Periclase-forsterite refractories from silica magnesite

Conclusions Periclase-forsterite refractories from silica magnesite of Beloretsk deposits are endowed with excellent properties.The density of periclase-forsterite brick is subject to a wide range of changes depending on the grain distribution of the mixture, molding pressure, sintering temperatures and the introduction of additives. The effect of additives on the sintering of periclase-forsterite mixtures from silica magnesite has the same pattern as in the sintering of pure magnesium or regular magnesite. The most effective sintering additives are titanium and zirconium dioxides. Additions of ZrO₂ produces a higher refractoriness-under-load of periclase-forsterite brick.Periclase-forsterite brick is highly-resistant in regenerator checkers of open-hearth furnaces. This is caused by peculiar changes in its mineralogical structure which occur during service, i.e. recrystallization of periclase in top layers which brings about higher density instead of looseness as in forsterite refractories bonded with unite.The forming and the properties of periclase-forsterite refractories as they depend on such factors as basic raw material, manufacturing methods and phase composition need further studies and large-scale testing in order to determine the rational areas of application.     

The influence of technological factors on the densification of forsterite green ware

Conclusions The grading of bodies made of dunite containing 20% additions of metallurgical magnesite ensuring a reduction in green porosity lies in the range 50–80% fraction 3–0.5 mm, 0–30% 0.5–0.088 mm and 20–50% finer than 0.088 mm.With an increase in fabricating pressure the relationship between the porosity of the green ware and grading diminishes.With a reduction in the grain sizes of the top and lower fractions the green porosity increases. An increase in moisture content from 4 to 6% in most cases increases the green porosity.An addition of 2–4% sulfite lye reduces the porosity (without a correction for pore filling by lye).The porosity of the green brick is greatly increased during firing. With the presence in the body of finely ground metallurgical magnesite the region of minimum porosity of fired specimens compared with the corresponding region for green brick moves to the side with the large content of fines.Dunite bodies with 20% fine magnesite giving the minimum porosity and shrinkage in firing should be used with the following grading: 10–40% fraction 3-0.5 mm, 10–40% 0.5–0.088 mm, and 50–70% finer than 0.088mm.An increase in the fines in the body leads to high shrinkage and deformation of the specimens in firing.     

Magnesite refractory with resin binder for the lining of oxygen-blown converters

Conclusions Unfired and fired magnesite refractories on a resin binder base are endowed with rather high density and mechanical strength and exhibit high refractoriness-under-load, increased resistance to elevated temperatures, satisfactory volumetric and thermal stability and conductivity and are air-stored over long periods of time without adverse effects.Regular crushed magnesite brick, fired Satka magnesite lumps and coarse-grained metallurgical powders are suitable for the production of carbon magnesite brick.Preliminary tests of carbon magnesite specimens corroborated the expedience of further production and testing in converter linings. In order to prevent the burning out of the binder, the production of this type of brick requires special heating conditions and lining preparation before the campaign.It is, therefore, recommended that carbon magnesite refractories be investigated in converter linings that are fully made of the above specimens.     

Spinel-bonded magnesite brick for high-tonnage electric arc furnaces

Conclusions The manufacture of an experimental batch of spalling resistant magnesite-chrome brick with a spinel binder has made it possible to improve the technological norms for the production of these parts and has shown the possibility of making them at the new shop at the Magnezit Plant.The parts produced show good characteristics: refractoriness-under-load of 2 kg/cm² — 1650–1720°; additional shrinkage during heating to 1650° with subsequent holding for three hours –0.1%; spalling resistance 7–13 water-heating-cooling cycles (heating to 1300°); apparent porosity 15–17%; compressive strength 620 kg/cm².To obtain parts with good physical-chemical properties it is essential to use MK magnesite powder; to add at least 6–8% industrial alumina to the charge (in terms of Al₂O₃); to make certain the magnesite-alumina mixture is highly dispersed so that it helps to complete the spinel formation reaction during the firing; to use a mixture of the following grain composition: not less than 20% fraction 3–1 mm; 55–60% finer than 0.5 mm, including 30–35% finer than 0.06 mm; to press the parts at 1200–1500 kg/cm²; to fire the parts at a temperature not less than 1600°, batching them far apart so as to avoid the formation of an uneven structure.The use of magnesite brick with a spinel binder for the walls of high-tonnage electric arc furnaces used to melt transformer steel ensures satisfactory strength of the walls in the slag belt and prevents the steel becoming contaminated with chromium.     

