Extruder and method for extruding cord reinforced tire components

Provided is an extruder and a method for extruding cord reinforced tire components, wherein the extruder has an extruder head with a die and a cord guide. The die is provided with a cross sectional profile that defines a first cross section of the extrusion material in the die, wherein the cross sectional profile has a profile height. The cord guide is arranged for guiding the cords into the die at a cord entry height. The extruder head is provided with first heating elements. The extruder has a control unit that is operationally connected to the first heating elements for generating an adjustable height temperature gradient in the extrusion material across the profile height to control swelling of the extrusion material relative to the cord entry height from the first cross section to a second cross section after the extrusion material leaves the die.

BACKGROUND

The invention relates to an extruder and a method for extruding cord reinforced tire components.

A known extruder comprises an extruder head for extruding cord reinforced tire components comprises a die defining a cross sectional profile through which an extrusion material is forced and a cord guide for guiding the reinforcement cords into the die. As soon as the reinforcement cords leave the cord guide and enter into the die, they are embedded into the extrusion material and are no longer guided by the cord guide. As the extrusion material is substantially uniform, the reinforcement cords are embedded in a constant position relative to the cross section of the tire component. An accurate positioning of the reinforcement cords with respect to the cross section of the tire component is critical to obtain the desired characteristics for the tire component. Usually, the reinforcement cords are prepositioned in the cord guide with respect to the cross section of the die within a tolerance of 5/100 millimeter.

It may be desirable to change the relative positioning of the reinforcement cords with respect to the cross section of the tire component to meet specific requirements for a specific batch of tire components. Currently, this requires replacing the extruder head with another extruder head having a different cord guide. As extruder heads are extremely expensive pieces of tooling, having a specific extruder head for each reinforcement cord position is very costly. Furthermore, interchanging extruder heads takes time and results in undesirable downtime of the extruder head.

It is an object of the present invention to provide an extruder and a method for extruding cord reinforced tire components, wherein the flexibility in positioning of the cords within the tire component can be improved.

SUMMARY OF THE INVENTION

According to a first aspect, the invention provides an extruder with an extruder head for extruding cord reinforced tire components, wherein the extruder head comprises a die for receiving an extrusion material and a cord guide for guiding cords into the die so that in use the cords are embedded in the extrusion material, wherein the die is provided with a cross sectional profile that defines a first cross section of the extrusion material in the die, wherein the cross sectional profile has a profile height, wherein the cord guide is arranged for guiding the cords into the die at a cord entry height with respect to the profile height, wherein the extruder head is provided with one or more first heating elements which are arranged to transfer heat into the extrusion material from a first side of the profile height, wherein the extruder further comprises a control unit that is operationally connected to the one or more first heating elements for generating an adjustable height temperature gradient in the extrusion material across the profile height to control swelling of the extrusion material relative to the cord entry height from the first cross section to a second cross section after the extrusion material leaves the die.

The adjustable height temperature gradient can cause a first viscosity and an associated first flow rate of the extrusion material in the bottom section that is unequal to a second viscosity and an associated second flow rate of the extrusion material in the top section. Through controlling the non-uniform viscosities and flow rates across the profile height, one can effectively control the swelling of the extrusion material from the first cross section to the second cross section after the extrusion material leaves the die. A lower viscosity allows the extrusion material to flow more easily through the die at a higher flow rate, while the velocity at which the cords are fed through the die remains constant. When the flow rate is higher than the cord velocity, the extrusion material will swell after leaving the die to a greater height with respect to the cord entry height. Therefore, one can control the final cord height in proportion to the height of the extrudate. The final cord height with respect to the height of the extrudate can be controlled to be proportionally different from the cord entry height with respect to the profile height. It is therefore no longer necessary to change extruder heads when a different cord position with respect to the cross section of the extrusion material is required. One can simply use the control unit in combination with the one or more first heating elements to adjust the range of the height temperature gradient to control the relative position of the cords with respect to the second cross section of the extrusion material.

