WO1992010322A1

WO1992010322A1 - Method of making intermeshing rotors or precision gears, whereby a patterned flank is machined by a rotor-shaped tool, and rotors or gears made by this method

Info

Publication number: WO1992010322A1
Application number: PCT/SE1991/000829
Authority: WO
Inventors: Sven-Åke ROSELL
Original assignee: Rosell Sven Aake
Priority date: 1990-12-05
Filing date: 1991-12-04
Publication date: 1992-06-25
Also published as: SE467864B; SE9003864L; SE9003864D0

Abstract

To minimize the clearances and the spread of the clearances between the interacting rotors in rotating machines of displacement type, working as compressors, expanders, pumps and similar machines, the flanks of at least one of the rotors (22) is in a preparative manufacturing operation given an overdimension (17) by cutting, chemical, electrical or plastic treatment which results in a rotor surface with closely located elevations in shape of ridges (19) or pyramides with a preferred run parallel to the run of the sealing zone between the interacting rotors. By rolling down against a special tool (30) or against the interacting rotor (20) itself, the elevations thereafter are pressed down to a part of their height to the contour (18) which gives the wanted minimized clearance towards the flank surfaces of the interacting rotor. The recesses between the elevations (19) can be filled with ceramic, polymeric or metallic material. At an alternative application on precision gears the clearance between the teeth (15, 16) is reduced in an analog way.

Description

Method of makin intermeshiπq rotors or precision gears, whereby a patterned flank is machined by a rotor-shaped tool, and rotors or πears made by thi^~ method.

This invention relates to a method for manufacturing of inter¬ acting rotors for rotating displacement machines and precision gearwheels where intermeshing engaging elements are unrolling relative each others during the rotation. The invention relates as well to rotors manufactured by the method.

The invention is primarily applicable on machines of displace¬ ment type equipped with scew- or tooth rotors. During the rota¬ tion of the interacting rotors one or more lobes or teeth with adequate geometrical shape on one of the rotors intermeshes with the corresponding gap of lobe or tooth on the other rotor. It is hereby necessary to keep the clearance between these intermeshing elements to a minimum to minimize the leakage losses and play to obtain best function, efficiency and precision. However, similar demand on minimized clearance and improved function exist from precision point of view (not from leakage point of view) also on gears for many machine tools and for the rotor synchronizing gears on several types of rotating compressors and expanders. The invention therefore has an important application also on precision gearwheels.

To minimize the clearances at applications as mentioned above one is today forced to machine the rotors and gearwheels on very accurate machines which is timeconsuming and expensive. Also with this expensive equipment one is forced to accept a - 2 -

relatively large spread of the dimensions for different samples of rotors and gearwheels and thereby also of the clearances in the final machine assembly.

The purpose of the invention is to make it possible to produce the wanted small clearances in a less expensive way and with considerable less spreading. Furthermore will it by the inven¬ tion be possible to manufacture conical rotors at a very low cost. This will be obtained by the characteristic properties mentioned in the patent claims below.

In the following some applications for the invention will be dealt with more in depth. To make it simpler the first descrip¬ tion will be for manufacturing of precision gearwheels, fol¬ lowed by a description of the application on rotors for dis¬ placement machines.

Figures

Fig.l shows schematically a fragmentaric sideview of two inter¬ meshing gearwheels manufactured by conventional methods.

Fig.2 is a section through two teeth on the driven gearwheel in Fig.l who have been shaped as per a first alternative of the invention.

Fig.3 shows section 3-3 in Fig.2 before rolled down.

Fig. shows section 3-3 in Fig.2 after rolled down.

Fig.5 shows in a way corresponding to Fig.2 a second alter¬ native.

Fig.6 shows an example of the run of the sealingzone, which is very important for certain applications of the invention, along a screw compressor rotor.

Fig.7 shows schematically a sideview of two intermeshing rotors when applying the invention. Fig.8 shows a section through the female rotor in Fig.7 shaped as per the invention.

