Title of Invention: MOLDING ELEMENT FOR MANUFACTURING A NOISE

REDUCING TREAD

FIELD OF INVENTION

(0001) The present invention relates to a molding element, in particular to a molding element for a mold used for manufacturing a tread for a tire having a closing device in a groove. BACKGROUND

(0002) A groove resonance is generated by occurrence of resonance in an air column defined between a groove in a tread and a road surface in contact with the tire. The frequency of this groove resonance is dependent on a length of the air column formed between groove and the road surface in the contact patch. (0003) This groove resonance has a consequence in an interior noise and an exterior noise on a vehicle equipping such tires, a frequency of which interior and exterior noise is often at around 1 kHz where human ear is sensitive.

(0004) In order to reduce such groove resonance, it is known to provide a plurality of closing device in the form of a thin flexible fence made of rubber-based material in each groove. It is effective that each flexible fence covers all or at least major part of the sectional area in the groove. Each flexible fence can extend from a groove bottom, or from at least one of a groove sidewall delimiting such groove. Because being relatively thin, each flexible fence has to bend for opening the groove section to flow water on the road surface, in particular on the wet road. (0005) Thanks to such flexible fences, the length of the air column is reduced so as to be shorter than the total length of groove in a contact patch, which leads to change the frequency of groove resonance. This change of resonance frequency makes the sound generated by the groove resonance less sensitive to human ear. (0006) For preserving function of drainage, in case of driving in rainy weather, it is necessary for such flexible fence to bend in a suitable way under the action of the pressure of water for opening the section of the groove. Several solutions have been proposed using this type of closing device to reduce groove resonance of the groove.

(0007) WO2013/178473A1 discloses, in Fig. 4, a method for manufacturing a tread for a tire provided with at least one flexible wall (closing device) in a groove, the method comprising steps of molding the tread with a groove and at least one connecting element arranged inside the groove transversely so as to connect sidewalls of the groove, and cutting the connecting element at the junction with each the sidewall of the groove. However with such method productivity of such tread is low, as the method requires additional process of cutting the connecting element after molding.

(0008) WO2013/120783A1 discloses, in Fig.3, a mold for molding a tread for a tire provided with at least one closing device, the mold comprising two cavities for the flexible fence separated by a first element.

(0009) The mold having the above cavities for the flexible fence has been manufactured through milling and/or casting process.

(0010) However, since milling and casting processes are complicated, the productivity of such molding element is low. Therefore, there is a need to improve productivity of the molding element for molding the tread provided with the flexible fence of the closing device. (0011) In addition, since it is difficult to form cavities with precise dimension through milling and/or casting process, it has been difficult to obtain a tread having a flexible fence with precise thickness so to obtain required bending by hydrodynamic pressure for liquid drainage. (0012) Therefore, there is a need for a molding element which can mold a flexible fence with precise thickness such that the molded flexible fence can appropriately bend by hydrodynamic pressure for liquid drainage.

(0013) Definitions:

(0014) A "tire" means all types of elastic tire whether or not subjected to an internal pressure.

(0015) A "tread" of a tire means a quantity of rubber material bounded by lateral surfaces and by two main surfaces one of which is intended to come into contact with ground when the tire is rolling.

(0016) A "mold" means a collection of separate molding elements which, when brought closer towards one another, delimit a toroidal molding space.

(0017) A "molding element" of a mold means part of a mold. A molding element is, for example, a mold segment.

(0018) A "molding surface" of a molding element means a surface of the mold that is intended to mold a surface of the tread. (0019) A "groove" is a space between two rubber faces/sidewalls which do not contact between themselves under usual rolling condition connected by another rubber face/bottom. A groove has a width and a depth.

(0020) It is thus an object of the invention to provide a molding element for a mold used for manufacturing a tread of a tire, such molding element can improve productivity for manufacturing a tread provided with a closing device in a groove while ensuring having precise thickness of the flexible fence of the closing device.

