Method of manufacturing heat exchange panels

A method for making a heat exchange panel comprising a plurality of sub-panels each comprising a finite length of a metal tube secured by welding to metal sheet material except at opposite end portions thereof which are small relative to said finite length, said method comprising continuously advancing both metal tubing and a metal sheet in separated relation to a weld point, said sheet having a face which is narrow relative to its length and which is wider than the thickness of said sheet, pressing said tubing and said face of said metal sheet together at said weld point and continuously removing said tubing and said metal sheet from said weld point, said tubing and said metal sheet having corresponding longitudinally continuous lengths at least several times said finite length of said tubing, supplying high frequency current to said tubing and said metal sheet upstream of said weld point to cause the facing surfaces thereof to reach welding temperature by the time that they reach the weld point thereby forming a longitudinally continuous weld between said tubing and said metal sheet during the time that said high frequency current is supplied to said tubing and said metal sheet, interrupting the supply of high frequency current to said tubing and said metal sheet each time that a length of said tubing substantially equal to but less than said finite length passes said weld point so that a portion of said tubing which is small in length relative to said finite length is not welded to said metal sheet, whereby there is provided a unit of a length several times said finite length and which comprises said tubing welded to said metal sheet along most of the length of the tubing but with weld interruptions spaced apart a distance substantially equal to said finite length, severing said unit at each weld interruption and intermediate the ends of said portion of said tubing to provide several of said sub-panels each having tubing thereon of said finite length welded to said metal sheet except at the end portions of said last-mentioned tubing, and assembling a plurality of said sub-panels in side-by-side relation to form said heat exchange panel.