MXPA96005919A - Prevulcanized pneumatic river band for recauchut - Google Patents

Abstract

The present invention relates to a pre-vulcanized tread designed to be joined to the wall of a pneumatic structure and which includes a crown and two lateral wings with a base, the transverse profile of which is flat or concave, and has an outer surface Each lateral wing has, starting from the crown, a region which is progressively used to a minimum thickness of the wing by a molding consisting of elastomeric material, where the transversal profile includes a point A which is the lateral side of the base and a point B which is a side side between the molding, point B extends beyond the point A in the direction of the structure on the surface of the molding between points A and B defines a surface of a cavity for the material which a modura ocn the structure, in which the distance between B and a tangent to the base in A is greater than or equal to the minimum thickness of the wing of the tapered region progressivame n

Description

PREVULCANIZED PNEUMATIC RIVER BAND FOR RECOVERY Field of the invention The subject of the present invention is a tread of a pre-vulcanized tire for retreading and, more precisely, the profile of the edges of the tread. The invention also relates to a tire obtained by using this tread.

BACKGROUND OF THE INVENTION It is known that a tire is constituted by a flexible housing that has approximately the shape of an open bull on the shaft side, and by a less flexible tread band which surrounds the periphery of the carcass and which secures the contact of the tire with the tire. floor. Thus, the tread is subject to faster wear than that of the carcass and, for a long time, it has been thought to replace this tread when w in order to reconstitute the tire REF: 23574 lower cost than that of a new tire. This reconstitution, called retreading in the most general case, in which it refers to the tread alone, resorts to various types of products and procedures; thus, the new tread can be used raw or prevulcanized: in the first case, the new tread, raw, previously applied on the carcass, is vulcanized in a mold similar to that used to make the new tire; in the second case, called "cold" retreading, the pre-vulcanized tread is applied on the carcass, with interposition of a layer of vulcanizable bonding rubber; the assembly is then surrounded, usually in whole or in part, with a sealed membrane, and then an autoclave is pressed under the vulcanization of the binding gum; This membrane is intended to ensure, during all or part of the vulcanization, a regular application of a pressure of several bars, especially in the critical area of union between the tread and the carcass.

The present invention relates to this second type of retreading. The screened band can be presented in different forms; you can prepare long, flat or preformed bands (transversally curved, for example), which are cut to the desired length at the time of retreading, or rings of determined length: the flat bands allow simple, safe retreading and effective, but present several disadvantages, reduction of the width of the tread in relation to that of the new tire, mediocre appearance, appearance of cracks during rolling; the bands with "bibs" are provided, laterally, with sharp extensions, which are also called "wings", intended to wrap (partially or completely) the shoulders of the tire; thus, the final appearance of the retreaded tire is improved, but these bands present a serious drawback, during rolling, cracks appear in the area where the tread joins the carcass, and these cracks progress dangerously, either in the form of detached areas of the tread, or as deep breaks in the carcass; the rings allow a better application on the casing and avoid the union of the two ends of the tread, but need more sophisticated positioning means, and do not prevent the appearance of cracks in the splice area.

It has been proven to avoid the occurrence of fissures by proposing tread wings as sharp as possible (EP 495 048, page 6, line 14) or by distributing the stresses in the area where the tread joins the carcass, practicing, for example, circumferential grooves on the outer sides of the tread (JP 6/191225). This last solution has decreased the bending stiffness of the wings and has thus facilitated its application on the shoulders of the tire carcasses, but has not involved a significant reduction in cracks in the critical area of connection with the carcass.

It has also been tried to improve the quality of the bonding in this critical area between the tread and the carcass after having ascertained that the joint rubber disposed between the carcass and the tread band could flow during its vulcanization to coat a part of the tire. the outer surface of the tread wing, part not prepared to solidly adhere to this joint rubber. For example, document US 5313745 proposes to grind the two inner and outer edges of the wings of the treads to improve their adhesion with the joint rubber. This solution has significantly improved the resistance to cracking or formation of cracks in the critical area, but this problem of cracks subsists and impairs the development of the technique of cold retreading, although, on the other hand, this is very interesting. Thus, the present invention aims to improve the quality and reliability of the joining of the tread with the carcass in the two circumferential zones of joining the edges of the tread with the carcass. In what follows, the term "pre-vulcanized tread" means a tread that has already undergone a vulcanization cycle, has led this cycle to a total, or partial, vulcanization; - «carcass» a tire that lacks only the tread, whether this tire is new or worn.

