Mechanical Technology Grade 12 Eastern Cape Mock 2020 Memo

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE GRADE 12 SEPTEMBER 2020 MECHANICAL TECHNOLOGY: AUTOMOTIVE MARKING GUIDELINE MARKS: 200 This marking guideline consists of 15 pages.

Downloaded from hlayiso.com 2 MECHANICAL TECHNOLOGY: AUTOMOTIVE (EC/SEPTEMBER 2020) QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC) 1.1 C (1) 1.2 B (1) 1.3 C (1) 1.4 A (1) 1.5 B (1) 1.6 C (1) [6] QUESTION 2: SAFETY (GENERIC) 2.1 Gas welding (PPE)  Eye protection   Overall / leather apron   Safety boots   Gloves  (Any 2 x 1) (2) 2.2 Safety rules that must be followed whilst the surface grinder is in operation:  Make sure that the sparks are of no danger to co-workers.   Do not force the material onto the grinding wheel.   Do not plunge grind.   Bring the material slowly into contact with the grinding wheel.   Never clean or adjust the machine whilst it is in motion.   Use cutting fluid.   Know where the emergency stop is located.   Stop the machine before any adjustment.   Keep tools clear from moving parts.  (Any 2 x 1) (2) Copyright reserved Please turn over

Downloaded from hlayiso.com (EC/SEPTEMBER 2020) MECHANICAL TECHNOLOGY: AUTOMOTIVE 3 2.3 Completing a task on any machine: Switch the machine off.  (1) 2.4 TWO safety measures to observe before switching the angle grinder on:  Make sure that there are no cracks or chips on the disc.   Make sure that the emery disc that is fitted is rated above the revolutions at which it is turned by the motor.   Make sure that the space between the tool rest and the emery disc does not exceed 3 mm.   Ensure that guards are in place.   Do not stand in front of the machine when switching it on; wait until it reaches its full speed.   Do not force or bump the work piece against the emery disc.   Grind only on the front surface of the wheel, not the sides.   All grinding machines must have a sign indicating the revolutions at which the spindle rotates.  (Any 2 x 1) (2) 2.5 Importance of a welding helmet:  To protect your eyes and face from ultra-violet rays and radiation  (1) 2.6 Types of workshop layouts:  Process layout   Product layout  (2) [10] Copyright reserved Please turn over

