Non-liquid coatings

Question 1

Define hot dip galvanising?

Answer 1

Hot dip galvanising is the process of coating iron or steel with a thin zinc layer, by passing the steel through a molten bath of zinc at a temperature around 820-860 f (460C)

Question 2

The usual galvanised coating consists of three distinct iron-zinc compounds

Answer 2

Gamma - 75% zinc and 25% iron
Delta - 90% zinc and 10% iron
Zeta - 94% zinc and 6% iron
Eta (outer layer) - 100% zinc (not considered seperate layer)

Question 3

A few safety issues the inspector should know when working around hot dip galvanising are?

Answer 3

Hot dipped articles stay hot, and to make sure the article is cool before touching it
Molten metal can splash out of the kettle and travel some distance
Nascent hydrogen may burn off in the air

Question 4

List several major stages of the hot dip process?

Answer 4

Surface preparation
Fluxing
Dipping
Post treatments
Inspection

Question 5

Explain the purpose of both caustic cleaning and acid pickling?

Answer 5

Caustic Cleaning - The steel is immersed in caustic solution to remove the dirt, oil and grease from the surface of the steel
Acid Pickling - The process where the item being prepared is immersed in a tank filled with either hydrochloric or sulphuric acid, which removes oxides and mill scale.

Question 6

What temperature does the galvanising kettle typically operate at?

Answer 6

820-860F (438-460C)