Pickling at home. Metal etching at home - stages of metal engraving

The starting metal for cold rolling is rolled stock obtained in hot rolling mills, called rolled stock. A mandatory operation in the production technology of cold-rolled products is metal for rolling. Since the surface of hot-rolled metal is covered with a layer of scale, it becomes necessary to remove it to obtain a high-quality metal surface.
The removal efficiency depends on its physicochemical composition, its thickness and structure, as well as on the etching conditions. Optimal pickling conditions are created when the scale

contains the maximum amount of wustite (iron oxide - FeO), and hematite (Fe2O3) is absent. This is due to the fact that wustite is highly soluble in acids, while hematite is an insoluble compound. Such conditions for the formation of scale are typical for low temperatures at the end of rolling. Reducing the temperature at which the strips are wound into a roll does not affect the thickness of the scale layer, but reduces the risk of hematite appearing on the edges and ends of the strip.

There are acid and mechanical. On pickling lines, scale is removed by combining both methods of removing it: first, the strip passes through a descaling machine and a skin-passing cage, where the scale is cracked and mechanically removed, and then the scale remaining on the strip is dissolved in acid solutions (chemical method).
based on the interaction of scale with acids. In this case, the scale undergoes chemical transformations and is separated from the base metal. In addition, scale removal also occurs as a result of the release of hydrogen gas, which accumulates under the scale and tears it away from the metal.

Known 2 etching method: immersing the metal in the bath and supplying the solution in the form of jets under pressure.

The most common acids used for pickling steel are sulfuric and. When using sulfuric acid, not only the dissolution of scale oxides occurs, but also pure iron, which leads to an increase in metal waste and an increase in acid consumption. Therefore, sulfuric acid etching is usually carried out in the presence of inhibitors - substances that slow down the process of dissolution of pure metal without reducing the rate of scale etching. The disadvantages of sulfuric acid etching also include: contamination of the etching solution with sludge, uneven removal of scale, lack of regeneration of spent etching solutions and low demand for the regeneration by-product - iron sulfate.

Etching in hydrochloric acid occurs in the outer and inner layers of scale. Hydrochloric acid dissolves not only wustite quite well, but also higher iron oxides. At the same time, the scale does not fall off to form sludge at the bottom of the bath or strip, but almost completely goes into solution. It is believed that metal losses during hydrochloric acid etching are ~25% less than during etching in sulfuric acid due to a decrease in the dissolution of pure iron. When etching in hydrochloric acid, the intensity of dissolution of scale increases, and over-etching is less common. Etching in hydrochloric acid results in a cleaner surface than etching in sulfuric acid. The great advantage of hydrochloric acid is the possibility of complete regeneration of spent hydrochloric acid etching solutions. Pickling, as a rule, is carried out in a hot solution, then the strip is wrung out by pairs of squeezing rollers, washed, dried, and the edge is trimmed. The strip processed in this way is transmitted to .

Artistic metal etching was first used by medieval gunsmiths. The decorations on their products were not inferior to those that came out of the hands of skilled jewelers. By etching, gunsmiths replaced one of the labor-intensive processes - hand engraving, without losing the previous artistic qualities.

Using the etching technique, you can reproduce a relief or in-depth ornament, plot, text on any metal. Now there are two methods of etching - chemical and galvanic. The galvanic method is simpler, because the electrolyte solution does not emit gases harmful to health, which are inevitable with the chemical method, and is more effective, since the contours of the etched pattern are clearer.

To engage in galvanic etching, you need to acquire a direct current source with a voltage of 4 - 7 V and make a bath of insulating material for the electrolyte - its structure can be seen in the figure.

An electrolyte is a saturated aqueous solution of iron or copper sulfate. The first is intended for steel and iron, the second - for copper, brass, bronze.

You can also use a saturated solution of table salt. In all cases, distilled water is desirable.

Before etching, it is necessary to solder a copper wire with a bent ring to the metal workpiece with tin. Holding it by the ring, lower the workpiece into a ten percent solution of caustic soda heated to 50 degrees for about five minutes. Then transfer to a fifteen percent sulfuric acid solution for one to two minutes, then rinse thoroughly in hot water. The workpiece is degreased.