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.     

Magnesite from Safonikha deposit

Conclusions Provided the Safonikha magnesite is blended, it can be used to make high-quality magnesite brick with a forsterite bond with apparent porosity 12–16%, bulk density 2.94–3.04 g/cm, compressive strength 1500 kg/cm and refractoriness-under-load of 2 kg/cm, 1670–1720°.The magnesite represented by the laboratory samples Nos. 1, 6, 8, 11, 13 and 14, and the second technological sample come up to the requirements for raw material for magnesite metallurgical powders. The magnesite in the remaining samples can also be used for making metallurgical powders, provided it is first enriched.     

PROPERTIES OF SANDSTONES AS A REFRACTORY MATERIAL*

Sandstories from Chungking were tested for their properties as a refractory material. Chemical, petrographical, rational, and sieve analyses were made; properties, such as porosity, refractoriness, specific gravity, thermal expansion, and resistance to spalling. were determined; and studies were made on changes in firing up to 1550°C. No inversion of the quartz grains in the rock into tridymite or cristohalite could be detected. The interstitial clay substances fused first, and the quartz grains then dissolved gradually into the glassy matrix on firing at high temperatures. Being free from mineralogical and structural changes, unusually low in thermal expansion and porosity, and good in spalling resistance after firing at high temperatures, sandstones are shown to be an excellent refractory if properly employed. Of the two kinds of rocks, the dense and the porous, the former was found much better in test for refractoriness under load. Prefiring of the material before lining in a furnace structure is desirable to eliminate the permanent expansion and to improve the resistance to spalling in the raw state.     

Melting refractory materials in the OKB-514 electric furnace and making parts for them

Conclusions The optimum conditions for melting magnesite into blocks using the OKB-514 electric furnace can be considered a voltage of 97 volts on the low side and a mean hourly charge of 50 kilograms. Of the methods of feeding powders to the furnace that were tried out, the continuous method is the most efficient.Parts with high properties can be machined from blocks of fused basic refractories.Parts made by the ceramic method from fused materials, including from a mixture of fused and sintered powders, are marked by high density (porosity 13–19%), refractoriness-under-load of 2 kg/cm higher than 1800°, and spalling-resistance of 5–15 heating-cooling cycles when cooled in water from 1300°.Using the OKB-514 furnace, with reduced periodic feeding, it is possible to produce fused magnesite containing up to 98% MgO when the initial raw material contains 90% MgO. The part of the block (10–15%) with the high MgO content can be separated during the finishing operation.     

Spinel-bonded magnesite brick with increased refractoriness-under-load

Conclusions We devised a technological system for manufacturing magnesite brick with increased density, refractoriness-under-load and thermal stability.The testing of this brick in the lining of the upper structure of an all-basic open-hearth furnace deserves attention.The use of magnesite brick manufactured by the devised technological system for the lining of basic steel-smalting converters is not advisable under present technological conditions.     

Production of chrome-magnesite brick from Shorzh deposit chromite

Conclusions Chromite from the Shorzh deposit has a dense structure and only minor quantities of minus 0. 5 mm particles after milling; this fact accounts for the production of green compact with a high bulk density without repressing.The negligible amounts of chromite fines eliminate the need for the introduction of magnesite grains into the batch since the latter have an adverse effect on the quality of refractories.The quality of chrome-magnesite brick made from Shorzh chromite is somewhat superior to that made from a mixture of Saranovo and Kempersayi chromite and fully meets the requirements of State Standards 5381-50.However, an experimental batch of refractories would have to be produced so as to arrive at final conclusions on the suitability of chromite from the Shorzh deposit for use as raw material in the production of chrome-magnesite bricks.     

