A METHOD AND A DEVICE FOR CONTROLLING THE ALIGNMENT BETWEEN REFINING SURFACES

Technical Field

The present invention relates to a method and a device for controlling the alignment between refining surfaces of two opposite refining discs rotatable in relation to each other, so that the gap width of the refining gap between the refining surfaces of the refining discs is kept constant for every diameter for a complete revolution, which refining discs are included in the refining apparatus for disintegrating and refining lignocellulose-containing material in a refining gap between the refining surfaces of the refining discs. Further, the present invention relates to a refining apparatus for disintegrating and refining lignocellulose-containing material in a refining gap between the refining surfaces of two opposite refining discs rotatable in relation to each other, comprising a device for controlling the alignment between the refining surfaces.

Background of the Invention

Refining apparatus or disc refiners of this type are used, inter alia, for highly concentrated refining, CTMP, TMP, fluffing and highly concentrated grinding of sack paper and other lignocellulose-containing material. They usually comprise two opposite refining discs rotatable in relation to each other, where often one re- fining disc is rotatable, a so called rotor, and one refining disc is non-rotatable, a so called stator, but in some refining apparatus both refining discs are rotatably arranged. Refining discs in this type of refining apparatus are provided with exchangeable refining segments which build up the refining surfaces of the refining apparatus. The refining segments comprise bars and intermediate grooves. Grinding occurs between the two refining surfaces which are kept at a certain distance from each other, whereby a space, a so called refining gap, is provided between the refining surfaces.

If the refining surfaces would come into contact with each other during operation, there is a risk of breakdown or at least wear on the refining surfaces, and with that a shortened operating performance. Further, the degree of alignment between the refining surfaces has a great importance regarding the quality of the ground material. When the degree of alignment between the refining surfaces is reduced, the quality of the ground material is deteriorated. An accurate control of

the refining gap and the alignment between the refining surfaces is thus of great importance.

One way of measuring the distance between the refining surfaces in a refining apparatus is disclosed in SE 416844, which discloses a device and a method for measuring the distance between two opposite surfaces, made of a magnetic conducting material, according to the reluctance method by means of a position sensor which is provided in one of the surfaces and is orientated in relation to the second surface so that the air gap between the surfaces is included in the circuit. The method comprises the use of a sensor having two windings pro- vided around a core, which are supplied with current so that they work in opposite directions and the currents are controlled so that the resulting magnetic flux through a direct current field meter located between the windings is always kept equal to zero, whereby the measurement result is attained by measuring the difference between the currents supplied to the windings. It is also known to make such a sensor displaceable from one of the surfaces towards the other surface, for position calibration.

SE 463396 discloses a device for indicating the axial contact position of the refining surfaces of two opposite refining discs rotatable in relation to each other and included in a disc refiner. A sensor sensing heat radiation is arranged to detect the heat radiation which arises through the friction as two refining surfaces contact each other during rotation in relation to each other. The sensor is positioned radially outside the refining discs.

SE 454 189 describes a method for controlling the production of mechanical pulp in a refiner process, where lignocellulose-containing material in pieces is refined when passing through the refining gap between two opposite refining discs rotating in relation to each other. The vibrations of at least one of the refining discs are measured by means of an accelerometer provided in the refining disc and are transformed to vibration energy, which, together with one or several of the process variables: production, size of the refining gap and material concentration, is used for controlling the properties of the produced pulp. Further, SE 454189 discloses that the condition of the refining segment can also be established by the measured vibration energy, which can be used for determining when it is time for exchanging refining segments, and different refining segment patterns and refining segment material can be compared.

GB 1 468649, upon which the preamble of claims 1 and 11, respectively, is based, discloses a method for adjusting the refining surfaces included in a refining apparatus, so that these are parallel when grinding wood chips into pulp, which refining apparatus comprises a stationary refining disc and a rotatable re- fining disc, the stationary refining disc being attached to the frame of the refining apparatus by means of three fixing pins of which at least one is heatable for instance by an electric current so its length is variable to achieve parallelism between the refining surfaces of the refining discs. The method comprises the steps of continuously measuring the axial force between the refining surfaces and maintaining this force at its maximum by shortening or lengthening the length of the heatable fixing pin. Said force is measured by measuring means provided on the rotation axis of the rotatable refining disc.

