KR20070083878A - Vacuum pump impeller - Google Patents

Abstract

The present invention relates to a vacuum pump impeller (10) comprising a shaft (14) made of steel and a piece of rotor (12) held by the shaft (14). The rotor is made of a material different from the steel of the shaft. The shaft 14 comprises an axial cavity 22, wherein the rotor 12 has an axial protrusion 16 disposed in the cavity 22 together in one or more of a positive engagement and a non-positive engagement. Include.

Description

Vacuum Pump Impeller {VACUUM PUMP IMPELLER}

The present invention relates to a vacuum pump impeller comprising a shaft made of steel and a piece of rotor made of a material different from the steel of the shaft and held by the shaft, and a method for manufacturing a vacuum pump impeller.

Various types, among others, are known vacuum pump impellers such as screw impellers, turbo impellers, rolling-piston impellers, sight-channel impellers. The vacuum pump impeller may be configured to be supported only at the axial end of one side such that the cantilever arrangement, ie the rotor is arranged in the protruding position. The impeller is operated at high speed, in part, so that high radial forces can be generated. For this reason, efforts have been made in designing the impeller, in particular to keep the weight of the rotor as low as possible and to provide the shaft with the best possible strength and rigidity. In practice, this is realized by attaching the rotor on the outer side of the steel shaft and by molding the rotor of a material of particularly light weight, such as aluminum. Since the rotor may expand larger than the shaft during operation due to high temperatures and high centrifugal forces, permanent and free play of the rotor may be achieved, for example, by welding, soldering, bonding, or axially deflected tooth engagement to the end side, tie rods, and the like. It can only be done in a difficult and complex way.

In view of the above, it is an object of the present invention to provide a vacuum pump impeller and a method for manufacturing a vacuum pump impeller that allows simple and permanent fixing of the rotor and shaft.

According to the invention, the above object is achieved by the features of claims 1 and 9 of the appended claims.

In the vacuum pump impeller of the present invention, the shaft is provided with a cavity on its axial end, and the rotor has a positive engagement in the axial cavity of the shaft and a non-positive. A corresponding axial protrusion is provided which is arranged in an engagement manner of any one or more of engagement (non-shaped fit engagement). Thus, the rotor is not fixed to the outside of the shaft but rather to the inside of the sleeved portion of the hollow steel shaft. Under the effect of the introduction of heat into the rotor and the effect of centrifugal forces as generated during operation, the rotor protrusions disposed in the shaft can be enlarged larger than the hollow shaft. Thus, during operation, especially in the case of high speed rotation, the connection between the rotor and the shaft will be stronger. This effect eliminates the need for holes in the shaft and rotor as well as the need for complex connection arrangements involving the use of tie rods and the like, thereby preventing breakage of the shaft or rotor by equalizing the resulting force flow. In addition, by omitting the complex fixation arrangement, the weight of the impeller is kept low, so that the bearing support can be simplified, especially in the case of high rotational speeds, for example when the turbo impeller is operated. Thus, with the impeller of the present invention, faster rotational speed and / or less weight and reduced structural size can be realized.

Preferably, each of the rotor protrusions and shafts comprises a suitably shaped portion inside the cavity for effecting positive engagement with each other in the axial and / or circumferential direction. By providing such a positive connection, a connection is created safely and easily between the rotor and the shaft.

According to a preferred embodiment of the invention, the rotor is a cast piece, the projection of which is integrally cast into the cavity of the shaft. Before casting the rotor, the shaft is inserted into the casting box by its portion comprising the cavity, and then the liquid rotor material is injected into the rotor casting box, and the liquid rotor material flows into the cavity of the shaft. In this way, the shaped parts in the cavity of the shaft are already transferred to the rotor protrusion when casting the rotor. No additional steps other than the manufacturing step of securing the rotor to the shaft are required. Thereby, the weight is then reduced and the occurrence of possible imbalances is prevented.

Preferably, the shaped portions described above are configured as grooves and bars. These grooves and bars can be arranged in the axial and circumferential directions, but can also be arranged in other directions. The exact shape and orientation of the bars and grooves will depend, among other things, on the thermal expansion behavior of the materials used for the rotors and shafts, the rotational speed and centrifugal forces generated during operation, and other constraints.

According to a preferred embodiment, the structure in which the wall thickness of the shaft on the rotor side end of the shaft decreases toward the opening of the cavity, that is, the wall thickness of the shaft casing continuously decreases toward the opening, so that the stiffness of the shaft end toward the opening of the cavity A configuration is provided that is weaker and the axial cavity opening is relatively elastic in the radial direction. This prevents relatively large and / or sudden changes in the moment of inertia of the shaft, otherwise it leads to high bending and / or torsional stresses—especially in the case of widespread changes of stress—premature fatigue with the occurrence of cracks May be caused. The risk of breakage of the rotor projections in this area is significantly reduced, whereby a compact size and a reduction in the weight of the projections of the rotor can be realized. The area of reduction in wall thickness as compared to the total length of the shaft may be less than 1/10 but longer than 3 mm.

