MECHANICAL TECHNOLOGY: WELDING AND METALWORK
GRADE 12
NOVEMBER 2020
MEMORANDUM
NATIONAL SENIOR CERTIFICATE

QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC)
1.1 A ✓(1)
1.2 D ✓ (1)
1.3 A ✓ (1)
1.4 C ✓ (1)
1.5 B ✓ (1)
1.6 B ✓ (1)
[6]

QUESTION 2: SAFETY (GENERIC)
2.1 Work procedures on machine:
Switch off machine. ✓ (1)
2.2 The horizontal band saw:

• No adjustments to machine or work piece✓
• Ensure sufficient coolant on work piece and blade. ✓
• Do not leave machine unattended while in operation. ✓
• Do not lean on machine.✓
• Keep hands clear from blade. ✓
  (Any 2 x 1)(2)

2.3 Surgical gloves:

• Prevent contamination of wound✓
• To prevent transmission of HIV/AIDS or any blood related diseases to the first aid helper. ✓(2)

2.4 Personal protective equipment (PPE) during arc welding:

• Welding helmet / Helmet✓
• Safety goggles / Face shield ✓
• Leather apron / Apron✓
• Leather gloves / Gloves ✓
• Leather spat / Spats ✓
• Safety boots / Safety shoes ✓
• Over-all ✓
• Skull cap✓
• Neck protection ✓
• Ear plugs / Ear muffs. ✓
• Respirator ✓
  (Any 2 x 1) (2)

2.5 Responsibility of the employer regarding the health and safety:

• Sufficient lighting ✓✓
• Sufficient ventilation✓✓
• Provide first-aid equipment✓✓
• Provide a safe / clean working environment ✓✓
• Provide personal protective equipment (PPE) ✓✓
• Provide safety training to employees ✓✓
  (Any 1 x 2) (2)

2.6 Responsible for administering first aid:
A qualified / trained first aid person ✓(1)
[10]

QUESTION 3: MATERIALS (GENERIC)
3.1 Tests to identify various metals:
3.1.1 Sound test:

• Tapping the metal with a hammer (any metal object) ✓ and identify the sound. ✓
• Dropping the metal on the floor ✓and identify the sound.✓
  (Any 1 x 2) (2)  

3.1.2 File test:
File the metal and pay attention to the bite of the file into the metal.✓The bigger the bite the softer the metal. OR The smaller the bite the harder the metal.✓ (2)
3.2 Purpose of heat treatment of steel:

• To change ✓ the properties ✓ of steel.
• To change ✓the grain structure ✓ of steel.
  (Any 1 x 2) (2)

3.3 Purpose of case hardening on steel:
To create a hard / wear resistance surface / case ✓ with a tough core. ✓ (2)
3.4 The tempering process for steel:

• Heat the steel to a temperature (temper colour) below the critical temperature. ✓
• Soak it at that temperature for a period.✓
• Quench / cool in an appropriate quenching agent. ✓ (water, brine, or oil) (3)

3.5 THREE factors for heat treatment of steel:

• Heating temperature / Carbon content ✓
• Soaking (Time period at temperature) / Work piece size✓
• Cooling rate / Quenching rate (Quenching medium) ✓ (3)

[14]

QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC)
4.1 B / D ✓ (1)
4.2 A ✓ (1)
4.3 C ✓ (1)
4.4 D ✓ (1)
4.5 B ✓ (1)
4.6 D ✓ (1)
4.7 A ✓ (1)
4.8 C ✓ (1)
4.9 D ✓ (1)
4.10 C ✓ (1)
4.11 B ✓ (1)
4.12 C ✓ (1)
4.13 A ✓ (1)
4.14 D ✓ (1)
[14]

QUESTION 5: TERMINOLOGY (TEMPLATES) (SPECIFIC)
5.1 Advantages of templates:

• Quicker to use to improve mass production ✓
• Accurate production ✓
• Cheap to manufacture ✓
• Unskilled labour will be able to use it ✓
• Avoid unnecessary wastages / cost effective ✓
• Uniformity in production ✓
• Can be reused. ✓
  (Any 2 x 1) (2)

5.2 Use of templates:
5.2.1 Thin metal is used for profile cutting machines ✓ (1)
5.2.2

• Hardboard templates is used for templates for gussets. ✓
• Hardboard templates are used for checking sizes. ✓
• Hardboard templates is used for marking of holes. ✓
  (Any 1 x 1) (1)

5.3 Components of a roof truss:

1. Rafter ✓
2. Purlin ✓
3. Internal bracing members / strut ✓
4. Gusset plate ✓
5. Main tie / Tie beam / Beam ✓ (5)

5.4 A mild steel ring material:
Calculate the dimensions of the required material:
Mean θ = Outside θ - plate thickness
= 280 - 12
= 268 mm

