Using electrolyte-plasma polishing (EPP) in product surface preparations for high-voltage electrochemical oxidation
Reducing aircraft weight for ensuring its operational safety is a topical problem. Metals are the basic structural materials in this sphere. The improving of metallic materials' characteristics by conventional methods (addition of alloying elements, improvement of thermo-mechanical hardening technology, etc.) has almost reached its limit at present. In this paper we present the studies of a new composite material based on aluminum oxide ceramic and diamond-like carbon, which may be successfully used in spacecraft slide units. The composite material was created in two stages. At the first stage a ceramic layer was formed. The formation was carried out on the basis of aluminum alloy 5052 by using high-voltage electrochemical oxidation method. In order to optimize the process, instead of chemical treatment the electrolyte-plasma polishing was applied for preliminary samples' preparation for oxidation. At the second stage the modified basis with a layer of aluminum oxide ceramic was treated by pulsed high-current flows of carbon plasma in the reaction hydrocarbon gas medium.
Application of an elektrolyte-plasma method of polishing for processing of field welds and surface preparation under coverings
The method of elektrolyte-plasma processing is known since 80th years of last century. A basis of the given method are proceeding on an anode and cathode surface in electrolyte of low concentration water solutions of neutral salts physical and chemical processes at giving of high (250-340 V) constant voltage.
Ways of perfection of technology of processing of a surface of metals and alloys by means of an elektrolyte-plasma method
The most important factor of acceleration of development is introduction of the new technologies, allowing to lower both energy consumption and possessing the best ecological and economic indicators. An example of such process is polishing of metals and alloys with the help of electrolyte plasma. Plasma-elektrolyte technology uses ecologically safe neutral low concentration water solutions of salts of ammonium (3–6 %) which in times are cheaper than toxic acid components which are used in electrochemical polishing. Thus for polishing 2–5 minutes and for removal of burrs 5–20 seconds there are required. In many cases the given technology would not demand special treatment facilities to utilize the waste electrolyte.
Methods of polishing which has received enough wide circulation in various branches of industry. The elektrolyte-plasma method of processing of a surface of metal articles in weak water solutions of neutral salts (2–6 %) is perspective. For polishing of metals the constant voltage 200–350 V and the density of a current 0,2–0,5 А/см2 are necessary. The process takes 2–5 minutes. The technology corresponds to modern technical, ecological, economic and social requirements.
Each method has the merits and demerits. So, machining receive a surface with the necessary parametres, however thus there is a pollution of a surface by an abrasive and mechanical deformation of coating surface of a article. Besides, application of this method is complicated at processing of details of the small size and the difficult geometrical form. The chemical method of processing allows to process products of the complicated form, but at polishing there is a pollution of a surface by products of reactions. After processing by this method it is necessary to perform additional operations on neutralisation and surface passivation. By means of an electrochemical method it is possible to process a surface of a various profile and the sizes, but use as a basis of the concentrated acid solutions, power consumption and ecological danger of process have not allowed to extend widely to this method, and now electrochemical polishing does not meet the requirements of modern manufacture.
On the threshold of 21 centuries for industrially developed countries which Byelorussia concerns also, more and more actual there is a maintenance of a sustainable development of the state which is understood as conducting economic activities taking into account preservation of natural resources and environment for present and the future generations. The major factor of strategy of a sustainable development is wide introduction of the new technologies directed on improvement of a condition of environment, and the emphasis becomes on decrease in formation of a harmful waste, instead of their clearings and processing. Reduction of quantity of formed wastes protects workers, inhabitants and environment is much better and more effective, than any technical control over emissions. Now the main accent is transferred in wildlife management on elimination of original causes of pollution, instead of its consequences. Economic gains of such policy abundantly clear.
For transition to a sustainable development it is necessary to change priorities in ecological and economic policy. For that it is necessary to pass from a principle «reactions and corrections» to «active preventive maintenance», i.e. now the main accent is transferred in wildlife management on elimination of original causes of pollution, instead of its consequences. In this case one of sustainable development primary factors is introduction ecologically safe, energy - and resource saving technologies. These technologies will allow to provide release of competitive production at smaller production costs and to improve environment.
