EP0368124A1 - Multistage Roots pump and its assembly method - Google Patents

Abstract

The pump comprises a stator constituted by an alternating succession of flanges (22) and stator rings (21) defining a series of compression chambers (20), and a rotor assembly composed of two shafts (24, 25) each comprising, in each compression chamber (20) a compression lobe (28), these compression lobes being attached and fixed to their shaft during assembly of the pump, thus making it possible to individually adjust the axial clearances between the lobes and the flanges, each lobe being composed of a body (29) and a flange (30) which is fixed to the body by screws (34) by compressing a set of two conical rings (32, 33) one of which (33) penetrates in the other by undergoing an axial narrowing ensuring the fixation of the lobe. The mounting method consists in using a mounting plate (23) having an extra thickness j penetrating inside the stator ring and corresponding to the desired clearance between the lobes and the flanges (22). The lobes are angularly positioned by means of rods (45) and they are positioned axially by pressing them against the mounting flange (23) by means of mounting screws (48). This done, the lobe is secured against its shaft by tightening mounting screws (34) which compress conical rings (32, 33) coming to tighten against the shaft.

Description

The present invention relates to a multi-stage roots pump comprising a stator and a rotor assembly, the stator defining a plurality of successive compression chambers, each compression chamber being limited axially by two flanges and radially by a stator ring, the rotor assembly being located inside the stator and consisting of two parallel shafts, each shaft comprising in each compression chamber a compression lobe which is attached and fixed, when the pump is mounted on its shaft, the shafts being supported by bearings in flanges located at the ends of the stator and comprising a synchronization gear located in a casing fixed to one of the end flanges, one of the shafts being driven in rotation by a drive motor.

French documents 2,517,755 (USA 4,504,201) and 660,528 disclose a multistage pump of this type.

In document 2 517 755, each stage of the stator is constituted by a kind of box without cover, which is closed during assembly by juxtaposition with the next stage, thus each stator stage forms a chamber axially limited by an integral flange of the floor considered and by a flange belonging to the previous floor. The rotors are mounted on the shafts in an unspecified manner but appear, in consideration of FIG. 1, keyed on the shafts.

In document 660,528, the stator is shown in FIG. 3 and appears to be in one piece, while for the rotors, the rotary pistons are mounted keyed on the shafts.

mm et donc d'atteindre des vides plus poussés que dans les machines actuelles, de l'ordre d'une décade.The object of the invention is to produce a modular multi-stage roots pump, with simple manufacturing parts allowing precise machining, and allowing very precise mounting, in particular of the position of the rotary lobes on the shafts so as to achieve a machine with very small lateral clearances between the lobes and the flanges, of the order of

mm and therefore reach deeper voids than in current machines, of the order of a decade.

The subject of the invention is therefore a multi-stage roots pump such as as defined above, characterized in that said flanges and stator rings are separate pieces stacked alternately and in that each compression lobe is composed of a body and a flange, the flange being fixed to the body by screws arranged axially, and compressing a set of two conical rings, one of which penetrates inside the other by undergoing a radial narrowing ensuring the fixing of the lobe on its shaft.

• a) on monte les deux arbres dans un flasque d'extrémité en y fixant leur position axiale,
• b) on monte l'engrenage de synchronisation sur les arbres,
• c) on place la première couronne statorique par dessus le flasque d'extrémité et on la fixe,
• d) on enfile un lobe de compression sur chaque arbre, la bride étant fixée au corps de lobe, mais sans serrage,
• e) on met en place un plateau de montage que l'on fixe contre la couronne statorique, ledit plateau de montage comportant sur sa face interne, à l'intérieur du périmètre délimitant la paroi interne de la couronne statorique, une surépaisseur j pénétrant dans la couronne statorique et correspondant au jeu axial souhaité entre les lobes et le flasque,
• f) on fixe la position angulaire des lobes au moyen de piges que l'on enfile dans des trous prévus dans les lobes, à travers des trous également prévus dans ledit plateau,
• g) les lobes sont plaqués contre le plateau de montage par le moyen de vis de montage s'appuyant contre le plateau de montage et dont les tiges pénètrent dans des trous lisses du plateau et viennent se visser dans des trous taraudés des corps de lobes, les tirant vers le plateau,
• h) on serre les vis de serrage des brides des lobes contre leur corps assurant ainsi la fixation axiale des lobes sur leur arbre respectif,
• i) on ôte les vis de montage de l'opération g,
• j) on ôte les piges de l'opération f,
• k) on ôte le plateau de montage et l'on vient placer et fixer le flasque suivant,
• l) on recommence cycliquement les opérations précédentes c à k jusqu'au dernier flasque à l'extrémité supérieure du stator.

