A method for adhesive forming of a large open composite shell with pre-buried dowel joint

Abstract

The application provides a large-opening composite shell bonding forming method of a pre-embedded pin joint, comprising the following steps: preparing a pre-embedded hanging pin joint, bonding an elastic layer / joint / thermal insulation layer, preparing a winding core mold, winding a composite material on the winding core mold, curing and forming the shell, and processing the hanging pin. The forming method of the application realizes uniform and stable winding of the fiber of the large-opening shell through the pre-embedded hanging pin joint, simplifies the winding forming process of the large-opening shell, avoids secondary processing of the winding layer and damage to the continuity of the fiber, and improves the axial bearing capacity of the large-opening shell through local reinforcement of the joint, bonding area of the joint and the thermal insulation layer, and length of the annular groove of the joint, so that the winding forming process and the bearing performance of the shell are considered.

Description

Technical Field

[0001] This invention belongs to the field of solid rocket motor composite material shell manufacturing, and specifically relates to a method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint. Background Technology

[0002] Carbon fiber composite shells, with their advantages of light weight, high strength, and high design flexibility, have been widely used in solid rocket motor shells. In recent years, solid rocket motors have faced requirements for high weight-to-weight ratio and high thrust-to-weight ratio, making large-aperture composite shells that allow for free propellant loading an important direction in the development of high-performance engines. However, for large-aperture composite shells, achieving both good fiber winding technology, strong joint load-bearing capacity, and excellent sealing performance undoubtedly presents challenges to the molding and manufacturing of large-aperture shells.

[0003] Large-opening composite material shells are primarily formed by winding prefabricated dummy heads, followed by cutting off the heads after molding to create the large-opening structure. Simultaneously, radial openings are made at the large-opening ends, connecting to the external structure via pins. The shell sealing structure utilizes embedded metal components within the winding layer to form a sealing surface, as illustrated in patent CN221277885U. To address the issue of high fiber consumption due to prefabricated dummy heads, large-opening winding is achieved by using hanging pins. However, after molding, the winding layer at the hanging pin locations requires secondary processing, disrupting the continuity of the wound fibers. While this molding method is technologically easy to implement, the connection structure is complex, the openings in the winding layer or secondary processing weaken the fiber strength, and the sealing surface is prone to deformation during the winding process, necessitating secondary processing and increasing the number of shell molding steps. To address these issues, this invention proposes a method for bonding and molding large-opening fiber-wound composite material shells with pre-embedded pin joints, balancing the winding molding process with the shell's load-bearing capacity. Summary of the Invention

[0004] In order to overcome the shortcomings of the existing technology, the inventors have conducted intensive research and provided a method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint. This method solves problems such as easy fiber slippage, weak axial load-bearing capacity, and secondary processing of the winding layer and sealing surface (i.e., the inner surface of the joint) during the molding process of the large-opening composite shell, and simplifies the shell winding molding process.

[0005] The technical solution provided by this invention is as follows:

[0006] A method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint includes the following steps:

[0007] Prepare two sets of connectors, a front connector and a rear connector. Machine annular grooves on the outer wall of the connectors. Embed yarn hanging pins in the annular groove area.

[0008] An elastic layer with pin holes is bonded to the outer surface of the joint; an insulation layer is bonded to the inner surface of the joint to obtain a joint with an elastic layer and an insulation layer.

[0009] The sand core mold is fitted onto the winding mandrel and positioned; the front and rear joints with elastic and heat insulation layers are fitted onto the front and rear sections of the sand core mold; the middle cylindrical section of the sand core mold is covered with a heat insulation layer, and the heat insulation layers of the front and rear joints are staggered and overlapped; at least one layer of dry fiber is wound on the outer surface of the above assembly, and the heat insulation layer is pre-vulcanized to obtain the winding mandrel.

[0010] The impregnated fiber bundles are wound on the winding mandrel. During the winding process, the yarn hanging pins pierce the impregnated fiber bundles, and reinforcing material is inserted to locally reinforce the annular groove of the joint.

[0011] The completed composite material shell is cured, demolded after curing, and the hanging pins of the protruding part of the composite material shell are removed to obtain a large-opening composite material shell with a pre-embedded pin joint.

[0012] The method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint provided by the present invention has the following beneficial effects:

[0013] (1) The present invention provides a method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint. The outer wall of the joint is processed with an annular groove. After the impregnated fiber bundle is wound and molded on the outside of the joint, an inlay structure is formed in the annular groove area, which improves the axial tensile strength of the joint. In addition, the hanging pin is pre-embedded in the annular groove area. The annular groove design provides a height space for the hanging pin to be implanted in the fiber winding layer. During the winding process, the hanging pin pierces the impregnated fiber bundle, realizing uniform and stable winding of the large-opening shell fiber, simplifying the winding and molding process of the large-opening shell, avoiding secondary processing of the winding layer, and destroying the continuity of the fiber.

[0014] (2) The present invention provides a method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint. The method involves using carbon cloth or pre-impregnated cloth to partially reinforce the annular groove of the joint. The reinforcement layer is located between the spiral and circumferential winding layers. The method also involves designing a specific bonding area between the joint and the insulation layer, and a specific annular groove length. This method effectively improves the axial pressure bearing capacity of the joint. The process is simple and efficient.

[0015] (3) The present invention provides a method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint. The glue-impregnated fiber bundles on the winding mandrel are wound in a spiral and circumferential alternating winding manner. This combined winding method can accurately match the shell load, which not only improves the circumferential bearing capacity of the shell but also ensures sufficient axial strength, thus achieving a balance between strength and stiffness. By adopting the method of determining the winding angle, spiral winding layer thickness and circumferential winding layer thickness of the spiral winding method given in the present invention, the fibers can be arranged according to the circumferential and axial stress distribution directions of the shell, so as to achieve efficient utilization of fiber strength and minimize material usage, thereby improving structural efficiency. Attached Figure Description

[0016] Figure 1 A schematic diagram of a large-opening fiber-wound composite material shell structure with a pre-embedded pin joint provided by the present invention;

[0017] Figure 2 This is a schematic diagram of the structure of the pre-embedded pin joint with a winding layer provided by the present invention;

[0018] Figure 3 A schematic diagram of the elastic layer / joint / insulation layer combination provided by the present invention;

[0019] Figure 4 This is a schematic diagram of the winding mandrel provided by the present invention.

[0020] Explanation of icon numbers

[0021] 1-Fiber winding layer; 2-Joint; 3-Elastic layer; 4-Hanging pin; 5-Insulation layer; 6-Winding mandrel; 7-Front positioning flange; 8-Rear positioning flange. Detailed Implementation

[0022] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0023] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0024] This invention provides a method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint. (See also: [link to method]). Figure 1 See partial image Figure 2 The molding method includes the following steps:

[0025] S1. Preparation of the joint for pre-embedded yarn hanging pins

[0026] Both ends of the composite material shell require pre-embedded yarn-hanging pins for connection to the external structure. The joints include a front joint and a rear joint. The outer wall of the joint is machined with an annular groove. After the resin-impregnated fiber bundles are wound and formed on the outside of the joint, they form an inlay structure within the annular groove area, which improves the axial tensile strength of the joint.

[0027] The fibers in the resin-impregnated fiber bundles are carbon fiber or glass fiber, and the resin is epoxy resin or phenolic resin.

[0028] The yarn hanging pin 4 is pre-embedded in the annular groove area. The annular groove design provides height space for the yarn hanging pin 4 to be implanted in the fiber winding layer 1. By pre-embedding the yarn hanging pin in the joint, the fiber of the large-opening shell is uniformly and stably wound, which simplifies the winding and forming process of the large-opening shell and avoids secondary processing of the winding layer, thus preventing damage to the fiber continuity.

[0029] The length L of the annular groove comp Determined by the following formula:

[0030]

[0031] In the formula, P is the set shell bearing pressure; D1 is the outer diameter of the joint groove; S comp K represents the interlaminar shear strength of the composite material. safe is the safety factor; k is the effective contact area coefficient.

[0032] The top taper of the yarn hanging pin is 15° to 45°, and the length is adjusted according to the actual winding requirements. The top of the tapered section needs to be rounded to avoid damaging the dipped fiber bundles during the winding process.

