焊接科学与工程专业英语 教学课件 ppt 作者 吴志生 柏艳红 黎穗琼 主编第3章.ppt

Chapter 3 Arc Welding Process 电弧焊接方法 3.Arc Welding Process 电弧焊接方法 Faced with a diversity of welding methods that increase year by year, we must adopt the following definition of welding: “Welding is the joining of metals and plastics by methods that do not employ fastening devices”. Technology of welding embraces a wide area:electronic circuits ,radio frequencies,photography and so on.Finally, welding has made important contributions to two outstanding technical creations of our time, the nuclear reactor and the aerospace rocket. As we know, there are in use about sixty methods of welding. No useful purpose would be served by listing all these methods. Instead, we shall begin a general description of the most available ones. 3.1 Shielded Metal-Arc Welding 焊条电弧焊 Definition an arc welding process wherein coalescence is produced by heating with an electric arc between a covered or “coated” metal rod called the electrode and the work. The work is made part of the welding circuit (Fig.3-1). This circuit includes a source of power, welding cables, an electrode holder, a ground clamp and the consumable welding electrode. Fig.3-1 Elements of a typical welding circuit for shielded metal-arc welding 3.1 Shielded Metal-Arc Welding 焊条电弧焊 Electrode being used 1 establishing the arc 2 supplying filler metal 3 The electrode covering performs the following functions: (1) Help stabilize and direct the arc for effective penetration. (2) Provide a gaseous shield to prevent atmospheric contamination. (3) Control surface tension in the pool to influence the shape of the bead formed when the metal freezes. (4) Act as scavengers to reduce oxides. (5) Add alloying elements to the weld. (6) Form a slag to carry off impurities, protect the hot metal, and slow the cooling rate. (7) Electrically insulate the electrodes. (8) Minimize spatter of weld metal. (9) Form a plasma to conduct current across the arc. 3.1 Shielded Metal-Arc Welding 焊条电弧焊 1