Abstract:
Injectable structural adhesives, methods of using the same, and products formed therewith, are described. The adhesive is introduced through a first opening into an internal cavity formed between two or more components. The adhesive is then permitted or forced to flow through the internal cavity, substantially filling the cavity, until it reaches a second spaced opening. Any air contained within the internal cavity is removed by the flow of the adhesive.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to injectable structural adhesives, and more particularly to injectable structural adhesives for joining components together that have an internal cavity formed therebetween, wherein the adhesive is injected into a first opening, the adhesive at least substantially filling the cavity, with any air in the cavity escaping through a spaced second opening.  
       BACKGROUND OF THE INVENTION  
       [0002]     Automobile fuel tanks are typically comprised of various plastic materials, such as high-density polyethylene materials. Recently, the use of rollover valves, in conjunction with fuel tanks, has increased in order to prevent fuel from escaping the fuel tank, e.g., when a rollover accident has occurred. The rollover valve assembly typically includes a plastic surface or structure that is intended to mate (e.g., concentrically through a snap-fit configuration) with and be bonded to a corresponding structure or surface formed on, or near the exterior surface of the fuel tank.  
         [0003]     Generally, it has been customary to bond the rollover valve assembly to the fuel tank by a process generally referred to as hot plate welding. Hot plate welding is generally unsuitable for welding large and irregularly shaped parts with difficult contours and joint lines. Hot plate welding uses a heated platen to radiate heat through close proximity and melt the joining surfaces. After the part interfaces have been melted, the parts are brought together to form a seal therebetween. Thus, in this particular application, only the peripheral surfaces of the rollover valve assembly and the fuel tank are typically bonded together.  
         [0004]     This method suffers from several disadvantages in that the peripheral bond may be susceptible to breaches or failures, e.g., due to either improper welding techniques and/or the corrosive characteristics of the various fuels contained within the fuel tank. Additionally, this method does not provide enhanced structural support to the bonded rollover valve/fuel tank assembly.  
         [0005]     Therefore, there exists a need for components formed with injectable structural adhesives and methods for accomplishing the same, including those suitable for bonding rollover valve assemblies to fuel tanks.  
       SUMMARY OF THE INVENTION  
       [0006]     In accordance with the general teachings of the present invention, two or more components are preferably bonded together with an adhesive. The respective components are preferably brought into contact with one another such that an internal cavity is formed therebetween. On an external surface of one of the components, at least two apertures are preferably formed therein, wherein the apertures are preferably spaced and still more preferably opposed from each other. The adhesive is then preferably introduced through one of the apertures into the cavity. As more adhesive is introduced, the adhesive is preferably allowed or caused to flow through the cavity towards the location of the other aperture or apertures. Once the adhesive reaches the other aperture or apertures, the introduction of any additional adhesive is preferably ceased. The adhesive preferably substantially fills the entire volume of the cavity. Any air that was initially contained within the cavity is preferably removed by the flow of the adhesive. The adhesive is then preferably allowed to cure or harden, thus providing enhanced structural support to the bonded components in addition to providing, a bonding function between the components.  
         [0007]     In accordance with a first embodiment of the present invention, a bonded component system is provided, comprising: (1) a first component; (2) a second component adjacent to the first component, the second component having at least two spaced apertures formed on an external surface thereof, wherein an area defining an internal cavity is formed between the first component and the second component; and (3) an adhesive material disposed within the cavity sufficient to bond the first component to the second component, wherein the adhesive material is introduced into the cavity through either of the apertures.  
         [0008]     In accordance with a second embodiment of the present invention, a bonded component system is provided, comprising: (1) a first component; (2) a second component adjacent to the first component, the second component having at least two substantially spaced and opposed apertures formed on an external surface thereof, wherein an area defining an internal cavity is formed between the first component and the second component; and (3) an adhesive material disposed within the cavity sufficient to bond the first component to the second component, wherein the adhesive material is introduced into the cavity through either of the apertures, wherein the adhesive material substantially completely fills the cavity.  
