EP1311763B1 - Pressure seal for a vacuum pump - Google Patents

Abstract

The invention concerns a vacuum pump consisting in the assembly of two stator half-shells (101, 102) and two directly mounted end parts (31, 32) with an interposed single-piece continuous pressure seal (33). The pressure seal (33) comprises two annular end parts (34, 35) generally parallel to each other and connected by two side-members (36, 37) which are generally perpendicular thereto. Thus, the number of components to be assembled to produce an multistage dry vacuum pump is reduced, while providing satisfactory impermeability to outside atmosphere.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to multi-stage dry vacuum pumps such as multi-stage Roots type pumps, Claw type or mixed Roots-Claw type, as described in the preamble of claim 1. Such a pump is known from EP-A-1,020,645.

Such multi-stage dry vacuum pumps are composed of several compression stages placed in series.

FIGS. 1 and 2 show a multi-stage Roots dry pump according to a known embodiment. Figure 2 illustrates in perspective a longitudinal section of the stator of such a pump Roots. One distinguishes in the stator 1, between a pumped gas inlet 2 and a discharge gas outlet 3, five successive compression chambers respectively 4, 5, 6, 7 and 8. The adjacent chambers are separated by a transverse wall respectively 9, 10, 11 and 12 each pierced with two holes such as the holes 13 and 14 of the transverse wall 12 for the passage of the shafts of two parallel rotors mechanically coupled to each other, not shown, and carrying compression lobes Roots or Claw type. The adjacent chambers are connected to each other by a gas passage pipe such as the gas channel 15 connecting the discharge of the first compression chamber 4 to the suction of the second compression chamber 5.

The rotor lobes, penetrating into the compression chambers 4-8, have a greater diameter than the rotor shafts passing through the holes 13 and 14. It is therefore not possible to axially engage an entire rotor in the stator 1 by simple axial displacement. It is not possible, either, to consider machining a stator 1 monobloc to achieve the cavities constituting the compression chambers 4-8.

In order to allow both machining and assembly, and to ensure a good seal, the stators of known dry vacuum pumps generally consist of the axial assembly of several stator elements, respectively 16, 17, 18, 19 and 20. , assembled according to their respective front walls, such as the front wall 21 of the stator element 16, with the interposition of respective annular seals 22, 23, 24, 25 and 26 compressed axially and insulating each compression chamber 4-8 with respect to the external atmosphere.

Such a Roots or Claw dry pump structure requires each stator element 16-20 to be machined separately, and then to carry out a long and delicate assembly operation of adapting the two rotor shafts in a support frame. to adjust the positioning of the lobes of the last compression chamber 8, to position the last stator element 20 with the annular seal 26, to adapt the lobes of the penultimate compression chamber 7, to bring about the penultimate stator element 19 with the annular seal 25, and so on until the first stator element 16. Knowing that the clearances between the rotor lobes and the stator walls are very small, for ensure a seal of each compression stage of the vacuum pump, it is understood that this assembly is particularly long and delicate, and it is estimated that it takes several hours of labor for this operation performed on a pump dry vacuum with five stages.

Another problem, in these known multi-stage dry vacuum pumps, is the difficulty of aligning the stator elements one after the other, being observed that the errors may accumulate between the first stator element 16 and the last stator element 20, so that it is difficult to control the games between the rotors and the stator in a series production.

The documents EP 0 476 631 A and JP 03 145594 A describe vacuum pump structures having a stator in two half-shells assembled radially according to a longitudinal assembly surface generally parallel to the axes of the rotors, the stator being closed in a sealed manner. at its ends by two end pieces inserted axially. These documents do not mention the interest of such a stator structure with two half-shells, and do not describe the means for sealing between stator and rotor.

The difficulty is in fact that it is necessary to ensure on the one hand the circumferential radial sealing in the assembly surface longitudinally of the two half-shells, to prevent the passage of gas between the outer atmosphere and the inner cavities of the pump, and simultaneously provide the axial end seal between the half-shells and the end inserts.

Conventionally, it can be imagined that the axial end seal is provided by annular seals such as those illustrated in FIGS. 1 and 2 in the known pump, and that the peripheral radial seal is provided by compressed longitudinal seals. between the half-shells. But the major disadvantage of this solution lies in the fact that there are creepage distances between the longitudinal seals ensuring the peripheral radial seal and the annular seals ensuring the axial end seal. The seal is therefore not satisfactory.

SUMMARY OF THE INVENTION

The problem proposed by the present invention is to design a new multi-stage dry vacuum pump structure, to reduce significantly the number of parts to assemble during assembly, facilitating assembly and reducing its duration, and while ensuring a satisfactory seal between the inner cavities of the vacuum pump and the outside atmosphere, in order to avoid any risk of pollution of the gases pumped by the external atmosphere, and all risks of pollution of the external atmosphere by the pumped gases.

