CA2755921A1 - Pulse cold gas dynamic spraying apparatus - Google Patents
Pulse cold gas dynamic spraying apparatus Download PDFInfo
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- CA2755921A1 CA2755921A1 CA 2755921 CA2755921A CA2755921A1 CA 2755921 A1 CA2755921 A1 CA 2755921A1 CA 2755921 CA2755921 CA 2755921 CA 2755921 A CA2755921 A CA 2755921A CA 2755921 A1 CA2755921 A1 CA 2755921A1
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- Prior art keywords
- pulse
- cgds
- converging
- nozzle
- generator
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C24/00—Coating starting from inorganic powder
- C23C24/02—Coating starting from inorganic powder by application of pressure only
- C23C24/04—Impact or kinetic deposition of particles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B12/00—Arrangements for controlling delivery; Arrangements for controlling the spray area
- B05B12/02—Arrangements for controlling delivery; Arrangements for controlling the spray area for controlling time, or sequence, of delivery
- B05B12/06—Arrangements for controlling delivery; Arrangements for controlling the spray area for controlling time, or sequence, of delivery for effecting pulsating flow
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B7/00—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas
- B05B7/16—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed
- B05B7/1606—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed the spraying of the material involving the use of an atomising fluid, e.g. air
- B05B7/1613—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed the spraying of the material involving the use of an atomising fluid, e.g. air comprising means for heating the atomising fluid before mixing with the material to be sprayed
- B05B7/162—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed the spraying of the material involving the use of an atomising fluid, e.g. air comprising means for heating the atomising fluid before mixing with the material to be sprayed and heat being transferred from the atomising fluid to the material to be sprayed
- B05B7/1626—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed the spraying of the material involving the use of an atomising fluid, e.g. air comprising means for heating the atomising fluid before mixing with the material to be sprayed and heat being transferred from the atomising fluid to the material to be sprayed at the moment of mixing
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Nozzles (AREA)
Abstract
The ultimate objective of this invention is to provide an improved Cold Gas Dynamic Spray (CGDS) apparatus capable of discharging powdered materials at greater velocities with higher deposition efficiency, as well as a greater variety of materials (e.g.
nanopowders). This objective is achieved by attaching a specialized device to an existent CGDS system. The device is a pulse-generator and is attached behind the converging portion of the De Laval-type nozzle. This device significantly increases the efficiency of the spray process in three ways.
First, it creates a higher pressure environment that introduces a wave of pulses to the exit stream, thereby increasing the speed of any introduced powder materials. Second, the addition of this device introduces steam to the overall process which also increases the speed of the exit stream. Third, the introduction of steam into the process also increases the drag co-efficient of any injected powders, thereby once again contributing to an increase in the velocity of the exit stream. This improved design and the resulting increased efficiency of the CGDS process also permits a greater choice in the type of powdered materials that may be used.
The pulse-generator generates detonation-type impulse waves by injecting hot compressed water into the low-pressure (vacuum) and high-temperature discharge chamber. The vacuum or low-pessure environment in the discharge chamber provides a greater pressure gradient for the creation of detonation-type impulse waves. The injections are repeated in a cyclical manner at a pre-determined frequency.
nanopowders). This objective is achieved by attaching a specialized device to an existent CGDS system. The device is a pulse-generator and is attached behind the converging portion of the De Laval-type nozzle. This device significantly increases the efficiency of the spray process in three ways.
First, it creates a higher pressure environment that introduces a wave of pulses to the exit stream, thereby increasing the speed of any introduced powder materials. Second, the addition of this device introduces steam to the overall process which also increases the speed of the exit stream. Third, the introduction of steam into the process also increases the drag co-efficient of any injected powders, thereby once again contributing to an increase in the velocity of the exit stream. This improved design and the resulting increased efficiency of the CGDS process also permits a greater choice in the type of powdered materials that may be used.
The pulse-generator generates detonation-type impulse waves by injecting hot compressed water into the low-pressure (vacuum) and high-temperature discharge chamber. The vacuum or low-pessure environment in the discharge chamber provides a greater pressure gradient for the creation of detonation-type impulse waves. The injections are repeated in a cyclical manner at a pre-determined frequency.
Description
Title PULSE COLD GAS DYNAMIC SPRAYING APPARATUS.
Field of the invention This invention relates to improvements in the spraying method to apply a coating using high kinetic energy of sprayed materials, in particular the Cold Gas Dynamic Spray (CGDS) process.
