Chemical etching of metal. Metal pickling at home

As you know, metal is quite difficult to process at home without special skills and tools, especially if it is such a hard metal as steel. Nevertheless, chemistry can be called to help: there is such a chemical process - electrolysis. It flows on the electrodes when an electric current passes through electrolyte solutions. Those. if you take a metal blank as an electrode, use ordinary salt water as an electrolyte, then when a current passes through it, the metal will begin to bleed, in other words, atoms from the surface of the metal will begin to “fly away”. Thus, metal processing does not always require any special skills and tools, because electricity can do everything for us.

In this article, we will consider how to etch an inscription or drawing on a metal plate. For this you will need:

• Plastic or glass container.
• Salt.
• Metal plate.
• Power supply 5 - 12 volts.
• Connecting wires.

Electrochemical engraving on metal

Metal etching sometimes replaces casting and engraving, it makes the whole process much easier. You can get a picture as a concave - embossed, and a convex - bas-relief. Metal etching at home can be chemical and galvanic. The first option is more toxic when used at home, so for starters we will use the second, it is also called electrochemical.

Equipment

You need to take a power supply or a transformer that can output from 4 to 7 V. In addition, you will need a dielectric bath, it must contain the necessary part and a second metal object that is connected to the anode.

To carry out the etching of the pattern on the metal, it is necessary to use it as iron sulphate. If a drawing is needed on a copper or brass surface, then you can also use it. The main thing is that the water be distilled.

Preparing the part for etching

In order for the etching to be uniform and in the right places, the part must be cleaned of dirt and degreased. For more convenient work, copper wire is soldered to the part with tin, it will be convenient to hold the object for it. To clean the surface, you need to lower the object to be converted into 10% sodium hydroxide, the temperature of which is 50 ° C, then into a 15% sulfuric acid solution and hold it there for two minutes, then rinse it in hot water. When the procedure is completed, the surfaces of the object will be completely cleaned, and of course, you cannot touch them with your hands.

Electrochemical etching of metal

We need to protect the places that shouldn't be pickled. To do this, it is necessary to apply a special mastic to these areas of the surface. It is made from three shares of wax and two - rosin, they are melted in a tin, stirring. After everything turns into a homogeneous mass, it is allowed to cool and divided into fragments. Each of them is placed in gauze, so that when pressed, as much mastic as necessary can seep through it. After that, the workpiece, which we will pickle, heats up. Now we take the created mixture, which was placed in gauze, and rub the surface with an even layer.

After cooling, the mastic becomes solid. From above it is covered with light water-soluble paint. It can be watercolor or gouache white. After that, the coating should dry. Then you can apply a drawing, it will hold well on the paint. It can be drawn with a pencil or translated through carbon paper. Then this contour must be scratched with a needle to the metal itself.

Now the etching of the metal by electrolysis begins, we connect one rod to the anode - plus, the other to the cathode - minus. To the first we connect the part on which the image will be applied, to the second any steel plate. After that, the process of etching the metal begins where the image was scratched.

If you need to create a multi-level drawing, everything is done in the same way as described above. Only the contours are checked every time, and when the smallest of them are etched to the prescribed depth, the part is removed and painted over with heated mastic using a brush. When it hardens, everything is repeated again until the next level of the drawing. In the process, an image is gradually created.

In this way, the metal is etched at home, after which the surface is washed with turpentine, and then polished, giving the product a finished look.

Etching chemical

Now let's look at how to create a pattern on a metal surface without the use of electrical appliances. To do this, we need chemicals that are freely sold in hardware stores. So, let's begin. For etching we need:

• "White Spirit";
• paint that does not dissolve in White Spirit;
• acetone;
• resin that is used to cover roofs;
• table salt;
• copper sulfate.

Part cleaning

To begin with, the part where the image is planned is cleaned with fine sandpaper and degreased. When the surface is ready, you need a place where the pattern will be applied, sealed with adhesive tape or something similar. After that, the rest of the surface, where chemical etching should not affect the metal, is painted over with paint. It can be of any color, as long as it is resistant to White Spirit.

When the paint dries, you can remove the adhesive tape. Beneath it is pure metal, ready to be painted on. Now on this "mini-canvas" you need to apply an image. It is made using resin, which is dissolved in White Spirit until it becomes liquid, like paint. She draws the desired image with a brush. What is good about such improvised paint is that if something does not work out in the drawing, then it will be possible to remove it by moistening a rag or cotton swab in White Spirit. If the drawing has very small details that did not turn out well with a brush, they can be corrected with a needle, scraping off the excess after drying.

