Cathode filament, cathode assembly, magnetron and microwave cooking appliance

Abstract

The application discloses a cathode filament, a cathode assembly, a magnetron and a microwave cooking electric appliance. The cathode filament is used for the magnetron, the cathode filament is in a spiral structure, the cathode filament comprises two non-main emission areas and a main emission area, the two non-main emission areas are connected to two sides opposite to the main emission area along the length direction of the cathode filament, and the pitch of the non-main emission area is greater than the pitch of the main emission area. In the cathode filament, the pitch of the non-main emission area outside the main emission area is greater than the pitch of the main emission area, the stress of the non-main emission area can be more dispersed, the stress of the cathode filament at the non-main emission area can be effectively reduced, and the breaking resistance of the cathode filament after carbonization is improved.

Description

[0001] Priority information

[0002] This invention claims priority and benefit to patent application No. 202411750386.8, filed with the China National Intellectual Property Administration on November 29, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of household appliance technology, and in particular to a cathode filament, cathode assembly, magnetron, and microwave cooking appliance. Background Technology

[0004] In related technologies, the magnetron is the heart of a microwave oven, and the heart of the magnetron comes from the cathode assembly assembled from the magnetron filament. As we know from the current production process, after the filament is carbonized (filament process), the ability of the filament to emit electrons is greatly improved. However, the carbonized filament is also significantly more brittle. Vibrations during the production process and slight collisions with the microwave oven can cause the filament to break. Once the filament breaks, the entire magnetron will be open-circuited and unable to generate microwaves. Even worse, if the filament breakage is not detected in time, consumers will find that the microwave oven does not work when they use it for the first time, which affects the user experience. Summary of the Invention

[0005] The present invention provides a cathode filament, a cathode assembly, a magnetron, and a microwave cooking appliance to solve at least one of the aforementioned technical problems.

[0006] The present invention provides a cathode filament for a magnetron, wherein the cathode filament has a helical structure and includes two non-main emitting regions and a main emitting region. Along the length of the cathode filament, the two non-main emitting regions are respectively connected to the opposite sides of the main emitting region, and the pitch of the non-main emitting regions is greater than the pitch of the main emitting region.

[0007] In the aforementioned cathode filaments, the pitch of the non-main emission area located outside the main emission area is greater than that of the main emission area, which makes the stress in the non-main emission area more dispersed. This can effectively reduce the stress of the cathode filament in the non-main emission area and improve the fracture resistance of the cathode filament after carbonization.

[0008] In some implementations, the non-primary emitter region satisfies the following condition: d1 / N1 is 0.15 to 0.25, where d1 represents the pitch of the non-primary emitter region and N1 represents the number of turns of the non-primary emitter region.

[0009] In some implementations, the main transmitting region satisfies the following condition: d2 / N2 is 0.15 to 0.30, where d2 represents the pitch of the main transmitting region and N2 represents the number of turns of the main transmitting region.

[0010] In some embodiments, the cathode filament is made of a tungsten alloy.

[0011] In some embodiments, the length of the cathode filament is 12 ± 0.5 mm.

[0012] In some implementations, the length of each of the non-primary emission regions is 4 mm, and the length of the primary emission region is 4 mm.

[0013] In some embodiments, the cathode filament includes a filament core and a carbonized layer, the carbonized layer covering the filament core at least in the circumferential direction, the filament core being made of lanthanum-tungsten material, and the carbonized layer being a lanthanum-tungsten carbonized layer.

[0014] In some embodiments, the thickness of the carbonized layer is 6% to 10% of the thickness of the filament.

[0015] In some embodiments, the thickness of the carbonized layer is 8% of the thickness of the filament.

[0016] In some embodiments, the thickness of the carbonized layer is 42 μm, and the thickness of the filament is 0.5 mm.

[0017] In some embodiments, the cathode filament material further includes at least one of yttrium, rhenium, lutetium, zirconium, and hafnium.

[0018] In some embodiments, the grain size of the filament core ranges from 0.4 μm to 2 μm.

[0019] In some embodiments, the cathode filament is capable of emitting electrons after being powered on and after being powered off.

[0020] An embodiment of the present invention provides a cathode assembly for a magnetron, the cathode assembly comprising the cathode filament of any of the above embodiments.

[0021] In some embodiments, the cathode assembly includes a support with two end caps, one end of each of the two non-main emission regions being disposed within the two end caps.

[0022] The magnetron provided by the embodiments of the present invention includes the cathode assembly of any of the above embodiments.

[0023] The present invention provides a microwave cooking appliance including the magnetron described in the above embodiment.

[0024] In some embodiments, the cathode filament includes a filament core and a carbonized layer, the carbonized layer covering the filament core at least in the circumferential direction, the filament core being made of lanthanum-tungsten material, and the carbonized layer being a lanthanum-tungsten carbonized layer, and the cathode filament is capable of emitting electrons at a minimum output power of 100 watts in the microwave cooking appliance.

[0025] In the aforementioned cathode assembly, magnetron, and microwave cooking appliance, the pitch of the non-main emission area located outside the main emission area is greater than that of the main emission area. This makes the stress in the non-main emission area more dispersed, thereby effectively reducing the stress of the cathode filament in the non-main emission area, improving the fracture resistance of the cathode filament after carbonization, and thus improving the reliability of the cathode assembly, magnetron, and microwave cooking appliance.

