The organization of technological operations in production in one form or another involves the preparation of equipment. These are devices that play an auxiliary but important role. These devices include crucibles. As a rule, these are small conical shaped containers in which heat treatment operations are performed. What are crucibles in the process? This is a tool, thanks to which various materials are processed in order to give them various operational qualities.
Crucible design
The crucible has a fairly simple device. Its main task is to contain materials when exposed to extreme temperatures, and the features are logically expressed by thermal protective properties. Another thing is that, depending on the material being serviced, the crucible can have different operational qualities in terms of chemical interaction with metals. So, what are crucibles from a structural point of view? This is a small cone-shaped tank, which can conditionally be divided into two parts - the upper and lower. In terms of functionality, the lower part is more important, since the greatest physical and thermal loads are imposed on it. As for the upper part, it can also have a high degree of technological responsibility if it is planned to use a full melting tank.
Crucible functions
As already noted, the crucible is used in the processes of melting metals as a supporting tank. However, even within the framework of this uncomplicated function, the specific tasks of such devices may differ. The most common use of the crucible is as a separate container for organizing metal melting. Thus, in particular, the metal charge is serviced in metallurgy. But there are other methods of application, including as part of induction equipment. It would seem, why do we need a crucible in an induction furnace, if it can be heated autonomously? There are many reasons for this. Firstly, to ensure the purity of the alloy itself and the supply of high temperatures. The crucible acts as a kind of utensil that protects the metal from impurities and unwanted gases. Secondly, the surfaces of the internal walls of the induction furnace are also protected. There is a third way to use crucibles. Using special mechanisms, metallurgists can move metal masses in the molten state using similar containers.
Types of Crucibles
Crucibles generally differ in the material used in the manufacture. Raw materials can be divided into two types - metals and non-metals. If we talk about the first group, then cast iron will be the most popular design basis. It is good primarily for its resistance to temperature influences and the possibility of safe contact with other metal alloys. However, these advantages only apply when comparing cast iron containers with other metal counterparts. Conversely, if you compare cast iron crucibles with non-metallic forms, you will find disadvantages in the form of high reactivity and oxidizability, not to mention the high cost of such a solution. Now you can turn to the second group of materials. What are non-metal crucibles? These are ceramic, clay and graphite products, which are characterized by resistance to thermal effects and oxidation processes. In addition , ceramics in no way affects the chemical composition of the alloy being served, which is also a plus. Practice shows that such crucibles can harmlessly accept alloys of palladium, chromium or cobalt. The most popular are graphite and clay products, which are worth considering separately.
Clay crucibles
The popularity of clay crucibles is due not so much to their positive operational qualities as to the availability and ease of manufacture. Usually, chamotte clay is used for such needs, which during the manufacturing process is subjected to three stages of processing - the creation of a working mass, molding and drying. This technology has replaced porcelain containers. They also gave in to molding without much effort, but in practice the use did not meet the requirements of strength and resistance to high temperatures. As a result, cracks and chips appeared. What are clay crucibles in practice? It is a stronger material than porcelain even at elevated temperatures. However, in other qualities of the same interaction with metal alloys, clay is not so harmless - at least against the background of alundum and graphite products. Nevertheless, economically, the use of clay crucibles more than justifies itself when it comes to small typical melt operations.
Features of graphite crucibles
Graphite and carbon products exhibit enhanced chemical and thermal resistance, which determines their value in metallurgy. For example, special graphite formulations can withstand about 3000 ° C. Obviously, such a crucible can be used for melting metal in almost all areas of the metallurgical industry. The equipment is used for the melt, distribution, bottling of non-ferrous and ferrous metals - including in combination with induction vacuum furnaces. The manufacturing technology of graphite crucibles allows you to precisely calculate their shape and size to the smallest detail. Most often, the dimensions are oriented to the specific design of the induction furnace. For example, cup-shaped forms are common, where other technological accessories are also present - nozzles, flanges, holes, etc. But graphite raw materials are much more expensive than other materials, therefore, tooling is used mainly in the professional field. Although there are exceptions when home masters dilute the compounds with cheaper materials.
Crucible for melting aluminum
With aluminum, you can work on graphite crucibles, which are able to provide a melting point in the range from 400 to 1400 ° C. In particular, the so-called mammoth crucibles are widely used. The widest temperature range for aluminum smelting is offered by universal containers. They provide both intense heating and direct melting. In the middle temperature range, an aluminum crucible is used, immersed in an electric furnace. Such forms, in addition to temperature resistance, are distinguished by protective coatings against corrosion and mechanical durability. The most stable crucibles for serving aluminum are used in gas furnaces, which provide a temperature regime of 1400 ° C. Less commonly used is a combination of crucibles with oil-fired furnaces.
Lead Crucible
Crucibles of almost all common types can be involved in lead melt, with the exception of fragile structures. For example, ceramic, porcelain and clay models are not recommended in this case. Of course, the same graphite crucible may become optimal, but its high cost limits the possibilities for application. It should be noted that the crucible for lead smelting is not so common in the professional sphere as in private households. Metal is used to make shots, weights, various molds and other devices that may be needed on the farm. The optimal solution for such a house melting may be the combined composition of graphite with affordable construction additives.
How to make a crucible with your own hands?
The main task of those who are faced with the need to make crucibles is to provide conditions for intensive drying or heating. At this point, you can effortlessly create a mold from the same clay. Next, a heating element is prepared - an inductor. This is a cylindrical structure made of heat-resistant material and a metal wire in the form of a wire. How to make a crucible with an inductor of this type from improvised materials? It is enough to prepare four electron tubes and connect them into a parallel circuit. After that, the shape of the future crucible is placed in the center and current is supplied through the generator set.
Conclusion
Thermal industrial equipment today is strictly segmented, which allows interested consumers to purposefully purchase the same furnaces designed specifically for the melting of metal billets. Against this background, the crucible seems to be a morally and technologically obsolete device, although it is structural simplicity that does not allow it to completely get out of production processes. But such products are not limited to industrial applications. It is enough to recall what crucibles are. The value of this device for domestic purposes is difficult to overestimate. This is a small container of available raw materials that can be performed by a home craftsman for his household needs. Of course, the quality of the products performed on such a snap will be rather low, but in particular needs, high accuracy of geometric parameters is rarely required.