US3921850A

US3921850A - Drum closure

Info

Publication number: US3921850A
Application number: US473720A
Authority: US
Inventors: Joseph E Powers
Original assignee: Kaiser Steel Corp
Current assignee: Shawmut Capital Corp; Security Pacific Business Credit Inc
Priority date: 1973-12-10
Filing date: 1974-05-28
Publication date: 1975-11-25
Anticipated expiration: 1992-11-25

Abstract

A closure for an opening in a bulk food storage drum such as a drum lined with interior coatings of plastic, film, tin, or the like, which also is capable of aseptic packing. The drum has an opening in one of the planar and panels thereof which opening is formed with an upwardly and outwardly flared lip which defines an acute angle with respect to the plane of the end wall. The lip is formed with minimal bending to avoid adversely affecting the film and the bond between the film and the material (e.g., steel) of which the drum is fabricated. A closure member or plug is fabricated of similar material having one side coated. The closure member has a cylindric mid-wall, at one end of which is a circular, fluid impervious disc and at the other end of which is an outwardly extending flange. The closure member fits into the opening and carries an O-ring type gasket which is distorted or caused to flow in response to movement of the member into the opening, thus forming a fluidtight closure. The surface portion of the drum wall beneath and outside of the lip is accessible for cleaning and painting, thereby avoiding accumulation of rust and/or material spilled during the filling of the drum.

Description

United States Patent 1191 Powers Nov. 25, 1975 [73] Assignee: Kaiser Steel Corporation, Oakland,

Calif.

[22] Filed: May 28, 1974 [21] Appl. No.: 473,720

Related U.S. Application Data [63] Continuation-in-part of Ser. No. 423,228, Dec. 10,

FOREIGN PATENTS OR APPLICATIONS 1,144,472 3/1969 United Kingdom 220/308 752,445 2/1933 France 220/310 Primary Examiner-William 1. Price Assistant Examiner-R0 E. Hart Attorney, Agent, or Firm-Naylor, Neal & Uilkema [57] ABSTRACT A closure for an opening in a bulk food storage drum such as a drum lined with interior coatings of plastic, film, tin, or the like, which also is capable of aseptic packing. The drum has an opening in one of the planar and panels thereof which opening is formed with an upwardly and outwardly flared lip which defines an acute angle with respect to the plane of the end wall. The lip is formed with minimal bending to avoid adversely affecting the film and the bond between the film and the material (e.g., steel) of which the drum is fabricated. A closure member or plug is fabricated of similar material having one side coated. The closure inember has a cylindric mid-wall, at one end of which is a circular, fluid impervious disc and at the other end of which is an outwardly extending flange. The closure member fits into the opening and carries an O-ring type gasket which is distorted or caused to flow in response to movement of the member into the opening, thus forming a fluidtight closure. The surface portion of the drum wall beneath and outside of the lip is accessible for cleaning and painting, thereby avoiding accumulation of rust and/or material spilled during the filling of the drum.

9 Claims, 12 Drawing Figures US. Patent Nov. 25, 1975 SheetlofZ 3,921,850

PRIOR ART FIE--ZA- PRIOR ART i 52 ail if r U.S. Patent Nov. 25, 1975 SheetZofZ 3,921,850

DRUM CLOSURE CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of commonly assigned, co-pending application for U.S. Pat. Ser. No. 423,228, filed Dec. 10, 1973.

FIELD OF THE INVENTION This invention relates to closures for drums and the like and more particularly to closures for drums that are lined and are used for bulk storing and shipping material such as foodstuffs, including aseptic packaging thereof.

In packing foodstuffs in large drums, one of the prac-' tices is to employ an aseptic technique. Such technique is characterized in that the foodstuff and the container are sterile and in a relatively cool state before the former is introduced into the latter. In employing the aseptic technique, it is important that all surfaces which the foodstuff is likely to contact be in a sterile condition. This is typically achieved by coating one surface of the container material (e.g., steel sheet) with an interior coating of plastic, film, tin, or the like and by forming the container and filling opening in such a manner that only the lined surface is exposed to the foodstuffs. Of particular importance is that the margin surrounding the opening be configured so that only the lined surface of the container material is exposed to contact by the foodstuff.

