US2042870A - Thermal insulating structure - Google Patents

Description

June 2, 1936. w. L. STAFFORD THERMAL INSULATING STRUCTURE Filed May 27, 1952 INVENTOR IVz'llz'am L.,$'tafford, 9%M

ATi'ORNEY 25 pores or voids.

Patented June 2, 1936 UNITED STATES PATENT OFFICE 2,042,870 THERMAL INSULATING STRUCTURE Application May 27, 1932, Serial No. 614,133

iclaims. (c1. 12-353 tory but impervious facing, in order to prevent .This invention relates to a monolithic thermal insulating structure and method of, making the same, and particularly to such a structure comprising a casting of an insulating concrete inte- 5 grally united at one face of the casting to a heatresistant facing material.

An object of the invention is to make a monolithic thermal insulating wallthat may be used in a. furnace without an independent protecting it) layer interposed between the insulating wall and the source of heat. A further object is to provide a monolithic, rigid, and relatively impermeable insulating layer and a monolithic layer of facing material adapted to withstand higher temlli peratures than the insulating layer, the two layers being integrally united and adherent to each other over a wide range of temperature. An additional object is to provide a method of combining the insulating with the more refractory material in 20 such manner as to produce a zone of graded mixing whereby abruptness of change in properties between the two layers is minimized.

There is a decided preference in thermal insulation for cellular material containing small An example of. such insulation is diatomaceous earth, in which the pores are of microscopic size. An objection to such insulation is that it is not sufilciently refractory for all purposes, as for direct exposure to very high 30 furnace temperatures. For this reason it is customary to protect diatomaceous earth insulating material with a layer of firebrick or other refractory material interposed between the diatomaceous earth'product and the source of heat,

85 or to use the diatomaceous earth insulation at temperatures not above those which can be with-v stood by the product without protection.

To protect cellular insulating products from the slagging action of furnace gases or from abra- 40 sion, there has been used heretofore a firebrick wall, as stated, or, if the temperature is not excessive, a wash of a cementitious product. The cementitious coating has been used in the form of a thin layer that does not show much tem- 45 perature difference between the utside.of the coating and the back side which adjoins the insulating material. l

There hasalso been described a refractory in- I sulating material containing pores, such as those 50 produced by heating an earthy product containing a substance adapted to develop gas, with the consequent formation of pores or voids, on

heating. Su' h a refractory insulating material containing relatively large voids has been used 55 in combination with similar and equally refracthe entrance of material into the voids, as, forexample, from a furnace which is insulated with the material containing the voids.

An example of a thermal insulating product containing small pores is that made as described in U. S. Patent 1,184,184 to Krieger. This product consists of fragments of kieselguhr (diatomaceous earth) in a partially fritted condition and a binder. A preferable form of. such insulation is made by first "calcining diatomaceous earth in lump form at approximately 1900 to 2000 R, cooling, and granulating and screening to 3 mesh and finer, suitably with a small proportion only or none of the material finer than 50 mesh. Four volumes of this granular calcined diatomaceous earth are then mixed with about 1 volume of Port-.

land cement and sufilcient water to give a workable concrete. The proportion of water may be varied to give the consistency desired. For many 0 purposes the water used in the mixture may be approximately 60 to 70% of the dry weight of the solids in the concrete. When this wet concrete is cast and allowed to stand until the hydraulic cementitious material becomes hard, there results an insulating diatomaceous concrete having a specific thermal conductance of about 2.4 British thermal units at a mean temperature of 1000" F. When the hardened product is used in a furnace wall, it is found that the concrete is non-refractory and that disintegration by heat becomes important when the outside of the hot surface, that is, the surface directed towards the source of. heat comes to have a temperature of about 1700 to 1900 F.

From the following description of the present invention it will be seen that there has now been constructed a monolithic thermal insulating wallcomprising a diatomaceous earth concrete that 7 may be used at a hot surface temperature that is very substantially higher than that at which the usual insulating concrete construction is satisfactory.

A preferred embodiment of the invention is illustrated in the drawings in which I Fig. 1 is a side elevational view of a monolithic insulating structure adapted for use as a wall such as a floor of a furnace.

Fig. 2 is an end elevational view of a granular calcined diatomaceous earth and Portland cement concrete casting with irregularities on one face adapted to increase the firmness of union of a later to be applied heat-resistant facing.

