Near-net-size forming method of light uniform composite material thermal protection shell

Abstract

The invention discloses a near-net size forming method of a light uniform composite material thermal protection shell, which comprises the following steps: preparing a fiber preform according to the boundary dimension of the thermal protection shell, and sleeving the fiber preform on a transfer tool; placing the mold and the fiber preform in a rotary oven for drying, mounting the mold after drying, and arranging sealing strips for sealing; a switch valve is installed, and vacuum detection is completed; closed mold RTM injection molding is adopted, an observation connector is arranged in the middle of an injection mold, and flow, pressure and outlet routes of different injection stages are controlled; heating and curing the light thermal protection shell precursor, and starting to demold when the temperature is 30-60 DEG C; and the light thermal protection shell is subjected to aftertreatment, and the dried thermal protection shell product is taken out. The defects that an existing thermal protection shell is single in moldable shape, poor in interface bonding, low in internal uniformity and poor in denudation resistance, and structural integrity is damaged due to machining are effectively overcome.

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 protection shell is the main heat protection structure of the outer layer of the spacecraft. It maintains the aerodynamic shape in the high-temperature aerodynamic environment and ensures the normal operation of the internal instrument components. It needs to be lightweight, resistant to ablation, heat-insulating and have a certain degree of anti-corrosion ability. The thermal protection shell material is mainly ablative composite materials. Its working mechanism is to dissipate its own mass to take away aerodynamic heat, reduce heat transfer, and realize reverse thermal radiation of heat in the environment, thereby realizing product thermal protection.

[0003] The dimensions of lightweight thermal protection shells are varied, consistent with the aircraft sections they protect, and are mainly cylindrical, conical, and special-shaped. Thermal protection shells are usually thin, and when used in high-temperature environments, the liquid phase melting surface should be kept stable, so the surface of the thermal protection shell should be flat and uniform to avoid heat accumulation in weak locations, and the shape should form steps along the airflow.

[0004] Most of the lightweight thermal protection shell products currently in use are low-density phenolic / quartz prepreg or phenolic / high-silica prepreg winding molding, which has the following technical problems: (1) Only rotational structures can be molded, and negative curvature structures and special-shaped structures cannot be prepared. In addition, wrinkles are easily formed inside the curved rotational body when it is adapted, causing internal defects; (2) Low-density prepreg tapes contain a lot of third-phase fillers, poor process performance, and poor internal resin rheological properties, making it difficult to fill completely; (3) The structure is formed by flat or oblique stacking, without z-axis connection, poor overall consistency, and surface erosion is prone 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, and bubbles accumulate in the preform during the molding process, 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 prone to 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: A near-net-size molding method for a lightweight uniform composite material thermal protection shell comprises the following steps: S1. Prepare fiber preforms according to the dimensions of the heat protection shell and put them on the transfer tooling; cylindrical and conical barrel preforms are prepared by fiber cloth / net tire needle punching or 2.5D weaving, and special-shaped structural parts are sewn twice; the preform volume density deviation value does not exceed 0.1g / cm 3 , thickness tolerance is controlled at ±0.1g / cm 3 The size of the transfer tooling is consistent with the core mold of the forming mold, and it is equipped with a positioning port and a positioning device; S2. Dry the mold together with the fiber preform frame in a rotary oven. After drying, cover the core mold with quartz fiber felt to avoid wrinkles and flash. Install the mold in sequence according to the quadrant mark and arrange the sealing strip for sealing. S3. Install the switch 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 it is determined that the sealing meets the requirements; S4. Heat and adjust the low-density phenolic resin to a viscosity of ≤100mPa.s to reach a usable state, add the resin glue solution into a water bath stirring pot, adjust the water bath temperature RT~45°C, seal the bottle mouth, set the stirring speed to 200~1000rad / min, add the curing agent in proportion, and stir for 20min~300min until the glue solution is 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 the internal bubbles and close the circulation; remove bubbles through the circulation equipment to avoid the overflow of the pore-forming agent inside the resin glue liquid caused by the process of removing bubbles under vacuum and low negative pressure conditions; S6. Closed-mold RTM injection molding is adopted, and an observation interface is set in the middle of the injection mold to control the flow, pressure and outlet route at different injection stages; it is conducive to the complete penetration of the glue in the fiber felt and convenient for removing internal defects of the product; vacuum-assisted RTM molding is not adopted to avoid the low-boiling point solvent in the low-density phenolic resin from continuously forming bubbles during the injection process, forming air trap defects in the fiber felt.