In principle, the vacuum pump impeller may comprise two shafts, each of which is arranged at each axial end of the rotor. However, it is preferred that only one shaft be provided which holds the axial end of the rotor. In this way, a vacuum pump impeller adapted for cantilever support is provided, in which a reduction in weight that can be realized by the construction of the present invention is particularly advantageous.

Preferably, the rotor material is a lightweight metal or plastic material. If the rotor is made as a casting piece, the rotor material must have a melting temperature that allows the rotor material to pour into the shaft cavity without damaging the steel shaft. In addition to lightweight metals, plastics or fiber-reinforced plastics can also be used for the rotor.

According to a method for manufacturing a vacuum pump impeller comprising a rotor with an axial protrusion and a steel shaft with a corresponding cavity formed therein, the following steps are provided:

Inserting a shaft having an axial cavity into the rotor mold,

Filling a liquid rotor molding material into the rotor mold and into the cavity of the shaft, and

Removing the vacuum pump impeller from the rotor mold after the rotor has cooled.

Using the manufacturing method described above, when providing a suitably shaped portion in the shaft cavity, a positive connection can be formed between the shaft and the rotor. In this way no additional parts will be needed to make a positive connection between the rotor and the shaft. This method is relatively simple and inexpensive.

According to an alternative method of manufacturing a vacuum pump impeller, arranging a shaft having an axial cavity into a drop-forge die for the rotor, into the rotor drop-forging die and into the cavity of the shaft Forging a red-hot rotor forging material, and removing the vacuum pump impeller from the drop-forging die.

When applying this method, advantages similar to those described in connection with the forming method are obtained.

In the following, some embodiments of the present invention are described in more detail with reference to the drawings.

1 is a longitudinal sectional view of a first embodiment of a vacuum pump impeller including a rotor machined after being driven into a shaft;

2 is a longitudinal sectional view of the shaft of the vacuum pump impeller.

3 is a longitudinal sectional view of a second embodiment of a vacuum pump impeller.

4 is a longitudinal sectional view of a third embodiment of a vacuum pump impeller.

5 is a longitudinal sectional view of a fourth embodiment of a vacuum pump impeller.

1 shows a vacuum pump impeller 10 used as one of two impellers of a screw vacuum pump. The vacuum pump impeller 10 consists essentially of two members, in particular one piece of rotor 12 made of aluminum, and one piece of steel shaft formed as a hollow shaft throughout its length; 14) and two members. The dashed line in FIG. 1 schematically shows the outline of the steel shaft 14 ′ and the rotor 12 ′ shown by the above components immediately after casting and before machining.

The rotor 12 comprises two members in its longitudinal direction, in particular an actuating portion 18 and a protrusion 16 having a helical structure 20 on its radially outer surface.

Slightly conical and / or cylindrical cavities 22 are provided over the entire length of the steel shaft 14, the cavities 22 being cast therein with a positive engagement between the cavities and the protrusions. 12, a protrusion 16 is provided. Internally of the cavity 22 of the shaft, longitudinal bars 24 and transverse bars 26 which engage the corresponding longitudinal and transverse grooves 30 of the protrusions 16 and constitute the shaped sections described above are provided. Are arranged.

On the rotor side end 32 of the shaft 14, the wall thickness of the hollow shaft decreases continuously toward the opening 34 of the cavity such that the stiffness of the shaft 14 in this region is reduced toward the rotor side end 32. do. The shaft end 32 has a large torque from the shaft 14 to the rotor 12 when the positive connection by the transverse bars and the grooves 24, 26, 28, 30, as shown, is not sufficient for this purpose. It may be provided with teeth in the axial direction so as to deliver. The shaft end 32 is inclined by about 5 ° with respect to the axis on its outer and inner surfaces. In the combination of the transverse bars and grooves 24, 26, 28, 30 of the rotor 12 and shaft 14-the bars and grooves have an inclined flank in cross section-this arrangement is characterized in that the rotor ( 12) and the thermal expansion effect caused by the different coefficients of thermal expansion of the two different materials that make up the shaft 14. In this way, the connection will always be reliably free of gaps.

For the manufacture of the vacuum pump impeller 10, the empty space of the shaft 14 ′ as shown in FIG. 4 is first placed into the molding box; The molding box is sealed and filled into the molding box while the rotor material aluminum is kept in the liquid state. In the process, the liquid aluminum also flows into the cavity 22 of the shaft, taking an external shape complementary to the shaft side bars 24 and 26. After cooling, the rotor 12 'and the shaft 14' are removed from the molding box and fed to a machining process, in which the rotor and shaft have their outer and inner surfaces as shown in FIG. The final shape is achieved on the surface.

In this manufacturing method, all shaped elements provided to absorb forces and torques can be produced by casting techniques. The use of a casting shaft will advantageously eliminate the need for further machining. In addition, this casting method can preshape all the elements with a casting radius useful for obtaining a good connection between the rotor 12 of aluminum and the shaft 14 of the steel due to the reduced notch effect. During casting of the rotor 12, the hollow shaft 14 functions as cooling iron, thereby allowing for a suitable cooling process in the rotor and thus increased non-porosity and better bonding force in the rotor material. Is obtained.

