JPH0315982B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for detecting and separating plastic pieces or rubber pieces mixed in pulp raw materials such as wood chips, or grains such as noodles and soybeans, and more specifically, a method for detecting and separating plastic pieces or rubber pieces mixed in pulp raw materials or grains such as grains. Alternatively, pieces of insulating material such as plastic pieces or rubber pieces are allowed to flow down in a thin layer onto a conductive inclined plate while being contaminated or mixed, and the surface electrometer placed above the plate is used to measure the The present invention relates to a method of detecting a difference in induced charge based on a difference in electrostatic properties of each substance, and automatically separating the insulating material piece from a conductive material based on the detection signal. In recent years, plastic products have been widely used in a variety of fields, and their applications are expanding more and more, but on the other hand, small pieces of unnecessary plastic products are getting mixed into pulp raw materials and grains.
This has caused problems in the processing of pulp raw materials and grains. For example, if small pieces of plastic bags, strings, tags, name tags, containers, toys, and other plastic products and rubber products (hereinafter collectively referred to as "plastics") are contaminated with wood chips, If this pulp is made into paper as it is, plastics will be mixed into the paper layer, causing holes in the paper and paper breakage. Non-wood pulp raw materials such as straw, bagasse,
The same is true when plastics are contaminated with linen, rags, cotton, linters, or even waste paper, and the situation described above is no different from that with wood chips. Plastics are generally chemically stable, so even when they are treated with chemicals under high temperature and high pressure during the pulping process, they are only deformed by heat at most, and even further broken into fine pieces by mechanical action such as a beating machine. Because of the crushing, it is extremely difficult to remove plastics from pulp slurry using conventional screens. Further, even if a centrifugal force type cleaner is used, since the difference in specific gravity between pulp and plastics is small, there is the disadvantage that separation efficiency is low despite consuming a large amount of power. Therefore, if the pulp raw material is contaminated with plastics, it is preferable to remove the plastics in advance. And if grains such as soybeans are contaminated with plastics, even if we only consider that the grains are edible,
It is desirable that plastics be removed before processing. The present inventors proposed a new detection/separation method to mechanically or electrically detect and remove the plastics, which had conventionally relied entirely on manual labor (Japanese Patent Application No. 113564/1983). (See No. 57-68782 and PCT/JP83/00016). The present invention has confirmed that plastics can be detected and separated by a method other than the method disclosed in the prior invention, and therefore proposes a new method for the detection and separation of plastics. As is well known,
Plastics are electrically insulating materials, while wood chips, straw, bagasse, hemp, rags, cotton,
Pulp raw materials such as linters and waste paper, and grains such as soybeans, have higher electrical conductivity than plastics. For this reason, due to the transshipment and transfer that pulp raw materials and grains undergo several times during the process from accumulation to processing, a considerable difference appears in the surface potential caused by friction between plastics and pulp raw materials and grains. Generally, this surface potential difference is further increased by actively performing treatments such as corona discharge. Incidentally, Table 1 shows the surface potential of plastics mixed in wood chips piled up in the open and the surface potential of plastics when the wood chips are transported by a conveyor.

[Table] In addition, while pulp raw material mixed with plastics was allowed to flow down through an inclined plate set at an angle of 45 degrees, a corona discharge was generated at an applied voltage of 6 KV from a discharge bar installed at a height of 3 cm above the inclined plate. Apply for seconds,
When the surface potential of plastics flowing down was measured on an inclined plate 3 cm from the electrode of the surface electrometer, the values were as shown in Table 2.