Downloaded from hlayiso.com 4 MECHANICAL TECHNOLOGY: AUTOMOTIVE (EC/SEPTEMBER 2020) QUESTION 3: MATERIALS (GENERIC) 3.1 MATERIALS DIFFERENT TYPES OF TESTS Sound Filing Bend Very dull sound  Easy  Cannot bend / Cast iron Snaps/breaks/ Fracturea easily  Medium metallic Easy  Benda easily  Mild steel sound  (6) 3.2 Heat treatment process:  Is the heating and cooling of metals in their solid state so as to change their properties  (1) 3.3 Hardness factors:  Workpiece size   Quenching rate   Carbon content  (Any 2 x 1) (2) 3.4 Heat treatment processes: 3.4.1 Tempering  Is a process applied to steel and it relieves the strains induced during the hardening process.   It decreases the degree of hardness   It increases toughness   It reduces brittleness   It gives steel fine grain structure  (Any 2 x 1) (2) 3.4.2 Annealing  Relieves internal stress   Softens the metal   Makes metal ductile   Refines the grain structure   Reduces brittleness  (Any 2 x 1) (2) 3.5 Hardness of steel depends upon  Carbon content  (1) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com (EC/SEPTEMBER 2020) MECHANICAL TECHNOLOGY: AUTOMOTIVE 5 QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC) 4.1 A (1) 4.2 C (1) 4.3 D (1) 4.4 B (1) 4.5 B (1) 4.6 D (1) 4.7 C (1) 4.8 D (1) 4.9 B (1) 4.10 A (1) 4.11 C (1) 4.12 D (1) 4.13 B (1) 4.14 A (1) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com 6 MECHANICAL TECHNOLOGY: AUTOMOTIVE (EC/SEPTEMBER 2020) QUESTION 5: TOOLS AND EQUIPMENT (SPECIFIC) 5.1 Bubble gauge: 5.1.1  Bubble gauge  (1) 5.1.2 A – King-pin inclination scale  B – Caster scale  C – Camber scale  D – Gauge zero scale  E – Mounting equipment on wheel  (5) 5.1.3  Caster angle   Camber angle   King-pin inclination  (3) 5.2 Set-up procedure to read camber:  Ensure that the wheels are in a straight ahead position.   Mount the bubble gauge on the centre of the wheel.   Zero the bubble gauge on the gauge zero scale.   Take the reading on the camber scale.   Do the same for the other wheels.  (5) 5.3 Dynamic balancing of wheels:  The plane of imbalance   The extent of unbalanced forces   The sense of direction of these forces (clockwise or counter clockwise / anticlockwise)   Run-out of the tyre and wheel assembly  (Any 3 x 1) (3) 5.4 Tools: 5.4.1 Turn table: To turn the front wheel 20° in and zero the bubble gauge  and then turn the wheel 20° out to check the castor reading  (2) 5.4.2 Wheel balancer: To balance the wheels of a vehicle  for static and dynamic balance.  (2) 5.4.3 Optical alignment tool: To check the toe-in  and toe-out of a vehicle  (2) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com (EC/SEPTEMBER 2020) MECHANICAL TECHNOLOGY: AUTOMOTIVE 7 QUESTION 6: ENGINES (SPECIFIC) 6.1 Causes of vibration:  The action of unbalance forces upon the shaft   The twisting effects of the power stroke  (2) 6.2 Types of vibration damper:  Friction face-type   Combined rubber and friction disc  (2) 6.3 In-built engine balance features: 6.3.1 Crankshafts are carefully balanced with webs extended and drilled to form balance mass piece at points opposite the connecting rods.  (2) 6.3.2 Connecting rods and pistons are kept as light as possible to reduce reciprocating forces.  (2) 6.3.3 Flywheels are carefully balanced and are usually fitted to the crankshaft flange in one position only.  (2) 6.4 Factors that determine engine configuration:  Number of cylinders   Position of cylinders   Engine layout   Firing order   Engine location and mounting  (Any 3 x 1) (3) 6.5 Types of engine configuration:  In-line engine   V-type engine   Horizontally opposed engine  (Any 2 x 1) (2) 6.6 Identification of an engine configuration: The crankshaft of a V-engine  (1) 6.7 Factors that determine the firing order:  The position of the crank on the crankshaft   The arrangement of the cams on the camshaft  (2) 6.8 Firing order of a 5-cylinder in-line engine: 12453 OR 13542  (1) 6.9 Turbocharger internal components: A – Turbine exhaust gas outlet  B – Turbine wheel OR impeller  C – Turbine exhaust gas inlet  D – Compressor air discharge  E – Compressor  F – Compressor air inlet  (6) Copyright reserved Please turn over

