Turbomolecular vacuum pump and method for mounting a splinter shield

Abstract

The invention relates to a turbomolecular vacuum pump (1) comprising a splinter shield (21, 31, 41) and a plurality of fastening screws (23), the heads (23a) of the fastening screws (23) being frustoconical, tapped holes (20) made in the stator (2) each having a rim (20a) of complementary frustoconical shape, the axes (A1) of through-openings (22) in the splinter shield (21) being radially offset towards the centre of a suction opening (4) in the vacuum pump (1) with respect to the axes (A2) of the tapped holes (20) when the fastening screws (23) are loosened, the axes (A1) of the through-openings (22) approaching axial alignment with the axes (A2) of the tapped holes (20) by guiding the frustoconical heads (23a) as the fastening screws (23) are tightened in the tapped holes (20) in the rim (20a) of complementary frustoconical shape in order to deform the splinter shield (21) by stretching and tensioning it.

Description

Description Title: Turbomolecular vacuum pump and method for mounting a spall filter Technical field of the invention

[0001] The present invention relates to a turbomolecular vacuum pump. The present invention also relates to a method for mounting a spall filter in a suction port of a turbomolecular vacuum pump. Technical background

[0002] Generating a high vacuum in an enclosure requires the use of turbomolecular vacuum pumps consisting of a stator in which a rotor is driven in rapid rotation on magnetic bearings, for example at a rotation of more than twenty thousand revolutions per minute.

[0003] The stator has a suction port that is connected to an outlet of a chamber whose pressure needs to be reduced, or to a flange on a valve or pipe. The suction port of turbomolecular vacuum pumps may be fitted with a "splinter guard" to prevent the accidental introduction of parts, such as screws, into the vacuum pump and their projection onto the rotor at full speed. The splinter guard also protects personnel from cuts caused by the rotor blades during operation of the vacuum pump.

[0004] These spall filters feature fairly large mesh sizes and a low axial thickness in order to minimize pressure losses that could impair pumping performance.

[0005] Some spall filters have a domed shape that can be reinforced by welding on an additional crossbar. The spall filter is received in the vacuum pump's suction port, where it is held in position by means of a retaining ring that fits into a corresponding groove. However, the elastic ring and the relatively wide and thick additional crossbar can be expensive. Furthermore, the volume occupied by the crossbar can impede the passage of pumped gas molecules and thus reduce pumping performance.

[0006] Other splinter filters have a flat shape and are fixed in the intake port by screws tightened around the periphery of the filter. However, these filters can deform under the effect of an impact and there is a risk that the deformed shatter guard will get too close to the rotor.

[0007] Another alternative is to stretch the anti-splinter filter before it is screwed in, either mechanically with a mechanical pre-stressing tool that pulls on its entire circumference (spider), or thermally (by heating it). However, these solutions can be complicated to implement because they require suitable mechanical or thermal stretching equipment. Furthermore, disassembly can be particularly difficult if it is not carried out with this same mechanical or thermal stretching equipment. Summary of the invention

[0008] One aim of the present invention is to provide a turbomolecular vacuum pump with enhanced blast-stop filter efficiency.

[0009] To this end, the invention relates to a turbomolecular vacuum pump comprising: - a stator and a rotor configured to rotate within the stator, the stator having a suction port, with tapped holes being provided in the stator around the suction port, - a shatterproof filter with through-holes around its periphery, - a plurality of fixing screws, each having a head, the fixing screws passing through the through holes of the splinter filter, characterized in that the heads of the fixing screws of the splinter filter are frustoconical, the tapped holes provided in the stator having a respective border of complementary frustoconical shape, the axes of the through holes of the splinter filter being radially offset towards the center of the suction hole relative to the axes of the tapped holes in the loose state of the fixing screws, the axes of the through holes of the splinter filter approaching axial alignment with the axes of the tapped holes by guiding the frustoconical heads of the fixing screws with the tightening of the fixing screws in the tapped holes of complementary frustoconical shape border to deform by stretching and tension the splinter filter.