As an alternative to the casting method described above, the impeller may be manufactured by a forging method performed in a similar manner.

3 shows a second embodiment of a vacuum pump impeller 50 comprising a radial compressor rotor 52 and a hollow shaft 54 shown in dashed lines. Conical rotor protrusion 56 is cast into conical shaft cavity 58. The positive connection between the radial compressor rotor 52 and the shaft 54 is effected by bars and grooves in the longitudinal axis and in the circumferential direction. The rotor space 52 'which is machined by the radial compressor rotor 52 is shown by a solid line.

The radial compressor rotor 60 is again shown in FIG. 4, which shows the blades 66 whose outer contours must be machined only by high-precision casting, inter alia, by melting, immediately after casting. . The shaft 67 includes a hollow portion 67 that does not extend throughout the length of the shaft but covers only about one third of the shaft length. The region of the hollow portion 67 is provided with a conical or cylindrical axial cavity 65, with the conical or cylindrical protrusions 63 of the rotor 62 disposed inside the axial cavity 65. Positive engagement is achieved between the rotor 62 and the shaft 64 by one or more eccentric rotor pins 68 disposed in the corresponding number of eccentric recesses 69 of the shaft 64. In order to prevent imbalance caused by shafts and rotors of different materials, one or more of the eccentric rotor pins 68 are arranged, for example, with two pins moved relative to each other by 180 °, or three pins moved relative to each other by 180 °. In order to achieve the best possible mass balance. 4 shows only one pin for convenience of illustration. The shaft space 64 'and the rotor space are shown in solid lines, and the rotor 62 and the machined shaft 64 completed by machining are shown in dashed lines.

5 shows a vacuum pump impeller 80 comprising a shaft 84 and a diagonal compressor rotor 82 provided with an axial cavity 86 extending along only one third of the axial length of the shaft 84. Illustrated. The axial cavity 86 of this shaft has a protrusion 88 of a corresponding rotor 82 disposed therein. The raw rotor 82 'and the raw shaft 84' are shown in solid lines, and the machined rotor 82 and the machined shaft 84 are shown in dashed lines.

When subjected to high mechanical and / or thermal stresses, cast rotors may reach their limits of stability and other methods and materials must be considered. The rotor 82 of the impeller 80 according to FIG. 5 must be hot-forged in the drop forging in which the shaft 84 with the cavity 86 was placed, for example a forged member made of aluminum. The stability of this rotor is improved not only by the forging behavior but also by the radial toothed shaft collar 90, which is effective in reducing the tension caused by the centrifugal force and for example compensating weights such as balance screws. Can be used to compensate for the imbalance by placement of and / or removal of material. In addition, to enhance the positive connection, a collar 92 can be formed that provides axial guidance with the corresponding mating groove 94.

The corrosion resistance of the aluminum rotor can be basically improved by eloxadizing or hard-anodizing.

Claims (10)

In a vacuum pump impeller 10 comprising a shaft 14 made of steel and a single piece of rotor 12 supported by the shaft 14 and made of a material different from the steel of the shaft, The shaft 14 includes an axial cavity 22, wherein the rotor 12 is disposed in the cavity 22 together in any one or more of a positive engagement and a non-positive engagement. Characterized in that it comprises a, Vacuum pump impeller. The method of claim 1, The protrusions 16 and the shaft 14 of the rotor comprise shaped portions 24, 26, 28, 30, respectively, inside the cavity 22, the shaped portions being connected to each other in the axial and circumferential directions. Characterized by forming a positive engagement with Vacuum pump impeller. The method according to claim 1 or 2, The rotor 12 is characterized in that it is a cast member with a projection 16 cast in the cavity 22 of the shaft, Vacuum pump impeller. The method of claim 2 or 3, Characterized in that the shaped portions 24, 26, 28, 30 are formed as grooves or bars, Vacuum pump impeller. The method according to any one of claims 1 to 4, On the rotor side end 32, the wall thickness of the shaft 14 is continuously reduced towards the opening 34 of the cavity, Vacuum pump impeller. The method according to any one of claims 1 to 5, The rotor 12 is characterized in that it is supported by a single shaft 14, Vacuum pump impeller. The method according to any one of claims 1 to 6, The material of the rotor is characterized in that the lightweight metal or plastic, Vacuum pump impeller. The method of claim 7, wherein Characterized in that the material of the rotor is aluminum, Vacuum pump impeller. As a method of manufacturing the vacuum pump impeller 10 according to any one of claims 1 to 8 by casting, Inserting the shaft 14 with the axial cavity 22 into the rotor mold, Filling a liquid rotor molding material into the rotor mold and into the cavity 22 of the shaft, and Removing the vacuum pump impeller 10 from the rotor mold after the rotor 12 is cooled, Method of making a vacuum pump impeller. As a method of manufacturing the vacuum pump impeller 80 according to any one of claims 1 to 8 by forging, Inserting a shaft 84 having an axial cavity 86 into the drop-forging die for the rotor, Forging a glowing rotor forging material into the rotor drop-forging die and into the cavity 86 of the shaft, and Removing the vacuum pump impeller 80 from the drop-forging die. Method of making a vacuum pump impeller.

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