WO2020225722A1

WO2020225722A1 - Method of manufacturing a hollow body

Info

Publication number: WO2020225722A1
Application number: PCT/IB2020/054236
Authority: WO
Inventors: Joseph David FRANKLIN; David Gregory BOTHA
Original assignee: Quality Equipment Holdings Limited
Priority date: 2019-05-06
Filing date: 2020-05-05
Publication date: 2020-11-12

Abstract

A method of manufacturing by rotational moulding of a hollow body such as a float for use in aquaculture. The float has a conduit extending through the outer shell with ends bonded to and integral with the outer shell so that the conduit forms an open passageway through the outer shell. The entry parts of the passageway at opposite ends of the float has a wider diameter than the conduit and which smoothly reduces to the diameter of the conduit. The method comprises positioning a preformed conduit within the mould cavity and rotationally moulding the outer shell around the preformed conduit such that the ends of the conduit bonded to and integral with the outer shell but open to the exterior. The radiused entry parts of the passageway reduces wear of ropes.

Description

METHOD OF MANUFACTURING A HOLLOW BODY

FIELD OF THE INVENTION

The invention relates to a method of manufacturing by rotational moulding a hollow body for use as a float particularly but not exclusively for use as a float in aquaculture.

BACKGROUND OF THE INVENTION

Rotational moulding is known and used to manufacture hollow articles of various types, including flotation devices used in the marine industry. Typically, rotational moulding involves heating and rotating the mould until the surface of mould cavity is coated with the plastics moulding material. As the mould cools, the plastics material solidifies and forms the hollow article.

Floats of various shapes and sizes can be manufactured by rotational moulding. Some floats have central passageways extending the length of the float for receiving ropes or cords. Floats having a central passageway are commonly moulded in two halves which are manually welded or bonded together around their circumference to form the complete article. This method is labour intensive and costly.

Mussel floats are used in mussel farming to support mussel cultivation and spat ropes that are suspended from horizontal rope structures that the mussel floats are attached to. Typical mussel floats are large hollow barrel like structures with rope attachment points at each end.

It is an object of the present invention to provide an improved or at least alternative method for manufacturing a hollow article, or to at least provide the public with a useful choice.

SUMMARY OF THE INVENTION

In broad terms, a first aspect of the invention comprises a method of manufacturing by rotational moulding a hollow body, the method comprising the steps of:

positioning a preformed conduit having opposing ends within the mould cavity of an open rotational mould,

closing the mould to contain the preformed conduit including the opposing ends thereof fully within the mould, and rotating the mould and coating the interior surface(s) of the mould cavity and the opposing ends of the preformed conduit with heated liquified moulding material to form an outer shell of the hollow body with the preformed conduit inside the outer shell and with the ends of the preformed conduit bonded to and integral with the outer shell but open to the exterior so that the conduit forms a passageway open at its ends through the hollow body.

In broad terms, a second aspect of the invention comprises a float comprising

a rotationally moulded outer shell,

a conduit extending through the outer shell and having ends bonded to and integral with the outer shell and open to the exterior so that the conduit forms a passageway open at its ends through the float, entry parts of the passageway at opposite ends of the float having a wider diameter than the conduit and which smoothly reduces to the diameter of the conduit.

The term "comprising" as used in this specification means "consisting at least in part of". When interpreting each statement in this specification that includes the term

"comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described with reference to the accompanying drawings, which show one or more embodiments by way of example only, in which :

Figure 1 is a perspective view of an embodiment of a float,

Figure 2 is one side view of the float of Figure 1,

Figure 3 is another side view of the float of Figures 1 and 2,

Figure 4 is a view of one end of the float of Figures 1-3,

Figure 5 is cross-section view along line C-C of Figure 4,

Figure 6 is an enlarged cross-section view of one end of the float,

Figure 7A is a perspective cross-section view of a similar embodiment of the float along line C-C of Figure 4,

