Flexible air bag core mold

Abstract

The flexible air bag core mold comprises a flexible air bag, a core shaft and an inflation device, and the core shaft penetrates through the flexible air bag and is fixedly connected with the flexible air bag; the core shaft is a hollow core shaft, a vent hole is formed in the core shaft, a hollow cavity of the core shaft is communicated with the flexible air bag through the vent hole, and the inflation device is communicated with the hollow cavity of the core shaft. Compared with a traditional sand core mold, the flexible air bag core mold has the advantages that the use efficiency is greatly improved, and repeated use of a winding shell manufactured subsequently is ensured, so that the cost is saved.

Description

Technical Field

[0001] This invention relates to the field of core mold technology, and specifically to a flexible airbag core mold. Background Technology

[0002] In aerospace equipment production, the main types of core molds currently used for molding composite rocket engine casings include all-metal core molds, low-melting-point alloy core molds, washable core molds, and modular assembly core molds. For molding large composite casings, all-metal core molds are too large in size, have too many parts, and are too heavy, making it difficult to guarantee assembly accuracy, and thermal expansion deformation at high temperatures cannot be controlled; low-melting-point alloy core molds generally contain heavy metal elements, such as lead, tin, and bismuth, which can harm the health of operators, and the casting process is also very difficult. More importantly, the melting temperature of the alloy must be reduced to a narrow range, otherwise the composite material will often be damaged when heated above the maximum solidification temperature without clamping force; washable sand core molds are too heavy, have large deflection deformation, and sand core production requires large molds, and the reuse rate after washing is low, resulting in high costs; modular assembly plaster core molds, although they can compensate for poor assembly accuracy through plaster layers, are prone to cracking in large-sized, thick-walled plaster layers, making it difficult to guarantee casing quality, and also have problems such as large weight, large deflection deformation, and long production cycles. Therefore, conventional core mold solutions do not meet the application requirements.

[0003] Currently, reusable inflatable core molds made from sewn fabric bladders coated with rubber are unsuitable for manufacturing rocket engines because they cannot expand uniformly and have poor dimensional stability. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a reusable flexible airbag core mold.

[0005] To achieve the above objectives, the present invention provides a flexible airbag core mold, comprising a flexible airbag, a core shaft, and an inflation device. The core shaft passes through the flexible airbag and is fixedly connected to it. The core shaft is a hollow core shaft with ventilation holes. The hollow cavity of the core shaft is connected to the flexible airbag through the ventilation holes, and the inflation device is connected to the hollow cavity of the core shaft.

[0006] Furthermore, the inflation device includes a hollow shell, an inflation pipe, an inflation nozzle, and a guide pipe. The inflation nozzle is vertically inserted into the hollow cavity of the hollow shell and communicates with the horizontally arranged guide pipe. One end of the inflation pipe is horizontally inserted into the hollow cavity of the hollow shell and connected to the air outlet of the guide pipe. The other end of the inflation pipe is connected to the mandrel through a coupling.

[0007] Furthermore, the method for preparing the flexible airbag includes the following steps: 1) Prepare a sand core mold of the required rocket engine casing dimensions; 2) Spray the sand core mold to prepare the bottom rubber layer of the flexible airbag. After the spraying is completed, let it air dry naturally until it is semi-dry, and then transfer the sand core mold into the oven for heating and curing. 3) Hoist the sand core mold with the bottom rubber layer onto the winding machine, and use the winding machine to wind the rubber-impregnated fibers until the fiber composite layer thickness is 0.2-0.3mm; 4) The surface of the flexible airbag is formed by rotary spraying of the fiber composite layer; 5) After removing the sand core mold inside the flexible airbag using room temperature water, place it in an oven and heat it to completely remove the internal moisture to obtain the flexible airbag.

[0008] Furthermore, step 1) also includes cleaning the surface of the sand core mold. The specific cleaning process is as follows: use a white cotton cloth soaked in 120# solvent oil to wipe and clean the surface of the sand core mold to ensure that the surface of the sand core mold is clean and free of dust and stains; the wiping range includes the entire outer surface of the sand core mold; wash repeatedly until there are no excess substances visible, and then let it air dry naturally. After cleaning the sand core mold surface, apply a layer of polytetrafluoroethylene release cloth, with no more than two layers; after application, ensure there are no bubbles, bulges, or delamination defects before cleaning the surface.

