CA2057614C

CA2057614C - High-performance extruder

Info

Publication number: CA2057614C
Application number: CA002057614A
Authority: CA
Inventors: Gerd Capelle; Gunther Meier
Original assignee: Hermann Berstorff Maschinenbau GmbH
Current assignee: KraussMaffei Berstorff GmbH
Priority date: 1990-12-14
Filing date: 1991-12-13
Publication date: 1997-01-28
Anticipated expiration: 2011-12-13
Also published as: CA2057614A1

Abstract

- 9 -A high-performance extruder is provided, wherein the pin-barrel and transfer mix mixing sections, which are known per se and have only been used individually hitherto, are jointly used in one extruder. The combination of both mixing systems permits the throughput of material to be increased in a surprising manner by 60 % to 100 %, whilst a constant mixing quality is maintained and the driving torque is halved.

Description

The invention relates to an extruder for processing and producing rubber and thermoplastic plastics materials.
In the field of extruder technology, it has long been known to construct an extruder so that metal pins protrude through its housing into the processing chamber for processing the extruded material in mixing sections. In addition, the flights of the extruder screw are interrupted at the locations where the pins protrude into the extruder housing. such extruders are known.
These extruders are distinguished by their very good mixing and homogenising effect upon the material to be processed and permit also an increased throughput of material through the extruder per unit of time whilst the r.p.m. of the screw remains constant. These advantages have resulted in pin-barrel extruders becoming the most commonly used mixing and homogenising extruders in the last lS years (not least as a consequence of constant improvement).
Independently of this, a mixing section for an extruder has been developed, which has become known as a 20 transfer mix mixing section. This mixing section is substantially characterised in that both the extruder screw and the internal wall of the extruder housing are provided with grooves and flights over a predetermined length, the thread depth of the extruder screw, when viewed in the longitudinal direction of the extruder housing, dec~easing to zero and subsequently increasing again at the same rate as the thread depth of the grooves in the housing respectively increases and decreases again. As a result of this configuration for the extruder screw housing, the extruded 30 material can be conveyed from the screw grooves into the housing and grooves, thereby having a good mixing effect upon the extruded material, and such conveyance is complete when the mixing section rotates.
Compared with the pin-barrel extruder, the transfer mix extruder could claim for itself a certain corner of the market, especially when the overall length of the extruder had A`

20576 ~ 4 to be kept small. However, the comparatively high cost of manufacture of the mixing section is a disadvantage of such a construction.
Since the technology for such mixing sections of extruders has not changed in the last 15 to 20 years, apart from detail improvements, the basic object of the invention was to create a new generation of mixing and homogenising extruders on the basis of known apparatus.
The extruder according to the present invention has lo great advantages over the mixing and homogenising extruders of the prior art.
According to the present invention there is provided an extruder for processing and producing rubber and thermoplastic plastics materials, comprising an extruder housing with an inlet and an outlet opening, and a drive unit for an extruder screw, which is disposed in the housing and is rotatable about a longitudinal axis of the screw, wherein the extruder has two mixing and homogenising sections,a first section and a second section, which are disposed one behind 20 the other, the first section being a pin-barrel section, and the second section being a transfer mix section.
According to the present invention, there is also provided an extruder for processing and producing rubber and thermoplastic plastics material, comprising:
- an elongatéd extruder housing defining a feed section in which a feed inlet is provided for feeding material to the extruder, and an outlet section having a material outlet opening for discharging molten material under pressure from the extruder;
- an extruder screw having a screw core and a helical flight, said screw being mounted for rotation in said housing about the longitudinal axis of said screw, said housing and said screw core defining therebetween a processing chamber, and means for driving said screw;
- said housing further defining a pin-barrel section in which at least one row of pins extend radially inwardly of the housing through the processing chamber toward the core of said screw, said helical flight of said screw being interrupted in the regions of said pins so as to accommodate rotation of said screw in such region; and - a transfer mix section defined by said housing longitudinally adjacent said pin-barrel section, the helical flight of said screw in said transfer mix section being constructed so that the thread depth of the areas between adjacent flight sections first decreases toward zero and then 10 increases from the feed side of the mix section to the outlet side, and wherein said housing in said transfer mix section is also formed with a helical flight generally aligned with the helical flight of said screw, said helical flight of said housing defining between adjacent flight sections thereof grooves which vary in depth and which are radially aligned with the area between adjacent flight sections of said screw, the depth of said grooves between adjacent flight sections of said housing first increasing and then decreasing from the feed side of the mix section to the outlet side, and being 20 generally inversely proportional to the thread depth between radially adjacent flight sections of said screw.
By utilising a laboratory extruder which has a pin-barrel section and a transfer mix section, it has been possible to ascertain that, while retaining the same mixing quality and the same screw r.p.m., the driving performance of the extruder could be reduced by 50%, and the throughput of material could be increased by 60% to 100%.
These excellent results also produce a 50% reduction in the driving torque, thereby resulting in a considerable 30 reduction in the drive costs. In addition, as a result of combining the pin-barrel mixing section and the transfer mix mixing section in accordance with the invention, the overall length of the mixing section required for the same mixing quality can be reduced by approximately 50~ compared with an extruder which operates only according to the pin-barrel principle.

