CORRECTION OF AN EXTREME CASE OF CRACKING IN THE DRYING OF BRICK1

I. In the manufacture of stiff-mud brick from a highly colloidal clay of low permeability to water, drying breakage was extremely high even though the drying was conducted at a very slow rate under high humidity conditions. Laboratory investigation yielded two methods of correcting the faults: (1) Preheating the clay for half an hour at a temperature between 400 °C and 500 °C increased the permeability to such an extent that brick made from the preheated clay could be dried rapidly without cracking. (2) Coagulating chemicals, such as aluminium chloride, ferric chloride, sodium chloride, and hydrochloric acid, in conjunction with moderate additions of grog, increased the permeability and thus improved the drying properties of the clay. II. Plant scale tests using ferric chloride, sodium chloride, and grog resulted in the production of brick which could be dried safely in a reasonable time. The fired brick were improved in quality as to strength and color. III. The chemical treatment of the clay using 1% ferric chloride and 0.5% sodium chloride with 10 to 15% grog was adopted for plant operation and resulted in increased production, lower cost of manufacture, and improved quality of product.     

INVESTIGATION OF THE EFFECT OF LOW-FIRED GROGS ON PROPERTIES OF SOFT-MUD BRICK*

Soft-mud brick were made from various mixtures of Hudson River clay and grog prepared by calcining the clay at 500°, 700°, and 900°C., and rate of drying tests were carried out. The brick were fired to cones 012, 08, and 04, and a special fast fire to cone 08 was also run. The various properties were compared with those of regular mix brick and all-clay brick. Brick made of a mixture of clay with 35% of 900°C. grog had particularly satisfactory properties such as to afford definite advantages as regards faster drying and accelerated firing.     

THE COMMERCIAL DEVELOPMENT OF A KAOLINIC FIRE BRICK1

The development of a kaolinic brick from Georgia clay is described. The high and continued shrinkage of this clay makes it necessary to fire the brick a t a very high temperature. A temperature of over 3000°F was required. The development of a kiln for the firing of the grog and brick was a problem that was satisfactorily solved. A light weight brick for use in marine boilers and a dense refractory for use in glass tanks were developed. The following physical properties of these two refractories are given and compared with other high grade bricks: (1) start of deformation under 25 Ibs. per sq. in. load, (2) 10% deformation under 25 Ibs. per sq. in. load, (3) start of permanent volume change without load, (4) mean coefficient of expansion, (5) cycles in 2900°F air-spalling test, (6) melting point, (7) thermal conductivity a t 1000, 2000 and 2750°F. Various successful applications of this type of brick are described.     

SUBSTITUTION OF TOPAZ,DOMESTIC KYANITE,AND SYNTHETIC MULLITE-CORUNDUM FOR INDIA KYANITE,I–III*

This report on the utilization of domestic materials as replacements for India kyanite has been divided into four parts, namely, (I) kyanite and other high-grade refractories, (II) effect of heat on kyanite and topaz, and (III) load resistance of refractories at elevated temperatures; (IV) will be published later.     

USE OF ALUMINUM METAL IN THE CERAMIC INDUSTRY I,PROPERTIES OF REFRACTORIES PRODUCED WITH MIXTURES OF ALUMINUM,FIRE CLAY,AND GROG*

The addition of aluminum metal powder to fire-clay-grog mixtures greatly increased the strength of the fired brick as a result of an aluminothermic reaction between the metal and the silica in the clay and grog. Because the reaction takes place at 930°C. and causes the temperature to rise rapidly, it is necessary to heat these refractories only to 930°C. to produce hard, well-fired brick. Such products have a high load-carrying capacity at furnace temperatures and also a fair spalling resistance.     

COMPARATIVE SERVICE TESTS OF GROSS ALMERODE AND DOMESTIC CLAY POTS1

Glass-drawing pots made from Gross Almerode clay proved to be superior in a service test to pots made from a synthetic siliceous domestic clay mixture. When removed from service the faces of the Gross Almerode pots are pitted. The faces of domestic clay pots are surface cracked. The blistering of the glass caused by this cracking is eliminated by substituting silica brick grog for fire clay grog.     

THE USE OF PLASTIC CLAY GROG IN PREVENTING SPALLING1

Effect of calcined clay grog on the properties of fire-brick .—A medium dense-burning clay was calcined at cone 8, then ground and mixed with plastic clay in various proportions up to 40 per cent. An air spalling test of the burned bricks showed that the grog increased the resistance to spalling about 5 per cent for each per cent of grog added. The results for other physical properties agreed with those found by previous observers; the bricks with grog were more porous and weaker mechanically but showed less drying and burning shrinkage.     

