Lesson Structure: Mechanics (Understanding and Working With Machines) BSS102

1  Introductory Mechanics

• Introduction
• Power Sources
• Engines
• Steam Engines
• Petrol Engine
• How an Engine Works
• The Operating Cycle
• Stages in a Four Stroke Spark Ignition Engine Cycle
• Stages in a Two Stroke Spark Ignition Engine Cycle
• Electric Motors
• Parts of an Electric Motor
• Types of Electric Motors
• Comparison of Electric and Petrol Engines
• Applied Tasks: Changing a Wheel, Mending a Puncture

2  Engine Features

• Measurements and Mechanical Principles: Force, Load, Pressure, Relationships in Pressure Measurements, Absolute Pressure, Force of Gravity, Centre of Gravity, Specific Gravity (Specific Weight), Density, Volumetric Efficiency, Vacuum, Work, Power, Energy, Bore, Piston Displacement, Compression Ratio (CR)
• How to Convert Imperial Measurements into Metric
• Engine Efficiency: How Does an Engine lose Power?
• Features of Electric Motors
• Applied Tasks: Spark Plugs, Checking for fouling and damage/ reading the spark plug

3  Machines and their Parts

• Parts of a Machine: Engine Systems, Lubrication System, Transmission System, Cooling System, Fuel System, Transmission System, Gearbox (transmission), Clutch (torque converter), Differential, Prop shaft/ drive shaft
• Power Source and Ignition: The Ignition System, Distributor, Coil pack
• Other Machines: Outdoor Multi Tools, Domestic Maintenance Equipment, Kitchen Equipment

4  Drive Mechanisms

• Introduction
• Cog Drive Machinery
• Belt Drive Machinery
• Transmission Drive Machinery
• The Transmission System
• Applied Tasks: Replacing Drive Belts

5  Managing Machinery Deterioration

• The Lubrication System
• The Cooling System
• Lubrication: Oil Viscosity, Delivering the Lubricant, Splash System, Pressure System, Combination Pressure and Splash
• Types of Lubrication Pumps
• Types of Filter Systems
• Materials Deterioation
• Metals – Ferrous: (Iron) Materials, Steels, Heat Treatments, Aluminium, Copper, Lead, Zinc, Tin, Nickel
• Non-Ferrous Alloys: Brass, Bronze, White Metal, Solder
• Seals
• Servicing Filters: Air Filters, Oil filters, Fuel Filters
• Servicing the Filters: Air Filters

6  Optimizing Machine Operation (Getting the most from Machines)

• Introduction: Adjustments, Controlling Power, Carburettors (for petrol engines), Types of Carburettors, How a Carburettor Controls the Fuel Mix, Number of Barrels
• Lubrication
• Exhaust Systems: Catalytic Converter, Muffler, Extractors
• Turbochargers: Intercooling, Wastegate, Blow off valves, Twin vs single turbo, Boost controller
• Superchargers: Temperature effects
• Applied Tasks: Servicing a Carburettor

7  Brake Systems

• Introduction
• Drum vs Disc Brakes
• Drum Brakes and Shoe (Pad)
• Disc Brakes
• Brake Systems –Pneumatic
• Hydraulic and Electric Brakes
• ABS (Anti-lock Brake System)
• Regenerative braking
• Applied Tasks: Servicing Brakes, Jacking up the vehicle to change or service brakes, Changing Disk Brakes, Changing Drum Brakes, Motorcycle Brakes, Push Bike Brakes

8  The Machine Workshop

• Introduction
• Tool Maintenance
• Work Bench
• Vices and Clamps
• Lifts, Ramps, Jacks, Ladders
• Tightening Pullers
• Pulleys
• Winches
• Generators, Battery Chargers
• Cleaning Equipment
• Grinders, Sharpening Equipment
• Work Pits and Hoists
• Measuring Equipment
• Spanners and Allen Keys
• How to Use Spanners
• Pliers and Grips
• Screwdrivers
• Files
• Cutting Equipment
• Hammers, Chisels and Punches
• Tap and Die Cutters
• Lubrication Equipment
• Drills
• Saws
• Soldering
• Welding: Oxy-fuel welding, Shielded metal arc welding (SMAW), Gas tungsten arc welding (GTAW), Gas metal arc welding (GMAW), Flux-cored arc welding (FCAW), Submerged arc welding (SAW), Electroslag welding (ESW), Electric resistance welding (ERW)

