US2793131A

US2793131A - Thermal insulating shape and method of manufacture

Info

Publication number: US2793131A
Application number: US286010A
Authority: US
Inventors: Mark E Binkley
Original assignee: Johns Manville
Current assignee: Johns Manville Corp; Johns Manville
Priority date: 1952-05-03
Filing date: 1952-05-03
Publication date: 1957-05-21
Anticipated expiration: 1974-05-21

Description

disclosed in the Kieselbach and Williams patent. ably the primary disadvantage is the inability to emf ploy the disclosed composition and procedure to fabricate insulating bodies for use at high temperatures, such as THERMAL INSULATING SHAPE AND METHOD 1 OF MANUFACTURE Mark E. Binkley, Somerville, N. J., assignor to Johns- Manville Corporation, New York, N. 1., a corporation of New York No Drawing. Application May 3, 1952, Serial No. 286,010

14 Claims. (Cl. 106-121) This invention relates to insulating blocks or shapes and more particularly to high temperature insulating shapes incorporating silica in the form of diatomaceous earth as a major ingredient.

The high temperature insulation shape and method of manufacture which form the subject of the present invention represent improvements on the High Temperature Insulating Shapes and Methods of Manufacture which are described in United States Patent No. 2,033,106 grant ed March 3, 1936 to Arthur B. Cummins and Patent No. 2,388,549 granted November 6, 1945 to Henry A. Kieselbach and Earl R. Williams.

Insulating blocks of the type described in the Cummins patent develop considerable shrinkage during the period of manufacture and cannot, therefore, be molded to precise dimensions. Such blocks must be molded and thereafter planed down or trimmed to the desired dimensions for their'intended use. The manufacture of finished blocks by such a method is, therefore, costly and time consuming and involves considerable loss of material in the form of trimming waste. The insulating blocks and method of their manufacture disclosed in the Kieselbach and Williams patent are an improvement upon those defined in the Cummins patent in that the composition of the blocks therein disclosed is such as to eliminate a substantial proportion of the shrinkage of such insulating bodies and to enable molding of the bodies to relatively true dimensions.

Various disadvantages, however, have been found in the block and method of manufacturing the same, as

Prob- 2000 F., having a desirable low density as, for example, a density of approximately 20 lbs./cu. ft. If such light weight products are formed in accordance with the Kieselbach and Williams procedure, they are generally unstable in insulating service at temperatures ranging in the neighborhood of 2000 F., due to the necessity of using a relatively high percentage of magnesium carbonate in the block to obtain such densities. While such blocks do not have the serious shrinkage characteristics of those defined in the Cummins patent, they still do exhibit shrinkage in an undesirable amount. Furthermore, the procedure outlined in the Kieselbach and Williams patent entails the step of casting the material or utilizing a plate and frame type filter press to form the body. Either manufacturing procedure, therefore, requires the provision of a large number of molds during forming and curing, thereby rendering the procedure relatively slow and expensive.

Accordingly, it is an object of the present invention to provide an improved method of manufacturing in sulatin-g shapes, particularly high temperature insulating shapes incorporating diatomaceous silica as a principal ingredient, whereby such shapes can be molded and cured to precise dimensions.

A more particular object of the present invention is to provide a precision piston press filter molded heat insulation shape adapted for use at elevated temperatures in the neighborhood of 2000 F. and having improved strength and insulation capacity during low or high temperature insulation service. I

A further object of the present invention is to provide a filter molded insulating shape adapted for use in high temperature insulating service and having a substantially lower density than heretofore obtained with insulating materials of comparable composition.

With the above and other objects and features in view, the invention consists in the improved insulating shapes and a method of manufacture hereinafter described and more particularly defined in the appended claims.

The insulation shape which forms the subject of the present invention incorporates diatomaceous earth as a principal ingredient. The composition of the herein-disclosed insulating bodies is somewhat similar to that defined in the Kieselbach and Williams patent and particularly differs from that disclosed in the Cummins patent in the same manner as does the patent to Kieselbach and Williams; that is, the composition herein-disclosed differs from the (himmins patent in that the principal bonding agent which is used in the manufacture of bodies in accordance with the invention comprises self-setting normal magnesium carbonate, rather than preformed basic magnesium carbonate. The composition of the blocks formed in accordance with this invention primarily differs from that defined in the Kieselbach and Williams patent in the inclusion of a relatively small amount of lime in the modable slurry composition containing diatomaceous silica, staple reinforcing fibers, and normal magnesium carbonate crystals.

