Which of the following marking media is used for filed or machine finished surfaces?

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ALP CBT 2 Fitter Previous Paper: Held on 21 Jan 2019 Shift 1
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  1. White lead power mixed with turpentine
  2. Chalk powder mixed with water
  3. Chalk powder mixed with methylated spirit
  4. Prussian blue oil paint

Answer (Detailed Solution Below)

Option 4 : Prussian blue oil paint
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Detailed Solution

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Concept:

Marking media is a substance that is applied on the surface of the metal to distinguish the marked line clearly.

Marking out is the preliminary work of providing guidance lines and centers before cutting and machining.

The different marking media are:

Whitewash:

  • It is applied to rough forging and castings with oxidized surfaces.
  • It is not recommended for a workpiece of high accuracy.

Prussian Blue:

  • It is used on filed or machine-finished surfaces.
  • This gives very clear lines but takes more time for drying than other marking media.

Copper Sulphate:

  • The solution is prepared by mixing copper sulfate in water and a few drops of nitric acid.
  • The copper sulfate is used on filed or machine-finished surfaces. It sticks to the finished surfaces well.
  • It needs to be handled carefully as it is poisonous.
  • Copper sulfate coating should be dried well before commencing marking as, otherwise, the solution may stick on the instruments used for marking.

Cellulose Lacquer:

  • This is a commercially available marking medium.
  • It is also used on the machined work surface.
  • It is made in different colors and dries very quickly.

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