A&A Coatings material is a blend of silicon-aluminum and polyester powders which was especially developed for machine element clearance control. Field testing in aircraft engines confirms that coatings of Aluminum-Polyester have a high degree of abradability with essentially no blade tip wear, excellent resistance to oxidation at temperatures up to (345° C) 650° F and good resistance to thermal shock.
Additionally, Aluminum-Polyester coatings have good resistance to impact and excellent internal strength. The microstructure is a continuous matrix of aluminum with fairly well dispersed particles of polyester. The aluminum provides good bond strength, good interparticle strength and good thermal properties. The polyester provides abradability and a low coefficient of friction.
Material Powder Characteristics
|Typical Composition:||Blend of Si-Al Alloy 60%|
|Typical Size Range:||-140 mesh +10 microns|
(-106 +10 microns)
Physical Properties of Coating
|Surface Texture As-Sprayed|
|Finish, As-Machined (microinches aa):||75-90|
|Coating Macrohardness:||R15y 68-78|
|Coating Weight (lb/ft2/.001″):||.0089|
|Thickness Limitation||None Apparent|
Clean substrate. Severe oxidation must be removed, grit blasting is recommended. Preheat to 95°C (200°F) to prevent formation of condensate.
The best finishes are obtained by machining, using a sharp pointed, high-speed steel tool bit, light feeds, fast work speed and fast traverse rate. The machined surface will be dull, rather than bright, as the result of particle pullout. It is recommended that the machined coating be thoroughly cleaned before the sprayed part is put into service. The coating appearance can be improved by buffing it with a soft brass wheel. However, this will smear the surface. The coatings should not be ground. The pressure and heat generated by grinding will compress the coating and alter its properties.