Method for extruding a semi-finished product made of elastomeric material

Abstract

The present invention relates to a method for extruding a semi-finished product made of elastomeric material, in which the elastomeric material is fed to an inlet channel (20a) of a gear pump (20) at an inlet pressure value and is dispensed through an outlet channel (20b) of the gear pump (20) at an outlet pressure value greater than the inlet pressure value. The method comprises detecting the outlet pressure value and adjusting the operation of the gear pump (20) based on the detection of the outlet pressure value to maintain a predetermined pressure difference between the outlet pressure and the inlet pressure. The above method is used in a method for building a tyre for vehicle wheels.

Description

Technical Field

[0001] This invention relates to a method for extruding semi-finished products made of elastomeric materials.

[0002] Preferably, the above method is used in a method for constructing a tire for a vehicle wheel. Background Technology

[0003] Tires for vehicle wheels typically include a carcass structure comprising at least one carcass ply formed by reinforcing cords bonded to an elastomeric material matrix. The carcass ply has end edges that engage with corresponding annular anchoring structures. These annular anchoring structures are arranged in a region of the tire commonly referred to as the “bead,” and each annular anchoring structure is typically formed by a substantially circumferential annular insert, with at least one filler insert applied at a radially outer position within the substantially circumferential annular insert. This annular insert, commonly referred to as the “bead core,” serves to firmly hold the tire in place within an anchor seat specifically provided in the wheel rim, thereby preventing the radially inner end flaps of the tire from disengaging from this anchor seat during operation.

[0004] A specific reinforcement structure can be provided at the tire bead, which has the function of improving the transmission of torque to the tire.

[0005] In tubeless tires, an airtight covering layer, often called a "liner," covers the inner surface of the tire.

[0006] The crown structure is connected in a radially external position relative to the carcass structure.

[0007] The crown structure includes a belt structure and a tread belt, the tread belt being located radially outward relative to the belt structure and being made of an elastomeric material.

[0008] The belt structure includes one or more belt layers that are radially juxtaposed with each other and have fabric or metal reinforcing cords that have a cross orientation and / or an orientation substantially parallel to the circumferential extension direction of the tire.

[0009] An elastomeric material layer, referred to as the "bottom belt," can be placed between the carcass structure and the belt structure. The function of this elastomeric material layer is to make the radial outer surface of the carcass structure as uniform as possible in order to facilitate the subsequent application of the belt structure.

[0010] An elastomeric material layer, referred to as the "bottom layer," can be arranged between the belt structure and the tread belt. This elastomeric material layer has suitable properties for achieving a stable connection between the tread belt and the belt structure.

[0011] Respective sidewalls made of elastomeric material are applied to the side surfaces of the carcass structure, each sidewall extending from one of the side edges of the tread strip to the corresponding annular anchoring structure.

[0012] Therefore, a tire used for a vehicle wheel includes multiple components made of an elastomeric material. As a non-limiting example, these components may include: tread belts, sidewalls, layers called underlay belts and / or underlays, linings, etc.

[0013] The aforementioned components can be made from a semi-finished product, which is made from an elastomeric material obtained through an extrusion process performed in an extrusion apparatus. The extruded semi-finished product is laid on a forming support. Depending on the component to be manufactured, the laying pattern can vary (e.g., based on adjacent coils and / or at least partially juxtaposed coils).

[0014] The term "elastomeric material" is used to refer to a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, such a composition also includes additives, such as crosslinking agents and / or plasticizers. Because a crosslinking agent is provided, this material can be crosslinked by heating to form the final product.

[0015] The phrase "semi-finished product made of elastomeric material" is used to refer to elongated components obtained according to the extrusion process of elastomeric material. Therefore, such semi-finished products are made solely of elastomeric material and typically have a flat shape.

[0016] The term "component made of elastomeric material" is used to refer to any component or part thereof of a tire obtained from the aforementioned semi-finished product made of elastomeric material.

[0017] The feeding direction of material within the reference extrusion unit is referred to as "downstream" and "upstream". Thus, assuming a feed direction from right to left, for example, a "downstream" position relative to any reference element means the position to the left of the reference element, while an "upstream" position means the position to the right of the reference element.

[0018] The term "thermal inertia" used to describe the structural unit of an extrusion apparatus is used to indicate the tendency of the structural unit to resist temperature changes; the greater the mass of the material constituting the structural unit, the greater the thermal inertia.

[0019] The “operating temperature” of a structural unit of an extrusion apparatus is used to indicate the temperature at which this structural unit is maintained during the extrusion process.

[0020] The term "output of a gear pump" is used to express the ratio between the actual volume of elastomeric material transported by the pump in one revolution and the internal free volume that the pump can theoretically transport in one revolution.

[0021] WO2012 / 001492, under the same applicant's name, describes an extrusion apparatus for extruding a semi-finished product made of an elastomeric material, used in a method for constructing tires for vehicle wheels. The extrusion apparatus comprises four distinct structural units. A first structural unit is defined by a hollow body having a longitudinal axis. The hollow body includes a loading hopper at its upstream end portion for loading the elastomeric material to be extruded. A second structural unit is defined by an extrusion screw rotatably mounted within the hollow body. The extrusion screw acts as a moving member for the elastomeric material within the hollow body. Specifically, the extrusion screw causes the elastomeric material to move from the upstream end portion of the hollow body to the downstream end portion of the hollow body. A third structural unit of the extrusion apparatus is defined by a gear pump assembly operatively associated with the hollow body at its downstream end portion. This gear pump assembly receives the elastomeric material conveyed by the extrusion screw and pushes it downstream under pressure. A fourth structural unit is defined by a nozzle associated with the gear pump assembly downstream of the gear pump assembly. The elastomeric material, propelled by a gear pump assembly, is stretched into a semi-finished form through this nozzle and then laid on the outer surface of the forming support.

