Consider aluminum. In fact, this is a fairly common metal that you want to engrave. For example: key fobs, flash drives, housings for some mobile phones - all these are products with aluminum coating.
What we know about aluminum is that it is a metal, has a melting point of about 600 degrees Celsius, has a high thermal conductivity and most often has aluminum oxide on its coating, which has a melting point of more than 1000 degrees Celsius. All this makes the engraving process not easy when it comes to heat treatment, but there is another option. Being a metal, it is a conductor, and if so, the electrolysis process has not been canceled. Here is the very solution that we will talk about!
In other words, this process is called aluminum etching. There is nothing difficult in this.
So, we need:
- a current source of 9-12 volts.
- ordinary table salt NaCl.
- a container made of dielectric (plastic is quite suitable).
- a nail or any iron object.
- water
- aluminum sample
- and of course, laser!
So the solution could be:
1. We prepare the drawing that we would like to apply to the aluminum surface.
For example, here's a bitmap.
2. Degrease the aluminum surface so that there are no air bubbles, and cover with tape, varnish, paint (optional).
3. We place an aluminum product on our 3D printer, and carry out the laser cutting process (to destroy surface layer and thus make open areas).
5. Source electric current We divide into 2 wires "plus" and "minus".
6. We attach an iron object to the minus and lower it into an aqueous solution.
7. We attach our object to the plus and lower it also into the solution.
8. We supply power to the current source.
9. The process of electrolysis (etching) in solution has begun. Depending on the current strength and the concentration of the solution, you can roughly estimate the time needed for etching. Usually 3-5 minutes.
10. We take out the product from the solution.
In fact, it is worth remembering that the product that needs to be engraved before being placed in the solution must be carefully isolated, with the exception of those areas where, in fact, the engraving should be applied.
This process can be carried out at home and in a small workshop. With this technology, anyone can become a metal (aluminum) engraver.
In our understanding, this is very practical and valuable knowledge. Please subscribe to Endurance updates!
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Etching various details at home from copper is already quite well known to modellers. But I always did not like the fact that the parts obtained by this method most often need to be painted - after all, for example, copper is practically not used in aviation.
How much more interesting it would be, I thought, if the parts were made of white metal, besides - this metal literally "rolls underfoot".
Many times I tried to poison aluminum from beer cans, but nothing good came of it. However, finally, I got a result that allows me to think that not everything is so hopeless..;)
As a material, a can of Red Bull Cola was cut. I read that some modellers prefer "Red Bull" due to the fact that the foil of cans with it is thinner.
The etching solution was the familiar "Mole", which is often used to remove paint from models.
The protective layer was a laser printer toner applied with an iron from a backing sheet from a self-adhesive film. This method is well known and I will not describe it in detail.
The aluminum of the can is coated on both sides with a protective layer. I removed this layer from one side sandpaper.
Why with one? Yes, because before that I deleted from both sides. But Mole "is not in vain used to remove paint. He peeled off the protective layer from reverse side which I did with white nitrate, and I got unpredictable double-sided etching instead of single-sided
Therefore, I decided to use, on the other hand, a transparent protective layer inside the jar for protection.
A drawing was transferred to the cleaned surface with an iron and the plate went for etching.
At first I etched aluminum with ferric chloride, but I could not achieve good results. In the article "Chemical milling of metals" based on the book "The ABC of Ship Modeling" I read: "Aluminum and its alloys are best etched in a 10-15% solution of caustic soda. It should be remembered that chemical milling occurs very slowly. When the solution is heated to 60— 80 ° in 20 minutes, a metal layer with a thickness of only 1 mm will dissolve. After etching, the part is thoroughly washed with water and polished.
Caustic soda in its pure form is unlikely to be sold to you, but Mole consists of caustic soda plus some additives. I used dry "Mole" in a bag.
I made a saturated solution (I filled it with water in a bottle so that the powder did not dissolve completely, but remained at the bottom).
ATTENTION! CAUSTOR SODIUM IS A VERY DANGEROUS SUBSTANCE! THE PRECAUTIONS ARE WRITTEN ON THE PACKAGING AND I WANT TO WARN THAT WHEN DISSOLVE IT MAY MELTE THE BOTTOM OF THE PLASTIC BOTTLE!
Therefore, it is better to use glassware.
After that, fill a jar of mayonnaise by one tenth and add water to get a "10-15% solution of caustic soda." I put the jar in an ice cream bucket, where I poured boiled water to maintain the temperature of the pickling solution at 60-80 ° C.
Etching occurs with the release of gas bubbles. They can easily control the process. I avoided very violent gas formation, since in this case the toner may peel off, and the etching, as it seemed to me, is very uneven.
If the reaction is very fast, then you can either dilute the solution more or lower the temperature.
I did not monitor the temperature (worked on the model), periodically adding hot water from the tap, and in about a couple of hours my plate began to shine through. The drawing was not completely etched, but I did not wait for this.
On that I had such considerations. First, due to lateral etching, the boundaries of the pattern deteriorate. Secondly, the toner did not fit well, and etching went through it, which was noticeable by the rare bubbles that formed right on the shaded areas.
Taking out the plate, I washed it in hot boiling water.
Then I washed off the toner.
The most commonly used aluminum etchant is an aqueous solution of sodium hydroxide with or without additives. It is used for general cleaning applications where oxide, grease or sub-surface detritus needs to be removed with a longer etch time to achieve a glossy or matte finish. This is used in the production of nameplates or decorative architectural elements, for deep engraving or chemical etching. This etching method is quite cheap, but at the same time it can become too complicated to perform.
