PLASTIC CONTAINER

Abstract

The present invention relates to a container (10) which is produced in a blow molding process and is made of thermoplastic material—preferably a bung drum—having a welded-on bung connector, prefabricated in an injection molding process and having an internal thread, for the storage and transport of liquid or free-flowing contents. In order to eliminate disadvantageous material distortion in blow-molded containers as a result of relatively long cooling times of thick locations, e.g. at threaded bungs and flash seams, according to the invention formed in the top (30) of the container (10) is a shortened welded bung connector (32), onto which a solid threaded welding head (12), prefabricated in an injection molding process and having an internal thread (20), is welded.

Claims

1.-8. (canceled)

9. A container made of thermoplastic material and produced in a blow molding process for the storage and transport of liquid or free-flowing contents, said container comprising: a shortened welded bung connector formed in the blow molding process on a top of the container and defining an opening in the top, said shortened welded bung connector having an obliquely upward facing first annular welding surface; and a bung connector part, prefabricated in an injection molding process and formed as an internally threaded, solid welding head, said solid welding head having an obliquely downward facing second annular welding surface complementary to the first annular welding surface, said first and second annular welding surfaces fixedly and non-detachably materially bonded to one another, said first and second annular welding surface each having a circular inner edge and a circular outer edge, wherein in an upright position of the container, said outer edges are situated above said inner edges.

10. The container of claim 9, wherein the first annular welding surface has a concave shape and the second annular welding surface has a convex shape.

11. The container of claim 9, wherein an outer side of the solid welding head—as viewed in a horizontal plane—has a dome shaped contour at least in a region of the second annular welding surface, and the first annular welding surface has a corresponding negative dome-shaped contour.

12. The container of claim 9, wherein an outer side of the solid welding head is essentially entirely dome-shaped.

13. The container of claim 9, wherein the shortened welded bung connector is configured as a circumferential beaded edge, said first annular welding surface arranged on the shortened welded bung connector directly on the opening in the top base of the container.

14. The container of claim 9, wherein the first annular welding surface is arranged on an upper edge of the welded bung connector, wherein the welded bung connector is formed respectively as a standard welded bung connector with a same diameter for conventional ¾-inch, 2-inch and 3-inch bung closures, regardless of a container size, onto which welded bung connector a correspondingly adapted standard threaded welding head with an external diameter of between 65 mm and 70 mm is welded, wherein an internally threaded opening of the standard threaded welding head is freely selectable for use of a ¾-inch, 2-inch or 3-inch bung closure.

15. The container of claim 9, wherein a color of the solid welding head is different from a color of the container as an indication of hazardous goods contents.

Description

[0041] The invention is explained and described in more detail below with reference to exemplary embodiments shown schematically in the drawings, in which:

[0042] FIG. 1 shows a perspective view of a blow-molded plastic container according to the invention in the form of a bung drum with welded-in threaded welding flanges,

[0043] FIG. 2 shows a cross-sectional view of a threaded welding head according to the invention,

[0044] FIG. 3 shows a partial cross-sectional view through a welded-in threaded welding flange,

[0045] FIG. 4 shows another partial cross-sectional view through a welded-in threaded welding head,

[0046] FIG. 5 shows a further partial cross-sectional view through a welded-in threaded welding head,

[0047] FIG. 6 shows a partial cross-sectional view of another embodiment of a welded-in threaded welding head.

[0048] FIG. 1 illustrates a bung drum made of thermoplastic material and denoted by the reference numeral 10 as a preferred exemplary embodiment of a blow-molded plastic container. Bung drums with an upper handling ring are available in a variety of drum sizes with a filling volume of from 30 liters to 300 liters. The most common are 220 liter bung drums with two bung closures in the top of the drum. According to the invention, the bung closures are each provided with a welded-in threaded welding head 12, prefabricated in an injection molding process, into which the customary bung fittings are screwed in order to close the bung opening 28 in a gas- and liquid-tight manner.

