JP4594336B2 - Solidification method - Google Patents

Description

  The present invention relates to a method for solidifying a liquid such as a molten metal or resin. More specifically, the present invention relates to a technique for refining a solidified structure (crystal structure obtained by solidifying a liquid).

  In general, since the metal material is more excellent in toughness as the crystal structure is more uniform and finer, various methods for uniformly refining the crystal structure have been studied.

Conventionally, the simplest method for miniaturizing the solidification structure of a metal material (crystal structure obtained by solidification) is to solidify before the crystal grains are coarsened by increasing the cooling rate of the molten metal. It is done.
However, in this method, a dendrite structure is formed in the vicinity of the surface of the ingot obtained by solidifying the molten metal, and an equiaxed structure is formed in the interior away from the surface of the ingot. It is difficult to obtain a uniform solidified structure.

  As one method for solving such a problem, there is known a method of accelerating nucleation in molten metal by immersing a vibrator in molten metal in a solidification process and applying ultrasonic vibration. For example, as described in Patent Document 1.

  However, this method has the following problems.

First, when the vibrator is immersed in the molten metal, the vibrator comes into contact with the molten metal, and is therefore eroded and worn by the molten metal. Further, the material constituting the vibrator is mixed into the molten metal and contaminates the molten metal.
More specifically, cavitation (bubbles) is generated in the molten metal due to the ultrasonic vibration of the vibrator, and an oxide film or the like generated on the liquid surface of the molten metal is removed by the cavitation. As a result of contact without passing through the oxide film, the reaction (including chemical reaction) between the molten metal and the vibrator is promoted, and the vibrator is worn out.
Also, when the upper mold of the mold is used as a vibrator, the mold release agent applied to the inner peripheral surface (contact surface with the molten metal) of the upper mold is removed by cavitation, so the molten metal vibrates during the solidification process. Firmly adheres to the child.
As a method for solving such a problem, it is conceivable to provide a mechanism such as an extrusion pin for peeling the fixed ingot from the upper mold, but it interferes with a mechanism for ultrasonically vibrating the upper mold as a vibrator. Therefore, it is not easy to provide.

  Second, when the vibrator is immersed in the molten metal, it is necessary to increase the output (vibration energy) of the ultrasonic vibration in order to apply ultrasonic vibration to the entire molten metal. For example, when a 20 kHz ultrasonic vibration is applied by immersing the vibrator in a molten aluminum alloy, the output needs to be set to about 200 kW.

  Thirdly, when an ultrasonic vibration is applied at high output by immersing the vibrator in molten metal, since the vibration is too strong in the region near the vibrator, crystal nuclei generated by the ultrasonic vibration are dissolved again. Therefore, it is difficult to efficiently increase the number of crystal nuclei in the molten metal and thereby refine the solidification structure.

Further, as a method of preventing the vibrator from being worn by immersing the vibrator in the molten metal, the vibrator is immersed in a molten salt or the like made of a material that does not chemically react with the molten metal and the vibrator. A method of applying ultrasonic vibration to a molten metal by bringing a molten salt or the like into contact with the molten metal is also known. For example, as described in Patent Document 2.
However, this method requires a step of removing the molten salt after solidification of the molten metal, and the productivity is not good, and even if the molten salt does not dissolve in the molten metal, it is caught in the molten metal. There is a problem that it may solidify.

As another method for solving the above problem, there is also known a method for applying vibration to a molten metal by applying a current and a magnetic field to the molten metal in a solidification process by high frequency induction without using a vibrator. For example, as described in Patent Document 3 and Patent Document 4.
Japanese Patent No. 3555485 Japanese Examined Patent Publication No. 7-84626 JP 2004-98111 A Japanese Patent No. 3007947

  In view of the above situation, the present invention provides a solidification method capable of obtaining a fine solidified structure while preventing wear of a vibrator.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, in claim 1,
A non-contact ultrasonic vibration step for applying ultrasonic vibration to the liquid by a vibrator arranged at a predetermined distance from the liquid surface of the liquid in the solidification process;
A contact ultrasonic vibration step of applying ultrasonic vibration to the liquid by a vibrator that is in contact with the solidified portion formed on the liquid surface of the liquid in the solidification process but not in contact with the molten metal ;
It comprises.

