We all know that CNC plasma cutting machines ionize high-velocity air jets that are ejected at high temperatures at the nozzles to form electrical conductors. When the current passes, the gas forms a high-temperature plasma arc, which is a cutting method. Plasma arc commonly used gases are: argon, hydrogen, nitrogen, oxygen, air and so on. Here are the characteristics of the five commonly used cutting gases:
I. Argon:
Argon gas does not react with any metal at high temperatures. The argon plasma cutting machine is very stable. The nozzles and electrodes used have a high service life. However, the argon plasma arc voltage is low, the helium value is not high, cutting can be limited, and the cut thickness is reduced by about 25% compared to air cutting. In addition, in the argon maintenance environment, the surface tension of the condensed metal is relatively large, which is about 30% higher than that in the nitrogen atmosphere, so that there will be more slagging problems. Even when using a mixture of argon and other gases, there is a tendency for sticky slag. As a result, pure argon is rarely used alone to stop plasma cutting.
Second, hydrogen:
Hydrogen is usually used as an auxiliary gas to mix with other gases. For example, the famous gas H35 (having a volume fraction of 35% hydrogen and other argon) is one of the strongest gases for plasma arc cutting. This is mainly due to hydrogen. Because hydrogen can significantly improve the arc voltage, so that the hydrogen plasma jet has a high enthalpy, when combined with argon gas, the plasma jet cutting can greatly improve. Normally, argon and hydrogen are used as cutting gas for metal materials with a thickness of 70 mm or more. If the water jet is used to further tighten the argon + hydrogen plasma arc, a higher cutting efficiency can be achieved.
Third, nitrogen:
Nitrogen is a commonly used working gas. Under the conditions of higher power supply voltage, nitrogen plasma arc has better stability and higher jet energy than argon, even if the liquid metal viscosity is high, such as stainless steel and In nickel-base alloys, the amount of dross on the lower edge of the cut is also small. Nitrogen can be used alone or in combination with other gases. For example, nitrogen or air is often used as working gas in automated cutting. These two gases have been the normative gases for high-speed cutting of carbon steel. Nitrogen is also sometimes used as starting gas for oxygen plasma arc cutting.
Fourth, oxygen and oxygen can improve the speed of cutting low-carbon steel materials. When oxygen is used to stop cutting, the cutting form is very similar to flame cutting. High-temperature and high-energy plasma arcs make the cutting speed faster, but it is necessary to use an electrode that resists high-temperature oxidation, and at the same time, the electrode stops shock protection during arcing to extend the electrode. Life expectancy.
V. The air contains about 78% nitrogen, so the use of air cutting dripping conditions and imagine the use of nitrogen when imagining; air also contains about 21% by volume of oxygen, due to the presence of oxygen, with The speed of air cutting of low-carbon steel materials is also high; at the same time, air is also the most economical working gas. However, when using air cutting alone, there are problems such as slag dregs, incision oxidation, nitrogen addition, etc., and the low life of electrodes and nozzles will also affect work efficiency and cutting costs. Since plasma arc cutting generally uses a power source with constant current or steep drop characteristics, after the nozzle height is increased, the current change is small, but the arc length is increased and the arc voltage is increased, thereby increasing the arc power; but at the same time, The arc length exposed to the environment increases, and the energy lost from the arc column increases. In the context of the combined use of the two elements, the former's role is often completely offset by the latter, which in turn reduces the effective cutting energy and results in a reduction in cutting. The usual manifestation is that the blowing force of the cutting jet is weakened, the residual slag at the lower part of the incision is increased, and the upper edge is over-melted to have a rounded corner. In addition, considering the shape of the plasma jet, the diameter of the jet shrinks outward after separating the muzzle, and an increase in the height of the nozzle inevitably causes an increase in the width of the slit. Therefore, choosing a nozzle height that is as small as possible is beneficial for improving the cutting speed and the cutting quality, but the double arc phenomenon may be caused when the nozzle height is too low. The use of a ceramic outer nozzle enables the nozzle height to be set to zero, that is, the end face of the nozzle is directly in contact with the cut surface, and a good effect can be obtained.