MECHANICAL TECHNOLOGY
GRADE 12
MEMORANDUM
NOVEMBER 2017
NATIONAL SENIOR CERTIFICATE

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

QUESTION 2: SAFETY
2.1 Surface grinder:

• Make sure the sparks are of no danger to co-workers. ✓
• Do not force the material onto the grinding wheel. ✓
• Do not plunge grind. ✓
• Bring the material slowly into contact with the grinding wheel. ✓
• Never clean or adjust the machine while it is in motion. ✓
• Use cutting fluid ✓
• Know where the emergency stop is located ✓
• Stop the machine before any adjustments ✓
• Keep tools clear from moving parts ✓
  (Any 3x1) (3)

2.2 Hydraulic press:

• To make sure there is no leakages. ✓
• To make sure that the readings are accurate. ✓
• To make sure the prescribed pressure is not exceeded. ✓(2)

2.3 MIG/MAGS welding:

• Working area must be well ventilated. ✓
• Make sure electrical parts are properly insulated. ✓
• Make sure the inert gas cylinder is fixed in an upright position. ✓
• Make sure the terminals are connected correctly to the right outlet points. ✓
• The operator should know how to use the equipment.✓
• The operator must be completely insulated by means of boots, gloves and rubber mats. ✓
• The work area must be partitioned off. ✓
• Use protective equipment. (Overall, gloves, apron, welding helmet etc.) ✓
• Ensure adequate fire precautions. ✓
• See that there is no oil or grease around the machine. ✓
• Ensure that the working area is clean. ✓
  (Any 3x1) (3)

2.4 Spring compressor:

• Make certain the compressor is strong enough for the spring ✓
• The compressor must be fitted correctly and firmly. ✓
• Ensure that the spring cannot slip out of position. ✓
• A uniform load must be applied. ✓
• Release the load carefully and also uniformly. ✓
• Do not use wire or ropes to compress the spring. ✓
• Do not hit with a hammer. ✓
• The hookes on the clamps shoul not be warned ✓
• Clamps must be evenly distributed ✓
• Do not exceed the maximum tension ✓
  (Any 2x1) (2)

[10]

QUESTION 3: TOOLS AND EQUIPMENT
3.1 Volt and ammeter:

• Voltmeter: connected in parallel to a circuit. ✓
• Ammeter: connected in series to a circuit. ✓ (2)

3.2 Uses of the multimeter:

• Direct current measurement (DC) ✓
• Alternating current measurement (AC) ✓
• Voltage measurement ✓
• Resistance measurement ✓
• Transistor test ✓
• Diode test ✓
• Continuity test ✓
• Temperature ✓
• Battery test ✓
  (Any 4x1) (4)

3.3 Compression Test:

• The piston rings are worn out. ✓✓
• Worn cylinders. ✓✓
• Cracked piston. ✓✓
  (Any 1x2) (2)

3.4 Tests:
3.4.1 A beam bending test is to investigate the deflection / bend ✓✓ of beams. (2)
3.4.2 A cylinder leakage tester is to check whether gases or air leaks ✓✓ from the cylinders / valve leak. (2)
[12]

QUESTION 4: MATERIALS
4.1 Properties of structures:
4.1.1 Cementite: hard ✓ and brittle ✓ (2)
4.1.2 Ferrite: soft ✓ and ductile ✓ (2)
4.2 Heating process of carbon steel:
4.2.1 Iron-Carbon ✓ Equilibrium ✓ Diagram (2)
4.2.2

1. = Ferrite and pearlite ✓
2. = Pearlite and cementite ✓
3. = Ferrite and austenite ✓
4. = Austenite and cementite ✓
5. = Austenite ✓ (5)

4.2.3 700 – 800 °C ✓✓ (2)
[13]

QUESTION 5: TERMINOLOGY
5.1 Screw thread terms:

5.1.3: NOTE: Any other corresponding point on the screw thread (5)
5.2 Milling processes:
5.2.1 Up-cut milling ✓ (1)
5.2.2 Down-cut milling ✓ (1)
5.3 Indexing:
Indexing =  40 
                   A
=  40 
    22
= 1 18  x  3 
      22      3
= 1  54 
       66
1 full turn and 54 holes on the 66-hole circle (6)✓✓✓✓✓✓
5.4 Dividing head:
5.4.1 The sector arm save time and removes the possibility of error in counting the number of holes for each move of the index pin. ✓ (2)
5.4.2 The index plate is equipped with accurate spaced holes on different-diameter circles. Each circle has a different number of holes. These circles allow the crank handle to be given an accurate part of a turn to obtain the desired spacing. ✓✓ (2)
5.4.3 The index pin can be set in the crank handle so that it can be dropped into calculated hole and lock the crank the hole circles. ✓✓ (2)
5.4.4 Ratio between worm and worm gear: 40:1 ✓✓ (2)
5.5 Gear terminology:
5.5.1 The pitch-circle diameter 'PCD'
module(m) = PCD
                        T
PCD = m x T
= 3 x 94
PCD = 282mm  (3)✓✓✓
5.5.2 The outside diameter:
outside diameter =  PCD + 2m
OD = 282+2(3)
OD = 288mm (2)✓✓
5.5.3 The dedendum:
Dedendum b = 1.157m
b = 1.157 x 3
b = 3.47mm

or

b = 1.25m
b = 1.25 x 3
b = 3.75mm (2)✓✓
5.5.4 The cutting depth:
Cutting dept = 2.157 x m
= 2.157 x 3
= 6.47 mm

or

Cutting depth = 2.25 x m
= 2.25 x 3
 = 6.75mm (2)✓✓
[30]

