BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate an embodiment of the invention and, together with a general description of the invention given above and a detailed description of a preferred embodiment given below, serve to explain the invention.
FIG. 1 illustrates a perspective view of a tire forming bladder according to one embodiment of the present invention;
FIG. 2 illustrates a cross-sectional view of the bladder illustrated in FIG. 1;
FIG. 3A illustrates a schematic cross-sectional view of the bladder of FIG. 1 being used in a tire mold to form a low aspect ratio tire;
FIG. 3B illustrates the tire bladder of FIG. 3A in which the bladder has expanded under pressure causing preferential contact between the sidewall portion of a green tire carcass and a tire mold;
FIG. 3C illustrates a schematic cross-sectional view of the tire bladder of FIG. 3B with increased expansion of the bladder causing full contact between a green tire carcass and a tire mold; and
FIG. 4 illustrates a prior art bladder design.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to FIG. 1, a preferred embodiment of a bladder 10 for forming a low aspect ratio tire is illustrated. In some embodiments, the aspect ratios produced are in the 45 series, the 40 series, and the 30 series, however, other series of low aspect ratio tires can be produced. The bladder 10 is formed of a flexible and expandable material, such as an elastomeric material, including butyl rubber. However, other types of materials apparent to those skilled in the art can be utilized to form the bladder 10. The bladder 10 can be formed using an injection molding process or other manufacturing technique readily apparent to those skilled in the art.
In the illustrated embodiment, the bladder 10 has a generally toroidal shape that generally corresponds to the shape of a low aspect ratio tire and that has an exterior surface 12 and an interior surface 14. The exterior and interior surfaces 12, 14 define an interior space 16 arranged to receive a central post (not shown) of a tire mold 30 (FIG. 3). The bladder 10 is connected to the post (not shown), usually by clamping, and is then inserted into the tire mold 30. The bladder 10 is designed to be pressurized during the process of forming/curing a tire and to expand under that pressure to engage a green tire carcass thereby urging the green tire carcass into contact with the tire mold 30.
FIG. 2 illustrates the three main portions of the bladder 10 positioned around the centerline 18 of the bladder 10. The first portion of the bladder 10 is a generally rectilinear and generally uniform thickness central portion 20 that extends axially outward from the centerline. In one preferred embodiment, the thickness or gauge of the central portion 20 is about 5 millimeters. The second portion of the bladder 10 extends from each of the ends of the central portion 20 and includes the shoulder portions 22 which are symmetrically positioned on either side of the centerline 18 and which have a generally arcuate cross section. The shoulder portions 22 begin at a location 23 where the thickness of the cross section of the bladder 10 is reduced. In one preferred embodiment, the thickness of the shoulder portions 22 is about 4 millimeters. The shoulder portions 22 are the portions of the bladder 10 that engage the transitional portion of the finished tire between the treads and sidewall.
The third portion of the bladder 10 is the clamping feet 24. The clamping feet 24 are used to secure the bladder 10 to a post (not shown) that is inserted into the center of the tire mold 30. The distance between the interior surface 25 of clamping feet 24 is represented by D1 in FIGS. 2 and 3A and the distance along the generally rectilinear portion of the exterior surface 12, which includes the central portion 20 and part of the shoulder portions 22, is represented by D2. Preferably, the distance D1 is less than the distance D2, which provides a wide rectilinear section of the exterior surface 12 that is longer in length than the distance between the clamping feet 24. In one preferred embodiment, the distance D1 is about 5.75 inches and the distance D2 is about 7.5 inches.
The central portion 20, shoulder portions 22, and clamping feet 24 are preferably one continuous membrane that is both expandable and readily deformable. The shape defined by the combination of portions 20 and 22 conforms generally to the profile of a low aspect ratio tire. Although clamping feet 24 are shown as having a cross-sectional width greater than that of the central portion 20 and shoulder portions 22, the present invention is not limited to such a construction. Those skilled in the art will recognize that other constructions may be used so long as the bladder 10 may be secured in position in the mold 30.
FIG. 3A illustrates the beginning stages of the curing process before the bladder is pressurized of a low aspect ratio tire using the bladder 10 illustrated in FIGS. 1 and 2. The bladder 10 attaches to the post (not shown) using dual clamps 26 positioned opposite from one another that serve to restrain the bladder 10 during the curing process. After the bladder 10 is attached to the post, it is inserted into a green tire carcass 28, both of which are placed in a mold 30. Advantageously the shape of the bladder 10 generally conforms to the shape of the green tire carcass 28, which improves the curing process of the green tire carcass 28 as described below.
