The Positorq brake can be used for three major types of applications:

1. To supply constant tension for unwind applications in industries such as paper, foil, steel, coating, plating, etc.
2. As an energy absorber (Dynamometer) to create a known controlled load on a system, usually for testing purposes.
3. Winch brakes to apply tension on the line is during unwind such as Drawworks auxiliary brakes, dynamic stopping and static holding.

How to Select a Positorq Tension Brake

The selection of a Positorq for a tension control application will vary depending on the type of tension application. The most common types of applications are:

1. Constant Unwind -The parent roll is continuously unwound as for plating, coating, laminating, etc.
2. Unwinding in Sets – The parent roll is wound onto several smaller rolls. In this application the parent roll will need to be stopped several times during the operation to change the smaller rolls.

For a Constant Unwind application the two Torque Requirements to be considered are:

1. The Torque to maintain constant tension.
2. The Torque to stop the inertia of the roll for a panic stop.

When Unwinding in Sets, there are three Torque Requirements to be considered.

1. The Torque to maintain constant tension.
2. The Torque to stop the roll Inertia only, (E-Stop).
3. The Total Torque to stop the roll Inertia and overcome tension at the first set stop.

The Total Torque Required when stopping at the first set stop is: (1)the total of the torque to maintain tension plus (2) the torque to stop the roll.

The larger of (1) The Total Torque required at set stop or (2) The Torque required for a Panic

Stop, should be used for selection purposes.

Note:

The same basic tension brake parameters are used for the winch brakes. There are some differences such as the drum diameter remains constant.

Determining Torque Capacity…

The following formulas are used to find the required torque capacity. Calculating the torque of a full roll and that at set stop is the same except for the difference in WK 2. and RPM.

(1) Tension Torque – Torque to maintain constant tension. Tt = Torque (Lb. Ft.) to maintain tension
D = Dia. Of Roll (Inches)
W = Width of Roll (Inches)
PLI = Tension (Lbs./Linear Inch)
PSI = Tension (Lb./Square Inch)
t = Thickness

(2) Stopping Torque – Torque required to stop roll. Ts = Torque (Lb. Ft.) for panic or set stop
WK2 = Inertia of roll when stopping (Lb. Ft.2)
RPM = Speed of roll when stopping
308 = Constant
t = Time to decelerate

(3) Total Torque – Total Torque required for set stop. TT = Torque (Lb. Ft.) at set stop
Tt = Constant tension torque at set stop
Ts = Stopping torque at set stop

(1) Thermal Horsepower to maintain tension – Torque to maintain constant tension. THPt = Thermal Horsepower (tension)
W = Width (Inches)
PLI = Tension (Lbs./Linear Inch)
FPM = Feet per Minute
33,000 = Constant

Thermal Horsepower relates to the amount of energy that must be absorbed, and is used to size the cooling system. Usually the thermal horsepower absorbed to maintain tension is satisfactory for calculating Cooling System Capacity, however in some cases where a very small PLI is required the thermal energy to stop the roll may be the limiting factor. The following formula can be used to determine the Thermal Horsepower.

Selection:
The correct Positorq unit is then selected based on the highest torque requirement and thermal horsepower rating.

The Cooling Unit is selected based on Thermal Horsepower.

How to Select a Positorq Absorber Brake

The Ideal Brake for High Torque – Low Speed Applications

In a Dynamometer Application normally a Positorq Brake is used to resist rotation of a shaft at some torque load. It can be used to absorb energy continuously as in product life testing, or for a short time for maximum load carrying capability. It can also be used to lock-up the shaft for destructive testing.

The Positorq Brake size is based primarily on torque and thermal horsepower. Sizing of the Positorq Brake should be done by application engineers at Force Control, however the following information will be required for sizing and determining cooling systems.

1. The first step is to determine the maximum continuous slip torque required at any speed. This is the torque at which the Positorq Brake is required to slip, absorbing energy continuously.
2. The next step is to determine the lock-up or holding torque required. This could be used for destructive testing or maximum load carrying ability.
3. Next determine the maximum heat load (Thermal Horsepower) to be dissipated. This can usually be determined by the maximum horsepower of the input driver. It can also be calculated by using torque and speed.
4. Determine the maximum speed in RPM required at the Positorq Brake.
5. Determine the minimum torque required at the maximum speed. Due to residual drag in the Positorq Brake, zero torque is not available depending on speed and Positorq size. Minimum torque is affected by brake size, number of discs, RPM, fluid flow and temperature.

Maximum Torque – Maximum torque at any speed. HP = Maximum continuous horsepower through each brake
Torque = Maximum Continuous Torque (Lb. Ft.) at each brake
RPM = Speed at brake
THP = Thermal Horsepower to be dissipated through each brake

Note:
There are many unique and specific requirements for load brakes such as response, cycle rates, minimum torque, mounting of the brakes, location of the cooling reservoir, and actuation type to name a few. A full review with one of our applications engineers should be completed before making decisions.