US2300137A - Fire resistant wallboard - Google Patents

Description

Patented Oct. 27, 1942 UNITED STATES PATENT OFFICE FIRE ansrsmn'r WALLBOARD Arthur 0. Salisbury, St. Helena, Oreg., assignor to Fir-Tex Insulating Board Co., St. Helena, Oreg.

No Drawing. Application March 27, 1940,

Serial N0. 326,275 I 2 Claims.

consumer must be in keeping with the commercial requirements. The fire-resistant wall board heretofore produced did not meet these requirements. By the methods previously practiced in the making of fire-resistant wall board, the inert material, for example, vermiculite, was either ground to a paste before being added to the pulp, or is a first added to the pulp and the admixture then ground to a paste by a specific refining process applied to the stock so produced. The board so produced, however, cannot be made on the usual machine, such as a fourdrinier. Vermiculite mixed with pulp and then reduced to a paste produces an excessively slow stock, because it tends to clog the drainage-wires of the machine; and besides, by such admixture,'a large portion of the vermiculite is carried away, and lost with the dilution still drained from the stock in forming the sheet on the wire of the machine.

Apparently it was heretofore believed that the fire-resistant quality of a fibrous wallboard depended upon the micaceous,,or inert, component being converted into a paste so that it would bedeposited on, and between the pulpfibers and coat the latter. But I found that such is not the case; that an eflicient fire-resistant fibrous wallboard is obtained if the inert material, i'or example, expanded vermiculite, be used 'inthe form of granules of predetermined particle size admixed with and disposed throughout the pulp stock. In my wall board the particles of inert material constitute mechanical blocks between adjacent sections of fiber, and function to intercept the transmission of sumcient heat from an ignited section capable of igniting an adjacent section. When my wallboard is subjected to intense heat the outer pulpfibers burn off, leaving the vermiculite particles exposed, which impose resistance to the ignition of further fiber; the vermiculite particles also seal the voids in the board against the entrance of air stimulating the combustion of the interior fibers of the board,

The stock produced by my method will not clog the meshes of the machine on which the board is formed; and besides, practically all the inert granules are retained in the stock during the 55 slstency of solids of about 1 /2 to 2% including draining ofl oi the dilution water on the wire. In short, I have discovered a commercially practical method, whereby a fire-resistant fibrous wallboard can be produced economically on the usual board-forming machines; and further discovered that the board so produced has a fireresistant quality at least fully equal to the board previously obtained by the old methods above described.

In order to produce my wall board, it is o! v course necessary that the granules of expanded vermiculite, or other inert material, be distributed throughout the thickness of the board produced. Expanded vermiculite granules will-float in water because having lesser density than water; but the granules will gradually absorb water, and in so doing the density of the granules increases, and finally exceeds that of water, causing the individual granules to sink and become submerged at diiferent levels, in accordance with their difierence in size; and thus the vermiculite, component becomes stratified, as it were, at all levels or horizontal planes in the sheet, while forming on the wire of the machine. I conceived that this characteristic of the micaceous granules could be used to advantage in making a fire-resistant wall board. In practicing my invention the expanded vermiculite granules, or other inert equivalent material, must not be introduced into the pulp stock until after all refining action on the pulp component has taken place; thus just ahead of the discharge of the admixture onto the wire of the sheet-forming machine.

Since the time within which said granules will absorb sufiicient water and cause them to sink to different levels in the stock-diluting water de-- pends upon the size of the granules, in order to obtain and assure distribution of the granules throughout the thickness of the sheet produced, I use only such granules of inert material as will be retained on a 20-mesh screen. In other words, I found that efliclent distribution of the expanded vermiculite granules throughout the body of the sheet produced, is assured by regulating the consistency of the stock discharged on the wire of the forming machine.

The sheet of composition flowed onto the wire of the machine must have a certain degree oi fluidity in order to obtain the best condition for forming the sheet of wall board to be produced.

The granules of expanded vermiculite reduce the fluidity of the composition but very little. I have used successfully a mixture having a conlarger-size granules is that they would tend to float to the top of the sheet of composition while carried on the wire in the length of time the composition must remain on the wire to effect its drainage of surplus water, and thus would concentrate the inert material in the upper stratum of the sheet, and correspondingly deprive its lower stratum of the inert material, and prevent proper distribution thereof throughout the sheet to assure the production of an emcient fire-resistant' wall board.

