EP3638438B1

EP3638438B1 - Die casting furnace system with ultrasonic unit for improved molten metal quality

Info

Publication number: EP3638438B1
Application number: EP18818914.6A
Authority: EP
Inventors: Randy S. BEALS
Original assignee: Magna International Inc
Current assignee: Magna International Inc
Priority date: 2017-06-16
Filing date: 2018-06-15
Publication date: 2022-01-19
Anticipated expiration: 2038-06-15
Also published as: EP3638438A4; WO2018232201A1; CN110769952A; US20200094315A1; EP3638438A1

Description

This PCT International Patent Application claims the benefit of U.S. Provisional Patent Application Serial No. 62/520,940 filed June 16, 2017 entitled "Die Casting Dosing Furnace With Ultrasonic Degassing System For Improved Aluminum Molten Metal Quality".

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates generally to a system and method for an improved quality of molten metal in a die casting holding furnace unit.

2. Related Art

This section provides background information related to the present disclosure that is not necessarily prior art.
Traditional dosing furnaces are closed holding furnaces with a spout for direct metal (e.g., liquid or molten metal) delivery into a cold chamber die casting machine. Traditional dosing furnaces are designed so the entire furnace has to pressurize for each cycle of the machine. When the metal level in the dosing furnace is pressurized, all of the metal in the dosing furnace physically moves upward. After a shot, the dosing furnace is depressurized and the metal returns to a lowest level. This type of oscillation can generate dross, sludge, oxides, etc. In addition, current dosing furnaces use porous plugs at the bottom of the dosing unit in order to degas or remove hydrogen from the metal (e.g., aluminum). A successful introduction of a rotary degassing unit inside a pressurized dosing furnace has not been achieved because this would cause issues with pressure tightness of the dosing furnace itself and introduce turbulence such as dross, oxides, etc. Attempts have been made to use ultrasonic degassing for small holding furnaces; however, the volume of metal in conventional dosing furnaces is too large for the ultrasonic degassing vibration / wave to be effective. Further relevant Prior Art is described in JP 2007 313 554 A , US 2017/ 056 971 A1 , US 5 913 358 A , WO 2016/ 071 613 A1 and US 2013/ 112 042 A1 . In particular, JP 2007 313 554 A describes a die casting furnace system comprising a die casting holding furnace unit having a cavity for holding a molten metal and a dosing unit.

SUMMARY OF THE INVENTION

This section provides a general summary of the present disclosure and is not a comprehensive disclosure of its full scope, which is defined in the appended claims, or all of its features, aspects, and objectives. In particular, it is provided a die casting furnace system having the features defined in claim 1. Further preferred embodiments are defined in the dependent claims.
A die casting furnace system includes a die casting holding furnace unit defining a cavity for holding a molten metal. The die casting furnace system also includes a dosing unit disposed or positioned within the cavity and defining a dosing area disposed in fluid communication with the cavity for receiving the molten material during a pressurization of the cavity. An ultrasonic unit is operably coupled with the dosing area and is configured to introduce a vibration into the received molten material for facilitating the removal of gases from the received molten material prior to the molten material traveling into a die casting machine.
By utilizing the die casting furnace system with a small dosing unit disposed inside of the die casting holding furnace unit, the ultrasonic unit operates with the optimum volume of molten metal (such as aluminum) in order to allow for the highest possible metal quality directly before the molten metal is introduced into the die casting machine. The present system also obtains the best combination of metal cleanliness and accuracy in a die casting furnace system by using the combination of ultrasonic unit with a dosing unit disposed within a cavity of the die casting furnace unit. The ultrasonic unit thus provides a large improvement in the melt quality of metal. In fact, as will be explained in more detail below, compared to Argon (Ar) rotary degassing and other systems, the amount of dross and/or hydrogen is reduced more than five times. Accordingly, the combination of a finitely sized dosing unit in combination with the ultrasonic unit advantageously provides for a lower hydrogen content, higher density, lower porosity number, and higher tensile properties of the treated molten metal relative to the prior art systems.
These and other objects, features and advantages of the present invention will become more apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Figure 1 is a cross-sectional side view of a die casting holding furnace system including a dosing unit illustrated during a refilling cycle;
Figure 2 is a cross-sectional side view of the die casting holding furnace system illustrating a dosing cycle;
Figure 3A is a cross-sectional side view of the die casting holding furnace system illustrating an ultrasonic unit operably coupled with the dosing unit;
Figure 3B is a magnified view of a portion of Figure 3A illustrating a probe of the ultrasonic unit positioned within a molten metal in the dosing unit for introducing a degassing agent and generating cavitation bubbles;
Figure 4 is a cross-sectional side view of the die casting holding furnace system illustrating an automatic grain refining unit operably coupled with the dosing unit;
Figure 5A is a cross-sectional side view of the die casting holding furnace system illustrating an automated feed unit for a metal matrix composite (MMC) operably coupled with the ultrasonic unit; and
Figure 5B is a magnified view of a portion of Figure 5A illustrating the probe of the ultrasonic unit positioned within the molten metal for introducing the degassing agent as well as ceramic particles received from the automated feed unit.

