DE29904411U1 - Screw compressor - Google Patents

Description

Screw compressor

The invention relates to a screw compressor of the type mentioned in the preamble of claim 1. The invention is preferably, but not exclusively, applicable to a screw compressor for generating a compressed air flow for the pneumatic transport of bulk materials, and in particular to a screw compressor designed for attachment to a silo vehicle.

Screw compressors are air compressors that operate on the displacement principle and have advantageous properties compared to other types of compressor, making them particularly suitable for the pneumatic transport of bulk materials. This is particularly true for so-called dry-running screw compressors, in which the screw rotors, which are synchronized by a synchronous gear, do not come into contact with one another or with the surrounding housing parts. No lubrication is therefore required in the compression chamber, so that it can be kept oil-free, thus avoiding any contamination of the compressed air with oil. Because the rotors run without contact, there is no wear in this area either, which would reduce the service life, and there is no abrasion that could contaminate the air being conveyed. Due to their operating characteristics, screw compressors are particularly suitable for achieving high pressure ratios and are insensitive to short-term pressure increases that could be caused by blockages in the pipes carrying the compressed air. Finally, they are lighter and have smaller dimensions, which makes them particularly suitable for mobile use, e.g. on silo vehicles.

The efficiency of such a screw compressor depends crucially on the smallest and most precisely defined gap possible between the pressure-side rotor faces and the adjacent end wall of the rotor housing. During operation, this gap should have a width that is, if possible, no greater than 100 μπα and should be maintained within very precise tolerances. The tolerances that affect the gap width are the result of the manufacturing tolerances of the components (rotor shaft journals, housing bores) and the axial play of the roller bearings used to support the shaft journals. Since these axial plays also have a manufacturing-related tolerance that can also change due to the installation and operating conditions, it has previously been common practice to set the rotor gap by trial and error during the manufacture of each individual compressor, namely by inserting washers of different thicknesses between the roller bearings pressed against the play stop and the associated housing contact surfaces. Since this meant that we had to rely on trial and error anyway, we also refrained from maintaining a particularly high level of precision in the manufacturing tolerances of the shaft journals and housing contact surfaces.

The invention is based on the object of designing a screw compressor of this type in such a way that, when assembling the compressor, a very precise maintenance of a predetermined gap between the rotor end faces and the housing end wall can be achieved, which gap does not depend on the axial play of the rolling bearings and their tolerances and does not require any trial and error using differently dimensioned washers when assembling the compressor.

The solution to the problem according to the invention is specified in claim 1. By using an arrangement free of axial play

By using angular contact ball bearings, any influence of a manufacturing-related difference in the axial play of the rolling bearings on the setting of the rotor gap is eliminated. This creates the prerequisite for specifying the width of the rotor gap to a very precisely defined value ¹ , namely by correspondingly precisely machining the length of a spacer ring surrounding the shaft journal, which serves as a spacer between the angular contact ball bearings and the rotor face and a predetermined oversize compared to the axial distance between two faces of the rotor housing facing the angular contact ball bearings or the rotor, which is also machined accordingly precisely. The spacer ring can have an additional function as a race for interaction with a sealing arrangement sealing the shaft journal.

An embodiment of the compressor according to the invention is explained in more detail with reference to the drawings. It shows:

Fig. 1 is a perspective view of the compressor with intake filter, seen from the side;

Fig. 2 is a vertical section through the compressor of Fig. 1;

Fig. 3 is a horizontal section through the compressor in the plane containing the two rotor axes;

Fig. 4 is a further perspective view of the compressor from below, seen from the suction end, with the suction housing and oil tank removed;

Fig. 5 is a detail of the perspective view according to Fig. 1, with a modified embodiment of the intake housing;

Fig. 6 is an enlarged detail of the sectional view of Fig. 2 in the area of the suction-side rotor bearing.

Fig. 7 is an enlarged detail of the sectional view of Fig. 3 in the area of the pressure-side rotor bearing.

