Closure plug improvement

Abstract

An externally threaded closure plug for tightly closing off the internally threaded opening in shipping and storage containers such as drums, pails and the like. The plug is formed as a cup having a bottom wall and threaded cylindrical sidewall terminating in a circumferentially enlarged rim. Immediately beneath the rim of the plug is an annular gasket seat defined by the undersurface of the plug rim, the plug sidewall at the thread root diameter and an annular retaining lip lying in a plane parallel to the undersurface of the plug rim.

Description

BACKGROUND OF THE INVENTION

[0001] This invention is directed to an improved container closure plug and more specifically a threaded plug having a unique gasket retaining feature.

[0002] In the shipping container industry it is most common to manufacture drums, pails and the like with one or more dispensing and/or fill openings. Such openings have an internal helical screw thread which merges into an unthreaded gasket sealing area. An externally threaded closure plug carrying an annular sealing gasket is threadedly engaged within the opening. Upon tightening the plug, the plug gasket is drawn down tightly against the unthreaded gasket sealing area to provide an effective sealing of the container. While many millions of drums and other containers have been sealed in this fashion, an occasional problem arises which this invention addresses. That problem has not only to do with sealing but also with unscrewing of the plug from the container opening. A critical relationship exists between the plug and its gasket on the one hand and the merger of the container opening thread into the opening gasket seat area on the other. This relationship is such that in practice upon applying the necessary torque to seal the plug in the container opening, the plug gasket becomes wedged against the run-out of the opening internal thread. When the plug is subsequently unscrewed it is an all to common occurrence that this gasket wedging action against the opening thread tightly grips the plug gasket. As the unscrewing action continues a tenuous condition ensues. Most notably as the plug travels out of the opening the gasket can remain ensnared on the internal opening thread so that the gasket gets pulled off of its gasket seat position on the plug. Continued rotation of the plug becomes extremely difficult as the gasket jams between the mating threads. Moreover, the gasket itself becomes severely damaged due to this shredding action which further diminishes the utility of the closure.

[0003] Another negative aspect of this gasket gripping condition is the tendency of the gasket to loop out of its gasket seat during torqueing of the plug. This problem occurs when the plug gasket movement around the unthreaded gasket seat of the opening becomes obstructed causing the gasket to bunch up and form a loop protruding from the edge of the opening. One way for such obstruction to occur is when the plug gasket again becomes ensnared on the opening thread run-out as the plug now is traveling into the opening. The resultant “looping” condition will most certainly create a leakage path and quite likely impart serious damage to the gasket. The commonality between these “gripping” and “looping” problems is, of course, the ability to retain the plug gasket in place on the plug gasket seat where it belongs and thus prevent it from being dragged onto the thread interengagement.

[0004] The prior art has recognized the desirability generally of providing some positive mechanical retaining means for keeping the plug gasket in place. For example, U.S. Pat. No. 5,211,304 to Stolzman discloses a plug construction wherein the gasket is securely retained on the undersurface of the plug rim with a mechanical interlocking arrangement. This arrangement, however, places the gasket radially outwardly of the plug thread and has no relationship whatsoever to any kind of gasket “gripping” or “looping” problem. Another prior art example is found in U.S. Pat. No. 2,906,429 to Marchyn which recognizes the “looping” problems but fails to provide a completely satisfactory solution. In this patent the plug has a special thread formation where the thread borders the gasket seat. Specifically the plug has a diminishing thread that continues around the lower edge of the gasket seat and acts as a partial barrier above the normal plug thread. This modified thread configuration, however, falls short of providing adequate protection against the “gripping” phenomenon as will be clearly seen hereinafter.

BRIEF SUMMARY OF THE INVENTION

[0005] According to the present invention, a closure plug is formed with a cylindrical threaded sidewall, the sidewall terminating in a circumferentially enlarged rim and having an annular gasket seat immediately under the plug rim in substantial axial alignment with the screw thread root diameter wherein a circumferential gasket retaining lip is interposed the plug gasket seat and the sidewall thread.

[0006] Also according to the present invention the closure plug is combined with a threaded container wall opening and has a resilient sealing gasket lying in close proximity to said internal thread whereby said gasket retaining lip prevents interengagement with said gasket and said opening thread.

