Patent Application
20060251821
The present invention is directed to coating technology and, more particularly, to pulsed detonation coating (sometimes also referred to as pulsed thermal spray (PTS)).
Several techniques have been used to implement thermal spray coating. One approach has been High Velocity Oxygen/Fuel System (HVOF), in which solid particles are injected in high velocity gas produced by reaction of oxidizer and a fuel at high pressure. Such systems typically are used for deposition at atmospheric pressure and primarily are used for coating metal alloys and cermets powders with particle sizes larger than about 10 μm. Other thermal spray coating techniques include plasma spray, in which particles are heated and accelerated by high temperature plasma produced by an electric discharge in an inert gas atmosphere. Plasma spray systems have been used for both atmospheric- and low-pressure coatings.
Thermal spray coating also has been implemented by intermittent detonations, e.g., by the use of a detonation gun (D-Gun). D-guns can be used for coating a wide variety of materials, such as metals, cermets, and ceramics. D-guns typically have a relatively long (often about 1 m), fluid-cooled barrel having an inner diameter of about one inch. Typically, a mixture of reactive gases, such as oxygen and acetylene, is fed into the gun along with a comminuted coating material in two phases. The reactive gas mixture is ignited to produce a detonation wave, which travels down the barrel of the gun. The detonation wave heats and accelerates the coating material particles, which are propelled out of the gun onto a substrate to be coated.
The detonation wave typically propagates with a speed of about 2.5 km/sec in the tube and can accelerate the particle-laden detonation products to a velocity of about 2 km/sec. However, coating particles never reach the velocity of detonation products due to inertia. In practice, particle velocities usually are lower than about 900 m/sec. The temperature of the detonation products often reaches about 4000 K. After the coating material exits the barrel of the D-gun, a pulse of nitrogen typically is used to purge the barrel. Newer designs of the D-guns allow operation frequencies of up to about 100 Hz. See, e.g., I. Fagoaga et al., “High Frequency Pulsed Detonation (HFPD): Processing Parameters” (1997).
One example of a gas detonation coating apparatus is illustrated in U.S. Pat. No. 4,669,658 to Nevgod et al. A barrel enclosed in a casing has annular grooves made on an inner surface of an initial portion thereof. A main pipe housing a spark plug and having annular grooves on its inner surface is inserted into the initial portion of the barrel. In operation, a gas supply means is turned on. The apparatus works in cycles, each cycle accompanied by gas flowing into the barrel and the main pipe through tubes, gas conduits, and additional pipes. After the gases fill the barrel, the gas mixture is ignited in each cycle with the aid of the spark plug. The detonation products are said to quickly heat up the walls of the barrel and the annular grooves.
According to Nevgod, the gases flowing into the barrel are heated up in two stages. During the first stage the gases are warmed up in the additional pipes heated up in cycles by the detonation products. The heat insulation tubes are said to prevent the pipes from cooling down. During the second stage, the gases are heated up in the barrel and partially in the main pipe. The annular grooves on the inner cylindrical surface of the initial portion of the barrel, the inner surface of the main pipe and on the inner surface of the cover on the end of the barrel, are said to enhance the efficiency of heat exchange with the gases due to an increase in the heat exchange area and due to gas turbulization. The gases are heated to a temperature approximating that of self-ignition. A plurality of ignition sites is provided to accelerate the burning process.
In current coating devices, the ranges of detonation temperature and pressure are intrinsically limited by the properties of the detonable mixture compositions and concentrations. Typical pressures produced by detonation waves in mixtures of common hydrocarbons and oxygen are on the order of about 50 atm in the detonation wave front (shock wave) and about 15 atm behind the detonation wave front. It is sometimes desirable for material processing to use higher pressures and higher temperatures than those which can be produced by detonation of common hydrocarbon/oxygen mixtures. On the other hand, it is sometimes desirable to process materials at temperatures and pressures that are significantly lower than those typical for detonation waves and detonation products.