Increasing the spalling resistance of fireclay refractories by adding combustible organic liquids and m ineral a dditives

Summary The combined addition of hydrophobic organic liquids and mineral (refractory) additions improves the structure and physico-mechanical properties of fireclay refractories. The spalling resistance is greatly increased.The spalling resistance of fireclay specimens assessed by the number of heat cycles before destruction with the combined action of mazut and mineral additives is 2.0–2.8 times greater than with the manufacture of the articles without these additives.The increase in spalling resistance occurs owing to the development of microcracks in the structure around the grains of grog, with a simultaneous reduction in the modulus of elasticity and coefficient of thermal expansion and also an increase in deformation before failure (/E) of the material.The addition to the hydrophobic organic liquid (mazut) of fine powders (magnesite, alumina) permits not only a considerable increase in spalling resistance, but also a certain reduction in the porosity and an increase in the strength of the products.Separate introduction of the additives (mazut on the grog, magnesite and kaolin to the bond) gives worse results compared with the above method (lower spalling resistance, increased expansion).Thus it was shown that the main factor determining the resistance of fireclay refractories against thermal strains is the nature of the contacts of the surfaces of the grains of grog and the bond.Semiplant testing of the method showed that the addition of 5% mazut and 5% calcined kaolin (or magnesite) doubled the life of fireclay saggers.     

FORMING PRESSURE OF DRY-PRESSED REFRACTORIES. II. THE EFFECT OF PRESSURE VARIATIONS ON FIRED PROPERTIES1

Laboratory tests of the dry-pressed fire brick revealt hat fired porosity varies inversely with the forming pressure. The change, however, is less marked at high pressures. The resistance to thermal spalling is considerably lowered by increased pressure. The course of spalling is traced for brick of various pressure and density. The relative importance of the various factors affecting spalling loss is discussed. In regard to the load test, increased pressure results in marked improvement with the highly plastic mixtures and more indifferent results when much flint clay is present. In general, firing shrinkage is increased by increased forming pressure, the phenomenon being explained as due to improved continuity of the material tending to further the pyrochemical reactions. The comparatively low pressures of mechanical presses are reaffirmed by a study of fired properties. A summary of the data indicates that by utilizing higher pressures, brick of greater density may be obtained which are greatly improved in appearance, in resistance to abrasion, and in load-carrying capacity, but with diminished resistance to thermal shock. It is indicated that higher forming pressures would partially obviate the necessity of firing ware to the present high temperatures.     

Study of the properties of pure types of fused magnesite for service in vacuum induction furnaces

Conclusions As regards the degree of sintering, the extent of the shrinkage, the thermal-shock resistance and the stability in contact with graphite at temperatures of service, the best material consists of fused magnesite containing 98–99% MgO, and the maximum grain size of the batch should be no more than 2 mm.Translated from Ogneupory No. 1, pp. 51–55, January, 1972.     

Effect of molding pressure on structural and densification behavior of microwave-sintered ceramic tool material

The die-pressed Al₂O₃-based ceramic compacts for microwave sintering were prepared using uniaxial molding pressure. Effect of molding pressure on density distribution, microstructure, and mechanical properties of both green and sintered compacts were studied by simulation and experiments. The results suggested that the density distribution of green compact showed obvious stratification phenomenon as the pressure increased. High pressure could increase the density of green compact but led to large density variation. Cracks were formed within the sintered compact due to the severe stress concentration at high molding pressure. Better mechanical properties were obtained at the pressure of 200-300°MPa. The optimal mechanical properties of Al₂O₃/Ti(C,N) ceramic tool were obtained at 1550°C with the soaking time of 10 minutes, which were as high as that of conventional sintering, but the sintering period was sharply shortened.     

