AU2016203935B2

AU2016203935B2 - Improvements to tank construction and methods of manufacture

Info

Publication number: AU2016203935B2
Application number: AU2016203935A
Authority: AU
Inventors: Peter John Snelling
Original assignee: THIN TANKS Pty Ltd
Current assignee: THIN TANKS Pty Ltd
Priority date: 2016-06-10
Filing date: 2016-06-10
Publication date: 2018-02-08
Anticipated expiration: 2036-06-10
Also published as: NZ721162A; ZA201604064B; AU2016203935A1

Abstract

A mould suitable for plastics moulding, the mould including a front surface, a back surface, and inwardly projecting hollow cylinders, each inwardly projecting hollow cylinder having a fluid sealed within the hollow section, the fluid being capable of absorbing heat from an external source and vapourisng so that on heating of the mould the fluid is heated to provide an even heating across an outer surface of the inwardly projecting hollow cylinders. 0 01l> n4ur

Description

FIELD OF THE INVENTION

This invention relates primarily to the manufacture and configuration of water tanks, in particular rectangular thin tanks for domestic water storage where the thin tank is designed to fit in confined spaces or adjacent to a structure with minimal intrusion into the surrounding area. In such rectangular tanks there has long been a problem of the vertical sides of the tank bowing outwards under the pressure of the static vertical water column as well as being able to provide a thin tank that has aesthetic appeal.

DESCRIPTION OF THE PRIOR ART

Rotational moulding is cycling process where polyethylene or other appropriate materials are placed inside a rotational mould as a powder. The mould is then heated to the desired temperature, the powder melts and, due to the rotational movement of the mould, the melted polyethylene forms an even coat over the internal surface of the mould. The process is made up of essential four steps: mould charging, mould rotation, mould cooling and removing the product from the mould.

The internal surface of the rotational mould must all be at the same temperature so as to obtain an even distribution of the melted polyethylene over the internal surfaces. Failure to provide an evenly heated surface of the mould can result in imperfections in the structure thus compromise the integrity of the product. As such, manufacturers of such products take positive steps to ensure complete heating of the mould surfaces.

Moulding thin tanks is a more difficult task, as it requires the structural inclusion of connections between the two vertical faces of the tank.

This can be done by including large holes between the two vertical faces, sufficiently large enough so as to allow hot air to circulate across the surface of the mould connecting the two faces in order to achieve the desired surface temperatures of the mould that allows the even distribution of the melted polyethylene material.

However the resulting product obtained from such a process contains visible holes or openings in the vertical face of the tank, which is not always desirable.

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In the alternative, stiffening features called “kiss-offs” can be incorporated into the mould and are created by using a inwardly projected cone formation on the inner surfaces of the mould, which causes the two walls of the part being moulded to be linked to each other. However, in the production of thin walled structures a kiss-off can be problematic to work with. In the moulds for thin walled structures, such as a thin thank, the inward projections are relatively small and are difficult to keep at the desired temperature as they are not directly in contact with the heated air. This results in uneven heating and cooling of the projections during the heating and cooling steps, requiring longer heating times to ensure the projections are heating to the required temperature, which results in increased production times for the product.

Additionally, a kiss-off is can be formed as an “almost” kiss-off where there is a slight gap between the two walls of the kiss-off. This approach addresses the issue that can be seen in some products where there is a slight blemish on the outer wall of the product but still retains most of the strength of the product as the opposite wall does not have to flex too far before the opposite kiss-off supports it.

However, this process is not applicable to thin walled tanks for holding liquids as the pressure comes from within the tank, forcing the walls and any “almost” kiss-offs away from each other. The only practical way to use a kiss-off for a thin tank is to ensure that the wall of the kiss-off is in contact with the opposing wall and this then creates an outer wall of the thin tank that has a series or blemishes or surface imperfections, which can look unsightly.