In all figures, identical or corresponding parts are designated by identical reference symbols.

The housing of the compressor shown in Fig. 1-4 consists of the following main parts: a gear housing 1, a rotor housing 3, an inflow housing 4, a suction housing 5 and an oil tank 7. Two rotors, namely a main rotor 9 (profile teeth) and a secondary rotor 11 (profile gaps), are rotatably mounted in the rotor housing 3. Their helical teeth and tooth gaps mesh with one another and form sealed chambers which move and shrink in the axial direction as the rotor rotates, thereby compressing the air taken in. During operation, the rotors are driven in such a way that their right-hand end in Fig. 1-3 is the suction side. Here, air is sucked in through inflow openings 13 provided on the front side of the rotor housing 3. The air is conveyed axially to the left by the intermeshing teeth and tooth gaps of the rotor pair and exits as compressed air at the pressure-side end of the rotors at an upwardly directed pressure outlet 15. The functional principle of a screw compressor is known and will not be explained in more detail here.

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The gear housing 1 has the shape of a disk-like stator. The drive shaft 17 of the compressor is mounted in bearings 16, 18 in it, the shaft journal 17a of which protrudes from the housing cover 49 and is connected to a rotary drive (not shown). The gear housing 1 also contains a drive gear consisting of a gear 19 fastened to the drive shaft 17 and a gear 21 fastened to the shaft journal 23 of the secondary rotor 11, through which the rotation of the drive shaft 17 is transmitted to the secondary rotor 11 with a suitable transmission ratio. Furthermore, the gear housing 1, i.e. also on the pressure side of the rotors 9, 11, houses the synchronization gear which ensures the synchronous running of these rotors, consisting of the intermeshing gears 25, 27 which are fastened to the shaft journal 23 of the secondary rotor and to the shaft journal 29 of the main rotor 9. The synchronizing gear ensures that the rotors 9, 11 mesh with each other with very little play but without contact. This makes it possible to manage without any oil lubrication between the rotors 9, 11, i.e. to create a dry-running compressor. This is particularly important if the compressor is to generate an air flow that is absolutely free of oil residues for the pneumatic conveyance of sensitive materials.

The gear housing 1, which is designed as a stand or disc, has on its lower base on both sides projecting fastening feet 31 with holes 33 for fastening screws, with which the entire compressor can be fastened to a suitable base, e.g. a vehicle.

For the purpose of constant lubrication of the drive gear 19, 21 and the synchronizing gear 25, 27, lubricating oil is injected into the area of the meshing of both gears, which is constantly circulated by an oil pump 45. A required supply of oil is kept in the oil tank 7, which communicates with the interior of the gear housing. Sealing arrangements 35 cooperate with the shaft journals 23, 29 of the rotors 9, which prevent oil from entering the rotors 9, 11 and thus the compression chamber of the compressor. These sealing arrangements will be explained in more detail below. Since the drive gear 19, 21 and the synchronizing gear 25, 27 are both arranged on the pressure side of the rotors 9, 11 and the suction side bearings of the rotors are grease-filled, as will be explained later, no oil lubrication is required on the suction side of the rotors (right in Fig. 1-3). Therefore, no oil lines are required, as in the usual design of screw compressors, through which oil can circulate from the pressure side to the suction side of the rotor and back.

