EP0111703B1 - Mill for fluid milling material - Google Patents

Abstract

A ball mill stator providing a milling space between a housing and a cover and a ring-like displacing body in the milling space with a V-shaped radial cross-section forming part of the rotor. The material being milled together with the balls flows around the displacing body from a feed inlet to an outlet along spiral paths. The milling media kept back at the milling gap are moved through a duct into an annular space and from this point through conveying ducts of an impeller outwards and re-enter the milling space at a small distance above the feed inlet. The impeller is sealed between the rotor and stator and is powered by a motor, or by a variable speed drive, run at a speed controlled by readings taken from different parts of the mill system such that the milling media is evenly distributed in the material being milled by which they are moved along making the milling operation more uniform and efficient. An adjustable milling ring together with the impeller form a coarse milling unit whose gap size may be changed like that of the inlet.

Description

The invention relates to a mill for flowable regrind with a grinding chamber receiving the regrind and in this freely movably provided grinding body, formed centrally between the stator and rotor, a good inlet and a good outlet, a separating device upstream of the good outlet for separating the grinding bodies and with a return device for recycling the separated grinding media in the area of the material inlet.

A ball mill of this type is known from DE-OS 2811 899. In this case, the grinding stock and grinding balls are kept in circulation in a grinding chamber which is limited in cross section by two conical surfaces, around a displacement ring of the rotor which is wedge-shaped in cross section, the material outlet and the material inlet being relatively tight the mill axis is arranged so that the grinding balls separated out by the separating device can be added to the incoming regrind through a return channel. This return channel passes through a disc of the rotor and is directed radially so that the conveying takes place under the action of centrifugal force.

In order to create a reasonably uniform distribution of the grinding stock and grinding media in mills of this type, the throughput speeds of the grinding stock and the grinding media must be in a specific relationship to one another. The throughput speed of the millbase can be influenced, for example, by the feed pressure and the rotor speed. The grinding media are taken away by the regrind, but the entrainment effect is mainly influenced by the viscosity of the regrind. The rotor speed also has a limited influence on the rotational speeds of the material to be ground and the grinding media. However, because a constant ratio of the circulation speeds cannot be achieved, the grinding results are always subject to certain fluctuations. Attempts have been made to change the rotational speed of the grinding balls by changing the dimensions of the return duct or the return ducts, but such changes can usually only be made when the machine is at a standstill when the machine is empty. In addition, the votes achieved in this way are still very unsatisfactory.

The invention takes a different approach and pursues the task of developing the mill described at the outset in such a way that the grinding process is made more uniform and the grinding result is improved by simplified and more precise coordination of the rotational speed of the grinding stock and grinding media.

To achieve this object, the feedback device for a positive change in the return speed of the grinding media in relation to the rotational speed of the material to be ground is provided with at least one separate conveying element of a conveying drive that can be operated at a speed different from the rotor drive.

In this way, regardless of all other drive processes and speeds, the rotational speed of the grinding media can be positively influenced and their optimal operating value can be approximated. It can be set at a very specific value if the operating conditions of the mill remain constant, as is usually the case for continuous operation. When the end product is put into operation, it is easy to set the operating speed of the conveying member and thus the necessary rotational speed of the grinding media by means of samples of the end product and, if necessary, to monitor and compensate for any changes in these conditions which may occur by means of further samples or measurements.

The aim is to achieve a size of the return speed such that the grinding media experience a certain amount of jam in front of the return device, which continues far into the grinding zone. If the return speed is too high, the contact pressure of the balls becomes too low, and the grinding effect of the mill deteriorates as the power consumption of the mill motor decreases. On the other hand, if the recirculation is too slow, there is an excessive backflow. As a result, the balls are pressed against each other too much and roll too little against each other and against the wall of the grinding chamber, which in turn reduces the grinding performance and increases the grinding temperature due to friction. In contrast, backflow and contact pressure are directly influenced by the selected return speed.

According to a first embodiment of the invention, the conveyor drive is provided completely independently of the rotor drive. This version is simple, but makes control difficult.

In contrast, a conveyor drive that runs with a certain fixed or variable transmission ratio to the rotor drive is more complex to manufacture and more precisely to control. For example, the rotor and conveyor element can be connected to a common drive via a speed change gear.

The conveying element is expediently designed as a centrifugal pump, which can act directly on the grinding media and, for example, has a pump wheel which rotates centrally to the mill axis. The dimensions and arrangements on the pump wheel can then be selected such that the rotation speed of the pump wheel is in the range of the rotation speed of the rotor in reasonably normal operation, and only certain changes in the speed up or down are selected for regulation, that is to say the grinding media do not have any abrupt changes in speed be subjected.

The central arrangement also enables a quite compact and functional design, especially when the pump wheel, each sealed, between the rotor and stator is inserted. The drives for the rotor and pump wheel are preferably connected from opposite sides.

The feed pump should form individual feed channels with a clear width that is slightly larger than the largest single or double cross-sectional dimension of the grinding media to be conveyed, in order to reliably prevent the grinding media from becoming blocked or jammed in the channels. Advantageously, only one or four to five grinding media should be able to pass through at the same time.

It is also advisable to provide the outlet of the centrifugal member and the material inlet axially closely adjacent in approximately the same circumferential area. Grist and grinding media are equally introduced radially into the grinding chamber.

If a grinding element is to be connected upstream of the material inlet, this grinding element is expediently formed between the pump wheel and the mill housing. Advantageously, the material inlet between the pump wheel and the mill housing forms an annular gap nozzle, which prevents the grinding media from flowing back when the mill is at a standstill and to which a set of interacting grinding surfaces on the pump wheel and mill housing connects. At least one of the two grinding surfaces can have teeth in the manner of a toothed colloid mill.

The clear width of the annular gap is at most half as large as the dimensions of the grinding media. Annular gap width and / or grinding gap width can also be changed by axial adjustment, in particular of a common grinding ring.

A control arrangement for controlling the conveyor drive, in particular, automatically, as a function of mill operating values and / or properties of the ground material, is used particularly advantageously here. Such a control arrangement can be connected, for example, to at least one sensor that detects the drive power, the torque and / or the speed of the mill drive. Likewise, the control arrangement can be connected to at least one sensor that detects the viscosity or the pressure of the ground material. The starting viscosity can be just as important as the viscosity achieved after the grinding process, as well as the ratio of the two viscosities. It goes without saying that other properties or state values of the ground material and further mill operating values can also be important.

Since the various measured values to be taken into account can form quite different controls for the conveyor drive, several sensors should be connected to a middle device, for example a computer, which, based on the various functions, forms a resulting control value for the conveyor drive based on the various functions.

• Fig. 1 einen Längsschnitt durch eine erfindungsgemässe Spaltkugelmühle,
• Fig. 2 ein zugehöriges Schaltbild.

The drawing shows the invention, for example. Show it:

• 1 shows a longitudinal section through a split ball mill according to the invention,
• Fig. 2 is an associated circuit diagram.

The stator 1 of the split ball mill shown in FIG. 1 is divided by the approximately horizontal parting line 2 into a lower mill housing 3 and a cover 4, which are flanged together in a sealing manner and braced by screws 5. It can be inserted between the clamping flanges annular intermediate members 6, which can be designed as sealing rings and / or as intermediate rings in order to be able to change the axial position of the rotor in the stator. The mill housing has a tapered housing wall 7 at the bottom which, with a recess 8 in the cover 4, delimits the double-conical grinding chamber 9 to the outside.

The housing wall 7 is enclosed on the outside by a cooling chamber 11, which in turn is delimited by a cooling housing 12 with a base 13 and annular walls 14, 15. In principle, the entire mill can be carried by this cooling housing 12, which is made in one piece with the mill housing 3. But you can also hang the mill housing 3 on the lid to be fixed to the stand.

Another cooling space 10 is formed in the cover 4, the bearing sleeve 17 rotatably carries a rotor shaft 19 in a known and therefore not shown manner, the lower end of which is in the hub shell 21 of the rotor 22, screwed to it by thread 23 and secured by a screw 24 is.

The rotor 22 has a rotor disk 26 extending from the hub cup 21, which has on its outer edge an annular hollow displacement body 27 with a double-cone cross section that is adapted to the shape of the housing wall 7. This displacement body is immersed in the grinding chamber 9 and forms a grinding gap 91 with the housing wall 7 with an approximately constant gap width a.

The interior of the displacement body 27 is divided by an approximately cylindrical partition 28 starting from the rotor disk 26. This ends at a distance b from the ring base 29 of this interior, which is thereby divided into an inner and outer annular chamber 31, 32 for internal cooling of the rotor or for Circulation of the cooling medium. The inner chamber 31 is connected via a predominantly radial channel 33 of the rotor disk 26 to an outer ring channel 34 in the rotor shaft 19. The outer ring chamber 32 is connected to a central bore 36 of the rotor shaft 19 via a comparable channel 35. Since the channels 33 and 35 are arranged diametrically, coolant flows downward in the inner annular chamber 31 and upward in the outer annular chamber 32 and has to flow tangentially around at least half the circumference of the partition wall 28 until it reaches the outside again. The inlet and outlet can also be tangential in order to achieve a rotating cooling flow and thus greater uniformity.

A pump wheel 39 is mounted centrally to the mill axis 37 between the rotor disk 26 and a high-lying inner flange 38 of the mill housing 3, which ends with a preferably axially adjustable grinding ring 41 seated on the inner flange 38 in the same cylinder surface 42. The pump wheel 39 is wedged onto the motor shaft 43 of a suitable drive, in particular an electric conveyor motor 44, which is suspended on the inner flange 38 via an intermediate ring 45. An annular space 47 is formed between the parts 38, 41, 39 and 45 by means of a mechanical seal 46, into which a feed line 48 opens from the underside and which is formed on the outlet side as an annular gap between the grinding ring 41 and the pump wheel 39 Good inlet 49 is in connection with the grinding chamber 9.

A pre-grinding unit 51, which is designed as a colloid mill by means of two toothings formed in the grinding ring 41 and the pump wheel 39, is connected upstream of the material inlet 49.

The raw material fed in from the line 48 thus flows through the annular space 47 and the pre-grinding unit 51 to the annular gap material inlet 49. The clear width of the annular gap is so much smaller than the cross-sectional dimensions of the ground material that this already prevents backflow when the mill is at a standstill. In addition, the clear width of the material inlet and the grinding gap of the pre-grinding unit can be changed by axially adjusting the grinding ring 41 by means of intermediate rings. From the inlet of the material, the material to be ground arrives downwards on the way of a conical spiral in the inner part of the grinding gap 91, again spiraling upwards on the outside of the displacement body 27 and radially inwards in the grinding gap on the upper side of the rotor disk 26. During this time, grinding balls 52 distributed approximately uniformly in the regrind are carried along. These grinding balls are repeatedly rotated by intermittent contacts with the rotor and roll alternately on the fixed and circumferential boundary surfaces of the grinding gap 91.

Since the entire displacement body 27 is rotated, there are numerous individual contacts in a limited space between the grinding balls and the particles of the material to be ground. The circulating flow of the millbase is essentially determined by the delivery pressure in the feed line 48, and the driving force exerted on the balls is significantly influenced by the viscosity of the conveyed millbase. However, this also results in a drive for the grinding balls, which is largely independent of the grinding material conveyance, and which press the front balls radially inward via the gap part 92 of the grinding gap.

While the relatively light ground material rises along the conical surface 53, the larger grinding balls already remain close to the top of the rotor disk 26 in the flat conical depression 54 or are retained in the outlet gap 55 which forms a separating device and which delimits a separating space 58 to the outside. The material freed from grinding media can thus pass through the outlet gap into the outlet line 59, which is guided to the outside by the bearing sleeve 17 and is shielded from the rotor shaft 19 and its drive.

The retained grinding balls, on the other hand, pass in the direction of arrow 63 from the separating space 58 via openings 64 in the rotor disk 26 into an annular space 65 between this rotor disk and the pump wheel 39. From this annular space 65, at least partially radially directed delivery channels 66 lead tightly to the common outer cylinder surface 42 Above the annular inlet 49. The cross section of the channels 66 is adapted to be larger than the diameter of the largest grinding balls used, which are thus thrown outwards by the rotation of the pump wheel 39 at a low radial speed. So that the ground material under the higher supply pressure cannot reach the outlet gap 55 in the opposite direction to the centrifugal direction 66 to 63, this supply pressure and the centrifugal force determined primarily by the rotational speed of the pump wheel 39 must be coordinated with one another. However, the speed n2 of the pump wheel 39 must also be matched at least to the speed n1 of the rotor 22. In addition, in order to maintain a uniform distribution within the goods, it must also be possible to adjust the viscosity.

The cross section of the channels 66 should either be selected so that only one or four to five balls can pass through it at the same time. In the first case, the diameter of the mostly cylindrical channels between 1.2 and 1.4 diameter of the grinding media is selected, while in the second case a channel diameter of 2.2 to 2.4 grinding media diameter is selected. In this way, it is achieved with greater certainty that grinding media cannot jam in the channels, but can move through quickly without great wall pressure.

The mill motor 67, which drives the rotor shaft 19 via a belt drive 68 according to FIG. 2, can in principle have a constant speed. As a rule, a variable speed drive will also be provided here. However, the conveyor motor 44 is controlled via a mediator device 69, which receives a first default value via a line 71 from an arithmetic unit 72, which is connected via line 73 to a first sensor 74, which constantly delivers first viscosity values from a first viscosity meter 75, which is connected to the feed line 48.

A further line 76 leads to the second sensor 77 of a second viscosity meter 78 on the outlet line 59, and a third line 79 leads to a sensor 80 provided directly or indirectly on the mill motor 67, which, for example, measures the current output, the current and / or or the speed of the engine delivers. Several of these quantities can also be sensed by separate measuring devices or transmitters can be passed on.

The middle device 69 is also connected via a line 81 to a computing unit 82, which in turn has three lines with sensors 83 for the pressure p1 in the feed line 48, 84 for the pressure p2 in the inlet part of the grinding chamber 9 and 85 for the pressure p3 in the outlet part the grinding chamber is connected.

Since only the speed of the conveyor motor 44 is to be controlled, it is necessary to form the suitable mean value from the various information. This can be done in a number of ways, in particular by means of electronic computing arrangements, which then transmit a single item of information and a single control command to the conveyor motor 44 via the middle device 69.

According to FIG. 2, the arithmetic units 72 and 82 already form first output values according to predetermined functions, which are averaged again in the common middle device 69. The subdivision shown in FIG. 2 can also be omitted if all sample values are fed to a common computer which forms the mean value and which is fed to the conveyor motor 44 after amplification.

Such a central computer 86 is provided according to FIG. 3. Instead of the feed motor 44, one controls a control device 87 for a continuously variable transmission 88, which is connected to a hollow shaft 89 guided to the pump wheel 39, through which the rotor shaft 19 runs downwards. Here, the line 79 led to the mill motor 67 is saved, since in principle there is a speed limitation of the conveyor drive to the mill motor. It is therefore not necessary to readjust if the speed of the mill motor changes, provided readjustment is not necessary due to other pulse values. Here, too, not all of the specified push buttons need to be connected, sometimes one single push button can be used.

In addition, the continuously variable transmission 88 can also be connected to the motor 67 outside the mill housing, so that there is no need for the rotor shaft 19 to pass through this housing.

If at all possible, the speeds of the rotor 22 and the pump wheel 39 should be approximately the same in normal operation in order to avoid unnecessary relative movements at the common interface. The viscosity measurement also does not have to be continuous, but can be carried out periodically, in which case it is then readjusted in stages. Usually, a single viscosity measurement is sufficient if the control function is determined based on experience. It goes without saying that further tactile values can also be used, for example a ball jam in the separating space 58. As a rule, it is also not disadvantageous if part of the ground material with the balls is fed back to the material inlet, that is to say undergoes a second processing operation. You can even significantly increase the mean throughput time using the grinding media conveyor, i.e. Allow the product to go through 1.5 to 3.5 times on average and thus homogenize it better.

Claims (23)

1. Mill for flowable material, comprising a grinding chamber (9) formed centrally between stator and rotor and accommodating the material to be ground and grinding bodies (52) freely movably provided therein, and further comprising a material inlet (49) and a material outlet (55), and a separating means upstream of the material outlet (55) and for separating out the grinding bodies and with a feedback means for returning the separated grinding bodies (52) back into the region of the material inlet, characterised in that the feedback means are, for a positive variation of the feedback speed of the grinding bodies (52) in relation to the peripheral speed of the material being ground, provided with at least one separate conveying means (39) of a conveyor drive (44, 88) adapted to be driven at a speed other than that of the rotor drive (67, 68).

2. Mill according to Claim 1, characterised in that the conveyor drive (44) is independent of the rotor drive (67).

3. Mill according to Claim 1, characterised in that rotor (22) and/or conveyor means (39) are connected to a common drive through a speed varying transmisison (88).

4. Mill according to Claim 1, 2 or 3, characterised in that the conveyor drive (24) is constructed to be infinitely regulable.

5. Mill according to one of Claims 1 to 4, characterised by the construction of the conveyor means (39) as a centrifugal pump.

6. Mill according to one of Claims 1 to 5, characterised in that the conveyor means (39) comprises a pump impeller rotating centrally in relation to the mill axis.

7. Mill according to Claim 6, characterised in that the pump impeller (39), in each case sealed, is incorporated between the rotor (22) and the stator (1 ).

8. Mill according to Claim 7, characterised in that the drives (57, 24, 88) or rotor (22) and pump impeller (39) are connected from opposite sides.

9. Mill according to Claim 5, 6 or 7, characterised in that the centrifugal pump (39) forms individual conveyor passages (66) having an inside diameter which is a little larger than the largest single or double cross-sectional dimension of the grinding bodies (52) which are to be conveyed.

10. Mill according to one of Claims 6 to 9, characterised in that the outlet of the pump impeller (39) and of the material inlet (49) are provided in an axially closely adjacent relationship, substantially in the same peripheral surface (42).

11. Mill according to one of Claims 1 to 10, with a grinding means upstream of the material inlet, characterised in that the grinding means (51) is formed between pump impeller (39) and mill housing (3).

12. Mill according to Claim 10 or 11, characterised in that the material inlet (49) forms between pump impeller (39) and mill housing (3) an annular gap jet adjacent to which there are inwardly co-operating grinding faces (51) on pump impeller (39) and mill housing (3).

13. Mill according to Claim 12, characterised in that at least one of the two grinding faces comprises a tooth system (51) after the manner of a toothed colloidal mill.

14. Mill according to Claim 12, characterised in that the inside diameter of the annular gap (49) and/or the grinding gap (51) can be varied by axial adjustment, particularly of a common grinding ring (41).

15. Mill according to one of Claims 1 to 14, characterised by a control arrangement for in particular automatic control of the delivery drive (44) as a function of mill operating values and/or properties of the material to be ground (Fig. 2).

16. Mill according to Claim 15, characterised in that the control arrangement is connected to at least one measured value transmitter (80, 83-85) which ascertains the drive output, the torque, the rotary speed, the pressure ration and/or the feed output.

17. Mill according to Claim 15, characterised in that the control arrangement is connected to at least one measured value transmitter (75, 78) which detects the viscosity of the material to be ground.

18. Mill according to one of Claims 14 to 16, characterised in that a plurality of measured value transmitters (75, 78, 80) are connected to an averaging unit (69, 82) which, according to predetermined functions, forms from the various measured values a resultant control value (71) for the delivery drive (44).

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