Torque Wrench

Torque wrenches are critical measurement instruments in assembly processes where fastener tension must be controlled for structural integrity, safety, or performance. Common types include click-type (which produce an audible and tactile click at the set torque), beam-type (which use a deflecting beam and pointer), digital (which use a strain gauge and electronic display), and dial-indicating (which show torque on an analog dial). Each type has different accuracy characteristics and appropriate applications.

Calibration of torque wrenches is performed by applying known loads and comparing the wrench's indication or click point to the reference value. This is done using a torque calibration system consisting of a calibrated torque transducer (load cell), a loading arm of known length, and a data acquisition system. Calibration points are typically taken at 20%, 60%, and 100% of the wrench's full-scale range, in both clockwise and counterclockwise directions where applicable. The standard accuracy specification for most click-type torque wrenches is ±4% of indicated value (per ISO 6789).

For calibration management, torque wrenches require special attention because they are subject to significant wear and abuse in production environments. ISO 6789 provides requirements for the design, calibration, and marking of torque wrenches. Calibration intervals are typically 6 to 12 months, but may need to be shorter for high-use applications. Torque wrenches should be stored at their lowest setting (for click-type) to preserve the spring mechanism, kept clean and lubricated, and never used as a breaker bar. Many quality systems require torque verification at the start of each shift for critical assembly operations.