CA1210114A - Method of detecting and sorting pieces of insulating materials admixed in small pieces of conductive materials - Google Patents
Method of detecting and sorting pieces of insulating materials admixed in small pieces of conductive materialsInfo
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- CA1210114A CA1210114A CA000443502A CA443502A CA1210114A CA 1210114 A CA1210114 A CA 1210114A CA 000443502 A CA000443502 A CA 000443502A CA 443502 A CA443502 A CA 443502A CA 1210114 A CA1210114 A CA 1210114A
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- chute
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- conveying surface
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Abstract
ABSTRACT
A method of detecting and sorting pieces of insulating materials admixed in small pieces of conductive materials, which comprises detecting and amplifying the surface potentials of the conductive materials and the insulating materials by a surface potentiometer on the basis of a time differentiation method, inputting the signal to a comparator, and sensing the presence of the insulating materials. This method is utilized to detect and sort plastics admixed in pulp and paper stuff or cereals.
A method of detecting and sorting pieces of insulating materials admixed in small pieces of conductive materials, which comprises detecting and amplifying the surface potentials of the conductive materials and the insulating materials by a surface potentiometer on the basis of a time differentiation method, inputting the signal to a comparator, and sensing the presence of the insulating materials. This method is utilized to detect and sort plastics admixed in pulp and paper stuff or cereals.
Description
TITLE OF THE INVENTION
METHOD OF DETECTING AND SORTING PIECES OF
INSULATING MATERIALS ADMIXED IN SMALL PIECES
OF CONDVCTIV~ MATERIALS
TECHNICAL FIELD
T}lis invention re:Lates to a me-thod of detecting and sor~ing pieces of insulating materials such as plastic or rubber pieces admixed in small pieces of conductive materials such as pu:Lp and paper stuff, eOg~' wood chips or cereals5 e.gO, noodles and soybeans. More particularly5 the invention relates to a method of electrically detecting plastic or rubber pieces admixed in pulp and paper stuff or cereals by the utilization of the difference in electrostatic properties between the conductive materials and -the insulating materials5 and manually or automatically removing the plastic or rubber pieces from the pulp and paper s-tuff or cerealsO
BACKGROUND ART
Recen-tly5 plastic products have been widely used in various fields, ancl-their utili-ties have a trend -to increase~ On the o-ther hanci, small chips of waste plas-tic produc-ts have been admixed in pulp and paper s-tuff or cereals and have accordingly caused a hindrance to processing -the pulp and paper stuff or cerealsO For example5 if small pieces of plastic bags5 braicls5 bands,-t;a~s5 name plates, receptacles~ -toys or o-ther plastic or rubber-~2~
products (which will be hereinafter called "plastics")are3 admixed in wood chips, and such wood chips are pulped as -they are, the plastics will be contained in a paper web layer, with the result that pores are formed in -the web layer or the web layer is easy to break. Such troubles will occur also when the plas-tics are admiY~ed in Straw, bagasse3 hemp, rag~ cotton3 linter, or waste paper of non-wood pulp and paper stuff.
Since the plastics are in general chemically stable, the plastics are subjected only to thermal deformation even in a liquor treatment at a high temperature and pressure in a pulping step. As the plastics are fur-ther pulverized into fine pieces by mechanical action of a beater, it is extremely difficult to remove the plastics from a pulp slurry by means of a screen of conventional type. As the difference in the speci-fic gravi-ty between the pulps and the plastics is slight~ the sorting efficiency is low for the large power consumed by a cleaner which utilizes a centrifugal force. Consequently, when the plastics are admixed in -the pulp and paper stu-ff, it is preferred -to remove the plas-tics in advance. When -the plastics are admixed in cereals such as soybeans, it is preferable -to remove the plas-tics before processing because -the cereals are used for food~
However, there exis-t no effective means at present to remove the plastics admixed in the pulp and paper stuff or cereals, and at present the plastics dispersed in -the pulp and paper stuff or cereals are found out (detec-ted) and picked up manually.
DISCLOSURE OF THE INVENTION
The present invention provides a method of electrically de-tecting plastics admixed in pulp and paper stuff or cereals and a method of removing the plastics therefrom by reJecting means operating in response to the detection signal in the previous methodO
The plastics are in general electrical insulators, while pulp and paper stuff such as wood chips, ~straw~ bagasse, hemp, rag, cotton, linter or waste paper or cereals such as noodles and soybeans has a high electrical conductivity as compared with the plastics. Therefore, it is normal that a considerable difference is produced in surface potentials generated by -the frl~ction between the plastics and the pulp and paper stuff or cereals owing to several times of re-.stacking or conveyance in the steps of stocking to processing and the su:rface potentia:L
difference is ~urther increased by posit:ively applying a corona discharg~e.
For example, the sur-face potentials o:E-the plastics admixed in wood chips whlch have been stored in the open air and those of the plastics in wood chips which have been conveyed by a conveyor are listed in Table 1 below.
Table 1 PlasticsSurface potentialSurface potential~-open-air storage conveyed polyethylene bag -70 volts -lO0 volts polypropylene-200 -300 plate polytetrafluoro-ethylene -100 -200 Carbon-containing rubber plate -50 -100 Polycarbonate film -100 -200 Polystyrene film -200 -300 Foamed styrene-50 -80 Vinyl chloride tape-70 -100 Nylon rope -50 -100 Sponge -~50 -~100 Wood chips -0 -0 ~2~ 4 ~The belt conveyor used had a belt 600 mm wide, a conveyance speed of 20 m/~lin and a conveyance distance of 10 m. The surface poten-tials of the plastics on the belt conveyor were measured by means of a sur~face poten-tiometer, -the electrodes of which were disposed 3 cm away from the conveyor.
(When a screw conveyor is used, the potential differences will be s-till larger because of larger friction.) Table 2 shows the surface potentials of the plastics admixed in pulp and paper stuff being conveyed on a conveyor, the measurements thereof being made by means of a surface potentiometer having electrodes disposed 2 cm away from the conveyor when a corona discharge was applied for 3 seconds at an applied voltage of 6 KV by a discharging bar disposed at a height of 2 cm above the conveyor.
Table 2 Plastics Surface potentials Polyethylene bag -300 volts Polypropylene -1000 Polyte-trafluoroethylene -3000 Carbon-contain:ing rubber plate -1000 Polycarbonate ~`ilm -1000 Polystyrene film -1000 Wood chips & non-wood pulp and paper stu~f ~
Table 3 shows the surface potentials of -the plastics admlxed in pulp and paper stu-ff flowing down a plate inclined at an angle of 45 , the measurement thereof being made by means of a surface potentiometer having electrodes disposed 3 cm away from the inclined plate when a corona discharge was applied for 3 seconds at an applied voltage of 6 KV by a discharging bar disposed at a height of 3 cm above the inclined plate.
Table 3 Plastics Surface potentials Polyethylene bag -200 volts Polypropyiene -600 Polytetrafluoroethylene-2000 Carbon-containing rubber plate -600 Polycarbona-te filln -60U
Polystyrene film -600 Wood chips & non-wood pulp and paper stuff 0 It was confirmed that high surface potentials were obtained by the corona discharge even when wood chips admixed with plastics contained much moisture, particularly when the chips were treated in advance by steam and hence the p:Lastics were moistened so as to prevent the chips from firing due to the corona discharge.
Tables 1 to 3 show the surface potentials of the plastics admixed in pulp and paper stuff, and the surface po-tentials of the plastics admixed in cereals such as noodles and soybeans were substantially the same thereas. As evident:Ly seen from Tables 1 to 3, the conductive pulp and paper stuff or cereals are not almost charged even if a corora discharge is ~z~
applied, while the insulating plastics is already charged at the time when the plastics are admixed in the pulp and paper stuff, the amount of charge is increased by -the friction at the time of conveyance and further increased by the corona discharge.
The present invention intends to electrically detect the plastics admixed in pulp and paper stuff or cereals by utilizing the elec-trical properties of the plastics as described above and to remove manually or by rejecting means to be described later the plastics from the pulp and paper stuff or cereals.
More particularly, a method of the present invention comprises the steps of distributing and moving pulp and paper stuff or cereals admixed with plastics on a relatively flat movable conveying surface such as a belt conveyor or an inclined immovable conveying surface such as a chute, measuring the surface potentials of the plastics mixed in wood chips by means of a surface potentiometer disposed above the conveying surface, the electrodes of said sur~ace potentiometer having an amplifier circuit of a time dieferentiating me-thod, input-ting -the time differentia-ted value to a comparator, sending the output of the comparator to an indicato,r such as a lamp or an alarm unit as requi:red and also to a timer, and stopping -the belt conveyor or the ~2~ L4 supply of the stuff or cereals or operating rejecting means for the plastics disposed in a suitable position above the conveyor or chute by means of the output signal o-f the timer delivered after the lapse of the set time -thereofO
Concrete means for sorting and removing the plastics in the wood chips by the method of the invention will now be generally listed.
