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60в среднем 98,6%, а максимум дифракционной эффективности составляет примерно 3,5%.
3. Заключение
В данной работе рассмотрена схема оптической нейронной сети и проанализировано применение корреляционного метода обработки изображений в нейронных сетях. Приведены результаты экспериментов по распознаванию изображений. Экспериментальные результаты показывают, что максимум дифракционной эффективности составляет примерно 3,5%.
Литература
1. Акаев А.А., Гуревич С.Б., Жумалиев К.М., Муравский Л.И., Смирнова Т.Н., Голография и оптическая обработка информации, Бишкек-Санкт-Петербург, - 2003. -572с.
2. Васильев В.Н., Павлов А.В., Оптические технологии искусственного интеллекта, СПбГУ ИТМО, - 2005.
3. Жээнбеков А.А., Сарыбаева А.А. Метод распознавания изображений на принципах двунаправленной ассоциативной памяти. Евразийский союз ученых, Актуальные проблемы в современной науке и пути их решения, Москва, 29-30 января 2016г. №1(22), Часть 3, с.148-151.
NEW EQUIPMENT FOR PRODUCTION OF SUPERHARD SPHERICAL TUNGSTEN CARBIDE AND OTHER HIGH-MELTING COMPOUNDS USING THE METHOD OF PLASMA ATOMIZATION OF ROTATING BILLET
Korzhyk V.
Doctor of Technical Sciences,
- Science Director of the Guangdong Institute of Welding (China-Ukraine E. O. Paton Institute of Welding),
Guangzhou, China,
- Head of Department of the Paton Welding Institute of the National Academy of Science of Ukraine, Kiev,
Ukraine Kulak L.
PhD (Eng.), Head of Department of Frantsevich Institute for Problems in Materials Science of the National
Academy of Science of Ukraine, Kiev, Ukraine
Shevchenko V.
Ph.D (Eng.), Senior Research Fellow of the Paton Welding Institute of the National Academy of Science of
Ukraine, Kiev, Ukraine Kvasnitskiy V.
Doctor of Technical Sciences, head of Department of National technical University of Ukraine "I. Sikorsky
Kyiv Polytechnic Institute", Kiev, Ukraine
Kuzmenko N.
PhD (Eng.), Senior Research Fellow, Frantsevich Institute for Problems in Materials Science of the National Academy of Science of Ukraine, Kiev, Ukraine
Hos I.
Research associate of the Paton Welding Institute of the National Academy of Science of Ukraine, Kiev,
Ukraine Khaskin V.
Doctor of Sciences, Senior Research Fellow Guangdong Welding Institute (China-Ukraine E. O. Paton Institute of Welding), Guangzhou, China
ABSTRACT
The article considers the results of studies confirm the promising of application of the technology of plasma rotary atomization of rotation billet to obtain granules of powders of high-melting-point materials, in particular tungsten carbide with sphericity over 90%, microhardness HV0.1 more than 30000 MPa characterized by high flow ability more than 7,5 s / 50 g. The universal installation for production of super-hard spherical tungsten carbide and other high-melting-point compounds by plasma atomization of rotating billets is designed for industrial application, is characterized by high degree of automation, allowing to adjust obtained powder particle size in a wide range.
Keywords: plasma rotary atomization, granules of powders, super-hard spherical tungsten carbide, high-melting compounds, velocity of the electrode rotation, particles size, microhardness, chemical composition.
Currently, in order to ensure high wear resistance their function purpose obtained using surfacing methof parts and tools, operating at significant dynamic ods are widely used. At that, the composite materials loads in the extreme conditions, the layers different in are widely used for the parts operating in conditions of
intense abrasive wear with the presence of moderate shocks, such as rolling drilling bits, tool joints, excavator tooth, crushing machines parts, cones of charging gears of blast furnaces.
In such surfacing compositions, the powders of high-melting compounds characterized by high hardness and strength, are used as a wear resistant component, for example, alloys of tungsten carbide WC + W2C (cast tungsten carbide), and as binder matrix the plastic and metal alloys are used. Cast tungsten carbide has unique complex of physical properties - high strength, ductility, hardness and high modulus of elasticity. In accordance with Ukrainian standards TUU 24.6-33876998-001-2006 the cast tungsten carbide contains 95,8-96,4% of tungsten and 3.6-4.0% of fixed carbon. The content of free carbon is not more than 0.05% , content of iron - 0.15%.
