Permanent magnet bearing insert

Abstract

A vacuum pump (1), preferably a turbo molecular pump, comprises a rotor shaft (9) configured to have one or more rotor blades (8) coupled thereto, and the rotor shaft (9) defines a bearing seat (7) housing a permanent magnet bearing in an interference fit configuration, the magnetic bearing insert comprises one or more permanent magnet alloy rings (3, 4, 5) of a rotor bearing half of a permanent magnet bearing and a radially outwardly extending sleeve (16) coupled thereto around an outer periphery of the or each permanent magnet alloy ring (3, 4, 5), and the outer surface of the permanent magnet bearing insert (3) engages with the inwardly facing wall of the bearing seat (7) to provide an interference fit wherein the coefficient of thermal expansion of the radially outwardly extending sleeve (16) is at least substantially the same as the coefficient of thermal expansion of the material of the rotor shaft (9) defining the engaged bearing seat wall.

Description

Technical Field

[0001] This invention relates to a magnetic bearing insert for a vacuum pump, a vacuum pump (particularly a turbomolecular pump) including the magnetic bearing insert, and a method for manufacturing the vacuum pump. The invention also provides the application of neodymium magnet alloys in permanent magnet bearing inserts or vacuum pumps. Background Technology

[0002] Vacuum pumps typically include an impeller in the form of a rotor, which is mounted on a shaft to rotate relative to a surrounding stator. For example, in a turbomolecular pump, multiple sets of moving rotor blades are located on a shaft and separated from each other, and can move between stationary blades during use to compress gas and typically deliver the compressed gas to an outlet pump (e.g., a rotary pump).

[0003] The shaft is supported by two bearings located at either end or between the two ends. Typically, the upper bearing (the one closest to the pump inlet) is a magnetic bearing, and the lower bearing is a rolling bearing.

[0004] Magnetic bearings are typically passive magnetic bearings, comprising an inner stator bearing half and an outer rotor bearing half, the outer rotor bearing half forming part of the rotor shaft of the vacuum pump. The outer rotor bearing half typically includes one or more annular permanent magnets, which are coaxially aligned with the rotation axis of the rotor shaft and the inner stator bearing half.

[0005] Typically, the permanent magnet rings in the inner stator bearing half and the outer rotor bearing half are magnetized and arranged opposite each other to generate a repulsive force between the two halves. Therefore, they allow the rotor to be radially suspended.

[0006] Permanent magnet rings are typically made of samarium cobalt alloys (such as SmCo5). Advantageously, these magnets have extremely strong resistance to demagnetization and exhibit good temperature stability, with the highest operating temperature typically between 250°C and 550°C, and the Curie temperature between 700°C and 800°C.

[0007] However, there is a desire to turn to other magnetic alloys, such as neodymium magnets, because their stronger magnetism facilitates the use of smaller magnets and ultimately enables more compact vacuum pump designs. However, it has been found that known vacuum pump design and manufacturing methods are not suitable for successfully fitting these alternative magnets into their bearings.

[0008] The present invention solves, at least to some extent, some or all of the problems in the prior art. Summary of the Invention

[0009] Therefore, in a first aspect, the present invention provides a vacuum pump, preferably a turbomolecular pump, comprising a rotor shaft configured to have one or more rotor blades coupled thereto, and the rotor shaft defining a bearing housing that is configured to receive a permanent magnet bearing insert in an interference fit configuration.

[0010] The magnetic bearing insert includes one or more permanent magnet alloy rings of the rotor bearing half of the permanent magnet bearing and a radially outwardly extending sleeve connected to the outer periphery of the permanent magnet alloy ring or each of the permanent magnet alloy rings.

[0011] The outer surface of the permanent magnet bearing insert engages with the inward-facing wall of the bearing housing to provide an interference fit.

[0012] Preferably, the coefficient of thermal expansion of the radially outwardly extending sleeve is at least substantially the same (i.e. the same or greater) as the coefficient of thermal expansion of the material of the bearing housing wall to which the rotor shaft is bounded, and preferably substantially the same.

[0013] In a related aspect, the present invention also provides a permanent magnet bearing insert for a vacuum pump, the vacuum pump including a rotor shaft having one or more rotor blades coupled thereto, and the rotor shaft defining a bearing housing configured to receive the magnetic bearing insert in an interference fit configuration.

[0014] The magnetic bearing insert includes one or more magnetized permanent magnet alloy rings of the rotor bearing half of the permanent magnet bearing and a radially outwardly extending sleeve connected to the outer periphery of the permanent magnet alloy rings or each of the permanent magnet alloy rings.

[0015] The outer surface of the permanent magnet bearing insert is configured to engage with the inward-facing wall of the bearing housing after insertion into the bearing housing.

