JP5590686B2 - Method for producing thermal protection composite material - Google Patents

Description

  The present invention relates to a method of manufacturing an ablator type thermal protection composite material that thermally protects an airframe by wearing an outer surface under severe heating conditions, and a thermal protection composite material manufactured by this method.

  When a recovery system such as a spacecraft enters the atmosphere of a planet such as the Earth from an earth orbit or planetary orbit, the aircraft is exposed to an aerodynamic heating environment. In order to prevent this aerodynamic heating from entering the machine, it is necessary to cover the outer surface of the machine with a thermal protection material. Among the collection systems, the collection capsules in particular have a severe heating environment that is exposed at the time of entry, and therefore employ an ablator type heat protection material that thermally protects the internal equipment by damaging the outer surface. Representative examples of such spacecraft include Apollo spacecraft, Galileo (Jupiter rush, 1995 rush), USERS spacecraft REV capsule (collected in 2003), and the like.

Among them, Galileo and REV capsules of USERS spacecraft use ablator made of CFRP suitable for high heating environment. This CFRP ablator has a density of about 1.5 g / cm ³ (see Non-Patent Document 5), is smaller than the density of aluminum alloy of about 2.7 g / cm ^{3, and has a} higher specific strength and specific rigidity, and excellent heat resistance. It is what. However, since this CFRP ablator accounts for a considerable part of the weight of the entire airframe, it has been required to further reduce the density.

For this reason, a lighter ablator has been actively researched at NASA in the United States, and as a result, PICA (Phenolically Impregnated Carbon Ablator) (see Non-Patent Documents 1 and 2) has been developed. PICA is an extremely lightweight ablator with a density of about 0.25 to 0.35 g / cm ³ and has already been adopted in the planetary explorer Stardust (launched in 1999).

  The ablator targeted by the present invention is a composite material produced by impregnating a reinforcing fiber such as carbon fiber with a matrix made of a thermosetting resin such as a phenol resin and then thermosetting and molding, and is exposed to a severe heating environment. When it is done, it heats itself and shields the heat input to the inside.

  The PICA is produced by making carbon fibers into short fibers with a diameter of 14-16 μm and a fiber length of 1600 μm in water slurry, mixing this with a water-soluble phenolic resin, vacuum casting, thermosetting and carbonizing. Is done. PICA is integrated from the initial stage of manufacture, and is different from the laminated ablator which is the object of the present invention (see Non-Patent Document 1).

  As ablator other than PICA, a laminated type having a structure in which a plurality of prepregs in which a reinforcing fiber is impregnated with a thermosetting resin is laminated is known (see, for example, Patent Documents 1 to 3). The laminated type ablator can control homogeneous impregnation or distributed impregnation by adjusting the amount of resin impregnated into the reinforcing fibers, the thickness of one reinforcing fiber to be used, the number of laminated layers, etc. There is an advantage that it is easy to achieve the target ablator thickness and density.

  In the above-mentioned patent document, in order to produce a laminated type ablator, it is described that after the prepreg is laminated, the resin is cured and the layers are integrated by heating in an autoclave.

JP 2003-48266 A JP 2002-292755 A JP 2001-278199 A

Tran et al., “Phenolic Impregnated Carbon Ablators (PICA) as Thermal Protection Systems for Discovery Missions”, NASA Technical Memorandum 110440, National Aeronautics and Space Administration, April 1997, pp.1-2 Tran, H., Johnson, C., Rasky, D. and Hui, F., “Phenolic Impregnated Carbon Ablators (PICA) for Discovery Missions”, AIAA-96-1191, 31ST AIAA Thermophysics Conference ”June 17-20 , 1996. Metzger, J. W., Engel, M. J. and Diaconis, N. S., “Oxidation and Sublimation of Graphite in Simulated Re-entry Environments”, AIAA Journal, Vol. 5, No. 3, March 1967. Shinichi Okuyama, Junro Kato, Tetsuya Yamada, Masaru Zako, “Thermochemical parameters affecting the oxidative wear of carbonized CFRP surfaces”, Carbon, 2004 [No.213], pp.128-133. Junichi Okuyama, Junro Kato, Tetsuya Yamada, “Research and development of REV ablator by arc heating”, Japan Aerospace Exploration Agency research and development report, USERS / REV capsule development research and post-flight analysis, JAXA-RR-04-045, ISSN 1349-1113, March 2005, PP.55-75.