To date, for surfacing of such compositions the arc methods, when the arc is a heat source, are more widely used in industry. Therefore, in the surfacing process the wear-resistant powders are usually heated up to a high temperature, which leads to their oxidation, changing of composition and destruction of powder particles.
Reinforcing grains can be partially dissolved in the alloy-bundle, deteriorating the properties of the composition. In addition to the structural state, phase and chemical homogeneity the shape of the cast tungsten carbide reinforcing particles significantly effects on the change of their physical and mechanical properties during the welding process. For example, research results obtained in paper [1] suggests that the particles of more spherical shape have higher density and strength, which has a positive effect on the wear resistance of the deposited layers.
In this connection, the great interest is the development of methods allowing producing powders of cast tungsten carbide and other high-melting-point materials of uniform composition, characterized by a high sphericity of the particles and having higher physical-mechanical properties. Therefore, it is important to find the ways which allow to provide increasing of sphericity of reinforcing wear resistant particles of cast tungsten carbide and other high-melting-point compounds with optimal structure, uniformity of their chemical and phase composition.
The objective of this work is the development of technology and high-performance equipment for production of superhard spherical tungsten carbide and other high-melting-point compounds by plasma atomi-zation of rotating billet.
Nowadays the most common technology for producing of cast tungsten carbide powders consists in production of billets from tungsten carbides WC+W2C by remelting of raw material charge in the electric resistance furnaces or by plasma arc method with a casting into mold to obtain an ingot, from which the nine fractions are separated by grinding and sieving classification. The minus material includes a grain size 0...0.04 mm, and the plus material - 1.6-2.5 mm.
The disadvantage of this technology is in that the conditions of ingot crystallization predetermine its heterogeneity in composition and structural state -alongwalls of the mold the fine crystalline structure is
formed due to the maximum overcooling, and in the zones under the conditions of less overcooling there is a possibility of their intense growth up to larger sizes due to reduction of amounts of crystallization grains.
It is known that materials with a coarse-crystalline structure have lower toughness and ductility, therefore are vulnerable to disintegration at lower external loads. Another disadvantage of this technology is that during grinding of ingots the defects are occurred in the forms of cracks and the powders retain all defects typical for casting, particularly heterogeneity in chemical composition, defects in the forms of pores, cavities and cracks, which greatly reduce wear resistance of deposited layers of such material.
One of the methods of producing of spherical particles from metals and alloys is the method of spraying of the melt jet by the high-speed flow of inert gas. However, the main disadvantage of this method is the capture of the inert gas into the center of the spherical grain and a large number of non-spherical particles [6]. Under the influence of high-speed flow of inert gas at the beginning there is a crushing of the jet on the dispersed particles in the form of films, which due to the action of surface tension forces are contracted into the spherical shape granules of with gas capture and formation of pores, leading to loss of physical and mechanical properties of the granules and primarily the strength.
The company "Sferomet" Ltd. developed the installation and technology for the production of spherical granules of metals and alloys using the method of rotary atomization of melt from skull crucible, rotating with a controlled speed [5]. In the presented installation the drop method for production of granules is used. Melting of solid raw material in the apparatus is performed by plasma directly in the crucible. However, direct heating of the solid charge requires substantial power, which leads to increased costs for the process implementation and reduces the productivity. In addition, direct heating through the charge do not allow completely dispose of the formation at the edge of the crucible of the solidificated mass of the melt. In the formation of solidificated mass of the melt the atomization process significantly slowed, and the obtained powder particles have a heterogeneous composition, microstructure and the shape, leading to reduction of quality characteristics of the obtained powder and its mechanical properties.
In addition, in the result of interaction of melt with the crucible material (graphite) we can observe an erosion of the latter, which requires constant monitoring of the condition and regular replacement of the crucible, it is necessary to provide quality and stable supply of electric current to the rapidly rotating crucible, the value of which has a significant impact on the heating of the melt.
The most promising is the method of rotary atomization from a liquid pool of the rotating electrode [4] made of tungsten carbide WC+W2C.
