WO2020254180A1

WO2020254180A1 - Extrusion device for preforming rubber mixtures of a tire tread

Info

Publication number: WO2020254180A1
Application number: PCT/EP2020/066183
Authority: WO
Inventors: Pablo LE-BIHAN; Nicolas LECHEVALIER
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2019-06-21
Filing date: 2020-06-11
Publication date: 2020-12-24

Abstract

The invention is directed to an extrusion device (10) for preforming an electrically conductive rubber mixture and one or more electrically non-conductive rubber mixtures of a tire tread, so that the assembly containing the electrically conductive rubber mixture and the coextruded electrically non-conductive rubber mixtures is given the desired profile by the extrusion orifice (40a) of the blade (40).

Description

Title: Extrusion Device for Preforming Rubber Mixtures of a Tire Tread Technical Domain

The present invention is directed to an extrusion process carried out by an extrusion device that enables production of a tread intended for the production of a tire having several mixtures. Such a device preforms an electrically conductive rubber mixture and one or more electrically non-conductive rubber mixtures into a tire tread in order to remove static electricity from the vehicle.

Background

In the field of tire manufacturing, extruded profiles are known that minimize the power of electrostatic discharges from a tire tread during driving. A tire that incorporates such a tread has at least one layer of an electrically conductive rubber mixture, the layer having a higher conductivity than the rest of the tread which is formed of one or more electrically non- conductive rubber mixtures. This tread is obtained, in the uncured state, by extruding these two types of rubber mixtures in parallel by bringing the two types of mixtures from one or more extruders into contact at the downstream end of a common extrusion head (see, for example, the process disclosed by patent EP1103391 and the extruded profile disclosed by publication W02003/016077).

Several extrusion heads are proposed by the prior art for producing treads having at least one layer of an electrically conductive rubber mixture. An extrusion head disclosed by patent EP2308666, for example, includes a multi-part extrusion head that cooperates with two fixedly mounted extruders, one of the parts being rotatably mounted with a third extruder carried by it, and the three extruders being arranged to co-extrude the same tread. In addition, an extrusion head described by French application 18/53731 of the Applicant includes at least one mobile end part capable of receiving a first extruder and having an extractable part. The extractable part, which includes an extrusion screw, is mounted so as to be movable relative to a member forming a housing for the extractable part between a first position, where it extends into the housing, and a second position, where it extends entirely outside the housing to make the interior of the extrusion head accessible (for example, to facilitate maintenance).

The invention disclosed herein combines the benefits of the known extrusion heads with the benefits of preforming both types of mixtures. The disclosed invention anticipates methods of production that combine these benefits to ensure quality cohesion between the two types of mixtures from the start of an extrusion cycle. This cohesion is achieved at a high operating speed of the extrusion device of the invention.

Summary of the invention

The invention relates to an extrusion device for preforming an electrically conductive rubber mixture and one or more electrically non-conductive rubber mixtures into a tire tread. The device includes a plurality of main extruders fixedly mounted to a frame, each dedicated to a rubber mixture selected from electrically conductive rubber mixtures and electrically non- conductive rubber mixtures, and that operate together to co-extrude the same tire tread through a common extrusion head. Each main extruder includes a respective conduit within which an extrusion screw rotates. The extrusion head includes fixed parts that serve to mount the extruders and movable parts that define between them flow channels that direct the flow of the respective rubber mixtures from the main extruders to flow channels of the extrusion head leading to a common outlet. The device also includes a sub-assembly that moves between a closed state, in which the device performs extrusion cycles, and an open state, in which the device is at rest. The sub-assembly includes a secondary extruder dedicated to the extrusion of an electrically conductive rubber mixture and having a sheath in which an extrusion screw is rotatably arranged, the sheath being connected to a geared motor that is also part of the sub-assembly of the device. The sub-assembly also includes a cassette having a preform with internal orifices that direct each flow of a selected rubber mixture towards an extrusion orifice of a blade of the cassette that is aligned with the common outlet of the extrusion head in the closed state of the sub-assembly. The preform and the blade are joined with an armature within which a flow channel extends between an armature inlet proximate to the extrusion screw of the secondary extruder of the subassembly, and an armature outlet proximate to the preform that establishes fluid communication with the preform to permit continuous flow along the extent of the flow channel of the armature; whereby the assembly of the electrically conductive rubber mixture and the co-extruded electrically non-conductive rubber mixtures are provided in the desired profile by the extrusion orifice of the blade.

