The essence of the process of chemical milling is the controlled removal of material from the surface of the workpiece by dissolving it in an etchant due to a chemical reaction. Areas of the workpiece that cannot be dissolved are covered with a protective layer of a chemically resistant material.
The removal rate of many materials is up to 0.1 mm / min.
Process advantages:
High productivity and quality of processing,
· The possibility of obtaining parts of complex configuration, both small and significant thickness (0.1-50) mm;
· Low energy costs (mainly chemical energy is used);
· Short cycle of production preparation and simplicity of its automation;
· Wastelessness due to the regeneration of process products.
During processing, material removal can be performed from the entire surface of the workpiece, to various depths or to the entire thickness of the part (through milling). Chemical milling includes the following main stages: preparation of the workpiece surface; applying a protective layer of the picture; chemical etching; removal of the protective layer and quality control of products (see Figure 3.1).
Surface preparation is cleaning it from organic and inorganic substances, for example, using electrochemical degreasing. The degree of purification is determined by the requirements for subsequent operations.
The application of a protective layer of the pattern is carried out by the following methods: manual and mechanized engraving on a continuous (varnish, wax) layer, by xerography, screen printing, offset, and also photochemical printing.
In instrument making, the most widely used method of photochemical printing, which provides small dimensions of products and high accuracy. In this case, to obtain a protective layer of a given configuration, a photomask is used (a photocopy of a detail on an enlarged scale on a transparent material). Liquid and film photoresists with photosensitivity are used as a protective layer. Liquid, the most widely used in the industry, require high quality cleaning of the surface of the workpieces. To apply them to the surface, one of the methods is used: immersion, watering, spraying, centrifugation, rolling, spraying in an electrostatic field. The choice of method depends on the type of production (continuous application or on individual workpieces); requirements for the thickness and uniformity of the formed film, which determine the dimensional accuracy of the pattern and the protective properties of the resist.
Rice. 3.1. General diagram of the technological process of chemical milling.
Photochemical printing of a protective pattern, in addition to the operation of applying the photoresist and drying it, includes the operations of exposing the photoresist layer through a photomask, developing the pattern and tanning the protective layer. Upon development, certain areas of the photoresist layer dissolve and are removed from the workpiece surface. The remaining layer of photoresist in the form of a pattern determined by a photomask, after additional heat treatment - tanning - serves as a protective layer during the subsequent operation of chemical etching.
The chemical pickling operation determines the final quality and yield of the product. The etching process takes place not only perpendicular to the surface of the workpiece, but also sideways (under the protective layer), which reduces the processing accuracy. The amount of undercutting is estimated through the etching factor, which is equal to, where H tr is the depth of etching, e is the amount of undercutting. The dissolution rate is determined by the properties of the metal being treated, the composition of the etching solution, its temperature, the method of feeding the solution to the surface, the conditions for removing the reaction products and maintaining the etching properties of the solution. Timely termination of the dissolution reaction ensures the specified processing accuracy, which is approximately 10% of the processing (etching) depth.
Etchants based on salts with an amine, an oxidizing agent, are currently widely used, among which chlorine, chlorine oxygen compounds, dichromate, sulfate, nitrate, hydrogen peroxide, and fluorine are most often used. For copper and its alloys, kovar, steel and other alloys, solutions of ferric chloride (FeCl 3) with a concentration of 28 to 40% (by weight) and a temperature within (20 - 50) C, which provide the dissolution rate (20 - 50) μm / min.
Among the known etching methods, a workpiece is submerged in a quiet solution; into a stirred solution; spraying the solution; spraying the solution; jet etching (horizontal or vertical). The best processing accuracy is provided by jet etching, which consists in the fact that the etching solution under pressure through nozzles is supplied to the surface of the workpiece in the form of jets.
Quality control of parts includes visual inspection of their surface and measurement of individual elements.
The chemical milling process is most beneficial in the manufacture of flat parts of complex configuration, which in some cases can also be obtained by mechanical stamping. Practice has established that when processing batches of parts in the amount of up to 100 thousand, chemical milling is more profitable, and over 100 thousand - stamping. With a very complex configuration of parts, when it is impossible to manufacture a stamp, only chemical milling is used. It should be borne in mind that the chemical milling process does not allow the manufacture of parts with sharp or right angles. The radius of rounding of the inner corner must be at least half the thickness of the workpiece S, and the outer corner must be more than 1/3 S, the diameter of the holes and the width of the grooves of the parts must be more than 2 S.
