U.S. patent application number 16/756644 was filed with the patent office on 2020-10-15 for screw rotor.
The applicant listed for this patent is Leybold GmbH. Invention is credited to Thomas DREIFERT, Roland MULLER, Nils OLESEN, Stefan WOLTER.
Application Number | 20200325897 16/756644 |
Document ID | / |
Family ID | 1000004956910 |
Filed Date | 2020-10-15 |
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United States Patent
Application |
20200325897 |
Kind Code |
A1 |
DREIFERT; Thomas ; et
al. |
October 15, 2020 |
SCREW ROTOR
Abstract
A screw rotor for screw vacuum pumps, comprising a rotor shaft
which bears at least two displacement elements. The displacement
element is conical in the conveying direction and the adjoining
conveying element has a cylindrical design.
Inventors: |
DREIFERT; Thomas; (Kerpen,
DE) ; WOLTER; Stefan; (Kerpen, DE) ; OLESEN;
Nils; (Koln, DE) ; MULLER; Roland; (Koln,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Leybold GmbH |
Koln |
|
DE |
|
|
Family ID: |
1000004956910 |
Appl. No.: |
16/756644 |
Filed: |
October 9, 2018 |
PCT Filed: |
October 9, 2018 |
PCT NO: |
PCT/EP2018/077471 |
371 Date: |
April 16, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04C 18/16 20130101;
F04C 2/16 20130101 |
International
Class: |
F04C 18/16 20060101
F04C018/16; F04C 2/16 20060101 F04C002/16 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 17, 2017 |
DE |
20 2017 005 336.5 |
Claims
1. Screw rotor for screw vacuum pumps, comprising a rotor shaft, at
least two displacement elements connected with the rotor shaft,
each having at least one helical recess, wherein a suction-side
displacement element is designed tapering in the conveying
direction, wherein a pressure-side displacement element is designed
substantially cylindrically.
2. Screw rotor of claim 1, wherein the suction-side displacement
element is designed to constantly decrease in the conveying
direction.
3. Screw rotor of claim 1, wherein the interior volume ratio is
greater than 8.
4. Screw rotor of claim 1, wherein the displacement element have
substantially the same diameter at the end faces directed towards
each other.
5. Screw rotor of claim 1, wherein the diameter of the
substantially cylindrical displacement element is smaller by 5-35%
than the suction-side diameter of the conical displacement
element.
6. Screw rotor of claim 1, wherein the tapering displacement
element has a volume ratio greater than 4.
7. Screw rotor of claim 1, wherein the at least cylindrical
displacement element has a volume ratio of 1 to 3.
8. Screw rotor of claim 1, wherein the diameter of the tapering
displacement element is 80 to 300 mm in the region of the pump
inlet.
9. Screw rotor of claim 1, wherein the diameter of the tapering
displacement element is 65 to 180 mm in the transition region to
the cylindrical displacement element.
10. Screw rotor of claim 1, wherein the diameter of the
substantially cylindrical displacement element is 65 to 180 mm in
the region of the outlet.
11. Screw rotor of claim 1, wherein the number of windings of the
cylindrical displacement element is greater than 6.
12. Screw rotor of claim 1, wherein the number of windings of the
tapering displacement element is 3 to 6.
13. Screw rotor of claim 1, wherein a further displacement element
is provided that is arranged upstream of the tapering displacement
element in the flow direction, the further displacement element
being preferably substantially cylindrical in shape.
14. Screw vacuum pump with a housing defining a suction chamber and
two screw rotors of claim 1 arranged in the suction chamber.
15. Screw rotor of claim 5, wherein the diameter of the
substantially cylindrical displacement element is smaller by 10-25%
than the suction-side diameter of the conical displacement
element.
16. Screw rotor of claim 6, wherein the tapering displacement
element has a volume ratio greater than 8.
17. Screw rotor of claim 11, wherein the number of windings of the
cylindrical displacement element is greater than 10.
