US 3659861 A
Particles having a core of a glazing material such as calcium fluoride surrounded by a shell of a metal that oxidizes at operating temperature are sprayed on a substrate to form a rubbing seal for a ceramic regenerator. The oxide of the metal forming these shells is non abradable to the ceramic regenerator. During engine operation the shell oxidizes and wears to expose appropriate amounts of the glazing material.
Description (OCR text may contain errors)
O 1 United States Patent 1 1 3,659,861 Rao et a1.  May 2, 1972 [541 PARTICULATE COATING FOR THE  References Cited RUBBING SEAL OF A GAS TURBINE UNITED STATES PATENTS REGENERATOR  I I v I D R w dh Y h 3,468,699 9/1969 Kremith ..117/100B nven OI'SI emu 8]) I 6 a0, 00 aven; CS
vamp. Hang, Grosselle, both OfMich 3,407,866 10/1968 Sawchuk ..165/9  Assignee: Ford Motor Company, Dearborn, Mich. Primary ExaminerSamuel B. Rothberg  Filed: July 6 1970 Att0rneyJohn R. Faulkner and Glenn S. Arendsen 1 pp 52,309 57 ABSTRACT Pt'lh' fl 1'1111' 52 US. Cl. ..277/96,277/D1G.6, 165/9, fig f f ijgfi g j f 15 7 2? 117/100 51 1111.0. ..F16j 15 54, C23C 11/16 fggf f'g l z. g g  Field ofSearch ..277 235 A, 96, D16 6; 165/9; ramlcregenem" em forming these shells is non abradable to the ceramic regenerator. During engine operation the shell oxidizes and wears to expose appropriate amounts of the glazing material.
4 Claims, 3 Drawing Figures Patented May 2, 1972 3,659,861
ATTORNEYS PARTICULATE COATING FOR THE RUBBING SEAL OF A GAS TURBINE REGENERATOR SUMMARY OF THE INVENTION This invention relates to US. Pat. application Ser. No. 854,397, filed Sept. 2, 1969, and entitled Rubbing Seal for High Temperature Ceramics.
Rubbing seals having surface layers consisting essentially of uniform mixtures of a glazing material and a matrix material have excellent wear and friction properties when used with ceramics operating at high temperatures. Such surface layers are difficult to prepare, however, and inherently provide a constant amount of glazing material regardless of the wear rate.
The rubbing seal provided by this invention is relatively easy to manufacture and exposes greater amounts of glazing material in those areas having higher wear rates to produce a more stable seal member having a much longer useful life. A seal member of this invention has a high temperature wear coating for rubbing against a relatively moving ceramic member that consists essentially of a plurality of particles having a core of glazing material surrounded by a shell of a metal capable of oxidizing at the operating temperature of the wear coating. The oxide of the metal shell does not abrade the ceramic member but instead wears off when the ceramic regenerator rubs against it to expose the glazing material. Greater amounts of glazing material are exposed in those portions of the seal member having higher wear rates until a balanced wear rate is achieved.
Useful core materials include calcium fluoride, barium fluoride, lithium fluoride, sodium fluoride, molybdenum disulfide, and tungsten selenide. Nickel, copper and cobalt are most useful as the shell materials, although any of the metals having oxides disclosed as useful matrix materials in the aforementioned patent application also can be used.
Coated particles can be made by any of a variety of techniques. Plasma spraying equipment is used to spray the coated particles onto a metal substrate having reasonably compatible thermal expansion properties. Typically substrates are nickel-chromium stainless steels or other high temperature alloys such as lncoloy 600 or 750 sold by International Nickel Co. or l-Iastalloy X sold by Union Carbide Co. Plasma spraying is carried out at a temperature where the metal shells weld themselves to the substrate and to each other to form a cohesive, integral surface layer made up of a substantially continuous matrix formed from the metal shells of the particles that contains a large number of evenly distributed particles of glazing material.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an exploded view of a disc type regenerator assembly for a gas turbine engine showing the relationship of the seal members to the regenerator.
FIG. 2 is a sectional view through one of the seal members.
FIG. 3 is an enlarged sectional view of a portion of the coating showing the final configuration of the particles.
