US3113361A

US3113361A - Refractory structures

Info

Publication number: US3113361A
Application number: US765541A
Authority: US
Inventors: Ronald H Cooper; Gerald M Corbett
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1958-10-06
Filing date: 1958-10-06
Publication date: 1963-12-10
Anticipated expiration: 1980-12-10

Description

De 10, 1963 R. H. cooPER ETAL 3,113,361

REFRACTORY STRUCTURES Filed Oct. 6. 1958 INVENTORS, Rona/dh( Coo/0er Gero/05% CO/e/i @wing l lq TfOR/Vfy United States Patent O 3,113,361 REFRACTRY STRUCTURES Ronald H. Cooper, tilare, and Gerald Ml. Corbett, Mitiland, Mich., assignors to The Dow Chemical Company, Midland, Mich, a corporation ot Delaware Filed @et o, 19Std, Ser. No. 765,541; l? Claims. (El. 22-l93) The present invention pertains to improved compositions for the fabrication of refractory structures that are duid-permeable and capable of 4Witbstandirug heat at extreme temperature elevations Isuch as is encountered from contact with molten metals, including iron and steel alloys. vIn particular, they invention concerns improved compositions that are especially suitable tor the lbtbrica` tion of refractory rings or spacers -vvhich are employed with -hot top Imolds in the casting of iron and steel ingots to protect the iron casing of the -hot .top on the mold from the action of the hot molten metal being poured. lt also has reference to a method for the fabrication of such structures with .the compositions and to the structures thereby provided. The present application is a continua tion-impart of copendn g applications for United States Letters Patent having Serial Number 612,287 and 612,288, respectively, both -led September 26, 1956, now United States Letters Patents Number 2,869,191 and 2,8o9,l96, respectivel Refractory `rings for hot tops which are positioned between .tne hot top and the top of the ingot mold in Washer- ]ilte fashion and which oftentimes have an annular configuration are conventionally prepared from one oi `several various compositions. By =way of illustration, they are frequently fabricated Ifrom a silicate bonded mixture of sand plus oil bearing shale and a small quantity of ferrous sulfate. Such mixtures may contain from 17 to 19 percent or more or less by Weight of sodium silicate solution as a binder material. Or they may be fabricated from refractory materials comprised essentially of clays admixed with either metal-lc oxides, carbon or granular colte.

Certain difficulties and disadvantages are commonly encountered fwit-h the conventional refractory bot `top rings. Sometimes, for example, tney may tend to adhere tenaciously and in la most objectionable manner to the solidified metal in 4the ingot that is in contact with them. in addition, the conventional retnactory rings for hot tops are somewhat brittle and iiragile and for this reason, are susceptible to a substantial incidence of breakage during their shipment and handling. Furthermore, some oi the conventional hot top rings, such as the silicate Ibon ed vanieties, require the emrlcyment ot considerable quantities of a binder material to be formulated in the compositions that are utilized tor their fabrication.

lt would be advantageous, and it is among the principe objectives of the present invention, to provide composi tions for fabrication into refractory hot top rings that would be capable of being fabricated into such structures having ample permeability and uniform good porosity to allow ecient gas evolution brom the molten metal being poured into ingots, little tendency to adhere or peel oft on 4the ingot, good characteristics of being readily disintegrated after employment at nich temperatures, little likelihood of breakage due to inherent brittleness vfragility, and modest binder requirements for their suitable fabrication. It would also be advantageous and beneficial, and it is also among the objectives of the invenice 2 tion, to provide a method for the fabrication of such structures Arom such compositions and to also provide the structures comprised of such compositions.

