Arc OK Signal & Expanded Metal Mode

[beefy]

I have a Hypertherm 1250 and may have a need to use "expanded metal mode", depending on the answer to this question.

I have a situation where for just a fraction of a second when the torch is switched on, it is over a small hole. In normal mode this causes a lost arc condition as soon as the torch fires, SO can I get around this by switching to "expanded metal mode".

My main question is: when in "expanded metal mode" does the 1250 give an "arc OK" signal as soon as the torch fires, whether the torch is over air (and hence only a pilot arc in the nozzle), or whether it's cutting the metal. Or the question re-phrased, when in expanded metal mode and the torch is switched on does the 1250 give out an arc OK signal for the duration the torch is on.

After this intial void (the small hole) it's solid metal all the way to the end of the cut. Does the 1250 operate any differently when in expanded metal mode, and is there any reasons why the cut or the nozzles could suffer. Remember the torch will only be over a void for a fraction of a second at the start of a cut.

Cheers,

Keith

[jimcolt]

The Arc Transferred output (also known as "arc ok") is a contact closure that occurs when current flow is detected on the work ground clamp. If the torch fires in the air...this contact will not close, if it fires in close proximity to the material being cut, the contact will close almost immediately (a few milliseconds) In expanded metal mode if you are cutting expanded metal....the arc transfer contact will open when you are over voids, and will close when on metal. You will also hear the arc power (amperage) ramping up when on metal and down to pilot arc current when over voids.

On expanded metal the nozzle will wear maybe twice as fast as on solid metal. On solid metal when in expanded metal cutting mode the nozzle will wear approximately 25% faster than in normal cut mode.....this is due to a small amount of leakage current to the nozzl that adds heat.

Jim Colt Hypertherm

I have a Hypertherm 1250 and may have a need to use "expanded metal mode", depending on the answer to this question.

I have a situation where for just a fraction of a second when the torch is switched on, it is over a small hole. In normal mode this causes a lost arc condition as soon as the torch fires, SO can I get around this by switching to "expanded metal mode".

My main question is: when in "expanded metal mode" does the 1250 give an "arc OK" signal as soon as the torch fires, whether the torch is over air (and hence only a pilot arc in the nozzle), or whether it's cutting the metal. Or the question re-phrased, when in expanded metal mode and the torch is switched on does the 1250 give out an arc OK signal for the duration the torch is on.

After this intial void (the small hole) it's solid metal all the way to the end of the cut. Does the 1250 operate any differently when in expanded metal mode, and is there any reasons why the cut or the nozzles could suffer. Remember the torch will only be over a void for a fraction of a second at the start of a cut.

Cheers,

Keith

[beefy]

Thanks very much Jim,

that answered my questions exactly.

Can't get that sort of support with a Chinese plasma cutter

Keith.

[beefy]

Actually Jim, another question has popped into my head.

When the torch first switched on and was over the void, there was still a blue "flame" coming from the torch. I'm guessing this is the initial pilot arc and is on for a certain time (attempting to find solid metal so to speak) before the torch switches off.

If this is the case do you know how long this pilot arc stays on after the torch is switched on.

Cheers,

Keith.

[jimcolt]

If you are in normal cutting mode the pilot arc will stay on for about 2 to 3 seconds ( I do not remember the exact timing), if in expanded metal mode it will stay on until the consumables melt. As soon as the arc finds metal the pilot extinguishes, the air flow and amperage ramps up and the arc is in transferred arc mode.

Pilot arc mode wears the nozzle orifice very rapidly....so it it recommended to keep the pilot arc time to a minimum.

Jim

Actually Jim, another question has popped into my head.

When the torch first switched on and was over the void, there was still a blue "flame" coming from the torch. I'm guessing this is the initial pilot arc and is on for a certain time (attempting to find solid metal so to speak) before the torch switches off.

If this is the case do you know how long this pilot arc stays on after the torch is switched on.

Cheers,

Keith.

[beefy]

Fantastic Jim, thanks so much.

Armed with the nitty gritty info you have given me I've worked out a solution to my problem, and it won't need expanded metal mode.

Cheers,

Keith.

[muzza]

Another one I've had to use Keith is just to hold a scrap of light gauge just covering the edge of the hole and as soon as the torch moves off the scrap and the height control brings the torch back down that little bit. PITA for lots of starts but easy fix for the odd hole or recut situation.
Murray

[beefy]

Thanks Murray,

I'll have to try that sometime, could have used that a few times in the past. I think I'm absolutely useless at thinking of simple solutions

It won't help me with what I'm playing with now, but it will be great for when something goes wrong at a pierce point and I have to start again.

Keith.