Background of the invention Prior art has already disclosed various processes and methods for spray coatings. The methods used vary as in the type of coating and its purpose. Coatings are most easily grouped according to their primary function, although a given coating may provide more than one basic function. The most important functional applications are for: thermal insulation, wear resistance, corrosion and chemical resistance, electrical conductivity or resistance, radioactive shielding, provision of dimensionally restorative coating and cosmetic repair.
Several techniques have been used to implement spray coatings, including widely used gas flame-spraying, arc spraying, plasma spraying, detonation spraying and high-velocity flame spraying. Of the multiple thermal processes, the detonation spraying process produces the highest quality coatings. More recently, a method called CGDS was developed. CGDS is a coating process whereby coatings can be produced without significant heating of the sprayed materials. In contrast to flame, arc and plasma spraying processes, with CGDS there is no melting of particles prior to impact with the substrate. The adhesion of particles in this process is secondary to their kinetic energy upon impact. In this process, very high particle velocities (300 to 1200 m/s) are obtained by accelerating an expanding gas stream to supersonic speeds through the use of a converging-diverging De Laval-type nozzle. The gas and particle temperatures remain well below the melting temperature of the sprayed material. As compared to the conventional thermal spray techniques, the distinguishing features of the CGDS process are as follows: the temperature of the sprayed material is always below the melting point and all sprayed materials remain in a solid state throughout the spraying process. This solid-state processing has several unique advantages, including: avoiding undesirable chemical changes (e.g. oxidation) and microstructure changes (e.g.
grain growth) during the deposition process, and producing minimal or even compressive residual stresses. Therefore CGDS is ideally suited for depositing oxygen-sensitive materials (e.g. Al, Mg, Ti, Cu, etc.), temperature-sensitive materials (e.g. nano-structured and amorphous materials) and phase-sensitive materials (e.g. carbide composites).
Field of the invention This invention relates to improvements in the spraying method to apply a coating using high kinetic energy of sprayed materials, in particular the Cold Gas Dynamic Spray (CGDS) process.
Background of the invention Prior art has already disclosed various processes and methods for spray coatings. The methods used vary as in the type of coating and its purpose. Coatings are most easily grouped according to their primary function, although a given coating may provide more than one basic function. The most important functional applications are for: thermal insulation, wear resistance, corrosion and chemical resistance, electrical conductivity or resistance, radioactive shielding, provision of dimensionally restorative coating and cosmetic repair.
Several techniques have been used to implement spray coatings, including widely used gas flame-spraying, arc spraying, plasma spraying, detonation spraying and high-velocity flame spraying. Of the multiple thermal processes, the detonation spraying process produces the highest quality coatings. More recently, a method called CGDS was developed. CGDS is a coating process whereby coatings can be produced without significant heating of the sprayed materials. In contrast to flame, arc and plasma spraying processes, with CGDS there is no melting of particles prior to impact with the substrate. The adhesion of particles in this process is secondary to their kinetic energy upon impact. In this process, very high particle velocities (300 to 1200 m/s) are obtained by accelerating an expanding gas stream to supersonic speeds through the use of a converging-diverging De Laval-type nozzle. The gas and particle temperatures remain well below the melting temperature of the sprayed material. As compared to the conventional thermal spray techniques, the distinguishing features of the CGDS process are as follows: the temperature of the sprayed material is always below the melting point and all sprayed materials remain in a solid state throughout the spraying process. This solid-state processing has several unique advantages, including: avoiding undesirable chemical changes (e.g. oxidation) and microstructure changes (e.g.
grain growth) during the deposition process, and producing minimal or even compressive residual stresses. Therefore CGDS is ideally suited for depositing oxygen-sensitive materials (e.g. Al, Mg, Ti, Cu, etc.), temperature-sensitive materials (e.g. nano-structured and amorphous materials) and phase-sensitive materials (e.g. carbide composites).
CGDS was introduced to the field through work done by Alkimov et al. as disclosed in U.S. Pat. No.
5,302,414 and by Kashirin et al. as disclosed in U.S. Pat. No. 6,402,050.
These two patents describe two different types of CGDS: an upstream-sprayed particle feeding technique (by Alkimov) and a downstream-sprayed particle feeding technique (by Kashirin).
The upstream-sprayed particle feeding CGDS system introduces the sprayed particles into the flow of gas at the converging portion of the nozzle co-axially. It uses high pressure and high temperature gases (e.g. helium) and has high deposition efficiencies. However, a common problem encountered in the operation of this system is nozzle-clogging, especially at the nozzle throat between the converging and diverging sections. Other disadvantages of this CGDS system are high operational and equipment costs.
