US2565340A - Insulation board - Google Patents

Description

loo-s Patented Aug. 21, 1951 CRQSS REFEREHCE UNITED STATES PATENT OFFICE INSULATION BOARD Harvey R. Anderson, Eureka, Pa., assignor to Keasbey and Mattison Company, Ambler, Pa., a corporation of Pennsylvania No Drawing. Application June 8, 1949,

Serial No. 97,907 7 8 Claims. (01. 10s-W This application is a continuation-in-part of my copending application for U. S. Patent, Serial No. 690,587, filed August 14, 1946, now abandoned.

This invention relates to heat insulating composition board, and a principal object of the invention is to provide a board of this class having generally improved physical characteristics.

More specifically, an object of the invention is to provide a heat insulating board of homogeneous structure susceptible of manufacture in the form of large sheets and exhibiting a relatively high strength for a material of the class exhibiting pronounced heat insulating characteristics.

Another object is to provide an improved insulation board suitable for use as bulkheads, fire barriers, heat insulating walls and the like, and composed essentially of chrysotil e asbestos, silivceous ilii hnira'ffilii'e PM Heretofore in the manufacture of boards of this class, the use of chrysotile asbestos fibres have been avoided for the reason that they failed to afiiordmard of the required density, strength and thermal characteristics, an i has been generally accepted that the best results were obtainable by use of asbestos fibres of the amosite type. Thus in U. S. Patent Nos. 2,326,516 and 2,326,517 it is specifically stated that to obtain a thermal conductivity of less than one and a minimum modulus of rupture of 1500 pounds per square inch in a heat insulating material of this -nature having a density of the order of 40 pounds per cubic foot, asbestos fibres of the amphibole variety having water of crystallization not hlgh er than per centsfiouldbe used. mchrysotile islclstos'fibrs'have in the neighborhood of 14. per cent Water, either as mm of or gstalligatignpr of both, and were, therefore, considered unsuitable for production of insulation board in accordance with the principles set forth in the aforesaid patents. .I have discovered, however, that so ti besto s possess the physical characteristics required for the formation of a thermal insulating sheet in which a thermal conductivity of less than one and a transverse strength in excess of 1500 pounds per square inch may be secured with a board density of 40 pounds per cubic foot or less. In accordance with my invention, it has been found possible to obtain transverse strengths in excess of 3,000 pounds per square inch at a density of substantially 40 pounds per cubic foot, together with a thermal conductivity of less than one at a mean temperature of 100 degrees Fahrenheit expressed as B. t. u.s per inch per hour per square foot per degree Fahrenheit.

I am aware of the fact that many chrysotile asbestos fibres do not have the characteristics required to produce a board of the above characteristics. These unsuitable fibres have a tendency to form in a water slurry a mass having great physical aflinity for water to an extent which interferes with removal of excess water in the formation of the sheet. This results in a sheet of high density in the area adjoining the face from which the water is removed and a very low density at the face to which pressure was applied. Thus the structure does not possess a uniform porosity or hardness, nor pores of a size conducive to a low heat transmission value. Further, such sheets require excessive surface preparation, with resultant material losses, as by sanding, to obtain a finish suitable for commercial application and even so, do not possess sufficient hardness to alleviate excessive damage in normal commercial use. Chrysotile fibres of the nature I have found suitable for a sheet of this type do not present such difliculty and, unexpectedly, produce a sheet with a low heat transmission and exceptionally high transverse strength for the aforesaid low density. The sheet may be made very close to the desired finished thickness and requires a minimum of sanding to provide a smooth and hard surface suitable for painting or other decorative finishing. The surface is of sufficient hardness to prevent scaling of applied decorative finish when subjected to the usual abrasive and impact loads in commercial use. Further, the sheet withstands processing procedures without the usual damage and resultant rejection of imperfect sheets common to a soft sheet. A board produced in accordance with my invention shows a materially improved strength as compared with the prior boards produced from amositefibre.

Chr sotile fibre suitable for use in the manufacture of the improved sfiee't He'rein described may be differentiated from unsuitable chrysotile mg by first establishing e c arac r o fibre from a specific source and then determining the grade from that source which may be used. This may be accomplished by means of the Quebec Standard" Asbestos Testing Machine in conjunction with a test of the wet volume of the fibre, milled to the extent giving the greatest bulk possible with that fibre.

To determine the suitability of a chrysotile fibre from a specific source, the fibre for this determination shall have a Quebec Standard Asbestos Testing Machine value not hi her than 2-8-4-2. If this fibre, after milling to the optimum state of bulk, has a wet volume value of at least 40 cubic inches per pound of fibre, the fibre from that source will possess the desired characteristics. The grade of fibre from that source having a wet volume value of 40 cubic inches per pound of fibre or greater will permit the manufacture of the type of sheet herein described.