Decorative etching solutions may contain 4-10% or more caustic soda, the operating temperature will be 40-90ºC, and it may also be necessary to use a wetting agent to dissipate grease and to obtain a light foam coating, as well as to use other additives. Normal operating temperature for cleaning and decorative processing is 60ºС. The figure shows the rate of metal removal at various concentrations and temperatures during a 5-minute pickling of 99.5% aluminum sheet. These curves apply to a freshly prepared solution, with lower values referring to the period after the aluminum has been immersed in the solution. Springe and Shval published data on the pickling rate of 99.5% pure aluminum sheet and extrusion of 6063 in sodium hydroxide solutions with a concentration of 10, 15, 20% at a temperature of 40 to 70ºС. Chaterjee and Thomas also did a detailed study of caustic soda pickling extrusion 6063 and sheets 5005, 3013.
Etching rate 99.5% aluminum in caustic soda.
Aluminum dissolves in caustic soda with the release of hydrogen and the formation of a compound aluminate, which exists only in an alkaline solution. The reaction that occurs in this case can be written in two ways:
The amount of free caustic soda decreases as the reaction proceeds, along with this, the etching rate also decreases, the electrical conductivity decreases, and the viscosity increases. If no sodium hydroxide is added to the bath at all, the reaction proceeds very slowly, but eventually the clear or brownish solution becomes milky white, from which point the etching rate starts to increase again, and rises to a value slightly less than initial etching rate. The reaction observed at this stage can be written as follows:
The formed alumina hydrate or Gibsite is in the form of a suspension, while the reaction also releases sodium hydroxide, which is so necessary for the continuation of etching.
Ionic structure of aluminate in solutions having high level pH is a rather complex issue, fortunately the operator is not actually concerned with this problem. Moulenard, Evans and McKeever conducted infrared and Raman spectra for solutions of sodium aluminate in water and deuterium oxide (heavy water), and they also studied the nuclear resonance spectrum for Na and Al. For aluminum concentrations below 1.5M, they derived 4 vibration zones, two of which were infrared active at 950 and 725 cm-1, as well as 3 Raman zones active at 725, 625 and 325 cm-1. For aluminum, there was also a thin resonance line. All these facts can be quite easily correlated with the existence of tetrahedral Al(OH)4-, which is the main carrier of aluminum in solution.
When the concentration of aluminum exceeds 1.5 M, a new vibrational zone appears at 900 cm-1 for the infrared zone and the Raman zone at 705 and 540 cm-1, while the nuclear resonance zone for aluminum will be significantly expanded without changing position. All these observations can be explained in terms of the condensation of Al(OH)4-, with an increase in concentration and the formation of Al2O(OH)62-, and in solutions of 6M sodium aluminate, these two forms coexist in parallel. It has been found that sodium hydroxide solution, when used continuously, will absorb aluminum until the volume of free sodium hydroxide is reduced to about one quarter of the original volume, after which etching with free sodium hydroxide will continue, oscillating at approximately the same level with amplitude , which depends on temperature, intensity of use and pause period. The hydrate will then slowly settle or crystallize on the bottom and sides of the tank to form a very hard hydrate which is very difficult to remove and unfortunately tends to settle on the surface of the heating coils. Here we observe the third reaction, i.e. the reaction of dehydrogenation of aluminum hydroxide with the formation of aluminum oxide:
The nature of this transformation is shown in fig. 4-10, where various amounts of aluminum are dissolved in 5% (wt) sodium hydroxide solution, and measurements are made on free sodium hydroxide immediately after each addition, and also after three weeks. Up to 15 g/l of aluminum remains completely in solution without changes in the amount of free sodium hydroxide, however, as soon as the precipitation of aluminum oxide begins, which occurs shortly before the appearance of a freely distinguishable precipitate, free sodium hydroxide is restored to 4%, i.e. up to 80% of its initial value. With prolonged use, this value for such a solution can range from 1 to 1.5%, sometimes rising to 2.5%, in case of downtime lasting several hours. A similar ratio also corresponds to a higher concentration of caustic soda, and these values are actually independent of temperature.
Effect of dissolved aluminum on free sodium hydroxide.
Another important influence of aluminum is that with an increase in the aluminum content, the etching rate decreases, and quite clearly, this is reflected in the figure. In practice, this means that if it is necessary to maintain a constant etching rate, it is necessary to increase the content of free sodium hydroxide as the amount of aluminum in the bath increases.
The final reaction in this case will occur between aluminum and water with the release of hydrogen and aluminum. In theory, pickling can thus continue indefinitely, with the loss of caustic soda occurring only as a result of entrainment. This method of working with the pickling tank is indeed applicable in practice, however, it is necessary to remember the need for periodic removal of the solid hydrate precipitate. According to current experience, when operating in this mode, the service life of the tank can be up to 2 years. Filtration of sodium hydroxide solutions has not been as successful due to the fact that very fine sediment tends to clog the filter very quickly, but otherwise no problems have been identified with this technique.
Etching rate in sodium hydroxide 50 g/l, sodium nitrate 40 g/l at 60ºС depending on aluminum concentration.
Chemical control of the solution, applied before precipitation or in a stable state after precipitation, includes the determination of total sodium and free sodium hydroxide. The content of the latter can be calculated with sufficient accuracy for practical application by titration with hydrochloric acid until the phenolphtoleic indicator loses its color. As an alternative, potentiometric titration can also be offered. To make up for losses due to entrainment, it is sufficient to maintain the total sodium hydroxide content at a fixed level, since it is not possible to control fluctuations in free sodium hydroxide in solution. For an accurate determination, in which carbonate and dissolved aluminum are also taken into account, a more complex calculation method is used, which is given in the table.
