EP0340510A2 - Airflow mill arrangement - Google Patents

Abstract

The invention relates to an airflow mill arrangement having a roller mill which has fixedly mounted mill rollers. The mill rollers can be pressed resiliently against a driven mill bowl. An integrated sifter is arranged over the roller mill. In this embodiment of the mill arrangement the mixture of material for milling and air is fed essentially from the roller mill centre to the mill bowl and the millrollers. Since, hitherto, the rotation of the mill rollers was brought about by means of a frictional connection to the material for milling or the milling bowl extreme loads and slip-stick effects could not be ruled out. In order to overcome these disadvantages, the invention employs the method of also separately driving the mill rollers in a combination, in which case speed of revolution and torque are configured in such a way that even in the case of a high degree of fineness of the material for milling a uniform mode of operation of the mill arrangement is ensured. <IMAGE>

Description

The invention relates to an airflow grinding system according to the preamble of claim 1.

Such an airflow grinding plant is e.g. known from DE-PS 20 19 005 and EP 0 173 065 A2 and shown in Fig. 1.

To clarify the problems existing in these conventional airflow grinding systems, such an airflow grinding system 1 with its essential assemblies and its mode of operation is briefly described below.

The airflow grinding system 1, which is on a foundation, is usually enclosed in an airtight manner by a housing 2. The grinding plant consists of a lower roller mill, above which an integrated classifier 11 is installed in the upper area. As the only component of the roller mill, the grinding bowl 3 is set in rotation via a drive 4. The regrind fed from above or from the side onto the grinding bowl 3 is comminuted between the resiliently pressed grinding rollers 9 and the grinding bowl 3. The grinding rollers 9 do not have a separate drive, but are set in rotation solely by the frictional connection between grinding bowl 3 or the grinding material present between them and the grinding bowl. The air flowing in via the feed channel 6 and the guide vane ring 16 conveys the mixture of finished and coarse material which is thrown off the grinding bowl 3 after being rolled over by the grinding rollers 9 Grain upwards in the area of the classifier 11. Due to the rotor 12, which is driven by its own rotor drive 14, oversize is rejected in accordance with the rotation and the rising volume flow of the air dust mixture 13, so that this, together with a partial air flow, is returned to the grinding bowl 3 in the area of a so-called vertebral sink 8 falls back. The fines or finished goods, on the other hand, leave the classifier 11 via the fines outlet 15.

These normally occurring flow conditions of the air / dust mixture are shown in FIG. 1 with broken lines as current threads. As can be seen from this, a vertebral sink 8 forms below the classifying rotor 12 in the center of the roller mill, wherein not only ground material particles, but also air or gas are almost returned downwards to the grinding bowl 3 in the circuit. This air / dust mixture is drawn in by the grinding rollers 3 and rolled over. The air naturally escapes.

Understandably, these flow conditions in the interior 7 of the airflow grinding system 1 strongly depend on the desired fineness of the product. With standard designs of such grinding plants, as are common in the field of cement raw material coal grinding, a dust is produced on average, which has a fineness of approx. 10% to 30% R DIN 0.09.

If you want to generate a much finer dust than 10% R DIN 0.09 with the airflow grinding system, the oversize rejected by the classifier 11 is also much finer. Since the buoyancy of the finest semolina in the air is higher than in the case of coarse semolina, the proportion of gravity that returns the oversize particles to the grinding bowl 3 also becomes lower. Ultimately, this means that an extremely highly ventilated "dust cloud" falls back on the grinding bowl or is returned. This cloud of dust can be compared to a liquid from a physical point of view due to its very low internal friction.

The problem that now arises in such conventional airflow grinding plants is that a strongly ventilated grinding bed is obtained on the grinding bowl 3, which is conveyed by the rotation of the grinding bowl in front of the grinding rollers 9. However, the grinding rollers 9 are only partially able to draw in this strongly ventilated grinding bed. As a result, the strongly aerated regrind builds up in front of the grinding rollers, whereby the air is displaced from the dust / air mixture. In this way, a continuously growing dust wave forms in front of the grinding rollers, which could be compared to a bow wave.

