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 =
                    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. 

  • VB = area  × stroke lenghtB
    π × D2B   × LB
          4
    π × (0,18)2  × 0,012
                4
    = 0,305 × 10-3 m3
    But VA= VB
    A× LA = VB
    AA × 0,06 = 0,305 × 10-3
    AA0,305 × 10-3
                0,06 ✔ 
    = 5,08 × 10−3 m2 ✔ 
    AA = πD2A
              4
    D2A = 4 × 5,08 × 10-3
                          π
    DA = √6,47 × 10-3
    DA = 0,80m
    = 800 mm ✔ (9)

9.1.2

  • Pressure at A = FA
                              A
    P   =    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 

  • PA = PB 
    PB = FB
            AB
    FB = 108,268 × 103 × AB ✔ 
    = 108,268 × 103 × 25,45 × 10−3 ✔ 
    = 2755,42 N 
    FB = 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 

  • NE =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

Last modified on Friday, 23 July 2021 12:26