Abradable coating
Encyclopedia
An abradable coating is a coating made of an abradable material – meaning if it rubs against a more abrasive
material in motion, the former will be worn whereas the latter will face no wear.
Abradable coatings are used in aircraft jet engine
s in the compressor and turbine sections where a minimal clearance
is needed between the blade tips and the casing.
In typical turbo machinery, the clearance between blade tips and the casing must account for thermal expansion as well as changes in concentricity due to shock loading events. To prevent catastrophic tip to casing contact, conservatively large clearances must be employed.
The role of abradable coatings is not only to allow for closer clearances, but to automatically adjust clearances, in-situ, to accept physical events and/or thermal scenarios that may be found in a devices operational history.
Abrasive
An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away...
material in motion, the former will be worn whereas the latter will face no wear.
Abradable coatings are used in aircraft jet engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
s in the compressor and turbine sections where a minimal clearance
Tip clearance
Tip clearance is the distance between the tip of a rotating airfoil and a non moving part.* Gas turbine: Rotor blade and casing* Propeller : Propeller and structure** Ground tip clearance * Wind turbine: Blade and tower...
is needed between the blade tips and the casing.
In typical turbo machinery, the clearance between blade tips and the casing must account for thermal expansion as well as changes in concentricity due to shock loading events. To prevent catastrophic tip to casing contact, conservatively large clearances must be employed.
The role of abradable coatings is not only to allow for closer clearances, but to automatically adjust clearances, in-situ, to accept physical events and/or thermal scenarios that may be found in a devices operational history.
Manufacturing
- Thermal spray : Many technics are available (Plasma, Flame, etc.).
- SinteringSinteringSintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature...
: HoneycombHoneycombA honeycomb is a mass of hexagonal waxcells built by honey bees in their nests to contain their larvae and stores of honey and pollen.Beekeepers may remove the entire honeycomb to harvest honey...
coatings are scintered on the casing - CastingCastingIn metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...
: in the case of polymer coating.