Tube mill

Details Tube mill Tube mill

2000-03-09

2001-10-09

Larson, Lowell A. (Department: 3725)

Solid material comminution or disintegration

Apparatus

Including means applying fluid to material

Reexamination Certificate

active

06299081

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a tube mill having a rotatably mounted milling tube with a grinding stock input end and a ground stock delivery end that is housed by a drop-delivery housing for delivering the ground stock and the mill gas.
Tube mills serve for crushing, or respectively, grinding, stock, which is usually transported in the rotary milling tube from the grinding stock input end to the ground stock delivery end using a mill air, or respectively, a drying gas, and is usually milled with the aid of grinding elements such as steel balls located in the mill tube, for which reason one speaks of air-swept mills, ball mills, and so on. It is known (EP-B-0184326) to arrange a delivery cone at the ground stock delivery end of a tube mill, which comprises openings that are distributed about the perimeter for delivering the ground stock and the mill gas. There, the delivery openings for the ground stock and the mill gas are housed by a stationary drop-delivery housing, in which the ground drops down, is delivered out below, and is transported to a downstream sifter, usually by a bucket elevator, whereas the mill gas, which is laden with finest grain, is drawn up out of the stationary product drop-delivery housing and likewise conducted to a sifter. The oversized material (grit) separated out by the sifter is re-circulated to the grinding stock input end of the tube mill. The tube mill and the at least one external sifter that has been necessary heretofore thus form a circulation milling system, whose construction, together with the necessary conveyor mechanisms such as bucket elevators and so on, requires relatively high outlay.
SUMMARY OF THE INVENTION
The invention is based on the object of designing a tube mill such that a simple and compact circulation milling system can be created therewith, given a low outlay terms of machinery, which system is capable of managing higher stock circulation rates without high operating costs.
What is characteristic of the inventive tube mill is that its drop-delivery housing is not a stationary, completely immobile component; rather, the drop-delivery housing consists of two spaced, stationary, non-rotating side faces between which a material conveyor ring is arranged, which is rotatably mounted and can be rotated by means of a rotary drive. This rotating material conveyor ring of the drop-delivery housing that surrounds the delivery opening for the ground stock and the mill gas rotates at, for instance, approximately 40-80% of the critical r.p.m.; that is, the material conveyor ring carries at least part of the mill's delivered stock to before or beyond the upper vertex of the ring and allows this stock material to drop; and namely, into an integrated sifting space formed in the intermediate space between the at least one ground stock delivery opening of the mill tube and the rotating material conveyor ring between the two stationary side faces of the drop-delivery housing. It would also be possible to have the material conveyor ring rotate more rapidly, and to strip the ground material from the inner wall of the ring using strippers.
For the sifting space that is integrated in the rotating material conveyor ring to function, it stands in connection with a sifting air inlet opening, to a delivery opening for sifting air and sifted fine material, and to a delivery opening for sifted oversized material in at least one of the two side faces. The space-consuming bucket elevators or other conveyance mechanisms for transporting the delivered stock of the mill to the integrated sifter are forgone, as is at least one external sifter that has always been required heretofore.
In the integrated sifting space of the drop-delivery housing with the rotating material conveyor ring, at least one rod basket of a dynamic sifter can be arranged, whereby the axis of the rod basket is situated parallel to the mill tube axis. The feeding of the mill's delivered stock to the integrated sifter, which can be a static and/or dynamic sifter, is accomplished in part by the rotating material conveyor ring and in part by the milling air and/or the sifting air. As a rule, the quantity of milling air is less than the quantity of sifting air that is required for sifting the mill's delivered stock, so that environmental air is usually drawn into the integrated sifting space to support the sifting. In the mill-drying of wet stocks, a hot gas flow can also be used for sifting.
The oversized stock of the sifter that is collected in the integrated sifting space, which is collected, or respectively, is separated from the sifting airflow, at the periphery of the at least one rotating rod basket in a dynamic sifter, is re-circulated to the grinding stock input of the tube mill via a conveyance mechanism, particularly an air conveyor trough, so that a compact circulation grinding system is realized.
A line for venting the sifting air, which is laden with fine material, runs from the sifting space integrated in the drop-delivery housing through an opening in at least one of the two side faces of the drop-delivery housing, said line leading to a separator for separating out the fine material from the sifting air.


REFERENCES:
patent: 3537658 (1970-11-01), Jurgenjanich
patent: 3712549 (1973-01-01), Cleemann
patent: 0184326 (1989-01-01), None

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