[0016] Typically, the sleeve of the permanent magnet bearing insert will be generally tubular. This sleeve can extend from a proximal end to a distal end. When positioned in the rotor shaft of a vacuum pump, the proximal end is usually positioned toward the low-pressure side of the rotor, while the distal end is usually positioned toward the relatively high-pressure section of the rotor.

[0017] The sleeve of the permanent magnet bearing insert can be a basically simple cylinder, or it can include other features.

[0018] One end of the sleeve may include a radially inwardly extending annular flange or other adjacent portion for retaining (multiple) permanent magnet alloy rings. In use, the permanent magnet alloy rings may directly abut against the radially inwardly extending annular flange or other adjacent portion. In some applications, this end may be the proximal end or the low-voltage end.

[0019] Such a radially inwardly extending annular flange or abutment can be an integral part of the sleeve, or it can be in the form of a ring or other insert inserted into the sleeve to provide abutment for (multiple) magnets or each magnet. The ring or insert can be held in place by snap-fit, interference fit, or other permanent or semi-permanent fastening methods.

[0020] In some applications, an adjacent ring or other abutment insert can be inserted at the end opposite to the one-piece ring to provide abutment to (multiple) magnets, thus providing abutment on both sides of (multiple) magnetic rings. Similarly, in some applications, two adjacent rings or abutment inserts can be inserted at opposite ends of the sleeve. This arrangement can also provide abutment at both ends of (multiple) magnetic rings.

[0021] One end of the sleeve may include a funnel-shaped inlet. This can facilitate pushing the permanent magnet ring into the funnel and / or forming an interference fit. In some applications, the funnel-shaped inlet may be located at the distal end of the sleeve or at a higher pressure end. Typically, before inserting the permanent magnet ring, the funnel-shaped inlet reduces the inner diameter of the sleeve from a diameter larger than the diameter of (multiple) permanent magnet rings to a diameter smaller than the diameter of (multiple) permanent magnet rings. After placement, the ring will typically be in an interference fit. After (multiple) permanent magnet rings are in place, an adjacent ring or other adjacent insert can be inserted through the funnel-shaped inlet to improve retention of (multiple) permanent magnet rings.

[0022] The ends of the sleeve may include tapered and / or stepped outer surfaces. This facilitates pushing the sleeve and / or bearing insert into the rotor shaft bearing housing. In some applications, the tapered and / or stepped outer surfaces may be located at the distal end or higher pressure end of the sleeve. However, in other applications (e.g., bell-shaped rotors), the tapered and / or stepped outer surfaces may be located at the proximal end or lower pressure end of the sleeve. Typically, the tapered outer surface increases the outer diameter of the sleeve from a diameter smaller than the inner diameter of the bearing housing to a diameter larger than the diameter of the bearing housing before the sleeve and / or bearing insert is inserted into the bearing housing. This facilitates pushing the sleeve and / or bearing insert into the bearing housing and / or forming an interference fit.

[0023] When positioned in the bearing housing on the rotor shaft, the end of the bearing insert can directly abut against a radially inwardly extending annular flange formed within the rotor shaft. This facilitates proper alignment of the rotor half of the permanent magnet bearing with the stator half of the permanent magnet bearing.

[0024] When the bearing insert is in place in the rotor's bearing housing, an additional abutment ring or (multiple) similar abutment inserts may be inserted into the rotor housing to abut against the sleeve and / or magnet. This additional abutment ring or abutment insert enhances the interference fit between the sleeve and the housing for better retention of the sleeve and / or magnet in place.

[0025] Bearing housings in the rotor shaft are typically in the form of cavities or recesses. Generally, the bearing housing is located near or towards the lower pressure end of the rotor shaft. However, in embodiments, the bearing housing may be located on the distal side of the rotor shaft, near or towards the relatively high pressure end, or at or towards both ends of the rotor shaft.

[0026] The bearing housing can be configured to slidably receive the bearing insert to achieve a tight engagement around the entire periphery of the bearing insert. Typically, the bearing housing has a generally circular cross-section along its length. The fit between the bearing housing and the bearing insert can be permanent or semi-permanent. However, this fit is sufficient to maintain the position of the permanent magnet bearing magnet during normal operation of the vacuum pump.

[0027] Typically, the bearing insert may include about 1 to about 10 permanent magnet alloy rings, more preferably about 2 to about 6 permanent magnet alloy rings, with 2 to 4 permanent magnet alloy rings being particularly preferred.

[0028] Preferably, the (multiple) permanent magnet alloy rings comprise neodymium iron boron (“neodymium”) magnets, preferably Nd2Fe 14 B; or samarium cobalt, preferably SmCo5 or Sm2Co. 17 Multiple neodymium magnets are particularly preferred. Typically, when multiple magnetic alloy rings are present, each magnetic alloy ring comprises substantially the same material.

