Patent Application
20230201917
The present disclosure relates to an electromagnetic vibration stirring device of semi-solid high pressure casting equipment and, more particularly, to an electromagnetic vibration stirring device of semi-solid high pressure casting equipment, the electromagnetic vibration stirring device being capable of controlling the structure of a semi-solid molten metal by applying electromagnetic vibration to the semi-solid molten metal.
Rheocasting is a process of producing a billet or a molded product from a semi-solid metal having a predetermined viscosity through casting or forging. The semi-solid metal is in a state in which a liquid phase and spherical solid particles coexist in an appropriate ratio in a semi-solid temperature range. Therefore, the semi-solid metal can change its shape even by a small force due to its thixotropic properties and can be easily cast like a liquid due to its high fluidity.
Semi-solid metals generally have fluidity at a lower temperature than molten metal, so that the temperature of a casting device can be lowered compared to the molten metal, thereby ensuring a prolonged lifespan of the device. In addition, when a semi-solid metal is extruded, turbulence is less likely to occur compared to a liquid state, so that the amount of air introduced during casting can be reduced. Furthermore, the use of semi-solid metals leads to reduced solidification shrinkage, improved workability, and lightweight products. Therefore, the semi-solid metals can be used in the field of advanced material forming technology, for example, in the field of materials for major lightweight aluminum parts of vehicles.
High pressure casting, which is one of the casting processes that can use semi-solid metals as casting materials, refers to a process in which a molten metal is forced into a mold, which has a hollow cavity of predetermined shape, and pressurized until solidification. In some cases, the structure of the molten metal in a semi-solid state is controlled by generating an electromagnetic field inside the molten metal through electromagnetic stirring.
With regard to high pressure casting using an electromagnetic stirring means, a technique has been developed to find a generation pattern of an electromagnetic field and an optimum stirring condition of a molten metal. However, when a magnetic field of about 100 Gauss is generated in an electromagnet of the electromagnetic stirring means, a coil may be disconnected due to overheating. Also, an impact on upper and lower molds of a high pressure casting device may be delivered to the electromagnetic stirring means, causing an error in the operation of the electromagnetic stirring means. This may lead to a problem in magnetic field formation. In addition, as the molten metal in a sleeve is rotated by the magnetic field, turbulence may be generated inside the molten metal. This turbulence may cause air to be introduced into the molten metal, resulting in a deterioration of the quality of castings.
An objective of the present disclosure is to provide an electromagnetic vibrating stirring device of semi-solid high pressure casting equipment, the electromagnetic vibrating stirring device having a magnetic field generating unit capable of suppressing overheating of an electromagnet to prevent disconnection of a coil due to overheating.
Another objective of the present disclosure is to provide an electromagnetic vibrating stirring device of semi-solid high pressure casting equipment, the electromagnetic vibrating stirring device being capable of controlling the structure of a semi-solid molten metal by applying periodic vibrations to the semi-solid molten metal.
Still another objective of the present disclosure is to provide an electromagnetic vibrating stirring device of semi-solid high pressure casting equipment, the electromagnetic vibrating stirring device having a magnetic field generating unit at a lower end or lower portion of a lower mold of the semi-solid high pressure casting equipment so that the magnetic field generating unit is protected against an impact on the mold.
The objectives of the present disclosure are not limited to the above-mentioned objectives, and other objectives not mentioned will be clearly understood by those skilled in the art to which the present disclosure belongs from the following description.
In order to accomplish the above objectives, the present disclosure provides an electromagnetic vibration stirring device of semi-solid high pressure casting equipment, the electromagnetic vibration stirring device including: a ring-shaped casing including an inner wall into which a sleeve is inserted and an outer wall spaced apart from the inner wall; and a magnetic field generating unit located between the inner wall and the outer wall of the casing, and including a plurality of electromagnets radially arranged at equal intervals around the sleeve in a circumferential direction of the sleeve, each of the electromagnets including a core and a coil surrounding the core. The magnetic field generating unit may generate a magnetic field by applying a current to the electromagnets in a clockwise or counterclockwise direction, and each portion of a semi-solid molten metal may be sequentially vibrated by the magnetic field along the circumferential direction of the sleeve, thereby controlling a microstructure of the molten metal.
The magnetic field generating unit may generate the magnetic field by applying the current to a pair of opposed electromagnets or a pair of non-adjacent electromagnets in the clockwise or counterclockwise direction.
The electromagnets of the magnetic field generating unit may be arranged such that the respective cores of the electromagnets are located perpendicular to a central axis of the sleeve.
The magnetic field generating unit may include a cooling channel formed in the coil of each of the electromagnets.
