The appearance of metal in people's lives has made it possible to significantly advance the technological progress of mankind. But in order to be able to create strong and reliable metal structures, it was necessary to develop a process for connecting the individual parts. It was the invention of welding that made it possible to achieve this result.
The characteristic features of cast iron necessitate the knowledge of many factors that influence the production of a high-quality weld. The most common currently considered to be the use of electrodes of various welding grades for cast iron, steel and various alloys.
Features of welding cast iron parts
The content of more than 2% carbon in the composition of cast iron causes a very low weldability of the surfaces of this metal. Therefore, to obtain a high-quality compound, a lot of effort is required to compensate for this negative property of the material.
The main feature of the welding process of cast iron products is the creation of uniform heating and cooling of the contact place of parts, otherwise the appearance of characteristic cracks in the joint surface is possible. Due to the active evolution of gases during the melting of cast iron alloys, porosity of the weld occurs.
Of course, the best way is to combine this capricious metal under the protection of argon. But this is a rather expensive technology. Therefore, welding of cast iron with an electrode at home is more common, which is cheaper and easier to carry out. The main thing is to qualitatively prepare the metal and, accordingly, choose a consumable. It is necessary that the cooling time of the base metal and the electrode coincide.
The correct selection of electrodes for cast iron welding must be carried out in accordance with their chemical composition.
Cast iron welding problems
To obtain a strong and reliable connection of metal products made of cast iron, it is necessary to overcome many problems that are caused by the following factors:
- the formation of a high-quality weld is complicated by the high fluidity of the liquid material;
- the formation of refractory oxides significantly complicates the conduct of welding;
- a sharp decrease in temperature in the welding zone causes the formation of bleached areas, which greatly increase the hardness of the material, which complicates the machining process;
- the cause of cracks is the uneven heating of the welding zone, as well as its further cooling;
- intensive gas evolution from a liquid metal leads to a negative appearance of internal pores.
Elimination of many negative welding factors is impossible without the correct use of special electrodes for cast iron. Consider this point in more detail.
Electrodes for welding
The electrodes are pieces of metal in the form of a bar. Their main purpose is to deliver to the junction of the components necessary for the correct flow of the welding method, as well as creating an electric closed circuit.
According to the material from which the rods are made, they can be:
- from copper;
- alloy steel;
- from bars of cast iron.
All steel products are processed with a composition containing ferrosilicon. Such electrodes are mainly used for joining simple products that are not subjected to heavy loads during operation. This material is great for welding cast iron with an electrode in home workshops.
Types of electrodes
The metal connection is made in the manufacture of special structures, as well as the removal of some casting defects. Selection of brands of electrodes is carried out depending on the solution of certain tasks:
- thickness and type of product;
- cold or hot welding;
- desired work quality;
- connection technology.
Electrode marking
The choice of electrodes is carried out in accordance with the marking, which is indicated on the rod and gives complete information about the components included in the product.
For the correct implementation of the task, it is enough to decipher the inscription on the rod. For example, the MNCh-2 electrode brand indicates that the product contains:
- M - about 30% copper;
- H - 66% nickel;
- H - indicates that the rod for welding cast iron;
- 2 - number, i.e. the ratio of components.
Electrodes for cold connection
Electrodes containing copper or nickel are suitable for this welding. Due to the fact that copper does not dissolve in cast iron, a uniform seam is formed. But nickel is highly soluble in metal, and almost does not come into contact with carbon. Therefore, the weld is perfectly processed, and it turns out without pores and cracks.
This kind of cast iron electrodes can be conditionally divided into three subspecies:
- 1. MNP-2. This brand contains nickel, iron and copper. Its application is possible for welding defects in casting and melting of metal. Using reverse current with such products, any cast iron can be welded. The seam is easy to process and has a high surface finish. The designs made by this brand of cast iron electrodes work perfectly in aggressive environments.
