PLASTIC HIGH VACUUM PIPING COMPONENTS

Abstract: The invention relates specifically to use of low cost thermoplastics such as PVC, and CPVC as high vacuum component material. We have discovered that when PVC or CPVC is exposed to high and ultra high vacuum pressures for a period of time, the outgas rate for these materials drops dramatically to levels that are well within required limits for high and ultra high vacuum applications, where vacuum pressures of 9x10-4 torr to 1x10-11 torr are required. Subsequently, it is a purpose of this invention through outgas reduction of the material with high and ultra high vacuum and or residual gas analysis determination of the outgas level to provide the user of the processed plastic components with a means (6) for determining the type and relative amount of contamination that the components would contribute to their vacuum process at the vacuum pressures that they intend to use.

Description: PLASTIC HIGH VACUUM PIPING COMPONENTS BACKGROUND OF THE INVENTION Field of the Invention (Technical Field) The invention relates specifically to the discovery that certain low cost thermoplastics such as PVC and CPVC can be excellent materials for the construction of high and ultra high vacuum components. Prior art vacuum use of these materials has been restricted to vacuum pump exhausts lines and rough vacuum. We have conclusively determined through the use of residual gas analysis that the prior bias against the use of said materials in said service relates to surface impurities that are either a residue of manufacture, a non vacuum compatible lubricant or a joining adhesive, not continuous outgas or permeation of the PVC or CPVC plastic material itself. Subseguently, when these materials are exposed to high vacuum pressures, said surface impurities are gradually eliminated. These type of surface contamination would by it's presence render any material unsuitable for high and ultra high vacuum service. We have used an outgas reduction process method to demonstrate the capability of PVC and CPVC plastic compounds to be suitable for use in the construction of high and ultra high vacuum systems, where vacuum pressures from 9xl0 "4 torr to lxlO "11 torr are required. We have also determined the relative purity level of the vacuum processed plastic components through the use of residual gas analysis. It should be noted that not all thermoplastic materials exhibit SUBS TUTE SHEET adequate high and ultra high vacuum performance. It is expected that through the invention evaluation of thermoplastics that other cost effective materials may be found in addition to PVC and CPVC. Background Art The vacuum industry has considered low cost thermoplastics such as PVC, or CPVC to be unsuitable as a material of construction for high and ultra high vacuum components. This relates primarily to the perceived outgassing rate of such plastic materials and, secondly, to the perceived rate at which gases are able to permeate through the plastic material into the contained vacuum pressure space, "outgassing" is the tendency of materials to release gases over time. The rate at which materials give off gas, or outgas, is particularly a problem in high and ultra high vacuum applications where systems are almost exclusively fabricated from expensive polished stainless steel components which have low outgassing characteristics. Metal components for high and ultra high vacuum piping are often supplied with a helium leak rate certificate but little or no information is currently supplied with vacuum piping components which specifies the outgas/permeation rate that these components produce. Low cost PVC and CPVC components are typically used in the construction of liquid transfer piping systems. Because these components are manufactured in very high quantity they are low in cost to end users. SUBSTITUTE SHEET SUMMARY OF THE INVENTION Certain low cost thermoplastic materials such as PVC and CPVC are excellent low cost high and ultra high vacuum materials. We have discovered that when a clean PVC or CPVC component is exposed to high and ultra high vacuum pressures for a period of time, the outgas rate for the PVC or CPVC component drops dramatically to levels which are well within required limits for high and ultra high vacuum applications where vacuum pressures from 9xl0 "4 torr to lxlO "11 torr are required. Subsequently, it is a purpose of this invention to show that low cost materials such as PVC and CPVC are suitable, and in certain cases superior to stainless steel, for high and ultra high vacuum component service. This is demonstrated through outgas reduction of surface impurities by exposing said materials to high and ultra high vacuum and through residual gas analysis determination of the outgas levels for said materials while exposed to high and ultra high vacuum pressures. It is also the intent of this invention to provide the user of these processed plastic components with documentation that shows the type and relative amount of contamination that the components would contribute to their vacuum process at a given vacuum pressure prior to the fabrication/installation of their system. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated into and form a part of the SUBSTITUTE SHEET specification, illustrate the preferred embodiment of the invention and, subsequently, are not to be construed as limiting the invention. Fig. 1 is an elevation view of a low cost PVC ball valve that has been modified for high and ultra high vacuum service by replacing the standard valve lubricant with a vacuum compatible lubricant; Fig. 2 is an elevation view of a low cost CPVC cross that illustrates the wide range of existing low cost PVC and CPVC rigid piping component shapes that can replace expensive metal component shapes in the fabrication of high and ultra high vacuum piping systems; Fig. 3 is an elevation view of a section of low cost flexible PVC tubing that can replace expensive flexible metal bellows tubing in high and ultra high vacuum piping systems where a flexible connection is required; Fig. 4 is a perspective view of a molded CPVC molecular drag pump rotor to show a complex shape, high and ultra high vacuum pump component that can be molded from plastic much more economically than it can be machined from aluminum or stainless steel; Fig. 5 is a perspective view of a molded PVC molecular drag pump stator/housing to illustrate further the ability to produce the two major components of a high vacuum molecular drag pump from molded plastic instead of machined metal; Fig. 6 is a perspective view of a typical system configuration for high and ultra high vacuum outgas evaluation / reduction of plastic piping SUBSTITUTE SHEET component material or material interior surface contamination; Fig. 7 is a perspective view of a typical system configuration for high and ultra high vacuum outgas reduction /evaluation of plastic piping component material or material surface contamination inside a vacuum chamber; Fig. 8 is an elevation view of a residual gas analysis xy bar chart display with the partial pressure levels of specific atomic mass units; Fig. 9 is an elevation view of an actual residual gas analysis spectra display during initial high and ultra high vacuum outgas reduction / evaluation of 2 ea. 8" diameter PVC tees; Fig. 10 is an elevation view of an actual residual gas analysis display spectra during final high and ultra high vacuum outgas reduction / evaluation of 2 ea. 8" diameter PVC tees. DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention is directed to a new use of thermoplastic material for the construction of components for high and ultra high vacuum environment generation and containment. We have proven that certain low cost thermoplastics such as PVC, the acronym for polyvinyl chloride and CPVC, the acronym for chlorinated polyvinyl chloride can replace expensive metal components in high and ultra high vacuum systems through the use of residual gas analysis evaluation. When said thermoplastic materials are exposed to high vacuum pressures, the surface impurities that initially are damaging to high and ultra high vacuum pressures are SUB S T I TUTESHEET gradually eliminated. We have used an outgas reduction process method to demonstrate the capability of PVC and CPVC plastic compounds to be suitable for use in the construction of high and ultra high vacuum systems, where vacuum pressures from 9xl0~ 4 torr to lxlO "11 torr are required. Additional thermoplastic materials can be used according to the invention provided that it meets the criteria of low permeability to prevent gas molecules from migrating through the material into the contained high or ultra high vacuum and low out¬ gassing characteristics which is the tendency of a material to give off gas molecules into a vacuum. It should be noted that not all thermoplastic materials exhibit adequate high and ultra high vacuum performance. We have incorporated a simple invention method to determined the relative purity level of the vacuum processed plastic components through the use of residual gas analysis. It is expected that through the invention evaluation of thermoplastics that other cost effective materials may be found in addition to PVC and CPVC. Referring