Thermal protection composite screw for aircraft and method for forming same

Abstract

The application relates to a heat-proof and heat-insulating composite screw for an aircraft and a forming method thereof, and belongs to the technical field of local heat protection of the aircraft. A fixing hole is arranged at the center of the bottom end of the plug body, a metal screw is arranged in the fixing hole, and one end of the metal screw extends to the lower side of the plug body. The application has the advantages of simple process, high preparation efficiency, and the like, can batch-produce the composite screw without threads, and the structure of the composite screw is reliable and durable, and the composite screw can be repeatedly disassembled for not less than 50 times. The application solves the problems that the existing split structure has poor process performance and is easy to collapse, and the short fiber structure of the integrated structure is discontinuous and has low structural strength.

Description

Technical Field

[0001] This invention relates to a heat-insulating composite screw for aircraft and its molding method, belonging to the field of local thermal protection technology for aircraft. Background Technology

[0002] Aircraft modules typically have external operating windows to facilitate the installation of individual components within the module and to allow for connections between modules. After installation, these windows are sealed with heat-insulating composite material covers and metal screws. Because the covers require metal screws for secure connection to the modules, and ordinary metal screws cannot withstand the aerodynamic and thermal loads experienced by the aircraft during flight, and because metal materials more easily transfer heat into the module's interior, potentially affecting aircraft safety, a combination of heat-insulating materials and metal screws is commonly used as the connection between the covers and modules.

[0003] There are two types of structures combining thermal insulation materials and metal screws: separate structures and integrated structures. In a separate structure, there is no connection between the thermal insulation material and the metal screw. This typically involves creating a stepped hole (reducing diameter hole) on the cap. The inner hole (small diameter hole) of the stepped hole is a smooth hole for the metal screw to pass through and connect to the compartment. The outer hole (large diameter hole) of the stepped hole is a threaded hole for installing a thermal insulation composite plug with external threads. Separate structures are simple to manufacture and install, but the external threads on the thermal insulation composite plug are inherently difficult to manufacture and are prone to chipping. Repeated disassembly and assembly increases the risk of damage, and some thermal insulation materials cannot be threaded. The most widely used integrated structure currently uses a method of integrally molding short-fiber prepreg and metal screws. This structure avoids the difficulty of molding threads in composite materials. However, the short-fiber structure is discontinuous and has low structural strength, making it prone to cracking and damage during repeated disassembly and assembly. Some products even show destructive damage after only 2-3 disassemblys. Furthermore, molding can only produce one piece per mold, resulting in low molding efficiency. Therefore, there is an urgent need to develop a composite screw that can avoid the difficulties of thread forming and has high structural stability. Summary of the Invention

[0004] The purpose of this invention is to provide a heat-insulating composite screw for aircraft and its molding method that is simple to process and has high manufacturing efficiency, thereby solving the problems of poor processability and easy tooth breakage of existing split structures, and discontinuous short fiber structure and low structural strength of integrated structures.

[0005] The technical solution of this invention is:

[0006] A heat-insulating composite screw for aircraft includes a metal screw and a plug body. The plug body has a fixing hole at its bottom center, into which a metal screw is installed. One end of the metal screw extends below the plug body. The plug body is cylindrical and made of quartz glass fiber woven in three dimensions. A clamping mesh formed by stitching woven yarns through the plug body corresponding to the metal screw in the fixing hole is provided. The clamping mesh is in contact with the metal screw to increase the installation strength of the metal screw. A resin coating layer formed by injection is provided on the outer surface of the plug body. A resin filling layer formed by injection is provided between the clamping mesh and the plug body.

[0007] The top end face of the plug body is symmetrically provided with operation holes.

[0008] The height of the plug body is 20~70mm; the diameter is 10~20mm.

[0009] The molding method of the above-mentioned heat-insulating composite screw includes the following steps:

[0010] 1) Prepare raw materials, including metal screws (rods), three-dimensional woven fabric, and phenolic resin;

[0011] 2) First, the three-dimensional woven fabric is impregnated with epoxy resin, bismaleimide resin, or phenolic resin to harden and shape the woven yarns.

