Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR PRODUCING A COATING MADE OF POWDERED MATERIALS
AND DEVICE FOR REALISING THE SAME
Technical Field
The present invention relates to the field of applying
and producing coatings from powder materials and more par-
ticularly to a method of producing a coating from powder ma-
terials and to a device for carrying out said method.
Background of the Invention
Known in the art is a method of producing a coating
from powder materials, which comprises introducing a start
ing powder material into a gas stream which accelerates ma
terial particles, shaping a high-velocity gas-and-powder
jet, and applying the powder material to the surface of an
article (Inventor's Certificate RU No. 1618778, C1. C23C
4/00, 1991).
This method suffers from the following disadvantages:
particles of a coating material cannot be accelerated by a
gas stream up to velocities close to those of the gas accel-
erating thereof, and the process of forming a coating cannot
be effected with relatively not high parameters of the work-
ing gas (air) with the pressure P < 10*105 N/mz.
Said disadvantages restrict the technological possi-
bilities of the method and involve considerable power in-
puts.
Also known in the art is a method of producing a coat-
ing from powder materials on the surface of an article whose
material is selected from the group consisting of metals,
alloys, dielectrics, which method comprises the steps of
forming an accelerating flow of a working carrier gas, in-
troducing particles of a powder material into this flow,
seeding the resulting gas-and-powder mixture into an accel-
erating supersonic nozzle, and applying the powder material
to the surface of an article by the gas flow (International
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Application WO 91/19016, C1. C23C 4/00, B05B 7/24, B05C
19/00, 1991).
For carrying this method into effect, a device is used,
comprising a spraying unit made as a supersonic nozzle with
a subsonic converging and a supersonic parts and an interme
diate nozzle, a means for feeding a compressed working car-
rier gas, and a means for introducing a gas-and-powder mix-
ture into the spraying unit (International Application WO
91/19016, C1. C23C 4/00, B05B 7/24, B05C 19/00, 1991).
The disadvantages of the known method and device are as
follows: limited possibilities of producing an adequate-
quality coating material due to the presence of a superfi-
cial oxide film on particles of the employed powder materi-
als and, as a result, the presence of oxides in the struc-
ture of the coating material; an insufficient effectiveness
of the particle acceleration process due to the deceleration
of particles in the compressed wall layer of gas at the sur-
face of the article being treated; insufficiently high phys-
icochemical properties of produced coatings; limited possi-
bilities of controlling the velocity of the gas flow and the
particles of the powder material from which the coating is
formed; the presence of friction and of the deceleration of
particles along the walls of the acceleration channel of the
supersonic nozzle, which lead to reducing the effectiveness
of the coating application process and the service life of
the spraying system. Said disadvantages interfere with pro-
ducing coatings having high physico-mechanical properties,
restrict the technological possibilities of producing a
high-quality coating from powder materials, and also inter-
fere with the provision of a high effectiveness of the coat-
ing application process and with the provision of a long
service life of the spraying system.
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Disclosure of the Invention
The problem underlying the described invention is the
provision of a method of preparing a coating from powder ma-
terial and a device for carrying this method into effect,
which would make it possible to broaden the technological
possibilities of producing coatings from various powder ma-
terials and from their mixtures, to improve the physico-
chemical properties of the resulting coating material, to
raise the effectiveness of the process of applying and form-
ing the coating, and to prolong the service life of the
spraying system.
The indicated technical result is attained owing to the
use of method of producing a coating from powder materials
and of a device for carrying this method into effect, the
essence of which is as follows:
The herein-proposed method of producing a coating from
powder materials, comprising the steps of forming an accel-
erating flow of a carrier gas, introducing particles of a
powder material thereinto, feeding the resulting gas-and-
powder mixture into an accelerating supersonic nozzle, and
applying the powder material by means of the gas flow to the
surface of an article, envisages that before feeding the
gas-and-powder mixture into the supersonic nozzle the mix-
ture is pre-accelerated by a gas inert with respect to the
starting powder material to a velocity defined by the number
0.3 < M <_ 1.0, where M is the Mach number, and accelerated
additionally by introducing the gas-and-powder mixture into
the core of the accelerating flow of the carrier gas, and
that before applying the coating powder material to the sur-
face of an article the powder particles are separated from
the gas. The accelerating flow of the working carrier gas is
formed in accordance with the square law of variation of the
profile of the accelerating supersonic nozzle area. This
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provides a possibility for a more effective utilization of
the gas flow energy.