Figure 7B is a similar cross-section view of a spherical embodiment of the float,

Figure 8 shows floats of Figures 1 to 7 in use in the vertical configuration, Figure 9A to 9C show the float of Figures 1 to 7 in use in various horizontal

configurations,

Figure 10A is a cross-section view of a rotational mould in the open position,

Figure 10B is cross-section view similar to Figure 10A but with the mould in the closed position, and with a preformed conduit positioned within the mould,

Figure IOC is a cross-section view similar to Figures 10A and 10B but with the mould in the closed position and rotating about an axis, and

Figure 10D is a cross-section view similar to Figures 10A-C but with the mould in the opened position and with the fully formed float.

DETAILED DESCRIPTION

The float

Referring to figures 1 to 7, the float 1 comprises a hollow body having an outer shell 2 and an internal conduit 3. The conduit 3 has opposing ends and extends through the outer shell 2, aligned with the longitudinal axis of the outer shell 2. The ends of conduit 3 are bonded to and integral with the outer shell 2 to form a passageway 4 through the float with ends that are open to the exterior of float 1. At opposite ends of the float are entry parts 5 which have a wider diameter than conduit 3. The entry parts 5 smoothly reduce to the diameter of the conduit 3. In an alternative embodiment, the ends of conduit 3 are closed to the exterior of float 1. The space between the conduit 3 and the outer shell 2 is enclosed and forms an air-tight compartment. The outer shell 3 may be elongate, and have any cross-sectional shape, for example cylindrical or ellipsoidal or square or rectangular. One or both ends of the outer shell 3 may be truncated to form a frustum. The outer shell 2 may be made from any suitable plastic polymer, for example thermoplastic polymers. The outer shell 2 and conduit 3 may comprise the same or different materials.

The conduit 3 may comprise any material or shape but is typically a thermoplastic tubular structure with a constant cross-sectional profile, for example, an extruded high- density polyethylene (HDPE) cylindrical pipe. Referring to figure 5, conduit 3 forms an open passageway 4 through float 1. Figure 6 shows in greater detail section D of figure 5 where the conduit 3 becomes integrally bonded to outer shell 2. Also shown in figure 6 is the entry part 5 of the passageway 4. The entry parts 5 at opposite ends of the float 1 comprises a wider diameter than the conduit 3 and gradually and smoothly reduces to the diameter of conduit 3. The rounded or radiused opening into the passageway 4 reduces wear on ropes. Referring to figures 5 and 6, the conduit 3 is shorter than the length of the float 1. For example, the conduit 3 may be about 1% to about 20% shorter than the length of the float but preferably about 2.5% to about 5% shorter than the length of the float. In other embodiments, the conduit 3 may be substantially the same length as the float 1. The preformed conduit 3 may be about 0.5m to 2m in length but preferably about 0.6m to about 1.5m in length.

The float 1 may comprise a volume/displacement of about 50 litres to about 400 litres but preferably about 100 litres to about 300 litres. The float 1 may also comprise a width-to-length ratio of about 1 :2 to about 1 : 5. The width-to-length ratio may be constant or may vary across the length of the float 1. For example, the widest section of float 1 may comprise a width-to-length ratio of about 1 :2 and the narrowest section of float 1 may comprise a ratio of about 1 : 5.

The outer shell 2 may include one or more formations such as handles and recesses in the float that facilitate a user to hold or manipulate the float 1 or for attaching lashing or ropes. The handle 7 comprises a gripping portion within a recess formed by a cut-out portion near an edge of the outer shell 2. Referring to figure 6, the cut-out extends into the outer shell 2 from one surface to another surface of the outer shell forming a channel between the two surfaces. Alternatively, the cut-out portion may only extend partially into the outer shell 2. As shown in figures 2 and 3, handle 7 is flushed with the surface of outer shell 2 and presents a hydrodynamic or low-drag profile. Recessed portion 8 provides additional means for holding or manipulating float 1. Recessed portion 8 may comprise any suitable shape, for example round, elliptical, or stadium (sausage-shaped). In another embodiment, handle 7 extends horizontally from the outer shell 2 towards an end of the float 1 (not shown). In this embodiment, the handle 7 comprises substantially flat sections (relative to the curved surface of outer shell 2) that advantageously prevents the float 1 from rolling when stored in the horizontal position.

