EP1408237A1 - Turbomolecular pump - Google Patents

Abstract

The turbomolecular vacuum pump has a rotor (5) with a metal turbine upstream rotor section (5a) and a HOLWECK (RTM) type composite material downstream section. The downstream section (5c) has a fibre reinforcement dedicated to the loads generated along the length of the shroud. The connection zone between the metal and composite sections is made of a composite with similar mechanical and thermal characteristics to the metal section. Claims include a method of making the rotor shroud.

Description

The present invention relates to vacuum pumps rapid rotation used to generate a high vacuum in a pipe and / or vacuum enclosure.

In the electronic components industry or micromechanical, we use machining or treatment processes by plasma performed in an enclosure where one must maintain a controlled vacuum atmosphere.

Vacuum generation requires the use of pumps able to quickly generate and maintain a high vacuum suitable for the machining or treatment process. We use generally turbomolecular type pumps, composed of a pump body in which a rotor is rotated fast, for example a rotation at more than thirty thousand revolutions per minute.

With such a high rotational speed, the rotor acquires very high kinetic energy, and undergoes high mechanical stresses which justify the choice of materials appropriate.

The rotor of a turbomolecular vacuum pump consists an upstream section (in the direction of gas flow) of the rotor with turbo-type blades and a downstream section (in the direction of gas flow) rotor in the form of a HOLWECK type skirt.

In the description and the claims, the expressions "upstream" and "downstream" respectively designate the parts of the pump unladen traveled first and last by the gases pumped into the direction of their flow, in operation.

The upstream section with turbo blades has a shape complex, which is made of a suitable metal such as aluminum or an aluminum alloy. The shape is too complex to allow economical production of a composite material.

The downstream section, in the form of a HOLWECK type skirt, is a thin wall of revolution, largely cylindrical, driven in rotation in a downstream section of stator having grooves helical with progressively reduced section.

The pumping performance of turbomolecular pumps high rotational speeds are today limited by the fact that you cannot increase the diameter of the HOLWECK skirt at beyond a maximum limit. We know that it is a priori possible increase pumping performance by increasing the diameter of the HOLWECK skirt. But such an increase turns out to be impossible to be carried out with the use of conventional materials, especially metallic, or even with composite materials based of metallic matrix containing reinforcing additives such than ceramics, powders or carbon fibers or other reinforcement materials. Indeed, the mechanical stresses stronger appear in this area of the rotor and are proportional to the density of the material constituting the skirt, squared the rotor speed and squared the rotor diameter.

To reduce the stresses in the HOLWECK skirt, you must including reducing its mass. To do this, we have already proposed rotors of which the downstream section in the shape of a HOLWECK skirt is in one composite material with organic matrix, based on resin charged with fibers. This solution offers the advantage of using a material having better mechanical properties. The downstream section is connects to the upstream section according to an annular connection zone. In this annular connection zone, the matrix composite material organic component of the HOLWECK skirt is joined to the section upstream metal.

But a difficulty then lies in the difference of mechanical and thermal properties between the composite material to organic matrix constituting the downstream section of skirt rotor HOLWECK and the metal or alloy constituting the upstream section of the rotor. Because of these differences in properties, constraints important mechanics appear in the annular area of connection when using the pump, i.e. in rotation speed of the rotor and in the presence of a temperature rise due to compression of the pumped gases. These mechanical constraints lead to embrittlement of the bonding area, and to a risk of rupture. Thus, the diameter of this connection zone does not may be increased too much.

Conversely, if we use a composite material with organic matrix whose mechanical and thermal properties are better compatible with those of the metal constituting the upstream section rotor, in particular giving flexibility allowing stress deformations, then these mechanical properties do not are more sufficient in the downstream area of HOLWECK skirt to hold the stresses to be borne during the rapid rotation of the rotor.

