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Solar Atmospheres Inc.
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Heavy Copper Electrodes Brazed to 225-lb Bars

SOUDERTON, Pa.—Solar Atmospheres, a specialist in vacuum heat treating and vacuum brazing, needed just one day recently to finish a difficult brazing job involving 130 copper bars. Its challenge was to silver braze three, 1-inch diameter copper rounds into the copper bars, which measured 3½ inches x 3 inches x 71 inches and weighed approximately 225 pounds each. As an end product, the copper electrodes are used in a process that manufactures a toxic gas used to produce flat-panel television screens.

The customer called Solar Atmospheres, whose large vacuum furnaces are capable of vacuum brazing 34 bars in a single furnace run, following unsuccessful attempts to torch braze the parts by hand. Solar reportedly brazed the bars at 1550°F, using a silver/28% copper (Bag-8) brazing alloy without braze flux. Instead, the bars were brazed in soft vacuum in the 10 Torr range, using partial pressure nitrogen to avoid evaporation of copper or braze alloy.

While the bars were in the furnace, 2-inch-thick graphite plates were used to support the 8,000-pound work load. Because copper melts at 1981°F, the bars would be very soft at brazing temperature and would distort if not completely supported and held level. Following brazing, the work load was cooled back to ambient temperature using nitrogen gas at a pressure of 5 psig, with a 300-hp radial gas blower and water-to-gas heat exchanger. On removal from the furnace, the copper was said to be "completely bright and scale-free," eliminating the need for cleanup.