SUMMARY OF THE INVENTION

(0021) The present invention provide a molding element for a mold used for manufacturing a tread of a tire having a plurality of contacting element delimited by a plurality of groove, the molding element having a molding surface for forming a contact face of the contacting elements intended to come into contact with ground during rolling and a groove forming rib portion for forming the groove comprising two opposed rib side faces for forming two opposed groove side faces and a rib top face connecting two rib side faces for forming a groove bottom, the groove forming rib portion providing at least one space opening to at least one of the rib side faces and/or to the rib top face and an insert being received in the space for forming a portion of the groove and a closing device in the groove, the molding element being characterized in that the insert is composed of a plurality of thin plates stacked in a direction along which the groove forming rib portion extends, comprises at least one forming plate assembly, the forming plate assembly comprises at least two notched plates of thickness , each of the notched plates includes at least one notch for forming a flexible fence of the closing device, and in that the notch in one notched plate has no area overlapping to the notch in the other notched plated adjacent thereto in sectional view in a direction along which the groove forming rib portion extends.

(0022) This arrangement improves productivity of a tread provided with a plurality of flexible fence of a closing device in a groove while ensuring having precise thickness of the closing device.

(0023) Since the insert is composed of a plurality of thin plates stacked in a direction along which the groove forming rib portion extends that is easier to form a shape necessary for forming a portion of the groove of the tread and the flexible fence of the closing device, processing duration for manufacturing such the insert decreases resulting improvement on productivity of the molding element for forming a tread provided with the plurality of flexible fence of the closing device in the groove.

(0024) Since the notched plate for flexible fence can prepared so as to precisely have a predetermined thickness, it is possible to form the plurality of flexible fence of the closing device with accurate thickness to permit a required bending of the flexible fence of the closing device for liquid drainage.

(0025) Since the insert comprises at least one forming plate assembly, the forming plate assembly comprises at least two notched plates of thickness ti including at least one notch for forming the flexible^ fence of the closing device and the notch on the adjacent notched plates in the forming plate assembly are not overlapped in sectional view in a direction along which the groove forming rib portion extends, it is possible to increase degree of freedom to design and to position the flexible fence of the closing device. (0026) In another preferred embodiment, the insert further comprises at least one support plate of thickness t2 without the notch, the support plate is provided on at least one end of the insert in a direction along which the groove forming rib portion extends.

(0027) According to this arrangement, it is possible to adjust easily the thickness of the insert for compensating the thickness of the space while ensuring precise thickness of the flexible fence of the closing device.

(0028) In another preferred embodiment, the insert further comprises at least one additional notched plate of thickness tl including at least one notch having an area overlapping to the notch in the notched plate in the forming plate assembly in sectional view in a direction along which the groove forming rib portion extends, and at least one support plate of thickness t2 without the notch is provided at least between the forming plate assembly and the additional notched plate.

(0029) According to this arrangement, it is possible to manufacture the flexible fences of the closing device effectively covering as broader cross sectional area of the groove as possible while maintaining, good productivity of the tread with the flexible fences as closing device, as the sectional area covered by each flexible fence can be reduced, and to have higher flexibility of an arrangement of the flexible fences.

(0030) In another preferred embodiment, t the thickness tl of the notched plate and the thickness t2 of the support plate are both at most equal to 2.0mm.

(0031) If these thicknesses tl of the forming thin plate and/or the thickness t2 of the support plate are more than 2.0mm, the closing device formed with the molding element would have important thicknesses that is difficult to bend with hydrodynamic pressure for liquid- drainage as these thicknesses will substantially be equal to the thickness of the flexible fence of the closing device. These thicknesses may be the same between tl and t2, may be different between tl and t

(0032) These thicknesses, theithickness tl of the forming thin plate and the thickness t2 of the support plate are preferably at most equal to 0.8mm, more preferably at most equal to 0.7mm and still more preferably at least equal to 0.02mm and at most equal to 0.6mm. (0033) In case multiple numbers of the forming thin plates are provided in one single insert and/or in one single forming plate assembly, the thickness tl of each the notched plate may vary. In case multiple numbers of the support plates are provided in one single insert, the thickness t2 of each the support plate may vary. (0034) In another preferred embodiment, the notch of the notched plate in the forming plate assembly opens to at least one of the rib side face, and wherein the notch of the additional notched plate opens to the rib top face.

