Process for uniting sleeve members by brazing

Claim 1

A process for uniting an assembly of a sleeve member and a tube, wherein the sleeve member is snugly inserted in the tube, with the outer surface of said sleeve member confronting and engaging the overlying surface of said tube, comprising: interposing a brazing member intermediate said confronting surfaces, then inserting in the bore of said sleeve at the location where the brazing is to occur an electrical resistance heating unit comprising an insulating, refractory, generally cylindrical elongate boron nitride mandrel that is formed with a lengthwise-extending bore and with enlarged diameter shoulder means at each of its ends respectively, and formed with helical recesses in its surface intermediate said shoulder means, a bare platinum-rhodium alloy wire disposed in said helical recesses and wound in the form of a generally helical coil having groups of windings in which the adjacent windings within each group of windings are substantially uniformly spaced from each other and said groups of windings are also spaced from each other lengthwise of said mandrel for providing electrical resistance heating, a pair of bare electrical lead members operatively connected to opposite ends of said wire respectively and electrically insulated from each other by interposed parts of said mandrel, one of said lead members being disposed in and extending through said bore, each of said shoulder means being formed with an aperture for the passage therethrough of one of said lead members, respectively, and each of said lead members extending through one of said apertures respectively, for electrical connection to the opposite ends of said wire, respectively, and then energizing said unit to heat the assembly to a temperature of at least 1000° C. to accomplish brazing.