EP1355758A1

EP1355758A1 - Profiled contour of a screw pump

Info

Publication number: EP1355758A1
Application number: EP02715419A
Authority: EP
Inventors: Ralf Steffens
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-01-19
Filing date: 2002-01-12
Publication date: 2003-10-29
Also published as: JP2004517261A; WO2002057044A1; KR20030079955A; DE10102341A1; CA2435040A1; US20040111884A1

Abstract

The invention relates to the production of screw pump rotors comprising a pitch and/or depth of teeth which can be modified along the axis of the rotor. By means of a simple profiled machine tool (7), a first part of the profiled flank contour is clearly defined along the rotor axis (8) by means of its specific tool guide mechanism, and is then produced in a definitive manner. The remaining second part of the profiled flank contour is then determined according to the rolling movement of the pair of rotors according to the first part of the profiled flank contour carried out by the tool, by means of an approximation which is as precise as possible. It is thus possible to obtain transversally different profiled contours according to the pitch and/or depth of teeth which can be modified along the axis of the rotor. A disk milling cutter is selected to be used as a profiled machine tool.

Description

Profile contour of a screw pump

The invention relates to the generation of the profile contour for the pair of spindle rotors of a screw pump with internal compression by changing the profile pitch and / or the tooth height along the rotor axis.

The invention further relates to a pair of screw spindles provided with the generated profile contour.

Screw pumps of this type are known, for example, from DE 29 34 065 A1, 195 30 662 A1 or from WO 01/57401 A1 and are becoming increasingly important, particularly in vacuum technology, that is to say as suction pumps, because of increasing obligations in environmental protection regulations and increasing operating and disposal costs and due to increased demands on the purity of the pumped medium, the well-known wet-running vacuum systems such as liquid ring machines and rotary vane pumps are increasingly being replaced by dry-compressing pumps. These dry compacting machines include screw pumps, diaphragm pumps, piston pumps, scroll machines and Roots pumps.

What these machines have in common, however, is that they do not yet satisfactorily meet the frequently demanded requirements for reliability and robustness, as well as size and weight, and at the same time a low price level.

Dry-compressing screw pumps are increasingly being used in vacuum technology because they, as typical two-shaft positive displacement machines, require this in a vacuum-specific manner Realize a high degree of compression simply by achieving the required multiple stages in an extremely uncomplicated manner by connecting several closed working chambers in series via the number of wraps per spindle rotor. Furthermore, the contactless rolling of the spindle rotors enables increased rotor speeds, so that, relative to the absolute size of the machine, nominal suction capacity as well as volumetric efficiency and delivery rate increase in an advantageous manner. In contrast to the known screw pumps that promote liquids, it is very important for gas-producing screw pumps to achieve an internal compression for reduced power consumption. According to the working principle of a displacement machine, the gas volume enclosed on the suction side is reduced by a selected factor during its transport to the outlet, in particular by reducing the pitch and / or the tooth height of the intermeshing screw spindles.

At the same time, for the contact-free rotation of the two displacement rotors designed as screw spindles with the smallest possible gap between the spindle profile flanks, a profile contour course is required which can be passed on in the x-y face cutting plane, ie perpendicular to the longitudinal axis z of the rotor, according to the known toothing law.

To produce screw rotors with a pitch that is variable in the longitudinal direction, a profile course that can be rolled off in accordance with the gearing law in the xy face section plane is selected in accordance with the known state of the art and in the direction of the rotor longitudinal axis along a screw line in the z-axis direction with different increments by “pulling up” in Developed in the sense of a "continuous stacking" so that in this way the desired screw rotor with an incline that changes in its longitudinal direction.

This can be easily represented or generated on a CAD system. However, considerable difficulties then begin during production, because it is mathematically clear and imperative that the spindle profile contour course for production changes depending on the pitch along the rotor axis. Because the flank contour clearly defined in the xy face section plane according to the gearing law must change mathematically clearly and imperatively both in the plane of the axial section and in the normal section in the described development in the longitudinal direction of the rotor along the chosen spiral or helix depending on the respective pitch, which in The longitudinal direction of the rotor follows a desired function course for realizing the internal compression. This is where the manufacturing difficulties start, because the fixed tools for creating the helical groove only follow the profile flank profile in the axial or normal cut, depending on the machining method selected. However, since the profile flank contours in these planes, as described above, change along the rotor axis depending on the respective value of the flank pitch, this production with the known tools is complex.

This problem is exacerbated by the so-called "comb production" at the rotor end on the outlet side: in the sense of an inner compression, the slope from the gas inlet side to the outlet side decreases by the value of the desired inner compression, so that the slope on the outlet side is the lowest the difficulty for the spindle rotor production, with the chosen tool with a decreasing profile tooth gap, to have to plunge relatively deep into the spindle rotor to be machined in order to generate the desired flank contour, which is because the rigidity of the selected tool is only possible to a limited extent.

