Patent Application
20150129692
The invention relates to a ball mill comprising at least two milling cup retainers arranged on a machine base plate, with each milling cup retainer being designed for a milling cup clamped in the milling cup retainer in a lying position, each milling cup having end-face milling cup ends and a filling of balls as milling bodies and comprises a drive which causes a rotational motion of the milling cup retainers.
A ball mill with the above mentioned features is known from WO 2009026990 A1. In said ball mill, as opposed to frequently used conventional planetary ball mills such as described in DE 197 12 905 C2 the movement paths of the balls inside the milling cup owing to the arrangement of the milling cup being aligned to the longitudinal axis flat or at an angle of 60 degrees in a lying position inside the milling cup changes in such a manner, that the end-face milling cup ends are involved in the crushing process as stop and grinding area. In this process, on the one hand, a periodic force motion component acts on the balls in direction of the side walls of the milling cup during the milling process caused by the rotation of the milling cup, while on the other hand, owing to the arrangement of the milling cup in a lying position, another additional force motion component is acting on the balls in the direction of the ends of the milling cup. Thus, it is achieved that when the balls move at the side walls of the milling cup the milling material to be ground is subjected mainly to friction and when the balls hit the milling cup ends the same are exposed to impact force. At the same time the milling material is thoroughly mixed owing to the movements of the balls in longitudinal direction of the milling chamber, exposing all particles of the milling material at the same time, thus improving the grinding efficiency. The severity of the friction- and impact components can be adjusted by setting or selecting the length and diameter of the milling cup in relation to the swing diameter and the diameter of the balls as well as the specific ball mass.
Insofar as both the milling cup retainers with their milling cups arranged inside in a lying position are mounted on a common machine base plate, it is proposed to use a spring-mass-valve as drive, by means of which the machine base plate is set into rotary motion causing the two milling cup retainers to move on said circular path. In case of said conventional ball mill this was found to be disadvantageous since the rotary motion caused by the spring-mass-valve was too uncertain for the movement paths of the balls taking place inside each milling cup.
Thus object of the invention is to improve a ball mill having the above mentioned design in a manner, in which the milling cups are put in a restraint-guided motion in order to achieve a precisely repetitive movement pattern of the balls.
According to the invention said problem is solved by the independent claims. Preferred embodiments are object of the related claims.
The invention is based on the general concept that each of the milling cup retainers, being arranged in pairs, is put into restraint-guided circular motion, oriented parallel to the plane of the machine base plate by means of a drive via two eccentric shafts connected to the milling cup retainers on faces opposite to each other in relation to an axis of symmetry of the milling cup, wherein on each of the eccentric shafts being put through the machine base plate and being assigned to one milling cup retainer each, a counter weight is arranged as mass equalizer for the milling cup retainer holding the milling cup clamped inside and which is connected to the eccentric shaft in relation to the longitudinal axis of the two eccentric shafts connected to the milling cup retainers and wherein the eccentricities for the two milling cup retainers of the eccentric shafts connected to the same are equal and the counterweights thereof are arranged on faces opposite each other in relation to the longitudinal axis of the milling cups and the milling cup retainers are put into a counter rotating, out-of-phase circular motion.
Thus it is possible to set a movement pattern in which the milling cups move on small circular paths, with the ratio of the diameter of the circular path on the one hand and the length of the milling cup being adjusted such, that by the impact of the milling material and the grinding balls hitting the milling cup ends a substantial part of the milling work takes place in the milling cup at the milling cup ends. But using eccentric shafts gives rise to the problem that during operation of the ball mill substantial unbalance forces and unbalance moments develop which have to be compensated. The problem of compensating unbalance forces being caused in the movement plane of the milling cup retainer is solved by providing an arrangement comprising of two milling cup retainers which are driven in a counter rotating and out-of-phase manner, which in this case is not sufficient since the drive of the eccentric shaft also causes unbalance moments because the milling cup retainers with their clamped milling cups which are connected to the upper ends of the eccentric shafts give rise to corresponding torques around an axis perpendicular to the plane, in which the milling cup retainers move, in the center between the milling cup retainers. Said torques change their operating direction in the same frequency in which the milling cups rotate, causing torsional vibration which, according to the invention, is compensated by an additional mass equalizer on each of the eccentric shafts in the zone below the milling cup retainer. For this purpose one counterweight each is arranged on the eccentric shaft which is installed at the face opposite the connection of the milling cup retainer on the upper end of the assigned eccentric shaft in relation to the longitudinal axis of the eccentric shaft. Additional unbalance moments result from the fact, that the centrifugal force acting on the milling cup retainer arranged at one end of the eccentric shaft and the centrifugal force acting on the counter weight arranged on the other end of the eccentric shaft cause a torque around axes extending in horizontal direction. Said unbalance moments rotate together with the rotation of the milling cups and counterweights around the vertical axis on the plane in which the milling cups move.
According to the invention the spatial unbalance problem of having to compensate unbalance forces and unbalance moments simultaneously is solved in that not only the unbalance forces caused by a rotating milling cup retainer are compensated by installing an additional second milling cup retainer driven in a counter-rotating and out-of-phase manner but moreover by providing counter weights on the eccentric shafts putting the milling cup retainers into rotation in a manner, in which the unbalance moments, being caused in the plane of the milling cup retainers after compensation of the unbalance forces, are also compensated.
In the context of the present invention the “lying” arrangement of the milling cups is defined in the same manner as in the generic WO 2009 026990 A1, namely as a flat or slanting arrangement being placed at an angle of 60 degrees.
The invention comprising an arrangement of two milling cups can also be realized in a design having multiples of two milling cups, for instance with four or six milling cups.
When, according to the invention, each of the milling cup retainers is connected to two eccentric shafts being arranged on faces of the milling cup retainer opposite to each other in relation to a symmetrical axis, in an alternative embodiment of the invention it can be provided, that each of the milling cup retainers is connected to an eccentric shaft on faces opposite to each other in relation to the longitudinal axis of the milling cup or that alternatively, each of the milling cup retainers is connected to one eccentric shaft each in the area of the end faces of the milling cup.
According to one embodiment of the invention it can be provided for each of the milling cup retainers to comprise a lower part receiving the milling cup in a lying or slanting position and which is connected to the two eccentric shafts on faces opposite to each other in relation to an axis of symmetry of the milling cup and an upper part linked to the lower part and overlapping the milling cup on top which can be clamped to the lower part.
Moreover, with ball mills the energy input required for the crushing process is of importance in so far as it is not supposed to cause inadmissible heating of the milling material. For instance, it is possible, that during heating of the milling material to be crushed, the glass transition temperature or softening temperature of plastic material is exceeded, causing sticking or clogging of the milling chamber. Thus, if cooling of the milling chamber or the milling cup is desired, the drive of the two milling cups via their assigned eccentric shafts according to the invention offers a good option for providing adequate cooling of the milling cups. Thus, according to a detailed embodiment of the invention, in order to cool the milling cup during the milling process it is provided for the two eccentric shafts connected to a milling cup retainer to have a hollow shaft body, through which a cooling medium can be conducted and that the milling cup retainer in which the milling cup is clamped is connected to the two eccentric shafts in a leak proof manner and designed having hollow spaces and that the one eccentric shaft assigned to the milling cup retainer is connected to a cooling medium inlet and the other eccentric shaft assigned to the milling cup retainer is connected to a cooling medium outlet.
Moreover it can also be provided for the lower part of the milling cup retainer to be provided hollow spaces in its connecting areas surrounding the ends of the two eccentric shafts as well as in a middle area forming a support for the clamped milling cup, in order to conduct a cooling medium through the same. Furthermore it can be provided that the upper part of milling cup retainer overlapping the milling cup comprises at least one hollow space in the middle part supported by the milling cup being connected to the hollow spaces of the connection areas for the cooling medium to be passed through.
The above described cooling of a milling cup or a milling cup retainer respectively by means of a cooling medium being passed through the eccentric shafts can be employed for all types of mills using eccentric shafts as drive or for which eccentric shafts can be used as drive. In this respect the use of the above explained principle of the invention is not restricted to ball mills having milling cups which are arranged in a lying position but can also be applied to all mills being operated by an eccentric shaft drive system.
Moreover, it can be provided that the milling cup ends of milling cups clamped in a lying or slanting position can be designed as flat, for example resulting in a cylindrical milling cup design in milling cups having a circular cross section,
Alternatively, it can be provided for the end-facing milling cup ends to be dome shaped.
Insofar as it is object of the invention, to dimension the masses of milling cups and retainers on the one hand and eccentric shafts with the attached counterweights on the other hand in such a manner, that filling the milling cup with milling material and if required, with balls, does not affect the unbalance compensation of the ball mill, it can also be provided in one embodiment of the invention for the counterweights which are arranged on the eccentric shaft below the milling cup retainer to be readjusted according to the mass of the retainer and the therein clamped milling cup. In the simplest scenario, readjustment can be done by attaching additional weights. Another option is radial displacement of the centers of gravity of the eccentrically mounted counter weights.
In the context of the invention, it makes sense to use oblong milling cups, in which the length specified for the longitudinal side and thus the space between the milling cup ends is greater than the diameter of the section extending between the milling cup ends. In this context it is practical to have differently shaped milling cups when realizing the invention. Thus, it can be provided for the respective milling cups to have a circular cross section or an elliptical cross-section or a rectangular cross-section with rounded corner areas, wherein in the last-mentioned embodiment the rounded corner areas of the respective milling cup when using grinding bodies inside the milling cup can have a radius corresponding the radius of the milling bodies. Differently shaped milling cups are also possible, for instance milling cups having an elliptical longitudinal section.
Within the scope of the invention it can be provided for the eccentricities of the connections of the milling cup retainers together with the corresponding eccentric shafts to be dimensioned equally, resulting in a circular movement of the milling cup retainers together with the clamped milling cups, with the longitudinal axis of the milling cups clamped in different milling cup retainers remaining during rotation of the same rotation in all positions in a parallel arrangement.
Alternatively, it can be provided for the eccentricities of the connections of the milling cup retainer together with the two respective eccentric shafts to be dimensioned differently, resulting in a rotational movement being initiated in the area of the milling cup retainer of the eccentric shaft having the smaller eccentricity, while on the opposite side of the milling cup retainer the eccentric shaft having the larger eccentricity causes a pendulum movement of the clamped milling cup. In this case only the eccentric shaft having the smaller eccentricity is driven while the other eccentric shaft is steered.
When the two eccentric shafts assigned to a milling cup retainer are firmly attached to their corresponding milling cup retainer with one of their ends and thus are firmly attached to each other, then, because of the manufacturing and assembly tolerances, there is no guarantee that the free lower ends of the eccentric shafts which are to be coupled to a drive medium such as a toothed belt or chain, engage with the common drive medium in a tension-free manner because the system is mechanically over determined. In order to prevent jamming of the eccentric shafts and drive medium one embodiment of the invention provides for both the eccentric shafts assigned to a milling cup retainer to be driven by a common drive medium and to set an equalizing play between the eccentric shaft and the drive medium.
For this purpose it can be provided that a toothed washer each is arranged on the end of the eccentric shaft opposite the milling cup retainer and the drive medium is designed as circulating toothed belt engaging with the tooth of the toothed washer and wherein on one of the two toothed washers the width of the gaps of the toothed washer is larger than the width of the tooth of the belt used. This is in particular the case when all eccentric shafts of a milling cup retainer arranged on a machine base plate are driven by a common tooth belt and in this case the compensating play is set on the toothed washer of one of the two eccentric shafts connected to the same milling cup retainer.
The drawing illustrates an embodiment of the invention described below, wherein show:
a-c a bottom view of the eccentric shafts assigned to the two milling cup retainers together with the drive medium
The ball mill 10 shown in
In the housing 11 a motor 21 is provided, protruding upwardly above the machine base plate 12, which drives the two milling cup retainers 13 arranged on the machine base plate 12 by means of a drive mechanism provided below the machine base plate 12.
As illustrated in
Moreover, as illustrated in
When the two drive sections 26 of the two eccentric shafts 25 having the same eccentricity are put in rotation by means of the driving mechanism driven by the motor 21, the milling cup 23 being clamped in the milling cup retainer 13 in a lying position moves on a circular path because the two external connecting areas 16, each connected to an eccentric shaft itself are moving on a circular path.
In as far as two milling cup retainers 13 together with their respective milling cups 23 are arranged on the machine base plate 12, the directions of movement of the two milling cups 23 on their respective circular paths are oriented each in opposing directions of movement together with opposing phases of motion in such a manner, that, when the ball mill 10 is in operation, the centrifugal forces acting on the milling cup retainers 13 with their clamped milling cups 23 are compensated above the machine based plate 12.
Since with this arrangement the centrifugal forces compensate each other on the plane, in which the milling cup retainers rotate, but the moments having alternating direction of rotation around a vertical axis remain on this plane, each of the eccentric shafts 25 is provided an additional counterweight 28 in the drive section 26 located below the machine plate 12 with the same being arranged on the face opposite the connecting area 16 of the milling cup retainer 13 located above the machine base plate 12 in relation to the longitudinal axis of the individual eccentric shafts 25. Thus, forces are balanced effectively on each of the eccentric shafts 25 during the circular movement of the milling cup retainer 13 connected to the same, which due to the fact, that two milling cup retainers 13 driven in counter rotation and phase opposition together with the connected eccentric shafts 25 are designed in the same manner, at the same time compensating the above described moment at the vertical axis on which the milling cup retainers 13 rotate as well as moments which are lying in this plane and which are initially caused by the centrifugal forces of the milling cup retainers 13 and the counter weights 28.
In order to provide cooling to the milling cup 23 during operation of the ball mill, the two eccentric shafts 25 are designed having an inner boring 31 as hollow-bored shafts. Accordingly, the two connecting areas 16 facing each other as well as the middle area 15 of the lower part 14 connecting the same are provided hollow spaces 32 which by means of a sealing element 33 fixed at the upper end of each of the eccentric shafts 25 and a sealing surface 34 formed on the milling cup retainers 13 serving as counter sealing element of the sealing element 33 are connected to the borings 31 of the two eccentric shafts 25. In this manner a gaseous or liquid cooling medium introduced into one of the two eccentric shafts 25 can flow via the corresponding eccentric shaft 25 and hollow spaces 32 provided in the lower part 14 to the eccentric shaft 25 connected on the opposite side to the milling cup retainer 13 as well as be discharged from the same. Accordingly, in the illustrated embodiment a cooling medium inlet 36 is provided on the lower end of the left eccentric shaft 25 and a cooling medium outlet 37 is provided on the right eccentric shaft. By designing the middle area 22 of the upper part 17 of each milling cup retainer 13 as having a hollow space 35 and by connecting the same to the hollow spaces 32 of the bottom part 14 it is ensured, that the cooling medium being introduced into the bottom part 14 of the milling cup retainer flows also through the upper part 17 of each retainer. In this manner the milling cup 23 is enclosed by cooled components allowing the temperature inside the milling cup 23 to be restricted during the crushing process.
a illustrates the driving concept according to the invention, wherein a revolving toothed belt 39 driven by a toothed lock washer 40 drives all four eccentric shafts 25 assigned to the milling cup retainers 13 as described in
The features, claims, summary and drawings, disclosed in the above description of the invention can be used individually or in any combination for realizing said invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102012105217.4 | Jun 2012 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/062402 | 6/14/2013 | WO | 00 |
