EP0721387B1 - Method and casting device for producing parts with a helically symmetrical outer contour - Google Patents

Description

The invention relates to a method for producing Rotors for screw compressors which have a section one screw-symmetrical to an axis of symmetry Have an outer contour.

The production of parts with a section by section screw-symmetrical outer contour, for example either starting from an edge material or from one forged or a cast roller into which by machining processes, for example milling, high-speed milling or grinding the screw symmetrical Outer contour is incorporated.

In this known method is a complex cutting Machining required, on the one hand, a high Material expenditure and on the other hand also a high processing effort has, in particular the high machining volume several machining operations required ultimately increases the required accuracy to reach.

From GB 2 229 121 is the manufacture of a Screw element known for extruders. Here is a Casting body by molding a model with screw-symmetrical outer contour and then this mold body used as part of a mold.

The invention has for its object a method to improve the generic type such that such parts with less effort and therefore cheaper can be produced.

This task is carried out in a process described in the introduction Art solved according to the invention in that Impression of the section with screw symmetrical Model having an outer contour in this section Molded body surrounding azimuthally to the axis of symmetry is produced and that with this mold body in a casting mold to solidify the shell Cast iron melt leading deterrent to the one to be manufactured Part of the corresponding cast iron cast is produced and that the mold under Sealing feed of the cast iron melt is poured out ..

The advantage of the method according to the invention is there too see that by the azimuthal surrounding area Mold body and pouring the same under Shell solidification of the cast iron melt leading to quenching already a screw-symmetrical outer contour having, in particular one-piece cast can be produced is. This is a significant reduction of the manufacturing effort achieved because of the geometry the screw-symmetrical outer contour is close to the final contour or true to the final contour. It also brings pouring under leading to shell solidification Quenching the cast iron melt has the advantages of doing so the one-piece cast body in particular defined high strength properties can be achieved and the Castings in particular have a high quality of themselves large cross-sectional differences extending material have and preferably preferably substantially homogeneous and in particular essentially free of pores and Cavities are.

Another advantage is that the mold poured out under the sealing feed of the cast iron melt is, so that especially with precipitated graphite the graphitization pressure is used to blow holes and to prevent pores in the cast.

To ensure a structure that is as homogeneous as possible across the cross-section receive, it is conveniently provided that the casting with vertically aligned axis of symmetry of the mold body will be produced.

With regard to the cast iron, which is used to manufacture the Part used according to the invention have so far been used no further details given. A homogeneous structure To get it, it is particularly advantageous if that Cast iron solidified in the mold essentially eutectically.

It is special for the homogeneity of the structure to be obtained cheap if the cast iron in the mold as Single substance system freezes.

This can be achieved in particular in that the Casting mold with a cast iron melt near the eutectic is fed.

Regarding the manufacture of the mold itself no details given. So it would be in the context of the present Invention conceivable that the mold alone Molded body includes. However, it is even more advantageous if for the manufacture of the mold the mold body as

Insert between two mold halves so that over the two mold halves further form elements of the to be produced and thus forming a one-piece component Castings can be specified and defined, but on the other hand the section of the screw-symmetrical outer contour also can be produced with a casting mold, although one screw-symmetrical outer contour not for casting molds with Mold halves is suitable because mold halves for screw symmetrical Outer contours often due to the lack of mold release cannot be produced between the mold half and the model are.

It is particularly advantageous in the context of the present Invention when the mold halves in the mold mask process or Mask molding processes are made because of this process the production of thin-walled and heat-conducting mold halves enables, which are necessary in order to Shell solidification of the cast iron melt required To enable deterrence. It also has the shape mask process the advantage that no draft angles are required are and thus the cast made with a smaller allowance than conventional casting processes.

It is particularly advantageous in the context of the invention Solution if the mold halves have a mold for at least one the section with the screw symmetrical Outer contour adjoining section of the part to be manufactured Form part.

With regard to the production of the mold body were in Connection with the previous description of individual Exemplary embodiments made no further details. That would be for example, the mold body by a variety of conceivable Surface processing methods can be produced.