OBJECT OF THE INVENTION

It is an object of the present invention to overcome, or at least substantially ameliorate, the disadvantages and shortcomings of the prior art.

Other objects and advantages of the present invention will become apparent from the following description, taking in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.

SUMMARY OF THE INVENTION

According to the present invention, although this should not be seen as limiting the invention in any way, there is provided a mould for a tank, the mould including a front surface, a back surface, a plurality of inwardly projecting hollow cylinders, each inwardly projecting hollow

2016203935 10 Jun2016 cylinder having a fluid sealed within, the fluid being capable of absorbing heat from an external source so that on a heating of the rotational mould the fluid is heated to provide an even heating across an outer surface of the inwardly projecting hollow cylinders.

In preference, each inwardly projecting hollow cylinder is substantially cone shaped.

In preference, the plurality of inwardly projecting hollow cylinders are located on an inner front surface and an inner back surface of the mould.

In preference, the plurality of inwardly projecting hollow cylinders are arranged in pairs.

In preference, the plurality of inwardly projecting hollow cylinders are arranged in pairs aligned with one another.

In preference, the inwardly projecting hollow cylinders hollow are cone shaped.

In preference, the inwardly projecting hollow cylinders are heat pipes

In preference, the fluid is water.

In preference, the mould is a rotational mould.

In preference, the tank is a water tank.

In preference, the water tank is a vertical water tank.

In preference, the vertical water tank is a slimline water tank or thin water tank.

In preference, the vertical water tank is a rectangular water tank.

In preference, the inwardly projecting hollow cylinders are partially filed with a liquid.

In preference, the liquid is water.

In preference, the inwardly projecting hollow cylinders are sealed to create a sealed inner chamber.

A rotationally moulded plastic tank having a main comportment bounded by a bottom wall, a front wall having a plurality of inwardly projecting protrusions, a back wall having a plurality

2016203935 10 Jun2016 of inwardly projecting protrusions and a top wall, wherein the inwardly projecting protrusions of the front wall and back wall are joined to one another.

In preference, the inwardly projecting cylinders of the front wall and back wall are integrally joined to one another during a moulding process.

In preference, the inwardly projecting protrusions are cone shaped.

In preference, the inwardly projecting protrusions of the front wall and back wall are joined to one another to provide support against deflection of the front wall and back wall relative to one another.

When the mould of the present invention is removed from the oven, the temperature of the mould must be reduced significantly so as to extract a solidified product and then reheated with a new load of polyethylene powder. During this cooling and reheating cycle, the connector (inwardly projecting hollow cylinders or heat pipes) remains at an elevated temperature with regards to the other internal surfaces of the mould. This temperature will remain above 100°C until the pressure within the sealed connector reduces sufficiently so as to allow the water to condense.

In this invention, the hollow cores within which a small volume of fluid, such as water although other fluids can be utilised as required, is sealed are just less than half the width separating the two vertical walls. The core half length connectors do not touch in the middle of the tank, but rather leave a small gap which seals with polyethylene and thereby closes what would otherwise be a visual hole through the tank.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example, an embodiment of the invention is described more fully hereinafter with reference to the accompanying drawings, in which:

Figure 1 is an embodiment of the tank of the present invention.

Figure 2 is a top view of the tank of figure 1.

Figure 3 is a front side view of figure 1.

Figure 4 is a side section view of figure 3 along section B-B.

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Figure 5 is a cross section view of figure 3 along section C-C

Figure 6 is perspective cross section view of figure 3 along section B-B.

Figure 7 is a perspective view of the cross section of figure 2 along section A-A showing the inside surface of the back wall.

Figure 8 is a cross section view of a mould for the tank of the present invention.

Figure 9 is an enlarged view of section D from figure 9.

