Screw rotor and method for manufacturing the same

Abstract

A screw rotor (1) made of polymer, the screw rotor (1) consisting of a shaft (2) and a rotor body (3) thereon, the polymer of the shaft (2) being reinforced with fibers (4), the shaft (2) featuring elements (5a, 5b) that engage with the rotor body (3) or corresponding elements (5c) on the rotor body (3), the elements (5a, 5b, 5c) being adapted to prevent axial and / or rotational movement of the shaft (2) relative to the rotor body (3).

Description

[Technical field]

[0001] The present invention relates to a screw rotor.

[0002] More specifically, the screw rotor according to the invention is directed to fluid injection compressors, expanders, and vacuum pumps. [Background technology]

[0003] Such screw rotors are conventionally manufactured from cast iron or steel and are either cast into a rough helical shape or forged into a rough cylindrical shape, which is then finished by coarse and fine grinding, filing, milling, and other cutting operations of the shaft and body of the screw rotor (with its helical profile) to obtain its final finished helical shape. Summary of the Invention [Problem to be solved by the invention]

[0004] This finishing is necessary because the casting process cannot achieve the very close tolerance features necessary to enable the final machine to function properly.

[0005] Even if such conventional screw rotors were to function properly, finishing by grinding, filing, milling, and other such processes is very laborious and time consuming.

[0006] Moreover, all this increases costs.

[0007] Another drawback is that a lot of material is machined away during the finishing process, resulting in lost or wasted raw material.

[0008] Another drawback is that such conventional screw rotors are heavy since they use cast iron or steel.

[0009] The object of the present invention is to provide a solution to at least one of the above mentioned and other disadvantages. [Means for solving the problem]

[0010] The subject of the present invention is a screw rotor made of a polymer, which is composed of a shaft and a rotor body thereon, the polymer of the shaft being reinforced with fibers, the shaft being characterized by elements that engage with the rotor body or corresponding elements on the rotor body, the elements being adapted to prevent the shaft from moving axially and / or rotationally relative to the rotor body.

[0011] By using polymers, the screw rotors are not only lighter than conventional metallic screw rotors, but also more corrosion resistant and easier to fabricate in complex shapes.

[0012] Such a screw rotor can be made, for example, by an injection molding process, which makes it possible to produce a rough helix that is already close to the final finished helix, and which would require limited or no finishing by cutting operations of the rough helix to bring it within the required tolerances.

[0013] Moreover, machining of the composite screw rotor is much simpler and easier than processing the cast iron or steel screw rotors.

[0014] This means that the finishing process requires much less work and time, resulting in significant cost savings.

[0015] Furthermore, since the starting point is already a raw spiral form that is close to the final form, less material is lost.

[0016] Although the present invention only requires the use of fiber reinforced polymer for the shaft, it does not preclude the rotor body from being manufactured from fiber reinforced polymer.

[0017] The element of an axis is the deviation of the axis into or from the surface of the axis, which means the deviation towards or away from the centerline of the axis.

[0018] The elements of the shaft and corresponding or matching elements on or in the rotor body provide a mechanical obstruction between the shaft and the rotor body so that axial forces and torques can be transferred from the shaft to the rotor body and vice versa. The elements may be located on the shaft itself, but the elements of the shaft may also be formed by intermediate bodies or keys located in designated recesses on the shaft.

[0019] Preferably, the fibres within the shaft extend primarily in the axial direction, which provides the necessary stiffness and strength to the shaft.

[0020] In the screw rotors of screw compressors, for example, it is known that very strong axial and gas forces act on the screw rotor, and for this reason it is very important that the shaft has the necessary stiffness.

[0021] The rotor body may be constructed of two or more concentric layers, with the inner layer featuring elements that engage with subsequent layers and prevent axial and / or rotational movement of one layer relative to the subsequent layer.

[0022] Such rotor bodies are used especially for manufacturing large screw rotors by injection molding, the maximum thickness of each layer is 8 millimeters.

[0023] By injection molding the rotor body in multiple steps or stages, the amount of material added at each step or stage can be limited, which makes it easier to monitor the injection molding process and the subsequent cooling process. This helps to optimize the final mechanical properties of the screw rotor. The elements are similar to the previously mentioned elements of the shaft and have the same function.