Fig.8A shows a partial section of the female rotor in Fig.8.

Fig.9 shows a section through an alternative male rotor that corresponds to the male rotor in Fig.7 and which has been shaped as per the invention.

Fig.10 shows a female rotor corresponding to Fig.9 and which has been shaped as per the invention.

Fig.lOA shows a partial section valid for both the rotor in Fig.9 and in Fig.10.

Fig.llA,B shows schematically two sideviews of female- and"^" male rotor in a tooth compressor at beginning of com¬ pression, A, and during ongoing compression, B.

Fig.12 shows a sideview of the female rotor in Fig.llA, B when shaped as per the invention.

Fig.l2A shows a partial section through the female rotor in Fig.12.

Gearwheels

Fig.l shows two intermeshing gearwheels, one, 15, driving and the other, 16, driven, who have been manufactured by conven¬ tional methods. The resulting clearance is S.

Fig.2 shows the driven gearwheel 16 shaped as per the inven¬ tion. The non-driven flank 17 of the toothgap has been given a contour 17 which is some tenth of a millimeter higher than the contour 18 which gives the wanted clearance against the driving wheel.

Fig.3 shows how the thus slightly overdimensioned contour 17 of the non-driven flank along its entire width has been given closely located elevations (distance e.g. 05 to 1 mm) with a shape of ridges, tops or pyramids 19 preferably with triangular equilateral or in relation to this more pointed triangular sec¬ tion (height e.g. 0.5 to 1 mm). By this is obtained that the overdimension with a minimum of pressforce (below some 40 tons) can be rolled down from the contour 17 in Fig.3 to the wanted contour 18 in Fig.4. The contour 17 can be obtained by different machining or shaping alternatives, e.g. cutting, chemical (etching), electrically (spark erosion) or plastic (knurling) to be selected optimized with regard to intended application, manufacturing costs and resulting finish.

Required pressforce at the rolling down operation can also be influenced by choice of type of pretreatment. For ridges 19 as in Fig.3 the required pressure is reduced when the top angle of the ridge is reduced. If e.g. a crossing type of pretreat¬ ment pattern is chosen which gives remaining pyramides, the required pressforce gets smaller than for ridges and is further reduced when the top angle of the pyramides is reduced. The rolling down to the wanted contour 18, marked in Fig.4, can be arranged by in a special machine press the driven wheel under rotation against a tool gearwheel and by gradually bringing it closer to this until the intended center distance has been obtained. The teeth of the tool gearwheel has been given the shape that gives the driven wheel its wanted contour to the non-driven flanks of the teeth.

As the different samples of the driven wheel who have been produced by this method will be for all practical purposes identical the spreading of the teeth clearance will almost entirely be depending on the variations of the teeth dimen¬ sions for the various samples of the driving wheel. This means a very important reduction of the variation of the teeth clea¬ rance compared to the conventionally manufactured gearwheels where the variation is depending on the normal spreading of the teeth dimensions of the two gearwheels.

A further reduction of the spreading of the teeth clearance will be obtained if the rolling down is done using the actual driving gearwheel as tool at the rolling down operation. The wanted clearance will be obtained by bringing the gearwheels somewhat closer to each other than what corresponds to nominal center distance. The variation of the teeth dimensions for the different samples of the driving gearwheel results in different degree of rolling down of the pretreated surfaces of the driven gearwheel samples why the variation of the teeth clearance between different pairs of driving and driven wheels will be very small.

The same result as has been described above can be obtained if the flanks of the driving gearwheel have been shaped for rolling down. The tool gearwheel will then have a shape that gives the wanted contour to the non-driving flanks of the driving gearwheel. Also in such a case the driven gearwheel can be used as tool. For gearwheels subject to low load it is pos¬ sible to shape e.g. the two flanks on the driven gearwheel for rolling down as shown in Fig.5. Rolling down can be done by tool gearwheel or by the actual intermeshing driving wheel.

Rotors for screw compressors

The circumstances are different for liquidinjected and for oilfree compressors why the application of the invention for these two types of displacement machines will be dealt with separately below.