Since in the previous design the grinding rollers 9 were driven only via the friction between the material to be ground and the grinding bowl or directly with the latter, the previous friction force drive did not work or only worked incompletely. This is because the coupling medium, which behaves like a dust wave, has properties like a liquid as a strongly ventilated grinding bed. The disadvantageous consequence of this is that the grinding rollers drop in their speed or even stop.

Only when enough air is displaced from the dust / air mixture of the strongly ventilated grinding bed, the coupling medium becomes stable enough, so to speak, to drive the grinding rollers again via the frictional engagement and to take them along. However, since a kind of wedge of dust quickly builds up in front of the grinding rollers due to a prolonged accumulation of such a growing dust wave, the further disadvantage inevitably arises of pulling the grinding bed quickly and continuously under the spring-loaded grinding rollers 9. The grinding rollers, which have dropped or even stopped due to these physical conditions, for example, have now jerked off the jammed dust wedge and must be accelerated. However, this means that there is currently a very high demand for drive energy since the inertia of the large roll masses has to be overcome.

The above-described functional sequences lead to a slip-stick effect on the grinding rollers, which manifests itself in strong mill vibrations. Apart from mechanical damage that can occur on the airflow grinding system due to this sliding and blocking effect, the disc throughput of the roller mills also affects and reduces the mill throughput.

Based on the disadvantages previously present in the prior art, the invention is therefore based on the object of constructing a generic airflow grinding system in such a way that a high degree of efficiency with regard to the mill throughput is achieved, in particular when a high degree of fineness of the grinding material is required, where possible the functional sequence becomes more uniform, so that impact loads during power consumption or in mechanical terms are largely reduced.

This object is achieved in a generic airflow grinding plant by the features of the characterizing part of claim 1.

The main idea can be seen, for example, in such a grinding system to depart from the sole drive of the grinding plate and instead to drive the individual grinding rollers in a manner of a combination in rotation.

At first glance, this appears to necessitate a higher investment in the plant, which is also associated with a higher energy requirement. In effect, the invention ultimately leads to the fact that a continuous operation of the roller mill avoids impact loads which can lead to increased mechanical wear. The same applies to the power requirement, which can be equalized in this way, which means that the design of these units is not designed for peak loads, as is the case with systems could occur according to the state of the art, must be aligned.

The grinding rollers are therefore forcibly driven by appropriately separately assigned drive devices, such as e.g. Electric motors driven at a speed that corresponds at least to the theoretical speed with a frictional connection between the grinding bowl and the corresponding grinding roller. This theoretical speed is understood to mean the speed that would occur if the grinding rollers were to rotate continuously as compared to a grinding bed existing in the prior art. The speed of the grinding rollers is advantageously chosen to be somewhat greater than the aforementioned theoretical speed. This ensures that there is no sliding or sliding or blocking of the grinding rollers with respect to the grinding bed or the grinding bowl, so that effective grinding of the material to be ground is actually achieved.

This speed of the grinding rollers should, if possible, be infinitely adjustable so that an adjustment or regulation according to the fineness of the desired material to be ground, the size of the grinding bed, the load condition or the running behavior of the roller mill is possible. The forcibly applied speed of the grinding rollers, with which a dust wave forming in front of the roller can be prevented in any case, is therefore an essential feature of the invention.
In addition, the drive torque T per grinding roller should be designed so that the drive torque T to be installed for a grinding roller is less than or equal to a value that results from the quotient of the torque of the grinding bowl T _{grinding bowl} and the number of grinding rolls.

Taking these two aspects into account, it can be ensured in any case in the invention that the An drive the grinding rollers rotated so that, so to speak, an advance compared to a pure friction drive, as is present in grinding plants in the prior art, is achieved.

Since such airflow grinding systems are often gas-tight encapsulated systems, in which the corresponding grinding rollers with their rocker arms are also integrated, the drive devices provided for the separate drive of the respective grinding roller are of any type, e.g. electrically, mechanically, hydraulically, expediently installed on the side remote from the grinding rollers. Drive devices, such as electric motors, which can be uncoupled from the housing of the grinding system, are particularly suitable. The drive devices can also be stored and held separately from the housing. It is essential that the output shaft of the drive device can be decoupled from the drive shaft for the grinding rollers.

