SURFACE TEXTURE FOR A TIRE TRAFFIC

Description

Field of invention

[0001] The present invention relates to the surface condition of tire treads baked in a vulcanization mold manufactured by three-dimensional printing (3D printing).

[0002] The invention proposes a texture of the tread surface of a tire which represents an optimal compromise between cost, aesthetics, and grip performance of the tire. Definitions

[0003] By convention, we define a reference (O, XX', YY', ZZ'), whose center O coincides with the geometric center of the tire, the circumferential XX', axial YY', and radial ZZ' directions respectively designate a direction tangent to the rolling surface of the tire according to the direction of rotation, a direction parallel to the axis of rotation of the tire, and a direction orthogonal to the axis of rotation of the tire.

[0004] By radially inner, respectively radially outer, we mean closer, respectively further from the axis of rotation of the tire.

[0005] Axially inner, respectively axially outer, means closer, respectively further from the equatorial plane of the tire, the equatorial plane of the tire being the plane passing through the middle of the tire tread and perpendicular to the axis of rotation of the tire.

[0006] A tire comprises a crown, intended to come into contact with the ground via a tread, the two axial ends of which are connected via two sidewalls with two beads ensuring the mechanical connection between the tire and the rim on which it is intended to be mounted.

[0007] Generally speaking, the person skilled in the art defines the tread of a tire primarily using the following design characteristics: the tread surface defining the total width of the tread, and the sculpture.

[0008] The "rolling surface" of the tread means the surface that includes all the points of the tire that will come into contact with the ground under normal driving conditions. These points that will come into contact with the ground belong to the contact faces of the blocks. For a tire, the "usual driving conditions" are the conditions of use defined, for example, by the ETRTO standard (European Tire and Rim Technical Organization). These conditions of use specify the reference inflation pressure corresponding to the load capacity of the tire indicated by its load index and its speed code. These conditions of use can also be called "nominal conditions" or "conditions of use". State of the art

[0009] 3D printing or additive manufacturing brings together processes for manufacturing parts in volume by adding or agglomerating material, by stacking successive layers. 3D printing makes it possible to create a real object: a designer draws the 3D object using a computer-aided design (CAD) tool. The resulting 3D file is processed by specific software that organizes the slicing of the different layers necessary to create the part. The slicing is sent to the 3D printer, which deposits or solidifies the material layer by layer until the final part is obtained. The principle remains close to that of a classic 2D printer, with this major difference: it is the stacking of layers that creates the volume.

[0010] The raw material is in the form of a powder, generally spherical, with a D90 particle size, most often between 20 and 45 µm. A D90 particle size means that 90% of the particles in the powder analyzed have a diameter between 20 and 45 µm. The powder is distributed in the machine either via a feed bin whose level is raised by a piston, or by a hopper. The powder is then spread by a roller or a doctor blade. The thickness of the layer varies depending on the material, the machine and the laser power but remains in the order of 20 to 100 µm.

[0011] To fuse a layer of powder, a source projects an energy beam onto the surface of this layer of powder, in a spot where such fusion occurs. The energy beam is then controlled so as to scan the surface in order to propagate this fusion over the entire surface of the layer. For example, the energy beam can be a laser which is generally of a power of 200W to 1000W.

[0012] Often, the process takes place in a controlled atmosphere enclosure (neutral gas, generally argon + control of the residual oxygen content) to avoid oxidation phenomena. The gas is chosen according to the nature of the material, but it is most often argon or nitrogen. Manufacturing begins from a plate, the parts will be welded to this plate at the end of manufacturing and this will require a cutting operation.

[0013] Conventionally, the energy beam scans different areas of the surface in a longitudinal direction and in a forward and return direction, alternately.

[0014] In particular, it has been proposed to control the energy source so that the task does not travel through each zone in a perfectly rectilinear translational movement in the longitudinal direction, but in a movement composed of a translation in the longitudinal direction and an oscillatory movement ("wobbling" in English). The oscillatory movement oscillates in particular in a transverse direction, so as to widen the weld pool.

[0015] Different oscillatory movements have been proposed.

[0016] One of them, which is generally called "circular mode", is such that the laser spot follows a trajectory comprising loops offset from each other in a longitudinal direction of the plate.

