Paper-making Means And Method

Abstract

For use in a fourdrinier section of a paper machine and/or the felt section of such a machine, a replacement for the fourdrinier wire and/or the felt which comprises a sheet of synthetic, open-celled, flexible foam such as polyurethane foam. According to one aspect of this invention, the foam may be reticulated to provide greater porosity. If the foam is employed as a fourdrinier "wire," the foam is provided with a reinforcing backing means which provides longitudinal strength but does not interfere with the porosity of the foam.

Description

BACKGROUND OF THE INVENTION paper-making

The fourdrinier table section of a papermaking machine includes a fourdrinier wire which is a wire cloth woven from metal such as phosphor bronze or synthetic fiber cloth. The fourdrinier wire allows drainage of the white water, but retains fibers. The principal materials employed in fourdrinier wire construction comprise specially annealed phosphor bronze and brass which are finely drawn to 0.010 to 0.040 inch in diameter and woven into a web of 50 to 150 mesh. The wire is woven into a web at a rate of 4 to 6 linear feet per day due to the stiffness and the fragile nature of the wire. Furthermore, since the fourdrinier wire is an endless belt, the warp wires must be brazed or welded end to end to produce a seam having the same strength as the base material and the same porosity as the remainder of the wire. Each warp wire must, therefore, be brazed end to end.

A further problem involved in employing a woven wire in the fourdrinier table section of a papermaking machine is the problem of short wire life, which is due principally to corrosion and abrasion. Typically, wire life may be from 5 to 50 days. When a wire is to be replaced, the papermaking machine must be shut down, and in older machines it is necessary to remove the table rolls, suction boxes, wire rolls, etc. from the fourdrinier frame. Newer machines are built with cantilevered or rollout fourdrinier tables which facilitate wire-changing operations. Such machines, however, are quite expensive.

Since the fourdrinier wire is quite fragile, it will not tolerate squeezing pressures, which may aid in removing the white water from the pulp. Although dandy rolls are employed to flatten out the top surface of the sheet which is laid on the fourdrinier wire, the dandy roll exerts relatively little pressure on the wire. Therefore, the white water is removed from the pulp by gravity flow and suction boxes.

SUMMARY OF THE INVENTION

This invention provides a replacement for a finely woven, metallic fourdrinier wire which comprises a synthetic, open-celled, flexible foam having porosity characteristics which are equal to the porosity characteristics of woven fourdrinier wires. The fourdrinier foam according to this invention may be a polyurethane foam and, according to a preferred aspect of this invention, may be a polyether or polyester foam which has been reticulated to skeletal structures according to the teachings found in U.S. Pat. No. 3,175,025, granted Mar. 23, 1965, to Geen et al., or may be a polyester foam which has been reticulated by alkaline solutions by kneading the foam in 10 percent caustic soda solution at 50.degree. C. and then washing the treated foam with dilute acetic acid and water.

Fourdrinier foam according to this invention eliminates the end-to-end seaming problem, the weaving problem, and the short life problem, and minimizes material cost. Furthermore, the fourdrinier foam according to this invention has a compressive strength which will permit the application of roll pressure to the pulp to drive white water out of the pulp. A particularly advantageous feature of the present invention is the fact that the fourdrinier foam may be foamed in place on a supporting belt without removing the belt from the fourdrinier table, thus eliminating long machine downtimes and dismantling operations.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic view of the fourdrinier table section of a papermaking machine showing a fourdrinier foam mounted thereon.

FIG. 2 is a perspective view of a length of fourdrinier foam produced in accordance with one aspect of this invention.

FIG. 3 is a perspective view of a section of fourdrinier foam produced in accordance with a further aspect of this invention.

FIG. 4 is a perspective view of a section of fourdrinier foam produced in accordance with a still further aspect of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, FIG. 1 diagrammatically illustrates the use of fourdrinier foam as a replacement for the conventional fourdrinier wire. The foam comprises an endless belt 10 which is trained around and between a breast roll 11 and a couch roll 12 on the fourdrinier table section of a papermaking machine. A plurality of table rolls 13 supports the belt 10 as a flat surface 13 allowing uniform drainage through the foam. Suction boxes 14 are employed to complete water drainage and dewater the pulp so that it can be self-supporting when it is delivered to the felt section of the papermaking machine.

