Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Dismantling of Machines
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Dismantling of Machines
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Subject: Electrical Installation And Maintenance Work
Class: Senior Secondary 3
Term: 2nd Term
Week: 8
Theme: Protective Devices And Maintenance
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Dismantle machines Identify front and back shield Record necessary data from the man plate.
Dismantling is the process of taking apart a machine or device into its constituent components.
It is essential for: Inspection: To check for worn parts, damage, or specific faults.
Repair: To replace faulty components or repair damaged parts (e.g., motor rewinding).
Cleaning: To remove dust, dirt, or debris that might impair performance.
Maintenance: To lubricate bearings, check insulation, or perform preventive maintenance.
Learning: To understand the internal structure and working principles of a machine. Safety is paramount when working with electrical machines. Adherence to these precautions is non-negotiable.
Disconnect Power: Always ensure the machine is completely disconnected from its power source. Implement a Lock-Out/Tag-Out (LOTO) procedure if available, especially in industrial settings.
Discharge Capacitors: If the machine has capacitors (e.g., single-phase motors), ensure they are safely discharged before touching any internal components to prevent electric shock.
Wear Personal Protective Equipment (PPE): Safety Glasses/Goggles: To protect eyes from flying debris.
Safety Gloves: To protect hands from sharp edges, dirt, and oil.
Safety Shoes: To protect feet from falling tools or components.
Clear Workspace: Ensure a clean, well-lit, and uncluttered workspace to prevent accidents and facilitate easy organization of components.
Use Correct Tools: Employ the right tools for each task to avoid damaging the machine or injuring oneself.
Secure the Machine: Place the machine on a stable workbench to prevent it from moving or falling during dismantling. The following tools are commonly used for dismantling small to medium-sized electrical machines: Screwdrivers: Flat-head and Phillips-head, various sizes.
Spanners/Wrenches: Open-end, ring, or adjustable types, for nuts and bolts.
Pliers: Combination, long-nose, and side-cutting pliers.
Hammers: Soft-face mallet (rubber or plastic) for gentle tapping, and a claw hammer for general use.
Bearing Pullers: For safely removing bearings from shafts.
Gear Pullers: If gears are present on the shaft.
Measuring Tape/Ruler: For taking dimensions.
Multimeter: For continuity checks or resistance measurements if required during inspection.
Marking Tools: Chalk, paint marker, or centre punch for marking components for reassembly.
Container/Trays: For organizing screws, bolts, and small parts.
Wire Brush/Cleaning Cloths: For cleaning components. Accurate identification of the front and back shields is essential for correct reassembly and understanding machine design.
Front Shield (Drive End - DE): Shaft Extension: This end always has the motor shaft extending outwards. This shaft is designed to connect to the mechanical load (e.g., pump, fan, gearbox) via a coupling, pulley, or gear.
Bearing Type: Often houses a more robust bearing (e.g., deep groove ball bearing) to handle radial and axial loads from the driven equipment.
External Appearance: Generally simpler in design, focused on providing a stable output shaft.
Back Shield (Non-Drive End - NDE): Cooling Fan: This end typically houses the cooling fan (inside or outside the shield, covered by a fan cover) which draws air over the motor body for cooling.
No Shaft Extension: The shaft usually terminates internally or has a very short extension for the fan.
Brush Gear (for DC/Universal Motors): In DC motors and universal motors, the brush gear (brushes, brush holders, commutator) is almost always located at the NDE, allowing for easier access for maintenance.
Terminal Box: The terminal box where external electrical connections are made is often located on the top or side of the main frame, but its proximity to the NDE is common.
Practical Differentiation: The easiest way to differentiate is the presence of the extended shaft at the Drive End (Front) and the cooling fan/brush gear at the Non-Drive End (Back).
This procedure outlines a typical approach to dismantling a small AC or DC motor. The exact steps may vary slightly depending on the machine type and design.
