A solid rocket engine nozzle closure

Abstract

The application provides a rocket engine tail nozzle closure, the pressure bearing surface of the closure is a spherical surface with an inner convex and outer concave shape, and reinforcing ribs are uniformly distributed in a radial manner on the concave surface; the thickness of the pressure bearing surface changes in a gradient manner, the thinnest part is in the center of the circle, and the thickness gradually increases towards the edge; the closure is integrally formed by injection molding; the injection molding material is short carbon fiber reinforced polyether ether ketone, which contains 10-30% short carbon fibers in terms of mass fraction. The application can take into account both low pressure sealing and high pressure reliable rupture: under the action of an internal and external pressure difference of 0.2±0.02 MPa, the adhesive interface is not detached, the closure is not ruptured or excessively deformed, and excellent air and liquid tightness is exhibited, while reliable rupture can occur in a pressure range of 0.20-1.5 MPa, and the number of fragments generated is 8-10 pieces and the size is small.

Description

Technical Field

[0001] This invention relates to the field of solid rocket motor technology, and specifically to a plug for the exhaust nozzle of a solid rocket motor. Background Technology

[0002] The tail nozzle plug of a rocket engine is a key component in a solid rocket engine. Its main function is to maintain the nozzle in a sealed state before engine ignition to prevent the intrusion of external foreign objects; and to reliably break and detach in time after ignition, thereby ensuring the smooth flow of gas and the normal launch of the rocket.

[0003] Traditional plugs, designed to ensure sealing performance, are often excessively robust, resulting in high pressure resistance. However, this makes timely and controllable rupture during engine ignition impossible, potentially leading to excessively high ignition pressure peaks or even explosions. Furthermore, the fragments produced after a rupture are few in number and relatively large, easily impacting the nozzle throat or the inner wall of the expansion section under high-speed exhaust flow, causing structural damage and severely impacting engine safety. Conversely, excessively thinning the plug to reduce burst pressure can lead to unexpected deformation or premature rupture under external pressure loads, causing sealing failure and resulting in ignition delay or failure, also posing a significant risk to engine performance. Summary of the Invention

[0004] The problem solved by this invention is to provide a rocket engine exhaust nozzle plug that can balance low-pressure sealing and high-pressure reliable rupture.

[0005] This invention is achieved through the following technical solution:

[0006] A rocket engine tail nozzle plug, wherein the pressure-bearing surface of the plug is a spherical curved surface with an inner convex and outer concave shape, and reinforcing ribs are provided in a radially evenly distributed manner on the concave surface;

[0007] The thickness distribution of the bearing surface varies in a gradient: it is thinnest in the central region and gradually thickens towards the edge.

[0008] The plug is integrally molded by injection molding; the injection molding material is polyetheretherketone reinforced with short carbon fibers, which contains 10-30% short carbon fibers by mass fraction.

[0009] The thickness of the bearing surface varies as follows: the thickness in the central region is 3.50~3.60 mm, and the thickness at the edge is 3.60~3.70 mm.

[0010] Furthermore, the reinforcing ribs are eight reinforcing ribs arranged in a star-shaped pattern.

[0011] The height of the reinforcing ribs gradually changes smoothly from the center to the edge, with the height of the reinforcing ribs at the center being 18~20.0 mm and the height of the reinforcing ribs at the edge being 0 mm.

[0012] Furthermore, the thickness of the reinforcing rib gradually decreases from the root to the top, with the root thickness of the reinforcing rib being 2.5~2.6mm and gradually decreasing to a thickness of 2.1~2.2mm.

[0013] The end face is sealed by epoxy adhesive bonding on the side of the plug, which can maintain structural integrity for several minutes under an internal and external pressure difference of 0.2±0.02 MPa: the plug does not crack and the bonding interface does not debond.

[0014] Furthermore, the plug reliably initiates rupture within a pressure range of 0.20~1.5 MPa, producing 8~10 fragments after breakage; the bonding interface remains intact and does not fracture.

