US3866842A

US3866842A - Grinding mill

Info

Publication number: US3866842A
Application number: US435854A
Authority: US
Inventors: Robert Linzberger
Original assignee: Buehler AG
Current assignee: Buehler AG
Priority date: 1973-01-24
Filing date: 1974-01-23
Publication date: 1975-02-18
Anticipated expiration: 1992-02-18
Also published as: ES422379A1; NL7400344A; DE2403351C3; FR2214526B1; CA1016923A; NL178753C; JPS5513782B2; NL178753B; GB1401415A; DE2403351B2; SU572183A3; DE2462414A1; IT1007568B; JPS49104381A; DD110435A5; FR2214526A1; CS170155B2; DE2403351A1

Abstract

A grinding mill has a housing which includes a feed hopper and a downwardly converging chamber located below the feed hopper and having an upper region and a lower region which is provided with an outlet. A pair of cooperating grinding rollers are arranged in substantially axial parallelism in the upper region of the chamber spaced from the feed hopper and define with one another a grinding gap from which ground material drops into the lower region. A first pneumatic conduit conveys material to be ground from the region of the feed hopper to the region of the grinding gap. A feeding arrangement feeds the ground material from the lower region through the outlet into a second pneumatic conduit, and a suction conduit is provided which has one open end portion communicating with the second pneumatic conduit and another open end portion located proximal to the grinding gap. The suction conduit serves to aspirate air from the first pneumatic conduit into the second pneumatic conduit via the region of the grinding gap, so as to maintain suction in this region and also-via the first pneumatic conduit-in the feed hopper.

Description

United States Patent Linzberger 1 Feb. 18, 1975 [541 GRINDING MILL 229,939 12/1969 U.S.S.R 241/47 [75] Inventor: Robert Linzberger, Saint Primary ExammerGranville Y. Custer, Jr. Gallen Bruggen Swltzefland Assistant Examiner1-Ioward N. Goldberg 1 1 Assigneei Gebluedel' Bllehlel' UZWil, Attorney, Agent, or Firm-Michael S. Striker Switzerland Filed: Jan. 23, 1974 Applv No.: 435,854

Foreign Application Priority Data Jan. 24, 1973 Switzerland 1012/73 Dec. 6, 1973 Switzerland... 17103/73 [52] US. Cl. 241/47, 241/225 [51] Int. Cl. B02c 23/02 [58'] Field of Search 241/47, 57, 58, 60, 62,

[56] References Cited UNITED STATES PATENTS 279,067 6/1883 Wolf 241/47 1,188,323 6/1916 Richardson. 241/57 1,991,757 2/1935 Lorentz 241/222 X 2,925,226 2/1960 Pratique 241/225 3,167,259 1/1965 Pitchford 241/47 X 3,468,488 9/1969 Karrer et al.. 241/225 X 3,545,686 12/1970 Brown 241/47 FOREIGN PATENTS OR APPLICATIONS 2,011,783 12/1969 Germany 241/62 [57] ABSTRACT conduit conveys material to be ground fromthe region of the feed hopper to the region of the grinding gap. A feeding arrangement feeds the ground material from the lower region through the outlet into a second pneumatic conduit, and a suction conduit is provided which has one open end portion communicating with the second pneumatic conduit and another open end portion located proximal to the grinding gap. The suction conduit serves to aspirate air from the first pneumatic conduit into the second pneumatic conduit via the region of the grinding gap, so as to maintain suction in this region and alsovia the first pneumatic conduitin the feed hopper.

26 Claims, 7 Drawing Figures HTENTEU FEB 1 8 5 SHEET 2 BF 7 FIG. 2,

GRINDING MILL BACKGROUND OF THE INVENTION The present invention relates to a grinding mill, and more particularly to a grinding mill wherein material is ground between two cooperating grinding rollers defining with one another a grinding gap.

