Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Equipment set-up (welding)
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Equipment set-up (welding)
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Subject: Welding & Fabrication
Class: Senior Secondary 2
Term: 1st Term
Week: 1
Theme: Workshop And Standard Workshop Practices
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identify the parts and accessories of the equipment for: gas welding arc welding 2. set-up the equipment for: gas welding arc welding
Gas welding primarily uses a flame produced by burning a mixture of oxygen and acetylene gases to melt and join metals. 2.1.
1. Parts and Accessories of Gas Welding Equipment:
1. Oxygen Cylinder: Description: A tall, heavy-duty steel cylinder containing oxygen gas under high pressure (typically up to 2200 psi or 150 bar). It has a right-hand threaded valve outlet.
Purpose: Supplies oxygen necessary for combustion and to achieve the high flame temperature required for welding.
Identification: Usually painted black (international standard) or blue in some regions; 'OXYGEN' stamped on the shoulder.
2. Acetylene Cylinder: Description: A shorter, thicker steel cylinder containing acetylene gas dissolved in a porous mass saturated with acetone. Acetylene is highly unstable under high pressure, so it's stored this way. It has a left-hand threaded valve outlet.
Purpose: Supplies the fuel gas that burns with oxygen to produce the welding flame.
Identification: Usually painted maroon or red; 'ACETYLENE' stamped on the shoulder.
3. Oxygen Regulator: Description: A pressure-reducing device attached to the oxygen cylinder valve.
It has two gauges: one showing cylinder pressure and the other showing working (hose) pressure. It uses a right-hand threaded inlet nut.
Purpose: Reduces the high cylinder pressure to a safe, usable working pressure for the torch and maintains a constant gas flow.
4. Acetylene Regulator: Description: Similar to the oxygen regulator but designed for acetylene, with two gauges. It uses a left-hand threaded inlet nut.
Purpose: Reduces acetylene cylinder pressure to a safe working pressure and maintains constant flow.
5. Hoses: Description: Flexible, non-porous rubber hoses designed to withstand gas pressure.
Purpose: Convey oxygen and acetylene from the regulators to the welding torch.
Identification: Oxygen hose is typically green or black, while the acetylene hose is red. Both have specific fittings for connection.
6. Welding Torch (Blowpipe): Description: The hand-held device where oxygen and acetylene are mixed and ignited. It has two valves for controlling gas flow (one for oxygen, one for acetylene) and a port for attaching various welding tips.
Purpose: Mixes the gases in precise proportions and directs the flame to the workpiece.
7. Welding Tips: Description: Interchangeable nozzles attached to the torch head, available in various sizes (e.g., 0, 1, 2, 3) with different orifice diameters.
Purpose: Controls the size and intensity of the flame. Larger tips produce a larger, hotter flame for thicker materials.
8. Spark Lighter/Friction Lighter: Description: A device used to safely ignite the gas mixture at the torch tip, producing a spark when a flint is scraped across steel.
Purpose: For safe ignition of the welding flame. Matches or cigarette lighters are unsafe and should NOT be used.
9. Cylinder Trolley/Cart: Description: A wheeled cart with chains or straps for securing cylinders.
Purpose: For safe transportation and securing of gas cylinders to prevent them from tipping over, which can damage valves or cause explosions.
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0. Flashback Arrestors (Safety Device): Description: Non-return valves installed between the regulator and the hose, or between the hose and the torch.
Purpose: Prevents a 'flashback' (flame travelling back into the hoses or cylinders) which can cause severe accidents. Highly recommended and often mandatory.
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1. Personal Protective Equipment (PPE): Welding Goggles: Protect eyes from intense light, heat, and sparks.
Welding Gloves: Heat-resistant gloves to protect hands from heat, sparks, and hot metal.
Leather Apron/Jacket: Protects body and clothing from heat and sparks. 2.1.
2. Step-by-Step Procedure for Gas Welding Equipment Setup:
1. Secure Cylinders: Place the oxygen and acetylene cylinders upright on a cylinder trolley or secure them to a wall or heavy object with chains to prevent accidental tipping. Ensure they are stable. 2. "Crack" Cylinder Valves: Briefly open and immediately close (crack) the cylinder valves using a cylinder wrench. This expels any dust or debris from the valve outlets, preventing contamination of regulators.
Oxygen cylinder valve (right-hand thread): Open slightly for a second, then close. Acetylene cylinder valve (left-hand thread): Open slightly for a second, then close.