[0015] Compared with existing technologies, it has the following beneficial effects:

[0016] The rocket engine exhaust nozzle plug provided by this invention can balance low-pressure sealing and high-pressure reliable rupture: under an internal and external pressure difference of 0.2±0.02 MPa, it can maintain structural integrity for 1 minute without debonding at the bonding interface, and the plug does not crack or deform excessively, exhibiting excellent airtight and liquid-tight performance without any leakage; while in the pressure range of 0.20~1.5 MPa, it can reliably rupture, producing 8~10 small fragments; at the same time, the bonding interface remains intact and does not break, ensuring that the plug falls off as a whole and ensuring the normal operation of the exhaust nozzle. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the plug structure of the present invention;

[0018] Figure 2 This is a diagram showing the fragments after the plug broke.

[0019] Among them, 1 is the plug, 2 is the pressure-bearing surface, and 3 is the reinforcing rib. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to embodiments. These descriptions are for illustrative purposes only and are not intended to limit the scope of the invention.

[0021] like Figure 1 As shown, a rocket engine tail nozzle plug has a pressure-bearing surface that is a spherical curved surface with an inner convex and outer concave shape, and is provided with radially and uniformly distributed reinforcing ribs on the concave surface.

[0022] The thickness distribution of the bearing surface varies in a gradient: it is thinnest in the central region and gradually thickens towards the edge.

[0023] The preparation of the pressure-bearing surface, reinforcing ribs, and plug is described in detail below.

[0024] To ensure the plug can maintain both low-pressure sealing and reliable high-pressure rupture:

[0025] Under an internal and external pressure difference of 0.2±0.02 MPa, the structure maintains its integrity for 1 minute: the plug does not crack, the bonding interface does not debond, there is no obvious plastic deformation, and excellent airtightness and liquid tightness are ensured without any leakage.

[0026] The rupture can be reliably initiated within a pressure range of 0.20~1.5 MPa: the plug breaks as required, ensuring rapid and unobstructed flow of gas in the tailpipe.

[0027] 1) The rocket engine exhaust nozzle plug provided by this invention is made of a material with moderate strength: it has strong resistance to low pressure, weak resistance to high pressure, and is prone to cracking into fragments under high pressure. Taking into account factors such as mechanical strength, creep, fatigue resistance, temperature resistance, and chemical stability, this invention selects polyetheretherketone (containing 10-30 wt% short carbon fiber) reinforced with short carbon fibers as the plug material, and integrally molds it by injection molding.

[0028] 2) Based on the material properties and molding process, the pressure-bearing surface of the plug adopts a spherical curved surface design with an inner convex and outer concave shape, and the thickness distribution changes in a gradient: the thinnest area is in the central region, and it gradually thickens towards the edge; and radial reinforcing ribs are evenly distributed on the spherical curved surface of the plug.

[0029] Specifically, the central area is the thinnest (thickness 3.50~3.60 mm, preferably 3.60 mm), and gradually thickens towards the edge (edge ​​thickness is 3.60~3.70 mm, and the thickest part is 3.70 mm).

[0030] The advantages of this design are:

[0031] a) Low-energy triggered fracture: Since the central region is the thinnest, the impact load is preferentially applied to this weak point, requiring only low energy to trigger the initial crack, ensuring reliable fracture within the set pressure range.

[0032] b) Controlled crack propagation: The crack extends radially outward from the center, and the gradually increasing thickness distribution makes the fracture process regular, avoiding the generation of large-sized fragments, thereby meeting safety requirements.

[0033] c) Optimization of fragment size: Through the design of radially distributed reinforcing ribs and thickness gradient of the spherical curved surface of the plug, the angle bisector of the reinforcing ribs is the weak stress area. Under pressure, the stress distribution of the plug and the thickness gradient work together to cause the plug to break into 8-10 small fragments, effectively reducing secondary risks. At the same time, the plug is reliably bonded with epoxy to achieve end face sealing, so that the bonding interface remains intact and does not break. Only after breaking into fragments will they all fall off.

