KR101028025B1 - Degassing apparatus for manufacturing cylinder head - Google Patents

Abstract

The present invention takes an excessive cost due to the flux and gas bubbling treatment while heating a large amount of molten metal for a long time to remove hydrogen gas that is the cause of pore defects during the casting of the cylinder head, the molten metal In order to suppress pore defects caused by hydrogen gas introduced by moisture in the atmosphere during the injection process, hydrogen gas removal is characterized in the injection cup mounted on the mold to degas the molten metal immediately before injection. Equipped with a device with an ultrasonic wave in the frequency band, a heating device for stirring the molten metal and a stirring device, it provides a cylinder head with improved fatigue characteristics by removing hydrogen gas in the molten metal in a clean and low-cost way without using flux or gas. Provided is a degassing device for manufacturing a cylinder head.

Cylinder head, ultrasonic with, degassing device, pore defect removal

Description

Degassing apparatus for manufacturing cylinder head

The present invention relates to a degassing apparatus for manufacturing a cylinder head, and more particularly, in the case of casting and manufacturing a cylinder head by a conventional molten metal treatment process, dissolved hydrogen gas is generated and remains in a metal structure by moisture in the atmosphere. In the removal of pore defects, a degassing apparatus for manufacturing a cylinder head capable of easily removing hydrogen gas generated in a manufacturing process of a cylinder head without undergoing expensive additional processes such as flux and gas bubbling treatment. will be.

In the casting process, in which a metal is melted and poured into a predetermined mold in relation to a cylinder manufacturing process, there is a high degree of freedom in manufacturing shape, but there is a problem in that defects occur in the product when neglected in process control. These defects are known to act as the starting point of the crack when the casting is subjected to a load, which adversely affects the mechanical properties depending on the distribution and amount thereof. Therefore, the core of the casting process is to make a healthy product free from defects, and for this purpose, management technology and casting technology of the molten metal, which is a metal melt, are important. Defects affecting the physical properties of the aluminum-silicon alloy include pores, inclusions, and eutectic silicon phases. In particular, the pores generated in the hollow space due to shrinkage during the solidification of the melt is the starting point of fatigue fracture, the larger the size and the surface / volume ratio, the worse the physical properties decrease as the distribution position is on the surface or gathered. On the other hand, when pore defects are well controlled, the fatigue properties depend on the process silicon phase, but the larger the size of the silicon and the closer the shape is to the bed, the larger the deterioration of physical properties. Therefore, in general, quantitatively manage the porosity and the degree of improvement in the manufacture of aluminum castings to secure the fatigue properties of the product.

The pore defect is a phenomenon in which the gas solubility of the hot water decreases rapidly during cooling of the molten metal, so that the gas in the dissolved state does not escape and remains in the metal coagulation structure, which is dissolved in the liquid aluminum used for the manufacture of the cylinder head. The only possible gas is hydrogen gas, and the moisture in the air usually causes dissolved hydrogen gas by the following reaction.

2Al _(l) + 3H ₂ O _(g) = Al ₂ O _{3 (s)} + 6H

In order to remove the hydrogen gas melt | dissolved by the above reaction, it is common to perform the degassing process which carries out stirring, inject | pouring a flux process process and inert gas into a molten metal. However, such a chemical melt treatment process is a concern of environmental pollution using chloride and gas, there is a problem that a large amount of the float floating. In addition, a separate heating device is required to prevent the temperature drop of the molten metal due to low temperature gas injection. However, the conventional method requires a large amount of energy cost to compensate for the drop in temperature of the molten metal because a large capacity is processed at a time.

On the other hand, when ultrasonic vibration is applied to the metal melt solution, the solubility in gas is lowered, and the pores of the cast product are reduced by escaping in the form of bubbles as shown below.

2H → H ₂

In other words, the application of ultrasonic waves to the aluminum-silicon alloy melt stimulates the nucleation of the gas bubble, thereby lowering the solubility of hydrogen in the melt and releasing hydrogen gas into the atmosphere. The effect is faster than it does, and there is no melt residue, so there is an advantage to configure a clean process.

Many studies and techniques of ultrasonic melt treatment can be classified into two types according to the treatment time, in which the melt is injected into the mold and the ultrasonic wave is applied before the injection. In order to maximize the effect, it is better to use the former case, but since the middle of the cylinder head is inserted with sand core, the shape is very complicated, so the effect is not reached to the corner. Application is fundamentally impossible due to the problem.

On the other hand, in the latter case, the treated melt is poured into a ladle, poured into an injection cup, and then injected into a mold from the injection cup. In addition, since the degassing effect by the ultrasonic wave only shows an improvement effect near the exciter to which vibration energy is transmitted, there is a problem that the efficiency of the retrofitting effect by the ultrasonic wave in the large scale degassing process is extremely inferior. In addition, since the ultrasonic wave is placed in a high temperature molten metal and operated for a long time, the heat durability is poor, so the equipment must be replaced frequently. Therefore, the size of the ultrasonic wave is limited to increase the efficiency.