Grinding mills of this general type are already well known and they are part of the state of the art. They are used for grinding various types of material that are admitted to the grinding gap via a feed hopper, frequently such materials as various types of foodstuffs. Generally speaking, the feeding of many of the materials to be ground proceeds satisfactorily in the prior-art grinding mills where the material supplied to the grinding gap has a substantially uniform veil of material. A pneumatic feed conduit is usedwhich serves to convey the material to the grinding gap, and at the air present at the end of the feed conduit is aspirated along the periphery of at least one of the grinding rollers in counterflow to the rotation of the same. This counteracts the tendency of the rapidly rotating grinding roller to take along the air in form of a boundary layer, and eliminates the interference which would otherwise be caused with the proper flow of the veil of material into the grinding gap.

The continuous removal of ground material and its conveying away is predominantly carried out in the prior art by a pneumatic suction conveying conduit; in some instances. a pressure conveying conduit is utilized. A suction conveying conduit has the advantage that the necessary suction which is required for the op eration of the pneumatic feed conduit can be directly communicated from below the grinding gap to above the grinding gap where the pneumatic feed conduit is located, whereas if a pressure conduit is used an injector will have to be interposed.

However, despite the many advantages possessed by this prior art type of grinding mill, there are certain disadvantages which must be rectified. In particular, it is not readily possible to provide for a uniform feeding via the pneumatic conduit of both lightweight and heavyweight materials to be ground, if uniform flowis to be achieved. To overcome this difficulty, it would be necessary to vary the air flow in the pneumatic feeding conduit, since an air flow which may be correct for feeding of heavyweight material may be excessive for lightweight material where too much of the light-weight material might be carried by the excessively strong air flow past the grinding gap and into the ground-material part of the mill, especially when the grinding rollers operate at high speed. However, the existing grinding mills cannot be so regulated to permit a variation in the air flow, and this therefore represents a substantial disadvantage.

SUMMARY OF THE INVENTION Accordingly, it is a general object of the invention to provide an improved grinding mill which avoids the aforementioned drawbacks.

More particularly, it is an object of the present invention to provide such an improved grinding mill wherein a reliable pneumatic feeding of material to be ground from the feed hopper to the grinding gap is assured under all circumstance, whether the material be light in weight or whether it be heavy.

Another object of the invention is to provide such an improved grinding mill which can be reliably and uniformly operatedeven at high rotational speed of its grinding rollers and at high throughput, i.e., in circumstances where a reliable and uniform feeding of the material to be ground is highly questionable in the priorart constructions due to the strong air currents which develop.

An additional object of the invention is to provide such an improved grinding mill in which any interference with the proper flow of the material and with the proper operation, resulting from variations in flow or pressure of air, will be reliably avoided.

Still a further object of the invention is to provide such an improved grinding mill wherein the various controls that most normally be carried out during the operation of the grinding mill, for instance the taking of samples or the like, can be carried out without the undesired escape of dust or the like, and in particular without causing any variation in the grinding effect itself, so that all controls and all samples that are taken will not be falsified by such undesiredinfluences.

In keeping with the above objects, and with others which will become apparent hereafter, one feature of the invention resides, in a grinding mill, in a combination which comprises wall means defining a' housing including a feed hopper and a downwardly converging chamber located below the feed hopper and having an upper region and a lower region provided with an outlet. A pair of cooperating grinding rollers are arranged in substantial axial parallelism in the upper region of the chamber spaced from the feed hopper and defining with one another a grinding gap from which ground material drops into the lower region. First pneumatic conduit means conveys material to be ground from the region of the feed hopper to the region of the grinding gap. Second pneumatic conduit means is provided, and feed means feeds ground material from the lower region through the outlet into the second pneumatic conduit means. Suction conduit means is provided, having one open end portion which communicates with the second pneumatic condiut means, and another open end portion which is located proximal to the grinding gap for aspirating air from the first pneumatic conduit means into the second pneumatic conduit means via the region of the grinding gap, whereby to maintain suction in the region of the grinding gap and via the first pneumatic conduit means in the feed hopper.

