Plasma cutting

plasma cutting machine

Plasma cutter

A plasma cutter It is a machine or tool capable of cutting metal parts of all kinds using high temperatures that can reach more than 20.000ºC. The keys to easily cutting metal, even high thicknesses, by this process are that very high temperature, the properties of plasma (the state to which the gas is brought by an electric arc), and polarization.

In the plasma state, that gas becomes conductive of electricity to be ionized. If it is passed through a very fine torch nozzle, it can be directed very precisely to where you want to cut. In other words, thanks to the high temperature (produced by a direct current electric arc) and by concentrating the kinetic energy of this gas, it can be easily cut with great precision.

plasma cutting machine

Note that there are electrodes that apply a Polarization between the torch or torch and the part to be cut. As they are opposite poles, the gas atoms are used as a "projectile" in one direction against the metallic surface, managing to pass through it. The good thing is that any gas can be used, although it is true that it should not be a reactive gas with the type of metal being cut ...

In addition to be able to choose any gas, another advantage is that the cut edges will not need subsequent treatments to correct imperfections generated during cutting, and there is no risk that the piece will be deformed by heat when concentrating it in a very specific point (unlike the oxicorte, which heats a larger area).

What is plasma

what is plasma, science

Plasma is the fourth state aggregation Of the mattery, since beyond the basic states of matter (solid, liquid and gas), there are more. In fact, it is rare that it is not as well known as the popular three, since it is the most abundant state in the universe.

If you remember what I mentioned in the previous section on polarization to direct the plasma jet, it makes sense when you know that plasma is a state similar to gas, but where the particles are electrically charged (they are ions), and using poles they can be jets of atoms / molecules wherever you want, similar to how electrons travel through a conductor. Maybe this way you will better understand the cutting procedure ...

To ionize, or transform a gas into plasma, you need to heat the gas or apply strong magnetic fields using a laser or microwave generator. In the case of plasma cutting, what is used is an electric arc to heat it, and that is why the ionized gas is transformed into a plasma.

Before continuing, I would like to explain that a Electric arc it is a phenomenon that we see in nature, like lightning. But you will also have seen it in some gadgets such as plasma balls, or if you are electronic you will know what happens in a capacitor when the dielectric breaks ... The arc is achieved by two electrodes of different signs in which the potential difference rises a lot and, although they are not in contact and are separated by air (a very good insulator), the air ends up “breaking”, producing a beam that goes from one electrode to another. In storms something similar happens between negatively charged clouds and positively land. Although clouds and land are separated by a large layer of insulating air, lightning jumps from one place to another ...

With that said, you may be wondering what is an ionWell, it can be an atom or molecule of any element or compound whose number of electrons has been altered. Remember that atoms or molecules are generally in an electric state of equilibrium, with the same amount of positive (proton) and negative (electron) charges, in addition to the neutral (neutron).

Explanation of plasma, anions, cations and electric charges

Thus, if an atom or molecule has been ionized and has an excess of electrons versus its steady state, then it will be an anion. Whereas if it has lost electrons and its positive charge predominates, then it will be a cation. The gas made up of these anions / cations will be that plasma we are talking about ...

And what I want to go to with this is that if it is in equilibrium (normal gas), then, by applying a negative or positive charge through two electrodes (one in the torch -, and another in the piece to be cut +), those atoms / molecules will do nothing. But having load Thanks to this arc that ionizes them, a negative electrode can attract cations and repel anions, and vice versa with a positive electrode. That is to say, they can be directed, in this case against the surface of the metal so that they are like projectiles, and at those temperatures, cut it as if it were butter ...

By the way, don't confuse that ion imbalance with radioactivity, since in that case it is when an atom is unstable due to a bad balance between the protons or neutrons of the nucleus (the electrons are in the crust orbiting around the nucleus, and they are the ones affected in the ionization process). In the case of radioactivity, when there is an imbalance between these protons and neutrons, the atom will become unstable and will need to release the excess neutrons or protons to reach equilibrium.

That emission to try to restore the balance is radiation, such as alpha particles (helium), beta particles (electrons or positrons) and gamma radiation (high energy photon). Perhaps it can lead you to confusion because this gamma electromagnetic wave is considered radiation ionizing, like X-rays, UV, or lasers. Therefore, it can be used to produce ions as well.

Plasma properties

Plasma has very interesting properties, some of them are vital for plasma cutting to work. For instance:

  • You have charged particles (ions). Because of that they respond to external electric, magnetic and electromagnetic fields.
  • Can conduct electricity better than gas.
  • Being composed of particles in a chaotic and highly energetic state, plasma produces its own electromagnetic radiation.
  • Depending on the temperature and electron density, there may be various types of plasma. For example, there are plasmas charged with one sign or another, as you saw earlier. And you will also find what they call cold plasma and hot plasma:
    • In the case of cold plasma it has a low electron density, and its temperature is cold (usually room temperature). For example, the one used in fluorescent and neon tubes to ionize the gas inside and that conducts and produces that luminescence when the current passes.
    • El hot pasma, is created when the gas is heated until the electrons have enough energy to free themselves from the atoms, with a high degree of electron density. This is what happens in the Sun, the one used by some scientists, or in the case of plasma cutting. In general, hot plasma will always be called the one that is ionized below 1% and if it is almost completely ionized it will be hot ...

As you can see, they are very peculiar characteristics that allow various industrial applications, such as cutting.

Type

types of plasma cutting

Within plasma cutting we can differentiate between various types different:

  • Manual plasma cutting: it is the plasma cutting that is done manually, with a plasma cutting group. The operator will be in charge of handling the cutting tip and cutting what he wants by moving his hand to direct the plasma jet.
  • CNC plasma cutting: Unlike the manual procedure, there are also tables or CNC machines that perform the cut automatically with greater precision and speed, for more precise cuts or industries in which a movement has to be repeated for multiple parts. In fact, CNC (Computer Numerical Control) is a system in which the cuts to be made are programmed by computer, and a machine or robot will be in charge of carrying out the programmed cut.
  • Plasma cutting by compressed air: Unlike traditional dry plasma, in 1963 it was possible to increase the speed by 25% thanks to the oxygen in the air. However, this oxygen leaves the cutting surface highly oxidized and the electrode rapidly erodes.
  • Water injection plasma cutting: Five years after air cutting, Hypertherm president Dick Couch invented this other type of cut, which uses water that is injected into the cutting area through a special nozzle radially. This results in a faster, better quality cut with less dross.
  • Plasma cutting with oxygen injection: It was developed in 1983, and instead of nitrogen oxygen gas is used for cutting and water at the tip of the nozzle. This helps reduce cutting electrode deterioration and cutting surface oxidation.
  • Dual flow plasma cutting: is the conventional or standard procedure. Use nitrogen gas plasma and a shielding gas such as carbon dioxide or oxygen in the cutting nozzle. Right in the center of the exit of the two gases will be the electrode. That is why it is called dual flow.

And even just out of curiosity, check out the technology of the water cut. Sure you find it really interesting.