In this way, you can etch a knife, keys, in general, any metal object. Now that the drawing is completely ready, you can proceed to the etching itself.

pickling solution

We need a liter of water, in which we need to dissolve 100 g of copper sulfate, and then add salt. It must be poured until it ceases to dissolve. The resulting mixture will have a blue color. However, after a metal object is immersed in it, the color will begin to change to green.

So, let's load the item. The chemical process starts immediately. In all this production, no substances harmful to health are emitted, so such metal etching at home is safe.

Actions in a chemical reaction

During the reaction, a plaque is formed, which will become more and more. It slows down the whole process, so you need to periodically wash it off with water. You should not do this with various brushes, brushes and other tools, because you can damage the paint. But she seems to be holding the whole drawing, and it will be a shame if, by etching a knife, for example, you inadvertently damage the drawing on it. This is a very delicate work that requires a firm hand and patience.

The depth of the pattern directly depends on the time during which the metal will remain in solution. There are no exact criteria, so each master must himself observe the course of a chemical reaction. And only after doing this several times, it will be possible to say with confidence how much time is needed for the manifestation of the desired pattern to the intended depth.

Advantages and disadvantages of electrochemical and chemical etching

The advantages of electrochemical metal etching at home include the fact that the pattern being created is clearer, this is clearly visible if you look at it with magnification. However, the downside is that this method requires an electrical device, which may not be for everyone.

The advantages of chemical etching include the fact that everything you need can be bought at a hardware store. These ingredients are cheap, and, most importantly, you do not need to look somewhere for a power supply or other devices capable of delivering from 4 to 7 V. However, the imperfect edges of the pattern are a minus.

Etching is a process in which part of the metal is removed from the surface by chemical means. This method is used for the final processing of the part, when preparing the workpiece before applying the coating (galvanic), as well as for creating all kinds of drawings, ornaments and inscriptions.

The essence of the method

Metal etching involves careful surface treatment. A protective coating is applied to the product, which is washed in place of the pattern. Then either acids or an electrolyte bath are used. Unprotected places are destroyed. The longer the exposure time, the deeper the etching of metals occurs. The drawing becomes more expressive and clear. There are various ways to obtain an engraving (inscription): the image itself or the background can be etched directly. Often these processes are combined. Multi-layer etching is also used.

Etching types

Depending on the substance used to destroy the surface of the material, the following etching methods are distinguished.

1. Chemical method (it is also called liquid). In this case, special solutions based on acids are used. Thus, ornaments and inscriptions are applied to the alloys.

2. Electrochemical etching of metal - involves the use of an electrolyte bath. It is filled with a special solution. Lead salts are also often used to prevent overetching. This method has a number of advantages. Firstly, the drawing is clearer, and the time required to complete the process is significantly reduced. In addition, such metal processing is economical: the volume of acid used is much less than with the first method. Another undoubted advantage is the absence of harmful gases (mordant does not contain caustic acids).

3. There is also an ion-plasma method (so-called dry). In this case, the surface is damaged minimally. This method is used in microelectronics.

Steel Pickling

Basically, this treatment is used to remove scale and various oxides. This procedure requires careful adherence to technology, since overetching of the base metal is undesirable. In the process, both a chemical method and electrolyte baths are used. Hydrochloric and sulfuric acids are used to prepare solutions. All parts require careful degreasing of the surface. Even a small fingerprint can ruin the workpiece. As a protective coating, varnish based on rosin, turpentine, and tar is used. However, it is worth remembering that the components are flammable substances, so the preparation of varnish requires great concentration and caution. After the metal processing is completed, the etching process itself takes place directly. Upon completion, the part must be cleaned of varnish.

Picklings used for steel

Very often, a solution of nitric acid is used to pickle steel. Also used is salt, tartar (with small additions of nitrogen). Hard steel grades are pickled with a mixture of nitric and acetic acids. Glyphogen is a special liquid based on water, nitric acid and alcohol. The surface is treated with this composition for several minutes. Then washed (solution of ethyl alcohol in purified water), dried quickly. This is a pre-treatment. Only after such manipulations are the workpieces placed in the pickling solution. Cast iron is well pickled in a solution of sulfuric acid.

