阅读说明：本技术 一种低密度近零烧蚀复合材料成型方法 (Low-density near-zero ablation composite material forming method ) 是由 王圆 王勇涛 何剑 陈永乐 孙晓莉 于 2021-08-19 设计创作，主要内容包括：本发明涉及到一种低密度近零烧蚀复合材料的成型方法,属航空航天飞行器防隔热层制备领域。本发明防隔热层材料为梯度材料设计,内层为低密度石英针刺毡隔热层材料,外层为高密度2.5D石英纤维机织物防热层材料,采用三维针刺的方式成型针刺毡,外层采用缝合工装预压后依次勾缝,确保织物尺寸合格。再合模整体RTM成型。整体使用低密度酚醛杂化树脂,防隔热层密度更低,整体性能更好,导热系数更低；织物采用梯度密度材料设计,兼顾了防隔热层防热要求及隔热要求；预制体采用缝合工装辅助制备,预制体外形尺寸更精确,成型出来的粗胚表观质量更好；产品采用一体化净尺寸成型,工艺更简单,产品制备周期更短,改善了二次成型导致的应力集中的问题。(The invention relates to a forming method of a low-density near-zero ablation composite material, belonging to the field of preparation of an aerospace craft thermal insulation layer. The heat-insulating layer is designed to be a gradient material, the inner layer is a low-density quartz needled felt heat-insulating layer material, the outer layer is a high-density 2.5D quartz fiber woven fabric heat-insulating layer material, the needled felt is formed in a three-dimensional needling mode, and the outer layer is subjected to prepressing by a sewing tool and then sequentially subjected to pointing, so that the qualified size of the fabric is ensured. And then the whole body is subjected to RTM molding. The whole use of low-density phenolic hybrid resin has lower density of the heat-proof and insulating layer, better integral performance and lower heat conductivity coefficient; the fabric is designed by adopting a gradient density material, and the heat-proof requirement and the heat-insulating requirement of the heat-proof and heat-insulating layer are both considered; the prefabricated body is prepared by the aid of a sewing tool, the external dimension of the prefabricated body is more accurate, and the apparent mass of a formed rough blank is better; the product is formed in an integrated net size mode, the process is simpler, the product preparation period is shorter, and the problem of stress concentration caused by secondary forming is solved.)

1. a low-density near-zero ablation composite material forming method is characterized in that: it comprises the following steps:

1) polishing the metal shell roughly by using 80-mesh sand paper, wiping the metal shell clean by using acetone, and standing for more than 30min to volatilize the acetone completely;

2) preparing a needled felt flat plate by using 2-5 layers of quartz needled net tires to perform Z-direction needling in advance, then laying the needled felt flat plate on a metal shell according to the required thickness, and performing Z-direction needling layer by layer to ensure that the needled felt can be tightly and tightly coated on the metal shell according to the shape;

3) after sewing of the needled felt is finished, 1-5 layers of 2.5D quartz woven fabrics are sewn on the surface of the needled felt by means of a sewing tool, the 2.5D quartz woven fabrics are firstly paved on the needled felt, then a sewing tool female die is assembled from two sides to the leeward side in sequence along the windward side of the cabin section for prepressing, the prepressing time is not less than 24h, after the prepressing is finished, the female die is disassembled, the woven fabrics and the needled felt are sewn, and the sewing direction is axial sewing, so that the woven fabrics and the needled felt are integrated;

4) in order to improve the structural strength of the lap joint, the lap joint can be covered with a layer of 0.2-1mm woven fabric, the woven fabric and the inner layer fabric are sewn and connected, and then a sewing tool female die is assembled for prepressing and shaping after sewing is finished, wherein the prepressing time is not less than 24 hours;

5) disassembling the metal shell assembly and the fabric prefabricated part from the sewing tool according to the disassembly sequence of the panel, the upper cover plate and the bottom plate;

6) cleaning resin on the surface of the die by using a copper sheet, and cleaning the inner molded surface of the female die by dipping absorbent gauze in absolute ethyl alcohol so as to enable the female die to be smooth and free of impurities; standing for more than 30min to completely volatilize alcohol, brushing a release agent, dipping a little release agent in clean cotton/absorbent gauze to coat the whole outer surface of the mold for 1 time, and wiping the whole mold with clean cotton; coating the release agent for 1 time every 20-30min, at least brushing for 2 times, placing for at least 1 hour after the last brushing for use, and then installing a sealing strip;