The novel features which are considered as characteristic for the invention are set forth in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with ad ditional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is-a somewhat diagrammatic vertical section through a first embodiment of the invention;

FIG. 2 is a view similar to FIG. 1, illustrating a second embodiment of the invention;

FIG. 3 is a view similar to FIG. 2, illustrating a third embodiment of the invention;

FIG. 4 is a view similar to FIG. 3, illustrating a fourth embodiment of the invention;

FIG. is a view similar to FIG. 4, illustrating a fifth embodiment of the invention;

FIG. 6 is a front view of another embodiment of the invention; and

FIG. 7 is a view similar to FIG. 1 but illustrating still a further embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring firstly to the embodiment illustrated in FIG. 1, it will be seen that reference numeral 1 identifies a housing including two frames 2 (only one shown) which are connected with one another by braces 3 extending normal to the plane of the drawing in FIG. 1, and by walls 4 extending in the same direction. Mounted in the housing are two

grinding rollers

6 and 7 of which the roller 6 is usually driven at a higher speed of rotation than the roller 7, with their direction of rotation being indicated by the arrows. The

rollers

6 and 7 define with one another a grinding gap from which ground material drops downwardly under the influence of gravity. The right-hand side of the housing 1 in FIG. 1 is the front side, that is the side which must be accessible to an operator, whereas the left-hand side is the rear side.

The grinding mill is provided with a funnel-shaped hopper 9 which extends over the entire length of the

rollers

6, 7, Le, normal to the plane of FIG. 1, and which communicates with a feed arrangement using a feed roller 10 and a damming member 11, the latter of which is pivotably mounted for movement about a pivot axis 12. The feed roller 10 and the damming member 11 together serve to distribute the material coming from the hopper 9, so that it will be supplied in form of an even veil of material into the grinding gap 15. The spacing of the member 11 with respect to the flows between them towards the gap 15, can be automatically regulated in a manner which is known per se and, therefore, need not be described herein. The inlet baffle 13 of a pneumatic feed channel is arranged downstream of the feed roller 10 and serves to guide the material from the feed roller 10 into the pneumatic feed channel 14 wherein it is conveyed to the grinding gap 15.

The walls 4 of the housing form a closed interior for the housing, except for the presence of aspiration openings 22 which will be discussed later, in which suction can be maintained to prevent the escape of dust and the like. The lower portion of the housing is configurated as a funnel-shaped region 19 which communicates via a lower outlet (shown, but not separately provided with a reference numeral) with a feeding arrangement through which ground material is removed from the funnel-shaped chamber 19.

In the region of the

rollers

6, 7 the walls 4 are so con-v feed roller 10, and thereby the quantity of material that tion conduit through which the ground material is removed. The conduit 31 is connected with an appropriate source of suction (not shown) and the injector 30 is provided with an inlet nipple 43 through which additional air may be allowed to enter, if necessary.

At the front side the grinding mill is provided in the upper region with a control flap 21 which forms an aspiration opening 22 together with the guide baffle 17, which opening 22 extends over the entire length (in direction normal to the plane in FIG. 1) of the housing. In the region of the gap 15, the channels 18 are provided with a throttle gap 23, and the channel 18 associated with the grinding roller 6 is formed in the region of the gap 15 with an aspiration-controlling slide 24. A suction conduit 41 extends to the region of the periphery of the roller 7, having an inlet end proximal to the grinding gap 15 and an outlet end which is connected with the conduit 31. A throttle 42 which in the illustrated embodiment is adjustable. is interposed in the suction conduit 41.

It will be appreciated that in operation, the material to be ground is admitted into the hopper 9 from where it is conveyed by the rotating feed roller 10 into the feed channel 14. A quantity of material being conveyed can be controlled by pivoting the member 11 so that it defines a larger or smaller gap with the periphery of the feed roller 10. The air that is being drawn through the feed channel 14 due to the suction exerted by the suction conduit 41, accelerates the material in the feed channel 14 and causes it to enter into the grinding gap 15 where it is ground.

It is an essential concept of the invention that the air flow conditions are controlled and maintained in optimum parameters in each operating condition of the mill. This is done by the presence of the suction conduit 41 which, because of the manner in which it communicates with the gap 15 and the channel 14, makes it possible to provide such a control in the region of the gap 15. In particular, the presence of the channel 41 makes it possible to maintain suction in the region of the gap 15 and thus also in the channel 14 and, to someextent, also in the hopper 9. Air is also drawn into the condiut 41 via the openings 22.

