Encapsulation of magnets with metal in permanent magnet thrusters

Abstract

The present invention relates to a permanent magnet thruster having a rotor yoke comprising a tubular element, wherein the tubular element holds a plurality of permanent magnets in contact with or at the location of the lateral surface of the tubular element. In a preferred embodiment, the plurality of permanent magnets are enclosed in magnet capsules made of a metal that has undergone hot isostatic pressurization.

Description

Technical Field

[0001] The present invention relates to a permanent magnet thruster having a rotor yoke with a tubular element, wherein the tubular element holds a plurality of permanent magnets in contact with the side surface of the tubular element or at a location on the side surface. In a preferred embodiment, the plurality of permanent magnets are encapsulated in magnet capsules made of a metal that has been subjected to hot isostatic pressing.

Background Art

[0002] Thrusters are widely used for the propulsion and / or steering of ships. Such thrusters are designed to provide a thrust that rotates a number of propeller blades submerged in water below the design waterline of the ship. Many such thrusters include a number of permanent magnets disposed on a rotor (rotor yoke). The propeller blades are coupled at one end to the rotor and at the other end to a hub such that the rotor with the propeller blades can rotate around the hub. The rotation is provided by a number of stator coils that can be magnetized by an electric current. Such a configuration of permanent magnets and magnetizable stator coils operates as an electric motor to impart rotation to the rotor.

[0003] Permanent magnets are made of materials that are prone to corrosion, especially when exposed to seawater (salt-containing water). For example, neodymium-type magnets are very prone to corrosion, and even a small amount of moisture in the atmosphere can cause the magnets to corrode. Corrosion of permanent magnets is highly undesirable because it leads to deterioration of the magnets in terms of strength, shape, and size, and the magnetic strength of the magnets deteriorates over time. In addition, there is a possibility that the chemicals formed as a result of corrosion may be of a type that should not be released into the seawater, and since such chemicals can be released from the magnets, the formation of such chemicals is a further environmental concern.

[0004] Since corrosion occurs due to the close contact between the surface of the permanent magnet and seawater, covering the surface of the permanent magnet to prevent such close contact can be an option.

[0005] However, such a covering should be strong enough to withstand the harsh conditions in seawater and should not significantly reduce the magnetic strength of the permanent magnet.

[0006] Furthermore, if covering the permanent magnets is to be considered, the manufacturing process should be relatively simple to avoid incurring excessive manufacturing costs in the production of the thrusters.

[0007] Therefore, thrusters with improved corrosion resistance are advantageous, and in particular, more efficient and / or reliable corrosion resistance of the permanent magnets used in the thrusters is advantageous. [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to provide a maritime thruster equipped with permanent magnets, wherein corrosion of the permanent magnets is at least reduced.

[0009] The present invention further aims to at least reduce corrosion of permanent magnets in maritime thrusters so that they can be used in harsh conditions in seawater.

[0010] The present invention further aims to at least reduce corrosion of permanent magnets in maritime thrusters, preferably without significantly reducing the magnetic strength of the permanent magnets, or even to have an equivalently large magnetic strength.

[0011] The present invention further aims to at least reduce corrosion of permanent magnets in maritime thrusters through a relatively simple manufacturing process.

[0012] The present invention further aims to provide an alternative to the prior art. [Means for solving the problem]

[0013] Therefore, the above object and several other object are intended to be achieved by providing a permanent magnet thruster in a first embodiment of the present invention, which permanent magnet thruster It is a rotor yoke, A tubular element that holds a plurality of permanent magnets in contact with or at the location of the side surface of the tubular element, Multiple propeller blades extending from the tubular element to a hub rotatably positioned inward on an axis, A rotor yoke including, A stator yoke located outside the rotor yoke and containing multiple stator coils that can be magnetized by electric current, Equipped with, The plurality of permanent magnets and the plurality of stator coils are configured to interact with each other such that the rotor yoke rotates when the plurality of stator coils are magnetized. The plurality of permanent magnets are enclosed in a magnet capsule made of metal that has undergone hot isostatic pressurization, and the magnet capsule encloses at least the uncovered surfaces of the permanent magnets that are facing away from the side surface in the radial direction of the tubular element and facing in the tangential and axial directions of the tubular element.

[0014] The metal from which the magnetic capsule is made is preferably stainless steel, titanium, bronze, especially nickel-aluminum bronze, and / or an alloy that is corrosion-resistant.

[0015] Capsules subjected to hot isostatic pressurization exhibit several highly distinctive material properties compared to other processes such as sintering or casting, including increased density (due to shrinkage) and a reduction in the amount of impurities in the absorbed gas.

[0016] The presence of a capsule that encloses at least the uncovered surface of the permanent magnet, along with the use of hot isostatic pressurization, essentially prevents contact between the uncovered surface of the permanent magnet and seawater. By shrinking the capsule through hot isostatic pressurization, an excellent seal is provided where the uncovered surface of the permanent magnet comes into contact with the inner surface of the capsule.

[0017] While complete encapsulation of the permanent magnet is preferable, it may be sufficient to encapsulate only some surface areas, such as the uncovered surfaces disclosed herein, by having a portion of the permanent magnet's surface area in close contact with the surface of the tubular element. Complete encapsulation preferably means that the surface of the permanent magnet is not exposed to the outside of the capsule at all.

