Cast iron is, as you know, an alloy of iron and carbon. Moreover, the content of the latter should exceed two percent. Depending on the state of carbon in the alloy, gray and white types of cast iron are distinguished . In the first form, carbon is in the form of graphite, in a free state, this leads to its good workability. Since this element is in a bound state in white cast iron , it is practically impossible to weld. At the break, the material has a light color.
How is cast iron welded? To begin with, this material is not the most suitable for this type of processing. When welding, it is deformed and cracks easily form 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, are not weldable. However, species having a fine-grained structure and a
light gray color are optimally suited for this
. Cast iron welding has such side effects: bleaching and, as a result, the appearance
of a layer of white cast iron at the place of
welding , which can not be processed; as already mentioned, cracking; increase in voltage in the welding zone; the weld pool metal can become porous due to carbon burnout while the formation of carbon dioxide. So, this process causes a lot of difficulties. Nevertheless, cast iron welding is used quite widely. It has three main methods: cold, half-hot and hot.
The first is the lack of preheating.
Cold welding of cast iron is performed by steel, cast iron and electrodes made of non-ferrous metals and alloys. The main thing here is to avoid strong heating in the heat affected zone. To do 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. Subsequent layers are applied with electrodes of a larger diameter, the coating can be either thin or thick.
One important rule - metal seams must be laid with small interruptions so that in the heat affected zone the temperature does not exceed sixty degrees.
If welding needs to be carried out on critical products, then special devices can be used. These are the so-called screwdrivers - special studs that are made of mild steel. Their purpose is to bind the weld metal with cast iron. Welding is carried out first around them, and then in the usual manner. When you need to brew any casting defects, cracks and other weak points, electrodes made of nickel or copper based alloys are often used. By promoting graphitization, they prevent the appearance 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 starting work with it. This method reduces the stress of the metal structure. The half-hot method is mutated hot. It consists in graphitization of the metal and general or local heating to a certain temperature. These methods are applied in different ways.
If it is necessary to weld individual parts from cast iron, then in this case the cold welding method is used. If the work is carried out at the enterprise, on an industrial scale, apply the hot method.