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.
Use of Copper-Tin Alloy
Bronze is an alloy composed mainly of Copper and Tin. The useful range of composition is 5 to 25 percent Tin and 75 to 95 percent Copper. The alloy is comparatively hard, resist surface wear and can be cast into shape or rolled into wire, rods and sheets very easily. In corrosion resistant properties Bronzes are superior to Brasses. It is used in hydraulic fittings, pump linings, making utensils, bearings, bushes, sheets, rods, wires and many other stamped and drawn articles. Some of the more common types of Bronzes and the special purpose Bronzes are described below.
When Bronze contains Phosphorus, it is called Phosphorus Bronze. A common type of wrought phosphor bronze has Copper 93.7%, Tin 6%, and Phosphorus 0.3 percent. Phosphorus increases the strength, ductility, and soundness of castings. The alloy possesses good wearing quality and high elasticity. The metal is resistant to salt water corrosion.
Uses – It is used for all average bearings in which wearing qualities are desired. Pump parts, lining, and propellers are examples of cast manufacture. A variety of phosphor bronze suitable for casting contains 11 percent Tin and 0.3 percent Phosphorus alloyed with Copper. This is used for bearings, which must carry heavy loads, worm wheels, gears, nuts for machine lead screws, springs etc.
Silicon bronze has an average composition of 96 percent Copper, 3 percent Silicon and 1 percent Manganese or Zinc.
Uses – It has good general corrosion resistance like Copper with higher strength. It can be cast, rolled, stamped, forged, pressed either hot or cold and can be welded by all the usual methods. Silicon bronze finds application in parts of boilers, tanks, stoves or wherever high strength and good corrosion resistance are required.
Manganese bronze is an alloy of Copper, Zinc, Lead and a little percentage of Manganese. The metal is highly resistant to corrosion. It is stronger and harder than phosphor bronze.
Uses – It is generally used for preparing bushes, plungers and feed pumps, rods, etc. Worm gears are frequently made from this bronze.
Gun metal contains 10 percent Tin, 88 percent Copper, and 2 percent Zinc. The Zinc is added to clean the metal and increase its fluidity.
Uses – It is not suitable for being worked in the cold state, but may be forged when at about 600C. The metal is very strong and resistant to corrosion by water and atmosphere. Originally, it was made for casting boiler fittings, bushes, bearings, glands, etc.
It contains 20 percent tin and the rest is Copper. It is hard and resistant to surface wear.
Uses – Bell metal is used for making bells, gongs, utensils, etc.