The author describes the specifics of molds for quasi-isostatic molding, which provide volumetric compression of preforms made of powdered materials and their waste-free production technology. The advantages of these molds compared to isostatic molds are discussed.The method of quasi-isostatic molding developed by us for producing a wide range of ceramic products is a simplified variant of isostatic molding ensuring three-axial volumetric compression of the material and, consequently, yielding products of uniform density with good physicomechanical and electric properties.The medium transmitting uniform isostatic pressure is a hard elastomer (synthetic caoutchouc), which simultaneously acts as part of the mold forming the outer or the inner surface of the preform. For instance, the elastic element in a mold designed to produce ceramic rings is the core forming the inner cavity of the ring, whereas in a mold for producing an article shaped as a solid cylinder, such element is the bushing that shapes the outer surface. Figure 1 shows possible schemes of compressing the matrix by means of the elastic medium: external compression from the periphery toward the center (a, b, c); inner compression from the center to the periphery (d, e); bilateral compression (inner and external) to form articles with a significant wall thickness ( f ).Molds for quasi-isostatic molding by their design, installation method, and operating techniques resemble molds for static molding. However, an article under quasi-isostatic compression exists in a more complex volumetrically stressed state than under traditional static compression, since the usual system of forces acting in static molding here is complemented by the reversible elastic energy of the press-buffer volumetric compression and its deformation.An elastic press-buffer is the main element in quasi-isostatic molding; therefore, in designing these molds a very significant issue is the choice of an accessible material for the elastic pressing element, which would ensure compaction of powder materials and reliable service of the mold in industrial conditions. We tested a wide range of elastomers in molds for molding ceramic products. Based on molding test results and data on physicomechanical properties, we have chosen the elastomer SKU-7l as the optimum material providing for articles with a uniform density throughout their volume and a smother (less rough) surface. This material has exceptionally high wear resistance and ability to operate under high pressure; its residual deformation is equal to zero

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As is well known [1][2][3][4], the isostatic method of pressing is one of the prospective methods in the production of refractories. The authors*of the present article developed a mold for making crucibles 150 mm high and 220 mm in diameter by the isostatic method using a "free matrix" scheme. The mold is shown in Fig. 1. It consists of a rigid matrix-ring 1, fitted on a thread in a flange 2 placed on the columns 3, and spring loaded on the axle of the press mold with springs 4. The external rigid-plunger 5 is connected with the upper plate 6. The internal elastically deformable plunger (press buffer) 7 made of polyurethane is fitted to the rigid cylindrical table-pusher 8 connected by means of a shaft 9 and an ejector 10 with the press ejector 11. The annular ejector 12 is installed concentrically on the table-pusher 8 on a cross piece 13, connected with a locking device 14. Two electromechanical vibrators 15 of the type PV-66 are fitted to the flange 2, and the intermediate plate 16 --to the bottom plate 17. The regulating supports 18 are placed on the upper plate 6.

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A classification method is provided for quasi-isostatic compaction of powder material objects. Schemes are considered for the action of compaction pressure on pressed material in relation to an assortment of pressed objects.The method of quasi-isostatic compaction is a fundamentally new version of isostatic compaction, combining successfully the advantages of the radial hydrostatic and static compaction methods, providing volumetric compression of pressed material. The method was developed for the first time in the Soviet Union, and there were no overseas analogs. The technology, developed for a broad range of objects, was introduced into 14 enterprises of the country. The method of volumetric (quasi-isostatic) compaction is the most economic and advanced procedure of all currently known isostatic and static compaction methods. Objects prepared by this method have high physicomechanical and electrical properties. The density of objects of aluminum oxide material is 94 -95% of theoretical, and with hydrostatic compaction of the same object this property does not exceed 85%. With static compaction the density of any objects of the same aluminum oxide material is 76 -82%.The compaction process is accomplished without using expensive isostats in dies, similar in construction to normal static compaction metal dies, using the equipment employed for static compaction. The sequence of production operations for quasi-isostatic compaction is similar to that for static compaction. The principle of quasi-isostatic compaction includes the fact that the medium transmitting a uniform pressure is an elastic material, i.e. synthetic rubber, that is similar to a quasiliquid, and transmits the applied pressure throughout the whole volume of a compacted object. Compared with hydrostatic compaction technology, the quasi-isostatic compaction method makes it possible to simplify considerably the technology and production equipment, to reduce capital expenditure and the production space, and to reduce production personnel. Compared with the static method, with quasi-isostatic (triaxial) compaction there is a considerable reduction in the metal content of the die and a reduction by several factors in the wear of metal surfaces. Industrial use of the quasi-isostatic compaction method creates a considerable saving in the national economy [1 -3].The quasi-isostatic compaction method has been used by us in order to prepare objects of a broad range: saggers (round, rectilinear, square), shells made of chamotte and alundum mixes, smooth rings with a diameter of 180, 190, 250, 370 mm and a height up to 250 mm, rings of ribbed configuration with a diameter of 156 mm made of aluminum oxide material, mixer balls with a diameter of 20, 30, 40, 50, 60 mm, powder condensers with a height of 170 and 120 mm, pipes of several standard sizes with a length of 65 and 160 mm (including with a wall thickness up to 1,5 mm), plates of several standard sizes (including with a size of 370´370´65 mm), crucibles, briquettes of cylindrical and rectangular shape, ro...