The On-line And Precise Measurement Principle And Method Of Refining Gap Of Disk Refiner For Papermaking

To measure, control and adjust the refining gap of disc refiner used widely for beating and high-yield pulping has been being one of the key technologies of disc refiner. The present technology in the world is based on keeping stable electric current value, that is, the refining power of disc refiner's host motor. In practice, the electric current value of disc refiner's host motor is influenced by the mobility of pulp flux and consistence and by impurity in pulp, and the scale value of the vernier doesn't contain the wearing gap between rotating tooth-disc and stable tooth-disc when disc's running. Therefore, the present technology has not made the Direct, Online and Precise Measurement of Refining Gap (DOPMRG) of disk refiner come true. DOPMRG is much necessary for improving the pulp-refining quality and ensuring the disc refiner to run safely.In the paper, firstly, the key technical demands to realize DOPMRG were brought forward. Secondly, the transducer satisfied with DOPMRG was screened out. Thirdly, the displacement-measuring theory, method, and in-and-out characteristic of the transducer screened out above were discussed when used for measuring the displacement of the rotating tooth-like metallic disk. Then, the condition, theory, technology and method about installing transducer on the disc refiner's stable disc, as well as the in and out characteristic of the transducer working under the different conditions of practical pulp refining, were researched and evaluated respectively. Finally, the calibration transform and program-converting flow of plate-gap arithmetic , as well as the basic program on computer, were studied showing.The main conclusions obtained in the paper are as follows:1. The eddy current sensor is best fit for measuring directly and accurately the displacement of the rotating tooth-like metallic disk with the conditions the disc refiner works under, and with the shape of the tooth-disc of disc refiner.2. The eddy current distribution on tooth-like metallic disk are: that there is a series of compound, abnormal, and closed circumfluent eddy current distribution in the tooth part, and that there is thicker circumfluent eddy current distribution around the edge area of tooth; but, that, in non-tooth (plane) part (below the underside of the alveolus), there is circumfluent eddy current distribution which is a series of circularity with one heart of the axes of the probe loop. If eddy current sensor is used for effectively measuring the surface displacement of tooth-like metallic disk, its probe should always cover with the same characteristic of sum of tooth and alveolus area, so as to bring about the stable eddy current characteristic.3. When the probe of eddy current sensor (Φ11 mm) measured the stable and rotating metallic tooth disc, the Sensor's Voltage (U)-Displacement (X) Response Curve (SVDRC (U-X)) showed the same changing rend as that obtained when it measured the metallic plane disc. When X was the same and closed to zero, the out-voltage U of sensor for the metallic tooth disc showed stepping up earlier than that of sensor for metallic plane disc. SVDRCs (U-X) of different metallic tooth discs with different tooth size were very closed.When the metallic tooth disc rotated at the speed of less than 760rpm (corresponding to the line speed of 172m/min), the value of U of SVDRC (U-X) waved in the range of±0.04v; while the value of U was steady when tooth disc's rotating speed was more than 760rpm, and the more the rotating speed, the steadier the value of U.With displacement of 0.6~7.20mm, obtained were the optimized linearity regression equations'parameters of in-and-out characteristic data of eddy current sensor of 9 testing tooth discs for captive and dynamic tests. The correlation coefficients of the 9 linearity regression response curves were all more than 0.999, and slops of the 9 linearity regression response curves were almost the same.4. There was non-linear edge effect of in-and-out characteristic of eddy current sensor when it measured the displacement of the border area of tooth-like metallic disc. The border area with non-linear edge effect was e<3mm (e represented the distance between the probe's radial end and the border of tooth-like metallic disc).5. When the probe of eddy current sensor was used for DOPMRG of disk refiner, the in-and-out characteristic of eddy current sensor did not be influenced by kinds, consistence, flux of the pulp refined. And when the stable and rotating discs worked respectively under three working conditions of stopping state without pulp, rotating state without pulp, and rotating state with pulp, the in-and-out specialities of eddy current sensor were almost consistent, and recurred very well when the stable disc advanced and fell back.6. There are four operating states for the refining disc: zeroing and obtaining initial gap, starting and running, advancing and falling back, and pausing. During the calibration transform as well as on-line acquisition and processing of the signal exported by the transducer measuring the refining gap of the disc refiner, the plate gap arithmetic and program-converting flows of four operating states are different.The paper did, for the first time in the world, open out the displacement measuring theory, method, and in-and-out characteristic of eddy current sensor when it was used for measuring the displacement of the rotating tooth-like metallic disk, which provided eddy current sensor with a new application of non-contact displacement measurement. The paper, also, indicated the theory, basic technical principle and method of DOPMRG of disk refiner, which settled the important base for guaranteeing pulp refining technic parameters to be put in practice on refiner and for enhancing the pulp refining technic controlling level. The paper's application will have great foreground and be spread fast.