Use of fireclay dust from rotary furnaces

Conclusions Dust removed by electric filters from the gases of rotary furnaces can be used for the preparation of firebrick articles. The composition of the bodies recommended is as follows; for standard brick 45% grog, 35% dust and 20% kaolin; for lightweight insulating brick 30% dust, 35% thermal-anthracite, 17.5% kaolin, and 17.5% Chasov-Yar clay.With combined firing into grog of kaolin and dust in the briquette it is possible to add not more than 20% dust; with an increase in the content the water absorption of the grog increases.When designing refractory factories in the complex of which we introduce rotary furnaces with electric filters, it is necessary to specify equipment for transporting dust into the body-preparation section with the aim of using it.The use of dust from rotary furnaces for the production of refractories will be a useful innovation for refractory workers in completing the directives of the 23rd congress of the party aimed at improving use of raw materials.The work was shared by L. S. Shchetina and S. D. Svidlo.     

New method of preparing batch for firebricks

Conclusions At the Konstantinov Red October factory they have developed and tested in production a new method for preparing batch for standard and cupola brick which will exclude various processes of grinding, screening and mixing clay and grog; the batch is obtained by combined grinding in centrifugal mills of lumps of grog and clay crushed to 120 mm whose moisture content can be as high as 20%.The standard and cupola brick obtained in production conditions from combined ground batch in external appearance and physicomechanical factors corresponds to the requirements of GOST and are as good as articles prepared by the usual factory method.By selecting the moisture content of the components and the working cycle for the centrifugal mill the combined grinding technique can be used to obtain batch for high-grog articles for which it is necessary to carry out extra tests.     

Firing arkalyksk clays into grog and obtaining products from it

Conclusions We obtained heat-technical and technological factors for the firing of Arkalyksk clays in rotary furnaces.On the basis of grog made from these clays we obtained class-A articles.Ladle brick made on the basis of grog from Arkalyksk clay shows a resistance of 1–3 heats greater than ordinary ladle brick.Translated from Ogneupory, No. 7, pp. 33–40, July, 1966.     

SUBSTITUTION OF TOPAZ,DOMESTIC KYANITE,AND SYNTHETIC MULLITE-CORUNDUM FOR INDIA KYANITE: IV,RAW TOPAZ AS HIGH-TEMPERATURE BOND FOR DOMESTIC KYANITE*

Raw topaz has been found to act as a high-temperature bond for both raw and calcined kyanite. It is thought that this bonding action is due in part to volatiles which emerge from the raw topaz between 1000° and 1200°C. Some of the topaz decomposition products are absorbed and retained by the calcined kyanite. Within the limits of this investigation, all refractories which contained either calcined or raw kyanite, or mixtures of the two, with a minimum of 10% raw topaz had a good structure and were well bonded. The results of the load tests indicated that increased firing temperatures in the preheat improved the load resistance, but excellent high-temperature resistance was obtained by preheating as low as 1300°C. in laboratory kilns.     

A STUDY OF THE EFFECT OF GROG ON PRESSURE TRANSMISSION IN DRY PRESSING1

A study of the dry-pressing characteristics of several fire brick and building brick clays was made by compressing them, at high and low pressures, into large shapes with a hydraulic press The clays do not effectively transmit the pressure into the interior. The finest grained clays are morc deficient in this respect. The result is a porosity gradient as high as 15% of the interior porosity between center and surface. Such a variation may account, in part, for the defects in dry-press ware. The addition of fired grog increases the pressure transmission. Some clays require more than 50% grog and some less for maximum pressure transmission and optimum results. Fireclay shapes as much as ten inches in thickness and of substantially uniform physical properties can be formed if the proper amount of grog is used.     

OBSERVATION ON THE EFFECT OF SILICON CARBIDE IN CLAY BODIES1

In these studies the distinction is made between silicon carbide in a clay body and clay-bonded silicon carbide. An increase of strength by replacement of grog particles was noted. Tests were made on various bodies containing as little as 10% Sic by weight and up to 67% by weight. Comparison of clay and grog bodies, clay grog, and SiC bodies, and clay and SiC bodies were carried out under the load-span test at various temperatures. The resistance of bodies containing SiC to the corrosion effect of various slags, particularly iron oxides with alkalis and alkaline earths, is given. A comparison is made with clay-grog bodies. The increase of conductivity of bodies containing SiC is apparent. Commercial application of SiC and clay bodies is discussed.     

Increasing the life of ladle brick

Conclusions A technology was developed for the manufacture of ladle brick of high resistance. The difference between the proposed method and that used at present is in the increase in alumina content of the bond part of the batch. The nonplastic may be ordinary grog made of first or second-grade clays normally used in the manufacture of ladle bricks. The optimum Al₂O₃ content in the bond part of the batch is 55–60%.A compulsory condition for increasing the service life of the ladle brick, in addition to a high content of alumina, is the density of the bonding part of the batch. Therefore, the firing temperature of the goods should be determined not by the porosity of the finished product in general, but by the porosity of the bond part of the batch.The chief norms for the manufacturing technology are as follows: a) a batch content of 50–55% ordinary grog made of first and second-grade clays, water absorption not more than 5%; b) a batch content of 50–45% mixture of combined grist of high-alumina grog and clay; the ratio of grog to clay in the mix should be from 6535 to 7030.The conclusions of the present article have been proved by manufacturing an industrial batch of goods and testing them in linings of ladles [14]. The technology has been included in a project for reconstructing the Bogdanovich refractories plant.     