The present invention is directed to a method and apparatus for producing a coating on a substrate using a pulsed detonation gun. In one embodiment, a pulsed detonation coating apparatus has a first section into which a detonable or reactive mixture is injected. The apparatus has a second section into which a coating precursor is injected. A detonable or reactive mixture is formed and ignited in the first section. The detonation or reaction products expand through the first section and into the second section where they contact the coating precursor. Detonation products containing the coating precursor are discharged through an outlet and contacted with a substrate to produce a coating. The multi-sectioned apparatus can be configured to provide temperature, pressure, and a chemical environment which accommodate desired processing conditions for the coating precursor.
In another embodiment, an object is coated at a reduced standoff between the outlet of a pulsed detonation coating apparatus and the coated surface. Conventional detonation coating generally uses a standoff of 8 to 25 cm. In this embodiment, the standoff can be about 5 cm or less and usually ranges from about 2 mm to about 4 cm, and often ranges from about 3 mm to 3 cm, about 4 mm to 2 cm, or about 5 mm to 1 cm. Such reduced standoffs facilitate coating the inside of tubes, especially at corners, and assures uniform material distribution. The apparatus makes coating at these short standoffs possible because of its small size and because of the small particle sizes that can be used in the coating systems.
In another embodiment, a pulsed detonation apparatus comprises a detonation gun having a smallest characteristic dimension of less than 10 mm, an igniter, and an outlet for discharging detonation products. A detonable mixture containing a coating precursor is formed in the detonation gun, and the detonable mixture is ignited to produce detonation products containing the coating precursor. The coating precursor is discharged through the nozzle and is contacted with the substrate to produce a coating. In this embodiment, the coating material can be injected into a detonation tube together with other components of the detonable mixture. Alternatively, the coating precursor can be injected into a coating precursor processing section having either the same or a different smallest characteristic dimension than that of the detonation tube, as in the previous embodiment.
In yet another embodiment, an amorphous metal alloy is coated on a substrate using a pulsed detonation gun. The method comprises providing a pulsed detonation gun having a detonation chamber, an igniter, and an outlet for discharging detonation products. A detonable mixture is injected in the detonation chamber, and a coating precursor containing a metal alloy which is amorphous, or which becomes amorphous after processing, is injected. The detonable mixture is ignited to produce detonation products, which accelerate the coating precursor through the outlet and into contact with the substrate to produce an amorphous metal alloy coating on the substrate. This technique also can be used for building amorphous coating layers on a preform as a method of producing bulk parts from amorphous materials.
The pulsed detonation gun of the present invention is particularly useful for directly depositing coating material(s) over internal surfaces of tubes and other hard-to-reach surfaces of a substrate, such as the inner surfaces of cylinders, the inner surfaces of converging/diverging shapes, the inner surfaces of rectangular tubes, the inner surfaces of shapes that are partially open, and the inner surfaces of various other non-cylindrical shapes.
The material(s) are deposited by high velocity gas products produced in intermittent detonations or an intermittent injection and deflagration process. The detonation tube and its associated fuel/oxidizer supply lines can be constructed at a sufficiently small scale that allows their insertion into long, small-diameter tubes, and permits their use in coating various other difficult-to-reach surfaces. Of course, the apparatus of the present invention also is useful for coating a wide variety of large-diameter tubes, such as gun barrels, tubes used in oil industries, tubes used in food industries, etc., as well as other large substrates including external surfaces thereof.
The detonation products produced by the pulsed detonation gun accelerate and heat the coating precursor or coating material particles to high kinetic energies, resulting in high quality coating depositions that can provide such properties as corrosion-, erosion-, and wear resistance. Existing thermal spray coating equipment is unsuitable for applying such coatings to the inner surfaces of small-diameter tubes and many other difficult-to-reach surfaces.
The present invention will now be described in more detail with reference to preferred embodiments of the invention, given only by way of example, and illustrated in the accompanying drawings in which:
The pulsed detonation coating apparatus of the present invention has utility in applying a wide variety of coating materials to a wide variety of substrates and is particularly useful in coating the inside surfaces of small-diameter tubes, as illustrated in
The term “detonation,” “detonation process,” and similar terms are used herein refer to a physical phenomena characterized by a shock wave propagating in front of a reaction front. The shock wave compresses the initial mixture to high pressures and high temperatures so as to initiate a very high rate of reaction behind its front. The detonation front propagates with supersonic speeds, typically on the order of about 1000 to 3000 m/sec.
