A near net shape forming method of a lightweight uniform composite thermal protection shell

Abstract

The application discloses a near-net-size forming method of a light uniform composite heat protection shell, and comprises the following steps: preparing a fiber preform according to the shape and size of the heat protection shell, and sleeving the fiber preform to a transfer tool; drying the mold together with the fiber preform in a rotary oven, sealing after drying by installing the mold and arranging a sealing strip; installing a switch valve and completing vacuum detection; adopting closed mold RTM injection forming, setting an observation interface in the middle of the injection mold, and controlling the flow, pressure and outlet route in different injection stages; heating and curing the light heat protection shell precursor, starting demolding when the temperature is 30-60 DEG C; and post-processing the light heat protection shell, and taking out the heat protection shell product after drying. The application effectively solves the defects of the existing heat protection shell, such as single formable shape, weak interface combination, low internal uniformity, poor anti-erosion capacity and structural integrity damage caused by machining.

Description

Technical Field

[0001] The invention belongs to the technical field of composite material heat protection shell molding, and relates to a near-net-size molding method for a lightweight and uniform composite material heat protection shell. Background Art

[0002] The thermal shell is the primary heat-protective structure on the outer layer of a spacecraft. It maintains its aerodynamic shape in high-temperature aerodynamic environments and ensures the normal operation of internal instrument components. It must be lightweight, ablation-resistant, heat-insulating, and have a certain degree of resistance to abrasion. The thermal shell is primarily made of ablative composite materials. Its working mechanism is to dissipate its own mass to remove aerodynamic heat, reducing heat transfer while achieving reverse thermal radiation to the environment, thereby achieving product thermal protection.

[0003] Lightweight thermal shells come in a variety of shapes and sizes, consistent with the aircraft sections they protect, primarily in cylindrical, conical, and irregular shapes. They are typically thin. When operating in high-temperature environments, the receding liquid melt surface must be stable. Therefore, the shell surface should be smooth and uniform to avoid heat accumulation in weak spots, and the shape should form steps that align with airflow.

[0004] The lightweight thermal protection shell products currently used are mostly low-density phenolic / quartz prepreg or phenolic / high-silica prepreg winding molding, which has the following technical problems: (1) It can only mold rotating body structures, and cannot prepare negative curvature structures and special-shaped structures. In addition, wrinkles are easily formed inside the curved rotating body when it is adapted, causing internal defects; (2) Low-density prepreg tapes contain a lot of third-phase fillers, poor process performance, poor internal resin rheological properties, and are difficult to fill completely; (3) The structure is formed by flat or oblique stacking, without z-axis connection, and the overall consistency is poor. Surface erosion is easy to occur after the resin matrix is ​​carbonized; (4) The negative pressure environment in the RTM and VARTM process steps is not fully compatible with the lightweight phenolic resin. During the molding process, bubbles accumulate in the preform, forming defects; (5) The molding cycle is long and the cost is high. The appearance dimensions cannot be accurately controlled, and the machined appearance surface is easy to cause damage to the thermal protection shell. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a near-net-size molding method for a lightweight, uniform composite material thermal protection shell.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for forming a near-net-size lightweight uniform composite thermal protection shell comprises the following steps:

[0008] S1. Prepare a fiber preform according to the dimensions of the thermal protection shell and place the fiber preform on the transfer fixture. Cylindrical and conical barrel-shaped preforms are made by needle punching of fiber cloth / mesh or 2.5D weaving. Special-shaped structural parts are sewn twice. The deviation of the preform volume density shall not exceed 0.1g / cm 3 , the thickness direction tolerance is controlled at ±0.1g / cm 3 The transfer tooling size is consistent with the core mold of the forming mold, and is equipped with a positioning port and positioning device;

[0009] S2. Place the mold together with the fiber preform frame in a rotary oven for drying. After drying, cover the core mold with quartz fiber felt to avoid wrinkles and flash. Install the mold in sequence according to the quadrant markings and arrange sealing strips for sealing.

[0010] S3. Install the on-off valve and complete the vacuum test; evacuate to a vacuum degree of ≤-0.095MPa, and the vacuum degree change is less than 0.002MPa within 5 minutes, and the sealing is determined to meet the requirements;

[0011] S4. Heat and adjust the low-density phenolic resin to a viscosity of ≤100 mPa.s, and it is ready for use. Add the resin glue solution to a water bath stirring pot, adjust the water bath temperature to RT~45°C, seal the bottle mouth, set the stirring speed to 200~1000 rad / min, add the curing agent in proportion, and stir for 20min~300min until the glue solution becomes clear.