[0022] JP2008229967 describes an extrusion apparatus comprising a screw and a gear pump for driving and conveying raw materials. The apparatus further includes: a detection region for the outlet pressure of the gear pump, wherein the outlet pressure at the outlet side of the gear pump is detected in the detection region; and a control region for the inlet pressure of the gear pump, wherein the inlet pressure at the inlet side of the gear pump is gradually controlled based on the outlet pressure, such that the outlet pressure of the gear pump is less than a pressure resistance value set at the outlet side of the gear pump at the start of extrusion.

[0023] In JP2019081288, JP2018030345, JP2012000949, JP2007237508,

[0024] Extrusion apparatus and methods are described in EP1638756 and EP3278951. Summary of the Invention

[0025] The applicant has observed that in extrusion processes used to construct tires for vehicle wheels, it is desirable for the elastomeric material discharged from the extrusion unit to have a continuous flow rate in order to avoid structural defects and / or discontinuities in the extruded semi-finished product (and therefore in parts made of the elastomeric material) and to allow the layup of the elastomeric semi-finished product on the forming support to be repeatable and identical to each other (and thus to have process reproducibility). To achieve the desired flow continuity, the gear pump needs to be continuously filled with the elastomeric material, which is typically achieved by adjusting the rotational speed of the extrusion screw to maintain a substantially constant pressure value upstream of the gear pump.

[0026] However, the applicant has observed that in an extrusion process performed by maintaining a constant inlet pressure into the gear pump, there may be undesirable variations in the flow rate and / or weight of the extruded semi-finished product during successive extrusion cycles of the same elastomer material and during a single extrusion cycle.

[0027] In attempting to identify the cause of this variation in the weight of the extruded semi-finished product, the applicant has observed a curve representing the pressure of the elastomeric material discharged from the gear pump over time (hereinafter also referred to as the "pressure curve") and has noted that the pressure of the elastomeric material discharged from the gear pump may vary during successive extrusion cycles of the same elastomeric material as well as during a single extrusion cycle.

[0028] The applicant believes that the pressure change of the elastomeric material discharged from the gear pump is determined by the viscosity change of the elastomeric material caused by the temperature change of the elastomeric material.

[0029] Specifically, the applicant believes that the pressure change of the elastomeric material discharged from the gear pump during successive extrusion cycles is determined by the fact that during the waiting time between two successive extrusion cycles, the elastomeric material downstream of the gear pump tends to cool due to the lack of mechanical action from the extrusion screw, thereby increasing its viscosity. The longer the waiting time, the greater the increase in viscosity. When a new extrusion cycle begins, the elastomeric material with higher viscosity causes an increase in pressure discharged from the nozzle, resulting in a pressure peak, which decreases as the extrusion cycle continues and the elastomeric material heats up due to the mechanical action of the extrusion screw.

[0030] The applicant has also noted that, during the same extrusion cycle, the pressure variation of the extruded semi-finished product is more pronounced when the initial viscosity of the elastomer material is higher. The applicant believes this is because it takes longer for the elastomer material to recover to a predetermined viscosity value (compared to the case of a lower initial viscosity value), thus requiring more time to reduce the pressure of the elastomer material discharged from the gear pump.

[0031] The applicant also believes that, during the same extrusion cycle, fluctuations in the pressure value of the extruded semi-finished product can be caused by the different thermal inertia of the structural units and small and localized changes in the composition of the elastomer material transported within the extrusion unit.

[0032] Upon further observation of the aforementioned pressure curves, the applicant has noted that, under the same conditions, the weight of the extruded semi-finished product is lower in an extrusion cycle that maintains a substantially constant inlet pressure to the gear pump and has a higher average pressure value, compared to the weight of the extruded semi-finished product found in an extrusion cycle with a lower average pressure value.

[0033] Therefore, the applicant has observed that pressure variations in the elastomer material discharged from the nozzle during the same extrusion cycle and during successive extrusion cycles result in weight variations per unit length of the extruded semi-finished product. Since the inlet pressure into the gear pump remains substantially constant, these pressure variations cause changes in the pressure difference between the gear pump inlet and outlet.

[0034] The applicant has demonstrated that changes in the pressure difference between the gear pump inlet and outlet cause changes in the instantaneous output of the gear pump. In particular, the applicant has demonstrated that an increase in the pressure difference between the gear pump inlet and outlet corresponds to a decrease in the instantaneous output of the gear pump and a consequent decrease in the amount (and therefore weight) of the extruded elastomer material, while a decrease in the pressure difference between the gear pump inlet and outlet corresponds to an increase in the instantaneous output of the gear pump and a consequent increase in the amount (and therefore weight) of the extruded elastomer material.

[0035] Reference JP2008229967 teaches to control the inlet pressure of the gear pump only at the beginning of the extrusion cycle and does not provide a solution to obtain a substantially constant extruded elastomer material in each extrusion cycle, while reference WO2012 / 001492 and other cited references do not provide a solution to the above problems.

[0036] However, the applicant has realized that since the flow rate of the elastomeric material discharged from the extrusion unit is substantially proportional to the instantaneous output of the gear pump, and since the instantaneous output of the gear pump is related to the pressure difference between the inlet and outlet of the gear pump, it is possible to obtain a substantially constant flow rate of the elastomeric material discharged from the extrusion unit while keeping the instantaneous output of the gear pump substantially constant. This result can be achieved by operating the gear pump such that the development of the elastomeric material pressure at the gear pump inlet substantially follows the development of the elastomeric material pressure at the gear pump outlet.

[0037] The applicant has finally discovered that by adjusting the pressure at the inlet of the gear pump according to the pressure at the outlet of the gear pump to maintain a predetermined difference between the inlet and outlet pressures, the amount of semi-finished product made of elastomeric material being laid remains substantially constant.

