How to stop dross buildup under torch as it cuts?

[AustinT]

Hi

I am using a self Made CNC plasma machine with a lincoln procutt 55 plasma cutter. Usually I cut 14 gauge with the smaller .028 nozzle. I am also using a THC. My problem is metal builds up between the torch and the workpiece as it cuts. If the torch is changing directions often then it does not matter as the pieces are wiped away or fall down the cut. When I am doing a long cut in one direction or big circles the dross builds up so bad that the torch will drag. What could be causing this?

[Torchhead]

Your getting dross on the TOP side with 14ga? WOW! What the heck does the back side look like!!? Either you are cutting at the wrong arc gap, using the wrong consumables or the air pressure is too low. What are the cut parameters you are using?

Current setting
Target Volts (Preset) on the THC
Feedrate
Air pressure

You have the workclamp on the material?
Is the THC holding a constant cut gap?

TOM caudle
www.CandCNC.com

[AustinT]

Thanks for the Reply Torchhead

I am cutting at 25 amps with the small .028 nozzle
The pressure is 75 psi and the feedrate is 52 ipm
I have tried a few THC settings , around 84 works great.


I need to explain better. The top of the plate looks great and the bottom dross usually pops off just by dropping it on the ground. The acid bath takes care of the rest. What is happening is a little round bead of molten metal starts to build between the tip and the workpiece. If the machine is cutting a file that changes directions alot then the bead just wipes off. If I am cutting a long straight line or a circle , then the bead grows until sometimes it can push the torch off of the intended path. I have been using a sharp stick to push the bead out before it gets too big. What has me stumped is it will happen when the machine travels one direction but not the other. I checked my torch and it is perpendicular to the table. Could water in the air line form the bead?

[Bigrhamr]

Do you have a cut chart for that Lincoln? I'm not familiar with it but 52 IPM sounds awfully slow for 14 gauge. By comparision my PMX 45 with 30 amp consumables has an optimum speed of about 120 IPM on 14 gauge.

[Alan Bradford]

Hi,
Is your Loncln a hand torch? Or are you using a hand cutting nozzle?
I do not know much about Lincoln, but the Hypertherm hand plasma nozzles have a flat notch cutout across the face of the nozzle.
(And the main Lincoln torch designer, if he is still there, used to work at Hypertherm!!!)
This is so that when you touch the nozzle to the plate the arc will not go out. It has a place for the Arg/Gasses to escape.
When you use this type of nozzle in a mechanized application, the edges of the notch will plug up with the slag from cutting.
Try a mechanized nozzle. It has a flat front face, as the THC prevents it from touching the plate.
Once again Im not sure if Lincoiln has diffrent types of nozzles , but this may be the problem.

It is also OK to spray the nozzle with Anti-Spatter Spray. This helps a bit.
Spray across the nozzle not straight up. The AS Spray will kill the electrode really, really, fast.

One other thing, are your nozzles lasting as long as they should/did?
A stuck Pilot Arc relay will cause more build up, slower cutting speeds and shorter nozzle life.

Good Luck,

[AustinT]

I dont have the chart for the feedrate but around 50 ipm works nice . I have bumped it up to 75 ipm but the dross is alot harder to remove from the back of the metal.

I am using a lincoln machine torch with the flat nozzle . I dont think lincoln has a nozzle with a groove ( or at least I have never noticed this option when ordering consumables ). I have been using anti spatter dip ,the kind you dip a mig nozzle in. Occasionally when the torch lifts up between cuts I rub some on the face of the nozzle with a foam painting brush. As for electrode life I can cut for around 3 hours before changing. The electrode always wears out first with a big pit or hole.
One thing , How important is it to have dry air? I always drain the compressor but there is still alot of water in the lines.

Thank You

[Alan Bradford]

Clean & Dry air is very imporntant.
I am not an Air expert, but any moisture in the air can reduce the electrode life. Oil in the air will rapidly kill an electrode.
I have never heard that water will cause top (or bottom) dross.
(Jim Colt are you out there!!!)
I always reccomend that your air be clean enough to spray paint with.
You can always find an automotive spray paint store, and they can help you get the right filters and seperators.

As for 3 hours of electrode life. Is that Elapsed Time or Arc On Time?
If you change the electrode every 3 hours while cutting, then the water in the air may be a problem.
If you change the electrode every 3 hours of Arc On Time then I would say your air is good.

Is your THC really working?
84 sounds a bit low. (Although as stated earlier I dont know much about the Big Red Stuff.)
Have you tried to raise the arc voltage to increase the torch to work distance?
Maybe you are too close to the plate and a little more space would help eliminate the problem.
Raising the Arc Voltagetoo high will start to round the top edge of the plate.
Too close and the cut angle starts to go negitive (Bottom wider than the top.)

Good Luck

[jimcolt]

Assuming that the consumables are in good shape (nozzle orifice perfectly round, no nicks, no cratering, inspect with a magnifier) then you are simply cutting way too slow.

You may want to increase current to 30 Amps, and increase cut speed to 100 ipm. Then, if there is still dross do a few test cuts while increasing the speed 10 ipm or so each time. The dross will be minimal somewhere between 100 and 150. The height should be almost dragging on the plate assuming you are using drag (hand cutting) consumables.

If you have any sign of moisture in the air...this will have a dramatic effect as well. Moisture changes the physics inside the torch, and will cause almost instant consumable damage that will cause cut quality issues.

Jim Colt Hypertherm

[AustinT]

Sounds like the first thing I need to do is clean the air up. The three hours I spoke of is the electrode life for the total elapsed time. The THC is working great and 84 puts me between a 1/16 and 1/8 of the plate as I cut. I will try and take a video of what is happening. Another clue is it only happens when the torch is traveling in a certain direction. If I cut one direction in a line I get buildup but if I cut the other direction It is clean. I know when its going to happen because sparks will come off the front of the plate as it cuts. If I cut the other direction there are no sparks.