[0024] The subject of the invention is also a method for manufacturing a screw rotor consisting of a shaft and a rotor body, characterized in that the screw rotor is made of a polymer, said method comprising the steps of: A) preparing an axle; B) injection molding the rotor body using a designated mold, using the stem as an insert into the mold; Includes.

[0025] By carrying out the process in at least two steps, the injection molding process of step B becomes much easier compared to an injection molding process in which the screw rotor is injection molded in a single step, and it is easier to monitor in the multi-step process according to the invention, especially with regard to material, dimensional shrinkage and reduction in mechanical properties.

[0026] Another advantage is that by using the shaft as an insert in the rotor body mold, the rotor body is cast on or around the shaft, so that the casting of the rotor body creates a thermal bond between the shaft and the rotor body.

[0027] This ensures that the shaft cannot move relative to the rotor body, because when injection molding the rotor body, the surface of the shaft can be reheated due to contact with the hot molten fiber-reinforced polymer injected into the shaft, thus causing a thermal bond with the rotor body material cast around the shaft.

[0028] Given the nature of the invention, and without these descriptions having any limiting nature, in the following some examples of preferred variants and methods for manufacturing a screw rotor according to the invention will be described with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0029] [Figure 1]FIG. 2 shows a schematic perspective view of a possible embodiment of a screw rotor according to the invention; [Diagram 2] FIG. 2 is an explanatory diagram showing the shaft of the screw rotor in FIG. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. [Figure 4] FIG. 2 is a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] FIG. 3 is a schematic diagram showing a modification of the embodiment of FIG. 2. [Figure 6] FIG. 3 is a schematic diagram showing a modification of the embodiment of FIG. 2. [Figure 7] FIG. 3 is a schematic diagram showing a modification of the embodiment of FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The screw rotor 1 according to the invention, shown diagrammatically in FIG. 1, consists of a shaft 2 and a rotor body 3 on the shaft 2 .

[0031] The screw rotor 1 can be used in a fluid injection compressor, an expander, or a vacuum pump.

[0032] In the embodiment shown, the rotor body 3 is cylindrical. However, it is not excluded that the rotor body 3 is conical. The advantage of using a conical rotor is that the forces are better distributed, which can increase the compression.

[0033] In FIG. 2, axis 2 is shown alone.

[0034] According to the invention, the screw rotor 1 is made of a polymer.

[0035] In this case, in terms of the present invention, at least the shaft 2 is made of a polymer reinforced with fibers 4, and although the rotor body 3 can be made of a polymer without fibers 4, in the embodiment shown in this specification and described below, the rotor body 3 is also made of a polymer reinforced with fibers 4.

[0036] The polymer may be, for example, a polyamide or a polyimide, although the invention is not limited thereto, and may be, for example, a polyetheretherketone (PEEK).

[0037] In some cases, the polymer can be a thermoset polymer, such as an epoxy, vinyl ester, or unsaturated polyester.

[0038] The fibres 4 preferably, but not necessarily, comprise carbon or glass fibres. The fibres may also comprise organic polymers, such as, for example, aramid fibres. Carbon nanotubes are also possible.

[0039] In a possible embodiment, the polymer reinforced with the fibers 4 is a so-called self-reinforced polymer, where the fibers are made of the same polymer as the mold.

[0040] Preferably, the self-reinforced polymer is a polymer polyamide, polyimide or PEEK reinforced with 10 to 60 weight percent of fibers 4. Preferably, the weight percent of fibers is between 25 and 45 percent.

[0041] It is not excluded that the shaft 2 is made of a different polymer than the rotor body 3, which may be made of a polymer reinforced or not reinforced with fibres 4.

[0042] Thus, for example, the polymer reinforced with the fibres 4 of the shaft 2 may have the same or a higher softening temperature than the polymer reinforced with the fibres 4 of the rotor body 3 .

[0043] The difference in softening temperatures of the different layers preferably varies between 0 and 20 degrees Celsius.

[0044] This leads to advantages in particular with regard to the production or manufacture of the screw rotor 1, as will be demonstrated below.