(0035) According to this arrangement, it is possible to manufacture the flexible fence of the closing device overlapping partly in sectional view of the groove for making a sound wave generated by groove resonance difficult to propagate between the flexible fences of the closing device with more precise distance between the flexible fences for effective attenuation of the groove resonance due to air column resonance of the groove. (0036) In another preferred embodiment, the thickness of the additional notched plate is different from thickness that of the notched plate in the forming plate assembly.

(0037) According to this arrangement, performance compromise by the flexible fences can be achieved. By making the thickness tl of the notched plate having the notch opening to the rib top face thicker than the thickness tl of the notched plate having the notch opening to the rib side face, it is possible to have a regular wear of the flexible fence extending from the groove bottom (formed via the notched plate having the notch opening to the rib top face) with tread wear by increased bending rigidity of the flexible fence extending from the groove bottom relative to the flexible fence extending from the groove sidewall (formed via the notched plate having the notch opening to the rib side face). Contrarily by making the thickness tl of the notched plate having the notch opening to the rib top face thinner than the thickness tl of the notched plate having the notch opening to the rib side face, it is possible to have easier bending of the flexible fence extending from the groove bottom (formed via the notched plate having the notch opening to the rib top face) even with reduced groove depth which results further improvement on drainage capability. (0038) In another preferred embodiment, the thickness of the additional notched plate is thinner than the thickness of the notched plate in the forming plate assembly.

(0039) According to this arrangement, it is possible to achieve easier bending of the flexible fence extending from the groove bottom (formed via the notched plate having the notch opening to the rib top face) even with reduced groove depth which results further improvement on drainage capability.

(0040) In another preferred embodiment, the insert comprises at least two support plates having at least two different thicknesses.

(0041) According to this arrangement, it is possible to increase manufacturing efficiency and flexibility of the molding element. By using the support plate having at least two different thickness t2 between each the notched plates, it is possible to increase degree of freedom of an arrangement of the flexible fences in the closing device. By using the support plate having at least two different thickness t2 one between the notched plates and other between the notched plate and a face of the space, a thickness of the insert can adjust easily for compensating a thickness of the space while ensuring precise thickness of the flexible fence of the closing device.

(0042) In another preferred embodiment, two ends of the insert in a direction groove along which the forming rib portion extends, are the support plates.

(0043) According to this arrangement, it is possible to adjust easily the thickness of the insert for compensating the thickness of the space while ensuring precise thickness of the flexible fence of the closing device.

BRIEF DESCRIPTION OF THE DRAWINGS

(0044) Other characteristics and advantages of the invention arise from the description made hereafter in reference to the annexed drawings which show, as nonrestrictive examples, the embodiments of the invention. (0045) In these drawings:

(0046) Fig.1 is a schematic plan view of a tread for a tire molded with a mold comprising a molding element according to embodiment of the present invention;

(0047) Fig.2 is an enlarged schematic plan view showing a portion indicated as II in Fig. l;

(0048) Fig.3 is a schematic cross sectional view taken along line ΙΙΙ-ΙΠ in Fig. l;

(0049) Fig.4 is a schematic perspective view of a portion of the molding element without an insert according to embodiment of the present invention;

(0050) Fig.5 is a schematic perspective view of a portion of the molding element with the insert according to embodiment of the present invention;

(0051) Fig.6 is a schematic view of a forming plate assembly according to embodiment of the present invention;

(0052) Fig.7 is a schematic exploded perspective view of the insert comprising the forming plate assembly according to embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

(0053) Preferred embodiments of the present invention will be described below referring to the drawings.

(0054) A molding element 1 for a mold used for manufacturing a tread 101 of a tire, a mold comprising the molding element 1, and a tread 101 molded and vulcanized using the mold according to an embodiment of the present invention will be described referring to Figs.1 to 7.

(0055) Fig. l is a schematic plan view of a tread for a tire molded with a mold comprising a molding element according to embodiment of the present invention. Fig.2 is an enlarged schematic plan view showing a portion indicated as II in Fig. l . Fig.3 is a schematic cross sectional view taken along line ΙΙΙ-ΙΠ in Fig. l . Fig.4 is a schematic perspective view of a portion of the molding element without an insert according to embodiment of the present invention. Fig.5 is a schematic perspective view of a portion of the molding element with the insert according to embodiment of the present invention. Fig.6 is a schematic view of a forming plate assembly according to embodiment of the present invention. Fig.7 is a schematic exploded perspective view of a configuration of the insert comprising the forming plate assembly according to embodiment of the present invention.

