Title of Invention	DEVICE FOR DEGASSING AND FILTERING PLASTIC MELTS
Abstract	The invention relates to a device for the extrusion of thermoplastic synthetic material featuring an extruder screw (2) which is mounted on a housing (1) including a plasticizing section (P) at the inlet side, a degassing section which is mounted upstream on a discharge section (A) and a conveying outlet (3) operating in the opposite direction which is located between the plasticizing section (P) and the degassing section (E). A flow channel (5) that contains a melt filter (4) is bridged over by at least one of the conveying outlets (3) in the opposite direction. To create favorable production conditions, the extruder screw (2) forms a similar conveying outlet (7) operating in the same direction between the conveying outlet (3) in the opposite direction and the downstream port (6) of the flow channel (5). The housing (1) has at least one degassing vent (8) at the transition area of the conveying outlet (3) operating in the opposite direction and the conveying outlet (7) operating in the same direction.

Title of Invention

DEVICE FOR DEGASSING AND FILTERING PLASTIC MELTS

Abstract

The invention relates to a device for the extrusion of thermoplastic synthetic material featuring an extruder screw (2) which is mounted on a housing (1) including a plasticizing section (P) at the inlet side, a degassing section which is mounted upstream on a discharge section (A) and a conveying outlet (3) operating in the opposite direction which is located between the plasticizing section (P) and the degassing section (E). A flow channel (5) that contains a melt filter (4) is bridged over by at least one of the conveying outlets (3) in the opposite direction. To create favorable production conditions, the extruder screw (2) forms a similar conveying outlet (7) operating in the same direction between the conveying outlet (3) in the opposite direction and the downstream port (6) of the flow channel (5). The housing (1) has at least one degassing vent (8) at the transition area of the conveying outlet (3) operating in the opposite direction and the conveying outlet (7) operating in the same direction.

