Grinding installation with several roller mills each with a refrigerated distribution cabinet

Abstract

The invention relates to a distribution dosing device (1) for a roller mill, comprising a housing (2) with at least one grinding material inlet (3), at least one grinding material outlet (4), a feed roller (5) arranged in the housing (2) for dosing the grinding material into a grinding space of the roller mill through the grinding material outlet (4), said feed roller being rotatable about a feed shaft (SA), a conveyor shaft (6) arranged in the housing (2) for distributing the grinding material along the feed roller (5), said conveyor shaft being rotatable about a transport shaft (FA), wherein the transport shaft (FA) is substantially parallel to the shaft of the feed roller (SA), and a first filling status sensor (7) arranged in the housing (2) for determining a first filling status of grinding material of the housing (2).According to the invention, a second filling status sensor (8) is provided in the housing to determine a second filling status of the grinding material in the housing (2). The grinding material inlet (3) and the first filling status sensor (7) are arranged at a first end of the feed roller (5) and the conveyor shaft (6), and the second filling status sensor (8) is arranged at a second end of the feed roller (5) and the conveyor shaft (6).

Description

[0001] The invention relates to a grinding plant with several roller mills and a control cabinet which has a cooling system.

[0002] In prior art roller mills, the material to be ground is introduced centrally into the inlet of the respective grinding section and accumulated. The material is then distributed outwards by gravity, possibly with the aid of a paddle roller, and conveyed by the feed roller into the grinding gap. A roller mill is disclosed, for example, in WO 93 / 06928 A1.

[0003] At the start of the grinding process, the fill level of the inlet is first manually set as the target level, for example, by an operator. It is important to ensure that, on the one hand, sufficient free buffer volume is available (level as low as possible), but on the other hand, that the material being ground reaches the ends of the discharge unit (level as high as possible). During operation, a measuring device (e.g., a force transducer) detects any deviation between the actual level and the target level. A control device ensures that the discharge is adjusted so that the actual level corresponds as closely as possible to the target level. Force transducers have the disadvantage that the fill level of the material being ground is not measured directly, but indirectly, and therefore requires calibration, which is highly dependent on the properties of the material being ground. This is also the case with all other current state-of-the-art measuring principles (e.g., capacitive sensors), although to a lesser extent.In the simplest state of the art, the material being ground flows towards the ends of the discharge unit solely by gravity. Therefore, it cannot always be guaranteed that material will be present at the ends of the discharge unit and can be discharged to the roller ends. If no material is conveyed into the grinding gap at the roller ends, serious damage can occur. Distribution devices (for example, paddle rollers) that assist in transporting the material to the ends of the discharge unit are also considered state of the art. A disadvantage of all state-of-the-art systems is that this distribution function is not automatically controlled or regulated during operation, independently of the material being ground.

[0004] A disadvantage of such roller mills is that the operator must manually define the fill level as the target level. This "empirical" setting of the target level is also intended to ensure the distribution of the ground material along the length of the feed roller. Checking / monitoring the distribution of the ground material along the feed roller, if done at all, is only done visually. In operation, it can happen that, due to an unsuitable selection of the target level and / or an unsuitable presetting of the distribution device, the ground material does not reach the ends of the discharge unit. Correct adjustment is difficult even for experts. With the ground material properties changing during operation, the risk of a malfunction is even greater at critical points using current technology. Furthermore, it is important that the ground material is not segregated when the product is fed into the center, as the product is not mixed at the inlet.The risk of segregated ground material in the inlet is particularly high when different qualities of ground material flow into the inlet through two or more feed pipes.

[0005] A distribution and metering device for a roller mill, as well as a roller mill itself, is described here. This device avoids the disadvantages of known designs and, in particular, enables optimal distribution of the material being ground along the metering shaft. Furthermore, it is intended to promote the mixing of the material being ground in the inlet area.

[0006] The distribution and metering device comprises a housing with at least one inlet for grinding material and at least one outlet for grinding material, as well as a feed roller arranged in the housing for metering grinding material into a grinding gap of the roller mill through the outlet for grinding material, which is rotatable about a feed roller axis.

