Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Types of Welding
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Types of Welding
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Subject: Plumbing And Pipe Fitting
Class: Senior Secondary 2
Term: 1st Term
Week: 6
Theme: Welding
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List three types of welding metallic pipes. List and identify various welding to ols and equipment.
the torch and ignited at the tip, producing a concentrated flame.
5. The flame is directed at the joint, heating the pipe edges to their melting point.
6. A filler rod (if needed, e.g., for steel pipes) is melted into the weld pool by the flame, filling the gap and creating a strong joint.
Application for Pipes: Excellent for welding thin-walled steel pipes, copper pipes (with brazing), and cast iron pipes. Frequently used for intricate work, small-diameter pipes, and repair of leaks in residential plumbing systems. It's also suitable for cutting metals.
Advantages: Portable, relatively inexpensive equipment for small scale, good control over heat input, no electricity required.
Disadvantages: Slower process, less efficient for thick materials, larger heat-affected zone (can cause distortion), fire hazard due to open flame and flammable gases.
Tools and Equipment for Gas Welding:
1. Oxygen Cylinder: Stores oxygen gas under high pressure (typically black cylinder).
2. Acetylene Cylinder: Stores acetylene gas under lower pressure (typically maroon or red cylinder, contains porous material soaked in acetone for stability).
3. Oxygen Regulator: Reduces and controls the flow rate and pressure of oxygen from the cylinder to the torch.
4. Acetylene Regulator: Reduces and controls the flow rate and pressure of acetylene from the cylinder to the torch.
5. Hoses: Colour-coded (green for oxygen, red for acetylene) flexible hoses to carry gases from regulators to the torch.
6. Welding Torch (Blowpipe): Mixes oxygen and acetylene in correct proportions and directs the flame through a nozzle (tip).
7. Torch Tips/Nozzles: Interchangeable components that dictate the size and shape of the flame, selected based on material thickness.
8. Spark Lighter/Striker: Used to safely ignite the gas mixture at the torch tip.
9. Filler Rods: Various metal rods (e.g., steel, copper, brass) used to add material to the weld pool.
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0. Goggles/Face Shield: Protect eyes from glare, heat, and sparks (shade 4-6 typically).
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1. Gloves: Heat-resistant gloves to protect hands.
C. Bronze Welding (Brazing)
Principle: Brazing is a joining process where a filler metal (bronze or brass alloy, typically copper-zinc based) is melted and flows into the joint between two close-fitting metal parts by capillary action. The key distinction is that the base metals themselves are not melted, only heated to a temperature above the filler metal's melting point but below the base metal's melting point. Flux is used to clean the surfaces and promote filler metal flow.
Process:
1. The joint area of the pipes is thoroughly cleaned.
2. Flux is applied to the joint to prevent oxidation and aid filler metal flow.
3. The base metals (pipes) are heated using a gas welding torch (oxy-acetylene or propane-oxygen) to the brazing temperature.
4. The brazing rod (bronze/brass) is touched to the heated joint, where it melts and is drawn into the joint by capillary action, creating a strong bond.
5. The assembly is allowed to cool slowly.
Application for Pipes: Extremely common for joining copper, brass, and bronze pipes, and also for joining dissimilar metals like steel to copper, or cast iron repair. Essential in plumbing for hot and cold water supply lines, refrigeration, and air conditioning systems.
Advantages: Joins dissimilar metals, produces strong, leak-tight joints, minimal distortion to base metals (as they don't melt), can join thin sections.
Disadvantages: Filler metal strength is typically lower than base metal strength, requires very clean surfaces, careful heat control is needed. Tools and Equipment for Bronze Welding (Brazing):
1. Gas Welding Setup: (As described above for Oxy-Acetylene Welding) - Oxygen and Acetylene Cylinders, Regulators, Hoses, Welding Torch with appropriate tips.
2. Brazing Rods: Filler metal rods made of bronze or brass alloys (e.g., CuZn alloys, often with silver or tin for lower melting points).
3. Brazing Flux: A paste or powder applied to the joint to remove oxides, promote wetting, and allow the filler metal to flow smoothly.
4. Cleaning Tools: Wire brush, abrasive cloth, files to prepare joint surfaces.
5. PPE: Goggles/Face Shield, Heat-resistant gloves.
Introduction to Welding: Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a molten pool of material that cools to a strong joint, often stronger than the base material. Pressure may also be used in conjunction with heat, or by itself, to produce a weld.