The float 1 may incorporate one or more reinforcing elements disposed within the enclosable air-tight compartment to increase the operational depth of float 1. The reinforcing element 6 may comprise any suitable geometric shape, for example, toroidal, hemispherical, spherical or dodecahedral. In some embodiments, the reinforcing element 6 may comprise one or more struts projecting radially from the conduit 3 towards the outer shell 2. In the embodiment shown in figure 7A, the reinforcing elements 6 comprise substantially disk-shaped structures projecting radially from around the conduit 3 towards outer shell 2 as shown in figure 7A. In another embodiment shown in figure 7B, the reinforcing element 6 comprises a spherical structure projecting radially from around the conduit 3 towards the outer shell 2. Multiple reinforcing elements 6 may be spaced along the length of the conduit as shown in figures 5 and 7. In use, the reinforcing elements 6 resist compression of the outer shell 2 when float 1 is subjected to increased atmospheric pressure. The reinforcing elements 6 may increase the effective operational depth of the float 1 to about 50m.

Application of the float

Float 1 may be used for any suitable marine applications, for example fishing or aquaculture industries. Depending on the application, float 1 may be used individually or as part of a network of floats to support object or objects under water. An offshore mussel farm may comprise a series of floats spaced along the of length of and supporting a horizontal headline or mainline 11. Each float may be attached to the headline or mainline 11 by a support lashing or rope 12. The headline or mainline 11 in turn supports a network of mussel cultivation ropes or spat ropes suspended from the headline or mainline 11 (not shown). The number of floats needed to support a mussel farm 10 depends on various factors including the displacement of the floats, operational depth of the floats, the length of the headline or mainline, and the total weight to be supported by the floats.

Traditional barrel-type mussel floats have rope attachment points such as eyelets at the ends of the floats. In use, support lashing or ropes tied to these traditional attachment points are subjected to the continuous motion of waves at sea which increases the stresses and wear on the ropes resulting in frequent breakage. Unlike traditional mussel floats, the float of the present invention uses the passageway 4 formed by conduit 3 as a rope attachment location.

Referring to figures 8 to 9C, the float 1 may be used in horizontal or vertical

configurations. Figure 8 shows floats 1 used in the vertical configuration. When used in the vertical configuration, a stopper knot is tied at one end of the support rope and the free end is received by the entry part 5 through passageway 4 and attached to the object to be supported, for example the headline or mainline 11. Figures 9A to 9C show floats 1 used in various horizontal configurations. Figure 9A shows two methods of attaching float 1 to a headline or mainline 11. In the method shown on the left side of figure 9A, a rope is received by entry part 5 through passageway 4 and each end of the rope is attached to object or objects (headline or mainline) to be supported. In the method on the right side of figure 9A, ropes are attached to handles of the float instead of passageway 4. In the horizontal configuration, parallel headlines or mainlines 11 may be supported. In the example shown in figure 9B, the handles of floats 1 are lashed to parallel headlines or mainlines 11. Figure 9C shows another horizontal configuration where a single headline or mainline is received by a series of floats 1. In both horizontal and vertical configurations, ropes received by the passageway 4 may move

independently from the floats reducing the stresses exerted on the ropes during continuous movement of the water. The smoothly radiused entry parts 5 further reduces the friction on the ropes to improve wear compared to traditional barrel-type mussel floats.

