Abstract:
A dispensing cartridge with a vented piston is disclosed. The piston includes a piston shell and a bleed plug. The arrangement of the piston shell and the bleed plug allows air to be vented through the piston until all of the air is vented out of the dispensing cartridge. With the air vented out of the dispensing cartridge, the piston self-into actuates into a closed sealed position in which the bleed plug forms a seal with the piston shell to prevent further fluid from flowing between the two elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application is a continuation of U.S. patent application Ser. No. 11/223,282 (pending), filed Sep. 9, 2005, which claimed priority from and claimed the benefit of U.S. Provisional Application Ser. No. 60/696,154 (expired), filed Jul. 1, 2005, the disclosures of which are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND 
     Pistons have been used for years in dispensing cartridges to dispense liquids from the cartridge. The issue has always been, especially with liquids that need to be dispensed at very precise ratios, how to keep air from getting trapped between the piston and the liquid in the cartridge when the piston is inserted into the cartridge during filling. In the very near past, pistons have been developed with integral bleed or ventilation outlets which allow the air to vent to atmosphere without the use of bleed shims or other means to separate the portion of the piston that forms a seal with the cartridge wall from the cartridge wall. These pistons formed with integral bleed or ventilation outlets have been very effective at increasing the efficiency with which air is evacuated from the dispensing cartridge and at decreasing the damage done to piston seals by bleed shims. 
     While pistons formed with integral bleed or ventilation outlets have been an improvement, significant drawbacks still remain. Such pistons require some separate or specialized device or mechanism to either keep the vent open during the filling process or to close the vent after a cartridge has been filled. None of the prior pistons automatically close during the filling process. None of the prior pistons are self-actuating. 
     Also, the design of some prior ventilating piston assemblies cause air to be trapped in the piston after the cartridge is sealed. Such trapped air is undesirable. The piston disclosed in U.S. Pat. No. 6,598,766 is an example of such a piston having the undesirable effect of trapping air in the piston after air has been evacuated from the dispensing cylinder. 
     Accordingly, there is a need for an improved piston for use in a dispensing cartridge. 
     SUMMARY 
     According to one aspect of the present invention, a piston includes a piston shell having an opening to atmosphere formed therein and a bleed plug having at least one bleed channel formed thereon. According to this aspect of the present invention, the bleed plug is disposed within the piston shell and is designed such that at a pre-determined pressure point the bleed plug moves into sealing engagement with the piston shell to form a seal. The bleed plug may have a sealing edge formed thereon, and the sealing edge, according to this aspect of the present invention, moves into sealing engagement with the piston shell to form a seal at the pre-determined pressure point. The piston shell further may have a seal surface formed therein with at least one notch formed on it, in which the sealing edge moves into sealing engagement with the seal surface of the piston shell to form a seal at the pre-determined pressure point. 
     According to another aspect of the present invention, the at least one bleed channel formed on the bleed plug is formed as two spiral channels. The bleed plug may further have a connecting structure formed thereon, such that, at the pre-determined pressure point, the connecting structure engages the opening to atmosphere formed in the piston shell. The connecting structure may have an opening formed therein and the connecting structure may be formed as a half-split, cylinder structure. 
     According to other aspects of the invention, the piston described above is utilized in a dispensing cartridge and in a method for venting air from a dispensing cartridge. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings where: 
         FIG. 1A  is a perspective view of an embodiment of a piston of the present invention from the liquid facing side; 
         FIG. 1B  is an exploded view of the piston depicted in  FIG. 1A ; 
         FIG. 2  is a perspective view of the piston depicted in  FIG. 1A  from the side of the piston that faces atmosphere; 
         FIG. 3A  illustrates a piston of the present in an open position inserted into a dispensing cylinder; 
         FIG. 3B  is a top view of a dispensing cartridge of the present invention; 
         FIG. 3C  is a longitudinal cross-sectional view taken along the line  3 C- 3 C in  FIG. 3B ; 
         FIG. 3D  is an enlarged view illustrating the interaction of the bleed plug and the piston shell in an open position; 
         FIG. 4  is longitudinal cross-sectional view with the piston in contact with liquid in the dispensing cylinder; 
         FIG. 5A  is longitudinal cross-sectional view with the piston full in contact with liquid in the dispensing cylinder and the piston in a closed position; and 
         FIG. 5B  is an enlarged view illustrating the interaction of the bleed plug and the piston shell in a closed position. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1A ,  1 B and  2 , an embodiment of a piston  20  of the present invention is depicted. As best seen in  FIG. 1B , the piston  20  in this embodiment has two components: a piston shell  22  and a bleed plug  24 . The two components  22 ,  24  of the piston  20  are made from a dimensionally stable and chemically inert material, such as thermoplastic or thermoset material in this embodiment. As depicted in  FIG. 1A , in an assembled configuration prior to being inserted into a cylinder  26  of a dispensing cartridge  27  ( FIG. 3A ), the bleed plug  24  seats in the piston shell  22  in an open non-sealed, first position. 
