GB2198409A - Plastics base member for fibreboard drum - Google Patents

Abstract

A base member (20) made of a plastics material has a circular section (22) and an upstanding peripheral wall (24), the free end of the peripheral wall being turned slightly radially outwardly. The base member is preferably of low density polyethylene and is moulded so that the circular section is thin, e.g. 2mm, a thickened section (26) together with radial ribs (28) being provided adjacent the upstanding peripheral wall. Annular corrugations (30) may provide flexibility and these corrugations together with the thickened portion and ribs are provided on the same side of the circular section as the upstanding wall so that the other side of the section can be generally planar. The base member is secured to an internally coated, cylindrical, convolutely wound, fibreboard body by means of a J-shaped metal band and by crimping and rolling (see Figure 1). The use of a caulking compound to prevent leaking may be avoided. <IMAGE>

Description

FIBREBOARD DRUMS The present invention relates to fibreboard drums, and in particular to such drums having a plastics base.

Fibreboard drums for bulk packaging have been known for at least 30 years. Such drums are generally produced by convolutely winding fibreboard, such as kraft board, to form a cylindrical sidewall.

A base is produced by laminating three circular plies of kraft board, the middle layer having a smaller diameter than those of the other two layers. The peripheral edge of the laminate are then turned up to provide a shallow dish-shaped base member. Preferably, the free end of the wall of the base member is turned slightly outwardly.

An annular metal band having an inturned J-shaped cross-section is then produced, the inner diameter of the band being marginally larger than the the outer diameter of the sidewall. The base is located in the band with its outturned wall in the hook of the J section and the sidewall is inserted so that it rests in the band with its bottom edge between the arm of the J section and the wall of the base member.

The assembly of sidewall, base member and band is then crimped and rolled. The crimping takes place on the side of the base member remote from its wall, and the rolling takes place on the other side of the base member to secure the base to the sidewall. The final configuration of the bottom of the drum is shown in Figure 1, to which reference is now made, in which the sidewall 1 is secured to the base 3 by means of the band 5. The sidewall 1 is forced into contact with the base 3 between the crimped section 7 and the rolled section 9 of the band 5.

The drum is completed by supplying a suitable lid, which may merely comprise a dish-shaped fibreboard member or may comprise a plastics or steel member located onto the sidewall using an adjustable metal band. Such lid arrangement are well known in the art.

Such a drum having a diameter of 470 mm can readily handle up to 200 kg of powder or similar dry goods or non-free flowing pastes and resins, or up to 115 1 of liquid products.

Since fibreboard is able readily to absorb liquids and thereby become weakened, it is necessary, if such drums are to contain liquids, to provide both the sidewall and the base member with liquid-impervious coatings, such as a layer of a plastics material. Such a layer 11 is shown in Figure 1. Moreover, it is necessary for the base to be sealed in a liquid-tight manner to the sidewall.

It is difficult to achieve such a liquid tight seal, even if the sidewall and the base are coated. The main reason for this is that, when the flat circular laminate is turned up to produce the dished base, the fibreboard of the base adjacent the junction of the wall and the flat portion becomes pleated and rucked. These pleats and rucks are not removed during the crimping and rolling operations, and therefore provide leakage paths for liquid escape.

It has therefore become the practice to caulk the seal between the base and the sidewall. This is generally carried out by placing a bead of caulking compound midway along the inside of the arm of the J section band prior to insertion of the sidewall. On such insertion, the bead is smeared onto most areas between the band, the sidewall and the base member.

On crimping and rolling the caulking compound is further spread, and tends to ooze into the drum on the side of the sidewall opposite the crimped area.

It is therefore necessary to wipe out the interior of the drum after the crimping and rolling operation.

It can thus be seen that forming a liquid-impervious fibreboard drum is a multi-step, labour intensive operation comprising cutting out three fibreboard circular layers one plastic coated), laminating them together, turning up the laminate to form the dished base, applying caulking compound to be band, crimping and rolling, and then wiping the interior of the thus formed drum.

However, even if all these steps are carried out correctly, it does not guarantee that the seal will be liquid-impervious. It is also well known that fibreboard changes its dimensions on absorbtion of water, but that the changes are anisotropic.

Generally, the changes in dimensions will be about an order of magnitude greater in the cross direction than in the machine direction.

It commonly occurs that when the circular laminate is produced, it is stored prior to turning down and insertion in a drum. During such storage, its moisture content is likely to change, and due to the anisotropic properties of the fibreboard the laminate will assume an elliptical rather than circular shape. On turning up, this will lead to a dish having a wall a varying height and of varying profile.