[0010] The splinter filter can thus be easily tensioned in a single operation when it is attached to the intake port. This limits deformation of the splinter filter in the event of an accidental impact. Furthermore, a taut splinter filter offers good mechanical resistance, resulting in low stress. Thickness. A thin shatterproof filter is also less susceptible to deformations induced by heating, particularly radiative heating. Furthermore, a thin shatterproof filter reduces costs and minimizes pressure drop.

[0011] The vacuum pump may also include one or more of the features described below, taken alone or in combination.

[0012] The deformation of the shatterproof filter can be elastic.

[0013] The thickness of the splinter filter in the axial direction is for example less than 2mm, such as less than 1mm, such as 0.6mm.

[0014] The deviation in the radial direction between the diameter of the circle in which the axes of the tapped holes are inscribed and the diameter of the circle in which the axes of the through holes of the splinter guard are inscribed in the loose state of the fixing screws can be between 0.5% and 5%, such as 1%.

[0015] The shatterproof filter is, for example, made of steel, such as stainless steel, or carbon fibers.

[0016] According to one embodiment, the splinter filter has at least two reinforcing radii extending radially from a central mesh of the splinter filter to a peripheral band of the splinter filter in which the through holes are provided.

[0017] According to one embodiment, the through-holes of the splinter guard of a pair are located on either side of a straight line aligned with a reinforcement radius, the through-holes of the pair being closer to each other than the through-holes of the adjacent pairs.

[0018] According to one example of implementation, the mesh of the splinter filter is hexagonal, the splinter filter having a honeycomb structure.

[0019] According to one embodiment, the meshes of the splinter filter are delimited on the one hand by rays of the splinter filter extending from a central mesh to a peripheral band of the splinter filter and on the other hand by concentric rings of the splinter filter crossing the rays.

[0020] The maximum size of the mesh of the splinter filter is, for example, less than 2 millimeters, such as less than 1 millimeter.

[0021] The invention also relates to a method for mounting a spall filter in a suction orifice of a turbomolecular vacuum pump as described above, in which: - a loosened spall filter is placed on the intake port with fixing screws passing through through holes in the spall filter by being inserted into associated tapped holes in the stator, the fixing screws being loosened, the axes of the through holes being radially offset towards the center of the intake port relative to the axes of the tapped holes, - Then, the fixing screws are tightened in the tapped holes to bring the axes of the through holes closer to axial alignment with the axes of the tapped holes. This is achieved by guiding the conical heads of the fixing screws within the complementary conical edges of the tapped holes, thereby deforming and tensioning the splinter guard. Brief description of the figures

[0022] Other advantages and features will become apparent upon reading the description of the invention, as well as the accompanying drawings, which show:

[0023] [Fig.1] Figure 1 shows a schematic axial cross-sectional view of an example of a turbomolecular vacuum pump.

[0024] [Fig.2a] Figure 2a shows an enlarged view of a detail of the turbomolecular vacuum pump of Figure 1 during the mounting of a splinter filter in a vacuum pump suction port with the fixing screws in the loosened state.

[0025] [Fig.2b] Figure 2b shows a view similar to figure 2a during the tightening of the fixing screws.

[0026] [Fig.2c] Figure 2c shows a view similar to figure 2a after tightening the fixing screws.

[0027] [Fig.3] Figure 3 shows a perspective view of a splinter guard filter of the turbomolecular vacuum pump of Figure 1.

[0028] [Fig.4] Figure 4 shows a perspective view of another example of the realization of a glare shield filter.

[0029] [Fig.5] Figure 5 shows a detail of the glare shield of Figure 4.

[0030] [Fig.6] Figure 6 shows another detail of the glare shield from Figure 4.

[0031] [Fig.7] Figure 7 shows a perspective view of another example of the realization of a glare shield filter.

[0032] In these figures, identical elements bear the same reference numbers. Detailed description

[0033] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Simple features of different embodiments can also be combined or interchanged to provide other embodiments, without departing from the scope of the invention as defined by the claims.

[0034] The axial direction is defined as the direction parallel to the axis of rotation ll of the vacuum pump rotor, and the radial or transverse directions are defined as those perpendicular to the axial direction.

