U.S. patent application number 11/415805 was filed with the patent office on 2006-12-14 for stator disc for a turbomolecular pump.
This patent application is currently assigned to PFEIFFER VACUUM GMBH. Invention is credited to Tobias Stoll.
Application Number | 20060280595 11/415805 |
Document ID | / |
Family ID | 36997487 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060280595 |
Kind Code |
A1 |
Stoll; Tobias |
December 14, 2006 |
Stator disc for a turbomolecular pump
Abstract
A stator disc for a turbomolecular pump has an inner ring (3),
an outer ring (4), and a plurality of vanes (2) formed of a stator
disc plane, extending between the inner and outer rings (3, 4), and
having, in connection regions of the vanes with the inner and outer
rings, respective radial webs (5) a circumferential width (S) of
which is smaller than a vane width (T).
Inventors: |
Stoll; Tobias;
(Angelburg-Goennern, DE) |
Correspondence
Address: |
ABELMAN, FRAYNE & SCHWAB
666 THIRD AVENUE, 10TH FLOOR
NEW YORK
NY
10017
US
|
Assignee: |
PFEIFFER VACUUM GMBH
|
Family ID: |
36997487 |
Appl. No.: |
11/415805 |
Filed: |
May 1, 2006 |
Current U.S.
Class: |
415/90 |
Current CPC
Class: |
F04D 29/542 20130101;
F04D 19/042 20130101; F05B 2230/10 20130101 |
Class at
Publication: |
415/090 |
International
Class: |
F01D 1/36 20060101
F01D001/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 11, 2005 |
DE |
10 2005 027 097.2 |
Claims
1. A stator disc for a turbomolecular pump, comprising an inner
ring (3); an outer ring (4); and a plurality of vanes (2) formed of
a stator disc plane, extending between the inner and outer rings
(3, 4), and having, in connection regions of the vanes with the
inner and outer rings, respective radial webs (5) a circumferential
width (S) of which is smaller than a vane width (T).
2. A stator disc according to claim 1, wherein the radial web (5)
is arranged at a half distance between opposite edges (20, 21) of a
respective vane.
3. A stator disc according to claim 1, wherein the circumferential
width (S) of a web (5) varies from about one/tenth to about
one/second of the vane depth (T).
4. A stator disc according to claim 1, wherein the stator disc is
formed of at least two identical disc sections.
5. A turbomolecular pump, comprising a housing including a flange
for connecting the pump with a pump-out recipient and having a
suction region, and an outlet; a rotor shaft arranged in the
housing and carrying a plurality of rotor discs provided with
vanes; a drive for driving the rotor shaft; and a plurality of
stator discs fixedly secured in the housing and arranged between
the rotor discs, at least one of the stator discs having a
plurality of vanes formed of a stator disc plane, extending between
the inner and outer rings (3, 4), and having, in connection regions
of the vanes with the inner and outer rings, respective radial webs
(5) a circumferential width (S) of which is smaller than a vane
width (T).
6. A method of forming a stator disc for a turbomolecular pump,
comprising the steps of producing semi-circular discs with
substantially radial slots by one of stamping and laser cutting;
forming circumferential slots at opposite ends of the radial slots;
and thereafter, curving out material between the radial slots so
that it is squeezed out of planes of the discs in such a way that
vanes with a web between a respective vane and at least one of the
outer and inner disc edges are formed.
7. A method according to claim 6, wherein all of the vanes are
formed at once.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a stator disc for a
turbomolecular pump and having a plurality of vanes curved out of
the disc plane and having their opposite ends connected with the
outer and inner rings of the disc.
[0003] 2. Description of the Prior Art
[0004] In turbomolecular pumps rotor and stator discs are
alternatively arranged, with the rotor discs being arranged on a
rapidly rotatable shaft. The stator discs are fixedly secured in
the pump housing. Both types of discs have vanes, and their
cooperation, together with a rapid rotation, produces the pumping
effect. It is known to produce the vanes of both types of discs by
milling them out of solid discs. This process is time-consuming and
expensive. That is why stamped stator discs are used. Such discs
are disclosed, e.g., in German Laid-Open Application DE-0S 37 22
164. In the disclosed process, solid discs are stamped out of sheet
metal. Then, radial slots are stamped out in the discs. In the last
step, the regions between the slots are set so that disc material
is squeezed out of the disc plane so that vanes are formed. The
regions, which are not set in inner and outer regions remain as
rings.