In comparison, the downstream-sprayed particle feeding CGDS system introduces the sprayed particles into the flow of gas at the diverging section of the nozzle radially. It uses lower pressure gases (e.g. air, nitrogen), is portable and is less expensive. Due to the lower particle velocities that can be reached with this system, only a limited number of materials can be deposited and the deposition efficiencies are much lower than the upstream-sprayed particle feeding CGDS system.
Summary of the invention The ultimate objective of this invention is to provide an improved Cold Gas Dynamic Spray (CGDS) apparatus capable of discharging powdered materials at greater velocities with higher deposition efficiency, as well as a greater variety of materials (e.g.
nanopowders). This objective is achieved by attaching a specialized device to an existent CGDS system. The device is a pulse-generator and is attached behind the converging portion of the De Laval-type nozzle. This device significantly increases the efficiency of the spray process in three ways.
First, it creates a higher pressure environment that introduces a wave of pulses to the exit stream, thereby increasing the speed of any introduced powder materials. Second, the addition of this device introduces steam to the overall process which also increases the speed of the exit stream. Third, the introduction of steam into the process also increases the drag co-efficient of any injected powders, thereby once again contributing to an increase in the velocity of the exit stream. This improved design and the resulting increased efficiency of the CGDS process also permits a greater choice in the type of powdered materials that may be used.
The pulse-generator generates detonation-type impulse waves by injecting hot compressed water into the low-pressure (vacuum) and high-temperature discharge chamber. The vacuum or low-pressure environment in the discharge chamber provides a greater pressure gradient for the creation of detonation-type impulse waves. The injections are repeated in a cyclical manner at a pre-determined frequency.
The injected water rapidly becomes a high-pressure impulse steam wave. These impulse steam waves accelerate when discharged through the pulse-generator and through the converging-diverging, De Laval-type nozzle, ultimately creating a greater velocity when reaching the exit point of the nozzle. These impulse steam waves are dragging any introduced powder materials and accelerating them towards a substrate. These impulse steam waves reach speeds of Mach 2 and higher in the diverging portion of the nozzle. For sphere-shaped, sprayed particles, the speed of the stream at Mach 2 and higher is a milestone achievement for optimizing the value of the drag co-efficient (Cd).
In addition, at various points between the nozzle throat and the substrate (depending upon various parameters) the pressure and the temperature drop create a saturated impulse steam wave, thereby causing portions of the steam in the wave to revert to a liquid state. The reintroduction of water in a liquid state at the last stage of the process does three things. It promotes agglomeration of the powdered particles in the exit stream. It causes water-hammering of the substrate which improves adhesion of the sprayed materials to the substrate. Finally, it cools down the nozzle which minimizes nozzle-clogging. The improved agglomeration of powdered particles is a critical/key benefit because it will permit the deposition of nanopowders; a hitherto unattainable objective in the prior art CGDS process.
Brief description of the drawings Figs. 1 and 3 are sectional views of a known, prior art CGDS apparatus.
Figs. 2 and 4 are sectional views of the CGDS apparatus embodying the present invention.
5,302,414 and by Kashirin et al. as disclosed in U.S. Pat. No. 6,402,050.
These two patents describe two different types of CGDS: an upstream-sprayed particle feeding technique (by Alkimov) and a downstream-sprayed particle feeding technique (by Kashirin).
The upstream-sprayed particle feeding CGDS system introduces the sprayed particles into the flow of gas at the converging portion of the nozzle co-axially. It uses high pressure and high temperature gases (e.g. helium) and has high deposition efficiencies. However, a common problem encountered in the operation of this system is nozzle-clogging, especially at the nozzle throat between the converging and diverging sections. Other disadvantages of this CGDS system are high operational and equipment costs.
In comparison, the downstream-sprayed particle feeding CGDS system introduces the sprayed particles into the flow of gas at the diverging section of the nozzle radially. It uses lower pressure gases (e.g. air, nitrogen), is portable and is less expensive. Due to the lower particle velocities that can be reached with this system, only a limited number of materials can be deposited and the deposition efficiencies are much lower than the upstream-sprayed particle feeding CGDS system.
Summary of the invention The ultimate objective of this invention is to provide an improved Cold Gas Dynamic Spray (CGDS) apparatus capable of discharging powdered materials at greater velocities with higher deposition efficiency, as well as a greater variety of materials (e.g.
nanopowders). This objective is achieved by attaching a specialized device to an existent CGDS system. The device is a pulse-generator and is attached behind the converging portion of the De Laval-type nozzle. This device significantly increases the efficiency of the spray process in three ways.