In particular, the technology and equipment for production of surfacing powders in the form of cast tungsten carbide using the method of rotary atomiza-tion had been developed in the E.O. Paton Electric Welding Institute of the National Academy of Sciences
of Ukraine (PWI NASU). This method allowed to obtain the granular tungsten carbide in the form of spherical particles of a given diameter [2, 3]. However, during the process of production of granular tungsten carbide powders in addition to spherical particles of regular shape the particles of tungsten carbide of non-spherical and elongated shape are formed, which has a negative effect on the quality of the surfacing of the composite layers.
For the production of powders of high-melting-point material using the method of rotary atomization the installation of VGU-3M, the principle of which is shown in Figure 1 [4] was developed at the Frantsevich Institute for Problems in Materials Science (IPMS NASU). The preliminary prepared electrode from tungsten carbide with a diameter 25 mm and a length 180200 mm was mounted by the authors in the holder in the chamber of the installation VGU-3M, the chamber had been filled with inert gas ambient consisting of a mixture of helium and argon, and that the end of the ingot had been melted using plasma.
After the formation of the liquid phase under the centrifugal forces, the drops of melt coming off of the
Figure
In the result of performed experiments, it was found that the distribution of the fractional composition of the atomized powders of tungsten carbide WC+W2C depends on the angular velocity of the rotating billet-ingot. The results obtained on the basis of experimental data are shown in Figure 2, from which it follows that for each angular speed of the electrode rotation, under otherwise equal process conditions, there is a maximum amount of powder of a certain size. This peak is shifted toward reducing the size of the atomized powders with increasing angular velocity of the electrode rotation.
edge of the molten bath at the end of the ingot are crystallized in free fall in the form of spherical particles. At this, the speed of cooling powders had been ranged between 103-106?C/s depending on the speed of the electrode, which also determines the fractional composition of the atomized powder. The electrode speed range had been varied in wide ranges from 5 up to 20 thousand r/min.
The obtained powders were separated and their fractional composition was determined by the sieve classification method. Then, using optical metallography and scanning electron microscopy the study and comparison of the microstructures of the initial electrode ingot, crushed and atomized cast tungsten carbide powders were performed. In addition, the measurement of microhardness by Vickers was performed and the strength of powders under static load was evaluated. At the last stage, the test of resistance to abrasion of coatings surfaced using various tungsten carbide powders was performed. At this, the wear of samples was determined by the weight loss on the length of distance covered.
Cast tungsten carbide powders produced by rotary atomization are characterized by an almost perfect spherical shape and visible defects on the surface are absent (Figure3,a,b). Besides, cast tungsten carbide spherical powders have a higher density compared to powders obtained by mechanical crushing and their microstructure is homogeneous and extremely fine- crystalline at the account of high cooling rate during crystallization.
1. Principle diagram of the installation for plasma rotary atomization [4]: 1 - electrode for atomization;
2 - plasmatron; 3 - atomization product.
Figure 2. Influence of the angular velocity of the electrode rotation on the fractional composition of the cast tungsten carbide powder atomized using centerless method [4]:1 - Vk = 12,5 m/s; 2 - Vk = 20,0 m/s; 3 - Vk =
30,0 m/s; 4 - Vk = 37,5 m/s.
In addition, there is a significant difference between physical and mechanical characteristics of the cast tungsten carbide powders produced by different methods. Microhardness (HV) of powders obtained by atomization is 24000-30000 MPa against 18000-21000 MPa for the crushed powder, the breaking load on the grain size 160 microns is 19,8 kGf and 7,3 kGf, respectively, and the average dynamic strength (load P = 5 kGf) 437 and 39 cycles, i.e. for spherical powders it is higher by more than in 11 times.
The results obtained in paper [4], indicate that the rotary atomization provides higher mechanical charac-
teristics of the cast tungsten carbide due to the formation of more uniform compared with crushed powders fine-grained structure (Figure 3,d), caused by high cooling rate, as well as by absence of visible surface defects (Figure 3,a,b). The results of comparative tests of resistance to abrasive wear of the surfaced layers from crushed cast tungsten carbide and obtained by rotary atomization showed that for spherical powders obtained by atomization the wear-resistance of the surfaced metal is higher in 2,5-3 times, and at the availability of the dynamic load created using a sample catcher, in 4-5 times.
