Abstract:
A tank piston is shown with an improved seal and wiper. The piston is used in conjunction with tanks used for transporting semi-solid and viscous materials such as grease, oil, ink, and the like. The improved seal consists of an annular rubber member with a hollow chamber filled with an open cell foam material such as polyurethane, or a gel such as silica gel. The material in the chamber is compressible and expandable to provide a seal about the piston. Optionally, the piston is provided with an annular wiper structure that extends about the outer forward periphery of the piston, and is forwardly angled at about 45° relative to an axis of the piston. The wiper has a beveled end that makes contact with the interior surface of the tank to provide a cleaning action. A complementary second wiper may be added near the outer rearward periphery of the piston. A preferred embodiment is also shown that uses a tiered support assembly.

Description:
This is a continuation-in-part of application for United States Patent, Ser. No. 08/926,821 filed Sep. 10, 1997, now U.S. Pat. No. 6,027,123, the specification of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to systems for the transportation and/or storing of viscous materials such as grease, oil, ink, and the like, and semisolid materials such as comminuted food products, and the like, in bulk quantity and, more particularly, to a tank and piston structure therefor. 
     BACKGROUND OF THE INVENTION 
     Tanks for the bulk transport and/or storage of semisolid and liquid materials of the kind comprising a tank with a movable piston therein are well known in the art. Examples of such tanks may be found in U.S. Pat. Nos. 3,828,988; 4,721,235; 5,114,054; and 5,341,726. The tanks usually have follower pistons with pneumatically expandable seals surrounding one end of the tank for seating the piston relative to the tank to accommodate changes in the interior cross-section of the tank. The seal is generally positioned between circumferential flanges affixed to the outer surface of the tank in order to axially retain the seal during movement of the piston. The tanks also generally have pads positioned about the piston and extending radially outwardly therefrom for preventing canting of the piston as the piston moves within the tank. 
     As indicated above, the prior art seals are usually hollow and capable of being filled with air to cause the seals to expand. The hollow portion or chamber of the seal may be filled and depleted of air through a valve structure in communication with the chamber and disposed within the piston. The valve is accessible through a rear opening in the piston. Since the seal is naturally between the outer surface of the piston and the inner surface of the tank, and is in contact with the inner surface of the tank as the piston reciprocates within the tank, the seal is subject to abrasion and wear. Also, because the seal is pneumatic, there is always the possibility that a puncture will develop and render the seal useless. Thus, although pneumatic seals are efficient, they are prone to failure. Furthermore, the friction created on the seal by the reciprocating piston may occasionally cause the seal to roll out of position. Additionally, pneumatic seals are difficult to fasten securely to the piston because they cannot be punctured by a fastener. 
     It has been suggested that the design of the seal be such as to effect a wiping action against the inner surface of the tank. This however, is subjecting the seal to more wear and exposing the seal to a greater possibility of failure. 
     In view of the above, it is an object of the present invention to provide an improved seal structure for a tank piston. 
     It is another object of the present invention to provide a piston seal that will accommodate expansion while providing a longer wear life. 
     It is yet another object of the present invention to provide a tank piston structure that includes an improved wiper structure. 
     It is still another object of the present invention to provide a tank piston that has an improved wiper structure for the inner surface of the tank, and having an improved seal structure that moves along the inner surface of the tank with less friction. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, an elastic, deformable seal structure for a tank piston includes an interior, annular chamber that is filled with an open celled foam material. The seal is preferably defined by an annular base coupled to a crown portion, which together define the interior, annular chamber. The open celled material may be rubber, polyurethane, or like resilient material that is compressible and is elastic to expand back substantially to its original volume. 
     The seal is substantially annular and disposed on the outer surface of the piston and surrounding the same, preferably near one end, and is axially retained by a circumferential groove or channel disposed in the outer surface of the piston. 
     In one embodiment of the seal, the crown portion is defined by a dome-shaped member. In another embodiment, the crown portion is defined by two axially spaced, parallel walls, each coupled to an angled top wall. The top walls join to form an apex. 
     According to another aspect of the present invention, the seal is surrounded by a friction reducing layer, possibly of Teflon®, which may be shrink-wrapped around the seal. The friction reducing layer specifically reduces the kinetic coefficient of friction between the seal and the inner surface of the tank. 
