GB2477850A

GB2477850A - Curing a component using a fluid heat transfer blanket in an autoclave

Info

Publication number: GB2477850A
Application number: GB1102062A
Authority: GB
Inventors: Alex Hewitt; Brian Grover
Original assignee: SFA Engineering Corp
Current assignee: SFA Engineering Corp
Priority date: 2010-02-08
Filing date: 2011-02-07
Publication date: 2011-08-17
Also published as: GB201001998D0; GB201102062D0

Abstract

An autoclave (1, Figure 1) comprises a pressure vessel 3, a tool 19 inside the pressure vessel for supporting a component 21 to be cured and a fluid heat transfer blanket 23 with a fluid flow channel (25, Fig. 3) extending along at least part of the blanket. The fluid flow channel comprises a fluid inlet (29, Fig. 3) and a fluid outlet (31, Fig. 3) connected to a source of temperature controlled fluid 34. The autoclave is arranged such that in use the fluid heat transfer blanket is in contact with and covers the part of the component to be cured, The fluid is delivered through the fluid flow channel to effect heat transfer between the fluid and the component in order to cure the component. Substantially the same pressure is applied to both the pressure vessel and the fluid. An autoclave fluid heat transfer blanket and a method of curing a component using an autoclave are also claimed.

Description

AN AUTOCLAVE, AN AUTOCLAVE FLUID HEAT TRANSFER

BLANKET AND A METHOD OF CURING A COMPONENT USING

AN AUTOCLAVE

The present invention relates to an autoclave, an autoclave fluid heat transfer blanket and a method of curing a component using an autoclave.

In a traditional autoclave a pressurised air or nitrogen atmosphere is circulated throughout the autoclave pressure vessel. Energy is added/extracted to/from the atmosphere in the vessel by a variety of mechanisms. The circulation of the atmosphere over the tool and the component to be cured allows the energy to be transferred into or out of the component to heat and cool it as required. This heat transfer cures the component. The component may be cured in the shape defined by the tool, or may be preformed in the desired shape and be supported by the tool. Non limiting examples of such a component include a component manufactured from composites, for example carbon fibre, such as an aircraft wing/fuselage, or a racing car chassis.

The traditional autoclave process is inefficient because: * heat transfer is directly related to the velocity and density of the circulated atmosphere; and * in addition to the component, all internal structures and the atmosphere in the autoclave, must also be heated and cooled.

Thus, the majority of energy used in the traditional autoclave process is parasitic and plays no part in curing the component.

For the traditional autoclave which used a gaseous atmosphere to transfer energy, the tool and component to be cured typically represent only around 16% of the mass heated. With power consumption for a large autoclave installation (e.g. to produce a wing cover or fuselage section for a commercial airliner) in the region of 4MW this is both a substantial cost, and a significant contributor to the aerospace industry's carbon consumption.

We have developed and commissioned a high pressure autoclave using water as the heat transfer medium instead of gas. This has the benefit that the energy transfer mechanism into the component to be cured is more efficient than for a gas atmosphere.

However, the parasitic losses are higher than a traditional autoclave due to the large mass of water and the need to insulate the pressure vessel externally, resulting in a greater mass of metal being subjected to the heating and cooling cycle.

The current invention stems from some work to provide an improved autoclave with increased efficiency.

According to a first aspect of the invention there is provided an autoclave comprising a pressure vessel, a tool inside the pressure vessel for supporting a component to be cured, a fluid heat transfer blanket comprising a fluid flow channel extending along at least part of the fluid heat transfer blanket, the fluid flow channel comprising a fluid inlet and a fluid outlet connected to a source of temperature controlled fluid, the autoclave being arranged such that in use the fluid heat transfer blanket is in contact with and covers the part of the component to be cured, the autoclave further comprising pressurising means operative to pressurise the pressure vessel and to pressurise the temperature controlled fluid, the autoclave being further operative to deliver the pressurised, temperature controlled, fluid through the fluid flow channel to effect heat transfer between the fluid and the component to be cured, to cure the component, the pressurising means being operative to apply substantially the same pressure to the pressure vessel and the fluid.

