Patent Application
20090283203
The present invention relates to a process for building pneumatic tyres, and to an apparatus for building pneumatic tyres based on said process.
A tyre generally comprises a carcass structure including at least one carcass ply having end flaps in engagement with respective annular anchoring structures, each usually made up of at least one substantially circumferential annular insert to which at least one filling insert tapering radially away from the rotation axis is applied.
A belt structure comprising one or more belt layers is associated with the carcass structure at a radially external position, said belt layers being disposed in radial superposed relationship with respect to each other and to the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre.
A tread band is applied to the belt structure at a radially external position, which tread band is also made of elastomeric material like other semi-finished products constituting the tyre.
A so-called “under-layer” of elastomeric material having properties adapted to ensure steady fastening of the tread band itself, can be interposed between the tread band and the belt structure.
Respective sidewalls of elastomeric material are also applied to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads.
It is to be pointed out, to the aims of the present description, that by the term “elastomeric material” it is intended a compound comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, this compound further comprises additives such as a cross-linking agent and/or a plasticizer, for example. Due to the presence of the cross-linking agent, this material can be cross-linked through heating, so as to form the final manufactured product.
In tyres of the tubeless type, the carcass ply is internally coated with a so-called liner consisting of a layer of preferably butyl-based elastomeric material having optimal air-tightness features and extending from one side of the beads to the other.
In tyres of the run flat type or for other particular uses, the carcass structure can be further provided with auxiliary support inserts of elastomeric material, placed at an axially internal position relative to each of the sidewalls. These auxiliary support inserts usually referred to as “sidewall inserts” lend themselves to support the loads transmitted to the wheel in case of accidental deflation of the tyre to enable the vehicle to run on, under safety conditions.
In many known processes for manufacture of a tyre, the carcass structure and belt structure, as well as the tread band, sidewalls and any other elastomeric structural element, are made separately from each other in respective work stations, and then stowed in storage stations or warehouses from which they are subsequently picked up for mutual assembly along a tyre building line.
It is to be pointed out that in this context by “component of elastomeric material” of the tyre it is intended any part of elastomeric material of the tyre (tread band, sidewalls, liner, under-liner, fillers in the bead region, inserts at the sidewalls in run flat tyres, abrasion-preventing inserts, for example), or a portion thereof, or yet the assembly formed of two or more of said parts or portions thereof.
More recently also production processes have been developed in which, as described in WO 00/35666 for example in the name of the same Applicant, components of elastomeric material of the tyre are obtained through delivery of an elastomeric elongated element from an extruder, for suitable distribution of same on a toroidal support carrying the tyre being processed, while rotation of said tyre around its axis is being caused. Simultaneously, the toroidal support hanging from a robotized arm, is moved in front of the extruder to cause transverse distribution of the elongated element and thus form a plurality of circumferential coils therewith, which coils are disposed in axial side by side relationship and/or radial superposition and the orientation and mutual-superposition parameters of which are adjusted so as to control the thickness variations to be given to the component of elastomeric material during manufacture, based on a predetermined deposition scheme previously set on an electronic computer.
In U.S. Pat. No. 5,171,394, components of elastomeric material of a tyre are formed on a rigid drum by means of a positive-displacement extruder having an outlet port of small sizes placed close to the surface to which the elastomer is to be applied. The components of elastomeric material are formed by actuation of the extruder relative to the surface of the toroidal support driven in rotation, concurrently with delivery of the elastomeric material in the form of a continuous elongated element.
U.S. Pat. No. 6,955,734 discloses obtaining components of elastomeric material of a tyre by laying an elastomeric elongated element on a forming support, said elongated element being delivered by a system comprising a screw extrusion unit terminating at a gear pump, downstream of which an extrusion head having a delivery nozzle is arranged. Disposed between the delivery nozzle and the forming support is a pair of guide rollers the outer cylindrical surfaces of which are mutually spaced apart to define a gauged passage; thus the elongated element is gauged as to its thickness during passage through the clearance defined between the rollers, and also guided and applied against the forming support by one of the guide rollers, elastically urged against the forming support itself.