Figure 3. External view of the powders obtained using the method ofplasma rotary atomization (a, b) and microstructure of crushed (c) and atomized (d) of the cast tungsten carbide powder.
The studies on the influence of the main parame- and mechanical properties were conducted at the labor-ters of the atomization process onto the fractional com- atory installation of the IPMS NASU (Figure 4). position, sphericity of powder granules and its physical
Table 1.
Chemical composition of the studied powders of cast tungsten carbide._
BatchNo Particlessize, microns Chemicalelementscontent, %
W C Fe V Cr Nb
Total Free
1 160-200 95.21 34.84 0.041 0.30 0.006 0.091 0.097
2 350-500 95.01 34.76 0.017 0.32 0.006 0.13 0.11
Figure 4. External view of the installation of the IPMS NASU for production ofpowders by the method ofplasma
rotary atomization (a) andplasmatron (b).
Under the optimal parameters of the technological process of atomization, the sphericity of powders was greater than 90% (Figure 5). The powder particles have a smooth surface with low roughness, surface defects such as cracks, cavities, etc. were not observed.
Then, using the method of sieve analysis, the obtained powders were separaed into 2 factions, 160-200 microns and 350-500 microns.The results of analysis of chemical composition of the powders of various fractions are shown in Table1, and the microstructure in Figure 6.
Figure 5. Surface morphology of the cast tungsten carbide powders obtained using the method ofplasma rotary atomization at the laboratory installation of the IPMS NASU.
Figure 6. Microstructure of the cast tungsten carbide powders obtained using the method ofplasma rotary atom-ization at the laboratory installation of the IPMS NASU: a) - fractions sizes 160-200 microns; b) - 350-500 microns.
The analysis of the obtained results shows that regardless of the powders dispersion value the structure of material is close to eutectic, characterized by a considerable dispersion and uniform distribution of phase components. The chemical composition also corresponds to the eutectic composition of the alloy with a minimum content of free carbon at the level 0.0170.041%. However, the alloy showed an increased content of impurities in the form of iron - 0.32% chromium - upto 0.13% and niobium, which is obviously related with the quality of the starting materials used in melting of the billets, and by the technology for obtaining the billets of cast tungsten carbide for atomization.
Microhardness (HV0.1) of powder particles depends a little on the fractions size and in all cases was in the range 29690-30250 MPa, which corresponds to the upper limit of the microhardness of particles of cast
tungsten carbide spherical powder obtained in paper [4]. Due to the high sphericity and smoothness of powders surface their flowability was better 7.5s / 50g.
Thus, the results of conducted studies confirm the perspective of application the technologyof plasma rotary atomization of the rotating billet for the production of granules of powders of high-melting-point materials, in particular of tungsten carbide, of high sphericity with high physical-mechanical properties.
To solve the problem of production of superhard spherical tungsten carbide and other high-melting-point compounds by plasma atomization of rotating billet, the equipment to produce powders (Figure 7) was designed in association of PWI NASU, IPMS NASU and National technical University of Ukraine "Kyiv polytechnic institute" (NTU "KPI").
Figure 7. Exterinal view of the installation for production of spherical powders of tungsten carbide and other high-melting-point materials by plasma rotary atomization.
Installation is the powder atomization chamber mounted on the two-level bridge and vacuum-tight connected to the chamber of mechanisms, powder collecting chamber, powder hopper and cassette for billets. Powder atomization chamber is a cylindrical structure having an inner diameter about 2 m and width about 0.3 m enhanced by reinforcement ribs, made of stainless steel. On the front wall of the powder atomization chamber the sliding rig with the plasmatron unit is installed.
