Patent Description:
It is known to use hollow containers made from thermoplastic material for storing a fluid, especially for storing a fuel, on a range of agricultural machines, such as tractors, combines, forage harvesters, and also in construction machines. It is preferable that vehicles of this type carry enough fuel to guarantee uninterrupted operating periods of e.g. <NUM> hours and more before the machine needs to be refuelled. This requires the use of large volume fuel containers. Since the installation space of these machines is limited, fuel containers are often designed to fit closely about the outer contours of the other components of the machines to make the most efficient use of the available space. This results in containers having unique and irregular shapes which may not be inherently stable. Therefore, it is common to reinforce a container with special tension members to increase its stability and prevent bulging of the containers' outer walls. However, these special reinforcements are sometimes difficult to apply. The unique container forms can also result in particular weak points in a container which are difficult to reinforce because they are hard to reach from the outside of the container or because there isn't enough space to reinforce these points. This can result in a reinforcement process which is very time consuming, leading to unacceptable costs.

A common option to achieve a greater stability and to prevent bulging is to use external straps or other tension members like rods or the like, which interact with the outer walls of the container. Use of such external reinforcement is disadvantageous as it takes up more space, which is limited in most cases. Furthermore, external reinforcing requires multiple assembly steps in sometimes hard to reach positions, resulting in a higher manufacturing time and costs. It is also known to locate tension members internally in a container to increase stability. An example of this is shown in European patent application <CIT>, in which tie elements are connected between opposing walls of a metal tank. Incorporating tie elements in the manner described increases the complexity of the manufacturing process and may create a leak point if not properly sealed. All these drawbacks are not desirable.

Where a container is moulded from plastic materials, it is known to integrate a hollow cross-member or tunnel into the container connecting opposing walls. However, if the cross-member is not aligned in the direction of the demoulding, a separate insert is needed. This adds additional manufacturing time and additional tooling costs. A further significant drawback is that such crossmembers reduce the internal volume of the container available for storing fluid.

<CIT> discloses a container of thermoplastic material having a support which extends between and is connected to opposing walls of the container. The support comprises at least one support strut extending between bases located on the opposing container walls. The support strut is operative in compression to support a load induced on the walls by a negative pressure in the container. A tensile force induced by positive pressure in the container is absorbed by at least one tension-resistant bracing element, which also extends between the opposed container walls. The tension-resistant bracing element is formed as a continuous band which is laced over holding brackets at the bases to pre-stress the bases against the support strut. This reinforcing arrangement is complex resulting in a time consuming and difficult manufacturing process. The use of internal struts in the form of hollow tubes reduces the internal volume of the container.

An older patent application <CIT> discloses a flexible gas container for motor vehicles, whereby the gas container is inflated once a gas is filled into the container. The sides of the container are braced with flexible tension members attached one end to the inner walls. All flexible tension members are connected at their other ends to an annulus of elastic cord. This annulus is stretched when the container is full of gas and imparts tension to the flexible members so as to hold the walls against outward bulging or distortion. The flexible members are preferably designed as stout ropes and are anchored to the inner wall of the container. A disadvantage with this system is that multiple tension members need to be vulcanized inside of the container and simultaneously connected to the annulus. This arrangement is not suitable for application to hollow containers made from thermoplastic material which are not inflatable in the manner described in <CIT>. Furthermore, the number of manufacturing steps to vulcanize multiple tension members inside of a rigid container is impractical, especially since the attachment points may be difficult to reach, for example where the container has an irregular shape.

<CIT> discloses a method of integrating an elongate reinforcing member into a container during moulding. The elongate reinforcing member is attached at its ends to the walls of the mould so that after moulding, the ends of the reinforcing member are incorporated into the walls of the container. The reinforcing element acts at least in tension to resist deformation of the container.

It is an objective of the present invention to provide an alternative method for manufacturing a container from a thermoplastic material which overcomes, or at least reduces, some or all of the limitations of known methods.

It is also an objective of the present invention to provide an alternative method for manufacturing a container from a thermoplastic material which enables internal reinforcement to be incorporated into a container more easily than the known methods.