         [0009]     In accordance with a third embodiment of the present invention, a gas tank system is provided, comprising: (1) a gas tank; (2) a rollover valve assembly adjacent to the gas tank, the rollover valve assembly having at least two substantially spaced and opposed apertures formed on an external surface thereof, wherein an area defining an internal cavity is formed between the gas tank and the rollover valve assembly; and (3) an adhesive material disposed within the cavity sufficient to bond the gas tank to the rollover valve assembly, wherein the adhesive material is introduced into the cavity through either of the apertures, wherein the adhesive material substantially completely fills the cavity.  
         [0010]     In accordance with a fourth embodiment of the present invention, a method is provided for forming a bonded component system, comprising: (1) providing a first component; (2) providing a second component adjacent to the first component, the second component having at least two spaced apertures formed on an external surface thereof, wherein an area defining an internal cavity is formed between the first component and the second component; and (3) disposing an adhesive material within the cavity sufficient to bond the first component to the second component, wherein the adhesive material is introduced into the cavity through either of the apertures.  
         [0011]     In accordance with a fifth embodiment of the present invention, a method is provided for forming a bonded component system, comprising: (1) providing a first component; (2) providing a second component adjacent to the first component, the second component having at least two substantially spaced and opposed apertures formed on an external surface thereof, wherein an area defining an internal cavity is formed between the first component and the second component; and (3) disposing an adhesive material within the cavity sufficient to bond the first component to the second component, wherein the adhesive material is introduced into the cavity through either of the apertures, wherein the adhesive material substantially completely fills the cavity.  
         [0012]     In accordance with a sixth embodiment of the present invention, a method is provided for forming a gas tank system, comprising: (1) providing a gas tank; (2) providing a rollover valve assembly adjacent to the gas tank, the rollover valve assembly having at least two substantially spaced and opposed apertures formed on an external surface thereof, wherein an area defining an internal cavity is formed between the gas tank and the rollover valve assembly; and (3) disposing an adhesive material within the cavity sufficient to bond the gas tank to the rollover valve assembly, wherein the adhesive material is introduced into the cavity through either of the apertures, wherein the adhesive material substantially completely fills the cavity.  
         [0013]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0015]      FIG. 1  is a perspective view of a fuel tank/rollover valve assembly, in accordance with the general teachings of the present invention;  
         [0016]      FIG. 2  is a partial sectional view of a fuel tank/rollover valve assembly, in accordance with one embodiment of the present invention;  
         [0017]      FIG. 3  is a partial sectional view of a fuel tank/rollover valve assembly, in accordance with an alternative embodiment of the present invention;  
         [0018]      FIG. 4A  is a partial sectional view of a detail of a fuel tank/rollover valve assembly, in accordance with a second alternative embodiment of the present invention;  
         [0019]      FIG. 4B  is a partial sectional view of a detail of a fuel tank/rollover valve assembly, in accordance with a third alternative embodiment of the present invention;  
         [0020]      FIG. 5  is a partial sectional view of a partially nested two-component assembly, in accordance with a fourth alternative embodiment of the present invention;  
         [0021]      FIG. 6  is a partial sectional view of a five-component assembly, in accordance with a fifth alternative embodiment of the present invention; and  
         [0022]      FIGS. 7A-7D  is a partial schematic view of a methodology illustrating the introduction of an adhesive material into a cavity of a fuel tank/rollover valve assembly, in accordance with a sixth alternative embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0024]     Furthermore, it should be appreciated that the present invention can be practiced with any number of different components, such as but not limited to fuel tanks, rollover valves, fuel spuds, fuel pumps, and the like.  
         [0025]     Referring to  FIG. 1 , there is shown a fuel tank  10  and a rollover valve assembly  12 . The rollover valve assembly preferably includes the rollover valve  12   a  itself, as well as a bracket member  12   b  that is fastened or otherwise attached to the rollover valve  12   a . In accordance with one embodiment of the present invention, it is preferred to bond, preferably permanently, the rollover valve assembly  12 , and more specifically the bracket member  12   b , to at least a portion of a surface of the fuel tank  10 .  
         [0026]     Referring to  FIG. 2 , there is shown a non-limiting example of a mating relationship between the fuel tank  10  and the rollover valve assembly  12 , specifically the bracket member  12   b  (the rollover valve  12   a  is not shown for purposes of clarity), so as to form an assembly  14 .  
