Masking fixture and method

Abstract

A fixture for selectively masking a turbine blade,includes a locator,with a separable receptacle,having portals,Guide bars,extend from the locator for guiding a pair of shield carriers,between deployed and retracted positions. Each shield carrier has a shield,projecting therefrom. In use, a turbine blade,whose root,includes a fir tree attachment,and a damper pocket,is mounted on the fixture so that the receptacle embraces the blade root. The shield carriers are translated along the guide bars until the shields penetrate through the portals and into the receptacle thus segregating the attachment,from the damper pocket,Masking powder,is then compressed into the receptacle to envelop the attachment while leaving the damper pocket unmasked. The fixture facilitates selective masking of the blade root so that when the receptacle and masked blade are subsequently exposed to a metal bearing vapor at an elevated temperature, the vapor coats the damper pocket but not the highly stressed attachment. In one variant of the invention, the shields are independent, consumable shields dimensioned and shaped to substantially conform to the size and shape of the damper pocket. The shields are made of a thermally decomposable material. In use, the shields are wedged into the damper pockets prior to blade masking. During the coating cycle, the shields decompose at a temperature lower than the temperature at which coating vapors are produced to expose the damper pocket to the vapors.