Permanent magnet bearing insert

Abstract

The present invention provides a vacuum pump (1), preferably a turbomolecular pump, comprising a rotor shaft (9) configured to have one or more rotor blades (8) coupled to the rotor shaft, wherein the rotor shaft (9) defines a bearing well (7) that receives a permanent magnet bearing insert in an interference fit configuration, the permanent magnet bearing insert comprising one or more permanent magnet alloy rings (3, 4, 5) of the rotor bearing half of the permanent magnet bearing, and a radially outward-extending sleeve (16) coupled to the or each permanent magnet alloy ring, wherein the outer surface of the permanent magnet bearing insert (3) engages with the inward-facing wall of the bearing well (7) to provide an interference fit, and the radially outward-extending sleeve (16) has a coefficient of thermal expansion at least substantially the same as the coefficient of thermal expansion of the material of the rotor shaft (9) that defines the bearing well wall to be engaged.

Description

[Technical Field]

[0001] The present invention relates to a magnetic bearing insert for a vacuum pump, a vacuum pump equipped therewith, in particular a turbomolecular pump, and a method for manufacturing a vacuum pump. The present invention further provides the use of neodymium magnet alloy in a permanent magnet bearing insert or a vacuum pump. [Background technology]

[0002] Generally, a vacuum pump has a rotor-type impeller mounted on a shaft that rotates relative to a surrounding stator. For example, in a turbomolecular pump, a series of movable rotor blades are arranged on the shaft, which are movable and isolated from stationary blades during use, compressing the gas and feeding it to an outlet pump, typically a rotary pump.

[0003] The shaft is supported by two bearing configurations located at each end or in the middle of the shaft. Generally, the upper bearing (the side closest to the pump inlet) can be a magnetic bearing, and the lower bearing is a rolling bearing.

[0004] Generally, magnetic bearings are passive magnetic bearings, comprising an inner stator bearing half and an outer rotor bearing half, with the outer rotor bearing half forming part of the rotor shaft of a vacuum pump. Generally, the outer rotor bearing half comprises one or more annular permanent magnets aligned coaxially with the rotor shaft's rotation axis and the inner stator bearing half.

[0005] Generally, permanent magnet rings in the inner stator bearing half and the outer rotor bearing half are magnetized and positioned relative to each other to create a repulsive force between the two halves. Thus, they can levitate the rotor radially.

[0006] Generally, permanent magnet rings are made from samarium-cobalt alloys such as SmCo5. Conveniently, these magnets exhibit high resistance to demagnetization and excellent temperature stability, with a maximum operating temperature generally between 250°C and 550°C and a Curie temperature of 700°C to 800°C.

[0007] However, there is a desire to move to other magnetic alloys, such as neodymium magnets, which have stronger magnetic force, enabling the use of smaller magnets and ultimately facilitating more compact vacuum pump designs. However, known vacuum pump designs and manufacturing methods have proven unsuitable for properly accommodating these alternative magnets in bearings. [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention addresses, to some extent, some or all of the problems of these prior art. [Means for solving the problem]

[0009] Accordingly, in a first aspect, the present invention provides a vacuum pump, preferably a turbomolecular pump, the vacuum pump comprising a rotor shaft configured to have one or more rotor blades coupled to the rotor shaft, the rotor shaft defining a bearing well for receiving a permanent magnet bearing insert in an interference fit configuration.

[0010] The magnetic bearing insert comprises one or more permanent magnet alloy rings in the rotor bearing half of the permanent magnet bearing, and a sleeve extending radially outward around the outer circumference of the or each permanent magnet alloy ring and coupled to the or each permanent magnet alloy ring.

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

[0012] Preferably, the radially outwardly extending sleeve has a coefficient of thermal expansion that is at least substantially the same (i.e., the same or greater) as that of the material of the rotor shaft defining the engaged bearing well, preferably substantially the same coefficient of thermal expansion.

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

[0014] The magnet bearing insert comprises one or more magnetized permanent magnet alloy rings of the rotor bearing half of the permanent magnet bearing and a radially outwardly extending sleeve coupled around the outer periphery of said or each permanent magnet alloy ring.

[0015] The outer surface of the permanent magnet bearing insert is configured to engage the inwardly facing wall of the bearing well after being inserted into the bearing well.

