TW202504694A - Coating removal system and methods of operating same - Google Patents

Abstract

A coating removal process includes providing a coating removal vessel having a sealable processing volume therein, providing a coating removal fluid, which reacts with the coating, at an elevated temperature above the ambient temperature surrounding the removal vessel, in the sealable processing volume, locating a component having a coating thereon to be removed in the processing volume, sealing the sealable process volume from the ambient surrounding the processing volume, heating the coating removal fluid to a temperature greater than the boiling point thereof at the pressure of the surrounding ambient, removing the coating from the component using the coating removal fluid at the temperature greater than the boiling point thereof at the pressure of the surrounding ambient, reducing the temperature of the coating removal fluid to a temperature less than the boiling point thereof at the pressure of the surrounding ambient, venting the sealable volume to the surrounding ambient, and removing the component from the processing volume.

Description

Coating removal system and method of operation thereof

The present disclosure relates to the field of cleaning of components used in semiconductor processing equipment, wherein material is deposited or formed on the surface of the component as a byproduct of a process performed in the processing equipment, and when the amount of deposit formed on the component can or will adversely affect processing in the processing equipment, the component is processed to remove a coating deposited thereon as a byproduct of a process performed in the processing equipment.

Components used in certain process environments such as process equipment such as process chambers often become coated with deposited materials or coated with byproducts of etch or material removal processes, wherein a deposition process or coating process is performed to coat an object in the process chamber, or an etch or material removal process is performed to etch or remove a coating on an object in the process chamber. Such a coating may be generated gradually, such as a coating that is generally thicker or thinner than a coating on an object being coated is formed or deposited on chamber components that are exposed to a process environment in a process chamber whenever an object is processed to be coated in a processing apparatus. Similarly, during an etching or material removal process, byproducts of the etching or material removal process may be deposited on walls or other surfaces of chamber components that are exposed to the process environment. This coating, when it reaches a certain thickness, can flake off the component and become a process contaminant, for example by becoming attached to the article being coated or by being deposited on a support provided to support the article within the article processing chamber or system, the coating can scratch the surface of the article being coated on its supported side in the processing chamber or system. Because process chamber components are typically high cost components of the processing chamber, the components are typically recycled for reuse one or more times. This recycling of the components requires that the coating formed on the component as a byproduct of the process to which the component is exposed be removed and the component cleaned, and the component can then be suitable for reuse. In some cases, a component will have a protective coating thereon prior to use in a process environment or process chamber, and removing the coating as a byproduct of the process environment may also remove some or all of the protective coating. In that case, the protective coating will also need to be replaced. Additional undesirable coatings may be the result of natural oxidation of the component or other effects, such as as a byproduct of combustion, for example in internal combustion engines, gas turbine engines, etc. Additionally, to refurbish the component, the byproduct coating needs to be removed. During refurbishment of a component that was exposed to a material on which the undesirable coating was formed as a byproduct of the use of the component, the undesirable coating on the surface of the component must be removed. Removal processes typically include: a) chemical processes, such as wet etching processes, in which the component is exposed to a liquid etchant and the chemical composition of the etchant reacts with the undesirable coating on the component to chemically remove the coating; b) dry etching techniques such as plasma etching, in which chemical species activated by the plasma react with the undesirable coating to remove the undesirable coating from the component; and c) physical removal processes, such as sandblasting, in which the component is bombarded with sand or particles to physically grind the undesirable coating away from the underlying surface of the component.

Combinations of these processes or techniques may also be used to remove undesirable coatings from components.

Many materials, such as certain metals, metal oxides, and other material coatings on underlying components are difficult or considered impractical or impossible to remove using wet or dry etching chemistries and techniques without also damaging the underlying components. For example, cobalt oxide and aluminum oxide, as well as other coating compositions, are generally not easily removed using chemical etching techniques. For example, the time used to remove the undesirable coating may be excessive, or possible chemistries that may be utilized for wet etching of the coating to remove the coating using known wet etching techniques may not effectively remove the undesirable coating at a sufficiently high removal rate to be commercially viable for use, or such possible chemistries may disadvantageously also etch underlying materials of the component. Additionally, the component having the undesirable coating removed therefrom may have critical dimensions, such as critical hole size, material thickness, or physical feature size, that need to be maintained within a manufacturer's tolerance or other specified tolerance to effectively reuse the component in the process chamber. In the event that the undesirable coating material reacts slowly with the etchant, and the etchant also reacts with the component material, the material will be removed from the component and the critical feature dimension may no longer exist in the component. When this occurs, the component can no longer be used for its intended purpose and will need to be replaced. Typically, the etchant material will have a greater etching or reaction rate with the material of the undesirable coating than the reaction rate with the underlying component. However, the undesirable coating will generally have a different thickness across the surface of the component, and the isotropic nature of wet etching will result in portions of the component surface being exposed to the etchant while other portions of the component remain covered in the undesirable coating material to be removed. As a result, overetching or removal of a portion of the underlying component may occur.

Some materials are not susceptible to removal by wet or dry etching techniques because the etch rate of the coating is so low that the time used to remove the coating is excessive. Here, the coating is usually removed by shot blasting or sand blasting, in which the coating is physically removed by small balls or grit that impact on the coating and lift the coating off the surface of the component. However, the underlying component surface becomes exposed to the impinging balls or grit and the balls or grit erode the exposed component surface, thereby removing material from the exposed component surface and causing dimensional changes that will ultimately require replacement of the component. In the case of components that are used in process chambers used in the manufacture of semiconductors, the dimensional integrity of the component is typically critical to at least one of electrical, fluid flow, temperature or other process properties, and thus critical to the repeatability of the manufacturing process. In the case of materials such as einsteinium oxide, aluminum oxide, and other difficult to remove materials, or their etch byproducts deposited on the component, shot blasting or sand blasting has been considered the only practical way to remove the coating because the reaction rate of the coating with the etchant is so slow that the time to etch away the undesirable coating has been considered commercially impractical.

Provided herein are methods and apparatus for removing coatings from surfaces of components, including at least one exterior surface of the component, a recessed surface of the component such as into a hole or opening in the component, an interior surface of the component accessible from the exterior of the component, or other component surface having a material to be removed adhered thereto or thereto. In one aspect, the coating removal container includes an outer body comprising a processing volume and an opening into the processing volume; a cover over the opening, the cover including a seal therein that is contactable with a surface of the outer body and the cover; a component holder that is removably positionable in the processing volume; and a heater configured to heat a cleaning fluid to a temperature greater than the cleaning fluid when supplied to the processing volume. a pressure regulator wherein, with the assembly holder positioned in the process volume and the cover sealingly connected to the vessel to close the opening and seal the process volume from the surrounding environment, a cleaning fluid positioned in the process volume can be heated to a temperature above its boiling point in the surrounding environment but is self-pressurized to a pressure sufficient to prevent the cleaning fluid from boiling in the pressure vessel.

In another aspect, a method for removing a coating from a component includes providing a coating removal container having a sealable processing volume therein; providing a coating removal fluid in the sealable processing volume, the coating removal fluid reacting with the coating at an elevated temperature above the temperature of an environment surrounding the removal container; positioning a component having a coating to be removed in the coating removal container in the processing volume of the coating removal container; sealing the sealable processing volume from the environment surrounding the processing volume; and heating the coating removal fluid to a temperature greater than the boiling point of the coating removal fluid at the pressure of the surrounding environment; using the coating removal fluid to remove the coating from the component at the temperature greater than the boiling point of the coating removal fluid at the pressure of the surrounding environment; reducing the temperature of the coating removal fluid to a temperature less than the boiling point of the coating removal fluid at the pressure of the surrounding environment; venting the sealable volume to the surrounding environment; and removing the component from the processing volume.

In another aspect, a coating removal system includes a containment container having an interior volume and a sealable door; and one or more coating removal containers configured to be received within the containment container.

In another aspect, a method of removing coating from an assembly includes providing a containment container having an interior volume and a sealable door; providing one or more coating removal containers configured to be received within the containment container; providing a coating removal liquid in the coating removal container; positioning an assembly into the coating removal container; positioning the coating removal container within the interior volume of the containment container, and closing the sealable door to seal the interior volume; and increasing the pressure and temperature of the coating removal fluid to a temperature greater than the boiling point of the coating removal fluid to maintain the coating removal fluid in a liquid state.

Herein, methods and apparatus are described for removing coatings from underlying components, such as components used in manufacturing equipment, including components used in semiconductor manufacturing equipment and exposed to semiconductor processing environments. Herein, a base component, i.e., a component under the conditions of being placed in a type of processing equipment and exposed to a process environment, has an underlying material composition, which may include a component composed of a single material, a part composed of several different materials, a coated part where the coating is intended to protect the underlying component material from exposure to the manufacturing environment, or other compositions.

