GB2137158A

GB2137158A - Thermoplastics Containers

Info

Publication number: GB2137158A
Application number: GB08308426A
Authority: GB
Inventors: Lewis Alfred Collins
Original assignee: RHEEM BLAGDEN Ltd
Current assignee: RHEEM BLAGDEN Ltd
Priority date: 1983-03-28
Filing date: 1983-03-28
Publication date: 1984-10-03
Also published as: ES8504010A1; MX159119A; FR2543484B1; SG41887G; GB2137158B; ZA841347B; GB8308426D0; MY8700628A; IT1173471B; DK85984A; SE468426B; DK161881C; DK161881B; DK85984D0; NO841129L; NZ207285A; BR8401393A; SE8401688L; IT8420212A0; FR2543484A1

Abstract

A thermoplastics container comprises a body portion 1 formed from a flat sheet by bending the sheet to produce a tube and welding together the ends of the sheet by hot- plate welding. The sheet ends are preferably butt-welded. End portions 2, 3 are attached to the body portion 1 by welding or adhesive; one end portion may be injection-moulded directly onto the body portion. The body portion can be ribbed or laminated, and the end portions may have configurations which facilitate stacking. <IMAGE>

Description

SPECIFICATION Improvements in Drums and Like Containers This invention relates to drums and like containers.

Of recent years, the use of steel in the manufacture of drums for the storage and transport of chemicals has been progressively supplanted by synthetic thermoplastic materials.

One technique widely used has been blow moulding. This technique is well understood but does lead to difficulties. One problem is that in the areas opposite the mould parting line the material tends to thin out due to the stretching of the parison. This results in thin corners on the top and the base of the containers.

Also, a blowmoulding always shrinks away from its true dimensions laid down in a product drawing and areas of greater wall thickness have a different shrinkage factor from those areas of less wall thickness. For example a container of square body section shrinks less along the mould parting line in comparison to the cross section in an angle of 900 to it.

Most blowmoulded containers can only be stacked 4 high when filled with the product to be packed and when submitted to outdoor conditions for periods exceeding 6 months.

It is often the case, however, that customers would prefer a stacking performance of 6 high, 9 high, or 12 high for longer periods with products of a specific gravity exceeding 1.0 g//cm3,m which cannot currently be achieved with a blowmoulded container in a commercially attractive weight and a specified even wall thickness distribution.

Further, many designs of blowmoulded containers are vulnerable to stress cracks when filled with an alkaline product or product of detergent composition and when submitted to superimposed loads in stacking piles.

Another technique used provides a drum with a body extruded into a desired section, and injection moulded end sections butt welded onto the body.

The use of extrusion for the body loads to the expense of large extrusion dies and this means that it is only economic for long production runs of given shape and thickness.

In accordance with the invention, there is provided a method of making a container of thermoplastic material comprising a body portion and two preformed end portions of thermoplastic material welded onto the body portion, in which the-body portion is formed from a flat sheet.by shaping a predetermined length of the flat sheetto form a tube of desired crosssection and welding the ends of the said length together by hot plate welding.

The flat sheets may be produced by extrusion, compression moulding or other suitable processes.

The ends of the length of sheet material are preferably butt welded together, but in certain circumstances it may be preferred to form an overlapping weld. The body portion may be of any suitable cross-section such as a circular cylinder, generally square or rectangular with rounded corners or even triangular, hexagonal or octagonal in section.

The preformed end portions may be formed by injection moulding, thermoforming, blow moulding or rotation moulding or any other suitable process, and they may be attached to the body portion in any suitable manner. They are preferably butt welded to the body portion by hot plate welding, but spin welding, ultrasonic welding or other bonding operations, e.g. by means of a suitable adhesive or the like, may be used. The injection moulded ends may be produced according to normal technology of moulding a top or bottom section of the container with a filler neck of final shape. Alternatively, there may be applied a technology where the bottom and top end are of the same geometry with the exception of the filler neck(s). In that case the filler necks could be moulded'without thread or filler-hole.Where the piece has to be the bottom end section, the neck could simply be machined off, resulting in a flat surface. Where the piece has to be the top end section, a thread could be cut inside or outside the straight filler neck if desired, and a hole could be machined through the diaphragm. The body portion and end portions may be of the same or difference thermoplastic materials, and any suitable material may be used such as polyethylene, polypropylene, polystrene, polyvinylchloride, polytetrafluoroethylene and so forth. The sheet of the body, however, may be co-extruded with one material in the middle section of the sidewall and an inner and an outer layer, resulting in a sandwich structure of the extruded sheet. That material combination may be required to give the sidewall of the drum predetermined mechanical or physical properties.

The preformed end portions and the body portion are normally assembled according to hot plate welding or the like after having been manufactured previously according to the relevant processes (e.g. injection moulding for the end portions and sheet extrusion and butt welding for the tubular body portion).

This means the three items have been cooled down and reached their preferred shape, as the shrinkage process of the thermoplastic material is completed. It may be preferably however, to hold the body portion in a fixed position and injection mould one end portion directly onto one side of it, thus avoiding one weld line created by hot plate welding.

The flat sheet to form the body portion may also be formed with reinforcement ribs which can be placed inside or outside the container or it can have a type of honeycomb structure inside its wall thickness which may help the mechanical properties of the body portion.

The reinforcement ribs may be positioned in horizontal or vertical direction of the body portion and they may fulfil different functions, depending on their position.

Horizontal ribs may be used as: a) aids to pick up a drum, b) rolling hoops, c) aids to prevent sidewalls of the drum collapsing under the influence of a superimposed load (stacking performance) or under the influence of a partial vacuum being drawn due to temperature differences on filler products with substantial partial vapour-pressure.

Vertical ribs may be used as reinforcements ribs on the inside or outside of a container e.g. to be located in the corners of a container of a square round or rectangular cross-section. The aforesaid ribs are provided to enhance vertical compression resistance.

By forming the body portion, from a flat sheet of material, the expense of a large number of extrusion dies, one for each required crosssection, is avoided.

By starting from a flat sheet, an additional advantage accrues in that the sheet can be preprinted while flat by a suitable printing method and may supply a better quality of printing in comparison to the printing of cylindrical, rectangular or square round body sections.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is an elevation of a typical form of a drum formed in accordance with the invention; Figure 2 is a top plan view of the drum of Figure 1; Figure 3 is a bottom plan view of the drum of Figure 1; Figure 4 is an enlarged section taken along the line A-A of Figure 2; Figure 5 is an enlarged section taken on the line B-B of Figure 3 showing in addition the stacking of two drums; Figure 6 is an elevation showing one form of sheet material from which the body may be formed; Figure 7 is an elevation of a drum body formed from sheet material as shown in Figure 6; Figure 7a is an elevation of an alternative form of drum body; Figure 7b is a horizontal section of the body of Figure 7a.

Figure 8 is a perspective view showing an alternative form of sheet material; Figure 9 shows a form of moulding which may be used as a basis for the top or the bottom of a drum; Figure 10 is a section through a bottom end moulding of a modified form; Figure 11 is a section through a top end moulding, also showing a Figure 10 bottom end in stacking relationship; Figure 12 is a plan view of the top end moulding of Figure 11; and Figure 13 is an elevation of a larger size of drum.

As illustrated in Figures 1 to 5 of the drawings, a drum consists of a body portion 1, an upper end portion 2 and a lower end portion 3. The body portion 1 is shown as being a circular cylindrical, and it is formed by bending a flat sheet of material with the aid of suitable former and butt welding the ends together by hot plate welding. The upper and lower portions 2 and 3 are preformed separately from the body portion 1 by injection moulding or otherwise.

