Heading 8515 covers electric welding, cutting, and surface-treating machines and apparatus. Heading 8468 covers the non-electric counterparts—gas-operated torches, gas welding machines, and other non-electric soldering or brazing equipment. If the apparatus uses an electric arc, resistance, or plasma as its energy source, it belongs under 8515; if it relies on combustion of gas or another non-electric heat source, it belongs here.

Yes. Gas-operated surface tempering machines and appliances are explicitly included in the heading's scope, even though their primary function is heat treatment rather than joining. They are classified under 846880 (other non-gas, non-8515 machinery) or 846820 depending on their operating principle, and their parts fall under 846890.