The channel 14- constitutes with the conduit 41 an independent feeding and air system, which makes'possible an optimum feeding of material to the gap 15, irrespective of the particular'type of material which is to be ground, and even at high speed rotation of the

roller

6, 7 and high throughput of material. The air flow in the channel 14 can be regulated, if necessary, by operating the throttle 42. The material supplied by the feed roller 10 is engaged by the air stream entering the channel 14 in the region of the inlet baffle 13, and is accelerated and flung at relatively high speed into the grinding gap 15. The air which issues in the region of the grinding gap 15 from the channel 14 is predominantly drawn into the suction conduit 41 and from there enters the conduit 31 where it serves as the conveying medium for the ground material which travels in the conduit 31. A part of the air which enters through the opening 22 is diverted via the slide 24 into the channel 18 and serves to introduce the ground material into the injector 30.

Theeffectiveness of the novel construction,'and the fact that the objects ofthe invention are achieved by it, can be readily demonstrated by removing a sample of the ground material. For this purpose, the door 26 is opened and it has been found that the air which is now drawn in through the opeining exposed by the door 26 does in no way influence the pneumatic feeding of material in the channel 14 or the conduit 31. The reason for this is that the air which is required for such feeding now enters at least in part through the opening exposed by the door 26, instead of enteringas previously via the slide 24. It has also been found that the uniform supply of material to the grinding gap 15 is in no way influenced by opening the door 26, because the air flow condition in the channel 14 is not varied thereby. This means, of course, that the grinding operation is not at all influenced when the door 26 is opened, a condition which is highly advantageous because it is, of course, necessary if a proper sample is to be obtained.

The throttle 42 could be omitted, if desired, but in many instances its presence will be effica cious because it permits a control of the air flow, the pressure conditions and largely also the material flow conditions in the grinding gap 15,- if and when necessary. The air flow could, of course, also be obtained in accordance with a desired parameter by appropriate dimensioning of the conduit 41 and/or the conduit 31.

As will be seen subsequently in the discussion of FIG. 3, the injector 30 could be eliminated in favor of a bucket wheel 44, but even in this case it is advantageous to aspirate the chamber 19. If additional air is required to be admitted for the operation, particularly in the lower portion of the conduit 3] intermediated the injector 30 and the point where the conduit 41 communicates with the conduit 31, then such additional air can be admitted via the inlet nipple 43 of FIG. 1.

Coming now to the embodiment in FIG. 2, it will be seen that this is reminiscent of that in FIG. 1, and that like reference numerals have been used to define like elements. In this embodiment, however, the suction conduit is identified with reference numeral 27 and extends partly around the periphery of the roller 7 and along the rear wall of the housing or more particularly of the funnel-shaped chamber 19. In order to prevent any interference in the proper operation of the suction conduit 27, for instance due to varying pressure conditions in the chamber 19, a seal 28 is interposed between the roller 7 and the conduit 27, so that the latter cannot directly communicate with the chamber 19.

It is advantageous to provide the injector 30 with a regulating baffle or adjustable control flap 30 to more effectively control the air flow conditions in the channel 14 and the feeding conditions in the ejector 30. This is a particularly advantageous arrangement because the advantages of the invention can be obtained with a very simple construction, and in particular no separate conduit is required which could interfere with the manipulations of personnel required to work on the mill.

Coming to the embodiment of FIG. 3, which again uses like reference numerals for like elements as in the preceeding embodiments, it will be seen that here the member 11 of FIG. 1 is replaced by a baffle 61 which is already known per se from the art and which is mounted for turning movement about a pivot 62. The purpose and operation of the member62 is the same as that of the member 11. The baffle 62 is provided with a longitudinally extending (normal to the plane of FIG. 3) arcuately curved portion 63 in order to guide the material to the inlet baffle 13 of the feed channel 14.