With constant pitch and constant profile tooth depth, as has been known for a long time in liquid-producing screw pumps because of the practically incompressible behavior of a liquid, there are no difficulties with the profile contour flanks that change in the longitudinal axis of the rotor in the axial or normal section plane. Only the desire for the longitudinally changing slope for performance-saving compression for compressible conveying media caused the described difficulties in production. Similar problems arise if, additionally or alternatively, the profile tooth height in the longitudinal axis of the rotor is changed in order to realize or increase the internal compression.

It is therefore the task of making the manufacture of screw rotor rotors as simple and inexpensive as possible with the implementation of an internal compression by means of an incline and / or tooth height which is variable along the rotor axis and of creating corresponding screw rotor rotors.

According to the invention, this object is achieved in that a simple profile machining tool clearly defines a final part of the profile flank through its own characteristic manufacturing process with its specific tool guide along the rotor axis and finally generates it permanently, and in that the remaining second part follows the profile flank contour in accordance with the rolling motion of the rotor pair This first part of the flank profile contour determined by the tool is determined by the greatest possible approximation, so that depending on the incline and / or tooth height which varies along the rotor axis, different profile contours in each case in the face cut surrender. For the generation of the profile contour, the first part of the profile contour is directly determined and definitely generated by a simple machining tool during its machining movement in the longitudinal axis of the rotor to produce the internal compression by changing the profile pitch and / or the tooth height, and the other part of the profile contour after this by the flank profile generated in the machining tool.

A “simple tool” is to be understood as a tool that is not tied to the workpiece. It is therefore not absolutely necessary to use a special, own or special tool to manufacture a desired spindle rotor as a workpiece.

Such a tool is understood to be a simple tool which produces different end cuts via the longitudinal axis of the rotor, this “simple tool” determining the profile contour.

This "simple", that is to say workpiece-independent tool, creates a certain profile flank during its processing through the workpiece at the desired profile tooth height or depth, the course of which, in addition to the tool geometry, is also caused by the movement of the tool relative to the workpiece. While the tool geometry is the origin - or the output size is no longer changed, but is initially selected as the starting size with regard to the smallest tooth gap width and a good profile approximation compromise as well as a low price, the controlled movement of the tool relative to the workpiece is decisive for influencing the profile geometry. There are various control options the tool movement, which depend on the selected machine tool and adapt to its possibilities are. A multi-axis machining center offers more possibilities, but the invention can also be carried out with a simple milling machine in which the milling cutter used as a simple tool can be inclined.

The options for controlling and moving the simple tool, which are specified by the processing machine, thus determine the profile flank shape for the spindle rotor. This tool movement is to be controlled in such a way that a suitable profile flank is created on the spindle rotor: For this purpose, a certain part of the profile flank generated in this way, preferably the base contour, i.e. the profile flank below the pitch circle, is applied to the other part, preferably to the head contour, according to the known toothing law , that is, the profile flank theoretically mapped above the pitch circle and thus generates the theoretical second part, that is, the head profile, corresponding to the first part, that is to say to the foot profile. This theoretical action according to the well-known gearing law takes place either via an envelope or analytically via mapping using profile gradient functions. The special feature of the two mirror rotors, which are identical in mirror image to each other, is used, which always roll the foot and head profile flanks in a corresponding manner.

Now the two second profile parts, i.e. the profile actually generated by the simple tool, are compared directly with this theoretical profile: Of course, a material crossing of the actual versus the theoretical contour in the sense of penetrating the rolling flanks must of course be avoided, whereas a material shortfall between actual and theoretical Contour in the sense of a flank gap is generally only to be minimized at first. This procedure is performed with a new slope value in each forehead cut repeated. This results in individual / specific profile contours, which can be optimized in different sections. In the area of large gradients, the line of contact (as the fixed location of all points of intervention) is drawn as close as possible to the intersection of the two outer diameters ("minimal blow hole") with at the same time minimal material shortfall between the actual and the theoretical contour in terms of a flank gap, whereas with a small gradient, The line of contact is kept shorter while at the same time the material falls below the permissible limit. The only input variable is the desired gradient along the spindle rotor axis.

This procedure differs significantly from the prior art, in which a reference profile is specified, which is kept constant for each face cut and which is best approximated.

The above-described invention can be carried out using known methods for producing spindle rotors, either by whirling, that is to say with an internal-axis tool movement, which requires a type of ring gear with inward-pointing turning steels, or by milling.

It is useful if the first part of the profile contour generated by the simple machining tool results in the entire profile of the foot profile below the pitch circle.

A side milling cutter can be selected as a simple machining tool for the first part of the profile contour. The simple machining tool for the first part of the profile contour can define and edit the two profile flank sides at the same time in the area of the smallest slope. The simple machining tool can generate the desired change in pitch by specifically controlling the rotational movement of the spindle rotor in relation to the movement of the machining tool along the spindle rotor axis.

