CURRENT "I'OPICS. 361
Electric Furnace Brazing Facilitates Manufacture of Insecticide Bombs.-Electric furnace brazing greatly facilitates the fabrication of insecticide bombs at the Aer-a-sol Division of the Bridgeport Brass Company, Bridgeport, Conn. Adoption of this method of brazing has inproved the quality of these bombs, simplified their construction, and lowered manufacturing costs. The containers, which are made of SAE-1010 steel .043-.049 inch thick and contain a liquid insecticide under about 90 pounds pressure, are fabricated at an average of approximately 10,000 per eight-hour shift. Two General Electric continuous furnaces are used.
Originally, these containers were fabricated by a bonding method which involved locally heating each joint and using brazing metal and flux. With this method, considerable difficulty was encountered after brazing in removing deposits of charred flux from the interior of the bombs. This was necessary since loose particles tended to clog the .008-inch diameter orifice of the specially designed dispensing valve of the bombs. In addition, there was the everpresent danger of corrosion from moisture trapped in the bomb. Furthermore. a large percentage of the containers leaked.
With electric furnace brazing, inexpensive copper is employed as the brazing metal, and no flux is required. Consequently, the bomb assemblies come fmln the furnaces clean and bright, no oxides or foreign matter are present, the corrosion and moisture hazard is eliminated, and the bonds are uniformly tighl and strong, testing almost 100 per cent. free from leaks. In addition, all fouc of the assembly joints are bonded simultaneously in a single trip through either of the two continuous furnaces.
With this brazing process, the assemblies are put together with the brazmetal preplaced near the joints to be brazed. .ks the containers pass through the heating chamber of the furnace, a reducing atmosphere frees the metal f:om any oxides present, prevents the steel from oxidizing, and thus prepare~ the parts to be wetted by the molten copper. When the brazing metal melts. it is drawn into the joints of the assemblies by capillary attraction and forms alloys with the steel. Transferred to the adjoining controlled atomospherc c~oling chamber, the solidifying alloys develop great strength, and the bombs gradually cool to a temperature at which it is safe for them to come in contact with the outside air without danger of discoloration because of oxidation.
Each of the roller hearth copper brazing furnaces used in this applicaation consists essentially of a heating chamber nine feet in length and an a(ljoining water-jacketed cooling chamber 30 feet long. The heating chamber is equipped with electric heating units rated 180 kw., divided into two 90-kxv. zones, each with separate power and temperature control. The heating units are made of heavy rolled ribbon, formed in sinuous loops, mounted in the roof of the chamber and on the side walls above and below the roller conveyor running through the chamber. The cooling chamber is made of two concentric; rectangular steel shells to provide a water jacket, and is divided lengthwise into three sections, each with a separate water circuit. The first section of the cooling chamber has automatic cooling water temperature control, to prevent condensation during idling periods.
Hollow cast alloy rolls are used throughout the charging vestibule, heating chamber, and the first section of the cooling chamber. Solid steel rolls are employed in the remaining sections. Water-jacketed, self-aligning rolh~r