7) and closing the mold: assembling the female die and the cover plate according to the die assembly requirement of the die, and locking the female die and the cover plate by using screws to ensure that the die assembly gap of the die is less than or equal to 0.1 mm;

8) and air tightness test: filling a nitrogen bottle to the mold cavity under the pressure of 0.2MPa, maintaining the pressure for 30min, wherein the display value of a pressure gauge is reduced by no more than 0.05 MPa;

9) cleaning the glue injection machine, weighing a proper amount of resin, transferring the resin into a charging barrel of the glue injection machine, and preheating the mould and the resin as required if the temperature is too low;

10) de-foaming the resin, connecting the charging barrel of the glue injection machine to a vacuum pump, vacuumizing and removing bubbles, wherein the vacuumizing time is 10-20 min;

11) connecting a ball valve at the glue inlet end of the mold to a glue injection machine through a tetrafluoride pipe, connecting a ball valve at the glue outlet end of the mold to a vacuum pump, starting the vacuum pump to vacuumize the mold, wherein the vacuumizing time is not less than 60 min;

12) and vacuum adsorption resin: opening a glue outlet valve of the glue injector, starting vacuum adsorption resin, and starting timing; after the rubber is completely discharged from the rubber discharge pipe on the small end face of the die, timing is finished;

13) and bubble discharging: filling a nitrogen bottle into the glue injection machine under the pressure of 0.1-0.3MPa, maintaining the pressure for 10min, discharging bubbles, closing the valve when no bubbles emerge from all the four glue outlets, and discharging the bubbles for 3 times according to the method until no bubbles exist; after the bubbles are discharged, closing the glue inlet valve and the glue outlet valve, and removing the glue injection pipe and the glue outlet pipe;

lifting the mould into an oven for heating and curing;

14) and curing: starting an oven to heat and solidify, wherein the solidification conditions are as follows: the temperature is between room temperature and 80 ℃, the temperature rise time is 120min, the heat preservation time is 90min, the temperature rise time is 50min at the temperature of between 80 ℃ and 105 ℃, and the heat preservation time is 500 min;

15) and post-treatment: naturally cooling to 40 ℃ after solidification, removing the mold, polishing burrs at each corner of the test piece by using a combination file, and then drying under the drying conditions: RT → 80 ℃, wherein the temperature rise time is 120min, the heat preservation time is 540min, the oven is closed after the drying is finished, the product is taken out after the temperature is naturally reduced to be below 40 ℃, and then the internal quality inspection is carried out to obtain the net size product.

2. The method of claim 1, wherein the method comprises the steps of: the thickness of the needled felt in the step 3 is 17-21mm, and the bulk density is 0.15-0.25g/cm³。

3. The method of claim 1, wherein the method comprises the steps of: in the step 3, the thickness of the woven fabric subjected to pointing is 2-4mm, and the fiber volume content is 37-45%.

4. The method of claim 1, wherein the method comprises the steps of: in the step 8, the preheating temperature can be determined according to the viscosity of the low-density resin, the viscosity of the resin is controlled within 200mPa, when the temperature is less than 15 ℃, the resin and the mold can be preheated to 25 ℃, and when the temperature is more than or equal to 15 ℃, the preheating is not needed.

5. The method of claim 1, wherein the method comprises the steps of: in the step 9, the vacuum degree of vacuum defoaming is-0.09 to-0.1 MPa.

6. The method of claim 1, wherein the method comprises the steps of: in the step 12, the vacuum degree of the vacuum adsorption resin is-0.09 to-0.1 MPa.

Technical Field

The invention relates to a forming method of a low-density near-zero ablation composite material, belonging to the field of preparation of an aerospace craft thermal insulation layer.

Background

The aerospace craft flies at high super-speed in the atmosphere and is influenced by serious pneumatic heating, the problem of heat insulation is a key problem in the design of the aerospace craft, and along with the development of the hypersonic aircraft in the atmosphere for a long time and in the whole process, the requirements of light weight, low ablation and high-efficiency heat insulation are provided for a heat insulation system.

The common preparation method of the heat-proof layer at present comprises a high-density woven fabric heat-proof layer and a low-density aerogel heat-proof layer, namely, 2-5 layers of high-density phenolic resin prepreg are arranged on the outer layer of a prefabricated body, grid areas with different sizes are prepared on the inner layer, and 5-20mm of low-density aerogel materials are filled in the grid areas. Aerogel and phenolic aldehyde preimpregnation material are connected through the mode that quartz fiber sewed up, through whole compression molding at last. The heat-insulating layer prepared by the process has good ablation resistance, high mechanical property and simple forming process. However, the heat-insulating layer material prepared by the process has a large number of high-density grid rib reinforced areas, so that the overall density of the material is higher, and the heat-insulating property of the high-density grid rib reinforced areas is poorer, so that the requirement of long-time hypersonic flight cannot be met.