Suitable blocks formed in accordance with this invention are molded from a relatively dilute slurry essentially containing, in percent of solids by weight, approximately 35-7 8% of diatomaceous earth, approximately 5-15 of staple reinforcing fiber, preferably asbestos fiber, approximately 2-7% of lime, preferably hydrated lime, approximately 0-10% bentonite clay, and approximately 5-50%' of self-setting normal magnesium carbonate in the form commonly referred to as A crystals of magnesium carbonate. The preferred blocks of this invention are suitable for high temperature insulating service as, for example, in the neighborhood of 2000 F. and preferably comprise the heat reaction product of a wet molded mixture containing, in percent of solids by weight, approximately 60-75% of calcined diatomaceous earth particles, approximately 10-12% of asbestos fiber, approximately 4-6% of lime, preferably hydrated, approximately 5-7% of bentonite clay, and approximately 14- 22% of self-setting normal magnesium carbonate crystals.

As may be clearly seen, the slurry composition used in this invention to form suitable insulating shapes contains a relatively small but significant amount of lime. Heretofore, lime has been purposely excluded from blocks of compositions comparable to those utilized inaccordance with this invention since the presence in the slurry of even a small amount of lime causes deterioration of the magnesium carbonate required for the binder matrix. The incorporation of the lime in the molding slurry, and hence in the finally fabricated insulating body, in accordance with this invention, does not detrimentally afiect the block; conversely, its use has been found to result in an insulating shape which exhibits, as compared to conventional insulating shapes of comparable compositions and those defined in the Cummins and Kieselbach and Williams patents, no substantial shrinkage from the wet precision molded form to that of the finally cured and dried body, ready for insulating service.

The procedure of manufacture utilized to form the insulating bodies of this invention essentially comprises forming voluminous flocks of lightly bonded, interlaced, self-setting normal magnesium carbonate crystals and staple reinforcing fibers in dilute aqueous suspension; mixing with the aqueous slurry of such flocks a substantial amount of a gelled slurry of diatomaceous earth, lime, staple reinforcing fiber, and, preferably, bentonite; partially dewatering and molding the wet solids content of the mixed slurry under pressure; immediately removingthe rm d o y rom. he molslrand dexel p n a shape-retaining e f t e thus ormed. body xheat ns.

As a n ia p n the process, an aque usslur x voluminous flocks of lightly bon ed, iILtQII8Q fI;SQ1 Q nsma m sium ar onate crystals. n v t p reinforcing fibersv is formed. Preferably, normal magnsium carbonate crystals are obtained. by, precipitating normal magnesium carbonate from. a. magnesiumbicarbonate solution by subjecting. the bicarbonate-solution to. severe. agitation, as by aeration, ata temperature. within the range IOU-120 F. After most-of the magnesium bicarbonate has been converted. to normal car-.

is then concentrated to asolids content preferablyiexceem.

ing 15% by weight, as by.filtering.or by decantations'i By limiting the time of aerating a. solutiomofmag-.

' tnaddsr additional gel-z, structure to: the; slurry' and gives it nesium bicarbonate liquor of, say, 3% concentration- (basic magnesium carbonate equivalent) within a-period of aboutone hour ata temperature of 80-130 F. with thoroughagitation, asin a turbo-aerator, areactive form of elongatedorthorhombic normal magnesium carbonate crystalsfcan be produced having; an average dimension of 20-40 microns in length and 2-4 microns in maximum thickness.-

A portion of the staple reinforcing fibers to be used in the insulating body of this invention is then added to the total requiredarnount of normal magnesium carbonate crystal 'slurry' in proportions normally ranging between 8 and 25% by weight of the normal magnesium carbonate crystals, or approximately 0.4l2.5% by weight of the solids in the finally formed molding slurry. The temperature of the thus formed fiber-crystal slurry should not at any time exceed about 120 F. up to this point. The, relatively cool fiber-crystal slurry is then diluted with a measured volume of hot water at a temperature above 140 F. and preferably between 180 and 210 F. The concentration of slurry solids after such dilution should preferably range from 1-8.5% by weight. The thus mixedhot water and slurry are agitated to secure a uniform suspension of slurry solids, after which the dilute slurry charge is allowed to stand quiescent until large flocks of crystal-fiber aggregates of substantial water-retaining capacity, somewhat resembling in appearance thick, incompletely cooked oatmeal porridge, arev and preferably within the range ISO-170 F. The length of the period ofzquiescentstanding to develop flocculation depends primarilyupon the temperature of the slurry andshould preferably range between 2 and 32 minutes.

