Method for managing the operation of an extruder following a stoppage of the extruder

Abstract

The invention relates to a method for managing the operation of an extruder (10), the extruder (10) generating an extruded product in the form of a strip, the extruder (10) comprising a hollow body (12) and at least one extrusion screw (14) mounted in the hollow body (12), the extruder (10) comprising two rollers for profiling the extruded product, the two profiling rollers (R1, R2) being mounted at the outlet (18) of the hollow body (12) of the extruder (10) so that the extruded product circulates between the two profiling rollers (R1, R2), the two profiling rollers (R1, R2) making it possible to drive the extruded product in a production direction when the extruder (10) is operating in production mode and delivering the extruded product continuously in the form of a strip. According to the management method, when the operation of the extruder (10) has stopped and just before resuming its operation in production mode, for a non-zero length of the extruded product to be driven in the opposite direction to the production direction by rotating the profiling rollers (R1, R2) in the opposite direction to the direction in which they drive the extruded product in the production direction.

Description

METHOD FOR MANAGING THE OPERATION OF AN EXTRUDER FOLLOWING A SHUTDOWN OF THIS EXTRUDER

[0001] The present invention relates to the management of the operation of an extruder following a stoppage of this extruder during an extrusion cycle or at the end of an extrusion cycle.

[0002] More specifically, the invention relates to extruders generating an extruded product in the form of a strip and whose outlet is equipped with two motorized rollers between which the extruded product in the form of a strip circulates.

[0003] For the purposes of tire manufacturing, various rubber compounds are produced and used in the form of strips.

[0004] A strip of rubbery mixture is for example produced using a screw extruder whose output is equipped with two motorized rollers allowing to manage the movements and profiling of the strip between the screw extruder and a downstream device using said strip generated by the extruder.

[0005] Often, the downstream device does not use the strip continuously but sequentially, resulting in intermittent operation of the extruder.

[0006] Furthermore, malfunctions can occur in the production line where the extruder is located and lead to extruder shutdowns.

[0007] During an extruder shutdown, a weakening of the extruded material strip was observed in the junction zone between the inside and outside of the extruder, typically between the two output rollers. This weakening of the strip in this junction zone is due to temperature differences between the inside and outside of the extruder and the release of tension in the extruded material.

[0008] The present invention aims to remedy this weakening of an extruded product in strip form when the extruder generating this extruded product is stopped.

[0009] To this end, the invention relates to a method for managing the operation of an extruder, the extruder generating an extruded product in the form of a strip, the extruder comprising a hollow body and at least one extrusion screw mounted in this hollow body, the extruder comprising two profiling rollers for the extruded product, the two profiling rollers being mounted at the outlet of the hollow body of the extruder so that the extruded product circulates between the two profiling rollers, the two profiling rollers enabling the extruded product to be driven in a direction of production when the extruder is in operation in production mode and delivers the extruded product continuously in the form of a strip.

[0010] In this management process according to the invention, during a stoppage of the operation of the extruder and just before resuming its operation in production mode, a non-zero length of the extruded product is driven in the opposite direction to the direction of production by rotating the profiling rollers in the opposite direction to the direction in which they drive the extruded product in the direction of production.

[0011] By reversing the direction of the strip, the portion of extruded product located in the junction zone between the product still inside the extruder and the product outside the extruder is reworked, remixed by the mechanical action of the profiling rollers, and reheated by its re-contact with one or more temperature-controlled parts. extruder temperature. Thus, the portion of the extruded product located in the junction zone regains mechanical characteristics almost identical to those of the product immediately after extrusion, making it less prone to breakage. Furthermore, this renewal of the mechanical characteristics of the extruded product in the junction zone also increases the acceleration and deceleration values ​​of the strip when the extruder resumes production mode, allowing it to reach its nominal operating speed more quickly and resulting in productivity gains.

[0012] When implemented, the management process according to the invention makes it possible to avoid a break in the extruded product when the extruder resumes operation in production mode, and therefore to limit the risks over the entire duration of use of the extruder.

