Mechanical Technology Grade 12 NSC November 2023 Memo (Eng)

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE GRADE 12 MECHANICAL TECHNOLOGY: WELDING AND METALWORK NOVEMBER 2023 MARKING GUIDELINES MARKS: 200 These marking guidelines consist of 22 pages. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 2 DBE/November 2023 NSC – Marking Guidelines QUESTION 1: MULTIPLE-CHOICE (GENERIC) 1.1 B (1) 1.2 A (1) 1.3 C (1) 1.4 C (1) 1.5 A (1) 1.6 B (1) [6] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 3 DBE/November 2023 NSC – Marking Guideline QUESTION 2: SAFETY (GENERIC) 2.1 Examination checks:  Severe bleeding   Internal bleeding   Head injuries   Neck injuries   Fractures   Vital signs   Physical abnormalities  (Any 2 x 1) (2) 2.2 Safety devices on the power-driven guillotine:  Finger protectors / Fixed guards / Blade guard   Rear view mirrors   Rear light curtains   Automatic sweep-away   Revolving warning lights   Two-hand / dual control device   Additional emergency buttons   Self-adjusting guards   Covered footswitch  (Any 2 x 1) (2) 2.3 Grinding wheel:  The wheel should be rated above the speed of the motor.   Check for cracks on the grinding wheel.   Check for chips on the grinding wheel.   Check that the arbor hole is the correct size.   Must not be contaminated by oil/fluids or grease.   Correct size of the wheel.   Correct type of wheel for the material.  (Any 2 x 1) (2) 2.4 Gas welding equipment – safety devices:  Valve guard   Flash back arrestor   Pressure regulator   C-clamps on hoses/Parallel hose clips   Acetylene spindle key must always be in place.   Cylinder valves.  (Any 2 x 1) (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 4 DBE/November 2023 NSC – Marking Guideline 2.5 Advantages of process layout of machines are:  High machine utilisation.   Better supervision.   Less interruption in the flow of work.   Lower equipment costs.   Better control of total manufacturing costs.   Greater flexibility.  (Any 2 x 1) (2) [10] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 5 DBE/November 2023 NSC – Marking Guideline QUESTION 3: MATERIALS (GENERIC) 3.1 Colour code of metal:  To identify the type of metal.   To identify carbon content especially after the metal was stored.   To identify the profile/size of the metal.  (Any 1 x 1) (1) 3.2 Tests to determine properties of steel: 3.2.1 Sound test:  Hardness   Softness  (Any 1 x 1) (1) 3.2.2 Bending test:  Ductility   Bend strength   Fracture strength   Resistance to fracture  Brittleness   Elasticity   Plasticity   Flexibility  (Any 1 x 1) (1) 3.2.3 Machining test:  Hardness   Strength  (Any 1 x 1) (1) 3.3 Reasons metal soaked during heat treatment:  To ensure uniform heat distribution  throughout the metal.   To achieve a uniform grain structure  after cooling the metal.  (Any 1 x 2) (2) 3.4 Case hardening:  Carburising   Nitriding   Cyaniding  (Any 2 x 1) (2) 3.5 Annealing process: Heating the steel slightly above AC3, (upper critical temperature)  soaking it for a required time/period  and then slow cooling  back to room temperature. (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 6 DBE/November 2023 NSC – Marking Guideline 3.6 Rapid quenching mediums:  Brine/Salt water   Water   Nitrogen   Oil  (Any 2 x 1) (2) 3.7 Heat treatment process: Tempering  (1) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 7 DBE/November 2023 NSC – Marking Guideline QUESTION 4: MULTIPLE-CHOICE (SPECIFIC) 4.1 A (1) 4.2 B (1) 4.3 C (1) 4.4 D (1) 4.5 A (1) 4.6 B (1) 4.7 A (1) 4.8 A (1) 4.9 D (1) 4.10 B (1) 4.11 A (1) 4.12 A (1) 4.13 D (1) 4.14 B (1) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 8 DBE/November 2023 NSC – Marking Guideline QUESTION 5: TERMINOLOGY (TEMPLATES) (SPECIFIC) 5.1 Brass ring calculations: 5.1.1 Mean Ø  InsideØ  Plate thickness  870  30   900 mm (2) 5.1.2 Mean circumference  π  Mean Ø  π  900   2827,43   2827 mm  (3) 5.2 Fusion weld symbols: (Symbols can be presented in any direction) 5.2.1 Square butt  (2) 5.2.2 V groove V  (2) 5.2.3 U butt  (2) 5.2.4 J butt  (2) 5.2.5 Flare-V  (2) 5.3 Weld symbol: 5.3.1 T-joint  (1) 5.3.2 Labels: A – weld all around  B – Site weld  C – Fillet weld  D – Tail  E – Pitch of weld  F – Length of weld  G – Size of weld  (7) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 9 DBE/November 2023 NSC – Marking Guideline QUESTION 6: TOOLS AND EQUIPMENT (SPECIFIC) 6.1 Types of metal:  Carbon steel/Steel   Aluminum   Brass   Copper   Cast iron   Cast steel   Stainless steel   Tool steel  (Any 3 x 1) (3) 6.2 Bench grinder:  Polishing   Sharpening of cutting tools and drill bits.   