FR2693147A1 - Repair of sandwich type composite material parts partic. aircraft radomes - with hot cured patch gas cooling element around repair area to prevent accelerated ageing of undamaged areas - Google Patents

Abstract

Composite material parts, partic. of sandwich construction are repaired with a hot curable patch put in place and then cured by:- (a) heating the part to be repaired to a limited temp. above ambient but less than the patch curing temp. or the temp. to cause accelerated ageing of the part; (b) heating the patch to curing temp.; (c) simultaneously cooling a zone around the patch to approximately the temp. in (a) so contg. the cure temp. to the repair zone. Also claimed is an application appts. comprising a heated former raising the part to the limited temp.; a heated mat applied against the patch to force it against the former and raise it to curing temp. A cooling element surrounds the heating mat. A temp. controller is connected to all three elements. USE/ADVANTAGE - Repair of composite material parts partic. civil aircraft radomes. Prevents accelerated ageing of the undamaged areas during repair.

Description

Method and installation for repairing parts made of composite material, in particular of the sandwich type
The invention relates to a method and an installation for repairing parts made of composite material, in particular of the sandwich type.

The expression "composite material" is intended to denote here a synthetic material essentially consisting of a hot-polymerizable binder and reinforcing fibers coated with this binder.

The binder usually consists of a resin, for example of the polyester, epoxy or phenolic type, mixed with a hardener capable of catalyzing the polymerization reaction of the resin, when the mixture is brought to a temperature above room temperature, by example at a temperature between 120 and 180 ° C.

The fibers, playing the role of reinforcement, are generally fibers of glass, polyamide, carbon, etc., woven to form a sheet.

The composite material can be of the monolithic type to form a simple "skin" or else of the sandwich type to form two skins between which an intermediate structure is placed, for example of the honeycomb type.

Composite materials of this kind find numerous applications, for example for the production of panels, fairings, aircraft radomes, etc.

For the repair of a piece of composite material of this kind, an insert is generally used in hot-polymerizable material which is placed in an area to be repaired of the piece and which is then heated to a temperature. sufficient to cause its polymerization and, consequently, its assembly to the part to be repaired.

To ensure the hot polymerization of the insert and its assembly with the part to be repaired, two methods are currently used.

The first method consists in placing the entire part as well as the insert in an autoclave or in an enclosure brought to a temperature sufficient to ensure the hot polymerization.

This first method has the major drawback of subjecting healthy parts of the part to a high temperature, that is to say to the temperature necessary for the polymerization of the added element.

this high temperature, which is generally between 120 and 180 ° C., leads to an accelerated aging of the part, from which it results in delamination, detachments, cracks, etc., and more generally a loss of mechanical characteristics.

The second method consists of placing a heating mat on the insert previously installed in the area to be repaired, to ensure polymerization when localized repairs are involved.

The main drawback of this second method is that it creates a significant temperature difference between the heated part and the unheated part of the part to be repaired. This has the consequence of creating delaminations in the healthy parts of the part, in particular in the case of parts made in sandwich.

The main object of the invention is to overcome the aforementioned drawbacks in order to avoid accelerated aging of the healthy parts of a part made of composite material to be repaired.

 It is also an object of the invention to provide a method and an installation making it possible to carry out repairs on parts made of composite material, under perfectly controlled conditions, to avoid heating of the healthy parts of the parts to be repaired.

 It is also an object of the invention to provide such a method and such an installation intended in particular for repairing radomes for civil transport aircraft.

The invention relates more particularly to a method of repairing a part made of composite material, according to which an insert made of hot-polymerizable material is placed in an area to be repaired of the part and heated to a temperature sufficient to cause its polymerization. .

According to an essential characteristic of the invention, the following operations are carried out in a controlled manner a) bringing the part by heating to a limited temperature, which is higher than ambient temperature, lower than the polymerization temperature of the added element and insufficient to cause accelerated aging of the part b) heating the added element to its polymerization temperature, previously placed in the area to be repaired of the part; and c) cooling a restricted peripheral zone of the part closely surrounding the zone to be repaired in order to maintain this peripheral zone at a temperature close to the limited temperature of the part and thus circumscribing the polymerization temperature to the zone to be repaired.

Thus, by bringing the part to a limited temperature, for example 60 ° C., phenomena of differential expansion between the part itself and the element added for repair, which is heated to polymerization temperature, are avoided. that is to say at a temperature generally between 120 and 180 c.

