Recently, there was an accident at a manufacturing plant where a friend of mine works. He told me that the plant’s production line, which is sizable, was shut down because an essential piece of equipment went offline. Although there was significant damage to the production line equipment, no one was injured.
Over the course of the investigation, which took several days, they were able to identify the problem. A bolt that had been used to fasten a part to some equipment loosened and broke, damaging a key component of the production line. And all this happened because an employee had installed a bolt using a torque wrench which was badly in need of calibration.
Everyone working at the plant learned an invaluable lesson from this incident: whether you are involved in production, engineering, field service repairs, installation, or simply a proud do-it-yourselfer, torque wrenches must be properly calibrated so they can be used with precision and safety.
Types of Torque Wrenches
Torque wrenches are either preset or adjustable. A preset wrench is set to work with specific fastening applications where there is one torque setting required, and it prevents the operator from changing the torque settings. On the other hand, an adjustable torque wrench features an external adjustment torque scale, which allows the operator to quickly adjust the torque setting on the tool as needed for different fastening needs.
There are some calibration differences between these two types to keep in mind. For a preset wrench or an adjustable wrench that will be checked at only one torque, the result will read either “go” or “no go.” “Go” means the wrench is within tolerance, while “No Go” indicates the wrench needs to be calibrated. You will not get the “go/no go” responses when checking the calibration of an adjustable wrench, and it is necessary to test at least three points with this type.
Besides the two basic categories of preset or adjustable, there are different types of torque wrenches available. These include click, cam-over, break-over and dial:
A cam-over wrench prevents a fastener or bolt from being under and over tightened. This type of wrench allows any user to deliver the correct torque with confidence, regardless of the task or the operator’s skill level.
This type of tool is used for torque auditing and torque measurement applications. The main pointer on the dial captures the finishing torque applied to the fastener with a memory pointer.
A torque wrench must be dependable and accurate, as precision is everything. As such, a quality torque wrench should comply with applicable performance and safety standards such as ISO 6789 and ASME B107. This way, you can be assured you have selected a torque wrench that is up to the work at hand.
Tools for Checking Torque Wrench Calibration
If you use a torque wrench with any frequency in the course of your work, it will go out of calibration eventually. A good rule of thumb is to have torque wrenches checked a couple times a year.
Here are some common tools you can use to check whether a torque wrench is properly calibrated:
This digital device is easy to use. It features a display that lets the operator know if the wrench is accurately calibrated. In addition, some analyzer units allow you to connect with various external torque sensors and has operating modes that let you conduct tests on different tools. If using a smartphone is easy for you, this analyzing tool will probably feel familiar. Some testers or analyzers do not need to sit on a level surface. Others should be mounted to a fixed surface like a workbench.
- The menu screen will display options, including “Quick Test,” “Units,” “Mode,” “Setup,” and “Filter.”
- Start by applying torque to the input of the analyzer..
- That movement is transmitted to an indicator, which rests on the maximum torque reading until it is set to zero.
- You will notice that the reading on the scale of the wrench is compared with the reading on the tester.
- Simply follow the device’s prompts to determine if the torque wrench needs to be calibrated.
- The analyzer will produce a reading indicating whether calibration is needed. As a bonus, these readings can be quickly uploaded to your computer.
This equipment provides quick and easy torque wrench calibration. The wheel ensures smooth manual loading and operates in both a clockwise and counterclockwise direction.
- First, think safety: secure the loader on a solid bench top or another stable surface.
- Place the torque wrench on the transducer, which is connected to the loading bench.
- To maintain greater accuracy, use the presetting position to eliminate accidental adjustments.
- The large handled wheel moves both clockwise and counterclockwise, which makes loading easier.
- Slide the loading device assembly along the reaction bar. The bar should allow enough clearance for the torque wrench to be installed.
- Choose the lowest capacity torque transducer to test the wrench.
- Ensure the wrench handle runs along the length of the reaction bar.
- Mount the wrench in the female square drive of the torque transducer.
- Now, slide the loading assembly along the reaction bar so the support spindle reacts against the normal hand position of the wrench. This will be the center of the wrench’s handgrip.
- If the wrench being tested has a square-drive ratchet, make sure the orientation of the ratchet allows maximum movement of the wrench handle by the support spindle.
- Position the spindle so the wrench keeps a horizontal position during testing.
- Before you load the equipment, secure the clamp plate.
- Smoothly turn the handwheel to apply load to the torque wrench.
- To measure the applied torque, there should be a torque transducer attached to a display instrument. This will show you if the wrench is properly calibrated.
Whatever tool you choose, it’s important to regularly check your torque wrench to see if it is in need of calibration. Taking such a proactive stance will help avoid any problems down the line.
Creating a Maintenance Schedule for Your Torque Wrench
Regardless of quality, eventually every torque wrench requires maintenance. As with many tools, a torque wrench should be professionally calibrated once a year, depending on how often it is used. Keeping in mind the old adage, “An ounce of prevention is worth an ounce of cure,” it’s advisable to check torque wrenches periodically for wear and tear or damaged components.
As part of a preventative maintenance schedule, an operator should monitor how often a torque wrench is used in a day and how many cycles and total hours it’s used for. Keep this information in an organized log you can easily check. A good rule of thumb is to have a torque wrench serviced after approximately 100,000 cycles. If parts of the wrench show excessive distress, it’s time for the wrench to be removed from service and repaired.
To make sure you won’t need to service your torque wrench more frequently than necessary, take good care of your tool. We recommended keeping a torque wrench in a case or using another storage system that ensures it lives in a clean and dry environment. You can clean a torque wrench regularly by using a cloth, without any liquids or chemicals, to wipe it down. Always keep a close eye on your torque wrench to ensure it is still in peak operating condition, and have a professional service it if you notice any signs of failure or damage.
The Importance of Proper Torque Wrench Calibration
After the mishap at his manufacturing plant, my friend and his colleagues were required to attend a workshop that reinforced the lesson they had learned: always work with tools that are in good operating condition. While it might seem like a hassle to frequently check the state of your tools, it is a small price to pay for increased safety and efficiency.
After all, what good is a bolt if it isn’t properly installed? A fastener that is poorly installed can loosen, leading to a failure and possibly a serious accident. When you take the time to properly calibrate your torque wrenches, the quality of your work is improved and the possibility of an accident is minimized.