Abstract:
A unitary plastic open head drum includes a first cylindrical sidewall closed at a bottom end with a bottom wall and open at an upper end. A second generally cylindrical sidewall is concentric to and extending at least partially the length of the first sidewall, providing sufficient stiffness to resist “elephant footing” of a bottom drum in a stack of drums.

Description:
FIELD OF THE INVENTION 
     This invention relates to containers and, more particularly, to an injection molded plastic drum with a reinforced sidewall. 
     BACKGROUND OF THE INVENTION 
     In one form of a conventional shipping and storage container, an enlarged drum is used. The drum may be, for example, a fifty five gallon drum. Such drums have found wide usage for shipping and storing liquid or granular products. For example, such drums have been used for storing food products and for storing hazardous products. 
     In its simplest form, a drum includes a single tubular sidewall closed at one end by a bottom wall. Such containers typically have either a fiberboard or metal sidewall of uniform thickness. More recently, plastic drums have found wide acceptance. 
     During shipping and storage, such plastic drums are often stacked to conserve space. When filled plastic drums are stacked, however, the additional weight bearing on a bottom drum in a stack may cause significant deformations of the bottom drum. In such a case, a lower portion of the bottom drum typically bulges outwards. resulting in an “elephant foot” shaped bottom drum. This deformation produces an internal pressure within the bottom drum, forcing the contents of the bottom drum to escape. 
     The present invention is intended to solve one or more problems discussed above in a novel and simple manner. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention there is provided a unitary plastic drum. 
     Broadly, there is disclosed herein a plastic shipping container including a unitary plastic drum having a generally cylindrical sidewall closed at a bottom end with a bottom wall and open at an upper end. The drum is of one-piece plastic construction. 
     It is a feature of the invention that at a lower section of the sidewall is double-walled. 
     It is another feature of the invention that a center section of the drum includes a diameter that decreases from the drum top downwards. 
     It is another feature of the invention that an upper section of the drum have a greater diameter than a diameter of the center section, thereby creating a conical ledge on the inner surface of the drum. 
     It is another feature of the invention that the lower section has a smaller diameter than the center section diameter such that a ledge is formed to aid in the nesting of empty drums. 
     It is yet another feature of the invention to include a second cylindrical sidewall concentric to and extending at least partially the length of the first sidewall. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a unitary plastic open head drum taken along the line  1 — 1  of FIG. 2; 
     FIG. 2 is a bottom plan view of the drum shown in FIG. 1; 
     FIG. 3 is a sectional view of a nested drum configuration. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the illustrated embodiment of the invention, as disclosed in the drawings, a container  10  is shown to comprise a unitary open head plastic drum  12  with an open top end  14 . The drum is formed of a suitable material, such as a molded synthetic resin. Advantageously, the resin is a thermoplastic which is suitable for injection molding. 
     With reference to FIG. 1, the drum  12  has a generally cylindrical sidewall  16  connected to a bottom wall  18  to define an interior space  20 . The drum  12  is open at the top end  14 . The sidewall  16  is approximately thirty seven inches tall, and includes an upper section  24 , a middle section  26 , and a lower section  28 . The upper section  24  and middle section  26  have a uniform wall thickness of approximately one quarter inch. The upper section  24  has a uniform diameter of approximately twenty four inches and connects to the middle section  26 , which is of a smaller diameter, forming a conical ledge  30 . The middle section  26  has a downwardly decreasing diameter, such that the sidewall  16  forms an angle of approximately two degrees with the vertical at the middle  10  section  26 . At the open end  14 , the upper section  24  includes a radially outwardly extending flange  32  which in turn is connected to an upwardly extending cylindrical lip  34  The cylindrical lip  34  forms a seal between the open end  22  and a cover (not shown). 
     The lower section  28  of the drum  12  includes an outer sidewall  38  with a diameter of approximately twenty inches and an inner sidewall  40  with a smaller diameter than the diameter of the outer sidewall  38 . With reference to FIG. 2, the lower section  28  is comprised of a plurality of radially extending ribs  42  sandwiched between the outer sidewall  38  and the inner sidewall  40 . The ribs  42  are circumferentially spaced with a major axis aligned substantially parallel to the longitudinal axis of the lower section  28 . The outer sidewall  38  has a downwardly decreasing thickness, whereas the inner sidewall  40  has a uniform thickness of approximately one quarter inch. The outer sidewall  38  and the inner sidewall  40  are approximately eight inches tall. The outer sidewall  38  of the lower section  28  has a diameter slightly less than a diameter of the bottom of the middle section  26 . An annular lip  43  connects the top of the inner sidewall  40  with the top of the outer sidewall  38 , forming an interior ledge  44  within the drum  12 . The bottom wall  18  has a uniform thickness of approximately one quarter inch and connects to the inner sidewall  40  of the lower section  28 . 
     The present invention sufficiently prevents “elephant footing” of the drum, and presents many advantages over the use of a conventional single sidewall lower section construction. To achieve an equivalent stiffness of the present double sidewall invention, a single sidewall lower section would have a thickness of at roughly one half inch. Such a thickness would require a greater amount of material than the present invention, thus increasing the drum weight and cost. Furthermore, a single sidewall with a one half inch thickness may be difficult to mold. The present invention overcomes these difficulties by exploiting a laminated construction wherein support ribs are sandwiched between two concentric sidewalls. More specifically, less material is used in the lower sidewall construction of the present invention since hollow cavities are formed between adjacent support ribs. Additionally, the structure exhibits good moldability since the inner and outer walls have a thickness that is typical in the conventional art. 
     To conserve space during shipping and storage, a plurality of empty drums are often nested within one another. As shown in FIG. 3, a drum  12 ′ identical to the drum  12  may be nested within the drum  12 . The bottom wall  18 ′ of the drum  12 ′ rests upon the interior ledge  44  of the drum  12 . Additionally, the exterior conical ledge  30 ′ of the drum  12 ′ rests upon the radially outwardly extending flange  32  and within the cylindrical lip  34  of the drum  12 .