To remove rough edges.   To remove excess material.   Buffing   Removing rust from metal.  (Any 3 x 1) (3) 6.3 Arc welding: 6.3.1 Labels of arc welding set up: A - Arc welding machine / Power source / Inverter  B - Electrode / Welding rod  C - Electrode holder / Welding rod holder D - Positive- / negative cable / Electrode cable E - Earth cable / negative cable / positive cable  (5) 6.3.2 Advantages of MIGS/MAGS welding:  Less distortion.   MIG/MAGS welding quality is better.   Fewer stops and starts.   MIG/MAGS works with many metals or alloys.   Greater deposition rates.   Less post welding cleaning (no slag to chip off weld).   Better weld pool visibility.   No stub end losses or wasted man hours caused by changing electrodes.   Low skill required to operate MIG/MAGS welding gun.   Can weld in any position.   The process is easily automated.   No fluxes required in most cases.  (Any 1 x 1) (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 10 DBE/November 2023 NSC – Marking Guideline 6. 4 Drill size: Drill size = Outside Ø - Pitch   Drill size = 10 -1,5 = 8,5 mm  (3) 6.5 Rolling machines:  Off-set pinch rolls   Horizontal pyramid rolls   Vertical rolls  (3) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 11 DBE/November 2023 NSC – Marking Guideline QUESTION 7: FORCES (SPECIFIC) 7.1 Beams: 7.1.1 Reaction RR: Take moment about (RL):    RR  7   4  1,5    5  3,5    3  5,5   6  17,5  16,5  40 40Nm  RR  7m RR  5,71N  Reaction RL: Take moment about (RR):    RL  7   3  1,5    5  3,5    4  5,5   4,5  17,5  22  44 44Nm  RL  7m RL  6,29N  (8) 7.1.2 Bending moments:  BMA = (6,29 N x 1,5 m) – (4 N x 0m) = 9,44 Nm  BMB = (6,29 N x 3,5 m) – (4 N x 2 m) – (5 N x 0 m)  = 14,02 Nm  BMC = (6,29 N x 5,5 m) – (4 N x 4 m) – (5 N x 2m) – (3 N x 0 m) = 8,60 Nm  (6) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 12 DBE/November 2023 NSC – Marking Guideline 7.1.3 Bending moment diagram. Scale: 1 m = 10 mm and 1 Nm = 10 mm. 4N 5N 3N A B C 14, 02 Nm   9, 44 Nm 8, 60 Nm    0 0 Note to marker: (6) ` Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 13 DBE/November 2023 NSC – Marking Guideline 7.2 Stress and Strain: 7.2.1 Area of the bar: F σ A F A  σ 65  103   5  106  13  10 3 m2 (3) 7.2.2 Diameter of a bar: πD2 A 4 4A  D    4 13  10 3    0,128655019 m  128,66 mm  (3) 7.2.3 Strain: σ ε  E 5  10 6  ε  75  10 9  6,67  10 -5  (2) 7.2.4 Change in length: L ε  OL L  ε  OL     6,67  10 5  250 mm    0,02 mm  (3)  Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 14 DBE/November 2023 NSC – Marking Guideline 7.3 Simple frame: 7.3.1 Space diagram: 220 N  1 mark for drawn to correct scale A  1 mark for labelling A, B B, C and D correctly D 30° 30° 1 mark for indicating C 10 m arrows correctly. 110 N 110 N NOTE: Draw to scale on transparency for marking purpose . Mark allocation is for indication of arrows. (3) 7. 3.2 Vector diagram: Scale 1 mm = 2 N a   d  c  b NOTE: Draw to scale on transparency for marking purpose. (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 15 DBE/November 2023 NSC – Marking Guideline 7.3.3 Magnitude and nature of force: Member Force (N) Nature AD 220 (216-224)  Strut  BD 220 (216-224)  Strut  CD 190 (186-194)  Tie  NOTE TO A MARKER: ALLOW FOR A DEVIATION OF 2 mm (UP OR DOWNWARDS). (6) [45] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 16 DBE/November 2023 NSC – Marking Guideline QUESTION 8: JOINING METHODS (INSPECTION OF WELD) (SPECIFIC) 8.1 Weld defects: 8.1.1 Slag inclusion  (1) 8.1.2 Incomplete penetration  (1) 8.2 Inspection of welds:  To check for weld quality.   To check for specification.  (2) 8.3 Welding defects: 8.3.1 Nick break test:  Lack of fusion   Internal quality   Porosity   Slag inclusion   Oxidized / burnt metal   Incomplete penetration  (Any 2 x 1) (2) 8.3.2 Guided bend test:  Quality of face of the weld joint.   Quality of root of the weld joint.   Degree of penetration.   Degree of fusion.  (Any 2 x 1) (2) 8.4 Non-destructive test: It is a method of testing a welded joint without destroying  the finished product.  (2) 8.5 Transverse cracks:  Preheat the base metal.   Using lower strength consumables.   Slow cooling after weld.  (3) 8.6 Crater crack:  It is caused by lack of filler at the end of the weld.   Metal of not good weldability  (Any 1 x 1) (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 17 DBE/November 2023 NSC – Marking Guideline 8.7 Advantages of liquid dye penetrant test:  Low cost.   