Mechanical Technology Grade 12 NSC November 2022 Memo (Eng)

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE GRADE 12 MECHANICAL TECHNOLOGY: WELDING AND METALWORK NOVEMBER 2022 MARKING GUIDELINES MARKS: 200 These marking guidelines consist of 20 pages. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 2 DBE/November 2022 NSC – Marking Guidelines QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC) 1.1 B (1) 1.2 B (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 2022 NSC – Marking Guidelines QUESTION 2: SAFETY (GENERIC) 2.1 Vital functions:  Breathing   Heart rate / pulse   State of consciousness  (Any 2 x 1) (2) 2.2 Safety glasses during grinding:  To prevent any injuries to the operator's eyes.   To protect eyes from sparks and debris.   To prevent blindness due to injury.  (Any 1 x 1) (1) 2.3 Type of guards:  Fixed guard   Automatic sweep-away   Self-adjusting / automatic guard   Electronic presence sensing device   Two-hand control device.  (Any 2 x 1) (2) 2.4 Precautions before gas welding operations can be undertaken:  An operator has been instructed on how to use the equipment safely.   A workplace is effectively partitioned off.   An operator uses protective equipment (PPE).   Ensure that fire equipment is at hand.   Ensure that the equipment is in a safe working condition.   Ensure the gas equipment is set-up correctly.   Ensure the area is well ventilated.   Ensure that the working area is safe.  (Any 3 x 1) (3) 2.5 TWO disadvantages of the product layout:  Lack of flexibility.   Optimum use of equipment is not possible.  (2) [10] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 4 DBE/November 2022 NSC – Marking Guidelines QUESTION 3: MATERIALS (GENERIC) 3.1 THREE properties:  Toughness   Hardness / Wear resistance   Softness   Case hardness   Ductility   Malleability   Elasticity   Brittleness   Strength  (Any 3 x 1) (3) 3.2 Heat treatment processes: 3.2.1 Tempering:  It consists of heating the hardened steel  to a temperature below its critical temperature (colour chart).   Soaking it at this temperature for a period of time,   Quenching/cooling it rapidly in water, brine or oil.  (4) 3.2.2 Hardening:  The steel is heated slightly higher than the upper critical temperature.   The steel is soaked at that temperature for the required time.   The steel is then rapidly cooled by quenching in water, brine or oil.  (3) 3.3 Examples of case-hardening:  Bearing cases   Bearing ball   Bearing needles   Crankshafts   Gears   Camshafts   Cylinder sleeves   Hammer head   Jack Hammer drill bits  (Any 2 x 1) (2) 3.4 Why steels are cooled down in still air away from draughts: This prevents sudden cooling of localised spots,  which might cause distortion/cracks.  (2) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 5 DBE/November 2022 NSC – Marking Guidelines QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC) 4.1 A (1) 4.2 C (1) 4.3 B (1) 4.4 B (1) 4.5 A (1) 4.6 C (1) 4.7 D (1) 4.8 B (1) 4.9 D (1) 4.10 A (1) 4.11 C (1) 4.12 C (1) 4.13 D (1) 4.14 B (1) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 6 DBE/November 2022 NSC – Marking Guidelines QUESTION 5: TERMINOLOGY(TEMPLATES) (SPECIFIC) 5.1 Steel ring calculations: 5.1.1 Mean Ø = Outside Ø - plate thickness = 920 - 45  = 875 mm  (2) 5.1.2 Mean circumference =   Mean Ø =  × 875  = 2748,89  = 2749 mm  (3) 5.1.3 Steel ring drawing: MEAN DIAMETER OUTSIDE DIAMETER 875 mm 920 mm DRAWING    THICKNESS  45 mm (4) 5.2 Weld symbols: 5.2.1 Weld all around  (1) 5.2.2 Flush  (1) 5.2.3 Convex  (1) 5.2.4 Grind  (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 7 DBE/November 2022 NSC – Marking Guidelines 5.3 Template makers tools:  Hand saws   Chisels   Plane   Hand drill and drill bits   Steel tape   Straight edge   Compass   Trammel pins   Carpenter's square   Protractor   Chalk line   Or any appropriate hand tool  (Any 2 x 1) (2) 5.4 Fillet weld on T joint:    10  40 - 90 ARC     If the T-joint was not  indicated, then (8) allocate mark here [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 8 DBE/November 2022 NSC – Marking Guidelines QUESTION 6: TOOLS AND EQUIPMENT (SPECIFIC) 6.1 Punch and shear machine:  Cutting steel profiles.   Punching holes in a steel plate.  (2) 6.2 Inert gas:  Stabilizers arc roots on the material surface.   Ensures a smooth transfer of molten droplets from the wire to the weld pool.   Prevents atmospheric contamination of the weld pool.   Prevents defects (Any other applicable defect).  (Any 2 x 1) (2) 6.3 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 factor required to operate MIG/MAGS welding torch.   Can weld in any position.   The process is easily automated.   No fluxes required in most cases.  (Any 2 x 1) (2) 6.4 Bending test:  To determine the materials ductility.   To determine the materials bend strength.   To determine the materials resistance to fracture.   To identify a weak point on the beam.  (Any 2 x 1) (2) 6.5 Power-driven guillotine:  A bottom cutting blade is fixed horizontally.   A top cutting blade moves downwards.   It is driven by an electric motor activated by a foot pedal.   It is driven by a flywheel, gearbox and axle.   It lowers the blade by eccentric motion or action.  (Any 4 x 1) (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 9 DBE/November 2022 NSC – Marking Guidelines 6.6 Hydraulic press labels: A – Adjustment hole  B – Pressure gauge / Gauge  C – Platform / Rest / Table  D – Cylinder / Piston / Plunger  E – Handle / Lever  F – Base / Stand / Legs  (6) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 10 DBE/November 2022 NSC – Marking Guidelines QUESTION 7: FORCES (SPECIFIC) 7.1 Simple Frames: 7.1.1 Space diagram: 200 N  B A  D 60o 30o C  10 m 150 N 50 N (3) 7.1.2 Force diagram: a   d  c  Note to marker: Marker must redraw the space and force diagrams according b to given scales for marking purposes. (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 11 DBE/November 2022 NSC – Marking Guidelines 7.1.3 Magnitude: Member Magnitude (N) AD 174  Note to marker: BD 100  Tolerance ± 2 mm CD 86  (3) 7.1.4 Nature of members: Member Nature AD Strut  BD Strut  CD Tie  (3) 7.2 Shear forces and bending moments: 7.2.1 The magnitude of the UDL/Point Load: UDL  6 N/m  5 m  30 N  (1) 7.2.2 The magnitude RL:    RL  10  40  2  30  4,5   20  9   80  135  180 395 RL   10  39,5 N  (5) 7.2.3 The magnitude RR:    RR  10   20  1   30  5,5    40  8   20  165  320 505  RR  10  50,5 N  (5) 7.2.4 The shear force at points A, UDL and B: SFA  39,5  20  SFA  39,5  20   19,5 N   19,5 N  SFUDL  39,5  20  30  SFUDL  19,5  30  OR  10,5 N   10,5 N  SFB  39,5  20  30  40  SFB  10,5  40   50,5 N   50,5 N  (6) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 12 DBE/November 2022 NSC – Marking Guidelines 7.2.5 Shear force moment diagram: 20 N 40 N 6N/m A B  39,5N   19,5N +  0 0  -10,5N -50,5N  (7) Note to marker: Marker must redraw the shear force diagram according to given scales for marking purposes.  ONLY if ALL components indicated are correct but incorrect scale used, then a 2-mark penalty is applied for incorrect scale.  ONLY if the diagram is correct according to scale but no values are indicated, then a 2-mark penalty is applied. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 13 DBE/November 2022 NSC – Marking Guidelines 7.3 Stress: 7.3.1 Maximum stress in MPa: Load Stress  Area 45000   0,8  10 5  56,25  10 8 Pa  5625 MPa  (2) 7.3.2 Safe working stress MPa: Maximum Stress Safety factor  Safe working Stress Maximum Stress Safe working stress   Safety factor 56,25  108 Pa   4  14,06  108 Pa  1406,25 MPa  (3) 7.3.3 Diameter: π  d2 Area  4 Area  4  d2  π 0,8  10 5  4 d  π  3,191 10 3 m d  3,19 mm  (3) [45] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 14 DBE/November 2022 NSC – Marking Guidelines QUESTION 8: JOINING METHODS (INSPECTION OF WELD) (SPECIFIC) 8.1 Arc welding process:  Rate of electrode burning.   Progress of the weld / weld speed.   Amount of penetration and fusion (melting).   Arc length.   The way the weld metal is flowing (no slag inclusion).   The sound of the arc, indicating correct current and voltage for the particular weld.   Electrode angle.  (Any 3 x 1) (3) 8.2 Oxy-acetylene welding:  Correct flame for the work on hand.   Correct angle of welding torch and welding rod.   Depth penetration and amount of fusion.   The rate of progress along the joint. (Any 2 x 1) (2) 8.3 Welding defects: 8.3.1 Undercut.  (1) 8.3.2 Incomplete penetration.  (1) 8.4 Welding defects: 8.4.1 Welding spatter:  Use correct welding voltage.   Set correct welding current.   Adequate shielding gas.   Use correct arc length.   Use anti spatter spray.   Use correct electrode angle.   Use correct welding speed.   Use correct polarity.   Use dry electrodes   Check weld ability of base metal/Carbon content.  (Any 2 x 1) (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 15 DBE/November 2022 NSC – Marking Guidelines 8.4.2 Porosity:  Avoid rust   Cleaning the welding surface.   Ensure that supply of shielding gas is not interrupted.   Avoid welding in windy conditions.   Use dry electrodes.   Lower the welding temperature   Ensure good weld ability of base metal  (Any 2 x 1) (2) 8.5 Welding defect: 8.5.1 Nick break test:  Slag inclusion   Porosity   Lack of fusion   Oxidised / burnt metal  (Any 2 x 1) (2) 8.5.2 Bend test:  Lack of fusion   Cracks   Incomplete penetration  (Any 2 x 1) (2) 8.6 Liquid dye penetrant:  Clean the surface to be tested.   