[0045] In this case, although this is not essential to the invention, the fibres 4 in the shaft 2 extend mainly in an axial direction X-X'.

[0046] This is shown diagrammatically in cross section in FIG.

[0047] Due to this orientation of the fibres 4, the shaft 2 has the necessary stiffness. It is well known that during machine operation, the shaft 2 is exposed to strong axial and gas forces at the location where the screw rotor 1 is mounted.

[0048] As can be seen from figure 3, the shaft 2 is a solid shaft 2. It is not excluded that the shaft 2 is hollow, where hollow means that a longitudinal cavity runs through the shaft 2. This prevents so-called flow problems during the manufacture of the shaft 2.

[0049] In this case, although not required, the fibres 4 of the rotor body 3 are randomly or randomly oriented.

[0050] According to the invention, as is evident from figures 2, 3 and 4, the shaft 2 is characterised by elements 5a, 5b.

[0051] Some of these elements 5a can engage with the rotor body 3 and some of these elements 5b can engage with corresponding elements 5c in the rotor body 3, all of which are designed such that the elements 5a, 5b, 5c prevent axial and / or rotational movement of the shaft 2 relative to the rotor body 3.

[0052] This will be explained with the aid of drawings.

[0053] As can be seen from Figures 2 and 3, the shaft 2 features two elements 5a in the form of ring-shaped projections, which projections on the shaft 2 in the axial direction X-X' are periodically symmetrical and coaxial with the centre line XX of the shaft 2.

[0054] Cyclically symmetric means that the sections or segments are repeated rotationally about a centerline.

[0055] These elements 5a relate in this case to ring-shaped projections, but these elements 5a can also include projections, grooves or rings of different shapes.

[0056] These elements 5a are capable of engaging with the rotor body 3 itself, as shown in FIG.

[0057] Such an element 5a is capable of transmitting axial forces from the shaft 2 to the rotor body 3 and vice versa.

[0058] In effect, these elements 5a constitute a stop for the rotor body 3 on the shaft 2 and vice versa, so that when an axial force is applied to the rotor body 3, this force can be transmitted to the shaft 2 via this stop.

[0059] It is not excluded to arrange these elements 5a at another location, further away from the end 6 of the shaft 2. In this case, these elements 5a do not engage with the rotor body 3 itself, but with corresponding elements 5c of the rotor body 3.

[0060] Furthermore, the shaft 2 features a number of elements 5 b which can engage with corresponding elements 5 c of the rotor body 3 .

[0061] In this case, these elements 5b are associated with projections along the axial direction XX' of the shaft 2, which gives the shaft 2 a hexagonal cross section.

[0062] As can be seen from a comparison of figures 1 and 2, these elements 5b are located on the axis 2 on which the rotor body 3 is disposed.

[0063] As can be seen in FIG. 4, the rotor body 3 features a corresponding element 5c which engages with a corresponding element 5b of the shaft 2.

[0064] By means of such elements 5b, 5c, torque can be transmitted from the shaft 2 to the rotor body 3. This is particularly suitable for driving the screw rotor 1 via the shaft 2 by means of a motor.

[0065] Instead of protrusions extending in the axial direction XX' grooves, rings etc. can likewise be used as elements 5b, 5c.

[0066] As can be seen from figures 1 and 2, in this case the shaft 2 features a coupling piece 8 on its surface 7, which features a thread 9 inside which a bolt can be placed.

[0067] By means of this bolt the shaft 2 can be connected for example to the drive shaft of a motor, or the like.

[0068] In the embodiment shown, the screw rotor 1 is composed of an axis 2 with a rotor body 3, although it is not excluded that the rotor body 3 itself is composed of two or more concentric layers, in which case the inner layer features elements 5b, 5c that engage with the subsequent layer and that prevent one layer from moving axially and / or rotationally relative to the subsequent layer.

[0069] In other words, the principle is fundamentally very similar to that of the shaft 2 and rotor body 3 described above.

[0070] In the case of large screw rotors 1, this is particularly advantageous during the manufacturing process as will be explained below.

[0071] The screw rotor of Figures 1 to 4 can be manufactured according to the method according to the invention.

