US 3739991 A
In a vibrating mill installation having a horizontally extending grinding chamber between a closed material feed device and a closed material discharge device the grinding chamber is provided between its ends with a plurality of serially arranged openings from which portions of gas are withdrawn by pipelines leading to the suction side of a blower or pump, while a cooling agent -such as liquid nitrogen-is introduced into the grinding chamber and cools the material being ground therein. The pressure side of the blower or pump is connected with the material feed device so that the still cool gas withdrawn from the grinding chamber is used to subject the material in the feed device to a preliminary treatment before the material to be ground enters the grinding chamber of the vibrating mill.
Description (OCR text may contain errors)
United States Patent Wehren et a1.
VIBRATING MILL Inventors: Peter Wehren; Helmut Haas;
Gerhard Demel, all of Cologne.
Germany Assignee: Klockner-Humboldt-Deutz Aktiengesellschaft,Cologne,Germany Filed: Sept; 29, 1971 Appl. No.: 134,795
Foreign Application Priority Data Oct. 5, 1970 Germany P 20 48 810.2
US. Cl. 241/45, 241/58, 241/153,
241/175 Int. Cl. B02c 19/16 Field of Search 241/17, 23, 24, 27,
 References Cited UNITED STATES PATENTS 2,031,710 2/1936 lhlefeldt 241/45 3,310,245 3/1967 Decker et a1. 241/175 X 3,510,074 5/1970 Edwards et a1. 241/175 X 1 ,iiiiiie i191,
3,658,259 12/1970 Ledergerber 241/65 X FOREIGN PATENTS OR APPLICATlONS 1,283,676 12/1961 France 241/175 Primary ExaminerGranville Y. Custer, .lr. Attorney-Singer, Stern & Carlberg  ABSTRACT In a vibrating mill installation having a horizontally extending grinding chamber between a closed material feed device and a closed material discharge device the grinding chamber is provided between its ends with a plurality of serially arranged openings from which portions of gas are withdrawn by pipelines leading to the suction side of a blower or pump, while a cooling agent such as liquid nitrogen-is introduced into the grinding chamber and cools the material being ground therein. The pressure side of the blower or pump is connected with the material feed device so that the still cool gas withdrawn from the grinding chamber is used to subject the material in the feed device to a preliminary treatment before the material to be ground enters the grinding chamber of the vibrating mill.
7 Claims, 1 Drawing Figure Pmmcom 3.139.991
I IN VE N TORS Peter Mk re), Helm! Haas 4 Gerlza rd Dene! VIBRATING MILL The invention relates to a grinding mechanism employing a vibrating mill having a closed material feed means and a closed material discharge means.
Grinding installations employing vibrating mills are preferably used for fine and superfine crushing or grinding operations. In this type of vibrating mills it is necessary that not only the material feed device, but also the material discharge device is closed so that the fine and superfine ground material cannot escape outwardly. Only in this manner is it possible to avoid losses of material and a contamination of the environment. It has now been discovered that in this type of vibrating mills the capacity of the grinding operation became considerably reduced. A reduction of the grinding capacity heretofore was avoided in that the vibrating mill was cooled from the outside by water. Such a watercooling operation, however, has disadvantages because when only a simple spraying or sprinkling is employed a considerable contamination of the environment took place, while on the other hand the employment of a water jacket around the vibrating mill leads to considerable difficulties in the construction of the installation.
It is an object of the invention to provide a structure for preventing a reduction of the grinding capacity of this type of vibrating mills, in that with reference to the longitudinal direction of the grinding space at one or more points in the rear of the material feed opening of the vibrating mills, a portion of the gases in the grinding space is being withdrawn. This structure avoids the disadvantages which are present when the vibrating mill is cooled with water.
