Thursday, April 1, 2010

THE BELL METAL Of INDIA

Any of several chemical elements that are usually shiny solids that conduct heat and can be formed into sheets are known as metals. The Metal Industry is primarily concerned with metallurgy and metalworking. At first the metals are extracted from the metal-ores found in their natural state deep within the earth and then these ores are purified through a detailed procedure to obtain the metals in their pure form, these processes comprise metallurgy. Then the pure form of the metal so obtained is used to manufacture structures as well as different machines and parts of machines. The procedures which involve the manufacturing of machines and other useful items from the metals so obtained through the metallurgical processes constitute metalworking.
This article tries to reveal the functioning of a cottage industry called Bell metal industry. This will help the people who are interested to know about the cottage industries.
Alloy
Alloys are formed by the mixturing of two or more metals. Alloys consist of tiny crystals called grains. In every grain the atoms are packed together in a particular geometric arrangement. Grain size determines particular characteristics in alloys. Eg: smaller grains make stronger alloys. The first alloy made by people was bronze. The oldest bronzes consisted of copper and arsenic it was in about 3500 BC.The manufacturing of alloys is also carried out in the Metal Industry through the proportionate homogeneous mixing of two or more metallic elements (metals in the pure state). The alloys so formed are mainly manufactured in order to enhance the natural properties of the metals by combining them together. Here we are going to describe one of the most popular as well as useful alloy of Tin and Copper; Bronze. The oldest alloy known to human beings is bronze mixture of copper and arsenic. The existence of Bronze dates back to 3500 BC. Gradually people replaced the arsenic with tin. The period in history between the Stone Age and the Iron Age became known as the Bronze Age. Bronze was commonly used to cast containers such as cups and urns. People made battle axes, shields, swords, ornaments and some times primitive stoves with Bronze.
It was the period when people used bronze for tools and weapons. It followed the Stone Age, when stone was the prime material. When iron tools became wide spread, the Bronze Age ended and the Iron Age began.
The Bronze Age is not a particular period of time. Some areas had their bronze age early, others had it late. In some places it lasted for a long time, and in others it was short or skipped altogether.
The earliest known use of bronze was in Sumer in Mesopotamia (now Southern Iraq), about 3500 BC. The Chinese began to use bronze during the Shang Dynasty (about 1766 BC to 1122 BC). During this period, the use of bronze became wide spread in Northern China. People continued to use bronze until some time between 1500 and 1000 BC. Then iron, which first appeared in Asia Minor, became common. The Bronze Age in most regions overlapped an earlier Stone Age and a later iron stage .because people did not stop using one material all at once. Some South American Indians had began to use bronze before white explores came. In short the oldest bronzes consisted of copper and arsenic. It was about 3500 BC. Over the next few hundred years, people discovered that mixing tin with copper produced a more useful bronze.
People began to make tools, ornaments and weapons out of this metal. This metal is much harder than pure copper and it is easier to melt and cast into useful shapes.
For special purposes Phosphorous, Lead, Zinc and other metals may be added in Bronze. For eg: Phosphorous hardens and strengthens Bronze. Because of reputation of Bronze for hardness and durability, the name has been adopted commercially for many Copper alloys that contain little or no tin but are similar in colour to Bronze. Eg: Brass (55% Cu + 45 % Zn), Zn is corrosive.
The Tin, which is used to make Bronze, is a costly metal. It has 600 per Kg. so the bell metal is also costly. Therefore except bells and cooking vessels. All other items are manufactured by Brass. Brass is an alloy of Copper and Zinc. In short some excellent Brass alloys have been in correctly called Bronze. Nowadays Brass is imported to India from Moradabad of UP. However it is usually understood that when the word Bronze is used by itself, the alloy will contain a considerable amount of Tin.