The plasmatron is fixed to the plasmatron unit using special mobile system, which allows regulation of position of plasmatron nozzle relatively the face of atomizing billet. The mechanisms of rotating and moving of the atomized billet, mechanism of billet heating and mechanism for billets feeding from the cassette are installed in the mechanisms chamber. The chamber of mechanisms of heating, rotation, and feeding of billets is coupled with cassette billets (100 billets). To the bottom of the atomization chamber the powder collection chamber is connected, to the bottom side of which the powder storage hopper is attached. Thea device for separating of powder from the gaseous medium is installed in the powder collection chamber. Powder storage hopper has a cylindrical structure and provides separation of powder from the stubs of atomized billets. The in-
stallation consists of a vacuum, gas and plasma systems. The vacuum system provides a pre- vacuum in the atomization chamber up to 5-10-4 Pa before supply of working gases mixture and before the start of the working cycle. The gas system is circulating and has a half-closed type. Filling the system and of technological elements of the installation for producing a powder mixture of working gases, is carried out from gas cylinders installed in the ramp.
The required given composition of the gas mixture is provided by the gas mixer. To cool the working gas mixture the system is equipped with heat exchangers, and for further purification of the mixture during operation of the installation - with the filters. The gas section of the plasma system is designed separated from the main circulating gas system. This solution allows to stabilize the parameters of the plasmatron operation during the process of powder atomization. The plasma system includes the plasmatron power 120 kW, which provides continuous operation within 8 hours. The installation design provides possibility to atomize billets of tungsten carbide and other brittle high-melting-point materials with diameters from 26 up to 30 mm in length 200-300 mm. The equipment is a fully automatic installation. The external view of some mechanisms of the installation is shown in Figure 8.
Figure 8. Exterinal view of the design elements and some mechanisms of the installation for production of spherical powders of tungsten carbide and other high-melting-point materials by plasma rotary atomization: a) - atomization chamber with powder collecting chamber; b) - chamber of mechanisms with cassette billets; c) -mechanism of rotating and moving of the billet; d) - mechanism offeeding of the billet from the cassette.
The principle of operation of the installation (Figure 9) is as follows: the starting material in the form of a solid cylindrical billets from the hard material of a given composition 11 from the position 1 using mechanism of feeding of the billets 19 is alternately fed from
the cassette billets 18 into the device for preheating of billets 17 into the position 2. By passing an electric current or heating from resistance heaters the preheating of billets is performed up to a temperature 0.2-0.6 from the melting temperature of starting material.
Figure 9. Flow chart of the installation for production of spherical powders of tungsten carbide and other high-
melting-point materials by plasma rotary atomization 1 - atomizationchamber; 2 - water-cooled disc; 3 -gaspassage channel; 4 - plasmajet; 5 -plasmatron; 6 - drivefor plasmatron movement; 7 - lid; 8 - powdercol-lecting chamber; 9 - powderseparator; 10 - powderhopper; 11 - billet; 12 - discsof rotation mechanism; 13 -body-frame of mechanisms chamber; 14 - holder; 15 - gasmixture flow; 16 - pusher-rod; 17 - device for billets
preheating; 18 - cassette; 19 - billetsfed mechanism.
Preheated billets, using the feeding mechanism 19 at push rod retracted from the pusher-rod 16, is fed into a special screwed holder 14, the position 3. In order to ensure stability and durability of the holder, it is made from heat-resistant alloy. Melting of preheated billet (in the position 3) is carried out by means of plasma jet 4 of the plasmatron 5. The rotation and movement of the billet from high-melting-point material in the process of its atomization are carried out by using the mechanism of rotation and moving of the billet, which in addition to the hoop also comprises a rotating discs 12 transmitting the rotational moment to the holder 14 and pusher-rod 16, rotating at a speed equal to the speed of rotation of the billet. The pusher-rod 16 provides a controlled translational motion of the billet in the direction of the plasmatron nozzle 5. The melting is carried out by concentrating the energy emitted by plasmatron 5 at the surface of the end of the rotating cylindrical billet 11, the axis of which lies in a horizontal plane. Mounted on the atomization chamber lid 7 the plasmatron 5 is
equiped with a drive of horizontal, vertical and angular displacement of the plasma torch 6, which ensures its exact positioning with respect to the billet end face, as well as allow atomizing billets of different diameters. As a result of plasma heating of preheated rotating billet from a high-melting point alloy at its end surface the melt is formed which, under the action on it of an centrifugal forces arising during high speed rotation of the billet, is atomized and dispersed in a gaseous mixture consisting of helium and argon. Flying melt drops, under the influence of surface tension forces become spherical and crystallized upon cooling in the ambient of gases mixture. The constant thickness of the melt layer formed on the billet end, is ensured by high stability of technological parameters of the plasmatron operation (the accuracy of sustentation of the given current of arc during plasmatron operation, is at least 2.5%) and the constancy of distance between the plasmatron nozzle and the end surface of atomized rotating billet. Control and regulation of the distance between
the billet and plasmatron are carried by a special control system, coupled with the control system of the installation.
