JPS63126987A - 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 paper pulp sieving device, 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. 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 stock is to trap and remove foreign substances such as plastics, bundled 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. It is therefore 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 test machines. 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 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 occurs, such as clogging of the screen 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, mainly long fibers of good quality, to escape toward the resect exit side.

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

(Means for Solving the Problems) Therefore, the present invention provides a pressure screen, which includes pressure sensors disposed at the inlet and outlet of paper stock, and a screen cylinder that is determined based on the pressure measurement values of the pressure sensors. A conversion device that generates a signal corresponding to a pressure loss value, and a means for adjusting the output rotation speed of a variable speed motor that drives the cleaning device based on the output signal from the conversion device,
This is a means to solve problems.

(Function) A variable speed motor is used to drive the pressure-type screen cleaning device, and pressure sensors are attached to the paper stock input section and output section, and the pressure loss value of the screen cylinder is calculated from the respective pressure measurement values. The rotation speed of the cleaning device is changed based on this pressure loss value.

The pressure loss value of the screen cylinder of a pressure screen is an important index when determining the operating state of the pressure screen. In other words, if the pressure loss value is relatively low and does not fluctuate, it is a normal and proper operating condition, and if the pressure loss value 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 pressure loss value shows an abnormally high value, it is possible to detect an operating condition such as a blockage in the screen cylinder. Therefore, the pressure loss value of this screen cylinder is detected, and the output rotation speed of the variable speed motor for driving the purifier is adjusted to a value suitable for the operating conditions at that time based on the pressure loss value and the tendency of change. This achieves long-term stable operation of the pressure screen.

(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.

Incidentally, since the reference numerals 1 to 10 in FIGS. 1 to 3 are the same as those in the conventional FIG. 4, 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 pressure sensor at the inlet of the stock, numeral 14 is a pressure sensor at the outlet, and numeral 15 is a screen using signals from the pressure sensor. a converter 16 for generating a signal corresponding to the pressure loss value of the cylinder 5; 16 receiving and receiving the signal corresponding to the pressure loss value;
17 is a control device that adjusts the rotation speed of the variable speed motor 12 based on the rotation speed setting signal.

Next, to explain the operation of the embodiment of FIG. Differences in positional water head and the like are corrected and converted into a signal proportional to the pressure loss of the screen cylinder 5.

For example, the pressure measured by the pressure sensor 13 is P, and the pressure measured by the pressure sensor 14 is P. , the supply flow rate of stock is QI, and the proportionality constants are CI and C2, then the pressure loss ΔP of the screen cylinder 5 is ΔP, = (Po P+)
CI C2・Q, -1---------・-・-(
1). Here, the proportionality constant C0 corresponds to a correction term that does not depend on the supply flow rate Q, such as the positional head difference of the detection part, and C2
corresponds to a correction term proportional to the supply flow rate Q, such as friction loss in the flow path.

In the case of a normal pressure screen, the third term on the right side of equation (1) is sufficiently small compared to the first and second terms, so ΔP - (
P o P +) Cr−−−−−−−−−−
-(2) has no practical problem. Of course, if the third term on the right side of equation (1) cannot be ignored due to the structure of the pressure screen, etc., a flow rate detector 18 such as an electromagnetic flowmeter is provided as shown in FIG. It is necessary to input a signal corresponding to the value into the converter 15 and obtain a signal proportional to the pressure loss value of the screen cylinder 5 using equation (1).

Moreover, the signal corresponding to the pressure loss value from the converter 15 is
The signal is taken into the calculation device 16 and simultaneously recorded (1) in the memory at prescribed time intervals.The calculation device 16 is preset with a reference level to be compared with the input signal corresponding to the pressure loss value. Evaluate the magnitude and level of the input signal. 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 less than a reference level corresponding to an abnormality, the setting signal that has been used to increase the rotation speed is canceled.

Further, if the input signal is smaller than the reference level corresponding to normality, a setting signal is output that slowly decreases 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. As for the input signal, in order to avoid excessive fluctuations in the setting signal, it is desirable to perform averaging processing using the signal value stored in the memory based on the current input signal. Furthermore, reference levels are determined based on operational experience and operational data from test machines, but in practice, the number of reference levels is not limited to two, normal and abnormal, but can be determined as desired depending on the characteristics of the pressure screen and operating conditions. The number is sufficient.

Next, the evaluation of the change tendency (trend) of the pressure loss value of the screen cylinder 5 can be basically achieved by mutually comparing the signal values stored in the memory at prescribed time intervals. For example, by subtracting the signal value stored immediately before from the current input signal value and storing it in memory as the amount of change, and processing these amounts of change using an appropriate averaging method, the trend of the pressure loss value can be calculated. A value is required. If the current value is positive, it indicates that the pressure loss value is increasing, and if it is larger than the reference level of the trend value corresponding to the preset abnormality, the rotation speed of the variable speed motor 2 is slowly increased. Outputs a setting signal to 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 greater than the reference level, a setting signal is output that slowly reduces the rotation speed of the variable speed motor 12, 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. In addition, detailed explanations of various display, recording, and alarm functions will be omitted, but
It can be incorporated appropriately. The specific types of variable speed motors 12 are roughly divided into DC motors and AC motors, and in the case of AC motors, motors with eddy current joints, shunt commutator motors, frequency conversion motors (inverter motors), etc. are applicable. can. - 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. . Further, it is desirable to set an upper limit rotation speed and a lower limit rotation speed in the control Il 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 device shown in FIG.

(Effects of the Invention) As described in detail below, according to the present invention, the pressure loss value of the screen cylinder can be set within a range that is carefully set according to the type, structure, and use of the pressure screen. The rotational speed of the cleaning device is adjusted depending on the current operating conditions. As a result, long-term stable operation is achieved, 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, making it possible to maintain stable operation over a long period of time. Problems with screens such as large power consumption, reduced removal rate of foreign matter in g-i Fl, and increased tendency of fibers to escape to the retract side can be solved. In particular, the effect of reducing power consumption is remarkable, and therefore, according to the means of the present invention, the rotation speed of the cleaning device can be reduced by 10 to 20% on average, and the power consumption is generally proportional to the 2.6th power of the rotation speed. Therefore, the reduction rate of power consumption is 28 to 60%.

[Brief explanation of the drawing]

Figures 1, 2 and 3 are side sectional views including a control circuit of a sieving device showing an embodiment of the present invention, Figure 4 is a side sectional view of a conventional sieving device, and Figure 5 is the same plane. It is a diagram. Explanation of main parts of the figure 5 - Screen cylinder 12 - Variable speed motor 13 - Population part sensor 14 - Outlet pressure sensor 15 - Conversion device 16 - Arithmetic device 17 - Control device 20 - Continuously variable transmission 21 - Control device

Claims (1)

[Claims] A pressure screen, comprising a pressure sensor disposed at the inlet and outlet of the paper stock, a conversion device for generating a signal corresponding to the pressure loss value of the screen cylinder from the pressure measurement value of the pressure sensor, and the conversion device. A sieving device comprising: means for adjusting the output rotation speed of a variable speed motor that drives a cleaning device based on an output signal from the device.