Tube mill

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.

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.

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 31a is arranged, at whose two rotor ends (in a
 dual realization) a stream 27a, 27b 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.