Cast iron in its composition is an alloy of iron and carbon, which may also include impurities and some alloying additives. This metal is widely used in industry for the manufacture of various supporting parts and structures. In domestic buildings, most of the sewer risers and heating radiators are made of cast iron.
The high carbon content makes it difficult to connect parts of cast iron with each other and with other metals. Violation of technological requirements often leads to quenching, and hence to an increase in the fragility of the metal. Therefore, before proceeding with the connection of cast iron structures, it is necessary to thoroughly study how to cook cast iron by electric welding, as well as the necessary materials and technology for performing such work.
Types of cast iron
The composition of cast iron includes not only carbon (2-6%) and iron, but also manganese (up to 1%), silicon (3%), phosphorus, sulfur, and also alloying additives - aluminum, vanadium, chromium, magnesium, nickel and some other components. It is alloying substances that give hardness, strength and ductility to the material, depending on its application.
Electric welding of cast iron is carried out depending on the shape and amount of carbon that is in the metal as graphite or cementite. It is for these indicators that cast iron is divided into the following types:
- White cast iron has a light colored fracture surface, since carbon in this metal is a form of cementite. The processing of such a material is difficult, due to its high hardness.
- In gray cast iron, carbon is in the form of graphite. The fracture surface of the metal is gray. Such cast iron is easy to metal work and has good casting properties.
- The heat treatment of white cast iron turns it into a malleable metal, which is widely used in mechanical engineering.
- Half-cast iron contains carbon in the form of cementite and graphite. This ratio gives the metal high wear resistance.
- Spherical graphite gives cast iron high strength. High-strength cast iron is used for the manufacture of high-quality oil and water pipes.
Features of cast iron welding
Before answering the question of whether it is possible to cook cast iron by electric welding, it is necessary to understand the features of the metal compound technological process. In its structure, as well as many physical properties, cast iron refers to alloys that are limitedly susceptible to the welding process.
During electric welding of cast iron at home, you need to pay attention to the following difficulties of this process:
- The formation of a high-quality seam complicates the fluidity of the cast iron alloy.
- Non-observance of the welding temperature leads to overheating of cast iron. This causes carbon to burn out in the weld pool and therefore increases pore formation.
- Also, the high temperature of the electric arc promotes the bleaching of cast iron at the welding site. This effect, due to the heterogeneity of the metal structure, leads to cracking of the seam.
- During welding, cast iron is able to oxidize, and a refractory oxide is created, the melting temperature of which is much higher than that of the starting material.
To avoid all these troubles when welding cast iron, it is necessary to responsibly treat the correct choice of operating mode.
Preparation of cast iron for welding
Before you cook cast iron by electric welding, it is necessary to prepare the edges of the joined surfaces. It is possible to carry out preliminary surface cleaning both manually and with an electric tool with a nozzle made of metal pile.
Further, it is necessary to make the cutting of edges to pure metal, since it is much more difficult to cook cast iron by electric welding in home workshops than steel.
Defective places of cast iron are cut according to the following rules:
- cutting is carried out strictly along the crack;
- non-through cracks are drilled with a drill, and then cut down to the main material;
- depending on the thickness of the metal, through cracks are cut from two or one side;
- it is recommended to weld a patch on closely located cracks, which should cover the defect by 15-20 mm from all sides.
After cleaning the surface and cutting the edges, thoroughly degrease the junction with acetone or solvent.
Basic cast iron welding methods
It is possible to cook cast iron both by electric welding and in an inert gas environment. The second method is mainly used for joining heterogeneous metals. Gas welding is used most often for repair work on sewer pipes, as well as restoration of automobile parts.
It is possible to cook cast iron by electric welding both hot, with preheating of workpieces, and the cold method, without heating the connection point. Welding with heating is technologically carried out in a more complicated way than a cold connection, so its use in domestic conditions is impractical.
Gas welding
Welding of cast iron in a cloud of protective gas is used to create a seam of high strength, which is achieved with a small penetration of the metal. The practical experience of the welder, as well as the choice of the correct mode of creating the weld, are of particular importance on the final result of the work.
The gas welding process is recommended to be performed with two torches. In this case, one torch provides preheating of the joint, and the second melts the wire and directly cast iron parts are welded. Cooling of the welded parts should be slow, so often covering the products with a layer of sand or asbestos is often used.
Hot welding cast iron
Welding of cast iron products with preheating of the edges of the joined surface is most often carried out at industrial enterprises. Workpieces can be heated in inert furnaces, as well as various special burners.
Warming up the weld point to 600–650 ℃ eliminates the possibility of tension and metal quenching at the joint.
The welding technology is as follows:
- Preliminary preparation of the junction.
- The product is positioned so that it is possible to weld with the lower position of the seam.
- The welding machine is configured to work with direct polarity. The current strength when welding cast iron is set much higher than the cooking of steel.
- The part is heated to a temperature of 300–600 degrees.
- The weld pool must be filled with molten metal during weld creation. It is recommended to stir the liquid melt with the tip of the electrode.
- After welding, it is better to leave the product in a cooling furnace, or fill it with heat insulating material. Slow cooling of cast iron is the key to a quality connection.
Of course, hot-metal welding of cast iron is considered to be labor-intensive work, but it is precisely these conditions that make it possible to obtain a joint without defects and with high quality.
Cold welding method
In cases where high requirements are not imposed on the weld, it is possible to cook cast iron by electric welding at home, both in the cold way and with slight heating.
Technological features of cold welding are as follows:
- A minimum power is set on the welding machine, which is permissible for a certain thickness of the electrode, in order to prevent overheating of the metal.
- Welding is carried out on reverse polarity current.
- The welding seam must be performed in segments of 30-50 mm.
- Overheating of the junction is eliminated with breaks or stitching in a checkerboard pattern.
- In multi-layer welding, each seam must be hammered.
The quality of the connection of cast iron depends entirely on the correct choice of electrodes.
Electrodes for cast iron welding
It is possible to cook cast iron by electric welding both with an electrode for cast iron and with products containing nickel or copper. Carbon does not combine with these non-ferrous metals; therefore, white iron is not formed in the weld. Most often, welding with such electrodes is carried out in several stages, with a break for cooling.
The following electrodes for cast iron are used for electric welding of cast iron products:
- OZCH-2 and OZCH-6 - electrodes based on copper and iron, which are used for welding gray or malleable cast iron;
- OZZHN-1 - this brand includes iron and nickel, which are very effective for ductile iron;
- MNP-2 - these products contain copper, nickel and iron, suitable for welding all types of cast iron.
Welding Safety Basics
Welding is classified as a hazard to the health of the welder. Therefore, compliance with safety precautions when welding cast iron is a prerequisite for work.
Key safety features include:
- all work must be carried out using personal protective equipment (mask, gloves, special suit and shoes);
- welding should be carried out in a well-ventilated area;
- welding equipment must be kept in good condition;
- electrical equipment must be properly grounded.
Cast iron refers to metals that are difficult to weld. Therefore, before starting the process of joining cast-iron products, it is necessary to carefully study the main nuances of the quality performance of such work.