Rigid masking devices and methods for in-SITU application of a spray-applied coating material onto a substrate surface

Abstract

Devices and methods are provided to mask a protected surface region of a substrate to prevent the spray-application of a coating material thereon. The protected surface region of a substrate may be masked against a spray-applied coating material by a rigid masking device having a masking plate that is sized and configured to mask the protected surface region of the substrate from the spray-applied coating material. The masking device is positionally secured to the substrate relative to the protected surface region of the substrate to be masked thereby such that the masking plate of the masking device is spaced above and overhangs the protected surface region of the substrate. In such a manner, therefore, the protected surface region of the substate is masked against spray-application of the coating material.

Description

RIGID MASKING DEVICES AND METHODS FOR IN-SITU APPLICATION OF A SPRAY-APPLIED COATING MATERIAL ONTO A SUBSTRATE SURFACEFIELD

[0001] The embodiments disclosed herein relate generally to devices and methods by which process vessels (e.g., pressure vessels used in corrosive application, autoclaves used in the mineral industry, tanks which hold corrosive media and the like) may be protected against corrosion by the application of a thermal spray (e.g., a field-applied metal alloy spray coating). In especially preferred forms, the embodiments disclosed herein relate to devices and methods whereby rigid masks are provided to ensure that the spray coating is not allowed to ingress onto sensitive machined surfaces or other selected surface areas.BACKGROUND

[0002] It is known in the art that process vessels employed in corrosive environments having vessel walls and components formed of carbon steel must be protected by corrosion-resistant materials. For example, it is known that autoclaves constructed of carbon steel experience significant corrosion that can destroy the vessel in a short time span if no corrosion-resistant measures are taken. Most process vessels when new are provided with internal surfaces having a corrosion protective surface coating. However, such protective coatings wear over time which in turn requires replenishment.

[0003] The typical process to field-apply a corrosion or erosion protective coating onto interior surfaces of a process vessel involves the application of a thermal spray coating material, usually a metal alloy material. During the field-application process, the surfaces to be sprayed with the thermal coating material are initially “clean-blasted” using a gritblasting media so as to remove any existing corrosion products or residue. Aggressive grit blasting of the surface provides a desired surface- roughened profile that will promote proper adherence of the subsequently applied thermal spray coating material. The profiled surface may then be subjected to thermal spray coating so as to apply the thermal coating material onto the surface at a specified thickness.

[0004] It is conventional practice to protect sensitive machined surfaces or other areas of the internal vessel surface by masking such sensitive surfaces or other areas with a rigid masking device, typically a rigid mask fabricated from suitable stainless steel (e.g., 300 series). Such a conventional masking practice is shown in accompanying FIG. 1 A whereby a rigid stainless steel mask 1 is attached to the substrate 2 so as to cover and protect the sensitive surface features 2a against the aggressive nature of the grit-blasting and subsequent thermal spray processes (shown schematically by the applicator spray head 3). The process will achieve a protective coating 4 having a specified thickness. When the rigid mask 1 is removed after the coating process, the sensitive surface 2a will be free of coating material as it was protected by the mask 1 during the spray application process. However, a hard edge 4a of the protective coating 2 is formed against the mask 1 which makes the coating 2 more susceptible to being damaged during use after the mask 1 has been removed (e.g., so-called edge failures of the coating).

[0005] It would therefore be highly desirable if improvements to providing spray-coated corrosion protection to process vessels could be provided which minimizes (if not overcomes entirely) the disadvantages of conventional masking techniques for protecting sensitive surface regions against the spray-coating process. It is towards providing such a need that the embodiments disclosed herein are directed.SUMMARY

[0006] In general the embodiments disclosed herein are directed toward devices and methods to mask a protected surface region of a substrate to prevent the spray-application of a coating material thereon. In some embodiments, the protected surface region of a substrate is masked against a spray-applied coating material by a rigid masking device having a masking plate that is sized and configured to mask the protected surface region of the substrate from the spray-applied coating material. The masking device is positionally secured to the substrate relative to the protected surface region of the substrate to be masked thereby such that the masking plate of the masking device is spaced above and overhangs the surface region of the substrate. In such a manner, therefore, the protected surface region of the substate is masked against sprayapplication of the coating material.