Mean circumference = π x meanθ
= π x 268
= 841,95mm
= 842 mm (5)

5.5 Abbreviation 'SANS':
South African ✓ National Standards ✓ (2)
5.6 Resistance weld:
5.6.1 Foil seam ✓ (1)
5.6.2 Flash or resistance butt ✓ (1)
5.7 Weld dimensions:

• 5 – size (width) of weld ✓
• 25 – length of weld ✓
• 50 – pitch of welds ✓ (3)

5.8 Position of the weld:
5.8.1 Weld on the arrow side ✓ (1)
5.8.2 Weld on both sides✓ (1)
[23]

QUESTION 6: TOOLS AND EQUIPMENT (SPECIFIC)
6.1 Pedestal drill machine:

1. = Table / Machine table / Working table / Platform ✓
2. = Chuck / Drill bit holder ✓
3. = Motor ✓
4. = Pillar / Column✓ (4)

6.2 Operating principles:
6.2.1 Horizontal band saw:

• The blade is tensioned around two pulleys. ✓
• The machine is driven by an electric motor.✓
• The blade is fitted so that it cuts in a continuously forward motion.✓
• The blade assembly is raised and lowered by hand or by hydraulic controls. ✓
• The metal being cut is held firmly in the stock clamp during the cutting process.✓
  (Any 4 x 1) (4)

6.2.2 Punch and cropper (shear) machine:

• It is an electrically driven machine. ✓
• It makes use of a flywheel and clutches ✓ to engage various shearing blades or punches. ✓ (3)

6.3 Primary function of flashback arrestors:
It prevents ✓ back-feeding/backfiring. ✓✓ (3)
6.4 Use of taps and dies:

• Taps are used to cut / clean✓ internal / nut screw threads ✓
• Dies are used to cut / clean ✓ external / bolt screw threads ✓ (4)

[18]

QUESTION 7: FORCES (SPECIFIC)
7.1 Frameworks:
7.1.1 Force diagram:

Markers need to draw the diagram to scale. (10)
7.1.2 Magnitude and nature of the members:

(18)
7.2 BEAMS:
7.2.1 Bending moments:
BM_B = (3,4 x 3)
= 10,2 kN.m

BM_C = (3,4 x l) - (4 x 4)
= 23,8 - 16
= 7,8 kN.m

BM_D = 0 kN.m
7.2.2 Shear force diagram: (3)

7.2.3 Bending moment diagram: (3)

7.3 Stress and Strain:
7.3.1 Maximum stress:
Maximum Stress = Maximum Load
                                      Area
=   8 x 10 ³
  0,08 x 10^-3
= 100 x 10⁶ Pa
= 100 MPa (3)

7.3.2 Safe working stress:
Safe Stress = Maximum Stress
                        Safety Factor
= 100 x 10⁶
         4
= 25 x 10⁶ Pa
= 25 MPa (2)
[45]

QUESTION 8: JOINING METHODS (INSPECTION OF WELDS) (SPECIFIC)
8.1 Welding spatter:

• Too high current / Amperage too high ✓
• Too long arc / Arc blow ✓
• Not using anti-spatter spray ✓
• Electrode angle too small ✓
• Welding speed too fast ✓
• Wet electrodes✓
• Gas-flow too high (gas welding)✓
• Incorrect polarity for electrode type✓
  (Any 4 x 1) (4)

8.2 Gas cutting:
8.2.1 Nozzle too high from surface:

• Excessive melting of the top edge. ✓
• Undercut at the top of the cut face with lower part square and sharp bottom corner. ✓ (2)

8.2.2 Nozzle too close to the surface:

• Top edge slightly rounded and heavily beaded.✓
• Cut face usually square with fairly sharp bottom corner.✓ (2)

8.3 Causes of weld defects:
8.3.1 Porosity:

• Dirty weld surface ✓
• Wet welding electrodes ✓
• Rust in the MIG wire electrode✓
• Interruption of shielding gas supply✓
• Welding in windy conditions where effectiveness of shielding gas is compromised ✓
• Wrong gas used on the specific metal✓
• Weld ability of parent metal not good ✓
• Wrong electrode used on the specific metal ✓
• Too high temperature ✓ (Any 2 x 1) (2)

8.3.2 Poor penetration:

• Welding current is too low ✓
• Travel speed is too fast ✓
• Incorrect electrode angle ✓
• Poor edge preparation✓
• Insufficient root gap✓
• Gas flow too low (gas welding) ✓(Any 2 x 1) (2)

8.4 Heat Affected Zone (HAZ) Cracks:

• Excessive hydrogen ✓
• High residual stress levels (work piece cooled too fast) ✓
• High carbon content on the base metal ✓
  (Any 2 x 1) (2)