[0007] The distribution and metering device further comprises a conveying shaft arranged in the housing for distributing ground material along the feed roller, which is rotatable about a conveying shaft axis, the conveying shaft axis being arranged parallel to the feed roller axis, and a first level sensor arranged in the housing for determining a first level of ground material in the housing. It is understood that individual sensors (e.g., sensor strips) can also be connected in combination to cover, for example, a greater height with such a combined level sensor.

[0008] The distribution and metering device also includes a second level sensor arranged in the housing for determining a second level of ground material in the housing, wherein the ground material inlet and the first level sensor are arranged at a first end of the feed roller and the conveying shaft, and the second level sensor is arranged at a second end of the feed roller and the conveying shaft.

[0009] The terms "at a first end" and "at a second end" mean that the first and second sensors are located at the first and last third of the feed roller, respectively. Preferably, the level sensors are located at the first and last quarter of the feed roller. The range specifications refer to the length of the feed roller in the axial direction.

[0010] The distribution and metering device is typically positioned above the grinding rollers of a roller mill. Material to be ground is fed into the housing of the distribution and metering device, where it forms a buffer that serves as a buffer for operating the roller mill, thus smoothing out small fluctuations in mass flow. The feed roller then conveys the material to the outlet of the distribution and metering device and from there into the grinding gap. The feed roller axis is preferably arranged parallel to the axis of the grinding rollers of the roller mill.

[0011] To ensure the distribution of the material being ground along the feed roller, a conveying shaft is provided. Rotation of the conveying shaft ensures that the material is conveyed in one direction along the shaft's axis, thus aiding in the distribution of the material by gravity. The conveying shaft is preferably designed as a screw conveyor or paddle roller. Furthermore, a conveying section of the shaft, i.e., the section of the conveying shaft that conveys the material being ground, preferably extends over at least half the axial length of the feed roller, and preferably over the entire axial length of the feed roller.

[0012] This design ensures that the feed roller is supplied with material along its entire length, thus preventing the grinding gap from operating without material feed in certain areas. Furthermore, the conveying shaft mixes the material being ground within the distribution and metering device, counteracting segregation caused by the formation of a screed cone (particularly due to the sieving effect).

[0013] The material inlet is located at one end of the feed roller and the conveying shaft. This means that, unlike in known devices, the material to be ground is not fed in the middle of the feed roller, but rather at one end of the feed roller and the conveying shaft. The first level sensor for determining the initial level of material to be ground is also located in this end. The height of the material being ground can be determined using this first level sensor.

[0014] A second level sensor is located at the other end of the feed roller and the conveying shaft. This allows a second material level, i.e., the height of the material being ground, to be determined.

[0015] Thus, a level sensor is positioned at each end of the feed roller (and the conveying shaft). The lateral arrangement of the material inlet and the placement of the level sensors allow conclusions to be drawn as to whether the feed roller is supplied with enough material along its entire length.

[0016] If the material inlet is not centrally located, the distribution and metering device is mirrored. The first level sensor is positioned below the material inlet, and two second level sensors are located at both ends of the feed roller and the conveying shaft. The conveying shaft is then designed so that material can be conveyed from its center to both ends by rotation. Preferably, the conveying shaft is designed in two parts, so that each half can move independently of the other half. It is evident that such a design is simply a mirror image of the distribution and metering device described herein.

[0017] The feed roller and the conveying shaft are preferably movable independently of each other. This means that the feed roller and / or the conveying shaft have a dedicated drive and are not, as known from the prior art, driven in a coupled manner. Preferably, the feed roller and the conveying shaft each have their own drive.

[0018] Preferably, the speed of the feed roller is controllable or adjustable depending on the initial fill level of the material being ground. This means that the speed of the feed roller is adjusted based on the initial fill level of the material being ground, as determined by the first fill level sensor.

[0019] Preferably, the feed roller is driven at a low speed if the initial material level is low. The speed is then increased if the initial material level rises.