【table】

[Example 1]

As shown in FIG. 1, the wood chips are sent from a storage container 1 containing wood chips via a vibrating feeder 3 after being leveled into a thin layer from the discharge end of the feeder. At the discharge end of the feeder, an inclined plate set at an inclination angle of 45 degrees, that is, a chip chute 2 is connected, and wood chips are supplied in a thin layer to the chip chute. On the other hand, above the transfer surface of the chip shoot 2, a needle-like corona discharge bar 6 connected to an air shower 4 and a high-voltage power supply 5 is provided to reduce dust attached to the wood chips being transferred and to perform corona discharge treatment. Charge. As the discharge bar, it is preferable to use an electrode in which a large number of needles are embedded in a rod-shaped insulator. In addition, the conductive chip chute 2 is grounded as shown in the figure, and the inclination angle of the chute is set to approximately 45 degrees as described above, so that the transport speed of the chips on the chute is 150 m/min. Set. Further, an electrode part 8 of a surface electrometer 7 having an amplifier circuit is installed at a distance of about 40 cm behind the corona discharge bar 6, and the time differential value of the amount of electric charge charged on the wood chips is measured. Configure it as follows. Bar electrodes 8a to 8 with a length of 30 cm are used as electrode parts.
As shown in FIG. 2, the electrodes c are arranged to cover one-third of the width of the chute 2, and a shield cover 9 can be attached to surround the electrodes. Note that the bar electrodes 8a to 8c may be arranged in two or three stages before and after the bar electrodes 8a to 8c. In this way, the amount of electric charge that the plastics in the wood chips are charged with is detected by the bar electrode, and this is amplified as a time differential value by the amplifier circuit of the surface electrometer 7. The output amplified by the surface electrometer 7 is
The voltage is introduced into the comparator 10 shown in the figure, and the comparator detects whether or not the potential is higher in absolute value than the reference potential. This point will be explained in detail below based on FIG. 3. The potential detected by the electrode 8 shows a waveform as shown in FIG. The waveform becomes as shown in b in the same figure, and further becomes an amplified waveform as shown in c in the same figure by the main amplifier 7B. By the way, code 7
C is a sensitivity setting element and defines the amplification factor.
As described above, the output of the surface electrometer 7 is led to the comparator 10, and by appropriately adjusting the level setting element 10A in the comparator 10, an arbitrary reference potential can be set. This reference (lower limit) potential is shown at 10a in c of the same figure.
, only the signal exceeding the potential level is taken out as a comparator output as shown in d of the figure, and this signal is introduced into the monostable amplifier 11 at the next stage. A time setting element 11A is attached to the amplifier, and the operating time of, for example, the lamp 12 or the alarm 13 is regulated by this element. The regulation time is indicated by the symbol Δt' in the figure e. In the above, for example, if the lower limit potential of the comparator 10 is set to -5 volts and a higher potential than this is detected in absolute value, the pilot lamp 12 is turned on by the detection signal, or the alarm 13 is turned on at the same time. Activate. Of course, the reference potential and amplification factor of the comparator in this case can be adjusted depending on the magnitude of the detected difference. When the detection signal of the comparator is emitted, it indicates that plastics are contained in the wood chips. Therefore, a separately installed timer 14 is activated, and after a certain period of time has elapsed, the operation of the belt conveyor 22 connected to the lower end of the chip chute 2 is stopped. The plastics contained in the water are removed manually. Thus, the present invention also includes a method for automatically detecting plastics contained in wood chips and manually removing them. According to this detection method, various plastics (polyethylene film, PP rope, Styrofoam, PVC tape, PP straw, pieces of PE trash can, PVC sheet, polyester film, polycarbonate, nylon, etc.) can be detected from wood chips and other conductive materials. The probability of plastics being removed was approximately 80% or more, and by passing the same type of plastic detector two or three times over an inclined plate, plastics could be detected and removed with a probability of approximately 95% or more. [Example 