WO2002057065A2

WO2002057065A2 - Vented extruder

Info

Publication number: WO2002057065A2
Application number: PCT/IB2002/000122
Authority: WO
Inventors: François-Marie FRANCI
Original assignee: Internova International Innovation Company B.V.
Priority date: 2001-01-18
Filing date: 2002-01-17
Publication date: 2002-07-25

Abstract

The invention concerns an extruder (100) comprising a first element (110) and a second element (130) cascade-mounted. Each element comprises a sheath (111, 131) wherein is housed an extruder screw, a raw material inlet (114, 134) and an outlet (115, 135) for transformed material. It further comprises a connecting part (150) provided with a buffer chamber (151) designed to receive the transformed material transformed by the first element and to transfer said transformed material into the second element. The connecting part comprises an extruder grate (156) at its outlet and filter (155) at its inlet. The second element comprises a venting orifice (136) arranged in the sheath upstream of the inlet for the material transformed by the first element.

Description

EXTRUDER DEGAZEUSE

Technical area

The present invention relates to a degasifier extruder, comprising a first element and a second element mounted in cascade and a buffer chamber disposed between said first element and said second element and arranged to receive the material transformed by said first element and to transmit thereafter said second element, and means for degassing the transformed material, said first element comprising a first sleeve in which is housed a first extrusion screw, a first drive gear motor of said first extrusion screw, a first orifice input of the raw material and a first outlet of the transformed material, and said second member having a second sleeve in which is housed a second extruder screw, a second drive gear of said second screw extrusion, a second inlet of the raw material and a second orifice of nettle of the transformed material, as well as degassing means.

Extruders are essential elements in the processing lines of plastic parts manufacturing lines. Extruders intended for extruding rubber or various plastics are used in particular for producing moldings or a profile whose shape and dimensions are defined by a die which equips the extrusion head, from a raw material which may be a natural elastomer or a synthetic elastomer.

The profiles are subjected to an operation called vulcanization which is usually carried out at atmospheric pressure and by heat treatment, for example by UHF (ultrahigh frequency) cooking, in salt baths or on a fluidized bed, etc. Because of this, heat treatment, it is essential to degas the raw material in the extruder. Under the effect of the rise in temperature during vulcanization, the residual gases included in the material tend to expand and cause unacceptable bulges on the finished product. The degassing operation is performed on a degassing extruder during the transformation of the material. This transformation takes place in the extruder which kneads the raw material initially in the form of granules or strips to make a homogeneous pasty material, under the effect of the heat generated by the heating means connected to the sheath, compression and shear induced by the rotation of the screw. The extrusion head is in fact a mold equipped at its output with a removable and interchangeable die which gives its shape to the extruded profile.

The problem of degassing also arises for certain plastics such as thermosetting plastics, in particular, but not exclusively.

Prior art

Some known extruders consist of two parts called cutting stages which comprise a one-piece screw consisting of two coupled screws arranged in line and separated by a rolling ring. The sleeve comprises, in its middle part, a degassing orifice coupled to a vacuum pump. This orifice is located just downstream of the rolling ring in order to achieve a good degassing. The necessary condition for achieving effective degassing is that the material entrained by the screw is well homogenized. This homogenization operation is performed by the upstream portion of the extrusion screw which delivers the material in thin strips around the rolling ring. An expansion causing a sudden drop in the pressure downstream of the rolling ring associated with the depression generated by the vacuum pump promotes the extraction of volatile substances from the material which travels in the extruder, pushed by the screw.

Although the principle of degassing is simple, the operation is complex in practice and depends on several factors. As mentioned above, the screw monobloc is in fact made up of two screws coupled in tandem, the first, arranged upstream, delivers the material through a rolling ring, in the second, disposed downstream which leads to the die. In order for degassing to be possible, it is essential that the degassing orifice be open and unobstructed, which implies that the flow rate of the first screw is identical to that of the second. This balance can not be achieved because the two screws are not identical.

