What Is a Torque Screwdriver?
Torque Screwdrivers are tools used in screw tightening operations that require torque control. Unlike ordinary screwdrivers, torque screwdrivers can tighten screws to a specified torque, and are therefore mainly used for automobile maintenance and assembly of precision equipment in factories.
There are manual and digital torque settings. In addition to manual screwdrivers, there are also electric torque screwdrivers, which are often used for assembly work in factories.
Usage of Torque Screwdrivers
Torque screwdrivers are mainly used for assembly of precision electronic parts and maintenance of bicycles in factories.
When these operations are performed with ordinary screwdrivers that do not allow torque settings, they can cause variations such as too high tightening torque and damage or too low tightening torque and screws not tightened completely, which can lead to product defects and a reduction in work efficiency by having to redo the work.
In contrast, a torque screwdriver can be used to tighten each screw. Torque Screwdrivers can solve this problem by controlling the torque for each operation.
In general, Torque Screwdrivers have replaceable bits, so they can be used with a variety of screw heads, just like regular screwdrivers.
Principle of Torque Screwdrivers
Torque Screwdrivers are available in the following two types of mechanisms:
- Dry Torque Screwdrivers Before use, the target torque is set by turning an adjustment ring. During screw tightening work, when the set torque value is reached, the clutch automatically disengages and idles to prevent over-tightening. It is a general torque driver mainly used for assembly work.
- Umbrella Type Torque Screwdrivers
This screwdriver has a scale on the driver to read the torque value. It has a scale on both sides, and the tightened torque value can be read on the scale.
In addition to the differences in mechanism described above, there is also a difference in whether the setting and reading are done analog or digital.
Calibration of Torque Drivers
Torque Screwdrivers are measuring instruments. It is important to calibrate it periodically to ensure that it functions at the correct torque value. However, there is no standard or law that defines the calibration cycle. Decide the calibration interval according to the regulations of the company that uses or manages the torque driver.
The unit of measurement for Torque Screwdrivers is cNm (centi-Newton meter).
To calibrate the Torque Screwdriver, fix the Torque Screwdriver horizontally, attach a 1 cm long calibration device to the torque sensing section, also horizontally, and hang a weight 1 cm from the Torque Screwdriver.
We will test whether the value of the weight and the torque display of the torque driver are within the specified accuracy range. If it is out of the accuracy range, adjust it and test again. As for the weight, use a weight that divides the full scale of the torque driver into equal parts, test the number of divisions, and record each value.
Calibrate in both clockwise (CW) and counterclockwise (CCW) directions.
There is also a calibration method using a dedicated verification device.
Air-Operated Torque Screwdrivers
Torque screwdrivers are used to measure screw tightening torque, but with a dry-running torque screwdriver, when dry-running occurs, the screw has been tightened to the set torque value.
This is because when torque exceeds the set torque value is applied to the torque screwdriver, the shaft idles and no further torque load can be applied.
There are two types of dry-running torque screwdrivers: those that allow the set torque value to be changed, and those that have a fixed torque value that cannot be changed (preset type). The idling type torque driver does not need to work while watching the torque value, so it is suitable for the work of continuously tightening screws with the same torque setting at the assembly site. Even non-idling torque screwdrivers have products that emit some kind of signal when the specified torque is exceeded.
Torque Screwdriver Bits
Most torque screwdrivers can use commercially available screwdriver bits with a 6.35 mm side-to-side diameter.