[0007] S7. Heat and cure the lightweight thermal protection shell precursor, and start demoulding when the temperature is 30-60°C. The disassembly sequence is opposite to 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, grind the end surface, and keep it flat.

[0008] As a preferred embodiment, in step S1, the proportion of the matrix and the proportion of the reinforcement in the composite material are calculated according to the performance index of the thermal protection shell, and the ratio of the matrix to the reinforcement is 1:0.2-4 in terms of mass fraction. The matrix is ​​selected from organic silicon hybrid lightweight phenolic resin, low-density phenolic resin, etc., and the reinforcement is selected from quartz, high silica or quartz / high silica mixed fiber preform, so as to ensure that the performance of the composite material after proportioning meets the performance index of the thermal protection shell.

[0009] As a preferred method, in step S2, the mold includes a base plate, a core mold, a flap mold, and a cover plate, and 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 a three-flap combination mold and a four-flap combination mold. Further preferably, the cavity surface of the mold is plated with a hard Cr layer, and the thickness of the coating is ≤0.01 mm.

[0010] As a preferred embodiment, in step S1, the fiber preform and the transfer tooling are placed in a silane coupling agent solution as a whole and immersed for 5 to 30 minutes, and evacuated 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.

[0011] As a preferred embodiment, in step S2, the drying process is: rotary drying at 80°C for 1-3 hours, with a rotation speed of 1-8 rad / min; rotary drying at 100°C for 0.5-1 hour, with a rotation speed of 1-8 rad / min, until the weight no longer decreases.

[0012] As a preferred embodiment, in step S6, the injection process is: 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 bubble 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: injection pressure 0.02~0.2MPa, injection flow rate 40~600g / min.

[0013] 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.

[0014] When discharging glue from the top glue outlet, the injection pressure is adjusted to 0.05~0.3MPa, the injection flow rate is ≤600g / min, and the injection process is kept stable until the bubbles are completely discharged from the glue outlet and the valve is closed.

[0015] As a preferred embodiment, in step S7, the heating curing process is: heating to 40-60°C, heating rate 0-3°C / min, keeping 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.

[0016] As a preferred embodiment, in step S8, the post-treatment process is: heating to 35-45°C, heating rate 0-3°C / min, keeping warm for 1-4h; heating to 55-65°C, heating rate 0-3°C / min, keeping warm for 1-16h, exhaust air 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.

[0017] The present invention has the following advantages: (1) The present invention adopts resin transfer molding to form a lightweight heat protection shell, which solves the problem that the wound heat protection shell cannot effectively adapt to the rotating body and special-shaped parts with curved busbars, avoids the wrinkles and splicing defects of the cut edges during the winding of the heat protection shell, and effectively ensures the integrity and uniformity of the product; (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 the B-stage resin chain segment in the low-density prepreg. The solution provided by the present invention has strong designability, high process stability and consistency, and accurate control over the resin state and the fiber preform structure. (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 increasing the interface bonding strength and improving the overall anti-ablation performance.

[0018] (4) The pressure and flow rate control in different injection stages was achieved, eliminating the phenomenon of continuous overflow of lightweight phenolic resin components caused by the negative pressure environment in the RTM and VARTM molding steps, and effectively improving the controllability of the internal quality of the product.

[0019] (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 cumbersome prepreg preparation process, which has low cost, short cycle, good product structure consistency, and strong stability in high-temperature aerodynamic environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The schematic diagram of the structure of the conical barrel thermal protection shell with the busbar as a curve; Figure 2 This is a schematic diagram of the injection mold structure of the cone barrel heat protection shell; Figure 3 This is a schematic diagram of the bottom plate structure of the injection mold for the conical barrel thermal protection shell; Figure 4 This is a schematic diagram of the top plate structure of the injection mold for the conical barrel thermal protection shell; Figure 5 This is a schematic diagram of the injection mold structure for the conical barrel thermal protection shell. DETAILED DESCRIPTION

[0021] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0022] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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.