It is furthermore an objective of the present invention to provide an alternative container made from a thermoplastic material having internal reinforcement which is easier to manufacture than known containers.

In accordance with a first aspect of the present invention there is provided a method of manufacturing a reinforced thermoplastic container, wherein the method comprising providing a mould having at least two mould parts, each mould part having an inner side and an outer side, characterized in that the method comprises:.

The at least one attachment element may comprise a base for attachment to the inner surface of the mould part and bracket to which the tension member is connected. The bracket may be a hook, a clamp, an eyelet or any other device, which is able to hold the tension member in place. More preferably at least the base portion of the attachment element is made from the same or a compatible thermoplastic material as used to form the container body.

In an embodiment, the method comprises use of a securing element to secure the attachment element to the inner side of said at least one mould part. The securing element may be applied to the outer side of the at least one mould part. The method may comprise connecting a base of the attachment element to an end of the securing element, whereby the securing element extends through a wall of a mould part and protrudes beyond in inner surface of the wall.

The securing element may comprise a threaded fastener inserted from outside of said at least one mould part through an aperture in the mould part to engage with a thread on the at least one attachment element. The aperture may be threaded. Alternatively, the securing element may be a safety pin, a magnet, a device with a bayonet connection or another device, which is able to attach the attachment element to the inner side of the mould part and be released from outside of the mould.

The method may comprise rotating the mould about two perpendicular axes in a cardanic fashion to evenly distribute the heated thermoplastic material over the internal surfaces of the mould parts. In other words, the container body may be moulded using rotational moulding techniques. Other methods to distribute the thermoplastic material could also be possible, for example blow moulding. Preferably, the thermoplastic material is distributed evenly on the inner side of the at least two mould parts to form a container with a nearly even wall thickness.

The method may comprise allowing the thermoplastic material to cool after it has been distributed over the inner side of the at least two mould parts to define the body of the container and subsequently detaching the at least one attachment element from the mould part. The method may comprise cooling the mould to allow the thermoplastic material to cool and set.

In an embodiment, the method comprises attaching at least two attachment elements to at least one of the mould parts and connecting the tension member between a plurality of the attachment elements. Preferably, at least one attachment element is attached to each of the at least two mould parts. Preferably, at least two attachment elements are located so as to be positioned on opposing walls of the container body in the completed container.

The tension member may be connected alternately to attachment elements located so as to be attached to opposing sides of the container body in the completed container.

The method may comprise connecting the tension member between a plurality of attachment elements in a meandering pattern.

The tension member can be attached to the attachment element(s) by a material based connection (chemical bond) or without one. If the tension member is attached to the attachment element(s) by a material based connection, then the tension member is preferably created out of the same thermoplastic material as that used to form the container body. In this case, the method can be configured so that the tension member is bonded to the attachment elements during distribution of the heated thermoplastic material. However it is also possible that the tension member is made from another suitable material and is connected attached to the attachment elements in a different way, for example by gluing. Alternatively the tension member can be mechanically connected to the attachment element(s) for example by pulling it through an eyelet, by hooking it up or any other way. Where at least some of the attachment elements are in the form of eyelets or hooks, the tension member may be fixed at its ends and passed through a series of attachment elements in succession so that it is held in tension between each consecutive pair of attachment elements in the series. Ends of the tension member may be secured together to form a closed loop and hold the tension member in tension. Alternatively, at least one end may be secured to a first attachment element. The other end may also be secured to an attachment element, which may be a different attachment element to the first attachment element, or it may be secured to another part of the tension member or to some other fixture in the container body.