Pickling of non-ferrous metals

Copper and alloys based on it are pickled with sulfuric, hydrochloric, phosphoric or nitric acids. The process is accelerated by solutions of chromates or nitrates. The first stage is the removal of scale, then the brass is directly etched. Aluminum (and its alloys) are etched in a solution of caustic alkali. For casting alloys, nitric and hydrofluoric acids are used. Spot-welded blanks are treated with phosphoric acid. Titanium alloys are also pickled in two stages. First - in caustic alkali, then in a solution of sulfuric, hydrofluoric, nitric acids. Titanium etching is used to remove the oxide film before electroplating. Molybdenum is treated with a solution based on sodium hydroxide and hydrogen peroxide. In addition, etching of metals (such as nickel, tungsten, for example) is carried out using water, hydrogen peroxide and formic acid.

There are several ways to etch boards. In the first case, water and ferric chloride are used. It can also be made independently. To do this, iron filings are dissolved in hydrochloric acid. The mixture is kept for some time. Also, etching of printed circuit boards is carried out using nitric acid. The whole process takes about 10 minutes. At the end of it, the board must be thoroughly wiped with baking soda, as it perfectly neutralizes the remnants of a caustic substance. Another etching composition includes sulfuric acid, water, hydrogen peroxide (in tablets). It takes much more time to etch boards with such a composition: hot water, table salt, blue vitriol. It is worth noting that the temperature of the solution should be at least 40 degrees. Otherwise, etching will take longer. Boards can also be etched using direct current. As dishes for this process, you can use glass, plastic containers (it does not conduct current). Fill the container with edible salt solution. It is he who is the electrolyte. As a cathode, you can take a copper (brass) foil.

Pickling process for other materials

Currently, this type of glass processing, such as etching, is widely used. Vapors of hydrofluoric acid, hydrogen fluoride are used. First, acid polishing of the surface is carried out, then a pattern is applied. After these manipulations, the product is placed in a bath with an etching solution. Then the glass is thoroughly washed and cleaned of the protective coating. As the latter, you can use a mixture based on beeswax, rosin, paraffin. Etching glass with hydrofluoric acid is used to give it a haze. There is also the possibility of color etching. Silver salts give the surface yellow, red, blue hues, copper salts - green, black, red. To obtain a transparent, shiny pattern, sulfuric acid is added to hydrofluoric acid. If deep etching is required, the process is repeated several times.

Pickling Safety

Metal pickling is a rather unsafe activity that requires a lot of concentration. This is due to work with aggressive materials - acids and their mixtures. First of all, for this process it is necessary to correctly choose a room with good ventilation. Ideal when pickling will use a fume hood. If one is not available, then it is necessary to take care of a respirator to avoid inhalation of harmful fumes. When working with acids, rubber gloves and an apron should be worn. Always have baking soda on hand, which - if necessary - can neutralize the effect of the acid. All pickling solutions must be stored in special containers (glass or plastic). Do not forget about the stickers, which will indicate the composition of the mixture, the date of preparation. There is one more rule: jars of acids should not be placed on high shelves. Their fall from a height is fraught with serious consequences. Artistic metal etching is not complete without the use of nitric acid, which is quite caustic. In addition, in some mixtures it can be explosive. Most often, nitric acid is used for sterling silver. Etching solutions are prepared by mixing acids with water. It is also worth remembering that in all cases the acid is added to the water, and not vice versa.

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 metal etching is used, why it is 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.

With the help of etching, the part is cleaned and surface adhesion is increased. This is done for the subsequent connection of a metal surface with another workpiece, before applying paint, enamel, electroplating and other protective coatings.

The method allows not only to quickly clean the part, but also to create the desired pattern on the metal surface. This method cuts out the thinnest channels and complex images on a metal surface. You can clean large parts or rolled products. The machining depth is adjustable to within a few microns, which allows the production of complex parts with small grooves and other complex features.

Application of pickling in industry

1. For removing the oxide film from parts made of carbon, low-alloy and high-alloy steel, titanium and aluminum.
2. To improve adhesion before electroplating and other types of protective coatings.
3. For preparation of a steel surface for hot dip galvanizing.
4. To conduct a macroanalysis to detect the formation of intergranular corrosion in stainless steels.
5. With this technology, small metal parts are processed, such as the gears of a wrist watch.
6. Copper processing is used for the manufacture of semiconductor microcircuits and printed circuit boards in electronics. This method is used to apply 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. By etching, relief images are obtained, drawn by removing a layer of metal according to a certain stencil.