[0016] Typically, the sleeve of the permanent magnet bearing insert can be generally tubular. The sleeve can extend from a proximal end to a distal end. When in the original position of the rotor shaft of the vacuum pump, the proximal end is typically disposed towards the low pressure end of the rotor and the distal end is typically disposed towards the relatively high pressure section of the rotor.

[0017] The sleeve of the permanent magnet bearing insert can be a substantially smooth cylinder or can include other features.

[0018] One end of the sleeve can include an annular flange or other abutment extending radially inwardly for retaining the permanent magnet alloy ring(s). In use, the permanent magnet alloy ring can directly abut against the annular flange or other abutment extending radially inwardly. In some applications, this end can be the proximal end or the low pressure end.

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

[0020] In some applications, a contact ring or other contact insert can be inserted at an end opposite the integral ring to provide contact portions on both sides of the magnet ring(s), thereby providing contact portions for the magnet(s). Similarly, in some applications, two contact rings or contact inserts can be inserted at each of the two ends of the sleeve. This arrangement can also provide contact portions for the magnet ring(s) at both ends.

[0021] One end of the sleeve can include a funnel-shaped inlet. This can assist in pushing the permanent magnet alloy ring into the funnel and / or forming an interference fit. In some applications, the funnel-shaped inlet can be the distal end or the high-pressure end of the sleeve. Typically, before the permanent magnet alloy ring is inserted, the funnel-shaped inlet is such that the inner diameter of the sleeve decreases from a diameter larger than the diameter of the permanent magnet alloy ring(s) to a diameter smaller than the diameter of the permanent magnet alloy ring(s). Typically, in its original position, the ring can be in an interference fit state. The contact ring or other contact insert can be inserted through the funnel-shaped inlet to strengthen its retention when the permanent magnet alloy ring(s) is in its original position.

[0022] One end of the sleeve may include a tapered and / or stepped outer surface. This can help to press the sleeve and / or bearing insert into the bearing well of the rotor shaft. In some applications, the tapered and / or stepped outer surface may be located at the distal or high-pressure end of the sleeve. However, in other applications, such as bell-shaped rotors, the tapered and / or stepped outer surface may be located at the proximal or low-pressure end of the sleeve. Typically, before the sleeve and / or bearing insert is inserted into the bearing well, the tapered outer surface is such that the outer diameter of the sleeve increases from a diameter smaller than the inner diameter of the bearing well to a diameter larger than the diameter of the bearing well. This can help to press the sleeve and / or bearing insert into the bearing well and / or form an interference fit.

[0023] When in its proper position within the bearing well of the rotor shaft, the end of the bearing insert can directly contact the radially inward-extending annular flange formed within the rotor shaft. This can help in the correct alignment of the rotor half and the stator half of the permanent magnet bearing.

[0024] When the bearing insert is in its original position in the rotor's bearing well, additional contact rings or similar contact inserts may be inserted into the rotor well to contact the sleeve and / or magnet. The additional contact rings or inserts complement the interference fit between the sleeve and the well and can hold the sleeve and / or magnet ring in place well.

[0025] Typically, a bearing well is a cavity or recess within the rotor shaft. Typically, the bearing well is located at or toward the proximal end (low-pressure end) of the rotor shaft. However, in some embodiments, the bearing well can be located at or toward the distal end (relatively high-pressure end) of the rotor shaft, or at or toward both ends of the rotor shaft.

[0026] The bearing well is configured to slidably receive the bearing insert, enabling a close fit around the entire circumference of the bearing insert. Typically, the bearing well has a generally circular cross-section along its length. The fit between the bearing well and the bearing insert can be permanent or semi-permanent. However, the fit can be sufficient to maintain the position of the permanent magnet during normal use of the vacuum pump.

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

[0028] Preferably, the permanent magnet alloy ring(s) are made of neodymium iron boron ("neodymium") magnets, preferably Nd2Fe 14 The material contains B, or samarium cobalt, preferably SmCo5 or Sm2Co17. Neodymium magnets are particularly preferred. Typically, if multiple magnet alloy rings are present, each contains substantially the same material.

