Engineering - Exam Papers - HL - Paper - 1992

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

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1.
(100 Marks)
Section A - 50 Marks
Give brief answers to any ten of the following :
(a) Give two precautions against the irritant effects of materials.
(b) Identify two main stages in the extraction of a metal from its ore.
(c) What is an n-ytpe semiconductor?
(d) Identify clearly the processes used to manufacture any two of the following:
(i) Brass Door Knocker;
(ii) Vehicle Reflector Lens;
(iii) Plastic Window Frames.
(e) What is the difference in structure between glass and ceramics?
(f) State two safety precautions related to the drilling machine.
(g) Identify two defects in the crystal structure of a metal.
(h) What is the main difference between thermoplastic and thermosetting adhesives?
(i) Explain the difference in elasticity between rubber and metals.
(j) Identify clearly the purpose of
(i) an optical pyrometer or
(ii) a computer interface.
(k) State two ways in which materials may be affected by environmental reactions.
(l) What is the function of
(i) a pneumatic valve or
(ii) programmable logic control (PLC)?
(m) Identify a technological feature associated with any one of the following:
(i) Robert MacGhee or
(ii) George Devol or
(iii) Charles Babbage.
Section B - 50 Marks
Answer all of the following :
(n) Identify the parts A, B and C of the robot shown in the diagram.
(o) (i) What are degrees of freedom and
(ii) How many are shown in the diagram?
(p) Describe briefly the main ways in which the moving parts of a robot are driven.
(q) Explain how control of the moving parts is effected.
(r) Identify two techniques for programming robots.
2.
(50 Marks)
(a) Referring to a tensile test, state two factors which influence the shape of load-extension curve.
Define
(i) stress and
(ii) tensile strength.
(b) The following results were obtained from a tensile test on a non-ferrous alloy of diameter 14 mm and gauge length 70 mm.
LOAD (kN) 10 20 40 60 80 100 107 109 105 95
EXTENSION (mm) 0.04 0.08 0.17 0.26 0.38 0.66 0.90 1.00 1.20 1.40
Plot the load-extension graph and determine:
(i) the tensile strength;
(ii) the 0.1% proof stress.
(c) State the principles involved in any two of the following non-destructive tests:
(i) magnetic;
(ii) ultrasonic;
(iii) radiographic.
In each case, state the suitability of the method for detecting internal or external flaws.
3.
(50 Marks)
(a) What is meant by the allotropy of a material?
Explain its significance in relation to carbon steel, giving details of structural and temperature changes.
(b) Referring to the given iron-carbon diagram:
(i) describe the phases at A, B, C and D;
(ii) identify the eutectoid point and explain what it represents;
(iii) describe the structural changes occurring in 1% carbon steel through rapid cooling from 1000°C.
(c) Answer any two of the following relating to the heat treatment of materials:
(i) State three relevant safety precautions to be observed.
(ii) Why does hardening occur in the flame hardening process?
(iii) Name three main requirements of a quenching oil.
4.
(50 Marks)
(a) Explain diffusion in metals.
Relate its importance to such processes as brazing and fusion welding.
(b) Copy the given lead tin diagram into your answer book.
Identify
(i) liquidus,
(ii) solidus,
(iii) solvus and
(iv) eutectic point
on your diagram.
State clearly what each term represents.
(c) Referring to the diagram, determine each of the following for the alloy with 25% tin:
(i) the temperature range in which solidification occurs;
(ii) the composition of the phases at 70°C and 230°C;
(iii) the ration of phases at 230°C.
5.
(50 Marks)
(a) Explain the function of
(i) a transformer,
(ii) rectifier and
(iii) capacitor
in changing mains alternating current into direct current for welding purposes.
(b) Explain
(i) arc voltage and
(ii) open circuit voltage
with regard to arc welding.
(c) Describe, with the aid of a diagram, the main features of one of the following processes:
(i) submerged arc welding or
(ii) resistance spot welding.
OR
(c) State three advantages of robotic control in a welding environment.
6.
(50 Marks)
(a) Explain the terms:
(i) monomer;
(ii) polymer;
(iii) copolymer.
(b) Identify three basic polymer structures with the aid of suitable diagrams.
Explain the role of chemical bonding in each case.
(c) Give the name of an additive used in polymers and explain its influence on properties.
(d) Describe, using diagrams, the production processes for any two of the following plastic products:
(i) electrical socket cover;
(ii) curtain rail;
(iii) dustbin.
Indicate the nature of the plastic used in each case.
7.
(50 Marks)
(a) Discuss three properties of cutting tool materials which are essential for efficient machining.
(b) Explain orthogonal cutting, indicating the significance of the forces acting on the cutter.
Calculate the power due to a feed of 0.4 mm/rev, a feed force of 500N and a spindle speed of 400 rev/min.       
(c) What is the main difference between generating and forming when machining?
State three advantages of grinding as against other types of metal machining process.
OR
(c) List the main features of a CADCAM system and explain, briefly, the benefits and limitations of such a system.
8.
(50 Marks)
(a) Describe the principle function of any three of the following:
(i) heat pump;
(ii) flywheel;
(iii) integrated circuit;
(iv) double-acting pneumatic cylinder;
(v) circuit breaker.
(b) Explain with the aid of suitable diagrams, how power is transmitted from an electric motor to the spindle of a drilling machine by means of:
(i) vee belt and pulleys;
(ii) gears.
Show how spindle speed may be varied in each case.
(c) Explain clearly how movement of a power hacksaw can be achieved by pneumatic means.
How may the speed of movement be varied and controlled?
OR
(c) Identify the components A, B, C, D and E in the given circuit diagram.
State the function of such a circuit.