18. Screw rotor of claim 17, wherein the number of windings of the
cylindrical displacement element is greater than 2.
19. Screw rotor of claim 3, wherein the interior volume ratio is
greater than 10.
20. Screw rotor of claim 19, wherein the interior volume ratio is
greater than 12.
Description
BACKGROUND
1. Field of the Disclosure
[0001] The disclosure relates to a screw rotor for a screw vacuum
pump.
2. Discussion of the Background Art
[0002] Screw vacuum pumps comprise a suction chamber in a housing,
in which suction chamber two screw rotors are arranged. Each screw
rotor comprises at least one displacement element with a helical
recess. Thereby, a plurality of windings is formed. With screw
vacuum pump, the goal is always to achieve an internal volume ratio
that is as high as possible. The internal volume ratio is the ratio
of the volume at the inlet of the vacuum pump to the volume at the
outlet of the vacuum pump. Screw vacuum pumps of the first
generation, such as e.g. the pumps LEYBOLD Screwline or BUSCH
Cobra, have an internal volume ratio of approx. 3 to 4. With vacuum
pumps currently on the market, such as e.g. the screw vacuum pumps
LEYBOLD DRYVAC or Edwards GKS, the volume ratio is 5 to 7.
[0003] To achieve low pressures at the pump inlet, a high energy
input is required and the power consumption of a corresponding
vacuum pump is very high, respectively.
[0004] It is an object of the disclosure to provide a screw rotor
for screw vacuum pumps with which it is possible to reduce energy
consumption.
[0005] The disclosure is based on the finding that it is possible
to reduce energy consumption by increasing the internal volume
ratio.
[0006] For a high internal volume ratio the outlet stages of the
pump must have a small delivery volume. However, small outlet
stages have a disadvantageous ratio between transport flow and
return flow, i.e. they are relatively leaky. Thus, only a rather
low pressure build-up can be generated with each single stage. In
order to still realize the major part of the compression in the
small outlet stages, a great number of outlet windings becomes
necessary.
[0007] Basically, two designs of screw rotors are known. These are
screw rotors with either a cylindrical or a conical outer
dimension.
[0008] With cylindrical rotors, the tooth space width at the outlet
must be chosen to be small for high internal volume ratios.
Thereby, the tooth height becomes rather large relative to the
tooth space width, which can be realized in manufacture only with
great effort and at high costs. However, with this rotor design, it
is readily possible to integrate a great number of small outlet
stages in the rotor (if the ratio of tooth height/tooth space width
allows for an economically feasible manufacture). Thus, the
geometrically installed volume ratio also becomes effective
thermodynamically.
[0009] With conical rotors, in contrast, the chamber volume
decreases steadily towards the outlet due to the tapering tooth
height, so that it is possible to produce small outlet volumes with
a ratio between the tooth height and the tooth space width that is
favorable under manufacturing aspects. However, it is difficult to
manufacture a plurality of stages with the low delivery volume,
since the tooth height decreases continuously due to the cone
shape. Although high geometric volume ratios are thus conceivable,
these hardly show the desired effect, since the compression occurs
in the larger stages due to the return flow through the gap.
[0010] It is further known to design staged rotors with two
cylindrical displacement elements having different diameters.
However, a great disadvantage of these staged rotors is the
discontinuous transition which is extremely difficult to
manufacture. Therefore, staged rotors are not common on the
market.
SUMMARY
[0011] The screw rotor of the disclosure comprises a rotor shaft
connected with at least two displacement elements, each
displacement element comprising at least one helical recess.
According to the disclosure a suction-side displacement element,
i.e. a displacement element arranged in the direction of the pump
inlet, in particular at the pump inlet, is designed to taper in the
conveying direction. The displacement element is arranged such that
is tapers in the conveying direction, i.e. towards the pump outlet.
