US2568237A - Batch for refractory masses and method of consolidating - Google Patents

Description

Sept. 18, 1951 F. E. LATHE BATCH FOR REFRACTORY MASSES AND METHOD OF CONSOLIDATING 7 Filed Aug. 5, 1946 4 Sheets$heet 1 Qa uh m m & n W5 1% mi M a Nfimw F. E. LATHE Sept. 18, 1951 BATCH FOR REFRACTORY MASSES AND METHOD-OF CONSOLIDATING 4 Sheets-Sheet 5 Filed Aug. 5, 1946 .1 w 0 ..O m m H 0A a a O D O O 0 0 O m m m w W w. w W. m m n n n w n T r r r r uomimk F. E. LATH E 2,568,237

4 Sheets-Sheet 4 10 70:30 mic l'rfEfi CLAY In v-en iamfi-Ziarney,

WEIGHT PERCENT s i 0 Mao-1;

BATCH FOR REFRACTORY MASSES AND METHOD OF CONSOLIDATING ept. 18, 1951 Filed Aug. 5, 1946 Q "9 IO 20 M o(5a.-4-2) CALC/NED DOLOMITE woo 2. .I a w m m 0 0 M w m w n w w m w w w w w w a a 2 w as 2 2 2 2 2 m Ua msmlb 40 WE/G-HT CALC/NED CLAY Patented Sept. 18, 1951 BATCH FOR REFRACTORY MASSES AND METHOD OF CONSQLIDATING Frank Eugene Lathe, ttawa, Ontario, Canada, assignor to Canadian Refractories Limited, Montreal, Quebec, Canada, a corporation of Canada Application August 3, 1946, Serial No. 688,264

In Canada July 16, 1946 7 Claims. (Cl. 1016-57) This invention relates to the. bonding of refractory materials, and in particular to a method ofconsolidating granular particles of refractory character, at a relatively low temperature, into highly refractory masses and shapes.

In the industrial application of refractoriesas, forexample, in forming furniace bottoms and in fettling open hearth and electric steel furnace banks-it is highly advantageous to use materials which will set" or be well consolidated, at a relatively low temperature. This will obviate the necessity of driving a furnace so hard as to damage the superstructure by partial fusion of the brickwork, which is a frequent result when material, too refractory in character, is to be consolidated in the furnace lining. By reducing the maximum temperature required, and shortening the period of-burning-in the bottom, important economies in both fuel and labour can be effected. By producing a more monolithic bottom, the absorption of steel and slag will be reduced, and the useful life of the refractory will be increased.

On the other hand, it is obviously important to have furnace linings made of materials sufficiently refractory that they will not fail at the highest working temperature. With the development for furnace superstructures of materials substantially more refractory than have previously been used, and the higher operating temperatures adopted as a result, the danger of breakouts and other types of hearth failure has been increased. lhis continued trend towards higher temperatures emphasizes the need for improvide hearth refractories.

It will be seen that these two desiderata in the properties of refractories-consolidation' at low temperature and resistance to failure at high temperature-are diametrically opposed. It is not too' much to say that for the past twentyfive years a major objective of research on refractories has been to devise ways and means of overcoming these defects. Much ingenuity has been shown in effecting compromises between the two objectives.

In the older practice, when it was desired to make a permanent hearth from Austrian mag-' nesite or other form of highly refractory periclas'e clinker (which cannot be burned to a monolithic mass at any permissible or readily attainable temperature) it was customary to mix with the clinker some 20-25% of slag, the purpose of which was tomelt at a relatively low temperature and thus act as a bond for the more refractory particles of periclase. However, the ultimate product was at best a mixture of the two materials-used, and the slag matrix remained as a weak componentfor an indefinite period, being subject to melting at maximum operating temperatures, to chemical attack by the constituents of the furnace charge, and to physical replacement in the bottom by molten steeL, Such practice, while still followed to some extent, has been largely superseded by more modern methods.

A major improvement was effected by the development of "magnesite clinkers containing, as essential constituents of the clinker particles, 9. sufilcient proportion of compounds of lower refractoriness, such as calcium ferrites and aluminates, to constitute a. self-bonding material. These have been called thermoplastic hearth refractories. jMcAnally (U. S. 1,305,475) used in his clinker 16-18%.015 lime and 8.0-8.5% of iron oxide plus alumina. His product could be sintered to a monolithic mass without the addition of slag, and has been widely imitated, but in his method improved setting was secured at the expense of, ultimate refractoriness, since any fluxes introduced become a permanent part of the hearth, and are converted to the liquid condition whenever the temperature rises sufliciently high. Using the same principle, McCaughey and Lee (U, S. 1,965,605) introduced similar proportions of calcium ferrites and aluminates into a clinker; of higher magnesia content. Seaton and Hartzell (U. S. 2,218,485) used two different magnesiar refractories, of such composition and in suchgproportions that, by their reaction with one another, dicalcium silicate, tricalcium aluminate and cal-, cium ferrite were said to be formed. The addition; of slag to bond such refractories was recognized as desirable, and in'fact was claimed. Later (U. S. 2,238,428), these investigators produced a refractory containing a minor proportion of monticellite (CaO.MgO.SiO2), and then converted the, latter to dicalcium silicate (2CaO.SiO'2) by heat; ing the refractory with a lime-bearing material. Lee (US. 2,292,644) similarly improved there? fractoriness'of a. material containing merwinite (3CaO.MgO.2Si02) by adding lime and heating. to convert at least a part of the merwinite to di-f calcium silicate. Lee objected to, the presence inj the primary refractory of monticellite, which, lie

said, lowered the'refractoriness too much.