One of the most commonly encountered problems with caustic soda etching is the tendency to pit or “burn” part or all of the part, which is accompanied by an increase in etch rate of up to 300%. This usually occurs in highly loaded solutions that are used so extensively that there is no way to recover. In this case, the hydrate crystallizes on the parts, which leads to an increase in the intensity of local etching, an increase in temperature and an effect on the grain boundaries, which has the properties of acid etching. It is sometimes difficult to avoid pitting in solutions of this type when trying to remove the anode film. If this happens, the temperature must be lowered.
Thus, it can be seen that, despite the apparent simplicity of the etching process, in practice many competing reactions can be observed, which must be recognized in order to obtain a good result. The main factors responsible for pickling are the content of free sodium hydroxide in the solution, the presence and amount of additives in the bath, the temperature of the solution, and the aluminum content of the solution. The influence of the composition of the solution has already been discussed previously, however, the temperature of the solution has a strong influence on the etch rate. Usually this factor is easy to control, but in practice, due to the exothermic nature of this reaction, it is often necessary to cool the pickling baths, especially when they are in continuous use. Most pickling baths are used at temperatures between 55 and 65°C, since at more high temperatures Contamination due to transfer etching may occur, especially on sheet materials.
Chemical solutions for pickling iron and steel
The simplest effective pickling solutions for iron and steel parts are dilute inorganic acids, especially 20% sulfuric acid, in which pickling is carried out at 45-50 ° C, or 20-25% hydrochloric acid, in which parts are pickled at room temperature. For etching, 10-15% orthophosphoric acid, heated to 60-70°C. Parts are etched in it, which will then be varnished or their surface will be left without further processing. If a galvanized surface coating is provided after pickling, then this bath is unsuitable.
Chemical etching of non-ferrous metal surfaces
Etching copper and brass
On brass, the solution forms a light yellow coating, on copper - light pink. The solution contains:
Nitric acid concentrated 250 ml;
- Hydrochloric acid concentrated 150 ml;
- Ethyl alcohol denatured 100 ml;
- Water 500 ml.
Parts are poisoned by briefly immersing them in a bath with a solution, after which they are removed and immediately washed with water.
Matt etched copper
After etching on copper, a rough (to matte) surface will be obtained. Bath composition:
Nitric acid 40% 600 g;
- Sulfuric acid concentrated 400 g;
- Sodium chloride 3 g;
- Zinc sulfate 2 g.
Brilliant etching of copper and its alloys
Sulfuric acid concentrated 500 ml;
- Nitric acid concentrated 500 ml;
- Hydrochloric acid concentrated 10 ml;
- Soot 5 g.
Working temperature baths 18-20°C. Fat-free parts are immersed in a bath with a solution for 10-30 seconds, after which they are removed, washed with water and dried.
Pickling solution for aluminum and its alloys
The aqueous solution contains:
Sodium fluoride 40 g/l;
- Caustic soda 50 g/l.
The operating temperature of the bath is 70-80°C, the processing time is about 1 minute.
Another aqueous solution contains
Chromium oxide 30 g/l;
- Sulfuric acid concentrated 150 g/l;
- The working temperature of the bath is 70°C, the processing time is 1-1.5 minutes;
The simplest way of decorative painting of steel products
Electrochemical method can be used to paint steel products in any color. If the paint layer is varnished, it will reliably protect the product from corrosion. The composition of the solution in which steel products are painted includes the following components:
blue vitriol 60;
- Refined sugar 90 g;
- Caustic soda 45 g;
- Water up to 1 liter.
Copper sulfate is dissolved in 200-300 ml of distilled water, then sugar is added to the resulting solution. Separately, caustic soda is dissolved in 250 ml of water and a solution of copper sulphate with sugar is added to it in small portions (with stirring). After mixing these two solutions, add distilled water to 1 liter. The part is cleaned, polished and degreased in a solution used in nickel plating, and then thoroughly washed in warm water. An additional electrode is made from red copper (preferably grades M0, M1). The part and electrode are connected to a battery from a flashlight (or other source direct current 4-6 V), and the copper electrode must be connected to the plus of the battery, and the part to the minus. The copper electrode is first lowered into the solution, and then the part. After 5-10 seconds, the battery is disconnected, and staining continues without electric current. Being in the solution from 2 to 25 minutes, the part is painted in the following colors (in the order of their appearance): brown, violet, blue, blue, light green, yellow, orange, red-lilac, greenish-blue, green, rose-red . The item can be taken out of the solution (checking the color) and lowered into the solution again - the process will proceed normally. When holding the part in the solution for more than 25-30 minutes, the process is cyclically repeated many times.
As the electrolyte evaporates, distilled water is added to the bath, since an increase in the electrolyte concentration worsens the quality of the color. To obtain more contrasting colors, 20 g of sodium carbonate (anhydrous soda) must be added to the finished electrolyte. If the coloring turned out to be unsuccessful, the film can be easily removed by wiping the part with ammonia. The painted parts are washed with water, dried and coated with a colorless varnish.
The easy way decorative finishes aluminum surface under mother-of-pearl
aluminum surface is cleaned wire brush, making small strokes in different directions(creating a certain pattern). Chips and dirt are removed from the surface with a clean rag. A clean aluminum surface is covered with an even layer of 10% sodium hydroxide solution (working temperature of the solution is 90-100°C). After the solution dries, a beautiful film with a pearly sheen forms on the aluminum surface. For better preservation, the film is covered with a colorless varnish. A more beautiful film is obtained if, before applying a solution of caustic soda, the product or part is heated to 80-90 ° C.
