FR3057197A1 - EXTRUDER AND METHOD FOR EXTRUSION OF A MIXTURE OF ELASTOMERS - Google Patents

Abstract

ABRIDGE: extruder for extruding an elastomer mixture comprising a screw (2) rotated about its longitudinal axis in a fixed sleeve having an inlet with a feed hopper (10) in a strip (30) elastomer mixture and an outlet of an extruded product. According to the invention, the extruder comprises a sensor (20) for measuring the longitudinal position of said band within the feed hopper (10).

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): MANUF FSE PNEUMATIQUES MICHELIN Limited partnership with shares.

Pty EXTRUDER AND METHOD FOR EXTRUDING A MIXTURE OF ELASTOMERS.

FR 3 057 197 - A1

SHORT: Extruder intended for the extrusion of a mixture of elastomers comprising a screw (2) driven in rotation about its longitudinal axis in a fixed sheath comprising an inlet provided with a supply hopper (10) in a strip (30) of mixture of elastomers and an outlet of an extruded product.

According to the invention, the extruder comprises a sensor (20) for measuring the longitudinal position of said strip within the feed hopper (10).

EXTRUDER AND METHOD FOR EXTRUDING A MIXTURE OF ELASTOMERS [001] The invention relates to the field of extrusion of mixtures of elastomers more particularly intended for the manufacture of tires. The invention also relates to the field of the extrusion of compositions with self-sealing properties used as an anti-puncture layer, and intended to fill the perforations thus making it possible to avoid the flattening of the tire during use.

In known manner, an extruder is used to homogenize a mixture of elastomers which is introduced by a feed hopper inside an extruder in order to shape it at the outlet thereof, the mixture being pressurized inside the extruder. In addition, the applicants have succeeded in developing a method for applying a mixture with self-sealing properties inside a tire using an extruder. The subject of the invention is a device and a method which relate to the filling of an extruder with material.

An extruder for elastomeric materials is generally fed from a strip of elastomeric mixture which is introduced via a feed hopper. In order to ensure correct operation of the extruder, the filling must be optimized for pre-established operating parameters thereof. Thus, it has been observed that, when filling is too large in relation to the operating flow rate of the extruder, the screw begins to slip and the mixture tends to heat up, which entails a risk of degradation of its properties. Conversely, insufficient filling causes discontinuities in the profile of the extruded product. It is therefore important to be able to adapt the filling of an extruder to its operating parameters.

Document FR 2294039 describes an extruder combined with a calender which offers a solution to compensate for the variation in the flow rate of the extruder. According to this document, the extruder outlet nozzle is mounted against the calendering cylinders and it forms with one of the calendering cylinders a compensating pocket. In operation, when the extruder delivers in excess, the compensating pocket fills and compensates for the excess pressure upstream of the calender. However, this document does not provide a solution for the case where the extruder throughput decreases. Furthermore, this solution cannot be applied to an extruder alone.

In known manner, when feeding an extruder from a strip of mixture of elastomers, the strip is swallowed by the rotation of the screw and, turning with the latter, it advances inside the extruder while at the same time forming a bead in the feed hopper. This bead ensures a volume of buffer product which guarantees the absence of discontinuities in the feeding. The presence, behavior and size of this feed bead are decisive in ensuring a stable flow rate of the extruder. Thus, to have optimum functioning of the extruder, a bead must always be present and be in rotation in the hopper of the extruder. Furthermore, the size of this bead is directly related to the operating regime of the extruder, a too large bead causing the mixture to heat up, while a too small bead is the cause of discontinuities in the geometry of the extruded product. It is therefore necessary to observe its presence and then to adjust the size of this bead. However, due to the fact that it has to rotate and modify its shape, cyclically during the rotation of the screw, but also randomly depending on the properties of the material, the results of measurement of the size of the bead are not sufficiently precise so that they can serve as a reference when it is desired to regulate the supply of the extruder.

