How does a plasma cutter work?
Plasma is a gas heated to a very high temperature and highly ionisted, it will be transferred to the arc power to the workpiece, high heat make the workpiece melts and blows off, forming the working state of plasma arc cutting, by the high-speed plasma momentum to exclude molten metal to form a process method of incision. Below to popularize the basic principles of plasma cutting machine.
Plasma cutting with different working gases can cut a variety of oxygen cutting difficult-to-cut metals, especially for non-ferrous metals (stainless steel, aluminum, copper, titanium, nickel) cutting effect is better; The speed can reach 5 to 6 times the oxygen cutting, the cutting surface is clean, the heat deformation is small, almost no heat impact area! Plasma cutting machines are widely used in automobiles, locomotives, pressure vessels, chemical machinery, nuclear industry, general machinery, engineering machinery, steel structures and other industries.
How it works?
1. After the compressed air enters the torch, two roads are distributed by the air chamber, i.e. the plasma gas and the auxiliary gas are formed. The plasma gas arc acts as a molten metal, while the auxiliary gas cools the components of the torch and blows out the molten metal.
2.Cutting power supply includes the main circuit and control circuit two parts, electrical principle: the main circuit includes contactor, high leakage resistance three-phase power transformer, three-phase bridge rectifier, high frequency arc coil and protection elements. The out-of-power feature seifrom the high leakage resistance to the steep. The control circuit completes the entire cutting process by a button switch on the torch: pre-ventilation-main circuit-power-supply-high-frequency arc-cutting-arc-stop.
3. The power supply of the main circuit is controlled by the contactor, the shortness of the gas is controlled by the solenoid valve, and the high-frequency oscillator is controlled by the control circuit to ignite the arc and stop the high frequency after the arc is established.
Plasma arc cutting process parameters
Various plasma arc cutting process parameters directly affect the stability of the cutting process, cutting quality and effect. The main cutting specifications are summarized below:
1. Empty voltage and arc column voltage. Plasma cutting power supply, must have a high enough empty load voltage, in order to easily lead the arc and make the plasma arc burning steadily. The empty voltage is generally 120-600V, while the arc column voltage is generally half the empty load voltage. Increasing the arc column voltage can significantly increase the power of the plasma arc, thus increasing the cutting speed and cutting a larger thickness of the metal sheet. Arc column voltage is often not reached by regulating the gas flow and increasing the shrinkage of the electrode, but the arc column voltage cannot exceed 65% of the empty load voltage, otherwise the plasma arc will be unstable.
2. Cutting current. Increasing the cutting current also increases the power of the plasma arc, but it is limited by the maximum allowable current, otherwise it will make the plasma arc column thicker, the width of the cut, and the electrode life decrease.
3.Gas flow. Increasing the gas-based flow can not only increase the arc column voltage, but also enhance the compression of the arc column, so that the plasma arc energy is more concentrated, the injection force is stronger, so that the cutting speed and quality can be improved. However, the gas flow is too large, but will make the arc column shorter, the loss of heat increased, so that the cutting capacity is weakened, until the cutting process can not be carried out normally.
4. In-electrode shrinkage. The so-called internal shrinkage refers to the distance from the electrode to the end face of the nozzle, the appropriate distance can make the arc in the cut mouth to get a good compression, to obtain energy concentration, high temperature of the plasma arc and effective cutting. Too large or too small distance, will cause the electrode serious burn, cut the mouth burned and reduce the cutting capacity. The indentation is generally 8-11mm.
5. Cut nozzle height. The height of the cut is the distance from the end face of the cut to the surface of the cut workpiece. The distance is generally 4 to 10mm. It is the same as the shrinkage of the electrode, the distance should be appropriate in order to give full play to the cutting efficiency of the plasma arc, otherwise it will reduce the cutting efficiency and cutting quality or make the cut mouth burned.
6. Cutting speed. The above factors directly affect the compression effect of the plasma arc, that is, affect the temperature and energy density of the plasma arc, and the high temperature and high energy of the plasma arc determine the cutting speed, so the above factors are related to the cutting speed. Under the premise of ensuring the quality of cutting, the cutting speed should be increased as much as possible. This not only increases productivity, but also reduces the amount of deformation of the cut part and the thermal impact area of the cut area. If the cutting speed is not suitable, the effect is reversed, and will increase the slag, the cutting quality is reduced.