The synthetic, open-celled, flexible foam forming the belt 10 is, preferably, an open-celled, polyurethane foam. The foam may be either polyether or polyester. The polyester foam may be produced by reacting a polyester with an organic isocyanate, such as tolylemediisocyanate, in the presence of an activator mixture. A polyether foam may be produced by reacting a polyol with an organic isocyanate, such as the previously mentioned isocyanate. These foams may be reticulated or reduced to a skeletal structure by utilizing a hydrolyzing agent, such as sodium hydroxide, to remove cell membranes. These foams may also be reticulated by subjecting the foam to a light pulse of sufficient intensity to remove the cell membranes. Such techniques are set forth in U.S. Pat. Nos. 3,175,030 and 3,175,025, granted to Geen and Geen et al., respectively.

Urethane foams have a structure which is similar to a screen. This is particularly true in the case of reticulated foam where the membranes between the cell structure are removed in accordance with the technique set forth above. White water has been successfully removed from a 99 percent water and 1 percent fiber slurry to produce a mat having an even distribution of fibers over the surface of the foam by employing a reticulated foam having a thickness of 3/16 inch and having approximately 60 pores to the inch. The mat produced has properties similar to mats produced by a 60-mesh wire screen. A microscopic study of the mat produced according to the present invention revealed that, as to fiber orientation and strength characteristics, there is no difference between such mat and mat produced on a wire screen. Furthermore, the mat exhibited less marking by the pore structure of the foam.

When used as a replacement for fourdrinier wire, foam must be reinforced, since foam does not have the tensile characteristics to be used in place of fourdrinier wire. Therefore, as is illustrated in FIG. 2, a fourdrinier belt 10a comprises polyurethane foam 15, which is reinforced by polyester cables 16 which extend in the direction of belt travel. The cable 16 may be bonded to the foam 15 by well-known heat-bonding procedures, or the foam may be foamed around the cables during the manufacture of the foam. If an in-place foaming operation is employed, it may be conducted after the cables are stretched between the breast roll 11 and the couch roll 12 without dismantling the machine.

According to a further aspect of this invention, and as is shown in FIG. 3, the foam 15 may be bonded to a coarse wire screen 17 to form a fourdrinier belt 10b. The foam 15 may be bonded to the screen or may be foamed in place in the manner indicated above.

According to a still further aspect of this invention, a fourdrinier belt 10c is illustrated in FIG. 4. The belt 10c comprises a thin, flexible metal or plastic sheet 18 having a multiplicity of apertures 19 therethrough. The foam 15 may be bonded to the sheet 18, or may be foamed in place, as indicated above.

Although the use of foam has been described herein as a replacement for the fourdrinier wire in the fourdrinier table section of a papermaking machine, it should be appreciated that such foam may also be employed in the press section of the machine as a replacement for the conventional blanketlike webs made of wool and synthetic fibers. The ability of polyurethane foam to resist roll pressure during the various squeezing operations makes such foam suited as a replacement for the conventional press felt webs.

It should further be appreciated that the conventional fourdrinier table section and the pressure section of the papermaking machine may be combined, since the fourdrinier foam is adapted to withstand roll pressure as indicated above.

The invention, therefore, is not restricted to the slavish imitation of each and every detail set forth above. Obviously, devices may be produced which change, eliminate, or add certain details without departing from the scope of the invention.

Claims

I claim:

1. A method of removing liquid from fibers in a papermaking process comprising the steps of depositing a slurry of liquid and fibers on a moving belt which comprises a flexible open-celled foam having a slurry-depositing surface consisting of said foam and an exposed opposite surface consisting of said foam, flowing the slurry onto the slurry-depositing surface and flowing the liquid through the open-celled foam from one surface to the exposed opposite surface while retaining fibers on the belt.

2. A method according to claim 1 wherein said belt is provided with longitudinal reinforcement means.

3. A method of removing liquid from fibers in a papermaking process comprising the step of extracting liquid from the fibers by pressing the liquid and the fibers against a flexible open-celled foam having a fiber-collecting surface consisting of said foam and an exposed opposite surface consisting of said foam so that the liquid passes through the foam to the exposed surface.

4. In the fourdrinier table section of a papermaking machine which has a breast roll and a couch roll, the improvement which comprises as the sole filter means an endless belt consisting of synthetic, open-celled, flexible foam trained between said rolls, said belt having longitudinal reinforcing means and having an exposed free slurry-depositing surface and an exposed opposite surface both surfaces consisting of said foam, means for depositing a liquid-fiber slurry on said slurry-depositing surface whereby a fibrous phase of said slurry may be retained on said depositing surface and whereby a liquid phase of said slurry may pass directly through said belt to said exposed opposite surface.

5. The improvement according to claim 4 wherein said belt is an open-celled, flexible polyurethane foam.

6. The improvement according to claim 5 wherein said polyurethane foam has been reduced to a skeletal structure by removing cell membranes.