[0026] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the cathode filament according to an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram showing the dimensions of the cathode filament according to an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the cathode assembly according to an embodiment of the present invention;

[0031] Figure 4 This is a cross-sectional schematic diagram of the magnetron according to an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram comparing the internal stress of the cathode filament of the present invention with that of the cathode filament of related technologies;

[0033] Figure 6 This is a schematic cross-sectional view of the cathode filament of an embodiment of the present invention;

[0034] Figure 7 This is a schematic diagram of the operation of the magnetron electrons according to an embodiment of the present invention;

[0035] Figure 8This is a metallographic cross-sectional view of the cathode filament material according to an embodiment of the present invention.

[0036] Figure 9 This is a partial schematic diagram of the metallographic cross-section of the cathode filament material according to an embodiment of the present invention.

[0037] Figure 10 This is a schematic diagram of the grain size distribution of the filament core of the cathode filament according to an embodiment of the present invention;

[0038] Figure 11 This is a schematic diagram of the grain morphology distribution of the filament core of the cathode filament according to an embodiment of the present invention.

[0039] Figure 12 This is a comparison diagram of the electron emission capabilities of the cathode filament in the embodiment of the present invention and the cathode filament in related technologies;

[0040] Figure 13 This is a circuit diagram of a frequency converter based on related technologies;

[0041] Figure 14 This is a schematic diagram illustrating the relationship between microwave output power and control current in related technologies;

[0042] Figure 15 This is a schematic diagram of the metal band structure in related technologies;

[0043] Figure 16 This is a schematic metallographic cross-section of the cathode filament material in a related technology.

[0044] Figure 17 This is a partial schematic diagram of the metallographic cross-section of the cathode filament material in the related technology.

[0045] Figure 18 This is a schematic diagram of the grain size distribution in the filament core of a cathode filament in a related technology.

[0046] Figure 19 This is a schematic diagram of the grain morphology distribution in the filament core of a cathode filament in a related technology.

[0047] Figure 20 This is a schematic diagram of the structure of a cathode filament in a related technology.

[0048] Explanation of key component reference numerals:

[0049] Cathode filament 100, magnetron 200, non-main emission area 12, main emission area 14, cathode assembly 102, bracket 16, connecting rod 18, cathode connector 20, end cap 22, anode assembly 24, anode cylinder 26, anode plate 28, interaction space 30, upper magnet 32, lower magnet 34, energy output window 36, filament 38, filament core 40, carbonization layer 42. Detailed Implementation

[0050] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0051] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0052] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection. They can refer to a mechanical connection or an electrical connection. They can refer to a direct connection or an indirect connection through an intermediate medium, and they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0053] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0054] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0055] Please refer to Figure 1 and Figure 4 The present invention provides a cathode filament 100 for use in a magnetron 200. The cathode filament 100 has a helical structure and includes two non-main emitting regions 12 and a main emitting region 14. Along the length of the cathode filament 100, the two non-main emitting regions 12 are respectively connected to opposite sides of the main emitting region 14, and the pitch of the non-main emitting regions 12 is greater than the pitch of the main emitting region 14.

[0056] In the aforementioned cathode filament 100, the pitch of the non-main emission region 12 located outside the main emission region 14 is greater than that of the main emission region 14, which makes the stress in the non-main emission region 12 more dispersed, thereby effectively reducing the stress of the cathode filament 100 in the non-main emission region 12 and improving the fracture resistance of the cathode filament 100 after carbonization.

[0057] Specifically, in Figure 1 The length direction of the cathode filament 100 is along the vertical direction. The cathode filament 100 can be used in the magnetron 200; please refer to... Figure 3 and Figure 4 The magnetron 200 includes a cathode assembly 102, which includes a bracket 16, connecting rods 18, and a cathode connector 20. The bracket 16 includes two end caps 22. One end of each of the two non-main emitting regions 12 is located within one of the two end caps 22. The cathode connector 20 is connected to the two end caps 22 via the two connecting rods 18. The cathode connector 20 can be connected to a power source, which can be provided by the filament windings of a transformer. Figure 3 As shown, when the power is turned on at the cathode connector 20, approximately 10A of current is supplied to the cathode filament 100 via the connecting rod 18. The cathode filament 100 spontaneously emits electrons under strong thermal resistance, which are then converted into microwaves by a high-voltage field and a high-magnetic field. Optionally, a slot is provided in the end cap 22, and one end of the non-main emission area 12 can be inserted into the slot, thereby effectively positioning the cathode filament 100.

[0058] The cathode filament 100 has a spiral structure; specifically, in... Figure 1In the illustrated embodiment, the cathode filament 100 has a cylindrical helical structure. During manufacturing, the cathode filament 100 with a cylindrical helical structure can be formed by winding filament material. Optionally, at least one of the number of turns, pitch, and length of the two non-main emitting regions 12 is the same, thereby reducing the cost of the cathode filament 100.

[0059] In related technologies, the magnetron is the most crucial component of a microwave oven. The microwaves generated by the magnetron are produced by electrons supplied by the heating of the cathode filament passing through a strong electromagnetic field to form electron spheres. Therefore, the cathode filament is also known as the heart of the magnetron. Please refer to... Figure 20 In related technologies, the cathode filament 300 has a cylindrical helical structure with a constant pitch. When the cathode filament 300 is energized, the strong heat creates significant stress within the filament, with the second and ninth turns exhibiting the greatest stress (counting from top to bottom). Vibrations during the manufacturing process and minor impacts from the microwave oven can cause the filament to break. Once the filament breaks, the entire magnetron 300 becomes an open circuit, preventing the generation of microwaves. Worse still, if a filament break is not detected in time, consumers may find the microwave oven malfunctioning upon first use, impacting user experience and damaging the company's brand image.

