Plasma cutting machine is vastly applied in automobile, locomotive, pressure vessel, chemical, engineering and ship machinery, nuclear industries.
Plasma cutting using various working gases can cut metals, which are difficult to cut with various types of oxygen, particularly when cutting non-ferrous metals (stainless steel, aluminum, copper, titanium, nickel). Its key advantage is to cut thinner metals. When the plasma cutting speed is high, particularly while processing regular slim carbon steel sheet, the speed may be 5-6 times more compared with the method of oxygen cutting, the cutting face is smooth, thermal deformation is little, the zone is less susceptible to heat.
At present, the plasma cutting machine for working gas (the working gas is a conducting medium of the plasma arch, it is also a coolant and removes molten metal in the gaps) has an evident influence on the features of the plasma arch, the outcome of cutting and processing velocity. Mostly applied plasma arch working gases are argon, hydrogen, nitrogen, oxygen, air, water vapor, and some mixture gases.
Various parameters of plasma cut process directly influence the stability, quality and efficiency of cutting process. Key cutting characteristics are described below in brief:
1. Open circuit voltage and column arch voltage
The plasma cut power supply should have a suitable high open-circuit voltage to inflame the arch easily and ensure continuous burning of the plasma arch. The open circuit voltage is usually 120-600 V, the arch voltage in the column is usually half the open circuit voltage. An increase in the arch voltage of the column considerably increases the power of the plasma arch, thus making the cutting velocity rise and ability to cut a thicker metal sheet. The arch voltage in the column can be gained through adjusting gas flow rate and increasing the electrode shrinkage, but the column arch voltage may not surpass 65% of the open circuit voltage, or else it causes plasma arch inconstancy.
2. Cutting electric current.
An increase in the cutting electric current may cause the plasma arch power to rise as well, and it is controlled through the utmost acceptable electric current, or else, the plasma column arch gets thicker, the slot breadth gets enlarged and the electrode service life reduces.
3. Gas stream.
Gas stream rate increase may cause the column arch voltage to rise and enlarge the column arch pressure, making plasma arch energy more concentrated and the ejecting strength stronger, which improves velocity and cutting performance. Yet, in case of high gas stream rates, the arch column becomes short, more heat gets lost making cutting ability weaker unless the cutting process is accomplished properly.
4. Electrode contraction.
Contraction relates to the space between electrode and the cutting nozzle end. At the proper distance, the arch gets proper pressure in the cutting nozzle and gets plasma arch with fortified energy and high temperature for efficient cutting. In case of extremely large or extremely short distances, the electrode burns too much, the cutting nozzle burns and the cutting capability gets reduced. Contraction is usually 8-11 mm.
5. Nozzle height
Cutting nozzle height depends on the space between the cutting nozzle end and the work piece face. The space is usually within 4 ~ 10 mm. The distance is the same as that of the electrode shrink, since the electrode must be suitable for fully utilizing cutting productivity of plasma arch, or else the cutting effectiveness and performance gets reduced, or the cutting nozzle gets burned.
6. Cutting speed
The previously mentioned factors have a direct influence on the plasma arch compression, as well as influence the plasma arch heat degree and energy concentration, and the great heat and energy of the plasma arch define cut velocity, so all the mentioned factors are connected with cutting speed. According to the premise of ensuring cutting quality, the cutting speed gets maximized. This not only increases efficiency, but reduces the degree of deformation of the cut pieces and the area of thermal influence of the slotted part. In case of improper cutting speed, the effect is reversed, and the adhering slag increases, and the cut performance is reduced.
7. Plasma cutting has a groove that can only be reduced, but not excepted.
Specific classification is the following:
1) Non-upright fracture surface due to cutting factors such as damage to consumables, too much or less air pressure, cutting velocity, etc., problems with the plasma power source are also possible.
2) The straight line of the cut is not direct, the guide in the corresponding course is not straight, this is also the main reason, and there may also be a change in the position of the cut during the cut based on a particular situation.
In addition to the general shape, the plasma cutting method is also obtained from water-compression plasma cutting. The most common methods are conventional plasma and air plasma cutting.
1) General cutting: conventional plasma cutting makes no use of shielded gas, working and cutting
gases get emitted out of the same nozzle. At the time the arch is triggered, the ion gas of a small stream is released as an ionization medium; a large gas flow is concurrently ejected to take away molten metal during cutting.
2) Air cutting. Air plasma cutting typically makes use of compressed air as the ion gas. This method is notable for low
price reduction and a proper source of gas. Compressed air is heated, decomposed and ionized in an electrode arch, as a result of which, oxygen cuts the metal, causing a chemical exothermic reaction that accelerates the cutting. Completely ionized air plasma possesses a high thermal enthalpy, so the arch energy and cutting speed are high.