Full Text	DEVICE FOR DEGASSING AND FILTERING PLASTIC MELTS [0001] The invention concerns a device for extruding thermoplastic synthetic products with an extruder screw mounted in a housing. The screw has a plasticizing section on the feed side thereof, a degassing section positioned upstream, that is, in front of a discharge section thereof, and an oppositely operating feed screw flight between the plasticizing section and the degassing section. The device further has at least one flow channel that bridges over the oppositely operating feed screw flight and has a melt filter. [0002] Plastics, especially plastic wastes, which must be degassed and/or cleaned before being further processed, need to be expediently degassed and processed. Printing, painting or soiling of waste and/or used plastics requires that the plastics be cleaned before further use. [0003] It is known (from WO 93/04841 A1) to melt plastic being reprocessed in an extruder, force it through a filter and degas it before further processing or granulation. To avoid an overflow of molten plastic from the plasticizing section to the degassing or discharge section, and to guarantee that all the molten plastic passes through the melt filter, an oppositely operating feed screw flight is arranged between the plasticizing section and the degassing section in the form of a feeding thread or sealing thread. The thread has a direction opposite to that of the screw thread of the plasticizing section, degassing section and discharge section. This known reverse feeding thread causes the return of a small fraction of the plastic that already passed through and had been cleaned by the melt filter back to the plasticizing section. This is supposed to prevent uncleaned plastic product from directly reaching the degassing and discharge section by bypassing the melt filter. The openings of the flow channel with the melt filter at the inlet and outlet sides are arranged right next to the reverse feeding thread to avoid dead spaces. This is supposed to prevent extended dwell times for the plastic product in the device which could cause heat damage to the plastic. A particular drawback of this device is that the feed screw sections with oppositely directed threads are in the nature of dynamic seals the tightness of which depends on the speed of the extruder screw. The viscosity of the plastic is also very important in this case, since plastic containing moisture forms vapors, and it cannot be prevented that moisture flows from the plasticizing section into the degassing section along these feed screw sections. Such vapors pass the filter and, amongst others, carry contaminants into the degassing section where they can again contaminate already filtered plastic, so that degassed and cleaned plastic of a uniform quality cannot be guaranteed. In addition, excessive degassing, caused for example by the moisture in the plastic, can cause undesirable pressure fluctuations in the device. [0004] In view of this prior art, it is an objective of the invention to overcome the aforementioned drawbacks and provide a device with improved degassing capability that prevents a direct material and/or gas flow from the plasticizing section into the degassing section via the feed screw flights between the sections. [0005] This is attained with an extruder screw that has a feed screw flight which operates in the same direction as the screw and is located between an oppositely operating feed screw flight and an opening of a flow channel for the plastic on an outlet side of the screw. The transitional zone between the two feed screw flights includes at least one degassing opening. [0006] The invention is based on the requirement that gas overflows between the plasticizing section and the degassing section must strictly be prevented for producing qualitatively uniform, cleaned and degassed plastic. This is achieved in accordance with the invention, in that, on the one hand, material flow from the plasticizing section to the degassing section is prevented by the oppositely operating feed screw flight. Likewise, the flow of already cleaned plastic from the degassing section to the plasticizing section is prevented by the feed screw flight that operates in the same direction and that is arranged between the oppositely operating feed screw flight and the opening of the flow channel to the outlet section of the screw. This separates the two sections and permits a degassing opening, a monitorable outlet opening, and/or a reduced pressure space to be arranged between the two screw sections. [0007] Gases and dirt particles entering the oppositely operating feed screw flight from the plasticizing section are therefore prevented in a simple manner from directly flowing into the degassing section and can be discharged from the device. This degassing and discharge can be deliberately supported in the usual manner by connecting the degassing space to a vacuum pump. Material overflows due to the emission of large amounts of gas caused, for example, by evaporating water can thereby be compensated for and suppressed in a simple manner. In accordance with the present invention, the pressures in the plasticizing and filtering sections are connected to the degassing and discharge section only via the flow channel, which assures a constant filling of the discharge screw and a constant degassing of the plastic. This also ensures that no dirt particles can be transported from the plasticizing section to the degassing section without having been passed through the melt filter. [0008] To reduce the wear of the oppositely rotating feed screw flight connected to the plasticizing section caused by uncleaned, plasticized plastic entering the feed screw flight, it is advantageous to connect the flow channel on the outlet side of the melt filter via at least one return channel, which preferably includes a check valve, to the oppositely operating feed screw flight of the extruder screw at the feeding side of the device. A deliberate, small backflow of clean plastic through the feed screw flight to the plasticizing section makes certain that no uncleaned plastic enters the oppositely operating feed screw flight. The check vale reliably prevents a flow of unfiltered plastic to the filtered side, especially during the startup phase of the device. [0009] To improve the degassing effect, a preferably threadless degassing space is provided between the oppositely operating screw flight of the extruder screw and the other screw flight operating in the same direction, which is defined by the extruder screw and/or the housing. Gases entering this area through the degassing opening are simply discharged from the device via the oppositely operating feed screw flight and the one operating in the same direction which reliably assures the desired pressure decoupling. [0010] To avoid a flow of plastic material through the oppositely operating feed screw flight towards the other feed screw flight that operates in the same direction due to a very low