It is reasonable to effect feeding of the gas-and
powder mixture into the accelerating nozzle with the cumula
tive flow of the accelerating carrier gas and of the gas in
ert to the powder material set in accordance with the rated
conditions of the accelerating nozzle.
The method envisages the use of air or of a mixture of
gases as the working carrier gas and the use of a gas or a
mixture of gases not reacting with the powdered components
of the powder material as the gas inert with respect to this
material.
Before the preliminary acceleration of the powder mate
rial, it is subjected to mechanical, electrochemical or
chemical treatment in a gaseous medium inert to the starting
powder material, and the powder material is supplied in a
flow of this medium into a metering feeder.
It is desirable that a gas with the temperature T <_ 300
K should be used as the gas inert to the powder material.
The gas-and-powder mixture may be introduced into the
core of the accelerating flow from the metering feeder in a
pulsed mode.
When applying the powder material to the surface of an
article, the latter may be brought in vibratory motion coax
Tally to the incident two-phase supersonic flow.
For enhancing the plasticity of the surface to be
coated, the article is subjected to superficial heating.
In the course of applying a coating, a potential may be
supplied to the article to be coated, the sign of this po
tential being opposite to that of the particles in the two
phase flow of the gas-and-powder mixture.
The essence of the invention, as regards the herein-
proposed device, is that the device for producing coatings
from powder materials, comprising a spraying unit made as an
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accelerating supersonic nozzle with a subsonic converging
and a supersonic parts and an intermediate nozzle, a means
for feeding a compressed working carrier gas, and a means
for introducing a gas-and-powder mixture into the spraying
5 unit, and a metering feeder, is provided with a means for
supplying an additional compressed gas inert to the powder
material, the intermediate nozzle is made as a supersonic
one, with the diameter of the nozzle exit section dsect.
smaller than the diameter of the critical section D~rit. of
the accelerating nozzle, and is arranged coaxially with the
possibility of translational displacement in the subsonic
converging part, the accelerating supersonic nozzle having
at the outlet of the supersonic part a linear portion which
passes into a portion with a curvilinear surface of a radius
R.
The device is provided with a unit for treating the
powder material with a view to activating and cleaning the
surface the particles of the coating material, with a gas
pulser connected to the means for introducing the gas-and-
powder mixture, with a vibrator for imparting vibrations to
the article being coated, and with a power supply source for
supplying a potential to the article.
Brief Description of Drawings
The invention is further explained by a particular ex
ample of its embodiment and by the accompanying drawings, in
which:
Fig. 1 shows a general view of a device for producing a
coating from powder materials;
Fig. 2 shows a spraying unit of the proposed device
with a means for introducing a gas-and-air mixture and sepa-
rating a two-phase flow into fractions.
Best Mode of Carrying the Invention into Effect
The device of the invention comprises a means 1 for
feeding a compressed gas inert to a coating material (to a
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mixture of powdered components), a shutoff valve 2, a unit 3
for the pretreatment of a powder material to remove an oxide
film from and to activate particles of the powder material,
a unit 4 for collecting the oxide film and the fine-
s dispersed fraction of the powder, a unit 5 for feeding the
treated powder material to a metering feeder 6, a shutoff
valve 7, a pulser 8 of the gas inert to the powder material,
a means 9 for feeding a working carrier gas (for instance,
air), a system 10 for controlling the working process of ap-
plying coatings, a heater 11 of the working carrier gas, a
unit 12 for the provision of translational axial displace-
ment of an intermediate supersonic nozzle 13, a chamber 14
for adjusting the carrier-gas flow, a centering perforated
sleeve 15, an accelerating nozzle 16 with a linear portion
17 which passes into a portion with a curvilinear surface 18
for varying the direction of motion of the gas flow, a means
19 for turning the gas flow away from the article being
coated 20, a means 21 for securing and rotating the article
being coated, a unit 22 for the translational displacement
of the article being coated, a vibrator 23, a power supply
source 24, a tube 25 for feeding 'the gas-and-powder mixture,
a tube 26 for feeding the working carrier gas.
