Patent Application
20110174460
The present invention relates to a method of manufacturing a casting for a mold for molding a tire of a sectional mold type, and particularly to a method of manufacturing a casting for a mold for molding a tire, wherein twist and warp deformation of each block of the casting is less likely to occur when the casting shrinks, the difference between the degrees of shrinkage of cope and drag is small, the casting, even if large-sized, can be produced in a relatively short molten metal solidifying time, and healthy castings can be easily obtained.
Molds for molding a tire are usually produced by a casting process because the design of the molds is intricate, and the molds have the property that the molds enclose thin plates such as sipes and blades made of different kinds of metal materials. Plaster casting is widely adopted as a method of manufacturing a casting for a mold for a tire. Other reasons why plaster casting is adopted are
(1) that castings having a melting point of up to about the melting point of an aluminum alloy can be manufactured with a high dimensional accuracy;
(2) that cutting process and assembly process can be easily performed at a stage of a plaster casting mold;
(3) that the plaster casting can flexibly deal with inserts for sipes or blades; and
(4) that an intricately designed shape can be accurately replicated by reverse casting from a rubber molding; or the like.
A mold dividing structure of a mold for a tire includes two types, that is, a two-piece mold in which the mold is divided into two pieces in the tire width direction and a sectional mold in which the mold is divided into 7 to 11 pieces in the tire circumferential direction. Among these structure, a sectional mold which has a low resistance at the time of molding and demolding of a tire and has a high dimensional accuracy is widely used. As the method of casting a sectional mold, for example, Patent Document 1 discloses a method of pouring molten metal by a low-pressure casting method, Patent Document 2 discloses a method of pouring molten metal by gravity casting using a tub for the exclusive use (chute), and Patent Document 3 discloses a method of pouring molten metal by gravity casting using a reusable runner-board.
Examples of characteristics of these method include (1) that, after the casting, the mold is processed into a sectional mold; (2) that the molten metal solidifying time differs between the upper portion and the lower portion per one sectional mold unit because tap holes are concentrated at the lower surface side, and (3) that a casting flask is applied as a chill.
Casting a casting for a mold for a tire by a sectional mold has advantages that twist and warp deformation of sectional mold block casting is less likely to occur when the casting shrinks, and that a casting productivity is high because the casting for a mold for a tire can be casted with one ring. However, in a conventional sectional mold, since a difference of molten metal solidifying time between the upper surface and the lower surface occurs and casting shrinkage increases at the portion where solidification is slow because a tap hole is on the side of the lower surface or the upper surface, there is a problem that a size difference between cope and drag is likely to occur.
Accordingly, an object of the present invention is to provide a method of manufacturing a casting for a mold for molding a tire, wherein twist and warp deformation of each block of the casting is less likely to occur when the casting shrinks, the difference between the degrees of shrinkage of cope and drag is small, the casting, even if large-sized, can be produced in a relatively short molten metal solidifying time, and healthy castings can be easily obtained.
To solve the above-described problems, the present inventor intensively studied to discover that the above-mentioned object may be attained by the following constitution, thereby completing the present invention.
That is, the method of manufacturing a casting for a mold for molding a tire of the present invention is a method of manufacturing a casting for a mold for molding a tire of a sectional mold type in which the mold is opened and closed by dividing the mold into a plurality of pieces in the circumferential direction, said method comprising
a process of manufacturing each of divided block castings by casting them individually, in which process, molten metal is poured into a casting mold where chills are disposed on four sides, the sides being an upper surface portion, a lower surface portion and both sides of circumferentially divided surfaces, and surrounding from four directions a design surface which is a contact surface with the mold, such that at least the chills surround said design surface continuously.
In the present invention, it is preferred that opposing said chills be respectively disposed symmetrically on said four sides, the sides being an upper surface portion, a lower surface portion and both sides of circumferentially divided surfaces. It is also preferred that a pair of tap holes to said casting mold be disposed symmetrically on said upper surface portion and lower surface portion, and a pair of tap holes to said casting mold be disposed symmetrically on said both sides of circumferentially divided surfaces. Further, it is preferred that a tap hole and/or a runner which provides the tap hole with molten metal be formed inside said chill.
By the present invention, a method of manufacturing a casting for a mold for molding a tire may be provided, wherein twist and warp deformation of each block of the casting is less likely to occur when the casting shrinks, the difference between the degrees of shrinkage of cope and drag is small, the casting, even if large-sized, can be produced in a relatively short molten metal solidifying time, and healthy castings can be easily obtained.
An embodiment of the present invention will now be described by way of the drawings.
Since, if a mold for a tire is ring casted by a conventional sectional mold as shown in
In the present invention, as for the back surface 4 side which is the opposing surface of the design surface 6, a disposition of chills for the block casting 1 is not particularly restricted. A chill may be in contact with the whole surface except for a hole portion of the dead head 5, or a chill may not be disposed and only a molding box may be used.
In the following embodiments 4 to 8, a suitable embodiment will be described in which opposing chills are respectively disposed symmetrically on four sides, the sides being an upper surface portion, a lower surface portion and both sides of circumferentially divided surfaces of the block casting 1.
In each of the embodiments 4 to 8, chills surround the design surface 6, and thus, the invention of the embodiments 4 to 8 can obtain the same effect as in the invention of the first embodiment. In addition, in the embodiments 4 to 8, by disposing respectively opposing chills symmetrically on four sides, the sides being an upper surface portion 2a, a lower surface portion 2b and both sides of circumferentially divided surfaces 3a, 3b of the block casting 1, the solidification of molten metal starts at about the same time from the upper surface portion 2a, the lower surface portion 2b and both sides of circumferentially divided surfaces 3a, 3b, and a size property in which the block casting 1 is symmetrical in up and down, left and right directions (arrow directions) is easily obtained. The disposition of chills on the back surface side 4 of the casting is not restricted.
