Plastic article or earthenware shaping or treating: apparatus – Reshaping – resizing or vulcanizing means for tire – tire...
Reexamination Certificate
2001-11-21
2004-11-16
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Reshaping, resizing or vulcanizing means for tire, tire...
C425S035000, C425S812000, C249S141000
Reexamination Certificate
active
06817848
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a mold for molding a tire. More particularly, the present invention relates to a mold for molding a tire to prevent spew (whisker projections) and burred extensions on a tire surface during tire molding, to allow the retention of the initial performance of a tire obtained and good external appearance, and to allow designing for reduction in the number of molds and their production costs as well as simplification of maintenance and inspection work.
(2) Related Art Statement
The molds for molding a tire are often manufactured by means of casting which fits for the forming of complicated shapes conforming to the surface shape designed as complicated shapes having numerous thin projections termed sharp corners or blades for a tire.
Molds for molding a tire manufactured by means of this casting are ordinarily divided into sub-molds, and these sub-molds are combined to form a predetermined form as a whole at the time of forming a tire. As a method for dividing the mold, a method for dividing into 7-11 sub-molds by cutting the predesigned form in the direction of the central axis along the circumference which are often called segmented molds (or sectional molds), and a method for dividing into 2 sub-molds by cutting the predesigned form in a direction perpendicular to the central axis, that is, in the direction of the tire diameter which are often called 2-piece molds (or One Cast Ring molds). Appropriate selection can be made in accordance with manufacturing conditions and the like.
Molding of a tire using this type of the mold is ordinarily performed by pressing a green tire, which has not been applied with a predetermined design and produced by pre-molding polymerized rubber materials and the like, to a mold. This type of the molding is called as compression molding.
In the course of such a compression molding, a number of closed spaces, which are called blockade spaces, are formed between the green tire and the projections and depressions such as ribs, blades, and the like formed on the mold surface, when a green tire is pressed into a mold. During molding, air within the blockades is not discharged therefrom, and thus, air bubbles are contained in the molded tire finally obtained. This is a problem when air bubble defects, such as air inclusions, are produced.
Further, after molding, molds for molding a tire should be ordinarily subjected to inspection and maintenance treatment, including periodic cleanings and the like, since the surface of the mold is roughened due to adherence of oils and fats and the like during repeated use. Depending on the mold, this cleaning and the like can become troublesome, requiring the introduction of long cleaning times and expensive equipment. This results in a problem that production costs of the articles produced increase.
To prevent the formation of the aforementioned air inclusions, methods of removing air from molds are usually implemented to cope with this situation.
As a means for removing air from the closed spaces, there have been conventionally employed two types of means; one of which is called a venthole type means and the other a non-spew or slit vent type means.
The method employing the venthole type means is such a one that air within blockades is discharged therefrom to the outside through air removal apertures called ventholes provided in the mold so as to make them lead to blockades. In the case of this method, the manufacturing costs of the mold are less expensive and this method has an advantage since one may employ, for maintenance and inspection, a simple blast method which comprises blowing media such as glass beads, resin beads, dry ice pellets, and the like to the interior surface of the mold with high-pressure air. However, spew (whisker projections) are formed on the final molded tire (the tire product) since air is discharged accompanying the outflow of raw tire material (a green tire) into ventholes when the venthole type means is used. There is a disadvantage in that the external appearance and initial running performance of the molded tire are deteriorated.
The method employing a non-spew or slit vent type means is such a method that air within blockades is discharged to the outside through gaps formed between sub-molds or slit-like air removal means provided in the predetermined locations; thus this method is superior in the external appearance with respect to a molded tire. Further, there is an advantage in that adverse effects on the initial running performance are not seen. The occurrence of spew can be prevented when a non-spew or slit vent type means is employed, however, it cannot prevent the formation of burred extensions. Further, in the case of this type of a mold, not only is the production cost of a mold expensive, but also there is a disadvantage in that clogging during molding occurs readily in addition to being more expensive. In addition to the above, with regard to maintenance and inspection, the mold should be broken down into every sub-mold if one employs a simple blast method. Thus, it requires several man-hours for cleaning by blasting. Further, since slit portions clog readily with repeated blasting and the contaminants accumulated in slit portions are difficult to remove, special cleaning methods such as chemical cleaning and plasma cleaning should be used. This requires long cleaning times and the introduction of expensive equipment. This is a disadvantage in that the production costs of the molded item increase.
As mentioned above, there are respective advantages and disadvantages in these two type means for air removal. Therefore, at present, one should choose a proper mold taking into consideration the use of tire to be produced, production costs, and the like. That is, at present, a mold equipped with a non-spew type means is used when a serious consideration must be given to the external appearance and the initial performance of a tire, with the acceptance of a relatively expensive production cost. On the other hand, however, a mold equipped with a venthole type means is used when a serious consideration must be given to the production costs of a mold and the running costs in tire molding, with the acceptance of a relatively poor external appearance and relatively poor initial running performance of a tire. Thus, a satisfactory balance between all aspects of the external appearance, the initial performance and the production costs of tire is desired.
In light of these circumstances, various types of measures are being proposed. For example, there is proposed in JP-A-9-141660 a mold equipped with air removal lids provided in ventholes. This air removal lid is provided with a movable lid insert comprising an axis and a lid head disposed thereon. This lid head is provided with a cavity and a surface having a circular-truncated-cone-shape on the opposite side of the cavity, and being mostly flat on the side near to the cavity. Further, this air removal lid is provided with a casing and is press fitted into the venthole together with this casing.
An air removal lid thus configured has the functions mentioned below. Namely, the lid insert is always pressed to upper side by means of a spring loaded with force. Moreover, the lid insert is, during compression molding using a green tire, pressed down in opposition to the loaded force of a spring by means of pressing a level surface of the lid head into a green tire. During this downward pressing, air can be removed through gaps, that is, air passages, formed between the casing and lid insert. Further, infiltration into air passages of the green tire can be prevented by interrupting air passages with such contact of the casing and the circular-truncated-cone-shaped surface when compression molding is completed. Furthermore, the lid insert is pushed upwardly again by means of a loaded spring in the cavity during removal of the vulcanized tire from the mold after vulcanization is completed.
Nonetheless, a mold provided with the air removal lid suffers, as mention
Burr & Brown
Mackey James P.
NGK Insulators Ltd.
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