RU2081202C1 - Method of coating application, its versions - Google Patents

Abstract

FIELD: technology of gas-dynamic application of coatings. SUBSTANCE: method includes introduction of powder of sprayed material into formed gas flow. Formed two-phase gas flow is accelerated in nozzle and particles are deposited on treated surface at particles temperature lower than melting point of sprayed material. To reduce energy consumption for particle acceleration, use is made of, either, prevention of possibility of formation of shock wave in two-phase flow, or at supersonic efflux of flow, conditions are provided at which velocity of particles in the wake of shock wave occurring between the nozzle edge and treated surface does not exceed the velocity of gas flow in the respective region of two-phase flow. To provide for high energy of particles of sprayed material, attained at supersonic efflux of two-phase flow from nozzle, preliminary shockless braking of flow before treated article shall be effected. EFFECT: higher efficiency. 19 cl, 1 dwg

Description

 The invention relates to coating technology, and more particularly to gas-dynamic coating methods, and can be used in various engineering industries.

 Currently, there are a number of coating methods, for example, various diffusion coating methods (cementation, aliasing, etc.), electroplating methods, ion-plasma coating methods [1] Each of the methods provides solutions to certain problems associated with the formation of surface coatings. properties of materials and has certain limitations and disadvantages. For example, small coating thicknesses, low productivity, high cost, and in some cases low consumer qualities.

 A known method of producing coatings based on the use of the gas-dynamic method [2] The method is as follows. First, a cold gas stream is formed using various gases, into which the powder of the sprayed material with a particle size of 1-200 microns and the required concentration of material is introduced. The particles introduced into the powder are accelerated to 650-1200 m / s and the surface of the product is treated with the obtained gas-powder mixture. In particular, the coating is carried out at Mach numbers at the nozzle exit 2.5-3, that is, at supersonic speeds.

 At supersonic speeds, shock waves should arise in front of the substrate, behind which a zone of gas of increased density and reduced gas velocity is formed, leading to a decrease in the particle velocity of the incident two-phase flow. This leads to both a decrease in the efficiency of the coating process and an increase in the energy costs of the process.

The closest analogue of the invention (two options) is a method of coating on the surface of the product. [4] The known method includes introducing into the gas stream a powder, the material of which is selected from the group consisting of metals, alloys, their mechanical mixtures or dielectrics, with a particle size of 1 to 50 microns, the formation of a gas-powder mixture with a mass flow rate of particles from 0.05 up to 17 g / s • cm ² and the direction of the gas-powder mixture to the treated surface of the product. In this case, a gas stream with particles is accelerated in a gas-dynamic nozzle to supersonic speeds and a supersonic jet of a given profile is formed, providing a speed of up to 1200 m / s for powder particles of the gas-powder mixture. The Mach number on the nozzle exit is 2.5-4. When implementing this method, there are also restrictions on the speed of particles accelerated in a two-phase flow. This is due to the deceleration of particles behind the shock wave caused by the flow around a two-phase supersonic stream of the workpiece surface.

 The basis of the invention (options) is to reduce the braking of particles of the sprayed material in the gas stream in the area between the nozzle exit and the surface to be treated. The solution to this problem is to create such conditions in a two-phase flow in the area from the nozzle exit to the surface to be treated, under which the velocity of the carrier gas or gas mixture always exceeds or at least equals the particle velocity.

 The technical result achieved by the implementation of the variants of the invention is expressed in the reduction of energy costs for creating coatings with desired properties (strength, porosity, adhesion, etc.) presented to the processed products.

 This technical result is achieved in the first embodiment of the coating method, including the introduction of powder into the generated gas stream, acceleration of the formed two-phase stream in the gas-dynamic nozzle and the deposition of particles from the accelerated stream onto the workpiece surface at a particle temperature lower than the melting temperature of the sprayed material, so that An accelerated two-phase flow prevents the occurrence of a shock wave and the inhibition of particles associated with it.

 The prevention of the occurrence of a shock wave in a two-phase flow can be achieved, firstly, by selecting the particle size, their concentration in the gas flow, the gas or gas mixture used, so that the gas flow velocity between the nozzle exit and the surface being treated is less than the speed of sound in the two-phase flow .

