GB2367546A

GB2367546A - A One-piece Moulded Container

Info

Publication number: GB2367546A
Application number: GB0119425A
Authority: GB
Inventors: Barry Mccormick
Original assignee: SHIELDTONE Ltd
Current assignee: SHIELDTONE Ltd
Priority date: 2001-08-09
Filing date: 2001-08-09
Publication date: 2002-04-10
Anticipated expiration: 2021-08-09
Also published as: GB0119425D0; GB2367546B

Abstract

A container, for use in containing and measuring mortar, comprising a base and side walls (10) formed as a unitary moulding of plastic material where the base includes support formations (20) which extend downwardly in normal use and remove the base of the container from the ground. The container can be formed by rotational moulding of linear low-density polyethylene.

Description

Container This invention relates to containers. Specifically, it relates to heavy-duty containers for transportation and storage of semi-liquid materials such as building mortar.

Mortar is often supplied to building sites in containers known as mortar tubs.

These tubs are used not only to contain the mortar on a building site, but also to measure the quantity of mortar that is actually delivered. While on site, mortar tubs can encounter an astounding degree of abuse ranging from improper and damaging handling by lifting equipment, to being dropped from a considerable height onto solid ground. Therefore, if it is to function as required throughout a reasonable life span, a mortar tub must be accurately made and extremely durable.

For some time, mortar tubs have been constructed from polyethylene, in particular, linear low-density polyethylene (LLDPE) using rotational moulding techniques.

While this moulding technique is not fast nor particularly efficient, the products that it produces have very favourable toughness and durability.

In an aim to improve the durability of mortar tubs, the present applicant company produced a new type of tub that is disclosed and claimed in its UK Patent No.

2320710. While this tub has proved to be a substantial improvement upon earlier designs, it has been found that particularly extreme examples of maltreatment can cause failure of the joint between two of its components. This can result in liquid mortar entering into substantially closed chambers of the tub, where it can solidify.

Because the solidified mortar cannot then be removed, problems can be encountered when an attempt is made to transport the tub for repair because of the excess weight of mortar that must be transported.

An aim of this invention is to provide a mortar tub that has even greater durability, and that does not tend to trap solidified mortar.

From a first aspect, this invention provides a container comprising a base and side walls formed as a unitary moulding of plastic material, in which the base includes a generally planar floor portion that constitutes a liquid-supporting floor for the container and a support formation that extends downwardly in normal use from the floor portion, the support formation including a substantially solid wall of plastic material.

It has been found that the unitary nature of the support formation, base and the side walls contribute to the strength of the container. Moreover, it has all of the functional features of the container disclosed in UK Patent No. 2320710 yet has no enclosed chambers within which mortar can be trapped. A small amount of mortar may flow into the top of the downwardly extending wall, but the quantity that can so do is so small as to be of negligible consequence. A complete container structure need include no box section or similar formation within which mortar can accumulate.

The wall of the support formation is most advantageously formed from plastic material that has been solidified in contact with opposed surfaces of a mould, while the floor portion and side walls are formed from plastic material that has solidified in contact with a single surface of the mould. This arrangement can provide the shape required to mould an embodiment of the invention without the need to provide cores within the mould.

A typical embodiment includes a plurality of such support formations.

When viewed in plan, the shape of the support formation may be essentially arbitrary, being chosen to best provide the functionality required. For example, the support formation may be formed as a wall that is a closed loop, whereby the support formation forms a void below the floor portion that is open in a downward direction only. Such a space cannot retain a liquid product, so is unlikely to accumulate material such as set mortar. Advantageously, the void is shaped to have across-section that tapers in an upward direction. Even if material can does solidify within the void, this taper ensures that the solid material can be removed readily. The support formation may conveniently be shaped as to be substantially rectangular in plan.