QUESTION 6: JOINING METHODS
6.1 Causes of undercutting:

• Current setting is too high ✓
• Current setting is too low ✓
• Faulty electrode manipulation ✓
• Arc length is too long ✓
• Welding speed is too fast ✓
• Incorrect electrode size ✓
  (Any 2x1) (2)

6.2 Prevention of slag inclusion:

• Chip off the slag from the previous weld runs before doing any further welding. ✓✓
• Increase the current setting. ✓✓
• Ensure that the joint is properly cleaned before any welding is done. ✓✓
• Ensure constant current flow. ✓✓
• Arc length must be shorter ✓✓
• Use dry electrodes
  (Any 1x2) (2)

6.3 Liquid dye penetrant test:

• Dye is sprayed onto the clean surface to be inspected ✓
• Allow a short time for the dye to penetrate, then remove excess dye with a solvent ✓
• Wash surface with water and allow to dry✓
• When the surface is dry spray a developer on the surface to bring out the colour in the dye which is trapped in the cracks or pin holes ✓ (4)

6.4 Advantages of using a MIGS/MAGS welding:

• Operator needs less skills ✓
• Continuous welds can be done without replacing electrodes✓
• Less cleaning of weld, (No slag to be removed) ✓
• It is a quicker process ✓
• Thin material can be welded easily ✓
• Can weld in any position ✓
• Create a better finish ✓
• High deposition rate ✓
• Less distortion ✓
  (Any 3x1) (3)

6.5 Gas flow meter:
Control the flow of rate of shielding gas ✓ and measure the flow rate. ✓ (2)
6.6 MIGS/MAGS welding process:

1. = Melted welding pool / Parent metal / Weld metal / Weld ✓
2. = Contact nozzle / Weld pistol / gun✓
3. = Gas shroud / Weld pistol / gun ✓
4. = Shielding gas ✓
5. = Earth clamp / Skelm / Earth cable ✓ (5)

Related Items

6.7 Shielding gas in MIGS/MAGS:

• To control the welding arc ✓✓
• Shield the molten pool from atmospheric gases ✓✓
  (Any 1x2) (2)

6.8 Earth cable:

• To complete the circuit ✓✓
• To maintain constant current ✓✓
• To prevent electric shock ✓✓
  (Any 1x2) (2)

6.9 THREE types of gasses used for MIGS/MAGS welding:

• Argon ✓
• Teral ✓
• CO₂ ✓
• Helium ✓
• Gas mixture ✓
  (Any 3x1) (3)

[25]

QUESTION 7: FORCES
7.1
(13)
7.2 Stress and Strain:
7.2.1 Stress in the bar:
A =  πD²   
          4
= π x 0.056²
         4
= 2.46 x 10^-3m^-2
σ =  F 
       A
=    40 x 10 ³
   2.46 x 10^-3
= 16260162.6Pa
= 16.26 x 10⁶Pa
= 16.26MPa (5)✓✓✓✓✓
7.2.2 Strain:
ε = σ 
     E
ε = 16.26 x 10⁶
        90 x 10⁹
= 0.18 x 10^-3(3)✓✓✓
7.2.3 Change in length:
ε = Δl
     ol
Δl = ε x ol
= (0.18 x 10^-3) x 0.85
= 0.15 x 10^-3m
OR
= 0.15 mm(3)✓✓✓
7.3 

Calculate A. Moments about B:
∑RHM = ∑LHM
(A x 12) = (960 x 6) + (750 x 8)
12A = 5760 + 6000
 12            12
A = 980N
Calculate B. Moments about A:
∑RHM = ∑LHM
(B x 12) = (750 x 4) + (960 x 6) + (300 x 12)
12B = 3000 + 5760 + 3600
12B = 12360
 12        12
B = 1030N (6)✓✓✓✓✓✓
[30]

QUESTION 8: MAINTENANCE
8.1 Pour point:
The lowest temperature ✓ at which a liquid will flow. ✓ (2)
8.2 Advantages of cutting fluids:

• Keep the work piece and cutting tool cool ✓
• It prolongs the life of the cutting tool ✓
• Ensure a better finish ✓
• It washes the cuttings/swarf away ✓
• It protects the machine by making the cutting process easier ✓
• Prevents rust ✓
• It increases the productivity because ✓
• It is possible to cut faster ✓
• It lubricates the machine ✓
  (Any 3x1) (3)

