Note: Descriptions are shown in the official language in which they were submitted.
1054765
This invention is related to extrusion apparatus for
processing rubber or plastic material.
Recent examples of prior art extruders include U. S.
patent No. 3,154,808 issued November 3, 1964 and assigned to
the assignee of the present invention and U, S. patent Nos.
3,865,355 issued on February 11, 1975 to T. J. Eau Claire and
3,869,111 issued March 4, 1975 to J. T. Matsuoku. The '355
patent describes an extruder having an auger feed tube attached
to the side of its hopper where additives may be entered into
the mix, The '111 patent discloses an extruding machine having
rotor members with axially accentuated blade portions.
The present invention provides a novel and continuous,
improved closed chamber apparatus for mixing and/or compounding
rubber, elastomer, plastics and like mixes.
The invention comprises a barrel having an elongated
bore therein, a rotor in the bore to process material fed to
the bore, and a carriage on which the rotor is mounted for
rotation, the carriage being mounted for movement toward and
away from the barrel wherein movement of the carriage away from
the barrel withdraws the rotor from the bore.
The apparatus comprises a piston and cylinder device,
for moving the carriage. The carriage comprises anti-vibration
mounting which permits minimization of any load on the rotor.
The drive means for rotating the rotor in the bore of the barrel,
is also mounted on the carriage. The carriage preferably runs
on rails during said movement toward and away from the barrel.
The apparatus may comprise one or more rotors, The
bore may have a cross section approximately of a figure eight
and two rotors with parallel axes which may be received one in
each part of the bore, the rotors having blades in a configura-
tion generally similar to that of the rotors of an internal
mixer, e.g., a "Banbury", Registered Trademark, mixer.
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The invention also includes an extruder comprising an
inlet through which material to be extruded can be introduced
into the bore at a rear, and an outlet leading from the bore at
a front. An extruder screw is mounted for rotation in the bore
with the rotor projecting rearwardly beyond the inlet.
In the operation of the extruder a conduit is provided
permitting passage of gas, but not material to be extruded,
rearwardly along the bore. A vacuum connection to the bore
is provided rearwardly of the inlet, so that suction applied
to the vacuum connection withdraws gaseous matter along the
conduit from the bore while material is extruded.
The extruder screw extends from a portion of the bore
in front of the inlet rearwardly beyond the inlet to the rear
of the bore, the thread of the screw in this instance providing
the said conduit permitting passage of gas. The vacuum con-
nection may comprise a sealing member disposed over the rear
end of the bore and sealed to the barrel, the sealing member
having means for connecting a suction pipe thereto for applying
suction to the rear of the bore.
The invention further provides a primary outlet lead-
ing from the bore at a front end portion of the barrel and a
secondary outlet leading from the bore at the rear end portion
of the barrel rearwardly of the inlet. An extrusion screw
extends along the bore at least from the secondary outlet to
forwardly of the inlet. Drive means rotates the rotor in the
bore in the operation of the extruder. The drive means is
operable to rotate the rotor in a first direction to cause its
screw portion to feed material supplied through the inlet for-
wardly along the bore and out of the primary outlet, or in a
second direction opposite to the first direction to cause the
screw portion to feed material supplied through the inlet rear-
wardly along the bore and out of the secondary outlet.
1054765
According to a further broad aspect of the present
invention there is provided a screw extruding machine for homo-
geneously mixing and extruding a thermoplastic material. The
machine comprises a feed hopper for feeding thermoplastic
material to the machine. At least one rotor is disposed in a
mixing bore of the machine for mixing the thermoplastic material
fed to the machine. An extruding screw is disposed in an ex-
truding bore of the machine, with the extruding bore being in
communication with the mixing bore. A sealable vacuum chamber
is disposed about the rearward end of the extruding screw. A
vacuum pipe is attached to the vacuum chamber permitting gaseous
evacuation of the material during machine operation. A scrap
outlet is included with the sealable vacuum chamber. Means is
also provided for reversing the extruding screw to cause un-
desirable material from being extruded through the screw bore,
the undesirable material being disposable through the outlet
disposed within the vacuum chamber.
The objects and advantages of the present invention
will become more apparent when viewed with the accompanying
drawings in which:
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Figure 1 is a diagrammatic view in front elevation of the illustrative
mixing and venting extruder;
Figure 2 is a diagrammatic view in front elevation showing a carriage
of the illustrative extruder in a retracted position; and
Figure 3 is a diagrammatic view in cross section showing a rear end
portion of an extruder portiion of the illustrative extruder.
