Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Divisional of co-pending U.S. patent application Ser. No. 09/303,702 filed May 3, 1999, the contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to apparatus and methods for sealing the rotating shaft of a fluid-containing housing, such as the drive shaft of a fluid-conveying pump. More particularly, the present invention relates to apparatus and methods for cooling a seal that utilizes the fluid conveyed by a pump to improve the performance of the seal. 
     BACKGROUND ART 
     Various types of pumps are utilized in fluid transporting systems in order to develop and maintain a desired amount of flow energy in the fluid. Many of these pumps require for their operation at least one rotatable shaft to drive a mechanical energy-transferring device such as a piston, impeller, or gear. Typically, the rotational power or torque transmitted to the shaft is generated in a motor disposed in remote relation to the pump housing. Thus, a portion of the shaft necessarily extends outside the housing through, for example, a bore in a wall of the housing, for direct or indirect linkage to the motor. The shaft is supported or mounted in the housing, but must be free to rotate at the interface of the housing and shaft in accordance with the operation of the pump. 
     A clearance of operationally-significant magnitude therefore exists between the bore of the housing wall and the shaft, even in a case where a bushing or like element is employed at the shaft housing or pump/atmosphere interface. It is recognized that over the range of operating pressures of the pump, this clearance presents a potential leakage point. Depending on the direction of the pressure gradient between the interior of the pump housing and the atmosphere, the leakage point may be characterized by fluid leaking out of the pump or air infiltrating into the pump. The leakage may contribute to a variety of undesirable conditions, including reduced pump efficiency, reduced economic life of the pump and related components, increased maintenance costs, and contamination or non-uniformity of the fluid being pumped. Accordingly, it is well understood that the pump must include some means for sealing the shaft at the interface. 
     The approach taken in the design of the shaft seal is especially critical in the context of gear pumps, which are utilized in a number of well-known applications to meter and discharge various types of fluids. A gear pump may generally be described as being a rotary, positive displacement pump. In its most basic design, the gear pump includes a pair of intermeshing spur, single-helical or double-helical (i.e., herringbone) gears disposed in a housing having narrow internal dimensional tolerances. One gear serves as the driving gear and is rotatable with a drive shaft, i.e., the shaft powered by a motor. The other gear serves as the driven gear and is rotatable on an idler shaft. The shafts are mounted in journal bearings on each side of gears. In operation, the gears create a pressure differential between a suction side and a discharge side of the gear pump housing. The working fluid is drawn into the housing at the suction side, is carried by the teeth of each gear in spaces defined by the teeth and one or more internal surfaces of the housing, and is squeezed out on the discharge side. This design results in a relatively constant rate of fluid flow with a minimum of drifting or slippage. The flow rate is dependent on gear rotational speed, but is largely unaffected by viscosity variations and pressure differential variations across the gear pump. 
     The performance characteristics of the gear pump make it especially useful in the processing of high-shear polymers such as rubber, PVC, and EDPM, where pressure, volume and uniformity of the flowing material must be controlled. For example, the gear pump may be used to transport synthesis polymeric material from a reaction vessel. The gear pump may also be used in connection with an extruder. A typical extruder includes an elongate barrel containing a rotating auger or screw. A hopper feeds pellets or granules of the polymeric material to the barrel, where the material is heated and melted as it is forced along the length of the barrel by the screw. In such an application, the gear pump is installed between the extruder and an extrusion die to pressurize and meter the polymer melt flow, and to dampen any pressure fluctuations or surges caused by the rotating screw of the extruder. Because the gear pump moves fluid more efficiently than the extruder and reduces the load on the extruder, the gear pump itself can be used to develop the high pressure needed in the fluid line. This enables the discharge pressure of the extruder to be separately adjusted to a reduced level in better accord with the extruder&#39;s own optimal operating point. Finally, the gear pump may be installed in line with two or more extruders as part of a compounding or mixing process to obtain similar advantages. 
     In view of the foregoing, it is readily apparent that the gear pump may produce not only a high pressure differential between the inlet and outlet fluid conduits communicating with the gear pump, but also a high pressure differential between the interior of the gear pump and the atmosphere. Thus, the problem of leakage in gear pumps may be potentially significant. 
