Cast iron is of interest for the construction industry, and for many areas of production. Its unique combination of technical and physical properties allows the manufacture of wear-resistant small parts and critical monolithic structures for the layout of engineering structures. But in each case, one or another form of processing of this alloy is required. The most affordable and modern method can be called cast iron welding by a semi-automatic machine, which in itself provides several options for the thermal effect on the workpiece.
Features of welding cast iron alloys
This is not the most convenient metal in terms of accessibility to thermal melt. The complexity of working with cast iron is determined by its following characteristics:
- Low melting point. The electric arc from the welding machine contributes to the release of high-density thermal energy, as a result of which the metal in the welding zone overheats. The workpiece can be deformed even in places that were not intended for processing, and impurities (silicon and manganese) are also heated.
- Risks of formation of a porous structure. The negative influence of oxygen on the structure of the molten metal makes it possible to form various kinds of defects. Therefore, special gas media are used to protect the workpiece from oxygen. In particular, welding of cast iron by a semi-automatic machine in a carbon dioxide environment is practiced as the most acceptable from the point of view of chemical reactions in the working area. But even this is not enough to minimize the risks of marriage after welding. Experts recommend using a flux-cored wire as an additional condition for obtaining a high-quality weld, which additionally reduces atmospheric air and stabilizes arc burning.
- Melt flow. Under high temperatures with the melting effect, cast iron quickly goes into a liquid state, which leads to yet another spectrum of difficulties. As a rule, fluidity becomes a problem in operations with sheet blanks, when there are risks of through melting with complete deformation of the element. This problem is solved using graphite pads that preserve the shape of the workpiece.
Semi-automatic welding basics
The main difference between semi-automatic welding (inverters) is the mechanization of the supply of consumables - an electrode or wire. A special feed unit can be used for this. Also during operation, a gas cylinder, gearbox and burner are used. Operations with cast iron are preferably performed in one of the following modes - MIG / MAG or TIG. Less commonly used is the manual MMA processing method, which is characterized by high quality melt. On powerful inverters, semi-automatic cast iron welding technology allows you to connect parts with a total thickness of up to 10 cm. However, thick workpieces can impose a high responsibility on the contractor. This is especially true of the initial stage of arc ignition, when it is necessary to maintain the stability of the torch and at the same time prevent the electrode from sticking to the surface of the workpiece.
Cold welding
Welding technology without the use of pre-heating the workpiece. From the point of view of organization, this is the most convenient method, but in terms of the quality of the result, it loses to the technique of forming a hot melt. As a rule, semi-automatic cold welding of cast iron is performed by electrodes, the coating of which gives the weld additional physical and chemical properties, like flux. Usually, electrodes with copper, iron, and nickel compositions are used. Such a coating under the influence of heat forms a structure protected from carbon inclusions, which improves the quality of the connection. It is recommended to use the cold welding method when working with large building structures.
Hot welding
At home, this method is unlikely to be realized, since preheating requires temperatures of about 400-600 ° C to be achieved. By the way, in industry, induction furnaces are used for such purposes. Work with heated products is much technically easier, but the main task of such preparation is to improve the quality of welding. Solid-state and at the same time brittle alloys can exhibit structural sensitivity to elevated temperature effects, therefore, parameters such as the accuracy of the torch direction and the correctness of the electrode and workpiece bundles come to the fore. Hot welding of cast iron and steel by a semiautomatic device allows you to connect elements with a clean weld and a minimum content of defective areas. After completion of the process, the workpieces are slowly cooled. An exposure of up to several days is required so that no cracks appear in the joint zone.
Preparation for work operations
Regardless of the method and equipment used for welding, cast iron billets require special training. Its surfaces must be cleaned of dirt, oil stains and, if possible, remove scale with traces of corrosion. Next, a chisel or angle grinder should extend the edges along the entire length. If it is planned to carry out repair of cracks by welding, then drilling of holes in the places of formation of defects is also initially performed. According to the created recesses, it will be easier to perform high-quality welding of cast iron semi-automatic with optimal penetration into the crack formation zone. Billets with a thickness of more than 5 mm are subjected to turning in order to obtain angular 50-60-degree bevels along the edges. Thin details, as noted above, are cooked using graphite pads, eliminating the risk of through burning.
The choice of wire for welding
Semi-automatic usually involves the use of wire. If the electrode is more likely to be used as a means of modifying the weld structure, then the wire in the case of cast iron machining performs the protection function. Today, special types of wire are produced for this metal - for example, from a steel alloy marked PP ANCH-1 (for the cold method). If it is planned to endow the structure with special properties, then cored wire is suitable. Specialists, in particular, praise the combined composition options based on silicon, copper and nickel. Welding of cast iron by a semiautomatic device with an ordinary aluminum wire with a thickness of about 1 mm is still relevant. With such a consumable, profile cast iron elements can be serviced, as well as large metal structures with direct current.
What to consider in organizing a protective environment?
Two aspects should be considered. Firstly, it is equipment that will supply gas to the burner. Secondly, the type and properties of the gas itself. For a technical organization, a cylinder with appropriate filling and mounting and connecting fittings with a nozzle, gearbox and other necessary equipment will be required. As for the second aspect, balanced welding of cast iron semi-automatic in carbon dioxide is the most common method. Carbon dioxide as such is self-sufficient and provides the necessary protection for welding. Another thing is that it does not always guarantee the stability of the arc, and during high-precision work it manifests itself not in the best way. An alternative would be an argon or carbon dioxide-argon mixture, which opens up more opportunities for obtaining modified alloyed alloys.
Semi-automatic cast iron welding process
Work begins with the ignition of the arc. The most comfortable version of this operation is offered in inverters with piezo ignition function and subsequent torch control using Arc Force and Hot Start technologies. The holder must be held at a 60-degree angle relative to the work surface. The seam is applied in several approaches - in layers. Final layers are laid across the tip of the wire. The event ends with the removal of slag and the adjustment of its temperature. To ensure a gradual and even cooling, the workpiece is filled with non-combustible material like asbestos.
Conclusion
Semi-automatic welding methods contain many technological nuances that involve different formats of work. Much depends on the gas environment and consumables. For example, a wire for welding cast iron by a semi-automatic machine can determine the ranges of optimal arc voltage and supplied current. But, of course, at a basic level, one should proceed from the requirements for the target procurement. Its characteristics and the parameters of the planned seam are taken into account, and the speed of the operation is also important in production.