SONOTRODE FOR PROCESSING OF LIQUID METALS AND A METHOD FOR PROCESSING OF LIQUID METALS

Abstract

An ultrasound sonotrode (101), the first end of which is adapted to be connected to a mechanical vibrations source, equipped with a working tip (105,205,405,805) at the opposite end of the sonotrode (101), equipped with a body (104) with a cooling jacket (103), sealed at the place of contact with the body (104) of the sonotrode (101) with the use of the first seal (106) and the second seal (107), characterized in that according to the invention the first seal (106) is placed at a distance less than or equal to 20 mm from the node of the standing wave excited in the sonotrode in the working conditions, and the second seal (107,207,407,507,607) is equipped with a resilient element (108,208,408,508,608) and is located at a distance less than or equal to 20 mm from the working tip (105,205 405,805). A method for metal alloying, in which the material is melted on the working tip (105, 205, 405, 805) of the sonotrode excited to mechanical vibrations, according to the invention characterized in that a sonotrode according to the invention is used.

Claims

1. Sonotrode (101), having a first end adapted to be connected to a mechanical vibrations source, and having a working tip (105,205,405,805) at the opposite end of the sonotrode (101), further having a body (104) with a cooling jacket (103), sealed with a first seal (106) and a second seal (107) at a place of contact with the body (104) of the sonotrode (101), characterized in that the first seal (106) is placed at a distance lower than or equal to 20 mm from the location of the node of a standing wave excited in the sonotrode in its working condition, and the second seal (107,207,407,507,607) is equipped with a resilient element (108,208,408,508,608) and is located at a distance less than or equal to 20 mm from the working tip (105,205,405,805).

2. Sonotrode according to claim 1, characterized in that the working tip is the working surface (205) of the body (104) of the sonotrode (101).

3. Sonotrode according to claim 1, characterized in that the working tip is an element (405, 805) detachably connected to the sonotrode.

4. Sonotrode according to any of claims from 1 to 3, characterized in that it is also equipped with an additional shield (510, 610) of the second seal (107,207,407,507,607).

5. Sonotrode according to any of claims from 1 to 4, characterized in that the second seal is a polymer seal (207) integrated with a metal resilient element (208).

6. Sonotrode according to any of the claims from 1 to 5, characterized in that the second seal is a diaphragm (407, 607) connected with the working tip.

7. Sonotrode according to claim 6 characterized in that the diaphragm is made of a material having thermal conductivity above 100 W/mK.

8. Sonotrode according to claim 7 characterized in that the diaphragm is made of a material with electrical conductivity above 20% IACS and has the diaphragm has stiffens lower or equal to 10 kN/mm in axial direction of the ultrasound system.

9. Sonotrode according to any of claims from 1 to 8, characterized in that the first seal is a elastomeric o-ring.

10. Sonotrode according to any of claims 1 to 9, characterized in that the body (104) is fitted with a resilient flange (712) near the first seal.

11. Method for metal processing in which the metal is melted on the working tip (105,205,405,805) of the sonotrode, excited to mechanically vibrate, characterized in that the sonotrode is a sonotrode as defined in any of claims from 1 to 10.

12. Method according to claim 11, characterized in that mechanical vibrations within the frequency range of 16 to 400 kHz are used.

13. A method according to the claim 11 or 12, characterized in that during the melting the sonotrode is placed in a vacuum chamber filled with argon.

14. A method according to any of the claims 11 to 13, characterized in that the melting is carried out with electrical current flow.

15. A method according to claim 14, characterized in that the diaphragm (407,607) is electrically conductive and the diaphragm (407,607) act as electric connector.

16. A method according to any of the claims 11 to 14, characterized in that the sonotrode cooling fluid is a fluid containing ethylene glycol.

17. A method according to any of the claims 11 to 14, characterized in that the sonotrode cooling fluid is a fluid containing oil mist.

Description

[0026] The subject of the present invention is shown in embodiments—

[0027] FIG. 1a shows an ultrasound system, a part of which is a sonotrode according to the invention with a transducer directly connected to the sonotrode, FIG. 1b shows an ultrasound system, a part of which is a sonotrode according to the invention with a transducer connected to the sonotrode through a waveguide,

[0028] FIG. 2a shows a sonotrode according to the first embodiment of the invention in a perspective, FIG. 2b shows a sonotrode according to the first embodiment of the invention in a longitudinal section,

[0029] FIG. 3 shows a magnification of second seal in the first embodiment,

[0030] FIG. 4a shows a sonotrode according to the second embodiment in a perspective, FIG. 4b shows a sonotrode according to the second embodiment in a longitudinal section,

[0031] FIG. 5 shows a magnification of the second seal in the second embodiment,

[0032] FIG. 6 shows a magnification of a variation of the second seal in the second embodiment,

[0033] FIG. 7a-c show a magnification of examples of sealing at the wave node,

[0034] FIG. 8 shows a sonotrode with the working tip during the liquid metal homogenization process.