The term “deflagration process,” as used herein, refers to a combustion process in which a reaction front propagates slowly through the mixture via diffusion and thermal initiation. Combustion of the unconfined mixture does not yield the high pressures that are characteristic of detonation. The combustion front propagates with subsonic speeds, typically on the order of about 1 to 30 m/sec.
The term “detonable mixture,” as used herein, refers to the components present in the detonation driver section at the time detonation is initiated. As discussed herein, in some cases a detonable mixture also is formed in the second section into which the coating precursor is injected. One example of a detonable mixture is oxygen and a fuel detonable in mixtures with oxygen. Another example of a detonable mixture is a monopropellant, such as nitromethane or nitrobenzene. As another example, a detonable mixture can comprise a detonable coating precursor and an oxidizer. The term “reactive mixture” refers to the components present in a volume at the time a deflagration process is initiated.
The term “coating precursor,” as used herein, refers to (1) material that can be heated and accelerated in a detonation process to form a coating, or (2) material that can react during a detonation process or a deflagration process to form a coating material in situ. The coating precursor can comprise, by way of example, particles such as metals, cermets, ceramics, polymers, or combinations thereof. The term “detonable coating precursor,” as used herein, refers to materials which function as both a coating precursor and as a fuel. Non-limiting examples of detonable coating precursors include gaseous and liquid metalorganic compounds, such as silane, disilane, germane, tungsten hexaflurade, trimethylboron, cadmium acetate, magnesium ethoxide, tantalum V-methoxide, tungsten V-ethoxide, zinc naphenate, and zirconium n-butoxide.
The coating precursor may be in a variety of physical forms. For example, the coating precursor may comprise metal particles, which can be pre-mixed with an inert carrier, fuel, or oxidizer before injection into the apparatus. During the detonation process, the coating precursor particles typically are heated and are liquefied or semi-liquefied. The resulting detonation products act as a carrier for the liquefied or semi-liquefied coating precursor, which forms a coating on the substrate. The coating precursor alternatively can be in the gaseous phase, and may form coatings, for example, upon interaction with the substrate via chemical reaction, physical sintering, or both.
Examples of fuels that can be used include, but are not limited to, those detonable in mixtures with oxidizer such as hydrogen, methane, propane, acetylene, or propylene. Also, detonable mixtures of liquid fuels and oxidizer can be used, e.g., kerosene/oxygen, alcohol/oxygen, benzene/oxygen and other similar mixtures. In addition, some detonable monopropellants can be used, such as nitromethane, nitroglycerin, or similar single-component fuels that can be detonated. Selection of a suitable fuel will be apparent to persons skilled in the art.
Non-limiting examples of oxidizers include oxygen, air, mixtures of oxygen and nitrogen, mixtures of oxygen and one or more inert gases such as helium and argon. The relative amounts of nitrogen or inert gases vary over a wide range and can be suitably selected by persons skilled in the art with the aid of no more than routine experimentation. The oxidizer also can be in liquid form. Examples of liquid oxidizers include hydrogen peroxide, nitric acid, hydroxylammonium nitrate, and the like.
For solid coating precursors, the size of particles can vary over a wide range. Often the mean particle size is about 100 μm, 50 μm, or less. Smaller micron particle sizes also can be used, such as those having a mean particle size of less than about 20 μm or 10 μm. Sub-micron sized particles can be used, e.g., having a mean particle size of less than 1 μm, and can have a mean particle size as small as about 100 nm, 10 nm, or less. The coating precursor typically is supplied in an inert liquid or gaseous carrier, such as water, nitrogen, argon, or helium.
The detonation apparatus can be (but is not necessarily) constructed of sufficiently small dimensions to enable the apparatus to easily fit into small-diameter tubes, e.g., tubes having a diameter of about 10 cm, 5 cm, 2 cm or even less. The detonation driver section and second section into which the coating precursor are injected are described herein primarily with reference to cylindrical shapes of which the internal diameter is the smallest characteristic dimension. However, the geometry of the sections is not limited to cylindrical shapes; for example, the detonation driver section and/or the coating precursor processing section may have a rectangular cross-section. In the context of non-cylindrical geometries, the term “diameter” refers to the diameter of a circle having the same area as the cross-sectional area of the non-cylindrical geometry. The diameter of a non-uniform cross-section refers to the diameter of a circle having the same area as the minimum cross-sectional area of the non-uniform section.
