Why a Perfect cut on Galanised Sheet?

[Normsthename]

I have had my homemade CNC Plasma up and running now for well over a year, and it has really earned its keep
Yesterday I got a job to cut a fireplace Plate out for someone.
It consisted of a 800mm x 250mm plate with 3 rectangle cutouts, and 3 round holes.
The material was 1.5mm Galvanised steel sheet supplied by the customer.
I was a little worried beforehand about how the plasma would cut the material, But it cut it absolutely superb!
There are absolutely no dross or even a burr and it looked like it had been cut on a Laser!
When I cut mild steel normally, it cuts OK but there is sometimes (usually) an easily removed dross that I have to remove.
Why did the Galvanised material cut so nicely?
I would love to get it to cut normal mild steel as nicely, I am really puzzled......

Andy

[jimcolt]

The dross does not adhere as easily on the galvanized zinc coating. However, by dialing in your speed and torch to work distance you can achieve the same cut on mild steel. 99% of the time people tend to cut gauge steel too slow.....and when it produces dross or warps they tend to go even slower! The dross free zone (dfz, a speed range that produces little or no dross, usually near the max penetration speed for a given thickness and process power level). Often...speeds to achieve dfz are above the speed capability of the cnc machine. For cutting thin gauge with plasma you should have a machine with acceleration in the 60 miligee range or higher, and the ability to cut at speeds in the 150 to 350 ipm range while maintaining torch to work distance. Plasma can cut very nicely on these materials....but needs excellent motion control to do so! Hypertherm introduced FineCut consumables a few years ago for some of its air plasma systems...these consumables are designed with higher energy density at lower power levels...allowing extremely good cut quality on materials thinner than 3/16"....at reasonable speeds.

Be careful with the fumes when cutting galvanized!

Jim Colt

[Normsthename]

Thanks Jim
I was using finecut consumables on a Hypertherm Powermax 1000

Be careful with the fumes when cutting galvanized!

I have an extractor running and I was aware of the nasty fumes produced by the galvanised coating.
Many years ago I used to weld Zintec material and that could make you very poorly if you breathed in the fumes too much....

Andy