The Quebec Standard Asbestos Testing Machine and its use is familiar to all in the asbestos industry and is the accepted standard for grading asbestos.

The wet volumes of the asbestos fibres are determined by means of a densitometer which measures the thickness of a wet filter cake of constant diameter which then permits the expression of the wet volume values in cubic inches. The apparatus consists of a piston of 1.75 inches in diameter fitted within a cylinder. The travel of the piston is measured to a thousandth of an inch by means of a dial gauge. One end of the cylinder has a filtering member of No. 5 Whatman filter paper supported by a perforated filtering plate attached to the cylinder, which allows the escape of liquid but retains any material in solid form. The piston is moved by air pressure of magnitude sufficient to exert 25 pounds per square inch on the sample. In use, the air pressure is applied to the piston and thus to the sample. The pressure is applied for a period of time of suflicient duration to allow the travel of the piston to cease. The slurried sample, three grams of fibre suspended in 50 milliliters of water, is thus pressed against the filtering member to form a filter cake. Since the diameter is a fixed value, the thickness measurement permits the calculation of the wet volume value of the filter cake in cubic inches.

According to the invention, the board may be formed from a water slurry of suitable chrysotile fibres as herein specified, fine silica, and hydrated me by qompressing and,removing excess water mold having a filteriyg'scree'rii 'The'formed 'Boaidftb 'a'hardf'sti'ohg, and .relatively flexible structure by subjecting it to elevated Lempergtures and pressures by means of steam. In carrying out thisprocss, it is preferaBle to open the chrysotile asbestos fibres to a great degree by passage through a fiberizing mill. This fibre may then be mixed with fine silica and hydrated lime by conventional means.

If preferred, the fine silica and hydrated lime may be fed through the mill togetheT'wdth the asbestos fibr e so as to obtain a blending of the dry ingredients simultaneously v'v'i't'hi the gpening of the fibres. rm'fy airxea*"rziatefia1tiics prepared'in the proper proportion are mixed with m to a sl ng; by conventional means. I prefer a quan ity ofwater in the neighborhood 1200 per cent of me o gyvergfit r me scird ingredients in the mixture. This aurryflirprcper ount to afford the desired density in the finished sheet, is then pressed to a solid blank form in a mold having its lower surface in the form of a screen or perforated sheet material to permit excess water to be substantially removed by application of pressure. Sheets in thickness of about inch to 1 inches may readily be produced in this manner. The formed sheet is then removed from the mold, placed on a fiat pallet and allowed to age from 2 to days at atmospheric conditions before the final curing at elevated temperature and pressure is effected as by autoclaving.

4 I have found that if sheets are allowed to age from 2 to 5 days before autoclaving. the'r'e'fi? very little tendency for t'fi'' 'sheets to swell or check along the edges, and that the sheets may 5 be autoclaved without the use of confining weights or clamps. Portland cement may be used together with the lmskeletonized binder prior to and during autoclaving. fie sheet is preferablygutoglaved atfrom iZjl I50 unasrnergs ua a; c .s eemrr u may be piled 'iifa' "solid 'pne forautoclaving or may be spaced at intervals to facilitate the entrance of steam into the sheets.

The sheets thus autoclaved are dri sub- 5 stantially bone dry condition in a suitable drier at a temperature above the boiling point of water, for instance, at about 250 degrees Fahrenheit. I thus obtain a sheet which is hard, has considerable fiexibility, is light in weight, and very strong. The sheet, although having relatively fiat surfaces, may be further finished by sanding or 'by other means as desired.

I havefound that it is possible to use 35 to 65 parts by weight of the specified chryspjilaeasr bestos to 100 parts of the finished dry sheet, de-

pending on the physical characteristics desired. To obtain maximum strength and good flexibility for a sheet of this nature, I prefer to use 50 per cent of the chrysotile begt os fib lle, as herein specified, to 100 parts of the finished dry sheet.

For example, a sheet made as heretofore described and composed of 50 parts of the specified chrysotile asbestos fib re, 25 parts comminuted siliclffafidaaparts hydrated Jime pxhibited a modiil iis of rupture of 3310 pounds per square inch at a density of 41.4 pounds per cubic foot with a thermal conductivity (measured in B. t. u.'s per inch per hour per square foot per degree Fahrenheit) of 0.76.

It is preferable to have the silica slightly in excess of stoichiometric proport ons with the lime in order that the lime will be substantially com pletely reacted.

1ltl'i6figh"p'roducing a less desirable sheet, I have found the use of minor amounts of chrysotile asbestos fibres not meeting the re uiremenfi of the chrysotile fibre Herein specifieagjasbesfis of the amphibole variet or small amounts of pulped cellulose along with chrysotile asbestos fibres aFhf'n'i s ecified may be permissible.

