WO2005084912A1

WO2005084912A1 - Method of producing a boiler comprising a perforated reinforcing by rotational moulding

Info

Publication number: WO2005084912A1
Application number: PCT/IB2004/002479
Authority: WO
Inventors: Marius Deon Smit
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-02-03
Filing date: 2004-08-03
Publication date: 2005-09-15
Anticipated expiration: 2006-08-03
Also published as: AP1868A; AP2005003235A0

Abstract

The invention concerns a method of producing a thermoplastic boiler (26). The method includes the steps of providing a perforated reinforcing (10) and locating the perforated reinforcing in a mould (14), an outer surface of the perforated reinforcing and an inner surface of the mould defining a moulding cavity (18). A thermoplastic material is placed inside the mould whereafter it is heated and moulded by way of rotational moulding. First an outer thermoplastic layer (20) is moulded inside the moulding cavity whereafter an inner thermoplastic layer (22) is moulded on an inner surface of the perforated reinforcing. The invention extends to a thermoplastic moulded product produced by the method, in particular a boiler for heating water.

Description

METHOD OF PRODUCING A BOILER COMPRISING A PERFORATED REINFORCING BY ROTATIONAL MOULDING

BACKGROUND TO THE INVENTION

THIS invention relates to a method of producing a thermoplastic product. In particular the invention is concerned with a method of producing a thermoplastic boiler.

Water for household use is normally heated in a boiler which is invariably installed between the ceiling and the roof of a house. Cold water is supplied to the boiler from the main water supply of the house where it is heated with an electrical element located inside the boiler. The electrical element is connected to a control system which monitors temperature conditions inside the boiler and allows electrical current to flow through the element in response to temperature measurements taken. From the boiler the water is supplied to a hot water tap through a plumbing network.

Traditionally boilers have been produced from steel. Unfortunately steel boilers are prone to rust and corrosion and as a consequence have to be replaced after only a few years of service. As boilers are relatively expensive items it would be beneficial if the lifetime of a boiler could be extended.

It has been proposed to produce boilers from thermoplastic materials, thermoplastic being better adapted to withstand the corrosive effects of water. Such thermoplastic boilers did not however exhibit the required strength and were not a commercial success.

It is an object of the invention to address the above problems. SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a method of producing a thermoplastic product comprising the steps of: providing a perforated reinforcing; locating the perforated reinforcing in a mould, an outer surface of the perforated reinforcing and an inner surface of the mould defining a moulding cavity; placing a thermoplastic material inside the mould; heating and moulding the thermoplastic material by way of rotational moulding; moulding an outer thermoplastic layer inside the moudling cavity; and moulding an inner thermoplastic layer on an inner surface of the perforated reinforcing.

Advantageously the method of producing a thermoplastic product includes the step of cooling the mould while the mould is rotating.

Preferably the perforated reinforcing is a hollow container having a plurality of perforations spaced over its surface. Typically the container is cylindrical in shape.

According to a second aspect of the invention there is provided a thermoplastic product comprising an inner thermoplastic layer, an outer thermoplastic layer and a perforated reinforcing sandwiched between the thermoplastic layers. Preferably the thermoplastic product is produced by way of rotational moulding.

More preferably the thermoplastic product is enclosed inside a shell.

Typically the shell acts as a mould for moulding the thermoplastic product during a rotational moulding process.

Advantageously the thermoplastic product is produced by rotational moulding polyethylene, polypropylene or a mixture of polyethylene and polypropylene.

Preferably the thermoplastic product is a container.

In a first embodiment of the invention the perforated reinforcing is cylindrically shaped and the thermoplastic material is polyethylene. In this embodiment the thermoplastic product is enclosed in a steel shell thereby to form a boiler for heating water.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the following drawings wherein:

Figure 1 shows a perspective view of a reinforcing for use in a method of producing a thermoplastic product in accordance with the invention;

Figure 2 shows a schematic representation of the reinforcing located inside a mould;

Figure 3 shows a schematic representation of a partially completed thermoplastic product inside the mould; Figure 4 shows a schematic representation of a completed thermoplastic product inside the mould;

Figure 5 shows a schematic representation of a boiler produced in accordance with the invention;

Figure 6 shows a perspective view of a portion of a second embodiment of a reinforcing for use in a method of producing a thermoplastic product of the invention;

Figure 7 shows a partial cross sectional view of a partially completed second embodiment of a thermoplastic product made in accordance with the method of the invention;

Figure 8 shows an exploded perspective view of a portion of the completed second embodiment of the thermoplastic product; and

Figure 9 shows a cross-sectional view of a water inlet valve for use in the second embodiment of the thermoplastic plastic product.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Persons skilled in the field of rotational moulding will be well familiar with the operation of a rotational mould. For ease of reference rotational moulding can be summarised as a moulding process for forming a hollow product which includes the step of rotating a mould while a thermoplastic material is heated. Typically a thermoplastic powder is placed inside a cold rotational mould whereafter the mould is closed and heated in an oven to temperatures of in the region of 260°C. Simultaneously to being heated, the mould is caused to rotate on vertical and horizontal axes. During rotation, the inner surface of the mould is coated with a melted thermoplastic. The mould is subsequently cooled to allow the melted thermoplastic to solidify in a desired shape. Finally rotation is ceased, the mould is opened and the thermoplastic product removed.

