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CAST IRON 237

Description and uses

Unitor Cast iron is a filler metal for welding cast iron, malleable iron and cast iron/steel joints.

The filler metal is extremely easy to work with, has high tensile strength and the structure and colour of cast iron. Welded connections are compact and machinable. The filler also fuses to oil contaminated cast iron. Typical uses are welding of cracked parts and building up worn surfaces such as gears and sprockets. The choice of method – gas welding or arc welding – for repairs to cast iron depends on the size, shape and thickness of the workpiece. As a general rule, gas welding is used for small machine parts and arc welding (cold welding) on larger, more complicated parts.

Adjust the flame to give a slight surplus of oxygen (oxidising). The area to be brazed must be properly cleaned and any casting skin removed. Round off any sharp edges or corners. Cracks must be surface ground or prepared with a 90° V-groove along the crack. It is usual to drill a hole at the end of the crack. Preheat the parts with a good spread of heat on either side, to 400– 600°C. Heat the end of the rod and dip it in th flux powder. The flux will stick to the hot rod. Heat the starting point to a dark red heat. Melt off a drop from the flux-coated rod into the groove and spread out by continually moving the torch, which should be kept at an angle of 15–30° to the workpiece. When the filler has flowed freely into the seam, melt off a new globule and repeat the procedure. Stir the weld pool with the filler rod. Weld with Leftward technique. After gas welding, allow the part to cool slowly in diatomite or dry sand. Surplus flux must be removed.

Brazing a cast iron manifold

Building up worn parts such as gear wheels

90°

Preparation of joint

3.05

Gas weld Leftward. Note that the weld pool must not be stirred with the filler rod

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