(0056) The tread 101 is a tread for a tire having dimension 205/55R16 and comprises a contact face 102 intended to come into contact with the ground during rolling, a plurality of groove 103 extending in a tire circumferential direction indicated as XX'. The groove 103 is delimited by two groove sidewalls 1031, 1032 facing each other and being connected b a groove bottom 1033. The groove 103 has a width W at a level of the contact face 102 and a depth D (as shown in Fig. 3). (0057) As shown in Fig: 1, a contact patch 106 has a contact patch length L in a tire circumferential direction when the tire with the tread 101 is mounted onto its standard rim and inflated at its nominal pressure and its nominal load is applied. According to 'ETRTO Standard Manual 2016' the standard rim for this size is 6.5J, the nominal pressure is 250kPa and the nominal load is 615kg. (0058) As shown in Fig. l, in the groove 103, a plurality of closing device 105 is provided. The closing device 105 comprises one first flexible fence 1051a and four second flexible fences 1051b for dividing an air column between the ground and the groove 103 in the contact patch 106 during rolling. The closing devices 105 are provided at a regular interval of distance P in the groove 103. The distance P is preferably shorter than the contact patch length L as to at least one closing device 105 in each groove 103 is always located in the contact patch 106 during rolling. (0059) The first flexible fence 1051a has a thickness of tl(a) and extends from the groove bottom 1033 of the groove 103.

(0060) The four second flexible fences 1051b have a thickness of tl(b). Two second flexible fences 1051b of four extend from one groove sidewall 1031 and other two second flexible fences 1051b extend from the other groove sidewall 1032. Two second flexible fences 1051b extending from the same groove sidewall 1031 , 1032 are offset each other in a circumferential direction in the groove 103. The first flexible fence 1051a is placed at a position circumferentially offset or distant from the four second flexible fences 1051b in the groove 103, as shown in Fig. 2. (0061) The thickness tl a) of the first flexible fence 105 la is thinner than the thickness tl(b) of the second flexible fence 1051b, as shown in Fig.2. Although the first and second flexible fences 1051a, 1051b partly overlap in a circumferential direction (in sectional view of the groove 103), the four second flexible fences 1051b do not overlap each other in a circumferential direction (in sectional view of the groove 103). The first and second flexible fences 1051a, 1051b cover at least equal to 70% of the cross sectional area of the groove 103, as shown in Fig.3.

(0062) As shown in Fig.3, the first flexible fence 1051a has a rectangular shape and extends from the groove bottom 1033 toward radially outward direction of the tread 101. The width of the first flexible fence 1051a is substantially equal to the width of the groove bottom 1033 at its bottom and the height of the first flexible fence 1051a is substantially equal to the depth D of the groove 103.

(0063) As shown in Fig.3, two of the second flexible fences 1051b have trapezoid shape and are positioned at radially inner positions, respectively. Remaining two second flexible fences 1051b have parallelogram shape and are positioned at radially outer positions, respectively. (0064) The axial length of each second flexible fence 1051b is shorter than the width W of the groove 103. The radial length of each second flexible fence 1051b is shorter than the depth D of the groove 103.

(0065) A radially outer edge of the second flexible fences 1051b provided at radially outer positions extends substantially parallel to the contact face 102. On the other hand, a radially inner edge of the second flexible fences 1051b provided at radially outer positions extends obliquely upwardly with respect to the groove bottom 1033.

(0066) A radially outer edge of the second flexible fences 1051b provided at radially inner positions extends obliquely upwardly with respect to the groove bottom 1033 so as to be substantially parallel to the radially inner edge of the second flexible fences 1051b provided at radially outer positions.

(0067) A radially inner edge of the second flexible fences 1051b provided at radially inner positions extends obliquely upwardly with respect to the groove bottom 1033 so as to form a generally triangular space thereunder with the groove bottom 1033. (0068) The tread 101 has the same structure as the conventional tread except for an arrangement regarding the closing device 105 and is intended to be applied to a conventional pneumatic radial tire and other non-pneumatic tire. Thus, description of the internal construction of the tread 101 will be omitted.

