Method and device for producing a two-part tire layer

Abstract: In a road vehicle tire, a two-part layer (2) of elastomeric material is preassembled by co-extruding a first and a second strip (19, 16) through a preforming plate die (26), through which extends at least one pair (27) of tapered flow channels (25a, 25b) having offset, side by side inlets (28, 29) with respective superimposed adjacent lateral portions (30, 32), and substantially coplanar outlets (33, 34) with respective adjacent lateral portions (35, 38) interconnected to define, between the two strips (19, 16), an L-shaped joint (20) wherein a lateral portion (21) of the second strip (16) has an edge (17) substantially contacting a lateral shoulder (22) of the first strip (19), and is superimposed on a thin annular appendix (23) projecting from the shoulder (22) of the first strip (19).

Description: The present invention relates to a method and a device of producing a two-part layer of a road vehicle tire. The present invention may be used to advantage for producing tire sidewall outer coating skims. Such a coating skim is normally defined by an abrasion strip and a lateral-wall strip arranged side by side and connected by a joint. As any expert knows, a two-part layer of the above type is produced by co-extruding the two strips of elastomeric material side by side and feeding the two strips to a die, by which they are so gripped as to adhere to each other along the facing lateral edges. The joint between the two strips is normally a straightforward butt joint, which has proved fairly unreliable when subjected normally to relatively severe stress by the nature and/or shape of the internal components of the tire adjacent to the joint. EP-0925903-A1 discloses the production of unvulcanized tread rubber for pneumatic tires. A pneumatic tire includes a low conductive rubber portion forming at least a cap rubber portion of the tread rubber which provides a tread surface of the tire; a narrow high conductive rubber strip extends in a radial direction of the tire at a widthwise center region of the cap rubber portion, and is exposed to the tread surface to form a discharge path for allowing electrostatic charges of a vehicle body to be discharged to a road surface. An unvulcanized tread rubber for the tire is obtained by passing a high conductive unvulcanized rubber through a passage extending from an extruder unit to the back side of an extrusion orifice, to form at least part of the remaining portion of the tread rubber; the high conductive unvulcanized rubber while passing through the passage is partly introduced into a narrow branch passage and passed through a slit-like opening having a cross-sectional shape which is substantially straight in a height direction of the extrusion head and situated in the vicinity of the back side of the extrusion orifice, to form the narrow strip of the high conductive rubber in a composite body of different kinds of unvulcanized rubbers. JP-04208443-A discloses a pneumatic tire, in which a rubber chafer and a side rubber are extruded into an integral form by a dual T-bar in order to prolong the tire life. A boundary part between a rubber chafer and a side rubber is oriented from inside in tire width direction to outside in the tire width direction and inclined from inside in tire radial direction to outside in the tire radial direction; the rubber chafer and the side rubber are extruded by a dual T-bar into an integral form. Accordingly, there is no occurrence of stepped parts at the boundary part between the rubber chafer and the side rubber. For this reason, upon vulcanization, no creek occurs at the boundary part between the rubber chafer and the side rubber, the separation of the boundary part is prevented and the tire life can be prolonged. It is an object of the present invention to provide a method and a device of producing a two-part layer, designed to produce, cheaply, easily and by co-extrusion, stronger, more reliable joints between the two parts than is currently possible. According to the present invention, there is provided a method and a device of producing a two-part layer of a road vehicle tire as recited in the attached claims. The invention will be described with reference to the accompanying drawings, in which: Figure 1 shows an exploded, partial view in perspective, from the output side, of a detail of a preferred embodiment of the extrusion device according to the present invention; Figure 2 shows a partial view in perspective, from the input side, of a first detail in Figure 1; Figures 3 and 4 show views in perspective, one from the input and the other from the output side, of another two details in Figure 1; Figure 5 shows a partial cross section of a tire produced using the extrusion device according to the present invention. Number 1 in Figure 1 indicates as a whole an extrusion device for extruding two layers of elastomeric material, each of which, as shown in Figure 5, defines a coating skim 2 of a respective sidewall 3 (only one shown in Figure 5) of a road vehicle tire 4. With reference to Figure 5, each sidewall 3 of tire 4 comprises, at the radially inner end, a bead 5 in turn comprising a bead bundle 6 coaxial with tire 4 and having a substantially triangular-section bead filler 7 with its base facing the outer lateral surface of bead bundle 6, and a vertex 8 facing radially outwards. Together with bead bundle 6, bead filler 7 defines a bead assembly 9, about which extends a respective lateral portion 10 of a body ply 11. Lateral portion 10 comprises an axially inner portion 12 lined with an innerliner 13; and a turn-up portion 14 located axially outwards of bead assembly 9, which is continued along sidewall 3 by a stiffening strip 15 contacting lateral portion 10 and extending radially outwards of vertex 8 along sidewall 3. Each skim 2 coats the relative sidewall 3 externally, extends about relative bead assembly 9, is