GB2227736A

GB2227736A - Plastic containers for liquids

Info

Publication number: GB2227736A
Application number: GB8902285A
Authority: GB
Inventors: Michael David Christy
Original assignee: Harcostar Ltd
Current assignee: Bulk Number Four Ltd
Priority date: 1989-02-02
Filing date: 1989-02-02
Publication date: 1990-08-08
Anticipated expiration: 2009-02-02
Also published as: GB8902285D0; GB2227736B

Abstract

A moulded plastics container useful in the transportation of liquids, comprises a body having a neck 12 of circular cross-section with an opening at its outer end 13. The neck 12 has a first internal screw-thread 14 adjacent its outer end 13 and a second internal screw-thread 16 between the first screw-thread 14 and the interior of the container. The major diameter of the second screw-thread 16 is smaller than the minor diameter of the first screw-thread 14. A bung with a corresponding external thread may engage the neck of the container so as to form a closure during normal use. During transportation two bungs may be used, one for each threaded portion. The screw thread 14 has a coarser pitch and greater thread depth than the second screw thread. The container may be formed from blow-moulding or rotational casting, or may be made of pieces welded together. <IMAGE>

Description

PLASTICS CONTAINERS This invent on relates to moulded plastics containers and n particular relates to neck configurations for the openings to such containers.

Moulded plastics containers intended for the transport of liquids frequently have an opening to the container defined by a neck generally of circular crosssectional shape, which neck is provided with internal and/or external screw-threads, to allow the fitment thereto of a suitable aorm of closure. In the case of a moulded plastics container intended for the bulk transport of liquids, and so having a volume in the range of from perhaps 20 litres up to 250 litres, the opening defined by such a neck may typically be of about 50 mm diameter and is often referred to as a "bung hole".

Prior to the introduction of large moulded plastics containers For the bulk transport of liquids, it was common to us metal containers for this purpose.

Often, such a container had an internally threaded neck defining a bung-hole: in the United Kingdom, the neck was conventionally threaded with a 2" British Standard Pipe Thread (2" BSP - about 50 mm diameter), either straight or tapered, and in the United States, the neck was conventionally threaded with a 2" American National Pipe Thread, again either straight (NIPS thread) or tapered (NPT thread). touring transport of a liquid, an externally threaded bung was engaged with the threads formed internally of the neck, and when the contents were to be removed from the container, the bung was removed and replaced by a fitting having a thread also engageable with the internal thread of the neck.As a consequence, a wide range of liquid dispensing equipment has been developed, in the United Kingdom all having 2" BSP threads, and in the United States all having 2" NP threads, such equipment including taps, outlet valves, pipe assemblies and pump mechanisms.

Modern blow-moulding techniques have allowed the cost-effective production of moulded plastics containers particularly suitable for the bulk transport of liquids, for such containers are relatively light, strong and resilient, as compared to a metal container of a comparable volume. However, it is found that a moulded plastics container cannot adequately be closed by means of an externally threaded bung similar to that employed in connection with metal containers (i.e. for example a 2" BSP or a 2" NP bung) and threaded into a corresponding internally-threaded neck provided on the plastics container. The thread form of a 2" BSP or 2" NP pipe thread (for instance) gives insufficient interengagement between the bung and the neck, and it is found that only a most unreliable closure can be obtained in this way.As a consequence, different thread forms have been developed for use with moulded plastics containers, with a much coarser pitch and with a significantly greater thread depth. However, the consequence of this is that the various fittings developed over flany years for use with metal containers having necks threaded internally with BSP or NP threads cannot be used with the plastics containers of corresponding sizes to the metal containers. In turn, this has led to a slower than expected acceptance of moulded plastics containers in the narketplace.

In an attempt to overcome the above-described problem, this Invention provides a plastics container having an opening defined by a neck of circular crosssection, the neck having a first internal screw-thread formed in a portion of the neck adjacent the outer end thereof and the neck having a second internal screwthread formed in a portion of the neck between said first internal screw-thread and the interior of the container, the major diameter of the second screw-thread being smaller than the minor diameter of the first screw-thread.

It will be appreciated that with a container of this invention, a secure closure may be provided by giving one of the first or second screw threads an appropriate profile for this purpose, which thread then may be engaged by a bung or other closure with a corresponding external thread. Such a bung or other closure may then be employed when the container is to be used to transport liquids from place to place. The other screw-thread may have a form corresponding to that conventionally used for metal containers, so that equipment developed for such containers may still be used with the moulded plastics container.

Most preferably, one of the first and second screw-threads has a coarser pitch and a greater thread depth than the other of the first and second screwthreads. Advantageously, the first screw-thread (that is, the screw-thread nearer the outer end of the neck) has a coarser pitch and greater thread depth than the second screw-thread.

In a typical example of mould plastics container of this invention, the second screw-thread (that is, the screw-thread nearer the container interior) may have a BSP or a NP pipe thread, conveniently of 2" nominal diameter. Then, the first screw-thread may take any suitable form to allow a secure closure of the plastics container with a corresponding bung, provided that said first screw-thread has a greater minor diameter than the major diameter of the pipe thread forming the second internal screw-thread. For example, the first internal screw-thread may have a square or Acme thread form, or a modified form of either of such thread forms.One such thread is known as a mouser thread, having a minor diameter of about 66 mm, a major diameter of about 71 mm and a pitch of 6 mm, the inwardly-facing flank of the thread in the neck being generally radial and the other flank being inclined at about 450.