In claim 2,
The predetermined distance in the non-contact ultrasonic vibration step is a second peak distance at which resonance of ultrasonic vibration occurs.

In claim 3,
The vibration direction of the vibrator is a direction substantially perpendicular to the liquid surface.

In claim 4,
In the contact ultrasonic vibration step, the liquid is pressurized.

  In the present invention, a fine solidified structure can be obtained while preventing the vibrator from being worn.

Below, one Embodiment of the solidification method which concerns on this invention is described using FIGS. 1-6.
As shown in FIGS. 1 and 2, one embodiment of the solidification method according to the present invention is a method of solidifying a molten metal 1 that is a molten Al—Si—Mg alloy (AC4CH). A vibration step S100 and a contact ultrasonic vibration step S200 are provided.
Although the molten metal 1 in the present embodiment is made of a molten state of an Al—Si—Mg alloy (AC4CH), which is an aluminum alloy used in so-called high-grade castings such as automobile wheels and aircraft engines, the present invention However, the present invention is not limited to this, and the present invention can be applied to applications for solidifying various liquid (molten) materials such as metal materials and resin materials.

  As shown in FIGS. 1 and 2, the non-contact ultrasonic vibration step S <b> 100 performs ultrasonic vibration on the molten metal 1 in a non-contact manner by the upper mold 2 arranged at a predetermined distance R from the liquid surface of the molten metal 1 in the solidification process. It is a process of giving.

  The upper die 2 is an embodiment of a vibrator in the coagulation method according to the present invention, and vibrates ultrasonically at a predetermined frequency. In the present embodiment, the upper mold 2 also serves as a movable mold (movable of the mold constituent members) forming the upper half of the mold 10 for molding the molten metal 1 into a predetermined shape.

As shown in FIG. 2, in the non-contact ultrasonic vibration step S100, first, the molten metal 1 is poured into the lower mold 3 which is a fixed mold constituting the lower half of the mold 10 and is subjected to a solidification process.
Here, “solidification process” means that (α) the temperature around the liquid (in this embodiment, the temperature of the lower mold 3) is kept at a temperature below the solidification point of the liquid (or the crystallization temperature of the primary crystal). Or (β) A state in which the liquid can solidify after a predetermined time has elapsed by lowering (cooling) the ambient temperature of the liquid below the freezing point (in other words, driving to solidify the liquid) State where force is generated).

Next, the upper mold 2 is disposed at a position where the distance from the liquid surface of the molten metal 1 to the lower surface of the upper mold 2 is R, and this is ultrasonically vibrated at a frequency of 20 kHz, and the molten metal 1 is ultrasonically vibrated without contact. Is granted.
At this time, the output of the ultrasonic vibration of the upper mold 2 is about 20 kW, which is about one tenth of the output (about 200 kW) of the ultrasonic vibration in the conventional solidification method in which the vibrator is immersed in the molten metal.

As shown in FIG. 3, when ultrasonic vibration is applied to the molten metal 1, the region near the liquid surface of the molten metal 1 vibrates and air convection occurs between the liquid surface of the molten metal 1 and the upper mold 2. The liquid level is cooled. Therefore, a large number of crystal nuclei 1a, 1a,... Nucleate in the vicinity of the liquid surface of the molten metal 1 facing the upper mold 2. In addition, due to ultrasonic vibration applied to the molten metal 1, gentle forced convection is generated in the molten metal 1 from the liquid surface to the bottom.
As a result, a large number of crystal nuclei 1a, 1a,... Nucleated near the liquid surface of the molten metal 1 are transported to the bottom of the molten metal 1 by forced convection without remelting, and settle there.

