Thread: Questions

Hi DD,
I will have a crack at it for you.

Perhaps if we could start with a bit of physics first to help form the mental picture.Its a bit different to straight out welding but its probably as straight forward as I can make it.

If you started with a block of ice and heated it, you get water.

Heat the water and you get steam. Heat the steam and you get superheated steam.

Now think about a block of steel. Heat it to a red heat say 918 degrees and introduce a jet of pure oxygen and it will oxidise.

Heat steel to 3,126 DEGREES (from memory) AND IT WILL MELT. Heat the steel to 60,000 degrees (hotter than the sun I am told) and it vaporises.

It takes a plasma to reach this temperature and it operates by jumping a small (in volume ) but high intensity arc from across a tungsten anvil to a nozzle cap with a tiny hole in it.Assisted by a high velocity jet of gas or compressed air it will vaporise the metal in its path.

The difference between oxy acetylene and plasma is that the oxy acetylene cut oxidises the heated metal, while the plasma heat it so intensely and quickly that it is mostly vaporised.
something to be very conscious of is the vapours released by the plasma process ,Stainless ,nickel and chromium carying metal,among others can be toxic. Be very aware before you cut and wear a respirator !
Yes you can cut down to a line and without distortion as the heat zone is very narrow and the travel speed is much higher than oxy.
Plasma can suffer from poor quality air supply which will cut out the tiny orifice in the cap and deteriorates the performance.
As far as a compressor is concerned that is usually another purchase. Some of the newer ones may have an inbuilt compressor. Look for a plasma unit that is filtered properly.A compressor could compress water and oil that will also pass plate scale and rust flakes through the plasma cap and erode / degrade the small orifice. The speed through the orifice is very high and I understand that is what does the damage.

Thats about as close as I can get it off the top of my head.

Grahame

I agree with Grahame for all of the above.

Have a little to add to the compressor though. I have used a small inverter plasma with a 12 cfm compressor and had a lot of trouble keeping the air pressure up. I had to stop and let the compressor catch up. I feel that maybe a 16+ cfm machine would have been better.

Robert.

Thanks Blokes for that info, I have a 16cfm compressor, any air tools that I use with it and I have a few gets connected to the water trap first followed by a lubricator. Of course I wont be using the lubricator with the Plasma cutter, I have one of those face mask respirator with changeable filters for different applications, would that do the job Graeme if I purchase the right filter for it.

D D

Hi,
I can't give you a definitive answer on that but I'd have to say that the filter type depends on the micron size of the heavy metal fume.

You might tell you filter supplier what you are plasma cutting and leave it to them to recommend the filter type and ( micron ) size.

Grahame