In certain embodiments, the extrusion head further includes a movable end part mounted movably with respect to the frame and having a sleeve for rotatably housing an extrusion screw of an additional extruder for introducing to the device one or more rubber mixtures selected from electrically conductive and electrically non-conductive rubber mixtures.

In certain embodiments, each electrically non-conductive rubber mixture includes at least one each of natural elastomers, synthetic elastomers and additives. In certain embodiments, the additives include silica.

In certain embodiments, each electrically conductive rubber mixture includes one or more carbon blacks.

In certain embodiments, the extrusion orifice is delimited by an upper wall and a lower wall to give the coextruded rubber mixtures the desired profile.

In certain embodiments, the sub-assembly of the device is moved in a linear or rotary manner. The invention also relates to a process for extruding a tire tread, including the following steps: -the step of providing the disclosed device with the sub-assembly in the closed state;

-the step of supplying an electrically non-conductive rubber mixture to at least one dedicated main extruder, this step including feeding the supplied electrically non-conductive rubber mixture to the preform;

-the step of supplying an electrically conductive rubber mixture to the secondary extruder of the device sub-assembly, which step includes feeding the electrically conductive rubber mixture to the flow channel of the armature to allow continuous flow along the extent of the flow channel of the armature between the secondary extruder of the sub-assembly and the preform; and

-the step of passing the assembly containing the electrically conductive rubber mixture and the electrically non-conductive rubber mixture(s) to the extrusion orifice of the blade so that the coextruded rubber mixtures are given the desired profile by the extrusion orifice.

In certain embodiments, the process further includes the step of moving the sub-assembly of the device from the closed state to the open state.

Other aspects of the invention will become evident from the following detailed description.

Brief Description of the Drawings

The nature and the various advantages of the invention will become more evident upon reading the following detailed description, together with the attached drawings, in which the same reference numbers designate identical parts everywhere, and in which:

Figure 1 represents a perspective view of a device for extruding a tire tread of the invention in a closed state.

Figure 2 represents a partial cross-sectional view of an extrusion head and a cassette of the extrusion device of Figure 1 in the P-plane.

Figure 3 represents an enlarged view of region A of Figure 2.

Figure 4 represents a perspective view of the extrusion device of Figure 1 in an open state.

Detailed Description Referring now to the figures, in which the same numbers identify identical elements, figures 1 to 4 represent an embodiment of an extrusion device (or "device") 10 of the invention. The device 10 is for preforming an electrically conductive mixture and one or more electrically non-conductive rubber mixtures to a tire tread to remove static electricity from the vehicle.

The device 10 includes a plurality of main extruders 12, 14, 16 the operate together to co extrude a single tire tread through a common extrusion head (or "extrusion head") 18. The device 10 also includes a frame 20 in relation to which the main extruders 12, 14, 16 are fixedly mounted and a known clamping means. As shown in Figures 1 to 3, the device 10 is in a closed state when the extrusion cycles start.

The extrusion head 18 of the device 10 includes fixed parts 24, 26, 28 that are used to mount the main extruders 12, 14, 16 (although three main extruders are shown in the figures, it is understood that two, three or more main extruders could be used). The extrusion head 18 also includes moving parts 30, 32, 34 that define between them flow channels that direct the flow of the respective rubber mixtures 36 from the main extruders 12, 14, 16. The flow channels lead to a common outlet 38 that is aligned with an extrusion orifice 40a of a blade 40

(described below) through which all the rubber mixtures are shaped together. This alignment is achieved in a closed state of the device 10 (represented by figures 1 to 3 and particularly by figure 1) when the extrusion cycles start.

In an embodiment, the main extruders 12, 14, 16 can be dedicated to the extrusion of electrically non-conductive rubber mixtures, each including natural and synthetic elastomers and additives (for example, silica). Alternatively, one or two main extruders 12, 14, 16 can be dedicated to the extrusion of electrically non-conductive rubber mixtures and the remaining main extruders can be dedicated to the extrusion of electrically conductive rubber mixtures.

In each embodiment, each main extruder is fed by one or more means for feeding the product to be extruded (not shown), and each includes a respective duct inside which an extrusion screw is driven in rotation (not shown) in a manner known to the person skilled in the art.

The extrusion head 18 further includes a movable end portion 42 movably mounted with respect to the frame 20. The movable end part 42 includes a sleeve 42a for rotatably accommodating an extrusion screw of an additional extruder (not shown). This additional extruder can be used to feed one or more electrically non-conductive rubber mixtures to the device 10. The extrusion head 18 can be selected from commercially available devices. For example, the extrusion head 18 may include features of the devices disclosed in publications JP2001-47494 and JP1566905.

The device 10 also includes a cassette 44 in which a preform 46 and a blade 40 are joined with an armature 48 of the cassette. The preform 46 includes internal orifices (not shown) that direct each respective flow of electrically non-conductive rubber mixture toward an extrusion port 40a of the blade 40. The extrusion port 40a is bounded by an upper wall 40a' and a lower wall 40a" to allow the assembly of all co-extruded mixtures (electrically conductive and electrically non-conductive) to achieve the desired profile. The preform 46 also includes the respective parts top preform 46a, middle preform 46b and bottom preform 46c that correspond to the flows of rubber mixtures.

The cassette 44 is part of a sub-assembly 50 of the device 10 that also includes a secondary extruder 52 dedicated to the extrusion of an electrically conductive rubber mixture having, in particular, one or more carbon blacks. The secondary extruder 52 includes a sleeve 54 in which an extrusion screw 56 is rotatably arranged. The sheath 54 is connected to a geared motor 58 that is also part of the sub-assembly 50. By movable, it is meant that this part can be brought between a closed state when the extrusion cycles start (as shown in Figure 1), and an open state in which the device 10 is stopped so as to permit maintenance and cleaning thereof (as shown in Figure 4).

The movement of the sub-assembly 50 can be realized in either a linear or rotary manner. The movement of the sub-assembly 50 is made by a known actuator (for example, a motor, a cylinder, and/or other hydraulic, pneumatic or equivalent means) to save extrusion cycle time by reaching a closing speed.

The armature 48 of the cassette 44 includes a flow channel 48a that extends between an armature inlet 48b in the vicinity of the extrusion screw 56 (and, in particular, in the vicinity of a screw tip 56a of the extrusion screw) and an armature outlet 48c in the vicinity of the preform 46 (and, in particular, in the vicinity of the top preform 46a). In the closed state of the device 10, the geared motor 58 rotates the extrusion screw 56 relative to the sheath 54 to feed the electrically conductive rubber mixture from the extrusion screw to the armature inlet 48b. A flange 60 or other known means can be used to provide a seal between the secondary extruder 52 and the armature 48. The armature outlet 48c, being in fluid communication with a dedicated internal orifice (not shown) in the top preform 46a, allows continuous flow along the length of the flow channel 48a of the armature 48. The electrically conductive rubber mixture is therefore preformed with the electrically non-conductive rubber mixtures at the extrusion port 40a of the blade 40.

During machine standstill phases, the device 10 can be easily maintained and cleaned. For example, referring to figure 4, where the device 10 is in the open state, the cassette 44 and its components (including all parts of the preform 46 and the armature) can be cleaned in order to remove residual material that could clog the ducts and orifices. Such maintenance prevents residues associated with co-extrusion of the tread, especially when changing mixtures. When initiating a cycle of an extrusion process, the device 10 is in the closed state as shown in Figures 1 to 3. In this state, the extrusion head 18 remains closed so that the moving parts of the extrusion head are kept locked against each other. In addition, in this state, the subassembly 50 of the device 10 is clamped so that the extrusion port 40a of the blade 40 is aligned with the common outlet 38 of the device (i.e., in the closed state of the device). The device 10 can then co-extrude a tread with good cohesion between the two types of rubber mixtures as soon as possible after the mixtures are fed to the blade 40.

