Single-Actuator Hydraulic Grips

Hydraulic grips are primarily used when test loads of 50 kN and over, with associated high gripping forces, are required (Fmax from 10 kN to 2500 kN possible).

  • The clamping pressure can be adjusted and reproduced with a high degree of accuracy.
  • Defined force application ensures optimum gripping of sensitive materials.
  • ZwickRoell's "Force Constant Hold" force stabilization system reliably protects the specimen from unwanted tensile or compression forces due to material flow or grip deformation during the closing and clamping process.
  • The ratio between gripping and tensile forces can be adjusted individually, ensuring that the specimen is held securely (at maximum tensile force approximately double gripping force is required).
Hydraulic grips

Key Advantages and Features

All of the components work together perfectly so you can rely on accurate, reproducible, repeatable and traceable testing results every time.  

Advantages and features

  • Hydraulic grips have an eccentric piston shape with a long piston stroke, achieving a deep clamping surface position and a large opening width.
  • The alignment of the jaws, specimen grips, and piston facilitates gripping of short specimens as well.
  • Defined force application ensures optimum gripping of sensitive materials.
  • Contact pressure can be reproduced exactly
  • Specimen grips can be installed in testing systems at three different angle settings (0°, 45°, and 90°).
  • T-slots in the lower part of the basic body serve as a mounting for the T-slot system, enabling the accommodation of smaller load cells, specimen grips, test tools, and fixtures (except hydraulic grips, type 8392, Fmax 10 kN).
  • Prismatic jaws (jaws with V-slots) can be rotated and have two-fold use: For round and flat specimens or for round specimens with various diameters (jaws with crosswise arranged V-slots)
  • The upper and lower grips can be opened and closed either individually or together via remote control or PC.
  • The ratio between gripping and tensile forces can be adjusted individually, ensuring that the specimen is held securely (at maximum tensile force approximately double gripping force is required).
  • Hydraulic grips are designed to offer optimal specimen feeding.
  • An adjustable, scaled stop ensures precise vertical specimen gripping for manual special feeding.
  • For easier specimen centering, a centering stop can be used.
  • For safety reasons, specimen tongs can be used to insert the specimen.

Operating principle 

The oil pressure is set at the hydraulic power pack according to the required closing pressure for the specimen grips. The control unit controls the closing and opening procedure separately for the top and bottom specimen grips.

Furthermore, the closing procedure is divided into a closing phase and gripping phase when a a universal hydraulic power pack is used. In the closing phase, the specimen is initially held on the upper end for safety reasons. During gripping, the full gripping force is applied. The force value is based on the expected tensile force.

Double-sided actuators

All hydraulic grips are equipped with double-sided actuators. This means the specimen grip opens hydraulically and not by means of spring return mechanism. The closing and opening pressure can be adjusted.

In contrast to single-acting actuators that open by means of a spring return mechanism, double-sided actuators ensure that the specimen grips always open safely . This also applies if the specimen is crooked or jammed. Additionally, the full opening stroke is not necessary because the opening procedure can be interrupted at any point using the Stop button. The opening stroke can be adjusted according to thickness. Especially with thin specimens, the test time is reduced and the risk of pinching parts of the body is minimized.

Single and double-sided closing specimen grips

Single-actuator hydraulic grips can be used for the symmetrical and asymmetrical gripping of specimens (for example, for shear tests). The thickness of the specimen is set by means of screw unit.

The single-actuator hydraulic grips are also available with a tandem cylinder to enable uniform force application to the specimen (especially suitable for tests on fabrics, textiles and geotextiles).

Double-actuator hydraulic grips always close symmetrically with respect to the tensile axis. This means the specimen is gripped in a precise axial position, thereby eliminating the need for thickness adjustment.

T-slotted system

The T-slotted system makes it possible to accommodate small load cells, specimen grips, test tools, and fixtures quickly, without having to dismantle the specimen grips.

T-slots are integrated in the gripping area of the specimen grip. These serve as mounts for the T-slotted mounting. The T-slotted mounting is clamped there. Other fixtures can now be mounted, saving time needed to mount other tools and fixtures.

