Casting in shell molds is also called shell casting. And abroad such a method of work is called Shell.
In the modern industrial industry,many different ways of casting. In addition to shell, also casting on investment models, as well as in metal forms and several other methods is also used. A common advantage of such methods of casting, when compared with sand molds, is that they enable us to obtain more accurate final materials in terms of their shapes and sizes. In addition, the amount of roughness on the surface of such products decreases. In more rare cases, it does happen that there is no need for subsequent machining after melting. In addition, the use of casting in shell molds and other methods contributes to the fact that it is possible to mechanize this process as much as possible, thereby increasing its automation. And this, of course, greatly increases the productivity of any industrial facility.
Speaking specifically about this method, heIt was first introduced in factories back in 1953. At the present time, the method is used quite widely. It is casting in shell molds, for example, most of the parts for the Kirovets tractor are manufactured. All the details that are produced by this method, are obtained the highest quality of steel or cast iron. By shell casting is meant a method in which the final result of the casting has a shape consisting of two sand-resin shells. This method of manufacturing parts is also used only in cases where it is necessary to create a part with small or medium dimensions, but with high accuracy. Examples of the application of this casting method can be engine parts or thin-walled castings.
With this method of work, you canget different parts for fans, motors, pumps or textile machines. However, the maximum length of the resulting product can not exceed 1 meter, and it can not be more than 200 kg.
The essence of casting in shell molds is basedon certain properties of thermosetting resins, which are part of sand-resin mixtures. The advantage due to which such components are used is that these resins have the property to harden and irretrievably harden if treated with a temperature of 200-250 degrees Celsius.
In order to make a shape for the subsequentcasting, it is necessary to have fine-grained quartz sand, which comes with the addition of a thermosetting resin, which is its binding element for obtaining a full shell shape. These materials, in particular, the resin is selected because it passes through a certain temperature barrier and hardens. The manufacturing process is as follows. First, the resin is heated to 140-160 degrees Celsius. Under the influence of such an environment, it turns into a liquid sticky mass that completely envelops the quartz sand shape.
The field of application of casting in shell forms is quite wide, and therefore the very process of making molds is brought to automatic or automated.
After the form is completely coveredresin, the temperature is increased to 200-250 degrees Celsius. This temperature threshold is sufficient to make the adhesive mass irreversibly harden and form a shape. Further, when the process of casting parts begins, that is, when the molten metal enters the mold, the temperature in it reaches about 600 degrees. This regime is sufficient for the resin not to melt, but burned, leaving pores on the very form that facilitate the escape of gases.
Like any other manufacturing process, this onehas its positive and negative qualities. If we compare this method of casting, for example, with casting into ordinary sand molds, then we can distinguish several of the following advantages:
However, there are some disadvantages of casting in shell molds. These include:
The process of forming the hull is carried out in six stages:
It is worth starting with the fact that the typical tolerances thatallowed in the manufacture of equipment can be 0.5 mm. Surface roughness is allowed in the range from 0.3 to 0.4 μm. Such limits are argued by the fact that fine sand is used. Also worth noting: the use of resin significantly contributes to the fact that the surface will be very smooth.
In order to engage in the production of suchforms and details, it is necessary to attend to the installation of the model-mold. The time required for installation is less than a week. After the completion of the installation, the quantity of produced products can reach from 5 to 50 pieces per hour. Such volumes of production per hour are quite real, but for this it is necessary to prepare the casting process accordingly. The main materials that will be required for casting are cast iron, aluminum, copper, and also alloys of these kinds of metals. Another necessary material will be an alloy using aluminum and magnesium.
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