The other heat-proof layer preparation method is that the heat-proof layer is prepared by two-time forming, the heat-proof layer and the light heat-insulating material are combined and then are sequentially cured and formed, the outer layer is 2-5 layers of high-density prepreg, the inner layer is 10-20mm of low-density cotton felt material, the outer layer material is formed by adopting a mould pressing process, and the inner layer material is formed by adopting an RTM process. The heat-insulating layer prepared by the process has low density and good heat-insulating property. However, the heat-proof and insulating layer prepared by the process has the problems of performance mismatching and thermal stress concentration among different materials, and the process is complex and the preparation period of the product is long.

Therefore, it is necessary to design an ultra-low density heat insulation material. The integral net size is required to be integrally formed, the process is simple, and the preparation period of the product is short; the ablation resistance is good, and the heat insulation performance is high; the integrity is good, and the requirement of long-time hypersonic flight of an aerospace vehicle can be met.

Disclosure of Invention

The invention aims to: provides a forming method of a low-density near-zero ablation composite material. The heat-proof layer material adopts a gradient density design, the inner layer is made of a low-density quartz needled felt heat-proof layer material, the outer layer is made of a high-density 2.5D quartz fiber woven fabric heat-proof layer material, the inner layer is made into a needled felt in a three-dimensional needling mode, the outer layer is made into a 2.5D woven fabric after being prepressed by a sewing tool, and the whole body is subjected to RTM glue injection molding. The heat-proof and insulating layer has good integrity, the process is simple, the appearance contour does not need to be processed, and the heat-proof and insulating layer is suitable for integral molding of large-size special-shaped products.

The technical scheme of the invention is as follows:

a method for forming a low-density near-zero ablation composite material. It comprises the following steps:

1) and polishing the metal shell roughly by using 80-mesh sand paper, wiping the metal shell clean by using acetone, and standing for more than 30min to volatilize the acetone completely.

2) And pre-Z-direction needling by using 2-5 layers of quartz needled net tires to prepare a needled felt flat plate, then laying the needled felt flat plate on a metal shell according to the required thickness, and carrying out Z-direction needling layer by layer. The needled felt can be tightly coated on the metal shell along with the shape. And then, covering and prepressing are used to ensure that the needled felt has certain thickness and density.

3) After the needling felt is sewn, 1-5 layers of 2.5D quartz woven fabrics are sewn on the surface of the needling felt by means of sewing tools, the 2.5D quartz woven fabrics are firstly paved on the needling felt, then a sewing tool female die is assembled from two sides to the leeward side in sequence along the windward side of the cabin section for prepressing, the prepressing time is not less than 24h, after the prepressing is completed, the female die is disassembled, the woven fabrics and the needling felt are sewn, and the sewing direction is axial sewing, so that the sewing tool female die becomes a whole.

4) And the lap joint is lapped and sewed by using drawstrings or butted and sewed, and in order to improve the structural strength of the lap joint, a layer of 0.2-1mm woven fabric can be covered on the lap joint part and is sewed and connected with the inner layer fabric. And after the sewing is finished, assembling a sewing tool female die for prepressing and shaping, wherein the prepressing time is not less than 24 h.

5) And disassembling the metal shell assembly and the fabric prefabricated part from the sewing tool according to the disassembling sequence of the female die side plate, the upper cover plate and the bottom plate.

6) And cleaning resin on the surface of the forming die by using a copper shovel, and cleaning the inner molded surface of the female die of the forming die by dipping absorbent gauze in absolute ethyl alcohol to ensure that the female die is smooth and free of impurities. Standing for more than 30min to completely volatilize alcohol, brushing a release agent, dipping a little release agent in clean cotton/absorbent gauze to coat the whole outer surface of the mold for 1 time, and wiping the whole mold with clean cotton. Coating for 1 time every at least (20-30) min, brushing for 2 times, and standing for 1 hr after the last brushing. And then installing the sealing strip.

7) Assembling the female die and the cover plate according to the die assembly requirement of the forming die, and locking the female die and the cover plate by using screws to ensure that the die assembly gap of the die is less than or equal to 0.1 mm.