In addition, the polymerization temperature is limited to the area to be repaired, that is to say to the insert, since the peripheral area of the part, closely surrounding the area to be repaired, is cooled under conditions controlled. This prevents the heat resulting from the heating of the insert from being transmitted to healthy parts of the part to be repaired, and in particular to the peripheral zone which immediately surrounds the zone to be repaired.

this peripheral zone is thus maintained at a temperature close to the room temperature; which is brought to reasonable values, for example to a maximum value of 80 C for the temperature values mentioned above.

Because the polymerization temperature is limited to the area to be repaired, the healthy parts of the part are not heated and therefore cannot undergo accelerated aging, unlike the processes of the prior art.

 According to another characteristic of the process of the invention, the limited temperature of the part, the temperature and the duration of polymerization of the added element, as well as the temperature of the restricted zone of the part, are adjusted. In this way, the repair of the part is carried out under perfectly controlled conditions according to the characteristics of the part and those of the polymerizable material from which the insert is formed.

In another aspect, the invention relates to an installation of a part made of composite material, which essentially comprises - a heating shaper capable of receiving the part by covering at least the area to be repaired and of bringing the part to a limited temperature, which is higher than room temperature, lower than the polymerization temperature of the insert and insufficient to cause accelerated aging of the part - a heating mat of dimensions adapted to those of the area to be repaired, suitable for being applied against the add-on element previously put in place in the repair area to heat the add-on element to its polymerization temperature - a cooling element capable of covering a restricted peripheral area of the part closely surrounding the area to be repaired to maintain this peripheral area at a temperature close to the limited room temperature and cir record the polymerization temperature in the area to be repaired; and - thermal regulation means coupled to the heating shaper, the heating mat and the cooling element.

According to another characteristic of the invention, the heating shaper has a shape adapted to that of the part so as to cover at least the area to be repaired.

Such a shaper is produced (unless it does not already exist due to previous or repetitive repairs, such as for example on aircraft radomes) by the known technique of "mold / counter mold" by taking an imprint of the part that covers at least the area to be repaired.

This shaper is made of composite materials and / or metal and comprises a heating network with adjustable temperature, which is advantageously formed by heating resistors incorporated in the shaper.

The temperature of the former is advantageously limited to a value of 60 ° C., which avoids the phenomena of accelerated aging of the part to be repaired.

In addition, according to another characteristic of the invention, this former includes a heat-insulating coating intended to avoid loss of energy.

According to another characteristic of the invention, the heating mat comprises a flexible mat capable of being cut to the desired dimensions, that is to say those of the area to be repaired, as well as a heating network with adjustable temperature.

This heating mat is advantageously made of an elastomer / silicone mixture, that is to say of a material resistant to a temperature of 250 C. The heating network of the carpet is advantageously formed of a network of resistive wires incorporated in the thickness carpet or glued to a surface of the latter.

The heating of the carpet is ensured under conditions of temperature and duration determined as a function of the conditions of polymerization of the added element. The maximum temperature of the heating mat is advantageously 180 C.

The cooling element forming part of the installation of the invention comprises an annular mattress, of dimensions adapted to those of the restricted peripheral zone, and housing at least one pipe suitable for being traversed by a refrigerant or cooling fluid.

The cooling of this peripheral zone is carried out under controlled conditions and prevents the temperature of the sound part of the part to be repaired from conduction on the periphery of the repair. The refrigerant or cooling fluid circulating in the cooling element can be gaseous or liquid.

According to another characteristic of the invention, the installation comprises a membrane capable of being applied in a leaktight manner to the part by covering the heating mat and the cooling element, as well as a vacuum pump capable of applying reduced pressure. in the space delimited by the membrane.

this membrane makes it possible to place the assembly under vacuum and to ensure the uniformity of the bonding of the repair.

The means of thermal regulation of the installation include temperature probes associated respectively with the heating shaper, the heating mat and the cooling element.

Advantageously, the regulating means also comprise means for adjusting the temperature of the shaper, the temperature and the operating time of the heating mat, as well as the temperature of the cooling element.

In the description which follows, given by way of example, reference is made to the appended drawings, in which - FIG. 1 is a partial elevation view of an installation according to the invention, intended for the repair of a radome d aircraft - Figure 2 is a partial sectional view along line II
Figure 1; and - Figure 3 is a detail, on an enlarged scale, of the installation of Figure 2.

