Engineers have to know the best and most economical materials 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. We can divide metals into ferrous and non-ferrous. 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. 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. Aluminium, copper, and the alloys (bronze and brass) are common non-ferrous metals.
Plastics and ceramics are non-metals; however, plastics may be machined like metals. Plastics are classified into two types – thermoplastics and thermosets. Thermoplastics can be shaped and reshaped by heat and pressure but thermosets cannot 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.
6.7 Draw similar diagrams displaying the connection between the following:
1. alloys, copper, brass, pure metals, aluminium, metals;
2. computer system, CPU, hardware, main memory, peripherals, software;
3. aeronautical engineering, civil engineering, electrical engineering, engineering, heating and ventilating, marine engineering, mechanical engineering.
Use the diagrams and the following table to classify the things described.
6.9 Match the symbols of chemical elements, their English names and their Russian equivalents. What are the properties of engineering materials containing these elements?
6.10 Join the pairs of sentences using however, therefore, because. Follow the models:
(a) Copper does not rust.
(b) Copper corrodes.
(a + b) Copper does not rust; howeverit corrodes.
(a) Cast iron is a brittle metal.
(b) Cast iron is not used to withstand impact loads.
(a + b) Cast iron is a brittle metal, thereforeit is not used to withstand impact loads.
(a) Titanium is used for aircraft frames.
(b) Titanium is light and strong.
(a + b) Titanium is used for aircraft frames becauseit is light and strong.
1. Chromium resists corrosion. Chromium is added to steels to make them rust-proof.
2. Manganese steel is very hard. Manganese steel is used for armour plate.
3. Bronze has a low coefficient of friction. Bronze is used to make bearings.
4. Nylon is used to make fibres and gears. Nylon is tough and has a low coefficient of friction.
5. Tin is used to coat other metals to protect them. Tin resists corrosion.
6. Tin is expensive. The coats of tin applied to other metals are very thin.
7. Stainless steels require little maintenance and have a high strength. Stainless steels are expensive and difficult to machine at high speeds.
8. Nickel, cobalt and chromium improve the properties of metals. Nickel, cobalt and chromium are added to steels.