In this embodiment, a compartment 65 is provided which is in part defined by the periphery of the grinding roller 6; it serves primarily to accommodate the air which issues-from the outlet end of the channel 14 and which is withdrawn via the suction conduit 66 that communicates with the compartment 65. The air flow could be regulated by an opening the cross section of which could be controlled if desired.

The suction conduit 66 communicates with the con duit 31 via a conduit portion that connects it first with the bucket wheel 44 interposed in the outlet of the chamber 19 and then with the lower end of the conduit 31. The bucket wheel 44 turns and discharges the ground material accomodated in each of its buckets or divisions, into the conduit which communicates with the conduit 31. A small gap 68 exists between the channel l4 and the roller 7, and a small amount ofthe air issuing from the channel 14 escapes from this-gap 68 along the roller 7 and into the chamber 19. The chamber 19 can be placed under suction, for instance via the conduit 66. This embodiment, incidentally, has the advantage that due to the cross-sectional configuration of the chamber 19 it is possible to locate the drive motor 69 which drives the

rollers

6, 7 and 10 in a manner not illustrated, but conventional, within the housing inter mediate the two frames 2 thereof, thereby both affording good access to the drive and at the same time providing a space-saving construction.

The embodiment in FIG/4 is reminiscent of that in FIG. 3, and like reference numerals identify like components as before. In FIG. 4, however, the suction conduit 66 is connected with the suction side of a blower 71. The pressure side of the blower 71 communicates with a conduit 72 which in turn is connected with the concuit 31, and injector 67 being formed which corresponds to the injector 30 of FIG. 1 in structure and in operation. In this particular embodiment, the conduit 31 could be operated as a pressure conduit or as a suction conduit, depending upon particularrequirements, by making simple modifications to convert from one type to another.

The embodiment of FIG. 5 is also reminiscent of that in FIGS. 3 and 4. Here, the conduit 72 is 'connectedvia an outlet 81 with the lower portion of the chamber 19.

A curved injector 82 communicates the outlet of the chamber 19 with the conduit 31.

In this embodiment, the orientation ofthe outlet 81 is such that air which is expelled from it into the chamber 19 has a main component of flow which is directed towards the injector 82. This embodiment is particularly suitable if materialis to be ground, and subsequently inserted into the conduit 31, which is difficult to convey and where the particular effect of the air stream issuing from the outlet 81 is required in order to aid the entry of the material into the injector 82. A seal is provided between the wall 84 of the channel 14 and the roller 7, to prevent the entry of air which travels around with the periphery of the roller 7, into the grinding gap 15.

In FIGS. 35 I have illustrated how the suction conduit 66 can be located in part at least outside the housing of the grinding mill. FIG. 6, by contrast, shows that a much more space-saving construction can be ob tained if the suction conduit 66 is so located that it is laterally adjacent the chamber 65, which can be given the configuration of the chamber 19 in FIG. 6, for example, and if the conduit 66 extneds along the frames 2 to the injector 67 and from there communicates with.

the conduit 31. In all other respects, the embodiment of FIG. 6 corresponds to the preceding embodiments.

FIG. 7, finally, illustrates yet a further embodiment of the invention which is highly advantageous. Like reference numerals again identify the same elements as in the preceding embodiments.

In FIG. 7, however, the feed hopper 9 has located in it a rotating vane wheel 16 or the like, which serves to constantly loosen up the material in the hopper 9 and prevent it from caking. The suction conduit 27 extends partly about the periphery of the roller 7 and extends along the rear wall 4 bounding the chamber 19, in a manner analogous to FIG. 2. A seal 28 is provided between the conduit 27 and the roller 7 to prevent interference of pressure variations in the chamber 19 with the conditions in the conduit 27.

in order to assure that the air conditions in the channel 14 and the feeding conditions in the injector 30 can be regulated at will, a flap 30 is provided in association with the injector 30. This is a particularly advantageous solution, because the control can be effected with very simple means. The flap 30' is, of course, pivotable about the indicated pivot axis, as is the flap 30' in FIG. 2.