[0017] The surface conditions of parts manufactured by 3D printing with scanning of an energy beam as described above are characterized by a succession of circular beads which give an unsightly appearance to the part which can hinder its successful marketing.

[0018] This phenomenon is observed for tires vulcanized in a mold manufactured by 3D printing. The tire's tread surface reproduces the inverted pattern of the mold surface with circular grooves inherited from molding.

[0019] The inventors set themselves the objective of improving the surface condition of the molded tire without degrading the industrial cost, and without degrading the grip performance while having an aesthetic more in line with customer expectations.

[0020] The invention also relates to the field of tire vulcanization molds, in particular sector-type molds.

[0021] A sector mold comprises several separate parts which, by relative approximation, delimit a quasi-toroidal molding space. In particular, a sector mold comprises two lateral shells for molding the tire sidewalls, and several peripheral sectors located between the shells for molding the tire tread. The approximation of all these parts is ensured by appropriate kinematics by a desired mechanism. The raw blank of the future tire must be firmly applied and held against the mold to obtain precise geometric dimensions and architecture and to print the tread pattern.

[0022] To form the tread patterns, the mold sectors include elements projecting from the radially inner surface of the sectors, these elements forming a negative of the patterns to be molded onto the tire tread. This negative is subsequently referred to as the "lining."

[0023] Therefore, the lining is formed by all the molding elements of the tread including the surface of the mold intended to be the rolling surface, as well as the projecting elements intended to form cutouts on the tread of the vulcanized tire (circumferential and axial grooves, sipe incisions, etc.). The lining also includes hollow elements such as, for example, the tire wear indicators.

[0024] Noting that the same tire dimension can be vulcanized with several different sculptures depending on the intended uses, the design of the mold by distinguishing on the one hand the removable lining and on the other hand the fixing supports, presents numerous advantages.

[0025] Thus, to adapt a mold to the manufacture of a tire with given sculptures, it is sufficient to successively attach the different lining elements to each support block of the mold sectors.

[0026] More specifically, a filling as used in the invention is characterized in that it comprises: a skin comprising first and second opposite surfaces, the first surface being intended to be in contact with a support block of a tire mold, the thickness of the skin being between 0.25 and 3 millimeters, and a plurality of protruding and recessed trim elements of the second surface of the skin, the trim elements being intended to form sculptures of a portion of a radially external surface of a tire, the skin and the protruding and recessed elements of the trim being produced in a single piece by 3D printing.

[0027] The lining, which includes protruding, hollow elements and is intended to be the sculpture of the tread, is in some cases of great complexity in shape depending on the desired tire performance. 3D printing manufacturing is adapted to this type of complexity by relying on computer-aided design modeling of the lining. Indeed, the laser can be controlled by a computer including a model of the part and the part can then be manufactured by successive sintering of superimposed layers of powder.

[0028] The inventors used this manufacturing technology to find a solution to the objective of improving the surface condition of the tire obtained by molding without degrading the industrial cost price, the grip performance while having an aesthetic more in line with customer expectations.

[0029] Patent document EP 2 799 250 A1 discloses a tire having characteristics similar to the preamble of independent claim 1. Statement of the invention

[0030] This objective has been achieved by a tire having a tread, portions of the tread surface of which intended to be in contact with a ground comprise a texture formed by an arrangement of contiguous pyramid-shaped elements, each pyramid-shaped element having a parallelogram-type base positioned on the tread surface, and an apex located at a radial distance H from the base, said base being defined by: a first pair of mutually parallel sides separated by a first pitch P1, and forming an angle Alpha with a circumferential direction; a second pair of mutually parallel sides separated by a second pitch P2, and forming an angle Beta with the circumferential direction of the tire; the first pair of parallel sides, and the second pair of parallel sides forming at their intersection the vertices of the parallelogram-type bases, constituting a mesh of the portions of the rolling surface, the angle Alpha is included in the interval between [15°; 75°], the angle Beta is included in the interval [-75°; -15°], and the normal distance from the apex H to the base is included in the interval [0.15 mm; 0.5 mm].

[0031] The texture of the tread of a tire of the invention constitutes a mesh of the portions of the tread surface containing neither cutouts, nor protruding parts, nor hollow parts.

