FR3060412A1 - METHOD FOR IMPROVING LOCAL THERMAL TRANSFER IN AN AUTOCLAVE AND DEVICE IMPLEMENTING SAID METHOD - Google Patents

Abstract

A method of improving the local heat transfer in an autoclave or oven (100) having an enclosure (10) in which a gas flows, and a mold (11) in which a structural part (12) is manufactured, said method comprising a preliminary step (200) of setting up said structural part in said mold, and characterized in that it comprises a step (201a) of installation, in the vicinity of the structural part (12), of a turbulator device ( 15) which locally increases the turbulence of a gas flow therethrough, a step (202a) for positioning the mold (11) and the structural part (12) at a predetermined location in the enclosure (10) of the autoclave, and a step (300) of execution of the cooking cycle of the autoclave (100) adapted to the structural part (12).

Description

® FRENCH REPUBLIC

NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY © Publication number: 3,060,412 (to be used only for reproduction orders)

©) National registration number: 16 62573

COURBEVOIE © Int Cl ⁸ : B 01 J 3/04 (2017.01), B 29 C 70/44, B 01 F 3/02

A1 PATENT APPLICATION

©) Date of filing: 16.12.16. (© Applicant (s): AIRBUS GROUP SAS Company by (30) Priority: simplified actions - FR. @ Inventor (s): CHATEL SYLVAIN. (© Date of public availability of the request: 22.06.18 Bulletin 18/25. ©) List of documents cited in the report preliminary research: Refer to end of present booklet (© References to other national documents ® Holder (s): AIRBUS GROUP SAS Company by related: simplified actions. ©) Extension request (s): (© Agent (s): IPSIDE.

METHOD FOR IMPROVING LOCAL THERMAL TRANSFER IN AN AUTOCLAVE AND DEVICE IMPLEMENTING SUCH A METHOD.

FR 3 060 412 - A1 (bj) Method for improving local heat transfer in an autoclave or an oven (100) comprising an enclosure (10) in which a gas circulates, and a mold (11) in which a part is manufactured structural (12), said method comprising a preliminary step (200) of placing said structural part in said mold, and characterized in that it comprises an installation step (201a), in the vicinity of the structural part ( 12), a turbulator device (15) which locally increases the turbulence of a flow of gas passing through it, a step (202a) of positioning the mold (11) and the structural part (12) at a determined location in the enclosure (10) of the autoclave, and a step (300) of executing the cooking cycle of the autoclave (100) adapted to the structural part (12).

100

Method for improving the local heat transfer in an autoclave and device implementing such a method

FIELD OF THE INVENTION

The present invention belongs to the field of manufacturing parts made of composite materials. The invention relates more particularly to a method for improving local heat transfer in an autoclave or an oven, during the production of structural parts made of composite materials.

STATE OF THE ART

The processes for developing parts in composite materials, and more particularly the processes for manufacturing structural parts in organic matrix composites, are known in the industry and allow their diversity to adapt to different requirements according to their fields of application.

In particular, the vacuum molding process in an autoclave is generally used for the manufacture of high performance parts and is widely used in the aeronautical industry. This process consists of vacuuming the part to be manufactured under a waterproof membrane followed by the application of a pressure and temperature cycle. This process allows the control of the manufacturing parameters of the structural parts. The manufacture of parts in an oven employs the same principles but without the application of a pressure cycle in the thermal enclosure of said oven.

In addition, the autoclave process ensures optimization of the porosity rate, control of the heating and cooling rates and the manufacturing temperature.

However, the manufacturing cycles in the autoclave process can have substantial durations, causing high production costs and preventing the generalization of such a process to mass production parts. Especially since these manufacturing means are controlled by a single global pressure and temperature imposed as a set point. Another known drawback of this process is the thermal gradient inside the autoclave, which is all the more important as the dimensions of the autoclave are large, thus reducing the useful volume of cooking of the pieces because of the heterogeneities. of temperature. In addition, the high values of temperature and pressure in the autoclave make it very difficult to measure fluid flow velocities (directing the heat exchanges by convection in the enclosure of the autoclave) and of the uniformity of the room temperature, and thereby to control the progress of manufacturing.

