Basic Information Selection Guide M451-110, August 2002 - Rexnord

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 (Nm) = System Peak Torque
or
System Peak kW x 9549
Selection Torque (Nm) =
rpm
B. REVERSING HIGH PEAK TORQUE
Selection Torque (Nm) = 1.5 x System Peak Torque
or
1.5 x Peak kW x 9549
Selection Torque (Nm) =
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 (Nm) = .5 x System Peak Torque
or
.5 x Peak kW x 9549
Selection Torque (Nm) =
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 (Nm) = 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.
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 37 kW
at its base speed and the system peak torque at the coupling is
estimated to be 17 000 Nm The coupling speed is 77 rpm at the
motor base speed. Drive shaft diameter is 100 mm and keyway
is 28 mm x 16 mm. Runout table roll diameter is 135 mm and
keyway is 36 mm x 20 mm. Shaft separation is 12 mm
maximum. Motor and drive shaft extensions are both 180 mm
long.
1. TYPE: From Page 7, to connect close coupled shafts (12 mm
gap), the double engagement Type G20 Steel Mill coupling
is the selection.
2. REQUIRED MINIMUM COUPLING RATING:
Use the Reversing High Peak Torque formula in Step 1B.
1.5 x 17 000= 25 500 Selection Torque
3. SIZE: From Table 1, Size 1040G20 coupling with torque rating
of 30 600 exceeds the selection torque of 25 500 Nm
4. CHECK: The maximum bore of 160 mm with square key,
allowable speed of 3600 rpm and Dimension M of 145 mm,
on Page 17, meet the requirements.
kW x 9549 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 Page 33.
The Falk Corporation, 1998, 2002. (M451-110) 11