Types of Welding Metallic Pipes: For plumbing and pipe fitting, several welding types are commonly employed, each suited for different materials, joint configurations, and environmental conditions.
The three primary types to focus on are:
A. Arc Welding (Shielded Metal Arc Welding - SMAW / Manual Metal Arc Welding - MMAW)
Principle: This method uses an electric arc between a consumable electrode (welding rod) and the workpiece (pipe) to melt the metals at the joint. The electrode is coated with a flux that disintegrates during welding, producing a shielding gas to protect the molten weld pool from atmospheric contamination (oxygen and nitrogen), and also forming a slag layer over the cooling weld.
Process:
1. The welding machine supplies current (AC or DC) to the electrode.
2. The welder strikes an arc by briefly touching the electrode to the pipe and then pulling it away slightly.
3. The intense heat of the arc melts both the electrode and the base metal.
4. The molten metal from the electrode and the pipe mix, forming a weld pool.
5. As the electrode is consumed, the welder moves it along the joint, creating a continuous weld bead.
6. The flux forms a protective slag that is chipped off after the weld cools.
Application for Pipes: Widely used for joining steel and stainless steel pipes of various thicknesses, especially in structural applications, heavy-duty plumbing, and industrial piping where strength is paramount. Suitable for both workshop and on-site work.
Advantages: Versatile, relatively low equipment cost, suitable for outdoor use and various positions, good for dirty or rusty material.
Disadvantages: Produces slag that needs to be removed, not ideal for very thin materials, requires skilled operators.
Tools and Equipment for Arc Welding:
1. Welding Machine (Power Source): Converts high voltage, low current power into low voltage, high current power suitable for welding. Can be AC (Alternating Current) or DC (Direct Current) or both.
2. Electrode Holder: A clamping device that securely holds the electrode and conducts welding current to it.
3. Ground Clamp: Connects the welding circuit to the workpiece, completing the electrical circuit.
4. Welding Cable: Heavy-duty insulated cables connecting the machine to the electrode holder and ground clamp.
5. Electrodes (Welding Rods): Consumable filler metal rods coated with flux, available in various sizes and compositions (e.g., E6013 for general purpose, E7018 for high strength).
6. Chipping Hammer: Used to remove slag from the finished weld bead.
7. Wire Brush: Used to clean the weld area before and after welding, and to remove remaining slag or spatter.
8. Personal Protective Equipment (PPE): Welding helmet (with appropriate filter lens), welding gloves, leather apron/jacket, safety boots.
B. Gas Welding (Oxy-Acetylene Welding - OAW)
Principle: This method uses the heat generated by the combustion of a fuel gas (commonly acetylene) and oxygen to melt the base metals and a filler rod. The flame temperature can reach over 3000°
C. No electrical current is involved.
Process:
1. Oxygen and acetylene gases are stored in separate cylinders under high pressure.
2. Regulators reduce the cylinder pressure to a safe working pressure for the torch.
3. Hoses carry the gases to the welding torch.
4. The gases are mixed in the torch and ignited at the tip, producing a concentrated flame.
5. The flame is directed at the joint, heating the pipe edges to their melting point.
6. A filler rod (if needed, e.g., for steel pipes) is melted into the weld pool by the flame, filling the gap and creating a strong joint. * Application for Pipes: Excellent for welding thin-walled steel pipes, copper pipes (with brazing), and cast iron pipes. Frequently used for intricate work, small-diameter pipes, and repair of leaks in residential plumbing systems. It's also suitable for cutting Teacher Activities: Introduction (10 minutes): Begin by engaging students with questions about how pipes are joined in their homes or communities (e.g., "How do plumbers fix leaky metal pipes?"). Introduce welding as a robust method for joining metals, especially pipes. State the learning objectives for the lesson. Explanation and Demonstration (30 minutes): Using visual aids (charts, diagrams of welding equipment, actual tools if available, or projected images), explain the three main types of welding: Arc Welding, Gas Welding (Oxy-Acetylene), and Bronze Welding (Brazing).
For each type: Describe the fundamental principle of operation. Detail the step-by-step process. Explain its application in joining pipes. Present and identify the key tools and equipment. Show diagrams or actual items for clear identification. Emphasize safety precautions associated with each method (e.g., electric shock for arc, fire/explosion for gas, fumes for all). Interactive Discussion and Q&A (15 minutes): Encourage students to ask questions for clarification. Ask probing questions to check understanding, e.g., "What is the main difference between arc welding and gas welding?" or "Why is flux important in arc and bronze welding?". Guide a discussion on typical scenarios where each welding type would be preferred in a Nigerian context (e.g., Arc for heavy steel structures, Gas for thin steel/copper repairs, Brazing for refrigeration lines).