[0029] Preferably, the coefficient of thermal expansion of the radially outwardly extending sleeve is at least substantially the same as, and more preferably substantially the same as, the coefficient of thermal expansion of the material of the bearing housing wall to which the rotor shaft is defined and engaged.

[0030] The present invention also provides a rotor for a vacuum pump, the rotor including a rotor shaft having one or more rotor blades coupled thereto, and the rotor shaft defining a bearing housing that is configured to receive a magnetic bearing insert in an interference fit.

[0031] The magnetic bearing insert includes one or more permanent magnet alloy rings of the rotor bearing half of the permanent magnet bearing and a radially outwardly extending sleeve connected to the outer periphery of the permanent magnet alloy ring or each of the permanent magnet alloy rings.

[0032] Preferably, the coefficient of thermal expansion of the radially outwardly extending sleeve is at least substantially the same as the coefficient of thermal expansion of the material of the bearing housing wall to which the rotor shaft is defined and joined.

[0033] Advantageously, the permanent magnet bearing inserts of various aspects of the present invention facilitate the inclusion of neodymium permanent magnets, etc., into the magnetic bearings of vacuum pumps.

[0034] It will be understood that permanent magnets are generally brittle and cannot withstand high tensile loads without fracturing. To control tensile stress, the rotor bearing half magnet is typically inserted into the rotor with an interference fit, thereby creating a radially inward compressive fit on the rotor bearing half magnet.

[0035] The material properties and dimensions of the permanent magnet and the rotor mean that the magnet expands less with temperature and centrifugal force than the rotor (which is typically made of aluminum). This results in a smaller amount of compression exerted on the rotor magnet by the rotor during use.

[0036] However, it will be understood that in order for the bearing to operate as intended, the residual compressive force at maximum speed and temperature must still be sufficient to hold the rotor bearing half magnet by the rotor, while keeping the tensile strain below the maximum permissible value for a given magnet (this can be referred to as minimum compressive force).

[0037] In addition, magnets can have minimum fit requirements. The minimum fit between magnets is the fit that generates the minimum compressive force as described above at the highest temperature and speed.

[0038] Additionally, the tolerances of the magnet and rotor result in a maximum fit, which can be defined as the “minimum fit requirement” plus manufacturing tolerances.

[0039] The compressive stress on the magnet and the overall stress in the rotor are highest when the maximum fit condition occurs. This typically occurs when the rotor is not rotating and the ambient temperature (and therefore the temperature of the rotor and bearings) is low (e.g., room temperature).

[0040] Additionally, the magnet is typically inserted into the rotor via a press, where the rotor is heated to a high temperature to minimize the required pressing force. The magnet can also be cooled to extremely low temperatures (such as in liquid nitrogen) to further reduce the required pressing force. The highest temperature the rotor can be heated to is typically limited by materials science factors, and the pressing force may also be limited by stress and practical considerations. Therefore, there are limitations on the maximum fit that can be achieved, which in turn limits the minimum fit requirements.

[0041] The inventors have found that the application of neodymium (NdFeB) magnets presents particular challenges because of their relatively low coefficient of thermal expansion and their susceptibility to demagnetization at relatively low temperatures (e.g., depending on the grade, starting from about 120°C).

[0042] Therefore, the minimum fit requirements are significantly higher than those for magnets such as NdFeB, and the maximum fit that can be achieved is reduced because cooling the magnets during fit operation does not help (since their coefficient of thermal expansion is negligible or negative), and depending on the rotor material, the maximum temperature they can be exposed to before significant demagnetization occurs is also reduced.

[0043] Using a sleeve allows for increased compression of the magnet, especially when the magnet is first inserted into the sleeve and then the assembly formed by the sleeve and the magnet is inserted into the rotor.

[0044] However, it has been found that, as seen in the prior art, permanent magnet bearing inserts made of materials with relatively low coefficients of thermal expansion (such as titanium) or more specifically, those with coefficients of thermal expansion lower than those of the rotor material (such as stainless steel in the case of aluminum rotors) are insufficient to accommodate NdFeB magnets in rotor bearing housings (especially aluminum rotor bearing housings).

[0045] In fact, while the thermal expansion of these materials relative to neodymium magnets can be controlled, the heating temperatures required to contract the magnets inside the sleeve and / or the pressing pressure required for maximum fit may be too high and / or may cause demagnetization of the magnets. Similarly, the heating temperatures required for the rotor to ensure the sleeves remain in contact during operation (especially if the rotor is made of aluminum) may weaken the rotor's strength.