  However, in the laminated type ablator, the adhesive force between the laminated layers is insufficient, so that the breakage may easily occur depending on the operation mode due to the shearing force, the peel force, the thermal stress, and the like. There is also a problem that it is difficult to achieve the same heat resistance as that of the ultralight ablator PICA.

Accordingly, an object of the present invention is to provide a method for producing a multilayer ablator by a simple technique that is less likely to cause a stress rupture problem and can achieve heat resistance equivalent to or superior to that of an ultralight ablator PICA. And

As a result of studying to solve the above-mentioned problems, the present inventors adopted an integral molding method by sintering using an electric furnace in thermoforming a laminated heat protection composite material and matted short fibers. The present inventors have found that the above problems can be solved by using felt-like fibers, and have completed the present invention.

That is, the present invention is a method for producing a heat-protective composite material comprising reinforcing fibers impregnated with a resin, wherein the reinforcing fibers are felt-like fibers obtained by matting short fibers, and the reinforcing fibers are thermosetting resins. Preparing a plurality of composite sheets (prepregs) impregnated with the above, laminating the plurality of composite sheets, and obtaining the heat protection composite material by performing integral molding by sintering using an electric furnace Features.

  The reinforcing fibers are preferably carbon fibers.

It is preferable that the felt-like fibers are formed by matting short fibers by needle punching or by using an organic binder .

  The thermosetting resin is preferably a phenol resin.

The heat protection composite material is desirably lightweight with a density of 1.0 g / cm ³ or less.

Note that the number of laminated composite sheets can be appropriately determined in consideration of the desired thickness of the heat protection composite material. Further, the plurality of composite sheets forming one heat protection composite material may have the same thickness or impregnation amount, or may be different from each other.
Furthermore, this invention relates also to the heat protection composite material manufactured by the manufacturing method mentioned above.

In the present invention, the adhesive strength between the laminated layers is improved, and a mechanically superior laminated lightweight heat protection composite material that is not easily broken by shearing force, peel force, thermal stress, etc. can be easily produced. In addition, it has become possible to produce a lightweight thermal protection composite material that has superior surface wear resistance compared to the ultralight ablator PICA currently used for planetary probes and the like by NASA. Furthermore, it became possible to manufacture a lightweight thermal protection composite material in which the density of the ablator can be easily controlled by controlling the resin content.

The graph which shows the heat processing conditions (temperature, time) in the hot press and electric furnace sintering of the lightweight thermal protection material in Example 1 and Example 2 Sectional view of the specimen used in the arc heating experiment of Example 1 Sectional view of the specimen used in the arc heating experiment of Example 1 Graph showing the relationship between the light-weight heat protective material and the surface mass attrition rate of PICA and (Pe / R _B) ^0.5 Example 1 Graph showing the relationship between the PCA surface mass wear rate and (Pe / R _B ) ^0.5 The graph which shows the thermal conductivity of Example 1 and the thermal conductivity of PICA, and the relationship of temperature. The graph which shows the relationship between the bending strength and bending elastic modulus, and temperature of the lightweight thermal protection material of Example 1. The graph which shows the relationship between the compression strength of the lightweight thermal protection material of Example 1, and a compression elastic modulus, and temperature. The graph which shows the relationship between the surface mass wear rate of the lightweight thermal protection material of Example 2 (a density of about 0.4 g / cm ³ ) and (Pe / R _B ) ^0.5. The graph which shows the relationship between the surface mass wear rate of the lightweight thermal protection material of Example 2 (a density of about 0.6 g / cm ³ ) and (Pe / R _B ) ^0.5.