Embodiments of the invention may advantageously include several spaced support formations. In such embodiments, in a space between adjacent support formations, the lowest part of the container is formed by a lower surface of the floor portion. This can conveniently be used as a lifting surface for the container. In such embodiments, the support formations may be dimensioned and spaced to form several such lifting surfaces, which are advantageously spaced for engagement with suitable lifting apparatus, such as a fork lift.

A particularly preferred form of a container embodying the invention is a moulding of polyethylene, of preference, linear low-density polyethylene (LLDPE), and most advantageously a rotational moulding of polyethylene. Typically, planar parts of the moulding may have a thickness in the range of 7 mm to 11 mm (e. g. approximately 9 mm).

A container embodying the invention may have a capacity of between 100 and 300 litres, and more particularly 200 to 250 litres. Typically, a container embodying the invention is a container for mortar; specifically, it may be for measuring a quantity of mortar in a commercial transaction, and for subsequent storage of mortar for use on a construction site.

From a second aspect, this invention provides a method of making a container according to the first aspect of the invention, in which fused plastic material is caused to flow within a mould, whereby the side walls and floor portion are formed by plastic material deposited in contact a single surface of the mould, and a wall of the support formation is formed by plastic material deposited in contact with two opposed surfaces of the mould.

The wall of the mould may be formed by solidifying material within a groove of the mould. The side walls and the floor are formed by solidifying material against a single surface of the mould. Plastic material can be caused to flow from the single surface into the groove. This can provide a finished moulding in which all parts of the moulding are highly integrated in a tough moulding with low internal stresses.

Most typically, the plastic material used in this aspect of the invention is polyethylene (for example, LLDPE), and the moulding process is a rotational moulding process. More specifically, the moulding process is one in which flow of plastic material is caused principally or entirely by the action of gravity (rather than by application of another force, such as is used in extrusion, injection moulding, vacuum forming, and so forth).

An embodiment of the invention will now be described in detail, with reference to the accompanying drawings, in which: Figure 1 is a sectional view of part of a container being a first embodiment of the invention; Figure 2 is a view from below of the container of Figure 1 ; Figure 3 is a side view of the container of Figure 1 ; and Figure 4 is a sectional view of part of a mould tool for use in the production of the container of Figure 1.

As shown in the drawings, a container embodying the invention is a mortar tub formed as a unitary moulding. This embodiment is a moulding of LLDPE formed by a rotational moulding process.

The container has side walls 10 and a base 12 that are arranged to form a volume within which a liquid or semi liquid product can be stored, and which has an upwardly-directed rectangular opening. Embodiments such as this have a liquid capacity of 250 or 300 litres. A typical thickness of the moulding in this application is approximately 10 mm, with a total weight of plastic material of 21 kg.

In plan, the base 12 is generally rectangular, and the side walls 10 extend generally upwardly from its four sides. The side walls 10 are angled to the vertical such that they taper away gently from one another and outwardly from the periphery of the base 12 towards the opening. A strengthening lip 14 is formed at an upper region of each of the side walls 10. In the event that the contents of the contents solidify, as might happen, for example mortar is left in the container for an extended time, the taper of the walls helps to ensure that the solid body can always be removed readily.

Several (three, in this case) supporting feet 20 extend downwardly from the base 12. Each foot is formed from a wall 22 that extends downwardly from the base 12, the wall forming a closed rounded rectangle in plan. The wall is shaped such that each foot 20 extends substantially entirely across a shorter dimension of the base 12, and the feet 20 are spaced apart along a longer dimension of the base 12. The wall 22 has a thickness that tapers gently in a direction away from the base 12. This forms a void 24 that is enclosed by the wall 22, the void being open in a downward direction, and tapering away from its opening. The container can be lifted by a fork lift, with its forks projecting between the feet 20 to engage on the underside of the base 12.

It will be recognised that voids such as the void 24 within each foot 20 will normally be formed using a double-skinned mould in a rotational moulding process. However, an aspect of this invention is to enable such a formation to be formed in a simple shell mould.