The objection to a smaller size of inert granules than such as retained on a -mesh screen is that they would be lost with the water in which held in suspension and drained from the sheet of composition; and the wall board produced would lack the mechanical blocks intended to insulate a burning or smoldering section of the wall board from adjacent sections,

It will be understood by all versed in the art to which my invention relates, that proper distribution of the expanded vermiculite granules throughout the thickness of the sheet produced is obtained by selecting granules of proper particle size and by regulating the consistency of the stock discharged on the wire. While expanded vermiculite granules float in water, because having a density less than water, the densities of the individual granules is changed by the amount of water they absorb while the stock is contained in the stock box; and thus when the stock is discharged on the wire of the board-forming machine, the granules of expanded vermiculite will be disposed at various levels in the sheet forming on the wire; and in that way be properly distributed throughout the thickness of the sheet of wall board produced.

Before the inert granules are mixed with the pulp stock, all refinement of the latter must be completed.

While the granules of expanded vermiculite vary in size, it is to be understood that the minimum and maximum sizes of the granules have been selected approximately as above stated. The strands of fiber constituting the web of my fiber board bind the components thereof firmly together. The adjacent sections of fiber composing the body of my wall board are effectively insulated from each other by the granules of expanded vermiculite enmeshed in the web of the fiber. In other words, the embedding of the granules of expanded vermiculite in the fiber composing the body of my wall board restricts the formation of the webs of fiber encompassing the expanded vermiculite granules to such as in combustion will be capable of generating only a small amount of heat; and the insulation effect of'the granules of expanded vermiculite is such as to confine the combustion of an ignited and smoldering section of my wall board, and prevent it from spreading by the transmission of high temperature to and the ignition of adjacent sections.

The composition for making my wall board may consist of about 35 to 55 parts by weight of wood pulp fiber, of the grade commonly used for making wall board and commingled with water to produce a pulp consistency, and about 65 to 45 parts by weight of expanded micaceous material, specifically expanded vermiculite, dimensioned as mentioned. These ingredients must be commingled by gentle agitation to obtain thorough intermixture of the fiber and micaceous material.

The wide range in the proportions of micaceous material and fiber is based upon the relative mechanical strength and fire-resistance requirements in the wall board produced. Wall board having the maximum amount of micaceous material is intended for use only in places where mechanical strength is not a factor.

I have found the employment of expanded micaceous granules of the size mentioned, as best for the making of my fire-resistant wall board. However, it may be'found that some other inert, porous material may be substituted for expanded vermiculite.

But when substituting other porous inert material for expanded vermiculite then the quantity of the substituted material must be determined relatively to its specific gravity as compared with that of expanded vermiculite. And if this factor would require the use of considerably larger amount of the substituted inertmaterial, the cost of the substituted inert material, or the increase in the weight of the wall board produced--and thus the increase in freight rates may not justify the substitution.

I claim:

1. A method of making fibrous, fire-resistant wall board comprising forming a stock of fiberpulp, completing all refinement of the fiber-pulp, intermixing with said fiber-pulp granules of an expanded vermiculite, said granules being selected in particle size within the approximate range as will pass through a 6-mesh screen and be retained on a 20-mesh screen, the resulting composite stock having a consistency suitable for mat formation on the wire of a Fourdrinier machine, limiting the period of contact of the expanded vermiculite with the water component of the stock so as to vary the densities of said different sized granules, then discharging on said wire the resulting stock, whereby said granules become disposed at various levels in the mat carried by said wire and are distributed throughout the fibers of the mat, and finally forming a board from said mat.

2. A method of making fibrous, fire-resistant wall board comprising forming a stock of fiberpulp, completing all refinement of the fiberpulp, intermixing with 35 to 55 parts of said fiber-pulp 65 to 45 parts of granules of an expanded vermiculite, said granules varying in particle size within the approximate range as-will pass through a 6mesh screen and be retained on a 20-mesh screen, the resulting composite stock having a consistency suitable for mat formation on the wire of a Fourdrinier machine, limiting the period of contact of the expanded vermiculite with the water component of the stock so as to vary the densities of said difierent sized granules, then discharging on said wire the resulting stock, whereby said granules become disposed at various levels in the mat carried by said wire and are distributed throughout the fibers of the mat, and finally forming a board from said mat.

ARTHUR C. SALISBURY.