The problem proposed by the present invention is to design a new turbo pump rotor structure molecular which allows, without risk of degradation of the rotor, withstand higher rotational speeds or exhibit a larger HOLWECK skirt diameter, in order to increase the pumping characteristics of the pump.

Another object of the invention is to design such a rotor structure which can be manufactured at low cost, with an industrializable process.

The pump according to the invention must support the conditions of usual operation, especially in temperature: the rotor must be able to withstand temperatures down to -20 ° C during transport, and rising up to + 150 ° C in operation.

Also, the rotor must have good qualities of centering, avoiding any risk of contact between the rotor skirt and the stator during operation at nominal speed.

The idea behind the invention is to design a HOLWECK skirt in an organic matrix composite material, the mechanical characteristics vary depending on the area longitudinal view of the skirt.

• le tronçon aval de rotor à jupe de type HOLWECK en matériau composite à matrice organique comprend une structure de renforcement à fibres qui confère à la jupe HOLWECK des caractéristiques mécaniques variant en fonction de la zone longitudinale considérée de la jupe,
• dans la zone annulaire de liaison, le matériau composite à matrice organique présente des caractéristiques mécaniques et thermiques proches de celles du métal ou alliage composant le tronçon amont de rotor,
• dans la zone aval de jupe, le matériau composite à matrice organique présente des caractéristiques plus appropriées pour tenir dans cette zone aval de jupe les contraintes mécaniques élevées résultant de la rotation rapide du rotor en fonctionnement.

Thus, the present invention provides a turbomolecular vacuum pump, comprising a rotor having an upstream section of rotor of turbo type and a downstream section of rotor in the form of a skirt of HOLWECK type, the upstream section of rotor being of a metal or alloy, the downstream rotor section being made of an organic matrix composite material, the downstream rotor section connecting to the upstream rotor section according to an annular connection zone; according to the invention:

• the downstream section of rotor with HOLWECK type skirt made of composite material with organic matrix comprises a fiber reinforcement structure which gives the HOLWECK skirt mechanical characteristics varying as a function of the longitudinal zone considered of the skirt,
• in the annular connection zone, the organic matrix composite material has mechanical and thermal characteristics close to those of the metal or alloy making up the upstream section of rotor,
• in the downstream region of the skirt, the composite material with an organic matrix has characteristics more suitable for holding in this downstream region of the skirt the high mechanical stresses resulting from the rapid rotation of the rotor in operation.

In practice, to withstand the high mechanical stresses resulting from the rapid rotation of the rotor in operation in the downstream area of HOLWECK skirt, the most appropriate characteristics of the composite material with organic matrix are very stiff, to reduce deformations under stresses, and to favor high own mechanical resonance modes.

According to a first embodiment, the structure of reinforcement includes long fibers wound in a helix according to constant pitch and coated with resin, the rate of resin being variable according to the longitudinal zone considered of the skirt.

According to another embodiment, the structure of reinforcement includes long fibers wound in a helix and coated with resin at a constant rate, the pitch of the propeller being variable according to the longitudinal zone considered of the skirt.

According to a third embodiment, the structure of reinforcement includes long fibers wound in a helix and coated with resin, the pitch of the propeller and the rate of resin being both variables according to the longitudinal area considered in the skirt.

According to all or part of the three embodiments previous, the step variation associated with the variation of the proportion of quantity of resin to quantity of fiber is likely, if no precaution is taken elsewhere, cause variations in diameter or thickness of the skirt composite. To control the outside diameter, especially in the HOLWECK part, suitable manufacturing tools are necessary. For example, and without limitation, a mandrel obtained by machining can be used.

In practice, to vary the pitch of the propeller according to the last two embodiments above, the propeller can advantageously have an angle close to 0 ° in the downstream area of the skirt, and have an angle greater than 0 °, for example 20 to 30 °, in and near the annular connection zone.

The above structure applies to different forms of skirt. According to a first embodiment, the skirt can be cylindrical.