JPH 06 231633 A discloses a known circumferential extrusion coating device with a crosshead for coating a rubber plastic lining cable. The circumferential flow channel of the cross head is divided into a plurality of zones, each with its own temperature regulating device. The temperature regulating device is controlled based on the measurements of a downstream flow temperature sensor. The goal of this known extrusion coating device is to provide an even coverage of the coating in the circumferential direction of the cable. Throughout JPH 06 231633 A, it is taught that the temperature distribution should be uniform and homogenous. JPH 06 231633 A explicitly discloses that any temperature gradient is lost and that thickness deviations in the radial direction, the circumferential direction and the longitudinal direction are prevented. JPH 06 231633 A does not disclose an extruder head for extruding cord reinforced tire components. Furthermore, JPH 06 231633 A does neither hint nor suggest a control unit that is arranged for purposely generating and controlling an adjustable height temperature gradient in the extrusion material across a profile height.

In an embodiment the one or more first heating elements are positioned at the die for transferring heat into the extrusion material from the first side of the profile height at the die. Preferably, the extruder is provided with flow channels that debouch into die, wherein the one or more first heating elements are positioned at the die downstream of the flow channels for transferring heat into the extrusion material from the first side of the profile height at the die. The position of the one or more first heating elements at the die allow for a better and/or direct control of the final cord height with respect to the cord entry height by generating a height temperature gradient at the die. It is noted that in the known crosshead of JPH 06 231633 A, the temperature regulating devices are located upstream of the die in the flow channels and, as such, are not arranged for accurately controlling the final cord height, if any, at the die.

In a preferred embodiment the height temperature gradient across the profile height is at least five degrees Celsius, and preferably at least ten degrees Celsius. Such a height temperature gradient can generate a noticeable difference in the amount of swelling of the extrusion material between the bottom section and the top section.

In an embodiment the one or more first heating elements comprises a plurality of the first heating elements distributed across the profile width. The plurality of first heating elements can more uniformly transfer the heat into the extrusion material from the first side.

In a highly versatile embodiment thereof the control unit is arranged for individually controlling the temperature of each of the plurality of first heating elements across the profile width. Thus, the heat being transferred into the extrusion material across the profile width from the first side can be accurately controlled.

In an embodiment the control unit is arranged for generating the height temperature gradient in the extrusion material across the entire profile width or substantially the entire profile width. The swelling of the extrusion material from the first cross section to the second cross section can thus be controlled across the entire profile width. Preferably, the control unit is arranged for generating the height temperature gradient uniformly in the extrusion material across the entire profile width or substantially the entire profile width. The extrusion material can thus be controlled to swell uniformly in the direction of the profile height across the entire profile width.

In a more elaborate embodiment the extruder head comprises one or more second heating elements which are arranged to transfer heat into the extrusion material from a second side of the profile height, opposite to the first side, wherein the control unit is operationally connected to the one or more first heating elements and the one or more second heating elements for generating the adjustable height temperature gradient in the extrusion material across the profile height to control the swelling of the extrusion material after the extrusion material leaves the die. One can simply use the control unit in combination with the one or more first heating elements and the one or more second heating elements to adjust the range of the height temperature gradient and/or the direction of increase of the height temperature gradient to control the amount and/or the direction of the swelling of the extrusion material.

In an embodiment the one or more second heating elements are positioned at the die for transferring heat into the extrusion material from the second side of the profile height at the die. Preferably, the extruder is provided with flow channels that debouch into die, wherein the one or more second heating elements are positioned at the die downstream of the flow channels for transferring heat into the extrusion material from the second side of the profile height at the die. The position of the one or more first heating elements and the one or more second heating elements at the die allow for a better and/or direct control of the final cord height with respect to the cord entry height by generating a height temperature gradient at the die. Again, it is noted that in the known crosshead of JPH 06 231633 A, the temperature regulating devices are located upstream of the die in the flow channels and, as such, are not arranged for accurately controlling the final cord height, if any, at the die.

In an embodiment the control unit is arranged for switching between a first mode in which the height temperature gradient is controlled to increase in temperature from the first side towards the second side and a second mode in which the height temperature gradient is controlled to increase in temperature from the second side towards the first side. The direction of the swelling can thus be directed towards the section at the side with the lowest viscosity, being the first side in the first mode and the second side in the second mode.