[0038] Therefore, in its first aspect, the present invention relates to a method for extruding a semi-finished product made of an elastomeric material.

[0039] Preferably, the elastomeric material is fed into the inlet channel of the gear pump.

[0040] Preferably, the elastomeric material has an inlet pressure value in the inlet channel.

[0041] Preferably, the elastomer material is dispensed through the outlet channel of a gear pump.

[0042] Preferably, the elastomer material has an outlet pressure value in the outlet channel.

[0043] Preferably, the outlet pressure value is greater than the inlet pressure value.

[0044] Preferably, the outlet pressure value is detected.

[0045] Preferably, the operation of the gear pump is adjusted based on the detection to maintain a predetermined pressure difference between the outlet pressure and the inlet pressure.

[0046] In a second aspect, the present invention relates to a method for constructing a tire for a vehicle wheel.

[0047] Preferably, a semi-finished product made of an elastomeric material is manufactured.

[0048] Preferably, a semi-finished product made of elastomeric material is laid on the forming support.

[0049] Preferably, in order to manufacture a semi-finished product made of an elastomeric material, an extrusion method according to the foregoing aspects is used.

[0050] The applicant believes that when the viscosity of the elastomer material increases, for example, due to the waiting time between one extrusion cycle and the next, and the outlet pressure at the gear pump outlet increases to a maximum reference value, the inlet pressure at the gear pump inlet can be increased to keep the pressure difference between the gear pump outlet and inlet equal to a predetermined pressure value. The specific instantaneous output of the gear pump and therefore the given flow rate of the elastomer material extruded per unit time correspond to such a pressure difference. When, for example, the viscosity of the elastomer material decreases due to heating by the extrusion screw, the outlet pressure at the gear pump outlet decreases, and the inlet pressure at the gear pump inlet can be reduced to ensure that the pressure difference between the gear pump outlet and inlet continues to be set to equal the predetermined pressure value. By continuously changing the inlet pressure at the gear pump inlet within a predetermined range of the inlet pressure, based on the outlet pressure at the gear pump outlet, the pressure difference between the gear pump outlet and inlet remains substantially constant and equal to the predetermined pressure value throughout the entire extrusion cycle duration, unaffected by possible, undesirable, and unpredictable changes in the viscosity of the elastomer material.

[0051] As described above, the specific instantaneous output of the gear pump and the given flow rate of the elastomeric material extruded per unit time correspond to this pressure difference. Such a flow rate therefore remains substantially constant throughout the entire extrusion cycle and in subsequent extrusion cycles. This constant flow rate allows for a substantially constant quantity (or weight) of the extruded semi-finished product and substantially repeatable process characteristics.

[0052] By providing inlet pressure variations within a predetermined inlet pressure range, it is also ensured that the gear pump is always properly fed under useful pressure conditions suitable for proper operation, thereby achieving operational integrity.

[0053] Only in exceptional circumstances and in any case of an extrusion time that is extremely short relative to the total extrusion time of the extrusion cycle, is a possible inlet pressure outside the predetermined inlet pressure range necessary to keep the amount of semi-finished product laid substantially constant during an extrusion cycle and in subsequent extrusion cycles.

[0054] In at least one of the foregoing aspects, the invention may have at least one of the preferred features described below.

[0055] Preferably, a predetermined minimum inlet pressure value is set before the elastomer material is fed into the inlet channel.

[0056] Preferably, a predetermined maximum inlet pressure value is set before the elastomer material is fed into the inlet channel.

[0057] Preferably, the predetermined range of the inlet pressure value is between the predetermined minimum inlet pressure value and the predetermined maximum inlet pressure value.

[0058] The predetermined minimum inlet pressure value can be set to the minimum pressure value that enables continuous filling of the gear pump given a specific elastomer material to be used.

[0059] Preferably, the predetermined minimum inlet pressure value is equal to or greater than 20 bar.

[0060] Preferably, the predetermined minimum inlet pressure value is equal to or greater than 30 bar.

[0061] Preferably, the predetermined minimum inlet pressure value is equal to or greater than 40 bar.

[0062] Preferably, the predetermined minimum inlet pressure value is equal to or greater than 50 bar.

[0063] Preferably, the predetermined minimum inlet pressure value is less than 70 bar.

[0064] The predetermined maximum inlet pressure value can be set to the maximum pressure value that will prevent the gear pump and / or the upstream extrusion screw from being damaged due to excessive feed pressure, given the specific gear pump to be used.

[0065] Preferably, the predetermined maximum inlet pressure value is equal to or less than 200 bar.

[0066] Preferably, the predetermined maximum inlet pressure value is equal to or less than 180 bar.

[0067] Preferably, the predetermined maximum inlet pressure value is equal to or less than 150 bar.

[0068] Preferably, the predetermined maximum inlet pressure value is equal to or less than 130 bar.

[0069] Preferably, the predetermined maximum inlet pressure value is greater than 120 bar.

[0070] Preferably, after the outlet pressure has been detected, a reference inlet pressure value is calculated as the difference between the outlet pressure value and the predetermined pressure difference.

[0071] Preferably, when the reference inlet pressure value is greater than the predetermined minimum inlet pressure value and less than the predetermined maximum inlet pressure value, the difference between the outlet pressure value and the inlet pressure value is set to be equal to the predetermined pressure difference.

[0072] Preferably, when the reference inlet pressure value is less than the predetermined minimum inlet pressure value, the inlet pressure is adjusted so that the inlet pressure value is set to be equal to the predetermined minimum inlet pressure value.