As an example, a tire tread extrusion process includes the step of providing the device 10 (or providing a system that includes the device 10). The process further includes a step of supplying to each main extruder 12, 14, 16 (and also to the additional extruder housed in the sheath 42a in the production methods using this extruder), a mixture selected from electrically conductive rubber mixtures and electrically non-conductive rubber mixtures, this step including the supply of each rubber mixture to the preform 46. The process further includes a step of feeding an electrically conductive rubber mixture to the secondary extruder 52 of the sub-assembly 50, this step including feeding the electrically conductive rubber mixture along the extent of the flow channel 48a of the armature 48 to allow continuous flow of the mixture between the secondary extruder 52 of the sub-assembly 50 and the preform 46. The process includes a final step of passing the electrically conductive rubber mixture and the electrically non-conductive rubber mixture to the extrusion orifice 40a of the blade 40 so that the co extruded rubber mixtures are conferred in the desired profile by the extrusion orifice.

In an embodiment of carrying out the extrusion process, the method further includes the step of moving the sub-assembly 50 from the closed state to the open state. This step may be performed between extrusion cycles to perform routine maintenance and cleaning of device 10

At the end of an extrusion cycle carried out by the device 10, one or more tire treads are produced having qualities that permit the dissipation of the electrical charges induced by the rolling of the tires incorporating these treads. These qualities shall be ensured while also preserving other performance qualities of the tires incorporating the treads produced by the disclosed device. In the field of tire manufacturing, it is in fact required that the tire possess various performance characteristics (for example, reduced rolling resistance, better wear resistance, comparable grip in wet and dry conditions, estimated mileage, etc.). Subject to very high stresses during tire rolling, in particular repeated compression, bending or curvature variations, these composites must in a known manner satisfy many technical criteria, sometimes contradictory, such as uniformity, flexibility, flexing and compression endurance, tensile strength, wear and corrosion resistance, and maintain these performances at a very high level for as long as possible. To this end, the disclosed invention does not compromise other characteristics but also applies itself to the reliable manufacture of treads, the aim being the preparation and mastery of the placement of co-extruded rubber mixtures (electrically conductive and non-conductive) to ensure good cohesion between them. The device 10 is therefore suitable for processing a variety of rubber mixtures (electrically conductive and non- conductive) without reducing industrial productivity.

An extrusion cycle performed by the extrusion device of the invention can be effected by PLC control and can include pre-programming of control information. For example, a process setting can be associated with the selected mixtures that are supplied to the main extruders 12, 14, 16 and 42a. This process setting can also be associated with the parameters delimited by the upper wall 40a' and the lower wall 40a" of the extrusion port 40a. A monitoring system could be set up for all embodiments. At least part of the monitoring system may be provided in a portable device such as a mobile network device (for example, mobile phone, laptop computer, network-attached portable device(s) (including 'augmented reality' and/or 'virtual reality' devices), network-attached wearable clothing and/or any combination and/or equivalent). In certain embodiments of the invention, the device 10 (and/or a system incorporating the device 10) may receive voice commands or other audio data representing, for example, a request for the current status of an extrusion cycle. A generated response may be represented in an audible, visual, tactile (for example, using a haptic interface) and/or virtual or augmented manner.

The device 10 may be trained (or a system that incorporates the device 10 may be trained) to recognize values representative of a tread exiting the device (for example, the preformed profile parameters at blade 40) and to make a comparison with target values. This step may include the step of training the device to recognize non-equivalences between the compared values. Each training step includes a classification generated by self-learning means. This classification may include, without limitation, rubber mixture parameters (electrically conductive and non-el ectrically conductive), extrusion cycle times and expected values at the end of an extrusion cycle in progress.

The terms "at least one" and "one or more" are used interchangeably. Ranges that are presented as "between a and b" include both "a" and "b" values.

