Seal

Abstract

 ABSTRACT
A secondary closure (22) for use with a screw cap closure which comprises a dish adapted to fit within the neck of a screw cap closure (14) characterised in that the dish has annular groove (26) about its external circumference adapted to receive an O-ring (28). The lower surface (24) of the dish is curved downwardly or radiused toward the interior of the drum. The external dimensions of the dish are such that the closure is an interference fit within the neck (10) and can only be removed by destroying the closure. The closure will resist internal pressures in the region of 1.5 - 2 bar (above ambient).

Description

[0001] This invention relates to an improved seal and in particular relates to an improved seal for use with cans, tanks or drums having screw caps.

[0002] Drums for carrying liquids are commonly provided with screw cap closure means. At a convenient place on the drum, usually the top face, an upstanding neck providing access to the interior of the drum carries a male thread. A complementary screw cap having a wad or seal in its inner face completes the closure. It is common practice to provide an additional closure for use on drums which are filled with a liquid at manufacture to prevent or at least reduce the likelihood of pilferage of the liquid. This closure commonly takes the form of a thin metallic dish or membrane which is an interference fit within the neck. The secondary closure requires to be removed by user before they can gain access to the contents of the drum and since this can only be done by destroying the seal it is readily apparent if a drum has been tampered with. However, the secondary closure does not normally provide an effective seal in the sense of being completely liquid-tight, and with most screw cap closures even with secondary closures of this type a small excess pressure within the drum, eg of 1.2 bar (3 psig), is often sufficient for the closure to leak.

[0003] The invention seeks to provide a secondary closure improved in the above respects.

[0004] According to the present invention there is provided a secondary closure for use with a screw cap closure which comprises a dish adapted to fit within the neck of a screw cap closure characterised in that the dish has annular groove about its external circumference adapted to receive an O ring.

[0005] Preferably also the lower surface of the dish is not flat but is curved downwardly toward the interior of the drum. By these means a secondary closure is provided which is capable of performing a liquid tight seal and resisting internal pressures an order of magnitude greater than was previously the case without leaking.

[0006] The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

figure 1 is a sectional view of a secondary closure in accordance with the invention;

figure 2 is a similar view to figure 1 of the closure in place beneath the screw cap.

[0007] Referring to the drawings, the outlet of a tank, can, or the like designed to carry liquid is a neck 10 carrying an external screw thread 12. The neck 10 co-operates with a cap 14 having a complementary thread 16. The cap 14 is provided with a wad 18 of sealing material. In a conventional closure it is the contact of the sealing material 18 with a raised lip 20 at the top of the neck 10 which provides the liquid proof seal. This seal is not especially resistant to internal pressure and indeed may well start to leak at internal pressures as low as 0.2 bar above atmospheric (3 psig).

[0008] The cap closure described above is conventional and would normally be used with a dished cylindrical anti-pilferage secondary closure. In accordance with the invention this is replaced by the secondary closure 22. The latter has a radiused lower face 24 and is provided with an annular groove 26 on its external circumference. The groove 26 receives an O-ring 28.

[0009] In use, the secondary closure 22 is placed within the neck 10 when the O-ring 28 provides an effective liquid-tight seal. The external dimensions of the dish 22 can be such that the closure is an interference fit within the neck 10 and can only be removed by destroying it, eg by inserting a screwdriver and levering it out. In this way the secondary closure 22 provides a pilferage barrier. However, the design of the secondary closure is such that it will resist very much higher pressures than hitherto without leakage, typically 2.5-3 bar (20-30 psig). This latter ability is especially important for containers carrying dangerous substances where stringent regulations are in force concerning the pressure resistance of the closure means.

[0010] The secondary closure of the invention provides a simple and economical solution to the problem of container closures being liquid tight and able to resist internal pressures.

Claims

1. A secondary closure for use with a screw cap closure which comprises a dish adapted to fit within the neck of a screw cap closure characterised in that the dish has annular groove about its external circumference adapted to receive an O-ring.

2. A closure as claimed in claim 1 in which the lower surface of the dish is curved downwardly toward the interior of the drum.

3. A closure as claimed in claim 2 in which the lower surface of the dish is radiused.

4. A closure as claimed in any of claims 1 to 3 in which the external dimensions of the dish are such that the closure is an interference fit within the neck and can only be removed by destroying the closure.

5. A closure as claimed in any of claims 1 to 4 which will resist internal pressures in the region of 1.5 - 2 bar (above ambient).

Drawing