The method has found wide application in electronics, radio engineering, electrical engineering and other industries in the production of printed circuit boards, integrated circuits, in the manufacture of various flat parts with a complex configuration (flat springs, raster masks for picture tubes of color TVs, masks with a pattern of circuits used in thermal spraying processes , razor nets, centrifuges and other parts).
Electrochemical sizing is based on the local anodic dissolution of the workpiece material in an electrolyte solution with intensive movement of the electrolyte between the electrodes.
The machinability of metals and alloys by the electrochemical method depends on their chemical composition and does not depend on their mechanical properties and structural state. The advantages of the method include high surface quality with an increase in processing productivity, no thermal effect on the part, and no wear of the tool electrode. Due to this, during electrochemical processing, a layer of a changed structure is not formed and the formation of burns, cracks, residual stresses, etc. on the surface is excluded.
Feasibility of application
The use of electrochemical processing turns out to be highly effective and economically feasible in the following main cases:
- for processing parts made of particularly hard, brittle or ductile materials (heat-resistant, hard and titanium alloys, stainless and hardened steels);
- for processing structurally complex assemblies and parts (gas turbine blades, dies, molds, casting molds, internal channels and cavities, etc.), even from materials that can be cut;
- to replace particularly laborious (including manual) operations (deburring, edge rounding, etc.);
- to obtain a high quality, including polished surface without defects in the surface layer.
It is advisable to classify the known types of electrochemical processing according to two defining characteristics - the mechanism of the metal destruction process itself and the method of removing the reaction products from the working zone. Based on this, we can name three main directions in which the development and implementation of electrochemical processing methods is going on: electrochemical-hydraulic (anode-hydraulic) processing, electrochemical mechanical processing and combined processing methods.
Electrochemical-hydraulic processing
Electrochemical-hydraulic treatment (also called electrochemical treatment in a flowing electrolyte) is based on the anodic dissolution of metal and the removal of reaction products from the working area by an electrolyte flow. In this case, the speed of the electrolyte flow in the interelectrode gap is maintained within the range of 5-50 m / s (using a pump providing a pressure of 5-20 kgf / cm2, or due to the rotation of the cathode-tool, continuously wetted by the electrolyte). The operating voltage is maintained within 5-24 V (depending on the material and technological operation), the gap between the electrodes is from 0.01 to 0.5 mm; the size of the gap is regulated by automatic tracking systems. Stainless steel, brass, graphite (the latter when processing at alternating or impulse voltage) are used as the material for the manufacture of the electrode-tool.
The energy intensity of this group of processes depends on the chemical composition of the processed material and the current efficiency. For most technological operations, it is 10-15 kWh / kg. The most common at present are the following types of electrochemical-hydraulic processing.
Copy-stitching operations carried out with the translational movement of the cathode-tool, the shape of which is copied on the product simultaneously over the entire surface (Fig. 5).
These operations are used in the manufacture of turbine blades, forging dies, etc. At a metal removal rate of 0.1-0.5 mm / min, a surface finish of 6-7 is achieved; with an increase in the processing speed to 1-2 mm / min, the surface finish rises to 8-9. The highest productivity obtained when machining cavities on the MA-4423 machine is 15000 mm3 / min at a current of 5000 amperes. The feed rate of the tool in the direction of metal removal is 0.3-1.5 mm / min when processing dies, molds and blades and 5-6 mm / min when piercing holes. Surface finish 6-9; processing accuracy 0.1-0.3 mm. Processing is carried out with minimal gaps (0.1-0.15 mm); the largest gaps (5-6 mm) - while processing large surfaces.
