... a steel tube, and then use high-frequency proximity effect and skin effect heating the tube side quickly to the welding temperature ... machines, steel butt cut, hopper, steel straightening, steel forming, high-frequency welding, to outer burr, cooling, pipe sizing, pipe straightening, cutting ... System of Forming 3.3 Seam Guide 3.4 High Frequency Induction Welding Machine 3.5 Roller System for Moving 3.6 ...