In an attempt to reach a balance between the flows of matter in the two floors, however, it is necessary to resort to artifices. One of them is to appropriately adjust the diameter of the rolling ring. This adjustment is however valid only for a specific flow and pressure condition which is a function of the section of the bushing used. The number of possible conditions being almost infinite, the adjustment of the diameter of the rolling ring is only a compromise that does not solve the problem of unbalance flows between the upstream screw and the downstream screw and degassing means equipping said second element.

Another artifice consists of adjusting the temperature so as to influence the viscosity of the material and consequently its flow rate. This can be done either upstream or downstream of the rolling ring. In practice, it has been found that the adjustment of the temperature gives only a limited result and does not make it possible to effectively manage the flows in the two screws and, consequently, to obtain an effective degassing of the material circulating in the extruder.

As a result, at present no degassing extruder of this type makes it possible to achieve flow equilibrium in the two stages, so that the extrusion of elastomers takes place more or less empirically with adjustments which constitute as much compromises difficult to manage. Various solutions have been proposed to overcome the drawbacks of this type of extruder and in particular two-stage extruders as described by US Pat. Nos. 4,117,063 and 4,134,714 illustrating two embodiments in which the extruders each comprise two elements arranged along two axes. perpendicular and each having a first and a second screw. The transformed material in the first element is directly transferred to the second element without specific treatment. The result is a bad degassing and consequently a random quality of the manufactured products.

The equipment illustrated by Japanese Publication No. 63209920 is very similar to the extruders described above and the disadvantages of the foregoing are found therein.

The equipment illustrated in Japanese Publication No. 60124232 is a two-stage extruder arranged parallel to each other and coupled through a chamber which is in fact a degassing device. The connection between the first stage and the degassing chamber is through dies. A vacuum pump is directly connected to the degassing chamber to evacuate the gases. This embodiment has a major disadvantage that is due to the risk of fouling of the mouth of communication with the vacuum pump. In addition degassing occurs in an area where the raw material has not yet undergone all its transformations and it is ineffective.

Presentation of the invention

The object of the present invention is to overcome all the disadvantages mentioned above by providing a degasing extruder capable of ensuring effective degassing of plastics and natural or synthetic rubber during the processing of the raw material into a homogeneous paste. This object is achieved by the extruder as defined in the preamble and characterized in that it comprises in that said buffer chamber is equipped with at least one extrusion grid mounted on a support and constituting a third outlet orifice which communicating the buffer chamber with said second input port of said second member to transfer said material transformed by said first member from said buffer chamber into said second member and to fragment it prior to introduction into said second member.

In a particularly advantageous manner, said extrusion grid comprises a series of through-openings arranged substantially along the axis of the buffer chamber. This extrusion grid is interchangeable and arranged on a support integral with the walls of the buffer chamber.

Preferably, said extrusion grid is disposed at said second inlet of said second element and has a cylindrical surface whose diameter corresponds to that of said second extrusion screw, so that the helical beads of this screw rub against the surface and fragment the transformed material exiting said buffer chamber through said through openings.

According to a particularly advantageous embodiment, said buffer chamber comprises at least one filter disposed at said third inlet orifice, in communication with said first outlet orifice of said first element.

Said filter is preferably interchangeable and mounted on a filter holder integrated in the walls of said buffer chamber.

According to an advantageous embodiment, the filter consists of at least one perforated plate and at least one mesh grid applied to at least one of the faces of the perforated plate. Said degassing means equipping said second element preferably comprise a fourth orifice called degassing orifice which is disposed upstream of said second inlet orifice of said second element.

Said degassing means are in communication with a source of depression. This vacuum source may be a vacuum pump coupled to the sheath of said second element in an area of this element which is upstream of the stream of transformed material.

Brief description of the drawings

The present invention and its advantages will become more apparent in the following description of a preferred embodiment, with reference to the accompanying drawings, in which:

FIG. 1 is a view in axial section of a conventional degassing extruder,

FIG. 2 is a view in axial section of a degassing extruder according to the invention,

FIG. 3A represents an enlarged section of the buffer chamber seen along an axial plane parallel to the longitudinal axes of the two elements of the extruder of the invention, and

- Figure 3B shows an enlarged section of the extrusion grid of the buffer chamber seen in an axial plane perpendicular to the longitudinal axes of the two elements of the extruder of the invention.

