High frequency current welding of metal strip to a metal part

#This invention relates to the welding of a metal part to a thin, flexible metal strip, and particularly, to the welding of a metal tube to a relatively thin and flexible metal strip or sheet, using high frequency electrical welding techniques.

#The welding together of metal parts using high frequency electric currents, i.e. a frequency of 50 kHz or higher, is well known in the art. See, for example, U.S. Pat. Nos. 2,821,619 and 3,319,040 and other patents assigned to the assignee of this application. In the high frequency welding methods, the parts are moved longitudinally and continuously, at relatively high speed and in separated relation, toward a weld point, at which they are pressed together, and in advance of the weld point, they are engaged by contacts which supply high frequency electric current thereto, the magnitude and frequency of the current being such that the surface portions to be joined reach welding temperature during the time that they move from the contacts to the weld point. When the parts have different thermal masses or conductivities, such as by reason of different dimensions or materials, problems are encountered in bringing both the surface portions of the parts to be welded together to the desired welding temperature at the time they are welded together. See, for example, U.S. Pat. Nos. 3,359,402 3,513,284, and 3,541,296. However, when one of the parts is a thin, flexible strip or sheet, additional problems are encountered in obtaining a uniform weld between the strip or sheet and the other part.

#The co-pending application of Wallace C. Rudd, Ser. No. 790,335, filed Apr. 25, 1977, entitled "Method of Manufacturing Heat Exchange Panels" and assigned to the assignee of this application, discloses methods and apparatus for using said high frequency electrical welding methods in the manufacture of heat exchange panels having metal strips with metal tubing welded thereto. Such methods and apparatus are entirely satisfactory when the metal tubing and the metal strip have similar thermal masses and the strip is thick enough to permit close control of the path followed by the strip between the contact engaging it and the weld point. However, when the strip is relatively thin, e.g. having a thickness in the range from 0.005-0.025 inch, problems are encountered in obtaining a uniform weld not only because it may have a thermal mass and conductivity which is low compared to the tubing, but also because undulations or variations in the path followed by the strip from the contact which engages it to the weld point cause non-uniform heating to the strip. As is known in the art, variations in the spacing between the current carrying parts as they approach the weld point cause variations in the heating of the parts because the current concentration is dependent on proximity effect which, in turn, is dependent on the spacing between the current carrying parts and the frequency of the current.

#Other objects and advantages of the present invention will be apparent from the following detailed description of the presently preferred embodiments thereof, which description should be considered in conjunction with the accompanying drawings in which:

#FIG. 1 is a side elevation view of preferred embodiment of the invention for welding a tube to a strip;

#FIG. 2 is an end elevation view, partly in cross-section, of the embodiment shown in FIG. 1 and is taken along the line 2--2 indicated in FIG. 1;

#In the embodiment illustrated in FIGS. 1-3, a thin, flexible metal strip 1, e.g. a strip of copper or aluminum, and a metal tube 2, e.g. a copper or aluminum tube, are pulled by apparatus well known to those skilled in the art in the direction of the arrows 3 and 4 indicated in FIG. 1. The tube 2 may have various diameters but generally speaking for solar heating exchangers will have an outside diameter of approximately one inch or less. The strip 1 with which the invention is concerned will be relatively thin, i.e. a thickness of from 0.005 to 0.025 inch and normally will have a width several times the diameter of tube 2, for example, a width from 4 to 18 inches.

#The strip 1 passes around a rotatable roll 5 which has an axis of rotation which is generally parallel to the upper and lower faces of the strip 1. Such roll 5 in combination with a rotatable roll 7, which has a peripheral groove 8 which embraces approximately half of the periphery tube 2, press the tube 2 and the strip 1 together at a weld point W. It is preferable that the rolls 5 and 7 be freely rotatable or "idler" rolls and it is desirable that the roll 5 not be a driving roll to avoid wrinkling or movement of the sheet 1 with respect to the surface of the roll 5 intermediate the contact 10 and the weld point W.

#In the preferred embodiment of the invention, the tube 2 is advanced toward the weld point W in a substantially straight line, but it may be advanced toward the weld point along a curved line. It is, however, important for current concentration purposes that the angle 9 between the lower surface of the tube 2 and the upper surface of the strip 1 as they approach the weld point be very small.