In an embodiment the one or more second heating elements comprises a plurality of the second heating elements distributed across the profile width. The plurality of second heating elements can more uniformly transfer the heat into the extrusion material from the second side.

In an embodiment the control unit is arranged for individually controlling the temperature of each of the plurality of second heating elements across the profile width. Thus, the heat being transferred into the extrusion material across the profile width from the second side can be accurately controlled.

In an embodiment each of the plurality of first heating elements is arranged opposite to one of the plurality of second heating elements in the direction of the profile height, wherein the control unit is arranged for generating the height temperature gradient between each set of two opposite heating elements. Thus, for each position across the profile width, the height temperature gradient can be generated by the heating elements on opposite sides of the profile height at that position.

In an embodiment the control unit is arranged for generating an adjustable width temperature gradient across the profile width in addition to the adjustable height temperature gradient in the profile height. The width temperature gradient can be particularly useful to ensure that the extrusion material reaches far ends of the profile width.

Preferably, the extruder head is provided with flow channels which are arranged to be in fluid communication with a supply of the extrusion material from a lateral end of the extruder head for receiving the extrusion material into the die parallel to the profile width, wherein the control unit is arranged for controlling the width temperature gradient so that it increases towards the distal end of the profile width with respect to the supply of the extrusion material. The extruder with a lateral supply of extrusion material is known as a ‘cross die’. The direction of increase of the width temperature gradient can be used to ensure that the extrusion material reaches the distal end of the cross sectional profile with respect to the extrusion material source.

In an embodiment the control unit is arranged for controlling the minimum temperature of the plurality of the first heating elements and the plurality of the second heating elements to at least eighty degrees Celsius, and preferably at least ninety degrees Celsius. The minimum temperature can corresponds to a maximum viscosity that is allowed for proper extrusion of the extrusion material.

In an embodiment the cross sectional profile comprises at least one tapering area, wherein the control unit is arranged for locally increasing the temperature in said at least one tapering area. The local increase in temperature can allow the extrusion material to flow more easily into tapering areas or other narrow areas of the cross sectional profile.

In an embodiment the extrusion in use cures to become an extrudate, wherein the cords are at a final cord height within the extrudate, wherein the extruder comprises a sensor for detecting the final cord height of the cords in the extrudate. The sensor can be used to validate the positioning of the cords within the extrudate.

Preferably, the sensor is an inductive sensor. The inductive sensor can electronically sense the proximity of the cords to the sensor, without damaging the extrudate.

Preferably the control unit is arranged for generating the height temperature gradient based on the measurements from the sensor. The feedback from the sensor to the control unit can improve the accuracy of the cord positioning and may even allow for in-line adjustments of the swelling.

In an embodiment the heat is arranged to be transferred conductively. The heat can thus be transferred indirectly, e.g. through the material of the extruder head into the extrusion material.

In a further embodiment the profile width extends in a horizontal or substantially horizontal direction, and/or wherein the profile height extends in a vertical or substantially vertical direction.

In an embodiment the cross sectional profile is elongate in the direction of the profile width with respect to a relatively small profile height.

In an embodiment the die has a cross sectional profile that is arranged to extrude sheets and/or films, in particular a tire tread.

According to a second aspect, the invention provides a method for extruding cord reinforced tire components with the use of the aforementioned extruder comprising an extruder head, wherein the extruder head comprises a die for receiving an extrusion material and a cord guide for guiding cords into the die, wherein the die is provided with a cross sectional profile that defines a first cross section of the extrusion material in the die, wherein the cross sectional profile has a profile height, wherein the extruder head is provided with one or more first heating elements, wherein the extruder further comprises a control unit that is operationally connected to the one or more first heating elements, wherein the method comprises the steps of receiving an extrusion material in the die, guiding cords from the cord guide into the die at a cord entry height with respect to the profile height so that the cords are embedded in the extrusion material, controlling the one or more first heating elements with the control unit to transfer heat into the extrusion material from a first side of the profile height for generating an adjustable height temperature gradient in the extrusion material across the profile height, and controlling swelling of the extrusion material relative to the cord entry height from the first cross section to a second cross section after the extrusion material leaves the die by adjusting the adjustable height temperature gradient.

