DETAILED DESCRIPTION OF THE INVENTION In that form of the present invention chosen for purposes of illustration in the drawing, FIGS.
1-4 show a tire casing, indicated generally at 10, mounted on a wheel rim 12 and having the cavity 14 of the tire casing 10 filled with a molded tire core 16 composed of a plurality of core sections 18, each formed of polypropylene foam beads fused together in accordance the process of the present invention.
In accordance with the present invention and illustrated in FIG.
5A, it has been found that excellent tire cores, such as the tire core 16 of FIG.
1, can be formed by filling a suitable mold with polypropylene foam beads and employing steam pressure to fuse the beads together into a polypropylene foam tire core, as indicated in FIG.
5A.
When the polypropylene foam beads are poured into the mold, they flow, much like a quantity of dry sand, because they are an assemblage of independent spheres, as seen in FIG.
5B.
However, when the steam is introduced into the mold, the pressure compresses the foam beads and the heat serves to fuse the walls of the foam beads together to form an integral framework, as seen in FIG.
5C, with a structure somewhat analogous to bone.
Polypropylene foam tire cores, such as that shown at 16 in FIGS.
1-4, have this bone-like structure, as seen in FIG.
2 and, h have a superior strength to weight ratio compared to prior art.
Consequently, less tire casing reenforcement is needed.
This, of course, is a distinct advantage in manufacturing tires.
Furthermore, polypropylene foam tire cores are found to have excellent barrier properties and low permeability to moisture.
Since there is no known solvent for polypropylene, polypropylene foam tire cores have the obvious advantage of not being susceptible to attack be oil, gasoline, hydrocarbon solvents or other chemicals.
In addition, molded polypropylene foam articles are found to have toughness and resistance to fatigue, properties ideally suited to tire cores.
Due to the low specific gravity of polypropylene, polypropylene foam tire cores can be made lighter, stronger and, therefore, more economical
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