In detail, the procedure is as follows: With a known simple side milling cutter as the first profile machining tool, which could also be a cutting whirling tool, the rotor blank is initially machined in such a way that the entire foot profile area is completely machined. The flank contour area below the pitch circle, i.e. deeper in the workpiece than the pitch circle, is defined as the base profile area, the pitch circle for the pair of spindle rotors, preferably rotating in opposite directions, corresponding to the center distance of the two spindle rotors.

The disk milling cutter - or, if appropriate, a swirl tool - is preferably designed in such a way that for the slightest incline, it can simultaneously completely machine the foot profile areas on the right and left tooth space flank sides. By advancing or advancing the side milling cutter in the longitudinal axis of the rotor - in which either the tool or the workpiece or both are moved relative to one another - the tooth gap width becomes wider as the incline increases, so that the side milling cutter initially changes the angle of inclination relative to the rotor axis machined a tooth gap flank side (in common parlance, for example, the "left" side) and then completely finished the remaining ("right") foot flank side in the subsequent processing step.

In order to realize the desired inner compression the flank inclination angle in relation to the longitudinal axis of the rotor changes in accordance with the desired gradient. The milling cutter - or an equivalent simple tool - is inclined in its machining angle with respect to the longitudinal axis of the rotor in accordance with the desired function profile of the flank pitch angle or adjusted in its inclination or - also spatially or in several planes - changed. This change in the angle of inclination for the rotary axis of the side milling cutter is known to be reliably achieved and guaranteed with the desired accuracy by modern production machines for the flank profile production during the tool movement along the rotor axis and can be controlled spatially precisely.

Instead of this repeatedly required longitudinal movement of the side milling cutter relative to the workpiece for machining the right and left foot profile flank with the larger pitch values and a correspondingly larger tooth gap width, it is alternatively also possible to machine the two tooth gap flank sides at the same time by a correspondingly excessive inclination of the side milling cutter, which, however, does somewhat less favorable profile contour.

For particularly simple profile flank approaches, it can also be loaned to keep a side milling cutter unchanged in its machining angle with respect to the longitudinal axis of the rotor and to control the desired variable pitch on the screw rotor by controlling the rotational movement of the workpiece in relation to the movement of the side milling cutter along the rotor axis to reach.

The idea of the invention remains common to all these possibilities, with a simple processing tool, preferred instruct a side milling cutter to finish machining the first part of the profile flank contour to be produced, preferably the entire base profile area.

Known standard side milling cutters with standard cutting inserts can advantageously be used as side milling cutters. After this processing step, the profile flanks of the spindle rotor below the pitch circle are completed. With this specification, there are now different profile contour profiles in the face cut (ie perpendicular to the longitudinal axis of the rotor). Subsequently, the foot profile profile that is clearly defined by the machining tool, for example a disc milling cutter, is transferred to the head profile profile in each face cut in accordance with the toothing law. This foot profile contour may not necessarily be able to comply with the known toothing law, but it is entirely sufficient to generate the resulting head profile contour, for example, by means of an “envelope” or by simulation of the rolling motion. A certain gap between the flanks of the interacting rotors is due to the non-contact Shifting is necessary anyway.

In addition, these screw pumps with the known profile contours (for example as a cycloid) have the known so-called “blow hole” or the “rounded tip opening” between the two rotors in the profile head area. Thus, the gap between the profile flanks, which in this invention results from the production-related generation of the profile contour, must always be seen in relation to these gap widths, which are present anyway and which determine the internal leakage to a much greater extent. Of course, this additional gap due to the manufacturing process can be minimized iteratively, for example, by simply varying the geometry of the machining tool, with a certain leakage between the flank rarely even being favorable in terms of better performance. Distribution is.

It is also particularly advantageous in this invention if the flank profiles of the foot and head profile profiles for the base and the counter rotor correspond to one another. As mentioned above, the screw spindle rotors are preferably operated in opposite directions at the same speed, wherein one spindle rotor can be referred to as a “basic rotor” and the other as a “counter rotor”. For reasons of production and uniform power conversion, it is desirable if the profile flanks of both rotors are designed identically and only the orientation of the pitch direction is reversed. One rotor rises to the left and the other rises to the right, this being achieved very simply by reversing the direction of inclination of the machining tool with otherwise the same manufacturing parameters. In each face section through both rotors, however, an identical profile course for the base and counter rotor is to be realized, and - as already mentioned - the face cut changes depending on the pitch course.

Favorably, by specifying the base profile contour on the basis of the machining tool, the entire flank profile is clearly determined under the condition of the identical profile, because the base profile of the base rotor always corresponds only with the top profile of the counter rotor and the top profile of the base rotor always only with the base profile of the counter rotor that after specifying a foot profile on the base rotor, this profile is transferred identically to the counter rotor and the resulting head profiles are then also identical.