In a preferred embodiment of the method the height temperature gradient across the profile height is at least five degrees Celsius, and preferably at least ten degrees Celsius.

In an embodiment the one or more first heating elements comprises a plurality of the first heating elements distributed across the profile width, wherein the method comprises the step of individually controlling the temperature of each of the plurality of first heating elements across the profile width.

In an embodiment the height temperature gradient is generated in the extrusion material across the entire profile width or substantially the entire profile width. Preferably, the height temperature gradient is generated uniformly in the extrusion material across the entire profile width or substantially the entire profile width.

In a more elaborate embodiment the extruder head comprises one or more second heating elements, wherein the control unit is operationally connected to the one or more first heating elements and the one or more second heating elements, wherein the method comprises the steps of controlling the one or more first heating elements and the one or more second heating elements with the control unit to transfer heat into the extrusion material from the first side and a second side opposite to the first side, respectively, of the profile height, for generating an adjustable height temperature gradient in the extrusion material across the profile height, and controlling the swelling of the extrusion material relative to the cord entry height from the first cross section to a second cross section after the extrusion material leaves the die by adjusting the adjustable height temperature gradient.

In an embodiment the method comprises switching the control unit between a first mode in which the height temperature gradient is controlled to increase in temperature from the first side towards the second side and a second mode in which the height temperature gradient is controlled to increase in temperature from the second side towards the first side.

In an embodiment the one or more second heating elements comprises a plurality of the second heating elements distributed across the profile width, wherein the method comprises the step of individually controlling the temperature of each of the plurality of second heating elements across the profile width.

In an embodiment each of the plurality of first heating elements is arranged opposite to one of the plurality of second heating elements in the direction of the profile height, wherein the method comprises generating the height temperature gradient between each set of two opposite heating elements.

In an embodiment the method comprises generating an adjustable width temperature gradient across the profile width in addition to the adjustable height temperature gradient in the profile height.

In an embodiment the method comprises the step of controlling the minimum temperature of the plurality of the first heating elements and the plurality of the second heating elements to be at least eighty degrees Celsius, and preferably at least ninety degrees Celsius.

In an embodiment the cross sectional profile comprises at least one tapering area, wherein the method comprises the step of locally increasing the temperature in said at least one tapering area.

In an embodiment the extrusion material cures to become an extrudate, wherein the cords are at a final cord height within the height of the extrudate, wherein the extruder comprises a sensor for detecting the final cord height of the cords in the extrudate, wherein the method comprises the step of controlling the height temperature gradient based on the measurements from the sensor.

The method provides for steps of using the aforementioned extruder and as such has the same advantages over the prior art as described before in relation to the corresponding features of the extruder.

In a particular embodiment of the method, the tire components are tire components of the group comprising breaker plies, body plies, cap strips, chafers or any other tire components with cords.

The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1A and 1Bshow an extruder1according to the invention, for extruding extrudate90in the form of cord reinforced tire components. The cord reinforced tire components are formed by embedding cords8, preferably steel or textile reinforcement cords, into an extrusion material9, preferably an elastomeric or rubber compound, during the extruding.

The extruder1comprises an extrusion material source2for supplying the extrusion material9in a supply direction S and an extruder head3for receiving the extrusion material9from the extrusion material source2in the supply direction S. The extruder head3comprises a die4for directing the extrusion material9from the supply direction S into an extrusion direction E while forming the extrusion material9into a desired shape of the extrudate as defined by the die4. The supply direction S is perpendicular to the extrusion direction E, such that the extrusion material9is supplied laterally or from a lateral end of the extruder1into the die4. A die4that is arranged for receiving the extrusion material9laterally is known as a ‘cross die’. The extruder1is provided with a cord guide5for guiding the cords8in a guide plane P in the extrusion direction E into the die4so that in use the cords8are embedded in the extrusion material9. The extruder1further comprises a control unit6and optionally a sensor7, for controlling parameters of the extrusion.

