Pre Technical Skills

 08/10/2020

METAL 

Metals are obtained from ores that are mined from the earth. Apart from mercury, most metals are solid and hard. 

Categories of Metals There are two groups of metals, namely; 

i. Ferrous metals 

ii. Non-ferrous metals 

 

Differences between Ferrous and Non-ferrous Metals 

Ferrous Metal                                    Non-ferrous Metal 

Ferrous metals contain iron with
varying percentage of carbon.      Non-ferrous metals do not contain iron or carbon. 

Ferrous metals corrode (rust)      Non-ferrous metals do not rust. 

Ferrous metals attract magnet.         Non-ferrous metals do not attract magnet. 

 

Examples of Ferrous and Non-ferrous Metals 

Ferrous Metals                                Non-ferrous Metals 

Low carbon steel                               Aluminium 

Medium carbon steel                      Copper 

High carbon steel                                  Lead 

Cast iron                                     Tin 

                                                         Zinc 

 

Properties (Characteristics) of Metals 

These are the qualities in a metals (material) that makes them particularly suitable for the manufacturing or making of an item. 

Examples: 

1. Physical properties 

2. Chemical properties 

3. Mechanical properties  

Physical Properties Chemical Properties Mechanical Properties 

Colour                        Fusibility                         Ductility 

Melting point                 Electrical conductivity Malleability 

Elasticity                 Thermal conductivity Brittleness 

Magnetism                    Plasticity                  Hardness 

Weight etc.             Toughness 

 

1. Colour: Colour helps in identifying metals and enhance their appearance. 

2. Melting point: The temperature at which metals become liquid vary from one metal to the other. 

3. Elasticity: It is the ability of a metal to return to its original shape when the force is applied on it is removed. 

4. Magnetism: This describes the ability of a metal to attract similar metals. 

5. Weight: Weight determines how light or heavy a metal is in weight. Cast iron is very heavy and aluminium is light in weight. 

6. Fusibility: It is the ability of a metal to melt when subjected to heat. 

7. Electrical conductivity: This describes the capability of a metal to conduct or transfer electricity. Example:  Copper wire and Aluminium wire  

8. Thermal-conductivity: It is the capacity of a metal to absorb, conduct or transfer heat. Example: 

Copper. 

9. Plasticity: Plasticity is the property of a metal to undergo enduring deformation under load when compressed. Example: Medium carbon steel.  

10. Ductility: It is the capacity of a metal to be drawn or stretched in its cold state without breaking. 

Example: Aluminium, copper etc. 

11. Malleability: This describes a metal which can be hammered, bent or rolled without breaking. 

Example: Aluminium, lead, tin, low carbon steel etc. 

12. Brittleness: A metal is said to be brittle if it can break easily when a force or load is applied to it suddenly. Example: Cast iron 

13. Hardness: A metal is said to hard if it can resist scratches, indents or wear. Example: High carbon steel, high speed steel etc. 

14. Toughness: It is the property that enables a metal to bend, twist or resist shock loads without breaking. Examples: Medium carbon steel etc.    

                                  21/10/2020

STEEL 

Steel mainly consists of iron and carbon. The carbon content in steel ranges from 0.1  to 1.5 . Examples of plain carbon steel are: 

1. Low carbon steel 

2. Medium carbon steel 

3. High carbon steel 

 

Low Carbon Steel 
The melting point of low carbon steel varies and has carbon content ranging 0.1  to 0.35 .  It is supplied in the form of rod, tubes, plates, strips, sheets, wires, bars etc. from the factory. 

 

Properties of Low Carbon Steel 

Low carbon steel is; 

1. Grey in colour                        4. Tough 

2. Fairly malleable                     5. High strength etc. 

3. Ductile 

 

Uses of Low Carbon Steel 

Low carbon steel is used for making the following items. 

1. Hinges                                              5. House gate 

2. Bolt and nut                                      6. Nails 

3. Screws                                               7. Rivets etc.  

4. Car body 

 

Medium Carbon Steel 
The medium carbon steel has carbon content ranging from 0.35  to 0.65  with varying melting point. The properties of medium carbon steel are improved by heat treating it. Examples of heat treating processes include; hardening, tempering, annealing and normalizing.  

 

Properties of Medium Carbon Steel 

Medium carbon steel is;  

1. Grey in colour                            4. Fairly hard 

2. Tough                                         5. Very strong 

3. Fairly brittle 

Uses of Medium Carbon Steel 

Medium carbon steel is used for making the following items. 

1. Hammer heads                     6. Rails 

2. Punches                                7. Pick axe 

3. Cold chisel                            8. Hinges  

4. Nails                                     9. Springs  5. Screws                                  10. Hoe etc. 

 

Cast Iron 

Cast iron is produced from re-melting of pig-iron and steel scraps in a furnace called cupola. Its carbon content ranges from 2.5% to 4.5% and about 92% to 95% of iron.  

Types of Cast Iron 

1. Grey cast iron                             3. Ductile cast iron 

2. White cast iron                           4. Malleable cast iron 

 

Properties of Cast Iron 

Cast iron is; 

1. Strong                                    4. Easily cast into various shapes 

2. Very brittle                            5. Cannot be forged etc. 

3. Self-lubrication  

 

Uses of Cast Iron Cast iron is used for making the following items. 

1. Box-iron                                       6. Bench vice body 

2. Cooking pot                                  7. Crankshaft  

3. Pipes                                             8. Engine blocks etc.  

4. Body of sewing machine 

5. Flying pan 

                                                                        28/10/2020

Heat Treatment Processes on Medium Carbon Steel

Heat treatment is a process used to improve the initial properties of ferrous metals precisely

medium carbon steel and high carbon steel. Examples are;

1. Annealing -> It is the process of making metal soft for easy machining.

2. Normalizing -> It is the process used to soften metals. The meatal is heated to a bright

cherry colour and allowed to cool in a still air.