An advantage of rotational moulding is that products are produced without pressure being applied thereto during the moulding process. This feature leads to products which are free of internal stresses and the associated problems which are often exhibited by products produced by way of injection moulding.

Figure 1 shows a perspective view of a reinforcing for use in a method of producing a thermoplastic product in accordance with the invention, generally indicated with the reference numeral 10. The reinforcing 10 of the present embodiment is generally in the form of a cylindrical steel container having two closed ends. The diameter of the reinforcing 10 is 475mm but it will be appreciated that this dimension could vary. As shown the cylindrical container has been perforated to have a plurality of perforations 12 spaced along its surface, the comparative size of the perforations relative to the container being exaggerated in Figure 1. The purpose of the perforations 12 will be explained below.

The reinforcing 10 comprises a body portion 11 to which two end portions 13.1 and 13.2 are welded at lines 15.1 and 15.2. A hot water outlet valve 30 and a safety valve 32 are connected to the end portion 13.1 while a water inlet valve 28 and an element socket 34 are secured to the end - portion 13.1. These connections are effected by way of welding. The operation of the water inlet valve 28, the hot water outlet valve, the safety valve 32 and the element socket 34 will be discussed below.

Although mention is made that the reinforcing depicted in the drawings is cylindrical in shape, it will be appreciated that a range of shapes could be employed.

In Figure 2 the perforated reinforcing 10 is shown located inside a mould 14. The mould 14 of this embodiment is an outside shell of a boiler which is to be used to heat water for domestic use in a house. Typically the mould will be produced from steel and will have a thickness of either 1.6mm or 2mm. The reinforcing 10 is secured to the inside surface of the mould 14 with suitable fasteners 16, in this embodiment bolts are used. A mould cavity 18 is formed by the space defined between the inside surface of the mould 14 and the outside surface of the perforated reinforcing 10. Due to the fact that the length of the fasteners 16 can be adjusted, the dimensions of the mould cavity 18 can as a result also be adjusted.

As is the case with a conventional rotational moulding process, a thermoplastic material 19 is placed inside the mould 14 whereafter the mould is closed and placed inside an oven, not shown. The oven is heated to temperatures in the region of 260°C. Simultaneously to being heated in the oven, the mould is rotated on vertical and horizontal axes. While the thermoplastic is heated, it will melt and become a liquid which can flow through the perforations 12 of the perforated reinforcing 10. Due to the rotation of the mould 14 the melted thermoplastic is allowed to fill the mould cavity 18 thereby to coat the inner surface of the mould 14 on one side and the outer surface of the perforated reinforcing 10 on the other side. This is illustrated in Figure 3 of the drawings.

Once the mould cavity 18 is filled with molten thermoplastic material, the remaining thermoplastic material coats the inside of the perforated reinforcing 10, the rotation of the mould 14 allowing an equal distribution of thermoplastic material. This is illustrated in Figure 4 wherein the thermoplastic material in the mould cavity 18 is shown to form an outer thermoplastic layer, indicated with the reference numeral 20, while the thermoplastic on the inside of the perforated reinforcing 10 forms a inner thermoplastic layer 22. The mould 14 is subsequently cooled to allow the thermoplastic layers 20 and 22 to solidify, whereafter rotation is stopped and the completed thermoplastic product removed from the oven.

Figure 5 shows a side view of a completed boiler 24 which comprises a shell, provided by the mould used during the rotational moulding process, which encloses a thermoplastic product generally indicated with the reference numeral 26. The thermoplastic product 26 comprises the outer and the inner thermoplastic layers 20 and 22, with the perforated reinforcing 10 sandwiched therebetween. In this embodiment of the invention the thermoplastic product 26 provides a protective cover for protecting the inside of the mould 14 against the corrosive action of water which is boiled in the boiler 24. It should be noted that the perforated reinforcing 10 will. deter the thermoplastic layers 20 and 22 from contracting and being placed under pressure due to internal material stresses.

As shown in Figure 5, the boiler 24 comprises the water inlet valve 28 for filling the boiler with water which is to be heated and the hot water outlet 30 from where heated water can be supplied to a hot water tap in a plumbing network. The boiler 24 further comprises the safety valve 32 which allows the boiler 24 to breath in order to prevent an uncontrolled escalation of pressure therein. The boiler 24 also includes an electrical element, not shown, for heating water inside the boiler 24. Electricity is supplied to the electrical element via the element socket 34. Finally the boiler 24 also includes a number of feet 36 allowing the boiler 24 to be placed securely on flat surfaces.