Forexample, whenvit takes eight minutes for aslurry of predetermined solids concentration to develop a flocculent oroatmeal condition at a temperature of 160 F., it has been found that. a period of about four minutes quiescent standing is necessary for a slurry of the same concentration to react to a fiocculent state at a temperatureof 170 F. Asisapparent, the time of quiescent standing decreases as the prereaction temperature of the slurry increases.-

The thus formed bonded, interlaced fiber-crystal flocks have sufl'icient cohesive strength so that they do not settle appreciably while in dilute aqueous suspension and have exceptionally high water-retaining capacity, which characteristics contribute to the light density of the blocks formed in accordance with this invention.

While this oatmeal slurryis being produced, aseparate slurry is formed with the diatomaceous earth, lime,

the remainder of the staple reinforcing fiber, and bentonite, if used. Preferably,rthese ingredientsarezinitially added to suflicicnt water to form a mixture havingv approximately the consistency of a thick mud. This initial mixing operation is followed-by aatreatment designed to develop extensive prereacti'on; flocculation, and volume expansion of the solidsto improve. the water-retaining capacity and gel characteristics of'the mixture. As a preliminary to this prereaction operation, this mixture is diluted with water to form; a slurrypreferably containi g at least about eight partsibyweightaofiwaters M10118 part of solids. Within such adilute. slurnyrit; is possible to obtain optimum volume expansionzandzformationof a prereacted lime. and silicagel having good; bulking, water-retaining, and free; filtering charatceristics'desirable for the, formation. of; the, blocks:' of. this invention; If bentonitetis; usedjn. thescomposition as is 1 preferred; for

light weight, high: temperature. insulating; blocks, thelime also serves, toflocculaterthezbentonite, .which. in turn better bulking, water-retaining, andi free filtering characteristi YHnstpIereactiOn. geleforminge treatment:is. carried :out by quiescent .reaction. in. thezslnrry. at .an; elevated :tem-

i perature .inthe.range-ofapproximately- 170a-2109 F. for

at? least fortyefiv'e: minutes..- Preferably; the slurry is heated. to a temperatureof approximately. 196 205 F. and: allowedato stands-quiescent with-periodic: mild agitationizfor' the desired meriodwof fime. Additionalstandingtimeis not detrimental to-.the-formatiow of theinsulatingblocks fabricated-in accordancecwitlr this invention since the bonding matrix of the'blocks is. not dependent upon the. formation-of a calcium silicate.

Afterboth the oatmeal slurry and the gel have been formed, theyare. mixed together to well disperse the flocks of each slurry, and the mixedslurry is then charged to a mold. As herein before indicated, the mixed-slurry thus formed is particularly adapted for piston press filter molding of the blocks ofthis invention. While it is clear thatthe slurry may-bemolded by conventional slower methods, suchas in a-plate and frame type filter press, it is apparentthat piston press filter molding is ideal to enable the rapid formation-0f light weight-insulating bodies with the use. of- 'a -minimum of apparatus, When theme-reacted mixed slurry is transferred into the piston= -press,- drainage of -water'startsimmediately and is accelerated by-thedeseentof the piston-ttQWar-d the'mold basesscreent As -the- -pistonde'scend'swithin the mold, thC' SO1idS content-of= amold chargeis compressed to precise; final blockdimensions under mechanical pressures, which, duringat least-the-initialstages ofthe molding-operation', should; be as highas-60 lbs./sq. in. when molding-blocks of; for=example,-20 lbs/cu: ft; density.

The wet moldedblockas-madein accordance with the present invention'has; adequate compressible strength so that it maybe immediately removed fromthe supporting mold base for transfer to a drying oven prefrablyoperated: at a temperature -of approximately 220'350 F., wherein the normal magnesium carbonate-in the body is converted to basic magnesium carbonate toform the binder matrix thereof.

As-a specific example of'this-invent-ion ahightemperature insulating block was formed in-the-followingmanner: Into 15 gallons of waterwere-mixed 1.0 lb. of amosite-asbestos fibers, 0.6 lb.-bentoniteclay,-.-6.4-lbs. of finely divided calcined diatomaceous-earth, and 0.5 lb. of hydrated lime.