Known solutions nevertheless make it possible to overcome the problems linked to the time and the rate of production in the autoclave process by using for example:

- a supply of thermal energy in conductive form, by a heat transfer fluid, or radiative, by radiant panels, inside the autoclave;

an increase in forced convection by an increase in the speed and or in the pressure, an optimization of the positioning of the mold in the useful cooking volume, a reorientation of the flows through rectifiers according to the geometries of the autoclave and structural parts to be manufactured.

The Canadian document CA 2762790 A1, by way of example, describes a method for optimizing the use of the volume of an autoclave by digital simulation, allowing a determination of the appropriate positions of the mold inside the autoclave and controlled modification of flows with grinders to improve the productivity of the autoclave.

This solution remains complex, however, requires a significant pre-treatment time and varies depending on the part to be manufactured and the configuration of the autoclave. This solution in fact allows an optimization of the use of the existing means without improving the efficiency of the means itself.

PRESENTATION OF THE INVENTION

On the basis of this state of affairs, the applicant proposes a solution which overcomes the limitations of the prior art and describes a method for improving the local heat transfer in an autoclave comprising an enclosure, a double-walled pipe fitted with a gas circulation fan. , and a mold in which a structural part is made, said method comprising a preliminary step of placing said structural part in said mold, said method comprising:

- a step of installation, in the vicinity of the structural part, of a turbulator device which locally increases the turbulence of any gas flow passing through it;

- a step of positioning the structural part at a determined location in the autoclave enclosure;

- a step of starting the autoclave cooking cycle adapted to the structural part.

The increase in turbulence in the flow of heating gas in the enclosure in fact makes it possible to promote heat exchanges by forced convection between said enclosure and the structural part to be produced during cooking.

This method is remarkable in that the step of installing the turbulator device in the vicinity of the structural part consists in positioning said turbulator device around the structural part so as to completely or partially cover the face of said part which will be the most exposed. heat transfer during cooking in the autoclave.

More particularly, the dimensions of the turbulator device are chosen as a function of the geometries and dimensions of the structural part produced in the autoclave as well as the materials of the tools used, so as to completely or partially cover the face of said part most exposed to convective heat transfer during cooking in the autoclave.

The method is therefore adaptable to different geometries of structural parts and can also be applied to several parts in the same manufacturing cycle.

In accordance with a particularly advantageous characteristic, the step of positioning the structural part in the autoclave consists in introducing the mold in which the part covered by the turbulator device is located in said autoclave in a location, previously determined by numerical simulation, which guarantees maximum efficiency of said turbulator device.

The invention also relates to a turbulator device for generating local turbulence for implementing the method as described, said turbulator device comprising one or more characteristics among movable or non-movable parts, corrugated surfaces, cavities, protuberances and / or any other formation favoring the appearance of local turbulence in the vicinity of said turbulator device when it is crossed by a flow of gas.

The presence of these formations creates controlled and predicted disturbances of the heating fluid flows in the enclosure.

In an advantageous embodiment of the invention, the turbulator device is a metal grid placed above the structural part placed in the mold of the autoclave.

The metallic grid comprises in one embodiment fixed elements, baffles for example which deflect the flow of gas and create turbulence, or rotary elements, which can be set in motion by a flow of gas in the enclosure, such blades, fins or blades which may or may not be motorized.

In one embodiment, the rotary elements are remotely controlled by a system outside the autoclave.

In particular, the process for improving the local heat transfer in an autoclave, according to the invention, is applied to the manufacture of structural parts made of composite materials in said autoclave.

The process described is particularly advantageous in the case of autoclaves for manufacturing high performance parts made of composite materials intended for the aeronautical industry for example.

The fundamental concepts of the invention having just been exposed above in their most elementary form, other details and characteristics will emerge more clearly on reading the description which follows and with reference to the appended drawings, giving by way of 'nonlimiting example an embodiment of a method for improving the local heat transfer in an autoclave and of a turbulator device implementing said method, in accordance with the principles of the invention.