According to the present invention, these desiderations and other advantages and benefits may be realized and the indicated obiectives may be achieved by a composition that 4consists essentially of a propender-ant proportion of relatively course sand; a binding proportion or an active powdered magnesium oxide catalyzed aqueous phenolic ld thermosetting resin; a small quantity of soda ash (sodium carbonate) or its equivalent; and benecially, 'another `quantity of a iinely divided blast furnace slag powder or particles. Advantageously, the composition may consist essentially of a preponderant proportion of relatively course sand; between about 3 and ll) percent by Weight, based on the weight of the composition, of an `'aqueous phenolic liquid thenmcseftting rcs-in binder that is catalyzed with from about l0 to 25 percent by weight, )based on the Weight of the resin `the composition, ci an active powdered magnesium oxide catalyst; between about il) :and 25 percent by Weight, based on the Weight of the resin in the composition, of anhydrous sodium carbonate; and between about llil and lil@ percent by Weight, based on ythe weight of the resin in the composition, of a finely divided blast furnace slag.

The compositions, freshly after being prepared, are plastic and ilcvfable coated sand mixtures that can be cold Worked to Iform desired structures While they are in a wet condition. f by Thus, they can be cold pressen as being rammed into mold forms, advantageously under pressures between about lb@ and i200 pounds per square inch, to form adesired structure of the agglomerated, integrated mixture. Or, if desired, `they can be deposited into desired forms with th assistance of a pneumatic blast otr spray operating under pressure, as, for example, in the neighborhood of Silpounds per .square inch, much in lthe manner of the core blowing techniques that are employed for sand compositions in certain types of foundry practice. During or after ythe wet formation of the structure, the agglomerated composition will self-set or auto-haarden to lan integrated, bonded magma structure, due primarily to the action ot the active magnesium oxide catalyst on the applied resin lthat coats the sand in the composition. The `self-setting or auto-hardening of the wet-formed composition ordinarily occurs within an hour at room temperature, after which the structure may be cured at tempo-natures between about 250 and 660 F. until it been completely ther-mcset to a strong rind form suitable for the intended employment. General-ly, the autohardencd structures may be satisfactorily cured by exposure to a .thermosetting temperature ci about 475- 500 E. rior a period of time of at least about 45 to 60 minutes.

The cured structure, when Iit is a refractory ring for hot tops, may then be employed to protect the casing of metal hot tops by preventing leakage of the molten metal from the mold. The extreme heat from the molten metal that is being poured will decompose and burn out the cured phenolic resin binder to leave a strong and uniformly porous refractory structure that provides an easy escape for the gases that are being evolved from the molten metal While restraining it, much in the manner of a sealing Washer, from leaking so as to damage the metal casing of the hot top being employed on the ingot mold. l-n this connection, care should be teilten when. curing tbe refractory structure prepared `according to the invention to utilize a suiciently high thermosetting temperature. The employment of too low a temperature for this purpose may not only cause a relatively weak structure to be encountered but may cause difficulties in the decomposition of the resin binder 4upon contact with heat from the molten metal or other source. improper-ly cured ring structures for hot tops may evolve considerable quantities of fire and smoke upon contact with the molten metal iand may severely carbonize the ingot being poured. In contrast, properly cured structures display greatly minimized tendencies for such behavior. An annular refractory ring for hot tops that has been prepared from a composition in accordance with the present invention is schematically illustrated in the accompanying drawing.

Any ordinary sand may be employed in the practice of the present invention, Advantageously, the sand that is employed has a fineness in accordance with the values proposed by the American Foundrymans Society (AFS) that is in the numerical range between about 25 and 125. Such sands, for example, as the varieties that are commonly employed las core sands including the types which are known Ias Berkeley Float Sand, Iuniata Sand, Lake Sand, Vassar Sand, Wedron Sand, Portage 40-60 Sand, Gratiot Bank Sand the like may be beneficially employed. lt is desirable that the sand be clean and substantially free from foreign metal oxides, clay, moisture and organic matter. YIn many cases, it may be more 4advantageous to employ a sand having `an AFS fineness nurnber from about 30 to 75.