     The bleed plug  24  has a bleed channel  28  formed therein. In this embodiment, the bleed channel  28  is formed as two spiral bleed channels formed on the exterior of the bleed plug  24 . The bleed channels  28  may be formed in any manner that allows air to pass between the bleed plug  24  and the piston shell  22 , while simultaneously preventing any liquid from attempting to pass through, when the bleed plug  24  is in the non-sealed, open position. The bleed plug  24 , in this embodiment, has a sealing edge  30  formed on the upper edge of the bleed plug  24 . The bleed plug  24 , in this embodiment, also has a connecting structure  32  with at least one opening  44  formed in the interior of the bleed plug  24 . In this embodiment, the connecting structure  32  is formed as a half-split, cylinder structure formed in the center of the interior of the bleed plug  24 . The connecting structure  32  in this embodiment has two openings  44  formed by the half-split in the cylinder structure. In other embodiments, other forms of connecting mechanisms, other than the connecting structure  32  discussed above, could be utilized. It is contemplated that other embodiments of the piston  20  would not incorporate a connecting structure at all. An example of such an embodiment would be one that utilizes an interference fit between the piston shell  22  and the bleed plug  24  to secure the piston shell  22  and the bleed plug  24  together in a closed, seal position. 
     As best seen in  FIG. 1B , the piston shell  22  has a thickened seal surface  34  formed integral to the interior of the piston shell  22 . The thickened seal surface  34  acts to reduce the inner diameter of the piston shell  22  at that point. The seal surface  34  has air passage notches  36  formed at various points along the circumference of the seal surface  34 . In the embodiment depicted, four notches  36  are formed in the seal surface  34 . Two notches  36  are visible in the view depicted in  FIG. 1B . The seal surface  34  in this embodiment also has a chamfered edge. As explained in detail below, the notches  36  formed in the seal surface  34  facilitate air passing through the piston  20  when the bleed plug  24  is in the open, non-sealed position. When the bleed plug  24  is moved into a closed, second position, the sealing edge  30  of the bleed plug  24  engages the seal surface  34  in an interference fit, forming a seal which stops air from flowing between the bleed plug  24  and the piston shell  22 . 
     In this embodiment, the piston shell  22  has a central opening  38 , best seen in  FIG. 2 , formed in the center of the back portion of the piston shell  22 . The piston shell  22  also has vent grooves  40  formed along the back of the piston shell  22 , which are in communication with the central opening  38 . A piston  22  is typically inserted into a dispensing cylinder  26  with a piston insertion rod. The vent grooves  40  function to allow air venting out from the piston interior to flow out from beneath and past the piston insertion rod when the piston  22  is being inserted into a cylinder  26 . 
     Referring to  FIGS. 3A-3D ,  4  and  5 A- 5 B, the process of inserting assembled pistons  20  into filled dispensing cartridge cylinders  26 , evacuating the air from the cylinders  26  and causing the pistons  20  to self-actuate to a closed, sealed position is depicted.  FIGS. 3A-3C  show pistons  20  inserted into the open ends of two filled cylinders  26   a ,  26   b . In the initial position depicted in  FIGS. 3A-3C , there is a space formed between each piston  20  and the top surface  50   a ,  50   b  of each liquid  52   a ,  52   b . It should be understood that even though the embodiment illustrated herein describes a dual cylinder system, the piston  20  of the present invention can be used with any cylinder  26  configuration (e.g., single cylinder, dual cylinder, etc.). A wide variety of liquids, having a very wide range of viscosities, may be used with the dispensing cartridge  27  and the piston  20  of the present invention. The liquids  52   a ,  52   b  depicted in the embodiment shown in the figures are relatively highly viscous liquids, such as the components of a caulking compound. Such high viscosity liquids create irregular static liquid surface profiles along the top surfaces  50   a ,  50   b  of the liquids  52   a ,  52   b , as can be seen in  FIGS. 3A and 3C . In the embodiment depicted in the  FIGS. 3A-3C , the liquids  52   a ,  52   b  in the cylinders  26   a,    26   b  form a “Hershey kiss”-type surface profile due to the liquids&#39; high viscosities. It should be noted that low viscosity liquids may also be used in the dispensing cartridge  27  of the present invention as well. The static liquid surface profile for such low viscosity liquids will generally be flat, as opposed to an irregular profile that a highly viscous material generates. 
