Heat exchange – Movable heating or cooling surface – Rotary drum
Reexamination Certificate
1999-05-27
2001-07-10
Atkinson, Christopher (Department: 3743)
Heat exchange
Movable heating or cooling surface
Rotary drum
C165S089000, C492S044000, C492S046000
Reexamination Certificate
active
06257321
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high production chill roll. More particularly, the present invention relates to a chill roll for cooling a web of material in the extrusion coating of paper and plastic film extrusion. The chill roll permits production rates which are higher than previously attainable by reducing the retention of heat in the outer shell of the chill roll. Furthermore, the chill roll of the present invention distributes coolant material throughout the inside of the chill roll to achieve uniform cooling across the surface of the chill roll.
2. Description of the Prior Art
Conventional chill rolls are used, in the formation of rolls of plastic and paper-based products, to cool the web of material passing around the surface of the chill roll. Commonly, water is passed through hollow cylinders, as the web of material passes around it. The production capacity of a chill roll is determined by a number of factors, including but not limited to: the diameter of the chill roll, the speed of rotation, the thickness of the outer surface of the roll, the effectiveness of the coolant material, and the uniformity of the cooling of the chill roll surface.
In most chill rolls water enters one end of the roll and exits the opposite end. As the water moves along the length of the chill roll it draws heat from the web of material traveling around the chill roll. Consequently, the side of the web closest to the water inlet is cooled to a much higher degree than the side of the web nearest the water exit. Such a temperature gradient across the chill roll lowers the production capacity of the system or produces inferior quality products.
Extrusion coating for applying plastic to paper requires chill rolls, or some means, to produce larger cooling capacity per unit area. The higher cooling capacity is due to the fact that plastic coatings, such as polyethylene, must be cooled to a temperature close to room temperature before it can be stripped from the chill roll. Furthermore, the diameter of the chill roll can not be so large that it creates a displacement of the extrusion die too far from a combining nip, which would cause a loss of coating adhesion, excessive neck-in of the coating, and other difficulties.
While the thickness of the outer shell of the chill roll can be made thinner to assist in the cooling of the web of material, such a reduction brings with it a reduction in the strength of the chill roll. At high speeds and high nip loads such a roll breaks down upon itself.
SUMMARY OF THE INVENTION
These and other deficiencies of the prior art are addressed by the present invention which is directed to a chill roll for cooling a web and includes a cylindrical outer roll having an inner and an outer surface, the inner surface of the outer roll having circumferential or helical structural projections spaced along its length forming circumferential or helical channels therebetween. The chill roll further has a cylindrical inner roll having an inner and an outer surface, and a diameter less than a diameter of the outer roll and may define an annular space between the outer surface of the inner roll and the inner surface of the outer roll, allowing a coolant material to flow into and out of the circumferential channels and to contact the inner surface of the outer roll to uniformly cool the outer surface of the outer roll. Alternately, the outer surface of the cylindrical inner roll may abut the structural projections.
A cylindrical middle shell may be disposed between the inner surface of the outer roll and the outer surface of the inner roll allowing passage of the cooling medium from the inner roll to be transferred into and out of the circumferential or helical channels through openings located along the middle shell. The middle shell allows the pressure distribution of the cooling medium to be profiled.
Based on the foregoing, it is an object of the present invention to provide a chill roll which develops even longitudinal cooling.
Another object of the present invention is to provide a chill roll which can operate at higher speeds without creating a decrease in the effectiveness of the cooling operation.
Still another object of the present invention is to provide a chill roll which has a greater inner surface area thereby increasing the heat transfer between the web and the cooling medium.
Yet another object of the present invention is to provide a chill roll which sufficiently cools the web of material without significantly increasing the diameter of the chill roll.
Another object of the present invention is to provide a chill roll having a unique design to distribute the cooling material throughout the chill roll.
REFERENCES:
patent: Re. 30302 (1980-06-01), Stamislaw
patent: 4453593 (1984-06-01), Barthel et al.
patent: 5078204 (1992-01-01), Loffredo et al.
patent: 406182896 (1994-07-01), None
Gibbons Charles E.
Watson Carter H.
Whillock Allan A.
Atkinson Christopher
Doyle Michael J.
Hoffman Wasson & Gitler
International Paper Company
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