Various Types Of Loads

Types of loads

Loads are classified into types;

Loads that provide active torques.

Loads that provide passive torques.

Active torques is due to either gravitational force or deformation in elastic bodies. The active torques due to gravitational pull is obtained in case of hoists, lifts or elevators and railway locomotives operating on gradients. Such torques is also developed during compression or release of springs.

When a load is moved upwards or a spring is compressed, the stored potential energy increases and the active torque developed opposes the action that takes place, i.e., the torque is directed against the upward movement or compression. On the other hand, when a load is brought downwards or a spring is released the stored potential energy decreases and torque associated with it aids the action.

Thus, it can be seen that the active torques continue to act in the same direction even after the direction of the drive has been reversed.

Passive torques is those due to friction or due to shear and deformation in inelastic bodies (lathes, fans, pumps etc.).

They always oppose motion, retarding the rotation of the driven machine. Moreover, with change in direction of motion, the sense of torque also changes.

For example, when a weight is being lifted up, the friction torque adds to the useful torque, but when lowered down it subtracts from the latter.

Loads can also be classified as;

(a) Continuous, constant loads: Centrifugal pumps or fans operating for a long time under the same conditions; paper-making machines etc.

(b) Continuous, variable loads: Metal cutting lathes; hoisting winches; conveyors etc.

(c) Pulsating loads: Reciprocating pumps and compressors; frame saws, textile looms and, generally, all machines having crank shaft.

(d )Impact loads: Apparent, regular and repetitive load peaks or pulses which occur in rolling mills, presses, shearing machines, forging hammers etc. Drives for such machines are characterized by heavy flywheels.

(e) Short time intermittent loads: Almost all forms of cranes and hoisting mechanisms; excavators; roll trains etc.

(f )Short time loads: Motor-generator sets for charging batteries; servomotors used for remote control of clamping rods of drilling machines.