The solution according to the invention consists in providing a continuous monobloc seal which ensures both types of sealing in a stator structure in two half-shells.

• le stator est réalisé par assemblage radial de deux demi-coquilles selon une surface d'assemblage longitudinale, chaque étage de compression étant ainsi contenu dans deux portions correspondantes de chacune des demi-coquilles, les deux demi-coquilles enfermant, une fois assemblées, l'ensemble des étages de compression ;
• un joint d'étanchéité monobloc continu assure à la fois l'étanchéité radiale périphérique dans la surface d'assemblage longitudinale des demi-coquilles, et assure l'étanchéité axiale d'extrémité entre les demi-coquilles et les pièces rapportées d'extrémité, pour isoler les étages de compression par rapport à l'atmosphère extérieure.

Thus, to achieve these objects as well as others, the invention provides a multi-stage dry vacuum pump composed of several compression stages placed in series, the pump having at least one rotor rotatably mounted in a closed stator sealingly at its ends by two end inserts; in addition :

• the stator is produced by radial assembly of two half-shells along a longitudinal assembly surface, each compression stage being thus contained in two corresponding portions of each of the half-shells, the two half-shells enclosing, once assembled, all the compression stages;
• a continuous monoblock seal ensures both radial circumferential sealing in the longitudinal assembly surface of the half-shells, and provides axial end sealing between the half-shells and the end inserts, to isolate the compression stages with respect to the external atmosphere.

According to an advantageous embodiment, the seal comprises two annular end portions generally parallel to each other and connected by two longitudinal members which are generally perpendicular to them.

In this seal structure, in the assembled state, the gasket longitudinal members are compressed laterally between the two half-shells in the longitudinal assembly surface, while the two annular end portions are compressed. between the two half-shells on the one hand and the respective end inserts on the other hand.

To ensure good compression of the first annular end portion of the seal, it is advantageous to provide a first end insert having an axial nose shaped to occupy a corresponding axial recess of the first end of the stator body constituted by the two half-shells assembled. In this way, the first annular end portion of the seal is compressed radially by the two half-shells on the axial nose.

Preferably, the axial nose comprises a peripheral annular groove for receiving said first annular end portion of the seal.

To facilitate the positioning of the seal and ensure good compression of the longitudinal members, at least one of the half-shells comprises in its longitudinal assembly surface two longitudinal grooves for receiving the longitudinal members of the seal.

The second annular end portion of the seal may simply be compressed axially by the second end insert against the end faces of the two half-shells.

Preferably, the two half-shells comprise, on their end faces of the second end, grooves shaped to receive said second annular end portion of the seal.

SUMMARY DESCRIPTION OF THE DRAWINGS

• la figure 1 est une vue en perspective éclatée d'une structure connue de stator de pompe à vide sèche multi-étagée ;
• la figure 2 est une vue en perspective en coupe longitudinale de la pompe de la figure 1, après assemblage du stator ;
• la figure 3 est une vue en perspective illustrant une première demi-coquille de stator et une première pièce d'extrémité de pompe à vide sèche selon un mode de réalisation de la présente invention ;
• la figure 4 est une vue en perspective éclatée montrant la première demi-coquille de stator et la première pièce d'extrémité après assemblage avec interposition d'un joint d'étanchéité selon l'invention, et montrant également la seconde demi-coquille de stator et la seconde pièce d'extrémité avant assemblage ;
• les figures 5 et 6 illustrent, en perspective selon deux angles différents, une demi-coquille de stator avec joint d'étanchéité, dans le mode de réalisation des figures 3 et 4 ;
• la figure 7 est une vue de côté montrant la face intérieure de la demi-coquille de stator des figures précédentes, avec le joint d'étanchéité en place ;
• la figure 8 est une coupe transversale de la demi-coquille et du joint de la figure 7 selon le plan de coupe A-A, avec les rotors montés ;
• la figure 9 est une vue en perspective du joint d'étanchéité selon un mode de réalisation de la présente invention ; et
• la figure 10 est une coupe transversale du joint d'étanchéité de la figure 9.

