Process and equipment for producing a rubber for a tire comprising a kneading step

In the process for producing a rubber for manufacturing a tire:

This application claims benefit of the filing date of PCT/FR2012/051042, filed May 11, 2012, which claims the benefit of FR1154190, filed May 13, 2011, the entire contents of each of which are incorporated herein by reference for all purposes.

BACKGROUND

The invention relates to the production of a rubber for manufacturing a tire.

2. Description of Related Art

It is known that the production of a rubber for a tire for the wheels of a vehicle involves successive mixing steps. Firstly, elastomeric materials are mixed with a charge of carbon black or silica. This mixing process takes place in the tank of a mixer and results in a rise of the temperature of the mixture, which may reach 170° C. for example. This mixture is then transferred to a station where it continues to be worked whilst being cooled. This working takes place by circulating the mixture between two cylinders so as to form it into a ply. The cooling means of the station lower the temperature to approximately 80° C.

It is known to add to the rubber a product that promotes vulcanization of the rubber during its subsequent baking. So as not to risk premature partial vulcanization of the rubber, the vulcanizing product is not incorporated at the same time as the other ingredients. It is therefore only once the above-mentioned steps have been carried out that the mixture is transferred to a finishing station, where the vulcanizing product is added to the mixture and is mixed therewith.

An arrangement of this type is described for example in document DE-11 2005 002546 T5.

But the properties of the rubber during the vulcanization process are very sensitive to the proportions of the ingredients forming the mixture. Thus, if the quantity of vulcanizing product is not added to the mixture in the correct proportions, vulcanization may therefore be either too quick, or insufficient, which in either case compromises the qualities of the rubber and those of the finished tire.

SUMMARY

The objective of the disclosure is to ensure that the correct proportions of the ingredients of the mixture forming the rubber are observed.

To this end, a process for producing a rubber for manufacturing a tire is provided, in which:a calendar forms a ply with a mixture of ingredients of the rubber whilst a conveyor moves the ply in a first direction,a mass of product other than the rubber is deposited on the ply, andthe conveyor moves the ply in a second direction, such that the mass is arranged between two faces of the ply extending one against the other.

The changing of the direction of the conveyor thus makes it possible to arrange the product between two portions of the ply. The rubber and the product are thus prevented from being separated from one another during the rest of the process for producing the rubber. It is thus ensured that the final proportions of the ingredients of the rubber are better observed.

The ply is advantageously circulated in the form of a closed loop.

This kneading thus makes it possible to work the rubber effectively and quickly.

A device comprising the calender and the conveyor may open the loop so as to form two free ends of the ply.

This opening makes it possible to easily discharge the ply.

The product forming the mass preferably comprises a compound promoting the vulcanization of the rubber.

The process of the invention is not limited to this case, since it also allows the addition to the mixture of complementary products other than a vulcanizing product, but is well suited to such a product, the observance of the proportions being of great importance.

The product is preferably deposited only once a temperature of the ply has become less than a predetermined threshold.

The rubber is therefore left to reach a temperature compatible with the addition of the product.

The ply is discharged from a device comprising the calender and the conveyor, advantageously together with the mass arranged between the two faces extending one against the other.

The complementary product is thus added to the rubber not as it arrives at the final mixing station, but before it leaves the station in which the ingredients, except for the product, are mixed. This product does not leave the mixture before the arrival at the finishing station. The attainment of a rubber having the expected properties is therefore favoured.

The conveyor preferably carries out the discharge in the second direction.

In accordance with the invention, a piece of equipment for producing a rubber, able to implement a method according to an embodiment of the invention, and comprising a calender, a first conveyor and a second conveyor able to dispense the mass directly onto a portion of the ply carried by the first conveyor, is also provided.

The production of a ply fold in which the product mass is arranged is thus facilitated.

These two conveyors ensure the movements in the respective, non-co-planar directions. The second conveyor preferably has an end arranged above and opposite the first conveyor. In addition, the second conveyor does not extend in the vertical extent of the calender and is therefore arranged neither above nor below the calender.

