Rotationally molded plastic waste container with integral channels for receiving lifting prongs and method

Abstract

A plastic waste container is rotationally molded with a hollow material carrying or holding compartment having a bottom, rear, front and opposed side walls. A plastic pocket defining a prong receiving channel, located on each side wall or on the bottom wall, is integrally formed and preferably molded with the compartment. The bottom wall extends upwardly and inwardly from a location adjacent the perimeter to form a convex dome with an upper surface above the perimeter in the range of about 3'' to 10''.

1 . A rotationally molded plastic waste container adapted to be lifted by the spaced prongs of a lifting mechanism comprising: 
 a hollow material carrying compartment having a bottom, rear, front, opposed side walls and an open top, the compartment extending downwardly from the open top, the bottom wall extending upwardly and inwardly from a location adjacent the perimeter forming a convex dome with an upper surface above the perimeter within the range of about 3″ to 10″; and    a plastic pocket defining a prong receiving channel integrally formed with and located on each compartment side wall.    
     
     
         2 . The waste container of  claim 1  further including a rib extending laterally across the dome section of the bottom wall.  
     
     
         3 . The waste container of  claim 2  wherein the bottom wall forms a generally planar upper surface extending about the perimeter within the range of about 4″ to 8″ and wherein the rib has an upper surface extending above the planar upper surface about 1″ to 3″.  
     
     
         4 . The waste container of  claim 3  wherein the rib is generally rectangular in cross-section.  
     
     
         5 . The waste container of  claim 4  further including a centrally disposed cavity extending downwardly from the top surface of the rib.  
     
     
         6 . The waste container of  claim 1  wherein the bottom wall extends upwardly from the perimeter at an acute angle to the horizontal within the range of about 14° to 22° to a center section.  
     
     
         7 . The waste container of  claim 6  further including a reinforcing rib extending laterally across the bottom wall and molded integrally therewith, the strut having generally vertically oriented sides terminating in a generally flat top surface.  
     
     
         8 . A rotationally molded plastic waste container adapted to be lifted by the spaced prongs of a lifting mechanism comprising: 
 a hollow material carrying compartment having a bottom, rear, front, opposed side walls and an open top, the bottom wall having a perimeter with a major portion of the bottom wall forming a convex-shaped dome extending upwardly and inwardly from adjacent the perimeter; and    a plastic pocket defining a prong receiving channel integrally formed with and located on each compartment side wall.    
     
     
         9 . The waste container of  claim 8  wherein the dome-shaped section comprises at least 70% of the bottom wall.  
     
     
         10 . The waste container of  claim 9  wherein the bottom wall extends upwardly from adjacent the perimeter at an acute angle to the horizontal within the range of about 14° to 22° to a center section.  
     
     
         11 . The waste container of  claim 10  further including a rib extending laterally across the dome-shaped section of the bottom wall.  
     
     
         12 . The waste container of  claim 11  wherein the dome-shaped section of the bottom wall forms a generally planar upper surface extending about the perimeter within the range of about 4″ to 8″ and wherein the rib has an upper surface extending above the planar upper surface about 1″ to 3″.  
     
     
         13 . A method of molding a plastic waste container comprising: 
 a) providing a mold defining a material holding compartment section having a bottom, front, rear and opposed side walls and a pair of removable core sections secured and spaced from the compartment section to accommodate molten material flowing from the compartment section around the removable cores to form pockets defining prong receiving channels;    b) biaxially rotating and heating the mold to rotationally mold the compartment and pockets surrounding the removable cores from a powered/molten plastic material; and    c) opening the mold and removing the core from the molded container.    
     
     
         14 . The method of  claim 13  wherein the mold includes a skirt section extending around each removable core and during the biaxial rotation of the mold, forming a skirt extending outwardly from each removable core, each skirt including at least two horizontally aligned c-shaped sections, one c-shaped section located adjacent the front and the other c-shaped section located adjacent the rear wall of the compartment.  
     
     
         15 . The method of  claim 14  wherein the mold includes a rim section around the top of the compartment section which is separated by one or more peripheral gaps from the compartment section and further including molding an enclosed rim around the top of the compartment by passage of the material through said peripheral gaps in the mold to form a partially enclosed interior void in the rim and venting air from the rim void to atmosphere.  
     
