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# Magnebrake® Engineering Calculations

See Below for Magnebrake® Engineering Calculations on the following applications:

Magnetic Particle Brake on a Non-Contact Unwind
Magnetic Particle Brake for Controlled Deceleration
Selection - Heat Dissipation (Slip Watts) vs. Speed Chart (RPM)

## Magnetic Particle Brake on a Non-Contact Unwind

Web Force (F)Web Speed (V)Core Diameter (d)Full Roll Diameter (D)
12 lbs. 200 fpm 3 in. 30 in.
##### 1. Calculate Torque (T)

T Start = 12 lbs. x 30in./24in = 15 lb. ft.
T Finish = 12 lbs. x 3in./24in. = 1.5 lb. ft.

##### 2. Calculation Speed (RPM)

RPM = Velocity/π(diameter)
RPM Start = 200 fpm / π x 30in./12in. = 25 rpm
RPM Finish = 200 fpm / π x 3in./12in. = 255 rpm

##### 3. Calculate Slipwatts (SW)

SW = T x RPM / 7.04
SW Start = 15 lb. ft. x 25 rpm / 7.04 = 53 Watts
SW Finish = 1.5 lb. ft. x 255 rpm / 7.04 = 54 Watts

##### 4. From Slipwatts vs RPM curves

The 25MB90S will dissipate 140 Watts at 255 rpm.

## Magnetic Particle Brake for Controlled Deceleration

1000 lb. ft.2 360 rpm 60 sec.
##### 1. Calculate Required Torque (T)

T = WK2 (rpm) / 308(t)
T = 1000 (360 rpm) / 308 x 60 = 19.5 lb. ft.

##### 2. Calculate Maximum Slipwatts (SW Max)

SW Max = T x RPM / 7.04
SW Max = 19.5 lb. ft. x 360 rpm / 7.04
SW Max = 997 Watts

##### 3. Calculate Average Slipwatts (SW Avg)

SW Avg = √[(t on / t on + t off) x 1/3 x SW Max2)]
SW Avg = √ [(1 min. / 2 min.) x 1/3 x 9972)]

SW Avg = 407 Watts
##### 4. From Slipwatts vs RPM curves

The 50MB90B20 will dissipate 450 Watts at 360 rpm.