The operational depth of mussel floats is the depth at which the float remains buoyant without fully collapsing due to atmospheric pressure. This is an important consideration when choosing the type, displacement, and/or the number of floats to use in a mussel farm. The weight supported by the mussel float increases significantly over time as the spat on the cultivation ropes develop into mature mussels. The increase in weight may cause the mussel floats to sink below the surface of the water. The mussel floats may continue to sink if the weight supported exceeds the buoyancy of the mussel floats.

When a float exceeds its effective operational depth, the mussel float may collapse resulting in the failure of the float. As discussed in the preceding paragraphs, incorporation of reinforcing elements 6 in the float of the present invention increases the depth at which the float can operate effectively. Compared to mussel floats of a similar size without reinforcing elements, a smaller number of the reinforced invention floats may be used to support a mussel farm of a similar size.

Manufacturing the float

Rotational moulding is commonly used to manufacture hollow articles of various types including floats with a central passageway. Such an article is typically rotationally moulded in two halves and welded or bonded together around their circumference to form the complete article. This method is generally costlier and more labour intensive.

Figures 10A to 10D illustrate the method of manufacturing by rotational moulding a hollow body of the present invention. The method broadly comprises the steps of positioning a preformed conduit 3 having opposing ends within the mould cavity of an open rotational mould, closing the mould to contain the preformed conduit including the opposing ends thereof fully within the mould, and rotating the mould and coating the interior surface(s) of the mould cavity and the opposing ends of the preformed conduit 3 with heated liquified moulding material to form an outer shell 2 of the hollow body with the preformed conduit 3 inside the outer shell and with the ends of the preformed conduit 3 bonded to and integral with the outer shell. The opposing ends of the preformed conduit 3 may be open to the exterior so that the conduit forms a passageway 4 open at its ends through the outer shell 2. Alternatively, the opposing ends of the preformed conduit 3 are closed to the exterior.

Referring particularly to figure 10A, a rotational mould having two mould parts 14 is shown in the open position with a support shaft 15 and mould plugs 16. A preformed conduit 3 is positioned on a support shaft 15 by sliding the preformed conduit 3 over the support shaft 15. The support shaft 15 helps to maintain the shape and prevent deformation (e.g. sagging) of the preformed conduit 3 when heat is applied during the moulding process. Mould plugs 16 are inserted into the opposing ends of the preformed conduit 3 and holds the preformed conduit 3 and support shaft 15 in the correct position in the mould cavity. Referring to figure 10B, the rotational mould is then closed with the preformed conduit 3 held within the mould cavity of the two rotational mould parts 14. The preformed conduit 3 is positioned longitudinally across the longitudinal axis of the rotational mould. In an alternative embodiment, the preformed conduit is supported in the mould cavity by mould plugs 16 without the need for a support shaft. The mould plugs 16 protrude into the mould cavity from opposite ends and form part of the surface of the mould cavity. The surface of mould plugs 16 forms part of the mould cavity is shaped to form entry parts 5.

Each mould part 14 may also incorporate formations (not shown) in the mould cavity to form integral handles or recesses in the fully formed float. A quantity of plastics moulding material, for example thermoplastic polymer, is loaded into the mould cavity before the mould is closed. Each mould part 14 may also comprise one or more pressure relief vents (not shown) that prevent excessive pressure build up in the mould cavity during the moulding process. Any vent holes formed in the outer shell as a result of the pressure relief vents may be hermetically sealed using any suitable methods. For example, a cap or cover may be spin welded to hermetically seal any vent holes in the outer shell.

