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Although dynamic systems rotating at high speed are designed to ensure concentric rotation, over time slight eccentricities can occur. Additionally, the inertial properties of rotation and thermal expansion can cause the turbine blade growth or a hard landing or maneuver loads in an aircraft can cause an unexpected occurrence of a fast blade incursion into the stationary component. It is therefore often necessary to design a gap between the rotating and stationary components of the system.

For gas turbine engines, such gaps in the gas path represent a loss of efficiency. A space of 0.125 mm (0.005 in) between the engine compressor blades and the outer casing can increase fuel consumption by 0.5%. Clearance control technologies minimize gap size by utilizing a surface that will abrade preferentially when contact is made with a mating part.

Solutions:

In rotary equipment such as compressors, gas turbines, and turbochargers, thermal and mechanical operational effects cause dimensional changes between the rotor and stator. These dimensional changes open gaps between the blade tips and the casing in gas path systems and between the seal and housing in labyrinth seal systems. 

In these applications, clearance control systems can be installed that consist of a sacrificial element and a cutting component. Thermal spray abradable coatings form effective sacrificial systems.

Learn more about the coatings for clearance control

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