How to use torque wrench: the purpose of tightening torque

If you are a mechanical enthusiast, you must have read some manual procedures more than once, using the torque to tighten or torque any nut or screw. You may think you don't need a tightening torque to replace the spark plug or reinterpret the bleed screw. However, statistical data show that in most cases, the strength of the screw exceeds the requirements, leading to fracture and thread damage.

In this tutorial, we will try to explain the meaning of tightening torque, its purpose and how to check it in a simple way.

The screw is a "fat" spring.

To understand how a screw works, you have to try to think of it as a very rigid spring, but it can be stretched by tightening (stretching) and maintaining tension because of the friction between its body and the extruded material.

Each screw can bear a certain tension. Under this tension, the screw will not stretch long enough and will eventually loosen. If the working stress is exceeded, the screw will deform and fracture.

Measure the voltage

Therefore, the key is to be able to measure the tension applied to each screw. Ideally, the tension can be measured directly, but this is very complex and impractical (although in high-tech applications, some screws are equipped with tension sensors).

In most applications, another indirect and less accurate estimation method is also used, that is, to measure the tightening torque or torsional force when rotating the screw, and to infer the tension and tension from the force.

Torque wrench

In the absence of technical details, we can define a torque wrench as a device that can measure the tightening screw or the torque of the screw (its tightening torque).

There are several types of dynamometer spanners, the most commonly used of which are:

• The simplest is the dial, the pointer tells us the deviation when tightening.

• A watch, very similar to the former, but with a dial and an internal rotating pointer.

• Jump or click. When the tightening torque (moving handle) is selected, the internal spring will be tightened and the key will slide. When the selected torque is reached, the "click" will be issued.

• Electronics. They have an internal sensor that measures tightening torque and makes sounds and vibrations when they arrive.

Unit of measurement

It is important to understand and understand the different units that provide us with tightening data. If you give us a unit of measurement different from our instrument, we have to convert them:

Metric system		Anglo Saxon system
Newton meter (Newton meter)	KGM (KGM)	LB ft (FT lb)	Lb in
1	0,10	0,7	8,9
5	0,50	3,7	44,3
10	1	7,4	88,5
20	2	14,7	177,0
30	3	22,1	265,5
40	4	29,5	354,0
50	5	36,9	442,5
60	6	44,2	531,0

 

For transformations, we can use tools, calculators, or tables that come with Google. Electronic dynamometers are usually converted automatically.

Some manufacturers provide us with a tightening torque plus an angle (usually used for cylinder head screws, crankshafts, etc.). For this purpose, we will use the dynamometer to tighten, and then use the goniometer or goniometer.

Some digital dynamometers have this built-in function.

Tips for use

When using dynamometer wrench, it is very important to understand its use and maintenance. For this reason, we will refer to the manufacturer's Manual (it is very important to read and understand). Similarly, we have to follow the tightening recommendations in the workshop manual of the vehicle we are working on, because sometimes, in addition to tightening torques, they also provide a tightening sequence so that parts are not distorted during assembly.

• They are delicate instruments, do not have to hit them or use them to loosen screws.
• They are usually saved with the dial set to 0, so as not to discalibrate them (see manual).
• Do not lubricate or grease the screws to be tightened, unless indicated in the workshop manual (if we modify the friction, we modify the tightening torque).
• They must be recalibrated from time to time (again, refer to the tool manufacturer's manual).
• If we use extenders, it must always be done at 90o so that the torque does not change.
• They're useless when they're stored. It is important to get used to its use at all times, reading the tightening torques of the manual and applying them with the tool (the torque of our forearm is very vague and depends a lot on what we have had breakfast).