Extrusion device and process for extruding a semi-finished product made of elastomeric material

Abstract

The invention relates an extrusion device (100) for extruding a semi¬finished product made of elastomeric material, comprising an extrusion body (10) extending along a feeding direction (A) and a pump (20) arranged downstream of the extrusion body (10) along said feeding direction (A). The extrusion body (10) comprises a hopper (30) for loading an elastomeric material and an extrusion screw (50) extending along said feeding direction (A) and having an inlet portion (50a) arranged close to the hopper (30) and an exit portion (50b) arranged close to the pump (20). The extrusion body (10) also comprises a motorised roller (40) arranged at the inlet portion (50a) of the extrusion screw (50) and configured to receive the elastomeric material from the hopper (30) and feed it to the extrusion screw (30). The extrusion screw (50) has a length and a diameter such that the ratio between length and diameter is comprised between 4 mm and 8 mm. The invention also relates to an extrusion process carried out through the aforementioned extrusion device (100).

Claims

1. A process for extruding a semi-finished product, comprising: providing a forced feeding of an elastomeric material through a motorised roller to an extrusion screw aligned with the motorised roller along a feeding direction; and moving the elastomeric material through the extrusion screw along the feeding direction; wherein the extrusion screw has a length and a diameter such that a ratio between the length and the diameter is comprised between 4 and 8.

2. The process according to claim 1, wherein the ratio is equal to about 6.

3. The process according to claim 1, wherein the motorised roller rotates at a first peripheral speed, the extrusion screw rotates at a second peripheral speed, and the first peripheral speed is lower than the second peripheral speed.

4. The process according to claim 1, further comprising cooling the motorised roller through a cooling fluid.

5. The process according to claim 1, further comprising adjusting a temperature at the motorised roller to a value lower than a temperature at the extrusion screw.

6. The process according to claim 1, wherein the elastomeric material is fed with a flow rate from about 25 cc/sec to about 45 cc/sec.

7. The process according to claim 1, wherein the extrusion screw comprises a pointed end portion provided with at least one thread.

Description

(1) Further characteristics and advantages of the present invention will become clearer from the following detailed description of a preferred embodiment thereof, made with reference to the attached drawings. In such drawings:

(2) FIG. 1 is a schematic view of a longitudinal section of a preferred embodiment of an extrusion device in accordance with the present invention;

(3) FIG. 2 is an enlarged perspective view of a detail of the extrusion device of FIG. 1.

(4) In FIG. 1, reference numeral 100 indicates an extrusion device in accordance with the present invention.

(5) The extrusion device 100 is used in a process for building tyres for vehicle wheels in order to make a component of the tyre made of elastomeric material. Such a component can for example be the tread band, the sidewall, the so-called under-belt and/or under-layer, the liner, etc.

(6) The aforementioned component is obtained by depositing a semi-finished product 150 made of elastomeric material on a forming support 500 which can rotate about a rotation axis R.

(7) Once deposition is complete, the forming support 500 is moved away from the extrusion device 100 leaving space for a new forming support in order to make a component made of elastomeric material of another tyre.

(8) Preferably, the extrusion device 100 is used to make the tread band of “HP” or “UHP” tyres or of winter tyres.

(9) The semi-finished product 150 deposited on the forming support 500 is obtained by extrusion in the extrusion device 100 of an elongated element 120 made of elastomeric material.

(10) The extrusion device 100 comprises an extrusion body 10 defined by a substantially cylindrical hollow body having a longitudinal axis X.

(11) The extrusion body 10 is mounted on a support block 200 that is located in a position adjacent to that taken up by the forming support 500 on which the semi-finished product 150 is deposited.

(12) The elongated element 120 is fed to the extrusion body 10 through at least one feeding roller 211 and at least one moving roller 212 mounted on the support block 200 upstream of the extrusion body 10, i.e. on the opposite side with respect to the forming support 500.

(13) The extrusion body comprises an extrusion screw 50 extending along the longitudinal axis X and configured to move the elongated element 120 inside the extrusion body 10 along a feeding direction A parallel to the longitudinal axis X.

(14) The extrusion screw 50 comprises opposite end portions 50a, 50b, namely an inlet portion and an exit portion, respectively.