DETAILED DESCRIPTION Referring to FIG. I, the housing of a gas turbine engine contains a substantially circular regenerator portion 10. A diametrical wall 12 separates a substantially circular passage in portion into two semi-circular gas flow passages 14 and 16. Hot exhaust gases flow upward through one of the passages and cooler air flows downward through the other passage in the conventional manner.
A cross arm seal 18 is positioned on top of wall 12 and is surrounded on opposite sides by C-shaped seals 20 and 22. Seals 18, 20 and 22 are held non-rotatably with respect to housing portion 12 by any conventional means (not shown).
A disc shaped ceramic regenerator 24 is positioned rotatably on top of seals 18, 20 and 22. Regenerator 24 is rotated relative to the seals by internal components of the engine. A D-shaped seal 26 is located above regenerator 24 and a cap (not shown) fits on top of housing portion 10 to hold the components in place.
Each of the surfaces of seal members 18, 20, 22 and 26 that rub against regenerator 24 has a coating consisting essentially of a plurality of welded particles 28. The sectional view of FIG. 2 illustrates the particulate coating on top of cross arm seal member 18. Several layers of particles 28 can be applied to each seal member as desired. For best results each coating contains a minimum of the equivalent of at least two or three layers of particles.
Referring also to FIG. 3, each particle consists essentially of a core 30 surrounded by a metal shell 32. Core 30 is a material capable of forming a glaze having a low coefficient of friction when rubbing against ceramic material at the anticipated operating temperature of the seal. Cross arm seal 18 typically operates at a temperature of about l,400 F. and preferably uses particles having cores of calcium fluoride surrounded by nickel shells. The C seal surrounding the passage carrying hot exhaust gases typically operates at about 800 F. and preferably uses particles having cores of lithium fluoride and sodium fluoride surrounded by shells of copper. The other C seal operates typically at a slightly cooler temperature of about 700 F. Its preferred particles have cores of a similar composition. D seal 26 operates at a relatively low temperature of about 600 F. and preferably uses particles having cores of molybdenum disulfide surrounded by shells of cobalt.
Each shell 32 is a metal capable of oxidizing at the operating temperature to an oxide that does not abrade the ceramic material of regenerator 24 but instead wears away under the rubbing action of the regenerator. The particles are plasma sprayed onto the metal substrate of the seal in a manner such that the shells 32 melt or weld together and to the substrate to form a cohesive coating containing a plurality of dispersed cores 30.
During engine operation, the combined effects of temperature and the rubbing action of the regenerator oxidizes the metals of the shells and rubs the oxide away to expose the core materials. The exposed core materials rapidly form a glaze having a low coefficient of friction.
Instead of plasma spraying the particles directly onto the metal substrate, the particles can be fabricated into the form of a separate sheet. The sheet is fastened mechanically by riveting, for example, to a substrate. This technique reduces repair costs and provides some improvement in the thermal shock resistance of the assembly.
Thus this invention provides an effective coating for the rubbing seals of a ceramic regenerator. The coating exposes its cores of glazing material according to the demands of each individual portion of the seal. Because of the composite structure of the coating, it is highly resistant to salt attack brought on by the presence of road salt in the air and gas streams of the engine.
1. A high temperature wear coating for rubbing against a ceramic member having relative motion, said wear coating consisting essentially of a plurality of particles having a core of lubricating material surrounded by a shell of a metal capable of oxidizing at the operating temperature of the wear coating, said shells of said particles being welded to each other to form an integral structure having dispersed therein a plurality of said cores, the oxide of said metal shell being non abradable to the ceramic member rubbing a against the coating.
2. The wear coating of claim 1 in which the shell is nickel, copper or cobalt and the core is calcium fluoride, barium fluoride, lithium fluoride, sodium fluoride, molybdenum disulfide, or tungsten selenide.
3. In a gas turbine engine having a ceramic regenerator mounted for rotation relative to an engine housing, a sliding seal for said regenerator comprising a metal substrate having a surface layer attached to one surface for rubbing against said ceramic regenerator, said surface layer comprising a plurality of particles, each of said particles having a core consisting of a glazing material surrounded by a shell of a metal oxidizable at the operating temperature of the coating, said shells being welded to each other to form an integral structure having dispersed therein a plurality of said cores.
4. The engine of claim 3 in which the cores of the particles 5 are calcium fluoride, barium fluoride, lithium fluoride, sodium fluoride, molybdenum disulfide or tungsten selenide.
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