Patent GB-516028-A (GB)
Title: Improvements relating to the manufacture of needles, small metal instruments and the like
IPC: B21G1/00
Filed: 1938-06-28
Abstract: 516,028. Heat-treating articles. EVERETT, S. J. June 28, 1938, Nos. 19140 and 21060. [Class 72] [Also in Group XXII] In the manufacture of metal articles such as knitting machine needles or sinkers, hypodermic, surgical or other needles, forceps, tweezers, tools or small metal instruments, aircraft propellers, structural parts of aircraft frames or wings or metal fishing rods, of the kind which are made from two or more parts and require one or more of the properties of high spring temper, strength, hardness or resistance to wear, two or more parts, one at least of which is of a work-hardened precipitation hardening alloy which hardens below 590‹C. are held in a jig. and hard soldered at a temperature-below 650‹C. and are then subjected to a heat treatment involving raising the temperature to a value not exceeding 590‹C. and then reducing from that value substantially without maintenance thereat. Two parts 1, 2 of a knitting machine needle, each consisting of an alloy of 63 per cent. nickel, 30 per cent. copper, 3.5 per cent. aluminium, 1.5 per cent. of iron and about 0.2 per cent. of carbon, as sold underneath Registered Trade Mark " K " Monel, and produced with work hardening, are placed together with solder wire 8, powder or strips in a jig of aluminium foil or of ironfoil coated with an antiflux such as graphite or chromicoxide, the foils having a melting point higher than the soldering temperature. The parts and foil are placed in a grooved metal block 3 having channels 5, 6 for the insertion of a rubber roller for folding the foil round the parts. The solder may have a melting point about 600‹C. Heating is now effected to 620-630‹C. to solder the parts. The parts are then heated to a temperature between 500‹C. and 590‹C. preferably at a rate of 100‹C. per hour. The temperature is not 'maintained at 590‹C. but is immediately reduced at about the same rate to 350‹C. Cooling is completed in the air. Heat treatment may be effected in a salt bath or in an electric furnace with forced draught. If the parts have been subjected to considerable cold working and soldering is effected at a low temperature, heating need not proceed to 590‹C. The metal jig may be replaced by a paste of 40 parts plaster of Paris and 60 parts brick dust or by moulding sand mixed with flour or by a moulded heat resistant cement or glass. An aluminium jig may be removed after use by treatment by caustic potash and an iron jig by treatment by hydrochloric acid, and the other kinds of jigs may be broken away after use. The jigs may be removed either prior to or subsequent to the heat treating operation. If one of the work parts consists of a nitrogen hardened or hardenable alloy such as a steel alloy containing 1.4-1.7 per cent. of chromium, 0.9 to 1.2 per cent. of aluminium and some molybdenum, and the other a work-hardened precipitation-hardened alloy, such as in joining latch parts and bearings or cam surfaces to a knitting machine needle body of " K " Monelmetal, the aluminium foil may be pressed over the bearing surfaces and into the rivet hole in the latch to prevent soldering of the latch to the rivet or bearings. If the latch parts have not been nitrided prior to assembly, this may be effected after completion of the article. In making propeller blades from a number of hollow drawn or stamped sections 9 of " K " Monel alloy the parts are soldered and heattreated on a stiffened steel frame covered with a sheet of aluminium. The parts are soldered and heat treated as previously described or the parts after soldering may be transferred at once to a furnace already at 590‹C.