[0012] S5. Place the resin glue liquid in the circulation device of the glue injection machine, maintain the temperature of the circulation pipe at 30~50℃, maintain the temperature of the circulation pump at 30~50℃, and the circulation flow rate at 80~600g / min. After 5~120min, remove all internal bubbles and close the circulation; remove bubbles through the circulation equipment to avoid the overflow of the pore-forming agent in the resin glue liquid caused by the vacuum and low negative pressure conditions.

[0013] S6. Use closed-mold RTM injection molding, and set an observation interface in the middle of the injection mold to control the flow, pressure and outlet route at different injection stages; this is conducive to the complete penetration of the glue in the fiber felt, making it easier to remove internal defects of the product; do not use vacuum-assisted RTM molding to avoid the low-boiling point solvent in the low-density phenolic resin from continuously forming bubbles during the injection process, which can form air trap defects in the fiber felt.

[0014] S7. Heat and cure the lightweight thermal protection shell precursor. Demolding begins when the temperature is between 30 and 60°C. The disassembly sequence is the opposite of the installation sequence.

[0015] S8. Post-process the lightweight thermal protection shell, take out the thermal protection shell product after drying, machine off the excess at both ends, grind the end surface, and keep it flat.

[0016] As a preferred embodiment, in step S1, the matrix and reinforcement ratios in the composite material are calculated based on the performance indicators of the thermal protective shell. The matrix:reinforcement ratio, calculated by mass, is 1:0.2-4. The matrix is ​​selected from a silicone hybrid lightweight phenolic resin, a low-density phenolic resin, or the like, and the reinforcement is selected from a quartz, high-silica, or quartz / high-silica hybrid fiber preform. This ensures that the composite material's performance meets the thermal protective shell's performance indicators after the proportions are adjusted.

[0017] As a preferred method, in step S2, the mold includes a base plate, a core mold, a flap mold, and a cover plate. The flap mold and the core mold are connected to the base plate and the cover plate respectively; the flap mold and the core mold are not in direct contact, and a reserved cavity is formed in the middle. The molding mold is designed and prepared according to the process simulation results, including two types of three-flap combination molds and four-flap combination molds.

[0018] Further preferably, the cavity surface of the mold is plated with a hard Cr layer, and the coating thickness is ≤0.01 mm.

[0019] As a preferred embodiment, in step S1, the fiber preform and the transfer tool are placed in a silane coupling agent solution and immersed for 5 to 30 minutes, and the solution is evacuated until no bubbles are generated inside; the silane coupling agent is prepared by weight in a ratio of water, ethanol, and KH550 of 1 to 3:87 to 93:6 to 10.

[0020] As a preferred embodiment, in step S2, the drying process is: rotary drying at 80°C for 1-3 hours at a rotation speed of 1-8 rad / min; rotary drying at 100°C for 0.5-1 hour at a rotation speed of 1-8 rad / min, until the weight no longer decreases.

[0021] As a preferred embodiment, in step S6, the injection process is as follows: initial pressure 0.15-0.3 MPa, flow rate 300-1000 g / min, adjustment level 6-20 g / time, injection temperature 30-40°C, and no bubbles or mixing in the injection tube;

[0022] After the resin glue is injected into the mold, the injection pressure is 0.05~0.2MPa, and the injection flow rate is 100~500g / min. The pressure and flow rate are adjusted according to the density of the fiber preform and the permeability of the resin glue to the fiber preform;

[0023] When glue is observed to flow out of the glue outlet in the middle, adjust the injection parameters to 0.02~0.2MPa injection pressure and 40~600g / min injection flow rate.

[0024] When no bubbles flow out of the glue outlet in the middle, close the interface valve, the injection pressure is 0.05~0.4MPa, and the flow rate is 100~1000g / min.

[0025] When discharging glue from the top glue outlet, adjust the injection pressure to 0.05~0.3MPa, the injection flow rate ≤600g / min, and keep the injection process smooth until the bubbles are completely discharged from the glue outlet and then close the valve.

[0026] As a preferred embodiment, in step S7, the heating and curing process is: heating to 40~60°C, heating rate 0~3°C / min, maintaining at 40~60°C for 0~4h; heating to 80~90°C, heating rate 0~2°C / min, temperature fluctuation ≤2°C, keeping warm for 24~40h; cooling to 60°C, cooling rate 0~0.5°C / min.

