Tire Cold Retreading Method

Abstract

A method for the cold retreading of a tyre (1) comprising the following steps: a removal step, during which the old, worn tread is removed from the tyre in order to expose an equatorial surface (2) of a casing (3) of the tyre (1); a deposition step, during which a cushion (4) and a pre-cured tread strip (6) provided with a tread pattern are deposited around the equatorial surface (2) of the casing (3); and a curing step, during which the cushion (4) arranged between the casing (3) and the pre-cured tread strip (6) is cured. The cushion (4) is manufactured with a compound comprising 1 to 30 phr of at least one conductive material chosen among graphite, graphene and a carbon black having a surface area which is greater than or equal to 300 m.sup.2/gr. The curing step comprises a connection step, during which said cushion (4) is connected to a heat or power source (S).

Claims

1-8. (canceled)

9. A method for a cold retreading of a tire, the method comprising: removing a tread from the tire in order to expose an equatorial surface of a casing of the tire; depositing a cushion and a pre-cured tread strip with a tread pattern around the equatorial surface of the casing, the cushion manufactured with a compound comprising 1 phr to 30 phr of at least one conductive material chosen among graphite, graphene, and carbon black having a surface area that is greater than or equal to 300 m.sup.2/gr; and curing the cushion arranged between the casing and the pre-cured tread strip, during which the cushion is connected to a heat source or a power source.

10. The method of claim 9, wherein the compound comprises 5 phr to 10 phr of the at least one conductive material.

11. The method of claim 9, wherein the cushion comprises at least one annular edge portion laterally projecting from the casing.

12. The method of claim 11, further comprising: arranging at least one annular heated portion of the heat source in contact with the at least one annular edge portion.

13. The method of claim 9, further comprising: prior to the curing step, depositing a filler in a fluid state on the pre-cured tread strip to form a filler coating that covers the pre-cured tread strip.

14. The method of claim 13, further comprising: following the curing step, removing the filler from the pre-cured tread strip.

15. The method of claim 13, further comprising: during the curing step, applying a radial pressure on the pre-cured tread strip by pressing, from an outside of the tire, against the filler coating.

16. The method of claim 15, wherein applying the radial pressure on the pre-cured tread strip comprises pressing a plurality of pressing bodies of a curing mold against the filler coating.

17. The method of claim 16, wherein each of the plurality of pressing bodies comprises a circular sector and the plurality of pressing bodies form a ring around the tire.

18. The method of claim 13, wherein the filler comprises a material that shrinks during curing.

19. The method of claim 18, wherein the shrinking material comprises clay.

20. The method of claim 9, wherein the cushion comprises raw rubber.

21. The method of claim 9, wherein the compound further comprises at least one of natural rubber, zinc oxide (ZnO), stearic acid, antioxidants, sulphur, accelerators, alkylphenol-formaldehyde resin, and combinations thereof.

22. The method of claim 9, wherein the step of curing further comprises curing the cushion arranged between the casing and the pre-cured tread strip at a temperature from 100° C. to 125° C.

23. The method of claim 9, wherein the step of curing further comprises curing the cushion arranged between the casing and the pre-cured tread strip at a pressure from 4 bar to 6 bar.

24. A tire which is retreaded via the cold retreading method of claim 9.

25. A method for a cold retreading of a tire, the method comprising: removing a tread from the tire in order to expose an equatorial surface of a casing of the tire; depositing a cushion and a pre-cured tread strip with a tread pattern around the equatorial surface of the casing, the cushion manufactured with a compound comprising at least one conductive material; connecting the cushion to a heat source or a power source; depositing a filler in a fluid state on the pre-cured tread strip to form a filler coating that covers the pre-cured tread strip; applying a radial pressure on the pre-cured tread strip by pressing, from an outside of the tire, against the filler coating; curing the cushion arranged between the casing and the pre-cured tread strip; and removing the filler from the pre-cured tread strip.

