Mechanical Technology Grade 12 NSC June 2022 Memo (English)

Downloaded from hlayiso.com SENIOR CERTIFICATE EXAMINATIONS/ NATIONAL SENIOR CERTIFICATE EXAMINATIONS MECHANICAL TECHNOLOGY: AUTOMOTIVE 2022 MARKING GUIDELINES MARKS: 200 These marking guidelines consist of 16 pages. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 2 DBE/2022 SC/NSC – Marking Guidelines QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC) 1.1 A (1) 1.2 B (1) 1.3 C (1) 1.4 D (1) 1.5 A (1) 1.6 C (1) [6] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 3 DBE/2022 SC/NSC – Marking Guidelines QUESTION 2: SAFETY (GENERIC) 2.1 Rated speed of a grinding wheel:  Because the wheel could burst/break if it turns faster than its revolution range. / Avoid an accident.   Effectiveness of the grinding process will be compromised.  (Any 1 x 1) (1) 2.2 Safety precautions of a band saw in operation:  Never leave the band saw unattended.   Use a push stick when cutting.   Hold the work piece firmly and flat on the table.   Don’t adjust the machine while working.   Don’t open any guard while the machine is on.   Make relief cuts before cutting tight curves.   Don’t force the material into the blade.   Keep hands clear from the action point.   Keep hands braced against the table.   Keep your hands on either sides of the blade and not in line with the cutting line and the blade.   Keep loose clothing clear from action point.  (Any 2 x 1) (2) 2.3 Stages in which first aid is applied:  Examination   Diagnosis   Treatment  (3) 2.4 Causes of accidents:  Unsafe acts   Unsafe conditions  (2) 2.5 TWO advantages of the product layout:  Handling of material is kept to a minimum.   Time period of manufacturing cycle is less.   Production control is almost automatic.   Control over operations is easier.   Greater use of unskilled labour is possible.   Less total inspection is required.   Less total floor space is needed per unit of production.  (Any 2 x 1) (2) [10] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 4 DBE/2022 SC/NSC – Marking Guidelines QUESTION 3: MATERIALS (GENERIC) 3.1 Tempering: Tempering is a process generally applied to steel to relieve the strains/brittleness/improve ductility  induced during the hardening process.  (2) 3.2 Annealing:  To relieve internal stresses  that may have been set up during working of metal.  To soften steel  in order to facilitate the machining process.  To refine their grain structure.   Reduce brittleness.   Make the steel ductile.  (Any 3 x 1) (3) 3.3 Normalising temperature:  Above  higher/upper critical temperature   Above  AC3 line.  (Any 1 x 2) (2) 3.4 Spark pattern for carbon steels: 3.4.1 High-carbon steel  (1) 3.4.2 Low-carbon steel / Mild steel  (1) 3.4.3 Cast-iron  (1) 3.5 Carbon diagram: A. Temperature range / °C  B. AC3 line / Higher/upper critical temperature line  C. AC1 line / Lower critical temperature line  D. Carbon content / % carbon  (4) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 5 DBE/2022 SC/NSC – Marking Guidelines QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC) 4.1 C (1) 4.2 B (1) 4.3 B (1) 4.4 D (1) 4.5 A (1) 4.6 C (1) 4.7 B (1) 4.8 A/C (1) 4.9 C (1) 4.10 B (1) 4.11 C (1) 4.12 A (1) 4.13 B (1) 4.14 D (1) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 6 DBE/2022 SC/NSC – Marking Guidelines QUESTION 5: TOOLS AND EQUIPMENT (SPECIFIC) 5.1 Wet compression test:  Pour/squirt some oil onto the piston through the spark plug hole.   Do the compression test.   Compare the readings to the dry compression test reading.  (3) 5.2 Functions: 5.2.1 Compression Test: Indicates  the compression pressure  created by piston in the cylinder. (2) 5.2.2 Cylinder Leakage Test:  Indicates the %  compressed air leakage from the cylinder.   