FR3059589A1 - EXTRUSION PROCESS USING A CROWN OF MOBILE FINGERS - Google Patents

Abstract

The extrusion process of elastomers or plastic products, carried out by means of an extruder (1), comprises the following successive steps: introduction of a first mixture of elastomers or plastic products into the extruder, once completing the introduction of the first mixture, introducing a second mixture of elastomers or plastic products into the extruder (1), the entire first mixture being located downstream of a section of a conduit formed by a support (4) of the extruder (1) and an extrusion screw (6), this section being orthogonal to an axis of the screw (6), reducing the section so as to prevent the second mixture from passing through the section, - degassing a section of the duct comprising the section, and - increasing the section so that the second mixture passes through the section.

Description

Holder (s): COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN Limited partnership with shares, MICHELIN RECHERCHE ET TECHNIQUE S.A. Limited company.

Extension request (s)

Agent (s): LLR.

154) EXTRUSION PROCESS BY MEANS OF A CROWN OF MOBILE FINGERS.

FR 3 059 589 - A1 (57) The process for extruding elastomers or plastic products, carried out using an extruder (1), comprises the following successive steps:

- introduction of a first mixture of elastomers or plastic products into the extruder,

- once the introduction of the first mixture has been completed, introduction of a second mixture of elastomers or plastic products into the extruder (1),

- the entirety of the first mixture being located downstream of a section of a conduit formed by a support (4) of the extruder (1) and an extrusion screw (6), this section being orthogonal to an axis of the screw (6), reduction of the section so as to prevent the second mixture from passing through the section,

- degassing of a section of the conduit comprising the section, and

- increasing the section so that the second mixture crosses the section.

The invention relates to processes for extruding or mixing elastomers or plastic products, in particular for the manufacture of wheel tires.

The function of an extruder is to heat a material or mixture of materials, to pressurize it and to produce it in the form of a profile with a predetermined section, such as a strip. Such a strip is for example wound on a support to form a raw tire blank intended to be cured to carry out the vulcanization of the rubber.

In the field of gum extrusion, industrial constraints make it necessary to configure the extrusion processes to allow the best compromise in flow / temperature / work / appearance for the most difficult outgoing product to implement. This constraint generally penalizes the extrusion performance of materials which are easier to extrude.

To avoid such a drawback, manufacturers have devised methods using a variable number of rings of movable fingers in an extruder. Movable finger crowns can then be likened to filters, and the process involves adding more finger crowns than the mixture is difficult to extrude. However, such a method is long to implement and requires either to stop the extruder each time the configuration is changed, or to operate the extruder under zero load while changing the configuration.

Processes of this type therefore have the disadvantage of not making it possible to manage changes of materials which are too different and of not making it possible to extrude the gum continuously or else at the cost of too large a volume of mixed product, unfit for industrial use.

The solutions known in the prior art to overcome this problem consist in using an extruder by type of mixture. These solutions result in a significant additional cost and size.

A problem not resolved by the state of the art is therefore the possibility of extruding mixtures of elastomers or plastic products of different or even very different natures according to a process allowing continuous extrusion and without mixing the various mixtures introduced into a same extruder.

The invention aims to remedy these drawbacks by providing an extrusion process allowing an extruder to extrude mixtures of elastomers or plastic products of different or even very different types, and this continuously.

To this end, there is provided according to the invention a process for the extrusion of elastomers or plastic products, which comprises the following successive steps:

- introduction of a first mixture of elastomers or plastic products into an extruder,

- once the introduction of the first mixture has been completed, introduction of a second mixture of elastomers or of plastic products into the extruder,

the entire first mixture being located downstream of a section of a duct formed by a support for the extruder and an extrusion screw, this section being orthogonal to an axis of the screw, reduction of the section of so as to prevent the second mixture from crossing the section,

- degassing of a section of the conduit comprising the section, and

- increasing the section so that the second mixture crosses the section.

Thanks to the obturation of the section, this process makes it possible to introduce the second mixture without waiting without risking that the two mixtures mix with each other.

