TIRE WITH A RETRACTABLE TREAD

Abstract

The invention relates to a tire (1) that can be regrooved at least once and whose tread, consisting of at least one first elastomeric compound forming at least the tread surface, has at least one circumferential groove (3) that can be regrooved. According to the invention, the material to be regrooved consists of at least one first layer of a second elastomeric compound, said second elastomeric compound having a volume resistivity ρ different from that of said first elastomeric compound, forming at least the tread surface. Figure for the abstract: Fig 1

Description

Title of the invention: TIRE WITH A REGRESSABLE TREAD

[0001] The present invention relates to a tire, with a radial carcass reinforcement and more particularly to a tire intended to equip vehicles carrying heavy loads, such as, for example, trucks, tractors, trailers or road buses.

[0002] Generally, in heavy-duty tires, the carcass reinforcement is anchored on both sides in the bead area and is radially surmounted by a crown reinforcement consisting of at least two superimposed layers formed of parallel wires or cables in each layer and crossed from one layer to the next at angles between 10° and 45° with the circumferential direction. These working layers, forming the working reinforcement, may also be covered by at least one protective layer formed of advantageously metallic and extensible reinforcing elements, known as elastic elements.It may also include a layer of low-extensibility wires or cables forming an angle of between 45° and 90° with the circumferential direction. This layer, called the triangulation layer, is radially positioned between the carcass reinforcement and the first crown layer, known as the working layer, which is formed of parallel wires or cables having angles of no more than 45° in absolute value. The triangulation layer, together with at least the aforementioned working layer, forms a triangulated reinforcement which exhibits little deformation under the various stresses it is subjected to. The essential role of the triangulation layer is to resist the transverse compression forces exerted on all the reinforcing elements in the crown area of ​​the tire.

[0003] Cables are said to be inextensible when said cables exhibit, under a tensile force equal to 10% of the breaking force, a relative elongation of at most equal to 0.2%.

[0004] Cables are said to be elastic when said cables exhibit, under a tensile force equal to the breaking load, a relative elongation of at least 3% with a maximum tangent modulus of less than 150 GPa.

[0005] The circumferential direction of the tire, or longitudinal direction, is the direction tangent to the periphery of the tire and defined by the rolling direction of the tire.

[0006] The axis of rotation of the tire is the axis around which it rotates in normal use.

[0007] A radial or meridian plane is a plane which contains the axis of rotation of the tire.

[0008] The circumferential median plane, or equatorial plane, is a plane perpendicular to the axis of rotation of the tire and which divides the tire into two halves.

[0009] The transverse or axial direction of the tire is parallel to the axis of rotation of the tire. An axial distance is measured along the axial direction. The expression "axially inside, respectively axially outside" means "whose axial distance measured from the equatorial plane is less than, respectively greater than".

[0010] The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular to it. A radial distance is measured along the radial direction. The expression "radially inside, respectively radially outside" means "whose radial distance measured from the axis of rotation of the tire is less than, respectively greater than".

[0011] Radially outside the top reinforcement, there is the tread usually made of polymeric materials intended to come into contact with the ground in the contact area between the ground and the tire.

[0012] It is known to provide the tread, that is, the part of the tire intended to come into contact with the ground during rolling and to wear down during rolling, with a tread pattern formed of raised elements delimited by cutouts such as grooves, whether circumferential, transverse, or oblique. The objective of such a tread pattern is to give the tread good rolling performance on dry pavement and on water-covered pavement, particularly in wet weather.

[0013] To improve tread performance without excessively reducing the shear stiffness of said treads, it is known to form a plurality of transversely or obliquely oriented edges on the tread surface in order to cut the water film on a road surface and ensure good contact between the tread and the road. One means of obtaining such edges consists of providing the tread with a plurality of cutouts, these cutouts having the form of grooves or incisions. In the present application, incisions are distinguished from grooves in that the incisions have a width suitable for allowing at least partial contact between the opposing walls delimiting these incisions during rolling, particularly during contact with the ground, which would not be the case for grooves under normal tire operating conditions.

[0014] For the purposes of the invention, a longitudinally or circumferentially oriented cutout is a cutout in which the mean plane of at least a portion of the walls of said cutout forms an angle of less than 10° with a longitudinal plane. This angle formed with a longitudinal plane may be oriented in either direction with respect to said longitudinal plane. A longitudinally oriented cutout may also to be a cutout whose walls undulate or zigzag around an average plane such as has just been described.

