DE3739250A1 - BLACKBOARD - Google Patents

Abstract

A light-weight panel, e.g. for aircraft, is manufactured by preparing a panel preform having a pair of surface members or skins (11, 12, 29, 30, 55, 56, 62, 64) separated and supported by an internal core in which spaces or interconnected pores provide vents to an edge of the panel, the wall surface members and the core comprising fibrous material, which may be carbon fibre, and using a pyrolysis process such as CVD to form a pyrolytic matrix around the fibres within the fibrous material, there being a flow of gas through the vents during the pyrolysis process. <IMAGE>

Description

The invention relates to a board and in particular, but not exclusively, building up Lightweight boards, for example for use in Aircraft construction.

In this description, the word "blackboard" is like this uses that it means a wall element that one area delimited by at least one edge has and can be flat, or with a curved Cross-section in one or more levels, like a Section of a cylinder, cone or one Bullet.

To build a board that has a high ratio Stiffness to weight, it is known such sheets of two thin layers one to produce the appropriate material by a lightweight inner core, for example from Honeycomb structure, are separated. The core can be from other Material as the layers are made.

The present invention is primarily concerned with with the problem of a lightweight board with high Rigidity and high strength with increased To create temperatures, in particular, but not exclusively for use in air and Space flight.

In the manufacturing method according to the invention a plate becomes a plate intermediate with two Wall panels made by a Core structure are separated and supported, in which Gaps or interconnected pores Create ventilation towards one edge of the panel that Wall panels and the core contain fiber material and a pyrolysis process is used to obtain a pyrolytic matrix around the fibers in the fiber material  to form a gas flow through the vents during the pyrolysis process.

A preferred method according to the invention for Production of a carbon / carbon composite panel involves forming a core assembly from a series of hollow elements made of carbon fiber that form spaces, what vents to an edge of the board manage to attach one at a time Carbon fiber panel on each side of the Kernes and the use of a pyrolysis process for Form a pyrolytic carbon matrix around the Carbon fibers, during the pyrolysis process there is a gas flow through the vents.

The invention also results in a panel according to one of the defined in the previous two paragraphs Procedure is established.

In this description and in the claims the term "pyrolytic matrix" means a matrix that by exposure to heat at a temperature above 400 ° C was generated to chemical decomposition of a To bring about matrix precursor material, such as for example the conversion of a Carbon bond to carbon with release gaseous by-products, or a chemical Decomposition of carbon in the spaces between Preform, such as the introduction of a carbon-containing gas and the splitting of the gas for carbon deposition (with the generation of gaseous by-products), and is limited to this. With the "decomposition" occurring at high temperature and "deposition" operations as described in this Context, it is important To create ventilation means to allow gases to penetrate and / or allow the board to escape, and the  Use of the terms "pyrolysis" and "pyrolytic Matrix "is intended to exclude matrices created by others chemical processes are produced in which it it is not necessary to enter or withdraw gases to let.

The wall panel elements and the core structure can be one Preform made of carbon fibers by a Carbon matrix is solidified, which by a chemical vapor deposition (chemical vapor deposition = CVD) was deposited to a To form carbon / carbon composite, or a Carbon matrix caused by a charring process was deposited from tar or resin, all of which Procedures are well known. Preferably that is Fiber material through the resin charring and / or CVD processes bound and stiffened. The carbon fiber can be non-graphitized, partially graphitized or be fully graphited, depending on the required thermal conductivity. she can be pre-carbonated or carbonized on site, e.g. B. from a fabric made of oxidized acrylic fiber (i.e., polyacrylonitrile fiber) Use of the term "pre-carbonized" is said be that the carbon fibers before insertion in the wall surface elements or the core structure completely were carbonized).

Alternatively, the core structure can be consolidated or nonwovens include open cell foam materials.

Other fiber materials, such as silicon carbide fibers or mixtures of carbon fibers with Silicon carbide fibers can be used. Around To achieve oxidation resistance at high temperatures, ceramic or glass ceramic fibers can be used will. The matrix can contain other materials  or include, such as antioxidants or other additives, or it can be, for example, a silicon carbide matrix be used.

Conversion processes can be used to convert a Convert fiber preform to other shapes; so can for example a carbon preform by a corresponding thermochemical process in Silicon carbide can be converted.

