PROCESSING OF MATERIALS – METALS AND ALLOYS

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Welcome to class! 

In today’s class, we will be talking about the processing of metals and alloys. Enjoy the class!

Processing of Materials – Metals and Alloys

Introduction to metals and alloys

Metals are materials used in producing some equipment used in everyday life. Metals always occur in nature as a compound such as an oxide or the sulphide, i.e. metal is produced from iron ore which is dug from the ground.

In its natural state iron-ore contains many impurities that are removed through smelting.

Metal processing:

Processing metals depends on the type of iron-ore used. First, the ore is physically crushed and then exposed to a combination of heat, chemical and other physical processes which makes it result in a liquid molten metal that can be poured and shaped.

As we know, the ore is obtained from beneath the earth and processed into pig-iron by removing most of the impurities. This whole process is carried out in a furnace.

Production of metals

1. Smelting
2. Casting
3. Alloying
4. Forming
5. Shaping
6. Finishing

• Smelting:

The metal ore is heated in a furnace e.g. blast furnace until the metal melts into liquid form. It is then separated from other impurities that have mixed with it.

• Casting:

The hot molten metal is poured into containers of different lengths and sizes called moulds. It is left there to cool and solidify to take up the shape of the mould.

• Alloying:

This is the mixing of two or more metals to obtain an improved metal. This process is carried out to improve the quality of certain metals in engineering.

Usually, a base metal, known as the parent metal, has up to 90% of the alloy material while the other 10% are just alloying agents.

For example:

1. Bronze = copper (78% to 95%) +tin(5 to 22%) +aluminum(5 to 20%)
2. Brass = Copper (10 to 35%) + Zinc (5 to 22%)

Importance of alloys

1. For strength.
2. Wear resistance.
3. It provides hardness.
4. Corrosion-resistance.

S/N	NAME OF ALLOY	MAIN PROPERTY	APPLICATION
1	Cast Iron	Brittle metal	It is used for making automobile cylinders and pistons
2	High Carbon Steel	It is worked upon in hot forming like forging and it is easily tempered	Used for making tools like punches, hammerheads, saws, chisels.
3	Low and Medium Carbon Steel	A group of malleable and ductile metals.	Used for making structural steelwork, automobile and vehicle parts.
4	Silicon Steel	Contain very good magnetic property.	Used for making laminations in the construction of transformers.

• Forming:

This is the method of processing metal either hot or cold into geometrical shapes by applying compressive or tensile forces of deformation.

Types of forming

1. Compressive forming: This is the use of pushing force to change the original shape of metal to the desired shape. There are two examples involved:

(a). Rolling: This is the use of rollers to flatten and reduce the thickness of metal.

(b). Extrusion: This is the method of forcing metal through a hole. This can be done through die forming (where the metal is stamped by a press around a die) or forging (where a localized force is applied to the metal).

2. Tensile forming: This is the method of using a pulling force to change the shape of a metal. This may include stretching, expanding and recessing of metals.

• Shaping:

This aspect of processing metals involves the use of the lathe machine to carry out milling, turning, etc operations.

Types of shaping

(I). Bending: Most metalwork project involves bending and folding, either cylindrically or as square-box shape. This changes the shape of the metal.

(ii). Drawing down: This is the process of stretching a metal by hammering.

(iii). Twisting: This is a beautification process in forging operation.

(iv). Upsetting: This is the process of increasing the thickness of metal. It is useful in processing bolt heads.

• Finishing:

This is the technique of giving metalwork a protective coat, smooth edges and surfaces in addition to an acceptable, improved final appearance.

Types of metal finishing

1. Buffing: This is the method of using wheels covered with soft cloth or leather to polish the surface of the metal.

2. Lacquering: This is the application of a lacquer to the metal surface to prevent corrosion.

3. Enamelling: This is the application of corrosion-resistant material, like plastics, on metal to make the surface glossy and hard.

4. Scratching: This is the use of a thin metal piece and steel brush for cleaning metal parts thoroughly to be finished.

5. Painting/spraying: This is the application of oil paint to metal for coating purpose.

6. Copper finishing: This is the oxidation of copper surface to form shades of different colours like purple, red, brown, etc.

7. Spot finishing: This is the forming of pressed spots on metal by the use of ornamental finishing and abrasive powder and oil spread over the metal. The spot is achieved by placing the metal over a spinning wood on a drill chuck.

8. Electroplating: This is the protective coating of a metal with other metal such as tin, zinc or chromium to prevent corrosion.

Note: A furnace is a solid structure in which a lot of heat energy is generated to produce metal. The different types of furnaces in which different types of metals are produced are:

• Bessemer converter
• Blast furnace
• Electric Arc-furnace
• Open Hearth furnace
• Cupola furnace
• Reverberating furnace
• Pudding furnace

 

In our next class, we will be talking about PROCESSING OF MATERIALS – CERAMICS, GLASS, PLASTICS AND RUBBER.  We hope you enjoyed the class.

Should you have any further question, feel free to ask in the comment section below and trust us to respond as soon as possible.

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