JPS63126988A - Screening apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a sieving device used in a pressure screen applied to a process for removing foreign matter from papermaking raw materials.

(Prior Art) A pressure screen, which has been well known as a sieving device for Gi pulp, has a paper stock population 1 in the upper part and a selected paper stock outlet 2 in the lower part, as shown in FIGS. 4 and 5. A casing 4 having a resect outlet 3, a screen cylinder 5 having a round hole or an elongated slit-like hole (hereinafter referred to as an opening) inside the casing 4, and a screen cylinder 5 that rotates at a small distance from the screen cylinder surface and a screen. - The cleaning device 6 serves to remove foreign matter trapped on the screen cylinder surface and keep the screen cylinder surface clean. The cleaning device 6 is connected to a motor 11 via a main shaft 7, a pulley 8 on the main body side, a belt 9, and a pulley 10 on the motor side.

The purpose of using such a pressure screen for paper stocks is to capture and remove foreign substances such as plastics, bound fibers, and undisintegrated pieces in the paper stock by trapping them on the screen cylinder surface.
The purpose is to efficiently allow fibers to pass through the openings of a screen cylinder. For this reason, it is essential that the cleaning device be rotated at a relatively high speed in order to prevent clogging of the screen cylinder apertures by foreign matter or fiber flocs in the paper stock. This rotation speed can be changed by replacing the motor side boolean, but since it is impossible to change it during operation, stable long-term operation is required based on operation data with similar stock and operation data from a test machine. In order to ensure this, a high rotational speed is selected taking into account the expected fluctuations in operating conditions during the operation period.

(Problems to be Solved by the Invention) In the conventional pressure screen, the rotation speed of the purifier is set at the most severe operating condition expected for the pressure screen during the operation period in order to ensure stable operation over a long period of time. A high rotational speed is selected with a margin of 10 to 20% added to the rotational speed of the cleaning device assuming the conditions. The rotational speed selected in this way is generally determined by changes in operating conditions or
No changes will be made unless there is a problem with the pressure screen, such as a clogged cylinder.

As a result, the cleaning device is operated at a considerably higher rotation speed than the optimal rotation speed corresponding to the operating conditions of the pressure screen at a certain point in time, which not only increases power consumption but also eliminates foreign particles in the paper stock. There were serious problems such as a decrease in the removal rate of fibers, and a tendency for fibers, especially long fibers of good quality, to escape toward the resect exit side.

The present invention has been proposed to solve the above-mentioned conventional problems.

(Lower stage for solving the problem) For this reason, the present invention is a pressure-type screen, which uses concentration sensors installed at the inlet and outlet of the paper stock, and from the concentration values measured by the sensors. Generate a signal corresponding to the reduction rate of the reject i! The converter is equipped with a converter, and a control means for controlling the output rotational speed of the variable gear that drives the purifier based on the output signal from the converter. It is intended as a means to solve the problem.

(Function) A variable speed motor is used to drive the pressure screen cleaning device, and a concentration sensor is installed at the inlet of the paper stock and the outlet of the resject. The rotation speed of the cleaning device is changed based on the Mal shrinkage ratio.

The retract fM shrinkage ratio, which is expressed as the ratio of the retract concentration to the inlet concentration of the pressure screen, is an important index for determining the operating state of the pressure screen. In other words, if the resect concentration ratio is relatively low and does not fluctuate, it is a normal and proper operating condition, and if the resect concentration ratio is relatively high and tends to increase gradually, the screen cylinder is becoming clogged. If there is a high possibility that this is the case, and if the resect concentration ratio shows an abnormally high value, it is possible to detect an operating condition such as a blockage in the openings of the screen cylinder. Therefore, by detecting the concentration of fibers at the inlet and outlet, the output rotation speed of the variable speed motor for driving the purifier can be determined from the value and change tendency of the resect Hi shrinkage ratio obtained by conversion at that point in time. By adjusting the value to suit the operating conditions, long-term stable operation of the pressure screen can be achieved.

(Embodiments) The present invention will be described below with reference to embodiments of the drawings. FIGS. 1 to 3 show embodiments of the present invention.

It should be noted that since the symbols 1 to ]O in FIGS. 1 to 3 are the same as those in the prior art shown in FIG. 4, a detailed explanation thereof will be omitted here. First, to explain the differences from the conventional one in Fig. 1, numeral 12 is a variable speed motor, numeral 13 is a density sensor at the inlet of the stock, numeral 14 is a density sensor at the resect outlet, and numeral 15 is a signal from the density sensor. Reject? Conversion device for generating a signal corresponding to a reduction ratio, 16B Rizek I->
3 a calculation device which receives a signal corresponding to the compression ratio and outputs a signal for setting the rotation speed of the variable speed motor; and 17 a control device that adjusts the rotation speed of the variable speed motor based on the rotation speed setting signal. .

Next, to explain the operation using the embodiment shown in FIG. 1, the concentration sensors 13 and 14 output a depth signal proportional to the fiber concentration, and can be of an optical type, an ultrasonic type, a radiation type, or a fluid friction loss type. Various types of concentration sensors have been put into practical use, and they are selected depending on the characteristics of the fibers in the stock, the amount added, etc., and the concentration range. Further, the signals from the concentration sensors 13 and 14 are converted by a converter 15 into signals proportional to the reject '4 reduction ratio.

In other words, the concentration at the inlet measured by the concentration sensor 13 is C+
If the concentration at the resect outlet measured by the 1-74 degree sensor 14 is C8, the resect concentration ratio KCR is K C
R=CR/C+ (11) Therefore, the conversion device 15 converts the signal according to equation (1).