Exemplary parts of this type include silicon carbide components such as rings, and metal components used in processing equipment such as shields, chambers, showerheads, exhaust ducts, etc. These components have critical thicknesses, critical hole sizes, and other critical feature sizes. The hole sizes, including diameter(s), taper, depth, etc. are considered critical to the effective use of shields in manufacturing environments, such as semiconductor processing chambers. It is well known that during use, films are formed as coatings on the surfaces of these components and must be removed after a certain period of time, deposition thickness, number of hours of process equipment operation, or other criteria. Because components are expensive, users of manufacturing equipment will clean and reuse them, which includes removing films that deposit on them during use, i.e., undesirable coatings. The number of times a component can be reused depends in part on how much of the component's underlying material is removed during the coating removal process, especially in critical size areas such as its pores. The desire of the component user is to remove the coating from the component and reuse the component as many times as possible.

Here, to remove the coating, a coating removal fluid is used at a temperature of the fluid above the boiling point of the fluid at atmospheric pressure, i.e., a removal fluid having an active chemistry therein that is capable of etching away, i.e., removing, the undesirable coating at room temperature (20° C.) but at an unacceptably low etching rate, or material from which the underlying coating cannot be removed at room temperature. This is accomplished by maintaining the removal fluid with the component disposed therein at a superatmospheric pressure, i.e., a pressure above the local ambient atmospheric pressure in which the process is performed, during exposure of the component to the coating removal fluid. Thus, the material of the undesirable coating deposited thereon during use of the component in the process chamber or manufacturing environment is in contact with a coating removal fluid at a temperature greater than its boiling point at normal or local atmospheric pressure, i.e., at or near 760 Torr. Alternatively, the removal fluid may be maintained at a temperature at which maintenance of the coating material fluid in a liquid state becomes difficult due to its excessive vaporization, such as at 70% to 100% of the boiling point temperature at atmospheric pressure.

Thus, in one aspect, a coating removal container 100 is provided that functions to contain the assembly therein at atmospheric pressure and provides a sealed environment to raise the temperature of the coating removal fluid therein to a temperature greater than the boiling point of the coating removal fluid at atmospheric pressure while maintaining conditions therein such that the removal fluid does not boil. This is achieved by maintaining the coating removal fluid in a sealed environment within the container 100 and then heating the fluid from a temperature below its boiling point in the surrounding environment to a temperature above that boiling point. Because the fluid volume is sealed, when the fluid emits vapor as it becomes close to its atmospheric pressure boiling point, the vapor is sealed within the fixed volume of the container. Because the vapor has a lower density than the coating removal fluid, the vapor will remain in the headspace above or on top of the coating removal fluid and will become pressurized as the temperature of the coating removal fluid increases, thereby creating a vapor pressure of the coating removal fluid, and from there releasing more vapor to become equal to the increased pressure in the headspace, and that pressure is sufficient to prevent the coating removal fluid from boiling, even if the coating removal fluid is at a temperature above its boiling point at atmospheric pressure. At such higher temperatures than can be achieved in a liquid coating removal fluid when the coating removal fluid is exposed to ambient atmospheric conditions, the etching rate of the coating material is significantly increased for a particular coating removal fluid chemistry. This allows wet etching removal of coatings on components that were not possible or practical using wet etchants in the prior art.

Here, in one embodiment, the coating removal container 100 is shown in cross-section in Figure 1 and generally includes a generally annular body 104 forming a processing volume 106, a removable cover 102 releasably secured to the body 104, a temperature maintenance system 108, a first fluid line 110 fluidly connected to the processing volume 106 through the cover 102, a second fluid line 112 fluidly connected to the processing volume 106 through the cover 102, and an inlet of a third fluid line 114 forming a fluid outlet, the third fluid line inlet being fluidly connected to the processing volume 106 through a base 116 of the body 104. The first fluid line 110 is closed with a rupture disc 120 at the end of the first fluid line distal to the cover 102. The rupture disc 120 is configured to break or rupture at a pressure below the pressure at which the coating removal container 100 would fail or would leak due to its overpressure condition. Alternatively, a pressure relief valve may be used in place of the rupture disc 120. The second fluid line 112 is connected to the collection container 199 via a vent valve 122 as shown in FIG. The vent valve 122 can be operated manually or automatically to allow fluid within the processing volume 106 to be released from the processing volume 106, including supergas vapor 124 generated by heating the removal fluid 126 therein in the head space 128 of the coating removal vessel 100. The third fluid line 114 is here configured to provide a fluid drain port to allow the removal fluid in liquid form to drain by gravity from the processing volume 106 of the coating removal vessel 100. Here, the drain valve 130 is connected to the end of the third fluid line 114 on the outside of the base 116 of the main body 104 by a flange connection 132. The drain valve 130 may have manual or automatic operation, or both, and is maintained in a closed condition during operation of the coating removal vessel 100 for removing coating from an assembly 200 schematically shown and disposed in the processing volume 106.

The body 104 is generally configured as a right annular shell having a circumferential container wall 134 extending circumferentially around the processing volume 106, a convex base wall 136 extending from a circumferential end wall 138 below the container wall 134, and a circumferential flange 152 forming an upper end wall 140 of the body 104. A landing surface 142 is provided on an inner surface 144 of the convex base wall 136 facing the processing volume 106 and delimiting a lower portion of the processing volume 106. The landing surface 142 may be a circumferential ledge extending from the inner surface 144 of the convex base wall 136 into the processing volume 106, a series of protrusions extending from the inner surface 144 of the convex base wall 136 into the processing volume 106 and spaced apart from each other along a circumferential path, a separate insert positioned on the inner surface 144 of the convex base wall 136 extending into the processing volume 106, or another structure. The landing surface 142 desirably extends in a direction perpendicular to the direction of gravity, i.e., generally horizontally and parallel to the upper end wall 140, and is configured to allow a component holder such as a cage or basket 146 to be placed thereon without sliding in a direction toward the container wall 134. The basket 146 is used to contain or accommodate one or more components 200 having one or more coatings thereon to be removed from the one or more components in the coating removal container 100 .

A temperature maintenance system 108 is provided to heat the removal fluid 126 in the processing volume 106 to a desired temperature for removal of one or more coatings on the component 200 in the processing volume 106, and to maintain the desired temperature of the removal fluid 126 during the coating removal process. The temperature of the coating removal fluid 126 fluid may be maintained at a single temperature or within a desired temperature range during removal of the coating from the component 200, or different temperatures or temperature ranges may be used at different times during the coating removal process. To provide this capability to the vessel 100, the temperature maintenance system 108 includes a heater 148 surrounding an exterior surface 150 of the vessel wall 104, and a cooling channel 151 extending through a circumferential flange 152 at its opposite first and second ends 154, 156 and extending within the processing volume 106 between the first and second ends and in contact with the removal fluid 126. Here, the cooling channel 151 is configured as a length of tubing through which a fluid coolant may flow, wherein the portion thereof within the processing volume 106 is configured in the shape of a positive annular coil 158 having a coil inner diameter 160. The coil inner diameter 160 is configured to be larger than the maximum width dimension of the basket 146 to allow the basket 146 to be freely placed into and removed from the processing volume, and to maintain a gap between the sides of the basket 146 and the adjacent surrounding surface of the coil 158 to allow removal fluid to exist therebetween. The opposite first and second ends 154, 156 of the cooling channel 151 are fluidly connected to a freezer 162 and a pump 164, schematically shown in FIG. 2, and the freezer 162 and the pump 164 are operatively connected to a system controller 166. A freezer 162 cools the fluid coolant flowing from the second end 156 of the cooling channel 151 and a pump 164 causes the frozen or cooled fluid to flow into the first end 154 of the cooling channel 151. The heater 148 is provided as a heating jacket or other heating system that can surround the exterior surface 150 of the container wall 134. The heater 148 can be provided as a single surrounding element such as a heating blanket, as a plurality of surrounding elements each less than the height of the container wall 134 and stacked one on top of the other, as individual heater segments disposed side by side around the exterior surface 150 of the container wall 134, or a combination thereof. The heater 148 or a separate separate portion thereof, when used, is a resistive heater operatively connected to a power supply 172, which is operatively connected to a system controller 166 (FIG. 2). A thermocouple 174 is positioned in the process volume and operatively connected to the system controller 166 by a thermocouple wire. The system controller 166 uses the thermocouple 174 to monitor the temperature of the removed liquid in the process volume. Although only one thermocouple 174 is shown, multiple such devices may be deployed at different locations within the process volume 106.

