Brass

Sham S. Misri

Brass is a mixture (alloy) consisting essentially of copper and zinc in variable proportions. Brass is harder and stronger than copper and it does not wear out easily. It is also cheaper than copper. This attractive, hard wearing metal has many uses in ornamental dishes, hardware, engineering, architecture and for musical instruments. The musical instruments (such as trumpets, trombones, orchestra and tubas) are made of brass. 

 

The bright metal objects are made of brass. It finds use in brass memorial tablets, bright metal fittings, utensils, or ornaments and empty cartridge shells.

There are many different kinds of brass, but all these contain copper and zinc. The amount of copper in brass varies from 50 percent to more than 95%. The other main metal, zinc, can be added in proportions up to 50%. Small amounts of these elements are often added for special purposes. These can be Tin, Nickel, lead, manganese, aluminum or iron.

When brass has 70 % copper it is a golden yellow colour. If the alloy has about 80% copper it becomes reddish in colour, and looks more like copper. Alloys with a lot of copper in them are quite soft and can be shaped either hot or cold. Brass with less than 60% copper is seldom shaped cold because it is too hard and brittle. The more zinc that is added to the mixture, the harder the brass becomes. Small quantities of nickel and tin are often added to make the brass harder and less likely to wear out.

Brass was probably discovered some time 1000BC by people who lived near the Black Sea in Turkey. They made brass by heating copper with charcoal and powdered zinc ore. Brass was extensively used in China after 220 BC, and soon thereafter by the Romans.

By the end of first century BC, the Romans were making brass coins. In Europe up to the 16^th century, brass was used mainly for decoration and memorial plates in churches.

In ancient documents, including the Bible, the term brass is often used to denote bronze (copper/tin alloy). The malleability of brass depends on its zinc content; brasses with more than 45% zinc are not workable. Alpha brasses contain less than 40% zinc; beta brasses (40–45% zinc) are less ductile than alpha brasses but stronger. A third group includes brasses with additional elements. Among these are lead brasses, which are more easily machined; naval, and admiralty brasses, in which a small amount of tin improves resistance to corrosion by seawater; and aluminum brasses, which provide strength and corrosion resistance where the naval brasses may fail.

Making Brass

One of the problems in making brass is the difference in the melting points of the two main ingredients. Copper melts at 1083 degrees centigrade, but zinc melts at only 419 degrees centigrade. If the metals were heated together the zinc would all boil away before the copper had melted. So the copper has to be heated first until it melts. Then solid zinc is added, and most of it melts quickly in the molten copper. A small extra amount of zinc is added to make up for the little that melts away.

Casting the brass

After the zinc and copper have melted and mixed, the brass is ready to be poured into molds preshaped to whatever is being made. To prevent the casting sticking to the mold a graphite coating or some oily substance is wiped around the inner side of the mold before the metal is poured in.

One of the most common types of brass is called cartridge brass. It consists of 70% copper and 30% zinc.

Nickel silver is another member of the brass family. It has no silver in it at all, but is an alloy (mixture) of copper, zinc and nickel. This metal which is also called German silver is used to make “silverware” for the table. It is plated with silver and looks just like pure silver. The plate can however wear off with use.

Some other alloys are: (Read in a rhyme)

Brass, Bronze, Bell metal,

German silver, Gunmetal,

Pewter, Solder, Type metal.