Patent Publication Number: US-6982105-B2

Title: Fuel tank having molded reinforcements and method of making same

Description:
This application is a divisional of application Ser. No.09/079,726 filed on May 15, 1998 and now U.S. Pat. No. 6,294,127. 

   TECHNICAL FIELD 
   The subject invention generally relates to marine fuel tank assemblies and, more specifically to a blow-molded fuel tank assembly having reinforced corners and a method of making same. The method includes the step of molding reinforcements over a portion of a plastic fuel tank body. 
   Traditionally, plastic containers, such as fuel tanks, have been molded by a variety of techniques such as roto-molding and blow-molding. Historically, blow-molded fuel tanks have been disfavored since their corners are inherently thin. The thin corners leads to inherent weaknesses in the fuel tanks. Because fuel tanks must meet stringent governmental standards for both permeation and fire resistance, the prior art blow-molded tanks have been disfavored due to their proclivity towards permeation of fuel and decreased resistance to fire. 
   The prior art has not successfully addressed the problems set forth above for blow-molded fuel tanks. Thus, there has been a need for an improved blow-molded plastic container assembly which provides increased strength, low permeability, and increased fire resistance. There has also been a need for an improved blow-molding method of manufacturing these container assemblies. 
   SUMMARY OF THE INVENTION 
   The improved storage tank assembly of the present invention provides a blow-molded fluid sealed tank assembly without weakened corners which are typical in blow-molded plastic fuel tanks. The container assembly includes a plastic container body and at least one corner reinforcement. The reinforcement is molded over an outer surface of at least one corner of the container body. The reinforcement includes a peripheral edge which is partially embedded in the outer surface of the container body. The peripheral edge is also partially deformed and becomes partially cohesive with the outer surface of the container body providing locking engagement between the reinforcement and the container body. 
   RELATED APPLICATION 
   In a method according to the present invention, a reinforcement is molded over the corner of a plastic container body leaving a portion of the reinforcement partially embedded in the molded container body. A mold is provided having an inner surface and an orifice, wherein the inner surface of the mold defines an outer surface of the container body. A reinforcement is disposed in the mold orifice with the portion of the reinforcement to be embedded into the container body positioned in the mold. The reinforcement also includes at least one peripheral edge which is partially embedded in the container body. A fluid thermoplastic material is introduced into the mold and forced against the inner surface of the mold and the peripheral edge of the reinforcement. The fluid thermoplastic material softens or partially melts the peripheral edge of the reinforcement. The peripheral edge is partially deformed forming a locking engagement between the container body and the reinforcement. The thermoplastic material comprising the container body and the thermoplastic material comprising the reinforcement can also cohesively bond together providing a secure seal between the container body and the reinforcement. Thus, sufficient thickness can be obtained at the corners without using greater amounts of plastic in the blow-mold process. 
   In the preferred embodiment, a blow-molded process is used to mold the container assembly. In this process, a fluid parison of thermoplastic material is introduced into the mold and a pressurized gas charge is introduced into the parison expanding the parison and confirming the parison to the inner surface of the mold. The thermoplastic reinforcement is preferably made by injection molding utilizing the same thermoplastic material as is used to form the container body. 
   The ability to produce parts with good material thickness in corners without making the balance of the part much too thick just to improve corners. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
       FIG. 1  is a perspective view of a plastic container assembly in accordance with the present invention; 
       FIG. 2  is a partial cross-sectional view of the reinforcement and container body of the assembly taken along line  2 — 2  of  FIG. 1 ; 
       FIG. 3  is a perspective view of the reinforcement in accordance with the present invention; 
       FIG. 4  is a cross-sectional view of the reinforcement during a molding step of a method in accordance with the present invention; 
       FIG. 5  is a cross-sectional view of a receiver in accordance with the present invention taken along line  5 — 5  of  FIG. 4 ; 
       FIG. 6  is a cross-sectional view of an alternative embodiment of the reinforcement in an orifice of a mold prior to a molding step of a method of the present invention; and 
       FIG. 7  is a cross-sectional view of an alternative embodiment of the container assembly in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a storage tank or container assembly according to the present invention is generally shown at  20 . The tank includes a container body  22  which defines an interior  24  of the tank assembly  20 . The container body  22  is constructed of a plastic material, such as a thermoplastic, of the type known in the art, which is preferably made by a blow-molding process or other known processes. The thermoplastic material which comprises the container body  22  is preferably a high density polyethylene plastic material and has a general thickness of approximately 2 to 4 millimeters. 