Easy to apply.   Easy to interpret.   Minimal training required.   Good for ferrous metals.   Good for non-ferrous metals.   Can be used in complex shapes/areas.   It is non-destructive.  (Any 3 x 1) (3) 8.8 Ultrasonic test  Clean the area on the metal to be tested.   Calibrate the equipment before commencement of testing.   Apply gel, oil or water to the area on the metal to be tested.   Move probe left-to-right along the area on the metal.   Soundwaves is sent and received by the equipment.   Interpret the flaws detected on oscilloscope.  (6) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 18 DBE/November 2023 NSC – Marking Guideline QUESTION 9: JOINING METHODS (STRESSES AND DISTORTION) (SPECIFIC) 9.1 Factors having effect on shrinkage:  Electrode type.   Electrode size.   Welding current.   Flame size.   Welding speed.   Rate of cooling during welding.   Rate of cooling after welding.   Workpiece size / thickness.  (Any 3 x 1) (3) 9.2 Peening:  A way to counteract  the shrinkage forces of a weld bead as it cools.   It is a technique used in welding  to help strengthen the joint.   It is the hammering  of the weld immediately after welding  is done. (Any 1 x 2) (2) 9.3 Types of strongbacks:  Clips   Yokes  (2) 9.4 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.   The important factor in hot-working is the finishing temperature.   Hot-working should be finished at a temperature just above the recrystallization temperature, so that a fine grain structure is obtained.   If the finishing temperature is too high, grain growth will occur while the metal is cooling above the recrystallization temperature.  (Any 3 x 1) (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 19 DBE/November 2023 NSC – Marking Guideline 9.5 Causes of residual stress in welds:  Heat present in the weld.   Quality of parent metal.   Quality of filler rod.   Quality of electrode.   Shape and size of weld.   Number of successive weld runs.   Comparative weight of weld and parent metal.   Type of welding joint used.   Welding method used to mitigate stress and distortion.   Type of structure of neighbouring joints.   Freeness of joint to be able to expand.   Freeness of joint to be able to contract.   Rate of cooling.  (Any 3 x 1) (3) 9.6 Types of distortions: 9.6.1 Longitudinal distortion.  (1) 9.6.2 Angular distortion.  (1) 9.7 Effects of cooling rates:  Distortion   Mechanical properties   Internal stresses   Potential cracking  (Any 3 x 1) (3) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 20 DBE/November 2023 NSC – Marking Guideline QUESTION 10: MAINTENANCE (SPECIFIC) 10.1 Lubrication: It is the process or technique of using a lubricant  between two surfaces.  (2) 10.2 Overloading the machine: 10.2.1 Punch and shearing machine:  Dulling or breaking blades/punches.   Putting strain on the motor.   Putting strain on the drive mechanism.  Machine will stop working.   Machine will cut out.  (Any 1 x 1) (1) 10.2.2 Guillotine machine:  Damage to the blade.   Damage to the hydraulic system.   Damage to the electric motor.   Machine will stop working.   Machine will cut out.  (Any 1 x 1) (1) 10.3 Tagging plates: It has multiple holes so that more than one technician  can lock out the machine simultaneously.  (2) 10.4 Maintenance:  Promote cost saving.   Improves safety.   Increases equipment efficiency.   Fewer equipment failure.   Improves reliability of equipment.  (Any 1 x 1) (1) 10.5 Friction:  By reducing drill speed.   By reducing feed speed.   By applying lubricant / (cutting fluid).  Use sharp drill bit.   Use correct drill bit.  (Any 1 x 1) (1) [8] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 21 DBE/November 2023 NSC – Marking Guideline QUESTION 11: TERMINOLOGY (DEVELOPMENT) (SPECIFIC) 11.1 Square to square Hopper (off centre): 11.1.1 A–2:    A - 2  180  350  4002 2 2  32400  122500  160000  314900  561,16 mm  (4) 11.1.2 B–3:    B - 3 = 410 +150 + 4002 2 2 = 168100 + 22500 +160000 = 350600 = 592,11 mm  (4) 11.1.3 C–4:    C  4  3802  902  4002  144400  8100  160000  312500  559,02 mm  (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 22 DBE/November 2023 NSC – Marking Guideline 11.2 Square to round transformer: 11.2.1 True length 5–6: D 56   12   500  12  130,90 mm  (2) 11.2.2 True length 3–6: 3 D D 36   36   12 4 3    500   500   OR   12 4  392,70 mm   392,70 mm  (3) 11.2.3 True length B–6:    B  6  3002  502  4002  90000  2500  160000  252500  502,49 mm  (4) [21] TOTAL: 200 Copyright reserved