[0049] An embodiment according to the present invention of a threaded welding head is illustrated in FIG. 2. The threaded welding heads 12 according to the invention can be designed in various sizes. Preferred sizes are ¾-inch, 2-inch and 3-inch threaded welding heads. The threaded welding heads 12 according to the invention can furthermore be provided with various types of thread, specifically either with a coarse thread and a seal seat arranged below the thread or with a fine thread and a seal seat arranged above the thread.

[0050] 2-inch threaded welding heads can moreover be formed with a customary BCS 70×6 thread.

[0051] The upper bung connector part, prefabricated in an injection molding process, is in the form of a solid threaded welding head 12 such as a spherical-dome ring element with a central bore for receiving an internal thread and a wall part enclosing the bore and having a wall thickness thickened by material accumulation.

[0052] The solid threaded welding head 12 with an internal thread 20 has an annular welding surface 22, which has a circular inner edge 24 and a circular outer edge 26, on the circumference. The outer side of the threaded welding head 12 can have a dome-like form on the circumference at least in the region of its annular welding surface 22. In a preferred embodiment, the outer side of the threaded welding head 12 has an almost entirely dome-like form. The spherical dome form of the threaded welding head 12 is represented by the circle indicated by a dashed line in FIG. 2 and has the shape of a three-dimensional spherical segment with a uniformly curved outer spherical zone as the dome-like outer side of the threaded welding flange.

[0053] The height of the annular welding surface 22 is defined by the arrow H(K).

[0054] FIG. 3 illustrates a threaded welding head 12 in the installed state in the case of a bung drum 10 with a circumferential handling ring. The bung opening 28 arranged in a bung hollow of the top 30 is enclosed by a welded bung connector 32. Formed on the upper edge of the welded bung connector 32 is an annular welding surface 14 with a negative dome-like contour, which has a circular inner edge 16 at the bottom and a circular outer edge 18 at the top. The welded-in threaded welding head 12 with a dome-like outer side accordingly comprises the annular welding surface 22 with a circular inner edge 24 and a circular outer edge 26. In this way, with normal upright positioning of the bung drum 10, the outer edges 18, 26 of the two welding surfaces 14, 22 lying one on top of the another are thus arranged higher than the inner edges 16, 24 of the two welding surfaces 14, 22. The mirror welding process, which is particularly suitable, is used for the welding operation on account of the comparatively large width of the welding surfaces, which is between 3 mm and 15 mm, preferably approx. 5 mm, running in the radial direction or obliquely. After the welding operation, the two annular welding surfaces 14 and 22 are connected or welded to one another in a materially bonded, fixed and non-detachable manner.

[0055] FIG. 4 illustrates the upper region of a bung drum 10, in the case of which, in an exaggerated form in the drawing, the top 30 is strongly upwardly convex or bulged outward—e.g. by virtue of subsequent cooling possibly under an excessively high internal pressure. As a result, the welded bung connector 32 is slightly warped and outwardly deflected here. The dome shape of the welded bung connector 32 also makes it possible for the internal thread 20 of the bung opening 28 to be oriented vertically even if the top 30 is “crooked”.

[0056] It is possible that, as a result of the slower cooling of thick locations, in particular along the flash seams of a plastic hollow body removed from the blow mold after the operation of shaping by blow molding, stresses internal to the material cause distortion, which can lower the top of the hollow body inward or downward. One such case is illustrated in FIG. 5 in an exaggerated form in the drawing, in which, in the case of the bung drum 10, the top 30 has lowered downward and the welded bung connector 32 is inclined toward the middle of the top 30. The vertical orientation of the dome-like threaded welding head 12 compensates the inclination of the welded bung connector 32, with the result that the internal thread 20 in the bung opening 28 with a screwed-in bung fitting is precisely oriented for the use of automatic screwing machines and filling lances in automatic filling installations and problems no longer arise.

[0057] In the context of the present invention, in a simple embodiment, the annular welding surface 14 on the container side and the corresponding annular welding surface 22 on the solid threaded welding head 12 can be formed as running obliquely in three dimensions. In that case, the bung opening 28 enclosed by the annular welding surface 14 in the top 30 of the bung drum 10 has an almost trapezoidal form when viewed in cross section. In a modified form, it is also possible for the annular welding surface 14 on the container side to be formed as concave and the annular welding surface 22 on the threaded welding head 12 to be formed as convex.

