MECHANICAL TECHNOLOGY
GRADE 12
NSC PAST PAPERS AND MEMOS
FEBRUARY/MARCH 2018

MEMORANDUM

QUESTION 1: MULTIPLE-CHOICE QUESTIONS 
1.1 C ✔ (1)
1.2 C ✔ (1)
1.3 B ✔ (1)
1.4 D ✔ (1)
1.5 C ✔ (1)
1.6 D ✔ (1)
1.7 A ✔ (1)
1.8 A ✔ (1)
1.9 A ✔ (1)
1.10 B ✔ (1)
1.11 A ✔ (1)
1.12 C ✔ (1)
1.13 B ✔ (1)
1.14 A ✔ (1)
1.15 D ✔ (1)
1.16 A ✔ (1)
1.17 C ✔ (1)
1.18 A ✔ (1)
1.19 B ✔ (1) 
1.20 A ✔ (1) [20]

QUESTION 2: SAFETY 
2.1 Spring tester 

• Use correct attachments of the valve spring tester to compress   the spring. ✔
• Do not exceed the prescribed pressure. ✔
• Ensure that the spring does not slip out. ✔
  (ANY 2 x 1) (2) 

2.2 Welding helmet 

• To protect your eyes against the dangerous ultra-violet rays. ✔
• To protect your skin against the dangerous ultra-violet rays. ✔
• To protect your eyes against the sparks. ✔
• To protect your skin against the sparks. ✔
  (ANY 1 x 1) (1) 

2.3 Spot welding  

• To prevent the electrodes from overheating. ✔ (1)

2.4 Testers  
2.4.1 Brinell tester 

• The tester must be mounted on the rigid spot on a workbench ✔
• The force must be applied at an angle of 90° to the test piece  ✔
• Do not exceed the prescribed load ✔
• Make sure the test piece is placed securely into position ✔ 
  (ANY 1 x 1) (1) 

2.4.2 Tensile tester 

• Make sure all safety guards are in place ✔
• Do not exceed the prescribed load ✔
• See that the test piece is securely placed in position ✔
• Make sure the dial indicator is mounted properly ✔
  (ANY 1 x 1) (1) 

2.4.3 Torsion tester 

• Fasten the tester to the workbench ✔
• When you add pieces of different mass, you should attach  them very gently otherwise you could get a skew reading of  the torsion on the rod ✔
• Get specification (torsion) of the different materials and of the  size rods you would like test ✔
  (ANY 1 x 1) (1) 

2.5 Bearing puller 

• Perpendicular or 90° to the bearing. ✔ (1)

2.6 Cylinder leakage tester 
2.6.1

• To prevent damage to the seals and tester ✔
• To ensure the correct reading ✔
  (ANY 1 x 1) (1) 

2.6.2

• To prevent damage to the tester and spark plug hole or  injector hole ✔
• To ensure the correct reading ✔
  (ANY 1 x 1) (1) [10]

QUESTION 3: TOOLS AND EQUIPMENT 
3.1 Testers 
3.1.1 Cylinder leakage tester 

• Is used to determine a leakage in the cylinder✔.
• Determine the volume of leakage✔ (2) 

3.1.2 Fuel pressure tester 

• Is used to test the fuel operating pressure in the system ✔
• Is used to test the fuel pressure in the fuel line that runs to  the direct injection. ✔ (2) 

3.1.3 Torsion tester 

• Is used to investigate the relationship between momentum or  torque applied to material ✔
• Is used to investigate influence of material length on torsional  deflection. ✔ (2) 

3.2 Reasons for high CO2 reading 

• Lean fuel mixture setting ✔
• Low compression ✔
• Faulty high tension leads ✔
  (ANY 2 x 1) (2) 

3.3 MIGS/MAGS-welding 
3.3.1 Reasons for using inert gas during MIGS/MAGS welding 

• Stabilises the arc on the parent metal ✔
• Shields the arc and weld pool from atmospheric gases like  oxygen ✔ (2) 

3.3.2 Advantages of MIGS/MAGS welding 

• Can weld in any position ✔
• Less operator skill required ✔
• Continuous welding can be done ✔
• Causes less deformation ✔
• Faster than arc welding ✔
• Minimal post weld cleaning ✔
• No slag removal is required ✔ 
  (ANY 2 x 1) (2) [12]

QUESTION 4: MATERIALS  
4.1 Characteristics of structures 
4.1.1 Austenite  

• Soft ✔
• Coarse grain structure ✔
• Non-magnetic ✔
  (ANY 2 x 1) (2) 

4.1.2 Ferrite  

• Soft ✔
• Ductile ✔
• Magnetic ✔
  (ANY 2 x 1) (2) 

