Grinding raw materials in the manufacture of cement

Claim 2

The improvement according to claim 2 wherein the step of separating the first part into said first and second portions is accomplished by reuniting said first part with the material forming said second part and subjecting the mixture so formed to a sifting operation.

Claim 3

The improvement according to claim 3 wherein simultaneously with said sifting operation the mixture is subjected to the flow of gas through the mill such that said first portion is entrained in said gas flow and carried out of the mill for collection.

Claim 4

The improvement according to claim 4 wherein at least a segment of said by-pass path coincides with the path of gas flow through the mill.

Claim 5

The improvement according to claim 5 wherein the path of gas flow and the by-pass path segment extend centrally through the secondary grinding zone.

Claim 6

The improvement according to claim 6 wherein said second portion of the first part is subjected to an ancillary crushing operation before reintroduction into the primary grinding zone.

Claim 7

The improvement according to claim 7 in which raw material is pre-crushed before entering the primary grinding zone and the grinding operation in both the primary and secondary grinding zones is carried out substantially by use of foreign grinding bodies.

Claim 8

The improvement according to claim 8 in which the raw material is moist raw material and wherein said gas flow is heated in order to dry the raw material simultaneously with the grinding thereof in the mill.

Claim 9

The improvement according to claim 6 wherein any ground material forming the second part which should have been initially separated for immediate entry into the secondary grinding zone is permitted to enter the secondary grinding zone during the by-pass operation.

Claim 10

In a rotary mill for grinding raw material which includes an inlet for the simultaneous introduction of raw material and a current of gas into the mill, a primary and at least one secondary grinding zone, and an outlet chamber for carrying finished fine ground material entrained in the current of gas out of the mill, said grinding zones being separated by perforated annular partitions adapted to allow substantially free passage of intermediate ground material between grinding zones, the improvement in combination therewith which comprises: a. a tubular conduit extending centrally through the secondary grinding zone in axially open communicating relationship between the outlet chamber and the primary grinding zone, said conduit defining the primary path of gas flow through the mill and said conduit being adapted to convey coarse ground material internally thereof in the direction of gas flow through the mill along a path by-passing the grinding operation in the secondary grinding zone.

Claim 11

The improvement according to claim 11 wherein said conduit is equipped with auxiliary conveying means comprising: a. scoop members adapted to advance said coarse ground material in the direction of gas flow through the conduit.

Claim 12

The improvement according to claim 12 wherein said conduit is provided with a series of perforations which define a path of entry for said intermediate ground material into said secondary grinding zone from the interior of said conduit.

Claim 13

The improvement according to claim 13 wherein the outlet chamber is provided with a screen member disposed in surrounding relation thereto for separating the ground material exiting from said chamber into fractions according to particle size by a sifting action.