Abstract:
In some implementations, apparatus and methods are provided through which a dynamic cryogenic seal is manufactured. In some implementations, the seal includes a retainer and a spring-seal assembly, the assembly being comprised of a main spring housing and fluorine-containing polymer seals. In some implementations, either a radial seal, or an axial (or “piston seal”) is provided. In some implementations, methods of manufacturing the dynamic cryogenic seal are also provided. In some implementations, the methods include assembling the components while either heated or cooled, taking advantage of thermal expansion and contraction, such that there is a strong interference fit between the components at room temperature. In some implementations, this process ensures that the weaker fluorine-containing polymer seal is forced to expand and contract with the stronger retainer and spring and is under constant preload. In some implementations, the fluorine-containing polymer is therefore fluidized and retained, and can not lift off.

Description:
ORIGIN OF THE INVENTION 
     The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to seals, and more particularly to dynamic cryogenic seals. 
     BACKGROUND OF THE INVENTION 
     Typical dynamic cryogenic seals use either a plastic jacket with a mechanical spring to energize the seal or a plastic coating on a mechanical seal. These are limited in life due to the high loads resulting from coefficient of thermal expansion (CTE) mismatch of the plastic and metallic parts, or the plastic coatings wear off with motion. 
     While many efforts have been made to improve plastic cryogenic seals, the state of the art designs all suffer from rolling or sliding of the weak plastic parts as the dynamic surfaces pass by. Metallic parts wear the plastic coating off after several cycles. 
     For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for improved dynamic cryogenic seal design. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The above-mentioned shortcomings, disadvantages and problems are addressed herein, which will be understood by reading and studying the following specification. 
     A dynamic cryogenic seal is provided. The seal includes a spring-seal assembly and retainers. The spring-seal assembly is comprised of a main spring housing and fluorine-containing polymer seals. The seal may be configured in either a radial implementation, or an axial (“pistol seal”) implementation. 
     Methods of manufacturing the dynamic cryogenic seal are also provided. The methods include assembling the components while either heated or cooled, taking advantage of thermal expansion and contraction, such that there is a strong interference fit between the components at room temperature. This process ensures that the weaker fluorine-containing polymer seals are forced to expand and contract with the stronger metallic retainers and spring, and are under constant preload. Thus the fluorine-containing polymer is fluidized and retained, and can not lift off. 
     Apparatus and methods of varying scope are described herein. In addition to the aspects and advantages described in this summary, further aspects and advantages will become apparent by reference to the drawings and by reading the detailed description that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric cross-sectional diagram of an illustrative seal according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 2  is an exploded isometric cross-sectional diagram of an illustrative seal according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 3  is an isometric cross-sectional diagram an illustrative seal according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 4  is an isometric diagram of an illustrative seal according to an implementation to provide a radial seal; 
         FIG. 5  is an isometric cross-sectional diagram of an illustrative main spring housing according to an implementation to provide a radial seal; 
         FIG. 6  is an exploded isometric cross-sectional diagram of an illustrative fluorine-containing polymer seal and retainer according to an implementation to provide a radial seal; 
         FIG. 7  is an isometric cross-sectional diagram of an illustrative fluorine-containing polymer seal and retainer according to an implementation to provide a radial seal; 
         FIG. 8  is an isometric cross-sectional diagram of an illustrative seal according to an implementation to provide a radial seal; 
         FIG. 9  is a cross-sectional diagram of an illustrative main spring housing according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 10  is a cross-sectional diagram of an illustrative fluorine-containing polymer seal according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 11  is a cross-sectional diagram of an illustrative retainer according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 12  is a cross-sectional diagram of an illustrative main spring housing according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 13  is a cross-sectional diagram of an illustrative main spring housing and fluorine-containing polymer seal according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 14  is a cross-sectional diagram of an illustrative main spring housing and fluorine-containing polymer seal according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 15  is a cross-sectional diagram of an illustrative main spring housing, fluorine-containing polymer seal, and retainer according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 16  is a cross-sectional diagram of an illustrative main spring housing, fluorine-containing polymer seal, and retainer according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 17  is a cross-sectional diagram of an illustrative main spring housing, fluorine-containing polymer seals, and retainer according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 18  is a cross-sectional diagram of an illustrative main spring housing, fluorine-containing polymer seals, and retainer according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 19  is a cross-sectional diagram of an illustrative main spring housing, fluorine-containing polymer seals, and retainers according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 20  is a cross-sectional diagram of an illustrative seal according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 21  is a cross-sectional diagram of an illustrative seal according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 22  is a cross-sectional diagram of an illustrative seal according to an implementation to provide an axial, or “piston,” seal; 
         FIG. 23  is a cross-sectional diagram of an illustrative seal according to either an implementation to provide a radial seal or an implementation to provide an axial, or “piston,” seal; 
         FIG. 24  is a cut-away diagram of an illustrative swaging tool and seal; 
         FIG. 25  is a cut-away diagram of an illustrative swaging tool and seal; 
         FIG. 26  is a flowchart of a method manufacture a seal; 
         FIG. 27  is a flowchart of a method manufacture a seal; and 
         FIG. 28  is a flowchart of a method manufacture a seal; 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific implementations which may be practiced. These implementations are described in sufficient detail to enable those skilled in the art to practice the implementations, and it is to be understood that other implementations may be utilized and that logical, mechanical, electrical and other changes may be made without departing from the scope of the implementations. The following detailed description is, therefore, not to be taken in a limiting sense. 
