Mechanical Technology Grade 12 NSC June 2022 Memo (English)

Downloaded from hlayiso.com SENIOR CERTIFICATE EXAMINATIONS/ NATIONAL SENIOR CERTIFICATE EXAMINATIONS MECHANICAL TECHNOLOGY: FITTING AND MACHINING 2022 MARKING GUIDELINES MARKS: 200 These marking guidelines consist of 26 pages. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 2 DBE/2022 SC/NSC Marking – Guidelines QUESTION 1: MULTIPLE-CHOICE QUESTIONS (GENERIC) 1.1 A (1) 1.2 B (1) 1.3 C (1) 1.4 D (1) 1.5 A (1) 1.6 C (1) [6] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 3 DBE/2022 SC/NSC Marking – Guidelines QUESTION 2: SAFETY (GENERIC) 2.1 Rated speed of a grinding wheel:  Because the wheel could burst/break if it turns faster than its revolution range. / Avoid an accident.   Effectiveness of the grinding process will be compromised.  (Any 1 x 1) (1) 2.2 Safety precautions of a band saw in operation:  Never leave the band saw unattended.   Use a push stick when cutting.   Hold the work piece firmly and flat on the table.   Don’t adjust the machine while working.   Don’t open any guard while the machine is on.   Make relief cuts before cutting tight curves.   Don’t force the material into the blade.   Keep hands clear from the action point.   Keep hands braced against the table.   Keep your hands on either sides of the blade and not in line with the cutting line and the blade.   Keep loose clothing clear from action point.  (Any 2 x 1) (2) 2.3 Stages in which first aid is applied:  Examination   Diagnosis   Treatment  (3) 2.4 Causes of accidents:  Unsafe acts   Unsafe conditions  (2) 2.5 TWO advantages of the product layout:  Handling of material is kept to a minimum.   Time period of manufacturing cycle is less.   Production control is almost automatic.   Control over operations is easier.   Greater use of unskilled labour is possible.   Less total inspection is required.   Less total floor space is needed per unit of production.  (Any 2 x 1) (2) [10] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 4 DBE/2022 SC/NSC Marking – Guidelines QUESTION 3: MATERIALS (GENERIC) 3.1 Tempering: Tempering is a process generally applied to steel to relieve the strains/brittleness/improve ductility  induced during the hardening process.  (2) 3.2 Annealing:  To relieve internal stresses  that may have been set up during working of metal.  To soften steel  in order to facilitate the machining process.  To refine their grain structure.   Reduce brittleness.   Make the steel ductile.  (Any 3 x 1) (3) 3.3 Normalising temperature:  Above  higher/upper critical temperature   Above  AC3 line.  (Any 1 x 2) (2) 3.4 Spark pattern for carbon steels: 3.4.1 High-carbon steel  (1) 3.4.2 Low-carbon steel / Mild steel  (1) 3.4.3 Cast-iron  (1) 3.5 Carbon diagram: A. Temperature range / °C  B. AC3 line / Higher/upper critical temperature line  C. AC1 line / Lower critical temperature line  D. Carbon content / % carbon  (4) [14] Copyright reserved Please turn over

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