[0018] The terms used herein are those commonly used by those skilled in the art. Some of the terms used are described below in detail.

[0019] Hot isostatic pressurization, abbreviated herein as "HIPping," refers to a manufacturing process in which one or more permanent magnets are encapsulated in a capsule preform made of metal, preferably stainless steel. The preform containing the magnets is exposed to high temperatures to remove any gases that may have been absorbed, and then, while maintaining the high temperature, is exposed to and compressed by an inert gas such as argon under increased isostatic pressure, causing the preform to contract and form a magnet capsule. Thus, the magnet capsule is said to have been made by hot isostatic pressurization, and the material obtained as a result of hot isostatic pressurization is called a hot isostatic pressurized material.

[0020] As used herein, the uncovered surface (of the permanent magnet) is preferably used to refer to a surface of the magnet that does not come into contact with another surface before the magnet capsule is given, and / or a surface that does not come into contact with water while the magnet is in use.

[0021] As used herein, a thruster refers to a maritime thruster, which is a device that produces hydrodynamic thrust, preferably directional thrust. Thrusters are mounted on ships and used for steering and / or propulsion.

[0022] The present invention, particularly preferred embodiments thereof, will now be described in more detail with reference to the accompanying drawings. The drawings illustrate the manner in which the invention may be practiced and are not to be construed as limiting other possible embodiments that fall within the scope of the appended claims.

Brief Description of the Drawings

[0023] [Figure 1] A three-dimensional view schematically shows a rotor yoke of a preferred embodiment of the present invention. For clarity, only one propeller blade and three permanent magnets are shown. [Figure 2A] A three-dimensional view schematically shows a rotor yoke of a preferred embodiment of the present invention. [Figure 2B] A three-dimensional view schematically shows a corresponding stator yoke of a preferred embodiment of the present invention. [Figure 3A] [[ID=十七]]A three-dimensional view schematically shows a segment of a preferred embodiment of the present invention. [Figure 3B] A cross-sectional view schematically shows a segment of a preferred embodiment of the present invention in FIG. 3A. [Figure 3C] A three-dimensional view schematically shows a segment of a preferred embodiment of the present invention disposed in a tubular element. [Figure 4A] A process related to the manufacture of a magnet capsule segment of a preferred embodiment is schematically shown. The cross-sectional view shown is a cross-sectional view along line A-A shown in FIG. 3A. [Figure 4B] A process related to the manufacture of a magnet capsule segment of a preferred embodiment is schematically shown. The cross-sectional view shown is a cross-sectional view along line A-A shown in FIG. 3A. [Figure 4C] A process related to the manufacture of a magnet capsule segment of a preferred embodiment is schematically shown. The cross-sectional view shown is a cross-sectional view along line A-A shown in FIG. 3A. [Figure 5] [[ID=三十五]]An embodiment of a magnet capsule segment is shown in which the orientation of the magnets is different from that disclosed in FIG. 4B. [Figure 6] An embodiment of a magnet capsule segment is shown in which the orientation of the magnets is different from that disclosed in FIG. 4B. [Modes for carrying out the invention]

[0024] Refer to Figure 1, which schematically shows a rotor yoke 2 for a permanent magnet thruster in a first preferred embodiment.

[0025] The rotor yoke 2 is part of a thruster that is submerged in water and coupled to the vessel, and rotates propeller blades to enable the vessel to be maneuvered and / or propelled in the water. The thruster may be an azimuth thruster, but the present invention is not limited to such an azimuth thruster.

[0026] In the embodiment disclosed in Figure 1, the rotor yoke 2 includes a tubular element 3. The tubular element 3 is typically a tubular structure having outward-facing sides and inward-facing sides. The sides are typically surfaces facing a direction having a normal vector with a component in the radial direction of the thruster. The tubular element 3 in Figure 3 holds a number of permanent magnets 4 in contact with or at the location of the outward-facing side 5 of the tubular element 3. However, the permanent magnets 4 can also be held in contact with the inward-facing side. Holding the magnets in contact with or at the location of the side typically refers to a situation where the magnets are coupled to the tubular element 3 in such a way that the rotational moment provided by the magnets causes the tubular element 3 to rotate. "At the location of the side 5" refers to the permanent magnets 4 being positioned slightly away from the side 5.

[0027] Five, six, seven, eight, or more propeller blades 10 are provided, extending inward from the tubular element 3 to the hub 11. In the embodiment of Figure 1, only one such propeller blade 10 is shown (for clarity), but in practice, many more propeller blades are provided. Such propeller blades 10 are typically arranged at equal intervals in the circumferential direction, for example, to prevent vibrations from occurring during rotation. Each propeller blade 10 is rotatably mounted on a shaft 12, which forms part of a structure (not shown) that connects the thruster to the ship.

[0028] Outside the rotor yoke 2, a stator yoke is positioned in the conventional manner for permanent magnet thrusters. The stator yoke contains multiple stator coils that can be magnetized by electric current. Thus, the combination of the rotor yoke 2 and the stator yoke is similar to an electric motor in that the rotor yoke 2 rotates when the stator coils are magnetized (unless the force acting on the rotor is greater than an overcomeable force). The multiple permanent magnets 4 and the multiple stator coils are configured in relation to each other such that the rotor yoke 2 rotates when the multiple stator coils are magnetized.

