JPS63135586A - 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 is conventionally well known as a sifting device for paper valves, has an inlet 1 for the stock at the top, an outlet 2 for the selected stock at the bottom, and an outlet 2 for the selected stock at the bottom, 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. It consists of a cleaning device 6 that serves to remove foreign matter trapped on the surface and keep the screen cylinder surface clean. This cleaning device 6 includes a main shaft 7, a pulley 8 on the main body side, a belt 9,
It is connected to a motor 11 via a motor side pulley 10.

The purpose of using such a pressure screen for paper stock is to capture and remove foreign substances such as plastics, bound fibers, and undisintegrated pieces in the paper stock onto the screen cylinder surface, and at the same time to efficiently remove the fibers from the screen cylinder. The purpose is to pass through the opening. For this reason, foreign matter or fiber lumps (
In order to prevent clogging of the screen cylinder apertures by flocs, it is essential to rotate the cleaning device at a relatively high speed. This rotation speed is 0 on the motor side.
However, since it is impossible to make changes during operation, predictions are made during the operation period to ensure long-term stable operation, based on operation data with similar stock and operation data from test a. The high rotational speed is selected taking into account the fluctuations in the operating conditions.

(Problems to be Solved by the Invention) In conventional pressure screens, the rotation speed of the purifier is set to the most severe operating conditions 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 an additional 10 to 20% margin in the rotational speed of the cleaning device assuming this. The rotational speed selected in this manner is generally not changed unless there is a major change in operating conditions or a malfunction of the pressure screen such as clogging of the screen cylinder occurs.

As a result, the cleaning device is operated at a considerably higher rotational speed than the optimal rotational speed corresponding to the operating conditions of the pressure screen at a given point in time, which not only consumes a large amount of power but also eliminates foreign particles in the paper stock. There were serious problems such as a reduction in the removal rate and an increased 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.

(Means for Solving the Problems) For this reason, the present invention is a pressure-type screen, in which density sensors are provided at the inlet and outlet of the paper stock, and the density measurement values of the density sensors are used to determine the density of the fibers passing through the fibers. This device is equipped with a converter that generates a signal corresponding to the cleaning rate, and a control device that adjusts the output rotation speed of a variable speed motor that drives the cleaning device based on the output signal from the converter. It is used as a means for point-solving.

(Function) A variable speed motor is used to drive the pressure screen cleaning device, concentration sensors are installed at the inlet and outlet of the paper stock, the fiber passage rate is determined from each concentration measurement value, and the fiber passage rate is based on this fiber passage rate. Change the rotation speed of the cleaning device, which has been set in advance.

The fiber passage rate, expressed as the ratio of the outlet 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 fiber passage rate is relatively high and does not fluctuate, it is a normal and appropriate operating condition, and if the fiber passage rate is relatively low and tends to gradually decrease, the screen cylinder is becoming increasingly clogged. If the fiber passage rate shows an abnormally low 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, and based on the fiber passage rate value and change tendency obtained by conversion, the output rotation speed of the variable speed motor for driving the purifier can be adjusted at that point in time. By adjusting the value to suit the conditions, long-term stable operation of the pressure screen can be achieved.

(Example) The present invention will be described below with reference to the embodiments shown in the drawings. Figs. 1 to 3 show a sieving device showing an embodiment of the present invention. Now, in Fig. 1, 1 to 10 are the same as those shown in Fig. 4, so a detailed explanation will be omitted.To explain the differences from Fig. 4, 12 is a variable speed motor, 13 is a paper stock. a concentration sensor at the inlet, 14 a concentration sensor at the outlet, 15 a conversion device for generating a signal corresponding to the fiber passage rate using the signal from the concentration sensor, and 16 receiving a signal corresponding to the fiber passage rate. 17 is a calculation device that outputs a setting signal for the rotation speed of the variable speed motor, and 17 is 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 of the embodiment configured as shown in FIG. 1, the concentration sensors 13 and 14 output a concentration signal proportional to the fiber concentration, and are of the optical type, ultrasonic type, radiation type, fluid friction loss. A variety of concentration sensors have been put into practical use, including those that utilize .

The signals from the concentration sensors 13, 14 are converted in a converter 15 into a signal proportional to the fiber passage rate. In other words, if the concentration at the inlet measured by the concentration sensor 13 is C+, and the concentration at the outlet measured by the fat degree sensor 14 is Cφ, then the fiber passage rate KA is KA-Cf/CI------ ------
(11), the conversion device 15 converts the signal according to equation (11).

In addition, when there is almost no change in the concentration of the supplied stock during the operation period, the fiber passage rate KA is KAocCp
(Since the relationship is 2+, the concentration sensor 13 at the inlet can be omitted as illustrated in FIG. 2. In this case, the conversion device 15 converts the concentration signal to match the calculation device 16 The signal corresponding to the fiber passage rate from the conversion device 15 is taken into the calculation device 16 and simultaneously stored in the memory at prescribed time intervals. A reference level is preset to be compared with the corresponding input signal to evaluate the magnitude and level of the input signal. For example, if the input signal is smaller 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 equal to or higher than the reference level corresponding to an abnormality, the setting signal for increasing the rotation speed up to this point is canceled.

If the input signal is greater 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 stored 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 in the fiber passage rate can basically be achieved by mutually comparing the signal values stored in the memory at specified time intervals. For example, the value obtained by subtracting the signal value stored immediately before from the current input signal value is stored in the memory as the amount of change, and by processing these amounts of change using an appropriate averaging method, the fiber passage rate can be calculated. A trend value is required. If this trend value is negative, it indicates that the fiber passage rate is decreasing, and if the absolute value of the trend value is greater than the preset reference level of the trend value corresponding to an abnormality, the variable speed motor 2
Outputs a setting signal that slowly increases the rotation speed.

When the absolute value of 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 positive and greater than the reference level, a setting signal is output that slowly reduces the rotation speed of the variable speed motor 2, and when the trend value becomes less than the reference level, the setting signal is canceled.

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. It is. 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, in the case of FIG. 3, there is no difference in operation and effect compared to the case of FIG. 1.

(Effects of the Invention) As described in detail above, according to the present invention, the fiber passage rate is set within a preset range depending on the type, structure, and application of the pressure screen. The rotation speed of the cleaning device is adjusted according to the operating conditions. As a result, while achieving long-term stable operation, the composition of the stock
The rotation speed of the cleaning device is adjusted to an appropriate speed according to changes in operating conditions such as concentration, temperature, and supply flow rate. It is possible to solve problems such as a decrease in the removal rate and an increase in the tendency of fibers to escape to the retract side. In particular, the effect of reducing power consumption is remarkable.According to the present invention, the rotation speed of the cleaning device can be reduced by 10 to 20% on average, and since the power consumption is generally proportional to the 2.6th power of the rotation speed, the power consumption can be reduced by 10 to 20% on average. The reduction rate will be 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 main parts of the figure 5 - Screen cylinder 12 - Variable speed motor 13 - Inlet concentration sensor 14 - Outlet concentration sensor 15 - Conversion device 16 - Arithmetic device 17 - Control device 20 - Continuously variable transmission 21 - Control device patent Applicant: Mitsubishi Heavy Industries, Ltd. Figure 1 Figure 4 Figure 5

Claims (1)

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