The magnetic field generating unit may generate a magnetic field of 500 to 1000 Gauss in a center region of the sleeve.
The respective cores of the electromagnets may be radially arranged at equal intervals of 60 degree angles on an inner surface of the outer wall of the casing, and the respective coils of the electromagnets may be coupled to the respective cores by insertion fitting.
The sleeve may be made of HK40 steel or ceramic.
The electromagnetic vibration stirring device may be located at a lower end or lower portion of a lower mold of the semi-solid high pressure casting equipment and may be coupled to a lower portion of the sleeve.
An electromagnetic vibration stirring device of semi-solid high pressure casting equipment according to the present disclosure has an advantage of suppressing overheating of an electromagnet through a cooling channel provided inside a coil of each electromagnet, thereby preventing disconnection of the coil due to overheating.
Another advantage is that it is possible to control the structure of a semi-solid molten metal by applying periodic vibrations to the semi-solid molten metal, thereby preventing formation of dendrites or destroying the dendrites. Still another advantage is that a magnetic field generating unit is located at a lower end or lower portion of a lower mold of the semi-solid high pressure casting equipment so that the magnetic field generating unit can be protected against an impact on the mold.
Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The embodiments are provided as example for those skilled in the art to be able to more clearly understand the spirit of the present disclosure. Accordingly, the present disclosure is not limited to the embodiments and may be achieved in other ways. Also, in the drawings, lengths, thicknesses, etc. of layers and regions may be exaggerated for convenient description. Throughout the drawings, the same reference numerals will refer to the same or like parts.
Referring to
After the molten metal A is injected into the sleeve 16 having a cylindrical hollow portion, the plunger 18 pressurizes the molten metal A injected into the sleeve 16 while moving inside the sleeve 16, causing the molten metal A to be forced into the mold. The molten metal A forced into a molding region between the upper mold 12 and the lower mold 14 is allowed to solidify for a predetermined period of time, and the casting operation is completed to produce a casting.
The electromagnetic vibration stirring device 100 of the semi-solid high pressure casting equipment 10 according to the embodiment of the present disclosure is coupled to an outer peripheral surface of the sleeve 16 and is configured to control the structure of a semi-solid molten metal A by applying electromagnetic vibration to the molten metal A to suppress the generation of dendrites.
In detail, the electromagnetic vibration stirring device 100 includes a casing 110 and the magnetic field generating unit 120. The casing 110 has a ring shape and includes an inner wall 112 into which the sleeve is inserted and an outer wall 114 spaced apart from the inner wall 112. In addition, to protect the magnetic field generating unit 120 located inside the casing 110 from outside, the casing 110 has a structure in which both upper and lower portions of the region between the inner wall 112 and the outer wall 114 are sealed. The casing 110 is made of a non-magnetic material so as not to interfere with a magnetic field generated by the magnetic field generating unit 120.
The magnetic field generating unit 120 is located between the inner wall 112 and the outer wall 114 of the casing 110, and includes a plurality of electromagnets 120 radially arranged at equal intervals around the sleeve 16 in a circumferential direction of the sleeve 16, each electromagnet 120 including a core 122 and a coil 124 surrounding the core 122. The magnetic field generating unit 120 generates a magnetic field by applying a current to the electromagnets 120 in a clockwise or counterclockwise direction. The magnetic field causes each portion of the semi-solid molten metal A to be sequentially vibrated by the magnetic field along the circumferential direction of the sleeve 16. When the magnetic flux of the magnetic field generated by the magnetic field generating unit 120 applies an impact to the inside of the molten metal A, a portion of the molten metal A is vibrated in a vertical direction, so that intermittent vibrational stirring in the vertical direction is achieved rather than rotational stirring. Therefore, without a rotational flow accompanied by turbulence with the semi-solid molten metal A, a vibrational flow accompanied by vibration of the molten metal A is generated, so that the microstructure of the semi-solid molten metal A is controlled by intermittent vibration of the molten metal A caused by the magnetic field impact. This prevents external air that may be introduced during rotational stirring by an electromagnetic field.
The magnetic field generating unit 120 generates a magnetic field by applying a current to a pair of opposed electromagnets or a pair of non-adjacent electromagnets in the clockwise or counterclockwise direction.
In detail, the magnetic field generating unit 120 generates a magnetic field sequentially in the circumferential direction by each pair of opposed electromagnets or each pair of non-adjacent electromagnets. For example, a pair of electromagnets 124-1 and 124-4, a pair of electromagnets 124-2 and 124-5, and a pair of electromagnets 124-3 and 124-6 generate respective magnetic fields by sequentially receiving a current in the counterclockwise direction. Alternatively, a pair of electromagnets 124-1 and 124-3, a pair of electromagnets 124-2 and 124-4, and a pair of electromagnets 124-3 and 124-5 generate respective magnetic fields by sequentially receiving a current in the counterclockwise direction.
