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Hydraulic Grips

Hydraulic grips are primarily used where test loads of 50 kN and above are required in combination with high closing forces.

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 actuator/double actuator

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.

Single actuator/double actuator

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