Techniques of Annealing Brass

Written by christien aguinaldo
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Techniques of Annealing Brass
Manufacturers of brass pipes rely on a series of processes, including annealing. (Jupiterimages/Photos.com/Getty Images)

Brass is an alloy metal composed mainly of copper and zinc. Since copper constitutes the major component, brass is categorised as a copper alloy. Though brass is stronger and harder than copper, it does not have the strength and hardness of steel. Nonetheless, it is a good conductor of heat, it can be moulded into different shapes and it has the ability to resist corrosion from saltwater. These properties of the alloy metal are ideal for making pipes, tubes, weatherstripping, screws, radiators, bullet casings and musical instruments. However, before brass is moulded into different items, it has to undergo a process known as annealing. During the manufacturing process, the brass is heated, which hardens the alloy and makes it difficult to cut and work with it. Furthermore, brass cannot be bent after the initial heating process. To make the brass soft and ductile, it is heated to a certain temperature and then cooled slowly. After brass undergoes the annealing process, it can be cut and shaped rather easily.

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Manufacturing Process for Brass

The raw materials are combined and then melted at a high temperature. The molten mixture is solidified and then put through a series of operations to change its shape and properties. The manufacturing process is dependent on the shape and properties the resultant brass metal should have. Typically, to make brass sheets, the raw materials are put through the processes of melting, hot rolling, annealing and cold rolling and finish rolling.

Melting

The raw materials are put into a furnace, which reaches a temperature of about 1049 degrees Celsius. Copper alloy scrap is used to make brass sheets and then based on the amount of zinc already present, more zinc is added. Thereafter, the molten metal is transferred to moulds and allowed to cool. Once the moulds are cool, the brass cakes are removed and transferred to the rolling area.

Hot Rolling

The brass cakes put into the furnace and reheated until the necessary temperature is reached. The temperature is set based on what shape and properties are desired in the end product. The reheated brass cakes are then put through steel rollers, which help to thin them out. Then they are put through a milling machine, known as a scalper, to remove oxides present on the surface. The oxides form when the hot metal gets exposed to air.

Annealing of Brass and Cold Rolling

The hot rolling makes the brass harder, and hence, it is more difficult to work with. It ends up losing its property of ductility. It has to be heated once again to make it more ductile. This process is referred to as annealing of brass. The temperature at which the annealing process occurs is dependent on the composition of the alloy and what properties the end product should have. Annealing of brass takes place in a furnace, and at times, nitrogen gas is put into the furnace to prevent the metal alloy from reacting with oxygen, which can form oxides on the surface of the alloy. After the annealing process, the brass is once more put through a series of rollers to reduce its thickness. This process is known as cold rolling, as the temperature of brass is much lower compared to what it was during the hot rolling process. The cold rolling alters the internal structure of the brass and this helps make the alloy stronger and harder. The thinner the brass gets, the stronger and harder it becomes.

Finish Rolling

The finish rolling helps to smoothen the surface of the brass. Thereafter, the alloy is then cut based on its intended use.

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