Screw compressor with multi-layered coating of the rotor screws

Abstract

The invention relates to a screw compressor comprising a compressor housing (11) having two rotor screws (1, 2) mounted axially parallel therein, which mesh with each other in a compression space (18), can be driven by a drive and are synchronized with each other in their rotational movement, wherein the rotor screws (1, 2) each have a single-part or multi-part base body (24) with two end faces (5a, 5b, 5c, 5d) and a profiled surface (12a, 12b) extending therebetween, and shaft ends (30) projecting beyond the end faces (5a, 5b, 5c, 5d), wherein at least the profiled surface (12a, 12b) is formed in multiple layers, comprising a first, inner layer (3) and a second, outer layer (4), wherein the first, inner layer (3) and the second, outer layer (4) both comprise or are formed from a thermoplastic synthetic material, wherein particles (25) or pores (32) supporting a running-in process are embedded in the second, outer layer (4) and the thermoplastic synthetic material defines a matrix for receiving the particles (25) or for forming the pores (32).

Claims

1. A screw compressor comprising a compressor housing having two rotor screws mounted axially parallel therein, which mesh with each other in a compression space, are driven by means of a drive and are synchronized with each other in their rotational movement, wherein the rotor screws each have a single-part or multi-part base body with two end faces and a profiled surface extending therebetween and shaft ends projecting beyond the end faces; wherein: at least the profiled surface is formed in a multilayer manner, comprising a first, inner layer and a second, outer layer, wherein the first, inner layer and the second, outer layer both comprise or are formed from a thermoplastic synthetic material, particles or pores supporting a running-in process are embedded in the second, outer layer and the thermoplastic synthetic material defines a matrix for receiving the particles or for forming the pores, respectively, and the screw compressor is an oil-free compressing, in particular dry compressing, screw compressor.

2. The screw compressor according to claim 1, wherein: the thermoplastic synthetic material for forming the first, inner layer and the second, outer layer is a semi-crystalline high-performance thermoplastic synthetic material.

3. The screw compressor according to claim 1, wherein: the thermoplastic synthetic material comprises a polyaryletherketone (PAEK) or at least substantially consists of a polyaryletherketone (PAEK) to form the first, inner layer and the second, outer layer.

4. The screw compressor according to claim 1, wherein: the thermoplastic synthetic material for forming the first, inner layer and the second, outer layer comprises polyetheretherketone (PEEK) or consists at least substantially of polyetheretherketone (PEEK).

5. The screw compressor according to claim 1, wherein: the first, inner layer is formed without particles or pores supporting a running-in process, but at least substantially homogeneously.

6. The screw compressor according to claim 1, wherein: the particles of the second, outer layer supporting a running-in operation comprise abrasive and/or lubricating particles.

7. The screw compressor according to claim 6, wherein: the particles comprise microspheres comprising aluminum oxide (Al2O3), silicon dioxide (SiO2) or of thermoplastic synthetic material.

8. The screw compressor according to claim 1, wherein: the particles comprise microspheres of glass comprising borosilicate glass, or are formed from glass comprising borosilicate glass.

9. The screw compressor according to claim 1, wherein: the particles of the second, outer layer, which support a running-in process, have a Shore hardness higher than that of the matrix defined by the thermoplastic synthetic material.

10. The screw compressor according to claim 1, wherein: the particles of the second, outer layer, which support a running-in process, have a Shore hardness lower than that of the matrix defined by the thermoplastic synthetic material.

11. The screw compressor according to claim 1, wherein: the first, inner layer is bonded to the second, outer layer by melting.

12. The screw compressor according to claim 1, wherein: the first, inner layer forms a substantially homogeneous coating and thus a corrosion protection layer.

13. The screw compressor according to claim 1, wherein: the second, outer layer defines a running-in layer which in the running-in process removes itself in regions and/or plastically deforms itself in regions, and thus adapts itself to the concrete operating conditions.

14. The screw compressor according to claim 1, wherein: the particles comprise graphite or are formed from graphite.

15. The screw compressor according to claim 1, wherein: the particles comprise: hexagonal boron nitride, carbon nanotubes (CNT), talc, polytetrafluoroethylene (PTFE), perfluoroalkoxy polymers (PFA), fluorinated ethylene propylene (FEP) and/or another fluoropolymer.