4.2 Iron-carbon equilibrium diagram  
4.2.1 Lower critical point (AC1) of steel 

• The structure starts to change ✔✔ (2)  

4.2.2 Higher critical point (AC3) of steel 

• The structure turns into complete Austenite ✔✔
• The steel completely loses its magnetic properties ✔✔ 
• The structure turns into its finest grain size ✔✔
  (ANY 1 x 2) (2)  

4.3 Reasons to enhance properties of a crankshaft 

• To produce a hard face with a tough core. ✔
• To induce toughness ✔ (2) 

4.4 Reasons for the tempering of a camshaft 

• To increase the lifespan of the camshaft ✔
• To eliminate brittleness caused by hardening. ✔
  (ANY 2 x 1) (2) 

4.5 Heat treatment process on piston rings 

• Hardening ✔ (1) [13] 

QUESTION 5: TERMONOLOGY
5.1 Key dimensions  
5.1.1 The width of the key 

• Width  = D
                 4
  = 120      ✔ 
       4 
  = 30 mm ✔ (2) 

5.1.2 The thickness of the key 

• Thickness  = D
                       6
  = 120      ✔ 
       6 
  = 20 mm ✔ (2) 

5.1.3 The length of the key

• Length = D × 15  ✔
  = 120 ×  15 ✔
  = 180 mm (2) 

5.2 Indexing 

•  Indexing = 40 
                     n
  =  40   ÷ 2        ✔ 
     124     2
  =   20           ✔ 
       62
  No full turns and 20 holes in a 62 hole circle (3) 

5.3 Height of screw the screw thread 

• H = 0 866
  = 3  × 0 866  ✔
  = 2 6  mm ✔ (2) 

5.4 Gear terminology 
5.4.1 Addendum = m 

• = 3 mm ✔ (1) 

5.4.2 Dedendum

• = 1,157 m                        or                       =1,25 m 
  = 1,157 x 3 ✔                                             =1,25 x 3 ✔ 
  = 3,47 mm ✔                                              =3,75 mm ✔ (2) 

5.4.3 Clearance

• = 0,157 m                        or                         =0,25m 
  = 0,157 x 3 ✔                                              =0,25 x 3 ✔
  = 0,47 mm ✔                                              =0,75 mm ✔ (2) 

5.4.4 

•  Module  =   PCD 
                        T
  PCD = m ×  T ✔
  = 3 ×  48   ✔
  = 144 mm ✔(2) 

5.4.5

• OD = PCD + 2m ✔ 
  = 144 + 2(3) 
   = 144 + 6 
   = 150 mm ✔ (2) 

5.4.6 Cutting depth

• = 2,157 m ✔                     or                     =2,25m ✔ 
  = 2,157 x 3                                                =2,25 x 3 
   = 6,47 mm ✔                                             =6,75 mm ✔ (2) 

5.4.7 Circular pitch

• = m x π✔
  = 3 x π
   = 9,42 mm ✔ (2) 

5.5 Setting of the lathe and cutting tool to cut a metric V-screw thread:

• Set the lathe to the correct speed for screw cutting ✔
• Set the lead screw according to the required pitch ✔
• Set the dial gauge to position with the required worm gear ✔
• Set the compound slide to half the included angle of the thread (30°) ✔
• Set the cutting tool centre height and 90° to the work piece with the  help of a centre gauge ✔
• Set cross slide and compound slide collars to zero with the tool  touching the work piece ✔ (6) [30] 

QUESTION 6: JOINING METHODS  
6.1 Welding defects 
6.1.1 Slag inclusion 

• Welding speed too fast ✔
• Not removing the slag from the previous weld run before  welding the next run ✔
• Current too low ✔ 
   (ANY 2 x 1) (2) 

6.1.2 Incomplete penetrations 

• Welding speed too fast ✔
• Faulty joint design ✔
• Electrode too large ✔
• Current too low ✔ 
   (ANY 2 x 1) (2) 

6.2 Atmospheric contamination during MIGS/MAGS welding 

• Inadequate shielding gas flow ✔
• Excessive shielding gas flow ✔
• Severely clogged nozzle ✔
• Damaged gas supply system ✔
• Excessive wind in the welding area ✔ 
  (ANY 2 x 1) (2)  

6.3 Nick break test 

• Make a hacksaw cut at both edges, through the centre of the weld ✔ 
• Place the saw-nicked specimen on two steel supports ✔
• Use a sledge hammer to break the specimen by striking it in the zone  where you made the saw cuts ✔
• Defects like incomplete fusion, slag inclusion and brittleness will be  exposed in the break ✔
• Any defects bring it to the attention to the welder to rectify it ✔ (5)