The extruder head3comprises a first extruder half31and a second extruder half32which, when mounted together as inFIGS. 1A and 1B, enclose the die4and the cord guide5with the guide plane P in between. The extruder halves31,32can be disassembled in a manner known per se to insert the cords8in between the extruder halves31,32at the cord guide5. In this example, the first extruder half31is located at the bottom of the extruder head3, and the second extruder half32is located at the top of the extruder head3or on top of the first extruder half31. The extruder head3comprises a first flow channel33in the first extruder half31and a second flow channel34in the second extruder half32. The flow channels33,34are in fluid communication with the extrusion material source2in the supply direction S, at a lateral end of the extruder head3, to direct separate flows of extrusion material9into the die4, as schematically shown with arrows F1and F2. The flow channels33,34extend laterally across the extruder head3to laterally distribute the extrusion material9, before debouching or merging into the die4from opposite sides of the guide plane P.

The die4is provided with an opening41having a cross sectional profile42that defines the shape of the extrusion material9in the die4. The cross sectional profile42has a profile width W and a profile height H1. In this example, the profile width W extends in a horizontal or substantially horizontal direction and the profile height H1extends in a vertical or substantially vertical direction. The cross sectional profile42is elongate in the direction of the profile width W and has a relatively small profile height H1with respect to the profile width W. As such, the die4is arranged for extruding sheets and/or films. The cross sectional profile42divides the extruder head3into a first side A below the profile height H1and a second side B above the profile height H1, in this example corresponding to the first extruder half31and the second extruder half32, respectively. In the die4, the extrusion material9has a first cross section C1. As shown inFIGS. 2A and 2Band inFIGS. 3A and 3B, the shape of the extrusion material9can be controlled to expand or swell from the first cross section C1inside the die4to a second cross section C2or a third cross section C3outside the die4that is larger in surface area than the first cross section C1. The heights of the expanded second cross section C2and the third cross section C3have been indicated with H2and H3, respectively. Swelling occurs when the extrusion material9is fed into the die4at a flow rate that exceeds the rate at which the cords8are fed into the die4in the extrusion direction E.

In this exemplary embodiment, the cross sectional profile42has a trapezoidal shape, comprising a straight or linear bottom edge43, a straight or linear top edge44extending parallel to the bottom edge43, and a first tapering or triangular area45and a second tapering or triangular area46connecting the bottom edge43to the top edge44at opposite ends of the profile width W. The shape of the exemplary cross sectional profile42is similar to and arranged for extruding the extrusion material9in the shape of a tire tread. It will however be evident to one skilled in the art that various cross sectional profiles are encompassed by the scope of the present invention.

The extruder head3is provided with one or more first heating elements, in this example a plurality of first heating elements35, and one or more second heating elements, in this example a plurality of second heating elements36. The first heating elements35extend in the first extruder half31and are arranged in direct contact with the material of the first extruder half31, usually metal, for transferring heat into the material of the first extruder half31, and ultimately, into the extrusion material9that is in direct contact with the first extruder half31at the first flow channel33and the die4. In particular, the one or more first heating elements are located downstream of the first flow channel33at or along the die4, for transferring heat into the material at the die4. As shown inFIG. 1Bthe first heating elements35extend in a part of the extruder head3that vertically below the die4. The second heating elements36extend in the second extruder half32and are arranged in direct contact with the material of the second extruder half32, usually metal, for transferring heat into the material of the second extruder half32, and ultimately, into the extrusion material9that is in direct contact with the second extruder half32at the second flow channel34and the die4. In particular, the one or more second heating elements are located downstream of the second flow channel at or along the die4, for transferring heat into the material at the die4. As shown inFIG. 1Bthe second heating elements36extend in a part of the extruder head3that vertically above the die4. Preferably, the heat is transferred conductively. However, other means of heat transfer, such as heat radiation, may also be applied. In this example, the first heating elements35and the second heating elements36are formed as integral channels within the respective extruder halves31,32for receiving a heating medium that is in direct contact with the respective extruder halves31,32. Alternatively, the first heating elements35and the second heating elements36may be formed as electrical heaters.