In summary, it has previously been proposed-.:

to make refractories which would set atattain able temperatures by (1) using in furnace'linings mixtures of slag and refractories high in-mag nesia, (2 introducing calcium ferrite and alumi;

mm? satee c r mbi gla' Recently, a different method pfj attach on the, problem has been made by the"introtluctiori of,

chemical bonds, such as sodium silicatef into masses of refractory clinker that are rammed into place, and thereby beeomes,-unnecessary to give the material a prolonged heat"treatment at high temperature in order to form a working bottom. This development has-proved; o f,.greatt importance in saving time and thereby increasing;

plant capacity, but it has not overcome the difficulty involved in the mtroduction of constituents of low melting-point, and refractories of this type have'been too expensive for general use in mam; taming-furnace banks}. 1

1% the latter purpose, so-c alled double-burned dolomite, containing a considerable proportion of iron-oxide, has'been -extensiyely used, along with raw ar id calcined dolomite, but 1' these materials aiiord"onlytemporary protection-tofurnace bank-sand their chifmeritis ini'act their cheapness.

' Inno case, it must-beemphasized, do these proposals-overcome'both of the major difficulties set out above; and at best they constituteonly'various degrees of compromise. Some methods do not 'sufiiciently lower the setting; temperature to effect maj or economiesin' burningin the-original harths or injfettlingfurnace banks; some per manently lower the r'efracto'ririess of the furnace materials to such a degree that subsequent service' is: impaired. In spite of theirindividual advantages, the problem remains essentially the same'-that of developinga material which will set rapidly at easily attainable temp'eraturesfand which will nevertheless have 's'ufiici'ent ultimate refractoriness to permit raising thefoperatin'g temperature to a point well above't-hat now used. Heretofore, 'no such material had been 'produced; 'In' the accompanyin drawingsare s'how'nmelt ing-point diagrams of Y actuar or hypothetical starting materials of the character herein described to facilitate a ready understanding of the invention. The temperatures given herein are mgeneme'ither those compiled by-'Sosman and Andersen, as given'on U; 'S'I'Steel Corporation Plates 1-4 Composition -'Temprature Phase Equilibrium Diagrams of the Refractory Oxides, dated Octoberf1933, or those given in comprehensivereviews by Hall and Insley, Degrees. c'entie grade are used throughout;

accordance with: the present invention an entirely newapproach to the problem hastherefore been made and, as willbeseen'belowit has been found that'bothf difiiculties can be overcome by. simple and highly 'fe'conomical me'ans." Not only is the consolidation of highly refractoryparticlesfib'rought about at alsubstantially lower tem- Pe e q et nmeihere ofo e' b n q isible w -I outthe'introdiicti 'or alkali metal compounds, but the ultimate 'refractoriness of the furnace lining or'refractory-"shapes is at the same time ub' iana t h ed In order to 'accomplish these desirable ends, it is'essential toselect particularist'arting materials. hese i m ea co i 'i'd l var ty of ari 1. 1: ii r qiimine a nd' f those combinations may it use'd'which belong to oral emanate, but only;

4 a very specific type. This acceptable type is invariably characterized by (1) reaction between the starting materials, under suitable conditions, to form a definite chemical compound of high refractoriness, and (2) the, formation between this chemical compoundand onei'of the starting materials-but not the otherof a product (usually of eutectic character) which substantially or completely melts to a liquid condition at thelo'w temperature desired. That is, the temperature of liquid formation between the compoundand one starting material must always be much below that of any eutectic or other liquid which may beformed between the compound and the second starting material, and obviously far lowenthanjhe melting-point of the compound itself.,

