Mechanical Technology Grade 12 NSC November 2018 Memo (Eng)

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE GRADE 12 MECHANICAL TECHNOLOGY: FITTING AND MACHINING NOVEMBER 2018 MARKING GUIDELINES MARKS: 200 These marking guidelines consist of 21 pages. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 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: Fitting and Machining 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.  (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  (Any 2 x 1) (2) 2.3 PPE for Hydraulic Press: • Overall  • Safety shoes / boots • Safety goggle  • Leather gloves  • 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 / treatment  • 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: Fitting and Machining 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 require 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: Fitting and Machining 5 DBE/November 2018 NSC – Marking Guidelines QUESTION 4: MULTIPLE-CHOICE QUESTIONS (SPECIFIC) 4.1 C (1) 4.2 A (1) 4.3 D (1) 4.4 A (1) 4.5 B (1) 4.6 A (1) 4.7 B (1) 4.8 B (1) 4.9 D (1) 4.10 C (1) 4.11 B (1) 4.12 D (1) 4.13 D (1) 4.14 C (1) TOTAL QUESTION 4: [14] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 6 DBE/November 2018 NSC – Marking Guidelines QUESTION 5: TERMINOLOGY (LATHE AND MILLING MACHINE) (SPECIFIC) 5.1 Advantages of using the tailstock to cut an external taper: • Long an accurate taper can be cut.  • The automatic feed can be used which result in a good finish.  (2) 5.2 Calculate the compound slide set-over: θ D−d  Tan = 2 2L θ 60 - 28 Tan =  2 2 × 85  = 0,188 θ = 10,66 °  2 OR 28 60 Ɵ 2 X 85 D−d X=   2 θ 16 Tan = 60 - 28  2 85 =  2 θ  = 10,66 ° = 16 mm 2 (5) 5.3 Centre gauge: • To measure the form and angle of the screw cutting tool angle while grinding the tool  • To set the screw cutting tool square/perpendicular to the axis of the work piece  (2) 5.4 Parallel key: Length: Length = 1,5 × diameter  = 1,5 × 42  = 63 mm  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 7 DBE/November 2018 NSC – Marking Guidelines 5.5 Advantages of up-cut milling: • Deeper cuts can be made as the cutting pressure on the cutter is lower than down cut milling.  • The process enables hard steel to be cut, because the total cutting pressure is absorbed by the material at the back of the edge.  • Metal with hard scale, such as castings or forgings, the cut is started under the scale where the material is softer which extends the life of the cutter.  • A quicker/course feed can be used.  • The strain on the cutter and arbour will be less.  • Vibration is limited  • Good finish  • Low noise level  (Any 2 x 1) (2) 5.6 Disadvantage of down-cut milling: • Vibration in the arbour is unavoidable.  • A fine feed must be used.  • When milling a material with hard scale the milling cutter will be damaged.  • Process takes time because of slower feed.  • Noisy process.  • Bad finish because of vibration.  (Any 2 x 1) (2) 5.7 Methods of centring a milling cutter: • Square and ruler method.  • Set-over method by milling machine dial.  • Dial indicator method  • Using reference points on digital read out equipment  (Any 2 x 1) (2) TOTAL QUESTION 5: [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 8 DBE/November 2018 NSC – Marking Guidelines QUESTION 6: TERMINOLOGY (INDEXING) (SPECIFIC) 6.1 Spur gear: Chordal tooth thickness: 90° 90° t c = Tmsin  t c = PCDsin  T T 90°  90°  = 50 × 3sin or = 150sin 50 50 = 50 × 3(0,03141)  = 150 × 0,03141  = 4,71 mm  = 4,71 mm  (4) 6.2 Calculate simple indexing: 40 Simple Indexing = N 40 =  13 1  =3 13 1 3 =3 × 13 3 3  =3 39  3 full turns and 3 holes in a 39 hole circle (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 9 DBE/November 2018 NSC – Marking Guidelines 6.3 Differential indexing: 6.3.1 Indexing required: 40 40 Indexing = = n 127 40 40 5  = = ÷ A 125 5 8  = 25 Indexing = 8 holes on the 25 hole circle  (3) 6.3.2 Change gears required: Dr A - n 40  = × Dn A 1 125 - 127 40  = × 125 1 2 40 = × 125 1 - 80 5  = ÷ 125 5 - 16 4 = × 25 4 - 64 =  100  (5) 6.3.3 Direction of rotation of index plate: The index plate will turn the opposite  direction as the index crank handle. (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 10 DBE/November 2018 NSC – Marking Guidelines 6.4 Calculate distance “x” between rollers: " x" = 150 + 2(AB ) − 2(CD) − 2r B A θ = BC tan  AB 60° BC AB = θ tan 35 =  tan 60° 35 = 20,207 mm  = 20,21 mm C θ = DE tan CD  E 15 CD = θ 15 tan  15 30° = C tan30° D = 25,98 mm  " x" = 150 + 2(AB ) − 2(CD) − 2r  = 150 + 2(20,21) − 2(25,98 ) − 2(15 ) = 150 + 40,42 − 51,96 − 30  = 108,454 mm = 108, 45 mm  (9) 6.5 Reasons for balancing work piece on a centre lathe: • Prevent unnecessary bearing loads  • Prevent excessive vibration  • To obtain a good finish  • To prevent clatter on the gear teeth  • To prevent the spindle from bending  (Any 2 x 1) (2) TOTAL QUESTION 6: [28] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 11 DBE/November 2018 NSC – Marking Guidelines QUESTION 7: TOOLS AND EQUIPMENT (SPECIFIC) 7.1 Hardness testers: • Brinell-hardness tester  • Rockwell-hardness tester  • Vickers  (Any 2 x 1) (2) 7.2 Moment tester: To determine the reactions  on either side of a simply loaded beam.  (2) 7.3 Tensile test: A piece of material is subjected to an increasing axial load  while measuring  the corresponding elongation  of the material. (3) 7.4 Depth micro-meter:     Reading = 100 + 11,00 + 0,50 + 0,09  = 111,59 mm (5) 7.5 Measure depth: Vernier calliper  (1) TOTAL QUESTION 7: [13] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 12 DBE/November 2018 NSC – Marking Guidelines QUESTION 8: FORCES (SPECIFIC) 8.1 Forces: (15) Horizontal Vertical Magnitudes Magnitudes Components  Components  1150cos0° 1150N  1150sin0° 0N 800cos150° -692,82N  800sin150° 400N  650cos200° -610,80N  650sin200° -222,31N  550cos270° 0N 550sin270° -550N  TOTAL: -153,62N  TOTAL: -372,31N  Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 13 DBE/November 2018 NSC – Marking Guidelines 8.2 Moments: 2800 N 700 N “x” O 1m 5m Calculate “x”: Take moments about O. ∑ RHM = ∑ LHM  700 × " x" = 2800 × 1 700 × " x" = 2800  2800  " x" = 700 " x" = 4 m  (4) 8.3 Stress and Strain: 8.3.1 Type of stress: Compressive stress  (1) 8.3.2 Stress: A= ( π D2 - d2 )  4 ( π 0,04 2 − 0,03 2 = ) 4 A = 0,55 × 10 -3 m2  σ =F  A 50 × 10 3 = 0,55 × 10 −3  σ = 90,91× 10 6 Pa σ = 90,91 MPa  (NO UNIT – NO MARK) (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 14 DBE/November 2018 NSC – Marking Guidelines 8.3.3 Change in length: σ Eε=  σ ε = E 90,91× 10 6 = 90 × 10 9 = 1,01× 10 −3  (IF ANY UNIT IS GIVEN – NO MARK) Δ ε =L  L Δ ε= ×L L  ( ) = 1,01× 10 −3 × (80 ) = 0,08 mm  (5) 8.3.4 Safety factor: Break stress Safety factor =  Safe working stress Break stress Safe working stress = Safety factor 600 × 10 6 =  4 = 150 × 10 6 Pa = 150 MPa  (3) TOTAL QUESTION 8: [33] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 15 DBE/November 2018 NSC – Marking Guidelines QUESTION 9: MAINTENANCE (SPECIFIC) 9.1 Lack of preventative maintenance: • Risk of injury or death.  • Financial loss due to damage suffered as a result of part failure and the waste of material.  • Loss of valuable production time.  (3) 9.2 Causes for the malfunctioning of chain drive systems: • Lack of or incorrect lubrication  • Lack of maintenance  • Overloading  • Misalignment of sprockets  • Incorrect chain tension  • Contamination of chain drive system such as dust or sand  (Any 2 x 1) (2) 9.3 Procedures to reduce the physical wear on a belt drive system: • Check the belt alignment.  • Checking the belt tension.  • Prevent overloading of the system.  • Keep the pulleys and belt clean.  • Check that all covers are secure.  (Any 2 x 1) (2) 9.4 Procedures to replace the belt on a belt drive system: • Ensure that the machine is switched off  • Release the tension on the belt  • Remove the belt from the pulleys  • Fit the correct size replacement belt onto the pulleys  • Check the pulley alignment  • Apply adequate tension according to specification and lock the system  (Any 5 x 1) (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 16 DBE/November 2018 NSC – Marking Guidelines 9.5 Properties of materials: 9.5.1 Poly vinyl chloride (PVC): • Flexible  • Rubber-like substance  • Makes a dull sound when dropped  • Tough  • Act as an insulator  • It is durable  • Highly resistant to oxidative material  • Oil, water and chemical resistant  (Any 1 x 1) (1) 9.5.2 Carbon fibre: • Strong  • Tough  • Light weight  • Good electrical conductor  (Any 1 x 1) (1) 9.6 Difference between “Thermoplastic” and “Thermo hardened (thermosetting)” composites: Thermoplastics can be reheated and deformed. / Recyclable  Thermo hardened cannot be reheated. / Non-recyclable  (2) 9.7 Examples of thermo hardened composites: • Carbon fibre or (Any application)  • Glass fibre or (Any application)  • Bakelite or (Any application)  • Teflon or (Any application)  (Any 2 x 1) (2) TOTAL QUESTION 9: [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 17 DBE/November 2018 NSC – Marking Guidelines QUESTION 10: JOINING METHODS (SPECIFIC) 10.1 Square thread: 10.1.1 The lead of the thread: Lead = pitch × no of starts  = 5×2 = 10 mm  (2) 10.1.2 The helix angle of the thread: θ = lead Helix angle tan  pitch cercumfrence 10  = π ×  outside dia − 1 pitch    2  10 = π × (82 − 2,5)  = 0,0400 θ = 2,29° / 2°17'24"  OR θ = lead Helix angle tan  pitch diameter 10  =  82 − 2,5 θ = 7,17° / 7°10'12"  (5) 10.1.3 The leading tool angle: Leading tool angle = 90° − (helix angle + clearance angle )  = 90° − (2,29° + 3°)  = 84,71° / 84°42'36" OR Leading tool angle = 90° − (helix angle + clearance angle )  = 90° − (7,17° + 3°) = 79,83° / 79°49'48"  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 18 DBE/November 2018 NSC – Marking Guidelines 10.1.4 The following tool angle: Following tool angle = 90° + (helix angle − clearance angle )  = 90° + (2,29° − 3°) = 89,29° / 89°17'24"  OR Following tool angle = 90° + (helix angle − clearance angle )  = 90° + (7,17° − 3°) = 94,17° / 94°10'12"  (2) 10.2 Measurements of a screw thread : 10.2.1 Metric screw thread  (1) 10.2.2 Crest / Major / External / Basic / Nominal / Outside diameter  (1) 10.2.3 Pitch  (1) 10.3 Angles of a square thread cutting tool: A – Helix angle  B – Clearance angle  C – Leading tool angle  D – Following tool angle  (4) TOTAL QUESTION 10: [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 19 DBE/November 2018 NSC – Marking Guidelines QUESTION 11: SYSTEMS AND CONTROL (DRIVE SYSTEMS) (SPECIFIC) 11.1 Advantages of a belt drive system compared to a chain drive system: • Silent operation  • Less expensive  • Drive can take place over a longer distance  • No lubrication needed  (Any 2 x 1) (2) 11.2 Hydraulics: 11.2.1 Fluid pressure: π 2 AA = d  4 π (0,032)2 = 4 = 0,8 × 10 −3 m2  FA p=  AA 120 = 0,8 × 10 −3 = 0,1492 × 10 6 Pa = 0,15 MPa or 149207,76 Pa  (NO UNIT – NO MARK) (4) 11.2.2 Diameter of the ram: F FB F p= A  = A  AA AB A A F A A × FB AB = B AB = p OR FA = 18 × 10 3  = (0,8 × 10 )× (18 × 10 )  −3 3 0,15 × 10 6 120 2 = 0,12 m 2  = 0,12 m  π 2 AB = d  4 4A d =π 4 × 0,12  = π = 0,39088 m  = 390,88 mm (6) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 20 DBE/November 2018 NSC – Marking Guidelines 11.3 Hydraulic symbols: One-way valve  (1) 11.4 Belt drives: Rotation frequency of the drive pulley: NDRD DR = NDND DN  N × D DN NDR = DN  D DR 80 × 240  = 75 = 256 r/min  (4) 11.5 Gear drives: 11.5.1 Rotation frequency of the output: N A Product of Driven gears = ND Product of Driver gears ND TA × TC  = N A TB × TD T × TC × N A  ND = A TB × TD 20 × 25 × 3000  =  35 × 30 1428,57 r/min ND =  60 = 23,81 r/sec  OR NB = NC = 1714,29 r/min NB × TB = NA × TA  NA × TA ND × TD = NC × TC  NB = TB NC × TC ND = 3000 × 20 TD = 35 1714,29 × 25  = = 1714,29 r/min  30 1428,57 r/min  = 60  = 23,81r/sec (6) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 21 DBE/November 2018 NSC – Marking Guidelines 11.5.2 Gear ratio: Product of the number of teeth on driven gears  Gear ratio = Product of the number of teeth on driver gears 35 30 = ×  20 25 = 2,1 : 1  (3) 11.6 Work done: Work done = F × s  = 250 × 15 = 3750 Joule or N.m  (2) TOTAL QUESTION 11: [28] TOTAL: 200 Copyright reserved Please turn over