U.S. patent application number 12/530601 was filed with the patent office on 2010-07-15 for vacuum pump.
Invention is credited to Emmanuel Uzoma Okoroafor.
Application Number | 20100178187 12/530601 |
Document ID | / |
Family ID | 38050354 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100178187 |
Kind Code |
A1 |
Okoroafor; Emmanuel Uzoma |
July 15, 2010 |
VACUUM PUMP
Abstract
A dry vacuum pump comprises a stator component and at least one
rotor component. To improve the tolerance of the pump to corrosive
gases passing through the pump, the stator component and/or said at
least one rotor component are formed from silicon-molybdenum (SiMo)
ductile iron.
Inventors: |
Okoroafor; Emmanuel Uzoma; (
Hampshire, GB) |
Correspondence
Address: |
Edwards Vacuum, Inc.
2041 MISSION COLLEGE BOULEVARD, SUITE 260
SANTA CLARA
CA
95054
US
|
Family ID: |
38050354 |
Appl. No.: |
12/530601 |
Filed: |
February 26, 2008 |
PCT Filed: |
February 26, 2008 |
PCT NO: |
PCT/GB08/50128 |
371 Date: |
February 8, 2010 |
Current U.S.
Class: |
418/55.2 ;
418/191; 418/206.9 |
Current CPC
Class: |
F04C 25/02 20130101;
F04C 18/123 20130101; F04C 2220/12 20130101; F05C 2201/0442
20130101; F05C 2201/0433 20130101; F04C 18/0215 20130101; F05C
2201/90 20130101; F04C 18/16 20130101; F04C 18/126 20130101 |
Class at
Publication: |
418/55.2 ;
418/206.9; 418/191 |
International
Class: |
F04C 25/02 20060101
F04C025/02; F04C 18/12 20060101 F04C018/12; F04C 18/02 20060101
F04C018/02; F04C 18/16 20060101 F04C018/16 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2007 |
GB |
0705971.0 |
Claims
1. A dry vacuum pump stator component, wherein the stator component
is formed from silicon-molybdenum (SiMo) ductile iron alloy.
2. A dry vacuum pump rotor component, wherein the rotor component
is formed from silicon-molybdenum (SiMo) ductile iron alloy.
3. A dry vacuum pump comprising a stator component and at least one
rotor component, wherein the stator component and/or said at least
one rotor component are formed from silicon-molybdenum (SiMo)
ductile iron alloy.
4. The pump according to claim 3, wherein the alloy contains
silicon in an amount from about 3.5 to about 5 wt %.
5. The pump according to claim 3, wherein the alloy contains
molybdenum in an amount from about 0.4 to about 1 wt %.
6. The pump according to claim 3, wherein said at least one rotor
component has one of a screw, Roots or Northey profile.
7. The pump according to claim 6, comprising first and second
intermeshing rotor components adapted for counter-rotation within
the stator component.
8. The pump according to claim 7, wherein intermeshing rotor
components are located on respective shafts, the pump comprising a
gear assembly for transmitting torque from one shaft to another, at
least one gear of the gear assembly being formed from SiMo ductile
iron alloy.
9. The pump according to claim 3, in the form of a multi-stage dry
vacuum pump in which the stator component defines a plurality of
interconnected pumping chambers each housing a respective pair of
rotor components each formed from SiMo ductile iron alloy.
10. The pump according to claim 3, in the form of a scroll pump in
which the stator component comprises a fixed scroll member having
an end plate with a first spiral wrap extending therefrom, and said
at least one rotor component comprises an orbital scroll member
having an end plate with a second spiral wrap extending therefrom
to intermesh with the first spiral wrap.
Description
[0001] Dry vacuum pumps are widely used in industrial processes to
provide a clean and/or low -pressure environment for the
manufacture of products. Applications include the pharmaceutical,
semiconductor and flat panel manufacturing industries. Such pumps
include an essentially dry (or oil free) pumping mechanism, but
generally also include some components, such as bearings and
transmission gears, for driving the pumping mechanism that require
lubrication in order to be effective. Examples of dry pumps include
Roots, Northey (or "claw"), screw and scroll pumps. Dry pumps
incorporating Roots and/or Northey rotor components are commonly
multi-stage positive displacement pumps comprising a stator
component defining a plurality of pumping chambers each housing a
respective pair of intermeshing rotor components. The rotor
components are located on contra-rotating shafts, and may have the
same type of profile in each chamber or the profile may change from
chamber to chamber.
[0002] Iron castings have for a long time been used in the
manufacture of stator and rotor components for dry vacuum pumps.
However, in the semiconductor industries the increasing use of high
flow rates of relatively corrosive gases such as chlorine, boron
trichloride, hydrogen bromide, fluorine and chlorine trifluoride
has lead to severe corrosion, and therefore relatively short
lifetime, of, cast iron stator and rotor components. Such corrosion
can lead to equipment failure, leakage of process gases and
possible process contamination, in addition to the costs associated
with the replacement of the pump or the corroded parts and
consequential process downtime.
[0003] In view of this, it is known to passively protect these
components by the formation of a resin or polymeric coating of a
fluoropolymer or polyimide material on the component surfaces which
are exposed to the corrosive gases. Such coatings have a tendency
to degrade with time, with the resultant peeling or flaking of the
coating exposing the underlying cast iron to the corrosive gases.
