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Author Topic: Physical buttons for plasma  (Read 87703 times)

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Offline Davek0974

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Re: Physical buttons for plasma
« Reply #390 on: November 20, 2016, 03:41:45 PM »
Ok, good the THC is off, one less thing.

Pilot arc is still HF but the arc is inside the torch and not from torch to metal. It won't be the issue though i think as all it might do is cause PC or motion problems and you don't have that it seems.

From the ESAB site...

Double Arc

A double arc is a condition which allows the nozzle to stay in the plasma circuit. As described, the nozzle should only be in the circuit during the pilot arc phase. If left in the circuit, the nozzle will carry cutting amperage which will destroy it.

Double arcing is caused by:

Standing pierce. The torch has to be positioned close enough to the work-piece to allow the pilot arc to contact the plate, so the main arc can transfer. Pierce spatter is ejected at a shallow angle during the initial pierce. As the arc penetrates the material the spatter becomes more vertical. This debris may connect the plate and nozzle, keeping the nozzle in the circuit even when the relay opens to remove it. This scenario may damage the front end of the torch.
Torch in contact with the plate. Cutting thin material. All automatic torch positioning systems utilize some initial height sensing method to position the torch above the plate. One method is the touch and retract method. The torch travels until it makes contact with the plate and retracts to the initial start height utilizing a timer or encoder. If the touch is not sensed properly, the torch may still be in contact with the material due to springing up or material warping. The nozzle will remain in the plasma circuit carrying cutting amperage, damaging it.

Pilot arc malfunction. This can occur if the pilot arc relay circuit fails to remove the nozzle. This can happen either with a shorted relay or resistor. Again the nozzle is left to carry more current than intended, damaging it.

Preventing the Double Arc

Double arcing usually occurs during the piercing sequence.

Some techniques which can help avoid double arcing are:

Creep move. The cutting machine is programmed at a reduced speed to begin machine movement on arc transfer. This speed is usually 5 to 10% of normal cutting speed and is for a given time period. Pierce spatter is being ejected away from the nozzle during this time. This reduces double arcing possibility.

Torch rising during standing pierce. On arc transfer the torch begins to pull away from the work- piece. This allows the pierce spatter to clear the nozzle. This retraction continues for a timed period, and then lowers to correct cutting height after the machine is moving at cutting speed.

Higher than normal initial height pierce (standing pierce). This allows the pierce spatter to miss the nozzle reducing the chances for a double arc. This method of prevention is the least effective.




So....
if you manually trigger an arc in free air, you should only see a low power pilot arc, not the full cutting arc, does your unit have current display? As there is no metal to complete the circuit, the unit should not switch to full power arc, just the pilot, if not  then maybe a dodgy pilot arc relay etc. You probably won't see this when manually cutting.

I would definitely not exceed the rated power for a nozzle/electrode, in fact my 45A unit cuts best at 43A, go figure :)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Physical buttons for plasma
« Reply #391 on: November 20, 2016, 04:36:42 PM »
Dave, nope no display, I think there may be a relay that clicks in then out again when the current is sensed but not sure, will have to listen for that.
The THC shows the Arc Ok only when the current flows with the main arc so that is fine.

Yes, saw that Esab info and there is also a Hypertherm description and that is what started me thinking it may be double arcing.

Did a vid of what happens, also put a good cut at the end of the vid for comparison , exactly same settings and code, one fine the other not.

https://youtu.be/jPcpDsdRcAQ

Offline Davek0974

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Re: Physical buttons for plasma
« Reply #392 on: November 20, 2016, 04:52:52 PM »
does look like double arc or failing to switch to full arc maybe.

if you have a clamp ammeter stick it round the work return cable, thats where my current sensor sits, see if it registers full current when messing around.

Even when working right, it can (and does) blow a nozzle sometimes, for no reason it seems, not usually as bad as yours - that is really destroyed. Mine tends to slightly blow out one side - it still cuts but has uneven angularity to the cut. Other times I can go for ages on one set of consumables.

Are you 100% certain there is no water in the air - put a bit of polished metal or a mirror under the nozzle and trigger the air flow for a minute or so, any muck will show up.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Physical buttons for plasma
« Reply #393 on: November 20, 2016, 05:21:22 PM »
Did an air test a while back but will do it again. Just used a bit of paper and let the air flow for a while, dry as a bone and no dirty marks, well except my fingerprints :D

Offline Hood

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Re: Physical buttons for plasma
« Reply #394 on: November 20, 2016, 05:22:50 PM »
Oh and I think it does switch to full arc as it always comes on strong then on the times it fails the arc goes all spread out and soft before it then comes back strong again.

Offline Davek0974

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Re: Physical buttons for plasma
« Reply #395 on: November 21, 2016, 02:14:49 AM »
Very odd, is there no help from TecArc?

Is there a support group? I can't see one on PlasmaSpider although i would certainly ask over there.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Physical buttons for plasma
« Reply #396 on: November 21, 2016, 03:02:48 AM »
Haven't contacted TecArc as yet, not 100% sure where the problem lies as it has only been a short time I have had it running.
I did find something interesting though in the early hours,  Jim Colt saying you get that all the time with Alu and that is what I have mostly been testing with because that is what I have most of.
He said that is why Hypertherm use shielded nozzles on their torches as it is almost impossible to get double arcing. So that now gives me something else to try out. The hand torch has a drag tip so in other words it is shielded. I can try that out on my machine torch and see how it performs, if it is ok I may get a spare drag tip and just remove the castellations  to give me the clearance required for machine cutting, think they are 1-2mm deep.
That may also explain why I have never seen this with the hand torch.

Offline Davek0974

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Re: Physical buttons for plasma
« Reply #397 on: November 21, 2016, 05:06:45 AM »
Jim is 99% right all the time, good guy.

Yes alu is a bitch, I hate the stuff on the plasma.

Cutting the castellations off a drag tip is what i did on the little 30XP unit as it has no machine torch - it works, try it.

HyperT recommend never cutting Alu on the 30A parts as they are not shielded either, i only use these for fine detail on stainless 1.2mm sheet.

Sounds like your on the way hopefully (did i say get a hypertherm ?? ) :)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Hood

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Re: Physical buttons for plasma
« Reply #398 on: November 21, 2016, 06:32:35 AM »
Well that is not the problem, put the long consumables in the machine torch with the drag tip and still the same.
Currently making up an adapter plate to hold the hand torch and will try that. If there is still a problem then the only thing I can think of is the machine or the something to do with the divider card wiring.

Offline Davek0974

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Re: Physical buttons for plasma
« Reply #399 on: November 21, 2016, 06:37:56 AM »
Thats not good.

Surely the divider card is only active/important when the THC is on?? Or does that send the ArcOk signal too? Still it should not affect the double arc issue.

Have you tried manual cutting with the drag tip again - it may be a problem in the plasma box??
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives