Mechanical Technology Grade 12 NSC November 2021 Memo (Eng)

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE GRADE 12 MECHANICAL TECHNOLOGY: FITTING AND MACHINING NOVEMBER 2021 MARKING GUIDELINES MARKS: 200 These marking guidelines consist of 24 pages. Copyright reserved Please turn over

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

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 7 DBE/November 2021 NSC – Marking Guidelines QUESTION 5: TERMINOLOGY (LATHE AND MILLING MACHINE) (SPECIFIC) 5.1 Advantages of compound slide method:  Tapers with large angles can be cut.   External and internal tapers can be cut.   The set-up is simple.  (Any 2 x 1) (2) 5.2 Taper cutting: 5.2.1 Length of taper: θ Dd Tan  2 2  Dd  2  θ tan 2 92  50 2   tan4 42 2  0,069926811  600,6279909   2  300,31 mm  (5) 5.2.2 Tailstock set-over: LD  d Set  over  2l 425,3192  50   2  300,31   29,74 mm  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 8 DBE/November 2021 NSC – Marking Guidelines 5.3 Key ways: 5.3.1 Width: D Width = 4 75 Width =  4 = 18,75 mm  (2) 5.3.2 Thickness: D Thickness = 6 75 Thickness =  6 = 12,50 mm  (2) 5.3.3 Length: Length = 1,5  diameter of shaft = 1,5  75  = 112,50 mm  (2) 5.4 Disadvantages of down-cut milling:  Vibration in the arbor is unavoidable.   A fine feed must be used.   When milling material with hard scale, the cutter teeth come directly in contact with the scale, which can damage the cutter.   The process is time consuming.  (Any 2 x 1) (2) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 9 DBE/November 2021 NSC – Marking Guidelines QUESTION 6: TERMINOLOGY (INDEXING) (SPECIFIC) 6.1 Gear terminology: 6.1.1 Pitch-circle diameter: PCD = m  T CP = m  π = 1,5  200  = 1,5  π = 300 mm = 4,71 mm  OR CP  T PCD  π 4,71 200  π  299,85 mm  (2) 6.1.2 Dedendum: Dedendum= 1,157  m Dedendum= 1,25  m = 1,157  1,5  OR = 1,25  1,5  = 1,74 mm  = 1,88 mm  (2) 6.1.3 Outside diameter: OD = PCD + 2  m OD = mT + 2 = 300 + 2(1,5)  OR = 1,5(200 + 2)  = 303 mm  = 303 mm  (2) 6.1.4 Working depth: WD = 2  m WD = 2  a = 2  1,5  OR = 2  1,5  = 3 mm  = 3 mm  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 10 DBE/November 2021 NSC – Marking Guidelines 6.2 Dovetails: W = 210 + 2(DE) m = W – 2(AC) – 2(R) 6.2.1 Maximum width distance of dove tail: (W) Calculate DE or y: DE tanθ  AD DE = tanθ  AD  = tan30°  45  = 25,98 mm  W = 210 + 2(DE)  = 210 + 2(25,98)  = 210 + 51,96 = 261,96 mm  (6) 6.2.2 Distance between the rollers: (m) Calculate AC or x: BC Tanθ  AC BC AC   Tanθ 17 AC   Tan30  29,44 mm  m = W - 2(AC) - 2(R)  = 261,96 - 2(29,44) - 2(17)  = 261,96 - 58,88 - 34 = 169,08 mm  (6) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 11 DBE/November 2021 NSC – Marking Guidelines 6.3 Milling of spur gear: 6.3.1 Indexing: 40 40 Indexing   N 137 40 40    A 140 4 2   14 2 8   28 Indexing : 8 holes on a 28 - hole circle  OR 12 holes on a 42 - hole circle  OR 14 holes on a 49-hole circle.  (3) 6.3.2 Change gears: (Markers to note alternative answers and calculations to award full marks if the answer is correct) Dr 40  A  n  Dn A Dr 40  140  137  Dn 140  40  3 140 120  140  12  14 12 2   14 2  Dr 24  48   OR Dn 28  56  (5) [28] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 12 DBE/November 2021 NSC – Marking Guidelines QUESTION 7: TOOLS AND EQUIPMENT (SPECIFIC) 7.1 Functions of a moment and force tester:  To determine the reaction on either side of a simple loaded beam.   To illustrate the concept of the triangle of force.  (2) 7.2 TWO hardness testers:  Brinell   Rockwell   Vickers  (Any 2 x 1) (2) 7.3 Precision measuring instrument:  Depth micrometer   Vernier caliper  (Any 1 x 1) (1) 7.4 Identify tester: Tensile tester  (1) 7.5 There are THREE ways that hardness is measured:  Resistance to penetration.   Elastic hardness.   