[0035] Figure 1 illustrates an example of the realization of a turbomolecular vacuum pump 1.

[0036] The turbomolecular vacuum pump 1 comprises a stator 2 in which a rotor 3 is configured to rotate at high speed in axial rotation, for example, at more than twenty thousand revolutions per minute. The pumped gases enter through a suction port 4 of the stator 2 and are discharged through a discharge port (not visible) of the turbomolecular vacuum pump 1. In operation, the discharge port is connected to a primary pump.

[0037] The stator 2 has a mounting flange 6 surrounding the suction port 4, for connecting the vacuum pump 1 to a chamber whose pressure is to be lowered or to a valve flange or other.

[0038] In one embodiment, the stator 2 comprises a housing 2a in which a recess 8 is provided, opening through the suction port 4, and includes at least two annular stator stages 9 received in the recess 8. The recess 8 is, for example, cylindrical. The stator 2 also includes a high-pressure sleeve 2b in which the discharge port of the vacuum pump 1 is provided.

[0039] The annular stator stages 9 are arranged between two successive bladed rotor stages 10 of the rotor 3. The annular stator stages 9 and the bladed rotor stages 10 follow one another axially along the axis of rotation 11 of the rotor 3 in the turbomolecular stage. Each bladed rotor stage 10 has inclined blades that extend in a substantially radial direction from a hub 11 of the rotor 3. The blades are evenly distributed around the periphery of the hub 11. The rotor 3 has for example more than four bladed rotor stages 10, as between seven and sixteen bladed rotor stages 10 (seven in the example illustrated in figure 1).

[0040] According to one embodiment, the rotor 3 has at least one skirt 5, called a Holweck skirt, downstream of the bladed rotor stages 10 in the direction of flow of the pumped gases, formed by a smooth cylinder, which rotates opposite helical grooves 7 of the stator 2, for example formed in the high-pressure sleeve 2b. The helical grooves 7 of the stator 2 allow the pumped gases to be compressed and guided towards the discharge port.

[0041] According to one embodiment, the rotor 3 further comprises an internal bowl 15, coaxial with the axis of rotation 11, arranged opposite a dome 17 of the stator 2, projecting below the rotor 3 and whose base is connected to the high-pressure bushing 2b. In operation, the rotor 3 rotates in the stator 2 without contact between the internal bowl 15 and the dome 17.

[0042] The rotor 3 is, for example, made in one piece (monobloc). The rotor 3 is fixed to a drive shaft 12 of the vacuum pump 1, driven in rotation in the stator 2 by an internal motor 16 of the vacuum pump 1. The motor 16 is, for example, arranged in the dome 17 of the stator 2, itself arranged under the internal bowl 15 of the rotor 3, the drive shaft 12 passing through the dome 17 of the stator 2.

[0043] The rotor 3 is guided laterally and axially by magnetic bearings and backup mechanical bearings, which support the rotor 3 drive shaft 12, located in the stator 2. The active magnetic bearings allow the rotor 3 to be kept levitating within the created magnetic field. Other electrical or electronic components, such as position sensors, can be housed in the stator 2 dome 17.

[0044] The suction port 4 is cylindrical and located at the end of the housing 2a. Regularly distributed tapped holes 20 are provided in the stator 2, here in the housing 2a, around the suction port 4. As more clearly seen in figure 2a, the tapped holes 20 extend in an axial direction parallel to the axis of rotation ll.

[0045] The vacuum pump 1 further includes a splinter filter 21 and a plurality of fixing screws 23.

[0046] The shatter filter 21 has a disc shape and cylindrical through orifices 22 distributed in a peripheral band 24 of the shatter filter 21 (figure 3).

[0047] The splinter guard 21 prevents the accidental introduction of parts into the vacuum pump 1 and their projection onto the rotor 3 of the vacuum pump 1 when it is running at full speed. The splinter guard 21 also protects personnel from cuts caused by the rotor blades 3 during operation of the vacuum pump 1.

[0048] The fixing screws 23 each have shanks 23b topped with heads 23a. The fixing screws 23 are, for example, made of steel, such as stainless steel.

