Plastic article or earthenware shaping or treating: apparatus – Reshaping – resizing or vulcanizing means for tire – tire...
Reexamination Certificate
2003-06-04
2004-10-19
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Reshaping, resizing or vulcanizing means for tire, tire...
C425S812000
Reexamination Certificate
active
06805540
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a flap ventlid installation assembly, a flap ventlid installation structure, a method for installing the flap ventlid installation assembly, and a mold for molding a tire. More particularly, the present invention relates to a flap ventlid installation assembly including a flap ventlid which can prevent the occurrence of spew (e.g., whisker projections) and burred extensions formed on a tire surface during tire molding to retain the desired initial performance or external appearance of the obtained tire in a satisfactory state and which can be simply installed in the tire mold. Clogging of mold ventholes due to penetration of rubber burrs can also be easily avoided. The present invention relates to a flap ventlid installation structure, a method for installing the flap ventlid installation assembly, and a mold for molding a tire.
(2) Related Art Statement
The molds for molding a tire are often manufactured by casting, which fits for forming complicated shapes conforming to a complicated surface shape designed to have numerous thin projections, such as sharp corners or blades for a tire.
Tire molds manufactured by casting are ordinarily divided into sub-molds, and these sub-molds are combined to form a predetermined whole form at the time of molding the tire. Methods for dividing the mold into sub-molds include a method of cutting the mold into 7-11 sub-molds along the circumference (segmented mold type) and a method of cutting the mold into 2 sub-molds in the direction of the central axis (one cast ring type). These methods can be optionally selected depending on the production conditions, etc.
Molding a tire using a divided mold type is ordinarily performed by compression molding which comprises pressing tire raw material (a green tire) comprising a polymerized rubber material into a mold before molding the application of the design.
In the course of such compression molding, closed spaces (i.e., blockade spaces) are formed between the green tire material and the mold surface on which projections and depressions such as ribs, blades, and the like are formed when the green tire material is pressed into the mold. During molding, air within the blockade spaces is not discharged therefrom, and thus, air bubbles are contained in the finally obtained molded tire. This is a problem in that air bubble defects called “bears” are produced.
Further, after molding, the tire molds should regularly be subjected to inspection and maintenance treatments, including periodic cleanings and the like, since the surface of the mold is roughened due to the adherence of oils and fats and the like during repeated use. Depending on the mold, this cleaning can become troublesome, requiring long cleaning times and expensive equipment. This results in a problem in that the production costs of the articles produced increase.
To prevent the formation of the aforementioned “bear” defects, methods of removing air from molds are usually implemented to cope with this situation. For example, as means for removing air from the closed spaces, two types of means have been conventionally employed, one of which is known as a venthole type means and the other is known as a non-spew or slit vent type means.
In methods employing venthole type means, air within blockades is discharged therefrom to the outside through air removal apertures called ventholes that are formed in the mold to lead to the blockades. In this method, the manufacturing costs of the mold are less expensive, and this method has an advantage since one may employ 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, for maintenance and inspection purposes. However, spew (whisker projections) is 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. This is a disadvantage in that the desired external appearance and initial running performance of the molded tire are deteriorated by the presence of the spew on the final molded tire.
In methods employing a non-spew or slit vent type means, 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 with respect to the external appearance of the final molded tire. Further, there is an advantage in that an adverse effect on the initial running performance is not seen. While the occurrence of spew can be prevented when a non-spew or slit vent type means is employed, however, the formation of burred extensions are not prevented. Further, in the case of this type of a mold, not only is the mold production cost expensive, but there is also a disadvantage in that clogging during molding readily occurs. In addition to the above, with regard to maintenance and inspection, the mold should be broken down into each sub-mold if one employs a simple blast method. Thus, several man-hours are required for cleaning by blasting. Further, since slit portions readily clog 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 longer cleaning times and introduces expensive equipment, which is a disadvantage in that the production costs of the molded products increase.
As mentioned above, there are respective advantages and disadvantages in these two type means for air removal means. 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 quipped with a non-spew type means is used when 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, a mold equipped with a venthole type means is used when serious consideration must be given to the production cost of a mold and the costs of molding the tire, with the acceptance of a relatively poor external appearance and relatively poor initial running performance of a finally molded tire. Thus, a satisfactory balance with respect to all the desired aspects, including the external appearance, the initial performance and the production costs of the tire, is sought after.
In light of these circumstances, various types of measures have been proposed. For example, in JP-A-9-11460, a mold that is equipped with air removal lids that are provided in ventholes is provided. The 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 is mostly flat on the side near to the cavity. Further, this air removal lid is provided with a casing and is press fit into the venthole together with this casing.
The air removal lid thusly configured has the functions mentioned below. Namely, the lid insert is always pressed to the upper side by means of a spring loaded with force. Moreover, during compression molding using a green tire, the lid insert is pressed down in opposition to the loaded force of a spring by means of pressing the level surface of the lid head into the 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 material 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 a
Burr & Brown
Mackey James P.
NGK Industries, Ltd.
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