The rear end wall portion 97 bounding the chamber 19 is removable, so as to facilitate access to the interior, particularly to the lower part of the conduit 27 and to the injector 30. An upright hollow shaft 90 is pro-' vided which constitutes an extension of the conduit 27 and reaches to the upper edge 91 of the housing 1, or to the level of the hopper 9. The upper open end of the shaft 90 is closed from the outside by a closure member 92 which is advantageously of wood, as illustrated in the cross-sectional showing of FIG. 7, and which airtightly closes the open end of the shaft 90 with a flange 93. A portion 94 of the member 92 extends into the shaft 90 and has a side facing towards the interior of the hopper 9 and being arcuately curved so that an opening 95 which communicates the hopper 9 with the shaft 90 is provided with an aerodynamically advantageous cross section.

A flap 96 is provided which can increase or decrease the effective cross section of the opening 95. The flap 96 could be replaced with another control member, for instance a sliding member or the like, and appropriate levers can be utilized for effecting this movement from the exterior of the mill. The flap 96-or analogous element must be so configurated that material which drops into the hopper 9 in the direction of the arrow, cannot enter into the opening 95 and thus cannot be carried along by the air stream which enters from the hopper 9 through the opening'95 into the shaft 90. On the other hand, there is nothing to interfere with the entry of such air through the opening 95, which means that excess air is removed from the hopper 9 and the escape of dust and the like is suppressed. Thus, the hopper 9 is constantly under a slight suction.

The rather surprising advantage which has been observed in connection with this embodiment is that both the conditions of air prevailing in the gap and the conditions of the air in the hopper 9 are both actively controllable with this embodiment. The quantity of air for the channel 14 and the excess air in the hopper 9 can both be removed and can be fully utilized for the pneumatic transportation of ground material which advances in the conduit 31. 9

Together with the construction of the hopper 9, the flap 96 or its analogous replacement consititutes a separator, inasmuch as very fine particles constituting a part of the material admitted into the hopper 9 can be carried by the air through the opening 95 and into the shaft 90. This is permissible because such very fine parts which are smaller than the particles of ground material can, of course, readily be admixed with the ground material particles without any difficulties. This solution makes it possible to eliminate many additional conduits, blowers, filters and the like, which were previously necessary, because the conduit 31 makes it possible to appropriately and properly control the entire air flow and air pressure conditions in the mill, and to regulate them to an optimum extent. 7

Particularly if the grinding mill according to the present invention is used for grinding foodstuffs for human use, for instance various grains or the like, it is frequently necessary to remove samples of the ground material directly from the chamber 19, in order to test for possible changes in the dimension of the gap 15 and consequent changes in the granulation of the ground product, changes in the moisture content or the like. For this reason, all grinding mills of the type in question are provided with a control door 26 through which such access is afforded. As previously already indicated, the advantages of the present invention are particularly emphasized when one attempts to remove such a sample, because the opening of the control door 26 in a grinding mill according to the present invention in no way influences the air flow and air pressure conditions in the grinding mill, and thus can under no circumstances disadvantageously. influence the operation of the mill.

The shaft 90 in the embodiment of FIG. 7 could, if desired, be provided with the member 92v at a lower level, and laterally rather than on top. However, in most instances it has been found that the location shown in FIG. 7 is the most advantageous one. It will be appreciated from a consideration of FIG. 7 that both the shaft 90 and the conduit 27 can be simply and readily cleaned if and when this is necessary, a consideration which is important in particularly those instances where foodstuffs for human consumption are being ground.

In addition to overcoming the disadvantages of the prior art, and thus meeting the objects of the invention, the grinding mill according to the present invention improves on the economy of operation which heretofore could be obtained with analogous grinding mills. Moreover, the transportation of ground material from the chamber 19 is completely independent of the supply of material to the grinding gap, and the grinding of the material in the gap. This means that in particular the entry of the material from the hopper 9 to the grinding gap 15 can be controlled to conditions which are considered optimum, under all circumstances and without having to consider the removal of the ground material. The infiltrated air" which enters when the door 26 is opened for removal of a sample or the like, does in no way influence the proper operation, such as the grinding itself, and thus it is now possible to obtain a sample which is not falsified by a temporary change in the operating conditions that occurs in the prior art when a door similar to the door 26 is opened.