In an embodiment, the tension member is initially connected to the attachment elements while the mould parts are still open. At least one end of the tension member is then led to the outside of the mould parts to be tensioned and fixated. Preferably, the at least one end is led out of the mould a point which defines part of the container which is not visible during the normal operation of the container. The tension member can be led to the outside of the mould for example between the edges of the mould parts which come in contact with each other once the mould parts are closed and the mould cavity is formed, or by extending through a wall of one of the mould parts, e.g. through an aperture in the mould part. In an embodiment, both ends of the tension member are led to the outside so a closed loop can be formed by connecting the two ends. After one or both ends of the tension member have been secured in position outside the mould, the mould parts are closed and the moulding process begins. This arrangement can be used for example if only two opposing walls are to be secured against bulging. In this case, only one attachment element is needed on a first side. The tension member is attached to this attachment element and both ends of the tension member extend on the other side through a wall of the mould. There they are tensioned and fixated. After the container body is removed from the mould, the ends of the tension member may be permanently secured together outside of the container body to hold the tension member in tension or the ends may become fused as part of the opposing wall of the container. Therefore it is possible to reinforce the container with only one attachment element, but in most cases multiple attachment elements are used.

Various ways to fixate the at least one end of the tension member outside of the mould parts are possible, for example using a clamp or any other suitable device.

The method may comprise tensioning the tension member. The tension member may be tensioned before or after moulding the container body.

The tension member may be made from the same or a compatible thermoplastic material as is used to form the container body. In which case, the method may be configured such that during moulding of the container body, the at least one tension member becomes fixed to each of the attachment elements by a chemical bond.

The method may comprise locating at least one end of the tension member outside of the mould prior to moulding of container body. The method may comprise tensioning the tension member and securing said at least one end outside of the mould prior to moulding the container body.

The method may comprise tensioning and fixing the tension member within the mould cavity prior to moulding the container body. In an embodiment, at least one of the mould parts comprises a port having an openable closure member, the method comprising accessing the mould cavity through the port after the mould parts have been brought together in order to tension and fix the tension member within the mould cavity.

In an embodiment, the method comprises distributing thermoplastic material on the tension member and the at least one attachment element to form at least one cross brace within the body of the container.

The at least one tension member is preferably flexible in a tension free state. The at least one tension member may be a tension rope.

Whilst at least one tension member is used, depending on the container design multiple tension members can be used. It is also possible to connect multiple tension members to the same attachment element.

The attachment elements are preferably located at specific positions so that in the finished container the attachment elements and tension member define an internal spatial tension structure which inhibit the container walls from bulging outwardly due to a positive internal pressure. These positions are for example possible weak points of the container, where the risk of bulging is higher. For example, these positions may be located at widespread sidewalls of the container having a low material stress, such as the middle of a widespread side wall. Therefore a stable container can be created, which doesn't require time consuming actions to install conventional reinforcing devices afterwards and whereby the tension members only require a very small volume.

In accordance with a further aspect of the invention, there is provided a reinforced thermoplastic container for storing a fluid, whereby the container is manufactured according to the method of the first aspect of the invention such that the least one attachment element is integrally moulded into a wall of the container body.

The container may be a fuel tank for an agricultural machine such as a tractor.

A major advantage of the invention is the ability to easily and inexpensively add additional reinforcement for a container by modifying an otherwise already finished moulding in a late stage of the development process.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which.

<FIG> shows a representation of an agricultural machine <NUM>, especially in the form of a tractor. The agricultural machine <NUM> comprises a chassis <NUM>, a cab <NUM>, a front axle <NUM>, a rear axle <NUM> and a hollow thermoplastics container <NUM> for storing a fuel.

The container <NUM> has a main body <NUM> moulded from a thermoplastic material. As illustrated in <FIG>, the container main body <NUM> defines an internal storage volume and an inlet <NUM> to allow access to interior volume. The container body <NUM> can be manufactured using a rotational moulding technique as is well known in the art. Since rotational moulding is a well know method of manufacturing hollow components such as containers from a thermoplastic material the process will not be described in detail. However, briefly, according to the known method a mould <NUM> comprises two or more mould parts 26a, 26b (shown in <FIG>) which can be brought together define a mould cavity <NUM> which defines the desired shape of the container <NUM>. A thermoplastic material is introduced into at least one of the mould parts 26a, 26b. The mould parts 26a, 26b are then closed and the thermoplastic material is heated till it is flowable. The closed mould <NUM> is rotated around two perpendicular axes in a cardanic fashion to evenly distribute the heated thermoplastic material over the internal surfaces <NUM> of the mould parts 26a, 26b. Once the thermoplastic material has been evenly distributed, the mould <NUM> and the thermoplastics material are cooled. Once the thermoplastic material has cooled down and solidified, the mould parts 26a, 26b are opened and the partially finished container body <NUM> is extracted. Initially after moulding the inlet <NUM> is closed and material is cut from the inlet <NUM> to form an opening. The basic process as briefly outlined above can be modified in accordance with any suitable adaptations known in the art.

The container <NUM> as so far described is conventional and for use as a fuel tank on a tractor will typically have a large internal volume and an irregular shape. Such a container <NUM> may have a tendency to bulge outwardly when full if not provided with additional reinforcement. In accordance with the invention, the method of manufacture as described above is modified so as to produce an integrated, internal spatial tension structure <NUM> that gives the container <NUM> stability and prevents, or at least reduces, bulging.

As illustrated in <FIG>, the spatial tension structure <NUM> comprises a number of attachment elements <NUM> integrally moulded into the walls of the container <NUM> and an elongate tension member <NUM> which is connected between the attachment elements <NUM>. The attachment elements <NUM> are distributed about the interior surface of the container <NUM>, with some being located on opposing walls of the container <NUM>. The tension member <NUM> is in the form of a tension rope or cable which is flexible, at least when not in tension. In use, the tension member <NUM> acts in tension where it connects between any two of the attachment elements <NUM> to resist those attachment elements <NUM> from separating along the line of the tension member <NUM>. Where the attachment elements <NUM> are located on opposite (e.g. facing) walls of the container <NUM>, this will help to resist the walls bulging outwardly. As shown most clearly in <FIG>, the attachment elements <NUM> may be in the form of eyelets through which the tension member <NUM> is threaded. A single tension member <NUM> may be used to interconnect all of the attachment elements <NUM>. However, in alternative arrangements, more than one tension member <NUM> can be used.

Attempting to incorporate the spatial tension structure <NUM> as described above into a container <NUM> after moulding would be difficult and could potentially create leakage points where fluid can exit the container <NUM>. To prevent this, the method of manufacture as described above is modified in accordance with an aspect of the invention so that the tension structure <NUM> is at least partially incorporated as an integral part of the container <NUM> as it is moulded.

The modified manufacturing process will now be described with reference to <FIG> and <FIG> in particular.

<FIG> shows a sectional view of a mould <NUM> for producing a container <NUM> using a rotational moulding method. The mould <NUM> has two parts 26a, 26b which each have an inner surface <NUM> and an outer surface <NUM>. The inner surfaces <NUM> of the mould parts define a mould cavity <NUM> when the parts 26a, 26b are assembled together. Prior to the two mould parts 26a, 26b being assembled together, a number of attachment elements <NUM> are secured to the inner surfaces <NUM> of the mould parts 26a, 26b at locations which correspond to the required positions of the attachment elements <NUM> in the completed container <NUM>. Four attachment elements 18a to 18d are illustrated in <FIG> for the purposes of describing the methodology but it should be appreciated that the number and location of the attachment elements <NUM> can be varied as required to provide a desired level of structural stability for any given container design.

As illustrated in an enlarged view in <FIG>, in the present embodiment the attachment elements <NUM> are in the form of eyelets, each having a ring or bracket 19a and a base 19b. The base 19b is in the form of a part cylinder having a central circular recess or bore with an internal thread 19c. An aperture with a matching internal thread <NUM> extends through a wall of the mould part 26a at the position where an attachment element <NUM> is to be located. Each attachment element <NUM> is secured to the inner surface <NUM> of a mould part 26a, 26b by means of a respective releasable fastening <NUM> in the form of a bolt or screw having a head portion and a shank with an external thread 34a. The external thread 34a corresponds to the internal threads 19c, <NUM> of the attachment element <NUM> and aperture. The bolt <NUM> is inserted from the exterior of the mould part 26a and is screwed into the internal thread <NUM> of the aperture until an end of the shank projects beyond the interior surface <NUM> of the mould part where it engages the internal thread 19c of the base 19b of the attachment element. The bolt <NUM> is tightened to securely clamp the base 19b to the inner surface <NUM> of the mould part so that no leakage can occur during moulding.

