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
06318984
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 tread of rubber mix intended to be fitted on a tire, the invention also relates to a mold equipped with this type of molding element.
French Patent Application No. 98-08653 discloses a molding element for molding in a tread an incision of cylindrical geometry defining a rubber block, the lateral wall of which is connected to the rest of the tread by rubber bridges.
In one variant presented in the aforementioned application, a molding element comprises at least two molding parts of generally cylindrical shapes said molding parts being mounted freely in rotation relative to each other about one and the same axis XX′. A first cylinder bears at least one molding blade wound at a first angle around the axis XX′ to form a helix and a second cylinder concentric to the first comprises at least one other molding blade wound around the same axis XX′ at a second angle of a sign opposite to the sign of the first angle. In this latter configuration, it is envisaged that the molding blades of said two cylinders are arranged such that the blades of the first cylinder and those of the second cylinder are in sliding contact with each other so as to form a sort of trellis defining a plurality of orifices intended to allow the rubber mix to pass during molding to form connecting bridges between the lateral wall of the molded block and the tread.
In this molding element proposed in the aforementioned application, the demolding of a tread after molding and vulcanization, that is to say, the extraction of said molding element from said tread, is made possible without breaking the bridges molded by the structure of the molding parts and their free mounting in rotation relative to the mold. In actual fact, the forces exerted by the rubber on the helical molding blades, during the demolding, create a resultant torque which causes the molding parts to turn about their axis XX′.
With this latter arrangement, it was noted, in particular after several molding operations, that the contact between the blades was insufficient and that films of rubber mix formed between said blades during molding. Consequently, after molding not a single incision but at least two non-interconnected incisions are obtained. The films of rubber mix form walls between the incisions which prevent the free circulation of fluids (air, water) from one incision to the other and isolate them from each other.
Furthermore, the forces exerted by the raw rubber mix at the time of molding and of penetration of the blades into said mix result in deformation of the molding blades, the consequence of which is an increase in the thicknesses of the molded films, and in gradual modification of the geometry of said blades. This deformation is all the more marked since the blades used are of low thickness compared with their length (which is frequently the case for molding incisions of a width of less than 2 mm).
The same defects are noted in the case of molding an incision which does not completely define a rubber block but has a trace on the outer surface of the tread, the geometry of which is in the form of a circle.
SUMMARY OF THE INVENTION
One object of the invention is to propose a molding element making it possible to mold in a tread an incision which is defined by two main walls connected by a plurality of connecting bridges of rubber mix, this molding element comprising two molding parts in contact with each other, said molding element not having the disadvantages which have been described above. Of course, the molding element according to the invention permits demolding without any breaking of the molded connecting bridges. “Demolding” is understood to mean that, with the molding element according to the invention, it is possible completely to extract said molding element from the tread after molding without causing breaking of the molded connection bridges.
To this end, the molding element according to the invention, intended to mold in a tread an incision of circular shape around an axis XX′, the main opposing walls of which are connected by a plurality of connecting bridges of rubber mix, comprises two molding parts, each molding part comprising a support extended by at least one molding blade for molding part of said incision. At least one of the molding parts comprises a support extended by a blade which is at least partially in a helix around the axis XX′ (that is to say that the blades of this molding part describe only a fraction of a complete revolution around XX′), said support being, mounted freely in rotation around XX′ relative to the other molding part.
Furthermore, the molding blades of a first molding part are provided with passages arranged so as to permit the engagement by sliding of the molding blades of the second molding part within said passages to form the molding element in the molding configuration and thus to form a plurality of orifices intended to allow the rubber mix to pass for molding the connecting bridges. Furthermore, to permit the engagement and disengagement (reverse movement to the engagement) of the blades of the second molding part in the passages provided on the first molding part, said second molding part is mounted to be mobile in translation in the direction XX′ relative to said first part.
This molding element makes it possible to mold in a tread an incision, the trace of which over the outer surface of said tread has the geometry of an are of a circle.
The molding element according to the invention also makes it possible to mold an incision, the trace of which over the outer surface of said tread has the geometry of a circle and defines a rubber block of cylindrical shape of axis XX′, this block of rubber having a lateral wall which is connected to the tread by a plurality of connecting bridges.
To this end, the molding element comprises two molding parts each formed of a support extended by at least one molding blade, the molding blades of at least one of the two molding parts having the form of a helix wound around an axis XX′, forming at least one complete turn. Furthermore, each molding part bearing at least one blade having the form of a helix is mounted to be mobile in rotation around XX′ relative to the other molding part.
This molding element is characterized in that:
the blades of a first molding part are provided with passages permitting the engagement by sliding of the blades of a second molding part to form the molding element in the molding configuration,
the second molding part, the blades of which are engaged in the passages in the first molding part, is assembled with said first part to form the molding element so as to be mobile in translation in the direction XX′ relative to the first molding part, in order to permit the engagement (and disengagement) of the blades of this second molding part within said passages.
In the present description, when reference is made to a first molding part of a molding element, this is defined as the one of the molding parts of said molding element the blades of which are provided with passages for engaging the blades of another molding part (referred to as second molding part).
At the moment of demolding, the relative movements of translation and rotation of the molding parts relative to each other systematically involves the breaking of any rubber films which may have been molded in the clearances existing between the passages provided on the blades of the first molding part and the blades of the second molding part.
A molding element according to the invention may be used equally well for equipping a mold for molding a tire or a mold for molding a tread intended, for example, for recapping a tire.
Another subject of the invention relates to a mold for molding a tread intended to be fitted on a tire, said mold molding at least one incision defining a rubber block of cylindrical shape connected to the tread on its lateral wall
Baker & Botts L.L.P.
Mackey James P.
Michelin Recherche ET Technique S.A.
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