JPH0247956B2 - IBUTSUJOKYOSOCHI - Google Patents

Description

Detailed Description of the Invention A. Field of Industrial Application The present invention aims to remove foreign substances such as plastics and rubber from pieces of substances such as wood chips and grains and their processed products (hereinafter simply referred to as pieces of material). The present invention relates to a device for removing the present invention.

B. Conventional technology In recent years, plastic products have become widely used, and small pieces of unnecessary plastic are often found in pulp raw materials, grains, etc. Foreign substances such as plastics and rubber have a small difference in specific gravity from those of wood and grains, so it is difficult to separate them using flotation methods or centrifugal separation methods. Conventionally, foreign substances have been separated and removed manually. Therefore, the present inventors have developed a foreign matter removal method that utilizes the difference in chargeability between a piece of material and an insulating material such as plastic. FIG. 3 shows the device, in which a discharge electrode 8 of a corona discharge device 7 is arranged on the upstream side of the conveyor 6 to charge the test material, and a detection electrode 10 of a surface electrometer 9 is placed on the downstream side. The peak of the surface potential is detected by comparing the differential output of the surface electrometer 9 with the reference voltage by the voltage comparator 17, and the timer 12 is activated by the output of this voltage comparator 17, and after a certain period of time, the peak of the surface potential is detected. The damper 13 is operated to remove foreign matter, and the surface potential is reduced by taking advantage of the fact that the charge decays faster on a conductive piece of material than on an insulating material such as plastic. Insulating foreign matter is detected by detecting peaks.

However, the foreign matter removing device shown in FIG. 3 has the following problems. In other words, if a material such as a wood chip has a high moisture content and the foreign object is wet due to rain, the electric charge will immediately escape even if it is charged, and the charged potential of both the chip and the foreign object will become low. Detection becomes difficult. Therefore, in such a case, it is advantageous to lower the reference voltage of the voltage comparator 17 because the foreign matter removal rate becomes higher. On the other hand, when the moisture content is low, the decay of the charge on the chip is small and the difference in surface potential between the chip and the foreign object is small, so it is necessary to increase the reference voltage. It is now possible to set it to .

However, as shown in Figure 4, for example, in the case of wood chips, the attenuation of the surface potential of charged wood chips suddenly begins to decrease as the water content decreases and reaches the 10% to 20% range. Since the variation in surface potential is large and the difference from the surface charge of plastics is becoming smaller, there is a high risk of malfunction even if the reference voltage is set strictly. Furthermore, when the water content is less than 10%, the attenuation of the surface potential becomes extremely small, and the difference in surface potential between the material and the insulating material becomes so small that it is practically impossible to detect foreign objects even if the reference voltage is finely adjusted. become.

C. Purpose of the Invention Therefore, the first object of the present invention is to provide a means that makes it possible to separate material fragments from insulating material fragments even when the moisture content of the material fragments is extremely high or extremely low. A second object is to eliminate the need for manual adjustment of the reference voltage by using the average output of the surface electrometer.

D. Structure of the Invention In order to achieve the above object, the present invention includes, in addition to the structure shown in FIG. In addition to the peak rate of change in charge, the average level of the rate of change in surface potential, such as surface charge, is detected, and the humidifying means and drying means are controlled based on this average level.

With this configuration, the surface potential meter used to detect the difference in charged potential between a piece of material and an insulating material can be used to detect the average level of the overall surface potential, thereby determining the water content of the material. By determining the moisture content and controlling the degree of humidification or drying, it is possible to keep the moisture content within a certain range, thereby creating a difference in chargeability between the test material and the insulating material. It can be done.

