Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C25/00—Adaptations of pumps for special use of pumps for elastic fluids
  • F04C25/02—Adaptations of pumps for special use of pumps for elastic fluids for producing high vacuum
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C18/00—Rotary-piston pumps specially adapted for elastic fluids
  • F04C18/08—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing
  • F04C18/12—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type
  • F04C18/126—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type with radially from the rotor body extending elements, not necessarily co-operating with corresponding recesses in the other rotor, e.g. lobes, Roots type
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C23/00—Combinations of two or more pumps, each being of rotary-piston or oscillating-piston type, specially adapted for elastic fluids; Pumping installations specially adapted for elastic fluids; Multi-stage pumps specially adapted for elastic fluids
  • F04C23/001—Combinations of two or more pumps, each being of rotary-piston or oscillating-piston type, specially adapted for elastic fluids; Pumping installations specially adapted for elastic fluids; Multi-stage pumps specially adapted for elastic fluids of similar working principle
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C18/00—Rotary-piston pumps specially adapted for elastic fluids
  • F04C18/08—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing
  • F04C18/12—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type
  • F04C18/123—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type with radially or approximately radially from the rotor body extending tooth-like elements, co-operating with recesses in the other rotor, e.g. one tooth
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C2210/00—Fluid
  • F04C2210/10—Fluid working
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C2220/00—Application
  • F04C2220/10—Vacuum
  • F04C2220/12—Dry running
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C2220/00—Application
  • F04C2220/30—Use in a chemical vapor deposition [CVD] process or in a similar process
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05C—INDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
  • F05C2201/00—Metals
  • F05C2201/04—Heavy metals
  • F05C2201/0433—Iron group; Ferrous alloys, e.g. steel
  • F05C2201/0436—Iron
  • F05C2201/0439—Cast iron
  • F05C2201/0442—Spheroidal graphite cast iron, e.g. nodular iron, ductile iron

Definitions

• the present invention relates to a vacuum pump, and particular to a vacuum pump suitable for pumping corrosive fluids.
• a known vacuum pump 50 is shown in Figure 7 which comprises a pumping mechanism 52.
• the pumping mechanism comprises a plurality of pumping stages 54 for pumping fluid along a fluid flow path 56 between an inlet 58 for fluid at high vacuum and an outlet 60 for fluid at low vacuum to atmospheric pressure. Five pumping stages 54 are shown.
• a motor 62 drives rotation of the rotors R relative to the stators S in each of the pumping stages 54.
• the fluid being pumped comprises a corrosive agent, such as fluorine
• corrosion is caused to the pumping mechanism 52. Over time, corrosion causes build up of deposits on the surface of components of the pumping mechanism which causes a reduction in the running clearances between the rotors R and the stators S of the pumping stages 54. After continued operation of the pump over many hours the corrosion can bring the rotors and stators of the pumping stages into contact causing pump failure.
• the present invention provides a vacuum pump for pumping corrosive fluid, the pump comprising: a pumping mechanism comprising a plurality of pumping stages along a fluid flow path between an inlet for fluid at high vacuum and an outlet for fluid at low vacuum, and wherein the material of the pumping mechanism at a first section of said flow path is less resistant to corrosion than the material of the pumping mechanism at a second section of said flow path downstream of said first section.
• Figure 1 shows a simplified section through a vacuum pump
• Figure 2 is a graph showing corrosive build-up over time against pump reference temperature for a pump having a pumping mechanism made from a material which is relatively non-corrosion resistant
• Figure 3 is a graph showing corrosive build-up over time against pump reference temperature for a pump having a pumping mechanism made from a material which is relatively corrosion resistant
• Figure 4 is a graph showing corrosive build-up over time against pump reference temperature for a pump having a pumping mechanism made from a material which is relatively non-corrosion resistant and a material which is relatively corrosion resistant;
• Figure 5 is a table showing properties of corrosion and non-corrosion resistant materials
• Figure 6 is a table showing an example of the constituents of a corrosion resistant material
• Figure 7 is a simplified section through a prior art vacuum pump.