These conditions are most clearly expressed in the form shown in Fig. 1, which is a hypothetical melting-point diagram of two starting materials, A- and B, of the type described, and havingmelting-points T1- and-T2, respectively. Inorder to make the illustration wholly general incharacterJthe basic temperature i's='take'n as T- a As shown, 62% of starting materialA reactsfwith 38%of starting material B-to form the compound AXBy, having a melting-point T3: of approximately T+1400L This compound 'in-turn forms with B a eutectic E1, witha melting-point T4 Of TH-300 and a composition of 25% A and'75 %--B/ With A, AxBy forms a eutectic Eacontaining '70,%A and 30% B} and having a melting-point -Taof T+1300. The-broken line indicates that eutectic formation between AxBy and A is not essential;' in case of a compound having an incongruent melting-point, the temperature of complete fusion ris'es" 'continuously from T4 to T1, with marked cha'ngein rate at R,- Which is technically known as the reaction point. The above-stated rule nevertheless applies, for AxB -still forms alowmelting product with-B but notlwith-AJ This distinction is fundamentaL Referring again to Fig. 1, and omitting consideration of the broken line, which applies to only a few cases, it may be pointed out that'the' curve is the locus of the temperature of complete fusion for everycombination of A and B. Aboveth line, at any composition Whatever, the melt is entirely liquid. At the five compositions corre spending to A, E2, AxBy} E1" and""B ther-e are definite-melting-points, these being T1, T5, T;-,-T4, and T2, respectively, At all other compositions; freezing and melting occur over a range of rem-1 perature. For example, at a composition of 50% each of A and B, freezing of'jthe wholly molten material begins at about- T-l-1'1'80"; when the com; Pound B n ar te as, a s l d; h s of course changes th composition of thereinainf ing liquid, and with a continued 'dropj'intemperature more of prey separates until the finalliqurd reaches the composition E1, I at a temperature T4; when it allsolidifies. Similarly, if a melt of: mposition pr ent dbr and, 20%,, Bite; coo1edfifrom'T+2000, for-example, mjss i r rhisl until a temperature of about T+ 1530: is reached, when A begins to separate, again. with a change inliquidcompositiong With furthencooling morle, Afseparates' untillthe liquid. compositionjEzj'is' reached, at a ,ternper'ature, T5, when complete, solidification 1 again resu ts; before there Q cariff. 5e.

anyfurth'er' temperaturedrop.

From this discussion it ,will'jbeobyious that. the. hatched; areas in the, hart represent comfiosi fi tioris which, arecompletelylso'lid atth'e tempe tures shown. simnar1y,"eiear"ar'eas, abdttife curves.- are those. of complete liquidity,-while stippled areas represent 'conditions'of compost tion and temperature inwhich liquid and solid (having different compositions) The actual procedure to be followed in carrying out the principles of this invention may now be explained for the general case of two starting materials, A and B, again with reference to Fig. 1, Both, it will be observed, are of a refractory character, although it may be assumed that the more refractory material A is to be the major constituent of the final product. First, one takes 25% of A and 75% of B (corresponding to the composition of E1), melts the mixture at a temperature T4 (T+300) and allows the product to solidify. Twenty parts of the crushed product (containing five parts of A and fifteen of B) are then mixed with eighty parts of A, of any" suitable grain size, and the mixture is formed into the desired shape, rammed into a furnace to form a permanent hearth, or thrown as fettling material into a hot furnace. When the temperature of the mass is raised to T+300, thethan that corresponding to AXB no more liquid can form until T+l300 (the'melting-point of E2) is reached. Mineralogically, the final refractory consists entirely of A and AxBy in equilibrium with each other; the relative amounts will de-' pend always of course, upon the proportions of the starting materials used.

In this case, it is evident that a very striking and important result has been brought about."

By using two refractory starting materials of the specified type, it has been possible through the application of the present invention to con-" solidate highly refractory particles of A into'a furnace hearth (mass-or shape) at a temperature 1000 degrees below that at which initial liquid formation can subsequently occur, and'in fact 900 degrees below the melting-pointof either starting material.

It is important to observe that the'two start ing materials do not have to be taken in the exact proportions corresponding to the eutectic E1 in order to form a low-melting product. -In the case of these two starting materials, alarge pro- 7 portion of liquid will be formed at T4 even though the composition may be varied, for example, anywhere from 40% A and 60% B to 12% Aand 88% of liquid E1 at T4 with 52% of solid B ,-and-,the

whole mass Will again be molten at T+90Q?, (The proportion of solid and liquid may be determined by measurement from the chart, or may be calculated algebraically; both methods are well known to students of phase equilibrium 'di'a grams.) j It may also be observed that when theproportion of starting material Bis greater than 38%;

some liquid will always be formed atTi, the' melting-point of the eutectic E'1,-whereas-'with co-exist in equilibrium. All of this is wellknown to students of phase equilibrium-diagrams, but is mentioned i here in order to clarify the subsequent discussion.

By the time the reaction is "di B. At the former composition, 59.5% of liquid E1 will form at T4 with 40.5% of SOHCLAXBL ancl complete liquidity will result at about.T-|-.900?-,=. while at the latter compositionthere will be 48 %J 38% or less there will be no liquid under the teiiiperature T5, which is the melting-point of A r/38%: of- B there will, of course; be none of either eutectic present, and no liquid will be formed below T3, at which temperature the compound AxBy melts completely. The low-melting constituent used in practice must therefore have a greater proportion of starting material B than is present in AxBy, and the only precaution necessary to eliminate all low-melting liquid in the ultimate product is to use enough of A in the final mixture to form the compound AxBy with all of the starting material B present. It may be advantageous to use a much greater proportion of A if this particular refractory is superior to AxBy' in the properties desired in the ultimate product.

In all the above discussion consideration has been given to the general case. Attention will now be called to combinations of actual startingmaterials of the same type. These cases are not all equally simple, but the essential features;-

enumerated above are identical, and such dlfierences as occur will be explained.