[0029] Permanent magnets are generally made from materials that are prone to corrosion, and such corrosion is clearly disadvantageous as it degrades the magnet in terms of both magnetic properties and size. Such corrosion is particularly pronounced in marine environments, including seawater, where salt in the water accelerates the progression of corrosion.

[0030] To prevent corrosion of the permanent magnets, multiple permanent magnets are enclosed in a metal magnet capsule 20. Such a capsule 20 is designed to shield the uncovered surfaces of the magnets that would otherwise be exposed to water during thruster operation. As will become clear below, such shielding can be achieved by completely enclosing the permanent magnets or by enclosing only the uncovered surfaces that would otherwise be exposed to water. In the latter case, in one embodiment, the magnets are arranged in contact with side 5 such that one or more uncovered surfaces face outward and one or more surfaces face inward, for example, in contact with side 5, and therefore do not need protection from water. In such an embodiment, the capsule 20 covers the outward-facing uncovered surfaces.

[0031] In general, it is preferable that the magnet capsule 20 encloses at least the uncovered surfaces of the permanent magnet 4 facing away from the uncovered side surface 5 in the radial, tangential, and axial directions of the tubular element 3.

[0032] The capsule 20 can be a tubular element in which a permanent magnet is fully or partially contained inside (with the surface of the permanent magnet facing the side surface 5 of the tubular element 3), or the capsule 20 can be composed of a plurality of capsule segments 21 as shown in Figure 2A.

[0033] Therefore, the magnet capsule 20 encloses at least the uncovered surface of each permanent magnet 4 facing the opposite side of the uncovered side 5, and the uncovered surface of each permanent magnet 4 facing the axial direction of the tubular element 3. However, the magnet capsule 20 can also completely enclose all of the permanent magnets 4.

[0034] The magnetic capsule 20 is made by subjecting a capsule preform, in particular to a hot isotropic pressurization treatment, to which one or more permanent magnets are enclosed. The preform is made of metal, preferably stainless steel. The preform can be a machined element, such as through a material reduction treatment or sintering treatment, and the machined element includes compartments configured to receive one or more permanent magnets, typically in a snug fit. With the permanent magnets in place in the compartments, the preform with the magnets is exposed to high temperatures to remove any gases that have been absorbed, and the preform is then compressed by exposure to an inert gas such as argon, which is pressurized at increased isotropic pressure while remaining at the high temperature. This causes the preform to shrink and form a magnetic capsule.

[0035] In embodiments where the magnetic capsule 20 is in the form of a tubular element, the magnetic capsule 20 can be positioned in contact with the tubular element 3 by press-fitting, with assistance from heating / cooling one of the elements, for example, by a thermal shrinkage process. Alternatively, or in combination, the magnetic capsule 20 can be fastened by screws, welding, or adhesive.

[0036] As shown in Figure 2A, a magnetic capsule can contain a number of magnetic capsule segments 21. In Figure 2A, one such capsule segment is highlighted with a dotted line. Each of the magnetic capsule segments 21 is made of metal and has undergone hot isostatic pressing treatment. Such a magnetic capsule segment 21 can contain one permanent magnet or a group of permanent magnets.

[0037] In embodiments where only one permanent magnet 4 is enclosed, the permanent magnet is typically enclosed by a magnet capsule segment 21 (see Figure 3A) that encloses at least the uncovered surfaces of the permanent magnet 4 facing radially to the tubular element 3, opposite the side surface 5, and facing tangentially and axially to the tubular element 3. “Radial,” “tangential,” and “axial” are shown in Figure 1. Such a capsule would cover the uncovered surfaces of the magnet that would otherwise be exposed to water, while the surface of the magnet facing the tubular element 3 may not be enclosed. However, as will be discussed in detail below, it is generally preferable to completely enclose the magnet.

[0038] If the magnetic capsule segment 21 contains a group of permanent magnets, such magnets are typically arranged side-by-side in the tangential direction of the tubular element 3 (the orientation of such magnets is shown in Figure 1).

[0039] In such embodiments, the magnetic capsule segment 21 faces the opposite side of the side 5 in the radial direction of the tubular element 3 and encloses at least the uncovered surfaces of the group of magnets 4 that are facing tangentially to the tubular element 3 and axially to the tubular element 3.

[0040] While permanent magnets are rectangular, it should be noted that the present invention is not limited to such rectangular magnets. When non-rectangular magnets are used, they still have uncovered surfaces facing the directions disclosed above, although such uncovered surfaces may be part of otherwise curved uncovered surfaces.

[0041] In summary, the magnetic capsule segment 21 can be disclosed as a structure that shields the magnet from exposure to water, preferably when positioned in contact with the tubular portion 3.

[0042] The orientation of magnet 4, and therefore the magnetization direction of the magnet with respect to the stator yoke, can be done according to what is normally practiced within the technical domain of permanent magnet thrusters to provide electric motor designs.

[0043] In one preferred embodiment, the magnetic capsule segment 21 encloses groups of four or more permanent magnets 4 arranged side-by-side in the tangential direction of the tubular element 3. The groups of four or more permanent magnets may preferably be arranged in two or more subgroups, where the tangential distance between the permanent magnets 4 within a subgroup is basically zero and less than the tangential distance between the subgroups.

[0044] In a preferred embodiment, the magnetic capsule segment 21 further encloses the uncovered surface of each permanent magnet 4 facing the side surface 5 in the axial direction of the tubular element 3, thereby completely enclosing one or more permanent magnets 4 within the magnetic capsule segment 21.