As 4has been indicated, the resin binder that is employed in the compositions of the present invention is a self-setting or auto-hardening mixture of an aqueous phenolic liquid resin, such as a phenol-formaldehyde liquid resin, and `an active powdered magnesium oxide catalyst that is capable of dehydrating :and auto-hardening the liquid resin at room temperatures to a dry, thermoplastic-thermosetting mass. Such a resin binder for insert filler materials is described in the copending application of Ronald Cooper covering lImproved Phenolic Resin `Compositions having Serial No. 612,283 that was filed on September 26, 1956, now U.S. Patent No. 2,869,194. Thus, the phenolic liquid resin that is employed may be a phenolformaldehyde condensation product, of the type that is oftentimes characterized as being a stage A resin, that has been prepared by reacting aqueous mixtures of phenol and formaldehyde, in a known manner, under the influence of basic catalysis. Such liquid resins usually h-ave a greater than 1:1 mole ratio of formaldehyde to phenol, respectively, in their compositions. it is oftentimes desirable for a phenolformaldehyde liquid resin to be employed that has a mole natio of formaldehyde to phenol in the neighborhood tof 1.4511. The solids content of the liquid resin should be at least 50 to 60 percent by weight and it may have a viscosity from about 100 to 1000 or 2000 centipoises at 77 F., and a pH from about 5 to 9. The active powdered magnesium oxide catalyst that is incorporated in such a phenolic liquid resin to achieve its auto-hardening properties may be a finely divided powder that has initial setting characteristics, measured as a function of time according to the procedure set forth in A.S.T.M. Specification No. C254-50Vl`, that is between about 0.1 and `6 hours. Generally, it is beneficial to utilize a magnesium oxide powder that has an average particle size not larger than about 40 mesh in the U.S. Standard Sieve Series and an initial setting time between about 0.5 and 3 hours, preferably (for most pronounced results) less than 1 hour.

The time that is required for a magnesium oxide catalyzed phenolic liquid resin to self-set or auto-harden due to the involved catalytic effect depends to a great extent upon the activity or initial setting time characteristics of the magnesium oxide powder and the proportion in which it is included with the phenolic liquid resin in the binder. This, of course, lim-its the time in which a cornposition prepared with such a liquid resin binder is plastic and fiowable so that it may be cold formed to a desired refractory structure (such as an annular ring for hot tops) as a wet, coated sand composition after its initial prepara-tion. Generally, more active magnesium oxide powders (materials having shorter initial setting times) and greater proportions of included catalyst resul-t in wet mixtures that auto-harden in shonter periods of time after their initial preparation. Compositions that are in accord-ance with those of the present invention may ordinarily be found to be auto-hardenable within about an hour of their initial preparation, especially when they are catalyzed by a powdered magnesium oxide that has an initial setting time of about 0.5 hour, or less.

The particulated blast furnace slag that may adv-antageously be employed in the compositions of the invention may be a typical slag, in finely divided form, of the type well known in the art that has been obtained from a blast furnace making basic iron. Such a slag is often found to contain about 48 percent by weight of a mixture of silica (SiO2) and alumina (A1203) in which the proportion of altunina may vary from 10 to l5 percent by weight of the entire slag yand about 48 percent by weight of a mixture of lime (CaO) and magnesia (MgO) in which the proportion of magnesia seldom if ever, exceeds, 10 percent by weigh-t of the entire slag, with the balance usually being comprised of minor proportions of calcium sulfide and ferrous and manganese oxides. Representative analyses of suitable blast furnace slags for employment in the practice of the invention are as follows:

Percent by weight Component Slag Xn Slag YH Silica (SiO2) 35. 02 34. 50 Alumina (AlzOs) 14. 99 13. 40 Limo (CaO) 114. 03 40. 70 Magnesia (ivIgO) 2. 72 5. 58 Ferrous Oxide (FeO) 1. 16 0. 65 Manganese Oxide (M110 1.08 0. 30 Sulfur (S) 1.35 1.09

Advantageously, the nely divided blast furnace slag that is utilized has an average particle size not larger than about mesh in the US. Standard Sieve Series. More coarse slag, as large as 20-40 mesh in average particle size, may also be employed. Of course, there is no minimum particle size limit on the slag, which may be used in as impalpable and finely divided a form as it may be obtained.

