h t s oude molen t h s - western cape · web viewwelding stands for: (1) a mainly industrial gas b...

MECHANICAL TECHNOLOGY

Grade: 12 Time: 3 hrs September 2011 Marks: 200

Examiner: Moderator: Instructions

1. Read through the whole question paper before you start any answers.2. Leave three lines clear at the top of the page for administrative purposes.3. Write the information in the block above at the top of your first answer page

and add your name in the top right hand corner.4. Number the pages you use and ensure that your name appears on the front of each page.5. Allocate time per question according to the marks available.6. Answers must be written in blue ink.7. If you need assistance, put up your hand to attract the attention to the invigilator. Out of respect

for the examination process and the other candidates, do not draw attention to yourself in any other way.

8. Do not attempt to communicate with any other candidate during the duration of the examination – i.e once exam papers are being distributed and until all have been collected.

9. Do your best!

Our business is growing people.

QUESTION ASSESSMENT STANDARDS

CONTENTS COVERED MARKS TIME

1 1-9 Multiple-choice questions 20 18minutes

2 6 Forces and systems and control 50 45minutes

3 2 Tools and equipment 20 18minutes

4 3 Materials 20 18minutes

5 1,4 & 5 Safety, terminology and joining methods 50 45minutes

6 7 & 9 Maintenance and turbines 40 36minutes

TOTAL 200180

minutes

2. MECHANICAL TECHNOLOGY SEPTEMBER 2011

GRADE 12

QUESTION 1 : (MULTIPLE CHOICE):Mark only the correct answer with a cross on the answer sheet provided. 1.1 Which precaution is not applicable when drilling stainless steel in the

drill press?(1)

A Use the correctly sharpened drill bitB Select the maximum speed possible for drillingC Never force the drill bit into the material D Use a brush or wooden rod to remove cuttings

1.2 Poor housekeeping results in many accidents in the workplace. Which of the following causes does not relate to housekeeping:

(1)

A Loose clothingB Untidy workshopC Tools not packed awayD Insufficient safety signage

1.3 CO testing is done to determine the percentage of …………in vehicle’s exhaust emissions.

(1)

A Nitrous oxideB Carbon dioxideC Nitrogen dioxideD Carbon monoxide

1.4 Hardness testing is performed on metals to determine: (1)A Young’s modulus for the metalB Ductility of the metalC Hardness of the metalD Strength of the metal

1.5 Compression testing is performed on internal combustion engines to: (1)A Test for cylinder leakageB Measure the pressure in the cylinder on its compression strokeC Test the power ratio of the engineD Measure the swept volume of the cylinder

1.6 Aluminium extrusions are usually made of: (1)A Ferrous metalsB Non ferrous metalsC Ferrous alloysD Non ferrous alloys

1.7 Which of the following is not true about perspex (1)A Perspex is a thermoplasticB Perspex can not be bonded with any glue or solventC Perspex is also known as acrylicD Perspex is resistant to most acids


GRADE 12

QUESTION 1 : (MULTIPLE CHOICE cont.):

1.8 White metal is used in: (1)A Xenon car headlightsB Tin foilC Main bearingsD Catalytic exhaust plates

1.9 The following type of milling cutter is placed on the arbor of a horizontal milling machine:

(1)

A T-slot cutterB End millC Woodruff key seat cutterD Involute cutter

1.10 Which of the following are not a set used on power saw blades: (1)

A Spiral setB Straight setC Raker setD Wave set

1.11 The included angle for grinding drill bit tips for use on easily drilled metals is:

(1)

A 118°B 90°C 135°D 60°

1.12 MIG welding stands for: (1)A Mainly Industrial GasB Metal Industrial GasC Mainly Inert GasD Metal Inert Gas

1.13 Which of the following should no be inspected while arc welding? (1)A Amount of fusion and penetrationB Regulator pressureC Sound of the arcD Way the molten metal is flowing

1.14 What welding defect does atmospheric contamination cause? (1)A PorosityB Slag inclusionC UndercuttingD Blow holes


GRADE 121.15 Stress is: (1)A An external force present in a material resisting an external loadB An internal force present in a material resisting an external loadC An external force present in a material resisting an internal loadD An internal force present in a material resisting an internal load

1.16 A round bar with a cross sectional area of 78,5 mm2 is subjected to a shearing force of 10kN. Calculate the stress in the bar.