It is particularly preferred that the suction-side displacement
element has an outer contour that is designed to constantly
decrease in the conveying direction. A conical design of the
suction-side displacement element, tapering in the conveying
direction, is particularly preferred. The cone angle is preferably
in a range from 2.degree. to 8.degree..
[0012] Further, a pressure-side displacement element, i.e. a
displacement element provided in the direction of the pump outlet,
in particular at the pump outlet, is designed substantially
cylindrically. The pressure-side displacement element may also be
designed to be slightly conical or slightly decreasing constantly
in the conveying direction. The substantially cylindrically
designed pressure-side displacement element has, in particular, a
diameter ratio from 1.1 to 1.0 between the suction-side diameter
directed towards the pump inlet and the pressure-side diameter
directed towards the pump outlet.
[0013] If so desired, further cylindrical and/or conical
displacement elements can be arranged on the rotor shaft. The
combination of a suction-side tapering, in particular conical
displacement element and a pressure-side substantially cylindrical
displacement element is essential according to the disclosure. This
allows to combine the advantages of both screw rotor designs. The
tooth height is reduced by the preferably conically designed
suction-side displacement element, so that it is possible to
provide the substantially cylindrical displacement element, which
adjoins the former element in the flow or conveying direction, with
a large number of outlet windings with small delivery volumes at a
small ratio between the tooth height and the tooth width. In a
particularly preferred embodiment it is thus possible to realize
internal volume ratios greater than 6, in particular greater than 8
and particularly preferred greater than 10.
[0014] Although more than two displacement elements may be
provided, a conical displacement element arranged on the suction
side and a cylindrical displacement element arranged on the
pressure side are provided in a particularly preferred embodiment.
Hereinafter, the disclosure will be described with reference to
this preferred embodiment, while further displacement elements may
be provided in each case.
[0015] It is preferred that the adjacent displacement elements in
particular abut against each other or contact each other by their
end faces directed towards each other, and that they are
substantially equal in diameter. Thus, a substantially stepless
transition is realized. When providing two displacement elements,
the diameter of the conical displacement element, starting from the
pump inlet, decreases to a diameter that corresponds to the
diameter of the cylindrical displacement element.
[0016] It is further preferred that the diameter of the cylindrical
displacement element is smaller by 5-35%, preferably 10-25%, than
the suction-side diameter of the conical displacement element, i.e.
in particular the diameter of the conical displacement element
provided at the inlet of the pump.
[0017] In a particularly preferred embodiment the lengths and the
diameters of the conical and the cylindrical displacement element
are chosen such that the greater part of the compression is
performed at a low suction pressure by the cylindrical displacement
element. In particular more than 70% of the compression performance
is provided by the cylindrical displacement element.
[0018] As such it is further preferred that the conical
displacement element has an internal volume ratio of more than 4,
in particular more than 8.
[0019] In a preferred embodiment the cylindrical displacement
element has an internal volume ratio greater than 1, in particular
greater than 3. The internal compression is preferably effected by
a decrease in pitch.
[0020] In the transition region between the in particular conical
displacement element and the substantially cylindrical displacement
element no continuous transition of the winding pitch has to be
provided. A step in the winding pitch is also possible so that an
internal compression is caused thereby. The internal compression
can thus be caused already in the transition and/or in the
cylindrical part.
[0021] For further improvement it is preferred according to the
disclosure that the ratio between the tooth height and the tooth
width is less than 3 in the outlet region of the vacuum pump. A
favorable manufacture is possible. In particular the ratio is in a
range from 1.8-2.2. In another preferred embodiment of the
disclosure the length of the substantially cylindrical displacement
element is 25-50% of the total profile length of the screw
rotor.
[0022] In another preferred embodiment the ratio between the outer
diameter of the displacement element at the pump outlet and the
outer diameter of the displacement element at the pump inlet is
less than 0.9, in particular less than 0.85.