The Applicant has verified that the tyres obtained by the above described building methods can have geometric and structural faults bringing about adverse effects both in terms of production waste and as regards the product quality. In particular, in spite of the attention and expedients adopted during manufacture of the individual components of elastomeric material through spiralling operations, the geometric and size accuracy of same often appears to be unsatisfactory. This problem is particularly apparent with reference to those components of elastomeric material that, after building of the tyre, must be submitted to a moulding operation of the so-called “imposed-volume” type, in which the tyre or given parts of same, the beads for example, are enclosed in a moulding cavity substantially having the same volume as that taken up by the material constituting the part itself submitted to moulding. In fact it has been verified that under this circumstance, small amounts of excess material in the component of elastomeric material submitted to moulding can prevent a correct closure of the mould and allow migration of the elastomeric material towards different tyre regions (in a radially external direction for example in the case of the beads), while material lacks of small amounts give rise to clear geometric and structural faults on the finished product.
The Applicant has also noticed that accuracy in working the components of elastomeric material is affected by different concurrent factors in the extrusion process, such as oscillations in the temperature and viscosity values of the elastomeric material within the strainer, wear of the inner members of the extrusion apparatus, pressure variations within the extrusion apparatus during the starting and stopping steps, and yet other factors that can hardly vary in a predictable and controllable manner.
In accordance with the Applicant's perception, all these variables cause as the final effect, more or less sudden important variations in the cross-section sizes of the elongated element applied to the forming support.
In accordance with the present invention, the Applicant has found the possibility of overcoming the above described problems by providing a pair of counter-rotating shaping rollers disposed downstream of the strainer for carrying out shaping of a continuous elongated element, and by executing during working, a constant control of the volumetric flow rate of the material passing between the shaping rollers, to modify the linear feeding speed of the material to the rollers in response to possible flow rate variations, so as to keep the elongated-element section variations within a predetermined range.
In more detail, in a first aspect the present invention relates to a process for building tyres, comprising the step of assembling components of elastomeric material on a forming support, in which at least one of said components of elastomeric material is manufactured by the steps of:
In accordance with a second aspect of the present invention it is proposed an apparatus for building tyres comprising:
When the monitoring device detects a flow rate that is lower than a predetermined minimum threshold, an increase in the feeding speed of the continuous thread element is carried out, said feeding speed being reduced when a flow rate higher than a pre-set maximum threshold is detected. Thus a careful control of the quantity of elastomeric material applied to the forming support is obtained. Consequently, a greater geometric and size accuracy of the individual components of elastomeric material of the tyre formed by deposition of the elongated element can be obtained.
Use of counter-rotating rollers to carry out forming of the elongated element further allows a continuous thread element of circular or approximately circular section to be extruded. Thus a more fluent and direct outflow of the elastomeric material can be provided from the outlet port of the extruder thus restricting the stresses usually imposed to the elastomeric material in the extruder's exit die that in the known art has important section variations to cause shaping of the elongated element in its final conformation. Thus all problems connected with wear of the surfaces of the dies used in the known art are eliminated as well as the drawbacks concerned with formation of deposits and incrustations within the die itself. It is also possible to reduce the temperature of the elastomeric material within the die, so that overheating and/or cross-linking initiation in the stopping steps of the laying operation does not occur.
Feeding of the elastomeric material to the shaping rollers can be carried out directly by the extruder, or by a pair of rollers or other driving devices operating downstream of the extruder itself. In this case, a storage step of the elastomeric thread element can be advantageously carried out at a storage length included between the extruder and the shaping rollers, so as to enable greater cooling and size stabilisation of the continuous thread element before it is disposed between the shaping rollers.
Shaping is preferably carried out by conducting the continuous thread element through a shaped clearance defined between the shaping rollers and preferably engaging said continuous thread element substantially on the whole cross-section outline extension of same, so as to give the formed elongated element a desired cross-section outline, preferably of trapezoidal form.
In a preferred embodiment, the flow rate of the elastomeric material between the shaping rollers is monitored by cyclically detecting the cross-section area of the continuous thread element immediately upstream of the shaped clearance, or the width of the elongated element immediately downstream of the shaped clearance. In the last-mentioned case, during shaping, at least one side edge of variable size depending on the flow rate of the elastomeric material between the shaping rollers can be advantageously formed on the elongated element, so as to increase accuracy and reading sensitivity of the elongated element width.
The feeding speed of the thread element towards the shaping rollers can be advantageously adjusted by modifying the delivery speed of the elastomeric material through the extruder, by intervening on the rotation of a feeding screw being part of said extruder and/or of a positive-displacement pump, of the gear type for example, possibly disposed upstream of an outlet port of the extruder.
Alternatively, the feeding speed of the thread element towards the shaping rollers is adjusted by acting on a driving device downstream of the extruder.