[0073] In this way, the gear pump is never fed with elastomeric material at a pressure lower than a predetermined minimum inlet pressure, thus allowing the gear pump to be fully and continuously filled with elastomeric material under every operating condition.

[0074] Preferably, when the reference inlet pressure value is greater than the predetermined maximum inlet pressure value, the inlet pressure is adjusted so that the inlet pressure value is set to be equal to the predetermined maximum inlet pressure value.

[0075] In this way, the gear pump is never fed with elastomeric material at a pressure higher than the predetermined maximum inlet pressure value, thus having a feed pressure that will not damage the gear pump and / or extrusion screw under each operating condition.

[0076] Preferably, the minimum outlet pressure value is predetermined.

[0077] Preferably, the maximum outlet pressure value is predetermined.

[0078] Preferably, the predetermined pressure difference is calculated based on the minimum outlet pressure value and the maximum outlet pressure value.

[0079] The applicant believes that an extrusion cycle can be performed by calculating a constant pressure difference based on the minimum and maximum outlet pressure values, wherein the inlet pressure at the gear pump inlet is not set to a value greater than the predetermined maximum inlet pressure value and lower than the predetermined minimum inlet pressure value for a considerable period of time during the extrusion cycle.

[0080] The time period refers to the period during which the reference inlet pressure value is greater than the predetermined maximum inlet pressure value and lower than the predetermined minimum inlet pressure value.

[0081] Preferably, the minimum outlet pressure value is predetermined by performing at least one reference extrusion cycle before feeding the elastomer material into the inlet channel.

[0082] Preferably, the maximum outlet pressure value is predetermined by performing at least one reference extrusion cycle before feeding the elastomer material into the inlet channel.

[0083] Preferably, the reference extrusion cycle is performed by the gear pump.

[0084] Preferably, the reference extrusion cycle is performed using the elastomer material.

[0085] In this way, the reference extrusion cycle can provide minimum and maximum outlet pressure values ​​that are similar to, even if not identical to, the minimum and maximum outlet pressure values ​​actually reached during an actual extrusion cycle.

[0086] The applicant believes that, in this manner, the instantaneous output of the gear pump is substantially constant over the entire extrusion cycle. This instantaneous output only differs from the constant value when the extrusion cycle exhibits an abnormal pressure profile, characterized by an outlet pressure peak at the gear pump outlet that is higher than the maximum outlet pressure of the reference extrusion cycle or lower than the minimum outlet pressure. Therefore, even when this occurs, it lasts only for a very short time (compared to the total duration of the extrusion cycle), thus allowing the significant periods of instability in the gear pump's instantaneous output to be minimized.

[0087] Preferably, if the type of elastomer material changes between one extrusion cycle and the next, a new reference extrusion cycle is performed to determine the minimum outlet pressure value and the maximum outlet pressure value.

[0088] Preferably, the predetermined pressure difference is calculated according to the formula DP = [(HEV + LEV) / 2] - [(PHIV + PLIV) / 2], where HEV represents the maximum outlet pressure value, LEV represents the minimum outlet pressure value, PHIV represents the predetermined maximum inlet pressure value, and PLIV represents the predetermined minimum inlet pressure value.

[0089] The applicant believes that there is a correlation between the maximum and minimum outlet pressure values ​​in any extrusion cycle, such that the maximum and minimum outlet pressure values ​​do not change independently of each other. The applicant has observed that, under the same elastomer material and nozzle conditions, successive extrusion cycles can have different pressure profiles, where an increase in the maximum outlet pressure value generally corresponds to an increase in the minimum outlet pressure value (not necessarily the same). Similarly, the applicant has observed that, under the same elastomer material and nozzle conditions, successive extrusion cycles can have different pressure profiles, where a decrease in the maximum outlet pressure value generally corresponds to a decrease in the minimum outlet pressure value (not necessarily the same).

[0090] The applicant believes that the formula DP=[(HEV+LEV) / 2]-[(PHIV+PLIV) / 2] makes it possible to calculate the predetermined pressure difference to be set, so that even for extrusion cycles whose pressure curves differ from those of the reference extrusion cycle, the instantaneous output of the pump remains substantially constant for most of the extrusion cycle.

[0091] Preferably, the outlet pressure is continuously and repeatedly detected during the feeding of the elastomer material.

[0092] Preferably, the reference inlet pressure value is calculated each time the outlet pressure is detected.

[0093] Preferably, the inlet pressure at the inlet of the gear pump is adjusted each time the outlet pressure is detected.

[0094] In this way, the inlet pressure at the gear pump inlet is continuously regulated by following the development of the pressure of the elastomeric material discharged from the gear pump.

[0095] Preferably, the calculation of the predetermined pressure difference is performed before dispensing the elastomer material.

[0096] Preferably, adjusting the inlet pressure includes adjusting the rotational speed of the extrusion screw that feeds the elastomer material into the gear pump. Attached Figure Description

[0097] Further features and advantages of the invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the accompanying drawings. In such drawings:

[0098] Figure 1 This is a schematic diagram of a longitudinal section of a preferred embodiment of an extrusion apparatus that can be used in the extrusion method according to the present invention;

[0099] Figure 2A and Figure 2B It means Figure 1 A block diagram of some components of the extrusion device;

[0100] Figure 3 This schematically and qualitatively illustrates how the speed of the extrusion screw changes. Figure 1 The development of inlet and outlet pressures at the inlet / outlet of the gear pump of the extrusion device over time, and the development of the flow rate of the elastomeric material extruded through the aforementioned extrusion device. Detailed Implementation

[0101] The present invention has a preferred embodiment in a method for constructing a tire for a vehicle wheel.

[0102] The aforementioned method preferably includes: constructing a carcass structure comprising at least one carcass ply and a pair of annular anchoring structures on a first forming support; and constructing a crown structure comprising at least one belt structure and a tread belt on a second forming support. The carcass structure and crown structure thus constructed are interconnected to obtain a green tire. This green tire is then transferred to a molding and vulcanizing line to obtain the final product.