The pulsed detonation coating apparatus of the present invention can be (but need not be) constructed substantially smaller than conventional D-guns, permitting its use for coating the inside surface of small-diameter tubes and various other difficult-to-reach substrate surfaces. The pulsed detonation coating apparatus can have a total length of about 200 cm or less. It is contemplated that coating guns of the present invention can have a total length of about 100 cm, 50 cm, 25 cm, 10 cm, 5 cm, 1 cm, or even less. For many applications, substantially larger dimensions can be used effectively. Larger devices may be needed, for example, for effectively coating large substrate surfaces. By way of example, the internal diameter (ID) of the detonation driver section and coating precursor processing section can be about 50 cm, 100 cm, or greater. In smaller devices, the ID of detonation driver and coating precursor sections can be substantially less, such as about 20 mm, about 10 mm, about 5 mm, or about 2 mm or less. By way of example, the ratio of the cross-sectional area, length, or volume of the detonation driver section to the corresponding cross-sectional area, length, or volume of the coating precursor processing section can range from about 100:1 to 1:100, from about 100:1 to 1:1, or from about 1:1 to 1:100.
One example of a multi-sectioned pulsed detonation coating apparatus has a relatively short 10 cm long×10 cm ID detonation driver section connected to a 10 cm long×50 cm ID coating precursor processing. Such a device is effective for coating large areas, for example, with polytetrafluoroethylene (melting point ˜470 K). The expanding detonation products (typical at 4000 K) from the 10 cm ID detonation driver section into the 50 cm ID coating precursor processing section will allow cooling and prevent overheating of the polytetrafluoroethylene particles, resulting in optimal coating conditions.
Processing at temperatures and pressures significantly lower than those typical for detonation propagating in hydrocarbon/oxidizer mixtures can be facilitated by using suspensions of particles in inert liquid and/or co-injecting with an inert gas (e.g., nitrogen, argon, helium). Alternatively, a reactive carrier liquid and oxidizer gas having relatively low detonation pressure and temperature can be injected through inlets 15 and 17, respectively. Such materials are not easily ignited by the spark ignition (i.e., ignition of the mixture can be avoided). With respect to the apparatus's geometry, a detonation driver section 20 having a relatively small volume and cross-sectional area (e.g., as shown in
The apparatus also can accommodate processing at higher detonation temperatures and pressures, e.g., using a configuration as shown in
The geometry of the apparatus also can be modified to increase or decrease the time of coating particle exposure to high temperature detonation products created in the detonation driver section 20 (and, if applicable, detonation products created in the second section 21). A shorter second section 21 will reduce particle exposure time. This is beneficial, for example, for processing nanostructure materials that can exhibit grain growth and lose nanostructure and other beneficial properties. In addition, some metastable material phases can be lost due to prolonged exposure to high temperature. For example, amorphous or glassy states of metal alloys can be lost due to overheating. Also, high temperatures can lead to graphitization of diamond, which is a metastable phase of carbon. On the other hand, a longer second section 21 will increase particle exposure time to high temperatures and can be useful, for example, for processing larger particles or materials with high melting points.
The cross-sectional area of the second section 21 also can be varied to increase or decrease temperature and pressure. For example, by reducing the cross-sectional area of the second section 21, as in the embodiment of
It sometimes may be advantageous to use a second section 21 that converges to a smaller outlet or diverges to a larger outlet. The ignition chamber 19 can either converge or diverge to the detonation driver section 20 (in the embodiments illustrated in
As an example of a diverging/converging configuration, the detonation driver section 20 can be generally spherical. The sphere can be connected to a cylindrical second section 21, e.g., via any of the above-described nozzle configurations. The various geometries of the detonation driver section 20 as described above can be used in combination with any of the above-described geometries of the second section 21. For example, both sections 20 and 21 can converge, both sections 20 and 21 can diverge, or both sections 20 and 21 can diverge and then converge. In addition, the detonation driver section 20 can have a bent end which joins the second section 21.
The detonation wave can be made to propagate somewhat faster in a converging configuration and generally will propagate at the same speed in a diverging configuration because it is driven mainly by energy released by chemical reactions. If the detonation wave reflects from a wall when running into a diverging nozzle, it will create higher pressures because most of the kinetic energy of the wave will be transferred into pressure. Thus, converging configurations could be used in the driver section 20 to increase pressure which will create wider shock wave and prolong exposure of the particles in the coating precursor processing section 21 to a high pressure, velocity, and temperature environment. Diverging configuration of the driver section 20 will create narrow shock waves in the coating precursor processing section 21 and will reduce time of exposure of the precursor material to high pressures, velocities and temperatures. The same strategy can be used in the coating precursor processing section 21. Gradually converging nozzles generally will increase the time the coating precursor material is exposed to high pressure, temperature, and velocity conditions. Gradually diverging nozzle generally will decrease the time the coating precursor material is exposed to high pressure, temperature, and velocity conditions.
The injection rates preferably are adjusted so that at the time detonation is initiated, the detonable mixture will mostly fill the detonation driver section 20 and the particle/liquid/gas suspension will mostly fill the second section 20. Usually the components will be co-injected simultaneously, although the components also can be injected sequentially.
Optionally, two or more coating precursors can be alternatively injected into the second section 21. The changing from one coating precursor to another coating precursor can be done at predetermined intervals (e.g., alternating each detonation, every other detonation, every fifth detonation, etc.) or can be actuated manually by an operator. Multiple coating precursors may be used, for example, to create a complex multi-layered coating material on a substrate using a single coating apparatus. When multiple coating precursors are employed, either a single coating precursor processing section can be used or, as discussed below, multiple coating precursor processing sections, e.g., in series or in parallel, can be used.
To help facilitate uniform distribution of coating precursor material inside of coating processing section 21, injection of the coating precursor can be accomplished using an injector 15′ that allows axial injection of coating precursor along the coating processing section 21 volume, as shown in
The detonable mixture is ignited by suitable igniter, such as a spark plug, laser, pyrotechnic device, or the like. Each detonation creates a detonation wave that propagates through the detonation driver section 20. The resulting high-temperature and high-pressure detonation products heat the coating precursor particles and accelerate the particles through the second section 21. The coating precursor particles are discharged through the detonation tube outlet and toward the inside surface of the substrate 25 to be coated. The frequency of detonations can vary over a wide range and can be suitably selected to meet the needs of a particular application, as will be apparent to persons skilled in the art. The operating frequency most often ranges from about 0.1 to 1,000 Hz.
The intermittent operation of the pulsed detonation coating apparatus avoids the need for separate cooling equipment because intermittent injection of the relatively cold gases between the brief periods of high-temperature detonation enables relatively low temperatures to be maintained in the walls of the detonation driver section 20 and second section 21. Nevertheless, to prevent damage to valves and other system elements, in some cases it may be advantageous to blow air or inert gas through the inner volume of the detonation tube over the valves and other elements of pulsed detonation coating apparatus, or to provide cooling in some other fashion. For example, cooling can be achieved by conventional methods such as circulating water or other cooling medium over external surfaces of the apparatus in specially designed channels.
Because of the intermittent exposure of the internal surfaces of the pulsed detonation apparatus to high temperature detonation products and low temperature injected material, in some cases effective cooling of the apparatus can be facilitated by providing a low thermal conductivity interface between the internal volume of the apparatus and bulk materials of the coating apparatus. In such cases, during the very short time of exposure of the internal volume to high temperature detonation products, only a very minimal amount of heat is transferred to the bulk body of coating apparatus. In practice, this can be implemented by coating the internal surfaces of the apparatus with zirconium oxide, aluminum oxide, or other materials with high thermal stability and low thermal conductivity. Other methods of providing a thermal barrier include inserting low thermal conductivity material into the internal volume or constructing parts exposed to high temperatures out of low thermal conductivity materials. It should be recognized that this technique generally is not effective for coating apparatuses based on continuous operation because it only delays (does not prevent) propagation of the hot front. In fact, this technique actually can increase internal surface temperature during continuous operation because outward heat transfer is restricted.
