External diameter of pulley, roller / belt conveyor -12

Belt conveyor moves conveyor belt forwards and conveys objects by rotating head pulley (roller) which winds the belt. The head pulley suggests a roller attached at the front edge of a belt conveyor, and it is rotated by a motor and moves belt forwards, therefore, it is also called a driving pulley.
In rubber belt conveyor, rubber is often wound around this head pulley to prevent belt from slipping. This is also the same for pulleys (rollers) of other parts than head pulley (roller).

1) Types of conveyor belt
When comparing rubber conveyor belt with resin belt, external diameter of pulley (roller) needs to be larger in rubber belt and it can be smaller in resin belt.

2)  Strength and tension of conveyor belt
Stress which pulls conveyor belt toward the moving direction is called strength or tension. As the tension gets larger, conveyor belt becomes hard to be bent and its thickness is increased. Therefore, external diameter needs to be made larger as strength and tension of conveyor belt increases.

Conveyor belt is bent the most when belt turns around pulleys (rollers) at head, tail or tensioned parts. As external diameter of these pulley (rollers) gets smaller, conveyor belt is bent more. When conveyor belt is largely bent near 180°, belt is folded and its load increased. So that connecting part of belt (endless part) is easily put out of joint or peeled off.
Also, in case that external diameter is smaller than one which is required for that conveyor belt, belt tends to stop moving forward because it slips and pulley (roller) spins. Belt does not move forward and object cannot be conveyed when belt slips. Bending degree of conveyor belt becomes smaller as external diameter of pulley (roller) gets larger, so that load on the belt becomes smaller and life time of the belt becomes longer. However, production cost of pulley (roller) will be expensive to make external diameter larger, therefore, the size needs to be well considered.

After installation, it is not recommended to replace belt readily when its belt is found to be not strong enough. Conveyor belt becomes thicker and hard to be bent as strength of belt increases. In case that pulley (roller) is used without replacing after increasing strength of conveyor belt, troubles such as endless part is peeled off, belt slips, etc. are likely to happen since external diameter is smaller than one required to move the belt. Also, load on belt will be increased and life time of belt will be shortened.

The following photo is about manufacturing head pulleys.