Laser ceramic alloy piston skirt

Abstract

A laser ceramic alloy piston skirt comprises a piston skirt body, an annular protrusion is arranged at the upper end of the piston skirt body, and a sealing groove is formed outside the annular protrusion. An inward protruding ring is arranged in the middle of the piston skirt body, and bolt holes and threaded holes are evenly distributed in the piston skirt body in the circumferential direction. The ceramic alloy layer is formed by melting, cooling and solidifying the ceramic alloy through laser beam scanning and heating; the inner layer of the ceramic alloy layer is rapidly fused with the surface layer of the piston skirt body through laser beam scanning heating, and then the transition layer is formed through cooling. And falling-off is absolutely avoided. And the environment is not polluted and is more environment-friendly. The relative wear resistance of the iron casting after laser surface ceramization is improved by more than 90% compared with the wear resistance of an untreated iron casting.

Description

Technical Field

[0001] The present invention relates to the field of machinery, in particular to a piston skirt of a two-stroke low-speed diesel engine, and specifically to a ceramic alloy piston skirt that is corrosion-resistant, high-temperature-resistant and wear-resistant. Background Art

[0002] According to statistics, over 90% of global trade is carried by seagoing vessels. Vessels are categorized by cargo type into oil tankers, bulk carriers, container ships, natural gas carriers, and other specialized vessels. These vessels are all powered by two-stroke, low-speed diesel engines. The piston skirt is an essential and crucial component of these engines. Two-stroke, low-speed diesel engines are categorized by design company, including engines from world-renowned brands such as MAN, WINGD, Rolls-Royce, Hyundai, General Motors, and Caterpillar. MAN and WINGD engines dominate the market, with MAN engines accounting for approximately 90% of the two-stroke, low-speed diesel engine market share. WINGD engines hold approximately 8% of the market share. Therefore, the newly developed piston skirt is primarily used as a spare part or accessory for MAN and WINGD engines. WINGD engines offer two piston skirt designs: copper ring-embedded and nitrided; MAN engines offer copper ring-embedded and molybdenum-plated. Each piston skirt design has its own advantages and disadvantages. To cope with the complex operating conditions of diesel engines, MAN currently primarily uses molybdenum-plated piston skirts. However, these piston skirts have significant drawbacks, including significant environmental pollution during manufacturing, impacting human health, and excessively high manufacturing costs. Taking all of these factors into consideration, MAN has developed a ceramic alloy piston skirt to meet the design and performance requirements of two-stroke, low-speed diesel engines. Summary of the Invention

[0003] In view of the above problems, the present invention provides a laser ceramic alloy piston skirt, which solves the problems of high temperature resistance, corrosion resistance and wear resistance of the piston skirt surface.

[0004] The laser ceramic alloy piston skirt of the present invention comprises a piston skirt body, characterized in that: an annular protrusion is provided at the upper end of the piston skirt body, and a sealing groove is provided on the outside of the annular protrusion; an inward convex ring is provided in the middle of the piston skirt body, and bolt holes are evenly distributed along the circumference on the surface between the two ends of the piston skirt body, wherein two symmetrical positions also have threaded holes; a ceramic alloy layer is provided on the outer circumference surface of the piston skirt body, and a transition layer is provided between the ceramic alloy layer and the outer circumference of the piston skirt body.

[0005] The laser ceramic alloy piston skirt of the present invention is further characterized by: the ceramic alloy layer is formed by pre-coating the outer circumference of the piston skirt body with a ceramic alloy layer, heating it through laser beam scanning, causing the ceramic alloy to fuse, and then cooling and solidifying it; the transition layer is formed by pre-coating the outer circumference of the piston skirt body with a ceramic alloy layer, heating it through laser beam scanning, causing the inner layer of the ceramic alloy layer to quickly fuse with the outer surface of the piston skirt body, and then cooling and solidifying it. The piston skirt has a diameter of 300-1080 mm.