. The air required for the transportation of material in the channel 14 can in its entirety be used for subsequent transportation of ground material in the-conduit 31, without requiring separate aspiration devices.

It goes without saying that the channels 18 may be provided for only one of the rollers 6 or for both of them. It is particularly advantageous if they are provided for both of the rollers, because this eliminates the so called fioating" of material and causes a partial cooling of the rollers which is desirable. In the case of embodiments such as those in FIGS. 4 and wherein a blower 71 is utilized, the conduit 31 can be operated as a pressure conduit, rather than as a suction conduit. However, if desired, it can nevertheless be in addition connected with a source of suction, in whichcase the conveying effectiveness will be further enhanced. However, it is then important to assure that the connection of the pressure side of the blower, such as the blower 71, with the conduit or passage having the feeding arrangement (such as the bucket wheel or the injector) therein be at the upstream side of the feeding arrangement.

The arrangement of FIG. 6 is particularly advantageous in terms of its reduced space requirements, because due to the fact that the conduit or conduits 66 are located laterally of the chamber 65 (equivalent to the chamber 19) extending along the back thereof, reduces the depth of the mill from the front towards the rear side thereof. It is particularly advantageous in applications where space is at a premium and where two of the grinding mills must always be arranged back-toback.

In the embodiment of FIG. 7, it is conceivable to eliminate the movable flap 96 (or its equivalent movable element) in favor of an opening 95 havine a fixed preselected effective cross-sectional area. The area can be readily determined empirically, independence upon the requirements which are made in a particular instance.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the type described above.

While the invention has been illustrated and described as embodied in a grinding mill, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

1. In a grinding mill, a combination comprising wall means defining a housing including a feed hopper and a downwardly convergent chamber located below said feed hopper and having an upper region and a lower re-- gion provided with an outlet; a pair of cooperating grinding rollers arranged in substantial axial parallelism in said upper region of said chamber spaced from said feed hopper and defining with one another a grinding gap from which ground. material drops into said lower region; first pneumatic conduit means for conveying material to be ground from theregion of said feed hopper to the region of said grinding gap; second pneumatic conduit means; feed means for feeding ground material from said lower region through said outlet into said second pneumatic conduit means; and suction conduit means having one open end portion communicating with said second pneumatic conduit means, and another open end portion located proximal to said grinding gap for aspirating air from said first pneumatic conduit means into said second pneumatic conduit means via the region of said grinding gap, whereby to maintain suction in the region of said grinding gap.

2. A combination as defined in claim'l, wherein said other open end portion is located adjacent the periphery of one of said grinding rollers.

3. A combination as defined in claim 1; and further comprising sealing means interposed between said one grinding roller and part of an edge bounding said other open end portion.

4. A combination as defined in claim 2, wherein said feed means comprises injector means for feeding the ground material by injector action into said second pneumatic conduit means,

5, A combination as defined in claim 4, wherein said injector means comprises an adjustable control flap for varying said injector action.

6. A combination as defined in claim 1, wherein said chamber is funnel-shaped and has a front wall and a rear wall; and wherein said suction conduit means extends along said rear wall.

7. A combination as defined in claim 6, wherein said suction conduit means forms a passage which extends partly about the periphery of one of said grinding rollers and is in part defined by said periphery.

8. A combination as defined in claim 6, wherein said suction conduit means includes a substantially vertical hollow shaft extending in the region of said rear wall from said lower region to the region of said feed hopper.

9. A combination as defined in claim 8, wherein said shaft has an opening; and further comprising remov able closure means which movably closes said opening of said shaft..

10. A combination as defined in claim 9, wherein said opening of said shaft is located in the region of said feed hopper. Y

11. A combination as defined in claim 8, wherein said shaft has an opening which communicates with the interior of said feed hopper; and further comprising varying means for varying the effective cross section of said opening of said shaft so that, depending upon the suction exerted in said feed hopper via said opening of said shaft, lightweight components of the material admitted into said feed hopper can be withdrawn from the latter and into said shaft via said opening of said shaft.