8.5 Visual inspection:

• Shape of the profile ✓
• Uniformity of the surface ✓
• Overlap ✓
• Undercutting✓
• Penetration bead ✓
• Root groove ✓
• Surface cracks ✓
  (Any 3 x 1) (3)

8.6 Ultrasonic test:

Gel should be put on the surface of the work piece.✓

• The sender/receiver is moved in a zigzag motion across the weld to broaden its detection range. ✓
• A high frequency sound wave is send into the metal. ✓
• When the wave is stopped, the sender serves then as a receiver. ✓
• The receiver monitors the waves as it is reflected through the metal. ✓
• Each wave is visually represented on an oscilloscope.✓
• The calibrated oscilloscope will then indicate the deviations in the waves which represents the defects in the metal.✓
  (Any 6 x 1) (6)

[23]

QUESTION 9: JOINING METHODS (STRESSES AND DISTORTION) (SPECIFIC)
9.1 Residual stress:
Residual stresses are stresses that exist in a metal ✓after cooling✓ (2)
9.2 Effect of hot working on steel:

• In hot working, deformation and recrystallization occur simultaneously so that the rate of softening is greater than work hardening. ✓
• Hot-working should be finished at a temperature just above the recrystallization temperature. ✓
• To obtain a fine grain structure.✓
• If the finishing temperature is too high, grain growth will occur while the metal is cooling above the recrystallization temperature and inferior properties will develop. ✓ (4)

9.3 Iron-carbon diagram:
9.3.1 Iron-carbon equilibrium diagram ✓ (1)
9.3.2

• Temperature / Degrees Celsius ✓
• Austenite✓
• Austenite and Cementite ✓
• Ferrite and Pearlite ✓
• Carbon content ✓ (5)

9.4 Result when metal is cooled rapidly:

• The metal sets up internal and external stresses. ✓
• Causes cracks on the surface of the metal. ✓
• Causes deformation.✓
• Hardness increases.✓
• Martensite forms. ✓
  (Any 2 x 1) (2)

9.5 Quenching media:

• Water ✓
• Brine✓
• Oil ✓
• Air ✓
• Metal / Molten salts ✓
• Lime✓
• Sand ✓
• Ash ✓
  (Any 4 x 1) (4)

[18]

QUESTION 10: MAINTENANCE (SPECIFIC)
10.1 Types of maintenance:

• Preventative✓
• Reliable centred ✓
• Predictive✓
• Routine ✓
• Corrective ✓
• Condition based ✓
• Reactive maintenance ✓
  (Any 2 x 1) (2)

10.2 Lockout on machines:
To ensure that nobody can turn on ✓the machine while maintenance is being carried out.✓ (2)
10.3 Rules to be observed before machine start up:

• Check if there is lock out tag✓
• Confirm that the machine is safe and operational.✓
• Check that all guards and safety devices are in position and operative. ✓
• Inform workers that the machine is being brought back into service. ✓
• Check that the area surrounding the machine is clear and that turning it on will not endanger anyone.✓
• Check that all relevant fasteners have been properly tightened.✓
• Check that all lockout devices have been removed.✓
• Turn on the machine's power supply. ✓
• Know where the stop switch or emergency switch is located. ✓
  (Any 2 x 1) (2)

10.4 Factors to be observed when selecting the cutting speed of a drilling machine:

• Type of material ✓
• Diameter of drill bit ✓
• Material of which the drill bit is made ✓
• Type of drill bit ✓
• Firmness with which the work is clamped ✓
• Condition of the machine ✓
• Use of cutting fluids ✓
• Rate of feed ✓
  (Any 3 x 1) (3)

[9]

QUESTION 11: DEVELOPMENT (SPECIFIC)
Square-to-round transition:
11.1 The true length FG:
IK = 300(2units)
IH = 150(1unit)
HK = 1√3 (1unit √3)

The true lengthFG:
Plan lengthFG = FK - GK
= 400 - 300
= 100mm

The true FG is equalto H'F
CG² = C'F² + FG²
= 400² + 100²
C'G = √170000
CG = 412,31 mm
True length C'G = √412,31² + 800²
= 900mm

11.2 Length CI, the sides CE and EI of triangle CEI must be calculated:
CE = CF - EF
= 400 - 150
= 250mm

ButEI = FH
HK = 1unit x √3
= 150√3
= 259,81mm

FH = FK - HK
= 400 - 259,81
= 140,19mm

CI² = CE² + EI²
= 250² + 140,19²
= √82153,24
CI = 286,62mm

TruelengthCI CI PerpendicularHeight
= 286,62² + 800²
= √722151,02
= 849,79mm (10)

11.3 JI is one-twelfth of the circumference:
True Length of JI Circumference = π x ^MD/₁₂
¹/₁₂ Circumference = 1884,9
                                      12
= 157,08 mm (3)
[20]
GRAND TOTAL: 200