However, it is particularly advantageous if the mold body by molding the model with molding material and then unscrewing the model from the mold body will be produced. It is also useful if the Molded body by molding in an outer mold container is produced with a defined outer contour, in particular when the mold body as an insert in a Half of the mold should be inserted, in which case the Half of the mold corresponding to the outer contour of the casting body Has recess.

Suitable for such a production of the mold body there is in particular a sand-molding process in which a molding of the model for the production of the Inner contour and, for example, the molded container Production of the outer contour of the mold body is carried out.

Regarding the way the final shape is made of the part with screw-symmetrical outer contour have not been previously specified made. It would be conceivable, for example, in particular lower requirements for the accuracy of the parts, this Can be produced directly ready for final contour using the master molding process.

However, it is particularly advantageous, in particular a to achieve high precision when the section with the screw-symmetrical outer contour as cast with oversize and then cutting to the usual shape is processed, so that in particular for screw compressors high accuracy of the outer contour can be achieved, but with little processing effort, because the screw symmetrical The outer contour can already be produced close to the final contour is.

The same goes for the section with the screw-symmetrical outer contour adjoining section, for example, shaft stub of the part, because in the area of this Wave end approaches a storage takes place and thus the Storage area for the bearings also with high accuracy must be processed.

Preferably, the cast after demolding Centering surfaces created by machining, the casting is then taken up on the centering surfaces and machined.

Finishing is done, for example, by milling in one clamping and subsequent grinding in one further tension.

However, it is particularly advantageous if the casting is carried out after Manufacturing of the centering surfaces in one clamping is finished. This is finishing grinding, preferably high speed grinding.

For accuracy, it is particularly advantageous if the Finishing is done on one machine.

It is even more advantageous if the production of the centering surfaces on the same machine as the finishing.

Regarding the cast iron used in the above described method no further information made.

In principle, all possible variants of cast iron melts would be usable, for example also a cast iron melt, which is created in cast iron with lamellar graphite. However, it is particularly advantageous, especially good ones Surface properties and good alternating load strength and especially to achieve good ductility if one Cast iron melt is used, in which cast iron in the cast with nodular graphite. The structure is preferred predominantly pearlitic and slightly ferritic.

The invention further relates to a casting device for manufacturing of rotors for screw compressors made of cast iron an outer contour that is screw-symmetrical to the axis of symmetry having section, this casting device especially for performing the above Variants of the inventive method is used.

The object of the invention is in such a casting device solved in that a mold a Section with the screw-symmetrical outer contour azimuthal to the axis of symmetry surrounding and closed a model with the screw-symmetrical outer contour has molded mold body and that the mold of one when pouring to solidify one into the mold introduced cast iron melt surrounding heat sink is.

With such a mold can be at the beginning described methods achieve the advantages mentioned, in particular a cast with a high degree of homogeneity, the also in the section with the screw-symmetrical outer contour is shaped close to the final contour or even true to the final contour, so that at least time-consuming processing operations are eliminated.

With regard to the design of the heat sink, none details given. It is advantageously provided that the heat sink is made of steel gravel, which one has high heat capacity to have a deterrent effect to achieve the solidification of the shell in the cast.

It is particularly advantageous here if the weight of the Heat sink at least 8 to 10 times the casting weight is.

In order to achieve good heat transfer, it is also advantageous if the wall thickness of the casting mold is a maximum of 10 mm is, it is preferably provided that the wall thickness is a maximum of 5 to 10 mm.

In principle, the casting mold could be made solely by the casting mold body be educated. However, it is particularly advantageous in particular, around which the screw-symmetrical outer contour section having to form additional sections, if the mold comprises two mold halves, into which the mold body is inserted.

The mold halves are preferably designed such that they have a shape for at least one sticking to the section the section adjoining the helical outer contour form the part to be manufactured.

A particularly precise casting can be achieved if the mold halves according to the mold mask or the mask molding process are produced, since it can be used to produce very precise shapes are.

The invention further relates to a rotor for screw compressors with a screw-symmetrical outer contour having compression section, wherein according to the invention the rotor has a cross-section that is free of pores and voids from cast iron with graphite precipitates and that Structure in the cross-section is rigidified on the outer contour side.