The thus formed slurry -was heated to- 200 F. and then allowed to stand quiescent for one. hour, during which time the slurry solids gelled with fiocculation and substantial volume expansion; Similarly, 1.2 gal. of a slurry containing, 2.5 lbs. of self-setting normal magnesium carbonate A crystals and 0.25 lb. of amosite asbestos fiber was diluted with gals. of water which had a temperature of 195 F. This diluted slurry was mixed by air or mechanical agitation for approximately 2 minutes and allowed to stand quiescent for about minutes, during which time large flocks of crystal-fiber aggregates of substantial water-retaining capacity formed. The gelled slurry containing the diatomaceous earth was then mixed with the thus formed fiber-crystal oatmeal slurry, and the mixed slurry charged to a filtering piston press wherein the block was precisely molded to dimensions of 2" in thickness, 12" in width, and 36" in length. After molding, the block was immediately removed from the mold and dried for 48 hours at 300 F., without exhibiting dimensional change. The thus formed block had a density of lbs/cu. ft. and a modulus of rupture of 64 lbs/sq. in. and easily withstood the soaking heat at insulating service temperatures of 2000 F.

When utilizing the hereinbefore disclosed procedure and slurry compositions, the insulating shapes of this invention may be molded to precise dimensions and exhibit no substantial amount of shrinkage in volume during the molding, curing, and drying operations. The high temperature insulating blocks according to the hereinbefore-defined preferred composition exhibit this nonshrinking characteristic during molding and drying, and also exhibit an excellent resistance to shrinkage at insulating service temperatures of approximately 2000 F. For example, a high temperature block of the preferred composition of this invention shrinks less than 2% linearly as compared to over 3% for those formed in accordance with the Kieselbach and Williams procedure. Additionally, these high temperature insulating blocks are not destroyed by soaking heat at these high temperatures, as are conventional magnesia insulating bodies. The blocks according to this invention have substantially dust-free, hard surfaces containing filter screen impressions and have a lower density and a higher ratio of modulus of rupture to density than comparable insulating blocks heretofore fabricated without using normal magnesium carbonate crystals. Blocks made in accordance with the present invention have a modulus of rupture to density ratio of at least 3 throughout the preferred density range of 15-25 lbs/cu. ft. and have a substantially lesser density for the same composition when compared to the insulating bodies formed in accordance with the hereinbefcre-mentioned Kieselbach and Williams patent.

Preferably, the diatomaceous earth utilized in the blocks should be reduced to finely divided or powdered form and, for blocks formed for high temperature insulating service, should be straight or flux calcined at temperatures not substantially less than the insulating service temperature at which the block will be used. In similar manner, the lime and bentonite utilized in this block should be in finely divided form to enable the formation of the desired gelled slurry. Asbestos fiber, preferably amosite fiber, is the most suitable staple reinforcing fiber for use in this invention, but conventional reinforcing fibers such as mineral wool, glass, etc, may be utilized to provide the bulking structure for the gelled and oatmeal slurries.

It will be understood that the details given are for the purpose of illustration, not restriction, and that variations within the spirit of the invention are intended to be included in the scope of the appended claims wherein the percentages set forth are in percent by weight of solids in the finally formed and molded slurry unless otherwise indicated.

What I claim is:

1. The method of manufacturing light weight insulating shapes which comprises forming an aqueous slurry containing approximately 5-50% self-setting normal magnesium carbonate crystals and approximately 0.41'2.5% staple reinforcing fibers having a temperature below approximately R, rapidly diluting and heating said slurry with hot water at a temperature and in amount suflicient to raise the temperature of the slurry to approximately 140-210 F., maintaining the thus diluted and heated slurry quiescent for 2-32 minutes to develop therein voluminous flocks of lightly bonded interlaced crystals and fiber, mixing with said fiber-crystal slurry a gelled aqueous slurry formed by subjecting a slurry containing approximately 35-78% diatomaceous earth, approximately 2-7% lime and approximately 2.5-14.6% staple reinforcing fiber and having a water to solids ratio of at least 8 to 1 to quiescent reaction of' said lime and diatomaceous earth at a temperature of approximately 170-2l0 F. for at least 45 minutes, partially dewatering and molding the wet solids content of the thus mixed slurry under pressure, and developing a shape-retaining set of the molded shape by heat to convert the normal magnesium carbonate crystals to magnesium basic carbonate.