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 6 DBE/2022 SC/NSC Marking – Guidelines QUESTION 5: TERMINOLOGY (LATHE AND MILLING MACHINE) (SPECIFIC) 5.1 Disadvantages of using compound slide method:  The automatic feed of the machine cannot be used.   Only short tapers can be cut.   It causes fatigue in the operator.   Poor finish.   Take longer time to cut.  (Any 2 x 1) (2) 5.2 Taper: 5.2.1 Length of taper: θ Dd tan  2 2 12 72  40 tan   2 2 32  2  tan 6  304,46   2  = 152,23 mm  (5) 5.2.2 Tailstock set-over: LD - d Set - over  2   x 70  152,2372 - 40 2152,23 x  23,36 mm  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 7 DBE/2022 SC/NSC Marking – Guidelines 5.3 Parallel key: 5.3.1 Width: D Width  4 102 Width   4  25,50 mm  (2) 5.3.2 Thickness: D Thickness  6 102 Thickness   6  17 mm  (2) 5.3.3 Length: Length = 1,5 x diameter of shaft = 1,5 x 102  = 153 mm  (2) 5.4 Disadvantages of gang milling:  The gang of cutters place more stress on the machine spindle bearings.   The cutters make the milling machine work harder.  (2) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 8 DBE/2022 SC/NSC Marking – Guidelines QUESTION 6: TERMINOLOGY (INDEXING) (SPECIFIC) 6.1 Spur gear: 6.1.1 Number of teeth: PCD Module  T 168 Module   42 Module  4  (2) 6.1.2 Circular pitch: CP = m x π PCD  π CP  =4xπ  T = 12,57 mm  OR 168  π   42  12,57 mm  (2) 6.1.3 Outside diameter: OD = PCD + 2(m) OD = m(T + 2) = 168 + 2(4)  OR = 4(42 + 2)  = 176 mm  = 176 mm  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 9 DBE/2022 SC/NSC Marking – Guidelines 6.2 W  135  2 y  m  W  2 x   2R  m  W  2 x  R  6.2.1 Maximum width distance of dove tail (W): Calculate y: h Tan θ  y y tanθ  35 h y  tan θ OR y  tanθ  h  35 y  tan30  35  y  tan 60  20,21 mm  y  20,21 mm  W = 135 + 2(y)  = 135 + 2(20,21)  = 135 + 40,42 = 175,42 mm  (6) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 10 DBE/2022 SC/NSC Marking – Guidelines 6.2.2 Distance between the rollers (m): Calculate x : R Tan α  x x R tanθ  x  12 Tan α x  tan  12  12 OR x  Tan 30 x  tan60  12  12 x  20,78 mm  0,5774 x  20,78 mm  m = W – (2 x ) – (2R)  = 175,42 – (2 x 20,78) – (2 x 12)  = 175,42 – 41,56 – 24 = 109,86 mm  OR m = W – 2( x +R)  m = 175,42 – 2(20,78 + 12)  m = 175,42 – 65,56 m = 109,86 mm  (6) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 11 DBE/2022 SC/NSC Marking – Guidelines 6.3 Milling of spur gear: 6.3.1 Indexing: 40 Indexing  n 40 Indexing  113 40 Indexing   110 40 5 Indexing   110 5 8 3 Indexing    22 3 24 Indexing   66 Approximate indexing: 24 holes on a 66-hole circle  (4) 6.3.2 Change gears: Dr 40  A  n  Dn A Dr 40  110  113   Dn 110 Dr - 3  40   Dn 110 Dr - 120 5    Dn 110 5 Dr - 24 2    Dn 22 2 Dr 48  Dn 44 (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 12 DBE/2022 SC/NSC Marking – Guidelines 6.4 Unbalanced work piece:  Unnecessary bearing loads   Excessive vibration   A bad finish   Work that is not perfectly round   Danger to the operator   Clatter on the gear teeth   A tendency to bend the spindle  (Any 2 x 1) (2) [28] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 13 DBE/2022 SC/NSC Marking – Guidelines QUESTION 7: TOOLS AND EQUIPMENT (SPECIFIC) 7.1 Tensile tester:  Yield stress   Ultimate tensile stress / Maximum stress   Elongation percentage / Ductility   Limit of proportionality   Limit of elasticity   Break stress  (Any 3 x 1) (3) 7.2 Brinell hardness tester: A - Work piece / Test piece  B - Steel Carbide ball / Indenter  C - Indentation diameter  (3) 7.3 Calculate cutting depth: Cutting depth = 0,613 x pitch = 0,613 x 1,75  = 1,07 mm  (2) 7.4 Depth micrometer reading:   17,36 mm (2) 7.5 Function of moment tester: To determine the reactions  on either side  of a simply