Cryogen shot blast deflashing system

Abrading – Machine – Sandblast

Reexamination Certificate

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Details

C451S088000

Reexamination Certificate

active

06283839

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention generally relates to a cryogen shot blast system and, more specifically, to a cryogen shot blast system having a recirculation system for particulate media.
Molded articles often have thin pieces of unwanted material extending therefrom called “flash” which must be removed from the articles for the articles to reach their desired final configuration. Removing flash from articles formed from flexible materials such as rubber, plastics, and the like, is difficult in view of the soft, elastic nature of the flexible materials. While various types of mechanical trimming operations have been proposed for use in removing unwanted flash, these methods have proven to be not economical in a number of applications.
In order to simplify and reduce the cost of flash removal, various attempts have been made for freezing or otherwise cooling molded articles to embrittle the thin sectioned flash, whereafter one or a combination of mechanical processes have been utilized to break-off, trim, or otherwise remove the frozen or embrittled flash. Some of these methods have utilized a two-stage process wherein the work pieces to be deflashed are cooled in a first stage to effect flash embrittlement, whereafter the work pieces are vibrated, tumbled, or otherwise mechanically treated in a second stage to break away or otherwise remove the embrittled flash. One method is to use a cryogen material, such as liquid nitrogen, to effect embrittlement of the work piece flash. As utilized herein, the term “cryogen” will be understood to refer broadly to substances which are fluids and are at temperatures of about −60 F. and below.
Two-stage processes of this type are undesirable from several viewpoints. They are time consuming to carry out because cooling the work pieces and removing their flash comprise separate steps that are carried out sequentially rather than concurrently. Inasmuch as the work pieces are cooled only once and will not be cooled again at other stages of the flash removal procedure, adequate time must be devoted at the outset to providing a thorough cooling of the work pieces to assure that they are refrigerated to an extent that their flash will remain embrittled throughout the remainder of the flash removal process. Sometimes the extensive degree of refrigeration which is required results in the generation of undesirable stresses and/or the formation of cracks or other types of structural defects in the work pieces. An equally troubling drawback of the two-stage processes is that, if there is a relatively large quantity of flash to be removed, the work pieces may not remain adequately embrittled during the entire time required for deflashing. Where such is the case, the work pieces are not properly deflashed.
These drawbacks have been overcome by shot-blast deflashing machinery which operate with a single flash embrittling and removing stage. For example, see U.S. Pat. Nos. 4,519,812, 4,598,501, 4,646,484, 4,648,214, and 5,676,588, the disclosures of which are expressly incorporated herein by reference in their entirety. While such machinery performs in an exemplary manner, there is a never ending desire to decrease the required time and/or cost of a deflashing operation. Accordingly, there is a need in the art for an improved cryogen shot-blast deflashing system.
SUMMARY OF THE INVENTION
The present invention provides a cryogen shot-blast deflashing apparatus which overcomes at least some of the above-described problems of the related art. The apparatus includes a treatment chamber for the work pieces, a throwing wheel adapted to propel particulate media into the treatment chamber to impact the work pieces in the treatment chamber, a cryogen supply system for introducing a flow of cryogen into the treatment chamber for embrittling at least selected portions of the work pieces in the treatment chamber, a recirculation system for recirculating particulate media back to the throwing wheel. The recirculation system includes a separator unit in communication with the treatment chamber, a media hopper in communication with the separator unit, a blower connected to the media hopper by a withdrawal conduit, and a supply conduit connecting the blower to the throwing wheel to return pressurized cryogen gas to the throwing wheel. The withdrawal conduit withdraws cryogen gas from the treatment chamber through the separator unit and the media hopper and at the same time pulls particulate media from the separator unit to the media hopper. A particulate media supply system introduces a metered flow of particulate media from the media hopper into flowing cryogen gas in the supply conduit to transport particulate media to the throwing wheel. Preferably, the recirculation system includes a second withdrawal conduit which is connected to the blower and is in communication with the treatment chamber to withdraw cryogen gas from the treatment chamber without passing through the separator unit.
According to another aspect of the present invention, a cryogen shot-blast deflashing apparatus includes a treatment chamber for work pieces, a throwing wheel adapted to propel particulate media into the treatment chamber to impact the work pieces in the treatment chamber, a cryogen supply system for introducing a flow of cryogen into the treatment chamber for embrittling at least selected portions of the work pieces in the treatment chamber, and a recirculation system for returning particulate media and cryogen gas back to the throwing wheel. The recirculation system includes a separator unit in communication with the treatment chamber, a withdrawal conduit in communication with the treatment chamber, a supply conduit connecting the withdrawal conduit and the throwing wheel to return pressurized cryogen gas to the throwing wheel, and a main blower connected to the withdrawal conduit for withdrawing cryogen gas from the treatment chamber and connected to the supply conduit for returning pressurized cryogen gas to the throwing wheel. The apparatus also includes a drop chute connecting the treatment chamber and the recirculation system to direct particulate from the treatment chamber to the separator unit. The drop chute has a downwardly sloped upper surface toward the separator unit and a plurality of spaced-apart openings along the upper surface for introducing streams of pressurized gas to assist movement of particulate through the drop chute from the treatment chamber to the recirculation system. Preferably, a plenum chamber is formed above the separator unit and is in communication with the treatment chamber so that an auxiliary blower can withdraw gas from the plenum chamber and provide pressurized gas to the plurality of openings.
According to yet another aspect of the present invention, a cryogen shot-blast deflashing apparatus includes a cryogenic chamber, a barrel supported within the cryogenic chamber and defining a treatment chamber for the work pieces, a throwing wheel adapted to propel particulate media into the treatment chamber to impact the work pieces in the treatment chamber, a cryogen supply system for introducing a flow of cryogen into the treatment chamber for embrittling at least selected portions of the work pieces in the treatment chamber, and a recirculation system for returning particulate media to the throwing wheel. The barrel is rotatable about a longitudinal axis and is pivotable to a dumping position wherein work pieces in the barrel are dumped from the barrel through an open end of the barrel. The recirculation system includes a separator unit in communication with the treatment chamber, a withdrawal conduit in communication with the treatment chamber, a supply conduit connecting the withdrawal conduit and the throwing wheel to return pressurized cryogen gas to the throwing wheel, and a main blower connected to the withdrawal conduit for withdrawing cryogen gas from the treatment chamber and connected to the supply conduit for returning pressurized cryogen gas to the throwing wheel. The apparatus also includes a drop chute connectin

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