DETAILED DESCRIPTION OF THE ENABLING EMBODIMENTS

Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a die casting holding furnace system 100, known as a dual chamber furnace, is generally illustrated in Figures 1-5. The die casting holding furnace system 100 includes a die casting holding furnace unit 102 defining a cavity 103 having a first storage capacity for holding a molten metal or molten material 104. The molten metal 104 may include aluminum, Al-Si-Mg alloy (300 series aluminum), or other metal or alloys. Furnace unit 102 is a closed holding furnace with a launder system to a die casting machine shot sleeve 106 for dispensing molten metal 106 from the die casting holding furnace unit 102 through the shot sleeve 104 to a die casting machine 108.
A dosing unit 110 is disposed or positioned within the cavity 103 and defines a dosing area 112 disposed in fluid communication with the cavity 103 for receiving the molten metal 104 during a refilling cycle. For example, Figure 1 illustrates the die casting holding furnace system 100 during this refilling cycle, in which a pressure, such as 60 millibars (mbar), is reduced or removed from being applied to the dosing area 112, causing the dosing area 112 to be filled with molten metal 104. In other words, during the refilling cycle, positive pressure inside of the die casting furnace unit 102 increases the level of molten metal 104 inside of the dosing unit 110 until the molten metal 104 reaches a specific level or range of levels. As illustrated in the Figures, the dosing area 112 defined by the dosing unit 110 has a second storage capacity that is smaller than the first storage capacity of the cavity 103 of the die casting furnace unit 102. As will be explained in more detail below, this smaller or finite size of dosing area 112 relative to the cavity 103 of the die casting furnace unit 102 provides for optimized processing of the molten metal 104 received during the refilling cycle before its introduction into the die casting machine 108.
As further illustrated in Figure 1, the dosing area 112 has an inlet 113 disposed in fluid communication with the cavity 103 for receiving the molten metal 104 from the die casting holding furnace unit 102 and an outlet 114 disposed in fluid communication with the shot sleeve 106. A check valve 115, such as a one-way ball valve, is disposed in the inlet 113 for allowing molten metal 104 to pass through the inlet 113 during the refilling cycle while preventing the molten metal 104 from returning to the cavity 103 once received within the dosing area 112.
Figure 2 illustrates the die casting holding furnace system 100 during a dosing cycle. The dosing cycle begins with a positive pressure produced inside the dosing unit 110, such as reapplication of the 60 mbar described above, so that the check valve 115 is closed and the molten metal 104 is discharged through the shot sleeve 106 and into the die casting machine 108. When a specific quantity of molten metal 104 is transported into the die casting machine 108, the dosing process terminates by reducing or relieving the pressure applied to the dosing unit 110. The specific quantity of molten metal 104 may be a predetermined amount. When the dosing cycle is finished, the level of molten metal 104 in the dosing unit 110 is at a lower level than the level of molten metal 104 before the dosing cycle began. After the dosing cycle is finished, the die casting holding furnace system 100 is ready for the refilling cycle to begin. As shown in Figure 1, the refilling cycle operates until the level of molten metal 104 within the dosing area 112 again returns to the specified level and the die casting holding furnace system 100 is ready for another dosing cycle to begin.
As best illustrated in Figure 3A, the die casting holding furnace system 100 includes an ultrasonic unit 116 operably coupled with the dosing area 112 and configured to introduce a vibration into the molten metal 104 received within the dosing area 112 after a refilling cycle. As will be explained in more detail below, the ultrasonic unit 116 facilitates the removal of gases from the received molten metal 104 prior to being dispensed to the shot sleeve 106. The ultrasonic unit 116 includes a probe 117 attached to the holding furnace unit 102 and extending downwardly to be positioned within the molten metal 104 disposed or received in the dosing area 112. The probe 117 is configured to generate the vibration, and additionally provide a degassing agent 118 within the dosing area 112 to interact with the molten metal 104 prior to the molten metal 104 traveling into the die casting machine 108. The degassing agent 118 functions to remove gases, such as hydrogen, from the molten metal 104 to provide a purification of the molten metal 104 entering the die casting machine 108. As discussed previously, the dosing area 110 has a defined or finite storage capacity that is smaller than the cavity 103 of the holding furnace unit 102. Accordingly, the ultrasonic unit 114 in combination with this finite storage capacity of the dosing area 112 provides for improved purification of the molten metal 104 because the ultrasonic unit is only treating molten metal 104 disposed within the dosing unit 110, and thus is more appropriately sized to efficiently and effectively degas the molten metal 104.