[0060] In this embodiment of the invention, by adjusting the pitch of the non-main emission region 12 and the main emission region 14, making the pitch of the non-main emission region 12 greater than the pitch of the main emission region 14, a non-equal pitch helical structure is formed to reduce the stress in the non-main emission region 12. In one example, the total number of turns in the two non-main emission regions 12 can be 8, and the number of turns in the main emission region 14 can be 3. If the two non-main emission regions 12 have the same number of turns, then the number of turns in each non-main emission region 12 is 4.

[0061] In one example, the total number of orbits for the two non-primary launch areas 12 can be 6, and the number of orbits for the primary launch area 14 is 5. If the two non-primary launch areas 12 have the same number of orbits, then each non-primary launch area 12 has 3 orbits.

[0062] In one example, the total number of turns in the two non-main emitting regions 12 can be 5, and the number of turns in the main emitting region 14 is 6. One non-main emitting region 12 has 3 turns, and the other non-main emitting region 12 has 2 turns. In this embodiment of the invention, the non-equidistant pitch helical structure can further disperse the stress in the non-main emitting regions 12, reducing the stress in the non-main emitting regions 12, especially the stress in the 2nd to 3rd turns. This, to a certain extent, improves the breakage resistance of the cathode filament 100 after carbonization, and enhances the reliability of the magnetron 200 and the microwave cooking appliance.

[0063] It is understood that the number of turns of the cathode filament 100 (the number of turns of the non-main emitting area 12 + the number of turns of the main emitting area 14) can be specifically set according to requirements, and this invention does not impose specific limitations on this.

[0064] Please combine Figure 2 The pitch of the non-main emission area 12 is d1, and the pitch of the main emission area 14 is d2, where d1>d2.

[0065] Please combine Figure 20 In related technologies, the cathode filament 300 has a constant-pitch helical structure. Figure 20 It can be seen that the main emission area of ​​the cathode filament 300 is relatively narrow. Figure 20 As shown in the dashed box, the cathode filament 300 requires a relatively long preheating time to generate microwaves, resulting in poor uniformity of electron emission in the main emission area, which negatively impacts the overall microwave conversion efficiency.

[0066] In this embodiment of the invention, the pitch of the non-main emission region 12 is greater than the pitch of the main emission region 14. That is, the distance between the rings in the main emission region 14 is smaller, and the rings in the main emission region 14 are more dense. This can improve the uniformity of electron emission in the main emission region 14 to a certain extent and have a positive impact on the microwave conversion efficiency.

[0067] The non-primary emission region 12 mentioned in this invention can refer to a portion of the cathode filament 100 located in the non-primary emission region 12 that does not emit electrons, or it can refer to a portion of the cathode filament 100 located in the non-primary emission region 12 that emits far fewer electrons than the portion of the cathode filament 100 located in the primary emission region 14. In other words, the microwaves generated by the magnetron 200 are mainly caused by electrons emitted by the portion of the cathode filament 100 located in the primary emission region 14. The primary emission region 14 is the main source of electrons and can also be called the main emission region. When the cathode filament 100 is energized, it is heated. The temperature in the middle of the cathode filament 100 is high, while the temperature on both sides is low. Therefore, after carbonization in the middle of the carbonization process, the carbonization layer in the non-primary emission region 12 is thin, while the carbonization layer in the primary emission region 14 is thick. The electron emission performance of the primary emission region 14 is strong, while the electron emission of the non-primary emission region 12 is poor or even non-emitted.

[0068] In some implementations, the non-main emission region 12 satisfies the following condition: d1 / N1 is 0.15 to 0.25, where d1 represents the pitch of the non-main emission region 12 and N1 represents the number of turns of the non-main emission region 12.

[0069] Therefore, the parameters of the non-main emission region 12 can be further optimized to further improve the breakage resistance of the cathode filament 100.

[0070] Specifically, d1 / N1 is between 0.15 and 0.25, that is, 0.15 ≤ d1 / N1 ≤ 0.25. In some examples, d1 / N1 = 0.15, 0.17, 0.18, 0.2, 0.22, 0.24, 0.25, or other values ​​between 0.15 and 0.25.

[0071] In one implementation, when the number of turns N1 of the non-main emission region 12 is constant, the pitch d1 of the non-main emission region 12 can be adjusted to reduce stress in the high-pressure region. In one example, d1 = 1.12 mm.

[0072] In some implementations, the main emission region 14 satisfies the following condition: d2 / N2 is 0.15 to 0.30, where d2 represents the pitch of the main emission region 14 and N2 represents the number of turns of the main emission region 14.

[0073] Therefore, the parameters of the main emission region 14 can be further optimized to improve the microwave conversion efficiency of the cathode filament 100.

[0074] Specifically, d² / N² is between 0.15 and 0.30, that is, 0.15 ≤ d² / N² ≤ 0.30. In some examples, d² / N² = 0.15, 0.17, 0.18, 0.2, 0.22, 0.23, 0.25, 0.27, 0.29, 0.30, or other values ​​between 0.15 and 0.30.

[0075] In one implementation, when the number of turns N2 of the main emission zone 14 is constant, the pitch d2 of the main emission zone 14 can be adjusted to control emission uniformity. In one example, d2 = 0.94 mm.