As will be further described herein, the heater 148 is used to heat the coating removal fluid 126 to its desired coating removal temperature under the control of a system controller 166 operatively connected to a power supply 172. The fluid flowing through the cooling channel 151 is used to remove heat from the removal fluid. By operation of the system controller 166 to cause cooling and heating of the coating removal fluid during a coating removal process on a component 200 in the processing volume 106, one or more desired set point temperatures or temperature ranges can be achieved and maintained during the coating removal process.

The cover 102 is configured to be releasably secured to a circumferential flange 152 forming an upper end wall 140 of the body 104. When removed, the processing volume 106 is accessible to place the basket 146 and the assembly 200(s) therein into or remove them from the processing volume 106. The fastening of the cover 102 to the circumferential flange 152 may be provided by clamps, bolts or the like, and in this case the cover 102 includes an upper surface 176 thereof protruding from the cover, a lifting hole 178 to which a crane or overhead lift may be connected for lifting the cover 102 off the upper end wall 140 of the body 104, and a plurality of fastener openings 180 extending through the cover and spaced apart from one another along a bolt circle 180. The circumferential flange 152 includes a number of studs 182 corresponding to the number of fastener openings 180, which exit generally perpendicular to the upper end wall 140 of the body 104. Each of the studs is arranged along the bolt circle and is spaced apart from one another along the bolt circle at the same spacing as the spacing of the fastener openings 180. Each screw 182 includes a base portion 184 extending from the upper end wall 140 of the main body 104 into the circumferential flange 152, and a threaded shank portion 186 extending away from the upper end wall 140 of the main body 104 at a position passing through the fastener opening 180 of the cover by a distance greater than the thickness of the cover 102.

To releasably secure the cover 102 to the body 104, the cover 102 is lowered onto the upper end wall 140 of the body 104 so that the shank portions 186 of the different screws 182 are aligned to enter each of the different fastener openings 180. The cover 102 is then further lowered so that the inner cover surface of the cover adjacent its periphery rests against the upper end wall 140 of the body 104. Thus, a portion of the shank portion 186 of each of the screws 182 extends outwardly of the outer cover surface 188 a distance sufficient to place the washer 190 and nut 192 on the protruding portion of each screw 182. By tightening the nut 192 on the threaded shaft, the inner cover surface is pressed against the upper surface of the upper end wall 140. To prevent outward fluid leakage between the inner cover surface and the upper surface of the upper end wall 140, a sealing groove 194 extends into the upper end wall 140 at a location inward of the bolt circle of the stud 182, and also extends circumferentially around and into the upper end wall 140. A sealing ring 196 is positioned in the sealing groove 194 so that the sealing ring 196 contacts the base 198 of the sealing groove 194 over the circumferential extension of the sealing groove. The sealing ring 196 and the sealing groove 194 are sized so that when the sealing ring contacts the base 198 of the sealing groove 194, the sealing ring 196 extends out of the sealing groove 194 in its free, uncompressed state. As the cover 102 is lowered onto the upper end wall 140, the inner cover surface engages this protruding portion of the sealing ring 196, and as the cover 102 is further lowered in the direction of the upper end wall 140, the sealing ring 196 becomes compressed to maintain contact between the sealing ring 196 and the base 198 of the sealing groove 194, and to maintain contact between the inner cover surface and the sealing ring 196. This seal of the interface area between the inner cover surface and the upper end wall 140 serves to prevent leakage of fluid through the interface surfaces thereof.

During the use of the removal container 100 to remove unwanted or undesirable coatings from the assembly 200, the assembly 200, or a plurality of assemblies, is placed into the basket 146, and the basket 146 with the assembly 200 therein is lowered into the removal fluid 126 present in the processing volume 106. The cover 102 is then lowered onto the upper end wall 140 and secured to the upper end wall 140 by placing a gasket 190 over each protrusion of each stud 182 and screwing a nut 192 onto the protrusion of each stud 182. The nut 192 is then tightened to secure each of the gaskets against the outer cover surface 188 and thereby secure the cover 102 to the body 104.

Once the cover 102 is secured to the body 104, the system controller 166 activates the power supply 172 to supply power to the heater 148 and activates the pump 164 to begin pumping the cooling fluid through the cooling channel 151. The cooling fluid may be pumped during, after, or during and after the heating of the removal fluid 126. When the desired temperature of the removal fluid is reached, the system controller 166 controls the freezer 162 to appropriately cool the cooling fluid that has absorbed heat while flowing through the cooling channel 151, and at the same time controls the operation of the heater 148 by varying the voltage, current, or both supplied to the heater 148 by the power supply 172 to maintain the desired temperature of the removal fluid 126.

When the basket 146 with the component 200 from which the coating is to be removed is placed into the removal fluid 126 and the cover 102 is secured to the upper end wall 140, the removal fluid and any air disposed between the removal fluid 126 and the cover 102 are under or exposed to atmospheric pressure. During the subsequent heating of the removal fluid to the desired process temperature for removing the coating on the component 200, the vent valve 122 and the drain valve 130 are maintained in the closed position and thus prevent the liquid from flowing out of the processing volume 106. Because the process volume 106 is sealed by the vent valve 122 and drain valve 130 positions and by the cover 102 connected to the upper end wall 140, vapor 124 will gradually form as the removal fluid 126 is heated. Because the vapor has a lower density than the removal fluid 126 in a liquid state and surrounding the component 200 to be processed, the vapor 124 will accumulate in the head space 128 above the liquid removal fluid 126. As this vapor 124 continues to develop, the pressure in the head space 128 increases to a level greater than the surrounding ambient atmospheric pressure. This pressure causes the vapor pressure of the liquid removal fluid to become equal to the increased pressure in the headspace, and thus the coating removal fluid, now at a pressure greater than atmospheric pressure, is at a pressure within the processing volume 106 having a higher boiling point than its boiling point at the ambient atmospheric pressure immediately surrounding the vessel 100. Thus, the removal fluid 126 in liquid form can be heated to a temperature well above its boiling point at the surrounding ambient atmospheric pressure because the vapor 124 that is gradually formed from the liquid removal fluid 126 will rise into the headspace 128 and cause the pressure within the processing volume 106 to increase further.

The etching or removal rate of the removal fluid 126 surrounding the component 200 increases as the removal fluid is heated to the desired processing temperature to remove the coating from the component 200. This increase allows the removal fluid to remove coatings that were previously removed using shot blasting or sand blasting or other physical removal techniques. Here, the chemistry of the removal fluid is selected to be relatively unreactive to the material of the component underlying the coating to be removed from the component, but sufficiently reactive to allow the coating to be removed from the component within a commercially reasonable period of time. When the coating is removed from the component, the cleaning process terminates, i.e., reaches the end point, after which the removal fluid is passively or actively cooled and the head space 128 is vented to atmospheric pressure via the second fluid line 112 and the vent valve 122.

Many process endpoint examples may be used to determine when to vent the processing volume 106 of the removal vessel 100 through the second fluid line 112 by moving the vent valve 122 to the open position. For example, the coating removal process time, temperature, etch rate, and thickness of the coating to be removed may be considered. The amount of time the part has been exposed to the elevated temperature removal fluid and the ramp time between the initial removal fluid temperature to the higher process temperature, and the ramp time from the higher process temperature to a temperature at which significant vapor is not gradually formed at atmospheric pressure are selected based on the thickness of the coating to be removed. Because the removal fluid will still react with the coating as the temperature is rising to the process temperature or falling to the open temperature of the removal fluid, the technician must take this into consideration to decide how quickly to ramp up and down the temperature, and how long to maintain the component 200 and the removal fluid surrounding the component 200 in a liquid state at a high temperature.

To remove the assembly 200 from the coating removal container 100, the system controller 166 controls the freezer 162 to continue cooling the cooling fluid that has absorbed heat while flowing through the cooling channel 151, and simultaneously controls the power supply 172 to stop supplying power to the heater 148. The system controller 166 may increase the flow rate of the coolant through the pump 164, increase the heat removal from the cooling fluid by the freezer 162 to reduce the temperature of the cooling fluid entering the coil 158, or both, to increase the heat removal from the removal fluid 126 and reduce the time until the removal fluid 126 is cooled to a temperature sufficient to allow the coating removal container to be drained and opened. When the temperature of the removal fluid 126 is below its boiling point at atmospheric pressure, the vent valve 122 can be opened to vent vapor from the headspace and equalize the pressure on or at the opposing outer cover surface 188 and inner cover surface. Venting can be performed at any time, before or after the temperature of the removal fluid 126 has dropped below its boiling point at atmospheric pressure. However, venting when the temperature of the removal fluid 126 is at or above its boiling point at atmospheric pressure can cause immediate boiling of the removal fluid unless the vent line is pressurized. Once the pressure in the headspace 128 equals the ambient pressure, the nut 192 is loosened from the stud 182, the washer 190 is removed, and the cover 102 is lifted off the body to allow access to the basket 146. The basket 146 is removed and replaced with an additional basket having one or more components 200 therein to perform the same coating material removal on the one or more additional components 200.