However, the method of GB 1 468649 assumes that the material intended for grinding has a certain moister content, which is defined as a dry matter content between 15 and 40 %, so that steam is generated between the refining surfaces, whereby this steam gives rise to the greater part of the pressure between the refining surfaces. The method is based on the conclusion that when the degree of parallelism between the refining surfaces reduces, the pressure between the refining surfaces reduces, which pressure reduction can be measured as a reduction of the axial force. When the pressure is at its maximum, the degree of parallelism is considered to be maximized. However, this means that when the material intended for grinding changes, for example regarding type, size and dry matter content, or the temperature in the refining gap changes, also the size of the maximum force attained when the degree of parallelism or alignment between the re- fining surfaces is at its maximum changes.

The Object of the Invention

The object of the present invention is thus to provide a method and a device which more effectively control the alignment between two opposite refining surfaces rotatable in relation to each other, which refining surfaces are included in a refining apparatus, in relation to prior art. The purpose is also to provide a refining apparatus provided with such a device.

Summary of the Invention

The above-mentioned objects are achieved by providing a method of the kind defined in the introductory part, which comprises the special measures which are mentioned in the characterizing portion of claim 1. By said measurement and comparison, a more effective control of the alignment between the refining surfaces is attained, so that the gap width of the refining gap between the refining surfaces of the refining discs is kept constant for every diameter of the refining surface for a complete revolution, and this is achieved independent of change in material intended for grinding, for example changes in dry matter content, size etc. or in the environment, for example changes in temperature or wear on the refining segment, in the region of the refining gap and refining discs. This results in an improved quality of the ground material, and the number of interruption of operation is kept at a minimum.

According to an advantageous embodiment of the method according to the present invention, the method comprises adjustment of the refining surface of at least one of the refining discs based on said comparison until substantially equal measurement results are obtained at all measurement positions, whereby a correct alignment is attained between the refining surfaces, so that the gap width is kept constant for every diameter for a complete revolution. By "substantially equal" is meant that the measurement results from all measurement positions are within a common and such a limited range that a satisfactory high degree of alignment between the refining surfaces is attained. This range should be within 10 % of the gap width, suitably within 5 % of the gap width, where the gap width is normally about 0.5 to 2 mm. The adjustment can, for example, be performed manually, for example by means of adjusting knobs, or by means of an automatic displacement of the refining surface, as described in GB 1 468649, or by connecting electrical stepping motors to the above-mentioned adjusting knobs. By said measurement, comparison and/or adjustment, a more effective control of the alignment between the refining surfaces is achieved, especially since the invention enables an effective control during operation, and where performing the measurement, comparison and/or adjustment during operation, during idle running and/or grinding, is an advantageous embodiment of the method according to the present invention.

The measurement is achieved by at least three sensors which are positioned at different measurement positions.

Alternatively, the measurement at the at least three measurement positions comprises non-contact measurement of the distance between the refining surfaces at each measurement position. This measurement can, for example, be performed by means of laser, by means of the reluctance method which is disclosed in SE 416844 etc.

According to the present invention, the measurement at the at least three measurement positions comprises measuring the vibrations at each measurement position. Alternatively, the measurement can, for example, comprise measuring the temperature at each measurement position, or measuring other parameters based upon which the alignment can be controlled by the present invention.

Further advantageous embodiments of the method according to the present invention are evident from the dependent claims. The above-mentioned objects are also achieved by providing a device of the kind defined in the introductory part, which comprises the special features which are mentioned in the characterizing portion of claim 6. Hereby, a more effective control of the alignment between the refining surfaces is attained so that the gap width is kept constant for every diameter of the refining surface for a com- plete revolution, and this is achieved independent of a change in material intended for grinding, or in the environment of the region refining gap and refining discs. Further, a device is provided which is uncomplicated and easy to install, both in connection with the assembly or set-up of the refining apparatus, or afterwards when the refining apparatus already is assembled or set-up, and consequently, an installation afterwards is not expensive.

