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Magnetic particle brakes generate braking torque by suspending magnetically susceptible powder particles between the rotor and stator. When DC current is applied to the coil, the particles form chains that transmit torque from the rotating shaft to the stationary housing. Torque output is nearly linear to applied current — increasing current increases torque, decreasing current reduces it. When the coil is de-energized, the particles disperse and the brake releases.
The defining characteristic of magnetic particle brakes is proportional torque control during continuous slip. Unlike friction brakes, which are designed to stop rotation, magnetic particle brakes are designed to run in a slipping condition indefinitely while maintaining a consistent, controllable braking torque regardless of shaft speed. This makes them the correct choice for tension control applications — not stopping applications.
Units are fully sealed. No wear particles escape into the machine environment and no external contaminants enter the brake. This makes them suitable for clean-room adjacent applications, printing equipment, and medical devices where contamination is not acceptable.
Electromate carries the Ogura OPB-N series electromagnetic magnetic particle brake. Torque range is 0.5 to 25 Nm (4.4 to 221 in-lbs). Optional fan kits are available on larger units for additional heat dissipation in heavy continuous-slip applications. Available in 24 VDC. Hollow bore and steel shaft configurations available.
Magnetic Particle Brakes – Frequently Asked Questions
How does a magnetic particle brake work?
A magnetic particle brake suspends magnetically susceptible powder particles between the rotor and stator. When current is applied, the particles form chains that couple the rotating shaft to the stationary housing and generate braking torque. Torque is nearly linear to applied current and is independent of shaft speed. When current is removed, the particles disperse and the brake releases.
What is a magnetic particle brake used for?
Magnetic particle brakes are used where precise, adjustable braking torque is required during continuous slip — not for stopping. Primary applications include web tension control on film, foil, and paper; wire drawing and winding; unwind and rewind reel control; and motor test stands. The nearly linear current-to-torque relationship makes them well suited for open-loop tension control using a simple variable DC supply or dancer arm feedback system.
What is the difference between a magnetic particle brake and a friction brake?
A friction brake is designed to stop rotation by clamping friction surfaces together. A magnetic particle brake is designed to run in a continuous slip condition while maintaining a set braking torque. Using a friction brake for continuous slip will cause rapid wear and heat buildup. Magnetic particle brakes are rated specifically for continuous slip operation and maintain consistent torque independent of slip speed.
Can magnetic particle brake torque be controlled?
Yes. Torque output is proportional to the current applied to the coil. A constant current power supply gives precise torque control. A variable DC supply gives general tension control. Ogura also offers dedicated power controllers for the OPB-N series. Response rates can be further increased using overexcitation circuits for applications requiring fast torque buildup.
What is the torque range of the Ogura OPB-N series?
The Ogura OPB-N series covers a torque range of 0.5 to 25 Nm (4.4 to 221 in-lbs) at 24 VDC. Max RPM is 1,800. Larger frame sizes are available with optional fan kits for increased heat dissipation in heavy continuous-slip applications.
Are magnetic particle brakes sealed?
Yes. Ogura OPB-N units are fully sealed. Magnetic particles are contained within the unit and cannot contaminate the machine or product. External contaminants also cannot enter the brake. This makes them suitable for printing equipment, medical devices, and other applications where particulate contamination is not acceptable.
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