Fig. 3 shows an end elevational view of a thermal insulating and heat resistin structure of a portion of the structure illustrated in Fig. 1,

and particularly an intermediate zone of gradedmixing.

In the various figures, like reference characters refer to like parts. Thus the thermal inulating structure comprises Portland cement I, granules of calcined dlatomaceous earth 2, a heat-resistant layer 3 united integrally to a face of the calcined diatomaceous earth and Portland cement concrete, and extensions into or mix- .tures 4 of the heat-resistant material with the said, concrete in an intermediate zone between the heat insulating material on one side and the more refractory material on the other. When the thermal insulating material is to be used in a side wall and when it must be cast in an upright position,-the casting of the insulating material may be made, allowed to take its initial set, and then provided with irregularities of surface such as those shown at 5 in Fig. 2, into which the heat-resistant material may be forced during the application of the latter to the insulating when these irregularities are. filled with the facing material, there are formed extensions 6 of one material into the other. when the sides of the irregularities are of such slope as to produce an opening which is more narrow-than the back part or the base of the irregularity, there is produced a dove-tailing effect, illustrated in Figs. 3 and 4, which'favors the firm anchorageof the heat resistant facing to a face of an upright layer of insulating material.

The application of the structure of the present invention to a furnace, such as a domestic oil-fired furnace, is illustrated in Fig. 4. It will be seen that the combustion chamber 8 is insulated at the front or left side with insulating concrete containing granular calcined diatomaeeous earth and Portland cement, the concrete being pr0tected from direct radiation from the combustion chamber by means of an. integrally united heat-resistant layercoated over and into the irregularities of surface of the insulating wall. The bottom of the furnace is insulated with a structure of the type illustrated in Fig. 1". The back side of the firebox, against which the flame from fuel ente through the pipe I may strike directly,- is constructed in conventional manner, with the insulating concrete protected 'by a wall of firebrick 9. f

detail which is not so evi-- Fig. 5 illustrates a dent in the other figures, all of which are drawn to a smaller scale. In Fig. I there may be an intermediate .zone IQ of raded 'mixing between the. insulating layer on the one side and the heat-resistant .or .more refractory 'layer on the other side.

The invention is. illustrated by the following examples.

. Example 1 A inpnolithic thermal insulating structure,

' suitablefor use in the door of afurnace, is constructedas follows.

side and the bottom with the,

somewhat ting. After hydraulic hardening, heat may be metal shell of a furnace door.

."iitwillbeseenthat' produced in Example 1.

aceous earth (so-called -C-3)' to 1 partby 5" volume of Portland cement. cast to a depth that may be This concrete is varied with the thoroughness of insulation desired. A depth that is satisfactory for most purposes is 5 inches. On top. of this casting, andhas v hardened, there is poured containing, besides water, approximately 75 parts by weight of fireclay grog, 2 parts of diaspore, and 23 parts of a quick hardening, high alumina hydraulic cement (so-called "Lumnite 15 cement, cement fondu, or calcium aluminate cement). The thickness of this layer of materials may be approximately a third of that of the insulating layer, say /2 to 2 inches, suitably about 1 tol inches. This material, while not a true refractory or adapted to withstand high furnace temperatures, is more heat-resistant than the insulating concrete and is adapted to withstand temperatures up to about 2300 to 2500 F.-

For best results, the Portland cement and granular calcined diatomaceousearth concrete is made up with a proportion of water that gives a fairly thick mixture, whereas the heat-resistant material of the kind described ismade up with water'to a fairly thin slurry.

After the water mixtures of both the insulating and the more refractory materials have been poured, the upper layer of heat-resistant material is pushed down at intervals into the floor layer, as by repeatedly inserting and withdraw- 3 ing ,a rod endwise, at intervals. This is sometimes referred to as "rodding. This rodding, or

-. mixing, approximately as illustrated at "I in Fig. 5.

. s After this rodding is,completed, the mixture is allowed to stand 'at atmospheric temperature, 45;

that is, without the application of external heat, until the two layers have hardened. Itshould beadded that the Lumnite cement, and also the Portland cement to a lesser extent, are warmed y the heat developed during the setapplied.