A moulding tool for use in manufacture of a container embodying the invention comprises two metal shells 30 each having defined within a void shaped as the outer shape of a container. The shells 30 are joined together at the region that will define the opening of the finished container so that two identical containers can be formed in one moulding operation. That much is conventional in rotational moulding. With reference to Figure 4, in manufacture of this embodiment, the wall 22 is formed within a V-shaped groove 32 in the wall of a rotational moulding tool.

In use, sufficient plastic material in granular form is introduced into one of the mould shells 30. Two shells 30 are then connected to seal the plastic material within a closed void. The assembled shells 30 are then heated to melt the plastic within them to a liquid. Simultaneously, the shells 30 are rotated such that the

liquid plastic flows within the void, under the action of gravity, to coat the entire internal surface of the void. During this process, plastic material flows into the groove 32, eventually to fill it. Once the groove 32 has been filled, plastic then flows over its top to form an essentially continuous base for the container.

It may be that the resulting base 12 is not entirely smooth in the region form which the wall 22 projects (as indicated at 34, in Figure 1). There may even be a cleft in the base 12 that extends some distance into the top of the wall 22. However, it has been found that the volume of such a cleft is sufficiently small that it can fill with mortar without significant addition to the weight of the container.

Short of complete destruction, one of the most significant types of damage that can occur to the container is that its base 12 can be holed. This will, of course, cause the content to leak, necessitating repair of the container. In this embodiment, mortar that leaks cannot become trapped and solidify in any location from which it cannot readily be removed. It has been found that when a container is holed in the base 12 above the void 24 of a foot 20, mortar will leak into the void. If the container is on a smooth surface, some of this mortar can be trapped there and solidify within the void 24. Because the void 24 is tapered as shown in Figure 1, solidified mortar will either fall from the void under its own weight, or with a relatively light tap upon the base 12.

Claims

Claims 1. A container comprising a base and side walls formed as a unitary moulding of plastic material, in which the base includes a generally planar floor portion that constitutes a liquid-supporting floor for the container and a support formation that extends downwardly in normal use from the floor portion, the support formation including a substantially solid wall of plastic material.
2. A container according to claim 1 in which, viewed in plan, the support is formed by a wall that is a closed loop, whereby the support formation forms a void below the floor portion that is open in a downward direction only.
3. A container according to claim 2 in which the void is shaped to have a cross-section that tapers in an upward direction.
4. A container according to any preceding claim in which the support formation is shaped as to be substantially rectangular in plan.
5. A container according to any preceding claim in which the wall of the support formation is formed from plastic material that has been solidified in contact with opposed surfaces of a mould, while the floor portion and side walls are each formed from plastic material that has solidified in contact with a single surface of the mould
6. A container according to any preceding claim which includes several spaced support formations.
7. A container according to claim 6 in which in a space between adjacent support formations, the lowest part of the container is formed by a lower surface of the floor portion that can be used as a lifting surface for the container.
8. A container according to claim 7 in which the support formations are dimensioned and spaced to form several such lifting surfaces spaced for engagement with suitable lifting apparatus, such as a fork lift.
9. A container according to any preceding claim being a moulding of polyethylene, of preference, linear low-density polyethylene (LLDPE).
10. A container according to claim 9 being a rotational moulding.
11. A container according to any preceding claim in which planar parts of the moulding may have a thickness in the range of 7 mm to 11 mm.
12. A container according to any preceding claim having a capacity of between 100 and 300 litres.
13. A container according to claim 12 having a capacity of 200 or 250 litres.
14. A container according to any preceding claim being a container for mortar.
15. A container according to claim 14 being suitable for measuring a quantity of mortar in a commercial transaction, and for subsequent storage of mortar for use on a construction site.
16. A container substantially as described herein with reference to the accompanying drawings.
17. A method of making a container, for example a container according to any preceding claim, in which method fused plastic material is caused to flow within a mould, whereby the side walls and floor portion are formed by plastic material deposited in contact a single surface of the

mould, and the wall of the support formation is formed by plastic material deposited in contact with two opposed surfaces of the mould.
18. A method according to claim 17 in which the wall of the support is formed within a groove of a mould.
19. A method according to claim 18 in which the side walls and the floor are each formed by solidifying material against a single surface of the mould.
20. A method according to claim 19 in which the plastic material is caused to flow from the single surface into the groove.
21. A method of making a container substantially as herein described with reference to the accompanying drawings.

