Patent Publication Number: US-2020300244-A1

Title: Seal assembly for high pressure single screw compressor

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to single screw compressors. In one aspect, the present invention relates to a seal between the discharge (high pressure) of high pressure single screw compressors and the suction (low pressure) of such compressors. 
     BACKGROUND OF THE INVENTION 
     Single screw compressors are used, for example, in compression systems, such as refrigeration systems, to compress a gas, such as refrigerant gas, for example “Freon,” ammonia, natural gas, or the like. A compressor generally uses a drive source to output compressed gas. Screw compressors, specifically, employ a housing in which a motor-driven main rotor having helical grooves thereon meshes with rotors on opposite sides of the main rotor to define gas compression chambers. It will be appreciated that a pressure differential is thereby created between a suction end cavity (lower pressure) and a discharge end cavity (higher pressure). 
     Standard single screw compressors operate at discharge pressures up to 350 psi, while high pressure single screw compressors operate at discharge pressures greater than 350 psi and up to 1500 psi. It will be appreciated that the design of various components may differ between a standard single screw compressor and those operating at high pressures. For example, high pressure single screw compressors experience a greater pressure differential between the suction end cavity and the discharge end cavity. The seal between the discharge cavity of a high pressure screw compressor and the suction cavity of a high pressure screw compressor must therefore accommodate the greater pressure differential than the seal for a standard single screw compressor. 
     Existing seals between the discharge and suction cavities can be machined directly to the rotor, as shown in PRIOR ART  FIG. 1 . In this case, the seal itself rotates with the main rotor. Alternatively, existing seals are provided as a separate part secured to the inside of the compressor housing, as shown in PRIOR ART  FIG. 2 . In these cases, the efficiency of the seal depends on the clearance which can be obtained between either the seal and the housing wall or rotor and the seal. The greater the distance, the less efficient the seal. The efficiency of the seal is also dependent on the amount of wear on the seal over time. 
     With respect to the seal shown in PRIOR ART  FIG. 1 , the clearance between the housing and the seal on the rotor cannot be significantly optimized because both the housing and the rotor are metal. That is, metal does not wear as readily as other materials and damage to the housing and/or rotor may occur if the clearance between the housing and the rotor is not sufficient. In contrast, when the seal is provided on the housing wall, it will be appreciated that two different seal surfaces are needed and optimizing the clearance can be difficult. 
     Accordingly, a need exists for a seal assembly for high pressure single screw compressors which addresses one or more of the above deficiencies or other problems. 
     SUMMARY OF THE INVENTION 
     In one aspect, a seal assembly is disclosed. The seal assembly is configured for use with a high pressure single screw compressor. The assembly comprises a seal body having a textured outer surface; and at least one attachment structure which fixedly attaches the seal body to, so as to be rotatable along with, a main rotor of the high pressure single screw compressor. The textured outer surface creates a labyrinthine path between a compressor housing and the seal body. 
     In another aspect, a high pressure single screw compressor is disclosed. The high pressure single screw compressor comprises a housing, a main rotor that is secured within the housing and rotatably driven by a main rotor drive shaft about a main rotor drive shaft axis, and operably engaged with a plurality of gate rotors that are also secured within the housing; and a seal assembly. The seal assembly comprises a seal body having a textured outer surface, and at least one attachment structure which fixedly attaches the seal body to, so as to be rotatable along with, the main rotor of the high pressure single screw compressor. The textured outer surface creates a labyrinthine path between the housing and the seal body. 
     Other embodiments, aspects, features, objectives and advantages of the seal assembly in accordance with embodiments of the present disclosure will be understood and appreciated upon a full reading of the detailed description and the claims that follow. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Features of the present disclosure, which are believed to be novel, are set forth with particularity in the appended claims. Embodiments of the disclosure are described with reference to the accompanying drawings and are for illustrative purposes only. The disclosure is not limited in its application to the details of construction or the arrangement of the components illustrated in the drawings. The seal assembly of the present disclosure is capable of other embodiments or of being practiced or carried out in other various ways. Like reference numerals are used to indicate like components. In the drawings: 
         FIG. 1  illustrates a prior art example of a seal for a high pressure single screw compressor; 
         FIG. 2  illustrates a further prior art example of a seal for a high pressure single screw compressor; 
         FIG. 3  is a top view, partly in cross-section and with portions broken away, of an exemplary high pressure single screw compressor employing a single screw rotor and a pair of star or gate rotors in accordance with embodiments of the present disclosure; and 
         FIG. 4  is a schematic illustration of a portion of the high pressure single screw compressor of  FIG. 3  which shows the seal assembly in further detail in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIG. 3 , numeral  10  designates an exemplary embodiment of a single screw compressor adapted for use in a compression system, such as a refrigeration system (not shown), or the like, and which may include a seal assembly  100  (not shown) in accordance with embodiments of the present disclosure. The single screw compressor  10  generally comprises a compressor housing  12 , a single main rotor  14  mounted for rotation in the housing  12 , and a pair of star-shaped gate or star rotors  16 ,  18  mounted for rotation in the housing  12  and engaged with the main rotor  14 . 