 It is advisable to use a powder consisting of particles ranging in size from 1 to 200 microns. Copper can be used as a spray material. It is desirable to maintain a relative mass content of copper particles in the gas stream of not more than 0.2.

 Helium can be used as a gas with a temperature of 300K, while the velocity of the gas stream at the exit of the nozzle is maintained equal to not more than 800 m / s.

 Air with a temperature of 700 K can also be used as a gas, while the velocity of the gas stream at the exit from the nozzle is maintained at no more than 440 m / s.

 Secondly, when a two-phase flow is accelerated to a supersonic speed, the occurrence of a shock wave and related undesirable phenomena (deceleration of accelerated particles) can be prevented by shockless inhibition of the flow between the nozzle exit and the treated surface to a speed less than or equal to the speed of sound in a two-phase flow.

 It is advisable to carry out flow inhibition by selecting the distance between the nozzle exit and the surface to be treated. For applying multilayer coatings and for coating on curved surfaces, it is necessary to ensure the movement of the workpiece relative to the accelerated two-phase flow.

 The above technical result is achieved in the second embodiment of the coating method, comprising introducing the powder of the sprayed material into the generated gas stream, accelerating the formed two-phase stream in the gas-dynamic nozzle and depositing particles from the accelerated stream onto the workpiece surface at a particle temperature lower than the melting temperature of the sprayed material, that according to the invention, the two-phase flow is accelerated until a supersonic speed is reached at which the velocity is often Itz of the sprayed material behind the front of the shock wave arising between the nozzle exit and the surface being treated does not exceed the value of the gas flow velocity in the corresponding region of the two-phase flow.

 When implementing this variant of the method, it is desirable to inhibit the two-phase flow, for example, by choosing the distance between the nozzle exit and the surface to be treated. Braking the supersonic flow to an acceptable speed level will provide a reduction in energy loss in the shock wave that occurs in front of the treated surface.

 As in the first embodiment of the method, it is advisable to use a powder consisting of particles ranging in size from 1 to 200 microns.

 As the sprayed material, for example, copper can be used.

 The choice of powder material depends on the desired properties of the coating.

 It is advisable that the relative mass content of copper particles in the gas stream does not exceed 0.2.

 For applying multilayer coatings and for coating on curved surfaces, it is necessary to ensure the movement of the workpiece relative to the accelerated two-phase flow.

 Air can be used as a gas at a temperature of 700 K. In this case, the gas flow velocity at the nozzle exit is equal to no more than 600 m / s.

 When helium is used as a working gas at a temperature of 300 K, the gas flow velocity at the nozzle exit is equal to not more than 1050 m / s.

 The essence of the proposed coating methods is based on the following physical principles.

 The velocities of gas and particles are selected from the condition of the maximum possible use of gas energy in the coating process. This condition can be realized either in the absence of shock waves in the region between the nozzle exit and the surface being processed, or in the presence of a shock wave, but at a gas velocity behind the shock wave equal to or greater than the particle velocity. In this case, the temperature of the particles is kept lower than the melting temperature of the sprayed material.

It is known that the presence of particles in a gas stream affects the magnitude of the speed of sound and, therefore, the formation of a shock wave and the magnitude of the parameters behind the shock wave. In particular, in the range of gas-dynamic parameters used in gas-dynamic spraying, the speed of sound in a two-phase flow is less than the speed of sound in a single-phase gas flow, therefore, shock waves will occur at lower velocities of the gas phase [4,5]
The condition for the occurrence of shock waves is determined using the Mach number M equal to the ratio of the flow velocity W to the speed of sound a _sound :
M W / a _sound > 1 (1)
The value of the speed of sound in a two-phase flow is determined by the particle size, particle concentration, the ratio of gas and particle velocities, their temperatures, thermophysical characteristics (specific capacities, gas constant, isoentropic index) and density ratio. There are also distinguished the so-called "frozen" speed of sound a _deputy and the "equilibrium" speed of sound a _{equal to} [4.5] Since a _deputy > a is _{equal to} the condition guaranteeing the absence of shock waves, will be
W _gas / a _{equal to} <1 (2)
When a two-phase flow is supersonic, the condition under which the gas velocity behind the shock wave is greater than or equal to the particle velocity is calculated from the frozen sound velocity corresponding to critical conditions [5]
W _part • W _gas ≅ a $\genfrac{}{}{0ex}{}{\text{2}}{\text{cr.zam}}$ (3)
at W _gas > a _cr
wherein W at the cut _{portions of} the particle velocity of the nozzle,
W _{gas the gas} velocity at the nozzle exit,
and _cr.zam critical speed of sound, calculated by the "frozen parameters".