DESCRIPTION OF THE PRIOR ART Known prior art closures include a lip surrounding the opening which is rolled on a relatively small or tight radius of curvature. Forming the closure in this manner unduly stresses the lining material with a serious risk of failure and possible harmful effect on the contents. The rolled lip also forms a virtually inaccessible concavity surrounding the opening from which it is difficult to clean foodstuffs or the like that have entered the concavity during filling of the drum. Such material may deteriorate with time and, although it is not in communication with the contents of the drum, create an unpleasant and unsanitary condition. Finally, the lip, when rolled totally, conceals the edge of the sheet material (typically, steel) of which the drum is made so that such edge cannot be coated with protective paint. Consequently, rust is likely to develop and, although not adversely affecting the contents of the drum, create an unpleasant and unsanitary condition.

With the prior art rolled configuration, sealing is achieved with a gasket. Either the gasket is specially fabricated at great expense or a gasket material is flowed into position on the lid and post cured. Moreover, the gasket is sealed by simple compression so that the quality of the seal is proportional to the care with which the closure is placed in the opening.

SUMMARY OF THE INVENTION The principal object of the present invention is to provide a drum closure that eliminates the above enumerated disadvantages present in known prior art structures. This object is achieved by the present invention by providing a lip surrounding the opening and integral with the panel in which the opening is formed, which lip is straight rather than rolled, the sole distortion occurring at a relatively large radius bend between the plane of the drum panel and the lip. Thus, the inte- 2 rior coating on the drum material is not adversely affected in forming a lip. Moreover, the lip is formed at an acute angle with respect to the plane of the drum wall in which the opening is formed so as to make the concavity beneath the lip accessible to cleaning and painting.

Another object is to provide a closure that employs a conventional O-ring for a sealing gasket and is arranged to optimally exploit the characteristics of the O-ring. This object is achieved by providing a closure member or plug having a cylindric wall and an outwardly extending flange that is generally perpendicular thereto and that is joined to the cylindric portion by an arcuate wall portion. An O-ring having a radius of curvature corresponding to the arcuate portion is employed and is contacted by the closure member throughout about of the O-ring periphery. When the closure member is forced into contact with the above mentioned lip, the O-ring deforms or flows because the upwardly facing lip surface against which the O-ring rests is angularly disposed with respect to both the cylindric wall and the flange of the closure member. The space between the closure member and the lip is thus generally triangular shaped whereby the O-ring can distort and effect a virtually perfect seal ,=therebetween.

A further object is to provide a closure structure which affords optimal compression of an elastic O-ring and is immune to.compressing the O-ring beyond its elastic limit.

Another object is to provide a temporary closure member or plug for the opening which is used during manufacture and completion of the drum and which closure member is left in place during shipment of the empty drum and until the drum is filled. The temporary closure member is-made of resilient molded plastic material which can be quickly snapped into place in the opening. The temporary closure member is arranged to avoid obstructing the concavity between the lip and the drum panel on which the lip is formed in order to facilitate cleaning and painting of the surfaces within such concavity.

The foregoing together with other objects, features and advantages of the invention will be more apparent after referring to the following specification and accompanying drawing.

BRIEF DESCRIPTION OF TIIE DRAWING FIG. 1 is a perspective view of a drum with the portions of the closure according to the present invention shown in exploded form.

FIG. 2A is a fragmentary view of a prior art closure typical of those used in drums lined with an interior coating.

FIG. 2B is a fragmentary view of a prior art closure typical of those used for drums lined with tin.

FIG. 3 is a fragmentary view, at enlarged scale, of a drum closure according to the present invention before full engagement of the closure plug.

FIG. 4 is similar to FIG. 3 with the closure plug in the fully closed or engaged position.

FIG. 5 is a fragmentary view of the upper extremity of the lip that encircles the opening according to the present invention.

Hg. 6 is a view of the opening with a temporary molded plastic closure member or plug in place.

FIG. 7 is an exploded perspective view of another embodiment of the present invention.

FIG. 8 is a cross-sectional view at enlarged scale of a fragment of FIG. 7 in the unsealed condition.

FIG. 9 shows the structure of FIG. 8 in a sealed condition.

FIG. 10 is a view similar to FIG. 8 of still another embodiment of the invention.