16. The screw compressor according to claim 1, wherein: said particles comprise: aluminum oxide (Al2O3), silicon carbide (SiC), silicon dioxide (SiO2), and/or glass, in particular borosilicate glass.

17. The screw compressor according to claim 1, wherein: layer thickness of the first, inner layer is 5 μm to 50 μm before running-in.

18. The screw compressor according to claim 1, wherein: the layer thickness of the second, outer layer is 10 μm to 120 μm before running-in.

19. The screw compressor according to claim 1, wherein: the base body of the rotor screw is formed from steel and/or cast iron.

20. The screw compressor according to claim 1, wherein: at least portions of the shaft ends are uncoated with a thermoplastic synthetic material.

21. The screw compressor according to claim 1, wherein: sections of said shaft ends are coated with the first, inner layer of thermoplastic synthetic material.

22. The screw compressor according to claim 1, wherein: in addition to the profiled surface of at least one rotor screw, one or both end faces are coated in multiple layers comprising a first, inner layer and a second, outer layer, wherein the first, inner layer and the second, outer layer both comprise or are formed from a thermoplastic synthetic material, wherein particles or pores supporting a running-in process are embedded in the second, outer layer and the thermoplastic synthetic material defines a matrix for receiving the particles or for forming the pores.

23. The screw compressor according to claim 1, wherein: inner walls, such as a jacket surface of a rotor bore, pressure-side and/or suction-side housing end faces of the compression space are coated at least with a first layer, preferably also with a second layer, wherein the first layer and the second layer both comprise or are formed from a thermoplastic synthetic material, and wherein particles or pores supporting a running-in process are embedded in the second, outer layer and the thermoplastic synthetic material defines a matrix for receiving the particles or for forming the pores.

24. The rotor screw for use in a screw compressor according claim 1, wherein the rotor screw comprises a one-piece or multi-piece base body with two end faces and a profiled surface extending therebetween as well as shaft ends projecting beyond the end faces, wherein at least the profiled surface is formed in a multilayer manner comprising a first, inner layer and a second, outer layer, wherein the first, inner layer and the second, outer layer both comprise or are formed from a thermoplastic synthetic material, wherein the particles or pores supporting a running-in process are embedded in the second, outer layer, and the thermoplastic synthetic material defines a matrix for receiving the particles or for forming the pores.

25. A method for applying a multilayer coating to a metallic surface to be coated of a rotor screw or a compression space of a screw compressor, comprising: pretreating the metallic surface to be coated, applying a first, inner layer which comprises a thermoplastic synthetic material or is formed therefrom, to the metallic surface to be coated or on an underlayer, which can be formed in particular as a pretreatment layer, and applying a second, outer layer to the first, inner layer, wherein the second, outer layer also comprises or is formed from a thermoplastic synthetic material, and wherein particles or pores supporting a running-in process are embedded in the second, outer layer and the thermoplastic synthetic material defines a matrix for receiving the particles or for forming the pores, wherein: the screw compressor is an oil-free compressing, in particular dry compressing, screw compressor comprising a compressor housing having two rotor screws mounted axially parallel therein, which mesh with each other in the compression space, are driven by a drive and are synchronized with each other in their rotational movement, wherein the rotor screws each have a single-part or multipart base body with two end faces and a profiled surface extending therebetween and shaft ends projecting beyond the end faces.

26. A method according to claim 25, wherein: the first, inner layer and/or the second, outer layer are applied as a wet paint or as a powder paint.

27. A method according to claim 25, wherein: the first, inner layer and the second, outer layer are baked in such a way that the thermoplastic synthetic material melts.

28. A method according to claim 25, wherein: pretreating the metallic surface to be coated comprises degreasing and preferably further conditioning of the metallic surface, wherein conditioning of the metallic surface comprises roughening the surface, blasting or etching, or applying a conversion layer by phosphating or applying a nanoceramic.