[0020] In particular, a control unit can be used to keep the initial material level essentially constant. The target value for this can be permanently programmed into the control unit, dependent on other factors, or adjustable by an operator. The speed of the feed roller is adjusted according to the deviation between the target and actual values ​​of the initial material level.

[0021] The speed of the conveying shaft is preferably also controllable or adjustable depending on the second material level. This means that the speed of the conveying shaft is adjusted depending on the second material level determined by the second level sensor.

[0022] Preferably, the conveying shaft is driven at a higher initial speed if the second material level is low. The speed is then reduced if the second material level rises.

[0023] In particular, it can be provided that the second material level is kept essentially constant by a suitable control unit. The target value for this can be permanently programmed into the control unit, dependent on other factors, or adjustable by an operator. The speed of the conveying shaft is adjusted depending on the deviation between the target and actual value of the second material level.

[0024] Changing the speed of the feed roller results in a corresponding increase or decrease in the amount of material being ground. Measuring the level of the second material being ground and adjusting the rotation of the conveying shaft accordingly ensures that the material is distributed along the entire length of the feed roller. The conveying shaft also mixes the material being ground.

[0025] The outlet for the ground material is preferably designed as a gap between the feed roller and a throttling device.

[0026] The throttling device preferably comprises a rotatable profile with a circular segment-shaped cross-section. Such a profile can, for example, be easily produced from a circular profile by removing / grinding off a circular segment. An advantage of this design is that the metering edge of the profile is stiffer than in known solutions where the throttling device comprises a flap composed of multiple elements. These elements must then be aligned to form a straight metering edge. Furthermore, a profile with a circular segment-shaped cross-section is more rigid than known solutions.

[0027] In such a device with a grinding material outlet designed as a gap between the feed roller and a throttling device, the gap width is preferably controllable or adjustable depending on the initial grinding material fill level. Particularly preferably, in such a case, the feed roller is operated at a constant speed and the grinding material discharge quantity is adjusted solely via the gap width.

[0028] The distribution and metering device preferably comprises a guide arrangement for directing the material to be ground to the feed roller. The guide arrangement is preferably designed as a sliding surface. The guide arrangement terminates with an edge that is spaced between 0.001 and 5 mm away from the feed roller. In radial section through the feed roller, the edge is positioned at an angular distance between 0° and 90° with respect to a perpendicular through the feed roller axis. In other words, the edge is positioned between the 9 o'clock and 12 o'clock positions.

[0029] This edge arrangement minimizes dead spaces around the feed roller, thus improving hygiene of the distribution and dosing unit. It also simplifies cleaning and emptying of the distribution and dosing unit.

[0030] The distribution and dosing device further comprises a control unit which is operatively connected to the first and second level sensors and by means of which the feed roller and / or the conveying shaft can be controlled / regulated. The control unit is arranged in a control cabinet with a cooling system that includes at least one Peltier element.

[0031] The control unit serves to control / regulate the rotation of the feed roller and the conveying shaft, and controls / regulates this in particular depending on the first or second fill level of ground material.

[0032] Of course, additional sensors can be connected to the control unit, which can also be used to control / regulate the feed roller and the conveyor shaft.

[0033] Due to the environmental conditions of a roller mill, the control unit must be protected from external influences (dust) and, for safety reasons (risk of dust explosion), must be securely housed and isolated from the environment as a potential ignition source. Previous solutions proposed a central control cabinet from which the entire system (multiple roller mills) is powered and controlled. The installation effort is considerable, as numerous cables must be run from the control cabinet to each individual machine.

[0034] The object of the present invention was to overcome this disadvantage. This object is achieved by a grinding system according to claim 1.

[0035] With a control cabinet mounted directly on the distribution and dosing device, the installation effort of previous solutions is eliminated. In particular, only three cables need to be connected to the control unit (power supply; data transmission, e.g., BUS; safety shutdown). Therefore, the device can be pre-installed and configured at the factory and simply needs to be connected to the respective cables at the installation site using a "plug-and-play" concept. To dissipate the heat generated during operation, the control cabinet includes at least one Peltier element for cooling the interior.