[0072] The method for producing a screw rotor 1 made of polymer reinforced with fibers 4 by injection molding basically involves: A) preparing an axle; B) injection molding the rotor body 3 using a designated mold, using said shaft 2 as an insert into the mold; This involves two steps:

[0073] Preferably, but not necessarily, the above step A includes injection molding the shaft 2 of the screw rotor 1 using a designated mold.

[0074] However, this is not essential to the invention. The shaft 2 can also be extruded, for example.

[0075] In step A, a mould can now be used with the elements 5a, 5b to injection mould the shaft 2, such that said elements 5a, 5b are formed on the shaft 2.

[0076] The polymer reinforced with fibres 4 can be injected into the mould in an axial direction X-X', with the aim of ensuring that the fibres 4 extend in the axis 2 in that direction.

[0077] Then, by using the shaft 2 as an insert in the mould of the rotor body 3, the corresponding element 5c will be efficiently and automatically formed in the rotor body 3.

[0078] By using a fiber 4 reinforced polymer for the shaft 2 that is different from the fiber 4 reinforced polymer used for the rotor body 3, the fiber 4 reinforced polymer used for the shaft 2 has the same or a higher softening temperature as the polymer used for the rotor body 3, and the shaft 2 will not melt or soften as a whole when the rotor body 3 is cast around it. In this way, the mechanical properties of the shaft 2 remain intact and the fibers 4 of the shaft 2 will not lose their orientation if the polymer of the shaft 2 softens somewhat.

[0079] With regard to step B, it is not excluded to carry out the injection molding of the rotor body 3 in two or more steps, in which, in each step, more material is added to the rotor body 3 by using a succession of base materials, and the rotor body parts produced in the previous steps are used as inserts in the subsequent molds.

[0080] Thus, the rotor body 3 itself can be made of two or more concentric layers, and the use of a base metal with the element 5c allows the element 5c to be provided on the inner layer, which engages with the subsequent layer cast around the inner layer.

[0081] This approach is particularly advantageous for large screw rotors 1 since the material added at each step can be more limited, and cooling can be monitored so that mechanical tensions do not develop or are significantly reduced.

[0082] If the rotor body 3 is conical, this has the advantage that the rotor body 3 can be demoulded, i.e. removed from the mould very easily.

[0083] To insert the aforementioned connecting parts 8 onto the surface 7 of the shaft 2 , the connecting parts 8 are placed in the mould of the shaft 2 at the location of the respective surface 7 of the shaft 2 .

[0084] The connecting piece 8 can therefore be integrated with the shaft 2 during the casting process.

[0085] Alternatively, after step B, said connecting part 8 can be placed in a designated cavity on the surface 7 of the shaft 2 by self-tapping.

[0086] It will be clear that in the embodiments shown and described in Figures 1 to 5 only a few of the possible embodiments of elements 5a, 5b are shown.

[0087] In another possible embodiment shown in FIG. 5, the elements 5 a, 5 b comprise at least one projection 5 b in the form of a spiral or helix around the axis 2 .

[0088] Instead of projections, the elements 5a, 5b may also be spiral or helical grooves.

[0089] The projections, or elements 5b, are arranged at the positions of the axis 2 on which the rotor body 3 is placed, so that corresponding elements are formed in the rotor body 3 during the injection moulding process.

[0090] The helical shaped element 5 b is capable of transmitting a combination of rotational and axial forces to prevent axial and rotational movement of the shaft 2 relative to the rotor body 3 .

[0091] FIG. 6 shows a further embodiment, in which the shaft 2 features an element 5 b that can engage with a corresponding element 5 c on the rotor body 3 .

[0092] In this case, this element 5 b is a ring-shaped projection around the axis 2 .

[0093] This element 5b is arranged at the position of the axis 2 on which the rotor body 3 is arranged. This element 5b is able to transmit axial forces from the axis 2 to the rotor body 3 and vice versa.

[0094] FIG. 7 shows yet another variant, in which the shaft 2 features a number of elements 5b in the form of elongated projections extending axially along the shaft 2 and distributed therearound.

[0095] Based on the above variants, it is clear that the elements 5a, 5b can be embodied in various ways and that the illustrated embodiment is in no way limiting.