• a multi-stage vacuum pump 10 for pumping corrosive fluid.
• a pumping mechanism 12 comprises a plurality of pumping stages 14 for pumping fluid along a fluid flow path 16 between an inlet 18 for fluid at high vacuum and an outlet 20 for fluid at low vacuum to atmospheric pressure. Five pumping stages 14 are shown in this example.
• a motor 22 drives rotation of a rotor R relative to a stator S in each of the pumping stages 14.
• Figure 2 shows a graph in which corrosion build-up over time (10,000 hours in this example) is plotted against pump reference temperature for the prior art pump.
• a first line shows build-up at the faces of the rotor and stator of a middle pumping stage along the flow path 56 and a second line shows build-up at the faces of the rotor and stator of a final pumping stage along the flow path 56.
• the middle pumping stage in this example is the 3 rd stage.
• Corrosive build-up is measured in microns and temperature is measured in degrees centigrade.
• the temperature used in the graph is a pump reference temperature taken at the final pumping stage.
• the temperature of the middle pumping stage is less than that shown in the graph but for simplicity has not been shown.
• the pump reference temperature increases during operation and the increase is dependent on a number of factors such as the type of fluid which is pumped and the work exerted by the pump.
• the material from which the pumping mechanism is made is relatively non-corrosion resistant.
• An example of such a material is SG iron. It will be seen from Figure 2 that corrosive build-up of the final stage is considerably greater than that of the middle pumping stage, particularly when the pump reference temperature is at 200 0 C. At this reference temperature, corrosive build-up at the final stage is just lower than 400 ⁇ m, whereas at the middle stage, build-up is only just higher than 50 ⁇ m.
• Figure 3 shows an equivalent graph as shown in Figure 2, except in this analysis the material from which the pump is made is relatively corrosion resistant.
• An example of such a material is Ni-rich SG iron.
• corrosive build-up at both the middle and final pumping stages is reduced, but build-up at the final pumping stage has been reduced by around 300 ⁇ m to just lower than lOO ⁇ m whereas build-up at the middle pumping stage has been reduced by only around 30 ⁇ m to around 20 ⁇ m.
• the pressure of fluid along the flow path 56 increases from the inlet 58 to the outlet 60 as fluid is compressed by each pumping stage 54, typically with the compression ratio increasing from one pumping stage to the next pumping stage along the flow path.
• the temperature of the fluid and the pumping mechanism also increases along the flow path.
• the fluid being pumped comprises a corrosive agent, such as fluorine
• a corrosive agent such as fluorine
• the amount of corrosion caused to the pumping mechanism 52 increases along the flow path 56 as temperature and pressure increase.
• Increased pressure increases the amount of corrosive molecules available for corroding the pumping mechanism and increased temperature increases corrosive reaction. Therefore, corrosive build-up is greater at the final pumping stage than at the middle pumping stage. Accordingly, pump failure occurs because of the reduction in running clearance at the final stage of the pumping mechanism where build-up is greatest. Whilst corrosion resistance can be increased as shown in Figure 3, pump failure often occurs at the final stage of the pumping mechanism.
• the first section 24 and the second section 26 comprise a respective plurality of pumping stages 14.
• the first section is adjacent to the second section along the fluid flow path.
• the first section comprises 1 st , 2 nd and 3 rd pumping stages whilst the second section 26 comprises 4 th and 5 th pumping stages.
• one of the first and the second sections may comprise a single pumping stage.
• the first section may comprise 1 st to 4 th pumping stages whilst the second section may comprise the 5 th pumping stage.
• stages 1 to 4 may be manufactured from a material which is less corrosion resistant.
• the first section may comprise the 1 st pumping stage and the second section may comprise the 2 nd to 5 th pumping stages.
• a graph equivalent to the graphs shown in Figures 2 and 3 is shown in Figure 4, which plots corrosive build-up against pump reference temperature for the pump shown in Figure 1.