[0015] For the purposes of this invention, a transversely oriented cutout is a cutout in which the mean plane of at least a portion of the walls of said cutout forms an angle of less than 35° with a radial plane. This angle formed with a radial plane may be oriented in either direction with respect to said radial plane. A transversely oriented cutout may also be a cutout in which the walls undulate or zigzag around a mean plane such as the one just described.

[0016] For the purposes of this invention, an obliquely oriented cutout is a cutout in which the mean plane of at least a portion of the walls of said cutout forms an angle with a radial plane of between 35° and 80°. This angle formed with a radial plane may be oriented in either direction with respect to said radial plane. An obliquely oriented cutout may also be a cutout in which the walls undulate or zigzag around a mean plane such as has just been described.

[0017] Combined with this need to improve grip performance through the presence of edges formed by the transverse cuts, it is also required that the performance of a tread be consistent, that is to say, that satisfactory performance be achieved even after partial wear, to a greater or lesser degree. Partial wear of a tread is understood to mean a state of wear corresponding to a tread thickness no greater than the total tread thickness that can be worn before the tire needs to be changed, particularly for regulatory reasons.

[0018] Heavy-duty vehicle tire treads can be regrooved (an operation by which new grooves can be cut), and tires with such treads bear the English word "Regroovable" or the symbol "U" on their sidewalls. Regrooving allows, on the one hand, for the extension of the heavy-duty tire's grip potential and, on the other hand, for a significant increase in mileage.

[0019] Regrooving heavy goods vehicle tires is a common and authorized operation due to its safety benefits and increased efficiency. For example, it is explicitly authorized by the French Highway Code (Article 4 of the decree of October 24, 1994) and recommended by the ETRTO (European Tyres and Rim Technical Organisation) and AFNOR (French Standardization Association) with standard NFR12714. For this operation, manufacturers are required to provide regrooving diagrams that are mandatory for the technicians responsible for this regrooving.

[0020] The groove heights on new tires are measurable and the groove heights after regrooving can be deduced from these regrooving diagrams.

[0021] As is known per se, the recutting of a groove can be carried out using a blade rounded heated, still often handled by an operator. Said blade, connected to a frame which rests on the tread surface, can be used manually in such a way as to follow quite faithfully the path of the groove on the tread surface, even in the case of a groove with a non-straight path.

[0022] Regrooving restores sharp edges and is usually intended to restore a tread depth corresponding to that of a half-worn heavy-duty tire. Standard recommendations aim for a post-regrooving depth of 5 to 6 mm, consisting of 3 to 4 mm of regrooving and 2 mm of remaining depth; in practice, regrooving is often carried out earlier at the initiative of the tire user, with remaining depths of between 4 and 5 mm, resulting in a post-regrooving depth of 7 to 9 mm, for tire tread depths when new of between 12 and 20 mm.

[0023] Regrooving a tire has several advantages. First, by restoring the tread depth to the tire, regrooving extends the tire's life.

[0024] Furthermore, since regrooving is carried out when the tread thickness is at its lowest and therefore when the tire has the lowest rolling resistance, the distance traveled is extended when the rolling resistance is lowest.

[0025] It has also already been described in document WO 2022 / 180325 of tyres exhibiting performance in terms of rolling resistance further improved throughout their rolling by combining one or more regrooving steps with particularly low tyre tread heights in the new condition.

[0026] There is currently a demand for the automation of these regrooving steps, particularly in the case of circumferential cutting. As explained previously, regroovable tires are supplied with regrooving patterns. Automating these regrooving steps requires a preliminary programming step of the regrooving machine to adapt it to the tire being regrooved. This means that if tires with different tread patterns need to be regrooved, the machine requires different programming. For each different regrooving operation, this programming negatively impacts the machine's productivity related to the actual regrooving process.

[0027] The inventors have set themselves the task of improving the productivity of an automatic regrooving of tires having circumferential cutouts that can be regrooved.

[0028] This objective has been achieved according to the invention by a tire, which can be regrooved at least once, comprising a crown reinforcement, itself radially capped by a tread, made of at least a first elastomeric compound forming at less the tread surface, joined to two bead ribs by means of two sidewalls, said tread comprising at least one circumferential regroovable cut forming at least one tread element constituting the tread of the tire, having a circumferential cut height when the tire is new and made of material to be regrooved in at least one regrooving step, said material to be regrooved being made of at least a first layer of a second elastomeric compound, said second elastomeric compound having a volume resistivity p different from that of said first elastomeric compound.