Chemical way of clarification of products and details from silumin (restoration)
Products and parts made of silumin (an alloy of aluminum with silicon) are quickly covered with an oxide film of dark tones. However, they can be shiny for a long time if they are lightened. Products or parts are cleaned and, if necessary, polished, then degreased, washed and immersed for 10-20 minutes in the following solution:
Chromic anhydride 100 g;
- Sulfuric acid concentrated 10 g;
- Water up to 1 liter.
The working temperature of the solution is 18-20°C.
After clarification, the products and parts are washed and dried, and so that the surfaces of the products and parts do not oxidize for a long time, they are covered with a colorless varnish.
What you need to know about polishing steel and non-ferrous metals
Polishing is used to improve the cleanliness of the surface of parts, devices, to eliminate traces of previous processing on them (strokes, scratches, small dents and the smallest irregularities). There are two types of polishing - preliminary and final. Pre-polishing is used to mechanically remove surface irregularities with loose abrasives (in a free state) or grains fixed on working surface polishing wheel. The final polishing is carried out with fine grinding powders or soft elastic wheels coated with fine polishing pastes. The finest surface finish is achieved by rubbing a piece of felt or woolen cloth lubricated with a special metal polishing paste. After polishing, the surface acquires a mirror finish.
Lime paste is used for polishing nickel, brass, aluminum and other metals, its composition (in%) is as follows:
Vienna lime 71.8;
- Ceresin 1.5;
- Stearic acid 2.3;
- Solidol T 1.5;
- Turpentine 2.2;
The composition of the paste (in%) for polishing steel and other metals:
Paraffin 20;
- Stearin 10;
- Technical fat 3;
- Micropowder M50 67;
Note
waxy and liquid materials mix and heat in a water bath (or over low heat). Then the dry ingredients are mixed into the hot mass.
GOI pastes are designed for polishing steel and other metals and are chromium oxide mixed with waxy substances. Pastes are produced in three grades: coarse, medium and fine. In the absence of chromium paste, oil paint chromium oxide diluted with kerosene can be successfully applied. Crocus paste (iron oxide) is sold in stores in ready-made(in dentures, they are used under the name "paste for gold"). Crocus paste is used for polishing brass, bronze, silver and other metals. Powder "Shine", diluted with machine oil, is used for fine polishing of metals.
Chemical polishing of metals
Metals can be polished chemically, i.e. by simply immersing the part or object in a bath of polishing solution without the use of electric current. For this purpose, you can use porcelain glasses or trays. The polishing solution consists of the following substances:
Phosphoric acid concentrated 350 ml;
- Nitric acid concentrated 50 ml;
- Sulfuric acid concentrated 100 ml;
- Sulphate or nitrate copper 0.5 g.
The operating temperature of the bath is 100-110°C. Polishing time from 0.5 to 4 min. When polishing, suffocating fumes are released, so the bath should be in a fume hood or outdoors.
This solution polishes aluminum and its alloys well. It is also suitable for polishing other metals, but the operating conditions (polishing time, temperature) must be different.
CHEMICAL TREATMENT OF METALS
Chemical nickel plating of steel, copper, brass and bronze products
Parts made of steel and copper alloys can be electroplated with nickel. Such a coating not only protects parts well from corrosion and gives them a beautiful appearance, but also has increased wear resistance. The advantage of chemical nickel plating is also that nickel is evenly deposited on all, including internal, surfaces of parts.
The part to be nickel-plated must be properly prepared: sanded, polished and degreased. Steel parts are degreased in a solution containing 20-30 g of caustic potassium (or caustic soda), 25-50 g of soda ash and 5-10 g of liquid glass(silicate glue); copper - in a solution containing (for the same amount of water) 100 g of trisodium phosphate and 10-20 g of liquid glass. Before nickel plating, copper parts must be held on the iron for 0.5-1 min. It should also be borne in mind that alloys containing more than 1-2% lead or cadmium are not amenable to chemical nickel plating.
Degreasing of steel and copper parts at room temperature ends after 40-60 minutes, at a temperature of 75-85°C - after 20-30 minutes. The part is then thoroughly washed in running water and immersed for 0.5-1 min in a 5% hydrochloric acid solution to remove the oxide film, after which it is washed again in water and immediately transferred to the nickel plating solution. In 1 liter of water heated to 60°C, dissolve 30 g of nickel chloride and 10 g of sodium acetate. Then the temperature is brought to 80 ° C, 15 g of sodium hypophosphate are added - and the solution is ready. A part is immersed in it, the temperature is raised to 90-92°C and maintained at this level until the end of the nickel plating process. At lower temperatures, the rate of the process slows down sharply, and when heated above 95°C, the solution may deteriorate.
Required amount(volume) of the solution depends on the area of the nickel-plated part. The ratio of this area (in square decimeters) to the volume of the solution (in liters) should be in the range of 2.5-3.5.
So, for example, at S/V=3 for 1 hour the thickness of the nickel layer will be 10 microns.
The chemicals used are not toxic, degreasing and nickel plating are not accompanied by the release of harmful gases.
Chemical copper plating of steel and cast iron parts
Quite easily, copper is chemically deposited on iron, steel and cast iron. The coverage is satisfactory.
To coat these metals, a solution is made up of the following substances:
Sulphate copper 8-50 g;
- Sulfuric acid concentrated 8-50 g;
- Water up to 1 liter.
Operating temperature 18-20°C. After thorough cleaning and degreasing, the parts are immersed for a few seconds in the solution. The parts coated with copper are removed from the solution, washed with water and dried.
Chemical chromium plating of metals
Parts made of steel, copper and brass are chemically chromium-plated in a solution containing:
Chromium fluoride 14 g;
- Sodium hypophosphate 7 g;
- Sodium citrate 7 g;
- Glacial acetic acid 10 ml;
- Caustic sodium (20% solution) 10 ml;
- Water up to 1 liter.