According to an advantageous embodiment of the device according to the present invention, the device comprises adjusting means for adjusting the refining surface of at least one of the refining discs based on the comparison of the comparison means until substantially equal measurement results are obtained at ail measurement positions, whereby a correct alignment is attained between the refining surfaces, so that the gap width is kept constant for every diameter for a complete revolution. Advantageously, the number of adjusting means is at least three, and can comprise fixing pins which are disclosed in connection with QB 1 468649. By "substantially equal" is meant the same as clarified above in con-

nection with the method. By said measuring equipment, comparison means and adjusting means, a more effective control of the alignment between the refining surfaces is provided, especially in the light of the fact that the device enables an effective control during operation, and where an advantageous embodiment of the device according to the present invention is the fact that measuring equipment, comparison means and/or adjusting means are/is arranged to perform the measurement, comparison and/or adjustment during operation, during idle running and/or grinding.

The measuring equipment of the device of the present invention com- prises at least three sensors which are provided at different measurement positions.

Alternatively, each sensor consists of a distance meter for non-contact measurement of the distance between the refining surfaces at the respective measurement position. Examples of advantageous distance meters are laser me- ters, inductive distance meters which are disclosed in SE 416844 and which are displaceably arranged, etc.

According to further advantageous embodiments of the device according to the present invention, each vibration sensor, provided at one of the refining discs for measuring the vibrations at the respective measurement position, con- sists for instance of an accelerometer, microphone etc. Alternatively, also temperature sensors for measuring the temperature can be provided at each measurement position, or other sensors for measuring other parameters, based upon which the alignment can be controlled by the present invention.

Further advantageous embodiments of the device according to the present invention emerge from the dependent claims.

The above-mentioned objects are also attained by providing a refining apparatus of the kind defined in the introductory part, where the device comprises the special features which are mentioned in any of the claims 6 to 10.

Brief Description of the Drawings The present invention will now be described, for exemplary purposes, in more detail by way of embodiments and with reference to the enclosed drawings, in which:

Fig. 1 is a schematic block diagram illustrating a first embodiment of the device according to the present invention, connected to a refining apparatus which is schematically shown in cross-section from the side, Fig.2 is a schematic block diagram illustrating a second embodiment of the device according to the present invention, connected to a refining apparatus which is schematically shown in cross-section from the side,

Fig. 3 shows an advantageous placement of the sensors of the first em- bodiment of Fig. 1,

Fig.4 shows an advantageous placement of the sensors of the second embodiment of Fig.2,

Fig. 5 is a flow diagram illustrating a first embodiment of the method according to the present invention, Fig. 6 is a flow diagram illustrating a second embodiment of the method according to the present invention, and

Fig. 7 is a diagram showing the relation between the vibration level of the stator and the change in refining gap of a refiner.

Detailed Descripϋon of Preferred Embodiments Fig. 1 shows a first embodiment of the device according to the present invention, connected to a refining apparatus, a so called disc refiner, of which only the refining housing is shown in Fig. 1 in cross-section, for disintegrating and refining lignocellulose-containing material in a refining gap 102 between refining surfaces 103, 104 of two opposite refining discs 105, 106 rotatabie in relation to each other, in the form of a rotatabie rotor 105 and a non-rotatable stator 106. The device comprises measuring equipment for measuring at at least three different measurement positions in the region of the refining gap 102 and the refining surfaces 103, 104, which measuring equipment comprises three inductive position sensors 107, 108, 100 provided at three different positions at the refining surface 104 of the stator 106, for measurement according to the reluctance method, where each position sensor 107, 108 109 is orientated in relation to the refining surface of the rotor 105 so that the refining gap 102 and the refining surface 103 of the rotor 105 are included as a part of the circuit, the reluctance of which is measured,