There are two basic alternatives for the separate drive of the grinding rollers. In the first alternative, the grinding roller is rotatably mounted in the rocker arm of the respective roller unit with a roller shaft rigidly attached to it. The drive device is then expediently attached to the rocker arm, so that rocking movements of the roller unit do not require separate compensation devices due to a different grinding bed height.
The second alternative of the drive implementation provides for a stationary hollow axis arranged in the rocker arm. The grinding roller is also held in rotation at the inner end of the hollow axis via roller bearings, for example axial and radial bearings. The actual drive takes place via a drive shaft which is guided through the hollow axis and which applies the required torque to the grinding roller on the roller side via a closing device.

This drive shaft is connected to the drive device at the other end, radial and axial adjustability, in particular gimbal type, of the entire shaft being possible via intermediate members. An electric motor provided, for example, as a drive device can in this case be fixed directly to the rocker arm or attached to the outside of the housing in such a way that it can be disconnected.

In both alternative embodiments, a spring device, which is at least in engagement with the rocking lever and is supported on a stationary part of the grinding system, is provided for applying the contact pressure of the roller against the ground material.

Instead of the above-mentioned mounting of the corresponding hollow shaft or roller shaft in a rocker arm, a direct mounting in the housing of the grinding plant can also be provided.

• Fig. 1 einen Aufriß durch eine Luftstrom-Mahlanlage gemäß Stand der Technik zur Verdeutlichung der Strömungs­verhältnisse;
• Fig. 2 schematisch einen axialen Schnitt durch eine erste Alternative des Antriebs einer Mahlwalze, wobei die Walzeneinheit mit Schwinghebel dargestellt ist;
• Fig. 3 eine axiale Ansicht teilweise im Schnitt auf eine zweite Alternative des Antriebs für eine Mahlwalze und
• Fig. 4 einen Aufriß durch eine erfindungsgemäße Luftstrom-­Mahlanlage, bei der einige Bezugszeichen und Bau­gruppen entsprechend der Fig. 1 beibehalten sind, je­doch mit einer Antriebsalternative, wie sie in etwa Fig. 2 entspricht.

The invention is explained in more detail below using two schematic exemplary embodiments. Show it:

• Figure 1 is an elevation through an airflow grinding system according to the prior art to illustrate the flow conditions.
• 2 schematically shows an axial section through a first alternative of driving a grinding roller, the roller unit being shown with a rocker arm;
• Fig. 3 is an axial view partly in section on a second alternative of the drive for a grinding roller and
• Fig. 4 is an elevation through an airflow grinding system according to the invention, in which some reference numerals and assemblies corresponding to FIG. 1 are retained, but with a drive alternative as it corresponds approximately to FIG. 2.

The airflow grinding system 1, as shown in elevation in FIG. 1, has already been described in detail in the introduction to the description to illustrate the disadvantages and problems that occur. Since individual assemblies of this grinding plant also match in the invention, matching assemblies are also identified with the same reference symbols in the further explanation.

In order to avoid disadvantages such as the slip-stick effect or mill vibrations in grinding plants according to the prior art, the respective grinding roller is also driven according to the invention in addition to driving the grinding bowl 3. The corresponding speed and the torque are coordinated so that an independent rotation of the corresponding grinding roller occurs in front of the roller without the formation of a material material bow wave. The direction of rotation between the grinding roller and grinding bowl at the grinding gap or regrind bed is directed in the same direction.

The exemplary embodiment according to FIG. 2 relates schematically to a first alternative for driving a grinding roller 20. The roller unit consisting of grinding roller 20 and rocking lever 25 is arranged so as to be pivotable about a rocker arm joint 34 on the housing or on its own foundation block on a bearing housing 35. The basic principle of this drive alternative is to provide a hollow shaft 23 rigidly fixed in the bushing 27 of the rocker arm 25, for example via a clamping device 36. The grinding roller is rotatably mounted on this hollow shaft 23 on the roll side, in FIG. 2 at the right end of the hollow shaft, via radial bearings 32 and angular bearings 33. The grinding roller 20, which in the example consists of the radially inner roller body 21 and the outer roller shell 22 forming a truncated cone, is driven with the appropriate torque via a drive shaft 24 which is guided in the hollow shaft 23 and is optionally supported.

