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Magnetic Particle Clutches – Proportional Tension Control
Magnetic particle clutches transmit torque between two rotating shafts using magnetically susceptible powder particles suspended between the input and output members. When DC current is applied to the coil, the particles form chains that couple the input and output members and transmit torque. Torque output is nearly linear to applied current and is independent of the slip speed between the two shafts. When current is removed, the particles disperse and the members rotate freely relative to each other.
The defining characteristic is controlled, adjustable torque during continuous slip. Both shafts rotate at all times — the clutch does not stop either shaft. It controls the torque transmitted between them while they run at different speeds. This makes magnetic particle clutches suited for tension control applications — unwind and rewind reel control, web handling, wire drawing, and torque limiting — where consistent slip torque is the requirement, not engagement or stopping.
Torque is set by controlling the coil current. A simple dancer arm system or variable DC supply is sufficient for open-loop tension control. Because torque is independent of slip speed, the output tension remains consistent regardless of reel diameter change or speed variation in the driven system.
All OPC-N and PC series units are fully sealed. Magnetic particles cannot escape to contaminate machine components or product, and external contaminants cannot enter the clutch. Hollow bore and steel shaft configurations are available.
Electromate carries two Ogura magnetic particle clutch series. The OPC-N is a compact unit for light torque applications. The PC series is the heavy-duty variant with forced air cooling for continuous high-cycle operation at higher torque levels.
Series Comparison Chart
Series
Torque Range
Max RPM
Bore Range
Voltage
Cooling
Duty
OPC-N
0.367–6 ft-lbs
1,800
5–15 mm
24 VDC
Passive (sealed)
Light continuous slip; small machinery and control systems
PC
Contact Electromate
Contact Electromate
Contact Electromate
24 VDC
Forced air (inlet/outlet ports)
Heavy continuous slip; high-cycle industrial tension control
Magnetic Particle Clutches – Frequently Asked Questions
How does a magnetic particle clutch work?
A magnetic particle clutch suspends magnetically susceptible powder particles between a rotating input member and a rotating output member. When DC current is applied, the particles form chains that couple the two members and transmit torque between them. Torque is nearly linear to applied current and independent of the slip speed between the shafts. When current is removed, the particles disperse and the members rotate freely relative to each other.
What is the difference between a magnetic particle clutch and a friction clutch?
A friction clutch is designed to engage two shafts and stop slip between them — it transmits full torque when engaged and zero torque when disengaged. A magnetic particle clutch is designed to transmit a controlled, adjustable torque while both shafts continue to rotate at different speeds. It is a continuous-slip device, not an engagement device. Using a friction clutch for continuous slip duty causes rapid wear and inconsistent torque. Magnetic particle clutches are rated specifically for continuous slip operation.
What is a magnetic particle clutch used for?
Magnetic particle clutches are used in web tension control for film, foil, paper, and textile processing; unwind and rewind reel control; wire and filament drawing; torque limiting on driven shafts; and motor test stands. The nearly linear current-to-torque relationship and speed-independent torque output make them suited for open-loop tension systems using a dancer arm or simple variable DC supply.
What is the difference between the Ogura OPC-N and PC series?
The OPC-N is a compact magnetic particle clutch for light torque applications (0.367 to 6 ft-lbs) in small machinery and control systems, with passive sealed cooling. The PC series is the heavy-duty variant with forced air cooling via inlet and outlet ports, designed for higher torque levels and continuous high-cycle industrial tension control where heat dissipation requirements exceed what passive cooling can handle.
Can magnetic particle clutch torque be controlled in real time?
Yes. Torque output is proportional to coil current. Varying the current varies the transmitted torque in real time, independent of shaft speed. A constant current supply gives fixed torque. A variable DC supply or dancer arm feedback system gives dynamic tension control. Ogura also offers dedicated power controllers compatible with the OPC-N and PC series for closed-loop tension control applications.
Are magnetic particle clutches sealed?
Yes. Both the OPC-N and PC series are fully sealed units. Magnetic particles are contained within the clutch and cannot escape to contaminate machine components or product. External contaminants and lubricants cannot enter the clutch. This makes them suitable for printing equipment, food processing adjacent machinery, medical devices, and other applications where particulate contamination is not acceptable.
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