26. The method of claim 25, wherein the compound comprises 1 phr to 30 phr of the at least one conductive material chosen among graphite, graphene, and carbon black having a surface area that is greater than or equal to 300 m2/gr.

27. The method of claim 25, wherein the cushion comprises at least one annular edge extending on a side of the casing.

28. The method of claim 27, further comprising the step of: arranging at least one annular heated portion of the heat source in contact with the at least one annular edge portion.

Description

[0028] Hereinafter there is a description of an embodiment of the invention, by mere way of explanatory and non-limiting example, with reference to the accompanying drawings, wherein:

[0029] FIG. 1 is a schematic view of a tire, in which the old, worn tread was mechanically removed, thus exposing an equatorial surface of a respective casing;

[0030] FIG. 2 is a schematic view of the wrapping of a cushion around a casing of a tire to be retreaded;

[0031] FIG. 3 is a schematic view of the wrapping of a pre-cured tread strip around the cushion with the interposition of the conductive element;

[0032] FIG. 4 is a schematic view of the application of a filler on the previously wrapped pre-cured tread strip;

[0033] FIG. 5 is a schematic view of a compression during the curing of a retreaded tire;

[0034] FIG. 6 is a schematic view of a removal of a filler from the pre-cured tread strip after curing.

[0035] In FIG. 1, number 1 indicates, as a whole, a tire, in which the old, worn tread was mechanically removed, thus exposing an equatorial surface 2 of a respective casing 3.

[0036] The procedure with which the old, used tread is removed is known and, since it is not relevant for the invention, it will not be discussed any further.

[0037] FIG. 2 shows a deposition step, during which a cushion 4 is wrapped on the equatorial surface 2 of the casing 3. As a person skilled in the art knows, the cushion is an intermediate strip of raw rubber, which fulfils a binding function between the casing of the used tire and the new, previously cured tread strip.

[0038] In particular, the cushion comprises an annular edge portion 4a, which extends on the side of the casing 3. This annular edge portion 4a has the function of providing an exposed side portion of the cushion, which is such that it can be connected to a heat or power source during the curing step, as explained more in detail below.

[0039] Table I shows the phr composition of the compound making up the cushion.

TABLE-US-00001 TABLE I Natural rubber 100 Carbon black 40 Zinc oxide 5 Stearic acid 1 Antioxidants 5 Sulphur 2.5 Accelerators 1 Alkylphenol-formaldehyde resin 9 Conductive material* 10 *The conductive material is chosen among graphite, graphene and carbon black having a surface area which is greater than or equal to 300 m.sup.2/gr.

[0040] Experiments have shown that the total quantity of conductive material must range from 1 to 30 phr in order for the heating to be effective for the purpose of curing. The total quantity of conductive material must preferably range from 5 to 15 phr.

[0041] FIG. 3 shows another operation of the deposition step, during which a pre-cured tread strip 6 is wrapped on the cushion 4. It should be pointed out that the pre-cured tread strip 6, since it has already been cured in a suitable mold, has a defined tread pattern.

[0042] FIG. 4 shows a coating step, during which, after the wrapping of the pre-cured tread strip 6 and before subjecting the tire 1 to a curing step, a filler 7 in the fluid state is deposited on the pre-cured tread strip 6. The filler 7 completely fills the pattern of the tread (namely, it penetrates the grooves of the tread pattern) and forms a coating which covers the pre-cured tread strip 6. In other words, the filler 7 creates a “negative” of the pre-cured tread strip 6.

[0043] In particular, the filler 7 is applied on the pre-cured tread strip 6 so as to completely cover it and, hence, have, on the outside, a flat equatorial surface (namely, a flat surface, i.e. without recesses and grooves). In other words, the filler 7 is used to form a coating that “levels off” the pre-cured tread strip 6, thus offering, towards the outside, a flat equatorial surface (namely, a smooth surface without recesses and grooves).

