An abradable coating is a coating made of an abradable material – meaning if it rubs against a more
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 by friction. While finishing a material often means polishing it to gain a smooth, reflec ...
material in motion, the former will be worn whereas the latter will face no wear. Abradable Coatings provide a .1 to .2% performance improvement compared to those without coating.
Abradable coatings are used in aircraft
jet engines in the compressor and turbine sections where a minimal
clearance is needed between the blade tips and the casing.
Abradable coatings have been in use by aero-engine manufacturers in some form or fashion for roughly 50 years
Abradable Powder Coatings provide an economical and environmentally friendly way to improve the efficiency of engines, compressors and pumps by fine-tuning the operational fit of internal components such as pistons, rotors and cases. In typical turbo machinery, the clearance between blade tips and the casing must account for thermal and inertial 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.
In small
Turboprop
A turboprop is a turbine engine that drives an aircraft propeller.
A turboprop consists of an intake, reduction gearbox, compressor, combustor, turbine, and a propelling nozzle. Air enters the intake and is compressed by the compressor. ...
aircraft, the angle at which abradable coating is applied is impacted by the necessity of the coating process performed at spray angles less than 60 degrees.
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
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Thermal spray
Thermal spraying techniques are coating processes in which melted (or heated) materials are sprayed onto a surface. The "feedstock" (coating precursor) is heated by electrical (plasma or arc) or chemical means (combustion flame).
Thermal sprayi ...
: Many techniques are available (Plasma, Flame, etc.).
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Sintering
Clinker nodules produced by sintering
Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.
Sintering happens as part of a manufacturing ...
:
Honeycomb
A honeycomb is a mass of hexagonal prismatic wax cells 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. Honey bees consume about of honey ...
coatings are sintered on the casing
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Casting
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
: in the case of polymer coating.
References
Gas turbine technology
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