JPH04111940A - Disintegratable core - Google Patents

Abstract

PURPOSE:To easily disintegrate and remove a core after casting, which bears high pressure of molten metal and does not develop breakage and penetration of the molten metal, by using sodium chloride as raw material and burning at the specific temp. after pressing and forming this raw material in a mold. CONSTITUTION:The disintegratable core 1 uses the sodium chloride with grain size set to 60-150mum as the raw material and this raw material is burnt at 670-720 deg.C after being pressed and formed in the mold, and shaped. Therefore, this bears the high pressure of molten metal in high pressure casting, and the penetration of molten metal and the breakage are not developed, and after casting, this is removed with good disintegration and cavity part of cooling hole, etc., in the casting can be formed as the desirable shape.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a collapsible core used in a casting method such as a molten metal forging method.

(Prior Art) As a collapsible core conventionally used in a casting process, there is one disclosed in, for example, Japanese Patent Laid-Open No. 60-72656. The invention disclosed in this publication relates to a method for manufacturing a piston for an internal combustion engine that has a cooling hole inside, but the specification also mentions that in the casting process of this manufacturing method, an annular cooling hole is formed inside the piston. It describes a core made of salt used to form a salt core.

This collapsible core contains, for example, sodium chloride (by weight)
NaCl) 96%, borax 2%, magnesium oxide (
SIgO) 1%, talc 1%, and particle size 200
・~500. After compacting the czm salt raw material into a link shape using a press, it was heated at 700°C for 20 minutes and sintered. This core is held in a piston mold by a cast-out pin, and the molten alloy is injected into the mold, and a rough piston material is produced by gravity casting or molten metal forging (high-pressure casting). After solidification, the cast body is removed from the mold and a water stream is supplied through the opening formed by the casting pin to collapse and remove the core, resulting in a piston with an annular cooling hole formed therein.

In the casting of alloy castings such as the above-mentioned piston, a so-called molten metal forging method (high pressure casting method) is used in which the molten alloy is solidified under high pressure in order to increase the strength of the cast alloy. It's starting to look like this. However, in this molten metal forging method, when the conventional salt core as described above is cast into the molten alloy as in the case of normal weight casting, the high pressure (500 to 2000 atmospheres) applied to the molten metal is required. Therefore, there was a problem in that the core was destroyed, or the molten metal penetrated into the gaps between the cores, making it impossible to form the required cooling holes.

In view of the above-mentioned problems, the present invention aims to provide a collapsible material that can be used in high-pressure casting to withstand the high pressure of molten metal, does not cause destruction or penetration of molten metal, and can be easily disintegrated and removed after casting. The purpose is to provide cores.

(Means for Solving the Problems) In order to achieve the above object, the collapsible core of the present invention uses sodium chloride with a particle size of 60 to 15C1 μm as a raw material, and presses and molds this raw material into a mold. After, 670~
It is made by firing at a temperature of 720°C. The sodium chloride raw material preferably contains 2 to 5% by weight of sodium borate and 2% or less of magnesium oxide.

(Function) When the collapsible core of the present invention constructed as described above is used in high-pressure casting, the molten metal does not penetrate or break under the molten metal pressure of 500 to 2000 atm, and it is removed with good collapsibility after casting. , desired cavities (cooling holes, etc.) are formed within the casting.

(Example) As mentioned above, the collapsible core of the present invention has a particle size of 50 to 15
Sodium chloride (hereinafter referred to as salt) set to 0 μm is used as a raw material, preferably contains 2 to 5% by weight of sodium borate and 2% or less of magnesium oxide as a binder, and this raw material is poured into a mold. It is formed by pressing and shaping, and then firing at a temperature of 670 to 720°C. All numerical values expressed in % below mean weight ratios.

In order to confirm the effect of this collapsible core, we investigated the salt particle size, firing temperature, amount of sodium borate, magnesium oxide (h
The levels of O) amount and talc amount were determined as shown in Table 1 below, and cores were molded for these various types and analyzed using the experimental design method.

Table 1 A core (salt core) 1 was molded using the mold shown in FIG. 1 under the above conditions.

In the mold shown in the figure, the outer diameter of the molds 2 and 3 is 55 mm,
The inner diameter d is 54.2 tnm, the clearance between the inner diameter d and the core type 4 is ÷0.01 +0.01, and the clearance C is 0.00 / 0.02.
The pressing force was 250 kg/ffl.

Salt particles having a particle size of 0 to 6 JtLm had a large frictional resistance between the particles, and a molded body could not be formed no matter what amount of binder was blended. In addition, the firing temperature is 720
℃ or higher, cracks were likely to occur after firing and the product could not be produced.

Therefore, we conducted an analysis on salt particles with a particle size of 6 to 150 μm or more and those with a firing temperature of up to 690°C.
Evaluation was conducted on three evaluation items: penetration, ■disintegrability, and ■strength. The evaluation method was as follows.

