Cast iron is one of the most common materials used in industry. Various methods are used in the production of parts, the most common of which is casting into the ground. This method involves the use of a special mixture from which the shape of the future part is created. Let’s consider them in more detail.
Types of molding mixtures for casting iron
To increase the strength and thermochemical characteristics of the molds of dimensional castings, they are dried. However, this technological process requires additional energy and time. To eliminate these problems, surface drying or casting of cast iron in cold-hardening mixtures (CHC) is often used. The latter method is most common in the manufacture of large ferrous metal products.
Composition of the molding mixture for cast iron
Depending on the requirements of the technological process, different types of materials are used. For example, chromomagnesite based on liquid glass are characterized by high thermochemical indicators. They are used in the manufacture of large-sized products from cast iron, stainless and heat-resistant steels. These mixtures are less pliable than analogues with a lingosulfanate base, which are used for the manufacture of rods. The disadvantages also include low gas permeability, which is why the thickness of the lining is not allowed to be made more than 15 mm.
For parts weighing less than 160 tons and with a wall thickness of up to 7 centimeters, a base of chromium ironstone is used. The thickness of the facing layer can vary from 25 to 150 millimeters. In this case, the grains of ironstone should be within 1-1.5 mm and contain no more than 40% dust. The humidity of the finished mixture cannot exceed 6-7%. Such a mixture does not require the addition of connecting elements, since a dense crust forms after drying. In order to increase strength, up to 3% of lignosulfonate can be added.
Zircon sands are used as the main component for the production of cast iron castings with high surface cleanliness. However, due to the high price, the distribution of such mixtures is limited. It is most expedient to use them for the production of products from precious metals and alloys.
Using cold-hardening mixtures
All of the above materials require drying. However, to reduce energy consumption in production, HTS mixtures are used that do not require heat treatment. The principle of hardening is that furan or other resins are added to the sand base, after which a chemical reaction takes place under the influence of a catalyst. As a result, hardening occurs.
The use of certain types of bases depends on the requirements of the technological process, including the cleanliness of the casting surface. Thus, finishing operations may require increased time and labor, which negatively affects the final cost of the finished product.
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