Hydrostatic molding of large refractory products

Dorodnyi, B. A.; Grinberg, Ya. M.; Kainarskii, I. S.; Degtyareva, É. V.; Orlova, I. G.

doi:10.1007/bf01281704

Cited by 2 publications

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“…the main shrinkage of the article occurs at pressures below 20 MPa. With further increase in the pressure densification is slight but the greenware is strengthened [15] which must be taken into account.…”

Section: Vi)mentioning

confidence: 99%

“…2) and depends on their properties, in particular the dispersion, hardness, and method of preparation [40]. The general rule is that, as with ordinary pressing, the curves for the densification of the powders are characterized by sections with different densification rates; with a rise in pressure their slope is strongly reduced [15,40].…”

Section: Vi)mentioning

confidence: 99%

“…Systematic studies of this method of pressing in the USSR have been made in the Central Research Institute for Ferrous Metallurgy [7][8][9][10],the All-Union Institute of Metallurgical Machinery [10][11][12][13], and also in the Ukrainian Scientific-Research Institute of Refractories [14][15][16][17].…”

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Isostatic pressing technology for refractory materials

Degtyareva

Grinberg

1982

Refractories

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Isostatic pressing is effected by multilateral, uniform, and smoothly increasing pressure, realized, in contrast to ordinary static and dynamic shaping, in rigid molds only through the freely deformable intermediate medium with obligatory complete demarcation of the pressed and pressing media. As a rule, during isostatic pressing the powder is poured into the elastic (rubber) shell which is sealed, placed inside a thick-walled metal container, and subjected to multilateral compression by the pressure of a liquid.The method of isostatic (hydrostatic) pressing is becoming widely used in the refractories, metallurgical, ceramics, and other industries. Abroad it is being used to make heatemitting cylindrical and spherical elements and graphite blocks for nuclear reactors, grinding bodies of various shapes, complicated small and large electrical insulators, special and transparent ceramics [i], long tubes and large crucibles for various purposes, large refractory blocks for glass melting and metallurgy [2][3][4] On an industrial scale the method of isostatic pressing of refractories and ceramics in the USSR was first used at the Luzhsk Abrasives Red Crucible Factory for preparing large crucibles and special ingot molds ~rom graphite--chamotte bodies [18], at the Semiluksk refractories factory for the mass production of graphite-~mullite--corundum ingot molds for bimetallic ingots, and in the Scientific-Research Institute of Building Ceramics for preparing large drain pipes [19].Isostatic pressing has a number of advantages over other methods of shaping refractories and ceramics: the possibility of preparing large and complex articles (including those from finely dispersed materials) which cannot be obtained by other means; obtaining high, uniformly dense and uniformly strong raw materials (greenware), which ensures low loss through buckling and cracking in firing; the possibility of increasing the density of the greenware at relatively low pressures and with low moisture contents, which provides the necessary density in firing the goods; providing for dense and high-density articles a big reduction in the sizes of the pores, with a reduction in the proportion of large pores, which gives, e.g., a higher corrosion resistance for zircon and mullite [20], and a reduced amount of sublimation for chromium oxide [21].Isostatic pressing is also advantageous energy-wise [22] since it creates the further possibility of reducing the porosity of the finished goods, not on account of the highenergy firing process, but on account of the lower energy consuming processes (preparation of body, pressing). The area of the intergrain contacts during isostatic pressing for the same pressure and other conditions being the same is about 38% higher than for ordinary static pressing in rigid molds. This boosts the rate of solid-phase reactions and somewhat reduces the shrinkage of the goods in firing.The disadvantages of isostatic pressing include the great complexity and high cost of the technological equipment and fittings, the high overhea...

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Section: Vi)mentioning

confidence: 99%

Section: Vi)mentioning

confidence: 99%

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Isostatic pressing technology for refractory materials

Degtyareva

Grinberg

1982

Refractories

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“…3-18; 2, pp. 1-291, In the Soviet Union experiments were carried out in the production of powders of synthetic magnesia and of refractories from these powders [3][4][5][6][7][8][9][10][11][12].…”

Section: Propertiesmentioning

confidence: 99%

“…The charging of the powder with vibration, the application of the hydraulic load, and the combination of vacuuming and compaction gave a green product of uniform density and well-formed configuration (the distortion index of the shape of the block Fd = 0.246-1.19% [12]). However, after firing some of the specimens were found to contain fissures and firecracks, obviously as a result of the orientation (flatwise) of the particles.…”

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Large chromic oxide bricks formed by isostatic pressure

1978

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Chromic oxide is a high-melting, chemically inert, and nonwettable material [1, p. 323] that is highly corrosion-resistant in the production of ordinary and other glass [2,3] so that it is used increasingly for the brickwork of the tank of glass furnaces [4, 5].The brickwork of glass furnaces is laid without mortar and must be constructed of large refractory bricks so that the number of joints in the lining is minimized. According to published data [5, 6], isostatic pressure molding is the most efficient method of producing high-quality large blocks, e.g., from chromic oxide. A relevant technology has been developed in the Ukrainian Scientific-Research Institute of Refractories [7].The known designs of isostatic pressure molding plant for large blocks do not give a uniform distribution of the working pressure on all sections of the material although it is the main idea of the isostatic method that the pressure should be uniform. The arrangements of the elements of the mold in isostatic pressure molding plant is shown in Fig. 1. Usually one of the sides (normally the top end) of the product lies against the rigid seal of the pressure vessel (in abuilt-in mold) or against the mold cover (in'a separate mold) so that this method of pressure molding is defined as semi-isostatic [8]. It does not give products of a true shape (Fig. lc) and the density of the product is slightly nonuniform. Vibrovacuum compaction does not prevent the product shape from being distorted (Fig. lf).These faults have been overcome in a mold design, which incorporates the principle described in an earlier communication [7], i.e., use is made of an additional elastic envelope through which the working fluid acts on the top end of the product being formed (Fig. li) so that the pressure is distributed evenly in all directions. The fluid can be admitted into the additional envelope before the start of pressure molding (Fig. lh) so that a hydraulic load is produced during the vibration of the vacuumed powder. This is a new feature in the technology of isostatic pressure molding.The present authors developed a technology for the isostatic pressure molding of large blocks on the basis of the above laboratory investigation.The products were formed from metallurgical chromic oxide OKh_M-1 (GOST 2912-73) containing 98.9-99.25% Cr203 in the form of flat crystals measuring predominantly 2-6 to 8-23 ~ (smallest diameter 1-3 ~, largest 80-150 p). The Chromic oxide was ground in a ball mill to particles finer than 6-10 ,~ and mixed with 4% WiO 2 [10].The moisture content of the mix and the type and amount of binder were decided with the aim of obtaining a green product of maximum strength and of producing a maximum degree of eonsotidation of the mix during the vibration process (Fig. 2). The data in Table 1 show that with water as the binder an increase in the moisture content of the mix from 2.8 to 5.5% does not influence the strength of the green product and other binders influence it only marginally. However, during drying at room temperature for 2-2.5 d...

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Hydrostatic molding of large refractory products

Cited by 2 publications

References 1 publication

Isostatic pressing technology for refractory materials

Isostatic pressing technology for refractory materials

Large chromic oxide bricks formed by isostatic pressure

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