It can be seen from the drawings that the end portions 2 and 3 can have central dimples 4 for reinforcement purposes, and the upper portion 2 is provided with a filler neck 5 which is shown threaded to receive a closure cap 6 (shown in phantom in Figure 4 only).

The upper portion 2 is provided with an upstanding peripheral wall or rim 7 to provide stackability despite the presence of the filler neck and closure cap 6 and of the dimples 4. This wall is provided with a gap 8 in the region of the filler neck 5 to facilitate pouring from the drum and also to ensure that rainwater or other liquids do not gather on the top of the drum. The wall 7 is integrally formed with the upper section 2 and is joined to the generally flat closure portion of the end portion 2 by means of a plurality of spaced reinforcing gussets 9.

The upper portion 2 is butt welded to the upper end of the body portion 1 by hot plate welding along the line indicated by 11 in Figure 4.

The lower portion 3 is provided with spaced down-turned pheripheral rims 12 and 13 which betweem them define a recess 14 which nests over the upstanding wall 7 of the subjacent drum when the drums are stacked. The rim 13 is reinforced by a series of spaced gussets 1 5.

The lower portion 3 is butt welded to the lower end of the wall 1 by hot plate welding along the line indicated by 1 6 in Figure 5.

It is envisaged in particular that drums of this construction will be used in sizes such as 1 5 litres, 20 litres and 25 litres. However, the manufacturing technique may be usable over a wide range of sizes, e.g. from 1 5 litres to 250 litres.

When using the hot plate welding, it may be necessary to provide some enlargement of the area to be welded by compression of the material, and these enlargements may, if appropriate, be smoothed off.

The upper portion 3 may have provision for a suitable carrying handle to be attached.

In addition, while the cross-section 2 is shown as having an upstanding wall 7 cooperating with the recess 1 5 for stacking, other stacking systems may be used. Also, the upper portion 2 may be convex while the lower portion 3 is concave to provide for nesting during stacking and substantial additional strength of the end portions 2 on 3. In such a domed arrangement, a filler spout may be incorporated in a recess in the dome.

Also, the filler neck may be either internally threaded to receive a threaded bung, externally threaded to receive a threaded cap, or plain to receive a crimped on closure Figure 6-shows a sheet 21 of plastics material such as polyethylene extruded with a pair of ribs 22. The sheet is shown as having side edges 23 and end edges 24. A sheet of suitable length is formed into a drum body by butt welding the end edges 24 together as shown in Figure 7 where the weld lin-e is indicate.d art 25. It-will be seen that the ribs 22 then extend horizontally on the body and act partially as rolling hoops and also as reinforcements. In an alternative arrangement, the side edges 23 of a suitably wide extruded sheet could be butt-welded together so that the ribs 22 then run vertically, i.e. parallel with the weld line.

25 as illustrated in Figure 7a. In either case7the- ribs 22 could be folded so as to be on the inside (as shown in Figure 7a) or the outside as shown in Figure 7) of the completed drum body. The arrangement of Figures 7a and 7b starts with a sheet having four ribs 22 and Figure 7b shows how these can be used to reinforce the corners of a generally square section drum body.

Figure 8 shows an alternative form of sheet material 26 which is somewhat thicker than the sheet 21 and is formed with an internal arrangement of hollows 27 giving a simple form of honeycomb structure. Ribs such as ribs 22 may be provided in such an arrangement if required.

Figure 9 shows a simple form of injection moulding which may be used for either the top or bottom end piece. A central portion 31, which may be domed or otherwise configured for integral reinforcement is provided with upward and downwardly extending flanges 32 and 33 respectively at its periphery. in addition, the central portion 31 is provided with two upstanding necks 34 and 35. If the elements is to be used as a lower end element, then the necks 34 and 35 will probably be removed by cutting and grinding, and the flange 33 can then be used to attach the portion to the lower end of the body.