First, it creates a higher pressure environment that introduces a wave of pulses to the exit stream, thereby increasing the speed of any introduced powder materials. Second, the addition of this device introduces steam to the overall process which also increases the speed of the exit stream. Third, the introduction of steam into the process also increases the drag co-efficient of any injected powders, thereby once again contributing to an increase in the velocity of the exit stream. This improved design and the resulting increased efficiency of the CGDS process also permits a greater choice in the type of powdered materials that may be used.
The pulse-generator generates detonation-type impulse waves by injecting hot compressed water into the low-pressure (vacuum) and high-temperature discharge chamber. The vacuum or low-pressure environment in the discharge chamber provides a greater pressure gradient for the creation of detonation-type impulse waves. The injections are repeated in a cyclical manner at a pre-determined frequency.
The injected water rapidly becomes a high-pressure impulse steam wave. These impulse steam waves accelerate when discharged through the pulse-generator and through the converging-diverging, De Laval-type nozzle, ultimately creating a greater velocity when reaching the exit point of the nozzle. These impulse steam waves are dragging any introduced powder materials and accelerating them towards a substrate. These impulse steam waves reach speeds of Mach 2 and higher in the diverging portion of the nozzle. For sphere-shaped, sprayed particles, the speed of the stream at Mach 2 and higher is a milestone achievement for optimizing the value of the drag co-efficient (Cd).
In addition, at various points between the nozzle throat and the substrate (depending upon various parameters) the pressure and the temperature drop create a saturated impulse steam wave, thereby causing portions of the steam in the wave to revert to a liquid state. The reintroduction of water in a liquid state at the last stage of the process does three things. It promotes agglomeration of the powdered particles in the exit stream. It causes water-hammering of the substrate which improves adhesion of the sprayed materials to the substrate. Finally, it cools down the nozzle which minimizes nozzle-clogging. The improved agglomeration of powdered particles is a critical/key benefit because it will permit the deposition of nanopowders; a hitherto unattainable objective in the prior art CGDS process.
Brief description of the drawings Figs. 1 and 3 are sectional views of a known, prior art CGDS apparatus.
Figs. 2 and 4 are sectional views of the CGDS apparatus embodying the present invention.
Detailed description of the preferred embodiments Fig.1 shows the prior art CGDS apparatus (1), where the low pressure (80 to 120 psi) gas supply (usually air or nitrogen) is heated in an electrical heater (19) to temperatures from 80 - 550 C and forced through the passage (11) into the back-cover (12) and the converging portion (14) of the nozzle (13). The back pressure at the nozzle discharge is lower than the critical pressure of the supplied gas and the Mach number of the gas stream at the throat (15) is Mach 1 and the flow is sonic. In the diverging portion (16) of the nozzle (13) the gas stream accelerates to supersonic velocities. When the required temperature of the supplied gas is reached (regulated by the control (18)), the powder materials are introduced to the stream from the powder feeder (17) and injected into this high velocity gas stream at the diverging portion (16) of the nozzle (13). At this point they are dragged by the gas stream and accelerated towards the substrate (5) to form a coating (6).
Fig.2 shows the CGDS apparatus (2) of the present invention whereby a pulse-generator (20) is inserted into the existing CGDS apparatus of the prior art (1). The pulse-generator body (21) is embedded and securely connected between the nozzle (13) and the back-cover (12). The injector (23) is inserted within the pulse-generator body (21) and together with the converging portion (14) of the nozzle (13) creates the pulse-generator chamber (22). The shapes of the conical portion (30) of the injector (23) and the converging portion (14) of the nozzle (13) make this portion of the pulse-generator chamber (22) into a converging or converging-diverging passage. The pulse-generator chamber (22) is embedded and securely connected with a passage (26) to the water heater (24). The passage (26) has an in-line solenoid valve (27) and an in-line check valve (29). The injector (23) links the supplied gas between the back-cover chamber (10) of the back-cover (12) and the converging portion (14) of the nozzle (13). The low pressure (80 to 200 psi) supplied gas (e.g. air, nitrogen or helium or any mixture thereof) is heated to temperatures of 400 -700 C in the electrical heater (19) and is forced through the passage (11) into the back-cover chamber (10) where it passes the injector (23) through the pulse-generator chamber (22), the throat (15) and the diverging portion (16) of the nozzle (13). As the heated supplied gas passes through, it heats the chamber (22) and the overall apparatus (20). At the throat (28) of the injector (23) the supplied gas has a sonic velocity and is accelerated through the diverging portion (16) of the nozzle (13). As this high velocity gas stream passes through the pulse-generator chamber (22) it creates a vacuum therein. The supplied gas is regulated by the control (18) and the temperature in the pulse-generator chamber (22) is regulated by the control (25). In order to reach the required temperature of the supplied gas (400 - 700 C) and to keep the CGDS apparatus portable and light, a secondary heater (not shown in the drawing) has to preheat the supplied gas before it reaches the primary heater (19). To achieve better control of the temperature in the pulse-generator chamber (22), a small band heater (not shown in the drawing) can be assembled around the pulse-generator body (21).
