MECHANICAL TECHNOLOGY
GRADE 12 
NSC PAST PAPERS AND MEMOS
SEPTEMBER 2017

MEMORANDUM 

QUESTION 1: MULTIPLE-CHOICE QUESTIONS 
1.1 A ✔ (1)
1.2 C ✔ (1)
1.3 B ✔ (1)
1.4 C ✔ (1)
1.5 D ✔ (1)
1.6 C ✔ (1)
1.7 A ✔ (1)
1.8 C ✔ (1)
1.9 B ✔ (1)
1.10 C ✔ (1)
1.11 A ✔ (1)
1.12 B ✔ (1)
1.13 D ✔ (1)
1.14 D ✔ (1)
1.15 A ✔ (1)
1.16 B ✔ (1)
1.17 C ✔ (1)
1.18 A ✔ (1)
1.19 D ✔ (1)
1.20 B ✔ (1)

[20] 

QUESTION 2: SAFETY 
2.1 Oil and grease are flammable and may cause a fire. ✔✔ (2) 
2.2

• Store full cylinders and empty ones separately. ✔ 
• Keep cylinders in a cool place. ✔ 
• Protect them from sunlight and other sources of heat. ✔ 
• Always store and use acetylene cylinders in an upright position. 
• Store oxygen and acetylene cylinders separately
• Never stack cylinders on top of one another. 
• Do not bang or work on cylinders. 
• Never allow cylinders to fall.
• Do not allow oil or grease to come into contact with oxygen fittings.
• Keep the caps on an oxygen cylinder for protection. (Any 3) (3) 

2.3

• An operator should be instructed to use a machine safely. ✔
• A workplace must be effectively partitioned off. ✔
• An operator must use protective equipment.
• Effective ventilation must be provided and maintained.
• Masks or hoods maintaining a supply of safe air for breathing must be  provided and used by the operators.
• The insulation of electrical leads must be satisfactory.
• The holder which contains the wire must be completely insulated. (Any 2) (2) 

2.4
2.4.1

• Make sure the centre or drill chuck is well secured before switching  on the machine. ✔
• Make sure the tail stock is well secured and locked when cutting  between centres. ✔ (Any 1) (1)

2.4.2

• Make sure the guard is well secured before switching on the  machine. ✔
• Machine guard must be in a good condition. ✔ (Any 1) (1) 

2.4.3

• Keep hands away from rotating chuck. ✔ 
• Don't leave the chuck key in the chuck. ✔
• Make sure the chuck is well secured before switching on the  machine. ✔
• Turn the chuck by hand to be certain that there is no danger of the  work piece striking any part of the lathe. ✔ (Any 1) (1) [10] 

QUESTION 3: TOOLS AND EQUIPMENT 
3.1

• Brinell hardness tester ✔
• Rockwell hardness tester ✔ 
• Vickers tester ✔ (Any 2) (2) 

3.2

• Check for worn cylinders ✔
• Check for worn piston rings ✔
• Check for worn pistons ✔
• Check for inlet valve leakage ✔
• Check for exhaust valve leakage ✔ (Any 3) (3) 

3.3 A tensile tester measures the resistance of a material to a static or slowly  applied tensile axial force. ✔✔ (2) 
3.4

• Rich mixture setting ✔
• Incorrect idle speed ✔
• Faulty choke creating a rich mixture (jammed in the closed position) ✔ (Any 2) (2) 

3.5

• Check if the measuring lead are inserted in the correct socket for the  measurement. ✔
• Turn the function switch to the desired function. ✔
• If you do not know what size of reading to expect, then switch to the  highest range first. ✔
• Connect the meter measuring lead probes to the correct points in the  circuit to be tested. (Any 3) (3) [12] 

QUESTION 4: MATERIALS 
4.1

• Low carbon steel ✔ 0,10 – 0,25% ✔✔
• Medium carbon steel ✔ 0,25 – 0,55% ✔✔
• High carbon steel ✔ 0,55 – 1,00% ✔✔ (9) 

4.2 The internal structural changes take place and it takes up an entirely new form  at a temperature of about 800 °C. ✔✔ (2) 
4.3 730° – 780 °C ✔✔ (2) [13]

QUESTION 5: TERMINOLOGY 
5.1

• Arbor cutters ✔ (1)
  e.g. plain, side, staggered-tooth, metal slitting saw and form cutters ✔✔ (Any 2 examples)(2)
• Shank cutters ✔ (1)
  e.g. end mills, T-slot, Woodruff key seat and fly cutter ✔✔ (Any 2 examples)(2) (6) 

5.2

• High abrasive resistance ✔
• Red hardness i.e. the hardness of the cutting edge must not be affected by  heat generated. ✔
• Edge toughness ✔ (Any 2) (2) 