Document FR 2180024 provides a solution to this problem and describes a device which makes it possible to adjust the filling of material in the feed hopper of an extruder. According to this document, the extruder comprises a feed hopper with two compartments delimited by a fixed wall. Thus, a first compartment is intended to receive a mixing strip using a feeding cylinder and a second compartment is intended for measuring the feeding bead. For this, the second compartment comprises a piston which is kept in contact with the material and which is caused to slide under the pressure of the bead. The piston rod includes two stops which actuate switches at the end of the stroke. When actuated, the switches control the flow of material into the feed hopper. This device certainly provides a solution to the problem of adjusting the filling of an extruder, but at the cost of a device which proves to be quite complex and unreliable over time and it is unsuitable for the sticky mixtures used for self-sealing materials. In addition, the extruder hopper must be modified to adapt it to the device.

The object of the present invention is to remedy the aforementioned drawbacks and to propose an extruder and a method for extruding mixtures of elastomers comprising means which make it possible to adjust the filling of the extruder in a simplified and reliable manner in time.

This objective is achieved with an extruder intended for the extrusion of a mixture of elastomers comprising a screw animated in rotation about its longitudinal axis in a fixed sheath comprising an inlet provided with a hopper for supplying a strip of elastomer mixture and an outlet of an extruded product and comprising means for controlling the filling of the extruder with mixture, characterized in that it comprises a sensor for measuring the longitudinal position of said strip within the feed hopper.

The extruder is fed with a strip of elastomer mixture which arrives inside the extruder through a feed hopper. The feed hopper is a generally tubular conduit with a main axis perpendicular to the longitudinal axis of the extruder. This duct is open outside the extruder and passes through the sheath to open above the extrusion screw, in the feeding zone of the extruder. The mixing strip is thus conveyed inside the extruder from feeding means external to the latter, for example from a feeding belt. Such a duct can have a rectangular, square or even circular cross section and is designed so that the insertion width is greater than the width of the strip. By insertion width is understood a longitudinal dimension of the hopper or a side of its section which extends in a direction parallel to the longitudinal axis of the extruder.

According to the invention, the extruder is provided with a sensor for measuring the longitudinal position of the strip within the feed hopper. Such a sensor can then be put in contact with a device for controlling the filling of the extruder. Thus, during tests carried out in the laboratory, the applicants were able to observe that the longitudinal position of the mixing strip in the hopper is directly linked to the size of the feed bead. Indeed, in operation, the bead is always located as close as possible to the exit from the feeding zone, as seen in the direction of advance of the mixture in the extruder. Thus, the bead always comes between the feed strip and the exit from the feed area. As a result, when it grows, it pushes the tape away from the exit from the feeding area. Conversely, when the bead decreases, the mixing strip advances towards the exit from the feeding zone. The movement of the mixing strip which feeds the extruder thus follows a path parallel to the longitudinal axis of the extruder. A position sensor which detects the longitudinal position of the mixing strip is then able to deliver relevant information relating to the filling of the extruder. When we then compare this position of the strip to a preset reference position, we can act in real time to control the supply of the extruder and adapt it to the operation of the latter.

Preferably, said sensor is a contactless sensor.

In one embodiment of the invention, the strip position measurement sensor is a displacement sensor of the feeler type, the rod of which comes into contact with one of the ends of the mixing strip in the hopper. However, a non-contact measurement sensor is preferred because it can accurately determine the position of the belt in the hopper and this for any type of mixture, without risk of contamination or fouling.

Advantageously, said sensor is connected to a central control unit of the extruder. This makes it possible to act on the operating parameters of the extruder such as the speed of the feed cylinder or the speed of the screw and those of the operation of the filling device and adjust them according to its filling in mixture.

[014] Preferably, said sensor is connected to a control unit of the means for supplying a strip of elastomer mixture. This makes it possible to act on the operating parameters of the feed means of the extruder, such as the feed speed of a feed belt.

In an advantageous embodiment of the invention, said control unit adjusts the speed of advancement of the strip as a function of the signal received from said sensor. This allows the feed to be adapted to the operation of the extruder.