Temperature and pressure of the water in the water heater (24) is regulated by the control (25). To avoid boiling the water in the water heater (24), the water temperature is set to 5 ¨ 10 C
below the water saturation temperature at the given pressures (e.g. for compressed water at 87 psi the water temperature should be 148 - 153 C). The control (25) also regulates the water injections via the solenoid valve (27).
These injections of water are repeated in a cyclical manner at a pre-determined frequency range (e.g.
1-20 injections per second) and strictly correlate with the injection of the discharged powder materials from the powder feeder (17). When the desired temperatures in both the pulse-generator chamber (22) and in the water heater (24) are reached, one drop of the hot compressed water is injected into the pulse-generator chamber (22). Instantaneously, a portion of the injected water (up to 30%) becomes flash steam. The remaining 70%+ of the water also rapidly converts to steam.
This rapid vaporization of the injected water generates detonation-type impulse steam waves. These impulse steam waves accelerate through the converging or the converging-diverging portion of the pulse-generator chamber (22) and through the diverging portion (16) of the CGDS nozzle (13).
These impulse steam waves reach speeds of Mach 2 and higher in the diverging portion (16) of the nozzle (13). For sphere-shaped, sprayed particles, the speed of the stream at Mach 2 and higher is a milestone achievement for optimizing the value of the drag co-efficient (Cd).
These impulse steam waves accelerate the powder materials injected into the high velocity gas stream at the diverging portion (16) of the nozzle (13) towards the substrate (5) to form a coating (6). If, in between the nozzle throat (15) and the substrate (5), the pressure and the temperature of the impulse steam waves drop to the saturation point then these waves become saturated and a portion of the steam waves revert to the liquid state as they move through the diverging portion (16) of the nozzle (13). Any steam reverting to a liquid state will promote water hammering of the sprayed materials for better adhesion of the sprayed particles to the subtrate (5) and, in addition, will cool down the nozzle (13).
This will also promote agglomeration of the powder particles and increase the efficiency of the spray process, as well as permit the deposition of nanopowders; a hitherto unattainable objective in the prior art CGDS process.
= CA 02755921 Fig.3 shows the prior art CGDS apparatus (3), where the high pressure (80 to 300 psi) gas supply (usually helium) is heated in an electrical heater (19) to temperatures from 80 - 550 C and forced through the passage (11) into the back-cover (12) and the mixing chamber (10).
When the required temperature of the supplied gas is reached (regulated by the control (18)), the powder materials are introduced to the mixing chamber (10) from the powder feeder (17) where they are mixed with the supplied gas and forced through the converging portion (14) of the nozzle (13). The back pressure at the nozzle discharge is lower than the critical pressure of the supplied gas and the Mach number of the mixed stream at the throat (15) is Mach 1 and the flow is sonic. In the diverging portion (16) of the nozzle (13) the mixed stream accelerates to supersonic velocities towards the substrate (5) to form a coating (6).
Fig.4 shows the CGDS apparatus (4) of the present invention where a pulse-generator (20) is inserted into the existing CGDS apparatus of the prior art (3). The pulse-generator body (21) is embedded and securely connected between the nozzle (13) and the back-cover (12). The injector (23) is inserted within the pulse-generator body (21) and together with the converging portion (14) of the nozzle (13) creates the pulse-generator chamber (22). The shapes of the conical portion (30) of the injector (23) and the converging portion (14) of the nozzle (13) make this portion of the pulse-generator chamber (22) into a converging or converging-diverging passage. The pulse-generator chamber (22) is also embedded and securely connected with the passage (26) to the water heater (24). The passage (26) has an in-line solenoid valve (27) and an in-line check valve (29). The injector (23) links the stream of the supplied gas and powder materials between the back-cover chamber (10) of the back-cover (12) and converging portion (14) of the nozzle (13). The high pressure (80 to 300 psi) supplied gas (e.g. helium) is heated to temperatures of 400 - 700 C in the electrical heater (19) and is forced through the passage (11) into the back-cover chamber (10) where it is mixed with the powder materials and forced through the injector (23) and the pulse-generator chamber (22), the throat (15) and the diverging portion (16) of the nozzle (13) towards the substrate (5) to form a coating (6). As the heated mixture of the supplied gas and the powder materials pass through the pulse-generator chamber (22), the mixture heats the chamber (22) and the overall apparatus (20). At the throat (28) of the injector (23) the mixture stream has a sonic velocity and is accelerated through the diverging portion (16) of the nozzle (13). As this high velocity mixture passes through the pulse-generator chamber (22) it creates a vacuum therein.