Indicates the location  of the leakage from the cylinder.  (Any 1 x 2) (2) 5.3 Gas analyser:  Inlet hose not to be stepped on.   Hose connection must be airtight, and valve closed.   No exhaust leaks.   Condensate must be blown out of the hose and pick-up probe.   Condenser must be drained after each test.   Filter on the condenser stand must be changed regularly.   Ensure test is done in a well-ventilated area.   On a 12v analyser, the battery clamps must be cleaned.   Make sure gas analyser is placed on a safe place.  (Any 4 x 1) (4) 5.4 Optical alignment gauges:  Centre the steering on your car.   Put each half of the tracking gauge against each of the front wheels.   Look through the periscope and you should see / identify the alignment mark.   Look through the periscope and align the vertical line with the triangle by moving the pointer arm.   Read off the toe-in or toe-out.  (5) 5.5 OBD-II scanner:  Plug the diagnostic tool into the OBD-II port.   Enter the vehicle's details into the scanner.   Turn on the vehicle’s ignition.   Start the diagnostic scan.   Interpret the trouble codes and make a diagnosis.  (5) 5.6 Wheel balance methods:  Dynamic balance   Static balance  (2) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 7 DBE/2022 SC/NSC – Marking Guidelines QUESTION 6: ENGINES (SPECIFIC) 6.1 Components driven by the crankshaft:  Flywheel   Camshaft   Supercharger   Connecting rod/Pistons   Oil pump   Water pump   Power steering pump   Air conditioning pump   Radiator fan   Distributor   Alternator   Transmission/gearbox  (Any 4 x 1) (4) 6.2 Combustion engines: 6.2.1 Rotating mass: The crank pin, big-end  and the lower two-thirds of the connecting rod.  (2) 6.2.2 Reciprocating mass: The pistons, gudgeon pins  and the upper third of the connecting rod.  (2) 6.3 Advantages of a six-cylinder V-engine over a six-cylinder straight engine:  Can be mounted in smaller engine compartments.   Improved power to weight ratio.   More compact engine.  (Any 2 x 1) (2) 6.4 Turbocharger: 6.4.1 Turbocharger parts: A – Compressor/Compressor housing/casing  B – Exhaust gas out/discharge  C – Turbine wheel/blades  D – Exhaust gas in  E – Compressed air out/discharge  (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 8 DBE/2022 SC/NSC – Marking Guidelines 6.4.2 Operation of the vanes in a variable geometry turbocharger at low speed:  At low-speed range the variable nozzle vanes are almost closed.   The vanes create a narrow path to the exhaust turbine blades.   The angle of the vanes, directs the gases to hit the blades at the correct angle   This causes the turbocharger to spin faster.  (4) 6.5 Types of superchargers:  Roots   Twin-screw   Centrifugal   Eccentric / sliding-vane  (4) 6.6 Disadvantages of superchargers compared to turbochargers:  Superchargers are less effective at increasing engine power at high revolutions.   Superchargers use engine power to drive it (parasitic).   Higher fuel consumption if generated power is not fully used.   More space required to mount the Roots supercharger.   Roots and twin-screw superchargers deliver air in bursts.   It is more expensive than a turbocharger.  (Any 3 x 1) (3) 6.7 Difference between twin-turbocharging and twin-charging: Twin-turbocharging uses two turbochargers  while twin-charging uses a combination of a turbocharger and a supercharger.  (2) [28] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 9 DBE/2022 SC/NSC – Marking Guidelines QUESTION 7: FORCES (SPECIFIC) 7.1 Definitions: 7.1.1 Work: Work is done when a force  overcomes resistance and causes movement.  (2) 7.1.2 Clearance volume: This is the volume above the crown of the piston,  when the piston is at TDC / combustion chamber.  (2) 7.2 The mean effective pressure represented: 7.2.1 Indicator diagram / Pressure-volume diagram  (1) 7.2.2 kPa/Pa or kN/m2 /Nm2  (1) 7.3 Calculations: 7.3.1 Swept Volume:  D2 SV  xL 4  x 7 2  65  x  4 10  250,15 cm 3  (3) 7.3.2 Original clearance volume: SV CV  CR  1 250,15   9 1   31,27cm3  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 10 DBE/2022 SC/NSC – Marking Guidelines 7.3.3 Stroke length: SV = CV ( CR - 1)   31, 27(10  1)   281, 42 cm 3   D2 SV  xL 4 SV x 4 L   x D2 281,42 x 4    x 7, 2 2  6,912 cm   69,12 mm  (7) 7.4 Calculations: 7.4.1 Indicated power: 10 L 100  0, 1 m  π D2 Area  4 π x 0,08 2   4  5,03 x 10 3 m2  2 500 N  60 x 2  20,83 firing strokes/sec  IP  PLANn     IP  1250  103  0,1  5,03  103  20,83  4   52387,45 W IP  52 , 39 kW  (7) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 11 DBE/2022 SC/NSC – Marking Guidelines 7.4.2 Torque: BP  2π NT 2500 N 60  41, 67 r/s  BP  T 2π N (46,08 x 103 )   2 x π x 41,67  176 Nm  (4) 7.4.3 Mechanical efficiency: BP Mechanical efficiency  x 100 IP 46,08  x 100  52, 39  87,96 %  (2) [32] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 12 DBE/2022 SC/NSC – Marking Guidelines QUESTION 8: MAINTENANCE (SPECIFIC) 8.1 Lean fuel mixture:  High oxygen (O2)   Low Carbon dioxide (CO2)   High Nitrogen oxide (NOx)  (3) 8.2 High hydrocarbon (HC) exhaust gas reading:  Incomplete combustion   Improper valve timing   Improper ignition timing   Faulty air management system   Blocked or restricted air-filter   Faulty temperature sensor   Faulty oxygen sensor   Excessive fuel pressure   Non-functioning PCV valve   Faulty catalytic convertor  (Any 3 x 1) (3) 8.3 Compression test: Causes Corrective Measures  Blown cylinder head gasket   Replace with new gasket   Cracked cylinder head   Replace/repair cylinder head  (4) 8.4 Bubbles in the radiator water:  Blown cylinder head gasket   Cracked cylinder head  (2) 8.5 Oil pressure test:  Oil pressure at idling speed.   Oil pressure at high revolutions.   Oil pressure when engine is cold.   Oil pressure when engine is hot.  (Any 3 x 1) (3) 8.6 Precautions while setting up the fuel tester:  Ensure that you wear the correct PPE e.g. safety goggles.   Ensure that the tester can read the fuel pressure of the engine.   Ensure that the place where you will couple the tester is clean before you remove the sender unit.   Ensure the rubber pipe on the tester is not perished.   Put the tester at a place on the engine that is safe from the running engine.   Ensure that there are no flammable materials in proximity.   Ensure that there is a fire-extinguisher.  (Any 4 x 1) (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 13 DBE/2022 SC/NSC – Marking Guidelines 8.7 Radiator pressure drop:  Repair leaks between components / gasket leaks.   Repair leaking hoses.   Tighten loose hose clamps.   Repair or replace leaking water pump.   Repair or replace corroded pipes.   Replace blown head gasket.   Repair or replace leaking radiator.   Repair or replace leaking cabin heater radiator.   Renew the heater tap.   Renew the welch or core plugs.  (Any 4 x 1) (4) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 14 DBE/2022 SC/NSC – Marking Guidelines QUESTION 9: SYSTEMS AND CONTROL (AUTOMATIC GEARBOX) (SPECIFIC) 9.1 Lock-up torque converter: 9.1.1 Function of the lock-up clutch:  The lock-up clutch improves efficiency   Prevents slip  (2) 9.1.2 Functions of a stator:  Redirects oil back to the impeller.   Increases the engine torque.  (2) 9.1.3 Lock-up clutch is engaged:  The oil pressure in the torque converter increases with engine speed.   