How set the parameters of plasma cutting machine?
1.Cutting electric current
The cutting electric current is the most importante parameter.It decide the cutting thickness and speed directly,also the cutting ability.
Influence
The cutting current increases, the arc energy increases, the cutting ability is improved, and the cutting speed is increased.
The cutting current increases, the arc diameter increases, the arc becomes thick and the cutting line becomes wide.
But if electric current is too big,the nozzle is easy to hurt.The hurt nozzle give bad influence to cutting result.So before cutting,we should set suitable electric current and nozzle according the metal thickness.
2.Cutting Speed
The best cutting speed needs test with certain machine and certain metal thickness.Because the different material,different thickness,diffrent melting point and thermal conductivity ,so the cutting speed is different.The main performance:
Increase the cutting speed appropriately can improve the result of cutting,the cutting line becomes narrow,the cutting surface becomes smooth and reduce the distortion.
If the cutting speed is too fast,the cutting line energy is lower than the required value, cut seam in the jet can't quickly melted cutting melt immediately blew and the formation of larger drag, accompanied by incision slag hanging, the surface quality of the incision down.
When the cutting speed is too low, because the cut is plasma arc anode, in order to maintain the stability of the arc's, anode spot or anode region must from recent arc cutting seam found near the conduction current place, at the same time will pass more heat to a radial jet, so make the incision became wide, on both sides of the notch of molten material in the bottom flange aggregation and coagulation, form is not easy to clean the slag hanging, and incision margin due to excessive heating and melting and the formation of fillet.
When the velocity is extremely low, as the incision is too wide, or even extinguished arc. Thus, good cutting quality and cutting speed are inseparable.
3.Arc voltage
We generally believe that the power supply is normal output voltage for cutting voltage.
Plasma arc cutting machine usually have high no-load voltage and working voltage, the use of high ionization energy in gas such as nitrogen, hydrogen or air, stability needed for the plasma arc voltage will be higher. When the current and voltage of the means of improvement of arc enthalpy and cutting ability. If the increase in the enthalpy, reduce the diameter of the jet and increase the gas flow, often can get faster cutting speed and cutting quality is better.
4.Work gas and gas flow
Working gas include cutting gas and auxiliary gas, some equipment also requires arcs gas, usually according to the types of cutting material, thickness and cutting method to choose proper working gas.Cutting gas need ensure the formation of plasma jet, but also need ensure the removal of molten metal oxides and incision.A large gas flow will take more heat from the arc, making jet length becomes shorter, resulted in cutting capacity is decreased and arc instability; too small gas flow the plasma arc lost due to the straightness and the cutting depth shallow, but also easy to produce hang slag; so the gas flow must with cutting current and speed very good cooperation.Now most plasma arc cutter control the gas flow according the gas pressure,because when the gun body aperture when the gas pressure control will control flow.When we choose different gas pressure of different thickness metal usually according the parameters from manufacture.If there are other special application, the gas pressure need to be determined by the actual cutting test. The most commonly used working gas: argon, nitrogen, oxygen, air, H35, ar - N2 etc..
Argon
Argon is hardly any reaction of metal at high temperature, argon plasma arc is stable. And the use of nozzle with electrodes have higher service life. But the argon plasma arc voltage is low, the enthalpy value is not high, cutting ability is limited, and cut the air than the thickness of the cut about 25% lower. In addition, in argon, protect the environment, the surface tension of molten metal is larger, about 30% higher than that in nitrogen environment, so there'll be more hang slag problem. Even using the mixture of argon and other gases will be cutting slag sticking tendency. Therefore, it is rarely used alone in pure argon plasma cutting.
Hydrogen
Hydrogen is often used as auxiliary gas and other gas mixed functions, such as the famous gas H35 (the volume fraction of hydrogen is 35%, the rest of the argon) is one of the strongest gas plasma arc cutting, the main enrichment in hydrogen. Because the hydrogen can significantly improve the arc voltage, the hydrogen plasma jet has high enthalpy, when mixed with argon plasma jet, the cutting ability is greatly improved. General of metal materials with the thickness of more than 70mm, commonly used as argon + hydrogen gas cutting. If the use of water jet to further compress argon + hydrogen plasma arc, also can obtain higher cutting efficiency.
Nitrogen
Nitrogen is a kind of common work gas, under the conditions of higher voltage and nitrogen plasma arc has better stability and higher than the argon gas jet power, even if is cutting liquid metal viscosity materials such as stainless steel and nickel base alloy, incision of inferior hanging slag quantity are few. Nitrogen can be used alone, also can use with other gas mixture, such as automatic cutting often use air or nitrogen as the working gas, the gas has become the standard high speed cutting carbon steel gas. Sometimes nitrogen is also used as an oxygen plasma arc cutting of arc gas.
Oxygen
The oxygen can improve the low carbon steel material cutting speed. Use oxygen cutting, cutting mode and flame cutting is difficult to imagine, plasma arc of high temperature and high energy of the cutting speed faster, but must with the use of high temperature oxidation resistance of electrode, and the electrode for arc anti impact protection, to prolong the electrode life.
Air containing volume fraction of about 78% of the nitrogen, so use air cut formed by the hanging slag and nitrogen for cutting very imagine; air also contains a volume fraction of about 21% oxygen, because the existence of oxygen, air cutting speed of low carbon steel material is also very high; at the same time the air is the most economical working gas. But the single use of air cutting, will hang slag and incision oxidation, nitrogen, and the electrode and the nozzle of the lower life will also affect the work efficiency and cutting costs. Five, the nozzle height: refers to the nozzle surface and the cutting surface distance, it constitutes a part of the whole arc length. Due to the power supply of plasma arc cutting generally use constant current or steep drop characteristic, nozzle height increased, the change in current is very small, but will the arc length increased and resulted in the increase of arc voltage, so that the arc power increase, but also to expose in the environment of arc length growth, increased energy loss in the arc column. In the two factors of the case, the former is completely offset by the latter, but will make the cut of the effective energy decreases, and the cutting capacity decreased. The performance is often a cut of the jet blow force is abate, incision of the lower residual slag increased, the upper edge of the melt and appear a round. In addition, considering the shape of plasma jet, jet diameter is expanded outward from the gun in, increase the height of nozzle will inevitably cause incision width increase. Therefore, selecting the nozzle height as small as possible to improve the cutting speed and cutting quality is beneficial, but may cause double arc phenomenon of the nozzle at low altitude. The ceramic nozzle can be set to zero nozzle height, or nozzle end direct contact surface is cut, you can get a good effect.
5.Cutting power density
In order to obtain high shrinkage of plasma arc cutting arc, cutting nozzles have adopted the smaller nozzle aperture, longer channel length and strengthen the cooling effect, which can increase the effective section of the nozzle in the current, arc power density increases. But at the same time compression also makes the arc power loss increase. Therefore, the actual used to cut energy efficient to smaller than the power output of the power and the loss rate generally between 25% - 50%, some methods such as water constricted plasma arc cutting energy loss rate will be greater, and in the cutting process parameter design or cutting the cost of economic accounting should consider this issue.
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