Mechanical Technology Grade 12 NSC November 2021 Memo (Eng)

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE GRADE 12 MECHANICAL TECHNOLOGY: WELDING AND METALWORK NOVEMBER 2021 MARKING GUIDELINES MARKS: 200 These marking guidelines consist of 23 pages. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 2 DBE/November 2021 NSC – Marking Guidelines QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC) 1.1 B (1) 1.2 A (1) 1.3 D (1) 1.4 A/C (1) 1.5 A (1) 1.6 C (1) [6] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 3 DBE/November 2021 NSC – Marking Guidelines QUESTION 2: SAFETY (GENERIC) 2.1 First-aid applications to an open wound:  Use surgical gloves.   Do not remove anything that is stuck to the wound.   Never use sticky plaster on the wound.   Cover the wound with a clean, lint-free cloth.   Avoid using any oily substances or lotions on wounds.   If necessary, cool wounds with cold water.   Apply pressure to prevent blood loss if necessary.   Avoid contact with blood from patient.   If the wound is on your arm, raise the arm above your head to stop the bleeding.  (Any 2 x 1) (2) 2.2 Surface grinder: (Already switched on)  Never leave the grinder unattended.   Switch off the machine when leaving.   Don’t try to stop revolving emery wheel with your hand.   Don’t adjust the machine while working.   Don’t open any guard while the machine is on.   Do not force the grinding wheel on to the work piece.   Approach the work piece slowly and evenly.   Don’t clean the machine while working.   Do not put hands near the work piece when grinder is in motion.   Don’t clean or adjust the machine while working.  Check for oil on the floor while working (spilling of cutting fluid on floor while working)   Check that the grinding wheel is running evenly.  (Any 2 x 1) (2) 2.3 Gauges calibrated:  To ensure accurate readings.   To prevent overloading.  (Any 1 x 1) (1) 2.4 Finger protectors’ hazards on power driven guillotines:  The finger protector prevents the hazards of getting the fingers cut by the blades.   To be crushed by the hold-downs.  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 4 DBE/November 2021 NSC – Marking Guidelines 2.5 Welding or flame cutting operation safety:  An operator has been instructed on how to use the equipment safely.   A workplace is effectively partitioned off.   An operator uses protective equipment.   Ensure that all equipment is in safe working condition.   Ensure that here are no flammable materials around the welding area.   Weld area must be well ventilated.   Fire extinguisher must be in close proximity.  (Any 2 x 1) (2) 2.6 Workshop layout: Product layout.  (1) [10] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 5 DBE/November 2021 NSC – Marking Guidelines QUESTION 3: MATERIALS (GENERIC) 3.1 File test: 3.1.1 Difficult  (1) 3.1.2 Easy  (1) 3.1.3 Difficult  (1) 3.2 Heat treatment: A. – Grain growth.  B. – Recrystallisation.  C. – Recovery.  (3) 3.3 Bending test:  Bend the test piece through a specific angle or around a mandrel or bar,  having a defined radius,  until a rupture in the metal occurs.  Place the material in a vice and bend it  then observe  the ductility of the material.  (Any 1 x 3) (3) 3.4 Purpose of case hardening: Creates a hard surface  with a tough core.  (2) 3.5 Quenching media for hardening:  Water   Brine (saltwater)   Oil   Soluble oil and water   Nitrogen air-infused air  (Any 3 x 1) (3) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 6 DBE/November 2021 NSC – Marking Guidelines QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC) 4.1 B (1) 4.2 B (1) 4.3 D (1) 4.4 C (1) 4.5 D (1) 4.6 A (1) 4.7 A (1) 4.8 B (1) 4.9 C (1) 4.10 B (1) 4.11 C (1) 4.12 B (1) 4.13 A (1) 4.14 D (1) [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 7 DBE/November 2021 NSC – Marking Guidelines QUESTION 5: TERMINOLOGY (TEMPLATES) (SPECIFIC) 5.1 Dimensions of the material: 5.1.1 Mean Ø  Outside Ø  Plate Thickness  960  60   900 mm  (2) 5.1.2 Mean circumference  π  Mean Ø  π  900   2827,43 mm  Round off to 2827 mm  (3) 5.2 Welding symbols: 5.2.1  (2) 5.2.2  (2) 5.2.3  (2) 5.2.4  (2) 5.2.5  (2) 5.3 Templates: 5.3.1 Flange template  (1) 5.3.2 Strip template  (1) 5.3.3 Web template  (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 8 DBE/November 2021 NSC – Marking Guidelines 5.4 Hand tools: (Due to the large number of alternatives, marker discretion must be used - discuss with IM).  Hand saws   Chisels   Plane   Handdrill and drill bits   Steel measuring tape   Straight edge   Compass   Trammel pins   Carpenter’s square   Protractor   Chalk line   Steel rule   Hammers   Centre punch   Callipers   Scribe   Combination square   Spirit level   Trammel  (Any 3 x 1) (3) 5.5 Template loft machines: (Due to the large number of alternatives, marker discretion must be used - discuss with IM).  