Referring to figure IOC, the mould is heated sufficiently to liquify the plastics moulding material and then rotated about one or more axis or axes to coat the surface(s) of the mould cavity (including sections of the mould plugs) and the opposing ends of the preformed conduit 2 with liquified plastics moulding material. The mould is then cooled sufficiently to harden the liquified plastics moulding material to form the outer shell 2 with the preformed conduit 3 inside the outer shell and to allow the ends of the preformed conduit to become bonded to and integral with the outer shell 2. Referring to figure 10D, rotational mould is opened and the fully formed float 1 with integral passageway 4 is removed from the mould. Thermal resistant cover may optionally be provided to the surface of the preformed conduit exposed to heat within the mould cavity. The thermal resistant cover protects the preformed conduit from deforming (e.g. sagging) when heat is applied during the rotational moulding process, particularly when the preformed conduit used has a similar or lower melting point than the plastics moulding material used in the moulding process.

Referring to the step illustrated in figure 10B, the method may further comprise the step of positioning in the mould cavity, a reinforcing element projecting radially from the preformed conduit towards the interior surface(s) of the mould cavity. Multiple said reinforcing elements may be spaced along the length of the preformed conduit to provide additional strength to the float. The reinforcing element may comprise any suitable shape or material as described in the preceding paragraphs. Preferably the reinforcing element comprises heat-stable and compression resistant material. The plastics moulding material may be any suitable plastic polymer, for example polyethylene. The preformed conduit may comprise a different material from the plastics moulding material used in the moulding process. For example, the preformed conduit may comprise a high-density polyethylene polymer while the plastics moulding material a low-density polyethylene polymer.

The foregoing description of the invention includes preferred forms thereof. Modifications may be made thereto without departing from the scope of the invention as defined in the accompanying claims.

Claims

1. A method of manufacturing by rotational moulding a hollow body, comprising the steps of:

2. The method of claim 1 comprising supporting the preformed conduit in the mould by plugs which enter the open ends of the preformed conduit.

3. The method of claim 2 wherein the plugs protrude into the mould cavity from

opposite ends of the mould cavity.

4. The method of any one of claims 1 to 3, wherein the preformed conduit further

comprises a thermal resistant cover.

5. The method of any one of claims 1 to 4, comprising also positioning in the mould cavity one or more reinforcing elements projecting radially from the preformed conduit towards the interior surface(s) of the mould cavity

6. The method of claim 5, wherein the reinforcing element or elements project radially from around the preformed conduit towards the outer shell.

7. The method of any one of claims 1 to 6, wherein the preformed conduit is from about 1% to about 20% shorter than the length of the hollow body.

8. The method of any one of claims 1 to 7, wherein the preformed conduit is from about 0.5m to about 2m in length.

9. The method of any one of claims 1 to 8, wherein the hollow body comprises a width- to-length ratio from about 1 :2 to about 1 : 5.

10. The method of any one of claims 1 to 9, wherein the moulding material comprises a thermoplastic polymer.

11. The method of any one of claims 1 to 10, wherein the preformed conduit is a plastics extrusion.

12. The method of any one of claims 1 to 11, wherein the outer shell comprises an

integrally formed handle.

13. The method of claim 12, wherein the integrally formed handle is within a recess open to the exterior into the outer shell.

14. A float comprising

a rotationally moulded outer shell,

15. The float of claim 14, comprising an internal reinforcing element or elements

projecting radially from the conduit towards the outer shell.

16. The float of either claim 14 or claim 15, wherein the reinforcing element is toroidal, hemispherical, spherical or dodecahedral in shape.

17. The float of any one of claims 14 to 16, wherein the conduit is from about 1% to about 20% shorter than the length of the float body.

18. The float of any one of claims 14 to 17, wherein the conduit is from about 0.5m to about 2m in length.

19. The float of any one of claims 14 to 18, wherein the hollow body comprises a width- to-length ratio from about 1 :2 to about 1 : 5.

20. The float of any one of claims 14 to 19, wherein the outer shell comprises a

thermoplastic polymer.

21. The float of any one of claims 14 to 20, wherein the conduit is a plastics extrusion.

22. The float of any one of claims 14 to 21, wherein the outer shell comprises an integrally formed handle.

23. The float of claim 22, wherein the integrally formed handle is within a recess open to the exterior into the outer shell.