Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Soldering
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Soldering
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Subject: Electrical Installation And Maintenance Work
Class: Senior Secondary 2
Term: 2nd Term
Week: 3
Theme: Workshop Practices
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Demonstrate the use of blow-lamp and pot and ladle for soldering big sizes of cables. Select sizes of thin cables and carry out soldering exercise on the joints.
Ensure the lamp is stable and on a non-combustible surface.
3. Soldering Pot and Ladle: Description: A pot, usually electrically heated or heated externally (e.g., by a blow-lamp), containing molten solder. A ladle is used to scoop and apply the molten solder.
Usage: Ideal for soldering very large cable lugs, battery terminals, or multiple cable joints where a large volume of solder is required, ensuring deep penetration.
Operation:
1. Preparation: Place bar solder into the pot.
2. Heating: Heat the pot (electrically or externally) until the solder melts and reaches the working temperature. A dross (oxide layer) will form on the surface, which should be skimmed off before use.
3. Application: The prepared cable joint (cleaned, fluxed, mechanically strong) is either dipped into the molten solder (for lugs) or the molten solder is scooped with a ladle and poured over the joint, ensuring it flows into all crevices.
Safety: Extreme caution is required due to large volume of molten metal. Wear heat-resistant gloves, eye protection, and protective clothing. Work on a stable, fire-resistant surface. Never add wet items to molten solder.
D. Other Tools: Wire Strippers: For safely removing insulation from cables without damaging conductors.
Pliers: To hold cables, bend wires, or provide mechanical strength.
Files/Sandpaper: For cleaning conductors.
Clamps/Vices: To hold workpieces steady.
Heat Sinks: Metal clips used to dissipate heat away from heat-sensitive components or insulation during soldering.
Cleaning Brush/Sponge: For cleaning soldered joints and soldering iron tips. 2.
3. Steps in Soldering (General Procedure)
1. Clean: Thoroughly clean the conductors to be joined using sandpaper, a wire brush, or a file. Remove all insulation, grease, dirt, and oxide layers. Cleanliness is paramount for a good joint.
2. Prepare Mechanical Joint: For most electrical joints, create a strong mechanical joint before soldering (e.g., twisting wires, forming a Western Union joint, crimping a lug). Soldering adds electrical conductivity and strengthens the joint but should not be the sole source of mechanical strength for many applications.
3. Apply Flux: Apply a thin layer of appropriate flux to the cleaned, mechanically prepared joint.
4. Heat: Apply heat to the joint (not the solder) until the conductors are hot enough to melt the solder.
5. Apply Solder: Touch the solder to the heated joint. The solder should melt and flow smoothly into the joint by capillary action, wetting all surfaces. Do not melt the solder directly with the heat source.
6. Remove Heat and Cool: Remove the heat source and allow the joint to cool undisturbed until the solder solidifies.
7. Clean Joint: Remove any flux residue, especially corrosive ones, using a suitable solvent (e.g., methylated spirit for rosin flux). 2.
4. Conductors and Heat Transfer Types of Conductors: Copper: Excellent electrical conductivity, good ductility (can be drawn into wires), corrosion resistant, relatively strong. Widely used for house wiring, motor windings, and general electrical applications in Nigeria.
Advantage: High conductivity, strong, flexible, good resistance to corrosion.
Disadvantage: More expensive than aluminum, heavier.
Aluminum: Good electrical conductivity (about 60% of copper's), lightweight, cheaper than copper. Used for overhead transmission lines, busbars, and sometimes large feeder cables in buildings (though special connectors are required due to oxidation issues).
Advantage: Lightweight, cheaper, good conductivity-to-weight ratio.
Disadvantage: Forms an insulating oxide layer quickly (making soldering difficult), less ductile than copper, lower mechanical strength, higher thermal expansion.
Other Conductors: Silver (best conductor but expensive), Gold (for corrosion resistance in critical electronics), Steel (for strength in overhead lines, usually copper-clad). Significance of Heat Transfer in Conductors: In Soldering: Heat transfer is critical. The heating tool (iron, blow-lamp) transfers thermal energy to the conductors. For the solder to melt and flow properly, the conductors themselves must reach the melting temperature of the solder. Efficient heat transfer from the tool to the workpieces ensures proper wetting and a strong, reliable joint. Poor heat transfer leads to 'cold joints'.