The method of the invention is carried into effect and
the device of the invention operates in the following man-
ner.
A gas inert to the coating material (to a mixture of
powdered components) is fed under a pressure, with the shut-
off valve open, from the means 1 to the unit 3 for the pre-
treatment of the powder coating material, said unit being
preliminarily filled with a required amount of a powder (a
mixture of powders). When the unit 3 for the pretreatment of
the powder material is thrown into action, oxide film is re-
moved from the surface of the powder material particles
therein by a mechanical or any other method. After the pre-
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treatment, waste substances in the form of oxide'film parti-
cles and non-calibrated fine-dispersed fraction of the pow-
der come to the unit 4. Then the particles of the powder
coating material are activated by an electromagnetic, ther-
mal, chemical or any other method, depending on the chemical
composition and physical properties of the powder material
(the mixture of powdered components). The activated parti-
cles are supplied with the help of the unit 5 into the me-
tering feeder 6. After filling the metering feeder 6 with
the powder material and with the gas inert to the powder ma-
terial, the units 3, 4, 5 are switched off, and the shutoff
valve 2 is closed, whereby supplying the gas inert to the
powder material is stopped.
For the process of producing a coating from powder ma
terials, a working carrier gas (for instance, air, nitrogen)
is supplied under a pressure from the feeding means 9 to the
system 10 for controlling the working process of applying
coatings, wherein the pressure is reduced to the required
working value. The gas whose pressure reduced to the re
quired value comes to the heater 11 of the gas, where the
gas is heated to a temperature corresponding to the rated
operating conditions. The heated working carrier gas comes
along the tube 26 for feeding the working carrier gas to the
chamber 14 for adjusting the carrier-gas flow, and then
through profiled apertures in the centering sleeve the work-
ing carrier gas is fed to the accelerating supersonic nozzle
16, wherein the carrier gas is accelerated to the velocity
required for applying and forming a coating. When the re-
quired parameters of the working carrier gas are reached,
the shutoff valve 7 is opened, whereby feeding of the gas
inert to the powder material is effected, which gas first
comes to the pulser 8, where it acquires a pulsating compo-
nent having a required frequency. From the pulser 8 the gas
inert to the powder material with the required frequency
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comes to the metering feeder 6 wherein, as the gas under
variable pressure is mixed with the particles of the powder
coating material, a gas-and-powder mixture is formed, in
which the powder particles are in the form of a suspension.
The resulting gas-and-powder mixture is fed in the form of a
two-phase flow through the tube 25 into the intermediate su-
personic nozzle 13 and then into the core of the accelerat-
ing flow of the carrier gas into the area of the critical
section of the accelerating supersonic nozzle 16. The re-
quired rated thermo- and gasdynamic parameters of the work-
ing carrier gas and of the pulsating gas-and-powder mixture
in the area of the critical section of the accelerating noz-
zle 16 are attained by displacing the intermediate super-
sonic nozzle 13. This displacement is performed in a trans-
latory manner along the axis of the nozzles, with the help
of the unit 12 for the provision of translational axial dis-
placement, for a distance depending on the velocity of flow
and the frequency of pulsations of the gas-and-powder mix-
ture in the area of the critical section of the accelerating
supersonic nozzle 16. When the required displacement is
achieved, the unit 12 for'the provision of axial displace-
ment of the intermediate supersonic nozzle 13 is switched
off. The pulsating mixture of particles with the gas inert
to them, issuing from the intermediate supersonic nozzle 13,
having the initial axial velocity 0.3 _< M _< 1.0 (where M is
the Mach number) , is mixed in the area of the critical sec-
tion of the accelerating supersonic nozzle 16 with the work-
ing carrier gas, and in this area the main acceleration of
the gas-and-powder mixture takes place. Having acquired the
required velocity along the channel of the accelerating su-
personic nozzle 16, the flow of the gas-and-powder mixture
adjusts the direction of its motion within the linear por-
tion 17, then the main part of the gas flow turns within the
portion with a curvilinear surface 18 and gets into . the en-
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trance portion of the means 19 for turning off the gas flow.