(0069) The groove 103 is provided with the plurality of closing device 105 each covering at least equal to 70% of the radial cross sectional area of the groove 103. Therefore, the length of the air column formed by the groove 103 in the contact patch 106 is shifted to a length whose groove resonance peak is outside of the frequency audible range for the human ear. Thus, groove resonance due to air column resonance of the groove 103 can be harmless. (0070) The flexible fences of the closing device 105 are provided each other with the offset in a direction the groove 103 extends. Therefore, it is possible to effectively improve groove resonance due to air column as a sound wave generated by groove resonance has difficulty to propagate between each the flexible fences of the closing device 105 in a direction the groove 103 extends.

(0071) The closing device 105 includes one first flexible fence 1051a and four second flexible fences 1051b, two of four second flexible fences 1051b extend from one groove sidewall 1031 and remaining two second flexible fences 1051b extend from the other groove sidewall 1032. Therefore, it is possible to effectively cover as broader cross sectional area of the groove 103 as possible by the closing device 105, while maintaining good productivity of the tread 101 with the flexible fences as closing device 105, as the sectional area covered by each flexible fence can be reduced, resulting in higher flexibility of an arrangement of the first and the second flexible fences 1051a, 1051b. (0072) Although the first flexible fence 1051a and the second flexible fence 1051b overlap partly in a circumferential direction (in sectional view of the groove 103), the second flexible fences 1051b do not overlap each other in a circumferential direction (in sectional view of the groove 103). Therefore, it is possible to further effectively attenuate groove resonance due to air column resonance of the groove 103 while increasing degree of freedom to design and to position the flexible fences of the closing device 105, as the sound wave generated by groove resonance has difficulty to propagate between each the flexible fences of the closing device 105.

(0073) The thickness tl a) of the first flexible fence 1051a is thinner than the thickness tl(b) of the second flexible fence 1051b. It is possible to have easier bending of the first flexible fence 1051a even with reduced groove depth, which results further improvement on drainage capability. (0074) Next, a molding element 1 for a mold used for manufacturing the tread 101 will be described referring to Figs.4, 5, 6 and 7.

(0075) As shown in Fig.4, the molding element 1 has a base portion 2 having a molding surface 2a intended to mold the contact face 102 of the contacting element 104. The base portion 2 has two side faces 11, 12 facing to circumferentially opposed directions. These side surfaces 11, 12 define circumferential extremities of the molding element 1.

(0076) In use, one side face 1 1 or 12 of one molding element 1 is contacted to the other side face 12 or 11 of the adjacent molding elements to form a mold. (0077) As shown in Fig.4, the molding element 1 also has a groove forming rib portion 3. The groove forming rib portion 3 has a trapezoid cross section and integrally extends from the molding surface 2a of the base portion 2 in a radially inward direction of the molding element 1.

(0078) The groove forming rib portion 3 includes two opposed rib side faces 31, 32 intended to mold two opposed groove side faces 1031, 1032, and a rib top face 33 intended to mold a bottom of the groove 1033. In case plurality of groove forming rib portions 3 is provided in one molding element 1, a radial position of the rib top face 33 can be the same among the these groove forming rib portions 3, or can be different among the these groove forming rib portions 3. (0079) The circumferential length of the groove forming rib portion 3 is shorter than that of the base portion 2 by length T. As shown in Fig.4, a circumferential end surface 3' of the groove forming rib portion 3 is placed at a position backwardly from the side face 12 of the base portion 2 by length T. Further, a rectangular area in the side face 12 below the groove forming rib portion 3 is backwardly offset from the side face 12 of the base portion 2 by length T so as to form a space 35, specifically a rectangular recessed space 35 having depth T.

(0080) The molding element 1 also comprises an insert 5 including an upper portion 5a having a trapezoid cross section identical to that of the groove forming rib portion 3 and a lower portion 5b having a rectangular cross section identical to that of the rectangular recessed space 35, as shown in Fig. 5.

(0081) The insert 5 is fixedly secured to the base portion 2 and the groove forming rib portion 3 such that the upper portion 5a abuts against the circumferential end surface 3' of the groove forming rib portion 3 and the lower portion 5b is received in the rectangular recessed space 35, as shown in Fig.5.