[0009] Further, the specific process of spraying in step 2) is as follows: Before spraying, adjust the spray gun pressure to 0.50-0.75MPa, turn on the rotating device to make the sand core mold rotate, and control the speed at 4-10r / min; during spraying, the width of each rubber layer is 0.05-0.10mm, and the interval between two adjacent layers is 10-20min; after the number of spraying layers is close to the theoretical thickness, use the needle punch method to measure the coating thickness. If it does not meet the requirements, continue spraying until the coating thickness meets the theoretical thickness.

[0010] Furthermore, in step 2), the curing temperature is 40-60℃ and the holding time is 8-12h.

[0011] Furthermore, the viscosity of the coating sprayed in step 2) is 18-24s.

[0012] Furthermore, after the winding is completed in step 3), continue to rotate for 1-2 hours.

[0013] Further, the specific process of rotary spraying in step 4) is as follows: adjust the spray gun pressure to 0.50~0.75MPa, turn on the rotating device to make the sand core mold rotate, and control the speed at 4~10r / min; start spraying, each layer is 0.05-0.10mm thick, and the interval between two adjacent layers is 5-10min; after the number of sprayed layers is close to the theoretical thickness, use the needle penetration method to measure the coating thickness. If it does not meet the requirements, continue spraying until the coating thickness meets the theoretical thickness; after the rotation is completed, send the sand core mold into the oven for heating and curing. The curing temperature is 40-60℃ and the heat preservation time is 8-12h.

[0014] Furthermore, the viscosity of the coating sprayed in step 4) is controlled at 18~24s.

[0015] Materials commonly used in the fabrication of solid rocket motor casings include metals and composite materials. Composite materials possess characteristics such as low density, high specific strength, and high specific modulus. For the fabrication of composite solid rocket motor casings, winding is a commonly used method. During the winding process, the cost and timeframe of mandrel fabrication play a decisive role in the overall cost and timeframe of casing fabrication. Therefore, the flexible airbag of this invention ensures a short fabrication cycle while reducing production costs. By providing an air source to the flexible airbag through an inflation device, the internal pressure of the flexible airbag is kept stable, thereby ensuring the stability of the mandrel's external dimensions. This allows for precise control of dimensional accuracy and thermal deformation, meeting the high-precision molding requirements of the composite material casing.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: the spraying technology used in the preparation process of the present invention is easy to control and allows for more flexible control over the molding thickness; the use of an inner rubber layer, a middle fiber reinforcement layer, and an outer reinforcing rubber layer fully ensures the sealing effect of the airbag and greatly improves its structural strength; the use of the flexible airbag core mold of the present invention greatly improves the efficiency of use compared with the traditional sand core mold, ensuring the repeated use of the subsequent production of the winding shell, thereby saving costs. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the flexible airbag core mold structure of the present invention; Figure 2 for Figure 1 Schematic diagram of the inflation device. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0019] like Figure 1The flexible airbag core mold shown includes a flexible airbag 1, a mandrel 2, and an inflation device 3. The mandrel 2 passes through the flexible airbag 1 and is fixedly connected to it. The mandrel 2 is a hollow mandrel with ventilation holes. The hollow cavity of the mandrel 2 communicates with the flexible airbag 1 through the ventilation holes, and the inflation device 3 communicates with the hollow cavity of the mandrel 2. Figure 2 The inflation device 3 shown includes a hollow shell 3.1, an inflation pipe 3.3, an inflation nozzle 3.5, and a guide pipe 3.2. The inflation nozzle 3.5 is vertically inserted into the hollow cavity of the hollow shell 3.1 and communicates with the horizontally arranged guide pipe 3.2. One end of the inflation pipe 3.3 is horizontally inserted into the hollow cavity of the hollow shell 3.1 and connected to the air outlet of the guide pipe 3.2. The other end of the inflation pipe 3.3 is connected to the spindle 2 through a coupling 3.4.

[0020] The flexible airbag provides support for the subsequent sprayed insulation layer and provides the inner surface of the sprayed insulation layer; the mandrel provides rotation and connection functions; the inflation device provides air to the airbag to ensure stable internal pressure, thereby ensuring the stability of the flexible mandrel's external dimensions.

[0021] The method for preparing a flexible airbag includes the following steps: 1) A sand core mold of the required rocket engine casing size is prepared using a molding die, and the surface of the sand core mold is cleaned and protected; Specifically: Wipe the surface of the sand core mold with a white cotton cloth soaked in 120# solvent oil to ensure that the surface of the sand core mold is clean and free of dust and stains; the wiping area includes the entire outer surface of the sand core mold; repeat the cleaning 2-3 times until there are no excess materials visible, and then let it air dry naturally for 30-50 minutes; After cleaning the sand core mold surface, attach a layer of polytetrafluoroethylene release cloth, with no more than two layers; after attaching, if there are no bubbles, bulges, or debonding defects, clean the surface using the same cleaning process described above.