In Electrical Operations: All electrical conductors generate heat when current flows through them due to their resistance (Joule heating, I2R losses). The ability of a conductor to transfer this heat away to the surroundings 2.
1. Definition of Soldering Soldering is a process used to join two or more metal items by melting and flowing a filler metal (solder) into the joint. The solder, having a lower melting point than the base metals, adheres to the surfaces of the workpieces without melting them, thereby forming a strong electrical and mechanical bond. The purpose of soldering in electrical work is to create a permanent, low-resistance electrical connection between conductors, ensuring the efficient flow of current. 2.
2. Materials and Tools for Soldering
A. Solder: Definition: A metallic alloy, typically with a low melting point, used as a filler material in soldering.
Types: Lead-Tin Solder (e.g., 60/40, 50/50): Historically common, but less environmentally friendly due to lead content. "60/40" means 60% tin and 40% lead. Lead-Free Solder (e.g., Sn99.3Cu0.7, SnAgCu alloys): Increasingly used due to environmental regulations and health concerns. Has a higher melting point than lead-tin solder.
Forms: Wire (solid core or flux-cored), bar, paste. For electrical work, flux-cored wire solder is common for soldering irons, while bar solder is used with soldering pots.
Properties: Good electrical conductivity, low melting point, good flow characteristics when molten.
B. Flux: Definition: A chemical cleaning agent applied to the surfaces to be soldered before and during the heating process.
Purpose:
1. Cleans surfaces: Removes oxides and other impurities that prevent proper wetting of the solder.
2. Prevents re-oxidation: Forms a protective barrier over the heated metal surfaces during soldering.
3. Aids solder flow: Reduces surface tension of the molten solder, allowing it to flow and spread evenly.
Types: Resin (Rosin)
Flux: Non-corrosive, used for general electrical and electronic work (e.g., for copper conductors). Available as a paste or incorporated into flux-cored solder wire. Acid Flux (e.g., Zinc Chloride): Corrosive, used for heavier gauge work, plumbing, or soldering metals like galvanized iron. Not suitable for electrical work as residues can cause corrosion and electrical leakage.
Application: Applied to the cleaned joint surfaces just before heating.
C. Heating Devices:
1. Soldering Iron: Description: An electrical tool with a heated tip used for melting solder.
Types: Pencil type (low wattage, for delicate work), pistol grip (higher wattage, general purpose), soldering stations (temperature controlled).
Power Ratings: Typically 15W to 60W for electronics, up to 100W for heavier wiring.
Usage: For soldering thin cables and electronic components.
Care: Keep tip clean and tinned (coated with a thin layer of solder) to ensure efficient heat transfer.
2. Blow-Lamp (Blowtorch): Description: A device that produces a high-temperature flame, typically fuelled by kerosene, propane, or butane. Used for heating large metal parts or heavy gauge cables for soldering.
Components: Fuel tank, pump (for kerosene types), burner, jet, air valve.
Operation (Kerosene Blow-lamp Example):
1. Fueling: Fill the tank with kerosene, ensuring not to overfill.
2. Priming: Pump air into the tank to pressurize it.
3. Preheating: Pour a small amount of methylated spirit (or kerosene) into the dish below the burner and ignite it. This preheats the burner to vaporize the kerosene.
4. Ignition: Once the preheating fuel burns out and the burner is hot, open the fuel valve slightly. The vaporized kerosene will ignite, producing a steady blue flame.
5. Adjusting Flame: Adjust the pump pressure and fuel valve for the desired flame size and intensity.
6. Shutting Down: Close the fuel valve completely and allow the flame to die out. Release remaining pressure from the tank.
Safety: Always operate in a well-ventilated area, keep away from flammable materials, wear protective gloves and eyewear. Ensure the lamp is stable and on a non-combustible surface.