[0032] The texture observable on the tread comprises a first bundle of segments parallel to each other making an angle Alpha with the circumferential direction between [15°; 75°], and a second bundle of segments two by two parallel making an angle Beta with the circumferential direction between [-75°; -15°]. The points at the intersection of the segments are the nodes of the mesh and correspond to the vertices of parallelograms which constitute the base of a pyramidal shape whose apex is located in the radially external direction passing the center of the parallelogram.

[0033] In some embodiments, the apex may be located radially inward of the parallelogram so as to form a hollow inverted pyramid.

[0034] The angles Alpha and Beta determine the orientation of the parallelograms in the tread plane. When Alpha and Beta are close to 15° in absolute value, the texture pattern is generally oriented along the circumferential direction, and when Alpha and Beta are close to 75°, the texture pattern is oriented along the axial direction of the tread.

[0035] Steps P1 and P2 determine the area of ​​the base of the pyramid shape. They correspond to half the length of the diagonals of the base parallelograms.

[0036] Preferably, the first step P1 and / or the second step P2 is constant, and even more preferably, the angle Beta is equal in absolute value to the angle Alpha. In this embodiment, the parallelograms are rhombuses. The texture has homogeneity and symmetry both in the circumferential direction and in the transverse direction.

[0037] Advantageously, the first step P1 of the first pair of sides of the basic parallelogram is less than or equal to 2*H / Tan(Alpha). Also advantageously, the second step P2 of the second pair of sides of the basic parallelogram is less than or equal to 2*H / Tan(Beta).

[0038] Advantageously, the texture of the portions of the rolling surface has a density of pyramid-shaped elements greater than or equal to 10 elements per square centimeter.

[0039] A second subject of the invention is a tire vulcanization mold which comprises a lining which reproduces the texture of the first claim after vulcanization of the tire. The particularity of this mold is to have a lining manufactured by 3D printing.

[0040] More specifically, the invention also relates to a vulcanization mold for a tire capable of cooperating with a curing press, said mold comprising two shells each ensuring the molding of a sidewall of the tire and a ring of sectors ensuring the molding of the tire tread, each sector comprising a support and a molding lining located radially inside the support, said lining comprising a skin comprising first and second opposite surfaces, the first surface being intended to be in contact with a support block of the mold, the second surface of the skin having a plurality of projecting and hollow elements intended to form the sculpture of the tread of a tire after vulcanization, characterized in that the second surface of the skin of the lining, between the projecting elements and the hollow elements, comprises a texture made of an arrangement of contiguous hollow pyramid-shaped elements,each pyramid-shaped element having a parallelogram-type base positioned on the skin, and an apex located at a distance H1 from the base, radially towards the inside of the lining.,

[0041] The distance H1 from the apex of the pyramidal shape to the parallelogram-type base positioned on the skin of the lining is determined so that after vulcanization of the tire in the mold this distance is equal to the distance H defined above.

[0042] Preferably, the texture of the skin of the filling comprises a density of hollow pyramid-shaped elements greater than or equal to 10 elements per square centimeter.

[0043] Finally, a third object of the invention is a 3D printing manufacturing method which is used for the production of the mold lining.

[0044] The invention proposes a method for manufacturing by 3D printing the lining of a vulcanization mold of a tire, said lining comprising a skin comprising first and second opposite surfaces, the first surface being intended to be in contact with a support block of the mold, the second surface of the skin having a plurality of projecting and hollow elements intended to form the sculpture of the tread of a tire after vulcanization, said method by 3D printing comprising the following steps: a. Scanning by an energy beam projected by a laser generator on the second surface of the skin so as to create a first series of segments parallel to each other making an angle Alpha with the circumferential direction between [15°; 75°]; b. Scanning the energy beam projected by a laser generator on the second surface of the skin so as to create a second series of segments parallel to each other making an angle Beta with the circumferential direction between [-15°; -75°]; c. The points at the intersection of the segments of the first series and the second forming the nodes of a mesh and corresponding to the vertices of parallelograms, scanning the energy beam projected by a laser generator at the center of each parallelogram so as to dig a pyramidal shape whose apex is positioned in the normal direction towards the inside of the lining. Description of Figures

