How the dynamometric key is used: What is the tightening torque

If you are fond of mechanics, surely you have read procedures more than once to use the tightening or torsion torque of some nut or screw. You may think you don't need a tightening torque to change spark plugs, or re -apprehend the exhaust screws. But statistics show that most of the time, the screws force more than necessary, leading to damaged breaks and threads.

In this tutorial we will try to explain in a simple way what the tightening torque means, what is its usefulness and how to check it.

A screw is a "fat" dock

To understand how a screw works, you have to try to see it as a very rigid dock, but that can be tightened when squeezing (stretches) and maintains the tension due to the friction that exists between your body and the material that squeezes.

Each screw is designed to support a certain tension. Below this tension, the screw will not stretch enough and end up loosening. If the working voltage is overcome, the screw will deform and break.

Measuring the tension

The key then consists of being able to measure the tension that we apply to each screw. Ideally, it would be to directly measure its stretching, but this is very complicated and unchanged (although, in high -tech applications, there are screws that have stretch sensors).

In most applications, another type of indirect and less precise estimate is used, consisting of measuring the tightening torque or torsional force when turning the screw and from this force deduce stretching and therefore the tension.

The dynamometric key

Without going into technicalities, we can define the dynamometric key as a device capable of measuring the torsion force with which we squeeze a screw or thread (its tightening torque).

There are different types of dynamometric keys, this are the most used:

• The simplest is that of Dial, where a pointer indicates the deviation generated when performing the tightening.

• Of clock, very similar to the previous one, but with a dial and a needle that rotates inside.

• Jump or click, where an internal dock is tense when selecting the tightening torque (moving the handle) and the key slides, emitting a “click” when you reach the selected pair.

• Electronic They have an internal sensor that measures the tightening torque and emits a sound and vibration when reaching it.

Units of measure

It is important to know and know how to interpret the different units in which we are presented with the tightening data. If they give us a measure in units other than those of our instrument, we will have to convert them:

Decimal Metric System		Anglo -Saxon system
Newton-meter (Nm)	kilogram-meter (kg-m)	LIBRAS-PIE (FT-LBS)	pounds-pulgated (in-lbs)
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 conversion, we can use the tables that come with the tool, a calculator or resort to Google. Electronic dynamometric usually conveys automatically.

Some manufacturers provide us with an angle tightening torque (it is usually used in butt, crankshaft, etc.). To do this we will apply the tightening with the dynamometric and then use a goniometer or angle meter.

Some digital dynamometric have this incorporated function.

Use tips

When working with a dynamometric key, it is essential to know its use and maintenance, for which we will resort to the manufacturer Manuel (it is very important to read and understand it). Similarly, we must follow the recommendations for tightening of the vehicle workshop manual with which we work, because sometimes, apart from the tightening torque, they also give us a tightening sequence so as not to distort the pieces during assembly.

• They are delicate instruments, do not hit or use them to loosen screws.
• They are generally saved with the dial to 0, so as not to barefoot them (manual consult).
• Do not lubricate or grease the screws to tighten, unless indicated in the workshop manual (if we modify friction, we modify the tightening torque).
• They must be emphasized from time to time (again, consult the manufacturer's manual).
• If we use extenders, we must always do it at 90º so that the torque is not modified.
• They are of no use when they are saved. It is important to get used to its use at all times, reading the tightening pairs of the manual and applying them with the tool (the torsion pair of our forearm is very inaccurate and depends a lot on what we have had breakfast).