FIG. 11 is a view of the embodiment of FIG. 10 in the sealed condition.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring more particularly to the drawing, reference numeral 12 indicates a drum that has a cylindric wall portion 14 and planar circular end walls, the upper one of which is indicated at 16. Centrally of planar end wall 16 is an opening 18 through which the container is filled. Circumscribing opening 18 and formed integral with end wall 16 is a lip 20. An O-ring sealing gasket 22 is compressed against the upper surface of lip by a closure member or plug 24, which plug is retained in place by deformation thereof in a more or less conventional way and is described in somewhat more detail hereinbelow.

The advantages of the present invention can best be appreciated in the context of the prior art as shown in FIGS. 2A and 2B. FIG. 2A is a typical form of closure 7 used in conjunction with plastic lined containers. The drum top 16 is formed with a generally circular lip 20 which terminates in an edge 26. In forming the prior art rolled lip 20, the lip is so tightly rolled as to jeopardize the integrity of the lining material on the rolled portion. Moreover, a virtually inaccessible space within the rolled lip is formed which space is extremely difficult to clean. Finally, edge 26, typically bare steel at the outset of the fabricating process, is substantially inaccessible to painting. The prior art closure of FIG. 2A requires a specially fabricated gasket member 28, which is expensive both to produce and to install, on the lip prior to installation of closure member 24'. The outer periphery of closure member 24' is provided with a rolled flange 30 which must be carefully formed so that gasket 28 is compressed throughout a substantial length.

FIG. 2B shows a known prior art structure that has been used with tin plated drum materials. End panel 16" has a rolled lip 20" which is substantially idetical to the 20' of FIG. 2A. Closure member 24" has a rolled lip 30' in which there is formed, during fabrication of the cover, a gasket 28'. The material of which gasket 28 is formed is poured into the concave space defined by lip 30' and then is raised to an elevated temperature to cure the same. Such elevated temperature may exceed the safe temperature to which the drum lining material can be elevated. In any event, the structure of FIG. 2B suffers from the same disadvantages as that described in connection with FIG. 2A in that an inaccessible unprotected edge 26' is formed and a concavity, difficult or impossible to clean, is also formed.

The principle parts of the present invention are shown most clearly in FIG. 3. In FIG. 3, it will be noted that lip 20 resides at an acute angle, preferably about 45, with the plane of end wall 16. Lip 20 is formed by bending the material of which panel 16 is made on a relatively large radius bend 32. Such large radius bend does not adversely affect the integrity of the plastic lining material indicated at 34 in FIG. 3. Moreover, the concavity, defined between the upper surface of wall 16 and the lower surface of lip 20, is accessible to cleaning and painting as will appear in more detail hereinafter. The closure member 24 includes a cylindric mid-wall 36 which has an outer diameter sufficient for entry into opening 18. At one end of cylindric midwall 36, the closure member includes an integral circular wall 38 and at the opposite end of the cylindric midwall is an outwardly extending annular flange 40. The region between flange 40 and mid-wall 36 is formed at a relatively large radius of curvature indicated at 42 so as to avoid impairing the integrity of coating layer 44 on the closure member.

An O-ring 22, having a relaxed radius corresponding to the radius of curvature of portion 42, is provided. The diameter of the central opening of the Oring is preferably slightly less than the outer diameter of cylindric mid-wall 36 so that the O-ring when installed on closure member 24 will be retained in place thereon. Any gasket which functions like an O-ring may be employed.

When drum 12 has been filled, closure 24 with O-ring gasket 22 in place is inserted into opening 18. The closure member is moved axially of the drum until the lower surface of flange 40 approaches the outer edge of lip 20. Although FIG. 4 shows flange 40 in actual contact with lip 20, such contact is not essential. Contact of flange 40 with the outer edge of lip 20, however, limits the amount of compression applied to O- ring 22 so as to avoid over compression of the O-ring. With closure member 24 in the lowered or closed position, a conventional tool (not shown) is introduced into the hollow center of the closure member and activated to distort the portion of cylindric mid-wall 36, thereby forming a re-entrant region 46 which retains the closure member in place. A study of FIG. 4 reveals several important advantageous characteristics of the present invention. Note that O-ring 22 has been caused to distort or flow because the O-ring is compressed between the arcuate portion between flange 44 and midwall 36 of the closure member and the upper surface of lip 20. Because the volume enclosed is a generally triangular shape, there is space into which the O-ring can flow. Thus, an extremely high quality seal is formed. Moreover, the concavity between the lower wall of lip 20 and the upper surface of drum wall 16 is accessible for cleaning, and if desired, so also is the space between the lip 20 and flange 44.