Circular saw   Planer   Drilling machine   Jig saw   Sanding machine   Shears for cutting cardboard   Welding machine   Angle grinder   Bench grinder   Guillotine   Cut–off power saw  (Any 2 x 1) (2) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 9 DBE/November 2021 NSC – Marking Guidelines QUESTION 6: TOOLS AND EQUIPMENT (SPECIFIC) 6.1 Operating principles of a resistance welding machine:  Current flows through a resistance to fuse plates together.   Two copper electrodes are pressed against the plates.   Heavy current is passed between the electrodes.   High resistance causes intense heat at the point.   The two plates melt and fuse together, forming a weld nugget or spot weld.  (5) 6.2 Arc welding: 6.2.1 A. Arc welding machine / Power source / invertor.  B. Earth clamp / “skelm”  C. Electrode / Rod / welding rod  D. Electrode holder  (4) 6.2.2  Holds the electrode.   Insulate the person welding   Provide current to the electrode   Used with electrode to weld  (Any 1 x 1) (1) 6.3 Cutting of threads:  Secure the die in die wrench/stock  and set die square to the shaft to be cut.   Rotate the die through half a turn in a clockwise direction  to cut the thread and then turn back a quarter of a turn  to break off waste.  Continue process until the die has reached the required length of thread  and adjust the centre and side screws until desired thread fit is achieved.  (6) 6.4 Advantages of using a punch machine:  Can punch holes faster.   Punch various hole profiles   Less effort is needed  (Any 1 x 1) (1) Pyramid rollers  Rolling sheet metal.  6.5  Used to roll round bars  (Any 1 x 1) (1) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 10 DBE/November 2021 NSC – Marking Guidelines QUESTION 7: FORCES (SPECIFIC) 7.1 Beams: 7.1.1 Calculating reactions: Taking moments about RL:    RR  10  (80  3 )  (60  5 )  (100  7 )  240  300  700  1240 RR  10  124 N  Taking moments about RR:    RL  10  (100  3 )  (60  5 )  (80  7 )  300  300  560 1160 RL  10 (8)  116 N  7.1.2 Calculating bending moments: Bending moments at B, C and D: BMB (116  3 )  348Nm  BMC (116  5 ) (80  2 )  420Nm  BMD (116  7 ) (80  4 ) (60  2 )  372Nm  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 11 DBE/November 2021 NSC – Marking Guidelines 7.1. 3 Bending moment diagram: 80 N 60 N 100 N A B C D  E 3m 2m 2m 3m RL = 116 N RR = 124 N  420 Nm   C 372 Nm 348 Nm D B    0 0 A E (7) NOTE: Draw the bending moment diagram to scale for marking purposes. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 12 DBE/November 2021 NSC – Marking Guidelines 7.2 Stress and Strain: 7.2.1 Diameter of a bar: F σ  A F  A σ 40  103   20  106  2  10  3 m2  πD 2 A 4 4A  D    4 2  10  3    0,05 046265 m  OR  50,46 mm  (6) 7.2.2 Strain: σ ε  E 20  106 ε   90  109  0,22  10 3  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 13 DBE/November 2021 NSC – Marking Guidelines 7.2.3 Change in length: L ε  OL L  ε  OL     0,22  10 3  2    0,44  10 3 m  0,44 mm  (3) 7.3 Stress and strain diagram: A: Limit of proportionality  B: Elastic limit  C: Yield point  D: Maximum stress  E: Break stress  (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 14 DBE/November 2021 NSC – Marking Guidelines 7.4 Simple frame: 7.4.1 Vector/Force diagram: 500 kN A B D 30° 60° C 10 000 125 kN 375 kN a    d c    b (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 15 DBE/November 2021 NSC – Marking Guidelines 7.4.2 Magnitude and nature of force: Member Force Nature AD 250 kN  Strut  BD 433 kN  Strut  CD 216 kN  Tie  (6) [45] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 16 DBE/November 2021 NSC – Marking Guidelines QUESTION 8: JOINING METHODS (INSPECTION OF WELDS) (SPECIFIC) 8.1 Arc welding aspects:  Rate of rod burning and the progress of the weld   Amount of penetration and fusion.   Observe for welding defects while welding   The sound of the arc indicating correct current and voltage for the particular weld.   Angle of electrode.   Arc length.   Size of molten pool while welding  (Any 3 x 1) (3) 8.2 Centreline cracks:  Aiming at width to depth ratio of 1:1.   Decreasing the current to prevent excess penetration.   Decreasing welding voltage   Slowing travel speed to achieve a flat to convex weld surface.   Use clamping device.   Pre – Heating   Use of correct electrode  (Any 2 x 1) (2) 8.3 Welding defects: 8.3.1 Lack of fusion:  Travel speed is too slow.   Wide weld joint.   Weld current too low.   Too big weaving action.   Included angle not correct.   Contaminated parent metal surface   Weld metal not permitted to roll in front of arc.   Arc not kept on leading edge of molten pool.   Travel speed too fast.   Excessive mill scale (iron oxide)  (Any 2 x 1) (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 17 DBE/November 2021 NSC – Marking Guidelines 8.3.2 Porosity:  Contaminated weld surface.   Wet or dirty electrodes.   Shielding gas supply is interrupted.   Welding in windy conditions.  (Any 2 x 1) (2) 8.3.3 Incomplete penetration:  Welding current too low.   Welding speed too fast.   Incorrect electrode angle.   