GB2399777A - Abradable seals for gas turbine engines - Google Patents

Abradable seals for gas turbine engines Download PDF

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Publication number
GB2399777A
GB2399777A GB0225472A GB0225472A GB2399777A GB 2399777 A GB2399777 A GB 2399777A GB 0225472 A GB0225472 A GB 0225472A GB 0225472 A GB0225472 A GB 0225472A GB 2399777 A GB2399777 A GB 2399777A
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GB
United Kingdom
Prior art keywords
coating
abrasive material
abradable
region
substrate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB0225472A
Other versions
GB0225472D0 (en
Inventor
Mark Henry Shipton
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rolls Royce PLC
Original Assignee
Rolls Royce PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Rolls Royce PLC filed Critical Rolls Royce PLC
Priority to GB0225472A priority Critical patent/GB2399777A/en
Publication of GB0225472D0 publication Critical patent/GB0225472D0/en
Publication of GB2399777A publication Critical patent/GB2399777A/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
    • C23C4/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D11/00—Preventing or minimising internal leakage of working-fluid, e.g. between stages
    • F01D11/08—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator
    • F01D11/12—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator using a rubstrip, e.g. erodible. deformable or resiliently-biased part
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D11/00—Preventing or minimising internal leakage of working-fluid, e.g. between stages
    • F01D11/08—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator
    • F01D11/12—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator using a rubstrip, e.g. erodible. deformable or resiliently-biased part
    • F01D11/122—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator using a rubstrip, e.g. erodible. deformable or resiliently-biased part with erodable or abradable material

Abstract

An abradable coating on, for example, a casing 2 of a gas turbine engine, comprises a first region 8 containing abrasive material and a second region 10 without the abrasive material. In normal operation, rotor blade tips penetrate the second layer 10 to form a seal between the rotor and the casing. If major incursions of the blade tips into the coating occur, the blade tips will be abraded by the abrasive material in the first layer 8, so preventing the blade tips from contacting a bondcoat 4 or the casing 2. This avoids the generation of extreme temperatures, which, in the case of titanium alloy components, could cause a titanium fire.