[0027] As a preferred embodiment, in step S8, the post-treatment process is as follows: heating to 35-45°C, heating rate 0-3°C / min, keeping warm for 1-4 hours; heating to 55-65°C, heating rate 0-3°C / min, keeping warm for 1-16 hours, exhaust volume 40-60L / m 3 , exhaust 1~2h, temperature fluctuation ≤2℃; heat up to 75~85℃, heating rate 0~3℃ / min, keep warm 20~40h, exhaust volume 40~60L / m 3 , exhaust for 2~4h, temperature fluctuation ≤2℃; heat up to 100~115℃, heating rate 0~3℃ / min, keep warm for 2~16h; cool down to 45~60℃, cooling rate 0.5~1.5℃ / min.

[0028] The present invention has the following advantages:

[0029] (1) The present invention adopts resin transfer molding to form a lightweight thermal protective shell, which solves the problem that the wound thermal protective shell cannot effectively adapt to the rotating body and special-shaped parts with curved busbars, avoids the wrinkles and splicing defects of the thermal protective shell during winding molding, and effectively ensures the integrity and uniformity of the product;

[0030] (2) Lightweight phenolic resin and fiber preforms are used to replace low-density prepregs, thereby avoiding the defects caused by the poor rheological properties of the third phase filler and B-stage resin segments in low-density prepregs; the solution provided by the present invention has strong designability, high process stability and consistency, and accurate control of the resin state and fiber preform structure.

[0031] (3) The fiber preform is surface treated with a silane coupling agent to introduce Si groups and generate chain segments on the fiber surface that can bind to the resin, thereby improving the interface bonding strength and the overall anti-ablation performance.

[0032] (4) The pressure and flow rate control in different injection stages was achieved, eliminating the phenomenon of continuous overflow of lightweight phenolic resin components due to the negative pressure environment in the RTM and VARTM molding steps, and effectively improving the controllability of the internal quality of the product.

[0033] (5) The use of closed mold injection and internal hard layer plating can achieve near-net size molding of the product, effectively ensuring product accuracy; the product surface does not require machining, and there is no need for tedious prepreg preparation process, which has low cost, short cycle, good product structure consistency, and strong stability in high-temperature aerodynamic environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the structure of the conical barrel thermal protection shell with a curved busbar;

[0035] Figure 2 This is a schematic diagram of the injection mold structure for the conical barrel thermal protection shell;

[0036] Figure 3 This is a schematic diagram of the bottom plate structure of the injection mold for the conical barrel thermal protection shell;

[0037] Figure 4 This is a schematic diagram of the top plate structure of the injection mold for the conical barrel thermal protection shell;

[0038] Figure 5 Schematic diagram of the injection mold structure for the conical barrel thermal protection shell. DETAILED DESCRIPTION

[0039] The present invention will be described in detail below with reference to the accompanying drawings.

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0041] Example:

[0042] This embodiment is a heat protection shell of busbar curve, and its appearance is as follows Figure 1 As shown, the large end diameter is 113.49mm and the small end diameter is 219.96mm.

[0043] Step 1: The thermal protection shell requires a density of 0.5~0.7g / cm 3 , calculate the raw material ratio according to density.

[0044] Step 2: Complete the corresponding mold design and preparation, and perform hard Cr plating on the mold cavity with a coating thickness of ≤0.01mm.

[0045] Step 3: Clean the mold cavity surface and runners, apply release agent, and form a dry film layer.

[0046] Step 4: Select low-density phenolic resin and fiber cloth / net tire needle punched preform as raw materials, with a bulk density of 0.31g / cm 3 , body density deviation +0.03g / cm3 The average value of the tolerance in the thickness direction of the large end is +0.08g / cm 3 , the average value of the tolerance in the direction of thickness of the small end is ≤0.05g / cm 3 .

[0047] Step 5: Prepare KH550 solution in the ratio of water: ethanol: KH550 = 2:91:7, stir at room temperature, stirring speed 600 rad / min, stirring time 4h.

[0048] Step 6: Place a positioning device on the transfer tool to prevent the fiber preform from sliding; place the fiber preform and the transfer tool in the solution and soak for 5 minutes, and evacuate until no bubbles are generated inside.

[0049] Step 7: Place the mold and fiber preform rack into a rotary oven and dry them as follows:

[0050] (1) Rotary drying at 80°C for 2.5 h, rotation speed 4 rad / min;

[0051] (2) Rotary drying at 100°C for 1 h at a rotation speed of 6 rad / min until the weight stops decreasing;

[0052] Step 8: Install the core mold and complete the sealing strip arrangement.

[0053] Step 9: Install the molding die according to the quadrant correspondence, with a maximum mold clearance of 0.05mm. Complete the sealing strip arrangement during the installation process.

