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Corrosion, finishing and production management

Mechanical finishes (polishing, brushing), plating (chrome, nickel, zinc), anodising (aluminium), enamelling, powder coating, and lacquering.

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  1. PDFCorrosion, finishing and production management – Metal Technology and Design notes (ZIMSEC A Level)47.5 KB

Corrosion

  • Electrochemical corrosion requires an anode, cathode and electrolyte; rusting of iron needs water and oxygen.
  • Galvanic corrosion occurs when dissimilar metals are in contact in an electrolyte; the more reactive metal corrodes.
  • Prevention: coatings (paint, powder coating, galvanising, electroplating), sacrificial protection (zinc anodes), cathodic protection, alloying (stainless steel) and design (avoid water traps and dissimilar metal contact).

Finishing

Mechanical finishes (polishing, brushing), plating (chrome, nickel, zinc), anodising (aluminium), enamelling, powder coating, and lacquering.

Production management

  • Production planning: process sheets, operation sequences, jigs and fixtures, batch sizes.
  • Quality: inspection, gauges (limit/go–no-go gauges), statistical process control, ISO standards.
  • Costing: materials, labour, overheads, profit.

Worked example: A batch of 50 brackets uses 15 kg of mild steel at US$1.20 per kg, 10 hours of labour at US$5 per hour and overheads of US$40. Find the cost per bracket.

Materials 18 + labour 50 + overheads 40 = 108; ÷ 50 = US$2.16 per bracket

Industry in Zimbabwe

Metal fabrication workshops, foundries, engineering firms supporting mining and agriculture; informal metalworkers (e.g. at Gazaland in Highfield, Harare) making scotch carts, ploughs and window frames.

Exam tip: Explain corrosion prevention by stating which part of the corrosion cell each method removes.

Check yourself

  1. What is galvanic corrosion?
  2. How does anodising protect aluminium?
  3. What is a go/no-go gauge?
Show answers
  1. Corrosion of the more reactive metal when two dissimilar metals are in electrical contact in an electrolyte.
  2. It thickens the natural oxide layer electrolytically, giving a hard, protective surface.
  3. A limit gauge that checks whether a dimension lies within its tolerance.
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