Other objects, features and advantages of the present invention will become apparent from the following description of particular embodiments, with reference to the accompanying figures, in which:

• Figure 1 is an exploded perspective view of a known multi-stage dry vacuum pump stator structure;
• Figure 2 is a perspective view in longitudinal section of the pump of Figure 1, after assembly of the stator;
• Fig. 3 is a perspective view illustrating a first stator half-shell and a first dry vacuum pump end part according to an embodiment of the present invention;
• FIG. 4 is an exploded perspective view showing the first stator half-shell and the first end piece after assembly with the interposition of a seal according to the invention, and also showing the second stator half-shell. and the second end piece before assembly;
• Figures 5 and 6 illustrate, in perspective from two different angles, a stator half-shell with seal, in the embodiment of Figures 3 and 4;
• Fig. 7 is a side view showing the inner face of the stator half-shell of the preceding figures, with the seal in place;
• Figure 8 is a cross section of the half-shell and the seal of Figure 7 along the cutting plane AA, with the rotors mounted;
• Figure 9 is a perspective view of the seal according to one embodiment of the present invention; and
• Figure 10 is a cross section of the seal of Figure 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the embodiment of FIGS. 3 to 10, the multi-stage dry vacuum pump according to the invention is a five-stage pump, in which the usual structural elements of a known pump of FIGS. 1 and 2 are found, marked with the same numerical references. Thus, the entry of the pumped gases 2, an outlet of gas that is not visible in the figures, the successive compression chambers 4, 5, 6, 7 and 8, the transverse walls 9, 10, 11 and 12 of compression chamber separation, the holes 13 and 14 for passage of the rotor shafts, and the gas passage pipe 15 between two successive compression chambers. In FIG. 8, the rotors 51 and 52 are also shown.

According to the invention, the stator is composed of two half-shells 101 and 102 respectively, which meet in a longitudinal assembly surface 30. Preferably, the longitudinal assembly surface 30 is flat and contains the respective axes II and II-II (Figure 3) of the two coupled rotor shafts.

In this way, after radial assembly of the half-shells 101 and 102, each compression stage of the pump, for example the first compression stage consisting of the first compression chamber 4 and the rotor lobes it contains, is contained in two corresponding portions of each of the half-shells 101 and 102. In other words, the two half-shells 101 and 102 enclose, once assembled, all the compression stages of the pump.

The main stator body thus constituted by the half-shells 101 and 102 assembled is sealed at its ends by two end inserts, respectively a first end piece 31 and a second end piece 32.

According to the invention, the seal between the external atmosphere and the internal cavities of the vacuum pump is achieved by a continuous monobloc seal 33. In the embodiment illustrated in the figures, and better visible in FIGS. 9 and 10, the seal 33 comprises two parts annular end 34 and 35 generally parallel to each other and connected by two longitudinal members 36 and 37 which are generally perpendicular to them. In this embodiment, adapted to the general stator structure described above, the longitudinal members 36 and 37 of the seal 33 are generally parallel to one another and are connected to the annular end portions 34 and 35 according to respective connection areas 38, 39, 40 and 41 diametrically opposite two by two.

As seen in FIG. 9, in this embodiment, the first annular end portion 34 is generally circular and of smaller diameter than the second annular end portion 35 which itself has an oblong shape to follow. the size of the coupled rotors offset vertically relative to each other. The beams 36 and 37 are axially connected directly to the respective upper and lower regions of the second annular end portion 35, while they are radially connected by elbows 42 and 43 to the first annular end portion 34.

In the embodiment of Figure 10, the seal 33 has a substantially circular cross section, visible on the section of the longitudinal members 36 and 37. However, it will be possible to use joints having cross sections of different shapes, for example square , rectangular, etc. The seals may be of elastomer, or of any suitable material such as a copper, aluminum or indium type metal.

Referring more particularly to Figures 3 and 4, it is seen that the first end insert 31 has an axial nose 44 shaped to occupy a corresponding axial recess 45 of the first end of the stator. The axial nose 44 comprises a peripheral annular groove 46 for receiving the first annular end portion 34 of the seal 33. In this way, in the assembled position, the first annular end portion 34 of the seal 33 is compressed radially by the two half-shells 101 and 102 on the axial nose 44 of the first end insert 31. The annular groove 46 may have a rectangular cross section, of a depth smaller than the diameter of the seal 33.

At least one of the half-shells 101 and 102, for example the half-shell 101, comprises in its longitudinal assembly surface 30 two longitudinal grooves 47 and 48 (Figure 3) to receive the longitudinal members 36 and 37 respectively of the seal Sealing 33, as seen in Figures 4 to 6. In this way, the longitudinal members 36 and 37 of the seal 33 are compressed laterally between the two half-shells 101 and 102 in the longitudinal assembly surface 30. The longitudinal grooves 47 and 48 may have a rectangular cross-section, with a depth less than the diameter of the seal 33.