In the example, the roller shell 22 is fixed rigidly, but replaceably, on the roller body 21 via a bolt device 48 and a clamping ring 49. On the inside on the right, the roller unit shown in FIG. 2 is closed off by a cap-like closure device 44. This termination device 44 and its fastenings 50 serve primarily to transmit the drive torque from the inner drive shaft 24 via a coupling member 45 and its rigid connection 46 to the actual grinding roller. At the same time, a dust-tight seal for the inner shafts and a counterbearing for the inclined bearing 33 is achieved by this termination device 44.

On the drive side, the inner drive shaft 24 is connected via a coupling shaft 43 to the output shaft 42 of a schematically indicated motor 26, e.g. an electric motor, in connection. This motor 26 is held by a fastening 41 on an end plate 39 which is fixed on the rocker arm 25. The output shaft 42 of the motor 26 projects into the hollow axis 23 through a corresponding opening 40. The shaft members are designed so that there is an axial adjustment in the direction of the longitudinal axis of the hollow axis, but also a radial adjustment. Universal joints or universal joints are also possible as coupling links.

As an example, it is shown how the roller unit is acted upon by a pressure spring 29 via a flange 28, this spring 29 being supported as a counter bearing in relation to a stationary part 30.

2 therefore both the grinding bowl 3 rotates about its axis of rotation 47 and - independently of it and designed with its own drive - the grinding roller unit, so that adverse effects, as set out above, are prevented by the separate drive of the grinding roller .

The dimensioning of the bore 31 of the hollow shaft 23 is based on the outer circumference of the coupling members or the drive shaft 24 and on the other hand on the required stability for taking up the roll load and roll rotation.

In the second alternative of driving a grinding roller 55, as is shown schematically and partially in axial section in FIG. 3, a roller shaft 56 connected to the grinding roller 55 is provided. This roller shaft is e.g. via bearings 53 rotatably mounted to absorb axial and radial forces in the bushing 52 of the rocker arm. The drive takes place here via a drive device 58 with a corresponding drive shaft 57. The rocker arm 25 is mounted in a manner similar to the aforementioned example via a rocker arm joint 34 relative to a bearing housing 35. The rocking lever 25 enables the compensating movements of the grinding roller 55 with respect to the grinding bowl 3 rotating about the axis 47. On the other hand, the rocking lever also serves to pivot the entire roller unit out of the corresponding housing of the grinding system. A e.g. A pressure spring 29 supported on a stationary part 30 of the housing acts, as in the previous example, on the grinding roller 55 via a flange 28 and the rocker arm 25.

The drive device 58 is fastened to the rocker arm 25 via a motor mount 54 in the example according to FIG. 3. The bearings of the roller shaft 56 are encapsulated, if possible, just like the actual drive device 58 in a dust-tight manner with respect to the interior 7 of the grinding system. In the exemplary embodiment, the roller-side closure is formed by a rounded roller cap 69.

The drive alternatives according to FIGS. 2 and 3 could be used, for example, in a mill 1 according to FIG. 1 operated in a vacuum.

In this mill 1, the rocker arm 10 lies essentially outside the housing 2, so that the drives 26 and 58, as shown in FIGS. 2 and 3 with respect to the rocker arms 25, 27 and 52, are also directly attached to the rocker arms 10 it is possible. In these alternatives, the drives therefore pivot with the corresponding rocker arms, for example around the articulation points 34.
FIG. 4 shows an airflow grinding system according to the invention in elevation, assemblies which largely correspond to the prior art being identified by the same reference numerals as in FIG. 1.
The airflow grinding system 60 shown in FIG. 4 has a grinding bowl 61 in the area of the roller mill, which has a dome-like central elevation 62 for distributing the supplied or circulating material to be ground onto the grinding path.
The millbase is supplied via a material feed channel 64 which runs centrally through the classifier 11 from top to bottom. A hollow rotor drive shaft 65 is rotatably provided around this channel for driving the rotor 12.

The drive device of the grinding roller 20 shown on the left corresponds approximately to the alternative shown in FIG. 2, the torque being applied to the grinding roller 20 via a drive shaft 24 running in a hollow shaft. A motor 26, which is held on the outer housing 2 via fastening struts 41, drives the grinding roller 20 separately via the drive shaft 42. The drive shaft 42 protrudes through an opening 63 in the outer housing 2 of the grinding system. The passage openings or bearings for the drive shafts are designed to be gas and dust-tight, which is not reflected in the schematic drawing.