[0023] Example: This embodiment is a heat protection shell of a busbar curve, and its appearance is as follows Figure 1 As shown, the diameter of the large end is 113.49mm and the diameter of the small end is 219.96mm.

[0024] Step 1: The thermal protection shell requires a density of 0.5~0.7g / cm 3 , calculate the raw material ratio according to density. 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.

[0025] Step 3: Clean the mold cavity surface and runners, apply release agent, and form a dry film layer.

[0026] Step 4: Select low-density phenolic resin and fiber cloth / net tire needle punched preform as raw materials, with a body density of 0.31g / cm 3 , body density deviation +0.03g / cm 3 The average value of the tolerance in the thickness direction of the large end is +0.08g / cm 3 , the average value of the small end thickness tolerance is ≤0.05g / cm 3 .

[0027] 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.

[0028] Step 6: Place a positioning device on the transfer tooling to prevent the fiber preform from sliding; soak the fiber preform and the transfer tooling in the solution for 5 minutes, and evacuate until no bubbles are generated inside.

[0029] Step 7: Place the mold together with the fiber preform frame into a rotary oven, and the drying process is as follows: (1) Rotary drying at 80°C for 2.5 h, rotation speed 4 rad / min; (2) Rotary drying at 100°C for 1 h at a rotation speed of 6 rad / min until the weight stops decreasing; Step 8: Install the core mold and complete the sealing strip arrangement.

[0030] Step 9: Install the molding mold according to the quadrant correspondence, with a maximum mold clearance of 0.05mm. Complete the sealing strip arrangement during the installation process.

[0031] Step 10: After the mold is installed and sealed, install the nozzle with the switch 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.

[0032] Step 11: Lift 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, evacuate to -0.095MPa, and there is no change in the vacuum degree within 5 minutes. At this time, it is determined that the mold sealing meets the requirements.

[0033] 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.

[0034] Step 13: Stir the resin at a constant temperature until the temperature reaches 40°C and seal. Weigh the curing agent in proportion, grind it and put it in an oven at 80°C for 15 minutes to dry. Turn on the resin stirrer at a stirring speed of 650rad / min, add the curing agent, and stir until the glue is clear.

[0035] 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.

[0036] 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.

[0037] Step 16: Set the injection parameters and start the resin injection. The process is as follows: (1) Initial pressure 0.3 MPa, flow rate 800 g / min, flow adjustment level 16 g / time, injection temperature 40 °C.

[0038] (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.

[0039] (3) Glue discharge from the middle interface: injection pressure 0.025 MPa, injection flow rate 80 g / min.

[0040] (4) Expel all bubbles from ports 3 to 6: Close the valve, injection pressure 0.12 MPa, flow rate 600 g / min.

[0041] (5) Glue discharge from outlets 7 to 10: injection pressure 0.05 MPa, injection flow rate 100 g / min. When there are no bubbles coming out of all the glue outlets, close all the switch valves.

[0042] Step 17: After injection, lift the mold to the curing area. The curing process is as follows: (1) Heat to 45°C at a rate of 2°C / min and maintain for 2 h.

[0043] (2) Raise the temperature to 85°C at a rate of 2°C / min and keep warm for 26 h.

[0044] (3) Cool down to 60°C at a rate of 0.5°C / min.

[0045] Step 18: Cool down to below 60°C, remove the mold, and demould the product.

[0046] Step 19: Post-process the thermal protection housing product. The processing process is as follows: (1) Heat to 45°C at a rate of 3°C / min and keep warm for 4 h.

[0047] (2) Heat to 65°C, heating rate 3°C / min, keep warm for 4 hours, open the exhaust system, exhaust volume 60L / m 3 , temperature fluctuation ±1℃.