Description

ABRADABLE COATINGS
This invention relates to abradable coatings, and is particularly, although not exclusively, concerned with abradable coatings for use in gas turbine engines.
The use of abradable coatings in gas turbine engines is well known. For example, GB 791568 discloses an abradable coating applied to the inner surface of a compressor casing. As a rotor rotates within the casing, the rotor blade tips contact the coating and, in effect, machine the coating to form a groove along which the blades of the rotor pass when the engine is at its normal operating temperature and speed. Consequently, gas flow paths between the rotor and casing are minimised, so improving the efficiency of the engine.
It is common to use titanium alloys in gas turbine engines, and in particular for rotor blades. Titanium is flammable, and will ignite at elevated temperatures in the presence of oxygen or carbon dioxide. Typically, the ignition temperature for titanium is 3300K.
In normal operation of a gas turbine engine, titanium alloy components are kept below the ignition temperature. However, in some circumstances, the ignition temperature can be reached, and a titanium fire will result. A titanium fire is an aggressive event which can cause major engine damage.
Some titanium fires are caused by frictional heating during heavy blade tip rubs upon an abradable coating or on the casing substrate material (for example steel). High radial incursions of a rotor may occur if the rotor becomes unbalanced or in the event of high g forces. Unbalancing of the rotor may follow damage such as the loss of one or more blades. This may cause the rotor tips to penetrate right through the abradable coating and to rub against the casing itself. The resulting friction generates extremely high temperatures, causing the titanium to ignite.
Even if the rotor tips do not penetrate entirely through the abradable coating, a large radial incursion may prevent normal clean removal of abradable material from the coating, and instead cause compression and smearing of the coating. The resulting friction may, again, raise the temperature at the sliding surfaces above the ignition temperature of titanium.
According to the present invention there is provided a coating on a substrate, the coating comprising a first region, adjacent the substrate, in which the coating contains or comprises an abrasive material, and a second region, over the first region, in which the coming comprises an abradabie material without the abrasive material, the second region providing a free surface of the coating.
A coating in accordance with the present invention may be used on a casing of a gas turbine engine. In normal operation of the engine, blade tips will abrade the coating to provide an adequate seal. However, if a major blade tip incursion takes place, the blade tips will reach the abrasive material which will abrade the blades in a relatively cool cutting process so preventing the blade tips from reaching the substrate, and avoiding temperature increases which could result in a titanium fire.
The abrasive material is preferably at least 0.5 mm, and more preferably at least 0.75 mm below the free surface of the coating. In a preferred embodiment, the abrasive material is approximately 1 mm below the free surface. In this context, the 'free surface' is the surface before any abrasion of the coating has occurred as a result of blade tip contact.
The abrasive material may, for example, comprise Alumina, Cubic Boron Nitride (CBN) or Zirconia.
The proportion of the abrasive material within the coating may vary with the depth of the coating. For example, the proportion of the abrasive material may be zero at the free surface of the coating and greater than 75% at the substrate. Preferably, the coating comprises 100% abrasive material at the substrate.
The present invention also provides a method of applying a coating to a substrate, the method comprising applying a first layer containing abrasive material and subsequently applying a second layer comprising an abradable material without the abrasive material.
In a preferred embodiment, the coating is applied by a spraying process, such as a thermal spraying or plasma spraying process.
The spraying process may be performed by means of a gun provided with two sources of material to be sprayed, one source providing abrasive material to the gun, and the other providing material which, when deposited, forms an abradable coating. Thus, during the spraying process, the proportion of abrasive material to the abradable- forming material may be varied as the coating builds up.
For a better understanding of the present invention, and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying Figure, which, in diagrammatic form, shows an abradable coating on a substrate.
The Figure represents a substrate 2 in the form of a steel casing of, for example, an HP compressor stage in a gas turbine engine. A bondcoat 4 is applied directly to the casing 2 and may, for example, take the form of a powder sprayed nickel/aluminium composition.
An abradable coating 6 is applied over the bondcoat 4. The abradable coating 6 is made up of two components, namely an abradable material and an abrasive material.
The abradable material preferably has a high thermal conductivity such as an Aluminium/Silicon/Polyester composition available from Sulzer Metco under the designation Metco 601 or an Aluminium/Silicon/Boron Nitride composition available from Sulzer Metco under the designation Metco 320. A typical thermal conductivity for the abradable material is 27.1 W/m K. Preferably the thermal conductivity should be greater than 20 W/m K, and more preferably above 25 W/m K. The abrasive material may be, for example, Alumina, Cubic Boron Nitride or Zirconia. A suitable composition is available from Saint Gobain Abrasives Limited under the designation B252, which comprises Cubic Boron Nitride having a particle size of 60-80 mesh.
The components of the coating 6 are not distributed equally through the depth of the coating. Instead, the abrasive component is confined to a region 8 of the coating 6 which is closest to the bondcoat 4. The outer region 10 of the coating, which provides the free surface 12, contains none of the abrasive material. By way of example, the depth do of the region 10 may be approximately 1 mm, and the depth d2 of the abrasivecontaining region 8 may be not less than 1.5 mm and not more than 2 mm.
Within the abrasive-containing layer 8, the proportion of abrasive material in the coating may vary. By way of example, the proportion of abrasive material to abradable material may vary from 0% in the outer region 10, to 100% in the region 8 adjoining the bondcoat 4. This can be achieved by feeding the coating forming materials separately to a spray gun, for example a plasma spray gun, with provision for adjustment of the flow rates of materials to the gun. Thus, when spraying on to the bondcoat 4 begins, only the abrasive feed material is supplied to the gun, so that 100% abrasive material is applied to the bondcoat 4. As the coating 6 builds up, the feed of material for the abradable coating starts, and the proportion of abrasive material is steadily reduced until it terminates altogether at the transition 14 between the regions 8 and 10. Thus the coating in the region 10 is built up using only the feed material for the abradable coating.
In normal operation of a gas turbine engine of which the casing 2 is a part, blade tip incursion into the coating 6 is confined to the region 10. If the engine is subjected to severe g forces, or if damage occurs which results in the rotor becoming out of balance, more severe blade incursion may occur, and the blade tips may reach the transition 14 and begin to penetrate into the abrasive-containing region 8. If this happens, the abrasive material will abrade the blade tips. This will be a relatively efficient cool cutting operation, and the lengths of the blades will be reduced without significant generation of heat. If, nevertheless, the blade tips penetrate further into the region 8, the increased proportion of abrasive material will increase the grinding effect on the blade tips, reducing the possibility that the blade tips may penetrate entirely through the coating 6 to the bondcoat 4 or the substrate material 2.
Since the rate of incursion of the blade tips into the coating may be very rapid during an out-of-balance event, the abrasive material needs to be highly abrasive in order to remove the blade tip material before contact with the bond coat or substrate occurs.
Consequently, the abrasive material should be very hard (ie a Vickers hardness in excess of 40 GPa - the hardness of Cubic Boron Nitride is approximately 45 GPa), and should have an angular particle structure.
The use of the coating 6 as described above consequently minimises the possibility of direct blade contact between the bondcoat 4 or the steel casing 2, so avoiding the possibility that a titanium fire may be started by frictional heat generation.

