MOULD FOR VULCANISING TYRES FOR VEHICLES

Abstract

A mould comprising a first and a second half-part (15a, 15b) that are mutually side-by-side along a geometric centring axis (X) in order to define a moulding cavity (16). An internal wall (16a) of the moulding cavity (16) has a first and a second series of slots (17a, 17b) having the respective axially outer terminal portions (19a) respectively in the first and in the second half-part (15a, 15b). The slots (17a, 17b) respectively belonging to the first and second series are circumferentially offset from each other and have respective axially inner terminal portion (20a, 20b) in proximity to an intermediate reference plane (P). A junction line (22) between the first half-part (15a) and the second half-part (15b) has an undulating progression astride the intermediate reference plane (P), to form alternatively arranged crests (23), each intersecting the axially inner terminal portion (20a, 20b) of one of the slots (17a, 17b).

Claims

1. Mould for vulcanising tyres for vehicles, comprising a first half-part and a second half-part that are axially opposite and mutually side-by-side along a geometric centring axis in order to define a moulding cavity arranged to house a tyre being processed; wherein the moulding cavity has an internal wall extended concentrically around the geometric centring axis and carrying a plurality of circumferentially-distributed slots configured for defining corresponding ribs on a radially outer portion of the moulded tyre; wherein each slot has an axially inner terminal portion arranged in proximity to an intermediate reference plane orthogonal to the geometric centring axis, and an axially outer terminal portion spaced from the intermediate reference plane; wherein said plurality of slots comprises a first series of slots having the respective axially outer terminal portions in the first half-part and a second series of slots having the respective axially outer terminal portions in the second half-part, wherein the slots respectively belonging to the first and second series are circumferentially offset from each other and have the respective axially inner terminal portions equidistant from the intermediate reference plane; wherein the first half-part and the second half-part are mutually couplable along a junction line that is extended according to an undulating progression astride the intermediate reference plane, to form crests alternatively arranged on respectively opposite sides with respect to the intermediate reference plane; wherein each of the slots belonging to the first and to the second series is intersected in proximity to its axially inner terminal portion by one of the crests formed by the junction line.

2. Mould according to claim 1, wherein the junction line has connection sections, each of which extended on the continuation of two contiguous crests, traversing the intermediate reference plane between two circumferentially adjacent slots, respectively belonging to the first and second series.

3. Mould according to claim 1, wherein each slot has a main section extended from the axially outer terminal portion and joined with the axially inner terminal portion, according to a direction that is tilted with respect to the latter.

4. Mould according to claim 3, wherein the main section and the axially inner terminal portion form a cusp having a vertex directed according to a circumferential direction.

5. Mould according to claim 4, wherein each crest of the junction line intersects the respective slot at the cusp.

6. Mould according to claim 4, wherein the crest of the junction line is extended along a bisector direction which symmetrically intersects the vertex of the cusp.

7. Mould according to claim 3, wherein the axially inner terminal portion of each slot is situated on the half-part of the mould opposite the half-part carrying the main section and the axially outer terminal portion of the same slot.

8. Mould according to claim 3, wherein the main section of each slot is extended obliquely with respect to the intermediate reference plane.

9. Mould according to claim 2, wherein the crests and the connection sections of the junction line each have a rectilinear extension.

10. Mould according to claim 2, wherein the crests and the connection sections of the junction line follow each other according to a polygonal chain progression.

11. Mould according to claim 2, wherein the crests and/or the connection sections of the junction line each have a curvilinear progression.

12. Mould according to claim 2, wherein the crests and the connection sections of the junction line are mutually connected according to a sinusoidal progression.

13. Mould according to claim 1, wherein the intermediate reference plane coincides with an axial middle line of the moulding cavity.

Description

[0042] Such description will be set forth hereinbelow with reference to the enclosed drawings, provided only as a non-limiting example in which:

[0043] FIG. 1 shows, in partially perspective sectional view, a tyre obtainable by the present mould;

[0044] FIG. 2 schematically shows, in cross section, the vulcanisation mould installed in a vulcanisation press, and arranged in open condition;

[0045] FIG. 3 shows the mould of FIG. 2 in closed condition;

[0046] FIG. 4 shows an enlarged detail of the mould with the half-parts side-by-side in closed condition;

[0047] FIG. 5 shows the detail of FIG. 4 in a possible embodiment variant of the invention.

[0048] With reference to the abovementioned figures, reference number 1 overall indicates a mould for vulcanising tyres for vehicles.