It can be provided that, during the reduction step, the section is reduced by at least 60%, in particular by at least 80%, and preferably by at least 96%, so as to prevent the second mixing. to cross the section.

In this way, a very large mixing range can be closed without changing the extruder configuration.

Advantageously, the section is only increased once a larger part, preferably all, of the first mixture, evacuated from a working area of the extruder.

In this way, it is certain that the second mixture will not mix with a large part, preferably all, of the first mixture, which represents a gain in material.

Advantageously, the second mixture is only introduced into the working area once a larger portion, preferably all, of the first mixture, located downstream of a working area of the extruder.

We can predict that the process will be automated according to a setpoint of at least one of the following parameters:

- pressure inside the support,

- a temperature inside the support,

- a temperature of at least one of the mixtures, and

- an aspect of at least one of the mixtures.

An extruder is also provided for elastomers or plastic products comprising:

- an extrusion screw, and

- Means capable of controlling the implementation of the method according to the invention.

Preferably, provision is made for the means to be self-adapting.

Also, a computer program is provided which includes, in recorded form, code instructions capable of controlling the implementation of a method according to the invention when it is executed on a computer.

We will now present an embodiment of the invention given by way of nonlimiting example and with the support of the appended figures in which:

- Figure 1 is an axial sectional view of the assembly of an extruder according to an embodiment of the invention;

- Figure 2 is an axial sectional view on an enlarged scale of a part of the assembly of Figure 1 illustrating the movable fingers of the extruder of Figure 1;

- Figure 3 is a sectional view along the plane III-III of Figures 1 and 2 showing fingers mounted movable relative to the support 4, in a retracted position;

- Figure 4 is a view similar to Figure 3 showing the movable fingers in an extended position; and

- Figure 5 is a diagram illustrating the regulation of the extruder according to predetermined input instructions.

- Figure 6 is a schematic sectional view along the plane lll-lll of Figures 1 and 2 illustrating the calculation of a shutter rate obtained according to one of the embodiments of the invention.

Figure 1 shows the entire extruder 1 of this embodiment. It comprises a frame 2 from which extends a support 4. An extrusion screw 6 is mounted mobile in rotation, inside the support 4, along a longitudinal axis 8. This axis is here horizontal. The screw is received coaxially in a cylindrical housing of the support with circular section in a plane perpendicular to the axis 8. The screw and the support therefore form an elongated passage intended to receive the mixture to be extruded.

In Figures 1 and 2, it is possible to distinguish different areas of the extruder. An upstream part of the extruder, with reference to the direction of travel of the mixture along the axis from right to left in the figures, extending upstream of the plane AO perpendicular to the axis 8, is called the zone of pressurizing Pr of the mixture to be extruded, preceded upstream by a feed zone provided with a mixing reception spout. The part of the extruder extending between the planes, parallel to each other, AO and A1 is a first work area, that between A1 and A2 is a second work area provided with fixed fingers B2 and that between A2 and A3 is a third work area, therefore downstream from the previous one. The set of areas between the planes AO and A3 is called working area B of the mixture to be extruded.

FIG. 2 is a view on an enlarged scale of the assembly of FIG. 1 better illustrating the extrusion screw 6. The extruder comprises fingers which can be distributed, preferentially according to the embodiments provided for by the invention, into two categories: fixed mounted fingers and movable mounted fingers 100.

Each of the fingers has a generally elongated cylindrical shape and has its longitudinal axis oriented in a direction radial to the axis 8 of the screw.

Fixed mounted fingers

In FIG. 2, a distinction is made between fixed fingers 112 to 612 located in planes B1 to B6 parallel to the planes AO, A1 and A2, located in the second work area, arranged in a constant pitch along the axis 8. These plans are numbered B1, B2, B3, B4, B5, B6, their exact number being the choice of geometry of the extruder of the skilled person. In each plane B, several fixed fingers, for example eight, are arranged uniformly distributed around the circumference of the support 4 and numbered 112, for the plane B1, 212 for the plane B2, etc. These fixed fingers provide the minimum work necessary for the extruded elastomeric mixtures which are used in the composition of a tire.

In FIGS. 3 and 4, in the plane III-III, a distinction is also made between fixed fingers 121.