Therefore, the structure of the semi-solid molten metal A in the sleeve 16 is controlled by periodically applying vibration to the molten metal A. In other words, by applying a current to each pair of opposed electromagnets of the magnetic field generating unit 120 in accordance with the sequence of (a), (b), and (c) of
Furthermore, when a current is applied to the opposed electromagnets or the non-adjacent electromagnets for less than 0.5 seconds, rotational stirring may occur. To prevent the occurrence of this rotational stirring, it is preferable that a magnetic field is generated by applying a current for equal to or more than 0.5 seconds. In this case, it is preferable that one cycle has a time period of less than 20 seconds to efficiently apply a uniform magnetic force to the entire molten metal A.
As described above, in the case of the casting method based on simultaneous application to the opposed or non-adjacent electromagnets of the plurality of electromagnets, a vibrational flow accompanied by vibration of the semi-solid molten metal A is achieved even when a magnetic field is generated, without a rotational flow accompanied by turbulence within the molten metal A. Therefore, the microstructure of the molten metal A is controlled by the vibration of the molten metal A caused by the magnetic field impact, thereby preventing external air that may be introduced during rotational stirring by the electromagnetic field. In addition, the amount of air contained in a billet is minimized and the generation and dispersion of nuclei are promoted, so that dendrite structures are refined and spheroidized, thereby minimizing the formation of internal voids. As a result, it is possible to produce a casting with a more stable quality compared to conventional microstructure control based on rotation.
Similar to the casting method based on simultaneous application to the opposed or non-adjacent electromagnets of the plurality of electromagnets, a current is periodically applied to three electromagnets 124-1, 124-3, and 124-5, a vibratory stirring effect may also be achieved.
The electromagnets of the magnetic field generating unit 120 are arranged such that the respective cores 122 of the electromagnets are located perpendicular to the central axis of the sleeve 16. In this case, the magnetic flux of the magnetic field generated by the magnetic field generating unit 120 and the sleeve 16 are located perpendicular to each other. Therefore, as an impact is applied to the molten metal A in the direction of the magnetic flux as illustrated in
The magnetic field generating unit 120 includes a cooling channel 124a formed in the coil 124 of each of the electromagnets. Therefore, cooling oil or cooling water flows directly along the inside of the coil 124, thereby reducing the heat generated by the coil 124 even in the presence of a large magnetic field of equal to or greater than 400 Gauss. As a result, a magnetic field is generated without disconnection of the coil 124, making it possible to continuously control the microstructure of the semi-solid molten metal A. The cooling channel 124a formed inside the coil 124 is connected to an external cooling channel 130 to continuously receive cooling oil or cooling water, and the cooling oil or cooling water heated by absorbing the heat of the coil 124 is discharged to outside through the external cooling channel 130.
In addition, the magnetic field generating unit 120 generates a magnetic field of 500 to 1000 Gauss with respect to a center region of the sleeve 16 and applies a magnetic field impact to the molten metal A located in the sleeve 16 to control the microstructure.
The magnetic field generating unit 120 includes the cores 122 radially arranged at equal intervals of 60 degree angles 110 on an inner surface of the outer wall 114 of the casing 110. The respective coils 124 are coupled to the respective cores 122 by insertion fitting. Therefore, the coils 124 are detached and replaced at the end of their lifespan, thereby reducing equipment replacement costs. For insertion fitting, each of the plurality of electromagnets has an open structure.
The sleeve 16 is made of HK40 steel or ceramic. The sleeve 16 made of a non-magnetic material such as HK40 steel or ceramic hardly absorbs a magnetic field even when a strong magnetic field is generated by the magnetic field generating unit 120 and minimizes a reaction such as vibration of the sleeve 16. Therefore, in the case of the sleeve 16 made of a non-magnetic material, the microstructure of the molten metal A in the sleeve 16 is controlled, while the sleeve 16 does not interfere with the strength of the magnetic field generated by the magnetic field generating unit 120. As a result, it is possible to produce a high-quality casting.
As illustrated in the section X of
Hereinafter, the electromagnetic vibration stirring device of the semi-solid high pressure casting equipment according to the present disclosure will be described with reference to the following experimental examples. However, the following experimental examples are only illustrative and are not intended to limit the scope of the present disclosure.