[0033] S2, Elastic layer / joint / insulation layer bonding

[0034] See Figure 3 Apply a layer of adhesive evenly to the outer surface of the connector 2 and bond it to the elastic layer 3 with pin holes; apply a layer of adhesive evenly to the bonding area of ​​the insulation layer on the inner surface of the connector 2 and bond it to the insulation layer 5 to obtain a connector with an elastic layer and an insulation layer.

[0035] The insulation layer 5 is made of EPDM rubber. The elastic layer 3 is made of nitrile rubber, which is used to improve the bonding strength between the fiber winding layer 1 and the joint 2 and to reduce the molding stress of the fiber winding layer.

[0036] The bonding length L between the joint and the insulation layer is determined by the following formula:

[0037]

[0038] In the formula, S 12 D1 is the shear strength between the insulation layer and the joint; D2 is the diameter of the bonding surface between the joint and the insulation layer.

[0039] S3. Prepare the winding core mold

[0040] The sand core mold is fitted onto the winding mandrel 6 and positioned by the front positioning flange 7 and the rear positioning flange 8. The front and rear joints, each with an elastic and insulating layer, are fitted onto the front and rear sections of the sand core mold. An insulating layer is wrapped around the middle section of the sand core mold, with the insulating layers of the front and rear joints overlapping in a staggered manner. After the insulating layer is wrapped, at least one layer of spiral and at least one layer of circumferential dry fiber are wound onto the outer surface of the above assembly to shape and constrain the insulating layer. The mixture is then placed in a curing oven for pre-curing of the insulating layer at a curing temperature of 100–120°C for 3–5 hours to obtain the winding mandrel. (See [link to relevant documentation]). Figure 4 .

[0041] The overlap length between the insulation layer covering the middle section of the sand core mold and the insulation layer of the front joint is 10-15mm; the overlap length between the insulation layer covering the middle section of the sand core mold and the insulation layer of the rear joint is 10-15mm.

[0042] S4, Composite material winding

[0043] According to the designed layup scheme, impregnated fiber bundles are wound onto the winding mandrel prepared in S3. Since the large-aperture composite shell is fully open at both ends, a front-to-back equal-aperture winding scheme is adopted. During the winding process, the yarn-holding pins pierce the impregnated fiber bundles to prevent fiber slippage, ensuring that the fibers wind along the designed winding path without deviating from the design trajectory. This achieves uniform and stable fiber winding, avoiding secondary processing of the winding layer and preventing damage to fiber continuity.

[0044] The resin-impregnated fiber bundles on the winding mandrel are wound using alternating helical and circumferential winding methods. The winding angle α of the helical winding method is determined by the following formula:

[0045]

[0046] In the formula, d1 is the set diameter of the front electrode hole; d2 is the set diameter of the rear electrode hole; D out The outer diameter of the winding core mold section.

[0047] Spiral winding layer thickness h α Determined by the following formula:

[0048]

[0049] In the formula, k s σ is the stress balance coefficient; fb To give the fiber strength.

[0050] Circumferential winding layer thickness h θ Determined by the following formula:

[0051]

[0052] During the winding process, carbon cloth or prepreg is used to locally reinforce the annular groove of the joint. The number of reinforcement layers can be adjusted according to the actual pressure bearing capacity of the shell. The reinforcement layers need to be staggered and overlapped to reduce the bridging of the impregnated fiber bundles and reduce local stress concentration.

[0053] The reinforcing layer in the annular groove of the joint is located between the spiral and circumferential winding layers. The reinforcing angles mainly include 0° and ±45°. The 0° and ±45° angles are reinforced with carbon cloth or prepreg. The 90° circumferential fiber winding outside the reinforcing layer compacts the 0° and ±45° reinforcing cloth through winding tension to avoid delamination defects after molding.

[0054] In addition, the number of yarn-hanging pins on the joint in step S1 can be calculated from the winding angle, as shown in the following formula:

[0055]

[0056] In the formula, R is the joint radius at the pin position, b is the bandwidth of the impregnated fiber bundle, and α is the winding angle.

[0057] S5, Shell curing and molding

[0058] The shell that has been wound in step S4 is placed in a curing oven for curing. After curing, it is demolded to form a large-opening composite material shell with a pre-embedded pin joint.

[0059] S6, Yarn hanging pin processing

[0060] The yarn hanging pins 4 of the protruding part of the composite material shell obtained in step S5 are cut off, and finally a large-opening fiber-wound composite material shell with pre-embedded pin joint is obtained.