The removal fluid chemistry may be changed by removing the coating removal fluid 126 by opening the drain valve 130 and allowing the removal fluid 126 to drain from the treatment volume 106. Thereafter, the inner walls of the body and cover are rinsed with, for example, a buffer, followed by one or more rinses with deionized water, and the drain valve 130 is moved to the closed position. With the cover 102 off the body 104 and the drain valve 130 in the closed position, new removal chemistry is poured into the treatment volume 106. Alternatively, the third fluid conduit 193 may be used to flow new removal fluid into the treatment volume 106. Here, a series of valves and at least one T-connection on the drain line downstream of the inlet of the third fluid line 114 can be configured to direct the spent removal fluid to a collection facility such as a collection container 199, or to allow fresh or different removal fluid to flow into the inlet of the third fluid line 114 and from the removal fluid reservoir 197 into the processing volume 106. For example, as shown in FIG. 2 , the drain valve 130 can be closed and the refill valve 191 opened, thereby allowing the removal fluid 126 in the removal fluid reservoir 197 to be transferred into the processing volume 106 by passing through the third fluid line 114. The refill valve 191 is then closed and the above-described cycle of operations for performing removal of the container 100 from the assembly is performed one or more times for the one or more assemblies 200 .

In another aspect, the component itself may be or provide a pressure vessel for performing coating removal from its interior at high temperatures. Here, for example, a process chamber itself is cleaned, wherein the interior walls of the chamber have been coated during processing of parts therein and the coating must be removed. Other components such as gas manifolds and process piping through which gases flow during use and which may form deposits on the interior surfaces of the manifold or piping may also be used in this manner to form an internal sealed environment for high removal fluid temperature removal of coatings, such as a temperature of at least 50% of the boiling point of the removal fluid at the local ambient atmospheric pressure, and above the boiling point of the removal fluid at the local ambient atmospheric pressure. Where the content volume of the assembly must have a deposited coating removed therefrom, the assembly may be used to provide a pressure vessel for containing a heat removal fluid heated to above its boiling point at atmospheric pressure if the content volume can be sealed and safely pressurized above the surrounding ambient pressure.

FIG. 4 schematically illustrates this assembly, where a manifold 222 is provided wherein in use, in a process environment, gases enter the interior of the manifold via a sealable threaded connection and exit the interior of the manifold via a sealable threaded connection. Here, the manifold 222 includes a hollow body 202 which may include internal baffles, internal tortuous paths, or other internal structures configured to enable two gas streams to mix therein (not shown). The first manifold inlet 204 and the second manifold inlet 206 include fluid conduits in fluid communication with the internal volume of the manifold 222, and the manifold 222 fluid outlet 208 is likewise in fluid communication with the internal volume of the manifold 222. Here, the manifold 222 itself provides a sealed pressure vessel for cleaning its internal surfaces. To enable this, the manifold is encased in an assembly heater 210 surrounding its outer surface, or alternatively placed in a furnace to heat the manifold 222 and the coating removal fluid therein to a temperature above the boiling point of the removal fluid 126 at the ambient atmospheric pressure.

Similar to the coating removal container 100, here, a rupture disk 212 is connected to and seals the second manifold inlet 206, and a pressure relief valve 214 is fluidly connected to the first manifold inlet 204 in a relief fluid line 216. Likewise, a manifold drain valve 218 is fluidly connected to the outlet 208 in a drain line 220.

To perform material removal on the interior surface of the manifold 222 or another component having an interior surface to be cleaned, the removal fluid is flowed to the interior of the manifold through the first manifold inlet 204, or alternatively, through the outlet 208, after which the pressure relief valve 214 is closed and the component heater 210 is powered and generates heat to increase the temperature of the removal fluid. Because the manifold drain valve 218 is likewise closed and the rupture disk 212 seals the second inlet 206, as the removal fluid is heated and develops its vapor or gas, the vapor or gas is trapped within the content volume of the manifold, and the pressure within the manifold 222 increases to a temperature at which the removal fluid 126 will evaporate or boil excessively at atmospheric pressure. Manifold 222 is maintained at this high temperature for a predetermined period of time to ensure complete removal of the undesirable coating on its interior surface, and then power to assembly heater 210 is removed and the manifold is allowed to return to a lower temperature. Pressure relief valve 214 is then moved to its open position, and manifold drain valve 218 is likewise moved to its open position, and the removal fluid is drained to a collection container such as that of FIG. 2 . To remove the residual removal fluid 126 therein, the interior of manifold 222 is then flushed with a buffer solution and then with deionized water to remove any residual removal fluid from its interior.

Referring now to FIG. 5 , an alternative configuration of a coating removal system is shown in which one or more coating removal containers 300 may be disposed inside a sealable containment container 302 , and the containment container is pressurized to enable ultra-large-scale wet or liquid etching of components in the coating removal container 300 . Here, in contrast to the removal vessel 100 of FIGS. 1-4 herein, the coating removal vessel 300 need not be independently pressurized relative to its surrounding environment, i.e., independently heated relative to the surrounding internal containment volume 304 of the containment vessel 302, and the coating removal vessel 300 is instead filled with a pressurized coating removal fluid while in the containment vessel 302 to allow or enable the pressure within the coating removal vessel 300 positioned therein to be maintained above the local atmospheric environment pressure surrounding the containment vessel 302. Here, the containment vessel 302 itself may be heated so as to maintain the fluid therein at or above the desired temperature of the coating removal fluid in the coating removal chamber 300. In this manner, the coating removal container 300 need not be constructed of a material having sufficient strength to withstand the pressure differential between its interior and exterior. Thus, the coating removal container can be constructed of a material selected for its resistance to reaction with the removal chemicals used to remove the coating from the parts and for its resistance to reaction with the reaction products of the removal process, and for facilitating cleaning of its surface.

The containment vessel 302 is here a pressure vessel having a generally annular main body shell 301 formed of, for example, stainless steel, having at one end thereof a hemispherical cap 303 welded to one generally annular end wall of the main body shell 303, and a door 320 hingedly connected to the opposite end of the main body shell 303. The door 320 can be opened to provide access to the containment volume 304 through the resulting opening 306, and closed and latched to allow the inner containment volume 304 to maintain a pressure higher than the ambient pressure. A latch is provided to tightly secure the door 320 relative to the open end 306 of the containment vessel, and one or more suitable seals are provided to create a pressure-resistant seal between the door 320 and the annular wall 307 of the containment vessel surrounding the open end 306. Alternatively, screws, washers and nuts may be used to secure the perimeter of the door 320 to the annular end wall 307 of the main housing 301.

In contrast to the configurations for removing coating from parts of FIGS. 1 to 4 herein, here, one or more parts from which the coating is to be removed are placed in one or more coating removal containers 300 at a location outside of a containment container 302. For example, the coating removal container 300 may be positioned on a wet bench and the parts from which the coating is to be removed are loaded therein on the wet bench. The coating removal container 300 may be configured to include a body that generally surrounds a processing space and has an opening thereof that is covered by a cover. Thereafter, the coating removal container 300 or container 300 is loaded into the open end 306 of the containment container 302. A shelf or base 310 is supported off the lower portion of the main housing 301 by a spacer 311 and the base 310 supports the coating removal container or container 300 thereon. The internal volume is fluidly connected to the volume of heated and pressurized coating removal fluid in the pressure vessel 400 so that the coating removal container 300 is selectively filled with fluid at or near the desired processing pressure and processing temperature of the coating removal fluid.

In one aspect thereof, the coating removal container(s) 300 are loaded with one or more components from which the coating is to be removed and are placed into a containment vessel without a coating removal fluid positioned therein. In this aspect, after the coating removal container(s) 300 are placed into the containment vessel 302, the coating removal fluid is transferred from the separation pressure vessel 400 into the coating removal container 300. After the coating removal container(s) 300 are placed therein and the containment volume 304 opening 306 is sealed with the door 320, the pressure of the containment vessel 302 is increased to a pressure greater than the ambient pressure surrounding the containment vessel 302. Each coating removal container 300 here includes a vent opening 294 extending through its cover so that the pressure within the containment volume 304 is connected to the internal volume of the coating removal container and thereby the pressure of the coating removal fluid to be loaded therein is maintained to or at the same pressure as the containment volume 304.