[0096] The invention is not limited to the exemplary embodiments shown and illustrated in the drawings, but rather the method and the screw rotor according to the invention can be realized in various variants without going beyond the scope of the invention. [Explanation of symbols]

[0097] 1 Screw rotor 2-axis 3 Rotor body 4. Fiber 5a, 5b, 5c elements

Claims

1. A screw rotor (1), characterized in that the screw rotor (1) is made of a polymer, the screw rotor (1) being composed of a shaft (2) with a rotor body (3) on the shaft (2), the polymer of the shaft (2) being reinforced with fibers (4), the shaft (2) being characterized by a first element (5a, 5b) engaging with the rotor body (3) or a corresponding second element (5c) of the rotor body (3), the first and second elements (5a, 5b, 5c) being adapted to prevent the shaft (2) from moving axially and / or rotationally relative to the rotor body (3), the first element (5a, 5b) comprising at least one groove or first protrusion in a helical shape around the shaft (2), the shaft (2) being hollow, the fibers (4) in the shaft (2) extending mainly in an axial direction (X-X'), The rotor body (3) is a single-layer structure.

2. 2. The screw rotor according to claim 1, wherein the overall shape of the rotor body (3) is cylindrical or conical.

3. 3. The screw rotor according to claim 1 or 2, wherein the rotor body (3) is at least partially made of a polymer reinforced with fibers (4).

4. The screw rotor according to claim 3, wherein the fibers (4) of the rotor body (3) are randomly or randomly oriented.

5. 5. The screw rotor according to claim 1, wherein the polymer forming the screw rotor is polyamide, polyimide, or PEEK.

6. The screw rotor according to any one of claims 1 to 4, wherein the polymer forming the screw rotor is a thermosetting polymer.

7. The screw rotor according to any one of claims 1 to 6, wherein the fibres (4) comprise carbon fibres or glass fibres.

8. The screw rotor according to any one of claims 1 to 7, wherein the fibres (4) comprise an organic polymer.

9. 9. The screw rotor according to claim 8, wherein the fibers (4) made of organic polymer are aramid fibers.

10. 5. The screw rotor according to claim 1, wherein the polymer forming the screw rotor is an aramid polymer reinforced with aramid fibers.

11. The screw rotor according to any one of the preceding claims, wherein the shaft (2) is made of a different polymer than the rotor body (3).

12. 6. The screw rotor according to claim 5, wherein the polymer of the shaft (2) has a softening temperature equal to or higher than that of the polymer of the rotor body (3).

13. 13. The screw rotor according to claim 1, wherein at the end face of the shaft (2), the shaft (2) is provided with a connecting part (8) having a screw thread (9) inside which a bolt can be placed.

14. A method for manufacturing a screw rotor (1) consisting of a shaft (2) and a rotor body (3), said screw rotor (1) being made of a polymer, said method comprising the steps of: A) providing a hollow shaft (2), the polymer of which is reinforced with fibers (4), the fibers (4) in the shaft (2) extending mainly in an axial direction (X-X'), the polymer of the shaft (2) being reinforced with fibers (4), the shaft (2) being characterized by a first element (5a, 5b) engaging with the rotor body (3) or a corresponding second element (5c) of the rotor body (3), the first and second elements (5a, 5b, 5c) being adapted to prevent the shaft (2) from moving axially and / or rotationally relative to the rotor body (3), the first element (5a, 5b) comprising at least one groove or first protrusion in a spiral shape around the shaft (2); B) injection molding the rotor body (3) using a designated mold, using the stem (2) as an insert into the mold; Including, The rotor body (3) is of single layer construction.

15. 15. The method according to claim 14, wherein the step A of preparing the shaft (2) comprises the step of injection molding the shaft (2) of the screw rotor (1) using a designated mold.

16. The method according to claim 15, wherein the polymer reinforced with fibres (4) is injected in an axial direction (X-X') into the mould to injection mould the shaft (2).

17. 17. The method according to any of claims 15 to 16, wherein in the mould for the shaft (2) a connection part (8) is placed as an insert in the mould at the location of the end face of the shaft, the connection part (8) being provided with a thread (9) inside which a bolt can be placed, or after step B, the connection part (8) is placed by tapping in a designated cavity in the surface (7) of the shaft (2).

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