[0005] The drawback of the known state of the art technology
consists in that in connection regions between the inner ring and
the vanes or between the vanes and the outer ring, a large degree
of deformation takes place. In addition, the forces with which the
necessary degree of deformation can be achieved, are very large.
This type of deformation leads to high stresses in the material
which results in the distortion of the disc and the necessary
process of straightening the disc. This adversely affects the
achievable precision of the disc shape. However, the disc shape
precision is very important when small clearances between the
rotor, stator and housing components need be achieved. The pump
output of turbomolecular pumps depends on the clearance
dimensions.
[0006] A further drawback of the known process consists in that the
process requires use of extravagant and, therefore, very expensive
tools. A flexible dimensioning of discs, which should be optimally
adapted to the operative range of a pump, i.e., to vacuum-technical
requirements, cannot be realized with justifiable costs at a small
number of workpieces.
[0007] The object of the invention is to eliminate these drawbacks
of the state of the art, to provide for use of cost-effective
manufacturing tools, and to achieve a high precision of stator
discs.
[0008] Another object of the invention is to eliminate the high
degree of the deformation.
SUMMARY OF THE INVENTION
[0009] These and other objects of the present invention, which will
become apparent hereinafter, are achieved by providing a stator
disc in which the vanes extending between the inner and outer rings
have in connection regions of the vanes with the inner and outer
rings, respective radial webs a circumferential width of which is
smaller than a vane width.
[0010] In comparison with the state of the art, the inventive
stator disc has a smaller deformable material region which,
moreover, requires a smaller degree of deformation. As a result,
stresses in the component are reduced, which eliminates
straightening costs. With the elimination of a need for
straightening, a higher precision of the disc measurements can be
achieved. Because of smaller deformation forces and fewer
operational steps are required, cheaper tools can be used. The
portion of the tool costs within overall manufacturing costs is
reduced, which makes adaptation of the stator disc to the
vacuum-technical requirements economical.
[0011] Because with the inventive stator disc, the disc dimensions
can be retained better than in the state of the art, the use of the
inventive stator disc in a turbomolecular pump results in reduction
of the clearances within the pumps and, thereby, in improvement of
the pumping action.
[0012] According to the inventive manufacturing method or process,
firstly, semi-circular disc members with substantially radial slots
are produced by stamping or laser cutting. Then, circumferential
slots are formed at opposite ends of the radial slots. Finally, the
material between the radial slots is curved out so that it is
squeezed out of planes of the discs in such a way that vanes with a
web between a respective vane and at least one of the outer and
inner disc edges are formed. This inventive manufacturing process
permits to achieve the above-described advantages regarding
deformation expenses and material stresses.
[0013] Arrangement of the web at a half distance between opposite
edges of a vane provides for a uniform loading of the web. The web
loading is caused by the different gas pressure above and beneath
the stator disc. Because of a symmetrical arrangement, the torques
which act on the web, have the same power but opposite signs. As a
result, no resulting torque appears on the radial axis of the vane
and the web. This reduces the loading of the material.
[0014] The maximum width of the web in the circumferential
direction or the circumferential width of the web is limited by the
fact that deformation and material stresses are increased with an
increased width. The minimum width is limited by the required
strength and heat transfer. The strength should insure that the web
is able to withstand the mechanical loads applied to the web as a
result, e.g., by an increased pressure drop across the stator disc.
In addition, the web has to have an appropriate cross-section that
would insure a satisfactory heat transfer. Advantageously, the
ratio of the web width to the vane width is selected within a range
from one/tenth to one/second.
[0015] A further manufacturing advantage results from forming the
stator disc of a plurality of identical disc sections. In this
case, only a single form for the disc section is necessary. This
also facilitates assembly as the disc sections cannot be mixed
and/or improperly combined.
[0016] A further manufacturing advantage is achieved by forming the
vanes in a single step, all at once, curving simultaneously all of
the vanes of a disc out of the disc plane. This permits to
significantly reduce the operational time.