In fabricating drum l2 and end wall 16 thereof, sheet material that is coated on one side with plastic, film, tin, or the like layer 34 is cut and bent into shape. The method of manufacture includes forming a circular opening in the end wall of the drum, said opening being bounded by an unfinished edge and a margin of said coating, and then bending the margin on an arcuate path to form the frusto-conical lip 20 circumscribing the opening and diverging therefrom. The bending step is performed so that the coating or layer is exposed to the boundary of the opening and the opposite surface of the lip resides at an acute angle relative to the end wall to define ,a concavity. When lip 20 is formed (see FIG. 5), the outer edge 48 as well as the lower surface 50 are bare steel. To avoid rusting, such bare steel surfaces are painted, typically by a spray painting apparatus indicated schematically at 52 in FIG. 6. It can be seen that both edge 48 and surface 50, as well as the upper surface of drum wall 16, are exposed to paint.

To avoid entry of paint to the interior of the drum, a temporary plastic closure member 54 is provided. Temporary closure member 54 is typically molded of resilient material so that it can be snapped into opening 18 before painting. The temporary closure member includes an inwardly rolled lip 56 and an inwardly sloped wall 58 which is disposed at an angle so as to be in parallelism with lip 20. Below sloped wall portion 58 is a curved portion 60 which is complemental to curved portion 32 of the lip. At the lower extremity of curved portion 60 is a re-entrant projection 62 which retains closure member 54 in place. Member 54 is completed by a circular wall 64 which can have one or more perforations 66. Perforations 66 permit movement of sufficient air through the cap to avoid pressure build-ups within the drum while in the empty condition that might otherwise dislodge the closure member.

After lip is formed on drum wall 16, closure member 54 is snapped in place as shown in FIG. 6 and painting of the bare metal surfaces can proceed. Full paint coverage is achieved in the concavity between lip 20 and the outer surface of panel 16 as well as of edge 48 of the lip.

When the drum is to be filled, closure 54 is removed. The foodstuffs or the like are then introduced through opening 18 and closure member 24 is inserted and distorted to the position shown in FIG. 4. At such position, the contents of the drum are exposed only to the 'internal coated surfaces of the drum and closure member and these surfaces are sealed to one another by the O- ring 22. Furthermore, the concavity between the lip and the upper surface of drum panel 16 is accessible for cleaning away of foodstuffs that may have been inadvertently spilled during the filling process. Moreover, the integrity of the film or tin'lining interior of drum 12 is preserved because the curves used in forming the parts of the closure member are of relatively large radius.

The inward movement of closure plug 24 in the embodiment of FIG. 3 is limited by contact of flange 40 with the outer edge of lip 20. Although this structure operates quite satisfactorily, it requires special care during formation of lip 20 to assure that the outer edge thereof is coplanar with drum wall 16 in order that O- ring 22 be uniformly compressed throughout its circumference. The embodiment of FIGS. 7-9 affords a different, and in some respects, superior, technique for limiting the inward movement of the plug. Becauseof the structural similarity between the embodiment of FIGS. I-7 and that of FIG. 3, similar characters of reference with the addition of the reference letter a are employed for corresponding parts. Thus, in the embodiment of FIGS. 7-9, there is an end wall 16a in which is a circular opening 18a through which the container is filled. Circumscribing opening 18a is a lip 20a which forms an upwardly exposed frusto-conical surface 21, the surface being lined with a layer 34a of suitable plastic material or the like. An O-ring gasket 22a circumscribes a eylindric mid-wall 36a of a closure plug 24a. The inner end of closure plug 24a has a circular end wall 38a which is integral with the mid-wall. On the end ofthe closure plug opposite wall 38a, there is a circular flange 40a that extends outward from mid-wall 36a. Between the radial extremities of flange 40a is a downward extending rib 41 which is radially spaced relative mid-wall 36a to contact frusto-conical surface 21 (See FIG. 9). Thus, the rib 41 limits the inward position of plug 24a with respect to opening 18a. Accuracy of the innermost position of the closure plug is important to optimally compress O-ring gasket 22a so as to produce a fluid-tight seal, without exceeding the elastic limit of the material from which the O-ring is fabricated; Because rib 41 makes surface contact with frusto-conical wall 21 accuracy of the spacing in the embodiment of FIGS. 8 and 9 is not dependent on accurately controlling the length of the lip 20a. Moreover, thestructure of FIGS. 8 and 9 is highly immune to damage.

contact with frusto-conical wall 21 and there retained by distortion of the inner region of mid-wall 36a, indicated at 46a; a triangular-shaped volume is formed by fr-usto-conical wall 21, the portion of flange 40d radi ally inward of rib 41 and the upper portion of mid-wall 36a. By proper dimensioning of the parts of the structure, the sealing qualities of O-ring gasket 22a are optimally exploited by compression-within such triangularshaped volume.

