MTS Series 249 Swivels - Manual (Page 31)

Checking for Swivel Bearing Backlash—System
Series 249 Rod Swivel Product Manual Maintenance 31
Checking for Swivel Bearing Backlash—System Response Method
When a swivel bearing is too loose, the amount of force measured as the actuator
moves from compression to tension can exhibit a small signal discontinuity
during the load reversal. The following figure shows this relationship for a
system designed to measure small changes in load.
Presence of Backlash During Load Reversals
Note The signal discontinuity from backlash might only be one component of
the load signal distortion. Be aware of other possible load signal
distortion sources in the force train, such as a loose mounting bolt.
If the test results appear to be adversely affected by the presence of swivel
bearing backlash, a small adjustment can be made to the swivel to determine
whether or not it is the cause of the problem.
Adjusting Backlash
Proper adjustment of the backlash enables the swivel to tilt and rotate without
damaging the bearing or distorting test results. If backlash appears to be the cause
of unacceptable test results, a small adjustment can be made to the swivel. If the
adjustment does not improve the test results, other possible sources of distortion
should be checked.
There is a direct relationship between the amount of clamping force required to
remove backlash and the frictional torque necessary to rotate the swivel. If the
backlash adjustment is too tight, high frictional torque will cause the spherical
bearing to overheat and eventually fail. To avoid this condition, the backlash
adjustment must be made in small steps, checked, and then if necessary
readjusted.
The following subsections contain the procedures required to complete the
adjustment process. The following table shows the type of clamping bolt and
clamping torque required by each swivel. The torque values identified in this
table are used in the following procedures. These procedures require the use of a
spanner and a torque wrench fitted with the appropriate size socket or hex key.