connected to a relative lateral edge of innerliner 13, and comprises an annular lateral-wall strip 19, and an annular abrasion strip 16, which is turned up into a U about relative bead assembly 9, and is defined laterally, on the axially outer side of relative bead assembly 9, by a sloping annular edge 17 substantially parallel to an equatorial plane 18 of tire 4. Lateral-wall strip 19 is connected to abrasion strip 16 by an L-shaped joint 20, wherein an annular lateral portion 21 of abrasion strip 16 extends with an edge 17 contacting a lateral annular shoulder 22 of lateral-wall strip 19, and is superimposed on a thin annular appendix 23 projecting from shoulder 22 and facing relative bead bundle 6. Obviously, shoulder 22 slopes at an angle complementary to that of relative edge 17, and defines, with relative appendix 23, a recess 24 engaged by a triangular peripheral portion of lateral portion 21 of abrasion strip 16. With reference to Figures 1 to 4, extrusion device 1 comprises two known double-outlet extruders (not shown), each outlet (not shown) of each of which feeds, in known manner not shown, a respective strip (not shown) of a respective elastomeric material to a respective preforming channel 25 formed through a preforming plate die 26 forming part of extrusion device 1. The four channels 25 of die 26 are arranged in side by side pairs 27, and each pair 27 comprises a channel 25a and a channel 25b arranged in a substantially side by side arrangement explained in detail later on. The outlets of channels 25a and 25b in each pair 27 of channels 25 communicate with a respective single known channel (not shown) of a known end die (not shown) for forming two coating skims 2 arranged specularly with respect to each other and for coating respective sidewalls 3 of tire 4. For which purpose, the two channels 25b are formed through die 26 in a substantially intermediate position with respect to the two channels 25a, so that channels 25 in each pair 27 are arranged specularly with respect to channels 25 in the other pair 27. As shown in Figure 2, the two channels 25a and 25b are tapered, and have respective substantially elongated rectangular inlets 28 and 29 arranged side by side in parallel, offset planes. At the end facing inlet 29, inlet 28 has a lateral portion 30, which is defined internally by a recess 31 extending .crosswise to the plane of inlet 28 and towards inlet 29, and is superimposed on a lateral portion 32 of inlet 29; which lateral portion 32 terminates facing and to the side of recess 31. As shown in Figure 2, the two channels 25a and 25b have respective substantially elongated rectangular outlets 33 and 34 arranged side by side in substantially the same plane. At the end facing outlet 34, outlet 33 has a lateral portion 35, which corresponds to lateral portion 30 of inlet 28, defines appendix 23 of lateral-wall strip 19, and is defined internally by a recess 36 communicating with and corresponding to recess 31. Recess 36 defines shoulder 22 and slopes with respect to the rest of outlet 33 to define, together with lateral portion 35, an acute dihedral 37 engaged by a lateral portion 38 of outlet 34 corresponding to lateral portion 32 of inlet 29, so that the two lateral portions 35 and 38 are interconnected by an L-shaped joint corresponding to respective L-shaped joint 20. Lateral portions 30 and 35 define the inlet and outlet ends of a lateral portion 39 of channel 25a, while lateral portions 32 and 38 define the inlet and outlet ends of a lateral portion 40 of channel 25b. With reference to Figure 1, die 26 comprises a substantially rectangular plate 41, which has a substantially horizontal longitudinal axis, is defined by an input surface 42 and an output surface 43 parallel to and opposite each other, and has, for each pair 27 of channels 25, a substantially rectangular cavity 44 formed through surface 42 and closed by an end wall 45 in which is formed a substantially rectangular through opening 46, which is substantially the same width as cavity 44, is smaller in height than cavity 44, and the top end of which substantially coincides with that of cavity 44. Cavity 44 and relative opening 46 are engaged by a block 47 shown in Figures 3 and 4 and comprising a plate 48, which is inserted inside cavity 44 and fixed to wall 45 by a screw 49; and a plate 50, which is fitted through opening 46. As shown in Figure 1, plate 50 is fixed in the correct position to plate 48 by two pins 51 and two screws 52, and is locked releasably against plate 48 and inside opening 46 by a retaining rod 53 fixed to surface 43 by screws 54 so that a top peripheral portion of the rod partly closes opening 46. As shown in Figures 3 and 4, lateral portions 39 and 40 of respective channels 25a and 25b are formed through block 47, while the remaining portions of channels 25a and 25b are defined by respective slots 55 and 56 formed through plate 41. More specifically, the input portions of lateral portions 39 and 40 are formed through plate 48, while the output portions of lateral portions 39 and 40 are formed through plate 50. Extrusion device 1 described provides not only for preassembling each abrasion strip 16 to the relative lateral-wall strip 19, thus greatly reducing the assembly time of tire 4, but also for producing an extremely precise L-shaped joint 20, which, given its structure, is easily capable of absorbing any stress transmitted by the relative turn-up portion 14 of body ply 11, and enables the use of body plies 11 with narrow turn-up portions 14. The easy-change blocks 47 of die 26 described provide for both changing the wear parts of die 26 cheaply and easily, and for altering the shape of joints 20 as required without changing plate 41. Finally, forming each block 47 by superimposing respective plates 48 and 50 makes lateral portions 39 and 40 of respective channels 25a and 25b easier to produce, and makes die 26 much easier to maintain and clean.

