In the last 10-15 years the role of outside-the-furnace vacuum treatment of steel has increased so much that this trend is now being assessed as one of the basic moves in develop~ ing steel melting production.The working conditions for ladles under these conditions are much more severe than those in ordinary steel ladles [I]. The combination of high temperatures, strong erosion of the metal, and variable thermal loadings all place high demands on the quality of the refractories~ Studies made at the Ukrainian Scientific-Research Institute of Refractories indicate the desirability of obtaining articles with a low porosity and high strength, thermal-shock resistance, and slag resistance [4].The quality of the bond is important to improve the properties of mullite--corundum articles; it should possess outstanding anitcorrosion properties. This is achieved by increasing the content of A1203 in the bond and introducing alloying additives into it, which reduce the wetting of the refractory by steel and slags [2].During the investigation of the effect of electrocorundum additions on the properties of mullite-corundum refractories, we used high-alumina chamotte ShMK-77.5, containing 77.5%* AI20~.The chamotte should contain 15-20% fractions 2-3 ~n, and not more than 10% < 0.5 mm to get the densest grain packing during pressing.The composition of the finely milled mixture of the materials obtained by combined grinding contained Polozhe kaolin PLK-0, which meets the requirements of Technical Specifications (TU) 14-8-137-75, and white electrocorundum EB-50 as specified by TU 48-01-53-71.The corundum has a high resistance to the action of both acid and basic slags, metals, and reducing and oxidizing agents. Moreover, the use of electrocorundum in high-alumina materials aids the sintering by imporoving the grain-size composition [3].Mullite--corundum specimens were prepared from batches using combined grinding for the white electrocorundum.The standard (batch No. i) was taken to be the batch for mullite--corundum articles produced in the high-alumina goods shop of the Zaporozhe Refractories Factory according to standard TIV-I-78.The batch No. 1 included 60% chamotte ShMK-77.5 and 40% finely milled mixture of the combined grist, consisting of 85% chamotte ShMK-77.5 and 15% kaolin PLK-0.Batches Nos. 2-4 differed from the standard batch because of the finely milled mixture, which contained respectively, 60, 75, and 85% electrocorundum (the remainder was PLK-0 kaolin).The white electrocorundum and kaolin were premixed in a laboratory ball mill for 2 h to ensure better distribution of the additive.The body was prepared in laboratory runner mills in the following way: the coarse chamotte was moistened with slip, then the combined grist was added.The slip was prepared with a solution of sulfite lye which had a density of 1.18 g/cm 3. The slip density after adding the kaolin was brought to 1.25 g/em ~. The total blending time was 20 min. The water content was 4.5%.The body was pressed on the PGA-100 laboratory hydraulic press at i00 MP...
UDC 666o762o!6o017:620.~!!.~ Recently the nondestructive (sonic) method has obtained ever increasing use in inspec tion of the quality of refractory parts. The use of this method under plant conditions makes it possible to increase the number of inspected parts without limit, which in the final analysis provides an objective evaluation of production quality.The use of the nondestructive method of inspection of the quality of finished production makes it possible:to increase labor productivity in inspection operations; to accelerate the inspection process; to save refractories as the result of those saved in nondestructive inspection; to improve sanitary and technical working conditions.The nondestructive method of inspection of the quality of finished refractory parts was developed by the All-Union Institute for Refractories [i, 2]. This method is based on establishment of a correlation relationship between the weight of a part and the frequency of its natural vibrations and also the open porosity, apparent density, and compressive strength.The experimental data were processed using a program in three stages.The program for the method was developed in Fortran language for EC computers in the Laboratory for Applied The original data are prepared for calculation of the full polynomial from two second power variables (that is, the values of m 2, f2, mf, f are calculated from sample data) and each of the variables is considered as optional for inclusion.The significance was verified at the 0.05 level, that is, the level of reliability is 95%.As the result of operation of the program an equation is produced which is considered suitable only if it contains terms only linear with respect to m and f (does not contain the terms m 2, f2, mf) and inclusion in the equation of the variable is necessary.If only the variable m is included in the equation, it is also unsuitable.
An indispensable condition of improvement of production operations is improvement in inspection of finished product quality. Existing methods of quality inspection of refractory parts involve cutting out of specimens and, consequently, destruction of parts. On the basis of many years of investigations All-Union Refractory Institute together with Zaporozh'e Industrial Institute and Zaporozh'e Refractory Plant has developed a nondestructive sonic method of quality inspection of finished refractory parts. This led to the development of GOST 25714-83. The method is based on establishment of a correlation relationship between the weight of parts and their frequency of resonant vibrations and also their properties (open porosity, apparent density, compressive strength).According to GOST 24555-81 all existing test units on which routine measurements or scientific-research work is done must pass metrological certification. For this purpose All-Union Refractory Institute has developed the industry standard specimen shown in Fig. 1. It is designed for certification and establishment of the accuracy characteristics of working test units for determination of the resonant frequencies of refractory parts according to GOST 25714-83. Documentation making it possible to certify nondestructive testing units has also been developed [1, 2].The nondestructive testing unit includes a G3-109 low-frequency generator, a Ch3-34 digital frequency meter, an S 1-68 oscillograph, and a receiving and transmitting system with transmitting and receiving piezoceramic transducers. Such units are used in acoustic inspection laboratories in three main shops of the plant. All units have undergone certification.The certification was done at 18~ a relative humidity of 50%, and an atmospheric pressure of 100 kPa with a voltage of 220 V and a frequency of 50 Hz. The certified characteristic is the resonant frequencies of the fundamental tone of the bending and longitudinal vibrations.The standardized accuracy characteristics of the test units are the maximum distance between the telescopic supports of the receiving and transmitting system for parts of normal dimensions and shaped simple and complex configuration, the working range of vibrations in the transducers of the receiving and transmitting system determined from the degree of attenuation, and the error in measurement of the resonant frequencies.In the first stage of certification an external inspection was made of the instruments and receiving and transmitting system of the test units.For standard production instruments there is existing evidence of state certification. The standards and technical documentation for the test unit was formulated in accordance with the requirements of GOST 24555-81 and GOST T 2.601-68-88. The standards and technical documentation includes method instructions for methods and means of tests MU MO 14-388-82-88, a technical description and instructions for use, and a service log.The limiting distance between the telescopic supports, 350 ram, was determined with a metal r...
Out-of-furnace vacuum treatment of steel is a promising method for improving its quality and is, consequently, finding ever-increasing application in the metallurgical plants of the Soviet Union and other countries [i]. The effectiveness (efficiency) of introducing vacuum treatment of steel depends to a large extent on the stability (life) of the monolithic lining of the ladles [2].The ladle lining is prepared from phosphate-bonded high-alumina ramming bodies [3]. The high-alumina bodies based on phosphate binders possess numerous advantages over the bodies prepared using other binders: higher thermal shock resistance, density, and strength and greater resistance to the action of molten metal and slag [4].
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