TWI504811B - Vacuum pump - Google Patents

Description

Vacuum pump

The present invention relates to a dry vacuum pump.

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. These pumps include a substantially dry (or oil-free) pump mechanism, but typically also include certain components for driving the pump mechanism (which require lubricating oil for effectiveness), such as bearings and transfer gears. Examples of dry pumps include Roors pumps, Northey (or "claw") pumps, screw pumps, and scroll pumps. A dry pump having a Roots and/or Norther rotor assembly is typically a multi-stage positive displacement pump comprising a stator assembly defining a plurality of pump chambers each accommodating a pair of mutually intermeshing rotors Component. The rotor assembly is located on the countershaft and may have the same type of profile or profile in each chamber that may vary from chamber to chamber.

Iron castings have long been used to make stator and rotor assemblies for dry vacuum pumps. However, in the semiconductor industry, the increasing use of relatively high corrosive gases of high flow rates, such as chlorine, boron trichloride, hydrogen bromide, fluorine gas and chlorine trifluoride, has led to severe corrosion, and This results in a relatively short service life of the cast iron stator and rotor assembly. In addition to the costs associated with the replacement of pumps or corroded parts and consequent process downtime, this corrosion can result in equipment failure, process gas leakage, and possible process contamination.

In view of this, it is known to passively protect such components by forming a resin or polymer coating of a fluoropolymer or polyimide material on the surface of the component exposed to the corrosive gas. These coatings have a tendency to degrade over time, with the final peeling or peeling of the coating exposing the underlying cast iron to corrosive gases. Another alternative is to form such components from nickel-rich cast iron (eg, ductile corrosion resistant Ni cast iron) or stainless steel with excellent corrosion resistance. However, corrosion resistant Ni cast iron and stainless steel are relatively expensive and difficult to machine, and thus do not provide a cost effective option for use in the manufacture of rotor and stator assemblies.

The present invention provides a dry vacuum pump comprising a subassembly and at least one rotor assembly, wherein the stator assembly and/or the at least one rotor assembly is formed from an austenitic tempered ductile iron.

The stator assembly can accommodate first and second intermeshing rotor assemblies that are adapted to reverse within the stator assembly. In a preferred embodiment, the rotor assembly has a Roots profile, although it may have a Norder or screw profile as desired.

The pump may be in the form of a multi-stage pump wherein the stator assembly defines a plurality of interconnected pump chambers that are arranged in series and each house a respective rotor assembly formed from an austempered ductile iron. The intermeshing rotor assembly can be located on each of the shafts, wherein the pump includes a gear assembly for transmitting torque from one shaft to the other, wherein at least one of the gear assemblies is preferably an anustempered ductile iron form.

Alternatively, the pump may be in the form of a scroll pump, wherein the stator assembly includes a fixed scroll member having an end plate having a first spiral cladding extending therefrom, and the at least one rotor assembly includes an end A rotary wrap member of the plate having a second spiral cover extending therefrom for intermeshing engagement with the first spiral cover. Each of the scroll members is preferably formed by ADI.

ADI preferably has a graphite spheroidization rate of at least 90%.

ADI preferably has a matrix of acicular ferrite and carbon stabilized austenite.

The ductile iron which has been austempered by austenite preferably comprises one or more of the following elements: carbon in the range of 3.4 to 3.5% by mass; in the range of 2 to 2.3% by mass; by mass Manganese in total in the range of 0.075 to 0.15%; molybdenum in total in the range of 3.4 to 3.5% by mass; nickel in total in the range of 1.2 to 1.4% by mass; and totaling in the range of 0.75 to 0.95% by mass Copper within range.

Referring to Figures 1 and 2, a multi-stage dry vacuum pump 10 includes a stator assembly 12 preferably formed of an austempered ductile iron (ADI) having a plurality of pump chambers 14, 16, 18 defined. , 20, 22 one series wall. An inlet conduit 24 for delivering gas to pump the inlet pump chamber 14 and a discharge conduit 26 for discharging the pumped gas from the discharge pump chamber 22 are also formed in the stator 12. The circumferential passages 28, 30, 32 and 34 formed in the stator 12 connect the pump chambers 14, 16, 18, 20, 22 in series.

The stator 12 houses a first shaft 36 and a second shaft 38 spaced from the first shaft 36 and parallel to the first shaft 36. 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 coupled to a drive motor 46 that is coupled together by a timing gear 47 such that in use the shafts 36, 38 rotate at the same speed but in opposite directions, as indicated by arrows 48 and arrows in FIG. 50 instructions. The gearbox 52 attached to the side of the pump 10 contains oil 54 for lubricating the timing gear 47. The timing gear 47 can be formed by ADI.

Within each pump chamber, the shafts 36, 38 support respective rotor assemblies 56, 58 that may also be formed by ADI. While a mixture of Roots and Nose profiles can be provided within pump 10, in this embodiment, rotors 56, 58 have a Roots-type profile within each pump chamber. The rotors 56, 58 are located in each of the pump chambers relative to the inner surface of the stator 12 such that the rotors 56, 58 can operate in a manner known per se.