A p~eferred embodiment of the invention will now be described as example without limitative manner having reference the attached drawings, wherein:
The single figure is a schematic view of a single-screw extruder according to the invention which has been cut open longitudinally.
one extruder screw 6 is disposed internally of the extruder housing 2 and is drivable about its longitudinal axis by a drive unit 5. In the region of its upstream end, the 10 housing 2 has an inlet opening 3 for receiving the material which is to be extruded with the material leaving the extruder, ready mixed, through the outlet opening 4.
In the feed section 9, the extruder screw 6 has a screw geometry which is suitable for drawing into the extruder, the material which has been supplied through the inlet opening 3 and for plasticising such material.
A pin-barrel section 7 is provided downstream of this feed section 9, and in said pin-barrel section two rows of pins schematically shown at 11 protrude radially through 20 the extruder housing 2 towards the screw core and into the processing chamber 14 of the extruder. The screw flights 12 are interrupted in the pin plane in this section 7, in order to avoid colliding with the pins 11.
Downstream of the pin-barrel section 7, there is disposed a transfer mix section 8, wherein, in this embodiment, the angles between the flights 12 of the extruder screw 6 and the flights 13 of the extrude~ housing 2 are greater than or equal to 105 and do not form any angles with one another which are complementary to 90.
The final processing section of the extruder screw 6 is formed by the pressure increasing section 10, in which the screw geometry is so selected that the pressure of the molten mass can be increased to the required tool pressure.
In addition to this embodiment, other possible A

embodiments are also conceivable for this high-performance extruder. Thus, for example, the transfer mix section 8 could also be disposed upstream of the pin-barrel section 7, although the illustrated embodiment produces better mixing and homogenising results. In addition, it may be mentioned here that the pin-barrel section also fulfils its mixing and homogenising task with more than the two illustrated rows of pins. In view of the ratio between costs and mixing quality, it is best to provide the pin-barrel section with one to five lo rows of pins.
The preferred length of the individual extruder sections, with an extruder length of 10 screw diameters (D), is substantially 3 D for the feed section, 1.5 to 2 D for the pin-barrel section, 2 to 2.5 D for the transfer mix sections, and approximately 3 D for the pressure augmenting section.
Independently of these particulars, however, additional processing sections may also be disposed upstream of, downstream of or between the pin-barrel and transfer mix sections, such as, for example, degassing or kneading 20 sections.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An extruder for processing and producing rubber and thermoplastic plastics material, comprising:
- an elongated extruder housing defining a feed section in which a feed inlet is provided for feeding material to the extruder, and an outlet section having a material outlet opening for discharging molten material under pressure from the extruder;
- an extruder screw having a screw core and a helical flight, said screw being mounted for rotation in said housing about the longitudinal axis of said screw, said housing and said screw core defining therebetween a processing chamber, and means for driving said screw;
- said housing further defining a pin-barrel section in which at least one row of pins extend radially inwardly of the housing through the processing chamber toward the core of said screw, said helical flight of said screw being interrupted in the regions of said pins so as to accommodate rotation of said screw in such region; and - a transfer mix section defined by said housing longitudinally adjacent said pin-barrel section, the helical flight of said screw in said transfer mix section being constructed so that the thread depth of the areas between adjacent flight sections first decreases toward zero and then increases from the feed side of the mix section to the outlet side, and wherein said housing in said transfer mix section is also formed with a helical flight generally aligned with the helical flight of said screw, said helical flight of said housing defining between adjacent flight sections thereof grooves which vary in depth and which are radially aligned with the area between adjacent flight sections of said screw, the depth of said grooves between adjacent flight sections of said housing first increasing and then decreasing from the feed side of the mix section to the outlet side, and being generally inversely proportional to the thread depth between radially adjacent flight sections of said screw.

2. An extruder according to claim 1, wherein said pin-barrel section is disposed upstream of the transfer mix section.

3. An extruder according to claim 1, wherein said feed section is upstream of the said pin-barrel section and said transfer mix section, and wherein material is extruded from said outlet section at the required tool pressure.

4. An extruder according to claim 1, wherein the length of said extruder is approximately 10 screw diameters (D), the length of said feed section is 3 D, the length of said pin-barrel section is 1.5 to 2 D, the length of said transfer mix section is 2 to 2.5 D, and the length of the outlet section where pressure is increased is substantially 3D.

5. An extruder according to claim 1, wherein a plurality of rows of pins are disposed in said pin-barrel section, said pins protruding radially into the processing chamber of the extruder housing, the screw flights of said screw being interrupted at the locations of said pins.

6. An extruder according to claim 1, wherein in said transfer mix section, the angles between the flights of the extruder screw and the flights of the extruder housing are greater than or equal to 105° and do not form any angles which are complementary to 90°.