EP1467922B1

EP1467922B1 - Closure plug

Info

Publication number: EP1467922B1
Application number: EP03700871A
Authority: EP
Inventors: Cornelis Am. Flange & MFG. Co. Inc VAN DE KLIPPE; Herman Kars
Original assignee: Greif International Holding BV
Current assignee: Greif International Holding BV
Priority date: 2002-01-17
Filing date: 2003-01-15
Publication date: 2007-08-15
Anticipated expiration: 2023-01-15
Also published as: ES2292930T3; BR0306963A; EP1467922B3; BRPI0306963B1; DE60315594T3; AU2003202017B2; NO20043428L; DE60315594T2; DE60315594D1; ES2292930T7; CN100341753C; RU2004124934A; RU2294870C2; CN1617820A; EP1467922A1; PL370538A1; WO2003062078A1; JP4475388B2; ATE370078T1; JP2005525271A

Abstract

An externally threaded closure plug (1, 60) for tightly closing off the internally threaded opening (23) in shipping and storage containers such as drums, pails and the like. The plug is formed as a cup having a bottom wall (2) and threaded cylindrical sidewall (23) terminating in a circumferentially enlarged rim (4). Immediately beneath the rim of the plug is a gasket seat (8, 64) defined by the undersurface (4a) of the plug rim, the plug sidewall and an annular gasket retaining lip (9, 61) lying in a plane parallel to the undersurface of the plug rim. In use, the plug is screwed into and out of a container wall opening, having an internally threaded portion (28) and an unthreaded portion (30), the sealing gasket (12) being compressed between the unthreaded opening portion and the plug gasket seat (8, 64, 72) and lying in close proximity to the internal thread. The gasket seat acts to prevent interengagement of the sealing gasket (12) and the opening internally threaded portion (28).

Description

BACKGROUND OF THE INVENTION

This invention is directed to an improved container closure plug and more specifically a threaded plug having a unique gasket retaining feature.
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.
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 travelling 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.
The prior art has recognized the desirability generally of providing some positive mechanical retaining means for keeping the plug gasket in place. U.S. Patent No. 2,906,429 (Marchyn ) 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.
Document U.S. Patent No. 4,768,677 (Kitsukawa ) discloses a closure plug wherein that the gasket retaining lip has a uniform continuous upwardly facing annular surface, a constant radial extension axially less than the outside radial extension of the crest of the helical screw sidewall thread and a cylindrical gasket seat.
Document DE 202 15 810U (DURA Automotive Systems Köhler GmbH) discloses a gas cap (10) for motor vehicles wherein a threaded cover (14) is with a seal (20); shown to have a semi-circular seat.

OBJECT OF THE INVENTION

An object of the present invention is to provide a closure plug that overcomes the problems of sealing gasket gripping and looping. A further object of one embodiment of the present invention is to provide a closure plug that fits a range of container openings

BRIEF SUMMARY OF THE INVENTION

According to the present invention, a closure plug is formed with a cylindrical sidewall having an external helical screw thread, a circumferentially enlarged rim, an annular gasket seat immediately under the plug rim and a continuous circumferential radially outwardly extending gasket retaining lip below the plug gasket seat, wherein the gasket seat flares radially outwardly and upwardly directly from the root of gasket retaining lip to meet the plug rim.
According to an embodiment of the present invention, the gasket seat is of frusto-conic shape.
According to another embodiment of the present invention, a resilient sealing gasket is stretched onto the gasket seat and assumes the shape of the gasket seat; the sealing gasket may assume the shape of a frusto-conic gasket seat.
Also according to the present invention, a closure plug in accordance with the present invention is combined with an opening in a container wall with a bushing, the bushing having a cylindrical wall with an internal helical screw thread and an upwardly extending, smooth gasket sealing area, the sealing gasket being substantially radially compressed between the bushing gasket sealing area and the plug gasket seat and lying in close proximity to the bushing internal helical screw thread.
A closure plug in accordance with the present invention provides a long sought after solution to the above mentioned "gripping" and "looping" problems in a simple straightforward manner.
In an example, the closure 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 between the plug gasket seat and the sidewall thread is the gasket retaining lip. The 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. The prior art critical relationship 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 gasket retaining lip. The resulting clean separation of the plug gasket from the container opening constitutes a significant improvement over the prior art.
It is accordingly a principal feature of the invention to provide an improved threaded closure plug for industrial size containers.
A more detailed feature is to provide a plug gasket seat with structure to positively retain the plug gasket thereon during screwing and unscrewing.
The above and further features of the present invention are set forth in the appended claims and are further described in the drawings wherein:

Fig. 1 is a part elevational part sectional view of a prior art closure plug.
Fig. 2 is a top plan view of a container closure combination incorporating the closure plug of Fig. 1.
Fig. 3 is part sectional part elevational view of the plug of Fig. 1 screwed into a container opening.
Fig. 4 is a view similar to Fig. 3 illustrating another prior art closure plug, with the plug in partially unthreaded position.
Fig. 5 is a part section detail of a metal closure plug in accordance with an embodiment of the invention.
Fig.6 is a view similar to Fig. 5 and including a sealing gasket.
Fig. 7 is part sectional part elevational view of a plastic plug, similar to the plug of Fig. 5, screwed into a container opening.
Fig. 8 is a view similar to Fig. 7, but with the plug in partially unthreaded position.