[0103] Alternatively, the present invention has a practically applicable method for constructing tires for vehicle wheels that can specify the direct manufacture of individual tire components on a generally annular single forming support in a predetermined sequence.

[0104] In the above method, components made solely of elastomeric material (such as, for example, tread belts, sidewalls, layers called underlay belts and / or underlays, filler inserts for annular anchoring structures, liners, underlay liners, sidewall inserts, reinforcing inserts, etc.) are obtained from a semi-finished product 150 made of elastomeric material. This is achieved through... Figure 1 In an extrusion apparatus 10 of the type shown, an elastomer material is extruded to obtain such a semi-finished product 150, and the semi-finished product is laid on a forming support 200 while the forming support moves about its own axis of rotation R so as to preferably lay the product according to adjacent and / or at least partially juxtaposed coils, depending on the part to be manufactured.

[0105] The extrusion apparatus 10 includes an extrusion body 11 defined by a generally cylindrical hollow body having a longitudinal axis X.

[0106] The extrusion body 11 is preferably mounted on the support block 12, which is located in a position adjacent to the position occupied by the forming support 200 on which the semi-finished product 150 is laid.

[0107] Elastomer material is fed into the extrusion body 11, for example, by at least one feed roller 13 and at least one guide roller 14, which are mounted on the support block 12 upstream of the extrusion body 11, i.e., on the opposite side relative to the forming support 200.

[0108] The extrusion body 11 includes an extrusion screw 15 that extends along a longitudinal axis X and is configured such that the elastomeric material moves within the extrusion body 11 in a feed direction A parallel to the longitudinal axis X.

[0109] The extrusion screw 15 includes opposing end portions, namely an inlet portion 15a and an outlet portion 15b.

[0110] Preferably, a motor assembly 16 mounted on the support block 12 provides rotational motion to the extrusion screw 15. A reduction gear 17 may be provided between the motor assembly 16 and the extrusion screw 15.

[0111] The extrusion body 11 includes a loading hopper 18 at the inlet portion 15a of the extrusion screw 15 for loading elastomeric material from the feed roller 13.

[0112] Again at the inlet portion 15a of the extrusion screw 15 and downstream of the loading hopper 18 relative to the feed direction A, the extrusion body 11 may include a motorized roller 40 configured to receive elastomeric material from the hopper 18 and feed it to the extrusion screw 15 along the feed direction.

[0113] The motorized roller 19 may be arranged below the hopper 18 and next to the inlet portion 15a of the extrusion screw 15; in other words, the motorized roller is not aligned with the extrusion screw 15. Alternatively, the motorized roller 19 may be arranged upstream of the inlet portion 15a of the extrusion screw 15, below the hopper 18 and aligned with the extrusion screw 15.

[0114] The extrusion apparatus 10 includes a gear pump 20 located downstream of the extrusion body 11, in other words, near the outlet portion 15b of the extrusion screw 15, through which the elastomeric material discharged from the extrusion body 11 passes.

[0115] The gear pump 20 includes an inlet channel 20a and an outlet channel 20b. The elastomeric material enters the gear pump 20 through the inlet channel and exits the gear pump 20 through the outlet channel. The inlet channel 20a is located downstream of the extrusion body 11, in other words, near the outlet portion 15b of the extrusion screw 15.

[0116] exist Figure 1 In the illustrated embodiment, nozzle 21 is associated with gear pump 20 on the side opposite to extrusion body 11. Elastomer material propelled by gear pump 20 is stretched through nozzle 21 to form a semi-finished product 150 having the desired shape and size, which is then laid on forming support 200.

[0117] In an alternative embodiment (not shown) of the extrusion apparatus 10, different devices (e.g., a pair of calendering rolls) suitable for giving the semi-finished product 150 the desired shape and size may be used instead of the nozzle 21 as the stretching member of the elastomeric material.

[0118] The outlet channel 20b of the gear pump 20 is located upstream of the nozzle 21.

[0119] The extrusion apparatus 10 also includes a plurality of thermal regulation units, each of which is designed to regulate the temperature in a specific area of ​​the extrusion apparatus 10.

[0120] Preferably, a heat regulation unit 22 associated with the extrusion body 11 at the hopper 18 and a heat regulation unit 23 associated with the extrusion body 11 at the extrusion screw 15 are provided so that the operating temperature of the region of the extrusion body 11 located upstream of the extrusion screw 15 can be maintained differently from the operating temperature of the region of the extrusion body 11 in which the extrusion screw 15 is disposed.

[0121] exist Figure 1 In the illustrated embodiment, a thermal adjustment unit 24 associated with the gear pump 20 and a thermal adjustment unit 25 associated with the nozzle 21 are also provided.

[0122] Each thermal control unit can be activated to heat the corresponding area to a predetermined operating temperature that may also differ from each other.

[0123] The extrusion apparatus 10 includes a first pressure sensor 26 configured to detect the pressure of the elastomeric material in the inlet channel 20a of the gear pump 20.

[0124] The extrusion apparatus 10 also includes a second pressure sensor 27 configured to detect the pressure of the elastomeric material in the outlet channel 20b of the gear pump 20.

[0125] The extrusion device 10 is configured to first perform a reference extrusion cycle during which an elastomeric material of the same type as the elastomeric material used to lay the semi-finished product 150 on the forming support 200 is fed into the extrusion device 10.

[0126] This elastomer material is fed into the extrusion body 11 through the hopper 18.