According to the present invention, the amount of gas is withdrawn from the grinding space or grinding chamber at a predetermined pressure. This permits one to determine in a simple manner the maximum permissible amount of gas to be withdrawn at which no reduction of the grinding capacity takes place, while on the other handfor instance when measuring first the grinding capacity and then determining the adjustment of the amounts of gas to be withdrawnsuch a method is very complicated and owing to the long delay period caused by the determination of the grinding capacity is also inaccurate. In accordance with the invention, the determination of the amount of gas to be withdrawn preferably takes place in such a manner that the adjustment of the predetermined pressure takes place by adjustable throttling means arranged in at least one of the pipelines connected with the gas withdrawal openings. This has the advantage that at the same time as the adjustment of the optimum amount of gas to be withdrawn corresponds to a maximum grinding capacity, a corresponding graduation of the adjustment of the pressures at the throttling points occurs and the flow of the gas will be in the same direction as the passage of the material to be ground through the grinding space. The gas which is withdrawn flows over the surface of the material being ground in the same direction in which the material in the grinding space is moved during the grinding operation. In this manner one also obtains the advantage that already sufficiently ground material at a suitable adjustment owing to the prevailing direction of the gas stream will leave the vibrating mill with increased speed which increases the grinding efficiency.
In accordance with the invention, the withdrawal of the gases from the grinding chamber takes place in such a manner that at the gas discharge openings a reduced pressure is produced. The reduced pressure at the gas withdrawal openings is suitably produced by the suction side of a blower or a pump. This has the particular advantage that, if necessary, the grinding space will have approximately the same pressure as the environment. Another advantage is that-for instance during the grinding of poisonous substances-the application of smaller negative pressure almost entirely prevents the escape of fine portions of the poisonous substances which owing to leaks of the mill may occur, but can now be controlled. The invention can also be applied with advantage to grinding operations in which the material to be ground is made brittle with the assistance of a refrigerant-for instance liquid nitrogen- -and therefore it is now possible to improve the grinding of different types of materials in vibrating mil1s-for instance plastics, which heretofore could not be ground at all.
The invention preferably employs a vibrating mill comprising two parallel grinding tubes. In this vibrating mill the material feed opening is connected to a material feed device which subjects the material to be ground to a preliminary treatment, such as a cooling device. The present invention is distinguished in this in that each grinding tube is provided with at least one withdrawal opening for the gases and these openings are connected by pipelines with a reduced pressure source. In this manner it is very simple to catch a pres sure rise in each grinding tube even when cooling agents are additionally introduced.
In accordance with the invention, the installation is provided with an adjustable throttle device in each pipeline which extends from a gas withdrawal opening to the reduced pressure source. In this manner it is possible to maintain a predetermined pressure in each grinding chamber. When a plurality of gas withdrawal openings is arranged in series, it is possible even when a relatively large amount of gas is to be withdrawn, to keep the speed of the individual withdrawn gas streams within limits above the one of the material being ground in the grinding chambers. At a too high gas speed the duration of the material in the grinding chamber and, therefore, the degree of reduction of the material would be too small. Preferably a blower or av pump whose suction sides are connected with the gas withdrawal openings of the grinding chambers is used as a source of reduced pressure.
In accordance with another object of the invention, the pressure side of the blower or the pump is connected by a pipeline with the feed device of the vibrating mill which is used for a preliminary treatment of the material to be ground. This feed device in this particular embodiment of the invention comprises a cooling device. The arrangement of the cooling device has the advantage that the gases which are withdrawn from the vibrating mill, in the event of the introduction of cooling agents into the grinding chamber, may still be exploited for the cooling or precooling of the material to be ground before they are discharged into the atmosphere. An advantage of this arrangement resides in the fact that the gases which are withdrawn from the grinding chamber during the movement through the material to be ground in the feed device will be freed of any dust because the latter will be deposited on the material to be ground while in the feed device. In the event that for technical grinding reasons this is not desired when grinding certain materials, the removal of the dust from the gases may take place prior to their introduction into the feed device-for instance in a cyclone dust separator. For an improved regulation, it is advisable that an adjustable throttle device be arranged in the pressure line between the blower and the heat exchange device.
Still another object of the invention is the arrangement of a material lock which is impermeable to gas between the feed device and the material receiving opening of the vibrating mill. This has the advantageous re sult that the gas flow which takes place in the grinding chamber moves only in the direction in which the material to be ground moves through the grinding chamber, so that the material passage through the mill is not impaired. Preferably, the material lock is constructed in the form of a so-called bucket wheel lock which assures an almost complete sealing of the grinding chamber with respect to the feed device with reference to the passage of the gases from the grinding chamber into the feeding device. Another advantage resides in the fact that the rotative speed of the bucket wheel lock in addition permits a simple manner of dosing of the material to be ground into the grinding chamber.