  Hereinafter, the present invention will be described in detail.

  The present invention provides a method for producing a heat-protective composite material comprising reinforcing fibers impregnated with a resin, preparing a plurality of composite sheets obtained by impregnating reinforcing fibers with a thermosetting resin, and laminating the composite sheets. Thus, the heat protection composite material is obtained by performing integral molding by heating and pressing such as hot pressing.

  The reinforcing fiber is not particularly limited as long as it can be used in an ablator, and specific examples thereof include carbon fiber and silica fiber. Among these, carbon fiber is preferable because of its excellent performance as an ablator.

  As the form of carbon fiber, generally, long fiber, short fiber, cloth, felt, and the like are known, and these can be used in the present invention. In particular, it is preferable to use a felt-like material. In the felt-like carbon fiber, the impregnation of the thermosetting resin between the fibers constituting the carbon fiber becomes more uniform, and the surface wear resistance performance of the heat protection composite material can be made higher. Further, the contact force between the felt surfaces can further improve the bonding force between the laminated layers. In addition, the felt here means what formed the short fiber into the mat by needle punch processing or using an organic binder.

  The thickness of the reinforcing fiber to be used is not particularly limited, and may be determined in consideration of the desired density of the heat protection composite material, but is usually in the range of about 1 to about 100 mm. In order to achieve homogeneous impregnation of the thermosetting resin in the thickness direction of the reinforcing fiber, it is preferable to make it as thin as possible.

  The thermosetting resin used in the present invention is not particularly limited as long as it can be used in an ablator. Specifically, phenol resin, silicon resin, epoxy resin, and the like can be given. In particular, phenol resin is preferable because it can provide an ablator that is lightweight and excellent in wear resistance.

  In the present invention, first, a plurality of composite sheets (so-called prepregs) are prepared by impregnating a reinforcing fiber with a thermosetting resin. In the impregnation, in order to reduce the viscosity of the thermosetting resin, a mixture of a diluent such as diethylene glycol and the thermosetting resin can be used. The temperature at the time of impregnation for promoting the three-dimensional diffusion of the thermosetting resin in the reinforcing fiber may be room temperature, and the pressure is preferably set to a reduced pressure condition. The amount of the thermosetting resin impregnated may be determined to an appropriate amount in consideration of the desired properties of the heat protection composite material, particularly the density.

  A plurality of composite sheets (prepregs) produced as described above are laminated. The number of laminated layers can be appropriately determined in consideration of the desired thickness of the heat protection composite material, and is usually in the range of 2 to several tens. However, if the amount is too small, there is an inconvenience for controlling the amount of impregnation and adjusting the thickness, density, etc., and if the amount is too large, the manufacturing process becomes complicated. Therefore, preferably in the range of about 3 to 10 sheets. is there. The plurality of composite sheets forming one heat protection composite material may have the same thickness or impregnation amount, or may be different.

  Next, integral molding is performed by subjecting the composite sheets stacked in a plurality of layers to pressurization and heating by a hot press. As a result, it is possible to obtain a heat protection composite material in which the bonding between the layers is strengthened and delamination hardly occurs. In the conventional integral molding by heating in an autoclave, the bonding strength between the layers of the obtained heat protection composite material is not sufficient, and the strength as the heat protection composite material does not reach a sufficient level. Here, the hot press refers to a processing method in which pressure is applied and compressed at a high temperature by, for example, uniaxial pressing. In this case, the pressing direction may be biaxial or triaxial. In the present invention, the thermosetting resin is cured at the same time as the integral molding is performed by applying a composite sheet laminated a plurality of sheets to a hot press machine.