[0054] Step 10: After the mold is installed and sealed, install the nozzle with the on-off valve. The installation position and corresponding number are as follows: Figure 2 As shown, the bottom injection ports are numbered 1 to 2, the middle observation ports are numbered 3 to 6, and the top ports are numbered 7 to 10.

[0055] Step 11: Hoist the mold to the vacuum detection area, open interface No. 1, keep all other interfaces closed, connect interface No. 1 to the vacuum pipeline, turn on the vacuum pump, and evacuate to -0.095MPa. If the vacuum degree does not change within 5 minutes, it is determined that the mold sealing meets the requirements.

[0056] Step 12: Take out the low-density phenolic resin glue from the refrigeration equipment, wait for its temperature to rise to room temperature, and use a viscometer to measure the viscosity of the resin glue. The viscosity at room temperature is 35mPa.s, and the resin is ready for use.

[0057] Step 13: Stir the resin at a constant temperature until it reaches 40°C and seal. Weigh the curing agent according to the proportion, grind it, and place it in an 80°C oven to dry for 15 minutes. Turn on the resin stirrer at a stirring speed of 650 rad / min, add the curing agent, and stir until the glue solution is clear.

[0058] Step 14: The circulation pipe temperature is 40°C, the circulation pump temperature is 40°C, the circulation flow rate is 150g / min, and after 45 minutes, the internal bubbles are removed and the circulation is closed.

[0059] Step 15: Connect the injection pipeline. The glue injection machine divides the injection port into two pipelines and connects them to injection ports 1 and 2 respectively. The remaining injection ports are connected to the collector and all the switch valves are opened.

[0060] Step 16: Set the injection parameters and start the resin injection. The process is as follows:

[0061] (1) Initial pressure 0.3 MPa, flow rate 800 g / min, flow adjustment level 16 g / time, injection temperature 40 °C.

[0062] (2) After the glue is injected into ports 1 and 2, the injection pressure is 0.1 MPa and the flow rate is 500 g / min.

[0063] (3) Glue discharge from the middle interface: injection pressure 0.025 MPa, injection flow rate 80 g / min.

[0064] (4) Expel all bubbles from ports 3 to 6: Close the valve, set the injection pressure to 0.12 MPa, and the flow rate to 600 g / min.

[0065] (5) Glue discharge from outlets 7 to 10: injection pressure 0.05 MPa, injection flow rate 100 g / min. When there are no bubbles at all the glue outlets, close all the switch valves.

[0066] Step 17: After injection, hoist the mold to the curing area. The curing process is as follows:

[0067] (1) Heat to 45°C at a rate of 2°C / min and maintain for 2 h.

[0068] (2) Raise the temperature to 85°C at a rate of 2°C / min and keep warm for 26 hours.

[0069] (3) Cool down to 60℃ at a cooling rate of 0.5℃ / min.

[0070] Step 18: Cool down to below 60℃, remove the mold and demould the product.

[0071] Step 19: Post-process the thermal protective housing product. The processing process is as follows:

[0072] (1) Heat to 45°C at a rate of 3°C / min and keep warm for 4 h.

[0073] (2) Heat to 65°C at a rate of 3°C / min, keep warm for 4 hours, open the exhaust system, and exhaust volume 60L / m 3 , temperature fluctuation ±1℃.

[0074] (3) Heat to 85°C at a rate of 3°C / min, keep warm for 24 hours, turn on the exhaust system, exhaust volume 60L / m3, and temperature fluctuation ±1°C.

[0075] (4) Raise the temperature to 105°C at a rate of 3°C / min and keep warm for 2 h.

[0076] (5) Cool down to 60℃ at a cooling rate of 0.8℃ / min.

[0077] Step 20: Take out the heat protection shell product and cut off the reserved margins at both ends.

[0078] Step 21: Use sandpaper to lightly smooth the rough edges at the end until they are flat. The heat shield is now ready.

[0079] The non-destructive testing of this embodiment adopts ultrasonic testing, and the testing is carried out in accordance with GJB 1038.1. There are no defects such as delamination, cracks, poly glue, and pores inside.