(0082) Thickness of the insert 5 is the same as the above offset length T of the circumferential end surface 3' of the groove forming rib portion 3 and the depth T of the rectangular recessed space 35. Therefore, the surface 5' of the insert 5 is flush with the side face 12 of the base portion 2. (0083) The insert 5 is fixed to the groove forming rib portion 3 by a fixing means such as a screw extending through a hole 351 in a groove forming rib portion 3 and a hole 55 in the insert 5.

(0084) The insert 5 may be fixed to the groove forming rib portion 3 by other manner such as welding, gluing, etc. In this case, the holes 55, 351 may not be provided. (0085) The insert 5 can be placed at any part of the groove forming rib portion 3. In case, a space for receiving the insert 5 is provided at a position which is not facing to the side face 11, 12 of the molding element 1, the insert 5 can be placed so as to be disclosed in WO2010/146180A1, for example.

(0086) A forming plate assembly 53 comprising two notched plates 51(51bl, 51b2) is provided in the insert 5. As shown in Fig.6, these two notched plates 51bl, 51b2 are closely contacted one another so as to form forming plate assembly 53. Each of the notched plates 5 lbl, 51b2 in the forming plate assembly 53 includes two notches 51 18 51 lbl , 511b2), respectively. That is, one notched plate 5 lbl in the forming plate assembly 53 includes two notches 51 lbl and the other notched plate 51b2 of the same forming plate assembly 53 includes two other notches 51 lb2.

(0087) When the insert 5 is received in the rectangular recessed space 35 of the molding element 1, one of notch 51 lbl (51 lb2) in one notched plate 5 lbl (51b2) opens to one rib side face 31, and the other notch 51 lbl (51 lbl) in the same notched plate 5 lbl (51b2) opens to the other rib side face 32. These notches 511b are used for forming the second flexible fence of 1051 the closing device 105. The notched plates 5 lbl, 51b2 in the forming plate assembly 53 are provided with a portion 55 for accepting fixing means, such as a screw.

(0088) Two notches 51 lbl, 51 lb2 in the same notched plate 5 lbl, 51b2 are separately provided and not communicated each other. The notches 51 lbl, 51 1b2 of different notched plate 5 lbl, 51b2 in the same forming plate assembly 53 do not have area overlapping each other in sectional view in a direction along which the groove forming rib portion 3 extends. In case more than two notched plates are provided in one forming plate assembly, a notch of one notched plate may overlap to a notch in a notched plate which is not placed adjacent to one notched plate. (0089) Since the forming plate assembly 53 in the insert 5 comprises two notched plates 51bl, 51b2 of thickness tlftlfb)) including two notches 51 lbl, 511b2 for forming the second flexible fence of 1051 the closing device 105 and the notch 51 lbl (51 lb2) in one notched plate 5 lbl (5 lb2) in the forming plate assembly 53 does not overlap the notch 51 lb2 (51 lbl) in the adjacent notched plate 51b2, 5 lbl in sectional view in a direction along which the groove forming rib portion 3 extends, it is possible to increase degree of freedom to design and to position the flexible fence 1051 of the closing device 105.

(0090) As shown in Fig.7, the insert 5 is composed of a plurality of thin plates stacked in a direction along which the groove forming rib portion 3 extends. As explained above, the insert 5 includes one forming plate assembly 53 comprising at least two notched plates 51(51bl, 51b2).

(0091) Each of the notched plates 51bl, 51b2 has thickness t lit 1(b)) and includes two notches 51 lbl, 51 lb2 which open to rib side face 31, 32 when the insert 5 is received in the space 35 of the groove forming rib portion 3. The notches 51 lbl , 51 1b2 are used for forming the first flexible fence 1051a of the closing device 105.