[0013] Advantageously, but not necessarily, the invention may also provide that: - the length of extruded product driven in the reverse direction before the extruder resumes operation in production mode is between 0.1 cm and 10 cm, and preferably between 0.1 cm and 5 cm, - the length of extruded product driven in the reverse direction before the extruder resumes operation in production mode is driven in the reverse direction at a speed between 1 and 10 m / min, preferably between 4 and 6 m / min, - the length of extruded product driven in the opposite direction before the extruder resumes operation in production mode is driven in the opposite direction with an acceleration of between 0.01 m / s 2 and 0.1 m / s 2 , preferably between 0.04 m / s 2 and 0.06 m / s 2 , - the ratio between the linear speeds of the drive surfaces of the extruded product of the two profiling rollers is between 0.5 and 1.5, for example between 0.9 and 1.1, and preferably equal to 1, - the two profiling rollers are driven in rotation by at least one motor and synchronized in rotation, - when the extruder stops operating, the management process provides, in addition to reversing the production direction of a non-zero length of extruded product by rotating the profiling rollers, for stopping the operation of the conveying device located downstream of the profiling rollers before stopping the rotation of the profiling rollers, or for rotating the extrusion screw in the opposite direction to the direction in which it rotates to extrude the strip product, or for moving the extruded product located downstream of the profiling rollers in the opposite direction to the production direction using the conveying device located downstream of the profiling rollers, - It is planned to increase the length of extruded product in contact with one of the profiling rollers by means of a third roller positioned downstream of the profiling rollers in the direction of production, - the extruded product is a strip with a thickness between 1 and 10 mm, preferably between 2 and 6 mm, and a width between 10 and 100 mm, preferably between 25 and 60 mm, - the extruded product is a rubbery mixture, - The extruded product is a rubbery mixture intended for the manufacture of tires, - at least one part or element of the extruder being temperature-controlled, the non-zero length of extruded product that is driven in the opposite direction to the production direction by the The profiling rollers are re-mixed and brought back into contact with that part or element of the extruder which is temperature-regulated. - When the extruder resumes operation in production mode and after a non-zero length of the extruded product has been driven in the opposite direction to the production direction by the profiling rollers, the acceleration of the extruded product is between 0.01 and 0.5 m / s 2 , - a non-zero length of the extruded product is driven in the opposite direction to the direction of production by rotating the profiling rollers when the stop time of the extruder operation is greater than or equal to a few seconds.

[0014] Other features and advantages of the invention will become apparent in the following description. This description, given by way of example and not limitation, refers to the attached drawings in which: - [Fig. 1] is a schematic view of an extruder that can be used with the management process according to the invention, generating an extruded product in strip form, and operating in production mode, - [Fig.2] is a schematic view of an extruder that can be used with the management process according to the invention, generating an extruded product in the form of a strip, and during a shutdown of its operation, - [Fig.3] is a schematic view of an extruder that can be used with the management process according to the invention, generating an extruded product in the form of a strip, and after a non-zero length of the extruded product has been driven in the opposite direction to the direction of production by rotating the profiling rollers located at the exit of the extruder, - [Fig-4] represents a schematic view of an extruder that can be used with the management process according to the invention, generating an extruded product in strip form, in operation in production mode, and equipped with a third conveyor roller.

[0015] The invention relates to a method for managing the operation of an extruder during a shutdown, and more specifically just before resuming production. The extruder is said to be in production mode when it continuously delivers the extruded product in strip form.

[0016] The management process according to the invention can in particular find application in the field of manufacturing rubber compound in strip form, especially intended for the manufacture of tires.

[0017] For example, the extruded product is a rubbery mixture intended for the manufacture of tires and includes natural and / or synthetic rubber mixed with various reinforcing fillers: carbon black, silica, with plasticizing agents: oil, resins, with vulcanizing agents: sulfur, zinc oxide, and with anti-aging agents and other chemicals.