[0046] The inventors have discovered that by providing a permanent magnet bearing insert comprising a radially outwardly extending sleeve whose coefficient of thermal expansion is at least substantially the same as that of the material of the rotor shaft configured to receive the magnetic bearing insert, an appropriate level of compression can be maintained during use and when no longer in use, while an acceptable press-fit insertion force can be employed without excessive heating of the magnet, sleeve, and / or rotor. Therefore, this invention facilitates the application of neodymium magnets in the magnetic bearings of vacuum pumps (particularly turbomolecular pumps), thereby reducing the required magnet size and potentially reducing the size of the bearing and / or vacuum pump.

[0047] The coefficients of thermal expansion mentioned herein refer to the linear coefficients of thermal expansion (CLTE) measured at 20°C (t0=20°C, t1=100°C). Unless otherwise stated, all measurements throughout this specification were obtained at 20°C and standard atmospheric pressure (101325 Pa).

[0048] The coefficient of thermal expansion of the sleeve can be at least substantially the same as, and preferably substantially the same as, the coefficient of thermal expansion of the material defining the bearing housing wall of the rotor shaft. More preferably, the sleeve is made of the material defining the bearing housing wall.

[0049] In this document, "substantially the same" can mean within about 10% of the given parameters, preferably within about 5% of the given parameters, and more preferably within about 1% of the given parameters.

[0050] Preferably, the coefficient of thermal expansion of the sleeve is approximately 1.5 × 10⁻⁶ times that of the material defining the bearing housing wall of the rotor shaft. -6 K-1 Within the range, preferably within about 0.25 × 10 -6 K -1 Within the range.

[0051] In this embodiment, the coefficient of thermal expansion of the material of the bearing housing wall to which the rotor shaft is defined has a coefficient of thermal expansion of approximately 8.6 × 10⁻⁶. - 6 K -1 Or larger, preferably about 10.1K -1 Or larger, preferably about 17.3 or larger, more preferably about 23K -1 Or larger.

[0052] Preferably, the sleeve comprises a material having a linear coefficient of thermal expansion of approximately 20 × 10⁻⁶. -6 K -1 Or larger, preferably about 23 × 10 -6 K -1 Or larger.

[0053] Preferably, the sleeve comprises a material having a linear coefficient of thermal expansion of approximately 20 × 10⁻⁶. -6 K -1 Or larger, preferably about 22 × 10 -6 K -1 Or larger, and the linear coefficient of thermal expansion of the material of the bearing housing wall to which the rotor shaft is bounded is about 23 × 10⁻⁶. -6 K -1 Or larger, preferably about 23 × 10 -6 K -1 Or larger.

[0054] Typically, the sleeve is made of a non-ferromagnetic material.

[0055] In this embodiment, the sleeve is made of aluminum. Typically, the cavity is defined by an aluminum portion of the rotor shaft, which is preferably made of a high-strength aluminum alloy.

[0056] In a particularly preferred embodiment, both the insert sleeve and the portion of the rotor shaft defining the rotor cavity for receiving the sleeve are made of aluminum, preferably a substantially identical aluminum alloy. For the avoidance of doubt, aluminum as referred to herein includes aluminum alloys, that is, alloys in which aluminum is the primary metal. Typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel, and zinc. Aluminum can be anodized or coated. 2000 series and 7000 series aluminum alloys are particularly suitable for this invention. Preferably, substantially the entire structure of the rotor shaft is made of aluminum.

[0057] Typically, the permanent magnet alloy ring, or each permanent magnet alloy ring, is connected to the sleeve via an interference fit. Preferably, the permanent magnet alloy ring(s) are connected to the sleeve before the sleeve is inserted into the cavity of the pump rotor.

[0058] In this embodiment, the magnetic bearing insert is machined after the permanent magnet alloy ring is attached to the sleeve, typically by machining the outermost radial wall of the sleeve after the magnetic alloy ring is attached. This in-situ machining is usually the final machining of the sleeve. Machining the sleeve after the magnet is in place allows for tighter tolerances compared to machining individual components before assembly.

[0059] Similarly, the rotor can be machined after the insert is in place. This is typically the final machining of the rotor. Likewise, machining the rotor after the insert (including (multiple) toroidal magnets) is in place can achieve tighter tolerances compared to machining the individual components before assembly.

[0060] To avoid ambiguity, in all embodiments and aspects, the permanent magnet alloy ring, or each permanent magnet alloy ring, may be magnetic. In embodiments, the permanent magnet alloy ring, or each permanent magnet alloy ring, comprises a neodymium magnet alloy.

[0061] Neodymium magnets (also known as NdFeB, NIB, or neodymium magnets) are permanent magnets made of an alloy of neodymium, iron, and boron, forming a typical Nd2Fe alloy. 14 B has a tetragonal crystal structure. Neodymium magnets are magnetized.

