Abstract:
A fluid storage tank assembly is provided which includes a tank having sidewalls, a bottom wall and a top wall, and a support columns positioned between the sidewalls. The support columns blend into the sidewalls to avoid sharp corners and the sidewalls join with the bottom wall and the top wall along rounded edges to avoid stress concentrations in the tank. The tank is rotationally molded of synthetic resin, and is provided with a plurality of detachably mounted discrete legs which thread into recesses in the bottom wall. The top wall includes an indentation, and the indentation and the reception surfaces atop the support columns receive the legs of a second fluid storage tank stacked thereon. A bottom protector provided as a relatively thin sheet of synthetic resin material has a plurality of holes therethrough to permit insertion of the threaded shanks of the legs to pass therethrough for coupling the protector to the bottom of the tank.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention concerns a fluid tank assembly capable of containing intermediate volumes of liquid in stacking relationship without additional reinforcement. More particularly, it is concerned with a tank which is rotationally molded of synthetic resin and wherein the walls of the tank are configured with corners including generally upright arcuate support portions to substantially retain the shape of the tank when filled, lifted from the bottom and/or stacked with similar tanks. The fluid tank assembly also has independent and removable support legs which facilitate stacking and retain a web-like bottom wall protector. 
     2. Description of the Prior Art 
     Various types of industrial liquids, including hazardous chemicals, are transported and stored in tanks and containers of a variety of sizes. These tanks have increasingly been manufactured of polyethylene or other synthetic resins for corrosion resistance, weight, and other reasons. These tanks have a storage capacity typically of from about 15 U.S. gallons to 793 U.S. gallons, and are often set on bases for lifting with a forklift. These bases underlie substantially the entire tank and may be complementally configured with the top of the tank as well as the bottom so that similar tanks and bases may be stacked one atop the other in the warehouse. Usually, such bases are separately attachable to the tank which contains the liquid. 
     Typically, these tanks have a specially designed shape and are formed with walls having a strong, rigid construction so that when several of the filled containers are stacked one on another, the container on the bottom of the stack has the load bearing capacity to support the total weight of the filled containers on top of it. Other types of containers have bases with stacking legs which surround the tank and extend above it, thereby protecting the tank and avoiding load transference through the walls of the tank. Among the tanks useful for transporting and storing industrial liquids are those shown in U.S. Pat. Nos. 5,490,603 and 6,079,580, both assigned to the assignee of the present invention. 
     Notwithstanding many beneficial features of these tanks, there remain several drawbacks. Tanks without stacking legs usually still require elaborate and expensive bases for stacking and dispensing liquid from the bottom outlet thereof, as well as to stabilize the tank and enable the tank to be lifted by a forklift. Moreover, in order to sustain the weight of filled tanks stacked thereon, the walls of the tank portion must be relatively thick and undamaged. Those fluid transportation and storage tanks having frames or stacking legs extending upwardly from their bases present significant advantages in terms of weight transfer, but are expensive to manufacture and may require the molding of three separate parts—the base and stacking legs, the tank, and the top protector. 
     Thus, there has developed a real need for an improved tank capable of handling industrial liquids, having good stacking characteristics with greater economy of manufacture. There is a further need for a tank having improvements in construction to maintain economy and still resist damage from fork lift tines and pallet jacks. There is additionally a need for improvements in the manner of elevating the bottom of the tank above a floor or other supporting surface. 
     SUMMARY OF THE INVENTION 
     These and other needs have largely been met by the fluid storage tank assembly of the present invention. That is to say, the invention hereof provides capabilities of storing intermediate amounts of liquid in a tank which is both self supporting and stackable when filled, and wherein the tank has very little deflection or dimensional difference between a filled and unfilled configuration. Furthermore, the tank avoids the need for a large base by employing legs which support the tank. The legs advantageously are removably mounted to the bottom wall of the tank, and retain an optional bottom protector in place in the manner of fasteners so that the protector acts as a shield between the bottom wall of the tank and pallet jacks or fork lift tines. 