  Regarding the conditions for hot pressing, the pressure and temperature usually change with time, but the change with time of pressure may be adjusted according to the desired density of the heat protection composite material. The change with time may be adjusted in consideration of the properties of the thermosetting resin to be used (specifically, a value recommended by the manufacturer of the resin as the temperature at the time of curing may be referred to). In order to further improve the bonding strength between the layers in the heat protection composite material, when phenol resin is used as the temperature at the time of hot pressing, a range of 90 ° C. to 180 ° C. is adopted, and the pressure is 1 kPa as a gauge pressure. It is preferable to employ a range of 5 MPa.

  Moreover, a heat-protective composite material with good heat resistance can be obtained by integral molding by sintering using an electric furnace instead of heating / pressurizing integral molding by hot pressing. As a temperature at the time of sintering in an electric furnace, when a phenol resin is used, a range of about 90 ° C. to 180 ° C. is adopted, and the temperature may be appropriately adjusted in consideration of a desired density of the heat protection composite material.

  When a phenol resin is used, the heat protection composite material obtained by the present invention is exposed to a severe heating environment, and a matrix resin (cured thermosetting resin) and a part of the reinforcing fiber are thermally decomposed and carbonized. This is a carbonized ablator that thermally protects the aircraft. Since it is a laminated heat protection composite material, it becomes possible to impregnate the resin uniformly with respect to the thickness direction of the composite material, thereby improving the heat resistance performance. In some cases, it is easy to intentionally distribute the resin impregnation amount in the thickness direction of the composite material by changing the resin impregnation amount for each prepreg to be laminated. It is also easy to adjust the thickness and density of the heat protection composite material to predetermined values.

In the present invention, as demonstrated in a later example, a lightweight heat protection material including an ultralight type having a density of 1.0 g / cm ³ or less can be manufactured. A heat-protective composite material having a density and thermal conductivity comparable to that of the ultralight ablator PICA and superior to PICA in surface wear resistance can be produced. Moreover, although it is a laminated heat-protective composite material, delamination does not occur, and strength problems are avoided.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1
Five pieces of felt-like carbon fibers (carbon felt manufactured by Nippon Carbon Co., Ltd.) having a thickness of 5 mm were cut out in a size of 160 mm in length and 180 mm in width. The weight of the cut-out felt-like carbon fibers was measured one by one and impregnated with the same weight of phenol resin (SC-1008: manufactured by Borden Chemical Inc.). At this time, a resin was put in a container, and carbon fibers were immersed therein. A roller was used so that the resin penetrated evenly. Also, the front and back resins were separately soaked separately.

The five prepregs thus obtained were laminated and set on a forming jig, and heated while applying pressure with a hot press. The temperature and pressure conditions during hot pressing are shown in FIG. The pressure during hot pressing was 0.1 MPa as a gauge pressure, the temperature was raised stepwise in the range of 90 to 180 ° C., and heating was continued for about 4 hours. As described above, a rectangular lightweight heat protection material having a density of about 0.2 g / cm ³ was manufactured. In addition, the said density is comparable as the density (0.25-0.35 g / cm < ³ >) of the well-known ablator PICA mentioned above.

  Next, the rectangular lightweight heat protection material was cut to obtain a cylindrical lightweight heat protection material having a diameter of 34 mm and a thickness of 10 mm.

  Below, the heat resistance characteristics of this lightweight thermal protection material were evaluated using an arc heating experimental apparatus.

  The arc heating experimental device is a gas of atmospheric composition, nitrogen gas, and argon gas heated by an arc heater and blown out into a vacuum chamber. The specimen is placed in this high-temperature, high-speed air stream, and the heat resistance and surface wear of the material. It is a device that evaluates.