[0007] The masking device according to some embodiments will include one or more spacer elements so as to space the masking plate in overhanging relationship above the protected surface region of the substrate. The masking device can be fabricated so as to provide virtually any geometric configuration that may be required. Thus, the masking device may be sized and configured so as to mask a protected substrate surface that is substantially circular or non-circular (e.g., a non-circular shaped protected surface region selected from the group consisting of elliptical, oval, pyriform and biconical shapes).

[0008] According to some embodiments, the masking device may include a flexible shroud around a perimetrical edge of the masking device. An inflatable bladder may also be optionally positioned around the perimetrical edge of the masking device.

[0009] These and other aspects and advantages of the present invention will become more clear after careful consideration is given to thefollowing detailed description of the preferred exemplary embodiments thereof.BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

[0010] The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative embodiments in conjunction with the drawings of which:

[0011] FIGS. 1 A and 1 B are schematic cross-sectional views of a conventional spray-coating masking device and the resulting spray-coated protective coating formed thereby, respectively;

[0012] FIG. 2A and 2B are schematic cross-sectional views of a masking device according to an embodiment of the invention disclosed herein and the resulting spray-coated protective coating formed thereby, thereby;

[0013] FIGS. 3A-3C are enlarged perspective view of the masking device schematically depicted in FIG. 2A, whereby FIG. 3A shows the masking device before the spray-application of coating material onto the substrate surface, FIG. 3B shows the masking device and substrate surface after the spray-application of the coating material and FIG. 3C shows the substrate after removal of the masking device;

[0014] FIGS. 4A-4C are perspective views of another embodiment of a rigid masking device according to the invention which is especially suited for protecting the internal (e.g., threaded) surface of a circular opening in the process vessel whereby FIG. 4A shows the masking device before the spray-application of coating material onto the substrate surface, FIG. 4B shows the masking device and substrate surface afterthe spray-application of the coating material and FIG. 4C shows the substrate after removal of the masking device;

[0015] FIGS. 5A-5D are perspective views of yet another embodiment of a rigid masking device according to the invention which is especially suited for protecting the internal surface of a large generally circular opening in the process vessel whereby FIG. 5A is a top perspective view showing the masking devices as assembled, FIGS. 5B and 5C are top and bottom exploded perspective views of the masking device shown in FIG. 5A and FIG. 5C is a cross-sectional elevational view of the masking device shown in FIG. 5A as taken along line 5D-5D therein; and

[0016] FIGS. 6A-6D are perspective views showing the embodiment of the rigid masking device depicted in FIGS. 5A-5D installed into a large circular opening of a process vessel prior to application of a spray-applied coating material whereby FIG. 6A is a top perspective view thereof, FIG. 6B is bottom perspective view thereof, FIGS. 6C shows the masking device and substrate surface after the spray-application of the coating material and FIG. 6D shows the coated substrate surface after removal of the masking device.DETAILED DESCRIPTION OF EMBODIMENTS

[0017] As is schematically shown in FIG. 2A and 3A-3B, a rigid masking device 10 is provided so as to mask a surface region 12a of a substrate 12 that should be protected from the spray-application of a coating material via the spray head 13. As is conventional, the spray head 13 is oriented at substantially a 90° angle relative to the substrate surface to which the coating material is applied. The masking device 10 will necessarily include a masking plate 10a which is fixed to and spaced above the protected surface region 12a by a spacer element 10b. Thespacer element 10b will typically have a thickness of between about 0.05” to about 0.25” as may be needed in dependence upon the specific surface region 12a to be protected. The masking plate 10a will typically have a thickness of between about 0.125” to about 0.375” and will be positionally but removably fixed to the spacer element 10b and the substrate 12 (e.g., by mounting bolts 1 1 shown in FIGS. 3A-3B) so as to extend away 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 positioning of the masking plate 10a will thereby establish an overhang edge section 10a1 of predetermined dimension (Doh) that is spaced above the protected surface region 12a. The predetermined overhang dimension Doh is dependent upon the dimensions of the protected surface region 12a, but typically has a minimum dimension of about 0.25”.