If desired, it is sometimes beneficial to add to the mixtures small quantities, in amounts between about l0 and 25 weight percent, based on resin weight, of such other materials as fusible silica glass powder. Such a beneficial supplemental additarnent tends to assist in binding the ring when it is under the influence of heat from the molten metal after the resinous binder has been decomposed. Conventional silica glass powders from borosilicate types of glass, such as those comprised of about 96 percent by weight of silica glass, 2.5 percent by weight of boron trioxide and the balance inert materials may' be employed in the practice of the invention. Beneficially, the silica glass powder that is used has a softening point of about 1290 F. and is a finely divided material, such as one that has an average particle size of finer, to any ultimate degree of fineness, than about 100 mesh in the US. Standard Sieve Series. The best results may often be obtained when the amount of the silica glass powder that is employed does not exceed the quantity of the organic resinous binder that is utilized in the composition.

In the formulation of the compositions of the invention, it is essential to achieve a uniform and thorough dispersion and interblending of all the ingredients. lt isV particularly advantageous to prepare the composition by intimately pre-mixing the powdered magnesium oxide cata-d lyst with the sand before homogeneously incorporating the liquid resin therein with suicient mixing to thoroughly coat the sand granules after which the soda ash and blast furnace slag particles or powder, if the latter is to be employed, can be intermixed homogeneously in the wet composition as may any other ingredients, such as fusible silica glass powder, that may be desired. The formulation can be readily achieved using many available varieties of efficient mixing and mulling apparatus.

The invention is further illustrated in and by the following examples wherein, unless otherwise indicated, all parts and percentages are to be taken by weight.

Example I A composition prepared according to the present in- The phenolic liquid resin had a formaldehyde to phenol mole ratio of about 1.45 :1, a solids content of about 50-60 percent, a pH of about 8 and a viscosity at 77 F. of about 300 centipoises. The constitution of the slag was about the same as that of the analysis given for slag Y in the foregoing specification. The composition was prepared by intimately premixing about 53.52 parts of the sand with about 0.48 part of the magnesium oxide powder. T o the dry mixture there was gradually added, with eicient continuous mixing, about 4.8 parts of the liquid resin to thoroughly coat the sand. About 0.24 part of the dry soda ash and 0.96 part of the blast furnace slag powder were then homogeneously dispersed in the wet mixture.

The wet mixture was then cold formed in a mold under a ram pressure of about 100 pounds per square inch into square ring structures for hot tops having about a 23/8 inch inside height, about a 1%. inch outside height, about a l inch peripheral lip portion, and inner and outer dimensions, respectively, of about and 271/2 inches with about 3 inch radii at the outer corners and about 11A inch radii at the inner corners. After being molded, and while remaining in the mold form, the cold formed ring structures were permitted to autoharden at room temperature to an agglomerated, composite, integral mass. This was accomplished in about an hour after which the rings were cured for about 60 minutes in a gas iired oven at a temperature of about 482 F. The thermoset rings could then be easily removed from the mold form by simple inversion thereof. They had an average density of about 110 pounds per cubic foot, an average tensile strength of at least about 650 pounds per square inch and an average compression strength of about 3,000 pounds per square inch. The finished rings performed excellently during tests in the pouring of ingots in het top molds. They did not permit the molten metal to leali nor did they fail in service or permit any damage to the metal casing of the hot top. They did not fire and smoke excessively from decomposition of the resin binder and had satisfactory porosity during the pour. In addition, they did not adhere to the ingots nor were they difficult to remove therefrom but disintegrated readily withing 1/2 hour of burn out.

Example II The procedure of Example I was essentially repeated to fabricate hot top rings with several other mixtures according to the present invention. in the following tabulation there is set forth the compositions of each of the mixtures and the average tensile strengths of the cured hot top rings prepared from them. The phenolic liquid resin that was employed for mixture B was the same as that used in the first example. The liquid resin employed in the remaining mixtures was a similar phenol-formaldehyde condensation product excepting that it had a solids content between 50 and 60 percent. The same type of slag as in the rst example was utilized throughout. In mixture R about 1.6 percent of a fusible silica glass powder from a borosilicate glass softening at about 1290 F. was uniformly incorporated in the composition.