To prevent overheating of the rotating and moving mechanisms of the cylindrical billet, the atomization chamber 1 is separated from the chamber of mechanisms 13, by means of water-cooled copper disc 2. At this between the billet 11 rotating in the holder and the water-cooled copper disk 2 the channel 3 is formed for the flow 15 of the cooling gas mixture circulating in a closed circuit. The shape and dimensions of the channel, as well as its spatial orientation provide deflection by the cooling gas flow of the molten spherical particles out of the plane of their expansion under the action of centrifugal force. This prevents the possibility of collision of melt drops flying under the action of centrifugal forces with already crystallized solid powder particles. The obtained powder particles are poured into the powder collecting chamber 8 and through the powder separator 9 from the gas mixture and collected into the powder hopper 10.
The use of special screwed holder 14 ensures reliable tightness of the billet to the pusher-rod 16, ro-tateing at a speed equal to the speed of rotation of the billet, which ensures reliable control of values of the progressive movement of the billet. The availability of a special holder 14 provides reliable contact and transmission of the rotational moment from the billet to the holder 11. Application of the holder provides reducing of the specific pressure on the surface of billets, made of high-melting-point material solid, rotating at high angular velocity.
This design provides the possibility of increasing the rotational speed of the billet preform and hence the dispersity of atomized melt particles, crystallizing upon cooling in gaseous medium into a spherical powder particles. In addition, the availability of the holder eliminates direct contact of the billet with the rotation mechanism elements (discs, drum), which significantly increases the durability of the whole mechanism. In its turn, the resistance of the holder is great as the angular velocity of the rotation of holder and billet are almost identical.
This design of installation can significantly improve the performance of the atomization process and resistance of rotating billets to cracking at the account of alternately preheating of billets before spraying and the use of rotating holder.
As the result we have achieved the increasing of dispersion of the obtained powders, the stability of their grain-size composition, to reduce the number of non-spherical granules in the production of powders from high-melting-point materials at the account of the molten particles deviation from the plane of expansion under the action of centrifugal force by the flow circulating in a closed circuit of the cooling gas mixture passing through the channel formed between the cylindrical billet rotating in the holder and a water-cooled copper disk, additional cooling by it of particles in flight.
The developed installation provides obtaining of spherical powders of tungsten carbide (WC+W2C) and other high-melting-point brittle material with disper-
sion 100-500 microns and sphericity up to 90%, hardness HV0.1 up to 31000 MPa. Such powder is characterized by high up to 9.0s / 50g flowability and conventional density up to 11,3 g/cm3.
The equipment is characterized by high performance of the atomization process and allows to obtaine up to 10 and more kilograms of spherical tungsten carbide powder per hour with a use factor of the billet more than 0.75 for the billets length 200 mm. Increasing of use factor of the billet is achieved by increasing its length, at this the maximum length of the billet from tungsten carbide for which the equipment is designed is 300 mm. The equipment is fully automatic and can simultaneously load up to 100 billets.