One of the most interesting cases is that of lime and silica (Fig. 2), which have meltingpoints of 2570 and 1728", respectively. They form: a highly refractory compound, dicalcium silicate (2CaO.SiO2) which has a melting-point of 2130"; The lowest-melting eutectic contains 36% lime and 64% silica, and this melts at 1438, whereas the eutectic between dicalcium silicate and lime has a, melting-point of 2065, 627 degrees higher and no liquid can form below this temperature if the proportion of lime to silica is that of di calcium silicate or greater. This case differs from the one described in Fig. 1 in that there is an in-- termediate compound, calcium metasilicate (CaQSiOz) having a, melting-point of 1544 and, strictly speaking, it is this compound which forms two low-melting eutectics. Both of these eutectics. it may be observed, have melting-points about 200 degrees below the ordinary operatingtem perature of an open hearth or electric steel fur nace, whereas the refractory eutectic between 'dlcalcium silicate and lime melts at a temperature far above any thing used in furnaces of these types.

Of the same type is the melting-point diagram of magnesia and silica, as shown in Fig. 3. The

compound between these two starting materials is the orthosilicate (2MgO.SiO2) forsterlte, which The low-melting, eutectic melts at 154'? and the high-melting" eutectic-between 'forsterite and magnesiawat" 1870, 323 degrees higher. The latter temperature has a melting-point of 1910".

is at least 200 degrees above ordinary open hearth temperatures, and if the magnesia content be high the percentage of liquid formed even at that temperature is relatively small. Magnesia itself has a melting-point of 2800.

cate has an incongruent melting-point, butthis is of no practical importance, and the re'sem-' blance is otherwise quite close. 7

Of some interest (but not illustrated) is the system lime-alumina. Both of these oxides are highly refractory. In this case there are several compounds,- of which the most refractory-is 3CaO.5Al2O3, havinga melting-point of 1735 and forming with'alumina a refractory eutectic melt- There aretwo low-melting eutectics', that between 3CaO.AlzOa and 5CaO.3AlzO3, melt- .ing at 1397, and thatbetween SCaOBAhOaanding at 1715".

This case differs" from that of lime and silica in that the metasilisimilar tothat of Fig, 1.

45aand 60 %i alumina,- can, be used satisfactorily:

tttbondv particleslof refractory 1 alumina, and providsidsthat theproportion of alumina in :the mix ture -be atleast that,in,.3CaO.5A12,Os (75.2%),;n quidcan form below 17 5*.

Qf; substantially different form, but corresp onding somewhat to thatof the dotted line of Fig, 1,

4Fi ,r4, of alumina and silica. In this case the low mglting eutectic, is exceptional in that. it-

ente s- .a qut 4% f-one a t n m er -.-;thiscase-silica. Its me1ting-point-is-1550". Then" fractorycompound 3A l2O3 .2Si O2 (mullite). has an incongr;uent melting point of I 1830 and olees-l outect cw m n aaw enemeltlng eutectic is eliminated the temperal ilgm ipm liquid' -is to increase the; overall 0f ir1itia1 liquid formationis raised by 280 it, Allthat is necessaryto-eliminate the alumina contentto 72% or higher, thecomposipgrtedjncomplete detail. The-refractory compg nd ba iumzirconate-lBaQZrOzlhas a-melting:

oint, of at. least-2600,,while the low-melting eutectic containing, about 10% (molecular) of zirconia melts at approximately l300"-. eutectic between ,barium zirconate. and zirconia The has a -,melting;point of approximately 2050, or

n gner 150. degrees.

All-of .theabove :e xamples, both. theoretical. and

raetiqal have dealt with, binary. systems, the two staigting,materialsbeing in-,;all-. cases. refractory oxides fQExactly the sameprinciple, however may be applied when there are three starting materials, or, to express -theidea differently, when ony.= .,of r the,starting materials, consists of twooxides whichlmay or, may not, exist-in chemical coin nation With eachother,

,illus tratesfthe general ,case, of three .refractorymxides, A, -B,r-&Ild-, C, having melting-,

points-ofabout, rr+19oo,, T+1600, and ir+2000zv respectively. As before, there is arefractorycompoundAxBy, which-forms a :lowmelting ,-.eutecticith-rB orvwith B and ,C, andahigh-melting eutectic with A, or with A and C. In the presence oi starting material, C themelting-points of both binary eutectics .ar e, lowered-somewhat, but it still holdsthat the lowest-melting eutectic be-, tween- A,,B and c (or, strictly. speaking, between assuming thatsB and -C are taken in constant propogtions; with-reference to eachotherand tha t lthe two eutectics lie on the same straight llne drawn -through :A to (B+C). This constant;

propgntioneof ,two starting materials, how-ever, is

afrequent commercial condition.

The, pseudobi-nary{melting-point diagram -of A and lliz-i-cnasderived from Fig,;6is shown-in Fig.

7, and it will be observed that it hasa form-very In this-casethecompoundAxB (as modified-by the-presence of about 10% of C) melts at about T l-1400, oneeutectic' melts at-T+300 and-the'other-at T+l200-j The principle already explained for -Fig-.;;1 cangbe-ap;

plied in exactly the same way in this caseby.

preforming a low-melting eutectic of A, B -,;and -C.