[0062] In this embodiment, the rotor shaft and one or more rotor blades are monolithic, i.e., made of a single piece of material. The rotor blades may extend radially outward from the rotor shaft in a series of axially separated, substantially planar arrays. This configuration of the rotor shaft may be referred to as a monolithic rotor.

[0063] Alternatively, one or more of the rotor blades may form part of an annular rotor blade array or multiple annular rotor blade arrays, which are coupled to the rotor shaft by an interference fit. Typically, the annular rotor blade array(s) are coupled to the rotor after the bearing insert is in place. Advantageously, this facilitates the introduction of further compression into the permanent magnet ring. Preferably, the rotor shaft is machined after the magnetic bearing insert is in place, but before the rotor blade array(s) are coupled to the rotor shaft. A rotor shaft with this configuration may be referred to as a multi-plate rotor(s).

[0064] Permanent magnets typically exhibit anisotropic thermal expansion, meaning the value of their coefficient of thermal expansion depends on the direction in which it is considered. Generally, the coefficient of thermal expansion that has the greatest impact on the expansion of the ring's diameter is the coefficient of thermal expansion in the circumferential or ring-shaped direction. Preferably, the coefficient of thermal expansion of the permanent magnet alloy ring in such a direction is less than about 16 × 10⁻⁻⁻⁶. 6 K⁻¹, more preferably in 4×10⁻ 6 K⁻¹ or less, and even more preferably 1×10⁻ 6K⁻¹ or less. Preferably, such a permanent magnet alloy ring is made of neodymium iron boron. Preferably, the ring is magnetized axially or radially.

[0065] In another aspect, the present invention provides a method for manufacturing a vacuum pump, preferably a turbomolecular pump, according to the foregoing aspects. The pump includes a rotor shaft configured to have one or more rotor blades coupled thereto, and the rotor shaft defines a cavity for receiving a magnetic bearing insert.

[0066] The method includes the following steps: a) providing a permanent magnet bearing insert according to a first aspect of the invention; and b) inserting the magnet bearing insert into a cavity of the rotor of a vacuum pump for receiving the magnet bearing insert and forming an interference fit.

[0067] In an embodiment of the method, prior to step a), the permanent magnet bearing insert is pre-assembled by inserting one or more permanent magnet alloy rings into the sleeve to form an interference fit.

[0068] In embodiments involving multiple rotors, after step b), one or more rotor blades are coupled to the rotor shaft, preferably using an interference fit. Preferably, after step b), the rotor shaft is machined in an intermediate step before coupling the one or more rotor blades to the rotor shaft.

[0069] In one embodiment, the permanent magnet bearing insert is cooled and / or a portion of the defining cavity of the rotor is heated before the permanent magnet bearing insert is inserted into the cavity.

[0070] In another aspect, the present invention provides the application of a neodymium magnet alloy in permanent magnet bearing inserts or vacuum pumps, particularly in the inserts or vacuum pumps described herein. The neodymium magnet alloy may be magnetic. Attached Figure Description

[0071] The invention will now be described with reference to the following drawings, which are intended to be non-limiting.

[0072] Figure 1 A magnetic bearing insert according to the invention is shown in place in an integral turbomolecular pump rotor.

[0073] Figure 2 A magnetic bearing insert according to the present invention is shown.

[0074] Figure 3 A magnetic bearing insert according to the invention is shown in place in a multi-stage turbomolecular pump rotor.

[0075] Figure 4 A rotor bearing including a bearing insert according to the invention is shown. Detailed Implementation

[0076] like Figure 1 As illustrated, the present invention provides a permanent magnet bearing insert (2), preferably for a turbomolecular pump rotor (1). In the illustrated example, the magnetic bearing insert (2) is positioned toward the relatively low-pressure end (6) of the rotor (1). The insert (2) is slidably mounted in a magnetic bearing housing (7) formed in the rotor (1). The bearing insert (2) is held in place within the bearing housing (7) by an interference fit.

[0077] In the illustrated embodiment, an interference fit is formed between the longitudinally extending and radially outward-facing circumferential wall of the insert and the longitudinally extending and radially inward-facing wall of the bearing housing. Typically, the interference fit causes the bearing insert and / or the magnetic ring or each magnetic ring to be in a compressed state within the rotor's operating temperature range (e.g., from about ambient temperature (e.g., 20°C) to about 90°C, or in other applications to about 120°C). Typically, the interference fit causes the bearing insert and / or the magnetic ring or each magnetic ring to be in a compressed state within the rotor's operating rotational speed range (e.g., up to about 100,000 rpm).

[0078] The illustrated bearing housing (7) includes a radially inwardly extending annular shoulder or shoulder (15). After insertion into the housing, the distal end of the insert rigidly engages with the shoulder or shoulder (15). This facilitates the precise positioning of the bearing insert (2) and thus the magnetic ring or each magnetic ring (3, 4, 5) within the rotor (1). Typically, a press is used to push the bearing insert (2) into the bearing housing (7) through the bearing housing opening.