BRIEF DESCRIPTION OF THE FIGURES

- Figure 1 shows a general diagram of the invention showing in longitudinal section an autoclave with a part in preparation, the elements of the drawing not necessarily being on the same scale;

- Figures 2a and 2b show two examples of the method according to two modes of implementation.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 represents a schematic diagram of the implementation of the method for improving the local heat transfer in an autoclave 100 according to the invention, said method applies in the case of autoclave manufacturing of structural parts made of materials composites intended in particular for the aeronautical industry, such as, for example, leading edges of wings in the case of secondary structures or parts of fuselages in the case of primary structures.

The autoclave 100, according to the embodiment of FIG. 1, mainly comprises an enclosure 10 used to receive the parts to be manufactured, internal walls 20 delimiting said enclosure and provided with an inlet opening 20a and a outlet opening 20b, external walls 40 resistant to the pressure prevailing in the autoclave and surrounding the internal walls 20, and a double-walled pipe 30 corresponding to the intermediate volume located between said internal walls and external walls.

The process described, object of the present invention, aims to locally improve the heat transfer in the vicinity of a mold 11 placed in the enclosure 10 of the autoclave 100 by a turbulating device 15, placed in the vicinity of said mold, producing local turbulence, said mold accommodating a structure 12 to be manufactured.

In the exemplary embodiment illustrated in FIG. 1, a gas is circulated in the double-jacket pipe 30 of the autoclave 100 via a fan 31 placed in said double-jacket pipe.

The double-jacket pipe 30 of the autoclave 100 is formed by a volume located between the internal walls 20 and the external walls 40 of said autoclave, the enclosure 10 in turn corresponds to the volume delimited by the internal walls 20.

The inlet opening 20a and the outlet opening 20b allow the enclosure 10 and the double-walled pipe 30 to communicate with each other, and are made, facing each other, in a vertical wall belonging to the internal walls 20 of the autoclave 100 to ensure general circulation of the gas in the enclosure.

The fan 31 blows the gas into the double-jacket pipe 30 of the autoclave 100, said gas then enters the enclosure 10 through the inlet opening 20a thus following a continuous circuit. The flow of the incoming gas 16a is then modified in the vicinity of the mold 11 by the turbulator device 15 obstructing it, said turbulator device disturbs the flow and generates local turbulence improving the homogenization of the temperature in the manufacturing zone as well as heat exchanges. The turbulator device 15 is shaped to produce turbulence and thereby increase the turbulence of the gas flow which reaches the mold and the part. The turbulator device 15 can be any assembly comprising moving parts, corrugated surfaces, cavities, protuberances and / or any other formation promoting local turbulence, causing traffic accidents and recirculations in the flow while remaining relatively transparent to the flow, such as a diffusion grid for example.

According to the principles of the invention, the modification of the gas flow in the vicinity of the mold containing the structural part can be described as active or passive depending on whether the turbulator device 15, responsible for creating local turbulence, contains moving parts, which can be controlled by a system outside the autoclave, or do not contain any.

In the case of an active modification of the flow, the turbulator device 15 comprises movable parts, each of which is animated by a rotational movement around a proper axis when it is traversed by the flow of gas. Such a turbulator device may for example be a metal grid of predetermined dimensions, which can be modular, and comprising rotary elements such as blades, fins or blades, said rotary elements being able to be motorized or simply driven by the movement of the gas. Thus, the movement of the mobile parts of the turbulator device 15 improve the diffusion and mixing of the gas in the autoclave thanks to the vortices generated by said mobile parts and in particular in an area surrounding the structural part in the vicinity of which said turbulator device is located.

In the case of a passive modification of the flow, the turbulator device 15 has no moving part and contains only fixed obstacles which disturb the flow of the gas by creating recirculation zones and therefore local turbulence. Such a turbulator device is for example a grid comprising elements which interfere with the natural path of the flow of gas in the enclosure and creates turbulence in it, these elements are for example baffles, like those used in the heat exchangers.

In both active and passive cases, which can be combined, the turbulator device 15 mainly comprises a grid. This is advantageous due to the incomplete nature of a grid-like structure which makes it possible to disturb gas flows easily. .