Figures 1 to 5 of the drawings show that the water inlet valve 28, the hot water outlet valve 30, the safety valve 32 and the element socket 34 comprise elongate tubes. Figure 6 shows a portion of a reinforcing 50 for use in a second embodiment of a thermoplastic product of the invention comprising a water inlet valve 52 and an element socket 54. In this embodiment both the water inlet valve 52 and the element socket 54 includes a flange 56 which is shaped as shown and includes a passage 57. Each flange further has holes 60 therein for receiving connecting members 58. Each connecting member 58 includes a recess 62, the purpose of which will be explained below.

Figure 7 shows a partially completed thermoplastic product 64 wherein the reinforcing 50 is enclosed between an outer thermoplastic layer 66 and an inner thermoplastic layer 68. During moulding an outer skin 70 is formed which covers the passage 57 and the holes 60. The passage 57 and the holes 60 are however easily re-opened by removing unwanted thermoplastic of the outer skin 70 with the use of a drill. Each flange 60 can hereafter receive a cover plate 72. Each cover plate 72 comprises a projecting portion 74 which is sized for sliding into the passage 57. In use a fluid seal 76 will be placed between the flange 56 and the cover plate 72. To secure the cover plate 72 to the flange 56, bolts 78 are provided having threaded portions 80 which can be received in the recesses 62 of the connector members 58 which in turn are located in the holes 60.

The assembled water inlet valve 52 is shown in Figure 9. This configuration provides a tight seal and prevents liquid which are stored in an operational thermoplastic product from leaking. Although not shown in will be appreciated that the tubes of the hot water outlet 30 and the safety valve 32 may be replaced with configurations as described directly above.

It will be appreciated that a range of thermoplastic products could be produced by way of a rotational moulding process in accordance with the present invention wherein the moulded thermoplastic product is removed from the mould. One example of such a thermoplastic product would be to produce a filter for a pump of a swimming pool which comprises an outer and an inner thermoplastic layer with a perforated reinforcing sandwiched therebetween.

A boiler comprising a thermoplastic product in accordance with the present invention addresses the problems highlighted in the background portion of the specification.

Claims

1. A method of producing a thermoplastic product comprising the steps of: providing a perforated reinforcing; locating the perforated reinforcing in a mould, an outer surface of the perforated reinforcing and an inner surface of the mould defining a moulding cavity; placing a thermoplastic material inside the mould; heating and moulding the thermoplastic material by way of rotational moulding; moulding an outer thermoplastic layer inside the moulding cavity; and moulding an inner thermoplastic layer on an inner surface of the perforated reinforcing.

2. A method of producing a thermoplastic product according to claim 1 wherein the perforated reinforcing is a hollow container having a plurality of perforations spaced over its surface.

3. A method of producing a thermoplastic product according to either claim 1 or claim 2 wherein the thermoplastic product is polyethylene.

4. A method of producing a thermoplastic product according to either claim 1 or claim 2 wherein the thermoplastic product is polypropylene.

5. A method of producing a thermoplastic product according to either claim 1 or claim 2 wherein the thermoplastic material is a mixture of polyethylene and polypropylene.

A thermoplastic product comprising an inner thermoplastic layer, an outer thermoplastic layer and a perforated reinforcing sandwiched between the thermoplastic layers.

7. A thermoplastic product according to claim 6 wherein the inner thermoplastic layer and the outer thermoplastic layer is moulded unto the perforated reinforcing by way of rotational moulding.

8. A thermoplastic product according to claim 7 wherein the thermoplastic product is enclosed inside a shell.

9. A thermoplastic product according to claim 8 wherein the shell acts as a mould during the rotational moulding of the thermoplastic mould.

10. A thermoplastic product according to claim 9 wherein the inner surface of the shell and the outer surface of the perforated reinforcing define a moulding cavity in which the outer thermoplastic layer is moulded.

11. A thermoplastic product according to any one of claims 5 to 10 wherein the thermoplastic layers are of polyethylene.

12. A thermoplastic product according to any one of claims 5 to 10 wherein the thermoplastic layers are polypropylene.

13. A thermoplastic product according to any one of claims 5 to 10 wherein the thermoplastic layers are a mixture of polyethylene and polypropylene.

14. A method of producing a boiler comprising the step of providing a thermoplastic product according to any one of claims 1 to 5.

15. A boiler comprising a thermoplastic product according to any one of claims 6 to 13

16. A method of producing a thermoplastic product substantially as herein described with reference to the illustrated embodiment.

17. A thermoplastic product substantially as herein described with reference to the illustrated embodiment.

18. A method of producing a boiler substantially as herein described with reference to the illustrated embodiment.

19. A boiler substantially as herein described with reference to the illustrated embodiment.