[Feckless]

Hi there,
How much dross is normal and how do you get rid of it ???
No matter what settings I use there is allways some dross on the underside of the parts and we use a chizle to remove it by hand, which is not fun, we use clean dry air on mild steel and I try to get the speed to a point where it just cuts the material by changing nozzle size, speed and amps. Is this the same for you or is there a solution, we don't have dual gas, hy-def. We use a TD151 with thc.
Interested to hear your stories.
Many Thanks,
Gordon

[Torchhead]

A totally dross free cut depends on so many factors that it's almost like the Holy Grail. If you cut anything but long straight lines or wide arcs the feedrate of the table will vary and produce dross. The type of material, precision of the tip gap (from the THC), air quality, consummables quality, direction of cut, current setting, quality of the workclamp connection and several other factors combine to limit/produce dross. Modern plasma torches do a better job that older ones but are not perfect. By the time you figure all of the perfect settings for a given type of material you will have your cut finished and it will change with the next piece.

Good cuts product low (small amounts of) dross on longer cuts That will fall off (mostly) if you drop the piece in a solid surface (old trick). We find that soaking steel in a weak HCL bath for several hours loosens most of the dross and makes cleaning easy and fast. It also removes mill scale. It won't remove oil or grease. If you use P&O steel then the acid bath is not needed and the scale should come off easily.

TOM CAUDLE
www.CandCNC.com

[jimcolt]

Their are plasma cutting processes that produce virtually no dross....such as high performance and high definition oxygen based plasma's. There also are techniques to eliminate....or at least minimize dross even with air plasma systems.

Dross is caused by:

1. Cutting too slow.....or cutting way too fast. In most cases their is a "dross free interval" in between too slow and too fast that produces little or no dross. Better process and torch designs have a wider dross free interval. Some torch designs have no dross free interval. I work for a plasma manufacturer....so I won't get too much into that argument on a public forum!
2. Damaged nozzle or shield. Many plasma users are not careful enough about pierce height and pierce delay times. Many of todays torch designs have the ability of providing for very long consumable life...it is not uncommon with an air plasma torch to achieve from 500 to 1500 pierces on one set of consumables. Just remember....one bad pierce can ruin a nozzle or a shield....they will still cut...but will produce dross and varying cut angles.
3. Improper torch height. Torch to work distance is critical to control dross and angularity.
4. Contaminated air. The air supply to the plasma must be clean, dry, and oil free. If you don't have devices between your compressor and your plasma that are designed to remove condensate and oil and particulates.....then you will at some time have contaminated air....especially during humid weather.
5. Correct consumables in your torch for the material and thickness you are cutting. A 60 Amp nozzle does not produce adequate energy density when operated at anything less than 60 Amps....and will produce dross. A 20 Amp nozzle will only last a few minutes if it is operated at over 20 Amps. A misture of an aftermarket nozzle with a genuine electrode do not usually work as well as all of the consumables produced by one manufacturer...stack up manufacturing tolerances will cause cut quality and parts life issues. Follow manufacturers specs for cutting each material type and thickness....these specs are in the manual for most major brand plasmas.
6. Air inlet pressure. Again follow the manufacturers specs....too high and the electrode will wear quickly and the torch may misfire, too low and the nozzle will wear quickly.

I could go on.....A good quality air plasma should be able to cut most materials almost dross free...assuming speed and height are correct and the consumable parts are in good shape.

Jim Colt