Pre-Dismantling Checks and Documentation: Record Nameplate Data: Before starting, carefully record all information from the nameplate (man plate). This is crucial for obtaining spare parts or for proper reassembly and operation. (See Section 2.7).
Visual Inspection: Note any external damage, loose connections, or unusual signs.
Marking: Before separating any major components (like end shields from the frame), use a chalk or a centre punch to make alignment marks across the mating surfaces. These marks ensure correct orientation during reassembly, maintaining dynamic balance and preventing misalignment issues. For instance, mark the frame and end shield at 12 o'clock, 3 o'clock positions, etc.
Disconnect Electrical Connections: Carefully disconnect the supply wires from the terminal box. Label them if necessary. If there are internal connections to components like capacitors or thermal protectors, disconnect and label them.
Remove External Accessories: Fan Cover: Unscrew and remove the fan cover, typically located at the non-drive end (back shield).
Fan: If secured by a nut or set screw, loosen it and carefully remove the cooling fan. A puller might be needed if it's press-fitted. Remove Brush Gear (for DC and Universal Motors): Locate the brush covers/caps. Unscrew and remove them. Carefully pull out the carbon brushes from their holders. Note their orientation. Remove the brush holder assembly if it can be detached easily. Note its position relative to the commutator.
Remove End Shields: Identify Fasteners: Locate the bolts or nuts holding the end shields to the main motor frame. These are usually long bolts extending from one end shield through the frame to the other end shield, or shorter bolts securing each shield independently.
Loosen Fasteners: Loosen these bolts gradually, criss-cross pattern, to avoid stressing the casing.
Separate End Shields: Gently tap the end shields with a soft-faced mallet to loosen them from the frame. Be careful not to damage the bearings or internal components. Front vs.
Back Shield: As the shields are removed, differentiate them. The front shield (drive end - DE) typically has the shaft extension for coupling to a load. The back shield (non-drive end - NDE) often houses the fan and possibly the brush gear in DC motors. (See Section 2.5).
Extract Rotor/Armature: Once the end shields are removed, the rotor (for AC motors) or armature (for DC motors) can be carefully withdrawn from the stator. Hold the rotor/armature by the shaft, avoiding contact with the windings or commutator/slip rings. Place it on a clean, soft surface to protect its components.
Inspect Stator Windings: With the rotor removed, the stator windings become fully visible. Observe the winding connection type (Star or Delta if identifiable from lead configuration). Note the condition of the insulation and the gauge of the winding wires. (See Section 2.8).
Remove Bearings (if necessary): If bearings need replacement, use a bearing puller to carefully remove them from the shaft or end shields. Never hammer bearings directly.
This topic holds significant practical relevance for Nigerian learners, directly linking classroom knowledge to local economic and community needs. Entrepreneurship in Motor Rewinding and Repair: The knowledge of dismantling is the foundational skill for establishing or working in motor rewinding businesses, a thriving industry in major Nigerian cities and towns (e.g., Alaba International Market in Lagos, Ariaria Market in Aba). Many burnt-out motors from pumps, grinding machines, and industrial equipment require rewinding rather than outright replacement, offering a cost-effective solution for consumers and a viable business for skilled technicians. Maintenance of Generators and Small Appliances: Almost every Nigerian household and small business relies on generators ("I better pass my neighbour," "Sumec Firman," etc.) due to inconsistent public power supply. The ability to safely dismantle a generator head for inspection, brush replacement, or minor repairs is a highly valuable skill. Similarly, repairing common home appliances like electric fans, blenders, and food processors begins with safe dismantling to access internal components, promoting self-reliance and reducing reliance on external repair services. Industrial and Agricultural Equipment Maintenance: In Nigeria's growing manufacturing sector (e.g., textiles, food processing) and agricultural industries (e.g., irrigation pumps, milling machines), electrical motors are ubiquitous. Technicians with skills in dismantling can perform routine maintenance, diagnose faults, and facilitate repairs, minimizing downtime and ensuring productivity. This directly contributes to local industrial development and food security.