Use of such an elliptical dished base member will lead not only to a seal of reduced efficiency in the lower areas of the wall but also to a less than perfect fit of the base member in the sidewall These problems can lead to an unsatisfactory seal and reduced overall seal strength. This is evidenced by the fact that, if a drum with an elliptical base is dropped so that the seal between the base and sidewall is broken, the point of failure is almost invariably adjacent the minor axis of the elliptical base.

The problems caused by the anisotropic properties of the base member can also arise after the drum has been produced. If the completed and filled drum is stored in different humidity conditions from those in which it was made, it may still assume an elliptical shape, with the accompanying loss of seal strength, or tensions may be set up in the base member, making it easier to rupture the seal.

A further problem with fibreboard drums is that, if the drum is stored in wet conditions, for instance on a concrete floor in a warehouse which is not totally weatherproof, the base may absorb so much moisture as to reduce to an unacceptable level the strength of the drum Although these problems with fibreboard drums have been known for many years, no proposals have been set forth for dealing with them It can thus be seen that, although fibreboard drums are generally very useful as bulk containers, they have significant drawbacks, in particular when used for containing liquids. It is an object of the present invention to overcome, at least in part, the above mentioned drawbacks.

According to a first aspect of the present invention, there is provided a base member for use in forming a fibreboard drum, comprising a circular section and an upstanding peripheral wall, the free end of the wall being turned slightly outwardly, the base member being made of a plastics material.

Preferably, the base member is made by a moulding process, such as injection moulding. Any suitable thermoplastic material may be used for such moulding.

The plastics material may be any one of which has sufficient strength to support the loads it is designed to carry, and sufficient resilience so that it can withstand the forces exerted on it during handling. Such plastics materials include polyethylene, polypropylene and polyvinylchloride.

A particularly preferred material is low density linear polyethylene. The plastics material may, if desired , be reinforced but this is generally unnecessary.

Preferably, the circular section of the base amber is generally as thin as possible, but is thickened towards its circumference to a thickness equivalent to that of a fibreboard base for the same purpose. Conveniently the circular section of the base member includes a plurality of radial ribs, preferably equally spaced, around its periphery.

Such thickened portions and ribs may be used to ensure that the base member can be used with the same tools as are used to crimp and roll conventional fibreboard drums.

In order to improve the strength and flexibility of the base member it is preferred that it includes a plurality of annular corrugations, preferably towards the circumference of the circular section. Preferably, the corrugations are sinusoidal, but other shape, such as saw tooth or box section, corrugations may also be used.

Advantageously the path length of the corrugated circular section is from 5 to 108 greater than the diameter of the circular portion.

Preferably, any thickened portions, ribs or corrugations are all formed on the same side of the circular section as the upstanding wall, whereby the side of the circular section remote from the wall is generally planar.

According to a second aspect of the present invention, there is provided a drum comprising a fibreboard sidewall, a plastics base and a metal band which has been crimped and rolled to seal the base to the sidewall.

Preferably, where the drum is intended for use with liquids, the sidewall is coated with a liquid-impervious coating, for instance of low density linear polyethylene.

Advantageously, the base is formed from a base member according to the first aspect of the invention or a member according to any of the preferred or optional embodiments thereof set out above.

The base member of the present invention is highly advantageous in that it can be made in a one step operation, such as by injection moulding.

Moreover, since the plastics material from which it is made is isotropic, it will retain the shape in which it was moulded.

Moreover, its use will lead to a more simple and economical process for the production of drums, since even where it is intended that the drums are to be used for containing liquids, it will not be necessary to apply any caulking compound or to wipe the inside of the drum after its formation. However, where the drum will encounter severe handling, it is advantageous to caulk the base to ensure adequate performance.

The drum thus produced will have highly advantageous properties. Since the formation of the base member involves no turning up of its edges, there will be no pleats or rucks to provide liquid leakage paths. The plastics material is isotropic and therefore the base member will not alter its shape during storage, thus ensuring that it has an even wall height and good fit in the sidewall prior to crimping and rolling. This will lead to an efficient and strong seal. The isotropic properties of the plastics material will ensure that, after formation of the drum, there will be no deteriotation in properties either due to a change in the shape of the base or due to absorbtion of liquid by the base.

It has also surprisingly been found that the drums of the present invention are significantly more resistant to rupture at the seal than are drums having fibreboard bases. For instance, a 120 1 (470 mm) fibreboard drum full of liquid will generally survive being dropped onto an edge of its seal from a height of about 0.6 metres. If an uncorrugated plastics base is used, the drop height increases to about 0.8 metres. If a corrugated plastics base is used, the drop height increases to about 1.0 metre.