Claims (32)

1 A coating on a substrate, the coating comprising a first region, adjacent the substrate, in which the coating contains or comprises an abrasive material, and a second region, over the first region, in which the coating comprises an abradable material without the abrasive material, the second region providing a free surface of the coating.
2 A coating as claimed in claim 1, in which the depth of the second region is not less then 0.5 mm.
3 A coating as claimed in claim 2, in which the depth of the second region is not less than 0.7 mm.
4 A coating as claimed in claim 3, in which the depth of the second region is approximately 1 mm.
A coating as claimed in any one of the preceding claims, in which the abrasive material is Alumina, Cubic Boron Nitride and/or Zirconia.
6 A coating as claimed in any one of the preceding claims, in which the abrasive material has a hardness of not less than 40 GPa.
7 A coating as claimed in any one of the preceding claims, in which the abradable material contains Aluminium.
8 A coating as claimed in claim 7, in which the abradable material comprises Aluminium and Silicon.
9 A coating as claimed in any one of the preceding claims, in which the abradable material includes a polymer.
A coating as claimed in claim 9, in which the polymer is a polyester.
11 A coating as claimed in any one of the preceding claims, in which, in the first region, the abrasive material is mixed with the abradable material.
12 A coating as claimed in claim 11, in which the proportion of abrasive material in the abradable material increases in the direction towards the substrate.
13 A coating as claimed in claim 11 or 12, in which the proportion of abrasive material at the substrate is not less than 75%.
14 A coating as claimed in claim 13, in which the coating is substantially 100% abrasive material at the substrate.
A coating as claimed in any one of the preceding claims, in which a bondcoat is disposed between the substrate and the coating.
16 A coating substantially as described herein with reference to, and as shown in, the accompanying Figure.
17 A casing for a gas turbine engine, the casing comprising a metallic substrate provided with a coating in accordance with any one of the preceding claims.
18 A gas turbine engine comprising a casing as claimed in claim 17, and a bladed rotor mounted for rotation in the casing, the blades of the rotor being made from a titanium alloy and being disposed to penetrate the second region of the coating during normal operation of the engine.
19 A method of applying a coating to a substrate, the method comprising applying a first layer containing abrasive material and subsequently applying over the first layer a second layer comprising an abradable material without the abrasive material.
A method as claimed in claim 19, in which the coating is applied by spraying.
21 A method as claimed in claim 20, in which the coating is applied by thermal spraying.
22 A method as claimed in claim 20, in which the coating is applied by plasma spraying.
23 A method as claimed in any one of the claims 20 to 22, in which material to form the coating is sprayed from a gun to which both abradable and abrasive materials are independently supplied.
24 A method as claimed in claim 23, in which the ratio of abrasive material to abradable material is reduced as the first layer is built up.
A method as claimed in claim 24, in which the proportion of abrasive material is reduced from 100% to 0% as the first layer is built up.
26 A method as claimed in any one of claims 19 to 25, in which the abrasive material is Alumina, Cubic Boron Nitride and/or Zirconia.
27 A method as claimed in any one of claims 19 to 26, in which the abrasive material has a hardness of not less than 40 GPa.
28 A method as claimed in any one of claims 19 to 27, in which the abradable material includes Aluminium.
29 A method as claimed in claim 28, in which the abradable material comprises Aluminium and Nickel.
A method as claimed in any one of claims 19 to 29, in which the abradable material comprises a polymer.
31 A method as claimed in claim 30, in which the polymer is a polyester.
32 A method as claimed in claim 19 and substantially as described herein.
GB0225472A 2002-11-01 2002-11-01 Abradable seals for gas turbine engines Withdrawn GB2399777A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0225472A GB2399777A (en) 2002-11-01 2002-11-01 Abradable seals for gas turbine engines

