Plasma Cut Holes are Beveled

[Retro]

Hi there,

i finally got everything working good enough to cut some parts. Today i wanted to try some stainless holes in 8 mm material. I already cut that raw stock and wanted to try 4 11mm mountingholes to save time on the drillpress.
I tried it with 950 mm/min and 60 Amp on my Kjellberg Plasma.

It cuts and i got nearly no dross which i'm happy with. BUT the bevel inside is awful. Could it be the consumables i'm working with or smth else?

Thats how the consumables look like after 8 Holes and (obviusly) 8 pierces. It got some black oxide type thing on them.

The Part:

[
Thats how my filter system looks like:

Two 0,05 and one 0,01 mm and after that again a 0,05 mm filter with water drain. No water in there. Got a water drain right behind the oil free compressor outside the building.

Can it be contaminated air? All new hoses and consumables. The Torch is true and square. It bevels all materials, not only stainless but this is a perfect example. From 2 mm to 10 mm steel, all beveled.
Any ideas?

[acourtjester]

The black stain on the consumables does look like contamination, but maybe not. You may check with another user of that cutter brand to see if its normal. On the beveling, If it is only on one side it could be torch alignment. If it fluctuates it could be an air flow problem. Member here have had "O" ring problems with Hypertherm torches, do not know the design of your torch. If you use a water table check the pattern of the air blast on the water surface, see if its directionable. You may need to lower the air pressure for a better look at that, it should be symmetrical.

[TJS]

For stainless I use Nitrogen. I don't use compressed air. This works for me however others have used compressed air for stainless and have had good results. Cut height also plays a role in bevel. Some bevel however is prevalent.
For holes I slow down 60% of book speed and lead in perpendicular and no lead out. Some overburn/overcut may be needed depending on the thickness.

[Retro]

The hole is not on one side beveled, its like diamenter top is 12 mm and the bottom 9 or so.

I don't know a single one who has the same machine like mine. I'm trying to change it to a Hypertherm in a short while.

I do use a watertable but the water level is somewhere 2 cm under the plate (3/4 of a inch roundabout).

And yes, nitrogen would be superior for stainless, but ignore the fact that its got a burned edge - nothing i worry about rn, the bevel is more important.

[djreiswig]

As TJS said, you need to cut holes at a slower speed than normal cuts to allow the arc to catch up with the torch. Do some sample cuts at different speeds to see what gives you the cleanest cut with the least bevel. I've tried down to 40% on some material.

[Retro]

Ok, i slowly beginning to see, why everyone is using a newer machine than mine. Mine is an 1989 Kjellberg GDR Machine with 3-phase power, 400 volt, 35 Amps and maximum 60 Amps output for 20 mm steel (not even 2 inch).
New machines get out of the half input amperage the same amount of output as mine. Time to look for a newer one. Is a Hypertherm 1100 for 1000 bucks woth it? I should get a Duramax Retrofit for the newer consumables...

Here are the results of nearly 2 hours of playing around and getting angry about my own machine.
Thats the best of 8 mm mild steel. All the others didn't even came out of the plate, because they melted together again.

Lots of dross everywhere and not even perfect straight edges. I changed the angles of the torch once again, but it the first two pictures are the best i can get out of it. I got the air up to 0,55 MPa (before 0,5 MPa), it helped a bit but the arc doesn't liked that very much.

I also replaced the very old hose to the plasma source with a brand new one.

[weldguy]

I would suspect air contamination judging by the carbon staining on your electrode and nozzle although with the description of your air supply system it sounds like it's all new so that baffles me but carbon staining is contaminates burning up. Was the plasma cutter previously used on another air system that may have contaminated your torch lead?

The bevel on one side is what I would suspect since the hole in your nozzle orifice is not longer round. The air should be swirling like a cyclone our of that nozzle hole but if its not round the cyclone is distorted and will blow off to one side and cause that. If you were to rotate that nozzle 180 degrees in the torch you would move your beveled edge to the other side of the hole.

Very curious about your air supply.

[Retro]

I start believing too that the machine torch is contaminated. I used the hand torch for a while and i can't remember the most of these problems. But how do i purge the lines? It's an water cooled torch btw.

[weldguy]

Ah yes, that could be the case. If it were me I would lay the torch and lead on the ground with the power source up higher and purge air through the torch for 5 minutes or so. Many plasma cutters have a purge option for setting the air pressure while air is flowing, this is ideal for this. Then reinstall the torch and just keep using it with clean dry air and it will improve over time.

[Retro]

As for the air supply:

I used to have an very old KAESER Compressor from the 1950s with 1500 l/min output. I "charged" the tank once a week and it held up for plasma cutting (it had a 750 Liter tank at 1 MPa). But it was too big. The compressor and the plasma used the same circuit. Both very high rated. So one had to move - it was the compressor obviously.
Now i got a very small silent compressor with a 10 Liter tank and 210 l/min output. Its enough for working with that plasma. It only uses 50l/min which is really low (but silent!).
It goes from the compressor into a water drain and from that to the hoses. Its one long hose around the shop and from that to the parts you saw on the top pictures. From those to another water drain and regulator (to 0,5 MPa) to the plasma.

