INSERT FOR A MOULD FOR VULCANISING TYRES FOR VEHICLE WHEELS, PROCESS FOR PRODUCING SAID INSERT AND PROCESS FOR VULCANISING TYRES

Abstract

The present invention relates to an insert (10) for a mould (1) for vulcanising tyres for vehicle wheels, the insert being arranged to be received in a seat (5) formed on a moulding surface (4) of the mould (1) and comprising a base surface (12) from which a plurality of projections (20) extends. Each projection comprises a lateral surface (21) extending away from said base surface (12), which lateral surface defines a tapered profile of said projection (20) away from said base surface (12), is inclined at an angle of between 10° and 25° with respect to a direction (X) perpendicular to said base surface (12), and has a roughness of between 4 and 11 μm. The invention is also related to a process for producing said insert and to a process for producing a tyre for vehicle wheels.

Claims

1. Insert (10) for a mould (1) for vulcanising tyres for vehicle wheels, the insert being arranged to be received in a seat (5) formed on a moulding surface (4) of said mould (1) and comprising a base surface (12) from which a plurality of projections (20) extends, each of which comprises a lateral surface (21) extending away from said base surface (12) towards a peak (23) of said projection (20) that is remote from said base surface, wherein said lateral surface (21): defines a tapered profile of said projection (20) away from said base surface (12), is inclined of an angle of between 10° and 25° with respect to a direction (X) perpendicular to said base surface (12), and has a roughness of between 4 and 11 μm.

2. Insert according to claim 1, wherein said projections (20) are substantially identical to one another.

3. Insert according to either claim 1 or claim 2, wherein said lateral surface (21) is inclined of an angle of between 15° and 25° with respect to said direction (X) perpendicular to said base surface (12).

4. Insert according to any one of the preceding claims, wherein said lateral surface (21) has a roughness of between 5.5 and 8 μm.

5. Insert according to any one of the preceding claims, wherein said base surface (12) has a roughness that is less than the roughness of said lateral surface (21).

6. Insert according to any one of the preceding claims, wherein said base surface (12) has a roughness of between 4.5 and 7 μm.

7. Insert according to any one of the preceding claims, wherein said projections (20) are raised with respect to said base surface (12) by a height of between 0.5 mm and 0.7 mm.

8. Insert according to any one of the preceding claims, wherein said projections (20) have a substantially circular cross section.

9. Insert according to any one of the preceding claims, wherein said projections (20) have a base (22) which has a diameter (D1) of between 0.40 and 0.49 mm.

10. Mould (1) for vulcanising tyres for vehicle wheels, comprising: at least one sidewall plate (3) on which a moulding surface (4) is defined which is intended for contacting an external surface of a sidewall (102) of a green tyre (100), a removable insert (10) that is received in a seat (5) formed on said moulding surface (4) and comprises a base surface (12) intended for contacting a portion of said external surface of the sidewall (102) of the green tyre (100), wherein said insert (10) is according to any one of the preceding claims.

11. Vulcanisation mould according to claim 10, wherein said base surface (12) is substantially continuous with said moulding surface (4).

12. Process for producing an insert according to any one of claims 1 to 9, comprising: providing a main body (11) of said insert, removing material from said main body (11) by means of laser so as to form a base surface (12) thereon with respect to which a plurality of projections (20) is raised, each of which comprises a lateral surface (21) extending away from said base surface (12) towards a peak (23) of said projection that is remote from said base surface (12), wherein said lateral surface (21) defines a tapered profile of said projection away from said base surface (12) and is inclined at an angle of between 10° and 25° with respect to a direction (X) perpendicular to said base surface (12), treating at least said plurality of projections (20) so as to obtain a roughness of said lateral surface (21) of between 4 and 11 μm.

13. Process according to claim 12, wherein at least said plurality of projections (20) is subjected to a sandblasting treatment.

14. Process according to claim 13, wherein said sandblasting treatment is carried out using glass microspheres which have a diameter of between 20 and 100 μm.

15. Process according to claim 12, wherein a coating layer is applied to at least said plurality of projections (20).

16. Process according to claim 15, wherein said coating layer is applied by means of depositing a composite material formed of polymeric particles dispersed in a metal matrix.