[0034] 3) Reinforcing rib design: Considering that the plug product has a convex-concave structure, the convex surface may flip when the pressure is below 0.2MPa. Therefore, eight reinforcing ribs are added to the concave surface in a star-shaped distribution to enhance the supporting structure capacity under pressure, thereby ensuring that it will not deform or crack below 0.2MPa.

[0035] (3.1) Height of stiffener

[0036] The stiffeners feature a smoothly transitioning height from the center to the edge (18-20.0 mm at the center, preferably 19.0 mm, and 0 mm at the edge), forming a gradient stiffness support system. This design offers the following advantages through mechanical matching and material optimization:

[0037] a. Load Adaptability Distribution: The star-shaped stiffener layout constructs a multi-directional constraint network, suppressing asymmetric deformation of the convex surface and improving stability. The deformation is greatest in the central region, where high stiffeners provide a "pillar effect" to directly resist central displacement; the edge stiffeners decrease in height to avoid abrupt changes in rigidity and reduce the risk of edge cracking caused by stress concentration.

[0038] b. Stress Distribution Optimization: Uniform height stiffeners can easily lead to insufficient central support or excessive edge constraint. Gradual stiffeners precisely match the pressure distribution, ensuring that the load is uniformly transmitted radially. The continuously varying stiffness distribution avoids local stress peaks, ensuring that the structure maintains controllable deformation under ultimate loads.

[0039] c. Lightweight: Material is retained only in critical load-bearing areas, resulting in a 20% to 30% weight reduction compared to uniform high-strength materials.

[0040] (3.2) Thickness of stiffener

[0041] The reinforcing ribs feature a smooth, gradually changing thickness design, with the thickest part (2.5~2.6mm) at the root where they connect to the pressure-bearing surface of the end cap, gradually thinning towards the top (2.1~2.2mm). This design, through mechanical optimization and process improvements, achieves a synergistic enhancement in structural performance, manufacturing feasibility, and product reliability.

[0042] a. Structural performance optimization

[0043] The root of a stiffener is typically a stress concentration area, bearing the maximum bending stress. Thickening the root significantly increases the moment of inertia, effectively dispersing bending stress and reducing stress concentration. Gradual thickness variation achieves a continuous transition in stiffness, while thinning at the top reduces local stiffness, effectively suppressing crack initiation caused by abrupt changes in stiffness. This improves the overall structural strength and reliability, ensuring the structure does not deform under a 0.2 MPa load.

[0044] b. It is beneficial for improving the injection molding process.

[0045] The thicker area at the root is prone to surface depressions due to cooling shrinkage; thinning at the top balances the overall shrinkage rate. Furthermore, the gradual thickness optimizes melt flow, preventing flow stagnation at the top due to excessive thickness and reducing the risk of short shots. Finally, this design naturally creates a draft angle, reducing ejection resistance and minimizing mold wear.

[0046] c. Reduce product weight

[0047] By increasing the thickness at the root and decreasing the thickness at the top, this design can minimize the amount of material used while ensuring structural strength.

[0048] 4) Injection molding

[0049] The plug is made of carbon fiber reinforced polyether ether ketone (PEEK) resin (containing 10-30% short carbon fiber by mass fraction, preferably 30%) and manufactured by injection molding.

[0050] The injection molding process and parameter control are as follows:

[0051] (4.1) Drying: Dry at 150℃ for 4 hours;

[0052] (4.2) Barrel temperature: 380-390℃ (rear) / 390-400℃ (middle) / 380-400℃ (front);

[0053] (4.3) Mold temperature: 200-210℃;

[0054] (4.4) Post-treatment: Treat at 160℃ for 5 hours.