DETAILED DESCRIPTION OF THE INVENTION

A prior art closure plug is illustrated in Figs 1 to 4 and is generally indicated at numeral 1, and is moulded from synthetic plastic resin to have 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 continuous annular surface 11 lying in a plane parallel to the undersurface 4a of the plug rim 4 and 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.
The container wall opening within which the plug 1 is threadedly engaged as clearly shown in Fig. 3 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.
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.
Fig. 4 illustrates unscrewing another prior art plug 40 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 the gasket seat creating a serious obstruction to normal closure functionality.
The embodiment of the invention illustrated in Figs 5 - 8 is a variant of the closure plug described with reference to Figs 1 to 3; like parts have been given like references. As shown in Figs. 5 and 6, a metal closure plug 60 in an example is cut and rolled from 1.15 mm drum end steel. The gasket retaining lip 61 is rolled to have a triangular, thread-like, cross-section having an included angle of 55°, a radial extension D1 less than the outside radial extension D2 of the crest of thread 7 and to lie in a plane parallel to the undersurface 4a of the plug rim 4. The upper flank 62 of the retaining lip 61 forms a continuous peripheral upwardly and outwardly facing surface above the screw thread 7. The diameter D3 of the inner root 63 of the lip 61 is less than the thread root diameter D4. The gasket seat 64 flares radially outwardly and upwardly to meet the rim 4 at essentially the same point that gasket seat 8 meets the rim in the first embodiment. A conventional gasket 12, of E.P.D.M., black nitrile or P.E., is stretched onto the gasket seat 64 and assumes the same generally flared shape; as shown in Fig. 6.
The effect of the geometry in this embodiment is that the radial extension D1 - D3 of lip 61 has gasket lifting and anti-grabbing and anti-looping functions. The reduced lip diameter enables the closure plug to fit a greater range of container openings. The flared gasket seat 64 has two advantages. Firstly it provides an increased volume for the sealing gasket 12 in the area between the closure plug lip 61 and the gasket sealing area 30 of the container closure bushing 21 and, secondly, the frusto-conic shape assumed by the stretched gasket 12 provides an increased area of contact between the gasket and the gasket sealing area 30 as the plug is being screwed into the bushing 21. The sealing gasket is "fed in" to the volume between the bushing sealing area 30 and plug seat 64, with the leading end of the gasket initially being subjected to lower (or even no) compression. Thus, advantageously, the initial contact band between the gasket and the closure bushing is partway up the side of the gasket.
This is seen most clearly in Figs. 7 and 8, of an embodiment of a closure plug, formed from a suitable plastics material, in which the plug threads, rim and lip 61 have a similar geometry to the embodiment shown in Figs. 6 and 7, but the plug is formed from a suitable plastics material. The effect of this increased area of contact and lower gasket leading end compression is to further mitigate against gasket looping during plug torqueing.
Another advantage of the geometry used for the lip 61 is that it reinforces the plug, enabling the plug in Figs. 5 and 6 to be formed from thinner gauge steel than used for prior art plugs, whilst still maintaining equivalent structural integrity.
Using standard gaskets, it is possible for the lip 61 to directly contact the closure bushing wall 23 in the region of the bushing thread run out 29 when the plug 60 is fully torqued home. An oversized gasket can be used to prevent such metal-to-metal contact if desired.
Various changes in or modifications of the gasket retaining plug of the invention can be made within the scope of the appended claims.

Claims

A closure plug formed with:-
i) a cylindrical sidewall (3) having an external helical screw thread (7);

ii) a circumferentially enlarged rim (4);

iii) an annular gasket seat (43) immediately under the plug rim; and,

iv) a continuous circumferential radially outwardly extending gasket retaining lip (61) below the plug gasket seat (64);
characterised in that:-

v) the gasket seat (64) flares radially outwardly and upwardly directly from the root (63) of gasket retaining lip (61) to meet the plug rim (4).
A closure plug as claimed in claim 1, wherein the gasket seat (64) is of frusto-conic shape.
A closure plug as claimed in claim 1 or claim 2, wherein the gasket retaining lip (61) has a radial extension (D1) less than the outside radial extension (D2) of the crest of external helical screw thread (7).
A closure plug as claimed in any of claims 1 to 3, wherein the diameter (D3) of the inner root (63) of the gasket retaining lip (61) is less than the diameter (D4) of the root of external helical screw thread (7).
A closure plug as claimed in any of claims 1 to 4, wherein the plug (60) is formed from metal or from moulded synthetic plastic resin
A closure plug as claimed in any of claims 1 to 4, wherein a resilient sealing gasket (12) is stretched onto the gasket seat (64) and assumes the shape of the gasket seat (64).
A closure plug as claimed in claims 2 and 6, wherein the sealing gasket (12) assumes the shape of the flared gasket seat (64).
A closure plug as claimed in any of claims 1 to 7, wherein the sealing gasket (12) is of E.P.D.M., black nitrile or P.E.
In combination, a closure plug as claimed in any of claims 6 to 8 and an opening in a container wall with a bushing (21), the bushing (21) having a cylindrical wall (23) with an internal helical screw thread (28) and an upwardly extending, smooth gasket sealing area (30), the sealing gasket (12) being compressed between the bushing gasket sealing area (30) and the plug gasket seat (8) and lying in close proximity to the bushing internal helical screw thread (28).