[0061] Example 1

[0062] S1. Preparation of pre-embedded pin joint

[0063] Prepare a yarn hanging pin with a length of 38mm and a diameter of Ф3mm. The top cone angle is 30° and it is rounded with R0.2. The depth of the connection hole between the joint and the yarn hanging pin is 2mm. The length of the local annular groove of the joint is 33mm through formula (1). The end of the joint is machined with a threaded connection hole to connect with the external structure.

[0064]

[0065] In the formula, P is the set shell bearing pressure, taken as 24MPa; D1 is the outer diameter of the annular groove of the joint, taken as 219mm; S comp The interlaminar shear strength of the composite material is taken as 70 MPa; K safeThe safety factor is set to 1.3; k is the effective contact area coefficient, set to 0.75.

[0066] S2, Elastic layer / joint / insulation layer bonding

[0067] Apply an adhesive to the outer surface of joint 2 and cover it with a 0.5mm thick nitrile rubber elastic layer; apply an adhesive evenly to the heat insulation bonding area on the inner surface of joint 2 and cover it with a 2mm thick EPDM rubber to form a joint with a heat insulation layer.

[0068] To increase the axial load capacity, the bonding length between the joint and the insulation layer can be calculated to be 286 mm according to formula (2).

[0069]

[0070] In the formula, S 12 D2 is the shear strength between the insulation layer and the joint, taken as 8MPa; D2 is the diameter of the bonding surface between the joint and the insulation layer, taken as 220mm.

[0071] S3. Prepare the winding core mold

[0072] The sand core mold is mounted on the winding mandrel 6 and positioned by the front positioning flange 7 and the rear positioning flange 8. The front and rear joints with elastic and heat insulation layers are mounted on the front and rear sections of the sand core mold. A 2mm thick EPDM rubber heat insulation layer is wrapped around the middle cylindrical section of the sand core mold and overlapped with the heat insulation layers of the front and rear joints by a staggered overlap length of 10mm. The heat insulation layers of the cylindrical section are overlapped circumferentially by a staggered overlap length of 15mm. After the heat insulation layer is wrapped, two layers of spiral and two layers of circumferential T800 carbon fiber are wound around the surface of the above assembly to shape and constrain the heat insulation layer. The assembly is then placed in a curing oven for pre-curing of the heat insulation layer at a curing temperature of 110℃ and a curing time of 4h.

[0073] S4, Composite material winding

[0074] Using the equal-hole method, the shell winding layup scheme is designed with a winding angle of 28.6°, as shown in formula (3). The impregnated fiber bundles are wound in alternating spiral and circumferential directions. The thickness of the spiral and circumferential winding can be calculated using formulas (4) and (5), resulting in 10 spiral layers and 7 circumferential layers. After the winding scheme is determined, the impregnated fiber bundles are wound on the winding mandrel prepared in S3. At the same time, local reinforcement is carried out on the annular groove of the joint. The number of reinforcement layers can be adjusted according to the actual shell pressure bearing capacity, and a 10mm staggered overlap should be reserved between each reinforcement layer to reduce fiber bridging and reduce local stress concentration. The reinforcement layer is located between the spiral and circumferential winding layers. The reinforcement angles mainly include 0° and ±45°. Carbon cloth or prepreg is used to reinforce 0° and ±45°. The 90° circumferential fiber winding outside the reinforcement layer is compacted by the winding tension of the 0° and ±45° reinforcement cloth.

[0075]

[0076] In the formula, d1 is the diameter of the front electrode hole, which is 110 mm; d2 is the diameter of the rear electrode hole, which is 110 mm; D out The outer diameter of the winding core mold section is 230mm.

[0077] Spiral winding layer thickness h α Determined by the following formula:

[0078]

[0079] In the formula, k s σ is the stress balance coefficient, taken as 0.65; fb The fiber strength is taken as 5900MPa.

[0080] Circumferential winding layer thickness h θ Determined by the following formula:

[0081]

[0082] In addition, the number of connector pins in step S1 can be calculated by the winding angle, as shown in formula (6). In this invention, the number of pins is 98.