3. Soldering Pot and Ladle: Description: A pot, usually electrically heated or heated externally (e.g., by a blow-lamp), containing molten solder. A ladle is used to scoop and apply the molten solder.
Usage: Ideal for soldering very large cable lugs, battery terminals, or multiple cable joints where a large volume of solder is required, ensuring deep penetration. * Operation:
1. Preparation: Place bar solder into the pot.
2. Heating: Heat the pot (electrically or externally) until the solder melts transfer is critical. The heating tool (iron, blow-lamp) transfers thermal energy to the conductors. For the solder to melt and flow properly, the conductors themselves must reach the melting temperature of the solder. Efficient heat transfer from the tool to the workpieces ensures proper wetting and a strong, reliable joint. Poor heat transfer leads to 'cold joints'.
In Electrical Operations: All electrical conductors generate heat when current flows through them due to their resistance (Joule heating, I2R losses). The ability of a conductor to transfer this heat away to the surroundings (heat dissipation) determines its current-carrying capacity. If heat is not effectively transferred, the conductor's temperature rises, potentially damaging insulation, increasing resistance, and leading to power losses or even fire hazards. This is why proper cable sizing and ventilation are crucial in Nigerian electrical installations (e.g., ensuring cables are not bundled too tightly in conduits). Worked
Example: Soldering a Heavy Cable Lug A technician needs to connect a 50mm2 copper cable to a main distribution board terminal using a copper lug. This requires a robust, low-resistance connection. Step-by-step procedure using a Blow-lamp and Soldering Pot/Ladle:
1. Preparation: Measure the cable and lug to determine the correct stripping length. Strip approximately 20-25mm of insulation from the 50mm2 copper cable using a heavy-duty cable stripper or a sharp knife (with extreme care). Clean the exposed copper strands thoroughly with sandpaper or a wire brush until shiny. Clean the inside of the copper lug with a wire brush to remove any oxidation. Apply a suitable rosin-based soldering flux (e.g., a non-corrosive paste) to both the cleaned cable strands and the inside of the lug.
2. Crimping (Mechanical Connection First): Insert the cleaned, fluxed cable strands fully into the lug barrel. Using a hydraulic crimping tool (appropriate for 50mm2 cable and lug), perform a secure crimp. This establishes the primary mechanical connection.
3. Heating and Soldering (Enhancing Electrical Connection): Heat the soldering pot with bar solder until the solder melts and reaches working temperature (typically 250-300°C for lead-tin solder). Skim off any dross. Place the crimped lug with the cable firmly in a vice or clamp, ensuring stability. Using a blow-lamp, gently and evenly heat the crimped lug and the exposed cable strands just below the crimped section. The goal is to bring the lug and cable to a temperature sufficient to melt the solder. Avoid direct, prolonged heating of the cable insulation. Once the lug and cable are hot enough, use a clean, preheated ladle to scoop molten solder from the pot. Pour the molten solder over the heated crimped joint, allowing it to flow by capillary action into the cable strands within the lug and cover the crimped area. Ensure full penetration and a shiny, continuous solder fillet. Continue applying small amounts of solder until the joint is fully filled and appears smooth and shiny.
4. Cooling and Cleaning: Remove the heat source (blow-lamp). Allow the joint to cool naturally and undisturbed until the solder solidifies. Do not quench with water. Once cool, clean off any flux residue using a brush and a suitable solvent (e.g., methylated spirit or a specific flux cleaner) to prevent corrosion. Visually inspect the joint for proper wetting, smoothness, and absence of voids or sharp points. This example illustrates the combination of mechanical connection (crimping) and soldering for robust, high-current applications common in Nigerian industrial or large-scale building installations. 3.
1. Teacher Activities: Introduction (10 minutes): Begin by briefly reviewing the previous topic and linking it to the need for secure electrical connections. Engage students with questions about how electrical wires are joined in real-life (e.g., in their homes, at construction sites). Introduce the topic of soldering, its importance, and safety.