Preferably, to increase the diameter of the skirt and thus improve the properties of the pump, the skirt may include an annular connection zone, a downstream section of cylindrical skirt larger in diameter than the annular connection zone and a zone intermediate connection between the annular connection zone and the downstream section of skirt. This increases the speed in rotation tangential of the skirt relative to the stator, which increases the compression ratio of the HOLWECK stage of the pump. Simultaneously, the increase in diameter makes it possible to accommodate a greater number of grooves in the HOLWECK part of the stator, increasing the pump flow.

a/ une étape consistant à enrouler en hélice des fibres longues sur le mandrin, en réalisant un enroulement à angle voisin de 0° dans les zones adjacentes aux deux extrémités du mandrin et un enroulement à angle supérieur à 0° dans la zone médiane du mandrin,

b/ une étape d'application et de durcissement de résine sur le mandrin portant les fibres enroulées en hélice,

c/ et une étape consistant à sectionner le manchon ainsi obtenu dans sa zone médiane pour obtenir deux jupes.

According to a particular characteristic, according to the upstream edge of the HOLWECK skirt, the reinforcing fibers can be cut. This results from an advantageous process for producing the HOLWECK type skirt, comprising:

a / a step consisting in helically winding long fibers on the mandrel, by carrying out a winding at an angle close to 0 ° in the zones adjacent to the two ends of the mandrel and a winding at an angle greater than 0 ° in the middle zone of the mandrel ,

b / a step of applying and curing resin on the mandrel carrying the helically wound fibers,

c / and a step consisting in cutting the sleeve thus obtained in its middle zone to obtain two skirts.

• la figure 1 est une vue schématique illustrant, en coupe longitudinale, une structure de pompe turbomoléculaire connue ayant un rotor monobloc en métal ;
• la figure 2 est une vue en perspective illustrant un secteur de rotor selon un mode de réalisation de la présente invention ;
• la figure 3 illustre la répartition des contraintes mécaniques sur le secteur de rotor de la figure 2, les pales de l'étage turbo ayant été enlevées ;
• la figure 4 est une vue de côté schématique illustrant la structure de rotor selon un premier mode de réalisation de la présente invention ;
• la figure 5 est une vue de côté illustrant schématiquement la structure de rotor selon un second mode de réalisation de la présente invention ;
• la figure 6 est une vue en perspective illustrant la structure de l'étage HOLWECK de stator entourant la jupe de rotor selon l'invention ;
• les figures 7 et 8 illustrent le module de YOUNG, respectivement dans le sens longitudinal et dans le sens transversal des fibres, en fonction de la proportion de fibres dans le matériau composite ;
• la figure 9 illustre la variation du module de YOUNG de la jupe en fonction de l'orientation des fibres par rapport au plan transversal de la jupe HOLWECK ;
• la figure 10 illustre la variation du coefficient de dilatation du matériau composite en fonction de l'angle que font les fibres par rapport au plan transversal de la jupe HOLWECK ;
• la figure 11 illustre le procédé de réalisation d'une jupe HOLWECK en matériau composite selon l'invention ; et
• la figure 12 illustre le procédé préférentiel de réalisation d'une jupe HOLWECK selon la présente invention.

Other objects, characteristics and advantages of the present invention will emerge from the following description of particular embodiments, given in relation to the attached figures, among which:

• Figure 1 is a schematic view illustrating, in longitudinal section, a known turbomolecular pump structure having a one-piece metal rotor;
• Figure 2 is a perspective view illustrating a rotor sector according to an embodiment of the present invention;
• FIG. 3 illustrates the distribution of mechanical stresses on the rotor sector of FIG. 2, the blades of the turbo stage having been removed;
• Figure 4 is a schematic side view illustrating the rotor structure according to a first embodiment of the present invention;
• Figure 5 is a side view schematically illustrating the rotor structure according to a second embodiment of the present invention;
• Figure 6 is a perspective view illustrating the structure of the stator HOLWECK stage surrounding the rotor skirt according to the invention;
• FIGS. 7 and 8 illustrate the YOUNG module, respectively in the longitudinal direction and in the transverse direction of the fibers, as a function of the proportion of fibers in the composite material;
• FIG. 9 illustrates the variation of the YOUNG module of the skirt as a function of the orientation of the fibers relative to the transverse plane of the HOLWECK skirt;
• FIG. 10 illustrates the variation of the coefficient of expansion of the composite material as a function of the angle that the fibers make with respect to the transverse plane of the HOLWECK skirt;
• FIG. 11 illustrates the process for producing a HOLWECK skirt in composite material according to the invention; and
• FIG. 12 illustrates the preferred method for producing a HOLWECK skirt according to the present invention.

We first consider Figure 1, illustrating a turbomolecular pump structure 1 secured to the wall 2 a vacuum chamber 3.

The turbomolecular pump 1 comprises a pump body 4 or stator in which a rotor 5 rotates at high speed axial rotation along the axis of rotation I. The pump body 4 has a coaxial suction port 6, through which penetrate the gases pumped 7, and a discharge orifice 8 through which are evacuated the outlet gas 9. The rotor 5 is rotated in the pump body 4 by an internal motor 10, and is guided laterally by magnetic or mechanical bearings 11 and 12.

The wall 2 of the vacuum enclosure 3 includes an orifice outlet 13, corresponding to the suction port 6 of the vacuum 1, and generally constitutes a closed enclosure isolated from outside and in which the vacuum pump 1 can create a vacuum control.

The rotor 5 comprises an upstream section of rotor 5a comprising blades such as the blade 5b, and comprises a section downstream of rotor 5c in the form of a HOLWECK type skirt. Facing the stretch upstream 5a of rotor, stator 4 comprises an upstream section of stator 4a with blades such as the blade 4b. Facing the downstream section of rotor 5c with HOLWECK skirt the stator 4 has a downstream section of stator 4c with helical grooves 4d of HOLWECK type tel as more apparent in Figure 6.

In FIG. 2, illustrating a rotor sector according to the present invention, we find the upstream section of rotor 5a having blades such as the blade 5b, and we find the downstream section of rotor 5c. The upstream rotor section 5a is made of a metal or alloy suitable, for example aluminum or aluminum alloy. The downstream section of rotor 5c with HOLWECK skirt is made of a material composite with organic matrix, based on resin filled with fibers reinforcement. The downstream section with HOLWECK 5c skirt is connected to the upstream section 5a along an annular connection zone 5d.

The reinforcing fibers can advantageously be glass fibers or carbon fibers, occurring under wick shape (up to several thousand filaments per wick) long wound continuously on a reel by a process filament winding. Resins can be resins thermoplastics (for example polyester ether ketone PEEK) or thermosets (eg epoxy).

According to the invention, the downstream section of rotor 5c with skirt HOLWECK in organic matrix composite material includes a internal fiber reinforcement structure which gives the skirt mechanical characteristics varying depending on the area longitudinal view of the skirt. We are trying to increase the stiffness of the organic matrix composite material in the downstream area 5th skirt or cylindrical section adjacent to the downstream end 5f of the rotor 5, in order to withstand the high mechanical stresses during of the rapid rotation of the rotor 5. Simultaneously, we seek a greater flexibility and greater expansion capacity thermal in the annular connection zone 5d, to follow the deformations which occur in the upstream section of rotor 5a in metal during the rapid rotation of the rotor and during its warming up.

Thus, in the annular connection zone 5d, the material organic matrix composite of the HOLWECK skirt has mechanical and thermal characteristics close to those of metal or alloy making up the upstream rotor section 5a.

Conversely, in the downstream region of skirt 5e, the material organic matrix composite has more characteristics suitable for holding in this downstream area of the 5th skirt the mechanical stresses resulting from the rapid rotation of the rotor in operation.

