The principle of operation of most plasmatrons with power from several kW to several megawatts is almost the same.
An electric arc is burning between the cathode, made of a refractory material, and the intensively cooled anode. Through this arc, the working fluid (PT) is blown through - a plasma-forming gas, which can be air, water vapor, or anything else. The ionization of RT occurs, and as a result, at the output, we obtain the fourth aggregate state of a substance, called plasma.
In high-power devices along the nozzle an emagnet magnet coil is placed, it serves to stabilize the plasma flow along the axis and reduce the anode wear.
This article describes the second construction, because The first attempt to obtain a stable plasma was not crowned with particular success. Having studied the device "Alplaza", we came to the conclusion that perhaps it is not worth repeating it alone. If anyone is interested, everything is very well described in the instructions attached to it.
Our first model did not have active anode cooling. Water vapor from a specially constructed electric steam generator was used as a working medium — a pressurized boiler with two titanium plates immersed in water and connected to a 220V network. The cathode of the plasmatron was a tungsten electrode with a diameter of 2 mm which quickly burned. The hole diameter of the anode nozzle was 1.2 mm, and it was constantly clogged. It was not possible to obtain a stable plasma, but there were still glimpses, and this stimulated the continuation of the experiments.
In this plasma generator, as a working medium, a steam-water mixture and air were tested. The output of the plasma turned out to be more intense with water vapor, but for stable operation it is necessary to overheat to a temperature of more than one hundred degrees so that it does not condense on the cooled plasmatron nodes. Such a heater has not yet been made, so the experiments so far continue only with air.
Photos of plasmatron viscera:
The anode is made of copper, the diameter of the nozzle opening is 1.8 to 2 mm. The anode block is made of bronze, and consists of two hermetically welded parts, between which there is a cavity for pumping coolant - water or antifreeze.
The cathode is a slightly pointed tungsten rod with a diameter of 4 mm, obtained from the welding electrode. It is additionally cooled by the flow of the working fluid supplied under pressure from 0.5 to 1.5 atm.
Here is a fully disassembled plasmatron:
Power is supplied to the anode through the tubes of the cooling system, and to the cathode through a wire attached to its holder.
Run, i.e. ignition of the arc is made by twisting the cathode supply handle until it contacts the anode. Then the cathode must immediately be moved to a distance of 2..4 mm from the anode (a couple of turns of the knob), and between them the arc continues to burn.
Power supply, connection of air supply hoses from the compressor and the cooling system - in the following diagram:
As a ballast resistor, you can use any suitable electric heater with a capacity of from 3 to 5 kW, for example, pick up several boilers connected in parallel.
The rectifier choke should be rated for current up to 20 A, our specimen contains about a hundred turns of thick copper wire.
Diodes fit any, designed for a current of 50 A and above, and a voltage of 500 V.
THIS DEVICE USES
BESTRANSFORMER POWER FROM THE NETWORK!
The air compressor for supplying the working fluid is taken automobile, and for pumping coolant through a closed loop, an automobile window washer is used. Power is supplied to them from a separate 12-volt transformer with a rectifier.
A little about future plans:
As practice has shown, this design also turned out to be experimental. At last stable work within 5 - 10 minutes is received. But to complete perfection is still far away.
Replaceable anodes gradually burn out, and it is difficult to make them out of copper, and even with thread, it would be better without threading. The cooling system does not have direct fluid contact with the replaceable anode, and because of this, heat transfer leaves much to be desired. A better option would be direct cooling.
Details are machined from the semi-finished products on hand, the design as a whole is too complex to be repeated.
It is also necessary to find a powerful isolation transformer, without it it is dangerous to use a plasma torch.
And under completion still pictures of the plasmatron when cutting wire and steel plates. Sparks fly almost a meter.