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The chill mold is what?

A mold is a reusable form for pouring metal. It can be either detachable (it consists of two parts), and it does not (shaking out the chill mold). Die-casting has several advantages over shell molding, but there are some drawbacks, for example, casting of castings requires additional heat treatment.

Benefits

During the casting process, intensive heat transfer from the molten metal to the chill mold occurs. This results in a higher density, better mechanical properties of the metal, higher accuracy, better structure and less roughness compared to sand castings.

The process of casting into chill molds differs also in that a metal mold (chill mold) can be used repeatedly. It is made of a material of high strength, due to which the working surface of the mold is performed more accurately. This increases the quality of the surface of the castings, and due to the high thermal conductivity of the casting, the castings quickly solidify.

Another advantage of chill casting before using sand molds is a smaller degree of further machining of the obtained castings, and this reduces the consumption of materials for molding.

Health and Ecology

Casting in chill molds increases productivity 2-3 times, because such labor-intensive operations as preparation of a mixture, cleaning and shaping of products are excluded from the process. Since production areas are also decreasing, the costs of repairs and the construction of new workshops are becoming significantly less.

Many harmful operations are eliminated from the process, such as knocking out molds, cleaning castings and cutting them. This contributes not only to improving the conditions of production, but also to reducing environmental pollution.

disadvantages

The manufacture of chill molds is quite expensive due to the laboriousness of the process itself. If there are undercuts in the castings, the cost of the chill is increased because of the need to complicate the design: inserts, disposable sand and split metal rods are used.

The life of the mold is determined by the number of castings of good quality, which can be obtained in it. The durability of the mold determines the economic feasibility of the process, especially in the process of casting steel and cast iron. Increasing the life of chill molds is one of the main technological tasks in this field of production.

Because of the rapid cooling and thickening of the melt, it is difficult to obtain long thin-walled products when casting into the chill mold. This also leads to the fact that cast iron castings acquire a hard, bleached layer. The form is malleable, this can lead to stresses and cracks in the castings. With the use of disposable sand bars, the accuracy of the castings is reduced, the roughness of the surface at the point of contact with the core rises.

Quality of castings

Casting and mold interact with high efficiency. The casting hardens and cools in the sand form much longer than in the chill mold, but the fillability in the sand mold is usually better, making the production process more difficult by casting castings from non-flowing alloys, and also restricts the parameters such as cast size and minimum thickness Walls. Casting of aluminum in chill mold (as well as copper and other non-ferrous metals) is the most demanded in Russia.

However, as a result of rapid cooling, it is possible to obtain a non-porous, fine-grained structure, which increases not only the strength, but also the plasticity of the resulting casting. In the manufacture of articles made of cast iron by chill casting, a number of problems arise: because of the unique crystallization in the castings, the formation of carbides and ferrite-graphite eutectics is possible. This reduces the toughness and wear resistance of cast iron. The bleached surface layer in such castings is very hard, so that the products are suitable for cutting only after heat treatment (annealing), which eliminates chaff.

The structure of the form

The chill mold is usually two half molds that are fastened with locks (pins), and immediately before starting the pouring of the molten metal the half molds are fixed with locks. Profits are carried out by feeding the casting through so-called bumps and ventilation plugs. Metal forms without the function of the connector are called shaking molds.

Before pouring, the working surface of the mold is treated with a layer of substance that protects the chill from the heat stroke from a sudden increase in temperature. This measure also prevents the casting from setting with the mold.

Steel and cast iron

Casting in the chill cast steel and cast iron occurs using pulverized quartz, graphite, liquid glass and refractory clay as a refractory coating. Before pouring, the chill must be heated to a certain temperature, which depends on the thickness of the walls of the casting and the alloy used.

The main requirement to which the material of the chill must meet is the resistance to thermal shock, which is unavoidable when pouring molten metal. For the production of molds use gray cast iron, high-strength cast iron, structural, carbon and alloy steel, as well as copper and aluminum alloys.

Coated chill mold

This is a kind of technology in which shell and chill casting combine their advantages, and the shortcomings of both methods are smoothed out. This technology is characterized not only by crack resistance but also by compliance, which makes it possible to produce castings of high accuracy, and if compared with shell molding, expensive molding material is consumed minimally.

The lined metal mold is manufactured by filling the space between the metal casting model and the inner surface of the die. The most commonly used are blowing and pouring methods. For filling, take a sand-resin mixture in which the binding element is phenol-formaldehyde resin (2-2.6%) and urotropine (about 10% by weight), as well as self-hardening (binder-liquid glass) and ceramic compounds (binder - ethyl silicate). The mold and mold model, having a temperature of 200 degrees, transfer the heat of the mixture, which solidifies and forms a layer of facing 3-5 mm thick. Conventional or sheath rods serve to make cavities in castings.

The casting process

The chill mold, covered with a layer of refractory material, heats up. The operating temperature should be at least two hundred degrees, but depends not only on the alloy used for pouring, but also on the size of the casting, the thickness of its walls and the properties that are required of it. After heating in the mold, it is possible to install rods, ceramic or sand, if this is of course required by the casting plan, and then the half-molds are joined and tightly locked with special clamps. If the casting takes place in the chill molding machine, then its own locking mechanism is used. After these preparations, molten metal can be poured into the chill mold.

When the casting has already acquired some strength, metal rods can be partially extracted from it. This subsequently facilitates the final extraction of the rods from the castings due to the reduced pressure on them from the solidifying metal.

After the casting has cooled down to the desired temperature, the chill mold can be opened. At this stage, the metal rods are extracted, and the castings are taken out of the mold. The sand rods are knocked out, the gains, spurs and springs are cut off, and the quality control of the product is carried out, after which the entire process can be repeated.

Before manufacturing a new casting, the plane of the connector and the surface of the die are carefully inspected. Refractory composition is applied once or twice per shift, but in case of detaching it from the working surface, it is necessary to restore the layer.
The chill must be brought back to the operating temperature, as it cools very much during the time that the casting is removed. If the product is thin-walled, the mold is strongly cooled; If the produced casting was sufficiently massive, the chill mold could be heated above the operating temperature, and then specially designed cooling systems are used, so that before the next pouring the mold will in any case be cooled.

Chill casting does not involve any complex and time-consuming action, excluding the process of cooling the casting to the desired temperature. Most operations can be performed by machines in automatic order, which is one of the important advantages of the method, but the main thing is that the chill mold is not a one-off form.

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