For the liquidinjected compressors synhronising of the rotors is normally not installed why one rotor, normally the male rotor, is driving the other while synchronisation is a necessity on oilfree compressors where the rotors to not be destroyed are not permitted to touch.

Furthermore are rotors and surrounding housings at liquid- injected compressors cooled by the injected liquid why the internal clearances are kept during the various running conditions.

For dry oilfree compressors the rotors are either not cooled at all or unsufficiently cooled by bores in the shaft center while surrounding housings often are cooled, entirely or partly. As the rotors by thermal expansion increase in diameter from inlet end towards outlet end the clearances between the two rotors and between rotors and surrounding housings become gradually smaller towards the outlet end during hot running conditions.

This becomes even more marked if the dry compression takes place in one step to 7 bar or higher. One is then forced to dimension the rotors so that rotorcontact at the hot outlet end is avoided during all running conditions. This gives unfavoura¬ bly big clearances along the rotors towards the cooler inlet end. An improved efficiency can be obtained if the rotors are made conical so that they give favourable clearances along the entire rotor length during hot running conditions. The manufac¬ turing costs for making conical rotors with up to now used methods are very high. However this invention gives the possi¬ bility to manuf cture conical rotors at a very low cost which will be apparent from what is said below.

Rotors for liquidinjected compressors

The circumstances are very similar to those for precision gear- wheels. However, an additional factor of high importance is that the small clearances also have to give optimal sealing along the sealingline between the rotors. Fig.6 shows drawn on the male rotor 20, one example on how the sealingzone 21 runs between the rotor 20 and the not shown intermeshing female rotor for a screw compressor with a certain type of conventional rotorprofile. Optimal sealing means that at the pretreatment of the surfaces one wants to make possible to roll down a great number of ridges 19 (Fig.8A) with smallest possible distance (e.g. distance as well as height 0.5 to l mm) who runs in parallel to the sealingline 21 along the entire length of the rotor 22 and distributed periferically around it. The ditches 23 between the ridges 19 can in this parallely running case be left non-filled or filled depending on the results of leakage tests. If for production technique reasons one wants to produce ridges or other patterns who cross the sealingzone, optimal sealing can still be obtained if the ditches that remain between the ridges after the rolling down operation are filled with suitable ceramic (heat-resistant) , polymeric (e.g. teflon-based) or metallic material. Filling with sealing material gives great freedom regarding choice of pretreatment pattern for the rolling down operation.

Fig.7 shows schematically a pair of intermeshing rotors, male rotor 20 and female rotor 22, who as per Fig.8 have the female rotor 22 shaped as per the invention. The concave parts A to B, C to D, E to F, etc. have got an overdimension with contour 17, Fig.8A, who is some tenth of a millimeter higher than the wanted contour 18 which gives the wanted optimal clearance towards the male rotor. The pretreatment of the concave parts AB, CD, EF, etc. of the female rotor before the rolling down to the wanted contour is done in the same ways as have been described above for gearwheels. The most favourable pattern from a sealing point of view is a large number of small ridges 19 as per Fig.δA who runs in parallel to the sealingline 21, Fig.6, between the rotors 20, 22 and who after the rolling down to the wanted contour 18 gets a section as per Fig.δA. Other patterns, e.g. ridges who are perpendicular to the rotor shaft are also possible but requires as mentioned above that re¬ maining ditches after the rolling down are filled with suitable sealing material as the ditches cross the sealingline and otherwise should cause leakage.

The rolling down to the wanted contour 18 marked in Fig.8A takes place by in a special machine pressing the female rotor 22 under rotation towards a male toolrotor, in Fig.7 marked with a dash-dotted line and the alternative indication 30, and by gradually bringing the female rotor closer to it, using the rotor 30 as a counterroll until intended center distance NM has been obtained. Alternatively the male rotor 20 itself could be used as a counterroll. The rotors 30, 20 who work as counter- rolls are given resp. have the shape that gives the concave parts AB, CD, EF, etc. of the female rotor 22 the wanted contour and thereby the wanted clearance towards the convex parts of the male rotors 20 (interlobe clearance) .

