Abstract: The invention relates to a method as well as to apparatus for combined grinding of at least two materials of differing grindability, such as clinker and limestone, wherein the material which is more difficult to grind is pre-crushed to a Blaine fineness of grinding of at least 700 cm.sup.2 /g and there-after is further ground together with the other material to produce the finished material.

Abstract: The invention relates to a method and a grinding plant for reduction of brittle material for grinding, in which material which has undergone primary reduction from a first grinding stage is delivered as fresh material to the second mill of a second grinding stage and finished product is removed from this second grinding stage, and in which the quantity of feed material of this second mill is kept constant when the quantity of finished product alters by altering the quantity of fresh material. This first grinding stage contains an air separator from which the fines are fed as fresh material to the second mill. In the event of alteration in the quantity of fresh material for the second grinding stage the quantity is kept constant by corresponding alteration of the fineness of separation of the separator of the first grinding stage.

Abstract: The invention relates to a material bed roller mill for crushing brittle material to be ground in the gap between two driven rollers which are pressed against one another with a high grinding force with a filling shaft for the delivery of material provided above the rollers. The width of the stream of material delivered to the roller gap can be altered with the aid of vertical guide walls which are adjustable at right angles to the vertical central plane of the roller mill while maintaining their vertical position. The column of material which is aligned vertically above the rollers creates pressure which is introduced fully into the material bed crushing and if required the column of material can be moved in the cross direction with respect to the rollers.

Abstract: The invention relates to a sifter in which the spiral for delivery of the air for sifting is divided into a plurality of channels lying one above another in which elements for setting the quantity of sifting air delivered to the individual channels are provided. In such a sifter the quantity of sifting air in the individual regions of the sifting chamber can be optimally adapted to the requirements, which leads to a substantial improvement in the degree of separation.

Abstract: A method and apparatus for the two-stage crushing of brittle material comprising a roll mill and a second mill downstream thereof, the output of the second mill being delivered to a sifter. The quantity of grit obtained in the sifting operation is divided between the roll mill and the second mill in such a way that the sum of the quantity of fresh material and the quantity of grit delivered to the roll mill remains constant.

Abstract: A method and apparatus for the two-stage crushing of brittle material comprising a roll mill and a mill connected downstream thereof, the output of the second mill being delivered to a sifter in which a second branch stream of the grit obtained in the sifting operation is returned to the roll mill and a further branch stream is returned to the second mill. A first control circuit keeps the sum of the quantity of fresh material and the quantity of grit constant, while a second control circuit divides the quantity of grit into two branch streams in such a way that the drive power of the roll mill remains constant.

Abstract: The invention relates to a roller mill with a sifter arranged above it which is provided with a deflecting rotor and an adjustable ring of guide vanes. Such a construction is distinguished by a particularly high degree of separation.

Abstract: A method and apparatus for two-stage crushing of material wherein the material is subjected to crushing first in a constant speed roll mill and then in a second mill. Grit resulting from the crushing is returned to the first mill in a proportion to maintain the filling level of combined fresh material and grit substantially constant even when the quantity of such fresh material changes.