29. A screw compressor comprising a compressor housing having two rotor screws mounted axially parallel therein, which mesh with each other in a compression space, are driven by means of a drive and are synchronized with each other in their rotational movement, wherein the rotor screws each have a single-part or multi-part base body with two end faces and a profiled surface extending therebetween and shaft ends projecting beyond the end faces; wherein: at least the profiled surface is formed in a multilayer manner, comprising a first, inner layer and a second, outer layer, wherein the first, inner layer and the second, outer layer both comprise or are formed from a thermoplastic synthetic material, wherein particles or pores supporting a running-in process are embedded in the second, outer layer and the thermoplastic synthetic material defines a matrix for receiving the particles or for forming the pores, respectively, wherein: the particles are present in microencapsulated form, wherein at least a first substance is surrounded by a second substance as a shell material.

Description

(1) The invention is explained in more detail below, also with regard to further features and advantages, on the basis of the description of embodiment examples and with reference to the enclosed drawings, wherein:

(2) FIG. 1 shows a transverse section of a pair of rotor screws according to the invention;

(3) FIG. 2 shows two interlocked rotor screws in perspective view;

(4) FIG. 3 shows an embodiment example of a rotor screw according to the invention, which here is specifically designed as a secondary rotor;

(5) FIG. 4 shows an embodiment example of a rotor screw according to the invention, which here is specifically designed as a main rotor;

(6) FIG. 5 shows a schematic cross-sectional view of a screw compressor;

(7) FIG. 6 shows an exploded view of a screw compressor;

(8) FIG. 7 shows a schematic embodiment of the multilayer coating of a rotor screw before running in;

(9) FIG. 8 shows a schematic embodiment of the multilayer coating of a rotor screw after running in;

(10) FIG. 9 schematically shows a merely single-layer coating of a section of a rotor screw;

(11) FIG. 10 shows an alternative embodiment of a multilayer coating of a rotor screw before running in;

(12) FIG. 11 shows the embodiment of the multilayer coating of a rotor screw according to FIG. 10 after running in;

(13) FIG. 12 shows a sequence of a preferred embodiment example of the coating process in accordance with the invention.

(14) FIG. 1 shows a transverse section of a pair of rotor screws according to the invention, comprising a rotor screw 1 designed as a secondary rotor and a rotor screw 2 designed as a main rotor. It is shown only purely schematically that a profiled surface 12a, 12b of rotor screw 1, 2 is coated in each case with first, inner layer 3 and second, outer layer 4. The rotor screws 1, 2 mesh with each other, i.e. they mesh with their teeth. The pitch circles already mentioned are marked with the reference symbol 22 for the rotor screw 1 designed as a secondary rotor and 21 for the rotor screw 2 designed as a main rotor.

(15) FIG. 2 shows the meshed rotor screws 1, 2 in perspective view. Both rotor screws 1, 2 with the already mentioned profiled surfaces 12a, 12b engage into each other or are meshed or screwed with each other. The profiled surfaces 12a, 12b are delimited perpendicularly to the respective rotor screw rotary axis by end faces 5a, 5b, 5c, 5d at the ends, wherein the end face 5a designates a pressure-side end face of the rotor screw 1 designed as a secondary rotor and the end face 5c designates a suction-side end face. In the case of the rotor screw 2 designed as the main rotor, the pressure-side end face is marked with the reference symbol 5b and the suction-side end face with the reference symbol 5d.

(16) Protruding axially over the end faces 5a, 5b, 5c, 5d are protruding shaft ends 30 which each form a shaft 16 in pairs for a rotor screw 1, 2. At the shaft ends 30 a rotor-side seal seat 7b for an air seal, a rotor-side seal seat 7a for an oil seal and a rotor-side bearing seat 9a, 9b are formed. The rotor-side seal seat 7b is designed for an air seal adjacent to the end faces 5a, 5b, 5c, 5d, whereas the rotor-side bearing seat 9a, 9b is provided more towards the distal end of the shaft end 30. Between the rotor-side bearing seat 9a, 9b and the rotor-side seal seat for an air seal 7b, the already mentioned rotor-side seal seat 7a for an oil seal is provided.