[0006] The laser-ceramic alloy piston skirt consists of a piston skirt body with a ceramic alloy coating on the outer surface. The ceramic alloy coating contains elements such as chromium, silicon, and boron. The piston skirt body is made of alloy cast iron. The ceramic alloy is pre-sprayed onto the outer working surface of the piston skirt. Under the action of a high-energy, high-density laser beam, the alloy cast iron on the piston skirt surface is rapidly heated and melted. The ceramic alloy quickly and evenly enters the piston skirt body and then rapidly cools and solidifies to form a chilled alloyed hardened layer. This layer consists of the surface ceramic alloy layer and a transition layer formed by the fusion of the two. The alloyed hardened layer is composed of high-hardness, ultra-fine martensite and ledeburite. The ceramic alloy layer can be of any thickness, selected according to the operating conditions.

[0007] When the alloying coating contains high chromium, silicon, and boron contents, the chromium, silicon, and boron contents of the alloyed layer are significantly higher than those of the substrate. Therefore, after laser ceramic alloying, the piston skirt surface not only possesses high hardness and wear resistance, but also exhibits excellent corrosion resistance and high-temperature resistance, with the overall performance generally increasing by more than 2 times in wear resistance. The greatest feature of this invention is that it allows the added coating and substrate to undergo sufficient metallurgical action, forming an alloyed coating with no distinct interface, ensuring a high metallurgical bond strength between the alloyed coating and the substrate. This is a purely chemical bond, directly melted into the substrate, and will never fall off. Furthermore, it does not pollute the environment, making it more environmentally friendly.

[0008] This invention is applicable to any marine low-speed diesel engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 These are the hardness test results of ceramic alloy tissue layer samples 1 and 2.

[0010] Figure 2 It is the AA cross-sectional view of the radial cross section of the piston skirt.

[0011] Figure 3 This is a top view of the piston skirt.

[0012] Among them: 1-piston skirt body, 2-ceramic alloy layer, 3-transition layer, 4-sealing groove, 5-threaded hole, 6-bolt hole. DETAILED DESCRIPTION

[0013] The present invention will be further described below with reference to the accompanying drawings.

[0014] Example 1. As shown in the accompanying drawings, the laser ceramic alloy piston skirt of the present invention comprises a piston skirt body 1, characterized in that: the upper end of the piston skirt body has an annular protrusion with a sealing groove 4 formed on the outer surface of the annular protrusion; the central portion of the piston skirt body has an inwardly facing convex ring; the surface between the two ends of the piston skirt body is uniformly distributed with bolt holes 6 arranged along the circumference, two symmetrical positions of which also have threaded holes 5; the outer circumferential surface of the piston skirt body is provided with a ceramic alloy layer 2, and a transition layer 3 is provided between the ceramic alloy layer and the outer circumference of the piston skirt body.

[0015] The laser processing system consists of a 5000-10000W high-power CO2 laser, a dedicated laser cooling system, an external optical path system, and a multi-functional laser CNC machining center. The piston skirt is cast, machined, and ground according to process requirements. The surface of the piston skirt undergoes laser ceramic surface alloying treatment using a specific processing technique. The alloy layer has a thickness of 0.25-0.3mm and a hardness of approximately HV710. Finally, the finished product is polished to meet the design and use requirements of the piston skirt. The ceramic alloy layer is pre-coated on the outer circumference of the piston skirt body, heated by laser beam scanning, and then cooled and solidified to form the ceramic alloy layer. The transition layer is pre-coated on the outer circumference of the piston skirt body, heated by laser beam scanning, and then cooled and solidified to form the transition layer.

[0016] This piston skirt with a ceramic alloy layer has no obvious interface between the ceramic alloy layer and the piston skirt body. During the operation of the piston skirt, the ceramic alloy layer will never fall off. It has high hardness and wear resistance, as well as good corrosion resistance. Figure 1 The hardness of the gray cast iron of the piston skirt body shown is about HV230. After ceramic alloying, a new ceramic alloy layer is formed with a layer depth greater than 0.6 mm. The hardened layer is greater than the alloy layer above HV713.

[0017] Test results show that the relative wear resistance of laser-ceramized cast iron parts is over 90% higher than that of untreated cast iron parts. In actual operation, the ceramic alloyed piston skirt can further improve the wear resistance, high temperature resistance, and corrosion resistance.