Preferably, application of the elongated element onto the forming support takes place by at least one roller or other applicator members operatively supported with respect to the shaping rollers and acting in thrust relationship towards the forming support. This applicator roller can advantageously be spaced from the shaping rollers, so that the latter do not hinder movement of the applicator roller on the surface of the forming support.
Further features and advantages will become more apparent from the description of a preferred, but not exclusive, embodiment of a process and an apparatus for building tyres, in accordance with the present invention. This description will be set out hereinafter with reference to the accompanying drawings, given by way of non-limiting example, in which:
With reference to the drawings, a plant for producing tyres comprising a building apparatus 2 according to the present invention has been generally identified with reference numeral 1.
Plant 1 is intended for manufacture of tyres 3 (
In run flat tyres or tyres intended for particular uses, auxiliary support inserts (not shown) can be further provided, of the type usually referred to as “sidewall inserts” for example, applied close to the sidewalls internally of the carcass ply 4 or between two paired carcass plies 4, and/or at an axially external position to said at least one carcass ply 4.
The building apparatus 2 may comprise a plurality of building stations 11, 12, 13, 14, 15, each being for example provided to form one component of the tyre 3 being processed directly on a forming support 16 preferably of toroidal conformation, having a forming surface 16a with a conformation corresponding to the inner conformation of the tyre 3 itself when building has been completed. Alternatively, one or more components of the tyre 3 being processed, instead of being directly manufactured on the forming support 16 of toroidal conformation, are provided to be obtained as semifinished products from preceding working steps and to be assembled to other components on a forming drum that can have a cylindrical conformation or other shape different from that of the forming support 16 described above.
By way of example, shown in
The building stations 11, 12, 13, 14, 15 can operate simultaneously, each on a respective tyre 3 being processed, carried by a respective forming support 16, sequentially transferred from a building station to the subsequent building station, via robotized arms 17 or other suitable devices.
Tyres 3 built by apparatus 2 are sequentially transferred to at least one vulcanisation unit 18 integrated into the plant 1.
In accordance with the present invention, at least one of the components of elastomeric material of tyre 3, such as liner 5, fillers 7a and/or other parts of elastomeric material of the beads 6, sidewalls 10, tread band 9, under-belt layer, tread band under-layer, abrasion-preventing inserts and/or others, is obtained by an assembly device generally denoted at 19.
The assembly device 19 comprises at least one extruder 20 provided with a cylinder 21 into which elastomeric material is introduced. The cylinder 21, heated to a controlled temperature included, just as an indication, between about 50° C. and about 100° C., operatively houses a rotating screw 22, by effect of which the elastomeric material is urged along the cylinder 21 itself, towards an outlet port 23 of the extruder 20. If required, the elastomeric material can be conveyed through a positive-displacement pump 24, a gear pump for example, that is operatively interposed between the rotating screw 22 and the outlet port 23, to ensure more uniformity of the flow rate therethrough.
Consequently, a continuous thread element 25 of raw elastomeric material having a substantially circular cross-section outline is delivered through the outlet port 23. Alternatively, the conformation of the outlet port 23 and, as a result, of the cross-section outline of the continuous thread element 25, can be of the ellipsoid type. In both said cases, the cross-section area of the outlet port 23 is preferably included between about 10 mm2 and about 200 mm2.
Said size features enable the continuous thread element 25 to be delivered at the desired linear speed corresponding to a so-called “target value” of the volumetric flow rate, included just as an indication between about 1 cm3/s and about 70 cm3/s, without too many deformations being imposed to the mass of the elastomeric material close to the outlet port 23. Thus it is advantageously possible to keep the elastomeric material temperature at the outlet port 23 to relatively reduced values, included between about 80° C. and about 110° C., by way of example.
The continuous thread element 25 coming from the extruder 20 is guided towards a shaping device 26 comprising at least one pair of counter-rotating shaping rollers 27. A first shaping roller 27a can be of substantially cylindrical conformation, while at least one second shaping roller 27b has at least one circumferential groove 28 of suitable conformation. Thus a shaped clearance 29 is defined between the mutually approached shaping rollers 27, which shaped clearance 29, in a lying plane containing the rotation axes of the rollers themselves has an area preferably included between about 50% and about 100% of the area of the outlet port 23 of the extruder 20.