(17) FIG. 3 shows an embodiment example of a rotor screw 1 designed as a secondary rotor, as already described in FIG. 2. Here too, the profiled surface 12a is coated with a first, inner layer 3 and a second, outer layer 4. The two end faces 5a, 5c are also coated with a first, inner layer 3 and a second, outer layer 4. The shaft ends, on the other hand, are only coated with a first, inner layer 3 between the end faces 5a, 5c and the bearing seats 9a (leaving out a second, outer layer 4), wherein the bearing seats 9a, however, are free, i.e. without a coating corresponding to the first, inner layer 3, i.e. without a coating with a thermoplastic synthetic material.

(18) FIG. 4 shows an embodiment example of a rotor screw 2 designed as the main rotor, as already described by reference to FIG. 2. Here too, the profiled surface 12b is coated with a first, inner layer 3 and a second, outer layer 4. The two end faces 5b, 5d are also coated with a first, inner layer 3 and a second, outer layer 4. The shaft ends, on the other hand, are only coated with a first, inner layer 3 between the end faces 5b, 5d and the bearing seats 9b (leaving out a second, outer layer 4), wherein the bearing seats 9a, however, are free, i.e. without a coating corresponding to the first, inner layer 3, i.e. without a coating with a thermoplastic synthetic material.

(19) FIG. 5 shows a schematic cross-sectional view of a screw compressor 20 with a compressor housing 11 and, mounted therein, two rotor screws 1, 2 which are meshed in pairs, namely a rotor screw 2 which is designed as a main rotor and a rotor screw 1 which is designed as a secondary rotor 1. The rotor screws 1, 2 are each mounted rotatably via suitable bearings 15 in a compression space 18 defined by a rotor bore 19 in the compressor housing 11 in a housing-side bearing seat 10. Seals 14b and 14c, which are each accommodated in a sealing seat 8a on the housing side for the oil seal and in a sealing seat 8b on the housing side for the air seal, prevent on the one hand the escape of compressed air from the compression space 18 and on the other hand the penetration of oil into the compression space 18. The compression space 18 in the compressor housing 11 is laterally limited by a rotor bore 18, which has two partial bores adapted to the diameters of the rotor screws 1, 2. At the end face, the compression space is limited by a pressure-side housing end face 6a and a suction-side housing end face 6b. Preferably, the pressure-side housing end face 6a, the suction-side housing end face 6b and the rotor bore 18 are also provided with the multilayer coating in accordance with the invention comprising a first, inner layer 3 and a second, outer layer 4.

(20) Via a synchronous gear 13 the rotor screws 1, 2 are fixed in their rotary position against each other and their profiled surfaces 12a, 12b, especially their respective rotor flanks are kept at a distance. A drive power can be applied to the shaft 16 of the rotor screw 2 designed as the main rotor, for example by means of a motor (not shown) via a coupling (not shown). A suction area 23 of the screw compressor can be seen at the suction-side end of the rotor screws 1, 2 which are screwed together in pairs.

(21) FIG. 6 shows an exploded view of an embodiment of a screw compressor 20. The compressor housing 11 limits the compression space 18. Ambient air is sucked in via a suction port 27 and enters the suction area 23 of the screw compressor. After compression via the rotor screws 1, 2, the compressed air is ejected from the compressor housing 11 via a pressure port 28.

(22) FIG. 7 illustrates the multilayer coating on the profiled surface 12a of rotor screw 1 along line A-A in FIG. 3. The first, inner layer 3 is first applied to a base body 24 of the rotor screw 1. On the first, inner layer 3—completely covering it—the second, outer layer 4 is applied. According to the invention, the second, outer layer 4 comprises particles 25 that support a running-in process, for example thin-walled hollow-glass microspheres. Alternatively or additionally, pores 32 can also be incorporated, which supports the plastic compressibility of the second, outer layer.

(23) FIG. 8 shows the multilayer coating along line A-A on a rotor screw 1 according to FIG. 3 after the running-in process.

(24) FIG. 9 shows an only integral coating on the shaft end 30 of the rotor screw 1, which is provided in the area of the rotor-side seal seat 7a for the oil seal and the rotor-side seal seat 7b for the air seal covering both seal seats 7a, 7b. In concrete terms, a section along line B-B is shown in FIG. 3. The first, inner layer here is arranged to cover the base body 24 and thus offers good and reliable corrosion protection.

