MECHANICAL TECHNOLOGY: WELDING AND METALWORK
GRADE 12
NATIONAL SENIOR CERTIFICATE EXAMINATIONS
MEMORANDUM
MAY/JUNE 2019

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

QUESTION 2: SAFETY (GENERIC)
2.1 Angle grinder:

• Do not use excessive force while grinding. ✓
• Ensure that the sparks do not endanger co-workers. ✓
• Keep hands clear from grinding disc. ✓
• Maintain a firm grip on the angle grinder. ✓
• Grinding disc fitted will not turn faster than the manufactures recommendation. ✓
• Make sure that there is no cracks or chips on the grinding disc
• Safety guard must be in place. ✓
• PPE must be worn.✓
• Beware of lockable switches in the on position when the machine is plugged in and switched on. ✓
• Check for defective cables. ✓
• Secure work piece properly. ✓
• Grinding angle to be away from body to prevent sparks directly on clothing. ✓
• Make sure disc does not wobble during cutting. ✓
  (Any 2 x 1) (2)

2.2 Welding goggles:

• To protect your eyes from the spatter / sparks. ✓
• To protect your eyes from the harmful rays / UV rays. ✓
• To ensure proper vision of the process. ✓
  (Any 2 x 1) (2)

2.3 PPE – Bench grinder:

• Overall ✓
• Safety goggles / face shield ✓
• Safety shoes ✓
• Safety gloves ✓
  (Any 2 x 1) (2)

2.4 Process and product workshop layout:

• The product layout ensures that the machines are arranged in the sequence of the manufacturing process of a product. ✓
• The process layout is based on the type of manufacturing process needed in the making of the product. ✓ (2)

2.5 Employer’s responsibility – equipment:

• They must provide and maintain equipment. ✓
• Ensure that the equipment is safe to use by employees.✓
• Provide safe storage for equipment. ✓
• Provide proper training of employees in the use of the equipment. ✓
• Enforce safety measures/ OHS acts and Regulations. ✓
• Employer must provide proper personal protective equipment (PPE) for the specific machines. ✓
  (Any 2 x 1) (2)

[10]

QUESTION 3: MATERIALS (GENERIC)
3.1 Tests to distinguish between metals:

• Bending test: ✓ hit with hammer. ✓
• Filing test ✓ file material. (colour and ease) ✓
• Machining test ✓ machine material. (type of shaving, ease and colour) ✓
• Sound ✓drop on floor. (high or low frequency) ✓
• Spark test. ✓Shape and colour of sparks. ✓
  (Any 4 x 2) (8)

3.2 Heat-treatment:
3.2.1 Tempering:
After hardening, the steel must be tempered.

• To relieve the strains induced.✓✓
• To reduce brittleness. ✓✓
  (Any 1 x 2) (2)

3.2.2 Normalising:
To relieve the internal stresses. ✓✓ (2)
3.2.3 Hardening:

• To produce extremely hard steel. ✓✓
• To enable it to resist wear and tear. ✓✓
  (Any 1 x 2) (2)

[14]

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

QUESTION 5: TERMINOLOGY (TEMPLATES) (SPECIFIC)
5.1 Roof truss:

1. – Purlin ✓
2. – Rafter ✓
3. – Incline tie ✓
4. – Tie beam ✓
5. – Shoe plate / Gusset plate ✓ (5)

5.2 Fillet weld on T-joint: 
(8)
5.3 Dimensions of the material:
5.3.1 MeanØ = Inside Ø + Thickness
= 215 ÷ 20
= 235 mm
Mean circumfrence = Fx MeanØ
= Fx 235
= 738.27 mm 
Round off to 740 mm (6)
5.3.2 
(4)
[23]

QUESTION 6: TOOLS AND EQUIPMENT (SPECIFIC)
6.1Punch and shear machine:

• Croppers are activated by hand or by foot. ✓
• A shear and punch machine is a heavy-duty machine for cutting steel profiles and punching holes into steel plates. ✓
• Croppers are electrically / hydraulically driven engaging various shearing blades to shear / punch different profiles. ✓
• Punches and corresponding dies need to be set to the desired size before punching. ✓
• They do not require cooling fluid because the shearing action does not develop a great deal of heat. ✓(5)