The supplied gas is regulated by the control (18), and the temperature in the pulse-generator chamber (22) is regulated by the control (25). In order to reach the required temperature of the supplied gas (400 - 700 C) and to keep the CGDS apparatus light, a secondary heater (not shown in the drawing) has to preheat the supplied gas before it reaches the primary heater (19). To achieve better control of the temperature in the pulse-generator chamber (22), a small band heater (not shown in the drawing) can be assembled around the pulse-generator body (21). Temperature and pressure of the water in the water heater (24) are regulated by the control (25). To avoid boiling the water in the water heater (24), the water temperature is set to 5 ¨ 10 C below the water saturation temperature at the given pressures (e.g. for compressed water at 87 psi the water temperature should be 148 - 153 C). The control (25) also regulates the water injections via the in-line solenoid valve (27). The water injections are repeated in a cyclical manner at a pre-determined frequency range (e.g. 1-20 injections per second). When the desired temperatures in both the pulse-generator chamber (22) and in the water heater (24) are reached, one drop of the hot compressed water is injected into the pulse-generator chamber (22). Instantaneously, a portion of the injected water (up to 30%) becomes flash steam. The remaining 70%+ of the water also rapidly converts to steam. This rapid vaporization of the injected water generates detonation-type impulse steam waves. These impulse steam waves accelerate through the converging or the converging-diverging portion of the pulse-generator chamber (22) and through the diverging portion of the CGDS nozzle (13). These impulse steam waves reach speeds of Mach 2 and higher in the diverging portion of the nozzle. For sphere-shaped, sprayed particles, the speed of the stream at Mach 2 and higher is a milestone achievement for optimizing the value of the drag co-efficient (Cd). If, in between the nozzle throat (15) and the substrate (5), the pressure and the temperature of the impulse steam waves drop to the saturation point then these waves become saturated and a portion of the steam waves revert to the liquid state as they move through the diverging portion (16) of the nozzle (13). Any steam reverting to a liquid state will promote water hammering of the sprayed materials for better adhesion of the sprayed particles to the subtrate (5) and, in addition, will cool down the nozzle (13). This will also promote agglomeration of the powder particles and increase the efficiency of the spray process, as well as permit the deposition of nanopowders; a hitherto unattainable objective in the prior art CGDS
process.
Fig.2 shows the CGDS apparatus (2) of the present invention whereby a pulse-generator (20) is inserted into the existing CGDS apparatus of the prior art (1). The pulse-generator body (21) is embedded and securely connected between the nozzle (13) and the back-cover (12). The injector (23) is inserted within the pulse-generator body (21) and together with the converging portion (14) of the nozzle (13) creates the pulse-generator chamber (22). The shapes of the conical portion (30) of the injector (23) and the converging portion (14) of the nozzle (13) make this portion of the pulse-generator chamber (22) into a converging or converging-diverging passage. The pulse-generator chamber (22) is embedded and securely connected with a passage (26) to the water heater (24). The passage (26) has an in-line solenoid valve (27) and an in-line check valve (29). The injector (23) links the supplied gas between the back-cover chamber (10) of the back-cover (12) and the converging portion (14) of the nozzle (13). The low pressure (80 to 200 psi) supplied gas (e.g. air, nitrogen or helium or any mixture thereof) is heated to temperatures of 400 -700 C in the electrical heater (19) and is forced through the passage (11) into the back-cover chamber (10) where it passes the injector (23) through the pulse-generator chamber (22), the throat (15) and the diverging portion (16) of the nozzle (13). As the heated supplied gas passes through, it heats the chamber (22) and the overall apparatus (20). At the throat (28) of the injector (23) the supplied gas has a sonic velocity and is accelerated through the diverging portion (16) of the nozzle (13). As this high velocity gas stream passes through the pulse-generator chamber (22) it creates a vacuum therein. The supplied gas is regulated by the control (18) and the temperature in the pulse-generator chamber (22) is regulated by the control (25). In order to reach the required temperature of the supplied gas (400 - 700 C) and to keep the CGDS apparatus portable and light, a secondary heater (not shown in the drawing) has to preheat the supplied gas before it reaches the primary heater (19). To achieve better control of the temperature in the pulse-generator chamber (22), a small band heater (not shown in the drawing) can be assembled around the pulse-generator body (21).
