Ultimately your Torque Wrench is used for tightening nuts and bolts accurately. The Australian Standard AS 4115 requires most torque wrenches to give a reading or "click" that is within +/-4% of the test equipment value.
If a torque value is too low, the component will not be stretched to create a clamping force, and similarly if the torque value is too high, you risk breaking the fastener. The risks associated with incorrect tension being applied can not only result in loss in downtime, but also lead to serious injury.
As wrenches can go out of calibration for varying reasons, ensuring a regular calibration programme is in place, will ensure you peace of mind that your tools are accurate and fit for any application.
Replacing old or worn wrenches should also be factored in. Sometimes the cost of repairing a wrench can be a similar cost to the value of the wrench itself. So, if you find you're spending money on it every time it is checked, it may be worth investing in a new replacement wrench that is of good quality.
Any torque wrench reading that is not within a +/-4% accuracy of the wrench setting does not comply with Australian Standard 4115-1993.
Calibration intervals set by national and international standards are either one year or 5000 cycles/clicks, whichever comes first. This may be too long in high usage applications or safety critical operations and more frequent checking and/or calibration may be necessary.
Ideal working temperatures are generally between +/-4°C & 43°C. Wrenches should be stored at room temperature (roughly between 18°C & 25°C). When a wrench is stored below freezing, you run the risk of developing condensation that can cause the internals to rust, affecting the accuracy and performance of the tool. Temperatures exceeding 48°C will cause the grease inside of the wrench to melt and seep out, affecting performance and accuracy also.
When not in use, it is recommended to reduce the setting to the minimum scale value (often 20% of the maximum). Adjusting the setting to zero should never be done as this can adversely affect the calibration of the wrench, if set for long periods without use.
If the torque wrench has not been used for a day or more, exercise the wrench about five times before use to redistribute any grease and get the parts moving evenly again. For safety critical or high volume applications it is common to check the wrench every day or every week where possible.
If you do forget to reduce the setting to minimum scale when not in use, re-adjust the torque to a mid-range scale, then tighten and loosen a fastener a few times to work the spring. Then set the wrench to the desired torque value ready for use.
Don't dismantle a wrench as it will affect the torque readings, and will require adjustment, as will dropping it and rough usage.
Tools should be kept clean and stored in a clean environment or box, they have moving parts, so dirt and dust can affect the internal mechanisms.
Tom will be able to provide you with any advice you may need to select the most appropriate Torque Wrench for the application it is required for.