[0029] In the context of the invention, the height of a circumferential cut is measured in a meridional cross-section of the tire and corresponds to the distance measured between the radially outer surface of the tread, forming the contact patch with the ground and extrapolated to disregard the cuts, and the surface of the bottom of the circumferential cut, said distance being measured in a direction normal to the radially outer surface of the tread. The bottoms of circumferential cuts are the radially innermost points of said circumferential cuts, disregarding the presence of elements such as wear indicators, regrooving depth indicator wells, or any other element whose sum of areas is less than 15% of the total area of ​​the circumferential cut.

[0030] For the purposes of the invention, the height of material to be regrooved is measured between the bottom of said at least one circumferential cut in the new condition and the bottom of said circumferential cut after the last regrooving. It can be determined from the regrooving plans associated with the tire.

[0031] The volume electrical resistivity p is measured statically according to ASTM D 257, p being expressed in ohm.cm.

[0032] The invention advantageously provides that several circumferential cuts of the tire are recut according to the invention during the same step.

[0033] The production of semi-finished products intended to form the tread part of the tire, made up of several elastomeric mixtures, can be carried out according to usual methods known to those skilled in the art, and in particular by co-extrusion of the mixtures during the preparation of the semi-finished product(s) intended to constitute at least part of the tread.

[0034] Regrooving on an automatic machine has been carried out on tires conforming to the invention without requiring specific programming of the automatic machine. For this purpose, the machine has been equipped with an electrical conductivity measuring device. Such a device is, for example, mounted on the regrooving head to make contact with the tire before the regrooving blade. One way The procedure involves, for example, starting the regrooving head from the edge of the tread and moving it helically across the tread surface while continuously measuring electrical conductivity. When a change in electrical conductivity is detected, the helical movement stops and becomes a circular motion, and regrooving begins while continuing to measure conductivity until another change in conductivity is detected.

[0035] According to a preferred embodiment of the invention, the first elastomeric mixture and the second elastomeric mixture have a difference in electrical resistivity p expressed in the form of log(p) greater than 3.

[0036] Preferably, one of the elastomeric mixtures is conductive and the other is non-conductive.

[0037] For the purposes of the invention, an elastomeric mixture is non-conductive when log(p) is greater than 8, the measurement being carried out on a new tire.

[0038] According to an advantageous embodiment of the invention, the first elastomeric mixture is an electrically conductive mixture and the second elastomeric mixture is an electrically non-conductive mixture.

[0039] According to this advantageous embodiment of the invention, the second elastomeric mixture has a volume resistivity p such that log(p) is greater than 8.

[0040] According to one embodiment of the invention, at least one cut being provided with at least two re-cutting steps, said material to be re-cut of said at least one cut provided with at least two re-cutting steps consists of at least two layers of radially superimposed elastomeric mixtures.Advantageously, the material to be recut from the said at least one cut consists of at least three layers of radially superimposed elastomeric mixtures, a second layer of a third elastomeric mixture radially inside the said first layer of elastomeric mixture and in contact with it, the said third elastomeric mixture having a volume resistivity p different from that of the said second elastomeric mixture, and a third layer of a fourth elastomeric mixture radially inside the said second layer of elastomeric mixture and in contact with it, the said fourth elastomeric mixture having a volume resistivity p different from that of the said third elastomeric mixture and the said fourth elastomeric mixture having a volume resistivity p different from that of the said first elastomeric mixture.

[0041] Preferably according to this embodiment of the invention, the third elastomeric mixture and the second elastomeric mixture have a difference in electrical resistivity p expressed in the form of log(p) greater than 3.

[0042] Preferably also according to this variant of the invention, the The fourth elastomeric mixture and the third elastomeric mixture have a difference in electrical resistivity p expressed in the form of log(p) greater than 3.

[0043] Preferably, according to this embodiment of the invention, the third elastomeric mixture has an electrical resistivity identical to that of the first elastomeric mixture, and preferably the third elastomeric mixture and the first elastomeric mixture are identical.

[0044] According to this embodiment of the invention, the fourth elastomeric mixture has a volume resistivity p such that log(p) is greater than 8.