[0083]

[0084] In the formula, R is the joint radius at the pin position, which is 109.5 mm; b is the bandwidth of the impregnated fiber bundle, which is 8 mm; and α is the winding angle.

[0085] S5, Shell curing and molding

[0086] The shell that has been wound in step S4 is placed in a curing oven for curing. After curing, it is demolded to form a large-opening composite material shell with a pre-embedded pin joint.

[0087] S6, Pin Processing

[0088] The yarn-hanging pins on the protruding part of the composite material shell obtained in step S5 are cut off, and finally a large-opening fiber-wound composite material shell with pre-embedded pin joint is obtained, which achieves a Ф230 shell pressure bearing capacity of ≥24MPa; stable fiber winding without slippage at a winding angle of 28.6°; and no need for secondary processing of the winding layer and sealing surface (i.e., the inner surface of the joint).

[0089] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0090] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint, characterized in that, Includes the following steps: Prepare two sets of connectors, a front connector and a rear connector. Machine annular grooves on the outer wall of the connectors. Embed yarn hanging pins in the annular groove area. An elastic layer with pin holes is bonded to the outer surface of the joint; an insulation layer is bonded to the inner surface of the joint to obtain a joint with an elastic layer and an insulation layer. The sand core mold is fitted onto the winding mandrel and positioned; the front and rear joints with elastic and heat insulation layers are fitted onto the front and rear sections of the sand core mold; the middle cylindrical section of the sand core mold is covered with a heat insulation layer, and the heat insulation layers of the front and rear joints are staggered and overlapped; at least one layer of dry fiber is wound on the outer surface of the assembly, and the heat insulation layer is pre-vulcanized to obtain the winding mandrel. The impregnated fiber bundles are wound on the winding mandrel. During the winding process, the yarn hanging pins pierce the impregnated fiber bundles, and reinforcing material is inserted to locally reinforce the annular groove of the joint. The completed composite material shell is cured, demolded after curing, and the hanging pins of the protruding part of the composite material shell are removed to obtain a large-opening composite material shell with a pre-embedded pin joint. The resin-impregnated fiber bundles are wound in an alternating spiral and circumferential manner on the winding mandrel; The reinforcing layer in the annular groove of the joint is located between the spiral and circumferential winding layers, and the reinforcing angles include 0° and ±45°. The 0° and ±45° angles are reinforced with carbon cloth or prepreg.

2. The method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint according to claim 1, characterized in that, The top of the hanging pin is conical, and the top of the conical section is rounded.

3. The method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint according to claim 1, characterized in that, The length of the annular groove on the connector L comp Determined by the following formula: In the formula, P The set pressure resistance of the shell; D 1 represents the outer diameter of the connector groove; S comp Interlaminar shear strength of the composite material; K safe For safety factor; k This is the effective contact area coefficient.

4. The method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint according to claim 1, characterized in that, The bonding length between the joint and the insulation layer L Determined by the following formula: In the formula, P The set pressure resistance of the shell; K safe For safety factor; k The effective contact area coefficient; S 12 The shear strength between the insulation layer and the joint; D 2 is the diameter of the bonding surface between the joint and the insulation layer.

5. The method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint according to claim 1, characterized in that, The winding angle of the spiral winding method α Determined by the following formula: In the formula, d 1 represents the set diameter of the front electrode hole; d 2 represents the set diameter of the rear electrode hole; D out The outer diameter of the winding core mold section.

6. The method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint according to claim 1, characterized in that, Spiral winding layer thickness Determined by the following formula: In the formula, k s This is the stress balance coefficient; σ fb To give the fiber strength; D out The outer diameter of the winding core mold section; P The set pressure resistance of the shell; K safe For safety factor; α The wrapping angle.

7. The method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint according to claim 1, characterized in that, Circumferential winding layer thickness Determined by the following formula: In the formula, k s This is the stress balance coefficient; σ fb Fibers exert strength; D out The outer diameter of the winding core mold section; P The set pressure resistance of the shell; K safe For safety factor; α The wrapping angle.

8. The method for bonding and molding a large-opening composite material shell with a pre-embedded pin joint according to claim 1, characterized in that, The number of yarn-hanging pins on the joint is determined by the following formula: In the formula, R The radius of the joint at the pin location. b The bandwidth of the resin-impregnated fiber bundle; α The wrapping angle.

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