Rice. 5. Scheme of piercing a hole by electrochemical method
Rice. 6. Machining with a rotating disc tool
Processing with a rotating disk tool (Fig. 6), which allows you to carry out profile, flat and circular external grinding with a non-abrasive tool to obtain a surface finish of 7-9 with a productivity on stainless steels up to 150-200 mm3 / min from a working area of 1 cm2 and 60-80 mm3 / min for hard alloys, it is used to obtain the profile of carbide threaded dies, shaped cutters, knurling rollers, making external spline grooves, cutting narrow slots, cutting workpieces (cutting width 1.5-2.5 mm; surface finish 6-7) as well as for the processing of permanent magnets. Processing is carried out with gaps of 0.01-0.1 mm; processing accuracy 0.01-0.05 mm, surface finish 6-9. The feed rate, depending on the depth of processing, ranges from 1 to 40 mm / min, the voltage is 6-10 V. When machining cemented carbide, alternating or pulsed currents are used.
Rice. 7. Scheme of electrochemical deburring: 1 - tool; 2 - insulating sleeve; 3-blank (anode); 4 - removable burr
Wire complex contour cutting on a copy of products from hardened, stainless steels and other difficult-to-machine materials allows the manufacture of die matrices, templates, through and blind grooves. Productivity of processing is up to 40 mm2 / min with a surface finish of 8 - 9. The accuracy of processing in straight cutting 0.02 mm, when cutting along the contour 0.06 mm. The maximum thickness of the workpiece to be cut is 20 mm (the given data were obtained on the MA-4429 machine).
Removing burrs from gears (Fig. 7), parts of hydraulic equipment, small radio engineering products, etc.
Manufacturing of grooves in special products.
Figured processing of bodies of revolution both at the end of the product and outside and inside. The processing accuracy when using a shaped cathode is 0.05-0.1 mm.
Electrochemical mechanical treatment
Electrochemical mechanical treatment is based on the anodic dissolution of metal and the removal of reaction products from the treated surface and from the working area using an abrasive and an electrolyte flow. This type of machining includes electrochemical grinding (electro-abrasive or electro-diamond machining), electrochemical machining with a neutral abrasive (grinding, honing and polishing) and anodic abrasive machining. In electro-abrasive and electro-diamond machining, metal removal is carried out not only due to the reaction of anodic dissolution, but also by grains of abrasive or diamond.
Productivity with electro-diamond grinding of hard alloys is 1.5-2 times higher than with diamond grinding, and the wear of a diamond wheel is 1.5-2 times less (when working with wheels on a bronze bond of Ml, on bonds M5, MB1 and MO13E, the wear of a wheel approximately the same as for diamond grinding); the surface finish is the same as for diamond grinding. In electrochemical grinding, the power consumed to drive the grinding wheel decreases several times. At the same time, the temperature of the surface layer drops sharply, due to which the appearance of cracks and burns is completely excluded. This method is widely used for sharpening carbide tools.
Electrochemical machining with neutral abrasives is used for flat, cylindrical and profile grinding, honing of internal cylindrical surfaces, and superfinishing. In all cases, the productivity of these operations is four to eight times that of machining.
Combined processing methods
The combined processing methods include electroerosive and electrochemical - ultrasonic.
The electroerosive-chemical processing method is based on the simultaneous occurrence of the processes of anodic dissolution and erosional destruction of the metal and the removal of reaction products from the working area by an electrolyte flow. During piercing operations, the cathode feed rate reaches 50-60 mm / min for steel, 20-30 mm / min for high-temperature alloys and 10 mm / min for hard alloys. In this case, the wear of the cathode-tool does not exceed 2.5%; processing accuracy 0.1-0.4 mm (according to experimental data).
This method can also be used for circular, flat and profile grinding, cutting workpieces made of difficult-to-machine materials. When cutting stainless steel blanks, the productivity is 550-800 mm2 / min; tool wear reaches 4-5%; processing accuracy 0.1-0.3 mm. Machines for this processing method are currently not produced.
The electrochemical processing method is based on the destruction of the metal by its simultaneous anodic dissolution and exposure to ultrasonic vibrations. This method is used for machining carbide drawing dies.
Chemical methods are called methods of processing materials in which the removal of a layer of material occurs due to chemical reactions in the processing zone. Advantages of chemical processing methods: a) high productivity, ensured by relatively high rates of reactions, primarily the lack of dependence of productivity on the size of the area of the treated surface and its shape; b) the ability to process particularly hard or viscous materials; c) extremely low mechanical and thermal effects during processing, which makes it possible to process parts of low rigidity with a sufficiently high accuracy and surface quality.
