Torque wrench calibration: processes and services

Torque wrenches are vital in ensuring the safety, quality and longevity of components in aerospace, automotive and precision engineering applications. Fasteners require a specific amount of torsional force to be secure; If they become over-tightened they can deform or break when your product is in use, or if the fastener is not tight enough it could come loose and break off during operation. 

As torque wrench accuracy is directly related to quality and safety in engineering applications, their readings need to be accurate and regularly calibrated; any reading inaccuracy can directly result in disaster. Because of this, ISO standards outline strict compliance factors to ensure the accuracy of torque equipment. 

But what are the torque related calibration standards, and what are the specific processes involved that businesses need to follow to ensure compliance?  

When should a torque wrench be calibrated?

The most recent international standard for torque calibration is split into two parts; ISO 6789 part 1 and part 2. Part 1 outlines the specific requirements for testing and quality conformance, with specific values such as maximum torque value and calculation deviation. Part 2 focuses on calibration specifically, outlining the requirements for accurate calibration, sources of measurement uncertainty, and the calculation of measurement error. Additionally, part 2 states the range of factors that determine the calibration interval for torque wrenches;

1. The standard stipulates that torque wrenches need to be calibrated at 12 months or every 5000 cycles, with a shorter interval if required by the business or user. 
2. If the torque wrench is subjected to an overload greater than their maximum torque value, has been recently repaired, or handled improperly, it will need to be calibrated. 
3. Under properly documented control test procedures, the user can determine their own calibration intervals. This requires full measurement traceability, documentation of measurement error, and calculation of measurement uncertainty. Moreover, staff and process competence is required at multiple levels.

Types of torque wrench

Beam

Beam torque wrenches consist of two attached beams that operate independently of one another. When in use, force is applied to the first beam that acts as the handle and deflects, whilst the secondary beam stays stationary. The end of the secondary beam acts as a pointer to a reading plate that accurately measures the newton metres (Nm) of torque applied. Beam torque wrenches are simple, reliable and accurate. 

Clicker

Clicker torque wrenches provide the ability to predetermine the value of desired torque. When in use, an inbuilt clutch mechanism will make a click sound once the desired torque has been applied. This mechanism makes clicker torque wrenches extremely precise, and are commonly used in the oil and gas industry. 

Dial

Dial torque wrenches represent quality control as opposed to being used to tighten or loosen bolts. They measure and display the specific Nm of torque, which can be set by the user to reliably verify and monitor values. Due to their extremely high precision, they are often used for verification in aerospace and automotive applications. 

Electronic 

Similarly to dial torque wrenches, electronic models are used for the verification of torque values. They differ in that they lack the internal mechanical systems to measure torque, and instead use an electronic sensor and display. Measurements can also be electronically saved and documented, making them useful for traceability and quality assurance. 

Manual calibration methods for torque wrenches

Torque analyser

A torque analyser is a simple to use electronic device that can be used on-site to monitor torque calibration in a fairly flexible manner. They utilise torque transducers to convert torsional mechanical input into electrical output signals, displaying the precise amount of force that is being applied. These can be used for regular checks, but often do not incorporate enough measurement uncertainty to be in line with full ISO 6789 standards.

Torque calibration bench

A torque calibration is a dedicated testing bed for the precision and accuracy of torque wrenches and equipment. They follow the strict guidelines of ISO 6789, which outlines the various positions and precise torsional input each type of wrench needs to be calibrated. For example, it states that “Type II setting torque tools shall be loaded on the calibration device with increasing force up to approximately 80% of the respective target torque value… The load shall be applied slowly and uniformly during a period of 0.5s to 4s.” 

The importance of UKAS calibration for industrial torque tools and equipment

Factors such as measurement uncertainty and measurement error calculation are vital components of ISO 6789 compliance. Moreover, these factors become increasingly important for industry grade equipment and tools. The standard outlines strict processes that must be followed to demonstrate compliant calibration; examples include ambient temperature that must be between 18-28°C, multiple loadings that must be performed at 20%, 60% and 100% of the wrench’s maximum tolerance, and reading deviations that are limited to ±4% -  ±6% depending on the tool.

Because of the intricacies leading to torque calibration compliance, UKAS accredited laboratories are trusted to perform torque testing that is in accordance with both ISO 6789 and ISO 17025 respectively. These laboratories represent the gold-standard of torque calibration, demonstrating complete competence from the facilities and processes to the staff performing the calibration. For businesses that lack the resources to meet the extensive torque calibration requirements of ISO 6789, a UKAS accredited laboratory provides precision, quality assurance, and peace of mind. 

Book your UKAS-accredited torque calibration

It is clear that the requirements for torque calibration compliance are extensive and precise. For a wide range of businesses, having a controlled, traceable and thoroughly documented calibration process in place is simply not possible; which is where DM Systems & Test comes in. 

Our laboratories are completely UKAS accredited to provide torque calibration in line with both ISO 6789 and ISO 17025. We have a team of expert engineers with the experience and knowledge to provide precision calibration for your torque wrenches and array of torque equipment. Better yet, we offer on-site calibration and have a fast turnaround time to minimise the impact to your operations. 

Is your torque equipment calibration date coming up? Contact us today to book the precision calibration you need without impacting your operations.