[0079] like Figure 2 As better illustrated in the diagram, the sleeve opening may be in the form of a funnel (13). The opening of the funnel has an inner diameter that is substantially the same as or larger than the outer diameter of the magnetic ring or each magnetic ring before it is inserted into the funnel. The end of the funnel may have an inner diameter smaller than the outer diameter of the magnetic ring or each magnetic ring before it is inserted into the funnel. The funnel-shaped inlet (13) to the sleeve facilitates the insertion of the magnetic ring or each magnetic ring (3, 4, 5) into the sleeve.

[0080] Similarly, in the embodiments and as Figure 2 As illustrated, the end of the sleeve may have a tapered (14) or stepped leading edge. Before being inserted into the bearing housing, the leading edge of the sleeve gradually transitions from an outer diameter smaller than the inner diameter of the bearing housing opening to an outer diameter larger than the inner diameter of the bearing housing opening. Similarly, the tapered leading edge of the sleeve facilitates the insertion of the sleeve (16) into the bearing housing (7).

[0081] The sleeve (16) may also include a radially inwardly extending annular lip (12) at its second end opposite the sleeve inlet (13). The annular lip (12) provides an abutment for the magnetic ring (3) of the bearing insert (2) to abut. This can facilitate the precise placement of the magnetic ring, or each magnetic ring, within the sleeve, rotor, and vacuum pump.

[0082] Figure 1 The rotor (1) shown in the diagram is a monolithic construction. That is, the rotor (1), including the rotor blades (8), rotor shaft (9), and rotor bearing housing wall (10), is entirely formed from a single piece of material. In this example, the material is aluminum alloy. Multi-part rotors are also considered, where the rotor blades are connected to the rotor shaft by an interference fit, typically after the bearing inserts are in place in the rotor bearing housing wall. In the embodiment described, the rotor shaft can be machined after the bearing inserts are in place but before the rotor blades are connected to the rotor shaft. This can improve tolerances.

[0083] Rotor blades (8) are arranged in a series of annular arrays extending radially outward from the rotor shaft (9). The size and spacing of the rotor blades will be determined according to the specific requirements of the pump under discussion; however, generally, both the size and spacing of the rotor blades decrease from the lower pressure end (6) of the rotor shaft (9) toward the relatively higher pressure end (11) of the rotor shaft (10). In the illustrated embodiment, the bearing housing (7) is positioned toward the lower pressure end of the rotor shaft (9). The bearing insert and (multiple) magnetic rings are held so that they are substantially coaxial with the axis of rotation (A) of the rotor shaft. In use, the bearing insert and (multiple) magnetic rings rotate around the axis of rotation (A) of the rotor shaft.

[0084] The permanent magnet bearing insert comprises multiple permanent magnet alloy rings (3, 4, 5), three in this example. The illustrated permanent magnet alloy rings are made of ferromagnetic material.

[0085] Typically, the sleeve is a monolithic structure. Usually, the sleeve is made of essentially a single material, but in embodiments, the sleeve may be coated and / or anodized.

[0086] Preferably, the sleeve comprises aluminum, is substantially composed of aluminum, or is composed of aluminum, wherein the aluminum is preferably an aluminum alloy selected from the 2000 series or 7000 series.

[0087] Preferably, the magnetic alloy ring or each magnetic alloy ring comprises a ferromagnetic material, is substantially composed of a ferromagnetic material, or is composed of a ferromagnetic material, wherein the ferromagnetic material is preferably Nd₂Fe. 14 B (neodymium magnet), SmCo5, Sm(Co,Fe,Cu,Zr)7, preferably Nd2Fe 14B or SmCo5. Neodymium magnets are particularly preferred, especially sintered neodymium alloys. The magnetic alloy rings, or each magnetic alloy ring, may be coated or electroplated, such as with nickel or zinc, or may be coated with polymers and / or paint.

[0088] Preferably, the permanent magnet bearing and / or vacuum pump are configured such that the magnetic alloy ring or each magnetic alloy ring does not exceed about 120°C during use.

[0089] Preferably, the Curie temperature of the magnetic alloy is from about 310°C to about 370°C.

[0090] As previously stated, the present invention also provides a method for manufacturing a vacuum pump, preferably a turbomolecular pump. The pump includes a rotor shaft configured to have one or more rotor blades coupled thereto, and the rotor shaft defines a cavity for receiving a magnetic bearing insert.

[0091] The method of the present invention will generally include the following steps: providing a permanent magnet bearing insert according to the present invention, and inserting the magnet bearing insert into a passive magnet bearing cavity of a vacuum pump rotor to form an interference fit.