(1) The ou-tput of a surface potentiometer amplified by an amplif:ier of a time differentiating method is applied to a comparator, and the OUtpllt signal of the comparator is applied to an indicator such as an alarm unit. When the amplified output of the surface poten-tial col.lected by the potentiometer exceeds a reference value set in the comparator, the comparator produces a signal, thereby turning on the lamp or ringing the alarm unit~ On the other hand, the output signal of the comparator is supplied also to a timer provided separately, and after the lapse o-E the set time of the timer the movable conveying surface (belt conveyor) is stopped or the supply of the woocl chips to the immovab:le conveying surface (chute) is s-topped~.
In other words, according to this method7 if tile plas-tics are admixed in the pulp and paper stuff) the presence of -tlle plastics is detected.!and amp'L:i~i`ed ~y -the surface ~l2~
potentiometer, and when the absolute value exceeds a predetermined value~ the alarm unit is actuated and the pilot lamp is lightened by the operation of the comparator, as well as the belt conveyor or the supply of s-tuff is stopped through the timer after the lapse of a predetermined time, thus only the plastics being removed from t;he pulp and paper stuff or cereals manually.
METHOD OF DETECTING AND SORTING PIECES OF
INSULATING MATERIALS ADMIXED IN SMALL PIECES
OF CONDVCTIV~ MATERIALS
TECHNICAL FIELD
T}lis invention re:Lates to a me-thod of detecting and sor~ing pieces of insulating materials such as plastic or rubber pieces admixed in small pieces of conductive materials such as pu:Lp and paper stuff, eOg~' wood chips or cereals5 e.gO, noodles and soybeans. More particularly5 the invention relates to a method of electrically detecting plastic or rubber pieces admixed in pulp and paper stuff or cereals by the utilization of the difference in electrostatic properties between the conductive materials and -the insulating materials5 and manually or automatically removing the plastic or rubber pieces from the pulp and paper s-tuff or cerealsO
BACKGROUND ART
Recen-tly5 plastic products have been widely used in various fields, ancl-their utili-ties have a trend -to increase~ On the o-ther hanci, small chips of waste plas-tic produc-ts have been admixed in pulp and paper s-tuff or cereals and have accordingly caused a hindrance to processing -the pulp and paper stuff or cerealsO For example5 if small pieces of plastic bags5 braicls5 bands,-t;a~s5 name plates, receptacles~ -toys or o-ther plastic or rubber-~2~
products (which will be hereinafter called "plastics")are3 admixed in wood chips, and such wood chips are pulped as -they are, the plastics will be contained in a paper web layer, with the result that pores are formed in -the web layer or the web layer is easy to break. Such troubles will occur also when the plas-tics are admiY~ed in Straw, bagasse3 hemp, rag~ cotton3 linter, or waste paper of non-wood pulp and paper stuff.
Since the plastics are in general chemically stable, the plastics are subjected only to thermal deformation even in a liquor treatment at a high temperature and pressure in a pulping step. As the plastics are fur-ther pulverized into fine pieces by mechanical action of a beater, it is extremely difficult to remove the plastics from a pulp slurry by means of a screen of conventional type. As the difference in the speci-fic gravi-ty between the pulps and the plastics is slight~ the sorting efficiency is low for the large power consumed by a cleaner which utilizes a centrifugal force. Consequently, when the plastics are admixed in -the pulp and paper stu-ff, it is preferred -to remove the plas-tics in advance. When -the plastics are admixed in cereals such as soybeans, it is preferable -to remove the plas-tics before processing because -the cereals are used for food~
However, there exis-t no effective means at present to remove the plastics admixed in the pulp and paper stuff or cereals, and at present the plastics dispersed in -the pulp and paper stuff or cereals are found out (detec-ted) and picked up manually.
DISCLOSURE OF THE INVENTION
The present invention provides a method of electrically de-tecting plastics admixed in pulp and paper stuff or cereals and a method of removing the plastics therefrom by reJecting means operating in response to the detection signal in the previous methodO
The plastics are in general electrical insulators, while pulp and paper stuff such as wood chips, ~straw~ bagasse, hemp, rag, cotton, linter or waste paper or cereals such as noodles and soybeans has a high electrical conductivity as compared with the plastics. Therefore, it is normal that a considerable difference is produced in surface potentials generated by -the frl~ction between the plastics and the pulp and paper stuff or cereals owing to several times of re-.stacking or conveyance in the steps of stocking to processing and the su:rface potentia:L
difference is ~urther increased by posit:ively applying a corona discharg~e.
For example, the sur-face potentials o:E-the plastics admixed in wood chips whlch have been stored in the open air and those of the plastics in wood chips which have been conveyed by a conveyor are listed in Table 1 below.
Table 1 PlasticsSurface potentialSurface potential~-open-air storage conveyed polyethylene bag -70 volts -lO0 volts polypropylene-200 -300 plate polytetrafluoro-ethylene -100 -200 Carbon-containing rubber plate -50 -100 Polycarbonate film -100 -200 Polystyrene film -200 -300 Foamed styrene-50 -80 Vinyl chloride tape-70 -100 Nylon rope -50 -100 Sponge -~50 -~100 Wood chips -0 -0 ~2~ 4 ~The belt conveyor used had a belt 600 mm wide, a conveyance speed of 20 m/~lin and a conveyance distance of 10 m. The surface poten-tials of the plastics on the belt conveyor were measured by means of a sur~face poten-tiometer, -the electrodes of which were disposed 3 cm away from the conveyor.
(When a screw conveyor is used, the potential differences will be s-till larger because of larger friction.) Table 2 shows the surface potentials of the plastics admixed in pulp and paper stuff being conveyed on a conveyor, the measurements thereof being made by means of a surface potentiometer having electrodes disposed 2 cm away from the conveyor when a corona discharge was applied for 3 seconds at an applied voltage of 6 KV by a discharging bar disposed at a height of 2 cm above the conveyor.
Table 2 Plastics Surface potentials Polyethylene bag -300 volts Polypropylene -1000 Polyte-trafluoroethylene -3000 Carbon-contain:ing rubber plate -1000 Polycarbonate ~`ilm -1000 Polystyrene film -1000 Wood chips & non-wood pulp and paper stu~f ~
Table 3 shows the surface potentials of -the plastics admlxed in pulp and paper stu-ff flowing down a plate inclined at an angle of 45 , the measurement thereof being made by means of a surface potentiometer having electrodes disposed 3 cm away from the inclined plate when a corona discharge was applied for 3 seconds at an applied voltage of 6 KV by a discharging bar disposed at a height of 3 cm above the inclined plate.
Table 3 Plastics Surface potentials Polyethylene bag -200 volts Polypropyiene -600 Polytetrafluoroethylene-2000 Carbon-containing rubber plate -600 Polycarbona-te filln -60U
Polystyrene film -600 Wood chips & non-wood pulp and paper stuff 0 It was confirmed that high surface potentials were obtained by the corona discharge even when wood chips admixed with plastics contained much moisture, particularly when the chips were treated in advance by steam and hence the p:Lastics were moistened so as to prevent the chips from firing due to the corona discharge.
Tables 1 to 3 show the surface potentials of the plastics admixed in pulp and paper stuff, and the surface po-tentials of the plastics admixed in cereals such as noodles and soybeans were substantially the same thereas. As evident:Ly seen from Tables 1 to 3, the conductive pulp and paper stuff or cereals are not almost charged even if a corora discharge is ~z~
applied, while the insulating plastics is already charged at the time when the plastics are admixed in the pulp and paper stuff, the amount of charge is increased by -the friction at the time of conveyance and further increased by the corona discharge.
The present invention intends to electrically detect the plastics admixed in pulp and paper stuff or cereals by utilizing the elec-trical properties of the plastics as described above and to remove manually or by rejecting means to be described later the plastics from the pulp and paper stuff or cereals.
More particularly, a method of the present invention comprises the steps of distributing and moving pulp and paper stuff or cereals admixed with plastics on a relatively flat movable conveying surface such as a belt conveyor or an inclined immovable conveying surface such as a chute, measuring the surface potentials of the plastics mixed in wood chips by means of a surface potentiometer disposed above the conveying surface, the electrodes of said sur~ace potentiometer having an amplifier circuit of a time dieferentiating me-thod, input-ting -the time differentia-ted value to a comparator, sending the output of the comparator to an indicato,r such as a lamp or an alarm unit as requi:red and also to a timer, and stopping -the belt conveyor or the ~2~ L4 supply of the stuff or cereals or operating rejecting means for the plastics disposed in a suitable position above the conveyor or chute by means of the output signal o-f the timer delivered after the lapse of the set time -thereofO
Concrete means for sorting and removing the plastics in the wood chips by the method of the invention will now be generally listed.
(1) The ou-tput of a surface potentiometer amplified by an amplif:ier of a time differentiating method is applied to a comparator, and the OUtpllt signal of the comparator is applied to an indicator such as an alarm unit. When the amplified output of the surface poten-tial col.lected by the potentiometer exceeds a reference value set in the comparator, the comparator produces a signal, thereby turning on the lamp or ringing the alarm unit~ On the other hand, the output signal of the comparator is supplied also to a timer provided separately, and after the lapse o-E the set time of the timer the movable conveying surface (belt conveyor) is stopped or the supply of the woocl chips to the immovab:le conveying surface (chute) is s-topped~.