A coating material can be synthesized in situ during an intermittent detonation or deflagration process. A coating precursor can be pre-mixed with oxidizer or fuel, and the components are co-injected into the second section 21 to form a detonable or reactive mixture. A detonable coating precursor also may be used, and can be co-injected with an oxidizer. When the detonable or reactive mixture is ignited, the coating precursor reacts in the high-temperature detonation or reaction products to yield coating materials that are accelerated through the second section 21, through the outlet and toward the substrate 25 to be coated.
In another embodiment, a pulsed detonation apparatus comprises a detonation gun having a smallest characteristic dimension of less than 10 mm, an igniter, and an outlet for discharging detonation products. For example, the smallest characteristic dimension of the apparatus shown in
In another embodiment, an amorphous metal alloy is coated on a substrate using a pulsed detonation gun. The method comprises providing a pulsed detonation gun having a detonation chamber, an igniter, and an outlet for discharging detonation products. A detonable mixture is injected in the detonation chamber, and a coating precursor containing a metal alloy that it amorphous (or becomes amorphous after processing) is injected. The detonable mixture is ignited to produce detonation products, which accelerate the coating precursor through the outlet and into contact with the substrate to produce an amorphous metal alloy coating on the substrate. The controlled processing conditions provided by the apparatus enable rapid heating and rapid cooling of the metal alloys, which preserve their amorphous state during detonation and coating. Preferably, the coating precursor is injected into a second section 21 in advance of the detonable mixture formed in the detonation driver section 20, e.g., as illustrated in
Any of the coating processes described herein can be implemented in a vacuum or reduced pressure environment. The lower pressures are particularly useful for coating with small particles and nanosized particles. For example, the substrate 25 can be situated in a low-pressure or vacuum chamber (not shown). The valves, controls, etc. preferably are disposed outside of the vacuum chamber for easy operator access, while the fuel, oxidizer, inert gas/precursor materials, and ignition lines are fed through the wall of the low-pressure or vacuum chamber without interfering with the vacuum or low-pressure environment. A vacuum pump can be used for creating and maintaining low-pressure or vacuum within the low-pressure chamber. The term “low pressure” refers to pressures lower than atmospheric (less than 1 atmosphere) and typically on the order of 10−1 of atmospheres and lower, often on the order of 10−2 to 10−3 atmospheres and lower. The term “vacuum” refers to pressures of 10−6 atmospheres and lower.
The low pressure environment provides a greater pressure gradient in relation to the detonation pressure, which imparts increased kinetic energy and impact energy to the coating particles, resulting in high quality coatings. The detonation products expand from the high-pressure, high-temperature environment of the detonation driver section 20 and second section 21 to the low-pressure environment of the low-pressure or vacuum chamber. By maintaining low pressure near the substrate 25, it is possible to produce high quality coatings using small-micron scale and even nanoscale-sized particles. The particles are effectively accelerated in the expanding detonation products and do not appreciably decelerate at the substrate because of the very small drag force in the low-density and low-pressure environment. In general, the drag force is smaller for smaller particles. In the low-pressure environment, the characteristic size of smaller (e.g., nanoscale) particles approaches that of the collision free path for molecules of the low-pressure carrying gas. Thus, small-micron size particles generally require lower pressures than do smaller, nanoscale particles for the same drag force at the substrate environment.
In the low-pressure or vacuum chamber, the coating precursor particles are accelerated to high velocities. The particle velocities can vary over a wide range depending on such factors as particle size, detonation pressure, detonation temperature, and the pressure in the low-pressure chamber. Typical particle velocities are in excess of about 2 km/sec., often 3 km/sec., 4 km/sec., 5 km/sec., or even higher. Because the high temperature detonation products heat the coating precursor particles, the coating particles generally are in a liquefied or semi-liquefied state.
The low-pressure environment also effectively removes or reduces the amount of carrier gases from the detonation products as the detonation products are accelerated toward the substrate 25, resulting in relatively low pressure at the substrate surface. This is especially significant for coatings using small-micron and nanosized particles, which are particularly susceptible to being decelerated and diverted away from the substrate by turbulent gas flow in the vicinity of the substrate surface. Such a problem is encountered, for example, in conventional HVOF coating processes.
