Casting of bronze and brass: features of technology and stages of the process
Casting of bronze allows to make products, characterized by exceptional decorative appeal. Casting technology from this alloy, based on copper, known for centuries, but even today it continues to improve.
The appearance of bronze products speaks of the painstaking work of the master, turning faceless metal into a work of art
History of technology
According to historians, age, which has a bronze casting, is 12 thousands of years. Initially, this technology was used to make jewelry and the simplest tools from bronze. Over time, this technology has improved, and today it is a method, with which to create many unique products from this alloy.
The current level of development of bronze casting allows to obtain from this copper alloy various items not only industrial, but also at home. Thanks to the invention of bronze, as well as the development of technologies for its processing, the main of which is casting, we can still enjoy the view of works of art today, which were created by masters in the Middle Ages and in ancient times.
Vintage bronze set of stationery
The most popular is bronze casting, as well as casting brass - another alloy, based on copper, acquired in the era of classicism and European baroque. It was in those days that people learned to use these materials for that, to create unique interior elements and decor.
Such alloys, created on the basis of copper, and today are actively used in the manufacture:
- items, which are used for interior design;
- gates and fences, perform not only decorative, but also a protective function;
- sculptural compositions and souvenirs;
- bas-reliefs and design elements of lighting fixtures - chandeliers and sconces;
- elements of stair structures and entrance groups.
Bronze casting for making knife handles
Many of these products, do not differ in large size and complexity of forms, can be made of bronze and brass not only industrial, but also at home.
Stages of artistic casting of bronze
In order to qualitatively perform casting of such metal, like bronze, it is necessary to follow a certain sequence of actions. First of all, the shape of the product should be reflected in the sketch, which is planned to be cast from bronze. Based on the sketch, professional artists and designers work on its creation at modern enterprises, specialists create drawings, which accurately reflects all the dimensions of the future casting. The drawing itself is the basis for making an accurate model, which is used for the production of molds.
To create a product model, which will be further made by bronze casting, different materials can be used, in particular:
- ivory;
- wood (preference is given to such varieties of this material, like a pine, alder, beech, linden);
- gypsum;
- different types of polymeric materials.
The cavities of the wax model of the future statuette are filled with clay, which will be removed after casting
To make the surface of the model as smooth as possible, it is grounded, putty and cover with several layers of varnish. Not only different materials can be used in the production of the foundry model, but also different constructive approaches. So, models can be:
- detachable (these are complex structures, consisting of several constituent elements, which can be interconnected with flat or complex surfaces);
- integral (monolithic models, the simplest type, most often used for casting at home);
- special (these include skeletal or molding patterns, which are used in those cases, when it is necessary to make a mold for making items, differing in a difficult configuration).
The next step after creating an accurate model of the future of bronze products is the manufacture of molds. For this purpose special devices and stock are used, and basic materials, which are used in this case, there are molding mixtures, created on the basis of clay and thoroughly cleaned quartz sand.
The longest stage of bronze casting is the formation - making a mold
In such a technological process, as casting, which is made of bronze and any other metal, the foundry mold plays a crucial role. It is in this form, the inner cavity of which must exactly repeat the cast product, pour molten metal, in it he cools down, forming the finished casting. Foundry molds, used as in production, and at home, can be single or multiple, which is determined not only by the material, from which they are made, but also the peculiarities of their design.
In order to compress and harden the mixture, from which the mold is made, did not collapse at that moment, when it begins to be affected by molten metal, it is placed in special devices, which are called opoki.
Opoka is often made of plywood or wood
The size of such crucibles, which can also be single - and multiple, completely depends on the geometric parameters of the future product. In flasks, which are usually made of metal, takes place as the creation of a mold, and the casting itself.
Informative video about the advantages and features of artistic bronze casting.
Subtleties of technology
In order to perform artistic casting of bronze or to make a product of practical purpose from this alloy, it is necessary first of all to receive the molten metal. Different types of furnaces are used for metal melting: induction, arc, flames, etc.. In the simplest case (when performing casting at home) for melting bronze, you can use a conventional gas burner, placing it under a special container for melting.