As mentioned above, in order to attain an up and down, left and right (arrow directions) symmetric solidification configuration of the block casting 1, dead head 5 necessarily needs to be disposed on the back surface 4 side, and the solidification of molten metal at the back surface 4 side of the block casting 1 needs to be delayed. Accordingly, the disposition of chills on the back surface 4 side is not necessary since it is not necessary to obtain the effect of a hamper by initially solidified layer of molten metal at the back surface 4 when the whole block casting 1 solidifies and is cooled to shrink.
In the following embodiments 9 to 11, a suitable embodiment will be described in which a pair of tap holes for a casting mold are disposed symmetrically on the upper surface portion and the lower surface portion, or in which a pair of tap holes for a casting mold are disposed symmetrically on both of the circumferentially divided surfaces.
In each of the embodiments 9 to 11, it is supposed that chills surround the design surface 6 continuously, and thus the invention of the embodiments 9 to 11 can obtain the same effect as in the invention of the first embodiment. In addition, in each of the embodiments 9 to 11, a heat input (overheat) condition by molten metal from the tap hole 7 from the start of pouring to the completion of pouring can also be made uniform in up and down, left and right directions, whereby such an advantage that in the block casting 1, it becomes easy to obtain a symmetrical size property in up and down, left and right directions is obtained.
In the following embodiment 12 to 15, a suitable embodiment will be described in which both or either of a tap hole(s) and a runner(s) which supply(ies) molten metal to a tap hole(s) are/is formed inside a chill 12.
In each of the embodiments 12 to 13, it is supposed that a chill 12 surround the design surface 6 continuously, and thus the invention of the embodiments 12, 13 can obtain the same effect as in the invention of the first embodiment. In addition, in these embodiments, by disposing the tap hole 7 inside the chill 12, molten metal at the tap hole 7 solidifies and is cooled immediately after the completion of pouring, and thus even in the case of the twelfth embodiment that the tap hole 7 is not disposed symmetrically in the up and down direction, an advantage that the block casting 1 solidifies and is cooled uniformly in up and down, left and right directions in the same manner as in the thirteenth embodiment can be obtained.
In the embodiments 14 and 15, the effect of the invention of the above-mentioned embodiments 12 and 13 can be further enhanced, and the embodiments 14 and 15 have an advantage that mounting and demounting of an external gate for every casting can be saved.
A method of manufacturing a casting for a mold for molding a tire of a sectional mold type of the present invention is characterized by a process of manufacturing each of divided block castings by casting them individually. Other processes such as a pattern manufacturing process, a reversing process of a rubber molding, a reversing process of a plaster casting mold, a drying process of a mold, a mold shakeout process and a casting mold spotting process may be performed as required according to known methods.
The present invention will now be described in detail by way of Examples thereof.
A rubber molding was manufactured by disposing in a molding box a wooden mold on which a tread pattern was formed and by pouring a silicone rubber material into the molding box. The material of the molding box was a synthetic wood (basic degree of shrinkage setting: 11.5/1000) and the rubber molding was silicone rubber molding having a plaster lining (thickness of rubber layer: 15 mm).
By pouring, into the rubber molding, a plaster (G-1 foam plaster manufactured by Noritake Gypsum Co., Ltd.: mixing water ratio: 70%, increase by foaming: 50%), a design surface portion being in contact with a casting mold (design surface φ: 600±20 mm, tire width size: 195±30 mm, casting thickness: 70 to 100 mm, whole casting height: 300±30 mm, divided sectors: 9 pieces/1 ring) was produced. the design surface portion was used for casting to obtain block castings of Examples 1 to 3 and Comparative Example 2, and a casting for a mold for a tire of Comparative Example 1. Basic sizes of the casting for a mold for a tire, and the methods of producing the castings are shown in combination in Table 1 below.
As for the dimensional accuracy of the as-cast castings for a mold for a tire manufactured in Examples 1 to 3 and Comparative Examples 1 and 2, four items: chord size, twist, circumferential warp and width direction warp were evaluated according to the evaluation method below.
chord size difference=actual casting size−size in drawing.
When the value of the chord size difference is a positive value, the casting chord size is larger than the size in the drawing. The difference between the upper chord size and lower chord size was calculated by the following:
difference between upper chord size and lower chord size=lower chord size−upper chord size.
When the value of the difference between upper chord size and lower chord size is a positive value, the chord size of the cope is smaller.
Table 2 shows that in Comparative Example 1 (conventional ring casting), the properties of twist, circumferential warp and width direction warp were preferable (both the average and variation were small), while the difference between the sizes of upper and lower chords was the largest. In Comparative Example 2 (conventional block casting), the difference between the sizes of upper and lower chords was small, while the properties of twist, circumferential warp and width direction warp were not preferable.
On the other hand, chord size difference in Example 1 was smaller than that in Comparative Example 1, and twist and warp deformation in Example 1 could be suppressed more than in Comparative Example 2. That is, it is known that a block casting method may be provided in which twist and warp deformation is less likely to occur when the casting shrinks and the difference between the degrees of shrinkage of cope and drag is small. The difference between the upper chord size and lower chord size in Example 2 could be suppressed further more than in Example 1. Further, in Example 3, twist and warp were similar to that of ring casting, while the difference between the upper chord size and lower chord size could be greatly improved as compared to ring casting.
From the above, by the present invention, also by using a block casting method, a dimensional accuracy property which is similar to that of a ring casting method or is better than that of a ring casting method may be obtained, and the present invention may make the most of high flexibility of dealing with a large-sized article, which is an advantage of a block casting method.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-233981 | Sep 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/060904 | 6/15/2009 | WO | 00 | 3/18/2011 |