When applying ultrasonic vibration in a non-contact manner, it is desirable to reduce the distance from the liquid surface to the vibrator as much as possible in consideration of the loss of vibration energy due to the medium. However, from the viewpoint of preventing deterioration of the vibrator due to radiant heat from the liquid surface of the molten metal and preventing the molten metal from splashing and adhering to the vibrator, the distance from the liquid surface to the vibrator should be increased. Is desirable.
In addition, since the vibrator has a predetermined area, not a point, and oscillates from the surface facing the liquid surface, resonance of ultrasonic vibration occurs, and depending on the distance from the liquid surface to the vibrator, Sonic vibration is amplified or canceled out.
Accordingly, the predetermined distance between the vibrator and the liquid surface in the non-contact ultrasonic vibration step is (1) a distance at which resonance of the ultrasonic vibration occurs and the ultrasonic vibration is amplified, and ( 2) It is desirable that the length be as short as possible within a range in which the influence of deterioration of the vibrator or the like can be suppressed.

  Here, the distance at which the resonance of the ultrasonic vibration occurs and the ultrasonic vibration is amplified is referred to as “nth peak distance (n: positive integer)”. The n-th peak distance Rn is expressed by Rn = (n / 2) × λ using the ultrasonic wavelength λ.

In the present embodiment, the ultrasonic vibration frequency of the upper mold 2 is 20 kHz and the sound velocity is about 320 m / sec, so that the wavelength λ = (320 × 10 ³ ) / (20 × 10 ³ ) = 16 [mm]. is there.
Therefore, the first peak distance R1 in this embodiment is 8 mm, and the second peak distance R2 is 16 mm.

However, in this embodiment, when the distance R between the upper mold 2 (the lower surface thereof) and the liquid level of the molten metal 1 is 8 mm which is the first peak distance, the nucleation is promoted near the liquid level of the molten metal 1. When the second peak distance was set to 16 mm, the effect of promoting nucleation in the vicinity of the liquid surface of the molten metal 1 was noticeable.
Therefore, it is desirable from the viewpoint of miniaturization of the solidified structure that the distance R between the upper mold 2 (the lower surface thereof) and the liquid surface of the molten metal 1 is the second peak distance (16 mm).
The reason why the effect of promoting nucleation was not so much observed at the first peak distance may be that resonance is less likely to occur if the distance is short because of the high straightness of ultrasonic waves.

As shown in FIG. 4, when a predetermined time has elapsed since the start of application of ultrasonic vibration to the molten metal 1, a solidified portion 1 b is formed on the liquid surface of the molten metal 1. In the solidified portion 1b, a large number of crystal nuclei 1a, 1a,... Generated inside the molten metal 1 are collected and solidified on the liquid surface to be in a solid state or a semi-molten state.
If the coagulation | solidification part 1b is formed, non-contact ultrasonic vibration process S100 will be complete | finished and it will transfer to contact ultrasonic vibration process S200.

  In this embodiment, the frequency of ultrasonic vibration of the upper mold 2 in the non-contact ultrasonic vibration step S100 is 20 kHz. However, the solidification method according to the present invention is not limited to this, for example, the type (composition) of the liquid, the liquid The frequency of the vibrator can be appropriately selected according to various conditions such as the amount, the temperature of the liquid, the viscosity of the liquid, and the shape of the container filled with the liquid.

The vibration direction of the upper mold 2 is a vertical direction, that is, a direction substantially perpendicular to the liquid surface of the molten metal 1.
With this configuration, it is possible to apply ultrasonic vibration to the liquid more efficiently than when the vibrator vibrates in a direction substantially parallel to the liquid surface, and thus nucleation of crystal nuclei in the liquid. It is possible to refine the solidified structure by promoting the above.

  As shown in FIGS. 1 and 5, the contact ultrasonic vibration step S <b> 200 is a step of applying ultrasonic vibration to the molten metal 1 by the upper mold 2 in contact with the solidified portion 1 b formed on the liquid surface of the molten metal 1 in the solidification process. is there.

In the contact ultrasonic vibration step S200, first, the upper mold 2 is lowered and brought into contact with the solidified portion 1b.
At this time, even if (1) the non-contact ultrasonic vibration step S100 is completed, the ultrasonic vibration of the upper mold 2 is once stopped, and the ultrasonic vibration is resumed after the upper mold 2 is brought into contact with the solidified portion 1b. The (2) ultrasonic vibration of the upper mold 2 may be continued during the transition from the non-contact ultrasonic vibration step S100 to the contact ultrasonic vibration step S200.