In the exemplary embodiment illustrated in FIG. 1, the turbulator device 15 comprises a grid allowing the formation of local turbulences, in the gas flow in the vicinity of said grid. In addition, the grid of the turbulator device 15 is placed above the structural part 12 so as to determine a sub-volume 17 of the enclosure 10 entirely enveloping the face of said part most exposed to thermal transfer by forced convection, said face here corresponds to a face of the part covered by a flexible and waterproof membrane 13. A partial vacuum is created in a volume between the membrane and the part.

The turbulator device 15 thus allows a modification of the forced convection around the structural part 12, placed in the mold 11, in a regime of turbulent flow of the heating gas in the enclosure 10, and an improvement in the mixing of said gas in said enclosure, in particular in the vicinity of the mold.

Indeed, the turbulator device 15 according to the illustrated embodiment and from its grid, generates local flows at the meshes of the grid, called blocking flows, opposite the vicinity of the structural part 12, to the general flow of the gas in enclosure 10. This has the direct effect of locally increasing the turbulence of the flow.

For example, for a flat room with a length of 2 m and above which is placed a grid at least 2 m in length generating multiple blocking flows in contact with the face exposed to the heating gas, via obstacles 1 mm high spaced 1 mm apart on said grid, the gain in heat transfer between said flat part and the gas is increased by 12% thanks to the blocking flows.

These results, verified during experiments, were measured for a gas heating the flat part in question with a speed of the gas, measured in the flow at the inlet of the enclosure, of 1 m / s and a difference of temperature between said flat part and said gas of 50 ° C.

The gain in thermal transfer is calculated from the dimensionless Nusselt number (Nu), characterizing the convective thermal transfer between the flat part and the gas as a function of the thermal conduction of said gas, with and without the presence of blocking fluxes by quantifying the ratio of the two Nusselt numbers in both cases.

As previously specified, the flow of the outgoing gas 16b is taken up at the outlet opening 20b by the fan 31 which then re-injects it into the pipes of the double-jacket pipe 30 of the autoclave 100.

The turbulence of the flow in the vicinity of the structural part being increased, the heat transfer between the heating gas of the enclosure and said structural part is therefore improved by a local increase in exchanges by convection.

FIG. 2a summarizes the main steps of the process for improving the heat transfer in an autoclave such as the autoclave 100 described. The method is implemented before the composite part is cooked and relates to the preparation and conditioning of said part so that the improvement in heat transfer occurs naturally during cooking in the autoclave .

The process which is the subject of the invention comprises:

- A preliminary step 200 of placing folds to form the structural part 12 in the mold 11 consisting of a layup phase, in the case of a composite part based on prepregs, followed by a placement phase on said piece of environmental tissue and the membrane 13 last. This preliminary step 200 relates to existing methods of vacuum manufacturing of a composite part in an autoclave;

- A step 201a of installation of the turbulator device 15 previously defined at the predefined location in the vicinity of the structural part 12 consisting in positioning the turbulator device 15 around the part 12 so as to completely cover the face of said most exposed part thermal transfer by convection during cooking in the autoclave. The turbulator device 15 is for example fixed directly on the mold 11 via supports mounted on said mold;

- A step 202a of positioning the mold 11 prepared at a determined location in the enclosure 10 of the autoclave 100 established by digital simulation for optimal efficiency of the turbulator device 15;

A step 300 of executing the cooking cycle, said cycle taking into account the improvement in heat exchanges, between the part 12 in question and the autoclave 100, resulting from the use of the turbulator device 15.

FIG. 2b represents a variant of the method of FIG. 2a by proposing to introduce the part 12 in the autoclave before installing the turbulating device 15 around said part. The method, according to the exemplary embodiment of FIG. 2a, therefore comprises:

- The preliminary stage 200;

- A step 201b of positioning the mold 11 and the structural part 12 which it contains at a determined location in the enclosure 10 of the autoclave 100;

- A step 202b of installation of the turbulator device 15 previously defined at the location of the preceding step 201b in the vicinity of the part 12 so as to completely cover the face of said part most exposed to heat transfer during cooking in the autoclave;

- Step 300 of execution of the part 12 cooking cycle.