Movable mounted fingers 100

In FIGS. 3 and 4, a distinction is also made between the fingers 100 mounted movable relative to the support 4, their exact number coming from the choice of geometry of the extruder, more particularly it is a function of the desired closure rate, of the internal diameter of the support and mechanical resistance to finger stresses.

Figures 3 and 4 are sectional views along the plane lll-lll of Figures 1 and 2. They illustrate an embodiment provided by the invention, in particular that in which the extruder has at least one finger 121 fixedly mounted relative to the support, inside which is housed a degassing valve 24.

Is also visible in Figures 3 and 4 the annular passage duct 107 formed between the screw and the support through which the mixture of elastomer or plastic products moves.

All the fingers, fixed and mobile, located in this cutting plane are arranged with their axes in the same plane. They form a star configuration. All the moving fingers are here identical to each other. All fingers are evenly distributed around the axis.

Apart from the fixed finger 121, all the other fingers 100 are mounted movable relative to the support 4 while being received in respective radial housings of the latter.

The extruder comprises, for each set of movable fingers lying in the same plane perpendicular to the axis, a flat annular ring 14 coaxial with the support and the screw. The crown extends outside the support and allows the fingers of the associated plane to be controlled.

The fingers are connected to the crown 14 by means of rollers 16 movable inside respective oblong through grooves 18 formed in the crown

14. Each finger is integral with a rod on which the corresponding roller is fixed while being mobile in rotation, the axis of rotation of the roller being parallel to the axis of the screw and distant from the latter.

The crown 14 is mounted movable in rotation around the axis 8 relative to the support while being guided by appropriate means. It is actuated for example by means of a jack 20 provided with a piston 22. The two ends of the jack are articulated respectively to the crown and to the frame. Thus, the rectilinear stroke of the piston 22 causes the rotation, relative to the support 4 and along the axis 8, of the ring 14. The grooves 18 then pivot around the axis 8 and thus allow the fingers 100 to move radially to the axis 8 towards the extrusion screw 6 or in the opposite direction. Thus, the stroke of the actuator 20 controls the position of the fingers 100 inside the support 4. The fingers 100 can therefore take any desired position between a fully retracted position (illustrated in FIG. 3) and a position completely extended from the passage (illustrated in Figure 4). In the retracted position, most of the distance between the finger housing and the screw core is occupied by the finger. In the extended position, this distance is left entirely free by the finger.

In a preferred embodiment, the movable fingers 100 each slide in a lubricated jacket 102. This makes it possible to reduce the force of the jack 20 to move the movable fingers 100.

When the movable mounted fingers 100 are in the retracted position, the extruder behaves as if it did not have this system. The pressure drop of the extruder is low: it is then possible to extrude mixtures requiring little work and a lot of flow. This position also allows the extruder to be drained quickly. Preferably, the fixed mounted fingers 112, 121 also help to drain the extruder.

When the fingers 100 mounted mobile are in the fully extended position, the work is maximum, the pressure drop is large and the screw begins to slip.

The extruder is therefore able to close, for each ring 14 connected to movable mounted fingers 100, a section of the passage duct thanks to the variable position of the fingers in the duct.

Depending on the position of the fingers, different obturation rates for this duct are therefore obtained. For example, at least 60% of a section of the conduit for a partially retracted position of the fingers, then as the ends of the fingers 100 move towards the axis 8, the extruder is able to seal at least 80% of the section, in order to finally achieve a closure of 96% of the section in a position where the diameter of the core of the extrusion screw 6 is close to a circle formed by the ends of the fingers 100. As an illustration, visible in FIG. 6, 20 fingers (19 movable mounted fingers 100 and one fixed mounted finger 121) of 18 mm diameter close 96% of a section of a conduit formed by an extrusion screw of 149.8 mm diameter having a 118 mm diameter core which rotates inside a 150 mm diameter support. The calculation is as follows: <14.98 \ ²

Total area

P = πχ I = 176.7 cm ² / ii. "\.