         [0027]     The fuel tank  10  preferably includes an area defining an aperture  16  formed therein. Around the aperture  16 , there is preferably formed a recessed U-shaped member  18  that preferably extends along the entire circumference of the aperture  16 . The U-shaped member  18  preferably defines an annular channel  20  between an external wall  22  and internal wall  24 . The internal wall  24  preferably includes a flange member  26  extending perpendicular to the internal wall  24 .  
         [0028]     The bracket member  12   b  preferably includes a substantially planar portion  26  and an annular protuberance  28  extending along the entire circumference of the underside  30  of the bracket member  12   b . The protuberance  28  is intended to mate, preferably in an offset or spaced apart manner, with the channel  20 . Thus, the protuberance  28  is preferably smaller in volume than the volume of the channel  20 .  
         [0029]     In order to maintain this offset arrangement, a spacer element  32 , such as but not limited to a gasket, washer, or the like, may be disposed between the bracket member  12   b  and the upper surface  34  of the fuel tank  10 . In this manner, a substantially hollow internal cavity  36  is defined by virtue of the fact that the bracket member  12   b  and the fuel tank  10  do not abut one another in a substantially flush manner.  
         [0030]     In order to allow-for the introduction of material into the cavity  36 , it is generally necessary to provide for at least one, more preferably at least two, and still more preferably more than two areas defining aperture  38 ,  40 , respectively, in the bracket member  12   b . In accordance with a preferred embodiment of the present invention, the apertures  38 ,  40 , respectively, are preferably substantially spaced from one another and still more preferably are substantially opposed from one another. The apertures  38 ,  40 , respectively, can be formed at the time of the manufacture of the bracket member  12   b  (e.g., injection molding, compression molding, and the like) or can be formed after the manufacture of the bracket member  12   b  (e.g., with the use of a stamp press, aperture press, awl press, or the like, and whether by hand or by aid of machine).  
         [0031]     By providing the apertures  38 ,  40 , respectively, an adhesive material  42  is operable to be disposed or otherwise placed into the cavity  36  (via either aperture  38  or  40 ) such that the cavity  36  is at least substantially completely filled with the adhesive material  42 . The arrows indicate the flow of adhesive material  42  through the cavity  36  if the adhesive material  42  had been initially introduced through aperture  38 . Conversely, if the adhesive material  42  had been initially introduced through aperture  40 , the direction of the arrows would be reversed indicating that the adhesive material  42  would flow towards aperture  38 .  
         [0032]     Once a sufficient amount of the adhesive material  42  is placed into the cavity  36 , it is preferably allowed to harden or cure so as to form a bond between the bracket member  12   b  and the fuel tank  10 . Additionally, the hardened or cured adhesive material  42  provides structural support to the assembly  14 . The detailed description of how the adhesive material  42  is introduced into, and how it substantially completely fills the cavity  36 , will be described herein.  
         [0033]     Any suitable adhesive material may be used in the present invention, provided that it is able to bond to the components to be bonded together. By way of a non-limiting example, with respect to the specific application of rollover valves and fuel tanks, adhesives that are capable of bonding to plastics, such as but not limited to HDPE, are preferred. In accordance with one embodiment of the present invention, acrylic-based adhesives are preferred, including but not limited to two-part acrylic adhesives. Additionally, the adhesive material may be introduced into the cavity by hand or may be injected by using mechanical aids, such as but not limited to pumps and the like.  
         [0034]     In accordance with a preferred embodiment of the present invention, the adhesive material is preferably a structural adhesive. More preferably, the adhesive material is a low energy surface adhesive (LESA) type material. Examples of LESA materials can be found with reference to commonly-assigned U.S. patent application Publication No. US 2003/0044553 to Ramanathan et al. and US 2003/0047268 to Korchnak et al., and U.S. Pat. Nos. 6,706,831 and 6,710,145 to Sonnenschein, the entire specifications of which are expressly incorporated herein by reference.  
         [0035]     Referring to  FIG. 3 , there is shown an alternative assembly  114  between an alternative fuel tank  110  and an alternative rollover valve assembly  112 , specifically the bracket member  112   a  (the rollover valve is not shown for purposes of clarity), in accordance with an alternative embodiment of the present invention.  