In addition, if there is almost no change in the concentration of the supplied paper stock during the operation period, the resect concentration rate KcR is KCR■CR------
Since the relationship is +21, the concentration sensor 13 at the inlet can be omitted as illustrated in FIG. In this case, the conversion device 15 converts the density signal so that it is compatible with the arithmetic device 16.

Further, a signal corresponding to the Rizeku BM reduction rate from the conversion device 15 is taken into the arithmetic device 16 and stored in the memory at prescribed time intervals. A reference level is preset in the arithmetic unit 16 to be compared with an input signal corresponding to the resect concentration rate, and the magnitude and level of the input signal are evaluated.

For example, if the input signal is greater than a reference level corresponding to an abnormality, a setting signal that rapidly increases the rotation speed of the variable speed motor 12 is output. In this state, when the input signal becomes lower than the reference level corresponding to an abnormality, the setting signal that has been used to increase the rotation speed is canceled.

If the input signal is smaller than the reference level corresponding to normality, a setting signal is output that slowly reduces the rotation speed of the variable speed motor 12. When the input signal returns to the reference level corresponding to normality from this state, the setting signal for decreasing the rotation speed up to this point is canceled. In order to avoid excessive fluctuations in the setting signal for the input signal, it is desirable to perform averaging processing using the signal value recorded in the memory based on the current input signal. Reference levels are determined based on operational experience and operating data from test machines, but in practice, the number of reference levels is not limited to two, normal and abnormal, but can be any number depending on the characteristics of the pressure screen and operating conditions. That's fine.

Next, the evaluation of the change trend of the Rizeku H7A shrinkage ratio can be basically achieved by mutually comparing the signal values stored in the memory at prescribed time intervals. For example, the value obtained by subtracting the signal value stored immediately before from the current input signal value is stored in memory as the amount of change, and these amounts of change are processed using an appropriate averaging method to calculate the result. A trend value of the a shrinkage ratio is determined. If this trend value is positive, it indicates that the resect concentration rate is increasing, and if it is larger than the reference level of the trend value corresponding to the recent abnormality, the rotation speed of variable speed motor 2 is slowly reduced. Outputs a setting signal to increase. When the trend value becomes less than the reference level from this state, the setting signal that has been used to increase the rotation speed is canceled.

Conversely, if the trend value is negative and its absolute value is greater than the reference level, a setting signal is output that slowly decreases the rotation speed of the variable speed motor 12, and when the absolute value of the trend value becomes less than the reference level, the setting signal is output. Release.

The above are the basic functions of the arithmetic unit 16, but in implementation, arbitrary combinations and modifications can be made depending on the characteristics and operating conditions of the pressure screen. Further, various display, recording, and alarm functions will not be explained, but can be incorporated as appropriate.

The specific types of the variable speed motor 12 are roughly divided into DC motors and AC motors, and in the case of AC motors, there are motors with eddy current joints, shunt commutator motors, frequency conversion motors (impark motors), etc. Applicable. - The force control device 17 receives the setting signal from the calculation device 16 and outputs a control signal that actually changes the rotation speed of the variable speed motor 12 according to the type and characteristics of the variable speed motor 12. be. Further, it is desirable to set an upper limit rotation speed and a lower limit rotation speed in the control device 17 for mechanical protection and stable operation of the pressure screen.

FIG. 3 shows another embodiment, in which a constant speed motor 19 and a continuously variable transmission 20 are used in combination to drive the cleaning device 6. Therefore, the control device 21 needs to match the type and characteristics of the continuously variable transmission. However, this embodiment also has no difference in operation and effect compared to the embodiment shown in FIG.

(Effects of the Invention) As explained in detail above, according to the present invention, the operating conditions at that time are adjusted so that the resect concentration ratio falls within a preset range depending on the type, structure, and application of the pressure screen. The rotation speed of the cleaning device is adjusted accordingly.

As a result, it is possible to achieve long-term stable operation, and at the same time, the rotation speed of the cleaning device is adjusted to an appropriate speed according to changes in operating conditions such as paper stock composition, concentration, temperature, and supply flow rate. This solves the problems of conventional screens, such as high power consumption, reduced removal rate of foreign matter from the paper stock, and increased tendency for fibers to escape to the reject side.

In particular, the effect of reducing power consumption is remarkable.Accordingly, according to the present invention, the number of revolutions of the cleaning device can be reduced by 10 to 20% on average, and power consumption is generally proportional to the number of revolutions to the 2.6th power. The reduction rate of power is 28-60%.

[Brief explanation of the drawing]

1, 2, and 3 are side sectional views including a control circuit of a sieving device showing an embodiment of the present invention, FIG. 4 is a side sectional view of a conventional sieving device, and FIG. 5 is the same plane. It is a diagram. Explanation of the main parts of the figure 5 - Screen cylinder 12 - Variable speed motor 13 - Person [J part concentration sensor 14 - Reject output part concentration sensor 15 - Conversion device 16 - Arithmetic device 17 - Control device 2〇 - Continuously variable transmission 21-Control device Figure 3

Claims (1)

[Claims] The pressure screen includes a concentration sensor installed at the inlet of the stock and at the outlet of the resect, a conversion device that generates a signal corresponding to the resect concentration rate from the concentration measurement value of the sensor, and a signal from the conversion device. A sieving device comprising: control means for adjusting the output rotation speed of a variable speed motor that drives a cleaning device based on an output signal.