In general, the effect of melt treatment is known to be drastically reduced when time is delayed or impact is applied. In the case of conventional gravity casting, molten metal from the melting furnace has two injection processes and an average of about two minutes as described above. There is a problem that the effect is reduced during the delay time. For this reason, it is most efficient to degas the molten metal in the injection cup mounted on the mold, but the existing gas injection type degassing process lowers the molten metal temperature due to the low temperature gas, thereby incurring energy costs to compensate for this. The process cycle time is long to secure the treatment time, and a large amount of dross is formed on the surface of the molten metal, so that defects occur when it is mixed during injection, and hot melt is splashed as the gas escapes from the molten surface. It is not applied at industrial sites because of the potential threat to safety.

Therefore, in the present invention, in the degassing apparatus for manufacturing a cylinder head, the apparatus having an ultrasonic wave in a frequency band characterized by hydrogen gas removal in an injection cup mounted on a mold when casting a cylinder head, and heating for molten insulation It is equipped with a device and a stirring device to degas the molten metal immediately before the injection of the mold, and unlike the existing molten metal treatment method, fatigue characteristics of the cylinder head are suppressed by suppressing pore defects caused by the inflow of hydrogen gas by atmospheric moisture during the process. In addition, the cylinder head is manufactured to prevent environmental pollution and reduce energy costs due to the additional process of flux and gas bubbling while heating a large amount of molten metal for a long time to remove hydrogen gas causing pore defects. Provide a degassing device for

In order to achieve the above object, the present invention provides the following configuration.

The present invention relates to a degassing apparatus for manufacturing a cylinder head, comprising: a guide formed on an inner wall of an injection cup, an ultrasonic excitation device provided on the guide, an agitator for the molten metal provided on the guide, and a lower portion of the injection cup. It provides a degassing device for producing a cylinder head, characterized in that it comprises a heater for maintaining at a predetermined temperature.

In addition, the degassing apparatus for producing a cylinder head, characterized in that to form a heat insulating wall for blocking heat between the injection cup and the mold so that heat generated in the injection cup by the heater is not transferred to the mold. To provide.

And, it provides a degassing device for producing a cylinder head, characterized in that it further comprises an oscillator for providing an electric force to the vibrator and agitator outside the injection cup.

Here, the stirrer provides a degassing apparatus for producing a cylinder head, characterized in that it comprises a propeller configured to be stirred up and down the molten metal in the injection cup according to the rotation.

In addition, the temperature of the molten metal in the injection cup provides a degassing device for producing a cylinder head, characterized in that to maintain the temperature of 678 ℃ to 692 ℃ by the heater.

In this case, the vibrator provides a degassing apparatus for producing a cylinder head, characterized in that installed on the guide in a position biased to the side wall separated by a predetermined distance from the center of the injection cup.

As described above, the degassing apparatus for manufacturing a cylinder head according to the present invention performs the degassing process by using an ultrasonic excitation method during the manufacture of the cylinder head, thereby providing a low-cost, eco-friendly method for manufacturing the cylinder head.

In addition, the ultrasonic excitation method not only improves the utilization efficiency of the ultrasonic excitation method during degassing by overcoming technical limitations such as treatment efficiency that may occur when gas is removed from the molten metal and equipment replacement due to high heat. In order to perform the molten metal treatment in the infusion cup just before the injection, there is an effect of improving the efficiency of pore defect removal through the molten metal treatment.

In the present invention for achieving the above object, in the degassing apparatus for manufacturing a cylinder head, ultrasonic waves capable of improving the porosity in the small-scale molten metal just before the molten metal injection in the conventional gravity casting method of the conventional casting method of aluminum-silicon-based alloy The present invention provides a degassing apparatus for manufacturing a cylinder head that can improve the fatigue characteristics of an aluminum cylinder head through the removal of hydrogen gas by configuring the excitation apparatuses and the molten metal thermostat and the stirring apparatus to assist the same.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figures 1a to 1c is a schematic diagram of the tilt type gravity casting method.

The molten metal (A) stabilized in the heating furnace is floated to the ladle (Ladle) and first poured into the injection cup 10 attached to the mold 20 (Fig. 1a), the mold shaft 20 is fixed to the rotating shaft 15 As a process in which the molten metal is injected into the mold 20 (FIG. 1C) while rotating relative to (FIG. 1B), the apparatus is simple and can be melted quickly and stably. Is the method used.

However, in such a gravity gravity casting method, the metal melt is melt-waited during the injection process into the injection cup 10 and the injection into the mold even if the metal melt is subjected to degassing and stabilization in a melting furnace or a heating furnace in advance. The contact between the liver is large, there is a disadvantage that the melt is unstable due to the impact during injection.