loaded  beam. (3) [13] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 14 DBE/2022 SC/NSC Marking – Guidelines QUESTION 8: FORCES (SPECIFIC) 8.1 System of forces: HORIZONTAL COMPONENT:  HC  50cos30  85cos0  75cos70     HC  43,30  85  25,65  HC   16,05 N  VERTICAL COMPONENT:  VC  50sin30  25sin90  75sin70     VC  25  25  70,48  VC   70,48 N  OR Force θ VC/y = Fsinθ HC/x = Fcosθ 50 N 30º VC = 50sin30º 25 N  HC = 50cos30º 43,30 N  85 N 180º VC = 85sin180º 0N HC = 85cos180º -85 N  25 N 270º VC = 25sin270º -25 N  HC = 25cos270º 0N 75 N 290º VC = 75sin290º -70,48 N HC = 75cos290º 25,65 N  Total -70,48 N  -16,05 N  R 2  VC 2  HC2 VC tan θ  HC R 2  ( 70,48)2 ( 16,05)2   70,48 θ  tan 1( )  16,05 R 2  5225,033 θ  tan 1(4,39) R  72,28 N   θ  77,17 OR 77 10' 12"     W    θ R S (15) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 15 DBE/2022 SC/NSC Marking – Guidelines 8.2 Moments: 8.2.1 Point load for UDL: 6 x 11 = 66 kN  (1) 8.2.2 Calculate A Take moments about B: ∑ RHM = ∑LHM A  11 (12  2,5)  66  5,5   75  11  11A  30  363  825 1218 A   11 A  110,73 kN  (3) 8.2.3 Calculate B Take moments about A: ∑ LHM = ∑RHM (B  11) (75  0) (66  5,5) (12  8,5)  11B  0  363  102 465 B 11  B  42,27 kN  OR A  B  75  66  12  B  153  110,73  B  42,27 kN  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 16 DBE/2022 SC/NSC Marking – Guidelines 8.3.1 The resistance area: πD 2 A 4 π(0,05) 2 A  4 A  0,00196 m 2 or 1,96  10 3 m 2  (2) 8.3.2 The stress in the material in MPa: F σ A 50  10 3  σ 1,96  10 3  σ  25510204,082 Pa σ  25,51 MPa  (3) 8.3.3 Strain in material: ΔL ε L 0,005 ε  3 ε  0,0017 OR 1,67  10  3  (No unit! If unit indicated, answer is wrong) (2) 8.4 Label stress and strain diagram: A – Limit of proportionality  B – Elastic limit  C – Yield point  D – Maximum stress  (4) [33] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 17 DBE/2022 SC/NSC Marking – Guidelines QUESTION 9: MAINTENANCE (SPECIFIC) 9.1 Main purpose of maintenance: To ensure that the machinery always operates at an optimal level.  (1) 9.2 Preventative maintenance: 9.2.1 Chain drives:  Cleaning uncovered drives.   Check sprocket teeth and link plate wear.   Check lubricants.   Checking the functioning of tensioning devices.   Inspecting chains regularly for elongation.  (Any 2 x 1) (2) 9.2.2 Belt drives:  Checking the wear and tear on belt.   Checking belt alignment.   Checking the tension setting.   Checking the tensioning devices.  (Any 2 x 1) (2) 9.3 Properties of EACH of the following nylon products: 9.3.1 Polyethylene (PET):  Stiff   Strong   Hard   Chemical resistance  (Any 2 x 1) (2) 9.3.2 Polypropylene (PP):  Good fatigue resistance   Heat resistance   Tough   Semi rigid   Good chemical resistant  (Any 2 x 1) (2) 9.3.3 Polystyrene (PS):  Good insulation properties   Water resistant   Odourless properties   Light weight  (Any 2 x 1) (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 18 DBE/2022 SC/NSC Marking – Guidelines 9.4 Factors influencing coefficient of friction:  Surface roughness/texture   Temperature   Type of lubricant   Type of friction  (Any 3 x 1) (3) 9.5 Thermo-hardened composites: This type of plastic goes through a chemical change during moulding that prevents reheating.  (1) 9.6 Types of belt drive systems:  V-belt   Wedge belt / Cog belt   Flat belt   Multi-groove belt   Toothed / Timing belt   Circular belt / Round belt   Poly V-belt  (Any 3 x 1) (3) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 19 DBE/2022 SC/NSC Marking – Guidelines QUESTION 10: JOINING METHODS (SPECIFIC) 10.1 Square Thread: 10.1.1 Pitch: Lead  Pitch  Number of starts Lead Pitch   Numberof starts 36 Pitch   3 Pitch  12 mm  (3) 10.1.2 Pitch diameter: P Dp  OD  2 12 Dp  70   2 Dp  64 mm  (2) 10.1.3 Helix angle of the thread: Lead Tan θ  π  PD 36  Tan θ  π  64  Tan θ  0,179049311 θ  10,15  OR 10 9 '  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 20 DBE/2022 SC/NSC Marking – Guidelines 10.1.4 Leading angle: Leading angle = 90° - (helix angle + clearance angle) = 90° - (10°9’ + 3°)  = 76°51’ or 76,85º  (2) 10.1.5 Following angle: Following angle = 90° + (helix angle - clearance angle) = 90° + (10°9’ - 3°)  = 97°9’ or 97,15º  (2) 10.2 Square thread cutting tool angles: 10.2.1 Square thread  (1) 10.2.2 A - Clearance angle  B - Leading angle  C - Following angle  D - Helix angle  (4) 10.3 Included angle of Metric V-thread: 60°  (1) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 21 DBE/2022 SC/NSC Marking – Guidelines QUESTION 11: SYSTEMS AND CONTROL (DRIVE SYSTEMS) (SPECIFIC) 11.1 Hydraulic calculations: 11.1.1 The fluid pressure in the hydraulic system in MPa: πd 2 A RAM  4 π(0,120) 2  A 4 A  11,31 10  3 m2  NOTE: Force of Ram = 4 500 kg x 10 m/s2 = 45 x 103 N F Ρ A  45  103 P 11,3  10-3 P  3,98 N  (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 22 DBE/2022 SC/NSC Marking – Guidelines 11.1.2 Force to be applied on the plunger: πd 2 A Plunger  4 π(0,032) 2  A 4 A  0,80  10  3 m2  F P A F  P A  F  3,98  106  0,80  10 3  F  3184 N  OR FA F  B A A AB  FA 45  103  0,8  103 11,31  103      45  103 0,8  103 FA   11,31  103  3184 N  (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 23 DBE/2022 SC/NSC Marking – Guidelines 11.2 Function hydraulic non-return valve: Used to provide one-directional oil flow and the fluid is not allowed to flow back.  (1) 11.3 Spring-loaded double-action control valve is used in a water line:  Protect water supplies from back flow.   Prevent water contamination.   Safety device if one valve is jammed.  (Any 2 x 1) (2) 11.4 Pressure gauges:  Bourdon tube gauge.   Schrader gauge.  (2) 11.5 Belt drive: 11.5.1 The rotational frequency: NDN  DDN  NDR  DDR NDR  DDR NDN   DDN 1320  0,085 NDN   0,375 299,2 NDN   60 NDN  4,99 r/sec  (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 24 DBE/2022 SC/NSC Marking – Guidelines 11.5.2 Power transmitted in Watt: (T  T2 )  D N Ρ 1 60   Ρ (275  120) π  0,375  4,99 P  911,199 Watt  OR P  T1  T2 π DN    275  120  π  0,085  1320 60  910,59 Watt  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 25 DBE/2022 SC/NSC Marking – Guidelines 11.6 Gear drive: 11.6.1 Number of teeth on TA: Ninput Product of the numberof teeth on driven gears  Noutput Product of the number of teeth on driving gears NF TA  TC  TE  NA TB  TD  TF 720 TA  45  50   320 20  25  20  2250  TA 2,25   10000 2250 TA  2,25  10000 22500 TA  2250 TA  10  (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 26 DBE/2022 SC/NSC Marking – Guidelines 11.6.2 Gear ratio: Product of the number of teeth on driven gears Gear ratio  Product of the number of teeth on driving gears 20  25  20  Gear ratio  10  45  50  Gear ratio  0,44: 1  OR NA Speed Ratio  NF 320   720   0,44 : 1  (3) [28] TOTAL: 200 Copyright reserved