Ways of Carrying Out the Invention With reference to FIG. 1, the traditional degassing extruder 10 shown mainly comprises a cylindrical sheath 11 in which is housed a one-piece screw 12 which is driven by a reduction motor 13 mounted to the upstream end of the sheath. The one-piece screw 12 is actually composed of two screw elements 12a and 12b assembled end-to-end and separated by a rolling ring 14. A first orifice 15 for input of the raw material is arranged near the upstream end of the one-piece screw 12 to allow the introduction into the extruder of plastics, thermoplastics or natural or synthetic rubber and any other components such as mineral fillers, oils, etc. At the level of the rolling ring 14 the sheath 11 is equipped with a second orifice 16, called vacuum well, which allows the connection of the inside of the extruder with a vacuum pump or the like to ensure degassing of the material being processed. At its downstream end, the extruder is equipped with a third orifice 17 formed in an extrusion head 18 provided for example with a die 19 which defines the shape and dimensions of the profile extruded by the extruder.

As explained above, degassing can not be effected efficiently and the settings to try to approach the optimal conditions are innumerable, laborious and often totally empirical.

The degasifier extruder 100 according to the invention represented by FIGS. 2, 3A and 3B comprises a first element 110 and a second element 130 coupled to each other and cascaded, each of these elements constituting an extruder per se, each of which may have a speed independent of the speed of the other. The first element 110 comprises a first sleeve 111 in which is housed a first extrusion screw 112, a first reduction motor 113 for driving said first extrusion screw 112, a first inlet orifice 114 for the raw material and a first outlet 115 of the transformed material. The second element 130 comprises a second sleeve 131 in which is housed a second extrusion screw 132, a second reduction motor 133 for driving said second extrusion screw 132, a second inlet orifice 134 for the raw material and a second outlet port 135 of the transformed material. The first member 110 is coupled to the second member 130 through a connecting piece 150 which connects the first outlet port 115 of the first member with the second inlet port 134 of the second member. This connecting piece 150 contains a buffer chamber 151 intended to collect the material transformed into said first element 110 and to transfer it into the second element 130. For this purpose, this buffer chamber 151 comprises a third inlet orifice 152 which communicates with the first outlet 115 of the first member 110 and a third outlet 153 which communicates with said second inlet 134 of said second member 130.

As shown in more detail in FIGS. 3A and 3B, the connecting piece 150 is provided with a clearance serving as a filter holder 154 in which a filter 155 is disposed near the third inlet orifice 52 of the buffer chamber 151. which communicates with the first outlet of the first element. This interchangeable filter advantageously consists of a perforated plate 155a and at least one more or less fine grid 155b and / or 155c. Moreover, this connecting piece 150 advantageously comprises an extrusion grid 156 placed nearby. the third outlet orifice 153 of the buffer chamber 151. This extrusion yoke makes it possible to deliver into the second inlet orifice 134 of the second element 130 fragments of material transformed in the first element. The extrusion grid is mounted on a support which is integral with the connecting piece and / or the sheath of the second element. It consists of an interchangeable plate provided with a multitude of through openings 156a. The upper surface 156b is substantially planar and the lower surface 156c has a circular sector-shaped section whose radius corresponds to the radius of the screw 132 of the second element 130. This surface 156c is located in the immediate vicinity of the helical beads of the screw 132. , or in rubbing contact with them in such a way that at each turn of the screw, these beads scrape the surface 156c and fragment the strands of material coming out of the through openings 156a in the form of cylindrical channels for real granulation of the material transformed in said first element. This granulation has the effect of considerably increasing the exchange surface of the material with its immediate environment which is the partial vacuum atmosphere prevailing in the upstream portion of the sheath of the second element 130 connected to a vacuum pump. This fragmentation of the material which increases the exchange surface considerably increases the efficiency of degassing. It is essential that the degassing occurs after the fragmentation, that is to say in the upstream zone of the second element. The degassed material will then be kneaded by the screw 132 of the second element and converted into a perfectly homogeneous extrudable paste.

Other accessories can be mounted in the connecting piece, for example a rolling ring, in order to increase the mixing and to make the material more homogeneous.

