Magnetic powder brake is the actuator in unwinding machine for tension control, it is through control magnetic powder brake output braking torque so as to produce relevant unwinding tension force. But because of magnetic powder brake's exciting current----braking torque or exciting voltage----braking torque static relationship is a pure lag and two capacity lags characters, especially when the coil electromagnetic time constant is large, the dynamic response capacity of the system is greatly constrained.

Because of these disvantage for magnetic powder brake, so as usually many users asopt air brake to replace magnetic powder brake, following are the advantage of pneumatic brake:
1. Through adjust air pressure to make braking force smooth and stable;
2. Good heat dissipation effect, so this air brake can be used in high frequency, high load and other bad working condition durably, idle rotating is also available;
3. Regulation air pressure volume to adjust braking force, eco-environment and large braking torque range;
4. Thicker friction pads, anti-wear and prolong service life, frictioin pads can be replaced when keep air brake structure completely.