2. The method of manufacturing light weight insulating shapes which comprises forming an aqueous slurry containing approximately 5-50% self-setting normal magnesium carbonate crystals and approximately 014- staple reinforcing fibers having a temperature below approximately 120 F., rapidly diluting and heating said slurry with hot water at a temperature and in amount sufiicient to raise the temperature of the slurry to approximately -2l0 F., maintaining the thus diluted and heated slurry quiescent for 2-32 minutes to develop therein voluminous flocks of lightly bonded interlaced crystals and fiber, mixing with said fiber-crystal slurry a gelled aqueous slurry formed by subjecting a slurry containing approximately 35-78% diatomaceous earth, approximately 2-7% lime, up to 10% bentonite and approximately 2.5-l4.6% staple reinforcing fiber and having a water to solids ratio of at least 8 to 1 to quiescent reaction of said lime and diatomaceous earth at a temperature of approximately -210 F. for at least 45 minutes, partially rewatering and molding the wet solids content of the thus mixed slurry under pressure, and developing a. shape-retaining set of the molded shape by heat to convert the normal magnesium carbonate crystals to magnesium basic carbonate.

3. The method of manufacturing light weight high temperature insulating shapes which comprises forming an aqueous slurry containing approximately 14-22% selfsetting normal magnesium carbonate crystals and approximately l-5.5% staple reinforcing fibers having a temperature below approximately 120 F., rapidly diluting and heating said slurry with hot Water at a temperature and in amount sufficient to raise the temperature of the slurry to approximately l40-2l0 F., maintaining the thus diluted and heated slurry quiescent for 2-32 minutes to develop therein voluminous flocks of lightly bonded interlaced crystals and fiber, mixing with said fiber-crystal slurry a gelled aqueous slurry formed by subjecting a slurry containing approximately 60-75% diatomaceous earth, approximately 4-6% lime and approximately 4.5- 11% staple reinforcing fiber and having a water to solids ratio of at least 8 to 1 to quiescent reaction of said lime and diatomaceous earth at a temperature of approximately 170-2l0 F. for at least 45 minutes, partially dewatering and molding the wet solids content of the thus mixed slurry under pressure, and developing a shaperetaining set of the molded shape by heat to convert the normal magnesium carbonate crystals to magnesium basic carbonate.

4. The method of manufacturing light weight high temperature insulating shapes which comprises forming an aqueous slurry containing approximately 14-22% selfsetting normal magnesium carbonate crystals and approxi- 'mately 1-5.5% staple reinforcing fibers having a temperature below approximately 120 F., rapidly diluting and heating said slurry with hot water at a temperature and in amount sufiicient to raise the temperature of the slurry to approximately 140-210 F., maintaining the thus diluted and heated slurry quiescent for 2-32 minutes to develop therein voluminous flocks of lightly bonded interlaced crystals and fiber, mixing with said fiber-crystal slurry a gelled aqueous slurry formed by subjecting a slurry containing approximately 60-75% diatomaceous earth, approximately 46% lime, approximately 5-7% bentonite and approximately 4.5-11% staple reinforcing fiber and having a water to solids ratio of at least 8 to ing body comprising the heat reaction product of a wet molded mixture of approximately 5-50% self-setting normal magnesium carbonate crystals, approximately 35- 78% finely divided diatomaceous earth, approximately 27% lime, and approximately 5-15% staple reinforcing fiber, said lime being present in the form of a hydrous calcium silicate from reaction with diatomaceous earth.

6. A precision molded, light weight thermal insulating body comprising the heat reaction product of a Wet molded mixture of approximately 5-50% selfsetting normal magnesium carbonate crystals, approximately 35- 78% finely divided diatomaceous earth, approximately 2-7% lime, up to 10% bentonite, and approximately 5- staple reinforcing fiber, said lime being present in the form of a hydrous calcium silicate from reaction with diatomaceous earth.

7. A precision filter molded thermal insulating body having a density of approximately 15-25 lbs/cu. ft. and a modulus of rupture to density ratio of at least 3, comprising the heat reaction product of a wet molded mixture of approximately 550% self-setting normal magnesium carbonate crystals, approximately 35-78% finely divided diatomaceous earth, approximately 2-7% lime, and approximately 5-15% staple reinforcing fiber, said lime being present in the form of a hydrous calcium silicate from reaction with diatomaceous earth.