to Fig. 1, the PVC/CPVC Ball Valve 1, is shown to illustrate our discovery that expensive stainless steel high and ultra high vacuum valves, can in many high and ultra high vacuum applications, be replaced by a low cost PVC ball valve that has been modified for high and ultra high vacuum service by replacing the standard valve lubricant with a vacuum compatible lubricant such as "KRYTOX" grease from Dupont. SUBSTITUTE SHEET Referring to Fig. 2, a 8" diameter PVC cross 2, is shown to illustrate our discovery that expensive large diameter stainless steel piping components, can in many high and ultra high vacuum applications, be replaced by a low cost PVC compon¬ ent that is actually superior to stainless steel in certain applications. Many other sizes and shapes of piping components can be used. Referring to Fig. 3, a 12" section of 4" diameter flexible PVC tubing 3, is shown to illustrate our discovery that an expensive section of metal bellows tubing can be replaced by a low cost flexible PVC section in certain high and ultra high vacuum piping applications where a flexible connection is required. Referring to Fig. 4, an injection molded CPVC molecular drag pump rotor 4, is shown to illustrate a complex shape, high and ultra high vacuum pump component that can be molded from plastic much more economically than it can be machined from aluminum or stainless steel. Referring to Fig. 5, a molded PVC molecular drag pump stator/housing 5, is shown to illustrate further the ability to produce the two major components of a high vacuum molecular drag pump from molded plastic instead of machined metal at a dramatic reduction in cost. Referring to Fig. 6, a typical system for high and ultra high vacuum outgas reduction / evaluation of thermoplastic piping component material or material ' interior surface contamination is shown. In this example, flexible PVC tubing 3 is SUBSTITUTE SHEET Capped 9 and connected to a High and ultra high Vacuum Outgas Reduction Manifold 8 and then subsequently evacuated by a High and ultra high Vacuum Pump 7 until a specific high and ultra high vacuum pressure, and or a outgas rate for each atomic mass unit between 0 and 100 is attained on a Residual Gas Analysis Device 6 which is connected to a Residual Gas Sensor 10. The said analysis device and sensor used in the invention discovery was the model » ppτ" from MKS instruments connection to an ALR "flyer" model PC. The results of this process are stored for customer distribution. Referring to Fig. 7, a typical system for high and ultra high vacuum outgas reduction / evaluation of entire thermoplastic piping components interior and exterior surfaces. In this example, the PVC / CPVC Ball Valve 1 is placed into a High and ultra high Vacuum Outgas Reduction Chamber 13 and evacuated by a High and ultra high Vacuum Pump 7 until a specific high and ultra high vacuum pressure, and or a specific outgas rate for each atomic mass unit between 0 and 100 is attained on a Residual Gas Analysis Device 6 which is connected to a Residual Gas Sensor 10. Referring to Fig. 8, a residual gas analysis bar chart is shown with bar levels which represent the Partial Pressure Reading Scale Levels 11 of individual atomic mass units such as the Atomic Mass Unit Four - Helium 12 and Atomic Mass Unit Twenty Eight - Nitrogen 14. The partial pressure for each atomic mass unit added together is equal to the total vacuum pressure. Through careful SUBSTITUTE SHEET monitoring of individual atomic mass unit partial pressures, it is possible to determine both the purity of the components which are undergoing high and ultra high vacuum outgas reduction and the integrity / effectiveness of the high and ultra high vacuum outgas reduction / evaluation system itself. Referring to Fig. 9, an actual residual gas analysis Initial Outgas Reduction Spectra 16 is shown. This actual data was taken 6 hours after 2 ea. 8" diameter PVC tees were connected to a High and ultra high Vacuum Outgas Reduction Manifold. The spectra shows numerous atomic mass units present in the composition of thermoplastic material / surface impurities outgassing into the manifold system. Referring to Fig. 10, an Outgas Reduction Spectra 17 is shown 72 hours after connecting the 8" PVC tees to the High and ultra high Vacuum Outgas Reduction Manifold. The only significant atomic mass unit outgas contributors are Seventeen and Eighteen which are the secondary and primary atomic mass units for water. These partial pressure levels for water vapor are very low for a unheated vacuum chamber showing that it may be easier to remove water vapor molecules from a thermoplastic system than it is in a stainless steel or aluminum chamber. SUBSTITUTE SHEET

