. Sheet metal workers' manual; a complete, practical instruction book on the sheet metal industry, machinery and tools, and related subjects, including the oxy-acetylen welding and cutting process . Figure 287.—Electric Butt Welder. wrhile testing several parts. When this setting is rightthe work can continue as long as the same sizes are be-ing handled. Copper, brass, tool steel and all other metals that areharmed by high temperatures must be heated quickly andpressed together with sufficient force to force all burnedmetal from the weld. In case it is desired to make a weld in the form of a E
. Sheet metal workers' manual; a complete, practical instruction book on the sheet metal industry, machinery and tools, and related subjects, including the oxy-acetylen welding and cutting process . Figure 287.—Electric Butt Welder. wrhile testing several parts. When this setting is rightthe work can continue as long as the same sizes are be-ing handled. Copper, brass, tool steel and all other metals that areharmed by high temperatures must be heated quickly andpressed together with sufficient force to force all burnedmetal from the weld. In case it is desired to make a weld in the form of a ELECTRIC WELDING 361 capital letter T, it is necessary to heat the part cor-responding to the top bar of the T to a bright red, thenbring the lower bar to the preheated one and again turnon the current, when a weld can be quickly made. Spot Welding.—This is a method of joining metalsheets together at any desired point by a welded spotabout the size of a rivet. It is done on a spot welder. Figure 288.—Clamping Dies of an Electric Butt Welder. (Figures 283, 284), by fusing the metal at the point de-sired and at the same instant applying sufficient pressure-to force the particles of molten metal together. The diesare usually placed one above the other, so that the workmay rest on the lower one while the upper one is broughtdown on top of the upper sheet to be welded. One of the dies is usually pointed slightly, the oppos-ing one being left flat. The pointed die leaves a slightindention on one side of the metal, while the other side isleft smooth. The dies may be reversed, so that the out- 362 SHEET METAL WORKERS MANUAL side surface of any work may be left smooth. The cur-rent is allowed to flow through the dies by a switch, whichis closed after pressure is applied to the work. There is a limit to the thickness of sheet metal thatcan be welded by this process, because of the fact thatthe copper rods can only carry a certain quantity ofcurrent without becoming unduly heat
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