Rigid masking device and method for in-situ application of coating material sprayed onto a substrate surface

Abstract

An apparatus and method for masking a surface area to be protected on a substrate to prevent a coating material from being sprayed onto the surface area to be protected are provided. The surface area to be protected on the substrate may be masked by a rigid masking apparatus having a masking plate whose size and shape are set to mask the area from a sprayed coating material. The masking apparatus is fixed in position to the substrate with respect to the surface area to be protected on the substrate to be masked, and accordingly, the masking plate of the masking apparatus is positioned to be spaced apart from and overhang the surface area to be protected on the substrate. In this way, the surface area to be protected on the substrate is masked from the spraying of a coating material.

Description

Technology Field

[0001] The embodiments of the present disclosure generally relate to an apparatus and method for protecting a process vessel (e.g., a pressure vessel used for corrosive applications, an autoclave used in the mining industry, a tank containing a corrosive medium, etc.) from corrosion by the application of thermal spraying (e.g., a metal alloy spray coating applied in the field). In a particularly preferred embodiment, the embodiments of the present disclosure relate to an apparatus and method provided with a rigid mask to prevent the spray coating from entering a sensitive processing surface or other selected surface area. Background Technology

[0002] It is known in the art that process vessels used in corrosive environments and having vessel walls and components formed of carbon steel must be protected by corrosion-resistant materials. For example, autoclaves made of carbon steel are known to undergo severe corrosion that can destroy the vessel within a short period of time if corrosion-resistant measures are not taken. Most process vessels are provided with internal surfaces having a corrosion-resistant protective surface coating when new. However, these protective coatings wear down over time, eventually requiring replenishment.

[0003] A typical process for applying a corrosion or erosion-preventive coating on the inner surface of a process vessel in the field involves the application of thermal spray coating materials, typically metal alloy materials. During the field application process, the surface to which the thermal coating material is sprayed is initially “clean-blasted” using a grit blasting medium to remove existing corrosion products or residues. Aggressive grit blasting of the surface provides a desirable surface roughness profile that facilitates proper adhesion of the subsequently applied thermal spray coating material. The surface thus profiled can then undergo thermal spray coating, allowing the thermal coating material to be applied to the surface to a specified thickness.

[0004] It is common practice to protect sensitive processing surfaces or other areas of the inner container surface by masking such sensitive surfaces or other areas using a rigid masking device, such as a rigid mask made of suitable stainless steel (e.g., 300 series). This conventional masking practice is illustrated in the attached FIG. 1a, where a rigid stainless steel mask (1) is attached to a substrate (2) to cover and protect sensitive surface features (2a) from the aggressive properties of grit blasting and subsequent thermal spraying processes (schematically illustrated by a sprayer spray head (3)). The process forms a protective coating (4) having a specified thickness. When the rigid mask (1) is removed after the coating process, the sensitive surface (2a) remains free of coating material because it was protected by the mask (1) during the spraying application process. However, the hard edge (4a) of the protective coating (2) is formed adjacent to the mask (1), which makes the coating (2) more susceptible to damage during use after the mask (1) is removed (e.g., so-called edge breakage of the coating).

[0005] Therefore, it would be highly desirable to provide improvements in providing corrosion protection for spray coatings on process vessels that minimize (even if not completely overcome) the disadvantages of conventional masking techniques for protecting surface areas sensitive to spray coating processes. The embodiments of the present disclosure are intended to meet this need.

[0006] Generally, embodiments of the present disclosure relate to an apparatus and method for masking a surface area to be protected on a substrate to prevent the application of a coating material by spraying it onto the said area. In some embodiments, the surface area to be protected on the substrate is masked by a rigid masking apparatus having a masking plate sized and shaped to mask the said area from the sprayed coating material. The masking apparatus is positionally fixed to the substrate with respect to the surface area to be protected on the substrate to be masked, so that the masking plate of the masking apparatus is positioned to be spaced apart from and overhang the surface area of ​​the substrate. In this way, the surface area to be protected on the substrate is masked from the spray application of the coating material.