Referring to the drawings in detail, and particularly to Figure 1, there
is shown a mixing and venting extruder 8 which comprises a mixing portion
10 and an extruding portion 12. The extruder 8 comprises an integral barrel
structure, 14 and 16, which can be regarded as being made up of a barrel
14 of the mixing portion 10 and a barrel 16 of the extruding portion 12. The
barrel 14 comprises a bore 18, as shown in Figure 3, having a cross section
approximately in the form of a figure eight, the barrel 16 having a cylindrical
bore 20. The barrel 16 runs generally from front to rear of the extruder 8
and the barrel 14 i8 disposed hori~ontally, at right angles to the barrel 16 with
a left-hand end portion above a rear end portion of the barrel 16, as shown
20 in Figure 1. The barrel structure, 14 and 16, of the extruder 8 is supported
by a frame 22.
The mixing portion 10 of the extruder 8 also comprises a carriage 24.
The carriage 24 comprises a base 26 on which are mounted rotatable wheels
28, the wheels being supported on and arranged to run along rails (not shown)
fixed to a reinforced concrete base 23. The rails are so disposed as to be parallel
with the bore 18. A support frame 30 of the carriage 24 is mounted on the
base 26 by anti-vibration mounting means comprising anti-vibration mounts
32 each of which obeys Hooke's Law, approximately. A rotor support member
30 34 is upstanding from a left-hand portion of the support frame 30, as shown
in Figures 1 and 2. A pair of parallel rotors 36 are supported for rotation in
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bearings (not shown) carried by the support member 34. The carriage 24
is so constructed and arranged that the rotors 36 are in alignment with the
bore 18 of the barrel 14 of the mixing portion 10. The bore 18, having in cross
section the approximate form of a figure eight, comprises two portions, each
forming part of a cylinder joined by a connecting portion. The rotors 36 are
received one in each of the part cylindrical portions of the bore 18 and, in
the operation of the extruder 8, rotate in such a fashion that the volume swept
by each rotor does not intercept the volume swept by the other rotor 36. The
10 rotors 36 have a configuration generally similar to the rotors of an internal
mixer, for example, a "Banbury" mixer. The rotors 36 are arranged to be
driven in the operation of the extruder 8 by drive means comprising an electric
motor 38 and a gear box 40, both mounted on the support frame 30 of the carriage
24.
The carriage 24 of the mixing portion 10 is movable, with the wheels
28 running along the rails (not shown), between an engaged position, as is
shown in Figure 1 and a retracted position, as shown in Figure 2. When the
carriage 24 is in the engaged position the rotors 36 are received in the bore
18 of the barrel 14 of the mixing portion 10 with a left-hand end portion 42 of
each rotor received in an associated bearing (not shown) in a left-hand portion
of the barrel 14. Spigots 44, only one shown in the drawings, project leftwardly
from the support member 34 and are received in corresponding holes to locate
the support member 34 in relation to the barrel 14 when the carriage is in the
engaged position, as shown in Figure 1. The support member 34 is clamped
to the barrel 14 by means of a clamp ring which engages over lips 46 on the
support member 34 and barrel 14.
The extruder 8 also comprises a cylinder 48 mounted on the frame 22
and a piston (not shown) slidable in the cylinder 48 and having a piston rod
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50 connected to the carriage 24, for moving the carriage 24 along the rails
toward and away from the barrel 14 between the engaged position and the retracted
position. As the carriage 24 is moved by the movement of the piston rod 50
from the engaged position toward the retracted position the rotors 36 are withdrawn
from the barrel 14 until the carriage 24 reaches the retracted position as shown
in Figure 2, in which the rotors 36 are completely clear of the barrel 14 permitting
access to the bore 18 of the barrel and to the rotors 36, for cleaning and/or
repair thereof.
The mixing portion of the mixing and venting extruder 8 further comprises
a hopper 52 from which material can be supplied through an inlet 54 into a
right-hand end portion of the bore 18. The barrel 14 has a passage 56 at a
left-hand portion thereof, providing an outlet through a bottom surface of
the barrel 14, the passage 56 opening into a rear end portion of the bore 20
of the extruding portion 12 of the extruder 8. A vent opening 58 is provided
at a left-hand end portion of the barrel 14 opening upwardly from the barrel
14.