[0076] In one embodiment, orthogonal experimental design showed that when d1 / N1 is 0.15 to 0.25 and d2 / N2 is 0.15 to 0.30, the maximum internal stress of the cathode filament 100 decreases by 21% (e.g., Figure 5 As shown in the figure, the microwave conversion efficiency of the cathode filament 100 is improved by 4.2%. Figure 5 In the figure, the unit of the vertical axis is MPa.

[0077] In some embodiments, the cathode filament 100 is made of a tungsten alloy.

[0078] This can improve the performance of the cathode filament 100.

[0079] Specifically, in one embodiment, the melting point of the tungsten alloy is typically between 3420 and 3800°C, which is much higher than that of ordinary metals. This allows the tungsten alloy to remain stable in high-temperature environments when used in the cathode filament 100, making it less prone to melting or deformation, thereby extending the service life of the magnetron 200.

[0080] Tungsten alloys also possess high hardness and strength, enabling them to withstand the impact and vibration of high-frequency electromagnetic fields, thus ensuring the magnetron 200 maintains stable performance even in harsh working environments. Tungsten alloys have excellent electrical conductivity, allowing current to flow smoothly through the cathode filament 100, generating sufficient heat to heat it. The heated cathode filament 100 emits more electrons, thereby improving the electron emission efficiency of the magnetron 200. Tungsten alloys exhibit excellent corrosion resistance, resisting corrosion from most acids, alkalis, and salts, allowing the tungsten alloy cathode filament 100 to maintain stable performance even in humid or corrosive environments.

[0081] Tungsten alloys include, but are not limited to, thorium tungsten, lanthanum tungsten, yttrium tungsten, and other tungsten alloys used in 200 filament magnetrons for microwave cooking appliances.

[0082] In some embodiments, the length L of the cathode filament 100 is 12 ± 0.5 mm.

[0083] Therefore, the length of the cathode filament 100 is adapted to the spatial structure of the magnetron 200.

[0084] Specifically, the length L of the cathode filament 100 is 12 ± 0.5 mm, that is, 11.5 mm ≤ L ≤ 12.5 mm. In some examples, L = 11.5 mm, 11.7 mm, 11.9 mm, 12 mm, 12.1 mm, 12.3 mm, 12.5 mm, or other values ​​between 11.5 mm and 12.5 mm.

[0085] During manufacturing, the cathode filament 100 can be formed by winding filaments to create a cylindrical spiral structure. In one example, the diameter of the cathode filament 100 is 0.5 mm.

[0086] In some implementations, the length of each non-main emission region 12 is 4 mm, and the length of the main emission region 14 is 4 mm.

[0087] Therefore, the cathode filament 100 is easy to manufacture.

[0088] Specifically, the two non-main emission areas 12 are located on opposite sides of the main emission area 14 along the length of the cathode filament 100. The length of each non-main emission area 12 is 4 mm, and the length of the main emission area 14 is 4 mm. That is to say, the length of each non-main emission area 12 is equal to the length of the main emission area 14. During the process of winding the filament 38 into a spiral shape, the manufacturing equipment can more easily control the lengths of the non-main emission areas 12 and the main emission area 14, thereby improving manufacturing efficiency.

[0089] In this embodiment of the invention, the pitch of the non-primary emitter region 12 is greater than that of the primary emitter region 14. When the lengths of the non-primary emitter region 12 and the primary emitter region 14 are equal, the number of turns in the non-primary emitter region 12 is less than the number of turns in the primary emitter region 14. The sparser turns in the non-primary emitter region 12 facilitate stress dispersion and reduce the likelihood of breakage. The denser turns in the primary emitter region 14 improve electron emission efficiency.

[0090] In one embodiment, the pitch of the non-main launch region 12 is greater than the pitch of the main launch region 14, and when the number of turns of the non-main launch region 12 and the main launch region 14 are equal, the length of the non-main launch region 12 is greater than the length of the main launch region 14.

[0091] In some embodiments, the filament 38 of the cathode filament 100 includes a filament core 40 and a carbonization layer 42, the carbonization layer 42 covering the filament core 40 at least in the circumferential direction, the filament core 40 being made of lanthanum tungsten, and the carbonization layer 42 being a lanthanum tungsten carbonization layer.

[0092] Therefore, the filament core 40 is made of lanthanum tungsten material, and the carbide layer 42 is made of lanthanum tungsten carbide layer. This reduces the work function of the cathode filament 100 to a certain extent and improves the migration ability of rare earth elements in the cathode filament 100. This can improve the electron emission capability of the cathode filament 100 to a certain extent, so that the magnetron 200 can adapt to the higher power requirements of microwave cooking appliances.

[0093] In related technologies, according to current market statistics, microwave ovens using magnetrons have a minimum output power of 500 watts or more. Lowering the power further will result in unstable microwave output, and in severe cases, no microwave output at all. For specific details, please refer to… Figure 13 Microwave ovens include inverters. The principle behind inverter power adjustment is that a control chip (IC) controls the switching on and off of two IGBTs (Insulated Gate Bipolar Transistors), maintaining a certain current in the system and thus providing a relatively stable power supply to the magnetron. Current I = Q / t (I is current, Q represents charge, and t is time). When the switching frequency of the IGBT increases, the amount of charge moving per unit time increases, and therefore the current increases; conversely, when the switching rate of the IGBT decreases, the current decreases accordingly. P = U*I (P is power, U is voltage, and I is current). When the voltage in the system remains constant, changing the magnitude of the operating current changes the output power. Please refer to... Figure 14The measured microwave output power was 600 watts, and the input current decreased by 40% compared to the normal current. When the microwave output power was below 500 watts, the input current decreased by about 50% compared to the normal current. The cathode filament emitted fewer electrons, making it difficult to form corresponding electron wheels in the cathode and anode, thus resulting in unstable microwave power.