The problem of “comb production” mentioned at the beginning is elegant and resolved in the manufacturing process described. disarmed by completely machining the entire flank area below the pitch circle, i.e. the foot profile, using a disk cutter or other simple tool. The tool rigidity is thus considerably improved and the design limits when determining the smallest pitch are correspondingly more favorable.

The implementation of the internal compression in a pair of screw rotor rotors by changing the profile pitch along the rotor axis is described in detail above as an example, because this form is the most common, because in this way the pump housing housing bypassing the two rotors is simply cylindrical in its area can be executed. As mentioned at the beginning, the tooth height can be used in addition or only on its own to implement the desired internal height

Compression can be changed. Because the volume of each working chamber is also changed in this way, which exactly corresponds to an internal compression. The procedure according to the invention can also be used directly or immediately with this approach of the tooth height changing along the rotor axis. For this purpose, only an additional movement of the tool or the side milling cutter is generated by changing the distance between the rotor axis and the tool axis during machining along the rotor axis in order to generate a changing tooth height via the longitudinal axis of the rotor. The previously described method for generating profile flanks remains identical and can be carried out separately or together with the change in slope. This specific change in the flank pitch angle and / or the distance between the two axes during machining in the longitudinal axis of the rotor can be carried out with no problem with modern processing machines.

An embodiment of the invention is shown in the drawings. fertilizer also described. It shows in a schematic representation:

Figure 1: A top or side view of a screw rotor with changing pitch along the rotor axis, with a milling cutter being shown as a simple machining tool for machining the profile flank contour, and

Figure 2: A partial longitudinal section of the rotor on an enlarged scale.

In the illustrated embodiments, Fig. 1 shows a plan view of a screw rotor 1 with an internal compaction by changes in the slope of 2 along the rotor axis, with the lower slope of m _Aeus A2 on one side of the rotor and the larger increase m _Eιn 2B on the other Side with the correspondingly different flank pitch angles ß 3A and 3B along the rotor axis. The manufacture with definition of the respective profile flank contour, based on the foot profile 4 below the pitch circle 5 and from the head profile 6 above the pitch circle, is now carried out according to the invention by a simple machining tool, for example as a disk milling cutter 7, which engages in the spindle rotor 1 by targeted movement along the rotor axis 8 generates the profile flanks. The axis 9 of the side milling cutter is now inclined during the rotor profile machining as a movement in the longitudinal direction of the rotor with respect to the rotor axis by the constant or variable angle y in order to produce the various flank inclination angles β in accordance with the above description in accordance with the desired internal compression.

To clarify the individual profile flanks is in the figure 2 shows an axial section enlarged with the pitch circle (as cylinder line 5), the foot profile contour (4- shown as a thick full line including the cylindrical foot circle diameter range, which is of course also finished by the side milling cutter) and the resulting head profile flank adjustment run (6- shown as dashed line without the cylindrical outer diameter).

LIST OF REFERENCE NUMBERS

1. Screw spindle rotor with its rotor longitudinal axis variable pitch

2. Profile pitch of the screw rotor

2A lower gradient m _A on the (outlet) side 2B greater gradient m _Eιn on the (inlet) side

3. Flank inclination _angle ß 3A lower pitch _angle ß _ÄUΞ on the (outlet) side 3B larger pitch _angle ß _AuΞ on the (inlet) side

4. Foot profile course

5th pitch circle

6. Profile profile

7. Profile machining tool (side milling cutter)

8. Rotor longitudinal axis

9. Axis of the profile machining tool

10. Inclination angle y between tool axis and rotor axis

Claims

claims

1. Method for generating the profile contour for the pair of spindle rotors of a screw pump with internal compression by changing the profile pitch and / or the tooth height along the rotor axis, characterized in that the first part of the profile contour is generated by a simple machining tool during its machining movement in the longitudinal axis of the rotor the internal compression is directly determined and definitely generated by changes in the profile pitch and / or the tooth height, and that the other part of the profile contour is determined according to this flank profile generated by the machining tool.

2. The method according to claim 1, characterized in that the profile contour of a screw pump, the first part of the profile contour generated by the simple machining tool results in the entire profile of the foot profile below the pitch circle.

3. The method according to claim 1 or 2, characterized in that the machining tool for the first part of the profile contour is a side milling cutter.

4. The method according to any one of claims 1 to 3, characterized in that the machining tool for the first part of the profile contour in the area of the smallest slope defines and processes the two sides of the profile flank simultaneously.

Method according to one of claims 1 to 4, characterized in that the simple machining tool by targeted control of the rotational movement of the spindle rotor generates the desired change in pitch in relation to the movement of the machining tool along the spindle rotor axis.