[0035] Sonotrode 101 according to the invention may constitute a part of an ultrasound system for liquid metal homogenization, such as systems shown in FIG. 1a and FIG. 1b: Sonotrode 101 needs to be connected to an ultrasound source, e.g. transducer 102—directly or through a waveguide 102a. In the sonotrode body 104, a standing wave is excited. For this to be possible, body 104 dimensions in the working temperature and transducer 102 frequency should be compatible. The working tip 105 of the sonotrode 101, placed at the opposite side of the sonotrode from the transducer 102, is in direct contact with the liquid metal. The working tip 105 of the sonotrode vibrates due to the vibrations, which results in homogenization of the liquid alloy and ensuring equiaxial grain growth during crystallization.

[0036] During the process, the sonotrode requires cooling—it is therefore equipped with a cooling jacket 103, fitted with an inlet 109a and an outlet 109b of the cooling fluid. The cooling fluid can be a liquid or a gas-liquid colloidal system, e.g. oil mist. The use of an oil mist allows for the energy absorbed during oil evaporation to be used for cooling. Jacket 103 in contact with the body 104 is sealed with the first 106 and second 107 seal. The first seal 106 is placed near the node of the standing wave in the body, so the displacement of the body in relation to the first seal 106 is negligible. The second seal 107 is placed near the antinode of the standing wave in the sonotrode body 104, so it needs to be movable.

[0037] Sonotrode body 104 as described in the embodiment below is half-waved, which means that in the working temperature and working frequency 20 kHz on the length from the base 104a to the end of the working tip 105, half the length of the sound wave fits. Therefore, there is only one distance value from the base 104a along the axis of the body 104, which assures no ultrasound longitudinal vibrations occur during sonotrode excitation. This is the distance in which wave node is located. Base surface 104a and working tip 105 surface is located in wave antinodes of the standing wave excited in the body 104. An expert is capable of routinely manufacturing a system with a length which is a multiple of half the standing wave and having similar function. For example, in some cases, integration of sonotrode and waveguide in one element is justified.

[0038] A sonotrode according to the first embodiment of the invention is a working element of the ultrasound system containing at least one ultrasound generator and ultrasound transducer working in a nominal frequency of 20 kHz.

[0039] The sonotrode is shown in perspective in FIG. 2a and in section in FIG. 2b. A sonotrode according to the embodiment contains a sonotrode body 104, cooling jacket 103, the first seal 106 and a working tip, which is the upper surface 205 of the body 104, and the second seal 207.

[0040] The cooling jacket 103 is ensured on a part of the sonotrode body closer to the working tip 205 and sealed with the first polymer seal 106 on which the body is fitted from one side, and on the other side sealed with a second seal 207 with a resilient element 208 near the working surface 205 constituting a working tip of the sonotrode.

[0041] Maximum stress in the working sonotrode occurs in its middle at a length of λ/4 (¼ of standing wave length in the given material-wave node). The sonotrode is fatigue-stressed with a frequency corresponding to the frequency of the ultrasound system. Stress in the sonotrode decreases with distance from the wave node as per the sine function. This means that the sonotrode in the λ/2 direction has much lower fatigue strength requirements. Absolute maximum stress values at sonotrode λ/4 depend mainly on the amplitude and density of the material (Roúca et al. Ultrasonic horns optimization; International Congress on Ultrasonics 2009) and exceed 400 MPa at high amplifications. Fatigue strength of most construction materials decreases as the temperature rises. The decrease is particularly significant after of homologous temperature (the ratio of working temperature to melting temperature). For example, the Ti6Al4V (ASTM grade 5) alloy reaches fatigue strength up to 600 MPa, which drops to below 100 MPa at temperatures over 1073 K. Similarly, in the case of tungsten alloys (Desimet), which reach up to 400 MPa of fatigue strength, the value drops to below 20 MPa at 1573 K.

[0042] Therefore, despite the existence of materials with high static strength in high temperatures, fatigue strength in this range is the main limitation in the ultrasound process. So far, the effective temperature limit of ultrasound systems, regardless of the cooling system or isolation, was about 1000 K, i.e. not much higher than aluminum melting point. System operation above this limit requires the use of expensive ceramic materials, such as silicon nitride or the use of a continuous sonotrode cooling system.

[0043] Providing a cooling system closer to the working tip of the sonotrode has made it possible to decrease the temperature in the part of the sonotrode most susceptible to damage. This was obtained at the expense of working conditions of the seal closer to the working tip. This seal is located at the antinode of the standing wave in the sonotrode body, which causes unfavorable working conditions. An expert not familiar with the present invention would conceivably not consider such a solution exactly due to the complex problem of ensuring adequate sealing.

