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US-12617167-B2 - Pneumatic tire curing method using a curing membrane comprising three drainage areas arranged in increasing order of depth

US12617167B2US 12617167 B2US12617167 B2US 12617167B2US-12617167-B2

Abstract

The method includes a step of deploying a curing membrane against an interior surface of the tire. The curing membrane has a contact surface with a drainage structure which comprises air-discharge channels and which is subdivided into a first drainage region, a second drainage region, and a third drainage reason. The first drainage region is pressed intimately against a crown region of the tire, the second drainage region is pressed intimately against a sidewall region of the tire, and the third drainage region is pressed intimately against a bead region of the tire. A mean depth of the channels of the third drainage region is strictly greater than a mean depth of the channels of the second drainage region, which is itself strictly greater than a mean depth of the channels of the first drainage region.

Inventors

  • Frederic Pialot
  • Jose Merino Lopez
  • ALAIN FAUGERAS

Assignees

  • COMPAGNIE GENERALE DES ETABLISSEMENTS MICHELIN

Dates

Publication Date
20260505
Application Date
20200602
Priority Date
20190606

Claims (19)

  1. 1 . A method for curing a tire, during which a curing membrane is deployed against a green tire in order to bring a contact surface of said curing membrane to bear against an interior surface of said green tire and thus press an exterior surface of said green tire against the walls of a curing mold so as to obtain a tire which has a crown region forming an annular tread around a central axis, and, on each side of an equatorial plane normal to said central axis, a bead region for securing said tire to a rim, and a sidewall region connecting the crown region to the bead region, the method further comprising the contact surface of the curing membrane is provided with a drainage structure which comprises air-discharge path channels cut into the contact surface to a depth equal to or greater than 0.05 mm, wherein said drainage structure is subdivided, at least on one side of the equatorial plane, into at least three drainage regions, these being a first drainage region which corresponds to a first annular portion of the contact surface, centered on the central axis, along which said contact surface will hug the crown region, a second drainage region which corresponds to a second annular portion of the contact surface, centered on the central axis, along which said contact surface will hug the sidewall region and the channels of which communicate with the channels of the first drainage region, and a third drainage region which corresponds to a third annular portion of the contact surface, centered on the central axis, along which said contact surface will hug the bead region and the channels of which communicate with the channels of the second drainage region, and a mean depth of the channels of the third drainage region, which is equal to a quotient of a volume occupied by the channels present in said drainage region by a surface area covered by these same channels in said drainage region is strictly greater than a mean depth of the channels of the second drainage region, said mean depth of the channels of the second drainage region being itself strictly greater than a mean depth of the channels of the first drainage region, and wherein all the channels of the first drainage region are a first family of channels formed by a repeating hexagonal pattern that extend continuously along a full length of the first drainage region including to the equatorial plane, wherein at least 50% of the channels of the first drainage region have a constant depth which is comprised between 0.05 mm and 0.25 mm.
  2. 2 . The method according to claim 1 , wherein a boundary between the first drainage region and the second drainage region follows a first parallel line along which the normal to the interior surface of the tire is inclined, with respect to the central axis, by a first declination angle which is comprised between 40 degrees and 85 degrees.
  3. 3 . The method according to claim 2 , wherein the first declination angle is between 45 degrees and 85 degrees.
  4. 4 . The method according to claim 3 , wherein the first declination angle is between 50 degrees and 80 degrees.
  5. 5 . The method according to claim 1 , wherein a boundary between the second drainage region and the third drainage region follows a second parallel line along which the normal to the interior surface of the tire forms, with respect to the central axis, a second declination angle which is comprised between zero degrees and 30 degrees.
  6. 6 . The method according to claim 1 , wherein the mean depth of the channels in the first drainage region is comprised between 0.05 mm and 0.25 mm.