[0092] Typically, before inserting the permanent magnet bearing insert into the rotor, the permanent magnet bearing insert is pre-assembled by first inserting permanent magnet alloy rings, or each permanent magnet alloy ring, into a sleeve and forming an interference fit therebetween. Typically, an external press is used to push the rings, or each ring, into the sleeve. In embodiments, the permanent magnet bearing insert is cooled and / or a portion of the rotor's defining cavity is heated before inserting the insert into the cavity.

[0093] After the magnetic alloy ring is in place, the sleeve can be machined. Typically, the surfaces of the sleeve that can form an interference fit with the rotor bearing housing are machined, such as the radially outward-extending circumferentially extending outer surface of the sleeve. Performing this machining step after the ring is in place can reduce tolerances and / or simplify manufacturing. This is usually the final machining of the sleeve.

[0094] Before insertion into the rotor, the insert may be cooled to a temperature below approximately 0°C, preferably below approximately -50°C, and preferably below approximately -75°C, for example, using dry ice or liquid nitrogen. Preferably, the portion defining the cavity of the rotor is heated to a temperature of approximately 100°C to approximately 150°C. After placement, the magnetic alloy rings, or each magnetic alloy ring and sleeve, are allowed to reach ambient temperature.

[0095] The rotor shaft can be machined after the insert is in place, for example, in the case of multiple rotors, by machining the surfaces of the rotor blades of the receiving annular array of the rotor shaft. Performing this machining step after the insert is in place can reduce tolerances and / or simplify manufacturing. Typically, this can be the final machining of the rotor. Figure 3A multi-piece rotor according to the present invention is shown.

[0096] In an embodiment, after the permanent magnet bearing insert is in place, one or more rotor blades (typically in the form of one or more annular arrays) are coupled to the rotor shaft, preferably using an interference fit.

[0097] The suitable vacuum pump for use with the permanent magnet bearing insert and rotor shaft described herein is the nEXT manufactured by Edwards Vacuums.

[0098] Figure 3 An embodiment of the present invention is shown, wherein the rotor (1) is a plurality of rotors. (The last part is incomplete and likely refers to a different embodiment of the invention.) Figure 1 and Figure 2 Similar or identical features are identified by corresponding reference numerals in the accompanying drawings. Figure 3 In the illustrated embodiment, the rotor (1) includes a rotor shaft (9) and rotor blades (8) of a plurality of separately formed annular arrays (17) connected thereto by an interference fit. The annular arrays (17) of rotor blades can be configured as a single monolithic structure or a plurality of blocks of one or more annular arrays. An annular array block or each annular array block itself can be a multi-array having two or more arrays in a single monolithic structure, or a single array having a single annular array.

[0099] As described above, preferably, in a multi-rotor configuration, the rotor blades are coupled to the rotor shaft after the magnetic bearing inserts are in place. This allows for improved compression of the (multiple) permanent magnet bearing rings.

[0100] Figure 4 An assembled permanent magnet bearing including a bearing insert according to the invention is shown.

[0101] As illustrated, the magnetic bearing comprises an inner stator bearing half and an outer rotor bearing half, the outer rotor bearing half forming part of the rotor shaft of the vacuum pump. The illustrated outer rotor bearing half comprises three annular permanent magnets (3, 4, 5) disposed in a permanent magnet bearing insert according to the invention. The bearing insert and the annular magnets are substantially coaxially aligned with the axis of rotation (A) of the rotor shaft (9). The bearing also includes an inner stator bearing half, which also comprises three annular permanent magnets (18, 19, 20).

[0102] The permanent magnet rings (18, 19, 20) illustrated in the inner stator bearing half and the permanent magnet rings (3, 4, 5) in the outer rotor bearing half are magnetized and arranged opposite each other to generate a repulsive force between the two halves. Thus, they cause the rotor shaft (9) to be radially suspended.

[0103] It will be understood that various modifications may be made to the illustrated embodiments without departing from the spirit and scope of the invention as defined by the appended claims in accordance with patent law.

[0104] Figure Labels 1. Turbomolecular pump rotor 2. Magnetic bearing insert 3. Magnetic ring 4. Magnetic ring 5. Magnetic ring 6. Low-pressure end of the rotor 7 Bearing housing 8 rotor blades 9. Rotor shaft 10 Rotor bearing housing wall 11 High-voltage end 12 Ring-shaped lips 13 Funnel-shaped inlet 14. Conical sleeve end 15. Shoulder / Stand-up Shoulder 16 sleeve 17. Circular Array 18 Magnetic Rings 19 Magnetic Rings 20 magnetic rings