As best illustrated in Figure 3B, the degassing agent includes both carrier gas 120 and cavitation bubbles 122 that are introduced into the molten metal 104 by the probe 117. Cavitation bubbles 122 can transport gases with them as they move throughout the molten metal 104, including to the surface of the molten metal 104. However, without any assistance, the cavitation bubbles 122 may collapse before reaching the surface. Thus, the carrier gas 120 can used to transport the cavitation bubbles 122 and dissolved gasses throughout the molten metal 104. The high-intensity ultrasonic vibration generated from the probe 117 of the ultrasonic unit 114 breaks up the carrier gas 120 bubbles as well as creates large numbers of cavitation bubbles 122. The carrier gas 120 bubbles can survive in the molten metal 104 because they do not dissolve in the molten metal 104. As the carrier gas 120 travels throughout the molten metal 104, the carrier gas 120 collects cavitation bubbles 122 containing dissolved gases and transports them uniformly throughout the molten metal 104, thereby improving degassing efficiency. In addition, the ultrasonic vibration also creates smaller degassing agent bubbles, which allows for more surface area while degassing the molten metal 104. After the ultrasonic unit 116 operates with the molten metal 104, the molten metal 104 travels through the die casting machine shot sleeve 106 toward and into the die casting machine 108.
To produce high quality aluminum alloy products, close control of the cast structure is required. An effective way to provide a fine and uniform as-cast grain structure is to add grain refiner 128, such as nucleating agents, to the molten metal 104 to control crystal formation during solidification. As best illustrated in Figure 4, the die casting holding furnace system 100 includes an automated grain refining unit 130 operably coupled with the dosing area 112 to introduce grain refiner 128 into the received molten metal 104. The grain refining unit 130 includes a wire rod 132 positioned in the dosing unit 110 as molten metal 104 refills the dosing area 112 to introduce the grain refiner 128. This step is performed between die cast machine (DCM) cycles. The grain refining unit 130 adds grain refiner 128 into the dosing unit 110 for direct contact with the molten metal 104. Grain refiner 128 can be a chemical, such as SiO₂ or TiB₂, added to the molten metal 104 or alloy to check grain growth.
As best illustrated in Figure 5A, the die casting holding furnace system 100 includes an automated metal matrix composite (MMC) feed unit 134 operably coupled with the ultrasonic unit 116 and configured to provide the ultrasonic unit 116 with ceramic particles 136. As best illustrated in Figure 5B, the ultrasonic unit 116 then releases both the degassing agent 118 and the ceramic particulates 136 into the molten metal 104 via the probe 117. The ceramic particles 136 feed directly into the ultrasonic wave for homogenous distribution throughout the molten metal 104. The ceramic particles 136 may comprise SiC, B₄C, nano alumina (Al₂O₃) decorated aluminum, or Si02 ceramic composite material or other suitable material.
The ultrasonic assist provided by the automated MMC feed unit 134 includes an electromagnetic pump 138 used for both Lorentz force stirring and Joule heating. As illustrated in Figure 5A, the electromagnetic pump 138 applies an alternating magnetic field (either single phase or multiphase) to a conductor to induce electric currents in the conductor, wherein the magnetic field acts as a nonintrusive stirring device, and passes electric currents through the conductor to produce heat. In other words, the electromagnetic pump 138 is a pump that moves molten metal 104 (i.e., liquid metal or any electrically conductive liquid) using electromagnetism. As molten metal 104 moves into the magnetic field, current passes through it, causing an electromagnetic force that moves the molten metal 104, together with the degassing agent 118 and ceramic particles 136. This prevents the ceramic particles 136 from settling in the molten Al-homogenous distribution prior to reaching the die casting machine 108.
As mentioned above, the ultrasonic vibration with degassing agent provided by the ultrasonic unit 116 in combination with the finite storage capacity of the dosing area 112 allows for a large improvement in the melt quality of the metal. For example, as established by Table 1 below, this combination accounts for a reduction of more than five times the amount of dross as compared to Argon rotary degassing. It also provides for a reduction in the amount of hydrogen as compared to other systems.

