Refrigeration – Processes – Treating an article
Reexamination Certificate
2002-06-17
2003-12-09
Doerrler, William C. (Department: 3744)
Refrigeration
Processes
Treating an article
C062S380000, C264S148000, C264S177190
Reexamination Certificate
active
06658864
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a method and apparatus for cooling extrusion articles, and more specifically to substantially vaporizing a liquid cryogen and then circulating the vaporized cryogen through a cooling chamber, through a cooling chamber including sizing and/or calibration tools, through a hollow in the article itself or a combination of the aforementioned to cool an extrudate. The invention is particularly useful as an extrusion chiller, and may also be utilized for chilling foods. 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.
BACKGROUND OF THE INVENTION
Certain continuously extruded materials, e.g., rubber products, plastic products, metal products, wood composites, must be cooled after passing through the extrusion operation in order to prevent deformation. In conventional extrusion operations, the extruded materials, be it hose, pipe, rod, bar or any other shape may deform from its own weight if the temperature was not decreased rapidly after leaving the extruder. Cooling the product rapidly creates at least a minimum amount of rigidity in the extrudate such that the manufacturer can cut, stack or otherwise handle the extrudate without unwanted deformation. If the product is not cooled effectively and quickly, the resultant deformation can lead to excessive rates of rejection of the manufactured or extruded product. Further, the rate at which the extrudate is cooled directly affects the rate at which product may be produced. In other words, the faster an extrudate is cooled, the faster the end product can be produced.
Historically, cooling water systems have 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 both solid and hollow extrusions and employs an external vacuum pump to create 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. However, cooling water systems have several drawbacks. Many products are adversely affected if contacted with water. Thus, extra care must be taken to avoid such occurrences. Extrusion speeds are limited because the cooling water generally has a well defined heat transfer capability and thus can only cool the fresh extrudate in accordance therewith. In practice, an optimum cooling temperature of approximately 50° F. is achievable from a cost-effective standpoint, which limits the manufacturer's ability to cool extrusions quickly. Additionally, cooling water systems require excessive floor space and also require treatments or special additive packages to prepare and maintain proper water chemistry, as well as to prevent scaling and bacterial growth, which add significantly to the cost thereof.
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 a 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 ambient temperature can be reduced to hundreds of degrees below zero (Fahrenheit) in a relatively short time, and much quicker than may be realized with a conventional cooling water system. The extreme difference in vaporized cryogen and the extruded product allows the manufacturer to quickly cool an extrudate.
However, prior methods of cryogenic cooling fail to realize the advantages, both in increased efficiency and in improved system control, that can be achieved by utilizing forced gas convection in combination with 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 gas 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 a liquid cryogen into the system. In contrast, utilization of forced gas 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. Such a forced gas convection system is disclosed by Thomas in U.S. Pat. No. 6,389,828, incorporated herein in its entirety by reference thereto.
The basis of forced gas convection is the principle that increasing velocity of a refrigerant over a heated surface, such as by blowing, 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. Forced gas convection cooling systems, as disclosed herein, take advantage of this “wind chill” affect in their ability to remove heat from an object faster with a constant temperature of a gas. In other words, if a 400° F. object is placed in a constant 75° F. atmosphere without velocity of the surrounding atmosphere, the transfer of energy from the object to the surrounding atmosphere by convection is much slower than if the atmosphere has a velocity over/around the object. An increase in velocity will increase the rate of energy transfer, even though the temperature of the atmosphere is constant. The rate of cooling can be increased or decreased by manipulating the velocity of the cooling medium as the temperature of the medium remains constant. This principle is advantageously utilized 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 is increased while simultaneously reducing the size, which is typically the length, of the cooling system.
However, the previous method disclosed by Thomas utilizes only a measurement of the ambient temperature within the cooling chamber to adjust the velocity and discharge of cryogen. An extrudate leaving a cooling chamber does not necessarily need to be cooled to an even temperature throughout, but may rely on “equilibrium cooling.” This principle is advantageously utilized according to the invention to significantly enhance the cooling efficiency of the system by creating and controlling the “wind chill” temperature during the cooling process in relation to a measurement of the temperature of the product after leaving the cooling chamber. The basis for “equilibrium c
Brandt Greg
Gieseking Chris
Randolph Lonnie
Thomas Michael
Winship Dave
Barnes & Thornburg
Doerrler William C.
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