According to the invention, a pre-lubricated tread comprises a crown and two lateral wings, with a base whose transverse profile is flat or concave and an outer surface, each lateral wing having, from the crown, a progressive thinning zone followed by a bead or ridge, consisting exclusively of elastomeric material, such that the transverse profile of the lateral end of said heel is convex and is progressively separated from the concave flat transverse profile of the base, such that, at point B of said profile lateral end of the heel in which the tangent is perpendicular to the tangent at the lateral end of the profile of the base, the distance separating said point B from said tangent at the lateral end of the profile of the base is greater than or equal to minimum thickness of the wing in the zone of progressive thinning. Advantageously, the bead is adjacent to a longitudinal groove, and the bead and throat are dimensioned to produce a decoupling between the bead and the body of the flange comprised between the crown and the throat in order to subtract the said bead from the stresses that are applied to the bead. They exert on the body of the wing. Preferably, the minimum thickness of the wing is located at the level of the longitudinal groove and the maximum thickness of the bead is greater than or equal to twice the minimum thickness of the wing. This minimum thickness is advantageously less than 3 mm. Thus, contrary to the practice of the person skilled in the art, which endeavors to give the retreaded tire the same profile as that of the new tire, the Applicant has found that, by replacing the progressive tapered splice of the wing of the tread. by a throat followed by a heel endowed with a substantial thickness in the area of connection between the tread and the casing, the mechanical stress of the splice zone is greatly diminished and the resistance to the formation of cracks in the critical zone. The presence of the bead also has the advantage of guaranteeing during the whole autoclave vulcanization phase, that the joining pressures of the lateral ends of the wings against the carcass are high and reproducible, which improves the quality and the reliability of the bonding in the critical zone. In a first embodiment, the lateral end of the bead has a cross-sectional profile in the form of a half-circle with a radius greater than or equal to the minimum thickness of the wing. In a second embodiment of the invention, the lateral end of the bead has a substantially rectilinear convex transversal profile and forms an angle with the transverse profile of the lateral end of the base or whose measurement is between 90 and 140 degrees and, preferably, between 110 and 130 degrees. According to a complementary feature, the transverse profile of the outer surface of the tread, at the heel, is substantially rectilinear and forms, with the substantially rectilinear profile of the lateral end of the bead, an angle ß whose measurement is less than or equal to sensibly 90 degrees. The geometry of the bead according to the invention, and especially in these two embodiments of the invention, has the advantage of defining, very precisely, how far the gum will flow. In fact, the cavity provided for this flow is delimited by the lateral end of the bead, the membrane that rests on the outer surface of the wing and the profile of the casing beyond the splice area. The pressure applied to the membrane during vulcanization is such that the gum can not infiltrate between the membrane and the outer surface of the bead beyond the intended cavity. Thus, these solutions involve the presence of a rubber band of juncture clearly delimited on the outer surface of the retreaded tire, which gives this tire a very aesthetic appearance. An exemplary embodiment of the invention will be described, given as being non-limiting, referring to the attached drawings, in which: Figure 1 is a transverse half-shear of a ring pre-vulcanized tread according to the invention;; Figure 2 is a cross-sectional view, on a larger scale, of a first embodiment of the edge of the wing of the tread of Figure 1, after its application on the carcass; Figure 3 is a view similar to Figure 2 of a second embodiment of the wing edge of the tread of Figure 1; - Figure 4 presents a flat tread with bibs consisting of two materials; Figures 5 (a) and 5 { b) are enlarged cut-outs of the first and second modes of embodiment of tread wing flaps.

Figure 1 shows a transverse half-section of pre-vulcanized tread band 1 comprising a rigid central part called crown 2 and a thinner lateral part 3 called "bib" or "wing". The wing 3 comprises a zone of progressive thinning 8 followed laterally by a heel 4. This tread 1 also has a base 11 intended to be applied against the outer surface 16 of a tire carcass 5 with interposition of a vulcanizable rubber bond 6. This base 11 ends laterally on the edge A, in which the profile of the wing 3, after application on the housing, separates from the profile of the housing 5. The base 11, at the level of the crown 2, is intended to be applied against the crown of the tire carcass and, at the wing level, to be applied against the shoulder, as well as, eventually, against the upper part of the carcass flanks. The tread 1 also comprises an outer surface 12 intended, after its application on a tire carcass, to constitute the outer surface of the tire. Said cutting of tread band corresponds, also, to a flat band transversely curved. The invention also applies to flat strips whose base has a completely flat transverse profile (see FIGS. 4 and 5).

