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: 11
Grade code: 3.2.2.LI.3
Strand code: 2
Sub-strand code: 2
Content standard code: 3.2.2.CS.1
Indicator code: 3.2.2.LI.3
Theme: METAL TECHNOLOGY
Subtheme: WELDING TECHNOLOGY
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Welcome, future engineers and artisans! Today, we are exploring two essential techniques in metal joining: soldering and brazing. Unlike fusion welding which melts the base metals, these processes are like using a strong, hot 'glue' to join metals together. In Ghana, these skills are vital everywhere – from the phone repairer in Circle who fixes a motherboard, to the plumber in your community installing water pipes, and the craftsman in Koforidua making beautiful brass jewellery. Mastering soldering and brazing opens doors to repairs, creation, and even entrepreneurship. It is a skill that demands precision, safety, and handwork.
A. What are Soldering and Brazing?
Soldering and brazing are metal-joining processes where a filler metal is heated above its melting point and distributed between two or more close-fitting parts by capillary action. The key principle is that the base metals (the parts being joined) are NOT melted. Only the filler metal melts, flows into the gap, and solidifies to create the bond. Capillary Action: This is the magic behind these processes. It is the ability of a liquid (the molten filler metal) to flow into narrow spaces without the assistance of, or even in opposition to, external forces like gravity. For this to work, the joint must be clean and the gap must be very small. B. Soldering
Soldering is a low-temperature joining process. Temperature: The process is carried out at temperatures below 450°C. Filler Metal ("Solder"): The filler metal is called solder. Traditionally, it was an alloy of tin and lead. Due to health concerns about lead, modern solders are often lead-free, containing tin, silver, and copper. Heat Source: A low-intensity heat source is used, such as: Soldering Iron: For electronics and delicate work. Soldering Gun: For slightly heavier jobs like joining electrical wires. Propane Torch: For plumbing work (joining copper pipes). Flux: A chemical cleaning agent is crucial. For electronics, rosin-based flux is used. For plumbing, a more aggressive acid-based flux is used. The flux does three things: Chemically cleans the metal surfaces. Prevents oxidation (formation of oxides) when the metal is heated. Helps the molten solder flow smoothly ("wetting"). Strength: Soldered joints are relatively weak and are not suitable for high-stress applications. They are primarily used for creating electrical conductivity or a waterproof seal.
Step-by-Step Soldering Process (Example: Joining two electrical wires): Preparation & Cleaning: Mechanically clean the ends of the wires with sandpaper or a wire brush to remove any insulation or dirt. The surfaces must be bright and shiny. Joint Assembly (Twisting): Twist the cleaned ends of the wires together neatly to ensure they have good physical contact. Applying Flux: Apply a small amount of rosin-based flux to the twisted joint. Heating the Joint: Heat the soldering iron. Touch the hot tip to the *joint* (the wires), not the solder. The goal is to heat the workpiece. This demonstrates the principle of heat transfer. Applying Solder: While the iron is heating the wires, touch the tip of the solder wire to the joint (on the opposite side from the iron tip). The heat from the wires should melt the solder, which will then flow into the joint via capillary action. Cooling and Inspection: Remove the solder wire first, then the soldering iron. Allow the joint to cool naturally without disturbance. A good joint looks shiny, smooth, and cone-shaped. C. Brazing