6.2 Plasma cutter:

• The basic cutting process involves creating an electrical channel of ionised gas; that is plasma, ✓from the plasma cutter itself through the work piece that is being cut. Thus forming a completed electric circuit back to the plasma cutter via a grounding clamp. ✓
• This is accomplished by compressed air that is blown toward the work piece through a focused nozzle at high speed. ✓
• A high frequency, electrical arc is then formed within the gas between an electrode near or integrated into the gas nozzle and the work piece itself. ✓ (4)

6.3 Internal Thread cutting process:

• Drill the required core / root / inside diameter. ✓
• Use the three taps in order. ✓
• Check thread with gauge / bolt when complete. ✓ (3)

6.4 Brinell hardness test:

• The Brinell hardness tester makes use of a steel ball as indenter. ✓
• A load is applied to the test piece. ✓
• The diameter of the indentation is measured with a microscope. ✓
• The diameter is used to determine the Brinell reading. ✓ (4)

6.5 Rockwell hardness testing over Brinell hardness testing:

• The advantages of the Rockwell Hardness method include the direct readout of the Rockwell Hardness number. ✓✓
• Rapid testing time. ✓✓
  (Any 1 x 2) (2)

[18]

QUESTION 7: FORCES (SPECIFIC)
7.1
(19)
7.2 Beams:
7.2.1 Reactions at the supports RL and RR:
R_L x 12 = (3 x 3) + (5 + 6) + (4 x 9)
R_L = 6.25N

R_R x 12 = (4 x 3) + (5 x 6) + (3 x 9)
R_R = 5.75N (4)
7.2.2 Bending moments:
BM_B = (6.25 x 3)
= 18.75 N.m

BM_C = (6.25 x 6) - (4 x 3)
= 25.5 N.m

BM_D = (6.25 x 9) - (4 x 6) - (5 x 3)
= 17.25 N.m (6)

7.2.3 Bending moments diagram:
(5)
SCALES: Space diagram:10 mm = 1 m
Bending moment diagram:5 mm = 1 N.m
7.3 Stress and Strain:
7.3.1 Stress in the shaft:
Area = DF² 
             4
=  F x (32 x 10^-3)²
             4
= 0.8 x 10^-3m²
σ =  Load 
Area
= 100 x 10³
    0.8 x 10^-3
= 125 x 10⁶Pa   or   125MPa (5)
7.3.2 Strain in the steel:
ε= ΔL 
     oL
= 0.5 
   120
=4.17 x 10^-3 (3)
7.3.3 Young’s modulus of elasticity:
E = σ 
       ε
=  125 x 10 ⁶ 
   4.17 x 10^-3
= 29.98 x 10⁹ Pa  or  29.98GPa (3)
[45]

QUESTION 8: JOINING METHODS (WELD INSPECTION) (SPECIFIC)
8.1 Factors to be observed during oxy-acetylene welding:

• Correct flame for the work at hand. ✓
• Correct angle of welding torch and rod. ✓
• Depth of fusion. ✓
• The welding rate. ✓
  (Any 2 x 1) (2)

8.2 Welding defects:
Incomplete penetration:

• Welding current too low.✓
• Welding speed too fast. ✓
• Incorrect welding angle. ✓
• Poor joint preparation. ✓
• Insufficient root gap. ✓
• Wrong polarity. ✓
• Arc length too short. ✓
• Wrong electrode used. ✓
  (Any 2 x 1) (2)

8.3 Methods reducing of welding defects:
8.3.1 Slag inclusion:

• Using well-maintained consumables. ✓
• Ensure adequate shielding gas. ✓
• Clean the joint properly.✓
• Slag must be removed before welding the next bead.✓
• Too slow welding movements. ✓
• Electrode too big. ✓
• Wrong or too big weaving action. ✓
  (Any 2 x 1) (2)

8.3.2 Centreline cracks:

• Aiming for a width-to-depth ratio of 1:1. ✓
• Decreasing the current to reduce excess penetration. ✓
• Decreasing welding voltage / current. ✓
• Slowing travel speed. ✓
• Reduce high carbon content in weld. ✓
• Welding while joint is under stress due to joint design, use clamping devices. ✓
  (Any 2 x 1) (2)

