Bài giảng Nhập môn điểu khiển quá trình công nghiệp - Chương 30: Fusion Welding Processes and Mechanical-Fastening Processes
Chapter 30
Fusion Welding Processes and
Mechanical-Fastening Processes
1
Fusion Welding Processes
hàn nóng chảy
2
Oxyacetylene Flame Types
Figure 30.1 Three basic types of oxyacetylene flames used in oxyfuel-gas welding
and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or
reducing, flame. The gas mixture in (a) is basically equal volumes of oxygen and
acetylene. (d) The principle of the oxyfuel-gas welding operation.
3
Oxyacetylene Torch
Figure 30.2 (a) General view of
and (b) cross-section of a torch
used in oxyacetylene welding.
The acetylene valve is opened
first; the gas is lit with a spark
lighter or a pilot light; then the
oxygen valve is opened and the
flame adjusted. (c) Basic
equipment used in oxyfuel-gas
welding. To ensure correct
connections, all threads on
acetylene fittings are left-handed,
whereas those for oxygen are
right-handed. Oxygen regulators
are usually painted green, and
acetylene regulators red.
4
Pressure-Gas Welding Process
Figure 30.3 Schematic illustration of the pressure-gas welding process; (a) before,
and (b) after. Note the formation of a flash at the joint, which can later be trimmed
off.
5
Gas-Tungsten Arc Welding
Figure 30.5 The effect of polarity and
Figure 30.4 (a) The gas tungsten-arc
welding process, formerly known as
TIG (for tungsten inert gas) welding.
(b) Equipment for gas tungsten-arc
welding operations.
current type on weld beads: (a) dc
current straight polarity; (b) dc current
reverse polarity; (c) ac current.
6
Plasma-Arc Welding Process
Hàn plasma
Figure 30.6 Two types of plasma-arc welding processes: (a) transferred, (b)
nontransferred. Deep and narrow welds can be made by this process at high
welding speeds.
7
Shielded-Metal Arc Welding
Hàn hồ quang
Figure 3
welding
operatio
Figure 30.8 A deep weld showing the buildup sequence of eight
individual weld beads.
8
Submerged-Arc Welding
Hàn hồ quang chìm
Figure 30.9 Schematic illustration of the submerged arc welding process and
equipment. The unfused flux is recovered and reused.
9
Gas Metal-Arc
Welding
Hàn có lớp khí bảo vệ
(MIG)
Figure 30.10 (a) Schematic illustration of the gas metal-arc welding process,
formerly known as MIG (for metal inert gas) welding. (b) Basic equipment used in
gas metal-arc welding operations.
10
Fluxed-Cored Arc-Welding
Figure 30.11 Schematic illustration of the flux-cored arc welding process. This
operation is similar to gas metal-arc welding, shown in Fig. 30.10.
11
Electrogas-Welding
Figure 30.12 Schematic illustration of the electrogas welding process.
12
Electroslag-Welding
Figure 30.13 Equipment used for electroslag welding operations.
13
Electrode Designations
14
Weld Bead Comparison
(a)
(b)
Figure 30.14 Comparison of the size of weld beads: (a) laser-beam or electron-
beam welding, and (b) tungsten-arc welding. Source: American Welding Society,
Welding Handbook (8th ed.), 1991.
15
Example: Laser Welding of Razor Blades
Figure 30.15 Detail of Gillette Sensor razor cartridge, showing laser spot welds.
16
Flame Cutting
Figure 30.16 (a) Flame cutting of steel plate with an oxyacetylene torch, and a
cross-section of the torch nozzle. (b) Cross-section of a flame-cut plate, showing
drag lines.
17
Weld Joint Structure
Figure 30.18 Grain structure in (a) deep weld
and (b) shallow weld. Note that the grains in the
solidified weld metal are perpendicular to their
interface with the base metal (see also Fig. 10.3).
(c) Weld bead on a cold-rolled nickel strip
Figure 30.17 Characteristics of a
typical fusion-weld zone in oxyfuel-
gas and arc welding.
produced by a laser beam. (d) Microhardness
(HV) profile across a weld bead.
18
Discontinuities and Defects in Fusion Welds
Figure 30.19 Examples of
various discontinuities in fusion
welds.
Figure 30.19 Examples of
various defects in fusion welds.
19
Cracks in Welded Joints
Nứt mối hàn
Figure 30.21 Types of cracks developed in welded joints. The cracks are caused
by thermal stresses, similar to the development of hot tears in castings (see also
Fig. 10.12).
20
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