GB2034628A

GB2034628A - Twin-screw, two-stage or multistage extruder having a double feed

Info

Publication number: GB2034628A
Application number: GB7843831A
Authority: GB
Original assignee: BERSANO T
Current assignee: BERSANO T
Priority date: 1978-11-09
Filing date: 1978-11-09
Publication date: 1980-06-11
Also published as: GB2034628B

Abstract

The first stage of a twin-screw, two-stage or multistage double feed extruder comprises at least one twin- screw extruder with double feed from hoppers T1, T2 and having opposite extrusion directions towards a common discharge bore F1. <IMAGE>

Description

SPECIFICATION Twin-screw, two-stage and multi-stage extruder having a double-feed There have been suggested in the latest years a number of two-stage extruders in various constructive embodiments which, however, both due to their high sale prices and their constructional intricacy, have not met with a widespread diffusion on the world market.

Even if, in our opinion, this is the ideal machine among all the types of extruders which are now present on the market, it did not enjoy of a favourable reception by the manufacturers of plastics material articles, above all because the type of mechanical union of the two stages did not permit an effective continuation and control of the gelling or plastification procedure any plastics material undergoes along the path between the feeding hopper and the extrusion die. Even if both the first stage, which is a twin-screw extruder with double feed and opposite extrusion directions, and the second stage, which is a conventional twin-screw extruder, are known, the subkect matter of this invention is the type and the form of union between the first and the second stages.Such a union permits to obtain a novel type of twin-screw, two- or multistage, doublefeed extruder. By virtue of the novel type and shape of the union, the twin-screw, two stage extruder in question permits to process any kind of thermoplastic materials while obtaining a thorough degassing, inasmuch as the possibility is afforded of controlling and varying at will the physical conditions of the material or the compound to be extruded, in correspondence with the degassing section.The experience has shown that such an extruder affords the opportunity of obtaining, concurrently with an excellent efficiency, a thorough homogeneousness of the extrudates together with the possibility of admixing materials of different kinds within a wide range, as various components can be introduced at preestablished points having certain pressures and temperatures (especially in the multistage version embodied with the same type and shape of interstage union).

In order that the embodiments of the twin-screw, two-stage version as well as that of the twin-screw, multistage version may be better understood, the following indications will be given: -the first stage with twin-screw and double feed and opposite extrusion directions is shown in Figure 1. The feed of the material(s) is carried out through the hoppers T1 and T2, whereas the extrusion of the materials takes place centrally through the bore F1 formed through the barrel C1.

The reduction and drive transfer gearbox and the thrust absorbing unit are diagrammatically indicated at R1,R2.

The rotary drive is impressed either by a variablespeed motor, Ml, or by a combined asynchronous motor-multispeed change gear, or by a hydraulic mover.

-the second stage is a conventional twin-screw extruder which is preferably fed from below by the twin-screw, double feed extruder having opposite directions of extrusion as shown in Figure 1.

-the twin-screw, two-stage extruder is shown in Figure 2, which is a diagrammatical longitudinal cross-sectional view and a diagrammatical transversal cross-sectional view. In this Figure there can be clearly seen a conventional twin-screw extruder united with a double-feed, contrary-extrusiondirection, twin-screw extruder of Figure 1 which feeds the conventional extruder from below.

-The multistage twin-screw extruder can be assembled both by matching several first stages as shown in Figure 1 with a conventional twin-screw so that a multistage twin-screw extruder as shown in Figure 3 is obtained, and by matching two first stages as shown in Figure 1 with a second stage which is still of the kind of the first stage (twin-screw, double-feed and contrary-extrusion-direction of Figure 1) and a conventional twin-screw extruder preferably fed from below, the result being a multistage extruder as shown in Figure 4.

In order that any doubt may be removed, there will be described hereinafter a possible embodiment as shown in Figure 2. The twin-screw, double feed extruder with opposite directions of extrusion receives the material(s) from the hoppers T1 ,T2. The two screws convey with their rotary motion the material towards the central point F1 wherefrom, through a variable-cross-section bore formed by interchangeable members D, the material is introduced from below upwards into the barrel C2 of the second stage. The screws of the second stage draw the pre-gelled material from the first stage and, with their rotary motions, convey it forward towards the extrusion head.

In the top section of the barrel C2 (in the case of feed from below) and in correspondence with the bore for the introduction of the pre-gelled material from the first stage, the degassing port G is provided. Stated otherwise, the material is heated and pre-gelled in the first stage and is introduced into the second stage and is cocurrently degassed and then compounded, gelled and extruded by the second stage.

The variable speeds of the screws of the first and the second stages and the variable cross-sectional area of the transfer bore from the first to the second stage permit to carry the material to the area of union between the first and the second stage under the desired pressure and temperature conditions, whereas the variable speeds of the screws of the second stage permit to maintain, in correspondence with the transfer bore a constant static pressure of the material and to carry out a complete degassing operation. Figure 5 shows in the three views a possible embodiment of an extruder of the twinscrew, two-stage kind actuated by hydraulic movers.

1. A twin-screw, two-stage or multistage, double feed extruder wherein the first stage is composed by at least one twin-screw extruder with double feed with contrary extrusion directions.

