JP2006125530A - Piston ring and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston ring capable of securing necessary wear resistance even if a hard film is not formed on an outer peripheral sliding part and a method of manufacturing the piston ring. <P>SOLUTION: A large number of minute dimples 2 are formed in at least the outer peripheral sliding part of the piston ring 1, nano crystal layers 3 are generated just below the dimples, and air shot peening equivalent to 10,000 to 50,000% in coverage is applied to the nano crystal layers 3 so that their thickness becomes 2 to 20 μm and its surface hardness becomes 800 to 1000 HV. In particular, when 20,000%<C<40,000%, hardness on the surface of the ring is 900 or higher and, therefore, high hardness can be provided to the ring and the ring can be securely prevented from being cracked. Except for the air shot peening, ultrasonic shot peening and flap wheel processing may be used for surface processing. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piston ring excellent in wear resistance used for, for example, an automobile engine and a method for manufacturing the same.

In order to improve the wear resistance of piston rings for automobile engines, etc., a chromium plating film, a nickel-based composite dispersion plating film, a thermal spray coating (molybdenum), a nitride coating, a PVD coating (TiC, Conventionally, a hard film such as TiN is formed. In addition, with higher engine output and lower fuel consumption, piston rings are required to have improved friction resistance and scuffing resistance on the outer periphery sliding surface and lower friction, and a hard coating on the outer periphery surface of the piston ring. Because it is not possible to meet the demand just by forming the shot ring peening on the outer peripheral surface of the piston ring base material in advance to form a minute dimple, and then forming a hard coating on the outer peripheral surface, It has been proposed that minute dimples similar to the dimples formed on the piston ring base material appear on the surface of the hard coating and act as a pool of oil to reduce friction (for example, patent documents) (See 1)
JP 2004-60873 A

  In order to improve wear resistance, the conventional piston ring has at least an outer peripheral sliding surface such as a chromium plating film, a nickel-based composite spray plating film, a thermal spray coating (molybdenum), a nitride coating, a PVD coating (TiC, TiN, etc.), etc. It was necessary to form a hard film. The same applies when shot peening is performed so as to form dimples that become oil pools on the outer peripheral surface of the piston ring base material, and the wear resistance cannot be sufficiently ensured only by the lubricating action of the oil pools. Furthermore, it was necessary to form a hard film such as a chromium plating film, a nickel-based composite sprayed film, a sprayed film (molybdenum), a nitride film, and a PVD film (TiC, TiN, etc.) on the surface.

  As described above, the conventional piston ring needs to form a hard film on at least the outer peripheral sliding portion in order to improve the wear resistance, and it takes a long time for the treatment, and the shape by heating may change. There was a problem that there was.

  The present invention has been made in view of the above problems, and it is an object of the present invention to provide a piston ring that can ensure the necessary wear resistance without forming a hard film on the outer peripheral sliding portion, and a method for manufacturing the same. And

  The present invention pays attention to the mechanical properties of a polycrystalline body having a crystal grain size of nanometer size that can be generated on the surface portion of the metal material by shot peening or the like, that is, the nanocrystal, particularly its high hardness and high strength, By forming a nanocrystal layer on at least the surface of the outer periphery sliding portion of the piston ring so that the hardness of the surface portion is 800 to 1000 HV, the resistance required for the piston ring is eliminated even if a hard coating is not formed on the surface. This is because it has been found that wearability can be ensured.

  That is, the piston ring of the invention according to claim 1 has a nanocrystal layer at least in the vicinity of the surface of the outer peripheral sliding portion, and the surface has a hardness of 800 to 1000 HV.

  This piston ring has a nanocrystal layer in the vicinity of the surface of the outer peripheral sliding portion, and the surface has a hardness of 800 to 1000 HV, and the hardness itself is high, so that a process for forming a hard film on the surface is not performed. However, it is possible to ensure the required wear resistance as a piston ring.

  The piston ring of the invention according to claim 2 has dimples formed by shot peening at least on the surface of the outer periphery sliding portion, and has a nanocrystal layer immediately below the dimples, and the hardness of the surface is 800 to 1000 HV.

  This piston ring has a nanocrystal layer directly below the dimples formed by shot peening on the surface of the outer peripheral sliding portion, and the surface hardness is 800 to 1000 HV, and the hardness itself is high. It is possible to ensure the required wear resistance as a piston ring without performing a process for forming a hard coating.

  The piston ring of the invention according to claim 3 has dimples formed by shot peening at least on the surface of the outer peripheral sliding portion, and has a nanocrystal layer immediately below the dimples, The ratio of the total surface area of the dimples to the processing area is 10,000 to 50,000% (coverage 10,000 to 50,000%).