Downloaded from hlayiso.com 8 MECHANICAL TECHNOLOGY: AUTOMOTIVE (EC/SEPTEMBER 2020) 6.10 Disadvantages of a turbocharger:  It can have lag problems.   It tends to heat up the air, reducing density.   Some require shut-down process.   It requires pressure lubrication for high speed bearings.   Its lubricant must be air cooled.   Over-revving must be controlled by waste gate.  (Any 3 x 1) (3) [28] QUESTION 7: FORCES (SPECIFIC) 7.1 Compression ratio: The compression ratio of an internal combustion engine is the ratio of compression of the inlet charge during the compression stroke  to the total volume of the cylinder.  (2) 7.2 Compression ratio: Swept volume: ∏𝐷2 𝑆𝑤𝑒𝑝𝑡 𝑣𝑜𝑙𝑢𝑚𝑒 = 𝐿  4 ∏(9.02 ) = × 11  4 = 700 cm3  𝑆𝑉+𝐶𝑉 Compression ratio =  𝐶𝑉 700+70 = 70  11 : 1  (6) 7.3 New compression ratio: ∏(9,612 ) Swept volume = × 11 4 = 797,865 cm3  797,865 + 70 Compression ration =  70 =12,4 : 1  (4) (4) 7.4 Methods used in raising compression ratio:  Remove shims between the cylinder block and cylinder head.   Fit thinner cylinder head gasket.   Machine metal from cylinder head.   Skim metal from cylinder block.   Fit piston with higher crown.   Fit crankshaft with longer stroke.   Increase the bore of the cylinders.  ( Any 4 x 1) (4) Copyright reserved Please turn over

Downloaded from hlayiso.com (EC/SEPTEMBER 2020) MECHANICAL TECHNOLOGY: AUTOMOTIVE 9 7.5 Indicated power: Indicated power is a measure to determine the total power developed by the burning of fuel in the combustion chamber of an internal combustion engine.  (2) 7.6 Power calculations: 7.6.1 Indicated power = P × L × A × N × n P = 1200000 Pa 86 L= 1000 =0,086 m  π𝐷2 A= 4 π× 0,092 =  4 =6,36 × 10-3 m2  4200 N = 60×2  = 35 r/s  N = 4 cylinders Indicated power = 1200000 × 0,086 × 6,36 × 10-3 × 35 × 4 = 91889,28 W = 92 kW  (7) 7.6.2 Brake power = 2 π NT 4200 N= 60 70 r/s  = 2 × π × 70 × 180  =211115,03 W =79168,13 W =79,2 kW  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com 10 MECHANICAL TECHNOLOGY: AUTOMOTIVE (EC/SEPTEMBER 2020) 7.6.3 𝐵𝑃 Mechanical efficiency = ×100% 𝐼𝑃 79,2 = × 100%  92 = 82,5%  (2) 7.7 Term definition: It is the percentage energy that an engine puts out due to mechanical losses as compared to the ideal engine power.  (2) [32] Copyright reserved Please turn over

Downloaded from hlayiso.com (EC/SEPTEMBER 2020) MECHANICAL TECHNOLOGY: AUTOMOTIVE 11 QUESTION 8: MAINTENANCE (SPECIFIC) 8.1 Reasons for high CO (carbon monoxide) reading: 8.1.1  Too rich mixture   Ignition misfire   Dirty or restricted air filter   Improper operation of the fuel delivery system   Faulty thermostat or coolant sensor   Non-functioning PVC valve system   Catalytic converter not working  (Any 3x1) (3) 8.1.2 Corrective measures:  Reset fuel mixtures.   Check for misfire and repair.   Replace air filter.   Check and correct fuel delivery system.  (Any 3 x 1) (3) 8.1.3 Gases analysed:  CO2   SO2   NO   HC   O2  (Any 3 x 1) (3) 8.2 Cylinder leakage testing:  Wet test  (1) 8.3 Cylinder leakage and causes: 8.3.1 Leakage inlet valve  (1) 8.3.2 Blown cylinder head gasket or cracked cylinder block  (1) 8.3.3 Piston rings are worn  (1) 8.4 Oil pressure testing:  Oil pressure when the engine is idling.   Oil pressure when the engine is cold.   Oil pressure when the engine is hot.   Oil pressure on high revolution.  (4) Copyright reserved Please turn over