As can be seen from Fig. 1 and Fig. 3, the rotor housing is attached to the gear housing 1 by means of a flange connection 37 in such a way that it protrudes freely from the gear housing 1. The oil tank 7, which has a flat box shape, is also attached to the gear housing 1 in such a way that it protrudes freely from the latter, approximately parallel to the rotor housing 3 and underneath it. The side walls of the oil tank 7 are provided with cooling fins 39. There is a relatively wide air gap 41 between the oil tank 7 and the underside of the rotor housing 3. With this arrangement of the rotor housing 3 and oil tank 7 relative to each other and to the gear housing 1, it is achieved that the heat transfer, in particular heat conduction, from the rotor housing 3 to the oil tank

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7 is reduced to a minimum. This prevents the heat generated by the air compression in the rotor housing 3 during operation of the compressor from leading to an undesirable heating of the oil supply in the oil tank 7, even though the oil tank 7 is directly connected to the gear housing. Due to the direct attachment (flange connection) of the oil tank 7 to the gear housing 1, it can communicate with the gear housing 1 via a large opening 43. Separate oil lines are no longer required.

An oil pump 45, which surrounds the drive shaft 17 and is driven by it, is used to circulate the oil inside the gearbox housing 1, or to generate an oil mist. The housing of the oil pump 45 has an outwardly projecting flange 47, which is used to center the

I attached housing cover 49. The oil pump 45 is attached to the gearbox housing 1 with 4 screws 51 (Fig. 3) and associated threaded holes.

Due to the arrangement of the drive gear 19, 21 and synchronizing gear 25, 27 on the pressure side of the rotors 9,

II, on the suction side, only the bearings 53 for the suction-side shaft journals 55, 57 are located in an inflow housing 4 which closes off the rotor housing 3 on the suction side and in which the inflow openings 13 leading to the interior of the rotor housing are formed between support ribs 14. Sealing arrangements 61 which interact with the shaft journals 55, 57 and which will be explained below are located in front of the bearings 53.

The ends of the suction-side shaft journals 55, 57 of the rotors 9, 11 that protrude beyond the bearings 53 are provided with a tool engagement for the attachment of a turning tool. In the embodiment shown in Fig. 6, the

Tool engagement consisting of two flats 63 for the attachment of an open-end wrench. The tool engagement can also have the shape of a square, hexagon, hexagon socket or the like. The shaft journals 55, 57 provided with the tool engagement are easily accessible by removing a housing cover 65 attached to the inflow housing 4 with screws.

By placing a turning tool on one or both of the suction-side shaft journals of the rotors 9, 11, it is possible to turn them by hand and thereby remove a blockage of the rotors, which can occur when dusty material, which is to be conveyed by the compressed air flow generated by the compressor, gets into the interior of the rotor housing 3 and between the rotors 9, 11 as a result of a material kickback. Such a blockage cannot usually be removed by turning the drive shaft journal 17a, since the drive gear 19, 21 has too high a gear ratio.

The inlet housing 4, which closes off the rotor housing 3 on the suction side and has the inlet openings 13, is surrounded at a distance by a large-volume intake housing 5 (indicated only by dash-dotted lines in Fig. 2 and Fig. 3), which is attached to a flange 67 of the rotor housing 3 by means of screws. In this intake housing 5, which is attached directly to the rotor housing 3, there is an intake filter for filtering the air taken in and/or a damper for soundproofing. In the embodiment shown in Fig. 1, the intake housing 5 contains a filter 6 made of a suitable porous or air-permeable filter material. The filter is located in an air flow path between an outer intake slot 69 and a passage slot 73 arranged in an inner partition wall 71, the intake slot 69 and the passage slot being so

are offset from one another so that the longest possible flow path for the air between the slots 69, 73 is formed by the filter 6.

Fig. 5 shows a modified embodiment of the intake housing 5, in which the air sucked in through the intake slot 69 and diverted by the deflection wall 71 with passage slot 73 flows through a silencer 75, e.g. made of suitable perforated metal sheets, before it reaches the space surrounding the housing cover 69 and flows through the inlet openings 13 into the interior of the rotor housing 3. It is also possible to design the intake housing 5 in such a way that it contains both a filter and a silencer.