The main advantages of the given installation are:
- has a high degree of automation ensures its continuous operation and atomization up to 100 pieces of billets without additional operations (billets load, powder unloadetc.). To achieve this goal in the design of the installation the special nodes are used to ensure its reliability, maximum interval of technical service, high resource of operating units and executing mechanisms;
- is intended for industrial production of disperse powders of tungsten carbide and other high-melting-point material of high sphericity, allows to adjust the size of obtained powder particles the within a wide range;
- in view of application of high-efficient vacuum and gas system in the installation design, it with the appropriate further equipping (replacement of mechanisms of rotation and movement of the billet) can be used for production of powders of any material on an industrial scale;
- high power specialized plasma system for heating of the billet with the automatic control and maintain system of the operating parameters of the plasma heating source is applied
- in the design of the plasmatron torch, the new (nanostructured) materials are used to ensure its long operation life and high reliability. The use of new materials allowed significantly increase the operating voltage of the plasmatron and its operation life in 2 and more times compared to conventional plasmatrones of the same capacity;
- the power supply has an increased efficiency coefficient, increased open circuit voltage and the operating voltage, improved dynamic characteristics;
- taking into account physical and technical characteristics of the tungsten carbide billets, the presence of porosity and susceptibility to cracking during plasma heating (tungsten carbide is brittle and is frightened of thermal shock) the installation is equipped with a specialized system of preliminary heating of billets with a special design of current leads providing reliable contact with the billet, regardless of its form errors. In addition, such system provides increased productivity of the installation and stability of the tungsten carbide at-omization process, reduction of gas saturation of the billets, that increases the stability of the parameters of the process of billets atomizatiom;
- availability in the design of rotation mechanism of the special holder for atomization of billet, provides
reduction of dynamic loads on the billet during it rata-tion at high speed, and ultimately the probability of its destruction during atomization;
- there is a possibility of maintenance of the plas-matron without depressurization of the operating chamber, which minimizes the time on its maintenance service, promotes ecological compatibility, performance of the powder atomization process and economic efficiency of the atomization process;
- for protection of mechanisms of rotation and movement of the billet from abrasion wera under the action of the solid powder particles, and to improve the operating resource of the mechanisms in the design of the installation the special gas dynamic seals of movable nodes are used without reducing the efficiency coefficient of nodes. Such gas-dynamic seals are wear-free and provide isolation of the powder atomization chamber from the chamber of supporting mechanisms, prevent the ingress the powder and dust of tungsten carbide and other synthesized compounds onto the moving parts of mechanisms. In addition, such original design provides considerable reduction of temperature of operation of moving units and mechanisms, which also significantly increases their operational life;
- to achieve high performance and automation of the atomization process the installation uses a special cassette for accumulation of billets providing stable uninterrupted supply of billets for atomization in an amount up to 100 items, and non-stop operation of the installation within several 8-hour shifts (a few working days). Its application allows to isolate billets previously prepared for atomization from the environment impact (air, moisture, etc.), which increases the purity of the chemical composition of the obtained powders granules of tungsten carbide and allows to perform the preparation of billets for atomization once every few days, that significantly reduces the consumption of energy and operating resources for preparatory operations (vacuum annealing);
- the gas system of the installation includes special receiver with pump intended for storage of the gases working mixture (previously used) at the opening of the installation for maintenance according to the established rules. Gases working mixture pumped into the receiver after the maintenance service is used in the process again, which can significantly reduce the loss of working gases, improve indicators of economic efficiency of the installation operation, reduce the production cost of powder and increase the sustainability of the process and equipment in general.
Conclusions
1. The results of studies confirm the promising of application of the technology of plasma rotary atomiza-tion of rotation billet to obtain granules of powders of high-melting-point materials, in particular tungsten carbide with sphericity over 90%, microhardness HV0.1 more than 30000 MPa characterized by high flow ability more than 7,5 s / 50 g.
2. The universal installation for production of super-hard spherical tungsten carbide and other high-melting-point compounds by plasma atomization of rotating billets is designed for industrial application, is
characterized by high degree of automation, allowing to adjust obtained powder particle size in a wide range.
3. Due to the use of new materials and innovative design and technological solutions the high reliability, maximum interval of technical service, high resource of operating units and executing mechanism of the equipment are ensured.
4. Due to the use of new high-power plasma system with power supply source with high efficiency coefficient and improved dynamic characteristics, the system of preliminary heating of billets, innovative gas systems, high performance vacuum system, the developed universal system for the production of granules of powders of high-melting-point material is also applicable for the manufacture of spherical powders of metals and alloys, including highly active, and provides lower costs of products (powder) with an increased productivity, economic efficiency of the atomization process and reduce the impact of atomization process on the environment.
Note: This work was support by the Financial Funding by Foreign Experts Program of China (No.WQ20124400119), the Innovative R&D Team of Guangdong Province (No.201101C0104901263), Chinese Program of Foreign Experts No.WQ20124400119, Guangdong Innovative Research Team Program No.201101C0104901263, China, Science and Technology Project of Guangdong province No.2015A050502039, Science and Technology Project of Guangdong province No.2016B050501002.
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