WO2016086268A1

WO2016086268A1 - Buoyancy module and method of forming

Info

Publication number: WO2016086268A1
Application number: PCT/AU2015/050757
Authority: WO
Inventors: David Cox
Original assignee: Matrix Composites and Engineering Ltd
Current assignee: Matrix Composites and Engineering Ltd
Priority date: 2014-12-02
Filing date: 2015-12-01
Publication date: 2016-06-09
Anticipated expiration: 2017-06-02

Abstract

A method of forming a buoyancy module for a subsea buoyancy system, including the steps of : forming a shell at least partially using an additive manufacturing process; introducing a buoyancy material into the shell; and sealing the shell.

Description

BUOYANCY MODULE AND METHOD OF FORMING

FIELD OF THE INVENTION The present invention relates to a buoyancy module and a method of forming a buoyancy module. More particularly, but not exclusively, the present invention relates to a buoyancy module for use in a subsea buoyancy system.

BACKGROUND OF THE INVENTION

Previously proposed methods of forming buoyancy modules have suffered a number of deficiencies, such as high costs, physical restrictions on size and/or shape, slow production time and inefficient use of materials. In one previous example, large shells for buoyancy modules were formed using rotational moulding techniques. The shells were then filled with a curable buoyancy material, the shell sealed and the material allowed to cure. As resins are commonly used in the buoyancy, heat is generated from the exothermic curing reaction and this heat can have a detrimental effect on the shell. To avoid excessive heat being generated, the volume of resin that can be used is limited, thereby limiting the size of the shell that can be produced using such a method. Although rotational moulding techniques provide a dimensionally consistent and repeatable product, they are not particularly cost effective unless a large number of identical parts are to be made, due to the costs associated with manufacturing a mould. As such, it has previously been expensive and difficult to manufacture buoyancy modules in limited quantities that are customised to a particular application or a customer's requirements.

In another previous example, a buoyancy module is formed by bonding together pieces of a buoyant material, such as a syntactic foam, which is then machined to a required shape. The machining process can be expensive and wasteful and a post -machining finishing operation is required to seal the block because the surface is very rough after machining if the buoyant material is formed of macrospheres.

Examples of the invention seek to solve, or at least ameliorate, one or more disadvantages of previous buoyancy modules.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a method of forming a buoyancy module for a subsea buoyancy system, including the steps of:

forming a shell at least partially using an additive manufacturing process;

introducing a buoyancy material into the shell; and

sealing the shell. According to a preferred embodiment, the method further includes the step of curing the buoyancy material after sealing the shell. The buoyancy material may be a syntactic foam comprising glass spheres suspended in a resin matrix. Preferably, the glass spheres are macrospheres, though alternatively the glass spheres may be microspheres. The method can further include the step of fixing a cover member to the shell to seal the shell. The cover member may be bonded to the shell using an adhesive or a welding process.

In a preferred embodiment, the additive manufacturing process is a fused deposition modelling process. Preferably, the fused deposition modelling process uses a printing head having a nozzle with a diameter greater than approximately 1mm, more preferably in the range of approximately 1mm to approximately 2mm, or greater than 2mm.

In some embodiments the shell is formed of a HDPE or Nylon material. Preferably, the material is deposited at a rate of at least approximately 300mm per second. In some embodiments, the shell is formed with a plurality of internal baffles separating internal compartments, the internal compartments being configured to be sealed from one another. The shell may also be formed with a plurality of separate internal cells. According to the present invention, there is also provided a buoyancy module manufactured using the above described method.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will be further described, by way of non-limiting example only, with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a buoyancy module of one embodiment of the invention; and

Figures 2 to 4 are a perspective views of alternative buoyancy modules.

DETAILED DESCRIPTION

With reference to Figure 1, there is shown a buoyancy module 10 according to a preferred embodiment of the present invention. The buoyancy module 10 is configured for use as part of a sub sea buoyancy system.

The buoyancy module 10 is manufactured by forming a shell 12 using an additive manufacturing process, which will be described further below. A buoyancy material (not shown) is introduced into the shell 12 and the shell 12 sealed. To complete the process, the buoyancy material is cured.

