Titanium in electroplating
Galvanic method of coating metals has received the widest distribution. To increase the intensity and efficiency of production and technological processes of electroplating, use new electrolytes, increase the temperature and increase the current density. This requires construction materials and equipment that meet the increased requirements of corrosion resistance. In addition to improving the technical parameters, it is extremely important to maximize the service life of the equipment, which depends on the quality of lining and structural materials. Despite the fact that there are quite a lot of materials for the safe operation of the equipment, problems related to its long service life and strength have not yet been resolved. Lead in chrome and other acid electrolytes, although it has chemical resistance, but is easily susceptible to mechanical failure. If the lead lining gets damaged, the body of the bath is subjected to severe corrosion.
Baths made of steel lined with viniplast, resistant to acid electrolytes, are used in the processes of nickel plating, copper plating, galvanizing, etc. But if the temperature is too high, the vinyplast sheets can crack from the temperature expansion. This is explained by the fact that the thermal expansion coefficient of vinyl plastic is six times greater than that of steel. This leads to a violation of the integrity of the lining, especially in the area of the welds, and later to the dissolution of the material from which the bath is made, under the influence of corrosion and contamination of the electrolyte composition. Even getting the minimum amount of corrosive constituents (impurities of heavy metals) in the electrolyte can cause a sharp drop in the quality of the coating. To resist this, rubber is used for lining. However, it also shows low efficiency due to the rapid aging and cracking of its coating. In addition, the process of lining and humification is expensive, because of low adhesion to certain metals. All the existing insulating and protective technologies for suspensions with the use of chemical resistant rubber, perchlorovinyl lacquer or tape allow the use of pendants for two to three months. Often to change or repair the suspension — an extremely time-consuming and economically unprofitable exercise.
Corrosion resistance of titanium
Of all materials demonstrating a high level of corrosion resistance in most electrolytes, titanium alloys are considered to be the most optimal for use. Titanium is known for its resistance to corrosive effects in virtually all electrolytes of an alkaline, slightly acidic and acidic nature. It is stable in etching solutions containing 10% H 2 SO 4 at a temperature of 75 ° C, but when the concentration increases to 18−20% starts to corrode rapidly. If nitric acid or its salts are added to the electrolyte as inhibiting additives, the process of corrosion destruction of titanium can be prevented. In this case, an oxide film forms on the surface of the metal, which prevents its dissolution. Titanium begins to quickly corrode also in electrolytes containing hydrofluoric or borofluoric acid. In all other cases, the use of titanium as a protective coating in galvanic engineering is extremely promising.
Equipment for electrotype
To perform pre-treatment and plating, baths, anode baskets, cathode drums, heating coils, suspensions, heat exchangers, pipelines, filters, pumps, etc. are used.
Baths made of titanium, intended for chrome plating, are made of alloy VT1−0. This technology has long been used by the automobile plant «Kommunar», as well as the plant for the production of measuring instruments in the city of Zaporozhye. The use of titanium in chrome plating baths increases the life of the titanium in five to seven times. When three baths made of alloy VT1−0 were installed in the Melitopol Engine Plant instead of traditional baths made of steel and lead, due to the increase in the duration of their use and the reduction of depreciation charges, the cost of electrolyte and the reduction of labor intensity and energy intensity, increase the annual income indicator.
In electrolytes, which are used in the processes of coppering, nickel plating, cadmium, brass, galvanizing and silvering, titanium practically does not undergo corrosion destruction, in addition to solutions of hydrofluoric acid and borofluoric acid. In addition, it is undesirable to use titanium in combination with media in which fluorine ions are located because of the difference in the rate of corrosion when using the anode circuit and switching off the current.
Replacement of baths made of carbon steel lined with viniplast or lead to titanium baths is expedient for stabilizing the production process: reducing the frequency of routine repairs, maintaining the purity of the electrolyte, increasing the quality of the coating, and, most importantly, being able to regulate the temperature or acid balance of the electrolyte. Stability of titanium alloys to corrosion in the above electrolytes makes it possible to reduce the wall thickness more than twice. This makes titanium baths and baths made of steel lined with viniplast, almost identical in value.
In the baths intended for nickel plating, galvanizing and coppering, three types of anodes are used: electrolytic, cast and rolled. The latter have become most common, since they dissolve most evenly, while electrolytic anodes tend to have more intensive dissolution and sludge formation.