Dimensional deep etching (chemical milling) is the most common chemical processing method. It is advisable to use this method for processing surfaces of complex shapes on thin-walled parts, obtaining tubular parts or sheets with a smooth change in thickness along the length, as well as when processing a significant number of small parts or round workpieces with a large; the number of places to be processed (perforation of the cylindrical surfaces of pipes). By local removal by this method from excess material in unloaded or lightly loaded, it is possible to reduce the total weight of aircraft and missiles without reducing their strength and rigidity. In the United States, the use of chemical milling has reduced the weight of a supersonic bomber wing by 270 kg. This method allows you to create new structural elements, such as sheets 1 of variable thickness. Chemical milling is also used in the manufacture of printed circuits for electronic equipment. In this case, in a panel made of insulating material, covered with copper foil on one or both sides, the sections specified by the circuit are removed by etching.
The technological process of chemical milling consists of the following operations.
1. Preparation of parts for chemical milling to ensure subsequent tight and reliable adhesion of the protective coating to the surface of the part. For aluminum alloys, this preparation is carried out: by degreasing in B70 gasoline; light etching in a bath with caustic soda 45-55 g / l and sodium fluoride 45-55 g / l at a temperature of 60-70 ° C for 10-15 minutes to remove the clad layer; rinsing in warm and cold waters and clarification in nitric acid followed by rinsing and drying. For stainless and titanium alloys, preparation of parts is carried out by etching for descaling in a bath with hydrofluoric (50-60 g / l) and nitric (150-160 g / l) acids or in a bath with electric heating up to 450-460 ° C in caustic soda and sodium nitrate (20%), followed by washing and drying, degreasing and light pickling with repeated washing and drying.
2. Application of protective coatings to the areas of the workpiece that are not subject to etching. It is produced by installing special overlays, chemically resistant adhering type templates or, most often, by applying paints and varnishes, which are usually perchlorovinyl varnishes and enamels, polyamide varnishes and materials based on non-oprene rubbers. So, for aluminum alloys it is recommended to enamel PVC510V, solvent RS1 TU MHP184852 and enamel KhV16 TU MHPK-51257, solvent R5 TU MHP219150, for titanium alloys - glue AK20, thinner RVD. For better adhesion of these coatings to the metal, the surface is sometimes pre-anodized. The application of paint and varnish coatings is carried out with brushes or spray guns with preliminary protection of the etching sites with templates or by immersion in a bath; in the latter case, the contour is marked on the dried protective film, then it is cut and removed.
3. Chemical dissolution is carried out in baths in compliance with the temperature regime. Chemical milling of aluminum and magnesium alloys is carried out in solutions of caustic alkalis; steels, titanium, special heat-resistant and stainless alloys - in solutions of strong mineral acids.
4. Cleaning after etching of parts made of aluminum alloys with an enamel protective coating is carried out by rinsing in running water at a temperature of 50 + 70 ° C, soaking the protective coating in hotter running water at a temperature
70-90 ° C and subsequent removal of the protective coating with knives manually or with soft brushes in a solution of ethyl acetate with gasoline (2: 1). Then produce clarification or light pickling and drying.
The surface quality after chemical milling is determined by the initial roughness of the workpiece surface and etching modes; usually it is 1-2 classes lower than the purity of the original surface. After etching, all the defects previously present on the workpiece. (risks, scratches, irregularities) retain their depth, but broaden, acquiring greater smoothness; the deeper the etching depth, the more pronounced these changes are. The surface quality is also influenced by the method of obtaining the workpieces and their heat treatment; the rolled material gives a better surface compared to stamped or extruded material. A large surface roughness with pronounced irregularities is obtained on cast blanks.
Surface roughness is influenced by material structure, grain size and grain orientation. Hardened and aged aluminum sheets have a higher grade of surface cleanliness. If the structure is coarse-grained (for example, the metal is annealed), then the finished surface will have large roughness, uneven, bumpy. The most suitable for chemical processing should be considered a fine-grained structure. It is better to treat carbon steel blanks by chemical milling before quenching, since in the case of hydrogenation during etching, subsequent heating helps to remove hydrogen. However, it is advisable for thin-walled steel parts to be hardened prior to chemical treatment, as subsequent heat treatment may deform them. The surface treated with chemical milling is always somewhat loosened due to etching, and therefore this method significantly reduces the fatigue characteristics of the part. Considering this, for parts operating under cyclic loads, it is necessary to polish after chemical milling.
