Plasma cutter setup

[kelvin2164]

Hi All
I have a large 240v plasma cutter, which, when new, cut 4mm steel like a hacksaw cut, with very little slag under the cut. I can no longer get that quality cut and the tips need replacing very often. Like about one metre of cut and replace the tip. The copper part seems to gouge out on the inside where it is against the stainless part.
I dont understand the principle. I imagine air must pass between these 2 parts and out the nozzle. Are they supposed to be in firm contact, as I can rotate the copper part by hand when all tightened up.
Please explain what I should be doing.
Pics enclosed. Forgive the quality. I dont know why they call it auto focus, when it doesn't.

 

[dennisa49]

Good day Kelvin,
It has been a while since I used a plasma.
The electrode and the nozzle should be both clean with an uninterrupted
air flow. Both hardware parts are consumables.
Be sure the electrode is screwing home in the hand piece and not shorting to the
nozzle.
The air must be dry, use two driers - one out of the compressor, one at the plasma inlet.
A paper filter at the plasma end offers the most consistent results.
My machine was a 240V said to be cappable of cutting 8 mm plate.
The 8 was really a stretch and mostly related to manufacturer's dreams.
It may also be the level of power you are asking the machine to deliver.
I hope this info is of use.
Regards,
Dennis

 

[Cogsy]

I've got some experience with plasma cutters, mostly CNC and up to about 25mm cut capacity. From memory (it's been a while for me as well) chewing through tips like that is normally the result of wet air, as Dennis says. You need a proper air dryer, not just the inline sediment traps that most people use. We had one machine start playing up like this even when the dryer was replaced and it was eventually tracked to a 'dip' in the fixed airline which had built up a reservoir of water over time. Once supplied with properly dry air it ran perfectly well again.

Dennis - the machine manufacturers normally quote the largest figure their machine will do, but there are 3 cut metrics used. One is maximum clean cut depth (the smallest figure and the one that you are really interested in) then maximum possible cut depth (higher figure but not a nice cut and is virtually impossible to attain) and the third figure, which is most often quoted or advertised is maximum penetration depth, which is the maximum thickness that you could pierce, eventually, but can't sustain a cut at this thickness. From memory one of our machines had something like 25mm max pierce, 18mm maximum cut and 12mm clean cut. The larger 3 phase machines that were actually capable of 25mm cuts were advertised with full disclosure of all 3 of the cut/pierce depths.

 

[kelvin2164]

A couple more pics. I bought a packet of inner stainless tips, and you can see from that pic that it doesnt screw down flush. All of them do this and I have none of the old ones to compare. I imagine an arc must be generated somewhere to produce the heat and wondered if the gap between the stainless part and the copper part is critical.
My unit has an inline paper cartridge dryer. Very old and probably past its use by date. I hear it is possible to dry them out in the oven?

 

[dennisa49]

Hello Kelvin,
I did have a similar issue with the electrodes.
It look as though you have the female thread on the electrode.
Check that the electrode is seating properly.
It could be as simple as the electrode may after market that not quite 100% suitable. See below ref the air gap.
You may find that the internal thread requires chasing.
Either buy a bottoming tap to suit the thread or use a grade 8.8 bolt
with a groove cut in it to chase the thread.
Then the electrode should then seat home.

Definitely replace the filter element or change the set up.
Some filters use dunny rolls as the filter medium.

There must be an air gap between the electrode and the nozzle.
Search for plasma cutting operations on the net the info should help.
The electrode uses the air to generate plasma which cuts the material. It will cut all metals, unlike oxy/acetylene.
Aluminium, copper, brass, steel etc.
Regards, Dennis

 

[kelvin2164]

Hi Dennis
I think that the problem is with the electrode not seating and being too close to the cap, as the cap gouges out on the inside (see fuzzy pic). Cant find anything on the internet that states a clearance figure. I'm still working on it.

 

[dennisa49]

Hello Kelvin,
I am not sure that you will find a gap setting.
The electrode normally seats at the correct depth and the nozzle should
match that. Damage to the nozzle would indicate that the plasma
is not being generated in the right spot.

If you know who the manufacturer is it could be worthwhile contacting
them and ask about the part numbers and seating info.

What make is it? A depending on the age it could be either Asian or European.

The search info was related to the plasma function of the machine.
Let me know the make, I would be happy to chase it up.
Regards
Denni s

 

[kelvin2164]

It's a Weldmac 40. I bought it about 10 years ago. I spoke to BOC (not much help, but a little) and I now recall that there may have been a spacer under the nozzle, to keep it at the correct distance from the electrode. I seem to have lost that. I bought it from Queensland Welding Supplies. Might go back there with my bits, see if they can help.

 

[rodw]

If you still have the manual or you can identify the torch make and model, you should have an exploded view of the cutting head that will identify the parts. The plasma cutters I have had have a ceramic spacer....

PS, I'm in Brisbane too!

 

[dennisa49]

Kelvin, I have posted a PM
regards Dennis