viscosity of the molten plastic, wear of the oppositely operating feed screw flight or the like, it is recommended to provide a further, oppositely operating feed screw flight section, preferably with smaller thread height, between the degassing space and the feed screw flight that operates in the same direction. [0011] To improve the flow density of the feed screw flight operating in the same direction, the extruder screw can be provided with a damming element in the vicinity of the opening of the flow channel at the discharge side of the screw. This damming element can be, for example, a ring element, a reduced pitch on the feed screw and/or an enlarged screw core diameter relative to the degassing section. The counterpressure of the plastic product against the feed screw flight operating in the same direction is thereby increased. [0012] The drawing shows in cross-section a practical example of a device incorporating the present invention. [0013] A device for the extrusion of thermoplastic synthetic products includes an extruder transport screw 2 mounted in a housing 1. The screw has a plasticizing section P on its feed side and a degassing section E arranged in front of a discharge section A. Between the plasticizing section P and the degassing section E is an oppositely threaded and therefore oppositely operating feed screw flight 3 that is bridged over by a flow channel 5 housing a melt filter 4. To prevent a direct flow of gases formed in the plasticizing section to the degassing section, extruder screw 2 has another feed screw flight 7 that operates in the same direction as the screw and is located between oppositely operating feed screw flight 3 and an opening 6 of the flow channel 5 into the degassing section (E). In the transitional area between the oppositely operating feed screw flight 3 and the feed screw flight 7 operating in the same direction there is a degassing opening 8 through which gases and contaminants entering the feed screw flight area can be advantageously discharged from the device 1 so that a decoupling of pressure is assured. [0014] Plastic to be processed is fed to device 1 via a filling opening 9. Extruder screw 2 melts the plastic in the plasticizing section P, and the molten plastic then passes along flow channel 5 and through melt filter 4. It is degassed in degassing section P. Degassing openings 10 connected to a vacuum pump 11 can optionally be provided in this area. When needed, a vacuum pump can be provided for degassing opening 8. Following the degassing process, the plastic is discharged from device 1 via discharge section A and can optionally be fed to a casting mold, a granulation head or the like. The two feed screw flights 3, 7 prevent plastic entering the area of the flight screws from the plasticizing section as well as from the degassing section. [0015] The outlet side of the melt filter 4 in communication with flow channel 5 is connected via a return channel 12 with a check valve 13 to the oppositely operating feed screw flight 3 of extruder screw 2. As a result, a small amount of already cleaned plastic is deliberately returned to the plasticizing section during operation of the device to prevent contaminated, wear-promoting plastic from entering the area where feed screw flight 3 is located. For improved degassing, a threadless degassing space 14 is provided between the oppositely operating feed screw flight and the one operating in the same direction of the extruder screw 2. An additional, oppositely operating feed screw flight section 15 with a relatively smaller thread height is arranged between degassing space 14 and the feed screw flight 7 that operates in the same direction to reliably prevent an overflow of plastic from the plasticizing side to the degassing side. The extruder screw 2 has a damming element 16 in the vicinity of the opening of the flow channel 5 on the outlet side in the form of a damming ring that increases the gas tightness of the feed screw flight 7 that operates in the same direction. WHAT IS CLAIMED IS: 1. A device for extruding thermoplastic synthetic products comprising a housing mounting an extruder screw, the screw including a plasticizing section on its feed side, a degassing section positioned arranged upstream of a discharge section of the screw and an oppositely operating feed screw flight between the plasticizing section and the degassing section, at least one flow channel including a melt filter and bridging over the oppositely operating feed screw flight, characterized in that the extruder screw (2) includes a further feed screw flight (7) operating in the same direction and arranged between the oppositely operating feed screw flight (3) and an opening (6) of the flow channel (5) at the discharge section of the screw, and at least one degassing opening (8) in the housing (1) in a transitional area between the oppositely operating feed screw flight (3) and the further feed screw flight (7) operating in the same direction. 2. A device according to Claim 1, characterized by at least one return channel (12) that preferably includes a check valve (13), and wherein the return channel extends from the flow channel (5) at an outlet side of the melt filter (4) to the oppositely operating feed screw flight (3) of the extruder screw. 3. A device according to Claim 1 or 2, characterized by a threadless degassing space (14) arranged between the oppositely operating feed screw flight (3) and the feed screw flight (7) operating in the same direction of the extruder screw (2). 4. A device according to Claim 3, characterized by a further oppositely operating feed screw flight section (15), preferably having smaller thread height, arranged between the degassing space (14) and the feed screw flight operating in the same direction. 5. A device according to one of the Claims 1 to 4, characterized in that the extruder screw (2) includes a damming element (16) arranged in a vicinity of an opening of the flow channel (5) to a discharge section of the screw. The invention relates to a device for the extrusion of thermoplastic synthetic material featuring an extruder screw (2) which is mounted on a housing (1) including a plasticizing section (P) at the inlet side, a degassing section which is mounted upstream on a discharge section (A) and a conveying outlet (3) operating in the opposite direction which is located between the plasticizing section (P) and the degassing section (E). A flow channel (5) that contains a melt filter (4) is bridged over by at least one of the conveying outlets (3) in the opposite direction. To create favorable production conditions, the extruder screw (2) forms a similar conveying outlet (7) operating in the same direction between the conveying outlet (3) in the opposite direction and the downstream port (6) of the flow channel (5). The housing (1) has at least one degassing vent (8) at the transition area of the conveying outlet (3) operating in the opposite direction and the conveying outlet (7) operating in the same direction.