[0127] The extrusion screw 15 rotates at a rotational speed suitable for obtaining the pressure required to produce the elastomeric material in the inlet channel 20a of the gear pump 20. This pressure is a function of known parameters, such as the properties of the elastomeric material (e.g., viscosity) and the operating temperature of the various zones of the extrusion unit 10 (temperature regulated by thermal control units 22, 23, 24, 25). These known parameters are the same as those used during the extrusion cycle of the elastomeric material to lay the semi-finished product 150 onto the forming support 200.

[0128] As an example, it is desirable to obtain a pressure of approximately 50 bar in the inlet channel 20a of the gear pump 20, which corresponds to a specific speed of the extrusion screw 15. The first pressure sensor 26 detects the pressure in the inlet channel 20a of the gear pump 20, thereby allowing the speed of the extrusion screw 15 to be changed if necessary, so that the elastomeric material reaches a pressure value equal to 50 bar in the aforementioned inlet channel 20a.

[0129] Preferably, this pressure value in the inlet channel 20a remains constant during the reference extrusion cycle.

[0130] The gear pump 20 is activated and the elastomeric material previously fed into the inlet channel 20a is pushed into the outlet channel 20b by the gear pump 20 so that it can be extruded through the nozzle 21.

[0131] The reference extrusion cycle is actuated to lay the desired amount of semi-finished product 150 onto the forming support 200 in time.

[0132] like Figure 2A As schematically illustrated, during the entire reference extrusion cycle, the second sensor 27 detects the pressure of the elastomeric material in the outlet channel 20b of the gear pump 20 and sends an RPS signal representing the detected pressure to the processing unit 30. The processing unit 30 determines and provides the maximum outlet pressure value HEV and the minimum outlet pressure value LEV reached by the elastomeric material at the outlet of the gear pump 20 during the reference extrusion cycle. These maximum outlet pressure values ​​HEV and LEV represent the upper and lower limits of the pressure curve of the reference extrusion cycle.

[0133] As an example, the applicant in Figure 1 Two reference extrusion cycles were performed in the extrusion apparatus of the type shown, in which two different elastomer materials were provided. In the first cycle, the maximum outlet pressure value HEV was 260 bar and the minimum outlet pressure value LEV was 150 bar. In the second cycle, the maximum outlet pressure value HEV was 290 bar and the minimum outlet pressure value LEV was 180 bar.

[0134] Subsequently, or before the reference extrusion cycle, obtain, calculate, or estimate the predetermined minimum inlet pressure value PLIV and the predetermined maximum inlet pressure value PHIV.

[0135] The predetermined minimum inlet pressure value PLIV is the minimum pressure value of the elastomeric material in the inlet channel 20a of the gear pump 20, which is sufficient to allow the gear pump 20 to be properly filled with the elastomeric material. Therefore, once the gear pump 20 in use and the type of elastomeric material that must be used in the extrusion cycle aimed at laying the semi-finished product 150 on the forming support 200 are known, the predetermined minimum inlet pressure value PLIV can be obtained, calculated, or estimated.

[0136] The predetermined maximum inlet pressure value PHIV is the maximum pressure value of the elastomeric material in the inlet channel 20a of the gear pump 20. Exceeding this maximum pressure value may damage the gear pump 20 and / or the extrusion screw 15 or cause it to malfunction under any circumstances. Therefore, once the gear pump 20 in use and the type of elastomeric material that must be used in the extrusion cycle intended to lay the semi-finished product 150 on the forming support 200 are known, the predetermined maximum inlet pressure value PHIV can be obtained, calculated, or estimated.

[0137] Typical values ​​for gear pumps used in extrusion methods for semi-finished products made of elastomeric materials, used in methods for constructing tires for vehicle wheels, are as follows: 150 bar as the maximum inlet pressure value PHIV and 30 bar as the minimum inlet pressure value PLIV.

[0138] The maximum outlet pressure value HEV, the minimum outlet pressure value LEV, the predetermined maximum inlet pressure value PHIV, and the predetermined minimum inlet pressure value PLIV are processed by the processing unit 30 to provide the predetermined pressure difference DP.

[0139] This processing can be performed by processing unit 30 (e.g., ... Figure 2A (Illustrative representation) Execution, execution by another processing unit (not shown), or manual execution by the operator.

[0140] In any case, the predetermined pressure difference DP is calculated according to the formula DP = [(HEV + LEV) / 2] - [(PHIV + PLIV) / 2], that is, by subtracting the average inlet pressure of the reference extrusion cycle from the average outlet pressure of the reference extrusion cycle.

[0141] At this point, an extrusion cycle aimed at laying the semi-finished product 150 on the forming support 200 for constructing a tire for a vehicle wheel can always be performed using the extrusion device 10 and the same elastomeric material used during the aforementioned reference extrusion cycle.

[0142] First, the areas of the extrusion unit 10 are temperature-regulated to reach the corresponding operating temperature (preferably equal to the temperature set in the reference extrusion cycle), and the forming support 200 is positioned close to the nozzle 21.

[0143] Then activate motor group 16.

[0144] The elastomeric material is fed into hopper 18 and from there into extrusion screw 15, and then into inlet channel 20a of gear pump 20 along feed direction A. The elastomeric material is then pushed into outlet channel 20b by gear pump 20 and then laid onto forming support 200 through nozzle 21.

[0145] like Figure 2B As illustrated in the diagram, during the movement of the elastomer material through the gear pump 20, the second sensor 27 detects the pressure of the elastomer material in the outlet channel 20b of the gear pump and sends a PES signal representing the detected outlet pressure value PE to the processing unit 30 (or another processing unit).

[0146] Therefore, processing unit 30 calculates the reference inlet pressure value PIR as the difference between the outlet pressure value PE and the predetermined pressure difference DP according to the formula PIR = PE - DP.