As can be seen in FIG. 4 and FIG. 7, the second end annular portion 35 of the seal 33 is compressed axially by the second end insert 32 of the stator against the two half-shells 101 and 102. In the illustrated embodiment, the two half-shells 101 and 102 comprise, on their end-end faces such as the end face 49 of the first half-shell 101 (FIG. 3), grooves such as the groove 50 in a conformed manner. to accommodate the second annular end portion 35 of the seal 33. The grooves such as the groove 50 may have a rectangular section, of lesser depth than the diameter of the seal 33. The grooves such as the groove 50 are connect to each other to form a continuous groove, and simultaneously connect at their point of connection with the longitudinal grooves 47 and 48 of the longitudinal joining surface 30.

For the assembly of a pump according to the invention, the seal 33 is fitted by engaging its first annular end portion 34 in the annular groove 46 of the axial nose 44 of the first end insert 31, then the first half-shell 101 is applied laterally against the axial nose 44. The longitudinal members 36 and 37 of the seal 33 are engaged in the longitudinal grooves 47 and 48, and a first half of the second annular end portion 35 of the seal 33 is engaged in the groove 50. It is then possible to mount the rotors, and easily position the lobes of the rotors in the chambers. Compression 4-8. The second half-shell 102 can then be adapted both laterally against the axial nose 44 and against the longitudinal assembly surface 30, by inserting the second half of the second annular end portion 35 of the seal 33 into the corresponding front groove of second half-shell 102. Finally, it is possible to bring axially the second end insert 32 against the end faces such as the face 49 of the half-shells 101 and 102.

The mounting of such a pump is much faster than that of known pumps generally used. At the same time, tightness is ensured very efficiently and satisfactorily.

The invention applies in particular to the constitution of a multi-stage primary pump type Roots, or type Claw, or Roots-Claw type.

Claims (11)

1. Dry multistage vacuum pump consisting of a plurality of compression stages (4-8) placed in series, the pump having at least one rotor rotatably mounted in a stator closed of its ends by two separate end caps (31, 32), the stator being obtained by radial assembly of two half-shells (101, 102) at a longitudinal assembly surface (30), each compression stage (4-8) thus being contained in two corresponding portions of each of the half-shells (101, 102) and the two half-shells (101, 102), when assembled, enclosing all of the compression stages (4-8), characterised in that, to isolate the compression stages (4-8) from the external atmosphere, a continuous one-piece seal (33) provides both a peripheral radial seal at the longitudinal assembly surface (30) of the half-shells (101, 102) and an end axial seal between the half-shells (101, 102) and the separate end caps (31, 32).
2. Vacuum pump according to claim 1, characterised in that the seal (33) has two generally parallel annular end portions (34, 35) joined by two longitudinal portions (36, 37) that are generally perpendicular to them.
3. Vacuum pump according to claim 2, characterised in that, in the assembled state, the longitudinal portions (36, 37) of the seal (33) are compressed laterally between the two half-shells (101, 102) in the longitudinal assembly surface, (30) and the two annular end sections (34, 35) are compressed between the two half-shells (101, 102), on the one hand, and the respective separate end caps (31, 32), on the other hand.
4. Vacuum pump according to either claim 2 or claim 3, characterised in that a first separate end cap (31) has an axial nose (44) shaped to occupy a corresponding axial recess (45) at the first end of the stator body consisting of the assembled two half-shells (101, 102), the first annular end portion (34) of the seal (33) being compressed radially onto the axial nose (44) by the two half-shells (101, 102).
5. Vacuum pump according to claim 4, characterised in that the axial nose (44) comprises a peripheral annular groove (46) adapted to receive said first annular end portion (34) of the seal (33).
6. Vacuum pump according to any one of claims 3 to 5, characterised in that at least one of the half-shells (101) comprises in its longitudinal assembly surface (30) two longitudinal grooves (47, 48) adapted to receive the longitudinal portions (36, 37) of the seal (33)
7. Vacuum pump according to any one of claims 3 to 6, characterised in that the second annular end portion (35) of the seal (33) is compressed axially by the second separate end cap (32) against the front faces (49) of the two half-shells (101, 102).
8. Vacuum pump according to claim 7, characterised in that the two half-shells (101, 102) comprise grooves on their second end front faces (49), (50) shaped to receive said second annular end portion (35) of the seal (33).
9. Vacuum pump according to any one of claims 2 to 8, characterised in that the seal (33) has a substantially circular cross section and is accommodated in grooves (46, 47, 48, 50) of rectangular cross section.
10. Vacuum pump according to any one of claims 1 to 9, characterised in that it constitutes a multistage primary pump of Roots, Claw or combined Roots-Claw type.
11. Vacuum pump according to any one of claims 2 to 9, characterised in that:

    - the longitudinal assembly surface (30) is plane and contains the axes (I-I, II-II) of the two coupled rotor shafts,

    - the longitudinal portions (36, 37) of the seal (33) are generally parallel to each other and joined to the annular end portions (34, 35) in respective joining areas (38-41) that are diametrally opposed in pairs.

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