In more detail, Table 1 is a comparison of various properties of 250 kg of a degassed Al-Si-Mg alloy after different degassing methods are used on the alloy. For example, using ultrasonic degassing on 250 kg of an Al-Si-Mg alloy results in a molecular hydrogen content of 0.17 cm³/g, a density of 2.706 g/cm³, a porosity number of 1-2, and tensile properties of a Unified Thread Standard (UTS) of 245 MPa (force per unit area) and 5.1% El (elongation). As compared to the other degassing methods, using ultrasonic degassing is a more beneficial method because it results in a lower hydrogen content, higher density, lower porosity number, and higher tensile properties.

Table 1

Degassing Method	H₂ Content (cm³/100 g)	Density (g/cm³)	Porosity Number	Tensile Properties
Degassing Method	H₂ Content (cm³/100 g)	Density (g/cm³)	Porosity Number	UTS (MPa)	El (%)
Starting melt	0.35	2.660	4	200	3.8
Ultrasonic degassing	0.17	2.706	1-2	245	5.1
Vacuum degassing	0.20	2.681	1-2	228	4.2
Argon lancing	0.26	2.667	2-3	233	4.0

In one embodiment, a low-cost and more effective grain refiner 128, such as SiO₂, is introduced to the molten metal 104 via the dosing unit 110. The grain refiner SiO₂ is less expensive than a more commonly used TiB₂ master alloy and is more effective at grain refinement. In reference to Tables 2-5, a SiC and/or B₄C ceramic composite material is added to the small dosing until the material becomes an in-situ MMC. This composite can have improved strength and modulus. The composite, however, may have lower ductility.
Table 2 is a comparison of the density characteristics of the in-situ MMC as ceramic composite material is added to the small dosing. For example, as the amount of ceramic composite material is added, the density of the MMC increases (i.e., from 2.65 g/cm³ with none added to 2.82 g/cm³ with the ceramic composite material constituting 15% of the MMC).
Table 3 is a comparison of the hardness characteristics of the in-situ MMC as ceramic composite material is added to the small dosing. For example, as the amount of ceramic composite material is added, the hardness of the MMC increases (i.e., from 62 HBW with none added to 72 HBW with the ceramic composite material constituting 15% of the MMC).
Table 4 is a comparison of the tensile modulus characteristics of the in-situ MMC as ceramic composite material is added to the small dosing. For example, as the amount of ceramic composite material is added, the tensile modulus of the MMC increases (i.e., from 75 GPa with none added to 125.25 GPa with the ceramic composite material constituting 15% of the MMC).
Table 5 is a comparison of the tensile properties of the in-situ MMC as ceramic composite material is added to the small dosing. For example, as the amount of ceramic composite material is added, the force per unit area of the MMC increases (i.e., from 205 UTS with none added to 260 UTS with the ceramic composite material constituting 15% of the MMC) and the elongation of the MMC decreases (i.e., from 15% El with none added to 13% El with the ceramic composite material constituting 15% of the MMC).
The die casting holding furnace system 100 having the combination of the dosing unit 110 and the ultrasonic unit 116 as described in this disclosure has various beneficial results. One beneficial result is ultra clean molten metal 104, such as molten aluminum. Another benefit is its dosing accuracy within +/-1%. Furthermore, the dosing is accurate when the dosing area 112 is both being refilled with molten metal 104 and pressurized simultaneously. This is unlike conventional systems that have issues pressurizing the system due the proportional valve getting confused during the refilling, changing metal level of the furnace, etc. Another benefit is better temperature control of the dosing metal.
Yet another benefit is that the die casting holding furnace system 100 allows for small additions of grain refiner 128, for example TiB₂ and/or SiO₂, to be added directly to the molten metal 104, resulting in homogeneous distribution due to ultrasonic wave. The die casting holding furnace system 100 also allows for small additions of ceramic particulates 136 to be added directly to the molten metal 104, resulting in homogeneous distribution due to ultrasonic wave that creates an in-situ MMC material.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the invention, as defined in the appended claims.