The equipment advantageously comprises cooling means within the calender.

Such means make it possible to accelerate the temperature drop of the rubber compared to the situation in which the calender would only have been cooled by contact with the ambient air.

The second conveyor preferably extends upstream of the calender with respect to a discharge direction outside the equipment by the first conveyor.

The equipment advantageously comprises a third conveyor, which is inclined with respect to the vertical direction and has an end located above the calender.

This conveyor makes it possible to circulate the ply in a closed loop.

Equally, the equipment may comprise cooling means within the third conveyor.

Here again, such means make it possible to accelerate the temperature drop of the rubber.

The second conveyor advantageously has an end located below the third conveyor.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

A station2of a piece of equipment for producing a rubber for a tire according to an embodiment of the invention has been illustrated inFIGS. 1 and 2. The tire may be a tire for the wheels of a lightweight vehicle, a passenger vehicle, a utility vehicle, a heavy goods vehicle, or else for the wheels of an engineering machine.

The station2comprises a lower horizontal belt4in the form of an endless band able to circulate whilst being held and driven between two rolls6, of which the axes defining the axes of rotation are horizontal and mounted rotatably relative to a frame8of the station. The two walls of the belt are horizontal.

Similarly, the station comprises a vertical belt8provided in the form of an endless band able to circulate whilst being held and driven between one of the rolls6and a roll10extending above the first-mentioned roll. The two walls of the belt8are vertical.

The station2also comprises a rising belt12in the form of an endless loop able to circulate whilst being supported and driven by an upper roll14and a lower roll16of greater diameter than the roll14. The roll14extends at a distance from the roll16in the horizontal direction and in the vertical direction. The belt12comprises inner cooling means33arranged between the two layers of the band or in at least one of the rolls6,10.

The station2further comprises a calender18comprising two identical cylinders20arranged in a mutually opposed manner with their geometric axes of rotation22parallel to one another. The two rolls extend at a distance from one another and above the horizontal belt. The calender comprises cooling means34within the rolls.

All the axes of the aforementioned rolls6,10,14,16as well as the axes22of the cylinders are horizontal and parallel to one another.

The station2also comprises a horizontal introduction belt24having a band in the form of a closed loop able to circulate whilst being held and driven by two rolls26having horizontal axes28parallel to one another and perpendicular to the aforementioned axes. The upper horizontal wall of the belt24moves in a direction25perpendicular to the direction29of movement of the wall of the lower belt4. In addition, the belt24is able to circulate such that the products arranged on its upper face are discharged therefrom via the end27located in the upper part ofFIG. 1. This end extends above the lower belt4, opposite the latter, approximately halfway between its ends formed by the rolls6.

Lastly, the station comprises a transfer belt30having a band provided in the form of a closed loop able to circulate whilst being held and driven by rolls32, of which only one is visible inFIG. 2. This roll has an axis parallel to that of the roll6and extends below the latter.

The roll14extends above one of the cylinders20, without covering the other cylinder20. The rising belt12extends above part of the introduction belt24and in particular from its discharge end. The roll16extends opposite the two belts4and8and the cylinder6supporting said two belts. The introduction belt24is located to the side of the calender18, without being arranged in the vertical extent thereof.

The equipment is controlled so as to carry out the process of the invention in the following manner.

In a station (not illustrated) of the equipment, a natural elastomer, a synthetic elastomer, and a charge formed for example by carbon black or silica are mixed in a tank, said station being arranged upstream of the station2. At this stage, vulcanizing product is not incorporated in the mixture.

At the end of this mixing phase, the mixture is discharged via a lower opening in the tank and this rubber mass35is transferred towards the station2of the equipment.