[0045] The invention will be better understood from reading the following description, given solely by way of example and with reference to the drawings in which: THE Figures 1-A , is an extract of the tread obtained after vulcanization of the tire representing the texture proposed by the invention. The Figure 1-B is the same representation as the Figure 1-A but seen from the computer-aided design (CAD) side. View 1-C is a magnification of the Figure 1-B which highlights the construction of the texture of the invention. Figures 2-A to 2-E illustrate commonly used mold terminology. The Figure 1-A is a perspective view of a mold fitting, the Figure 2-B is a perspective view of a mold sector comprising a support block and the lining shown in the Figure 2-A fixed on said support block; the Figure 2-C is a top view of the sector of the Figure 2-B , there Figure 2-Dis a sectional view of the sector of the Figure 2-B finally the Figure 2-E is an example of a mold with its sectors including the fittings attached to it. The Figures 3-A, 3-B, and 3-C represent partial views of mold linings obtained by 3D printing. Graph 3-B is an enlargement of view 3-A to highlight the texture proposed by the invention, in comparison with conventional textures visualized on the Figure 3-C formed from concentric circle patterns. The Figure 3-D is a magnification of the Figure 3-B with the texture pattern of the invention showing the texture with pyramid-shaped elements. The figure 4 represents a mold whose lining is manufactured by 3D printing. The Figure 5 represents the diagram of the operating principle of 3D printing manufacturing. The trim with its components, skin, protruding elements, hollow elements are manufactured in one piece by 3D printing. Detailed description of the invention

[0046] There Figure 1-C shows the details of the construction of the tire tread pattern with the general reference 1. We can see the pyramid-shaped pattern (ABCDE), represented by the reference 2, whose base is the parallelogram (ABCD). The sides AB and DC are parallel and make an angle Alpha with a circumferential direction (XX'), as for the sides DA and CD, they are also parallel and make an angle Beta with this same circumferential direction. The apex E is positioned radially outside the tread surface. The Figure 1-B is the computer-aided design modeling of the tread surface from the pattern shown on the Figure 1-C , and finally the Figure 1-A is an extract of the tread surface after vulcanization of the tire.

[0047] There Figure 2-A represents a portion of trim 14 limited to the sector displayed on the Figure 2-B . More specifically, a gasket 14 as used in the invention is characterized in that it comprises: a skin 18 comprising first 20 and second 22 opposite surfaces, the first surface being intended to be in contact with a support block 12 of a tire mold, the thickness of the skin 18 being between 0.25 and 3 millimeters for a vulcanization mold of a passenger car tire, and a plurality of protruding and hollow lining elements 24 of the second surface 22 of the skin, the lining elements 24 being intended to form sculptures of a portion of a radially external surface of a tire.

[0048] It has been represented on the Figure 2-B a sector, designated by the general reference 10 of a sector mold for vulcanizing a tire. The sector 10 comprises a support block 12 and a lining 14 attached to the support block 12.

[0049] The support block 12 is formed by a solid steel block comprising in particular a support surface 16 intended to receive the lining 14. The support surface 16 is substantially smooth and has a shape substantially matching the general curvature of the tread of the tire to be molded.

[0050] The lining 14 comprises a skin 18 containing first 20 and second 22 opposing surfaces, the first surface 20 being intended to be in contact with the support surface 16 of the support block 12.

[0051] The skin 18 further comprises a plurality of trim elements 24 projecting from the second surface 22, the trim elements 24 being intended to form the sculptures of a portion of the tread of the tire to be molded.

[0052] Among the lining elements 24, there are in particular slats 26 intended to form circumferential slots in the tread of the tire, or circumferential cords 28 intended to form a longitudinal groove on the tread of the tire.

[0053] The different cords 28 are connected by axial strips 30 so as to form a network of trim elements 24.

[0054] There Figure 2-Erepresents the general reference mold 3 in the open position. The shells which are intended to mold the sidewalls of the tire are not shown. Each sector is generally made of steel or cast iron. The molding lining 14 is generally made of an aluminum alloy. In a known manner, several sectors 10 are arranged side by side circumferentially around the axis of symmetry VV' of the mold and form a ring, the sectors being radially movable by means of a device comprising a crown (4) which encompasses the sectors. The crown 4 is shown on the figure 4 .