[0147] If the reference inlet pressure value PIR is greater than the predetermined minimum inlet pressure value PLIV and less than the predetermined maximum inlet pressure value PHIV, the extrusion screw 15 is actuated by the motor assembly 16 at a rotational speed such that the pressure generated in the inlet channel 20a of the gear pump 20 is equal to or as close as possible to the outlet pressure value PE minus the constant pressure value DP.

[0148] Preferably, the pressure generated in the inlet channel 20a is between 98% and 102% of the outlet pressure value PE minus the constant pressure value DP.

[0149] When the extrusion cycle is very similar to the reference extrusion cycle (because this is expected to occur normally with very few exceptions), the formula used to calculate the predetermined pressure difference DP ensures that the reference inlet pressure value PIR is always between the predetermined minimum inlet pressure value PLIV and the predetermined maximum inlet pressure value PHIV.

[0150] As an example, using the values ​​HEV=260 bar, LEV=150 bar of the first reference cycle illustrated above, and the typical values ​​PHIV=150 bar and PLIV=30 bar provided above, the formula for calculating the predetermined pressure difference DP gives a DP value equal to 115 bar. Assuming the extrusion cycle has a pressure curve similar to that of the reference extrusion cycle, the maximum outlet pressure value PE detected by the second outlet sensor 27 will be equal to 260 bar, and the minimum outlet pressure value PE detected by the second outlet sensor 27 will be equal to 150 bar. The reference inlet pressure value PIR, calculated as PIR=PE-DP, will be between 145 bar and 35 bar, and therefore will always be less than the predetermined maximum inlet pressure value PHIV and greater than the predetermined minimum inlet pressure value PLIV. It should be noted that the reference inlet pressure value PIR will be between the predetermined minimum inlet pressure value PLIV and the predetermined maximum inlet pressure value PHIV, even if the maximum outlet pressure value PE detected by the second outlet sensor 27 and the minimum outlet pressure value PE detected by the second sensor in the extrusion cycle are different from the above-mentioned maximum outlet pressure value and minimum outlet pressure value, for example, equal to 265 bar and 145 bar respectively.

[0151] Using the values ​​HEV=290 bar, LEV=180 bar of the second reference cycle illustrated above, and the typical values ​​PHIV=150 bar and PLIV=30 bar provided above, the formula for calculating the predetermined pressure difference DP yields a DP value equal to 145 bar. Assuming the extrusion cycle has a pressure curve similar to that of the reference extrusion cycle, the maximum outlet pressure value PE detected by the second outlet sensor 27 will be equal to 290 bar, and the minimum outlet pressure value PE detected by the second outlet sensor 27 will be equal to 180 bar. The reference inlet pressure value PIR, calculated as PIR=PE-DP, will be between 145 bar and 35 bar, and therefore will always be less than the predetermined maximum inlet pressure value PHIV and greater than the predetermined minimum inlet pressure value PLIV. It should be noted that the reference inlet pressure value PIR will be between the predetermined minimum inlet pressure value PLIV and the predetermined maximum inlet pressure value PHIV, even if the maximum outlet pressure value PE detected by the second outlet sensor 27 and the minimum outlet pressure value PE detected by the second outlet sensor 27 of the extrusion cycle are different from the above-mentioned maximum outlet pressure value and minimum outlet pressure value, for example, equal to 295 bar and 175 bar respectively.

[0152] If the reference inlet pressure value PIR is lower than the predetermined minimum inlet pressure value PLIV (due to an abnormal pressure curve in the extrusion cycle), the motor assembly 16 actuates the extrusion screw 15 at a rotational speed such that the pressure generated in the inlet channel 20a of the gear pump 20 is equal to or as close as possible to the predetermined minimum inlet pressure value PLIV.

[0153] Preferably, the pressure generated in the inlet channel 20a is between 98% and 102% of the predetermined minimum inlet pressure value PLIV.

[0154] If the reference inlet pressure value PIR is greater than the predetermined maximum inlet pressure value PHIV (due to an abnormal pressure curve in the extrusion cycle), the motor assembly 16 actuates the extrusion screw 15 at a rotational speed such that the pressure generated in the inlet channel 20a is equal to or as close as possible to the predetermined maximum inlet pressure value PHIV.

[0155] Preferably, the pressure generated in the inlet channel 20a is between 98% and 102% of the predetermined maximum inlet pressure value PHIV.

[0156] The detection of the outlet pressure value PE and the calculation of the reference inlet pressure value PIR are performed continuously throughout the extrusion cycle, preferably at predetermined and sufficiently short time intervals, to obtain continuous adjustment of the inlet pressure value in the inlet channel 20a of the gear pump 20.

[0157] For example, these predetermined time intervals are equal to each other and fall between 0.01s and 0.1s.

[0158] In this way, the inlet pressure value in the inlet channel 20a of the gear pump 20 substantially corresponds to the outlet pressure value PE in the outlet channel 20b of the gear pump 20 minus a predetermined pressure difference DP. The gear pump 20 therefore operates at a specific instantaneous output. This is in Figure 3 The diagram illustrates how, by properly controlling the speed of the extrusion screw 15 (the curve of the solid thin line), it can be ensured that after the initial transient, the inlet pressure of the gear pump 20 (the curve of the dotted line) follows the outlet pressure of the gear pump 20 (the curve of the dashed line) at a predetermined pressure difference, thereby obtaining a substantially constant flow rate of the extruded elastomer material (the curve of the solid thick line) and thus obtaining a specific instantaneous output of the gear pump 20.

[0159] The only deviation allowed by the constant instantaneous output of the gear pump 20 occurs when the reference inlet pressure value PIR in the inlet channel 20a is less than the predetermined minimum inlet pressure value PLIV or greater than the predetermined maximum inlet pressure value PHIV.