3. Hardening -> It is the process of heating metal to a temperature of about 100°C to 900°C

and cooled in either brine (salt solution), oil or water rapidly.

4. Tempering -> It is a process of heating hardened steel to a temperature of about 200°C to

300°C and quenched in water. This is done to remove the brittleness and hardness of the

metal.

 

Aluminium

Aluminium is obtained from bauxite by an electrolytic process. Caustic soda is added to the

bauxite to obtain alumina and then reduced to aluminium electrically.

 

Properties of Aluminium

1. Bluish-white in colour.

2. The melting point of aluminium is about 650°C.

3. Light in weight.

4. Malleable, ductile and soft.

5. Resistant to corrosion.

6. Good conductor of heat and electricity.

 

Uses of Aluminium

1. Roofing sheet        6. Food cans

2. Bucket                    7. Kettle

3. Cooking utensil     8. Dustbin

4. Aircraft body         9. Overhead power cable

5. Kitchen sink         10. Louvre frames and blades etc.

 

Copper

Copper is produced from the ore known as pyrite.

Properties of Copper

1. Copper is reddish in colour.

2. Melting point of copper is about 1100°C.

3. Malleable, ductile and tough.

4. Copper is heavy in weight.

5. Resistant to corrosion

6. A good conductor of heat and electricity. Etc.

Uses of Copper
1. Electrical plug pins, wires, cables etc.     5. Water pipes

2. Telephone wires                                       6. Alloyed with zinc to form brass

3. Soldering iron (bit)                                  7. Rings and jewelries

4. Boilers                                                     8. Alloyed with tin to form bronze etc.

 

Lead

Lead is obtained from the ore called galena.

Properties of Lead

1. Lead is bluish-grey in colour.

2. Melting point of lead is about 372°C.

3. Lead is heavy.

4. Lead is very soft, malleable and ductile.

5. Resistant to corrosion. Etc.

 

Uses of Lead

1. Lead acid battery.

2. Covering electrical cables.

3. Constituent in paint.

4. Mixed with tin to make soft solder. Etc.

11/11/2020

SAFETY PRECAUTION 

Safety: The word safety refers to freedom from danger, injury and damage to the craftsman  and others. 

Accident: Accident in the workshop is unexpected event associated with injury, loss, or  harm. It is typically sudden in nature. 

Types of accidents that occur in the workshop: 

i. Falls v. Slips (Trips) 

ii. Cuts vi. Muscle strain 

iii. Bruises vii. Being hit by falling objects 

iv. Explosions. viii. Inhaling toxic fumes etc. 

Causes of accident in the workshop 

i. Carelessness v. Poor ventilation 

ii. Forgetfulness vi. Walking into objects 

iii. Inattentiveness vii. Poor lightening 

iv. Tiredness (Fatigue) viii. Fight at work etc. 

REASONS FOR OBSERVING SAFETY RULES 

In the workshop, there are rules to be observe to prevent accident. If these rules are properly  observed; 

1. The craftsman will be protected from injury. 

2. The tools or equipment will be protected from being damaged. 

3. The workpiece will not be damaged or wasted.  

PROTECTIVE CLOTHING 

For proper safety of the working force, the following protective clothing should be properly  use to prevent accident in the workshop. 

1. Overcoat         7. Goggles 

2. Helmet            8. Overall 

3. Safety shoes/boots 9. Apron 

4. Gloves             10. Nose mask 

5. Cap                  11. Ear plug (muff) 

6. Full mask         12. Safety belt

18/11/2020

PERSONAL SAFETY 

There are measures or rules and regulations to be observed to prevent accident or injuries to  the craftsmen. Examples of these rules include: 

1. Wear safety shoes to protect your feet. 

2. Wear goggles to protect the eye when grinding. 

3. Wear proper protective clothing when working with dangerous liquids. 4. Never talk to anyone operating electrical equipment and machinery. 5. Tools being carried should always point downwards. 

6. Make sure workpiece is securely fixed before work commences. 

7. Craftsmen with any health problems that may affect workplace safety must report these to  the supervisor. 

8. Do not leave anything inflammable near fire. 

9. Wash hands after using equipment and materials. Etc.  

SAFE USE OF TOOLS 

The following rules should be observed to prevent accident when using tools and equipment  in the workshop. 

1. Use files with handle. 

2. Select the tool for the right job. 

3. Do not use hammer with loosed head. 

4. Give tool to fellow craftsmen by the handle. 

5. Obtain permission before using any tool or machine in the workshop.  6. Notify the workshop supervisor of any faulty or broken equipment. 

Reasons for Taking Care of Tools  

If tools are properly cared for, they will; 

1. Last longer, 

2. Keep their appearance, 

3. Keep their cutting edges sharp, 

4. Keep their accuracy.

Care and Maintenance of Tools 

After every practical session or work: 

1. Clean tools with a piece of cloth, 

2. Wash tools with water where necessary, 

3. Soak a piece of cloth in an oil and rub over the tool where necessary, 4. Sharpen cutting tools when the cutting edge is blunt, 5. Grind cutting tools when the cutting edge is damaged, 6. Chisels and saws should be hung on the rack or cabinet. NB: Places tools can be kept in the workshop include; 

i. Tools box, 

ii. Tools cabinet or rack, 

iii. Tools shelve etc.