Temperature and pressure of the water in the water heater (24) is regulated by the control (25). To avoid boiling the water in the water heater (24), the water temperature is set to 5 ¨ 10 C
below the water saturation temperature at the given pressures (e.g. for compressed water at 87 psi the water temperature should be 148 - 153 C). The control (25) also regulates the water injections via the solenoid valve (27).
These injections of water are repeated in a cyclical manner at a pre-determined frequency range (e.g.
1-20 injections per second) and strictly correlate with the injection of the discharged powder materials from the powder feeder (17). When the desired temperatures in both the pulse-generator chamber (22) and in the water heater (24) are reached, one drop of the hot compressed water is injected into the pulse-generator chamber (22). Instantaneously, a portion of the injected water (up to 30%) becomes flash steam. The remaining 70%+ of the water also rapidly converts to steam.
This rapid vaporization of the injected water generates detonation-type impulse steam waves. These impulse steam waves accelerate through the converging or the converging-diverging portion of the pulse-generator chamber (22) and through the diverging portion (16) of the CGDS nozzle (13).
These impulse steam waves reach speeds of Mach 2 and higher in the diverging portion (16) of the nozzle (13). For sphere-shaped, sprayed particles, the speed of the stream at Mach 2 and higher is a milestone achievement for optimizing the value of the drag co-efficient (Cd).
These impulse steam waves accelerate the powder materials injected into the high velocity gas stream at the diverging portion (16) of the nozzle (13) towards the substrate (5) to form a coating (6). If, in between the nozzle throat (15) and the substrate (5), the pressure and the temperature of the impulse steam waves drop to the saturation point then these waves become saturated and a portion of the steam waves revert to the liquid state as they move through the diverging portion (16) of the nozzle (13). Any steam reverting to a liquid state will promote water hammering of the sprayed materials for better adhesion of the sprayed particles to the subtrate (5) and, in addition, will cool down the nozzle (13).
This will also promote agglomeration of the powder particles and increase the efficiency of the spray process, as well as permit the deposition of nanopowders; a hitherto unattainable objective in the prior art CGDS process.
= CA 02755921 Fig.3 shows the prior art CGDS apparatus (3), where the high pressure (80 to 300 psi) gas supply (usually helium) is heated in an electrical heater (19) to temperatures from 80 - 550 C and forced through the passage (11) into the back-cover (12) and the mixing chamber (10).
When the required temperature of the supplied gas is reached (regulated by the control (18)), the powder materials are introduced to the mixing chamber (10) from the powder feeder (17) where they are mixed with the supplied gas and forced through the converging portion (14) of the nozzle (13). The back pressure at the nozzle discharge is lower than the critical pressure of the supplied gas and the Mach number of the mixed stream at the throat (15) is Mach 1 and the flow is sonic. In the diverging portion (16) of the nozzle (13) the mixed stream accelerates to supersonic velocities towards the substrate (5) to form a coating (6).
Fig.4 shows the CGDS apparatus (4) of the present invention where a pulse-generator (20) is inserted into the existing CGDS apparatus of the prior art (3). The pulse-generator body (21) is embedded and securely connected between the nozzle (13) and the back-cover (12). The injector (23) is inserted within the pulse-generator body (21) and together with the converging portion (14) of the nozzle (13) creates the pulse-generator chamber (22). The shapes of the conical portion (30) of the injector (23) and the converging portion (14) of the nozzle (13) make this portion of the pulse-generator chamber (22) into a converging or converging-diverging passage. The pulse-generator chamber (22) is also embedded and securely connected with the passage (26) to the water heater (24). The passage (26) has an in-line solenoid valve (27) and an in-line check valve (29). The injector (23) links the stream of the supplied gas and powder materials between the back-cover chamber (10) of the back-cover (12) and converging portion (14) of the nozzle (13). The high pressure (80 to 300 psi) supplied gas (e.g. helium) is heated to temperatures of 400 - 700 C in the electrical heater (19) and is forced through the passage (11) into the back-cover chamber (10) where it is mixed with the powder materials and forced through the injector (23) and the pulse-generator chamber (22), the throat (15) and the diverging portion (16) of the nozzle (13) towards the substrate (5) to form a coating (6). As the heated mixture of the supplied gas and the powder materials pass through the pulse-generator chamber (22), the mixture heats the chamber (22) and the overall apparatus (20). At the throat (28) of the injector (23) the mixture stream has a sonic velocity and is accelerated through the diverging portion (16) of the nozzle (13). As this high velocity mixture passes through the pulse-generator chamber (22) it creates a vacuum therein.
