ROLLER MILL

The present invention relates to a roller mill for grinding particulate material such as cement raw materials, cement clinker and similar materials, said roller mill comprising a substantially horizontal grinding table and at least one roller operating interactively therewith, said roller rotating about a roller shaft which is connected to a vertical central shaft via a hinged connection which allows the roller to move freely up and down in a plane comprising the centreline of the roller shaft.

A roller mill of the aforementioned kind is known for example from the published German patent application No. 2061422. This known mill is arranged so that the rollers rotate about the central shaft while the grinding table is stationary. In the known mill the grinding force required for grinding the material is generated partly by the own weight of the roller and the roller shaft and partly by the gyroscopic effect from the rollers and partly from the centrifugal force acting upon the rollers. In the known mill the total grinding force which is applied by the rollers during the operation of the mill to the material deposited on the table will thus depend on the velocity at which the rollers rotate about their own axis and about the central shaft. The roller mill may further incorporate force means, mechanically or hydraulically operated, for generating the desired grinding pressure. Also the grinding table may be arranged giving it the ability to rotate in the same or in the opposite direction of the rollers in order to enhance the capacity of the mill. During the operation of roller mills of the aforementioned kind it is often desirable in a simple way to be able to regulate the specific grinding pressure which is applied to the material, without having to change the rotational velocity of the rollers or the grinding table and hence the total grinding force. Also, it is desirable to have the ability to prevent uneven wear on rollers and grinding table, respectively.

It is the objective of the present invention to provide a roller mill by means of which it will be possible to regulate the specific grinding pressure on the basis of a substantially constant grinding force, i.e. at constant rotational velocities for the

rollers and the grinding table while at the same time uneven wear on the rollers and the grinding table can be avoided.

This is achieved by a roller mill of the kind mentioned in the introduction, and being characterized in that it comprises means for regulating the angular position of the roller relative to the horizontal plane of the grinding table during the operation of the roller mill.

Hence it will be possible to regulate the specific grinding pressure being applied to the material during the operation of the roller mill. This is due to the fact that when the angular position of the roller is altered relative to the grinding table, the area of the grinding surface of the roller which subjects the material to a compressive force will also be changed, thereby causing the total grinding force to take the form of a changed specific grinding pressure. At the same time it will be possible to regulate the wear pattern on the roller and the grinding table so that uneven wear on these parts is avoided. This is due to the fact that the wear sustained by the roller and the grinding table will be changed in form as well as scope when the angular position of the roller in relation to the grinding table is changed.

Since the roller is supported by the grinding table and the roller shaft is connected to the vertical, central shaft via a hinged connection which allows the roller to move freely up and down in the plane comprising the centreline of the roller shaft, it will be possible to alter the angular position of the roller relative to the grinding table quite simply by forming the grinding table with means for regulating its position in the vertical direction or by forming the hinged connection with means for regulating the position of its centre of rotation in the vertical direction. In a roller mill comprising several rollers, the roller shafts may further be inter-connected through a pull/pressure system which when rotating about the hinged connections will pull the roller shafts against one another or pushing the roller shafts away from one another, respectively, thereby altering the angular position of the rollers relative to the grinding table.

The means for regulating the position of the centre of rotation of the hinged connection in the vertical direction may for example comprise an eccentric provided in the hinged connection; however, it is preferred that these means comprise means for regulating the axial position of the vertical shaft and hence also the vertical position of the hinged connection.

The means for regulating the axial position of the vertical shaft may in principle be made up of any type of actuator, such as for example a spindle, a toothed gearing or similar means which is driven by a motor. However, it is preferred that these regulating means for the vertical shaft comprise a dual-action cylinder/piston device which may either be pneumatically or hydraulically operated.

The invention will now be described in further details with reference to the drawing, being diagrammatical, and where

Fig. 1 shows a section of a roller mill according to the invention where the roller is shown in three different angular positions relative to the grinding table,

Fig. 2 shows a first embodiment of the roller mill according to the invention, and

Fig. 3 shows a second embodiment of the roller mill according to the invention, and

Fig. 4 shows a third embodiment of the roller mill according to the invention.

In Fig. 1 is seen a section of a roller mill 1 which comprises a horizontal grinding table 3 and a roller 4 operating interactively herewith, said roller being connected to a vertical shaft 5. The roller 4 rotates about a horizontal roller shaft 6 which is connected to the vertical shaft 5 via a hinged connection 7 which will allow the roller 4 during its rotation about this connection to move freely up and down in a plane comprising the centreline 12 of the roller shaft.

According to the invention the roller mill 1 comprises means for regulating the angular position of the roller 4 relative to the horizontal plane of the grinding table 3 during the operation of the roller mill. Fig. 1 shows the roller 4 in three different positions where its grinding surface forms an angle α relative to the grinding table 3. In the three examples shown, the specific grinding pressure which is applied to the material during the operation of the roller mills will exhibit variations partly because the grinding area is different and partly because the horizontal mean distance between the hinged connection and the actual grinding area is different. Also, the actual grinding area will be different in the three examples, and this entails that the wear pattern on the roller and grinding table, respectively, will also be different, hence allowing it to be regulated so that a more uniform distribution of wear is attained when different angular positions of the roller are chosen.

In Fig. 2 is seen a first embodiment of the roller mill according to the invention which comprises means in the form of an actuator 10 for regulating the position of the grinding table 3 in the vertical position, whereas in Fig. 3 is seen a second embodiment where the hinged connection 7 comprises an eccentric 11 for regulating the position of the centre of rotation of the hinged connection 7 in the vertical direction.

In Fig. 4 is seen a preferred embodiment of the roller mill according to the invention where the central shaft 5 can be moved up and down in the vertical direction through the use of an actuator 12 which in the shown example comprises a dual-action cylinder/piston device 12 which is fitted at the bottom of the shaft 5 and serving both as an axial and a radial bearing for the shaft 5. In the shown embodiment, rotation of the roller shaft 5 of the roller mill and hence the rollers 4 is effected using a drive means 13 which may, for example, consist of an electrical motor comprising a rotor 14 which is connected to the shaft 5 and an annular stator 15 which is fixed to the frame structure 16 of the mill where the rotor 14 is arranged so that it will be capable of axial movement in the magnetic field. During the operation of the roller mill, the central shaft 5, and hence the centre of rotation of the hinged connection 7, may via a pipe 17 to the dual-action cylinder/piston means 12 be lifted in the vertical direction so that the roller is

slanted away from the shaft 5 or lowered via a pipe 18 in the vertical direction so that the roller is slanted inward towards the shaft 5.