[0029] Preferably, the radially outward-extending sleeve has at least substantially the same coefficient of thermal expansion as the material of the rotor shaft defining the bearing well wall to be engaged with, and preferably, their coefficients of thermal expansion are substantially the same.

[0030] The present invention further provides a rotor for a vacuum pump, the rotor comprising a rotor shaft having one or more rotor blades coupled to the rotor shaft, the rotor shaft defining a bearing well for housing a magnetic bearing insert in an interference fit configuration.

[0031] The magnetic bearing insert comprises one or more permanent magnet alloy rings in the rotor bearing half of the permanent magnet bearing, and a sleeve extending radially outward coupled around the outer circumference of the permanent magnet alloy rings.

[0032] Preferably, the radially outward-extending sleeve has a coefficient of thermal expansion at least substantially the same as the coefficient of thermal expansion of the rotor shaft material defining the bearing well wall to be engaged.

[0033] Advantageously, the permanent magnet bearing insert according to an embodiment of the present invention facilitates the inclusion of neodymium permanent magnets or the like in the magnetic bearing of a vacuum pump.

[0034] As is understood, permanent magnets are generally brittle and cannot withstand high tensile loads without cracking. To suppress tensile stress, rotor bearing half magnets are typically inserted into the rotor in an interference fit, creating an inward radial compression fit on the rotor bearing half magnets.

[0035] The material properties and dimensions of the permanent magnets and rotors are typically such that the magnets expand less due to temperature and centrifugal force than the rotors, which are made of aluminum. As a result, the amount of compression applied to the rotor magnets by the rotor during use is reduced.

[0036] However, as can be understood, for the bearing to function as intended, the residual compression at maximum speed and temperature must still be sufficient to hold the rotor bearing half magnets to the rotor while keeping tensile strain within limits that do not exceed the maximum allowable value for a given magnet (this is sometimes called minimum compression).

[0037] In addition, the magnets have a minimum mating requirement. The minimum mating between magnets is the mating that produces the minimum compression effect described above at the highest temperature and highest speed.

[0038] In addition, tolerances in the magnet and rotor lead to maximum mating, which can be defined as the sum of the minimum mating requirement and manufacturing tolerances.

[0039] When maximum engagement occurs, the compressive stress on the magnet and the stress on the entire rotor reach their maximum. This typically occurs when the rotor is not rotating and the ambient temperature (and consequently the temperature of the rotor and bearings) is low (e.g., room temperature).

[0040] Furthermore, the magnets are typically inserted by a press machine with the rotor heated to a high temperature to minimize the required pressing force. In some cases, the magnets may also be cooled to extremely low temperatures, such as in liquid nitrogen, to further minimize the required pressing force. The maximum temperature the rotor can reach is often limited by materials science issues, and the pressing force may also be limited by stress and practical considerations. Therefore, there are limits to the maximum achievable mating, which in turn limits the minimum mating requirement.

[0041] The inventors have found that the use of neodymium magnets, particularly NdFeB magnets, presents unique challenges due to their extremely low coefficient of thermal expansion and their tendency to demagnetize at relatively low temperatures (which vary depending on the grade, but for example, from around 120°C).

[0042] Consequently, the minimum mating requirement is much higher than that of NdFeB magnets, and the maximum achievable mating is reduced. This is because cooling the magnet during the mating process is ineffective (as the coefficient of thermal expansion is negligible or negative), and also depends on the rotor material, as it is affected by the maximum temperature to which significant demagnetization occurs.

[0043] The use of sleeves allows for high compression of the magnets, especially when the magnets are first inserted into the sleeves and then the sleeve and magnet assembly is inserted into the rotor.

[0044] However, as seen in prior art, permanent magnet bearing inserts made from materials with relatively low coefficients of thermal expansion, such as titanium, or more specifically, materials with lower coefficients of thermal expansion than rotor materials (e.g., stainless steel for aluminum rotors), have been found to be insufficient for housing NdFeB magnets in rotor bearing wells, particularly aluminum rotor bearing wells.

[0045] In fact, while the thermal expansion of these materials relative to neodymium magnets can be suppressed, the heating temperature required to contract the magnet within the sleeve and / or the pressing force required to achieve maximum mating may become inappropriately high and / or cause demagnetization of the magnet. Similarly, especially if the rotor is made of aluminum, the heating temperature required for the rotor to ensure that the sleeve maintains contact during operation may lead to weakening of the rotor.