Full Text

DEVICE FOR DEGASSING AND FILTERING PLASTIC MELTS
[0001] The invention concerns a device for extruding thermoplastic synthetic products with
an extruder screw mounted in a housing. The screw has a plasticizing section on the feed
side thereof, a degassing section positioned upstream, that is, in front of a discharge section
thereof, and an oppositely operating feed screw flight between the plasticizing section and the
degassing section. The device further has at least one flow channel that bridges over the
oppositely operating feed screw flight and has a melt filter.
[0002] Plastics, especially plastic wastes, which must be degassed and/or cleaned before
being further processed, need to be expediently degassed and processed. Printing, painting or
soiling of waste and/or used plastics requires that the plastics be cleaned before further use.
[0003] It is known (from WO 93/04841 A1) to melt plastic being reprocessed in an extruder,
force it through a filter and degas it before further processing or granulation. To avoid an
overflow of molten plastic from the plasticizing section to the degassing or discharge section,
and to guarantee that all the molten plastic passes through the melt filter, an oppositely
operating feed screw flight is arranged between the plasticizing section and the degassing
section in the form of a feeding thread or sealing thread. The thread has a direction opposite
to that of the screw thread of the plasticizing section, degassing section and discharge section.
This known reverse feeding thread causes the return of a small fraction of the plastic that
already passed through and had been cleaned by the melt filter back to the plasticizing
section. This is supposed to prevent uncleaned plastic product from directly reaching the
degassing and discharge section by bypassing the melt filter. The openings of the flow
channel with the melt filter at the inlet and outlet sides are arranged right next to the reverse
feeding thread to avoid dead spaces. This is supposed to prevent extended dwell times for the
plastic product in the device which could cause heat damage to the plastic. A particular
drawback of this device is that the feed screw sections with oppositely directed threads are in
the nature of dynamic seals the tightness of which depends on the speed of the extruder
screw. The viscosity of the plastic is also very important in this case, since plastic containing
moisture forms vapors, and it cannot be prevented that moisture flows from the plasticizing
section into the degassing section along these feed screw sections. Such vapors pass the filter
and, amongst others, carry contaminants into the degassing section where they can again
contaminate already filtered plastic, so that degassed and cleaned plastic of a uniform quality

cannot be guaranteed. In addition, excessive degassing, caused for example by the moisture
in the plastic, can cause undesirable pressure fluctuations in the device.
[0004] In view of this prior art, it is an objective of the invention to overcome the
aforementioned drawbacks and provide a device with improved degassing capability that
prevents a direct material and/or gas flow from the plasticizing section into the degassing
section via the feed screw flights between the sections.
[0005] This is attained with an extruder screw that has a feed screw flight which operates in
the same direction as the screw and is located between an oppositely operating feed screw
flight and an opening of a flow channel for the plastic on an outlet side of the screw. The
transitional zone between the two feed screw flights includes at least one degassing opening.
[0006] The invention is based on the requirement that gas overflows between the plasticizing
section and the degassing section must strictly be prevented for producing qualitatively
uniform, cleaned and degassed plastic. This is achieved in accordance with the invention, in
that, on the one hand, material flow from the plasticizing section to the degassing section is
prevented by the oppositely operating feed screw flight. Likewise, the flow of already
cleaned plastic from the degassing section to the plasticizing section is prevented by the feed
screw flight that operates in the same direction and that is arranged between the oppositely
operating feed screw flight and the opening of the flow channel to the outlet section of the
screw. This separates the two sections and permits a degassing opening, a monitorable outlet
opening, and/or a reduced pressure space to be arranged between the two screw sections.
[0007] Gases and dirt particles entering the oppositely operating feed screw flight from the
plasticizing section are therefore prevented in a simple manner from directly flowing into the
degassing section and can be discharged from the device. This degassing and discharge can
be deliberately supported in the usual manner by connecting the degassing space to a vacuum
pump. Material overflows due to the emission of large amounts of gas caused, for example,
by evaporating water can thereby be compensated for and suppressed in a simple manner. In
accordance with the present invention, the pressures in the plasticizing and filtering sections
are connected to the degassing and discharge section only via the flow channel, which assures
a constant filling of the discharge screw and a constant degassing of the plastic. This also
ensures that no dirt particles can be transported from the plasticizing section to the degassing
section without having been passed through the melt filter.