  This piston ring has a nanocrystal layer directly below the dimples formed by shot peening on the surface of the outer peripheral sliding portion, and the degree of shot peening is equivalent to a coverage of 10,000 to 50,000%. Since the ratio of the total surface area of the dimples to the total processing area of processing is 10,000 to 50,000%, the hardness of the surface is 800 to 1000 HV, and the hardness itself is high, and therefore a process for forming a hard film on the surface Even if it does not perform, it becomes possible to ensure required abrasion resistance as a piston ring.

  The degree of shot peening can be adjusted by the material of the workpiece, the material of the shot material, the shape, the particle size, the projection speed and the projection time. In general, it can be represented by coverage (C) indicating the ratio (%) of the total surface area (B) of the dimples to the total processing area (A) of shot peening. That is, the degree of shot peening can be expressed by C = B / A. And when this C value is 10000% to 50000%, the required hardness (800 to 1000 HV) can be obtained. When C <10000%, the required hardness (800 to 1000 HV) cannot be obtained, and when C> 50000%, cracks may occur on the surface of the piston ring. More desirably, 20000% <C <40000%.

  A piston ring according to a fourth aspect of the present invention is the piston ring according to the first, second, or third aspect, wherein the nanocrystal layer has a thickness of 2 to 20 μm.

  This piston ring has a nanocrystal layer with a thickness of 2 to 20 μm in the vicinity of the surface of the outer periphery sliding portion, and has a surface hardness of 800 to 1000 HV and its own hardness, or the outer periphery sliding portion. A nanocrystal layer with a thickness of 2 to 20 μm directly under the dimples formed by shot peening on the surface of the metal, and the surface hardness is 800 to 1000 HV, and the hardness itself is high, or the outer periphery slides Surface has a nanocrystal layer with a thickness of 2 to 20 μm immediately below the dimples formed by shot peening, and the degree of shot peening is equivalent to a coverage of 10,000 to 50,000%. Is 800 to 1000 HV, and the hardness itself is high. For this reason, even if a treatment for forming a hard film on the surface is not performed, Required wear resistance can be ensured as tons ring. If the thickness of the nanocrystal layer is less than 2 μm, it is difficult to obtain sufficient wear resistance. If the thickness of the nanocrystal layer exceeds 20 μm, cracks may occur at the boundary due to the difference between the inside and the surface hardness. is there.

  Moreover, the manufacturing method of the piston ring of the invention which concerns on Claim 5 gives surface processing to the at least outer periphery sliding part of a piston ring, produces | generates a nanocrystal grain in the surface vicinity, and the hardness of this surface is 800-1000HV. It is characterized by increasing to.

  By manufacturing the piston ring by this method, the required wear resistance can be ensured without performing a process of forming a hard film on the surface. Therefore, a process for forming a hard coating is not required, and it can be manufactured at a low cost, and a shape change due to heating can be prevented from occurring.

  According to a sixth aspect of the present invention, there is provided a piston ring manufacturing method according to the fifth aspect, wherein the surface processing is performed by air shot peening processing, ultrasonic shot peening processing or flap wheel processing. It is characterized by being.

  Pneumatic shot peening, ultrasonic shot peening and flap wheel machining are suitable for processing a plurality of piston rings at once, for example, in a cylindrical shape, so that at least the surface of the outer periphery sliding portion of the piston ring can be processed. Surface processing for increasing the hardness of the surface to 800 to 1000 HV can be efficiently performed by generating nanocrystal grains in the part. In particular, air shot peening is desirable in terms of mass productivity.

  As described above, according to the present invention, a treatment for forming a hard coating such as a chromium plating coating, a nickel-based composite spray coating, a spray coating (molybdenum), a nitride coating, a PVD coating (TiC, TiN, etc.) on the surface is performed. Even if it is not, it can be set as the piston ring which has required abrasion resistance, the piston ring can be manufactured at low cost, and the shape change by heating can be prevented from occurring.

  FIG. 1 shows a cross-sectional structure of a piston ring according to an example of an embodiment of the present invention. The piston ring 1 has a substantially rectangular cross section, and a large number of minute dimples 2 are formed at least on the outer periphery sliding portion. A nanocrystal layer 3 is generated immediately below the dimple 2, and the thickness of the nanocrystal layer 3 is increased. Is processed by air shot peening corresponding to a coverage of 10000 to 50000% so that the hardness of the surface becomes 800 to 1000 HV.