6.4 Reasons for destructive tests 
6.4.1 Bend test 

• To determine the ductility/elongation ✔✔ of the weld metal. (2)  

6.4.2 Machinability test 

• To determine the welds hardness ✔ and its strength. ✔ (2)  

6.5 X-ray test 

• To detect internal defects in the weld metal✔✔ (2)

6.6 Weld crater 

• Forms where welding is resumed at the bottom of the previous weld instead  of on the top ✔✔ (2) 

6.7 MIGS/MAGS welding 
6.7.1 Welding process 

• MIGS/MAGS welding ✔ (1)  

6.7.2 Labelling 

• A. Parent metal ✔
• B. Arc ✔
• C. Electrode wire ✔
• D. Gas shroud ✔
• E. Shielding gas ✔ (5)  [25]

QUESTION 7: FORCES 
7.1 Resultant 

• ∑HC = 200 +  210cos60 - 190cos 40º  ✔
  = 200 + 105 - 145.55  ✔ ✔  ✔
  = 159,45  N   ✔ (4)
• ∑VC = 210sin 60º + 190sin 40º - 185 
  = 181,87 + 122,13 - 185 ✔✔
  = 119 N ✔ (3) 

OR  

2 2 2 

• E² =  HC² + VC²
  E = √ 159,45² + 119²
  E = 198,96 N  ✔ ✔ 
   (3) 
  Tan θ = VC✔ 
               HC
  =     119               
    159,45N
  = 36,74º E 
  E = 198,96N 36,73º south of west  ✔ 
  OR 
  = 36º 44' minutes south of west ✔  (3) 

7.2 Stress and Strain  
7.2.1 Resistance area 

• A = π (D² -  d²)
                   4
  = π (0,056² -  0,038²)  ✔ 
                   4 
  = 1,33 × 10^-3m²   ✔ (2) 

7.2.2 Stress 

• Stress  =  force
                  area 
  stress =   20 × 10³   
                1,33 × 10^-3
  =15037593,98  Pa
  Stress= 15,04MPa ✔(3) 

7.2.3 Strain 

• Strain  = Δl    ✔
                OL 
  Strain = 50 - 49,975 
                     50
  Strain = 0,025
                 50
  = 0,5 ×  10^-3  ✔ (3) 

7.2.4 Young’s Modulus of Elasticity 

•  Youngs Modulus of Elasticity = Stress   ✔ 
                                                     Strain 
  E = 15,04 × 10⁶ 
             0,5 10^-3 
  = 30,08 × 10⁹  Pa
  = 30,08 GPa ✔ (3) 

7.3 Moments  
7.3 
Calculate B. Moments about A: 

• ∑LHM =∑ RHM 
  ( B × 6) = (300 × 1,5) + (850  × 3) ✔
  6B = 3000    ✔ 
  6           6     
  B = 500N  ✔

Calculate A. Moments about B: 

• ∑RHM =∑LHM 
  (A ×  6) =(850 ×  3) +(300 ×  4,5) + (600 ×  6)
  6A = 2550 + 1350 + 3600
  6A = 7500    ✔ 
  6           6     
  B = 1250N  ✔(6) [30] 

QUESTION 8: MAINTENANCE  
8.1 Reason using SAE 20W50 

• This to ensure that the oil is able to satisfy the operational ✔ requirements  over a range of temperature ✔ from start-up to running hot. (2) 

8.2 Maintain V-belt drive systems 

• Check the contact surfaces of the pulley to prevent the belt from being  damaged.✔
• Check the belt condition and replace if it is worn.✔
• Correct installation procedure must be followed. ✔
• Belt drives should be well guarded to prevent foreign objects to come  into contact with the belts and pulleys.✔
• Keep guard mesh free of papers, rags, etc. that can cause insufficient  air flow. ✔
• Check that the belt deflection is according to specification. ✔
• Store replacement belts in a cool, well ventilated place. ✔
• Correct alignment of pulleys. ✔
  (ANY 2 x 1) (2) 

8.3 Flash point 

• It is the lowest temperature ✔ at which the oil gives off vapours ✔ which can  ignite. ✔ (3) 

8.4 Maintaining cutting fluid  

• Avoid contamination of the cutting fluid by draining and regularly  replacing it. ✔
• Always clean the machine's splash tray of metal cutting after use. ✔
• Regularly wipe cutting fluid splashes of machine parts. ✔
• Ensure that the sump is topped up from time to time and check that  there is sufficient flow of cutting fluid to the cutting tool. ✔
  (ANY 2 x 1) (2) 