[0045] According to a preferred embodiment of this variant of the invention, the fourth elastomeric mixture has an electrical resistivity identical to that of the second elastomeric mixture and preferably even the fourth elastomeric mixture and the second elastomeric mixture are identical.

[0046] Preferably also according to this variant of the invention, the fourth elastomeric mixture and the first elastomeric mixture have a difference in electrical resistivity p expressed in the form of log(p) greater than 3.

[0047] Advantageously according to the invention, the second layer radially intercalated between the first layer and the third layer has a thickness less than or equal to 1 mm.

[0048] In the context of the invention, the thickness of an elastomeric mixture layer is measured radially between its radially outer surface and its radially inner surface.

[0049] Such a thickness of the second layer consists of using this second layer only to stop the re-excavation phases.

[0050] Advantageously, the width of the second layer has an axial width less than that of the circumferential cut. Preferably, the distance between a wall of the circumferential cut and an end of the second layer is greater than the width of the electrical conductivity measuring device associated with the recutting head.

[0051] Successive regrooving of a cut designed to be regrooved at least twice was carried out on an automatic machine on tires according to the invention without requiring specific programming of the automatic machine, as in the case of a single regrooving. As before, continuous measurement of the electrical conductivity on the tread surface allows the different regrooving stages to be triggered successively. When a change in electrical conductivity is detected, regrooving is initiated while continuing the conductivity measurement until another change in conductivity is measured. Indeed, during the second regrooving phase, when the second layer is visible, the regrooving phase starts when a change in Conductivity is detected at the level of the third layer, which is apparent between the wall of a circumferential cut and the end of the second layer. The thickness of the second layer is advantageously designed to be removed during this re-grooving, the end of the re-grooving being triggered after the removal of the third layer and the detection of a new change in conductivity upon contact again with the first elastomeric compound appearing radially beneath the third layer.

[0052] The invention as just described is particularly well suited to the regrooving of tires such as those described in document WO 2022 / 180325, after regrooving, the height of said at least one regrooved circumferential cut being greater than or equal to 70% of the height of said at least one regroovable circumferential cut of the tire in the new condition.

[0053] Advantageously in the case of the tires described in document WO 2022 / 180325, the height corresponding to the distance between the tread surface in the new condition and the bottom of the circumferential cutouts after the last regrooving of such tires is greater than or equal to 200% of the height between the bottom of the circumferential cutout and the tread surface when the tire is new.

[0054] Advantageously still, the height corresponding to the distance between the tread surface in the new condition and the bottom of the circumferential groove after the last regrooving is greater than or equal to 250% of the height between the bottom of the circumferential groove and the tread surface when the tire is new.

[0055] The invention as just described is also particularly well suited to the regrooving of tires such as those described in patent application PCT / EP2023 / 057206 which, in addition to the description of the tire according to document WO 2022 / 180325, provides for the presence of at least one incision, flush with the tread surface when the tire is new and having a height when the tire is new greater than the height of a regroovable circumferential groove of the tire in the new condition and advantageously equal to the height corresponding to the distance between the tread surface in the new condition and the bottom of said at least one circumferential groove after the last regrooving.

[0056] According to a preferred embodiment of the invention, the height of said at least one incision of the tire in the new condition is greater than 90% of the height corresponding to the distance between the tread surface in the new condition and the bottom of said at least one groove after the last regrooving.

[0057] Preferably, the height of said at least one incision of the tire in the new condition is equal to the height corresponding to the distance between the tread surface in the new condition and the bottom of the grooves after the last regrooving.

[0058] Such tires according to the invention also have the advantage in com Compared to conventional regroovable tires, improved rolling resistance performance while maintaining similar wet grip properties and substantially identical mileage until complete tire wear.

[0059] Indeed, in the case of such tires, the combination of a tread thickness substantially identical to that of a more conventionally designed tire with reduced groove heights when new compared to those of more conventionally designed tires makes it possible to significantly increase performance in terms of rolling resistance.

[0060] Indeed, for tread thicknesses similar to those of more conventionally designed tires, the height of the grooves after regrooving exceeding 70% of the height of the grooves in the new condition means that the height of the grooves in the new condition is reduced compared to that of more conventionally designed tires.

[0061] According to either embodiment of the invention described above, the portion of the tread constituting the areas likely to form the contact surface of the tire with the ground may consist of at least two radially superimposed layers of elastomeric compounds, with at least a fifth elastomeric compound forming the tread surface of the tire after complete wear of the first elastomeric compound. The conductivity differences described above between the first elastomeric compound and the second, third, and fourth elastomeric compounds should be understood as the differences with said at least fifth elastomeric compound when it forms the tread surface.