The fluid heat transfer blanket is in contact with the component to be cured, and thus energy is transferred from the fluid to the component or vice versa primarily by conduction.

The fluid heat transfer blanket may cover all or part of the component to be cured.

The fluid heat transfer blanket may comprise a plurality of fluid flow channels.

The fluid flow channels of the fluid heat transfer blanket may be arranged such that the temperature of at least some of which can be controlled independently.

The flow rate of fluid through at least some of the fluid flow channels may be controlled by control valves.

The autoclave may comprise at least one temperature sensor operative to generate a signal indicative of at least one of the temperature of the fluid and the fluid heat transfer blanket. The temperature sensor may comprise a thermocouple. The temperature sensor may be provided on the fluid heat transfer blanket, or on the fluid inlet or outlet, or on pipework connecting the fluid heat transfer blanket to the source of temperature controlled fluid.

The autoclave preferably comprises at least one pressure sensor operative to generate a signal indicative of the pressure of the temperature controlled fluid in the fluid heat transfer blanket. The pressure sensor may be a pressure transducer for example.

The pressure sensor may be provided on at least one of the fluid heat transfer blanket, the fluid inlet or outlet, or pipework connecting the fluid heat transfer blanket to the source of temperature controlled fluid.

Preferably the source of temperature controlled fluid is fed by an energy storage system comprising a plurality of reservoirs of fluid, each reservoir being operative to store fluid at a different temperature to another reservoir. Thus there may be for example a reservoir of heating fluid and a reservoir of cooling fluid.

The fluid heat transfer blanket may comprise at least one insulating layer on a part of the blanket not in contact with the component to be cured in use.

According to a second aspect of the invention there is provided an autoclave fluid heat transfer blanket for placing in contact with and curing a component in an autoclave, the blanket comprising a fluid flow channel extending along at least part of the fluid heat transfer blanket, the fluid flow channel comprising an inlet and outlet enabling a connection to a source of temperature controlled fluid, the fluid heat transfer blanket being arranged such that it can be placed in contact with the component to be cured so as to cover the part of the component to be cured, the blanket being arranged to receive pressurised, temperature controlled fluid delivered through the fluid flow channel to effect heat transfer between the fluid and the component to be cured, to cure the component.

According to a third aspect of the invention there is provided a method of curing a component using an autoclave, comprising steps of: supporting the component on a tool in an autoclave pressure vessel; providing a fluid heat transfer blanket comprising a fluid flow channel extending along at least part of the fluid heat transfer blanket, the fluid flow channel comprising a fluid inlet and a fluid outlet; moving at least one of the tool or the fluid heat transfer blanket into contact with the component so that the blanket covers the part of the component to be cured; connecting the fluid inlet and fluid outlet of the fluid heat transfer blanket to a source of temperature controlled fluid; pressurising the autoclave vessel; pressurising the temperature controlled fluid; delivering the pressurised temperature controlled fluid through the fluid flow channel of the fluid heat transfer blanket such that heat transfer occurs between the fluid and the component to be cured, to cure the component; controlling the pressure of the pressure vessel and the fluid to apply substantially the same pressure to the pressure vessel and the fluid.

Other aspects of the present invention may include any combination of the features or limitations referred to herein.

The present invention may be carried into practice in various ways, but embodiments will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a perspective view of a prior art autoclave; Figure 2 is a perspective view of an autoclave in accordance with the present invention, with part of the wall of the pressure vessel of the autoclave cut-away to reveal the interior; and Figure 3 is a perspective view of a fluid heat transfer blanket in accordance with the present invention.

With reference initially to Figure 1, a prior art autoclave 1 comprises a vertical pressure vessel 3 supported by a support framework 5. The autoclave 1 comprises a lid 7 moved into and out of sealing engagement with the upper end of the pressure vessel 3 by a lid support frame 9.