5.3

• Turn the part to be threaded to the major diameter of the thread ✔ 
• Set compound slide 300 to the right and set tool up accurately in the tool  post. ✔ 
• Check index plate of the quick-change gearbox and move the levers for  the necessary pitch of the thread. ✔
• Start lathe and set cutting tool to touch work piece. Set dial to zero on  cross feed and compound slide. ✔ 
• Move the cutting tool a short distance off to clear the end of the work piece  and feed compound slide 0,05 mm inward. ✔
• With lathe turning, engage half-nuts in the correct line on the chasing dial,  putting the first cut in progress. ✔ 
• Withdraw the cutting tool quickly and disengage the half-nut lever return  the carriage to the starting point of thread and check with thread gauge to  see if thread pitch is correct. ✔ 
• Repeat with successive cut until thread is complete. (Max. 7 x 1) (7) 

5.4
5.4.1

• Form cutters ✔
• Profile cutters ✔ (Any 1) (1)

5.4.2

• Number of turns = 40  = 1  7
                                33✔     33✔
  1 Full turn and 7 holes in a 33 hole-circle ✔ (3) 

5.5 

1. Side and face milling cutters ✔
2. Spindle nose ✔
3. Vice fixed jaw ✔ 
4. Parallels ✔
5. Work piece ✔ 
6. Shoulder width ✔ 
7. Collars and spacers ✔
8. Vice movable jaw ✔ (8) 

5.6

1. Major/Crest diameter ✔ 
2. Pitch diameter ✔ 
3. Minor or Root diameter ✔ (3) [30]

QUESTION 6: JOINING METHODS 
6.1

1. Regulator ✔ 
2. Flow meter ✔ 
3. Continuous wire reel ✔ 
4. Wire feed roller unit ✔ 
5. Gun conduit ✔ 
6. Welding gun ✔ 
7. Weld pool ✔ 
8. Work piece ✔ 
9. Earth clamp ✔ (9) 

6.2 

1. Parent metal ✔ 
2. Molten pool ✔ 
3. Continuous electrode wire ✔ 
4. Nozzle ✔ 
5. Gas shroud ✔ (5) 

6.3 

• X-ray testing ✔ 
• Liquid dye penetrant ✔ 
• Ultrasonic testing ✔ (3) 

6.4

• Make a hacksaw cut at both edges through the centre of the weld. ✔
• Use a sledge hammer to break the specimen by striking it in the zone  where you made the saw cuts. ✔
• The weld metal exposed in the break should be completely free from slag  inclusions and contain no gas pockets greater than 1,6 mm. ✔ (4) 

6.5 To protect the weld area from oxygen and water vapour. ✔✔ (2) 
6.6

• Solid metals entrapped in the weld metal or between the weld metal and  the base metal. ✔
• Weld temperature is too low. ✔ 
• Included angle is too small. ✔ 
• Repeating a weld without removing the previous slag. ✔ 
• High viscosity of the molten metal. ✔ (Max. 2) (2) [25] 

QUESTION 7: FORCES 
7.1
7.1.1 A force is a push or a pull movement. ✔ (1)
7.1.2 It is a system in balance. ✔ (1)
7.1.3 It is a conversion of multiple forces into one. ✔ (1)
7.2
7.2.1

• • Stress = F 
                  A
    A  =     F     
           Stress
    πD² =    F     
     4       Stress
    D² =     F × 4   
             π × stress
    D = √ 4 × 40 × 10³
              π × 20 ×10⁶
    D = √2,546
    D = 0,05045 m 
    D = 50,45 mm ✔ Diameter of bar (6) 

7.2.2

• E = Stress 
         Strain
  Strain =  20 × 10⁶
                90 × 10⁹ ✔ 
  = 2,222 × 10⁻⁴ ✔ (2) 

7.2.3

• Strain = Change in lenght 
                 Original lenght✔ 
  Change in length = Strain × Original length ✔ 
  = 0,177 mm ✔ (3) 

7.3

• X-component = 280 N + 300 Cos 30° - 400 Cos 30° ✔✔ 
  = 193,39 N ✔ 
  • Y-component = 300 Sin 30° + 400 Sin 30° - 170 ✔✔ 
    = 150 + 200 + 170 
    = 180 N ✔ 
  • R² = X² + Y²
    = 193,39² + 180² ✔ 
    = √69799,69 
    R = 264,19 N - resultant ✔
• Calculation of the direction: 
  Tan Ɵ =   180    
                193,39 ✔ 
  = 0,931 
  = 42,95° ✔ (10) 

7.4

• Reaction at A:
  B × 6,2 = (496 × 3,1) + (350 × 7,9) ✔ 
  = 1537,6 + 2765 ✔ 
  B = 693,96 N ✔
• Reaction at B:
  (A × 6,2) + (350 × 1,7) = (800 × 6,2) + (496 × 3,1) ✔ 
  (A × 6,2) = 4960 + 1537,6 – 595 ✔ 
  A = 952,03 N ✔ 
  A + B = 693,96 + 952,03 = 1645,99
  Downwards = 800 + 496 + 350 = 1646
  The beam is in equilibrium (6) [30]

QUESTION 8: MAINTENANCE 
8.1

• It prevents the shavings or metal chips from sticking and fusing to the  cutting tool. ✔
• It will carry the heat generated by the turning process. ✔
• It flushes away shavings/metal chips. ✔ 
• It improves the quality of the finish of the turned surface. ✔ (Max. 3) (3) 