     The detailed description is divided into three sections. In the first section, apparatus of implementations are described. In the second section, implementations of methods are described. Finally, in the third section, a conclusion of the detailed description is provided. 
     Apparatus Implementations 
       FIG. 1  is an isometric cross-sectional diagram of illustrative seal  100  according to an implementation to provide an axial, or “piston,” seal. Seal  100  solves the need in the art to achieve an effective seal in a cryogenic environment by avoiding the problems conventional seals encountered due to the high loads resulting from coefficient of thermal expansion (CTE) mismatch between plastic and metallic parts, premature wear of the weaker plastic parts caused by metallic parts, and rolling or sliding as the dynamic parts pass by. In this illustration, seal  100  is implemented in such a way to provide an effective seal for an axially moveable object within a concentric passage. 
     Seal  100  comprises an assembly, e.g. assembly  102 , and a retainer, e.g. retainers  106  and  108 , which is coupled to assembly  102 . Assembly  102  comprises a main spring housing, e.g. housing  104 , assembled with a fluorine-containing polymer seal, e.g. seal rings  110  and  112 , wherein the fluorine-containing polymer bears compressive loads and wherein the fluorine-containing polymer has a fluidized state. 
     Seal rings  110  and  112  must be weaker than retainers  106  and  108 , as well as housing  104 . This ensures seal rings  110  and  112  follow retainer rings  106  and  108 , as well as housing  104 , as seal  100  expands and contracts in response to temperature changes. By forcing seal rings  110  and  112  to follow retainer rings  104  and  106 , as well as housing  104 , the fluorine-containing polymer contained therein is kept under constant pressure, thus fluidizing and retaining the fluorine-containing polymer. Therefore, the fluorine-containing polymer does not crack or split as the mechanical parts move. 
     The fluidized fluorine-containing polymer stays in the swaged gland volume as the free surface of seal rings  110  and  112  are able to “freeze” and plug the fluidized fluorine-containing polymer from flowing out. As pressure is applied to the face of seal rings  110  and  112 , the fluidized material below the surface acts as a spring and keeps the solid surface in contact with the small imperfections of the dynamic surface, housing  104  moves the seal for larger deflections, and the pressure energized features keep the pressure in seal  100  above the system pressure, thus providing a leak free seal under dynamic applications. Seal  100  also has the ability to be easily replaced as needed. 
       FIG. 2  is an exploded isometric cross-sectional diagram of illustrative seal  100  according to an implementation to provide an axial, or “piston,” seal. In order to avoid the high loads resulting from CTE mismatch, premature wear, and rolling or sliding, seal rings  110  and  112  can be formed from a fluorine-containing polymer. Suitable materials for forming seal rings  110  and  112  include, but are not limited to, polytetrafluoroethylene (Teflon), perfluoroalkoxy (Teflon-PFA), and fluorinated ethylene propylene (Teflon-FEP). A high-strength material must be used to form retainers  106  and  108 , as well as housing  104 . This material cannot move more than a specified, controlled amount, and must be able to withstand the seal stress. Suitable materials for forming retainers  106  and  108 , as well as housing  104 , include, but are not limited to an austenitic nickel-based superalloy and stainless steel. 
       FIG. 3  is an isometric cross-sectional diagram of seal  100  according to an implementation to provide an axial, or “piston,” seal. In  FIG. 3 , the edges of retainers  106  and  108  have not yet been swaged over housing  104 . 
       FIG. 4  is an isometric diagram of illustrative seal  100  according to an implementation to provide a radial seal. In this illustration, seal  100  is implemented in such a way to provide an effective seal for the radial gap between objects. Housing  104 , retainers  106  and  108 , and seal ring  110  are all shown. 