Accuracy of chemical milling ± 0.05 mm. depth and not less than +0.08 mm along the contour; the radius of curvature of the notch wall is equal to the depth. Chemical milling is usually carried out to a depth of 4-6 mm and less often up to 12 mm; at a greater depth of cut, the surface quality and machining accuracy deteriorate sharply. The minimum final thickness of the sheet after etching can be 0.05 mm, therefore, chemical milling can be used to machine parts with very thin bridges without warping, to process them on a cone by gradually immersing the part in the solution. If it is necessary to etch from both sides, it is necessary either to position the workpiece vertically so as to allow the evolved gas to rise freely from the surface, or etch in two steps - first on one side, and then on the other. The second method is preferable, since with a vertical position of the workpiece, the upper edges of the cutouts are processed worse due to gas bubbles entering there. When making deep cuts, special measures (eg vibration) should be used to remove gas from the surface to be treated that interferes with the normal process. Control of depth, etching during processing is carried out by immersion. Simultaneously with the preparation of control samples, direct control of dimensions with thickness gauges such as an indicator bracket or electronic, as well as through automatic weight control.
Chemical milling performance is determined by the rate at which material is removed in depth. The etching rate increases with an increase in the temperature of the solution by about 50-60% for every 10 ° C, and also depends on the type of solution, its concentration and purity. Stirring the solution during the etching process can be done with compressed air. The etching process is determined by an exothermic reaction, therefore, the supply of compressed air cools it somewhat, but mainly the constancy of temperature is ensured by placing water coils in the bath.
Immersion etching has a number of disadvantages - manual labor, partial breakdown of protective films on untreated surfaces. When processing a number of parts, the jet etching method is more promising, in which the alkali is supplied by nozzles.
A means of increasing the productivity of chemical milling is the use of ultrasonic vibrations with a frequency of 15-40 kHz; in this case, the processing productivity increases by 1.52.5 times - up to 10 mm / h. The chemical treatment process is also significantly accelerated by the action of directional infrared radiation. Under these conditions, there is no need to apply protective coatings, since the metal is subjected to strong heating along a given heating circuit, the rest of the sections, being cold, practically do not dissolve.
The etching time is established empirically on control samples. The etched workpieces are removed from the pickling machine, washed in cold water and treated at a temperature of 60-80 ° C in a solution containing 200 g / l of caustic soda to remove emulsion, paint and BF4 glue. The finished parts are thoroughly washed and dried in a stream of air.
Improving the conditions for roughing workpieces by cutting by first removing the skin by pickling is another example of the dissolving effect of a reagent. Before pickling, the workpieces are blasted with sand in order to remove scale. Etching of titanium alloys is carried out in a reagent consisting of 16% nitric and 5% hydrofluoric acids and 79% water. According to foreign literature, etching in salt baths is used for this purpose, followed by rinsing in water and then repeated etching in acid etchants for final cleaning of the surface.
The chemical action of the technological environment is also used to improve conventional cutting processes; Methods of material processing based on a combination of chemical and mechanical action are finding more and more widespread use. Examples of already mastered methods are the chemical-mechanical method of grinding hard alloys, chemical polishing, etc.
Ya.M. I'm Polish
ELECTROLYTIC MILLING METHOD
INTERIOR CONNECTING WINDOWS
DUCTS IN PARTS OF ALUMINUM AND ITS ALLOYS
Stated February 8, 1957. No. 566488 n Committee on Inventions and Discoveries iri Soneta of the USSR Ministers
The invention relates to methods for electrolytic milling of connecting windows of internal channels in parts made of aluminum and its alloys.
Known methods of this kind do not make it possible to perform internal connection of channels in hard-to-reach places. According to the invention, to obtain such channels, copper tubes are used, which serve to supply and remove the electrolyte and are the cathode. A solution of neutral salt is used as an electrolyte, for example, a solution of technical sodium chloride.
The proposed method of electrolytic milling is illustrated by a drawing.
