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TECHNOLOGY OF ETCHING AND SPEYKI OF METALS
In addition to the above described etching of metals by a chemical route, there is another method of etching using a galvanic battery. This tool has many advantages in chemical. The etching operation itself is galvanized much faster, and the contours of the etched pattern are sharper and more distinct. Corrosive acids do not enter into the mordant, as a result of which no harmful gases to health are formed.
If we examine through a magnifying glass a picture etched chemically, then it turns out that the edges of the individual recessed lines are also uneven, and the deeper the line, the more etched it is. In the case of galvanic etching, the edges of individual lines are completely smooth, but the walls of the recesses are vertical. The method of pre-finishing the item described above is also used for electroplating. The processed object, the anode servant, is suspended in a bath containing a mordant on a wire that is soldered with tin solder to an uncovered room; place of adhesion varnish. The other end of the wire is connected to a plate of the same metal that serves as the cathode. Iron is used as a mordant for steel as iron sulphate or a solution of ammonia; for copper, brass and bronze - a solution of copper sulphate; for zinc - zinc vitriol or zinc chloride solution. If different parts of the pattern need to be etched to different depths, then after some period the pores of the object are removed from the bath, rinsed those rooms that do not need to be etched deeper, they also apply a protective coating on them, but then hang the object back into the bath and continue etching.
1 part alcohol
1 part chromic acid
10 parts of water.
1 part alcohol
1.5 parts of acetic acid,
1 part of antimony chloride (antimony oil),
10 parts of water.
8 parts of alcohol
5 parts of tin dichloride,
80 parts water.
Chemical methods of metal etching
By etching is called a means of reproduction using organic means of drawings, ornaments, inscriptions, etc. on the surface of metal objects.
Etching is done in a couple of ways: it is possible to coat the substance on which the mordant acts, all the features of the surface of the pattern; it is possible, on the contrary, to protect all gaps from the action of acids, leaving the features and surfaces of the pattern free. If you then cover the entire surface with acid, then in the first case the image will turn out slightly raised, in the other - the image will come out in-depth.
No matter how simple it is, at the main eye, the etching operation, beginners often fail, especially when etching thin and complex patterns.
Before applying the protective coating, the surface to be treated should be thoroughly cleaned from a thin layer of rust, and the grease also on other mud. The fat adhering to the surface can be removed by washing in alcohol or gasoline, calcining or, finally, boiling in a solution of soda or caustic sodium.
The item cleaned from tina also is immersed in a 10% solution of sulfuric acid and left in it until a gloomy rust deposit disappears. After that, the treated surface can be polished, if the type of the object also allows its appointment does not contradict this operation. But such pre-polishing is not necessary. It is impossible to touch the cleaned surface with bare fingers, as if they always have more or less fatty substance, but the mordant does not affect the fat.
When the etched surface is cleaned so that it has a fresh metallic luster, proceed to the application of a protective coating. A good coating can be prepared as follows: 1 share of asphalt is melted as well 2 parts of mastic, the mash is mixed and 2 elements of white wax are added to it. Upon cooling, this composition is molded into balls and cones, which are wrapped first in a rag from a thin dense cloth, and from above - in a dry taffeta. The composition is applied to the surface as follows: the object being processed is heated up plus, pressing lightly on the surface, driving it evenly with the mass wrapped in taffeta; at the same time the composition also melts through the rag, covering the rubbed surface with a thin layer. At what time this coating will harden, it is covered with a thin layer of lead white, finely pounded, also dissolved in gum arabic solution. Then with the help of blue paper on the white surface translate the desired image or inscription. All rooms that need to be etched, are scraped to the surface of the metal. Even the thinnest shading of a picture can be reproduced with a thin and sharp engraving needle.
If they want to etch a simple figure or inscription, then the safety coating can be diluted with some kind of liquid, such as turpentine, up to the consistency of thick oil paint. This coating can reproduce the desired image by hand with a needle or even a steel pen.
When applying a protective coating, it is necessary to ensure that the metal surface is completely dry, otherwise the coating will stick badly in some places, however, the acid can penetrate at that time to the metal and also etch the rooms, which should remain intact.
The mordant for copper, brass, bronze and silver products is the following mixture: 3 elements of a saturated aqueous solution of copper nitrate and 1 share of a saturated acetic solution of ammonia.
The following mixture is also recommended for iron: 400 water elements, 2-3 drops of nitric acid, 15 parts of calomea (mercury dichloride) and 1 part of tartaric acid.
The object to be etched is dipped in a clay glazed cuvette (bath) into which the appropriate solvent is poured. If the treated surface is flat, then you can install it in a horizontal position, scoop a flange of wax with a finger-thick edge and pour the corresponding acid into the flat cuvette thus obtained. At what time the etching is considered finished, the object is rinsed in clean water, but the protective coating is removed by heating or it is washed off with turpentine. If a number of pickling remains in the grooves, then over time it will corrode the metal surface in places deeper than required. To avoid this, the washed object is placed in a few minutes in lime water, which neutralizes the rest of the acid.
The old way of etching
This old one is also an excellent means of decorating forged products approximately forgotten, even nowadays the chemical industry alienates the best opportunities for this work. When decorating small items, such as locks, furniture and door hinges, etc., this tool can be successfully used. Etching can be positive or negative . Etching of patterns in the form of dimples is called positive, with negative etching, the ornament remains on the surface, but the surface around it is etched. The whole etching process consists of three stages:
drawing the main acidproof covering on a surface;
In case of positive etching, an acid-resistant coating is applied to the polished and degreased surface of the product. After drying, the needle is applied drawing. Then the surface is protected with wax and the product is immersed in a ceramic bath with pickling solution. When negative etching do the opposite. First of all, a drawing or an ornament is also applied to the surface to be treated, and a coating is applied to the drawing with a thin brush. After drying, the pattern is retouched with a needle, and then they do the same, as if with positive etching. The composition of the acid-resistant coating: two paraffin elements, two mastic resin elements and one share of bitumen. This mixture is dissolved in turpentine. Diluted acids are used as etching solutions. Steel is poisoned in an aqueous solution of sulfuric acid (1:10 ratio). Brass is also used to pickle copper with nitric acid diluted with water. Water is added so much that small bubbles appear in the drop. If the bubbles are intense, the solution is still too strong. At what time the product will go to a sufficient depth, it is removed from the pickling bath and thoroughly washed in clean water. The coating layer is removed after weak heating of the product with turpentine.
Some objects, as it is known, cannot be soldered at high temperature, without in any way subjected to damage. For such items the following composition is recommended.
The copper precipitated in the powdered state is mixed in a porcelain mortar with concentrated sulfuric acid to form a non-coarse doughy mass, to the total weight of which add little by little, with constant stirring, 70 elements of mercury. At what time a homogeneous amalgam is obtained in this way, it is washed well in hot water to remove the acid and then it is allowed to cool. After 10-12 hours, the amalgam is so hard that it shreds tin. In this form, the composition is already quite ready for use, for which it is heated up to the consistency of softened wax and solder objects; cooled down, this amalgam very well own welded parts.