Any fastener, or for that matter, any bolted joint which has a load attached to it, is torque dependant. Hence, the tightening force is of paramount importance. The bolted joint has a torque value and this value signifies the tightness of that particular joint or nut. In other words, the bolt is preloaded, and force plays a part in preloading the joint. The wrench assures checks and certifies and measures the torque value of the joint.
You will come across different kinds and categories of torque wrenches such as simple ones with the beam and specialized wrenches which do more than just measure the resistance of bolt to movement. This blog post doesn’t seek to highlight the different kinds of torque wrenches because if that’s what you’re looking for, all you have to do is google it. Instead, this blog post aims to highlight what lies inside the device.
If your goal is to tighten up a bolted joint, you rely on the efficiency of the click type torque wrench. Ensuring the optimum torque value, you are provided with a click which indicates that the task has been done. The click conveniently indicates the completion of the task and the realization of the value, but what actually happens to make the instrument click?
We had a customer who accidently destroyed his original $100 click-centric wrench. It is important to note that when you put away your wrench, it is best practice to ensure that the setting is backed off. By doing this, you are basically stopping the spring which lies inside from getting compressed. When our customer manipulated the settings and made the necessary adjustments on his wrench, the bottom handle became loose. Despite becoming loose, the handle didn’t get detached. Instead, it showed axial movement and spun freely. As a result of this disruption, the calibration settings of the device were affected.
Our customer sent his wrench in to our Repair/Calibration department to restore the calibration. At Excel, we offer complimentary evaluations but you are expected to pay for the freight. An approximate charge for the calibration of a torque wrench is around $85.00. The other option for our customer would have been to invest in a new wrench. He did end up purchasing two wrenches; one new and one used.
Click-centric wrenches are effective in many ways. If you are dealing with joints that are tight, you can use this particular type of device at your convenience; just wait until you hear the clicking sound. You do not need to wait for the dial, as is necessary for the beam-centric torque wrenches. If you are using the beam-centric option, you have to see the pointer, and then realize that your objective has been fulfilled. The dial type wrenches with beams do not include a ratchet. It is not always easy to access the figure when you are working at home, without a hoist.
I removed both the retaining ring and the arm pin from the wrench. The removal of thesecomponents made it easy for the removal of the ratchet. The device’s body tube made way for the removal of the ratchet.
The grip happens to be clamped in such a way that it finds an easy access to the screw which can be adjusted. The nuts serve as the link of connection, helping to clamp the grip to the screw which can be adjusted. It is necessary to manipulate the grip in order to get the reading of the torque value. When you turn and manipulate the device’s grip assembly in such a way that you can move up the calibration scale, the screw also gets manipulated. These manipulations, in turn, compress the spring of the tightening device. The grip, as well as the screw moves and rotates, but they move at different speeds. Their rotational speed is not relative. These changes account for the compression of the spring. The spring seeks to outdo this compression by expanding itself. This expansion then creates the force on the wrenching mechanism, and as a result of this force, you’ll hear the clicking sound.
In a device that is properly calibrated, you can easily move and manipulate the grip. Similarly, you can move and manipulate the adjustable screw. The calibration takes place when the grip, together with the adjustable screw moves up and then goes down. This movement ensures calibration. In a device that is properly calibrated, the reading produced by the grip and that of the barrel marking are found to be similar. As a user, you can read the figure to find out the tightness of the bolted joint. The nuts, the screw, and the grip are adjusted and clamped in such a way that the device is well calibrated.
After restoring the washer, the spring with the cup to its original place. Next, I want to highlight the functioning of the device’s cam assembly, Ratchet assembly and the pawl.
The wrench’s cam assembly has four different components. The cam is shaped out in the form of a cylinder. Other than the cam, the assembly includes a cage, a spring and quite a few balls. The component that shapes out as a cage keeps the balls organized. The cage doesn’t take loads. The assembly facilitates anti-windup and prevents the other components from dashing against the device’s barrel. When the force is applied, the pawl gets activated and in turn, influences the spring.
Installation of the pin that fixes the arm and getting the retaining ring attached become convenient. That’s because the head of the ratchet facilitates easy installation. The role of the pin is to hold and connect the assembly in such a way that it doesn’t drift apart. The pin serves as the pivot of connection.
As the grip backs down, the assembly receives little or no resistance. So, there is no reason to exert pressure on the device’s ratchet assembly so as to bring its arm pin right back inside. With the help of the following diagrams, you can understand the positioning and placement of the device’s torque spring, cam assembly, pawl and the ratchet lineup.
See how the head of the ratchet and the assembly that facilitates anti wind-up have small little squares? The instrument’s tilt box is found trapped between the tiny squares. The spring exerts pressure, and as result, the tilted box finds itself trapped. The wrench is now assembled. It is interesting to note that the lowermost part of the ratchet setup lies on the top, the device’s cam assembly lies beneath it and the pawl finds itself juxtaposed between both the components.
After changes have been made, how will the device tighten up a bolted joint?
If you apply turning force, the spring’s preload gets affected, and this gives rise to a new series of clamping force. The force you apply is overcome by the next series of force. The pressure influences the pawl. The ratchet setup also gets affected by the pressure series that is created. It touches the barrel to produce the clicking sound.
You should not turn the wrench once you hear the clicking sound. The wrench is automated in such a way that it prevents the exertion of extra pressure. But if you keep pushing, you will only end up adding to the torque value, so you will not get the correct figure. It is important that you treat the click as an indicative signal, and stop pushing once the value is realized.
The click type wrench has no frictional wear. Grease is used to slither the internal part. So, moisture fails to affect the overall functionality of the device. You can undertake as many as five thousand cycles with this special variety of click centric corded and cordless torque wrench, but there are two things to remember. After every testing cycle, you need to get the pressure backed off. Secondly, you need to be cautious while dialling and backing down the pressure.
In summation, wrenches are a precision device. They should be handled with care, gentleness and caution. Do not subject your wrenches to any kind of impact and use only for tightening purposes. Once the job is done, safeguard your tool in its original box. If you handle your wrench carefully, it will be sure to serve you over a long period of time.