[0055] THE Figures 3-A, 3-B, 3-C and 3-D are relative to the mold obtained by 3D printing. The Figure 3-Ais a portion of the lining 14 comprising the skin 18 with the texture of the invention but on the mold side, that is to say that it is the reverse pattern of that of the tire tread. References 100 and 120 are examples of protruding and hollow elements which will imprint the tread after molding.

[0056] There Figure 3-B is a magnification of the filling portion of the Figure 3-A which more clearly shows the pattern of the invention110 carried by the skin 18 of the lining 14.

[0057] There Figure 3-C represents the classic surface state obtained by 3D printing with concentric circles revealing 115 cords which print the tire after vulcanization. The Figure 3-A is precisely the improvement of this 3-C surface condition.

[0058] There figure 4illustrates by a partial sectional view of a sector 10 of a vulcanization mold where the main parts of the mold are seen. The lining 14 is fixed on a support 12, generally made of steel or cast iron. The lining 14 is generally made of an aluminum alloy and carries the negative of the tread pattern of the tire. A crown 4 surrounds the sectors 10 so as to allow the operations of opening and closing the mold. The shell 5 ensures the molding of the sidewalls and comprises an interface 7 with the lining 14. The shell 5 and the crown 4 are carried by a plate 6. The crown 4 has a radially inner surface of frustoconical shape which cooperates with the radially outer surface of frustoconical shape of the sectors 10.

[0059] Trim 14 is made by 3D printing. The pattern of the Figure 3-Dformed around a pyramidal shape 2 is reproduced on the surface 22 of the skin 18 between the projecting and recessed trim elements 24.

[0060] There Figure 5 shows the schematic diagram of 3D printing manufacturing.

[0061] Before 3D printing manufacturing, the first step is to model the part to be manufactured using computer-aided design (CAD) software, which defines the morphological constraints of the part to be produced. The next step is to import the previous data into software that defines the development strategy for the object, as well as the process parameters. Instructions are then sent to the 3D printing manufacturing machine for the production of the object in its physical form.

[0062] So on the Figure 5, the part to be produced is gradually manufactured on a removable plate 230 which is identified by a local axis system (X1, X2, X3). The plane (X1, X2) being parallel to the plane of the plate 230, and the direction X3 being orthogonal to this same plane. The plate 230 is supplied with powder by the feed chute 220, a powder layer equalization system 250 spreads the powder over a homogeneous thickness. The laser generator 270 directs the laser beam onto an optical system 210. The movement of the laser on the plate 230 is done using an optical chain 210 which is in fact a system of oscillating mirrors controlled by the CAD data. The manufactured part 260 is welded to the support 240.

[0063] To produce the mold lining, which generates the texture of the tire's tread surface, the laser of the 3D printing manufacturing process traces on the skin of the lining a first beam of segments parallel to each other making an angle Alpha with the circumferential direction between [15°; 75°], and a second beam of segments two by two parallel making an angle Beta with the circumferential direction between [-75°; -15°]. The points at the intersection of the segments are the nodes of the mesh and correspond to the vertices of the parallelograms. Each parallelogram is hollowed out in its center by the laser so as to form an inverted pyramid.

[0064] The main parameters of the 3D printing manufacturing process used for the invention are: the laser power [100 - 1000 W], the laser scanning speed [0.1 - 5 mm.s-1], the laser spot diameter [50 - 200 µm], adjustable by adjusting the distance between the surface of the powder layer and the laser focal point, the powder layer thickness [20 - 200 µm], the laser spacing [25 - 200 µm] which corresponds to the spacing between two adjacent and parallel laser passage lines. It is generally less than the laser spot diameter in order to obtain an overlapping area.

[0065] The invention has been described in relation to a sector-type mold. It can also be implemented in relation to a mold of another type. Tests

[0066] To validate the invention, the test was carried out on a tire of standardized dimension according to ETRTO (ETRTO: European Tire and Rim Technical Organization): 13R22.5 TL 156 / 151 K. The inflation pressure is 875 kilos Pascal for a load to be carried in simple assembly of 3450 kilos.

[0067] The tire has been tested according to regulation UN / ECE / R117 which covers the mandatory performance thresholds before the marketing of tires in Europe issued by the United Nations Economic Commission for Europe (UN / ECE).

[0068] The results of the tests carried out here concern grip on wet and snowy surfaces.

[0069] Compared to the standard provided for by the regulation (SRTT), the tire of the invention presents an improved performance in wet grip of 120%, and on snow an improvement of 185%.