(0092) The notch 511bl (511b2) in one notched plate 51bl (51b2) in the forming plate assembly 53 does not overlap to the notch 51 lb2 (51 lbl) in the adjacent notched plate 51b2 (51bl) in sectional view in a direction along which the groove forming rib portion 3 extends. (0093) The insert 5 comprises an additional notched plates 51(5 la) has a thickness tl (tl(a)). Thickness tl(a) is different from the thickness tl(b of the notched plates 5 lbl, 51b2 in the forming plate assembly 53. The additional notched plates 51a includes a notch 511a which opens to the rib top face 33 when the insert 5 is received in the space 35 of the groove forming rib portion 3. The notch 511a is used for forming the first flexible fence 1051a of the closing device 105. The notch 51 1a in the additional notched plate 51a in the forming plate assembly 53 overlaps to the notch 511b2, 51 lbl in the notched plate 51b2, 5 lbl in the forming plate assembly 53 in sectional view in a direction along which the groove forming rib portion 3 extends. (0094) The insert 5 further comprises two support plates 52(52a) of thickness t2(t2(a)) without the notch. Two support plates 52a are provided at extremities of the insert 5 in a direction along which the groove forming rib portion 3 extends.

(0095) The insert 5 further comprises one additional support plate 52(52b) of thickness t2(t2(b)) without the notch. Thickness t2(b) is different from the thickness t2(a) of the two support plates 52a at two extremities of the insert 5. The additional support plate 52b is placed between the forming plate assembly 53 and the additional notched plate 51a.

(0096) Thus, in the present embodiment, the insert 5 comprises one forming plate assembly 53 including two notched plate 51bl, 51b2, one additional notched plates

51a, two support plates 52a at two extremities of the insert 5 and one additional support plate 52b.

(0097) In this present embodiment, the thickness tUa is thinner than the thickness tl(b). and the thickness t2(a) is thicker than the thickness t2(b). (0098) The thickness tl of all the notched plates 51 (51a, 51bl, 51b2) and the thickness t2 of all the support plates 52 (52a, 52b) are at most equal to 2.0mm. The thickness tl of the notched plates and the support plate is preferably at most equal to 0.8mm, more preferably at most equal to 0.7mm and still more preferably at least equal to 0.02mm and at most equal to 0.6mm. (0099) In the present embodiment, all the notched plates and support plates is provided with a hole 55 as a portion for receiving fixing means. However, in case any elements for fixing the insert 5 to the rectangular recessed space 35 of the groove forming rib portion 3 is not necessary, the hole 55 may not be provided. (0100) Any material able to resist to a force applied during vulcanization, for example metal, resin, plastic or composite material, is usable for configuring both the notched plate 51 and the support plate 52.

(0101) The notched plates 51, comprised in the forming plate assembly 53 or not, and the support plates 52 may be prepared, for example cutting a steel sheet via a wire or a laser.

(0102) The notched plates 51, comprised in the forming plate assembly 53 or not, and the support plates 52 may be covered completely or partly with a non-stick material for better and easier demolding. The non-stick material is, for example xylane. (0103) Since the insert 5 is composed of a plurality of thin plates stacked in a direction along which the groove forming rib portion 3 extends, that is easier to form a shape necessary for forming a portion of the groove of the tread 101 and the flexible fence 1051 of the closing device 105, processing duration for manufacturing such the insert decreases resulting improvement on productivity of the molding element 1 for forming the tread 101 provided with the plurality of flexible fence 1051 of the closing device 105 in the groove 103.

(0104) Since the insert 5 comprises one forming plate assembly 53, the forming plate assembly 53 comprises two notched plates 51bl, 51b2 of thickness tl b includes two notches 5111 , 511b2 for forming the flexible fence 1051 of the closing device 105 and the notches 511 lbl, 51 1b2 on the adjacent notched plates 51bl, 51b2 in the forming plate assembly 53 have no overlap in sectional view in a direction the groove forming rib portion 3 extends, it is possible to increase degree of freedom to design and to position the flexible fence 1051 of the closing device 105.

(0105) Since a thickness of the plurality of thin plates composing the insert 5 have narrow tolerance in thickness than other processes, it is possible to form the plurality of flexible fence 1051 of the closing device 105 with accurate thickness to permit a required bending of the flexible fence 1051 of the closing device 105 for liquid drainage.

(0106) Since the insert 5 further comprises three support plates without the notch, it is possible to easily adjust the thickness of the insert for compensating the thickness of the space by using support plates the while ensuring precise thickness of the flexible fence of the closing device.

(0107) Since the thicknesses of the notched plates and the support plate are at most equal to 2.0 mm, it is possible to ensure satisfactory bending capability of the flexible fence 1051 of the closing device 105 with hydrodynamic pressure for liquid drainage as these thicknesses will substantially be equal to the thickness of the flexible fence 1051 of the closing device 105.

