This month we have a special guest blog from Edward Simpson at RS Calibration. Morehouse welcomes guest blogs from others in the calibration industry. Edward is a seasoned Calibration and Technical Engineer working for RS Calibration Services. Edward has a knack for finding faults in machines and does not rest until they are rectified to perfection. He lives in Pleasanton, CA and can be contacted anytime for matters related to machines. Edward has written several articles for various magazines and we welcome his take on knowing a torque wrench better.
Know a Torque Wrench Better with this Ultimate Guide
A torque wrench is one of the most indispensable tools to have in your toolbox. Before choosing the one perfect for your requirement, you need to be aware of the various types of torque wrenches available, their calibration and factors affecting the calibration. All of these points are essential. Let’s take a look at them:
What are the different types?
There are multiple varieties of torque wrenches available which cater to diverse application needs. Listed below are a few of them:
- Electronic Wrench - These are easy to program and set specific limits, which are aligned to the accurate torque level for important and frequently performed applications. The strain gauge attached to the torsion rod transmits a signal to the transducer device for calculating the torque per unit force. The reading is then displayed on the LED screen. These types of torque wrenches have memory sticks within them, which record the readings in a way so that they can be accessed through computers.
- Hydraulic Wrench - These wrenches are used for applying the required amount of torque strength to the fasteners, and are often utilized for automotive jobs. With an adequate amount of pressure, the nut or the bolt is tightened according to the pre-calibrated level of torque.
- Click Wrench - This is a slightly sophisticated version of a socket wrench. The torque level can be easily preset through a clutch mechanism. Its high-precision design ensures that the clutch automatically starts slipping out and uses a shut-off mechanism when the torque level reaches the predefined level.
- Plumbers Wrench – This kind of wrenches are particularly designed so that they can be used with couplings on the soil pipes. They are pre-calibrated to slip out when the predefined level of torque is reached, and hence are suitable for specific kinds of jobs only.
- Beam Wrench - It is one of the most basic types. Its lever arm has some elasticity which allows it to bend for applying the desired amount of pressure. When not in use, the indicator rests parallel with the lever arm, and when the torque is applied, the scale shifts to provide the required reading.
You can choose the type of tool best suitable for your needs. However, the thumb rule for a well-performing torque wrench is appropriate calibration. Described below are the various aspects you need to keep in mind to ensure that the tool delivers precise results:
Apart from verifying accuracy, calibration measures the reliability of the tasks performed by the wrench day in and day out. With the permissible window of calibration error set at 5%, any fault beyond that may adversely affect the overall performance of the wrench.
When to calibrate?
One of the most common questions which almost every torque wrench owner has struggled with is how frequently should the torque wrench be calibrated. The key here to avoid erroneous results is to remember that ‘one-size-fits-approach’ should never be applied when it comes to your instrument calibration. For instance, calendar-based calibrations are a preferred path for many, but it does in no way assure that your tool will remain in perfect working condition. Simply put, you can narrow down the need of calibrating your torque wrench to – a) how often and b) how intensively the tool has been used.
Some professionals believe that the performance of the tool is affected between 2,500 to 3,000 repetitions. Hence, it is the generally recommended parameter for calibrating a torque wrench tool.
What factors affect calibration?
Temperature, type and frequency of usage, and also how the torque wrench tool is handled and stored – are all crucial factors that affect the tool’s calibration requirements. Depending on how frequently or rarely the tool is used, the type of application it is used for and the manufacturer’s instructions can guide the owner in a correct manner. Also, it is essential to keep in mind the temperature of the surroundings in which the tool operates. Preferably, it should be calibrated in similar temperature conditions, to reduce or eliminate calibration errors.
Morehouse thanks Edward for his guest blog. Please remember that the views expressed here are from Edward Simpson and not Morehouse Instrument Company. We feel Edward has provided a very nice introduction into torque wrench calibration. There are many other things that need to be considered depending on the type of wrench and your overall accuracy requirements. Most Click type wrenches may need to be stored at a 20 % preload and should never be backed off to 0. Some torque wrenches that do not state impact free may actually loosen the fastener and so on. It is always important to evaluate all parameters when selecting and calibrating torque wrenches.
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