The continuous thread element 25 fed via the shaping rollers 27 is such shaped that it forms an elongated element 30 having a predetermined cross-section outline corresponding to the conformation of the shaped clearance. As clearly shown in
Operating close to the shaping rollers 27 is at least one device 31 for monitoring at least one parameter indicating the volumetric flow rate of the continuous thread element 25. The monitoring device 31 interacts with at least one adjusting device 32 to adjust the volumetric flow rate for feeding the continuous thread element 25 towards the shaping rollers 27.
The monitoring device 31, for instance, may comprise an ultrasonic detector 33 of the laser beam or other type, positioned immediately upstream of the shaping rollers 27 (
In accordance with a further preferred solution, shown in
The width-reading sensibility of detector 33 can be increased by providing at least one lateral interspace 35 in the outline of the shaped clearance 29. In the example shown, two lateral interspaces 35 are provided which extend on respectively opposite sides in the extension of the major base side 30a of the trapezoidal outline of the clearance itself, preferably in order to give the shaped clearance 29 a maximum width “A” at least as large as a maximum acceptability value “B” for the elongated element width 30.
The presence of the lateral interspaces 35 causes formation of two tab-shaped projections 36 during shaping of the continuous thread element 25, in the extension of the major base 30a of the elongated element 30, which projections 36 have a thickness “S” included, by way of example, between about 0.1 mm and about 0.5 mm. Due to the relatively reduced thickness, the tab-shaped projections 36 show a noticeably variable width depending on variations, even if of small value, in the flow rate of the elastomeric material through the shaped clearance 29. In fact, due to the trapezoidal conformation of the shaped clearance 29, the elastomeric material acceding to the clearance itself tends to fill the portion close to the minor base of the trapezoidal conformation and to subsequently expand into the region of the major base. A residual part of the elastomeric material will therefore fill the lateral interspaces 35 to a more or less important degree depending on the flow rate through the shaped clearance 29. As a result, even small variations in the flow rate give rise to important size variations in the tab-shaped projections 36 formed along the edges of the elongated element 30 and, consequently, in the width “D” of the elongated element 30 itself at a given instant. The linear speed of the continuous thread element 25 being known, as it is detectable in case of need by an encoder (not shown) associated with a driving motor of the shaping rollers 27 for example, an electronic processing unit 34 being part of the adjusting device 32 can easily calculate the corresponding flow rate at each reading cycle carried out by detector 33.
A comparator 34a associated with the electronic processing unit 34 compares the flow rate parameters cyclically detected by detector 33 with an ideal flow rate value stored beforehand, in order to enable the adjusting device 32 to adjust the feeding speed of the continuous thread element 25 towards the shaping rollers 27 so that the volumetric flow rate through the shaped clearance 29 and the outlet port 23 shall be maintained substantially equal to said predetermined target value, with a difference preferably less than 0.5%.
In more detail, when detector 33 detects a width of the elongated element corresponding to, or smaller than a predetermined minimum acceptability value “C”, the adjusting device 32 enables an increase in the feeding speed of the continuous thread element 25 towards the shaping rollers 27. Vice versa, when detector 33 detects a width of the elongated element corresponding to or greater than a predetermined maximum acceptability value “B”, the adjusting device 32 enables a reduction in the feeding speed of the continuous thread element 25 towards the shaping rollers 27. The width “D” of the elongated element is therefore maintained within said minimum and maximum acceptability values.
Adjustment of the feeding speed of the thread element can be carried out by modifying the delivery speed of the elastomeric material through the extruder 20, acting for instance on the rotation speed of the rotating screw 22 or, in the presence of the positive-displacement pump 24, modifying the driving speed of the pump itself.
In an alternative embodiment, as shown in the dashed box in
An applicator device 42 operating downstream of the shaping rollers 27 applies the elongated element 30 coming from the shaping rollers 27 onto the forming support 16. During application, the forming support 16 carried in overhanging by one of said robotized arms 17, is driven in rotation and suitably moved in front of the applicator device 42 to distribute the elongated element 30 in the form of coils disposed in side by side relationship and/or superposed, so as to form a liner 5 for example, or any other component of elastomeric material of the tyre 3 being processed.
The applicator device 42 comprises at least one roller or other applicator member 43 operatively supported relative to the shaping rollers 27, to some distance therefrom, and acting in thrust relationship towards the forming support 16, by effect of a pneumatic actuator 44 for example, to apply the elongated element onto the forming support 16 itself.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IT2006/000614 | 8/9/2006 | WO | 00 | 2/3/2009 |
