Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
2000-05-16
2002-07-02
Silverman, Stanley S. (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S341000, C162S336000, C162S216000
Reexamination Certificate
active
06413376
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a headbox to uniformly distribute a reactive, aqueous suspension of calcium sulfate hemi-hydrate crystals and fibers across the width of a foraminous wire mesh in a water-felting process to form a uniform gypsum/fiber web. More specifically, the headbox of the present invention may be used to distribute hot suspensions of calcium sulfate hemi-hydrate crystals and lignocellulose fibers, such as paper fibers or wood fibers, although the headbox of the present invention also may be used to distribute suspensions of other dense crystals and any fibrous materials.
BACKGROUND AND PRIOR ART
The process of water felting dilute aqueous dispersions of various fibrous materials is a well-known commercial process for manufacturing many types of paper and board products. In this process, an aqueous dispersion of fiber, binder and other ingredients, as desired or necessary, is flowed onto a moving foraminous support wire, such as that of a Fourdrinier or Oliver mat forming machine, for dewatering. The dispersion may be first dewatered by gravity and then dewatered by vacuum suction means; the wet mat is then pressed to a specified thickness between rolls and the support wire to remove additional water. The pressed mat is then dried in heated convection or forced air drying ovens, and the dried material is cut to the desired dimensions.
U.S. Pat. No. 5,320,677 to Baig describes a composite material made from gypsum and host particles of a reinforcing material, such as lignocellulose fibers, hereinafter sometimes referred to as gypsum/wood fiber board. The composite material is produced by mixing gypsum and host particles of a stronger substance, such as wood fibers, in a dilute aqueous slurry. The slurry is heated in an autoclave, preferably under pressure, to convert the gypsum to calcium sulfate alpha hemihydrate. The hot, converted slurry is discharged through a headbox onto a continuous felting conveyor of the type used in paper making operations, where the slurry is dewatered to remove as much uncombined water as possible before rehydrating the hemihydrate back to gypsum. The resulting material is a homogeneous mass comprising gypsum crystals physically interlocked with the discrete host particles. The resulting mat is then dried in heated convection or forced air drying ovens, and the dried board is cut to the desired dimensions.
In order to produce the best composite product it is essential to spread the hot, reactive gypsum/fiber slurry uniformly across the width of the felting conveyor. The headbox of the present invention functions to spread the aqueous gypsum/fiber slurry over a moving wire screen much like the headboxes used in papermaking. However, the aqueous gypsum/fiber slurry differs from conventional papermaking stock in that the aqueous gypsum/fiber slurry is hot and reactive and has much higher solids than traditional papermaking slurries. The aqueous gypsum/fiber slurry to which the present invention pertains is comprised of two materials having markedly different densities. For example, the gypsum/fiber slurry may contain as much as 30% by weight of solids, of which from 80-97.5% by weight is high-density gypsum and 2.5-20% by weight is low-density paper fibers. Because of the disparate density of the components, the aqueous gypsum/fiber slurry must be constantly agitated, but the agitation must be in a manner that avoids breaking down the friable acicular calcium sulfate hemihydrate crystals. The particular nature of the aqueous gypsum/fiber slurry imposes special requirements on the headbox design.
In the formation of gypsum/fiber board products using such a water felting process, one measure of board quality is the formation property, that is, the degree of uniformity of distribution of solid components or fibers in the finished board. This formation property, while dependent upon many factors inherent in individual water felting process machines, is determined to a large extent by the flow pattern of gypsum/fiber stock from the sluice of the headbox onto the Fourdrinier wire or the web formation surface, and by the flocculated or unflocculated state of the fibers in the gypsum/wood fiber stock flow. Thus, if the gypsum/fiber stock flow onto the formation surface is uneven across the width of the surface, is uneven throughout the course of the machine run, or if the gypsum/fibers deposited onto the formation surface are in a non-uniformly flocculated state, the finished board will show stripes, ripples, density spots, strength variations and the like, characteristic of nonuniform distribution of fiber components. It is obvious, of course, that in the manufacture of quality board the formation property must be stringently controlled to insure a completely uniform distribution of gypsum/fibers onto the formation surface both by presenting an even stock flow and unflocculated fibers in the stock flow. Accordingly, control of the evenness of the stock flow and the flocculation of the fibers is very important inasmuch as even slight variations in gypsum/fiber stock flow or slight variations in the flocculation of the gypsum/fibers are sufficient to introduce serious non-uniformity to the finished board.
It is the general object of the present invention to provide a headbox for a Fourdrinier machine that produces a uniform distribution of the gypsum/fiber stock across the width of the Fourdrinier wire.
A more specific object of the Invention is to provide a headbox for a Fourdrinier machine having an improved structure for controlling the factors contributing to the formation property of the gypsum/fiber board produced thereby, particularly where low slurry flow rates and/or high solids contents are required.
Another object of the Invention is to provide improved turbulence generating distribution rolls by means of which the formation property of a gypsum/fiber board may be better controlled.
Another object of the invention is to provide improved distribution rolls for the headbox of a Fourdrinier machine by means of which sufficient controlled turbulence is introduced into the gypsum/wood fiber stock flowing therein to maintain the gypsum/wood fiber stock in a controlled state of flocculation.
Another object of the invention is to provide a distribution roll for the headbox of a Fourdrinier machine having an improved grid structure, preferably a diamond pattern, by means of which fibers in the gypsum/fiber stock are maintained in a controlled state of flocculation and the velocity profile of the gypsum/fiber stock flow is smoothed.
An additional object of the invention is to provide improved turbulence generating distribution rolls having sufficient openness to effectively smooth the velocity profile of the gypsum/wood fiber stock flowing in the headbox and of sufficient rigidity so as to be substantially unflexible when supported at its ends for rotation about its longitudinal axis.
A more specific object of the invention is to provide improved turbulence generating distribution rolls for which the surface solidity is less than 80% and which is sufficiently rigid to prevent flexing when the structure is supported at its ends for rotation about its longitudinal axis.
Another specific object of the invention is to provide improved turbulence generating distribution rolls having a solidity of between 65% and 80% of the area of its cylindrical surface, that is, an openness of between 20% and 35%.
BRIEF DESCRIPTION OF THE INVENTION
The present invention is a headbox for distributing a hot aqueous dispersion of calcium sulfate hemi-hydrate crystals and non-gypsum fiber uniformly across the width of the forming wire of a Fourdrinier machine or the like. The headbox of the present invention is described herein in the context of distributing a hot suspension of gypsum crystals and lignocellulose fibers, such as paper fibers or wood fibers, as described in U.S. Pat. No. 5,320,677 to Baig. However, the headbox of the present invention may also be used to distribute suspensions of other dense crystals and any fibrous material.
Egan Donald E.
Janci David F.
Lorenzen John M.
Silverman Stanley S.
United States Gypsum Company
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