The extruding portion 12 of the mixing and venting extruder 8 comprises
a rotor, namely an extrusion screw ff0 mounted for rotation in the bore 20 of
the barrel 16 of the extruding portion 12. The barrel 16 ha~ an inlet provided
by the pas~age 56 which forms the outlet from the bore 18 of the barrel 14 of
the mixing portion 10 of the extruder 8. The extruding portion 12 of the extruder
8 comprises an outlet, not shown at a front end portion of the barrel 16. The
outlet from the barrel 16 is in the form of a suitably shaped orifice, for example
a slot type die for extrusion of film, or a pelletizing head where pellets would
be formed.
The extruding portion 12 further comprises drive means 62 including
a motor and gear box, for rotating the extrusion screw 60 in the bore 20.
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The drive meanæ 62 is connected to a rearwardly extending drive shaft portion
61 of the extrusion screw 60.
The extruding portion 12 of the extruder further comprises a vacuum
connection comprising a housing 64 in sealing engagement with the barrel
structure, 14 and 16, about the rear of the bore 20 of the barrel 16. The threaded
portion of the extrusion screw 60 projects rearwardly beyond the end of the
bore 20 into the chamber defined by the housing 64. The extrusion screw 60
comprises a sealing portion 66 intermediate the threaded portion and the drive
10 shaft portion 61 of the screw, the sealing portion rotating in a hole 68 in a rear
plate of the housing 64. Sealing members, not shown, form a vacuum tight
seal between the sealing portion 66 and the rear plate of the housing 64. A
vacuum pipe 70 leads upwardly from the chamber of the housing 64 and can
be connected by a suitable pipe arrangement to a suction device, not shown.
A secondary outlet 72 leads from the chamber of the housing 64 for elimination
of scrap material and the like. A door 74 normally seals the secondary outlet
72 .
In the operation of the extruder 8 material to be extruded, for example
pellets of plastics material, molten low density polythene supplied straight
from the polythene forming reactor, or powdered rubber and an appropriate
curing 6ystem, are supplied to the hopper 52 of the mixing portion 10. Where
the extruder 8 is to be fed with a molten plastics material, the flow of plastics
material from the reactor is not exposed to the air and may be supplied direct
to the inlet 54 of the barrel 14. The carriage 24 is in the engaged position,
as shown in Figure 1. The rotors 36 are driven by the electric motor 38 through
the gear box 40, the rotors subjecting material reaching the bore 18 of the
barrel 14 through the inlet 54 from the hopper 52 to intensive working thus
to thoroughly mix and homogenize the materials. Pellets of plastics material
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~(~5476S
which are supplied to the hopper are melted in the mixing portion 10 and then
thoroughly homogenized. The construction and arrangement of the barrel
14 and the rotors 36 is such that the rotors only exert a very small force on
the material in the bore 18 tending to urge it leftwardly, as shown in Figure
1, along the bore 18 from the inlet 54 towards the passage 56 providing the
outlet from the mixing portion. In the steady state operation of the extruder
8 to extrude material, the extrusion screw 60 is rotated in such a direction
as to urge material entering the bore 20 of the extruding portion 12 through
10 the passage 56 from the mixing portion 10, forwardly, along the bore, from
left to right as shown in Figure 3. The material forced forwardly along the
bore 20 is extruded through the primary outlet of the extruding portion 12
to provide the extruded product. The temperatures of the mixing portion 10
and the extruding portion 12 are controlled to maintain the material in the extruder
in the appropriate condition.
The output of the extruder is controlled by the extruding portion 12,
provided that the mixing portion 10 is kept supplied with an adequate quantity
of raw materials through the hopper 52. As hereinbefore mentioned, the mixing
portion is designed BO that very little pressure is exerted on material in the
bore 18 of the mixing portion. Thus material is withdrawn from the mixing
portion 10 through the passage 56 by rotation of extrusion screw 60 as the material
is required, there being little or no tendency for the mixing portion to force
material through the passage 56 into the extruding portion 12; however, sufficient
pressure is generated to ensure that the passage 56 is kept substantially filled.