[0017] The novel features of the present invention, which are
considered as characteristic for the invention, are set forth in
the appended claims. The invention itself, however, both as to its
construction and its mode of operation, together with additional
advantages and objects thereof, will be best understood from the
following detailed description of preferred embodiment, when read
with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The drawings show:
[0019] FIG. 1 a cross-sectional view of a turbomolecular pump with
stator discs according to the present invention;
[0020] FIG. 2 a plan view of a stator disc according to the present
invention; and
[0021] FIG. 3 a perspective view of a section of a stator disc
according to the present invention, with the cut-out showing a web
between a vane and an outer disc.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] A turbomolecular pump 10, which is shown in FIG. 1, has a
housing 11 with a flange 12 for connecting the pump 10 with a
pumped-out recipient. The flange 12 contains a suction region 13.
The turbomolecular pump 10 has an outlet 14 from which the
compressed gas is expelled. The turbomolecular pump 10 has a rotor
shaft 15 which is supported in bearings 17 and is driven, with high
speed, by a drive 18. The rotor shaft 15 carries a plurality of
discs 16, each carrying vanes. Stator discs 1, which are likewise
provided with vanes, are arranged between the rotor discs 16 and
are fixedly secured in the housing 11. The stator discs 1 are hold
at a distance from each other by spacer rings 19. The pumping
action produced by a rapid rotation of the rotor discs 16 and their
cooperation with the stator discs 1.
[0023] The stator disc 1 according to the present invention, which
is used in the turbomolecular pump 10 and a plan view of which is
shown in FIG. 2, is formed of two half-discs 6 and 7 which are
mounted about the rotor shaft from opposite sides upon assembly of
the turbomolecular pump. The stator disc 1 has an outer ring 4 with
which it is held in the housing of the turbomolecular pump, and an
inner ring 3. Between the outer ring 4 and the inner ring 3, there
are arranged a plurality of vanes 2. The vanes are formed upon
formation, in a solid material, substantially radial slots 8 and
slots 9 in the circumferential direction. As a result of formation
of slots 8 and 9, webs 5 are formed in connection regions between
the outer and inner rings and the vanes. The circumferential width
of the webs is designated with S, and the vane width is designated
with T. The vane width T is greater than the web depth S.
[0024] FIG. 3 shows a perspective view of a cut-out of the stator
disc 1 that clarifies how the vanes are formed in a disc plane. In
the connection region between the outer ring 4 and the vane 2, the
plane of which is inclined relative to the disc plane, the web 5 is
formed. With the web, the circumferential width S of which is
smaller than the vane width T, the amount of the to-be-deformed
material is reduced. The radial dimension of the web is designated
with R. Conventionally, the deformation region along the
circumference is as large as the depth T. At a large inclination of
the vane relative to the disc plane, a very significant deformation
of the material takes place, with the above-discussed drawbacks.
With formation of the web 5, a significant deformation is not any
more necessary. The deformation is essentially limited to the
shorter region S, which permits to obtain the above-discussed
advantages. The dimensions S and R cannot be made arbitrary small.
The geometrical dimensions of the web are selected based on a load
carrying ability and a maximum possible heat transfer. Within the
pump, in particular in the rotor, a large amount of heat is
generated as a result of compression and friction of the compressed
gasses. Another source of heat is the drive which operates not
without losses. This heat is transferred from the rotor to the
stator discs by radiation, and it should be able to be removed by
the webs. A ratio of S to T of 1:10 to 1:2 proved itself to be
favorable and practical.
[0025] Additional advantages are achieved when the web 5 is
arranged at a half distance between the vane edges 20 and 21.
[0026] In the first step of the process of forming the stator disc
1, first, semi-circular discs with the substantially radial slots 8
are produced by stamping or laser cutting. The further treatment is
carried out in such a way that at the ends of the radial slots,
further slots 9 in the circumferential direction, are produced, so
that a web 5 is formed between the vane 2 and at least the inner
ring 3 or the outer ring 4. Finally, the material between the
radial slots is so curved that it is squeezed out of the disc plane
in such a way that a vane 2 is formed. For squeezing the material
out, the disc, e.g., is placed between upper and lower forms, with
the two forms being pressed against each other.
[0027] Though the present invention was shown and described with
references to the preferred embodiment, such is merely illustrative
of the present invention and is not to be construed as a limitation
thereof and various modifications of the present invention will be
apparent to those skilled in the art. It is therefore not intended
that the present invention be limited to the disclosed embodiment
or details thereof, and the present invention includes all
variations and/or alternative embodiments within the spirit and
scope of the present invention as defined by the appended
claims.
* * * * *