[0012] 3) Drill an mounting hole along the axial direction at the center of the bottom of the three-dimensional woven fabric after the impregnation treatment, and then insert the metal screw into the hole;

[0013] 4) The metal screw is inserted into the hole and the corresponding three-dimensional braided part of the mounting hole is sewn with quartz fiber braided yarn through stitch. The through stitch quartz fiber braided yarn forms a clamping mesh in the three-dimensional braid to strengthen the strength of the three-dimensional braid. At the same time, the through stitch quartz fiber braided yarn causes radial contraction of the three-dimensional braid to improve the clamping force of the three-dimensional braid on the metal screw, thereby improving the installation strength of the metal screw.

[0014] 5) After the through-stitching is completed, a composite prefabricated body of three-dimensional woven fabric and metal screws is obtained;

[0015] 6) Place the composite preform into the mold, inject phenolic resin into the mold cavity using RTM injection, and then heat and cure it for 12-36 hours under the conditions of pressure of 0.01MPa~1.2MPa and temperature of 80~170℃. After that, take it out and drill the operating hole symmetrically on the top end face of the plug body to obtain the finished heat-insulating composite screw.

[0016] The beneficial effects of this invention are as follows:

[0017] This invention features a simple process and high manufacturing efficiency, enabling the mass production of threadless, reliable, and durable composite screws. Furthermore, these composite screws can withstand at least 50 reassemblies and disassemblies. It solves the problems of poor manufacturability and easy thread breakage in existing split-structure designs, and the discontinuous short-fiber structure and low structural strength in integrated designs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the heat-insulating composite screw of the present invention;

[0019] Figure 2 This is a cross-sectional view of the heat-insulating composite screw of the present invention.

[0020] In the diagram: 1. Metal screw, 2. Plug body, 3. Operating hole, 4. Resin filling layer, 5. Resin coating layer, 6. Hoop mesh. Detailed Implementation

[0021] This heat-insulating composite screw for aircraft includes a metal screw 1 and a plug body 2. The plug body 2 is a cylinder with a height of 20-70mm and a diameter of 10-20mm, made of quartz glass fiber woven in three dimensions. Operating holes 3 are symmetrically arranged on the top end face of the plug body 2 for inserting a tightening wrench during assembly. A fixing hole is provided at the center of the bottom end of the plug body 2, and a metal screw 1 is installed in the fixing hole, with one end of the metal screw 1 extending below the plug body 2. A clamping mesh 6, formed by weaving yarns stitched through the plug body 2 corresponding to the metal screw 1 in the fixing hole, is provided in contact with the metal screw 1 to increase the installation strength of the metal screw 1. A resin coating layer 5 formed by injection is provided on the outer surface of the plug body 2; a resin filling layer 4 formed by injection is provided between the clamping mesh 6 and the braided yarns of the plug body 2.

[0022] The forming method of the above-mentioned heat-insulating composite screws is as follows:

[0023] Prepare the raw materials, including metal screws (rods) 1, three-dimensional woven fabric constituting the plug body 2, and phenolic resin.

[0024] First, the three-dimensional woven fabric is impregnated with phenolic resin to harden and shape the woven yarn. Then, a fixing hole (mounting hole) is drilled axially at the center of the bottom of the impregnated three-dimensional woven fabric, corresponding to 1 / 3 of the length of the metal screw 1. Finally, the metal screw 1 is inserted into the hole.

[0025] After the metal screw 1 is inserted into the hole, the corresponding three-dimensional braided part of the mounting hole is sewn together with quartz fiber braided yarn (the braided yarn can also be made of high silica fiber, glass fiber, or carbon fiber) in a through-stitch manner. This through-stitched quartz fiber braided yarn forms a clamping mesh 6 within the three-dimensional braided material, thereby strengthening the plug body 2 (three-dimensional braided material). At the same time, the through-stitched quartz fiber braided yarn exerts radial pressure on the three-dimensional braided material, forcing it to contract inward, thus increasing the clamping force of the three-dimensional braided material on the metal screw 1 and improving the installation strength of the metal screw 1. The sewing method is not limited to through-stitch (it can also be grout stitch, lock stitch, or oblique stitch, or a combination of these methods). During the through-stitching process, the braided yarn is required to be inserted at a 360° angle on the outer circumference of the three-dimensional braided material, so that it deviates from the center after contacting the metal screw 1, thus creating a tendency to wrap around the metal screw 1, thereby improving the tightness (stability) of the metal screw 1 within the mounting hole. After sewing, a composite preform of three-dimensional woven fabric and metal screw 1 is obtained; that is, a heat-insulating composite screw semi-finished product.