Area of the screw core = π xf ——j = 109.36 cm ²

Area of the section of a finger = 3.02 cm ² Area of duct 107 unobstructed = 176.7 - 109.36 - (20 x 3.02) = 6.94 cm ² ! 6.94 \

Shutter rate = 11 - -r = -r =) x 100 = 96%

V 176.7 J

A shutter of 0% corresponds to the retracted position of the fingers.

The rings 14a and 14b illustrated in Figure 2 are exactly the same. Their operation is described with the support of FIGS. 3 and 4 as explained above.

The extruder is capable of closing several sections of the conduit in this way according to the number of rings arranged along the axis 8 along its support 4.

As illustrated in FIG. 2, the sections can be located downstream of the working area provided with fixed fingers B, for example the section located in the plane of the crown 14b, but also upstream of the working area provided with fingers fixed B, for example the section located in the plane of the crown 14a which is immediately downstream of the pressurization zone. The sections can also be located directly downstream of the pressurization zone, as is the case with the crown 14a.

The extruder is also equipped with sensors. These sensors allow the collection of data during the operation of the extruder, inside or at the exit of the extruder, about different physical quantities specific to the mixture or to the extruder.

For example, one or more temperature sensors, of the thermocouple type, can be installed in the passageway of the extruder to determine the temperature inside the extruder or the temperature of the mixture during extrusion, it also possible to install a temperature sensor of the mixture at the outlet of the extruder to verify that the mixture is at the appropriate temperature to be used directly at its outlet.

One or more pressure sensors can also be installed inside the extruder. For example, they are of the Dynisco brand according to one of the embodiments of the invention. They make it possible to control the internal pressure of the passage duct. Indeed, depending on the closure of one or more sections of the duct, the internal pressure can be very high (which can even reach around 1000 bars, or 108 Pa, for a closure of around 96% of a section). It is also desirable to precisely control the pressurization of the mixture and therefore to have a pressure sensor in the pressurization zone of the extruder.

Better control of the internal pressure of the extruder, at different places in the extruder, allows better control of the flow rate of the mixture to be extruded. The flow and pressure inside the extruder are linked. The flow rate of the mixture to be extruded through the extruder pipe is one of the parameters that determine the work applied to the mixture by the extrusion screw. It is therefore desirable to also have one or more flow sensors within the extruder. Thanks to these, it is possible, for example, to control the flow rate of entry into the mixture duct, the flow rate through a closable section of the duct or the flow rate at the extruder outlet.

It is also best to control the roughness and appearance of the mixture. This can be apprehended according to the thickness of the mixture or its texture (lumpy or not). To carry out this control, the extruder can be equipped with thickness sensors, for example laser sensors, or even CCD cameras which allow control of the texture of the mixture and can therefore be considered as aspect sensors. In addition, the roughness sensors that can equip the extruder generally use optical technology.

This extruder is capable of extruding a very wide range of mixtures so that all of the rubber mixes used to produce a tread for a tire blank can be extruded by the same extruder. These differences between the mixtures are expressed according to the Mooney plasticity index.

To characterize the plasticity of a material, an oscillating consistometer is used as described in French standard NF T 43-005 (1991). The Mooney plasticity measurement is carried out according to the following principle: the composition in the raw state (i.e., before baking) is molded in a cylindrical enclosure heated to 100 ° C. (37325 K). After one minute of preheating, the rotor turns within the test tube at 2 revolutions / minute and the torque useful for maintaining this movement is measured after 4 minutes of rotation. The Mooney plasticity (ML 1 + 4) is expressed in Mooney unit (MU, with 1 MU = 0.83 Newton.meter). The lower the Mooney value, the lower the viscosity before cooking and the better the processability of the composition.

As an example of the wide range of extruded mixes, the rubber mixes used to create a tread assembly are: a first 100% natural rubber material to make an undercoat with a Mooney index ML1 + 4 from 80 to 110, then a second material to make the 100% synthetic rubber tread with a Mooney index ML1 + 4 from 70 to 100 followed by a third material to make the sidewalls composed of a mixture of natural rubber / synthetic rubber (20% to 80% natural rubber) with an index of

Mooney from ML1 +4 from 50 to 100.

