The chief ores of Zinc are zinc blende (zinc sulphide) and calamine (zinc carbonate). In the extraction of the metal, the ore is first roasted in a reverberatory furnace to convert the sulphide to oxide, and in the case of calamine, to drive off carbonic acid and water. The roasted ore is then reduced either in a furnace or by electrolysis process. Zinc is fairly heavy, bluish-white metal used principally because of its low cost, corrosion resistance and alloying properties. The melting point of Zinc is 419C.
The protection of Iron and Steel from corrosion is done more often with Zinc than with any other metal coating. The oldest and most important methods of applying the Zinc coating are known as galvanizing. When rolled into sheets, Zinc is used for roof covering and for providing a damp proof non-corrosive lining to containers, etc. Zinc casts well and forms the base of various die-casting alloys.
The most widely used copper-zinc alloys are Brass and Muntz metal.
This is fundamentally a binary alloy of Copper with as much as 50 percent Zinc. Various classes of Brass, depending on the proportion of Copper and Zinc are available for various uses. Suitable types of Brass lend themselves to the various processes like casting, hot forging, cold forging, cold rolling into sheets, drawing into wire. It can be extruded through dies to give special shaped bars. The melting point of Brass ranges from 800C to 1000C.
Properties. The alloy is non-corrosive. Air, water and some acids do not appreciably affect it. It is soft, ductile and has tensile strength with good fusibility and surface-finish characteristic. It is non-magnetic. By adding small quantities of other elements, the properties of brass may be greatly changed, as for example; the addition of 1 or 2 percent of Lead improves the machining quality of Brass. Small amount of Tin is sometimes added to Brass to increase its hardness.
Uses. Brasses are used in hydraulic fittings, pump fittings, pump linings, in making utensils, bearings, bushes, etc.
It contains 40 percent Zinc and 60 percent Copper. Sometimes, a small percentage of Lead is also included. It is stronger, harder, and more ductile than common Brass. It is excellently suited for working at 700C to 750C but not for cold working.
Muntz metal is used for a wide variety of small components of machines, electrical equipment, fuses, ordinance works, and for bolts, rods, tubes, etc. It is widely employed in making such articles, which are to resist wear.