     
         16 . The method of  claim 15  wherein the removable cores are located on opposed side walls of the compartment and wherein the mold includes a skirt section extending outwardly from each side wall around a respective removable core and during the biaxial rotation of the mold forming a skirt extending outwardly from each side wall of the compartment, each skirt including at least two horizontally aligned c-sections, one c-section located adjacent the front wall and the other c-section located adjacent the rear wall of the compartment.  
     
     
         17 . The method of  claim 15  wherein the removable cores are located adjacent the bottom wall of the compartment, the skirt forming step further includes integrally molding a plurality of skirts extending upwardly and downwardly from each of the respective pockets during rotation of the mold.  
     
     
         18 . The method of  claim 16  wherein the skirt forming step further includes integrally molding a plurality of struts extending from each of the respective pockets during the rotation of the mold.  
     
     
         19 . The method of  claim 18  wherein said upper struts are joined to the rim.  
     
     
         20 . A method of rotationally molding a container defining a material holding compartment having a bottom, front, rear and opposed side walls and a lifting prong receiving channel on each side wall comprising: 
 a) providing a mold having an interior space defining a compartment forming section and a skirt and a removable pocket forming section on each side wall of the compartment forming section with one or more gaps extending between at least a portion of each of the skirt/pocket forming sections and the compartment forming section of the mold, the gaps being dimensioned to be bridged over during the molding process, the pocket forming sections defining a channel for accommodating lifting prongs, the skirt forming sections extending outwardly from the compartment forming section and around the pocket forming sections;    b) placing a sufficient amount of powdered/molten plastic material in the mold to provide the desired thickness to the molded container;    c) biaxially rotating and heating the mold to allow the plastic material to flow over and progressively adhere in successive layers to the mold surface to form the compartment and the portion of skirts and pockets not separated by the gaps; and    d) passing the plastic material through the gaps, during the compartment forming step, to form the portion of the skirts and pockets separated form the compartment section by the gaps and allowing the material to bridge over the gaps.    
     
     
         21 . The method of  claim 20  wherein: 
 a) the provided mold defines a rim forming section at the free end of the container walls with one or more peripheral rim gaps between the intersection of the rim and compartment forming sections; and    b) passing the plastic material through the rim gaps during the compartment forming step to form the rim.    
     
     
         22 . The method of  claim 21  wherein the pocket forming sections of the mold are arranged to form generally rectangular pockets each having an inner wall forming a portion of the respective compartment side wall and wherein the skirt forming sections of the mold are arranged to form a plurality of spaced c-sections surrounding the pocket with intervening strut sections, the strut sections forming generally u-shaped struts extending upwardly from the c-sections and joined to the wall of the compartment.  
     
     
         23 . The method of  claim 22  wherein the forming of the skirts and pockets creates partially enclosed spaces between the skirts and pockets and venting the spaces to atmosphere.  
     
     
         24 . The method of  claim 20  wherein the skirt forming sections of the mold are arranged to additionally form generally u-shaped struts extending downwardly from the c-sections and joined to the wall of the compartment.  
     
     
         25 . The method of  claim 20  wherein a plurality of spaced caster plate receiving nuts are located on the interior of the mold bottom wall adjacent each comer whereby the nuts will be encapsulated in the bottom wall of the finished container.  
     
     
         26 . The method of  claim 21  wherein the mold defines a hinge ear forming section for forming a plurality of hinge ears on the back rim of the container open to the partially enclosed voids in the rim and to the material holding compartment and passing the plastic material to the hinge ear forming section during the compartment forming step.  
     
     
         27 . A rotationally molded plastic waste container adapted to be lifted by the spaced prongs of the lifting mechanism comprising: 
 a hollow material carrying compartment having a bottom, rear, front and opposed side walls and an open top; and    a pair of spaced parallel plastic pockets integrally molded with the compartment bottom wall, each pocket defining a prong receiving channel.    
     
     
         28 . The container of  claim 27  wherein each pocket has a top, bottom, and side walls with the top wall forming a portion of the compartment bottom wall and further including a skirt integrally molded with the container compartment and extending around the bottom and side walls of each pocket.  
     
     
         29 . The container of  claim 28  wherein each skirt forms a plurality of c-sections extending around the bottom and side walls of each pocket and a plurality of strut sections adjacent the c-sections with each strut section extending along the compartment bottom wall on each side of the respective c-sections.