As the different samples of the female rotor that have been produced in this way become practically identical the spread of the interlobe clearance will be almost entirely depending on the variations of the dimensions of the different samples of the male rotor. This means a considerable reduction of the variation of the interlobe clearance compared to conventional¬ ly manufactured rotors where the variation is depending on the normal spread of dimensions for the two rotors.

A further reduction of the spread for interlobe clearance can be obtained if the rolling down, as said above, is done by using the actual male rotor as the tool. The wanted clearance is obtained by bringing the rotors somewhat closer to each other than the nominal center distance. The variation between max. and min. dimension of the convex parts of the different samples of the male rotor results in different degree of rolling down of the pretreated surfaces on the female rotors why the variation of interlobe clearance between different pairs of rotors will be very small.

Same result as described above will be obtained if instead the convex parts of the male rotor 20 have been shaped for rolling down. The rolling down operation takes place in the same was as described above against either a female tool rotor or alter¬ natively against the actual female rotor 22. For cases where the specific surface pressure between the rotor surfaces be¬ comes critical it is appropriate to pretreat only the non- loaded which means the non-driving surfaces for rolling down as described above for gearwheels. The rolling down can be done as per the alternative described above.

Rotors for dry oilfree compressors

As the rotors by the synchronization are prevented from touching, both rotors can be pretreated for rolling down of the actual parts if so wanted. The patterns of the pretreatment can not give any mechanical problems as they after the rolling down are not touching.

Furthermore, by different degree of rolling down along the rotors they can be given the wanted slightly conical contour which gives optimal small clearances along the entire rotor length during hot running conditions. This is obtained by using toolrotors which have been made conical to the appropriate degree for the rolling down operation.

Regarding the pretreatment for rolling down same as has been said above regarding rotors for liquid injected compressors is valid. However, if a pretreatment pattern has been chosen which requires filling of remaining ditches it is necessary to con¬ sider that the filling material must stand the higher tempera¬ tures in dry oilfree compressors. Fig.9, 10 and lOA shows how male- and female rotors have been shaped as per the invention. Pretreatment is for the female rotor given to the surfaces A to B, C to D, E to F, etc. and for the male rotor to the sur¬ faces G^Λ to H', I' to J', K' to L', etc. At the rolling down operation the pretreated female rotor 22 is pressed against a tool male rotor which gives the female rotor its wanted con¬ tour including conicity. In the same way the pretreated male rotor 20 is under rotation pressed against a tool female rotor which gives the male rotor its wanted contour including coni¬ city.

The time consuming and costly procedure for manufacturing conical rotors by conventional methods is by application of the invention limited to include only the toolrotors. If these are made of a suitable material that can be hardened the wear on them during the rolling down operation will be very small why the toolrotors can be used for manufacturing of a big number of production rotors.

Rotors for tooth compressors

As example a single-toothed compressor has been chosen. How¬ ever,the invention is equally applicable on multitoothed com¬ pressors. Fig.11 shows schematically the rotors 24, 25 in a single-tooth compressor. For a tooth compressor the sealing line between the rotors is a straight line in parallel with the rotor shafts. The rotors 24, 25 rotate without touching thanks to not shown synchronizing gears. Fig.12, 12A shows the female rotor 24 shaped as per the invention. The rotor surface A over B to C, which during running will seal against the male rotor 25, has from flank to flank been given a contour 17, Fig.l2A, which is some tenth of a millimeter higher than the wanted contour 18.

The optimal pretreatment consists of a big number of small ridges 19 parallel with the sealing line along the circum¬ ference of the female rotor 24 from point A over point B to C and from flank to flank. The rolling down of the pretreated circumference of the female rotor 24 to the wanted contour 18 can be done by pressing the emale rotor under rotation against a male tool rotor who gives the female rotor its wanted contour when the intended center distance has been obtained.

