Low speed engine exhaust valve disc for large ships

Abstract

The application discloses a large ship low-speed engine exhaust valve disc and a preparation method thereof. According to the working principle of a ship two-stroke engine, the working condition of an exhaust valve and the failure characteristics of the exhaust valve, the bottom surface of the new exhaust valve disc is designed with annular protrusions. The number of the annular protrusions is 1-5, the distance of the first annular protrusion from the center is 10-80 mm, the distance of the second annular protrusion from the center is 80-150 mm, the width d is 1-50 mm, and the height e is 1-8 mm. The annular protrusions on the bottom surface of the exhaust valve disc change the gas vortex direction in the cylinder, break the scouring and ablation of the vortex group on the bottom surface of the exhaust valve disc, and destroy the heat transmission along the bottom surface of the valve disc. Without changing the existing material, increasing the difficulty of heat treatment process and manufacturing cost, the service life of the large ship low-speed engine exhaust valve can be effectively prolonged, and the operation cost of the ship can be reduced.

Description

Technical Field

[0001] This invention relates to a valve disc and its preparation method, specifically a valve disc for a low-speed engine exhaust valve used in large ships and its preparation method, belonging to the field of ship exhaust valve preparation technology. Background Technology

[0002] High-temperature corrosion and exhaust gas erosion are major challenges in the exhaust passages of marine two-stroke engines. As a critical component of these engines, the exhaust valve's service life is most significantly affected by these factors. After prolonged use, the bottom surface of the exhaust valve disc ablates, reducing its effective thickness and overall structural strength. This can lead to valve disc deformation, decreased valve surface sealing, and an increased risk of ablation and perforation failure. Therefore, marine two-stroke engine designers have established ablation limits for the exhaust valve stem and disc thickness. Exhaust valve stems with ablation depths exceeding these limits must be repaired or scrapped.

[0003] After investigation, the applicant discovered that although the bottom surface of the exhaust valve of a marine two-stroke engine exhibits ablation and depression characteristics as described above after long-term use under actual operating conditions, the ablation is not uniform and downward. Instead, the deepest ablation occurs at a certain distance from the center. Due to the excessive ablation depth in some local areas, the exhaust valve becomes unusable. A comparison of the ablation characteristics of exhaust valve bottoms made of different materials shows that the ablation characteristics are consistent, indicating that the occurrence of this characteristic is unrelated to the material of the exhaust valve bottom surface. According to the in-cylinder combustion model analysis of a marine two-stroke engine, in addition to high-temperature ablation, the bottom surface of the exhaust valve bottom is also affected by the scouring effect of combustion gases. During the compression and combustion process of the combustion gases in the cylinder of a marine two-stroke engine, the formation of vortices in the combustion gases is the cause of the uneven ablation of the exhaust valve bottom surface.

[0004] For the reasons mentioned above, major marine two-stroke engine designers worldwide are continuously upgrading exhaust valve disc materials, selecting high-temperature and corrosion-resistant materials with excellent performance. A well-known example is the addition of a certain amount of Cr to nickel-based alloys to form high-chromium nickel-based high-temperature alloys (such as DSA760). Although this can effectively improve the service life of exhaust valves, the high-performance materials are limited by key technologies such as smelting, forming technology and processes, and heat treatment processes, which leads to an increasing difficulty in processing exhaust valves. As a result, the production and manufacturing costs of exhaust valves for low-speed engines in large ships have increased significantly, and the operating costs of ships have continued to rise. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a valve disc for exhaust valve of low-speed engine of large ships that has a reasonable structure, stable performance, and is resistant to high temperature and corrosion.

[0006] To solve the above technical problems, the present invention proposes the following technical solution: a valve disc for a large marine low-speed engine exhaust valve, comprising a valve disc, a disc bottom, and a protrusion. The valve disc is made of austenitic heat-resistant material or Ni-based high-temperature alloy, and its microstructure is a single-phase solid solution characterized by equiaxed grains. Its composition includes: SNCrW / NiCr20TiAl / NiCr22Mo9Nb / NiCr29Fe4 / NiCr38Al4. The protrusion is located below the disc bottom and is distributed in a ring around the center of the disc bottom. The connection between the protrusion and the disc bottom plane is an arc-shaped connection without sharp corners.