[0018] Once the masking device 10 is positionally secured to the substrate 12, the coating material may be spray-applied onto the substrate 12 thereby forming a coating layer 14 of predetermined thickness thereon. The separation of the masking plate 10ba and the overhang of the edge section 10a1 relative to the protected surface region 12a will thereby allow a “shadowing” effect to be achieved by the coating material. That is, a tapered edge 14a will be formed at boundary region between the protected surface region 12a and the coating 14 such that the tapered edge 14a gently slopes (tapers) from the predetermined thickness of the coating 14 to the protected surface region 12a (see FIGS. 2B and 3C). Such tapering or feathering / shadowing of the coating material edge 14a will thereby prolong the life of the coating 14 and minimize coating failure which is encountered with conventional masking techniques as discussed above with respect to FIGS. 1 A and 1 B.

[0019] An embodiment of a masking device 20 which is especially suited for protecting the inner (threaded) surfaces of an opening 22a into a process vessel 22 is shown in FIGS. 4A-4C. As is shown, the maskingdevice 20 includes a masking disc 20a that is spaced above the surface of the process vessel 22 and is sized so as to overhang the edge of the opening 22a thereby providing protection to the inner surface thereof. Following the spray-application of the coating material to form a coating 24 of specified thickness, therefore, a tapered annular edge region 24a will be formed adjacent the opening 22a due to the shadowing effect provided by the overhanging edge of the masking disc 20a.

[0020] A further embodiment of a masking device 30 that is especially adapted to protecting surfaces associated with a relatively large circular or non-circular (e.g., generally elliptical, oval, pyriform, biconical or the like) opening in a process vessel is shown in accompanying FIGS. 5A- 5D. In this regard, the masking device 30 will include an upper masking plate 30a formed of mirror-image plate halves 30a1 , 30a2 and a mounting plate assembly 30b comprised of an annular mounting collar 30b1 and an adjacent mounting plate 30b2. A number of spacers 32 are provided in cooperation with nut and bolt assemblies 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 sandwiched between the annular mounting collar mounting collar 30b1 and the adjacent mounting plate 30b2. A circumferential inflatable bladder 38 is in turn sandwiched between a base plate 38a and the mounting plate 30b of the mounting plate assembly 30. The base pate 42 and hence the bladder 38 are positionally fixed to the mounting plates assembly 30 by a circumferential series of cooperating nuts, bolts and spacer sleeves, a representative few of which are identified in FIG. 5D as numerals 44a, 44b and 44c, respectively.

[0021] In order to allow manual manipulation of the masking device 30 and / or the masking plate 30a, a pair of handles 46a, 46b may be rigidly connected to the top surface of the respective masking plate halves 30a1 , 30a2, respectively. Similarly, in order to allow manual manipulation of themounting assembly 30b, a pair of handle slots 48 may be formed in the mounting plate 30b2.

[0022] In use, as shown in FIGS. 6A-6D, the masking device 30 can be positioned within an opening 50 associated with the process vessel 52 such that the masking plate 30a will be exposed to the spray- applied coating material. Positioning of the masking device 30 will entail providing radial slits in the shroud 36 so that corresponding radial sections of the shroud 36 can be wrapped around the inflatable bladder 38 in a deflated state and overlap with one another as may be needed.

[0023] Once positioned in the opening 50 of the process vessel 52, the bladder 38 may be inflated by introducing compressed air through the inflation tube 54 (see FIG. 6B). The inflation of the bladder 38 will therefore positionally restrain the masking device 30 within the opening 50 and form a seal therewith by virtue of the overlapped radial sections of the shroud 36. With the masking device 30 positionally secured, the coating material can then be spray applied as has been described previously to form a coating 58 (see FIG. 6C). Upon removal of the masking device 30, the coating 58 will include a tapered edge section 58a adjoining the protected (and uncoated) opening 50.

