Handbook on Japanning: 2nd Edition eBook

This eBook from the Gutenberg Project consists of approximately 49 pages of information about Handbook on Japanning.
coating against corrosion.  A piece of lead-coated iron placed in water will show decided evidences of corrosion in twenty-four hours.  This is to be attributed to the porous nature of the coating, whether it is applied by the hot or wet (acid) process.  The lead does not bond to the plate as well as either of the other metals—­zinc, tin, copper, or any alloys of them.  The following table gives the increase in weight of different articles due to hot galvanizing:—­

-------------+ | Description of | Weight of Zinc | Percentage | | Article | per Square foot | of Increase | | | | of Weight | +--------------------------+--------------------------+-----
--------+ | Thin sheet-iron | 1.196 oz. | 18.2 | | 5/16-in. plates | 1.76 " | 2.0 | | 4-in. cut nails | 2.19 " | 6.72 | | 7/8-in. die bolt and nut | approximately 1.206 oz. | 1.00 | +--------------------------+--------------------------+-----

Tin is often added to the hot bath for the purpose of obtaining a smoother surface and larger facets, but it is found to shorten the life of the protective coating very considerably.

A portion of a zinc coating applied by the hot process was found to be very brittle, breaking when attempts were made to bend it; the average thickness of the coating was .015 inch.  An analysis gave the following result:  tin, 2.20; iron, 3.78; arsenic, a trace; zinc (by difference), 94.02.  A small quantity of iron is dissolved from all the articles placed in the molten zinc bath, and a dross is formed amounting in many cases to 25 per cent of the whole amount of zinc used.  The zinc-iron alloy is very brittle, and contains by analysis 6 per cent of iron, and is used to cast small art ornaments from.  A hot galvanizing plant, having a bath capacity of 10 feet by 4 feet by 4-1/2 feet outside dimensions, and about 1 inch in thickness, will hold 28 tons of zinc.  With equal amounts of zinc per unit of area, the zinc coating put on by the cold process is more resistant to the corroding action of a saturated solution of copper sulphate than is the case with steel coated by the ordinary hot galvanizing process; or, to put it in another form, articles coated by the cold process should have an equally long life under the same conditions of exposure that hot galvanized articles are exposed to, and with less zinc than would be necessary in the ordinary hot process.  The hardness of a zinc surface is a matter of some importance.  With this object in view aluminium has been added from a separate crucible to the molten zinc at the moment of dipping the article to be zinced, so as to form a compound surface of zinco-aluminium, and to reduce the ashes formed from the protective coverings of sal-ammoniac, fat, glycerine, etc.  The addition of the aluminium also reduces the thickness of the coating applied.  Cold and hot galvanized plates appear to stand abrasion equally well.  Both pickling and hot galvanizing reduce the strength, distort and render brittle iron and steel wires of small sections.

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Handbook on Japanning: 2nd Edition from Project Gutenberg. Public domain.
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