  7. 7 . The method according to claim 1 , wherein the mean depth of the channels in the second drainage region is comprised between 0.25 mm and 0.45 mm.
  8. 8 . The method according to claim 1 , wherein at least 50% of the channels of the second drainage region have a constant depth which is comprised between 0.25 mm and 0.45 mm.
  9. 9 . The method according to claim 8 , wherein at least 50% of the channels of the third drainage region have a constant depth which is comprised between 0.45 mm and 1.20 mm.
  10. 10 . The method according to claim 9 , wherein at least 80% of the channels of the third drainage region have the constant depth which is comprised between 0.45 mm and 0.60 mm.
  11. 11 . The method according to claim 8 , wherein at least 80% of the channels of the second drainage region have the constant depth which is comprised between 0.25 mm and 0.45 mm.
  12. 12 . The method according to claim 1 , wherein the mean depth of the channels in the third drainage region is comprised between 0.45 mm and 1.20 mm.
  13. 13 . The method according to claim 1 , wherein the first drainage region comprises the first family of channels have a depth comprised between 0.05 mm and 0.25 mm, a width comprised between 0.4 mm and 1.5 mm, and a first repeat pitch comprised between 2 mm and 15 mm.
  14. 14 . The method according to claim 1 , wherein the second drainage region comprises a second family of channels which are formed by repeating a second hexagonal pattern which gives the channels of said second family a depth comprised between 0.25 mm and 0.45 mm, a width comprised between 0.4 mm and 1.5 mm, and a second repeat pitch comprised between 2 mm and 15 mm.
  15. 15 . The method according to claim 1 , wherein the third drainage region comprises a third family of channels which are formed by repeating a third pattern in parallel straight bands which gives the channels of said third family a depth comprised between 0.45 mm and 1.20 mm, a width comprised between 0.4 mm and 2 mm, and a repeat pitch comprised between 4 mm and 40 mm.
  16. 16 . The method according to claim 1 , wherein at least 80% of the channels of the first drainage region have the constant depth which is comprised between 0.05 mm and 0.25 mm.
  17. 17 . The method according to claim 1 , wherein the curing membrane has a portion of greater thickness in a vicinity of each of its feet and has a simple thickness, which is less than the greater thickness, in a vicinity of the equatorial plane.
  18. 18 . A tire obtained by a method according to claim 1 , said tire thus having on its interior surface three distinct annular portions, centered on the central axis of the tire, which are situated, on the one same side of the equatorial plane, respectively beneath the crown region thereof, beneath the sidewall region thereof, and beneath the bead region thereof, and which contain ribs of a height equal to or greater than 0.05 mm, which correspond to the respective impressions, in negative, of the channels of the distinct first, second and third drainage regions, and which are dimensioned in such a way that a first annular portion has a mean rib height strictly less than a mean height of the ribs of a second annular portion, said mean height of the ribs of the second annular portion being itself strictly less than a mean height of the ribs of a third annular portion.
  19. 19 . The tire according to claim 18 , wherein the first annular portion comprises ribs the height of which are comprised between 0.05 mm and 0.25 mm, and a width of which are comprised between 0.4 and 1.5 mm, and which are arranged in a hexagonal first pattern that repeats with a first repeat pitch comprised between 2 mm and 15 mm, the second annular portion comprises ribs the height of which are greater than the height of the ribs of the first annular portion and comprised between 0.25 mm and 0.45 mm, and a width of which are comprised between 0.4 and 1.5 mm, and which are arranged in a hexagonal second pattern that repeats with a second repeat pitch comprised between 2 mm and 15 mm, equal to the first repeat pitch, and the third annular portion comprises ribs the height of which are greater than the height of the ribs of the second annular portion and comprised between 0.45 mm and 1.2 mm, and a width of which are comprised between 0.4 mm and 2 mm, and which are arranged either in a hexagonal third pattern that repeats with a third repeat pitch equal to or greater than the second repeat pitch and comprised between 4 mm and 40 mm or in a third pattern of parallel straight bands which repeats at a third repeat pitch strictly greater than the second repeat pitch and comprised between 4 mm and 40 mm.