In an article 1 provided with two or more channels 2, it is required to make a channel 3 connecting the first two channels. To do this, an insulating-sealing tube 4 is inserted into one of the channels 2, inside which 1 there are copper tubes 5 and 6, which serve to supply and drain electrolyte. serve as a cathode, Electrolyte is continuously pumped through tube 5 by a pump. Under the action of the current and the mechanical action of the electrolyte jet, anodic dissolution of the metal of the article occurs in the direction of the electrolyte jet. Through tube 6, the electrolyte enters the collector and then back into the feed pump.
For the processing of aluminum products, a 10–20% -HblH solution of technical sodium chloride is used as an electrolyte. The current density must be equal to 10 € ”
Current source voltage 15†”
25th century With the selection of the appropriate electrolytes, the method can be used for the development of other metals. No. 110679
The subject of the invention
Resp. editor L. G. Golaidsky
Standardgiz. Subp. to print 14 / 1H 1958 Volume O, I25 and. l. Circulation 85O, ceis 28 iop.
Printing house of the Committee for Inventions and Discoveries under the Council of Mpiistroi of the USSR
Moscow, Neglinnaya, 23. Zak. 1980
1. A method of electrically milling connecting windows of internal channels in parts made of aluminum and its alloys, consisting in the fact that an electrolyte stream is directed to the surface to be treated, and the product and the electrolyte stream are connected to a direct current source, from and t c M that, in order to create the possibility of making holes in hard-to-reach places, copper tubes are used to supply and drain the electrolyte, connected to the negative pole of the current source.
2. The method according to and. 1, characterized in that a solution of technical sodium chloride is used as the electrolyte.
Similar patents:
The invention relates to equipment for electrochemical analysis and can be used as a sensor in the composition of polarographic equipment
The invention relates to the field of electroplating and can be used in the electrical industry, in instrument making and for decorative purposes in the production of consumer goods. The method is characterized in that the anode of silver and silver alloys and the metal cathode are immersed in an electrolytic bath and a voltage of 280-370 V is applied to them at an anode current density of 0.4-0.8 A / cm2 and at a temperature of an aqueous electrolyte solution of 20-40 ° C, while an aqueous solution containing ammonium chloride, ammonium citrate and tartaric acid is used as the electrolyte in the following ratio of components, wt%: ammonium chloride 3-10; ammonium citrate 2-6; tartaric acid 1-3; water rest. The technical result consists in polishing the silver or silver-containing part - the anode and obtaining silver oxide on the cathode surface.
The invention relates to the field of electrochemical processing of workpieces from non-ferrous metals, and in particular to the aqueous electrolyte solution used for processing. The electrolyte solution contains citric acid with a concentration in the range from 1.665 g / l to 982 g / l, ammonium bifluoride with a concentration from 2 g / l to 360 g / l and not more than 3.35 g / l of strong acid. Surface treatment of the workpiece includes exposing the surface to a bath of aqueous electrolyte solution, adjusting the bath temperature to less than or equal to 85 ° C, connecting the workpiece to the anode of the DC power supply, and immersing the cathode of the DC power supply in the bath and passing less than 255,000 amperes of current through the bath. square meter. The invention makes it possible to use an aqueous electrolyte solution for processing various non-ferrous metals, while the electrolyte is environmentally friendly and does not create hazardous waste. 6 n. and 23 p.p. f-crystals, 12 dwg., 9 tab.
The invention relates to the field of electrochemical methods for processing metal surfaces, including decorative processing. The method includes processing the silver surface in an aqueous solution of sodium thiosulfate Na2S2O3 × 5H2O - 790 g / l at a temperature of 35 ± 2 ° C using pulsed unipolar and bipolar rectangular currents of the following amplitude-time parameters: tp = 0.1-10.0 ms , trep.imp = 0.1-10.0 ms, the duration of the delay of the current pulse of negative polarity tg = 0.1-10.0 ms, tpause = 0.1-10.0 ms, the amplitude current density in the pulse of positive polarity iimp = 0-5 A / cm2, amplitude current density in a pulse of negative polarity iotr.imp = 0-5 A / cm2 and processing time 0.5-15.0 minutes, and the current is unipolar when iotp.imp = 0. The technical result is the formation of passive decorative films resistant to external influences of the environment on the surface of a 925 sterling silver alloy. 3 ill.
K .: Tehnika, 1989 .-- 191 p.