- Electrodes of the OZCh-2 and OZCh-6 brand contain copper and iron in their composition. OZCh-6 is used for welding thin parts. The connection is carried out by reverse DC. OZCH-2 are similar to the previous brand, but have an acid strapping.
- OZZHN-1 or 2, as well as OZCh-3 or 4 are composed of nickel and iron. Increased requirements for the quality of the connection are achieved by OZCH-3 electrodes for welding high-strength or gray cast iron. OZCH-4 is used to dock parts that are impacted. To connect the vertical parts of the mechanism, electrodes for cast iron with the marking OZZHN-1 or 2 are suitable.
Electrodes steel cast iron TsCh-4 are considered the most common brand. Perfect for joining any type of cast iron (gray, malleable, durable). Docking is done in the lower position, it is possible with heating, or it can be without. If there is a high-current apparatus, then work can be done with alternating voltage. But the best quality indicators of the weld can be achieved with direct current.
Hot welding cast iron
Using the method of hot joining cast iron, it is possible to obtain a seam of the same composition and density with the base metal of the product. The properties of the weld are almost no different from cast iron, so it is easily processed. Of course, there are problems with the organization of the docking process itself, especially the difficulty arises with uniform heating of the joint. And also the inconvenience causes a long duration of the welding process.
The use of hot welding compensates for all the disadvantages of the cold method. There are three main types of heating of the welding zone:
- 150-200 ℃ - warm heating;
- 300-400 ℃ - semi-hot heating;
- 500-600 ℃ - hot welding.
Overheating of the joining parts can lead to a change in the structure of the metal. Therefore, heating should be carried out slowly and not more than 650 ℃. It is also necessary to slowly produce and surface cooling.
Electrodes for hot casting of cast iron
Hot welding is carried out with the following cast iron electrodes:
- Steel electrodes of the UONI or ANO brands are widespread.
- Gray cast iron is well welded with OMCH-1 electrodes. The diameter of these electrodes can be from 3 mm to 6 mm. Structurally, they are cast iron rods coated with a special coating.
- Electrodes for cast iron labeled “A” are well suited for arc welding. Brand "B" is considered universal, and is well suited for any welding. Their diameter can range from 4 mm to 16 mm. Qualitative characteristics of the weld are increased due to the special additive “termite”, which slows down the cooling process of cast iron.
Non-consumable electrode welding
Another type of joining cast iron billets is the process of joining non-consumable electrodes. In this case, tungsten, graphite or carbon rods are used. It is very important to correctly select the filler material and strictly adhere to the joining technology.
Good quality joining of cast iron can be achieved by using steel rods with nickel, aluminum and copper.
Welding with rods made of coal or graphite is done in direct forward current. Moreover, the current strength is set depending on the diameter of the electrode.
Argon arc welding is most often used when connecting with a tungsten rod. With such welding, the diameter of the electrode is selected in accordance with the thickness of the workpieces.
Thick-walled cast iron welding
If the workpieces have a thickness of more than 20 mm, then for the high-quality connection, several electrodes are used, which include the following materials:
- copper rod with a diameter of not more than 5 mm;
- brass bar with a section of less than 3 mm;
- UONI electrode less than 4 mm in cross section.
The welding process proceeds due to the heat generated during the transition of the welding arc from one rod to another. Cooling of the junction occurs slowly, which positively affects the quality of the seam.
Such prefabricated electrodes are of high cost. Therefore, for welding cast iron with an electrode at home, an inverter uses homemade electrodes. For their manufacture, it is necessary to put a copper tube on a regular steel electrode or wind a wire, which must be protected with a special coating.
The coating is made from a crushed coating of electrodes mixed with iron powder and silicate glue. Then, an electrode is dipped into such a creamy mixture, after which it is dried and calcined. Layer thickness - no more than two millimeters.
There are many electrodes for cast iron welding. Therefore, it is necessary to carefully and responsibly approach the correct choice of material, in accordance with the requirements of welding technology. Even a minor error leads to a decrease in the quality of the connection of cast iron products, and these are cracks and porosity of the metal.