The pressure in the containment volume 304 can be gradually increased in one or more steps to be greater than or equal to the pressure that will be formed or exists in the coating removal container 300 positioned therein. In another aspect, the pressure in the coating removal volume 298 of the coating removal container 300 can be monitored, and the pressure in the containment volume 304 is increased or decreased based on the pressure in the coating removal volume 298 to adjust the pressure of the coating removal fluid in the coating removal volume 298. In the aspect of the material removal system shown in Figures 5-7, the fluid under pressure within the containment volume is maintained at an elevated temperature to supply heat to the coating material fluid within the coating removal vessel 300. After processing the assembly to remove coating from one or more parts in the coating removal vessel 300, as the temperature of the removal fluid decreases, the pressure within the containment volume 304 may be reduced, but maintained above or equal to that temperature required to prevent boiling of the coating removal fluid in the coating removal volume 298. The pressure within the containment vessel 302 is brought to the pressure of its surrounding environment before the door 320 of the containment vessel 302 is opened. In this aspect, coating removal container(s) 300 may be loaded with parts and placed into containment container 302 during multiple part coating removal processes, i.e., reused, and removed from the containment container for loading parts into or unloading parts from the coating removal container(s).

The coating removal system of FIG. 5 generally includes a containment chamber or vessel 302 having an internal containment volume 304, one or more of the removable coating removal vessels 300 replaceably positioned therein, and a facility connected to at least one of the containment vessel 302 or the removable coating removal vessel 300 and configured to control the pressure and temperature of the coating removal process. In FIG. 5 , the facility is connected between the system controller 324 and the containment vessel 302 and includes one or more containment vessel pressure sensors 326, one or more containment vessel temperature sensors 328, and a containment vessel heater control line 330. The one or more containment vessel pressure sensors 326 and the one or more containment vessel temperature sensors 328 are configured to provide electrical signals indicative of the pressure and temperature within the containment volume 304. However, as described above, the one or more containment vessel pressure sensors 326 and the one or more containment vessel temperature sensors 328 may be connected to directly monitor the pressure and temperature of the interior volume of the coating removal vessel(s) 300. The controller 324 is configured to receive these signals and send containment vessel heater control signals to the containment vessel heater power supply 332, which is connected to one or more containment vessel heaters 360 ( FIG. 6 ) disposed about the exterior surface of the containment vessel. The controller 324 controls the power output of the containment vessel heater power supply 332 to the containment vessel heater 360 based on a desired temperature set point for the walls of the containment volume 304 or containment vessel 302.

Here, to pressurize the containment volume 302, a separate pump 434 or multiple pumps may be provided and the pump is connected to a source of fluid to pump the fluid into the containment vessel 302 to increase the pressure or the containment volume. In another aspect, the containment volume 304 may be maintained at atmospheric pressure. In another aspect, the same pressure vessel 400 used to fill the coating removal chamber(s) 300 with the coating removal fluid may be used to supply the coating removal fluid to the containment volume 304 of the containment vessel. In FIG. 5 , the pressure vessel 400 supplies the coating removal fluid as a liquid directly to the coating removal vessel(s) 300. The pressure vessel 400 includes an outer circumferential wall 404 and upper and lower hemispherical caps 406, 408 that sealingly enclose a pressurizable volume 402. A pump 410 is provided in communication with the inner pressurizable volume 402 of the pressure vessel via a pump line 412. The pump 410 is connected to a fluid supply line 412 to allow fluid to be pumped into the pressurizable volume 402. The fluid supply line 412 is connected to a source of fluid to be used as a coating removal fluid that is supplied to the coating removal chamber(s) 300 for performing a coating removal process. One or more pressure vessel temperature sensors 416 and pressure sensor 414 are provided to supply signals indicative of the pressure and temperature of the pressurizable volume 402, or the wall temperature of the pressure vessel 400, to the controller 324. The controller 324 is configured to send a pressure vessel heater power supply signal to a pressure vessel heater power supply 418, which supplies power to one or more jacket heaters 420 on the exterior of the pressure vessel 400.

The pressurizable volume 402 of the pressure vessel 400 is fluidly connected to the interior volume of the coating removal chamber(s) 300 to enable the supply of pressurized fluid therein, and the removal of pressurized fluid from the coating removal vessel(s) 300. In FIG. 5 , a pressurized fluid fill line 422 extends from a lower portion of the pressurizable volume 402, through a valve 424, through an upper portion of the containment vessel 302 and into an upper interior portion of the coating removal chamber 300. In the case where multiple coating removal chambers 300 are processed together in a single containment volume, fill line 422 is branched to simultaneously fill multiple coating removal container(s) 300 with coating removal fluid. A fluid return line 430 extends from a lower portion of the coating removal container(s) 300 through a return valve 428, through the lower wall of the containment volume 304, and thence to an upper portion of the pressurizable volume 420.

In operation of the coating removal system of FIG. 5 , with the containment vessel 302 at a local ambient pressure 322, in other words, at local atmospheric pressure, the door 320 of the containment vessel 302 is opened, and the coating removal vessel 300 that has been processed in the high pressure and high temperature environment of the containment volume 304 but has been cleaned or substantially cleaned of the coating removal fluid is removed from the containment volume 304 through the opening 306 after the door 320 has been opened. The parts therein are removed for further processing and new parts from which the coating has been removed are loaded into the same or a different one of the coating removal containers 300, after which the coating removal container(s) 300 are loaded through the opening 306 and placed on the base 310 in the containment container 302. The door 320 is then closed and latched to seal and isolate the containment volume 304 of the containment container 302 from the surrounding environment 322.

The pressure vessel 400 is filled or nearly filled with the coating removal fluid 432 to be transferred or flowed to the containment vessel 302 prior to loading of the coating removal vessel 300 into the containment volume. Here, the pressure vessel 400 may be operated to maintain a desired fluid pressure and temperature of the coating removal fluid 432 therein as the parts or assemblies and the coating removal vessel 300 are removed and loaded into the containment vessel. For example, the temperature of the coating removal fluid 432 in the pressure vessel 400 can be maintained at a temperature above the temperature at which it would boil at atmospheric or ambient pressure 322, and the pump 410 is used to increase the coating removal fluid 432 in a liquid state to flow into the pressurizable volume 402 and increase the pressure of the fluid in the pressurizable volume 402 to approximately greater than one atmosphere to ten or more atmospheres. Thus, the coating removal fluid can be maintained at a desired process pressure and temperature for use in removing coatings from assemblies for immediate delivery to the coating removal vessel(s) 300 in the containment vessel 302 once the door 320 is closed and the opening is sealed. The use of the pressure vessel 400 to maintain the coating removal fluid at a temperature at or near the removal process temperature and to flow that fluid at or near the coating removal process pressure and temperature into the coating removal vessel(s) 300 reduces the time required to process parts in the coating removal vessel 300 because the need to heat the fluid in situ using a heating blanket or other type of heater can be eliminated.

Once the coating removal container(s) 300 having the parts or assemblies 200 from which the coating is to be removed are loaded into the containment container 302, and the door 320 is closed and sealed, the valve 424 is opened to allow the coating removal fluid 432 to flow from the pressure vessel 432 to the coating removal container 300 in the containment volume 304. The higher pressure in the pressurized volume 402 may cause the coating removal fluid 432 to flow into the coating removal container 300. Here, the cover of the coating removal container 300 includes a vent opening 294, whereby the pressure in the containment volume 304 is transmitted to the content volume of the coating removal container 300. Thus, the coating removal vessel 300 can be filled solely by the pressure differential between the higher pressure vessel 400 and the lower pressure containment volume 304 when the pressure in the containment volume 304 is maintained at a pressure slightly lower than that of the coating removal fluid 432 but at a pressure at which the coating removal fluid 432 will not boil at its entry temperature into the coating removal vessel.