In order to conduct an arc heating experiment, a specimen having the structure shown in FIGS. 2 and 3 was manufactured. First, two holes with a depth of 5 mm were drilled in the manufactured material, and a thermocouple was attached. Then put this in bakelite. Since the diameter of the manufactured material was 34 mm and the inner diameter of the bakelite was 33 mm, the inner diameter was shaved with a micro grinder so that the material was stuck in the bakelite tube. After that, a test piece was made by filling the heat insulating material.
An arc heating test using the above-described specimen and test apparatus with the lightweight thermal protection material was performed, and data such as the wear mass of the lightweight thermal protection material was obtained. FIG. 4 shows the relationship between the measurement result of the surface mass wear rate m _DS obtained based on this heating test and (Pe / R _B ) ^0.5 . Also shown were determined on the basis of the non-patent document 2, the relation between m _DS and (Pe / R _B) ^0.5 about PICA in FIG.

When the material is graphite, the relationship between the surface mass wear rate m _DS (kg / (s · m ² )) and (Pe / R _B ) ^{0.5 in} the diffusion-limited oxidation region (about 1500K to about 3000K) is expressed by Equation 1. (See Non-Patent Document 3).

In the above equation, the surface mass wear rate m _DS is defined by the following equation and is a parameter representing the wear rate due to heating of the ablator surface.

Where Δh: surface wear thickness of the ablator due to heating (m), ρv: density of base material before heating of ablator (kg / m ³ ), t: heating time (s), C ₀ : diffusion dependent oxidation Constant (Diffusion-controlled mass-transfer constant. Kg / (s ・ m ^3/2・ Pa ^1/2 )), P _e : Stagnation point pressure (Pa), R _B : Blunt radius (m) of the specimen tip It is. If the tip of the specimen is flat, R _B is the half of the specimen cylinder diameter 2.463 (= 1 / 0.637 ²⁾ times the value is used.

FIG. 4 shows the value of C ₀ (see Non-Patent Documents 4 and 5) obtained by assuming that Equation (1) is approximately established for the lightweight thermal protection material (ablator material) of Example 1. Incidentally, specimens of the present embodiment, since a flat plate, R _B is using 1/2 2.463 (= 1 / 0.637 ²⁾ times the value of the specimen cylinder diameter. 4 and 5 also show the PICA diffusion-dependent oxidation constant C ₀ obtained by the same method as described above based on Non-Patent Document 2. From the figure, when the value of (Pe / R _B ) ^0.5 is in the range of 100 to 200, C ₀ of the lightweight thermal protection material of Example 1 is 4.74 × 10 ⁻⁵ kg / (s · m ^3/2 · Pa ^1/2) a and, _{C 0} of PICA is found to be ^{9.45 × 10 -5 kg / (s} · m 3/2 · Pa 1/2). That is, the diffusion-dependent oxidation constant of the lightweight thermal protection material of Example 1 is about 50% of PICA, and the lightweight thermal protection material of Example 1 has excellent surface wear resistance while having a density equivalent to PICA. I found out.
Furthermore, from the above arc test results, no delamination or the like was observed in the heated ablator specimen. As a result, it was confirmed that the adhesive strength between the laminated layers was improved, and the laminated thermal barrier composite material was not easily broken by shearing force, peel force, thermal stress, and the like.

  The thermal conductivity of this lightweight thermal protection material was measured under various temperature conditions using a laser flash method. The result is shown in FIG. 6 together with the thermal conductivity of PICA. From FIG. 6, it can be seen that the lightweight thermal protection material of Example 1 has the same thermal conductivity as PICA.

  Below, the bending and the compressive strength test of the lightweight thermal protection material were performed, and the mechanical characteristic at the time of changing temperature was confirmed.

  A material having a size of 5 × 10 × 50 mm was used as the bending test product, and a material having a size of 5 × 10 × 15 mm was used as the compression test product.

  The results of bending and compressive strength tests are shown in FIGS.

  From FIG.7 and FIG.8, the lightweight thermal protection material of a present Example has bending strength, bending elastic modulus, compressive strength, and compressive elastic modulus in the range which does not have a problem in design and operation. I understand. The lightweight thermal protection material prevents the inflow of heat by thermal decomposition and carbonization of the resin at a temperature exceeding about 150 ° C., and this is because the density decreases due to carbonization as the temperature rises. Thus, it is considered that the compressive strength and the compressive elastic modulus are reduced.