Now prepare the mastic. Melt 4 parts of varnish, 2 parts of rosin, 3 parts of wax in a tin box or jar and stir until a homogeneous mass is obtained. Cut the cooled mastic into small pieces and wrap each piece in a strong, thin cloth. You will get some kind of tampons. Move the swab over the surface of the slightly heated workpiece, pressing lightly, and the metal will be covered with a thin, uniform layer of mastic. The entire workpiece must be covered with mastic.

When the mastic layer has hardened, white or yellow watercolor paint is applied to it and gently rubbed with your finger. A drawing or text is applied to the surface primed in this way with a pencil. Using a sharp knife and needles, scrape out the mastic in those places where, according to the plan, there should be indentations.

Place the workpiece prepared in this way in the electrolyte, hanging it by the ring from the rod with the “plus” terminal. This is the anode. Hang a plate of any metal to the cathode (minus sign) and connect the current.

If different etching depths are required, remove the product from the solution from time to time and use a brush to cover with mastic those places that have been sufficiently etched. Having achieved the desired result, turn off the current, unsolder the wire, rinse the product with turpentine and proceed1 to the final finishing - grinding and polishing.

If your creative design requires a more decorative finish, you can use nitro enamel of various colors. Degrease the product with gasoline, then evenly fill the etched areas with enamel. Dry the enamel under an electric lamp, making sure that dust does not fall on the paint.

When finishing an item, try your hand at tauching - this is the inlay of metal with another metal - soft, ductile, contrasting in color.

Etch grooves in the product with a depth and width of 0.7 - 1 mm. Take copper wire (and if the product is made of copper, then aluminum) with a cross-section one-fifth larger than the etched groove. Then burn the wire (there is no need to anneal aluminum) and drive it into the groove, hitting the punch with a hammer, the end of which should correspond to the width of the groove so that there are no nicks left on the product.

After finishing the tasselling, polish the product to a shine and, having previously degreased it, coat it with varnish - it will protect the metal from corrosion.

Pickling is a metal processing process in which a layer of a certain thickness is removed from the surface under the influence of active chemicals (acids or salts with an acidic reaction), as well as direct current in an electrolyte bath.

Metal etching can serve various purposes and be used in industry and at home. The surface of an item subjected to etching receives a number of technological and decorative properties and allows one to examine its microstructure in a metallographic microscope, remove scale and other non-metallic inclusions from the surface, obtain the necessary jewelry ornament or prepare it for soldering.

Etching, also called electrochemical engraving, is most often used at home or in the garage to obtain relief images on various objects with decorative functions. Most often, it is used on steels with high hardness, the processing of which with conventional engraving tools requires great effort. This process is not very difficult even in the absence of artistic skills, if you follow its technology.

Metal surface preparation

In order for the etching process to proceed at a high speed and the thickness of the removed layer to be the same, all dirt and traces of oils should be removed from the surface of the product. For this purpose, ordinary detergents and cleaning products used for washing dishes and warm water are suitable. After washing and drying, the surface should be wiped with fiber soaked in a solvent, which, in addition to degreasing, helps remove residual moisture.

Separately, it is worth mentioning the quality of surface treatment. Mirror polishing is subsequently guaranteed to give a good contrasting pattern even with a small etching depth. But if its implementation is impossible for some reason, the surface can be treated with sandpaper so that the risks from it go in one direction. This will also give a good optical effect.

Drawing

To apply a design to metal, you can use a lot of different methods that work according to the same mechanism: areas that are not subject to etching are protected from exposure to an aggressive environment or electrolyte.

Method No. 1

The most affordable way is to apply regular nail polish to the protected areas. However, it has a number of significant disadvantages:

• The viscosity of the varnish does not allow the lines to be thin enough to obtain highly complex patterns;
• Good ability in visual arts required;
• Correcting inaccurate lines is difficult.

