Testing of industrial textile fibres: capstan design overcomes problem of premature failure

  • Pneumatic cord and yarn grips in capstan design evenly distribute gripping force
  • Application: industrial textile fibres, including Aramid and UHMwPE
  • New feature: interchangeable clamping blocks

Aramid and UHMwPE are synthetically prepared fibres that are stronger per weight than steel. However when tested with a traditional side acting grip, they are likely to exhibit internal slippage in the jaw, where one or more fibre is slipping past the others. The fibres are also likely to fail where stress is concentrated at the jaw faces. This kind of challenge is much harder to detect and can lead to low maximum strengths and/or inaccurate results. The company Instron, a leading provider of testing equipment to evaluate the mechanical properties of materials, offers an easy solution designed specifically to overcome the problem of premature failure for industrial textile fibres.

Capstan design evenly distributes the gripping force

The pneumatic cord and yarn grips of Instron incorporate a capstan design that evenly distributes the gripping force over the curved surface of an involute specially designed to maximize breaking load. The capstan provides support for the specimen, making the transition from the free-stressed length of specimen to the rigidly clamped portion gradually rather than abruptly, thus minimizing breakage of the specimen adjacent to the jaw face. The capstan also incorporates a smooth guide horn, which assists in rapid specimen loading and prevents damage to individual fibres during specimen insertion. This allows for greater failure loads to be recorded.

Additionally, the clamping mechanism can be activated automatically and through a footswitch to allow for two-handed specimen insertion and hands-free grip operation.

pneumatic cord and yarn grip

New feature: interchangeable clamping blocks

Instron Pneumatic Cord and Yarn Grips (2714-04x), which test up to 2 kN, are designed with interchangeable clamping blocks that accommodate fibres or yarns. This cost-effective new feature allows customers to utilize the same grip body as the common actuator and carrier for a range of application-specific clamping blocks. Whereas before the addition of the interchangeable clamping blocks, it was necessary for a lab to purchase a full set of grips, with grip bodies, grip faces, and single purpose capstans.

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