The structural components of the extruder, an example of sensors allowing data collection and an example of mixtures that can be extruded by the extruder having been described, we will now describe the possible uses of the extruder.

Usually, an extruder is configured to allow the best compromise between flow / temperature / work / appearance for the most difficult outgoing product to implement. This constraint penalizes the extrusion performance of materials that are easier to work with. The process of the invention makes it possible to configure the extruder continuously according to the incoming mixtures. The proposed principle makes it possible to vary the flow section of the material, therefore the pressure drop of the extruder to optimize the compromise between flow / temperature / work / appearance.

The process is carried out as follows.

Before the introduction of the first mixture, the position of the fingers 100 is defined according to the physical properties desired at the outlet of the extruder of the first mixture. The work applied by the screw 6 to the mixture, called shearing, is therefore initially fixed.

The first mixture is introduced into the extruder, it crosses the pressurization zone A, then arrives in the working zone B of the extruder.

It now extends in the conduit through one or more of the sections which can be closed off by means of the different crowns 14 driving the fingers 100. Depending on the position of the fingers 100 in the sections, the shear of the mixture by the screw 6 is more or less great . For example, in the fully extended position, the work is maximum, and the pressure drop is great. This allows the material to be worked at different levels of consistency generated by the rise in its temperature and at different intensities.

At this stage, the first mixture being introduced into the extruder, the second mixture is introduced there. The extruder was not stopped on this occasion and continues to operate normally.

As soon as the first mixture begins to leave the extruder, the data collections by the sensors (visible in FIG. 2) make it possible to correct the initial positions of the fingers 100 if necessary. As illustrated in FIGS. 2 and 5, regulation of the process is carried out (symbolized by the letter R). The process becomes self-adaptive thanks to the self-adaptive technical means of the extruder controlled by returns (temperature, appearance, roughness, flow rate, pressure symbolized by the letters T, A , Rg, D and P in Figure 5). Of course, if the sensors present inside the extruder but not at the exit of the extruder indicate an abnormal pressure, temperature or flow, a correction is made without waiting for the exit of the first mixture. A process regulation is thus carried out. For example, the appearance of the gum extrudate at the outlet of the extruder is measured, for example in the form of a strip. If the appearance deteriorates, we order (symbolized by the letter C in Figure 5) for example the output of the fingers 100 of one (or more) crown (s) in order to increase the level of work and of improve the appearance of the product. It is checked that the modification of the position of the fingers does not cause an increase in temperature beyond the tolerances. It must also be checked that the pressure upstream of the finger crowns is not too excessive.

As the first mixture comes out of the extruder with the desired physical properties, it is used immediately.

While the first mixture is extruded by the screw 6 according to different shear intensities (the more the movable mounted fingers 100 come out, the more the work, ie the shear increases and this until the almost total closure of the section). the second mixture arrives in the pressure zone A. To prevent the two mixtures from mixing, the passage section of the conduit is reduced downstream of which the entire first mixture is located.

The reduction is obtained by advancing the fingers 100 movably mounted in the conduit. According to the Mooney index of the second mixture, the required filling is more or less large. For example, it can be 60%, or 80% or even 96%. This reduced section is located at the entrance or exit of work area B but not necessarily. In this case, it may be section 14b or 14a. The reduced section can also be located in the middle of working area B, thus delimiting a clean working area between two closed sections.

Generally, there is a section of the extruder, delimited downstream by the closed section, considered to be mainly filled with gas. It is therefore useful to degas this section. The degassing contributes to the continuity of the outgoing product, without inclusion of air and without noise pollution. The degassing valve 24 makes it possible to carry out this operation. It is located in the closed section, in a fixed finger 121 or not. It is closed when a rubber pressure is detected and opens mechanically when the rubber pressure detected at this crown is zero.

Once the degassing has been carried out, the passage section is increased, by virtue of the removal of the movable fingers 100. According to the Mooney index of the second mixture, the increase is more or less significant before the second mixture can cross the closed section. It is also possible, alternatively or not, to wait until a greater part of the first mixture is discharged before the step of increasing the section begins.