[0046] The inventors have found that by providing a permanent magnet bearing insert comprising a radially outward-extending sleeve having at least substantially the same coefficient of thermal expansion as the material of the rotor shaft defining a cavity configured to receive the magnet bearing insert, an appropriate compression level can be maintained both during and after use, while allowing an acceptable interference fit insertion force to be applied without requiring excessive heating of the magnet, sleeve, and / or rotor. Accordingly, the present invention facilitates the use of neodymium magnets in magnet bearings of vacuum pumps, particularly turbomolecular pumps, reducing the size of the required magnets and potentially reducing the size of the bearing and / or vacuum pump.

[0047] In this specification, references to the coefficient of thermal expansion refer to the linear thermal expansion coefficient (CLTE) measured at 20°C (t0=20°C, t1=100°C). Throughout the specification, unless otherwise specified, all measurements are performed at 20°C and standard atmospheric pressure (101325 Pa).

[0048] The sleeve may, as a whole, have a coefficient of thermal expansion at least substantially the same, preferably substantially the same, as the material of the rotor shaft defining the bearing well wall. More preferably, the sleeve is made from the material defining the bearing well wall.

[0049] Here, "substantially the same" may mean within approximately 10%, preferably within approximately 5%, and more preferably within approximately 1% of the given parameter.

[0050] Preferably, the sleeve can have a coefficient of thermal expansion within about 1.5×10 -6 K -1 or less, preferably within about 0.25×10 -6 K -1 or less.

[0051] In an embodiment, the coefficient of thermal expansion of the material of the rotor shaft defining the engaged bearing well wall is about 8.6×10 -6 K -1 or more, preferably about 10.1 K -1 or more, more preferably about 17.3 K -1 or more, still more preferably about 23 K -1 or more.

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

[0053] Preferably, the sleeve comprises a material having a linear coefficient of thermal expansion of about 20×10 -6 K -1 or more, preferably about 22×10 -6 K -1 or more, and the material of the rotor shaft defining the engaged bearing well wall has a linear coefficient of thermal expansion of about 23×10 -6 K -1 or more, preferably about 23×10 -6 K -1 or more.

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

[0055] In an embodiment, the sleeve is aluminum. Typically, the cavity is defined by an aluminum portion of the rotor shaft, preferably 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 that receives it are made of aluminum, preferably substantially the same aluminum alloy. To avoid misunderstanding, references to aluminum in this specification include aluminum alloys, i.e., 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, and 2000 series and 7000 series aluminum alloys are particularly suitable for the present invention. Preferably, substantially the entire rotor shaft is made of aluminum.

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

[0058] In the embodiment, the magnetic bearing insert is machined after the permanent magnet alloy ring is coupled to the sleeve, and typically, the radial outermost wall of the sleeve is machined with the magnet alloy ring coupled to the sleeve. Typically, this machining in its original position is the final machining of the sleeve. Machining the sleeve with the magnet in its original position can achieve tighter tolerances compared to machining individual parts before assembly.

[0059] Similarly, the rotor can be machined with the inserts in their original positions. Typically, this is the final machining of the rotor. In this case as well, machining the rotor with the inserts (including the ring magnets) in their original positions can achieve tighter tolerances compared to machining the individual parts before assembly.

[0060] To avoid misunderstanding, in all embodiments and aspects, the above-mentioned or each permanent magnet alloy ring may be a magnet. In embodiments, the above-mentioned or each permanent magnet alloy ring includes a neodymium magnet alloy.

[0061] Neodymium magnets (also known as NdFeB, NIB, or neo-magnets) are permanent magnets made from an alloy of neodymium, iron, and boron, typically Nd2Fe 14 It forms a tetragonal crystal structure of B. Neodymium magnets are magnetized.

[0062] In the embodiment, the rotor shaft and one or more rotor blades are integrally formed, i.e., integrally molded from the same material. The rotor blades are a series of substantially flat arrays spaced apart axially and may extend radially outward from the rotor shaft. The rotor shaft of this structure may be called an integrally cast rotor.

