METHOD AND APPARATUS FOR FORMING A COMPOSITE APEX

Abstract

A method for forming a composite apex, the method comprising the steps of: forming a coextruded strip of a first compound and a second compound, wherein the second compound is a compound different than the first compound, wherein the apex is formed from winding the coextruded strip while varying the ratio of the first compound to the second compound.

Claims

1. A method for forming a composite apex, the method comprising the steps of: forming a coextruded strip of a first compound and a second compound, wherein the second compound is a compound different than the first compound, wherein the apex is formed from winding the coextruded strip while varying the ratio of the first compound to the second compound.

2. The method of claim 1 wherein the radially outer portion of the apex is 100% of the second compound.

3. The method of claim 1 wherein the radially inner portion of the apex is formed from a coextruded strip having a ratio of 95% of the first compound and 5% of the second compound.

4. The method of claim 1 wherein the apex is formed from a dual layer of strip lamination.

5. The method of claim 1 wherein the second compound is selected for high stiffness.

6. The method of claim 1 wherein the coextruded strip is formed by: extruding a first compound through a first extruder and a first gear pump and into a first passageway of a coextrusion nozzle; extruding a second compound through a second extruder and a second gear pump and into a second passageway of the coextrusion nozzle; and wherein the first and second passageways are joined together immediately upstream of the die outlet of the coextrusion nozzle.

7. The method of claim 6 wherein the coextrusion nozzle has an insert which divides the nozzle into a separate first and second passageway.

8. The method of claim 7 wherein the insert has a distal end for positioning adjacent a die outlet of the coextrusion nozzle, wherein the distal end has an elongated flat portion.

9. The method of claim 1 wherein the ratio of the volume of the first compound to the volume of the second compound is varied by changing the ratio of the speed of the first gear pump to the second gear pump.

10. The method of claim 6 wherein the ratio of the first gear pump to the second gear pump may be varied during operation of the system.

11. The method of claim 7 wherein the insert is removable.

12. The method of claim 7 wherein the insert has a rectangular cross-sectional shape.

13. The method of claim 1 wherein the strip is formed in a continuous manner.

14. The method of claim 1 wherein the strip is applied in a continuous manner to a tire building machine to build a tire component.

15. A method for forming a tire component, the method comprising the steps of: providing a tire, forming a coextruded strip of a first compound and a second compound, wherein the second compound is a compound different than the first compound, wherein the tire component is formed from winding the coextruded strip onto the tire building drum while varying the ratio of the first compound to the second compound.

16. The method of claim 1 wherein the second compound comprises a rubber composition having a shear storage modulus G measured at 1% strain and 100 C. according to ASTM D5289 ranging from 23 to 31 MPa.

17. The method of claim 1 wherein the first compound comprises a rubber composition having a shear storage modulus G measured at 1% strain and 100 C. according to ASTM D5289 ranging from 1.4 to 2.3 MPa.

18. The method of claim 1 wherein the radially outer strip windings have an axis X-X oriented in the radial direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention will be described by way of example and with reference to the accompanying drawings in which:

[0021] FIG. 1A shows a meridional cross-section of a radial ply pneumatic tire according to the present invention;

[0022] FIG. 1B shows a cross-section of the bead section of FIG. 1A;

[0023] FIG. 2A is a perspective view of a coextruded strip of 90% of a first compound and 10% of a second compound of the present invention;

[0024] FIG. 2B is a perspective view of a coextruded strip of 95% of a first compound and 5% of a second compound;

[0025] FIG. 3 is a cross-sectional view of a composite apex of the present invention;

[0026] FIG. 4 is a perspective view of a dual compound apparatus for forming a coextruded strip onto a tire building drum;

[0027] FIG. 5 is a cross-sectional view of the dual compound apparatus of FIG. 4; and

[0028] FIG. 6 is a perspective cutaway view of a coextrusion nozzle of the present invention, while FIG. 7 is a side cross-sectional view of the coextrusion nozzle of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

[0029] FIG. 1A illustrates a cross-sectional view of a pneumatic tire 1 having a tread 5, a belt structure comprising one or more belts 7, and a carcass 9. The carcass 9 has an innerliner 11, at least one radial ply 13, two sidewalls 12, 12, and two opposed bead areas 14,14 having an annular bead wire 15. FIG. 1B shows a cross-section of the bead areas 14 of FIG. 1A. The bead areas 14 have an axially-inner apex 16 formed of a first material and an axially-outer apex 18 formed of a second material. Thus, in this example of a prior art apex configuration, two different apexes are used having different stiffness properties in order to have the desired overall properties.

[0030] FIG. 3 illustrates a cross-sectional view of an apex profile 200 of the present invention that can be substituted with the apexes of FIG. 1A and FIG. 1B. The apex 200 is formed by strip lamination, or by winding a continuous coextruded strip 210 of two discrete layers of green rubber onto a tire building drum 18 or a shaped green carcass. The continuous coextruded dual strip 210 is shown in FIG. 2A, and is a dual layer of a first rubber compound 212 and second rubber compound 214, wherein each rubber compound has different properties. Each strip 210 has an axis X-X.

[0031] The first layer 212 is formed from a first rubber compound which is typically used to form an apex. The second compound is preferably a rubber compound preferably having high stiffness properties. The first and second rubber compounds of the strip are formed in discrete layers 212,214, and thus are not mixed together.