Method No. 2

First you need to apply a protective layer to the entire surface of the product. To do this, you can use primers GF-021, XV-062 or bitumen varnish, available in auto parts and household goods stores. After the coating has completely dried, you can use a gel pen or a thin marker to draw the contours of the future image. An experienced artist can be hired for this task.

Next, from a copper (or brass) wire or rod, the diameter of which is selected based on the ease of holding in the hand, you need to make a needle with a pointed end and scratch the primer along the image lines to the metal. Harder needle material may damage the polish on the surface of the product.

Already at this stage you can evaluate the relief of the future ornament. To obtain areas with different depths of metal etching, for example, contours and penumbra, this process can be carried out in two or more cycles.

Important! The primer should not chip off during the process. Before applying the design, you should experiment and make sure that it is suitable for the job.

Method No. 3

You will need a laser printer, glossy paper, image processing software and an iron. The selected picture must be formatted (adjusted to size, mirrored) and printed. The most affordable source of glossy paper is women's magazines.

The printed image is applied to the surface, covered with a regular landscape sheet (to protect the iron) and ironed. After cooling, the paper is washed off under running water, and the toner layer remains on the metal surface.

This method is often used for etching printed circuit boards. Its main drawback is that the design is applied only to a straight surface.

Important! The gloss is difficult to see under water. After drying, you need to make sure that it does not remain on the product.

Care must be taken to protect all surfaces of the product. Various substances can be used for this. You can cover the back surface with ordinary plasticine: it is a good dielectric.

Metal etching methods

The choice of a specific method depends on many factors: the chemical activity of the metal, the availability of chemical reagents and safety considerations.

Chemical etching

It is performed in a container with the active substance. For carbon steels, solutions of weak acids may be suitable: citric, acetic. Hydrochloric acid works well. Pickling in battery electrolyte, nitric acid and rust converter should be treated very carefully: the process can release toxic gaseous substances, so it is better not to work with such reagents in the absence of a fume hood and good ventilation.

One of the safest substances is a saturated solution of ferric chloride. It can be bought in stores that sell radio components. The advantages of the solution are its almost unlimited service life (when working with iron alloys) and the coloring of the etched surface in an even gray color.

The process time is selected experimentally depending on the concentration of the reagent used and the activity of the metal.

Electrochemical etching

Many stainless and acid-resistant steels, for example, 40Х13, 95Х18, 08Х10Н18, 03Х12Н14М2, do not react to acids, so an electrochemical method is used for etching them.

It will require an electrolyte bath made of plastic or glass, wires, terminals and a direct current source. A saturated solution of table salt will work as an electrolyte. When choosing a container for it, you should remember that the process can proceed quite violently, so its volume should be 2 times larger than that of the electrolyte.

You can use rechargeable batteries as a current source, but it is better to use a charger (3 - 10A) with an ammeter and the ability to adjust the current parameters to select their optimal value. The workpiece is connected to the anode (positive contact) using terminals and a conductor; any stainless plate placed in the bath parallel to the front surface of the workpiece can be used as a cathode. After this, the device is connected to the network.

The entire process can take from two minutes to half an hour, depending on the current strength and the area of ​​the pattern. The etching depth should be controlled by periodically removing the part from the bath. At the same time, do not forget to turn off the power.

At the end of the process, the protective coating can be removed with a suitable solvent and the results of the work can be assessed. Thanks to good adhesion of the etched surface, it is possible to create a colored pattern.

To do this, the entire surface of the product is blown out of a cylinder with nitro-enamel, and after it dries, it is wiped with a piece of clean leather, felt or other non-abrasive material. The paint is removed from the polished surface, remaining only in the depressions.

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Select the image you want to etch onto the steel. You can draw the image by hand or reproduce an existing image on the surface of the steel. Depending on the image transfer method you choose, you may end up with either a very simple pattern or a rather complex one.

• If you're planning on reproducing an existing pattern, then choose something with a high contrast of black and white.
• If you plan to make and sell prints of your etched designs, select a public domain image or obtain permission from the copyright holder if one exists.