[0036] The insulation between the exterior and interior is advantageous here, so that potential ignition sources are not in contact with the roller mill environment.

[0037] The roller mill comprises at least two rollers that define a roller gap for grinding material, wherein the roller gap is supplied with material from the material outlet of the distribution metering device.

[0038] The material to be ground is fed to the roller mill via the distribution and metering device described above.

[0039] The ground material is fed to the distribution and dosing device via the ground material inlet and then leaves the distribution and dosing device through the ground material outlet.

[0040] Preferably, the speed of the feed roller is controlled or regulated depending on the initial material level. In particular, the speed of the feed roller is adjusted proportionally to any deviation between a target value of the initial material level and the actual value of the initial material level.

[0041] Preferably, the speed of the conveying shaft is controlled or regulated depending on the level of the second material being ground. In particular, the speed of the conveying shaft is adjusted inversely proportional to any deviation between a target value of the second material being ground and the actual value of the second material being ground.

[0042] Preferably, if the distribution and metering device is configured with a grinding material outlet formed as a gap between the feed roller and a throttling device, the gap width is controlled or regulated depending on the initial grinding material level. The rotational speed of the feed roller is kept particularly constant (i.e., not changed during operation). The gap width is adjusted proportionally to any deviation between a target value of the initial grinding material level and the actual value of the initial grinding material level.

[0043] In addition to machine control elements, the control cabinet contains at least one power electronics component for operating the main drive motors of the rolls of the roll mill and / or the drive motors of the roll mill's power supply unit. Preferably, the power electronics component is selected from the group consisting of safety switches, main switches, soft starters, frequency converters (inverters), and high-voltage cables.

[0044] The present invention thus relates to a grinding plant with several roller mills, wherein each roller mill comprises at least two rollers arranged in a housing, a grinding material inlet, a grinding material outlet, a distribution and metering device, and a control unit for controlling and / or regulating the roller mill, characterized in that the control unit of each roller mill is arranged in a control cabinet with a cooling system, which is arranged directly on the distribution and metering device of the respective roller mill, wherein the cooling system in particular comprises at least one Peltier element, and that all connecting lines of the respective roller mill are connected via its control unit in the control cabinet of the roller mill.

[0045] The insulation between the exterior and interior is advantageous here, so that potential ignition sources are not in contact with the roller mill environment.

[0046] The invention is described in more detail below with reference to a preferred embodiment in conjunction with the figures. The figures show: Fig. 1 a schematic sectional view of the distribution and metering device for the grinding plant according to the invention in a plane parallel to the feed roller shaft; Fig. 2 a schematic sectional view of the distribution and metering device for the grinding plant according to the invention in a plane perpendicular to the feed roller shaft; and Fig. 3 a schematic perspective view of a roller mill for the grinding plant according to the invention with a distribution and metering device and a control cabinet.

[0047] In the Figure 1 and 2A distribution and metering device 1 is shown schematically. The distribution and metering device 1 comprises a housing 2 with a material inlet 3 and a material outlet 4. A feed roller 5, rotatable about a feed roller axis SA, and a conveying shaft 6 are arranged in the housing 2 above the feed roller 5 in the direction of material flow. In this case, the conveying shaft is designed as a screw conveyor and is rotatable about the conveying shaft axis FA, which is parallel to the feed roller axis SA. Motors 15 and 16 are provided to drive the feed roller 5 and the conveying shaft 6, respectively. The motors 15 and 16 are operatively connected to a control unit 12 (shown schematically by the dashed line).

[0048] In the housing 2 are arranged two level sensors 7 and 8, which are designed to determine the level of the ground material in the housing and are also in operative communication with the control unit 12.

[0049] The first level sensor 7 is located in the area of ​​the material inlet 3 at one end of the feed roller 5 and the conveying shaft 6. The second level sensor 8 is located at the other end of the feed roller 5 and the conveying shaft 6. Thus, there are two level sensors 7 and 8 located at the two ends of the feed roller 5 and the conveying shaft 6. The material inlet 3 is also not located centrally, as in known devices, but is positioned above the first end of the feed roller 5 and the conveying shaft 6.