The installation shown in Figures 1 and 2 comprises a frame 10 provided with four rollers 12 for its movement on the ground. On the chassis 10 is mounted an inclined support 14 carrying a ball ring 16 on which is removably mounted a shaper 18.

Thanks to the ball ring 16, the shaper 18 can turn on itself around an axis XX inclined by an angle A, here 45, relative to the horizontal. The shaper 18 has here the shape of a paraboloid of revolution whose axis coincides with its axis of rotation XX. Shaper 18 constitutes a kind of mold suitable for receiving a part 20 of composite material which, in the example, is an aircraft radome. The part 20 is immobilized in the shaper 18 by at least one fixing 21.

Shaper 18 has a shape adapted to that of the radome 20 and it can be made from an impression of the radome, unless it already exists due to previous or repetitive repairs on a radome of the same type.

The shaper 18 is made of composite material and / or metal and it comprises a wall 22 in which are incorporated heating resistors 24 supplied by an electric cable 26 passing through a hole 28 in the support 14 (FIG. 2) and connected to a control unit 30. In the thickness of the wall 22 is also housed a temperature sensor 32 connected by an electric cable 34, which also passes through the hole 28, to the control unit 30. On the external face of the wall 22 is provided with a heat-insulating coating 36 to avoid energy loss. Shaper 18 is intended to bring the radome to a limited temperature which, in the example, is 60 C.

The radome 20 has a wall 38 of synthetic composite material, for example of the sandwich type, which is placed in contact with the internal surface of the wall 22 of the shaper 18. The wall 38 of the radome 20 comprises an area to be repaired in which has been put in place an insert 40 (Figure 3) formed of a polymerizable hot, compatible with the material from which the wall 38 of the radome is formed. The insert 40 is placed in contact with the internal surface of the wall 22 of the shaper and it has an external peripheral edge 42 coming into contact with an internal peripheral edge 44 of the area to be repaired.

 The installation of the invention further comprises a heating mat 46 of dimensions adapted to those of the area to be repaired and therefore of the insert 40. The heating mat 46 is formed from a flexible material, for example made of an elastomeric mixture / silicone resistant to a temperature of 250 C. The heating mat 46 incorporates a network of resistive wires 48 which are connected to the control unit 30 by means of an electric cable 50. In addition, the heating mat 46 comprises a cooling probe 52 which is connected to the control unit 30 by means of an electric cable 54.

The heating mat 46 allows the added element 40 to be brought to an adjustable temperature, generally between 120 and 180 c, to allow its polymerization.

The installation of the invention further comprises a cooling element 56 suitable for covering a restricted peripheral zone 58 of the radome 50 which closely surrounds the zone to be repaired. In the example, the peripheral zone 58 has a generally annular configuration and it is internally limited by the internal edge 44 of the radome 20.

The cooling element 56 is a mattress adapted to the dimensions of the area to be repaired and it has internal pipes 60 for the circulation of a cooling or cooling fluid, liquid or gaseous. The pipes 60 are connected by conduits 62 to the control unit 30.

The cooling element 56 also comprises a temperature probe 64 connected to the central unit 30 by an electric cable 66.

The central control unit 30 makes it possible to adjust the temperature of the zone 58 to limit it to reasonable values, for example 80 ° C. maximum.

The installation further comprises a membrane 68 suitable for being applied in a sealed manner to the radome by covering the heating mat 46 and the cooling element 56. The seal between the membrane 68 and the radome 20 is ensured by a flange d peripheral sealing 70. The membrane 68 is connected to a vacuum pump 72 via a conduit 74, which makes it possible to apply a reduced pressure in the space delimited by the membrane 68.

The installation of the invention operates as follows.

After placing the radome 20 in the heating shaper 18, the insert 40 is placed in the area to be repaired.

The heating mat 46 is then installed, previously made to the dimensions of the area to be repaired; and it is connected to the central control unit 30. The temperature probe 52 is also installed, which is also connected to the central unit 30. the latter is set to the desired temperature and duration of polymerization.

Around the area to be repaired, the cooling element 56 is installed, which is connected to the central unit 30 by the conduits 62.

The temperature probe 64 is also installed in the peripheral zone 58, which is connected to the control unit 30.

this central unit controls the circulation of the cooling fluid and it is adjusted so that the temperature of the restricted peripheral zone 58 is much lower than the polymerization temperature, while being barely higher than the temperature of the heating shaper 18, which is limited at around 60 C in the example considered.

The membrane 68 is then placed and the assembly is placed under vacuum.