The structure so made may be installed in the Example 2 {The procedure a'nd materials arethe same as under Example 1,

inch. This thin layer is then partly stirred into the top portion of the lower layer containing the insulating concrete, to givea mixed layer, after which there is then added the rest of the heat-resistant material, to give a total thickness of layer of such material about equal to that sample a I p Forms are erected and a conventional mixture 7 of granular calcined diatomaceous earth and Portland cement is cast- I notches may be shaped roughly during the casting operation by having casting is set and the forms with the attached blocks of wood are removed, the irregularities may be shaped with a chisel, to produce side walls that converge in the direction of the face of the block provided with the irregularities or depressions; After the irregularities have been formed, or directly after the casting has partially hardened, in case no irregularities are to be used, there is applied to the face of the wall, which during use is to be nearest to the source of heat, a layer of refractory or heat-resistant material of the kind described under Example 1. In applying this layer of heat-resistant material to one face of the insulating concrete, one side of the form which was used originally for retaining the Portland cement and granular calcined diatomaceous earth concrete may be moved back, that is, away from the face, a suflicient distance to allow casting a layer of heat-resistant material of the desired thickness between the face of the concrete and the form in its new position. or the heatresistant layer may be applied in some cases by trowelling on. However, the latter method is somewhat complicated by the fluidity of the mixture of the heat-resistant material and water at the time the heat-resistant material is applied. This diiiiculty may be minimized by trowelling on and allowing the heat-resistant material to take its initial set in several successive thin layers instead of one thick layer. 7

The properties of the insulating structure made according to the present invention are such as to adapt it to eirtensive commercial use as a means of restricting the flow of heat. Thus the insulating layer of the structure has its usual efficiency as a thermal insulator. Also, the heat-resistant layer is sufliciently thick to offer substantial resistance to the flow of heat. While this may not be so very important directly in the total resistance of the struct I e to heat transfer, it is important in lowering substantially the temperature on. the hot side of the layer of insulating material. With this structure there is produced a wall that will withstand 300 to 600 degrees F. higher temperature on the hot surface than is the case when the heat-resistantlayer is omitted and the conventional, thermal insulating, granular calcined diatomaceous earth concrete is used without a protecting layer. It will be understood that theextent of the increase in temperature that may be withstood by the wall will vary in part with the thickness of the heat-resistant layer. In gener when increased temperature resistance is desired, there should be avoided very thin wash coatings,

' such as have been used heretofore, over insulating brick walls, for other purposes than that of increasing the resistance -to high temperatures.

The insulating material in the present structure contains a cellular or such as the granular calcined diatomaceous earth. which is bonded together by non-refractory cementitious material hardened by setting at atblocks of wood project into the form at selected locations. After the or separate as the temperature of porous refractory void-containing product,

mospherlc temperature. The wall has satisfactory resistance to crushing.

The insulating layer itself is rigid and has sub are enclosed by cement, in the preferred embodiment of the invention, to give an overall effect of non-porosity. The cellular particles may be embedded in and surrounded by non-porous material.

Maintaining the integral union, over a wide range of temperatures, of a rigid facing layer and an insulating layer that is also rigid, involves a problem that is absent when the insulating layer is more or; lessyieldable and adapted to undergo change of shape or volume under the influence of stresses of even minor magnitude and without cracking. The problem is further complicated when the insulating layer contains a high proportion of Portland cement. A Portland cement casting, when heated through a wide temperature pansion at higher temperatures.

In spite of these difficulties, the present invention provides a structure, comprising a rigid insulating concrete integrally united to a rigid facing of different material, that does not crack apart the structure is varied, for example, from atmospheric up to furnace temperature. Thus, a furnace containing such a structure may be heated or cooled, say, from 2300 to 2400 F. on the hot face to atmospheric temperature, without destroying the bond between the layersof the'two different materials.

The heat-resistant material, comprising a high proportion of the granular fireclay grog and a lesser proportion of the cementitious material of the quality of Lumnite, not only hardens when its wet mixture is allowed to stand, but also probably undergoes partial fritting or vitrification of its outside surface on being strongly heated. The final set-of the outside surface of the heat-resistant material is partly ceramic in nature and is not developed fully until after the wall structure including the Portland cement has been heated.

In a modification of with its heat-resistant facing and insulating backing containing hydraulic cementitious material may be subjected to an elevated temperature before the cementitious material has taken its final set.