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to and the benefit of PCT Patent Application No. PCT/EP2020/065215 filed on 2 Jun. 2020, entitled “PNEUMATIC CURING METHOD USING A CURING MEMBRANE COMPRISING THREE DRAINAGE AREAS ARRANGED IN INCREASING ORDER OF DEPTH,” and French Patent Application No. FR1906013, filed on 6 Jun. 2019, entitled “PNEUMATIC CURING METHOD USING A CURING MEMBRANE COMPRISING THREE DRAINAGE AREAS ARRANGED IN INCREASING ORDER OF DEPTH”. BACKGROUND 1. Field The present disclosure relates to the field of methods for manufacturing tires, and more particularly the field of methods for curing pneumatic tires. 2. Related Art It is known practice to obtain a tire by first of all producing a green tire, of toroidal shape, and then by pressing said green tire against the walls of a curing mold using an inflatable curing membrane which serves to confer upon the tire the definitive shape thereof, and to vulcanize said tire. The green tire is generally obtained by laying and winding onto a drum a plurality of components, usually including an airtight film known as an “inner liner”, a carcass ply, rubber-based reinforcing plies reinforced with reinforcing threads, and a pair of annular bead wires intended to reinforce a bead region used for attaching the tire to a rim. In order to mold the tire, a curing membrane is deployed against the interior surface of the green tire so as to press the exterior surface of said green tire against the walls of the mold, these themselves being arranged according to the definitive shape of the tire and provided with linings which correspond to the negative impression of the tread pattern. Advantageously, the inflating of the curing membrane is performed using a pressurized heat-transfer fluid which is able not only to exert the pressure required for shaping the tire, but also to supply heat which contributes to the vulcanizing of said tire thus shaped. Of course, it is necessary, when deploying the curing membrane, to remove the air that is initially trapped between said curing membrane and the interior surface of the green tire, this being so as to avoid the appearance of air pockets liable to lead to defects on the interior surface of the tire, which defects could prejudice the appearance, the performance, or even the cohesion of said tire. In this regard, it is known practice to provide on the surface of the curing membrane a drainage structure comprising channels which form air discharge pathways, allowing the air to be removed to vents present for that purpose in the mold. However, the person skilled in the art is then faced with contradictory requirements. Specifically, in order to encourage effective drainage and removal of the air, the temptation would be, on the one hand, to cover the largest possible area of the curing membrane with channels, by providing the highest possible surface density of such channels, this being so as not to leave, on the interior surface of the green tire, regions that are not drained and, on the other hand, to provide said channels with the greatest possible depth, so as to have a high capacity for the flow of air through the cross section of the channels. However, when the curing membrane is pressed intimately against the interior surface of the green tire, it is found that the airtight film or “inner liner” with which said green tire is lined, enters the channels and substantially adopts the shape of said channels. This then results in an increase in the developed surface area of said airtight film and therefore, through a plastic deformation phenomenon of the striction type, results in a reduction in the thickness of said airtight film. In order to avoid a weakening of the airtight film, and to thus guarantee the airtightness and longevity of the tire, it is therefore necessary to limit the surface irregularities of the curing membrane. SUMMARY The objectives assigned to the disclosure therefore seek to overcome the aforementioned disadvantages and to propose a novel curing method, together with a corresponding novel curing membrane, which ensures both effective removal of air during molding and a high and repeatable quality of the tire obtained. In particular, the disclosure proposes to restrict as far as possible the depth of the channels of the drainage structure, so as to limit the inner liner striction effects. The objectives assigned to the disclosure are achieved by means of a method for curing a tire during which a curing membrane is deployed against a green tire in order to bring a contact surface of said curing membrane to bear against an interior surface of said green tire and thus press an exterior surface of said green tire against the walls of a curing mold so as to obtain a tire which has a crown region forming an annular tread around a central axis Z, and, on each side of an equatorial plane normal to said central axis Z, a bead region for securing said tire to a rim, and a sidewall re