For a vibration stirring experiment for the electromagnetic vibration stirring device of the semi-solid high pressure casting equipment according to the present disclosure, a crucible was manufactured using SUS304. The crucible was manufactured to have an upper diameter of 120 mm, a lower diameter of 72.5 mm, and a height of 260 mm. To compare magnetic field intensities for respective positions on the crucible, as illustrated in
To measure a magnetic field strength as a function of a position on the crucible, currents of 20A, 40A, 60A, 80A, and 120A were applied to the magnetic field generating unit of the electromagnetic vibration stirring device according to the embodiment of the present disclosure.
After the magnetic field generating unit was placed on the outside of the crucible as illustrated in
In the same manner as in Experimental Example 1, a magnetic field was generated according to each current, after which a magnetic field strength as a function of a position on the crucible was measured. The measurement of the magnetic field strength was performed by applying each current to a pair of opposed electromagnets for 0.5 second and then to a next pair of opposed electromagnets located clockwise of the previous pair for 0.5 second.
The same procedure was performed as in Experimental Example 2, except that each current was applied to a pair of non-adjacent electromagnets in the counter clockwise direction.
The same procedure was performed as in Experimental Example 2, except that each current was applied to a pair of adjacent electromagnets in the counter clockwise direction.
In the same manner as in Experimental Example 1, a magnetic field was generated according to each current, after which a magnetic field strength as a function of a position on the crucible was measured. The measurement of the magnetic field strength was performed by sequentially applying each current to individual electromagnets in the counter clockwise direction.
In the same manner as in Experimental Example 1, a magnetic field was generated according to each current, after which a magnetic field strength as a function of a position on the crucible was measured. The measurement of the magnetic field strength was performed by randomly applying each current to individual electromagnets.
To compare magnetic field intensities in the presence or absence of the sleeve, each current was simultaneously applied to opposed electromagnets for 0.5 second both in the presence and in the absence of the sleeve made of HK40 steel. A magnetic field strength as a function of a position on the crucible was measured by periodically repeating the application of the current in the clockwise direction.
After placing the molten metal in the electromagnetic vibration stirring device according to the embodiment of the present disclosure, currents of 40A, 60A, 80A, and 120A were applied to the magnetic field generating unit in such a manner that each of the currents was simultaneously applied to opposed electromagnets for 0.5 second in the clockwise direction. A change in temperature per minute of the molten metal at the points α and β of
Referring to
In the case of the vertical axes X and Y, a magnetic field in the case of simultaneous application to opposed electromagnets was the largest, and a magnetic field in the case of simultaneous application to non-adjacent electromagnets was the second largest. In addition, a magnetic field in the case of simultaneous application was larger than that in the case of independent application. In the case of simultaneous application to adjacent electromagnets, the magnetic field was canceled, indicating that the magnetic field was reduced compared to other simultaneous application methods. However, in the case of the vertical axis Z, i.e., the edge region, a magnetic field in the case of simultaneous application to adjacent electromagnets was the largest. This may indicate that the effect of an electric field due to the current in two adjacent cores and coils was stronger than that of the magnetic field due to the magnetic flux. In the vicinity of the two adjacent cores, electromagnetic forces generated from the cores are combined. Therefore, in the case of simultaneous application to adjacent electromagnets, a strongest electromagnetic force is generated at the edge region where electromagnetic forces generated from the adjacent electromagnets are combined to form a larger force, while a weakest electromagnetic force is generated at the center region and ¼ regions.
The results of Experimental Example 7 are illustrated in Table 1 below.
As can be seen in Table 1, the sleeve made of a non-magnetic material had little influence on a magnetic field generated by the magnetic field generating unit. That is, the sleeve made of a non-magnetic material could transmit a magnetic field to the molten metal in the sleeve without causing a reduction in the magnetic field strength or a deformation of the magnetic field generated by the magnetic field generating unit.
Referring to
The point α illustrated in
The peripheral regions of the points α and β illustrated in
From all the results, when each pair of opposed electromagnets or each pair of non-adjacent electromagnets sequentially generated the magnetic field in the circumferential direction, or the magnetic field in the range of 500 to 1000 Gauss was generated, or the current in the range of 80 to 120 A was applied, an effective magnetic field could be generated at a relatively low current, the distribution in temperature of the molten metal could become uniform, and vibrational stirring of the semi-solid molten metal could be effectively performed.
While the present disclosure has been described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the technical idea and scope of the present disclosure and such changes and modifications belong to the claims of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2019-0064348 | May 2019 | KR | national |
This application is a Rule 53(b) Divisional of U.S. Application No. 17/595,959 filed Nov. 30, 2021, which is a National Stage of International Application No. PCT/KR2020/003579 filed Mar. 16, 2020, claiming priority based on Korean Patent Application No. 10-2019-0064348 filed May 31, 2019, the entire disclosures thereof are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17595959 | Nov 2021 | US |
| Child | 18115674 | US |
