MTS Series 646 Hydraulic Collet Grips - Manual (Page 45)

Series 646 Hydraulic Collet Grips Installation 45
Grip Alignment
This section describes how to align the rotation of the grips. The following
information applies only to the axial grips because you can adjust the actuator
rotation with the axial-torsional grips. The grips can be rotated several ways:
with spiral washers, shim washers, and it might be possible to rotate the actuator
rod to achieve the desired orientation.
Spiral washers can offer up to 30° of rotation. They are also used to preload the
connector studs to prevent backlash. Spiral washers are installed between each
grip and the mating member of the force train. They are used to preload the
connector stud. When placing the spiral washers on the connector stud, rotate the
washers until they are fully closed; this is the minimum thickness for the spiral
washers.
Shim washers are used to adjust the rotation of the upper and lower grips on the
mounting studs so they are aligned with each other. Each shim kit includes
washers of different thicknesses and are for a specific stud size. A combination of
the shims can change the rotation of the grip with reference to the point at which
the grip is tightened into position. Contact MTS Systems Corporation for
information about the appropriate shim kit for your application.
Shim washers are not necessary on the actuator side of the force train if the
actuator can be rotated.
How to Preload the Spiral Washers
The connector studs must be preloaded to prevent backlash. Preloading the
connector studs requires that a full tensile load be applied to a specimen mounted
in the grips. Therefore, it is assumed that the system hydraulics and the hydraulic
grip supply are operational.
Required equipment
The procedure requires that the spiral washers be installed on each connector stud
in the force train. You will also need two spanner wrenches.
Note Sometimes you might have multiple fixtures in the force train that have
different force ratings. When installing the fixtures pretensioned with
spiral washers, install the fixtures with the highest force rating first. Then
install any other fixtures from the highest to the lowest force rating.
Procedure
1. Select force control at the system controller.
2. Turn on the system hydraulic pressure.
3. Select a dummy specimen that will withstand a tensile force 10 to 20%
greater than the maximum force to be applied during the test.
4. Adjust the output pressure of the hydraulic grip supply to the correct level.
5. Install the dummy specimen in the grips.