Mechanical Technology Fitting & Machining (Eng) Memo

May-June 2019 — Grade 12 / Matric — Mechanical Technology

Memo 2019 Grade 12 English

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🎯 200 marks 📄 16 pages 📝 110 items found 📚 3 topics

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110

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Q1— Section header —

1.1(1\

1.2(1\

1.3(1\

1.4(1\

1.5(1\

1.6(1\ [6]6

Q2— Section header —

2.1Angle grinder: Do not use excessive force while grinding. Ensure that the sparks do not endanger co workers. Keep hands clear from grinding disc. Maintain a firm grip on the angle grinder. Grinding disc fitted will not turn faster than the manufactures

2.2Welding goggles: To protect your eyes from the spatter / sparks. To protect your eyes from the harmful rays / UV rays. To ensure proper vision of the process. (Any 2 x 1\ (2\

2.3Bench grinder: Overall Safety goggles / face shield Safety shoes (Any 2 x 1\ (2\

2.4Process and product workshop layout: The product layout ensures that the machines are arranged in the sequence of the manufacturing process of a product. The process layout is based on the type of manufacturing process

2.5

Q3— Section header —

3.1Tests to distinguish between metals: Bending test: hit with hammer. Filing test file material. (colour and ease\ Machining test machine material. (type of shaving, ease and colour\ Sound

3.2Heat treatment:

3.2.1Tempering: After hardening, the steel must be tempered. To relieve the strains induced. To reduce brittleness. (Any 1 x 2\ (2\

3.2.2Normalising: To relieve the internal stresses. (2\

3.2.3Hardening: To produce extremely hard steel. To enable it to resist wear and tear. (Any 1 x 2\ (2\ [14]14

Q4— Section header —

4.1(1\

4.2(1\

4.3(1\

4.4A or (1\

4.5(1\

4.6(1\

4.7(1\

4.8(1\

4.9(1\

4.10(1\

4.11(1\

4.12(1\

4.13(1\

4.14(1\ [14]14

Q5— Section header —

5.1Compression test:

5.1.1Wet test Dry test (2\

5.1.2Reasons for low compression: Worn cylinders Worn piston rings Worn piston Leaking inlet valve Leaking exhaust valve Leaking cylinder head gasket Cracked cylinder Cracked piston

5.2Static imbalance: A small mass or weight is applied to the wheel rim diametrically opposite the heavy spot until the wheel is in balance. (2\

5.3Cylinder leakage tester:

5.3.1Components of cylinder leakage tester: Spark plug adapter / connector Meter / gauge Flexible air hose Compressed air coupling Control valve / knob (5\

5.3.2Cylinder leakage test reasons: Loss in power. Low compression. To determine if the cylinder head gasket has blown. Oil consumption due to excessive leakage past the oil piston rings. identify leaking valves

5.4Reasons for a high CO reading: High idle speed Too rich mixture Ignition misfire Clogged air filter Improper operation of the fuel supply

5.5Wheel alignment gauge:

5.5.1Bubble gauge (1\

5.5.2

5.6Diagnostic scanner: The vehicle identification number (VIN\ The make and the model of the vehicle The engine type (Any 2 x 1\ (2\ [23]23

Q6— Section header —

6.1Balancing of engine

6.1.1Engine crankshaft: Static balance Dynamic balance (2\

6.1.2Methods to balance a crankshaft: Static balance: By fitting balance mass pieces to the crank webs by removing metal from the crank webs. Dynamic balance: Vibration is r educed by removing

6.1.3Factors that cause vibration: Mechanical unbalance caused by unbalanced moving parts Power unbalancing caused by uneven pressure on the piston and crankshaft The crankshaft and flywheel assembly is not statically

6.2Firing order factors: The position of the cranks on the crankshaft The arrangement of the cams on the camshaft The number of cylinders. (Any 2 x 1\ (2\

6.3Vibration damper: It is a mass fitted to the crankshaft on the opposite side of the flywheel to counteract the torsional vibration of the crankshaft. (2\

6.4Supercharger:

6.4.1Type of supercharger: Centrifugal type (1\

6.4.2Supercharger parts: Air inlet port Air outlet port Rotor (impeller Vane (fins (4\

6.5Advantages of engine with supercharge More power is developed compared to a similar engine without a supercharger An engine with a s upercharge

6.6Operation of the turbocharger: The exhaust gases from the engine are routed to the turbine wheel to enable the turbine wheel to spin at very high speed. The gases are then channel ed out of the housing and wheel assembly

6.7Turbo charger disadvantage against a super charger: Require lubrication. Suffers from lag. Tend to heat the air, reducing density. Needs to be controlled from over revving by the waste gate. Some turbochargers

6.8High altitude: At high altitude less oxygen is available for combustion and therefore the performance will be weaker than at sea level. (2\ [28] 1028

Q7— Section header —

7.1Compression Ratio Is the ratio between the total volume of a cylinder when the piston is at bottom dead centre to the volume of the charge in a cylinder when the piston is at top dead centre. (2\

7.2Compression ratio calculations:

7.2.1498,76 (8,4\ Volume Swept (3\

7.2.266,50 498,76 498,76 Ratio Compressio (3\

7.2.3New bore diameter 89,4 8,94 79,97 79,97 66,50 66,50 66,50 Ratio

7.3Power calculations

7.3.11250 radius Force Torque 1250 Force (3\

7.3.2cylinders strokes/se power 2400 11,31 0,12 0,14 1000 KPa

7.3.394,25 94247,78 Power Brake (3\

7.3.478,32 120,34 94,25 100% Efficiency Mechanical (3\ [32]32

Q8— Section header —

8.1

8.2Exhaust pressure test: Determine if the catalytic converter is blocked Determine if sil ncer is blocked Decrease in power output Lack of high speed power Poor fuel consumption Overheating

8.3Radiator cap test: Install the cap on the cooling system pressure tester Increase the pressure in the tester while watching the pressure gauge. The pressure cap should release air at a rated pressure stamped on

8.4Fuel pressure test manufacturers specifications Fuel pressure before fuel pump. Fuel pressure before the carburettor. Fuel pressure at idle speed. Fuel pressure high revolutions.

8.5Compression test:

8.5.1High tension lead: The ignition system will be disabled to prevent electrical shock. (2\

8.5.2Fuel injectors disconnected: To prevent unburned fuel entering the exhaust system and from entering the tester. To prevent fuel from entering the cylinders and causing oil dilution (Any 1 x 2\ (2\

8.5.3Throttle valve fully open: To obtain the correct amount of air entering the cylinder and to obtain a correct reading. (2\

8.5.4Recording the readings: The reading obtained during the compression test can be compared to the specification reading to check if the pressure is correct or not. (2\

8.6Wet test procedure Add oil to that cylinder which has a low reading. Carry out compression test as for dry test, if the reading increases it indicates that the piston rings are worn. [23] 1423

Q9— Section header —

9.1Methods of cooling the automatic transmission: By using a special oil cooler alongside the engine cooling radiator and circulating transmission fluid through it. Circulating transmission fluid through the bottom radiator tank.

9.2Advantages of automatic transmission: It reduces driving fatigue Greater reduction of wheel spin under bad road conditions. The vehicle can be stopped suddenly without the engine stalling. The system dampers all engine torsional vibrations.

9.3Purpose of automatic gearbox To relieve the driver of clutch and gear shift operation

9.4Gear ratio on torque: The higher the gear ratio the lower the torque transferred and the lower the gear ratio the higher the torque transferred.

9.5Advantages of torque converter: Torque increases automatically Smooth transfer of to que Minimum servicing is required To absorb shocks (Any 2 x 1\ (2\

9.6Automatic gearbox

9.6.1Brake (1\

9.6.2Brake band labels: Lever shaft Lever Strut Brake band Anchor Band adjuster (6\

9.6.3Brake bands function: To enable the annulus to come into a stationary position to change to another ratio. (1\ [18] 1518

Q10— Section header —

10.1Preliminary wheel alignment check Kerb mass against the manufacturers specifications Uneven wear on the tyres Tyre pressure Run out on the wheels Correct preload on the wheel bearings Kingpins and bushes

10.2out on turns: This toe out effect in a turn gives a true rolling motion to the front wheels in a corner without scuffing. (2\

10.3Dynamic balance of the wheel and tyre assembly: Dynamic balance of the wheel and tyre assembly refers to the equal distribution of all weights around the axis of rotation in all rotation parts. (1\

10.4Reasons of the speed control system: The speed control system is to control the throttle opening electronically. To keep the vehicle speed constant. (2\

10.5Disadvantages of the speed control: The system is expensive. High maintenance costs if the system becomes faulty. (2\

10.6Diode: The function of the diode is to permit current to flow in only one direction and to block it from flowing in the opposite direction. (2\ 16

10.7Advantages of an electric fuel pump: Immediate supply of fuel when the ignition switch is turned on. Low operation noise. Less discharge pulsation of fuel. Compact and light design. Prevents fuel leak and vapour lock.

10.8Aspects that an injector needs to fulfil: Precise fuel flow rate Good linearity Wide active range Good spray characteristics No leakage Silent operation Durability

10.9Ackerman principle:

10.9.1Ackerman angle steering principle / geometry (1\

10.9.2Parts Rear axis ongitudinal axis Steering arms Front wheels Extended centre lines from steering arms Intersection (6\

10.9.3If the centre lines of the steering arms are extended they will intersect on the longitudinal axis of the vehicle. (2\

10.10Alternator

10.10.1Rotor assembly (1\

10.10.2Parts slip ring brushes pole pieces (3\

10.10.3The function of the rotor assembly is to provide a rotating electro magnet to generate current (1\ [32 TOTAL:

Topics Identified

CircuitsMaterialsConstruction

Mark Allocation

Total200 marks

Sections6 + 10 + 14 + 14 + 23 + 28 + 32 + 23 + 18 = 168 marks

Paper information

SubjectMechanical Technology

Year2019

SessionMay-June

TypeMemo

PaperSee title

LanguageEnglish

Pages16

Downloads7

Examination context

Decade2010s

Years ago7y

Season—

Start day—

Exam period—

Days since exam—

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