21. A method according to claim any one of claims 17 to 20 in which the plastic material used in this aspect of the invention is polyethylene.

22. A method according to any one of claims 17 to 21 in which the moulding process is a rotational moulding process.

23. A method according to any one of claims 17 to 22 in which the moulding process is one in which flow of plastic material is caused principally or entirely by the action of gravity.

24. A method of making a container substantially as herein described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows Claims 1. A rotationally moulded mortar tub comprising a base and side walls formed as a unitary moulding of plastic material, in which the base includes a generally planar floor portion that constitutes a liquid supporting floor for the container and a support formation that extends downwardly in normal use from the floor portion, the support formation including a substantially solid wall of plastic material, there being no volume enclosed by the moulding below the floor within which mortar can accumulate to cause significant addition to the weight of the container.

2. A mortar tub according to claim 1 in which, viewed in plan, the support is formed by a wall that is a closed loop, whereby the support formation forms a void below the floor portion that is open in a downward direction only.

3. A mortar tub according to claim 2 in which the void is shaped to have a cross-section that tapers in an upward direction.

4. A mortar tub according to any preceding claim in which the support formation is shaped as to be substantially rectangular in plan.

5. A mortar tub according to any preceding claim in which the wall of the support formation is formed from plastic material that has been solidified in contact with opposed surfaces of a mould, while the floor portion and side walls are each formed from plastic material that has solidified in contact with a single surface of the mould 6. A mortar tub according to any preceding claim which includes several spaced support formations.

7. A mortar tub according to claim 6 in which in a space between adjacent support formations, the lowest part of the container is formed by a lower surface of the floor portion that can be used as a lifting surface for the container.

8. A mortar tub according to claim 7 in which the support formations are dimensioned and spaced to form several such lifting surfaces spaced for engagement with suitable lifting apparatus, such as a fork lift.

9. A mortar tub according to any preceding claim being a moulding of polyethylene, of preference, linear low-density polyethylene (LLDPE).

10. A mortar tub according to any preceding claim in which planar parts of the moulding may have a thickness in the range of 7 mm to 11 mm.

11. A mortar tub according to any preceding claim having a capacity of between 100 and 300 litres.

12. A mortar tub according to claim 11 having a capacity of 200 or 250 litres.

13. A mortar tub according to any preceding claim being suitable for measuring a quantity of mortar in a commercial transaction, and for subsequent storage of mortar for use on a construction site.

14. A mortar tub substantially as described herein with reference to the accompanying drawings.

15. A method of making a mortar tub according to any preceding claim, in which method fused plastic material is caused to flow within a mould in a rotational moulding process, whereby the side walls and floor portion are formed by plastic material that is deposited in contact a single surface of the mould, and the wall of the support formation is formed by plastic material deposited in contact with two opposed surfaces of the mould.

16. A method according to claim 15 in which the wall of the support is formed within a groove of a mould.

17. A method according to claim 16 in which the side walls and the floor are each formed by solidifying material against a single surface of the mould. 18. A method according to claim 17 in which the plastic material is caused to flow from the single surface into the groove.

19. A method according to claim any one of claims 15 to 18 in which the plastic material used is polyethylene.

20. A method according to any one of claims 15 to 19 in which the moulding process is one in which flow of plastic material is caused principally or entirely by the action of gravity.