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0225472A GB2399777A (en) 2002-11-01 2002-11-01 Abradable seals for gas turbine engines

Publications (2)

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GB0225472D0 GB0225472D0 (en) 2002-12-11
GB2399777A true GB2399777A (en) 2004-09-29

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1801472A2 (en) 2005-12-22 2007-06-27 Kabushiki Kaisha Toshiba Sealing device
EP1908925A3 (en) * 2006-09-28 2011-01-26 United Technologies Corporation Ternary carbide and nitrate thermal spray abradable seal material
US8132414B2 (en) 2005-10-31 2012-03-13 Kabushiki Kaisha Toshiba Steam turbine and hydrophilic coating material used therefor
US8545175B2 (en) 2009-07-03 2013-10-01 Rolls-Royce Plc Rotor blade over-tip leakage control
EP2927432A1 (en) * 2014-03-31 2015-10-07 Rolls-Royce plc Gas turbine engine, method of manufacturing a gas turbine engines and fan casing
EP3020931A1 (en) * 2014-10-31 2016-05-18 United Technologies Corporation Abrasive rotor coating with rub force limiting features
US20190085865A1 (en) * 2017-09-19 2019-03-21 United Technologies Corporation Turbine engine seal for high erosion environment

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4291089A (en) * 1979-11-06 1981-09-22 Sherritt Gordon Mines Limited Composite powders sprayable to form abradable seal coatings
US4349313A (en) * 1979-12-26 1982-09-14 United Technologies Corporation Abradable rub strip
US4566700A (en) * 1982-08-09 1986-01-28 United Technologies Corporation Abrasive/abradable gas path seal system
GB2242143A (en) * 1990-03-23 1991-09-25 Rolls Royce Plc Abradable seal coating and method of making the same

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4291089A (en) * 1979-11-06 1981-09-22 Sherritt Gordon Mines Limited Composite powders sprayable to form abradable seal coatings
US4349313A (en) * 1979-12-26 1982-09-14 United Technologies Corporation Abradable rub strip
US4566700A (en) * 1982-08-09 1986-01-28 United Technologies Corporation Abrasive/abradable gas path seal system
GB2242143A (en) * 1990-03-23 1991-09-25 Rolls Royce Plc Abradable seal coating and method of making the same

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8132414B2 (en) 2005-10-31 2012-03-13 Kabushiki Kaisha Toshiba Steam turbine and hydrophilic coating material used therefor
EP1801472A2 (en) 2005-12-22 2007-06-27 Kabushiki Kaisha Toshiba Sealing device
EP1801472A3 (en) * 2005-12-22 2007-07-11 Kabushiki Kaisha Toshiba Sealing device
AU2006252116B2 (en) * 2005-12-22 2009-07-02 Kabushiki Kaisha Toshiba Sealing device
EP1908925A3 (en) * 2006-09-28 2011-01-26 United Technologies Corporation Ternary carbide and nitrate thermal spray abradable seal material
US8017240B2 (en) 2006-09-28 2011-09-13 United Technologies Corporation Ternary carbide and nitride thermal spray abradable seal material
US8545175B2 (en) 2009-07-03 2013-10-01 Rolls-Royce Plc Rotor blade over-tip leakage control
EP2927432A1 (en) * 2014-03-31 2015-10-07 Rolls-Royce plc Gas turbine engine, method of manufacturing a gas turbine engines and fan casing
US9752593B2 (en) 2014-03-31 2017-09-05 Rolls-Royce Plc Method of manufacturing a gas turbine engine having a fan track liner with an abradable layer
EP3020931A1 (en) * 2014-10-31 2016-05-18 United Technologies Corporation Abrasive rotor coating with rub force limiting features
US20190085865A1 (en) * 2017-09-19 2019-03-21 United Technologies Corporation Turbine engine seal for high erosion environment
EP3456928B1 (en) * 2017-09-19 2021-09-08 Raytheon Technologies Corporation Blade outer air seal for gas turbine engines in high erosion environment
US11149744B2 (en) * 2017-09-19 2021-10-19 Raytheon Technologies Corporation Turbine engine seal for high erosion environment

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