Lesson Notes By Weeks and Term v4 - SHS 1
WELDING TECHNOLOGY
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WELDING TECHNOLOGY
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Subject: Applied Technology
Class: SHS 1
Term: 2nd Term
Week: 11
Grade code: 1.4.2.LI.3
Strand code: 4
Sub-strand code: 2
Content standard code: 1.4.2.CS.1
Indicator code: 1.4.2.LI.3
Theme: METAL TECHNOLOGY
Subtheme: WELDING TECHNOLOGY
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Look around you. The burglar proof on the windows, the gate to your school, the metal frame of your desk, even the body of the "tro-tro" you ride in—all these were likely made using welding. Welding is the process of joining pieces of metal together, and it is a fundamental skill in construction, manufacturing, and repair work all across Ghana. Understanding the different types of welding and knowing where to use them is crucial for any student of technology. In this lesson, we will focus on two of the most common types: Gas Welding and Electric Arc Welding, and we will explore their specific applications in our everyday lives.
What is Welding? Welding is a fabrication process that joins materials, usually metals, by using high heat to melt the parts together and allowing them to cool, causing fusion. Think of it as melting the edges of two pieces of metal so they flow into each other and become one solid piece when they cool down. Often, a filler material (called a welding rod or electrode) is added to the joint to form a strong bond.
We will focus on the two most common types you will see in local workshops. Gas Welding (Oxy-acetylene Welding)
This is one of the oldest and most versatile welding processes. How it works: Gas welding uses the flame produced by burning a mixture of two gases: Oxygen and Acetylene. This flame, which can reach temperatures over 3,200°C, is directed by a torch onto the metal parts to be joined. The intense heat melts the edges of the metal. The welder then adds a separate metal rod, called a filler rod, into the molten pool to add more material and create a strong joint as it cools. Key Characteristics: Less Intense Heat: Compared to arc welding, the heat is less concentrated. This gives the welder more control. Slower Process: It takes longer to heat the metal to its melting point. Good for Thin Metals: The lower heat intensity makes it ideal for welding thin sheets of metal without burning holes through them. Portable: The gas cylinders can be moved around, making it useful for on-site repairs. Common Applications in Ghana: Car Body Repairs: When a car's body is dented or rusted, welders often use gas welding to repair the thin metal panels because it provides delicate control and avoids warping or burning the thin sheet metal. Repairing Leaky Containers: For fixing small holes in thin metal containers like buckets, barrels, or local water tanks ("polytank" frames), gas welding is gentle enough. Plumbing and Pipe Fitting: It is used for brazing and soldering copper pipes used in plumbing and air-conditioning systems. Artistic Metalwork: For creating sculptures or intricate designs with thin metal rods, the control offered by gas welding is superior. Electric Arc Welding (e.g., "Stick Welding" or SMAW)
This is the most common type of welding you will see in roadside workshops in Ghana used for construction and fabrication. Its formal name is Shielded Metal Arc Welding (SMAW). How it works: Electric arc welding uses electricity to create an extremely hot arc (like a small, continuous lightning bolt) between an electrode (the welding stick) and the metal workpiece. This arc is incredibly hot (over 5,500°C) and instantly melts the metal and the tip of the electrode. The molten electrode metal mixes with the molten base metal to form the weld. The electrode is coated with a material called flux, which burns to create a protective gas shield around the weld, preventing it from reacting with air and becoming weak. This also forms a protective layer called slag on top of the cooling weld, which is chipped off later. Key Characteristics: Intense, Concentrated Heat: The electric arc is extremely hot and melts metal very quickly. Fast and Efficient: It is much faster than gas welding. Strong Welds: It creates very strong, deep welds, making it perfect for structural work. Good for Thick Metals: The intense heat makes it excellent for joining thick and heavy pieces of steel. Common Applications in Ghana: Fabricating Burglar Proofs and Gates: Security items need to be extremely strong. Arc welding creates powerful joints that can withstand force, making it the standard for all security metalwork. Making Metal Furniture: The frames for school desks, metal chairs, and tables are joined using arc welding for strength and durability. Construction: Used in building construction to join steel beams and columns that form the skeleton of large buildings. Heavy Machinery and Vehicle Frame Repair: Repairing the chassis of a truck, a "tro-tro," or farm equipment requires strong welds that arc welding provides. Making Local Containers: Fabricating large metal boxes ("chop boxes"), water tankers, or storage containers from thick steel plates. Summary Comparison