  The coverage is a value (C) indicating the ratio (%) of the total surface area (B) of the dimple to the total processing area (A) of the shot peening process, and C = B / A represents the degree of the shot peening process. When the value of C is 10000% to 50000%, the hardness of the ring surface is 800 to 1000 HV, and the hardness necessary for the sliding surface of the piston ring can be obtained. When C <10000%, the required hardness (800 to 1000 HV) cannot be obtained. When C> 50000%, cracks may occur on the ring surface. And especially when 20000% <C <40000%, the hardness of the ring surface is 900 or more, a large hardness is obtained, and the occurrence of cracks can be reliably prevented.

  The air shot peening uses a general air shot peening apparatus, and projects the shot material onto the outer peripheral sliding surface of the piston ring 1 at high speed with high-pressure air.

  The degree of shot peening processing can be adjusted by the material of the piston ring 1, which is the workpiece, the material of the shot material, the shape, the particle size, the projection speed, and the projection time.

  The material of the piston ring 1 is martensitic stainless steel, for example. In addition, any material that can form dimples may be used, such as austenitic stainless steel, ferritic stainless steel, Si—Cr, and cast iron.

  The material of the shot material is, for example, ceramic, glass, metal, and the like, and is not particularly limited. However, the shot material needs to have higher hardness than the material of the piston ring 1. Further, the shape of the shot material is desirably a substantially spherical shape in which dimples are easily formed, and the particle diameter is desirably 10 to 100 μm. The shot material is preferably projected at a speed of 100 to 300 m / s, and more particularly about 200 m / s. The projection time is preferably 5 to 10 minutes.

  The surface processing may be ultrasonic shot peening processing, flap wheel processing, or the like in addition to air shot peening processing.

  Martens with a composition of% by weight, C: 0.7%, Si: 0.52%, Mn: 0.49%, P: 0.032%, Cr: 12.2%, the balance being iron and inevitable impurities Using a site-based stainless steel oil tempered wire as a material, it is formed into a piston ring shape with a substantially rectangular cross-section, and air shot peening is applied to the surface of the outer periphery sliding part, changing the shot material projection time to change the coverage. Then, nanocrystal grains were generated on the surface, and the hardness of the surface was examined. The material of the shot material is C: 1.0%, Si: 1.3%, Mn: 1.0%, the balance is high carbon steel made of iron and inevitable impurities, the shape is substantially spherical, the particle size is about 50 μm, The projection speed is 200 m / s. The result is shown in FIG.

  FIG. 2 is a graph showing the relationship between coverage and surface hardness (Vickers Hardness). In order to obtain a hardness of 800 HV or more, it is necessary to set the coverage to 10,000% or more, and it is understood that a hardness exceeding 900 HV can be obtained at a coverage of 20000% or more.

  FIG. 3 is a photomicrograph showing a state where nanocrystals generated on the surface of the outer peripheral sliding portion of the piston ring are generated. The thickness of the nanocrystal layer is 2 to 20 μm.

It is sectional drawing (a) of the piston ring which concerns on an example of embodiment, and its A section enlarged view (b). It is a graph which shows the relationship between the coverage of the piston ring of an Example, and the hardness (Vickers Hardness) of a surface. It is a microscope picture of the outer periphery sliding part cross section of the piston ring of an Example.

Explanation of symbols

1 Piston ring 2 Dimple 3 Nanocrystal layer

Claims (6)

A piston ring having a nanocrystal layer in the vicinity of the surface of at least the outer peripheral sliding portion, and having a hardness of 700 to 1000 HV. A piston ring having dimples formed by shot peening at least on the surface of an outer peripheral sliding portion, a nanocrystal layer immediately below the dimples, and a hardness of the surface of 800 to 1000 HV. It has dimples formed by shot peening at least on the surface of the outer periphery sliding portion, and has a nanocrystal layer immediately below the dimples, and the ratio of the total surface area of the dimples to the total processing area of the shot peening is 10000 Piston ring characterized by ˜50000% (coverage 10000-50000%). The piston ring according to claim 1, 2 or 3, wherein the nanocrystal layer has a thickness of 2 to 20 µm. A manufacturing method of a piston ring, characterized in that at least an outer peripheral sliding portion of the piston ring is subjected to surface processing to generate nanocrystal grains in the vicinity of the surface, and the hardness of the surface is increased to 800 to 1000 HV. 6. The method of manufacturing a piston ring according to claim 5, wherein the surface processing is air shot peening processing, ultrasonic shot peening processing or flap wheel processing.

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