[0160] Once the semi-finished product 150 has been laid on the forming support 200, the extrusion unit 10 is stopped, thereby interrupting the extrusion process, and the forming support 200 is picked up and removed from the extrusion unit 10 to continue with the subsequent tire construction steps.

[0161] After the new forming support is positioned in the position previously occupied by the forming support 200, a new extrusion cycle can be started again, and the above operations can be repeated in the same way.

[0162] A reference extrusion cycle is performed when the type of elastomer material to be extruded changes, because the reference extrusion cycle does not need to be repeated before each new extrusion cycle that lays the semi-finished product on the same or different forming supports.

[0163] The applicant conducted tests in which the same extrusion apparatus was used and in which the same elastomer material was used to repeat several extrusion cycles.

[0164] According to the test, the first set of extrusion cycles was performed by setting a constant inlet pressure in the inlet channel of the gear pump, and the second set of extrusion cycles was performed by the extrusion method according to the invention.

[0165] In the first set of extrusion cycles, the extrusion cycles are executed with different time intervals between one cycle and the next. In the second set of extrusion cycles, the same time interval is set between one extrusion cycle and the next.

[0166] At the end of each extrusion cycle, the extruded elastomer material is weighed.

[0167] The tests highlight that, relative to the weight difference between extrusion cycles with more and less elastomer material in the first set of extrusion cycles, the weight difference between extrusion cycles with more and less elastomer material in the second set of extrusion cycles (according to the invention) is less than about 85%.

[0168] Such tests thus highlight that the method of the present invention enables the achievement of the desired constant flow rate during repeated extrusion cycles.

[0169] The invention has been described with reference to some preferred embodiments. Various modifications may be made to the above embodiments, all of which remain within the scope of protection of the invention as defined by the appended claims.

Claims

1. A method for extruding a semi-finished product made of an elastomeric material, the method comprising: An elastomer material is fed into the inlet channel (20a) of a gear pump (20), the elastomer material having an inlet pressure value in the inlet channel (20a); The elastomer material is dispensed through the outlet channel (20b) of the gear pump (20), the elastomer material having an outlet pressure (PE) value in the outlet channel (20b) that is greater than the inlet pressure value; Detect the outlet pressure (PE) value; The operation of the gear pump (20) is adjusted based on the detection to maintain a predetermined pressure difference (DP) between the outlet pressure (PE) and the inlet pressure; Predetermine the minimum outlet pressure value (LEV) and the maximum outlet pressure value (HEV). The predetermined pressure difference (DP) is calculated based on the minimum outlet pressure value (LEV) and the maximum outlet pressure value (HEV).

2. The method according to claim 1, wherein the method comprises: Before feeding the elastomer material into the inlet channel (20a), a predetermined minimum inlet pressure value (PLIV) and a predetermined maximum inlet pressure value (PHIV) are set. After the outlet pressure (PE) has been detected, a reference inlet pressure value (PIR) is calculated as the difference between the outlet pressure (PE) value and the predetermined pressure difference (DP).

3. The method according to claim 2, wherein, When the reference inlet pressure value (PIR) is greater than the predetermined minimum inlet pressure value (PLIV) and lower than the predetermined maximum inlet pressure value (PHIV), the difference between the outlet pressure value (PE) and the inlet pressure value is set to be equal to the predetermined pressure difference (DP).

4. The method according to claim 2, wherein, When the reference inlet pressure value (PIR) is lower than the predetermined minimum inlet pressure value (PLIV), the inlet pressure is adjusted so that the inlet pressure value is set to be equal to the predetermined minimum inlet pressure value (PLIV).

5. The method according to claim 2, wherein, When the reference inlet pressure value (PIR) is greater than the predetermined maximum inlet pressure value (PHIV), the inlet pressure is adjusted so that the inlet pressure value is set to be equal to the predetermined maximum inlet pressure value (PHIV).

6. The method according to claim 2, wherein, The predetermined minimum inlet pressure (PLIV) value is equal to or greater than 20 bar.

7. The method according to claim 2, wherein, The predetermined maximum inlet pressure (PHIV) is equal to or less than 200 bar.

8. The method according to claim 1, wherein, The minimum outlet pressure (LEV) and the maximum outlet pressure (HEV) are predetermined by performing at least one reference extrusion cycle before feeding the elastomer material into the inlet channel (20a).

9. The method according to claim 8, wherein, The reference extrusion cycle is performed by the gear pump (20).

10. The method according to claim 8, wherein, The reference extrusion cycle is performed using the elastomer material.

11. The method according to claim 2, wherein the method comprises: Predetermine the minimum outlet pressure value (LEV) and the maximum outlet pressure value (HEV). The predetermined pressure difference (DP) is calculated based on the minimum outlet pressure value (LEV) and the maximum outlet pressure value (HEV). The predetermined pressure difference (DP) is calculated according to the formula DP = [(HEV + LEV) / 2] - [(PHIV + PLIV) / 2], where HEV represents the maximum outlet pressure value (HEV), LEV represents the minimum outlet pressure value (LEV), PHIV represents the predetermined maximum inlet pressure value (PHIV), and PLIV represents the predetermined minimum inlet pressure value (PLIV).

12. The method according to claim 1, wherein, The outlet pressure (PE) is continuously and repeatedly monitored during the feeding of the elastomer material.

13. The method according to claim 1, wherein, Adjusting the inlet pressure includes adjusting the rotational speed of the extrusion screw (15) configured to feed the elastomeric material into the gear pump (20).

14. A method for constructing a tire for a vehicle wheel, the method comprising: Manufacturing a semi-finished product (150) made of elastomeric material; The semi-finished product (150) made of the elastomeric material is laid on the forming support (200); The manufacture of the semi-finished product (150) made of the elastomeric material includes performing the method according to any one of claims 1 to 13.

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