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18. Some applications of cast iron as a hard-facing material

Material. Low-carbon (mild-steel) workpiece, cast iron welding rod (not electrodes used for welding cast iron) or pieces of broken cast iron; powdered borax or a commercial cast-iron or bronze-welding flux.

Additional tools. Grinding equipment if this work is performed on tools.


Where steel suitable for the making and repairing of ploughshares, ridger points, landsides and similar equipment is not available, the smith often has to use low-carbon steels. They may also have to be used in toolmaking. For several kinds of tools the wearing life of parts subjected to abrasion can be prolonged by refacing the most affected parts of jobs.

Where there is a lack of suitable steels, there is almost always a lack of modern hard-facing and wear-resisting materials. Even when available, they are often too expensive for use in rural areas of developing countries. In addition, they usually require electric-arc or oxyacetylene welding equipment, which again is not always available. Nevertheless, given a good blacksmith's fire, flux, cast iron and a little practice, cast iron can be applied to low-carbon steels that, when quenched from high temperature, will give a very hard surface. Although not as effective as the use of modern alloys, this treatment does prolong the life of wearing parts and allows some tools to be made from low-carbon steels.

The application of cast iron is far from a new idea. It has been used by smiths for many generations and was of prime importance when only wrought iron and pig or cast iron were available. The process is made possible because of the difference in the melting temperatures of wrought iron and low-carbon steel and that of cast iron. Wrought iron melts at more than 1 500°C, mild steels at about 1 420°C and cast irons at 1 280° to 1 350°C, depending on how much carbon is present in the iron. Cast iron passes through a "pasty" stage when melting and does not become really fluid until a fluxing agent is applied.

If cast-iron welding rod is used, the application is fairly easy. If broken pieces of cast iron are used, they should be of fairly thin section. Pieces from old cylinder blocks or cylinder heads of motor vehicles are quite good. Pieces need to be of sufficient length to be held in tongs without overheating. Flux should be placed close to the fire, perhaps on a metal dish.

The workpiece is heated at the part to be treated to a bright yellow or nearly white heat. While this heating is taking place, the cast iron is also heated. As the cast iron nears the melting point, it will sag toward the fire. Dip the cast iron in to the flux, reheat a little and then apply it to the job by rubbing it on to the heated part of the work. The cast iron can be spread fairly easily on to the work and a buildup will be observed. Sufficient thickness is 1 to 2 mm. More can be deposited if needed. During this operation the work remains in the fire. Allow it to cool to a dull red heat and quench it in water. No additional work is required on jobs such as those shown in Figs 172 to 175.

Agricultural engineering in development

Figure 172

Agricultural engineering in development

Figure 173

For hammers and suchlike only the faces are treated in turn and, after quenching, these need to be ground smooth. It is a good idea to practise this operation on a scrap piece of mild steel with cast iron and flux before attempting it on an important job. You will learn by experience the best angles to hold the job in the fire and how to judge temperatures.

Although cast iron is a very brittle material, it is so modified during this operation, as well as being backed up by the tough mild steel, that it can be used with confidence on hammer faces without fear of cracking.

Figure 172 shows one method of repointing a ploughshare. Holes are drilled or punched at equal centres as shown at XXX. These holes need to be only about 8 mm in diameter. A piece of mild steel about 40 x 4 mm and of sufficient length is curved to match the share and drilled or punched in the same way. The working end and its opposite are hard-faced. The piece is riveted into position and will give good service. When it is worn, the rivets can be removed and the piece reversed and used again. (H in the figures indicates the position of hard-facing.)

A replacement landside can be treated at the points of greatest wear (Fig. 173). Ridger body points and coulters can also be made or repaired and treated (Figs 174 and 175). Many more ways to use the technique can be found. If a smoother finish is required, a little light hammering can be carried out on the deposit at red heat to smooth the surface before quenching.

It must be stressed that only wrought iron or mild steel can be treated in this way.

Agricultural engineering in development

Figure 174

Agricultural engineering in development

Figure 175

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