Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Patent
1998-09-21
2000-08-22
Johnstone, Adrienne C.
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
152548, 152563, 156134, B60C 908, B60C 911
Patent
active
061056472
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to radial tires and to reinforcements serving to reinforce the carcass of such tires.
Such carcass reinforcements are known to consist of at least one ply, hereinafter referred to as `radial ply` or `radial carcass ply,` prepared in the form of a semifinished product and consisting essentially of an elastomer matrix reinforced with threads. These reinforcing threads, hereinafter referred to as `radial threads,` are arranged at regular intervals, parallel to each other, in a substantially radial direction (substantially perpendicular, that is, to the circumferential direction), that is to say conventionally a direction making an angle of about 90.degree..+-.10.degree. with the tangent to the circumferential direction of the tire.
Each radial ply normally takes the form of a continuous annular element formed, in fabrication of the carcass reinforcement on a drum, by cutting fabric strips or widths, then assembling the two edges of the cut on the drum by a joint, also known as a `weld,` to connect the two edges. According to the rules of the prior art these fabric strips are always cut between two radial threads and parallel to them, so as not to cut them. Hence the weld thus obtained has an orientation that may be called radial, like that of the reinforcing threads.
Two types of joints or welds are currently in use: the so-called `butt` weld, made by butting the two ends (that is, without superposition of the two edges), and the so-called `lap` weld (that is, with superposition, overlapping, of the two edges). In the case of a radial tire carcass for passenger cars or vans, with carcass reinforced by non-metallic threads, in particular textile threads, a lap weld is ordinarily used.
This invention refers specifically to an improvement made in the lap welds of radial plies forming the carcass reinforcements of radial tires.
As the name implies, the technique of lap welding consists in covering one edge of a ply with the other edge, maintaining a certain distance, and forming the bond by applying pressure. After curing of the tire, this type of weld offers great solidity, due to the larger surface area of adhesion available between the overlapping parts.
However, this lap weld has some disadvantages. Because of a double thickness of fabric, the density of radial threads is in effect multiplied by two in the lapped area. By `thread density` is meant, in known manner, the number of threads per unit length of ply, in a direction perpendicular to the axes of the threads. The presence of these `double` threads (double layer of threads) has the result in particular that under the action of the tire inflation pressure, and hence the application of tension to the radial carcass ply, each radial thread present in the weld will undergo about two times less tension and elongation compared to a radial thread located outside of the weld. Furthermore, in known manner, the radial threads, if subject to thermal shrinkage, will show a different contraction upon curing of the tire according to whether they are inside or outside of the weld.
The above phenomena result in a discontinuity of the properties of the carcass ply at the weld, in particular of the rigidity, and consequently a lack of uniformity in the manufactured tire. This discontinuity and lack of uniformity, greatly localized, may be especially damaging to the appearance, the outward aspect, of the tire, since it generally manifests itself by producing a more or less pronounced hollow in the side walls of the inflated tire. As is known, this depression or deformation of the side walls, described also by the term "indentation," is generally more pronounced, the smaller the modulus of elasticity of the reinforcing thread.
The above fault in appearance, well known and especially visible when for example polyester threads are used, is sometimes disadvantageous to the successful marketing of the tire; if this flaw is too pronounced, it may even make the manufactured tire unmarketable, so that it will be destroyed, which
REFERENCES:
patent: 2688996 (1954-09-01), Loomis
patent: 4325423 (1982-04-01), Seitz et al.
Champilou Yves
Panighel Bruno
Johnstone Adrienne C.
Michelin & Recherche et Technique S.A.
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