[0026] The composite preform is placed in the mold, and phenolic resin is injected into the mold cavity using RTM injection. Then, it is heated and cured for 12 to 36 hours under the conditions of pressure of 0.01MPa~1.2MPa and temperature of 80~170℃. After that, it is taken out and the operating hole 3 is symmetrically drilled on the top end face of the plug body 2 to obtain the finished heat-insulating composite screw.

[0027] When using this heat-insulating composite screw, it is first placed into the stepped hole on the hatch. The metal screw 1 of the heat-insulating composite screw extends downwards from the small-diameter hole of the stepped hole to the corresponding threaded hole port of the compartment. Then, a special wrench is used to rotate the composite screw through the operating hole 3 to install and fix the hatch. Because the plug body 2 of the composite screw is located in the large-diameter hole of the stepped hole on the hatch, and the metal screw 1 is embedded in the bottom of the plug body 2, it can effectively block the aerodynamic heat loads experienced by the aircraft during flight, preventing heat transfer to the metal screw 1 and the interior of the compartment. It is particularly suitable for connecting aircraft hatches and compartments. Furthermore, this invention has a simple process, high manufacturing efficiency, and can mass-produce threadless, reliable, and durable composite screws. These composite screws can be repeatedly disassembled and reassembled at least 50 times. It solves the problems of poor manufacturability and easy thread breakage in existing split structures, and the discontinuity and low structural strength of integrated short-fiber structures.

Claims

1. A molding method for heat-insulating composite screws used in aircraft, characterized in that: It includes the following steps: 1) Prepare raw materials, including metal screws (1), three-dimensional braided fabric, and phenolic resin; 2) First, the three-dimensional woven fabric is impregnated with resin to harden and shape the woven yarns. 3) Drill a mounting hole along the axial direction at the center of the bottom of the three-dimensional woven fabric after the impregnation treatment, and then insert the metal screw (1) into the mounting hole; 4) After the metal screw (1) is inserted into the mounting hole, the three-dimensional braided part corresponding to the mounting hole is sewn together with braided yarn, so that the sewn braided yarn forms a clamping net (6) in the three-dimensional braided material to strengthen the strength of the three-dimensional braided material. At the same time, the braided yarn that passes through the sewn part forms radial contraction on the three-dimensional braided material to increase the clamping force of the three-dimensional braided material on the metal screw (1), thereby increasing the installation strength of the metal screw (1). 5) After the through stitching is completed, a composite prefabricated body of three-dimensional woven fabric and metal screw (1) is obtained; 6) Place the composite preform into the mold, inject phenolic resin into the mold cavity using RTM injection, and then heat and cure for 12-36 hours under the conditions of pressure of 0.01MPa~1.2MPa and temperature of 80~170℃. After taking it out, drill the operation hole (3) symmetrically on the top end face of the plug body to obtain the heat-insulating composite screw product. The suturing method is one or a combination of through-hole suture, outrigger suture, lockstitch, and oblique suture; The resin used for impregnation of the three-dimensional woven fabric is one of epoxy resin, bismaleimide resin, or phenolic resin. The braided yarn is quartz fiber braided yarn, or high silica fiber braided yarn, or glass fiber braided yarn, or carbon fiber braided yarn.

2. The molding method for a heat-insulating composite screw for aircraft according to claim 1, characterized in that: Step 6) The heat-insulating composite screw includes a metal screw (1) and a plug body (2). The bottom center of the plug body (2) is provided with an installation hole, and the metal screw (1) is installed in the installation hole. One end of the metal screw (1) extends to the bottom of the plug body (2). The top end face of the plug body (2) is symmetrically provided with operation holes (3).

3. The molding method for a heat-insulating composite screw for aircraft according to claim 2, characterized in that: The plug body (2) is cylindrical and is made of quartz glass fiber in a three-dimensional weave.

4. The molding method for a heat-insulating composite screw for aircraft according to claim 2, characterized in that: The plug body (2) corresponding to the metal screw (1) in the mounting hole is provided with a clamping mesh (6) formed by stitching braided yarn. The clamping mesh (6) is in contact with the metal screw (1) to increase the installation strength of the metal screw (1).

5. A molding method for a heat-insulating composite screw for aircraft according to claim 2, characterized in that: The outer surface of the plug body (2) is provided with a resin coating layer (5) formed by injection; a resin filling layer (4) formed by injection is provided between the clamping mesh and the plug body.

6. A molding method for a heat-insulating composite screw for aircraft according to claim 2, characterized in that: The height of the plug body (2) is 20~70mm; the diameter is 10~20mm.

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