Qualifying The Right Tension Braking System

Pneumatic friction brakes and magnetic particle brakes are two types of braking systems commonly used in web converting and roll-to-roll manufacturing. While both brakes can be used to control the tension of a moving web, there are a number of differences that should be considered prior to specifying a system.

OPERATING PRINCIPLE
Pneumatic friction brakes use air pressure to apply friction to a rotating surface, whereas magnetic particle brakes use magnetic fields to control the amount of torque applied to a rotating shaft.

Dual Disc Pneumatic Friction Brakes

CONTROL METHOD
Pneumatic friction brakes are typically controlled by regulating the air pressure applied to the brake, while magnetic particle brakes are controlled by varying the strength of the magnetic field.

RESPONSE TIME
Magnetic particle brakes are generally faster to respond to changes in torque requirements than pneumatic friction brakes. This is because the magnetic field can be adjusted quickly, whereas air pressure changes take longer to propagate through the system.

HEAT DISSIPATION
For a given brake diameter, pneumatic friction brakes generally provide higher heat dissipation capacity than magnetic particle brakes. This is primarily due to the physical characteristics of each brake and its surface area available for cooling airflow. Some magnetic particle brakes incorporate active cooling capability by way of piped air channels, which can increase heat removal capacity beyond what a passively cooled magnetic particle brake is capable of. It should also be mentioned, magnetic brakes generate less heat during operation, which helps to negate some of the cooling advantages that pneumatic brakes enjoy on paper.TORQUE RANGE
While magnetic particle brakes enjoy an advantage in terms of response speed and fine torque adjustment, pneumatic friction brakes have the advantage of delivering a much wider torque range for a given brake diameter. The wide torque range comes with a caveat, however. Air cylinders or pistons must be turned off to optimize torque to air pressure ratio during operation in order to maintain high response. This can be accomplished by actuating cylinder shutoff valves progressively as the material roll reduces in diameter on the unwind.

RPMS & LINE SPEED
In general, pneumatic friction brakes can maintain significantly higher RPMs than magnetic particle brakes, enabling higher line speeds.

ENVIRONMENTAL IMPACT
During operation, pneumatic brakes emit brake dust as a byproduct of friction stresses. In contrast, magnetic particle brakes emit no contaminants during operation, so they remain the preferred solution for clean-room or hygiene-sensitive applications.

Magnetic Particle Brakes

MAINTENANCE
Pneumatic friction brakes require periodic maintenance to ensure that the brake pads are not worn beyond their material thickness and that air pressure can be maintained within a specified operating range. Magnetic particle brakes require less maintenance, but they may need to be periodically cleaned to prevent buildup of magnetic particles on the braking surfaces.

COST
Pneumatic friction brakes are generally less expensive than magnetic particle brakes, but the exact cost will depend on the specific application and the size and capacity of the brake required.

Overall, both pneumatic friction brakes and magnetic particle brakes have their advantages and disadvantages. Selecting the right braking system for your process should be based on the performance characteristics that fit best within your system requirements such as responsiveness, heat dissipation, torque, speed or environmental impact.