The present invention relates to the profile of the heel 4 of the wing 3, which will be described more in detail referring to figures 2, 3 and 5. In this figure 2 is again the heel 4 of the wing 3 of the band of rolling 1, after its application on the casing 5; a layer of rubber glue 6 has been interposed between the carcass and the tread 1 in order to ensure its adhesion after vulcanization, in autoclave for example, of this gum 6. Prior to this vulcanization, and after the assembly of the tread 1 on the casing 5, a flexible membrane 7 is placed around this assembly that covers the outer profile of the assembly, then the assembly thus prepared is placed in an autoclave whose internal pressure is brought to 5 or 6 bar (500 or 600 kPa), and the temperature at about 115 ° C for a time of the order of two hours. The membrane 7 is fixed in a sealed manner, so that a relative vacuum can be established between the membrane and the tire, forcing the latter to adapt perfectly to the outer profile of the assembly and ensuring strong pressure throughout the vulcanization time. effective application of the tread 1 on the casing 5, especially in the critical area of splicing. According to the invention, in FIGS. 1, 2 and 5 (a) it is seen, starting from the crown 2, that the profile of the wing 3 of the tread 1 comprises, successively, a progressive thinning zone 8, a circumferential groove. 9 of minimum thickness emin and then a circumferential bead 4. Preferably, the maximum thickness emax of the bead 4 is at least equal to twice the minimum thickness of the wing 3 at the level of the circumferential groove 9. The minimum thickness emin is less than 3 mm, on the order of 1 to 2 mm, even less if possible. The circumferential groove 9 is thus a means of mechanical decoupling, which, because of the thickness of the heel 4, is very effective and effectively allows to limit the tension tensions generating the cracks experienced during rolling at the level of the junction zone between the wing 3 and the housing 5. Preferably, this decoupling means is a single circumferential groove 9 with a very rounded profile. The radius of this throat can advantageously be more than 5 times the minimum thickness of the wing.

In the embodiment of FIGS. 2 and 5 (a), the heel 4 has a straight section whose lateral end 13 has a rounded convex shape. The point B corresponds to the point of the transverse profile of the lateral end 13 of the bead 4 in which the tangent TB is perpendicular to the tangent TA at the lateral end A of the profile of the base 11. The distance d that separates B from this tangent TA it must be greater than or equal to the minimum thickness of the wing, which is at the level of the longitudinal groove 9. Thus, this bead according to the invention has a substantial thickness in the area of connection between the carcass and the tread. Here, the profile of the lateral end has substantially the shape of a semicircle. And the radius r of this semicircle is markedly greater than the minimum thickness Tmj.n of the throat 9. The lateral end 13 of the heel 4, the outer profile of the housing 5, and the base of the membrane 7, define a cavity 14, which is filled during vulcanization by the binding gum 6 made fluid by the heat. Due to the pressure applied by the membrane 7 on the heel 4, the gum 6 can not infiltrate between the membrane 7 and the heel 4, consequently, the yield zone of the gum 6 is well controlled and gives place a very aesthetic splice area after the removal of the membrane 7. Figures 3 and 5 (b) present a second embodiment of a wing 20 according to the invention. In this case, the wing comprises, as above, a mechanical decoupling throat 9, followed by a heel 21. The lateral end 22 of the heel 21 is connected at A with the base 11 and at B with the outer surface 12 of the band. rolling. This lateral end 22 has a substantially rectilinear cross section between the points A and B, forming in A with the transverse profile of the lateral end of the base 11 of the heel 21 an angle whose measurement is between 90 and 140 degrees and, preferably, between 110 and 130 degrees. In this range of preferred values, this angle favors a reproducible application pressure transmitted by the membrane 7 to the area of junction between the carcass and the tread band, around A, during the whole time of autoclaving of the whole of the carcass with the tread. The transverse profile of the outer surface 12 of the tread at the level of the heel 21 is, in this example, substantially rectilinear and forms at B with the lateral end 22 of the bead a beta angle of measurement less than or equal to 90 degrees. This transverse profile of the outer surface at the level of the heel is here substantially parallel to the base 11. Consequently, there is a strong application pressure of the membrane 7 on the outer surface 12 at the level of the heel 21 to the edge B and thus, a particularly precise definition of the area of junction between the joint rubber 6, after its creep during vulcanization, and the heel 21. This line segment 22 thus forms a kind of slope where the joint gum 6 it can flow freely without being able to infiltrate further. This results, as before, in a very appreciable aesthetic aspect of the splice zone between the tread flange 20 and the carcass 5. According to the invention, the distance d that segars B from the tangent TA of the profile of the The lateral end of the base 11 at A is notably greater than the minimum thickness of the emin wing, and the maximum thickness emax of the bead 21 is greater than twice this minimum thickness emin. These two wing geometries 3, 20, which are less fragile, also imply that the treads according to the invention are much easier to handle during all manufacturing and assembly operations than the treads with sharp wings. In addition, the preparations of the base and the lateral end of the heels 4, 21 are also facilitated for a bond with the gum. These preparations can be made, for example, by brushing or grinding. Figure 4 shows a flat tread 10 with bib according to the invention made with two different elastomeric materials. The decoupling throat 9 and the bead 31 are again found with geometries close to those of figure 3. The crown 2 is made as above with a constituent elastomeric material, usually, of the treads. On the other hand, the wings 30 are made of an elastomer material of composition and hardness similar to those of the outer flanks of the tires. The separation surface 32 between the two materials is located substantially at the level of the junction between the wings and the crown. Accordingly, the mechanical stiffness of the wings 30 is reduced, as well as the stresses experienced by the critical splicing zone between the lateral end of the wings and the housing, and the resistance to crack formation is also improved. Naturally, this solution can be applied to all types of pre-vulcanized treads. The applicant has carried out tests on tires of dimensions 275/70 R 22, 5 and 315/70 R 22.5 (heavy-duty trucks) which had been retreaded with pre-vulcanized treads comprising, respectively, sharp wings of a known type , and wings comprising a heel according to the invention. These tests have shown a very significant improvement in the resistance to crack formation in the critical area of splice between the tread and the carcass and, thus, a significant gain in fatigue resistance for the retreaded tire. The retreading process described above comprises the use of a flexible membrane during the vulcanization phase. It is also possible not to use a sealed membrane. It is then spoken of vulcanization "without membrane". This procedure is more delicate than the previous one and needs to take special measures during the assembly of the tread with the carcass, to guarantee the tightness in the critical splice zone, but it has the advantage of being less expensive.

The new tread geometry according to the invon thus gives excellresults with this membraneless process, although the extension of the yield of the gum is less controlled. Naturally, the treads according to the invon can also be used to make new tires from new vulcanized housings. It is noted that with respect to this date, the best method known by the applicant to carry out the presinvon , is the convonal for the manufacture of the objects to which it refers. Having described the invon as above, the contof the following is claimed as property:

Claims (12)

1. Pre-vulcanized tread pattern, characterized in that it comprises a crown and two lateral wings, with a base whose transversal profile is flat or concave and an outer surface, each side wing having, from the crown, a progressive thinning zone followed by a heel formed exclusively of elastomeric material, such that the transverse profile of the lateral end of said heel is convex and progressively separates from the flat or concave transverse profile of the base, such that, at point B of said profile of the lateral end of the bead in which the tangent is perpendicular to the tangent at the lateral end of the profile of the base, the distance separating said point B from said tangent of the lateral end of the profile of the base is greater than or equal to the minimum thickness of the wing in the zone of progressive thinning.

2. Pre-vulcanized tread according to claim 1, characterized in that the junction zone between the progressive thinning zone and the heel is a longitudinal groove.

3. Pre-vulcanized tread according to claim 2, characterized in that the minimum thickness of the wing is located at the level of the longitudinal groove.

4. Pre-vulcanized tread according to claim 3, characterized in that the maximum thickness of the bead is greater than or equal to twice the minimum thickness of the wing at the level of the longitudinal groove.

5. Pre-vulcanized tread according to one of claims 2 to 4, characterized in that the radius of the longitudinal throat is greater than or equal to 5 times the minimum thickness of the wing.

6. Pre-vulcanized tread according to one of claims 1 to 5, characterized in that the minimum thickness of the wings is less than 3 mm.

7. Pre-vulcanized tread according to one of claims 1 to 6, characterized in that the lateral end of the heel has a cross-sectional profile in the form of a half-circle with a radius greater than or equal to the minimum thickness of each wing.

8. Pre-vulcanized tread according to one of claims 1 to 6, characterized in that the lateral end of the heel has a substantially rectilinear transverse profile and forms an angle with the transverse profile of the lateral end of the base. ¿Whose measurement is appreciably between 90 and 140 degrees.

9. Pre-vulcanized tread according to claim 8, characterized in that the angle has a measurement comprised between 110 and 130 degrees.

10. Pre-vulcanized tread according to one of claims 8 or 9, characterized in that the transverse profile of the outer surface, at the heel, is substantially rectilinear and forms with the substantially rectilinear lateral end of the heel profile an angle ß whose size is less than or equal to substantially 90 degrees.

11. Pre-vulcanized tread according to one of claims 1 to 10, characterized in that the crown and the wings are made of two different elastomeric materials, of compositions and hardnesses similar to those of the constituent elastomeric materials, respectively, of the treads and the outer flanks of the tires. .

12. Tire characterized in that it is obtained by mounting a carcass and a pre-vulcanized tread according to one of claims 1 to 11.