[0022] 2) Spray the sand core mold to prepare the bottom rubber layer of the flexible airbag, with each layer being 0.05-0.10 mm wide and the interval between adjacent layers being 10-20 minutes; when the number of spray layers is close to the theoretical thickness, use the needle punch method to measure the coating thickness, and the coating thickness should be 0.5-0.7 mm; after spraying, let it air dry naturally until semi-dry, then transfer the sand core mold into an oven for heating and curing, with a curing temperature of 40-60℃ and a holding time of 8-12 hours; Among them, polytetrafluoroethylene film is used to protect the spraying site and prevent the sprayed paint from causing environmental pollution. Prepare the spray coating according to the technical requirements, and use a Fork-4 cup to test the viscosity of the coating. The viscosity should be controlled between 18-24s. Specifically: Before spraying, adjust the spray gun pressure to 0.50-0.75 MPa, turn on the rotating device to rotate the sand core mold, and control the speed at 4-10 r / min. Begin spraying, with each rubber layer width being 0.05-0.10 mm, and an interval of 10-20 minutes between adjacent layers. After the number of sprayed layers approaches the theoretical thickness, use the needle penetration method to measure the coating thickness. The required coating thickness is 0.5-0.7 mm. If it does not meet the requirement, continue spraying until the coating thickness meets the theoretical thickness. After the theoretical thickness meets the requirements, allow it to air dry until semi-dry, then transfer the core mold into an oven for heating and curing. The curing temperature is 40-60℃ and the holding time is 8-12 hours. Once the oven temperature drops below 50℃, the sand core mold can be removed. Then, use 80-grit sandpaper to roughen the surface of the silicone rubber, ensuring there is no reflective surface. Next, use ethyl acetate to clean the surface of the silicone rubber and let it air dry for at least 30 minutes.

[0023] 3) Hoist the sand core mold with the bottom rubber layer onto the winding machine, and use the winding machine to wind the rubber-impregnated fibers until the fiber composite layer thickness is 0.2-0.3mm; In this process, the adhesive material for winding is prepared according to the process requirements, the fibers for winding are prepared, and the fibers are impregnated in the adhesive material in preparation for winding. Set the relevant parameters, check if the equipment is in good condition, and use a winding machine to wind the fiber composite layer. The required thickness of the fiber composite layer is 0.2-0.3mm. Continue rotating for 1 hour after wrapping to prevent uncured adhesive from dripping.

[0024] 4) The flexible airbag surface of the fiber composite layer is formed by rotary spraying, with each pass being 0.05~0.10mm wide and the interval between adjacent passes being 5-10 minutes. After the number of spray passes approaches the theoretical thickness, the coating thickness is measured using the needle punch method, and the required coating thickness is 0.5~0.7mm; Among them, the spray coating was prepared according to the technical requirements, and the viscosity of the coating was tested using a Fork-4 cup, with the viscosity controlled between 18 and 24 s. The specific process is as follows: Adjust the spray gun pressure to 0.50~0.75MPa, turn on the rotating device to rotate the sand core mold, and control the speed at 4~10r / min. Begin spraying, with each coat being 0.05-0.10mm thick and an interval of 5-10min between adjacent coats. After the number of sprayed coats approaches the theoretical thickness, use the needle penetration method to measure the coating thickness. The required coating thickness is 0.5-0.7mm. If it does not meet the requirement, continue spraying until the coating thickness meets the theoretical thickness. After the thickness meets the requirements, continue to rotate the sand core mold for 1-2 hours to prevent uncured silicone rubber from dripping. After rotation, the sand core mold is placed in an oven for heating and curing at a temperature of 50-60℃ for 18-24 hours. The sand core mold can be removed once the oven temperature is below 50℃.

[0025] 5) After removing the sand core mold inside the flexible airbag with room temperature water, place it in an oven and heat it to completely remove the internal moisture. The heating temperature is 70-80℃ and the heating time is 6-8 hours. At the same time, inspect the outer surface of the flexible airbag for defects such as missing adhesive, bulges, delamination, detachment, wrinkles, peeling, and sagging. If the surface is free of defects, proceed to the next process; if the above defects are present, polishing and repair are performed. The specific process is as follows: Use room temperature water to remove the sand core mold inside the flexible airbag, then clean the inside thoroughly, and wipe the inside of the flexible airbag with a clean white cotton cloth to ensure that there is no residual water inside; The flexible airbag is placed in an oven and heated to completely remove internal moisture. The heating temperature is 70-80℃ and the heating time is 6-8 hours. Once the oven temperature is below 50℃, the flexible core mold can be removed.