E. Embodiment FIG. 1 shows a schematic system diagram of an embodiment of the apparatus of the present invention, in which wood chips (several mm thick) as a material to be inspected in a hopper 1 are transferred onto a conveyor 3 by a vibrating feeder 2. It will be withdrawn and supplied. Next, the wood chips are transferred to a second conveyor 6 that is faster than the conveyor 3, and after being spread out thinly so that the wood chips do not overlap each other, they are passed under the discharge electrode 8 of the corona discharge device 7 and charged. . The discharge electrode 8 is installed at a height of several centimeters above the conveyor belt and across the width of the belt, and a voltage of several kilovolts is applied to it. conveyor 6
is constructed of a wire mesh and is grounded, and the corona discharge current flows through the conveyor 6 to the ground. The detection electrode 10 of the surface electrometer 9 is installed several tens of centimeters downstream from the discharge electrode 8 at approximately the same height as the discharge electrode 8, and the conveyor 6 has a speed of about 100 m/min. A wood chip traverses the distance in about 0.3 seconds. The output of the surface potential meter 9 is applied to the detection circuit 11, where the peak and average level of the surface potential are detected, and the peak detection output is used as the timer 1.
2 to operate the damper 13 after a certain period of time, and control the moisture regulator 14 based on the average level detection output to adjust the amount of water supplied to the fountain nozzle 4 and the amount of hot air supplied to the hot air dryer 5. There is.

FIG. 2 shows the configuration of the detection circuit 11.
The output of the surface electrometer 9 is applied to the differentiating circuit 15, and the output is amplified by the amplifier circuit 16, and then the voltage comparator 1
7 and a reference voltage, and this comparison output is used as a peak detection output. Furthermore, the output of the surface electrometer 9 is applied to the smoothing circuit 18 to be averaged, and the output is applied to the voltage comparator 19 and compared with a set value. When this average level falls below the set value, the moisture content of the wood chips is determined. In such a case, the water from the fountain nozzle 4 is stopped and only the hot air dryer 5 is operated to lower the moisture content of the wood chips. Adjust within the appropriate range. Furthermore, if the average level exceeds the upper limit set value, it indicates that the moisture content of the wood chips is extremely low. Increase the moisture content of the chips and adjust it within the appropriate range. Further, the output of the smoothing circuit 18 is input to a level setting circuit 20, so that the reference voltage of the peak detection voltage comparator 17 can be automatically set to an optimum value according to the average moisture content.

F. Effects of the Invention As described above, according to the device of the present invention, if the moisture content of a piece of material such as a wood chip is out of the appropriate range and no difference in surface potential occurs between it and the insulating material, the transfer By moistening the object or drying the surface, the chargeability can be differentiated, and by detecting the average level of surface potential using a surface electrometer, the average level can be automatically determined. There is an advantage that the moisture content can be controlled to an optimum state.

It should be noted that it is a preferred embodiment of the present invention to remove dust by subjecting the material pieces supplied to the hopper to a vibrating screen or the like in advance, since this allows the above-mentioned surface potential to be measured more accurately. In addition, in this embodiment, one detection electrode is used, but two detection electrodes are arranged in the front and back, separated in the transport direction of the conveyor, and peak detection is performed using the detection potential of one detection electrode. The detection potential of the other electrode may be smoothed to detect the average level, or the moisture content of the material to be tested may be detected from the difference in the average level of the detection potentials of the front and rear detection electrodes, and this may be controlled. It's okay.

[Brief explanation of drawings]

Fig. 1 is a schematic system diagram of the device of the present invention, Fig. 2 is a block circuit diagram of the same essential parts as above, Fig. 3 is a schematic system diagram of a conventional device of this kind, and Fig. 4 is a diagram showing the moisture content and surface of wood chips. It is a relationship graph with electric potential. 1... Hopper, 2... Vibration feeder, 3... Conveyor, 4... Fountain nozzle, 5... Hot air dryer,
6... Second conveyor, 7... Corona discharge device,
8...discharge electrode, 9...surface electrometer, 10...detection electrode, 11...detection circuit, 12...timer, 1
3...Damper, 14...Moisture adjustment device, 15...
Differential circuit, 16...Amplification circuit, 17...Voltage comparator, 18...Smoothing circuit, 19...Voltage comparator, 2
0...Level setting circuit.

Claims (1)

[Claims] 1. A discharge electrode is installed on the upstream side of the conveyor to charge the test material by corona discharge, and a detection electrode is installed on the downstream side to detect the surface potential of the test material. A foreign matter removing means that operates at the timing of peak detection is provided directly below or downstream of the detection electrode, and a humidifying means and a drying means are provided upstream of the discharge electrode and are controlled based on the average level. What is claimed is: 1. A foreign matter removal device comprising: