LIFELIGN® COUPLINGS

How to Select
Formula Selection Method
The Standard Selection Method can be used for most coupling
selections. The procedure below should be used for:
High Peak Loads
Brake Applications (where the disc brake or brakewheel is to
be an integral part of the coupling, consult Falk for design
options.)
High Frequency Axial Sliding
Shear Pin Couplings
Providing system peak torque and frequency, duty cycle, and
brake torque rating will allow for a more refined selection using
the Formula Selection Method.
1. High Peak Loads: Use one of the following formulas for
applications using motors, with torque characteristics that are
higher than normal; applications with intermittent operations,
shock loading, inertia effects due to starting and stopping and
or system induced repetitive high peak torques. System Peak
Torque is the maximum torque that can exist in the system.
Select a coupling with a torque rating equal to or greater than
selection torque calculated below.
A. NON-REVERSING HIGH PEAK TORQUE
Selection Torque (lb-in) = System Peak Torque
or
The user provided shear torque value must be based on a system
analysis. It is recommended that the shear torque value be at least
225% of the normal transmitted torque value for non-reversing
applications to avoid breaking the shear pins due to fatigue during
motor start-up. For reversing applications, the recommended shear
torque setting is 300-400% of normal torque to avoid fatigue
failures. If the connected equipment cannot tolerate these torque
levels, expect to replace the shear pins more frequently.
FORMULA SELECTION EXAMPLE — High Peak Load:
Select a gear coupling to connect a gear drive low speed shaft to
a reversing runout mill table. The electric motor rating is 50 hp at
its base speed and the system peak torque at the coupling is
estimated to be 150,000 lb-in. The coupling speed is 77 rpm at
the motor base speed. Drive shaft diameter is 4.000" and keyway
is 1.000" x .500". Runout table roll diameter is 5.250" and
keyway is 1.250 x .625". Shaft separation is .500" maximum.
Motor and drive shaft extensions are both 7.00" long.
1. TYPE: From Page 7, to connect close coupled shafts (.50"
gap), the double engagement Type G20 coupling is the
selection.
2. REQUIRED MINIMUM COUPLING RATING:
Use the Reversing High Peak Torque formula in Step 1B.
1.5 x 150,000 = 225,000 Selection Torque
3. SIZE: From Table 1, Size 1040G20 coupling with torque rating
of 270,900 exceeds the selection torque of 225,000 lb-in.
4. CHECK: The maximum bore of 5.75", Table 13, Page 38,
allowable speed of 3600 and Dimension M of 5.70", on Page
19, meet the requirements.
System Peak HP x 63,000
Selection Torque (lb-in) =
rpm
B. REVERSING HIGH PEAK TORQUE
Selection Torque (lb-in) = 1.5 x System Peak Torque
or
1.5 x Peak HP x 63,000
Selection Torque (lb-in) =
rpm
C. OCCASIONAL PEAK TORQUES (Non-Reversing) — If a
system peak torque occurs less than 1000 times during the
expected coupling life, use the following formula:
Selection torque (lb-in) = .5 x System Peak Torque
or
.5 x Peak HP x 63,000
Selection Torque (lb-in) =
rpm
For reversing service, select per Step B, above.
2. BRAKE APPLICATIONS: If the torque rating of the brake
exceeds the motor torque, use the brake rating as follows:
Selection Torque (lb-in) = Brake Torque Rating x S.F.
3. HIGH FREQUENCY AXIAL SLIDING: For Type GL couplings;
if axial movement occurs more than 5 times per hour, add .25
to the service factor.
HP x 63, 000 x ( S. F. . 25)
Selection Torque
rpm
4. SHEAR PIN COUPLINGS: When selecting Type GR couplings,
make certain that the required shear torque is within the
minimum/maximum range for the coupling size selected. Refer
to Pages 35 and 50.
© The Falk Corporation, 1992, 2004. (451-110) 11