Possibilities of small furnaces, which can be made yourself, quite enough for that, to perform melting of non-ferrous metals and their alloys, which also include brass and bronze.
To melt a small amount of bronze requires a refractory brick and a gas burner
The most important stage of bronze casting is filling the mold with molten metal. No matter what, that such pouring lasts all 1-2 minutes, the correctness of its implementation directly affects the quality characteristics of the finished product. Improper fillings can result in the following defects, as:
- junctions;
- burns;
- slag sinks;
- invisible.
On these bronze castings shells were formed due to poor cleaning of the crucibles before pouring
When casting brass and bronze products of small size, the molten metal is not poured from the crucible, in which it was heated, and with the help of a special device, used as a hand bucket or spoon.
Metal, which is already poured into a mold, it must be allowed to cool to the required temperature, which, depending on the brand of alloy used may vary. The procedure for removing the finished product from the mold depends on, what type it is - single or multiple. In the first case, it is simply broken with a hammer, and the casting is removed with ticks. Reusable forms, in accordance, no need to break: they are simply opened for the connecting surface and the castings are carefully removed from them.
The elongated form just needs to be refined. This is the refinement, that from a surface of a product gutters are removed, vapor, profit and bay, formed in the process of casting. Such an operation, which can be performed with a variety of mechanical tools, called chopping.
Giving the cast product an attractive appearance
Product, which has just been removed from the mold, looks quite unpresentable. On its surface may remain burnt molding mixture and other surface defects are detected. The first step in bringing a bronze object to normal is to clean it. Metal brushes or grinders are used to perform this procedure (as a working body on them the wire circle is established).
Though, that brass and bronze differ in good fluidity and at performance of molding well fill all deepenings in the form, it is almost impossible to get a thin picture on the finished product. To form a similar pattern, use such finishing operation, as coinage. It is performed using a special tool. Depending on the complexity and subtlety of the drawing, which must be formed on the surface of the cast bronze product, the minting operation may take a different amount of time.
Hand minting bronze figurine
It should be borne in mind, that stamping is the most creative stage of the casting procedure, that depends on the quality and diligence of its implementation, how the product will look like in the end. That is why it is necessary to approach performance of such operation very responsibly and with the maximum accuracy.
Depending on the plan of the master, performing casting of bronze or brass, as well as from requirements to decoration, the surface of the casting can be covered with artificial patina, gilding, silver, a layer of nickel or chromium. Items, which have a complex structure, often not completely cast, and separate parts, which then need to be connected properly. This connection is made using special locks, originally provided in the design. In order not to confuse such locks and correctly compare their elements with each other, they are often labeled.
Casting on centrifugal technology
For the production of bronze products in the factory, to wear resistance of which there are increased requirements, such technology is often used, as centrifugal casting. It is used to cast bronze products, used in mechanical engineering and other industries. Here, in particular, include:
- gears;
- elements of worm compounds;
- bushings for various purposes;
- loving;
- bushings;
- rings;
- inserts, etc..
Centrifugal casting technology involves, that molten bronze fills the form under its own weight, and under the influence of centrifugal forces. Foundry molds are placed in special equipment. Depending on that, in which plane is the rotation of the molds, installed in such equipment, it can be of vertical or horizontal type.
Centrifugal casting scheme
Equipment of any type, which is used to perform casting of bronze by centrifugal technology, has the following structural elements:
- crucible, in which the metal is melted;
- approach, by which the molten metal is fed into molds;
- exhibit;
- electric motor, which is used as the main drive and provides rotation of forms;
- drive elements: pulleys, it's raining, key-belt transmission.
Due to the peculiarities of this technology, with its help it is possible to carry out high-quality casting of bronze products, differing even in a very complex configuration. Due to the use of centrifugal forces, which press the molten metal to the walls of the mold, the casting surface has a high density and, in accordance, high wear resistance.
Naturally, that to perform casting with this technology is possible only in production conditions and in the manufacture of parts in large series, as in unit production such method is economically impractical.