[0062] As mentioned previously, according to its embodiments of the invention, the production of the semi-finished products intended to form the tread part of the tire can be carried out according to usual methods known to those skilled in the art, and in particular by co-extrusion of the mixtures during the preparation of the semi-finished product(s) intended to constitute at least part of the tread.

[0063] According to one embodiment of the invention, the crown reinforcement of the tire is formed of at least two working crown layers of inextensible reinforcing elements, crossed from one layer to the other making angles with the circumferential direction between 10° and 45°.

[0064] According to other embodiments of the invention, the top reinforcement also comprises at least one layer of circumferential reinforcing elements.

[0065] One embodiment of the invention further provides that the top reinforcement is radially supplemented on the outside by at least one additional layer, called a protective layer, of so-called elastic reinforcing elements, oriented with respect to the circumferential direction rential with an angle between 10° and 45° and in the same direction as the angle formed by the inextensible elements of the working layer which is radially adjacent to it.

[0066] According to any one of the embodiments of the invention mentioned above, the top reinforcement can be further completed, radially inside between the carcass reinforcement and the radially inner working layer closest to said carcass reinforcement, by a triangulation layer of inextensible metallic steel reinforcing elements making, with the circumferential direction, an angle greater than 60° and in the same direction as that of the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement.

[0067] Other advantageous details and features of the invention will become apparent from the description of examples of embodiments of the invention with reference to Figures 1 to 3, which represent: - [Fig. 1], a meridian view of a diagram of a pneumatic tire according to a first embodiment of the invention, - [Fig.2], a meridian view of a diagram of a tire according to a second embodiment of the invention, - [Fig.3a] to [Fig.3e], a schematic representation of the steps of regrooving a tire tread according to a third embodiment of the invention.

[0068] The figures are not shown to scale for ease of understanding. Figures 1 and 2 represent only a half-view of a tire which extends symmetrically with respect to the axis XX' which represents the circumferential median plane, or equatorial plane, of a tire.

[0069] In Figures 1 and 2, the tire 1, size 315 / 70R22.5, comprises a radial carcass reinforcement 2 anchored in two beads around wires, not shown. The carcass reinforcement 2 is formed of a single layer of wire cords. The carcass reinforcement 2 is held in place by a crown reinforcement 5, itself capped with a tread 6. The tread has three grooves 3 forming four ribs 4.

[0070] The lower areas and bulges of the tire 1 are in particular not shown in the figures.

[0071] In figures 1 and 2, the vertex reinforcement 5 is formed radially from the inside to the outside: - of a first working layer 51 formed of inextensible metal cables, continuous over the entire width of the layer, oriented at an angle al, - a layer of circumferential reinforcing elements 53 formed of elastic steel wire cables 21.23, with a 2 mm pitch, and - a second working layer 52 made of inextensible metal cables, continuous across the entire width of the layer, oriented at an angle a2 and crossed with the metal cables of the first working layer.

[0072] The axial width L5i of the first working layer 51 is equal to 246 mm.

[0073] The axial width L52 of the second working layer 52 is equal to 228 mm.

[0074] As for the axial width L53 of the layer of circumferential reinforcing elements 53, it is equal to 200 mm.

[0075] In [Fig. 1], according to the invention, the grooves 3 are of the regroovable type. As illustrated in [Fig. 1], the grooves 3 consist of a single layer A forming the bottom of the grooves in the new state and corresponding to a single regrooving.

[0076] The height on new HN3 tire of grooves 3 is equal to 7.5 mm.

[0077] The HR height of the grooves 3 after regrooving is equal to 9.5 mm.

[0078] This HR height corresponds to a recut of 7.5 mm when the remaining height of the initial groove is 2 mm, a value close to the generally permitted legal limit corresponding to the minimum height and corresponding to the wear indicators. This limit is symbolized by line 7 in [Fig. 1].

[0079] The height not measurable before this regrooving and corresponding to the distance between the bearing surface in the new state and the bottom of a groove 3 after the regrooving is thus equal to 15 mm.

[0080] Figure 2 illustrates a tire whose grooves 23 can be regrooved twice. The grooves 23, when new, consist of three layers B, C, and D forming the bottom of the grooves and corresponding to these two regroovings. Layer D is designed with a width less than that of the groove and a thickness of approximately 1 mm.