17. Process according to claim 16, wherein said metal matrix comprises a nickel and phosphorus alloy.

18. Process according to either claim 16 or claim 17, wherein said polymeric particles are tetrafluoroethylene-based particles.

19. Process according to claim 15, wherein said coating layer is applied by means of galvanically depositing metallic chromium.

20. Process according to either claim 16 or claim 19, wherein said deposition is carried out until the coating layer has a thickness of between 5 and 15 μm.

21. Process according to any one of claims 12 to 20, wherein said removal of material by means of lasers is carried out using a power of between 20 and 60 KW, a frequency of between 100 and 300 KHz and a speed of between 800 and 1500 mm/s.

22. Process for producing a tyre for vehicle wheels, comprising: building a green tyre (100), and moulding and vulcanising said green tyre in a mould (1) according to either claim 10 or claim 11.

Description

[0086] The features and advantages of the invention will become clearer from the detailed description of a preferred exemplary embodiment thereof, illustrated by way of indication and in a non-limiting manner with reference to the accompanying drawings, in which:

[0087] FIG. 1 is a schematic cross-sectional view of a portion of a vulcanising mould for tyres for vehicle wheels, fitted with an insert produced in accordance with the present invention;

[0088] FIG. 2 is a schematic view on an enlarged scale of the portion of the mould denoted by II in FIG. 1;

[0089] FIG. 3 is a schematic sectional view of the insert of FIG. 2 when decoupled from the mould;

[0090] FIG. 4 is a plan view from above of the insert of FIG. 3;

[0091] FIG. 5 is a schematic sectional view on a further enlarged scale of a portion of the insert indicated by V in FIG. 3;

[0092] FIG. 6 is a schematic view of a portion of a sidewall of a tyre obtained using the mould of FIG. 1.

[0093] With reference to the accompanying figures, a mould for vulcanising tyres for vehicle wheels produced in accordance with the present invention is denoted overall by 1.

[0094] The mould 1 has a conventional overall general structure and comprises a closed moulding chamber in which a green tyre 100 is received for the moulding and vulcanisation process.

[0095] The tyre 100 has a generally toroidal shape developed around a rotational axis and comprises a tyre structure that is conventional per se, on which an elastomeric material tread band 101 is arranged in a radially outer position, on which tread band there is defined a tread surface intended for contact with a road surface, as well as a pair of sidewalls 102, extended from the ends of the tread surface towards the rotational axis.

[0096] With reference to the radial and axial directions of the tyre 100 when it is received in the mould 1, the moulding chamber is delimited radially by a plurality of heads 2, generally at least 8, which are suitably shaped to form annular sectors and which are intended as a whole to contact the tread band 101, and axially by a pair of sidewall plates 3, which are substantially intended to contact the tyre sidewalls 102. Both the heads 2 and sidewall plates 3 may be moved away from each other to allow the mould to be opened and the green tyre to be inserted into the moulding chamber and removed once it has been moulded and vulcanised.

[0097] A heating device 7 is associated with the heads 2 and sidewall plates 3 to transmit to the green tyre the heat necessary to reach the temperature intended for vulcanisation.

[0098] Inside the moulding chamber of the mould 1, a membrane, which is conventional per se and not shown in the accompanying figures, may be provided and may be expanded to compress the green tyre 100 against the inner walls of the heads 2 and sidewall plates 3 at a predetermined pressure.

[0099] On the inner walls of the mould 1 intended to come into contact with the green tyre, corresponding pluralities of raised portions and recesses are suitably formed so as to obtain, by moulding on the radially outer surface of the tread band 101, the configuration of the tread pattern and, on the sidewalls 102, writing and images useful, for example, for providing visible information to the user regarding the characteristics of the tyre 100.

[0100] In particular, on at least one sidewall plate 3, and preferably on both sidewall plates 3, a moulding surface 4 is defined and is intended to contact the outer surface of a tyre sidewall 102.

[0101] On the moulding surface 4 of the sidewall plate 3 there is also provided, in a suitable position, a seat 5 to accommodate, with the option of removal, an insert 10.

