Cast iron welding with electrode
If a car manifold leaks or a crack in a cast iron pipe, seek help from a welder. But unlike mild steels, cast iron is much less weldable. Frequent defects are pores on the surface of the seam, and after welding work, you can hear cracking of the product, which indicates the formation of microcracks in the peri-seam area. In industrial applications, this high-carbon metal is joined with pre-preparation of the product by heating the material with induction currents, and ensuring that it cools down smoothly. But how do you solve the problem at home? Electrode welding of cast iron at home is done with a conventional inverter. Get a quality connection is possible, properly preparing the surface of the product and correctly selecting welding modes.
Methods of welding cast iron
Two basic techniques are mainly used for welding cast iron parts: hot and cold. Also, the semi-hot method of welding such metal can be used.
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Cold welding method
This method allows you to weld cast iron without preheating the parts. It is especially important when constructions have quite big dimensions.
Mandatory condition of this method is the use of special electrodes.
Usually choose consumables that contain iron, copper and nickel. These elements do not lead to the formation of alloys with carbon, from which the weld does not get too brittle.
Hot and semi-hot methods
These are more reliable methods of welding cast iron. Parts are preheated either in furnaces or special induction heaters (industrial scale).
The main thing is to follow the temperature regimes. Cast iron can not be heated more than 600 degrees. Otherwise begins the process, which they try to avoid during welding. change of structure and bleaching (formation of white cast iron).
This method can be of several types, depending on how high it is heated. For example, the half-hot method heats parts between 350 and 400 degrees, and the warm method heats parts between 250 degrees.
After welding is complete, the parts must be cooled slowly (sometimes up to 5 days!) so that the weld doesn’t crack from the temperature dropping too quickly.
Hot welding methods are more labor intensive. But allow you to get a quality joints.
How to weld a cast iron plate
There are many ways to weld cast iron in general, these are inverter, cold welding, hot welding, semi-hot.
Preparation of cast iron before the welding process is mandatory. An angle grinder with a petal wheel is used for cleaning. As soon as the rust layer is removed it is necessary to treat the plate with solvent for degreasing. In the process of preparation it is necessary to pay attention:
- Studs. There are two types of welding with the use of supporting elements, and without them.
- Edge trimming.
- Using special electrodes.
Choice of brewing method
- Hot. It is considered the main and most suitable for this type of material. The essence of welding is that before you start working with electrodes you need to heat the metal to a high temperature.
- Semi-Hot. This method is identical to the previous one, except for the heating temperature, it must be less.
- Cold. Characterized by a large number of technological processes, but without heating.
How to weld a cast iron plate
There are many ways to weld cast iron in general, it is an inverter, cold welding, hot welding, semi-hot.
Preparing the plate
Preparation of cast iron before the welding process is mandatory. An angle grinder with a petal wheel is used for cleaning. Once the rust layer is removed you need to treat the board with a solvent to degrease it. Attention must be paid to the preparation process:
- Studs. There are two types of welding with or without support elements.
- Edge trimming.
- Using special electrodes.
Choosing a broiling method
- Hot. Considered basic and most appropriate for this type of material. The essence of welding is that the metal must be heated to a high temperature before the electrodes can be used.
- Semi-Hot. This method is identical to the previous one, except for the temperature of heating, it should be less.
- Cold. Characterized by a large number of technological processes, but does not involve heating.
How to clean a cast iron stove
Many indoor wood stoves are made entirely of thick cast iron. While this material is effective at containing the fire and providing heat to the room, it also needs to be cleaned from time to time. Ashes in a cast iron furnace will accumulate in the furnace after each use, and the interior may be covered with ash and smoke residue. You can clean the stove by regularly cleaning the furnace and using a wire brush and sandpaper to clean the outside.
How to weld cast iron
Cast iron parts are joined by gas, termite, casting, electroslag, arc welding and brazing. Welding works are carried out without heating (cold welding of metal), with local or general heating of the product.
The process involves mechanical processing for welding, shaping of the welded parts, preheating, welding works proper and slow cooling afterwards.
