Arc Voltage and Material Thickness

[Stout]

Using the cut chart from my PM1250 and T80M, the cut distance is always the same for all sizes of nozzles:1/16". Why is the arc voltage for a 40 amp nozzle cutting 10 gauge 146 volts and 134 volts for a 60 amp nozzle? The cut quality of the 40 amp value, 146 volts, is quite poor. Is the cut chart incorrect or could my Micro Edge controller be setup incorrectly in regards to reading the arc voltage from the voltage divider to set cut height? The 40 amp value that produces a much better cut is 134 volts on this machine.

The torch does seem to be much higher off of the plate at the 146 volt setting. I could stop a cut and get a measurement to check the cut height.

From the cut chart for 1/4" mild steel:
80 amp 134 volts
60 amp 138 volts
40 amp 149 volts
These are all supposed to keep a 1/16" torch to work distance?

As a side note, the Micro Edge cut chart for a T80M torch does not have a 40 amp option so I am forced to use the T100M torch in the setup. The values are the same for the two torches as I have checked the user manual. Just letting you know.

[jimcolt]

The arc voltages listed in Hypertherm's cut charts are based on laboratory testing in actual cut conditions. The voltages are intended as a starting point ....and it is expected that the operator will adjust the voltage (once the rest of the cut parameters are set) so the the cut height of the torch matches the physical cut height (.062" or 1/16") required in the manual. Since arc voltage relies on a lot of variables....it can vary quite a bit from the book suggested values from system to system, and from cutting job to cutting job. Here are a few things that affect the voltage / height relationship:

- Cut speed....if you go faster at a given voltage...the torch will get further away from the plate, slower will be closer.
- Air pressure, air flow, air purity will affect height.
-condition of the table slates...dirty slats will make the torch run closer to the plate.
-condition of the consumables....nozzle wear and electrode wear will make the torch run closer. It is normal to have to increase arc voltage through the life of a set of consumables

Hope this helps.



Jim Colt Hypertherm

Originally Posted by Stout Using the cut chart from my PM1250 and T80M, the cut distance is always the same for all sizes of nozzles:1/16". Why is the arc voltage for a 40 amp nozzle cutting 10 gauge 146 volts and 134 volts for a 60 amp nozzle? The cut quality of the 40 amp value, 146 volts, is quite poor. Is the cut chart incorrect or could my Micro Edge controller be setup incorrectly in regards to reading the arc voltage from the voltage divider to set cut height? The 40 amp value that produces a much better cut is 134 volts on this machine. The torch does seem to be much higher off of the plate at the 146 volt setting. I could stop a cut and get a measurement to check the cut height. From the cut chart for 1/4" mild steel: 80 amp 134 volts 60 amp 138 volts 40 amp 149 volts These are all supposed to keep a 1/16" torch to work distance? As a side note, the Micro Edge cut chart for a T80M torch does not have a 40 amp option so I am forced to use the T100M torch in the setup. The values are the same for the two torches as I have checked the user manual. Just letting you know.

[Stout]

My question is more in regards to if the speed is the same for the three nozzles listed below and the air is the same, why would the arc voltage be different to maintain the 1/16" working distance? The arc voltage varies by the distance between the cathode and the anode. Not by the material or the current. Correct?

So if all parameters are equal for each nozzle, except of course for the material being cut, then they should all have the the arc voltage. I'd think.

[jimcolt]

The arc voltage is based on the resistance of the arc....which is created by the diameter and length of the arc. At higher amperage the arc is larger in diameter.....and when you cut thicker material...the arc is longer as it's "anode feet" attach to the materials from top to bottom. Further.....when you slow the cut speed....the arc gets longer (if the torch is at a fized height) as the arc must reach further to connect to the anode (material being cut)... The arc resistance (and voltage) will also change if gas pressure changes....or if moisture or particulates are in the gas....or if a different type of gas is used.

Jim Colt Hypertherm

Originally Posted by Stout My question is more in regards to if the speed is the same for the three nozzles listed below and the air is the same, why would the arc voltage be different to maintain the 1/16" working distance? The arc voltage varies by the distance between the cathode and the anode. Not by the material or the current. Correct? So if all parameters are equal for each nozzle, except of course for the material being cut, then they should all have the the arc voltage. I'd think.