In the same way as for the first mixture, once the second mixture begins to leave the extruder, the data collected by the sensors located at the exit of the extruder allow dynamic control of the position of the fingers to adjust if necessary the shear applied to the mixture in a working zone B of the extruder.

This process defined by its successive stages is therefore automated according to a setpoint of at least one of the following parameters:

- pressure inside the support,

- a temperature inside the support,

- a temperature of at least one of the mixtures,

- an aspect of at least one of the mixtures.

- roughness of at least one of the mixtures.

Generally, the extruder is controlled using this process according to several of these parameters as explained above.

The extruder can be provided with computer control means controlled by at least one computer program. This program includes, in recorded form, code instructions capable of controlling the implementation of the process when it is executed on a computer of the extruder. In particular, it is possible to save:

- the characteristic data of the mixtures to be extruded,

- the desired characteristics at the output of the mixtures to be extruded, and

- the geometric characteristics of the structural elements of the extruder.

An advantage of the process described above is that it makes it possible to better control the change of incoming materials, while ensuring the continuity of the outgoing product and also to limit the volume of mixed product.

Another advantage is that it optimizes the flow / temperature / work / appearance compromise of the outgoing product. This process implemented by the extruder therefore achieves a high level of flexibility. The system also makes it possible to manage variations in the product contained in the extruder during transient phases (shutdown, restart, filling, emptying).

It also makes it possible to compensate for the geometric variations of the extruder (general wear, mechanical dispersion). It also makes it possible to compensate for the variability of the incoming product (dimensions, suppliers, aging). In contrast to a conventional extruder in which the flow decreases with wear, an extruder equipped with this process maintains the flow by opening the flow section.

The system makes it possible to manage the change of incoming materials, while ensuring the continuity of the outgoing product and also to limit the volume of mixed product. Preferably, the method avoids mixing the first material and the second material (mixture of non-conforming properties which must be removed in the form of scraps). It also eliminates falls during the mixture change.

Of course, many modifications can be made to the invention without departing from the scope thereof.

In a variant, not illustrated in the figures, the crown 14 is absent, each movable finger 100 being actuated by its own jack, the jacks of all the fingers being connected to a central control unit.

Claims (10)

Claims 1. Process for the extrusion of elastomers or plastic products, characterized in that it comprises the following successive steps: - introduction of a first mixture of elastomers or plastic products into an extruder (1), - once the introduction of the first mixture has been completed, introduction of a second mixture of elastomers or of plastic products into the extruder (1), - the entirety of the first mixture being located downstream of a section of a conduit formed by a support (4) of the extruder (1) and an extrusion screw (6), this section being orthogonal to an axis of the screw (6), reduction of the section so as to prevent the second mixture from passing through the section, - degassing of a section of the conduit comprising the section, and - increasing the section so that the second mixture crosses the section. 2. Method according to the preceding claim wherein, during the reduction step, it reduces by at least 60%. 3. Method according to claim 1 wherein, during the reduction step, the section is reduced by at least 80%. 4. The method of claim 1 wherein, during the reduction step, the section is reduced by 96%. 5. Method according to any one of the preceding claims, in which the section is only increased once a greater part, preferably all, of the first mixture evacuated from a work area (B ) from the extruder. 6. Method according to any one of the preceding claims, in which the second mixture is not introduced into the working area until a greater part, preferably all, of the first mixture located downstream of a work (B) of the extruder. 7. Method according to any one of the preceding claims, automated according to a setpoint of at least one of the following parameters: - a pressure inside the support (4), - a temperature inside the support (4), - a temperature of at least one of the mixtures, - an aspect of at least one of the mixtures and - roughness of at least one of the mixtures. 8. Extruder (1) for elastomers or plastic products comprising: - an extrusion screw (6), and means suitable for controlling the implementation of the method according to any one of claims 1 to 7. 9. Extruder (1) according to the preceding claim wherein the means are self-adapting. 10. Computer program which comprises, in recorded form, code instructions capable of controlling the implementation of a method according to any one of claims 1 to 7 when it is executed on a computer. 1/6 COS < 14a 2/6 CM D) LL Ξ [at] 3/6 c ω ο. 4/6 c <0 CL