[0049] The mould 1 is particularly aimed for making tyres of the type exemplified in FIG. 1 and overall indicated with 2, comprising one or more carcass plies 3 having preferably cords made of metallic material or possibly textile material. Two anchoring annular structures 4, each comprising at least one so-called bead core 5 preferably carrying an elastomeric filler 6 in radially outer position, are engaged with respective end flaps 3a of the carcass ply/plies 3. The anchoring annular structures 4 are integrated in proximity to zones normally identified with the name “beads”, at which the engagement normally occurs between the tyre 2 and a respective mounting rim (not depicted).

[0050] A belt structure 7 can be circumferentially applied around the carcass ply/plies 3, and a tread band 8 is circumferentially superimposed in radially outer position with respect to the carcass ply/plies 3 and to the possible belt structure 7. Two sidewalls 9, each extended from the corresponding bead to a corresponding lateral edge of the tread band 8, are applied in laterally opposite positions on the carcass ply/plies 3.

[0051] The tread band 8 has a so-called “tread design” comprising a first series of ribs 10a and a second series of ribs 10b that are axially opposite, each extended transversely, preferably according to a direction that is oblique, with respect to the circumferential extension of the tread band 8 and alternatively intercalated with respective surface slots 11.

[0052] The ribs 10a, 10b respectively belonging to the first and second series are mutually offset in a circumferential direction and have respective axially inner apices 12 preferably arranged in proximity to an axial middle line plane M of the tyre 2. Preferably, the axially inner terminal portions of the ribs 10a, 10b respectively belonging to the first and to the second series are equidistant from the axial middle line plane M. More particularly, in the illustrated example, said axially inner apices 12 each terminate at or substantially at the axial middle line plane M.

[0053] From the axially inner apex of each rib, a main portion 13 is extended that leads to an axially outer apex 14, preferably arranged in proximity to the respective axially outer edge of the tread band 8.

[0054] Preferably, the main portion 13 has an extension that is tilted with respect to a circumferential direction, and the axially inner apex of each rib 10a, 10b is extended according to a direction that is angled with respect to the main portion 13.

[0055] The above-described tread design is formed during a moulding and vulcanisation treatment of the tyre 2 within the mould 1.

[0056] The mould 1 has a first half-part 15a and a second half-part 15b, axially opposite along a geometric centring axis X, which coincides with a geometric rotation axis of the tyre 2. The half-parts 15a, 15b are mutually side-by-side starting from an open condition, in which they are mutually spaced from each other as in FIG. 2, up to a closed condition in which the half-parts themselves mutually mate in order to define a moulding cavity 16 arranged to receive the tyre 2 being processed.

[0057] The green tyre 2, previously built in a known manner, is introduced between the half-parts 15a, 15b arranged in the open condition, and subsequently closed in the moulding cavity 16 following a mutual approach of the half-parts 15a, 15b. In a per se known manner, the tyre 2 closed in the moulding cavity 16 is subjected to a combined action of heating and pressing against an internal wall of the moulding cavity 16. The pressing determines the formation of the tread design and of possible graphic motifs and/or indications impressed for example in the zones of the sidewalls 9, while the administration of heat determines the molecular cross-linking of the elastomeric 5 materials employed in the attainment of the tyre 2 and its consequent geometric and structural stabilisation.

[0058] The moulding cavity 16 reproduces, in reverse image, the shape of the tyre 2 with the tread design to be obtained, and therefore has an internal wall 16a extended concentrically around the geometric centring axis X and carrying a first and a second series of circumferentially-distributed slots 17a, 17b, each configured in order to define one of the aforesaid ribs 10a, 10b on the tread band 8 of the moulded tyre 2.

[0059] Each slot 17a, 17b has a main section 18a, 18b extended from an axially outer terminal portion 19a, 19b to an axially inner terminal portion 20a, 20b of the slot 17a, 17b itself. The main sections 18a, 18b of the slots 17a, 17b respectively belonging to the first and to the second series, and/or at least the axially outer terminal portions 19a, 19b of the same, are respectively situated in the first half-part 15a and in the second half-part 15b of the mould. The axially inner terminal portions 20a, 20b of the slots 17a, 17b belonging to the first and to the second series are in turn situated at or nearby an intermediate reference plane P orthogonal to the geometric centring axis X, while the axially outer terminal portions 19a, 19b are spaced therefrom. In the illustrated example, such intermediate reference plane P coincides with an axial middle line of the moulding cavity 16 and of the tyre 2 being processed, but in some embodiments it can be axially offset with respect to the axial middle line itself.

[0060] The slots 17a, 17b respectively belonging to the first and second series are circumferentially offset with respect to each other and have the respective axially inner terminal portions 20a, 20b equidistant from the intermediate reference plane P. More particularly, in the illustrated example, each of the axially inner terminal portions 20a, 20b terminates at the intermediate reference plane P, i.e. at zero or substantially zero distance therefrom.