2] Next, an example will be presented in which conductive substances including plastics are partially removed automatically without using human hands. In the apparatus shown in FIG. 4, a hopper 15 is attached to the lower end of the tip 2, which is an inclined plate, and branch pipes 17a and 17b having a distribution damper 16 are disposed in the hopper, and a drive source 18 for the damper 16 is connected to the hopper 15. The signal of the above-mentioned timer 14 is supplied. However, normally, the damper 16 is set at the position shown by the chain line in the figure, so that the conductive substance discharged from the inclined plate 2 is stored in the receiver 20. If plastics are mixed in the conductive material, their presence is automatically detected as described above, the timer 14 is activated, and the damper 16 is activated after a predetermined period of time has elapsed.
is switched to the position shown with a solid line in the figure. In such a case, the conductive material containing plastics is stored in the plastics receiver 19 via the branch pipe 17b, and the chips not containing plastics are supplied to one of the receivers 20 for automatic sorting. . [Embodiment 3] As a method for removing plastics mixed in the conductive material, a method as shown in FIG. 5 can also be used. That is, in this case, a reciprocating plastic receiver 24 attached to the piston rod of the cylinder 23 is provided to the lower end discharge part of the inclined plate 2. The spool valve 25 is switched, thereby automatically removing the plastics. Incidentally, the entire removal device is indicated by the reference numeral 26. [Embodiment 4] FIG. 6 shows an example in which a plurality of inclined plates equipped with the detection means of the present invention are provided along the transport direction, and this will be specifically explained below. A vibrating screen 31 is disposed at the discharge end of a hopper 30 for wood chips, which are conductive materials, and ionized air generators 32 and air showers 33 are disposed approximately alternately above the screen. In this way, the vibrating screen 31 simultaneously removes the vibrating wood chips and the dust adhering to the plastics. These dust particles are typically slightly positively charged and conductive, making them particularly harmful to the plastics they are intended to remove, but are beneficial in that they can be removed before they are detected. It is. The air shower 33 is effective in removing dust together with the vibrating screen, and in addition, in the case of the device shown in FIG.
Since the ionized air generator 32 is attached, the following effects are achieved. By the way, the device 3
As an example, as shown in FIG. 7, 2 has a configuration in which a counter electrode 32b is provided in the vicinity of a needle electrode 32a of a corona bar, and serves to ionize the surrounding air. As mentioned above, dust attached to wood chips and plastics may be positively charged, and it is highly likely that this dust is electrostatically attached to the plastics. Even in such a case, when ionized air is blown through the device 32, it has the effect of breaking the electrostatic bond and making dust removal easier. The chips from which the dust has been removed as described above are guided to the vibrating feeder 34 in FIG.
5 in a thin layer. Chipshoot 35
Another chip chute 36 is provided on the discharge end side of the chip chute 36, and an automatic opening/closing machine 37 is provided therebetween and on the discharge side of the latter chip chute 36 to automatically remove the detected plastics as described below. Make sure to remove it. By the way, on the upper surfaces of the chute 35 and 36, a corona discharge device 38 is provided on the upstream side thereof.
After arranging the electrodes, the electrode section 39 of the surface electrometer is attached to the downstream side thereof, and the surface potential difference is detected separately in the same manner as in the first embodiment. The processing after detection is as already described. In addition, in each of the above embodiments, the chute 2 or 35, 36, which is an inclined plate, can be formed into a surrounding structure as shown in FIG. 8, and in this case, it is not affected by the surrounding wind. There is an advantage. Further, as shown in FIG. 9, an automatic opening/closing window 22 is disposed on the lower surface of the chute 2 or 35, 36, and its drive mechanism 22A is activated by a signal from the timer 14 to open the window 22. If this is done, wood chips mixed with plastic will be automatically separated by this method as well. The following page shows a list of operating conditions for each of the above examples.