The first heating elements35and the second heating elements36are distributed parallel to or across the profile width W of the cross sectional profile42. Preferably, the first heating elements35and the second heating elements36are evenly distributed across the profile width W so that heat can be evenly transferred into the extruder halves31,32and ultimately the extrusion material9. Most preferably, for each of the first heating elements35, there is a second heating element36opposite to it in the direction of the profile height H1. As shown inFIG. 1Athe first heating elements35in the first extruder half31are arranged at a constant distance in the direction of the profile height H1to the bottom edge43of the cross sectional profile42, while the second heating elements36in the second extruder half32are arranged at a constant distance in the direction of the profile height H1to the top edge44and the tapering areas45,46. Consequently, the at least the second heating elements36which are positioned at the second side B above the tapering areas45,46are closer to the guide plane P and the first heating elements35across from the profile height H1.

The heat generated by each of the first heating elements35and the second heating elements36is adjustable in a manner that will be described in more detail hereafter.

As shown inFIG. 1B, the cord guide5is formed at the mating between the extruder halves31,32. The cord guide5comprises a plurality of known, mutually parallel guide channels (not shown) formed in one or both of the extruder halves31,32and arranged for guiding each of the cords8in the guide plane P towards the die4. The guide plane P extends between the extruder halves31,32at a cord entry height H4with respect to the bottom or the bottom edge43of the cross sectional profile42. The cord guide5extends up to the die4, but not into the die4. The cords8are introduced from the cord guide5into the die4at the cord entry height H4and are immediately embedded at said cord entry height H4into the extrusion material9flowing into the die4from both sides A, B of the profile height H1from the flow channels33,34. For the purpose of the invention, the cord entry height H4is expressed as a relative or proportional value, in particular as a percentage of the profile height H1. In this example, the cord entry height H4is approximately 50% of the profile height H1. The cord entry height H4and/or the guide plane P split the cross sectional profile42into a lower section47below the cord entry height H4and a upper section48above the cord entry height H4. Each section47,48receives a volume of extrusion material9, which volumes together embed the cords8from the opposite sides A, B of the guide plane P.

The control unit6, as shown inFIG. 1A, is operationally connected to each of the first heating elements35and each of the second heating elements36for individually controlling the heat or the temperature of the heat of each of the aforementioned heating elements35,36. The control unit6is specifically arranged for controlling the first heating elements35and/or the second heating elements36to generate an adjustable height temperature difference, delta or gradient G1, G2in the extrusion material9across the profile height H1, as schematically shown in temperature graphs inFIGS. 2A and 2BandFIGS. 3A and 3B. The height temperature gradient G1, G2causes a non-uniform viscosity in the extrusion material9across the profile height H1. More specifically, the height temperature gradient G1, G2causes the viscosity of the extrusion material9in one of the lower section47and the upper section48to be unequal to the viscosity of the extrusion material9in the other of the lower section47and the upper section48.

The method for extruding cord reinforced tire components with the use of the aforementioned extruder1is described with reference to a normal condition as shown inFIGS. 1A and 1B, a first mode as shown inFIGS. 2A and 2Band a second mode as shown inFIGS. 3A and 3B.

In the normal condition ofFIGS. 1A and 1B, the control unit6is arranged for setting each of the first heating elements35and each of the respective second heating elements36opposite to the first heating elements35in the direction of the profile height H1to the same or substantially the same temperature, so that the temperature in the extrusion material9across the profile height H1is substantially constant. This also applies to a condition in which the first heating elements35and the second heating elements36are inactive. The cords8entering the die4from the cord guide5at the cord entry height H4will be embedded in the extrusion material9flowing into the die4from both sides A, B of the guide plane P. In the normal condition, the viscosity in the extrusion material9is substantially constant across the profile height H1. As a result, the flows F1, F2of extrusion material9in the lower section47and the upper section48have an equal viscosity and thus flow with the same velocity and volumetric rate in the extrusion direction E. Therefore, the extrusion material9after leaving the die4does not swell or swells uniformly towards both sides A, B. As a result the cords8will substantially remain at the cord entry height H4, in this example at approximately 50% of the profile height H1.