[0094] As can be seen from the above, the microwave output power is controlled by the switching frequency of the IGBT. However, the thorium tungsten filament used in the existing magnetrons has a drastic reduction in the number of electrons in the filament below a certain current, making it impossible to use microwave ovens below wattage. For example, it cannot be used in some low-power cooking scenarios (such as microwave heating milk, microwave boiling milk, etc.), which affects the further promotion of microwave ovens.

[0095] In this embodiment of the invention, the filament core 40 is made of lanthanum-tungsten material, and the carbide layer 42 is a lanthanum-tungsten carbide layer. For example... Figure 15 As shown, when a metal is heated, electrons gain energy and undergo energy level transitions. The work done by an electron escaping from the metal surface (Fermi level) (vacuum level) is called the work function. The smaller the work function, the easier it is for electrons to escape from the metal surface. Therefore, based on this characteristic, this invention uses lanthanum to replace the original thorium, making the work function of the cathode filament 100 of this invention lower than that of the original thorium-tungsten filament. Furthermore, the filament 38, including lanthanum-tungsten material, can be further carbonized to adapt to the operating conditions of the magnetron 200. For example, a lanthanum-tungsten carbonized layer can be formed on the outer layer of the filament 38 using a carburizing reaction after methane cracking, while the uncarbonized interior forms the filament core 40. This enhances the migration ability of rare earth elements in the cathode filament 100 material and simultaneously homogenizes the entire emission surface, thereby improving the electron emission capability of the cathode filament 100 to a certain extent, allowing the magnetron 200 to adapt to the higher power requirements of microwave cooking appliances. Furthermore, orthogonal design can be performed on multiple experimental parameters of the carbonization reaction to ultimately achieve the desired result. Figure 8 and Figure 9 The results of carbonization layer 42 are shown.

[0096] The filament core 40 has two main functions. First, it stabilizes the spiral structure of the cathode filament 100. Second, it forms a lanthanum-tungsten carbide layer. This lanthanum-tungsten carbide layer has electron emission capability, primarily due to the electrons generated by the reaction of lanthanum with tungsten carbide and ditungsten carbide. During this process, lanthanum is consumed. Because of the consumption of lanthanum in the carbide layer 42, a concentration gradient is created, allowing the lanthanum in the filament core 40 to diffuse to the carbide layer 42 for timely replenishment, thereby ensuring the continuous electron emission capability of the cathode filament 100.

[0097] The carbide layer 42 covers the filament core 40 at least in the circumferential direction, so that during the operation of the cathode filament 100, the carbide layer 42 emits electrons outward, and the filament core 40 can continuously and timely replenish lanthanum to the carbide layer 42 through diffusion. Optionally, in one embodiment, the carbide layer 42 covers the filament core 40 in both the circumferential and longitudinal directions.

[0098] Please combine Figure 16 and Figure 17 , Figure 16 This is a cross-sectional view of the thorium-tungsten filament material in related technologies. Figure 17 This is a partially enlarged view of the cross-section of a thorium-tungsten filament from a related technology. Figure 16 and Figure 17 It can be seen that in the relevant technologies, the filament core is blocky with coarse grains and weak bonding, and the carbide layer is mostly blocky tungsten carbide.

[0099] Please combine Figure 8 and Figure 9 , Figure 8 This is a cross-sectional view of the filament 38 of the cathode filament 100 comprising lanthanum-tungsten material according to an embodiment of the present invention. Figure 9 This is a partially enlarged cross-sectional view of the filament 38 of the cathode filament 100 comprising lanthanum-tungsten material according to an embodiment of the present invention. Figure 8 and Figure 9 As can be seen, in this embodiment of the invention, the internal structure of the filament core 40 is compact and has strong fracture resistance. The carbide layer 42 is predominantly composed of fine, layered tungsten carbide, which increases the electron emission channel and enhances the electron emission capability of the cathode filament 100.

[0100] Based on actual testing, please combine... Figure 12 When tested without a magnetic field, the original filament received a total electron current of 360mA at the anode under a current of 9A, while the lanthanum-tungsten filament received an electron current of 692mA under a current of 9A.

[0101] It is understood that the ratio of lanthanum to tungsten can be determined according to specific needs, such as power requirements and cost, and the process parameters of the carbonization process can also be determined according to the design performance. This invention does not impose specific limitations on this.

[0102] In some embodiments, the thickness of the carbonized layer 42 is 6% to 10% of the thickness of the filament 38.

[0103] Therefore, the long-term electron emission capability of the cathode filament 100 can be guaranteed to a certain extent.

[0104] Specifically, please combine Figure 6The thickness of the carbonized layer 42 is D1, and the thickness of the wire 38 is D2. The thickness of the carbonized layer 42 is 6% to 10% of the thickness of the wire 38, that is, 6% × D2 ≤ D1 ≤ 10% × D2. Figure 6 In the middle, the filament 38 is cylindrical, the thickness D2 of the filament 38 is the diameter of the filament 38, and the thickness D1 of the carbonized layer 42 is the difference between the diameter of the filament 38 and the diameter of the filament core 40.

[0105] In some examples, D1 = 6% × D2, 6.5% × D2, 7% × D2, 7.5% × D2, 8% × D2, 8.5% × D2, 9% × D2, 9.5% × D2, 10% × D2, or other values ​​between 6% × D2 and 10% × D2.