Therefore, in the present invention, in order to solve the problem according to the molten metal injection timing on the principle of casting to obtain the best efficiency, the molten metal treatment period is configured to be performed in the injection cup 10 immediately before the mold injection.

On the other hand, in the degassing apparatus for manufacturing a cylinder head of the present invention, the effect is quickly shown for degassing treatment, there is almost no drop in the melt temperature, and the injection cup 10 is used by using an ultrasonic excitation method suitable for application to the injection cup structure. The ultrasonic wave was applied directly to the molten metal in the apparatus to remove dissolved hydrogen gas, thereby improving the quality of the cast product.

2 is a cross-sectional view specifically showing a degassing apparatus for producing a cylinder head of the present invention. As shown in FIG. 2, the degassing apparatus for manufacturing a cylinder head of the present invention, as in FIG. 1, is applied to a molten metal in a cylinder head casting apparatus including an injection cup 10 and a mold 20 configured to be rotatable. Including an oscillator 70 made of a piezoelectric element and a cylindrical titanium alloy including an amplifier and an agitator 40 for evenly transmitting the effects of ultrasonic excitation in the molten metal to directly apply ultrasonic waves. It is composed. Preferably, the guide 30 is formed on the inner side wall of the infusion cup 10 and the exciter 50 and the stirrer 40 are installed on the formed guide 30 so that the ultrasonic wave is wide enough in the molten metal. It is configured to perform the excitation and agitation, the oscillator 70 is installed outside the injection cup 10 through the respective power source 45, 55 to block the negative effects that the oscillator 70 may have.

In this case, the portion of the vibrator 50 immersed in the molten metal is subjected to heat-resistant coating, the location of the installation of the vibrator 50 and the stirrer 40 is to make a large contact area with the molten metal, it is difficult to enter and exit the hot water It is also set to a position where residues on the surface caused by contact between the molten metal and the atmosphere are sufficiently removed so that it cannot be mixed into the molten metal. That is, since the residues generated on the surface are difficult to be removed due to the accumulation of residues on the surface near the center of the injection cup 10, the exciter 50 is not disposed near the center of the injection cup 10, the predetermined wall from the center to the side wall When installed in a position sufficiently biased by the distance of, as a preferred embodiment of the present invention, in the degassing apparatus for manufacturing a cylinder head, four exciters 50 are installed in a square with each other on the guide 30, the above Two agitators 40 may be installed between the four exciters 50 to configure sufficient stirring of the molten metal. In addition, in the degassing apparatus for manufacturing a cylinder head according to the present invention, the vibrator 50 is fixed on the guide 30 for efficient gas removal so that the molten metal is poured into the injection mold 20 in the injection cup 10. Configure it to work while it is complete.

As shown in FIG. 2, the stirrer 40 is disposed between the vibrators 50 to maximize the degassing effect and is supplied to the vibrator 50 with a new molten metal by stirring. Ultrasonic excitation is performed with respect to the whole molten metal. In this case, the stirrer 40 is a stirrer 40 having a propeller, it is preferable that the propeller is configured in an oblique shape so that the upper and lower melt can be mixed.

The lower portion of the injection cup 10 is provided with a heater 60 for maintaining the temperature of the molten metal at a higher temperature than the process of manufacturing a general cylinder. The temperature of the molten metal is higher than the general standard of the conventional cylinder fabrication. Unlike the gas injection type, the ultrasonic excitation causes hydrogen gas to spontaneously rise into the molten metal. Therefore, when the fluidity of the molten metal drops, it is difficult to reach the surface. This is to increase the flow rate of the melt by sufficiently raising the temperature. Preferably, the temperature of the molten metal is maintained at about 690 ° C higher than 650 ° C corresponding to the temperature of the molten metal in the conventional casting process.

However, in this case, a heat insulation wall 25 is installed between the injection cup 10 and the mold 20 so that the temperature rise of the injection cup 10 by the heater 60 is not transmitted to the mold 20. It is preferable to.

The improvement and degassing effect by the ultrasonic excitation are realized by different mechanisms. As the degree of the effect is different according to the ultrasonic excitation characteristics such as frequency and excitation width, the excitation band and the method must be taken differently to maximize the efficiency. Can be.

The experiment in Table 1 measures the time required to reduce the hydrogen gas content of the melt at 700 K at 10 Kg from 0.2 mg / 100 ml to 0.1 mg / 100 ml. This experiment shows that the degassing effect is maximized at relatively low frequency (20 ~ 30kHz), and the degassing efficiency increases with increasing output (or amplitude).