In other words, according to this method7 if tile plas-tics are admixed in the pulp and paper stuff) the presence of -tlle plastics is detected.!and amp'L:i~i`ed ~y -the surface ~l2~
potentiometer, and when the absolute value exceeds a predetermined value~ the alarm unit is actuated and the pilot lamp is lightened by the operation of the comparator, as well as the belt conveyor or the supply of s-tuff is stopped through the timer after the lapse of a predetermined time, thus only the plastics being removed from t;he pulp and paper stuff or cereals manually.
(2)When the presence of plastics is detected by a comparator connected with a potentiome;ter, a pilot lamp is lightened,an alarm unit rings, then a scraper disposed above a belt conveyor or a chute is actuated after some time through a timer so as to automatically remove the pulp and paper stuff or cereals containing plastics sideways from the conveyor or the chuteO
(3) A d~vice for removing plastics from pulp and paper stuff or cereals is installed at the exhausting end of a be.lt conveyor, and automatically moved in a timely manner to remove wood chips containing plastics, then said wood chips being moved to some other place where the plastics are removed therefromO
(4)An automatic opening and closing mechanism, or a window adapted to open and c.Lose automatically~ is provided on an inclined conveying surface down which wood chips~ etc~ flow. When a potentiometer- detects plastics) a detection signal thereof opens said window~
th~ough which the wood chips containing the plastics fallO
The compara-tor used in the method of the invention is adapted to set in advance the lower limi-t (reference value) of the absolute value of the differentiated value of the measured potential and to automatically discriminate whether the measured value is larger than the lower limit or not. Thus) the comparator is a kind of potential comparator.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic vertical sectional view illustrating an example of an apparatus~ including a belt conveyor as a movable conveyirg surfaceg for carrying out the method of the present invention, Fig. 2 is a s¢hematic lateral sectional view illustrating an example of stationary electrodes for detecting surface potentials in the apparatus in Fig~ 1.
Fig. 3 is a circuit diagram showing a circuit arrangement of a poten-tial detec-tor together with signal waveforms of respective uni-tsO
Fig. 4 is a lateral sectional view showing a dovice for removing plastics ussd in the apparatus.
Fig. 5 is a partial plan view of the device.
Fig. 6 is a longituclinal sectlonal view partly il~ustrating another exampLe of the device for removing ~2~ 4 the plas-tics.
Figo 7 is a schematic side view of another example of the apparatus for carrying out the method of the presen-t inventionO
Figo 8 is an explanatory view showing an example of an ionic air generatorO
Figso 9 -to 13 show still another example of the apparatus; including a chute as an immovable conveying surface) for carrying out -the method of the present invention~
Figo 9 is a schematic side view illustrating said apparatusO
Figo 10 is a schematic lateral sectional view illustrating an example of stationary electrodes for detec-ting surface poten-tials in said apparatusO
Figo 11 is a schematic side view illustrating a chute apparatus.
. Fig. 12 is a perspective view illustrating an enclosed chute in which wood chips flowO
Fig. 13 is a perspective view illus-trating a chute having a w:indow adapted to open and close automa-tically~
BEST MODE FOR CA~RYING OUT THE INVENTION
:[n order -to eEfec-tive:Ly detect the sureace po-tentials of plastics admixed in pulp and paper stuff or cereals, it is preferred to make wood chips thin and move them on a belt conveyor as a movable conveying surface or let them flow down a chute as an immovable conveying surface. The plas-tics to be detected for the presence by a surface potentiomerer inc1ude polystyrene, polyethylene, polyvinyl chloride, polycarbonate;
polyethylene -terephthalate, polytetrafluoroethylene, polypropylene, polyvinylidene chloride, polyvinyl fluoride;
polyvinylidene fluoride, epoxy resin, polyacrylic resin3 polyamide, milamine resin, polybutadiene, syn-thetic high molecular compound including copolymer with the same, cellophane, and rubbers, all of which have lower charge attenuating velocity as compared with the pulp and paper stuff or cereals. The size of the detectable plastics is larger than 1 mm , but even if the plastics is less than 1 mm in size, the plastics having remarkable charging property such as polystyrene, polye-thylene~
polypropylene, or polyester can be sufficiently detected by a po-tentiome-ter.
Non-wood pulp and paper stuff sueh as straw, bagasse~ hemp, rag, eotton, linter, or waste paper contains less quanti-ty of moisture as compared with wood ehips) ancl contains less than 5 -to 6 ~ by weightO
Consecluently, even if the non-wood pulp and paper stuff is eorona clischarged, a suff:icient potential difference ~2~
may not be obtained between -the non-wood pulp and paper stuff and the plastics~ Accordingly~ when the non-wood pulp and paper stuff is treated, i-t is preferred to moisten the non-wood pulp and paper stuff at the upstream side of the position of the surface potentiomeker (a-t the upstream side of -the position of a discharging bar in case of performing corona discharging)~
For instance, waste paper, newspaper and rag selected as non-wood pulp and paper stuff had water contents in the range of 4 to 6 % by weightO They were distributed in a thin layer on a conveyor belt having a width of 600 mm and moving at a speed of 8 m/min, and corona discharged by means of electrodes of 10 ~V installed at a height of 4 cm above the conveyor belt. Then -the surface potentials thereof were measured by means of a surface potentiome-ter installed at a height of 4 cm above the conveyor belt at positions isolated by 30 cm from the electrodesO Their surface potentials thus measured were -50 to -lOO volts.
On the other hand, when they were similarly corona discharged after being sprayed with water by means of a shower pipe installed at a height of 40 cm above the conveyor belt so as to adjus-t their water con-tent to a range of 9 to 12 ~ by weight, their surface poten-tials were only O -to 2 volts. These data apply also to a case where pulp and paper stuf-f in a thin layer flows down a chute a-t a speed of lG0 m/min~ said chute having a width of 1000 mm and an inclination of 45 , and the surface potentials o-f the stuff are measured by means of a surface potentiometer disposed a-t a heigh-t of 4 cm above said chute.
Means formoistening the non-wood pulp and paper stuf-f is not always limited in the invention, but the moistening is generally performed by spraying water over the surfaces of paper or fibers by means of a noz~le shower, etc. moistening by steam is also effectiveO It is always preferable to adjust the wa-ter content of the non-wood pulp ans paper stuff to the range of 9 to 60 % by weight. In this case, it is also possible to adjust the water conten-t after the paper or fibers mixed with the plastics are put on a conveyor belt, and it is rather preferable to moisten the paper or fibers after putting them in a thin layer on the conveyor belt because this ensures rela-tively uniform moistening adjustment. In this case, the shower pipe is preferably ins-talled at a height of 20 -to 50 Clll above -the conveyor belt to spray wa-ter over the paper or fibersO
In carrying ou-t -the methocl o-f -the invention, it is preferable but not indispensable to apply a corona ~2~ 4 discslarge to pulp and paper stuff or cereals conveyed on a conveyor or moved by gravity on a chute, so as to increase the potentials of plastics mixed in the stuff or cerealsO Since dusts are frequently adhered to the plastics admixed in the pulp and paper stuff Ol~ cereals~ it is effective to perform corona discharging after the pulp and paper stuff or cereals are supplied to -the conveyor through a vibrating screen or a vibrating feeder and, if necessary, the dusts adhered to the plastics are further removed by an air shower, in order to increase the charging potentials of the plastics.
When the air shower is employed, the dusts might be charged at a plus potential and adhered to the plastics, and therefore it is desirable to neutralize in advance the charge of the dusts by using ioni~ed air produced by a static eliminating barO The voltage of the corona discharge is normally in the range of I to 50 KV,and it is normal to adjust tsle distance between the corona discharging bar made, for example, of stylus electrodes and a conveyor hel-t which is a paired electrode to 3 to 20 cm.
The surface po-tentiometer necessary to carry ou-t the method of the present invention has an amplifier circuit for performing a tisne diEferentiating method, it is preferable to approach the electrodes to tsle flow of pulp and paper stuff or cereals as near as - 16 _ ..... , .. ~
~2~
possible without contacting themO In -the cace of corona discharge, it is preferable to approach the electrodes to the discharging position as near as possibleO
In this manner, even if the charging charge of the plastics due to -the corona discharge is attenuated, it is possible to detect the potential clifference of the plastics from the pulp and paper stuffo ~lowever; it is desirable to ensure tha-t -the high voltage of the corona discharge or the increase of the earth potential by spark discharge does not exert a bad influence, with saicl approach, upon the surface potentiometer or an integrated circuit contained in electronic circuits such as the arnplifier circuit or the comparator.
It is also possible to use a checking mechanism or circuit to check whether the electronic circuits are in nomal operation.
It is preferable~ that the electrodes of the surface potentiometer are of a bar type because they measure the surface potentials of the plastics moving on the wide belt conveyor or chute, and -they normally have a leslgth of a ~ew to 100 cmO
Additionally, since the surface potentiome-ter employed ;.n the me-thocl of -the inventi.on has an amplifier circui-t for a -time differentiating method, the presence of the plastics can be sufficiently detec-ted even when the passing veloci-ty of -the plastics passing under the electrodes is high or when the charging density is small. This is because the charge induced at the electrodes of -the surface poten-tiometer due to the approach of the charged plastics to the electrodes is amplified -to a time differentiated value, and the amplified value is outputted to the comparator~
Accordingly~ in case of a conveyor it is possible to arbitrarily select the moving speed of the conveyor in a range of 1 to 300 m/min. In case of a chute, it is possible to arbitrarity select the flowing speed of the wood chips, etc. in a range of 10 to 400 m/min by changing the inclination of the chuteO
The present invention will be further described in detail with reference to accompanying drawingsO
As shown in Fig. 1, wood chips contained in a storage unit 1 are con-tinuously dropped onto a belt conveyor 2 through a vibration feeder 3, and flattened so that the chips become a thin layer on -the conveyorO
An air shower 4 and sty:Lus corona discharging bars 6 connected to a high voltage power source 5 are prov:ided above the conveying surface o~ the conveyor 2, -thereby clusts adhered -to the wood chips being reduced and corona discharge being performed to charge the wood chips. Preferably the electrodes of discharging bars comprise a number of s-tyluses buried in bar-shaped insulators. The conductive belt conveyor is grounded as shown in Fig. 1., and is operated at a speed of 50 m/min for exampleO The electrode unit 8 of a surface potentiometer 7 having an amplifier circuit is provlded in a position about 40 cm behind the bars 6 so as to measure the time differentiated value of the quantity of charge stored at the wood chipso The bar electrodes 8a to 8c each having a length of 30 cm are arranged, as shown in Fig. 2, so that each of them shares 1/3 of the width of the belt conveyor 2, and a shielding cover9 is mounted so as to surround the electrodes. The electrodes 8a to 8c may be arranged longitudinally in two or three stagesO
In this manner~ the quanti*y of charge stored in the plastics in the wood chips is detected by the bar electrodes, and the charge is amplified as the time differentiated value by the amplifier circuit of the surface potentiometer An output ampl:ified by the surface potentiometer 7 is appl.ied to a comparator 10 in Fig. 1, and detected by the comparator as to whether the absolute value thereof is higher than a reference potential.
The above operation will be described in nore detail with reference to Figs. 3. The surface potertial detected by the electrodes 8 exhibits a waveform as shown in Fig. 3(a). ~ince the detected signal is applied to a differentiation type amplifier 7A in the surface potentiometer 7, the waveform becomes a pattern as shown in Fig. 3(b), and is further amplified by a main amplifier 7B in the waveform as shown in Fig. 3(c), Reference symbol 7C
represents a sensitivity set-ting element for defining the amplification factor. The output of the surface potentiometer 7 is applied to the comparator 10 as described above, and an arbitrary reference ~oltage can be set by suitably adjusting a level setting element lOA in the comparator 10. The reference (lower limit) potential is represented by symbol 1Oa in Fig~ 3(c)o ~nly the signal exceeding the reference po-tential level is produced as the output of the comparator as shown in Fig. 3(d), and applied to a monostable multi-vibrator llof next stage. A time setting element 1lA i~ attache~ to the monostable multi-vibrator 11 so as to define the operating time of a lamp 12 or an alarm unit 13.
The defining time is shown by symbol ~t' in Fig. 3(e).
, When the lower lim:it of potential isg for exampleg set to -5 volts in the comparator 10 and the absolute value of the signal is detected to be higher than the lower limit of potential 9 the pilot lamp 12 is energized by the detection signal~
or the alarm unit 13 is simultaneously operatedO
In -this case, the reference poten-tial of the comparator and -the amplification factor of the amplifier circuit are adjustable according to the magnitude of -the detected potential difference.
When the detection signal is produced from the comparator, the presence of the plastics is notified by the means described above, and a timer 14 separately mounted is operated by the signal, and stops a drive drum 2a in the conveyor 2 a~ter the lapse o~ a predetermined period of timen Subsequently3 the plastics admixed in the wood chips on the belt conveyou is manually removedO
The present invention thus includes a me-thod of automatically detecting the plastics admixed in the wood chips and manually removing the plastics therefromO
According to the method of the present invention, the probability of de-tecting various plastics (polyethylene film, polypropylene (PP) rope, foamed s-tyrol~ polyvinyl chlor:ide tape~ PP straw, polyethylene (PE) dust box broken pieces, polyvinyil chloride shee-t) polyester fi:lm, polycarbonate; or nylon) from the wood chips or o-ther conductive substances is higher than about 80 ~.
When -the wood chips were passed two or three times through a conveyor equipped with~ the same plastics detector; the plastics were detected and removed with a probability of more than 95 %.
An example of the inven-tion in ~hich conductive ma-terials containing plastics are automatically partly removed will be described. In the apparatus shown in Fig71, a hopper 15 is mounted a-t the exhaust end of the belt conveyor 2, branch tubes 17a, 17b having a damper 16 are arranged at the hopper, and the signal of the timer 14 is supplied to an actuator 18 o-f -the damper 160 The damper l6 is normally a-t the position designated by a chain line in Fig. 1 so that the conductive materials eshausted from the conveyor 2 flow into a reservoir container 200 When the plastics are admixed in the materials~ the presence of the plastics is automatically detected as described above~ the timer 14 is operated, and -the damper 16 is switched to the position as designated by solid lines in Fig~ 1 after -the lapse of a predetermined period of -timeO At this time -the materials conta:ining -the plasti.cs flow through the branch -tube 17b into a plastic container 190 The ch:ips con-taining no plastics are supplied to the other con-tainer 20 as mentioned above.
rrhus~ automatic sorting :i.s perfomed.
As a method of removing plastics admixed in conductive materials, means shown in Figs. 4 and 5 or Fig. 6 may be adopted. In the arrangement shown in Figs 4 and 5, a vertically movable scraper 21 is disposed obliquely in a plan view just above -the belt conveyor 2 for conveying the conductive materials, and the changeover valve of an elevation cylinder 22 is operated by said detection signal and the output signal from the timer 140 The scraper 21 is normally raised upwardly as shown by solid lines in Fig. 4, and when the conductive materials admixed with the plas-tics have arrived at a predetermined position, the scrapter 21lis moved downwardly by the above-described signals, thereby the materials being automatically removed as shown by an arrow in Fig~ 5.
In the arrangement shown in Fig. 6, a reciprocating plastic container 24 mounted on a piston rod of a cylinder 23 is arranged at the exhaust end of the conveyor 2.
In this arrangement~ a spool valve 25 of a solenoid type is switched via the output signal of the timer 14, and the plastics are thereby automatically removedO ~he entire plastics removing dcvice is generally designated by numeral 26.
F:ig. 7 shows an arrangement :in which a plurality o~ conveyors pro~ided wi-th -the detecting means of the invention are disposed in the direction of conveyance there of 0 This arrangement will now be described in detail.
A vibrating screen 31 is arranged at the exhaust end of a hopper 30 ~orelectrically conductive wood chips9 and an ionic air generator 32 and an air shower 33 are substantially alternately installed above the screen.
Dus-ts adl-ered to the wood chips and plas-tics vibra-ted by the screen 3~ are simultaneously removed. Since the dusts are normally slightly charged positively and are conduc-tive, they are particularly de-trimental to the plas-tics to be removed, but the dusts are removed before the detectionO The air shower 33, as well as the vibrating screen 31, is er~ective for removing the dusts. In addition, in the arrangement in Fig. 7, the ionic air generator 32 is further installed, and the ~ollowing advantages are obtained. The generator 32 has paired electrodes 32b in the vicinity of the stylus electrodes 32a of a corona bar as shown in Fig. 8, and is adapted to ionize the air in the environment. The dusts adhered to the wood chips or plastics may be charged positive]y as mentioned above~ and may be electrostatically adhered to the plastics.
Even in this case , when ionic air is sprayed through the generator 32, the elec-trostatic bond is released so as -to facilitate the removal of the dusts.
The chips, from which the dusts are thuæ removed, are introduced to a vibrating ~eeder 34 in Fig. 7, and a predetermined q-lan-tity o~ chips are supplied in a thin layer ~z~
onto the next belt conveyor 35 ~ Another conveyor 36 is provided at the exhaust side of the belt conveyor 35, automatic swi-tches 37 being respectively provided between the conveyors 35 and 36 and at the exhaust side of the conveyor 36.
Thus -the plastics detected as described below are automatically removed.