A tool is provided inside the pressure vessel 3 and this supports a component to be cured. The tool may simply support the component, or may additionally comprise a surface or surface against which the component engages such that the tool surface shapes the component in use.

A temperature controlled water supply system 11 supplies water to the pressure vessel 3 via pipework 13. During heating, heat energy is transferred from the water to the component to be cured. During cooling, heat energy is transferred from the component to the water.

In accordance with the present invention the autoclave pressure vessel 3, in this example shown in horizontal orientation, comprises a pressurised fluid inlet 15 and a pressurised fluid outlet in the form of vent 17. The interior of the pressure vessel 3 is provided with a tool 19 which in this example has a curved upper surface 19A which supports the component 21. It will be appreciated that the tool 19 may be of any desired shape, size or profile as required to manufacture the component required. The tool 19 may be used to shape some or all of the component 21 during curing, or simply to support the component 21 if the component 21 is preformed in the desired shape.

The pressure vessel 3 further comprises a fluid heat transfer blanket 23 that is draped over the component 21, the component 21 thus being sandwiched between the blanket 23 and the tool 19.

The fluid heat transfer blanket 23 comprises a plurality of fluid flow channels. The energy transfer fluid, which is preferably water, is pumped through the channels in the blanket 23 which functions as a cover placed over, and in contact with, the component 21 to be cured.

The fluid heat transfer blanket 23 incorporates temperature sensors such as thermocouples for process monitoring of the fluid temperature and/or the blanket 23, and an insulating layer to reduce energy transmission to the surrounding atmosphere.

Referring additionally to Figure 3, the blanket 23 comprises an elongate hollow flexible panel in this example, defining a plurality of discrete internal fluid flow channels 25 the temperature of each of which may be independently controlled. Each channel 25 defines an elongate fluid flow path through the blanket 23.

Each fluid flow channel 25 is provided with a pair of fluid connectors the first of which functions as a fluid inlet 29, the second of which functions as a fluid outlet 31.

Each channel 25 is provided with a plurality of temperature sensors 33 spaced along each flow channel 25.

Each connector 29, 31 is connected via a suitable manifold and pipework 32 to a source of temperature controlled fluid 34, this being external of the pressure vessel 3. The fluid temperature can be controlled to supply heat or cooling to the blanket 23 and therefore to the component 21. The temperature controlled fluid is controlled in use to be at the same pressure as the pressure within the pressure chamber 3, as applied to the component 21.

The pressures of both the pressure chamber 3 and the temperature controlled fluid in the blanket 23 are closely controlled by use of solenoid control valves, pressure transducers and control means comprising a programmable logic controller (PLC) based control system and a SCADA operator system for monitoring the pressures concerned.

It is envisaged that other types of control means could alternatively or additionally be used.

The blanket 23 further comprises at least one layer 35 of thermally insulating material, this being arranged on the upper face of the blanket 23, opposite to the face that rests on the component 21. The insulating material may be of any desired form, and multiple layers of material may be provided as required.

In use, the component 21 is placed on the tool 19 in the pressure vessel 3, the fluid heat transfer blanket 23 is moved into contact with the component 21 to be cured, and the component 21 is subjected to pressure by pressurising the pressure chamber 3. The same pressure is also applied to the temperature controlled water supply to the blanket 23. In this way, pressures on the fluid heat transfer blanket 23 are equalised and there is no restriction to fluid flow through the blanket 23.

Heating and/or cooling are applied to the component 21 via the fluid in the fluid channels 25, each of which can be controlled by means of control valves that can restrict or increase the fluid flow into each channel 25 relative to the other channels 25 to optimise the process and ensure even heating and/or cooling over all the required parts of the component 21. It will be appreciated that the blanket 23 is arranged to provide localised, precision controlled heating and cooling to the required parts of the component 21 as required and indeed individual channels 25 can be heated and/or cooled rapidly or vice versa. Thus the blanket 23 enables the temperature applied to the component 21 to be controlled relatively quickly and accurately to ensure that a precise pressure/temperature-time profile is adhered to. The provision of pressurised fluid to the blanket 23 enables the temperature of the water in the blanket to far exceed the normal boiling point at atmospheric pressure.

