Plastic article or earthenware shaping or treating: apparatus – Reshaping – resizing or vulcanizing means for tire – tire...
Reexamination Certificate
2000-03-10
2001-11-20
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Reshaping, resizing or vulcanizing means for tire, tire...
C425S046000, C425S438000, C425SDIG005
Reexamination Certificate
active
06318983
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a novel type of molding element intended to be fitted in a mold for molding a cutout in a rubber tread intended, for example, for a tire; the invention also relates to molds equipped with this type of molding element.
In FR 2 759 321, there is proposed a mold for molding a tread of a tire, this tread comprising a tread pattern provided with incisions, the main walls defining the incisions being connected by at least one connecting bridge so as to maintain a satisfactory level of rigidity for said tread. The mold described in this application is formed of two parts which come into contact with each other in the molding position and each part bears at least one molding element for molding, an incision. In the molding configuration, certain of said molding elements of one mold part are in contact with certain molding elements of the other mold part, their end walls cooperating to form orifices intended to allow the rubber to pass during molding and thus to mold the bridges connecting the walls of the incision. After molding, it is possible to open the two mold parts without breaking said rubber bridges.
Although this technique does make it possible to produce connecting elements between the walls of a cutout, it however requires manufacturing the tread separately before assembling it with suitable means on a tire without a tread to finish the manufacture of said tire. An additional operation is then necessary to join the tread to the tire thus covered. It is therefore costly owing to the large number of operations, and requires very special attention in the transport and assembly phases for forming the tire.
In another French application, 98-08653, there was proposed a molding element for molding a rubber block in a tread, the lateral surface of said block being connected to the tread by at least one rubber connecting bridge. This molding element comprises molding blades mounted on a head which can turn about an axis substantially parallel to the direction of molding/demolding of the mold part equipped with said molding element. To obtain connecting bridges connecting the walls of the rubber block, it was proposed, for example, to arrange two series of blades on two concentric cylinders, each blade of a cylinder being crossed and in contact with blades of the other cylinder so as to define, in the molding configuration, orifices permitting the molding of said bridges. During the demolding under the action of the displacement of the mold part bearing this molding element, the vulcanized rubber exerts contact actions which force the cylinders bearing the blades to turn relative to each other. This process. notwithstanding that it is highly advantageous and achieves high-performance, once the number of molding elements becomes very large, requires a very great demolding force which increases the complexity of production of the apparatus in displacing the mold parts during the demolding operation.
This problem is furthermore a general problem which arises when the number of molding elements becomes very large, whatever their structure (this is a current tendency in all categories of tires for passenger vehicles or heavy vehicles).
SUMMARY OF THE INVENTION
The object of the invention is to propose an element molding a cutout in a tread which makes it possible to obtain a cutout, the rubber walls of which defining said cutout are connected together by at least one rubber bridge, said molding element not having the disadvantages which have been mentioned above. In particular, a molding element according to the invention permits a reduction in the costs of manufacturing a tread provided with cutouts of this type by reducing the number of manufacturing operations and by permitting demolding without there being any breaking of the connecting bridges, while reducing the forces necessary for this demolding operation.
“Demolding” is understood to mean that, by the mere opening movement of the mold part bearing the molding element according to the invention, it is possible completely to extract said molding element from the tread once said tread has been molded.
To this end, the molding element according to the invention intended to mold a cutout in a rubber tread is composed of at least two molding parts intended to project on the molding surface of a mold for molding said tread. Each molding part is provided with lateral walls and end walls limiting said lateral walls. Said molding parts are functionally arranged between them to define, in the molding configuration, at least one orifice intended for molding a rubber connecting bridge between the walls of the cutout.
The molding element is characterized in that at least one molding part is mounted to be mobile at least in translation in the direction of demolding relative to the other molding parts of said element so as to form, during a first phase of the demolding, at least one passage of sufficient dimensions to allow the connecting bridges molded in the final phase of demolding to pass in order to permit complete demolding of the molding element from the molded tread without breaking said bridges.
During this final phase of the demolding, the molding part or parts of the molding element which have remained in the tread are entrained by the mold for molding the tread and will force the rubber connecting bridges to deform sufficiently to permit said parts to emerge from the tread.
In a first variant, the molding element according to the invention is composed of at least two molding parts intended to project on the molding surface of a mold for molding said tread, each molding part being provided with lateral walls and end walls joining the lateral walls, the lateral walls being intended to mold in the tread the main walls defining said cutout, said main walls being connected by at least one rubber connecting bridge.
In the molding position, the molding parts of the molding element are arranged so that one wall of a molding part is in contact with a wall of another molding part, the geometries of the end walls of said molding parts being functionally arranged to define at least one orifice permitting the rubber to pass during molding for molding a connecting bridge between the walls of the cutout.
This molding element is characterized in that: at least one of the molding parts is mounted to be mobile relative to the molding part with which it defines at least one orifice, such that, under the action of the demolding forces exerted by the rubber after vulcanization, each molding part is displaced relative to the other molding parts to create at least one passage of sufficient dimensions to allow each molded connecting bridge to pass and thus to permit the demolding of the rubber tread in a single operation without breaking the rubber bridge(s).
Depending on the geometry of the desired cutout and the geometry of that of the rubber bridges between the main walls of said cutout (both the form of the cross-sections of said bridges and their distribution), it is advantageous to provide for the mobile part of the molding element to comprise an end wall arranged to be able to move relative to another part of the molding element, while remaining in contact with an end wall of said other part (said wall of the other part acting as a guide ramp for the displacement of the mobile part during demolding). If the angle, other than zero, formed by the guide ramp with the direction of demolding is referenced cc, the greater this angle &agr; (yet always remaining less than 45°) the more the passage formed is widened, the result of which is to make demolding easier.
In another variant, a molding element according to the invention may furthermore comprise at least one molding part mounted to be mobile in rotation relative to at least one other molding part, for example in the event that a molding part comprises at least one blade wound in a helix for molding an incision of helicoidal shape.
A molding element according to the invention may be used equally well in a mold for molding a tire or in a mold for mol
Kaczorwski Jean-Claude
Lavialle Georges
Lopez José Merino
Peyron Georges
Baker & Botts L.L.P.
Mackey James P.
Michelin Recherche ET Technique S.A.
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