The amount of work carried out on material by the mixing portion 10
is determined by the speed of rotation of the rotors 36 and by the temperature
at which the material in the bore is maintained. For controlling the temperature
of material in the bore 18 the temperature of the barrel 14 is controlled and
1054765
means are provided for supplying a liquid cooling medium e. g. water to the
barrel 14. For heating the barrel 14, thermocouples being provided to measure
the temperature of the barrel and to effect control of the temperature. The
temperature of the barrel 16 of the extruding portion 12 is likewise controlled
and can be cooled by a liquid e. g. water cooling medium, or heated electrically.
In the operation of the extruder 8 a temperature differential may arise
between the mixing portion 10 and the extruder portion 12. Such a temperature
differential may cause expansion of, for example, the extruding portion 80
that the bore 18 is moved out of alignment with the rotors 36 of the mixing portion
10 by as much as 10 to 15 thousandths of an inch. The mounting of the support
frame 30 for the rotor 36 on the anti-vibration mounts 32 allows the rotors to
move slightly with the expan~ion of the extruding portion 12 without a substantial
load being placed on the rotors. In the absence of the anti-vibration mounts
a much greater load would be placed on the rotors and this would lead, in
a relatively short time, to metal fatigue in the rotors leading to fatigue failure.
As the extruder operates to extrude material through the primary outlet
from the bore 20 of the barrel 16 of the extruding portion 12, suction is applied
through the vacuum pipe 70 to the chamber of the housing 64 at the rear of
the bore 20. A vacuum of about 28 to 30 inches of Mercury may be applied
through the pipe 70. Application of thi~ vacuum to the chamber of the housing
64 removes gaseous matter from the material being processed by the extruder
8, the gaseous matter flowing rearwardly along the bore 20 from the region
of the passage 56 along the screw flight into the chamber of the housing 64
through the vacuum pipe 70. The seal between the rear plate of the housing
and the sealing portion 66 of the extrusion rotor, and the sealing outlet door
30 74 prevent air leaking into the chamber from the atmo~phere. Presence of
material being processed in the bore 18 of the mixing portion 10 and in the
lOS4765
bore 20, in front of the passage 56, of the extruding portion 12 prevents air
from the atmosphere being drawn through the bores 20 or 18. In addition to
this vacuum venting, gaseous matter may leave the material being processed
through the vent opening 58. If desired, a small amount of suction, for example
a vacuum of three to four inches of water, may be applied to the vent opening
58, or the vent opening 58 may vent directly to the atmosphere. The vacuum
venting provided by the vacuum connection i~ useful in removing free ethylene
gas, where material processed is molten polyethylene fed to the extruder direct
from the reactor which gas can be returned to the reactor. The vacuum venting
is also u6eful for processing hygroscopic materials, for example acrylonitrile-
butadiene-styrene copolymer, the vacuum venting removing water vapor.
Vacuum venting may eliminate the need for a pre-drying stage in which hydroscopic
materials are dried in a separate operation before they are fed to the mixing
portion of the extruder.
When the extruder is to be started up from cold or is to be used to process
different material or is started up from an empty condition, the material issuing
from the mixing portion 10 through the passage 56 into the bore 20 wi~l be
~0
inadequately mixed and homogenized because it will not have been subjected
to sufficient intensive working. For example, where plastics material i8 supplied
to feed hopper 52 in the form of solid pellets, the material issuing through
the passage 56 may include some solid lumps of unmelted material. It is undesirable
that this incompletely homogenized material should be extruded through the
primary outlet from the extruding portion 12. The inhomogenieties are likely
to block holes in a pellet plate or to form a blockage in part of a slot type die
where such are being used, or where dies with a larger orifice are in use,
30 the extrudate is likely to be nonuniform and thus of poor quality. One past
practice has been to remove the actual die from the end of the extruding portion
lQ5476S
1 - and to allow material to issue from the end of the barrel 16 of the extruding
portion 12 freely until such time as the material issuing from the barrel 16 is
of uniform quality, however this practice is troublesome and time-consuming.
During the initial starting up, the drive means 62 is caused to drive
the extrusion screw 60 in a direction opposite that in which the extrusion screw
60 runs during its normal operation thus to drive material issuing into the
bore 20 from the passage 56 rearwardly along the bore 20 into the chamber
of the housing 64. The door 74 i8, during starting up, in an open position
10 thus opening the eecondary outlet 72 from the bore 20 and allowing the
inhomogeneous material from the mixing portion to issue from the outlet 72.