8:; The; temperatur 10f; tinitial liquid; formation Y therebyraised .909, degrees:

mpassaincfromvthel general o the Specific): One maytalsa S ;i i.-Fig;,8,the two starting ma terialssilica,andscalcined dolomite, and plotthe,

meltin epqint ccurveas a pseudobinary system. It is; seeni,that the compound dicalcium silicate can, -co,-exist-:with.periclase. Complete fusion of a=. low-melting;pro duct, with a silica content of about,,50%l can ,be made to occur, at 1358,'but. by,--burning;;it.with sufiicient lime to form di-,- calcium;silicate.with all of the silica thus intro-'- dueed;the-temperature-of initial liquid formation,-can;- be raised by 622degrees to 1980. This particular, chart does; not show a high-melting eutectic, since thcwpseudobinary line does notpass -throll l it,-but. such a eutectic neverthe-l, less exists, with; 1980 as its approximate melting- PQ nt-.,

Anotheri case of a pseudobinary is that of Fig., 9,-which illustratesrthe sameprinciple when applied-to magnesia, and a hypothetical clay containing silica-and alumina in the proportions .70; to 30., This case is of special interest in that the magnesia-decomposes the clay to form not one, but; two,-compounds, thesebeing forsterite and spinel (MgOAlzOs), which can co-exist in. equilibrium. Liquid formation can take place at atemperature as low as 1347, with complete fusion;

at 1362,, yetalllow-rmelting liquids can be eliminated, ;by,.heating with suflicientmagnesia, the; temperature ofinitial. liquid formation then becoming about,\1700, or substantially the melting-point-of, ,pure silica. In products of high; magnesia ,content, -relativelylittle liquid will be formed, seven at,.this temperature.

It,,is,ob.vio,us-that, if a low-melting rock ormineral-of, suitable composition .be available, this may. be, ,used in, place of an artificial, product madebyfusion of the two starting materials. For 1 example, both diopside (CaO.MgO.2SiO2) and tremolite ,(CaQBMgOASiOz). melt below 1400, wollastonitew (CaQSiOz) at 1544, cordierite. (ZMgQZAlzOsfiSiOzlat- 1530 and enstatite' (Mgqsiozxat 1547 These minerals; are of commOnpccurrencein pyroxenites, amphibolites rand; relatedzrocks,

Now thatl-theuprinciple of the invention has beemfullymxplained andillustrated, it may beaccurately redefined asa method of consolidat-. incl-refractory; granulan materials, at a relatively low temperature, into masses or shapes of a highly rci factory character, which comprises (a) thesselectionof-two refractory'materials of the type illustrated in; Fig. 1 (or of more than two, as illustratedin Fig. '7), characterized by the formation :betweemthem-of at least one highly. refractorychemical compound, which compound unites pr reacts with, the first but not with then second-, star ting; material to form an intermediate'pompound,eutectic or other product of rela-' tively low irefractorinessflb) forming by'any con-- venlentmeans said intermediate compound, eutec tic; or other product of low refractoriness, or utiliZing-a, natural mineralorrock of similar chemical composition and properties, (0) using said intermediate product of low refractoriness, while'in amolten condition but at a relatively .low temperature, toconsolidate, particles .cf the second, refractory starting material into masses "or; shapes andndl converting. said masses or shapes byvthe application of heat intohighly refractory, ceramically, bondedbodies through the substan tlal elimlnation ,of the-said-intermediate prodnot of low refractoriness by means of its reaction with the second refractory starting material.

The starting materials must always be of the specific type described above, but it is-not essential that, as taken for commercial use, they be in the particular form mentioned. For example, lime and magnesia have been given as starting materials, whereas in practice it may be more convenient to use limestone, magnesite, brucite, or "dolomite, all of which on the application of heat are readily converted into the corresponding oxide or oxides. So also one may use diaspore (A12O3.H2O) as a source of alumina, and barite (BaSOi) of barium oxide, and as sources of more than one oxide such minerals as wollastonite, serpentine (3MgO.2ISiO2-2HZO), and kaolinite (AlzO3.2SiO2.2H2O). In every case, however, the combination of oxides chosen must be such that they fall into the particular type described, There may also be used as a major starting. material-a clinker containing magnesia associated with more limethan that necessary to form dicalciumi silicate with all the silica present in it. In such a case, the magnesia is substantially inert and the excess of lime acts as one starting material, while the other is siliceous, like serpentine, diopside, wollastonite or quartzite.

As already intimated, the initial product of relatively low refractoriness need not be a true eutectic between AxBy and the first starting material. For some applications a low-melting compound such as pseudowollastonite (melting-point 1544) or,5CaO.3AlzOs (melting point 1458) may bejsatisfactory. If a considerable proportion of low-melting product is to be used, it is not essen tialrthat it be wholly liquid, but only that the actual quantity of liquid present at the desired temperature be sufiicient to consolidate the refractory particles with which it is mixed.