Portland cement an oxide of any of the alkaline saith metals may be used as a substitzfie for lime in the 5m der, although lime is preferred, and when Portland cement is thus used, the ratio of cement to silicious material is, preferably, about 2 to 1. When oxides of alkaline earth metals other than lime are used and reaction is too slow, an accelerator such as sodium carbonate may be used to speed the reaction. As the sili- 00 ceous material, diatomaceous earth is preferred.

It will be understood that the details given are for the purpose of illustration and not limitation or restriction, and that variations within the spirit of the invention are intended to be included 55 in the scope of the appended claims.

I claim:

1. As a new article of manufacture, a iight weight, hardand strong heat-insulating sheet material composed essentially of chrysotile asbestos fibres, whose characteristics are such that when gradingnot higher than 2-8-4-2 as determined on the Quebec Standard Asbestos Testing Machine, have a minimum wet volume value of 40 cubic inches per pound of fibre, and a hydraulic binder selected from the group consisting of the product resulting from the reaction in admixture with moisture of hydrated lime and finely divided silica substantially in stoichiometric proportions, the product resulting from the reaction in admixture with moisture of Portland cement and finely divided silica, substantially in the proportions of two parts of Portland cement to one part of silica, and mixtures thereof, said fibres constituting from 35 per cent to 65 per cent of the dry weight of the finished material, and said material having a density of less than 45 pounds per cubic foot, a modulus of rupture substantially in excess of 1200 pounds per square inch, and a thermal conductivity of less than one when measured at a mean temperature of 100 degrees Fahrenheit.

2. A heat-insulating sheet material in accordance with claim 1 wherein the elements of the said binder have been reacted substantially to completeness under the influence of steam.

3. A heat-insulating sheet material in accordance with claim 1 wherein the hydraulic binder consists of the product resulting from the reaction in admixture with moisture of hydrated lime and finely divided silica substantially in stoichiometric proportions.

4. A heat-insulating sheet material in accordance with claim 3 wherein the elements of said hydraulic binder binder have been reacted substantially to completeness under the influence of steam.

5. A heat-insulating sheet material in accordance with claim 1 wherein the hydraulic binder consists of the product resulting from the reaction in admixture with moisture of Portland cement and finely divided silica in substantially the proportions of two parts of Portland cement to one part of finely divided silica.

6. A heat-insulating sheet material in accordance with claim 5 wherein the elements of said hydraulic binder have been reacted substantially to completeness under the influence of steam.

7. A heat-insulating sheet material in accordance with claim 1 wherein the reactants in said hydraulic binder include both hydrated lime and Portland cement.

8. A heat-insulating sheet material in accordance with claim 7 wherein the elements of said hydraulic binder have been reacted substantially to completeness under the influence of steam.

HARVEY R. ANDERSON.

REFERENCES CITED UNITED STATES PATENTS Name Date Smith June 3, 1947 Number EXAMINEF

Claims (1)

1. AS A NEW ARTICLE OF MANUFACTURE, A LIGHT WEIGHT, HARD AND STRONG HEAT-INSULATING SHEET MATERIAL COMPOSED ESSENTIALLY OF CHRYSOTILE ASBESTOS FIBRES, WHOSE CHARACTERISTICS ARE SUCH THAT WHEN GRADING NOT HIGHER THAN 2-8-4-2 AS DETERMINED ON THE QUEBEC STANDARD ASBESTOS TESTING MACHINE, HAVE A MINIMUM WET VOLUME VALUE OF 40 CUBIC INCHES PER POUND OF FIBRE, AND A HYDRAULIC BINDER SELECTED FROM THE GROUP CONSISTING OF THE PRODUCT RESULTING FROM THE RACTION IN ADMIXTURE WITH MOISTURE OF HYDRATED LIME AND FINELY DIVIDED SILICA SUBSTANTIALLY IN STOICHIOMETRIC PROPORTIONS, THE PRODUCT RESULTING FROM THE REACTION TION IN ADMIXTURE WITH MOISTURE OF PORTLAND CEMENT AND FINELY DIVIDED SILICA, SUBSTANTIALLY IN THE PROPORTIONS OF TWO PARTS OF PORTLAND CEMENT TO ONE PART OF SILICA, AND MIXTURE THEREOF, SAID FIBRES CONSTITUTING FROM 35 PER CENT TO 65 PER CENT OF THE DRY WEIGHT OF THE FINISHED MATERIAL, AND SAID MATERIAL HAVING A DENSITY OF LESS THAN 45 POUNDS PER CUBIC FOOT, A MODULUS OF RUPTURE SUBSTANTIALLY IN EXCESS OF 1200 POUNDS PER SQUARE INCH, AND THERMA, CONDUCTIVITY OF LESS THAN ONE WHEN MEASURED AT A MEAN TEMPERATURE OF 100 DEGREES FAHRENHEIT.