     According to yet another aspect of the present invention, a circumferential wiper structure extends from the outer surface of the piston near the discharging end of thereof, and is in abutting relationship with the inner surface of the tank. The end of the wiper abutting the inner surface of the tank preferably includes a bevel. Optionally, a second wiper may be disposed at the opposite end of the tank. 
     In one form, the wiper is an elongated circumferential ring that extends at a 45θ angle, relative to an axis of the piston, towards the inner surface of the tank. The ring may be formed of a suitable plastic. 
     In the preferred embodiment of the seal, a support strip is placed between the open cell foam material and the base portion. The support strip is preferably made of the same material as the seal itself. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above-recited features, advantages, and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     It is noted, however, that the appended drawings illustrate only typical embodiments of this invention and is therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. Reference the appended drawings, wherein: 
     FIG. 1 is a longitudinal cross-sectional view of an end portion of a tank showing a piston in partial cross-section, movable within the tank, in accordance with the present invention; 
     FIG. 2 is an enlarged sectional view of a portion of the piston showing the seal mounted in its channel; 
     FIG. 2A is an enlarged sectional view of a portion of the piston showing an alternate embodiment of the present seal mounted in its channel; 
     FIG. 3 is an enlarged sectional view of the seal depicted in FIGS. 1 and 2; 
     FIG. 3A is an enlarges sectional view of the seal of FIG. 3 with an optional friction reducing layer; 
     FIG. 4 is an enlarged sectional view of an alternate embodiment of the present seal depicted in FIGS. 1 and 2A; 
     FIG. 4A is an enlarged sectional view of the seal of FIG. 4 with an optional friction reducing layer; 
     FIG. 5 is an enlarged sectional view of a portion of the piston showing the seal mounted in its channel with a pair of wipers coupled to the piston body; 
     FIG. 6 is an exploded sectional view of the components in the preferred embodiment of the seal; 
     FIG. 7 is an enlarged sectional view of the assembled seal of FIG. 6; and 
     FIG. 8 is an enlarged sectional view of the seal of FIG. 7 with an optional friction reducing layer. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1, there is shown a portion of a tank, designated  10 , defined by a generally cylindrical wall  11 , preferably formed of a suitable metal in order to effectively contain the material to be stored and/or transported therein (hereinafter “the material”). The wall  11  defines a generally cylindrical interior volume or space  12  of the tank that is bounded by an interior or inner surface  14  of the wall  11 . The tank  10  has an opening  16  at one end thereof, which for convenience will be deemed the front of the tank  10 . The opening  16  is a combination inlet and outlet for introducing and removing the material respectfully into and out of the tank volume  12 . 
     Disposed within the volume  12  is a tank piston  18  of a generally cylindrical configuration and preferably formed of a suitable metal. The outside diameter of the piston  18  is slightly less than the inner diameter of the tank  10  such that the piston  18  is movable back and forth within the tank  10 . The piston  18  divides the whole interior volume  12  of the tank  10  into a front volume  22  forward of a curved front portion  20  of the piston  18  and a rear volume  21  rearward of a curved rear portion  19  of the piston  18 . The front and rear volumes  22 ,  21  are variable depending on the position of the piston  18  within the tank. The front volume  22  receives and holds the material. The more material, the larger front volume  22  becomes with the rear volume  21  becoming less as the piston  18  moves rearward. As the material exits the tank  10  the rear volume  21  becomes greater with the front volume  22  becoming less as the piston  18  moves forwardly. It should be immediately understood that the above describes the introduction of the material into the front volume  22  of the tank  10  via the opening  16  and the evacuation of the material from the front volume  22  of the tank  10  via the opening  16 . 
     The piston  18  is defined by the curved front portion or wall  20  and the rear portion or wall  19  and a middle, generally cylindrical portion or wall  23 . Disposed on the outside surface or periphery  24  of the wall  23  of the middle portion  23  are two sets of anti-canting pads  26  and  28 . The anti-canting pads  26  are disposed in an annular pattern about the piston  18  proximate the front portion  20  while the canting pads  28  are disposed in an annular pattern about the piston  18  proximate the rear portion  19 . The anti-canting pads  26 ,  28  extend radially outward from the surface  24  and are respectfully fastened thereto by bolts that extend through the wall  23  and are secured by nuts  27 ,  29  on the inner surface  25 . The anti-canting pads  26 ,  28  abut the inner surface  14  of the wall  11  to prevent the piston  18  from canting within the tank  10 . The pads are preferably of a low friction material (e.g. nylon) to permit the piston  18  to move freely within the tank  10 . Of course, alternate devices may be used to accomplish this result. The pads  26 ,  28  are axially and circumferentially spaced on the piston surface  24  accordingly. 