[0044] Sonotrode body 104 is made of materials with a high ratio of tensile modulus to density, high fatigue strength and low acoustic loss. Typically, materials used in the state of the art are titanium or aluminum alloys. Considering the fact that the sonotrode material conducts heat from the working surface to the cooling liquid, materials with high thermal conductivity are particularly suited for this application. An expert in ultrasound materials would also be able to suggest other materials depending on the characteristics of the processed medium, for example tungsten or copper alloys.

[0045] Sonotrode body 104 according to the embodiment is made of aluminum PA7A alloy and has a length of 136 mm in a temperature of 297 K. It has an axially symmetric shape, beginning and ending in cylindrical shape. In the working temperature and during the process, standing wave node is located 70 mm from the working surface 205.

[0046] In the embodiment, the sonotrode body 204 shape was designed to obtain a stepped sonotrode in order to amplify the vibration amplitude four times, which is determined by the ratio of the base 104a surface area to the working surface 205. A change in sonotrode profile between the first and the second cylindrical part is made in such a way as to ensure the edge to be rounded to a radius of 10 mm.

[0047] An expert is capable of routinely suggesting different sonotrode profile changes, e.g. a sonotrode with logarithmic amplification, sonotrode without an axis of symmetry or with additional ribbing, depending on the particular needs and the selected material. Changes in sonotrode profile have a negligible impact on the location of the wave node. However, tests have shown that sonotrode wave node in the range of useful frequencies is usually within the range of half the length of the sonotrode and half the length of the sonotrode enlarged by 20 mm.

[0048] The first seal 106 is located at 70 mm from the working tip of the sonotrode, in the standing wave node. Therefore, it is not exposed to longitudinal vibrations.

[0049] At half sonotrode body 104 length, at the location of minimal longitudinal vibrations in the wave node, the first cooling system seal is placed. Tests have shown that within a distance less than 20 mm from the node, the vibration amplitude is low enough for typical static sealants to be used. This observation is particularly significant due to the fact that the location of the wave node depends on the sonotrode body 104 profile, as well as the temperate and temperature distribution in the body of the sonotrode. In the embodiment, the second seal is an o-ring compressed by the water jacket flange. An elastomeric o-ring is compressed around the sonotrode, creating a closing of the cooling system between the jacket 103 and the body 104.

[0050] Sonotrode body 104, on the surface 104a in direct contact with a transducer or a waveguide has an internal thread for the system assembly. Due to the presence of the cooling jacket 103 in the part of the sonotrode closer to the working surface 205, the surface in direct contact with the transducer 104a is heated only through mechanical losses in the system. Therefore, typical ultrasound state-of-the-art methods may be used for joining the parts and the conservation of the coupling.

[0051] In the present embodiment, the second seal located next to the working surface 205 is a polymer seal 207, integrated with a resilient element 208 at the end of the jacket 103 and tightened on the end of the sonotrode body 104, as shown in detail in FIG. 3. This ensures the simplicity of the system in case low amplitude ultrasounds and low cooling liquid pressure are used. There are also other possible solutions for sealing near the working chamber, discussed below in subsequent embodiment.

[0052] In FIG. 4a and FIG. 4b a sonotrode according to the second embodiment with the working tip 405, screwed in the sonotrode body 104, connected to diaphragm 407 containing a diaphragm resilient element 508, as shown in FIG. 5. Diaphragm 407 is pressed against the sonotrode body 104 with the working tip 405. Additionally, as shown in FIG. 5, the sonotrode can be equipped with a shield 510 of the diaphragm 407 , protecting it from the sprayed material. An effective solution is to equip the jacket 103 with a plate and to use this plate to press the diaphragm 407 to the shield 510.

[0053] In an embodiment shown in FIGS. 4a and 4b, the sonotrode is equipped with a working tip screwed into the sonotrode body. The working tip may be made from the same material and a different material than the sonotrode body. In a preferable embodiment of the invention, the working tip is made from high-melting materials, such as tungsten or molybdenum alloys. The working tip can also act as an element pressing the seal against the sonotrode body, as shown in FIG. 5. After the working tip has undergone degradation, the diaphragm is also replaced, which ensures failure-free sealing. The mass of the working tip 405 preferably does not exceed 0.03 kg due to the system overload.

[0054] Diaphragm 407 could be made of various materials. In lower working temperatures, fluorinated technopolymer is recommended, e.g. Viton. In the case of higher temperatures, a metal diaphragm should be used, e.g. made of 316 steel. Preferably, the diaphragm is made of 0,5 mm thick Ampcoloy 95-copper based material with thermal conductivity above 100 W/mK and electrical conductivity above 20% IACS, and has a stiffness equal to or lower than 10 kN/mm in the axial direction of the ultrasound system. This allows for heat transfer from the working tip 405 to the cooling liquid to be increased. System sealing takes place directly at the place of contact of the working tip and the diaphragm. The use of an additional shield 510 is particularly recommended in higher working temperatures.