[0008] To reduce the wear of the oppositely rotating feed screw flight connected to the
plasticizing section caused by uncleaned, plasticized plastic entering the feed screw flight, it
is advantageous to connect the flow channel on the outlet side of the melt filter via at least
one return channel, which preferably includes a check valve, to the oppositely operating feed
screw flight of the extruder screw at the feeding side of the device. A deliberate, small
backflow of clean plastic through the feed screw flight to the plasticizing section makes
certain that no uncleaned plastic enters the oppositely operating feed screw flight. The check
vale reliably prevents a flow of unfiltered plastic to the filtered side, especially during the
startup phase of the device.
[0009] To improve the degassing effect, a preferably threadless degassing space is provided
between the oppositely operating screw flight of the extruder screw and the other screw flight
operating in the same direction, which is defined by the extruder screw and/or the housing.
Gases entering this area through the degassing opening are simply discharged from the device
via the oppositely operating feed screw flight and the one operating in the same direction
which reliably assures the desired pressure decoupling.
[0010] To avoid a flow of plastic material through the oppositely operating feed screw flight
towards the other feed screw flight that operates in the same direction due to a very low
viscosity of the molten plastic, wear of the oppositely operating feed screw flight or the like,
it is recommended to provide a further, oppositely operating feed screw flight section,
preferably with smaller thread height, between the degassing space and the feed screw flight
that operates in the same direction.
[0011] To improve the flow density of the feed screw flight operating in the same direction,
the extruder screw can be provided with a damming element in the vicinity of the opening of
the flow channel at the discharge side of the screw. This damming element can be, for
example, a ring element, a reduced pitch on the feed screw and/or an enlarged screw core
diameter relative to the degassing section. The counterpressure of the plastic product against
the feed screw flight operating in the same direction is thereby increased.
[0012] The drawing shows in cross-section a practical example of a device incorporating the
present invention.
[0013] A device for the extrusion of thermoplastic synthetic products includes an extruder
transport screw 2 mounted in a housing 1. The screw has a plasticizing section P on its feed
side and a degassing section E arranged in front of a discharge section A. Between the

plasticizing section P and the degassing section E is an oppositely threaded and therefore
oppositely operating feed screw flight 3 that is bridged over by a flow channel 5 housing a
melt filter 4. To prevent a direct flow of gases formed in the plasticizing section to the
degassing section, extruder screw 2 has another feed screw flight 7 that operates in the same
direction as the screw and is located between oppositely operating feed screw flight 3 and an
opening 6 of the flow channel 5 into the degassing section (E). In the transitional area
between the oppositely operating feed screw flight 3 and the feed screw flight 7 operating in
the same direction there is a degassing opening 8 through which gases and contaminants
entering the feed screw flight area can be advantageously discharged from the device 1 so
that a decoupling of pressure is assured.
[0014] Plastic to be processed is fed to device 1 via a filling opening 9. Extruder screw 2
melts the plastic in the plasticizing section P, and the molten plastic then passes along flow
channel 5 and through melt filter 4. It is degassed in degassing section P. Degassing
openings 10 connected to a vacuum pump 11 can optionally be provided in this area. When
needed, a vacuum pump can be provided for degassing opening 8. Following the degassing
process, the plastic is discharged from device 1 via discharge section A and can optionally be
fed to a casting mold, a granulation head or the like. The two feed screw flights 3, 7 prevent
plastic entering the area of the flight screws from the plasticizing section as well as from the
degassing section.
[0015] The outlet side of the melt filter 4 in communication with flow channel 5 is connected
via a return channel 12 with a check valve 13 to the oppositely operating feed screw flight 3
of extruder screw 2. As a result, a small amount of already cleaned plastic is deliberately
returned to the plasticizing section during operation of the device to prevent contaminated,
wear-promoting plastic from entering the area where feed screw flight 3 is located. For
improved degassing, a threadless degassing space 14 is provided between the oppositely
operating feed screw flight and the one operating in the same direction of the extruder screw
2. An additional, oppositely operating feed screw flight section 15 with a relatively smaller
thread height is arranged between degassing space 14 and the feed screw flight 7 that
operates in the same direction to reliably prevent an overflow of plastic from the plasticizing
side to the degassing side. The extruder screw 2 has a damming element 16 in the vicinity of
the opening of the flow channel 5 on the outlet side in the form of a damming ring that
increases the gas tightness of the feed screw flight 7 that operates in the same direction.