As the different samples of the female rotor who have been produced in this way become practically identical will the spread of the interlobe clearance almost entirely depend on the variation of the dimensions of the different samples of the male rotor. This means a considerable reduction of the varia¬ tion of the interlobe clearance compared with conventionally manufactured rotors where the variation depends on the normal spread of the dimensions of the two rotors.

A further reduction of the spread of the interlobe clearance will be obtained if the rolling down takes place using the actual male rotor as tool for the rolling down operation. The wanted clearance will be obtained by bringing the rotors some¬ what closer than the nominal center^distance. The variation between the maximum- and minimum dimension of the different samples of the male rotor results in different degree of rolling down of the pretreated surfaces of the female rotor why the variation of the interlobe clearance between different pair of rotors will be very small.

Claims

PATENT CLAIMS.

1. Method for manufacturing of interacting rotors for rotating displacement machines and precision gearwheels where inter¬ meshing engaging elements (20, 22, 15, 16) are unrolling relative each other during the rotation, c h a r a c t e ¬ r i z e d t h e r e b y, that at least one of the flanks of the engaging elements (at 17) in a preparative manu¬ facturing operation by pretreatment of at least one of the rotors (22, 20, 24, 16) is given a clearancereducing over- dimension (17) in shape of a pattern of closely located pointed elevations (19) separated by recesses (23), and that, by rolling down against a toolrotor (30, 20) the elevations thereafter are pressed down to a part of their height to a contour (18) who gives the wanted minimized clearance towards the flanks of the engaging elements on the interacting rotor.

2. Method according claim 1, c h a r a c t e r i z e d t h e r e b y, that as toolrotor is used the interacting rotor (20, 22) itself, which during rotation is pressed against the other rotor until the rolling down has given intended centerdistance between the rotors in running condition.

3. Method according claim l, c h a r a c t e r i z e d t h e r e b y, that the roolrotor when manufacturing rotors for screwcompressors is shaped slightly conical to obtain clearance equalization along the rotorlength when the manu¬ factured rotor is running.

4. Method according claim 1, c h a r a c t e r i z e d th e r eb y, that the elevations (19) are shaped as ridges or pyramides, for screwcompressors preferably ridges who run in parallel to the sealing zone (21) between the inter¬ acting rotors (20, 22).

5. Method according claim l or 4, c h a r a c t e r i z e d t h e r e b y, that remaining recesses (23) are filled out with heatresistant polymeric, ceramic or metallic material.

6. Method according claim 1 or 4, c h a r a c t e r i z e d t e r e b y, that the overdi ension of the flanks (at 17) in shape of elevations (19) is produced by cutting, chemical or electric method.

7. Method according claim 1 or 4, c h a r a c t e r i z e d t h e r e b y, that the overdimension (17) in shape of elevations (19) is produced by deforming the flank surfaces plastically as by knurling.

8. Rotorpair manufactured according any of the methods described in the claims above for manufacturing of inter¬ acting rotors for rotating displacement machines and preci¬ sion gearwheels, where intermeshing engaging elements (20, 22, 15, 16, 24, 26) are unrolling relative each other during the rotation, c h a r a c t e r i z e d t h e r e b y, that at least one of the flanks of the engaging elements

(at 17) on at least one of the rotors (22, 20, 15, 16, 24, 26) is equipped with a pattern of closely located pointed elevations (19) separated by recesses (23) the tops of those elevations (19) are deformed by rolling down to a contour (18) for the mentioned flank (18) which is adapted to mini¬ mize its clearance towards the flanks of the engaging elements on the interacting rotor.

9. Rotorpair according claim 8, c h a r a c t e r i z e d t h e r e b y, that the recesses (23) between the eleva¬ tions (19) are filled out with heatresistant material, polymeric, ceramic or metallic.

10. Rotorpair according claims 8 or 9, c h a r a c t e r i ¬ z e d t h e r e b y, that the elevations (19) are shaped of ridges or pyramides with flat tops.