[0048] (3) Raise the temperature 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.

[0049] (4) Raise the temperature to 105°C at a rate of 3°C / min and keep warm for 2 h.

[0050] (5) Cool down to 60°C at a rate of 0.8°C / min.

[0051] Step 20: Take out the heat protection shell product and cut off the reserved margins at both ends.

[0052] Step 21: Use sandpaper to lightly smooth the rough edges at the ends until they are flat. The heat protection housing is now ready.

[0053] The non-destructive testing of this embodiment adopts ultrasonic testing, and the testing is carried out according to GJB 1038.1. There are no defects such as delamination, cracks, polyadhesive, and pores inside.

[0054] The present invention is not limited to the above-mentioned 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 near-net-size molding method for a lightweight uniform composite thermal protection shell, characterized in that: The steps include: S1. Prepare a fiber preform according to the outer dimensions of the heat protection shell, and put the fiber preform on a transfer tool; S2, drying the mold together with the fiber preform frame in a rotary oven, installing the mold after drying, and arranging the sealing strip 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 ≤100mPa.s to reach a usable state, add the resin glue solution into a water bath stirring pot, adjust the water bath temperature RT~45°C, seal the bottle mouth, set the stirring speed to 200~1000rad / min, add the curing agent in proportion, and stir for 20min~300min until the glue solution is clear; S5. Place the resin glue liquid in the circulation device of the glue injection machine, keep the circulation pipe temperature at 30~50℃, keep the circulation pump temperature at 30~50℃, and the circulation flow rate at 80~600g / min. After 5~120min, remove all the internal bubbles and close the circulation; S6, adopt closed mold RTM injection molding, set an observation interface in the middle of the injection mold to control the flow, pressure and outlet route at different injection stages; S7. Heat and cure the lightweight thermal protection shell precursor, and start demoulding when the temperature is 30-60°C. The disassembly sequence is opposite to 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, grind the end surface, and keep it flat.

2. A near-net-size molding method for a lightweight uniform composite material thermal protection shell according to claim 1, characterized in that: In the step S1, the proportion of the matrix and the proportion of the reinforcement in the composite material are calculated according to the performance index of the thermal protection shell, and the ratio of the matrix: the reinforcement is 1:0.2-4 in terms of mass fraction.

3. The near-net-size molding method of a lightweight uniform composite material thermal protection shell according to claim 1, characterized in that: 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.

4. The near-net-size molding method of a lightweight uniform composite material thermal protection shell according to claim 3, characterized in that: The cavity surface of the mold is plated with a hard Cr layer, and the thickness of the layer is ≤0.01 mm.

5. The near-net-size molding method of a lightweight uniform composite material thermal protection shell according to claim 1, characterized in that: In the step S1, the fiber preform and the transfer tooling are placed in a silane coupling agent solution as a whole 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.

6. The near-net-size molding method of a lightweight uniform composite material 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, with a rotation speed of 1-8 rad / min; rotary drying at 100°C for 0.5-1 hour, with a rotation speed of 1-8 rad / min, until the weight stops decreasing.

7. The near-net-size molding method of a lightweight uniform composite material thermal protection shell according to claim 1, characterized in that: In step S6, the injection process is: 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 bubble 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: injection pressure 0.02~0.2MPa, injection flow rate 40~600g / min. 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, the injection pressure is adjusted to 0.05~0.3MPa, the injection flow rate is ≤600g / min, and the injection process is kept stable until the bubbles are completely discharged from the glue outlet and the valve is closed.

8. The near-net-size molding method of a lightweight uniform composite material thermal protection shell according to claim 1, characterized in that: In step S7, the heating curing process is: heating to 40-60°C, heating rate 0-3°C / min, keeping 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.

9. The near-net-size molding method of a lightweight uniform composite material thermal protection shell according to claim 1, characterized in that: In step S8, the post-treatment process is: heating to 35-45°C, heating rate 0-3°C / min, keeping warm for 1-4h; heating to 55-65°C, heating rate 0-3°C / min, keeping warm for 1-16h, exhaust air 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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