Ventilation – Clean room
Patent
1994-02-24
1996-05-21
Joyce, Harold
Ventilation
Clean room
454 60, F24F 316
Patent
active
055184502
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and apparatus for protecting a surface and, in particular, thought not exclusively, to a method and apparatus employing a flow of a protective fluid. The invention may be used, for example, in the manufacture of electronic equipment, in precise mechanical engineering and instrumentation, and medical engineering for the treatment of abacterial chambers.
Modern industrial production is characterized by the use of materials having a high uniformity of composition and accuracy of machining (Clean Rooms. Ed. By Hayakawa. 1990. Mir Publishing House, Moscow, pp. 44-58). It is impossible to manufacture such products without creating a special production environment which is capable of ensuring predetermined conditions in production rooms for long periods of time. It is most efficient to maintain an ultraclean environment in production rooms with laminar air flow (laminar flow is a flow in which the intensity of transfer processes is close to a level determined by molecular movement).
The velocity of contaminant particles in a laminar flow is determined by molecular movement, and such velocity is several times lower than the velocity of the flow proper. For this reason the particles can penetrate only to a small depth into the flow because they are very soon washed off the flow. In such a case, the degree of contamination of a surface to be protected depends on the degree of cleaning of the laminar flow proper. In addition, the direction of air flows carrying fine particles can be predicted with the laminar flow so as to prevent them from getting to the surface being protected. For this reason this circulation method is most suitable and is widely used for producing high-purity fluids.
Vertical or horizontal circulation has been used so far for maintaining a high cleanliness of the environment within clean rooms.
Two methods for protecting surfaces are known. One method resides in washing off, with a laminar air flow, fine particles released from a source of contamination to reduce the contamination down to such as level as to prevent the penetration of the particles into a zone near to the surface being protected. The second method involves forming a flow of highly clean air in a zone near to the surface being protected in order that it moves in parallel with the surface so as to prevent fine particles from the interior space of the room getting to the surface of an object being protected. This method of protection is efficient, but it has a number of disadvantages and, in particular, it calls for substantial investment, i.e. the special equipment of the rooms and a high operating cost. With this method, gases and vapors released at various production steps propagate throughout the entire room, and a high degree of cleaning of the incoming flow is necessary. This results in the need to have multiple cleaning filters, and the release of dust in the room is to be prevented so that requirements imposed upon clothing, equipment and operating procedures are rather stringent.
In the manufacture of miniature products which require especially clean conditions (Clean Rooms. Ed. by Hayakawa. 1990. Mir Publishing House. Moscow. pp. 58, 59), e.g. in making extra ELSIs, the effective protection of the surfaces of products against dust can be ensured within a relatively small space with an ultraclean environment. The method involves producing a laminar flow of an ultraclean fluid to flow over the surface being protected.
This method allows power consumption to be reduced, since the size of ventilation and filtering devices is smaller; and the requirements imposed upon the cleanliness of the whole room are lower. The system does not call for protective chambers so that it can be integrated into a continuous automatic production process. The method for forming a flow of an ultraclean fluid does not, however, allow turbulence to be avoided, hence it is not reliable enough.
The above-described method may be carried out by means of an apparatus for providing a local clean space (Clean Rooms. Ed. by
REFERENCES:
patent: 3776121 (1973-12-01), Truhan
patent: 4009647 (1977-03-01), Howorth
patent: 4037830 (1977-07-01), Poluzzi
patent: 4412849 (1983-11-01), Shahani
Clean Rooms, Ed. by Hayakawa, 1990, Mir Publishing House, Moscow, pp. 44-58.
Patent Abstracts of Japan, vol. 7, No. 132 (E-180)(1277), Jun. 9, 1983 of JP A 58-48423, Mar. 22, 1983.
Joyce Harold
Overseas Publishers Association
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