Refractoriness is a relative, rather than an absolute, term. Copper refining furnaces may .be operated at 1100 and copper converters at 1250, basic brick may be burned at 1450-1550, open hearth furnaces may require 1650 and electric steel furnaces 1750"; a refractory suitable for the first two applications might be quite inadequate in refractoriness for steel production. It is therefore not possible to state categorically at what temperature low-melting products lying within the scope of this invention should form liquid, but as a general rule it may be said that the invention relates to low-melting products forming at least 50% of liquid at 1450, 75% of liquid at 1500, or wholly molten at 1550". It also includes, regardless of the actual temperature, all systems of the type defined when the temperature of consolidation or setting of the refractory particles by means of a low-melting product is at least 220 degrees centigrade-below the temperature at which liquid formation will occur when equilibrium has been established in the ultimate refractory. A large temperature difference of this kind is characteristic of the invention, and

thedifierence will usually be substantially greater than 200 degrees.

In discussing systems involving the use of pure starting materials, one can speak with confidence .as to the temperature of initial liquid formation and the degree of melting. That is not the case, however, when commercial starting materials are used, for the presence of impurities almost invariably reduces the temperature of liquid formation. Similarly, impurities may make it impossible to eliminate all liquid from the final product. It will be evident that some potential sources of raw materials, because of theircontent' of im purities, must be rejected altogether for application in the practice of this invention. In the practical examples which follow it will be assumed that impurities do not occur in the raw materials in sufficient quantity to afiect the re sults to any substantial degree.

The scope of the invention is so broad, and the possible applications of the principles involved are so numerous, that the cases mentioned below" are not intended to'do more than provide typical examples. The invention is by no means limited in scope. by the particulardisclosures made herein,'but only by thebroad application of the principles involved in them.

If the low-melting product to be used in the consolidation of refractory particles is to-be'preformed, any suitable method of production may be adopted. For example, if dolomite and quartzite areto be used in the proportions'required to produce a material melting below 1400", the operation can be carried out in an electric'furnac'e,

'or evenin a blast furnace or cupola. The molten product issuing from the furnace maybe allowed to solidify and then" be crushed to'the desired size, or the molten stream may be granulated by breaking it up with aJ'et of water, steam or air, and allowingthe droplets tofall intoa body of water.

If sin'tering rather than complete fusio'nis desired, a rotary kiln may be used to'advantage'. Such equipment, with' appropriate temperature control, can be used for the production of'any low-melting product, and is particularly advantageous when the' product-contains, at the temvperature of operation, a considerable proportion of solid as well as liquid constituent. Under these conditions the product will usually issue from the kiln in the form of clinker, and can be used' with or without crushing-according to its particle size.

The use of natural minerals in place of syn- 'thetic low-melting products has'already'bee'n dealt with above.

V v I CaseI There is requireda material for burning in successive layers of .magnesite' tojform the permanent bottom of an open hearth steel furnace, the object being to replace the magnesite-slag mixture so long-but rather inefiectivelyused for this purpose One may first prepare by the fusion of serpentine, oldfireclay brick and quartzite, a low-melting material containing 20 MgO, 20 A1203 and 60% SiOz. This is crushed to pass a screen of four-meshes totheinch and is mixed with magnesiteclinkerof the same grain size-in-proportions of 20 to 80,- and the mixture is thrown into a hot furnace. As soonas thematerial reaches a temperature of..1350 thelow-melting product fuses! and bonds the highly refractory particles together.- Subsequent heat treatment of the bot: tom during the, ordinary. burning-in process brings about reaction between the constituents and consolidates the mass so that the final bottom consists of 84 MgC), 4 A1203 and 12% SiOz,

.in the .forni' of periclase, spinel and ,forsterite.

aromas? than burned: dolomite,- be resistant-toslag attack, andibdhard at 1750,".

Two par-tsofraw. dolomite and one'of quartz orsandstone are melted toform; a=- slag containing 30 CaO,'21'MgO and 49% SiO2, and-melting between 1350 and 1400. This product is granulated in water, mixed with four-mesh dolomite (burned without theaddition of iron oxide) in equal: proportion, and the product is used for 'iettiing; Owing to the formation of 50% liquid at1'400 and the immediate-absorptionof thisliquid'by theburn-ed dolomite, setting-is extremely rapid. The consolidated product consists exclusively' of periclase and dicalciumsilicata'and forms no liquid below 19.80% Since the slag consists=:-almost exclusively of dicalcium and tricalciumvsilicate, with-a little calcium carbide, caleium fiuoride, magnesia, and other minor constituents,- it" has no actiononthe'banks. (If desired, thedolomitecould be used raw, but it- IS usually more economical topreburn'it. If desired;- one'could alsoadd 'tothe final mixture a small proportion of calcium phosphate orother suitable stabilizing agent to prevent the subsequent dusting of the dicalcium silicate on cooling, but this is a refinement which does notappreciably affect'the procedure or productgand does notconstituteia part of the present invention.)

