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4.6 PERMANENT JOINTS

As it was mentioned above, permanent joints are joints which are impossible to disconnect
without the damage of connecting parts. Let’s consider such types of joints, as joints by welding,
soldering, cementing.

4.6.1 WELDED JOINTS

Welding is a permanent method for making joints. Welding has replaced riveting in many
industries because of saving in labour as well as material and reduction in weight by the use of
lighter plates and the elimination of all overlaps and rivets. Standard steel shapes, plates and bars
may be welded together to make machine frame, bases, jigs and fixtures, etc. For joining of very
high pressure steam pipes, welding is the only acceptable process. The aircraft, automotive and ship
building industries have developed welding as a major fabricating method for aluminium
magnesium and steel.
Welding is defined as the localized, intimate union of metal parts in the plastic or plastic and
molten state, with the application of blows or mechanical pressure or the union of parts in the
molten state without any pressure. There are three main methods of welding, viz., forge welding,
electric resistance welding and fusion welding, which may further be classified as shown in Fig.
4.33.

Figure 4.33 – Types of welding

The most common welding used in manufacturing of machinery is arc welding but gas
welding is also used.
Arc welding is carried out with the help of a voltaic arc between an electrode and welded
parts. The gas welding is conducted by flame of hot gas which is burned in the stream of oxygen.
At the resistance welding heating is carried out a heat which is selected at flowing of the
powerful electric current through welded parts in the place of contact between them. The resistance
welding is divided into butt and spot.
There are five basic form of welded joints, namely, edge, butt, lap, corner and tee. The
various types of welded joints are shown in Fig. 4.34.

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