Engineers have to know the best and most economical to use. Engineers must also understand the properties of these materials and how they can be worked. There are two kinds of materials used in engineering metals and non metals. The former contain iron and the latter do not contain iron. Cast iron and steel, which are both alloys, or mixtures of iron and carbon, are the two most important ferrous metals. Steel contains a smaller proportion of carbon than cast iron contains. Certain elements can improve the properties of steel and are therefore added to it. For example, chromium may be included to resist corrosion and tungsten to increase hardness. Alumunium, copper, and brass, are common non ferrous metals.
Study the following statements carefully.
1. Non metals are used by engineers.
2. Cast iron contains more carbon than steel.
3. Chromium imoroves the properties of steel.
4. Copper contains iron.
5. Bronze is an alloy.
Plastics and ceramics are non metals, however, plastics may be mahined like metals. Plastics are classified into two types thermoplastics and thermosets. Thermoplastics can be shaped and reshaped by heat and pressure but thermosets can not be reshaped because they undergo chemical changes as they harden. Ceramics are often employed by engineers when materials which can withstand high temperatures are needed.
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