Induction welding of tubes

Claim 1

IN AN APPARATUS FOR WELDING A LONGITUDINAL OPEN SEAM IN A TUBULAR SHAPE OF WELDABLE METAL IN WHICH THE TUBULAR SHAPE IS PROGRESSIVELY ADVANCED THROUGH A WELDING ZONE WHERE THE EDGE PORTIONS OF THE SEAM ARE HEATED BY AN INDUCED ELECTRIC CURRENT OF HIGH FREQUENCY TO WELDING TEMPERATURE AND THE HEATED EDGES ARE FORCED TOGETHER BY PRESSURE ROLLS TO EFFECT A WELD, THE IMPROVEMENT WHICH COMPRISES AN INDUCTION COIL POSITIONED AROUND THE TUBULAR SHAPE AND ADAPTED TO INDUCE IN THE TUBULAR SHAPE A CIRCUMFERENTIALLY FLOWING ELECTRIC CURRENT, A PERMEABLE MAGNETIC MEMBER POSITIONED INSIDE AND AS CLOSE AS PRACTICABLE TO THE TUBULAR SHAPE AND WITHIN THE INFLUENCE OF THE MAGNETIC FIELD ESTABLISHED BY SAID INDUCTION COIL, SAID PERMEABLE MAGNETIC MEMBER DIRECTLY UNDERLYING THE OPEN SEAM AND A PORTION OF THE WELD, AND A SEAM GUIDE EXTENDING INTO SAID OPEN SEAM AND ADAPTED TO MAINTAIN A SEAM WIDTH OF AT LEAST ONE-FOURTH INCH AT A DISTANCE WITHIN THE RANGE OF 4 TO 7 INCHES IN ADVANCE OF SAID WELDING ZONE AND THEREBY PREVENTING THE TUBULAR SHAPE ACTING AS A SHIELD AROUND THE MAGNETIC MEMBER WHEREBY THE MAGNETIC MEMBER EFFECTIVELY SERVES TO INCREASE THE CURRENT FLOW IN THE TUBULAR SHAPE AND THE SPEED OF WELDING BY LOWERING THE IMPEDANCE OF THE COMBINATION OF INDUCTION COIL AND TUBULAR SHAPE.