[0058] In a particularly preferred embodiment, the annular welding surface 14 on the container side is arranged on the upper, somewhat widened edge of the weld bung connector 32 of shortened form which encloses the container opening 28 in the top 30 of the container 10. In this respect, the welded bung connector 32 is formed respectively as a standard welded bung connector with the same diameter of e.g. 65 mm for the conventional ¾-inch, 2-inch and 3-inch bung closures, regardless of the container size, onto which welded bung connector a correspondingly adapted standard threaded welding head 12 with likewise always the same diameter of e.g. 70 mm is welded, the opening 36 of which, which has an internal thread, can be freely selected for the use of the conventional ¾-inch, 2-inch and 3-inch bung closures.

[0059] A frequently used threaded welding head is designed for a bung closure or bung fitting BSC 70×6 for steel sealing caps.

[0060] It is thus possible for e.g. bung drums in the container sizes 60 I, 120 I, 220 I or 250 I which have a standard welded bung connector 32 of shortened form to always be produced with the same diameter of 65 mm, without the mold insert in the blow mold having to be interchanged for various bung opening diameters or for various bung plug sizes (¾-inch, 2-inch, 3-inch). As a result, significantly higher numbers of drums can be produced; this is possible also because shorter cooling times or cycle times are required for the standard welded bung connectors 32 of shortened form. Depending on the customer demand, prefabricated standard threaded welding heads with always the same diameter, with a freely selectable color and with a freely selectable size of the bung fitting and thread type (coarse thread, fine thread) and sealing seat (above or below the thread) can be welded onto the standard welded bung connectors of shortened form.

[0061] Threaded welding heads can be prefabricated for the following bung closures:

[0062] BCS 70×6, 2″ Butress, 2″ NPS, BCS 56×4, BCS 38×6 and others. In this respect, the external diameter of the threaded welding heads remains always the same at approx. 65 to 70 mm. Only the diameter of the central threaded opening is variable for the various bung closures, in that case the wall thickness increasing with the smaller bung openings.

[0063] By virtue of the manufacture by blow molding of bung drums with standard welded bung connectors of shortened form, there is still the option of inserting a thin-walled inliner into the prefabricated bung drum and welding on the thin-walled inliner connector inside the standard welded bung connector before the desired threaded welding head e.g. of the color yellow is welded onto the standard welded bung connector. The yellow color of the threaded welding head can designate e.g. a bung drum with an inserted inliner, since this is otherwise not visible from the outside without opening the bung closures.

[0064] Furthermore, FIG. 6 illustrates an embodiment in which the annular welding surface 14 on the container side is formed virtually without a connector and directly in the bung opening 28 in the top 30 of the bung drum 10. In this respect, in addition, a circumferential bead edge 34 can be formed on the upper edge of the bung opening 28 on the top 30. As a result, it is possible—if desired—to increase the width of the annular welding surface 14. This embodiment is particularly intended for smaller containers such as canisters or small bung drums which have only a shallow bung hollow or do not have a deeper-recessed bung hollow at all to protect a bung connector.

CONCLUSION

[0065] The present invention teaches how the advantages of blow molding technology—large numbers of items at comparatively low production costs—can be combined in a simple manner with the advantages of injection molding technology —precise geometric dimensions on the sealing seats and screw threads on the container side.

LIST OF REFERENCE NUMERALS

[0066] 10 Plastic container (e.g. bung drum) [0067] 12 Threaded welding head (10) [0068] 14 Annular welding surface on the container side (10) [0069] 16 Circular inner edge on the container side (14) [0070] 18 Circular outer edge on the container side (14) [0071] 20 Internal thread (12) [0072] 22 Annular welding surface on the flange side (12) [0073] 24 Circular inner edge on the flange side (22) [0074] 26 Circular outer edge on the flange side (22) [0075] 28 Container opening (30) [0076] 30 Top (10) [0077] 32 Welded bung connector (30) [0078] 34 Circumferential beaded edge (30) [0079] 36 Opening in the threaded welding head (12) [0080] H.sub.(K) Height of the welding surface (22)