8.2

• Formation of gum, acids and lacquer may be left by the oil to coat the  surfaces. ✔
• Oil loses its viscosity after a while due to excessive heat transfer which  results in friction of lubricating efficiency. ✔ 
• Metal particles deposit in the oil due to metal and metal contact. ✔(Max. 3) (3) 

8.3
8.3.1 It is the lowest temperature at which the oil gives off vapours which  can ignite ✔✔ (2) 
8.3.2 It is the lowest point at which a liquid remains ‘pourable’ (meaning it  still behaves like a fluid) ✔✔ (2) 
8.4

• It must be water resistant, it must not mix ✔
• Rust/Corrosion resistant ✔
• Good for load pressure ✔ 
• High melting point ✔ 
• Low freezing point ✔ (Any 3) (3) 

8.5

• To provide friction between the clutch and pressure plate ✔ 
• To connect the flywheel to the gearbox shaft ✔ (2) [15] 

QUESTION 9: SYSTEMS AND CONTROL 
9.1
9.1.1 First calculate the volume of cylinder B. 

• V_B = area  × stroke lenght_B
  = π × D²_B   × L_B
        4
  = π × (0,18)²  × 0,012
              4
  = 0,305 × 10^-3 m³
  But V_A= V_B
  A_A × L_A = V_B
  A_A × 0,06 = 0,305 × 10^-3
  A_A = 0,305 × 10^-3
              0,06 ✔ 
  = 5,08 × 10⁻³ m² ✔ 
  AA = πD²_A
            4
  D²_A = 4 × 5,08 × 10^-3
                        π
  DA = √6,47 × 10^-3
  DA = 0,80m
  = 800 mm ✔ (9)

9.1.2

• Pressure at A = F_A
                            A_A 
  P_A    =    550       
           5,08 × 10⁻³ ✔ 
  = 108,268 × 10³ Pa 
  = 108,27 kPa ✔ (2) 

9.1.3 Note: Pressure at A is equal to pressure at B 

• P_A = P_B 
  P_B = F_B
          A_B
  F_B = 108,268 × 10³ × A_B ✔ 
  = 108,268 × 10³ × 25,45 × 10−³ ✔ 
  = 2755,42 N 
  F_B = 2,76 kN ✔ (4)

9.2
9.2.1 Compressive stress ✔ (1) 
9.2.2

• A = π(D² - d²)
                4
  = π(0,04²) - (0,03²)
                     4
  = 0,55 × 10^-3 m²
  stress = force 
               area
  =    23 × 10³  
     0,55 × 10³
  =  41818181,8 Pa ✔ 
  = 41,82 MPa ✔ (5) 

9.3
9.3.1 Rotation of motor 

• N_E =80 × 40 × 90
             30 × 20✔ 
  = 288000
         600 
  = 480 r/min ✔ (2) 

9.3.2

• No slip occurs ✔ 
• It is much stronger ✔ 
• More accurate ✔ 
• Last longer ✔ (Any 2) (2) [25]

QUESTION 10: TURBINES 
10.1

• The supercharger fills the cylinder with an increased pressure that is higher  than atmospheric pressure. ✔
• The compression pressure in the cylinder is increased. ✔
• The volumetric efficiency of the engine is increased. ✔ (Any 2) (2) 

10.2

• Used in racing cars ✔ 
• Four-stroke compression ignition engines in heavy vehicles ✔
• Earth moving equipment ✔ 
• Aircraft engine to overcome loss of power owing to height above sea  level ✔ (Any 2) (2) 

10.3

• A turbine is driven by the exhaust gas from a pump, most often an internal  combustion engine, to spin an impeller whose function is to force air into  the pump’s intake or air supply. ✔
• The shaped fins on the impeller move the air around to the outer edge of  the impeller into the housing. ✔
• In doing so, the moving fins leave a low pressure behind it. ✔ 
• Air, under atmospheric pressure, rushes in to fill the low pressure at the  centre of the impeller. ✔
• By spinning at a relatively high speed, the compressor turbine draws in a  large volume of air and forces it into the engine. ✔
• As the turbocharger’s output – flow volume exceeds the engine’s  volumetric flow, air pressure in the intake system begins to build. ✔ 
• The speed at which the assembly spins is proportional to the pressure of  the compressed air and total mass of air flow being moved. ✔ 
• Since a turbo will spin faster than is needed, the speed must be controlled  and thus it is also the property used to set the desired compression  pressure. ✔ (8) 

10.4

• Kinetic energy is the steam which is converted to mechanical energy to  cause rotation. (mechanical energy) ✔
• Steam at very high temperature and pressure is directed to the turbine. ✔ 
• Nozzles are used to direct the pressure onto the blades. ✔
• The blades are attached to the turbine and shaft causing it rotate. ✔
• This is mechanical energy created by the impulse and the reaction effort of  the steam jet. ✔ (5) 

10.5

• Water turbines ✔ 
• Gas turbines ✔ 
• Wind turbines ✔ (3) [20] 

TOTAL: 200