 Thus, one of the options for eliminating the influence of shock waves on the process of dispersing particles of the sprayed material and their deposition on the surface to be treated is to take into account the effect of particles on the speed of sound and, as a result, the use of subsonic and sound modes of the outflow of a two-phase flow.

 In the second embodiment, if it is necessary to use a supersonic regime of the outflow of a two-phase flow to ensure the specified coating properties, the influence of the arising shock waves on the process of acceleration and deposition of particles is reduced due to the fact that the gas flow rate behind the shock wave front is ensured (by preliminary calculation of the process parameters) or equal to the particle velocity. That is, the particles must be accelerated without braking in the gas flow in the area between the nozzle exit and the surface to be treated.

 One of the possible ways to implement these options for solving the technical problem is to provide shockless braking of a supersonic two-phase flow in front of the surface to be processed at an acceptable speed level both for a supersonic outflow mode (for the second option) and for an audio or subsonic mode (for the first option).

Braking of a supersonic flow can be realized by pre-selecting the distance between the nozzle exit and the workpiece surface. The length is selected based on condition (2) or (3) taking into account the braking (changing) characteristics of the speed of the calculated gas supersonic jet [6,7] or a two-phase supersonic jet [8,9]
The proposed options for the formation of a gas flow with particles were tested when coating copper powder on substrates of various materials. Air was used as the working gas with initial parameters R _o (10-20) • 10 ⁵ Pa, T ^* 600-700 K. Particles of copper powder with sizes in the range of 10-40 microns were used. The coating was stably provided up to the lower limit for the initial pressure in the range of selected temperatures. The speed of the particles ranged from 400 to 600 m / s, depending on the dispersion of the particles, and the gas velocity from 600 to 800 m / s. At the same time, at the lower pressure limit, condition (3) was satisfied, which ensured minimal losses from shock waves arising in the flow.

 Variants of the claimed method of coating are illustrated by the attached drawing, which shows a diagram of the installation with which the proposed invention is carried out.

 The installation for implementing two variants of the coating method comprises a source 1 of compressed working gas, a particle supply device 2, a heater 3, a mixing chamber 4, a gas-dynamic nozzle 5, a protective chamber 6, a processed substrate 7 and a separation device 8.

 The implementation of the first variant of the method is carried out using this installation as follows.

 Part of the working gas from the source 1 is supplied to the particle supply device 2, and the rest to the heater 3. The two-phase stream formed in the device 2, consisting of the working gas and particles of the sprayed material, is fed into the mixing chamber 4, where the set initial flow temperature and relative mass content of particles of the sprayed material. The resulting mixture (two-phase flow) is sent to the gas-dynamic nozzle 5, where it accelerates to the required speed. In the process of preparing the mixture and its acceleration, the temperature of the particles is ensured lower than the melting temperature of the sprayed material. The resulting high-speed jet is directed to the treated surface of the substrate 7 of the coating object, resulting in the deposition of particles of the sprayed material on the surface of the substrate and the formation of a coating with desired properties.

 If necessary, the substrate 7 can move relative to a high-speed jet (rotational and / or translational). This should be used for multilayer coatings, with relatively large sizes of the treated surface and coating on curved surfaces. The nozzle 5 and the substrate 7, and, if necessary, the mixing chamber 4, are placed in the protective chamber 6. After processing the substrate 7, the working fluid comes from the chamber 6 into the separation device 8, where the particles of the sprayed material are separated from the working gas.

 To prevent the occurrence of a shock wave in an accelerated two-phase flow, the particle size, their concentration in the gas stream and the gas used are chosen so that the gas flow rate between the nozzle exit and the treated surface is less than the speed of sound in the two-phase flow.

 The particle size for implementing the method is selected in the range from 1 to 200 microns.

