【正文】 s raw materials has brought with it a need for faster movement of these material from the point of extraction to the point of process or usage and transporting these materials through the process plant and disposing of the waste in the shortest possible time. Many methods of material handling are employed from wheel barrows to dump trucks or shuttle cars, to pneumatic ducts carrying pulverised particles in an air stream. In this line of movement, belt conveyors play a very important part in the reliable carrying of material over long distances at a petitive cost. Each method of material conveying has its advantages and disadvantages. One of the problems with belt conveyors is that soft friable material can be degraded, particularly in loading and unloading. If the maintenance of lump size is important, this can present difficulties on a plicated conveyor system. Conveyor systems have bee larger and more plex and drive systems have also been going through a process of evolution and will continue to do so. Bigger belts require more power and has brought the need for larger individual drives as well as multiple drives such as 4 drives of 1000 kW each on one belt. Shaft mounting of the plete drive unit is another change which has brought with it the requirement for more pact and lighter drive units. This tends to favor a right angle drive configuration with the motor next to the belt and hardened gears to reduce the dimensions and mass of the drive. 2. Drive Ratio and Belt speeds Depending on the quantity, size, distance and characteristics of the material to be conveyed, the absorbed power, width, tensile requirements and top cover thickness of the belt will be decided. Large volume conveyor belts run in the range of 2 to 6 metre/second and the allowable bend radius of the belt determines pulley diameters which for large belts is of the order of 0,8 to 1,5 m giving pulley speeds between 50 and 125 rpm. Assuming that 4 pole motors are used, this gives a reduction ratio required between 12:1 and 30:1. Most modern gear manufacturers do not use a higher ratio per stage than 5:1, which means that speed reducers will be either 2 or 3 stage reduction. (Except for small powers where worm reducers, or torque arms and V belt drives may be used). There is a misconception that one can reduce the cost of the gearspeed reducer by using a 6 or 8 pole motor, but even an 8 pole motor on the higher speeds would require a reduction above 6:1and a 2 stage unit would still be required. The bulk of the cost of a gearbox is related to the low speed shaft torque and therefore having determined this, there is generally no economic advantage at all in using anything but a 4 pole motor. The motor manufacturers, because of size and volume, generally supply 4 pole motors at the lowest price, and as a rule therefore, a 4 pole motor is the best choice with a gearbox of the appropriate ratio to arrive at the desired conveyor shaft speed. Where ball and roller bearings are used in the electric motors some manufacturers prefer 6 pole or even 8 pole speeds for motors over 1000 kW. . Choice of Single or Multiple Drive Having calculated the power required to drive the belt and having considered the belt tension and angle of contact, a decision can be taken on whether the belt should be fitted with single or multiple drive. This decision is often influenced by