Refrigeration – Processes – Treating an article
Reexamination Certificate
2000-06-14
2002-04-02
Doerrler, William C. (Department: 3744)
Refrigeration
Processes
Treating an article
C062SDIG001, C264S237000
Reexamination Certificate
active
06363730
ABSTRACT:
BACKGROUND
This invention relates generally to a method and apparatus for cooling articles, and more specifically to vaporizing a liquid a cryogen in a chamber and then circulating the vaporized cryogen through cooling circuits in a tool for cooling the tool itself or, such as where the tool is a calibrator, to cool an extrusion passed through the calibrator. Additionally, the tool itself may be disposed in a cooling chamber in which vaporized cryogen is circulated. The invention is particularly useful as an extrusion chiller. Additionally, many other applications of the invention will become apparent to those skilled in the art upon a review of the following specification and drawings.
Historically, water has been utilized as the primary medium for cooling articles, including extrusions. For example, conventional extrusion chilling systems employ a “cooling” chamber downstream from the extruder. The extrusion is fed through the cooling chamber, wherein the extrusion can be sprayed with water, or partially/fully submerged in water in order to chill the extrusion. Various other components may also be included in such systems, such as a vacuum sizing chamber intermediate the extruder and the cooling chamber. The vacuum sizing chamber can be used for hollow extrusions and employs a vacuum to assist the extrusion in maintaining its shape while it cools. Water can also be used in the vacuum chamber to cool the extrusion while the vacuum supports the shape.
Coolant mediums other than water which have been used in cooling processes can be referred to collectively as refrigerants, including cryogens. Cryogens include liquid nitrogen, liquid carbon dioxide, liquid air and other refrigerants having normal boiling points substantially below minus 50° F. (−46° C.). Prior art methods of cooling articles using cryogens disclose the benefits of fully vaporizing the cryogen into a gaseous refrigerant prior to contact with the articles to be cooled. Cryogens due to their extremely low boiling point, naturally and virtually instantaneously expand into gaseous form when dispersed into the air. This results in a radical consumption of heat. The resilient temperature can be reduced to hundreds of degrees below zero (Fahrenheit) in a relatively short time. However, prior methods of cooling fail to realize the advantages, both in increased efficiency and in improved system control, that can be achieved according to the invention by utilizing forced air convection in combination with the nitrogen or any other refrigerant. Some disadvantages of prior art cryogenic cooling systems include lower efficiency and limited options for controlling the cooling process. Such systems generally rely exclusively on the cooling effect of the refrigerant, to lower the ambient temperature and chill the article. Although prior art methods utilize forced convection to ensure complete vaporization of the cryogen, no methods use forced air convection to control the rate of cooling of the article by controlling the wind chill temperature. Consequently, the only control variable in the prior art methods to adjust (lower) the temperature is the introduction of liquid cryogen into the system. In contrast, the utilization of forced air convection adds a wide range of variable control to adjust the effective temperature, up or down, by controlling the velocity at which the refrigerant, is circulated over/around the article to be cooled.
The basis of forced air convection is the principle that blowing a refrigerant over a heated surface greatly enhances the transfer of heat from that surface. In the context of cold temperatures, this principle is probably better known indirectly, from the commonly used phrase “wind chill” temperature, which is frequently reported on TV or radio by weather announcers. In that context, wind chill temperature is what the temperature outside “feels” like, taking into account the ambient temperature and the prevailing velocity of the wind. The stronger (higher velocity) the wind, the lower the temperature “feels,” compared to if there were no wind present. This principle is advantageously utilized according to the invention to significantly enhance the cooling efficiency of the system by creating, and controlling, “wind chill” temperature during the cooling process. As a result, the efficiency of the process can be increased while simultaneously reducing the size, which is typically the length, of the cooling system.
Another type of prior art cooling system utilizes a device called a “calibrator,” and typically multiple such calibrators, to cool extrusions. A calibrator is a tool which generally has a central opening through which the extrusion is fed, the central opening having a surface which is generally in contact with the surface of the extrusion as it is fed therethrough. As a result of contact with the surface of the extrusion, heat is conducted to the calibrator away from the extrusion thus cooling the extrusion. To enhance the heat transfer from the extrusion, cooling circuits, internal passages, are provided in the calibrator through which a coolant is circulated. Typically, the coolant is water, but liquid nitrogen is also known to have been used to some degree. However, circulating liquid nitrogen through the cooling circuits has met with some difficulties regarding contact of the liquid nitrogen with the calibrators. Moreover, it has been found that it is preferable to first vaporize a liquid cryogen, such as liquid nitrogen, and then to circulate the super cold vapor/refrigerant through the cooling circuits instead of the liquid cryogen, which thus requires a system for vaporizing the liquid cryogen prior to circulation through the cooling circuits of the calibrator.
Accordingly, there is a need for a method and apparatus for cooling articles which can provide improved efficiency and can also reduce the size of the cooling system, and also an alternative cooling system for circulating vaporized cryogen through cooling circuits in calibrators.
SUMMARY
A method and apparatus for cooling articles is provided which can utilize the dispersion of a liquid cryogen into a chamber wherein the liquid cryogen is substantially vaporized and then circulated through either a separate cooling chamber, containing the article to be cooled, or through internal cooling circuits in a tool, such as a calibrator, to cool the article. The vaporized cryogen can be further circulated though a cooling chamber in which the tool is disposed. The vaporized cryogen can be circulated at a controllable velocity, over/around the tool and the article to be cooled, in order to regulate the rate of cooling by controlling the wind chill temperature, based upon the principles of forced air convection.
A presently preferred cryogen is liquid nitrogen. The liquid nitrogen can be dispersed into a feed chamber in a controlled manner using an valve, which itself can be operated by a controller, such as a microprocessor. Since the temperature in the feed chamber is much higher than the boiling point of the liquid nitrogen, a high BTU (British Thermal Unit) and expansion rate is captured thereby producing an extremely effective refrigerant. The feed chamber can be communicated with a cooling chamber into which the vaporized cryogen can be circulated by a fan, or other device for circulating air and/or vaporized cryogen. Either the feed chamber or the cooling chamber can be vented to dissipate pressure generated as the liquid nitrogen rapidly expands to gaseous form. The fan can preferably be a variable speed fan, or other variable speed device for circulating the vaporized cryogen through the cooling chamber at a controllable velocity to take advantage of principles of forced air convection. The fan can be located in the feed chamber to aid in substantially vaporizing the liquid cryogen. However, considering the relatively high temperature utilized in the cooling chamber compared to the boiling point of the cryogen, even without the fan, the liquid cryogen will virtually completely and instantaneously vaporize as it is inj
Bessemer Robert H.
Thomas Michael R.
Buchanan Ingersoll P.C.
Doerrler William C.
The Conair Group, Inc.
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