[0007] The instant closure of the instant invention presents a long sought after solution to the above mentioned “gripping” and “looping” problems in a simple straightforward manner. The plug is formed with a cylindrical threaded sidewall and a disc like bottom wall. The sidewall terminates in a circumferentially enlarged rim and has an annular gasket seat immediately under the rim. Interposed the plug gasket seat and the sidewall thread is a circumferential gasket retaining lip. A resilient sealing gasket is stretched over the plug gasket seat occupying the vertical space between the plug rim and the retaining lip. The above described plug is screwed into a container wall opening having an internal screw thread and an inwardly facing gasket sealing area. In accordance with the invention the critical relationship heretofore existing between the plug gasket and the container opening thread now becomes quite inconsequential. As the plug is backed out of the threaded container opening the gasket is firmly held in place on the plug gasket seat by the novel retaining lip. The resulting clean separation of the plug gasket from the container opening constitutes a significant improvement over the prior art.

[0008] It is accordingly a principal object of the invention to provide an improved threaded closure plug for industrial size containers.

[0009] A further object is to provide a threaded closure plug having a new and improved gasket seat construction.

[0010] A more detailed object is to provide a plug gasket seat with structure to positively retain the plug gasket thereon during screwing and unscrewing.

[0011] Further and more detailed objects will in part be apparent and in part pointed out as the description of the invention taken in conjunction with the accompanying drawing proceeds.

[0012] The above and further features of the present invention are set forth in the appended claims and are further described in the drawings wherein:

[0013] FIG. 1 is a part elevational part sectional view of the closure plug in accordance with the invention.

[0014] FIG. 2 is a top plan view of the container closure combination.

[0015] FIG. 3 is part sectional part elevational view of the plug screwed into the container opening.

[0016] FIG. 4 is a view similar to FIG. 3 but with the plug in partially unthreaded position.

[0017] FIG. 5 is a view similar to FIG. 4 illustrating the prior art.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The closure plug of the invention generally indicated at numeral 1 has a disc like bottom wall 2 surrounded by a cylindrical sidewall 3 terminating in a circumferentially enlarged rim 4. The interior of the plug 1 has a series of wrench engaging lugs 5 for imparting screwing and unscrewing torque to the plug. The plug sidewall 3 has a pilot portion 6 extending from the bottom wall 2, an external helical screw thread 7 and a gasket seat 8 positioned immediately below the plug rim 4. Here it is important to note that the gasket seat 8 lies in plane axially aligned with the plug thread root diameter. This relationship is beneficial in assuring a sufficient gasket volume between the plug and the mating container opening surface to close off any leakage path. The plug sidewall 3 is formed with a circumferential retaining lip 9 at the upper end of the thread 7 which extends radially outwardly in axial alignment with the thread crest. As clearly seen in FIG. 1 the plug thread runs out and terminates at the point 10 within the lip 9 leaving a uniform upwardly facing annular surface 11 immediately above the thread termination 10. A resilient annular sealing gasket 12 having a substantially square cross sectional shape is stretched over the plug so as to hug the gasket seat 8. The gasket thus positioned is snugly clamped between the undersurface 4a of the plug rim 4 and the upper surface 11 of the retaining lip 9 making dislodgement of the gasket 12 from the gasket seat 8 quite unlikely.

[0019] The container wall opening within which the plug 1 is threadedly engaged is clearly shown in FIG. 2 and consists of a container wall 20 within which a bushing generally indicated at numeral 21 is inserted in a conventional manner. The bushing 21 has a circumferentially extending polygonal base 22, a cylindrical wall 23 extending therefrom and terminating in a radially outwardly curled bead 24. The container wall 20 overlies the polygonal base 22 in a mating embossment 25 and has an upstanding substantially cylindrical neck 26 which extends within the bushing curl 24. A bushing gasket 27 is compressed between the bushing 21 and the surrounding surfaces of the container wall 20. An internal helical screw thread 28 is formed on the bushing wall 23 extending from the base 22 to a thread run-out point 29 at the start of the bead 24. The upwardly extending unthreaded bead portion immediately above the thread run-out point 29 forms a smooth gasket sealing area 30.