(1)

A 156,32 MpaB 210,34 MpaC 127,39 MpaD None of the above

1.17 State which of the following statements is true: (1)A Viscosity of liquids decreases as temperature decreasesB Viscosity of liquids decreases as temperature increasesC Viscosity of liquids increases as temperature increasesD Viscosity of liquids are not affected by temperature

1.18 The following is an example of: (1)

A Reverse motion linkageB 1st class leverC 2nd class leverD 3rd class lever

1.19 In hydraulic systems the following is not true (1)A The pressure is uniform throughout the systemB Volume is directly proportional to pressureC Hydraulics are used to obtain mechanical advantageD Hydraulic systems must have pressure relief safety valves

1.20 The concepts lag and boost are only applicable to: (1)

A Twin screw superchargersB Roots superchargersC TurbochargersD Centrifugal superchargers


Load Fulcrum

Force

GRADE 12

QUESTION 2 : (Applied mechanics chapter 6)

2.1 Draw a neat labelled diagram of the stress strain diagram. 8 X ½ (4)

2.2 At which point in the stress strain diagram is Young’s Modulus no longer true?

(1)

2.3 A steel cable with a diameter of 12 mm is subjected to a tensile test using a hydraulic tensile tester. When a load of 30 kN is applied to the cable, it causes it to lengthen by 0,01 mm. The original length is 1m.

2.3.2 Calculate the following for the test piece:2.3.2.1 The tensile stress in the cable (3)2.3.2.2 The strain in the cable (2)2.3.2.3 Young’s Modulus (2)

2.4 In designing a machine you are required to calculate belt lengths for both the open- and crossed-belt drive systems. The following specifications are given:

The diameter of the driving pulley is 400 mm. The diameter of the driven pulley is 150 mm. The centre distance between the pulleys is 550 mm.

2.4.1 Calculate the belt length for an open-belt drive system. (2)2.4.2 Calculate the belt length for a crossed-belt drive system. (2)

2.5 An electric motor rated at 7 kW at a speed of 1500 r/min is required to pump water in an air conditioning unit. The suppliers only stock an electric motor that generates a torque of 45 Nm at 1 500 r/min. Will this motor be powerful enough to meet the requirements? Motivate your answer.

(3)


GRADE 12

2.6 In the figure below the load applied on piston B induces a force of 500 N on this piston in a hydraulic jack. Piston B moves 5 mm upwards. The area of piston A is 0,012 m2 and that of piston B is 0,20 m2.

Calculate the following:2.6.1 The force applied in piston A (4)2.6.2 The distance 'x' in millimeters, that piston A moves downwards (5)2.6.3 The effect it will have on the distance 'x' if the length of the

hydraulic press is doubled. Motivate your answer.(2)

2.6.4 Give another example where this type of hydraulic system is used. (2)

2.7 The mechanical advantage of a differential wheel and axle lifting machine, used as a winch is 6. A load of 1,6 kN is lifted when an effort 'F' is applied. The diameters of the pulleys are 200 mm (D), 140 mm (d2) and 110 mm (d1) respectively.


2000 mm

x mm

5 mm

GRADE 12

Calculate the following:2.7.1 The magnitude of the applied effort 'F' (2)2.7.2 The velocity ratio (2)2.7.3 The percentage with which the efficiency of the system will

increase if pulley A is replaced by another pulley twice its size.(2)

2.8 A three-start square thread with a crest diameter of 14 mm and a pitch of 2 mm is to be cut on a shaft using a centre lathe to manufacture the screw of a scissor jack. Assume a clearance angle for the cutting tool of 3°.

Calculate the following:2.8.1 The helix angle of the thread (3)2.8.2 The leading angle of the cutting tool (2)2.8.3 The following angle of the cutting tool (2)2.8.4 How can more travel on the scissor jack be achieved with the

same number of turns of the crank handle?(3)

2.9 A single-plate friction clutch with an effective diameter of 0,15 m is used to transmit torque of 56Nm at 3 000 r/min in an engine/generator combination. The clutch plate has a friction material on both sides. The total applied force on the pressure plate is 2,5 kN.

2.9.1 Determine the coefficient of friction of the clutch plate. (2)

[50]

8. MECHANICAL TECHNOLOGY SEPTEMBER 2011 GRADE 12

QUESTION 3 : (Tools and equipment) 3.1 Name the instrument in the following diagram and state its primary

function.(2)

3.2 State the steps (in correct order), which must be performed when using the instrument above.

(6)

3.3 What is the purpose of fitting catalytic converters to vehicle exhaust systems?

(2)

3.4 What do the hissing noises at the following places indicate when using the cylinder leakage tester?

3.4.1 The carburetor (1)3.4.2 The exhaust pipe (1)3.4.3 The dipstick hole (1)

3.5 A stainless steel test specimen was hardness tested using a Brinell hardness tester and the following result was achieved: 75 HB 10/500/30. Interpret the result and explain what it represents.