     The leakage problem is further exacerbated when the gear pump is used to process viscous fluids. For example, in polymeric material processing the bearings selected for the gear pump are typically hydrodynamic and self-lubricating. That is, instead of using a separate lubrication method such as a forced oil circulation system, the gear pump and bearings are designed with flow paths for diverting a portion of the incoming polymer melt flow and circulating that portion between the bearings and shafts prior to discharge from the gear pump. The radial clearance provided in the bearing permits a wedgeshaped polymeric film to develop between the journal and the bearing as the shaft rotates. As a result, a hydrodynamic pressure is generated in the film that is sufficient to float the journal portions of the shafts and support the loads applied to them. And since the journal portion of the rotating shaft does work on the polymeric film and induces shear stresses therein, the frictional heat energy produced raises the film temperature. Consequently, the heated and pressurized polymer melt flowing in the vicinity of the shaft/housing interface has a high tendency to leak out from the pump. 
     Previous sealing solutions have not adequately controlled the leakage problem observed in gear pumps. In one application typical of the prior art, the sealing means took the form of a packing seal. A packing seal is constructed of one or more layers, windings or gaskets constructed of packing material such as graphite-impregnated cotton. The packing material is compressed within a packer or stuffing box. The stuffing box is usually disposed adjacent to the main pump housing. The main shaft of the gear pump extends outside the housing and through the stuffing box, such that the compressed packing material is squeezed against the shaft. 
     Apart from its general ineffectiveness in environments marked by high pressure differentials, the packing seal suffers from several other problems The compressed packing material, although treated with graphite, is nonetheless abrasive enough to produce substantial frictional contact with the shaft and thereby accelerate wear and deterioration of the shaft as well as the packing material itself, inviting frequent replacement of both. Additionally, the excessive frictional contact engendered by the packing material causes the pump to work harder, which lowers output and efficiency. 
     An attempt to improve the utility of the packing seal in the context of polymer processing is disclosed in U.S. Pat. No. 4,515,512 to Hertell et al. The gear pump disclosed in the Hertell patent includes a stuffing box attached to an end wall of the main pump housing. The stuffing box is thus adjacent to and outside of the housing. The drive shaft of the gear pump extends through a bore in the end wall of the housing, through the stuffing box, and to the outside. There is no seal directly located in the clearance or gap created between the shaft and the bore of the gear pump housing end wall Accordingly, the fluid being pumped has a relatively unrestricted path by which to flow through the gap and into the stuffing box. 
     The Hertell patent provides two sets of gaskets, which are packed within the stuffing box in annular disposition around the shaft and the inner contour of the stuffing box. An annular cavity in the stuffing box separates the two gasket sets. A plurality of springs are circumferentially spaced in the annular cavity between the between the two gasket sets. The end of the stuffing box opposite the main pump housing is capped with a threaded flange annularly disposed around the shaft. Adjustment of the flange maintains axial compression of the gaskets in the direction of the gear housing, thereby maintaining frictional contact between the gaskets and the shaft. Within the annular cavity, the springs provide a biasing force to maintain a volume in the cavity between the two gaskets sets, as well as assist in compressing the gaskets. An inlet an outlet tube are placed in communication with the cavity and lead to a remote solvent reservoir, which stores a polymer solvent such as glycol. This arrangement serves to circulate and cool the solvent in the annular cavity. 
     In operation, some of the pressurized polymeric material in the housing of the gear pump in the Hertell patent tends to leak through the gap in the end wall in the direction of the stuffing box. However, the pump is configured with a bypass line such that the pressure in the gap is essentially equalized to the pressure on the suction side of the pump. This creates a pressure gradient in the direction of the stuffing box to the gear pump housing, so that polymer solvent tends to travel from the annular cavity of the stuffing box toward the housing. In this manner, it is intended that the solvent meet the leaking polymer and dissolve it. 
     It should be apparent from the foregoing that the concept disclosed in the Hertell patent is primarily directed at protecting the packing seal from leaking polymeric material by incorporating a complex and burdensome polymer solvent circulation system into the gear pump. That is, this concept does not focus on preventing leakage of fluid from the pump housing. In practice, the concept may improve the life of the packing material of the seal, but does not resolve the afore-described problems associated with the packing seal itself. Moreover, the solvent circulation system introduces additional problems. For instance, the Hertell patent acknowledges that, due to the pressure gradient, some of the solvent supplied may reach the interior of the gear pump and be discharged with the polymer melt flow. Such a result is clearly undesirable where even moderate quality control of the polymer product is specified. Also, the range of use of the Hertell system is limited, as many high-pressure/high-viscosity/high-temperature applications could be expected to overcome the capacity of the solvent system to prevent polymeric material from flooding the stuffing box, degrading or overwhelming the packing material, and leaking to the atmosphere. Another approach to sealing a gear pump operating in a highly viscous environment is disclosed in U.S. Pat. No. 4,699,575 to Geisel et al., which avoid use of a stuffing box. In the Geisel patent, a plurality of annular bushings constructed of a resilient plastic are press-fitted onto the drive and idler shafts of an adhesive gear pump, at locations between each gear and each journal bearing of the gear pump. The gear pump is configured with means for circulating an incompressible lubricant grease at high pressure throughout the gear pump, and through gaps located in proximity to the plastic bushings. The circulation means requires, among other things, several grease fittings for charging the circulation system, several internal passages within the gear pump, and high-pressure outlet relief valves leading to the atmosphere. According to the Geisel patent, the adhesive flowing through the gear pump is prevented from creeping past the bushings because the gaps are kept continuously filled with the incompressible grease. This approach presents many of the same disadvantages as described in regard to the Hartell patent, in that it specifies a system for circulating an additional material through the gear pump and accordingly introduces unnecessary complexities. 
     The first valid approach toward solving, rather than mitigating, the leakage problem in polymer processing applications is believed to be disclosed in U.S. Pat. No. 4,336,213 to Fox. In the gear pump disclosed therein, a seal is provided directly at the housing/shaft interface, and uses the polymeric material itself to complete the seal. The seal includes a cylindrical sleeve that is inserted onto the portion of the shaft extending beyond the pump housing. The seal member has a flange at the end of the sleeve opposite the pump housing. A plurality of holes are circumferentially disposed around an annular shoulder portion of the flange, through which bolts may be inserted to tightly secure the seal to the housing in annular disposition with the shaft. When inserted onto the shaft, the cylindrical inner surface of the sleeve abuts the outer surface of the shaft. Accordingly, the inner surface of the sleeve and the outer surface of the shaft together define a clearance or gap which becomes the potential leakage point for the gear pump. 
     The seal in the Fox patent is characterized in part by the fact that a shallow helical channel is formed on the inner surface of the sleeve. The helical channel extends substantially along the entire length of the inner surface The orientation or “hand” of the helical path taken by the channel is opposite to that of the shaft rotation. Thus, during operation of the gear pump, polymeric material entering the clearance between the sleeve and shaft tends to travel in the helical channel. However, given the opposite orientation of the helix, the leaking material is effectively pumped back toward the interior of the pump housing and thus is prevented from leaking to the outside. In essence, the configuration of the sleeve, flanged and bolted to the housing, provides a mechanical seal while the polymeric material opposed by the helical channel provides a viscous, relatively static seal. Furthermore, the existence of the polymeric material in the clearance significantly reduces friction therein. Accordingly, this design has been highly effective as a seal for gear pumps operating over a considerable range of pressures, temperatures and viscosities. 
     In U.S. Pat. No. 4,471,963 to Airhart, an attempt was made to improve upon the design disclosed in the Fox patent. As in the Fox patent, the seal provided in the Airhart patent includes a cylindrical sleeve that is flanged and bolted to the housing of the gear pump. Two helical channels are formed on the inner surface of the sleeve and are axially separated by a relatively deep and wide annular cavity. The first helical channel begins at a point proximate to the pump housing and terminates in fluid communication with the annular cavity. On the opposite side of the annular cavity farthest from the housing, the second helical channel communicates with the annular cavity and terminates at a point proximate to the outer end of the sleeve. The orientation of the first helical channel is the same as that of the rotating shaft, and hence polymeric material leaking from the gear pump had a high tendency to flow through the first helical channel and accumulate in the annular cavity. On the other hand, the second helical channel has an opposite orientation, such that it impedes outwardly axial flow of polymeric material beyond the annular cavity. 
     The seal in the Airhart patent is characterized in that means are provided for actively cooling the polymeric material accumulated in the annular cavity so as to create a polymeric plug. Two bores are drilled at diametrically opposite sides of the flange and communicate with an annular passageway formed within the solid cross-sectional portion of the cylindrical sleeve of the seal. The bores are connected via tubing to a circulation system. During operation of the pump, water or other coolant is circulated through the bores and the annular passageway to carry heat away from the polymeric material present in the seal, thereby solidifying the polymeric material and forming the plug. 
     The approach for improving the helically-channeled seal disclosed in Fox by active cooling is at first glance attractive. However, as in the case of the Hertell and Geisel patents, the seal in the Airhart patent requires external equipment and conduits to circulate an additional fluid through the pump. This adds to the cost and complexity of the gear pump, and introduces additional areas of maintenance. 
     The present invention is therefore provided to solve these and other problems associated with the prevention of leakage of rotating shafts in general, and specifically with the prevention of leakage at the shaft/housing interface of gear pumps operating in polymer processing applications. 
     DISCLOSURE OF THE INVENTION 
     In accordance with the present invention, an improved sealing apparatus is provided with structure for passively cooling the seal. In one embodiment, an air-cooled shaft seal comprises an annular body having an inner surface and an outer surface. One or more helical channels are formed on the inner surface. A plurality of external surfaces such as radial fins are disposed in axially spaced relationship on the outer surface, and extend radially in a direction away from a longitudinal axis of the annular body. The external surfaces present a substantially increased surface area through which heat energy is transferred from polymeric material contained in the seal to the atmosphere. In systems where viscous material such as polymer melt or adhesive is being processed, the structure of the present invention permits a substantial amount of heat energy dissipation, and is effective to form a relatively static and frictionless seal or plug in the helical channel itself, without the need for an annular cavity or external active heat transfer equipment. 
     In another embodiment, a gear pump for transporting a viscous material under pressure comprises a housing having first and second sides, wherein each side has a hole. A shaft is disposed in the housing and extends through the first and second holes of the housing. The shaft has a first outer section disposed outside the housing beyond the first hole and a second outer section disposed outside the housing beyond the second hole. A sealing member is annularly disposed around the shaft and defines an annular space between an inner surface of the sealing member and the outer surface of the shaft. The sealing member has a first portion disposed in the first hole and a second portion disposed outside the housing. In addition, the sealing member includes a plurality of external surfaces disposed in axially spaced relationship on the second portion. The shaft upon which the sealing member is installed may be the drive shaft of the gear pump. 
     Therefore, it is an object of the present invention to provide an improved seal for a rotating shaft. 
     It is another object of the present invention to provide a shaft seal for a pump which is adapted to cool material leaking therein without the use of active cooling means. 
     Some of the objects of the invention having been stated hereinabove, other objects will become evident as the description proceeds, when taken in connection with the accompanying drawings as best described hereinbelow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective cut-away view of a conventional gear pump using a packing seal; 
     FIG. 2 is a vertical cross-sectional view of a typical gear pump showing the fluid moving operation of the gear pump; 
     FIG. 3 is a side elevation view of a portion of a polymer processing system wherein a gear pump is utilized; 
     FIG. 4 is a perspective view of a gear pump seal of the prior art that includes a helical channel; 
     FIG. 5 is a perspective cut-away view of a gear pump of the prior art that includes the seal of FIG. 4; 
     FIG. 6A is a side cross-sectional view of a sealing member according to the present invention; 
     FIG. 6B is a perspective view of the sealing member of FIG. 6A; 
     FIG. 7A is a side cross-sectional view of another sealing member according to the present invention; 
     FIG. 7B is a perspective view of the sealing member of FIG. 7A; 
     FIG. 8 is an exploded view of a gear pump including sealing members according to one embodiment of the present invention; 
     FIG. 9 is a perspective view of a third sealing member according to the present invention; 
     FIG. 10A is an enlarged fragmentary cross-sectional view of a helical groove of a sealing member according to the present invention; and 
     FIG. 10B is an enlarged fragmentary cross-sectional view of another helical groove of a sealing member according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following embodiments of the present invention are described with particular application to the field of polymer processing. It will be readily understood, however, that the broad teachings of the present invention have utility in any application wherein passive cooling of a shaft seal improves sealing performance. 
     FIGS. 1 and 2 illustrate the main components of a conventional gear pump generally designated  12 . Gear pump  12  has a main housing  14  with a suction side  16  and a discharge side  18 . A drive shaft  20  and an idler shaft  22  are mounted within main housing  14  in parallel relation. Drive shaft  20  includes a driving gear  24  and idler shaft  22  includes a driven gear  26  meshing with driving gear  24 . Each shaft  20 ,  22  is rotatably mounted in one or more journal bearings  28 . Bearings  28  are typically hydrodynamic and self-lubricating. Drive shaft  20  extends through a sealing side  30  of main housing  14  and includes a keyway  32  or similar means for coupling drive shaft  20  with transmission and prime moving means (not shown) such as a gear reduction box and motor, respectively. A packing or stuffing box  34  is formed on or attached to sealing side  30  of main housing  14 . Stuffing box  34  contains packing material  36  compressed against drive shaft  20 , as described above, and is closed with a flange  38  bolted thereto. 
     As best shown in FIG. 2, main housing  14  has an inlet port  41  on suction side  16  and an outlet port  42  on discharge side  18 . In operation, the rotating shafts  20 ,  22  cause gears  24 ,  26  to mesh in the direction shown by the arrows A. This movement creates a pressure differential across gear pump  12 . Accordingly, material is drawn into main housing  14  on suction side  16  and is carried in spaces  44  defined by teeth  46  and internal chambers  48  of housing  14 . The material is then discharged at high pressure on discharge side  18 . In most cases, gear pump  12  effectively dampens the undesirable conditions occasioned by screwbeat  51  and surge  52  from an upstream extruder and provides a uniform, pressurized flow of material for further processing. 
     FIG. 3 illustrates gear pump  12  installed in a typical polymer processing application. A hopper  54  delivers pelletized or granulated polymer feedstock to an extruder  56 . Extruder  56  includes an auger or screw  58  and means for heating and melting the polymer feedstock. Auger  58  and gear pump  12  are powered by motors  59 ,  60 . Extruder  56  and motor  59  are mounted on appropriate support means  61 . Melted polymeric extrudate exits extruder  56  and flows toward gear pump  12  along a process line or conduit  62 . A screen or filter means  64  may be interposed between extruder  56  and gear pump  12 . From discharge side  18  of gear pump  12 , the pressurized and heated polymeric extrudate flows through a die  66 . Depending on the particular application, die  66  is adapted to extrude a sheet tube or other profile. Other components such as cooling units and slitters (not shown) may be installed downstream of die  66  as needed. 
     FIGS. 4 and 5 illustrate a shaft sealing member generally designated  70  without the passive cooling means of the present invention. Sealing member  70  includes a cylindrical body  72  with a central cylindrical bore  74  and outer surface  76 . A helical channel  78  is formed in cylindrical bore  74 . Sealing member  70  is mounted to drive shaft  20  of gear pump  12  with helical channel  78  turning in a direction opposite to that of rotation of drive shaft  20 . Helical channel  78  and cylindrical body  72  together define a continuous clearance space  79  wrapped around drive shaft  20  within sealing member  70 . When gear pump  12  is placed in operation, polymeric material leaking axially into sealing member  70  from main housing  14  of gear pump  12  tends to enter helical channel  78 , wherein drag forces of oppositely oriented helical channel  78  oppose further leakage. In many applications, sealing member  70  does not provide a satisfactory seal because outer surface  76  of cylindrical body  72  and outer surfaces of sealing side  30  of gear pump  12  cannot sufficiently cool the leaking polymeric material residing therein. 
     FIGS. 6-11 illustrate practical applications of the present invention for improving the sealing effect of a shaft seal, which retain the benefits accruing from a helical-type channel but avoid the use of external circulation equipment or other active cooling means. Referring to FIGS. 6A and 6B, a sealing member generally designated  80  includes a body or sleeve generally designated  82  and has an inner surface  84  defining a cylindrical bore  86 . Sleeve  82  is preferably cylindrical as shown, but other cross-sectional shapes may be provided if desired. A helical groove or channel  88  is formed on inner surface  84  along an axial length of cylindrical bore  86 . Helical channel  88  begins at a point on an inner end  91  of sleeve  82  communicating with the interior of a gear pump. On an outer end  92  of sleeve  82 —that is, the end of sleeve  82  open to the atmosphere outside the gear pump—a plurality of axially spaced external surfaces are included, preferably in the form of cooling fins  94  that extend radially from an outer surface  96  of sleeve  82 . Fins  94  may be formed by reducing the diameter of a first section  98  of sleeve  82  to define a flange  101  of larger diameter on a second section generally designated  103  of sleeve  82 , then cutting into flange  101  at axially spaced intervals. Alternatively, flange  101  and fins  94  are provided as separate elements and secured onto sleeve  82  such as by press-fitting. A plurality of mounting bores  104  are drilled through fins  94  and flange  101  at circumferential intervals around cylindrical bore  86 , through which bolts may extend to secure sealing member  80  to a gear pump. 
     Sealing member  80  is preferably constructed of stainless steel. If press-fitted onto sleeve  82 , the material selected for fins  94  may be different than that of sleeve  82  in order to tailor the heat transfer properties of sealing member  80  to specific needs. 
     The dimensions of sealing member  80  will depend upon the size of the gear pump and shaft used, as well as the internal temperatures expected to be developed in the proximity of the sealing area. The following dimensions are given as an example. Sleeve  82  has an overall axial length of 1.65″ of which first section  98  has an axial length of 0.78″. First section  98  has an outside diameter of 2.0″ and second section  103  with fins  94  has an outside diameter of 3.0″, such that fins  94  have a radial height of 0.5″. Inner surface  84  of sleeve  82  forming cylindrical bore  86  has an inside diameter of 1.02″. Outer and inner surfaces  96 ,  84  of sleeve  82  together define an annular thickness  106  of approximately 0.5″. As best seen in FIG. 10A, helical channel  88  has a depth of 0.01″ from inner surface  84  of sleeve  82  into annular thickness  106  and has an axial width of 0.125″. The helix angle of helical channel  88  is such that helical channel  88  makes two turns per inch of axial length of sleeve  82 ; however, the helix angle could be varied along the axial length of sleeve  82 . The width of lands  108  between each section of helical channel  88  is 0.125″. Each fin  94  has a thickness or axial width of 0.09″. Fins  94  are spaced apart at intervals of 0.06″. 
     The number of fins  94  formed or disposed on sleeve  82  are shown to be four, but the precise number may be varied. More importantly, the number and dimensions of fins  94  are specified so as to provide a substantial increase in the surface area available for transfer of heat energy from polymeric material present in helical channel  88  to the atmosphere. The increase in the amount of heat energy removed by the mechanisms of conduction and convection is obtained without the use of a coolant circulation system. Moreover, fins  94  constitute a passive heat transfer device that is much more efficient and simple than an active cooling device. 
     FIGS. 7A and 7B illustrate another sealing member generally designated  120  according to the present invention. Sealing member  120  can be more effective than, and thus preferred over, sealing member  80  shown in FIGS. 6A and 6B for many high-viscosity/high-temperature polymer processing applications. Similar features shared between sealing member  120  in FIGS. 7A and 7B and sealing member  80  in FIGS. 6A and 6B are designated using the same reference numerals. 
     With respect to sealing member  120  in FIGS. 7A and 7B, the diameter of second section  103  of sleeve  82  is considerably reduced. This results in a reduced annular thickness  106 . In addition, the width of fins  94  is reduced. By comparison to sealing member  80  in FIGS. 6A and 6B, the diameter of second section  103  with fins  94  is reduced from 3.0″ to 2.0″, such that fins  94  have a radial height of 0.336″. Annular thickness  106  of sleeve  82  is reduced from 0.5″ to 0.15″. The width or thickness of fins  94  is reduced from 0.09″ to 0.06″. These reduced dimensions result in reduced mass and cross-sectional areas of sealing member  120  and, consequently, improved rate of heat dissipation from the journal area of sealing member  120  during operation of the gear pump. The reduced thickness of fins  94  enables a greater number of fins  94  to be used for the same axial length of sleeve  82 , if desired. It should also be noted that the reduced dimensions do not affect the amount of surface area available for heat transfer. 
     In operation, sealing member  120  (or sealing member  80 ) is fitted onto one or both ends of a drive shaft  122  of a gear pump  124 , as shown in FIG.  8 . End plates  126  of gear pump  124  include mounting holes  128  to receive sealing members  120 . A portion of the pressurized polymeric material flowing within gear pump  124 , especially that portion distributed through journal bearings  131  on either side of gears  129 , tends to leak in an axially outward direction into clearance spaces in end plates  126  at the sealing members  120 . The leaking portion enters helical channels  88  of sealing members  120 . Fins  94  on sealing members  120  take full advantage of the temperature gradient between drive shaft  122  and the atmosphere, thereby contributing to a rapid cooling of the polymeric material contained in helical channels  88 . At least a portion of the polymeric material in helical channels  88  consequently solidifies to form a frictionless mechanical plug or seal and prevent polymeric material from escaping through sealing members  120 . 
     FIG. 9 illustrates a third embodiment of the invention, sealing member  130 , that includes two helical channels  132 ,  134  within cylindrical bore  86 . Helical channels  132 ,  134  both run along the same axial length of sleeve  82 , preferably 180 degrees out of phase with each other on the circumference of the cylindrical bore  86 . This configuration may be preferred in order to increase the amount of cooled polymeric material available to form the seal. In other cases, one or more additional channels may be needed in order to enable the cross-sectional areas of the channels to be reduced while retaining a sufficient sealing area for the associated shaft. In still other cases, each helical channel  132 ,  134  may be sized differently from each other to achieve different dynamic effects in sealing member  130 . 
     FIGS. 10A and 10B illustrate two of many suitable cross-sectional profiles for helical channel  88 . The rectangular profile shown in FIG. 10A has been found to be suitable under the conditions thus far tested, and therefore is preferred. The profile shown in FIG. 10B is analogous to the inverse flight of a screw thread and presents an alternative. The exact profile chosen will depend upon several fluid mechanical properties, such as those used to determine the Reynolds number in a fluid system. In the case where two or more helical channels  88  are used, the profile of each channel  88  may differ to achieve different sealing effects. 
     It will be understood that other embodiments of the present invention may be manufactured in a variety of ways, and that these other embodiments are contemplated to fall within the scope of the present invention. For instance, the shape, number and configuration of cooling fins  94  may be changed. It will also be understood that other types of channels or grooves may be utilized in cylindrical bore  85  of sleeve  82 . In the embodiments shown in the Figures, the twisting or turning path taken by helical channel  88  around a shaft provides a large sealing area for the shaft and the orientation or “hand” of the helix shape in opposition to shaft rotation slows down the leakage rate to afford the polymeric material time to solidify. These effects, however, may be emulated in other types of winding or labyrinthine channels, although the helical path is preferred and relatively easy to form. 
     It will be further understood that various other details or features of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims. in other types of winding or labyrinthine channels, although the helical path is preferred and relatively easy to form. 
     It will be further understood that various other details or features of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims.

Technology Category: 2