[0102] The insert 10 comprises a main body 11, on which there is defined a base surface 12, turned towards the outside of the sidewall plate 3 when the insert 10 is received in the seat 5, as well as a stem 13 extended from the main body 11, on the opposite side to the base surface 12.

[0103] On the sidewall plate 3 there is also provided a locking device 8 to engage the stem 13 and hold the insert 10 firmly engaged in the seat 5.

[0104] This locking device may be of the screw type, or snap type, or magnetic type, or it may adopt any other system suitable for holding the insert 10 inside the seat 5 removably.

[0105] Preferably, from the main body 11 there is also extended, in an eccentric position, a pin (not shown in the figures) intended to be received in a dedicated recess formed inside the seat 5. The engagement of the pin in the corresponding recess is necessary so that the insert 10 may be fully received in the seat 5 and ensures that the insert 10 is coupled to the seat 5 only with a predetermined orientation.

[0106] Preferably, the main body 11 has a profile tapered away from the base surface 12, so as to allow a substantially tight fit with the sidewall plate 3, and so as to prevent, as far as possible, any elastomeric material from entering the seat 5.

[0107] As already mentioned, the base surface 12 is arranged inside the moulding chamber and is intended to contact the tyre sidewall 102.

[0108] The coupling of the insert 10 in the seat 5 is such that the base surface 12 is substantially continuous with the moulding surface 4 of the sidewall plate 3, without any significant steps at the transition between the two surfaces.

[0109] In addition, the base surface 12 has a curved profile, quite similar to the profile of the moulding surface 4, so as to maintain the continuity of the overall surface trend.

[0110] The base surface 12, seen from above (FIG. 4), has a generally rectangular form with rounded corners, and on it there are identified an upper edge 14, a lower edge 15, connected to each other by a pair of opposite side edges 16.

[0111] In the preferred example described herein, the base surface 12 has a length of approximately 34 mm and a height of approximately 19 mm.

[0112] The upper edge 14 is positioned in the seat 5 in a radially outer position, intended to face the tread surface of the tyre 100, while the lower edge 15 is positioned in the seat 5 in a radially inner position, intended to face the ends (the beads) of the tyre 100.

[0113] Preferably, to facilitate the insertion of the insert 10 into the seat 5 with the correct orientation, the upper edge 14 is connected to the side edges 16 with a first radius of curvature, while the lower edge 15 has a second radius of curvature, smaller than the first radius of curvature.

[0114] In particular, the first radius of curvature is about 7 mm, while the second radius of curvature is about 5 mm.

[0115] A substantially square central area 18, with sides of approximately 15 mm, is defined on the base surface, and in said area there is a QR code produced in the ways described hereinafter, surrounded by a framing area 19 of approximately 2 mm, which is substantially smooth, and two opposite lateral areas 17, in which information of alphanumerical nature may be provided.

[0116] On the base surface 12, there is formed a plurality of projections 20, extended from the base surface 12 along a direction X substantially perpendicular thereto.

[0117] The projections 20 are substantially identical to one another and have a truncated cone profile defined by a lateral surface 21 extended from a base 22, which is part of the base surface 12, towards a peak 23.

[0118] The lateral surface 21 is inclined at an angle A of approximately 20° to the direction X and has a roughness Ra between approximately 6 to and approximately 7 μm.

[0119] Each projection 20 also has a height H of approximately 0.6 mm and a diameter varying between a value D1 of approximately 0.45 mm at the base 22 and a value D2 of approximately 0.1 mm at the peak 23.

[0120] The base surface 12 preferably has a roughness lower than the roughness of the lateral surface 21, for example between 5 and 6 μm.

[0121] The projections 20 are arranged inside the central area 18 according to a predetermined configuration, depending on the coded information contained in the QR code (see FIG. 4, for example). In particular, the central area 18 is subdivided into basic square areas P with a side length of 0.5 mm, and each of these basic areas P comprises a projection 20 which, under consideration of the dimensions of the base 22, occupies the basic area almost fully with a free margin of a few hundredths of a millimetre, or, alternatively, comprises only the base surface 12.

[0122] The insert 10 is formed in accordance with one of the processes described below.