         [0036]     The fuel tank  110  preferably includes an area defining an aperture  116  formed therein. Around the aperture  116 , there is preferably formed a recessed and angled C-shaped member  118  that preferably extends along the entire circumference of the aperture  116 . The C-shaped member  118  preferably defines an annular channel  120  between a shoulder member  122  and a flange member  124 . On a top surface  126  of the fuel tank  110 , an annular rim member  128  is formed, the purpose of which will be described herein.  
         [0037]     The bracket member  112   a  preferably includes a substantially planar portion  130  and an annular edge member  132  extending along the entire circumference of the bracket member  112   a . In accordance with a preferred embodiment of the present invention, the edge member  132  is preferably angled so as to abut or otherwise engage the rim member  128 . Additionally, a portion of a wedge-shaped member  134  of the bracket member  112   a  preferably abuts or otherwise engages a surface  136  of the flange member  124 . In this manner, the bracket member  112   a  is preferably offset or spaced apart from the fuel tank  110  so as to define a substantially hollow internal cavity  138  by virtue of the fact that the bracket member  112   a  and the fuel tank  110  do not abut one another in a substantially flush manner. Additionally, this configuration eliminates the need for a spacer element, as previously described in the first embodiment.  
         [0038]     As with the previously described embodiment, in order to allow for the introduction of material into the cavity  138 , it is generally necessary to provide for at least one, more preferably at least two, and still more preferably more than two areas defining aperture  140 ,  142 , respectively, in the bracket member  112   a . In accordance with a preferred embodiment of the present invention, the apertures  140 ,  142 , respectively, are preferably substantially spaced from one another and still more preferably are substantially opposed from one another. The apertures  140 ,  142 , respectively, can be formed at the time of the manufacture of the bracket member  112   a  (e.g., injection molding, compression molding, and the like) or can be formed after the manufacture of the bracket member  112   a  (e.g., with the use of a stamp press, aperture press, awl press, or the like, and whether by hand or by aid of machine).  
         [0039]     By providing the apertures  140 ,  142 , respectively, an adhesive material  144  is operable to be disposed or otherwise placed into the cavity  138  (via either aperture  140  or  142 ) such that the cavity  138  is at least substantially completely filled with the adhesive material  144 . The arrows indicate the flow of adhesive material  144  through the cavity  138  if the adhesive material  144  had been initially introduced through aperture  140 . Conversely, if the adhesive material  144  had been initially introduced through aperture  142 , the direction of the arrows would be reversed indicating that the adhesive material  144  would flow towards aperture  140 . Once a sufficient amount of the adhesive material  144  is placed into the cavity  138 , it is preferably allowed to harden or cure so as to form a bond between the bracket member  112   a  and the fuel tank  110 . Additionally, the hardened or cured adhesive material  144  provides structural support to the assembly  114 .  
         [0040]     It should be appreciated that the configurations of the C-shaped member  118 , channel  120 , shoulder member  122 , flange member  124 , and wedge-shaped member  134  can be varied depending, in part, on the particular packaging and/or application requirements. Referring to  FIGS. 4A and 4B , an alternative shoulder member  122   a  is shown wherein the roundness of the shoulder member  122   a  has been replaced with more squared-off surfaces and angles. Additionally, an alternative wedge-shaped member  134   a  is shown wherein the softly angled surfaces thereof have been replaced with a sharply angled triangle-like surface that is deeply recessed within a corresponding surface of an alternative C-shaped member  118 a defining a similar deeply recessed alternative channel  120   a.    
         [0041]     Without being bound to a particular theory of the operation of the present invention, it is believed that the joint designs shown in  FIGS. 4A and 4B , it is believed that a reduction in the level of peel forces on both sides of the joint will be realized, when there is a force applied from below. By way of a non-limiting example, the use of surfaces that are angled with respect to one another, rather than surfaces that are substantially horizontal (e.g., flush) with respect to one another, will be better able to resist peel forces applied thereto. The exact degree of the angle is not thought to be critical to the present however, provided that the chosen degree enables the joint to at least partially resist peel forces applied thereto. By way of a non-limiting example, the angle of each surface is preferably in the range of about 1 degree to about 89 degrees, still more preferably in the range of about 30 degrees to about 60 degrees, and most preferably about 45 degrees.  