[0018] As illustrated in Figure 1, an extruder 10 capable of generating an extruded product P in the form of a strip B generally comprises a hollow body 12, also called a barrel, and an extrusion screw 14 mounted in this hollow body. Alternatively, the extruder 10 could also comprise two or more screws, interpenetrating or tangent, co-rotating or counter-rotating and mounted in a hollow body comprising a housing shaped to receive these screws.

[0019] For example, the hollow body 12 and the extrusion screw 14 extend lengthwise around a horizontal central axis AC. The hollow body 12 includes at least one inlet 16 for introducing the product to be extruded into the extruder.

[0020] The hollow body 12 includes at least one outlet 18, also called an arch, through which the product P is extruded. This outlet 18 is equipped with a die (not shown) preforming the extruded product P.

[0021] During extruder operation in production mode, product P is extruded by the extrusion screw 14 in a production direction SP from the inlet 16 to the outlet 18 of the extruder. More precisely, rotating the extrusion screw 14 in an extrusion direction SE allows product P to be extruded in the production direction SP from the inlet 16 to the outlet 18 of the extruder. The inlet 16 of the hollow body 12 and the extruder is located upstream of the extrusion screw 14 with respect to the production direction SP. The outlet 18 of the hollow body 12 and the extruder is located downstream of the extrusion screw 14 with respect to the production direction SP.

[0022] To shape the extruded product P into a strip B and to transport the extruded product P to another production device DP located downstream of the extruder 10 in the direction of production, the extruder 10 includes two profiling rollers R1, R2 for the extruded product P. The production device DP located downstream of the profiling rollers R1, R2 of the extruder 10 is, for example, a conveying device for the strip B to an assembly machine that uses the strip B to produce a tire blank. This conveying device is for example a roller conveyor including conveying rollers for strip B or a belt conveyor including a conveying belt for strip B. These two profiling rollers R1,R2 are mounted at the outlet 18 of the hollow body 12 of the extruder so that the extruded product P flows between the two profiling rollers R1,R2.Preferably, these two profiling rollers R1, R2 are mounted as close as possible to the outlet 18 of the extruder's hollow body 12. For example, the two profiling rollers R1, R2 have central axes A1, A2 that are parallel to each other and perpendicular to a vertical plane PV. For example, the two central axes A1, A2 of the two profiling rollers R1, R2 are fixed relative to the extruder. For example, the first profiling roller R1 is mounted above the second profiling roller R2. The space E between the two profiling rollers R1, R2 corresponds approximately to the thickness of the extruded product strip and ensures contact and adhesion between the upper surface SS and the lower surface SI of the extruded product strip B and the drive surfaces S1, S2 of the extruded product on the two profiling rollers R1, R2.When the extruder is operating in production mode and continuously delivering the extruded product P in strip form, the two profiling rollers R1, R2 drive the extruded product in the production direction SP. In the example illustrated in Figure 1, when the extruder 10 is operating in production mode, the first profiling roller RI, mounted above the second profiling roller R2, is driven in a counterclockwise direction SA around its central axis Al, while the second profiling roller R2 is driven in a clockwise direction SH around its central axis A2.

[0023] For example, the extruded product P shaped by the profiling rollers R1,R2 is a strip B with a thickness between 1 and 10 mm, preferably between 2 and 6 mm, and having a width between 10 and 100 mm, preferably between 25 and 60 mm.

[0024] During a shutdown of the extruder 10, as illustrated in Figure 2, a junction zone ZJ appears in the extruded product P between the product still inside the extruder and the product outside the extruder, which is susceptible to rupture when the extruder resumes production. This junction zone ZJ also includes the portion of the extruded product strip located between the two profiling rollers R1, R2. A bead of rubbery material can form in this junction zone ZJ due to the reduction in pressure applied to the extruded product P between the extruder 10 and the profiling rollers during the extruder shutdown.

