Coated porous metal panel

Abstract: A coated porous metal panel (10) includes a first outer surface (12) on one side of the panel (10), a second outer surface (14) on the other side of the panel (10), a plurality of laterally offset discharge and inlet pores (22,34) in respective ones of the first and the second outer surfaces (12,14), an internal chamber (32) in the panel (10) communicating with each of the inlet and discharge pores (22,34) so that tortuous gas flow paths are formed through the porous metal panel (10), and a shield lamina (16) mechanically clamped against the second outer surface (14). The shield lamina (16) has shield pores (42) aligned with the inlet pores (34) to permit gas flow into the inlet pores (34). A plurality of extraction passages (36) are formed in the panel (10) between the internal chamber (32) and the second outer surface (14) and directly behind each of the discharge pores (22). When the coating material (48) is sprayed on the first outer surface (12) with the shield lamina (16) not attached to the panel (10), surplus coating entering the discharge pores (22) passes through the extraction passages (36) for collection behind the panel (10). The shield lamina (16) blocks the extraction passages (36) to prevent gas flow into the extraction passages (36) and short circuiting of the tortuous gas flow paths in the porous metal panel (10).

Description: This invention relates to coated porous metal panels and to a method of making such a panel. Porous metal panels are described in United States patents US-A-3,584,972 and US-A-4,004,056. United States patents US-A-4,338,360 and US-A-5,130,163 describe methods of applying thermal barrier coating on porous metal panels with minimum deposit of coating material in the pores of the panel. The present invention seeks to provide an improved coated porous metal panel. According to an aspect of the present invention, there is provided a method of making a coated porous metal panel as specified in claim 1. According to another aspect of the present invention, there is provided a coated porous metal panel as specified in claim 3. The coated porous metal panel includes a first outer surface having a pattern of discharge pores therein, a second opposed surface having a pattern of inlet pores therein laterally offset from the discharge pores and connected to the discharge pores through an internal chamber of the panel, and a shield lamina mechanically clamped against the second opposed surface. The shield lamina has a plurality of shield holes arrayed in the same pattern as the inlet pores so that when the shield lamina is in place, the inlet pores are exposed to a source of coolant gas. The panel further includes a plurality of extraction passages behind respective ones of the discharge pores and opening through the second opposed surface. When the shield lamina is in place, the extraction passages are blocked to foreclose entry of coolant gas into the extraction passages. In the method of making the above embodiment of coated porous panel, coating material is sprayed generally perpendicularly to the first outer surface with the shield lamina not in place. Most of the coating material deposits on the first outer surface to form a coating thereon. Surplus coating material entering the discharge pores passes completely through the panel by way of the extraction passages and is collected behind the second opposed surface. After the coating is applied, the shield lamina is mechanically clamped against the second opposed surface to block the extraction passages. In alternative embodiments, mechanical blockers, such as pins or the like, may be inserted in the extraction passages from the second outer surface to project into the discharge pores and thereby physically block entry of coating material into the discharge pores, the blockers being removed after the coating is applied and the extraction passages being closed by the shield lamina as described above. An embodiment of the present invention is described below, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a fragmentary, partially broken-away, exploded perspective view of an embodiment of coated porous metal panel; Figure 2 is an elevational view in cross-section of a portion of the coated porous metal panel of Figure 1; Figure 3 illustrates one of the steps of an embodiment of method of forming the panel of Figure 1; Figure 4 illustrates another step in the embodiment of method of forming the panel of Figure 1; and Figure 5 shows the coated porous metal panel of Figure 1. Referring to the drawings, a coated porous metal panel 10 is illustrated as a laminated structure which can be fabricated by alternate methods, including casting. The laminated panel 10 includes a first lamina 12, a second lamina 14, and a shield lamina 16. The first lamina 12 has an outer surface 18 forming a first outer surface of the panel 10 which is adapted for exposure to a high temperature heat source (not shown), an inner surface 20, and a plurality of discharge pores 22 arrayed in a regular first grid or pattern. The second lamina 14 has an outer surface 24 forming a second surface of the panel 10 which is adapted for exposure to a source of coolant gas under pressure, not shown. The side of the second lamina opposite the outer surface 24 is etched or chemically machined to form an inner surface 26 interrupted by a plurality of integrally formed raised pedestals 28 each having a flat bonding surface 30 thereon. The second lamina 14 is diffusion bonded to the first lamina 12 at the abutting interfaces between the inner surface 20 and the bonding surfaces 30 on the pedestals 28. The inner surfaces 20, 26 of the first and second laminas are spaced apart by the pedestals 28 and form therebetween an internal chamber 32 of the porous metal panel. The second lamina 14 has a plurality of inlet pores 34 passing therethrough arrayed in a regular second grid or pattern which is laterally offset relative to the first pattern of the discharge pores 22. Accordingly, each of the inlet pores 34 is laterally offset relative to each of the discharge pores 22 so that gas flow from the inlet pores to the discharge pores is constrained to follow tortuous flow paths through the internal chamber 32. The second lamina 14 further includes a plurality of extraction passages 36 passing therethrough arrayed in the first pattern so that each of the discharge pores 22 has directly behind it one of the extraction passages 36. The shield lamina 16 has an inner surface 38 facing the outer surface 24 of the second lamina and an outer surface 40 facing the aforesaid source of coolant gas under pressure. The shield lamina 16 has a plurality of shield pores 42 passing therethrough arrayed in the second pattern. The shield pores 42 are at least as large as the inlet pores and preferably slightly larger. A plurality of cylindrical rivet bodies 44, shown in Figures 4 and 5, are welded or otherwise rigidly attached to the second lamina 14 substantially perpendicularly to the outer surface 24 thereof. The rivet bodies 44 are received in a corresponding plurality of clearance holes 46 in the shield lamina 16 when the inner surface 38 of the shield lamina is juxtaposed the outer surface 24 of the second lamina. A mounting bracket 47 may conveniently be fitted over the rivet bodies 44 against the outer surface 40 of the shield lamina for mounting the porous metal panel 10 on a support structure (not shown). Heads are formed on the rivet bodies 44 rigidly to secure together the shield lamina 16, the bracket 47, and the first and second laminas 12,14. The shield pores 42 overlay the inlet pores 34 for maintaining exposure of the inlet pores to the source of coolant gas under pressure. The remaining, solid portion of the shield lamina 16 blocks the extraction passages 36 to prevent entry of coolant gas into the extraction passages though the outer surface 24 of the second lamina. With the shield lamina in place, coolant gas under pressure enters the inlet pores 34 through the shield pores 42, circulates in tortuous paths through the internal chamber 32 for cooling the panel by convection, and exits through the discharge pores 22 to form a protective film between the panel and the heat source. As seen best in Figures 3 to 5, a thermally resistant coating 48 is applied to the porous metal panel 10 by a method including the steps of mechanical surface preparation and spray coating. The aforesaid steps are performed with the shield lamina 16 not attached and may include grit blasting the outer surface 18 of the first lamina and spray application from spray apparatus 52. The coating 48 may include a bond coat 54 such as NiCrAlY on the grit-blasted outer surface 18 and a top coat 56 such as Yttria-stabilized zirconia over the bond coat. The apparatus 52 sprays the bond coat and top coat material generally perpendicularly to the outer surface 18. Necessarily, a surplus fraction of the coating material sprayed towards the outer surface 18 enters the discharge pores 22. The extraction passages 36, being directly behind the discharge pores, form through passages which conduct the surplus coating material directly through the second lamina for collection behind the latter. The presence of the extraction passages 36 behind the discharge pores effectively short circuits the internal chamber 32 and the inlet pores 34 to minimize deposit of surplus coating material in the internal chamber 32 and in the discharge and inlet pores 22, 34. In succeeding steps of the method, the shield lamina 16 and bracket 47 are assembled over the rivet bodies 44 and clamped against the second lamina 14 as described above. Other fastening techniques, such as threaded studs welded to the second lamina, may be used. The extraction passages 36 permit use of other techniques for precluding deposit of surplus coating material in the internal chamber 32 and in the discharge and inlet pores 22, 34. For example, mechanical blockers such as pins may be inserted into the extraction passages 36 from behind the second lamina 14. The pins may extend to just beyond the outer surface 18 completely to preclude entry of surplus coating material into the discharge pores. Then, at the conclusion of the spray operations, the pins are withdrawn to expose the discharge pores and the shield lamina is attached as described above. Alternatively, a mask may be introduced into the extraction passages to fill the discharge pores from behind. The mask precludes entry of surplus coating material into the discharge pores and may be chemically or thermally removed following coating.

