JPS6260181B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for casting parts having a cylindrical portion, such as engine cylinder blocks, and particularly to a sand mold used in the casting method to prevent cracking due to thermal expansion of the core used in the casting method. .

Molds such as cylinder blocks are constructed by combining a large number of cores. When combining cores, a heat-resistant adhesive is used to secure the cores together and to prevent melt from leaking from the combined surface of the cores during pouring. If the core is fixed with
If such a core crack occurs, the cast product cannot be used as a product.

In addition, the contact surfaces between the cores include a portion that needs to be fixed to each other by pasting them together, and a portion that must not be fixed in order to absorb thermal expansion of the cores. In either case, if there is a gap, hot water will leak from that area, so it is necessary to seal the gap.

Conventionally, fixed sealing members have been put to practical use, but there is no suitable sealing method that allows relative movement between the cores. The conventional method of sealing parts that allow relative movement will be explained in the case of a cylinder block mold as shown in FIGS. 1 and 2.

A box-shaped formwork 13 is filled with sand 8, and a rail core 3 having a conical portion 9 and a cylindrical portion 1 are placed inside the box-shaped formwork 13.
4, and insert the conical part 1b and cylindrical part 1a of the crankcase core 1 into the conical part 9 and the cylindrical part 14, respectively. Then, wedges 4 and 5 are driven between the end of the rail core 3 and the end of the crankcase core 1, which are part of the sand mold body, and the mold 12 filled with sand 7 is then placed in the mold. 13 to form a mold.

In this way, the cylinder head attachment part A, the cylinder part B, and the crankcase part C are cast on the outside of the crankcase core 1. In order to prevent hot water from leaking to the left from the end of the cylinder head mounting part A, the cylindrical part 1a of the rail core 1 is attached to the right end of the conical part 9 of the rail core 3, as shown in FIG. A cylindrical part 10 having an inner diameter slightly larger than the outer diameter is formed, and a step part 21 is provided between the conical part 9 and the cylindrical part 10. On the other hand, the cylindrical part 1 of the core 1
A step portion 22 is provided between a and the conical portion 1b. When assembling the cylindrical portion 1a of the core 1 to the rail core 3, a gap s is provided between the stepped portion 21 and the stepped portion 22 in consideration of thermal expansion of the cylindrical portion 1a.
Further, an adhesive 2 is provided between the conical part 9 and the cylindrical part 10.
4 and fix both.

However, in reality, the cylindrical part 10 and the cylindrical part 1
When hot water flows into the space between the stepped portions 21 and 22 from the gap between the stepped portions 21 and 22, and the hot water in this portion solidifies first, the axial expansion due to thermal expansion of the cylindrical portion 1a is hindered, and the cylindrical portion 1a As shown by reference numeral 15, the core 1 may crack and hot water may leak into the interior of the core 1.

SUMMARY OF THE INVENTION In view of these problems, it is an object of the present invention to provide a sand mold that prevents the leakage of hot water from the mating surface of the core and prevents the core from cracking due to thermal expansion.

Another object of the invention is to obtain a sand mold that can be implemented without any modification to conventional molds.

For this purpose, the present invention forms an annular step at a right angle to the longitudinal axis at the end of the core, and between the step and the opposite step in the hollow part of the sand mold body, By interposing a seal packing made of a compressible material such as paper with a thickness that absorbs the thermal expansion of the core, leakage of hot water is prevented and the thermal expansion of the core is absorbed. It is something.

The present invention will be described based on an embodiment. As shown in FIG. 3, a seal packing 20 is installed between a portion that requires sealing, that is, a step portion 21 and a step portion 22. There is no need to use any special adhesive between the rail core 3 and the conical portion 1b of the crankcase core 1.

As described above, by installing the seal packing 20, when the crankcase core 1 is surrounded by molten metal due to pouring, thermal expansion occurs.
This thermal expansion is absorbed by the gap s provided in advance between the stepped portions 21 and 22. That is, when the crankcase core 1 thermally expands in the axial direction, the stepped portion 2
2 compresses the seal packing 20.
Even if the molten metal enters from the gap between the cylindrical portion 10 and the cylindrical portion 1a, it is blocked by the seal packing 20 and cannot enter between the stepped portions 21 and 22.

The seal packing 20 made of paper or the like has an oxygen-poor condition inside the mold, so it will not burn out due to the molten metal and will carbonize and solidify.
It does not impair sealing performance.

For the seal packing 20, soft paper or pulp is practical from a cost standpoint, but other suitable materials may be used.

According to the present invention, the seal packing interposed in the combined part of the core has a cushioning effect that absorbs thermal expansion of the core, and a sealing effect that prevents molten metal from flowing into the gap between the combined part of the core. demonstrate. Therefore, compared to the conventional method, not only can the occurrence of casting burrs be significantly suppressed, but also the excellent effect of preventing cracking due to thermal expansion of the core can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view showing a general assembled state of a mold using a core, Fig. 2 is a partial sectional view showing the state of pouring in the same mold, and Fig. 3 is a side sectional view showing the state of pouring in the same mold. FIG. 2 is a cross-sectional view similar to FIG. 2; A: Head mounting part, B: Cylinder part, C: Crankcase part, 1: Crankcase core, 1a:
Cylindrical part, 1b: Conical part, 3: Rail core, 4,
5: Wedge, 6: Core, 7, 8: Sand, 9: Conical part, 10: Cylindrical part, 12, 13: Formwork, 14: Cylindrical part, 20: Seal packing, 21, 22: Step part.

Claims (1)

[Claims] 1. An annular step is formed at the end of the core at right angles to the longitudinal axis, and between the step and the opposite step in the hollow part of the sand mold body, the heat of the core is A sand mold that prevents leakage and absorbs thermal expansion of the core by interposing a seal packing made of compressible material such as paper with a thickness that absorbs expansion.