Welding of cast iron

Cast iron is, as you know, an alloy of iron and carbon. In this case, the content of the latter should exceed two percent. Depending on the state of the carbon in the alloy, gray and white types of cast iron are distinguished . In the first form, the carbon is in the form of graphite, in a free state, this causes its good workability. Since in white cast iron this element is in a bound state, it is almost impossible to weld it. In the fracture material has a light color.

How is cast iron welded? To begin with, this material is not the most suitable for this kind of processing. When welding, it deforms and cracks are easily formed in it. This is due to the special structure of carbon in its fracture. Oiled cast irons, as well as those that have undergone the effects of various aggressive environments, can not be welded. However, for this purpose, the species having fine-grained structure and light gray color are optimal . Welding of cast iron has such side effects: bleaching and, as a result, the emergence of a layer of white cast iron at the site of welding , which can not be processed; As already mentioned, the formation of cracks; Increase in stress in the welding zone; Metal weld pool can become porous due to the burning out of carbon with the simultaneous formation of carbon dioxide. So, this process causes a lot of difficulties. Yet cast iron welding is used quite widely. It has three main methods: cold, half-hot and hot.

The first is the absence of preheating. Cold welding of cast iron is made by steel, cast iron and made of non-ferrous metals and alloys by electrodes. The main thing here is to avoid strong heating in the zone of thermal influence. For this, when using steel electrodes, the first layer is applied with small diameter electrodes with a low carbon content, a thin coating. The current strength at this stage of operation should not exceed 90 amperes. The subsequent layers are applied with electrodes of larger diameter, the coating can be either thin or thick.

One important rule is that metal seams should be applied with small interruptions, so that in the zone of thermal influence the temperature does not exceed sixty degrees.

If welding is to be carried out on critical products, then special devices can be used. These are so-called screwdrivers - special studs, which are made of mild steel. Their purpose is to tie the weld metal to the cast iron. Welding is performed first around them, and then - in the usual manner. When it is necessary to brew any casting defects, cracks and other weak points, electrodes made of nickel-based or copper-based alloys are often used. By promoting graphitization, they prevent the emergence of a wide whitening zone. Welding of cast iron at home is mainly done in a cold way. In this case, any of the types of electrodes listed above can be used.

Hot welding of cast iron involves heating the workpiece before working with it. This method reduces the stress of the metal structure. A half-hot method is a modified hot one. It is in the graphitization of metal and general or local heating up to a certain temperature. These methods are applied in different ways.

If it is necessary to weld individual parts from cast iron, then a cold welding method is used. If the work is carried out at the enterprise, on an industrial scale, a hot method is used.