[0018] This ceramic alloy layer and transition layer are alloyed hardened layers composed of ultra-fine martensite and ledeburite with high hardness. The ceramic alloy layer can be of any thickness, selected based on the application requirements. It is a purely chemical bond, directly melted into the base material, and will never flake off. It is also environmentally friendly and pollution-free. After ceramic alloying, a new ceramic alloy layer is formed, with a depth greater than 0.6mm, and the hardened layer is greater than that of alloy layers above HV713.

[0019] The test results show that the relative wear resistance of cast iron parts after laser surface ceramicization is more than 90% higher than that of untreated cast iron parts.

[0020] Example 2. The laser ceramic alloy piston skirt of the present invention (see accompanying drawings) comprises a piston skirt body, characterized by a ceramic alloy layer formed on the outer surface of the piston skirt. The ceramic alloy coating contains elements such as chromium, silicon, and boron. The piston skirt body is made of alloy cast iron. The ceramic alloy is pre-sprayed onto the outer working surface of the piston skirt. Under the action of a high-energy, high-density laser beam, the alloy cast iron on the piston skirt surface is rapidly heated and melted, then rapidly cooled and solidified to form a chilled, alloyed, hardened layer. A transition layer is formed between the ceramic alloy layer and the outer circumference of the piston skirt body. This transition layer is where the ceramic alloy quickly and evenly enters the piston skirt body and rapidly cools and solidifies to form a chilled, alloyed, hardened layer. The alloyed, hardened layer is composed of high-hardness, ultrafine martensite and ledeburite. The ceramic alloy layer can have any thickness, selected based on operating conditions. When the alloying coating contains high chromium, silicon, and boron content, the chromium, silicon, and boron content of the alloyed layer is significantly higher than that of the base body. Therefore, after laser ceramic alloying, the piston skirt surface not only possesses high hardness and wear resistance, but also excellent corrosion resistance and high-temperature resistance. Overall, the wear resistance is generally improved by more than 2 times. The laser ceramic alloy piston skirt comprises a piston skirt body, with an annular protrusion at the upper end of the piston skirt body and a sealing groove on the outer surface of the annular protrusion; an inward-facing protrusion at the middle of the piston skirt body; bolt holes evenly distributed along the circumference between the two ends of the piston skirt body, two of which are also symmetrically provided with threaded holes; a ceramic alloy layer is provided on the outer circumference of the piston skirt body, and a transition layer is provided between the ceramic alloy layer and the outer circumference of the piston skirt body. The ceramic alloy layer is formed by pre-coating the outer circumference of the piston skirt body with a layer of ceramic alloy, heating it with a laser beam, and then cooling and solidifying it; the transition layer is formed by pre-coating the outer circumference of the piston skirt body with a layer of ceramic alloy, heating it with a laser beam, and then rapidly fusing the inner layer of the ceramic alloy layer with the outer surface of the piston skirt body through laser beam scanning and heating, and then cooling and solidifying it.

[0021] The key feature of this invention is that it allows for full metallurgical interaction between the additive coating and the base material, forming an alloyed coating with no distinct interface. A transition layer exists where the ceramic alloy layer gradually transitions to the piston skirt body, ensuring a high metallurgical bond between the alloyed coating and the base material. This purely chemical bond, directly melted into the base material, will not flake off. Furthermore, it is environmentally friendly and does not pollute the environment.

Claims

1. A laser ceramic alloy piston skirt, comprising a piston skirt body, characterized in that: The upper end of the piston skirt body has an annular protrusion with a sealing groove on the outside; the middle part of the piston skirt body has an inward protrusion, and the surface between the two ends of the piston skirt body has bolt holes evenly distributed along the circumference, two of which are symmetrically located with threaded holes; the outer surface of the piston skirt body is provided with a ceramic alloy layer, and there is a transition layer between the ceramic alloy layer and the outer surface of the piston skirt body.

2. The laser ceramic alloy piston skirt according to claim 1, characterized in that: The diameter of the piston skirt is 300-1080mm.

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