One embodiment of a base member of the present invention is now described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a fragmentary sectional view of a conventional fibreboard drum; and Figure 2 is a fragmentary sectional view of the base member of the invention.

Referring now to Figure 2 of the drawings, there is shown a base member 20 for use in forming a drum according to the invention. The base member 20 is made as an injection moulding from low density linear polyethylene.

The base member 20 has a circular section 22 and an upstanding wall 24 at its peripheral edge.

The free end 26 of the wall 24 is turned outwardly so that the wall has a generally J-shape. The outside face of the wall need not be exactly perpendicular to the circular section 22 and is preferably inclined so that the free edge has a slightly greater diameter than the circular section 22.

The circular section 22 has an annular thickened section 26 adjacent its circumference.

Also adjacent its circumference and at regularly spaced intervals therearound are twelve radial ribs 28. The thickened section 26 and the ribs 28 have a thickness which is equal to the thickness of a conventional fibreboard base for the same purpose.

The base member 20 can therefore be used in the same crimping and rolling apparatus as is used to form conventional fibreboard drums.

The circular section 22 has formed in it four sinusoidal annular corrugations 30 which provide sufficient flexibility in the base member 22 to enable it easily to withstand the stresses placed on it during formation, handling, use and misuse (such as dropping).

The outside diameter of the circular section 22 is 46.9 cm, and the path length along a diameter but following the corrugations is 49.7 cm. The path length is therefore 6.0% larger than the diameter.

The height of the upstanding wall 24 is 2 cm, the height of each corrugation is 0.6 cm, and the thickness of the circular section 22 and wall 24 in general is 2 mm. Bowever, at its thickened section 26 and ribs 28, its thickness is 0.45cm.

The distance from the circumferential edge of the circular section 22 to the end of the innermost corrugation is about 8.8 cm.

The dimensions given above are those preferred for a 47 cm diameter, 120 1 liquid containing drum. These dimensions can be varied, or altered to suit a different size drum. For instance, a smaller drum may only require three corrugations and may not require any ribs.

The base member 20 is used to form a drum according to the present invention in a manner analogous to that described with respect to conventional fibreboard drums. If the drum is to be used to contain liquids, the fibreboard sidewall will be coated with, for instance, a polyethylene coating. Using the base member of the present invention, it may be unnecessary to use a caulking compound since, during the crimping and rolling operation, the coating on the sidewall will become welded to the base member, thus forming a liquid impervious seal. Moreover, since there will be no pleats or rucks in the base member, no liquid leakage paths will be formed.

It has been found that a drum according to the invention can be stored under varying degrees of humidity, or even standing in water, without being adversely effected. Moreover, the such a 120 1 (47cm) drum full of water can be dropped directly onto one edge of its base from a height of up to 1.0 metre without rupturing.

It can thus be seen that the base member and drum of the present invention represent a significant advance in the fibreboard drum art.

It will be appreciated that the above embodiment of the present invention has been described purely by way of illustration and that modifications of detail can be made without departing from the scope of the invention

Claims (13)

1. A base member for use in forming a fibreboard drum comprising a circular section and an upstanding peripheral wall, the free end of the wall being turned slightly outwardly, the base member being made of a plastics material.

2. A base member as claimed in claim 1 wherein the circular section of the base member is generally as thin as possible, but is thickened towards its circumference to a thickness equivalent to that of a fibreboard base for the same purpose.

3. A base member as claimed in claim 1 or claim 2 where in the circular section of the base member includes a plurality of radial ribs around its periphery.

4. A base member as claimed in any one of the preceeding claims wherein the base member further comprises a plurality of annular corrugations.

5. A base member as claimed in claim 4 wherein the path length of the corrugated circular section is from 5 to 10% greater than the diameter of the circular portion.

6. A base member as claimed in any of the preceeding claims wherein any thickened portions, ribs or corrugations are all formed on the same side of the circular section as the upstanding wall, whereby the side of the circular section remote from the wall is generally planar.

7. A base member as claimed in any of the preceeding claims wherein the base member is made by a moulding process.

8. A base member as claimed in any of the preceeding claims wherein the plastics material is low density polyethylene.

9. A base member according to claim 1 substantially as herein before described with reference to the accompanying drawings.

10. A drum comprising a plastics base as claimed in any of the preceeding claims, a fibreboard sidewall and a band to seal the base to the sidewall.

11. A drum as claimed in claim 10 wherein the sidewall is coated with a liquid-impervious coating.

12. A drum as claimed in claim 11 wherein the liquidimpervious coating is low density linear polyethylene.

13. A drum substantially as described herein with reference to the accompanying drawings.