JPH0310422B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a mold particularly suitable for manufacturing a cast product having a locally enlarged portion, and more specifically,
The present invention relates to an improvement in a mold that effectively prevents shrinkage cavities that tend to occur in the above-mentioned locally enlarged areas.

Conventional technology Generally, cast products shrink due to the solidification of the molten metal, so if there is a locally enlarged part such as a flesh intersection, heat dissipation is delayed in that part, creating a hot spot that delays the solidification of the casting, causing the product to shrink. Nests are likely to occur. Of course, the shape of the meat intersection should be designed with shrinkage cavities in mind so that it does not become a hot spot, but in cases where it is necessary to take measures against shrinkage cavities due to the casting plan, Methods such as replenishing molten metal using a riser and speeding up the cooling and solidification of areas where shrinkage cavities occur using a chiller have been taken.

Problems to be Solved by the Invention However, there is a limit to the replenishment of molten metal using the above-mentioned feeder, and there are also disadvantages such as a decrease in yield and additional man-hours required for weir folding, polishing, etc. Also,
When using a cold metal, if the shape of the area where the shrinkage cavity occurs is not a flat surface, but has a complicated shape such as a circle or a stepped shape, it will be difficult to insert it.
It is easy to cause secondary defects such as sand bites and scratches, and in addition, there is the problem that it takes a considerable amount of man-hours to manage the chilled metal and remove the flash that forms on the side surface of the chilled metal when it is used. . Therefore, some companies have adopted the back metal method disclosed in Japanese Patent Publication No. 34-2105, and have also used a method in which the thickness of the shell in the area where the shrinkage cavity occurs is made thinner, thereby providing a cooling effect using a die. However, the most fatal drawback is the high cost.

The problem to be solved by this invention is to economically eliminate hot spots that occur in locally enlarged areas and to effectively prevent the occurrence of shrinkage cavities.

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems, and the first invention is to provide a structure in which the required length is A second invention is characterized in that a thin plate-shaped molten metal leakage cavity is formed respectively, and a second invention is characterized in that a chiller is loaded in the cavity for holding a chiller formed so as to face the molten metal leakage cavity. A configuration is adopted.

Effect When pouring metal into the mold of the first invention, the product cavity is filled with molten metal, but this is the part of the product cavity where hot spots are generated and shrinkage cavities are likely to occur. The above molten metal leakage sky
As the molten metal flows and is connected to the thin walled part formed in the form of a flash, a cooling starting point is created in the area where the shrinkage cavity occurs due to the rapid cooling of the thin walled part. It turns out. In other words, the generation of hot spots is suppressed, solidification progresses from the surface of the casting toward the feeder or the center of the product, and shrinkage cavities are completely eliminated at least from the processed area of the surface layer.

Furthermore, according to the mold according to the second invention, the thin-walled portion is cooled more rapidly by the action of the chiller, and the chiller does not directly act on the product part. The cooling ability of the portion where shrinkage cavities are likely to occur is further promoted without causing the above-mentioned secondary defects.

Embodiment Hereinafter, an embodiment in which the present invention is embodied in a mold for a crankshaft of an internal combustion engine will be described with reference to the drawings.

In addition to cast products, cast products made of spheroidal graphite cast iron are also commonly used for crankshafts.