It is also an object of the invention to provide the material discharge opening of the vibrating mill with a material lock which is impermeable to gas, preferably a bucket wheel lock, since in this manner the adjustment of the pressure prevailing in the grinding chamber and the adjustment of the speed of the gas flow in the grinding chamber by means of adjustable throttling devices may be substantially facilitated.
For the purpose of explaining the invention, reference is made to the accompanying drawing.
A vibrating mill is shown which includes two horizontally disposed grinding tubes 2 and 3 which are connected with each other and are vibratorily supported and provided with an out-of-balance drive, and has its material feed opening 4 connected by means of a flexible intermediate member 5 with a material feed device 6. This material feed device 6 is used for a preliminary treatment of the material to be ground and in the present instance comprises a cooling device. The cooling device is connected by a pipeline 7 with a substantially horizontally disposed conveyor device 8-for instance comprising a vibrating conveyor tubeand the latter receives the material to be ground from a supply bin 9.
The two grinding tubes 2 and 3, which are both filled with grinding bodies, are connected with each other by a pipeline 10 in such a manner that the material to be ground passes first through one of the tubes 2 and then through the other one of the tubes in series. The material discharge opening 11 of the grinding tube 3 is connected by a flexible intermediate tubular member 12 with a collecting container 13 into which the ground material is discharged. In place of the illustrated series arrangement of the grinding tubes 2 and 3, it is also possible to arrange these tubes parallel with each other depending upon the type of material to be ground in the vibrating mill.
In the connecting line 14 between the cooling device 6 and the material feed opening 4 and also between the material discharge opening 11 and the collecting container 13 are arranged a bucket wheel lock 15 and 16, respectively, for adjusting the material feed and the material discharge, respectively.
In the cooling device 6 which preferably is constructed in such a manner that a direct contact between the material to be ground and the cooling agent is possible, a cooling agent is introduced whichdepending upon the degree of cooling required-comprises a gas or a liquid or a vaporous cooling agent, for instance nitrogen. The cooling device is preferably constructed so that the liquid or vaporized nitrogen cannot directly reach the vibrating mill. For the maintenance of the low temperature, additional nitrogen is introduced in closed quantities directly into the grinding chamber either in a liquid or in a vapor form. This is accomplished preferably in the range of the point at which the material to be ground enters the grinding tube, namely at the range of the material feed opening 4 in the grinding tube 2 and in the range of the connecting pipe 10, where the latter is connected with the grinding tube 3.
The grinding tube 2 and also the grinding tube 3, with reference to the direction of movement of the material as indicated by the arrows 30 and 30, are provided in the center of their grinding chambers and at their ends with gas withdrawal openings 17, 18 and 19, 20, respectively, and these openings are each connected by suitable flexible intermediate tubular members with pipelines 21, 22, 23 and 24. For the purpose of avoiding cold losses these pipelines up to the flexible connecting members are heavily insulated. The pipelines 21, 22, 23 and 24 areconnectecl with a manifold 25 and the latter is connected with the suction side of a blower 26. In each of the pipelines 21, 22, 23 and 24 is arranged a pressure gauge 27. Furthermore, looking in the direction of the flow of the gases, in the rear of each pressure gauge is arranged an adjustable throttling device 28. The pressure side of the blower 26 is connected by a pipeline having a throttle 28 and gauge 27, 29 the cooling device 6. If the material to be ground is, for instance, cooled with liquid nitrogen, then for the purpose of saving nitrogen the gases withdrawn by the pipeline 29 are introduced for a preliminary cooling of the material to be ground into the material feed devices which are connected with the cooling device 6.