8) And filling 0.2MPa of air pressure into the die cavity through a nitrogen bottle, maintaining the pressure for 30min, and ensuring that the display value of a pressure gauge is reduced by no more than 0.05 MPa.

9) The glue injection machine is cleaned, a proper amount of resin is weighed and transferred to a charging barrel of the glue injection machine, and if the temperature is too low, the mold and the resin can be preheated as required.

10) And (3) defoaming the resin, namely connecting the charging barrel of the glue injection machine to a vacuum pump, vacuumizing and discharging bubbles, wherein the vacuumizing time is 10-20 min.

11) And connecting the ball valve at the glue inlet end of the mold to a glue injection machine through a tetrafluoride pipe, connecting the ball valve at the glue outlet end of the mold to a vacuum pump, opening the vacuum pump to vacuumize the mold, wherein the vacuumizing time is not less than 60 min.

12) And opening a glue outlet valve of the glue injection machine, starting vacuum adsorption resin, and starting timing. And finishing timing after the rubber outlet pipes on the small end surfaces of the molds are completely discharged.

13) And filling 0.1-0.3MPa pressure into the glue injection machine through a nitrogen bottle, maintaining the pressure for 10min, discharging bubbles, closing the valve when no bubbles emerge from the four glue outlets, and discharging the bubbles for 3 times according to the method until no bubbles exist. And after the bubbles are discharged, closing the glue inlet valve and the glue outlet valve, and removing the glue injection pipe and the glue outlet pipe. And (4) lifting the die into an oven for heating and curing.

14) And starting the oven to heat and solidify, wherein the solidification conditions are as follows: the temperature is between room temperature and 80 ℃, the temperature rise time is 120min, the heat preservation time is 90min, the temperature rise time is 50min at the temperature of between 80 ℃ and 105 ℃, and the heat preservation time is 500 min.

15) Naturally cooling to 40 ℃ after solidification is completed, removing the mold, polishing each corner burr of the test piece by using a mixed file, and then drying: RT → 80 ℃ (temperature rise time 120min, heat preservation time 540 min), closing the oven after drying, naturally cooling to below 40 ℃, and taking out the product; then carrying out internal quality inspection to obtain a net-size product.

The thickness of the needled felt in the step 3 is 17-21mm, and the bulk density is 0.15-0.25g/cm³。

In the step 3, the thickness of the woven fabric subjected to pointing is 2-4mm, and the fiber volume content is 37-45%.

In the step 8, the preheating temperature can be determined according to the viscosity of the low-density resin, the viscosity of the resin is controlled within 200mPa, and when the temperature is less than 15 ℃, the resin and the mold can be preheated to 25 ℃. When the temperature is more than or equal to 15 ℃, preheating is not needed.

In the step 9, the vacuum degree of vacuum defoaming is 0.09 to 0.1 MPa.

In the step 12, the vacuum degree of the vacuum adsorption resin is 0.09 to 0.1 MPa.

The invention has the beneficial effects that:

the outer layer of the prefabricated body is made of a high-density 2.5D quartz fiber woven fabric heat-proof material, the inner layer of the prefabricated body is made of a low-density quartz fiber needled felt heat-insulating material, the prefabricated body is integrally molded by glue injection at one time, and the composite material with the nano-pore structure is prepared by adopting a sol-gel process. The material structure is comparatively homogeneous, and the enhancement district is less, and whole is nanometer pore structure combined material, and the heat-proof quality is good, does not have the poor region of heat-proof quality.

The system material reinforcing material is quartz fiber fabric, the resin is low-density phenolic hybrid resin, the resin is injected and cured at one time and integrally formed, and the problems of performance mismatch and thermal stress concentration caused by different resins and different curing processes can be solved. And the process is simple and the preparation period is short.

The prefabricated body is sewn after being pre-pressed by a sewing tool, the size of the prefabricated body is accurate, and the prepared product has the defects of apparent rubber shortage, resin enrichment and the likeLess. According to the process method, the density of the material system heat-proof and heat-insulating material can reach 0.5-0.65g/cm³Compared with the currently common 0.8-1.2g/cm³The dense heat-proof and insulating material has great advantages in light weight, and is an important development direction of the subsequent heat-proof and insulating materials for aerospace aircrafts.

Detailed description of the preferred embodiment 1

And (3) polishing the metal shell roughly by using 80-mesh sand paper, wiping the metal shell clean by using acetone, and standing for more than 30min to volatilize the acetone completely.