To minimize the harmful effect of slime, the anodes are placed in special bags of «belting» or «chloride», which were previously treated with hydrochloric acid. In this case, the waste reaches only twenty to thirty percent of the total weight of the anodes. The use of anode baskets made of titanium is extremely promising. Back in 1959, the firm «Ford» developed and put into operation the first anode containers made of titanium. Due to this, the expenses for the maintenance of equipment were significantly reduced, and the duration of daily work increased by four hours.
Anode baskets are designed to increase the overall productivity of the plant. In addition, in order to add the anode material to the container, it is not necessary to discharge the remaining solution from the bath. The anode material is consumed almost in its entirety, maintaining a constant density and ensuring maximum efficiency of its operation. Since 1959, they have been used for cyanic and acid copper-plating, cyanic white brass, and brilliant nickel plating. Introduction to the domestic production process of baskets made of titanium made it possible to create a completely dissolving anode.
The use of anode baskets made of titanium alloy VT1−0 at the Melitopol Motor Plant has significantly increased the annual economic indicator for the production of nickel-plated parts used in power units. The main indicator of the economic efficiency of this innovation is a hundred percent use of nickel anodes, whereas up to the time of introduction of this technology only 70% of all anodes were used. In addition, the need to use copper hooks, which were previously used for the installation of new anodes, was lost, the labor cost indicator for the replacement of anodes was reduced.
Zaporozhye plant «Kommunar» on the automatic line of electroforming managed to escape from the ratio of income and total consumption of anodes from nickel, later unused, which was 30%. Titanium baskets made of alloy VT1−0 made it possible to significantly reduce the consumption of anodes from nickel and simplify the maintenance of baths when adjusting the electrolyte level.
Anode baskets with special hooks for hanging are created from sheets of titanium with a thickness of 0.8−1 millimeter. Calculation of the cross section of hooks is based on the calculation of low values of thermal conductivity and current density, which is less than 1A / dm.
For carrying out the process of high-speed tinning, titanium baskets are used, which are pre-filled with granular tin acting as an anode. Such anodic material can significantly increase the productivity of electrolytic tinning by increasing the active current density, which is distributed over the entire area of the anode in the basket.
The described titanium baskets, designed according to different schemes, have gained wide popularity in the processes of nickel plating, tinning, copper-plating and galvanizing, since they allow to use the anode material to the end, and thus to save expensive raw materials: nickel, tin, copper, and others. In addition, it is possible to use pigs, granules, ingots of primary material, which cost much less than their rolling anode equivalents.
In order to achieve a qualitative precipitation of the parent metal, it is required to maintain a stable temperature balance during the galvanic process. Today, heaters and coils of lead, leaded carbon steel, stainless steel are still often used. The problem is that after only two to three months they fail under the influence of the aggressive chemical environment of the electrolyte and high temperature. If necessary in this case, permanent repair work and replacement of heaters, there is an undesirable violation of the temperature stable balance, and consequently, the costs for operating the equipment also increase.
The use of titanium in heat-exchange equipment is more advantageous in comparison with the above materials. This explains the growing popularity of titanium in Western production. So, the English company «Dean Produkti Incorporated» is engaged in the release of its own development of all-titanium panels used to heat the electrolyte. The American company «Imperial Chemical Industrial» is engaged in the production of titanium coils, and the American society «Kontimet» produces titanium heat exchangers for heating electrolytes of various types (even chrome ones). Due to the absence of corrosive products on the external surface of the heat exchanger, the necessary heat transfer values are achieved by reducing the heating surface up to 45%, which is an indisputable advantage.
Even having half the heat conductivity, rather than lead or steel, titanium makes it possible to create pipes of heaters with much thinner walls, since it has high corrosive and mechanical strength. This implies the equality of the price of coils from leaded carbon as well as stainless steel and equipment from titanium grades VT1−00 and VT1−0. In addition, the use of titanium alloys can significantly reduce the cost of operating equipment, increasing the operating time by four to six times.
Even in ordinary baths for chrome plating, titanium coils will serve for many years. The plant «Kommunar» in Zaporozhye uses, for the purpose of heating the electrolyte, chromium-plated titanium heaters 3 m in length and 2.5 mm in diameter, which replaced the obsolete lead coils with a length of 7 meters and Ø 6 millimeters. For four years of operation, this type of equipment has provided invaluable economic advantages. Titanium heaters are also used on dozens of automatic lines of the Tambov Mechanical Plant.
