This section is from the book "An Elementary Outline Of Mechanical Processes", by G. W. Danforth. Also available from Amazon: An elementary outline of mechanical processes.
This consists of covering articles of iron or steel with a coating of zinc for the purpose of resisting corrosion.
Articles to be galvanized must first be pickled in a dilute acid to remove or loosen all surface dirt and scale. Upon lifting from this bath, the articles are well brushed with brooms or steel brushes and are washed with fresh water from a hose. They are then placed in a second bath of weak acid (usually HCl) to insure a clean metallic surface and must be taken directly from this bath to a "flux tank" to avoid rusting, which would occur if exposed unduly to the air. The fluxing mixture consists of a solution of sal ammoniac kept hot by steam pipes and covered with beef tallow, and is used to neutralize the acid of the two preceding baths. From the fluxing bath articles are lifted dripping, and immediately lowered into the galvanizing bath, known as the "zinc pot." This bath consists of molten zinc, which soon becomes covered with flux and dross, and is protected by these from the oxidizing action of the air. The zinc pot is an iron tank which is surrounded by brick walls with space enough between the walls and the tank to maintain a coke fire for keeping the zinc melted.
Small articles are lowered for a moment into the zinc bath in wire baskets. They are lifted out and allowed to cool.
The best grade of galvanized sheets is produced by feeding the sheets taken directly from the fluxing bath into a machine which is submerged in the zinc pot. This machine is merely a series of rolls which draw the sheet into the bath, carry it down near the bottom, and finally send it out over the further edge of the pot. These rolls insure an even coating of zinc over the surface of the sheet and roll down all lumps and uneven places. Sheets from the zinc pot are placed on edge in racks to cool, and are then run through straightening rolls and sorted to pick out sheets which are imperfectly galvanized. The imperfect sheets are returned to the second acid bath if very imperfect, or are bundled and sold as "seconds" if only slightly imperfect. All sheets are branded before bundling for market.