With several intrinsic benefits of plasma cutting technology playing in its favor to make it the first choice in metal cuttings, it will be pertinent to look at the ways one can reduce the production cost.
In metal cutting projects where air plasma cutting machines are used, the production cost can be greatly influenced by the judicious use of electrodes and the preventive maintenance/cleaning of the instrument, as explained below. But a brief about the basics of plasma cutting will be a good starting point for better understanding.
Plasma is an ionized gas that conducts electricity. This property makes it lethal when it comes to cutting of electrically conductive materials, both ferrous and non-ferrous. Plasma cutting is popularly used for cutting of steel, stainless steel, aluminum, brass, copper, and many other materials.
For industrial purposes, plasma is created by ionizing an electrically neutral gas by adding energy to it. In most cases, compressed air is used as gas and electricity for energy. The ionization process takes place inside a chamber that has an electrode on one side and a nozzle with an orifice on the other.
The air inside the chamber gets ionized by the electric arc sent through the electrode and force its way out through the nozzle, thus creating a constricted flow of plasma. The more electricity added via the electrode, the hotter the plasma arc becomes, to increase the cutting capacity and efficiency.
The components used in the formation of a plasma arc are the shield, retaining cap, electrode, nozzle, and the swirl ring.
Although all five parts are called consumables and needed to be changed from time to time, electrodes and nozzles demand more attention and are often replaced for higher cutting speed and better cut quality.
But studies show that the replacement of the consumables can be brought down by their proper uses coupled with the preventive maintenance of the entire system. Read on -
Electrode consumption or wear is usually very quick at the beginning and at the end of its life. In the middle portion, the wear is slow and predictable. Usually, there are fewer starts per electrode when longer cuts are performed. This tells us that the consumables will last longer if you have fewer starts.
In a plasma torch, the nozzle and electrode have different wear rates. There are factors like the torch design, power level, and technique of the operator that decide the wear rates. You can solve any problem in cut quality and efficiency by changing the individual consumable parts.
It is important that the copper body of the electrode remains shiny even when it has reached the end of its usual life - any heat discoloration caused by a cooling issue will turn it greyish. The extremely high operating temperature of the electrode makes its tip wear.
If you notice the pit to be off-centered in a used electrode, it means there could be a problem with the gas flow that may have occurred due to a wrong gas flow setting or a damaged or incorrect swirl ring. A deep electrode pit may indicate that the electrode is almost exhausted.
Sometimes, electrodes are blamed for the poor cut quality and are discarded by the operator when the problem may be due to other factors such as wrong gas pressure, cutting speed, etc
The life and wear of the nozzle can be more difficult to assess compared to the electrodes. The orifice of the nozzle and also the inside and outside must be checked thoroughly to assess the wear. The orifice bore should be perfectly round shaped on the outside and must not have any nick. The cut quality is affected by the shape of the orifice. The orifice of a new nozzle generally has a sharp round edge which eventually becomes smoothened.
By the same logic, the inner bore of the nozzle must also be perfectly round without any nick or heavy arc marks.
The orifice and the inner bore are the two areas that greatly influence the intensity of the plasma arc. Their shape and surface must be spot on. A few grey or white residue or some black or grey swirl marks in the bore are common and won’t affect the performance much.
Besides the consumables and maintenance factors, the performance of an advanced plasma cutting system can also vary significantly by other aspects such as the performance of the CNC machine, CAM software, height control, etc.
For example, blaming the plasma torch and changing electrodes may not always solve a cut quality issue. The problem may lie somewhere else. You need to inspect every part of your plasma cutting system to pinpoint the problem area.
Every component has to perform optimally and work in synergy to result in best cut speed, quality, and consumable’s life in order to bring down the production cost. The preventive maintenance of the entire plasma system is necessary following the guidance from the manufacturer for higher efficiency, longer life, and lower cost.
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