In practice, the fiber reinforcement structure of the downstream section with skirt type HOLWECK 5c includes long fibers helically wound at the periphery of the skirt. The fibers are embedded in resin, the resin being polymerized.

We can for example consider Figure 11, which illustrates schematically a process for making a resin skirt armed with long fibers wound in a helix: a mandrel 14 is rotated around a shaft 15, and the mandrel has an external surface whose shape conditions that of the skirt to achieve. The reinforcing fibers are in the form of a wick wound on a reel 16. The wick is unwound from the reel 16, passes through a resin tank 17, is guided by a wire guide 18 which the helical winding on the mandrel 14 during the rotation of the mandrel. Depending on the relative speed of rotation of the shaft 15 and longitudinal translation of the wire guide 18 according to the arrow 19, the wick is arranged on the mandrel 14 according to a propeller whose the pitch can be chosen by the operator.

FIG. 4 illustrates a first embodiment of a rotor 5 according to the present invention.

In this embodiment, the rotor 5 comprises the upstream section of metal rotor 5a with the blades such as the blade 5b, and includes the downstream section of rotor 5c, in the form of a skirt cylindrical tubular type HOLWECK.

The 5d annular connection zone and an intermediate zone of connection 5g which is adjacent to it have an internal structure reinforcement such as their mechanical characteristics and are close to those of the metal or alloy composing the upstream section of rotor 5a. For this, the reinforcement structure includes long fibers wound in a helix at a pitch relatively large, the fibers making with the transverse plane an angle greater than 0 °, for example from 5 ° to 20 ° depending on the desired mechanical properties. In the downstream area of the 5th skirt, the long fibers are wound in a helix with an angle close to 0 °, forming contiguous turns which significantly improve the mechanical resistance of the skirt.

FIG. 5 illustrates a preferred embodiment of rotor 5 of a turbomolecular pump according to the present invention. We finds, in rotor 5, the upstream section of rotor 5a for example identical structure to that of the embodiment of the figure 4, and a downstream section of rotor 5c whose diameter varies in depending on the position considered along the longitudinal axis: the skirt of the downstream section of rotor 5c comprises the annular zone of link 5d, the downstream section of skirt 5th cylindrical with larger diameter as the annular connection area 5d, and an area connection intermediate 5g with diameter gradually crescent that links the 5d annular bond area cylindrical and the downstream section of skirt 5th cylindrical.

In this second embodiment, the annular zone of 5d bond has reinforcing fibers at an angle not zero with the transverse plane, while the downstream section of skirt 5e and possibly the intermediate connection area 5g have contiguous fibers forming with the transverse plane a angle close to 0 °.

Thanks to the reinforcement by fibers at zero angle, the downstream section of 5th cylindrical skirt may have a diameter significantly higher, which increases the tangential speed of the skirt relative to the stator for the same angular speed of rotation of the rotor, and this allows the number of grooves 4d in the stator section HOLWECK 4c (Figure 6).

The advantage of this composite skirt structure is explained in relation to FIG. 3. We have illustrated, on this figure, the mechanical stresses undergone by the rotor during a rapid rotation of the rotor: in the annular connection area 5d, the constraints are relatively low, while in the downstream section of skirt 5e the constraints illustrated by the arrows 5i are much larger, about 3 to 4 times larger in the embodiment illustrated in the figure. In the zone connection intermediary 5g, the constraints increase gradually when approaching the downstream section of skirt 5e. Thus, in the annular connection zone 5d, the fibers so as to give the composite material of the skirt a some flexibility and some expansion capacity thermal, to follow the dimensional variations of the section upstream of rotor 5a made of metal. However, to support the higher mechanical stresses in the downstream section of 5th skirt, it is necessary to arrange the reinforcing fibers of so as to ensure good rigidity of the skirt, good concentricity, and relative resistance to vibrations.