As shown in FIG. 5, when the upper mold 2 is ultrasonically vibrated in a direction substantially perpendicular to the liquid surface while the upper mold 2 is in contact with the solidified portion 1b, ultrasonic vibration is imparted to the molten metal 1 through the solidified portion 1b. Is done.
As a result, a larger number of crystal nuclei 1a, 1a,... Are generated in the region near the solidified portion 1b, and a solidified structure composed of fine crystal grains starts to be formed in the region near the solidified portion 1b.
Further, nucleation of a large number of crystal nuclei 1a, 1a... In the region near the solidified part 1b and forced convection from the liquid surface to the bottom are maintained, and the crystal nuclei 1a. 1a... Rides on forced convection and is transported to the bottom of the molten metal 1 and settles there. Then, the crystal nuclei 1a, 1a,..., Settled on the bottom of the molten metal 1 grow and a solidified structure composed of fine crystal grains begins to be formed at the bottom of the lower mold 3 as well.
In this way, in the contact ultrasonic vibration step S200, a solidified structure composed of fine crystal grains is formed from the upper part (near the liquid surface) and the lower part (bottom part) of the molten metal 1, so that the ambient temperature of the molten metal 1 is not much. If not low (the driving force for solidification is not so great), all of the molten metal 1 is occupied by a solidified structure composed of equiaxed fine crystal grains before the dendrite structure is formed.

  Further, in the contact ultrasonic vibration step S200, the upper mold 2 is in contact with the solidified part 1b in a solid state or semi-molten state, but not in contact with the molten metal 1. Therefore, the upper mold | type 2 is eroded by contact with the molten metal 1, and it prevents that it wears out (or suppresses significantly).

  Even after the solidified part 1b is generated, the ultrasonic wave is not transferred to the contact ultrasonic vibration step S200, and the upper mold 2 is ultrasonically separated from the solidified part 1b without contacting the upper mold 2 with the solidified part 1b. When vibrated, the upper mold 2 can be prevented from being worn, but cannot be efficiently applied to the molten metal 1 through the solidified portion 1b, and subsequent nucleation of the crystal nuclei 1a, 1a,. The Rukoto.

In the case of the present embodiment, the ultrasonic vibration is applied to the molten metal 1 and the molten metal 1 is pressurized by pushing the upper mold 2 downward into the opening on the upper surface of the lower mold 3 in the contact ultrasonic vibration step S200. .
And all the molten metal 1 solidifies by cooling the circumference | surroundings of the molten metal 1 holding the state to which the ultrasonic vibration was provided while being pressurized.

By applying pressure, it is possible to more efficiently apply ultrasonic vibration to the molten metal 1 that has not solidified in the substantially central portion of the mold 10 and promote nucleation of the crystal nuclei 1a, 1a,. is there.
As a result, as shown in FIG. 6, an ingot 4 having a predetermined shape corresponding to the mold 10 and having a solidified structure made of equiaxed fine crystal grains of about several tens of μm from the surface to the inside is obtained. .
The solidified structure of the ingot 4 consists of equiaxed crystals from the surface to the inside, and its Vickers hardness is HV68. In contrast, the solidified structure of an ingot obtained by a conventional solidification method (ingot obtained by cooling alone without using ultrasonic vibration at all) develops a dendrite structure near the surface, and the crystal grains are coarse overall. (About 100 μm) and Vickers hardness is HV57, which is lower than that of the present example.

  Depending on the type of molten metal and the shape (size) of the inside of the container (mold), the liquid may be solidified at normal pressure without pressurizing the liquid in the contact ultrasonic vibration step.

  In the present embodiment, the upper mold 2 serves as a part of the mold 10 which is a container for filling the molten metal 1. However, the present invention is not limited to this, and the container filled with the liquid and the vibrator are separated. But it ’s okay.

