1" plate cut. pm65 or oxy-fuel for best cut?

[tnttracy]

i've got some 1" plate i need to cut and normally if its over 100" i just go straight to oxy-fuel to avoid hitting duty cycle on the pm65.

on this job i'm wanting the absolute best cut i can get, mostly thinking about the edge taper. i haven't been able to find much information on the subject.

so what do you all think? anybody have a chart for taper? and if plasma is the best i know it will change as the consumable wears, so at what point do i change it out? i would think before the normal 1/16 pit in the electrode, maybe half that?

thanks for any help!

[jimcolt]

First, if you have to do any piercing, the Powermax65 is not recommended for piercing over 5/8". Piercing 1" with the 65 will destroy nozzles and shields rapidly. 8 inches per minute will be the cut speed, assuming you edge start (no damage to nozzle/shield) then expect about a 1 to 2 degree taper with the 65. Duty cycle may /may not be an issue on a 100" cut on 1" plate....it depends on the ambient air temp (duty cycle is based on 104 degrees F) as well as input line voltage (better duty cycle if running on higher input voltage or 3 phase). You might get through 100" of continuous cut, then again you may not!

Oxy-fuel, if set up correctly (correct tip, correct gas pressure, correct height, correct speed) will cut 1" steel at about 12 ipm, can pierce it (about 7 to 10 seconds) and will cut with less than 1 degree of taper. There will be a much larger heat affected zone and a rougher cut edge, but nice cuts.

The issue often with oxy-fuel is that it requires expertise from the operator, while Plasma can be set at book specs (Hypertherm anyway!) and expect it to cut as advertised.

If I had both processes and I could cut the part without having to pierce (drill a hole or edge start) then I would use the Powermax65. If piercing was necessary or I needed a slightly straighter edge, then I would use the oxy-fuel.

Normally we at Hypertherm would specify at least a 125 amp air plasma or a 200 amp (or 260 or 300 0r 400 if you really want nice 1" cuts at 60 ipm!) for cutting 1" steel on a production basis. You are asking a lot of a 65 amp plasma!

Jim Colt Hypertherm

[tnttracy]

thanks jim

when plasma cutting would having water touch the underside of the plate help the edge taper any? the haz? the horrible taper on corners? maybe even putting an 1/8" round would help over hard 90degree turns.

it seems counter intuitive that the plasma would have less haz in this case seeing that it travels slower but i assume thats because its heat of burning is instant. just out of curiosity say 4' into a straight cut at that point would oxy-fuel have a smaller haz or is plasma always going to be smaller, despite the lack of amperage?

i went ahead with the job, i did it with the pm65. i was lazy and didn't want to change over to oxy-fuel, plus figured i'd push the pm65 to see how far it will go. i edge started and connected the the parts to make it one continuous cut about 210" and it come out great. i let it cool down before moving on the the next cuts but was supprised the internal fan kicked down in just a few minutes, maybe i'll push it further next time. i cant damage it right? it will just shut itself down? wish i could get the corners better. would love a bigger machine but thats not a priority currently.

[tnttracy]

the cut...

[Gamelord]

Impressive cut.....more impressive is that it did exactly what Jim said it would.

[tnttracy]

thanks jim

when plasma cutting would having water touch the underside of the plate help the edge taper any? the haz? the horrible taper on corners? maybe even putting an 1/8" round would help over hard 90degree turns.

it seems counter intuitive that the plasma would have less haz in this case seeing that it travels slower but i assume thats because its heat of burning is instant. just out of curiosity say 4' into a straight cut at that point would oxy-fuel have a smaller haz or is plasma always going to be smaller, despite the lack of amperage?

JIm, or any body have any insight or answers???

[jimcolt]

Water contacting the material can lessen the heat affected zone, but can cause hydrogen embrittlement of the cut edge and more dross. Taper with water in contact usually is worse.

Mt experiences with HAZ between plasma and oxy-fuel is when you are using a productive power level on the plasma....for 1" we recommend using an oxygen plasma of 200 amps or as high as 400 amps. More power, squarer edges, less corner washout, faster speeds (which produce a smaller HAZ).

Even at 65 amps though...the heat affected zone is smaller with plasma. If you watch 1" being cut with oxy-fuel....you will see a red glow for a while after the cut is done....not with plasma. I do not know the exact reason.

On the cuts shown....I would have looped the corners for mech better quality. Jim Colt Hypertherm

[KIDTech]

http://plasmaspider.com/viewtopic.php?f ... 39#p119239

That's my post on cutting 1.125.