WHAT IS CLAIMED IS:
1. A device for extruding thermoplastic synthetic products comprising a
housing mounting an extruder screw, the screw including a plasticizing section on its feed
side, a degassing section positioned arranged upstream of a discharge section of the screw
and an oppositely operating feed screw flight between the plasticizing section and the
degassing section, at least one flow channel including a melt filter and bridging over the
oppositely operating feed screw flight, characterized in that the extruder screw (2) includes a
further feed screw flight (7) operating in the same direction and arranged between the
oppositely operating feed screw flight (3) and an opening (6) of the flow channel (5) at the
discharge section of the screw, and at least one degassing opening (8) in the housing (1) in a
transitional area between the oppositely operating feed screw flight (3) and the further feed
screw flight (7) operating in the same direction.
2. A device according to Claim 1, characterized by at least one return
channel (12) that preferably includes a check valve (13), and wherein the return channel
extends from the flow channel (5) at an outlet side of the melt filter (4) to the oppositely
operating feed screw flight (3) of the extruder screw.
3. A device according to Claim 1 or 2, characterized by a threadless
degassing space (14) arranged between the oppositely operating feed screw flight (3) and the
feed screw flight (7) operating in the same direction of the extruder screw (2).
4. A device according to Claim 3, characterized by a further oppositely
operating feed screw flight section (15), preferably having smaller thread height, arranged
between the degassing space (14) and the feed screw flight operating in the same direction.
5. A device according to one of the Claims 1 to 4, characterized in that
the extruder screw (2) includes a damming element (16) arranged in a vicinity of an opening
of the flow channel (5) to a discharge section of the screw.

The invention relates to a device for the extrusion of thermoplastic synthetic material
featuring an extruder screw (2) which is mounted on a housing (1) including a plasticizing
section (P) at the inlet side, a degassing section which is mounted upstream on a discharge
section (A) and a conveying outlet (3) operating in the opposite direction which is located
between the plasticizing section (P) and the degassing section (E). A flow channel (5) that
contains a melt filter (4) is bridged over by at least one of the conveying outlets (3) in the
opposite direction. To create favorable production conditions, the extruder screw (2) forms a
similar conveying outlet (7) operating in the same direction between the conveying outlet (3)
in the opposite direction and the downstream port (6) of the flow channel (5). The housing
(1) has at least one degassing vent (8) at the transition area of the conveying outlet (3)
operating in the opposite direction and the conveying outlet (7) operating in the same
direction.

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Patent Number

272683

Indian Patent Application Number

4345/KOLNP/2008

PG Journal Number

17/2016

Publication Date

22-Apr-2016

Grant Date

19-Apr-2016

Date of Filing

27-Oct-2008

Name of Patentee

EREMA ENGINEERING RECYCLING MASCHINEN UND ANLAGEN GESELLSCHAFT M.B.H.

Applicant Address

FREINDORF, UNTERFELDSTRASSE 3, A-4052 ANSFELDEN

Inventors:

#	Inventor's Name	Inventor's Address
1	HELMUTH SCHULZ	HIRSCHGASSE 16/12, A-4020 LINZ

PCT International Classification Number

B29C 47/60

PCT International Application Number

PCT/AT2007/000185

PCT International Filing date

2007-04-24

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	A 713/2006	2006-04-27	Austria