   The tank assembly  20  also includes a plurality of fixtures  26 ,  28 ,  30 . Fixtures  26 ,  28 ,  30 , are pre-fabricated pieces and comprise, for example, an injection molded thermoplastic material. Fixtures  26 ,  28 ,  30  preferably comprise a high density polyethylene thermoplastic material. For reasons set forth below, the container body  22  and fixtures  26 ,  28 ,  30  preferably are made from the same thermoplastic material. However, fixtures  26 ,  28 ,  30  will be thicker than the material container body  22 . Typically, fixtures  26 ,  28 ,  30  will have a general thickness of approximately 4 to 7 millimeters. Fixtures  26 ,  28 ,  30  can each have a portion embedded in the container body  22 , as described below. Each fixture  26 ,  28 ,  30  provides an opening into the interior  24  of the tank assembly  20 . Each fixture has a cap associated therewith which seals the interior  24  to retain a fluid in the interior  24  of the container assembly  20 . 
   The tank assembly  20  illustrated in  FIG. 1  is a fuel tank of the type utilized in the marine industry. The fuel tank  20  includes an inlet cap  28  associated with fixture  26  through which fuel can be pumped into the fuel tank  20 . The fuel tank  20  also includes a fuel gauge assembly and a fuel line assembly  31  both associated with the fixtures  28  and  30 , respectively. Fuel disposed in the tank  20  is drawn through the fuel line assembly  31  and is conveyed through a fuel line to an engine. Although a fuel tank is illustrated, it should be understood that this invention extends to other types of containers. Thus, the invention will be described generally as relating to a conventional container assembly. 
   As shown in  FIG. 1 , each fixture  26 ,  28 ,  30  has a threaded outer surface which receives the cap  27 ,  29 ,  31 , respectively. The fixtures  26 ,  28 ,  30  allow for interchangeable components to be used. The fixtures  26 ,  28 ,  30  are uniformly designed receptacles adapted to receive any desired components. As should be apparent, the components illustrated could be assembled in the various fixture openings. For example, the cap  27  could be mounted in the middle and the fuel gauge  28  could be mounted on the end. 
   The fixtures  26 ,  28 ,  30  are embedded in the plastic container body  22 . This is shown and described in greater detail in co-pending application U.S. Ser. No. 08/704,130, assigned to the assignee of the present invention, and incorporated herein by reference. 
   Referring to  FIGS. 1-3 , the container assembly  20  is shown having its top, bottom, and side walls intersecting in at least corner  32 . The corner  32  includes a reinforcement  40  disposed on an outer surface  34  of the corner  32 . Referring specifically to  FIG. 3 , the corner reinforcement  40  can include an indexing pin  42  disposed on a surface thereof which provides a mechanism for inserting and retaining the corner reinforcement  40  in a mold, which will be discussed in greater detail below. 
   Referring specifically to  FIG. 2 , the corner reinforcement  40  has a co-extensive peripheral edge  44 . The peripheral edge  44  has a substantially tapered cross-section. The peripheral edge  44  of the corner reinforcement  40  is partially embedded in the outer surface  34  of the container body  22 . That is, upon molding of the tank body  22 , the molten thermoplastic material comprising the tank body  22  engulfs a portion of the peripheral edge  44 . The thermoplastic material which comprises the outer surface  34  of the corner substantially engulfs a bottom surface  45  of the peripheral edge  44  and substantially covers a top surface  46  of the peripheral edge. However, the plastic material comprising the tank body  22  is not disposed over any other portion of the corner reinforcement  40 . 
   The peripheral edge  44  of the corner reinforcement  40  can also become partially cohesive with the outer surface  23  of the tank body  22 . That is, if compatible thermoplastic materials are utilized for both the corner reinforcement  40  and the tank body  22 , the materials comprising the respective parts can form a cohesive bond therebetween. Additionally, the peripheral edge  44  of the reinforcement  40  can be partially deformed by the hot thermoplastic material comprising the tank body  22  and can thus provide locking engagement between the reinforcement  40  and the container body  22 . That is, the deformed peripheral edge  44  allows for a mechanical lock to be formed between the deformed peripheral edge  44  having the material comprising the tank body  22  disposed thereover. 