• Figure 4 shows at 200 0 C that corrosive build-up at the final stage of the pumping mechanism has been reduced from around 400 ⁇ m as shown in Figure 2 to just lower than lOO ⁇ m as is the case with a corrosion resistant pump according to Figure 3.
• corrosive build-up at the middle, or 3 rd , stage is the same as that shown in Figure 2 for a non-corrosion resistant pump.
• the corrosive buildup of the middle stage is around 50 ⁇ m which is less than that of the final stage even though the middle stage is made from a non-corrosion resistant material (e.g. SG iron) and the final stage is made from a corrosion resistant material (e.g. Ni-rich iron). Therefore, there is no benefit to be gained from making both the first section and the second section of a pumping mechanism from a corrosion resistant material and doing so would unnecessarily add to the cost of a pump.
• a non-corrosion resistant material e.g. SG iron
• a corrosion resistant material e.g. Ni-rich iron
• Materials should be selected for the first and second sections so that the build-up of corrosive deposits at the first section is less than or equal to the build-up of corrosive deposits at the second section.
• the components of said pumping stages are fabricated from selected materials such that the build-up of corrosion deposits in each stage during pumping of corrosive gas is generally equal one stage to another stage. In this way, the materials for the various pumping stages can be selected in a cost efficient manner whilst maintaining acceptable resistance to corrosion.
• the rotor R and stator S of each pumping stage 14 of the second section 26 is made from a Nickel rich iron, whilst the rotor R and stator S of each pumping stage 14 of the first section 24 is made from an SG (spheroidal graphite) iron.
• Nickel is resistant to fluorine but if the fluid being pumped contains other corrosive agents it would be desirable to select an appropriately resistant material.
• the first section of the pumping mechanism may be made from materials other than SG iron.
• the first section may be made from a corrosion resistant material for instance NI-rich SG iron, whilst the second section may be made from a more corrosion resistant material such as cast stainless steel or nickel alloy.
• Figure 5 shows three examples of both SG iron and Ni-rich SG iron. It is preferable to select materials for the first and second section with similar linear expansion coeff ⁇ cients.
• Ni-res D-5S is a preferred corrosion resistant material as its linear expansion coefficient is 12.6 m/mK which is similar to the coefficient of SG iron of 12.5 m/mK.
• Ni-rich SG iron material which exhibits good corrosion resistant properties and also good strength and stiffness in high temperature conditions are shown in Figure 6.
• Nickel content is relatively high between 24 % and 32 % by weight.
• the same or similar material is preferably used for the rotor R and stator S in each section to avoid problems associated with having components of different thermal expansion coefficients.
• the vacuum pump 10 is shown in simplified form in Figure 1.
• the vacuum pump may comprise a claw type pumping mechanism or roots type pumping mechanism or other type of dry pumping mechanism, particular in which running clearance between components of the pumping mechanism is required to be small to increase efficiency.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Applications Or Details Of Rotary Compressors (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)
• Compressors, Vaccum Pumps And Other Relevant Systems (AREA)

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• 2009
  • 2009-04-29 GB GBGB0907298.4A patent/GB0907298D0/en not_active Ceased
• 2010
  • 2010-03-31 KR KR1020177014638A patent/KR20170063990A/ko active Search and Examination
  • 2010-03-31 US US13/263,947 patent/US20120045322A1/en not_active Abandoned
  • 2010-03-31 CN CN201080018922.5A patent/CN102414449B/zh active Active
  • 2010-03-31 KR KR1020117025564A patent/KR20120007014A/ko active Search and Examination
  • 2010-03-31 EP EP10712149A patent/EP2425137A2/en active Pending
  • 2010-03-31 JP JP2012507816A patent/JP5636042B2/ja active Active
  • 2010-03-31 WO PCT/GB2010/050572 patent/WO2010125368A2/en active Application Filing
  • 2010-03-31 BR BRPI1009368A patent/BRPI1009368A2/pt not_active Application Discontinuation
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