Metal pretreatment. simple recipes

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FACTORY TECHNOLOGIES AT HOME - SIMPLE RECIPES
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Metal pretreatment. Simple recipes and tips

Factory technologies - simple recipes

Directory / Factory technology at home - simple recipes

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Subject to chemical coloring metal objects must be thoroughly cleaned of dirt and grease. First, objects, depending on the hardness of the metal, are cleaned with steel wire or bristle brushes. They also use pumice stone and sandpaper. If the fat is poorly removed, then stains will remain on the treated surface.

There are many ways to remove fat. Usually they use a mixture of burnt lime and soda. You can also remove fat by immersing objects in a decoction of a soap root, in gasoline, petroleum (petroleum) ether, carbon tetrachloride and others.

Usually, the cleaned object is immersed in several vessels in turn; first washed with a solvent that was already in use and therefore containing fat, then with a purer solvent, and finally with a completely pure one. After some time, the most contaminated solvent is poured out of the first vessel and the liquid of the second vessel is used instead, then from the third, and pure solvent is poured instead of the last. Items after solvent treatment are cleaned with lime using a brush and rinsed in water.

Cleaning is also practiced by immersion for 20-30 minutes in a hot 10% solution of caustic soda or potassium. With this treatment, vegetable and animal fat turns into soap, which is easily removed by washing. Vaseline, paraffin and lubricating oils are hardly saponified by alkalis, so objects contaminated with these substances are usually washed with some kind of solvent, mostly gasoline. Since hot alkalis corrode tin, lead, zinc and British metal, it is better to clean these metals with a hot 3-5% soda solution. Aluminum should not be cleaned with either caustic alkali or soda.

You should not take cleaned items with your hands, as there are always oily secretions on the skin. Usually, objects are tied to a wire of the same metal and lowered into solutions on the wire. You can also use wooden tongs. A sign of complete removal of fat is uniform wetting of the surface of the object with water. In greasy places, water remains in the form of large drops. After the metal surface is cleaned of grease, it is well washed.

If the metal surface is covered with a layer of oxide, then it is subjected to special chemical cleaning. A thin layer of oxide can be removed by immersing the object for 15-25 minutes in a 5% solution of tartar, but usually various cleaning acid mixtures are used to free metals from oxides. We give several recipes, and note that such processing is sometimes carried out to obtain clean matte or shiny metal surfaces, when it is not intended to subject them to chemical staining in the future.

Cleaning of copper, brass and bronze

10 wt. hours of concentrated sulfuric acid are added in small portions to 7,5 wt. including concentrated nitric acid (and not vice versa; mixed in a glass chemical flask). The mixture is allowed to cool and 5 g of table salt are added for each kilogram of the mixture. The object is immersed in this mixture for 1-2 seconds, making sure that there are no air bubbles on the object. Then the object is taken out, the acid mixture is allowed to drain and the object is quickly washed by immersion in a vessel with a large amount of water. After such treatment, the surface of the metal becomes yellow. If a grayish spot appears on the surface of the metal after treatment with acids, then the object is immersed in a solution of 100% zinc chloride in 1 liter of water, removed and slightly heated until it dries. After rinsing with water, the surface becomes clean.

To obtain a matte surface, a mixture of 2 kg of concentrated nitric acid, 1 kg of concentrated sulfuric acid, 10 g of sodium chloride and 15-40 g of zinc sulfate is used. The more the object remains in this solution, the more matte it takes on. Next, the item is well washed and quickly dried in sawdust.

Iron and steel can be freed from oxide by immersion in concentrated nitric acid, to which a small amount of pine soot is added. After immersion, rinse with water, immerse in a 4% soda solution and rinse again with water. The oxide layer on steel can be removed by immersion in a solution of 4 wt. parts of sulfuric acid 66 °Be and 1 wt. hours of water. For pure iron, another 5% sulfuric acid solution is used.

To clean silver, preheat it and then drop it into a solution of 1 wt. parts of sulfuric acid 66 °Be in 5 wt. hours of water. You can also use a boiling solution of 2 wt. tsp table salt and 1 wt. tsp cream of tartar in a small amount of water or a solution of 60 g of borax in 100 wt. hours of water. You can also clean with ammonia.

Plaque on gold is removed using a clean rag moistened with a 3% borax solution. To purify zinc, use a solution of 1 wt. parts of sulfuric acid 66 °Be in 16 wt. hours of water. If the oxide layer is large, use a cooled mixture of equal parts of 66 °Be sulfuric acid and 36 °Be nitric acid. The object is immersed in this mixture for 1-2 seconds, removed and rinsed well with water. If you want to give it a matte surface, then before treating it with acids, immerse it in a solution of zinc nitrate salt (this salt can be obtained by dissolving zinc in nitric acid). If the zinc object was coated with a layer of copper, then this layer can be removed by immersion in a solution of 3 wt. parts of concentrated nitric acid in 1 weight part of water, followed by a good rinse.

Tin and lead after treatment with a soda solution are well cleaned with brushes. No less important is the processing of metals after painting. In order to remove chemical residues, the item must be thoroughly rinsed in clean water. For drying, objects are immersed in warm sawdust of woody, non-resinous tree species or placed in a drying cabinet for several hours. Usually, after painting, to protect against harmful atmospheric influences, as well as various gases, objects are covered with a transparent varnish. The most suitable material for these purposes are celluloid varnishes. You can also apply a thin layer of neutral vegetable oil or wax dissolved in gasoline (1 part by weight of wax to 16 parts by weight of gasoline).

The coloring of metal surfaces by applying a thin coating of another metal is based on the ability of metals to displace other metals from salt solutions. For example, when a zinc or iron stick is immersed in a solution of copper sulfate, the metals change places: zinc or iron goes into solution, and the corresponding amount of copper falls out of the solution and is deposited on the zinc or iron stick. The formation of sediment stops when a thin coating of metal forms on the object. Usually, staining is applied by simple dipping, boiling and rubbing.

Some metals (less electropositive) do not liberate from salts by simply immersing them in a solution of salts of another metal, but liberation can be induced if the metal is brought into contact (contact) with some strongly electropositive metal. For example, in a solution of a double salt of tartaric acid, copper and potassium, iron will only be coated with copper when it is brought into contact with zinc.

With this contact method, the metal layer can be somewhat thicker than with simple immersion. In this method, metals are immersed in a liquid, after which they are touched with a contact metal.

Zinc and aluminum are mainly used as contact metals. Objects to be painted are usually placed on a clay sieve and immersed in a solution with constant stirring.

Author: Korolev V.A.

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