[0049] The fixing screws 23 pass through the through holes 22 of the splinter filter 21 and are inserted into the associated tapped holes 20 of the stator 2 to secure and tension the splinter filter 21 in the suction hole 4.

[0050] The number and distribution of the through holes 22 corresponds of course to those of the tapped holes 20 of the stator 2 and to the number of fixing screws 23. There are for example between six and twenty, such as eight or twelve, through holes 22, fixing screws 23 and tapped holes 20, for example regularly distributed around the suction hole 4.

[0051] The heads 23a of the fixing screws 23 of the anti-splash filter 21 are frustoconical.

[0052] The tapped holes 20 made in the stator 2 have a respective rim 20a of complementary truncated conical shape.

[0053] The axes A1 of the through holes 22 of the splinter guard 21 are radially offset towards the center of the suction hole 4 relative to the axes A2 of the tapped holes 20 when the fixing screws 23 are loosened (Figure 2a). In other words, the diameter of the circle in which the axes A1 of the through holes 22 of the splinter guard 21 are inscribed is smaller than the diameter of the circle in which the axes A2 of the tapped holes 20 are inscribed when the fixing screws 23 are loosened.

[0054] The fixing screws 23 are considered to be loose as long as the heads 23a are not in contact with the edges 20a of the tapped holes 20. The splinter filter 21 is then centered in the suction orifice 4 by the shanks 23b of the screws 23 bearing against the external edges of the through orifices 22 of the splinter filter 21.

[0055] For example, there is between 0.5% and 5% difference, such as 1% difference, in the radial direction, between the diameter of the circle in which the axes A2 of the tapped holes 20 are inscribed and the diameter of the circle in which the axes A1 of the through holes 22 of the splinter guard 21 are inscribed in the loose state of the fixing screws 23.

[0056] The axes A1 of the through holes 22 of the splinter guard 21 are brought into close axial alignment with the axes A2 of the tapped holes 20 by guiding the frustoconical heads 23a of the fixing screws 23. Tightening the fixing screws 23 in the tapped holes 20 of the complementary frustoconical rim 20a deforms the splinter guard 21 by stretching and tensioning it (Figure 2b). Since the height of the frustoconical heads 23a is greater than the thickness of the splinter guard 21, the frustoconical rim 20a of the tapped holes 20 allows the fixing screw 23 to be tightened sufficiently to stretch the splinter guard 21 and produce tension.

[0057] The deformation of the splinter filter 21 can be elastic so that after stretching the splinter filter 21, it can return to its initial relaxed shape with the loosening of the fixing screws 23.

[0058] The 21 anti-splash filter, for example, is made of steel, such as stainless steel, or carbon fiber. Stainless steel and carbon fiber have elastic moduli that allow the 21 anti-splash filter to be thin. These materials also offer good resistance to high temperatures. A 21 anti-splash filter made of stainless steel has the added advantage of being resistant to corrosive gases.

[0059] The thickness of the splinter filter 21 in the axial direction is, for example, less than 2 mm, such as less than 1 mm, such as 0.6 mm. This small thickness allows the splinter filter 21 to remain elastic, inexpensive, and to limit pressure losses.

[0060] The mesh of the splinter filter 21 can be hexagonal, with the splinter filter 21 having a honeycomb structure. These mesh shapes allow for the transfer of forces from mesh to mesh without making the splinter filter 21 become flexible.

[0061] Other mesh shapes are possible, as we will see later. In particular, the meshes are not necessarily regular; they can be organic.

[0062] The maximum dimension of the mesh of the splinter filter 21 (in the plane of the splinter filter) is for example less than 2 millimeters, such as less than 1 millimeter.

[0063] We are looking for the thinnest and most open 21 shatterproof filter possible.

[0064] During the assembly process of the spatter-proof filter 21 in the suction port 4 of the turbomolecular vacuum pump 1, the spatter-proof filter 21 is placed loosely onto the suction port 4 of the vacuum pump 1 with the fixing screws 23 passing through the through orifices 22 of the anti-splinter filter 21 and inserted into the associated tapped holes 20 of the stator 2, the fixing screws 23 being loosened (figure 2a).