Preparation of defect area for welding consists of its thorough cleaning and cutting of welded edges.
Removal of through cracks or welding defects on the edge of the parts is performed using graphite forms, preventing the flow of molten metal from the weld pool. Moulds are made of graphite plates, joined by casting compound, which includes silica sand mixed with liquid glass.
Arc welding with cast-iron electrode is carried out using cast rods with diameter of 8 to 12 mm, on which special graphitizing coatings are applied. The coating includes ferrosilicon, termite, graphite, marble, aluminum (powder), liquid glass and titanium ore. Castings and castings are heated to 300 700 oC. Welding is performed with cast iron electrodes or flux-cored wire with ceramic rod additives. Preheating is performed in special furnaces, so that after welding is complete, cooling of the entire product is performed evenly and cracks are not formed.
Hot welding of cast iron is performed at high amperage of welding current without interruption until the defect is fully welded. For example, to weld an electrode with a diameter of 8 mm a current of 600 A is required, with a diameter of 12 mm a current of 1000 A. Work is performed with direct current of reversed polarity.
Arc welding of cast iron with a carbon electrode is performed with carbon or graphite rods. As the filler material are used pig iron rods, and for deoxidation and protection of the bath use a flux consisting of ground to a powder and calcined at 400 oC anhydrous technical borax. It is possible to use a mixture consisting of 23% of technical borax, 50% of sodium nitrate and 27% of soda. Welding with carbon electrodes with diameter of 8 20 mm is carried out at direct direct current of 280 600 A with the use of converters PSM 1000, rectifiers BAM 1601, transformers TDF 1601.
The welding process requires continuous maintenance of a large volume of liquid metal in the weld pool and its thorough mixing. To slowly cool the welded parts, they should be covered with fine charcoal or dry sand.
Cold method of welding works
This type of welding is used more often for cast iron. Preparation of defective areas involves scraping, milling, drilling, and other metalwork until a clean metal surface is obtained. The defects located further apart than 20 mm are drilled or cut out separately, if they are located closer to each other the defective area is cut out completely.
Placing of studs for weld hardening
In practice, several variants of cold welding are used: copper-iron, copper-nickel, nickel, iron-nickel, steel and other electrodes.
Using copper-nickel and copper-steel electrodes, it is possible to obtain clad metal that is well machinable. Cladding is formed by one-layer or multi-layer beads.
Welding with steel electrodes is performed as follows. In order to create a firm layer of clad metal, pins are inserted into the cast iron workpiece and then welded. This method is used when repairing bulky and heavy cast iron parts. With this method, the weld metal contains an increased amount of carbon, which increases its hardness and promotes the formation of cold and crystallization cracks. Two methods are used to reduce this hardness:
Carbon content is reduced by reducing the depth of penetration of the base metal or the process of joining the metal is performed on a layer of oxidizing flux, with m up to 30% of scale, which serves as a carbon oxidizer.
The structure of the weld metal and its chemical composition are similar to the structure of gray cast iron, which is achieved by applying a thick layer of graphitizing coating on the steel rod, which consists of 30% graphite and 30% ferrosilicon. Steel electrodes are widely used when repairing small irrelevant cast iron products, which do not require any treatment after welding.
Cold welding zone
Copper-iron electrodes are used when welding single defects or small imperfections, which cause leaks on the castings of critical applications, working under pressure. The weld metal from these electrodes is perfectly machinable. The welded joint is a mechanical mixture of iron-carbon alloy and copper, joined to the base metal by common steel crystals, as well as by partial penetration of copper into the micropores of iron.
Copper-nickel electrodes are mainly used when welding cast defects on the working surfaces, which are unacceptable local increase in hardness.
Iron-nickel electrodes are used for welding individual small defects on critical surfaces of gray or ductile iron castings.
Nickel electrodes of the brand are used to repair minor defects in critical items.