[0007] Based on the actual characteristics of the exhaust valve disc end face after long-term use, and combined with in-cylinder combustion model analysis, it is determined that during actual use, the exhaust valve disc end face is subjected to high-temperature erosion in addition to being affected by combustion gas scouring. The tip of the vortex may be the area with the deepest erosion on the bottom of the exhaust valve disc. Due to the excessive erosion depth in this area, the exhaust valve becomes unusable. Therefore, breaking the scouring and erosion of the vortex at the bottom of the disc can effectively improve the service life of the exhaust valve. With the cylinder's external dimensions and injection angle unchanged, adding an annular protrusion structure at the front end of the severely eroded area can change the vortex direction, reducing the scouring and erosion on the bottom of the disc. This invention does not improve product life through the upgrading of high-performance materials, but instead takes a different approach, designing the valve disc bottom structure from a completely new perspective: the in-cylinder combustion environment of marine low-speed engine exhaust valves and the unique high-temperature erosion failure characteristics of the disc bottom surface. This achieves the technical effect required by this invention.

[0008] Furthermore, the material of the bottom of the disc and the protrusion is the same as that of the valve disc. The valve disc is formed by integral die forging, and the bottom of the disc and the protrusion are formed by turning in one step.

[0009] Furthermore, the bottom of the disc and the protrusion are integrally formed and are made of a different material than the valve disc, including Ni-based superalloys NiCr22Mo9Nb or NiCr29Fe4. The Ni-based superalloys contain the following essential elements by mass percentage: Cr: 22-35%, Fe ≤6%, Al: ≤5%, Mo: 5-25%, Cu: 0.5%, with the balance being Ni.

[0010] Furthermore, the number of protrusions is 1 to 5, wherein the distance b from the center of the first protrusion outward from the center of the disc bottom is 10 to 80 mm, and the distance c from the center of the second protrusion outward from the center of the disc bottom is 80 to 150 mm. The position and distance of the annular protrusions are determined based on the shape and position of the vortex formed by fuel injection and combustion in the cylinder of a marine low-speed engine. Because the shape and position of the vortex in the cylinder of marine low-speed engines of different cylinder diameters are different, the set distance of the annular protrusions on the bottom of the exhaust valve disc is also different. The first two annular protrusions in this invention can already change the direction of the gas vortex in the cylinder, break the scouring and erosion of the vortex cluster on the bottom surface of the exhaust valve disc, and disrupt the heat transfer along the bottom plane of the valve disc. Adding more annular protrusions can cover all current product models.

[0011] Furthermore, the surface of the protrusion has a rounded transition, and its cross-section has an inverted trapezoidal structure.

[0012] Furthermore, the width d of the connection surface between the protrusion and the bottom of the plate ranges from 1 to 50 mm.

[0013] The present invention is characterized by the following: While maintaining the same external dimensions and injection angle of the low-speed engine cylinder for marine applications, the valve disc provided by the present invention adds an annular protrusion to the front end of the severely eroded area on the bottom surface of the exhaust valve disc. This alters the direction of the gas vortex within the cylinder, breaks the erosion of the vortex cluster on the bottom surface of the exhaust valve disc, and disrupts heat transfer along the bottom plane of the valve disc. Without changing existing materials or significantly increasing manufacturing costs and process difficulty, the service life of the exhaust valve can be effectively improved and the operating costs of the ship reduced simply by improving the structure of the bottom surface of the exhaust valve disc. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the bottom structure of the exhaust valve disc of a marine two-stroke engine in the prior art.

[0015] Figure 2 This is a schematic diagram of the bottom structure of the exhaust valve disc of the marine two-stroke engine in this invention.

[0016] Figure 3 This is a schematic diagram of the actual shape of the annular protrusion on the bottom surface of the exhaust valve disc in this invention.

[0017] Figure 4 This is a schematic diagram showing the shape and dimensions of the annular protrusion on the bottom surface of the exhaust valve disc in Example 1.

[0018] Figure 5 This is a schematic diagram showing the shape and dimensions of the annular protrusion on the bottom surface of the exhaust valve disc in Example 2.

[0019] Figure 6 This is a schematic diagram showing the annular protrusion on the bottom surface of the valve disc disrupting the turbulent flow of the exhaust valve when it is closed.