Claims

A die casting furnace system (100), comprising:
a die casting holding furnace unit (102) defining a cavity (103) for holding a molten metal (104);

a dosing unit (110) disposed within said cavity (103) and defining a dosing area (112) disposed in fluid communication with said cavity (103) for receiving the molten metal (104) during a pressurization of said cavity (103); and

an ultrasonic unit (116) operably coupled with said dosing area (112) and configured to introduce vibration into the received molten metal (104) for facilitating the removal of gases from the received molten metal (104), wherein said ultrasonic unit (116) includes a probe (117) extending into said dosing area (112) to establish said operable coupling between said ultrasonic unit (116) and said dosing area (112) and additionally introduce a degassing agent into the received molten metal (104).
A die casting furnace system (100) as set forth in Claim 1, wherein said cavity (103) of said die casting holding furnace unit (102) has a first storage capacity and said dosing area (112) of said dosing unit (110) has a second storage capacity being less than said first storage capacity.
A die casting furnace system (100) as set forth in Claim 2, wherein said dosing area (112) has an inlet (113) disposed in fluid communication with said cavity (103) for receiving the molten metal (104) from said die casting holding furnace unit (102) and an outlet (114) disposed in fluid communication with a shot sleeve (106) for dispensing the molten metal (104) from said dosing unit (110) and into a die casting machine (108) after treatment with said degassing agent.
A die casting furnace system (100) as set forth in Claim 3, wherein said degassing agent includes a carrier gas and said probe (117) is configured to generate an ultrasonic vibration for breaking up said carrier gas and introducing a plurality of cavitation bubbles into the received molten metal (104).
A die casting furnace system (100) as set forth in Claim 4, further comprising an automated grain refining unit (130) operably coupled with said dosing area (112) to introduce grain refiner into the received molten metal (104).
A die casting furnace system (100) as set forth in Claim 5, wherein said automated grain refining unit (130) includes a wire rod (132) positioned within said dosing area (112) to establish said operable coupling between said automated grain refining unit (130) and said dosing area (112).
A die casting furnace system (100) as set forth in Claim 6, wherein said grain refiner includes at least one of SiO₂ or TiB₂.
A die casting furnace system (100) as set forth in Claim 4, further comprising:
an automated metal matrix composite feed unit (134) operably coupled with said ultrasonic unit (116) and configured to provide said ultrasonic unit (116) with ceramic particles; and

said probe (117) configured to introduce said ceramic particles into the received molten metal (104) along with said carrier gas and said cavitation bubbles.
A die casting furnace unit (100) as set forth in Claim 8, wherein said ceramic particles include at least one of SiC, B₄C, or nano alumina (Al₂O₃) decorated aluminum.
A die casting furnace unit (100) as set forth in Claim 8, further comprising an electromagnetic pump (138) operably coupled with said shot sleeve (106) for moving the molten metal (104) dispensed from said outlet (114) of said dosing area (112) through said shot sleeve (106) and preventing said ceramic particles from settling out of the dispensed molten metal (104) prior to reaching the die casting machine (108).
A die casting furnace unit (100) as set forth in Claim 10, wherein said electromagnetic pump (138) is configured to generate both Lorentz force stirring and Joule heating of the dispensed molten metal (104).
A die casting furnace unit (100) as set forth in Claim 3, wherein said inlet (113) of said dosing area (112) includes a check valve (115) for allowing molten metal (104) to pass through said inlet (113) during said pressurization of said cavity (103) of said die casting holding furnace unit (102) and preventing the molten metal (104) from returning to said cavity (102) once received within said dosing area (112).
A die casting furnace unit (100) as set forth in Claim 1, wherein said die casting holding furnace unit (100) is a closed holding furnace.
A die casting furnace unit (100) as set forth in Claim 1, wherein said probe (117) is secured to said die casting holding furnace unit (102) and extends downwardly into said dosing area (112).