[0007] A masking device according to some embodiments includes one or more spacer elements to cause the masking plate to be spaced apart from the surface area to be protected of the substrate in an overhang relationship. The masking device may be manufactured to provide almost any geometric configuration that may be required. Accordingly, the size and shape of the masking device may be set to mask the surface to be protected of the substrate which is substantially circular or non-circular (e.g., a surface area to be protected of a non-circular shape selected from the group consisting of elliptical, oval, pear-shaped, and biconical shapes).

[0008] According to some embodiments, the masking device may include a flexible shroud around the periphery edge of the masking device. Additionally, an inflatable bladder may be optionally placed around the periphery edge of the masking device.

[0009] These and other aspects and advantages of the present invention will become more apparent by carefully considering the detailed description of the preferred exemplary embodiments below. Brief explanation of the drawing

[0010] The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary and non-limiting embodiments together with the drawings: FIGS. 1a and FIGS. 1b are schematic cross-sectional views showing a conventional spray coating masking device and a spray-coated protective coating formed by it, respectively; FIGS. 2a and 2b are schematic cross-sectional views illustrating a masking device according to an embodiment of the invention according to the present disclosure and a spray-coated protective coating formed thereby; FIGS. 3a to 3c are enlarged perspective views of a masking device schematically illustrated in FIG. 2a, where FIG. 3a illustrates the masking device before a coating material is sprayed onto the surface of a substrate, FIG. 3b illustrates the masking device and the surface of the substrate after the coating material is sprayed, and FIG. 3c illustrates the substrate after the masking device has been removed; FIGS. 4a to 4c are perspective views showing a rigid masking device according to another embodiment of the present invention particularly suitable for protecting the inner surface (e.g., threaded) of a circular opening within a process vessel, FIG. 4a shows the masking device before a coating material is sprayed and applied, FIG. 4b shows the masking device and the substrate surface after the coating material is sprayed and applied, and FIG. 4c shows the substrate after the masking device is removed; FIGS. 5a through 5d are perspective views showing a rigid masking device according to another embodiment of the present invention particularly suitable for protecting the inner surface of a relatively large, generally circular opening within a process vessel, FIG. 5a is a top perspective view showing the masking device in an assembled state, FIGS. 5b and 5c are top and bottom exploded perspective views of the masking device shown in FIG. 5a, FIG. 5c is a cross-sectional elevation view of the masking device shown in FIG. 5a taken along line 5D-5D; and FIGS. 6a to 6d are perspective views showing an embodiment of the rigid masking device illustrated in FIGS. 5a to 5d installed in a large circular opening of a process vessel before the application of a spray-applied coating material, FIG. 6a is a top perspective view thereof, FIG. 6b is a bottom perspective view thereof, FIG. 6c shows the masking device and the substrate surface after the coating material has been spray-applied, and FIG. 6d shows the coated substrate surface after the masking device has been removed. Specific details for implementing the invention

[0011] As schematically illustrated in FIGS. 2a and FIGS. 3a through 3b, a rigid masking device (10) is provided to mask a surface area (12a) of a substrate (12) that is to be protected from the spray application of a coating material through a spray head (13). Typically, the spray head (13) is oriented at a substantially 90° angle with respect to the surface of the substrate to which the coating material is applied. The masking device (10) essentially comprises a masking plate (10a) that is fixed and spaced apart from the surface area (12a) to be protected by a spacer element (10b). The spacer element (10b) typically has a thickness of about 0.05 inches to about 0.25 inches as needed, depending on the specific surface area (12a) to be protected. The masking plate (10a) generally has a thickness of about 0.125 inches to about 0.375 inches and is positionally but detachably fixed to the spacer element (10b) and the substrate (12) (e.g., by the mounting bolt (11) shown in FIGS. 3a and 3b) so as to extend spaced apart from the edge of the spacer element (10b) parallel to the surface of the substrate (12) to be spray-coated by the coating material. Such placement of the masking plate (10a) is spaced apart by a certain dimension (D) above the surface area (12a) to be protected thereby. oh The overhang edge portion 10a1 of ) is formed. A predetermined overhang dimension (D oh ) varies depending on the dimensions of the surface area (12a) to be protected, but generally has a minimum dimension of about 0.25 inches.