Excellent results were obtained in the utilization during ingot pouring with hot top molds of all lof the annular hot top rings fabricated from; each of the above mixtures.

As -is apparent, structures other than hot top rings intended for other uses, including -uses rat normal temperatures, may also be fabricated with advantage from the compositions of the invention.

Certain changes and modifications in the practice of the present invention can be entered into readily without departing substantially from its intended spirit and scope. Therefore, it is to be fully understood that the invention is not to be limited or otherwise restricted to or by the foregoing deictic description and specification.

tatheir, it is to be interpreted and construed in the light of what is set forth and defined lin the hereto appended claims.

What is claimed is:

1. Composition for the fabrication of porous refractory structures which consists essentially of a preponderant proportion of relatively coarse sand; between about 3 and l0 percent by weight, based on the weight of the composition, of an aqueous phenolic resin liquid binder that is catalyzed with from 10 to 25 percent by w-eight, based on the weight of the resin in the composition, `of an active powdered magnesium oxide catalyst having an initial setting time of .less than about six hours, said resin being a phenol-forma1dehyde condensation pro-duct that has a greater than 1:1 mole ratio of formaldehyde to phenol, respectively, a solids content of at least about 50 percent by weight, a pH between about 5 and 9, and a viscosity at 77 F. of between about 100 and 2000 centipoises; between about 10 and 25 percent by weight, based on the weight o-f the resin in the composition, of anhydrous sodium carbonate; and between about 10 and 100 percent by weight, based on the weight of the resin in the composition, of nely divided blast furnace slag particles.

2. The composition of claim l in the form of a wet, plastic and ilowable mixture.

3. The composition `of claim 1, wherein the sand has an AJFS neness number between about 25 and 125.

4. The composition of claim l, wherein the sand has an AFS iineness number between about 30 and 75.

5. The composition of claim l, wherein the aqueous phenolic liquid thermosetting resin is a phenol-formaldehyde condensation product that has about a 1.45:1 mole ratio of formaldehyde to phenol, respectively, a solids content yo-f at least about 50 percent by Weight, a pH between atbou-t 5 and 9 and a viscosity at 77 F. between about and 1,000 centipoises.

6. The composition of claim l, wherein the magnesium oxide catalyst is a finely divided powder that has an initial setting time of less than about 1 hour.

7. The composition of :claim l, wherein the magnesium oxide catalyst is a nely divided powder that has an initial setting time of about 0.5 hour and an average particle size not larger than about 40 mesh in the US. Standard Sieve Series.

8. The composition of claim 1, wherein the divided. blast furnace slag powder has an average particle size not larger than about 100 mesh in the U.S. Standard Sieve Series.

9. The composition of claim 1 and including in addition to the mentioned ingredients, a small quantity of between about l() and 25 percent by weight, based on the weight of the resin in the composition, of a fusible silica glass powder uniformly dispersed therein.

10. Method for the preparation of a composition that is particularly adapted toprovide porous refractory structures which comprises uniformly dispersing ya binding proportion of between about 3 and 10 percent by weight, based on the weight of the resulting mixture, of an aqueous phenolic l-iquid thermosetting resin with a mixture of a preponderant proportion of sand and a catalytic quantity of between about 10 and 25 percent by weight, based on the weight of the resin in the mixture, `of an active powdered magnesium oxide for auto-hardening the phenolic liquid resin and subsequently interblending in the resulting Wet mixture a small quantity of between about 10 and 25 percent by weight, based on the weight of the resin in the mixture, .of soda ash 'and another quantity of between about 10 and 100 percent by weight, based on the weight of fthe resin in the mixture, of a particulated Iblast furnace slag, said magnesium loxide catalyst having an Vinitim setting time olf less than about six hours, said resin being a phenol-formaldehyde condensation product that has a greater than 1:1 mole raltio of formaldehyde to phenol, respectively, a solids content of at least 50 percent by weight, a pH between about 5 and 9 and a viscosity at 77 F. between about 100 and 2000 centipoises.