     The compressor housing  12  includes a cylindrical bore (not shown) in which the main rotor  14  is rotatably mounted. The bore is open at its suction end  27  and is closed by a discharge end wall (not shown). The main rotor  14 , which is generally cylindrical and has a plurality of helical grooves  25  formed therein defining compression chambers, is provided with a rotor shaft  26  which is rotatably supported at opposite ends on bearing assemblies  28  mounted on the housing  12 . The rotor shaft  26  drives rotation of the main rotor  14  about a main rotor shaft axis. 
     The compressor housing  12  includes spaces  30  therein in which the star or gate rotors  16 ,  18  are rotatably mounted and the rotors  16 ,  18  are located on opposite sides (i.e., 180 degrees apart) of the main rotor  14 . Each of the rotors  16 ,  18  has a plurality of gear teeth  32  and is provided with a rotor shaft  34  which is rotatably supported at opposite ends on bearing assemblies mounted on the housing. Each of the rotors  16 ,  18  successively engages a groove  25  in the main rotor  14  as the latter is rotatably driven by a motor (not shown) and, in cooperation with the wall of the bore (not shown) and specifically its end wall (not shown), defines a gas compression chamber. 
       FIG. 4  is a schematic illustration of a portion of the single screw compressor of  FIG. 3 . Specifically,  FIG. 4  shows a portion of the suction end cavity  27  with the main rotor  14  and housing  12  forming a discharge cavity  29 . A seal assembly  100  is provided between the suction end cavity  27  and the discharge cavity  29 . As will be appreciated in view of the description above in relation to  FIG. 3 , the suction end cavity  27  is generally a low-pressure cavity, with pressure in the suction end cavity  27  being around 30 psi in standard operating conditions. Compression of gases results in a high pressure in the discharge cavity  29 . In standard single screw compressors, the pressure in the discharge cavity  29  is around 150-300 psi. However, in the high-pressure single screw compressors of the present disclosure, pressures in the discharge cavity  29  range from 350 psi to 2000 psi. In the embodiment shown, the pressure in the discharge cavity  29  is from 350 psi, or 400 psi, or 500 psi, or 750 psi to 800 psi, or 1000 psi, or 1200 psi, or 1500 psi, or 2000 psi. 
     In an embodiment, the difference in pressure between the suction end cavity  27  and the discharge cavity  29  is greater than or equal to 150 psi, or greater than or equal to 200 psi, or greater than or equal to 250 psi, or greater than or equal to 300 psi, or greater than or equal to 350 psi, or greater than or equal to 400 psi, or greater than or equal to 450 psi, or greater than or equal to 500 psi, or greater than or equal to 550 psi, or greater than or equal to 600 psi. 
     In an embodiment, the difference in pressure between the suction end cavity  27  and the discharge cavity  29  is up to 600 psi, or 700 psi, or 800 psi, or 900 psi, or 1000 psi, or 1250 psi, or 1500 psi, or 1750 psi, or 2000 psi. 
     In contrast to the prior art seal shown in PRIOR ART  FIG. 1 , the seal assembly  100  is not machined directly to the main rotor  14 . Further, in contrast to the prior art seal shown in and PRIOR ART  FIG. 2 , the seal assembly  100  is not an independent component fixedly attached to the interior of the housing  12 . Rather, the seal assembly  100  in accordance with embodiments of the present disclosure is an independent component fixedly attached to the main rotor  14 . 