Claims

1. A vacuum pump, preferably a turbomolecular pump, comprising a rotor shaft configured with one or more rotor blades coupled thereto, and defining a bearing seat configured to accommodate a permanent magnetic bearing insert with an interference fit, wherein the magnetic bearing insert comprises one or more permanent magnet alloy rings of a rotor bearing half of a permanent magnetic bearing and a radially outwardly extending sleeve coupled to an outer periphery of the or each permanent magnet alloy ring, and an outer surface of the permanent magnetic bearing insert engages with an inwardly facing wall of the bearing seat to provide the interference fit, wherein a coefficient of thermal expansion of the radially outwardly extending sleeve is at least substantially the same as a coefficient of thermal expansion of a material of the rotor shaft defining the engaged bearing seat wall. The coefficient of thermal expansion of the radially outwardly extending sleeve is substantially the same as a coefficient of thermal expansion of a material of the rotor shaft defining the engaged bearing seat wall. The permanent magnet alloy ring or each permanent magnet alloy ring is coupled to the sleeve with an interference fit. The permanent magnet alloy ring is coupled to the sleeve prior to the sleeve being inserted into the bearing seat of the pump rotor.

2. Vacuum pump according to claim 1, wherein, The magnetic bearing insert is machined after the permanent magnet alloy ring is coupled to the sleeve.

3. A vacuum pump according to claim 1 or claim 2, wherein, The rotor is final machined after the insert is installed.

4. A vacuum pump according to any preceding claim, wherein, The bearing seat is defined by an aluminium portion of the rotor shaft; and / or wherein the sleeve is of aluminium.

5. A vacuum pump according to any preceding claim, wherein, The permanent magnet alloy ring or each permanent magnet alloy ring comprises a neodymium magnet magnetised in an axial or radial direction.

6. The vacuum pump of any one of claims 3 or 4, wherein, The rotor shaft and one or more rotor blades are monolithic, and / or wherein one or more of the rotor blades form part of an annular rotor blade array coupled to the rotor shaft with an interference fit.

7. A vacuum pump according to any preceding claim, wherein, 11. A method of manufacturing a vacuum pump, preferably a turbomolecular pump, according to any one of claims 1 to 10, the pump comprising a rotor shaft configured with one or more rotor blades coupled thereto, and defining a bearing seat for receiving a magnetic bearing insert, the method comprising the steps of: a) providing a permanent magnetic bearing insert comprising one or more permanent magnet alloy rings of a rotor bearing half of a permanent magnetic bearing and a radially outwardly extending sleeve coupled to an outer periphery of the or each permanent magnet alloy ring; and b) inserting the magnetic bearing insert into a rotor bearing seat of the vacuum pump rotor and forming an interference fit, and wherein a coefficient of thermal expansion of the radially outwardly extending sleeve is at least substantially the same, preferably substantially the same, as a coefficient of thermal expansion of a material of the rotor shaft defining the engaged bearing seat wall; optionally wherein the permanent magnetic bearing insert is cooled and / or a portion of the rotor defining the bearing seat is heated prior to the bearing insert being inserted into the bearing seat.

8. A vacuum pump according to any preceding claim, wherein, The permanent magnetic alloy ring has a coefficient of thermal expansion in the circumferential direction of less than about 4 x 10 −6 K -1 .

9. A vacuum pump according to any preceding claim, wherein, ​ 10. A vacuum pump according to any preceding claim, wherein, ​ ​ ​ ​ ​ 12. The method of claim 11, wherein, Prior to step a), the permanent magnetic bearing insert is pre-assembled by inserting the permanent magnetic alloy ring into the sleeve and forming an interference fit, and / or wherein after step b) one or more rotor blades are coupled to the rotor shaft.

13. A permanent magnetic bearing insert for a vacuum pump, the vacuum pump comprising a rotor shaft having one or more rotor blades coupled thereto and defining a bearing seat configured to receive the magnetic bearing insert in an interference fit configuration, wherein the magnetic bearing insert comprises one or more permanent magnetic alloy rings of a rotor bearing half of a permanent magnetic bearing and a radially outwardly extending sleeve coupled thereto around an outer periphery of the or each permanent magnetic alloy ring, and an outer surface of the permanent magnetic bearing insert is configured to engage with an inwardly facing wall of the bearing seat upon insertion into the bearing seat, wherein a coefficient of thermal expansion of the radially outwardly extending sleeve is at least substantially the same, preferably substantially the same, as a coefficient of thermal expansion of a material defining the engaged bearing seat wall of the rotor shaft.

14. A vacuum pump according to any one of claims 1 to 10 comprising a permanent magnetic bearing insert according to claim 13.

15. Use of a neodymium magnetic alloy in a vacuum pump according to claims 1 to 10 or 14 or in a permanent magnetic bearing insert according to claim 13; or use of a neodymium magnet in a vacuum pump according to any one of claims 1 to 10.

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