Sealing device on a shaft journal of a dry-running helical rotary compressor

A sealing arrangement on a rotor shaft peg of a dry-running rotation screw compressor for establishing a seal between the rotor (1) and the oil-lubricating bearing (7) of the shaft peg (3) has a labyrinth slit seal (11), located closer to the rotor, and a lip seal ring (13), located closer to the bearing, and in between an annular space (27) with ventilation opening (29) towards the bottom. The shaft peg bears a bearing race (25) made of a hardened material, which acts in cooperation with the lip sealing ring (13), and which can also extend above the area of the labyrinth slit seal (11).

In dry-running rotation screw compressors, no oil for lubrication, cooling
 and sealing is introduced between the rotors into the sealing space. The
 ribs of the main runner and the nuts of the secondary runner form a "dry"
 engagement which nevertheless achieves a seal between them. Such screw
 compressors are particularly suited because they allow the absence of oil
 in the seal space in applications in pneumatic conveyor installations, for
 example, for filling and emptying silos, tanks, tanker vehicles and
 similar instruments with bulk goods. In particular, in the pneumatic
 conveyance of sensitive goods such as foods or chemicals it is important
 that the conveyance air stream is free, to a high extent, of oil
 particles.
 In the case of dry-running screw rotors, an appropriate seal of the shaft
 peg must be used to prevent oil from the oil-lubricated bearings of the
 shaft pegs to reach the sealing space as a result of leakage along the
 shaft pegs. It is already known from GB A 1189856, to arrange on the shaft
 peg of rotation screw compressor, next to each other, a conventional
 sealing ring and an oil sealing ring, which are separated from each other
 by an annular space which is connected to the external air. However,
 because of the high level of abrasion, ordinary sealing rings are unsuited
 for establishing seals of rapidly rotating shaft pegs, which can reach
 circumferential speeds of 55-150 m/sec. On the other hand, it is known to
 use two adjacent, contact-free, labyrinth seals to seal the shaft peg of a
 dry-running rotation screw compressor; of the labyrinth seals, the one
 located closest to the oil-lubricated bearing is in the form of an oil
 return threading. However, it has been shown that such contact-free
 labyrinth seals cannot always reliably prevent the leakage of oil along
 the shaft peg to the seal space, particularly if there is high pressure
 differential on the suction-side of the seal. From DE A 24 41 520, a shaft
 seal is known for a screw rotor seal with water injection, which presents
 several sealing hoops surrounding the rotor pegs, and located between the
 annular chambers, of which one is applied to the ring chamber with the gas
 densified by the compressor, as a barrier gas, and the other ring chamber
 is a drainage chamber for bearing oil drainage. The sealing hoops are
 labyrinth seal hoops, of which one also can be a contact seal. This shaft
 seal is a dynamic seal, which uses pressurized barrier gas, which must be
 shunted from the conveyor gas stream of the compressor, and which thus
 entails an output loss.
 It is an object of the invention to provide a sealing arrangement which
 works without barrier gas, which presents a particularly high sealing
 effect and, nevertheless, good abrasion resistance, for a shaft peg of a
 dry-running rotation screw compressor.
 For achieving the object, the invention provides a sealing arrangement on a
 rotor shaft peg of a dry-running rotary screw compressor for establishing
 a seal between the rotor and an oil-lubricated bearing of the shaft peg.
 The sealing arrangement has a labyrinth gap seal closer to the rotor and a
 lip seal ring closer to the bearing and in between an annular space with a
 ventilation opening towards the atmosphere. The shaft peg carries a
 bearing ring made of hardened material which cooperates with the lip
 sealing ring.