     Also disposed on the outer surface or periphery  24  of the piston  18  between the front portion  20  and the pads  26  is a circumferential groove or channel  35  (see FIG.  2 ). Disposed at least partly within the channel  35  is an elastic seal structure  68 . FIG. 2A shows an alternate seal structure  36  disposed within channel  35 . 
     With additional reference to FIGS. 3 and 3A the seal  68  is preferably formed of an elastic material such as rubber, VITON®, neoprene, nitrile, or other suitable material. The seal  68  is defined by an annular base  70  formed of a rubber as again described above, to which is coupled an annular dome-shaped (in cross-section) cap or crown  72 . The cap  72  and base  70  define an annular cavity or chamber  74  which is filled with an open celled foam  76 . Such open celled foam material  76  may be a rubber compound, polyurethane, or the like which is elastically compressible, to provide and impart a resiliency effect to the seal structure  68 . Optionally, a gel, such as silica may be used in place of the open celled foam material  76 . 
     As shown in FIG. 3A, an optional an outer layer  77  may be disposed about the seal  68  to reduce the kinetic coefficient of friction as the seal moves across the inside surface  14  of the tank  10 . The outer layer  77  may be made of any suitable low friction material, such as teflon, rayon, nylon, or any high-density alkenes. It is preferable that such outer layer  77  be shrink wrapped around the seal  68  to provide the best friction reduction. 
     Referring to FIGS. 2A,  4 , and  4 A there is shown an alternative embodiment of a seal, generally designated  36  that may be used. It should here be understood that various seal configurations may work, as long as they have an interior cavity filled with an open celled foam as described above with reference to the seal  36 . The seal  36  is defined by an annular base portion  50 , a first or left perpendicular annular wall portion  52 , a second or right perpendicular annular wall portion  54 , a first or left angled annular wall portion  56 , and a second or right angled annular wall portion  58 . The first perpendicular wall portion  52  is attached to the base portion proximate one end thereof, while the second perpendicular wall portion  54  is attached to the base portion proximate another end thereof. The first angled wall portion  56  is attached at one end to a top end of the first perpendicular wall portion  52 , while the second angled wall portion  58  is attached at one end to a top end of the second perpendicular wall portion  54 . The other ends of the first and second angled wall portions  56 ,  58  are joined together to form an apex  60 . Preferably, the wall portions are integrally formed such that the seal  36  is substantially seamless. The wall portions  52 ,  54 ,  56 ,  58 , form a crown or cap, and an annular interior hollow, cavity, or chamber  62  that is filled with an open celled foam material  64 . Such open celled foam material  64  may as described above in reference to celled foam material  76 . To prevent the base  50  from bowing outward (i.e. to keep it flat) it is possible with this embodiment of the seal  36  to provide a base  50  that is somewhat thicker than the other walls  52 ,  54 ,  56 ,  58 . An optional outer layer  65  may be disposed around seal  36  in the same manner as outer layer  77 . 
     It should here be understood that various seal configurations may work, as long as they have an interior cavity filled with an open celled foam as described above with reference to the seals  36  and  68 . With any embodiment of the seal that may be used, a plurality of cotter pins  80  may be used to further prevent the seal from rolling out of the channel  35 . The cotter pins  80  may be inserted through two sidewalls  44 ,  48  defined by channel  35  and through the celled foam material of the seal. 
     Referring back to FIG. 2A again, the seal  36  is where the apex  60  is abutting the inner surface  14 , and the first and second angled wall portions  56 ,  58  are radially downwardly compressed. Compression of the seal  36  between the piston and the inner surface of the tank prevents the intrusion of the material from the front volume  22  and the rear volume  21 . Also, because the cavity  62  of the seal  36  is filled with the resilient foam material  64 , the walls of the seal tend to radially outwardly expand, particularly if the base  50  is made thicker than the remaining walls. Thus, if a puncture or rupture occurs in the seal, there will be no deflation of the seal as in “air seals” nor a significant loss of the sealing effect. It should be recognized that after a certain amount of wear and tear, even the present seal would need replacement. However, the lifetime of the present seal is generally greater than the “air seals.” 
