A metal is one of the basic elements in nature. Of the 92 or more known elements more than 70 are metal. Metal are good conductors of electricity and heat. Physically they are generally hard, heavy, and tenacious. An alloy is a combination of two or more metals. For example, brass is a mixture of copper and zinc. In the shop, all these materials are called metals even if some are actually alloys. There are two basic kinds of metals and alloys: ferrous and nonferrous metals.
The term ferrous comes from the Latin word ferum which means iron. Ferrous metals are those which contain iron or a considerable quantity of iron. Ferrous metals include the following:
- Iron. A chemical element which is crystalline in nature. To metalworkers, pure iron is relatively a soft metal so it is combined with other metals.
- Cast Iron. When iron is melt from its ores, it generally combines with a percentage of carbon from the coal or coke used for its heating. The result is cast iron.
- Gray Cast Iron. Contains from 2.5 to 3.5 percent carbon. This kind of cast is most used in casting.
- White Cast Iron. When the percentage of carbon is from 2.0 to 2.5, cast iron possesses extreme hardness but also becomes brittle. In metalworks where hardness is desired and brittleness can be tolerated, white cast iron is most suited. It is used extensively in the production of machine parts.
- Malleable Cast Iron. Where ductility is desired, malleable cast iron is used rather than forging parts together. This type of cast iron may be bent or distorted under stress. It can load up to a certain limit without breaking.
- Wrought Iron. Is almost pure iron containing a little slag (one to two percent). It is used in ornamental iron work and for many commercial purposes. It contains no carbon so it is almost rust proof. The presence of sulfur causes wrought iron to be brittle when hot.
- Steel. Simple steel is an alloy of iron and carbon containing no other element. Commercial steels, however, are plain carbon steels containing manganese and small quantities of silicon, phosphorus, sulfur, and traces of other elements. Its carbon content is from a few hundredth of a percent to 1.4 percent. Plain carbon steel seldom contains more than 1.4 percent carbon. There are, however, steels which contain up to 2.0 percent. Aside from carbon, various other elements are added to give steel different properties suitable for different applications:
- Phosphorus. Improves hardness of steel and makes it more resistant to scratching and abrasions. Phosphorus, however, weakens steel against shocks and vibrations.
- Manganese. Improves the strength, hardness, and soundness of steel. Hardness and brittleness result if a considerable amount of this metal is added to steel.
- Nickel. Increases the strength and toughness of steel. This is added to steel to produce armor plates.
- Vanadium. Increases ductility of steel. It improves tensile strength, increases the electric limit of steel, and makes steel resistant to shocks. It renders steel nonfatigable. This type of steel is most suited for making spring, gears, and axles.
- Aluminum. Increases soundness of ingots and casting.
- Sulfur. Increases the brittleness of steel.
- Molybdenum. Render steel hard even at high temperature. It produces the so-called high speed steel which makes steel suitable for crankshafts, propeller shafts, guns, rifle barrels, and broiler plates.
The nonferrous metals are metals without iron but are as useful as iron in metalworks. Nonferrous metals include the following:
1. Aluminum. A very light metal which is gradually taking the place of iron in many application. This metal is malleable, ductile, and a good conductor of heat and electricity. It is a cheap substitute to the more expensive copper in many electrical installations.
2. Copper. Another very useful seddish-brown metal. It is malleable, ductile, and is next to silver in electrical and thermal conductivity. It is extensively employed in many electrical applications. When copper is alloyed with zinc, brass is produced. When alloyed with tin, bronze is produced.
3. Zinc. Used extensively in dry cells and batteries. It is used as sacrificial anodes attached to the hulls of sea-going vessels and in coating iron to produce galvanized iron.
4. Tin. Very malleable and can be rolled into very thin sheets. It is used in coating insides of pipes used for conveying drinking water. It is also plated insides cans used to conserve foodstuff due to its high resistance to tarnishing.
5. Lead. One of the densest metals. It is soft and can be cut with a knife. A two millimeter thick sheet may be bent or straightened with bare hands. It has been used extensively in plumbing but it being replaced by other metals. One popular application is the galvanized iron roofing, where lead washers are used.
6. Brass. An alloy of copper and zinc. The color may vary from red to yellowish-white depending on the percentage of zinc. It is used in producing many articles such as Muslim brass works, bells, commutators, slide contacts, and many others.
7. Bronze. An alloy of copper and tin. It has a better appearance and greater strength than bass. It is used in bushings and in many other applications.
8. Babbit metal. An alloy of tin, antimony, and copper. It is a good electrical and heat conductor.9. Monel metal. An alloy of copper, nickel, and a small percentage of iron. It is used extensively in the manufacture of ship’s propeller.
10. Muntz metal. A special form of bronze with 60 percent copper and 40 percent tin. It is used in application where hard brass is required.
Different metals have distinct characteristics and properties which make them suitable for specific purposes. The following are the usual properties of different metals:
- Hardness. Allows a metal to resist penetration. The harder the metal the less likely it is to change in shape. Hardness can be increased by hardening or heat treating.
- Brittleness. Makes a metal break easily. Certain kinds of cast iron are brittle and break when dropped. Hardness and brittleness are closely related since hard metals are more brittle than soft metals.
- Malleability. Allows a metal to be hammered or rolled out into thin sheets without breaking or cracking.
- Ductility. Allows a metal to be drawn out into thin wires without breaking. Copper is very ductile and therefore makes very good wire.
- Elasticity. Allows metals to return to its original shape after bending. Steel used in making springs is a good example.
- Fusibility. Allows metals to become liquid easily and join with other metals to form an alloy.
- Machinability. Involves several properties. Some of these are the rate at which the material can be removed in machining, the chip, the amount of tool wear, and the kind of surface finish.