[0020] Figure 7 This is a schematic diagram showing the annular protrusion on the bottom surface of the valve disc disrupting the gas flow when the exhaust valve is in the open state. Detailed Implementation

[0021] Example 1

[0022] The structural diagram of the valve disc, disc bottom, and annular protrusion on the disc bottom surface of the marine two-stroke engine exhaust valve in this embodiment is shown below. Figure 4 As shown, all three are made of the same material, and the materials that can be selected include: austenitic heat-resistant steel SNCrW or Ni-based high-temperature alloy NiCr20TiAl / NiCr38Al4, whose main chemical composition meets the requirements of Table 1, and whose room temperature mechanical properties meet the requirements of Table 2. The exhaust valve disc is integrally formed by die forging, and the disc bottom and the annular protrusion on the disc bottom surface are formed by turning in one piece.

[0023] Table 1

[0024] C% Si% Mn% P% S% Cr% Ni% W% Fe% Al% Ti% Cu% SNCrW 0.30 1 1 ≤0.04 ≤0.03 20 10 2 - - - - NiCr20TiAl - - - - - 20 margin - ≤3 1.5 2.5 - NiCr38Al4 0.10 1.00 - - - 37-39 margin - - 3-4 - 0.50

[0025] Table 2

[0026]

[0027] In this embodiment, the exhaust valve disc of the marine two-stroke engine has a diameter of 288.6 mm. Two annular protrusions are designed on the bottom surface of the disc. The distance between the first annular protrusion and the center of the bottom of the disc is 40 mm, and the distance between the second annular protrusion and the center of the bottom of the disc is 110 mm.

[0028] like Figure 6 As shown, in this embodiment, the cross-section of the annular protrusion on the bottom surface of the exhaust valve disc is an inverted trapezoid. The width of the surface connecting with the bottom surface of the disc is 24mm, the width of the other plane is 10mm, the height is 3mm, and the sharp corner is transitioned by a radius of 3mm.

[0029] Example 2

[0030] The difference between this embodiment and Embodiment 1 lies in the materials used for the bottom and annular protrusions of the exhaust valve disc on the marine two-stroke engine. The valve disc material is the same as that in Embodiment 1, comprising austenitic heat-resistant steel SNCrW or Ni-based high-temperature alloy NiCr20TiAl / NiCr38Al4. The material used for the weld overlay of the bottom and annular protrusions comprises Ni-based high-temperature alloy NiCr22Mo9Nb or NiCr29Fe4, with the main chemical composition meeting the requirements of Table 3 and the room temperature mechanical properties meeting the requirements of Table 4. In this embodiment, the bottom and annular protrusions are integrally formed by GMAW welding on the bottom of the exhaust valve disc using an additive manufacturing method. The height of the additive manufacturing includes the thickness of the valve disc alloy and the height of the annular protrusion. The shape of the bottom and annular protrusions is formed by one-time machining.

[0031] Table 3

[0032] C% Si% Cr% Mo% Fe% Nb% Fe% Al% Ti% Cu% Co% Ni% NiCr22Mo9Nb ≤0.5 22 9 ≤5 3.5 - - - - margin NiCr29Fe4 ≤0.15 - 27-31 20 2.5-6 0.5-2.5 ≤3 2.5-4 ≤1 ≤0.3 ≤0.12 margin

[0033] Table 4

[0034]

[0035] In this embodiment, the exhaust valve disc of the marine two-stroke engine has a diameter of 534mm. The bottom surface of the disc is designed with three annular protrusions. The distance between the first annular protrusion and the center of the bottom of the disc is 50mm, the distance between the second annular protrusion and the center of the bottom of the disc is 150mm, and the distance between the third annular protrusion and the center of the bottom of the disc is 220mm.

[0036] like Figure 7 As shown, in this embodiment, the cross-section of the annular protrusion on the bottom surface of the exhaust valve disc is an inverted trapezoid. The width of the surface connecting with the bottom surface of the disc is 30mm, the width of the other plane is 15mm, the height is 5mm, and the sharp corner is transitioned by an arc of R5mm.