Other arrangements for releasably securing an attachment element <NUM> to the mould <NUM> can be adopted, such as a bayonet fitting for example. If the material from which the attachment elements <NUM> are made permits, they could be secured in position using magnetic attraction. In this case, a suitable material could be incorporated into the base 19b. The attachment elements <NUM> could also be secured using a non-permanent adhesive or the like or indeed by any other suitable method. A mixture of different methods for securing the attachment elements <NUM> to the inner surfaces of the mould parts can be used. Further, it will be appreciated that the attachment elements <NUM> can take other forms than an eyelet such as a hook or indeed any suitably shaped bracket 19a to which the tension member <NUM> can be connected and tensioned.

Once all the attachment elements <NUM> are secured to the mould parts 26a, 26b and before the mould parts 26a, 26b are fully closed, the tension member <NUM> is connected between the attachment elements <NUM> in a suitable pattern to provide the required structural stability. In the exemplary embodiment illustrated in <FIG>, the four attachment elements 18a, 18b, 18c, 18d are shown arranged generally at the corners of a square, with two 18a, 18c attached to the inner surface of one of the mould parts 26a which will form a first wall of the container and the other two 18b, 18d attached to the inner surface of the other of the mould parts 26b which will form an second wall of the container opposing the first wall. In the example illustrated, a first end of the tension member <NUM> is secured to a first one of the eyelets 18a on a first of the mould parts 26a. The first end of the tension member <NUM> may be bonded to the attachment element <NUM>, secured using a mechanical fastening, tied to the eyelet, or secured in any other suitable manner. The tension member <NUM> is threaded through the remaining eyelets, extending in a lateral direction to an opposing second eyelet of a second attachment element 18b on the opposite mould part 26b, in a diagonal fashion to a third eyelet of a third attachment element 18c on the first mould part 26a, passing in a lateral direction to a fourth eyelet of a fourth attachment element 18d on the second mould part 26b opposite from the third eyelet before passing in a diagonal manner back through the first eyelet. The second end 20a of the tension member <NUM> extends out of the mould <NUM> between the mould parts 26a, 26b where they define the inlet <NUM> so that it locates where a section of the moulded container <NUM> which is to be removed after moulding is to be produced. Once the tension member <NUM> has been attached to all the eyelets and the required thermoplastic material to form the container <NUM> introduced into at least one of the mould parts 26a, 26b, the mould parts 26a, 26b are fully closed. Using the second end region 20a of the tension member <NUM> which protrudes from the mould <NUM>, the tension member <NUM> is stretched to place it in tension and fixed in position using a suitable clamp (not shown). Other components <NUM> which are to be integrated into the moulded container may also be secured to the inner surface <NUM> of one or other of the mould parts 26a, 26b. This might include, for example, metal flanges for holding sensors or withdrawal units and the like.

The container <NUM> is now moulded using known rotational moulding techniques. Briefly, the thermoplastic material is heated until it is flowable. Then the mould <NUM> is rotated in a cardanic fashion around two perpendicular axes so that the heated flowable thermoplastic material is distributed almost evenly over the inner walls <NUM> of the mould parts 26a, 26b so that a hollow container <NUM> having outer walls of a nearly even thickness is formed. During this process, the flowable thermoplastic material will encase at least the base parts 19b of the attachment elements <NUM> but will usually also coat the tension member <NUM> and the eyelets 19a. In an embodiment, at least the base 19b of the attachment elements <NUM> is made of the same thermoplastic material as the container walls, or at least a compatible material, such that the thermoplastic material used to form the walls of the container <NUM> and the attachment elements <NUM> form a chemical bond. The base 19b will effectively melt and form an integral part of the wall of the container <NUM>. Alternatively, the attachment elements <NUM> may be designed so that the thermoplastic material of the container walls forms a mechanical bond with the attachment elements <NUM> as it solidifies. The tension member <NUM> may also be made of the same thermoplastic material as the container walls or a compatible material such that the tension member <NUM> is bonded to the eyelets 19a during the moulding process. After the container <NUM> is moulded and the thermostatic material has cooled, the attachment elements <NUM> and any utility elements <NUM> are detached from the mould parts 26a, 26b by releasing the securing elements <NUM>. The mould parts 26a, 26b can then be separated and the container <NUM> de-moulded. An opening is formed in the inlet <NUM> of the container <NUM> by removing the section of material through which the second end of the tension member extends and the second end region 20a of the tension member <NUM> is trimmed.