Since only the component 21, fluid heat transfer blanket 23, and the temperature controlled water are heated/ cooled the energy requirements are substantially reduced compared to a traditional autoclave with parasitic losses in the region of 60%.

Due to the relatively small mass of temperature controlled water required, an energy storage system in which hot and cold water reservoirs are maintained independently, further reduces the energy consumption. The final energy cost may be approximately 25 to 30% of a traditional autoclave. For the example of an aircraft wing cover autoclave, this would translate to a reduction in installed power of up to 3MW, with attendant savings in capital, infrastructure and running costs.

Because the energy is transferred by conduction into and out of the component 21 there is no requirement for a circulating fan or fans within the pressure chamber 3.

Heating and cooling are equally efficient which is advantageous over alternative low energy autoclave processes which concentrate on the efficiency of heating the component (e.g. microwave, induction) but neglect the cooling requirement. Cooling the component can be similarly important in both energy consumption and overall process time, as heating.

Thus, the costs of the manufacturing process are dramatically reduced without compromising the structural integrity or traceability of the product.

The following benefits are therefore provided: * Reduction in capital cost * Significantly reduced running costs * Improved process time * Existing tooling can be used without modification * Through life inspection and maintenance of the main vessel is simplified * Dual purpose machine can be used for primary cure, hot de-bulk and post cures, eliminating the need for a separate oven.

It is envisaged that the fluid heat transfer blanket be formed from any suitable, flexible material having sufficient heat resistant and thermally conductive properties. The blanket may be formed from two sheets of material sandwiched together with integrally moulded fluid channels.

Examples of suitable materials include silicon sheet, a low temperature nylon, or an organic polymer thermoplastic such as Polyether ether ketone (PEEK). PEEK is a semi-crystalline thermoplastic having mechanical and chemical resistance properties that are retained to high temperatures.

It will also be appreciated that the blanket 23 be of any desired shape, size and profile, and may comprise only one channel 25 or any other number of channel 25 as required. Likewise any desired number of temperature sensors, pressure sensors and control valves can be provided. It is envisaged that it may be sufficient to have only one temperature sensor and/or only one pressure sensor, at the fluid inlet/outlet to the blanket 23, or in the pipework connecting the blanket 23 to the source of temperature controlled fluid. One or more temperature sensors and/or pressure sensors may be provided per channel 25.

In the production of high quality cured composite components it is customary to enclose the composite into a vacuum bag prior to cure. The bag is flexible plastic or similar material. The bag is often divided into zones. Each zone has a vacuum draw and vacuum sense quick release coupling bonded into the bag. Suction lines run from the quick release couplings out of the autoclave pressure vessel. Suction is applied to the bag which extracts air from the composite material. Instead of a complete bag, a single sided sheet or "foil" is often used which is laid over the composite and the edges bonded to the tool to provide an air tight seal. After cure the bond line is broken and the foil removed. It is envisaged that the fluid heat transfer blanket 23 could also be utilised in this way.