2. A twin-screw, two-stage or multistage double

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Twin-screw, two-stage and multi-stage extruder having a double-feed There have been suggested in the latest years a number of two-stage extruders in various constructive embodiments which, however, both due to their high sale prices and their constructional intricacy, have not met with a widespread diffusion on the world market. Even if, in our opinion, this is the ideal machine among all the types of extruders which are now present on the market, it did not enjoy of a favourable reception by the manufacturers of plastics material articles, above all because the type of mechanical union of the two stages did not permit an effective continuation and control of the gelling or plastification procedure any plastics material undergoes along the path between the feeding hopper and the extrusion die. Even if both the first stage, which is a twin-screw extruder with double feed and opposite extrusion directions, and the second stage, which is a conventional twin-screw extruder, are known, the subkect matter of this invention is the type and the form of union between the first and the second stages.Such a union permits to obtain a novel type of twin-screw, two- or multistage, doublefeed extruder. By virtue of the novel type and shape of the union, the twin-screw, two stage extruder in question permits to process any kind of thermoplastic materials while obtaining a thorough degassing, inasmuch as the possibility is afforded of controlling and varying at will the physical conditions of the material or the compound to be extruded, in correspondence with the degassing section.The experience has shown that such an extruder affords the opportunity of obtaining, concurrently with an excellent efficiency, a thorough homogeneousness of the extrudates together with the possibility of admixing materials of different kinds within a wide range, as various components can be introduced at preestablished points having certain pressures and temperatures (especially in the multistage version embodied with the same type and shape of interstage union). In order that the embodiments of the twin-screw, two-stage version as well as that of the twin-screw, multistage version may be better understood, the following indications will be given: -the first stage with twin-screw and double feed and opposite extrusion directions is shown in Figure 1. The feed of the material(s) is carried out through the hoppers T1 and T2, whereas the extrusion of the materials takes place centrally through the bore F1 formed through the barrel C1. The reduction and drive transfer gearbox and the thrust absorbing unit are diagrammatically indicated at R1,R2. The rotary drive is impressed either by a variablespeed motor, Ml, or by a combined asynchronous motor-multispeed change gear, or by a hydraulic mover. -the second stage is a conventional twin-screw extruder which is preferably fed from below by the twin-screw, double feed extruder having opposite directions of extrusion as shown in Figure 1. -the twin-screw, two-stage extruder is shown in Figure 2, which is a diagrammatical longitudinal cross-sectional view and a diagrammatical transversal cross-sectional view. In this Figure there can be clearly seen a conventional twin-screw extruder united with a double-feed, contrary-extrusiondirection, twin-screw extruder of Figure 1 which feeds the conventional extruder from below. -The multistage twin-screw extruder can be assembled both by matching several first stages as shown in Figure 1 with a conventional twin-screw so that a multistage twin-screw extruder as shown in Figure 3 is obtained, and by matching two first stages as shown in Figure 1 with a second stage which is still of the kind of the first stage (twin-screw, double-feed and contrary-extrusion-direction of Figure 1) and a conventional twin-screw extruder preferably fed from below, the result being a multistage extruder as shown in Figure 4. In order that any doubt may be removed, there will be described hereinafter a possible embodiment as shown in Figure 2. The twin-screw, double feed extruder with opposite directions of extrusion receives the material(s) from the hoppers T1 ,T2. The two screws convey with their rotary motion the material towards the central point F1 wherefrom, through a variable-cross-section bore formed by interchangeable members D, the material is introduced from below upwards into the barrel C2 of the second stage. The screws of the second stage draw the pre-gelled material from the first stage and, with their rotary motions, convey it forward towards the extrusion head. In the top section of the barrel C2 (in the case of feed from below) and in correspondence with the bore for the introduction of the pre-gelled material from the first stage, the degassing port G is provided. Stated otherwise, the material is heated and pre-gelled in the first stage and is introduced into the second stage and is cocurrently degassed and then compounded, gelled and extruded by the second stage. The variable speeds of the screws of the first and the second stages and the variable cross-sectional area of the transfer bore from the first to the second stage permit to carry the material to the area of union between the first and the second stage under the desired pressure and temperature conditions, whereas the variable speeds of the screws of the second stage permit to maintain, in correspondence with the transfer bore a constant static pressure of the material and to carry out a complete degassing operation. Figure 5 shows in the three views a possible embodiment of an extruder of the twinscrew, two-stage kind actuated by hydraulic movers. CLAIMS

2. A twin-screw, two-stage or multistage double feed extruder as claimed in claim 1, wherein the match between the first and the second stage is preferably made from below upwards in direct drive relationship.

3. A twin-screw, two stage or multistage double feed extruder as claimed in claim 1 or 2, wherein at the point of connection between the first and the second stage the apparent specific gravity or the degree of compactness of the material to be extruded can be modified by acting upon the transfer bore which is of the interchangeable-member type irrespective of the speed of rotation of the screw of the first stage.

4. Atwin-screw, two stage or multistage double feed extruder as claimed in claim 1, 2 or 3, wherein said first stage comprises a plurality of twin-screw extruders with double feed with contrary extrusion directions disposed substantially parallel to each other and said second stage comprises one twinscrew extruder traversing all the extruders of the first stage at right angles thereto.

5. A twin-screw, two stage or multistage double feed extruder substantially as described with referpence to any one of the examples shown in the accompanying drawings.