and so that each position sensor 107, 108109 is pushable out from the refining surface 104 of the stator 106 for moving into contact with the refining surface 104 of the rotor 105, for calibration. Each position sensor 107, 108, 109 comprises two windings provided around a core, which are supplied with current so that they work in opposite directions and the currents are controlled so that the resulting magnetic flux through a direct current field meter located between the windings is always kept equal to zero, and the difference between the currents supplied to the windings is measured. A corresponding position sensor is disclosed in SE 416844. Further, the measuring equipment comprises current generators 110 for feeding current to the position sensors 107, 108, 109, control means 111 for controlling the displacement and calibration of the position sensors 107, 108, 109, and signal processing means 112 for processing the signals from the position sensors 107, 108, 109. The device comprises a control device 113 which is connected to the current generators 110, the control means 111 and the signal processing means 112, from which the control device 113 receives signals. Further, the control device 113 is connected to three adjusting means 114, 115, 117 for adjusting the refining surface 104 of the stator 106, advantageously, the adjusting means 114, 115, 117 being evenly distributed around the circumference. The control device 113 comprises comparison means 116 for comparing the measurement results of the position sensors 107, 108, 109 with each other, and correct alignment is established if these measurement results are substantially equal. The control device 113 is arranged to control the adjusting means 114, 115, 117 for adjusting the refining surface 104 of the stator 106 based on the comparison by the comparison means 116 until substantially equal measurement results are obtained from the three position sensors 107, 108, 109, whereby correct alignment between the refining surfaces 103, 104 is attained. The measuring equipment 107, 108, 109, 110, 111, 112, the comparison means 116 and the adjusting means 114, 115, 117 are arranged to perform said measurement, comparison and adjustment during operation. Fig.2 shows a second embodiment of the device according to the present invention, connected to a refining apparatus 201 , in the form of a so called CD-refiner (Conical Disc), of which only the refining housing is shown in Fig.2 in cross- section. The device comprises measuring equipment for measuring at four different measurement positions in the region of the refining gap 202 and the refining

discs 205, 206, a rotor 205 and a stator 206, which measuring equipment comprises four vibration sensors 207, 208, 209, 210, in the form of four accelerome- ters 207, 208, 209, 210, provided at four different positions at the stator 206 for measuring the vibrations at the respective measurement position. In this embodi- ment, the accelerometers 207, 208, 209, 210 are provided at that side of the stator 206 which is opposite the refining surface 204 and are attached to the bolts 220, the purpose of which are to keep the refining disc 206 with refining segments in position, which refining segments build up the refining surface 204. Thus, these bolts 220 transmit vibrations from the refining surface 204 to the opposite side of the stator 204 and to each accelerometer 207, 208, 209, 210. This is an effective installation of the accelerometers 207, 208, 209, 210 when the device is installed afterwards when the refining apparatus is already assembled or set-up. However, also other installation positions of the accelerometers 207, 208, 209, 210 are possible. If the device is installed at the same time as the refining apparatus is as- sembled, the accelerometers 207, 208, 209, 210 are advantageously positioned as close to the refining surface as possible, for example immediately under said refining segments. The accelerometers 207, 208, 209, 210 are arranged to measure the amplitude and frequency of the vibrations at the respective measurement position. Further, the measuring equipment comprises a current generator 211 for feeding current to the accelerometers 207, 208, 209, 210, filtering means 212 for filtering the signals received from the accelerometers 207, 208, 209, 210, and sampling means 213 for sampling the filtered signals. The device comprises a control device 214 which is connected to the current generator 211, the filter means 212 and the sampling means 213 from which the control device 214 re- ceives the sampled signals. Further, the control device 214 is connected to three adjusting means 215, 216, 218 for adjusting the refining surface 204 of the stator 206, advantageously, the adjusting means 215, 216, 218 being evenly distributed around the circumference. The control device 214 comprises comparison means 217 for comparing the measurement results of the accelerometers 207, 208, 209, 210 with each other, and correct alignment is established if these measurement results are substantially equal. The control device 214 is arranged to control the adjusting means 215, 216, 218 for adjusting the refining surface 204 of the stator 206 based on the comparison by the comparison means 217 until substantially equal measurement results are obtained from the four vibration sensors 207, 208,