Claims: WHAT WE CLAIM IS : CLAIM 1. A new use for thermoplastic material, comprising: a vacuum-component made of thermoplastic material for use in vacuum systems having operating pressures below roughing pressures. CLAIM 2. The vacuum-component made of thermoplastic material according to claim 1, said vacuum-component being used in a vacuum system having a vacuum of between 9 X 10~ 4 torr and 1 X 10~ 9 torr. CLAIM 3. The vacuum-component made of thermoplastic material according to claim 1, in combination with a vacuum system having a vacuum of between 9 X 10~ 4 torr and 1 X 10 ~9 torr, said vacuum-component forming at least a part of said vacuum system. CLAIM 4. The vacuum-component made of thermoplastic material according to claim 3, wherein said vacuum-component comprises at least one of a: tubular piping; pump; rotor of a pump; valve; cross-component; and flexible, tubular member performing the functions of a bellows. CLAIM 5. The vacuum-component made of thermoplastic material according to claim 1, wherein said component is made of at least one of the following: polyvinylchloride, and chlorinated polyvinyl chloride. SUBSTITUTE SHEET CLAIM 6. The vacuum-component made of thermoplastic material according to claim 1, wherein said component is made of a thermoplastic material having low gas-permeability, and low outgassing- rates when used in a steady-state vacuum system. CLAIM 7. A method of using thermoplastic material, comprising: producing a vacuum-component made of thermoplastic material for vacuum systems having operating vacuum-pressures below roughing vacuum- pressures. CLAIM 8. The method according to claim 7, wherein said step of producing a vacuum-component comprises producing a vacuum-component for use in a vacuum system having a vacuum of between 9 X 10 torr and 1 X 10 "9 torr. CLAIM 9. The method according to claim 7, wherein said step of producing a vacuum-component comprises producing a vacuum-component for use in a vacuum system having a vacuum of between 9 X 10 torr and 1 X 10~ 9 torr, and installing said vacuum-component in said vacuum system. CLAIM 10. The method according to claim 7, wherein said step of producing a vacuum-component comprises making said vacuum-component into one of a: tubing; valve; pump; cross-shaped member; and rotor. S U BSTITUTE SHEET CLAIM 11. The method according to claim 7, wherein said step of producing comprises choosing a thermoplastic material that has low gas-permeability and low outgassing in its steady-state operation. CLAIM 12. The method according to claim 11, wherein said step of producing comprises: shaping said thermoplastic material into a desired component-shape; and, thereafter, reducing the outgassing of said component- shape before the steady-state use of said component- shape in a vacuum-system; said step of reducing comprising evacuating at least the interior surfaces of said component- shape to a vacuum-pressure approximately equal the vacuum-pressure of the system in which said component-shape is to be used. CLAIM 13. The method according to claim 12, wherein said step of reducing comprises additionally evacuating all exterior surfaces to said vacuum- pressure. CLAIM 14. The method according to claim 11, wherein said step of evacuating comprises coupling said component-shape to a vacuum-pumping system, and creating said vacuum thereby in the interior of said component-shape. CLAIM 15. The method according to claim 13, wherein said step of reducing comprises placing said component-shape in a vacuum-chamber having a vacuum- pressure approximately equal the vacuum-pressure of SUBSTITUTE SHEET the system in which said component-shape is to be used. CLAIM 16. The method according to claim 12, further comprising measuring the residual gas outgassed during at least a portion of said step of evacuating; said step of measuring comprising determining the presence and rate of outgassing of each residual gas. CLAIM 17. The method according to claim 12, further comprising operatively coupling said component-shape into a vacuum-system having a vacuum-pressure approximately equal to said vacuum- pressure used during said step of evacuating said component-shape. CLAIM 18. The method according to claim 11, further comprising operatively coupling said vacuum- component into a vacuum-system. CLAIM 19. A method of evaluating thermoplastic material for potential use in vacuum systems having vacuum-pressures below roughing pressure, comprising: subjecting at least a portion of the surface-area of the thermoplastic material being evaluated to a vacuum