[0026] 6) Assemble the flexible airbag, mandrel, and inflation device, then inflate it and observe the deformation of the flexible airbag during inflation, such as whether there are bulges or protrusions on the surface; after inflation, check the maintenance of the shape of the flexible airbag.

Claims

1. A flexible airbag core mold, characterized in that: It includes a flexible airbag, a mandrel, and an inflation device. The mandrel passes through the flexible airbag and is fixedly connected to it. The mandrel is a hollow mandrel with ventilation holes. The hollow cavity of the mandrel is connected to the flexible airbag through the ventilation holes, and the inflation device is connected to the hollow cavity of the mandrel.

2. The flexible airbag core mold according to claim 1, characterized in that: The inflation device includes a hollow shell, an inflation pipe, an inflation nozzle, and a guide pipe. The inflation nozzle is vertically inserted into the hollow cavity of the hollow shell and communicates with the horizontally arranged guide pipe. One end of the inflation pipe is horizontally inserted into the hollow cavity of the hollow shell and connected to the air outlet of the guide pipe. The other end of the inflation pipe is connected to the spindle through a coupling.

3. The flexible airbag core mold according to claim 1, characterized in that: The method for preparing the flexible airbag includes the following steps: 1) Prepare a sand core mold of the required rocket engine casing dimensions; 2) Spray the sand core mold to prepare the bottom rubber layer of the flexible airbag. After the spraying is completed, let it air dry naturally until it is semi-dry, and then transfer the sand core mold into the oven for heating and curing. 3) Hoist the sand core mold with the bottom rubber layer onto the winding machine, and use the winding machine to wind the rubber-impregnated fibers until the fiber composite layer thickness is 0.2-0.3mm; 4) The surface of the flexible airbag is formed by rotary spraying of the fiber composite layer; 5) After removing the sand core mold inside the flexible airbag using room temperature water, place it in an oven and heat it to completely remove the internal moisture to obtain the flexible airbag.

4. The flexible airbag core mold according to claim 1, characterized in that: Step 1) also includes cleaning the surface of the sand core mold. The specific cleaning process is as follows: use a white cotton cloth soaked in 120# solvent oil to wipe and clean the surface of the sand core mold to ensure that the surface of the sand core mold is clean and free of dust and stains; the wiping range includes the entire outer surface of the sand core mold; wash repeatedly until there are no excess materials visible, and then let it air dry naturally; After cleaning the sand core mold surface, apply a layer of polytetrafluoroethylene release cloth, with no more than two layers; after application, ensure there are no bubbles, bulges, or delamination defects before cleaning the surface.

5. The flexible airbag core mold according to claim 1, characterized in that: The specific process of spraying in step 2) is as follows: Before spraying, adjust the spray gun pressure to 0.50-0.75MPa, turn on the rotating device to make the sand core mold rotate, and control the speed at 4-10r / min; during spraying, the width of each rubber layer is 0.05-0.10mm, and the interval between two adjacent layers is 10-20min. Once the number of spray coats approaches the theoretical thickness, the coating thickness is measured using the needle penetration method. If the thickness does not meet the requirements, spraying continues until the coating thickness meets the theoretical thickness.

6. The flexible airbag core mold according to claim 1, characterized in that: In step 2), the curing temperature is 40-60℃ and the holding time is 8-12h.

7. The flexible airbag core mold according to claim 1, characterized in that: The viscosity of the coating sprayed in step 2) is 18-24s.

8. The flexible airbag core mold according to claim 1, characterized in that: After the winding is completed in step 3), continue to rotate for 1-2 hours.

9. The flexible airbag core mold according to claim 1, characterized in that: The specific process of rotary spraying in step 4) is as follows: adjust the spray gun pressure to 0.50~0.75MPa, turn on the rotating device to make the sand core mold rotate, and control the speed at 4~10r / min; start spraying, with each layer having a thickness of 0.05-0.10mm and an interval of 5-10min between adjacent layers; After the number of spray coats approaches the theoretical thickness, the coating thickness is measured using the needle punch method. If it does not meet the requirements, spraying continues until the coating thickness meets the theoretical thickness. After rotation, the sand core mold is sent into the oven for heating and curing. The curing temperature is 40-60℃ and the holding time is 8-12h.

10. The flexible airbag core mold according to claim 1, characterized in that: In step 4), the viscosity of the sprayed coating is controlled at 18~24s.

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