During curing, the clamps 26 hold the bladder 10 inside of the mold 30 with each of the clamps 26 having an outside clamp 32 and an inside clamp 34 to clamp around the clamping feet 24. The green tire carcass 28 is surrounded by the mold 30, which has a top half 36 and a bottom half 38 that can move apart relative to each other enabling removal or placement of the green tire carcass 28. The mold 30 also includes ribs 39 and grooves 40 formed on the interior surface 41 of the mold 30 to form the treads and tread grooves on the green tire carcass 28 during the curing process. Besides the two-piece mold 30 illustrated in FIG. 3A, a variety of other types of molds can be utilized in forming the green tire carcass 28. For instance, segmental molds are commonly utilized in forming low aspect ratio tires.
As illustrated in FIG. 3B, after the green tire carcass 28 is positioned in the mold 30, the bladder 10 is pressurized. As the pressure is increased inside of the bladder 10, as illustrated by the arrows, the shoulder portions 22 which have a cross-sectional thickness or first gauge 42 that is thinner than the cross-sectional thickness or second gauge 44 of the central portion 20 of the bladder 10, expand at a faster rate than the central portion 20. The central portion 20 having the thicker second gauge 44 will stretch and expand at a slower rate than shoulder portions 22 having the thinner first gauge 42. Advantageously, the expansion at the shoulder portions 22 results in increased pressure on the green tire carcass 28 in the corner areas 46 of the green tire carcass 28 as compared to bladders used to form standard aspect ratio tires. This increased pressure in the corner areas 46 results in an improved quality and uniform contact between the green tire carcass 28 and the mold 30 in the corner areas 46 and, thereby, higher quality low aspect ratio tires are obtained than can be obtained using traditional bladders.
Referring now to FIG. 3C, the fully pressurized bladder 10 is illustrated pressing the green tire carcass 28 against the entire surface of the mold 30. Because the bladder 10 expands more rapidly in the shoulder portions 22 than the central portion, the bladder 10 is able to urge the green tire carcass 28 into full engagement with the mold 30 without any gaps. The result is a uniformly formed low aspect ratio tire created from the green tire carcass 28. Although the preferred embodiment achieves the desired results by reducing the thickness or gauge 42 of the bladder 10 in the shoulder portions 22 as compared to the thickness or gauge 44 of the central portion 20, the present invention is not limited to such a construction. For example, the bladder 10 could be formed such that the material in the shoulder portions 22 has a lower modulus of elasticity than the material in the central portion 20 such that the shoulder portions 22 expand at a greater rate than does the central portion 20 under a given pressure. Persons skilled in the art will recognize that other variations are available that enable the shoulder portions 22 of the bladder 10 to expand more readily under a given pressure than the central portion 20.
Referring now to FIG. 4, the advantage of the bladder 10 of the present invention over a conventional bladder 48 is illustrated. Since the conventional bladder 48 has a generally uniform gauge, it fails to adequately expand across and conform to all areas of the green tire carcass 50. Instead, a gap area 52 is frequently left between the bladder 48 and the green tire carcass 50 in the corner areas between the tread area 54 and sidewall areas 56. The result is that the transitional part of the green tire carcass 50 from the tread area 54 to the sidewall area 56 is frequently poorly formed. The conventional bladder 48 therefore produces low aspect ratio tires of marginal quality for at least the reason that the pressure applied to the shoulder areas of the bladder 48 is inadequate.
Referring now to FIGS. 5A-D, multiple bladder embodiments are illustrated for use with different types of tire molds. The first bladder embodiment 58a is directed to a bladder for use with Bag-O-Matic® type LARC curing presses. The profile of this bladder is similar to the one described in FIGS. 1-4. The second bladder embodiment 58b is directed to another type of bladder for use with a NRM type LARC curing press. This bladder has a profile with an irregularly shaping clamping foot and a curved clamping foot. The third bladder embodiment 58c is directed to another type of bladder for use with KRUPP & AUTOLOK LARC curing presses. This bladder has a profile with an extended clamping foot and a thick clamping foot. The fourth bladder embodiment 58d is directed to yet another type of bladder for use with KOBE type LARC curing presses.
The invention has been described in the context of exemplary embodiments. Those skilled in the art will appreciate that additions, deletions and modifications to the features described herein may be made without departing from the principles of the present invention. Accordingly, the following is claimed:
Patent Application
20080084007
