Process and apparatus for producing finned tubing

Claim 1

A PROCESS FOR APPLYING A HELICAL FIN TO THE EXTERIOR OF A TUBE, WHICH COMPRISES THE STEPS OF APPLYING ROLLING STRESS TO THE OPPOSITE SIDES OF LONGITUDINALLY EXTENDING AREAS OF A THIN STRIP OF METAL SO AS TO ADVANCE THE STRIP THEREBETWEEN AND DIFFERENTIALLY THIN THE STRIP ALONG SUCH LONGITUDINALLY EXTENDING AREAS IN A DIRECTION FROM ITS INNER TO ITS OUTER EDGE AND THEREBY FORM IT INTO A HELICAL FIN AS IT IS SO ADVANCED, PROVIDING NO MORE THAN RELATIVELY SMALL SUPPORT FOR AN INTERMEDIATE AREA OF THE STRIP BETWEEN SAID LONGITUDINALLY EXTENDING AREAS SO THAT IT IS RELATIVELY UNTHINNED AND CAUSED TO PART AT A SERIES OF LOCATIONS ALONG ITS LENGTH AS SAID LONGITUDINALLY EXTENDING AREAS ARE THINNED, AND ROTATING THE TUBE AND SIMULTANEOUSLY MOVING THE TUBE AND STRIP RELATIVE TO ONE ANOTHER ALOONG THE AXIS OF THE TUBE SO THAT THE HELICAL STRIP MAY BE GUIDED ABOUT THE TUBE.