209, 210, whereby correct alignment between the refining surfaces 203, 204 is attained. The measuring equipment 207, 208, 209, 210, 211, 212, 213, the comparison means 217 and the adjusting means 215, 216, 218 are arranged to perform said measurement, comparison and adjustment during operation, Fig. 3 shows a front view of the stator 106 of Fig. 1 in cross-section, and shows schematically an advantageous placement of the position sensors 107, 108, 109. The position sensors 107, 108, 109 are installed at the refining surface 106 of the stator 106 substantially along one and the same diameter of this refining surface. Fig.4 shows a front view of the stator 206 of Fig.2 in cross-section, and shows schematically an advantageous placement of the vibration sensors 207, 208, 209, 210. The vibration sensors 207, 208, 209, 210 are positioned substantially symmetrically along the periphery of the refining surface 204 of the stator 206. Although, the sensors of the above-mentioned embodiments are installed at the stator, it is also possible to provide them in a corresponding may at the rotor. Instead of sensors which measure the vibrations and the distance according to the reluctance method, respectively, it is also possible to use other sensors which measure other parameters, based upon which the alignment can be controlled. Fig.5 shows a flow diagram illustrating a first embodiment of the method according to the present invention. First, the position sensors are calibrated, at 501, which position sensors are of the type described in connection with Fig. 1, by pushing the position sensors out from the refining surface of the stator and moving them into contact with the refining surface of the rotor. Thereafter, a non-contact measurement of the distance between the refining surfaces at each measurement position according to the reluctance method is performed, at 502, at three different measurement positions in the region of the refining gap and the refining surfaces by means of three position sensors positioned at different measurement positions, where each position sensor measures the reluctance in a circuit in which at least the refining surface of the rotor and the refining gap are included. The measurement of the distance is performed substantially along one and the same diameter of the refining surface of one of refining discs. After this, the signals/measurement results from the position sensors are processed, at 503. The measurement results are analysed, at 504, which analysis comprises comparison of the measurement

results with each other. Hie refining surface of the stator is adjusted based on said comparison in step 504 until substantially the same measurement results are obtained at all measurement positions, whereby correct alignment between the refining surfaces is attained. Thereafter, this process is preformed recurrently during the operation of the refining apparatus.

Fig. 6 shows a flow diagram illustrating a second embodiment of the method according to the present invention. First the vibrations at four different measurement positions in the region of the refining gap and the refining discs are measured, at 601, by measuring the amplitude and frequency of the vibrations, and this is performed by means of four accelerometers positioned at different measurement positions. The measurement of the vibrations is performed in one and the same refining disc, advantageously, as close to the refining surface of the refining disc as possible. Advantageously, first the frequency is observed and the frequency determines which amplitude shall be the leading one. Thereafter, the signals/measurement results received from the accelerometers are filtered, at 602, so that noise is filtered out. The filtered signals are sampled, at 603, after which the sampled signals are analysed, at 604, which analysis comprises comparison of the measurement results with each other. The refining surface of the stator is adjusted, at 605, based on said comparison in step 604 until substantially the same measurement results are obtained at all measurement positions, whereby correct alignment between the refining surfaces is attained. Thereafter, this process is preformed recurrently during the operation of the refining apparatus.

By "substantially equal" is meant that the measurement results from all measurement positions are within a common and such a limited range that a sat- isfactory high degree of alignment between the refining surfaces is attained.

Instead of measuring the vibrations and distances according the reluctance method, respectively, it is also possible to measure other parameters, based upon which the alignment can be controlled.

Fig.7 shows a diagram showing the relation between the vibration level of the stator and change in refining gap of a refiner, where the y-axis shows the vibration level in the stator at a measurement position, and the x-axis shows the position of the rotor.