US 3667977 A
Description (OCR text may contain errors)
ke-vz \i ilnited States Patent 015 3,667,977 Patented June 6, 1972 3,667,977 EXPLOSION-PROOF ASBESTOS-CEMENT SHAPES James E. Harbison, Ambler, Pa., assignor to Certain- Teed Products Corporation, Ardmore, Pa. No Drawing. Filed Feb. 6, 1970, Ser. No. 9,423 Int. Cl. C04b 31/08 US. Cl. 106-99 3 Claims ABSTRACT OF THE DISCLOSURE Asbestos-cement shapes are formed from a furnish containing a small quantity of Zegetable fibers distributed therein, the shapes being formed by screw extrusion, thereby providing articles or shapes in which fibers extend randomly from the exterior surface of the shapes into the interior regions thereof and thus provide bleed channels through which vapor formed in the interior may escape when the shapes are subjected to heating, with consequent substantial elimination of tendency to explode.
This invention relates to explosion-resistant asbestoscement shapes, especially adapted for use as structural members, pipes and the like, and to a method for manufacturing such explosion-resistant shapes.
It is known that when asbestos-cement shapes are subjected to substantial and rapid heating, they exhibit a marked tendency to explode, shatter or break up. For example, when a building such as a house formed of or containing asbestos-cement structural parts is subjected to fire, for instance a fire in the contents of the house, the high temperature to which the asbestos-cement shapes are subjected results in evaporation of moisture contained within the mass of the shape. This heating, especially if it is relatively rapid, frequently causes the shape to literally explode or break apart, often with resultant violent scattering of fragments of the shape over substantial distances. This effect is hazardous not only to properly, but also to persons within close range.
The present invention is concerned with asbestos-cement shapes especially suitable for use as structural components of buildings in which tendency to explode is substantially eliminated and in which this is accomplished without appreciable loss of strength or other desirable physical characteristics of the asbestos-cement material of which the shapes are formed. In general, this is accomplished according to the invention in consequence of the use of fibers of a certain type in the furnish from which the shape is made, and also in consequence of the use of a certain particular manufacturing technique for forming the shapes from the fiber containing furnish.
First, with reference to the fibrous material, it is contemplated to employ a small percentage of vegetable fibers preferably wood fibers which are characterized by relatively great freeness. Free'ness is a term used with respect to fibers, especially wood fibers, employed in the manufacture of paper, roofing felts, fibrous hardboard or fibrous insulating board. In general relatively great freeness indicates that the fibers will drain freely when mixed with water to prepare a pulp. A more specific freeness test is referred to more fully hereinafter.
According to the present invention, a small percentage of wood fibers, for instance about 0.7% by weight of the dry ingredients, is added to and mixed with the other ingredients of the asbestos-cement furnish. The water required is then added and the shapes or articles are formed from the resultant mixture.
Although asbestos-cement shapes, pipes or the like may be made from such a mixture by a va'i'iety of different techniques, it is herein contemplated that the articles be prepared by screw extrusion of the furnish, the extrusion being carried out promptly after the water has been added to the dry ingredients, and the shapes being cured after delivery from the nozzle of the extruder.
An important reason for the preference for the use of screw extrusion according to the present invention is that this type of fabrication results in a type of distribution of the fibers throughout the mass of the article being made such that many of the fibers have one end adjacent to an exposed surface of the shape and the other end located in the interior of the article. Although extrusion has a tendency to cause some fiber orientation in certain areas or zones, the fiber orientation and distribution is nevertheless three-dimensional in character, with the result that many fine channels are provided in the interior of the material terminating in pores at the surface of the article. Such channels, even through occupied by the fiber itself, nevertheless represent flow paths through which vaporgenerated in the interior may pass to the surface of the article and thus be liberated without de velopment ofinterior localized areas of high pressure such as to cause explosion.
In contrast to the foregoing, with certain other known techniques for forming shapes from asbestos-cement furnish or mixes, vegetable fibres of the kind herein contemplated for use would have a tendency to stratify or to become concentrated in localized areas. For example with types of fabricating operations in which lamination is employed to form an article, the overwhelming bulk of fibers, if present, would tend to lie in planes paralleling the planes of lamination.
It is therefore of importance according to the present invention not only to utilize vegetable fibers but also to form the shapes or articles by screw extrusion, since by the use ofsuch extrusion, the distribution and random orientation of the fibers is maximized, with the result that a smaller total quantity of fibers may be employed, thereby providing the highly desirable explosion-proof characteristic while minimizing loss of strength and other desirable physical properties.