     As shown in  FIG. 4 , the seal assembly  100  is composed of a seal body  110  fixedly attached to the main rotor  14  using one or more attachment structures  130 . Specifically, in the embodiment shown, the seal body  110  is disposed around at least a portion of the circumference of the main rotor  14 , and preferably around substantially the entirety of the main rotor  14 . That is, in an embodiment, the seal body  110  is arcuate, and preferably disc-shaped to substantially or completely surround a circumference of the main rotor  14 . 
     Further, in the embodiment shown in  FIG. 4 , a cross-section of the seal body  110  is generally rectangular. In an embodiment, the seal body  110  has a consistent cross-sectional geometry along the length of the seal body  110 . 
     When viewed in cross-section as in  FIG. 4 , the side surfaces  112 ,  116  and inner surface  114  which abuts the main rotor  14  are generally smooth, while the outer surface  118  which faces the interior of the main housing  12  is textured to create a labyrinthine path from the suction end cavity  27  to the discharge cavity  29  between the seal body  110  and the housing  12 . In the embodiment shown, the labyrinthine path on the outer surface  118  of the seal body  110  is formed by a plurality of grooves of approximately the same depth along the arcuate outer surface  118  of the seal body  110 . The grooves are evenly spaced along the outer surface  118 . It will be appreciated that in further embodiments, the labyrinthine path may be formed using any surface texture which accomplishes the creation of the labyrinthine path, including, for example, and not limited to, grooves, teeth, channels, serpentine channels, bumps, stippling, and combinations thereof, any or all of which may be consistently, symmetrically or evenly spaced or positioned along the outer surface  118 , and any or all of which may have the same or different height or depth from or into the seal body  110 . 
     As mentioned above, in the embodiment shown, the seal body  110  entirely surrounds the main rotor  14  at a circumferences of the main rotor  14 . In other words, in the embodiment shown in  FIG. 4 , the seal body  110  is generally ring-shaped or disc-shaped having an outer diameter and an inner diameter. The thickness of the seal body  110  is consistent across all of the seal body  110 . 
     Importantly, the seal body  110  is not made of metal. Rather, the seal body  110  is made of a resin material, and more preferably a thermoplastic material or thermoset material. As used herein, the term “thermoplastic material” refers to a polymer or resin which once set in solid form, can again become pliable or moldable upon application of heat. As used herein, the term “thermoset material” refers to a polymer or resin which, once set in a solid form, does not again become pliable or moldable upon the application of heat. In other words, thermoplastic materials can be re-melted and re-formed several time, while thermoset materials once formed cannot be again melted and re-formed—they are permanently in the set form. In a particular embodiment, the thermoplastic material or thermoset material is a polyphenylene sulfide resin. 
     Further, in an embodiment, the thermoplastic or thermoset material is carbon or glass reinforced. That is, the thermoplastic or thermoset material contains carbon fibers, including woven carbon fibers, or glass fibers. In a particular embodiment, the thermoplastic or thermoset material comprises from 10%, or 15%, or 20%, or 25%, or 30%, or 40% or 50%, or 60% based on the total weight of the thermoplastic or thermoset material. 
     In an embodiment, the thermoplastic or thermoset material is a thermoplastic material having from 20%, or 30% to 40%, or 50% woven carbon fibers or glass fibers, based on the total weight of the thermoplastic material. In a further embodiment, the thermoplastic material is a polyphenylene sulfide resin having from 20%, or 30% to 40%, or 50% woven carbon fibers or glass fibers. 
     In an embodiment, the thermoplastic or thermoset material having carbon or glass fibers has a specific gravity from 1.25 g/cc, or 1.30 g/cc, or 1.35 g/cc, or 1.40 g/cc, or 1.45 g/cc, or 1.50 g/cc to 1.55 g/cc, or 1.60 g/cc, or 1.65 g/cc, or 1.70 g/cc, or 1.75 g/cc, as measured in accordance with ASTM D792. In an embodiment, the thermoplastic of thermoset material having carbon or glass fibers has a specific gravity from 1.45 g/cc, or 1.50 g/cc to 1.55 g/cc, or 1.60 g/cc, or 1.65 g/cc, or 1.70 g/cc. 
     In an embodiment, the thermoplastic of thermoset material having carbon or glass fibers has a tensile strength from 90 MPa, or 95 MPa, or 100 MPa, or 110 MPa, or 120 MPa to 130 MPa, or 140 MPa, or 150 MPa, or 160 MPa, or 170 MPa, or 175 MPa, as measured in accordance with ISO 527. 