[0012] When the masking device (10) is fixed in position on the substrate (12), the coating material can be sprayed onto the substrate (12), thereby forming a coating layer (14) of a predetermined thickness thereon. Accordingly, the spacing of the masking plate (10a) with respect to the surface area to be protected (12a) and the overhang of the edge portion (10a1) allow a “shadowing” effect by the coating material to be achieved. That is, a tapered edge (14a) is formed in the boundary area between the surface area to be protected (12a) and the coating (14), and this tapered edge (14a) is gently inclined (tapered) from a predetermined thickness of the coating (14) to the surface area to be protected (12a) (see FIG. 2b and FIG. 3c). Tapering or feathering / shadowing of the coating material edge (14a) thereby extends the life of the coating (14) and minimizes coating breakage that occurs in conventional masking techniques as discussed in relation to FIG. 1a and FIG. 1b above.

[0013] An embodiment of a masking device (20) particularly suitable for protecting the inner (threaded) surface of an opening (22a) into a process vessel (22) is illustrated in FIGS. 4a to 4c. As illustrated, the masking device (20) includes a masking disk (20a) that is spaced above the surface of the process vessel (22) and sized to overhang the edge of the opening (22a), thereby providing protection for the inner surface. Thus, after a coating material is sprayed and applied to form a coating (24) of a predetermined thickness, a tapered annular edge region (24a) is formed adjacent to the opening (22a) due to the shadowing effect provided by the overhang edge of the masking disk (20a).

[0014] Additional embodiments of a masking device (30) particularly adapted for protecting surfaces associated with relatively large circular or non-circular (e.g., generally elliptical, oval, pear-shaped, double-conical, etc.) openings within a process vessel are illustrated in the attached FIGS. 5a through 5d. In this regard, the masking device (30) comprises an upper masking plate (30a) formed by plate halves (30a1, 30a2) that are mirror images of each other, and a mounting plate assembly (30b) consisting of an annular mounting collar (30b1) and an adjacent mounting plate (30b2). A plurality of spacers (32) are provided in cooperation with a nut and bolt assembly (34) so ​​as to maintain a desired separation distance between the masking plate (30a) and the mounting plate assembly (30). A flexible shroud or skirt (36) is fitted between the annular mounting collar (30b1) and the adjacent mounting plate (30b2). The circumferentially expandable bladder (38) is again sandwiched between the base plate (38a) and the mounting plate (30b) of the mounting plate assembly (30). The base plate (42) and thus the bladder (38) are positionally secured to the mounting plate assembly (30) by a series of circumferentially arranged interacting nuts, bolts, and spacer sleeves, the representative parts of which are identified by reference numerals 44a, 44b, and 44c, respectively, in FIG. 5d.

[0015] To enable manual operation of the masking device (30) and / or the masking plate (30a), a pair of handles (46a, 46b) may be rigidly connected to the upper surface of each masking plate half (30a1, 30a2). Similarly, to enable manual operation of the mounting assembly (30b), a pair of handle slots (48) may be formed in the mounting plate (30b2).

[0016] When in use, as illustrated in FIGS. 6a through 6d, the masking device (30) may be placed within an opening (50) associated with the process vessel (52), so that the masking plate (30a) is exposed to the spray-applied coating material. The placement of the masking device (30) involves providing radial slits in the shroud (36), so that corresponding radial portions of the shroud (36) may be wrapped around an expandable bladder (38) in a contracted state and may overlap each other as needed.

[0017] Once placed within the opening (50) of the process vessel (52), the bladder (38) can be expanded by introducing compressed air through the expansion tube (54) (see FIG. 6b). Thus, the expansion of the bladder (38) positionsally restrains the masking device (30) within the opening (50) and forms a seal with it by the overlapping radial portions of the shroud (36). With the masking device (30) positionally fixed, the coating material can be sprayed and applied as previously described to form the coating (58) (see FIG. 6c). When the masking device (30) is removed, the coating (58) includes a tapered edge portion (58a) adjacent to the protected (and uncoated) opening (50).

[0018] Although the present invention has been described with reference to specific embodiments, various modifications may be conceived within the scope of the art. Accordingly, the present invention should not be understood as being limited to the disclosed embodiments, but rather is intended to encompass various modifications and equivalent configurations included within the spirit and scope thereof.

