Sooner or later, each welder encounters various cast iron products. This material is a rather brittle alloy having a high thermal conductivity. Like steel, cast iron is an alloy of carbon with iron. The difference between the two is in the amount of the first. If the steel contains about 2.14% carbon, then in the iron its content can reach 6.65%. It is this that causes low ductility, poor ductility, and difficult weldability of this material. Next will be considered how to cook cast iron.
The scheme of hot welding.
Features of cast iron welding
Cast iron is a widespread construction material, which has a relatively low cost, good machinability and excellent casting properties. But some of its features greatly impede welding, namely:
- High tendency to crack. This is due to its heterogeneity and the processes of bleaching and hardening that occur in the heat-affected zone during cooling of the hot material.
- The high fluidity of the molten material, which greatly complicates the creation of high-quality weld.
- Burnout of carbon during heat treatment, which leads to the formation of pores.
- When welding, refractory acids are formed, which have a higher melting point than that of cast iron.
The above features of this material make its welding not only difficult, but not always predictable with respect to the final result. This is especially noticeable at home, when cast iron of an unknown brand is welded with non-compliance with the technological process. No one is immune from the fact that after the formation of a seam cracks will follow it.Back to table of contents
Preparation for work
To weld the iron yourself, it is necessary to prepare such tools and materials:
Classification of welding methods.
- welding machine;
- emery wheel with a flexible shaft;
- cold chisel;
- electric drill with a set of drills for metal;
- induction heating apparatus (blowtorch or flame burner);
- Electrodes for cast iron welding.
Before welding cast iron, it is necessary to conduct proper preparation of the joints of individual parts. Edges are cut using a portable emery wheel with a flexible shaft or a chisel. To avoid spalling of the material, it is necessary to cut it in thin layers (chip thickness should be no more than 1.0 mm). Defective areas are treated to untainted metal with the help of drills, chisels, cones, scrapers, the dimensions of which depend on the size of the defect.
When preparing and cutting a defective place, it is necessary to observe some conditions:
Options for welded joints.
- Cutting is done strictly along the crack.
- Depending on the thickness of the iron and convenience, through cracks are cut from one or two sides. Places of the end of cracks before it is drilled.
- One-sided cracks at a distance of 9 mm from their ends are drilled with a drill, the diameter of which should be a few millimeters larger than the width of the defect, after which they are cut down to solid metal.
- On the cracks that are placed close to each other, weld the patch in the same way as when closing the holes.
When brewing holes repair its edges are aligned with a chisel. After that, the surface of the product is cleaned with an emery wheel at a distance of 20-30 mm from the edge of the hole. Next, cut out the required thickness and shape of the patch of low carbon steel. It should cover the hole by 16-22 mm from all sides.
To reduce the stress that appears in the material during welding, the edges of the patch are folded 25-30 °. Next, the patch is placed on the damaged place and the electrode is overlapped with an electrode.Back to table of contents
Methods of welding cast iron
Cast iron welding is used in the manufacture of welded-cast structures or in the repair work. Depending on the operating conditions of the product, various requirements are imposed on the welds: from decorative embedding of small external defects to obtaining high-quality welds, the strength of which should be no worse than the base metal.
Cast iron can be welded by arc welding with a carbon or metal electrode, a gas apparatus or in another way. In most cases, the choice of a particular method is determined by the state of the element being welded. Depending on the preheating temperature, cast iron welding is divided into:
The first type is used in the elimination of small or medium defects, when the cracks are small in size, and also in the case where the deposited material cannot be cast iron for various reasons. When performing cold welding, it is not necessary to preheat the part.
Hot welding is used when the metal to be welded is cast iron, which in its performance characteristics is similar to the main material of the part.Back to table of contents
Hot iron welding
The technology of such welding is much more complicated than the cold method, but it can be used to reduce the risk of cracking on the seam to almost zero. Before welding, it is necessary to warm the surface of the part evenly, since the main cause of cracks is a large temperature difference between the weld and the base.
Before heat treatment of the product, it must be well fixed in a rigid frame in order to reduce stress, which can lead to the appearance of cracks.
If the heat is local, then the rigid frame can not be applied.
The cast iron product is made to be heated using induction heating devices using currents of 50 Hz frequency. If such a device is not available, you can use a horn, a blowtorch or a fiery torch. The scheme of hot welding.
When sealing defects at the edges of the product, or welding through cracks, it is better to use graphite molds that prevent liquid material from escaping from the weld pool. Before welding, it is necessary to qualitatively prepare the defective place, that is, clean it from dust, dirt and separate the part to form cavities, which allows for better access to the welding site.
In the process of work, it is necessary to strictly follow the technological process: observe the volume of molten iron and stir it with the end of the filler rod or electrode. Cooling the product should be gradual, not allowing rapid cooling. Small items can cool from 4 hours to 2 days, and large ones up to 5-6 days.Back to table of contents
Cold welding by electrodes
For quality cold welding, special electrodes based on copper or nickel should be used. Copper does not react with carbon and does not dissolve in iron, therefore the weld seam is non-uniform, with the presence of high-strength high carbon iron.
Nickel is dissolved in iron, does not form compounds with carbon, in connection with which there is practically no section of bleached cast iron, and the weld material has a small strength and is easy to process.
To date, there are a large number of different types of electrodes for cast iron: copper-iron, iron-nickel, iron-copper-nickel. The most common types of electrodes are presented in the table.
|Mark||Diameter, mm||Type of weld metal||Purpose|
|OZCH-2||3; four; five||Copper based alloy||Elimination of defects in the elements of ductile and gray cast iron|
|OZCH-6||2; 2.5; 3; four; five||Copper based alloy||Welding thin-walled parts from ductile and gray cast iron|
|MNCH-2||3; four; five; 6||Copper-nickel||Welding parts from ductile, high strength and gray cast iron|
|OZZHN-1||2.5; 3; four; five||Iron nickel||Welding high strength and gray material|
|OZZHN-2||3||Iron nickel||Welding high strength and gray material|
|OZCH-3||2.5; 3; four; five||Nickel-based alloy||Welding of gray and ductile iron parts|
|OZCH-4||2.5; 3; four; five||Nickel-based alloy||Welding of gray and ductile iron parts|
These electrodes allow to perform welding work not only on the bottom surfaces, but also on vertical ones. The method of welding with special electrodes is indicated in the instructions for them. They are mainly used when working with direct current of reverse polarity. The main rule of cast iron welding is that when working, it is necessary to weld metal as little as possible. For these purposes, it is recommended to use a small current and electrodes of small diameter. After applying each seam, a break should be taken to reduce the temperature of the product to 45-65 ° C.Back to table of contents
Cast iron welding with steel electrodes
This method of welding is the most affordable, but in many cases it gives poor quality of the weld. This is due to the fact that the weld steel has an unstable bond with the cast iron due to different shrinkage.
When welding with steel electrodes, due to the penetration of cast iron, the carbon content in the weld metal is very high (1.1-1.8%). The material of the roller, aimed at cast iron, is a hardened high-carbon steel with a high content of manganese, flint, and sometimes sulfur, phosphorus and other substances that have been converted from cast iron.
Rapid cooling leads to an increase in the strength of the deposited material and metal in the near-weld zone. Between the weld metal and the base, a layer of bleached cast iron with a width of about 1 mm is formed, and then a wider layer of hardened cast iron. The welding seam, made by a steel electrode, is not amenable to further processing with a cutting tool. The third layer is the electrode material.
Some welders use other techniques to weld cast iron products, but the methods listed above are the most effective. Knowing all the technological nuances of welding, you can create a reliable joint that will allow you to use the product for a long time.