Lamp Production Research Articles

Manufacture of Electric Lamps

ONE of the exhibits at the Faraday Centenary Exhibition last September which attracted much attention was that showing some of the operations in the manufacture of electric lamps. Only a few of the operations could be demonstrated, but much further information on the subject is contained in an article on “The Mass Production of Electric Incandescent Lamps” in Engineering for March 25. The article contains a description of the new Wembley Lamp Factory of the General Electric Co., Ltd., which has a capacity of 25,000,000 lamps a year. All the machines used are illustrated, and many interesting facts are given about the manufacture of the components of a lamp. The tungsten for the filament is obtained from the ore scheelite. It is first prepared in the form of powder, which is subjected to very great pressure and then treated in an atmosphere of hydrogen, first at about 1200° C., and then at about 3000° C. Sixty drawings are required to reduce the original 1 mm. rod to a filament 0.015 mm. in diameter, and a tungsten bar ¼ in. square and 10 in. long can be drawn into 15 miles of filament. The leading-in wires, which used to be of platinum, are now of copper-covered nickel-steel. The important operation of exhausting the lamps and then filling them with gas is done on capstan machines, each holding twentyfour lamps. Vacuum pumps reduce the pressure in them to a few thousandths of a millimetre of mercury, heat from an oven drives off moisture and adsorbed gas, and, while still hot, the lamps are filled with a mixture of nitrogen and argon, the internal pressure when cold being about two-thirds of an atmosphere.