       FIG. 5  is an isometric cross-sectional diagram of housing  104  according to an implementation to provide a radial seal. In this illustration, retainer  104  is shown prior to assembly or swaging. Prior to assembly, housing  104  is cooled in liquid nitrogen. 
       FIG. 6  is an exploded isometric cross-sectional diagram of seal ring  112  and retainer  108  according to an implementation to provide a radial seal. In this illustration, seal ring  112  and retainer  108  are shown prior to assembly. Prior to assembly, both seal ring  112  and retainer  108  are heated to approximately 300 degrees Fahrenheit. 
       FIG. 7  is an isometric cross-sectional diagram of seal ring  112  and retainer  108  according to an implementation to provide a radial seal. In this illustration, seal ring  112  and retainer  108  are shown subsequent to assembly. The main spring housing is not shown. Retainer  108  is shown prior to swaging. 
       FIG. 8  is an isometric cross-sectional diagram of seal  100  according to an implementation to provide a radial seal. In this illustration, seal  100  is shown fully assembled. Force sufficient to swage retainers  106  and  108  is applied, ensuring the fluorine-containing polymer contained in seal rings  110  and  112  is captured. After swaging, the face of seal rings  110  and  112  are trued flat. 
       FIG. 9  is a cross-sectional diagram of housing  104  according to an implementation to provide an axial, or “piston,” seal. In this illustration, the main spring housing, housing  104 , is shown prior to assembly. Illustrative dimensions are also shown. 
       FIG. 10  is a cross-sectional diagram of seal ring  110  according to an implementation to provide an axial, or “piston,” seal. In this illustration, the outboard seal, seal ring  110 , is shown prior to assembly. Illustrative dimensions are also shown. The inboard seal ring mirrors the dimensions of seal ring  110 . 
       FIG. 11  is a cross-sectional diagram of retainer  106  according to an implementation to provide an axial, or “piston,” seal. In this illustration, the outboard retainer, retainer  106 , is shown prior to assembly. Illustrative dimensions are also shown. The inboard retainer mirrors the dimensions of retainer  106 . 
       FIG. 12  is a cross-sectional diagram of housing  104  according to an implementation to provide an axial, or “piston,” seal. In this illustration, housing  104  is shown prior to assembly. 
       FIG. 13  is a cross-sectional diagram of housing  104  and seal ring  110  according to an implementation to provide an axial, or “piston,” seal. In this illustration, housing  104  and seal ring  110  are shown prior to assembly. Before assembling, housing  104  will be cooled and seal ring  110  will be heated. 
       FIG. 14  is a cross-sectional diagram of housing  104  and seal ring  110  according to an implementation to provide an axial, or “piston,” seal. In this illustration, cooled housing  104  and heated seal ring  110  are shown subsequent to assembly. The assembly process is performed while housing  104  remains cooled and seal ring  110  remains heated. At room temperature, there is an interference fit between the components. 
       FIG. 15  is a cross-sectional diagram of housing  104 , seal ring  110 , and retainer  106  according to an implementation to provide an axial, or “piston,” seal. In this illustration, retainer  106  is shown prior to assembly with housing  104  and seal ring  110 . Before assembling, housing  104  and seal ring  110  will be cooled, and retainer  106  will be heated. 
       FIG. 16  is a cross-sectional diagram of housing  104 , seal ring  110 , and retainer  106  according to an implementation to provide an axial, or “piston,” seal. In this illustration, cooled housing  104 , cooled seal ring  110 , and heated retainer  106  are shown subsequent to assembly. The assembly process is performed while housing  104  and seal ring  110  remain cooled, and retainer  106  remains heated. At room temperature, there is an interference fit between the components. 
       FIG. 17  is a cross-sectional diagram of housing  104 , seal rings  110  and  112 , and retainer  106  according to an implementation to provide an axial, or “piston,” seal. In this illustration, seal ring  112  is shown prior to assembly with housing  104 , seal ring  110  and retainer  106 . Before assembling, housing  104 , seal ring  110 , and retainer  106  will be heated, and seal ring  112  will be cooled. 
       FIG. 18  is a cross-sectional diagram of housing  104 , seal rings  110  and  112 , and retainer  106  according to an implementation to provide an axial, or “piston,” seal. In this illustration, heated housing  104 , heated seal ring  110 , heated retainer  106 , and cooled seal ring  112  are shown subsequent to assembly. The assembly process is performed while housing  104 , seal ring  110  and retainer  106  remain heated, and seal ring  112  remains cooled. At room temperature, there is an interference fit between the components. 
