GB2076953A - A method for manufacturing a rotary regenerator seal cross arm assembly - Google Patents

Abstract

A method for manufacturing a regenerator cross arm seal assembly uniformly stressing a cross arm substrate member 36 to a flattened condition; fixedly securing the substrate member 36 to a holding fixture to maintain it flat between the opposite ends at the top surface 72 of the substrate member, bond coating the top surface 72 to form an oxidation resistant surface 74 thereon, plasma spray coating a layer 78 of nickel oxide on the bond coating to prevent contamination thereof by subsequently applied wear surface material, plasma spray depositing a nickel oxide/calcium fluoride wear coating 82 to a uniform depth across the plasma spray coating of nickel oxide for defining a wear surface of concave form; double coating the substrate member 36 by applying a like coating to the back side surface 88 of the substrate and thereafter heat treating the coated substrate member to produce a thermally induced growth stress in the wear surface coating and back side coating that substantially equalizes the prestress in the substrate member thereby to produce a resultant flat wear surface on the cross arm assembly when the substrate member is placed in a gas turbine engine regenerator and operated under temperature conditions in the order of 1400 DEG F (760 DEG C). <IMAGE>

Description

SPECIFICATION Ir A method for manufacturing a seal cross arm assembly This invention relates to cross arm assemblies for sealing between high and low pressure paths through a hot inboard seal assembly and more particularly to a method for manufacturing such cross arm assemblies to form a substantially flat wear face thereon.

One problem in sealing gas flow passages through a rotary regenerator assembly for use in gas turbine engines having turbine engine temperatures in the range of 1400"F (760to) or at temperatures in excess of 1400"F (760"C) is that of maintaining a wear face on an inboard seal assembly in a flat disposition with respect to the hot seal surface of a rotary regenerator matrix disc so as to prevent excessive gas bypass across the cross arm portion of a regenerator seal assembly.

Hot side regenerator seal assemblies have a cross arm connected to rim components of the seal which prevent gas bypass between high and low pressure gas passes in the regenerator assembly. The cross arm is spring biased and pressure loaded against a rotary matrix disc and it must have a wear coating with a flat wear surface that rides against the rotating matrix disc of the regenerator assembly. Otherwise, undesirable bypass of gas can occur from one side of the cross arm seal assembly to the opposite side thereof across the rotating flat face of the regenerator disc. In the past it has been difficult to fabricate cross arms with flat wear surfaces since heat treatment to stabilize coating growth has produced stresses that bend the cross arm substrate.

A method for manufacturing a seal cross arm assembly for a rotary heat exchange regenerator according to the present invention comprises the steps of forming a cross arm substrate memberhav- ing free opposite ends thereon joined by a center segment having side edges between the opposite ends and including a wear face surface and a back side surface, equally stressing the member to a flattened condition, locating the substrate member in a holding fixture to maintain it flat between the opposite ends at the wear face surface of the substrate member, bond coating the wear face surface to form an oxidation resistant surface thereon, plasma spray coating a layer of nickel oxide on the bond coating to prevent contamination thereof by subsequently applied wear surface material, plasma spray depositing a nickel oxide/calcium fluoride wear coating to a uniform depth across the plasma spray coating of nickel oxide for defining a wear surface of concave form, coating the backside surface with a stress compensating coating for counterstressing the substrate member to compensate the previously formed bow therein, and thereafter heat treating the double coated substrate member to produce a thermally induced growth stress in the wear surface coating and back side coating that substantially equalizes the prestress in the substrate member thereby to produce a resultant substantially flat wear surface on the cross arm assembly when the substrate member is placed in a gas turbine engine regenerator and operated under temperature conditions in the order of 1400 F (760 C).