Operating temperature around 80°C. Cleaned and degreased parts are metallized within 3-8 hours. chemical chromium plating steel objects, it is recommended that they be chemically coppered first. Parts with a deposited chromium layer are washed in water and dried.
Chemical nickel plating of metals
The nickel plating solution consists of the following substances:
Nickel-ammonium sulphate 50 g;
- Ammonium chloride 40 g;
- Water up to 1 liter.
A small amount of metallic zinc is added to the solution and continuously stirred.
Chemical coloring of pewter products in bronze color
Tin products are well painted in bronze color by a chemical method. Products are immersed in a solution or wiped with a cloth soaked in a solution consisting of the following substances:
Sulphate copper 25 g;
- ferrous sulfate ferrous 25 g;
- Water up to 500 ml.
Then the product is dried, brushed, wiped with a cloth and again immersed in a solution consisting of the following substances:
Acetic acid copper 100 g;
- Acetic acid 10% 400 ml.
After that, the product is dried. If desired, it can be polished and covered with a transparent varnish.
"Gilding" of brass
Brass and products from it in the air quickly fade and oxidize. To protect polished items from oxidation, brass parts are often coated with a special golden lacquer. A simpler and more affordable method is as follows: after thorough cleaning and polishing, the brass part is immersed in a 10-15% solution of some kind of alkali to remove fats from its surface. Then the part is washed in water and dipped in a weak (2-3%) solution of sulfuric or hydrochloric acid for 1-2 seconds. Good results are obtained if brass is immersed in a solution of sodium bisulfite, then washed in water and immersed in a solution of copper acetate, heated to 36-40 ° C.
Depending on the time during which the part is in solution, brass is painted from a light golden color to the color of pure gold and even to a reddish-violet hue. The color of the color is monitored by removing the part from the solution from time to time. After painting, the part is washed with water and dried in air. The color is permanent and does not change over time. Acetic acid copper is commercially available, but you can cook it yourself. To do this, dissolve 5 g of copper sulfate in 0.5 liters of water, then mix with a solution of lead acetate (pharmacy lead lotion or lead sugar).
The second solution is made up of 8 g of lead acetate and 0.5 l of water. When the solutions are mixed, lead sulphate precipitates, and copper acetate remains in the solution. This solution will serve as the working solution. The precipitate can be filtered off or left at the bottom of the vessel.
Coloring copper under gold
4 g of caustic soda and 4 g of milk sugar are dissolved in 100 g of water, boiled for 15 minutes, then, with constant stirring, 4 g of a solution of saturated copper sulfate are added in small doses. Well-cleaned copper products are immersed in the hot mixture. Depending on the duration of action, they acquire a different color - from gold, green to complete black.
Golden lacquer for brass (brass passivation)
Passivation of brass produces a stable protective film similar to gilding. This film is not afraid of moisture, so anglers passivate brass spinners. The cleaned, polished and degreased part is dipped for 1 s into a solution prepared from 1 part of nitric and 1 part of sulfuric acid, and immediately transferred to a strong solution of potassium dichromate (chromic acid) for 10-15 minutes.
After that, the part is washed and dried.
Chemical staining of brass
The cleaned, degreased and washed part is immersed in one of the following solutions.
1st solution:
Hyposulfite 11 g;
- Lead sugar 39 g;
- Water up to 1 liter.
Solution temperature 70°C.
2nd solution:
In 250 ml of boiling water dissolve 10 g of caustic soda and 10 g of milk sugar. Then, stirring continuously, add 10 ml of a concentrated solution of copper sulphate to the solution.
Within 3-10 minutes, the part, which is in one of the solutions, turns golden, bluish, blue, purple and, finally, iridescent.
When the desired color is obtained, the part is taken out, dried and polished with a cloth.
Brass acquires a bluish-black color when the prepared part is immersed for 1-3 minutes in the following solution:
Ammonia (25% ammonia) 500 ml;
- Bicarbonate (or carbonate) copper 60 g;
- Brass (sawdust) 0.5 g.
After mixing the components, the solution is vigorously shaken 2-3 times, after which the part is immersed in it.
Brass turns brown when the part is immersed in one of the following solutions.
1st solution:
Hyposulfite 50 g;
- Copper vitriol 50 g;
- Water up to 1 liter.
Solution temperature 70°C.
2nd solution:
Sodium sulfide 100 g;
- Water up to 1 liter.
Solution temperature 70°C.
3rd solution:
Acetic lead 30 g;
- Hyposulfite 90 g;
- Water up to 1 liter.
The temperature of the solution is 80-90°C.
To prepare the 3rd solution, you need to dissolve both substances separately in half the volume of water, then drain them together and heat to 80-90°C. After painting, the part is washed with warm water, dried and covered with a colorless varnish.
The easy way to silver
As a silvering composition, spent hyposulfite (fixer) is used, which is no longer suitable for fixing photographic films or photographic paper. The method is extremely simple. The copper part is cleaned to a shine, boiled in a soda solution and washed thoroughly with water. Then immersed in used hyposulfite. After a while, silver will settle on the part. After washing with water, the part is dried and polished with a cloth. The quality of silver plating and the adhesion strength of silver to copper depends on the concentration of silver in the hyposulfite solution.
Silver plating of metal parts in a hot way
This method can be used to silver any metal. It consists in the following: a cleanly processed part is immersed on a zinc tape in a boiling solution consisting of the following components:
Iron-cyanogen potassium 120 g;
- Potash 80;
- Silver chloride 7.5 g;
- Distilled water up to 1 liter.
The silvering process ends after the complete coverage of the surface of the part with silver. The part is then removed from the solution, washed and polished. It should be remembered that when the solution boils, harmful substances, so boiling should be done outdoors or under a hood.