The supplied gas is regulated by the control (18), and the temperature in the pulse-generator chamber (22) is regulated by the control (25). In order to reach the required temperature of the supplied gas (400 - 700 C) and to keep the CGDS apparatus light, a secondary heater (not shown in the drawing) has to preheat the supplied gas before it reaches the primary heater (19). To achieve better control of the temperature in the pulse-generator chamber (22), a small band heater (not shown in the drawing) can be assembled around the pulse-generator body (21). Temperature and pressure of the water in the water heater (24) are regulated by the control (25). To avoid boiling the water in the water heater (24), the water temperature is set to 5 ¨ 10 C below the water saturation temperature at the given pressures (e.g. for compressed water at 87 psi the water temperature should be 148 - 153 C). The control (25) also regulates the water injections via the in-line solenoid valve (27). The water injections are repeated in a cyclical manner at a pre-determined frequency range (e.g. 1-20 injections per second). When the desired temperatures in both the pulse-generator chamber (22) and in the water heater (24) are reached, one drop of the hot compressed water is injected into the pulse-generator chamber (22). Instantaneously, a portion of the injected water (up to 30%) becomes flash steam. The remaining 70%+ of the water also rapidly converts to steam. This rapid vaporization of the injected water generates detonation-type impulse steam waves. These impulse steam waves accelerate through the converging or the converging-diverging portion of the pulse-generator chamber (22) and through the diverging portion of the CGDS nozzle (13). These impulse steam waves reach speeds of Mach 2 and higher in the diverging portion of the nozzle. For sphere-shaped, sprayed particles, the speed of the stream at Mach 2 and higher is a milestone achievement for optimizing the value of the drag co-efficient (Cd). If, in between the nozzle throat (15) and the substrate (5), the pressure and the temperature of the impulse steam waves drop to the saturation point then these waves become saturated and a portion of the steam waves revert to the liquid state as they move through the diverging portion (16) of the nozzle (13). Any steam reverting to a liquid state will promote water hammering of the sprayed materials for better adhesion of the sprayed particles to the subtrate (5) and, in addition, will cool down the nozzle (13). This will also promote agglomeration of the powder particles and increase the efficiency of the spray process, as well as permit the deposition of nanopowders; a hitherto unattainable objective in the prior art CGDS
process.
Claims (3)
1. A pulse-generator for use in a cold gas dynamic spray apparatus comprising:
a pulse-generator body mounted coaxially behind a converging-diverging nozzle with an injector mounted in a cylindrical chamber thereof;
means for connecting a supply of heated gas with a converging-diverging nozzle; and means for creating a low-pressure chamber;
a pressurized water heater with in-line valves;
means for injecting compressed hot water into a low-pressure chamber; and means for injecting water in a cyclical manner at a pre-determined frequency;
a pulse-generator body mounted coaxially behind a converging-diverging nozzle with an injector mounted in a cylindrical chamber thereof;
means for connecting a supply of heated gas with a converging-diverging nozzle; and means for creating a low-pressure chamber;
a pressurized water heater with in-line valves;
means for injecting compressed hot water into a low-pressure chamber; and means for injecting water in a cyclical manner at a pre-determined frequency;
2. A pulse-generator as claimed in claim 1 wherein the conical shape of the injector and the converging portion of the converging-diverging nozzle create a converging passage for steam.
3. A pulse-generator as claimed in claim 1 wherein the conical shape of the injector and the converging portion of the converging-diverging nozzle create a converging-diverging passage for steam.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2755921 CA2755921A1 (en) | 2011-10-21 | 2011-10-21 | Pulse cold gas dynamic spraying apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2755921 CA2755921A1 (en) | 2011-10-21 | 2011-10-21 | Pulse cold gas dynamic spraying apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2755921A1 true CA2755921A1 (en) | 2013-04-21 |
Family
ID=48173945
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2755921 Abandoned CA2755921A1 (en) | 2011-10-21 | 2011-10-21 | Pulse cold gas dynamic spraying apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2755921A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2023070189A1 (en) * | 2021-10-28 | 2023-05-04 | Zygmunt Baran | Dental apparatus for air abrasion and polishing |
-
2011
- 2011-10-21 CA CA 2755921 patent/CA2755921A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2023070189A1 (en) * | 2021-10-28 | 2023-05-04 | Zygmunt Baran | Dental apparatus for air abrasion and polishing |
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