High frequency in-line, electrical welding apparatus for small diameter metal tubing

Claim 1

Apparatus for welding together at a weld point the edges of a thin metal strip formed substantially into a small diameter tube with said edges extending longitudinally of the tube, said apparatus comprising means for longitudinally advancing said tube toward said weld point, a pair of downstream electrical contacts engageable with said tube and disposed adjacent said weld point, one of said pair of contacts being engageable with said tube at one of said edges thereof and the other of said pair of contacts being engageable with said tube at the other of said edges thereof, a pair of upstream electrical contacts engageable with said tube and spaced from said downstream pair of contacts by a distance sufficient to permit said edges to reach welding temperature as they reach said weld point, one of said upstream pair of contacts being engageable with said tube at one of said edges thereof and the other of said second pair of contacts being engageable with said tube at the other of said edges thereof, a source of electrical current of a frequency of at least 50 kilohertz, means connecting one terminal of said source to both of said upstream contacts, means connecting the other terminal of said source to both of said downstream contacts, said last-mentioned means including a proximity conductor extending from adjacent said upstream contacts to said downstream contacts in closely spaced relation to the path of both said edges as they are advanced from said upstream contacts to said downstream contacts, each contact of said upstream and said downstream contacts being independently movable toward and away from, and being urged toward, said tube, one contact of said pair of downstream contacts being movable along a path which extends substantially parallel to a first plane parallel to and intersecting the longitudinal axis of said tube and the other contact of said pair of downstream contacts being movable along a path which extends substantially parallel to a second plane parallel to and intersecting the longitudinal axis of said tube but which extends at an acute angle to said first plane and one contact of said pair of upstream contacts being movable along a path which extends substantially parallel to a third plane parallel to and intersecting the longitudinal axis of said tube and the other contact of said pair of upstream contacts being movable along a path which extends substantially parallel to a fourth plane parallel to and intersecting the longitudinal axis of said tube but which extends at an acute angle to said third plane, and means for controlling the positions of said edges relative to each other and to said proximity conductor comprising downstream guiding means adjacent said downstream contacts and at said weld point and upstream guiding means spaced from said downstream guiding means in the direction opposite to the direction of advance of said tube by a distance no greater than the distance between said upstream contacts and said weld point, each of said guiding means having a surface engageable with said tube for maintaining said edges in opposed relation and both said surface of said upstream guiding means and said surface of said downstream guiding means being shaped, in cross-section, to maintain said tube with a non-circular cross-section as it is advanced from said upstream guiding means to said downstream guiding means.