With reference to FIG. 7, it will be noted that wall 16a of the container is formed with an annular reinforcing ring 70 which is integral with top wall 16a and concentric with opening 18a. The ring has

oblique wall portions

72 and 74 which are oriented obliquely of wall 16a so as to afford rigidity to the portion of the wall that bounds opening 18a. Thus, when the closure plug ,is moved to the closed position of FIG, 9, the likelihood of relative movement between lip 20a and the closure plug is virtually eliminated.

The embodiment of FIGS.10 and 11 affords the advantages described hereinabove in connection with FIGS. 3 and 4 and FIGS. 8 and 9. Because of the structural similarity, reference characters with theaddition of a reference letterb are used to designated parts in FIGS. 10 and 11 that correspond to the similar parts in FIGS. 3 and 4 and FIGS. 8 and 9. More specificallyfthe drum has a planar end wall 16b from which extends, upward and outward, a lip 20b which circumscribes an opening 18b. Lip 20b defines an upwardly exposed frusto-conical wall 21b. A closure plug 24b has a generally cylindric mid-wall 36b, at one end of which is a circular end wall 38b and atthe opposite end of which is an annular flange 40b which extends radially outward .from the mid'wall. Mid-wall 36 at the region thereof adjacent but spaced downward from flange 40b is formed with a rib 41b which extends throughout the circumference of the mi d-wall and is uniformly spaced below the flange throughout the periphery thereof. Before closure plug 24b is introduced into opening 18b, an O-ring gasket 22b is placed around midwall 36b and moved between flange 40b and rib 41b, as shown in FIG. 10. Rib 41b is positioned so that it limits the inward travel of closure plug 24b by contact with frustoconical wall 21b. Because the position and configuration of rib 41b can be control-leg very accurately with swaging techniques or the like, the innermost position of the closure plug is accurately established. As can be seen in FIG. 11, when mid-wall 36b is distorted outward, as at 46b, a triangular volume is defined'by frusto-conical wall 21b, the lower surface of flange 40b and It will be noted in FIG. 9 that, when rib 41 is in as to facilitate placement of protective coatings on the surface of the material opposite that on which the lining is present. The closure is so arranged that material, which might accidentally be spilled on the exterior surface of the drum during filling thereof can be completely removed. Finally, the closure is configured so as to achieve an optimum O-ring seal so as to assure freshness and cleanliness of the product contained in the drum.

Although several embodiments of the invention have been shown and described, it will be obvious that other adaptations and modifications can be made without departing from the true spirit and scope of the invention. For example, while the invention has been described with reference to a drum coated with plastic, film or tin, it should be understood that it is not limited to use with such drums.

What is claimed is:

1. A closure for a drum having at least one generally planar end wall with an opening therein, said closure comprising: a portion of said end wall bounding said opening and defining a lip integral with said end wall, said lip extending axially and radially outward around said opening, residing at an acute angle with respect to said planar end wall, being of a single thickness and having all surfaces exposed to the exterior of the end wall, a smooth conical interior surface merging into said opening and an outwardly exposed distal edge, said distal edge being concentric with said opening and residing in a plane substantially parallel with said end wall; a closure plug having a cylindric mid-wall and including an O-ring gasket circumscribing said mid-wall, a circular wall integral with and extending across one end of said mid-wall, and an annular flange integral with and extending outward from said mid-wall at the end of the mid-wall opposite said circular wall, said mid-wall having a diameter sized to fit within said opening and an axial extent such that said circular wall is interior of said drum end wall when said flange is in contact with the distal edge of said lip, said closure plug being deformable so that the portion of said mid-wall adjacent said circular wall can be radially expanded to retain said closure plug in said opening and distort said O-ring gasket into engagement with the smooth conical interior surface of the lip and the surfaces of the closure plug opposed thereto to seal said closure, said plug, lip and O-ring being so proportioned that distortion of the O-ring is within its elastic limit when the flange of the plug is in contact with the distal edge of the lip.

