User Manual

DescriptionItemDescriptionItem
Cylinder13Wedges3
Grip Piston14Specimen Guide (flat specimens
only)
4
Preload Chamber15Wedge Chamber5
End Cap16Hydraulic Release6
Piston Extension17Hydraulic Pressure7
Hydraulic Release18Preload Chamber8
Hydraulic Pressure19End Cap9
Grip Piston10
About Gripping Specimens
The grips provide a constant, hydraulically actuated gripping force regardless of the applied test loads. 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. When actuated, the preload chamber locks
all moving grip parts in position, thus eliminating backlash when cycling between tension and compression.
The specimen can then be cycled from full tension through zero to full compression with no backlash.
Once a specimen is positioned between the grip wedges, hydraulic pressure is applied to the preload chamber.
This pressure pulls the wedge chamber toward the piston, forcing the wedges to clamp the specimen. The
pressure applied to the preload chamber can be adjusted to a level which clamps the specimen securely, but
does not damage the specimen by applying excessive gripping force.
About Wedges
Each grip model has its own selection of wedges. Not all wedge options are available for all grip models.
Three types of wedges are available for use with the grips: flat wedges, round wedges, and vee-notched
wedges.
• Flat wedges grip flat specimens. Both narrow and wide wedges are available.
• Round wedges can only grip a round specimen of a specific diameter.
• Vee-notched wedges can grip a range of round specimens.
Flat wedge surfaces can be finished with diamond serrations, with a Surfalloy coating, or a smooth finish.
• Diamond serrated surfaces can grip materials such as soft steels and plastics.
• Surfalloy surfaces can grip hard or brittle materials. Surfalloy incorporates a grit onto the wedge surface.
20 Series 647 Hydraulic Wedge Grips Reference Manual
Introduction