[0025] The management method according to the invention aims to prevent the breakage of the strip of extruded product P in this junction zone ZJ when the extruder resumes operation in production mode.

[0026] To this end, and as illustrated in Figure 3, the management method according to the invention provides that, during a shutdown of the extruder and just before resuming operation in production mode, a non-zero length L of the extruded product P is driven in the opposite direction to the production direction SP by rotating the profiling rollers R1, R2 in the opposite direction to the direction in which they drive the extruded product in the production direction SP. This non-zero length L of the extruded product P driven in the opposite direction to the production direction SP corresponds substantially to the junction zone ZJ in the extruded product P between the inside and outside of the extruder. The reversal of the extruded product P advantageously eliminates the ridge of rubbery material that can form in the junction zone ZJ during an extruder shutdown.

[0027] In the example illustrated in Figure 3, when a non-zero length L of the extruded product P is driven in the opposite direction to the production direction SP, the first profiling roller RI mounted above the second profiling roller R2 is driven in a clockwise rotation SH around its central axis Al, while the second profiling roller R2 is driven in a counterclockwise rotation SA around its central axis A2.

[0028] For example, the length L of extruded product carried in reverse before the extruder resumes production operation is between 0.1 cm and 10 cm, and preferably between 0.1 cm and 5 cm. This length L of extruded product P carried in reverse before the extruder resumes production operation is limited by the capacity of the extruded product P material to stretch without breaking and by the quantity of product P that can be drawn back towards the extruder without causing a malfunction when production resumes. Therefore, to enable the implementation of the management method according to the invention, a minimum free length LL of extruded product P must be present between the profiling rollers and the production device DP located downstream of the extruder.This minimum free length LL of the extruded product P is intended to allow the extruded product P to be stretched when it is driven in the opposite direction by the profiling rollers. For example, in the case of a rubbery material intended for tire manufacturing, a free length LL at least 5 times greater than the length L of the extruded product P driven in the opposite direction is available between the profiling rollers R1, R2 and the production device DP.

[0029] The management process according to the invention involves mixing and reworking the extruded product P at a low speed and low acceleration when it is reverse-driven before the extruder resumes operation. For example, the non-zero length L of extruded product P, reverse-driven before the extruder resumes production mode, is reverse-driven at a speed between 1 and 10 m / min, preferably between 4 and 6 m / min. For example, the non-zero length L of extruded product P, reverse-driven before the extruder resumes production mode, is reverse-driven with an acceleration between 0.01 m / s 2 and 0.1 m / s 2 , preferably between 0.04 m / s 2 and 0.06 m / s 2 .

[0030] For example, when the extruder is in production mode, the extruded product P is moved at a speed between 50 and 200 m / min, with accelerations between 0.01 and 0.5 m / s 2 .

[0031] Advantageously, and in addition to preventing disruptions due to breakage of the extruded product strip P in the junction zone ZJ when the extruder resumes production, the mixing and working of the junction zone ZJ achieved by driving a non-zero length of extruded product in the opposite direction also increases the acceleration of the extruded product when the extruder resumes production. This allows the extruder, and more generally the production line in which it is installed, to reach its nominal operating speed more quickly. For example, when the extruder resumes production and after driving a non-zero length L of the extruded product in the opposite direction to the production direction SP by the profiling rollers, the acceleration of the extruded product P is between 0.1 and 0.5 m / s². 2 .

[0032] To prevent blistering of the extruded product after it has been driven in the opposite direction, the management process provides that the two profiling rollers R1, R2 are driven in rotation at substantially identical speeds. For example, the ratio between the linear speeds of the drive surfaces SI, 52 of the extruded product P of the two profiling rollers is between 0.5 and 1.5, for example between 0.9 and 1.1, and preferably equal to 1. To this end, the two profiling rollers R1, R2 are, for example, driven in rotation by the same motor and synchronized in rotation by means of a mechanical element for transmitting rotational motion, such as a chain, a belt, or a gear.

[0033] In cases where reverse drive of the extruded product P is more complex to implement due to the characteristics of the material constituting this extruded product P, the mechanical environment of the extruder, or a significant length of extruded product P to be reverse driven, the management method according to the invention may provide for: - stop the operation of the conveyor device located downstream of the profiling rollers before stopping the rotation of the profiling rollers R1, R2, or - rotate the extrusion screw 14 in the opposite direction to the extrusion direction SE in which it rotates to extrude the product P into strip B, or - move the extruded product P located downstream of the profiling rollers in the opposite direction to the production direction SP using the conveying device located downstream of the profiling rollers.

[0034] By stopping the operation of the downstream conveying device before stopping the rotation of the profiling rollers R1 and R2, the profiling rollers R1 and R2 deliver an excess length of product P that corresponds approximately to the length of extruded product P, which will then be conveyed in the opposite direction to the production direction. This delayed shutdown of the extruder is used for example when the extruded P product is difficult to stretch or if it is desired to limit its deformation.

[0035] By rotating the extrusion screw 14 in the opposite direction to the extrusion direction SE in which it rotates to extrude the product P into strip B, the objective is to reduce the compression of the extruded product P inside the extruder to promote the reintroduction of a certain amount of extruded product P inside the extruder when a non-zero length of the extruded product is driven in the opposite direction to the production direction.

[0036] By moving the extruded product P located downstream of the profiling rollers in the opposite direction to the production direction SP, for example in translation, using the conveyor located downstream of the profiling rollers, the aim is to avoid stretching the extruded product when a non-zero length of the extruded product is conveyed in the opposite direction to the production direction. In this case, the conveyor, its conveyor belt, or at least one of its conveyor rollers is mounted to move, for example in translation, relative to the extruder 10 and the profiling rollers.

[0037] To increase the length of the extruded product P in contact with one of the profiling rollers R1, R2, a third roller R3 can be provided, positioned downstream of the profiling rollers R1, R2 in the production direction SP. In the example shown in Figure 3, the third roller R3 increases the length of the extruded product P in contact with the second roller R2. This ensures the adhesion of the extruded product P to the second profiling roller R2 and thus guarantees that the extruded product P is driven by the profiling rollers in the production direction SP or in the opposite direction. For example, the third roller R3 is located below the two profiling rollers R1, R2 in a vertical direction. For example, the third roller R3 is located at a distance D between 5 and 50 cm from the two profiling rollers R1, R2. This third roller R3 is preferably mounted to rotate freely around its central axis A3.This third roller R3 is inserted between the profiling rollers R1, R2 and the production device located downstream.

[0038] Generally, an extruder 10 includes at least one temperature-controlled part or element. For example, the outlet 18 of the extruder's hollow body 12 is temperature-controlled. To this end, the outlet 18 includes one or more channels (not shown) for the circulation of a fluid used to regulate the temperature of the outlet 18 and thus of the extruded product P. For example, the fluid is used to maintain the extruder outlet 18, and therefore the extruded product P, at a desired temperature. Also, the non-zero length L of the extruded product P that is driven in the opposite direction to the production direction SP by the profiling rollers R1, R2 is remixed and brought back into contact with this temperature-controlled part or element of the extruder. Thus, the extruded product P is heated in the junction zone ZJ and is less likely to break when the extruder resumes operation in production mode.

[0039] The method for managing the operation of an extruder according to the invention is particularly intended for use when the extruder 10 is stopped for several tens of seconds or several minutes, for example at the end of an extrusion cycle or during a pause in an extrusion cycle. According to the invention, a non-zero length L of the extruded product P is driven in the opposite direction to the production direction SP by rotating the profiling rollers R1, R2 when the extruder's operating stoppage time is greater than or equal to a few seconds.