The invention further relates to a method for mounting a roots pump as defined, characterized by the succession of the following operations:

• a) the two shafts are mounted in an end flange by fixing their axial position there,
• b) the synchronization gear is mounted on the shafts,
• c) the first stator ring is placed over the end flange and fixed,
• d) a compression lobe is threaded on each shaft, the flange being fixed to the lobe body, but without tightening,
• e) a mounting plate is put in place which is fixed against the stator ring, said mounting plate comprising on its internal face, inside the perimeter delimiting the internal wall of the stator ring, an additional thickness j entering the stator crown and corresponding to the desired axial clearance between the lobes and the flange,
• f) the angular position of the lobes is fixed by means of rods which are threaded into holes provided in the lobes, through holes also provided in said plate,
• g) the lobes are pressed against the mounting plate by means of mounting screws pressing against the mounting plate and the rods of which penetrate into smooth holes in the plate and are screwed into tapped holes in the lobe bodies, pulling them towards the plateau,
• h) the clamping screws of the lobe flanges are tightened against their body, thus ensuring the axial fixing of the lobes on their respective shafts,
• i) the mounting screws of operation g are removed,
• j) we remove the rods from operation f,
• k) remove the mounting plate and place and fix the flange following,
• l) the preceding operations c to k are cyclically repeated until the last flange at the upper end of the stator.

According to a particular preferred embodiment, the flange of a compression lobe comprises four clamping screws for its fixing against its body, thus, during operation d), the flange of each lobe is only fixed to its respective body by two of these four screws and without tightening, then, during operation g), two so-called mounting screws are used provided with washers pressing against the mounting plate, these two mounting screws being screwed into the two tapped holes in each lobe body, not occupied by clamping screws, then under operation h), tighten the two clamping screws and then carry out operation i), we then place in place of the two mounting screws removed, the two remaining tightening screws to which the tightening torque is applied, then continue operations j) to l) indicated above.

• La figure 1 montre en vue éclatée un lobe de compression d'une pompe roots multiétagée selon l'invention.
• La figure 2 est une vue selon l'axe de la machine d'une pompe selon l'invention, sans flasque de séparation, permettant de voir une chambre de compression, deux lobes et une couronne statorique.
• La figure 3 est une vue partielle de la pompe selon l'invention, la montrant au cours de son montage, cette vue correspond à une coupe selon III-III de la figure 2.

The invention will be clearly understood in the light of the description of an exemplary embodiment, given below with reference to the appended drawing in which:

• Figure 1 shows in exploded view a compression lobe of a multi-stage roots pump according to the invention.
• Figure 2 is a view along the axis of the machine of a pump according to the invention, without separation flange, allowing to see a compression chamber, two lobes and a stator crown.
• FIG. 3 is a partial view of the pump according to the invention, showing it during its assembly, this view corresponds to a section on III-III of FIG. 2.

Referring to the figures, the roots pump of the invention comprises a stator and a rotor assembly. The stator defines a plurality of compression chambers such as the chamber 20. Each chamber 20 is bounded radially by a stator ring 21 and axially by two lateral flanges, separating the chambers from one another. In FIG. 3, only the first lateral flange 22 is seen, which is the lower end flange. In this figure, we also see only the first chamber 20 and that the first stator ring 21. Thus, after the first stator ring 21 is placed a second flange 22 which comes to rest on the upper end of the stator ring 21. This second flange, not shown, has its internal surface at the same level as its support against the stator ring 21, in the same way as the first end flange 22 shown. In FIG. 3, the part which rests on the upper end of the stator ring 21 is not a lateral flange 22, but a simple mounting plate 23, the role of which will be explained below. The stator is thus constituted by an alternative series of flanges 22 and stator rings 21 up to the upper end flange.