having vacuum-pressure approximately equal to the vacuum-pressure of a system in which it may be potentially used; and detecting the residual gas outgassed during at least a portion of said step of subjecting; SUBSTITUTE SHEET said step of detecting comprising determining the presence and rate of outgassing of residual gas. CLAIM 20. The method of evaluating thermoplastic material for potential use in vacuum systems having vacuum-pressures below roughing pressure according to claim 19, wherein said step of detecting comprises measuring the rate of outgassing of residu¬ al gas to determine if said thermoplastic material has low gas-permeability and low outgassing characteristics in its steady-state operation. CLAIM 21. The method of evaluating thermoplastic material for potential use in vacuum systems having vacuum-pressures below roughing pressure according to claim 20, wherein said step of subjecting comprises exposing said at least a portion of the surface-area of the thermoplastic material being evaluated to the vacuum for a predetermined period of time; said predetermined period of time being equal to the length of time it would normally take to remove most outgassing of residual gases from said surface-area based on the flow-rate of the vacuum-system in which it is being tested. CLAIM 22. The method of evaluating thermoplastic material for potential use in vacuum systems having vacuum-pressures below roughing pressure according to claim 19, further comprising; before said step of subjecting, shaping said thermoplastic material into a desired SUBSTITUTE SHEET component-shape having a hollow interior surface- area, and an exterior surface area; and, said step of subjecting comprises evacuating at least the interior surface-area to said vacuum. CLAIM 23. The method of evaluating thermoplastic material for potential use in vacuum systems having vacuum-pressures below roughing pressure according to claim 19, wherein said step of subjecting comprises forming a vacuum having a minimum total vacuum pressure of 1 X 10~ 6 torr to which said at least a portion of the surface-area of the thermoplastic material is exposed. CLAIM 24. The method of evaluating thermoplastic material for potential use in vacuum systems having vacuum-pressures below roughing pressure according to claim 20, wherein said step of measuring comprises exposing said at least a portion of the surface-area of the thermoplastic material being evaluated to the vacuum for a period of time equal to the length of time for a predetermined, minimal outgassing rate to be achieved for each atomic mass unit between 0 and 100 of the residual gas indicative of said low gas-permeability and low outgassing in its steady-state operation. CLAIM 25. A system for evaluating thermoplastic material for potential use in vacuum systems having vacuum-pressures below roughing pressure, comprising: SUBSTITUTE SHEET a vacuum-source for creating a vacuum; coupling means coupling said vacuum-source to said thermoplastic material for exposing at least a portion of said thermoplastic material to said vacuum; a residual gas measuring system operatively coupled to said coupling means for detecting and measuring the outgassing of residual gas from said at least a portion of said thermoplastic material, whereby it may be determined if the thermoplastic material is suitable for use as a vacuum-component for vacuum-pressures below roughing pressures. CLAIM 26. A system for evaluating thermoplastic material for potential use in vacuum systems having vacuum-pressures below roughing pressure according to claim 25, wherein said coupling means coupling said vacuum-source to said thermoplastic material comprises a vacuum-chamber in which said thermoplastic material is placed. CLAIM 27. A system for evaluating thermoplastic material for potential use in vacuum systems having vacuum-pressures below roughing pressure according to claim 25, wherein said thermoplastic material comprises a component-shape having an interior surface and an exterior surface; said coupling means coupling said vacuum-source to said thermoplastic material comprising at least one hollow-connector having an end secured to an end of said component- shape, whereby said interior surface of said component-shape is exposed to said vacuum-source, and said exterior surface is exposed to ambient. SUBSTITUTE SHEET

Inventors: CLAYTON R DALLAS, GRENCI CHARLES, CLAYTON, R., DALLAS, GRENCI, CHARLES
Applicants: CLAYTON R DALLAS, GRENCI CHARLES, CLAYTON, R., DALLAS, GRENCI, CHARLES
Application year: 1993
Main classification: G01M3
IPC codes: B01L3, B29D23, B29K27, F16L41, G01N1, G01N27