Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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.
(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~
-- 10 --
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
- 12 --
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
- 14 -
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
EXAMPLE 1
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
- 18 -
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
- 19
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
- 20 -
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 %.
EXAMPLE 2
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.
EXAMPLE 3
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.
EXAMPLE 4
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
- 23 -
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
- 24 -
~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
250 600 5 10 40
3 5 900 5 10 40
~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
3 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)
- 26 -
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~
EXAMPLE 5
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
- 28 -
~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
- 29 -
L4
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~
- 30 -
~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
- 31 -
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)
50 3O 5 7 40
6 50 600 5 10 4
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
- 32 -
~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)
_
130 5 1 -5
130 5 1 -5
.,
- 33 -