The invention and how it may be performed are hereinafter particularly described with reference to the accompanying drawings, wherein a preferred embodiment of the present invention is clearly shown, and in which: Figure 1 is an end elevational view of a regenerator seal cross arm assembly manufactured by the method of the present invention; Figure 2 is a block diagram of a process sequence utilized in practising the present invention; Figure 3 is a top elevational view of a regenerator cross arm on a process holding fixture; Figure 4 is an enlarged, fragmentary sectional view taken along the line 4-4 of Figure 3; Figures Sand 6 are cross sectional views of the cross arm assembly following a first wear surface coating sequence and preparatory to a second back side coating sequence; and Figure 7 is a cross sectional view of the cross arm assembly following the method sequence of Figure 2.

Referring now to the drawings, in Figure 1 a gas turbine engine block 10 is illustrated having a seal support platform 12 therein in which is supportingly received an inboard or hot gas side seal assembly 14 for use in gas turbine engine regenerator systems.

The seal assembly 14 is, more specifically, the type set forth in United States Patent No.3,542,122 (Bracken, Jr.). Such seals include a cross arm 16 interconnected at opposite ends thereof to generally semicircularly configured rims 18,20. The rim 20 constitutes a low pressure rim seal which, together with the cross arm 16, seals the peripheral extent of a low pressure opening 22 which directs low pressure exhaust gas to the hot side of a rotary regenerator matrix disc 24. Rim 18 and cross arm 16 seal the perimeter of a high pressure passage 26 for directing preheated, compressed air to a combuster. Disc 24 has a flat surface located in sealing engagement with the exposed wear surfaces of the seal assembly 14 which are shown in Figure 1.

More particularly, the cross arm 16 has a wear face 28 thereon and the rim portions 18 and 20 have wear faces 30 and 32 thereon. In such arrangements, a spring seal system is interposed between the seal support platform 12 and a backside portion of the cross arm and low and high pressure rim portions 20,18. Examples of such biasing systems are shown in United States Patent No. 3,542,122 (Bracken, Jr.).

In accordance with the present invention, the cross arm 16 of the above illustrated seal assembly 14 is processed to eliminate wear face warpage produced during plasma spray processing methods. By practicing the present invention it has been found that a double, multiple coating can be imposed on the metallic substrate of a cross arm seal assembly so as to prevent end-to-end warpage of a wear face surface following a heat treatment process to growth stabilize the plasma spray coatings for subsequent long term durability in gas turbine engine operation wherein the hot side matrix face can reach temperatures in the order of 1000"F (538"C) to 1400"F (760"C).

zone particuierly, in practicing the present inven tion, a process is utilized having the basic steps set forth in the block diagrams of Figure 2. The first stsp includes that of forming a cross arm blank 36 of high nickel alloy steel. The blank 36 has opposite free ends thereon illustrated as being arcuate end seg ments 38,40 each having a locating tab 42, 44 thereon, respectively, for locating the cross arm 16 at an indexed relationship with respect to the seal sup port platform 12.The cross arm blank 36 defines a metallic substrate between the arcuate segments 38 and 40 with a first arm portion 46 extending along one radial line from an arm center point 48 and a second arm portion 50 extending along a second radial line from center point 48. Each of arm portions 46,50 diverge from the arcuate segments 38 and 40 along opposed edges 52, 54 on the arm portion 46 and opposed edges 56, 58 on the arm portion 50.

Thus, the arm portions have a variable width from their point of connection at the arcuate segments 38, 40 to a center segment 60 having an apex 62 thereon. Thus, the substrate in the blank 36 has a complex geometry and shape between the opposite ends thereof. In such arrangements, during the processing of a cross arm member for use in an inboard assembly 14 it is necessary to thermally stabilize various bond and wear surface coatings that are plasma spray coated on the substrate defined by the cross arm blank 36. Heretofore, it has been found that such heat stabilization can cause a bend to occur in the length of the cross arm between the arcuate segments 38,40.Accordingly, the present invention includes a specific processing sequence that is aimed at eliminating such bends so that the resultant cross arm assembly will have a relatively flat wear surface thereon at the wear face 28 so that it will uniformly seal across the width of a matrix disc 24 on the hot surface thereof to seal between the low pressure opening 22 and the high pressure inlet air opening 26 formed between the cross arm 16 and the high pressure rim 18.