Since the rocker arms 25, 27 are arranged within the housing 2 in this airflow grinding system 60, direct fastening of the drive 26 to the rear of the rocker arm 27 is prohibited. Rather, the drive 26 must now be fastened to the outside of the mill housing 2 via the holder 41 . The pivoting movements of the rollers 20 are therefore compensated for by the drive shafts 24 by universal adjustability, which can be achieved in particular by universal joint connections.

In the overall function, the separate drive of the individual grinding rollers 20 prevents the material to be backed up in front of the rollers, thereby avoiding sliding or blocking effects which cause the roller mill to run unevenly and also bring about greater wear and tear. The drive units can be designed for a low maximum output, since impact stresses, as can still occur in the prior art, are largely prevented. The throughput performance even with a regrind with high required fineness can be significantly improved in this way.

Claims (10)

1. Airflow grinder
with a roller mill which has at least one stationary grinding roller which can be pressed against a rotatingly driven grinding bowl,
with an integrated sifter arranged above the roller mill,
the ground material-air mixture being fed to the grinding bowl and the grinding rollers essentially from the center of the roller mill,
characterized by
that in addition to the grinding bowl (3), the grinding roller (20; 55) has a separate drive device (26; 58), by means of which the grinding roller (20; 55) is forcibly rotatable in the same direction as the grinding bowl (3), which at least the theoretical speed with frictional engagement between the grinding bowl (3) - with or without regrind - and the grinding roller (20; 55) corresponds, or is greater than this theoretical speed. 2. Airflow grinding plant according to claim 1, with a plurality of grinding rollers,
characterized by
that a drive torque between 0 and a value T _{roller is} applied to each grinding _roller (20; 55), which is determined by the equation

is determined, where T _{grinding bowl is} the driving torque of the grinding bowl and T _{roller is} the maximum driving torque of a grinding _roller . 3. Airflow grinding plant according to claim 1 or 2,
characterized by
that the speed of the grinding rollers (20; 55) is adjustable, in particular continuously adjustable. 4. Airflow grinding plant according to claim 3,
characterized by
that the speed of the grinding rollers (20; 55) is adjustable depending on the fineness of the material to be ground, the bed size, the load condition or the running behavior of the roller mill. 5. Airflow grinding plant, in particular according to one of claims 1 to 4,
with a roller mill which has a plurality of stationary grinding rollers which can be pressed resiliently against a rotatingly driven grinding bowl,
with an integrated classifier arranged above the roller mill, the ground material / air mixture being fed to the grinding bowl and the grinding rollers essentially from the center of the roller mill,
with a separate drive device with which the grinding rollers can forcibly be rotated at a speed,
characterized
that the forced rotational speed of each grinding roller (20; 25) takes place in the same direction as the grinding bowl (3) and is greater than the theoretical speed with frictional engagement between the grinding bowl (3) and the respective grinding roller (20; 25), and
that each grinding roller (20) is mounted on a fixed hollow shaft (23) in which a drive shaft (24, 42, 43, 45) for the grinding roller (20) is arranged, the drive of the drive shaft on that of the grinding roller (20) facing away. 6. Airflow grinding plant according to claim 5,
characterized by
that the drive shaft (24, 42, 43, 45) is adjustable, in particular in the radial and axial directions. 7. Airflow grinding plant according to claim 5 or 6,
characterized by
that on the side of the roller mill center (8) oriented side of the hollow shaft (23) a closing device (44) for sealing the hollow shaft (23) against the interior (7) of the grinding system (60) and for torque transmission to the grinding rollers (20) is provided. 8. Airflow grinding plant according to one of claims 1 to 4,
characterized by
that each grinding roller (55) is rigidly connected to a roller shaft (56) which is rotatably mounted in the housing (2) of the grinding system (60) or an oscillating lever (25, 52) assigned to the grinding roller (55), the roller shaft (56 ) is rigidly or elastically coupled to the drive device (58). 9. Airflow grinding plant according to one of claims 1 to 8,
characterized by
that an electrical, mechanical or hydraulic drive device (26; 58) is provided. 10. Airflow grinding plant according to one of claims 1 to 9,
characterized by
that the drive device (26; 58) is provided on or separate from the housing (2) of the grinding system (60) or a stationary part of the grinding system.

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