In the first mode and the second mode, as shown inFIGS. 2A and 2BandFIGS. 3A and 3B, respectively, the control unit6is arranged to control the height temperature gradient G1, G2to ultimately affect and/or change the swelling of the extrusion material9after it leaves the die to an extent in which the relative position of the swollen, second cross section C2of the extrudate90relative to the cord entry height H4is lowered. To achieve this, the control unit6is arranged for generating an adjustable height temperature gradient G1, G2that increases from the second side B towards the first side A of the profile height H1. Specifically, the control unit6is either arranged for activating the first heating elements35only, or alternatively is arranged for setting first heating elements35to a higher temperature than the temperature of the respective second heating elements36. In each case, a disproportional amount of heat is transferred into the extrusion material9from the first side A of the profile height H1to increase the viscosity of the extrusion material9in the lower section47with respect to the extrusion material9in the upper section48.

The temperature height gradient G1, G2generates a non-uniform viscosity in the extrusion material9across the profile height H1. The flow F1of extrusion material9flowing at the lower section47has a lower viscosity than the other flow F2, resulting in a higher flow rate than the other flow F1in the upper section48. In particular, the velocity at which the extrusion material9flows through the lower section47in the extrusion direction E is higher than the velocity at which the cords8are fed in the same extrusion direction E. This results in a surplus volume of extrusion material9leaving the die4from the lower section47under a relatively high pressure and expanding in the direction of the first side A. The shape of the extrusion material9swells or expands from the first cross section C1in the die4towards the second cross section C2outside the die4and then cures to form the extrudate90.

As a result, the cords8extending at the cord entry height H4become situated at a final cord height H5with respect to the height H2of the extrudate90that is relatively or proportionally higher than the cord entry height H4with respect to the profile height H1. In particular, in this example, the final cord height H5is at approximately 60% of the height H2of the extrudate90with respect to the bottom (side A) of the extrudate90. In other words, the thickness of the extrusion material9in the extrudate90at the first side A has increased with respect to the thickness of the same extrusion material9when it was contained in the die4.

In the second mode, as shown inFIGS. 3A and 3B, the control unit6is arranged for generating an adjustable height temperature gradient G1, G2that increases from the first side A towards the second side B of the profile height H1. Specifically, the control unit6is either arranged for activating the second heating elements36only, or alternatively is arranged for setting second heating elements36to a higher temperature than the temperature of the respective first heating elements35. In each case, a disproportional amount of heat is transferred into the extrusion material9from the second side B of the profile height H1to increase the viscosity of the extrusion material9in the upper section48with respect to the extrusion material9in the lower section47.

As a result, the third cross section C3is expanded with respect to the first cross section C1in the direction of the second side B. As a result of the increased height H3of the second cross section C3, the cords8become situated at a final cord height H6with respect to the height H3of the second cross section C3that is relatively or proportionally lower than the entry cord height H4with respect to the profile height H1. In this example, the final cord height H6is only 40% of the height H3of the second cross section C3. In other words, the thickness of the extrusion material9above the final cord height H6is substantially thicker than the thickness of the extrusion material9that was above the cord entry height H4when the extrusion material9was still contained in the die4.

In each of the aforementioned modes, the control unit6is arranged for generating a local increase in temperature (not shown) or an additional, adjustable width temperature difference, delta or gradient G3, G4, and thus an additional, adjustable non-uniform viscosity, in the extrusion material9across the profile width W. The width temperature gradient G3, G4is schematically shown inFIGS. 2A and 2BandFIGS. 3A and 3Bin temperature graphs. Preferably, the control unit6is arranged to control the first heating elements35and the second heating elements36such that the width temperature gradient G3, G4increases from the extrusion material source2towards the distal end of the cross section profile42with respect to the extrusion material source2. As a result, the temperature of the second heating elements36in the first mode increases as a result of the width temperature gradient G3from a first temperature T1to a second temperature T2in the profile width W, while the temperature of the first heating elements35in the first mode increases as a result of the width temperature gradient G4from a third temperature T3to a fourth temperature T4. Similarly, the temperature of the first heating elements35in the second mode increases as a result of the width temperature gradient G3from the first temperature T1to the second temperature T2in the profile width W, while the temperature of the second heating elements36in the second mode increases as a result of the width temperature gradient G4from the third temperature T3to the fourth temperature T4.