[0065] The axes A1 of the through holes 22 of the splinter filter 21 are radially offset towards the center of the suction hole 4 relative to the axes A2 of the tapped holes 20. The heads 23a are not in contact with the edges 20a of the tapped holes 20. The shanks 23b of the screws 23 bear against the outer edges of the through holes 22 of the splinter filter 21.

[0066] Then, the fixing screws 23 are tightened into the tapped holes 20, which brings the axes A1 of the through holes 22 of the splinter guard 21 closer to axial alignment with the axes A2 of the tapped holes 20 by guiding the frustoconical heads 23a of the fixing screws 23 into the complementary frustoconical edges 20a of the tapped holes 20 (Figure 2b). Tightening the fixing screws 23 generates mechanical tension in the splinter guard 21, allowing it to be deformed by stretching and tightened.

[0067] After tightening, the splinter filter 21 is centered and tensioned in the suction orifice 4, the axes A1 of the through orifices 22 of the splinter filter 21 are axially aligned with the axes A2 of the tapped holes 20 (figure 2c).

[0068] The splinter filter 21 can thus be easily tensioned in a single operation when it is fixed in the suction port 4. This limits deformation of the splinter filter 21 in the event of an accidental impact. Furthermore, a taut splinter filter 21 offers good mechanical strength, allowing for a thin profile. A thin splinter filter 21 is also less susceptible to deformation caused by heating, particularly radiative heating. In addition, a thin splinter filter 21 reduces costs and minimizes pressure losses.

[0069] The operation can be reversible due to the possible elastic properties of the splinter filter 21. The splinter filter 21 can return to its initial relaxed shape by loosening the fixing screws 23.

[0070] Figures 4 to 6 show a second example of the implementation of the shatterproof filter.

[0071] In this example, the splinter filter 31 has at least two reinforcing radii 25, such as between four and eight, such as six, to better distribute the tension in the mesh of the splinter filter 31.

[0072] The reinforcing rays 25 extend radially from a central mesh of the splinter filter 31 (figure 6) to the peripheral band 24 in which the through holes 22 are provided (figure 5).

[0073] For example, there is an even number N of regularly distributed 25 reinforcement radii, the 25 reinforcement radii being arranged over N / 2 diameters.

[0074] In the case of hexagonal meshes, six reinforcing radii 25 extend radially from each vertex of the central mesh to the peripheral band 24.

[0075] The reinforcing radii 25 help to reduce the stresses exerted on the central meshes of the tensioned splinter guard 31.

[0076] According to one embodiment, the through-holes 22 of the spall filter 31 (and the associated tapped holes 20 of the stator 2) of one pair are located on either side of a straight line aligned with a reinforcing radius 25, the through-holes 22 (and the associated tapped holes 20) of the pair being closer to each other than the through-holes 22 (and associated tapped holes 20) of the adjacent pairs (Figure 4). In this configuration, the pairs of through-holes 22 limit the mechanical stresses exerted at the base of the connection between the reinforcing radius 25 and the peripheral strip 24.

[0077] The other characteristics of this example implementation are similar to those of the first example implementation.

[0078] Figure 7 shows a third example of the implementation of the 41 glare shield filter.

[0079] In this example, the mesh of the splinter guard 41 is delimited, on the one hand, by radii of the splinter guard 41 extending from a central mesh, for example in the shape of a disk, to a peripheral band 24 of the splinter guard 41, and on the other hand, by concentric rings of the splinter guard 41 intersecting the radii. This configuration allows for a better distribution of mechanical stresses and greater homogeneity of the mechanical tension exerted in the splinter guard 41.

[0080] The other characteristics of this example implementation are similar to those of the first example implementation.