[0123] On the central body 11, appropriately shaped, there is identified the surface intended to remain turned towards the outside when the insert 10 is received in the seat 5. This surface is then subjected to a treatment of material removal by laser differently in the various areas, so that in some areas the material is removed uniformly, defining the base surface 12, this being substantially smooth, while in other areas the processing is carried out by removing the material present around specific portions of the main body, so as to form the projections 20.

[0124] The positioning of the basic areas provided with projections 20 and of the basic areas formed only by the base surface 12 is predetermined depending on the QR code to be moulded on the tyre sidewall 102.

[0125] In particular, the laser treatment is carried out maintaining the beam substantially perpendicular to the surface being processed and using a power between 20 and 60 KW, a frequency between 100 and 300 KHz and a speed between 800 and 1500 mm/s.

[0126] The laser treatment leaves both the base surface 12 and the peak 23 of the projections 20 with micro grooves, whereas the lateral surface 21 of the projections 20 has a profile with micro steps, which, at the ends, may be hook-shaped.

[0127] Such irregularities of the surfaces define their roughness and, in addition, determine the tendency of the elastomeric compound to adhere thereto.

[0128] At the end of the material-removal step, the roughness of the surfaces and above all the ability of the elastomeric compound to be removed from the insert without tearing is not yet at the desired levels, and therefore the base surface 12 and its projections 20 are subjected to a further treatment which, in a first preferred embodiment, is a sandblasting treatment.

[0129] In particular, the sandblasting is conducted by throwing a jet of glass microspheres with dimensions of between 20 and 100 μm, in the absence of water, from a distance of 10 to 50 cm at a pressure of approximately 5-10 bar.

[0130] Following this treatment, the crests of the irregularities of the surfaces are smoothed, and, in particular, any micro hooks and the micro points present on the lateral surfaces 21 of the projections 20 are rounded.

[0131] This makes it possible to sensibly increase the ability of the elastomeric compound to be detached from the mould, thus also increasing the difference in roughness between the base surface 12 and lateral surface 21.

[0132] In particular, after the sandblasting treatment, the base surface 12 has a roughness between 5 and 6 μm, and the lateral surface 21 has a roughness between 6 and 7 μm.

[0133] In a second preferred embodiment, the base surface 12 and the projections 20 thereof, at the end of the laser treatment, are subjected to a coating treatment that involves the application of a coating layer.

[0134] In a first exemplary embodiment of the coating treatment, the insert may be treated by depositing, on the base surface 12 and on the projections 20, a composite material formed by particles based on tetrafluoroethylene and dispersed in a matrix based on a nickel-phosphorus alloy.

[0135] In particular, the matrix is an alloy formed by 87%-90% nickel and 10-13% phosphorus and contains from 20% to 30% by volume of tetrafluoroethylene particles less than 1 μm in size.

[0136] In a second exemplary embodiment, the coating layer, which is about 5-15 μm thick, is applied to the base surface 12 and to the projections 20 by galvanic deposition of metallic chrome.

[0137] The insert 10, once prepared, is positioned in the seat 5 and coupled at the stem 13 by the hooking device 8, so as to be firmly held on the sidewall plate 3 and with the base surface 12 substantially aligned with the moulding surface 4.

[0138] The correct positioning of the seat 5 is favoured by the different curvature of the connections of the upper and lower edges to the lateral edges and by the provision of the pin.

[0139] The vulcanising and moulding process of the tyre 100 is carried out in the usual manner, introducing the green tyre into the moulding chamber, closing the mould 1, expanding the internal membrane, and heating the mould.

[0140] During this step, the green tyre sidewall 102 is pressed against the mould surface 4 and the base surface 12 of the insert. In this way, the surface of the sidewall 102 is imprinted with that which is formed in relief on the base surface 12a of the insert. In particular, a QR code 105 is obtained, as in the central area 18 of the insert 10, and is formed by the plurality of recesses corresponding to the projections 20 and by the substantially smooth surface corresponding to the base surface 12 between the projections 20.

[0141] Once the vulcanising step is complete, the mould 1 is opened and the moulded and vulcanised tyre 100 is removed.

[0142] Thanks to the features of the present invention, the QR code 105 is intact, without any portions of the compound torn between the recesses and with an optimal contrast between dark basic areas and light basic areas, such that the QR code may be read easily and accurately by an optical reader.