[0045] Figure 3 is shown to illustrate a preferred embodiment of segment 21. Figure 3A shows the magnetic capsule segment 21 in three dimensions, and Figure 3B is a cross-sectional view along line AA shown in Figure 3A. In the embodiment disclosed in Figure 3, the magnet is completely enclosed by the magnetic capsule segment 21 to form the magnetic capsule segment.

[0046] Figure 3B also discloses an optional backing element 22. As shown, the magnetic capsule segment 21 further encloses the backing element 22, which is positioned between the side surface 5 of the tubular element 3 and the contact surface of the permanent magnet 4 facing the side surface 5 of the tubular element 3 (when this segment is positioned in contact with the tubular element 3 as shown in Figure 2). In the shown embodiment, the magnetic capsule segment 21 further encloses the surface of the backing element 22 facing the uncovered side surface 5 and the surface of the backing element 22 facing the axial and tangential directions of the tubular element 3, thereby completely enclosing the permanent magnet 4 and backing element 22 within each of the segments 21.

[0047] The backing element 22 is particularly useful in embodiments in which the magnetic capsule segment 21 having the permanent magnet 4 is fastened to the rotor yoke 2 by screws. In such embodiments, the internal screw threads can be provided within the backing element, accessible by an opening provided in a portion of the magnetic capsule segment 21 facing the side 5. This allows the magnetic capsule segment 21 to be attached by screws extending through the tubular element 3, as shown by the screw 18 shown in Figure 2A.

[0048] The backing element 22 is made from a material usable in connection with hot isostatic pressing, meaning that when the magnet capsule segment is subjected to hot isostatic pressing, the compression of the backing element 22 is equivalent to the compression of the permanent magnet, preventing, or at least minimizing, the geometric strain of the magnet capsule segment 21 that results from the hot isostatic pressing. Preferably, the backing element 22 is made from the same metal as the capsule, but preferably a different metal from the metal of the magnet capsule, such as carbon steel, can be used.

[0049] In a preferred embodiment, at least some of the permanent magnets 4 are arranged side by side in the tangential direction of the tubular element 3, and the tangential distance between the permanent magnets 4 is greater than zero. In such an embodiment, the permanent magnets 4 are preferably arranged at equal intervals in the tangential direction.

[0050] In a preferred configuration of the permanent magnets, at least some of the permanent magnets 4, such as all of the permanent magnets 4, each have two sides facing tangentially to the tubular element 3, and at least some of the permanent magnets 4, such as all of the permanent magnets (4), are arranged such that two adjacent permanent magnets 4 abut each other along at least a portion of their sides.

[0051] Since many preferred embodiments of the thruster will be used in seawater, some corrosion in the magnetic capsule or magnetic capsule segment may be acceptable, but generally, it is preferable to prevent or at least mitigate corrosion of the magnetic capsule / magnetic capsule segment. To achieve this, the metal from which the magnetic capsule / magnetic capsule segment is made is a corrosion-resistant material such as stainless steel.

[0052] As presented herein, the permanent magnets 4 are preferably arranged side-by-side on the outside of the tubular element 3 or on the inside of the tubular element 3. However, to improve efficiency, it is preferable to place the permanent magnets on the outside of the tubular element 3. The inside refers to the side facing the hub 11, and the outside refers to the opposite side.

[0053] Since the tubular element 3 in contact with or positioned in the same location as the magnetic capsule 20 or magnetic capsule segment 21 typically has curvature, such as the radius of the tubular element 3, it is sometimes preferable to form the outer surface 6 of the magnetic capsule 20 or magnetic capsule segment 21 to have curvature (R) in the tangential direction of the tubular element 3. However, in the embodiments shown in Figures 3A to 3C, a portion of the magnetic capsule segment facing the tubular element 3 (bottom surface) is flattened. The surface of the tubular element 3 is formed to resemble a flat surface by including a piecewise flat surface as shown in Figure 3C (only one magnet-encapsulating element 21 is shown so that the surface of the tubular element 3 is visible). It is also preferable that the surface of the capsule 20 or capsule segment 21 has curvature on the surface away from the tubular element 3, because this allows for a smaller gap between the rotor yoke 2 and the stator yoke.

[0054] The manufacturing of the magnetic capsule 20, or the magnetic capsule segment 21 containing the permanent magnet, is disclosed in Figure 3 and will be described in detail with reference to the magnetic capsule segment shown in Figure 4. For ease of reference to Figure 3, the process in Figure 4 is shown with the magnetic capsule segment 21 oriented in the same way; however, in actual implementations, the magnetic capsule segment 21 may be manufactured advantageously upside down (relative to the orientation in Figure 4).

[0055] In Figure 4B, examples of the orientation of the poles of magnet 4 are also shown with the symbols "N" for the north pole and "S" for the south pole. The opposite polarity shown in Figure 4B is obtained by magnetization. The apparatus is used to hold down the magnet capsule segment 21 and magnetize each magnet beneath it. If the magnets were soft objects, they would move and attract each other. However, since the magnets are essentially fixed in place within the magnet capsule segment, they cannot move and therefore create the magnetic field necessary to allow rotation later.

[0056] Figure 5 discloses an example in which the two poles within the magnetic capsule segment 21 are oriented in opposite directions, indicated by the symbols "N" for the north pole and "S" for the south pole. Figure 5 shows the same cross-sectional view AA used in Figure 4B.

