Description

Electroslag welding is a mechanised method of making vertical and near-vertical welds, with a maximum slope of 15 from the vertical. It is intended for welding very thick materials (40 mm and up), although it can also be used for thinner materials.

Figure 9.1: Electroslag welding.

The process is started by striking an arc between the electrode and the workpiece. Flux is fed into the joint, and melts to form a bath of slag that increases in depth as more flux is added. When the temperature of the slag, and thus also its electrical conductivity, has increased sufficiently, the arc is short-circuited and the current is carried by the molten slag, maintaining its temperature by resistive heating.

The molten metal is prevented from escaping from the joint by water-cooled copper shoes, which may be fixed or arranged to travel with the welding head. The weld is formed between them and the surfaces of the joint. The welding head moves up the joint as welding progresses. One or more filler wires may be used, depending on the thickness of the plate. If the material is very thick, the welding head may weave.

The benefits of the method include:

• High productivity

• Low cost for joint preparation

• Single pass, regardless of the plate thickness

• No angular deformation when making butt joints

• Little transverse shrinkage

• Little risk of hydrogen embrittlement.

A drawback of the method is that the high heat input means that the weld and HAZ cool only slowly,...