The crankshaft 1 shown in Fig. 1 is an example of the above-mentioned cast product, and the mold in this case is cut off by a common air surface that includes the axis of each crank pin 2, and is separated into upper and lower molds. be done. Figure 2 shows a product cavity 2a corresponding to the above-mentioned crank pin 2.
This figure shows a partial cross section of the mold taken longitudinally, and the cut line is indicated by the symbol P. Due to its natural shape, the crankshaft 1 tends to generate hot spots in the crank pin 2 surrounded by the crank cheek 3, and therefore shrinkage cavities occur frequently on the surface of the product. It is being The occurrence of this defect is particularly noticeable in the case of green molding.
It is represented by a mark. A thin plate-shaped molten metal leakage gap 4 is provided in the upper mold of the mold, extending along the cut line and connected to the product cavity 2a indicated by the cross mark. The molten metal leakage cavity 4, which is a feature of the present invention, is not limited to a thin plate shape as in the illustrated embodiment, and its shape can be arbitrarily selected, as various shapes are known for ordinary weirs. Its length is also determined so that the thin wall portion 4a formed by the molten metal leakage cavity 4 has sufficient heat capacity to appropriately accelerate the cooling rate of the portion where defects are likely to occur. Incidentally, the diameter of the crank pin 2 shown in this example is 52 mm, and the molten metal leakage gap 4
The width, thickness, and length of each are 28mm x 3.5mm x 80mm.
mm. In addition, the above-mentioned molten metal leakage cavity 4 may be formed depending on the shape of the part of the casting product where defects are particularly likely to occur.
It is also possible to provide it optionally without following the cutting line P.

When the upper and lower molds are aligned and molten metal is poured into them, the molten metal that has flowed into the product cavity 2a also enters the molten metal leakage gap 4 and fills it. Therefore, the thin wall portion 4a formed in the shape of a flash by the molten metal leakage gap 4 cools rapidly, and a cooling starting point is created at the X-marked portion of the crank pin 2 that is connected to the thin wall portion 4a where hot spots are likely to occur. . As a result, the cooling rate of the part is increased and the shrinkage cavities, which are very common, are completely eliminated or at least driven internally and prevented from appearing in the surface working area.

The symbol 5 in Fig. 2 is a chiller,
After molding, it is loaded into a cold metal holding cavity 6 formed in the lower mold so as to face the molten metal leakage gap 4, in the same manner as the core is inserted. When the chiller 5 is used in this manner, the molten metal guided into the molten metal leakage gap 4 also fills the cavity 6, and the cooling of the thin wall portion 4a is further promoted by contact with the chiller 5. As a result, the cooling ability of the area marked with an x where shrinkage cavities are likely to occur is further promoted. In this case, the effects of secondary defects such as sand bites and scratches that occur due to the use of conventional cooling metals do not extend to the crank pin 2 part, which is absorbed by the thin wall part 4a and becomes a product. Moreover, there is an advantage that the cleanliness control of the chiller 5 is not required to be strict.

The cooled and solidified crankshaft 1 is taken out through a demolding process, but as clearly indicated by hatching in FIG. Since it can be separated from the raw material, the same amount of post-processing is required as for normal kimiri finishing.

Effects of the Invention Since this invention is a mold that takes measures against shrinkage cavities as described in the claims, there is no effect on the product due to secondary defects, which is seen in the use of conventional cooling metals. Even when a chilled metal is used, it has the advantage of not requiring strict control in consideration of secondary defects, and there is no decrease in yield or increase in the burden of post-processing as would be the case with countermeasures using a riser. However, it has an excellent economic effect.

Furthermore, compared to the back metal method, (1) there is a large difference in the lance bead, and productivity is extremely high. (2) There is no need to use expensive dies or resin-coated sand, and there is no need for firing costs, resulting in low costs. (3) Since it can be applied to green molds, it is easy to integrate with other main mold lines and respond to construction changes. It has various features.

[Brief explanation of the drawing]

FIG. 1 is a plan view illustrating a crankshaft manufactured using the mold of the present invention, and FIG. 2 is a partial sectional view of the mold taken longitudinally through a product cavity portion corresponding to the crank pin portion of the crankshaft. 1... Crankshaft, 2a... Product cavity, 4... Molten metal leakage gap, 4a... Thin wall portion, 5
... Cold gold, 6 ... Blank space.

Claims (1)

[Scope of Claims] 1. A mold characterized in that thin plate-like molten metal leakage cavities of a required length are formed in series with product cavity parts where cavities are likely to occur. 2. Form a thin plate-shaped molten metal leakage cavity of the required length connected to the product cavity part where cavities are likely to occur, and furthermore, in a cavity for holding a cold metal formed so as to face the molten metal leakage cavity. A mold characterized by being filled with cold metal.