[Retro]

Ah yes, that could be the case. If it were me I would lay the torch and lead on the ground with the power source up higher and purge air through the torch for 5 minutes or so. Many plasma cutters have a purge option for setting the air pressure while air is flowing, this is ideal for this. Then reinstall the torch and just keep using it with clean dry air and it will improve over time.

It wouldn't work with the torch only on more pressure on the airline? Its rated smth round 0,5 MPa. So more would maybe destroy it, right?
And yes, it got a purge switch.

[weldguy]

Ah yes, that could be the case. If it were me I would lay the torch and lead on the ground with the power source up higher and purge air through the torch for 5 minutes or so. Many plasma cutters have a purge option for setting the air pressure while air is flowing, this is ideal for this. Then reinstall the torch and just keep using it with clean dry air and it will improve over time.

It wouldn't work with the torch only on more pressure on the airline? Its rated smth round 0,5 MPa. So more would maybe destroy it, right?
And yes, it got a purge switch.

I wouldn't over pressurize it, just let it purge for 5 minutes or so but if your torch lead has low lying areas the moisture may not make it out so laying it flat on the floor and straight while purging would help. If thats too much trouble just purge it for 5 minutes and lift up any low lying torch lead to allow any moisture to move down the line then just use it and hopefully after a few hours of use your will see improvements.

[weldguy]

As for the air supply:

I used to have an very old KAESER Compressor from the 1950s with 1500 l/min output. I "charged" the tank once a week and it held up for plasma cutting (it had a 750 Liter tank at 1 MPa). But it was too big. The compressor and the plasma used the same circuit. Both very high rated. So one had to move - it was the compressor obviously.
Now i got a very small silent compressor with a 10 Liter tank and 210 l/min output. Its enough for working with that plasma. It only uses 50l/min which is really low (but silent!).
It goes from the compressor into a water drain and from that to the hoses. Its one long hose around the shop and from that to the parts you saw on the top pictures. From those to another water drain and regulator (to 0,5 MPa) to the plasma.

I see. Well what you have for filters in my opinion is not sufficient as they will remove most raw water and some particulate but nothing to eliminate humidity in the air. A good desiccant filter would do that for you. Also your compressor is very small so it will likely be making a lot of heat which end up producing more moisture in your air supply. I like the 3 stage filters like this one here https://www.plasmaspider.com/shop/dryer_sharpe6760.html

[Retro]

Its small, yes, but i only gets on every now and then. Not every 5 minutes. More likely 20 minutes or so. If it would get hot and cools down again, i would assume some drops of water in my water separator. But not a single one. In all 4 of them. Between the compressor and the plasma are 10 meters (30 feet smth like that). The compressor stands outside, its cold outside, under 10 °C.

[Retro]

Alright, i demounted it and let purge for 10 minutes. It pumped the air a little up and made a bigger hole in the nozzle to get everything out. I put a piece of paper in front of it to see if any water comes out. None. Ok so far.

Another test: Brand new consumables everywhere and then try to cut again. 5 Pierces later and 10 cm cutting path these look awful. Like worn out after a long time using them. The hole in the nozzle is also worn out. I'm getting somewhat exhausted by this cutter. The really cheap one with the extremly strong issues of bringing death to my controller board cut better. And it only cost smth round 800 bucks. This one here cost new over 3000. Maybe. I don't know, old german technology. The true creators of plasma cutting!

Look at these photos:

That were original consumables. One of the last ones i have. They are not longer available.

[acourtjester]

"I start believing too that the machine torch is contaminated" I would agree with that. A new clean air supply will not cure it, your consumables show that. If the torch is contaminated it may also affect the flow of the plasma stream adding to the bad cutting, and consumable death.

[Retro]

Is there any chance of "curing" the torch? If it had a seperate Airhose i could blow a cleaning pad trough it.

[weldguy]

I have never seen anything go that bad let alone that fast and not see obvious signs of air contamination. I am stumped.

[Retro]

Maybe smth goes wrong with that torch since its water cooled.

[Retro]

Alright, i got in touch with Kjellberg and they're very helpful since this machine is over 3 decades old. I can send the torch in and they check it since the HF-Ignition too makes some issues too.
I don't know the price for repairing it and i hope they can make it longer to fit into the cable chains to make it more tidy.

I'll keep you updated.

[adbuch]

Thanks for the update. Good luck!!
David

[weldguy]

I didn't realize it was a water cooled torch, that could certainly cause if a seal was leaking or something. Thanks for the update, hopefully they can fix you up. Let us now.

[Retro]

Yesterday i sent my torch to Kjellberg to check it. We will see what happens. They also attach a longer hose. I still don't now any price.

[Rodw]

I think aside from the contaminated air possibility, trying to cut an 11 mm hole in 8mm sheet is asking too much of most plasma cutters, let alone a 30 year old one! Bevellig is to be expected. Once you slow down to 60% as suggested, the dross will build up becaue you are no longer respectung the cut chart.
Sometimes you are better off spotting hole position and drilling. I have one part with 10mm, 11mm and 6mm holes and we need 200 a month. I've never considered plasma cutting them. Outsourcing to a laser cutter gives me tap ready holes (6.8mm diameter for 8mm tap). Plasma case hardens the edges so you can't really clean out the bevelled holes with a drill.

[adbuch]

I think this is great advise - spot and drill the holes, or laser cut as Rodw suggests.
David