Figures 9 and 10 illustrate the effect of the angle the fibers relative to the transverse plane of the skirt, on the one hand on the mechanical resistance evaluated by the YOUNG module longitudinal, on the other hand on the coefficient of expansion thermal.

On curve A of figure 9, the YOUNG module is at a maximum A2 for an angle of 0 °, i.e. when the fibers are in a transverse plane. The YOUNG module decreases sharply when the fiber angle increases to an angle of 20 ° approximately, then it decreases more slowly as increasing the angle.

On curve B of Figure 10, the coefficient of dilation increases regularly when the angle increases between fibers and the transverse plane.

Thus, in the annular connection zone 5d (FIGS. 4 and 5), a fiber angle greater than 0 ° is chosen, for example a 10 ° angle to position at point A1 of curve A in the figure 9, and to go to point B1 of curve B in figure 10: relatively low YOUNG modulus and coefficient of expansion relatively high thermal. On the other hand, in the downstream area of the skirt 5th (Figures 4 and 5), we choose a fiber angle close to 0 °, so that we place ourselves at point A2 of curve A of figure 9 and at point B2 of curve B in FIG. 10: maximum YOUNG modulus, and minimum coefficient of thermal expansion.

In these two variable angle embodiments of fibers compared to the transverse plane, a difficulty lies in the fact that the skirt section having to present mechanical characteristics of flexibility occupies one end of the skirt, namely the annular connection zone 5d. Indeed, in this area, the fibers must have a non-zero angle by in relation to the transverse plane, and these fibers must be wound in several layers to achieve sufficient reinforcement. So, when a helical fiber is wound in the direction of the upstream end of the annular connection zone 5d, this makes an angle to the end of the skirt, and you have to move the thread guide in the other direction as soon as the fiber reaches this end. Reversing the winding direction is not easy, and it a way must be found to facilitate this operation.

a/ une étape consistant à enrouler en hélice des fibres longues sur un mandrin en réalisant un enroulement à angle voisin de 0° dans les zones 20 et 21 (figure 12) adjacentes aux deux extrémités du mandrin et un enroulement à angle supérieur à 0° dans la zone médiane 22 du mandrin ;

b/ une étape d'application et de durcissement de résine sur le mandrin portant les fibres enroulées en hélice ;

c/ et une étape consistant à sectionner le manchon 23 ainsi obtenu, transversalement au milieu 24 de sa zone médiane 22, permettant ainsi d'obtenir deux jupes identiques, sous réserve de prévoir initialement un mandrin symétrique par rapport à sa zone médiane 22.

The invention provides such a means by a particular method of producing a HOLWECK type skirt for a turbomolecular vacuum pump, the method comprising:

a / a step consisting in helically winding long fibers on a mandrel by making a winding at an angle close to 0 ° in the zones 20 and 21 (FIG. 12) adjacent to the two ends of the mandrel and a winding at an angle greater than 0 ° in the middle zone 22 of the mandrel;

b / a step of applying and curing resin on the mandrel carrying the helically wound fibers;

c / and a step consisting in cutting the sleeve 23 thus obtained, transversely in the middle 24 of its central zone 22, thus making it possible to obtain two identical skirts, subject to initially providing a mandrel symmetrical with respect to its central zone 22.

During the sectioning step of the middle zone 22, the fibers wound in a helix at an angle greater than 0 ° in said central zone 22 are cut. It does not affect the qualities mechanical of the skirt obtained. On the contrary, it allows great regularity of winding of the fibers, and therefore a great regularity mechanical properties of the skirt in the annular zone of link.

In the embodiments illustrated above, the mechanical properties of the composite material are obtained in modulating the pitch of the fiber winding helix, i.e. the angle that the turns of fibers make in relation to the plane transverse.

Alternatively, long fibers are helically wound and coated with resin, the helix having a pitch constant.