Activity Facilitation (20 minutes): Organise students into small groups. Provide diagrams or pictures of various welding tools and equipment. Instruct groups to identify and label the tools for each welding type. Circulate, observe, and provide guidance to groups.
Summarisation (5 minutes): Reiterate the key types of welding discussed and the primary tools associated with each. Conclude by highlighting the importance of proper welding techniques and safety in plumbing.
Student Activities: Active Listening and Note-Taking: Students will listen attentively to the teacher's explanations and take comprehensive notes on the types of welding, their principles, and associated equipment.
Observation and Identification: Students will observe charts, diagrams, or actual welding equipment displayed by the teacher, focusing on identifying different tools.
Group Discussion and Labelling: In small groups, students will discuss and label diagrams of welding setups, identifying components for arc, gas, and bronze welding.
Q&A Participation: Students will actively participate in class discussions, asking questions for clarity and contributing to the understanding of different welding methods and their applications.
Drawing and Sketching: Students may be asked to sketch simple diagrams of a welding torch or an arc welding setup and label its parts.
Question 1: List three types of welding methods commonly used for joining metallic pipes.
Solution: Arc Welding (Shielded Metal Arc Welding - SMAW) Gas Welding (Oxy-Acetylene Welding - OAW) Bronze Welding (Brazing)
Commentary: This directly assesses the first performance objective by requiring recall of the main welding types.
Question 2: For Gas Welding, identify any three essential tools or equipment.
Solution: Three essential tools/equipment for Gas Welding are: Oxygen Cylinder Acetylene Cylinder Welding Torch (or Regulators, Hoses, Spark Lighter)
Commentary: This question targets the second performance objective, focusing on specific tools for one welding type.
Question 3: Describe the primary function of the flux coating on an arc welding electrode.
Solution: The primary function of the flux coating on an arc welding electrode is to protect the molten weld pool from contamination by atmospheric gases (oxygen and nitrogen). It does this by creating a shielding gas around the arc and forming a protective slag layer over the cooling weld. This prevents oxidation and ensures a stronger, cleaner weld.
Commentary: This moves beyond simple listing to require a basic understanding of a component's role, reinforcing the identification objective.
Question 4: Explain how Bronze Welding differs from Arc Welding in terms of how the base metals are joined.
Solution: In Arc Welding, the base metals (pipes) are melted along with the filler rod (electrode) to form a molten weld pool that fuses the parts together. In contrast, Bronze Welding (Brazing) involves heating the base metals only to a temperature above the filler metal's (bronze/brass rod) melting point, but below the base metals' melting point. The filler metal then flows into the joint by capillary action, joining the parts without melting the base metals themselves.
Commentary: This question encourages comparative thinking and deeper understanding of the principles of two different welding types.
Community Water Projects and Plumbing Repairs: Knowledge of welding types is essential for plumbers and pipe fitters involved in community water supply projects. For example, Arc welding is critical for joining large steel pipes in municipal water distribution networks, ensuring robust, leak-proof joints. Gas welding or brazing is frequently used for repairing smaller diameter residential copper pipes or mending burst galvanized iron pipes in homes and public buildings, preventing water wastage and ensuring access to potable water. Fabrication of Metal Structures and Artisanal Work: Many Nigerian artisans and small businesses are involved in fabricating metal products like security gates, window grilles (burglar proofs), handrails, and furniture frames. Arc welding is the primary method for these applications due to its versatility with steel. Understanding the different welding processes allows students to appreciate how these everyday items are constructed, potentially inspiring them to pursue entrepreneurial ventures in metal fabrication. Industrial Maintenance and Oil & Gas Sector: In industries such as breweries, food processing plants, and especially the oil and gas sector (e.g., in the Niger Delta), various types of pipes transport liquids and gases. Skilled welders are indispensable for the installation, repair, and maintenance of these critical piping systems. The choice of welding method (e.g., TIG for high-integrity stainless steel pipes, Arc welding for robust carbon steel pipes, or Brazing for refrigeration lines) directly impacts the safety and efficiency of operations, ensuring continuous production and preventing environmental hazards.