And (3) pre-Z-direction needling is carried out on 5 layers of 0.4mm quartz needled net tires to prepare a 2mm needled felt flat plate, then 10 layers of needled felt flat plates are laid on a metal shell according to the required thickness, and Z-direction needling is carried out layer by layer. The needled felt can be tightly coated on the metal shell along with the shape, and then pre-pressed by using a process covering, wherein the pre-pressing time is not less than 12h, so that the thickness of the needled felt is 20 (-1, 1) mm.

After the needled felt is sewn, 1 layer of 4mm2.5D quartz woven fabric is sewn on the surface of the needled felt by means of a sewing tool, the 2.5D quartz woven fabric is firstly paved on the needled felt, then a sewing tool female die is assembled from two sides to the leeward side in sequence along the windward side of the cabin section for prepressing, the prepressing time is not less than 24 hours, after the prepressing is completed, the female die is disassembled, the woven fabric and the needled felt are sewn, and the sewing direction is axial sewing, so that the woven fabric and the needled felt are integrated.

The lap joint is sewed by a drawnwork lap joint mode, a layer of 1mm woven fabric is covered on the lap joint part, and the woven fabric and the inner layer fabric are sewed and connected. And after the sewing is finished, assembling a sewing tool female die for prepressing and shaping, wherein the prepressing time is not less than 24 h.

And disassembling the metal shell assembly and the fabric prefabricated part from the sewing tool according to the disassembling sequence of the female die side plate, the upper cover plate and the bottom plate.

And cleaning resin on the surface of the forming die by using a copper shovel, and cleaning the inner molded surface of the female die of the forming die by dipping absorbent gauze in absolute ethyl alcohol to ensure that the female die is smooth and free of impurities. Standing for more than 30min to completely volatilize alcohol, brushing a release agent, dipping a little release agent in clean cotton/absorbent gauze to coat the whole outer surface of the mold for 1 time, and wiping the whole mold with clean cotton. Coating for 1 time every at least (20-30) min, brushing for 2 times, and standing for 1 hr after the last brushing. And then installing the sealing strip.

Assembling the female die and the cover plate according to the die assembly requirement of the forming die, and locking the female die and the cover plate by using screws to ensure that the die assembly gap of the die is less than or equal to 0.1 mm. And (3) filling the pressure of 0.2MPa to the die cavity through a nitrogen bottle, maintaining the pressure for 30min, and ensuring that the display value of a pressure gauge does not decrease to be less than 0.05 MPa.

And cleaning the glue injection machine, weighing a proper amount of resin, transferring the resin into a charging barrel of the glue injection machine, and preheating the mould and the resin as required if the temperature is too low. And connecting the charging barrel of the glue injection machine to a vacuum pump, vacuumizing and removing bubbles for 10-20 min.

And connecting the ball valve at the glue inlet end of the mold to a glue injection machine through a tetrafluoride pipe, connecting the ball valve at the glue outlet end of the mold to a vacuum pump, and starting the vacuum pump to vacuumize the mold, wherein the vacuumizing time is not less than 60 min. And opening a glue outlet valve of the glue injection machine, starting vacuum adsorption resin, and starting timing. And finishing timing after the rubber outlet pipes on the small end surfaces of the molds are completely discharged.

And (3) filling 0.2MPa pressure into the glue injection machine through a nitrogen bottle, maintaining the pressure for 10min, discharging bubbles, closing the valve when no bubbles emerge from the four glue outlets, and discharging the bubbles for 3 times according to the method until no bubbles exist. And after the bubbles are discharged, closing the glue inlet valve and the glue outlet valve, and removing the glue injection pipe and the glue outlet pipe. And (4) lifting the die into an oven for heating and curing.

Starting an oven to heat and solidify, wherein the solidification conditions are as follows: the temperature is between room temperature and 80 ℃, the temperature rise time is 120min, the heat preservation time is 90min, the temperature rise time is 80-105 ℃, the temperature rise time is 50min, and the heat preservation time is 500 min. Naturally cooling to 40 ℃ after solidification, removing the mold, polishing burrs at each corner of the test piece by using a combination file, and then drying under the drying conditions: and (3) RT → 80 ℃ (the temperature rise time is 120min, and the heat preservation time is 540 min), closing the oven after drying is finished, and naturally cooling to below 40 ℃ to take out the product. Then carrying out internal quality inspection to obtain a net-size product.

In order to show various performances of the heat-proof and insulating layer prepared by the invention, a comparison test is carried out on the heat-proof and insulating layer prepared by the invention and the heat-proof and insulating layer prepared by the two-time forming process under the same condition, and the specific results are as follows:

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