Corona dischargers 38 are respectively arranged above the conveyors 35 and 36; and the elec-trodes 39 of surÇace potentiometers are disposed at the downstream side -thereof so that the differences in surface potential are individually detected in the same manner as in Example lo The treatment after the de-tection is as already described~
Operating conditions in the above respective examples will be listed in tables belowO
Table 4 Ex. Conveyor Conveyor Distance between Voltage I~terval speed width bar and applied to between bar (m/rnin) (mm) conveyor bar and elect-(cm) (KV) rode (cm) 150 300 5 7 a,o ~L%~
Nwnber of Distance be- Distance be- Time set Lower limit electrodes -tween elect- tween elect- in timer value set in rode and the rode and the (sec) comparator end of surface of conveyor conveyor (m) (cm) (V) 1 2 5 2.4 -5 2 2 5 2.4 -5 Operating conditions of example 4 Applied voltage of ionic air generator: 7 KV
Spraying amount of air shower: 200 liters/min Vibrating screen: Model RVS-450 made by Shinko Electric Co., Ltd.
~ (Capacity: Max. 0014 m3/min) Vibrating feeder: Model F-22BDT made by Shinko Electric Co., Ltd.
(Capacity: Max. 0.12 m3/min) Table 5 Conveyor Conveyor Feeding Applied vol~age speed width amount of corona discharge (m/min) (cm) (m3/min) (KV) Front belt 80 60 OoO8 11 conveyor Rear belt 80 60 0O08 11 conveyor Corona Distance be- Distance be- Number of discharger tween bar tween bar electrodes (Linear type) and conveyor and electrode ~Icm) (cm) one~ 5 row 5 80 2 one~ 5 row 5 80 2 Distance be- Distance be- Time set Lower limit value tween elect- tween elect- in timer set in comparator rode and the rode and the (sec) end of surface of conveyor conveyor (cm) (cm) (V) 130) 5 l -5 130 5 1 -.5 ~2~
As shown in Figs D 9 and 10~ wood chips contained in the storage unit 1 are sent out through the vibration feeder 3 in a flattened thin layer. The outle-t of the vibra-tion feeder 3 is connected to a chip chute 102 inclined a-t an angle of about 45~ and the wood chips are supplied in a thin layer to the chip chute 102.
The air shower 4 and the stylus corona discharging bars 6 connected to the high voltage power source 5 are provided above the conveyirlg surface of -the chip chute 102 thereby dusts adhered to the wood chips being reduced and corona discharge being performed to charge the wood chips.
Preferably~ the electrodes of the discharging bars 6 comprise a number of styluses buried in bar-shaped insulators.
The conductive chip chute 102 is grounded as shown in Fig~ 9 and inclined at an angle of abou-t 45 as mentioned above so that the wood chips move thereon at a speed of 150 m/min~
The electrode unit 8 of -the surface potentiometer 7 having an ampliEier circuit is provided in a position about 40 cm behind the bars 6 so as to measure -the time differentiated value of the ~uanti-ty of charge stored a-t -the wood chips.
The bar electrodes 8a to 8c each having a length of 30 cm are arranged; as shown in Fig. 10, so -that each of them shares 1/3 of the width of the chute 102, and -the ~29L~ 4 shielding cover 9 is moun-ted so as to surround the electrodes~
The electrodes 8a to 8c may be arranged longitudinally in two or three stages. In this manner, -the quan-tity of charge stored in the plastics in the wood chips is de-tected by the bar el.ectrodes~ and the charge is amplified as the -time differentia-ted value by the amplifier circuit of -the sur:face potentiometer 7. An output amplified by the surface potentiometer 7 is applied to the comparator 10 in Figo 9;
and detected by the comparator as to whether the absolute value thereof is higher than a reference potential~
In these respects~ Example 5 is the same as ~xample 1O
When the detec-tion signal is produced from the comparator 109 the presence of the plastics is notified by the means described above, and the timer 14 separately disposed is actuated by the signalO After the lapse of a predetermined period of time~ the timer 14 stops a belt conveyor 103 disposed under said chip chute 102 and also stops the vibration feeder 30 Now~ plastics admixed in the wood chips on the bel-t conveyor 103 are removed thereerom by handO
EXA~PLE 6 In this examp:Le, the method of the present invention is applied to the same chute as :i.n said ~xample 5, and the plastics are removed automatically~ not by hanclO
The same removing means as in said Examples 2 and 3, that is~
the device represented by numeral 26 is Fig~ 1 or 6~ is disposed at the exhaust end of the chip chute 102~ and the plastics are automa-tically remove~ from the wood chips by the same method as in said Examples 2 and 3O
EX~MPL~ 7 Fig. 11 shows an arrangement in which a plurality of chutes prov:ided with the detecting means of the invention are disposed in the ~irection of conveyance there o~O
This arrangemen will now be described in detail.
The vibrating screen 31 is arranged at the exhaust end of the hopper 30 for electrically conductive wood chips and the ionic air generator 32 and the air shower 33 are substantially alternately installed above the screenO
Dusts adhered to the wood chips and plastics vibrated by the screen 31 are simultaneously removedO Since the dusts are normally slightly charged positively and are conductive, they are particularly detrimental to the plastics to be removed~
but the dusts are removed be~ore the detectionO The air shower 33, as well as the vibrating screen 31j is effective for removing the dustso In addition, in the arrangement in Figo 11, the ionic air generator 32 is further installed.
'I'herefore, even when the dusts adhered to the wood chips Ot' plastics are charged positively~ :ion:ic ai:r can be sprayed through -the generator 32~ and the electrostatic bond is released thereby so as to facilitate the removal of -the dustso The chips~ Erom which the dusts are thus removed~
~æ~
are introduced into the vibrating feeder 34 in Figo 11~
and a prede-termined cluantity of chips are supplied in a thin layer onto -the next chip chu-te 104. Another chip chute 105 is provided at -the exhaust side of the chip chute 104~ the automatic switchss 37 being respectively proveded be-tween the chip chutes 104 and 105 and at -the exhaust side of -the ch:ip chute lOSo Thus the plastics detected are au-toma-tically removed through the switches 37 in the same manner as in Example 40 The corona dischargers 38 are respectively arranged above the chutes 104 and 105, and the electrodes 39 of the surface potentiometers are disposed at the downstream side thereof so that the differences in surface potential are individually detected in the same manner as in Example lo In this case~ the detection can be made more effectively.
In sajd Examples 5 to 7, the chute 102 or the chutes 10~ 105 may be enclosed as shown in Figo 12 (See numeral 1060) so as to eliminake the influence of wind.
Wood chips containing -the plastics are automa-tically separated also when a winclow 107 adap-ted to open and close automatically is disposed at -the bottom of each chute as shown in ~':ig~ 13j -the driving mechanism 107A of sa:id window 107 being actuated by the signal Oe said timer 14 so as to open the window 107.
Operating conditions in the above respective examples will be listed in tables below.
Table 6 Ex, Cllip Chute Distance be- Voltage Inte~val speed width tween bar applied to between on cllute (mm) and chute bar bar and (m/min) (cm) (KV) electro~e _ (cm) Ex. Number of Distance be- Time set Lower limit electrodes tween elect~ in timer value set in rode and the (sec) comparator surface of chute (cm) (V) 2 5 2.4 5 6 2 5 2.4 -5 Operating conditions of example 7 Applied voltage of ionic air genera-tor: 7 ~V
Spraying amount of air shower: ZOO liters/min vibrating screen: Model RVS-450 made by Shinko Electric Co., Ltd.
(Capacity: Max. O~t4 m3/min) Vibrating fceder: Modcl E-2213D'r made by Shinko ~2~
Electric CoO, Ltd.
(¢apacity: Max. 0.12 m3/min) Table 7 Chip Chute Feeding Applied voltage speed width amount of corona discharge (m/min) (cm~ (m3/min) (KV) Front chute 80 60 0. o8 11 Rear chute 80 60 0.08 11 Corona Distance be- Distance be- Number of discharger tween bar tween bar electrodes (Linear type) and chute and electrode (cm) (cm) ....
one, 5 row 5 80 2 one, 5 row 5 80 2 Distance be- Distance be- Time set Lower limit value tween elec-t tween elect- in timer set in comparator rode and the rode and the (sec) end of chute surface of (cm) chute (cm) (V) _ .,
th~ough which the wood chips containing the plastics fallO
The compara-tor used in the method of the invention is adapted to set in advance the lower limi-t (reference value) of the absolute value of the differentiated value of the measured potential and to automatically discriminate whether the measured value is larger than the lower limit or not. Thus) the comparator is a kind of potential comparator.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic vertical sectional view illustrating an example of an apparatus~ including a belt conveyor as a movable conveyirg surfaceg for carrying out the method of the present invention, Fig. 2 is a s¢hematic lateral sectional view illustrating an example of stationary electrodes for detecting surface potentials in the apparatus in Fig~ 1.
Fig. 3 is a circuit diagram showing a circuit arrangement of a poten-tial detec-tor together with signal waveforms of respective uni-tsO
Fig. 4 is a lateral sectional view showing a dovice for removing plastics ussd in the apparatus.
Fig. 5 is a partial plan view of the device.
Fig. 6 is a longituclinal sectlonal view partly il~ustrating another exampLe of the device for removing ~2~ 4 the plas-tics.