[0057] Figure 6 discloses an example in which the poles within the magnetic capsule segment 21 are oriented in opposite directions, indicated by the symbols "N" for the north pole and "S" for the south pole. Figure 6 shows the same cross-sectional view AA used in Figure 4B.

[0058] First, a preform 27 is manufactured. The preform 27 can be provided by sintering or by material reduction processes such as milling or turning. The preform includes a cavity 29 that is shaped and sized to receive the permanent magnet 4 and the backing element 22, preferably in a snug fit. The preform 27 is shown in cross-sectional view in Figure 4A.

[0059] Once the preform 27 is manufactured, referring to Figure 4B, the permanent magnet 4 is placed in the cavity 29 and positioned in the intended orientation and location within the magnet capsule segment 21. The backing element 22 is then placed in the cavity and abuts against the surface of the permanent magnet 4 as shown. A closing member 28 is positioned to close the opening of the cavity that has received the permanent magnet 4 and the backing element 22.

[0060] The closing member 28 is then welded to the preform 27, and a vacuum unit is created by hot isostatic pressurization.

[0061] It should be noted that the closing member 28 and the preform are preferably made of the same material.

[0062] The method for providing the magnetic capsule segment 21 is applicable to a single permanent magnet or a group of permanent magnets, such as multiple permanent magnets. As shown in Figure 4B, two groups of permanent magnets 4 are arranged side by side in the preform 27. While it is considered within the scope of the invention to encapsulate different magnets in the capsule segment 21 and to use different magnets in the permanent magnet thruster, it is generally preferable to encapsulate magnets of the same material in the capsule segment 21 and to use magnets of the same material in the permanent magnet thruster.

[0063] The preform 27, having magnets, backing elements 22, and closing members 28, undergoes a hot isostatic pressurization treatment as shown in Figure 4C. The hot isostatic pressurization treatment is carried out in a pressure tank 30 configured to withstand the relatively high pressure and temperature that spreads during the hot isostatic pressurization treatment. During the hot isostatic pressurization treatment, the pressure (indicated by the arrow labeled "P") and the temperature (indicated by the arrow labeled "Q") are increased.

[0064] Hot isostatic pressurization is typically performed using argon gas at 900°C to 1100°C and a hot isostatic pressurization pressure of 100 MPa to 200 MPa for 2 to 5 hours. After the hot isostatic pressurization stage, the furnace is switched off and the magnets are slowly cooled to room temperature to prevent residual stress and cracking. While the appropriate cooling rate for "slow cooling" can be determined experimentally, in a preferred embodiment, the furnace for hot isostatic pressurization is switched off and the sealed magnets are cooled over 5 hours from, for example, 1000°C to room temperature (e.g., 20°C). Therefore, in a preferred embodiment, a cooling rate of 200°C per hour is used. However, cooling rates in the range of 100°C to 300°C per hour have been found to be suitable with respect to the present invention.

[0065] Due to the aforementioned tight fit, shrinkage and shape changes after hot isostatic pressing are minimized, making final machining easier if necessary. Furthermore, the hot isostatic pressing process also benefits the magnet itself by removing internal pores and improving its magnetic properties.

[0066] The permanent magnet used in connection with a preferred embodiment of the present invention is preferably made of an alloy of neodymium, iron, and boron, Nd2Fe 14 The permanent magnets are neodymium magnets (NeFeB), samarium cobalt (SmCo5) magnets, and / or AlNiCo (aluminum, nickel, cobalt) magnets that form a tetragonal crystal structure. The permanent magnets related to the present invention are preferably in solid form rather than powder form before encapsulation.

[0067] Before encapsulating one or more magnets in the magnetic capsule segment 21 and performing the hot isostatic pressurization treatment as presented herein, the magnets may preferably be demagnetized (unless they are already non-magnetic or demagnetized). Such demagnetization offers several advantages. Because neodymium magnets have a very strong magnetic force (when magnetized), placing, for example, two magnets in the preform shown in Figure 4A and arranging the closure member 28 in the preform can be a very difficult task if the magnets are not demagnetized. This is particularly difficult if the magnets are spatially separated, as shown in Figures 4A and 4B, and / or if the encapsulating material has magnetic properties. However, if the magnets are demagnetized, handling them becomes technically easier and safety concerns are reduced.

[0068] The permanent magnets are magnetized after hot isostatic pressing. However, it is generally preferable to perform magnetization after the magnet capsule segments 21 are positioned in contact with the rotor yoke, because this makes it technically easier to attach the magnets to the rotor yoke compared to when the magnetization is performed before the magnets are attached to the rotor yoke. If magnetization is delayed until the magnet capsule segments are positioned in contact with the rotor yoke, the magnet capsule segments 21 can be machined as needed, as there is no need to consider problems caused by magnetism when fixing the magnet capsule segments to each other and / or to the machine used to machine the magnet capsule segments.

[0069] Magnetization is achieved by exposing the enclosed magnet to a magnetic field.

[0070] It should be noted that, depending on the permanent magnet used and the temperature during the hot isostatic pressing process, the temperature of the magnet may exceed the Curie temperature at which the magnet is demagnetized. Therefore, in such embodiments, actively performed demagnetization will not result in undesirable side effects.