8.4 Porosity:
Porosity refers to cavity-type pores ✓ (bubbles or gas pockets) formed by gas✓ during the solidification ✓ of molten weld metal. (3)
8.5 Non-destructive test:
The welded joint is not ✓destroyed ✓ in the process of testing. (2)
8.6 Ultrasonic test:

• To detect internal flaws. ✓
• To detect surface flaws. ✓ (2)

8.7 Visual inspection:

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

8.8 Nick break test:

• Make a hacksaw cut at both edges, through the centre of the weld. ✓
• Place specimen on two steel supports.✓
• Use a sledge hammer to break the specimen in the area of the cuts.✓
• Inspect the exposed weld metal in the break  for incomplete fusion, slag inclusion, etc. ✓ (5)

[23]

QUESTION 9: JOINING METHODS (STRESSES AND DISTORTION) (SPECIFIC)
9.1 Shrinkage in welding:
Shrinkage is a form of plastic deformation ✓ where the metal has deformed as a result ✓ of contraction ✓ on cooling. ✓ (4)
9.2 Factors affecting distortion and residual stress:

• If the expansion that occurs when metal is heated is resisted, then deformation will occur. ✓
• When contraction that occurs on cooling is resisted, then a stress will be applied. ✓
• If that applied stress causes movement, then distortion occurs. ✓
• If the applied stress does not cause movement, then there will be residual stress in the welded joint. ✓ (4)

9.3 Back-step welding:
(6)
9.4 Factors affecting the temperature of cold worked steel for re-crystallisation:

• The prior amount of cold work.✓
• The temperature and time of annealing process. ✓
• Composition of the metal. ✓
• The melting point. ✓ (4)

[18]

QUESTION 10: MAINTENANCE (SPECIFIC)
10.1 Effect of overloading:
10.1.1 Power saw:

• Driving motor will be damaged. ✓
• Excessive strain on the driving system. ✓
• The cutting blade will be damaged. ✓
• The blade may deflect and result in a skew cut. ✓
  (Any 1 x 1) (1)

10.1.2 Bench grinder:

• Result in malfunction due to excessive loads on the spindle bearings, grinding wheel and machine motor. ✓
• Overloading will wear the grinding wheel excessively and unevenly. ✓
• It shortens the life span of the spindle bearings and motor. ✓
  (Any 1 x 1) (1)

10.2 Effect of friction:
10.2.1 Drill bit of a pedestal drill:

• Due to the heat caused by friction the cutting edge of the drill bit softens / blunt.✓
• Lifespan of the drill bit will be reduced. ✓
  (Any 1 x 1) (1)

10.2.2 Rolling machine’s bearings:
Journals and bearings will prematurely wear out. ✓(1)
10.3 A punch and a shearing machine:

• Check the condition of the switch gear, wiring and isolation. ✓
• Ensure that the isolator is lockable. ✓
• Check the condition of the stop / start equipment. ✓
• Check the operation of emergency stop where fitted. ✓
• Check connections of electrical wiring. ✓
  (Any 2 x 1) (2)

10.4 Record keeping:

• Monitoring of the machine’s condition✓
• Monitoring of the maintenance costs on the machines. ✓
• Upholding the warranties and guarantees. ✓
  (Any 2 x 1) (2)

[8]

QUESTION 11: TERMINOLOGY (DEVELOPMENT) (SPECIFIC)

11.1.1 Length of IJ:
Plates A and D.
IJ = IL - JL
IJ = 300 - 150
IJ = 150mm (3)

11.1.2 True length of AE:
True Length AE = √IE² + AI² + VH²
AE = √150² + 350² + 450²
AE = 589.49mm
= 590mm (6)

11.1.3 Length of MK:
MK = LK - LM
MK = 350 - 200
MK = 150mm (2)

11.1.4 The True length of DH:
True length of DH = √HK² + KD² + VH²
DH = √150² + 150² + 450²
DH = 497.49mm
SAY 498 mm(6)
11.1.5 Pattern for plates A: (2)

11.1.6 Pattern for Plate C: (2)

[21]
TOTAL: 200