The rotor assembly, located inside the stator comprises two parallel shafts 24 and 25 mounted on ball bearings 26, 27 carried by the flanges 22 located at the ends of the machine.

The shafts 24 and 25 are each equipped, in each chamber 20, with a compression lobe 28.

These compression lobes 28 are not in one go with the shafts 24 and 25, but are attached to these shafts and fixed on them during assembly of the pump, thus making it possible to individually adjust the axial clearances.

The compression lobes 28 being attached to the shafts during assembly, the separation flanges are each in a single part.

Figure 1 shows in exploded view a compression lobe 28. It comprises a lobe body 29 and a flange 30. The flange 30 is used to compress, by means of a washer 31 a set of two conical rings 32 and 33 , so as to fix the lobe on its tree. Tightening is carried out by means of four clamping screws 34 which pass through smooth holes in the flange 30 and are screwed into tapped holes 35 in the body 29. The ring 33 enters the ring 32, and when the screws are tightened 34, the ring 33 undergoes a radial narrowing ensuring the fixing of the lobe 28 on its shaft. The washer 31 and the flange 30 can be made in one piece.

Each lobe 28 further comprises two smooth, blind, tracing holes 36 used to position the lobes respectively relative to one another during assembly.

.Returning to Figure 3, we see that beyond the flange end 22, the shafts comprise a synchronization gear composed of two pinions 37 and 38 mounted respectively on the shafts 24 and 25. This gear is located inside a casing 39 fixed by screws 40 to the flange of end 22. In operation, the casing 39 contains lubricating oil. The compression chambers 20 are isolated from this oil by lip seals 41 and 42. The shaft 24 is rotated by a drive motor, not shown. It should be noted that on each shaft, the compression lobes, in the different successive chambers, are offset from one chamber to the next, angularly, by $\frac{\text{π}}{\text{2}}$

.

The different flanges 22 and stator rings 21 are positioned between them by centering pins and fixed to each other by screws.

We will now describe the pump mounting process, referring to Figure 3.

We start by axially positioning the shafts 24 and 25 in the end flange 22 with the bearings 26, 27 and the seals 41 and 42. We then mount the pinions 37 and 38 on the shafts 24 and 25. We then place and fix the first stator ring 21, then, on each shaft, a compression lobe 28 is threaded. Two of the four tightening screws 34 are only put in place, but without applying a tightening torque. We see in Figure 2, on each lobe 28, these two screws 34, arranged symmetrically relative to the axis of their shaft. In Figure 3, we see only one screw 34 on the left lobe. The lobes are positioned angularly "within sight" so that the free housings (FIG. 2) 43 in the flanges 30 for the clamping screws 34 coincide with the position of the holes 44 made in the mounting plate 23 when we come to put this tray in place. This so as to allow the positioning of positioning rods 45 in the base holes 36 (FIG. 1) of the lobes 28 through holes provided in the plate 23, ensuring precise angular positioning and blocking of the lobes 28. On therefore comes to place the mounting plate 23 and introduce these pins 45. The mounting plate 23 is positioned by two pins 46 and fixed by four screws against the stator ring 21. This mounting plate 23 has on its internal face and inside the perimeter delimiting the internal wall 47 of the stator ring 21, an additional thickness j penetrating into the stator ring, and which corresponds to the desired axial clearance between the lobes 28 and the flange 22 which will be placed next, and which does not include any additional thickness. Then the lobes 28 are pressed against this mounting plate 23 using for each lobe, two mounting screws 48 which are screwed into the two tapped holes 35 not occupied by clamping screws. These mounting screws 48 are supported by means of support washers 49, against the upper face of the mounting plate 23. By thus screwing these two screws 48, the lobe is pressed against the underside of the mounting plate 23.