 Most preferably, particles with a size of 5 to 100 microns are used.

 For applying a copper coating to the product, the relative mass content of copper particles in the gas stream should be no more than 0.2.

 To reduce the cost of implementing the method, air should be used as the working gas.

Thermophysical properties of air:
Gas constant R 287 J / kg • K
Heat capacity C _rg 1000 J / kg • K
The index of isentropes K _g 1.4
The heat capacity of copper C _to 397.7 J / kg • K.

При значении коэффициента скольжения частиц (относительно газового потока) ε=W_к/W_г, (где W_к cкорость частиц напыляемого материала, а W_г скорость газового потока), порядка 0,7, что соответствует размерам частиц более 1 мкм, скорость частиц на срезе сопла при W_г а_равн будет равна
W_к=ε•W_г=308 м/c
Для получения более высоких скоростей частиц меди необходимо использовать в качестве рабочего газа гелий.By setting the value of the braking temperature of the gas phase [5,6] T $\genfrac{}{}{0ex}{}{\text{*}}{\text{g}}$ = 700 K and the relative mass content of copper particles in the air stream κ _k = 0.2, we can determine the value of the equilibrium speed of sound in a two-phase stream:

When the particle slip coefficient (relative to the gas flow) is ε = W _k / W _g , (where W _{k is the} particle velocity of the sprayed material, and W _{g is} the gas flow velocity), of the order of 0.7, which corresponds to particle sizes greater than 1 μm, the particle velocity at the nozzle exit when W and _{r equals} equals
W _k = ε • W _g = 308 m / s
To obtain higher speeds of copper particles it is necessary to use helium as a working gas.

Thermophysical characteristics of helium:
Gas constant R 2080 J / kg • K
Heat capacity C _rg 5200 J / kg • K
The index of isentropes K _g 1.67.

By setting the braking temperature of the gas phase T $\genfrac{}{}{0ex}{}{\text{*}}{\text{g}}$ = 300 K and the relative mass content of copper particles in helium κ _k = 0.2, it is possible to determine the value of the equilibrium speed of sound in a two-phase flow, following the above calculation procedure.

and _equal ≈ 808 m / s
at K '1.653 and R' 1733.3 J / kg • K.

 With a particle slip coefficient ε of the order of 0.7, it is possible to determine the velocity of copper particles at the nozzle exit.

W _k = ε • W _g = 563.5 m / s
The above calculation examples confirm the possibility of reducing energy consumption for accelerating particles in a gas stream at a level of achieved speeds of up to 560 m / s by providing a sound or subsonic regime for the outflow from the nozzle of a two-phase stream. When these modes are implemented, the possibility of the occurrence of a shock wave is excluded and, therefore, the deceleration of particles in the gas flow behind the shock wave is prevented, which is characteristic of a supersonic flow around a workpiece.

 From the presented estimated calculations, it follows that for the implementation of the specified mode according to the first embodiment of the invention, for the selected initial data, the gas flow velocity at the nozzle exit should not exceed 440 m / s when using air as a working gas, 800 m / s when using helium.

 In the case when it is necessary to provide a higher particle velocity, determined by the properties of the applied coating, it is possible to increase the speed of the two-phase flow to supersonic values. In this case, it is necessary to brake the flow in front of the work surface without impact, at least to sound speed. Braking is carried out by increasing the distance from the nozzle exit to the work surface.

 The implementation of the second variant of the coating method is carried out similarly to the first variant in accordance with the above list of operations using the described installation with the exception of the choice of processing modes.

 The second variant of the method is implemented if it is necessary to disperse the particles of the sprayed material to higher speeds compared to the achieved level of speeds (<approx> 800 m / s) provided by the first variant of the method. The need for higher particle speeds is determined by the specified properties of the sprayed coating and the material properties of the processed product.

 This method variant is characterized by the fact that the two-phase flow is accelerated in the gas-dynamic nozzle 5 until a supersonic speed is reached at which the particle velocity of the sprayed material behind the shock wave front arising between the nozzle exit and the surface being treated does not exceed the value of the gas flow velocity in the corresponding region of the two-phase flow in accordance with condition (3).