[0023] Moreover it is particularly preferred that the diameter of
the tapering displacement element is 80-300 mm in the region of the
pump inlet. In the transition region between the tapering
displacement element and the substantially cylindrical displacement
element, the diameter is preferably 65-180 mm. Correspondingly, in
a preferred embodiment, the outer diameter of the substantially
cylindrical displacement element is also 65-180 mm, wherein in case
of a cylindrical displacement element also tapering slightly this
diameter may also be somewhat smaller than the diameter in the
transition region.
[0024] In a preferred development of the disclosure, the number of
windings of the cylindrical displacement element is at least 6 or
preferably at least 10 and particularly preferred at least 12. By
providing a great number of windings of the cylindrical
displacement element the major part of the compression can be
performed by the same.
[0025] In a preferred embodiment the in particular conical
suction-side displacement element has 3-6 windings.
[0026] The individual displacement elements are preferably formed
as separate components and are connected to the rotor shaft e.g. by
being pressed thereon. However, it is also possible that individual
or all displacement elements are formed integrally with the rotor
shaft.
[0027] The rotor shaft further preferably comprises cylindrical
subs at both ends that serve as bearing seats. However, it is also
possible to support the screw rotor in an overhung manner, i.e. on
one side.
[0028] Basically the screw rotor of the disclosure can be
manufactured from known materials, such as steel, cast iron or
aluminum, with the advantage of the disclosure being realizable in
particular with screw rotors of steel or cast iron.
[0029] In a preferred development of the disclosure a further
displacement element is provided on the suction side. The further
displacement element is thus arranged upstream of the in particular
conical displacement element that tapers in the conveying
direction. The further displacement element preferably is an also
substantially cylindrical displacement element. Here, it is
preferred that the pitch of the windings of this further
displacement element decreases in the conveying direction.
[0030] Further, the disclosure relates to a screw vacuum pump with
two screw rotors arranged in a suction chamber defined by a
housing. Here, the two screw rotors are designed or developed
according to the disclosure, as described above.
[0031] The disclosure will be explained hereinafter in more detail
with reference to a preferred embodiment and to the accompanying
drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The FIGURE is a schematic side view of an embodiment of a
screw rotor according to the disclosure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0033] The screw rotor illustrated comprises a rotor shaft 10
supporting two displacement elements 12, 14. The two cylindrical
ends 16, 18 of the rotor shaft serve to receive bearings for
supporting the screw rotor in a pump housing. It is also possible
to support the rotor shaft in an overhung manner, i.e. on one
side.
[0034] The displacement element 12 on the right in the FIGURE is
conical and tapers in the conveying direction 22 from a pump inlet
20 which is arranged on the right in the FIGURE but not illustrated
therein, towards a pump outlet 24 which is arranged on the left in
the FIGURE but not illustrated therein. A helical recess 26 of the
conical displacement element 12 is designed such that the volume
decreases. This is achieved on the one hand due to the conical
outer shape of the displacement element 12 and on the other hand
due to the inner portion 28 of the displacement element 12 widening
in the conveying direction. Individual chamber volumes formed by
the two meshing screw rotors thus reduce their respective volume in
the conveying direction 22.
[0035] In the embodiment illustrated in which only two displacement
elements 12, 14 are provided, an end face 30 of the displacement
element 12 which is directed towards the pump outlet 24 or towards
the pressure side of the pump, abuts on an end face 32 of the
cylindrical displacement element 14. The end face 32 is directed
towards the pump inlet or in the direction of the suction side of
the vacuum pump. The diameters of the two displacement elements 12,
14 are substantially the same in the region of the end faces 30,
32.
[0036] The cylindrical displacement element 14 has a helical recess
34 as well.
[0037] In the embodiment illustrated the same has a constant pitch,
wherein a decrease in pitch is also possible in the conveying
direction 22 for further compression. Due to the recess 34 8
windings are formed in the embodiment illustrated.
* * * * *