(0108) These thicknesses, the thicknesses of the notched plate and the support plate are preferably at most equal to 0.8mm, more preferably at most equal to 0.7mm and still more preferably at least equal to 0.02mm and at most equal to 0.6mm.

(0109) Since the insert 5 further comprises one additional notched plate 51a of thickness tl(a) including at least one notch 51 1a overlapping with the notch in the forming plate assembly 53 in sectional view in a direction along which the groove forming rib portion 3 extends, and one support plate 52b of thickness t2(b) without the notch is provided between the forming plate assembly 53 and said other notched plate 51, it is possible to manufacture the flexible fences 1051 of the closing device 105 effectively covering as broader cross sectional area of the groove 103 as possible while maintaining good productivity of the tread 101 with the flexible fences 1051 as closing device 105, as the sectional area covered by each flexible fence 1051 can be reduced, resulting in higher flexibility of an arrangement of the flexible fences 1051. (0110) Since the notches Sl lbl, 511b2 in the forming plate assembly 53 partially overlap with the notch 511a in the additional notched plate 51a, it is possible to manufacture the flexible fence 1051 of the closing device 105 overlapping partly in sectional view of the groove 103 for making a sound wave generated by groove resonance difficult to propagate between the flexible fences 1051 of the closing device 105 with more precise distance between the flexible fences 1051 for effective attenuation of the groove resonance due to air column resonance of the groove 103.

(0111) Since the thickness tl(a) of the notched plate 51a having the notch 51 1a opening to the rib top face 33 is different from the thickness tl(b) of the notched plate 51bl, 51b2 having the notch 51 lbl, 511b2 opening to the rib side face 31, 32, performance compromise by the flexible fences 1051 can be achieved. By making the thickness tl(a) thicker than the thickness t l(b). it is possible to have a regular wear of the flexible fence 1051 extending from the groove bottom 1033 (formed via the notched plate 51a having the notch 511a opening to the rib top face 33) with tread wear by increased bending rigidity of the flexible fence 1051 extending from the groove bottom 1033 relative to the flexible fence 1051 extending from the groove sidewall 1031, 1032 (formed via the notched plate 51 having the notch 511 opening to the rib side face 31, 32). Contrarily by making the thickness 1 (a) of the notched plate 51a thinner than the thickness tl(b) of the notched plate 51ba, 51b2, it is possible to have easier bending of the flexible fence 1051 extending from the groove bottom 1033 (formed via the notched plate 51 having the notch 51 1 opening to the rib top face 33) even with reduced groove depth which results further improvement on drainage capability.

(0112) Since the insert 5 comprises at least two support plates 52 having at least two different thicknesses t2, it is possible to increase manufacturing efficiency and flexibility of the molding element 1. (0113) By using the support plate 52 having at least two different thickness t2 between each the notched plates 51, it is possible to increase degree of freedom of an arrangement of the flexible fences 1051 in the closing device 105. By using the support plate 52 having at least two different thickness t2 one between the notched plates 51 and other between the notched plate 51 and a face of the rectangular recessed space 35, a thickness of the insert 5 can adjust easily for compensating a thickness of a space including the rectangular recessed space 35 while ensuring precise thickness of the flexible fence 1051 of the closing device 105.

(0114) Since two end ^' s of the insert 5 in the direction groove forming rib portion 3 extends are the support plates 52a, it is possible to adjust easily the thickness of the insert 5 for compensating the thickness of the rectangular recessed space 35 while ensuring precise thickness of the flexible fence 1051 of the closing device 105.

(0115) The invention is not limited to the examples described and represented and various modifications can be made there without leaving its framework.

(0116) Reference Numerals

1 molding element 1 1, 12 side face

2 base portion

2a molding surface

3 groove forming rib portion 31, 32 rib side face

33 rib top face 35 space 351 hole insert

1 notched plate

11 notch

2 support plate

3 forming plate assembly 5 hole

101 tread

102 contact face

103 groove

1031, 1032 groove side face 1033 groove bottom

104 contacting element

105 closing device

1051 flexible fence

106 contact patch