After checking the installation, the displayed temperatures are checked and operation is carried out: the vacuum pump 72, the heating network of the shaper 18, the heating mat 46, the cooling element 56 as well as a temperature recorder 76 which is coupled to the central controller 30.

The radome 20 is thus brought to a temperature limited to around 60 ° C., which homogenizes the phenomena of expansion between the whole of the radome to be repaired and the insert 40, while reducing the difference between the temperature of the radome and the polymerization temperature of the insert 40 placed in the area to be repaired.

 The cooling element 56 circumscribes the polymerization temperature to the added element 40 in the area to be repaired.

Therefore, the healthy parts of the radome are not subjected to high temperatures and the composite material from which the radome is formed does not undergo accelerated aging phenomena.

A repair is then carried out which leaves the part in its normal aging cycle, which is very important in particular in aeronautical maintenance.

Of course, the invention is susceptible of numerous variants and is not limited to the repair of an aircraft radome.

In each case, the conformator is adapted to the shape of the part to be repaired. Similarly, the repair can be done by means of one or more added elements.

Claims (10)

Claims 1. Method for repairing a part made of composite material, in which an insert (40) made of heat-polymerizable material is placed in a repair area of the part (20) and heated to a temperature sufficient to cause its polymerization, characterized in that the following operations are carried out in a controlled manner a) bringing the part (20) by heating to a limited temperature, which is higher than the ambient temperature, lower than the polymerization temperature of the added element (40 ) and insufficient to cause accelerated aging of the part b) heating to its polymerization temperature the added element (40), previously installed in the area to be repaired of the part (20); and c) cooling a restricted peripheral zone (58) of the part (20) to maintain this restricted zone at a temperature close to the limited temperature of the part (20) and thus circumscribing the polymerization temperature to the zone to be repaired. 2. Method according to claim 1, characterized in that one regulates the limited temperature of the part (20), the temperature and the duration of polymerization of the insert (40) and the temperature of the restricted zone (58 ) of the part (20). 3. Installation for repairing a part made of composite material, comprising means for placing an insert (40) made of heat-polymerizable material in an area to be repaired of the part (20) and means for heating the element added (40) to a temperature sufficient to cause polymerization, characterized in that it comprises - a heating shaper (18) capable of receiving the part (20) by covering at least the area to be repaired and bringing the part to a limited temperature, which is higher than room temperature, lower than the polymerization temperature of the insert (40) and insufficient to cause accelerated aging of the part - a heating mat (46) of dimensions adapted to those of the area to be repaired, suitable for being applied against the insert (40) previously placed in the area to be repaired to heat the insert (40) to its temperature ure of polymerization - a cooling element (56) suitable for covering a restricted peripheral zone (58) of the part (20) closely surrounding the zone to be repaired in order to maintain this restricted zone at a temperature close to the limited temperature of the part and circumscribe the polymerization temperature to the area to be repaired; and - thermal regulation means (30) coupled to the heating shaper (18), the heating mat (46) and the cooling element (56). 4. Installation according to claim 3, characterized in that the heating shaper (18) has a shape adapted to that of the part (20) to cover at least the area to be repaired. 5. Installation according to one of claims 3 and 4, characterized in that the heating shaper (18) comprises a heating network (24) at adjustable temperature and a heat-insulating coating (36). 6. Installation according to one of claims 3 to 5, characterized in that the heating mat (46) comprises a flexible mat capable of being cut to the desired dimensions and a heating network (48) at adjustable temperature. 7. Installation according to one of claims 3 to 5, characterized in that the cooling element (56) comprises an annular mattress of dimensions adapted to those of the restricted peripheral zone (58), housing at least one pipe (60 ) suitable for being traversed by a refrigerant or cooling fluid. 8. Installation according to one of claims 3 to 7, characterized in that it comprises a membrane (68) suitable for being applied in a sealed manner to the part (20) by covering the heating mat (46) and the element cooling (56), as well as a vacuum pump (72) capable of applying reduced pressure in the space delimited by the membrane.  9. Installation according to one of claims 3 to 8, characterized in that the thermal regulation means comprise temperature probes (32, 52, 64) associated respectively with the heating shaper (18), the heating mat (46) and to the cooling element (56). 10. Installation according to one of claims 3 to 9, characterized in that the thermal regulation means comprise means (30) for adjusting the temperature of the heating shaper (18), the temperature and the operating time of the heating mat ( 46) and the temperature of the cooling element (56).