This material can be collected and put back in the hopper 52. During the starting
up, vacuum i6 not applied to the chamber of the housing 64. When the material
issuing from the secondary outlet 72 is of uniform and acceptable quality, the
door 74 is closed to seal the chamber of the housing 64 and the drive means
62 i8 caused to rotate the extrusion screw in a direction to drive material along
the bore 20 forwardly towards the primary outlet from the bore 20. At the
same time a vacuum is applied to the chamber of the housing 64. Rotation of
the screw 60 to drive the material in the bore 20 forwardly removes much of
the material from the chamber of the housing 64, a small plug of material may
remain in the secondary outlet 72, which plug may be removed at a later stage.
The use of a secondary outlet in this manner is convenient and avoids the
troublesome removal of the extrusion dies from the front end of the extruding
portion which has hitherto been a known practice.
When it i~ desired to gain access to the bore 18 of the barrel 14 of the
mixing portion 10 or to the rotors 36, the extruder 8 is first emptied of material,
so far as possible, by stopping feed to the hopper 52 and allowing the extruding
portion 12 and the mixing portion 10 to operate until no extrudate issues from
10547~S
1 the primary outlet of the extruding portion 12. The drive means 62 of the extruding
portion 12 and the motor 38 of the mixing portion 10 are stopped. The clamp
ring i~ removed from the lips 46 on the barrel 14 and on the rotor support
member 34. The piston and cylinder device is then operated by admitting oil
under pres6ure to the cylinder 48 to move the piston rod 50 out of the cylinder
48 to thus move the carriage 24 to the right, viewing Figure 1, to its retracted
position in which it is shown in Figure 2. Previous machines have comprised
a mixing portion and an extruding portion in which the barrel of the mixing
10 portion i8 spaced from the barrel of the extruding portion and acces6 to the
interior of the barrel and to the rotors has been obtained by removing the barrel
from the rotors, the rotors and drive therefor being fixed. As hereinbefore
mentioned, it is necessary to supply cocling fluid and heating means to the
barrel as well as thermocouples with their necessary connecting wires. Past
machines have had to have flexible connectors for all these services, or alternatively
the services have had to be disconnected. A large number of connections were
involved and it was both time consuming and inconvenient to remove the barrel.
In the case of the present invention, the moving of the carriage to wimdraw
the rotors 36 from the barrel 14 necessitates only the use of a flexible electrical
supply wire to the electric motor, or alternatively, a readily disconnectable
electric ~upply to the motor 38. However there is only a single connection
involved and the problem is therefore much simpler than in me case of the
previous machines. Furthermore, the use of spaced apart barrels for the mixing
portion and extruding portion of known machines demanded that the barrels
of both the mixing portion and the extruding portion be sufficiently rigid in
their own right to withstand the stresses generated during operation of me
machine. The integral barrel structure used means that the barrel 16 of the
extruding portion gains in rigidity from the fact that it is fixed to the barrel
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14 of the mixing portion 10 and vice versa, the necessary rigidity being thereby
achieved with the use of less metal. This integral barrel structure means
that the bores of the barrel of the mixing portion can be positioned closer to
the bore of the barrel of the extruding portion than was possible in the known
machines thus leading to a shorter connecting passage between the bores of
the two barrels than has been possible in known extruding machines. This
shorter connecting passage has a much lower resistance to flow therethrough
than was the caee in the known machines and leads to better flow control of
material through the extruder than was readily achievable in the known extruding
machines .
Although the opening 58 of the illustrative extruder is primarily intended
as a vent opening, it may also be used to feed additional materials to the extruder.
For example> in making glass fiber reinforced plastics extruded sections,
it is necessary to subject the plastics material to intensive working but, on the
other hand, intensive working tends to break up the glass fibers into undesirably
small lengths. Accordingly, it is desirable to feed the glass fibers into the plastics
material at a stage of operation after the plastics material has already undergone
the majority of its intensive working and this can be achieved by 6upplying the
glass fiber to the extruder through the opening 58. Openings may be provided
in the barrel 14 of the mixing portion 10 or in the barrel 16 of the extruding portion
12 at other positions for supply of additives or for venting purposes, if desired.
However care mu6t be taken to avoid so-called "vènt plugging" which can lead
to poor quality extruded material.
Though this invention has been described with some degree of particularity,
it is intended to be exemplary only, and not interpreted in a limiting sense.