[0070] The invention was presented for passenger car and heavy goods vehicle tires, but in reality it is applicable to any type of tire.

Claims

1. Tyre (1) provided with a tread of which portions of the tread surface that are intended to be in contact with the ground comprise a texture formed by an arrangement of contiguous elements of pyramidal shape, each element of pyramidal shape having a base of parallelogram type positioned on the tread surface, and an apex situated at a radial distance H from the base, said base being defined by: ▪ a first pair of mutually parallel sides spaced apart from one another by a first pitch P1, and forming an angle alpha with a circumferential direction of the tyre, ▪ a second pair of mutually parallel sides spaced apart from one another by a second pitch P2, and forming an angle beta with the circumferential direction, ▪ the first pair of parallel sides and the second pair of parallel sides, which form, at their intersection, the vertices of the bases of parallelogram type, constituting a mesh of the portions of the tread surface, characterized in that the angle Alpha is in the range [15°; 75°], in that the angle Beta is in the range [-75°; -15°], and in that the normal distance from the apex H to the base is in the range [0.15 mm; 0.5 mm].

2. Tyre (1) according to Claim 1, wherein the first pitch P1 and / or the second pitch P2 is constant.

3. Tyre (1) according to either of the preceding claims, wherein the angle Beta is equal in terms of absolute value to the angle Alpha.

4. Tyre (1) according to one of the preceding claims, wherein the first pitch P1 of the first pair of sides is less than or equal to 2*H / Tan (Alpha).

5. Tyre (1) according to one of the preceding claims, wherein the first pitch P2 of the first pair of sides is less than or equal to 2*H / Tan (Beta).

6.

12. Tyre (1) according to one of the preceding claims, wherein the texture of the portions of the tread surface has a density of elements of pyramidal shape that is greater than or equal to 10 elements per square centimetre.

7. Vulcanization mould (3) for a tyre according to one of Claims 1 to 6, able to cooperate with a curing press, said mould having two shells (5) that each ensure the moulding of a sidewall of the tyre and a ring (4) of sectors (10) that ensures the moulding of the tread of the tyre, each sector (10) having a support (12) and a moulding lining (14) situated radially on the inside of the support (12), said lining (14) having a skin (18) comprising opposing first (20) and second (22) surfaces, the first surface (20) being intended to be in contact with a support block (12) of the mould, the second surface (22) of the skin having a plurality of protruding and recessed elements (24) intended to form the tread pattern of the tread of a tyre after vulcanization, characterized in that the second surface (22) of the skin (18) of the lining (14), between the protruding elements and the recessed elements (24), comprises a texture made of an arrangement of recessed contiguous elements of pyramidal shape, each element of pyramidal shape having a base of parallelogram type positioned on the skin, and an apex situated at a radial distance H1 from the base, radially towards the inside of the lining (14).

8. Mould (3) according to Claim 7, wherein the texture of the skin (18) of the lining (14) comprises a density of recessed elements of pyramidal shape that is greater than or equal to 10 elements per square centimetre.

9. Method for manufacturing, by 3D printing, the lining (14) of a mould for vulcanizing a tyre according to either of Claims 7 and 8, said lining (14) having a skin (18) comprising opposing first (20) and second (22) surfaces, the first surface (20) being intended to be in contact with a support block (12) of the mould, the second surface (22) of the skin (18) having a plurality of protruding and recessed elements intended to form the tread pattern of the tread of a tyre after vulcanization, said 3D printing method involving the following steps: a. Scanning by a beam of energy projected by a laser generator (270) onto the second surface (22) of the skin (18) so as to create a first series of mutually parallel segments forming an angle Alpha with the circumferential direction of between [15°; 75°]; b. Scanning of the beam of energy projected by a laser generator (270) onto the second surface (22) of the skin (18) so as to create a second series of mutually parallel segments forming an angle Beta with the circumferential direction of between [-15°; -75°]; c. The points at the intersection of the segments of the first series and of the second forming the nodes of a mesh and corresponding to the vertices of parallelograms, scanning of the beam of energy projected by a laser generator (270) at the centre of each parallelogram so as to hollow out a pyramidal shape of which the apex is positioned in the normal direction towards the inside of the lining.