The pressurised oil is channelled to the lock-up clutch piston.   The lock-up clutch piston pushes the friction plate against the clutch friction surface attached to the housing.   Since the friction plate is splined to the impeller, it connects the impeller and turbine.   The turbine and impeller begin to turn as one.  (5) 9.2 Automatic gearbox: 9.2.1 Double epicyclic gear train.  (1) 9.2.2  Three forward   One reverse  (2) 9.3 Cooling the hydraulic transmission fluid in an automatic transmission:  The hydraulic transmission fluid is circulated through an oil cooler at the radiator. /Oil is cooled by circulating through the bottom tank of the radiator.   The airflow over the transmission sump allow for cooling of the oil.  (2) 9.4 Differences between the construction of a manual transmission and automatic transmission: Manual Automatic  Less complex design.   More complex design.   Different gear sets used to  Same gear sets used to obtain obtain different gear ratios.  different gear ratios.   Cluster and simple gear trains  Epicyclic-gear trains used.  used.   Dry clutch used when changing  Wet clutch used to engage gears.  gears.  (Any 2 x 2) (4) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 15 DBE/2022 SC/NSC – Marking Guidelines QUESTION 10: SYSTEMS AND CONTROL (AXLES, STEERING GEOMETRY AND ELECTRONIC) (SPECIFIC) 10.1 Pre-checks on vehicle suspension before wheel alignment:  Correct preload on the wheel (hub) bearings   Kingpins and bushes   Suspension ball joints for wear, locking and lifting   Suspension bushes for excessive free movement   Steering box play and whether secure on chassis   Tie-rod ends   Sagged springs, which includes riding height   Ineffective shock absorbers   Spring U-bolts   Chassis for possible cracks and loose cross-members  (Any 3 x 1) (3) 10.2 Toe out on turns: Outer wheel  Inner wheel  Outer  steering  20° angle  Inner  23° steering angle NOTE: Steering angles should be different. If degrees indicated are the same, candidate loses the TWO marks. Angles sizes shown are just an example. (6) 10.3 Faults toe-out on turns:  Wear on the suspension parts   Wheel bearing wear   Steering system wear  (Any 2 x 1) (2) 10.4 Static balancing:  Mount the wheel so that it is free to spin on a spindle.   Spin the wheel slowly.   If the wheel is out of balance, it will always come to rest at the same point,  the ‘heavy spot’, at the bottom.  To correct static imbalance, a small weight is fitted to the wheel rim by trial and error, opposite the ‘heavy spot’.   Repeat until the wheel stops at random positions.  (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Automotive 16 DBE/2022 SC/NSC – Marking Guidelines 10.5 Electronic Control Unit (ECU) functions: 10.5.1 Air-induction system: The air-induction system measures  and controls  the air required for the combustion. (2) 10.5.2 Ignition system: The purpose of the ignition system is to ignite  the air/fuel mixture in the combustion chamber at the correct time.  (2) 10.6 Catalytic convertor gases:  Hydrocarbons (HC)   Carbon monoxide (CO)   Nitrogen oxide (NOx)  (Any 2 x 1) (2) 10.7 Labels common rail direct injection (CRDI) system: A. Common rail  B. High pressure pump / pump / diesel pump  C. Diesel/fuel filter  D. Injectors  (4) 10.8 Function of the pressure regulator:  It keeps the pressure  in the common rail at a specified pressure.   It relieves excessive pressure  in the common rail.  (Any 1 x 2) (2) 10.9 The alternator: 10.9.1 Component: A. Rotor  B. Capacitor  (2) 10.9.2 Winding connection: Star / Y  connected stator windings (1) 10.9.3 Diodes: Six (6)  (1) [32] TOTAL: 200 Copyright reserved