Spray the liquid dye penetrant onto the surface.   Allow liquid dye to penetrate.   Remove excess dye with a cleaner / water.   Spray a developer onto the surface to bring out the colour / Using a UV light to show defects.   Observe surface for defects.  (6) 8.7 Ultrasonic test:  Internal flaws   External flaws  OR  Slag inclusion   Undercut   Porosity   Incomplete penetration   Cracks   Lack of fusion  (Any 2 x 1) (2) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 16 DBE/November 2022 NSC – Marking Guidelines QUESTION 9: JOINING METHODS (STRESSES AND DISTORTION) (SPECIFIC) 9.1 Electrode size:  The larger/thicker the electrode diameter  the higher the welding temperature,  the greater the potential to cause deformation.   The smaller/thinner the electrode diameter  the lower the welding temperature,  the lesser the potential to cause deformation.  (Any 1 x 3) (3) 9.2 Methods of reducing distortion:  Do not over weld   Use intermittent welding   Place welds near the neutral axis   Use as few passes as possible   Use backstep welding   Anticipate the shrinkage forces   Plan the welding sequence   Use strongbacks   Use clamps, jigs and fixtures   Pre-heating the workpiece   Tack welding   Allow slow cooling after welding.  (Any 2 x 1) (2) 9.3 Disadvantages:  Restraining force provided by clamps, fixtures and jigs increases internal stresses in the welded joint.   Increases the residual stress because the welded joint is not allowed to expand or contract.  The metals movement is severely restricted and result in increased stress. (Any 2 x 1) (2) 9.4 Elastic deformation: Elastic deformation occurs when the joint recovers  to its original position once the stress have been removed.  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 17 DBE/November 2022 NSC – Marking Guidelines 9.5 Factors responsible for setting up residual stress:  Heat present in the weld.   Qualities/type of parent metal.   Qualities/type of filler rods.   Qualities/type of electrode.   Shape and size of weld.   Number of successive weld runs.   Comparative weight of weld metal and parent metal.   Type of welding joint used.   Welding method used to mitigate stress and distortion.   Type of structure of adjacent joints.   Freeness of joint to be able to expand and contract.   Rate of cooling.   Stresses already present in the parent metal.  (Any 3 x 1) (3) 9.6 Iron carbon diagram: A – Ferrite  B – Ferrite + Pearlite  C – Pearlite  D – Pearlite + Cementite  E – Austenite + Ferrite  F – Austenite  (6) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 18 DBE/November 2022 NSC – Marking Guidelines QUESTION 10: MAINTENANCE (SPECIFIC) 10.1 Malfunctions in machines:  Seized bearings and bushes.   Excessive worn journals.   Excessive rust.  (Any 2 x 1) (2) 10.2 Pedestal drilling machine:  Visual checks of electrical wiring, switches, etc.   Verify that all guards are secure and function correctly.   Lubricate moving parts.   Use moisture-penetrating oil spray to prevent rust.   Check for availability of specific tools.   Check the run-out of the spindle.   Inspect drive belts for wear.   Ensure the drive belt is correctly tensioned.   Check the condition of the rack and pinion mechanisms.   Ensure cuttings are removed.   Inspect the Morse taper sleeves for burrs/scratches.   Machine is properly secured to the floor.  (Any 2 x 1) (2) 10.3 Service records:  Assist in the monitoring of the condition of the machines.   Assist in upholding warranties.   Assist in keeping a history of maintenance and repairs.  (Any 2 x 1) (2) 10.4 Major and Minor service: Major service allows for on-going service procedures that are designed to maintain machines and equipment in premium working condition.  Minor service is designed to minimize major mechanical and electrical failures, by employing the principle of preventative maintenance.  (2) [8] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 19 DBE/November 2022 NSC – Marking Guidelines QUESTION 11: TERMINOLOGY (DEVELOPMENT) (SPECIFIC) 11.1 Uses of hoppers:  Storage of loose materials.   Ventilation ducting.   Gravity flow hoppers.  (Any 2 x 1) (2) 11.2 Hopper: 11.2.1 Square  to square  hopper. (2) 11.2.2 True length: (a) A–2:    A  2  6002  2002  6002  360000  40000  360000  760000  871,78 mm  (4) (b) A–X:    A  X  200  400  6002 2 2  40000  160000  36000  560000  748,33 mm (4) (c) X–Y:   X  Y  200  6002 2  40000  360000  400000  632,46 mm (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 20 DBE/November 2022 NSC – Marking Guidelines 11.3 Cone frustum: 11.3.1 True length 1–2. πd 1 2   12 π  300   12  78,54 mm  (3) 11.3.2 True length A–B. π D A B  12 π  600  12  157,08 mm (3) [21] TOTAL: 200 Copyright reserved