2015 Designer's Notebook - 2

Engineering Application and Web Tension Information

Torque:

Example:

A force that produces or tends to produce rotation. It is
measured by multiplying the amount of force applied by its
perpendicular distance from the axis of rotation (lever arm).

A cable is wound around a drum of 30.5 cm
(12 inch) radius (R) and is supporting
a weight (F) of 22.7 kg (50 lbs).
What torque is being applied to the drum?

Torque (TQ) = Force (F) x Radius (R)
Solution:

TQ = F x R

TQ = F x R = 22.7 kg x .305 m = 6.9 kg-m
Typical units of measure for torque are pound-inch,
pound-feet, newton-meters, and kilogram-meters.

Power:

or
TQ = F x R = 50 lb x 12 inches = 600 lb-in

HP = Force (lb) x Velocity (fpm)

The rate at which work is done or energy is transmitted.
Typical units of measure for power are watts or horsepower.
One horsepower is equivalent to the amount of work required
to lift 33,000 lbs one foot in one minute.

33,000

or
1HP = 745.7 Watts

Relating Power to Torque:
Torque and speed of rotation are directly related to force and
velocity in the following equations by radius. Therefore, the
horsepower formula can be expressed as follows:
TQ = F x R
F = TRQ

FxV
HP = 33,000

HP = Torque (lb-ft) x RPM

RPM = V

2πR

5252

x 5252
TQ = HP RPM

V = RPM x 2πR

Slip Heat:
The heat generated when more horsepower is put into a clutch
or brake than is taken out. Expressed in slip watts (SW).

that substituted slip RPM for RPM and converts 1HP to 746
watts.

If horsepower is being transmitted through the unit on a
one-to-one basis (or lock-up condition), ignore slip heat
calculations.

Slip heat must be calculated for each application. The curves in
the catalog showing heat dissipation capacity of the individual
brake or clutch are based upon continuous duty, and no "derating" or "service" factors need be applied. The unit can be
applied up to or on the curve for all normal applications. If
applied over the curve, life of the unit will be greatly reduced.

Magnetic particle units, however, are generally used in a
slipping or controlled torque condition, and slip heat becomes
a factor in selecting a unit. To determine the slip heat or the
"slip watts" the unit must dissipate, use the following formula:
Slip Heat = Torque (RPM7in - RPM out)
This formula may look unusual, but is the familiar horsepower
formula from above,
HP = Torque (lb-ft) x RPM
5252

2

Engineering Application and Web Tension Information

Heat dissipation of the unit is dependent on the cooling effect
of the outer rotating member. This outer member is labeled or
can be determined by rotating both shafts. The shaft that turns
the fins is the outer rotating member and should normally be
driven at the higher RPM.



Table of Contents for the Digital Edition of 2015 Designer's Notebook

Table of Contents
2015 Designer's Notebook - Cover1
2015 Designer's Notebook - Cover2
2015 Designer's Notebook - Table of Contents
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2015 Designer's Notebook - Cover3
2015 Designer's Notebook - Cover4
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