JPS5973147A - Casting method - Google Patents

Abstract

PURPOSE:To enable prevention of cracking in a thin-walled part in the stage of producing a casting having the thin-walled part in continuation with a thick- walled part by packing sand in the longitudinal through-hole of a core provided freely communicatively with the hole opend in the top and bottom surfaces of a casting mold and using such core thereby cooling forcibly the thick-walled part from the central part. CONSTITUTION:A molten metal is charged through a sprue 5 into a casting mold 8. A shutter 13 is released to discharge the dry sand 12 packed in the longitudinal through-hole 10 of a core 7 and the holes 9A, 9B of a casting mold 8 through the hole 9B when the molten metal on the surface in contact with the core 7 begins to solidify upon lapse of a prescribed time after completion of charging. Then, the core 7 is decomposed and discharged at the same instant. As a result, the vertical through-hole in a boss 1A part is made continuous with the holes 9A, 9B of the mold 8 and the atmospheric air flows vigorously as shown by an arrow on account of a difference in temp. The inside surface of the through-hole in the part 1A is thus forcibly cooled and therefore the cracking of the thin-walled impeller 1B continuous with the part 1A is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a casting method for castings, such as impellers and pump casings for pumps and water turbines, in which a thin wall portion is continuously formed in a thick wall portion.

Cast products such as impellers and pump casings for pumps and water turbines, in which a thin wall part is continuously formed on a thick wall part, have a large cooling time difference between the thick wall part and the thin wall part during casting. Cracks are likely to occur at the edges that contact the thicker parts.

If the material of the casting is a metal that can be easily repaired by welding, such as ordinary cast steel or stainless cast steel, such cracks can be fixed by applying overlay welding after casting, even if it takes a certain amount of time to make the product. I can do it. However, if the cast material is a metal that is difficult to repair by welding, such as ordinary cast iron, ductile cast iron, or high chromium cast iron, the above-mentioned cracks become a fatal defect, and the casting cannot be used as a product.

Therefore, metallurgy has been conventionally provided in order to artificially speed up the cooling of the portions where cooling is delayed as described above.

FIG. 1 is a longitudinal sectional view showing a conventional casting method when the casting is an impeller. The impeller 1 consists of a thick boss part IA having a vertical through hole 2 in the center, and a thin in-wave part IB continuous with the boss part IA.

In casting such an impeller 1, conventionally, a metallurgical metal 4 is attached to a part of the solid core 3 forming the thick-walled boss portion 1A in close contact with the through hole 2, and a sprue 5 of the boss portion IA is A metallurgy 6 is brought into contact with the end face on the side far from the boss part 1.
The cooling of A was promoted and the aim was to prevent cracks from occurring in IB, which is a thin wall that covers one boss part.

However, such conventional methods are not effective enough to prevent cracks, so it is recommended to cast impellers and guide casings made of non-repairable materials such as high chromium cast iron, which provides particularly excellent wear resistance. Therefore, there has been a strong desire to develop a method that can reliably prevent the occurrence of cracks.

As a result of intensive research to solve the two problems, the inventors of the present invention have discovered that the use of metallurgy, etc., lacks cooling capacity, and the use of cooling water, etc., results in too rapid cooling, which has the opposite effect. From this, we obtained the knowledge that cooling the thick wall from the center using flowing air is effective in preventing cracks in the thin wall.

The present invention has been made based on the above findings, and has a through hole in the vertical direction at the center of the thick part, and when casting a casting in which the thick part is continuous with the thin part, the through hole is The core used for forming is a hollow core with a vertical through hole that can freely communicate with the hole opening on the upper and lower surfaces of the mold, the vertical through hole of the hollow core is filled with sand, and then the mold is filled with sand. Pouring the metal, and after completing the pouring, removing the sand in the hollow core and the vertical through hole of the hollow core, opening the through hole, and forcibly cooling the thick part by the air flowing inside the through hole. It has the following characteristics.

Next, the casting method of the present invention will be explained based on the drawings.

FIG. 2 shows a longitudinal sectional view of an example of an impeller cast by the method of this invention. In this embodiment, a hollow core 7 is used to form the upper and lower through holes of the thick boss portion 1A of the impeller 1 to be cast.

The hollow core 7 has holes 9A and 9B opened on the upper and lower surfaces of the mold 8.
This vertical hole 10 and the holes 9A and 9B of the mold 8 are filled with dry sand 12 during modeling.
In order to prevent this dry sand 12 from flowing out, the hole 9 of the mold 8 is
Install several shutters 13 at the lower end of B○ In this state, pour the metal from the sprue 5 into the mold 8, and after the pouring is completed, after a predetermined period of time has passed, the hot water begins to solidify on the surface in contact with the hollow core 7. When the shutter 13 is opened, the dry sand 12 filled in the vertical through hole 10 of the hollow core 7 and the holes 9A and 9B of the mold 8 is discharged down from the hole 9B of the mold 8, and The air child 7 is also disassembled and discharged. As a result, as shown in FIG. 3, the upper and lower through holes of the boss portion IA are connected to the holes 9A and 9B of the mold 8, and the atmosphere flows violently as shown by the arrows in FIG.

This atmospheric flow is generated in the through hole of the boss part A due to the temperature difference, and thereby the inner surface of the through hole of the boss part IA is effectively forcedly cooled.

FIG. 4 shows a longitudinal sectional view of a guide casing 11 during casting as another embodiment of the present invention. In this case, the only difference is the shape of the hollow core 7' used, and the process is exactly the same as that for casting the impeller 1 described above, effectively forming the thick bearing part 11A of the core 7'. Vertical hole 1
0' can be forcedly cooled by the flowing atmosphere.

Therefore, the nof side vane 11. The guide casing 11 can be cast without cracking.

As described above, according to the method of this invention, the pon 70,
When casting castings where a thin wall part is continuously formed on a thick wall part, such as an impeller for a water wheel or a pump 0 casing, a hollow core is used to forcefully cool the thick wall part using flowing air at the appropriate time. Since it can be applied to a wide range of surfaces, excellent industrial effects can be brought about, such as obtaining castings of excellent quality without cracking in thin walled parts.

[Brief explanation of the drawing]

Fig. 1 is a vertical sectional view showing an impeller being cast by a conventional casting method, and Figs. 2 and 3 are longitudinal sectional views showing an impeller being cast by the method of the present invention. , and FIG. 4 is a longitudinal sectional view showing a state in which the id casing is being cast. In the drawings, ■...Impeller, IA...Boss part, IB...Blade,
2... Through hole, 5... Sprue, 7, 7'... Hollow core, 8... Mold, 9A, 9B... Hole, 10.10'
... Vertical hole, 11... Guide casing, 11A.
... Bearing part, 11B... Guide vane, 12... Dry sand, ]3... Shutter. Applicant: Ebara Corporation Agent: Natsuo Shiotani (and 2 others)

Claims (1)

[Claims] When casting a casting that has a vertical through hole in the center of the thick wall and a thin wall continuous to the thick wall, the core used to form the through hole is inserted into the hole that opens on the top and bottom surfaces of the mold. A hollow core is formed with a freely communicating vertical hole, the vertical hole of the hollow core is filled with sand, and then the metal is poured into the mold, and after the pouring is completed, the hollow core and the hollow core are A casting method characterized in that the sand in the vertical through-hole is removed to open the through-hole, and the thick part is forcibly cooled by the atmosphere flowing inside the through-hole.