The process sequence includes preforming a platform 0.092 inches (2.34 mm) thick which is vacuum annealed at 1600 F (8710C) for two hours. A surface preparation is then conducted wherein the cross arm blank 36 is degreased with a suitable solvent such as perchlorethylene or is cleaned by a cheese cloth dampened with acetone. Surface preparation is followed by blasting both surfaces of the cross arm blank 36 with sixty grit aluminium oxide particles directed against the opposite flat surfaces of the cross arm blank 36 under an application pressure of 60 psi (413.7 kPa) with the grit blasting applicator being located six inches (152.4 mm) from the cross arm blank 36. Such grit blasting will equally stress the blank 36 at the start of the process sequence of the present invention.Following grit blasting, all loose particles are removed from the cross arm by use of compressed air or by cleaning the part with cheese cloth dampened with acetone. Thereafter, the clean equally stressed cross arm blank 36 is located in a holding fixture 64 shown in Figure 4. The holding fixture 64 is preferably prefabricated from a block of Hastelloy-X (R.T.M.) material to have a recess 66 congruent to the perimeter of blank 36.

In the illustrated arrangement, the exposed sur face 68 of the fixed cross arm blank 36 is masked define the other perimeter 70 of a wear surface 72 on the seal cross arm blank 36 that will be coated with desired material coating layers.

As shown in Figure 2, once the part has been fixed and masked the part and the fixture are preheated to 175"F to 200"F (79.4"C to 93.3"C). Then, the wear su r- face 72 is coated with a bond coat 74. Coat 74 is plasma spray deposited on the wear surface 72. One suitable bond coat is a nickel chrome bond coating such as Metco 443 which is applied to a uniform thickness of from four to six mils (0.10160.1524 mm) completely across the area bounded by the perimeter70 shown in Figure 3.The bond coat plasma spray should be applied at an impingement angle of 900, plus or minus 15 , and at a distance of from four to five inches (101.6-127 mm) from the part to be sprayed. In one working embodiment, the spray parameter included the use of an SG1 B gun system 76 having a noule S1-3-F and an electrode S1-3-R, all manufactured by Plasmadyne Corp. The carrier gas is argon applied at a rate of 65 cubic feet per hour (1.841 cubic metres/hour) and helium at a rate of 15 cubic feet per hour (0.425 cubic metres/hour). The spray gun system is electrically connected to a source of power of 500 amps. at 45 volts.

A 1 000A powder feed of Plasmadyne Corporation is used to apply the nickel/chrome bond coating material. The feed gear has thirty teeth and it is set at a dial setting of 30. An argon carrier gas for the powderfeed is applied at a rate of fifteen cubic feet per hour (0.425 cubic metres/hour) at an external powderfeed port.

Following application of the bond coat, the process includes plasma spray application of a wear surface barrier coat 78 to coverthe exposed bond coat surface 80. The barrier coat 78 is preferably 100% nickel oxide which is applied uniformly to a depth of 10 mils (0.254 mm) across the bond coat surface 80. The barrier coat 78 is selected to have a chemistry to prevent migration of contaminate materials between a bond coat and an outer wear coat.

The spray coating apparatus and the spray parameters for application of the barrier coat are those used to apply the bond coat 74 as stated above.

In accordance with the present invention, a finish coat or seal wear coat layer 82 is plasma sprayed onto an outer surface 84 of the barrier coat 78. Preferably, the wear coat is a composition of nickel oxide (NiO) and calcium fluoride (CaF2) in the range of 60%-85% NiO and 15%-40% CaF2. The above powders are measured by weight percent and are blended in a twin shell blender or equivalent until they are thoroughly mixed and then they are applied with plasma spray apparatus having the above stated parameters.

In the illustrated arrangement, the wear coat layer 82 is applied to a uniform depth of 30 mils (0.762 mm) across the outer surface 84 of the previously applied barrier coat 78. More particularly, at this point in the method of manufacture, the work piece is coated on one side as seen in Figure 5. The piece has a maximum bow, concave to the wear face 86.

The piece is then inverted as seen in Figure 6 and it is light grit blasted on backside 88 to clean up the work piece prior to a double coat process applied on the back side as set forth in the sequence of Figure 2.