The powder particles of the coating material, having a large
mass and sluggishness, continue their rectilinear motion
till they collide with the surface of the article being
coated. When the necessary thermo- and gasdynamic conditions
for applying the coating are attained, the article 20 to be
coated, which is secured in the means 21 for securing the
article, is set in (back-and-forth or rotary) motion. Then
the vibrator 23, connected with the unit 22 for the dis-
placement of the article, and the power supply source 24,
which feeds to the article 20 a potential whose sign is op-
posite to that of the moving particles, are switched on.
This is how the process of applying a coating to and forming
a coating on the surface of an article occurs.
As the gas inert to the powder material, a gas (a mix-
ture of gases) may be chosen, which does not react chemi-
cally with the powder material of the coating, for instance,
nitrogen, argon, helium, krypton, and others. The choice is
determined by particular requirements to the properties of
the resulting coating, its structure, and the composition of
the material of the latter.
Removal of the oxide film from the surface of the pow-
der particles of the coating material, activation of the
particles, and their preliminary acceleration by the gas in-
ert to the particles, prevent oxidation of the coating mate-
rial and make it possible, when applying and forming a coat-
ing, to obtain chemically pure materials, without oxides in
their structure, to improve substantially their structure,
physicochemical and technological properties.
The coefficient of utilization of the coating material
being applied, the adhesion, cohesion and its structure de-
pend on the impact velocity of the coating particles being
applied with the surface of the material.
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Preliminary acceleration of the particles of the coat-
ing material by the gas inert to them at a temperature T 5
<_ 300 K, with the velocity of the accelerating gas of 0.3 5
< M 5 1.0, and introducing the gas-and-powder mixture into
5 the core of the carrier gas accelerating the particles make
it possible to increase substantially the velocity of the
particles of the coating material to a velocity close to
that of the accelerating gas and thereby to make maximum use
of the energy of the gas jet accelerating the particles. In-
10 troducing the powder mixture into the core of the accelerat-
ing flow of the carrier gas eliminates the effect of decel-
eration of the particles by the walls of the flow-through
part of the supersonic accelerating nozzle, prolongs the
service life of the device, increases the coefficient of
utilization of the coating material being applied. For
eliminating the effect of decelerating the coating particles
in the compressed near-wall gas layer, which originates as
the supersonic gas jet falls upon the surface of the arti-
cle, in the method of the invention the gas flow is turned
and moved away from the surface of the article being
treated. Turning of the gas flow is brought about by the
physical effect which originates as the plane-parallel flow
of gas flows around the curvilinear surface of radius R.
Thus, turning of the gas flow and moving it away from the
surface of the surface of the article being treated elimi-
nate the appearance of the compressed near-wall gas layer on
the surface of the article, and the coating particles con-
tinue their rectilinear motion, reach the surface of the ar-
ticle with the velocity which they acquired in their inter-
action with the gas flow accelerating them. Thereby, it be-
comes possible, with smaller energy parameters of the gas
flow, to apply particles of the of the coating material with
higher impact velocities with the surface of the material of
the article. As a result, the power inputs are reduced, the
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coefficient of utilization of the coating material is in-
creased, and the structure, quality and properties of the
coating material are improved.
Setting the cumulative rate of flow of the working car
s rier gas and of the gas inert to the powder coating material
in accordance with the calculated conditions of the gas flow
issue from the accelerating nozzle is the regime in which
the pressure in the exit section of the accelerating super
sonic nozzle corresponds to the pressure of the ambient me
dium. Under this condition the velocity of the gas flow is-
suing from the supersonic nozzle will be maximum. Any
changes in the parameters of the carrier gas, such as tem-
perature, pressure, kind of gas, lead to off-design condi-
tions of the issue, i.e., to a loss of the gas flow velocity
and, consequently, of the velocity of particles of the coat-
ing material being applied.