8.5 Functions of the clutch plate 

• It provides friction between the flywheel and pressure plate. ✔
• It serves as a link between the clutch and the gearbox main shaft. ✔ (2) 

8.6 Reasons for skimming the flywheel 

• To remove the grooves caused by the clutch plate. ✔
• To ensure a full contact surface between the flywheel and the clutch  plate. ✔
• To prolong the life of the clutch plate. ✔
  (ANY 2 x 1) (2)

8.7 Properties of grease 

• It must be water resistant, it must not mix with water ✔
• Prevents rust/corrosion ✔
• Good for load pressures ✔
• High melting point ✔
• Low freezing point ✔
• Prevent gumming ✔
• Be able to lubricate ✔
• High viscosity ✔
  (ANY 2 x 1) (2) [15]

QUESTION 9: SYSTEMS AND CONTROL
9.1 Gear drives  
9.1.1 Rotation frequency of input shaft 

• N_A = T_B × T_D × T_F
  N_F    T_A × T_C × T_E
  N_A = T_B × T_D × T_F × N_F
                T_A × T_C × T_E
  = 30 × 46 × 80 × 160
           20 × 18 × 42
  = 1401,90r/min  (3) 

9.1.2 Velocity ratio 

• VR=  N_A
           N_F
  VR= 1401,90
             160
  = 8,76: 1  ✔ (2) 

9.2 Belt drives 
9.2.1 Rotation frequency of driver pulley

• N_DR × D_DR = N_DN × D_DN
  N_DR  = N_DN  × D_ND
                   D_DR
  = 733,33 × 0,36
               0,24
  = 200r/min  (3) 

9.2.2 Power transmitted 

• P = (T₁ - T₂)πDn
                  60
  P=  (360 - 90)π × 0,36 ×  733,33
                            60
  = 3732,20 Watts
  =3,73 kW   (2) 

9.2.3 Belt speed 

•  Belt speed = πDN
                          60
  =  π ×  0,36 ×  733,33
                  60
  = 13,83m.s^-1 ✔  (2) 

9.3 Hydraulics 
9.3.1 Fluid pressure 

• A_B = πD²
              4
  =   π0,04²
            4
  = 1,26 × 10^-3m²
• P_B =   F    
           A_B    
  =      275          
     1,26 × 10^-3
  =  218253,97  pa
  or
  = 218,25  kPa     (5) 

9.3.2 Diameter of piston B 

• P_B =P_A
  P_B = F_B 
            A_B
  A_B = F_B
           P_B
  A_B = 5,56  × 10³   
        218,25 × 10³
  A_B = 25,48 × 10^-3m²
  A_B = πD²
            4
  D_B = √A_B × 4
                 π
  = √25,48 × 10^-3 × 4
                   π
  =0,18 m 
  or
  =180 mm  (4) 

9.4 ABS 

• ABS prevents wheels from skidding ✔ when breaking hard ✔ in difficult  conditions. (2) 

9.5 ECU 

• Electronic Control Unit ✔ (1) 

9.6 Traction Control 

• Prevent wheels from spinning. ✔
• Improves road holding ✔
  (ANY 1 x 1) (1) [25]

QUESTION 10: TURBINES 
10.1 Reaction turbines 

• Francis ✔ 
• Kaplan ✔ 
• Tyson ✔ 
  Gorlov ✔  (ANY 2 x 1) (2) 

10.2 Supercharger boost 

• Boost refers to the increase in intake manifold pressure ✔  that exceeds  normal atmospheric pressure✔  (2) 

10.3 Blowers 

• Roots ✔ 
• Centrifugal ✔ 
• Vane-type ✔ 
• Twin screw type ✔ 
  (ANY 2 x 1) (2) 

10.4 Gas turbine 

• A = Clean air inlet ✔
• B = Compression ✔
• C = Combustion ✔
• D = Exhaust ✔
• E = Turbine ✔
• F = Combustion chamber ✔ (6) 

10.5 Application of a gas turbine 

• Jet engines ✔
• Naval ships ✔ 
• Hi-performance vehicles and boats ✔ 
• Generating electricity ✔
  (ANY 2 x 1) (2) 

10.6 Advantages of a gas turbine 

• Less complex than internal combustion piston engines ✔
• Only one moving part (Common shaft for: compressor and turbine) ✔ 
• Operate at higher revolutions per minute ✔ (ANY 2 x 1) (2) 

10.7 Waste gate 

• A waste gate is a valve that diverts exhaust gases away from the turbine  wheel ✔  to regulate the turbine/compressor speed and boost.✔  (2) 

10.8 Oil cooler 

• To cool the oil ✔  that lubricates the turbocharger bearings and shaft. ✔  (2) [20] 

TOTAL: 200