The method can therefore include step 200 as the only preliminary step in the first exemplary embodiment, and steps 200 and 201b as preliminary steps in the second exemplary embodiment. In the first case, the group of steps 400a comprises the steps from 201a to 300 and characterizes the method. In the second case, the group of steps 400b includes steps 202b and 300 and characterizes the method.

The process for improving the local heat transfer in an autoclave thus described, can be applied to all kinds of thermal chambers with or without internal pressure (autoclaves or ovens) and structural parts, regardless of their geometries and their dimensions. The process is also independent of the location of the structural part inside the autoclave enclosure because the said process can be adapted to different locations within the enclosure, and therefore pale the limits imposed by the useful volume. previously difficult to overcome in the autoclave.

The method can be applied for an autoclave in order to manufacture several parts simultaneously by using different turbulating devices simultaneously and at different locations in the same autoclave according to the need for each of the parts produced at the same time in said autoclave.

The process which is the subject of the present invention then makes it possible to reduce the cooking and cooling time of the structural parts produced in an autoclave employing said process, to limit the persistent thermal heterogeneities in large pieces after the autoclave cycle, to increase the productivity while limiting the cost of modifying the heating system of the autoclave in situ, and increasing the useful volume of cooking in the autoclaves.

The method for improving the local heat transfer, as described, is intended for all manufacturers of structural parts made of composite materials using ovens or autoclaves, and is applicable both in the case of polymerization of thermosets and in case of crystallization of thermoplastics.

Claims (11)

1. Method for improving the local heat transfer in an autoclave (100) comprising an enclosure (10) in which a gas circulates, and a mold (11) in which a structural part (12) is produced, said method comprising a step preliminary (200) for placing said structural part in said mold, and characterized in that it comprises: - A step (201a) of installation, in the vicinity of the structural part (12), of a turbulator device (15) which locally increases the turbulence of a gas flow passing through said turbulator device; - A step (202a) for positioning the mold (11) and the structural part (12) at a determined location in the enclosure (10) of the autoclave; - A step (300) of execution of the autoclave (100) cooking cycle adapted to the structural part (12). 2. Method according to claim 1, in which the step (201a) of installing the turbulator device (15) in the vicinity of the structural part (12) consists in positioning said turbulator device so as to completely cover the face of said part. most exposed to convective heat transfer during cooking in the autoclave. 3. Method according to one of claims 1 or 2, wherein the dimensions of the turbulator device (15) are chosen according to the geometries and dimensions of the structural part (12) so as to completely cover the face of said structural part most exposed to convective heat transfer during cooking in the autoclave. 4. Method according to any one of the preceding claims, in which the step (202a) of positioning the mold (11) and the structural part (12) in the autoclave (100) consists in introducing said mold into which finds said part covered by the turbulator device (15) in the enclosure (10) of said autoclave at a location previously determined by digital simulation. 5. Method according to any one of the preceding claims, in which the structural part (12) produced in the autoclave (100) is made of composite material. 6. Method according to any one of the preceding claims, in which the turbulator device (15) implemented comprises one or more characteristics among moving parts, corrugated surfaces, cavities, or protuberances, favoring the appearance of turbulence. local in the vicinity of said turbulator device when it is crossed by a gas flow. 7. The method of claim 6, wherein the turbulator device implemented comprises a grid provided with rotary elements which can be set in motion by the gas flows present in the enclosure. 8. The method of claim 7, wherein the rotary elements are motorized. 9. The method of claim 8, wherein the rotary elements are controlled remotely by a system outside the autoclave. 10. The method of claim 6, wherein the turbulator device implemented comprises a grid provided with baffles deflecting the flow of gas passing through said turbulator device and creating local turbulence in the vicinity of said grid. 11. Autoclave (100) intended for cooking a structural part (12) characterized in that it comprises a mold (11) adapted to receive the structural part during step (300) of the method according to one of previous claims, and in that it comprises a turbulator device (15) arranged 5 in the vicinity of the structural part, when said structural part is installed in the mold, so as to locally increase the turbulence on one face of the structural part during step (300). 1/1 100 300  1 i 1 | 1 300   1 1 1