The containment volume pressure relief valve 362 is fluidly coupled to the containment volume 304 so that pressure in the containment volume 304 can be vented to prevent back pressure therein that prevents a sufficient amount of pressurized fluid from covering the components in the coating removal chamber(s) 300. A pump 364 is fluidly coupled to the containment volume 304 to pressurize the containment volume 304, and the containment volume pressure relief valve 362 is configured to open at a pressure greater than the process pressure of the parts or components in the coating removal chamber 300. By using the pump 364 and the containment volume pressure relief valve 362 to control the pressure in the containment volume 304, and thus the pressure differential between the containment volume 304 and the pressure of the coating removal fluid 432 entering the coating removal vessel 300, the flow rate of the coating removal fluid into the coating removal vessel(s) 300 is controlled. The amount of coating removal fluid distributed to each tank can be controlled or determined by a fluid sensor on the inside wall of the coating removal vessel(s), a flow meter on the fill line(s) 422, or other methods. The pump 410 can be operated during the filling of the coating removal container(s) 300 to maintain the pressure of the coating removal fluid 432 at or above the pressure required to prevent boiling of the fluid as it enters the coating removal container 300, and if the containment volume pressure relief valve 362 is opened to vent the containment volume 304, maintain that pressure above the pressure in the containment volume 304. Once the coating removal vessel(s) 300 are filled with hot coating removal fluid at a temperature greater than that at which it would boil at atmospheric pressure and at a pressure sufficient to prevent it from boiling in the coating removal vessel 304, the fill valve 424 is closed and the coating removal process is performed. If desired, heat from the fluid in the containment volume that rises to or exceeds the process temperature is transferred through the walls of the coating removal vessel 300 to heat the coating removal fluid therein, or vice versa. The one or more containment vessel heaters 360 preferably maintain the fluid in the containment vessel 302 at or above the desired process temperature to reduce heat loss of the coating removal fluid from the coating removal vessel 300. If the pressure in the containment volume 304 drops, the fill pump 434 can be activated to provide additional fluid to the containment volume 304 to maintain the desired process pressure in the coating removal vessel(s) 300 fluidly coupled to the containment volume. The controller 324 is electrically wired to the fill valve 424 and the return valve 428 to control their opening and closing with electrical control signals from the controller 324.

The pressure vessel 400 coupled to the coating removal vessel(s) 300 allows the coating removal fluid 432 to be recovered for reuse. Thus, as the process of removing coating from parts in the coating removal vessel(s) approaches its end, the pressure in the pressure vessel 400 decreases below that in the containment vessel 302. Once the coating removal process is complete, the return valve 428 is opened by the controller 324 and the higher pressure pressurized fluid in the coating removal vessel 300 flows into the lower pressure pressurizable volume 402 of the pressure vessel 400. A pressure vessel relief valve 423 is provided to allow the headspace above the returning pressurized fluid to vent and prevent back pressure from building up, thereby preventing refilling of the pressure vessel 400 with the pressurizable fluid 432. As the pressurized fluid returns to the pressure vessel 400, a pump 434 may be used to selectively deliver a fluid, such as ambient air, into the containment vessel to maintain sufficient pressure therein to maintain the fluid therein greater than that in the pressure vessel 400. At the same time, power to the containment vessel heater 360 is removed, thereby allowing the containment vessel to begin cooling to a temperature at which the containment vessel will be safe for opening the door 320. Once the pressurized fluid is returned to the pressure vessel 400, under operation of the controller 324, the vent valve 428 is switched to a closed position to isolate the pressurized volume 402 and the containment volume 304 from each other, and the containment vessel 302 is vented through the containment vessel pressure relief valve 362 or another valve. Similar to the aspects of Figures 1-4 herein, cooling coils may be provided to be immersed in the pressurized fluid in the pressure vessel 400 to more accurately control the temperature of the pressurized fluid. The coils may also be used to cool the walls of the containment vessel 302 after the pressurized fluid is removed. Other cooling of the containment vessel 302 may be used, such as one or more blowers to blow air over the exterior of the containment vessel. The coating removal fluid returned to the pressure vessel 400 is heated and pressurized in the pressure vessel if necessary, and maintained at that pressure and temperature until the containment vessel 302 is reloaded with a new coating removal vessel(s) 300 for processing the assembly 200 therein to remove the coating therefrom. Although a single pressure vessel 400 is shown connected to a single containment vessel 302, multiple containment vessels 302 may be connected to a single pressure vessel 400. In this case, the pressure vessel 400 may be refilled with coating removal fluid after filling the coating removal vessel(s) 300 in the first containment vessel 302 to heat and pressurize the pressurized fluid to fill the coating removal vessel(s) 300 in another containment vessel. Alternatively, the pressure vessel pressurization volume 402 may be sized to hold sufficient pressurized fluid to fill the coating removal vessels 300 in two or more containment vessels. Additionally, two or more pressure vessels 400 may be connected to a single containment vessel to enable one of the pressure vessels to be at process temperature and pressure while the fluid in the coating removal vessel(s) 300 is discharged into another pressure vessel 400. Additionally, different ones of the pressure vessels 400 may contain different types of coating removal fluids.

In this aspect of the coating removal system, the coating removal container 300 is configured substantially the same as the coating removal container 100 of Figures 1-4 herein, except that the coating removal container 300 is not pressure resistant. In other words, the coating removal containers include one or more vent openings 294 extending through the wall of the coating removal container to allow fluid, or at least fluid pressure, to be transmitted between the coating removal volume 298 and the surrounding enclosure volume 304 of the coating removal container. This allows the pressure within the coating removal container 300 to be the same pressure as that in the containment volume 304, so that the material of the coating removal container does not need to be a high-strength material that can maintain a higher pressure within the coating removal volume 298 than on the outside of the coating removal container 300, thereby allowing the user of the system greater freedom in the choice of materials used in the coating removal container 300. Although pressurization of the containment volume is described herein as using air or a gas, a liquid such as deionized water or the coating removal fluid 432 may be used to pressurize the containment volume 304. Referring now to FIG. 8 , yet another aspect of a coating removal system is shown, where the coating removal vessel 300 is configured to be heated and simultaneously cooled to maintain a desired temperature of the coating removal volume 298 and any removal fluid therein, as in the case of the coating removal vessel 100. Here, the lower portion of the coating removal vessel 300 is configured as a fluid reservoir, and a cage, platform, or other containment structure, such as the cage of FIG. 2 , is positioned above the reservoir so that a fluid volume of coating fluid at room temperature (approximately 20 degrees Celsius) is positioned below the part from which the coating is to be removed in the coating removal vessel 300.

Referring to Fig. 8, a modification of the coating removal system of Figs. 5-7 is shown, wherein the containment vessel of Fig. 8 is used, but schematically shown in Fig. 8, the coating removal vessel(s) of Figs. 5-7 are used, but here are individually heated, and thus do not require a pressure vessel 400. Here, the coating removal vessel 300 is contained within the containment volume of the containment vessel, but the individual coating removal vessels are individually heated to gradually form vapor of the coating removal fluid to pressurize the individual coating removal vessels 300. Similar to the coating removal vessel 100 of FIGS. 1-4 , this coating removal vessel 300 includes a temperature maintenance system 108 ( FIG. 1 ) including a heater 148 surrounding an exterior surface 150 of the coating removal vessel wall 104, and a cooling channel 151 extending through a circumferential flange 152 at its opposite first and second ends 154, 156 and extending within the coating removal volume 298 between the first and second ends and in contact with the removal fluid 126. Here, the cooling channel 151 is configured as a length of tubing through which a fluid coolant can flow, wherein the portion thereof within the processing volume 106 is configured in the shape of a positive annular coil. The inner diameter of the coil is configured to be larger than the maximum width dimension of the basket 146 (FIG. 1) to allow the basket 146 to be freely placed into and removed from the coating removal volume 298, and to maintain a gap between the sides of the basket 146 and the adjacent surrounding surface of the coil 158 to allow removal fluid to exist therebetween. The opposing first and second ends 154, 156 of the cooling channel 151 are fluidly connected to the freezer 162 and pump 164 schematically shown in FIG. 5 by fluid quick connects or other types of connectors, and the freezer 162 and pump 164 are operatively connected to the system controller 166. Here, a first cooling fluid line 312 extends through the wall of the containment vessel 302 to be connected between the first end 154 of the cooling channel 151 and the cooling fluid pump 164, and a second fluid line 314 extends between the second end 156 of the cooling channel 151 and the freezer 162. The freezer 162 is fluidly connected to the coolant pump 164 so that a continuous fluid loop for pumping to the cooling fluid is created. The freezer 162 cools the fluid coolant flowing from the second end 156 of the cooling channel 151, and the pump causes the frozen or cooled fluid to flow into the first end 154 of the cooling channel 151. The first fluid line 312 and the second fluid line 314 may be bifurcated such that a first portion thereof extends to a wall of the containment vessel and a fluid connector positioned to allow fluid to pass through the wall of the containment vessel, and a second portion thereof leads from the fluid connector to an opposite end of the cold channel 151. Here, the second portion may be flexible and include a second pipe fitting at its cold channel 151 end to connect to the cold channel. Flexibility allows for easier connection of the first fluid line 312 and the second fluid line 314 to the cold channel.

