Abstract:
To construct a tube mill such that a simple and compact circulation grinding system can be created therewith, with little outlay in terms of machinery, that can also manage higher stock circulation rates without high operating costs, a tube mill is disclosed whose drop-delivery housing consists of two spaced stationary non-rotating side faces, between which a rotatably mounted material conveyor ring is arranged, which can be rotated; whereby a sifting space with a dynamic sifter and/or a static sifter is integrated in this so constructed drop-delivery housing.

Description:
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&#39;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&#39;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&#39;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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention and its additional features and advantages are detailed with the aid of the schematically illustrated exemplifying embodiment. Shown are: 
     FIG. 1 is a side view, partly in a vertical section, of the inventive tube mill system with an integrated sifter, configured into a circulation grinding system; 
     FIG. 2 is a cross-section along the line II—II of FIG. 1; 
     FIG. 3 is a detailed cross-section along the line III—III of FIG. 2; and 
     FIG. 4 is the invention as applied in what is known as a two-chamber tube mill with central delivery. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The tube mill of FIG. 1 comprises a rotatably mounted milling tube  10  with a grinding stock input end on the night side and a ground stock delivery end on the left side. At the delivery end, the milling tube  10  is connected to a delivery cone  11 , via which the tube mill is driven by a motor  12 . The grinding stock is guided from the supply bunker  13  into the mill tube  10 , which is filled with grinding bodies such as balls, via a metering apparatus  14  and an intake chute  15 . Milling air  16  is also drawn in to the mill tube  10  at the input end. In the mill-drying of wet stock, a hot gas flow can also be used as milling air  16 . Several openings  17  for delivering the ground stock and the milling air are arranged so as to be distributed about the perimeter of the mill delivery cone  11 . 
     The delivery cone  11  with its delivery openings  17  for ground stock and milling air is surrounded by a drop-delivery housing, which inventively consists of two spaced stationary non-rotating side faces  18  and  19 , between which a rotatably mounted, rotatable material conveyor ring  20  is arranged, which ring terminates the drop-delivery housing exteriorly at the periphery of the side faces  18 , 19 . The material conveyor ring  20  can be rotated on rollers  21  and  22 , and the rotation of the material conveyor ring  20  is accomplished via its cylindrical shell; for instance, by means of the driven bearing roller  22  or some other drive mechanism engaging the conveyer ring. The ground stock that has been delivered from the delivery openings  17  of the tube mill drops onto the inner wall of the rotating material conveyor ring  20 , which wall may be provided with lift elements, as warranted; whereby, the rotation rate of the ring  20  lies below what is known as the critical rate; that is, the ring  20  carries the ground stock into the region of the upper vertex of the ring and lets this stock material drop, specifically into a sifting space  23  that is arranged above the delivery cone  11  in the drop-delivery housing, the housing of which space is formed by the two side faces  18 ,  19 . As illustrated in the exemplifying embodiment of FIG. 1, the material conveyor ring  20  can surround the edges of the two spaced side faces  18 ,  19  at its two sides; however, the two edges of the ring  20  can also be arranged within the two spaced side faces  18 , 19 . 
     As emerges from FIGS. 2 and 3, sifting air intake openings  24 ,  25  and a delivery opening  26  for sifting air and sifted fine material (FIG. 1) are arranged in at least one of the two side faces  18 ,  19  of the drop-delivery housing, from which latter opening a line  27  for venting the sifting air that is laden with sifted fine material runs, said line leading to a separator  28  for separating the fine material  29  from the sifting air  30 , which is vented by an induced draft ventilator (not illustrated). 
     According to the exemplifying embodiment, at least one rod basket  31  of a dynamic sifter is arranged in the sifting space  23  of the drop-delivery housing, whereby the rod basket axis is situated parallel to the milling tube axis. The sifted oversized material that collects on the periphery of the rotating rod basket  31  (which is driven by the rod basket drive motor  32 ) is re-circulated to the grinding stock input of the tube mill via a conveyance element  33 , particularly an aerial conveyor trough for grit. 
     From the sectional illustration of FIG. 2, it is evident from the arrows drawn there that the mill tube  10  and the material conveyor ring  20  of the drop-delivery housing can turn in the same direction. Different directions would also be possible, however. The sectional illustration in FIG. 2 further shows that plate type baffles  34  for guiding the sifted-air/ground-fine-material flow  35  are arranged in the drop-delivery housing in the flow path from the ground stock delivery openings  17  of the tube mill to the rotor of the rod basket sifter  31 . 
     FIG. 4 shows that the invention can also be used in a two-chamber tube mill with central delivery. In this two-chamber mill the ground stock delivery openings  17  of the drop-delivery housing, which surrounds the two grinding chambers  36 ,  37  and which is likewise composed of the two spaced stationary non-rotating side faces  18 , 19  and the rotatable material conveyor ring  20 , are arranged in the central longitudinal region. In the sifting space of the drop-delivery housing of the two-chamber mill, at least one sifter rod basket  31   a  is arranged, at whose two rotor ends (in a dual realization) a stream  27   a ,  27   b  of sifting air which is laden with sifted fine material is respectively vented, whereby the sifted oversized material that has collected on the periphery of the two halves of the rod basket is re-circulated to the grinding stock input of the one grinding chamber  36 , on one hand, and to the grinding stock input of the other grinding chamber  37 , on the other hand. 
     The invention can be applied not only in tube mills with a central drive, but also in tube mills with other drives, for instance toothed ring drives. 
     As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.