[0081] The height on new HN23 tire of the grooves 23 is equal to 6 mm.

[0082] The height HRides grooves 23 after the first re-grooving and removal of layer B is equal to 7 mm. Layer D and partially layer C are then visible.

[0083] This HRi height corresponds to a 5 mm recut when the remaining height of the initial groove is 2 mm, a value close to the generally permitted legal limit corresponding to the minimum height and the wear indicators. This limit is symbolized by line 71 in [Fig.2].

[0084] The height not measurable before a first re-grooving and corresponding to the distance between the bearing surface in the new state and the bottom of the groove after the first re-grooving is thus equal to 11 mm.

[0085] The HR2 height of the grooves 23 after the second re-grooving and removal of layers D and C is equal to 6 mm.

[0086] This HR2 height corresponds to a 4 mm deep groove when a remaining groove height of 2 mm is present, a value close to the generally permitted legal limit corresponding to the minimum height. This limit is symbolized by line 72 on the [Fig.2].

[0087] The height not measurable before the two re-groovings and corresponding to the distance between the running surface in the new state and the bottom of the sprockets 23 after the second re-grooving is thus equal to 15 mm.

[0088] The tire shown in [Fig. 2] has two regrooving operations at different stages of tire wear. Advantageously, according to the invention, the grooves are regrooved simultaneously at each regrooving stage.

[0089] According to other embodiments of the invention, the regrooving of the various grooves of a tire can be staggered over time. According to these embodiments, the tire may have some of these grooves that can be regrooved only once and other grooves that can be regrooved several times. A tire could thus have a combination of grooves such as those illustrated in [Fig. 1] and grooves such as those illustrated in [Fig. 2].

[0090] In the case of [Fig.3a], which illustrates the tread 36 of a tire in its new condition, the central groove 331 can be recut once and the grooves 332 can be recut twice.

[0091] The four ribs 34 forming the part of the tread intended to come into contact with the ground are made of the first elastomeric compound.

[0092] The layer A' forming the bottom of the circumferential groove 331 that can be recut, identical to that described in the case of [Fig.1], is made up of the second elastomeric mixture.

[0093] The layers B' and C' forming the largest recuttable volumes of the circumferential grooves 332, similar to those described in [Fig.2], are made up respectively of the second and fourth mixtures chosen in this embodiment identical and identical to the elastomeric mixture constituting layer A'.

[0094] According to one embodiment of the invention, the layers B' and C' are radially separated by a layer D' made of a third elastomeric mixture and having a thickness on the order of a millimeter and a width less than that of the circumferential grooves 332. The third elastomeric mixture is chosen to be identical to the first elastomeric mixture forming the rib 34.

[0095] Tires were made in accordance with [Fig.3a] on the basis of the elastomeric mixtures described below. First Mixture Second Mixture NR 80 100 BR 20 N234 48 NonN550 17.5 Stearic Acid 1 6PPD- 1.3DIMETHYL 8UTYL PHENYL PARAPHEITr'LENE-DfAMINE 2.5 ZNO 3 5 Sulfur 1.5 4 Accelerator (CBS).... 0.9 1.5 IggCpj <4.6 >9

[0096] The values ​​of the constituents are expressed in pce (parts by weight per hundred parts of elastomers).

[0097] The first mixture is therefore constitutive of the ribs 34 and of the layer D'.

[0098] The second mixture constitutes layers A', B' and C'.

[0099] Fig. 3b illustrates the tread 36 after initial wear and before the first regrooving, the depth of the circumferential grooves 332 being approximately 2 mm.

[0100] Figure 3c illustrates the tread 36 after a first regrooving. This first regrooving consisted of removing layer A' from the circumferential groove 331 and layers B' in the grooves 332, revealing in these circumferential grooves 332 layers D' and part of layers C'.

[0101] In the case of regrooving on an automatic machine, as explained previously, the regrooving head, associated with a continuous electrical conductivity measuring device, starts from an edge of the tread 36 and follows a helical path around the tire until it encounters a change in electrical conductivity at the level of the second compound of a layer B' of a circumferential groove 332. The regrooving head is then moved circumferentially and activated to regroove the tire and remove layer B' of a circumferential groove 332. The regrooving stops when a change in electrical conductivity is again measured at layer D'. The helical movement then resumes in the same way as before until the electrical conductivity of layer A' of the circumferential groove 331, consisting of the second compound, is measured.Similarly, the re-grooving head is then activated to remove layer A' from the circumferential groove 331. The re-grooving stops when the conductivity of the first mix is ​​measured again. since it appears at the bottom of the circumferential groove 331 after the disappearance of layer A'. The last stage of this re-grooving then starts according to the same principle as before to remove layer B' from the second circumferential groove 332.