The detonation reaction produces a brief period of extremely high temperature and high pressure inside the detonation driver section 21. Typical detonation temperatures are on the order of 4000 K, and pressures on the order of 20-30 atmospheres and higher. The period of each detonation most often is less than about 10−3 sec. and can be as small as about 10−4 sec., 10−5 sec., or even less. Shorter periods of detonation can reduce or avoid appreciable local heating of the substrate, and also can permit operation at high frequencies, e.g., as high as 1000 Hz or higher. Shorter periods of detonation also can help avoid or reduce particle grain growth, particularly with nanosized particles.
The detonation apparatus outlet may include configured openings and/or a nozzle for directing the detonation products toward the substrate 25 to produce a coating. A wide variety of configurations are possible and may be particularly adapted for coating the inside surfaces of the small-diameter tubes and various other difficult-to-reach portions of substrates, such as the inner surfaces of cylinders, the inner surfaces of converging/diverging shapes, the inner surfaces of small rectangular tubes, the inner surfaces of shapes that are partially open, and the inner surfaces of various other non-cylindrical shapes. Several examples of showerhead and nozzle configurations are illustrated in
The detonation gun outlet may include a plurality of openings, such as in a “showerhead” type configuration, as illustrated in
As illustrated in
The intermittent detonations advantageously enable the surface of the substrate to cool between coated layers. This enables high deposition rates of coating materials, such as metals or ceramics, onto a wide variety of substrates, especially those, such as plastic, that have low melting point surfaces. If necessary, the surface of the substrate can be subjected to rapid temperature quenching, for example after each detonation exposure or at other suitable intervals. This can be done, for example, by intermittently spraying nitrogen onto the substrate surface between exposures. Quenching can be also achieved by injecting liquids such as water, ethyl alcohol, or inert gases such as helium or argon between the cycles into the detonation driver section 20.
At particle velocities in excess of 2 km/sec., some particles will fuse into coatings, even at low temperatures, and create a strong bond with the substrate surface. Excessive heating of the substrate surface can result in previously coated layers being damaged. By avoiding overheating of the substrate surface, the intermittent detonation process of the present invention permits high quality coatings to be applied at high coating rates.
The multi-section pulsed detonation coating apparatus can have more then one driver section 20 and/or more then one coating precursor processing section 21. Plural driver sections may be desirable, for example, to initiate detonation of a detonable mixture that could not be easily initiated by a spark plug, or to reduce the distance of deflagration-to-detonation transition. For example, an acetylene/oxygen mixture could be used in a first driver section and a methane/air mixture in a second driver section. Detonation of the acetylene/oxygen mixture can be easily initiated by spark discharge, and this detonation wave will propagate into second driver section and initiate detonation of the methane/air mixture. If methane/air mixture is initiated directly with a spark discharge, the transition from deflagration to full detonation wave can take tens of meters. It is contemplated that even more than two detonation driver sections may be desirable to meet the needs of some particular processing conditions.
Two or more coating precursor processing sections may be desirable, for example, for creating composite materials where different materials are injected in each section. Use of multiple sections will allow optimization of the environment to which each component of the composite is exposed. The sections could be of different geometry, e.g., different length and cross-sections, to allow greater flexibility of material processing. For example, as shown in
Another variation of a multi-sectioned pulsed detonation gun is shown in
When plural coating precursor processing sections are used, they may have the same or similar dimensions (e.g., cross-sectional areas, lengths, and volume), or the dimensions may vary significantly. For example, the ratio of the cross-sectional area, length, or volume of one coating precursor processing section to the corresponding cross-sectional area, length, or volume of another coating precursor processing section can range from about 100:1 to 1:100, from about 100:1 to 1:1, or from about 1:1 to 1:100.
While particular embodiments of the present invention have been described and illustrated, it should be understood that the invention is not limited thereto since modifications may be made by persons skilled in the art. The present application contemplates any and all modifications that fall within the spirit and scope of the underlying invention disclosed and claimed herein.