3. Attach Regulators: * Oxygen Regulator: Attach the oxygen regulator to the oxygen cylinder trolley or secure them to a wall or heavy object with chains to prevent accidental tipping. Ensure they are stable. 2. "Crack" Cylinder Valves: Briefly open and immediately close (crack) the cylinder valves using a cylinder wrench. This expels any dust or debris from the valve outlets, preventing contamination of regulators.
Oxygen cylinder valve (right-hand thread): Open slightly for a second, then close. Acetylene cylinder valve (left-hand thread): Open slightly for a second, then close.
3. Attach Regulators: Oxygen Regulator: Attach the oxygen regulator to the oxygen cylinder valve. The fitting is typically right-hand threaded. Tighten firmly with a wrench.
Acetylene Regulator: Attach the acetylene regulator to the acetylene cylinder valve. The fitting is typically left-hand threaded. Tighten firmly with a wrench.
4. Attach Hoses: Connect the green/black oxygen hose to the oxygen regulator outlet and to the oxygen inlet on the welding torch (usually marked 'OXY' or 'O'). Connect the red acetylene hose to the acetylene regulator outlet and to the acetylene inlet on the welding torch (usually marked 'ACET' or 'AC'). Ensure all hose connections are tight. Flashback arrestors should ideally be installed at this stage, either at the regulator or torch end of the hoses.
5. Attach Welding Tip: Select the appropriate welding tip size for the job and securely attach it to the torch head. Ensure it is finger-tight, then use a spanner for a final snug tightening.
6. Open Cylinder Valves: Oxygen Cylinder: Open the oxygen cylinder valve fully (all the way open), then turn it back a quarter turn. This prevents the valve from seizing in the fully open position. Observe the high-pressure gauge on the oxygen regulator for cylinder pressure.
Acetylene Cylinder: Open the acetylene cylinder valve only 1/2 to 3/4 of a turn. This allows for quick closure in an emergency. Observe the high-pressure gauge on the acetylene regulator.
7. Set Working Pressures: Oxygen: Turn the adjusting screw on the oxygen regulator clockwise until the desired working pressure (low-pressure gauge) is indicated (e.g., 20-30 psi for welding).
Acetylene: Turn the adjusting screw on the acetylene regulator clockwise until the desired working pressure (low-pressure gauge) is indicated (e.g., 5-7 psi for welding).
Note: Specific pressures vary based on tip size and material thickness. Refer to manufacturer's charts.
8. Check for Leaks: * Before ignition, apply a leak-detection solution (soapy water) to all connections (cylinder-regulator, regulator-hose, hose-torch). Look for bubbles, which indicate a leak. If leaks are found, close cylinder valves, depressurize, and tighten connections or replace faulty components. Never proceed with leaks. the workpiece.
Importance: A good electrical connection is vital for a stable arc and to complete the welding circuit. Avoid clamping to painted surfaces or rusted areas.
4. Insert Electrode into Holder: Select the appropriate type and size of electrode for the welding job. Open the jaws of the electrode holder and firmly insert the bare end of the electrode (not the flux-coated part) into the clamp, typically at a 45 or 90-degree angle. Ensure it is securely held.
5. Connect Machine to Power Supply: Once all connections are made and checked, plug the welding machine into the appropriate power outlet. Ensure the power outlet is rated for the machine's current draw and is properly earthed.
6. Switch On Machine and Set Current: Turn on the welding machine. Adjust the welding current (amperage) according to the electrode size and type, and the thickness of the material being welded. Reference manufacturer guidelines or welding charts.
7. Wear PPE: * Before striking an arc, ensure all necessary PPE (welding helmet, gloves, apron, safety boots) are worn correctly. --- Arc welding uses an electric arc struck between a coated electrode and the workpiece to melt and join metals. 2.2.
1. Parts and Accessories of Arc Welding Equipment:
1. Welding Machine (Power Source): Description: Converts AC power into a suitable welding current (AC or DC). Can be transformer-based (AC), rectifier-based (DC), or inverter-based. Has terminals for connecting welding cables and controls for current adjustment.
Purpose: Provides the electrical energy needed to create and sustain the welding arc.
2. Electrode Holder: Description: A spring-loaded clamp with an insulated handle, designed to securely hold the welding electrode.
Purpose: Grips the electrode and transmits the welding current to it. Allows the welder to manipulate the electrode.
3. Earth Clamp (Ground Clamp): Description: A clamp, usually spring-loaded, used to establish an electrical connection between the welding machine and the workpiece or welding table.
Purpose: Completes the electrical circuit, allowing current to flow from the machine, through the electrode, through the arc, through the workpiece, and back to the machine.
4. Welding Cables: Description: Heavy-duty, insulated copper cables designed to carry high welding currents.
There are two main cables: the electrode cable and the earth cable.