DETAIFED DESCRIPTION OF THE INVENTION

Figure 1 shows a preferred embodiment of the present invention. In this preferred embodiment there is a water tank 10 having a front wall 12 and an opposing back wall 14. Focated on both the front wall 12 and the back wall 14 are a series of spaced apart vertical channels 18 extending from the top wall 20 to the bottom wall 24. These vertical channels 18 provide additional support to the structure of the tank 10. On the sides 26 of the tank 10 are series of spaced apart horizontal channels 28, which provide support against horizontal and vertical flexing of the main tank. Openings 30 are located on the top wall 20. Other openings may be incorporated into the tank 10 as required and dictated by intended use.

In figure 2 the front wall 12 shows the spaced apart vertical channels 18 with spaced apart openings 40 arranged in line within the vertical channel 18. These openings 40 (40a - 40g) are spaced apart at increasing distances from one another so that the distance between opening 40a are and 40b is less than the distance between the openings 40f and 40g.

In this way, the openings 40 at a lower area 50 of the tank 10 are closer together then the openings in the upper area 52. This configuration provides increased strength where is needed most, towards the lower area 50 of the tank 10 where the pressure from the vertical column of water is greatest compared to the upper area 52. This orientation of the openings 40 also provides for the most economical use of material.

Figure 3 shows the cross sectional view of figure 2 with the tank 10 and the front wall 12 and back wall 14 with the plurality of openings 40a-40h on the front wall 12 each of which is opposite an opening 42a - 42h on the back wall 14.

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The openings 40 and 42 extend substantially into the main chamber 13 of the tank 10 to provide a front and rear hollow cones. The cylinders 45 on the front face 12 terminate at the base 60. On the back wall 14, the opposite openings 42 also extend inwardly to form cylinders 46 which terminate in the base 62. This results in an annular support portion 64, which is a substantially vertical rib section in Figure 4, between the two cylinders 45 and 46 on the front and back walls 12 and 14 respectively.

The support portions 64 are integrally formed during the moulding process of the tank 10 and are not thermally welded nor spin welded. The meeting of the cylinders 45 and 46 results with the support portion 64 results in a structural element or connector that spans from the inner surface of the front wall 12 to the inner surface of the back wall 14 providing substantial support across the width of the tank. This greatly increases the structural integrity of the sides of the tank to resist the outward pressure on the inner sides of the tank by the pressure of the water column. The strength of the water tank 10 is further enhanced by arranging the support portions 64 closer together at the lower area 50 of the tank 10.

If desired, for aesthetic purposes, the openings in the front and back walls (12 and 14) can be sealed by the insertion of face plugs.

The moulding element 100 to mould the tank 10, includes a front wall 110 having an inner surface 115, a back wall 120 with an inner surface 125. A top section 117 and a bottom section 118 complete the mold 100 form.

Projecting from the inner surface of the mould 100 is a plurality of inwardly extending heat transfer projections (130a-130g and 132a-132g), often referred to as heat pipes.

The heat transfer projections 130a-g and 132a-g are hollow 134 and are filled with a liquid, such as water, and sealed within so that when heat is applied to the surfaces 115 and 120, the fluid also heats up and transfers the heat from the surfaces 115 and 120 along the heat transfer projections 130a-g and 132a-g, in an even manner, right to the surfaces of each of the projections 131 and 133. As the heat transfer projections 130a-g and 132a-g (heat pipes) heat up, the water within the interior also heats up, and can reach temperatures in excess of the boiling point of the fluid, thus resulting in the fluid vapourizing to a gas, which increases the pressure inside the heat transfer projections 130a-g and 132a-g.

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The liquid inside the hollow sections 134 of the heat transfer projections 130a-g and 132a-g are sealed in that they are not in any fluid communication with an outside source of liquid, as regular heat pipes used in the moulding industry are. The hollow section 134 of the present invention have a liquid inside and are partially fdled so as to have an air space although that space may be fdled with a gas, such as an inert gas, so as to provide space for the formation of the vapour.