Resistance to abrasion / scratching / file test.  Sound test (dropping it on the floor and listen to the sound). (Any 3 x 1) (3) 7.6 Screw thread height:   (2) 7.7 Measuring instrument: Vernier caliper  (1) 7.8 Interchangeable extension: To measure depths greater than 25 mm.  (1) [13] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 13 DBE/November 2021 NSC – Marking Guidelines QUESTION 8: FORCES (SPECIFIC) 8.1 Calculate resultant: VERTICAL COMPONENT:     HORIZONTAL COMPONENT:     OR VC/y = Fsinɵ HC/x = Fcosɵ -45sin90° OR 45sin270° -45 N  120cos0° 120 N  -70sin30° OR 70sin210° -35 N  -70cos30° OR 70cos210° -60,62 N  185sin45° OR 185sin135° 130,82 N  -185cos45° OR 185cos135° -130,82 N  Y = 50,82 N  X = -71,44 N    VC  45sin9070sin30185sin45 VC  4535130,82   VC  50,82N    R  (15) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 14 DBE/November 2021 NSC – Marking Guidelines 8.2 Moments: 9,5 kN 80 kN 4,5 kN 2,5 m 2,5 m 10,25 m A B 8.2.1 Point load for UDL:   (2) 8.2.2 Take moments about B: (A  10,25) (4,5  5,25) (80  7,75) (9,5  10,25)  10,25A  23,625  620  97,375 741 A  10,25 A  72,29 kN  (3) 8.2.3 Take moments about A: (B  10,25) (9,5  0) (80  2,5) (4,5  5)  10,25B  0  200  22,5 222,5 B  10,25 B  21,71 kN  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 15 DBE/November 2021 NSC – Marking Guidelines 8.3.1 The stress in the material in MPa:   (2) 8.3.2 The diameter of the mild steel shaft: F πd 2 σ A A 4 F A  4  πd 2 A  σ A 4 2 3 d2   πd 90  10 π   4 14,59  106 A 4 3 d 90  10  4 π πd2  14,59  106 OR d 6,17  10   4  3 πd2  0,0247 π 0,0247 d 0,007855887  d2  π d  0,088633441 m  d  7,85  10 3  d  88,63 mm  d  0,08863 m  d  88,63 mm  (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 16 DBE/November 2021 NSC – Marking Guidelines 8.3.3 Original length:    (3) [33] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 17 DBE/November 2021 NSC – Marking Guidelines QUESTION 9: MAINTENANCE (SPECIFIC) 9.1 Preventative maintenance:  Planned or scheduled maintenance.   Condition-based maintenance.  (2) 9.2 Preventative maintenance of gear drive systems:  Checking and replenishment of lubrication levels.   Ensuring that gears are properly secured to shafts.   Cleaning and replacement oil filters.   Reporting excessive noise, wear, vibration and overheating for expert attention.  (Any 3 x 1) (3) 9.3 Purpose of jockey pulley:  The jockey pulley helps setting the tension on the system.   To increase the angle of contact in an open belt drive.  (Any 1 x 1) (1) 9.4 Properties of materials: 9.4.1 Teflon:  Water resistant.   Resistant to grease.   Resistant to heat.   Resistant to corrosion.   Can withstand high temperatures.   Need no lubricants.   Electrical insulator   Thermoplastic /Easy to be reshaped / recycled. (Any 2 x 1) (2) 9.4.2 Nylon:  Tough.   Hard-wearing.   Cheap.   Needs no or little maintenance.   Can withstand high temperatures.   Need no or little lubricants.   Is light.   Can absorb shock.   Resistant to chemicals.   Non-toxic.   Thermoplastic /Easy to be reshaped.  Has high load-bearing strength  (Any 2 x 1) (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 18 DBE/November 2021 NSC – Marking Guidelines 9.4.3 Vesconite:  Wear resistant.   Low friction.   Operate with little or no lubrication.   Easy to machine.   Load carry higher than white metal.   Cost effective material.   Gives long life span.   Performs well, in unhygienic, dirty and un-lubricated environments.   Low maintenance.   Low or no water absorption   High chemical resistance   Versatile   Can handle high temperatures   Thermoplastic /Easy to be reshaped  (Any 2 x 1) (2) 9.5 Use of material: 9.5.1 Polyvinyl chloride (PVC): (Due to the large number of alternatives, marker discretion must be used - discuss with IM).  Electrical cable isolation.  Electrical pipes.   Water pipes.   