Figo 7 is a schematic side view of another example of the apparatus for carrying out the method of the presen-t inventionO
Figo 8 is an explanatory view showing an example of an ionic air generatorO
Figso 9 -to 13 show still another example of the apparatus; including a chute as an immovable conveying surface) for carrying out -the method of the present invention~
Figo 9 is a schematic side view illustrating said apparatusO
Figo 10 is a schematic lateral sectional view illustrating an example of stationary electrodes for detec-ting surface poten-tials in said apparatusO
Figo 11 is a schematic side view illustrating a chute apparatus.
. Fig. 12 is a perspective view illustrating an enclosed chute in which wood chips flowO
Fig. 13 is a perspective view illus-trating a chute having a w:indow adapted to open and close automa-tically~
BEST MODE FOR CA~RYING OUT THE INVENTION
:[n order -to eEfec-tive:Ly detect the sureace po-tentials of plastics admixed in pulp and paper stuff or cereals, it is preferred to make wood chips thin and move them on a belt conveyor as a movable conveying surface or let them flow down a chute as an immovable conveying surface. The plas-tics to be detected for the presence by a surface potentiomerer inc1ude polystyrene, polyethylene, polyvinyl chloride, polycarbonate;
polyethylene -terephthalate, polytetrafluoroethylene, polypropylene, polyvinylidene chloride, polyvinyl fluoride;
polyvinylidene fluoride, epoxy resin, polyacrylic resin3 polyamide, milamine resin, polybutadiene, syn-thetic high molecular compound including copolymer with the same, cellophane, and rubbers, all of which have lower charge attenuating velocity as compared with the pulp and paper stuff or cereals. The size of the detectable plastics is larger than 1 mm , but even if the plastics is less than 1 mm in size, the plastics having remarkable charging property such as polystyrene, polye-thylene~
polypropylene, or polyester can be sufficiently detected by a po-tentiome-ter.
Non-wood pulp and paper stuff sueh as straw, bagasse~ hemp, rag, eotton, linter, or waste paper contains less quanti-ty of moisture as compared with wood ehips) ancl contains less than 5 -to 6 ~ by weightO
Consecluently, even if the non-wood pulp and paper stuff is eorona clischarged, a suff:icient potential difference ~2~
may not be obtained between -the non-wood pulp and paper stuff and the plastics~ Accordingly~ when the non-wood pulp and paper stuff is treated, i-t is preferred to moisten the non-wood pulp and paper stuff at the upstream side of the position of the surface potentiomeker (a-t the upstream side of -the position of a discharging bar in case of performing corona discharging)~
For instance, waste paper, newspaper and rag selected as non-wood pulp and paper stuff had water contents in the range of 4 to 6 % by weightO They were distributed in a thin layer on a conveyor belt having a width of 600 mm and moving at a speed of 8 m/min, and corona discharged by means of electrodes of 10 ~V installed at a height of 4 cm above the conveyor belt. Then -the surface potentials thereof were measured by means of a surface potentiome-ter installed at a height of 4 cm above the conveyor belt at positions isolated by 30 cm from the electrodesO Their surface potentials thus measured were -50 to -lOO volts.
On the other hand, when they were similarly corona discharged after being sprayed with water by means of a shower pipe installed at a height of 40 cm above the conveyor belt so as to adjus-t their water con-tent to a range of 9 to 12 ~ by weight, their surface poten-tials were only O -to 2 volts. These data apply also to a case where pulp and paper stuf-f in a thin layer flows down a chute a-t a speed of lG0 m/min~ said chute having a width of 1000 mm and an inclination of 45 , and the surface potentials o-f the stuff are measured by means of a surface potentiometer disposed a-t a heigh-t of 4 cm above said chute.
Means formoistening the non-wood pulp and paper stuf-f is not always limited in the invention, but the moistening is generally performed by spraying water over the surfaces of paper or fibers by means of a noz~le shower, etc. moistening by steam is also effectiveO It is always preferable to adjust the wa-ter content of the non-wood pulp ans paper stuff to the range of 9 to 60 % by weight. In this case, it is also possible to adjust the water conten-t after the paper or fibers mixed with the plastics are put on a conveyor belt, and it is rather preferable to moisten the paper or fibers after putting them in a thin layer on the conveyor belt because this ensures rela-tively uniform moistening adjustment. In this case, the shower pipe is preferably ins-talled at a height of 20 -to 50 Clll above -the conveyor belt to spray wa-ter over the paper or fibersO
In carrying ou-t -the methocl o-f -the invention, it is preferable but not indispensable to apply a corona ~2~ 4 discslarge to pulp and paper stuff or cereals conveyed on a conveyor or moved by gravity on a chute, so as to increase the potentials of plastics mixed in the stuff or cerealsO Since dusts are frequently adhered to the plastics admixed in the pulp and paper stuff Ol~ cereals~ it is effective to perform corona discharging after the pulp and paper stuff or cereals are supplied to -the conveyor through a vibrating screen or a vibrating feeder and, if necessary, the dusts adhered to the plastics are further removed by an air shower, in order to increase the charging potentials of the plastics.
When the air shower is employed, the dusts might be charged at a plus potential and adhered to the plastics, and therefore it is desirable to neutralize in advance the charge of the dusts by using ioni~ed air produced by a static eliminating barO The voltage of the corona discharge is normally in the range of I to 50 KV,and it is normal to adjust tsle distance between the corona discharging bar made, for example, of stylus electrodes and a conveyor hel-t which is a paired electrode to 3 to 20 cm.
The surface po-tentiometer necessary to carry ou-t the method of the present invention has an amplifier circuit for performing a tisne diEferentiating method, it is preferable to approach the electrodes to tsle flow of pulp and paper stuff or cereals as near as - 16 _ ..... , .. ~
~2~
possible without contacting themO In -the cace of corona discharge, it is preferable to approach the electrodes to the discharging position as near as possibleO
In this manner, even if the charging charge of the plastics due to -the corona discharge is attenuated, it is possible to detect the potential clifference of the plastics from the pulp and paper stuffo ~lowever; it is desirable to ensure tha-t -the high voltage of the corona discharge or the increase of the earth potential by spark discharge does not exert a bad influence, with saicl approach, upon the surface potentiometer or an integrated circuit contained in electronic circuits such as the arnplifier circuit or the comparator.
It is also possible to use a checking mechanism or circuit to check whether the electronic circuits are in nomal operation.
It is preferable~ that the electrodes of the surface potentiometer are of a bar type because they measure the surface potentials of the plastics moving on the wide belt conveyor or chute, and -they normally have a leslgth of a ~ew to 100 cmO
Additionally, since the surface potentiome-ter employed ;.n the me-thocl of -the inventi.on has an amplifier circui-t for a -time differentiating method, the presence of the plastics can be sufficiently detec-ted even when the passing veloci-ty of -the plastics passing under the electrodes is high or when the charging density is small. This is because the charge induced at the electrodes of -the surface poten-tiometer due to the approach of the charged plastics to the electrodes is amplified -to a time differentiated value, and the amplified value is outputted to the comparator~
Accordingly~ in case of a conveyor it is possible to arbitrarily select the moving speed of the conveyor in a range of 1 to 300 m/min. In case of a chute, it is possible to arbitrarity select the flowing speed of the wood chips, etc. in a range of 10 to 400 m/min by changing the inclination of the chuteO
The present invention will be further described in detail with reference to accompanying drawingsO
As shown in Fig. 1, wood chips contained in a storage unit 1 are con-tinuously dropped onto a belt conveyor 2 through a vibration feeder 3, and flattened so that the chips become a thin layer on -the conveyorO
An air shower 4 and sty:Lus corona discharging bars 6 connected to a high voltage power source 5 are prov:ided above the conveying surface o~ the conveyor 2, -thereby clusts adhered -to the wood chips being reduced and corona discharge being performed to charge the wood chips. Preferably the electrodes of discharging bars comprise a number of s-tyluses buried in bar-shaped insulators. The conductive belt conveyor is grounded as shown in Fig. 1., and is operated at a speed of 50 m/min for exampleO The electrode unit 8 of a surface potentiometer 7 having an amplifier circuit is provlded in a position about 40 cm behind the bars 6 so as to measure the time differentiated value of the quantity of charge stored at the wood chipso The bar electrodes 8a to 8c each having a length of 30 cm are arranged, as shown in Fig. 2, so that each of them shares 1/3 of the width of the belt conveyor 2, and a shielding cover9 is mounted so as to surround the electrodes. The electrodes 8a to 8c may be arranged longitudinally in two or three stagesO
In this manner~ the quanti*y of charge stored in the plastics in the wood chips is detected by the bar electrodes, and the charge is amplified as the time differentiated value by the amplifier circuit of the surface potentiometer An output ampl:ified by the surface potentiometer 7 is appl.ied to a comparator 10 in Fig. 1, and detected by the comparator as to whether the absolute value thereof is higher than a reference potential.