[0106] The thickness of the carbonized layer 42 is 6% to 10% of the thickness of the filament 38. The thickness ratio of the carbonized layer 42 is moderate. During the long-term use of the cathode filament 100, it can ensure that the filament core 40 can continuously supply lanthanum to the carbonized layer 42 to a certain extent, so that the carbonized layer 42 has a long-term stable electron emission capability.

[0107] Verification has shown that the thickness of the carbide layer 42, which includes the lanthanum tungsten carbide layer, in the embodiments of the present invention is 6% to 10% of the thickness of the wire 38, which is 16% thicker than the carbide layer in related technologies. Moreover, the carbide layer 42 in the embodiments of the present invention is mostly composed of layered channels with a larger crystal gap area, which is more conducive to increasing the electron emission capability of the wire 38.

[0108] Optionally, in one embodiment, the thickness of the carbide layer 42 in the main emission region 14 is 6% to 10% of the thickness of the filament 38. It is understood that the thickness of the carbide layer 42 decreases from the main emission region 14 towards the non-main emission regions 12 on both sides. In one embodiment, please refer to... Figure 1 The cathode filament 100 has 12 turns. The upper non-main emitting region 12 has turns 1 to 4, the main emitting region 14 has turns 5 to 8, and the lower non-main emitting region 12 has turns 9 to 12. Turns 1 to 2 and turns 11 to 12 of the cathode filament 100 have virtually no carbonized layer 42. Turns 3 to 4 and turns 9 to 10 have relatively thin carbonized layers 42, which cannot form a stable electron output. The main emitting region 14 has relatively thick carbonized layers 42 in turns 5 to 8, which can form a stable and sufficient number of electrons.

[0109] In some embodiments, the thickness of the carbonized layer 42 is 8% of the thickness of the filament 38.

[0110] Therefore, the thickness of the carbonized layer 42 can be further prioritized.

[0111] Specifically, the emission performance of the cathode filament 100 is positively correlated with the thickness of the carbide layer 42. Increasing the thickness of the carbide layer 42 will increase the brittleness of the cathode filament 100. Therefore, in order to balance the emission performance and vibration resistance of the cathode filament 100, the thickness D1 of the carbide layer 42 is 8% of the thickness D2 of the wire 38.

[0112] In some embodiments, the thickness of the carbonized layer 42 is 42 μm (micrometers), and the thickness of the filament is 0.5 mm (millimeters).

[0113] This is beneficial for increasing the electron emission capability of the cathode filament 100.

[0114] Specifically, in this embodiment, the thickness of the carbide layer 42 is D1 = 42 μm, and the thickness of the wire 38 is D2 = 0.5 mm. As a comparative example, the thickness of the thorium tungsten carbide layer is about 35 μm. In the cathode filament 100 of this embodiment, the carbide layer 42 is mostly in the form of layered channels, and the increased crystal gap area compared to the comparative example is more conducive to increasing the electron emission capability of the cathode wire 100.

[0115] In some embodiments, the cathode filament 100 is made of at least one of yttrium, rhenium, lutetium, zirconium, and hafnium.

[0116] This can improve the electron emission capability, melting point, and / or saturated vapor pressure of the cathode filament 100.

[0117] Specifically, adding yttrium to the cathode filament 100 can enhance the electron emission capability of the cathode filament 100, and adding rhenium to the cathode filament 100 can increase the high melting point characteristic of the cathode filament 100, thereby extending the service life of the cathode filament 100.

[0118] In one embodiment, any one or any two or three of lutetium, zirconium, and hafnium can increase the saturated vapor pressure and melting point of the cathode filament 100, hindering the volatilization of lanthanum, thereby achieving a balance between the volatilization and diffusion of the main functional element lanthanum and better maintaining the dynamic balance of lanthanum.

[0119] In one embodiment, the cathode filament 100 material further includes yttrium, rhenium, lutetium, zirconium, or hafnium; that is, yttrium, rhenium, lutetium, zirconium, or hafnium can be added to the lanthanum-tungsten material. In another embodiment, the cathode filament 100 material further includes any two, three, four, or five of yttrium, rhenium, lutetium, zirconium, and hafnium; that is, any two, three, four, or five of yttrium, rhenium, lutetium, zirconium, and hafnium can be added to the lanthanum-tungsten material.

[0120] The proportions of yttrium, rhenium, lutetium, zirconium, and hafnium can be determined based on factors such as the performance enhancement of electron emission capability, the maximum operating temperature of the cathode filament 100, and the saturated vapor pressure. This invention does not impose specific limitations on these proportions.

[0121] The aforementioned added elements may be present in the filament core 40 and the carbonized layer 42.

[0122] Optionally, in one embodiment, the cathode filament 100 contains more than 98% tungsten matrix and no more than 2% lanthanum and other additive elements. It is understood that the present invention does not limit the tungsten content, lanthanum content, or the proportions of other additive elements in the cathode filament 100.

[0123] In some embodiments, the grain size of the filament core 40 ranges from 0.4 μm to 2 μm.

[0124] This is beneficial for increasing the electron emission capability of the cathode filament 100.

[0125] Specifically, the grains in the filament core 40 can be lanthanum-tungsten alloy grains, or lanthanum-tungsten alloy grains with other additive elements. The grain size ranges from 0.4 μm to 2 μm. Please refer to... Figure 10 and Figure 11 The average grain size of the lanthanum-tungsten alloy in the embodiments of the present invention is compared with that in the comparative example (e.g.) Figure 18 and Figure 19 The thorium-tungsten grains are small and uniformly distributed, which helps to increase the electron emission capability of the cathode filament 100.