Etching types

The main types of metal processing used in the industry:

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

electrolytic etching

Electrolytic or galvanic metal processing is used for quick cleaning of parts, engraving and 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, lead is used as the material for the anode, and the electrolyte is a solution of hydrochloric acid, sulfuric acid, or an alkali metal salt. In the process of electrolysis, gaseous hydrogen is actively released at the cathode, which interacts with iron and detaches scale. The metal surface in the cathodic method is actively saturated with hydrogen, which increases the brittleness of the workpiece. Therefore, for thin-walled products, the cathode method is not used.
2. Anode electrochemical cleaning. This is the most common method in mechanical engineering. The process consists in mechanical tearing off the oxide film on the anode with oxygen and mixing metal molecules with the electrolyte. The 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 products becomes clean, with a slight roughness, and the metal dissolves in the electrolyte. With this method, there is a risk of reducing the thickness of the workpiece and overpicking.

chemical etching

The chemical treatment method is used to clean the surface of a part from an 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 acidic or alkaline solution, molten salt and kept for the desired time interval. The required cleaning time can be from 1 to 120 minutes.

The purification process occurs due to the release of hydrogen during the interaction of acid with the metal. Acid molecules penetrate through pores and cracks under the oxide film. There they interact with a metal surface, hydrogen is released. The released gas breaks off the oxide film and cleans the part.

Simultaneously with the oxides, the metal to be treated dissolves in the acid. Corrosion inhibitors are used to prevent this process.

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 enter into a chemical reaction with the molecules of the material being processed. Allows you to make high-precision notches, grooves with an accuracy of 10 nm. The technology is applied in microelectronics.

The plasma-chemical method involves the 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 have a high reactivity. These gases actively interact in the gas discharge plasma. In contrast to 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.

Etchant

Etching 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 brittleness of the material and reduce the possibility of overetching.

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 steps. 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.

A thick layer of scale that forms on stainless steel is removed during its production with 75-85% sodium hydroxide melt with 20-25% sodium nitrate. After that, in 15-20% nitric acid, complete removal of oxides is carried out.

The processing of aluminum and alloys based on it is used to remove a refractory oxide film from the surface of the workpiece. For this, 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 fluoride to the alkali makes this process more uniform.

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, hydrochloric or nitric acid is used 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;
• iron chloride;
• ammonium persulfate.

This white paper 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, various patterns can be applied to the metal, complex microcircuits can be created, and microscopic channels of the desired shape can be made.

Figure 2.2 shows how a board can be made from foil textolite without etching. It is necessary to separate the sections of the board from each other with grooves running along the lines, as in the figure, cutting them with a cutter from a hacksaw blade (pictured), while the foil should cut through. In this case, you do not need to draw tracks, but you can clean the board from oxides, degrease, cut grooves, drill holes for parts and immediately solder. We can say, by making a groove, we separate the patches on the board, interconnected by a track, from other such patches and tracks. After soldering, you should get something similar to the bottom photo. In this way, you can make almost any of the simplest boards, at one time, when I hadn’t poisoned boards yet, I even made a board with one 14-leg Dip chip in the package, but it wasn’t easy, so if possible, it’s better to make boards with microcircuits by etching. You can part the board in sprint layout by printing. You can also manually on a piece of paper in a cage, referring to the circuit diagram, applying the details and marking the places of future holes in the board with dots. Having parted, you need to glue the resulting drawing to the prepared piece of textolite with electrical tape, and you can directly core on a piece of paper. After cutting, it is necessary, by switching the tester to the sound continuity mode, touching in turn, all adjacent sections with the probes of the tester, check all sections in this way, if at the same time a beep sounds, then there is a short circuit between these sections (the foil is not completely cut or chips from the foil closed the sections) . Of course, this check can also be done with a tester in ohmmeter mode, but with sound continuity, possible short circuits on the boards are easier to detect. Since there is no way to tin contact points - pads, I recommend dropping a drop of alcohol-rosin flux for high-quality soldering, you can make it yourself (dissolved in ethyl alcohol 97% powdered rosin in a ratio of 50 alcohol / 30 rosin).

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