDI applied our algorithm via a PLC to the system and wa-la. THis can be seen on our website:



www.conveyor-dynamics.com

Booster drives offer advantage to lower belt strength, and allow reduced vertical and horizontal curves which may also reduce civil and structural costs. Booster drive use must be evaluated in its entirety considering all factors such as : complexity, total costs of system, maintenance, and what if scenarios.

Some booster drive systems have been abandoned do to their inherent stability flaws. Full PID feedback control is usually not acceptable. The belt has an elastic memory that should not be allowed to be fed by positive perturbations of the elastic response.

Coal boosters (figure 8 belt path) with in-line chute-transfer may not be useable for ore with clay like, wet, fine product that cannot be readily cleaneed from belt and pulleys.

THe description of all attributes is not managable in a brief dissertation in this forum.

CDI has worked on many such systems and can give aid if needed.

Lawrence Nordell

Conveyor-Dynamics, Inc. ■

Hi Shane

A year or so ago we extended a 2km curved overland conveyor to 4.5km. It is curved nearly all the way carries 3000t/h at 4.1m/sec on a 1050mm wide belt with a simple gravity take up at the head end.

Since it was only originally meant to take 2100 t/h, we had to put an intermediate tripper type drive half way round the curve.

The conveyor now has 3 x 260kW drives at the head and one 260kW drive in the middle, (all with TSS fluid couplings).

To make it work the intermediate drive is started last with a delay of about 4 seconds.

Since the original conveyor was 4 years old, the new drives were not identical to the old ones, as the new motor speeds were marginally faster 1490rpm vs 1475rpm.

This caused head aches trying to balance the absorbed powers untill we found spare motors of similar speed as adjusting the oil fills did not really give the desired result.

As to where to put the intermediate drive, it simply has to go where you will get the optimum tension distribution for the conveyor profile. When correctly positioned, it does wonders for the belt class requirement.

The transfer point at the tripper needs to be carefully designed though, due to the range of tensions there, and the tendancy for reducing sag when the power comes through to trap rocks.

If this is similar to your application I can always give you more info and experiences via

gspriggs@global.co.za

Good luck ■