     In greater detail, the assembly of the invention most preferably includes a tank and a plurality of removable support legs, and may also include a bottom protector of a relatively thin web of material which is held in position adjacent a bottom wall of the tank by the legs. The side walls of the tank are substantially curvilinear, with the tank including integrally molded support columns at its corners, whereby the tank presents a generally polygonal shape in horizontal cross-section. The support columns are integral with the side walls, receive liquid therein and thus, together with the side walls, top wall and bottom wall define the liquid receiving chamber. The preferred side walls are curvilinear rather than lying in flat, upright planes, and thus are somewhat arcuate either in vertical section, horizontal section, or possibly both vertical and horizontal section and merge into rounded corners along at least the top edge. The support columns are generally curved in horizontal section and may be generally of oppositely extending frustoconical portions or generally cylindrical in configuration. The support columns receive fluid therein and need not extend in a full circular in horizontal section but only a segment thereof, as the support columns are hollow to receive liquid as a part of the chamber formed by the support columns and the walls of the tank. The bottom wall preferably includes an integrally formed diagonally extending reinforcing channel extending from the center toward the support columns at the corner, with the top wall preferably similarly configured. The bottom wall adjacent the reinforcing channel is preferably somewhat arcuate whereby the reinforcing channel acts as a bottom support beam with the arcuate bottom wall to transfer the weight of the liquid carried within the tank to the support columns and to distribute the load to the vertical walls. The bottom deck of each of the ribs forming the reinforcing channel is substantially co-planar to provide an even engagement surface for facilitating lifting of the tank assembly by a fork lift or pallet jack. While the portions of the reinforcing channel atop the support columns are preferably flat and stepped downwardly relative to the top deck of the ribs of the reinforcing channel by an adjacent arcuate margin to provide reception surfaces for legs of a similar tank assembly stacked thereon, the reinforcing channel at the bottom of the support columns is preferably provided with internally threaded recesses to receive a threaded shank on the feet. In addition, the intersection of the diagonally extending ribs of the reinforcing channel is preferably indented in the top wall and a recess is threaded in the bottom wall to permit attachment of a leg thereto. The bottom wall of the tank is preferably provided with an outlet threaded to receive a pipe or valve thereon, while the top wall may include a threaded collar to receive a cap and a threaded internal neck for mounting of a bung. The tank is preferably made by rotational molding of polyethylene or other suitable synthetic resin. 
     The legs are also molded of polyethylene or other synthetic resin, either by blow molding, rotational molding or injection molding. The legs are provided with a shoulder for retaining the bottom protector in position and a threaded shank sized and threaded complementally to the recesses in the bottom wall of the tank. 
     The optional bottom protector is configured for positioning beneath the bottom wall of the tank and includes openings therein sized to receive the shanks of the but abut the shoulders of the legs. The bottom protector is a relatively thin web or sheet of material which helps avoid damage to the bottom wall and distribute force from the fork lift tines to the reinforcing channel. Thus, the legs serve the dual purpose of elevating the tank above the floor and holding the bottom protector in position. 
     In use, a plurality of tanks may be stacked one atop the other, even when filled. The bottom surface of the legs of the upper tank assembly rest on and are held in position by the margins or rims on the diagonally extending reinforcing channel in the top wall. Because each of the support columns and the center indentation in the reinforcing channel are recessed below the channel and face outwardly from the center, the upper tank may be readily lifted off the lower tank but resists lateral movement relative thereto. The arcuate configuration of the sidewalls and the integrated support columns cooperate to bear the load of the tank as well as assemblies positioned thereon. Pallet jacks or fork lift tines are provided ready access because the legs elevate the bottom wall and the bottom protector above the floor, and the bottom protector, which may be readily replaced, helps to isolate the bottom wall of the tank from damage caused by the pallet jacks or fork lift tines. 
     These and other advantages will be readily apparent to those skilled in the art with reference to the description and drawings presented herewith. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a right upper front perspective view of the fluid tank assembly of the present invention having a bottom protector attached by legs coupled to the bottom wall of the tank; 
     FIG. 2 is a front elevational view thereof, showing the recesses at the tops of the support columns; 
     FIG. 3 is a top plan view thereof, showing the center indentation at the intersection of the diagonally extending, generally X-shaped reinforcing channel on the top wall; 
     FIG. 4 is a bottom plan view of the tank without the bottom protector or legs attached; 
     FIG. 5 is a vertical cross-sectional view taken along line  5 — 5  of FIG. 3, showing the arcuate side walls and rounded corners of the tank; 
     FIG. 6 is a vertical cross-sectional view taken along line  6 — 6  of FIG. 3, showing the threaded attachment between the legs and the recesses in the bottom wall and the transition between the side wall and the support column; 
     FIG. 7 is a vertical cross-sectional view taken along line  7 — 7  of FIG. 3 showing the arcuate side walls and showing a discharge pipe in phantom; 
     FIG. 8 is an enlarged fragmentary vertical sectional view showing the positioning of the legs when two tank assemblies are in superposed, stacked relationship; and 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawing, a fluid tank assembly  10  for transportation and storage of liquids and in accordance with the present invention preferably includes a tank  12 , a plurality of legs  14  and a bottom protector  16 . The tank  12 , legs  14  and bottom protector  16  are molded of synthetic resin such as high density polyethylene. The tank  12  is of a capacity in the range of 15 U.S. gallons to 793 U.S. gallons, and may receive thereon a cap  18  and a bung  20  to aid in filling, venting and emptying the tank, as well as an outlet  22  for receiving a discharge pipe shown in phantom which may include a valve or other regulating member. The legs  14  are preferably configured for removable mounting to the tank  12  without the necessity of tools. 