Then applied to the two tightening screws 34, the tightening torque provided using a screwdriver 50. This action has the effect of compressing the two rings 32 and 33 and tightening them against the shaft 24 (or 25). We can then remove the mounting screws 48 and place and tighten the other two clamping screws 34.

Then simply remove the pins 45, then remove the mounting plate 23. Then place the second flange 22, then the second stator ring 21, and repeat the previous operations cyclically to the last flange 22 end superior.

Once the assembly is complete, the pump is arranged horizontally.

Of course, the pump has a suction port and a discharge port and each chamber has an intermediate discharge communicating with an intermediate suction of the next chamber, this by orifices made in the flanges 22, but this is known and does not do not part of the invention and has not been shown.

Claims (3)

1 / Multi-stage roots pump comprising a stator and a rotor assembly, the stator defining a plurality of successive compression chambers (20), each compression chamber being limited axially by two flanges (22) and radially by a stator crown (21), the rotor assembly being located inside the stator and consisting of two parallel shafts (24, 25), each shaft comprising in each compression chamber (20) a compression lobe (28), which is attached and fixed, during mounting the pump on its shaft, the shafts being supported by bearings (26, 27) in the flanges (22) located at the ends of the stator and comprising a synchronization gear (37, 38) located in a casing (39) fixed to one of the end flanges, one (24) of the shafts being driven in rotation by a drive motor, characterized in that said flanges (22) and stator rings (21) are separate pieces stacked alt ernatively, and in that each compression lobe is composed of a body (29) and a flange (30), the flange being fixed to the body by screws (34) arranged axially, and compressing a set of two rings conical (32, 33) one of which (33) penetrates internally into the other undergoing a radial narrowing ensuring the fixing of the lobe on its shaft. 2 / A method of mounting a multi-stage roots pump according to claim 1, characterized by the succession of the following operations: a) the two shafts (24, 25) are mounted in an end flange (22) by fixing their axial position there, b) the synchronization gear (37, 38) is mounted on the shafts, c) the first stator ring (21) is placed over the end flange (22) and fixed, d) a compression lobe (28) is threaded onto each shaft, the flange (30) being fixed to the lobe body, but without tightening, e) a mounting plate (23) is put in place which is fixed against the stator ring (21), said mounting plate comprising on its internal face, inside the perimeter delimiting the internal wall of the stator ring (21) an extra thickness j entering the stator crown and corresponding to the desired axial clearance between the lobes and the flange, f) the angular position of the lobes (28) is fixed by means of rods (45) which are threaded into holes (36) provided in the lobes, through holes also provided in said plate, g) the lobes are pressed against the mounting plate (23) by means of mounting screws (48) pressing against the mounting plate and the rods of which penetrate into smooth holes in the plate (44) and are screwed in tapped holes (35) of the lobe bodies, pulling them towards the plate (23, h) the clamping screws (34) of the lobe flanges are tightened against their body, thus ensuring the axial fixing of the lobes (28) on their respective shaft (24, 25), i) the mounting screws (48) are removed from operation g, j) we remove the rods (45) from operation f, k) the mounting plate (23) is removed and the following flange (22) is placed and fixed, l) the preceding operations c to k are cyclically repeated until the last flange (22) at the upper end of the stator. 3 / A method according to claim 2, characterized in that, the flange (30) of a compression lobe (28) comprising four clamping screws (34) for fixing against its body (29), during the operation d) of claim 4, the flange of each lobe is fixed to its respective body only by two of these four screws (34) and without tightening, in that during operation g, two said screws are used. mounting (48) provided with support washers (49) against the mounting plate, these two mounting screws being screwed into the two tapped holes (35) of each lobe body, not occupied by clamping screws (34 ), in that under operation h, the two clamping screws (34) are tightened and then operation i is carried out, then the two mounting screws (48) removed are placed, the two screws remaining tightening (34) to which the tightening torque is applied, then operations j to l are continued.

Images