In another advantageous embodiment of the invention, said central unit adjusts the synchronization ratio between the speed of the screw and the speed of advance of the strip as a function of the signal received from said sensor. In this embodiment, action is taken both on the speed of the screw and on that of the feed means.

Advantageously, said sensor is mounted on the feed hopper. The sensor is thus placed as close as possible to the strip so as to improve its measurement accuracy.

[018] Preferably, said sensor is located outside of the hopper. In this case, contamination of the sensor with the material of the mixture and / or any measurement errors due to the temperature of the mixture or to the fumes emitted by it is avoided.

Preferably, said sensor is an optical sensor. In this case, a sighting window of the sensor is arranged in the side wall which faces the sensor of the hopper, or even this wall is made transparent.

Preferably, an optical sensor of the laser sensor type is used having a beam diameter greater than 5 mm, see a laser sensor with linear projection so as to be able to clearly target the width of the strip and thus ensure good accuracy of measurement for different bandwidths and their lateral displacement within the hopper.

[021] Advantageously, the extruder comprises a feed cylinder arranged inside the sheath opposite the feed hopper and rotated about an axis parallel to the longitudinal axis of the screw. Such a feed cylinder makes it possible to better drive the strip in contact with the extrusion screw. The speed of rotation of the feed cylinder is then controlled according to the signal received from the position sensor.

[022] In an advantageous alternative embodiment of the invention, the extruder receives the supply of a strip of elastomer mixture from a gear converter. Such a gear converter works on the principle of a gear pump and makes it possible to provide a first treatment to the mixing strips before they arrive in the feed hopper. The signal received from the sensor for measuring the position of the mixing strip is then used to control the speed of rotation of the gears of the converter.

[023] The objective of the invention is also achieved with a process for extruding a mixture of elastomers from a strip of mixture of elastomers which feeds an extruder in which the filling of the hopper is controlled. feed to the extruder according to the position of the belt in the feed hopper.

Indeed, with such a method, we manage to control the filling of the extruder quickly and efficiently, because the measurement of the longitudinal position of the strip in the feed hopper allows it to be used directly for control the supply of the extruder with a mixing strip.

Preferably, that the longitudinal position of the strip is measured with a non-contact measurement sensor.

[026] Advantageously, the measurement sensor is connected to a central control unit of the extruder and to a control unit of the supply means.

In an advantageous embodiment of the invention, the speed of the supply means is adjusted as a function of the signal received from said sensor.

In another advantageous embodiment of the invention, the synchronization ratio between the speed of the screw and the speed of advance of the supply means is adjusted as a function of the signal received from said sensor.

[029] The following description is based on the following figures which represent several embodiments of the invention, where:

Figure 1 is a perspective view of an extruder according to a preferred embodiment of the invention;

Figure 2 is a schematic view which illustrates the operating principle of the extruder of the invention;

Figure 3 is a schematic cross-sectional view made in the feed area of the extruder according to another embodiment;

Figure 4 is a schematic view which illustrates the operating principle of the extruder of Figure 3.

The extruder shown in Figure 1 comprises a sleeve 1 inside which rotates a screw 2 driven in rotation about a longitudinal axis XX ′ by an electric motor and a reduction gear 3. The sleeve 1 a a generally cylindrical shape and comprises an inlet 4 for supplying a mixture of elastomer and an outlet 5 which is provided, in known manner, with an extrusion nozzle (not shown in the drawings) to give the shape and the desired profile for the extruded product. The extruder is supplied with a strip of elastomer mixture which arrives at the inlet 4 from the feed means 6.

[031] Such a mixture comprises all the constituents which form part of a formulation of a composition for a tire, such as for example elastomers, in particular diene elastomers, reinforcing fillers, non-reinforcing fillers, plasticizers, vulcanization additives, protection. The mixture can also be of the self-sealing composition type for a tire, the composition of which is described in application FR 2 955 587 of the applicant.

In the example shown in FIG. 1, the supply means 6 comprise a gear converter 7 driven by an electric motor 8. The mixing strip enters inside the gear converter 7 while being brought there. at an inlet 9 and it leaves the converter through an outlet opening situated opposite the first and communicating with a feed hopper 10 of the extruder. A gear converter works on the principle of a gear pump, it includes two pairs of toothed wheels with axes parallel to each other and perpendicular to the direction of flow of the material as defined between the inlet and the outlet of the converter. The toothed wheels are made so as to mesh with each other, a single axis receiving the engine torque. The converter is supplied with one or more bands of elastomer mixture. The mixture is driven by the gear wheels inside the converter housing, it is worked by the gears so that its properties are improved at the outlet. We can thus begin the work of plasticizing the material inside the converter before feeding the extruder with a strip whose outlet section can also be modified compared to that which is introduced into the converter. Such a gear converter is for example of the ROTOMEX ZX 75/50 type from the company TROESTER.

According to the invention, the extruder comprises a sensor 20 capable of measuring the longitudinal position of the strip 30 inside the feed hopper 10. In the example illustrated in the figures, the sensor 20 is a optical sensor connected to a central extruder control unit. The sensor 20 is mounted on a rigid support 12 secured to the hopper 10. The sensor 20 targets the strip 30 inside the hopper 10 through the side wall 11 of the hopper. More particularly, an aiming window with dimensions greater than those of the sensor beam is arranged in the side wall 11 so as to be able to pass the beam through the window in the direction of the strip 30.

[034] The sensor 20 is preferably a reflection laser sensor, the beam of which has a diameter greater than 5 mm. The sensor targets the width of the strip 30 and its beam has a sufficiently large diameter to always target the width of the strip, even during lateral displacements of the latter. In fact, during the supply of the mixing strip, as a function of the tensile force Ft (FIG. 3) exerted on the strip which passes between the screw 2 and a supply cylinder 25, the strip 30 can undergo lateral displacements (it is understood in the direction of the width of the hopper and perpendicular to the longitudinal direction of the latter) of the order of a few mm to about 20 mm. In a variant, a laser sensor with linear projection is used, for example of the type whose optics comprises a cylindrical lens, the length of the line of the sensor having a dimension greater than 5 mm so as to clearly target the width of the strip 30 A laser sensor allows precise measurement even in a smoke and high temperature atmosphere released by the mixture inside the hopper 10.

[035] Figure 2 illustrates, by a block diagram, the operation of the device of the invention. Note the screw 2 which is caused to rotate about its longitudinal axis X-X ’when the drive motor 3 of the screw receives a command from a central control unit 40 of the extruder. The central control unit 40 is connected to the sensor 20 which measures the position of the strip 30 within the hopper 10. The hopper 10 has a longitudinal dimension or width "L" clearly greater than the width "I" of the strip 30. The strip 30 is swallowed when the screw 2 rotates and advances inside the extruder while at the same time forming a bead 35 in the feed hopper 10. In operation, it has been observed that the bead is located always as close as possible to the exit from the feed zone, as seen in the direction of advance of the mixture in the extruder. Thus, the bead 35 is always interposed between the strip 30 and the outlet 36 of the feeding zone. Therefore, when it grows, it pushes the strip 30 opposite the outlet 36 of the feed area. Conversely, when the bead 35 decreases, the strip 30 advances towards the outlet 36 from the feeding zone. The movement of the strip 30 which feeds the extruder thus follows a path parallel to the longitudinal axis X-X ’of the extruder according to the arrows indicated by A in FIG. 2 over the width L of the hopper 10.

The sensor 20 is an optical reflection sensor whose beam points to the width of the strip 30. It reads the position of the strip 30 within the hopper 10 and thus delivers relevant information relating to the filling of the extruder . When this position of the strip is then compared with a preset reference position, it is possible to act in real time to control the speed of advance of the strip 30 by controlling the feed means 6 of the extruder and to adapt the speed. of movement of the strip 30 during operation of the extruder.

In the example of FIG. 1, the speed of rotation of the input shaft in the gear converter 7 is controlled.

