CHROME REFRACTORIES FOR THE OPEN HEARTH2

This is not a technical paper but a compilation of notes on chrome ore, and the various forms in which it is used in open hearth furnaces, with a discussion of recent improvements in chrome brick that have permitted their broader use. Also some performance data secured through the courtesy of many companies and individuals operating open hearth furnaces.     

SPECIFIC HEATS OF CHROME AND MAGNESIA REFRACTORIES*

The previous work in the field is surveyed, the method of preparing the samples is described, and chemical, petrographic, and screen analyses and photomicrographs of the samples are presented. Specific-heat determinations were made by the method of mixtures in a calorimeter using carbon tetrachloride; the calorimeter and the auxiliary equipment are described; and the procedures for determining the heat capacity of the calorimeter system and for the specific heats of the test samples are given in detail. The results are summarized, tabulated, and compared with published data. In addition to the bibliography of the papers mentioned in the article, an additional section (Section B), which served as a background for the study, is included.     

TESTING COKE OVEN REFRACTORIES1

General Reluirements are stated for mat, bench walls, checker work, regenerator korbels, main flues, division walls, oven chambers and jamb blocks. The following Tests are described:—inspection, reheating tests on three qualities, bending test. Requirements and specifications are discussed. The latter part ofthe paper deals with Apparent density and Permanent expansion. It is shown that the relation between them is a linear one and a chart is given. The average of thirty-nine determinations gives an apparent density, for Western brick, 0.016 higher than for Pennsylvania brick, due to the fact that the Western ganister is slower to transform than the Eastern.     

REFRACTORIES UNDER LOAD CONDITIONS1

Life factors.—The life of fire clay slabs, rings and saggers is influenced by a number of factors, both mechanical and chemical. The chief factors controlling the life of the slabs are (1) proper selections of clays and grog, (2) medium absorption or porosity, (3) strength in the unburned state, (4) proper and thorough blending and preparation of the mix, (5) proper pressing so as to insure freedom from flaws, (6) proper drying, (7) proper setting in the kilns and especially (8) initial burn. These factors are briefly discussed. Setting.—The manner of setting grinding wheels, using large slabs is described. This manner of setting causes transverse bending stress to be set up in the slab and shear stresses to develop. This shearing force, in connection with the large size and the high temperature (cones 11 to 12), make severe conditions for the slab to withstand. Shape and size.—The rate of heating and the size and shape of the slabs are additional factors. Round slabs, up to about 20° in diameter have a decidedly longer life when made in two half sections as compared with the solid shape. Larger slabs have longest life when split up into four sections, while if solid they will fail in one burn. Warping of the slabs, as well as cracking, causes failure. In general, if the width of area of the load is held constant, and length of span of the slab is increased, deformation and cracking is slightly increased. If the span is held constant, and the width or load area is increased warpage is greatly increased, especially as the number of burns under load increases. Cracking also increases in direct proportion to increase in width. These features are more pronounced the longer the span. Ultimate failure at high temperatures.—When not due to structural defects, failure is brought about by a gradual decrease in mechanical strength from burn to burn, so that fire-clay slabs under transverse load at such temperatures have decided limitations     

REFRACTORIES FOR OIL-GAS MANUFACTURE1

The present investigations of refractories by the oil-gas industry on the Pacific Coast were stimulated by sporadic independent tests in the past whereby it was observed that different qualities of fire brick not only had varying lengths of service but also had an apparent influence on the amount and quality of gas made and on the efficiency of gas manufacture. The essential differences in generator design, including that of brick-work construction, in the two-shell type of generator as compared with the single-shell generator are such that longer refractories life is obtained in the former type. The operations in the manufacture of oil gas for the two-generator types are briefly discussed, showing that the refractories are subjected to alternating oxidizing and reducing conditions. Other causes contributing to ultimate refractories failures are carbon deposition in the brick, abrasion of hot gases and the impinging of long flames on the brick, heavy checker-brick loads on arches, faulty construction of arches, and erratic working conditions. In addition, super-saturated steam, heavy hydrocarbons, and salts and sulphur in the oil, are contributing causes to checker-brick disintegration, especially in the generator zones where the oil and steam are introduced. It is hoped that specifications for refractories may be drawn up from the results of practical service tests now being conducted. The heat-transfer and heat-absorption properties of various refractories, such as conductivity, specific heat, density, diffusivity, heat capacity, and time required for the refractories to reach near-heat saturation, are discussed, particular attention being given to their possible application as oil-gas generator checker brick. The need for more complete and accurate data on the fundamental constants necessary in heat-transfer calculations is pointed out. Researches on refractories with thermal properties superior to fire brick are now being conducted in generators in an endeavor to increase gas capacity and operating efficiency along the lines indicated by theoretical considerations.     