■Evaluation of penetration rate: As shown in Figure 2 (aj), set the core 1 in the mold 5, pour 720'C molten aluminum alloy 6 into the mold 5, and press down the punch 7. 2000
A pressurizing force of kg,/crF is applied to solidify the molten metal. The solidified and cooled cast body is taken out and the core 1 is cut as shown in Figure (b), and the cross-sectional area of the molten metal permeation part 8 is measured and calculated as (permeation part area, 7/core area) x 100 ( %〉 is the penetration degree.

■Evaluation of collapsibility: As shown in Figure 3 ia), water jet was applied to the salt 10 filled in the pores of the resin 9.
) 11 is sprayed to make the volume (cc) of the cavity 12 formed as shown in Figure (b) collapsible.

■Strength evaluation: As shown in Figure 4, 3 for core 1
A point bending test (fulcrum spacing B.50+nm) was conducted, and the strength (w/h~2) was measured using an autograph manufactured by Shimadzu Corporation.

The results of the evaluation of these three items are shown in FIG. From this Figure 5, the following two things were discovered. That is, 1) Talc (talc) is unnecessary, at least from the perspective of these three evaluation items.

2) Magnesium oxide (MgO) contributes to improving strength, but as the amount increases, permeability and disintegration deteriorate. 0
~2% is appropriate.

3) The smaller the amount of sodium borate, the better the disintegration and strength, but it worsens the permeability. 2 to 5% is appropriate.

4) The higher the firing temperature, the higher the penetration rate and strength.
Cracks occur at temperatures above 720°C. Therefore, 670-7
20'C is appropriate.

5) The finer the salt particle size, the better the overall properties.

However, it cannot be formed with a diameter of 601 x m or less. Therefore, 6
0 to 150. zzm is appropriate.

From the above findings, the collapsible core of the present invention has a particle size of 50 to
150. Using sodium chloride set in itm as raw material,
Preferably 2-5% sodium borate in this raw material;
The material contains 2% or less of magnesium oxide, and after pressing and molding this raw material in a mold, it is fired at a temperature of 570 to 720'c.

Next, a method for removing the core encased in the casting when a rough piston casting material is cast using the collapsible core of the present invention will be described.

In the conventional gravity casting method (gravity casting), two or more holes are made through the outer surface of the casting in the collapsible core part that is cast inside the casting, and from one hole 15 kg, /
The conventional method was to remove the core by spraying a pressurized water stream with a pressure of about Cl1. This is a collapsible core with sufficient strength and penetration resistance to withstand gravity casting.
A low-pressure power pump causes water to flow in from the inlet, and the core flows out to the outlet while being split in two directions.

However, for a collapsible core with strong strength and high permeation resistance, such as the one of the present invention, which can be used to form a casting using a high-pressure solidification method such as a molten metal forging method, conventional removal methods such as those described above cannot be used. The core cannot be removed sufficiently. Therefore, a method is adopted in which the core of the raw casting material is removed using a high-pressure water stream, a nozzle shaped to give directionality to the water stream, and a core removal jig.

Figure 6 is a front view of the device used in this core removal method;
FIG. 7 is a sectional view taken along line AA. Reference numeral 21 in the figure is a worksheet for installing the piston rough material 22 in which the collapsible core 1 is cast. One nozzle 23, 24 is attached to each of the left and right worksheets 21, and each nozzle 23, 24 communicates with a pipe 25 connected to a high-pressure pump (not shown), so that high-pressure water flows from the tip toward the core 1. It is designed to be sprayed. The tips of the nozzles 23, 24 have a curved shape as shown in an enlarged view in FIG.

The crown surface 22a of the piston rough material 22 is shown in the worksheet 21.
After the piston blank 22 is attached to the piston, it is pressed and fixed by a holding arm 26.

When removing the collapsible core 1 from the piston rough material 22,
A high-pressure water stream of 50 to 200 kg/alt from a high-pressure pump is injected onto the collapsible core 1 from the tips of the nozzles 23 and 24. The water jet direction of the nozzles 23 and 24 is one direction along the annular shape of the core 1 (counterclockwise direction in Fig. 7).
Nozzle 2 on the worksheet 21 on the right side of the diagram
The water flow coming out from 3 removes the core 1 on the upper left in Figure 7.
Meanwhile, the nozzle 24 of the left worksheet 21 removes the core 1 in the lower right half. The collapsed salt in the core 1 is discharged from the outlet 27 along with the water flow 6 Next, the piston rough material 22 on the left and right work sheets 21 is replaced and the same removal operation as before is performed, and the remaining half of each Core 1 is removed. (Piston rough material 2 on the same worksheet 21
2 may be set in a position rotated by 180° to perform the removal work on the second floor. ) In this way, by performing the removal work for each of the left and right halves of the core as one cycle, complete removal is possible without leaving anything behind. Furthermore, since a high-pressure water stream is used and the nozzle jet direction is directional, even a high-strength core compatible with high-pressure coagulation, such as the product of the present invention, can be completely removed.

Next, the core removal status of the piston with cooling holes that was cast using the collapsible core as described above and the core was removed.
A method for inspecting the state of cooling hole formation will be described.

