Marine Engineering Nathan: March 2011

Tuesday, 22 March 2011

The Production Process of Brass

Brass is a non-iron based that is a very versatile metal and has been used over the years in many different industries and in many different shapes and sizes. Brass is quite a soft metal that can be moulded easily into different forms for example; plate, sheet, strip, foil, rod, bar, wire, and billet depending on the final stages of the manufacture process.

The manufacturing process or brass varies from each stock pile as not every batch will be the same. The process is also effected by where the brass is manufactured as one plant may have a different process from the next, but the most common way to manufacture it is as follows;

1. The first stage in the making of the metal is melting specific scrap metal together in an electric furnace where it is heated to over 1000 degrees Celsius. If any other metals are required for the particular brass formation they are also added in this step if they were not present in the scrap metal.

2. Next the molten metal is poured into moulds and allowed to solidify into slabs called cakes. In some cases the metal s poured continuously so it forms a extra long slab.

3. Then when the cakes of metal are cooled and have solidified they are released from the moulds and are taken to the rolling area where they are stored.

4. The next step is “hot rolling”. The cakes are placed in a furnace and are reheated until they reach the desired temperature. The temperature may vary depending on what the final shape of the object will be.

5. The heated cakes of metal are then feed through a series of opposing steel rollers which will then reduce the thickness of the steel by 75% while doing this the width of the metal is increased as it is pressed down.

6. The brass, which is now much cooler, passes through a milling machine called a scalper. This machine cuts a thin layer off the outer faces of the brass to remove any oxidised metal which may have formed on the surfaces as a result of the hot metal's exposure to the air.

7. As the brass is hot rolled it gets harder and more difficult to work. It also loses its ability to be stretched further. So before the brass can be shaped further it has to be heated again so it softens up again and can be moulded more easily, this process is called “ annealing”. The annealing temperatures and times vary according to how much zinc or other metal scrap was added in step 1. In every method the atmosphere inside the furnace is filled with a neutral gas like nitrogen to prevent the brass from reacting with oxygen. If this occurs it will oxidise and will become a green colour.

8. The annealed pieces of brass are then fed through another series of rollers to further reduce their thickness. This step is called cold rolling because the temperature of the rollers are much lower than that used in the hot rolling step. Cold rolling changes the internal structure of the brass and increases its strength and hardness. The more the thickness is reduced, the stronger and harder the metal becomes.

9. Steps 7 and 8 may be repeated a few times if the manufacturer want thinner, stronger metal.

10. The finished metal is then given an acid bath to rinse and clean it.