MTS Series 646 Hydraulic Collet Grips - Manual (Page 16)

Series 646 Hydraulic Collet Grips 16 Introduction
About Series 646 Hydraulic Collet Grips
The Series 646 Hydraulic Collet Grips are mounted in a load unit to secure the
specimen under test. Hydraulic pressure to the grips is supplied by an external
hydraulic grip supply.
Grip Cross Section
About Gripping Specimens
The grips provide a constant, hydraulically actuated gripping force regardless of
the applied test loads. When hydraulic pressure is applied, it pulls the grip
housing towards the piston, forcing the collet to clamp the specimen. The
pressure applied to the preload chamber locks all moving grip parts in position.
This eliminates backlash when cycling between tension and compression.
The specimen gripping force is adjustable to prevent specimen damage by the
grips or specimen slippage during the test. Each grip (upper and lower) is
independently actuated.
Collet Sets
The grips require collet inserts to accommodate the type of specimen. Various
specimen geometries may be easily accommodated by changing only the collet
sets. Three types of collets are available; round, flat, and threaded.
Spiral Washers
The optional Model 601 Spiral Washers are commonly used when installing axial
grips. They provide fatigue-resistant connections between elements of the force
train and minimize the effects of backlash.
The spiral washers are placed over the connector studs and adjusted to place a
constant preload on the stud. The spiral washers also minimize the possibility of
backlash due to loose-fitting or worn stud threads. When cyclic loads below the
tensile force level of the preload are applied to the connections, the load is
Preload Chamber Grip Piston
Grip Housing
Collet
Hydraulic
Release
Port
Hydraulic
Pressure
Port