[0055] An alternative for the diaphragm 407 is the use of a stiff jacket seal 607, made from e.g. the same material as the body 104 and the cooling jacket and to ensure the presence of a flexible elastomer 608 between the seal and the end of the body 104, as shown in FIG. 6. After the additional shield 610 is used, the flexible elastomer 608 can be compressed between the seal 607 and the shield 610. The seal 607 constitutes a plate of the cooling jacket 103—in the present embodiment of the invention, the plate is 1 mm thick—the same as the other jacket walls. Compression is realized through a plate by cooling liquid pressure. Due to the low plate thickness, the system is flexible enough not to destroy the polymer seal in low ultrasound amplitude conditions, while simultaneously allowing for high cooling liquid pressure to be used.

[0056] Due to the interaction with the liquid material and the possibility of generation of additional ultrasound modes, vibrations in the body 104 of the sonotrode are not limited to the axial direction. Radial vibrations are also present. In such case, the location of the first seal. next to the node of the base mode does not assure the lack of displacement of the body in relation to the cooling, jacket. This may lead to excessive wear of the first seal and/or leaks due to mechanical overload.

[0057] Therefore, in the present embodiment the sonotrode was provided with an elastic flange 712, which isolates the rest of the system from sonotrode body 104 vibrations. The flange is shown in detail in FIG. 7a. Flange 712 may be an element of the monolithic body—FIG. 7a or may be pressed on the sonotrode body FIG. 7b.

[0058] If the radial vibrations are low, an ordinary seal 706c may be used, as shown in FIG. 7c.

[0059] The sonotrode and its components may be made from different materials depending on the processed material type and the processing temperature. An embodiment illustrating the working principle of the sonotrode according to the invention and a method for metal homogenization was described below in relation to FIG. 8.

[0060] Sonotrode according to the embodiment shown in FIG. 8 works in a vacuum chamber as a component of ultrasound-assisted system for plasma melting of metals. A chamber according to the example is pumped out four times to an absolute pressure of 20 mbar, and then filled with 5.0 purity argon to an absolute pressure of 1200 mbar.

[0061] The body of the sonotrode 104 ensures amplitude amplification of 1:4 and is made of Grade 5 titanium alloy (Ti6Al4V). Is equipped with a thread 811.

[0062] The sonotrode is equipped with a working tip 805 made of technical grade tungsten. The working tip has a mass of 20 g and is made in the form of a M8 screw with a hexagonal head and a semicircular recess.

[0063] Working frequency in the temperature of 297 K of the sonotrode with the working tip was 20200 Hz. Working frequency is overstated due to thermal expansion of the sonotrode material in the working conditions. Between the working tip 805 and the body 104 of the sonotrode, a diaphragm 507 is placed, with a thickness of 0.8 mm made of Glidcop 60 material and containing a flexible part 508. Above the diaphragm, a diaphragm shield 510, made of 316 steel is placed. Diaphragm separates the cooling liquid 812 from the vacuum chamber.

[0064] In the present example, the cooling liquid is a mixture of ethylene glycol and water in 20:80 proportions, with a temperature of 15 degrees centigrade and liquid expenditure of 5 l/min. The addition of glycol restricts cavitation in the liquid and limits ultrasound power losses. Diaphragm 507 is sealed directly through pressing the working element 805 to the body 104 of the sonotrode and directly on the body of the cooling jacket.

[0065] Liquid metal 813 is melted via a plasma arc 815, sustained between a tungsten electrode 814 and the working element 805 and diaphragm 507, which simultaneously constitutes a connector electrode of the ultrasound system to the system sustaining arc discharge. In the example it is assumed to use direct current of 100 A applied for 30 s until a 3 g sample of Ti7Al6Nb alloy is melted. Amplitude at the working tip is 10 micrometers.

[0066] After the sample is melted, the plasma arc 815 is extinguished and the alloy melts with a simultaneous influence of the ultrasounds. This allows the prevention of dendritic structure forming and to obtain microstructure similar to recrystallized materials, i.e. equiaxial grains.

[0067] Person skilled in the art having learned the teachings of the description above will be able to suggest other materials and mechanical solutions for the seals, while maintaining the essence of the invention, which is to begin cooling of the sonotrode near the working tip or even at the very working tip location. An expert would easily notice that the proposed methods of embodiment of the first seal can be used for virtually every single described examples of embodiment of the invention.

[0068] An expert would be easily able to scale the sonotrode as per the embodiment to a different working frequency, as well as to suggest mechanical vibration sources, particularly ultrasounds.