As to the behaviour of such a fettling material under the action of heat, it'may be said that until initial: fusion takes place the. granular masson the-banks is soft and friable, as when originally mixed; The appearance of liquid produces in the mass'a mushy condition; like that of wet snow. 'As-the form'ationofrefractory compounds proceeds, the mass becomes progressively'harder -'anddrier-,and when the reaction; is complete the consolidated material is usually 'very hard, with no =si'gn 'ofliquid. With-differentstarting materials-,- -the change in character of the material used "for fettling varies somewhat, owing to differehces: in the amount: and viscosity-of the; liq;- uid present, the rate at which theyflnal reactions proceed, and other factors. Frequently, however, materials of the type described will pass through "all, "of, these. stages befor O n ry fettling fractories show an'y'sign offsetting whatever.

Case-3 Difiiculty is encountered in burning 'zir'conia brick, owing to the high temperature required for the development of a bond'to provide the necessary. strength in; the final product. Some means are required of'producin'g a bond at a lower "temperature, and at the same timeof developing a stronger b'rick,fo'f adequate refractoriness.

"Oneilrst, prepares a eutectic containing 90 BaO "and 10% ZrO2, and the'n introduces 10% 'of this, "a'sja fine constituent, into granular zirconia to be used in making brick. The molded; brick are burned at 1400, a temperature easily attainable in any refractory brick'kiln. At 1350 the eutectic melts, and when reaction with the 'zirconia and consolidation are complete a strong ceramic bond is'efie'cted, and no liquid can, form below 2030, a refractoriness which is. more than adequate. In, a. similar way, forsterite, mullite, and other types of brick of excellentstrength and high refractoriness can, be made at relatively low tend,- neretures.

Case 4 -.practice, the furnace is-heated to... working temperature and then cooled before putting; in the first charge. Cracks form, owingto thermal con traction, and steel would subsequently penetrate these, weakening the bottom and increasing its thermal conductivity. There is required a refractory material with which the cracks canb'e filled to prevent the penetration of steel.

Instead of preparing a highly refractory material and attempting to fill the cracks with it (which would be practically impossible) one picpares a low-melting product by .sintering ina rotarykiln at a temperature of 1400 a mixture of serpentine, clay, and kyanite to make a product containing 17 MgO, 36 A1203, and 47% S102. At this temperature there is good clinkering action without complete fusion. The furnace is heated to 1500 and sufiicient ofthe crushed sinter is then thrown into it, especially along the cracks, to fill them. adequately, with some excess. The material immediately melts and runs into; the cracks, where it slowly reacts with the magnesia walls to-form forsterite and spinel, havingmelt ingpointsof 1910 and 2135, respectively. These refractory compounds will remain solid atfthe highest; temperature of the furnace, and by con.- solidating the whole bottom, effectively prevent the penetration of steel or slag.

Case 5 It is desired to lower the setting temperature of one of the common thermoplastic fettlingrefractories which, in spite of its content. of calcium ferriteand aluminata inthe absence or slag re;- mains in a loose condition on the furnace banks until the temperature rises above 1600. It is also an objective to increase the ultimate martian;- ness of this material, which. is definitely plastic @1650 a V I The thermoplastic refractory contains (exclue sive of its dead-burning agents, which may for the moment be regarded as impurities) approxima'tely 12 MgO, 21 CaO and 7%. S102. Sincetlie lime contentis, approximately 60% -greater than that required to form the refractory compound dicalciurnfsilicate, the magnesia may be takenas periclase and neglected in the calculation of siliceous flux'to be added; hence the system is essentially binary. There is-available as a low;- melting material a quantity of the mineral diopside (CaO.MgO.2SiOz). Enough of this will. be added to form in the final product only dicalcium silicate from all lime and silica present. Calculation shows that the quantity required is 8.5 parts, which will be used with 91.5 parts of the thermoplasticrefractory. The diopside is crushed to 20 mesh, mixed with the thermoplastic refractory, and thrown. onto the banks of an open hearth furnace. as a fettling material. The diop side melts at 1395, thereby lowering the setting temperature by more than 200. degrees, and subsequently reacts. with and consolidates thethermoplastic refractory to bring about a substantial increase in its refractoriness. Both of these results are, important advantages. (Actually, the addition of the siliceous low-melting diopside breaks up the calcium ferrite and aluminateQa nd replaces them with more refractory dicaljci um silicate, magnesium ferrite and magnesium amminate (spinel), but the elimination of these fluxes is not a part of the invention.)

This procedure i in striking contrast with the practice, disclosed in the prior art, of adding, a

material high in lime to refractories which are, to

some degree thermoplastic due to-the presence in, them of orthosilicates of-low refractoriness (monticellite and merwinite). The new method greatly lowers the setting temperatures of the major refractory by providing a siliceous, lowmelting material between the grains to be bonded, instead of actually raising the setting temperature by introducing between the plastic grains a calcareous material of high refractoriness. The consolidating reaction between the liquid low melting constituent and the highly refractory particles readily takes place under normal burning conditions.