9  Machine Maintenance and Repair

• Introduction
• Servicing a Typical Motor Car
• Inspect Oil levels/Engine/transmission – Change oil filter, fuel filter
• Changing spark plugs/ cleaning / gapping resizing /Installing
• Inspect Coolant levels
• Inspect tyre pressure/tread condition (should be done regularly if not every 6 months)
• Change Fuel Filter
• Check brakes – brake fluid
• Wheel Alignment
• Power steering fluid
• Electrics – indicators, brake lights, headlights, windscreen wipers and fluid, hazard lights, horn
• Replacing light bulbs
• Servicing Garden Equipment
• Oil
• Dirty Spark Plugs
• Mowers
• Changing Mower Blades
• Chainsaws
• Outdoor Electric Machines
• Treating Rust
• Painting Metal

Learning Goals: Mechanics (Understanding and Working With Machines)  BSS102

1. Explain how different types of engines and motors work.
2. Describe the features that differentiate the quality and work capacity of engines; one from another.
3. Describe the scope and nature of components of a machine.
4. Explain different ways of converting the movement of energy to perform useful work tasks.
5. Describe how machinery can deteriorate over time, and responses to both prevent and repair deterioration.
6. Explain how engines and motors have their power output regulated.
7. Explain the mechanisms used to slow or stop any form of motion by applying force.
8. Describe machinery workshop tools and equipment, and explain their safe and appropriate use in maintaining and repairing machinery.
9. Describe some routine machine maintenance and repair tasks.

THE LUBRICATION SYSTEM

Any piece of metal, regardless of how smooth and polished it may look to the sight or touch, is covered with tiny irregularities and projections. When two highly polished metal surfaces are brought together, and one forced to slide over the other, the projections grip each other, causing resistance to the sliding.

This resistance is called FRICTION. Friction results in wear of the metals. The amount of friction depends on the type of material, amount of pressure and the nature of the surfaces.

Lubrication reduces friction, and this occurs when some substance, either liquid or solid is put between two rubbing surfaces. Lubrication also reduces wear and heat that would otherwise occur. The lubrication system must distribute the lubricant so that at no instance is there metal to metal contact in any moving parts.

There are different types of lubrication systems, for different types and sized engines, e.g. the splash feed system (see diagram below) and the force feed system. Although the lubricant acts as a coolant, some sort of cooling system is also necessary in an engine (cooling methods are discussed in the following section).

Oil contamination can occur so it is necessary to change the oil regularly, after a certain number of operating hours. Moisture contamination can occur in an engine due to condensation and also as a result (by-product) of the cooling process itself. Dirt may enter through the air intake of the engine, so it is important to regularly change or maintain the air filter. Tractors, particularly, operate in very dirty environments and for this reason they are fitted with a special mechanism called an oil bath air cleaner. Carbon and soot by products also cause oil contamination.

The Cooling System

When a motor or engine is operating it produces a significant amount of heat. To prevent damage to the engine it is necessary to keep the engine at a correct temperature. Operating an engine at overly high temperatures causes structural damage to engine components, and overly cool operating temperatures mean the fuel will not vaporise properly. The two main methods for cooling engines are air cooling and water cooling.

Air cooling is mainly used in small engines (single cylinder) or for machinery like potato harvesters, lawn mowers and elevators. A blast of air is directed on the cylinder and cylinder head, both of which are finned (see diagram below). These fins increase the surface area of the cylinder and provide a larger surface area through which the heat can spread. Air cooled systems are simple and reliable, but are less efficient than water cooled systems as air has a lower heat capacity, so more air is needed to produce the same effect as water. Over-heating can occur if the fins become blocked with dirt, as this reduces the surface area to be cooled.

Water cooling is more effective for use in multi-cylinder engines. The engine cylinders are completely surrounded with a water jacket. The water extends to the cylinder head where there is an outlet to the radiator. There is another outlet at the bottom of the radiator connecting back to the water jacket surrounding the cylinders. Water flows around this system.

The radiator is composed of a head tank and a bottom tank. Between these there are a lot of thin tubes and metal plates that greatly increase the surface area to be cooled. This is the core of the radiator. Behind the radiator core there is a fan that operates via a pulley system connected to the crank shaft of the engine. This fan blows cool air onto the radiator. The cooled air circulates back through the engine.

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General

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