In one embodiment, a cover member 14 is fixed to the shell 12. The cover member 14 may entirely, substantially or partially seal the shell 12. In this regard, in some embodiments the cover member 14 may be formed as a separate lid or cover that seals the shell 12 when fixed thereto, in other embodiments the cover member 14 may be formed in pieces that progressively seal the shell 12, or the cover member 14 may be configured to received a plug or sealing element the seal the shell 12. Although the cover member 14 is shown as being an upper lid, the shell 12 may be formed so that a cover member can close any side or a base of the shell 12. Also, the cover member 14 may also be formed using an additive manufacturing process or using alternative forming processes and/or using different materials. For example, the cover member 12 may be moulded using injection or rotation moulding techniques, or it may be cut from a preformed sheet of plastic or a metallic material. The cover member 14 may be bonded to the shell 12 using an adhesive or a welding process, though it is envisaged that mechanical fixing means, or combinations of the foregoing, may also be provided.

In a preferred form, the buoyancy material is a syntactic foam comprising a plurality of hollow spheres, preferably glass spheres, suspended in a resin matrix which is filled in an uncured form and, after fixing the cover member 14 to the shell 12, heated to cure the foam. Fixing the cover member 14 to the shell 12 ensures that all of the air within the shell is displaced so that air bubbles are not introduced and thus cannot collapse through high hydrostatic pressure encountered in use.

Preferably, the buoyancy material is introduced when the shell has an open upper portion so that a large opening is available for receiving the buoyancy material. The cover member 14 may then be fixed to the shell 12, leaving at least a small space through which resin can be pumped and a vent space through which are can escape. By fixing the cover member 14 to the shell 12 before the resin is introduced, problems with resin expansion and sealing of the cover member 14 are avoided.

It will be appreciated that other foams or buoyancy materials may also be suitable for introduction into the shell 12. For example, polyurethane foam or polyethylene foam may also be used. It will also be appreciated that the shell may be entirely or partially filled, and different buoyancy materials may be combined to fill the shell 12. In the described embodiment, the additive manufacturing process is a fused deposition modelling, or 3D printing process, using a printing head having a nozzle with a diameter greater than approximately 1mm, preferably in the range of approximately 1mm to approximately 2mm, or greater than 2mm. It will be appreciated that other additive manufacturing process, such as SLA or SLS processes for example, may be utilised in forming the shell. Also, the fused deposition modelling process may be performed using two or more printing heads to increase production speed. Previously, fused deposition modelling processes have generally been used for producing a limited number of small parts, such as prototypes for example. Small diameter printing heads, i.e. heads having a diameter of 0.2mm to 0.4mm, have been used to provide a sufficiently high resolution and dimensional accuracy so that post forming processes are not required or minimised. However, the appearance of a buoyancy module for a subsea buoyancy systems is not as critical, which allows fused deposition modelling processes to be used.

Although the appearance of the module is not as important as for parts previously made using fused deposition modelling processes, due to size of the shell, which may be 2.5m long, 2.0m wide and 0.75m high with a wall thickness of 4mm, or even larger, the speed at which the process can be performed is important and determines whether the shell can be made on a cost effective basis. To achieve sufficient process speed, a printing head having a nozzle diameter as described above is used and the forming apparatus configured so that material is deposited at a rate of at least about 300mm per second. It is envisaged that such a process could form a shell 12 of such a size in about 8 to 16 hours.

In the described embodiment, the shell 12 is formed of a HDPE or Nylon material such as glass filled Nylon 12, though it will be appreciated that other materials such as ABS, PLA or other thermoplastics may similarly be used. Previously, the use of HDPE in a fused deposition modelling process has been avoided due to material shrinkage issues, though given that the appearance of the module is not critical, it is envisaged that it will be acceptable for present purposes.

The fused deposition modelling process may be performed by a machine configured to use raw material in the form of pellets. In alternative forms, pre-extruded filament is used.

Also, given the size of the shell 12, the process may be performed with the part formed on a heat bed and/or within a heated enclosure.