[0037] Examples 3-5

[0038] Table 6 Comparison of Annular Protrusion Designs on the Bottom Surface of Exhaust Valve Disc

[0039]

[0040] The bottom surface structure of the exhaust valve disc used in the low-speed engine of large ships described in Examples 3-5 can be made of materials and manufactured using the same process as in Example 1 or Example 2, and will not be repeated here.

[0041] Figure 6 and Figure 7 This is a schematic diagram illustrating how the annular protrusion on the bottom surface of the valve disc in this embodiment disrupts the erosion of the gas vortex under different conditions.

[0042] In this invention, the material used for the bottom of the exhaust valve disc has increased Cr and Al content. Cr can improve the strength and hardness of steel, enhance its high-temperature mechanical properties, and provide good corrosion resistance and oxidation resistance. Al can refine grains, lower the brittle transition temperature of steel, improve its oxidation resistance, and enhance its resistance to hydrogen sulfide corrosion.

[0043] in, Figure 6 This diagram illustrates the exhaust valve in the closed state. When the exhaust valve of a two-stroke marine engine is closed, during in-cylinder compression combustion, the combustion gas circulates within the cylinder. At this time, the upper part of the combustion gas vortex is positioned at the bottom surface of the exhaust valve disc, and it propagates outward along the bottom surface. The reason for this combustion gas vortex circulation within the cylinder is due to the fuel injection method and cylinder shape of the two-stroke marine engine. Therefore, the scouring of the combustion gas vortex at the bottom of the exhaust valve disc results in the deepest erosion of the valve disc bottom within the boxed area. Through comparison with the erosion characteristics of the exhaust valve disc bottom of existing NI80A materials and extensive testing, it was found that all exhaust valve disc bottoms exhibit the same characteristics. This proves that the generation of this scorching characteristic is unrelated to the material. Furthermore, as demonstrated by the aforementioned embodiments, the annular protrusion structure at the bottom of the valve disc in this invention breaks the propagation of the combustion gas vortex on the bottom surface, preventing excessively deep local erosion that could affect the valve disc strength and lead to its scrapping.

[0044] When the exhaust valve is open, the high-temperature combustion gases inside the cylinder flow along the edge of the exhaust valve into the exhaust valve passage and are then discharged. Figure 7 As shown. In actual operation, the alloy layer of the exhaust valve edge is significantly eroded and consumed after being eroded by high-temperature gas for a long time. The annular protrusion of the present invention can resist the transmission of high-temperature gas along the edge surface of the exhaust valve, thereby effectively reducing the erosion loss of the exhaust valve edge.

[0045] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A valve disc for exhaust gas of a large marine low-speed engine, characterized in that: The valve disc comprises a valve plate, a plate bottom, and a protrusion. The valve plate is made of austenitic heat-resistant material or a Ni-based high-temperature alloy, and its microstructure is a single-phase solid solution characterized by equiaxed grains. Its composition includes: SNCrW / NiCr20TiAl / NiCr22Mo9Nb / NiCr29Fe4 / NiCr38Al4. The protrusions are located below the bottom of the disk, and are distributed in a ring shape with the center of the bottom of the disk as the center. The connection between the protruding part and the bottom plane of the plate is an arc-shaped connection without sharp corners; The material of the bottom plate and the protrusions is the same as that of the valve plate. The valve plate is integrally forged, and the bottom plate and the protrusions are formed by turning in one piece. The bottom plate and the protrusions are integrally formed and are made of a different material than the valve plate, including Ni-based high-temperature alloys NiCr22Mo9Nb or NiCr29Fe4. The Ni-based high-temperature alloys contain the following essential elements by mass percentage: Cr: 22-35%, Fe ≤6%, Al: ≤5%, Mo: 5-25%, Cu: 0.5%, with the balance being Ni. The number of protrusions is 1 to 5, wherein the distance b from the center of the first protrusion outward from the center of the bottom plate is 10-80 mm, and the distance c from the center of the second protrusion outward from the center of the bottom plate is 80-150 mm.

2. The valve disc of the exhaust valve for large marine low-speed engines according to claim 1, characterized in that: The surface of the protrusion has a rounded transition, and its cross-section has an inverted trapezoidal structure.

3. The valve disc of the exhaust valve for large marine low-speed engines according to claim 1, characterized in that: The width d of the connection surface between the protrusion and the bottom of the plate ranges from 1 to 50 mm.

Images