Claims

CLAIMS1. An autoclave comprising a pressure vessel, a tool inside the pressure vessel for supporting a component to be cured, a fluid heat transfer blanket comprising a fluid flow channel extending along at least part of the fluid heat transfer blanket, the fluid flow channel comprising a fluid inlet and a fluid outlet connected to a source of temperature controlled fluid, the autoclave being arranged such that in use the fluid heat transfer blanket is in contact with and covers the part of the component to be cured, the autoclave further comprising pressurising means operative to pressurise the pressure vessel and to pressurise the temperature controlled fluid, the autoclave being further operative to deliver the pressurised, temperature controlled, fluid through the fluid flow channel to effect heat transfer between the fluid and the component to be cured, to cure the component, the pressurising means being operative to apply substantially the same pressure to the pressure vessel and the fluid.
2. The autoclave of claim 1 wherein the fluid heat transfer blanket is in contact with the component to be cured, and thus energy is transferred from the fluid to the component primarily by conduction.
3. The autoclave of claim 1 or 2 wherein the fluid heat transfer blanket is adapted to cover all or part of the component to be cured.
4. The autoclave of any one of the preceding claims wherein the fluid heat transfer blanket comprises a plurality of fluid flow channels.
S. The autoclave of claim 4 wherein the temperature of at least some of the fluid flow channels of the fluid heat transfer blanket can be controlled independently.
6. The autoclave of claim 5 wherein the flow rate of fluid through at least some of the fluid flow channels is controlled by control valves.
7. The autoclave of any one of claims 1 to 6 wherein the fluid heat transfer blanket comprises at least one temperature sensor operative to generate a signal indicative of at least one of the temperature of the fluid and the fluid heat transfer blanket.
8. The autoclave of claim 7 wherein the temperature sensor comprises a thermocouple.
9. The autoclave of claim 7 or claim 8 wherein the temperature sensor is provided on at least one of the fluid heat transfer blanket, the fluid inlet or outlet, or pipework connecting the fluid heat transfer blanket to the source of temperature controlled fluid.
10. The autoclave of any one of the preceding claims comprising at least one pressure sensor operative to generate a signal indicative of the pressure of the temperature controlled fluid in the fluid heat transfer blanket.
11. The autoclave of claim 10 wherein the pressure sensor comprises a pressure transducer.
12. The autoclave of claim 7 or claim 8 wherein the pressure sensor is provided on at least one of the fluid heat transfer blanket, the fluid inlet or outlet, or pipework connecting the fluid heat transfer blanket to the source of temperature controlled fluid.
13. The autoclave of any one of claims 1 to 12 wherein the source of temperature controlled fluid is fed by an energy storage system comprising a plurality of reservoirs of fluid, each reservoir being operative to store fluid at a different temperature to another reservoir.
14. The autoclave of any one of claims 1 to 13 wherein the fluid heat transfer blanket comprises at least one insulating layer on a part of the blanket not in contact with the component to be cured in use.
15. An autoclave fluid heat transfer blanket for placing in contact with and curing a component in an autoclave, the blanket comprising a fluid flow channel extending along at least part of the fluid heat transfer blanket, the fluid flow channel comprising an inlet and outlet enabling a connection to a source of temperature controlled fluid, the fluid heat transfer blanket being arranged such that it can be placed in contact with the component to be cured so as to cover the part of the component to be cured, the blanket being arranged to receive pressurised, temperature controlled fluid delivered through the fluid flow channel to effect heat transfer between the fluid and the component to be cured, to cure the component.
16. A method of curing a component using an autoclave, comprising steps of: supporting the component on a tool in an autoclave pressure vessel; providing a fluid heat transfer blanket comprising a fluid flow channel extending along at least part of the fluid heat transfer blanket, the fluid flow channel comprising a fluid inlet and a fluid outlet; moving at least one of the tool or the fluid heat transfer blanket into contact with the component so that the blanket covers the part of the component to be cured; connecting the fluid inlet and fluid outlet of the fluid heat transfer blanket to a source of temperature controlled fluid; pressurising the autoclave vessel; pressurising the temperature controlled fluid; delivering the pressurised temperature controlled fluid through the fluid flow channel of the fluid heat transfer blanket such that heat transfer occurs between the fluid and the component to be cured, to cure the component; controlling the pressure of the pressure vessel and the fluid to apply substantially the same pressure to the pressure vessel and the fluid.
17. An autoclave and fluid heat transfer blanket substantially as described herein and as shown in Figures 2 and 3.
18. A fluid heat transfer blanket substantially as described herein and as shown in Figures 2 and 3.