         [0042]     Although the previous description related primarily to rollover valves and fuel tanks, it should be appreciated that the present invention is equally applicable to other types of components, assemblies, and systems, regardless of their configurations.  
         [0043]     Referring to  FIG. 5 , there is shown an assembly  200  including a first member  202  nested, at least partially, within a second member  204 , in accordance with another alternative embodiment. These members,  202 ,  204 , respectively, can be cross-sectionally configured in any number of shapes, including but not limiting to cylinders, squares, rectangles, and the like. By way of a non-limiting example, the members  202 ,  204 , respectively can be comprised of pipes, conduits, tubes, hoses, and the like.  
         [0044]     In this embodiment, two apertures,  206 ,  208 , respectively, are provided on the second member  204 . Because the first member  202  is offset from the internal surface  210  of the second member  204 , a substantially hollow cavity  212  is formed. As with the previous embodiments, an adhesive material  214  is preferably introduced into the cavity  212  through one of the apertures  206  or  208 . In this manner, the first and second members,  202 ,  204 , respectively, are bonded together, wherein the cured and/or hardened adhesive material  214  provides structural support to the assembly  200 . The arrows indicate the flow of adhesive material  214  through the cavity  212  if the adhesive material  214  had been initially introduced through aperture  206 . Conversely, if the adhesive material  214  had been initially introduced through aperture  208 , the direction of the arrows would be reversed indicating that the adhesive material  214  would flow towards aperture  206 .  
         [0045]     Referring to  FIG. 6 , there is shown a relatively complex assembly  300  including five members  302 ,  304 ,  306 ,  308 , and  310 , respectively, in accordance with yet another alternative embodiment. Although these members  302 ,  304 ,  306 ,  308 , and  310 , respectively, are shown as being substantially rectangular, they can be cross-sectionally configured in any number of shapes, including but not limiting to cylinders, squares, and the like.  
         [0046]     In this embodiment, the members  302 ,  304 ,  306 ,  308 , and  310 , respectively, have been brought into contact so as to abut or otherwise engage at least one other member. Because the members  302 ,  304 ,  306 ,  308 , and  310 , respectively, are offset from one another to one degree or another, a substantially hollow cavity  312  is formed. In this embodiment, two apertures,  314 ,  316 , respectively, are provided on one of the members, in this case member  302 , and another member, in this case  310 . It should be appreciated that the placement of the apertures,  314 ,  316 , respectively, are chosen, in part, on the basis of how best to ensure that an adhesive material can flow so as to at least substantially completely fill the cavity  312 , and as such, contact the relevant surfaces of members  302 ,  304 ,  306 ,  308 , and  310 , respectively. As such, the apertures,  314 ,  316 , respectively, are preferably substantially spaced and opposed from one another, to the extent possible.  
         [0047]     As with the previous embodiments, the adhesive material  318  is preferably introduced into the cavity  312  through one of the apertures  314  or  316 . In this manner, all of the members  302 ,  304 ,  306 ,  308 , and  310 , respectively, are bonded together, wherein the cured and/or hardened adhesive material  318  provides structural support to the assembly  300 . The arrows indicate the flow of adhesive material  318  through the cavity  312  if the adhesive material  318  had been initially introduced through aperture  314 . Conversely, if the adhesive material  318  had been initially introduced through aperture  316 , the direction of the arrows would be reversed indicating that the adhesive material  318  would flow towards aperture  314 .  
         [0048]     The present invention can also be practiced with any types of components that nestingly engage one another, such as but not limited to windows/window sills, Intake manifolds, radiators, vacuum canisters, and the like.  
         [0049]     Referring to  FIGS. 7A-7D , a non-limiting example of a method of introducing the adhesive material into the cavity of the assembly is shown, in accordance with the general teachings of the present invention. Although the assembly  400  depicts a rollover valve bracket  402  being bonded to a fuel tank  404 , it should be appreciated that the methodology can be applicable to other components, assemblies, and systems, including those previously described.  
         [0050]     Referring to  FIG. 7A , the cavity  406  is shown as being completely empty, except of course, for any air contained therein. A nozzle  408 , connected to a source of adhesive material (not shown), is brought into proximity to one of the apertures  410  provided in the rollover valve bracket  402 . It should be appreciated that other methods of introducing the adhesive material are contemplated by the present invention, including manually introducing the adhesive materials.  