Radiographic techniques and ultrasonic flaw detection methods have conventionally been used for internal inspection of such cast articles. However, the radiographic method is expensive because the inspection equipment consists of an X-ray oscillator and a detection unit, and for objects with complex shapes such as pistons, the internal shape of the cooling hole must be visually determined. That is extremely difficult. CAT, which has been attracting attention recently, has a sufficient discrimination accuracy, but it takes a long time (about 5 minutes) to take in and analyze X-ray data, and is not suitable for 100% inspection. Due to its principle, ultrasonic inspection cannot express the shape of piston cooling holes, so it cannot detect cracks or deformations caused by molten metal insertion. Therefore, when inspecting the cooling holes of pistons cast using the collapsible core of the present invention, fluids such as air, water, oil, etc. were flowed into the cooling holes, and the pressure loss or flow rate between the inlet and outlet was measured. However, we have adopted a system that determines that cooling hole formation is defective if the pressure loss is greater than a predetermined value or if the flow rate is less than a predetermined value.

Figure 9 shows a piston to which this inspection method is applied. Reference numeral 31 denotes a cooling hole which is formed inside the piston 30 by the collapsible core of the present invention and is to be inspected after the core is removed as described above. It communicates with the oil jet inlet hole 32 and the oil jet outlet hole 33. Inspection jigs 34a and 34b are pressed through rubber seals 35 to prevent fluid from leaking. is installed.

FIG. 10 shows an outline of the piping in the first embodiment of this inspection method, in which the fluid pipeline is connected to the inlet side inspection jig 34a via a column 36 and a pressure control valve 37. A pressure gauge 38 is installed between the pressure control valve 37 and the inlet inspection jig 34a. The outlet side inspection jig 34b is exposed to the atmosphere via a flow meter 39.

To inspect the cooling holes 31, the sockets 36 are opened and fluid (oil, water, air, gas) is allowed to flow. After the pressure control valve 37 adjusts the pressure gauge 38 to a constant pressure Po, the flow meter 39 measures the flows 'j# and Qo. Flow rate Q.

It is a well-known fact that the flow rate Qo decreases as the loss resistance that occurs inside the piston cooling hole 31 increases. can be judged. That is, if the cooling hole 31 is clogged or collapsed, the loss resistance K will increase and the flow rate Q will increase. decreases.

1-P For example, if Qo

FIG. 11 shows an outline of piping in a second embodiment of this inspection method. In this example, a cock 36, a flow control valve 40,
Flow meter 39. The inlet inspection jig 34a is connected in this order, and a differential pressure gauge 41 is provided in parallel between the cooling hole 31 and the outlet. Let the fluid flow.

The flow rate control valve 40 has a flow rate Q. = CQnSt.

If the loss resistance K of the piston/cooling hole 31 increases, the pressure loss (differential pressure) ΔP between the person and the outlet of the cooling hole 31 increases.

That is, ΔP = KQ'.

For example, if it is -1.2 x ΔP - ΔP° or more, it is determined that cooling hole formation is defective.

As described above, this inspection method makes a judgment by quantifying whether or not oil easily passes through when an oil jet is actually inserted into the cooling hole. Compared to the ultrasonic flaw detection method, it is possible to better understand the actual cooling hole formation status, and it is also inexpensive, allows for high-speed judgment, and is suitable for 100% inspection.

(Effect of the invention) As mentioned above, the collapsible core of the present invention has a particle size of 60 to 15
Use sodium chloride set at f1 person Lm as a raw material, preferably containing 2 to 5% sodium borate and 2% sodium borate in this raw material.
The following magnesium oxide is stored, this raw material is pressed into a mold, molded, and then fired at a temperature of 570 to 720°C, so it can withstand the high pressure of molten metal in high-pressure casting. After casting, it is removed with good disintegrability, making it possible to form cavities such as cooling holes in the casting as desired.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing an example of a mold used for molding a collapsible core, Figure 2 is a diagram showing a method for evaluating the degree of penetration of a collapsible core, and Figure 3 is a diagram showing the collapse of a collapsible core. Figure 4 is a diagram showing how to evaluate the strength of collapsible cores. Figure 5 is a diagram showing the evaluation and analysis results of permeability, collapsibility, and strength of collapsible cores. , FIG. 6 is a front sectional view of a device used for removing collapsible cores, FIG. 7 is a sectional view taken along line A-A in FIG. 6, and FIG. 8 is an enlarged view of the nozzle tip in FIG. 6. Fig. 9 is a diagram showing a piston whose cooling holes cast using a collapsible core are inspected, Fig. 10 is a piping schematic diagram of an embodiment of the piston cooling hole inspection method, and Fig. 11 is the same. FIG. 7 is a schematic diagram of piping in another embodiment of the inspection method. ■...Disintegrable core. Patent applicant: Accunicia Co., Ltd.

Claims (2)

[Claims] (1) Use sodium chloride with a particle size of 50 to 150 μm as a raw material, press this raw material into a mold, mold it, and then
A collapsible core characterized by being fired at a temperature of 70 to 720°C. (2) 2 to 5% by weight in the sodium chloride raw material
The collapsible core according to claim 1, comprising sodium borate of 2% or less and magnesium oxide of 2% or less.