8. A precision molded thermal insulating body having a density of approximately 15-25 lbs/cu. ft. and a modulus of rupture to density ratio of at least 3, comprising the heat reaction product of a wet molded mixture of approximately 5-50% self-setting normal magnesium carbonate crystals, approximately 35-78% finely divided diatomaceous earth, approximately 2-7% lime up to 10% bentonite, and approximately 5-15% staple reinforcing fiber, said lime being present in the form of a hydrous calcium silicate from reaction with diatomaceous earth.

9. A precision molded thermal insulating body adapted for use in high temperature insulating service, comprising the heat reaction product of a wet molded mixture of approximately 14-22% self-setting normal magnesium carbonate crystals, approximately 60-75% finely divided diatomaceous earth, approximately 4-6% lime, approximately 5-7% bentonite, and approximately 10-12% asbestos fiber, said lime being present in the form of a hydrous calcium silicate from reaction with diatomaceous earth.

10. A precision molded thermal insulating body adapted for use in high temperature insulating service and having a density of approximately 15-25 lbs/cu. ft. and a modulus of rupture to density ratio of at least 3, comprising the heat reaction product of a wet molded mixture of approximately 14-22% self-setting normal magnesium carbonate crystals, approximately 60-75% 8 finely divided diatomaceous earth, approximately 4-6% lime, approximately 5-7% bentonite, and approximately 10-12% asbestos fiber, said lime being present in the form of a hydrous calcium silicate from reaction with diatomaceous earth.

11. The method of manufacturing light weight insulating shapes which comprises forming an aqueous slurry of lightly bonded voluminous flocks of approximately 5 to 50% self-setting normal magnesium carbonate crystals and approximately 0.4 to 12.5% staple reinforcing fiber, said lightly bonded voluminous flocks being formed by maintaining a dilute slurry of the normal magnesium carbonate crystals and staple reinforcing fiber at a temperature of approximately to 210 F. for a period of about 2 to 32 minutes, mixing with said fiber-crystal slurry a gelled aqueous slurry containing approximately 35 to 78% diatomaceous earth, approximately 2 to 7% lime and approximately 2.5 to 14.6% of staple reinforcing fiber, said gelled aqueous slurry being formed by maintaining a dilute slurry of the diatomaceous earth, lime and staple reinforcing fiber at a temperature of approximately to 210 F. for at least 45 minutes, partially dewatering the wet solids content of the thus formed mixed slurry, and developing a shape-retaining set of the molded shaped by heating to convert the normal magnesium carbonate crystals to magnesium basic carbonate.

12. The method of manufacturing light weight insulating shapes which comprises forming an aqueous slurry of lightly bonded voluminous flocks of approximately 5 to 50% self-setting normal magnesium carbonate crystals and approximately 0.4 to 12.5 staple reinforcing fiber, said lightly bonded voluminous flocks being formed by maintaining a dilute slurry of the normal magnesium carbonate crystals and staple reinforcing fiber at a temperature of approximately 140 to 210 F. for a period of about 2 to 32 minutes, mixing with said fiber-crystal slurry a gelled aqueous slurry containing approximately 35 to 78% diatomaceous earth, approximately 2 to 7% lime, up to 10% bentonite and approximately 2.5 to 14.6% staple reinforcing fiber, said gelled aqueous slurry being formed by maintaining a dilute slurry of the diatomaceous earth, lime, bentonite and staple reinforcing fiber at a temperature of approximately 170 to 210 F. for at least 45 minutes, partially dewatering and molding the wet solids content of the thus formed mixed slurry, and developing a shape-retaining set of the molded shape by heating to convert the normal magnesium carbonate crystals to magnesium basic carbonate.

13. The method of manufacturing light weight insulating shapes which comprises forming an aqueous slurry containing, in percent of solids by weight, approximately 5 to 50% self-setting normal magnesium carbonate crystals and approximately 0.4 to 12.5 staple reinforcing fiber, heating said slurry to raise its temperature to approximately 140 to 210 F., maintaining the thus heated slurry quiescent for about 2 to 32 minutes to develop therein voluminous flocks of lightly bonded interlaced crystals and fiber, mixing with said fiber-crystal slurry a gelled aqueous slurry formed by subjecting a slurry containing, in percent of solids by weight, approximately 35 to 78% diatomaceous earth, approximately 2 to 7% lime and approximately 2.5 to 14.6% staple reinforcing fiber and having a water to solids ratio of at least 8 to 1 to quiescent reaction of said lime and diatomaceous earth at a temperature of approximately 170 to 210 F. for at least 45 minutes, partially dewatering and molding the wet solids content of the thus mixed slurry, and developing a shape-retaining set of the molded shape by heat to convert the normal magnesium carbonate crystals to magnesium basic carbonate.