In place of the granular calcined diatomaceous earth there may be used some other insulating material, suitably one containing voids or cells and made into granular form. Thus, there may be used the product described in U. S.' Patent 1,812,376 to Ross and Lambie, and comprising a material produced by heating cyanite. Or there may be used, in place of the diatomaceous earth, a product made, as described in U. S. Patent 1,583,521 to Boynton, by heating a slurry of earthy material that develops gas during such heating. In cases where the insulating layer is not to be exposed to high temperatures, granular diatomaceous earth that has not been calcined may be used.

In place of the Portland cement in the insulating concrete, there may be used another binding material. Thus, there may be used the .cal-

the invention, the casting, o

cium aluminate cement described above, although 7 lation at high temperatures as 'tion by volume of binding agent.

the use of the latter is at present not recommended because of its cost. v

In place of the insulatin concrete containing granular calcined diatomaceous earth, there may be used a concrete containing voids, such as a concrete sold under the name Porete and made by casting a mixture of cement, water, a foam producing and stabilizing substance, and :air, the air being in the form of bubbles or foam distributed throughout the rest of the material. Such voids, however, are not as effective in heat insuthe smaller pores in diatomaceous earth. Such a concrete containing voids should not be used in structures in which the concrete is exposed to temperatures at which Portland cement fails.

It is preferred 'to'use an insulating and also heat-resisting layer containing each a large proportion of granular material and a lesser propor- The explanation for the better adherence obtained with the high proportion of granular material (granules in the insulating layer and grog in the heat-resistant layer) and the minimized tendency to separation with change of temperature may be the eifect of the granules in localizing the tendency to cracking of the structure with changes in temperature and/or in making the layer containing the granules somewhat less brittle.

In place of the Lumnite cemen't, inits mixture with diaspore and fire-clay grog, as the facing material, there may be used another cementitious material, as, for example, a doublecalcinedJiigh lime content cement, suitably containing 65 to 69% of lime, calculated as calcium oxide, and sold under the name Incor cement. Incor cement and grog compositions are less-- refractory than Lunmite cement and grog compositions.

As a substitute for the diaspore theremay be used another hydrous mineral aluminum oxide or hydroxide, as, for example, ground raw bauxite. The diaspore, or aluminum droxide, serves the function of increasing the cast. If this function is not desired or necessary, such materials may be omitted from the composition.

The flreclay gro which has been described as being used as a major ingredient of the heat-re sistant mixture is a refractory and .is suitably 6- mesh and finer but free from any large proportion of very fine material. As grog, there :may be used a refractory aggregate havinga suitably low coeflicient-of thermal expansion, as, for expheric temperature, and a ample, fused alumina, mullite, silicon carbide. as

substitutes for in whole or in part.

Since many variations from the illustrative details given may be made. it is intended that variations within the spirit of the invention should be included within the scope of the claims.

What I claim is:

1. A monolithic thermal insulating structure comprising a thermal insulating layer, containthe nreclay grds.

ing a cellular material and Portland cement hardened by setting at approximately atmos heat-resistant facing layer integrally united to the insulating layer, said facing layer containing a large proportion of granular refractory material and a lesser proportion of a hydraulic cementitious material.

2'. A thermal insulating structure comprising in combination a monolithic casting of a mixture of granulated calcined diatomaceous earth and Portland cement and a heat-resistant protective layer of facing material containing approximately 75 percent of calcined fireclay rog. approximatealuminate cement.

ly 2 percent of a hydrous aluminum oxide, and approximately 23 percent by' weight of calcium ture comprising in combination sumixture of lightweight granules and a binder therefor, of the type of hardened Portland cement, a'protective facing material adapted to withstand higher.temperatures than the'said mixture and adhered thereto,- and an intermediate zone of graded mixing between the mixture and facing material, whereby there are eliminated marked inequalities of coefficient of'thermal expansion between adjacent portions of the structure.

4. A monolithic thermal insulating structure comprising 'a thermal insulating layer, containing granular calcined diatomaceous earth of particle .size finer than and Portland cement in the proportion proximately one volume of the cement a heat-resistant facing layer integrally united to the insulating layer, said facing. layer containingapproximately 3-mesh of apto four volumes of the calcined diatomaceous earth, and 45 n

Images