Mechanical Technology Grade 12 NSC November 2012 Memo (Eng)

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE GRADE 12 MECHANICAL TECHNOLOGY NOVEMBER 2012 MEMORANDUM MARKS: 200 This memorandum consists of 17 pages. Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 2 DBE/November 2012 NSC – Memorandum QUESTION 1: MULTIPLE-CHOICE QUESTIONS 1.1 B (1) 1.2 A (1) 1.3 D (1) 1.4 B (1) 1.5 A or B  (1) 1.6 B (1) 1.7 A (1) 1.8 C (1) 1.9 D (1) 1.10 A (1) 1.11 D (1) 1.12 B (1) 1.13 B (1) 1.14 C (1) 1.15 A (1) 1.16 C (1) 1.17 D (1) 1.18 A (1) 1.19 C (1) 1.20 D (1) [20] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 3 DBE/November 2012 NSC – Memorandum QUESTION 2: TOOLS AND EQUIPMENT 2.1 Causes of low compression: • Worn cylinders  • Worn compression rings  • Worn piston  • Worn valves  • Worn head gasket  (Any 3 x 1) (3) 2.2 Torsion: Torsion is the twisting action in a member  caused by two opposing moments along the longitudinal axis.  (2) 2.3 Multimeter: A – LCD display screen  B – Range selector switch  C – 10 A DC terminal socket (Input terminal)  D – VΩmA terminal socket (Input Terminal)  E – Common terminal socket  (5) 2.4 Cylinder leakage tester: • Listen at the carburettor and/or inlet manifold for hissing noise.  (inlet valve is leaking)  • Listen to the exhaust pipe or exhaust manifold for a hissing noise.  (exhaust pipe is leaking)  • Listen for hissing noise in the dipstick hole.  (piston rings worn)  • Remove the filler cap on the tappet cover and listen for hissing noise.  (rings are worn)  • If you see bubbles in the radiator water,  (the cylinder head gasket is blown or the cylinder block is cracked)  (Any 3 x 2) (6) 2.5 MAGS/MIGS – meaning • MAGS: Metal Arc Gas Shielded  • MIGS: Metal Inert Gas Shielded  (2) 2. 6 MAGS/MIGS gases • Argon  • CO 2  • Helium  (Any 2 x 1) (2) [20] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 4 DBE/November 2012 NSC – Memorandum QUESTION 3: MATERIALS 3.1 Non-ferrous materials and composites: • Non-ferrous Metals are metallic and composites are non-metallic.  • Non-ferrous metals are original substances and composites are combinations of two or more materials.  (Any 1 x 2) (2) 3.2 Compressive strength test: 3.2.1 Material A has the highest compressive strength.  (1) 3.2.2 The material that can resist a large compression force will have little deformation or compression, and has a higher compressive strength.  (2) 3.3 Carbon steel: • Low-carbon steel  • Medium-carbon steel  • High-carbon steel  (3) 3.4 Carbon steel – properties: • Greater hardness is obtained  • Tensile strength is increased  • Ductility is decreased  • Welding ability is decreased  (4) 3.5 Uses and properties of engineering materials: 3.5.1 Uses of Duralumin: It is used to make the following: • Bars  • Sheets  • Piston rods  • Tubes  • Rivets  • Motorcar and aircraft parts  (Any 2 x 1) (2) Properties of Duralumin: o Lightweight  o High tensile strength  o Good resistance to corrosion  o Hardens with age  (Any 2 x 1) (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 5 DBE/November 2012 NSC – Memorandum 3.5.2 Uses of PVC: It is used to make: • Pipes and fittings  • Cable and services ducting  • Roofing and ceiling systems and membranes  • Healthcare materials  • Automotive industry materials  (Any 2 x 1) (2) Properties of PVC: • Lightweight  • Weather resistant  • Rigid or flexible  • Clear or coloured  • Good electrical insulator  • Good resistance to corrosion  (Any 2 x 1) (2) [20] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 6 DBE/November 2012 NSC – Memorandum QUESTION 4: SAFETY, TERMINOLOGY AND JOINING METHODS 4.1 Beam bending tester: • Make sure that the object to be tested is firmly secured.  • Make sure that all the holding devices are properly fitted.  • Check components of tester for wear.  • Check for leaks at the hydraulic pump ram and hose.  • Make sure that the tester is clean and free from oil and grease.  (Any 3 x 1) (3) 4.2 Gas cylinders: • Store full cylinders apart from empty cylinders.  • Keep in cool, dry place away from sunlight.  • Acetylene cylinders should be stored in an upright position.  • Oxygen cylinders should be stored away from acetylene cylinders.  • Do not allow cylinders to fall.  • No oil and grease should come into contact with oxygen cylinders and fittings.  (Any 3 x 1) (3) 4.3 Milling operations: 4.3.1 Upcut milling: • Less vibration occurs.  • Less strain on the cutter and arbor.  • There is positive pressure on the feed screw spindle and its nuts because of the direction of the cutter.  • A coarser feed may be used.  (Any 2 x 1) (2) 4.3.2 Down-cut milling: • Deeper cuts can be made because the force of the cutter is downwards.  • A finer finish is obtained.  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 7 DBE/November 2012 NSC – Memorandum 4.4 Indexing: 4.4.1 40 Indexing =  A 40 =  60 4× 4  = 6× 4 16 20 26 28 34 36 44 = or or or or or or  24 30 39 42 51 54 66 16 holes on the 24-hole circle or 20 holes on the 30-hole circle or 26 holes on the 39-hole circle or 28 holes on the 42-hole circle or 34 holes on the 51-hole circle or 36 holes on the 51-hole circle or 44 holes on the 44-hole circle (4) 4.4.2  = ( A − n )× = (N − n )× Dr 40 Dr 40 OR Dv A Dv N  = (60 − 63)× = (60 − 63)× Dr 40 Dr 40 Dv 60 Dv 60 Dr − 120 Dr − 120  = = Dv 60 Dv 60 Dr − 12 × 4 Dr − 12 × 4 = =  Dv 6 ×4 Dv 6 ×4 Dr − 48 56 64 Dr − 48 56 64 = or or = or or  (5) Dv 24 28 32 Dv 24 28 32 Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 8 DBE/November 2012 NSC – Memorandum 4.5 Cutting feed: V = πDN  V N=  πD 20  N= π × 0,08 N = 79,577 r/min  f = f1 × T × N  f = 0,08 × 14 × 79,577  f = 89,13 mm/min  (7) 4.6 Ultrasonic test: • A high frequency sound wave is send into the metal for a very short period of 1 to 3 microseconds.  • The same unit which was used to send the sound wave then acts as a receiver to listen to the ultrasonic waves it reflected through the metal.  • This cycle is repeated from one to five million times per second. • The oscilloscope is calibrated only to pick up defects of a size that would be considered harmful.  • The oscilloscope wave pattern is also calibrated to show the distance between the searching unit and any defects found.  (5) 4.7 Weld defects: 4.7.1 Slag inclusion: Causes: • Included angle too narrow  • Rapid cooling  • Welding temperature too low  • High viscosity of molten metal.  • Welding second run without removing slag  (Any 2 x 1) (2) Prevention: • Increase the included angle.  • Let the welded metal cool slowly  • Pre-heat the metal  • Remove slag before welding a second run  (Any 1 x 1) (1) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 9 DBE/November 2012 NSC – Memorandum 4.7.2 Undercutting: Causes: • Faulty electrode manipulation  • Arc length too long  • Current too high  • Welding speed too fast  (Any 2 x 1) (2) Prevention: • Use a uniform weaving movement in butt joint  • Use the correct electrode  • Use the correct current  • Weld slowly  (Any 1 x 1) (1) 4.8 Milling Cutters: 4.8.1 Spur gear – Involute cutter  4.8.2 Groove – Side-and-face cutter or end mill or slot drill  4.8.3 Rack – Involute cutter/Fly cutter  4.8.4 Blind hole – Flute-end mill  (4) 4.9 Dividing head of a milling machine: A = Index plate  B = Index crank  C = Sector arms  D = Single-start worm  E = Wormwheel/gear  (5) 4.10 Classification of milling cutters: Arbor cutters  (1) Examples: Plain cutter , side cutter, staggered-tooth cutter, slitting-saw cutter, angular cutter, profile/form cutters, side-and-face cutter, helical cutter  (Any 1 x 1) (1) Shank cutters  (1) Examples: End mill; shell end mill; T-slot cutter and Woodruff keyseat cutter (Any 1 x 1) (1) [50] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 10 DBE/November 2012 NSC – Memorandum QUESTION 5: MAINTENANCE AND TURBINES 5.1 Clutch 5.1.1 Parts: A. Crankshaft  B. Clutch plate  C. Gearbox shaft  D. Diaphragm spring  E. Pressure plate  F. Flywheel  (6) 5.1.2 Functions: • To provide friction between the clutch and pressure plate  • To connect the flywheel to the gearbox shaft  (4) 5.1.3 Causes of slip: • Oil on the friction surfaces  • Worn friction surfaces  • Lack of compressive force on the friction surfaces caused by weak springs  • Lack of compressive force on the friction surfaces caused by incorrect clutch settings  • Uneven friction surfaces  • Overheating  (Any 3 x 1) (3) 5.1.4 Clutch types: • Single-disc clutch  • Multi-disc clutch  • Centrifugal clutch  (Any 2 x 1) (2) 5.2 Functions of lubricating oil: • Provides lubrication between contact surfaces  • Resists oxidation  • Prevents rust  • Avoids foaming  • Resists carbon forming  • Prevents corrosion  • Resists extreme pressure  (Any 3 x 1) (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 11 DBE/November 2012 NSC – Memorandum 5.3 Cutting fluid: • Avoid contamination of the cutting fluid by draining and regularly replacing it.  • Always clean metal cuttings from the machine’s splash tray after use.  • Regularly wipe cutting fluid splashes off machine parts when machine is stationary.  • Ensure that the sump is topped up from time to time, and check that there is sufficient flow of cutting fluid to the cutting tool.  • Check for correct ratio of cutting fluid to water.  (Any 3 x 1) (3) 5.4 Supercharger 5.4.1 Centrifugal type  (1) 5.4.2 Parts: A. Inlet port  B. Outlet port  C. Rotor  D. Vane  (4) 5.4.3 Operation: • The engine drives the rotor  • Air is drawn in behind the rotor  • The air is forced around into a decreasing volume  • This raises the pressure of the air  • The air is forced into the inlet manifold and into the cylinders  (5) 5.4.4 Advantages of a supercharger: • More power is developed compared to a similar vehicle without a supercharger  • Supercharged engines are more economical per given kilowatt output  • Less fuel is used compared to engine mass  • Power loss above sea level is eliminated  (Any 3 x 1) (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 12 DBE/November 2012 NSC – Memorandum 5.5 Steam turbines: • Condensing turbines  • Non-condensing turbines  • Reheat turbines  • Extracting turbines  • Induction turbines  (Any 3 x 1) (3) 5.6 Advantages of gas turbine: • High power output from a given weight of engine.  • The torque output permits a notable simplification of the transmission system.  • Smooth vibrationless running due to absence of reciprocating parts.  • No rubbing parts such as piston so that internal friction and wear are almost eliminated.  • Easy starting.  • Can use a wide range of fuels without expensive anti-knock additives.  • Low lubricating oil consumption.  • No water cooling system needed.  • Non-poisonous exhaust gases gives very little trouble with pollution.  • Requires little routine maintenance.  (Any 3 x 1) (3) [40] Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 13 DBE/November 2012 NSC – Memorandum QUESTION 6: FORCES, SYSTEMS AND CONTROL 6.1 Hydraulics: 6.1.1 Fluid pressure: Rounded off Fully extended πD 2 πD 2 AA =  AA =  4 4 π × (0,038 ) π × (0,038 ) 2 2 = = 4 4   = 1,13 × 10 −3 m 2 = 0,001134114 m 2 F F P= A P= A  AA  AA 300 300 P=  P= 1,13 × 10 −3 0,001134114  = 0,27 MPa  = 264523,45 Pa  (5) 6.1.2 Load lifted by piston B: Rounded off Fully extended πD 2 πD 2 AB =  AB =  4 4 π × (0,175 ) π × (0.175 ) 2 2 = = 4 4 = 24,05 × 10 −3 m 2  = 0,024052818 m 2  FB FB P=  P=  AB AB FB = AB × P  FB = AB × P   = (0,024052818 × 264523,45  = (24,05 × 10 −3 ) × 0,27 × 10 6 = 6,49 kN  = 6362,54 N  (6) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 14 DBE/November 2012 NSC – Memorandum 6.2 Stress and Strain: Tensile force: Rounded off Fully extended ΔL  ΔL  ε= ε= OL OL 0,2 0,2 = = 300 300 = 0,66 × 10 −3  = 0,0006666  σ σ E=  E=  ε ε σ = E×ε σ = E×ε = 245 × 10 9 × 0.66 × 10 −3  = 245 × 10 9 × 0,000666666   = 163333333,3 Pa  = 161.7 × 10 Pa 6 F F σ= σ= A  A  F =σ×A F =σ×A   = 161,7 × 10 × 2,2 × 10 6 −6  = 163333333,3 × 2,2 × 10 −6  = 355,74 N  = 359,33 N  (9) 6.3 Belt drives: 6.3.1 Rotation frequency of the driven pulley: driven pulley: N A × DA = N B × DB N × DA  NB = A DB 1000 × 0,25 = 0,35  = 714,29 rpm r/min  (3) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 15 DBE/November 2012 NSC – Memorandum 6.3.2 Power transmitted: P= (T1 − T2 )πDN 60  P= (200 − 90 )× π × 0,25 × 1000  60 P = 1439,90 Watts P = 1,44 kW  (3) 6.3.3 Belt speed: πDN  v= 60  π × 0,25 × 1000 = 60  v = 13,09 m.s −1 (3) 6.4 Gears: 6.4.1 Rotation frequency of the output shaft: N F TA × TC × TE N F Product of driven gears = or =  N A TB × TD × TF N A Product of driver gears TA × TC × TE × N A 24 × 20 × 42 × 1440  NF = = TB × TD × TF 40 × 48 × 90  24 × 20 × 42 × 1440 NF = = 168 rpm r/min 40 × 48 × 90  = 168 rpm r/min (4) 6.4.2 Velocity ratio: NA VR =  NF 1440 VR = 168 VR = 8.57 : 1  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 16 DBE/November 2012 NSC – Memorandum 6.5 Differential wheel and axle: 6.5.1 Mechanical advantage: W  MA = F 2400 MA = 400 MA = 6  (2) 6.5.2 Velocity ratio: 2D VR =  d1 − d 2 2(210 )  VR = 160 − 140 420 VR = 20 VR = 21 : 1  (3) 6.5.3 Mechanical efficiency: MA ηmech = × 100%  VR 6 = × 100% 21 = 28.57%  (2) Copyright reserved Please turn over

Downloaded from hlayiso.com Mechanical Technology 17 DBE/November 2012 NSC – Memorandum 6.6 Clutches: 6.6.1 Diameter of clutch plate: T = μWnR  T R=  μWn 336  R= 0,4 × 3500 × 2 R = 0,12 m D = 2 × 0,12  D = 0,24 m = 240 mm  (5) 6.6.2 Power transmitted at 3500 rpm in kW: 2π NT P=  60 2 × π × 3200 × 336 P=  60 P = 112,59kW  (3) [50] TOTAL: 200 Copyright reserved