When the mould cools down, the gas inside the heat transfer projections 130a-g and 132a-g can condense back to a liquid state and thus the stored energy in the form of the elevated temperature of the vapour and the associated high pressure from the vapourisation (expansion) of the liquid is released.

This then ensures that the heat transfer projections 130a-g and 132a-g are evenly heated during the moulding process and also then at the cooling phase, these sections of the mould are able to retain a portion of the heat, when the formed product 10 is removed during the cooling cycle, so as to reduce the amount of time required to get the mould back up to working temperature for forming the next product.

This differs then to known heat pipes in which may be constructed from a solid material that is in direct contact with a circulating liquid, such a circulating water flow through a section of the mould. Such moulds are complex to produce and thus expensive.

The heat transfer projections 130a-g and 132a-g are arranged in a grid pattern so that the heat transfer projections 130a-g on the inner surface 115 of the front wall 110 are substantially mutually aligned with the heat transfer projections 132a-g on the inner surface 125 of the back wall 120. The heat transfer projections 130 and 132 extend outwardly from the respective inner walls but do not contact one another. The ends 131c and 133c of the heat transfer projections are adjacent one another leaving a small gap 140 between them. This then allows fluid plastic material to flow between the ends 132a and 132b to allow the formation of the support portion 64 in the tank 10.

This ensures that the support portions 64 are formed in the strongest manner so that the structural integrity of the front and back wall of the tank is in no way compromised. This contrasts those tanks or containers of the prior art that have internal support structures that consist of either inwardly projecting indentations that abut one another or by employing

2016203935 10 Jun 2016 standard known kiss-offs that result in the formation of blemishing of a surface of the tank or container. In addition, the heat transfer projections as described may be readily incorporated into any mould as required by those skilled in the filed, without the need for expensive time consuming mould construction that required water channels throughout the mould.

Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures can be made within the scope of the invention, which is not to be limited to the details described herein but it is to be accorded the full scope of the appended claims so as to embrace any and all equivalent devices and apparatus.

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Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A mould, the mould including a front wall with an inner surface, a back wall with an inner surface, a top section and a bottom section, each of the inner surfaces having a plurality of inwardly projecting hollow cylinders, each inwardly projecting hollow cylinder having a fluid sealed within, the fluid being capable of absorbing heat from an external source and vapourisng so that on heating of the mould the fluid is heated to provide an even heating across an outer surface of the inwardly projecting hollow cylinders.
2. The mould of claim 1, further characterised in that each inwardly projecting hollow cylinder is substantially cone shaped.
3. The mould of claim 2, further characterised in that the plurality of inwardly projecting hollow cylinders are located on an inner front surface and an inner back surface of the mould.
4. The mould of claim 3, further characterised in that the plurality of inwardly projecting hollow cylinders are arranged in pairs.
5. The mould of claim 4, further characterised in that the plurality of inwardly projecting hollow cylinders are arranged in pairs aligned with one another.
6. The mould of claim 5, further characterised in that the inwardly projecting hollow cylinders are cone shaped.
7. The mould of any one of claims 1-6, further characterised in that the inwardly projecting hollow cylinders are heat pipes.
8. The mould of claim 1, further characterised in that the fluid is water.
9. The mould of any one of claims 1-6, further characterised in the mould is a rotational mould.
10. The mould of claim 9, further characterised in that the mould is for a tank.
11. The mould of claim 10, further characterised in that the tank is a water tank.

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12. The mould of claim 11, further characterised in that the water tank is a vertical water tank.
13. The mould of claim 12, further characterised in that the vertical water tank is a slimline water tank or thin water tank.
14. The mould of claim 13, further characterised in that the vertical water tank is a rectangular water tank.
15. The mould of claim 4, further characterised in that the plurality of inwardly projecting hollow cylinders arranged in pairs have ends that are adjacent to one another with a gap there between.
16. The rotationally moulded plastic tank of claim 15 produced by the mould any one of claims 1-15.

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