(25) FIG. 10 shows an alternative multilayer coating for a profiled surface 12a, 12b on a rotor screw 1, 2. Instead of the particles 25 described in FIG. 8, pores 32 are embedded in the second, outer layer, which were worked in, for example, by a foaming process before or during the application of the second, outer layer, for example in the wet paint process.

(26) FIG. 11 shows the multilayer coating according to FIG. 10 after a running-in process. It can be seen that some areas of the layer have been removed or compressed. Also some of the pores 32 are removed with parts of the layer or compressed due to the absorbed counter pressure so that a plastic deformation of the second, outer layer 4 as running-in layer was achieved.

(27) FIG. 12 schematically shows a flow chart for a possible design of the coating process. In a step sequence S01 to S04, the metallic surface to be coated is pretreated, for example the surface of a rotor screw to be coated. Step S01 involves degreasing the surface by burning it off at high temperature (pyrolysis). In the subsequent step S02, the surface is blasted, in particular sandblasted. After blasting, a step S03 follows, in which the surface is cleaned again chemically, for example using acetone. In step S04, a nanoceramic coating is then applied to the embodiment example described here.

(28) This is followed by application of the first, inner layer 3, wherein the first, inner layer 3 is applied as a wet paint in the present example. However, alternative processes are also conceivable, for example dry application as powder coating. The wet paint for the first, inner layer is prepared beforehand, wherein the thermoplastic synthetic material in the form of PEEK is mixed in powder form in water with dispersing agent. A suspension is formed, which is applied to the pre-treated surface in step S10. In a subsequent step S11, the applied wet paint is dried or deaerated. In step S11, the rotor screw coated with the wet paint for the first coat is heated to approx. 120° C. for evaporation of the water. In one step S12, which can optionally also be omitted, the first layer is baked on. Baking takes place at temperatures of approx. 360° C. to 420° C., for example in a convection oven or inductively, until the PEEK has melted and a homogeneous layer has formed.

(29) The second layer is applied in steps S20, S21, S22 which are analogous to steps S10, S11, S12. A wet lacquer is prepared again for this purpose, wherein appropriately—but not necessarily—the same thermoplastic synthetic material is used as for the application of the first layer—comprising or having PEEK as the thermoplastic synthetic material. For this purpose, the PEEK in powder form is mixed with the particles supporting the running-in process, for example the thin-walled glass microspheres, in particular made of borosilicate glass, together with water and dispersing agent. The second, outer layer 4 is applied in step S20 directly onto the first, inner layer 3, which has already been baked in the present example. However, it is also possible to leave step S12, i.e. the baking of the first layer, aside and baking the first, inner layer 3 and the second, outer layer 4 together. The application of the second, outer layer in step S20 is followed by a step of drying or ventilating of the second, outer layer. For this purpose, the rotor screw to be coated is heated up again to approx. 120° C. in step S21 or maintained at this temperature. After sufficient drying of the second, outer layer, the second, outer layer is baked in step S22 at temperatures of approx. 360° C. to 420° C., for example in a convection oven or in an inductive manner.

(30) Optionally, a step S23 (not shown) may follow, which should preferably be avoided. In a step S23, the second, outer layer 4 could be regrinded in order to achieve the desired dimensioning by regrinding when the second, outer layer with oversize is formed. As already mentioned, however, it is preferred to achieve the desired dimensioning of the layer structure with the methods shown by reference to FIG. 12.

LIST OF REFERENCE SYMBOLS

(31) 1, 2 Rotor screw 3 First, inner layer 4 Second, outer layer 5a, 5b, 5c, 5d End faces 6a Pressure-side housing end face 6b Suction-side housing end face 7a Rotor-side seal seat for an air seal 7b Rotor-side seal seat for an oil seal 8a Housing-side seal seat for an oil seal 8b Housing-side seal seat for an air seal 9a, 9b Rotor-side bearing seat 10 Housing-side bearing seat 11 Compressor housing 12a, 12b Profile area 13 Synchronous gear 14b Seal 14c Seal 15 Bearings 16 Shaft 18 Compression space 19 Rotor bore 20 Screw compressor 21 Pitch circle (main rotor) 22 Pitch circle (secondary rotor) 23 Suction area 24 Base body 25 Particles 27 Suction port 28 Pressure port 30 Protruding shaft ends 32 Pores