         [0051]     Referring to  FIG. 7B , the nozzle  408  is at least partially inserted into the aperture  410  and adhesive material  412  is introduced therethrough into the cavity  406  with the adhesive material flowing or otherwise being forced to flow into the cavity  406  proximate the aperture  410 . It should be appreciated that all other paths for exiting must be substantially sealed off to the flowing adhesive material  412 , otherwise the flowing adhesive material  412  will travel along unintended paths and may not adequately fill the cavity  406 .  
         [0052]     Referring to  FIG. 7C , the nozzle  408  continues to dispense additional amounts of adhesive material  412  through the aperture  410  with the adhesive material flowing or otherwise being forced to flow further through the cavity  406  towards the other substantially spaced and opposed aperture  414 .  
         [0053]     Referring to  FIG. 74 , the nozzle  408  continues to dispense additional amounts of adhesive material  412  through the aperture  410  with the adhesive material flowing or otherwise being forced to flow further through the cavity  406  proximate to the other substantially spaced and opposed aperture  414 . If the adhesive material is relatively viscous, an optional source of suction or vacuum  416  may be applied to the other aperture  414 , so as to draw the adhesive material  412  towards the other aperture  414 . It should be appreciated that adhesive materials of any viscosity may be used in the practice of the present invention, provided that they can be disposed within the  406  so as to substantially completely fill the same. Although the flow of adhesive material  412  through the cavity  406  is seen as commencing at aperture  410 , it should be appreciated that the flow of adhesive material  412  could alternatively have commenced at aperture  414 .  
         [0054]     Once the adhesive material  412  flows out, or nearly out of the other aperture  414 , the flow of adhesive material  412  is preferably ceased. If any adhesive material  412  does flow out of the other aperture  414  and spill not the surface  418  of the rollover valve bracket  402 , it can be easily wiped up, e.g., with a damp cloth or the like.  
         [0055]     It should be appreciated that this process can be automated and performed by computer-programmed robots, e.g., on an assembly line. By way of a non-limiting example, the assembly  400  can be placed on an assembly line, apertures could be punched in the surface of the rollover valve bracket  402 , and a precise, pre-measured amount of adhesive material  412  can be injected into the aperture  410 , such that it substantially completely fills the cavity  406  such that the adhesive material  412  does not spill out from the other aperture  414 .  
         [0056]     In order to determine the flow characteristics of the adhesive material, the following test was performed, as described in Example I, below:  
       EXAMPLE I  
       [0057]     The flow of the adhesive was tested by mocking up a joint design using transparent plastic cups. The cups were placed one in the other with the outer cup having two apertures drilled at opposite ends. A two-part acrylic adhesive was injected in one aperture until it started coming out of the aperture on the other side. The adhesive had a Brookfield viscosity of 20,000 cps, as measured at 20 rpm with spindle number 7. A two-part pneumatic gun was used to dispense the adhesive at a pressure of 30 psi. There were two joints mocked up, one with a thickness of 0.7 mm and one with a thickness of 2 mm. The adhesive completely filled the cavity both times without any detectable air gaps.  
         [0058]     In order to determine the strength of the resulting bonds between the components, the following test was performed, as described in Example II, below:  
       EXAMPLE II  
       [0059]     Three sample HDPE joints were mocked up with 7 mm thick HDPE, similar to the joints shown in  FIG. 3 . A two-part acrylic adhesive with a Brookfield viscosity of 50,000 cps was injected in one aperture, using a 2-part pneumatic gun at 40 psi, until it came out of the other aperture. The adhesive used was of the Low Energy Surface Adhesive (LESA) type and was obtained from Dow Chemical (Midland, Mich.) under the designations Lot Nos. 200302273-14-1 and  200302273- -4-2. The adhesive was allowed to cure for 24 hours, and then, using an Instron machine, the upper part of the joint was pushed while the lower was constrained. In all three samples the HDPE failed in substrate failure mode. The force of failure for each sample was as follows: 2891 N, 3011 N, and 3176 N, respectively. After the joints failed, they were cut into four pieces to see how uniformly the respective cavities were filled. In all cases, there were no visible voids in the respective bond lines.  
         [0060]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.