[Table] Operating conditions of Example 4 Applied voltage of ionized air generator: 7KV Spraying amount of air shower: 200/min Vibrating screen: RVS-450 type manufactured by Shinko Electric Co., Ltd. (Capacity: Max. 0.14 m ³ /min) Vibratory feeder: F-22BDT type manufactured by Shinko Electric Co., Ltd. (Capacity: Max.0.12m ³ /min)

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a skeletal side view showing an example of an apparatus for carrying out this method, FIG. 2 is a skeletal cross-sectional view showing an example of a fixed electrode for surface potential detection in the same apparatus, and FIG. A wiring diagram showing the circuit configuration of the potential detection section is shown, and signal waveforms of each section are also shown. FIG. 4 is a skeletal side view of a device showing another embodiment for carrying out the present method, FIG. 5 is a cross-sectional view showing a plastics removal device that can be used in the device, and FIG. 6 is a further A skeletal side view of the present device showing another embodiment, FIG. 7 is an explanatory diagram showing an example of an ionized air generating device, and FIG. 8 shows a case in which an inclined plate for allowing wood chips to flow down is surrounded. FIG. 9 is a perspective view showing a case where an automatic opening/closing window is attached to the conveyance surface of the chute, which is an inclined plate. 1: Storage device, 2, 35, 36: Inclined plate (chip shoot), 3, 34: Vibration feeder, 4, 3
3: Air shower, 5: Power supply, 6, 38:
Corona discharge bar, 7, 39: Surface potentiometer, 7A:
Differential amplifier, 7B: Main amplifier, 7C: Sensitivity setting element, 8, 8a to 8c, 39: Surface electrometer electrode, 9: Shield cover, 10: Comparator,
10A: Level setting element, 11: Monostable amplifier,
12: Lamp, 13: Alarm, 14: Timer, 1
5: hopper, 16: damper, 17a, 17b: branch pipe, 18: drive source, 19, 20, 24: receptor, 21: belt conveyor, 22: automatic opening/closing window,
22A: Drive device, 23: Reciprocating cylinder, 2
5: Spool valve, 26: Remover, 30: Hopper, 31: Vibrating screen, 32: Ionized air generator, 37: Automatic switch.

Claims (1)

[Scope of Claims] 1. Small pieces of conductive material mixed with pieces of insulating material are distributed in a thin layer on the inclined plate and flowed down on the inclined plate, and the conductive material is made to flow down the inclined plate, and is arranged to face the transfer surface of the inclined plate. In this state, the electrode of the surface electrometer is arranged, and the electric charge induced on this electrode is time-differentiated and amplified, and the amplified value is inputted from the surface electrometer to the comparator, and the input potential is set to the comparator. An output signal generated from the comparator when the reference potential exceeds the reference potential is introduced into a timer, and the supply of the material piece to the inclined plate is stopped by the output signal generated by the timer according to the set time of the timer. , the removing means attached to the inclined plate is operated without stopping the inclined plate, and the inclined plate is made of a material having at least a surface opposite to the electrode conductive. A method for detecting and separating pieces of insulating material mixed in small pieces of conductive material. 2. The method according to claim 1, wherein a corona discharge device is provided upstream of the electrode position of the surface electrometer with respect to the transport direction of the substance flowing down on the inclined plate, and a corona discharge is applied to the substance on the inclined plate. Detection separation method. 3. The detection and separation method according to claim 2, in which a dust removal device is provided upstream of the installation position of the corona discharge device to remove dust attached to the substance with respect to the transport direction of the substance flowing down on the inclined plate. . 4. The detection and separation method according to claim 3, wherein the dust removal device is a vibrating screen. 5. The detection and separation method according to claim 3, wherein the dust removal device is an air shower. 6. Upstream of the installation position of the dust removal device with respect to the flow direction of the substance flowing down on the inclined plate,
6. The detection and separation method according to claim 5, wherein the substance is subjected to ionized air treatment. 7. The detection and separation method according to claim 1, wherein the removing means is a branch pipe with a distribution damper installed at the discharge end of the inclined plate. 8. The detection and separation method according to claim 1, wherein the removing means is a reciprocating receiver installed at the discharge end of the inclined plate. 9. The detection and separation method according to claim 1, wherein the removing means is an automatic opening/closing window attached to the transfer surface of the inclined plate. 10. The detection and separation method according to claim 1, wherein the transport speed of the substance can be adjusted by changing the inclination angle of the inclined plate. 11. The method according to claim 1, wherein an inclined plate comprising a closed chute is used. 12. The detection and separation method according to claim 1, wherein the insulating substance is plastics and the conductive substance is pulp raw material or grains.