While specific embodiments of the disclosed device have been illustrated and described, it is understood that various changes, additions and modifications may be made without deviating from the spirit and scope of this disclosure. Consequently, no limitations should be imposed on the scope of the described invention except those set forth in the claims annexed hereto.

Claims

1. An extrusion device (10) for preforming an electrically conductive rubber mixture and one or more electrically non-conductive rubber mixtures into a tire tread, the device (10) comprising:

a plurality of main extruders (12, 14, 16) fixedly mounted to a frame (20), each dedicated to a rubber mixture selected from electrically conductive rubber mixtures and electrically non-conductive rubber mixtures, and that operate together to co-extrude a tire tread through a common extrusion head (18), each main extruder comprising a respective conduit within which an extrusion screw rotates;

the extrusion head (18) comprising fixed portions (24, 26, 28) for mounting the main extruders and movable portions (30, 32, 34) defining flow channels therebetween that direct the flow of the respective rubber mixtures from the main extruders to flow channels in the extrusion head leading to a common outlet (38); and

a sub-assembly (50) that moves between a closed state, in which the device performs extrusion cycles, and an open state, in which the device stops, the sub-assembly comprising: a secondary extruder (52) dedicated to extruding an electrically conductive rubber mixture and having a barrel (54) in which an extrusion screw (56) is rotatably disposed, the barrel (54) being connected to a geared motor (58) that is also part of the subassembly (50) of the device; and

a cassette (44) comprising a preform (46) with internal orifices that direct each flow of a selected rubber mixture to an extrusion orifice (40a) of a blade (40) of the cassette that is aligned with the common outlet (38) of the extrusion head in the closed state of the sub- assembly, the preform (46) and the blade (40) being joined with an armature (48) within which a flow channel (48a) extends between an armature inlet (48b) near the extruder screw of the secondary extruder (52) of the sub-assembly (50), and an armature outlet (48c) in proximity to the preform (46) that establishes fluid communication with the preform to allow continuous flow along the extent of the flow channel (48a) of the armature (48);

whereby the electrically conductive rubber mixture and the coextruded electrically non-conductive rubber mixtures are provided in the desired profile by the extrusion orifice (40a) of the blade (40).

2. The device (10) of claim 1, wherein the extrusion head (18) further comprises a movable end portion (42) movably mounted with respect to the frame (20) with a sleeve (42a) for rotatably housing an extrusion screw of a further extruder for feeding one or more electrically non-conductive rubber mixtures to the device.

3. The device (10) of claim 1 or claim 2, wherein:

each electrically non-conductive rubber mixture comprises at least one of natural elastomers, synthetic elastomers and additives; and

each electrically conductive rubber mixtures comprise one or more carbon blacks.

4. The device (10) of claim 3, wherein the additives comprise silica.

5. The device (10) of any one of the preceding claims, in which the extrusion orifice (40a) is delimited by an upper wall (40a¹) and a lower wall (40a") that confer the desired profile to an assembly containing the co-extruded rubber mixtures.

6. The device (10) of any one of the preceding claims, in which a movement of the sub- assembly (50) of the device is carried out in either a linear or a rotary manner.

7. A method of extruding a tire tread, comprising the following steps:

the step of providing a device (10) of any one of claims 1 to 6 with the sub-assembly (50) in the closed state;

the step of providing a mixture selected from electrically conductive rubber mixtures and electrically non-conductive rubber mixtures to at least one dedicated main extruder, which step comprises feeding each selected rubber mixture to the preform (46);

the step of providing an electrically conductive rubber mixture to the secondary extruder (52) of the sub-assembly (50) of the device, which step comprises feeding the electrically conductive rubber mixture to the flow channel (48a) of the armature (48) to allow continuous flow along the extent of the flow channel of the armature between the secondary extruder (52) of the sub-assembly (50) and the preform (46); and

the step of passing the assembly containing the electrically conductive rubber mixture and the electrically non-conductive rubber mixture to the extrusion orifice (40a) of the blade (40) so that the coextruded rubber mixtures are given the desired profile by the extrusion orifice.

8. The method of claim 7, further comprising the step of moving the sub-assembly (50) of the device from the closed state to the open state.