It is particularly advantageous if the rotor in the Area of its screw-symmetrical outer contour shell-solid structure made of cast iron with graphite precipitates having.

Furthermore, the invention relates to a part made of cast iron with a screw-symmetrical to an axis of symmetry Outer contour, in particular a rotor for one Screw compressor with a screw symmetrical Compression section having an outer contour, which according to the invention is characterized in that this one over a cross section of the section with screw symmetrical Outer contour has a homogeneous structure.

It is particularly advantageous if the structure in the Cross section is completely free of pores and voids, whereby pores and cavities are to be understood as cavities, which are visible and larger than about 1/10 mm in diameter are.

Such a part is preferably accessible that this is according to an embodiment of the above Process is made.

A particularly preferred embodiment of a part of the invention has in addition to the screw symmetrical Outer contour of other shaped elements, for example Wave approaches that also with the screw-symmetrical outer contour cast in one go are, so that the structure, for example by the seal supply available structure, through the entire extends in one piece and thus also the properties associated with this structure with the simple inexpensive manufacture refer to this whole one-piece body.

Fig. 1

einen Längsschnitt durch einen Schraubenverdichter, bei welchem als Rotoren Teile mit schraubensymmetrischer Außenkontur Verwendung finden;

Fig. 2

einen Schnitt längs Linie II-II in Fig. 1 und insbesondere durch die Rotoren mit schraubensymmetrischer Außenkontur;

Fig. 3

einen senkrechten Schnitt durch eine Vorrichtung zum Herstellen eines Abgusses für einen derartigen Rotor;

Fig. 4

einen Längsschnitt durch eine Vorrichtung zur Herstellung eines Gießformkörpers für eine Gießform gemäß Fig. 3;

Fig. 5

eine Darstellung einer ersten Aufspannung eines erfindungsgemäßen Abgusses für einen Rotor zur mechanischen spanabhebenden Bearbeitung; und

Fig. 6

eine Darstellung einer zweiten Aufspannung des Abgusses zur Fertigbearbeitung.

Further features and advantages of the invention are the subject of the following description and the graphic representation of the invention. The drawing shows:

Fig. 1

a longitudinal section through a screw compressor, in which parts with a screw-symmetrical outer contour are used as rotors;

Fig. 2

a section along line II-II in Figure 1 and in particular through the rotors with screw-symmetrical outer contour.

Fig. 3

a vertical section through a device for producing a cast for such a rotor;

Fig. 4

a longitudinal section through a device for producing a mold body for a mold according to FIG. 3;

Fig. 5

a representation of a first clamping of a casting according to the invention for a rotor for mechanical machining; and

Fig. 6

a representation of a second clamping of the casting for finishing.

The parts produced according to the invention are, for example Rotors 10, 12 shown in FIGS. 1 and 2 Screw compressors 14, each of the rotors 10 and 12 as a one-piece part with a section 16 or 18 screw-symmetrical outer contour, simplified below referred to as a screw-symmetrical section, formed is in which an outer contour of the rotors 10, 12 several helical to an axis of symmetry or screw axis 20 or 22 extending screw combs 24 or 26, which have different cross-sectional shapes, the Cross-sectional shapes are designed so that the Screw combs 24 and 26 of the two rotors 10 and 12 interlock tightly. The cross-sectional shape of the Screw combs 24 and 26 are different, however mutually adjusted so that with each other rotating rotors 10 and 12 of these compresses a medium becomes.

For this purpose, the rotors 10 and 12 are in one piece with 30 designated housing arranged, which is the screw symmetrical Sections 16 and 18 are essentially sealing encloses.

Each of the rotors 10 and 12 is also still on both sides of the symmetrical sections 16 and 18 and coaxial to the symmetry axis 20 or 22 integrally molded shaft ends 32 or 34 and 36 or 38 provided with which the Rotors 10 and 12 are rotatably supported in the housing 30. One of the shaft ends or the shaft end 36 is there led to a drive motor, not shown in Fig. 1 and driven by it.