[0071] In a preferred embodiment, the magnets are demagnetized by the hot isostatic pressing treatment such that the permanent magnets are demagnetized by a temperature exceeding the Curie temperature of the permanent magnets during the hot isostatic pressing treatment.

[0072] The permanent magnets are preferably solid pieces of a magnetizable material, that is, they are not powdered substances before the encapsulation and hot isostatic pressurization treatment.

[0073] Preferably, the permanent magnets are neodymium magnets, samarium cobalt magnets, and / or alnico (AINiCo) magnets. While it is considered within the scope of the present invention to encapsulate different magnets in the capsule segment 21, it is generally preferable to encapsulate magnets of the same material in the capsule segment 21.

[0074] While the present invention has been described in relation to specific embodiments, it should not be construed as being limited to the examples presented. The scope of the present invention is defined by the appended set of claims. In relation to the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Nor should references to elements such as “a” or “an” be construed as excluding plurals. Nor should the use of reference numerals in the claims for elements shown in the figures be construed as limiting the scope of the present invention. Furthermore, individual features described in different claims may, in some cases, be advantageously combined, and references to these features in different claims do not preclude the possibility or benefit of combining features. Itemized list of preferred embodiments

[0075] Item 1 Rotor yoke (2), A tubular element (3) that holds a plurality of permanent magnets (4) in contact with the side surface (5) of the tubular element (3) or at the location of the side surface (5), Multiple propeller blades (10) extend inward from the tubular element (3) to a hub (11) rotatably positioned on the shaft (12), Rotor yoke (2) including, A stator yoke (2) is positioned outside the rotor yoke (2) and includes a plurality of stator coils that can be magnetized by electric current, Equipped with, The plurality of permanent magnets (4) and the plurality of stator coils are configured to rotate the rotor yoke (2) when the plurality of stator coils are magnetized. The plurality of permanent magnets are enclosed in a magnet capsule (20) made of metal that has undergone hot isostatic pressurization, and the magnet capsule (20) encloses at least the uncovered surfaces of the permanent magnets (4) that are facing away from the side surface (5) in the radial direction of the tubular element (3) and facing in the tangential and axial directions of the tubular element (3). Permanent magnet thruster.

[0076] Item 2 The permanent magnet thruster (1) according to item 1, wherein the magnet capsule (20) comprises a number of magnet capsule segments (21) made of metal and each subjected to hot isostatic pressurization, each of which magnet capsule segments encloses one of the permanent magnets or a group of the permanent magnets arranged side by side in the tangential direction of the tubular element (3), and each of the one of the permanent magnets or the group of permanent magnets is enclosed by magnet capsule segments (21) that enclose at least the uncovered faces of each of the permanent magnets or the group of magnets (4) that are facing away from the side surface (5) in the radial direction of the tubular element (3) and facing in the tangential direction of the tubular element (3) and in the axial direction of the tubular element (3).

[0077] Item 3 Each of the magnet capsule segments (21) encloses a group of four or more permanent magnets (4) arranged side-by-side in the tangential direction of the tubular element (3), and the group of four or more permanent magnets is arranged in two or more subgroups, where the tangential distance between permanent magnets (4) within a subgroup is basically zero or less than the tangential distance between subgroups, as described in item 2, for the permanent magnet thruster (1).

[0078] Item 4 Each of the magnetic capsule segments (21) further encloses each uncovered surface of the permanent magnet (4) facing the uncovered side surface (5) in the axial direction of the tubular element (3), so that the permanent magnet (4) within the magnetic capsule segment (21) is completely enclosed by the magnetic capsule segment (21), as described in item 2 or 3.

[0079] Item 5 The permanent magnet thruster according to item 2 or 3, wherein the magnet capsule segment (21) further encloses a backing element (22) positioned between the side surface (5) of the tubular element (3) and the contact surface of the permanent magnet (4) facing the side surface (5) of the tubular element (3), and each of the magnet capsule segments (21) further encloses the surface of the backing element (22) facing the uncovered side surface (5) and the surface of the backing element (22) facing the axial and tangential directions of the tubular element (3), so that the permanent magnet (4) and the backing element (22) within each of the magnet capsule segments (21) are completely enclosed by the magnet capsule segment (21).

[0080] Item 6 The backing element (22) is preferably made of a metal such as carbon steel, different from the metal of the magnet capsule, as described in item 5 of the permanent magnet thruster.

[0081] Item 7 A permanent magnet thruster (1) according to any one of items 1 to 6, wherein the permanent magnet is completely enclosed by the magnetic capsule.

[0082] Item 8 The permanent magnet thruster according to any one of items 1 to 7, wherein the metal from which the magnetic capsule is made is selected from the group consisting of stainless steel, titanium, and bronze, particularly nickel-aluminum bronze.

[0083] Item 9 The permanent magnet thruster according to any one of items 1 to 8, wherein the permanent magnets (4) are arranged side by side on the outside of the tubular element (3) or on the inside of the tubular element (3).

[0084] Item 10 A permanent magnet thruster according to item 9, wherein the outer surface (6) of the magnetic capsule (20), or, if dependent on any one of items 2 to 6, the magnetic capsule segment (21) described in any one of items 2 to 6, has a curvature (R) in the tangential direction of the tubular element (3).