Purpose: Conduct electricity from the welding machine to the electrode holder and from the workpiece (via the earth clamp) back to the machine.
5. Electrodes (Welding Rods): Description: Consumable metal rods with a flux coating. The core wire melts to form the weld metal, while the flux coating provides shielding gas, slag, and arc stabilization. Available in various types and sizes (e.g., E6013, E7018).
Purpose: Serves as the filler metal and provides protection to the weld pool.
6. Chipping Hammer: Description: A hammer with a pointed chisel on one end and/or a flat peening end on the other.
Purpose: Used to chip off the slag (solidified flux residue) that forms over the weld bead.
7. Wire Brush: Description: A stiff-bristled brush, usually steel.
Purpose: Used to clean slag and spatter from the weld area and prepare the base metal before welding.
8. Welding Helmet/Screen: Description: A head-worn or hand-held device with a dark filter lens (shade 10-14 for arc welding) that protects the eyes and face from intense UV/IR radiation, heat, and spatter. Auto-darkening helmets are common.
Purpose: Essential for protecting the welder's eyes and face from arc flash and sparks.
9. Personal Protective Equipment (PPE): Welding Gloves: Heavy-duty, heat-resistant leather gloves to protect hands from heat, sparks, and electrical shock.
Leather Apron/Jacket: Protects body and clothing from sparks and heat.
Safety Boots: Protects feet from falling objects and electrical shock. 2.2.
2. Step-by-Step Procedure for Arc Welding Equipment Setup:
1. Ensure Power OFF and Disconnected: Before making any connections, ensure the welding machine is switched OFF at the machine and disconnected from the mains power supply (unplugged). This is a critical safety step to prevent electrical shock.
2. Connect Welding Cables to Machine: Identify the output terminals on the welding machine (usually marked for electrode holder and earth clamp, sometimes with polarity indicators + and -). Connect the electrode holder cable to the appropriate terminal (e.g., positive for DC Electrode Positive (DCEP), also known as Reverse Polarity, which is common for general-purpose welding). Connect the earth clamp cable to the other terminal (e.g., negative for DCEP). Ensure connections are tight and secure.
3. Attach Earth Clamp to Workpiece: Securely attach the earth clamp directly to the workpiece or to a clean, bare metal section of the welding table that is in direct electrical contact with the workpiece.
Importance: A good electrical connection is vital for a stable arc and to complete the welding circuit. Avoid clamping to painted surfaces or rusted areas.
4. Insert Electrode into Holder: Select the appropriate type and size of electrode for the welding job. Open the jaws of the electrode holder and firmly insert the bare end of the electrode (not the flux-coated part) into the clamp, typically at a 45 or 90-degree angle. Ensure it is securely held.
5. Connect Machine to Power Supply: * Once all connections
Understanding welding equipment setup is a foundational skill with extensive relevance in the Nigerian context, integrating with various aspects of community, economy, and environment.
Community and Infrastructure Development: Application: Welders with proficiency in equipment setup are essential for constructing and maintaining local infrastructure such as market stalls, community water tanks, gates, school fences, and signposts. In rural areas, this skill can be used to repair farm implements like ploughs, hoes, and irrigation pipes, directly supporting agricultural productivity.
Integration: This skill enables local artisans to contribute to durable community structures, reducing reliance on imported goods and fostering self-sufficiency. It also empowers individuals to start small businesses, offering fabrication and repair services that directly address local needs. Industrial Growth and Economic Empowerment: Application: Nigeria's burgeoning manufacturing and oil & gas sectors require skilled welders for fabrication, installation, and maintenance of machinery, pipelines, and structural steel. Correct equipment setup is the first step in ensuring quality welds that meet industry standards. Skilled welders are highly sought after in these sectors, providing stable employment and contributing to national economic output.
Integration: Equipping students with these skills prepares them for formal employment in factories, construction companies, and repair workshops, thereby reducing unemployment. It also provides a pathway for entrepreneurship, allowing individuals to establish their own welding and fabrication ventures, creating job opportunities for others. Environmental Sustainability through Repair and Recycling: Application: Instead of discarding broken metal items, proficient welders can repair them, extending their lifespan. This applies to vehicles, furniture, industrial parts, and even art pieces. Properly setting up welding equipment allows for precise repairs that prevent waste.
Integration: This practice aligns with principles of a circular economy and environmental sustainability by reducing the amount of metal waste sent to landfills. It promotes a culture of repair and recycling, which is vital in a resource-constrained environment, offering cost-effective solutions for individuals and businesses while minimizing environmental impact. For example, fixing a broken metal chair rather than buying a new one saves resources and reduces waste. ---