The method as outlined above can be modified in various ways.

In one alternative embodiment, the tension member <NUM> is threaded through the eyelets 19a in a loop and both ends passed out of the mould <NUM> at a suitable location where an aperture in the container <NUM> is to be produced after moulding, such as the inlet <NUM>. In this case, both ends of the tension member <NUM> can be used to stretch and tension the tension member <NUM> and secured in place, say by means of a clamp or the like, before the container <NUM> is moulded. After moulding of the container <NUM> is complete, both ends of the tension member <NUM> can be trimmed.

In a further alternative, the tension member <NUM> is not fused or bonded to the attachment elements <NUM> during the moulding process. In this embodiment, the tension member <NUM> may not be fully tensioned prior to moulding the container body <NUM> but tensioned sufficiently that it does not interfere with the moulding process and one or both ends secured outside the mould <NUM>. After moulding of the container body <NUM> is complete, the inlet <NUM> aperture is produced and the tension member <NUM> is fully tensioned and secured in position. Typically, at least one end of the tension member <NUM> will extend through the inlet <NUM> and can be used to stretch and tension the tension member before the tension member is secured in its tensioned state. In this case, part of the tension member <NUM> proximal the free end 20a could be clamped to another portion of the tension member <NUM> inside the container using a suitable clamp or clip or it may be secured to an attachment element <NUM> located near the inlet. If desired, a special attachment element for use in tensioning can be located proximal to the inlet <NUM> for this purpose. If two ends of the tension member <NUM> extend outside of the container body <NUM> through the inlet <NUM>, these may be clamped together once the tension member <NUM> is tensioned so that the tension member <NUM> forms a continuous loop and any excess trimmed.

In a still further embodiment, one or both of the mould parts 26a, 26b is provided with an access port (indicated schematically by broken lines <NUM> in <FIG>) having a flap or other closure member which can be opened to allow access to the interior cavity <NUM> of the mould <NUM> after the mould parts 26a, 26b have been closed together. The access port or ports <NUM> provide access to the tension member <NUM> inside the mould cavity <NUM> so that it can be fully tensioned and secured in its tensioned state. In this embodiment, it may not be necessary for any part of the tension member <NUM> to be fed outside of the mould <NUM>. Once the tension member <NUM> has been tensioned and secured, the access port or ports <NUM> is/are closed and the container body <NUM> is moulded. In this embodiment, the tension member <NUM> may or may not be bonded or fused to the attachment elements <NUM> during moulding of the container body <NUM>. In a further alternative, the tension member <NUM> may be affixed to each attachment element <NUM> using an adhesive or a mechanical fastening prior to moulding of the container body <NUM>. In a still further embodiment, the tension member <NUM> may be elastic and may be stretched into position before the mould parts 26a, 26b are fully closed such that the once the mould parts 26a, 26b are fully closed the tension member <NUM> is still sufficiently tensioned to prevent, or at least reduce, bulging of the container walls.

It is a particular advantage of the method of manufacture according to the invention that the attachment elements <NUM> can be positioned anywhere in the container <NUM> so that possible weak spots of the container <NUM>, e.g. side walls of the container <NUM> with low material stress, can be reinforced precisely. This method enables a fairly complex reinforcing tension structure <NUM> to be produced which could not be introduced into the container <NUM> after moulding. Since the attachment elements <NUM> and the tension member <NUM> are integrated inside of container <NUM> as it is moulded, the time needed for the manufacturing process can be greatly reduced in comparison with the prior art methods of reinforcement.