An advantage of directly attaching the intake housing 5, which contains a filter and/or a silencer, to the rotor housing 3 in such a way that it surrounds the inflow housing 4 at a distance is that a separate arrangement of a filter and/or silencer and a connecting line between this and the suction side of the compressor can be omitted. This results in a particularly simple, compact and robust arrangement. A further advantage is that the air sucked into the intake housing 5 flows around and cools the outside of the inflow housing 4 containing the shaft journal bearings before it enters the interior of the rotor housing 3 through the inflow openings 13. This achieves effective cooling of the rotor bearings on the suction side.

Fig. 6 shows an enlarged sectional view of the bearing and sealing of the shaft journal 55 of the rotor 9 in the inflow housing 4. The shaft journal 57 of the other rotor 11 is supported and sealed in an analogous manner. The shaft journal 57 of the other rotor 11 is supported and sealed in an analogous manner.

The shaft journal 57, which is provided with tool engagement (flats 63), is mounted in the middle part of the inflow housing 4, which is designed like a hub, by means of a roller bearing 53 which is arranged between a shoulder of the shaft journal 57 and a locking ring 83 which engages in an annular groove of the shaft journal. Since, as explained above, no oil lubrication is to take place on the suction side of the rotors 9, 11, the roller bearing 53 is preferably designed as an encapsulated bearing with a lifetime grease filling so that it does not require any subsequent lubrication. A race 85 is attached to the shaft journal 57 adjacent to the roller bearing 53, preferably shrunk on. The race 85, which can be a commercially available race for a roller bearing, for example, is made of steel with a specially hardened circumferential surface. Two sealing lips of a lip seal ring 87 work together with this, which seals the interior of the rotor housing 3 against the roller bearings 53. On the side of the lip seal ring 87 facing the rotor housing 3, a protective ring 89 is arranged between the lip seal ring 87 and an inner shoulder 4a of the inflow housing 4, the inner circumference of which faces the outer surface of the race with a very small gap, but without contact. The protective ring 89 and the lip seal ring 87 are fixed, preferably glued, against each other and against the inner shoulder 4a of the inflow housing 4 in the bore of the housing.

The function of the protective ring 89 is as follows: During operation, the compressor generates a compressed air flow by sucking in air on the suction side and blowing out compressed air at the discharge port 15, which can be used, for example, for the pneumatic transport of dusty material. In the event of operational faults, compressed air can flow back from the pressure side to the suction side of the rotors, which creates the risk

that particles of the dust-like material carried by the air stream enter the rotor housing 3 and from there to the shaft journals of the rotors. In the event of such a material kickback, the protective ring 89 protects the lip sealing ring 87 from dust particles getting under the sealing lips of the lip sealing ring 87 and impairing the sealing effect.

The suction-side bearing arrangement shown in Fig. 6 and described above has the further advantage that it can be removed from the shaft journal 57 without having to remove the rotor 9 or 11 or change the precise setting of the rotors relative to one another. The bearing and sealing arrangement can be removed from the shaft journal in the following way:

After removing the intake housing 5, the housing cover 65 of the inflow housing 4 is removed so that the shaft journal 57 with its locking ring 83 becomes accessible. The locking ring 83 is removed. The screws connecting the inflow housing 4 to the rotor housing 3 are then loosened. The entire inflow housing 4 can now be removed together with the roller bearings 53, lip seal rings 87 and protective rings 89 contained therein. This means that the suction-side roller bearings 53, which are the parts that need to be replaced most quickly due to the limited service life of their grease filling, can be easily replaced without the rotors 9, 11 having to be adjusted to one another and to the housing or even removed.

Fig. 7 shows in a sectional view corresponding to Fig. 3, but on a larger scale, the bearing and sealing of the pressure-side shaft journals 29, 23 of the rotors 9, 11 on the pressure-

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side end of the rotor housing 3. The bearing and sealing arrangement for the shaft journal 29 of the rotor 9 is described below. The arrangement for the shaft journal 23 of the rotor 11 is designed in a completely analogous manner.