Bell Metal Industry
This is a traditional cottage industry. Bell metal workers belong to Moosari community. Moosari, Blacksmith, Goldsmith, Carpenter and Mason are the five groups called Viswakarma. Moosari is doing bell metal and brass casting. The main difference between these two works is that, bell metal products have no permanent moulds but in brass casting permanent moulds are present. In bell metal works 100 % hand made workers are involved. No need of any kind of machinery. They make the tools themselves. (But nowadays very rarely it is imported from Andra Pradesh).so this industry is under the department of handicrafts and khadi and village industry. The main raw materials for this industry are clay, wax, castor oil, fire wood, coconut shells, and coconut husk, cow dung and metals. The main metal used in this industry is bell metal.
There is a famous definition for handicraft i.e.: “TWO PIECE NEVER BE SAME”. In the hands of skilled artisans or “moosaris” of kerala, the process of casting bell metal has evolved to its ultimate, to produce single piece casting weighing u to a tone. The perfection of casting technology and alloy composition through an unbroken tradition of many countries has resulted in diverse product forms varying from bells to cooling vessels. The stand proof to a rich visual language and style, a strength shared by all craft traditions of India.
Bell Metal
Bell metal is an alloy of copper and tin in the ratio of 78: 22. This alloy in a particular fixed ratio of 78% of 99.9 pure copper and 22 % of tin was first invented by the Germans. They used this metal to make church bells. Because, this alloy has special sound damping characteristics that give these bells a rich tone. Thus this alloy got the name BELL METAL .Nowadays bell ghams are used for the production of bells. But a musical effect is not present in these types of bells.
Production Process
The process of casting is known as “varku” in Malayalam makes use of natural bees wax in a unique way. A layer of wax is wrapped around a rigid clay core. All the intricate details ands designs of the final product are worked in to the wax by hand. The wax model is covered again in clay and allowed to dry. This three layered mould is heated in a furnace to remove the wax, leaving a cavity between the clay core and the outer clay mould. Melted bell metal is poured into the mould and takes the shapes of the wax model. After cooling minimum 24 hours, the clay core and outer mould are broken open. The cast form is then finished and polished by chiseling and filing. This is done for the shining of the vessel.
The entire operation is skill intensive and performed with the simplest tools. For the alloy, tin and copper are recovered from scrap. All the in gradients including the clay and wax are recycled leaving no wastage. The most important part of this work is the preparation of mould. This mould is not readily available and not a machine made one. This is fully made manually. Only clay and wax is used for the preparation of mould.
The temperature of the mould and the metal fluid should be equal. This is generally 900c to 950 c[1] .the same temperature of both the mould and the melted fluid ensure the smooth flow of the liquid to the hollow portion without any hindrance. This is a highly skilled job. Only the practical knowledge of the workers is used here. In short it is a 100% handy craft phenomena. That is there are any instruments for the measurement of temperature.100% success is not expected in this type of moulding process. Generally 20% damage or defect is expected. That is about 20% of manufacturing loss are occurs.
Properties and Uses
The strongest bronze contains a high percentage of tin and little lead. Alloys with a high tin content also have a low melting point. They are preferred for intricate ornamental castings such as statues. When bronze is to be used for this purpose, lead is often added to the alloy. The result is a cheaper alloy that is easier to cut. Lead is also added to bronze when the manufactured article will need to be lubricated. For e.g.: bearings are made from leaded bronze. Bronze that contains only phosphorous and tin wears best against steel when no lubricating agent is used. Because it is easily cast in large shapes. It is used for making bells.
Most alloys resist corrosion. Statues and bells made of bronze will wealthier to a beautiful brown colour or develop a green patina (film) characteristic of copper. After such films form, bronze corrodes very slowly. Because of these bronze articles frequently last hundred of years. This metal generally will not react with acids. So it is very healthy to prepare food in the vessels made out of bell metal. This metal cannot be welded. This is a heavy and brittle one. If fallen down it may develop cracks, even break into pieces.
Here we are talking about the Bell Metal. Its an alloy with high proportion of tin to copper was the material used for making utensils for ritual and household use. Bell Metal did not tarnish easily and suitable for serving dishes. Traditionally the plate’s tumblers or bowls were forged out of lump of on anvils and steel shapers by a team, heating and beating the metal simultaneously. Bigger pots are shaped and forged in parts and joined or brazed with soldering paste finished and polished. In this article we saw the cottage industry of bell metals and their production as a whole.
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