Multilayer structure in welding works
Arc welding using electrodes made of austenitic cast iron coated with a current-conducting layer and designed for welding cast defects and repair welding. Welding works are performed with direct current of direct polarity. The conductive layer of the electrodes has good conductivity, so the arc burns between the metal rod and the product, and also between the product and coating alternately.
Gas welding of cast iron is rarely used and is limited to repair work (welding castings cavities, surfacing of worn surfaces, removing external defects). The best result is achieved by welding with an acetylene-oxygen mixture, so other flammable mixtures are practically not used for welding cast iron. Welding is carried out with pre-heating, general and local.
For general heating used muffle furnaces, induction heating, horn, capable of heating small parts to 300 400 ° C, and large up to 600 700 ° C. For local heating, gas burners or blowtorches are used. Because of the great fluidity of cast iron, welding is only performed in the lower positions of the weld. The welding bath is protected by fluxes fed manually.
Gas welding can help you cut the metal qualitatively. Read more about the process in this article.
Read about basic welding concepts and the welding process at https://elsvarkin.ru/texnologiya/kak-varit-metall-vidy-svarki/ link.
Electrode welding of cast iron at home
Cast iron is an alloy of carbon and iron, which also contains alloying additives and impurities. Parts made of cast iron are widely used not only in industrial and manufacturing fields, but also in everyday life. Cast iron products for private purposes: plumbing fixtures, fence structures, car parts and more. Active use of this alloy leads to the need for welding.
The main difficulties of welding cast iron, which are faced by home craftsmen:
- Due to the fluidity of the alloy it is recommended to weld in the lower spatial position;
- failure to follow temperature regimes leads to overheating of cast iron, which can cause pore formation and stresses in the welds;
- Cast iron in the molten state can release gases, which will adversely affect the quality of the connection;
- Accelerated or uneven heating or cooling can contribute to cracks.
To get a quality connection of cast iron products at home it is necessary to consider these specific characteristics, as well as properly prepare the work surface, correctly select the mode of welding and the electrode.
Thermal expansion of different materials must be taken into account during installation. For example, bricks and cast iron are affected by high temperatures in completely different ways. If the hob is walled up against the brickwork during installation, the hob will soon collapse due to the expansion of the metal.
- Leave a horizontal 5 mm gap between the heating structure and the panel. Thanks to it the thermal expansion between the objects will be compensated, the period of operation will be increased.
- The hob must be installed in a strictly horizontal position on a level base. the tiles must not play. To determine whether there are no deviations on the horizon, use a construction level. The largest of the cast-iron circles for the stove is placed over the furnace compartment.
- The panel is mounted on the clay-asbestos compound. These materials are resistant to high temperatures. The solution can be made by yourself, grinding and mixing the components with water, or dilute already ready-bought. Its consistency should be similar to liquid sour cream. When installing make sure that the horizontal gaps are left empty, otherwise the stove will quickly collapse.
Restoring, Refurbishing, Removing Rust and Installing a Cast Iron Wood Stove!
To heat the oven for the first time after installing the surface should be done in a special way: after installing the panel, warm it up to 640 degrees for 8 hours, adding 70-80 degrees per hour. When you reach the desired temperature the iron cools down until the fuel burns through.
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Through gradual heating, the internal stress of the cast iron is released and the stove becomes more durable. The procedure has a positive effect on the further work of the stove and tile, preventing bending and cracking.
Installation on a metal stove follows the same principles. But it should be taken into account that cast iron is a heavy material, so the brick structure is capable of deforming under its weight. Additional reinforcement of the furnace with a cast-iron corner is required. It is possible to apply a “prop” from another resistant material.
The benefits of cast iron
Cast iron provides the product inertial heat transfer, which means that the slow cooling surface contributes to the even warming of the room. The cooking decks are cast in SC 15-20 iron (carbon combined with iron), which is famous for its strength and resistance to fire.
Phosphorus, sulfur, silicon and manganese added to the composition enhance the chemical and physical properties. That is why cast iron structures are not subject to temperature fluctuations and remain intact for quite a long time of operation. In addition, any cast iron structures will not be subject to corrosion due to the rust layer covering them.