MISSOURI HARD FLINT CLAY FIRE BRICK1

The hard flint clay obtained in the diaspore pits of Missouri, which has exceedingly low bonding properties and high shrinkage, but a P.C.E. value of cone 34, with the use of as low a percentage of flint clay grog as 20%, can be bonded into a strong brick, free of physical defects and of super-refractory quality. Excessively high forming pressure is not required. A small addition of bentonite adds materially in bonding the clay. The results of spall, hot load, cold compression, porosity, shrinkage, and reheat tests are presented.     

RATE OF DECOMPOSITION OF KYANITE AT VARIOUS TEMPERATURES*

The rate at which North Carolina kyanite of various grain sizes decomposes into mullite and glass in the range 1350° to 1600 °C. is given. Kyanite from other sources is also discussed.     

SOME EXPERIMENTS WITH ZIRCON AND ZIRCONIA REFRACTORIES*

This is a record of the results of five years' research on refractory uses for a chemically purified grade of zircon and electrically fmed zirconia of high purity. The products investigated included semi-permanent foundry molds, refractory brick and cements, ladle nozzles, and crucibles. Electric firing and a small oil-fired tunnel kiln are described. Sintered zircon grog was found superior to electrically fused grog. Zircon brick made with 50% grog, using 20% milled zircon for the permanent bond and fired at 1600°C for an hour, showed no firing shrinkage, very slight volume change, and high compressive strength at 1600°C. They were extremely resistant to spalling but did not resist basic slags or metallic oxides very well a t high temperature. Zircon-bonded magnesite brick were more refractory than ordinary magnesite, more resistant to spalling, and had about the same slag resistance magnesite. Zirconia was more refractory than zircon and had better slag resistance. Lime-bonded zirconia crucibles of good spalling resistance were made, but the cost was higher than that of zircon. The effects of various binders are discussed.     

THE PROPERTIES OF REFRACTORIES IN THE METALLURGY OF ZINC1

A study has been made of some of the properties of clays, grogs, and body mixtures used by various zinc smelters for the manufacture of zinc retorts. Only minor differences were observed in the properties of the clays. No attempt has been made to offer any of the results as conclusions. The investigation tends to confirm the following points; that the use of reclaimed retort material in the grog for new retorts is of doubtful economy; that, if old bricks or shapes are used as grog, care should be taken that they were originally made of good quality clay and that they are free from slag; that some flint clay of good quality and properly calcined is advisable for at least a part of the grog; and that zinc in a clay or body mixture markedly affects the refractoriness by lowering the deformation value.     

SOME EXPERIMENTS ON THE FIRECRACKING OF TERRA COTTA1

Firecracking .—occurs on terra cotta under certain conditions and is characterized by the appearance of sharp, hair-line cracks extending into the body. The experiments were made by firing large typical pieces of terra cotta made from various clays and grogs and cooling them at different rates. The tendency to firecrack was observed after weathering. The absorption, porosity and transverse strength of the various bodies were determined. Rate of Cooling .—All bodies similar to those used in practice showed a tendency to firecrack when cooled rapidly and all were free from cracks when cooled slowly. The rate of cooling has a much greater effect on the tendency to firecrack than the composition or physical properties of the body. Effect of Clay .—Three of the four sandy clays showed a decided tendency to firecrack, due to the difference in the expansion and contraction behavior of sand and clay in heating and cooling. The sandy clays showed more tendency to firecrack than the non-sandy, vitrifying clays. The tendency of a clay to develop firecracks in a body depends to a very large extent upon the character of the clay itself, regardless of the impurities it contains. The presence of sandy material and the character of the clay appear to have a much greater effect on the tendency to firecrack than the absorption, porosity or transverse strength of the body. No relation was found to exist in these experiments between the porosity and transverse strength of a body and its tendency to firecrack. Effect of Grog .—The greatest tendency to firecrack was found on a body with all grog finer than 40-mesh, but a body with all grog coarser than 40-mesh did not appear to have much less tendency to firecrack than the average. Increase of grog reduced the tendency to firecrack. The kind or source of the grog used does not have as much effect on the tendency to frecrack as the size and amount. The kind of grog is of much less importance in this respect than the kind of clay.     

OBSERVATIONS ON THE PROPERTIES OF CLAYS AND CLAY-GROG BODIES

Determinations of shrinkage, absorption, and transverse strength were made on a series of clays and clay-grog bodies fired together. Highly porous grog bodies are obtained with tight burning clays when the latter possess high shrinkage. This is due to the formation of crevices between the clay and grog particles, and to produce a tight grog body the clay must be of low shrinkage and low porosity.