     In another embodiment, the thermoplastic or thermoset material having carbon or glass fibers has a tensile strength from 15 kpsi, or 18 kspi, or 20 kpsi, or 22 kpsi to 25 kpsi, or 27 kpsi, or 30 kpsi, or 35 kpsi, as measured in accordance with ASTM D638. 
     In another embodiment, the thermoplastic or thermoset material having carbon or glass fibers has a tensile strength) (90°) from 550 MPa, or 600 MPa, or 625 MPa, or 650 MPa to 675 MPa, or 700 MPa, or 725 MPa, or 750 MPa, or 775 MPa, or 800 MPa, or 850 MPa, or 900 MPa, as measured at 20° C., or 23° C. (50% relative humidity), or 80° C. 
     In an embodiment, the thermoplastic or thermoset material having carbon or glass fibers has a glass transition temperature from 80° C., or 90° , or 100° C. to 110° C., or 120° C., or 130° C. 
     In an embodiment, the thermoplastic or thermoset material having carbon or glass fibers has a melting temperature from 250° C., or 260° C., or 270° , or 280° C. to 290° , or 300° C., or 310° C., or 320° C., or 330° C., or 350° C. 
     In an embodiment, the thermoplastic or thermoset material has one, some or all of the following properties:
         i) from 20%, or 30% to 40%, or 50% woven carbon fibers or glass fibers; and/or   ii) a specific gravity from 1.45 g/cc, or 1.50 g/cc to 1.55 g/cc, or 1.60 g/cc, or 1.65 g/cc, or 1.70 g/cc; and/or   iii) a tensile strength from 90 MPa, or 95 MPa, or 100 MPa, or 110 MPa, or 120 MPa to 130 MPa, or 140 MPa, or 150 MPa, or 160 MPa, or 170 MPa, or 175 MPa, as measured in accordance with ISO 527; and/or   iv) a tensile strength from 15 kpsi, or 18 kspi, or 20 kpsi, or 22 kpsi to 25 kpsi, or 27 kpsi, or 30 kpsi, or 35 kpsi, as measured in accordance with ASTM D638; and/or   v) a glass transition temperature from 80° C., or 90° , or 100° C. to 110° C., or 120° C., or 130° C.; and/or   vi) a melting temperature from 250° C., or 260° C., or 270° , or 280° C. to 290° , or 300° C., or 310° C., or 320° C., or 330° C., or 350° C.       

     In an embodiment, the thermoplastic or thermoset material has at least one, at least two, at least three, at least four, at least five, or all six of properties (i)-(vi). 
     As used herein, the term “attachment structures” refers to hardware components, assemblies and/or adhesive compounds which can be used to fixedly attach the seal body  110  to the main rotor  14 . In the embodiment provided in  FIG. 4 , the one or more attachment structures  130  is a screw which passes through the seal body  110  and extending partially into the main rotor  14 . However, in further embodiments, the one or more attachment structures may include, and is not limited to, screws, bolts, clips, adhesives, welds, and combinations of these and other structures or assemblies. 
     As further shown in  FIG. 4 , and in accordance with embodiments of the present disclosure, the seal body  110  is shown as attached to and partially set into the rotor  14 . That is, in the embodiment shown, the seal body  110  itself makes up a portion of the rotor  14  near the edge of the rotor  14  nearest the suction end cavity  27 . In further embodiments, the seal body  110  may be connected to a surface of the rotor  14  so as to extend away from the rotor  14  or, in further embodiments, set entirely into the rotor  14  (i.e., such that material of the rotor is in contact with both arcuate sides  112  and  116  of the seal body  110 . 
     It will be appreciated that, because the seal body  110  is fixedly attached with the rotor  14 , the high pressure seal assembly  100  will rotate with the rotor  14 . Because the seal body  110  is made of a thermoplastic or thermoset material, the material will wear against the metal housing  12  if in contact with the housing. The clearance, or space, between the housing  12  and the seal body  110 , and particularly the outer surface  118  of the seal body  110 , can therefore be optimized. In particular, in an embodiment, the distance between the outer surface  118  of the seal body  110  and the inner surface of the housing  12  is from 0 μm, or greater than 0 μm, or 0.01 μm, or 0.05 μm, or 0.1 μm, or 0.5 μm, or 1.0 μm, or 5.0 μm to 10 μm, or 25 μm, or 50 μm, or 100 μm, or 250 μm, or 500 μm, or 1000 μm. 
     It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.