[0102] Fig. 3d illustrates the tread 36 after a second wear, the depth of the circumferential grooves 332 being approximately 2 mm.

[0103] Figure 3e illustrates the tread 36 after the second regrooving. This second regrooving consists of removing layers D' and C' in grooves 332.

[0104] Following the same principle as the first re-grooving, the second re-grooving begins with a helical movement of the re-grooving head until the electrical conductivity of layer C' of a circumferential groove 332, formed from the second mixture, is measured. This measurement triggers the second re-grooving of the circumferential groove 332 and the removal of layers C' and D' from this circumferential groove 332. The narrower width of layer D' compared to that of the circumferential groove 332 allows for the measurement of the electrical conductivity of layer C', which triggers the re-grooving. The re-grooving stops when the conductivity of the first mixture is measured again, as it appears at the bottom of the circumferential groove 332 after the disappearance of layers D' and C'. The final stage of this re-grooving then starts according to the same principle as before to remove layers D' and C' from the second circumferential groove 332.It should be noted that when the regrooving head, coupled with the electrical conductivity measuring device, passes along a helical path through the central groove 331, no change in electrical conductivity is detected since the only elastomeric mixture measured is the first mixture. Therefore, no regrooving is triggered when passing through the central groove 331.

Claims

Demands

1. Tire (1), regroovable at least once, comprising a crown reinforcement (5), itself radially capped by a tread (6), made up of at least a first elastomeric compound forming at least the tread surface, joined to two beads by means of two sidewalls, said tread (6) having at least one circumferential cut (3) regroovable forming at least one tread element constituting the tread of the tire, having a circumferential cut height (HN3) (3) when the tire is new and made up of material to be regrooved in at least one regrooving step, characterized in that said material to be regrooved consists of at least a first layer (A, A', B, B') of a second elastomeric compound and in that said second elastomeric compound has a volume resistivity p different from that of said first elastomeric compound.

2. Pneumatic (1) according to claim 1, characterized in that at least one circumferential groove (3) recuttable is recuttable at least twice.

3. Pneumatic (1) according to any one of claims 1 or 2, characterized in that the first elastomeric mixture and the second elastomeric mixture have a difference in electrical resistivity p expressed in the form of log(p) greater than 3.

4. Pneumatic (1) according to any one of the preceding claims, characterized in that the first elastomeric mixture is an electrically conductive mixture and the second elastomeric mixture is an electrically non-conductive mixture.

5. Tire (1) according to any one of the preceding claims, characterized in that, after regrooving, the height (HR) of said at least one regrooved circumferential cut (3) is greater than or equal to 70% of the groove height (HN) of said at least one regroovable circumferential cut (3) of the tire in the new condition.

6. Tire (1) according to any one of the preceding claims, characterized in that the height corresponding to the distance between the tread surface in the new condition and the bottom of the circumferential cutouts (3) after the last regrooving of such tires is greater than or equal to 200% of the height (HN) between the bottom of the circumferential cutout (3) and the tread surface when the tire is new.

7. Tire (1) according to any one of the preceding claims, said tread (6) having at least one incision, flush with the tread surface when the tire is new, having a height between the bottom of said at least one incision and the tread surface when the tire is new, characterized in that the height of said at least one incision of the tire in the new condition is greater than the height of said at least one circumferential cut (3) recuttable of the tire in the new condition.

8. Tire (1) according to claim 7, characterized in that the height of said at least one incision of the tire in the new condition is greater than 90% of the height corresponding to the distance between the tread surface in the new condition and the bottom of said at least one circumferential cut (3) after the last regrooving.

9. Tire (1) according to claim 7 or 8, characterized in that the height of said at least one incision of the tire in the new condition is equal to the height corresponding to the distance between the tread surface in the new condition and the bottom of said at least one circumferential cut (3) after the last regrooving.

10. Tire (1) according to any one of the preceding claims, characterized in that said tread comprises, at least locally, at least two layers of radially superimposed elastomeric mixtures in the tread.

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