Transfer your design onto the surface of the steel. You can translate the pattern using one of the following methods. However, keep in mind that no matter the transfer method, the result will be the opposite of the image produced by etching onto the steel. If you plan to use the etched plate solely as a decoration and not for printing with it, then this will not matter to you.

• The oldest method of transferring images is to coat steel with a liquid varnish or wax-like substance (such as beeswax), or even enamel paint or nail polish. This coating is called soil. You can scratch your image directly into the ground using needles or cutting tools. (This process is reminiscent of wood carving.) The primer will serve as a resist, isolating the areas of steel it coats from the action of the etching acid.
• Another method is to cover the surface of the steel with permanent marker marks in the areas you don't want to etch. To determine the best resist, you will have to experiment with several permanent markers of different brands and colors.
• The third method is to create a stencil that is transferred to steel using an iron, either by photocopying the image onto transfer paper, or by printing it on glossy photo paper with a laser printer. Place the paper face down on the steel surface and, using an iron set to high temperature, smooth it with smooth circular movements for 2-5 minutes. (If you're using transfer paper, press down gently; if you're using photo paper, press down firmly with the iron.) You can then remove the paper. (The transfer paper will peel off on its own, and removing the photo paper requires placing it in a tray of hot water to soften it.) The transferred ink will become a resist for the etching acid.

Pickling is the process of cleaning and processing a metal workpiece. Chemical, acidic, alkaline, electrochemical - there are many ways to perform this technological operation. Where is metal etching used, why is it used in industry, what are the processing methods using this technology, all these issues are discussed in detail in the article below.

What is etching

This is a technology for removing the top layer from the surface of a metal part. The technology is used to clean workpieces from scale, rust, oxides and remove the top layer of metal. Using this method, the top layer is removed to search for internal defects and study the macrostructure of the material.

Using etching, they clean the part and increase surface adhesion. This is done for the subsequent connection of the metal surface with another workpiece, before applying paint, enamel, galvanic coating and other protective coatings.

The method allows you not only to quickly clean the part, but also to create the desired pattern on the metal surface. Using this method, the finest channels and complex images are cut out on a metal surface. You can clean large parts or rolled products. The processing depth is adjustable with an accuracy of several microns, which makes it possible to produce complex parts with small grooves and other complex elements.

Application of etching in industry

1. For cleaning parts made of carbon, low-alloy and high-alloy steel, titanium and aluminum from oxide film.
2. To improve adhesion before applying galvanic and other types of protective coatings.
3. To prepare steel surfaces for hot-dip galvanizing.
4. To conduct macroanalysis to detect the formation of intergranular corrosion in stainless steels.
5. This technology is used to process small metal parts, such as watch gears.
6. Copper processing is used to make semiconductor chips and printed circuit boards in electronics. This method applies a conductive pattern to the microcircuit.
7. For quick cleaning of hot rolled metal products, heat-treated parts, from oxides.
8. In the aircraft industry, this technology is used to reduce the thickness of aluminum sheets to reduce the weight of the aircraft.
9. In the manufacture of metal inscriptions and drawings. Etching produces relief images drawn by removing a layer of metal according to a specific stencil.

Types of etching

The main types of metal processing used in industry:

• electrolytic - there are cathode and anodic;
• chemical;
• plasma.

Electrolytic etching

Electrolytic or galvanic metal processing is used to quickly clean parts, apply engravings and produce grooves. Metal parts are immersed in an acid or salt electrolyte. The part becomes a cathode - a negative electrode or an anode - a positive electrode. Therefore, two types of electrolytic etching are classified - cathodic and anodic.

