Abstract: The invention relates to an apparatus for the classification of solid materials, preferably that of hard and highly pure materials, comprising a housing provided with an inlet stub, fine fraction outlet stub and a coarse fraction outlet stub as well as vane-crowns. The fluid carrying the material to be separated or classified radially passes through two vane-crowns with the vanes oriented at an angle to the tangent of the vane-crowns. Upon passage through the first vane-crown the separating or classifying chamber is reached whereupon the coarse fraction is separated out and the fluid flows radially through the second vane-crown whereupon the flow becomes axial with the fluid exiting against gravity and the separated material being collected below in a closed storage tank associated with the coarse product outlet stub.

Abstract: The present invention relates to a priming or body paint having active anti-corrosive and surface cleaning effect containing binding material, pigment and optionally solvent, filler and/or additives, characterized in that said pigment, optionally in addition to other known pigments, comprises:(a) 30-70% parts by weight, preferably 40-55% by weight of alumina hydrate (Al/OH/.sub.3),(b) 20-55% by weight of at least of one of atoxic oxides, hydroxides, oxide hydroxides, carbonates or phosphates of amphoteric elements or metals of variable valency possessing less valency than the maximum, in case of aluminum the oxide or hydroxide thereof,(c) 0-50% by weight, preferably 2-15% by weight of calcium and/or magnesium carbonate,and the grain size thereof is <20 .mu.m, preferably 2-10 .mu.m.

Abstract: An air-jet mill provided with pregrinding chambers and inner sizer suitable for fine grinding (below 10 .mu.), for cryogenic grinding and also for surface treatment during grinding of hard, elastic and/or thermoplastic materials.During operation there are no moving components to be exposed to heavy wear, and an inner sizer, forming an integral part of the grinding space, uses the energy left after grinding in the system to enable a sharp sizing or separation of fine fractions.

Abstract: A system and an associated process are described for the determination of grain size distribution of particles in suspension. The suspension is settled in a settling tank and optical density measurements of the suspension are taken and from this the grain size distribution is determined. According to the invention, the suspension is homogenized by circulating it in the settling tank, then circulating is stopped and the optical density is repeatedly measured in the settling tank on at least three points with deviating spacings. The equipment described is a settling tank (1) for the suspension, a device for the measurement of optical density in the settling tank (1) and a computing unit calculating the grain size distribution from the optical density values measured. The settling tank (1) is equipped with a means for the circulation of the suspension and there are at least three measuring heads (2,3,4,5,6) along the settling tank (1) sensing the optical density.

Abstract: According to the process the grains are led to the surface or ducts of a rotary element farther in than the flange of the rotary element, thus the coarse grains are led to the flange of the rotary element in a counterflow to the sizing medium. In a housing on an impeller deflecting elements are arranged, the carrier medium and the mixture of material to be sized are fed into the housing by medium inlet tubes, and led out by coarse and fine fraction outlet tubes or nozzles, and one inlet disc is arranged above the impeller so that they form an annular assorting space which is divided by deflecting elements into segments, and a passage connected to the inlet tube of the sizing medium is formed between the mantle of the inlet disc and the inner wall of the housing at its upper end, where ducts leading into the assorting space are arranged in the inlet disc farther in than its flange, and which are connected to the carrier medium inlet tube.

Abstract: An improved process for accelerating the digestion process in the Bayer alumina process is provided which promotes both the goethite-hematite conversion and a more perfect and quick dissolution of the diaspore. The above is achieved by carrying out the digestion in the process of 5-20% by weight calculated on the dry weight of the bauxite of a novel hydrogarnet catalyst.

Abstract: An improved process for the enrichment of bauxites with unfavorable textures and low qualities via flotation and carried out after selective agglomeration. According to the process of the invention a water-soluble prepolymer of low chain length is added to the slurry as flocculating agent, thereafter the polymerization is started again by heating the slurry and/or adjusting its pH and/or adding a catalyst thus converting the polymer chain fragments adhered onto the gangue with high surface activity into a cross-linked resin, and finally the slurry is subjected to flotation in the presence of a conventional flotation aid.