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Publication Date: 2017-Apr-28
Document File: 5 page(s) / 115K

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An exhaust system for a coating furnace is filled with a particulate material effective to scrub exhaust gases without the detrimental effects of water filtering.

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This is the abbreviated version, containing approximately 42% of the total text.

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[0001] An exhaust system for a coating furnace is filled with a particulate material

effective to scrub exhaust gases without the detrimental effects of water filtering.


[0002] Numerous coating methods are known for applying protective coatings to

workpieces such as gas turbine engine components. One known process is vapor phase

aluminide ("VPA"). In the VPA process, a donor material including an aluminum alloy

and an activator are placed in a furnace along with the workpieces. Heating of the donor

material forms a reactive aluminum halide vapor. This vapor is circulated by a flow of

inert gas and condenses on the workpieces, forming the protective coating. The process

also creates spent coating gases which must be filtered to prevent the release of

undesirable materials into the environment.

[0003] Conventional VPA furnaces typically use an exhaust system that incorporates a

water-filled tank as an exhaust filter. This water-filled tank allows the spent coating gases

to escape from the coating chamber, condensing out the aluminum halide vapor, and

permits metering of the coating chamber gas flow by creating a slight back pressure in

the exhaust system.

[0004] There are numerous problems with the use of water in the exhaust filter. As the

coating gases travel through the water-filled chamber, the water becomes more dense and

acidic because the exhaust constituents are dissolved in the water. As the viscosity of the

water increases, this slows the flow of the coating exhaust gases and increases the gas

back pressure to the point that the gases cannot effectively leave the coating chamber.

Coating activator crystals can deposit in the exhaust piping and in the coating chamber

itself. In some circumstances the water in the exhaust tank could flow back into the

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coating chamber, contaminating the parts.

[0005] Described herein is a coating furnace exhaust system which uses solid phase

particulate matter to filter spent exhaust gases.


[0006] The concept may be best understood by reference to the following description

taken in conjunction with the accompanying drawing figure which is a schematic,

partially-sectioned drawing of a coating apparatus including an exhaust filter.


[0007] Referring to the drawings wherein identical reference numerals denote the same

elements throughout the various views, FIG. 1 depicts an exemplary coating apparatus

10. While the illustrated coating apparatus is used for a VPA coating process, it will be

understood that the concept described herein could be used to extract the exhaust gases of

any kind of coating process or industrial process.

[0008] The apparatus 10 includes a furnace or coating chamber 12 which is an enclosed

vessel. Means are provided for heating the coating chamber 12 to a suitable process

temperature which may be (for example) on the order of 1100°C (2000°F). In the