ISBN 5-335-00257-3
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In electrochemical milling, a coating made of any acid-resistant paint applied on a stencil can serve as a protective coating. The pickling solution in this case consists of 150 g / l sodium chloride and 150 g / l nitric acid. Etching occurs at the anode at a current density of 100-150 A / dm2. Copper plates are used as a cathode. After the termination of the process, the cathodes are removed from the bath.
Electrochemical milling is more accurate than chemical milling.
PRE-TREATMENT OF ALUMINUM AND ITS ALLOYS
To ensure strong adhesion of the electrolytic coating to aluminum, an intermediate layer of zinc, iron or nickel is applied to the surface of the latter (Table 21).
CHEMICAL AND ELECTROCHEMICAL POLISHING
A smooth metal surface can be obtained by chemical or electrochemical (anodic) polishing (Tables 22, 23). The use of these processes makes it possible to replace mechanical polishing.
When oxidizing aluminum, mechanical polishing is not enough to achieve a shiny surface, after which chemical or electrical
21. Solutions for pretreatment of aluminum
Orthophosphoric Ki Ice Acetic Orthophosphoric Ki
280-290 15-30 1-6
Acid Orange * For:
dye 2
pinned surface
1st treatment with intermediate
ratu-ra. WITH
4. OrTHOPHOSPHORUS!
Triethane! lamin
500-IfXX) 250-550 30-80
Triethanolamine Catalin BPV
850-900 100-150
Ortofs of phrtoic acids Chromic thhydrnd
* PS mining products are processed by the washing line in the same flow rate 6A / dm2
Trochemical polishing When polishing precious metals by chemical or electrochemical methods, their losses are completely eliminated. Electrochemical and chemical polishing can be not only a preparatory operation before electroplating, but also the final stage of the technological process. It is most widely used for aluminum. Electrochemical polishing is more economical than<ими-ческое.
The current density and the duration of the electropolishing process are selected depending on the shape, size and material of the products.
TECHNOLOGY OF COATING PROCESSES
SELECTION OF ELECTROLYTES AND PROCESSING MODES
The quality of the metal coating is characterized by the structure of the deposit, its thickness and uniformity of distribution on the surface of the product. The structure of the precipitate is influenced by the composition and pH of the solution, the hydrogen released together with the metal, the electrolysis mode - by the
polishing
M 41
with SS
Density
„|§..
Cathodes
From sent
Carbonaceous
I-IL
15-18
1,63-1,72
12XI8H9T, svshsho
1-5
10-100
From steel 12Х18Н97
H: rust
From styles 12Х18Н9Т Aluminum and 3-5 20-50 - (aluminum) stainless
0.5-5.0 20-50 1.60-1.61 Of copper or Evin - Copper and its
temperature, flow density, rocking, filtration, etc.
To improve the structure of the precipitate, various organic additives (glue, gelatin, saccharin, etc.) are introduced into the electrolytes, complex salts are precipitated from solutions, the temperature is increased, continuous filtration is used, etc. The released hydrogen can be absorbed by the precipitate, contributing to an increase in fragility and porosity. , and the appearance of points of the so-called pitting. To reduce the effect of hydrogen on the quality of the sediment, the parts are shaken during the process, oxidizing agents are introduced, the temperature is increased, etc. The porosity of the sediment decreases with an increase in its thickness.
The uniform distribution of the sediment on the surface and the delium depends on the scattering power of the electrolyte. The best scattering power is possessed by alkaline and cyanide electrolytes, much less - by acidic ones, and the worst - by chromic ones.
When choosing an electrolyte, it is necessary to take into account the configuration of the products and the requirements that are imposed on the NNM. For example, when covering products of a simple shape, you can work with simple electr> -
lntamn that do not require heating, ventilation, filtration; when coating products of complex shape, solutions of complex metal salts should be used; for covering internal and hard-to-reach surfaces - internal and additional anodes, filtration, mixing; to obtain a shiny coating - electrolytes with complex gloss-forming and leveling additives, etc.
GENERAL DIAGRAM OF THE TECHNOLOGICAL PROCESS
The coating process consists of a series of sequential preparatory, coating and finishing operations. Preparatory operations include mechanical processing [of parts, degreasing in organic solvents, chemical or electrochemical degreasing, etching and polishing. Finishing treatment of coatings includes dehydration, clarification, passivation, impregnation, polishing, and brushing. After each operation