Patent GB-1245274-A (GB)
Title: Method and apparatus for brazing
Inventor: MILLER HARRY EDMOND
IPC: B23K1/012
Filed: 1968-10-22
Abstract: 1,245,274. Combustion control apparatus. PYRONICS Inc. 22 Oct., 1968, No. 50120/68. Heading F4B. [Also in Division B3] In brazing a workpiece hot gas is projected to cause turbulence of the gas about the workpiece with scrubbing on all sides, the temperature of the gas being close to the melting temperature of a brazing alloy provided on the workpiece to bring the workpiece to a uniform temperature just below the said melting temperature and then hot gas at a higher temperature is projected to melt the brazing alloy. A heat exchanger assembly 10 comprising U-shaped tubes 12 of copper, aluminium or steel extending through galvanized steel tube sheets 13 with aluminium fins 14 between the tube sheets and return bends 16 on the free ends of the tubes 12 with rings of brazing material e.g. copper zinc or copper-phosphorus alloy for joining the bends 16 to the tubes 12 is arranged on a work-holder 21 movable by wheels 26 on tracks 27 by a pneumatic motor 28 to carry the assembly into the mouth 22 of a brazing box 23. Burners 35 at the top of the box 23 burn a mixture of gas and air from a gas line 45 and a line 48 supplied with air from a blower 51, the gas being ignited by a pilot 53. The flames 55 provide streams 58 of high temperature flue gas in a laminar flow pattern in a chamber 34 and excess fuel gas is provided to give a reducing flue gas at about 3000‹ F. The temperature of this gas is reduced before applying it to the work by mixing it with cool flue gas derived from a diverted and cooled portion of the high temperature gas or preferably from a separate source. The separate source is a burner 83 where mixed gas and air from the line 48 are burnt. The reducing flue gas at about 3000‹ F. is passed through a chamber 88 into a cooler 84 where water circulates about the gas duct 89, the water supply being controlled by a valve 95 responsive to a temperature sensor 96 in the water discharge line 93. The duct 89 communicates with the cool flue gas duct 66 and another duct 97 branches off the duct 66 and makes additional passes through the cooler before communicating with the cold flue gas duct 81. The cool flue gas is injected into the brazing box 23 from duct 66 to flow through a chamber 65 and through ports 61 to mix with the flames 55 and the high temperature flue gas stream 58 to form cool stream 62 encasing stream 58. The chamber 34 at its lower end converges inwardly to an orifice 72 which opens into an expansion chamber 73 above the mouth 22. The flue gases are thus compressed and expanded near the mouth and flow across the work with a turbulent scrubbing action and out through ports 36 communicating with an exhaust chamber 37 from which the gas is withdrawn by a pump 39. The cold reducing gas may enter the chamber 73 to turbulently scrub the work before being exhausted from ports 36. In operation with the work below the mouth 22 and mixed gases flowing, the work is moved up to the mouth, the valves supplying burners 35 are fully opened and the mixed reducing flue gases now at a temperature above the melting temperature of the brazing material preheat the work. An electronic temperature sensor detects the temperature of the bends 16 and causes the gas/air supply to the burners 35 to be reduced and the flue gases now flow until uniform heating of the work is obtained. The gas/air to the burners 35 is then increased so that the flue gases melt the brazing material. The burners 35 are then turned off and the cool flue gas supply is stopped, cold flue gas at a temperature of about 100‹ F. then flowing to cool the work. In a modified apparatus a burner generates a flame and the resultant flue gas passes into a furnace from where a portion of the flue gas is caused to pass through a cooler and then into a box where it meets the uncooled flue gas. In this case the cool flue gas cools the brazed workpiece.