The component then cracks This can be prevented by a low temperature stress

The component then cracks this can be prevented by a

This preview shows page 10 - 13 out of 73 pages.

The component then cracks. This can be prevented by a low temperature stress relief annealing process. This low temperature does not cause recrystallization but is sufficient to remove the locked up stresses by allowing the atoms to move small distances nearer to their equilibrium positions. (V) TEMPERATURE For all chemical reactions there is a critical temperature below which they will not take place. Since corrosion is the result of chemical or electrochemical reactions, corrosion is retarded or stopped altogether at low temperatures. On the other hand, corrosion is at its worst in the hot, humid atmosphere of the tropical rain forests, and equipment for use in such environments has to be ‘tropicalized’ if it is to have a reasonable service life.
Image of page 10
~ Page 11 of 73 ~ High temperatures alone do not increase the rate of corrosion, and corrosion is virtually non-existent in arid desert areas of the world. Failure of mechanical devices in desert environments is due generally to the abrasive effect of the all- pervasive sand.
Image of page 11
~ Page 12 of 73 ~ EXERCISE 1. Briefly explain the difference between the terms ‘corrosion’ and ‘erosion’ as applied to metals. 2. Describe the main difference between ‘wet’ and ‘dry’ corrosion. 3. Briefly explain why: (a) The tin film coating of tinplate must not be broken during forming processes. (b) The zinc coating of galvanised wire netting is eaten away before the wire it is protecting. 4. Explain why sheet copper is resilient to urban pollution when used as a roofing material. 5. Describe the essential difference(s) between electroplating and anodising. 6. Differentiate between the processes of chromating and chromising. 7. Describe the essential difference(s) between electroplating and the cementation process. 8. Give three (3) examples of plastic coated metal components in a home. 9. Explain the importance to the paint system of: (a) The primer; and (b) The gloss paint. 10. Describe what is meant by the terms: (a) Atmospheric corrosion; and(b) Galvanic corrosion. 11. Discuss four (4) factors which affect the corrosion of metallic components and assemblies. 12. (a) Describe in detail how metals such as aluminium, copper and zinc resist corrosion. (b) Discuss the main factors responsible for the degradation of polymeric materials in service. 13. State briefly what is meant by the terms: 14. Explain why sherardized steel-work in an industrial, urban environment should also be painted. 15. Explain: (a) How low carbon steel components can be protected by the process of galvanising and explain why the coating is said to be ‘sacrificial’; (b) Why the surface of a metal component must be carefully prepared prior to painting and how this may be performed. (c) How paint systems are classified according to the method by which the paint dries and hardens, and describe the various coats which are used to build up a complete paint system.
Image of page 12
Image of page 13

You've reached the end of your free preview.

Want to read all 73 pages?

  • Fall '19

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors