Abstract:
A valve bushing for an injection molding apparatus and method of use is disclosed. This includes an actuator, a manifold having an internal channel for the flow of melted resin, a valve stem, having a longitudinal axis, and is operatively connected to the actuator and movable within at least a portion of the internal channel of the manifold, and a valve bushing that at least partially encircles the valve stem along the longitudinal axis, wherein the valve bushing includes a projecting member so that when pressure is applied to a bottom portion of the valve bushing, that deflection of the valve bushing occurs along the longitudinal axis of the valve stem, which is then translated into radial constriction by the projecting member of the valve bushing to reduce leakage.

Description:
BACKGROUND OF INVENTION 
       [0001]    Valve bushings utilized in injection molding equipment require a precise fit between the stem and the bushing to ensure that excessive leakage of resin does not occur. Resins that have a melt flow index (“MFI”) of greater than 80 can excessively leak even with a small gap. Leakage is becoming an increasing challenge as new low viscosity resins continue to emerge. However, a tight fit between the stem and the bushing can cause the stem to seize. Also, the manufacturing tolerances that are required to prevent leaks are very exacting and costly. 
         [0002]    An approach that has been utilized to address this situation is the use of coatings and/or treatments of not only the valve stem but the valve bushing to prevent resin leakage. This provides for a very expensive approach for dealing with this problem. 
         [0003]    Another approach to this situation is disclosed in U.S. Pat. No. 6,840,758 (Babin et al.). This patent discloses a spacer that is compressed between an actuator block and a manifold block. The compression causes the spacer to radially compress to cause the bushing to prevent seepage from traveling up the valve stem and the bushing. However, if too much pressure is applied to the spacer, then valve stem seizure will occur. Also, too little compression may provide leakage. 
         [0004]    Still another approach is disclosed in U.S. Pat. No. 6,159,000 (Puri et al.), which discloses a guide sleeve that has a narrow portion that clings to the outside of the valve stem. However, this guide sleeve does not assert any additional pressure to block the flow of resin, especially low viscous resin having a high MFI. 
         [0005]    U.S. Pat. No. 6,729,871 (Sattler et al.) discloses the utilization of a cooled bush that increases the viscosity of the melted thermoplastic material in the gap between the stem and the bush. In this manner, leakage is prevented even when the gap is large; however, additional energy and resources are required to provide the cooling, and in this manner there are also issues created involving maintenance. A similar approach is to require cooling to a back plate to increase resin viscosity and prevent resulting leakage. This again is a very costly approach with regard to not only initial expenditures but also energy costs as well as ongoing maintenance. 
         [0006]    U.S. Pat. No. 5,518,393 (Gessner) discloses a bushing having a melt channel for mating with a melt channel in a manifold in which the bushing is housed and with an axial channel in a nozzle body. The bushing is sized to fit within a bore in the manifold in an attempt to reduce the possibility of leakage between the bushing and the manifold. However, there is nothing in this structure that will provide additional constriction on the valve stem to reduce resin leakage in the presence of heat, pressure and a high MFI resin. 
         [0007]    U.S. Pat. No. 4,344,750 (Gellert) discloses an electrically heated sprue bushing seated in a well in the cavity plate with a centrally extending melt runner passage which branches radially outward with separate channels leading to a number of edge gates in the cavity plate. An air gap is provided to insulate the hot sprue bushing from the surrounding cooled cavity plate and a hollow seal is provided at each gate to convey the melt across the air gap. This heating of the metal applies the pressure to reduce resin flow. This is a feature that requires significant energy consumption as well as more maintenance due to increased complexity. 
         [0008]    U.S. Pat. No. 5,885,628 (Swenson et al.) discloses an injection molding nozzle for disposition in a mold. The nozzle is for injecting melt into a cavity of the mold, and includes a body having a through bore extending therethrough for receiving the melt. A nozzle member surrounds the body at a position upstream of the nozzle piece and has an inner surface contacting the body and an outer surface contacting the mold that forms a seal against melt flow upstream from the nozzle member. Swenson et al. does not apply any additional pressure to the valve stem to prevent resin flow when resin is flowing in the nozzle. 
         [0009]    U.S. Pat. No. 6,555,044 (Jenko) discloses a bushing held in the manifold by a nut that traps a back-up pad. When this nut is tightened, a metal “O” ring seals tightly to reduce plastic leakage along the bore of the bushing. However, “O” rings eventually wear out and with vibration; the nut can loosen up to allow resin flow. 
         [0010]    The present invention is directed to overcoming one or more of the problems set forth above. 
       SUMMARY OF INVENTION 
       [0011]    In an aspect of this invention, an injection molding apparatus is disclosed. This injection molding apparatus includes an actuator, a manifold having an internal channel for the flow of melted resin, a valve stem, having a longitudinal axis, and is operatively connected to the actuator and movable within at least a portion of the internal channel of the manifold, and a valve bushing that at least partially encircles the valve stem along the longitudinal axis, wherein the valve bushing includes a projecting member so that when pressure is applied to a bottom portion of the valve bushing, that deflection of the valve bushing occurs along the longitudinal axis of the valve stem, which is then translated into radial constriction by the projecting member of the valve bushing to reduce leakage. 
         [0012]    In another aspect of this invention, an injection molding apparatus is disclosed. This injection molding apparatus includes an actuator, a manifold having an internal channel for the flow of melted resin, a valve stem, having a longitudinal axis, and is operatively connected to the actuator and movable within at least a portion of the internal channel of the manifold, and a valve bushing that at least partially encircles the valve stem along the longitudinal axis, wherein the valve bushing includes a projecting member, and an upper member that is positioned adjacent to the projecting member so that when pressure is applied to a bottom portion of the valve bushing, that deflection of the valve bushing occurs along the longitudinal axis of the valve stem, which is then translated into radial constriction, by the projecting member of the valve bushing being wedged against a contacting surface of the upper member, to reduce leakage. 
         [0013]    In yet another aspect of this invention, an injection molding apparatus is disclosed. This injection molding apparatus includes an actuator, a manifold having an internal channel for the flow of melted resin, a valve stem, having a longitudinal axis, and is operatively connected to the actuator and movable within at least a portion of the internal channel of the manifold, a valve bushing that at least partially encircles the valve stem along the longitudinal axis, and includes a projecting member, wherein the projecting member includes a top portion having a ferrule, which includes resilient metal, and an upper member that is positioned adjacent to the projecting member so that melted resin, without force against a bottom portion of the valve stem, can apply pressure to the ferrule, which is then translated into radial constriction, by the projecting member of the valve bushing being wedged against a contacting surface of the upper member, to reduce leakage. 
         [0014]    In still yet another aspect of this invention, a valve bushing for use in an injection molding apparatus is disclosed, which includes an actuator, a manifold having an internal channel for the flow of melted resin, and a valve stem, having a longitudinal axis, and is operatively connected to the actuator and movable within at least a portion of the internal channel of the manifold. The valve bushing includes a projecting member so that when pressure is applied to a bottom portion of the valve bushing, that deflection of the valve bushing occurs along the longitudinal axis of the valve stem, which is then translated into radial constriction by the projecting member of the valve bushing to reduce leakage, wherein the valve bushing that at least partially encircles the valve stem along the longitudinal axis. 
         [0015]    In still another aspect of this invention, an injection molding apparatus is disclosed. This injection molding apparatus includes an actuator, a manifold having an internal channel for the flow of melted resin, and a valve stem, having a longitudinal axis, and is operatively connected to the actuator and movable within at least a portion of the internal channel of the manifold, is disclosed. The valve bushing includes a projecting member so that when pressure is applied to a bottom portion of the valve bushing, that deflection of the valve bushing occurs along the longitudinal axis of the valve stem, which is then translated into radial constriction by the projecting member of the valve bushing to reduce leakage, wherein the valve bushing that at least partially encircles the valve stem along the longitudinal axis. 
         [0016]    In another aspect of this invention, a method for utilizing an injection molding apparatus is disclosed. The method includes utilizing a valve bushing that at least partially encircles the valve stem along a longitudinal axis, wherein the valve bushing includes a projecting member so that when pressure is applied to a bottom portion of the valve bushing, that deflection of the valve bushing occurs along the longitudinal axis of the valve stem, which is then translated into radial constriction by the projecting member of the valve bushing to reduce leakage, wherein the valve stem is operatively connected to an actuator and movable within at least a portion of an internal channel of a manifold. 
         [0017]    In yet another aspect of this invention, a method for utilizing an injection molding apparatus is disclosed. The method includes utilizing a valve bushing that at least partially encircles the valve stem along a longitudinal axis, wherein the valve bushing includes a projecting member, wherein the projecting member includes a top portion having a ferrule, which includes resilient metal so that melted resin can apply pressure to the ferrule which is then translated into radial constriction by the projecting member of the valve bushing to reduce leakage even if no pressure is applied to a bottom portion of the valve bushing. 
         [0018]    These are merely some of the innumerable aspects of the present invention and should not be deemed an all-inclusive listing of the innumerable aspects associated with the present invention. These and other aspects will become apparent to those skilled in the art in light of the following disclosure and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]    For a better understanding of the present invention, reference may be made to the accompanying drawings in which: 
           [0020]      FIG. 1  is a sectional view through an injection molding apparatus of the present invention having a valve bushing in accordance with a preferred embodiment of the present invention; 
           [0021]      FIG. 2  is an isolated view of valve bushing, as shown in  FIG. 1 , in accordance with the preferred embodiment of the present invention; 
           [0022]      FIG. 3  is a sectional view through an injection molding apparatus of the present invention having a valve bushing in accordance with an alternative embodiment of the present invention; 
           [0023]      FIG. 4  is an isolated view of valve bushing, as shown in  FIG. 3 , in accordance with an alternative embodiment of the present invention; 
           [0024]      FIG. 5  is an illustrative schematic that illustrates the function of the valve bushing, in an exaggerated state to creating a wedging effect, without a valve stem to support the inner diameter in accordance with the alternative embodiment of the present invention as shown in  FIG. 3 ; 
           [0025]      FIG. 6  is a graphical representation of contact pressure on a valve stem as a function of the distance from the tip of the bushing in accordance with the alternative embodiment of the present invention as shown in  FIG. 3 ; and 
           [0026]      FIG. 7  is an illustrative schematic that illustrates a modification of the alternative embodiment of the present invention as shown in  FIG. 3  utilizing a ferrule having a resilient metal, e.g., resilient steel, located at the top portion of the valve bushing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Referring initially to  FIG. 1 , a hot runner valve gate system for injecting resin into a mold, or the like, is illustrated and is generally indicated by numeral  10 . The system includes a backing plate  12  and a manifold plate  14 . The system also includes a nozzle assembly  18  for introducing melted resin into a mold cavity  20 . The nozzle assembly  18  is located within the manifold plate  14  and includes a nozzle housing  22  with a nozzle tip  24  secured thereto. There is a heater (not shown) that is at least partially positioned on an outside diameter of the nozzle housing  22 . The heater may be any suitable heater known in the art to which current is provided by way of an electric cable. There is a wide variety of heat conductive materials that can be utilized for the nozzle housing  22 , and an illustrative, but nonlimiting, example includes steel. Also, there is a wide variety of heat conductive materials that can be utilized for the nozzle tip  24 , and an illustrative, but nonlimiting, example includes copper alloys. 
         [0028]    The nozzle housing  22  includes an axial channel  36  through which melted resin can flow. The nozzle tip  24  surrounds a terminal portion of the axial channel  36 . There is a valve stem  42  that controls the opening and closing of the melt channel opening  68  located in the gate insert  40  that controls the flow of melted resin into the mold cavity  20 . There is an insulator  66  that occupies the space between the nozzle tip  24  and the gate insert  40  and also contains a melt channel opening  68  located therein. There are cooling channels  72  in the gate insert  40  that allow the melted resin to solidify in the mold cavity  20  prior to the opening of a mold (not shown). 
         [0029]    The valve stem  42  can be made of a wide variety of shapes and materials. An illustrative, but nonlimiting, embodiment of a valve stem  42  includes a steel rod. The valve stem  42  extends through a passageway  44  in a manifold  30  and into the nozzle housing  22 . The passageway  44  connects to a melt channel  46  located in the manifold  30 . The end of the valve stem  42  that is located opposite to the gate insert  40  is connected to a piston head  48  by means of a threaded clamp  50 . 
         [0030]    There is an actuator that is generally indicated by numeral  51 , which includes a piston  52  having a piston head  48  that is housed within a cylinder  54  and the backing plate  12 . Fluid, e.g., pneumatic air, is selectively provided through a first channel  64  into an upper chamber  73  to apply downward pressure on the piston  52 . The downstroke of the piston  52  causes the valve stem  42  to close and/or reduce the cross-sectional area of the gate insert  40  to restrict or stop the flow of melted resin into the mold cavity  20 . Fluid, e.g., pneumatic air, is selectively provided through a second channel  67  into a lower chamber  71  to apply upward pressure on the piston  52 . The upstroke of the piston  52  causes the valve stem  42  to open and/or increase the cross-sectional area of the gate insert  40  to allow the flow of melted resin into the mold cavity  20 . 
         [0031]    The manifold  30  is formed between the manifold plate  14  and the backing plate  12  and is separated from the manifold plate  14  and the backing plate  12  by an air gap  56 . The manifold  30  includes the melt channel  46  that forms a portion of the hot runner system that transports melted resin from a source (not shown) to the gate insert  40  associated with a mold cavity  20 . The manifold  30  houses a valve bushing  32 . There is a wide variety of materials that can be utilized for the manifold  30 , which can include any suitable metal or heat conducting material known in the art. The valve bushing  32  is preferably, but not necessarily, formed of flexible metal, e.g., strong steel, which has a predictable flexibility when shaped correctly and which can constrict under pressure. The valve bushing  32 , which includes an aperture  34 , surrounds a portion of the valve stem  42 . There is also a melt channel opening  62  that is in fluid relationship with the melt channel  46  in the manifold  30  and the axial channel  36  in the nozzle assembly  18 . 
         [0032]    There is a disk spring  28  that will deflect as the cylinder  54 , the manifold  20 , and the nozzle housing  22  expand due to an increase in temperature. This disk spring  28  will create a resilient spring action in the nozzle assembly  18 , which is independent of sealing action created by the valve bushing  32  and the manifold  30  as well as between the valve bushing  32  and the backing plate  12 . The disk spring  28  is mounted on a nozzle insulator  74 , where the nozzle insulator  74  is adjacent to and supports the nozzle housing  22 . 
         [0033]    Referring now to  FIG. 2  and as previously discussed above, mounted within the manifold  30  is the valve bushing that is indicated by numeral  32 . When melted resin enters the melt channel  46  in the manifold  30 , the melted resin then passes into a melt channel opening  62  in the passageway  44 . The melted resin applies upward pressure against a lower, end portion  80  of the valve bushing  32 . This upward injection pressure  81  on the lower, end portion  80  deflects the valve bushing  32  and moves the valve bushing  32  upward axially  82  along the passageway  44 . There is a projecting member  86  extending outward from the valve bushing  32  within the air gap  56 . 
         [0034]    Preferably, the projecting member  86  is traverse to the passageway  44 , and preferably in an angle α is in a range from about twenty degrees to about seventy degrees from a line that is perpendicular to the longitudinal axis of the valve stem  42 ; more preferably, the angle α is in a range from about thirty degrees to about sixty degrees from a line that is perpendicular to the longitudinal axis of the valve stem  42 ; most preferably, the angle α is in a range from about forty degrees to about fifty degrees from a line that is perpendicular to the longitudinal axis of the valve stem  42  where the optimal value of angle α is forty-five degrees from a line that is perpendicular to the longitudinal axis of the valve stem  42 . The projecting member  86  preferably includes at least one leg portion extending downward from the projecting member  86  in preferably a vertical direction to contact a portion, which is the upper surface  76  of the manifold  30  and the lower portion of the air gap  56 . In the preferred illustrative, but nonlimiting, embodiment, there is a first leg portion  88  and a second leg portion  90 . 
         [0035]    Therefore, the valve bushing  32  forms a cantilever structure that is preferably but not necessarily m-shaped, in cross-section, so that when the previously described upward force from injection pressure  81  is applied to the valve bushing  32 , axial movement, indicated by arrows  82 , is then translated to radial deflection, indicated by force arrows  94 , of the valve bushing  32  to constrict and reduce resin flow from melt channel opening  62  between the aperture  34  of the valve bushing  32  and the valve stem  42 . The reactive support for the valve bushing  32  is located outside the aperture  34  of the valve bushing  32  and can possibly reduce or eliminate any cooling needed for the backing plate  12 , previously shown in  FIG. 1 . The axial force due to a cantilever-effect causes the aperture  34  within the valve bushing  32  to constrict in a radial direction as shown by the force arrows indicated by numeral  94 . It is the application of injection molding pressure  81  against the lower, end portion  80  of the valve bushing  32  that creates the restriction of the stem aperture  34 . As an illustrative, but nonlimiting, example, with a nozzle force of 6,000 pound-force, the aperture  34  can constrict by less than 1 micron, but with the same nozzle force of 6,000 pound-force with an injection pressure of 20 kilo-pound per square inch, the aperture  34  can constrict by 6 microns. There is a seal  60  that is located between the valve bushing  32  and an upper surface  76  for the manifold  30 . This operates to prevent plastic leakage between the manifold  30  and the valve bushing  32  through passageway  44 . 
         [0036]    There is a first, alternative embodiment that is shown in  FIG. 3  of a hot runner valve gate system for injecting resin into a mold or the like, which is illustrated and generally indicated by numeral  100 . The system includes a backing plate  12  and a manifold plate  14 . The system also includes a nozzle assembly  18  for introducing melted resin into a mold cavity  20 . The nozzle assembly  18  is located within the manifold plate  14  and includes a nozzle housing  22  with a nozzle tip  24  secured thereto. There is a heater (not shown) at least partially positioned on an outside diameter of the nozzle housing  22 . The heater may be any suitable heater known in the art to which current is provided by way of an electric cable. There are a wide variety of heat conductive materials that can be utilized for the nozzle housing  22  and an illustrative, but nonlimiting, example includes steel. Also, there is a wide variety of heat conductive materials that can be utilized for the nozzle tip  24  and an illustrative, but nonlimiting, example includes copper alloys. 
         [0037]    The nozzle housing  22  includes an axial channel  36  through which melted resin can flow. The nozzle tip  24  surrounds a terminal portion of the axial channel  36 . There is a valve stem  42  that controls the opening and closing of the melt channel opening  68  located in the gate insert  40  that controls the flow of melted resin into the mold cavity  20 . There is an insulator  66  that occupies the space between the nozzle tip  24  and the gate insert  40  and also contains a melt channel opening  68  located therein. There are cooling channels  72  in the gate insert  40  that allow the melted resin to solidify in the mold cavity  20  prior to the opening of a mold (not shown). 
         [0038]    The valve stem  42  can be made of a wide variety of shapes and materials. An illustrative, but nonlimiting, embodiment of a valve stem  42  includes a steel rod. The valve stem  42  extends through a passageway  44  in a manifold  30  and into the nozzle housing  22 . The passageway  44  connects to a melt channel  46  located in the manifold  30 . The end of the valve stem  42  that is located opposite to the gate insert  40  is connected to piston head  48  by means of a threaded clamp  50 . 
         [0039]    There is an actuator that is generally indicated by numeral  51 , which includes a piston  52  having a piston head  48  that is housed within a cylinder  54  and the backing plate  12 . Fluid, e.g., pneumatic air, is selectively provided through a first channel  64  into an upper chamber  73  to apply downward pressure on the piston  52 . The downstroke of the piston  52  causes the valve stem  42  to close and/or reduce the cross-sectional area of the gate insert  40  to restrict or stop the flow of melted resin into the mold cavity  20 . Fluid, e.g., pneumatic air, is selectively provided through a second channel  67  into a lower chamber  71  to apply upward pressure on the piston  52 . The upstroke of the piston  52  causes the valve stem  42  to open and/or increase the cross-sectional area of the gate insert  40  to allow the flow of melted resin into the mold cavity  20 . 
         [0040]    The manifold  30  is formed between the manifold plate  14  and the backing plate  12  and is separated from the manifold plate  14  and the backing plate  12  by an air gap  56 . The manifold  30  includes the melt channel  46  that forms a portion of the hot runner system that transports melted resin from a source (not shown) to the gate insert  40  associated with a mold cavity  20 . The manifold  30  houses a valve bushing  32 . There is a wide variety of materials that can be utilized for the manifold  30 , which can include any suitable metal or heat conducting material known in the art. The valve bushing  132  is preferably, but not necessarily, formed of flexible metal, e.g., strong steel, which has a predictable flexibility when shaped correctly and which can constrict under pressure. The valve bushing  132 , which includes an aperture  134 , surrounds a portion of the valve stem  42 . There is also a melt channel opening  62  that is in fluid relationship with the melt channel  46  in the manifold  30  and the axial channel  36  in the nozzle assembly  18 . 
         [0041]    There is a disk spring  28  that will deflect as the cylinder  54 , the manifold  20 , and the nozzle housing  22  expand due to an increase in temperature. This disk spring  28  will create a resilient spring action in the nozzle assembly  18 , which is independent of sealing action created by the valve bushing  132  and the manifold  30  as well as between the valve bushing  132  and the backing plate  12 . The disk spring  28  is mounted on a nozzle insulator  74 , where the nozzle insulator  74  is adjacent to and supports the nozzle housing  22 . 
         [0042]    Referring now to  FIG. 4  and as previously discussed above, mounted within a manifold  30  is the valve bushing that is indicated by numeral  132 . When melted resin enters the melt channel  46  in the manifold  30 , the melted resin then passes into a melt channel opening  62  in the passageway  44 . The melted resin applies upward pressure  81  against a lower, end portion  180  of the valve bushing  132 . This upward injection pressure  81  on the lower, end portion  180  deflects the valve bushing  132  and moves the valve bushing  132  upward axially  82  along the passageway  44 . 
         [0043]    There is a projecting member  186  extending outward from the valve bushing  132  within the air gap  56 . When melted resin enters the melt channel  46  in the manifold  30 , the melted resin then passes into a melt channel opening  62  in the passageway  44 . The melted resin applies upward pressure  81  against a lower, end portion  180  surrounding an aperture  134  for the valve bushing  132 . This injection pressure  81  is applied to the lower end portion  180 , which deflects the valve bushing  132  and moves the valve bushing  132  upward axially  82  along the passageway  44 . 
         [0044]    There is a projecting member  186  extending outward from the valve bushing  132  within the air gap  56 . The projecting member  186  preferably includes an angled surface  187 . The projecting member  186  is adjacent to and in direct contact with an upper member  188 . The upper member  188  preferably includes resilient material, such as, but not limited to, a resilient metal such as steel. Also, the upper member  188  preferably includes an angled surface  189 . The angled surfaces  187  and  189  are preferably in an angle α that is in a range from about twenty degrees to about seventy degrees from a line that is perpendicular to the valve stem  42 ; more preferably, the angle α is in a range from about thirty degrees to about sixty degrees from a line that is perpendicular to the valve stem  42 ; most preferably, the angle α is in a range from about forty degrees to about fifty degrees from a line that is perpendicular to the valve stem  42 , where the optimal value of angle α is forty-five degrees from a line that is perpendicular to the valve stem  42 . 
         [0045]    There is a seal  160  that is located between the valve bushing  132  and an upper surface  76  for the manifold  30  in the lower portion of the air gap  56 . This operates to prevent plastic leakage between the manifold  30  and the valve bushing  132  through passageway  44 . Preferably, but not necessarily, there is a leg portion  199  on the upper member  188  that is in direct contact between the upper surface  76  for the manifold  30  in the lower portion of the air gap  56 . 
         [0046]    The valve bushing  132  is also shown in  FIG. 5  that illustrates an angle mismatch between angled surface  187  of the projecting member  186  and the angled (contacting) surface  189  of the upper member  188 . The image on  FIG. 5  shows the function of the valve bushing  132  operating as a wedge in an exaggerated state without the presence of a valve stem  42  to support the inner diameter. The solid outline, indicated by numeral  202 , depicts the un-deformed state when there is no injection pressure applied, and the dotted outline, indicated by numeral  204 , shows how injection pressure causes the valve bushing  132  to move in the axial direction, which causes the passageway  44 , as shown on  FIG. 4 , to constrict due to the conical-type interface at the opposing end. The deflection experienced due to injection pressure should be elastic so that the valve bushing  132  will spring back to its un-deformed state as the pressure is lowered. This operates to prevent contact between the manifold  30  and the valve bushing  132  but does cause the aperture  134  to radially constrict around the valve stem  42 , as shown in  FIG. 4 . There is a graphical representation of the force, indicated by numeral  148 , that is exerted by the cylinder  54  for the actuator  51 , see  FIG. 3 . 
         [0047]      FIG. 6  is a graphical representation that is generally indicated by numeral  210  showing the valve bushing  132 . This graphical representation is indicated by numeral  216 , which is the contact pressure on the valve stem  212  as a function of the distance from the tip of the bushing  214 , which is the condition when applied injection pressure is shown. 
         [0048]    A modification of the alternative embodiment is shown in  FIG. 7  and is generally indicated by numeral  220 . This modification includes a valve bushing  232  having a top portion  222  that includes a ferrule  224 . The ferrule  224  preferably includes resilient material, such as, but not limited to, a resilient metal such as steel. This resilient material is retained by the ferrule  224  to the top portion  222  of the valve bushing  232 . 
         [0049]    The ferrule  224  responds by constricting an aperture  234  under the pressure exerted by the melted resin alone. The greater the amount of pressure provided by the melted resin, the greater the amount of sealing force provided by the ferrule  224 . The solid outline, indicated by numeral  202 , depicts the un-deformed state when there is no injection pressure applied, and the dotted outline, indicated by numeral  204 , shows how injection pressure causes the valve bushing  232  to move in the axial direction, which causes the passageway  44 , as shown on  FIG. 4 , to constrict due to the conical-type interface at the opposing end. The deflection experienced due to injection pressure should be elastic so that the ferrule  224  for the valve bushing  232  will spring back to its un-deformed state as the pressure is lowered. This operates to prevent plastic leakage between the manifold  30  and the valve bushing  232 . 
         [0050]    The various valve bushing examples shown above illustrate a novel valve bushing and associated method of use. A user of the present invention may choose any of the above valve bushing embodiments, or an equivalent thereof, depending upon the desired application. In this regard, it is recognized that various forms of the subject invention could be utilized without departing from the spirit and scope of the present invention. 
         [0051]    Other aspects, objects and advantages of the present invention can be obtained from a study of the drawings, the disclosure and the appended claims. Thus, there has been shown and described several embodiments of a novel invention. As is evident from the foregoing description, certain aspects of the present invention are not limited by the particular details of the examples illustrated herein, and it is therefore contemplated that other modifications and applications, or equivalents thereof, will occur to those skilled in the art. The terms “have,” “having,” “includes” and “including” and similar terms as used in the foregoing specification are used in the sense of “optional” or “may include” and not as “required.” Many changes, modifications, variations and other uses and applications of the present construction will, however, become apparent to those skilled in the art after considering the specification and the accompanying drawings. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is limited only by the claims that follow.