Mechanical Technology Grade 12 NSC November 2017 Memo (Eng)

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE GRADE 12 MECHANICAL TECHNOLOGY NOVEMBER 2017 MARKING GUIDELINES MARKS: 200 These marking guidelines consist of 18 pages. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 2 DBE/November 2017 NSC – Marking Guidelines QUESTION 1: MULTIPLE-CHOICE QUESTIONS 1.1 B (1) 1.2 C (1) 1.3 D (1) 1.4 B (1) 1.5 C (1) 1.6 D (1) 1.7 D (1) 1.8 C (1) 1.9 B (1) 1.10 B (1) 1.11 A (1) 1.12 C (1) 1.13 B (1) 1.14 B (1) 1.15 B (1) 1.16 D (1) 1.17 B (1) 1.18 B (1) 1.19 B (1) 1.20 A (1) [20] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 3 DBE/November 2017 NSC – Marking Guidelines QUESTION 2: SAFETY 2.1 Surface grinder: • Make sure the sparks are of no danger to co-workers.  • Do not force the material onto the grinding wheel.  • Do not plunge grind.  • Bring the material slowly into contact with the grinding wheel.  • Never clean or adjust the machine while it is in motion.  • Use cutting fluid  • Know where the emergency stop is located  • Stop the machine before any adjustments  • Keep tools clear from moving parts  (Any 3x1) (3) 2.2 Hydraulic press: • To make sure there is no leakages.  • To make sure that the readings are accurate.  • To make sure the prescribed pressure is not exceeded.  (2) 2.3 MIG/MAGS welding: • Working area must be well ventilated.  • Make sure electrical parts are properly insulated.  • Make sure the inert gas cylinder is fixed in an upright position.  • Make sure the terminals are connected correctly to the right outlet points.  • The operator should know how to use the equipment.  • The operator must be completely insulated by means of boots, gloves and rubber mats.  • The work area must be partitioned off.  • Use protective equipment. (Overall, gloves, apron, welding helmet etc.)  • Ensure adequate fire precautions.  • See that there is no oil or grease around the machine.  • Ensure that the working area is clean.  (Any 3x1) (3) 2.4 Spring compressor: • Make certain the compressor is strong enough for the spring  • The compressor must be fitted correctly and firmly.  • Ensure that the spring cannot slip out of position.  • A uniform load must be applied.  • Release the load carefully and also uniformly.  • Do not use wire or ropes to compress the spring.  • Do not hit with a hammer.  • The hookes on the clamps shoul not be warned  • Clamps must be evenly distributed  • Do not exceed the maximum tension  (Any 2x1) (2) [10] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 4 DBE/November 2017 NSC – Marking Guidelines QUESTION 3: TOOLS AND EQUIPMENT 3.1 Volt and ammeter: • Voltmeter: connected in parallel to a circuit.  • Ammeter: connected in series to a circuit.  (2) 3.2 Uses of the multimeter: • Direct current measurement (DC)  • Alternating current measurement (AC)  • Voltage measurement  • Resistance measurement  • Transistor test  • Diode test  • Continuity test  • Temperature  • Battery test  (Any 4x1) (4) 3.3 Compression Test: • The piston rings are worn out.  • Worn cylinders.  • Cracked piston.  (Any 1x2) (2) 3.4 Tests: 3.4.1 A beam bending test is to investigate the deflection / bend  of beams. (2) 3.4.2 A cylinder leakage tester is to check whether gases or air leaks  from the cylinders / valve leak. (2) [12] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 5 DBE/November 2017 NSC – Marking Guidelines QUESTION 4: MATERIALS 4.1 Properties of structures: 4.1.1 Cementite: hard  and brittle  (2) 4.1.2 Ferrite: soft  and ductile  (2) 4.2 Heating process of carbon steel: 4.2.1 Iron-Carbon  Equilibrium  Diagram (2) 4.2.2 A = Ferrite and pearlite  B = Pearlite and cementite  C = Ferrite and austenite  D = Austenite and cementite  E = Austenite  (5) 4.2.3 700 – 800 °C  (2) [13] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 6 DBE/November 2017 NSC – Marking Guidelines QUESTION 5: TERMINOLOGY 5.1 Screw thread terms: 5.1.3: NOTE: Any other corresponding point on the screw thread (5) 5.2 Milling processes: 5.2.1 Up-cut milling  (1) 5.2.2 Down-cut milling  (1) 5.3 Indexing: 40 Indexing = A  40 = 22  18 3 =1 × 22 3  54 =1 66     1 full turn and 54 holes on the 66-hole circle (6) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 7 DBE/November 2017 NSC – Marking Guidelines 5.4 Dividing head: 5.4.1 The sector arm save time and removes the possibility of error in counting the number of holes for each move of the index pin.  (2) 5.4.2 The index plate is equipped with accurate spaced holes on different-diameter circles. Each circle has a different number of holes. These circles allow the crank handle to be given an accurate part of a turn to obtain the desired spacing.   (2) 5.4.3 The index pin can be set in the crank handle so that it can be dropped into calculated hole and lock the crank the hole circles.   (2) 5.4.4 Ratio between worm and worm gear: 40:1   (2) 5.5 Gear terminology: 5.5.1 The pitch-circle diameter 'PCD' PCD Module(m) =  T PCD = m × T  = 3 × 94 PCD = 282 mm  (3) 5.5.2 The outside diameter: Outside diameter = PCD + 2m  OD = 282 + 2(3) OD = 288 mm  (2) 5.5.3 The dedendum: Dedendum b = 1,157 m or b = 1,25m  b = 1,157 × 3 b = 1,25 × 3 b = 3,47 mm b = 3,75 mm  (2) 5.5.4 The cutting depth: Cutting depth = 2 ,157 × m or Cutting depth = 2,25 × m  = 2 ,157 × 3 = 2,25 × 3 = 6 ,47 mm = 6,75 mm  (2) [30] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 8 DBE/November 2017 NSC – Marking Guidelines QUESTION 6: JOINING METHODS 6.1 Causes of undercutting: • Current setting is too high  • Current setting is too low  • Faulty electrode manipulation  • Arc length is too long  • Welding speed is too fast  • Incorrect electrode size  (Any 2x1) (2) 6.2 Prevention of slag inclusion: • Chip off the slag from the previous weld runs before doing any further welding.  • Increase the current setting.  • Ensure that the joint is properly cleaned before any welding is done.  • Ensure constant current flow.  • Arc length must be shorter  • Use dry electrodes (Any 1x2) (2) 6.3 Liquid dye penetrant test: • Dye is sprayed onto the clean surface to be inspected  • Allow a short time for the dye to penetrate, then remove excess dye with a solvent  • Wash surface with water and allow to dry  • When the surface is dry spray a developer on the surface to bring out the colour in the dye which is trapped in the cracks or pin holes  (4) 6.4 Advantages of using a MIGS/MAGS welding: • Operator needs less skills  • Continuous welds can be done without replacing electrodes  • Less cleaning of weld, (No slag to be removed)  • It is a quicker process  • Thin material can be welded easily  • Can weld in any position  • Create a better finish  • High deposition rate  • Less distortion  (Any 3x1) (3) 6.5 Gas flow meter: Control the flow of rate of shielding gas  and measure the flow rate.  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 9 DBE/November 2017 NSC – Marking Guidelines 6.6 MIGS/MAGS welding process: A = Melted welding pool / Parent metal / Weld metal / Weld  B = Contact nozzle / Weld pistol / gun  C = Gas shroud / Weld pistol / gun  D = Shielding gas  E = Earth clamp / Skelm / Earth cable  (5) 6.7 Shielding gas in MIGS/MAGS: • To control the welding arc  • Shield the molten pool from atmospheric gases  (Any 1x2) (2) 6.8 Earth cable: • To complete the circuit  • To maintain constant current   • To prevent electric shock   (Any 1x2) (2) 6.9 THREE types of gasses used for MIGS/MAGS welding: • Argon  • Teral  • CO 2  • Helium  • Gas mixture  (Any 3x1) (3) [25] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 10 DBE/November 2017 NSC – Marking Guidelines QUESTION 7: FORCES 7.1 (13) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 11 DBE/November 2017 NSC – Marking Guidelines 7.2 Stress and Strain: 7.2.1 Stress in the bar: πD 2  A= 4 π × 0 ,056 2 = 4  = 2 ,46 × 10 −3 m 2 F σ=  A 40 × 103  = 2,46 × 10-3  = 16260162.6 Pa = 16 ,26 × 106 Pa = 16 ,26 MPa (5) 7.2.2 Strain: σ ε=  E 16 ,26 × 10 6 ε=  90 × 10 9 = 0 ,18 × 10 −3  (3) 7.2.3 Change in length: Δl ε=  ol Δl = ε × ol  ( = 0 ,18 × 10 −3 )× 0,85 −3 = 0 ,15 × 10 m OR  = 0 ,15 mm (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 12 DBE/November 2017 NSC – Marking Guidelines 7.3 Moments: 750 N 300 N 960 N 6m 4m 8m A B Calculate A. Moments about B: ∑ RHM = ∑ LHM (A × 12) = (960 × 6) + (750 × 8)  12A 5760 + 6000 = 12 12 A = 980 N  Calculate B. Moments about A: ∑ LHM = ∑ RHM (B × 12 ) = (750 × 4) + (960 × 6) +( 300 ×12)  12B = 3000 + 5760 + 3600 12B 12360 = 12 12 B =1030 N  (6) [30] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 13 DBE/November 2017 NSC – Marking Guidelines QUESTION 8: MAINTENANCE 8.1 Pour point: The lowest temperature  at which a liquid will flow.  (2) 8.2 Advantages of cutting fluids: • Keep the work piece and cutting tool cool  • It prolongs the life of the cutting tool  • Ensure a better finish  • It washes the cuttings/swarf away  • It protects the machine by making the cutting process easier  • Prevents rust  • It increases the productivity because  • It is possible to cut faster  • It lubricates the machine  (Any 3x1) (3) 8.3 'ATF': Automatic transmission fluid  (2) 8.4 Main parts of a clutch: Pressure plate  clutch plate  release bearing (Thrust bearing)  (3) 8.5 Results of a stretched chain: • The chain weakens  • Generates friction  • Vibration occurs  • Becomes noisy  • Derails easily  • Tends to break easily  (Any 3x1) (3) 8.6 Causes of belt slip: • Incorrect tension (loose)  • Oil on the contact surfaces  • Worn belts  • Incorrect pulley alignment  • Overloading  • Not the correct size  (Any 2x1) (2) [15] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 14 DBE/November 2017 NSC – Marking Guidelines QUESTION 9: SYSTEM AND CONTROLS 9.1 Gear drives: 9.1.1 Rotation frequency of the output shaft: N F T A × TC × TE = N A TB × TD × TF T A × TC × TE NF = × NA  TB × TD × TF 30 × 20 × 50  NF = × 2300 40 × 60 × 70 = 410,71 r/ min  (3) 9.1.2 Velocity Ratio: N NOUTPUT VR = INPUT VR = NOUTPUT NINPUT 2300  410,71  = or = 410,71 2300 = 5,6 :1  = 1 : 0,178  (2) 9.2 Belt Drives: 9.2.1 Rotation frequency of the driven pulley: V = πDn  V n= πD 32 = π × (0 ,26 ) nr / min = 39 ,18× 60 nr / min = 2350,6 r / min (3) 9.2.2 Tensile force in the tight side: T1 = 2 ,5 T2 T = 2 ,5 × T  1 2 = 2 ,5 × 140 = 350 N  (2) 9.2.3 Power transmitted: P = (T1 − T2 )v  P = (350 − 140 ) × 32  = 6720 Watts  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 15 DBE/November 2017 NSC – Marking Guidelines 9.3 Hydraulics: 9.3.1 Fluid pressure: πD 2 AA =  4 π 0.02 2 = 4 = 0 ,31 × 10 −3 m 2  F pA =  AA 300 = Pa 0 ,31 × 10 −3 = 967741,94 Pa  = 0 ,97 × 10 6 Pa = 0 ,97 MPa (4) 9.3.2 Stroke at piston B: πD 2 AB =  4 π 0.075 2 = 4 = 4 ,42 × 10 −3 m 2  VB =VA AB × LB = AA × LA  A × LA LB = A AB = (0,31× 10 )× 185 −3 4 ,42 × 10− 3 =12 ,98 mm  (4) 9.4 Traction control: It prevents the wheels from spinning   (2) 9.5 Safety belt: Safety belts need to be activated (buckle up) by the driver/passenger   (2) [25] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 16 DBE/November 2017 NSC – Marking Guidelines QUESTION 10: TURBINES 10.1 Water turbine: • Waterwheel  • Pelton  • Turgo  • Michell-Banki  • Jonval turbine  • Reverse overshot waterwheel  • Archimedes’ screw turbine  (Any 1x1) (1) 10.2 Runaway speed of a water turbine: Runaway speed of a water turbine is its speed at full flow  and with no shaft load  (2) 10.3 Water turbine: 10.3.1 Type of turbine: • Reaction turbine  • Kaplan turbine  (Any 1x1) (1) 10.3.2 A. Wicket gate  B. Rotor  C. Stator  D. Shaft  E. Water flow  F. Blades  (6) 10.3.3 Advantages of water turbine: • Water turbine blades continue to turn on cloudy windless days unlike sun and windy system.  • No water is consumed in this process  • More reliable  • Environmentally friendly with no pollution  • More economical than steam turbines  • Can be mounted vertically to take up less space  (Any 3x1) (3) 10.4 Function of turbo and superchargers: To increase  volumetric efficiency  of an internal combustion engine. (2) 10.5 Compressor used in a turbocharger: Centrifugal  (1) 10.6 Turbocharger: Exhaust gasses  (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 17 DBE/November 2017 NSC – Marking Guidelines 10.7 Advantage of a turbocharger: • It is driven by exhaust gasses  • No power from engine is used  • Power loss above sea level is eliminated  • More power is developed compared to a similar vehicle without a turbocharger  • Less fuel is used compared to engine mass  • To increase volumetric efficiency  (Any 1x1) (1) 10.8 Advantage of a steam turbine: • It is compact  • No lubrication is needed  • It is more economical  • Converts heat energy into mechanical energy  • Greater thermal efficiency  • Direct drive  • Low maintenance  • High power to weight ratio  (Any 2x1) (2) [20] GRAND TOTAL: 200 Copyright reserved