FIG. 1 is a portion of an axial section through a screw compressor, and it
 shows diagrammatically one of the rotors, for example, the main runner
 (rib rotor) 1, whose shaft peg 3 is located in a bearing in housing 5,
 namely the roller bearing 7. The roller bearing 7 is oil lubricated,
 preferably by means of a lubrication installation (not shown) which
 produces an oil mist.
 A housing ring 9, which is rigidly connected to the housing, is inserted in
 the housing 5. In the section of the housing ring 1 located closer to the
 rotor 1, a labyrinth slit seal 11 in the form of several adjacent ring
 ribs is adapted to its internal circumferential surface. This labyrinth
 slit seal acts contact-free together with the cylindrical circumferential
 surface of the section 3a of the shaft peg 3 to achieve the gas seal.
 A lip seal ring 13 is inserted in the housing ring 9 at the section of the
 housing ring 9 located closer to the roller bearing 7; it is represented
 in greater detail in FIG. 2.
 The lip seal ring 13 represented in FIG. 2 consists of an external holder
 ring 15 and an internal holder ring 17, between which two lip rings 19, 21
 and a flat seal 23 consisting of flexible elastomer materials are inserted
 with tension. The sealing lips 19a, 21a of the two lip rings 19, 21 have
 different lengths. The sealing lip 19a of the lip ring 19, which is bent
 into the direction of the bearing 7, is longer than the sealing lip 21a of
 the sealing ring 21, which is bent in the direction towards the rotor.
 In the area of the lip seal ring 13, a bearing race 25 is attached on a
 section 3b of the shaft peg 3; preferably it is attached by shrinkage. The
 bearing race 25, which can be, for example, a conventional commercial
 bearing race for a roller bearing, is made of steel with specially
 hardened circumferential surface, to which the lips 19a and 21a of the lip
 seal ring 13 are applied. The external diameter of the bearing race 25 is
 smaller than the external diameter of section 3a of the shaft peg which
 works in cooperation with the labyrinth slit seal 11.
 The hardened and extremely precisely machined, for example, polished,
 external surface of the bearing race 25 produces a particularly
 abrasion-reducing application surface for the sealing lips of the lip
 sealing ring 13. The lip rings 19, 21 are preferably made of an elastomer
 material based on fluorocarbon polymers.
 In the housing ring 9, between the labyrinth slit seal 11 and the lip seal
 ring 13, a circumferential ring space 27 is formed, which is connected,
 through an opening 29 of the housing ring 9, with a space 31 of the
 housing 5, which is open to the atmosphere.
 Between the bearing 7 and the lip seal ring 13, on the shaft peg 3 is
 attached a ring 33 with an external flange, which forms a spray shield,
 which prevents the direct entry of oil droplets sprayed into the bearing 7
 toward the lip seal ring 13.
 During the operation of the screw compressor, the labyrinth slit seal 11
 works in the conventional manner as a gas seal, whereas the lip seal ring
 13 functions as an oil seal with particularly high sealing effect, where
 leakage from oil from the bearing 7 past the lip seal ring 13 in the
 direction of the labyrinth slit seal 11 is prevented with high
 reliability. The step located in the area of the ring space 27 of the
 housing ring 9 between the external surface of the bearing race 25 and the
 external surface of the section 3a of the shaft peg prevents the creep of
 oil along the surface. Any volatile components of the oil, which reach the
 area of the ring space 27, escape through the ventilation opening 29 into
 the external air.
 In the embodiment variant represented in FIG. 3, the shaft peg 3 of the
 dry-running rotor 1 of a screw compressor is placed in a bearing in the
 housing 5 by means of oil- or fat-lubricated roller bearings 7 in the
 housing 5. A second rotor, which engages in a known manner with rotor 1,
 is indicated by the reference numeral 2.
 As in the embodiment variant according to FIG. 1, in the housing 5, a lip
 seal ring 13 adjacent to the roller bearing 7 and a labyrinth seal ring 11
 adjacent to the rotor 1 are inserted. In between, there is a ring space
 27, which is in connection, through a ventilation opening 29 with the
 ventilation duct 31 of the housing, and through it with the external air.
 On the shaft peg 3, bearing race 25 is attached, for example, by shrinkage,
 which has an axial length such that it works in cooperation, not only with
 the lip seal ring 13, but also extends over the area of the labyrinth seal
 ring 11. The specially hardened and polished bearing race 25 in the
 preceding embodiment variant normally does not come in contact with the
 lip seal ring 11. However, should, a contact nevertheless be established
 between the lip seal ring 11 and the bearing race 25 as a result of an
 operational disturbance, then the shaft peg 3 is not damaged as a result,
 only the bearing race 25 is damaged. Thus, by simply replacing the bearing
 race 25, the correct sealing state can be reestablished. In addition, the
 extended bearing race according to FIG. 3 also has the advantage that it
 can be used as a spacer between the front surface 1a of the rotor 1 and
 the roller bearings 7. It is only then that it becomes possible, by an
 exact measurement of the axial length of the bearing race 25, to achieve
 simultaneously a very precise setting of the front-side slit between the
 front surface 1a of the rotor 1 and the corresponding front surface of the
 housing 5.