According to the invention, the manufacture of the rotors 10 or 12, for example the rotor 10 in a in Fig. 3 as Whole with 40 casting device, which one Bucket 42 comprises, in which one designated as a whole with 44 Casting mold is arranged in which a casting 10 'of Rotor 10 can be produced, the entire casting 10 ' integrally molded part, which both the screw symmetrical section 16 'as well as the two Stub shaft 32 'and 36' includes, by the designation of the individual elements with a dash is brought that this is not the final measure but have an oversize.

The casting mold 44 in turn comprises two mold mask halves 46 and 48, which according to the known shape mask method, for example described in the book "Foundry Molding Materials", VEB-Verlag Technik Berlin, edition 1955, author: Dr. R. Grochalski are made. These mold mask halves 46 and 48 form a shape for the shaft ends 32 'and 36 ', which is on both sides of the screw symmetrical Section 16 'extend.

The mold for casting the screw symmetrical section 16 'is formed by a mold body 50, which the screw-symmetrical section 16 'in the azimuthal direction encloses closed to the axis of symmetry 20 and in a corresponding recess 52 of the two mold mask halves 46 and 48 is inserted. For example, points to this the casting mold body 50 is cylindrical to the axis of symmetry 20 Outer surface 54 and end faces 56 and 58 and the recess 52 has an inner cylinder surface 60 and ring surfaces 62 and 64 delimiting them and forms with these a precisely fitting receptacle for the mold body 50.

A division plane 70 of the two mold mask halves 46 and 48 is placed so that in this the axis of symmetry 20 of the rotationally symmetrical section 16, which is simultaneously the axis of symmetry for the two shaft ends 32 'and 36' forms.

The casting mold comprises the two mold mask halves 46 and 48 and the mold body 50 inserted into it. This is arranged in the bucket 42 so that the axis of symmetry 20 runs in the vertical direction. Furthermore, the mold still surrounded by a heat sink 72 in the bucket 42, which from a bed surrounding the mold 44 Steel gravel is formed. The bed of steel gravel surrounds the entire mold 44 and has a mass, which is about 8 to 10 times the mass of the cast 10 'of the rotor corresponds.

To provide an effective cooling effect through the heat sink 72 reach, the mold 44 is designed so that it is preferably one between the casting 10 'and the heat sink 72 lying wall thickness of 5 to 8 mm, so that a suitable thermal coupling between the in the mold filled cast iron melt and the heat sink 72 is possible.

The casting mold body 50 is produced as shown in FIG. 4, by means of a whole designated 80 Molding device having a molding container 82 in which a model 84 for the screw symmetrical Section 16 'can be used. The molded container 82 includes a bottom 86 and can be closed by a cover 88, an inner wall 90 of the molding container 82 the cylindrical Outer surface 54, the bottom 86, the end face 58 and the cover 88 define the end face 56. Of the Cover 88 is designed so that it is a one The outer contour of the model 84 has the corresponding opening 92, so that the model 84 with its screw symmetrical The outer contour extends through this opening and thus can also be screwed through the cover 88 is.

The model 84 is also non-rotatably connected to a shaft 94, which is displaceable in the direction of its axis of rotation 96 a drive wheel 98 penetrates, but rotatably with the Drive wheel 98 is connected so that by rotating the drive wheel 98 the entire model 84 through the cover 88 can be unscrewed.

Model 84 is preferably guided exactly the opening 92 formed in accordance with the outer contour Cover, which in the direction of the axis of symmetry 20, which runs coaxial to axis 96, has a length that at least approximately the extent of the model 84 in the Mold container 82 corresponds.

The model 84 is used to manufacture the mold body 50 screwed far into the mold container 82 until it with his End face 100 is seated on the bottom 86 of the molded container 82. Subsequently, openings 102 are made using a Core shooter sand under pressure in the space between the model 84 and the molded container 82 with the bottom 86 and the cover 88 shot and in conventional Solidified so that the solidified sand the mold body 50 forms. After solidification is done by turning of the drive wheel 98, the model 84 from the mold body 50 unscrewed, then the cover 88 is lifted off and the mold body 50 is removed from the mold container 82.

This mold body 50 is then in the two after one conventional mold mask halves produced 46 and 48 can be used to mold 44 form.

The mold mask halves 46 and 48 are one for the mold mask process usual sand-resin mixture and hardened.