The width temperature gradient G3, G4may be particularly useful to ensure that the extrusion material9reaches the distal end of the cross sectional profile42with respect to the extrusion material source2. The local increase in temperature (not shown) may result in the extrusion material9more easily flowing into the tapering areas45,46or other narrow areas of the cross sectional profile42.

Depending on the mode, the control unit6is arranged for the heating elements35,36on one side A, B of the profile height H1to the first temperature T1or, in the case of the aforementioned width temperature gradient G3, G4, to a temperature range between the first temperature T1and the second temperature T2, while setting the heating elements35,36at the other side A, B to a third temperature T3or, in the case of the aforementioned width temperature gradient G3, G4, to a temperature range between the third temperature T3and the fourth temperature T4. Each heating element35,36at the one side A, B is set to a temperature that is higher than the temperature of the respective heating element35,36opposite or vertically opposite to the heating element35,36in the direction of the profile height H1, at the other side A, B. The temperature difference between each of the first heating elements35and their respective opposite second heating elements36is preferably at least five degrees Celsius, and more preferably at least ten degrees Celsius. Similarly, the range of the height temperature gradient G1, G2in the extrusion material9across the profile height H1is preferably at least five degrees Celsius, and more preferably at least ten degrees Celsius.

The control unit6is arranged for generating the adjustable height temperature gradient G1, G2across the entire profile width W to ensure a uniform control of the swelling of the first cross section C1to the second cross section C2with respect to the cord entry height H4. In particular, the control unit6is arranged for controlling the first heating elements35and the second heating elements36as a first group and a second group offset with respect to the first group with the height temperature gradient G1, G2. The control unit6is arranged for adjusting the range or amount of the height temperature gradient G1, G2and/or the width temperature gradient G3, G4. The control unit6is further arranged for switching between the first mode and the second mode, thereby changing the direction of the height temperature gradient G1, G2.

In the exemplary modes as shown inFIGS. 2A and 2BandFIGS. 3A and 3B, the first temperature T1is eighty (80) degrees Celsius, the second temperature T2is one-hundred (100) degrees Celsius, the third temperature T3is eighty-five (85) degrees Celsius and the fourth temperature T4is one-hundred-and-twenty-five (125) degrees Celsius. The temperatures T1-T4are adjustable and can be variably controlled by the control unit6, depending on the type of extrusion material9, the desired cord height H2, H3and/or optimization of the distribution or swelling of the extrusion material9across the profile width W. In this exemplary embodiment, the first heating elements35and the second heating elements36are used to heat the extrusion material9up to a minimum temperature corresponding to a maximum viscosity that is allowed for proper extrusion of the extrusion material9. For an extrusion material9in the form of a typical elastomeric compound for tire components, the minimum temperature is at least eighty (80) degrees Celsius, and preferably at least ninety (90) degrees Celsius. Consequently, the first temperature T1of the second heating elements36in the first mode is at least equal to the aforementioned minimum temperature.

In the aforementioned modes, the control unit6is programmed based on given data about rubber compounds and their respective viscosities under various temperatures T1-T4. The actual cord height H2, H3may be experimentally validated by cutting extruded tire components to reveal the second cross section C2or the third cross section C3and the relative position of the cords8therein. The findings from the experimental validation can subsequently be used to improve the data and programming of the control unit6. Additionally or alternatively, the optional sensor7, as shown inFIG. 1B, can be provided at the exit of the die4where the extrusion material9exits the extruder head in the extrusion direction E. The sensor7is used to determine the actual cord height H2, H3of the cords8in the extrusion material9. In this example, the sensor7is an inductive sensor that electronically senses the proximity of the metallic cords8in the extrusion material8. The sensor7is operationally connect to the control unit6for sending signals indicative of the proximity of the cords8with respect to the sensor7to the control unit6. The control unit6can therefore determine if the actual cord height H2, H3with respect to the second or third cross section C2, C3corresponds to the desired cord height H2, H3and, if necessary, adjust the temperatures of the first heating elements35and the second heating elements36improve the actual cord height H2, H3with respect to the desired cord height H2, H3. This feedback between the sensor7and the control unit6can further improve the accuracy of the extruder1and may even allow for in-line adjustments of the swelling.