The heater 148 for heating the coating removal vessel 300, and thus the part(s) and coating removal fluid therein, is provided as a heating jacket or other heating system that may surround the exterior surface 150 of the vessel wall 134 of the coating removal vessel 300. The heater may be provided as a single surrounding element, as a plurality of surrounding elements each having a height less than the height of the vessel wall 134 and stacked one upon another, as individual heater segments disposed side by side around the exterior surface 150 of the vessel wall 134 as a vertically extending heater strip, or a combination thereof. Each coating removal container 300, or the heater 148 on a separate separate portion thereof, when used, is operatively connected to a power supply 172 by wiring 173, which is operatively connected to the system controller 166. A plurality of wirings, each dedicated to a heater 148 or heaters associated with one coating removal chamber, may be used, or the wiring 173 may include a main cable from which individual wires or cables extend to individual heaters 148 associated with each coating removal container 300. A variable controller 351 is disposed between each of the coating removal containers 300 and the power supply 172 to adjust the power supplied to each of the heaters 148. Alternatively, a plurality of power supplies 172 allow a power supply to be dedicated to the heater(s) 148 associated with each individual coating removal container 300. A thermocouple 174 is positioned in the coating removal volume 298 of each coating removal container 300 and is operatively connected to the system controller 166 by a thermocouple wire. The system controller 166 uses the thermocouple 174 to monitor the temperature of the removal liquid in the coating removal volume 298. Although only one thermocouple is shown, multiple such devices may be deployed at different locations within the coating removal volume 298. By varying the power supplied to the heater 148 and the flow of cooling fluid to the cooling channel 151 of each coating removal container 300, the temperature of the coating removal fluid can be controlled.

The containment vessel 304 is configured as a pressurizable volume capable of maintaining a seal and structural integrity at a pressure greater than the pressure surrounding the containment vessel, which in use is typically the local ambient atmospheric pressure. During operation of a process for removing a coating from a part(s), the containment vessel 302 is actively pumped with a relatively non-reactive gas such as nitrogen or air, or an inert gas such as argon, to increase the pressure therein, i.e., in its containment volume 304. The containment volume 304 may be maintained at a pressure greater than, for example, 1.1 times the ambient pressure, greater than 1 to 1.5 times the ambient pressure, greater than 1 to 2 times the ambient pressure, or greater, such as ten times greater than the ambient pressure. The containment vessel 302 and the door 320 are assembled from stainless steel, which provides sufficient strength to withstand the pressure differential between the containment volume 304 and the ambient pressure.

The containment volume 302 is connected to a gas source or fluid source, such as a supply of nitrogen or a gas that is inert or relatively non-reactive with the coating removal fluid, via a gas supply 336 coupled to a pump 334. The pump is configured to pump gas into the containment volume to achieve a pressure greater than the atmospheric pressure surrounding the containment vessel 302. The pump 334 may be a compressor. A fluid removal line 338 is fluidly coupled to the containment volume to draw fluid from the containment volume 304. Here, fluid removal line 338 is connected to valve 340, which can be changed to change the fluid conduction through valve 340, and a foreline 341 extends from the valve to a recovery container 342, which is configured to intercept the coating removal fluid that condenses and flows into it. The recovery container is connected to a vacuum source 344 via a valve 346, which can be a facility vacuum system of a vacuum pump.

In one method of using the coating removal container 300, one or more parts having coating to be removed therefrom are positioned in the coating removal container 300. In one aspect, the coating removal container 300 is removed from the containment container 302 through the opening 306 when the door 320 is open, and the one or more parts positioned in the coating removal container are replaced with the parts or assemblies from which the coating is to be removed. The coating removal container 300 is then positioned on a base or platform 310 and connected to the power supply 172, the controller 166, and the first and second fluid supply lines 312, 314 are connected to the first and second ends 154, 156 of the cooling channel 151. The door 320 is then closed to seal the containment volume 304 from the surrounding environment 322. In another aspect, the coating removal container 300 is maintained within the containment volume 304, and the parts or assemblies from which the coating is to be removed are transferred through the opening 306 and placed in the coating removal container 300 on the platform 310. Thereafter, the door 320 is closed to seal the containment volume 304 from the surrounding environment 322. The pump 334 is then operated to increase the pressure in the containment volume 304 by pumping gas into the containment volume 304. The pump 334 may be operated to pump the containment volume 304 to a predetermined pressure greater than that of the surrounding environment 322, or the pump may be operated to simply maintain the pressure in the containment volume 304 at or greater than the pressure in the coating removal vessel (300). The heater(s) 148 are powered to heat the coating removal fluid to a desired temperature greater than its boiling point at atmospheric pressure. As the temperature in the coating removal vessel(s) 300 increases, vapor of the coating removal fluid is gradually formed. In one aspect, the coating removal container 300 includes one or more vent openings 294 so that the pressure of the containment container is transmitted into the coating removal container 300. In this aspect, the pressure within the containment volume 304 can be maintained above the pressure at which significant vapor is developed from the coating removal fluid, or maintained below the pressure at which the coating removal will begin to boil based on the temperature of the coating removal fluid. In another aspect, the vent opening 294 includes a pressure relief valve connected thereto, which can be connected to a controller and operated by the controller to open the vent passage when the pressure in the coating removal container 300 reaches an undesirable pressure. If necessary, the pressure in the containment vessel is controlled using the pump 334 and vacuum system 334 to maintain the containment volume pressure at a sufficiently high level to prevent the coating removal fluid from boiling when the coating removal fluid is heated to the higher temperatures used in the coating removal process. In addition, once the desired containment volume 304 pressure is achieved, the valve 350 on the fluid inlet to the containment volume 304 from the pump 334 can be closed and the pump disengaged, with the valve 340 likewise closed. If there is a pressure drop in the containment volume 334, the pump 334 can be restarted by starting the pump 334 after opening the valve 350.

After an appropriate amount of time has elapsed to ensure that the coating has been removed from the part, pump 334, if not already disengaged and isolated from the containment volume, is disengaged and isolated from the containment volume 304 by closing valve 350, and valve 340 opens to allow the containment vessel to vent to vacuum line 344, which may be just below the ambient pressure of the containment vessel 302. Then, when the containment volume has regained the pressure of the environment 322 surrounding the containment vessel 302, the door 320 is opened so that the parts, or the coating removal container with the parts therein, can be removed from the containment vessel and another collection of parts returned to the containment volume and within the coating removal container(s) to be processed.

Although the containment vessel 302 is described herein as being pressurized with a gas, the containment volume may also be pressurized with a liquid.

Table 1 sets forth exemplary chemistries useful for removing exemplary coatings from exemplary underlying materials. The coatings in Table 1 have previously been deemed impossible or impractical to remove using a chemical removal process, i.e., a wet etching process. Thus, blasting or shot blasting to remove the coatings, and subsequent inherent removal of the material of the underlying component 200, are the only processes used to remove such coatings. Therefore, the useful life of the underlying component 200 is limited by the coating removal processes because critical dimensions of such components 200 will be produced from the manufacturer's specifications of the component after one or more coating removal processes. Table 1 The material underlying the component that forms the coating to be removed The coating to be removed Removal of fluid chemicals Removal fluid temperature Process time to remove coating Titanium Alumina KOH/ _H2O 150-300C 1-48 hours Titanium Ethylene oxide KOH/ _H2O 150-300C 1-48 hours Titanium Alumina NaOH/H ₂ O 150-300C 1-48 hours Titanium Ethylene oxide NaOH/H ₂ O 150-300C 1-48 hours Titanium Alumina NaOH/H ₂ O 150-300C 1-48 hours Silicon Carbide Alumina NaOH/H ₂ O 150-300C 1-48 hours Silicon Carbide Ethylene oxide NaOH/H ₂ O 150-300C 1-48 hours Silicon Carbide Alumina KOH/ _H2O 150-300C 1-48 hours Silicon Carbide Ethylene oxide KOH/ _H2O 150-300C 1-48 hours

In each case described in Table 1, the process temperature at which the removal of the coating was performed was above the boiling point of the removal fluid at atmospheric pressure. For example, a NaOH/ _H2O solution of 10% NaOH and 90% _H2O has a boiling point of 105°C, and a solution of 50% NaOH and 50% _H2O has a boiling point of 140°C. KOH/ _H2O solutions have boiling points in the range of 140°C to 150°C. In each case of Table 1, the process temperature was above the boiling point of the removal chemical used to remove the coating at atmospheric pressure. In addition, KOH and NaOH removal chemicals are known to be relatively unreactive with silicon carbide and titanium, the materials of the underlying components in Table 1. Additionally, at the temperature ranges in which the KOH and NaOH solutions described in Table 1 may be used in the baths where the solutions are exposed to atmospheric pressure, the coating removal rates are so low that it is not commercially feasible to remove such coatings using wet etching techniques. Thus, herein, in each coating removal step, it is believed that less than 0.1% to 0.5% of the underlying material of the component is removed. Thus, the amount of coating removal and component reuse is substantially increased as opposed to using shot blasting or sand blasting for coating removal of components having such underlying material compositions.