In the illustrated arrangement, the exposed surface of the fixtured cross arm blank 36 is masked to define an outer perimeter 70 of a wear surface on the back side 88 of seal cross arm blank 36 that will be coated with desired material coating layers. The back side perimeter is congruent to thewearface.

As shown in Figure 2, once the part has been fixed and masked the part and the fixture are preheated to 175"F to 200"F (79.4"C to 93.3"C). Then the wear surface is coated with a bond coat 90. Coat 90 is plasma spray deposited on the back side 88. The bond coat 90 is a nickel chrome bond coating such as Metco 443 which is applied to a uniform thickness of from four to six mils (0.1016-0.1524 mm) completely across the area bounded by a perimeter like perimeter 70 shown in Figure 3 so that the blank 36 will be coated across the same area of both the wear side and backside thereof.The bond coat plasma spray should be applied at an impingement angle of 900, plus or minus 15 , and at a distance of from four to five inches (101.6-127 mm) from the part to be sprayed. A SG1B gun system 76 having a nozzle S1-3-F and an electrode S1-3-R, all manufactured by Plasmadyne Corp. are also used on the backside and are operated in the same manner and with the same accessories as used in the wear side sequence of coatings.

Following application of the bond coat 90 the process includes plasma spray application of a wear surface barrier coat 92 to cover the exposed bond coat surface 94. The barrier coat 92 is preferably 100% nickel oxide which is applied uniformly to a depth of 10 mils (0.254 mm) across the bond coat surface 94. The barrier coat 92 is selected to have a chemistry to prevent migration of contaminate materials between a bond coat and an outer wear coat.

The spray coating apparatus and the spray parameters for application of the barrier coat are those used to apply the bond coat 90 as stated above.

In accordance with the present invention, a finish coat or back side wear coat 96 is plasma sprayed onto an outer surface 98 of the barrier coat 92. Preferably, the backside wear coat is a composition of nickel oxide (NiO) and calcium fluoride (CaF2) in the range of 60%-85% NO and 15%-40% CaF2. The above powders are measured by weight percent and are blended in a twin shell blender or equivalent until they are thoroughly mixed and then they are applied with plasma spray apparatus having the above stated parameters.

In the illustrated arrangement, the back side wear coat layer 96 is applied to a uniform depth of 30 mils (0.762 mm) across the outer surface 98 of the previously applied barrier coat 92. The double coating of the substrate or cross arm blank 36 will counterstress it to partially compensate the intermediate bow as shown in Figure 6.

In some applications, this back side coating may extend seal life by enabling the seal to be reversed once wear face 28 is worn. The double coating of material on the wear surface and back side of metallic substrate material of the cross arm blank 36 is subjected to a heat treatment cycle wherein the part is heated in air to a temperature in the range of 1 6000F (871 C) for a time period in the order of sixteen hours. During this heat treatment step, it has been found necessary to cover the outer surface 88 of the wear face with a thermal insulation blanket to eliminate overheating of the coat due to excess radiation from furnace elements which are in a line of sight relationship to the surface coatings on the metal substrate defined by the cross arm blank 36.

Heretofore, it has been found that such thermal heat treatment steps, applied to an unrestrained metal substrate, caused the cross arm to bend between the ends thereof to a degree where a wear surface thereon was not sufficiently flat to conform to the hot inboard surface of a rotary matrix disc during gas turbine engine operation. As a result, undesired gas bypass occurred thereacross which caused a loss of efficiency.

The specific sequence of steps discussed above and outlined in Figure 2 of heat treating of the member in a restrained flat condition stabilizes the wear surface coating.

A substantially flat wear coat surface 28 on the arm 16 enables it to be operated at equilibrium conditions of gas turbine engine operation and in sealing relationship to the flat hot inside surface of the rotary matrix disc 24 and yet retain a substantially flat wear face 28 that will be undistorted between the arcuate segments 38,40 when indexed with respect to the seal support platform 12.