Another alternative is to form these components from a nickel-rich
cast iron, for example ductile Ni-resist, or a stainless steel
having superior corrosion resistance. However, Ni-resist cast iron
and stainless steel are relatively expensive and s difficult to
machine, and so do not provide cost-effective options for use in
the manufacture of the rotor and stator components.
[0004] The present invention provides at least one dry vacuum pump
stator component, wherein the stator component is formed from
silicon-molybdenum (SiMo) ductile iron alloy.
[0005] The present invention also provides at least one dry vacuum
pump rotor component, wherein the rotor component is formed from
silicon-molybdenum (SiMo) ductile iron alloy.
[0006] The present invention also provides a dry vacuum pump
comprising a stator component and at least one rotor component,
wherein the stator component and/or said at least one rotor
component are formed from silicon-molybdenum (SiMo) ductile iron
alloy.
[0007] The alloy may contain silicon in an amount from about 3.5 to
about 5 wt %. The alloy may contain molybdenum in an amount from
about 0.4 to about 1 wt %.
[0008] The stator component may house first and second intermeshing
rotor components adapted for counter-rotation within the stator
component. In the preferred embodiment, the rotor components have a
Roots profile, although they could have a Northey or screw profile
as required.
[0009] The pump may be in the form of a multi-stage pump in which
the stator component defines a plurality of interconnected pumping
chambers arranged in series and each housing respective rotor
components formed from SiMo ductile iron alloy. The intermeshing
rotor components may be located on respective shafts, with the pump
comprising a gear assembly for transmitting torque from one shaft
to another, with at least one gear of the gear assembly preferably
being formed from SiMo ductile iron alloy.
[0010] Alternatively, the pump may be in the form of a scroll pump
in which the stator component comprises a fixed scroll member
having an end plate with a first spiral wrap extending therefrom,
and said at least one rotor component comprises an orbital scroll
member having an end plate with a second spiral wrap extending
therefrom to intermesh with the first spiral wrap. Each of the
scroll members is preferably formed from SiMo iron alloy.
[0011] Preferred features of the present invention will now be
described, by way of example only, with reference to the following
drawings, in which:
[0012] FIG. 1 is a cross-section through a multi-stage dry vacuum
pump; and
[0013] FIG. 2 is a view along line A-A in FIG. 1.
[0014] With reference to FIGS. 1 and 2, a multi-stage dry vacuum
pump 10 comprises a stator component 12, preferably formed from
silicon-molybdenum (SiMo) ductile iron alloy, having a series of
walls that define a plurality of pumping chambers 14, 16, 18, 20,
22. An inlet conduit 24 for conveying gas to be pumped to the inlet
pumping chamber 14, and an exhaust conduit 26 for exhausting pumped
gas from the exhaust pumping chamber 22, are also formed in the
stator 12. Passages 28, 30, 32 and 34 formed in the stator 12
connect the pumping chambers 14, 16, 18, 20, 22 in series.
[0015] The stator 12 houses a first shaft 36 and, spaced therefrom
and parallel thereto, a second shaft 38. Bearings 40 for supporting
the shafts 36, 38 are provided in the end plates 42, 44 of the
stator 12. One of the shafts 36 is connected to a drive motor 46,
the shafts being coupled together by means of timing gears 47 so
that in use the shafts 36,38 rotate at the same speed but in
opposite directions, as indicated by arrows 48 and 50 in FIG. 2. A
gear box 52 attached to the side of the pump 10 contains oil 54 for
lubricating the timing gears 47. The timing gears 47 may be formed
from SiMo ductile iron alloy.
[0016] Within each pumping chamber, the shafts 36, 38 support
respective rotor components 56, 58, which may also be formed from
SiMo ductile iron alloy. In this embodiment, the rotors 56, 58 have
a Roots-type profile within each pumping chamber, although a
mixture of Roots and Northey-type profiles may be provided within
the pump 10. The rotors 56, 58 are located in each pumping chamber
relative to an internal surface of the stator 12 such that the
rotors 56, 58 can act in an intermeshing manner known per se.
[0017] In use, gas is urged into the pump 10 through the inlet
conduit 24 and passes into the inlet pumping chamber 14. The gas is
compressed by the rotors 56, 58 located within the inlet pumping
chamber 14, and is fed by passage 28 into the next pumping chamber
16. The gas fed in the pumping chamber 16 is similarly compressed
by the rotors 56, 58 therein, and fed by the passage 30 to the next
pumping chamber 18. Similar gas compressions take place in the
pumping chambers 18, 20 and 22, with the pumped gas finally being
exhaust from the pump 10 through exhaust conduit 26.
[0018] The SiMo ductile iron alloy preferably contains silicon from
about 3.5 to about 5 wt %, and/or molybdenum in an amount from
about 0.4 to about 1 wt %.
[0019] The use of SiMo ductile iron alloy to manufacture the stator
component 12 and/or the rotor components 56, 58 of the pump 10
makes the pump 10 particularly suitable for pumping corrosive gases
such as chlorine, boron trichloride, hydrogen bromide, fluorine and
chlorine trifluoride. In comparison to the more expensive Ni-resist
material, which are currently around four to five times more
expensive than SiMo ductile iron alloy, SiMo ductile iron alloy has
superior hardness, specific strength ratio and F.sub.2 corrosion
susceptibility. This can enable the stator and rotor components,
and the timing gears, to have relatively high wear and corrosion
resistance with reduced component weight and costs for equivalent
or improved performances.
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