Claims

DEMANDS 1. A method for managing the operation of an extruder, the extruder generating an extruded product in the form of a strip, the extruder comprising a hollow body and at least one extrusion screw mounted in this hollow body, the extruder comprising two profiling rollers for the extruded product, the two profiling rollers being mounted at the outlet of the hollow body of the extruder so that the extruded product flows between the two profiling rollers, the two profiling rollers enabling the extruded product to be driven in a production direction when the extruder is operating in production mode and continuously delivers the extruded product in the form of a strip, the management method being characterized in that, during a shutdown of the extruder's operation and just before resuming its operation in production mode,A non-zero length of the extruded product is driven in the opposite direction to the production direction by rotating the profiling rollers in the opposite direction to the direction in which they drive the extruded product in the production direction.

2. Method of managing the operation of an extruder according to claim 1, wherein the length of extruded product driven in the reverse direction before resuming operation of the extruder in production mode is between 0.1 cm and 10 cm, and preferably between 0.1 cm and 5 cm.

3. Method of managing the operation of an extruder according to any one of the preceding claims, wherein the length of extruded product driven in the reverse direction before the resumption of operation of the extruder in production mode is driven in the reverse direction at a speed of between 1 and 10 m / min, preferably between 4 and 6 m / min.

4. A method for managing the operation of an extruder according to any one of the preceding claims, wherein the length of extruded product driven in the opposite direction before the extruder resumes operation in production mode is driven in the opposite direction with an acceleration of between 0.01 m / s 2 and 0.1 m / s 2 , preferably between 0.04 m / s 2 and 0.06 m / s 2 .

5. Method of managing the operation of an extruder according to any one of the preceding claims, wherein the ratio between the linear speeds of the drive surfaces of the extruded product of the two profiling rollers is between 0.5 and 1.5, for example between 0.9 and 1.1, and preferably equal to 1.

6. Method of managing the operation of an extruder according to claim 5, wherein the two profiling rollers are driven in rotation by at least one motor and synchronized in rotation.

7. A method for managing the operation of an extruder according to any one of the preceding claims, wherein, during a shutdown of the extruder, the management method provides, in addition to driving a non-zero length of extruded product in the opposite direction to the production direction by rotating the profiling rollers, that: - stop the operation of the conveying device located downstream of the profiling rollers before stopping the rotation of the profiling rollers, or - rotate the extrusion screw in the opposite direction to the extrusion direction in which it rotates to extrude the product into strips, or - move the extruded product located downstream of the profiling rollers in the opposite direction to the direction of production using the conveying device located downstream of the profiling rollers.

8. Method of managing the operation of an extruder according to any one of the preceding claims, wherein it is provided to increase the length of extruded product in contact with one of the profiling rollers by means of a third roller arranged downstream of the profiling rollers in the direction of production.

9. Method of managing the operation of an extruder according to any one of the preceding claims, wherein the extruded product is a strip having a thickness of between 1 and 10 mm, preferably between 2 and 6 mm, and having a width of between 10 and 100 mm, preferably between 25 and 60 mm.

10. Method of managing the operation of an extruder according to any one of the preceding claims, wherein the extruded product is a rubbery mixture.

11. Method of managing the operation of an extruder according to claim 10, wherein the extruded product is a rubbery mixture intended for the manufacture of tires.

12. Method of managing the operation of an extruder according to any one of the preceding claims, wherein, at least one part or element of the extruder being temperature regulated, the non-zero length of extruded product which is driven in the opposite direction to the direction of production by the profiling rollers is remixed and brought back into contact with that part or element of the extruder which is temperature regulated.

13. A method for managing the operation of an extruder according to any one of the preceding claims, wherein, upon resuming operation of the extruder in production mode and after a non-zero length of the extruded product has been driven in the opposite direction to the production direction by the profiling rollers, the acceleration of the extruded product is between 0.01 and 0.5 m / s 2 .

14. Method of managing the operation of an extruder according to any one of the preceding claims, wherein a non-zero length of the extruded product is driven in the opposite direction to the direction of production by rotating the profiling rollers when the stop time of the operation of the extruder is greater than or equal to a few seconds.

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