It is particularly advantageous, especially if a good one Cooling of the screw-symmetrical section 16 'is required is the mold body 50 made of a mixture of quartz sand, To produce chrome ore and zircon sand.

The mold 44 embedded in the heat sink 72 is at vertical alignment of the axis of symmetry 20 over a Feeder 104 with an essentially eutectic cast iron melt poured out, the cast iron melt in the

Casting mold 44 essentially eutectic and due to the Quenching by the heat sink by solidifying the shell stiffens. Furthermore, the supply takes place in the way of Seal feed analogous to that known from gravity die casting Seal feeding (e.g. in the technical essay by Dipl. Ing. K. Näser with the title HD special casting in "The Constructor" 3/83 described), so that by forming in the mold 44 Graphitization pressure the formation of cavities is prevented. A cast iron melt is preferably used such melt used that the casting 10 'a structure from spheroidal graphite cast iron, so that preferably a GGG material, in particular GGG70, is created.

The structure is advantageously essentially pearlitic and slightly ferritic, preferably approximately 95% pearlitic and approximately 5% ferritic.

After the casting 10 'has been removed from the mold, the mechanical one is carried out machining, for example only by Milling or only by grinding in the area of the screw symmetrical Section 16 ', so that after removal of the Oversize of the screw-symmetrical section 16 of the rotor 10 arises and further appropriate processing takes place of the stub shafts 32 'and 36' to the stub shafts Get 32 and 36.

The casting 10 'is preferably clamped after removal from the mold and in this clamping centering surfaces are machined, which are either recordings for tips or at least one Holder for clamping the workpiece or non-rotatable Hold and another such recording or recording embrace for a bit.

In particular, as shown in FIG. 5, the Cast 10 'in the screw-symmetrical section 16', preferably in the end regions 16a 'and 16b' with one each Clamping jaw set 110a and 110b clamped, such a Tensioning the screw symmetrical section 16 'therefore is simply possible because it uses the form mask process is manufactured and therefore already based on this Casting process high accuracy in the area of the peripheral surface, in which a clamping with the jaw sets 110a and 110b.

In this first clamping shown in FIG. 5 by means of the clamping jaw sets 110a and 110b are processed from end faces 112a and 112b of the screw symmetrical Section 16 'and the shaft ends 32' and 36 '.

For example, in the shaft stub 32 ' Connection to the face 112a the processing of a Cylinder surface 114 and following this the processing one set back from the cylinder surface 114 Cylinder surface 116, which is preferably for receiving the Camp serves.

The machining follows the cylinder surface 116 an end threaded portion 118.

An end face 120 of the stub shaft end 32 'is edited at least in such a way that a conical Centering hole 122 is introduced coaxially to the axis 20.

In addition, for example, following the front 112b the shaft stub projection 36 'is also processed in such a way First, machining a cylinder surface 124, which adjoins the end face 112b, then the Machining a set back from the cylinder surface 124 Cylinder surface 126, which is preferably a Forms the frustum of the shaft and then the processing an end driving surface 128, which also is set back radially with respect to the cylinder surface 126, he follows. Then another is processed Front 130 of the shaft end 36 'in that also a conical centering hole 132 coaxial with the axis 20 is introduced.

All machining operations are preferably carried out in the first clamping on the end faces 112a and 112b and the cylinder surfaces 114, 116, 124, 126 and 128 in the form of a pre-turning of these areas.

After machining the centering surfaces, the casting 10 ' recorded with these and either with milling and finished a subsequent grinding operation or in one machine in one setup, especially finished by high-speed grinding.

For example, in the second setup, as in Fig. 6, the casting 10 ′ in the centering bores 122 and 132 added between tips 134 and 136 and additionally in the area of the clamping surface 128 by means of jaws 138 Torque initiation excited.

In this second setup, shown in FIG. 6 Finishing is carried out between the tips 134 and 136 of the cylinder surfaces 114, 116, 124 and 126 and the End faces 112a and 112b and also finish grinding of the screw-symmetrical section 16 'to achieve the final outer contour of this screw symmetrical Section.

After processing the casting 10 'in the clamping according to 6, the rotor 10 'according to the invention is finished.

The clamping surface 128 remains on the finished part preserved and does not interfere with the use of the same.