[0085] Item 11 A permanent magnet thruster (1) according to any one of items 1 to 10, wherein at least some of the permanent magnets (4) are arranged side by side in the tangential direction of the tubular element (3), the tangential distance between the permanent magnets (4) is greater than zero, and the permanent magnets (4) are preferably arranged at equal intervals in the tangential direction.

[0086] Item 12 A permanent magnet thruster according to any one of items 1 to 11, wherein at least some of the permanent magnets (4), such as all of the permanent magnets (4), each has two uncovered sides facing tangentially to the tubular element (3), and at least some of the permanent magnets (4), such as all of the permanent magnets (4), are arranged so that two adjacent permanent magnets (4) abut each other along at least a portion of their uncovered sides.

[0087] Item 13 The permanent magnet thruster described in any one of items 1 to 12, wherein the permanent magnet (4) is a rectangular parallelepiped.

[0088] Item 14 Each of the aforementioned permanent magnets is a solid of magnetizable material before the aforementioned encapsulation, as described in any one of items 1 to 13, for a permanent magnet thruster.

[0089] Item 15 The permanent magnet thruster described in any one of items 1 to 14, wherein the permanent magnets are, respectively, neodymium magnets, samarium cobalt magnets, and / or alnico magnets.

[0090] Item 16 A method for providing a segment containing multiple permanent magnets, wherein the permanent magnets are arranged side by side and enclosed by a magnet capsule segment (21) that completely encloses each of the permanent magnets (4), and the method is The enclosed magnet is held in an argon gas atmosphere at a temperature in the range of 900 to 1100 degrees Celsius and a pressure in the range of 100 MPa to 200 MPa for 2 to 5 hours. Subsequently, in order to prevent residual stress and cracking of the magnet, the enclosed magnet is cooled to a temperature of about 20°C, preferably at a cooling rate in the range of 100° to 300°C per hour. Methods that include...

[0091] Item 17 The method according to item 16, wherein the permanent magnet is demagnetized by hot isostatic pressurization, typically by causing the permanent magnet to be demagnetized at a temperature exceeding the Curie temperature of the permanent magnet.

[0092] Item 18 The capsule segment (21) includes a preform (27) configured to receive the magnets side by side and a closing member (28) configured to close the preform (27), and the method is performed before the hot isostatic pressing treatment. To provide a demagnetized permanent magnet, the permanent magnet is demagnetized, The demagnetized magnet is placed inside the preform (27), and the capsule segment (21) is closed by joining the closing member (28) to the preform (27), preferably by welding. The method described in item 16, including the subsequent steps.

[0093] Item 19 The method according to item 16 or 17, wherein the demagnetized magnet is magnetized after hot isostatic pressurization.

[0094] Item 20 The method according to item 19, wherein the magnetization is performed after the magnet capsule segment is positioned in contact with the rotor yoke of a permanent magnet thruster as described in any one of items 1 to 15.

[0095] Item 21 The method according to any one of items 16 to 20, wherein each of the permanent magnets is a solid of magnetizable material before the sealing and hot isostatic pressurizing treatment.

[0096] Item 22 The method according to any one of items 16 to 21, wherein the permanent magnets are, respectively, neodymium magnets, samarium cobalt magnets, and / or alnico magnets. [Explanation of Symbols]

[0097] 1. Thruster 2 Rotor yokes 3 Tubular elements 4 Permanent Magnets 5 Side view 6 External surface 10 propeller blades 11 Hubs 12 axes 18 screws 20 Magnetic Capsules 21 Magnetic Capsule Segments 22 Backing elements 24 axis direction 25 Radial 26 Tangential direction 27 Preform 28 Closing member 29 Cavity 30 pressure tanks R curvature

Claims

1. Rotor yoke (2), A tubular element (3) that holds a plurality of permanent magnets (4) in contact with the side surface (5) of the tubular element (3) or at the location of the side surface (5), Multiple propeller blades (10) extend from the tubular element (3) to a hub (11) that is rotatably arranged inward on an axis (12), A rotor yoke (2) including, A stator yoke is provided which is located outside the rotor yoke (2) and includes a plurality of stator coils that can be magnetized by electric current, Equipped with, The plurality of permanent magnets (4) and the plurality of stator coils are configured to rotate the rotor yoke (2) when the plurality of stator coils are magnetized. The plurality of permanent magnets are enclosed in a magnet capsule (20) made of metal that has undergone hot isostatic pressurization, and the magnet capsule (20) encloses at least the uncovered surfaces of the permanent magnets (4) that are facing away from the side surface (5) in the radial direction of the tubular element (3) and facing in the tangential and axial directions of the tubular element (3). Permanent magnet thruster.

2. The permanent magnet thruster (1) according to claim 1, wherein the magnet capsule (20) comprises a plurality of magnet capsule segments (21) made of metal and each subjected to hot isostatic pressurization, each of the magnet capsule segments (21) encloses one permanent magnet or a group of permanent magnets arranged side by side in the tangential direction of the tubular element (3), and each of the one permanent magnet or the group of permanent magnets is enclosed by the magnet capsule segments (21) that enclose at least the uncovered faces of each of the permanent magnets or the group of magnets (4) that are facing away from the side surface (5) in the radial direction of the tubular element (3) and facing in the tangential direction of the tubular element (3) and in the axial direction of the tubular element (3).