[0032] The first layer thickness of the first compound is preferably in the range of about 0.3 mm to about 2 mm, and more preferably in the range of about 0.6 to about 1.2 mm. The second layer thickness of the second compound preferably has a thickness in the range of about 0.01 mm to about 0.2 mm, more preferably about 0.01 mm to about 0.1 mm. The overall width of the strip 230 is in the range of about 10 mm to about 50 mm, more preferably 20-40 mm. The term about as used herein means a variation of +/10%.

[0033] The coextruded strip 210 shown in FIG. 2A is a dual layer strip of a first layer 212 having a ratio of 90% of the first compound. The dual layer strip 210 has a second layer 214 having a ratio of 10% of the second compound. FIG. 2B illustrates a a dual layer strip 210 having a first layer 212 formed of the first compound and a second layer 214 formed of the second compound, wherein the dual layer strip has a ratio of 95% of the first compound to 5% of the second compound. The apparatus used to form the continuous coextruded strip is described in the paragraphs below and is shown in FIGS. 4-7. The apparatus can form the coextruded strip while instantaneously varying the ratio of the first compound to the second compound.

[0034] The coextruded strip forming apparatus 10 is used to form the desired apex profile 200 shown in FIG. 3 by rotating the drum 18 (or carcass) and then applying a continuous coextruded strip 210 by continuously winding the strip directly onto the tire carcass or drum. As shown in FIG. 3, the annular strip windings 220,222,224 are overlapped or stacked in the radial direction. In the strip windings nearest the bead, preferably the first three step windings 220,222,224, have a strip composition preferably in the range of 90-100% of the first compound, while the second compound is in the range of 0-10% by volume of the strip. The midportion of the apex which correspond to strip windings 226-236, the strip composition is preferably 50% first compound, and 50% of a second compound. The radially outer portion of the apex that is radially outward of the midportion corresponds to strip windings 238-244, the strip composition is preferably 80% first compound, and 20% of a second compound. The radially outermost portion of the apex that corresponds to strip windings 246-258, the strip is preferably 100% first compound.

[0035] The stiffness may be characterized by the dynamic modulus G, which are sometimes referred to as the shear storage modulus or dynamic modulus, reference may be made to Science and Technology of Rubber, second edition, 1994, Academic Press, San Diego, Calif., edited by James E. Mark et al, pages 249-254. The shear storage modulus (G) values are indicative of rubber compound stiffness which can relate to tire performance. The tan delta value at 100 C. is considered as being indicative of hysteresis, or heat loss.

[0036] In a first embodiment, the second rubber compound comprises a stiff rubber composition having a shear storage modulus G measured at 1% strain and 100 C. according to ASTM D5289 ranging from 18 to 32 MPa, and the first rubber compound comprises a rubber composition having a shear storage modulus G measured at 1% strain and 100 C. according to ASTM D5289 ranging from 1.2 to 10 MPa. In a more preferred embodiment, the second rubber compound comprises a rubber composition having a shear storage modulus G measured at 1% strain and 100 C. according to ASTM D5289 ranging from 23 to 31 MPa, and the first rubber compound comprises a rubber composition having a shear storage modulus G measured at 1% strain and 100 C. according to ASTM D5289 ranging from 1.4 to 2.3 MPa.

Coextruded Strip Forming Apparatus

[0037] As shown in FIGS. 4-7, the coextruded strip forming apparatus 10 includes a first extruder 30 and a second extruder 60, preferably arranged side by side in close proximity. The first extruder 30 has an inlet 32 for receiving a first rubber composition A, while the second extruder 60 has an inlet 62 for receiving a second rubber composition B. Each extruder functions to warm up the rubber composition to the temperature in the range of about 80 C. to about 150 C., preferably about 90 C. to about 120 C., and to masticate the rubber composition as needed. The coextruded strip forming apparatus 10 is mounted upon a translatable support bar 16, that can translate fore and aft in relation to a tire building machine 18.

[0038] The first compound is extruded by the first extruder 30 and then pumped by the first gear pump 42 into a nozzle 100, while at the same time the second compound is extruded by the second extruder 60 and then pumped by the second gear pump 44 into the coextrusion nozzle 100.

[0039] The coextrusion nozzle 100 has a removable insert 120 that functions to divide the nozzle into a first and second flow passageway 122,124. The removable insert 120 is preferably rectangular in cross-sectional shape. The removable insert 120 has a distal end 130 with tapered ends 132,134 forming a nose 136. The nose 136 is positioned adjacent the nozzle die exit 140 and spaced a few millimeters from the die exit 140. The region between the nose 136 and the die exit 140 is a low volume coextrusion zone 150 that is high pressure. In the low volume coextrusion zone 150, the first compound flowstream 122 merges with the second compound flowstream 124 forming two discrete layers 212,214 joined together at an interface 215.

[0040] The coextrusion nozzle 100 is preferably mounted upon a rotatable head 70.

[0041] The volume ratio of the first compound to the second compound may be changed by varying the ratio of the speed of the first gear pump of the first compound to the speed of the second gear pump of the second compound. The dual coextruded strip forming apparatus 10 can adjust the speed ratios on the fly, and due to the small residence time of the coextrusion nozzle, the apparatus has a fast response to a change in the compound ratios. This is due to the low volume of the coextrusion zone.

[0042] Variations in the present inventions are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.