l1. Method for fabricating porous refractory structures which comprises preparing a wet, auto-hardenable mixture of a preponderant proportion of sand with a binding proportion of an active powdered magnesium oxide catalyzed aqueous phenolic liquid thermosetting resin, said magnesium oxide catalyst having an Iinitial setting time of less than about six hours, said resin being a phenol-formaldehyde condensation product that has a greater than 1:1 mole ratio of formaldehyde to phenol, respectively, a solids content of at least 50 percent by weight, a pH between about 5 and 9 and a viscosity at 77 F. between about 100 and 2000 centipoises, said resin being present in said mixture in `an amount between about 3 and 10 percent by weight, based on the weight of 4the mixture, and being catalyzed with between about and 25 percent by weight, based on the weight of the resin in the mixture, of said magnesium oxide; :said mixture containing a small quantity of between `about 10 and 25 percent by weight, based on the weight of the resin in the mixture, of soda ash and another quantity of between about 10 and 100 percent by weight, based on the weight of the resin in the mixture, of finely divided blast furnace slag particles; forming said wet mixture into a desired structure while it is in a plastic and ilo-Wable condition and before it has auto-hardened; permitting said formed mixture to auto-harden to an agglomerated, integral structure; and subsequently curing the integral, formed mixture at a thermosetting temperature between about 250 F. and 600 F. into a rigid structure.

12. The method of claim 11, wherein said mixture is cold formed as a wet, plastic and owable mass under a pressure Ibetween about and 1200 pounds per square inch. v

13. The method of claimll,l wherein the formed, auto-hardened -mixture is cured at a temperature of about i-75500 F. for a period of time of at least about 45 minutes.

14. The method of claim 10, and including in addition to the mentioned steps, adding rto said resulting wet mixture, along with the soda ash and blast furnace slag, between about 10 and 25 percent by weight, based on the weight of `the resin in the mixture, of a fusible silica glass powder having an average particle size not larger than about 100 mesh in the U.S. Standard Sieve Series.

15. The method of claim 11, and including in addition to the mentioned steps, preparing said wet mixture to contain along with said other ingredients 4between about 10 and 25 percent by weight, based on the weight of the resin in the mixture, of a fusible silica glass powder having an average particle size not larger than about 100 mesh inthe U. S. Standard Sieve Series.

16. A cured, rigid formed structure prepared lfrom a composition that is in accordance with the composition set forth in claim 1.

17. A refractory ring for hot tops prepared from a composition that is in accordance with the composition set forth in claim 1.

References Cited in the le of this patent UNITED STATES PATENTS 2,133,245 Brice et al. Oct. 1l, 1938 2,861,307 Froberger Nov. 25, 1958 2,869,191 Cooper et al. Ian. 20, 1959 2,869,196 Cooper et al Jan. 20, 1959 2,870,110 Cooper et al. Jan. 20, 1959

Claims

11. METHOD FOR FABRICATING POROUS REFRACTORY STRUTURES WHICH COMPRISES PREPARING A WET, AUTO-HARDENABLE MIXTURE OF A PREPONDERANT PROPORTION OF SAND WITH A BINDING PROPORTION OF AN ACTIVE POWDERED MAGNESIUM OXIDE CATALYZED AQUEOUS PHENOLIC LIQUID THERMOSETTING RESIN, SAID MAGNESIUM OXIDE CATALYST HAVING AN INITIAL SETTING TIME OF LESS THAN ABOUT SIX HOURS, SAID RESIN BEING A PHENOL-FORMALDEHYDE CONDENSATION PRODUCT THAT HAS A GREATER THAN 1:1 MOLE RATIO OF FORMALDEHYDE TO PHENOL, RESPECTIVELY, A SOLIDS CONTENT OF AT LEAST 50 PERCENT BY WEIGHT, A PH BETWEEN ABOUT 5 AND 9 AND A VISCOSITY AT 77*F. BETWEEN ABOUT 100 AND 2000 CENTIPOISES, SAID RESIN BEING PRESENT IN SAID MIXTURE IN AN AMOUNT BETWEEN ABOUT 3 AND 10 PERCENT BY WEIGHT, BASED ON THE WEIGHT OF THE