The shaft journal 29 is mounted in the pressure-side end wall of the rotor housing 3 by two roller bearings 91, 93 arranged next to one another, which are designed as so-called angular contact ball bearings. Angular contact ball bearings that are commercially available are ball bearings whose balls are gripped by the outer and inner race only on one side or the other of the radial center plane. The two angular contact ball bearings 91, 93 are arranged next to one another in mirror symmetry. Such an arrangement of angular contact ball bearings has the property that it is completely free of play in the axial direction. A shaft nut 95 arranged on the shaft journal 29 fixes the angular contact ball bearings 91, 93 in the axial direction on the shaft journal 29. The outer race of the angular contact ball bearing 93 rests against an inner shoulder 97 of the rotor housing 3.

Between the angular contact ball bearing 93 and the rotor 9 there is a section of the shaft journal 29, onto which a race ring 101 is fastened, preferably shrunk. This race ring 101, like the previously described race ring 85 according to Fig. 6, is made of steel with a specially hardened circumferential surface. The sealing lips of a lip seal ring 103 rest on the surface of the race ring 101, which seals the compression chamber of the rotor housing 3 against the oil-loaded gear and bearing area. The hardened and extremely precisely machined, e.g. polished, outer surface of the race ring 25 provides a particularly wear-reducing contact surface for the sealing lips of the lip seal ring 103.

Between the lip seal ring 103 and the rotor 9 there is also a labyrinth seal ring 105 which has several adjacent ring ribs on its inner circumference which face the outer surface of the race ring 101 with a very small gap but without contact and form a labyrinth gap with it. Although the race ring 101 does not normally come into contact with the labyrinth seal ring 105, it is nevertheless advantageous for the race ring 101 to also extend over the area of the labyrinth seal ring 105. The labyrinth gap seal is normally a contactless seal, but under extreme operating conditions there may be contact between the ring ribs of the labyrinth seal ring 105 and the race ring 101. If the race ring 101 were not present, grooves would be created on the shaft journal 29, damaging it and rendering the rotor 9 unusable. Thanks to the presence of the race ring 101, in such a case only the race ring 101 needs to be replaced, so that the rotor 9 can be used again, provided it is otherwise undamaged.

Between the labyrinth sealing ring 105 and the lip sealing ring 103 there is an annular relief chamber 107 which is connected to the atmosphere via a ventilation channel 109 (see Fig. 7 and Fig. 2). The ventilation channel 109 formed inside the rotor housing 3, the so-called lantern, runs downwards from a point between the two shaft journals 29 of the rotors 9, 11 and opens out at the bottom of the rotor housing 3. The top of the oil tank 7, which is provided with the cooling fins 39, is located at a distance from the mouth of the lantern 109. A straight access path to the mouth of the lantern 109 from below is blocked by the oil tank 7.

Fig. 4 shows a perspective view of the compressor from below with the oil tank 7 removed, so that the screw holes 44 for fastening the oil tank 7 and the large connection opening 43 through which the oil tank communicates with the gear housing are visible in the front wall of the gear housing 1. Furthermore, in Fig. 4, the intake housing 5 is removed from the suction-side end of the rotor housing 3, so that the view is clear of the inflow housing 4 with its support ribs 14 and the inflow openings 13 leading to the interior of the rotor housing 3. Fig. 4 also shows the mouth of the lantern (ventilation duct) 109 on the underside of the rotor housing 3. As can be seen from Fig. 4, projections 111 are provided on both sides of the mouth of the lantern 109 on the underside of the rotor housing 3, which shield the mouth of the lantern 109 against straight-line access from the side. These projections 111 can be formed by oil drainage channels. The mouth of the lantern 109 is thus located in a protected location to which a straight access path is not possible either from below (due to the oil container 7) or from the side (due to the projections 111). This prevents, for example, when cleaning the compressor using a high-pressure spray device, the high-pressure water jet from being directed directly at the mouth of the lantern 109, which could cause water to enter the annular space 107 and thus the area of the lip sealing ring 103 and the labyrinth sealing ring 105.