Directions of expansion of technological possibilities of a method of elektrolitno-plasma influence use of jet currents of electrolit is perspective. It will allow to reduce power consumption of process of polishing. Tests of processing of products with use of devices which create jet currents of electrolit are already conducted. Local influence on a surface of products will allow to save power and material resources and as considerably will expand a scope of a method of elektrolitno-plasma processing and the list of processed products, including the large-sized. For the purpose of development of this perspective direction research of laws of influence is carried out elektrolitno-plasma technology on metals and alloys электролитной plasmas at jet currents of electrolit. Persons interest is represented by processing of internal remote surfaces, deep apertures, lengthy products etc.
One of the basic directions of use of elektrolyte-plasma technology (EPT) — surface preparation under the subsequent protective or wearproof coverings. As an example we will consider frictional disks. Operation on preparation of a basis of frictional disks under the precoating traditionally carried out galvanic or electrochemical methods, demands considerable expenses and time, not speaking already about environmental problems. The purpose of use EPТ in this case consists in as much as possible to simplify and reduce the price of preparation of a surface of disks from the carbonic steel 65G.
The ecological factor at processing of materials along with economic is the major. One of the basic advantages of elektrolyte-plasma technology is relative ecological compatibility in comparison with other kinds of processing. Naturally, for each metal and an alloy different structures of electrolytes, as a rule, are used, therefore by consideration of ecological questions of processing the approach should be concrete. Today the greatest experience is saved up on processing austenitic and ferritic stainless steels.
Processes of updating of surfaces of current-carrying materials (reduction of roughnesses, formation of shine, decrease of surface stress, removal of burrs, blunting of sharp edges) are considered at processing of articles by an elektrolyte-plasma method in solutions of salts of low concentration. The basic laws of processes and the phenomena proceeding on border metal-electrolyte are established. Features and advantages of new ecologically pure technology of updating of surfaces are shown. Technical and economic aspects of use of the elektrolyte-plasma equipment are considered.
Surface polishing is the major process at manufacturing of metal products of mass production both technical and a household purposes. Existing mechanical methods of polishing are labour-consuming, difficult and often lead to undesirable structural changes in a surface of products, creation of the additional stresses, making negative impact on operational properties. Widely applied electrochemical methods of polishing of metal products have high cost, basically because of use of expensive acid electrolytes which besides do the big ecological harm to environment. In this connection the major value is given to working out and implementation of new technological processes of the polishing having high efficiency, good ecological and economic indicators. Rather new elektrolyte-plasma method of processing of a surface meets the specified requirements and is applied to polishing of metal products at many enterprises of Russia, Ukraine, Belarus, thus successfully competes to widespread mechanical and electrochemical ways of polishing in acids. The elektrolyte-plasma technology has higher technical characteristics of process, such as speed of processing of a product, a class of cleanliness of its surface, absence of introduction of parts of an abrasive and surface degreasing.
Last years in the industry wide application for finishing technological operations was received by a way of polishing of the products, based on a method of electropulse processing of a surface of a product. This way provides reception of high quality of a surface of a processed product.
Surface polishing is the mass technological process which constantly extends in industry. Existing mechanical methods are labour-consuming and result in undesirable structural changes in a surface of products. Therefore practical interest is represented by the new methods which are not deforming a surface.
Within the limits of the program «Energy Saving» a energy-efficient method of heat treatment of expensive boiler pipes from the austenitic stainless steel has been found. This ones has saved up a limited level of damages of structure during the operation. The method and the device for local, thermocyclic, regenerative heat treatment of lengthy pipes in electrolyte is offered.
One of the perspective directions, received the wide circulation in various branches of industry , is elektrolyte-plasma processing of a surface of metal articles in water solutions of salts of low concentration (2... 6 %). The given technology satisfyes to modern technical, economic, ecological and social requirements. Polishing of metals occurs in the field of the voltage 200-350 V, density of a current 0,2... 0,5 А/sm2, duration of polishing 2... 5 minutes.
In this paper the process of elektrolyte-plasma polishing and its fields of application are described. Authors suggest to use a method of elektrolyte-plasma polishing for deactivation and clearing of a surface of the equipment of the Nuclear Power Plant.
The method of High Voltage Electrochemical Oxidation (HVEO) of aluminium and its alloys has been developed. It was found that obtained aluminium oxide layers have thickness up to 70 µm, microhardness is over 8 GPa, surface roughness of 0.1-0.3 µm and thermal conductivity is about 3.5 W/m·K. A breakdown voltage of oxidized samples can reach 2500 V. The HVEO technique provides high physical and mechanical properties of oxide coatings. It is characterized by a low power consumption that makes it competitive among other methods of aluminum oxidizing.