     In greater detail, the tank  12  has a substantially continuously molded outer wall  24  including sidewalls  26 ,  28 ,  30  and  32 , a bottom wall  34  and a top wall  36 . The sidewalls, bottom wall and top wall a curvilinear but not of a continuous curvature. As shown in the drawings, the tank  12  has a generally polygonal shape as opposed to generally spherical or cylindrical. In the preferred embodiment shown herein, the tank  12  is generally square in horizontal cross-section, although other generally polygonal shapes could be provided. The sidewalls define four corners with support columns  38 ,  40 ,  42  and  44  located at the respective corners. The support columns each include a generally frustoconical upper support member  46  which narrows in cross section moving from a bottom to top direction, a transition section  48  of generally cylindrical shape, and a generally frustoconical lower support member  50  which narrows in cross section moving from a top to bottom direction. The tank  12  has a fluid storage chamber  52  within the outer wall  24 , and the support columns form a part of the outer wall and thus receive liquid therein. 
     The four sidewalls  26 ,  28 ,  30  and  32  are generally curved in the Y axis (in vertical section) as shown by FIG. 4, and may also be curved in the X axis as illustrated by the top plan and bottom views of FIGS. 3 and 4. The sidewalls  26 ,  28 ,  30  and  32  merge into the bottom wall  34  along a bottom edge  54  and merge into the top wall  36  along a top edge  56 . The bottom edge  54  and top edge  56  are rounded to provide a transition to the sidewalls and to avoid stress concentrations. Thus, the top edge  56 , and the bottom edge  54  along sidewalls  28 ,  30  and  32  and bottom wall  34  which do not include an outlet sump  58 , have a radius of curvature preferably of at least 10% of one-half of the distance between the bottom wall and the top wall. 
     The bottom wall  34  includes an X-shaped reinforcing channel  60  formed therein, the reinforcing channel  60  extending between the support columns as shown in FIG.  4 . The reinforcing channel  60  acts as a support beam and cooperates with the adjacent bottom wall areas to transfer loads carried thereby to the sidewalls and support columns acting as a suspension truss. The reinforcing channel  60  presents diagonally extending raised ribs  62  and  64  which are oriented approximately 90° from one another and have an intersection  66 . The ribs  62  and  64  extend downwardly relative to adjacent portions of the bottom wall  34 . Recesses  68 ,  70 ,  72  and  74  are provided in the bottom wall  34  and positioned below each of the support columns  38 ,  40 ,  42  and  44 , respectively, and have internal threads  76  therein. A central recess  78  is located at the intersection  66  and also has internal threads  76  on a threaded upright sleeve  80 , and together with the end wall  82  of the recesses  68 ,  70 ,  72 ,  74  and  78 , provide additional reinforcement for the bottom wall  34 . The ribs  62  and  64  each include opposed downwardly extending siderails  81  and a bottom deck  83 , the decks  83  of each of the ribs  62  and  64  being substantially coplanar to proved even surfaces for lifting of the tank  12  by a fork lift or pallet jack. 
     The top wall  36  also includes an X-shaped reinforcing channel  84  which includes raised ribs  86  and  88  having an intersection  90 , the ribs  86  and  88  being in substantial vertical alignment with the ribs  62  and  64  and having side rails  89  and a top deck  91 . An indentation  92  relative to the top deck  91  is provided at the intersection  90 , which has a reception surface  94  which is substantially co-planar with reception surfaces  96  of the reinforcing channel which are vertically aligned with and atop the support columns as shown in FIG.  5 . The reception surfaces  96  at the ends of the ribs  86  and  88  each have an arcuate margin  98  on the inboard area toward the intersection  90  which aid in locating the legs  14  of a similar fluid tank  10  assembly thereon as shown in FIG.  8 . The top wall also includes a threaded collar  100  for receiving the cap  18  and an internally threaded neck  102  for threadably mounting the two-part removable bung  20 . 