(Example 2)
Five prepregs obtained in the same manner as in Example 1 were placed in an electric furnace and sintered. The temperature conditions at that time are first kept at a relatively low temperature for 120 minutes in order to dissipate moisture contained in the carbon fibers, and then at a higher temperature for an additional 120 minutes in order to keep the thermosetting resin on the carbon fibers. Heated. Thereafter, the electric furnace was turned off and gradually cooled. Thus, a rectangular lightweight heat protection material having a density of about 0.4 g / cm ³ was manufactured.

Next, while using the manufactured lightweight thermal protection material, a specimen similar to that in Example 1 was manufactured, and heat resistance characteristics were evaluated using an arc heating experimental apparatus similar to that in Example 1. FIG. 9 shows the measurement results of the surface mass wear rate m _DS , the relationship of (Pe / R _B ) ^0.5 and the diffusion-dependent oxidation constant C ₀ . From the figure, when the value of (Pe / R _B ) ^0.5 is in the range of 80 to 140, C ₀ of Example 2 is 7.7 × 10 ⁻⁵ kg / (s · m ^3/2 · Pa ^1/2 ). It can be seen that it is. For _{C 0} of PICA is ^{9.45 × 10 -5 kg / (s} · m 3/2 · Pa 1/2), diffusion-dependent oxidation constants lightweight thermal protection components of the second embodiment of figures PICA The density of the lightweight thermal protection material of Example 2 is about 80%, which is slightly higher than that of PICA, but the surface wear resistance performance is more excellent.

Further, a light-weight heat protection material having a density of about 0.6 g / cm ³ was manufactured by the same method as that for the light-weight heat protection material having a density of about 0.4 g / cm ³ . Furthermore, while using the manufactured lightweight thermal protection material, the same test body as Example 1 was manufactured, and the heat resistance characteristics were evaluated using the same arc heating experimental apparatus as Example 1. FIG. 10 shows the measurement result of the surface mass wear rate m _DS , the relationship of (Pe / R _B ) ^0.5 and the diffusion dependent oxidation constant C ₀ . From the figure, it is understood that C _{0 of} this example is 9.0 × 10 ⁻⁵ kg / (s · m ^3/2 · Pa ^1/2 ). For _{C 0} of PICA is ^{9.45 × 10 -5 kg / (s} · m 3/2 · Pa 1/2), lightweight thermal protection material of the present Example 2 (a density of about 0.6 g / cm ³ approximately ) Diffusion-dependent oxidation constant was found to be comparable or slightly better than PICA.

  The heat protection composite material produced by the present invention is lightweight and has good heat resistance characteristics, and does not cause delamination, so that the outer surface of planetary entry machines and recovery capsules, fairing of high-speed flying objects such as rockets and missiles, It can be used to coat propulsion system nozzles and the like.

1 Lightweight thermal protection material 2 Bakelite tube 3 Insulation 4 K-type thermocouple

Claims (6)

A method for producing a thermal protection composite material comprising a reinforcing fiber impregnated with a resin,
The reinforcing fibers are felt-like fibers obtained by matting short fibers, preparing a plurality of composite sheets obtained by impregnating the reinforcing fibers with a thermosetting resin, laminating the plurality of composite sheets, A method for producing a thermal protection composite material, comprising obtaining the thermal protection composite material by performing integral molding by sintering using an electric furnace. The felt-like fibers by needle punching, or process according to claim 1, wherein by using an organic binder in which the short fibers was matted. The process according to claim 1 or 2 wherein the thermosetting resin is a phenolic resin. The manufacturing method according to claim 1, wherein the felt-like fibers are carbon fibers. The manufacturing method according to any one of claims 1 to 4 , wherein the heat protection composite material is an ultralight material having a density of 1.0 g / cm ³ or less. The heat protection composite material manufactured by the manufacturing method in any one of Claims 1-5 .

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