Cross arms processed by the present invention have been measured to have a flatness measured end-to-end of the cross arms in the order of fifteen to twenty-five mils (0.381-0.635 mm) in a slightly concave mode which is considered, for purposes of a running seal in a gas turbine engine with spring back-up biasing systems, to be sufficiently flat to adequately seal between the pressure conditions of gas flow through the low pressure opening 22 and the high pressure opening 26.

The present invention provides an improved method of manufacture of regenerator seal assemblies with growth stabilized wear surface coating layers on a cross arm substrate member by processing the cross arm portion to have an initial flatness and thereafter coating both sides of the substrate to equally stress the substrate member back to an endto-end flat condition so that stresses are balanced to hold a flat wear surface which can be spring biased and pressure loaded into conformity with the rotating regenerator disc of a rotary regenerator system for use in gas turbine engine applications thereby to prevent undesirable gas bypass across the wear face of the cross arm portion of a hot side regenerator seal assembly.

Preferably the method of manufacturing regenerator seal cross arm assemblies according to the present invention used is one wherein a cross arm member is processed by restraining it on a substrate of high nickel alloy steel having a surface configured to receive free end portions of the member and a center segment between the ends and to restrain side edges so that the member will initially be in a flattened condition; thereafter coating one surface of the member with layers of material including an inner bond coat, an intermediate nickel oxide barrier coat and an outer plasma sprayed coating of nickel oxide/calcium fluoride wear material having a uniform depth across the member which causes a slight bow in the member between its ends; then coating the backside surface of the member with layers of material including an inner bond coat, an intermediate nickel oxide barrier coat and an outer plasma sprayed coating of nickel oxide/calcium fluoride wear material having a uniform depth across the backside surface to correct the slight bow and return the substrate to near flatness and thereaftersubjecting the double coated member to a heat treat cycle in the order of 1600cm (871 cm) for sixteen hours to produce heat stabilized growth of the double coating layers on the substrate member so that when the cross arm is located in a regenerator seal assembly and operated at turbine iniet temperatures in excess of 1400"F (760"C) a relatively undistorted wear face surface will be presented to a flat surface of a rotary regenerator matrix disc to prevent excessive gas bypass across the cross arm assembly during turbine engine operation.

Claims (3)

1. A method for manufacturing a seal cross arm assembly for a rotary heat exchange regenerator comprising the steps offorming a cross arm substrate member having free opposite ends thereon joined by a center segment having side edges between the opposite ends and including a wear face surface and a back side surface, equally stressing the member to a flattened condition, locating the substrate member in a holding fixture to maintain it flat between the opposite ends at the wear facets surface of the substrate member, bond coating the wear face surface to form an oxidation-resistant surface thereon, plasma spray coating a layer of nickel oxide on the bond coating to prevent contamination thereof by subsequently applied wear surface material, plasma spray depositing a nickel oxide/calcium fluoride wear coating to a uniform depth across the plasma spray coating of nickel oxide for defining a wear surface of concave form, coating the backside surface with a stress compensating coating for counterstressing the substrate member to compensate the previously formed bow therein, and thereafter heat treating the double coated substrate member to produce a thermally induced growth stress in the wear surface coating and back side coating that substantially equalizes the prestress in the substrate member thereby to produce a resultant substantially flat wear surface on the cross arm assembly when the substrate member is placed in a gas turbine engine regenerator and operated under temperature conditions in the order of 1400"F (760 C).

2. A method for manufacturing a seal cross arm assembly for a rotary heat exchange regenerator according to claim 1, in which the method for coating the backside surface with a stress compensating coating comprises bond coating the backside surface to form an oxidation resistant surface thereon, plasma spray coating a layer of nickel oxide on the backside bond coating to prevent contamination thereof by subsequently applied wear surface material, and then plasma spray depositing a nickel oxide/calcium fluoride wear coating to a uniform depth across the backside plasma spray coating of nickel oxide.

3. A method for manufacturing a seal cross arm assembly for a rotary heat exchange regenerator substantially as hereinbefore particularly described and as shown in Figures 2 to 7 of the accompanying drawings.