       FIG. 19  is a cross-sectional diagram of housing  104 , seal rings  110  and  112 , and retainers  106  and  108  according to an implementation to provide an axial, or “piston,” seal. In this illustration, retainer  108  is shown prior to assembly with housing  104 , seal rings  110  and  112 , and retainer  106 . Before assembling, housing  104 , seal rings  110  and  112 , and retainer  106  will be heated, and retainer  108  will be cooled. 
       FIG. 20  is a cross-sectional diagram of seal  100  according to an implementation to provide an axial, or “piston,” seal. In this illustration, heated housing  104 , heated seal rings  110  and  112 , heated retainer  106 , and cooled retainer  108  are shown subsequent to assembly. The assembly process is performed while housing  104 , seal rings  110  and  112 , and retainer  106  remain heated, and retainer  108  remains cooled. At room temperature, there is an interference fit between the components. Housing  104  is shown prior to swaging. 
       FIG. 21  is a cross-sectional diagram of seal  100  according to an implementation to provide an axial, or “piston,” seal. In this illustration, housing  104  is shown subsequent to swaging. Force sufficient to swage housing  104  is applied, ensuring the fluorine-containing polymer contained in seal rings  110  and  112  is captured. 
       FIG. 22  is a cross-sectional diagram of seal  100  according to an implementation to provide an axial, or “piston,” seal. In this illustration seal rings  110  and  112  are shown subsequent to being trimmed and finished to a true flat. 
       FIG. 23  is a cross-sectional diagram of seal  100  according to either an implementation to provide a radial seal or an implementation to provide an axial, or “piston,” seal. In this illustration, retainers  106  and  108  are shown subsequent to swaging over housing  104 . Force sufficient to swage retainers  106  and  108  is applied, ensuring the fluorine-containing polymer contained in seal rings  110  and  112  is captured. 
       FIG. 24  is a cut-away diagram of swaging tool  2400  and seal  100  according to an implementation to provide a radial seal. Swaging tool  2400  comprises a component that is operable to trap liquid fluorine-containing polymer; is operable to compress the fluorine-containing polymer; and is operable to swage the retainer or the main spring housing. Swaging tool  2400  further comprises a drive shaft, e.g. drive shaft  2402 , having a first end and a second end, the first end operable coupled to the component that is operable to swage the retainer or the main spring housing; a cap, e.g. cap  2404 , having a circular hole, the drive shaft extending through the hole; and a nut, e.g. nut  2406 , operably coupled to the second end of the drive shaft. The component that is operable to trap further comprises a seal, e.g. seal  100 . 
       FIG. 25  is a cut-away diagram of swaging tool  2400  and seal  100  according to an implementation to provide a radial seal. In this illustration, nut  2406  is visible, as is seal  100 . 
     Method Implementations 
     In the previous section, apparatus of the operation of an implementation was described. In this section, the particular methods performed by such an implementation are described by reference to a series of flowcharts. 
       FIG. 26  is a flowchart of a method manufacture a seal. Method  2600  solves the need in the art to achieve an effective seal in a cryogenic environment by avoiding the problems conventional seals encountered due to the high loads resulting from coefficient of thermal expansion (CTE) mismatch between plastic and metallic parts, premature wear of the weaker plastic parts caused by metallic parts, and rolling or sliding as the dynamic parts pass by. 
     A fluorine-containing polymer seal, e.g. seal rings  110  and  112 , is heated at block  2602 . The seal may be heated to about 300 degrees Fahrenheit. The fluorine-containing polymer may be comprised of polytetrafluoroethylene (Teflon), perfluoroalkoxy (Teflon-PFA), or fluorinated ethylene propylene (Teflon-FEP). 
     A main spring housing, e.g. housing  104 , is cooled at block  2604 . The main spring housing may be cooled in liquid nitrogen. 
     The heated main spring housing and the cooled seal are assembled, forming an assembly, e.g. assembly  102 , at block  2606 . At room temperature, there is an interference fit between the two. The Teflon is weaker so it follows the main spring housing as it warms. 
     The assembly, e.g. assembly  102 , is cooled at block  2608 . The assembly may be cooled in liquid nitrogen. 
     A retainer, e.g. retainers  106  and  108 , is heated at block  2610 . The retainer may be heated to about 300 degrees Fahrenheit. 
     The cooled assembly and the heated retainer are assembled at block  2612 . At room temperature, there is an interference fit between the components. 
