No abstract

Possibilities are studied of reinforcing refractory objects and unmolded materials with carbon fibers produced domestically. It is shown that with specific treatment fibers are effectively distributed within refractory materials, they reinforce them efficiently, increasing strength and thermal shock resistance, and they remain in refractory objects and dense concretes up to a heat treatment temperature of 1600°C.The reduction in the specific consumption of refractories for a unit of basic product (steel, cement, glass, etc.) is moving along the path of improving the quality of refractories and the production of new, more resistant forms of refractories, replacement of small-piece refractory objects by unmolded refractory materials, with production and use of new refractories not requiring manual labor. Another worldwide tendency in the refractory market is more extensive use of carbon-containing materials and objects exhibiting a valuable set of properties from the point of view of refractory operation, i.e. high heat resistance and corrosion resistance to melts based on iron, and high mechanical strength. Recently a tendency has been observed in increasing the specifications for refractories and mainly for achieving quality uniformity even as a result of an increase in cost. One method for improving the quality of refractory materials is reinforcement.Reinforced materials are composite materials, within whose composition there is additionally a fiber filler distributed within the volume. In a number of properties, including ultimate tensile strength and shear strength, impact and fatigue strength, crack resistance, fracture toughness and thermal shock resistance, reinforced materials surpass traditional materials, and this ensures their high efficiency in applications.Reinforcement with a fiber changes the behavior of the matrix of a refractory as a component of a specific structure, and this makes it possible to create the required strength reserve, retaining structural integrity even after development hairline cracks. In addition, as a result of a combination of fiber and matrix the refractory forms an additional set of composite material properties, whose components do not exhibit them individually. In particular, presence of an interface between the reinforcing elements and the matrix markedly increases crack resistance and increases material resistance to spalling. Thus, in composites an increase in static strength leads not to a reduction, but to an increase in fracture toughness. For example, introduction of silicon carbide fibers (whiskers) into a bauxite mix in an amount of 2 -4 wt.% increases the fracture toughness from 1.3 to 1.9 MPa 1/2 [1].Introduction of filaments (fibers) into a refractory charge provides three-dimensional volumetric strengthening and an increase in material endurance, a reduction in shrinkage during heat treatment, as a result of which there is a significant increase in crack resistance and impact strength. Volumetric reinforcement of a refractory makes it possible to reduce the ...

No abstract

No abstract

Compositions have been developed for nonshrinking vibrocast thermally insulating light refractory concretes with densities of 1.0, 1.3, 1.5, and 1.8 g/cm 3 for temperatures of use up to 1400°C. The structure and properties have been examined for the concrete of density 1.3 g/cm 3 .Advances in metallurgy and other branches of industry impose new requirements on the properties of light-weight refractories, and one needs better refractories with a combination of properties providing the reduction of energy, materials, labor, and time during production.Although there has been a general reduction in the production and use of refractory materials, there has been an increase in the proportion of production for unmolded refractories having many advantages over the usual ones. Out of all forms of unmolded refractories, the commonest have been refractory concretes, both traditional ones with high contents of cement and low-cement new-generation ones.When heat-insulating refractories are used in industrial ovens, there is 20 -70% reduction in the consumption of fuel, and it is possible to accelerate substantially the firing in batch ovens while also reducing the wall thicknesses in ovens and domes. If the thermal insulation is provided by high porosity, then the mass of the lining is also reduced.It is important to develop light concretes with low density and thermal conductivity, which can be transported in the form of dry mixtures and from which one can produce the lining by vibrocasting directly at the user=s plant.This study was performed to develop compositions for light refractory concretes with various densities on the basis of available and cheap raw materials. The basic concept was to use a light spherical aluminosilicate filler with closed porosity, which would allow one to use the minimum amount of water to obtain the vibrational flow state. Eliminating water from the structure of the concrete leads to the structure becoming more open and weaker, so the task is to minimize the amount of treatment water, including by the use of deflocculants and the addition of ultrafine powders.Rod specimens were shaped by vibration in demountable metal molds. The molds containing the specimens were kept for 24 h in a moist medium at room temperature. Then the