1. Cathodic etching. The method is used to remove scale from the surface of carbon steel products after hot rolling or oil quenching. In cathodic etching, the material for the anode is lead, and the electrolyte is a solution of hydrochloric, sulfuric acid or an alkali metal salt. During the electrolysis process, hydrogen gas is actively released at the cathode, which interacts with iron and removes scale. During the cathode method, the metal surface is actively saturated with hydrogen, which increases the fragility of the workpiece. Therefore, the cathode method is not used for thin-walled products.
2. Anodic electrochemical cleaning. This is the most common method in mechanical engineering. The process involves mechanically tearing off the oxide film on the anode with oxygen and mixing metal molecules with the electrolyte. An electrolyte is a solution of acids or salts of the metal being processed. Lead, copper and other metals are used as the cathode. During anodic treatment, the surface of the product becomes clean, with slight roughness, and the metal dissolves in the electrolyte. With this method, there is a risk of reducing the thickness of the workpiece and over-etching.

Chemical etching

The chemical treatment method is used to clean the surface of a part from oxide film, scale and rust for workpieces made of the following materials:

• ferrous metals;
• stainless and heat-resistant steels;
• titanium and its alloys;
• aluminum

For etching, sulfuric, hydrochloric or nitric acid is used. The workpiece is immersed in an acid or alkaline solution, molten salt and kept for the required time interval. The required cleaning time can range from 1 to 120 minutes.

The cleaning process occurs due to the release of hydrogen when the acid interacts with the metal. Acid molecules penetrate through pores and cracks under the oxide film. There they interact with the metal surface and hydrogen is released. The released gas tears off the oxide film and cleans the part.

Simultaneously with the oxides, the metal being treated dissolves in the acid. To prevent this process, corrosion inhibitors are used.

Plasma etching

With the ion-plasma method, cleaning and removal of the surface layer occurs by bombarding the part with ions of inert gases that do not react chemically with the molecules of the material being processed. Allows you to make high-precision notches and grooves with an accuracy of up to 10 nm. The technology is used in microelectronics.

The plasma-chemical method involves excitation of plasma in a chemically active medium, which causes the formation of ions and radicals. Active particles falling on a metal surface cause a chemical reaction. In this case, light compounds are formed, which are removed from the surrounding air by vacuum pumps.

The method is based on chemical reactions that occur when using reactive gases, such as oxygen, which are highly reactive. These gases actively interact in the gas discharge plasma. Unlike plasma treatment in inert gases, with this cleaning method, the active gas reacts only with certain molecules.

The disadvantage of this method is the lateral expansion of the grooves.

Etchants

Pickling of carbon steels is carried out in an 8-20% solution of sulfuric or 10-20% hydrochloric acid. With the obligatory addition of corrosion inhibitors (KS, ChM, UNIKOL) to eliminate the fragility of the material and reduce the possibility of over-etching.

Products made of stainless or heat-resistant steel are processed using a solution consisting of: 12% hydrochloric, 12% sulfuric, 1% nitric acid. If required, processing is done in several stages. The first is that scale is loosened in 20% hydrochloric acid. The second stage is immersion in a 20-40% nitric acid solution to completely remove surface contaminants.

The thick layer of scale that forms on stainless steel is removed during its production by 75-85% molten caustic soda with 20-25% sodium nitrate. After which, complete removal of oxides is carried out in 15-20% nitric acid.

Processing of aluminum and alloys based on it involves removing the refractory oxide film from the surface of the workpiece. For this purpose, alkaline or acidic solutions are used. Usually 10-20% alkali is used, at a temperature of 50-80 ºС, the etching procedure takes less than 2 minutes. The addition of sodium chloride and sodium fluoride to the alkali makes this process more uniform.

The purification of titanium and its alloys, carried out after heat treatment, is carried out in several stages. At the first stage, scale is loosened in concentrated caustic soda. Then the scale is removed in a solution of sulfuric, nitric or hydrofluoric acid. To remove the remaining pickling sludge, use hydrochloric or nitric acid with the addition of a small amount of hydrofluoric acid.

When processing copper and its alloys, etchants from hydrogen peroxide, chromic acid and the following salts are used:

• copper chloride;
• ferric chloride;
• ammonium persulfate.

This information material describes in detail the pickling process used in metallurgical plants. The method allows you to quickly clean the metal surface from oxides, scale, rust and other contaminants. Thanks to etching, it is possible to apply various designs to metal, create complex microcircuits and make microscopic channels of the desired shape.