Bronze casting

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Detailed torso with separate head as cast bronze, cape chased and forged , Eastern Mediterranean, approx. 100 BC BC, Israel Museum , Jerusalem .

The bronze casting is a casting method in which liquid bronze , an alloy of copper and tin , is poured into a mold to produce a desired article made of bronze. Typical products were and are u. a. Bells , epitaphs , sculptures , tools, cannons , mirrors and jewelry.

history

The bronze casting has a long tradition that goes back to the Neolithic . In the 4th millennium BC, people began to melt and pour copper. The first evidence of cast copper in Central Europe is found in crucibles from the Pfyn culture , Switzerland. From around 2200 BC Tin-bronze appears regularly in Central Europe.

Besides the cold working of the bronze, the bronze casting is the most important production process of the Bronze Age, as it is gradually replacing the production of stone tools. The reusability of the metal, which can be melted down again as often as required, is a great advantage.

In the course of history, several molding processes have emerged: casting in permanent molds and casting in lost molds .

Casting in permanent molds

For copper materials, permanent forms can be made from stone, as found since the Bronze Age, and from metal. Metal molds are much younger and are called permanent molds . Nowadays steel molds are used in industry. For the craft, only casting in lost forms is profitable. In the modern world, bronze casting primarily plays a role for artists, as other materials are more resilient and more economical than bronze.

Pouring into lost forms

introduction

In the literature, the lost wax process is often equated with the lost form process. This is not technically correct as sand molds are also one of the lost molds that are destroyed after casting. The lost wax technique should therefore be referred to as the lost model technique. Demands on the molding material are malleability , gas permeability, mechanical strength before casting and good disintegration after casting, to name just the most important. The casting is usually done in cold molds, which must first be fired dry. It is important to ensure that all chemically bound crystal water is removed.

Bronze casting with master model

The following article describes the production of a wax positive using a so-called plaster mold. The wax positive is required to create a shape using the lost wax technique. Since the silicone rubber compounds are a relatively new development, a traditional way is described here with which wax models can also be produced without silicone rubber. Even before wax was used, molding sand was used to make the casting molds. A piece shape consists of individual pieces that mold parts of the model in such a way that no undercuts are created that would make it impossible to remove the pieces. After all the plaster pieces have been made and the piece shape is ready, the plaster pieces are removed one after the other to expose the plaster positive. The pieces of plaster are watered and then put together. The resulting cavity is then brushed or swiveled with liquid wax. After the wax has cooled down, the individual pieces of plaster can be removed and the wax model can be removed. The more or less large number of plaster pieces resulted in numerous seams on the wax that had to be reworked before the casting mold was made.

Operation

First, a plaster negative is created from the plaster of paris model of the figure or the final shape. The mold to be cast must be divided into several small sections, since otherwise larger models or very detailed samples cannot be produced. Then the positive plaster is cast and touched up. Partial casts avoid the undercut and result in a piece shape (negative shape), whereby the plaster positive is retained. Then the piece form is put together and lined with wax on the inside and then the core mass is poured in. Individual pieces of the piece form are removed and the wax is removed from the mold in this way. Then the wax is revised. A mixture of tin and copper is used as casting material for bell casting, and a mixture of copper, tin and zinc for the casting of statues. After these have cooled down, the individual parts are removed and put together according to the plaster model, usually by melting. Finally, the pouring edges and joints must be plastered.

Artist as a bronze caster

See also

literature

Web links