(15) As shown in FIG. 2, the exit portion 50b of the extrusion screw 50 comprises a pointed end portion 51 provided with a thread 52. In particular, the thread 52 is an extension of the thread provided on the remaining portion of the extrusion screw 50. In this way, the threaded portion of the extrusion screw 50 has a length greater than that of a conventional extrusion screw, which unlike the extrusion screw 50 has a pointed end portion without threads.

(16) With reference to FIG. 1, the extrusion screw 50 has a length L greater than 500 mm, preferably greater than 700 mm.

(17) The extrusion screw 50 has a length L lower than 1500 mm, preferably lower than 1300 mm.

(18) In the preferred embodiment of the present invention, the length L of the extrusion screw 50 is comprised between 500 mm and 1500 mm, more preferably between 700 mm and 1300 mm.

(19) The extrusion screw 50 has a diameter D lower than 250 mm, preferably lower than 220 mm, more preferably lower than 190 mm.

(20) The extrusion screw 50 has a diameter D greater than 100 mm, preferably greater than 120 mm, more preferably greater than 170 mm.

(21) In the preferred embodiment of the present invention, the diameter D of the extrusion screw 50 is comprised between 100 mm and 250 mm, more preferably between 120 mm and 220 mm, even more preferably between about 170 mm and about 190 mm.

(22) The ratio between length L and diameter D of the extrusion screw is comprised between 4 and 8, preferably between 5 and 7, for example equal to about 6.

(23) The extrusion screw 50 is driven in rotation by a motor group 55.

(24) For example, like in the exemplifying embodiment shown in FIG. 1, the motor group 55 is mounted on the support block 200 upstream of the extrusion body 10 and provides the rotation motion to the extrusion screw 50 through a reduction gear 56 also arranged upstream of the extrusion body 50.

(25) The extrusion body 10 comprises, at the inlet portion 50a of the extrusion screw 50, a hopper 30 for loading the elongated element 120 coming from the rollers 211, 212.

(26) Again at the inlet portion 50a of the extrusion screw 50, and downstream of the hopper with reference to the path followed by the elongated element 120, the extrusion body 10 comprises a motorised roller 40 configured to receive the elongated element 120 coming from the hopper 30 and feed it to the extrusion screw 50 along a feeding direction A parallel to the longitudinal axis X.

(27) The motorised roller 40 can be arranged under the hopper 30 and on a side of the inlet portion 50a of the extrusion screw 50, i.e. not aligned with the extrusion screw 50. Alternatively, the motorised roller 40 can be arranged upstream of the inlet portion 50a of the extrusion screw 50, under the hopper 30 and aligned with the extrusion screw 50.

(28) Preferably, the extrusion device 100 also comprises a cooling unit for cooling the motorised roller 40. Such a cooling unit can be one of the heat-control units 60, 65, 67, 68 discussed below. Alternatively, the motorised roller 40 can be cooled with a direct flow of water adjusted through a thermostatic valve.

(29) The motorised roller 40 is driven in rotation by a motor group 45 distinct from the motor group 55 that moves the extrusion screw 50.

(30) For example, like in the exemplifying embodiment shown in FIG. 1, the motor group 45 is mounted on the support block 200 on a side of the extrusion body 10 and provides the rotation motion to the motorised roller 40 through a reduction gear or a (belt or chain) transmission system, not visible in the attached figures.

(31) The provision of distinct motor groups for the extrusion screw 50 and the motorised roller 40 makes it possible to drive in rotation the motorised roller 40 at a different rotation speed from that of the extrusion screw 50. Preferably, the rotation speed of the motorised roller 40 is lower than that of the extrusion screw 50.

(32) In the preferred embodiments of the invention, the ratio between rotation speed of the motorised roller 40 and rotation speed of the extrusion screw 50 is comprised between about 0.2 and about 0.8.

(33) The extrusion device 10 comprises, downstream of the extrusion body 10, i.e. close to the exit portion 50b of the extrusion screw 50, a pump 20, preferably of the gear type, through which the elastomeric material exiting from the extrusion body 10 passes.

(34) In the example embodiment shown in FIG. 1, a nozzle 21 is associated with the pump 20 on the opposite side to the extrusion body 10. The elastomeric material pushed by the pump 21 is drawn through such a nozzle 21 to form a semi-finished product 150 having the desired shape and size, which is then deposited on the forming support 500.