[0020] The sealing relationship between the plug 1 and bushing 21 in fully torqued condition as depicted in FIG. 3 shows the plug gasket 12 tightly compressed between the plug gasket seat 8 and the bushing sealing area 30. Quite noticeably the gasket 12 is also axially restrained between the rim undersurface 4a and the upper surface 11 of the retaining lip 9. Moreover it can be seen that the gasket 12 in this tightened position lies in contact with the bushing thread helical run-out and termination point 29. The continuous annular upper surface of the retaining lip maintains a constant axial spacing from the rim under surface 4a and prevents the gasket 12 from at any point becoming ensnared in the bushing thread 28. Upon unscrewing of the plug as shown in FIG. 4, the retaining lip 9 very clearly lifts the plug gasket 12 away from the bushing thread 28 and up off of the gasket sealing area 30. It is due to this clean separation of the plug gasket from the surrounding bushing surfaces that the heretofore common gasket “gripping” and gasket “looping” problems have been eliminated.

[0021] Turning to FIG. 5 which in contrast shows a typical prior art condition wherein a prior art plug 40 is unscrewed from an internally threaded container wall opening neck 41. Here the plug gasket 42 sits on the gasket seat 43 formed at the root diameter of the plug thread but the plug thread 44 simply diminishes indicated by numeral 45 as it approaches the gasket seat 43. Under these prior art conditions it can be seen that as the plug is backed off, the gasket 42 has almost no axial support supplied by the diminished thread 45. As a result the gasket becomes easily ensnared between the interengaging closure threads and is pulled off of the gasket seat creating a serious obstruction to normal closure functionality.

[0022] Various changes in or modifications of the gasket retaining plug of the invention would suggest themselves to those skilled in the art and could be made without departing from the spirit or scope of this invention. For example, the invention plug could be either molded from synthetic plastic resin or machined from metal. It is accordingly intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as being illustrative and not in a limiting sense.

Claims

1. A closure plug formed with a cylindrical sidewall having a helical screw thread, said sidewall terminating in a circumferentially enlarged rim, an annular gasket seat immediately under said plug rim in substantial axial alignment with said screw thread root diameter and a circumferential gasket retaining lip interposed said plug gasket seat and said sidewall thread.

2. The closure plug as in claim 1, wherein said sidewall thread runs out and terminates at a point within said retaining lip; leaving a uniform upwardly facing annular surface immediately above said thread termination.

3. An externally threaded closure plug for tightly sealing off an internally threaded container wall opening, said plug formed with a cylindrical sidewall, a helical screw thread formed on said sidewall, a circumferentially enlarged rim surrounding one end of said sidewall an annular gasket seat formed in substantial axial alignment with said screw thread root diameter on said sidewall interposed said rim and said screw thread and circumferential gasket retaining means formed on said sidewall interposed said thread and said gasket seat.

4. A closure plug as in claim 3 including a sealing gasket positioned on said gasket seat.

5. A closure plug as in claim 4, said sealing gasket being tightly confined within the radially opening annular groove formed by said rim and said gasket seat and said gasket retaining means.

6. A closure plug as in claim 3 and said gasket retaining means extending radially outwardly from said gasket seat.

7. A closure plug as in claim 6 and said gasket retaining means presenting a continuous annular surface substantially parallel to said rim.

8. In combination an externally threaded closure plug and a container wall opening, said container wall opening having an internally threaded portion and an unthreaded portion, said closure plug having a cylindrical sidewall, a screw thread on said sidewall, a circumferentially enlarged rim surrounding said sidewall, an annular gasket seat formed on said sidewall, a gasket compressed between said unthreaded opening portion and said gasket seat, said gasket lying in close proximity to said internal thread and gasket retaining means on said plug sidewall interposed said plug thread and said gasket seat preventing interengagement of said gasket and said opening internally threaded portion whereby unimpeded unscrewing of said plug and gasket as an undisturbed unit is effected.

9. The combination as in claim 8 wherein said container wall unthreaded portion extends upwardly and radially outwardly from said gasket retaining means.

10. The combination as in claim 8 and said sealing gasket being tightly confined by said rim and said gasket retaining means.

11. The combination as in claim 10 and said gasket retaining means presenting a continuous annular surface substantially parallel to said lip rim.

12. The combination as in claim 11 and said gasket retaining means extending radially outwardly to a point spaced from said opening unthreaded portion.