Claims: A method of making a coated porous metal panel (10) comprising the steps of forming a metal panel (12,14) which includes a first outer and a second opposed surface (18,24); forming a plurality of discharge pores (22) in the first outer surface (18) arrayed in a first pattern; forming a plurality of inlet pores (34) in the second surface (24) arrayed in a second pattern offset from the first pattern, such that the discharge pores are offset from the inlet pores; forming an internal chamber (32) in the panel communicating with the inlet pores and the discharge pores; forming a plurality of extraction passages (36) in the panel extending between the internal chamber and the second surface and arrayed in the first pattern such that the extraction passages are substantially aligned with the discharge pores; spraying a coating material substantially perpendicularly to the first outer surface to form a coating (48) on the first outer surface; capturing surplus coating material entering the discharge pores by conducting surplus coating material through corresponding extraction passages; forming a shield lamina (16) including a plurality of shield pores (42) therein at least as large as the inlet pores and arrayed in the second pattern; and mechanically securing the shield lamina to the panel (12,14) in juxtaposition to the second surface thereof with the shield pores substantially aligned with corresponding inlet pores and the extraction passages blocked by the shield lamina. A method according to claim 1, wherein the step of mechanically securing the shield lamina to the panel includes the steps of attaching a plurality of posts (44) to the panel extending substantially perpendicularly to the second surface; forming a corresponding plurality of attaching apertures (46) in the shield lamina for receiving the posts; and forming clamping means (47) on the posts for clamping the shield lamina to the second surface of the panel. A coated porous metal panel (10) including a first outer and a second opposed surface (18,24); a plurality of discharge pores (22) in the first outer surface arrayed in first pattern; a thermally resistant coating (48) on the first outer surface (18); a plurality of inlet pores (34) in the second surface (24) arrayed in a second pattern offset from the first pattern, such that the inlet pores are offset from the discharge pores; an internal chamber (32) in the panel communicating with the inlet pores and the discharge pores, a plurality of tortuous gas flow paths being formed within the internal chamber between the inlet and discharge pores; a plurality of extraction passages (36) between the internal chamber and the second surface arrayed in the first pattern such that the extraction passages are substantially aligned with the discharge pores; a shield lamina (16) in juxtaposition with the second surface and including a plurality of shield pores (42) substantially aligned with the inlet pores, the extraction passages being blocked by the shield lamina; and attachment means (44,47) for rigidly clamping the shield lamina to the second surface.

Inventors: JUNOD LARRY ALLEN, JUNOD, LARRY ALLEN
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1993
Main classification: C23C4
IPC codes: B32B3, F01D5, F23R3, C23C22, C23C4, B05D3, C25C5, B32B7, B32B15