Lesson Notes By Weeks and Term v4 - SHS 3
WELDING TECHNOLOGY
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WELDING TECHNOLOGY
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Subject: Applied Technology
Class: SHS 3
Term: 1st Term
Week: 12
Grade code: 3.2.2.LI.4
Strand code: 2
Sub-strand code: 2
Content standard code: 3.2.2.CS.1
Indicator code: 3.2.2.LI.4
Theme: METAL TECHNOLOGY
Subtheme: WELDING TECHNOLOGY
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In our communities, we see welders creating beautiful and strong metal products every day, from the school gates and burglar-proof windows that keep us safe, to the metal chairs we sit on. However, the work of a metal fabricator does not end after the last spark of the welding machine. To create a professional, durable, and functional product, we must know how to join parts that may need to be removed later and how to protect the finished product from our climate's biggest enemy: rust. This lesson focuses on these two critical final stages: using mechanical fasteners and applying protective and decorative finishes.
This lesson is divided into two main parts: Mechanical Fasteners and Metal Finishes. Part A: Mechanical Fasteners
A mechanical fastener is a device used to mechanically join or affix two or more objects together. Unlike welding, which creates a permanent, monolithic joint, most mechanical fasteners create non-permanent or semi-permanent joints, meaning they can be disassembled without destroying the components.
Key Types of Mechanical Fasteners: Bolts and Nuts Description: A bolt is a threaded fastener with an external male thread, designed to be used with a nut (which has an internal female thread). Tightening the nut draws the clamped materials together. Components: Bolt Head: Can be hexagonal (most common), square, or round (carriage bolt). Shank: The unthreaded part of the bolt. Thread: The helical ridges that engage with the nut. Nut: A block with a threaded hole. Washers: Often used with bolts. Flat washers distribute the load over a wider area. Spring washers prevent the nut from loosening due to vibration. Ghanaian Context/Example: Imagine a metal-frame school desk with a wooden top. You would not weld the wood to the metal. Instead, you would drill holes through the wood and the metal frame and use bolts, nuts, and washers to secure the top. This allows the wooden top to be easily replaced if it gets damaged. Screws Description: A screw is a fastener similar to a bolt, but it is designed to cut its own internal thread into one of the materials being joined. It does not typically require a nut. Key Difference from Bolts: A bolt passes through unthreaded holes in components and is tightened with a nut. A screw threads into one of the components. Types & Examples: Machine Screws: Have fine threads and are used to fasten metal parts together, often into a pre-tapped (threaded) hole. Self-Tapping Screws: These are very common in Ghana. They can form their own thread in a pre-drilled hole in sheet metal. Ghanaian Context/Example: When fixing corrugated iron or aluminium roofing sheets to a metal roof structure (purlins), artisans use self-tapping roofing screws. These screws often have a rubber washer to prevent water leakage. Rivets Description: A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite the head is called the tail. To install, the rivet is placed in a punched or drilled hole, and the tail is "upset" (deformed) so it expands to about 1.5 times the original shaft diameter, holding the rivet in place. Types & Examples: Solid Rivets: Require access to both sides. Used in heavy construction. Blind Rivets (or "Pop" Rivets): These are extremely useful as they can be installed from one side of the workpiece. A special tool, a rivet gun, is used to set them. Ghanaian Context/Example: Think of the classic metal trunks ("chop boxes") used by students. The hinges, handles, and locks are often attached to the sheet metal body using pop rivets. They are also used to repair holes in aluminium cooking pots. Part B: Metal Finishes
A metal finish is a coating or treatment applied to the surface of a metal product. It serves two main purposes: Protection: To protect the metal from corrosion (rusting), abrasion, and chemicals. Aesthetics: To improve the appearance, colour, and texture of the product.