Method and apparatus for manufacturing tyres for vehicle wheels

摘要

In a method of manufacturing tires for vehicle wheels, a green tire, once formed, is transferred into a vulcanization mold and pressed against the holding walls of a molding cavity. Concurrently with the pressing step, a fluid present between the green tire and the holding walls is evacuated through vent valves. The tire is brought into contact with the closing head of each valve so as to push it toward a closed position at which the closing head forms a contact seat spaced apart from the inner surface of the molding cavity in order to define an embedding recess between the inner surface of the molding cavity and the closing head.

主权项

1. A method of manufacturing tyres for vehicle wheels, comprising the steps of:
a) forming a green tyre; b) transferring the green tyre into a vulcanisation mould having holding walls defining an inner surface of a moulding cavity, said inner surface conforming in shape to the final conformation to be given to the green tyre; c) pushing the green tyre toward said holding walls of said mould; d) evacuating a fluid present between an outer surface of said green tyre and the holding walls of said mould, said evacuating step comprising the steps of:
d1) arranging a vent valve in said holding walls, said vent valve comprising a duct, the duct having an inlet end opening onto said inner surface of said moulding cavity and an outlet end opening outwards of the mould, and a closure member comprising a closing head and a substantially cylindrical stem which are axially movable relative to said duct, the closing head comprising a proximal portion and an intermediate portion, the proximal portion comprising a first truncated cone tapering toward the stem at a first angle and having a first upper diameter and a first lower diameter, the first upper diameter being larger than the first lower diameter, the intermediate portion comprising a second truncated cone tapering toward the stem at a second angle smaller than the first angle and having a second upper diameter and a second lower diameter, the second upper diameter being greater than the second lower diameter,
wherein the intermediate portion extends in a continuation of the proximal portion and the first lower diameter of the proximal portion is substantially equal to the second upper diameter of the intermediate portion, andwherein the intermediate portion is adjacent the stem and the second lower diameter of the intermediate portion is greater than a diameter of the stem, defining an annular abutment surface on a lower surface of the intermediate portion, the annular abutment surface abutting with a spring;d2) carrying out an open position of said vent valve, while preventing substantial misalignments of the closure member relative to the duct by said intermediate portion at said open position; andd3) transferring said fluid from the moulding cavity to the duct through a connecting passage confined between an inner wall of said duct and the closing head of the closure member set to the open position; e) bringing the green tyre into contact with the closing head of the closure member, pushing the latter into the duct so as to achieve a closed position of said vent valve; f) forming a first contact seat in said inlet end by contacting the proximal portion of the closing head to the inner wall of the duct in order to obstruct said connecting passage, said first contact seat being formed at a position spaced apart from said inner surface of the moulding cavity so that an embedding recess is defined between the inner surface of the moulding cavity and the closing head of the closure member in the closed position; and g) forming a second contact seat in said inlet end by contacting the intermediate portion of the closing head to the inner wall of the duct.