Seal for a joint or juncture – Seal between relatively movable parts
Reexamination Certificate
1999-11-05
2001-11-20
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
C277S500000, C277S906000
Reexamination Certificate
active
06318727
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for maintaining a fluid seal with a moving substrate. More particularly, this invention relates to a pressure chamber designed to maintain uniform sealing contact with a moving substrate despite the existence of deflection forces resulting from a pressure differential between ambient conditions and the inside of the pressure chamber.
BACKGROUND OF THE INVENTION
An air press is a mechanical device that is designed to assist in removing water from a moving web. The air press includes a positive pressure chamber, i.e. a pressure plenum placed in sealing relation with a moving substrate, and a negative pressure chamber, i.e. a vacuum device, positioned on the opposite side of the moving substrate. The moving substrate may include a tissue web sandwiched between two supporting fabrics, and the pressure differential across the moving substrate establishes airflow through the substrate. The airflow is normally used to dewater a tissue web.
The effectiveness of such an air press, as well as the effectiveness of many other types of pressure chambers, is partly a function of the seal quality that the pressure chamber forms with the moving substrate. As used herein, a “moving substrate” can refer to a paper web, a paper manufacturing felt or fabric, a roll surface, or a sandwich of a paper web between two supporting or transfer fabrics. Unfortunately, the difficulty associated with maintaining a proper seal increases, as the cross-machine length of the pressure chamber becomes longer or the pressure differential from ambient is increased. Specifically, the pressure differential between the interior of the pressure chamber and ambient conditions generates deflection forces tending to cause the pressure chamber to bow in the cross-machine direction away from the moving substrate. The bowing of the pressure chamber away from the moving substrate compromises the chamber's seal to the moving substrate. This can result in leakage either into or out of the pressure chamber or a cross-machine direction variation in load that can result in accelerated local fabric wear.
A “pressure chamber”, as used herein, refers to a chamber in which the interior is at a pressure either higher or lower than atmospheric pressure.
The bowing phenomena are especially problematic on a paper machine because the pressure chamber can only be restrained from deflection on the two ends outside the manufactured web. Structural restraints positioned at locations between the ends would interfere with the paper manufacturing process, and generally are not feasible in a modern papermaking machine. Current papermaking economics dictates a paper machine as wide as possible, and what frequently limits the ability to build a wider paper machine is deflection of the cross-machine components.
Current methods for reducing the deflection of cross-machine components include increasing the cross-section of the component and hence its second moment of inertia or machining an intentional deflection into the component opposite the component's deflection when in a paper machine. A larger cross-section reduces deflection; however, this leads to an increase in the dimensions of the component that may not be practical because of limited space and greater cost. As an example, minimization of the cross-machine deflection of a paper machine roll is critical to proper tracking of fabrics and felts. Wider paper machines require roll diameters that are much larger in diameter, when compared on a proportional basis, to the increase in width between the narrower paper machine and the wider paper machine. Because the required roll diameter dramatically increases, the cost of these rolls and the space needed also dramatically increases. It is important to note that increasing the size of the components can reduce the deflection, but such an increase never eliminates the deflection.
Deflection is controlled by a material property called Young's Modulus. Young's Modulus is defined as the ratio of applied unit load, expressed as stress, to the elongation, expressed as strain, of the specimen. A higher Young's Modulus means a specimen will not deflect as much under a given load when compared to a specimen with a lower Young's Modulus. A potential method of reducing deflection could be to select a material with a higher Young's Modulus. Metals, particularly iron-bearing alloys such as steel and stainless steel, already have the highest Young's Modulus for commonly available materials. Thus, few opportunities exist for alternate material selection from which to construct paper machine components in a cost-effective manner.
Another method of reducing the effect of deflection is to manufacture the components in such a manner that the component is deflected when in the unloaded state. The component then assumes a “zero deflection state” upon application of the load. Actually, the component still is deflected due to the load, but is deflected to a desired position upon application of the load. This is accomplished by applying the expected load to the component, while it is supported at its ends, and then machining the component to the desired profile. This process is effective where the load is constant and known, but it is evident that the desired profile is only possible at the load applied during machining. If the actual load varies, or is different from the applied load during machining, the component will not have the desired profile while in use.
For all these methods, it is important to note that deflection continues to be proportional to the load or force applied to the component. For example, cross-machine deflection of a pressure chamber is proportional to the actual pressure in the chamber. Furthermore, any deflection of the cross-machine components in a paper machine is undesirable. The previous methods help to control deflection, with the aforementioned disadvantages, but the deflection of the component remains.
Therefore, what is needed is a pressure chamber that eliminates sealing problems caused by cross-machine deflection of the pressure chamber. Such a pressure chamber's cross-machine deflection will not change as the internal pressure of the chamber is changed. Relatedly, what is also lacking and needed is a more efficient method for treating a moving substrate with a fluid in a pressure chamber.
SUMMARY OF THE INVENTION
Briefly, this invention relates to an apparatus for maintaining a fluid seal with a moving substrate. The apparatus includes an enclosure and a cap. The enclosure has a first surface and a second surface with the first surface being in sealing contact with the moving substrate. The cap functions to seal off the second surface of the enclosure. The cap is secured to the enclosure at at least two spaced apart locations and the cap has a non-secured portion that is capable of deflecting independently of the enclosure. The apparatus further includes means for introducing a pressurized fluid into the enclosure. The pressurized fluid creates a net force on the enclosure of zero and an upward force on the cap which causes a portion of the cap to deflect. The deflection of the cap allows the first surface of the enclosure to remain in sealing contact with the moving substrate.
The general object of this invention is to provide a pressure chamber, which seals to a moving substrate, such that the deflection of the chamber due to a pressurized fluid does not interfere with the seal to the moving substrate. A more specific object of this invention is to provide a pressure chamber, suitable for use in a paper manufacturing process, to dewater a paper web by means of pressurized air.
Another object of this invention is to provide a pressure chamber that uses a minimum of materials, and weighs less than a pressure chamber reinforced by use of additional materials in an attempt to reduce pressure deflections.
A further object of this invention is to provide a pressure chamber that functionally can minimize leakage of the pressur
Beres John L.
Charlier Patricia A.
Connelly Thomas J.
Kimberly--Clark Worldwide, Inc.
Knight Anthony
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