  In this embodiment, only the upper die 2 (upper die) is ultrasonically vibrated in the contact ultrasonic vibration step S200. However, the present invention is not limited to this, and the lower die is also superposed in the contact ultrasonic vibration step. A configuration in which sound waves are vibrated may be used.

  In this embodiment, both the non-contact ultrasonic vibration step S100 and the contact ultrasonic vibration step S200 are configured to apply ultrasonic vibration by the same upper mold 2, but the present invention is not limited to this, and each step is performed. It is good also as a structure which provides ultrasonic vibration using a respectively different vibrator | oscillator.

In this embodiment, the frequency of ultrasonic vibration is set to 20 kHz in both the non-contact ultrasonic vibration step S100 and the contact ultrasonic vibration step S200. However, the present invention is not limited to this, and ultrasonic waves having different frequencies for each process. It is good also as a structure which provides a vibration.
From the viewpoint of preventing the vibrator from being deteriorated by radiant heat from the molten metal in the non-contact ultrasonic vibration process, resonance of the ultrasonic vibration occurs by making the frequency of the ultrasonic vibration of the vibrator as low as possible. Although it is desirable to increase the distance at which the ultrasonic vibration is amplified (distance that becomes the n-th peak), there is a problem that if the frequency is too low, it overlaps with the human audible range and the surrounding work environment deteriorates. Therefore, the lower limit of the ultrasonic vibration frequency of the vibrator is desirably about 15 kHz.

  In the present embodiment, the amplitude (vibration energy) of the ultrasonic vibration is the same in both the non-contact ultrasonic vibration step S100 and the contact ultrasonic vibration step S200, but the present invention is not limited to this, and is different for each step. It is good also as a structure which provides the ultrasonic vibration of an amplitude.

  In addition, the main purpose of the present invention is to uniformly refine all of the solidified tissue, but the amplitude of ultrasonic vibration and ultrasonic vibration in the non-contact ultrasonic vibration process and the contact ultrasonic vibration process are reduced. It is also possible to control the solidified tissue by appropriately adjusting the application time, ambient temperature, and the like. For example, the average crystal grain size of the solidified structure is changed between the upper part and the lower part of the ingot, the lower part is a solidified structure composed of equiaxed crystals, and the upper part is a dendrite structure.

The flowchart which shows one Embodiment of the solidification method of the molten metal which concerns on this invention. The side surface cross-sectional schematic diagram which shows the initial stage of the non-contact ultrasonic vibration process of one Embodiment of the solidification method of the molten metal which concerns on this invention. The side surface cross-sectional schematic diagram which shows the intermediate stage of the non-contact ultrasonic vibration process of one Embodiment of the solidification method of the molten metal which concerns on this invention. The side surface cross-sectional schematic diagram which shows the final stage of the non-contact ultrasonic vibration process of one Embodiment of the solidification method of the molten metal which concerns on this invention. The side surface cross-sectional schematic diagram which shows the initial stage of the contact ultrasonic vibration process of one Embodiment of the solidification method of the molten metal which concerns on this invention. The side surface cross-sectional schematic diagram which shows the final stage of the contact ultrasonic vibration process of one Embodiment of the solidification method of the molten metal which concerns on this invention.

1 Molten metal (liquid)
1a Crystal nucleus 1b Solidification part 2 Upper mold (vibrator)

Claims (4)

A non-contact ultrasonic vibration step for applying ultrasonic vibration to the liquid by a vibrator arranged at a predetermined distance from the liquid surface of the liquid in the solidification process;
A contact ultrasonic vibration step of applying ultrasonic vibration to the liquid by a vibrator that is in contact with the solidified portion formed on the liquid surface of the liquid in the solidification process but not in contact with the molten metal ;
A coagulation method comprising:   2. The molten metal solidification method according to claim 1, wherein the predetermined distance in the non-contact ultrasonic vibration step is a second peak distance at which resonance of ultrasonic vibration occurs.   The coagulation method according to claim 1 or 2, wherein a vibration direction of the vibrator is a direction substantially perpendicular to a liquid surface.   The coagulation method according to any one of claims 1 to 3, wherein the liquid is pressurized in the contact ultrasonic vibration step.

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