     The support columns  38 ,  40 ,  42  and  44  are substantially vertical when the tank assembly  10  is in normal use. While the upper support member  46  and the lower support member  50  extend from the sidewalls, the transition area  48  blends into the sidewalls without sharp corners or curvatures. For example, while the sidewalls  28  and  30  are oriented at substantially right angles to one another, the transition area  48  of the support column  38  positioned at the intersection between the adjacent sidewalls  28  and  30  is arcuate in horizontal section, having a radius of curvature of at least about 5% of the distance between sidewalls  28  and  32 , and also sidewalls  30  and  34 . The transition area substantially blends and merges into the sidewalls  28  and  30  as it turns the corner so that no appreciable edge is noticeable between the transition area  48  and the sidewalls  28  and  30 . Thus, as seen in FIGS. 5,  6  and  7  looking at the inner surface of the sidewalls and support columns which is substantially smooth and continuous therebetween, the effect is to provide an outer wall  24  which is substantially smooth and continuous without edges at least in the area of the transition areas  48  located substantially midway between the top wall and the bottom wall, but alternatively could include planar wall segments as a part thereof. The curvilinear walls serves to avoid stress concentrations in the tank  12  and makes it more capable of supporting loads placed thereon. It may be appreciated that the cross-sectional view shown in FIG. 6 would be substantially the same if the section were taken along a plane rotated 90° counterclockwise as seen in FIG.  3 . 
     The legs  14  are commonly configured with one another, each having a base  104  extending upwardly to a shoulder  106  and a threaded shank  108  complementally sized to thread into the recesses of the bottom wall  34 . The legs  14  are of sufficient height to permit a forklift or pallet jack to be inserted below the bottom wall  34 . The base  104  is preferably substantially cylindrical so as to be symmetrical, thereby permitting tolerance in manufacturing regarding the orientation of the threads, and is of a transverse dimension complemental to be received in the indentation  92  and to fit atop the reception surfaces  96  of the reinforcing channel  84  atop the support columns. Thus, the base  104  preferably has an outer radius which is complemental with the curvature of the arcuate margins  98 . 
     The bottom protector  16  is preferably molded as a sheet or web which substantially conforms in contour to the bottom wall  34  of the tank  12 . It includes a front pan  110  providing access to the outlet pipe or discharge valve, and deflectors  112  around the edge. The bottom protector further includes holes  114  therethrough which are positioned in registry with the recesses of the bottom wall  34 . The holes  114  are of a diameter to permit the threaded shanks  108  of the legs  14  to pass therethrough and into the recesses, but to engage the shoulders of the legs  14  so that the bottom protector is thereby held in place. 
     In use, the tank  12  may be readily tipped to one side because of its light weight, and the outlet pipe or valve installed in the outlet  22 . The bung  20  may be installed in the top wall  36 , and the bottom protector  16  positioned on the bottom wall  34  so that the legs  14  may be threaded into the recesses to thereby hold the bottom protector in place. This completes the tank assembly  10 , which is then ready to be filled through the collar and the cap  18  threaded thereon. The tank assembly  10  may also be lifted onto another tank assembly  10  as shown in FIG.  8 . In this stacked arrangement, the bases  104  of the legs  14  are received on the reception surfaces  96  atop the support columns, with the leg positioned in the central recess  78  located in the indentation  92  as shown in FIG.  8 . It may be appreciated from FIG. 8 that ample clearance is still provided between the legs  14  and between the bottom wall  34  of the upper tank assembly  10  and the top wall  36  of the lower tank assembly  10  that the tines of a forklift may be easily inserted therebetween to permit lifting and removal of the upper tank assembly  10 . The engagement of the legs  14  with the top wall  36  around the indentation and the arcuate margin  98  inhibit relative lateral movement between the upper tank assembly  10  and the lower tank assembly  10  as illustrated in FIG.  8 . The weight of the tank assemblies is evenly transferred to the legs  14 , thus inhibiting collapse and leakage of the contents of the tanks  12 . 
     Although preferred forms of the invention have been described above, it is to be recognized that such disclosure is by way of illustration only, and should not be utilized in a limiting sense in interpreting the scope of the present invention. Obvious modifications to the exemplary embodiments, as hereinabove set forth, could be readily made by those skilled in the art without departing from the spirit of the present invention. For example, externally threaded extensions could be molded into and extend from the bottom wall with the legs having internal threads for receipt thereon. The support columns may be substantially cylindrical instead of frustoconical. Further, the tank could be configured with an outer wall of a variety of shapes, including a substantially continuously arcuate shape such as a sphere with three, four or more support columns molded into the perimeter for support. Additional threaded recesses could be provided to permit additional legs to be mounted, or the leg  14  located in the central recess  78  could be eliminated. 
     The inventor hereby states his intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of his invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set out in the following claims.