   As shown in  FIG. 2 , the outside wall of the corner  34  coexists with the corner reinforcement  40 . That is, although the corner reinforcement  40  is disposed about the outside corner  34 , both the outside corner  34  and the reinforcement  40  exist independently. A void space or gap  48  can be formed during the molding operation. 
   Referring to  FIG. 7 , an alternative embodiment of the present invention is shown. In this embodiment, an alternative corner assembly is shown. The corner assembly  50  includes a corner reinforcement  54  molded to an outer surface  52  of a corner. The reinforcement  54  includes a peripheral edge  56  and a vent hole  58 . The vent hole is provided to allow for the exchange of fluid between the reinforcement  54  and the hot thermoplastic material comprising the outside corner  52 . The vent  58  allows for the elimination of the void  48  shown in FIG.  2 . 
   In  FIGS. 4-6 , a process of the present invention is illustrated. As shown in  FIG. 4 , the corner reinforcement  40  is placed in an orifice  82  of a mold  80 . An inner surface  84  of the mold  80  defines an outer surface  23  of the container body  22 . The corner reinforcement  40  is disposed in the mold  80 . The corner reinforcement  40  is secured in the mold  80  by inserting the pin  42  into an indexing mechanism  86 . The indexing mechanism  86  includes a receiver  90  is disposed in an aperture  92  of the mold  80 . The receiver  90  includes a cylindrical portion  94  disposed in the aperture  92 . The cylindrical portion  94  includes a bore  96  adapted to receive and retain the pin  42  of the corner reinforcement  40  therein. The receiver  90  further includes a base portion  98  disposed in a recess  104 . The base portion  98  is laterally displaceable within the recess  104 . 
   Springs  100  disposed in bores  102  laterally bias the receiver  90  within the aperture  92 . When the pin  42  of the corner reinforcement  40  is disposed within the bore  96  of the receiver  90 , the springs  100  provide a lateral force on the receiver  90  to force the corner reinforcement  40  into engagement with the inner surface  84  of the mold  80 . This mechanism insures that the corner reinforcement  40  will be maintained in its proper position during the molding operation and to allow controlled movement of the corner reinforcement  40  due to molding forces and thermodynamic effects such as expansion and contraction of the materials disposed within the mold  80 . A keeper plate  106  disposed adjacent to the base portion  98  and the recess  104  retains the indexing mechanism within the mold  80 . 
   As discussed above, a vent hole  58  can be disposed in the corner reinforcement  54 . With reference to  FIG. 6 , the mold  80  includes a vent  120  disposed in fluid communication with the vent hole  58  of the corner reinforcement  54  to allow for the flow of fluid therebetween. 
   In the process of the present invention, a hot fluid thermoplastic material is simultaneously disposed over both the inner surface  84  of the mold  80  and the peripheral edge  44 ,  52  of the corner reinforcement  40 ,  54 . This step can be performed, for example, by any plastic molding method which is well known in the art. The preferred plastic molding method is blow-molding. In this process, a molten parison of fluid thermoplastic material may be disposed in the interior  81  of the mold  80 . A pressurized gas, such as air, is then blown into the parison in the mold  80 , thereby expanding the parison and conforming the parison to the inner surface  84  of the mold  80 . The hot fluid thermoplastic material contacts the peripheral edge  44 ,  52  of the corner insert  40 ,  54  and can begin to soften or even melt at least a portion of the peripheral edge  44 ,  52 . 
   The fluid thermoplastic material cools and hardens forming the container body  22 . As the fluid thermoplastic material cools, limited shrinkage of the thermoplastic material can occur, drawing the peripheral edge  44 ,  52  and the container body  22  together. The peripheral edge  44 ,  52  can be deformed, thereby producing locking engagement with the container body  22 . Additionally, as discussed above, cohesive bonding between the peripheral edge  44 ,  52  and the fluid plastic material comprising the container body  22  can also occur. 
   A preferred description of this invention has been disclosed; however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied in order to determine the true scope and content of this invention.