14. The method of manufacturing light weight insulating shapes which comprises forming an aqueous slurry containing, in percent of solids by weight, approximately 5 to 50% self-setting normal magnesium carbonate crystal and approximately 0.4 to 12.5% staple reinforcing fiber, heating said slurry to raise its temperature to approximately 140 to 210 F., maintaining the thus heated slurry quiescent for about 2 to 32 minutes to develop therein voluminous flocks of lightly bonded interlaced crystals and fiber, mixing with said fiber-crystal slurry a gelled aqueous slurry formed by subjecting a slurry containing, in percent of solids by weight, approximately 35 to 78% diatomaceous earth, approximately 2 to 7% lime, up to 10% bentonite and approximately 2.5 to 14.6% staple reinforcing fiber and having a water to solids ratio of at least 8 to 1 to quiescent reaction of said lime and diatomaceous earth at a temperature of approximately 170 to 210 F. for at least 45 minutes, partially dewatering and molding the wet solids content of the thus mixed 10 slurry, and developing a shape-retaining set of the molded shape by heat to convert the normal magnesium carbonate crystals to magnesium basic carbonate.

References Cited in the file of this patent UNITED STATES PATENTS 1,279,975 Boeck et al. Feb. 24, 1918 1,819,893 Grieder Aug. 18, 1931 2,033,106 Cummins Mar. 3, 1936 2,209,754 Abrahams et al July 30, 1940 2,275,032 Greider et al. Mar. 3, 1942 2,388,549 Kieselbach et al Nov. 6, 1945 2,415,647 MacArthur et al Feb. 11, 1947 2,428,555 Cummins et al. Oct. 7, 1947 2,536,073 McGarvey Ian. 2, 1951

Claims

1. THE METHOD OF MANUFACTURING LIGHT WEIGHT INSULATING SHAPES WHICH COMPRISES FORMING AN AQUEOUS SLURRY CONTAINING APPROXIMATELY 5-50% SELF-SETTING NORMAL MAGNESIUM CARBONATE CRYSTALS AND APPROXIMATELY 0.4-12.5% STAPLE REINFORCING FIBERS HAVING A TEMPERATURE BELOW APPROXIMATELY 120*F., RAPIDLY DILUTING AND HEATING SAID SLURRY WITH HOT WATER AT A TEMPERATURE AND IN AMOUNT SUFFICIENT TO RAISE THE TEMPERATURE OF THE SLURRY TO APPROXIMATELY 140-210*F., MAINTAINING THE THUS DILUTED AND HEATED SLURRY QUIESCENT FOR 2-32 MINUTES TO DEVELOP THEREIN VOLUMINOUS FLOCKS OF LIGHTLY BONDED INTERLACED CRYSTALS AND FIBER, MIXING WITH SAID FIBER-CRYSTAL SLURRY A GELLED AQUEOUS SLURRY FORMED BY SUBJECTING A SLURRY CONTAINING APPROXIMATELY 35-78% DIATOMACEOUS EARTH, APPROXIMATELY 2-7% LIME AND APPROXIMATELY 2.5-14.6% STAPLE REINFORCING FIBER AND HAVING A WATER TO SOLIDS RATIO OF AT LEAST 8 TO 1 TO QUIESCENT REACTION OF SAID LIME AND DIATOMACEOUS EARTH AT A TEMPERATURE OF APPROXIMATELY 170-210*F. FOR AT LEAST 45 MINUTES, PARTIALLY DEWATERING AND MOLDING THE WET SOLIDS CONTENT OF THE THUS MIXED SLURRY UNDER PRESSUR, AND DEVELOPING A SHAPE-RETAINING SET OF THE MOLDED SHAPE BY HEAT TO CONVERT THE NORMAL MAGNESIUM CARBONATE CRYSTALS TO MAGNESIUM BASIC CARBONATE.