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

Si eres aficionado a la mecánica, seguro que más de una vez has leído en algún manual procedimientos para utilizar el par de apriete o de torsión de alguna tuerca o tornillo. 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

Para entender cómo funciona un tornillo, hay que intentar verlo como un muelle muy rígido, pero que se puede tensar al apretarlo (se estira) y mantiene la tensión debido a la fricción que existe entre su cuerpo y el material que aprieta.

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. Lo ideal sería poder medir directamente el estiramiento del mismo, pero esto resulta muy complicado y poco práctico (aunque, en aplicaciones de alta tecnología, existen tornillos que disponen de sensores de estiramiento).

En la mayoría de aplicaciones, se utiliza otro tipo de estimación indirecta y menos precisa, consistente en medir el par de apriete o fuerza torsional al girar el tornillo y a partir de esta fuerza deducir el estiramiento y por lo tanto la tensión.

The dynamometric key

Sin entrar en tecnicismos, podemos definir la llave dinamométrica como un dispositivo capaz de medir la fuerza de torsión con la que apretamos un tornillo o rosca (su par de apriete).

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.

• De salto o click, donde se tensa un muelle interno al seleccionar el par de apriete (moviendo el mango) y la llave se desliza, emitiendo un “click” al llegar al par seleccionado.

• 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.

Algunas dinamométricas digitales disponen de esta función incorporada.

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.

• Son instrumentos delicados, no hay que golpearlos ni utilizarlos para aflojar tornillos.
• 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).