100: coating removal container 102: removable cover 104: substantially annular body 106: process volume 108: temperature maintenance system 110: first fluid circuit 112: second fluid circuit 114: third fluid circuit 116: base 120: rupture disk 122: vent valve 124: supergas 126: fluid removal 128: head space 130: drain valve 132: flange connection 134: circumferential container wall 136: convex base wall 138: lower circumferential end wall 140: upper end wall 142: landing surface 144: inner surface 146: cage/basket 148: heater 150: external surface 151: cooling channel 152: circumferential flange 154: first end 156: second end 158: positive annular coil 160: coil inner diameter 162: freezer 164: pump 166: system controller 172: power supply 173: wiring 174: thermocouple 176: upper surface 178: lifting hole 180: fastener opening 182: screw 184: base portion 186: threaded shank portion 188: outer cover surface 190: gasket 191: refill valve 192: Nut 193: Third fluid conduit 194: Sealing groove 196: Sealing ring 197: Removal fluid reservoir 198: Base 199: Collection container 200: Assembly 202: Hollow body 204: First manifold inlet 206: Second manifold inlet 208: Fluid outlet 210: Assembly heater 212: Rupture disc 214: Pressure relief valve 216: Release fluid line 218: Manifold drain valve 220: Drain line 222: Manifold 294: Vent opening 298: Coating removal volume 300: Coating removal container 301: generally annular main body housing 302: sealable containment vessel 303: hemispherical cap 304: surrounding inner containment volume 306: open end 307: annular wall 310: base 311: spacer 312: first cooling fluid line 314: second fluid line 320: door 322: local ambient pressure/ambient environment 324: controller 326: containment vessel pressure sensor 328: containment vessel temperature sensor 330: containment vessel heater control line 332: containment vessel heater power supply 334: pump 336: gas supply 338: fluid removal line 340: Valve 341: Foreline 342: Recovery container 344: Vacuum source 346: Valve 350: Valve 351: Variable controller 360: Containment container heater 362: Containment volume pressure relief valve 364: Pump 400: Pressure vessel 402: Pressurizable volume 404: Outer circumferential wall 406: Upper hemispherical cap 408: Lower hemispherical cap 410: Pump 412: Pump line/fluid supply line 414: Pressure sensor 416: Pressure vessel temperature sensor 418: Pressure vessel heater power supply 420: Sheath heater 422: Pressurized fluid fill line 423: Pressure vessel relief valve 424: Valve 428: Return valve 430: Fluid return line 432: Coating removal fluid 434: Separation pump

FIG. 1 is a schematic cross-sectional view of a coating removal chamber;

FIG. 2 is a schematic illustration of the coating removal chamber of FIG. 1 showing the connection of the coating removal chamber to peripheral equipment useful for the operation of the coating removal chamber;

Figure 3 is a plan view of the coating removal container of Figure 1; and

FIG4 is a schematic diagram of the assembly assembled to provide its own pressurizable internal volume for cleaning thereof;

FIG. 5 is a schematic diagram of an alternative material removal system in which a separate coating removal chamber or vessel is processed within a containment vessel;

Figure 6 is a side view of the containment vessel in Figure 5;

Figure 7 is a plan view of the pressure vessel in Figure 5;

FIG. 8 is a schematic diagram of another alternative coating removal system.

Domestic storage information (please note in the order of storage institution, date, and number) None Foreign storage information (please note in the order of storage country, institution, date, and number) None

200:Components

294: Ventilation opening

298: Coating removal volume

300:Coating removal container

301: Generally annular main body shell

302: Sealable containment container

303: Hemispherical cap

304: Surrounding internal resistance volume

306: Open end

307: Ring wall

310: Base

311: Spacer

320: Door

322: Local environmental stress/surrounding environment

324: Controller

326: Containment vessel pressure sensor

328: Containment container temperature sensor

330: Containment container heater control line

332: Containment vessel heater power supply

360: Containment container heater

362: Containment volume pressure relief valve

364: Pump

400: Pressure vessel

402: Pressurizable volume

404: Outer circumferential wall

406: Upper hemispherical cap

408: Lower hemispherical cap

410: Pump

412: Pump line/fluid supply line

414: Pressure sensor

416: Pressure vessel temperature sensor

418: Pressure vessel heater power supply

420: Sheath heater

422: Pressurized fluid fill line

423: Pressure vessel relief valve

424: Valve

428: Return valve

430: Fluid return line

432: Coating removal fluid

434: Separation pump

Claims (10)

A method for removing a coating from a component, the method comprising the following steps: Providing a coating removal container, the coating removal container having a main body and a sealable processing volume located in the main body; Providing a coating removal fluid in a liquid state and under ambient pressure in the sealable processing volume, the coating removal fluid reacting with the coating at an elevated temperature higher than the ambient temperature surrounding the removal container; Positioning the component having the coating to be removed in the coating removal container in the processing volume of the coating removal container; Sealing the sealable processing volume from the ambient environment surrounding the processing volume; heating the coating removal fluid to a temperature greater than the boiling point of the coating removal fluid at the pressure of the surrounding environment while maintaining the coating removal fluid in a liquid state; using a temperature maintenance system to heat and cool the coating removal fluid during the removal of the coating from the component; removing the coating from the component using the coating removal fluid in a liquid state at a temperature greater than the boiling point of the coating removal fluid at the pressure of the surrounding environment; Using the temperature maintenance system to reduce the temperature of the coating removal fluid to a temperature less than the boiling point of the coating removal fluid at the pressure of the surrounding environment, the temperature maintenance system includes a heater surrounding an exterior surface of the coating removal container, and a cooling channel extending through the body of the coating removal container at opposite first and second ends thereof and extending within the processing volume between the first and second ends and in contact with the coating removal fluid; venting the sealable volume to the surrounding environment; and removing the assembly from the processing volume. The method of claim 1, further comprising the step of removing the coating from the component in the coating removal vessel, wherein less than 0.05% of the material of the component is removed by the removal fluid. The method of claim 2 further comprises the steps of removing the removal fluid that has been exposed to the coating to be removed from the component from the processing volume and providing fresh removal fluid to the processing volume. The method as described in claim 1, wherein the coating to be removed is one of benzimidazole or aluminum oxide, and the material of the component is silicon carbide or titanium. A method for removing a coating of at least one of ferroxene oxide or aluminum oxide from an underlying material containing at least one of silicon carbide or titanium, the method comprising the following steps: Under the pressure of the surrounding environment, the coating is exposed to a removal fluid, the removal fluid reacts with the coating at a temperature at which the removal fluid is liquid under the atmospheric conditions of the pressure of the surrounding environment, but does not react with the underlying material on which the coating is located; While keeping the removal fluid in a liquid state, the removal fluid exposed to the coating is heated to a temperature greater than the temperature at which the removal fluid is liquid under the atmospheric conditions of the pressure of the surrounding environment, and the coating is continuously exposed to the removal fluid; Maintaining the temperature of the removal fluid exposed to the coating at a first temperature greater than a second temperature at which the removal fluid is liquid under atmospheric conditions of the pressure of the surrounding environment while continuously exposing the coating to the removal fluid; Using a temperature maintenance system to heat and cool the removal fluid during the removal of the coating from the underlying material; Removing the coating by reacting the coating with the removal fluid; and Thereafter reducing the temperature of the removal fluid to a temperature at which the removal fluid is liquid under atmospheric conditions of the pressure of the surrounding environment, or to a temperature less than a temperature at which the removal fluid is liquid under atmospheric conditions of the pressure of the surrounding environment. The method of claim 5, wherein the removal fluid does not etch the underlying material of the component. The method of claim 5, wherein the coating comprises at least one of bismuth oxide or aluminum oxide, and the component material comprises at least one of silicon nitride or titanium. The method of claim 7, wherein the removal fluid comprises at least one of KOH or NaOH. A method for removing a coating from a component, the method comprising the following steps: Providing a containment container having an interior volume and a sealable door; Providing one or more coating removal containers, the one or more coating removal containers being configured to be contained within the containment container; Providing a coating removal fluid in the coating removal container under atmospheric pressure; Positioning a component inside one of the one or more coating removal containers with the interior of the one or more coating removal containers exposed to ambient atmospheric pressure; Positioning the coating removal container within the interior volume of the containment container and closing the sealable door to seal the interior volume; While maintaining the coating removal fluid in a liquid state, increasing the pressure and temperature of the coating removal fluid to a temperature greater than the boiling point of the coating removal fluid at the pressure of the surrounding environment; and using a temperature maintenance system to heat and cool the coating removal fluid during the removal of the coating from the component. The coating removal method as described in claim 9 further comprises the steps of: providing a pressure source, the pressure source selectively fluidly connected to the internal volume of the containment vessel; and allowing a pressurized fluid to flow from the pressure source into the containment vessel.