8.3 'ATF':
Automatic transmission fluid ✓✓ (2)
8.4 Main parts of a clutch:
Pressure plate ✓ clutch plate ✓ release bearing (Thrust bearing) ✓ (3)
8.5 Results of a stretched chain:

• The chain weakens ✓
• Generates friction ✓
• Vibration occurs ✓
• Becomes noisy ✓
• Derails easily ✓
• Tends to break easily ✓
  (Any 3x1) (3)

8.6 Causes of belt slip:

• Incorrect tension (loose) ✓
• Oil on the contact surfaces ✓
• Worn belts ✓
• Incorrect pulley alignment ✓
• Overloading ✓
• Not the correct size ✓
  (Any 2x1) (2)

[15]

QUESTION 9: SYSTEM AND CONTROLS
9.1 Gear drives:
9.1.1 Rotation frequency of the output shaft:
N_F = T_A x T_C x T_E
N_A    T_Bx T_D x T_F
N_F = T_A x T_C x T_E x N_A
         T_B x T_D x T_F
N_F =  30 x 20 x 50  x 2300
         40 x 60 x 70 
=410.71r/min (3)✓✓✓
9.1.2 Velocity Ratio:
VR = N_INPUT
         N_OUTPUT
=  2300 
   410.71
= 5.6:1 (2)✓✓

or

VR = N_OUTPUT
          N_INPUT
= 410.71
    2300
= 1:0.178
9.2 Belt Drives:
9.2.1 Rotation frequency of the driven pulley:
V = πDn
n =  V 
      πD
=    32   
  πx(0.26)
n_r/min = 39.18 x 60
n_r/min = 2350.6r/min (3)✓✓✓
9.2.2 Tensile force in the tight side:
T₁  = 2.5
T₂
T₁ = 2.5 x T₂
=2.5 x 140
=350N (2)
9.2.3 Power transmitted:
P = (T₁ - T₂)v
P = (350 - 140)x 32
=6720 watts (3)✓✓✓
9.3 Hydraulics:
9.3.1 Fluid pressure:
A_A = πD²
          4
= π0.02²
      4
= 0.31 x 10^-3m²

P_A =  F 
         A_A
=      300      Pa
    0.31 x 10^-3
= 967741.94Pa
= 0.97 x 10⁶Pa
= 0.967 MPa (4)✓✓✓✓
9.3.2 Stroke at piston B:
A_B = πD²
         4
= π0.075²
        4
= 4.42 x 10^-3m²

V_B = V_A

\A_B x L_B = A_B x L_A
L_B =  A_A x L_A
            A_B
= (0.31 x 10^-3) x 185
           4.42 x 10^-3
= 12.98mm (4)✓✓✓✓
9.4 Traction control:
It prevents the wheels from spinning ✓✓(2)
9.5 Safety belt:
Safety belts need to be activated (buckle up) by the driver/passenger ✓✓ (2)
[25]

QUESTION 10: TURBINES
10.1 Water turbine:

• Waterwheel ✓
• Pelton ✓
• Turgo ✓
• Michell-Banki ✓
• Jonval turbine ✓
• Reverse overshot waterwheel ✓
• Archimedes’ screw turbine ✓
  (Any 1x1) (1)

10.2 Runaway speed of a water turbine:
Runaway speed of a water turbine is its speed at full flow ✓ and with no shaft load ✓ (2)
10.3 Water turbine:
10.3.1 Type of turbine:

• Reaction turbine ✓
• Kaplan turbine ✓
  (Any 1x1) (1)

10.3.2

1.  Wicket gate ✓
2.  Rotor ✓
3.  Stator✓
4.  Shaft ✓
5.  Water flow ✓
6.  Blades✓ (6)

10.3.3 Advantages of water turbine:

• Water turbine blades continue to turn on cloudy windless days unlike sun and windy system. ✓
• No water is consumed in this process ✓
• More reliable ✓
• Environmentally friendly with no pollution ✓
• More economical than steam turbines✓
• Can be mounted vertically to take up less space ✓
  (Any 3x1) (3)

10.4 Function of turbo and superchargers:
To increase ✓ volumetric efficiency ✓ of an internal combustion engine. (2)
10.5 Compressor used in a turbocharger:
Centrifugal ✓ (1)
10.6 Turbocharger:
Exhaust gasses ✓ (1)
10.7 Advantage of a turbocharger:

• It is driven by exhaust gasses ✓
• No power from engine is used ✓
• Power loss above sea level is eliminated ✓
• More power is developed compared to a similar vehicle without a turbocharger ✓
• Less fuel is used compared to engine mass✓
• To increase volumetric efficiency ✓
  (Any 1x1)(1)

10.8 Advantage of a steam turbine:

• It is compact✓
• No lubrication is needed ✓
• It is more economical ✓
• Converts heat energy into mechanical energy ✓
• Greater thermal efficiency✓
• Direct drive ✓
• Low maintenance ✓
• High power to weight ratio ✓
  (Any 2x1) (2)

[20]
GRAND TOTAL: 200