[0050] From the Figure 2Furthermore, the structure of a throttling device 10 is visible, which is used to adjust a gap 9 that serves as the grinding material outlet 4 of the housing 2. The throttling device 10 comprises, in addition to actuators and bearings, an elongated profile 11 with a circular segment-shaped cross-section. By rotating the profile 11 (schematically represented by the dashed line), the gap width of the gap 9 can be adjusted.

[0051] From the Figure 2The arrangement of the guide assembly 18, which is designed as a chute, is also visible. The guide assembly terminates with an edge 19 close to the surface of the feed roller 5. The edge 19 is positioned so that no material being ground can get under the feed roller 5 or remain in the feed chamber; for example, the edge 19 can be positioned at an angular distance of 0° to 90° with respect to a plumb line through the feed roller axis SA. This arrangement reduces the dead space around the feed roller and facilitates the residual emptying / cleaning of the distribution / metering device 1. A casing 20 adjoins the edge 19 for sealing. In the prior art, the feed chamber largely surrounds the feed roller (discharge roller), creating a dead zone below the feed roller (discharge roller) which cannot be completely emptied during operation and would therefore have to be cleaned manually when the system is at a standstill.This dead zone can be an unwanted habitat for insects, etc. Therefore, when designing edge 19, care should ideally be taken to ensure that no such dead zone can form.

[0052] When the distribution and metering device 1 is operated, material to be ground is fed in through the material inlet 3. By rotating the conveying shaft 6, the material to be ground is conveyed from the first end towards the second end of the feed roller 6. This distribution is monitored by the second level sensor 8. If the second material level (actual value) measured by the second level sensor 8 deviates from a target value for the second material level, the speed of the conveying shaft 6 is adjusted accordingly, so that more or less material to be ground is conveyed to the other end of the feed roller 5.

[0053] Simultaneously, the feed roller 5 is driven. If the first material level measured by the first level sensor 7 (actual value) deviates from a target value for the first material level, the speed of the feed roller 5 is adjusted accordingly so that more or less material is discharged, thus keeping the fill level of the housing constant.

[0054] In the Figure 3 A roller mill 14 with a distribution and metering device 1 for the grinding plant according to the invention is visible. Of particular note is the control cabinet 13, which is arranged on the roller mill and houses the control unit 12 and is cooled by Peltier elements 17 (of which only the cooling fins are visible). Other ATEX-compliant cooling systems are also conceivable, for example, liquid cooling, especially water cooling; ATEX-compliant fans; etc.

Claims

1. Milling plant with several roller mills (14), each roller mill (14) comprising at least two rollers arranged in a housing (2), a material inlet (3), a material outlet (4), a distribution-dosing device (1) and a control unit (12) for controlling and / or regulating the roller mill (14), characterized in that for each roller mill (14), the control unit (12) is arranged in a switch cabinet (13) with a cooling system, which is arranged directly on the distribution-dosing device (1) on the respective roller mill (14), wherein the cooling system particularly comprises at least one Peltier element (17), and that all connection lines of the respective roller mill (14) are connected via its control unit (12) in the switch cabinet (13) on the roller mill (14).

2. Milling plant according to claim 1, characterized in that three lines for power supply, data transmission and safety shutdown are connected to the control unit (12).

3. Milling plant according to claim 1 or 2, characterized in that insulation is provided between the exterior and interior of the switch cabinet (13).

4. Milling plant according to one of claims 1 to 3, characterized in that in the switch cabinet (13) there is additionally contained at least one power electronic component, which serves to operate the main drive motors of the rollers of the roller mill and / or the drive motors of a feeding unit of the roller mill.

5. Milling plant according to claim 4, characterized in that the power electronic component is selected from the group consisting of safety switch, main switch, soft starter, frequency converter (inverter) and high-current lines.

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