The mechanism of formation of top and bottom dross during plasma cutting were studied and a theory was developed for the case of top dross which agrees well with experiment. Techniques were developed, involving secondary gas flows around the plasma jet and a rotating brush following the plasma jet, which very greatly reduced top-dross formation. Similarly the use of jets under the cut was shown to reduce under-dross to negligible proportions. Thus, by using these techniques, the quality of plasma cutting can be greatly improved and the speed greatly increased without the formation of excessive top dross. Tests done with thin gage stainless steel were successful and are described in detail.

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