Pendants and accessories
Titanium has also been widely used in the creation of suspensions for anodizing parts made of aluminum and its alloys. So, simple aluminum frames are extremely quick to oxidize and begin to break down. To prolong the average time of their operation for more than four to six weeks, the frame must necessarily be exposed to an alkaline environment. In this case, the titanium frame in similar operating conditions does not show signs of beginning destruction even after years. Suspension from titanium also showed their best qualities in the processes of tinning and galvanizing. They are not subject to corrosion, which allows you to avoid the loss of their valuable material, extend the life of the parts and reduce the cost of repairs.
The production of titanium suspensions and frames is quite easy. The only limiting nuance is the use of joints by soldering with hard and soft solder. It is also undesirable to connect the parts with bolts and rivets, since these junctions can malfunction in the transmission of electric current. The maximum reliability factor is demonstrated by a connection using welding.
One of the British companies specializing in the production of washing machines, uses in its technical arsenal more than sixty tools made of titanium, for anodizing aluminum parts, as well as over four hundred aluminum devices with titanium tips. Repair galvanic suspension is quite expensive, long and time consuming. The use of titanium elements of production makes it possible to minimize the number of such repair operations. In addition, titanium for a long time maintains electrical conductivity at a fairly high level.
Experience of use
In Zaporozhye, at the electrical equipment plant, as well as at the Kommunar plant, aluminum suspensions were previously used in the processes of anodizing and electropolishing aluminum parts. Then the life of the suspension was only one month. After the introduction of the production of suspensions from titanium, this time was able to extend more than a year. Quantitatively, this can be represented as a ratio of 15 titanium suspensions instead of 816 aluminum suspensions, which must be used within one year of operation.
The English company Aitzi develops new projects and produces titanium suspensions of varying design complexity. After thousands of work cycles, the corrosion in the titanium equipment of their production is only 0.025 of the value of the cross section of the entire suspension.
German companies «Riedel», «Blasberg» and others intensively use suspensions of different designs in electrolytes with a base of sulfuric acid (mainly during anodizing). Most often used suspension from titanium or aluminum with titanium contacts. However, all-titanium structures are more successful in application.
Titanium equipment used to equip ventilation systems also helps in reducing the costs of operation and maintenance, improves the quality of work, extends the life of the equipment. Although the initial investment in the installation of a titanium ventilation system is two to three times higher than the cost of standard ventilation from steel, but the titanium quality performs its functions five to six times longer. For more than one year Zaporozhye Automobile Plant has successfully used a titanium ventilation system.
When the production capacity of workshops specializing in metal coatings increases, more care must be taken to clean up the waste water that contains a large number of toxic components (acids and their salts) that are formed during the etching of metals and their hydroxides from anodic purification. In the baths of galvanizing, coppering, cadmium, there are a large number of metal alkaloids and toxic cyanides, whose concentration should be less than 0.1 mg / l, and the chromium content in chromic and chromium baths should not exceed 0.5 mg / l.
For the purification of sewage from slag and toxins, special neutralization plants are used. In addition to these harmful substances, sewage also contains a lot of chemical compounds that aggressively affect the condition of the purification system and the drain system. In the event that sewage treatment plants are only being built or undergoing major overhaul, tanks for collecting spent substances, discharge pipelines, pumping equipment and stop valves are recommended to be made of titanium. The use of this metal increases the operational endurance and extends the service life of the entire equipment system.
A similar system with a capacity of 10 cubic meters, designed for wastewater treatment with an increased chromium content and associated compounds, has been built and has been successfully operating for several years at a transformer plant in the city of Zaporozhye. At the same time, during the entire operation in the recovery bath and the drainage pipeline, not a single case of corrosive destruction was observed.
Numerous experience in the use of titanium in galvanic constructions proves the feasibility of using titanium elements. This concerns the reliability, quality, durability and economic benefits of using this material. The use of titanium equipment in production is an indicator of the progressiveness of the company, keeping track of its current trends and taking care of performance indicators, reducing labor intensity, reducing heavy maintenance work for personnel, increasing the quality of coatings, saving electrolyte, water, electricity, steam, reducing cycle time, increasing durability of equipment, improvement of working conditions and growth of production culture.
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