The function and application of abradable sealing coating

       In order to form an ideal sealing state between the blades and the casing of high-speed rotating machinery (compressors, gas turbines, etc.) to obtain the largest hydrodynamic pressure difference, abradable coating technology can be used to improve the efficiency of the whole machine and reduce energy consumption , prolong the service life of the whole machine. In the manufacture of aero-engines, the use of abradable coatings can successfully reduce the gap between the rotor and the casing. For clearance control between the compressor turbine and the outer ring, the ideal result is that friction does not cause damage to the turbine or other compressor components, such as bearings or gears; after friction, the surface of the abradable coating is extremely smooth, and Uncoated material transfers to the turbine. If the residual surface is not smooth, it will negatively affect the airflow direction, which will affect the efficiency of the machine; if the abradable material is transferred to the turbine, it may cause an imbalance, which will also affect the performance of the compressor. Up to now, a series of abradable coating materials have been developed for the air path sealing problem of jet engine. The use of abradable coatings can be used not only for surface air seals to reduce clearances, but also for labyrinth seals to channel cooling air, reduce engine compressed air losses, and maintain rotor shaft pressure balance.



In addition to the use of flame sprayed pure aluminum coatings as abradable coatings in the early days, most of the currently used abradable coatings are composed of two materials, namely metal body and non-metallic filler. The function of the filler is to weaken the metal The integrity of the body enhances the abradability of the coating. The spray powder used for the abradable coating is a mixed powder or agglomerated powder composed of two materials.



Using plasma spraying or powder flame spraying technology, a soft abradable coating is sprayed on the compressor casing, and a hard wear-resistant cobalt-coated tungsten carbide coating is sprayed on the end of the compressor blade, which can form an ideal between the two. It is an advanced manufacturing technology developed rapidly in the aerospace sector in the 1970s and one of the important applications of modern thermal spraying technology.