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Will the plasma surface cleaner produce corona discharge and spark discharge:
The plasma surface cleaning machine is composed of a vacuum (low pressure) plasma surface cleaning machine and an atmospheric (atmospheric pressure) plasma surface cleaning machine; corona machine and spark machine discharge are two states of gas discharge, and there are essential differences between the two, the applicable scenes and Different objects are processed.
The corona of the plasma surface cleaner, also called unipolar discharge, occurs in the high-voltage field area near the gas end, edge or coil. It is located in the electrical pressure state before the electrical breakdown point; it is electrical discharge Typical phenomenon. Assuming that the corona current is large, the corona is a visible glow discharge. When the current is small, the entire corona will become darker. The results include electrostatic discharge, which is the electrostatic form of corona; brush discharge, which is luminous discharge in an uneven electric field. DC corona, that is, corona discharge under the action of an electrostatic field, is generated when the air pressure is high (above 1 standard atmosphere) and the electric field distribution is extremely uneven. The inhomogeneity of the electromagnetic field is caused by the extremely small radius of curvature of the surface of one or two electrodes. The electrode structure can be for the needle, facing the plate, metal wire to the coaxial cylinder, two parallel metal wires, etc. In short, at least one of the electrode surfaces has a small radius of curvature.
The corona discharge is self-discharge. The plasma surface cleaner does not need any catalyzer, and the discharge current is generally 10-6~10-3A. The corona layer is a kind of corona layer characterized by strong spatial ionization and excitation when the electric field is unevenly distributed and the electrode surface is close to a strong electric field. At a standard atmospheric pressure of corona discharge, the breakdown electric field is about 3MV per meter or 30KV per centimeter (KV). If the local electric field at the needle tip or filament is greater than the breakdown electric field, a corona will be generated around the end protrusion. In the corona initiating electrode, there is only a small radius of curvature, the so-called unipolar corona. The unipolar corona has a positive corona and a negative corona, which is determined by the polarity of the corona initiating electrode. The discharge mechanism of the positive and negative corona is different, and the space charge distribution is beneficial to the positive corona, so the breakdown voltage of the negative corona is higher than that of the positive corona.
When the two electrodes are both electrodes with a small radius of curvature, a bipolar corona is formed. The positive corona and the negative corona exist at the same time, and the current through the outer zone is bidirectional and consists of positive and negative charged particles. Under the same conditions, the onset voltage of bipolar corona is lower than that of unipolar corona. The corona discharge mechanism is different from the plasma surface cleaner.
The plasma surface cleaner also has spark discharge and corona discharge under higher pressure (Pd greater than 1500mmHg.mm); however, the difference between spark discharge and corona discharge is that its electric field is uniform, and the power of the power source is not too high. In large cases, the transition from Tangsheng discharge to spark discharge. Spark discharge is also a kind of self-sustained discharge. Under atmospheric pressure, the ignition voltage of spark discharge is equal to the ignition voltage, also known as spark potential. When other conditions remain unchanged, spark discharge determines the distance between electrodes. This method is somewhat similar to adjusting the electrode distance of a plasma surface cleaner.
After the discharge is started, strong ionization occurs between the electrodes, and the temperature between the electrodes is very high (thermal ionization can occur), so the resistance between the electrodes is small, the conductivity is high, and a large current flows. A large voltage drop is generated on the resistor, and the voltage drop distributed between the poles is reduced, which is not enough to maintain the existence of spark discharge. The spark will be extinguished after a short time. After the spark is extinguished, the voltage between the poles will rise again and the discharge will restart. Therefore, the shape of the spark discharge is a bunch of shiny and curved filaments, which quickly pass through the discharge interval, and then quickly extinguish, alternately one after another.
The larger the inter-electrode capacitance of the discharge gap, the longer the charging time and the lower the discharge frequency; the discharge duration is only 10-8~10-6s, after which it may be converted to arc discharge. When the capacitor poles are connected in parallel, the amplitude of the pulse current can be increased, and each discharge cycle can be prolonged, but the discharge frequency will be reduced.
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