(5)

3.6 Name two other types of hardness testers (2)

[20]

9. MECHANICAL TECHNOLOGY SEPTEMBER 2011 GRADE 12

QUESTION 4 : (Engineering materials)

Non-ferrous alloys and polymers are used broadly in industry today for manufacturing various components due to their composition and properties.

4.1 In table format compare and contrast the following non-ferrous metals with reference to composition, properties and uses:

4.1.1 White metal (3)4.1.2 Duralumin (3)4.1.3 Brass (3)

4.2 Name 3 advantages and 3 disadvantages of using thermoplastics over using thermosetting plastics.

(6)

4.3 Give the full name of the following abbreviations of plastics and state one use of each one.

4.3.1 (1)

4.3.2 (1)

4.4 Why is Teflon such a versatile engineering material? (3)

[20]


GRADE 12

QUESTION 5 : (Safety, terminology and joining methods)

5.1 When sharpening a drill bit on a bench grinder, certain steps need to be followed to ensure safety. State how you would ensure that no accidents occurred while sharpening the drill bit.

(4)

5.2 Why must oil or grease never be used on or near the oxy-acetyleneregulator?

(1)

5.3 What is the purpose of the dividing head on a milling machine? (2)

5.4 Name FOUR methods of indexing when using the milling machine. (4)

5.5 A gear with 112 teeth must be machined on a milling machine. Calculate the required indexing and change gears for cutting the gear. Use the Cincinnati dividing head and the given change gears. (Use N = 120.)

(10)

5.6 When arc welding mild steel there are certain possible welding defects that may occur during the welding process. State ONE possible cause and ONE correction method for each of the following welding defects:

5.6.1 Porosity (2)5.6.2 Weld craters (2)5.6.3 Undercutting (2)

5.7 Which 4 safety precautions must be applied when MIG welding? (4)

5.8 Name 4 aspects that should be inspected during the oxy-acetylene process.

(4)

5.9 What are the 2 main purposes of ultrasonic testing? (2)

5.10 Describe the ultrasound testing process and state 2 advantages of ultrasound testing.

(6)

5.11 Explain how the nick-break test is performed? (3)

5.12 Name one advantage of destructive testing over non-destructive testing.

(1)

5.7 Describe the process used when performing the dye penetrant test to find welding defects and state two advantages of using this test method.

6 X ½ (3)

[50]


GRADE 12

QUESTION 6 : (Maintenance and turbines)

6.1 Describe what is meant by the term viscosity of oil. (2)

6.2 What is the difference between an oil’s viscosity and its viscosity index?

(2)

6.3 What does it mean if gear oil has a good demulsibility index? (1)

6.4 Name 4 other characteristics of good quality gear oils. (4)

6.5 Mineral oil is pumped from oil reserves below the earth’s crust as shown in the diagram below.

Name 2 other origins of oils used in mechanical systems and give specific examples of where each type is usually used.

(4)

6.6 What is the purpose of a torque converter in an automatic transmission?

(2)

6.7 Which type of gear system is used in an automatic transmission and state 3 advantages of using this type of system?

(4)


GRADE 12

6.8

The oil in the diagram above is classified as SAE 20W-50 engine oil.Explain what each component of this classification means.

(4)

6.9 Name 4 guidelines for using cutting fluid (water soluble oil) when machining objects on lathes and milling machines.

(4)

6.10 Why are turbochargers more efficient than superchargers? (2)

6.11 What advantages do superchargers have over turbochargers? (4)


GRADE 12

6.12 Eskom has recently built a gas turbine plant in Atlantis called ANKERLIG. The purpose of the plant is to generate additional electricity at times of high demand.

The turbines are very effective at generating large amounts of power, very quickly but have the disadvantage that they are not energy efficient.

Explain why this type of turbine is not very energy efficient.

(2)

6.13 Aeroplanes use very similar types of gas turbines call jet engines. Why are they more effectively used in the propulsion of aircraft than to generate power?

(2)

6.14 Name the following supercharger and state why it is very commonly used.

(3)

[40]

Total 200

MECHANICAL TECHNOLOGY ANSWER BOOK

QUESTION 1 : (MULTIPLE CHOICE):Answer this question on the sheet providedChoose only one correct answer

NAME:

GRADE:

TEACHER:

DATE:

1.11 A B C D

1.12 A B C D

1.13 A B C D

1.14 A B C D

1.15 A B C D

1.16 A B C D

1.17 A B C D

1.18 A B C D

1.19 A B C D

1.20 A B C D

1.1 A B C D

1.2 A B C D

1.3 A B C D

1.4 A B C D

1.5 A B C D

1.6 A B C D

1.7 A B C D

1.8 A B C D

1.9 A B C D

1.10 A B C D

h t s oude molen t h s - western cape · web viewwelding stands for: (1) a mainly industrial gas b...

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