[0063] Alternatively, one or more rotor blades may form part of an annular rotor blade array(s) and be coupled to the rotor shaft by an interference fit. Typically, the annular rotor blade array(s) is coupled to the rotor with the bearing inserts in their original positions. Advantageously, this can facilitate further compression introduction to the permanent magnet rings. Preferably, the rotor shaft is machined before coupling the rotor blade array(s) to the rotor shaft, with the magnet bearing inserts in their original positions. A rotor shaft in this configuration can be called a multiblock rotor(s).

[0064] In many cases, permanent magnets exhibit anisotropic thermal expansion, and therefore the value of the thermal expansion coefficient depends on the direction considered. Often, the thermal expansion coefficient that has the greatest influence on the expansion of the ring diameter is the thermal expansion coefficient in the circumferential or hoop direction. The thermal expansion coefficient of a permanent magnet alloy ring in such a direction is preferably about 16 × 10⁻⁶. -6 K -1 Less than, more preferably 4 × 10 -6 K -1 Less than 1 × 10 -6 K -1 It is less than [value missing]. Preferably, such a permanent magnet alloy ring is made of neodymium iron boron. Preferably, the ring is magnetized in the axial or radial direction.

[0065] In another embodiment, the present invention provides a method for manufacturing a vacuum pump, preferably a turbomolecular pump, according to the above embodiment. The pump comprises a rotor shaft configured to have one or more rotor blades coupled to the rotor shaft, the rotor shaft defining a cavity for receiving a magnetic bearing insert.

[0066] The method includes a) preparing a permanent magnet bearing insert according to a first aspect of the present invention, and b) inserting the magnet bearing insert into a cavity of a vacuum pump rotor to accept it and form an interference fit.

[0067] In this embodiment of the method, the permanent magnet bearing insert is pre-assembled before step a) by inserting the permanent magnet alloy ring(s) into the sleeve to form an interference fit.

[0068] In embodiments relating to a multiblock rotor, one or more rotor blades are coupled to the rotor shaft, preferably by interference fit, after step b). Preferably, the rotor shaft is machined in an intermediate step after step b) but before the one or more rotor blades are coupled to the rotor shaft.

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

[0070] In another aspect, the present invention provides the use of a neodymium magnet alloy in a permanent magnet bearing insert or vacuum pump, and more particularly in the above insert or vacuum pump. The neodymium magnet alloy can be a magnetic material.

[0071] The present invention will be described below with reference to non-limiting drawings. [Brief explanation of the drawing]

[0072] [Figure 1]This shows the magnetic bearing insert according to the present invention in its original position within the integrally cast turbomolecular pump rotor. [Figure 2] This shows a magnetic bearing insert according to the present invention. [Figure 3] This shows the magnetic bearing insert according to the present invention in its original position within the rotor of a multi-block turbomolecular pump. [Figure 4] This shows a rotor bearing equipped with a bearing insert according to the present invention. [Modes for carrying out the invention]

[0073] As shown in Figure 1, the present invention provides a permanent magnet bearing insert (2) preferably for a turbomolecular pump rotor (1). In the illustrated embodiment, the magnet bearing insert (2) is positioned toward the relatively low-pressure low-pressure end (6) of the rotor (1). The insert (2) is slidably incorporated into a magnet bearing well (7) formed in the rotor (1). The bearing insert (2) is held in place within the bearing well (7) by an interference fit.

[0074] In the illustrated embodiment, an interference fit is formed between a circumferential wall extending longitudinally and facing radially outward of the insert and a wall extending longitudinally and facing radially inward of the bearing well. Typically, the interference fit is such that the bearing insert and / or the magnet rings are compressed over the operating temperature range of the rotor, which is, for example, ambient temperature (e.g., 20°C) to about 90°C, or about 120°C in other applications. Typically, the interference fit is such that the bearing insert and / or the magnet rings are compressed over the operating rotational speed range of the rotor (e.g., up to about 100,000 rpm).

[0075] The illustrated bearing well (7) comprises an annular shoulder or ledge (15) extending radially inward. When inserted into the well, the distal end of the insert securely engages with the shoulder or ledge (15). This helps in the precise positioning of the bearing insert (2), and therefore the above or each of the magnet rings (3, 4, 5), within the rotor (1). Typically, the bearing insert (2) is pressed into the bearing well (7) from the bearing well opening using a press.