The above operation will be described in nore detail with reference to Figs. 3. The surface potertial detected by the electrodes 8 exhibits a waveform as shown in Fig. 3(a). ~ince the detected signal is applied to a differentiation type amplifier 7A in the surface potentiometer 7, the waveform becomes a pattern as shown in Fig. 3(b), and is further amplified by a main amplifier 7B in the waveform as shown in Fig. 3(c), Reference symbol 7C
represents a sensitivity set-ting element for defining the amplification factor. The output of the surface potentiometer 7 is applied to the comparator 10 as described above, and an arbitrary reference ~oltage can be set by suitably adjusting a level setting element lOA in the comparator 10. The reference (lower limit) potential is represented by symbol 1Oa in Fig~ 3(c)o ~nly the signal exceeding the reference po-tential level is produced as the output of the comparator as shown in Fig. 3(d), and applied to a monostable multi-vibrator llof next stage. A time setting element 1lA i~ attache~ to the monostable multi-vibrator 11 so as to define the operating time of a lamp 12 or an alarm unit 13.
The defining time is shown by symbol ~t' in Fig. 3(e).
, When the lower lim:it of potential isg for exampleg set to -5 volts in the comparator 10 and the absolute value of the signal is detected to be higher than the lower limit of potential 9 the pilot lamp 12 is energized by the detection signal~
or the alarm unit 13 is simultaneously operatedO
In -this case, the reference poten-tial of the comparator and -the amplification factor of the amplifier circuit are adjustable according to the magnitude of -the detected potential difference.
When the detection signal is produced from the comparator, the presence of the plastics is notified by the means described above, and a timer 14 separately mounted is operated by the signal, and stops a drive drum 2a in the conveyor 2 a~ter the lapse o~ a predetermined period of timen Subsequently3 the plastics admixed in the wood chips on the belt conveyou is manually removedO
The present invention thus includes a me-thod of automatically detecting the plastics admixed in the wood chips and manually removing the plastics therefromO
According to the method of the present invention, the probability of de-tecting various plastics (polyethylene film, polypropylene (PP) rope, foamed s-tyrol~ polyvinyl chlor:ide tape~ PP straw, polyethylene (PE) dust box broken pieces, polyvinyil chloride shee-t) polyester fi:lm, polycarbonate; or nylon) from the wood chips or o-ther conductive substances is higher than about 80 ~.
When -the wood chips were passed two or three times through a conveyor equipped with~ the same plastics detector; the plastics were detected and removed with a probability of more than 95 %.
An example of the inven-tion in ~hich conductive ma-terials containing plastics are automatically partly removed will be described. In the apparatus shown in Fig71, a hopper 15 is mounted a-t the exhaust end of the belt conveyor 2, branch tubes 17a, 17b having a damper 16 are arranged at the hopper, and the signal of the timer 14 is supplied to an actuator 18 o-f -the damper 160 The damper l6 is normally a-t the position designated by a chain line in Fig. 1 so that the conductive materials eshausted from the conveyor 2 flow into a reservoir container 200 When the plastics are admixed in the materials~ the presence of the plastics is automatically detected as described above~ the timer 14 is operated, and -the damper 16 is switched to the position as designated by solid lines in Fig~ 1 after -the lapse of a predetermined period of -timeO At this time -the materials conta:ining -the plasti.cs flow through the branch -tube 17b into a plastic container 190 The ch:ips con-taining no plastics are supplied to the other con-tainer 20 as mentioned above.
rrhus~ automatic sorting :i.s perfomed.
As a method of removing plastics admixed in conductive materials, means shown in Figs. 4 and 5 or Fig. 6 may be adopted. In the arrangement shown in Figs 4 and 5, a vertically movable scraper 21 is disposed obliquely in a plan view just above -the belt conveyor 2 for conveying the conductive materials, and the changeover valve of an elevation cylinder 22 is operated by said detection signal and the output signal from the timer 140 The scraper 21 is normally raised upwardly as shown by solid lines in Fig. 4, and when the conductive materials admixed with the plas-tics have arrived at a predetermined position, the scrapter 21lis moved downwardly by the above-described signals, thereby the materials being automatically removed as shown by an arrow in Fig~ 5.
In the arrangement shown in Fig. 6, a reciprocating plastic container 24 mounted on a piston rod of a cylinder 23 is arranged at the exhaust end of the conveyor 2.
In this arrangement~ a spool valve 25 of a solenoid type is switched via the output signal of the timer 14, and the plastics are thereby automatically removedO ~he entire plastics removing dcvice is generally designated by numeral 26.
F:ig. 7 shows an arrangement :in which a plurality o~ conveyors pro~ided wi-th -the detecting means of the invention are disposed in the direction of conveyance there of 0 This arrangement will now be described in detail.
A vibrating screen 31 is arranged at the exhaust end of a hopper 30 ~orelectrically conductive wood chips9 and an ionic air generator 32 and an air shower 33 are substantially alternately installed above the screen.
Dus-ts adl-ered to the wood chips and plas-tics vibra-ted by the screen 3~ are simultaneously removed. Since the dusts are normally slightly charged positively and are conduc-tive, they are particularly de-trimental to the plas-tics to be removed, but the dusts are removed before the detectionO The air shower 33, as well as the vibrating screen 31, is er~ective for removing the dusts. In addition, in the arrangement in Fig. 7, the ionic air generator 32 is further installed, and the ~ollowing advantages are obtained. The generator 32 has paired electrodes 32b in the vicinity of the stylus electrodes 32a of a corona bar as shown in Fig. 8, and is adapted to ionize the air in the environment. The dusts adhered to the wood chips or plastics may be charged positive]y as mentioned above~ and may be electrostatically adhered to the plastics.
Even in this case , when ionic air is sprayed through the generator 32, the elec-trostatic bond is released so as -to facilitate the removal of the dusts.
The chips, from which the dusts are thuæ removed, are introduced to a vibrating ~eeder 34 in Fig. 7, and a predetermined q-lan-tity o~ chips are supplied in a thin layer ~z~
onto the next belt conveyor 35 ~ Another conveyor 36 is provided at the exhaust side of the belt conveyor 35, automatic swi-tches 37 being respectively provided between the conveyors 35 and 36 and at the exhaust side of the conveyor 36.
Thus -the plastics detected as described below are automatically removed.
Corona dischargers 38 are respectively arranged above the conveyors 35 and 36; and the elec-trodes 39 of surÇace potentiometers are disposed at the downstream side -thereof so that the differences in surface potential are individually detected in the same manner as in Example lo The treatment after the de-tection is as already described~
Operating conditions in the above respective examples will be listed in tables belowO
Table 4 Ex. Conveyor Conveyor Distance between Voltage I~terval speed width bar and applied to between bar (m/rnin) (mm) conveyor bar and elect-(cm) (KV) rode (cm) 150 300 5 7 a,o ~L%~
Nwnber of Distance be- Distance be- Time set Lower limit electrodes -tween elect- tween elect- in timer value set in rode and the rode and the (sec) comparator end of surface of conveyor conveyor (m) (cm) (V) 1 2 5 2.4 -5 2 2 5 2.4 -5 Operating conditions of example 4 Applied voltage of ionic air generator: 7 KV
Spraying amount of air shower: 200 liters/min Vibrating screen: Model RVS-450 made by Shinko Electric Co., Ltd.
~ (Capacity: Max. 0014 m3/min) Vibrating feeder: Model F-22BDT made by Shinko Electric Co., Ltd.
(Capacity: Max. 0.12 m3/min) Table 5 Conveyor Conveyor Feeding Applied vol~age speed width amount of corona discharge (m/min) (cm) (m3/min) (KV) Front belt 80 60 OoO8 11 conveyor Rear belt 80 60 0O08 11 conveyor Corona Distance be- Distance be- Number of discharger tween bar tween bar electrodes (Linear type) and conveyor and electrode ~Icm) (cm) one~ 5 row 5 80 2 one~ 5 row 5 80 2 Distance be- Distance be- Time set Lower limit value tween elect- tween elect- in timer set in comparator rode and the rode and the (sec) end of surface of conveyor conveyor (cm) (cm) (V) 130) 5 l -5 130 5 1 -.5 ~2~
As shown in Figs D 9 and 10~ wood chips contained in the storage unit 1 are sent out through the vibration feeder 3 in a flattened thin layer. The outle-t of the vibra-tion feeder 3 is connected to a chip chute 102 inclined a-t an angle of about 45~ and the wood chips are supplied in a thin layer to the chip chute 102.
The air shower 4 and the stylus corona discharging bars 6 connected to the high voltage power source 5 are provided above the conveyirlg surface of -the chip chute 102 thereby dusts adhered to the wood chips being reduced and corona discharge being performed to charge the wood chips.
Preferably~ the electrodes of the discharging bars 6 comprise a number of styluses buried in bar-shaped insulators.
The conductive chip chute 102 is grounded as shown in Fig~ 9 and inclined at an angle of abou-t 45 as mentioned above so that the wood chips move thereon at a speed of 150 m/min~
The electrode unit 8 of -the surface potentiometer 7 having an ampliEier circuit is provided in a position about 40 cm behind the bars 6 so as to measure -the time differentiated value of the ~uanti-ty of charge stored a-t -the wood chips.