Vibratory motions of the article being treated in the
case of synchronous introducing in the pulsed mode of the
gas-and-powder mixture into the core of the accelerating
flow of the carrier gas are effected in such a manner that
feeding the gas-and-powder mixture occurs at the moment when
the article being treated moves in a direction opposite to
that of the flow of particles of the coating material. In
this case the velocity of moving particles of the coating
material and the velocity of displacing the article being
treated are added together. As a result, the velocity of
collision of the particles with the surface increases. This
leads to an increase in the depth of penetration of the par-
ticles into the surface of the material of the article, in
the extent of their plastic deformation, in the coefficient
of utilization of the coating material, to an improvement in
the structure of the coating and its technological proper-
ties.
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In order to intensify the course of mechanical and
chemical processes in the superficial layer of the material
of the article on collision of particles of the coating ma-
terial with the surface of the article in the method of the
invention, the article is subjected to surface heating to a
temperature at which the plasticity of the surface of the
material of the article is close to the plasticity of the
coating material. This makes it possible to apply coatings
having a smaller hardness to harder and less plastic sur-
faces of articles. In this case the properties of the tran-
sition zone (material of the particles and material of the
article) change sharply, the structure of this zone and, as
a consequence, adhesion of the coating, becomes improved. In
the transition zone there is also formed an intermetallic
compound on application of a metal to a metal, consisting of
the material of the coating particles being applied and of
the material of the article. Solid particles, while moving
in the gas flow, acquire a charge having a definite value
and sign due to friction with gas, against each other, and
on the walls of the flow-through part of the gas channel.
The value and sign of the charge depend on the material of
the particles. When in the method of the invention an oppo-
site-sign potential is fed to the surface of the article be-
ing coated, there occurs an increase in the velocity of the
charged particles as they approach to the surface of the ar-
ticle, and a micro-arc discharge originates on collision.
Acting on the moving flow of charged particles by dif-
ferent electromagnetic methods and by the value of the po
tential fed to the article, it is possible to regulate the
process of applying and forming the coating.
This makes it possible to vary the structure, proper-
ties and quality of the coating in the course of applying
thereof.
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The structural feature of the means for introducing the
gas-and-powder mixture make it possible to effect axial in-
troducing of the coating particles with the starting eeloc-
ity into the core of the working carrier-gas flow accelerat-
ing said particles, obviating the interaction of particles
of the coating material with the walls of the accelerating
nozzle 16 under the conditions of dsect. ~
Thereby it becomes possible to prolong the service life
of the device, to make maximum use of the energy of the gas
flow for increasing the kinetic energy of the particles of
the coating material, to carry into effect the process of
coating formation with relatively not high starting parame-
ters of the carrier gas, to increase the coefficient of
utilization of the material being applied.
The device of the invention may be used for producing
multifunctional coatings and materials from various powdered
components selected from the group comprising metals, alloys
or mechanical mixtures thereof, as well as dielectrics and
organic compounds.
Owing to the provision of conditions which allow acti-
vating the particles and rule out the presence of an oxide
film on their surface, the range of materials used for the
application of coatings by the method of the invention may
be substantially broadened.
So, the described method and device for producing coat-
ings from powder materials make it possible to intensify the
process of applying and forming coatings from various pow-
ders and their mixtures, to obtain a coating material with-
out the presence of oxide inclusions in its structure, to
improve the structure and physicochemical properties of the
coating material, to increase the coefficient of utilization
of the coating material, to reduce the energy parameters of
the gas flow, to broaden the possibility of controlling the
process of applying and forming coatings, to obtain materi-
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als in coatings with unique properties, to broaden the tech-
nological and functional possibilities of the process for
producing coatings.
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Industrial Applicability
The present invention may be used in metallurgy, me-
chanical engineering, radio- and electronic engineering and
other industries for improving the technological and phys-
5 icochemical properties of articles, for restoring various
worn-out parts, and for imparting specific properties to the
surface of articles.