[0080] The present invention is not limited to the aforementioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A method for forming a near-net-size lightweight uniform composite thermal protection shell, characterized in that: The steps include: S1. Prepare a fiber preform according to the dimensions of the heat protection shell, and place the fiber preform on a transfer tool; S2. Place the mold together with the fiber preform frame in a rotary oven for drying. After drying, install the mold and arrange sealing strips for sealing. S3. Install the switch valve and complete the vacuum test; S4. Heat and adjust the low-density phenolic resin to a viscosity of ≤100 mPa.s, and it is ready for use. Add the resin glue solution to a water bath stirring pot, adjust the water bath temperature to RT~45°C, seal the bottle mouth, set the stirring speed to 200~1000 rad / min, add the curing agent in proportion, and stir for 20min~300min until the glue solution becomes clear. S5. Place the resin glue liquid in the circulation device of the glue injection machine, maintain the temperature of the circulation pipe at 30~50℃, maintain the temperature of the circulation pump at 30~50℃, and the circulation flow rate at 80~600g / min. After 5~120min, remove all internal bubbles and close the circulation; S6, using closed mold RTM injection molding, with an observation interface set in the middle of the injection mold to control the flow rate, pressure and outlet route at different injection stages; S7. Heat and cure the lightweight thermal protection shell precursor. Demolding begins when the temperature is between 30 and 60°C. The disassembly sequence is the opposite of the installation sequence. S8. Post-process the lightweight thermal protection shell, take out the thermal protection shell product after drying, machine off the excess at both ends, and grind the end surface to keep it flat; In step S1, the matrix ratio and reinforcement ratio in the composite material are calculated based on the performance index of the thermal protection shell, and the matrix: reinforcement ratio is 1:0.2-4 in terms of mass. In step S2, the mold includes a base plate, a core mold, a flap mold, and a cover plate, wherein the flap mold and the core mold are connected to the base plate and the cover plate respectively; the flap mold and the core mold are not in direct contact, and a reserved cavity is formed in the middle; In step S6, the injection process is as follows: initial pressure 0.15-0.3 MPa, flow rate 300-1000 g / min, adjustment level 6-20 g / time, injection temperature 30-40°C, and no bubbles or mixing in the injection tube; After the resin glue is injected into the mold, the injection pressure is 0.05~0.2MPa, and the injection flow rate is 100~500g / min. The pressure and flow rate are adjusted according to the density of the fiber preform and the permeability of the resin glue to the fiber preform; When glue is observed to flow out of the glue outlet in the middle, adjust the injection parameters to 0.02~0.2MPa injection pressure and 40~600g / min injection flow rate; When no bubbles flow out of the glue outlet in the middle, close the interface valve, the injection pressure is 0.05~0.4MPa, and the flow rate is 100~1000g / min; When discharging glue from the top glue outlet, adjust the injection pressure to 0.05~0.3MPa, the injection flow rate ≤600g / min, and keep the injection process smooth until the bubbles are completely discharged from the glue outlet and then close the valve.

2. The method for forming a lightweight, uniform composite thermal protection shell of near-net size according to claim 1, characterized in that: The surface of the mold cavity is plated with a hard Cr layer, and the thickness of the layer is ≤0.01 mm.

3. The method for forming a lightweight, uniform composite thermal protection shell of near-net size according to claim 1, characterized in that: In step S1, the fiber preform and the transfer tool are placed in a silane coupling agent solution and immersed for 5 to 30 minutes, and vacuumed until no bubbles are generated inside; the silane coupling agent is calculated by weight, and the ratio of water, ethanol, and KH550 is 1 to 3:87 to 93:6 to 10.

4. The method for forming a near-net-size lightweight uniform composite thermal protection shell according to claim 1, characterized in that: In step S2, the drying process is: rotary drying at 80°C for 1-3 hours at a rotation speed of 1-8 rad / min; and rotary drying at 100°C for 0.5-1 hour at a rotation speed of 1-8 rad / min, until the weight no longer decreases.

5. The near-net-size molding method for a lightweight, uniform composite thermal protection shell according to claim 1, characterized in that: In step S7, the heating and curing process is as follows: heating to 40-60°C, heating rate 0-3°C / min, maintaining at 40-60°C for 0-4 hours; heating to 80-90°C, heating rate 0-2°C / min, temperature fluctuation ≤ 2°C, maintaining for 24-40 hours; cooling to 60°C, cooling rate 0-0.5°C / min.

6. The near-net-size molding method for a lightweight, uniform composite thermal protection shell according to claim 1, characterized in that: In step S8, the post-treatment process is as follows: heating to 35-45°C, heating rate 0-3°C / min, keeping warm for 1-4 hours; heating to 55-65°C, heating rate 0-3°C / min, keeping warm for 1-16 hours, exhaust volume 40-60L / m 3 , exhaust 1~2h, temperature fluctuation ≤2℃; heat up to 75~85℃, heating rate 0~3℃ / min, keep warm 20~40h, exhaust volume 40~60L / m 3 , exhaust for 2~4h, temperature fluctuation ≤2℃; heat up to 100~115℃, heating rate 0~3℃ / min, keep warm for 2~16h; cool down to 45~60℃, cooling rate 0.5~1.5℃ / min.

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