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TECHNOLOGY OF THINNING AND SPARKS OF METALS
Glossary of terms
In addition to the chemical etching described above, there is another etching method using a galvanic battery. This tool has many advantages over the chemical. The galvanic etching operation itself proceeds much faster, and the contours of the etched pattern are more sharp also distinct. The composition of the mordant does not enter corrosive acids, so that no harmful gases are created for the health of the gases.
If we consider through a magnifying glass a pattern etched by a chemical method, it turns out that the margins of individual deepened lines are also uneven, the deeper the line, the wider it is etched. With galvanic etching, the margins of individual lines are completely smooth, but the walls of the depressions are vertical. The method of preliminary finishing of the object described above is also used in galvanic etching. The treated object, an anode servant, is suspended in a bath containing a mordant on a wire that is soldered with tin solder to an uncovered room; the place of adhesion is varnished. The other end of the wire is connected to a plate of the same metal serving as the cathode. As a mordant for steel, iron is also used iron sulphate or a solution of ammonia; for copper, brass also bronze - copper sulphate solution; for zinc - zinc sulfate or a solution of zinc chloride oxide. If different parts of the pattern are to be etched to different depths, then after a certain period of time the object is taken out of the bath, the rooms that do not need to be etched deeper are also rinsed, they also put a protective coating on them, but then the object is again suspended in the bath and the etching is continued.
Ingredients for etching:
1 part alcohol,
1 part of chromic acid,
10 parts of water.
1 part alcohol,
1.5 parts of acetic acid,
1 part antimony chloride (antimony oil),
10 parts of water.
8 parts of alcohol,
5 parts of tin dichloride,
80 parts of water.
Chemical methods of etching metals
Etching is 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 cover with the substance on which the mordant acts, all the features of the surface of the figure; on the contrary, it is possible to protect all gaps from the action of acids, leaving the features and surfaces of the pattern free. If then cover the entire surface with acid, then in the first case the image will be slightly embossed, in the other - the image will come out in-depth.
No matter how simple, for the main eye, the etching operation, beginners often fail, especially when etching thin also complex drawings.
Before applying a protective coating, the surface to be treated should be thoroughly cleaned from a thin coating of rust, grease is also another type. Adhered to the surface of fat can be removed by washing in alcohol or gasoline, by calcination or, finally, by digesting soda or sodium hydroxide in the solution.
Purified from the silt, as well as fat, the object is immersed in a 10% solution of sulfuric acid and is also left in it until the gloomy rust disappears. After that, the surface to be treated can be polished, if the type of the object also allows its appointment does not contradict this operation. But such a preliminary polishing is not necessary. Do not touch the cleaned surface with your bare fingers, as if there is always more or less fat on them, however, the fat of the mordant does not work.
When the etched surface is so cleaned that it has a fresh metallic sheen, they begin to apply a protective coating. A good coating can be prepared as follows: 1 part of the asphalt is melted as well, 2 parts of the mastic are mixed, mixed and 2 elements of white wax are added to it. On cooling this compound is formed into balls and cones, which are wrapped first in a rag from a thin dense cloth, and on top - into a dry taffeta. The composition is applied to the surface in the following way: the workpiece is heated plus, slightly pressing on the surface, driving it evenly with a mass wrapped in a taffeta; while the composition melts also seeps through a rag, covering a thin layer of a rubbed surface. At what time this coating will harden, it is covered with a thin layer of lead white, finely ground also dissolved in the solution of gum arabic. Then, using a blue paper on the snow-white surface, translate the required pattern or inscription. All rooms that need to be etched are scraped to the surface of the metal. A thin sharp engraving needle can also reproduce even the finest of the drawings.
If you want to etch a simple figure or an inscription, then the protective coating can be diluted with some liquid, for example turpentine, down to the consistency of thick oil paint. On such a coating, you can reproduce the desired image from the hand with a needle or even a steel pen.
When applying a protective coating, it must be ensured that the metal surface is completely dry, otherwise the coating will not adhere well in places, but the acid can penetrate at that time to the metal and also etch the rooms that must remain untouched.
The following mixture serves as a stain for copper, brass, bronze and silver products: 3 elements of a saturated aqueous solution of nitric acid also 1 part of a saturated acetic solution of ammonia.
For iron, the following mixture was also recommended: 400 water elements, 2-3 drops of nitric acid, 15 parts of calome (dichloromethane), and 1 part of tartaric acid.
An etched object is lowered into a clay glazed cuvette (bath) in which the appropriate solvent is poured. If the surface to be treated is flat, then it can be installed horizontally, the edge of the wax with the thickness of the finger should be molded and the corresponding acid should be poured into the flat cuvette thus obtained. At what time the etching is considered complete, the object is rinsed in clean water, but the protective coating is removed by heating or washed away with turpentine. If some amount of etch remains in the indentations, then eventually it will dissect the metal surface in places deeper than required. To avoid this, the washed object is put in lime water for several minutes, which neutralizes the acid residue.
An ancient etching method
This old also a wonderful means of decorative finishing forged products is almost forgotten, although in our days the chemical industry alienates for this work the best opportunities. When decorating small items, such as locks, furniture, door hinges, etc., this tool can be used successfully. Etching can be positive or negative . Positive is the etching of patterns in the form of depressions, with negative etching the ornament remains on the surface, however, the surface around it is etched. The entire etching process consists of three stages:
application of the basic acid-resistant coating on the surface;
In case of positive etching, an acid-resistant coating is applied to the polished, non-fattened surface of the product. After drying, the needle is applied with a pattern. Then the surface is protected with wax and the product is immersed in a ceramic bath with etching solution. Negative etching is reversed. Preliminarily, a pattern or ornament is applied to the surface to be treated, and a thin brush is applied to the pattern. After drying, the pattern is retouched with a needle, and also proceeds in the same way as if with positive etching. The composition of acid-resistant coating: two elements of paraffin, two elements of mastic resin are also one share of bitumen. This mixture is dissolved in turpentine. Diluted acids are used as etching solutions. Steel is etched in an aqueous solution of sulfuric acid (ratio 1:10). To etch copper, brass also uses 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 be etched to a sufficient depth, it is removed from the pickling bath and also thoroughly washed in clean water. The layer of the coating is removed after a weak heating of the product with turpentine.
Some objects, as it is known, can not be soldered at high temperature, without in any way spoiling. For such items, the following composition is recommended.
The copper precipitated in the powder state is mixed in a porcelain mortar with concentrated sulfuric acid until a stiff, dough-like mass is obtained, to the total weight number of which, gradually adding 70 mercury elements with unchanged stirring. At what time in this way a homogeneous amalgam is obtained, it is well washed in hot water to remove the acid and then allows it to cool. After 10-12 hours, the amalgam becomes so hard that tin shreds. In this form, the composition is already quite ready for use, for which it is heated up to the consistency of the softened wax also solder the objects; having cooled down, this amalgam very strongly own soldered parts.