As can be explained with reference to Fig. 7, the race 101 mounted on the shaft journal 29 also serves as a spacer element, which serves to maintain a very precisely measured gap between the pressure-side face of the rotor 9 or 11 and the face 113 of the rotor housing 3 facing it. For the efficiency of the compressor,

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sensor, it is crucial that the gap on the pressure-side face of the rotor 9 or 11 is as small and precisely defined as possible. According to the invention, this gap is precisely set and maintained in such a way that, when machining the rotor housing 3, the distance a between the face 113 facing the rotor 9 and the contact shoulder 97 for the roller bearing 93 is manufactured to a predetermined value with very close tolerances. The length b of the race 101, which is used as a spacer element between the roller bearing 97 and the face of the rotor 9, is also ground to a value with correspondingly precise tolerances which is oversized compared to the distance a and corresponds exactly to the width of the gap to be set between the rotor 9 and the rotor housing 3. This adjustment of the gap based on the difference in length of the distances a and b is possible because, according to the invention, angular contact ball bearings 91, 93 are used in a symmetrical arrangement, which, as mentioned, result in a bearing arrangement that is completely free of axial play. Since the contact surfaces between the outer bearing ring and the housing shoulder 97 on the one hand and between the inner bearing ring of the roller bearing 93 and the race 101 on the other hand serve as axially play-free reference surfaces, a correspondingly precise adjustment of the rotor front gap is obtained by sufficiently precise machining of the distance a. of the housing shoulders and the length b of the race 101. The adjustment of the rotor front gap once achieved is retained even when the temperature changes, since the influence of the different thermal expansion of the rotor housing 3 and the race 101 is negligible. The adjustment of the rotor front gap, which was previously required for compressors of this type during assembly by inserting shims of different thicknesses in accordance with the manufacturing tolerance fluctuations, is no longer necessary.

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Claims (2)

1. Screw compressor with two rotors mounted axially parallel in a rotor housing ( 3 ), which engage with each other with helical teeth and tooth gaps and, during operation, convey air from a suction-side end towards a pressure-side end of the rotor housing ( 3 ) and thereby compress it, a gear housing ( 1 ) arranged at the pressure-side end of the rotor housing ( 3 ), in which a drive shaft ( 17 ) with drive gear ( 19 , 21 ) for the rotors ( 9 , 11 ) is mounted and oil lubrication is provided for the drive gear,
a synchronizing gear ( 25 , 27 ) coupling the rotors ( 9 , 11 ) to form a synchronous, counter-rotating, contact-free synchronous coupling
and a bearing arrangement arranged at the suction-side end of the rotor housing ( 3 ) for the shaft journals ( 55 , 57 ) of the rotors ( 9 , 11 ),
characterized in that the pressure-side shaft journal ( 23 , 29 ) of each of the two rotors ( 9 , 11 ) is supported by an axial play-free arrangement of angular contact ball bearings ( 91 , 93 ),
that the angular contact ball bearing ( 93 ) closest to the rotor ( 9 , 11 ) rests against an inner shoulder ( 97 ) of the rotor housing ( 3 ) and against a spacer ring ( 101 ) surrounding the shaft journal ( 29 ),
and that the axial length b of the spacer ring ( 101 ) is larger by an excess than the distance a of the inner shoulder ( 97 ) of the rotor housing from the end face ( 113 ) of the rotor housing ( 3) facing the rotor (9 ) such that the excess of the race determines the width of the gap between the end face of the rotor ( 9 , 11 ) and the inner end face ( 113 ) of the rotor housing. 2. Screw compressor according to claim 1, characterized in that the spacer ring ( 1 ) is a hardened race with a polished surface, with which a sealing arrangement ( 103 , 105 ) surrounding this race ( 101 ) for the shaft journal ( 23 ) or ( 29 ) interacts.