Seal for a joint or juncture – Seal between relatively movable parts – Close proximity seal
Reexamination Certificate
2000-03-02
2002-01-01
Sandy, Robert J. (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Close proximity seal
Reexamination Certificate
active
06334617
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to resilient composite abradable materials, and particularly to abradable materials for use in the compressor sections of gas turbine engines, and particularly in the low compressor section of such engines.
Modern large gas turbine engines have axial flow compressors which include multiple circular airfoil arrays mounted at the periphery of rotatable disks. Adjacent each set of moving compressor airfoils is an array of stationary airfoils. The efficiency of such a compressor is strongly affected by air which leaks around the ends of the moving airfoils. The typical approach to minimize such leakage is to provide an abradable air seal with which the compressor airfoil outer ends interact to minimize leakage.
U.S. Pat. No. 3,575,427 describes the abradable seal materials similar to those which are currently in use in engines produced by the assignee of the present invention. The seal material of U.S. Pat. No. 3,575,427 comprises a resilient matrix material containing a dispersion of friable hollow glass microspheres.
Applicants currently use such materials which comprise a silicone rubber matrix containing 15 to 50 volume percent of hollow glass microspheres as an abradable air seal material.
The evolution of gas turbine engines has been in the direction of higher operating temperatures. Temperatures in the compressor section of the engine have increased moderately, while temperatures in the combustor in turbine section have increased substantially since the development of the material described in U.S. Pat. No. 3,575,427.
In gas turbine engines with glass microballoon containing seals, when the abradable seals abrade, the glass microspheres are carried through the combustor and turbine sections of the engine. In modern engines, the temperatures in the combustor and turbine sections, are sufficiently high to cause the glass microspheres to soften or melt. It has been occasionally observed that these softened or melted glass microspheres have adhered to engine components and have blocked air cooling holes. Blockage of cooling holes is detrimental to engine component longevity.
Accordingly, it is an object of this invention to describe an abradable material for use in modern high temperature gas turbine engines. It is another objective of the invention to describe an abradable material which whose constituents will not subsequently adhere to combustor and turbine components. It is yet another object of the invention to describe a compressor of abradable material which exhibits higher erosion resistance over temperatures ranging from room temperature to 400° F. than the currently used material and is usable in temperatures up to 450° F., and exhibits desirable abradability characteristics.
SUMMARY OF THE INVENTION
Broadly stated, the invention comprises a high temperature resilient material comprised of a high temperature capable silicone polymeric material which contains a dispersion of high temperature capable organic particles. The particles are selected from a material which is stable to at least 400° F. The particles are present in the seal in an amount of about 10 wt %.
The silicone polymeric matrix is selected so as to be thermally stable at temperatures in excess of 300° F. and preferably in excess of 450° F. Most preferably the silicone polymeric matrix can withstand short temperature spikes of up to 550° F. without undue deterioration.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention comprises a matrix containing a particle or low aspect ratio (<10:1) fiber dispersion.
The phrase “abradable silicone polymer matrix” or ASPM is used herein as a defined term for a material that is a resilient one or two part silicone polymer catalyzed by a precious metal selected from the group consisting of Ru, Rh, Pd, Os, Ir, Pt and mixtures thereof, which is thermally stable at least 300° F. The cured ASPM material has a room temperature tensile strength of greater than 400 PSI, an elongation to failure of greater than 100%, and a Shore A (Durometer) hardness of from 15-50.
Preferably the ASPM material is a demethyl or methyl phenyl silicone.
Preferably the ASPM material contains a transition metal oxide selected from the group consisting of oxides of V, Cr, Ce, Mn, Fe, Co, Ni, or other transition metal and mixtures thereof with iron oxide being particularly preferred. The transition metal oxide acts as a thermal or thermal oxidative stabilizer.
Preferably the ASPM material is produced from a mixture of a vinyl terminated polymer having a molecular weight of 1,000 g/mol to 1,000,000 g/mol; a silane crosslinker having a molecular weight of 300 g/mol to 10,000 g/mol and a precious metal catalyst, most preferably Pt. The ASPM may also contain a reinforcing file such as fumed silica.
Preferably the room temperature tensile strength of the cured ASPM material exceeds 1,000 PSI.
Preferably the room temperature elongation to failure of the cured ASPM ma exceeds 800%.
Preferably the Shore A Durometer hardness of the cured ASPM material is about 15 to about 40.
Preferably the cured ASPM material is oxidation resistant, exhibiting less 2% weight loss after 100 hours (using a 1″×1″×¼″ sample) at 300° F., and most preferably at 400° F. exposure in air.
Preferably the cured ASPM material is thermally stable, losing less than 20% of its tensile strength after 100 hours at 300° F., and preferably 400° F.
The phrase “abradable organic filler particles” or AOFP is used herein as a defined term meaning a material that is hard, organic, and that retains useful properties at 300° F. The AOFP material must contain less than about 2% S to ensure proper curing of the ASPM material. The AOFP material must have a glass transition temperature which exceeds 300° F. and a room temperature impact strength in excess of 0.5 ft-lb/in
x
to reduce the likelihood of particle breakage during abrading conditions in engine operation.
Preferably the AOFP material retains useful mechanical properties at temperatures in excess of 500° F.
Preferably the AOFP material contains less than about 2 wt % F so that the products of AOFP material combustion are not corrosive to gas turbine materials.
Preferably the AOFP material contains less than about 1 wt % S and less than about 1 wt % F.
Preferably the AOFP material produces only gaseous combustion products when combusted in a gas turbine engine at temperatures in excess of 2,000° F. generally oxidizing conditions.
Many organic materials contain fillers such as mica, glass particles etc. Preferably the AOFP material does not contain fillers. If fillers are present they must either combust completely, or be non combustable with softening temperatures in excess of 2500° F. and preferably in excess of 3000° F. Non combustable fillers preferably have a particle size of less than 1 mil.
Preferably the AOFP material has a glass transition temperature exceeds about 400° F.
Preferably the AOFP material has a Deflection Temperature, measured according to ASTM D 648, at 1.8 MPa, which exceeds about 400° F., and preferably exceeds 500° F.
Preferably the AOFP material has a room temperature tensile strength which exceeds 10 ksi.
Preferably the AOFP material has a room temperature elongation to failure which exceeds 1%.
Preferably the AOFP material has a room temperature Izod impact strength which exceeds 1.0 ft-lb/in.
The particles which are added to the matrix material serve to slightly weaken the matrix material, and make it more abradable. It is well within the ability of one skilled in the art to select the proper amount of particulate material for a matrix material having particular qualities to achieve the desired degree of abradability. We prefer to use from about 5 to about 20 weight percent particles.
The particles are preferably selected from the group consisting of polyamides, polyimides, polyamide-imides, as well as other thermoplastic and thermoset materials which are stable in the gas turbine compressor operating environment.
We particularly prefer a polyamide-imide known as Torlon 40
Putnam John W.
Watson Charles R.
Sandy Robert J.
Schwing Karlena D.
United Technologies Corporation
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