Engineering - Exam Papers - HL - Paper - 1990

300 Marks
Answer Question 1, Sections A and B and FOUR other questions.

Structure | TEDs | Plastics | Metallurgy | Metrology | Steels & Iron | Information Tables | Exam Papers | Syllabus
1.
(100 Marks)
Section A - 75 Marks
(a) What principle toxic effects may result from working with certain materials?
(b) Why is silicon a semiconductor?
(c) Identify the main type of lattice defect in metals.
(d) State two disadvantages of adhesives related to the joining of engineering materials.
(e) Distinguish between electrostatic and magnetic ore dressing.
(f) Identify processes used to manufacture
(i) plastic footballs,
(ii) motor car shells and
(iii) printed circuit boards.
(g) Explain why quality of surface finish is important in precision machining.
(h) What environmental factors affect the corrosion rate of metals?
(i) Differentiate briefly between ionic and metallic bonding.
(j) State two precautions relating to the use of compressed air.
(k) What is elastic memory with reference to thermoplastics?
(l) Why do metals tend to harden as a result of cold forming?
(m) State two reasons for using pneumatic systems in industry.
(n) Differentiate briefly between graphite and diamond with regard to stricture.
(o) Outline a particular contribution to technology by any one of the following:
(i) Henri Coanda or
(ii) John Dunlop or
(iii) Germain Sommeiller.
Section B - 25 Marks
(p)
How is the piston returned in a pneumatic cylinder which is
(i) single-acting, and
(ii) double-acting?
(q) Some of the main features of a pneumatic circuit are shown in the diagram.
Identify A, B and C.
(r) Explain how such a circuit operates.
(s) Explain the term cushioned cylinder.
(t) What is sequential control?
2.
(50 Marks)
(a) Name the two main classes of materials testing and list three tests appropriate to each class.
(b) Distinguish between macroscopic and microscopic examination of metals.
(c) The given diagram shows the load-extension graph for a ductile material.
(i) Explain what the regions A and B represent.
(ii) Why is the load at which fracture occurs less than the maximum load?
(iii) Explain, step by step, what occurs if the test specimen is loaded to point C and then unloaded.
(iv) Explain how the 0.1% proof load may be found from the load and hence calculate the proof stress, given that the specimen has a cross-sectional area of 80 mm2 and a gauge length of 80 mm.
3.
(50 Marks)
(a) Referring to the given iron-carbon diagram:
(i) describe the phases represented at A, B, C and D;
(ii) identify clearly the eutectic point and explain what it represents.
(b) A eutectoid reaction occurs at 723°C for 0.83% carbon steel.
(i) Compare the eutectic and eutectoid reactions.
(ii) What practical use is made of the eutectoid reaction?
(c) Describe any method by which 0.5% carbon steel may be surface hardened.
4.
(50 Marks)
(a) Explain the terms:
(i) interstitial solid solution;
(ii) substitutional solid solution;
(iii) intermetallic compound.
(b) The melting points of two metals A and b are 270°C and 630°C, respectively. The given table shows the temperature at which solidification begins and ends, when various alloys of the metals are cooled from liquid to solid.
(i) Using the graph paper supplied, draw a thermal equilibrium diagram according to the given data;
(ii) Label the diagram and discuss its main features.
AMOUNT OF B IN ALLOY (%) 0 10 20 30 40 50 60 70 80 90 100
TEMPERATURE AT START OF SOLIDIFICATION (°C) 270 332 400 445 492 524 552 580 603 618 630
TEMPERATURE AT END OF SOLIDIFICATION (°C) 270 272 280 300 318 340 368 404 449 510 630
(c) Determine from the diagram:
(i) the compositions of the phases present at 450°C for the alloy containing 60% of B
(ii) the ratio of the phases present at 450°C.
5.
(50 Marks)
(a) Discuss the general information which may be obtained from the code used to classify welding electrodes.
(b) The diagram shows a type of circuit used to provide welding current from a 220V ac power supply.
(i) Name the devices shown at A and B and sate their functions.
(ii) Using a suitable diagram, show the path and direction of current flow when P is positive and Q is negative.
(iii) Why is component X required in the circuit?
(iv) Sketch graphs showing the input and output currents.
(c) State three advantages of automatic welding.
OR
(c) Outline the main characteristics of a robot arm to be used for the auto mated welding of bicycle frames.
6.
(50 Marks)
(a) Differentiate between addition polymerisation and condensation polymerisation. What is copolymerisation?
(b) Explain the role of covalent bonding in polymer structures. Hence explain why the properties of thermoplastics differ so markedly from thermosets. Illustrate your answer with suitable examples.
(c) Compare the effects of stress on the structure of thermoplastics, thermosets and elastomers.
Describe a manufacturing process using any one of these materials.
7.
(50 Marks)
(a) Describe the basic theory of metal cutting with reference to the mechanism of chip formation.
(b) Identify the forces A and B acting at the tip of a single-point tool as shown in the diagram.
Which force is most significant in terms of power consumption?
When a shaft of 60 mm diameter is machined at 150 rev/min, the cutting force is 3 kN; calculate the power consumed.
(c) Compare the use of three different types of machine tool for machining flat surfaces.
OR
(c) Explain, briefly, each of the following terms:-
(i) computer numerical control (CNC) machining;
(ii) computer aided design (CAD);
(iii) computer aided manufacture (CAM).
8.
(50 Marks)
(a) Describe the principle function of any three of the following:
(i) strip heater;
(ii) thermocouple;
(iii) ratchet mechanism;
(iv) pneumatic flow regulator;
(v) electronic transistor.
(b) Explain with the aid of a diagram, the operation of the automatic feed mechanism on a centre lathe.
OR
(b) Identify the components A, B, C, D, E and F in the circuit diagram.
What is the function of this circuit?
(c) Explain, with the aid of a diagram, the operation of a mechanism or system to enable an entrance barrier for a car park to function automatically.