Mechanical Technology Grade 12 NSC November 2018 Memo (Eng)

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE GRADE 12 MECHANICAL TECHNOLOGY: WELDING AND METALWORK NOVEMBER 2018 MARKING GUIDELINES MARKS: 200 These marking guidelines consist of 19 pages and Annexure A. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 2 DBE/November 2018 NSC – Marking Guidelines QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC) 1.1 A (1) 1.2 C (1) 1.3 A (1) 1.4 B (1) 1.5 D (1) 1.6 A (1) TOTAL QUESTION 1: [6] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 3 DBE/November 2018 NSC – Marking Guidelines QUESTION 2: SAFETY (GENERIC) 2.1 Angle grinder: (Before using) • The safety guard must be in place before starting.  • Protective shields must be placed around the object being grinded to protect the people around.  • Use the correct grinding disc for the job.  • Make sure that there are no cracks in the disc before you start.  • Protective clothing and eye protection are essential.  • Check electrical outlets and cord/plugs for any damages.  • Ensure that lockable switch is disengaged.  • Ensure that the disc and the nut are well secured.  • Ensure that the removable handle is secured.  • Remove all flammable material from the area.  • Secure the work piece.  (Any 2 x 1) (2) 2.2 Welding goggles: • To protect your eyes against sparks  • To protect your eyes against heat  • To be able to see where to weld  • To protect your eyes from UV rays / bright light  • To protect your eyes from smoke  (Any 2 x 1) (2) 2.3 PPE for Hydraulic press: • Overall  • Safety shoes  • Safety goggle  • Leather gloves  • Leather apron  • Face shield  (Any 2 x 1) (2) 2.4 Workshop layouts: • Process layout  • Product layout  (2) 2.5 Employer’s responsibility regarding first-aid: • Provision of first-aid equipment  • First aid training  • First-aid services by qualified personnel  • Any first aid procedures  • Display first aid safety signs  • First aid personnel must be identified by means of arm bands or relevant personal signage  (Any 2 x 1) (2) TOTAL QUESTION 2: [10] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 4 DBE/November 2018 NSC – Marking Guidelines QUESTION 3: MATERIALS (GENERIC) 3.1 Bending test: • Ductility  • Malleability  • Brittleness  • Flexibility  (Any 1 x 2) (2) 3.2 Heat-treatment: 3.2.1 Annealing: • To relieve internal stresses  • To soften the steel  • To make the steel ductile  • To refine the grain structure of the steel  • To reduce the brittleness of the steel  (Any 2 x 1) (2) 3.2.2 Case hardening: • To produce a wear resistant surface  and it must be tough enough internally  at the core to withstand the applied loads. • Hard case  and tough core.  (Any 1 x 2) (2) 3.3 Tempering process: • To reduce  the brittleness  caused by the hardening process. • Relieve  strain  caused during hardening process. • Increase  the toughness  of the steel. (Any 1 x 2) (2) 3.4 Factors for heat-treatment processes: • Heating temperature / Carbon content  • Soaking (Time period at temperature) / Size of the work piece  • Cooling rate / Quenching rate  (3) 3.5 Hardening of steel: • Steel is heated to 30 – 50°C above the higher critical temperature. (AC 3 )  • It is then kept at that temperature to ensure (soaking) that the whole structure is Austenite.  • The steel is then rapidly cooled by quenching it in clean water, brine or oil.  (3) TOTAL QUESTION 3: [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 5 DBE/November 2018 NSC – Marking Guidelines QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC) 4.1 B (1) 4.2 A (1) 4.3 B (1) 4.4 B (1) 4.5 A (1) 4.6 B (1) 4.7 D (1) 4.8 D (1) 4.9 C (1) 4.10 C (1) 4.11 A (1) 4.12 D (1) 4.13 B (1) 4.14 B (1) TOTAL QUESTION 4: [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 6 DBE/November 2018 NSC – Marking Guidelines QUESTION 5: TERMINOLOGY (TEMPLATES) (SPECIFIC) 5.1 Template loft: The template loft is separated from the workshop because… • it is quieter.  • the lighting is better.  • all equipment is at hand.  • it is a permanent base.  • marking on the floor enhance accuracy.  (Any 2 x 1) (2) 5.2 Purpose of purlins: • The purlins support  the roof covering  • Stabilizes  the trusses.  (Any 1 x 2) (2) 5.3 A steel ring calculation: 5.3.1 Dimensions of the required material: Mean diameter = Outside diameter − plate thickness  = 880 − 50  = 830 mm  Mean circurmference π = × Mean diameter  π = × 830  = 2607,52mm  2608 mm of 50 x 50 mm  square steel bar is required to fabricate the ring. (7) 5.3.2 880  830    50 Mean diameter Material Outside diameter thickness (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 7 DBE/November 2018 NSC – Marking Guidelines 5.4 Resistance weld symbols: 5.4.1 Spot weld  (1) 5.4.2 Seam weld  (1) 5.5 Welding symbols: A. Tail  B. Weld symbol (Fillet weld)  C. Pitch of weld  D. Site weld  E. Arrow  F. Weld all round  (6) TOTAL QUESTION 5: [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 8 DBE/November 2018 NSC – Marking Guidelines QUESTION 6: TOOLS AND EQUIPMENT (SPECIFIC) 6.1. Working Principles: 6.1.1 Guillotine: • A bottom cutting blade is fixed horizontally.  • With a top cutting blade moving downwards.  • It is driven by an electric motor, flywheel, gearbox and axle  by eccentric motion / action / hydraulic action.  OR • It is activated manually by foot  with lever action.  (4) 6.1.2 Bending rolls: • A bending roll has two fixed rollers next to each other rotating in unison (Manually or Electrical motor).  • A third roller is adjustable, moving in between the two rollers.  • The third roller applies downward pressure onto the metal.  • That causes the metal to deflect and ultimately form the round shape desired.  (4) 6.2. Regulators on gas cylinders: Regulators reduce  the cylinder pressure  to operating or working pressure.  (3) 6.3 Press machine: • The press machine is used for installing  or removing  components on mechanical devices / machines.  • To press  profiles  onto material  (Any 1 x 3) (3) 6.4 MIGS/MAGS welding process: A – Weld pool / weld bead / molten metal  B – Electrode wire / electrode  C – Gas shroud / electrical contact / nozzle / contact tip  D – Shielding gas  (4) TOTAL QUESTION 6: [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 9 DBE/November 2018 NSC – Marking Guidelines QUESTION 7: FORCES (SPECIFIC) 7.1 Forces in members: SCALE: Vector diagram 1 mm = 5 N 200 N 300 N B  A F C E G 225 N D 275 N      MEMBER MAGNITUDE NATURE AE 260 N  STRUT  BF 135 N  STRUT  CG 317,5 N  STRUT  FG 27,5 N  STRUT  ED 130 N  TIE  EF 27,5 N  TIE  GD 160 N  TIE  (20) NOTE: Use a tolerance of 2 mm + and – on the vector diagram. = a tolerance of 10 N + and – on the answer. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 10 DBE/November 2018 NSC – Marking Guidelines 7.2 Bending moments: 8 kN 4 kN 6 kN A B C D E 2m 3m 3m 2m RL RR 7.2.1 Moments about RR   RL × 10 = (8 × 8 ) + (4 × 5 ) + (6 × 2) 96 RL =  10 RL = 9,6kN  Moments about RL   RR × 10 = (6 × 8 ) + (4 × 5 ) + (8 × 2) 84 RR =  10 RR = 8,4kN  (8) 7.2.2 Bending moments at point A, B, C, D and E: Scale 2 mm = 1 kN.m Moment at A = 0 kN.m  B = RL × 2 = 19,2 kN.m  C = (RL × 5 ) − (8 × 3 ) = 24 kN.m  D = (RL × 8 ) − (8 × 6 ) − (4 × 3 ) = 16,8 kN.m  E = (RL × 10 ) − (8 × 8 ) − (4 × 5 ) − (6 × 2) = 0 kN.m  (5) 7.2.3 (5) NOTE: Use a tolerance of 2 mm + and – on the bending moment diagram. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 11 DBE/November 2018 NSC – Marking Guidelines 7.3 Stress and strain: π 2 A=d  4 π 2 A = (0,02)  4 A = 0,314 × 10 −3 m2  Load Stress = Area  Load = Stress × Area   ( ) ( Load = 80 × 106 × 0,314 × 10 −3 ) Load = 25,133 kN  (7) TOTAL QUESTION 7: [45] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 12 DBE/November 2018 NSC – Marking Guidelines QUESTION 8: JOINING METHODS (WELD INSPECTION) (SPECIFIC) 8.1 Factors to be observed during 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.  • The distance of the nozzle from the parent metal.  (Any 2 x 1) (2) 8.2 Abbreviation 'HAZ': Heat Affected Zone  (1) 8.3 Causes of weld defects: 8.3.1 Spatter: • Disturbance in the molten weld pool.  • Too low welding voltages.  • Too high welding current / amps.  • Inadequate shielding gas flow.  • Too fast travel speed  • Arc length too long  • Wet electrode  • Wrong polarity  • Arc length too short  • Wrong included electrode angle  • Wrong electrode used  • Arc blow  (Any 2 x 1) (2) 8.3.2 Undercutting: • Too fast travel speed  • Rapid solidification  • Too low arc voltage  • Arc length too long  • Excessive welding current  • Too slow movement over weld  • Current / amps too high  • Electrode too big  • Wrong electrode  • Wrong included electrode angle  • Excessive weaving  • Wrong joint design  (Any 2 x 1) (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 13 DBE/November 2018 NSC – Marking Guidelines 8.3.3 Incomplete penetration: • Welding current too low  • Too fast travel speed  • Incorrect electrode angle  • Poor edge preperation  • Insufficient root gap  • Electrode too big  • Wrong electrode  • No pre-heating done  • Wrong shielding gas used  • Too long arc  (Any 2 x 1) (2) 8.4 Types of cracks: 8.4.1 Transverse cracks: • Pre-heating the base metal  • Using lower strength consumables / welding rod  • Slow cooling after welding  • Use clamping device.  • Weld toward the unrestrained side of the weld.  (Any 2 x 1) (2) 8.4.2 Centreline cracks: • Ensure that width-to-depth ratio is 1:1.  • Decrease the current to decrease excess penetration.  • Decreasing welding voltage setting or slowing travel speed to achieve a flat to convex weld surface.  • Use clamping device.  (Any 2 x 1) (2) 8.5 Differences between non-destructive and destructive tests: • Non-destructive test does not destroy the welded joint.  • Destructive test destroys the welded joint.  (2) 8.6 Ultrasonic test: • No defects will occurs during a ultrasonic test  • Detect internal  flaws as well as surface flaws.  • Porosity  • Slag inclusions  • Cracks  (Any 1 x 2) (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 14 DBE/November 2018 NSC – Marking Guidelines 8.7 Nick break test for internal defects: • Slag inclusion  • Porosity  • Lack of fusing  • Oxidised metal  • Burned metal  (Any 2 x 1) (2) 8.8 Machinability test: • To determine the hardness  and strength of the welded joint. • To determine  the machinability.  (Any 1 x 2) (2) 8.9 Visual requirements of welds: • Shape of the profile  • Uniformity of the surface  • Overlap  • Free from any external defects  • Penetration bead  • Root groove  (Any 2 x 1) (2) TOTAL QUESTION 8: [23] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 15 DBE/November 2018 NSC – Marking Guidelines QUESTION 9: JOINING METHODS (STRESSES AND DISTORTION) (SPECIFIC) 9.1 Residual stress: Residual stresses are stresses that exist  in a metal after cooling / welding.  (2) 9.2 Factors affecting grain size: • The amount of cold work.  • The temperature and time of annealing process.  • The composition and constitution.  • The recrystallisation temperature of cold worked metal.  • The melting point.  (Any 2 x 1) (2) 9.3 Quenching medias: • Oil  • Water  • Sand  • Air  • Brine / Salt water  • Lime  • Liquid salts  • Molten lead  • Ash  (Any 2 x 1) (2) 9.4 Weld distortion: • Distortion in a weld results from the uneven expansion and contraction (warping)  of the weld metal  and adjacent base metal  during the heating and cooling cycle  of the welding process. (4) 9.5 Factors that affect 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 this 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.  (Any 2 x 2) (4) 9.6 Result when metal is cooled rapidly: • Rapid cooling of metal results in large temperature differences  between the internal and external areas  of the metal that set up stresses,  which cause cracks  on the surface. • It will harden  and the grain structure  will change.  (Any 1 x 4) (4) TOTAL QUESTION 9: [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 16 DBE/November 2018 NSC – Marking Guidelines QUESTION 10: MAINTENANCE (SPECIFIC) 10.1 Reasons maintenance: • Promote cost saving  • Improves safety  • Increases equipment efficiency  • Fewer equipment failure  • Improves reliability of equipment  (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 Reasons for service records: • Assist in the monitoring of the condition of the machines.  • Assist in upholding warrantees.  • Assist in keeping a history of maintenance and repairs.  (Any 2 x 1) (2) 10.4 Methods of reducing friction: • By reducing both drill speed and feed speed.  • By applying lubrication. (cutting fluid)  • Use the correct drill bit  • Drill a pilot hole  (Any 2 x 1) (2) TOTAL QUESTION 10: [8] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 17 DBE/November 2018 NSC – Marking Guidelines QUESTION 11: TERMINOLOGY (DEVELOPMENT) (SPECIFIC) 11.1 Use of transformers: Transformers are used to connect  ducting sections of dissimilar  shapes to each other.  (3) 11.2 On-centre hopper: (1) Off-centre hopper: (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork 18 DBE/November 2018 NSC – Marking Guidelines 11.3 Truncated cone: 11.3.1 Base circumference: Circumferenceπ = × Base diameter  π = ×1400  = 4398,23 mm  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork DBE/November 2018 NSC – Marking Guidelines 11.3.2 Main radius (AC): Triangles ABC and CED has the same shape: AC : DC = BC : EC AC BC Thus =  DC EC BC × DC From where AC =  EC Base Dia − 800 and CE =  2 1400 − 800 =  2 CE = 300 mm  For : DC DC2 = DE2 + CE2  DC = 12002 + 3002  DC = 1236,93 mm  rounded = 1237 mm BC × DC AC = EC 700 × 1237 =  300 = 2886,17 mm  rounded = 2886 mm (10) 11.3.3 Small radius (AD): AD = AC − DC  = 2886 − 1237  AD = 1649 mm (1649,24 mm)  (3) TOTAL QUESTION 11: [21] GRAND TOTAL: 200 Copyright reserved

Downloaded from hlayiso.com Mechanical Technology: Welding and Metalwork DBE/November 2018 NSC – Marking Guidelines Annexure A Question 7.1 The CM need to redraw to check the scale and to photocopy it to a transparency. 31.75 mm 28.87 mm 60.00° 40.00 mm 5.77 mm 55.00 mm 60.00 mm 63.51 mm 60.00° Question 7.2.3 48.00 mm 38.40 mm 33.60 mm 30.00 mm Copyright reserved