Although it has been known to employ sawdust and even certain fibrous materials in cement mixes'of various kinds for various purposes, it is important in the practice of the presentinvention to utilize fibers of relatively great freeness, as already indicated above, and to employ such fibers in only very low concentration. A fiber content of from 0.10% to 2.00% by weight of the dry ingredients is usable, most advantageously from about 0.25% to about 1.0%. These percentages are here given on the basis of the weight of the dry ingredients used in making up the furnish. However, when an article is made from such a furnish, the percentage of the fibrous material will be essentially the same in the ultimate cured or dried article, because the addition of water and the subsequent curing only alters the weight by a small amount as compared with the initial dry ingredients.
Although vegetable fibers of different types may be utilized, wood fibers are preferred, and the wood fibers used may be of the same type as employed in making roofing felt, insulating fiberboard or hard fiberboard. Fibers utilized for 'such purposes have much greater freeness than do the wood fibers employed in the manufacture of paper. As a specific test of the freeness of the fibers preferably used according to the present invention, after preparing a slurry or pulp by adding the fibers to water, the fibers may be placed upon a screen or positioned in some other manner to permit free drainage, and the fibers have a degree of freeness usable according to the invention if they readily drain down to less than 70% water content by weight. Most advantageously, the fibers should readily drain down to a water content at least as low as 3 50%. At any point below the 70% level, the fibers can be handled as a solid, rather than as a slurry, and this is of importance from the standpoint of facilitating and enhancing the fiber distribution and random orientation contemplated by the invention.
The relatively great freeness of the fibers as referred to facilitates preparation of the furnish because such fibers may readily be mixed in the same manner as a dry ingredient.
The furnish should contain both asbestos and cement and may also contain other ingredients if desired, for instance silica. In any event, the cement should constitute at least about 40% by weight of the dry ingredients and may even run up to about 85 or 90% of the dry ingredients. The asbestos should constitute from about 5% to about 60% by weight of the dry ingredients. In general the Portland cements are suitable for the purposes ofv the present invention, especially those known to the trade as Types I, II, HI and III-A in their normal powder form.
Although a variety of types of asbestos fibers may be employed, any of the seven grade fibers are preferred, a typical and especially advantageous type being Canadian Quebec chrysotile slip fiber.
The furnish may be prepared for extrusion in the manner referred to in copending application of Joseph L. Cangelosi and Frederick E. Hawkins, Ser. No. 767,892 filed Sept. 9, 1968, now issued as Pat. No. 3,529,981, Sept. 22, 1970, and assigned to the assignee of the present application. Specific compositions of furnish as referred to in said copending application may here be utilized, but with the addition of a small percentage of the fibers contemplated for use according to the present invention.
A comparative example indicating a formulation both with and without the fibrous material is indicated just below:
EXAMPLE A Percent Portland cement 4 6 /9 Silica 31 Asbestos fiber 22% EXAMPLE B Percent Portland cement 46.2 Silica 30.8 Asbestos fiber 22.3 Wood fiber .7
It will be seen that these formulations are identical except for the addition of the wood fibers in Example B.
After the addition of the same quantity of water to each (about 25 pounds for each 100 pounds of the dry ingredients), building components were extruded from these two formulations and the components were subjected to astandard fire test (ASTM Test Ell9-67), in which the components were subjected to a temperature of 1500 F. The components made from the formulation of Example A exploded and the components made from the formulation of Example B did not explode.
1. An asbestos-Portland cement extrusion having from about 0.25% to 1.00% by weight of fibrous material dispersed therein, the fibrous material consisting of vegetable fibers characterized by freeness sufficient to readily drain to less than 70% of water content, and the fibers being distributed and randomly oriented throughout the mass of the extrusion to define a plurality of fine fibershaped channels through which vapors may flow from the interior of said extrusion to its surface.
2. An asbestos-cement extrusion as defined in claim 1 in which the fibrous material comprises wood fibers.
3. An asbestos-cement extrusion consisting essentially of from about 40% to 85% by weight of Portland cement and from about 5% to by weight of asbestos, and having from about 0.10% to 2.00% by weight of fibrous material dispersed therein, the fibrous material consisting essentially of wood fibers characterized by freeness sufficient to readily drain to less than of water content, and the fibers being distributed and randomly oriented throughout the mass of the extrusion to define a plurality of fine fiber-shaped channels through which vapors may flow from the interior of said extrusion to its surface.
References Cited UNITED STATES PATENTS 3,529,981 9/1970 Hawkins et a1. l0699 2,144,213 1/1939 =Bassett et al. l0699 1,314,772 9/ 1919 Viens l0699 1,961,525 6/ 1934 Ofiutt l0699 889,569 6/ 1908 Albrecht l0699 JAMES E. POER, Primary Examiner W. T. SCOTT, Assistant Examiner US. Cl. X.R. 106-93