Artificial leather.   Cling wrap.   Credit / bank / phone cards.  Window frames.   Fences.   Furniture.  (Any 1 x 1) (1) 9.5.2 Glass fibre: (Due to the large number of alternatives, marker discretion must be used - discuss with IM).  Boats.  Motor vehicles bodies.   Transparent roof sheeting.   Petrol tanks.   Swimming pools.   Furniture.   Fruit and salad bowls.   Ornaments.   Fishing equipment.  (Any 1 x 1) (1) 9.6 Difference between thermoplastic and thermo-hardened composites: Thermoplastic can be re-heated  and reshaped again  where a thermo- hardened plastic cannot be re-heated,  to be softened, shaped  and moulded again. (4) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 19 DBE/November 2021 NSC – Marking Guidelines QUESTION 10: JOINING METHODS (SPECIFIC) 10.1 Screw thread:  Square thread   Acme thread   V-screw thread   Trapezium thread / Buttress thread  (Any 3 x 1 ) (3) 10.2 Square Thread: 10.2.1 Pitch diameter: Lead Pitch  Numberof starts 36   2  18 mm  P PD  OD  2 18   80  2  71 mm  (4) 10.2.2 Helix angle of the thread: Lead Tanθ  π  PD 36  Tanθ  π  71  θ  tan 10,161396562    9,17  (4) 10.2.3 Leading angle: Leading angle = 90° - (helix angle + clearance angle) = 90° - (9,17° + 3°)  = 77,83°  (2) 10.2.4 Following angle: Following angle = 90° + (helix angle - clearance) = 90° + (9,17° - 3°)  = 96,17°  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 20 DBE/November 2021 NSC – Marking Guidelines 10.3 Multiple screw threads:  They provide more bearing surface than single start screw thread / does not strip easily.   To provide faster linear movement.   They are more efficient as they lose less power to friction compared to single start screw threads.  (3) [18] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 21 DBE/November 2021 NSC – Marking Guidelines QUESTION 11: SYSTEMS AND CONTROL (DRIVE SYSTEMS) (SPECIFIC) 11.1 Hydraulics: 11.1.1 The fluid pressure:     (4) 11.1.2 Force at ram:       OR F f 2  D d2 F 25 2   120 352  25  1202  F 352  F  293,88kN  (5) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 22 DBE/November 2021 NSC – Marking Guidelines 11.2 Functions hydraulic reservoir:  A fluid storage tank.   Promotes air separation from the fluid.   Support for the pump and electric motor.   Promotes heat dispersion.   Acts as a base plate for mounting control equipment.  Permits contaminants to settle at the bottom in order to be drained.  (Any 1 x 1) (1) 11.3 Efficiency of pneumatic systems:  Pneumatic tools are environmentally friendly.   Last long.   It is robust (powerful / less force required)   Easy to use.   It is compact.   Easy to maintain as there are so few working parts.  (Any 2 x 1) (2) 11.4 Applications for pneumatic systems: (Due to the large number of alternatives, marker discretion must be used - discuss with IM).  Drills.   Brake systems.   Jackhammers   Nail guns   Missiles   Doors   Spray guns   Air blow guns   Air socket wrench   Grinders  (Any 2 x 1) (2) 11.5 Belt drives: 11.5.1 Rotation frequency:    (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 23 DBE/November 2021 NSC – Marking Guidelines 11.5.2 Power transmitted: T1 (T  T )π DN Ratio  Ρ 1 2 T2 60 T1 T2  Ρ (300  120 )π  0,8  5,4  Ratio  300 T2  P  2442,90 Watt 2,5 T2  120 N  P  2,44 kW  (4) 11.6 Gear drives: 11.6.1 Rotation frequency: Ninput Product of teeth on driven gears  Noutput Product of teeth on driver gears TA  TC  NA N(D)OUTPUT   TB  TD 30  20  2300  N(D)OUTPUT  40  60  N(D)OUTPUT  575 r/min  (4) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology: Fitting and Machining 24 DBE/November 2021 NSC – Marking Guidelines 11.6.2 Gear ratio: Product of teeth on driven gears Gear ratio  Product of teeth on driver gears 40  60  Gear ratio  30  20  Gear ratio  4 : 1  OR NA Speed ratio  ND 2300   575   4 :1  (3) [28] TOTAL: 200 Copyright reserved