Chemical silvering
1. Several sheets of "Unibrom" matte photographic paper are cut into pieces and dipped into a solution of fixing salt (salt is diluted in the volume of water indicated on the package).
The cleaned and degreased part is placed in this solution and rubbed with an emulsion layer of paper until a dense layer of silver forms on the surface of the part. After washing in warm water, the part is wiped with a dry cloth.
2. Add 1-2 ml of ammonia and 2-3 drops of formalin to 300 ml of spent fixer (remaining after printing photos) (the solution is stored and handled only in the dark).
The cleaned and degreased part is placed in the solution for 0.5-1.5 hours, then washed in warm water, dried and wiped with a soft cloth.
Silver Paste
Parts made of copper, bronze, brass, copper-plated iron can be silver plated with pastes.
1. Silvering paste is prepared as follows: in 300 ml of distilled water or water obtained from the ice of household refrigerators, dissolve 2 g of silver nitrate (lapis) and add a 10% sodium chloride solution to the solution until precipitation stops silver chloride precipitate. This precipitate is washed 5-6 times in running water. Separately, 20 g of hyposulfite and 2 g of ammonium chloride (ammonia) are dissolved in 100 ml of distilled water. Then silver chloride is added in small doses to the resulting solution until it stops dissolving. The resulting solution is filtered and mixed with finely ground chalk to the consistency of thick sour cream. The previously degreased part is rubbed with paste using cotton wool or gauze until a dense layer of silver forms on its surface, after which the part is washed with water and wiped with a dry rag.
2. The polished and degreased part is rubbed with a cloth or a piece of soft leather, on which a paste of the following composition is applied:
Silver chloride 6 g;
- Table salt 8 g;
- Acid potassium tartrate (tartar) 8 g.
The listed substances are ground in a mortar and stored in a dark container; before use, the mixture is diluted with distilled water until a liquid paste is obtained. When the part is covered with a layer of silver, it is washed in water and rubbed to a shine with a soft flannel.
3. Silvering paste is prepared as follows: pour 2 g of ammonia, 4 g of cream of tartar and 1 g of silver nitrate (lapis) into a vessel, add a little distilled water until a semi-liquid slurry is obtained. Then, with a cloth coated with paste, the polished and degreased part is rubbed to a silver sheen.
Chemical method of silvering non-metallic materials
Non-metallic parts, such as plastics, glass, ceramics, wood, etc., can also be metallized chemically. The solution below for silvering non-metallic materials gives very good results, especially for glass plating (silvering mirror surfaces, vessels, flasks of incandescent lamps, reflectors for projection equipment, etc.).
The composition of the bath for silvering includes the following substances
Composition A
Silver nitrate 12 g;
- Ammonium nitrate 18 g;
After complete dissolution of the substances, the solution is topped up with distilled water to 750 ml.
Composition B
Caustic soda (chemically pure) 19 g.;
- Distilled water 500 ml.
After complete dissolution of caustic soda, the solution is topped up with distilled water to 750 ml.
Composition B
Sucrose 12.5 g;
- Tartaric acid 1.5 g;
- ode distilled 125 ml;
The solution is boiled for 20 minutes, and then topped up with distilled water to 500 ml.
All solutions are stored separately in dark vessels with ground stoppers.
A solution for silvering is obtained by mixing compositions A and B, to which composition C is added immediately before silvering. Parts intended for silvering are thoroughly cleaned in a hot soda solution, rinsed running water and immersed in a bath of freshly prepared solution. The working temperature of the solution is 18-20°C. Silvering time - 10 min. The plating can be carried out two or three times in succession, but each time in a fresh solution. Silver-plated parts are dried at a temperature of 50°C for 1 hour, and at a temperature of 18-20°C - for 24 hours. From glass, porcelain or ceramics, the silver layer can be easily removed with nitric acid.
Dyeing silver items purple by chemical means
Silver or silver-plated objects turn purple in a solution consisting of the following substances:
Sodium sulfate anhydrous 12.5 g;
- Sodium carbonate 5 g;
- Water 500 ml.
The solution is heated to 80°C and the object is immersed in it for a few seconds. The item is then allowed to dry. The surface of the object can be coated with a transparent varnish.
chemical solution for dyeing silver items black
Silver or silver-plated objects turn black after boiling them in a solution of sodium sulphate (100 g per 500 ml of water). After boiling in this solution, the objects are dried and covered with a transparent varnish.
Gilding metal products hot way
In a glass vessel, 20 g of nitric acid and 20 g of hydrochloric acid are mixed. 1 g of gold is dissolved in this mixture. When gold dissolves, 1 g of antimony chloride and 1 g of pure tin are added to the solution. The vessel with the solution is placed in hot water and boiled until the tin dissolves, after which 20 g of a saturated solution are added. boric acid. Products intended for gilding are cleaned, polished and boiled in a solution of caustic potassium or sodium hydroxide. The solution is applied to the product with a brush; the dried product is heated on the flame of an alcohol lamp or on a charcoal fire. After heating, a good gilding is obtained, which does not require polishing. Store the solution in a glass vessel with a ground stopper in a dark place.
Gilding without external source contact gilding is used to obtain very dense and uniform coatings, characterized by high adhesive strength, and if a large coating thickness is not required. Electrolysis by this method does not need an external current source. The potential difference necessary for the deposition of gold is created by a galvanic cell, in which the coated item serves as the cathode, immersed in the gilding electrolyte, and the anode is a zinc plate, which is in a concentrated sodium chloride solution and connected to the item with a wire, as shown in Fig. 1. For electrolysis, any heated gilding electrolyte from those indicated in the table can be used.