The advantage of the invention is that a high accuracy of the finished machined workpiece is accessible, for example selecting suitable finished No need for pairs of rotors, since all the rotors are sufficient high precision can be produced with little machining are.

Claims (22)

1. Process for the production of rotors for screw compressors having a section with an outer contour which is spirally symmetrical to an axis of symmetry, characterized in that by making a mould from a master having the section with a spirally symmetrical outer contour a casting mould member surrounding this section in an azimuthally closed manner with respect to the axis of symmetry is produced, and that with this casting mould member a cast iron casting corresponding to the part to be produced is made in a casting mould with chilling leading to the shell hardening of the cast iron melt, and that the casting mould is filled by feeding the cast iron melt.
2. Process as defined in claim 1, characterized in that the casting takes place with the axis of symmetry of the casting mould member standing vertical.
3. Process as defined in any one of the preceding claims, characterized in that the cast iron hardens in the casting mould essentially eutectically.
4. Process as defined in any one of the preceding claims, characterized in that the casting mould is supplied with a cast iron melt near to the eutectic.
5. Process as defined in any one of the preceding claims, characterized in that for the production of the casting mould, the casting mould member is placed as insert between two mould halves.
6. Process as defined in claim 5, characterized in that the mould halves are produced in a shell moulding process or shell mould casting process.
7. Process as defined in claim 5 or 6, characterized in that the mould halves form a mould for at least one section of the part to be produced adjoining the section.
8. Process as defined in any one of the preceding claims, characterized in that the casting mould member is produced by making a mould from the master with moulding material and subsequently screwing the master out of the casting mould member.
9. Process as defined in any one of the preceding claims, characterized in that the casting mould member is produced with a defined outer contour by making a mould in an outer mould container.
10. Process as defined in any one of the preceding claims, characterized in that the section with the spirally symmetrical outer contour is produced as a casting with overmeasure and subsequently machined down to the final shape.
11. Process as defined in claim 10, characterized in that the casting is provided with centering surfaces and then machine finished.
12. Process as defined in claim 11, characterized in that the casting is held in the region of the spirally symmetrical outer contour for the provision with the centering surfaces.
13. Process as defined in claim 11 or 12, characterized in that the machine finishing is carried out with a single setup at the centering surfaces.
14. Process as defined in any of claims 10 to 13, characterized in that the machining down to the final shape is carried out on one machine.
15. Casting device for the production of rotors for screw compressors made of cast iron and having a section with an outer contour which is spirally symmetrical to an axis of symmetry, in particular, for carrying out the process as defined in any one of the preceding claims, wherein a casting mould (44) comprises a casting mould member (50) surrounding the section (16) with the spirally symmetrical outer contour in an azimuthally closed manner with respect to the axis of symmetry (20) and moulded by means of a master (84) having the spirally symmetrical outer contour, and wherein the casting mould (44) is surrounded by a cooling body (72) leading during casting to the shell hardening of a cast iron melt introduced into the casting mould (44).
16. Casting device as defined in claim 151 characterized in that the cooling body (72) consists of steel pebbles.
17. Casting device as defined in claim 16, characterized in that the weight of the cooling body (72) is eight to ten times the casting weight.
18. Casting device as defined in any one of claims 15 to 17, characterized in that the wall thickness of the casting mould (44) is at the most 10 mm.
19. Casting device as defined in any one of claims 15 to 18, characterized in that the casting mould (44) comprises two mould halves (46, 48) into which the casting mould member (50) is inserted.
20. Casting device as defined in claim 19, characterized in that the mould halves (46, 48) form a mould for at least one section (32', 36') of the part to be produced adjoining the section (16) with the spirally symmetrical outer contour.
21. Casting device as defined in claim 19 or 20, characterized in that the mould halves (46, 48) are produced by the shell moulding process or shell mould casting process.
22. Rotor for screw compressors having a compression section with a spirally symmetrical outer contour, characterized in that the rotor (10, 12) is a casting made of cast iron, that the rotor (10, 12) has in cross section a pore-free and cavity-free structure with graphite separations, and that the structure is in cross section shell-hardened at the outer contour thereof.

Images