Hydraulic grips

Hydraulic specimen single actuator specimen grips

Fmax 50 kN, 100 kN, 250 kN

Advantages and features

  • Defined force application ensures optimum gripping of sensitive materials.
  • Unwanted forces acting on the specimen are compensated for during the gripping process by Zwick’s "Force Constant Hold" feature when the grips are used in conjunction with ZwickRoell hydraulic power-packs, the testControl electronics, and testXpert III testing software.
  • Small load cells, specimen grips, test tools and fixtures can be quickly accommodated via the optional mounting unit and without having to dismantle the specimen grips.
  • Prismatic jaws (jaws with V-slots) can be rotated and have two-fold use: For round and flat specimens or for round specimens with various diameters (jaws with crosswise arranged V-slots)
  • Excentric offset between piston and piston rod allows specimen grips with short clamping lengths to be tested as well.
  • The upper and lower grips can be opened and closed either individually or together via remote control or PC.
  • For safety reasons, specimen tongs can be used to insert the specimen.

Function description

Hydraulic grips are single-sided closing and can be used for symmetrical and asymmetrical gripping.

The opposing jaw can be steplessly adjusted.

Two horizontal T-slot pairs are found in the specimen grip. The larger slot is for insertion of the T-slotted system to accommodate smaller load cells and specimen grips. The smaller slot is for inserting/guiding additional accessories.

You can insert the specimen vertically and in the center using the specimen gripper. The slot of the specimen grips is used as a guide. Using a specimen gripper helps minimize the risk of injury when inserting and removing specimens from the specimen grips. Such risks are the pinching of body parts between the jaws or the burning of body parts on hot specimens.

Technical data, Fmax 50 kN

Item No.

317176[1]

Type

8801

Test load Fmax

50

kN

Adjustability of the opposing jaw

Stepless

Operating principle/identification

Single-sided closing

Operating pressure

12 ... 300

bar

Gripping force at max. pressure

100

kN

Dimensions

Height

205

mm

Width

365

mm

Width with screw unit, open completely

395

mm

Depth

132

mm

Gripping travel

35

mm

Opening width, max. with jaws

See table of jaws (specimen thickness)

Gripping of the specimen

The specimen must be gripped with at least 2/3 of the jaw height

Connection, stud

Ø 36/60[2]

mm

Ambient temperature

+10 ... +35

°C

Weight per specimen grip, approx.

37

kg

Scope of delivery

2

pieces

  1. Recommended and approved for strain rate control to the standards DIN EN ISO 6892-1:2009 and ASTM E8-09
  1. These specimen grips can be offered with a 36 mm or 60 mm connection (selection made using parts list alternatives).

Technical data, Fmax 100 kN

Item No.

317178[1]

Type

8802

Operating principle/identification

Single-sided closing

Adjustability of the opposing jaw

Stepless

Test load Fmax

100

kN

Operating pressure

12 ... 300

bar

Gripping force at max. pressure

255

kN

Dimensions

Height

303

mm

Width

423

mm

Width with screw unit, open completely

461

mm

Depth

170

mm

Gripping travel

35

mm

Gripping of the specimen

The specimen must be gripped with at least 2/3 of the jaw height

Connection, stud

Ø 60

mm

Ambient temperature

+10 ... +35

°C

Weight per specimen grip, approx.

70

kg

Scope of delivery

2

pieces

  1. Recommended and approved for strain rate control to the standards DIN EN ISO 6892-1:2009 and ASTM E8-09

Technical data, Fmax 250 kN

Item No.

317180[1]

Type

8803

Adjustability of the opposing jaw

Stepless

Operating principle/identification

Single-sided closing

Test load Fmax

250

kN

Operating pressure

12 ... 480

bar

Gripping force at max. pressure

410

kN

Opening width, max. with jaws

59

mm

Dimensions

Height

303

mm

Width

423

mm

Width with screw unit, open completely

423 (461)

mm

Depth

170

mm

Gripping travel

70

mm

Gripping of the specimen

The specimen must be gripped with at least 2/3 of the jaw height

Connection, stud

Ø 60

mm

Ambient temperature

+10 ... +35

°C

Weight per specimen grip, approx.