     With reference to FIGS. 1 and 5, the piston  18  may include an essentially annular wiper generally designated  38  preferably formed of a plastic such as nylon or the like. The wiper  38  in the embodiment shown extends about the piston  18  from the area forming a juncture between the curved front portion  20  and the cylindrical middle portion  23 . The wiper  38  is angled upwardly relative to a major axis of the piston  18  towards the inner surface of the tank. If a wiper  38  is used it should extend at a 45θ angle relative to the piston axis. The end of the wiper  38  abutting the inner surface of the tank has a bevel  39  such that a flat portion of the bevel abuts the inner surface of the tank. This provides a wiping or scraping action against the inner surface of the tank to clean the same. 
     In the embodiment shown in FIGS. 1 through 5, the wiper  38  is mounted to the piston  18  by disposing a lower portion  82  of the wiper  38  within a circumferential groove or channel  84  axially spaced parallel to the seal channel  35 . The channel  84  defines two sidewalls  86 ,  88 . The sidewall  86  closest to the front of the piston  18  should be at 45° relative to the piston axis. If the sidewall  86  is vertical or at an angle other than 45°, a fill material  90  should be disposed against the sidewall  86  as shown in FIG.  5 . The fill material  90  may be metal, polymer, or any other material that can provide a smooth 45° surface for the wiper  38 . The wiper  38  may then be secured to the fill material  90  or angled sidewall as appropriate by means of a screw or nut  92  and a bolt  94 . Optionally a second wiper  38   a  may be disposed near the rear of the piston  18 , in mirror image to the first wiper  38  (i.e. the bevel  39   a  of the rear wiper  38   a  is oriented in the opposite direction of wiper  38 ). 
     Referring now to FIGS. 6 through 8, a preferred embodiment of the seal  100  is shown generally. The seal  100  is similar to the seal  36  of FIGS. 2A,  4 , and  2 A. Unlike the seal  36 , the seal  100  has an annular base portion  102  that is the same thickness as the wall portions,  104 ,  106 ,  108 , and  110 . A thickness of 0.375″ has been discovered to be effective. The annular chamber  112  defined by the annular base  102  and the wall portions  104 ,  106 ,  108 , and  110  is filled with the support assembly  114 . 
     The support assembly  114  comprises one or more open cell foam material layers  116 ,  118  and a support strip  120 . The support assembly  114  is combined into an integral part by placing an adhesive between the various components layers—the foam material layers  116 , and  118  and the support strip  120 . After the adhesive cures, the edges of the support assembly  114  are cut down, possibly with a band saw, to match the approximate profile of the annular chamber  112 . FIG. 6 shows how the cuting has left beveled surfaces  122  on the support assembly  114  to correspond to the wall portions  106  and  108 . 
     It is best if a small section of the support strip  120  extends beyond the open cell foam material layers  116 ,  118 . This allows the entire support assembly  114  to be pulled through the annular chamber  112 , the open cell foam material layers  116 ,  118 , thus being compressed during this process. After the support assembly  114  is in place, it is given time to relax, the protruding portion is removed after which the ends of the two ends of the seal  100  may be glued together thereby forming a ring. 
     It has been discovered that a support strip of 0.25″ works well with 0.375″ walls in the seal. The support strip  120  is preferably made of the same material as the base portion  102  (and wall portions  104 ,  106 ,  108 ,  110 ). The support strip  120  performs two functions. It provides rigidity to the support assembly  114  facilitating its insertion into the annular chamber  112 . It also provides extra support to the base portion  102  to limit the amount of bowing that occurs. In FIGS. 7 and 8 it can be seen that the base portion  102  will bow slightly even with the support strip  120 . By the time the seal is formed into a ring and placed around the piston, this bowing becomes negligible. It should be noted that it is ideal not to have any gaps remaining in the annular chamber  112  after the support assembly  114  is in place. Of course this is not always possible, but any gaps should be kept to an absolute minimum. The compression of the open cell foam material layers as they are inserted into the chamber helps in this regard. Lastly, FIG. 8 shows that the optional outer layer  124  may be added to this embodiment similar to the outer layer  77  of FIG.  3 A. 
     While the foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims, which follow.