(35) In an alternative embodiment (not shown) of the extrusion device 100 of the present invention, as member for drawing the elastomeric material, instead of the nozzle 21, it is possible to use a different device suitable for giving the semi-finished product 150 the desired shape and size (for example a pair of calender rollers).

(36) The extrusion device 100 also comprises a plurality of heat-control units each intended to adjust the temperature at a specific area of the extrusion device 100.

(37) In particular, a heat-control unit 60 associated with the extrusion body 10 at the hopper 30 is provided and a heat-control unit 65 associated with the extrusion body 10 at the extrusion screw 50 is provided, so as to be able to keep the area of the extrusion body 10 upstream of the extrusion screw 50 at a temperature lower than that of the area of the extrusion body 10 in which the extrusion screw 50 is provided. Such a provision is particularly useful in the case in which elastomeric materials with low viscosity are used.

(38) In this case, for example, the area of the extrusion body 10 at the hopper 30 is kept at a temperature comprised between about 25° C. and about 30° C., whereas the area of the extrusion body at the extrusion screw is kept at a temperature comprised between about 50° C. and about 90° C.

(39) In the exemplifying embodiment shown in FIG. 1, a heat-control unit 67 associated with the pump 20 and a heat-control unit 68 associated with the nozzle 21 are also provided. Downstream of the nozzle there a conveyor belt can be provided; in this case, a heat control of the nozzle 21 is not necessary.

(40) The heat-control units are controlled by an electric panel (not shown) also provided on the support block 200.

(41) Advantageously, the provision of the electric panel and of the heat-control units 60, 65, 67 and 68 on the support block 200 allows that in order to activate the extrusion device 100 it is necessary to simply connect it to the electrical power network and to the air and water feeding circuits.

(42) With the extrusion device 100 described above, it is possible to set at the outlet of the extrusion body 10 and upstream of the pump 20 pressure values comprised between about 30 bar and about 80 bar, preferably equal to about 50 bar. This makes it possible to ensure the desired consistency of flow rate for feeding flow rates comprised between about 25 cc/sec and about 45 cc/sec, even in the case of use of elastomeric materials with low viscosity and in the case of discontinuous extrusion processes.

(43) A preferred embodiment of an extrusion process for extruding a semi-finished product made of elastomeric material is now described. In particular this process can be carried out by the extrusion device 100 described above to make a component made of elastomeric material of a tyre for vehicle wheels.

(44) Once the forming support 500 has been positioned close to the extrusion device 100, the motor groups 45 and 55 are activated, thus driving the motorised roller 40 and the extrusion screw 50 in rotation at the desired rotation speed. In particular, the motorised roller 40 is preferably driven at a rotation speed lower than that of the extrusion screw 50.

(45) The heat-control units 60, 65, 67 and 68 are also activated, by adjusting the temperature of the various areas of the extrusion device 100 to the desired values. In particular, the area of the extrusion body 10 upstream of the extrusion screw 50 is brought and kept to a temperature lower than that of the area of the extrusion body 10 in which the extrusion screw 50 is provided.

(46) The elongated element 120 is taken from a collection bench and arranged manually on the rollers 211, 212, which are moved to bring the elongated element 120 inside the hopper 30.

(47) The elongated element 120 passes from the hopper 30 to the motorised roller 40 and from the latter is forcibly fed to the extrusion screw 50 and then to the pump 20 proceeding along the feeding direction A.

(48) During the feeding of the elongated element 120 towards the extrusion screw 50 the motorised roller 40 is cooled through a cooling fluid, preferably water.

(49) The elastomeric material coming out from the pump 20 passes through the nozzle 21 and is drawn to form the semi-finished product 150, which is deposited on the forming support 500.

(50) Once the deposition of the semi-finished product 150 on the forming support 500 is complete, the extrusion device 100 is deactivated, thus interrupting the extrusion process, and the forming support 500 is picked up and taken away from the extrusion device 100 to proceed with the subsequent tyre building steps.

(51) The extrusion process can start again, repeating the operations described above identically, following the positioning of a new forming support in the position previously occupied by the forming support 500, so as to build a component made of elastomeric material of another tyre also on this new forming support through deposition on such a forming support of the semi-finished product 120 obtained through the extrusion device 100.

(52) The present invention has been described with reference to some preferred embodiments. Different changes can be made to the embodiments described above, still remaining within the scope of protection of the invention, defined by the following claims.