Exemplary embodiments of the invention are described below explained in more detail with reference to the drawing; in the Drawing shows

Fig. 1 is a schematic cross-sectional view of a portion of a panel produced by a method of the invention,

Fig. 2, 3, 4 and 5 representations similar to Fig. 1 alternative board structures, manufactured using the method according to the Invention, and

Fig. 6 is a schematic cross-sectional view of part of a panel during the manufacture position.

The panel 10 in FIG. 1 contains two outer wall surface elements or outer layers 11 and 12 which are connected to and separated from one another by a core structure 13 .

The core assembly 13 consists of a series of interconnected hexagonal tubes 16, 17 and 18 which are formed of impacted oxidized acrylic fiber to provide a unitary assembly in which the tubes are connected by webs 20, 21 and 22 from the knit fabric.

During manufacture, the tubes 16, 17 and 18 are brought into a hexagonal shape by inserting appropriately shaped molded parts (e.g. made of carbon) and then subjected to a carbonization process. The molded parts are then replaced by destructible or decomposable supports. The outer layers 11 and 12 of carbon fiber fabric are then easily bonded to the outer surfaces of the tubes using an appropriate resin adhesive, as shown in FIG. 1. The assembly is held flat between carbon plates during curing and carbonization of the resin, and the resulting free-standing panel is then subjected to chemical vapor deposition of carbon to densify both the core 13 and the outer layers 11 and 12 .

By using hollow elements in the form of tubes 16, 17 and 18 , which run parallel to the plane of the plate 10 , the plate structure is well suited for the penetration and passage of chemical vapors through the spaces 23, 24, 25 which extend parallel to the plate plane and to all parts of the structure, and to vent at the edges of the board, so that a uniform coating of the necessary compacting carbon matrix is possible.

Alternatively, the core and / or the Pre-impregnated with an appropriate resin which is then carbonized and again results the open structure of the core spaces through which non-carbon components of the resin can escape in gas form.

The structure shown in FIG. 2 is similar in all respects to that of FIG. 1, but here the tubes 26, 27 and 28 are integrally connected to one another so firmly that they touch one another without connecting webs, and they are between the outer layers 19 and 30 arranged in circular cross-sectional shape.

The structure of FIG. 3 also comprises tubes 36, 37 and 38 of circular cross section, but they are again by webs 31, 32, 33 connected together. Any desired distance and any possible cross-sectional shape of the tubes can be achieved by modifying the assembly process and using appropriate shapers.

Fig. 4 shows a panel 40 , which is constructed in the same way as that just described, but the core structure 42 is here constructed by triangular tubes 43, 44, 45 with enclosed spaces 46, 47 and 48 for ventilation to the edge of the panel. The fabric or knitted fabric forming the core structure 42 can be knitted as an integral structure with connecting seams at the edges 50, 51 and 52 of the adjacent tubes, or it can be produced from woven, non-woven or knitted fabric web, these webs being arranged around corresponding shaped elements in the illustrated configuration are folded.

An advantage of the core structure according to FIG. 4 is the large connecting area that the side walls of the triangular tubes 43, 44 and 45 offer for the contact of the respective outer wall layers 55 and 56 .

FIG. 5 shows part of a panel 60 in which the outer layers 62 and 64 are attached to a core assembly of tubes 66 and 67 which is generally similar to that shown in FIG. 2, but in this case the tubes 66, 67 provided with flattened cross-sectional shapes in order to enlarge the bonding area of the tubes with the outer layers 62, 64 .

The manufacture of boards according to the invention in the following using exemplary embodiments explained.

Embodiment 1

For producing a panel according to Fig. 5 has been oxidized to acrylic fiber integrally knitted tubes 66, 67 formed, each tube mm a nominal diameter of 10 mm, a crotch width of about 12 and had a nominal wall thickness of 1 mm.

Graphite rods of 10 mm diameter were in the knitted tubes used and resulted during the subsequent carbonation or Charring a support that ensured that the knitted tubes have their circular cross section kept. The carbonization of the acrylic fibers was by heating in a nitrogen atmosphere, removing Compounds made of nitrogen, carbon, hydrogen and oxygen and converting the fibers to carbon carried out. The temperature was measured at a rate of 100 ° C / h to 1020 ° C ± 10 ° C and 4 h on this Value held. An overpressure of nitrogen was at continuous flow during heating and Always maintain later cooling.