[0126] In some examples, the grain size is 0.4 μm, 0.6 μm, 0.8 μm, 0.87 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.45 μm, 1.6 μm, 1.8 μm, 2 μm, or other values ​​from 0.4 μm to 2 μm. In one example, the average grain size is 0.87 μm.

[0127] In some embodiments, the cathode filament 100 is capable of emitting electrons after being powered on and after being powered off.

[0128] Therefore, even after a power outage, the cathode filament 100 maintains a strong and stable operating performance.

[0129] Specifically, the carbonized layer 42 of the cathode filament 100 in this embodiment of the invention has a strong secondary back-bombardment capability. During the operation of the magnetron 200, after the cathode filament 100 is energized and emits electrons, the power to the cathode filament 100 can be cut off. Even after the power is cut off, the cathode filament 100 can still emit electrons to enable the magnetron 200 to generate microwaves for heating food. More specifically, under the influence of the magnetic field of the magnetron 200, some of the emitted electrons will bounce back to the carbonized layer 42. The bounced electrons collide with the carbonized layer 42, thereby causing the carbonized layer 42 to continuously emit new electrons. For example, one bounced electron can cause the emission of two new electrons, and two bounced electrons can cause the emission of four new electrons, etc. Therefore, even if the power to the cathode filament 100 is cut off (equivalent to 0 amp current) after it is energized and emits electrons, the carbonized layer 42 can continue to emit electrons stably under the action of secondary back-bombardment, enabling the magnetron 200 to continuously and stably output microwaves to heat food.

[0130] Please combine Figure 3 and Figure 4 The present invention provides a cathode assembly 102 for use in a magnetron 200. The cathode assembly 102 includes the cathode filament 100 of any of the above embodiments.

[0131] In the aforementioned cathode assembly 102, the pitch of the non-main emission area 12 located outside the main emission area 14 is greater than that of the main emission area 14, which makes the stress in the non-main emission area 12 more dispersed, thereby effectively reducing the stress of the cathode filament 100 in the non-main emission area 12 and improving the fracture resistance of the cathode filament 100 after carbonization.

[0132] Specifically, please combine Figure 4 The magnetron 200 includes an anode assembly 24, which includes an anode cylinder 26 and multiple anode plates 28. One end of each anode plate 28 is connected to the sidewall of a receiving cavity within the anode cylinder 26 and is spaced apart along the circumferential direction of the anode cylinder 26. The other ends of the multiple anode plates 28 are suspended to form a receiving space. A cathode filament 100 is disposed in the receiving space, and an interaction space 30 is formed between the cathode filament 100 and the anode plates 28. Please refer to... Figure 4 and Figure 7The working principle of the magnetron 200 is as follows: When the magnetron 200 is working, a DC voltage (such as a DC voltage of several kilovolts) is applied between the cathode filament 100 and the anode plate 28. Simultaneously, the upper magnet 32 ​​and lower magnet 34 of the magnetron 200 provide a magnetic field to the interaction space 30. The DC electric field and DC magnetic field within the interaction space 30 are perpendicular to each other. The cathode filament 100 emits electrons, which are accelerated by the electric field and deflected by the magnetic field, resulting in stable oscillating motion within the interaction space 30. The electron velocity is proportional to the ratio E / B, where E is the electric field strength and B is the magnetic flux density. The energy gained by the electron stream emitted by the cathode filament 100 from the electric field in the interaction space 30 is transferred to a high-frequency field under certain conditions and output as microwaves through the energy output window 36.

[0133] In some embodiments, the cathode assembly 102 includes a support 16, which includes two end caps 22, with one end of each of the two non-main emission regions 12 disposed within the two end caps 22.

[0134] This facilitates the installation of the cathode filament 100.

[0135] Specifically, the end cap 22 is provided with a slot, and one end of the non-main emission area 12 can be placed in the slot, thereby allowing the cathode filament 100 to be easily installed on the bracket 16. The cathode assembly 102 also includes connecting rods 18 and cathode connectors 20, which are connected to the two end caps 22 respectively via the two connecting rods 18. The cathode connectors 20 can be connected to a power source, which can be provided by the filament windings of a transformer.

[0136] Please combine Figure 4 The magnetron 200 provided in this embodiment includes the cathode assembly 102 of any of the above embodiments.

[0137] The microwave cooking appliance provided by the present invention includes the magnetron 200 of the above embodiment.

[0138] In the aforementioned magnetron 200 and microwave cooking appliance, the pitch of the non-main emission area 12 located outside the main emission area 14 is greater than that of the main emission area 14, which makes the stress in the non-main emission area 12 more dispersed, thereby effectively reducing the stress in the cathode filament 100 in the non-main emission area 12 and improving the breakage resistance of the cathode filament 100 after carbonization.

[0139] Specifically, microwave cooking appliances include, but are not limited to, microwave ovens, microwave-steam-grill combos, and integrated cooktops. The magnetron 200 can be used as a microwave source, and the microwaves generated by the magnetron 200 can be guided into the cooking cavity of the microwave cooking appliance via a waveguide to cook the food inside the cooking cavity.