Degassing time (seconds)

Print

1 kW

2 kW
3 kW



Frequency
25 kHz

75.7
71.1
69.5
45 kHz

78.0
75.9
76.1
65 kHz

77.1
77.2
75.3

As a preferred embodiment of the present invention, the production of the cylinder head was performed by casting by applying the present technology to the aluminum A356 alloy. The alloy used was A356, the composition of which is shown in Table 2, and after dissolution and stabilization, the temperature was 692 ° C when injected into the injection cup and maintained at 685 ± 7 ° C during the application of ultrasonic waves. The injection volume is 10.5 Kg, and in preserving and preheating the injection cup, the preheating is only required when the molten metal is first injected, and then the preheating time is set to be very short.

Al

Si
Mg
Fe
Ti
B
Bal.

7.0
0.41
0.07
0.02
0.0005

In this regard, the heater 60 installed in fear of the temperature drop may be configured so that the heater 60 is not required when an insulation treatment is added to the injection cup 10, but the work is performed for a large capacity in which the capacity of the molten metal is increased. In consideration of the case, it is preferable to install the heater (60). The degassing device was installed two in the injection cup in the equipment of Figure 2 transversely, in each device ultrasonic wave was 1.5kW, 25kHz for 1 minute, the excitation width was an average 100㎛. In order to confirm the effects of the present invention, the unprocessed castings and the treated castings were manufactured and compared, respectively.

The amount of dross in each process could not be compared directly because the degassing process was not carried out in a separate heating furnace, but the amount of melt in the cup was decreased. In Table 3, the porosity was reduced by 80% with ultrasound, and the SDD (Secondary Dendrit Arms Spacing) was also improved by 20%.

division
Organizational Analysis

Porosity (%)

SDAS (㎛)
Before sonication

2.6
35.8
After sonication

0.46
29.2

As can be seen in the tissue photographs of FIGS. 3A and 3B, the shape of the silicon is also rounded as a whole (FIG. 3A) as compared to the case where the ultrasonic treatment is not performed, resulting in an effect similar to that of the improvement. Table 4 measures the hydrogen gas of the molten metal. Ultrasonic excitation reduced hydrogen gas by approximately 40%. Table 5 shows that the physical properties were improved by improving the mechanical properties and reducing the pore defects. In particular, the elongation was greatly increased, and the fatigue strength was also improved.

division

Hydrogen gas content (mg / 100mL)


Average
One

2
3
After sonication

0.05
0.08
0.07
0.07
Before sonication

0.13
0.2
0.18
0.17

Properties

Ultrasonic Treatment
No ultrasonic treatment
Yield strength (MPa)

228
220
Tensile Strength (MPa)

315
287
Elongation (%)

11
3.5
Fatigue Strength (MPa)

155
138

Therefore, the effect of the degassing apparatus for manufacturing a cylinder head of the present invention is more than the result of the technology applying the existing degassing process, so that the cylinder head of good quality can be cast at low cost without waste of environment and energy when applying the present invention. It can be seen that.

While the invention has been described with reference to the preferred embodiments, those skilled in the art will appreciate that modifications and variations of the elements of the invention may be made without departing from the scope of the invention. In addition, many modifications may be made to particular circumstances or materials without departing from the essential scope of the invention. Therefore, the invention is not limited to the details of the preferred embodiments of the invention, but will include all embodiments within the scope of the appended claims.

1A to 1C are cross-sectional views schematically showing a tilt gravity casting method for producing a cylinder head.

2 is a cross-sectional view of a degassing apparatus for manufacturing a cylinder head of the present invention.

3a and 3b is a photograph of the internal tissue according to whether or not the ultrasonic treatment.

<Description of Symbols Used in Main Parts of Drawings>

10: infusion cup 50: agitator

20: mold 60: heater

30: guide 70: oscillator

40: stirrer

Claims (6)

In the degassing apparatus of the cylinder head casting apparatus for producing a cylinder head by a tiltable gravity casting method using a rotatable injection cup and a mold, A guide formed on the inner wall of the injection cup; A vibrator fixedly installed on the guide at a position biased from the center of the injection cup to the side wall, wherein four are formed in a rectangular shape on the guide; A stirrer installed on the guide between the four exciters to stir the melt; A heater installed at a lower portion of the infusion cup to maintain a temperature of the melt at 678 ° C. to 692 ° C .; Degassing device for producing a cylinder head, characterized in that it comprises a. The method of claim 1, wherein a heat insulating wall for blocking heat between the injection cup and the mold to prevent the heat generated in the injection cup by the heater to form the mold for removing the cylinder head, characterized in that Gas device. The degassing apparatus of claim 1, further comprising an oscillator configured to provide an electric force to the vibrator and the stirrer outside the injection cup. The degassing apparatus for manufacturing a cylinder head according to any one of claims 1 to 3, wherein the stirrer includes a propeller configured to vertically stir the molten metal inside the injection cup as it rotates. delete delete

Images