The operation of the installation is substantially as follows:
The material to be ground is taken by the vibrating tube conveyor 8 from the supply bin 9 and is conveyed into the pipeline 7 and by the latter into the cooling device 6. In the cooling device 6 the material to be ground comes into direct contact with liquid nitrogen and is sufficiently cooled so that the material becomes brittle and a very good grindability is obtained, or the grindability is improved therewith. The bucket wheel lock 15 delivers the material to be ground to the feed opening 4 of the grinding tube 2 of the vibrating mill in dosed quantities. Since the movement of the material to be ground in the grinding tubes of the vibrating mill takes place according to the displacement principle, the material to be ground moves under the influence of the continuously newly supplied amounts of material and under the vibrating movements of the grinding tubes first in the direction of the arrow 30 through their grinding tube 2 and is crushed or ground therein by the grinding bodies; then the material ground is transferred by the connecting pipe 10 into the grinding tube 3 in which the grinding operation is completed and the material is ground still more. The bucket wheel lock 16 then transfers the completely ground material from the vibrating mill into the collecting container 13.
Since the grinding or crushing operation which takes place in the vibrating mill is accompanied by a release of heat, it is necessary to introduce a cooling agent into the vibrating mill for the purpose of maintaining a low temperature. This is accomplished, for instance, by introducing liquid nitrogen through a nozzle 31 adjacent the material feed opening 4 into the grinding chamber 2 and by introducing liquid nitrogen into the grinding tube 3 by means of a nozzle 32.
The pipelines 21 and 22 and also 23 and 24, respectively, withdraw a portion of the vaporized nitrogen by the operation of the blower 26. The throttles in these pipelines are now so adjusted that the pipelines 22 and 24 will each withdraw a somewhat larger partial stream of nitrogen than is done by the pipelines 21 and 23, respectively. In this manner the assurance is gained that the gas flow in the grinding tubes will always be in the same direction as the material to be ground as it moves through the grinding tubes.
The gaseous, but still cold nitrogen which is withdrawn from the vibrating mill is introduced by the pipeline 29 into the upper range of the cooling device 6 and is used for a preliminary cooling of the material to be ground, This nitrogen gas leaves the installation in an opposite direction than the direction in which the terminal to be ground is moved, namely upwardly through the pipe 7 and through the vibrating conveyor 8 and finally through the supply bin 9 as indicated by the arrow above the bin 9. The fine particles of the material which are withdrawn from the grinding space in this manner will be deposited on the material to be ground so that the nitrogen gas which escapes into the atmosphere is free of dust. If necessary, the collecting container 13 may be connected by a pipeline 33 with the manifold 25 of the blower 26 so that any nitrogen which reaches the collecting container 13 via the bucket wheel lock 16 may be removed.
The invention is not limited to a vibrating mill such as has been described in the foregoing, but may also be used in the same manner with other constructions of a vibrating mill and may even be used in connection with intermittently operating vibrating mills.
What we claim is:
l. A vibrating mill installation having a closed material feed means and a closed material discharge means and therebetween means for grinding the material introduced into said mill, said means for grinding said material comprising two parallel. disposed horizontal grinding tubes each of which is provided with at least one opening used for the withdrawal of gas from the interior of said grinding tubes, means forming a source of reduced pressure, and pipelines connecting said openings with said source of reduced pressure.
2. A vibrating mill installation according to claim 1, including an adjustable throttling device in each pipeline connecting a gas withdrawal opening in said grinding tubes with said source of reduced pressure.
3. A vibrating mill installation according to claim 1, including a pipeline connecting the pressure side of said means forming a source of reduced pressure with said closed material feed means,
4. A vibrating mill installation according to claim 1, including a pipeline connecting the pressure side of said means forming a source of reduced pressure with said closed material feed means, and an adjustable throttling device in said pipeline leading to said closed material feed means.
5. A vibrating mill installation according to claim 1, including a material lock which is impermeable to gas arranged between the material feed device and the inlet of the first one of said two grinding tubes.
6. A vibrating mill installation according to claim 1, including a material lock which is impermeable to gas arranged between the material feed device and the inlet of the first one of said two grinding tubes, said material lock comprising a bucket wheel lock.
7. A vibrating mill according to claim 1, including a collecting means connected with said material discharge means and a material lock which is impermeable to gas arranged in the connection between said material discharge means and said collecting means.