Gilding by immersion is based on the creation of a potential difference at the boundary of the surface of the coated metal and the electrolyte layer adjacent to it. Coatings good quality formed only on brass or brass-plated parts. Therefore, details from other metals are preliminarily brassed (minimum layer thickness 1-2 microns). The gilding process automatically stops when a layer of gold with a thickness of about 0.1 microns is obtained, but the coating is dense, glossy and has good adhesion to the surface of the parts.
Compositions of solutions and modes of operation during gilding by immersion
Removal of poor quality gold plating
To remove poor-quality coatings, gilded silver items are suspended as anodes in a 5% hydrochloric acid solution at a temperature of 18-20°C. Iron or lead plates serve as cathodes. Anode current density 0.1 - 1 A / dm?. Copper pendants. In addition, the gold coating can be removed in the "royal vodka". "Aqua regia" is a mixture of acids (50% nitric acid mixed in 50% hydrochloric acid). The mixture is used for etching copper, brass, iron, steel, zinc, etc. This solution acts on metals almost instantly; corrosion and dirt disappear, and the surface of the metal becomes shiny or, more often, matte. Jewelers use this mixture to determine pure gold.
Note
When using active acids, safety rules must be strictly observed. It should be remembered that when diluting an acid with water (for example, sulfuric acid), it is necessary to pour the acid into the water, and not vice versa, otherwise the acid will splash, which can lead to severe burns.
Simple Ways extraction of silver from spent hyposulfite (fixer)
Only a part of the silver contained in the photosensitive layer of the photographic material is spent on the construction of a photographic image. Most of the silver goes into the fixer and developer and can be isolated and collected.
1st way.
Allows you to highlight pure silver. It consists in the following: iron shavings or small iron nails, well washed from fat with gasoline, are poured into a vessel with an exhausted fixer. The solution is shaken from time to time. After 7-10 days, the solution is drained and the nails are dried in air. The silver deposited on the nails crumbles as a black powder, which can then be smelted into ingots.
2nd way.
The depleted fixer and an equal volume of spent metholhydroquinone developer are poured into one vessel. A 30% sodium hydroxide solution is added to the resulting mixture at the rate of 100 ml for each liter of used fixer. Silver is deposited in the form of the finest pure silver powder. The process takes at least 48 hours.
The silver precipitate formed during this time is filtered off and dried. The remaining aqueous solution of sodium thiosulfate, i. fixer, can be reused in work.
3rd way.
A polished sheet of brass is placed in the spent fixer, which is in a glass vessel. After 48 hours, almost all of the metallic silver from the depleted solution will settle on it. After precipitation, the sheet is washed well with water and dried. Then a layer of silver is carefully scraped off its surface.
4th way.
To 1 liter of the used fixing solution add 5-6 g of sodium hydrosulfite and 5-6 g of anhydrous soda. After 19-20 hours, metallic silver formed in the form of a black fine powder is filtered, and the silver-free fixing solution is acidified with sodium bisulfite and reused for work.
5th way.
To do this, prepare a 20% solution of sodium sulfate and pour it into the spent fixer at the rate of 20 ml of the solution for each liter of fixer. After thoroughly mixing the solution, it is allowed to settle for a day. The solution is then decanted from the precipitate, and the precipitate is dried on paper. The precipitate is silver sulfide. Precipitation is carried out in the open air or with enhanced ventilation, to reduce the release of hydrogen sulfide, the spent fixing solution is first alkalized.
PAINTING OF METALS
Coating of metal with varnish "moiré"
Before coating with "moire" varnish, the surface of the metal part is degreased by heating in an oven (oven) for 15-20 minutes at a temperature of 80-100 ° C, then primed with heat-resistant enamel, puttied with varnish putty and dried. When the part dries well, it is treated with pumice stone with water and sandpaper, wiped dry, covered with an even layer of moire varnish with a spray gun and placed for 10-15 minutes in an oven with a temperature of about 80 ° C.
The pattern of the pattern depends on the thickness of the coating and the duration of the heating of the part. When a pattern is formed on the part, it is taken out of the oven for a short time for partial cooling, and then placed back in the oven for the final drying of the varnish. At a temperature of 120-150°C, the varnish dries completely within 30-40 minutes, and at a lower temperature - within 2-3 hours.
To protect the painted surface from dusting, it is covered with celluloid varnish: celluloid is dissolved in acetone to the consistency of liquid oil varnish and applied to the surface in an even layer with a swab. After the acetone dries, a strong protective film remains on the surface.
A resistant coating is obtained if BF-2 glue is added to the aluminum paint. Glue BF-2 is dissolved in alcohol until the thickness of the enamel, then dry aluminum powder is poured into the resulting solution and thoroughly mixed, after which alcohol is added again until normal viscosity is obtained.
The paint prepared in this way lays down well when painting with a brush or with a spray gun, it does not crumble and retains its appearance for a long time.
Painting of steel products under aluminum
To give steel products beautiful view and protect them from corrosion, the metal is often coated with aluminum paint - varnish with aluminum powder. To do this, 15 g of the powder is poured into a colorless nitrolac diluted with acetone (110 g).
In the same proportion, the paint can be diluted not in nitro-lacquer, but in celluloid glue - acetone, in which 5-10 g of x-ray film, cleaned of emulsion, is dissolved.
The surface of the product is pre-cleaned thoroughly and then a thin layer of paint is applied using a spray gun.
A resistant coating is obtained if BF-2 glue is added to the aluminum paint. Glue BF-2 is dissolved in alcohol until the thickness of the enamel, then dry aluminum powder is poured into the resulting solution and thoroughly mixed, after which alcohol is added again until normal viscosity is obtained. The paint prepared in this way lays down well when painting with a brush or with a spray gun, it does not crumble and retains its appearance for a long time.
