text: The present invention relates generally to aspirating face seals between rotor and stator assemblies and, more particularly, to an abradable seal land for an aspirating face seal starter tooth.
  Aspirating face seals minimize leakage of a fluid, such as compressed air or combustion gases, by restricting flow between an area of high pressure and an area of low pressure. Aspirating face seals (AFS) control leakage by compensating for variations in the gap which may exist between a rotor and stator. Such seals have been disclosed for use in rotating machinery, including but not limited to, gas turbine engines used for power generation and for aircraft and marine propulsion.
  Fluid leakage through gas turbine engine seal assemblies may significantly increase fuel consumption and adversely affect engine efficiency. Additionally, fluid leakage may cause damage to other components and/or increase overall engine maintenance costs. Because of the location of the seal assemblies and/or the operating environment, some known seal assemblies may deteriorate over time.
  Some embodiments of aspirating face seals are configured as oppositely facing rotatable first and non-rotatable second seal elements. The rotatable first seal element is attached to, or is a monolithic portion of, the rotor. Likewise, such seals typically have the stator supporting the non-rotatable second seal element which is attached to, or a monolithic portion of, a slider. Retraction springs, typically coil springs, are used to separate or retract the non-rotating second seal element from the rotating first seal element during low or no power conditions. The non-rotatable second seal element is mounted on the slider supported by the stator. Examples of such aspirating face seals are disclosed in patent applications from General Electric Company in Ser. Nos. 2016/41013072 and 2016/41016504, filed in INDIA, assigned to the present Assignee, the General Electric Company, and incorporated by reference. Ser. No. 2016/41013072 is entitled “ANTI-CONING ASPIRATING FACE SEAL” and was filed in India on Apr. 14, 2016. Ser. No. 2016/41016504 is entitled “ASPIRATING FACE SEAL TOOTH CONFIGURATION” and was filed in India on May 11, 2016.
  U.S. Pat. No. 6,676,369 to Brauer, et al., issued Jan. 13, 2004, and entitled “Aspirating Face Seal with Axially Extending Seal Teeth”, discloses a gas turbine engine aspirating face seal including a rotatable engine member and a non-rotatable engine member and a leakage path therebetween. Annular generally planar rotatable and non-rotatable gas bearing face surfaces circumscribed about a centerline are operably associated to the rotatable and non-rotatable engine members respectively. Radially inner and outer tooth rings axially extend away from a first one of the rotatable and non-rotatable gas bearing face surfaces across the leakage path and towards a second one of the gas bearing face surfaces. An auxiliary seal includes an annular restrictor tooth extending radially across the leakage path from a second one of the rotatable and non-rotatable gas bearing face surfaces towards the first one of the rotatable and non-rotatable gas bearing face surfaces. Coiled springs are utilized to separate the gas bearing face surfaces.
  Known seal designs include a starter tooth mounted on a rotatable engine member. The starter tooth is an annular labyrinth seal tooth designed and operable to sealingly engage a corresponding abradable starter seal land. The starter seal abradable land is typically an abradable coating on an interior surface of an annular slider axially slidingly mounted on the annular non-rotatable engine member.
  It is also important to note that aspirating face seal technology uses phrases such as “air bearing”, “air dam”, and “air flow”, wherein it is understood that the word “air” is used to describe the working fluid of the seal. The working fluid of an aspirating face seal can include, without limitation, compressed air, combustion gases, and/or steam. Note that an aspirating face seal is a non-contacting seal in that the first and second parts or rotatable and non-rotatable seal elements of the seal are not intended to touch, but may for short periods of time, during which they experience what are known as rubs.
  One potential cause of air bearing contact is an aggressive rub between the rotor starter tooth and the slider abradable land or coating. As the tooth wears into the coating, heat generated by the rub causes the slider air bearing surface to distort. In addition, the starter tooth rub forces prevent or inhibit the slider from retracting. These two effects lead to air bearing contact. Heat generated by the contact creates a large thermal gradient across the slider air bearing face, which can cause the surface to crack. To prevent this problem, starter tooth rubs must be minimized or eliminated when the seal is closed.