Plastic article or earthenware shaping or treating: apparatus – Reshaping – resizing or vulcanizing means for tire – tire...
Reexamination Certificate
1999-06-18
2001-03-13
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Reshaping, resizing or vulcanizing means for tire, tire...
C425S046000
Reexamination Certificate
active
06200118
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a mold for molding a tire, said mold containing at least one molding element designed to mold a cut in said tire; this invention also concerns a molding element designed to mold a cut in a tire.
In order to mold a cut in a tire tread, a mold made up of a plurality of mold members is ordinarily used, each of said members being able to contain a plurality of molding elements projecting on the molding surface of said mold members. The term “cut” is understood to embrace grooves (at least 3 mm wide) as well as incisions (that is, grooves less than 3 mm wide).
A molding element generally contains two parts: a first part forming the molding part of the molding element projects on the molding surface of the mold, and a second part situated in the extension of the first is anchored in the mold. The anchorage of said second part is, for example, for a mold made by casting, obtained at the time of casting of the material constituting said mold, said material trapping said second part of the molding element during the phase of cooling of said material.
During molding and vulcanization of the tire, the molding part of the molding element is sunk inside the rubbery material constituting the tire in order to form a cut. After vulcanization of the tire, the components of the mold are moved in their proper mold stripping direction and gradually separate from one another so as to release the molded tire by carrying the mold elements along with them to extract them from the tire.
Producing a tire having durable rolling performances can be accomplished by the use of incisions, the geometry and/or mean orientation of which appreciably evolve(s) with wear of the tire tread. However, when such incisions are molded, usually by means of rigid molding elements, the mold stripping of said elements is sometimes very difficult (for it necessitates a force that increases with the number of molding elements of this type), and is even impossible without risking damage to the tire (by tearing away rubber compound parts).
For example, French Application 2,722,145 discloses a tread containing a plurality of elements in relief, some of them being provided with incisions, whose mean direction on the rolling surface gradually changes with the wear of said tread. As soon as the change of orientation becomes great, it is clear that obtaining such an incision by means of a molding element containing a rigid wire forming the molding part of the same geometry is difficult, at least in the mold stripping phase (that is, of extraction of said molding element). The term “wire” is understood to embrace blades.
The same is true when a molding element contains at least one rigid wire having a helical or twisted shape or any geometry entailing the existence of a torque resulting from torsion being exerted on the molding part during mold stripping. In order not to damage the appearance of the tread during said mold stripping operation, the use of this type of element necessitates particular precautions usually incompatible with the demands of industrial production.
SUMMARY OF THE INVENTION
To overcome these difficulties, a mold is proposed for molding a tire tread, said mold being formed by a plurality of members, each mold member comprising a molding surface for molding a part of the surface of said tread and being movable in a molding/mold stripping direction.
In addition, at least one mold member is provided with at least one molding element for molding at least one incision in said tread, said molding element embodying two parts situated, one an extension of the other, a first part forming the molding part of the molding element and projecting on the molding surface in order to mold said incision in the tread and a second part rotatable about an axis XX′, merged with the direction of molding/mold stripping of the mold member, and intended to be mounted in a seat provided in the mold member.
The mold member is characterized in that it is provided with means of mounting and fastening the second part of the molding element in the seat provided in the mold, said mounting means allowing rotation of the molding element on its axis XX′ during at least the mold stripping phase.
The first part of the molding element is intended to mold at least one incision in the tire; for that purpose, it contains at least one wire, the geometry of which is such that during mold stripping, the contact forces of the rubber surrounding said first part create a resultant torque about the main direction XX′ of the element tending to turn said molding element on XX′. The free rotary mounting of said molding element makes possible and facilitates extraction of the molding part from the molding element out of the tire during mold stripping.
A variant embodiment consists of mounting the second part of the molding element in free rotation on a cylinder-shaped base, said base being arranged in turn to be rigidly mounted in rotation in a seat provided in a mold member. This arrangement makes it possible to avoid wear of the mold member created by friction with the rotary moving part of the molding element.
It can advantageously be arranged to combine a relative rotary motion of the molding element in relation to the mold and a translational motion of the same molding element in relation to the mold, in order to facilitate penetration and/or extraction of the molding part in or out of the rubber. For this purpose, a generally cylinder-shaped seat of main axis XX′ is provided for receiving a molding element whose part inserted inside the seat is capable of turning about said direction XX′; in addition, means are provided for moving said molding element in direction XX′ in said seat. Complementary means can also be provided to ensure a given position of the molding element in the molding configuration.
It is also of interest to arrange for the presence of means of rotation before or during the operation of molding and/or mold stripping, whether or not there is a possibility of displacement of the molding element in its seat; this rotation can advantageously be synchronized with displacement of the element along XX′ (corresponding to the mold stripping movement of the mold member and/or to the movement inside the seat of the molding element).
In known manner, the molding elements used to mold cuts in a tire are formed either directly on the mold used for molding said tire during manufacture of the mold, or formed separately and slipped on the mold during its manufacture or afterwards. The method of manufacture of molds and that of molding of tires limit the possibilities of molding shapes of cuts to shapes that can be stripped from the mold without cutting or tearing away the rubber compound after its vulcanization.
Molding elements making it possible to mold unstrippable incisions (that is, containing undercut parts) are known, for example, from French Patent Application No. 97/05194; however, the use of such molding elements demands a deformation of the molding part during mold stripping, which deformation can become permanent after a more or less large number of moldings.
To remedy these problems, a molding element is proposed to equip a mold member molding a rubber compound article like a tire or tractor tread in order to make at least one incision in said tread, which mold member can be driven in a molding and/ or mold stripping motion in a predetermined direction. The molding element according to the invention is characterized in that it comprises:
a body equipped with a head extended by a molding part, said molding part being intended to project on the molding surface of the mold member in order to mold at least one incision in the tread;
the head containing at least one circular cylinder of axis XX′ defining the main axis of the molding element, and means of mounting said molding element in the mold member, said means cooperating with said member in order to permit a rotation of the head about XX′ relative to the mold, when the molding part o
Auxerre Pascal
Kaczorwski Jean Claude
Lopez José Merino
Baker & Botts L.L.P.
Mackey James P.
Michelin Recherche ET Technique S.A.
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