As a precision technician, you use a torque wrench to achieve the exact tightness you need to extract maximum performance. However, the only way you can be sure a fastener is tight enough to resist vibration, but not so tight as to strip the threads or stretch the bolt beyond its yield point, is through torque wrench calibration. Properly calibrated torque wrenches will deliver accurate torque readings within specified tolerances, assuring safety, maximizing machine efficiency, and extending fastener life.
The Nuts and Bolts of Torque
Tightening a nut onto a bolt causes the bolt to elongate. Like a stretched spring, the bolt tries to return to its normal length, and in doing so, creates clamping action. Clearly, proper tightness is important to ensure a machine or component operates properly and that parts do not break off due to high-stress loads or loosen and fail as a result of weather or vibration. Torque is a measurement of turning power, expressed in pounds per foot (or Newtons per meter in metric countries). This standard is calculated by multiplying the length of the tool by the force applied to it. For instance, a 14-inch wrench with 30 pounds of force applied to the handle will exert 420 foot pounds of torque.
The clamping force required depends on the product being assembled or maintained. The fastener being used, the loads the component will be subjected to, lubrication, weather, vibration, and other factors determine the proper torque.
The Right Tool for the Job
Because the force applied to a wrench is almost always delivered by a person, it is difficult to measure. Enter the torque wrench. When working within specifications, a torque wrench works by either continuing to tighten a fastener until a user-set torque limit is reached or by using a scale to indicate how much torque is being applied and relying on the user to stop when reaching the desired torque. As mentioned, they only work when properly calibrated. More expensive torque wrenches generally not only operate under more exact tolerances, but also can be expected to remain within specifications longer. Still, all torque wrenches should be recalibrated often to ensure proper readings and clamp force. ISO 6789 calls for torque wrench testing annually or after every 5,000 uses, but more frequent calibration may be appropriate, especially in high-tech and critical life-safety applications.
Testing and Calibration
In addition to the 5,000 uses/one-year recommendation, recalibrate torque wrenches whenever they are subjected to abnormal conditions:
- Maltreatment – Torque wrenches are delicate instruments. Using them as a breaker bar or extending the reach with pipes is never recommended. Overloading torque wrenches or accidentally dropping them are good ways to make them inaccurate. Any time a torque wrench is used or handled improperly, it must be recalibrated.
- Working Conditions – Subjecting a torque wrench to inclement weather or extreme temperatures can introduce moisture into the working parts. Rust, water, dust, and solvents can affect accuracy.
- Poor Storage – Torque wrenches should be dialed back and stored at their lowest setting to avoid subjecting the tension spring to a prolonged load. Test any wrench that is stored in a setting above the lowest mark (or all the way to zero, which could cause other components to shift slightly).
Professional calibration services can test and adjust torque wrenches back to factory specifications, but for every day (or every week) checks right in the garage or production floor, a portable calibrator can be used to ensure wrenches remain within acceptable parameters.
Do-it-yourself methods are imprecise, time-consuming and labor intensive, requiring marking the wrench and employing heavy weights to check torque ratings. The Torque Wrench Validator from Mountz offers quick torque wrench testing to ensure the tools fall within acceptable limits. Designed exclusively as a torque tester (it’s not suitable for power tools) the Validator makes it easy to test regularly to ensure optimal efficiency. This torque wrench checker is fast – a green light indicates the wrench is within the specified tolerance; a red light means the tool needs to be calibrated.
Winner of a 2017 Pro Tool Innovation Test and Measurements Award, the Validator is compact and lightweight with a torque testing range capacity from 40 to 200 foot pounds. It offers significant advantages over competitors’ products including:
- Three operation modes: Peak, First Peak, and Track.
- Three units of measurements: Foot Pounds, Newtons per Meter, and, Kilograms per Meter.
- Battery-operated. 9-volt lithium ion rechargeable battery and universal charger (100-240 VAC) included.
- Easy-to-read menu settings and LCD display.
- Numerous mounting options.