2. A closure, according to claim 1, wherein said annular flange is substantially perpendicular to said cylindric mid-wall and wherein said flange is joined to said mid-wall by an integral arcuate wall portion extending therebetween, said O-ring gasket having a radius of curvature corresponding to said arcuate wall portion and being distorted into sealing condition in response to movement of said flange into contact with the outer edge of said lip.

3. A closure, according to claim 2, wherein the surface of said lip and the surfaces of said flange and said mid-wall that are in contact with said O-ring gasket have thereon a layer of inert material bonded thereto.

4. A closure, according to claim 1, wherein the acute angle between said lip and said planar end wall is about 45.

5. A closure for a drum having at least one generally planar circular end wall with an opening therein, said closure comprising: a portion of said end wall bounding said opening and defining a lip integral with said end wall and extending axially and radially outward around said opening, said lip residing at an acute angle with respect to said planar end wall so as to define a frustoconical wall concentric with said opening, said lip being of a single thickness and having all surfaces exposed to the exterior of the end wall and an outwardly exposed distal edge; a closure plug having a cylindric mid-wall, a circular wall integral with and extending across one end of said mid-wall, and an annular flange integral with and extending outward from said mid-wall at the end of the mid-wall opposite said circular wall, said mid-wall having a diameter sized to fit within said opening and an axial extent such that said circular wall is interior of said drum end wall when said flange is in a fixed spatial relation to said frusto-conical wall; and an O-ring circumscribing said mid-wall adjacent said annular flange, said closure plug mid-wall being deformable so that the portion of said mid-wall adjacent said circular wall can be radially expanded to retain said closure plug in said opening and compressively distort said O-ring within a volume bounded by said frustoconical wall, said flange and said mid-wall; and means for limiting inward movement of said closure plug to establish said spatial relation and to establish said volume at a magnitude to compress said O-ring within the elastic limit thereof.

6. A closure, according to claim 5, wherein said inward movement limiting means comprises an outer edge on said lip concentric with said opening and residing in a plane substantially parallel with said end wall, said flange having a radial extent sufficient to contact said edge thereby limiting inward movement of said closure plug.

7. A closure, according to claim 5, wherein said inward movement limiting means comprises a downward extending rib formed on said flange and adapted to contact said frusto-conical wall thereby limiting inward movement of said closure plug.

8. A closure, according to claim 5, wherein said inward movement limiting means comprises a rib on said mid-wall, said rib extending radially outward sufficient to contact said frusto-conical wall thereby limiting inward movement of said closure plug, said O-ring being disposed intermediate said rib and said flange.

9. A closure, according to claim 5, wherein said container end wall is formed with an integral reinforcing ring circumscribing said opening, said ring having at least one integral oblique wall portion disposed obliquely of said end wall.

Claims

4. A closure, according to claim 1, wherein the acute angle between said lip and said planar end wall is about 45*.

5. A closure for a drum having at least one generally planar circular end wall with an opening therein, said closure comprising: a portion of said end wall bounding said opening and defining a lip integral with said end wall and extending axially and radially outward around said opening, said lip residing at an acute angle with respect to said planar end wall so as to define a frusto-conical wall concentric with said opening, said lip being of a single thickness and having all surfaces exposed to the exterior of the end wall and an outwardly exposed distal edge; a closure plug having a cylindric mid-wall, a circular wall integral with and extending across one end of said mid-wall, and an annular flange integral with and extending outward from said mid-wall at the end of the mid-wall opposite said circular wall, said mid-wall having a diameter sized to fit within said opening and an axial extent such that said circular wall is interior of said drum end wall when said flange is in a fixed spatial relation to said frusto-conical wall; and an O-ring circumscribing said mid-wall adjacent said annular flange, said closure plug mid-wall being deformable so that the portion of said mid-wall adjacent said circular wall can be radially expanded to retain said closure plug in said opening and compressively distort said O-ring within a volume bounded by said frusto-conical wall, said flange and said mid-wall; and means for limiting inward movement of said closure plug to establish said spatial relation and to establish said volume at a magnitude to compress said O-ring within the elastic limit thereof.