Plastic and nonmetallic article shaping or treating: processes – Prestressing solid body and uniting in stressed condition
Reexamination Certificate
1999-11-12
2002-05-14
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Prestressing solid body and uniting in stressed condition
C249S063000, C249S083000, C264S259000, C264S275000, C264S328200, C264S334000, C425S543000, C425S577000, C425S443000
Reexamination Certificate
active
06387311
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns the manufacture of elastic casings as supports used inside tires to bear the weight in case of a flat. More specifically, it concerns the manufacture of supports which have a generally inextensible belt at their base, made by means of reinforcing wires of the type that usually reinforces tires.
Patent Application EP 0,796,747 describes a particular example of such a support. In FIG. 1 of Patent Application EP 0,796,747, it can be seen that the base 10 of the support is reinforced by wires 11 arranged substantially at zero degree relative to a plane perpendicular to the axis of rotation of the support.
In the present invention, “wire” is understood to mean monofilaments as well as multifilaments, or assemblages like cords, plies or even any type of equivalent assemblage, whatever the material and treatment of those wires, such as surface treatment or coating or presizing in order to favor adhesion to the rubber. “Zero degree” is understood to mean an angle measured relative to the circumferential direction, that is, relative to a plane perpendicular to the axis of rotation of the support, thus following the usual conventions for tires. The angle is said to be “substantially” zero degree, because the reinforcement making it possible to oppose centrifugation of the support is created by winding of a wire or strip of parallel wires, with a certain pitch, the result being that the angle will not be zero degree in the strict sense, but, in practice, at least locally, slightly greater than zero degree, in order to be able to sweep the entire width desired.
A suitable material for creating such a support is rubber.
Different methods of manufacture of a molded object are known: compression molding, transfer molding and injection molding. Compression molding implies the introduction of the necessary volume of rubber inside the mold before closing it, while transfer molding and injection molding both imply closing of the mold before introduction of the necessary volume of rubber inside. The choice depends, notably, on the quantities planned, injection molding, while more expensive in initial investment, having a lower marginal cost, making possible a more uniform pressure and temperature during the vulcanization reaction and enabling a greater geometric quality to be attained.
But injection and transfer molding lend themselves poorly to producing nonhomogeneous products which are reinforced by flexible reinforcements. In particular, said processes, involving the introduction of material in a closed mold, are ill-suited for use when the reinforcement is a ply of wires, for the wires do not stay in place in the mold, or they stay in place very poorly. The rubber fed into the mold tends to displace the wires when it fills the mold. It therefore poses a major problem to ensure precise positioning of the wires in the vulcanized support. This is why the force feeding of rubber into a closed mold has not been adopted for wire-reinforced rubber parts. It is, for example, well known that tires are not injection molded; first of all, a rough blank is made very close to the final shape of manufacture of the tire, the blank containing the reinforcing wires inserted in the proper places between the different layers of rubber, and the molding is carried out by enclosing the necessary molding elements around the blank.
SUMMARY OF THE INVENTION
The object of the invention is to manufacture a support, such as described in patent application EP 0,796,747, by force feeding material into a previously closed mold, while making sure that the position of the reinforcing wires desired by the designer of the support is fully respected.
The invention proposes a method of manufacture of a support intended to be mounted on a vehicle rim, said support having an axis of rotation, a base defined by a substantially cylindrical radially inner face designed to be mounted around said rim, a crown designed to support the weight and a body between said base and said crown, said base having a substantially inextensible circumferential reinforcement, the radially outer face of said crown having a shape departing from the cylindrical shape, the body containing a plurality of axial recesses emerging from said support on at least one side,
said method of manufacture using a mold having an axis corresponding to said axis of rotation, said mold comprising:
an inner core for molding the radially inner face,
a crown molding ring, said ring comprising at least two parts radially separable from each other, said separable parts making it possible to mold said radially outer face of said crown,
at least one shell containing a plurality of axial fingers for laterally molding said body and said recesses, said core, said ring and said shell cooperating to define, at least partially, a closed cavity for molding said support,
said core comprising at least two components and being capable of assuming a molding configuration in which its components form a circumferentially continuous molding surface for molding said radially inner face, the molding surface being defined by a reference diameter &PHgr; corresponding generally to the inner diameter of said support, said core also being capable of assuming a mold stripping configuration different from the molding configuration, defined by an overall length E around said molding surface less than the product of &pgr; and reference diameter &PHgr;, said method of manufacture comprising the following steps:
prefabricating a ring having said circumferential reinforcement;
establishing the mold stripping configuration of said core;
installing said ring on said core;
establishing the molding configuration of said core;
closing the mold and then force feeding into the mold an injectable material which is elastic in final state;
axially separating said shell containing axial fingers, at least partially, in relation to at least one of the components that are the molding ring and the core;
then establishing the mold stripping configuration of said core and radially separating said parts from the crown molding ring;
discharging said support.
In the context of the present invention, a nonpneumatic casing designed to be used alone in normal service will be considered equivalent to a support, an accessory intended to be mounted inside a tire in order to provide it with a means of temporary operation at zero pressure, adjustments of choice of materials and/or of design of the product itself not being the subject of the present patent invention. In other words, this invention is not limited to a specific application of the product. Its use is advantageous whenever molding or mold stripping becomes rather difficult, for example, because the object manufactured is reinforced, notably, by wires. It is not limited to a particular material, provided that the material meets the needs of the support in terms of characteristics in final state and, for the manufacturing phase, provided that the material can be force fed into a closed mold through mold filling ducts.
The invention proposes using pressurized feeding into a closed molding cavity, in combination with an inner core in several parts, whereas single-part cores are generally used when injection or transfer molding is employed because closing of the mold poses no problem, since that occurs prior to filling, and mold stripping of the product generally adapts quite well to stresses on the latter, since it is in a reticulated or vulcanized state, therefore possessing good mechanical properties. Thus, the invention uses, for example, a core in several parts for molding a support whose radially inner face can be directly or easily stripped from the mold, even outside a single-part core, said radially inner face forming a surface presenting, in relation to a strippable surface parallel to the axis of rotation, deviations not exceeding a few millimeters. In general, said core presents a molding configuration and a mold stripping configuration, different in shape from the preceding one, facilitating not only mold
Lacour Jean-Charles
Voisin Didier
Baker & Botts L.L.P.
Michelin & Recherche et Technique S.A.
Vargot Mathieu D.
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