The important factors in selecting a magnetic particle clutch or brake are:

• The maximum and minimum torque required - LB. FT. 

• The amount of heat generated - Slip Watts 

• Shaft speed - RPM

​

Torque 

The torque rating of a MAGNECLUTCH or MAGNEBRAKE is its maximum torque capability.  Continuous permissible values of torque depend on the speed and slip watts rating of the unit and can be much lower than maximum torque values.  For some applications, the torque required may be known.  For others, such as web handling, accelerating or stopping a load, or overload protection, torque must be calculated using the formulas below. 

 

​Torque = Force (lb.) x Radius (in.)

Torque = Tension per unit width (lb./in.) x Radius (in.) x Width (ft.)

Torque = WR²(RPM) / 308(t)

​WR² = Inertia in lb. ft.²

t = time in seconds 

308 is a constant 

Torque = hp(5250) / rpm

 

RPM & Heat Dissipation Considerations 

Slip heat occurs when more power is put into a clutch or brake than is taken out.  If power is transferred on a 1 to 1 basis ("locked condition"), slip heat is not generated.  When the speed of the input shaft is greater than the speed of the output shaft, the unit is said to be slipping.  Clutches have an output shaft, and so the difference in RPM (Input RPM - Output RPM) is the slip RPM.  Brakes have no output shaft, so the "slip RPM" of a brake is the RPM of the input shaft.  Magnetic particle clutches and brakes are generally used in continuous slipping, controlled torque situations, and slip heating is a controlling factor in selection of a unit. 

​​

We use the term "slip watts" for the heat energy which must be dissipated.  To calculate slip watts for your application, use the equations below.  In some situations, it may be necessary to convert lineal velocity to RPM before calculating slip watts.  Slip watts for your application should be referenced against the slip watts vs RPM curves in our product performance and outline documents when selecting a clutch or brake.  Performance and outline documents can be found on each product page.  The data given on the slip watts vs RPM curves represents the average, continuous dissipation capacity of units operating under slip conditions.  For base mounted clutches and brakes, the RPM on the slip watts vs RPM curves is the speed of the outer rotating member which is the input side and should generally be spun at the higher RPM.  For shaft mounted brakes, the RPM is the speed of the input shaft.  And for flange mounted clutches, the RPM is the speed of the outer rotating member, not the motor speed.   To ensure the life of the unit, the clutch or brake should not be applied over its respective slip watt vs RPM curve for any significant period of time.  ​

 

To calculate clutch slip watts: 

SW = Torque x (Input RPM - Output RPM) / 7.04

​

To calculate brake slip watts:   

SW = Torque x RPM / 7.04​

 

*Divide by 5252 to find hp; 1 hp = 746 watts

​​

To convert lineal velocity to RPM, use the equation below.

RPM = Web Speed (fpm) / π x Diameter (ft.) 

​