     To evacuate the air from the space formed between the pistons  20  and the liquids  52   a ,  52   b , the pistons  20  are pressed into the cylinders  26   a ,  26   b  in the direction indicated by the arrow in  FIG. 3C . As the pistons  20  are pressed into the cylinders  26   a ,  26   b , the air trapped between each piston  20  and their respective liquid  52   a ,  52   b  is pushed through the piston  20  and out to atmosphere. Referring to  FIGS. 3C and 3D , the flow path of the exiting air is indicated by arrows  54 . The air trapped between a piston  20  and a liquid  52  hits the bottom of the bleed plug  24  and spreads to the outer edge of the bleed plug  24  where it is forced, in this embodiment, into the two spiral bleed channels  28  formed along the exterior of the bleed plug  24 . From the two spiral bleed channels  28 , the air flows around the sealing edge  30  of the bleed plug  24  and, depending on the position of the sealing edge  30  in relation to the seal surface  34 , through the notches  36  formed in the seal surface  34  of the piston shell  22 . From the notches  36 , the air continues to flow into and through an annular chamber  42  formed between the bleed plug  24  and the piston shell  22 . From the annular chamber  42 , in this embodiment, the air passes through the openings  44  formed in the connecting structure  32  and then out of the piston  20  to atmosphere through the opening  38 . In other embodiments, the piston  20  may be formed such that air being evacuated from the piston  20  passes straight from the notches  36  out through the opening  38 . As described above, if the piston  20  is being pushed in with a piston insertion rod, the air will travel from the opening  38  to and through the vent grooves  40  along the back of the piston shell  22  to vent to atmosphere. 
     As depicted in  FIG. 4 , as the pistons  20  are pressed further into the cylinders  26   a ,  26   b , the air continues to flow through the pistons  20  in the manner described above, even after the bleed plugs  24  come into contact with their respective liquids  52   a ,  52   b.    
     As the pistons  20  are pressed forward, less and less air remains in the space between the piston  20  and the liquid  52  and more and more liquid  52  contacts the piston  20 . As the liquids  52   a ,  52   b  press back against their respective bleed plugs  24  and start entering their respective spiral bleed channels  28 , the bleed plugs  24  are pressed further into their piston shells  22 . As the bleed plugs  24  are pressed further into their piston shells  22 , the sealing edges  30  on the upper edge of each bleed plug  24  are pressed along each seal surface  34  to a point above the notches  36  formed in each seal surface  34  creating an interference fit, as depicted in  FIGS. 5A-B . As a consequence, a seal is formed between the sealing edge  30  and the seal surface  34 , such that air no longer flows around the sealing edge  30 . Simultaneously, the connecting structure  32  for each piston  20  is pushed into its respective opening  38  in the piston shell  22 . In this embodiment, the half-split cylinder structure of each connecting structure  32  compresses as it moves into the opening  38 , and each connecting structure  32  literally snaps into place within the opening  38 . At this point, air is evacuated from each cylinder  26   a ,  26   b  between the liquids  52   a ,  52   b  and their respective pistons  20 , and each cylinder  26   a ,  26   b  is sealed. No air is trapped in the annular chambers  42  of the pistons  20  because the openings  44  formed in the connecting structures  32  allow air in the annular chambers  42  to vent to atmosphere through openings  38 . 
     While the invention has been discussed in terms of certain embodiments, it should be appreciated that the invention is not so limited. The embodiments are explained herein by way of example, and there are numerous modifications, variations and other embodiments that may be employed that would still be within the scope of the present invention.