Downloaded from hlayiso.com 12 MECHANICAL TECHNOLOGY: AUTOMOTIVE (EC/SEPTEMBER 2020) 8.5 Causes of low fuel pressure reading:  Faulty fuel pump   Blocked or restricted fuel filter   Cracked or restricted fuel line   Clogged pump inlet strainer   Low voltage to fuel pump   Faulty fuel pressure regulator   Faulty fuel pump relay   Empty fuel tank  (Any 3 x 1 ) (3) 8.6 Cooling system pressure testing:  Water hoses   Water pump   Radiator   Corroded core plugs   Interior heater radiator   Faulty radiator cap  (Any 3 x 1 ) (3) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com (EC/SEPTEMBER 2020) MECHANICAL TECHNOLOGY: AUTOMOTIVE 13 QUESTION 9: SYSTEMS AND CONTROL (AUTOMATIC GEARBOX) (SPECIFIC) 9.1 Purpose of automatic gearbox: To relieve the driver of clutch and gearshift operation, thereby allowing the driver to concentrate on driving the vehicle  (2) 9.2 Advantages of an automatic gearbox  It reduces driving fatigue.   It ensures reduction of wheel spin under bad road condition.   The vehicle can be stopped suddenly without the engine stalling  The system puts a damper on/muffles all engine vibrations.  (Any 3 x 1) (3) 9.3 Torque converter: 9.3.1 Torque converter  (1) 9.3.2 Parts A – One-way clutch  B – Turbine  C – Pump  D – Turbine shaft  E – Gearbox housing  (5) 9.3.3 Torque converter functions:  Transfers engine torque to the transmission.   Multiplies the engine torque.   Provides a direct drive from engine to transmission.   It muffles/puts a damper on all engine vibrations.   It acts as flywheel.  (Any 3 x1 ) (3) 9.3.4 Function of parts: It sets the fluid in motion at high pressure to the turbine,  thereby causing the turbine to rotate with great torque.  (2) 9.4 Torque multiplication: As the car speed increases,  the torque multiplication tapers off gradually.  (2) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com 14 MECHANICAL TECHNOLOGY: AUTOMOTIVE (EC/SEPTEMBER 2020) QUESTION 10: SYSTEMS AND CONTROL (AXLES, STEERING GEOMETRY AND ELECTRONICS) (SPECIFIC) 10.1 Properties of a good steering mechanism:  Light and easy to control   Free from vibration and road shocks   Self-centring   Able to operate effectively under the influence of the suspension and braking system   It must be as direct as possible to reduce too much driver’s attention.  (Any 4 x 1) (4) 10.2 Toe-in Steering wheel  Wheel  Toe-in  FRONT (4) 10.3 Alignments: 10.3.1 Caster angle: It gives self-centring action to the steering thereby keeping the wheels in straight ahead position. (2) 10.3.2 Ackermann principle: To avoid the need for tyres to slip sideways  when following the path around a curve. (2) 10.3.3 King pin inclination: To bring the front wheel back to the straight ahead position  after rounding a corner without any driver effort.  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com (EC/SEPTEMBER 2020) MECHANICAL TECHNOLOGY: AUTOMOTIVE 15 10.4 Camber: 10.4.1 Positive camber.  (1) 10.4.2 A – Tyre  B – Vertical line  C – Centre line  D – Positive camber angle  E – Lower control arm  F – Road surface  (6) 10.4.3 Positive camber angle is the outward tilt  of a front wheel away from The vehicle when viewed from the front.  (2) 10.5 Factors to be taken into account before attempting alignment adjustment:  Kerb mass must be checked against the manufacturer’s specifications   Uneven wear on tyres   Tyre pressure   Run-out on wheels   Kingpins and bushes   Suspension ball joints for wears   Suspension bushes for excessive free movements   Tie-rod ends   Sagged springs   Ineffective shock absorbers   Spring U-bolts   Chassis for possible cracks   Wheel must be balanced   Wheel alignment specifications   Drive shaft CV-joints  (Any 5 x 1) (5) 10.6 Purpose of wheel balancing: To avoid shimming and bouncing of wheel assembly which can cause wearing of the steering mechanism and suspension parts.  (2) 10.7 Wheel balancing:  Static balance   Dynamic balance  (2) [32] TOTAL: 200 Copyright reserved Please turn over