 When using copper as a spray material with a particle size of 1 to 200 μm with a relative mass content of copper particles in the gas stream equal to 0.2, the parameters of the two-phase stream are selected as follows. Consider an example of the choice of parameters when using air as a working gas.

При выборе размера частиц более 1 мкм на срезе сопла имеет место отставание частиц от потока газа, которое можно оценить с помощью коэффициента скольжения

, зависящего от размера частиц, их формы, плотности, вязкости и температуры газа.Let the braking temperature [6] of the gas phase T $\genfrac{}{}{0ex}{}{\text{*}}{\text{g}}$ corresponds to the value of T _g 700 K, then based on the well-known thermophysical characteristics of air and copper, it is possible to determine the critical speed of sound calculated by the "frozen" parameters

When choosing a particle size of more than 1 μm at the nozzle exit, there is a lag of particles from the gas flow, which can be estimated using the slip coefficient

depending on the size of the particles, their shape, density, viscosity and temperature of the gas.

,
где

коэффициент скорости [6]
Задавая значение коэффициента ε=0,7, получим

,
что соответствует скорости газа
W_газа≅ λ•a_кр.зам≈ 600 м/с
и скорости частиц
W_частиц=ε•W_газа=405 м/с.Using the coefficient ε, we can write condition (3) in the form

,
Where

speed coefficient [6]
Setting the value of the coefficient ε = 0.7, we obtain

,
which corresponds to the gas velocity
W _gas ≅ λ • a _cr.sam ≈ 600 m / s
and particle speeds
W _particles = ε • W _gas = 405 m / s.

 If the obtained value of the particle velocity does not meet the specified requirements for the applied coating, then it is necessary to use a working gas, for example helium.

Основываясь на известных теплофизических характеристиках гелия и на выбранных условиях скольжения ε=0,7, можно определить скорость газа и частиц.Let the gas phase inhibition temperature T $\genfrac{}{}{0ex}{}{\text{*}}{\text{g}}$ corresponds to the value of T _g 300 K, then the critical speed of sound calculated by the "frozen" parameters is

Based on the known thermophysical characteristics of helium and on the selected slip conditions ε = 0.7, it is possible to determine the velocity of gas and particles.

.Gas velocity

.

 Particle velocity.

W _k = ε • W _gas = 732 m / s
In the case when it is necessary to ensure a higher particle velocity by increasing the speed of the two-phase flow at the nozzle exit, the supersonic flow in front of the surface to be treated should be braked unshocked. Braking is carried out by increasing the distance from the nozzle exit to the work surface.

The spraying conditions of various materials require a certain particle energy, determined by their speed [1]
Depending on the required speed of the particles and their physical properties (density, shape, size, heat capacity, etc.), following the proposed variants of the invention, the working gas and its parameters (temperature, pressure and velocity of outflow from the nozzle) are selected, as well as the distance between the cut nozzle and work surface.

Achieved when using the claimed invention, the technical result, expressed in the reduction of energy consumption, can be estimated using known results obtained by the implementation of the prototype method [3]
In particular, in comparison with the known results [3] where the Mach number at the nozzle exit when using helium as the working gas was 2.5–4, when implementing the claimed coating method, the required particle energy is achieved with a Mach number of 1.7. With equal initial temperatures <SEapprox> 300 K), this allows to reduce the initial pressure of the working gas by eight times, which corresponds to a decrease of approximately three times the energy expended on gas compression.

 The proposed variants of the invention can be used in various industries: metallurgy, mechanical engineering, aircraft manufacturing, shipbuilding, agricultural machinery, automotive, instrument making, electronic engineering. The invention is intended for the restoration of various parts and for the formation of anticorrosive, electrically conductive, antifriction, hardening, magnetically conductive, dielectric and other coatings on products made of metals, ceramics and dielectrics. The proposed variants of the coating method can also be used to obtain multilayer, combined, for example metal-polymer and multifunctional coatings.

Literature
1. Theory and practice of hardening materials in extreme processes. Novosibirsk, 1992, p. 146-147.

