Page 97 of 561

SOLUTIONS: Cast Iron

Searing

Even after filling there will still be graphite present in the surfaces to be joined. Graphite is a refractory material, which can inhibit "tinning". By playing the inner cone of an oxidising flame from the welding torch over the surfaces off the groove, most, if not all, of this graphite can be burnt away. This process, which is called "searing" should be practiced as a matter of course before attempting to braze weld cast iron.

2.07

Preheating

After the searing is completed, preheat the part(s) to 400–600 °C with a wide spread of heat to each side. Remember that cast iron is one of the more brittle and crack-sensitive base metals. Thus care should be exercised in the preheating to ensure that it is even and uniform.

Braze welding

When braze welding cast iron the flame should be adjusted to have a slight surplus of oxygen (oxidising flame).

Joining is done with the filler metal Unitor Castiron 237. This filler metal is extremely easy to work with, has high tensile strength and the structure and color of cast iron. Welded connections are compact and machinable. The filler also fuses to oil impregnated cast iron.

Typical uses are welding of cracked parts and building up worn surfaces such as gear and gear wheel teeth. Use Castiron 237 in combination with Castiron Flux 236F. Heat the end of the rod and dip it in the flux powder. The flux will stick to the rod

96

Heat the starting point to a dark red heat. Touch the rod to the surface and melt off a drop from the rod into the groove and spread it out by continually moving the torch, which should be held flat at an angle of about 15 - 30° to the workpiece, and approximately 1 cm above the groove. When the filler has flowed freely into the seam, melt off a new drop and repeat the procedure.

Braze leftward

When the brazing work is completed, the part should be allowed to cool slowly in kieselgur or dry sand. Surplus flux must be removed by hot water and brushing.

Alternatively, where a hardwearing surface is required, the joining can be done with the filler rod Unitor FC-Wearbro 262, applying the same technique as described for Castiron 237.

Unitor FC-Wearbro 262 has a low bonding temperature. However, the strength and machinability is lower than for Castiron 237.

Technical details on the rods are found in the section "Consumables".