[0055] Specific implementation examples are given below.

[0056] The plug has a spherical curved surface structure with an inner convex and outer concave shape, and its curvature is defined by the radius of the sphere.

[0057] Specifically, the radius of the sphere is 571 mm (SR571), and the diameter of the plug is 300~320 mm.

[0058] The thickness distribution of the pressure-bearing surface of the plug varies in a gradient: it is thinnest in the central area (3.50~3.60mm, preferably 3.55mm) and gradually thickens towards the edge (3.60~3.70mm, preferably 3.65mm).

[0059] The concave surface of the plug is provided with eight reinforcing ribs distributed in a cross shape. The height of the reinforcing ribs decreases continuously from the center area to the edge (preferably 18.80~19.50mm at the center until the edge is flush), and the thickness gradually decreases from the root to the top (preferably 2.6mm at the root and gradually decreases to 2.2mm).

[0060] The plug is bonded with epoxy adhesive. Before bonding, the bonding surface is sanded. After applying the adhesive and fixing, it is cured at room temperature for 24 hours before use.

[0061] 5) Perform a pressure test on the plug.

[0062] Fragments after the plug breaks, such as Figure 2 As shown;

[0063] Its pressure resistance and breakage results are as follows:

[0064] 1) Under an internal and external pressure difference of 0.2±0.02 MPa, it can maintain structural integrity for 1 minute without debonding at the bonding interface, and without cracking or excessive deformation of the plug or gas leakage.

[0065] 2) It can reliably break within a pressure range of 0.20~1.5 MPa, producing 8~10 pieces of uniform size; at the same time, the bonding interface remains intact and does not break.

[0066] The embodiments given above are preferred examples for implementing the present invention, and the present invention is not limited to the above embodiments. Any non-essential additions or substitutions made by those skilled in the art based on the technical features of the present invention are within the protection scope of the present invention.

Claims

1. A rocket engine exhaust nozzle plug, characterized in that, The pressure-bearing surface of the plug is a spherical curved surface that is convex on the inside and concave on the outside, and reinforcing ribs are set in a radially evenly distributed manner on the concave surface; The thickness distribution of the pressure-bearing surface varies in a gradient: it is thinnest in the central region and gradually thickens towards the edge; The plug is integrally molded by injection molding; the injection molding material is polyetheretherketone reinforced with short carbon fibers, which contains 10-30% short carbon fibers by mass fraction. The height of the reinforcing rib changes smoothly from the center to the edge, and the thickness of the reinforcing rib gradually decreases from the root to the top.

2. The rocket engine exhaust nozzle plug as described in claim 1, characterized in that, The thickness of the bearing surface varies as follows: the thickness in the central region is 3.50~3.60 mm, and the thickness at the edge is 3.60~3.70 mm.

3. The rocket engine exhaust nozzle plug as described in claim 1 or 2, characterized in that, The reinforcing ribs consist of eight ribs arranged in a star-shaped pattern.

4. The rocket engine exhaust nozzle plug as described in claim 3, characterized in that, The height of the reinforcing rib at the center is 18~20.0 mm, and the height of the reinforcing rib at the edge is 0 mm.

5. The rocket engine exhaust nozzle plug as described in claim 3, characterized in that, The thickness of the reinforcing rib at the root is 2.5~2.6mm, and gradually decreases to 2.1~2.2mm.

6. The rocket engine exhaust nozzle plug as described in claim 1, characterized in that, The end face is sealed by epoxy adhesive bonding on the side of the plug, which can maintain structural integrity for several minutes under an internal and external pressure difference of 0.2±0.02 MPa: the plug does not crack and the bonding interface does not debond.

7. The rocket engine exhaust nozzle plug as described in claim 1 or 6, characterized in that, The plug reliably initiates rupture within a pressure range of 0.20~1.5 MPa, producing 8~10 fragments after breakage; the bonding interface remains intact and does not fracture.

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