Claims

Claim 1 A method for masking a surface area to be protected of a substrate from a spray-applied coating material, wherein the method comprises: (a) providing a rigid masking device having a masking plate having a size and shape set to mask a surface area to be protected of a substrate from a spray-applied coating material; and (b) fixing the masking device to the substrate with respect to a surface area of ​​the substrate to be masked so that the masking plate of the masking device is spaced apart from and overhangs above the surface area of ​​the substrate, thereby masking the surface area to be protected of the substrate from the spray application of the coating material. Claim 2 A method according to claim 1, wherein step (b) comprises providing one or more spacer elements such that the masking plate is spaced apart from the surface area to be protected of the substrate in an overhang relationship. Claim 3 A method according to claim 1, wherein the masking plate of the masking device is set in size and shape to mask a substantially circular or non-circular substrate surface. Claim 4 A method according to claim 3, wherein the masking device is configured in size and shape to mask a non-circular substrate surface selected from the group consisting of elliptical, oval, pear, and double conical shapes. Claim 5 The method of claim 3, wherein the masking device comprises a flexible shroud around the perimeter edge of the masking device. Claim 6 A method according to claim 3, wherein the masking device comprises an expandable bladder disposed around the periphery edge of the masking device. Claim 7 A method for applying a coating material to the surface of a substrate while simultaneously masking a selected surface area of ​​the substrate to prevent the application of the coating material, wherein the method comprises the following steps: (a) positionally fixing a rigid masking device to a substrate, the masking plate having a size and shape set to mask a selected surface area of ​​the substrate from the application of a spray-applied coating material, wherein the edge portion of the masking plate is spaced apart from and overhangs the selected surface area of ​​the substrate, thereby masking the selected surface area from the application of the coating material; (b) spray-applying a coating material onto the surface of the substrate to form a coating of a predetermined thickness thereon; and (c) forming a tapered edge of the coating applied according to step (b) along the boundary area between the coating and the surface area to be protected due to a shadowing effect achieved by the overhang of the masking plate. Claim 8 A method according to claim 1, wherein step (b) is performed by directing the spray of coating material onto the surface of a substrate at a substantially 90° angle. Claim 9 A method according to claim 7, wherein step (a) comprises providing a spacer element to the masking device such that the masking plate is spaced apart from the surface area to be protected of the substrate in an overhang relationship. Claim 10 A method according to claim 7, wherein the masking plate of the masking device is set in size and shape to mask a substantially circular or non-circular substrate surface. Claim 11 A method according to claim 10, wherein the masking device is configured in size and shape to mask a non-circular substrate surface selected from the group consisting of elliptical, oval, pear, and double conical shapes. Claim 12 The method of claim 10, wherein the masking device comprises a flexible shroud around the perimeter edge of the masking device. Claim 13 A method according to claim 10, wherein the masking device comprises an expandable bladder disposed around the periphery edge of the masking device. Claim 14 A masking device for masking a surface area to be protected of a substrate from a spray-applied coating material, wherein the masking device comprises: a rigid masking plate having a size and shape set to mask a surface area of ​​a substrate from a spray-applied coating material; and a spacer element configured to position an edge area of ​​the masking plate in an overhang relationship spaced apart from the surface area to be protected of the substrate. Claim 15 The masking device of claim 14, wherein the masking device comprises a plurality of spacer elements configured to position the edge regions of the masking plate in an overhang relationship spaced apart from the surface region to be protected of the substrate. Claim 16 In claim 14, the masking plate of the masking device is a masking device whose size and shape are set to mask a substantially circular or non-circular substrate surface. Claim 17 In claim 16, the masking device is a masking device whose size and shape are set to mask a non-circular substrate surface selected from the group consisting of elliptical, oval, pear, and double conical shapes. Claim 18 In claim 14, the masking device comprises a flexible shroud around the periphery edge of the masking device. Claim 19 The masking device of claim 14 comprises an expandable bladder disposed around the periphery edge of the masking device. Claim 20 In claim 14, the masking plate is a masking device having at least one handle.

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