Abrading – Machine – Sandblast
Reexamination Certificate
2001-07-31
2003-06-03
Morgan, Eileen P. (Department: 3723)
Abrading
Machine
Sandblast
C451S053000, C451S039000, C451S040000
Reexamination Certificate
active
06572457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to cryogenic cleaning systems, and more particularly, to a system and method for controlling the humidity within the workspace of a cryogenic aerosol spray cleaning system by circulating the workspace atmosphere through a dehumidifier to eliminate the need to purge the workspace prior to each cleaning cycle.
2. Description of the Prior Art
Precision cleaning using solid, liquid, or gaseous carbon dioxide, or other cryogenic based cleaning materials and methods, including mixed carbon dioxide 20 phases, solid or liquid argon sprays, liquid nitrogen sprays, and even ice (H
2
O), or combinations of these materials and methods, has been disclosed by patents and prior art publications. The cryogenic spray cleaning technologies disclosed by the prior art have evolved in response to many commercial, industrial, and practical concerns, including environmental concerns, and the need for better and more effective cleaning methods for both particle and organic-based contamination.
Carbon dioxide snow cleaning was first disclosed by S. A. Hoenig around 1985. The process typically involves cleaning, using a source of fluid (i.e., liquid or gaseous) carbon dioxide provided at a certain enthalpy condition (i.e., temperature and pressure). Such liquid carbon dioxide (or gaseous carbon dioxide if proper adiabatic conditions are met by the nozzle design) is passed at high velocity through an orifice of a spray nozzle. Upon exiting the orifice, a stream of dry ice particles having varying sizes and densities and traveling at varying velocities is directed at a workpiece for removal of contaminates deposited on a surface thereof. The stream of dry ice particles may be combined with CO
2
gas, nitrogen or other dry gases to boost 10 the dry ice velocity.
Another form of cryogenic cleaning uses macroscopic CO
2
pellets and was first described by Rice et al. in U.S. Pat. No. 3,676,963, and by Fong in U.S. Pat. No. 4,038,786. This snow cleaning method feeds dry ice pellets into a dry carrier gas stream such as nitrogen or dry compressed air, at a pressure typically in the range of between 40 and 300 psi and possibly greater. The dry ice pellets are accelerated toward the surface of a workpiece at such high velocity that even thick coatings such as paint can be removed.
One limitation in cryogenic spray cleaning methods is the fact that extremely cold streams (e. g., typically −60° C. for carbon dioxide snow cleaning) of cleaning medium are applied to the surface of the workpiece being cleaned. Consequently, when the cleaning processes are conducted at room temperature, or in any unsealed and uncontrolled environment, condensation can form on the workpiece surface being cleaned, or on the spray nozzle. The moisture condensation, present as water, frost, or ice, interferes with and impedes the cleaning process. Prior art attempts to eliminate moisture include direct heating, heating with blanketing gases or heating only specific portions of the surface of the workpiece, insulating the cleaning chamber, cleaning in vacuum environments, purging with nitrogen, air or other dry inert gases, purging using specially constructed chambers, and other methods utilized to produce dry environments.
Patents directed to clean and dry chambers for cryogenic spray cleaning systems and methods typically include vacuum chambers and/or require purging a clean dry box with a dry inert gas. For example, U.S. Pat. No. 4,631,250 to Hayashi was the first to mention indirectly the need for a sealed chamber for a cleaning system that had mixed CO2 and nitrogen for cleaning a wafer surface. The sealed chamber included a vacuum exhaust line for removal of contaminants. Of course, a vacuum environment also assists in moisture reduction.
Another attempt to control the humidity in the cleaning chamber of a cryogenic cleaning system is disclosed in U.S. Pat. No. 5,316,560 to Krone-Schmidt et al. This patent discloses purging an enclosed space (i.e., a cleaning chamber) with dry nitrogen gas to control the humidity within the chamber. Essential to this system is the chamber within a chamber design having a purged airlock between the enclosed interior cleaning chamber and the exterior of the system. The system disclosed by this reference requires lengthy purge times to dry out the cleaning chamber before initiation of a cleaning cycle, and may therefore not be practical for cleaning a large workpiece in a large volume cleaning chamber.
In U.S. Pat. No. 5,315,793 to Peterson et al., an apparatus for precision cleaning using CO
2
snow or other cryogenic sprays is disclosed. The apparatus disclosed is intended only as a final cleaning station and has some design features in common with U.S. Pat. No. 5,316,560. The dryness of the sealed chamber is maintained by vacuum or by an external inert gas purge. The preferred method for maintaining a dry environment involves pumping out and then back-filling the chamber with a dry gas after each cleaning cycle, i.e., to purge the cleaning chamber.
Cryogenic argon spray cleaning developed as an alternative to CO
2
snow cleaning. Cryogenic argon spray cleaning, and, in parallel, cryogenic nitrogen spray cleaning, were first mentioned in U.S. Pat. No. 5,062,898, and later in U.S. Pat. No. 5,294,261, and still further developed in U.S. Pat. No. 5,209,028, all to McDermott et al. These patents disclose the nozzles and cleaning stations for cryogenic argon spray cleaning, and methods and procedures for ensuring a dry cleaning station based upon a flush gas for removal of contaminants.
Further developments in cryogenic argon spray cleaning are disclosed in U.S. Pat. No. 5,486,132 to Cavalier et al. and in U.S. Pat. No. 5,366,156 to Bauer et al., wherein argon spray cleaning methods and apparatus are extended to include cryogenic nitrogen or mixed argon and nitrogen. These patents also clearly discuss means to reduce and prevent moisture condensation from forming on the apparatus, nozzles, argon or nitrogen lines, and on the workpiece surface to be cleaned.
Moisture elimination methods discussed and claimed included purge means, such as dry gas purge methods with purge ports and purge gas sources, providing a vacuum about the cryogenic argon lines and nozzle, providing thermal insulation and barriers and positive pressure within the enclosures, and other suggestions unrelated to the present invention.
A means for eliminating moisture in a CO? dry ice pellet system cleaning apparatus is disclosed in U.S. Pat. No. 5,651,723 to Bjornard et al. The apparatus disclosed therein includes separate load locks for loading and unloading a workpiece, a cleaning chamber between the two load locks, and the necessary equipment to provide airflow through the cleaning chamber and apparatus and to purge the cleaning chamber. Dry compressed air is required for accelerating the dry ice pellets only. A dry environment was ensured in the load locks by purge methods and all chambers were kept at positive pressures to keep moisture out.
Systems and apparatus for maintaining a dry and clean manufacturing environment abound within the electronic, chemical and pharmaceutical industries. However, none of the known systems, apparatus, methods, processes, etc. use a dehumidifier in conjunction with a cryogenic spray cleaning process to control the humidity within a cleaning chamber, thereby obviating the need for time-consuming and expensive purging of the cleaning chamber. For large cleaning chambers, purging as a means for controlling humidity within a cleaning chamber becomes cost-prohibitive, and therefore, commercially impractical.
The present invention overcomes the shortcomings of the prior art by providing a system and method for controlling the humidity within the workspace of a cryogenic aerosol spray cleaning system by circulating the workspace atmosphere through a dehumidifier placed in the airflow path of the cleaning system. The present invention obviates the need to purge the workspace atmosphere at any time during a cleaning cycl
DePalma Philip W.
Sherman Robert
Applied Surface Technologies
Fortunato David
Morgan Eileen P.
Riker, Danzig
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