After carbonization, the graphite rods were removed and rolled-up paper tubes 70 ( Fig. 6) were inserted into the knitted tubes. The tendency of the paper tubes to roll up gave a small compressive force from the outside, as indicated by arrows in Fig. 6, so as to support the knitted tubes. The tubes were then coated with resin and glued to separately formed cover or skin layers 62, 64 , the manufacture of which will be described later. The paper rolls gave a support that could then be easily removed.

The skin or skin layers 62, 64 were made from a non-woven fabric of aligned, oxidized acrylic fibers arranged in two layers, the fibers of each layer being perpendicular to those in the other layer, and these two layers were easily pricked together . The fiber layers were carbonized in a similar process to that used for the knitted tubes.

The tubes and the outer layers were then (separately) evenly coated with a mixture of about 50% phenolic resin (Cello Bond J22255 from BP Chemicals) and acetone so that the resin was distributed at 0.05 g / cm ² the total area of each component resulted.

The outer layers were then placed on both sides of the knitted tubes, as shown in Fig. 2, the fibers of the respective outer surface layer being parallel to the axes of the tubes. The panel assembly and core thus formed was then pressed to a total thickness of 10 mm (set by spacers) between flat graphite plates, with a layer of silicone treated paper on each side preventing the resin from sticking to the plates. A pressure force of 7000 N / m ² was then applied to each panel by weight loading the panels. The paper tubes allowed the knitted tubes to deform into the shape shown in FIG .

After drying overnight, the resin in the panel was heated to cure while maintaining a 10 mm gap between the graphite plates. The temperature was first held at 80 ° C for 1 h and then raised at a rate of 6 ° C / h, with holding times of 2 h at 120 ° C, 3 h at 150 ° C, 3 h at 175 ° C and 4 h at 210 ° C. After the resin had hardened, the spacers were removed and a slight pressure of about 15 N / m ^{2 was applied} through the flat graphite plates in order to prevent deformation during the carbonization.

The resin was then heated in nitrogen carbonized. The temperature was measured at a rate of 20 ° C / h up to 750 ° C and 50 ° C / h up to 1050 ° C, and held at 1050 ° for 4 hours. A nitrogen overpressure with continuous flow was during heating and the subsequent cooling continuously maintain.

After carbonization, the tablet was unsupported. The charred paper tube and the silicone-treated Paper was removed.

The sheet was then chucked at the edges in an apparatus and subjected to high temperature deposition treatment for 500 hours in a vacuum furnace supplied with low pressure methane, the methane then being broken down to form in the matrix between the fibers of the sheet to deposit carbon by a CVD process. The amount of carbon deposited was on the order of 0.4 g / cm ² panel area (ie based on the area of one side surface of the panel).

The panel obtained had the following components and Characteristics:

% By weight Knitted carbon fiber tubes21  Carbon fiber skin 12 Charred resin carbon matrix11 CVD carbon matrix56

Average specific
Wall density = 1.18 g / cm ³ Average specific
Total weight = 0.62 g / cm ³ total thickness = 10 mm basis weight = 0.62 g / cm ² thickness of each outer layer = 1 mm

Embodiment 2

A knitted oxidized acrylic fiber structure in general the same as in embodiment 1 was according to Embodiment 1 assembled and carbonized. In this example, the outer layers were made from one Eight-layer velvet fiber fabric (A0021 from Fothergill Engineering fabrics using 1000-filament yarns made from acrylic-based carbon fibers (T300) from Toray).

Each outer skin consisted of a single layer of one resin-soaked tissue and the skin layers were too both sides of the knitted tubes so constructed that the Fibers aligned at 0 ° or 90 ° to the tube axis were.

The carbonization and CVD processes were then carried out in the same way as in embodiment 1.

