Welding Metallurgy. Sindo Kou. Читать онлайн. Newlib. NEWLIB.NET

Автор: Sindo Kou
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Техническая литература
Год издания: 0
isbn: 9781119524915
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      a) Process code: SMAW, shielded metal arc welding; SAW, submerged arc welding; GMAW, gas−metal arc welding; FCAW, flux cored arc welding; GTAW, gas–tungsten arc welding; PAW, plasma arc welding; ESW, electroslag welding; OFW, oxyfuel gas welding; EBW, electron beam welding; LBW, laser beam welding.

      b) Thickness: S, sheet, up to 3 mm (1/8 in.); I, intermediate, 3−6 mm (1/8−¼ in.); M, medium, 6−19 mm (¼−¾ in.); T, thick, 19 mm (¾ in. and up); X, recommended.

      1.1.1.3 Types of Joints and Welding Positions

Schematic illustration of the five basic types of weld joint designs. Schematic illustration of the typical weld joint variations. Schematic illustration of the four welding positions.

      1.1.2 Solid‐State Welding Processes

      In addition to fusion welding processes, various solid‐state welding processes have also been developed. Some of them are shown as follows:

      1 (a) Friction Stir Welding:Friction stir welding (FSW)Friction stir spot welding (FSSW)

      2 (b) Friction Welding:Linear friction welding (LFW)Rotary friction welding (RFW)

      3 (c) Fast‐Collision Welding:Explosion welding (EXW)Magnetic pulse welding (MPW)

      4 (d) Diffusion Welding

      1.2.1 The Process

Schematic illustration of the oxyacetylene welding including (a) overall process and (b) welding area enlarged. Schematic illustration of the three types of flames in oxyacetylene welding.

      Source: Welding Journal, 1969, © American Welding Society.

      1.2.2 Three Types of Flames

      1.2.2.1 Neutral Flame

Schematic illustration of the chemical reactions and temperature distribution in a neutral oxyacetylene flame.

      1.2.2.2 Reducing Flame

      When excess acetylene is used, the resulting flame is called a reducing flame. The combustion of acetylene is incomplete. As a result, a greenish acetylene feather between the inert cone and the outer envelope characterizes a reducing flame (Figure 1.9b). This flame is reducing in nature and is good for welding aluminum alloys because aluminum oxidizes easily. It is also good for welding high‐carbon steels (also called carburizing flame in this case) because excess oxygen can oxidize carbon and form CO gas porosity in the weld metal.

      1.2.2.3 Oxidizing Flame

      When excess oxygen is used, the flame becomes oxidizing because of the presence of unconsumed oxygen. A short white inner cone characterizes an oxidizing flame (Figure 1.9c). This flame is preferred when welding brass because copper oxide covers the weld pool and thus prevents zinc from evaporating from the weld pool.

      1.2.3 Advantages and Disadvantages

      The main advantage of the OAW process is that the equipment is simple, portable, and inexpensive. Therefore, it is convenient for maintenance and repair applications. However, due to its limited power density, the welding speed is very low and the total heat input per unit length of the weld is rather high, resulting in large heat‐affected zones (HAZs) and severe distortion. The OAW process is not recommended for welding reactive metals such as titanium and zirconium because of reactions with CO and H2.