[0024] While reference has been made to particular embodiments of the invention, various modifications within the skill of those in the art may be envisioned. Therefore, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope thereof.

Claims

WHAT IS CLAIMED IS:1 . A method to mask a protected surface region of a substrate from a spray-applied coating material, the method comprising:(a) providing a rigid masking device having a masking plate that is sized and configured to mask the protected surface region of the substrate from the spray-applied coating material; and(b) positionally securing the masking device to the substrate relative to the surface region of the substrate to be masked thereby such that the masking plate of the masking device is spaced above and overhangs the surface region of the substrate thereby masking the protected surface region of the substate against spray-application of the coating material.

2. The method according to claim 1 , wherein step (b) includes providing one or more spacer elements so as to space the masking plate in overhanging relationship above the protected surface region of the substrate.

3. The method according to claim 1 , wherein the masking plate of the masking device is sized and configured so as to mask a substrate surface that is substantially circular or non-circular.

4. The method according to claim 3, wherein the masking device is sized and configured so as to mask a non-circular shaped substrate surface selected from the group consisting of elliptical, oval, pyriform and biconical shapes.

5. The method according to claim 3, wherein the masking device comprises a flexible shroud around a perimetrical edge of the masking device.

6. The method according to claim 3, wherein the masking device comprises an inflatable bladder positioned about a perimetrical edge of the masking device.

7. A method to apply a coating material to a surface of the substrate while simultaneously masking a selected surface region of the substrate to prevent application of the coating material, the method comprising the steps of:(a) positionally securing to the substrate a rigid masking device having a masking plate that is sized and configured to mask the selected surface region of the substrate from the application of the spray-applied coating material such that an edge portion of the masking plate is spaced above and overhangs the selected surface region of the substrate thereby masking the same against the application of the coating material;(b) spray-applying the coating material onto a surface of the substrate to form a coating of predetermined thickness thereon; and(c) allowing a tapered edge of the coating applied according to step (b) to form along a boundary region between the coating and the protected surface region due to a shadowing effect achieved by the overhang of the masking plate.

8. The method according to claim 1 , wherein the step (b) is practiced by directing a spray of the coating material onto the surface of the substrate at substantially a 90° angle.

9. The method according to claim 7, wherein step (a) includes providing the masking device with a spacer element so as to space the masking plate above in overhanging relationship to the protected surface region of the substrate.

10. The method according to claim 7, wherein the masking plate of the masking device is sized and configured so as to mask a substrate surface that is substantially circular or non-circular.1 1 . The method according to claim 10, wherein the masking device is sized and configured so as to mask a non-circular shaped substrate surface selected from the group consisting of elliptical, oval, pyriform and biconical shapes.

12. The method according to claim 10, wherein the masking device comprises a flexible shroud around a perimetrical edge of the masking device.

13. The method according to claim 10, wherein the masking device comprises an inflatable bladder positioned about a perimetrical edge of the masking device.

14. A masking device to mask a protective surface region of a substrate from spray-applied coating material, the masking device comprising: a rigid masking plate that is sized and configured to mask the surface region of the substrate from the spray-applied coating material; and a spacer element adapted to position an edge region of the masking plate in spaced overhanging relationship to the protective surface region of the substrate.

15. The masking device according to claim 14, wherein the masking device comprises a plurality of spacer elements each adapted to position an edge region of the masking plate in spaced overhanging relationship to the protective surface region of the substrate.

16. The masking device according to claim 14, wherein the masking plate of the masking device is sized and configured so as to mask a substrate surface that is substantially circular or non-circular.

17. The masking device according to claim 16, wherein the masking device is sized and configured so as to mask a non-circular shaped substrate surface selected from the group consisting of elliptical, oval, pyriform and biconical shapes.

18. The masking device according to claim 14, wherein the masking device comprises a flexible shroud around a perimetrical edge of the masking device.

19. The masking device according to claim 14, wherein the masking device comprises an inflatable bladder positioned about a perimetrical edge of the masking device.

20. The masking device according to claim 14, wherein the masking plate has at least one handle.

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