[0076] As clearly shown in Figure 2, the sleeve opening can 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 above or each magnet ring before insertion. The end of the funnel can have an inner diameter that is smaller than the outer diameter of the magnet ring before insertion. The funnel-shaped inlet (13) into the sleeve facilitates the insertion of the above or each magnet ring (3, 4, 5) into the sleeve.

[0077] Similarly, in the embodiment shown in Figure 2, the end of the sleeve may have a tapered (14) or stepped front edge. The front edge of the sleeve is tapered from an outer diameter smaller than the inner diameter of the bearing well opening to an outer diameter larger than the inner diameter of the bearing well opening before insertion. In this case as well, the tapered front edge of the sleeve facilitates insertion of the sleeve (16) into the bearing well (7).

[0078] The sleeve (16) may further comprise an annular lip (12) extending radially inward at a second end opposite the sleeve inlet (13). The annular lip (12) provides an abutment to which the magnetic ring (3) of the bearing insert (2) can abut. This can help in the precise positioning of the above or each magnetic ring within the sleeve, rotor, and vacuum pump.

[0079] The rotor (1) shown in Figure 1 is a one-piece structure. That is, the entire rotor (1), including the rotor blades (8), rotor shaft (9), and rotor bearing well wall (10), is formed from a single material. In this case, it is an aluminum alloy. A multi-part rotor is also envisioned in which the rotor blades are joined to the rotor shaft by an interference fit, typically when the bearing inserts are in their original positions within the rotor bearing wells. In this embodiment, the rotor shaft can be machined before joining the rotor blades to the rotor shaft, while the bearing inserts are in their original positions. This can improve tolerances.

[0080] The rotor blades (8) are arranged in a series of annular arrays extending radially outward from the rotor shaft (9). The size and pitch of the rotor blades will be determined according to the specific requirements of the pump in question, but generally both the size and pitch of the rotor blades decrease from the low-pressure end (6) of the rotor shaft (9) towards the relatively high-pressure high-pressure end (11) of the rotor shaft (10). In the illustrated embodiment, the bearing well (7) is located towards the low-pressure end of the rotor shaft (9). The bearing insert and magnetic ring are held substantially coaxial with the rotation axis (A) of the rotor shaft. During use, the bearing insert and magnetic ring rotate around the rotation axis (A) of the rotor shaft.

[0081] The permanent magnet bearing insert comprises multiple permanent magnet alloy rings (3, 4, 5), of which there are three in this example. The illustrated permanent magnet alloy rings are made from a ferromagnetic material.

[0082] Typically, the sleeve is a single-piece structure. Typically, the sleeve is made of substantially a single material, but depending on the embodiment, it may be coated and / or anodized.

[0083] Preferably, the sleeve is made of aluminum, substantially aluminum, or aluminum, preferably an aluminum alloy selected from the 2000 series or 7000 series.

[0084] Preferably, the magnetic alloy ring is made of a ferromagnetic material, preferably Nd2Fe 14 B (neodymium magnet), SmCo5, Sm(Co,Fe,Cu,Zr)7, preferably Nd2Fe 14 The magnets contain or consist essentially of B or SmCo5, or consist of these. Neodymium magnets are particularly preferred, especially sintered neodymium alloys. The above or each magnet alloy ring can be coated or plated, such as nickel plating or zinc plating, or polymer and / or lacquer coatings can be used.

[0085] Preferably, the permanent magnet bearing and / or vacuum pump is configured so that the magnetic alloy ring does not exceed approximately 120°C during use.

[0086] Preferably, the magnetic alloy has a Curie temperature of about 310°C to about 370°C.

[0087] As described above, the present invention further provides a method for manufacturing a vacuum pump, preferably a turbomolecular pump. The pump comprises a rotor shaft configured to have one or more rotor blades coupled to the rotor shaft, the rotor shaft defining a cavity for receiving a magnetic bearing insert.

[0088] The method of the present invention generally includes the steps of preparing a permanent magnet bearing insert according to the present invention, and inserting the magnet bearing insert into the cavity of a passive magnet bearing of a vacuum pump rotor to form an interference fit.

[0089] Typically, the permanent magnet bearing insert is pre-assembled before the step of insertion into the rotor by first inserting the above-mentioned or each permanent magnet alloy ring into a sleeve and forming an interference fit between them. Typically, the above-mentioned or each ring is pressed into the sleeve using an external press. In embodiments, the permanent magnet bearing insert is cooled and / or the rotor portion defining the cavity is heated before the insert is inserted into the cavity.

[0090] The sleeve can be machined with the magnetic alloy ring in its original position. Typically, the sleeve surface that can form an interference fit with the rotor bearing well, for example, the outer surface extending circumferentially outward from the sleeve, is machined. Performing this machining with the ring in its original position reduces tolerances and facilitates manufacturing. Typically, this can be the final machining of the sleeve.

[0091] Before insertion into the rotor, the insert is cooled to below approximately 0°C, preferably below approximately -50°C, and more preferably below approximately -75°C, using dry ice or liquid nitrogen. Preferably, the rotor portion defining the cavity is heated to approximately 100°C to approximately 150°C. In its fixed position, the above or each magnet alloy ring and sleeve can reach ambient temperature.

[0092] With the inserts in their original positions on the rotor shaft, machining of the rotor shaft can be performed. For example, in a multiblock rotor, the rotor shaft surface that receives the annular array of rotor blades is machined. Performing this machining step with the inserts in their original positions reduces tolerances and facilitates manufacturing. Typically, this can be the final machining of the rotor. Figure 3 shows a multiblock rotor according to the present invention.

[0093] In the embodiment, 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, with the permanent magnet bearing inserts in their original positions.

[0094] The vacuum pump suitable for use with the permanent magnet bearing inserts and rotor shafts described herein is the Edwards Vacuums nEXT.

[0095] Figure 3 shows one embodiment of the present invention in which the rotor (1) is a multiblock rotor. Similar or identical features are identified by numbers corresponding to those in Figures 1 and 2. In the exemplary embodiment of Figure 3, the rotor (1) includes a rotor shaft (9) and an annular array (17) of a plurality of separately formed rotor blades (8) coupled thereto by interference fit. The rotor blade annular array (17) can be provided as a single monolithic structure or as a plurality of blocks of one or more annular arrays. The above or each annular array block can be a multi-array having two or more arrays within a single monolithic structure, or a mono-array having a single annular array.

[0096] As described above, preferably, in a multi-block rotor, the rotor blades are coupled to the rotor shaft with the magnetic bearing inserts in their original positions. This allows for improved compression of the permanent magnet bearing ring(s).

[0097] Figure 4 shows an assembled permanent magnet bearing equipped with a bearing insert according to the present invention.

[0098] As shown in the figure, 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) provided within a permanent magnet bearing insert according to the present invention. The bearing insert and the annular magnets are aligned substantially coaxially with respect to the axis of rotation (A) of the rotor shaft (9). The bearing further comprises an inner stator bearing half containing three annular permanent magnets (18, 19, 20).

[0099] The permanent magnet rings (18, 19, 20) of the inner stator bearing half and the permanent magnet rings (3, 4, 5) of the outer rotor bearing half are magnetized and positioned relative to each other to create a repulsive force between the two halves. Thus, they cause the rotor shaft (9) to levitate radially.

[0100] It should be understood that various modifications are possible to the embodiments shown without departing from the spirit and scope of the invention as defined by the attached claims, as interpreted in accordance with patent law. [Explanation of Symbols]

[0101] 1 Turbomolecular pump rotor 2 Magnetic bearing inserts 3 Magnetic rings 4 Magnetic Rings 5 Magnetic Rings 6. Low-pressure end of the rotor 7 Bearing wells 8 rotor blades 9. Rotor shaft 10 Rotor bearing well wall 11 High-voltage end 12 Ring Lip 13 Funnel entrance 14 Tapered sleeve end 15 Shoulder / Shelf 16 sleeves 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 to have one or more rotor blades coupled to the rotor shaft, wherein the rotor shaft defines a bearing well for receiving a permanent magnet bearing insert in an interference fit configuration, The magnetic bearing insert comprises one or more permanent magnet alloy rings in the rotor bearing half of the permanent magnet bearing, and a sleeve extending radially outward that is coupled around the outer circumference of the or each permanent magnet alloy ring. The outer surface of the permanent magnet bearing insert engages with the inwardly facing wall of the bearing well to provide an interlocking fit. A vacuum pump wherein the radially outward-extending sleeve has a coefficient of thermal expansion at least substantially the same as the coefficient of thermal expansion of the material of the rotor shaft defining the bearing well wall to be engaged.

2. The vacuum pump according to claim 1, wherein the radially outward-extending sleeve has substantially the same coefficient of thermal expansion as the material of the rotor shaft defining the bearing well wall to be engaged.

3. The vacuum pump according to claim 1 or 2, wherein the aforementioned or each permanent magnet alloy ring is coupled to the sleeve by an interlocking fit.

4. The vacuum pump according to any one of claims 1 to 3, wherein the permanent magnet alloy ring is coupled to the sleeve before the sleeve is inserted into the bearing well of the pump rotor.

5. The vacuum pump according to any one of claims 1 to 4, wherein the magnetic bearing insert is machined after the permanent magnet alloy ring is coupled to the sleeve.

6. The vacuum pump according to claim 3 or 4, wherein the rotor is subjected to final machining after the insert is fitted.

7. The vacuum pump according to any one of claims 1 to 6, wherein the bearing well is defined by the aluminum portion of the rotor shaft, and / or the sleeve is made of aluminum.

8. The aforementioned permanent magnet alloy ring is approximately 4 x 10 -6 K -1 A vacuum pump according to any one of claims 1 to 7, having a coefficient of thermal expansion in the circumferential direction of less than .

9. The vacuum pump according to any one of claims 1 to 8, wherein the aforementioned or each permanent magnet alloy ring includes a neodymium magnet magnetized in either the axial or radial direction.

10. The vacuum pump according to any one of claims 1 to 9, wherein the rotor shaft and one or more rotor blades are integrally constructed, and / or one or more of the rotor blades form part of an annular rotor blade array coupled to the rotor shaft by interference fit.

11. A method for manufacturing a vacuum pump, preferably a turbomolecular pump, according to any one of claims 1 to 10, wherein the pump comprises a rotor shaft configured to have one or more rotor blades coupled to the rotor shaft, the rotor shaft defines a bearing well for receiving a magnetic bearing insert, and the method is a) A step of preparing a permanent magnet bearing insert, wherein the permanent magnet bearing insert comprises one or more permanent magnet alloy rings in the rotor bearing half of a permanent magnet bearing, and a sleeve extending radially outward around the outer circumference of the or each permanent magnet alloy ring and coupled to the or each permanent magnet alloy ring, b) Inserting the magnetic bearing insert into the rotor bearing well of the vacuum pump rotor to form an interference fit, Includes, The radially outward-extending sleeve has at least substantially the same, preferably substantially the same, coefficient of thermal expansion as the material of the rotor shaft defining the bearing well wall to be engaged. A method wherein, optionally, the permanent magnet bearing insert is cooled and / or the portion of the rotor defining the bearing well is heated before the bearing insert is inserted into the bearing well.

12. The method according to claim 11, wherein the permanent magnet bearing insert is pre-assembled before step a) by inserting the permanent magnet alloy ring into the sleeve to form an interference fit, and / or one or more rotor blades are coupled to the rotor shaft after step b).

13. A permanent magnet bearing insert for a vacuum pump, wherein the vacuum pump comprises a rotor shaft to which one or more rotor blades are coupled, and the rotor shaft defines a bearing well configured to receive the magnet bearing insert in an interlocking fit configuration. The magnetic bearing insert comprises one or more permanent magnet alloy rings in the rotor bearing half of the permanent magnet bearing, and a sleeve extending radially outward around the outer circumference of the or each permanent magnet alloy ring and coupled to the or each permanent magnet alloy ring. The outer surface of the permanent magnet bearing insert is configured to engage with the inwardly facing wall of the bearing well after insertion into the bearing well. A permanent magnet bearing insert wherein the radially outward-extending sleeve has a thermal expansion coefficient at least substantially the same, preferably substantially the same, as that of the material of the rotor shaft defining the engaging bearing well wall.

14. A vacuum pump according to any one of claims 1 to 10, comprising the permanent magnet bearing insert according to claim 13.

15. Use of a neodymium magnet alloy in a vacuum pump according to any one of claims 1 to 10 or 14, or in a permanent magnet 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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