To give the interior associations with the aristocratic style of the Middle Ages, decor masters have long used brass, and especially often - bronze. Casting from these alloys and now makes it possible to create monumental masterpieces that can decorate any home.
Bronze: properties
In art casting, alloys are more often used than pure metal. Bronze is especially popular - an alloy of copper with tin (an additive and an alloying element) in various proportions. If zinc is added instead of tin, then the result is brass, and if nickel is nickel silver. Copper in combination with aluminum, beryllium or silicon is also considered bronze. The alloying element is indicated in the designation:
- BrO5, where tin is 5%;
- BrOS5-25: composed of 5% tin and 25% lead.
What technological properties does bronze have? Casting is possible when the material reaches fluidity. The temperature at which copper melts is 1083 ° C. When tin is added to it, the threshold decreases to 800 ° C, which greatly facilitates the process of heating the raw material. After solidification, the product shrinks to 1%. Depending on the components, bronze products will vary in hardness. With a minimum amount of tin, they can be forged, at a concentration of 20% or more, they become hard and brittle. Plasticity is added by the introduction of lead. The addition of zinc makes the material more resistant to corrosion.
Bronze: cast
Significant preparatory work precedes metal melting. One part is related to the manufacture of the model. At this stage, the sculptor sculpts the sample on a scale of plastic material. Then translates it into life size in gypsum or clay. A reverse cast is taken from this transition model. The complex form has several components and is assembled in parts. Heated wax is poured into it. By wrapping the form, they achieve uniform distribution over the entire surface. After cooling, a model of the future sculpture, made in wax, is formed. The author completes the details, corrects the flaws.
The overwhelming majority of art castings made of bronze and brass are carried out using such lost wax forms ("waxes"). The sculpture is hollow with a wall thickness of 2 - 5 mm. Otherwise, if the metal filled the entire mold, then the massive casting would be too heavy, and a lot of material would be required. And the matter is not only in its high cost. When pouring, it would be necessary to immediately melt all its amount, and this automatically increases the size of the hearth and furnace, complicates the process of feeding the alloy to the mold. In addition, shrinkage of the material will lead to inevitable deformation, which will lead to distortion of the shapes and individual details of the composition.
Process features
After creating the wax form, the next step begins. The caster is taken over. He creates his mold for pouring molten metal. Stencil is covered with a special heat-resistant composition in several layers. First, such a liquid ceramic is poured into a waxy mold. At this stage, the core is created - "blockhead." After it hardens with the same composition, the model is carefully covered outside, setting the required number of “pilots”, where bronze will be sent.
Casting becomes possible after sintering (calcining) the mass at high temperature. As a result of this process, a durable ceramic shell is formed. The wax is evaporated through airmen and air vents. The result is a hollow shape. After pouring with metal, it breaks. The inner layer of ceramics can be left or also removed through the process hole.
Bronze casting at home
You can get an alloy product in earthen form. At home, if you have a template in this way, you can make a bronze cast. But you need to be prepared for the fact that accurate copying of small details cannot be achieved and there is a revision. The form is disposable, but the earth itself (a mixture of clay and sand) can be used repeatedly. Usually make detachable forms, consisting of two parts. But you can make it whole if you use a wax model. After sintering, the clay form is boiled in water, wax through the summer floats to its surface.
High-quality casting can be obtained if the mold is preheated. Copper and tin are heated in a steel crucible. Use coal hearth or muffle furnaces. After complete melting, the metal is kept at high temperature for a few more minutes and poured into the flyer with a thin continuous stream. After cooling, the product is further processed. First, the metal frozen in the flyers is chopped off. Places are being cleaned. Thin details are formed during the minting process. The product is ground, polished, if necessary covered with a patina.