In use, gas is pushed into the pump 10 via the inlet conduit 24 and into the inlet pump chamber 14. The gas is compressed by the rotors 56, 58 located within the inlet pump chamber 14 and fed by the passage 28 into the next pump chamber 16. The gas fed into the pump chamber 16 is similarly compressed by the rotors 56, 58 located therein and fed by the passage 30 to the next pump chamber 18. Similar gas compression occurs in the pump chambers 18, 20 and 22, wherein the pumped gas is ultimately discharged from the pump 10 via the discharge conduit 26.

The use of austenitic tempered ductile iron (ADI) to manufacture the stator assembly 12 and/or rotor assemblies 56, 58 of the pump 10 makes the pump 10 particularly suitable for pumping corrosive gases such as chlorine, boron trichloride, hydrogen bromide. , fluorine gas and chlorine trifluoride.

ADI has superior hardness, higher specific strength ratio, and comparable F ₂ corrosion sensitivity compared to the more expensive corrosion resistant Ni materials currently about four to five times more expensive than ADI. This enables the stator and rotor assembly and timing gear to have relatively high wear and corrosion resistance with respect to reduced component weight and cost for equal or improved performance.

As an example, the tempered ductile iron (ADI) used to fabricate the stator assembly 12 and/or the rotor assemblies 56, 58 and/or the timing gear 47 may include the following elements (by mass):

The ADI preferably has a graphite spheroidization rate of at least 90% and preferably has a number of spheroidal particles in the range of 150 to 300/mm ² . ADI preferably has a major matrix of acicular ferrite and carbon-stabilized austenite, which is substantially free of carbides, inclusions or porosity. These characteristics of ADI enable the material to meet the performance requirements of semiconductor processing equipment, notably the sufficient friction and mechanical properties at high temperatures and corrosion resistance.

10. . . Pump

12. . . Stator/stator assembly

14. . . Pump chamber

16. . . Pump chamber

18. . . Pump chamber

20. . . Pump chamber

twenty two. . . Pump chamber

twenty four. . . Inlet pipe

26. . . Discharge pipe

28. . . Circumferential channel

30. . . Circumferential channel

32. . . Circumferential channel

34. . . Circumferential channel

36. . . axis

38. . . axis

40. . . Bearing

42. . . End plate

44. . . End plate

46. . . Drive motor

47. . . Timing gear

48. . . arrow

50. . . arrow

52. . . Gearbox

54. . . oil

56. . . Rotor/rotor assembly

58. . . Rotor/rotor assembly

1 is a cross section through a multistage dry vacuum pump; and FIG. 2 is a view along line A-A in FIG.

12. . . Stator/stator assembly

twenty two. . . Pump chamber

26. . . Discharge pipe

34. . . Circumferential channel

36. . . axis

38. . . axis

48. . . arrow

50. . . arrow

56. . . Rotor/rotor assembly

58. . . Rotor/rotor assembly

Claims (14)

A dry vacuum pump for pumping chlorine gas, boron trichloride, hydrogen bromide, fluorine gas and chlorine trifluoride, comprising a certain subassembly and at least one rotor assembly, wherein the stator assembly and/or the at least one rotor assembly It is formed by ductile iron that has been tempered by Auschine. The pump of claim 1, wherein the at least one rotor assembly has one of a screw profile, a Roots profile, or a Norther profile. The pump of claim 2, comprising a first and second intermeshing rotor assembly adapted to reverse within the stator assembly. A pump according to claim 3, in the form of a multi-stage dry vacuum pump, wherein the stator assembly defines a plurality of interconnected pump chambers arranged in series and each accommodating a pair of respective rotor assemblies, each rotor assembly being Formed by ductile iron of austempered tempering. The pump of claim 3, wherein the intermeshing rotor assemblies are located on respective shafts, the pump including a gear assembly for transmitting torque from one shaft to the other, at least one gear of the gear assembly being austenitic The formation of ductile iron in tempering. A pump according to claim 1, which is in the form of a scroll pump, wherein the stator assembly comprises a fixed scroll member having an end plate having a first spiral cover extending therefrom, and the at least A rotor assembly includes a rotary scroll member having an end plate having a second spiral cover extending therefrom for intermeshing engagement with the first spiral cover. The pump of any one of claims 1 to 6, wherein the austenitic tempered ductile iron has a graphite spheroidization rate of at least 90%. The pump of any one of claims 1 to 6, wherein the austenitic tempered ductile iron has a matrix of acicular ferrite and carbon stabilized austenite. The pump of any one of claims 1 to 6, wherein the austenitic tempered ductile iron comprises carbon in a total amount ranging from 3.4 to 3.5% by mass. The pump of any one of claims 1 to 6, wherein the austenitic tempered ductile iron comprises a total of 2 to 2.3% by mass. The pump of any one of claims 1 to 6, wherein the austenitic tempered ductile iron comprises manganese in a total amount ranging from 0.075 to 0.15% by mass. The pump of any one of claims 1 to 6, wherein the austenitic tempered ductile iron comprises molybdenum in total in the range of 3.4 to 3.5% by mass. The pump of any one of claims 1 to 6, wherein the austenitic tempered ductile iron comprises nickel in total in the range of 1.2 to 1.4% by mass. The pump of any one of claims 1 to 6, wherein the austenitic tempered ductile iron comprises copper in a total amount ranging from 0.75 to 0.95% by mass.