3. Each of the magnet capsule segments (21) encloses two, four, or more groups of the permanent magnets (4) arranged side by side in the tangential direction of the tubular element (3), the group of four or more permanent magnets is arranged in two or more subgroups, and the tangential distance between the permanent magnets (4) within the subgroup is basically zero or less than the tangential distance between the subgroups, the permanent magnet thruster (1) according to claim 2.

4. Each of the magnet capsule segments (21) further encloses each uncovered surface of the permanent magnet (4) facing the uncovered side surface (5) in the axial direction of the tubular element (3), so that the permanent magnet (4) within the magnet capsule segment (21) is completely enclosed by the magnet capsule segment (21), as described in claim 2 or 3.

5. The permanent magnet thruster according to claim 2 or 3, wherein the magnet capsule segment (21) further encloses a backing element (22) positioned between the side surface (5) of the tubular element (3) and the contact surface of the permanent magnet (4) facing the side surface (5) of the tubular element (3), and each of the magnet capsule segments (21) further encloses the surface of the backing element (22) facing the uncovered side surface (5) and the surface of the backing element (22) facing the axial and tangential directions of the tubular element (3), so that the permanent magnet (4) and the backing element (22) within each of the magnet capsule segments (21) are completely enclosed by the magnet capsule segment (21).

6. The permanent magnet thruster according to claim 5, wherein the backing element (22) is preferably made of a metal different from the metal of the magnet capsule, such as carbon steel.

7. The permanent magnet thruster (1) according to any one of claims 1 to 6, wherein the permanent magnet is completely enclosed by the magnetic capsule.

8. The permanent magnet thruster according to any one of claims 1 to 7, wherein the metal from which the magnet capsule is made is selected from the group consisting of stainless steel, titanium, and bronze, particularly nickel-aluminum bronze.

9. The permanent magnet thruster according to any one of claims 1 to 8, wherein the permanent magnets (4) are arranged side by side on the outside of the tubular element (3) or on the inside of the tubular element (3).

10. The permanent magnet thruster according to claim 9, wherein the outer surface (6) of the magnet capsule (20), or, if dependent on any one of claims 2 to 6, the magnet capsule segment (21) described in any one of claims 2 to 6, has a curvature (R) in the tangential direction of the tubular element (3).

11. The permanent magnet thruster (1) according to any one of claims 1 to 10, wherein the permanent magnets (4) are arranged side by side in the tangential direction of the tubular element (3), the tangential distance between the permanent magnets (4) is greater than zero, and the permanent magnets (4) are preferably arranged at equal intervals in the tangential direction.

12. A permanent magnet thruster according to any one of claims 1 to 11, wherein at least some of the permanent magnets (4), such as all of the permanent magnets (4), each has two uncovered sides facing tangentially to the tubular element (3), and at least some of the permanent magnets (4), such as all of the permanent magnets (4), are arranged such that two adjacent permanent magnets (4) abut each other along at least a portion of the uncovered sides.

13. The permanent magnet thruster according to any one of claims 1 to 12, wherein the permanent magnet (4) is a rectangular parallelepiped.

14. The permanent magnet thruster according to any one of claims 1 to 13, wherein each of the permanent magnets is a solid of a magnetizable material before the encapsulation.

15. The permanent magnet thruster according to any one of claims 1 to 14, wherein the permanent magnets are each a neodymium magnet, a samarium cobalt magnet, and / or an alnico magnet.

16. A method for providing a magnet capsule segment including one permanent magnet or a group of permanent magnets, wherein the permanent magnets of the group of permanent magnets are arranged side by side, and the magnets or the group of permanent magnets are enclosed by the magnet capsule segment (21) which completely encloses each of the permanent magnets (4), and the method is The magnetic capsule segment is subjected to hot isostatic pressurization treatment of the enclosed magnet (4) by holding it in an argon gas atmosphere at a temperature in the range of 900 to 1100 degrees Celsius and a pressure in the range of 100 MPa to 200 MPa for 2 to 5 hours. Subsequently, in order to prevent residual stress and cracks in the magnet, the magnet capsule segment is cooled to a temperature of approximately 20°C, preferably at a cooling rate in the range of 100° to 300°C per hour. Methods that include...

17. The method according to claim 16, wherein the magnet is demagnetized by the hot isostatic pressurization treatment, typically by causing the permanent magnet to be demagnetized at a temperature exceeding the Curie temperature of the permanent magnet.

18. The capsule segment (21) includes a preform (27) configured to receive the magnets side by side and a closing member (28) configured to close the preform (27), and the method is performed before the hot isostatic pressing treatment. To provide a demagnetized permanent magnet, the permanent magnet is demagnetized, The capsule segment (21) is closed by placing the demagnetized magnet inside the preform (27) and joining the closing member (28) to the preform (27), preferably by welding. The method according to claim 16, further comprising the following subsequent step.

19. The method according to claim 16 or 17, wherein the demagnetized magnet is magnetized after the hot isostatic pressurization treatment.

20. The method according to claim 19, wherein the magnetization is performed after the magnet capsule segment is positioned in contact with the rotor yoke of a permanent magnet thruster according to any one of claims 1 to 15.

21. The method according to any one of claims 16 to 20, wherein each of the permanent magnets is a solid of a magnetizable material before the sealing and hot isostatic pressurizing treatment.

22. The method according to any one of claims 16 to 21, wherein the permanent magnets are each a neodymium magnet, a samarium cobalt magnet, and / or an alnico magnet.

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