The rubber mass35passes in the calender18between the cylinders20turning in opposite directions and forms a ply. The lower belt4is moved such that its upper wall moves towards the left as indicated inFIG. 3. The vertical belt8is moved such that its right-hand wall moves upwards. The rolls14and16are turned in a clockwise direction such that the upper wall of the belt12rises during the movement of this belt.

During its passage through the calender, the rubber forms a ply which deposits on the upper wall of the lower belt4and is transferred in the direction of the vertical belt.

An operator places an end part of this ply around the lower roll16, such that this part is driven over the rising belt, passing between this belt and the vertical belt8. The ply travels over the rising belt12, passes the roll14, and falls again in the direction of the calender, where it accumulates again.

A closed-loop ply is thus formed, which circulates continuously in the clockwise direction, as indicated inFIG. 3, from the calender to the lower belt, then over the rising belt and again through the calender, and does so a number of times. During this movement, the rubber accumulates in the calender upstream of the rolls so as to reform a ply at the exit of said rolls. This circulation thus causes continued mixing and kneading of the ingredients. During this movement, the cooling means34lower the temperature of the rubber, which additionally experiences a lowering of its temperature due to its contact with the air and the other elements of the station2. Whereas its temperature reached 170° C. before its arrival at the station, it reaches approximately 80° C. at the end of this circulation. These values are given merely by way of example. The circulation of the ply for example takes within one and four minutes, preferably over two minutes.

To end this circulation, a reversal of the direction of movement of the rising belt12is commanded, as illustrated inFIG. 4, whilst continuing the rotation of the cylinders20as before. This leads to a rupture of the ply between the roll14and the calender and therefore to the opening of the loop. At the same moment, the reversal of the direction of movement of the lower belt is commanded so as to initiate the movement of the ply in the direction of the transfer belt30in the direction31, that is to say to the right in the figures.

At the same moment also, a block of vulcanizing product36is introduced into the station. This product is a mixture of sulphur and a retarder product, for example. This block, in this case, has a rectangular parallelepipedic shape. It forms a product mass proportioned to the constituents of the mixture forming the rubber. The block36is introduced via the belt24, which guides the block via its upper wall as far as the discharge end27and dispenses it directly onto a portion37of the ply carried by the lower belt4and thus being located in the lower half of the latter. The block is therefore arranged on an upper face38of a portion37of the ply of which the kneading at the station2is now complete since this portion will no longer pass again through the calender. At the moment of deposition of the block on the ply, part of the ply is still carried over the entire upper face of the rising belt12, and another part is carried by the calender20, through which it is passing for the last time.

During the continuation of the movements of the different elements of the station2, the portion37of the ply carrying the block is moved therewith towards the right, whereas the end portion39of the ply passing through the calender is moved progressively over this portion so as to cover it and also the block. The block is therefore arranged between the inner faces of the two portions37,39of the ply extending one against the other and one above the other. A two-layer fold or arrangement is thus formed, in which the block is housed. It should be noted here that the end of the belt24is located upstream of the calender with respect to the movement of the belt4towards the right.

The continuation of the movement of the rising belt discharges the other end part of the ply towards the horizontal belt. The ply is transferred progressively over the transfer belt30.

Still in the same configuration with the block between the two ply portions, the assembly is then sent towards a finishing station, where the ply and the vulcanizing block are mixed.

The rubber35and the vulcanizing block36are thus transported from the station2towards the station following the equipment in a configuration such that the block is enveloped in the ply. As a result, material losses of vulcanizing product are avoided during the transfer of this assembly.

It should be stressed that the block36is not mixed with the rubber of the ply35and is not kneaded therewith within the station2. These procedures are only performed in a subsequent station of the equipment. It is also stressed that the block is arranged against a face of a part of the ply of which the kneading was completed in the station2.

The equipment may comprise control means42able to control all or some of the process steps just described. These means advantageously comprise one or more computers having microprocessors and memories as well as a program comprising code instructions able to control the execution of these steps when these instructions are run on a computer.

Of course, numerous modifications can be applied to the invention, without departing from the scope thereof.