 2. USSR Author's Certificate N 1618778, С 23 С 4/00, Publication 1991.

 3. International Application (PCT) WO 91/19016, C 23 C 4/00, 05 B 7/24, B 05 C 19/00, 1991.

 4. G. Wallis. One-dimensional two-phase flows. M. Mir, 1972, p. 293-294.

 5. Two-phase monoi polydisperse gas flows with particles. M. Engineering, 1980.

 6. Sergel O.S. Applied fluid dynamics, M. Mechanical Engineering, 1981, p. 337-341.

 7. Abramovich G.N. Applied Gas Dynamics, M. Nauka, 1974, pp. 112-142.

 8. Zuev Yu. V. Lepeshinsky I.A. Some results of calculating a two-phase turbulent jet. Collection: Turbulent two-phase flows, Tallinn, 1982.

 9. Kireev V.I. Vainovsky A.S. Numerical modeling of gas-dynamic flows. M. MAI, 1992, p. 154-162.

Claims (19)

 1. The method of coating, including the introduction of the powder of the sprayed material into the generated gas stream, the acceleration of the formed two-phase stream in the gas-dynamic nozzle and the deposition of particles from the accelerated stream on the surface to be treated at a particle temperature in the stream lower than the melting temperature of the sprayed material, characterized in that at cooling of particles prevents the possibility of a shock wave in an accelerated two-phase flow.  2. The method according to claim 1, characterized in that the occurrence of a shock wave in a two-phase flow is prevented by selecting the particle size, their concentration in the gas flow, the gas or gas mixture used, so that the gas flow velocity between the nozzle exit and the surface to be treated is lower sound velocity in a two-phase flow.  3. The method according to claim 1, characterized in that the possibility of a shock wave in the flow is prevented by preliminary unstressed braking between the nozzle exit and the treated surface to a speed less than or equal to the speed of sound in a two-phase flow.  4. The method according to claim 3, characterized in that the shockless braking of the two-phase flow is carried out by selecting the distance between the nozzle exit and the surface to be treated.  5. The method according to any one of claims 1 to 4, characterized in that they use a powder consisting of particles of a size of 1,200 microns.  6. The method according to any one of claims 1 to 5, characterized in that copper is taken as the sprayed material.  7. The method according to claim 6, characterized in that the relative mass content of copper particles in the gas stream is not more than 0.2.  8. The method according to claim 1, characterized in that the gas used is helium with a temperature of 300 K, while the gas flow velocity at the exit of the nozzle is maintained no more than 800 m / s.  9. The method according to p. 1, characterized in that the gas used is air with a temperature of 700 K, while the velocity of the gas stream at the outlet of the nozzle is maintained no more than 440 m / s.  10. The method according to any one of claims 1 to 9, characterized in that the workpiece is moved relative to the accelerated flow.  11. A coating method, comprising introducing a powder of the sprayed material into the generated gas stream, accelerating the formed two-phase stream in the gas-dynamic nozzle and depositing particles from the accelerated stream onto the surface to be treated at a particle temperature in the stream lower than the melting temperature of the sprayed material, characterized in that the two-phase the flow is accelerated until a supersonic speed is reached, at which the particle velocity of the sprayed material behind the shock front arising between the cutoff the nozzle and the surface does not exceed the magnitude of the gas flow velocity in the corresponding region of two-phase flow.  12. The method according to p. 11, characterized in that it additionally provides shockless braking of the two-phase flow between the nozzle exit and the surface to be treated.  13. The method according to p. 12, characterized in that the shockless braking of the two-phase flow is carried out by selecting the distances between the nozzle exit and the surface to be treated.  14. The method according to any one of claims 11 to 13, characterized in that a powder consisting of particles from 1 to 200 microns in size is used.  15. The method according to any one of claims 11 to 13, characterized in that copper is used as the sprayed material.  16. The method according to clause 15, wherein the relative mass content of copper particles in the gas stream is supported by no more than 0.2.  17. The method according to claim 11, characterized in that air with a temperature of 700 K is used as a gas, while the gas flow velocity at the exit of the nozzle is maintained equal to not more than 600 m / s.  18. The method according to claim 11, characterized in that the gas used is helium with a temperature of 300 K, while the velocity of the gas stream at the exit of the nozzle is maintained no more than 1050 m / s.  19. The method according to any one of claims 11 to 18, characterized in that the workpiece is moved relative to the accelerated flow.