     Swaging is performed on the edge of the retainer or the main spring housing at block  2614 . The swaging may be performing with a swaging tool that comprises a drive shaft having a first end and a second end, the first end operable coupled to the component that is operable to swage the retainer or the main spring housing; a cap having a circular hole, the drive shaft extending through the hole; and a nut operably coupled to the second end of the drive shaft. Swaging the edge of the retainer or the main spring housing further comprises trapping the fluorine-containing polymer; compressing the fluorine-containing polymer; and swaging either the retainer or the main spring housing. 
     The face of the seal is finished to true flat at block  2616 . 
       FIG. 27  is a flowchart of a method manufacture a seal. Method  2700  solves the need in the art to achieve an effective seal in a cryogenic environment by avoiding the problems conventional seals encountered due to the high loads resulting from coefficient of thermal expansion (CTE) mismatch between plastic and metallic parts, premature wear of the weaker plastic parts caused by metallic parts, and rolling or sliding as the dynamic parts pass by. 
     A heated fluorine-containing polymer seal, e.g. seal rings  110  and  112 , and a cooled main spring housing, e.g. housing  104 , are assembled at block  2702 . 
     This assembly, e.g. assembly  102 , is cooled at block  2704 . 
     The cooled assembly and a heated retainer, e.g. retainers  106  and  108 , are assembled at block  2706 . 
     Swaging is performed on the edge of the retainer or the main spring housing at block  2708 . The swaging may be performing with a swaging tool that comprises a drive shaft having a first end and a second end, the first end operable coupled to the component that is operable to swage the retainer or the main spring housing; a cap having a circular hole, the drive shaft extending through the hole; and a nut operably coupled to the second end of the drive shaft. Swaging the edge of the retainer further comprises trapping the fluorine-containing polymer; compressing the fluorine-containing polymer; and swaging the retainer. 
       FIG. 28  is a flowchart of a method manufacture a seal. Method  2800  solves the need in the art to achieve an effective seal in a cryogenic environment by avoiding the problems conventional seals encountered due to the high loads resulting from coefficient of thermal expansion (CTE) mismatch between plastic and metallic parts, premature wear of the weaker plastic parts caused by metallic parts, and rolling or sliding as the dynamic parts pass by. 
     A fluorine-containing polymer seal, e.g. seal rings  110  and  112 , is cooled at block  2802 . The seal may be cooled in liquid nitrogen. The fluorine-containing polymer may be comprised of polytetrafluoroethylene (Teflon), perfluoroalkoxy (Teflon-PFA), or fluorinated ethylene propylene (Teflon-FEP). 
     A main spring housing, e.g. housing  104 , is heated at block  2804 . The main spring housing may be heated to about 300 degrees Fahrenheit. 
     The heated main spring housing and the cooled seal are assembled, forming an assembly, e.g. assembly  102 , at block  2806 . At room temperature, there is an interference fit between the two. The Teflon is weaker so it follows the main spring housing as it warms. 
     The assembly, e.g. assembly  102 , is heated at block  2808 . The assembly may be heated to about 300 degrees Fahrenheit. 
     A retainer, e.g. retainers  106  and  108 , is cooled at block  2810 . The retainer may be cooled in liquid nitrogen. 
     The heated assembly and the cooled retainer are assembled at block  2812 . At room temperature, there is an interference fit between the components. 
     Swaging is performed on the edge of the retainer or the main spring housing at block  2814 . The swaging may be performing with a swaging tool that comprises a drive shaft having a first end and a second end, the first end operable coupled to the component that is operable to swage the retainer or the main spring housing; a cap having a circular hole, the drive shaft extending through the hole; and a nut operably coupled to the second end of the drive shaft. Swaging the edge of the retainer or the main spring housing further comprises trapping the fluorine-containing polymer; compressing the fluorine-containing polymer; and swaging either the retainer or the main spring housing. 
     The face of the seal is finished to true flat at block  2816 . 
     CONCLUSION 
     A dynamic cryogenic seal is described. Although specific implementations are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific implementations shown. This application is intended to cover any adaptations or variations. For example, although the main spring housing and retainers are described as being comprised of stainless steel or an austenitic nickel-based superalloy, one of ordinary skill in the art will appreciate that implementations can be made in other metals that provide the required function. 
     In particular, one of skill in the art will readily appreciate that the names of the methods and apparatus are not intended to limit implementations. Furthermore, additional methods and apparatus can be added to the components, functions can be rearranged among the components, and new components to correspond to future enhancements and physical devices used in implementations can be introduced without departing from the scope of implementations. One of skill in the art will readily recognize that implementations are applicable to future dynamic cryogenic seal devices, different dynamic cryogenic seals, and new dynamic cryogenic seals. 
     The terminology used in this application is meant to include all seals, and dynamic cryogenic seal environments and alternate technologies which provide the same functionality as described herein.