Claims: A method of producing a two-part layer (2) of a road vehicle tire (4); the method comprising the step of co-extruding two strips (19, 16) of a respective elastomeric material side by side, feeding the two strips (19, 16) to a preforming die (26), and adhere the two strips (19, 16) to each other in the preforming die (26); a first strip (19) is fed through a first flow channel (25a) of the preforming die (26) between a first inlet (28) and a first outlet (33), and a second strip (16) is fed through a second flow channel (25b) of the preforming die (26) between a second inlet (29) and a second outlet (34); the method being characterized in comprising the step of bringing an edge (17) of a lateral portion (21) of the second strip (16) in contact with a lateral shoulder (22) of the first strip (19) through the flow channels (25a, 25b), superimposing the lateral portion (21) of the second strip (16) on a thin annular appendix (23) projecting from the shoulder (22) of the first strip (19), and interconnecting the two strips (19, 16) with an L-shaped joint (20). A method as claimed in Claim 1, and comprising the step of making a coating skim of a sidewall (3) of a tire (4) using said two-part layer (2) by forming a lateral-wall strip of the tyre (4) using said first strip (19) and forming an abrasion strip (16) of the tyre (4) using said second strip (16). A method as claimed in Claim 1 or 2, and comprising the step of forming simultaneously two said two-part layer (2) using a same preforming die (26) having two side by side pairs (27) of flow channels (25a, 25b). A device for producing a two-part layer (2) of a road vehicle tire (4), the device comprising a preforming plate die (26), through which extends at least one pair (27) of tapered flow channels (25a, 25b) for co-extruding and connecting together a first and a second strip (19, 16); a first flow channel (25a) of the preforming die (26) has a first inlet (28) and a first outlet (33), and a second flow channel (25b) of the preforming die (26) has a second inlet (29) and a second outlet (34); the device being characterized in that said inlets (28, 29) are separated, are arranged side by side, and have respective superimposed adjacent lateral portions (30, 32); said outlets (33, 34) are separated, are coplanar, and have respective adjacent lateral portions (35, 38), which are interconnected each other by an L-shaped joint; at the end facing the second outlet (34), the first outlet (33) has a first lateral portion (35) defined internally by a first recess (36), which communicates with and corresponds to a second recess (31) of the first inlet (28) and slopes with respect to the rest of the first outlet (33) to define, together with the first lateral portion (35), an acute dihedral (37) engaged by a second lateral portion (38) of the second outlet (34). A device as claimed in Claim 4, wherein said layer (2) is a coating skim of a respective sidewall of said tire; said first and said second strip (19, 16) are a lateral-wall strip (19) and an abrasion strip (16). A device as claimed in Claim 5, wherein said preforming die (26) has two side by side said pairs (27) of flow channels (25a, 25b); the two channels (25a, 25b) in each pair (27) are arranged specularly with respect to the two channels (25a, 25b) in the other pair (27). A device as claimed in one of Claims 4 to 6, wherein said lateral portions (30, 32) of said inlets (28, 29) define, together with the respective said lateral portions (35, 38) of said outlets (33, 34), the opposite ends of respective lateral portions (39, 40) of the respective said channels (25a, 25b); said die (26) comprising a flat supporting plate (41), and, for each said pair (27) of said channels (25a, 25b), a block (47) fitted removably through said plate (41); said lateral portions (39, 40) of said channels (25a, 25b) being formed through said block (47); and said channels (25a, 25b) having the remaining portions defined by respective through slots (55, 56) formed through the supporting plate (41). A device as claimed in Claim 7, wherein said block (47) comprises a first and a second plate (48, 50) superimposed and connected to each other; input portions of said lateral portions (39, 40) of said channels (25a, 25b) being formed through said first plate (48); and output portions of said lateral portions (39, 40) of said channels (25a, 25b) being formed through said second plate (50). A device as claimed in Claim 8, wherein said supporting plate (41) comprises, for each said block (47), a rectangular cavity (44), which is engaged by said first plate (48) and closed by an end wall (45) through which is formed a rectangular through opening (46) engaged by said second plate (50). A device as claimed in Claim 9, wherein said opening (46) is smaller in height than said cavity (44); said first plate (48) being positioned contacting said end wall (45), and being connected to the end wall (45) by removable fastening means (49).

Inventors: TOMLINSON GORDON MALCOM, TOMLINSON, GORDON MALCOM
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 2001
Main classification: B29C47
IPC codes: B29D30, B60C13, B29C47, B29K21, B60C15