The second element is provided with degassing means which in this case consist essentially of a fourth orifice 136 formed through the sleeve 131 and which is connected to a vacuum source (not shown), for example a vacuum pump. This fourth orifice is disposed upstream of the second inlet orifice 134 of the second element, in an end zone of the extrusion screw 132 situated between its so-called active zone defined as being located between the inlet orifice of the material and the extrusion head, and the reducing motor 133 for driving the extrusion screw 132. This zone is a so-called neutral zone which contains practically no material while being in perfect communication with the latter. The depression created in the so-called neutral zone and the free communication between the so-called active zone and the so-called neutral zone make it possible to ensure very efficient degassing and unequaled quality of raw material.

In addition, since the degassing operation is no longer subject to flow equilibrium constraints in both parts of the extruder. traditional monobloc as described with reference to Figure 1, the original geometry of the extruder according to the invention with its buffer chamber, is suitable for the use of screws having profiles that can be very different, perfectly suited to the functions that they have to assume in each of the two elements that make up the extruder. Moreover, by its original construction, the maintenance operations are facilitated because the parts that can be closed, such as the filter and the extrusion grid, are very accessible and can be replaced or cleaned easily, without both. elements containing the extrusion screws are not involved in these interventions. The dimensions of the mesh and the perforated plate of the filter can be adapted according to the specific needs depending in particular on the treated material. Similarly the extrusion grid of the connecting piece can be adapted and changed quickly as needed.

The present invention is not limited to the preferred embodiment described, but may undergo various modifications or variations obvious to those skilled in the art.

Claims

A degassing extruder comprising a cascaded first member (110) and a second member (130) and a connecting piece (150) having a buffer chamber (151) disposed between said first member and said second member and arranged thereon to receive the material transformed by said first element and then to transmit it to said second element, and degassing means of the transformed material, said first element (110) comprising a first sheath (111) in which is housed a first screw of extruding (112), a first reduction motor (113) for driving said first extrusion screw (112), a first inlet (114) for the raw raw material and a first outlet (1 15) of the transformed material, and said second member (130) having a second sleeve (131) in which is housed a second extrusion screw (132), a second reduction motor (133) for driving said second extruder screw usion (132), a second inlet (134) of the raw material and a second outlet (135) of the transformed material, and degassing means (136), characterized in that said connecting piece is equipped with at least one extrusion grid (156) mounted on a support and constituting a third outlet (153) which communicates the buffer chamber (151) with said second inlet port (134) of said second element (130) for transferring this material transformed by said first member (110) from said buffer chamber (151) into said second member (130) and fragmenting it prior to introduction into said second member (130).

2. extruder according to claim 1, characterized in that said extrusion grid (156) comprises a series of through openings disposed substantially along the axis of the buffer chamber (151).

3. Extruder according to claim 1, characterized in that said extrusion grid (156) is interchangeable and disposed on a solidarity support the connecting piece (150) and / or the second sleeve (131) of said second member (130).

4. Extruder according to claim 1, characterized in that said extrusion grid (156) is disposed at said second inlet orifice

(134) of said second member (130) and having a cylindrical surface having a diameter corresponding to that of said second extrusion screw (132), such that the helical beads of said screw rub against the surface and fragment the transformed material exiting said buffer chamber (151) through said through openings.

5. Extruder according to claim 1, characterized in that said buffer chamber (151) comprises at least one filter (155) disposed at said third inlet orifice (152), in communication with said first outlet orifice (115) of said first element.

6. Extruder according to claim 1, characterized in that said filter is interchangeable and mounted on a filter holder (154) integrated with the walls of said buffer chamber (151).

7. Extruder according to claim 1, characterized in that said filter consists of at least one perforated plate and at least one mesh grid applied to at least one of the faces of the perforated plate.

8. Extruder according to claim 1, characterized in that said degassing means equipping said second element (130) comprises a fourth orifice (136) said degassing orifice which is disposed upstream of said second inlet orifice (134) of said second element (130).

9. Extruder according to claim 1, characterized in that said degassing means are in communication with a source of depression.

0. Extruder according to claim 1, characterized in that said vacuum source is a vacuum pump coupled to the sheath of said second element (130) in an area of this element which is upstream of the stream of transformed material.