I claim:

1. A method of consolidating refractory materials, which comprises mixing discrete particles comprising essentially refractory oxide material from a group consisting of lime, magnesia, alumina and zirconia with non-refractory material comprising essentially a low-melting compound of said oxide and being one of a group consisting oi calcium silicate and calcium magnesium silicate when said oxide is lime and lime with magnesi-a present, magnesium silicate and magnesium aluminum silicate when said oxide is magnesia, barium zircon-ate when said oxide is zirconia, and aluminum silicate when said oxide is alumina, said non-refractory material becoming liquid at a temperature between 1321 and 1550 C., the mixture containing not less than 50% by weight of said discrete particles, and heating the mixture to not less than 1321 C. to melt said nonrefractory material, and thus consolidate said particles into a highly refractory mass.

2. A method of consolidating refractory materials which comprises forming an intimate mixture of two types of materials, the first type being granular particles consisting essentially of refractory oxide material from a group consisting of lime, magnesia, alumina and zirconia, and the second type comprising essentially a low-melting compound of the oxide material and being one 01' a group consisting of calcium silicate and calcium magnesium silicate when the oxide material is lime and lime with magnesia present with the molecular ratio of lime to silica in the mixture not less than 2.0, magnesium silicate when the oxide material is magnesia with the molecular ratio of magnesia to silica in the mixture not less than 2.0, magnesium aluminum silicate when the oxide material is magnesia with a molecular ratio of magnesia to silica in the mixture not less than 2.0 and additional magnesia to alumina not less than 1.0, aluminum silicate when the oxide material is alumina with the molecular ratio of alumina to silica in the mixture not less than 1.5, and barium ziroonate when the oxide material is zlrconia with the molecular ratio of zirconia to baryta in the mixture not less than 1.0, and heating the mixture to not less than 1321 C. to melt said non-refractory compound and thus consolidate said particles into a highly refractory mass,

3. A method as defined in claim 1 wherein the non-refractory compound is a preformed material.

4. a method as defined in claim 1 wherein the 65 method is carried out in a furnace lining.

5. A batch material for refractory masses and shapes, which comprises an intimate mixture of discrete particles comprising essentially refractory oxide material from a group consisting of 14 lime, magnesia, alumina and zirconia, and nonrefractory material comprising essentially a lowmelting compound of said oxide material and being one of a group consisting of (a) calcium silicate and calcium magnesium silicate when the oxide material is lime and lime with magnesia, (1)) magnesium silicate and magnesium aluminum silicate when the oxide material is magnesia, (0) aluminum silicate when the oxide material is alumina, (d) barium zirconate when the oxide material is zirconia, and said mixture containing not less than 50% by weight of said discrete particles, whereby when the mixture is heated to liquefy said non-refractory material the whole 0 mass consolidates into a product which does not melt below 1800 C.

6. A batch material for refractory masses and shapes, which comprises an intimate mixture of two types of materials, the first type being granular particles consisting essentially of refractory oxide material from a group consisting of lime, magnesia, alumina, and zirconia, and the second type consisting essentially of a low-melting compound of the refractory oxide and being one of a group consisting of (a) calcium silicate and calcium magnesium silicate when the oxide is lime and lime with magnesia present with the molecular ratio of lime to silica in the mixture not less than 2.0, (1)) magnesium silicate when the oxide is magnesia with the molecular ratio in the mixture not less than 2.0, (0) magnesium aluminum silicate when the oxide is magnesia with a molecular ratio of magnesia to silica in the mixture not less than 2.0 and additional magnesia to alumina not less than 1.0, ((1) aluminum silicate when the oxide is alumina with the molecular ratio of alumina to silica in the mixture not less than 1.5 and (e) barium zirconate when the oxide is zirconia and the molecular ratio of zirconia, to baryta in the mixture not less than 1.0, whereby when the mixture is heated to liquefy said non-refractory material the whole mass consolidates into a product which does not melt below 1800 C.

7. A method as defined in claim 2 wherein the mixture is heated to a temperature of not less than 1550 C. to melt the non-refractory material and thus consolidate the particles into a highly refractory mass.

FRANK EUGENE LATHE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,300,631 Meyer Apr. 15, 1919 2,015,446 Cape et al Sept. 24, 1935 so 2,089,970 Lee Aug. 17, 1937 2,207,557 Sell July 9, 1940 2,238,428 Seaton et a1 Apr. 15, 1941 FOREIGN PATENTS Number Country Date 396,532 Great Britain 1933 OTHER REFERENCES May 11, 1943.

Claims (1)

1. A METHOD OF CONSOLIDATING REFRACTORY MATERIALS, WHICH COMPRISES MIXING DISCRETE PARTICLES COMPRISING ESSENTIALLY REFRACTORY OXIDE MATERIAL FROM A GROUP CONSISTING OF LIME, MAGNESIA, ALUMINA AND ZIRCONIA WITH NON-REFRACTORY MATERIAL COMPRISING ESSENTIALLY A LOW-MELTING COMPOUND OF SAID OXIDE AND BEING ONE OF A GROUP CONSISTING OF CALCIUM SILICATE AND CALCIUM MAGNESIUM SILICATE WHEN SAID OXIDE IS LIME AND LIME WITH MAGNESIA PRESENT, MAGNESIUM SILICATE AND MAGNESIUM ALUMINUM SILICATE WHEN SAID OXIDE IS MAGNESIA, BARIUM ZIRCONATE WHEN SAID OXIDE IS ZIRCONIA, AND

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