[0061] As is more visible in FIGS. 4 and 5, the main section 18a, 18b of each slot 17a, 17b is extended obliquely with respect to the intermediate reference plane P, and it is joined with the respective axially inner terminal portion 20a, 20b according to a direction that is tilted with respect to the latter. The main section 18a, 18b and the respective axially inner terminal portion 20a, 20b therefore form a cusp 21a, 21b having a vertex directed according to a circumferential direction.

[0062] The half-parts 15a, 15b of the mould 1 coupled in the closed condition define a mutual junction line 22 which is extended circumferentially along the internal wall 16a of the moulding cavity 16. Such junction line 22, unlike known solutions in which it has a rectilinear progression along a circumferential direction, is extended advantageously according to an undulating progression astride the intermediate reference plane P.

[0063] More particularly, the junction line 22 forms crests 23 alternatively arranged on respectively opposite sides with respect to the intermediate reference plane P, consecutively interconnected by connection sections 24.

[0064] In the illustrated example, the crests 23 and the connection sections 24 of the junction line 22 each have a rectilinear extension and follow each other according to a polygonal chain progression. In at least one possible embodiment variant, the crests 23 and the connection sections 24 of the junction line 22 can also each have a curvilinear progression, and/or be mutually connected according to a sinusoidal progression.

[0065] Each of the connection sections 24 is extended on the continuation of two contiguous crests 23, traversing the intermediate reference plane P in a position comprised between two circumferentially adjacent slots 17a, 17b, respectively belonging to the first and second series. Each of the slots 17a, 17b belonging to the first and to the second series is in turn intersected by one of the crests 23 formed by the junction line 22. The intersection of each crest 23 with the respective slot 17a, 17b occurs in proximity to the axially inner terminal portion 20a, 20b of the slot itself, more precisely at the aforesaid cusp 21a, 21b formed in the transition between the main section 18a, 18b and the same axially inner terminal portion 20a, 20b. Preferably, the crests 23 formed by the junction line 22 are extended each along a bisector direction which symmetrically intersects the vertex of the respective cusp 21a, 21b, by dividing the latter between the first and the second half-part 15a, 15b of the mould 1.

[0066] Due to the undulated extension of the junction line 22, the axially inner terminal portions 20a, 20b of the slots 17a, 17b respectively belonging to the first and to the second series are respectively situated in the second half-part 15b and in the first half-part 15a. Consequently, the axially inner terminal portion 20a, 20b of each slot 17a, 17b is situated on the half-part (e.g. the first half-part 15a) of the mould 1 opposite the half-part (e.g. the second half-part 15b) carrying the main section 18a, 18b and the axially outer terminal portion 19a, 19b of the same slot 17a, 17b.

[0067] The undulated extension of the junction line 22 between the half-parts 15a, 15b of the mould 1 considerably simplifies the moving apart of the half-parts themselves during the opening of the mould 1, offering an improved distribution of the stresses transmitted to the various parts of the tyre 2 for the purpose of its removal from the moulding cavity 16. In particular, it was found that the positioning of each of the axially inner terminal portions 20a, 20b—in the half-part 15a, 15b opposite that which houses the remaining parts of the respective slot 17a, 17b—resolves the problems emerging in the prior art in relation to the opening of the mould 1. Indeed, when the tyre 2 is elastically deformed in order to allow the ribs 10a, 10b formed on the tread band 8 to exit from the slots 17a, 17b present in the internal wall 16a of the moulding cavity 16, the exit of the axially inner terminal appendices of the ribs 10a, 10b from the respective axially inner terminal portions 20a, 20b of the slots 17a, 17b occurs with relative ease and with a significant reduction of the stresses transmitted between the rigid parts of the mould 1 and the corresponding deformable parts of the tyre 2.

[0068] In particular, there is no excessive concentration of the stresses—which tends to be formed in the prior art at the cusps 21a, 21b formed in proximity to the axially inner terminal portions 20a, 20b. This is also ascribable to the fact that the orientation of the main sections 18a, 18b of the slots 17a, 17b, opposite that of the axially inner terminal portions 20a, 20b positioned in the opposite half-part, generates—during the opening of the mould 1—force components that tend to rotate the tyre 2 around the geometric rotation axis thereof, facilitating the disengagement thereof from the slots 17a, 17b in a progressive manner and with an improved distribution of the stresses.

[0069] Thus, an advantageous reduction or elimination of the production defects is attained, also protecting the mould 1 and the mechanical components of the vulcanisation press from high stresses.