SOME PROPERTIES OF CHROME SPINEL1

Five chrome ores covering a wide range of chemical composition from different localities were studied and their behavior at high temperatures was ascertained. The properties determined are chemical and mineralogical composition, thermal expansion (25 to 1250°C), specific gravity changes after various heat treatments, and X-ray characteristics.     

NOTE ON REFRACTORIES ENGINEERING1

A brief outline of training necessary to fit one for work as a Refractories Engineer. Nature of the work, its present-day importance and one verbal illustration of the work of such an Engineer.     

OIL FIRING OF REFRACTORIES1

Notes on the construction and condition of kilns used for refractories, comments on the results obtained when firing with fuel oil, and data on the equipment and operation of the kilns, are discussed in this paper.     

REFRACTORIES FOR FLAT ARCHES1

Arch construction is discussed, describing present method of placing fire clay tile. Tile are suspended on cast iron hangers by means of a tee-shaped slot molded in the top end of each tile, giving room for expansion in every direction. Larger quantities of heat units are released, more intense chemical reactions and there is ample shearing strength and small loss from weight or pressure.     

PRODUCER GAS FOR BURNING REFRACTORIES1

History of installations in the United States of producer gas for burning fire brick. Causes of failure or abandonment of producer gas firing. Continuous regenerative kiln necessary for successful burning at high temperatures with producer gas. The compartment kiln, fired with producer gas, best adapted for general refractories. Advantages of the compartment kiln over the car tunnel kiln. Essential features of continuous kilns for the successful burning of refractories. Special features of gas producers for ceramic kilns. Temperatures from producer gas. Economy of producer gas as compared with natural gas, oil and powdered coal. Investigation of designs and methods of operating gas producers.     

THE THERMAL EXPANSION OF REFRACTORIES1

The thermal expansion or contraction of a number of typical refractories has been measured up to 1700°C in a neutral or slightly oxidizing atmosphere. In nearly every case the expansion curve has been carried to a higher temperature than given by previous data. In a few cases the expansion curve has been obtained for materials that have not been studied in this way before. It is believed that the expansion curve of a brick, if carried to the softening point, gives valuable information as to the performance of that brick in service.     

THE ELECTRICAL RESISTIVITY OF REFRACTORIES1

The electrical resistivities of flint fire clay, kaolin, magnesite, sillimanite, silica, diaspore, Maryland, Italian and Indian talcs were determined at temperatures up to 1500°C. Tests were made in an atmosphere of nitrogen, by the Wheatstone bridge method, using 45-volt 1000 cycle alternating current. With the exception of magnesite, the rate of decrease of resistivity decreases with an increase in temperature. The investigation indicates that the resistivity of a complex ceramic body, especially if it is open and porous, is not constant for a given temperature above the temperature at which its most fusible mixture melts. Resistivity is affected by the amount of impurities present, decreasing with an increase of impurities. As was shown in the tests of Italian talc, the resistivity is not only dependent upon the amount of impurities, but also upon their distribution. Within the limits of the voltage used, the resistivity is independent of the potential applied.     

SILICON-CARBIDE REFRACTORIES FOR WATER-GAS GENERATORS1

A discussion of the problems involved in water-gas generator refractories is given and the steps in the development leading to the present highly satisfactory silicon-carbide air-ventilated Bernitz type blocks are given. Actual operating costs of typical installations are given. It is shown that generator capacities have been increased as much as 50% and fuel reductions have been so large that a real saving in net operating costs has resulted from the installation of this-type of lining. Many generators have now been lined and economically operated with air ventilated silicon-carbide blocks.