If the portion is to be used as an upper end portion, then the central portion 31 will be pierced in the region of one or both of the necks 34, 35 as indicated by the dotted lines 36. If only one filler neck is required, then obviously only one piercing will be made and the other neck may be removed if required. The neck or necks retained can then be provided with either internal or external threading if required to receive a bung or closure cap.

Where a bottom end member as shown in Figure 5 is used, and the drums are stacked, it may be that the rim 12, which has to transfer the whole weight of the stack to a pallet or other support surface, may be damaged or distorted. In order to improve the stackability, an arrangement such as shown in Figures 10 to 12 may be used.

In this arrangement, the rim or skirt 1 2 is assisted in its support role by a series of spaced annular ribs 41, 42, 43 centered on the axis of the drum.

These ribs bear on the pallet surface and relieve the load on the skirt or rim 12. Figure 11 shows how a corresponding upper end has a filler neck 44 entering a localised dimple 45, and it also shows how the upper end is provided with a shoulder 46 which cooperates with the rim or skirt 12 to support part of the weight, while the upstanding wall 7 still passes inside the rim 12 to provide further support for the superjacent drum.

Figure 12 shows how the shoulder 46 is interrupted in the region of a pair of connection zones 47 for a conventional wire handle 48, and it also shows a reduction in the width of the shoulder 46 in the region of a gap 49 in the wall 7 adjacent the filler neck 44. Also shown in Figure 12 are tapered zones 51 on the wall 7 leading down into the gap 49. Again, although the neck ring is shown as being provided with an external thread, and a screw cap is shown in position, it is to be understood that the neck ring may be internally threaded to take a buttress bung, or may be left unthreaded so as to take a crimped on or other form of closure.

While the invention has so far been described in relation to drums which are suitable for man handling and stacking, e.g. a capacity range of 1 5 to 30 litres, it will be understood that the similar technology of manufacture may be applied to drums of larger capacity, e.g. 50 litres to 250 litres. Such drums can be provided with or without any facility for nesting together when stacked but could have flat topped flanges for skirts in abutment with each other. Figure 13 shows such an arrangement in which a drum has a body provided with rolling hoops 61 formed by integral ribs. The upper and lower end portions are each provided with flanges 62 forming skirts or upstanding rims respectively. Figure 1 3 also shows the upper end portion as being provided with two necks 63 of different sizes. These may of course be of the same size, or one neck may be omitted if desired. It is even possible, for the body itself to be provided with a body bung fixture 64, and in this case it is possible that one or both necks 63 could be omitted. As for the smaller sizes, the skirt 62 is preferably provided with drainage holes to release rainwater. The top of the drum maybe configured so as to facilitate mechanical handling.

Various modifications may be made within the scope of the invention.

Claims

1. A method of making a container of thermoplatic material comprising a body portion and two preformed end portions of thermoplastic material welded and the body portion, in which the body portion is formed from a flat sheet by shaping predetermined length of the flat sheet to form a tube of desired cross-section and welding the ends of the said length together by hot plate welding.

2. A method as claimed in claim 1, in which the ends of the length are butt welded.

3. A method as claimed in claim 1 or 2, in which the preformed end portions are butt welded onto the body portion.

4. A method as claimed in claim 3, in which the end portions are butt-welded to the body portion by hot plate welding.

5. A container made by a method as claimed in any of claims 1 to 4.

6. A container as claimed in claim 5, in which the end portions having stacking formations adapted to nest with the stacking formation of an adjacent similar container, the said stacking formation being in the form of circumferential rims standing proud of a generally flat closure portion.

7. A container as claimed in claim 6, in which the rings are joined to the closure portion by a series of reinforcing gussets.

8. A container as claimed in claim 5, in which the end portions are formed from a common moulding.

9. A container as claimed in claim 5, 6 or 7, in which the lower end portion is provided with a series of annaular ribs substantial coplanar with the lower most plane of the lower end portion.

10. A container as hereinbefore described with reference to the accompanying drawings.