12. A combination as defined in claim 11, wherein said varying means comprises a pivotally suspended flap which is so configurated as to direct material which is being admitted into said hopper away from opening said shaft.

13. A combination as defined in claim 11, wherein said varying means comprises a slide member which is so configurated as to direct material which is being admitted into said hopper, away from said opening of said shaft.

14. A combination as defined in claim 11, wherein said shaft has an additional opening located upwardly of the first-mentioned opening; and further comprising a removable closure member closing said additional opening and having a portion which extends into said shaft towards said first-mentioned opening, said portion of said closure member having a side facing towards said first-mentioned opening and being rounded so as to define a flow guide for matter entering via said first-mentioned opening.

15. A combination as defined in claim 1, wherein said first pneumatic conduit means forms a throttling gap with one of said grinding rollers.

16. A combination as defined in claim 1; and further comprising throttling means interposed in said suction conduit means.

17. A combination as defined in claim 16, wherein said throttling means comprises an adjustable throttling flap for varying the suction which acts in the region of said grinding gap and in said feed hopper.

18. A combination as defined in claim 1, wherein said wall means comprises a wall portion which together with one of said grinding rollers defines a compartment that communicates with said grinding gap; and wherein said other open end portion of said suction conduit means communicates with said compartment.

19. A combination as defined in claim 1; and further comprising means defining a throttling gap between one of said grinding rollers and said other open end portion of said suction conduit means.

20. A combination as defined in claim 1; and further comprising blower means having a suction side connected with said suction conduit means, and a pressure side connected with said first pneumatic conduit means upstream of said grinding gap.

21. A combination as defined in claim 20, wherein said feed means comprises a conduit communicating with said outlet and with said suction conduit means; and wherein said suction side of said blower means communicates with said conduit upstream of said outlet and said suction conduit means.

22. A combination as defined in claim 20, wherein said feed means comprises injector means communicating with said outlet; and wherein said pressure side of said blower means has a discharge opening which communicates with the interior of said chamber in said lower region and has such an orientation that air expelled from said opening has a major component of movement in direction towards said outlet.

23. A combination as defined in claim 1, wherein said feed means comprises a bucket wheel.

24. A combination as defined in claim 1, wherein said feed means comprises injector means.

25. A combination as defined in claim 1; and further comprising aspiration openings provided in said wall means and communicating with the interior of said housing.

26. A combination as defined in claim 1; and further comprising curved guide baffle means defining with at least one of said grinding rollers an air channel which partly surrounds the periphery of said one grinding roller and communicates with said chamber.

Claims

1. In a grinding mill, a combination comprising wall means defining a housing including a feed hopper and a downwardly convergent chamber located below said feed hopper and having an upper region and a lower region provided with an outlet; a pair of cooperating grinding rollers arranged in substantial axial parallelism in said upper region of said chamber spaced from said feed hopper and defining with one another a grinding gap from which ground material drops into said lower region; first pneumatic conduit means for conveying material to be ground from the region of said feed hopper to the region of said grinding gap; second pneumatic conduit means; feed means for feeding ground material from said lower region through said outlet into said second pneumatic conduit means; and suction conduit means having one open end portion communicating with said second pneumatic conduit means, and another open end portion located proximal to said grinding gap for aspirating air from said first pneumatic conduit means into said second pneumatic conduit means via the region of said grinding gap, whereby to maintain suction in the region of said grinding gap.

2. A combination as defined in claim 1, wherein said other open end portion is located adjacent the periphery of one of said grinding rollers.

4. A combination as defined in claim 2, wherein said feed means comprises injector means for feeding the ground material by injector action into said second pneumatic conduit means.

5. A combination as defined in claim 4, wherein said injector means comprises an adjustable control flap for varying said injector action.

9. A combination as defined in claim 8, wherein said shaft has an opening; and further comprising removable closure means which movably closes said opening of said shaft.

10. A combination as defined in claim 9, wherein said opening of said shaft is located in the region of said feed hopper.