[0044] In the embodiment shown in FIG. 4, the filler 7 is applied on the pre-cured tread strip 6 by means of an applying device 8 after the pre-cured tread strip 6 has been wrapped around the casing 3 (namely, when the pre-cured tread strip 6 has an annular shape).

[0045] According to a preferred embodiment, the filler 7 can be made of clay, which has the advantage of being easy to be found, not very expensive and recyclable for further retreading operations or in general. Furthermore, the natural shrinking of the clay when dry also allows the filler 7 to be easily removed from the pattern of the tread.

[0046] FIG. 5 shows a curing and compression step, during which the tire 1 is housed inside a curing mold 9, which consists of a plurality of pressing bodies 10, which are each shaped like a circular sector and form, all together, a ring designed to contain, on the inside, the tire 1.

[0047] According to the figure, the mold 9 comprises a heat source indicated with S and represented with a broken line.

[0048] The heat source S comprises at least one heated annular surface, which, during the curing step, is arranged in contact with the annular edge portion 4a of the cushion 4. In this way, thanks to the thermal conductivity of graphite or graphene or a carbon black having a surface area which is greater than or equal to 300 m.sup.2/gr, the cushion 4 is entirely heated at a temperature that is such as to cause the curing thereof.

[0049] This solution offers the great advantage of not having to subject the entire tire to a heating process, with the consequence both that already cured parts of the tire do not risk being deteriorated and that the curing step is quicker.

[0050] Each pressing body 10 is radially moved (hence, is radially pushed against the tire 1) by an actuator 11 (for example a pneumatic or hydraulic cylinder). According to a preferred embodiment, the actuators 11 are designed to apply on the pressing body 10 a radial pressure towards the centre (namely, a radial pressure compressing the tire 1) with an adjusted force, which is determined in such a way that, during the curing process, the tire 1 (namely, the pre-cured tread strip 6 which is part of the tire 1) is radially compresses with a desired pressure; by way of example, the actuators 11 could use, in order to radially push the pressing bodies 10, a pneumatic or hydraulic system with an adjusted pressure or they could use a completely mechanical system provided with adjusted springs.

[0051] During the curing process, the tire 1 is kept at ambient pressure and a radial pressure is mechanically applied to the pre-cured tread strip 6 by means of the pressing bodies 10 of the curing mold 9 and with the interposition of the filler 7. In other words, the pressing bodies 10 of the curing mold 9 press against the filler 7, which has, on the outside, a smooth surface (hence, the pressure exerted by the pressing bodies 10 is distributed in a uniform manner on the entire filler 7); the filler 7 transmits the pressure exerted by the pressing bodies 10 in a uniform manner to the entire pre-cured tread strip 6, since the filler 7 is homogeneously distributed on the entire pre-cured tread strip 6 (namely, even in all the grooves of the tread pattern). As a consequence, the filler 7 acts like a “distributor” of the pressure exerted by the pressing bodies 10 on the entire pre-cured tread strip 6, since it is a coating that reproduces in negative the shape of the pre-cured tread strip 6.

[0052] FIG. 6 shows a removal step, during which, after the curing step, the filler 7 is removed from the pre-cured tread strip 6 by means of a suitable removal device 12 and with this operation the tire 1 retreading process ends.

[0053] To sum up, the cold retreading method according to the invention makes sure that the curing step is carried out without using autoclaves and by subjecting the sole cushion to heating. This leads to the important advantage of having a quicker and safer curing (avoiding the safety problems caused by the use of autoclaves) and of preventing, to a significant extent, the already cured parts of the tire from having to undergo a heating process, which could jeopardize them. These results are obtained thanks to the particular composition of the cushion, which allows it to be heated after having been connected to a heat source or to a power source.

[0054] Furthermore, the fact that the pre-cured tread strip is covered with the filler prevents manufacturers from having to use vacuum envelops, thus avoiding the complicated tire dressing/undressing procedures and the risks of breaking of the envelops.