70

kg

Scope of delivery

2

pieces

  1. Recommended and approved for strain rate control to the standards DIN EN ISO 6892-1:2009 and ASTM E8-09
Hydraulic grips

Hydraulic specimen grips for fleece and other compressible specimens

Fmax 10 kN (single-sided closing)

Advantages and features

  • The jaws can be be changed quickly and easily without tools if the application changes. The jaws are thus automatically centered.
  • A very wide opening allows for quick and easy insertion of highly compressible specimens.
  • Accurate test results along with a high cycle rate that is made possible by central insertion of the sample with the aid of an easily adjustable centering stop.
  • The constant gripping force allows for repeatable test results.
  • Short specimens can also be gripped due to the special design of the specimen grip.
  • Reliable testing results are guaranteed with the optimal interaction between the hydraulic power pack, the electronics, and the testing software. The force-zero control prevents unwanted forces on the specimen during the gripping process.

Function description

Hydraulic grips are single-sided closing and can be used for symmetrical and asymmetrical gripping.

The opposing jaw can be steplessly adjusted.

The closing and gripping pressure of the specimen grip can be set steplessly and reproducibly via a hydraulic power pack. The specimen is held securely and jaw breaks are prevented during the test.

Technical data, Fmax 10 kN

Item No.

320719[1] [2]

Type

8392

Operating principle/identification

For fleece and other compressible specimen

Test load Fmax

10

kN

Operating pressure

10 ... 150

bar

Gripping force at max. pressure

20

kN

Dimensions

Height

152

mm

Width

359

mm

Depth

76

mm

Opening width, max. with jaws, thickness 5 mm

78

mm

Gripping travel

50

mm

Gripping of the specimen

The specimen must be gripped with at least 1/2 of the jaw height

Connection, stud

Ø 20

mm

Ambient temperature

+10 ... +35

°C

Weight per specimen grip, approx.

12.1

kg

Scope of delivery

2

pieces

  1. Recommended and approved for strain rate control to the standards DIN EN ISO 6892-1:2009 and ASTM E8-09
  1. Includes connecting hoses

Applications

  • Specimen material:
    Geotextile, geogrids, geocomposites, fleece, felt, knitted fabrics, technical textiles
  • Specimen shape:
    Flat specimens
  • Type of loading:
    Tensile

Advantages and features

  • The jaws can be be changed quickly and easily without tools if the application changes.
  • The constant gripping force allows for repeatable test results.
  • Reliable testing results are guaranteed with the optimal interaction between the hydraulic power pack, the electronics, and the testing software. The force-zero control prevents unwanted forces on the specimen during the gripping process.
  • Sensitive textile specimens (for example, glass fabrics and coated fabrics) can also be securely and gently held. The special tandem cylinder allows for very high gripping forces.
  • The optimized workflow guarantees optimum operator safety during rapid and accurate positioning of technical textiles and geotextiles.

Function description

Using a specimen work panel, textile specimens can be gripped in a slat easily and without deformation. The slat with the specimen is guided into the specimen grip via a telescopic rail. This allows specimens to be inserted perpendicularly and centrically so the operator does not need to reach into the gripping area.

Technical data

Item No.

317677

317669

316734

Type

8393

8493

8593

Test load Fmax

50

100

250

kN

Operating pressure

50 ... 450

50 ... 350

50 ... 480

bar

Gripping force at max. pressure

300

600

1200

kN

Dimensions

Height

255

340

352

mm

Width

390

500

550

mm

Depth

260

315

345

mm

Opening width, max. with jaws

35

35

35

mm

Gripping of the specimen

The specimen must be gripped with at least 2/3 of the jaw height

Connection, stud

Ø 36

Ø 60

Ø 60

mm

Ambient temperature

+10 ... +35

+10 ... +35

+10 ... +35

°C

Weight per specimen grip, approx.

65

160

235

kg

Scope of delivery

2

2

2

pieces

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