[0140] In some embodiments, the filament 38 of the cathode filament 100 includes a filament core 40 and a carbonized layer 42, the carbonized layer 42 covering the filament core 40 at least in the circumferential direction, the filament core 40 being made of lanthanum tungsten, the carbonized layer 42 being a lanthanum tungsten carbonized layer, and the cathode filament 100 being capable of emitting electrons at a minimum output power of 100 watts in a microwave cooking appliance.

[0141] Therefore, the cathode filament 100 can be adapted to more application scenarios of microwave cooking appliances.

[0142] Specifically, microwave cooking appliances with magnetrons 200 are used in scenarios requiring low power, such as microwave heating milk or microwave boiling milk. In one embodiment, the minimum output power of the microwave cooking appliance is 100 watts. The cathode filament 100 of this embodiment can emit electrons even when the minimum output power of the microwave cooking appliance is 100 watts, enabling the microwave cooking appliance to operate normally and provide heating for low power requirements.

[0143] Actual testing showed that when the cathode filament 100 is used in a microwave cooking appliance with an output power of 100 watts, the microwave cooking appliance can operate stably and heat the food.

[0144] In summary, in the technical solution of the present invention, 1) by adjusting the pitch and number of turns of the non-main emission area 12 and the main emission area 14, the maximum internal stress can be reduced by 21%, and the failure rate of the cathode filament 100 can be significantly reduced; 2) the effective area of ​​the cathode filament 100 in the main emission area 14 is more concentrated, the electron emission uniformity is increased, and the microwave conversion efficiency can be improved by 4.2%.

[0145] Furthermore, the cathode filament 100 of this embodiment can be made of lanthanum-tungsten material or lanthanum-tungsten material with other additives, replacing the original thorium-tungsten cathode filament, reducing the electron work function by 20% compared to the original material. The thickness of the lanthanum-tungsten carbide layer formed after carbonization treatment accounts for 6% to 10% of the thickness of the filament 38, and the carbide layer 42 is distributed in layers. Its emission capability is improved by 92% compared to the original product. The carbide layer 42 of this embodiment can make its secondary back-bombing capability strong, enabling continuous emission of secondary electrons. Thus, after the cathode filament 100 emits electrons after heating, it can still operate stably under power failure (0A current). When the minimum output power of the microwave cooking appliance is 100 watts, the cathode filament 100 can also enable the magnetron 200 to output stable microwaves, allowing the microwave cooking appliance to heat the food.

[0146] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0147] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A cathode filament for use in a magnetron, characterized in that, The cathode filament has a spiral structure and includes two non-main emitting regions and a main emitting region. Along the length of the cathode filament, the two non-main emitting regions are respectively connected to the opposite sides of the main emitting region, and the pitch of the non-main emitting regions is greater than the pitch of the main emitting region.

2. The cathode filament according to claim 1, characterized in that, The non-main emission region satisfies the following condition: d1 / N1 is 0.15 to 0.25, where d1 represents the pitch of the non-main emission region and N1 represents the number of turns of the non-main emission region.

3. The cathode filament according to claim 1, characterized in that, The main transmitting region satisfies the following condition: d2 / N2 is 0.15 to 0.30, where d2 represents the pitch of the main transmitting region and N2 represents the number of turns of the main transmitting region.

4. The cathode filament according to claim 1, characterized in that, The cathode filament is made of tungsten alloy.

5. The cathode filament according to claim 1, characterized in that, The length of the cathode filament is 12±0.5mm.

6. The cathode filament according to any one of claims 1-5, characterized in that, Each of the non-primary emission regions has a length of 4 mm, and the primary emission region has a length of 4 mm.

7. The cathode filament according to claim 1, characterized in that, The cathode filament includes a filament core and a carbonized layer. The carbonized layer covers the filament core at least in the circumferential direction. The filament core is made of lanthanum-tungsten, and the carbonized layer is a lanthanum-tungsten carbonized layer.

8. The cathode filament according to claim 7, characterized in that, The thickness of the carbonized layer is 6% to 10% of the thickness of the filament.

9. The cathode filament according to claim 7 or 8, characterized in that, The thickness of the carbonized layer is 8% of the thickness of the filament.

10. The cathode filament according to claim 7 or 8, characterized in that, The thickness of the carbonized layer is 42 μm, and the thickness of the filament is 0.5 mm.

11. The cathode filament according to claim 7, characterized in that, The cathode filament material also includes at least one of yttrium, rhenium, lutetium, zirconium, and hafnium.

12. The cathode filament according to claim 7, characterized in that, The grain size of the filament core ranges from 0.4 μm to 2 μm.

13. The cathode filament according to claim 7, characterized in that, The cathode filament is capable of emitting electrons after being powered on and continuing to emit electrons after the power is turned off.

14. A cathode assembly for a magnetron, characterized in that, The cathode assembly includes the cathode filament as described in any one of claims 1-13.

15. The cathode assembly according to claim 14, characterized in that, The cathode assembly includes a support, which includes two end caps, with one end of each of the two non-main emission areas located inside the two end caps.

16. A magnetron, characterized in that, Includes the cathode assembly as described in claim 14 or 15.

17. A microwave cooking appliance, characterized in that, Including the magnetron of claim 16.

18. The microwave cooking appliance according to claim 17, characterized in that, The cathode filament comprises a filament core and a carbonized layer, wherein the carbonized layer covers the filament core at least in the circumferential direction. The filament core is made of lanthanum-tungsten material, and the carbonized layer comprises a lanthanum-tungsten carbonized layer. The cathode filament is capable of emitting electrons when the minimum output power of the microwave cooking appliance is 100 watts.

Images