A plastics container of this invention may be made in a variety of ways, using conventional plastics moulding techniques. For example, the container could be blow-moulded, or a rotational casting process may be employed. The container could be made in more than one piece, the pieces then being welded together to form the complete container. In this latter case, parts - such as just the neck - could be made by an injectionmoulding process.

The transportation of certain classes of liquids is permitted only in a container having two distinct seals or closures, in order to provide greater security.

For example, in the case of a metal container, it is common to provide a bung engaged with the internal screw-threads of the neck, and also to provide a crimped-on metal seal over and around the exposed portion of the container neck. An advantage of a container of the present invention is that the regulations relating to the transportation of such classes of liquids may be satisfied by providing two separate closures engaged respectively with the first and second internal screw-threads of the neck, whereby access to the interior may be gained only by sequentially removing the outer closure and then the inner closure, engaged respectively with the two sets of screw threads.

By way of example only, one specific embodiment of blow-moulded plastics container arranged in accordance with this invention will be described in detail, reference being made to the accompanying drawing, which is a cross-sectional view through the neck portion of the container.

In the accompanying drawing, there is shown the neck portion of an otherwise conventional blow-moulded plastics container including a top wall 10 formed integrally during the moulding operation with a side wall 11, the top wall including an upstanding neck 12.

Formed in the portion of the neck 12 nearer the outer end 13 thereof is a first internal screw-thread 14, and formed in the portion of the neck between the first internal screw-thread 14 and the inner end 15 of the neck is a second internal screw-thread 16. As will be appreciated from the drawing, the first internal screw-thread 14 is of a relatively coarse form as compared to the second internal screw-thread 16, and the minor diameter of the first internal screw-thread 14 is greater than the major diameter of the second internal screw-thread 16. Between the first and second internal screw-threads 14 and 16 there is a shoulder 17 adapted to provide an engagement surface for a sealing member (not shown). Annular ribs 18 are formed around the external surface of the neck 12.

It will be appreciated that for the normal closure of the container, a bung (not shown) having an external screw-thread corresponding to the first internal screwthread 14 may threadingly be engaged with that thread in the neck. A suitable sealing member (such as an O-ring) may be disposed on the bung, so as sealingly to engage the shoulder 17. In view of the thread form of the first internal screw-thread 14, a secure closure for the container may thus be achieved.

When the container is to be filled or emptied, the filling or emptying equipment may have a portion externally-threaded for engagement with the neck of a container, the form of this thread being standardised to allow use of the equipment on different containers. In the case of the container of this embodiment, the equipment may be engaged with the screw-thread 16, following the removal of the bung. Though the screwthread 16 provides a less secure interengagement than thread 14, in view of the lesser thread depth formed in a plastics material, nevertheless an adequate interengagement may be achieved for many purposes, other than actual transportation of the container itself.

If a further seal is required for the closure engaged with the first screw-thread 14, then an appropriate form of seal (such as a crimped metal seal) may extend over the neck 12 and be crimped into engagement with the ribs 18.

In a typicai embodiment of blow-moulded plastics container of this invention, the first internal screwthread 14 is a Mauser thread of about 66 mm minor diameter, 71 mm major diameter, and 6 mm pitch. The second internal screw-thread 16 may be a NPSM pipe thread of 2" nominal diameter, having 11.5 tpi. One of these threads 14 or 16 may be formed during the blowmoulding operation in a manner known in the art, the other screw-thread being formed subsequently, for example by means of a thread-tapping operation.

Claims

1. A plastics container comprising a body having a neck of circular cross-section and being open at its outer end, the neck having a first internal screwthread formed in a portion of the neck adjacent the outer end thereof and a second internal screw-thread formed in a portion of the neck between said first internal screw-thread and the interior of the container, the major diameter of the second screwthread being smaller than the minor diameter of the first screw-thread.

2. A container according to claim 1, wherein one of the first and second screw-threads has a coarser pitch and a greater thread depth than the other of the first and second screw-threads.

3. A container according to claim 2, wherein said one of the first and second screw-threads has a square or Acme profile, or a modified square or Acme profile.

4. A container according to claim 2 or claim 3, wherein the first screw-thread has a coarser pitch and greater depth than the second screw-thread.

5. A container according to any of the preceding claims, which has been made by a blow-moulding or rotational casting process.

6. A container according to any of the preceding claims which has been made by a fabrication process from more than one moulded piece, which pieces are welded together to form the complete container.

7. A plastics container as hereinbefore described with reference to and as illustrated in the accompanying drawing.

8. A container according to any of claims 1 to 7 in combination with a pair of externally-threaded bungs adapted for screw-threaded interengagement with the first and second screw-threads respectively in the neck of the container, whereby the neck may be closed by sequential interengagement of the tor bungs with the respective screw-threads.