MTS Model 680-01 High-Temperature Grips - Manual (Page 27)

Model 680.01 High-Temperature Grips 27
Preload the Spiral Washers
The components in the force train must be preloaded to prevent backlash during
operation. Preloading is done while a high tensile load is applied to a dummy
specimen mounted in the grips. While this load is applied, the spiral washers are
adjusted to remove any slack in the force train. When the applied load is
removed, the force train remain preloaded.
The load to be applied while preloading the studs should be at least 10% greater
than the maximum load that the force train will experience during actual testing.
Or, to preload the studs for grip operation at full rated load, the studs should be
preloaded to about 110% of the grips fatigue rating.
The procedure requires that the spiral washers be installed on each connector stud
in the force train. The spiral washers should be set to minimum thickness You
will also need two spanner wrenches.
1. Select force control.
2. Turn on the system hydraulic pressure.
3. Select a dummy specimen that will withstand a tensile force 10%– 20%
greater than the maximum force to be applied during the test.
4. Install a dummy specimen in the grips according to the appropriate
procedure.
The next step may apply a force greater than the force train capacity.
Exceeding the tensile load capacity of any element in the force train can
cause personal injury or equipment damage.
It is necessary to temporarily exceed the tensile load capacity to achieve the
requirements of Step 5 in this procedure. This is accomplished by increasing the
output pressure of the HPU.
5. Apply a static tensile force 10%– 20% higher than the maximum force to be
applied during testing.
If the spiral washers are not sufficiently tightened, the connector stud can
break when subjected to cyclic loads.
Improper preloading of the connector stud can cause eventual fatigue
resulting in connector stud breakage.
Sufficiently tighten the spiral washers as described in Step 6.
WARNING
CAUTION