The finished panel had the following components and Characteristics:

% By weight Knitted carbon fiber tubes37 Carbon fiber outer layers 5 Charred resin-carbon matrix13 CVD carbon matrix45

Average specific
Wall density = 1.1 g / cm ³ Average specific
Total density = 0.71 g / cm ³ total thickness = 9 mm basis weight = 0.64 g / cm ² thickness of each skin = 0.25 mm

Embodiment 3

An array of integrally knitted fiber tubes based on oxidized acrylic and non-woven fiber skin layers was made as in Example 1, but in this example the array was carbonized in a single process, completely avoiding the use of resin or any other binder. 10 mm diameter graphite rods were inserted into the knitted tubes and the fiber skin layers were placed so that the fibers of the outer surfaces were parallel to the tube axis. The arrangement was held between two flat graphite plates during the carbonization under a constant compressive force of approx. 7000 N / m ² . The carbonization cycle was similar to that for the skin and core fibers in embodiment 1. The constant pressure force, together with the tendency of the fibers to shrink and ripple during carbonization, "caught" the skin layers and the tube cores.

After carbonization, the 10 mm rods and the flat plates were carefully removed. The fiberboard obtained retained the shape achieved by the plates and the rods (see FIG. 2), it was self-supporting and could be handled easily. It was then supported at its edges in a graphite device so that gas could flow past it and through the hollow tubes of the core during a subsequent CVD infiltration process as described in Example 1. The amount of carbon deposited in the CVD process was approximately 0.6 g / cm ² .

The finished panel had the following components and Characteristics:

% By weight Knitted carbon fiber tubes18 Carbon fiber skin layers 10 CVD carbon matrix72

Average specific
Wall density = 1.4 g / cm ³ Average specific
Total density = 0.72 g / cm ³ total thickness = 11.5 mm basis weight = 0.83 g / cm ² thickness of each skin = 1 mm

Embodiment 4

A panel was made in the same manner as described in Embodiment 3, but non-circular graphite rods were used to support the tubes in the initial carbonization process, so that after carbonization, a non-circular cross-section as shown in Fig. 5 resulted, and this became subjected to the CVD process described in embodiment 3.

The use of rigid graphite shaped bars for Internal support in the process after Embodiment 4 resulted in a larger one Interface between the core of knitted tubes and the skin layers, so that an improved Connection between the core and the skin layers through the initial carbonization process was created.

The finished panel had the following components and Characteristics:

% By weight Knitted carbon fiber tubes15 Carbon fiber skin layers15 CVD carbon matrix70

Average specific
Wall density = 1.4 g / cm ³ Average specific
Total density = 0.51 g / cm ³ total thickness = 12 mm basis weight = 0.55 g / cm ² thickness of each skin = 1 mm

According to the exemplary embodiments described Manufactured boards had the advantage of being small  specific weight and high rigidity. A Main characteristic is that by the core extending spaces are provided that the passage of gases in chemical vapor deposition (CVD) or the escape of gases during resin charring allow for compression. The blackboard can easily be used Use of suitable devices for carbonization and compacting in required curved shapes be formed.

Certain types of panels according to the invention, in particular Non-graphitized carbon / carbon plates Bundles can also be used at very deep Temperatures may be suitable as they are mechanical Strength with low thermal conductivity perpendicular to the board (through the cavities in the core structure) connect.

Although two in the described embodiments wall panels separated by a core structure the core can also be one or more Reinforcing element (s) included, e.g. B. can be a Multi-layer construction at least two stacked Hollow core structures with an intermediate one Skin layer included.

Claims (26)