不同熔炼工艺对电熔方镁石的影响

为了提高电熔方镁石品位,合理利用资源,以菱镁矿为原料制备电熔方镁石。研究了不同石墨电极（分别是直流空心电极、直流实心电极、交流空心电极和交流实心电极）对电熔方镁石的影响。通过对电熔方镁石的体积密度、显气孔率、物相组成和显微结构进行分析,结果表明：电熔方镁石坯体在靠近皮砂位置结晶最好,晶体发育比较完整;使用空心电极制备出的电熔方镁石结构致密,晶粒尺寸大。用交流空心电极制备出的电熔方镁石体积密度最大、显气孔率低、晶界平直,形成了较大尺寸的方镁石晶粒。     

Unfired magnesite refractories in resin phosphate bonding

Conclusions A process has been developed for producing unfired, dense, thermal-shock and slag-resistant magnesite refractories with a resin-phosphate binding.One feature of this process is the molding of the articles with an addition of orthophosphoric acid but without heating from a mass containing coarse (> 0.5 mm) magnesite grains and also fine magnesite grains (< 0.5 mm) coated with resin.Translated from Ogneupory, No. 7, pp. 56–58, July, 1979.     

玄武岩熔液对耐火材料的侵蚀

为深入了解玄武岩高温熔体对耐火材料的侵蚀行为,参照ASTM C621—1984(2001)分别对致密氧化铬砖、致密锆英石砖和熔铸锆刚玉砖(AZS-33)进行了1 500℃72 h的玄武岩熔液侵蚀试验,并对侵蚀后试样进行了显微结构对比分析。侵蚀试验结果表明,致密氧化铬砖的抗熔融玄武岩侵蚀性最好,其次是致密锆英石砖,最差的是熔铸AZS-33砖,其在液面线处出现严重剥落现象。显微结构分析表明:致密氧化铬砖结构均匀,与玄武岩熔液反应性小,同时与玄武岩渣中的成分形成尖晶石致密层阻止了渣的进一步渗透;致密锆英石砖表面与玄武岩熔液反应产生很薄的脱锆层和玻璃相,并且其致密均匀的结构也阻止了渣的进一步渗透;熔铸锆刚玉砖的显气孔率虽然很低,对玄武岩熔液有较好的抗渗透性,但其液相量较多,因此抗侵蚀性相对较差。     

Increasing the thermal efficiency of a rotary kiln for firing dolomites from various deposits

Conclusions More uniform firing of dolomite of various fractions can be achieved by reducing the upper limits of the dolomite particle size to 10–12 mm and excluding fractions < 5mm. Considering the low resistance of chrome-magnesite brick in the firing zone it is necessary to use periclase-spinel brick.The use of GVM burners for burning natural gas in rotary kilns increases the output of the kiln and reduces the consumption of fuel when burning dolomite. These burners can be recommended for installation in rotary kilns for firing magnesite, chamotte, lime, etc.Translated from Ogneupory, No. 4, pp. 23–26, April, 1973.     

Highly spalling resistant periclase-spinel brick (A Discussion)

Conclusions We established in principle the possibility of manufacturing in production conditions roof periclasespinel brick with a high spalling resistance by introducing ground chromite into the coarse grained part of the batch.Incorporating 18% coarse chromite into the granular part of the batch before mixing it with the finely milled magnesite powder increases the average spalling resistance of periclase-spinel refractories by a factor of 1.4. However, the existing production scheme is responsible for serious variations in spalling resistance. The other factors (with the exception of the refractoriness under load, which is reduced by 60°) correspond to the levels for ordinary PShSO products.Although comparative testing in the roof of an oscillating open-hearth furnace showed that spallingresistant periclase-spinel brick is highly wear resistant in such conditions, supplementary investigations of the industrial factors are required in order to obtain the special structure which increases the thermal shock resistance and makes it stable, and also slows down the melt saturation of the products.Translated from Ogneupory, No. 8, pp. 13–19, August, 1967.     

NiO直接电化学还原制Ni制片条件对阴极片孔隙率影响研究

本文研究了NiO直接电化学还原制取Ni工艺过程中制片条件对阴极片孔隙率影响。设计正交实验研究了成型过程中粘结剂的浓度和用量、球磨时间和成型压力对阴极片孔隙率的影响。结果表明,其中成型压力影响最大。利用SEM、测定孔隙率等手段研究了成型压力、烧结时间和烧结温度对NiO片的影响。结果表明:三者对孔隙率影响程度由大到小依次为:烧结温度、成型压力、烧结时间;随着烧结温度压力和成型压力的增大,试样孔隙率逐渐减小;而烧结时间对试样孔隙率的影响不大。