It is a further advantage that the tension member <NUM> and the attachment elements <NUM> are initially separate, only being connected after the attachment elements are secured to part of the mould. This enables different special tension structures <NUM> to be produced for different containers using standard tension members <NUM> and attachment elements <NUM>. There is no requirement to manufacture a specific tension structure <NUM> for use in a given container. Using the method of manufacture according to the invention, a reinforcing tension structure <NUM> which is precisely adapted to reinforce a container <NUM> of any given shape can be produced. The reinforcing tension structure <NUM> can be as complex or as simple as required.

<FIG> illustrate an exemplary tension structure <NUM> for an L shaped container <NUM> which is relatively long and thin and which would be difficult to reinforce using the conventional reinforcing methods. As illustrated, the tension member <NUM> connects the attachment elements <NUM> in a meandering pattern. In this regard, the tension member <NUM> can be arranged to extend between attachment elements <NUM> in any suitable direction, including laterally across the container <NUM> from one wall <NUM> to another <NUM>, in a diagonal fashion from one wall <NUM> to another <NUM>, or even between attachment elements <NUM> on the same wall. The designer will be able to create a suitable structure <NUM> to reinforce any give container shape in an optimal fashion using known engineering principles.

As can be seen from the illustrations, the attachment elements <NUM> and the tension member <NUM> do not require much space inside of the container <NUM> and so have little impact on the volume of the container <NUM>. This is a big advantage compared to other solutions mentioned in the state of the art.

Whilst it is expected that most containers <NUM> will be provided with at least two attachment elements <NUM> interconnected by a tension member <NUM>. It is possible that the principles outlined above can be adapted to enable a tensioning structure <NUM> be produced using only one attachment element <NUM>. For example, a single attachment element <NUM> may be located on one mould part 26a or 26b where it will become embedded or fused into a wall of the container <NUM>. The tension member <NUM> is attached to the attachment element <NUM> and its ends passed out of the mould <NUM> at a position spaced from the attachment element <NUM> where an opposing wall of the container <NUM> is to be formed. After the container <NUM> is moulded and released from the mould <NUM>, the tension member <NUM> is stretched and tensioned and the ends secured together outside of the opposing wall. The tension member <NUM> will be effective to prevent the walls from bulging. Alternatively, the tension member <NUM> may be fully tensioned prior to moulding and the arrangement configured such that the tension member <NUM> is fused into the wall on the side where it passes out of the mould <NUM>.

The attachment elements <NUM> and the tension member <NUM> can be made from any suitable materials which are suitable for submersion in the fluid to be held by the container <NUM>.

Whilst the method is particularly suitable for use with rotational moulding of the container body <NUM>, it may be adapted for use with other moulding techniques provided the attachment elements <NUM> can be secured inside the mould cavity <NUM>.

Claim 1:
A method for the production of a reinforced thermoplastic container (<NUM>), the method comprising providing a mould (<NUM>) having at least two mould parts (26a, 26b), each mould part (<NUM>) having an inner side (<NUM>) and an outer side (<NUM>), characterized in that the method comprises:
releasably securing at least one attachment element (<NUM>) to the inner side (<NUM>) of at least one of the mould parts (26a, 26b),
subsequently connecting a tension member (<NUM>) to the at least one attachment element (<NUM>),
adding a thermoplastic material onto the inner side (<NUM>) of at least one of the at least two mould parts (26a, 26b),
closing the at least two mould parts (26a, 26b) to produce a mould cavity (<NUM>),
heating the thermoplastic material and
distributing the thermoplastic material at the inner side (<NUM>) of the at least two mould parts (<NUM>) to create a moulded body (<NUM>) of the reinforced container (<NUM>) in which the at least one attachment element is fixedly integrated into a wall of the container body.