1. A method for producing a building board, characterized in that a board ( 10; 40; 60 ) is produced with two wall surface elements ( 11, 12; 55, 56; 62, 64 ) separated by a core element ( 13; 42 ) and are supported in which spaces ( 23, 24, 25; 46, 47, 48 ) or interconnected pores create vents to an edge of the panel, the wall panels and core being made of fiber materials and using a pyrolysis process to a pyrolytic matrix to form the fibers in the fibrous material while maintaining a gas flow through the vents during the pyrolysis process. 2. A method for producing a carbon / carbon composite panel, characterized in that a core structure ( 13; 42 ) is prepared from a series of hollow elements ( 16, 17, 18; 26, 27, 28; 36, 37, 38; 43, 44, 45; 66, 67 ) made of carbon fiber, which define spaces ( 23, 24, 25; 46, 47, 48 ) through which vents are created to one edge of the panel that two carbon fiber wall surface elements ( 11, 12 ; 55, 56; 62, 64 ) are individually attached to each side of the core assembly and that a pyrolysis process is used to form a pyrolytic carbon matrix around the carbon fibers while maintaining gas flow through the vents during the pyrolysis process. 3. The method according to claim 2, characterized in that the carbon fibers of the core structure ( 13 ) are formed on the spot by carbonization of a preform made of carbonizable fiber material. 4. The method according to claim 2, characterized in that the core ( 13; 42 ) is formed by carbonization of a preform made of oxidized acrylic fiber. 5. The method according to any one of claims 2 to 4, characterized in that the carbon fibers of the wall surface elements ( 11, 12; 55, 56; 62, 64 ) are formed on the spot by the carbonization of carbonizable fiber material. 6. The method according to claim 5, characterized in that the carbon fibers of the wall surface elements ( 11, 12; 55, 56; 62, 64 ) are formed on the spot by carbonization of oxidized acrylic fibers. 7. The method according to claim 2, characterized in that the core ( 13; 42 ) is formed from precarbonized fiber material. 8. The method according to claim 2, characterized in that the wall surface elements ( 11, 12; 55, 56; 62, 64 ) are formed from precarbonized carbon fiber material. 9. The method according to claim 2, characterized in that the core structure from a series of tubes ( 16, 17, 18; 26, 27, 28; 36, 37, 38, 43, 44, 45; 66, 67 ) is formed. 10. The method according to claim 9, characterized in that the tubes are made of knitted fabric. 11. The method according to claim 10, characterized in that shaped elements ( 70 ) are used for forming the tubes. 12. The method according to any one of claims 9 to 11, characterized in that the tubes ( 26, 27, 28; 36, 37, 38 ) are formed with a circular cross section. 13. The method according to claim 11, characterized in that the tubes ( 16, 17, 18, 26, 27, 28; 36, 37, 38; 43, 44, 45; 66, 67 ) through during the application and curing of a resin non-rigid inner supports are supported. 14. The method according to claim 13, characterized in that the tubes ( 16, 17, 18, 26, 27, 28; 36, 37, 38; 43, 44, 45; 66, 67 ) through during the application and curing of the resin inserted winding tubes ( 70 ) are supported. 15. The method according to claim 13 or 14, characterized in that the wall surface elements ( 62, 64 ) with the core structure ( 66, 67 ) are connected by a curable resin and that pressure is applied to the two components during the curing of the resin to flatten the pipe cross-section. 16. The method according to any one of claims 9 to 11, characterized in that the tubes ( 16, 17, 18 ) are provided with a non-circular cross-section by inserting inner supports. 17. The method according to claim 10, characterized in that webs ( 20, 21, 22, 31, 32, 33 ) are formed from the knitted fabric for connecting the tubes. 18. The method according to any one of claims 9, 10, 11, 15 or 16, characterized in that the tubes ( 16, 17, 18 ) are deformed into a hexagonal cross section. 19. The method according to claim 9 or 10, characterized in that the tubes ( 43, 44, 45 ) are formed with a triangular cross section. 20. The method according to any one of claims 2 to 19, characterized in that the tubes ( 43, 44, 45 ) are formed from folded fabric. 21. The method according to any one of claims 2 to 20, characterized in that the wall surface elements ( 11, 12; 55, 56; 62, 64 ) are made of non-woven fiber webs. 22. The method according to any one of claims 2 to 20, characterized in that the wall surface elements ( 11, 12; 55, 56; 62, 64 ) are made from woven webs. 23. The method according to claim 2, characterized in that the core structure is formed from non-woven material. 24. The method according to claim 2, characterized in that the core is made of an open cell foam material is formed. 25. A panel formed by a method according to one of the preceding claims, characterized in that the panel comprises two wall surface elements ( 11, 12; 55, 56; 62, 64 ) which are separated and supported by a core structure ( 13; 42 ). which comprises spaces or interconnected pores for ventilation to an edge of the board, the wall surface elements and the core being made of a fiber material consolidated by a pyrolytic matrix. 26. Carbon / carbon composite panel, produced by a method according to one of claims 1 to 24, characterized in that the panel comprises two wall surface elements ( 11, 12; 55, 56; 62, 64 ), each with one side of a core structure ( 13; 42 ) which comprises a series of hollow elements ( 16, 17, 18; 26, 27, 28; 36, 37, 38; 43, 44, 45; 66, 67 ), which spaces ( 23, 24 , 25; 46, 47, 48 ) for ventilation to an edge of the panel, the hollow elements and the wall surface elements being composed of carbon fibers stiffened by a pyrolytic carbon matrix.