The Manufacturing Process Of Brass
The manufacturing process used to produce brass involves combining the appropriate raw materials into a molten metal, which is allowed to solidify. The shape and properties of the solidified metal are then altered through a series of carefully controlled operations to produce the desired brass stock.
Brass stock is available in a variety of forms including plate, sheet, strip, foil, rod, bar, wire, and billet depending on the final application. For example, brass screws are cut from lengths of rod. The zigzag fins used in some vehicle radiators are bent from strip. Pipes and tubes are formed by extruding, or squeezing rectangular billets of hot brass through a shaped opening, called a die, to form long, hollow cylinders.
The differences between plate, sheet, strip, and foil are the overall size and thickness of the materials. Plate is a large, flat, rectangular piece of brass with a thickness greater than about 0.2 in. (5 mm)—like a piece of plywood used in building construction. Sheet usually has the same overall size as plate, but is thinner. Strip is made from sheet that has been cut into long, narrow pieces. Foil is like strip, only much thinner. Some brass foil can be as thin as 0.0005 in (0.013 mm).
The actual manufacturing process depends on the desired shape and properties of the brass stock, as well as the particular machinery and practices used in different brass plants. Here is a typical manufacturing process used to produce brass sheet and strip.
1 The appropriate amount of suitable copper alloy scrap is weighed and transferred into an electric furnace where it is melted at about 1,920°F (1,050°C). After adjusting for the amount of zinc in the scrap alloy, an appropriate amount of zinc is added after the copper melts. A small amount of additional zinc, about 50% of the total zinc required, may be added to compensate for any zinc that vaporizes during the melting operation. If any other materials are required for the particular brass formulation, they are also added if they were not present in the copper scrap.
2 The molten metal is poured into molds about 8 in x 18 in x 10 ft (20 cm x 46 cm x 3 m) and allowed to solidify into slabs called cakes. In some operations, the melting and pouring are done semi-continuously to produce very long slabs.
3 When the cakes are cool enough to be moved, they are dumped out of the molds and moved to the rolling area where they are stored.
4 The cakes are placed in a furnace and are reheated until they reach the desired temperature. The temperature depends on the final shape and properties of the brass stock.
5 The heated cakes are then fed through a series of opposing steel rollers which reduce the thickness of the brass step-by-step to about 0.5 in (13 mm) or less. At the same time, the width of the brass increases. This process is sometimes called breakdown rolling.
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 oxides which may have formed on the surfaces as a result of the hot metal's exposure to the air.
Annealing and cold rolling
7 As the brass is hot rolled it gets harder and more difficult to work. It also loses its ductility, or ability to be stretched further. Before the brass can be rolled further, it must first be heated to relieve some of its hardness and make it more ductile. This process is called annealing. The annealing temperatures and times vary according to the brass composition and desired properties. Larger pieces of hot-rolled brass may be placed in a sealed furnace and annealed together in a batch. Smaller pieces may be placed on a metal belt conveyor and fed continuously through a furnace with airtight seals at each end. In either method, the atmosphere inside the furnace is filled with a neutral gas like nitrogen to prevent the brass from reacting with oxygen and forming undesirable oxides on its surface.
8 The annealed pieces of brass are then fed through another series of rollers to further reduce their thickness to about 0.1 in (2.5 mm). This process is called cold rolling because the temperature of the brass is much lower than the temperature during hot rolling. Cold rolling deforms the internal structure of the brass, or grain, and increases its strength and hardness. The more the thickness is reduced, the stronger and harder the material becomes. The cold-rolling mills are designed to minimize deflection across the width of the rollers in order to produce brass sheets with near-uniform thickness.
9 Steps 7 and 8 may be repeated many times to achieve the desired thickness, strength, and degree of hardness. In some plants, the pieces of brass are connected together into one long, continuous sheet and are fed through a series of annealing furnaces and rolling mills arranged in a vertical serpentine pattern.
10 At this point, the wide sheets may be slit into narrower sections to produce brass strip. The strip may then be given an acid bath and rinse to clean it.
11 The sheets may be given a final cold rolling to tighten the tolerances on the thickness or to produce a very smooth surface finish. They are then cut to size, stacked or coiled depending on their thickness and intended use, and sent to the ware-house for distribution.
12 The strip may also be given a final finish rolling before it is cut to length, coiled, and sent to the warehouse.