By using a fused deposition modelling process, the shell 12 can be formed with a plurality of internal baffles 16 separating internal compartments 18, the internal compartments being configured to be sealed from one another. In other words, the shell 12 has a plurality of separate, individual internal cells 18. Previously, it was difficult to manufacture buoyancy modules having internal compartments due to the complexity of the mould required and a general incompatibility with rotational moulding processes that were previously used. An advantage of providing separate individual cells is that they can be individually filled, thereby limiting the volume of resin that is being cured so as to minimise heat generated and distortion of the shell. In this regard, introducing the buoyancy material may be performed in two steps, with every second cell being filled and once the buoyancy material cured, the remaining cells filled and allowed to cure. Distortion due to weight of the buoyancy material can also be avoided.

One advantage of having separate individual cells is that the effect of damage, impact, fatigue or otherwise, to the module can potentially be minimized. In this regard, crack propagation can be eliminated so that a small crack does not grow into a single large crack travelling through the buoyancy block so that the entire block is damaged from a small localised crack (which in fact may be caused from fatigue rather than impact). For example, if a single cell is damaged, the buoyancy of the entire module is not necessarily compromised, thereby providing some redundancy and potentially improving the useful life span of the module.

Another advantage of using a fused deposition modelling process is that shells having custom shapes and/or sizes can be formed with relative ease, provided that a CAD model can be created. In this regard, irregular or complex shapes having either or both curved and straight surfaces may be formed and Figures 1 to 4 illustrate differently configured shells 112, 212, 312 that are provided for different applications. In the event that much larger shells are required, it will be appreciated that the shell may be formed in two or more parts having complimentary shapes that are configured for engagement to join multiple section together. In the example shown in Figure 4, with each part has a corresponding section of a dovetail 20 that allows individual modules to be joined. Using a fused deposition modelling process also allows the shell 12 to be more easily formed with additional design features, such as internal ribs or gussets 322 as shown in Figure 4, to provide additional reinforcement for increased stiffness. Previously, reinforcement elements were required to be separately manufactured and inserted into the shell, increasing the cost of the module. Such features assist when a pressure or vacuum filling process is used for introducing resin. A vent or air escape aperture 324 is also provided to assist in the step of introducing the buoyancy material into the shell 312.

The embodiments have been described by way of example only and modifications are possible within the scope of the invention disclosed.

Claims

1. A method of forming a buoyancy module for a subsea buoyancy system, including the steps of:

forming a shell at least partially using an additive manufacturing process;

introducing a buoyancy material into the shell; and

sealing the shell.

2. A method of forming a buoyancy module as claimed in claim 1, further including the step of curing the buoyancy material after sealing the shell.

3. A method of forming a buoyancy module as claimed in claim 1 or claim 2, wherein the buoyancy material is a syntactic foam comprising glass spheres suspended in a resin matrix.

4. A method of forming a buoyancy module as claimed in any preceding claim, further including the step of fixing a cover member to the shell to seal the shell.

5. A method of forming a buoyancy module as claimed in claim 4, wherein the cover member is bonded to the shell using an adhesive or a welding process.

6. A method of forming a buoyancy module as claimed in any preceding claim, wherein the additive manufacturing process is a fused deposition modelling process.

7. A method of forming a buoyancy module as claimed in claim 6, wherein the fused deposition modelling process uses a printing head having a nozzle with a diameter of greater than approximately 1mm.

8. A method of forming a buoyancy module as claimed in claim 6 or claim 7, wherein the shell is formed of a HDPE or Nylon material.

9. A method of forming a buoyancy module as claimed in any one of claims 6 to 8, wherein material is deposited at a rate of at least approximately 300mm per second.

10. A method of forming a buoyancy module as claimed in any preceding claim, wherein the shell is formed with a plurality of internal baffles separating internal compartments, the internal compartments being configured to be sealed from one another.

11. A method of forming a buoyancy module as claimed in any preceding claim, wherein the shell is formed with a plurality of separate internal cells.

12. A buoyancy module manufactured using the method of any preceding claim.