Torque Calibration Equipment

Torque calibration equipment is needed due to the accuracy of torque tools drifting over time, because of springs in the mechanism relaxing, components wearing out and tools getting damaged through overload or misuse.

If a torque tool applies a precise amount of torque, it prevents under-tightening, which can cause safety hazards because fasteners aren't tight enough and may become loose, and over-tightening, which can cause damage to the fastener and the material it is connected to.

How often torque calibration needs carrying out depends on several factors, such as -

• How critical the application is?
• How frequently the tool has been used?
• Are there any quality standards that need to be adhered?

There is no general hard and fast rule on when torque tools should be calibrated, but for critical applications, more frequent calibration is recommended to ensure accuracy. We would recommend calibrating a torque tool every 6-12 months or every 5,000 cycles (this number does differ between manufacturers), but that time frame may be smaller if it is used heavily, or if the tool is used in a particular sector, such as medical device manufacturing or aerospace. This is because there will likely be quality systems specified by ISO, ASME or UKAS to ensure that torque tools are calibrated frequently and these will probably be defined by internal procedures.

If your torque tool produces inconsistent results, such as inconsistent clicking, slipping or signalling, or if the tool feels noticeably easier or harder to operate, or it has been dropped or shows signs of wear, then it likely requires calibration. It will also need calibrating if it has reached or passed its calibration due date, which is often 6–12 months from the last calibration.

Some industries are regulated for traceability and accuracy, like the aerospace and medical device manufacturing industries, and will have calibration intervals already defined, regardless of whether the torque tool appears to be performing accurately.

It is important to maintain torque calibration equipment properly to preserve its accuracy and reliability, as well as ensure it continues meet compliance and quality standards. Some ways to ensure that torque calibration tooling is looked after is to -

• Keep it clean and protected - Always keep calibration equipment clean, dry and free from dust, oil and debris. Ensure that surfaces are wiped after use and store the equipment in its protective case or in a controlled environment, which doesn't expose the tool to moisture, vibration or extreme temperatures.
• Use within rated limits - Never exceed the rated torque capacity of the torque analyser or sensor, because overloading torque calibration equipment can permanently damage sensors and invalidate any future calibration. 
• Follow calibration schedules - Ensure that the equipment gets recalibrated at regular intervals and this should be traceable to recognised standards, such as ISO or UKAS.
• Maintain records - Keep clear calibration and maintenance records, including certificates, service history and verification results. This provides traceability and ensures that the torque tooling being calibrated is also accurate.

Digital calibration equipment isn't necessarily more accurate than mechanical calibration equipment, because mechanical equipment can be just as accurate when well designed, properly maintained and correctly calibrated. However digital equipment does have some benefits, such as -

• It provides clear and easy-to-read results.
• Reduces operator subjectivity.
• Provides data logging and automated reporting, making it superior for traceability of tooling performance, which is important in certain sectors, such as medical device manufacturing and aerospace.
• Has built-in tolerance checks, as well as pass/fail indicators, which can clearly be seen by the operator.

Yes, many calibration devices are compatible with a range of torque tools, including both torque screwdrivers and torque wrenches.

It would be rare that one calibration tool would be able to service a torque screwdriver and a torque wrench though, because both tools operate at vastly different torque levels. Torque screwdrivers operate at much lower torque values than torque wrenches, with torque values often measured in centinewton metres (cNm), inch-ounces (oz-in) or small newton-metre ranges (Nm), whereas torque wrenches work at medium to high torque levels, which are nearly always measured in Nm.

Torque calibration equipment should comply with recognised international standards, which are designed to ensure reliability, traceability and accuracy in professional and industrial settings. These standards are usually set from recognised bodies, such as ASME, ISO and UKAS.

A few examples of some of the standards they have introduced, includes -

ISO 6789-1:2017 - Specifies the conformance testing and marking requirements for hand torque tools used for controlled tightening of screws and nuts.

ISO 6789-2:2017 - Specifies the method for the calibration of hand torque tools and describes the method of calculation of measurement uncertainties for the calibration.

ASME B107.300 - Provides performance and safety requirements for manually operated torque instruments, commonly used for mechanical measurement of torque for control of the tightness of threaded fasteners.

The accuracy required for torque calibration equipment should be at least four times (4:1 ratio) more accurate than the torque tool being calibrated. This means that a torque screwdriver could have an accuracy of ±1%, so the torque calibrator would need to be at ±0.25% accuracy. This ensures reliable results and reduces measurement uncertainty.

Some industries that are regulated, such as aerospace, automotive and medical device manufacturing, will have minimum accuracy requirements as well as or internal quality procedures, which may produce even stricter tolerances, as well as traceability requirements.