The bar electrodes 8a to 8c each having a length of 30 cm are arranged; as shown in Fig. 10, so -that each of them shares 1/3 of the width of the chute 102, and -the ~29L~ 4 shielding cover 9 is moun-ted so as to surround the electrodes~
The electrodes 8a to 8c may be arranged longitudinally in two or three stages. In this manner, -the quan-tity of charge stored in the plastics in the wood chips is de-tected by the bar el.ectrodes~ and the charge is amplified as the -time differentia-ted value by the amplifier circuit of -the sur:face potentiometer 7. An output amplified by the surface potentiometer 7 is applied to the comparator 10 in Figo 9;
and detected by the comparator as to whether the absolute value thereof is higher than a reference potential~
In these respects~ Example 5 is the same as ~xample 1O
When the detec-tion signal is produced from the comparator 109 the presence of the plastics is notified by the means described above, and the timer 14 separately disposed is actuated by the signalO After the lapse of a predetermined period of time~ the timer 14 stops a belt conveyor 103 disposed under said chip chute 102 and also stops the vibration feeder 30 Now~ plastics admixed in the wood chips on the bel-t conveyor 103 are removed thereerom by handO
EXA~PLE 6 In this examp:Le, the method of the present invention is applied to the same chute as :i.n said ~xample 5, and the plastics are removed automatically~ not by hanclO
The same removing means as in said Examples 2 and 3, that is~
the device represented by numeral 26 is Fig~ 1 or 6~ is disposed at the exhaust end of the chip chute 102~ and the plastics are automa-tically remove~ from the wood chips by the same method as in said Examples 2 and 3O
EX~MPL~ 7 Fig. 11 shows an arrangement in which a plurality of chutes prov:ided with the detecting means of the invention are disposed in the ~irection of conveyance there o~O
This arrangemen will now be described in detail.
The vibrating screen 31 is arranged at the exhaust end of the hopper 30 for electrically conductive wood chips and the ionic air generator 32 and the air shower 33 are substantially alternately installed above the screenO
Dusts adhered to the wood chips and plastics vibrated by the screen 31 are simultaneously removedO Since the dusts are normally slightly charged positively and are conductive, they are particularly detrimental to the plastics to be removed~
but the dusts are removed be~ore the detectionO The air shower 33, as well as the vibrating screen 31j is effective for removing the dustso In addition, in the arrangement in Figo 11, the ionic air generator 32 is further installed.
'I'herefore, even when the dusts adhered to the wood chips Ot' plastics are charged positively~ :ion:ic ai:r can be sprayed through -the generator 32~ and the electrostatic bond is released thereby so as to facilitate the removal of -the dustso The chips~ Erom which the dusts are thus removed~
~æ~
are introduced into the vibrating feeder 34 in Figo 11~
and a prede-termined cluantity of chips are supplied in a thin layer onto -the next chip chu-te 104. Another chip chute 105 is provided at -the exhaust side of the chip chute 104~ the automatic switchss 37 being respectively proveded be-tween the chip chutes 104 and 105 and at -the exhaust side of -the ch:ip chute lOSo Thus the plastics detected are au-toma-tically removed through the switches 37 in the same manner as in Example 40 The corona dischargers 38 are respectively arranged above the chutes 104 and 105, and the electrodes 39 of the surface potentiometers are disposed at the downstream side thereof so that the differences in surface potential are individually detected in the same manner as in Example lo In this case~ the detection can be made more effectively.
In sajd Examples 5 to 7, the chute 102 or the chutes 10~ 105 may be enclosed as shown in Figo 12 (See numeral 1060) so as to eliminake the influence of wind.
Wood chips containing -the plastics are automa-tically separated also when a winclow 107 adap-ted to open and close automatically is disposed at -the bottom of each chute as shown in ~':ig~ 13j -the driving mechanism 107A of sa:id window 107 being actuated by the signal Oe said timer 14 so as to open the window 107.
Operating conditions in the above respective examples will be listed in tables below.
Table 6 Ex, Cllip Chute Distance be- Voltage Inte~val speed width tween bar applied to between on cllute (mm) and chute bar bar and (m/min) (cm) (KV) electro~e _ (cm) Ex. Number of Distance be- Time set Lower limit electrodes tween elect~ in timer value set in rode and the (sec) comparator surface of chute (cm) (V) 2 5 2.4 5 6 2 5 2.4 -5 Operating conditions of example 7 Applied voltage of ionic air genera-tor: 7 ~V
Spraying amount of air shower: ZOO liters/min vibrating screen: Model RVS-450 made by Shinko Electric Co., Ltd.
(Capacity: Max. O~t4 m3/min) Vibrating fceder: Modcl E-2213D'r made by Shinko ~2~
Electric CoO, Ltd.
(¢apacity: Max. 0.12 m3/min) Table 7 Chip Chute Feeding Applied voltage speed width amount of corona discharge (m/min) (cm~ (m3/min) (KV) Front chute 80 60 0. o8 11 Rear chute 80 60 0.08 11 Corona Distance be- Distance be- Number of discharger tween bar tween bar electrodes (Linear type) and chute and electrode (cm) (cm) ....
one, 5 row 5 80 2 one, 5 row 5 80 2 Distance be- Distance be- Time set Lower limit value tween elec-t tween elect- in timer set in comparator rode and the rode and the (sec) end of chute surface of (cm) chute (cm) (V) _ .,
Claims (12)
1. A method of detecting and sorting pieces of insulating materials admixed in small pieces of conductive materials, which comprises distributing said small pieces of conductive materials in a thin layer on a movable conveying surface having conductivity or an inclined immovable conveying surface having conductivity, conveying said materials thereby, time differentiating and amplifying a charge induced at the electrodes of a surface potentiometer disposed above said conveying surface, inputting the amplified value from said surface potentiometer into a comparator, sending an output signal generated by said comparator to a timer when the input potential of said comparator exceeds a refernce potential set in said comparator, and stopping the operation of said movable conveying surface or the supply of said materials or operating removing means attached to said conveying surface without stopping said operation or supply in response to an output signal delivered by said timer according to the set time thereof.
2. A method as claimed in Claim 1, wherein a corona discharger is provided at the upstream side of the electrode position of said surface potentiometer with respect to the direction of conveyance of said materials on said conveying surface, said corona discharger being adapted to apply a corona discharge to said materials on said conveying surface.
3. A method as claimed in Claim 2, wherein a dust removing device is provided at the upstream side of the position of said corona discharger with respect to the direction of conveyance of said materials on said conveying surface, said dust removing device being adapted to remove dusts stuck to said materials.
4. A method as claimed in Claim 3, wherein said dust removing device is a vibrating feeder.
5. A method as claimed in Claim 3, wherein said dust removing device is an air shower.
6. A method as claimed in Claim 5, wherein said materials are treated with ionic air at the upstream side of the position of said dust removing device with respect to the direction of conveyance of said materials on said conveying surface.
7. A method as claimed in Claim 1, wherein said removing means comprises branch tubes with a damper disposed at the exhaust end of said conveying surface.
8. A method as claimed in Claim 1, wherein said removing means is a reciprocating container disposed at the exhaust end of said conveying surface.
9. A method as claimed in Claim 1, wherein said insulating materials are plastics and said conductive materials are pulp and paper stuff or cereals such as noodles and soybeans.
10. A method of detecting and sorting pieces of insulating materials admixed in small pieces of conductive materials, which comprises distributing said small pieces of conductive materials in a thin layer on an inclined immovable conveying surface which is a chute, letting said materials flow down said chute, the electrodes of a surface potentiometer being disposed above said chute, time differentiating and amplifying a charge induced at said electrodes, inputting the amplified value from said surface potentiometer into a comparator, sending an output signal generated by said comparator to a timer when the input potential of said comparator exceeds a reference potential set in said comparator, and stopping the supply of said materials to said chute or operating removing means attached to said chute without stopping said supply in response to an output signal delivered by said timer according to the set time thereof, said chute having a conductive surface opposing said electrodes.
11. A method as claimed in Claim 10, wherein the conveyance speed of said materials can be adjusted by changing the inclination of said chute.
12. A method as claimed in Claim 10, wherein said immovable conveying surface is an enclosed chute.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/JP1983/000016 WO1984002980A1 (en) | 1983-01-18 | 1983-01-18 | Method of detecting and insolating piece of insulating substance between small pieces of conductive substance |
| JPJP83/00016 | 1983-01-18 | ||
| JP58171335A JPS6064246A (en) | 1983-09-19 | 1983-09-19 | Method for detecting and separating insulating material piece mixed in conductive material in small piece state |
| JP58-171335 | 1983-09-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1210114A true CA1210114A (en) | 1986-08-19 |
Family
ID=26424026
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000443502A Expired CA1210114A (en) | 1983-01-18 | 1983-12-16 | Method of detecting and sorting pieces of insulating materials admixed in small pieces of conductive materials |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1210114A (en) |
-
1983
- 1983-12-16 CA CA000443502A patent/CA1210114A/en not_active Expired
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