We then provide a variable resin rate depending on the area longitudinal view of the skirt. For example, in the area 5d connection ring, a higher resin level is provided, and, in the downstream region of the 5th skirt, a resin content is provided inferior. Mechanical resistance is thus increased in the downstream section of skirt 5e, while flexibility is increased in the annular connection zone 5d, as illustrated in FIGS. 7 and 8 respectively showing the variations of Young's modulus longitudinal (curve C) and transverse Young's modulus (curve D) as a function of the fiber content (complement to 1 of the fiber content resin).

If necessary, depending on the desired properties of the skirt, you can vary both the pitch of the propeller and the rate of resin according to the longitudinal zone considered of the skirt.

The present invention is not limited to the modes of which have been explicitly described, but it includes the various variants and generalizations contained in the field of the claims below.

Claims (9)

Turbomolecular vacuum pump, comprising a rotor (5) having an upstream rotor section (5a) of turbo type and a downstream rotor section (5c) in the shape of a HOLWECK skirt, the upstream rotor section (5a) being a metal or alloy, the downstream rotor section (5c) being made of an organic matrix composite material, the downstream rotor section (5c) connecting to the upstream rotor section (5a) according to an annular connection zone (5d),
characterized in that : the downstream rotor section (5c) with a HOLWECK type skirt made of an organic matrix composite material comprises a fiber reinforcement structure which gives the HOLWECK skirt mechanical characteristics varying as a function of the longitudinal zone considered of the skirt, in the annular connection zone (5d), the organic matrix composite material has mechanical and thermal characteristics close to those of the metal or alloy making up the upstream section of rotor (5a), in the downstream region of the skirt (5e), the organic matrix composite material has characteristics more suitable for holding in this downstream region of the skirt (5e) the high mechanical stresses resulting from the rapid rotation of the rotor (5) in operation. Turbomolecular vacuum pump according to claim 1, characterized in that the reinforcing structure comprises long fibers wound in a helix at a constant pitch and coated with resin, the rate of resin being variable according to the longitudinal zone considered of the skirt. Turbomolecular vacuum pump according to claim 1, characterized in that the reinforcing structure comprises long fibers wound in a helix and coated with resin at a constant rate, the pitch of the helix being variable according to the longitudinal zone considered of the skirt. Turbomolecular vacuum pump according to claim 1, characterized in that the reinforcing structure comprises long fibers wound in a helix and coated with resin, the pitch of the helix and the rate of resin both being variable according to the longitudinal zone considered from the skirt. Turbomolecular vacuum pump according to one of claims 3 or 4, characterized in that the propeller has an angle close to 0 ° in the downstream region of the skirt (5e), and has an angle greater than 0 ° in and near of the annular connection zone (5d). Turbomolecular vacuum pump according to any one of claims 2 to 5, characterized in that the skirt is cylindrical. Turbomolecular vacuum pump according to any one of claims 2 to 5, characterized in that the skirt has an annular connection zone (5d), a downstream section of skirt (5e) cylindrical with a larger diameter than the annular connection zone (5d), and an intermediate connection zone (5g) between the annular connection zone (5d) and the downstream section of skirt (5e). Turbomolecular vacuum pump according to any one of claims 2 to 7, characterized in that , according to the upstream edge of the skirt, the reinforcing fibers are cut. Method for producing a HOLWECK type skirt for a turbomolecular vacuum pump according to any one of Claims 3 to 8, characterized in that it comprises: a / a step consisting in helically winding long fibers on a mandrel (14), by carrying out a winding at an angle close to 0 ° in the zones (20, 21) adjacent to the two ends of the mandrel (14) and a winding at angle greater than 0 ° in the middle zone (22) of the mandrel (14), b / a step of applying and curing resin on the mandrel carrying the helically wound fibers, c / and a step consisting in cutting the sleeve (23) thus obtained in its central zone (22) to obtain two skirts.

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