What you need to know about paint incompatibility and the perception of paint color
All components of the paint - chemical substances. Metals (copper, zinc, aluminum), which are part of paints in the form of powder, affect the corrosion of the painted metal surface and the binder. Metal oxides and salts affect the binder, accelerating film formation. Dissimilar types of binder cannot be combined with each other, and some oil paints obtained on the same binder, but based on different pigments, cannot be mixed.
Pigment incompatibility.
When mixing pigments, it is very important to take into account the nature of their interaction. In case of incompatibility of pigments, their destruction and loss of anti-corrosion properties occur.
When mixing paints with incompatible pigments, their color is lost.
Binder incompatibility.
Oil paints can only be mixed with oil paints (on a homogeneous basis), glyptal paints with glyptal paints, pentaphthalic paints with pentaphthalic paints, epoxy paints with epoxy paints, bituminous varnishes with asphalt and coal tar varnishes, etc. However, all thick oil paints can be diluted with drying oils and varnishes made on the basis of only light natural and artificial resins, excluding asphalt and bituminous resins.
Incompatibility of paint with surface material. All primers without exception can be applied to the steel surface: oil, phosphating, protective, glyptal, phenol-formaldehyde, on vinyl chloride copolymers, ethinol, acrylic, etc.
The site outlines the basics of electroplating technology. The processes of preparation and application of electrochemical and chemical coatings, as well as methods for quality control of coatings. The main and auxiliary equipment of the electroplating shop is described. Information on the mechanization and automation of galvanic production, as well as sanitation and safety precautions is given.
The site can be used for vocational training of workers in production.
The use of protective, protective-decorative and special coatings makes it possible to solve many problems, among which an important place is occupied by the protection of metals from corrosion. Corrosion of metals, i.e., their destruction due to the electrochemical or chemical action of the environment, causes enormous damage to the national economy. Every year, as a result of corrosion, up to 10-15% of the annual output of metal in the form of valuable parts and structures, complex instruments and machines goes out of use. In some cases, corrosion leads to accidents.
Electroplating are one of effective methods corrosion protection, they are also widely used to impart a number of valuable special properties to the surface of parts: increased hardness and wear resistance, high reflectivity, improved anti-friction properties, surface electrical conductivity, easier solderability, and, finally, simply to improve the appearance of products.
Russian scientists are the creators of many the most important ways electrochemical processing of metals. Thus, the creation of electroforming is the merit of Academician B. S. Jacobi (1837). The most important work in the field of electroplating belongs to the Russian scientists E. Kh. Lenz and I. M. Fedorovsky. The development of electroplating after the October Revolution is inextricably linked with the names of scientific professors N. T. Kudryavtsev, V. I. Liner, N. P. Fedotiev and many others.
Much work has been done to standardize and normalize coating processes. The sharply increasing volume of work, mechanization and automation of electroplating shops required a clear regulation of processes, careful selection of electrolytes for coating, selection of the most effective methods for preparing the surface of parts before the deposition of electroplated coatings and final operations, as well as reliable methods for quality control of products. Under these conditions, the role of a skilled electroplating worker increases sharply.
The main objective of this site is to help students of technical schools in mastering the profession of an electroplating worker who knows modern technological processes used in advanced electroplating shops.
Electrolytic chromium plating is effective way increasing the wear resistance of rubbing parts, protecting them from corrosion, as well as the method of protective and decorative finishing. Significant savings are provided by chromium plating when restoring worn parts. The process of chromium plating is widely used in the national economy. A number of research organizations, institutes, universities and machine-building enterprises are working on its improvement. More efficient electrolytes and chromium plating modes are emerging, methods are being developed to increase mechanical properties chrome-plated parts, as a result of which the scope of chrome plating is expanding. Knowledge of the basics of modern chromium plating technology contributes to the fulfillment of the instructions of normative and technical documentation and the creative participation of a wide range of practitioners in the further development of chromium plating.
The site developed the issues of the influence of chromium plating on the strength of parts, expanded the use of effective electrolytes and technological processes, introduced a new section on methods to improve the efficiency of chromium plating. The main sections have been redesigned taking into account the nporpecsivnyh advances in chrome plating technology. The given technological instructions and designs of suspension fixtures are exemplary, guiding the reader in matters of choosing chrome plating conditions and in the principles of designing suspension fixtures.
The continuous development of all branches of mechanical engineering and instrument making has led to a significant expansion of the field of application of electrolytic and chemical coatings.
By chemical deposition of metals, in combination with galvanic metal coatings are created on a wide variety of dielectrics: plastics, ceramics, ferrites, glass-ceramic and other materials. The manufacture of parts from these materials with a metallized surface ensured the introduction of new design and technical solutions, improved quality of products and cheaper production of equipment, machines, and consumer goods.
Plastic parts with metal coatings are widely used in the automotive industry, the radio engineering industry and other sectors of the national economy. The processes of metallization of polymeric materials have become especially important in the production of printed circuit boards, which are the basis of modern electronic devices and radio engineering products.
The brochure provides the necessary information about the processes of chemical-electrolytic metallization of dielectrics, the main regularities of the chemical deposition of metals are given. The features of electrolytic coatings during metallization of plastics are indicated. Considerable attention is paid to the technology of production of printed circuit boards, as well as methods for analyzing solutions used in metallization processes, as well as methods for their preparation and correction.
In an accessible and entertaining way, the site introduces physical nature in the features of ionizing radiation and radioactivity, the effect of various doses of radiation on living organisms, methods of protection and prevention of radiation hazard, the possibilities of using radioactive isotopes to recognize and treat human diseases.