In another example, shown in Figures 3 and 4, the strip arrives in the feed hopper 10 either from a gear converter 7, as in the previous example, or from a belt feed. In this example, the extruder comprises a feed cylinder arranged inside the sheath 1 opposite the feed hopper 10. The feed cylinder 25 is rotated by a clean drive motor around 'an axis Y-Y' parallel to the longitudinal axis X-X 'of the screw 2. FIG. 4 illustrates by a schematic view the arrangement of the cylinder 25 relative to the screw 2 and the arrangement of the mixture at l inside the barrel 1 of the extruder.

The band 30 is driven inside the extruder passing between the screw 2 and the supply cylinder 25. In this example, the speed of rotation of the supply cylinder 25 is modified as a function of the signal. received from sensor 20.

Advantageously, the signal delivered by the sensor 20 to the central control unit 40 of the extruder is used to modify the synchronization ratio between the speed of the screw 2 and the speed of rotation of the cylinder. food 25.

[041] Other variants and embodiments of the invention can be envisaged without departing from the scope of its claims.

[042] Thus, one can use a displacement sensor of the electrically operated feeler type, for example of the potentiometric or magnetostrictive type.

[043] Alternatively, the sensor is connected directly to the control unit for the supply of the mixing strip.

Claims (16)

1. Extruder intended for the extrusion of a mixture of elastomers comprising a screw (2) driven in rotation about its longitudinal axis in a fixed sheath (1) comprising an inlet (4) provided with a feed hopper (10) in a strip (30) of mixture of elastomers and an outlet (5) of an extruded product, characterized in that it comprises a sensor (20) for measuring the longitudinal position of said strip within the feed hopper (10). 2. Extruder according to claim 1, characterized in that said sensor (20) is a contactless sensor. 3. Extruder according to one of the preceding claims, characterized in that said sensor (20) is connected to a central control unit (40) of the extruder. 4. Extruder according to one of the preceding claims, characterized in that said sensor (20) is connected to a control unit (50) of the supply means (6) in strip (30) of mixture of elastomers of l 'extruder. 5. Extruder according to claim 4, characterized in that said control unit (50) adjusts the speed of advance of the strip (30) according to the signal received from said sensor (20). 6. Extruder according to one of claims 3 or 4, characterized in that said central control unit (40) adjusts the synchronization ratio between the speed of the screw (2) and the speed of advance of the strip (30 ) as a function of the signal received from said sensor (20). 7. Extruder according to one of the preceding claims, characterized in that said sensor (20) is mounted on the feed hopper (10). 8. Extruder according to one of the preceding claims, characterized in that said sensor (20) is located outside the feed hopper (10). 9. Extruder according to one of the preceding claims, characterized in that said sensor (20) is an optical sensor. 10. Extruder according to one of the preceding claims, characterized in that it comprises a feed cylinder (25) arranged inside the sheath (1) opposite the feed hopper and which is driven in rotation about an axis parallel to the longitudinal axis of the screw (2). 11. Extruder according to one of the preceding claims, characterized in that it receives the strip feed (30) of mixture of elastomers coming from a 5 gear converter (7). 12. Method for extruding a mixture of elastomers from a strip (30) of mixture of elastomers which feeds an extruder in which the filling of the feed hopper (10) of the extruder is controlled as a function of the position of the strip (30) in the feed hopper (10). 10 13. Method according to claim 12, characterized in that the longitudinal position of the strip (30) is measured with a contactless measuring sensor (20). 14. Method according to claim 13, characterized in that said sensor (20) of measurement is connected to a central control unit (40) of the extruder and to a control unit (50) of the supply means ( 6). 15. The method of claim 14, characterized in that one adjusts the speed of advance of the strip (30) according to the signal received from said sensor. 16. Method according to claim 14, characterized in that the synchronization ratio between the speed of the screw and the speed of advance of the supply means is adjusted as a function of the signal received from said sensor. 30571 ⁹⁷ 2/3