Key Concept Explanation (20 minutes): Explain the definition of soldering, types of solder and flux, and the general steps of soldering. Use diagrams or actual samples of solder and flux. Explain the properties and uses of copper and aluminum conductors, highlighting their advantages and disadvantages.
Tool Demonstration (30 minutes): Blow-lamp: Demonstrate the safe operation of a blow-lamp (priming, lighting, adjusting flame, shutting down). Emphasize safety precautions (ventilation, non-flammable surface, PPE). If live demonstration is not feasible/safe, use videos or detailed diagrams.* Soldering Pot and Ladle: Demonstrate heating solder in a pot (if available), skimming dross, and using a ladle to scoop molten solder. Explain its application for large cables. Emphasize extreme safety with molten metal.
Soldering Iron: Demonstrate the safe use of a soldering iron (tinning the tip, heating a joint, applying solder). Show how to make a simple joint on thin wires. Practical Application Demonstration (30 minutes): Demonstrate Objective 1: Perform a step-by-step soldering demonstration of a large cable lug onto a thick cable using the blow-lamp and/or soldering pot/ladle method (as outlined in the worked example). Explain each step clearly, emphasizing safety and quality.
Demonstrate Objective 2: Perform a step-by-step soldering demonstration of a simple joint (e.g., pigtail, Western Union) on thin cables using a soldering iron. Show proper cleaning, twisting, flux application, heating, and solder flow.
Supervision and Guidance (40 minutes): Divide students into small groups. Distribute materials (cable offcuts, lugs, solder, flux, tools).
Supervise students as they practice: Preparing large cables for soldering. Preparing thin cables for soldering. Practicing the actual soldering under close supervision, focusing initially on heat application and solder flow before attempting full joints. Continuously monitor safety practices and provide immediate corrective feedback.
Q&A and Reinforcement (10 minutes): Address student questions and clarify any misunderstandings. Summarize key learning points, emphasizing safety and quality. 3.
2. Student Activities: Active Listening and Note-taking: Pay close attention to teacher explanations and demonstrations, taking detailed notes on procedures and safety.
Questioning: Ask clarifying questions during explanations and demonstrations.
Observation: Carefully observe all demonstrations of tool operation and soldering techniques.
Practical Preparation: In groups, practice stripping and cleaning different sizes of electrical cables.
Mechanical Joint Formation: Practice making simple mechanical joints (e.g., twisting thin wires).
Supervised Soldering Practice: Under direct teacher supervision, learners will: Practice using a soldering iron to make joints on thin cables, focusing on proper heating and solder application. Practice preparing a large cable and lug, and if resources permit, observe and assist in the blow-lamp/pot and ladle process for large cables. Identify and correct common soldering faults (e.g., cold joints, too much solder).
Safety Adherence: Strictly follow all safety instructions and wear appropriate Personal Protective Equipment (PPE) – safety goggles, gloves.
Group Discussion: Discuss observations and challenges encountered during the practical session.
Domestic and Commercial Electrical Installations: In Nigeria, electricians frequently use soldering for robust connections in house wiring, especially for joining smaller gauge cables in junction boxes or connecting flexible wires to rigid ones. For example, connecting a ceiling fan's wiring to the main circuit often involves soldering for a secure and long-lasting connection. In commercial settings, heavy-duty soldering might be used for main feeder connections or earthing system joints in markets or office complexes. Repair of Electronic Appliances and Automotive Electrics: Soldering is indispensable in repairing everyday electronic devices common in Nigerian households and workshops, such as faulty televisions, radios, electric irons, blenders, and even rechargeable fans. Automotive technicians in Nigeria rely heavily on soldering to repair broken wires in vehicle wiring harnesses, re-solder connections in car alternators or starters, or fix corroded battery cable terminals, ensuring vehicle reliability. Renewable Energy Systems and Telecommunications: With the growing adoption of solar power in Nigeria, technicians use soldering to make reliable connections in solar panel systems, including connecting wires to charge controllers, inverters, and battery banks (for smaller gauge wires and specific terminals). In telecommunications, soldering is used for joining communication cables, repairing network equipment, and making secure connections in base stations, especially in remote areas where reliable infrastructure is crucial.