Claims

DEMANDS

1. Turbomolecular vacuum pump (1) comprising: - a stator (2) and a rotor (3) configured to rotate in the stator (2), the stator (2) having a suction port (4), tapped holes (20) being provided in the stator (2) around the suction port (4), - a shatterproof filter (21, 31, 41) having through-holes (22) at its periphery, - a plurality of fixing screws (23), each having a head (23a), the fixing screws (23) passing through the through holes (22) of the splinter guard (21, 31, 41), characterized in that the heads (23a) of the fixing screws (23) of the splinter guard (21, 31, 41) are frustoconical, the tapped holes (20) provided in the stator (2) having a respective rim (20a) of complementary frustoconical shape, the axes (A1) of the through holes (22) of the splinter guard (21, 31, 41) being radially offset towards the center of the suction hole (4) relative to the axes (A2) of the tapped holes (20) in the loosened state of the fixing screws (23), the axes (A1) of the through holes (22) of the splinter guard (21 31,41) approaching axial alignment with the axes (A2) of the tapped holes (20) by guiding the frustoconical heads (23a) of the fixing screws (23) with the tightening of the fixing screws (23) in the tapped holes (20) of complementary frustoconical rim (20a) to deform by stretching and tension the splinter guard (21, 31, 41).

2. Vacuum pump (1) according to the preceding claim, characterized in that the deformation of the shatterproof filter (21, 31, 41) is elastic.

3. Vacuum pump (1) according to any one of the preceding claims, characterized in that the thickness of the splinter guard filter (21, 31, 41) in the axial direction is less than 2mm, such as less than 1mm, such as 0.6mm.

4. Vacuum pump (1) according to any one of the preceding claims, characterized in that the deviation in the radial direction between the diameter of the circle in which the axes (A2) of the tapped holes (20) are inscribed and the diameter of the circle in which the axes (A1) of the through orifices (22) of the splinter filter (21, 31, 41) are inscribed in the loosened state of the fixing screws (23) is between 0.5% and 5%, such that 1%.

5. Vacuum pump (1) according to any one of the preceding claims, characterized in that the splinter guard filter (21, 31, 41) is made of steel, such as stainless steel, or carbon fibers.

6. Vacuum pump (1) according to any one of the preceding claims, characterized in that the splinter filter (31) has at least two reinforcing radii (25) extending radially from a central mesh of the splinter filter (31) to a peripheral band (24) of the splinter filter (31) in which the through orifices (22) are provided.

7. Vacuum pump (1) according to the preceding claim, characterized in that the through orifices (22) of the splinter filter (31) of a pair are located on either side of a straight line aligned with a reinforcement radius (25), the through orifices (22) of the pair being closer to each other than the through orifices (22) of the adjacent pairs.

8. Vacuum pump (1) according to any one of the preceding claims, characterized in that the meshes of the splinter filter (21, 31) are hexagonal, the splinter filter (21, 31) having a honeycomb structure.

9. Vacuum pump (1) according to any one of claims 1 to 7, characterized in that the meshes of the splinter filter (41) are delimited on the one hand, by rays of the splinter filter (41) extending from a central mesh to a peripheral band (24) of the splinter filter (41) and on the other hand, by concentric rings of the splinter filter (41) crossing the rays.

10. Vacuum pump (1) according to any one of the preceding claims, characterized in that the maximum dimension of the mesh of the splinter filter (21, 31, 41) is less than 2 millimeters, such as less than 1 millimeter.

11. A method for mounting a spall filter (21) in a suction port (4) of a turbomolecular vacuum pump (1) according to any one of the preceding claims, wherein: - a loosened splinter filter (21, 31, 41) is placed on the suction port (4) with fixing screws (23) passing through through ports (22) of the splinter filter (21, 31, 41) by being inserted into associated tapped holes (20) of the stator (2), the fixing screws (23) being loosened, the axes (A1) of the through ports (22) being radially offset towards the center of the suction port (4) relative to the axes (A2) of the tapped holes (20), - then, the fixing screws (23) are tightened in the tapped holes (20) to bring the axes (A1) of the through holes (22) closer to axial alignment with the axes (A2) of the tapped holes (20) by guiding the frustoconical heads (23a) of the fixing screws (23) in the borders (20a) of complementary truncated conical shape of the tapped holes (20) so as to deform and tension the shatter guard filter (21, 31, 41).

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