Lesson Notes By Weeks and Term - Junior Secondary School 3

TERM: 2ND TERM

SUBJECT: BASIC TECH

CLASS: JSS 3

Reference Materials

• NERDC, INTRODUCTORY TECHNOLOGY FOR JSS, BOOK 3
• EVANS, INTRODUCTORY TECHNOLOGY FOR JSS, BOOK 3

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WEEK 3

TOPIC: METAL FINISHING�

CONTENT�

• Definition���
• Buffing (buffering)
• Scratching and brushing�
• Spot or copper finishing
• Lacquering��
• Enameling�
• Tinning and Plating�
• Painting
• Hammered finishing�

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Definition�

Metal finishing can be defined as process of working on metal surface for decorative and preservative treatment.�

Metal finishing is essential so as to prevent rusting to make the metal look nice and takes time to wear out.

Metal finishing includes the following:

1. Buffing (buffering)
2. Scratching and brushing�
3. Spot or copper finishing
4. Lacquering��
5. Enameling�
6. Tinning and Plating�
7. Painting
8. Hammered finishing�

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Evaluation

1. Define metal finishing
2. State 8 methods off metal finishing�

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BUFFING�

This is the process of polishing metal surfaces using a special wheel with soft leather that mops the metal. The mops are usually soft leather or calico, charged periodically with the polishing compounds such as lime, Tripoli, crocus and rouge, emery flour or pumice

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Buffering is the smoothing and brightening of a surface by an abrasive compound pressed against it by a soft wheel or belt.

SCRATCHING�

These are processes of making ornamental profiles on metals and hardened steel. Scratching is done by thoroughly cleaning the surface of the metal, covering it with a melted wax or asphalt and allowing it to dry. The face of the metal is then scratched with a scriber to show the metal as desired for marking.

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SPOT OR COPPER FINISHING�

Spot finished is a form of ornamental finishing. The emery and oil will then be clean round the spot made be a wooden drill, which will as patterns. While copper finishing is the application of copper of different colours to spot.

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LACQUERING�

The lacquer to be used here is different from that described under wood finishes. This lacquer prevents rusting or corrosion of the metals because it is harder and tougher than enamel. A thin film of this lacquer is used for cans of soft drink so that the metal beneath can be seen.��

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ENAMELING������������

This is used to apply colours on as decoration to metal surface. The surface finishes are hard and glossy when dry. Enameling is done by applying powdered glass.�

It is applying�

• heating (hot enameling)����
• Brushing�
• Spraying�
• Cold enameling� for plastic�

Car body are enameled (dipped, painted and baked)

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TINNING AND PLATING

Tinning of a piece of metal is done by coating the finished products (steel) with tin. This prevents poisoning as in electric kettle originally made with copper.

PAINTING

This takes various forms. These include: galvanizing (dipping of the object in melted zinc and then heating to produce an alloy). Bronzing (painting with a powdered brass or bronze mixed with banana oil)�

. Red lead painting (uses as protective coats for machinery. It is necessary that object to be painted must be thoroughly sanded and prime coated.

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HAMMERED FINISHING�

This involves the use of punches with different points or rounded ends on the both sides of metal. It is then painted black or given a smoke finish, while the high spots are polished with abrasive paper and lacquered.

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Evaluation�

1. State 8 methods of metal finishing and explain.

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Reading Assignment�

Read METAL FINISHING

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Reference Materials���

1. EVANS, Introductory Technology for JSS, book 3, pages 124 - 129

Weekend Assignment��

• Which of the following is the process of polishing metals with wheel having soft leather mops? (a) spot finishing (b) buffering (c) scratching (d) enameling�
• Which metal finishing methods prevents poisoning of metal originally made with copper? (a) spot finishing (b) buffering (c) scratching (d) enameling
• Which of the following is a form of ornamental finishing? (a) spot finishing (b) buffering (c) scratching (d) enameling�
• Which of the following is used for cans of soft drink? (a) lacquering (b) buffering (c) scratching (d) enameling�
• The following are methods of metal finishing except___ (a) lacquering (b) buffering (c) sanding (d) enameling

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Theory�

1. State and explain 5 methods of metal finishing�
2. Briefly discuss the following (i) galvanizing (ii) bronzing�

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