Poor joint preparation.   Insufficient root gap.   Electrode too big.   Too long arc.   Contaminated weld surface.  (Any 2 x 1) (2) 8.4 Setting oxy-acetylene torch flame to a neutral flame:  Open acetylene torch valve ¼ turns or less and ignite.   Adjust the acetylene torch valve further until the black smoke disappears.   Open oxygen torch valve until the flame is no longer burning yellow.   Inner cone of the flame must be rounded.  (Any 3 x 1) (3) 8.5 Guided bend test:  Specimen is placed across the supports of the die.   Apply force to the specimen to bend into shape of the die.   Determine the percentage of elongation of the weld metal.  (3) 8.6 Free bend test:  Determine the ductility of the weld.   Determine the ductility of the heat – affected area adjacent to the weld.   Determine the percentage of elongation  (Any 2 x 1) (2) 8.7 Types of dye:  Type A: Fluorescent that emits visible light when viewed using a Black light.   Type B: Brightly coloured liquid dyes that can be inspected in regular light.  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 18 DBE/November 2021 NSC – Marking Guidelines 8.8 Nick-break test:  Determines internal  quality of the weld metal.   Reveals internal defects  such as slag inclusions, porosity and lack of fusion.  (Any 1 x 2) (2) [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 19 DBE/November 2021 NSC – Marking Guidelines QUESTION 9: JOINING METHODS (STRESS AND DISTORTION) (SPECIFIC) 9.1 Causes of residual stress in welds:  Heat present in the weld.   Qualities of parent metal, filler rod or 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 and contract.   Rate of cooling.   Stresses already present in the parent metal.  (Any 2 x 1) (2) 9.2 Factors of cooling rate:  Size of work piece.   Weld thickness.   Thermal conductive properties of parent metal.  (Any 3 x 1) (3) 9.3 Effect of cold working:  The effect of cold working is to break down the crystal structure  elongating the grains.   An elongated and distorted crystal structure of this kind gives the metal greater hardness  and tensile strength.   Reduces ductility.   Referred to as work hardening.  (4) 9.4 Effects of welding speed on distortion:  Increase in welding speed increases distortion due to larger flame in oxy-acetylene welding.   Larger diameter electrode requires increased current causing more localised heat.   Causing more residual stress.  Causing more distortion.  (Any 3 x 1) (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 20 DBE/November 2021 NSC – Marking Guidelines 9.5 Quenching media:  Water   Oil   Brine   Liquid salts   Sand   Air   Ash   Lime   Molten lead   Nitrogen air-infused air  (Any 3 x 1) (3) 9.6 Reducing welding distortion:  Do not over-weld.   Intermittent welding.   Place welds near the neutral axis.   Use a few passes as possible.   Use back step welding.   Anticipate the shrinkage forces.   Use clamps, jigs and fixtures.   Use strongbacks.   Heating metal before welding. (pre- heating)   Slowing the cooling rate  (Any 3 x 1) (3) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 21 DBE/November 2021 NSC – Marking Guidelines QUESTION 10: MAINTENANCE (SPECIFIC) 10.1 Locking out of machine:  Isolation switches must be switched off.   The only key to the lock is in possession of the person carrying out the maintenance / Each maintenance person must have own lock.  (2) 10.2 Tagging plates: More than one technician can lock out machine simultaneously.  (1) 10.3 Minor service for a power-driven guillotine: The minor service is designed to minimise  major mechanical and electrical failures.  (2) 10.4 Cutting fluid:  Keep the blade cool.  Keep the work piece cool   Prolong the life span of the blade   Washes cuttings away   Improves cutting efficiency   Reduces friction during cutting process.   Better finish given to workpiece.   Also prevents further corrosion.  (Any 2 x 1) (2) 10.5 Overloading a rolling machine:  Limit the life span of components   Can result in costly damage   Damage to bearings/bushes   Damage to gearbox   Damage to motor  (Any 1 x 1) (1) [8] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 22 DBE/November 2021 NSC – Marking Guidelines QUESTION 11: TERMINOLOGY (DEVELOPMENTS) (SPECIFIC) 11.1 True length of AC: AC 2  AB 2  BC 2 90  50 but BC   2 40  2  20 mm  AC 2  AB 2  BC 2  502  202  AC  2500  400   53,85 mm   54 mm  (6) 11.2 Development: Square/rectangle  to round  transformer / transition piece / on centre.  (3) 11.3 Square to rectangle on centre hopper: 11.3.1 True length of A-1:    A  1  200  1302  5002 2  40000  16900  250000  306900  553,99   554 mm (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 23 DBE/November 2021 NSC – Marking Guidelines 11.3.2 True length of C-2:    C  2  470  200  5002 2 2  220900  40000  250000  510900  714,77  715 mm  (4) 11.4 Hoppers: 11.4.1 Square to rectangle  hopper off centre  (2) 11.4.2 Square to square  hopper on centre  (2) [21] TOTAL: 200 Copyright reserved