JP2000179692A - Piston ring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve seizure resistance of a piston ring. SOLUTION: A compound plating coat with silicon nitride grains with an average grain diameter of 0.5-10 μm dispersed at 5-30 vol.% in alloy base material containing 1-15 wt.% of phosphorous and the rest formed of nickel, is formed at least on the outer peripheral sliding surface of a piston ring, and network cracks are formed on the surface of the compound plating coat. The network cracks are formed on the surface of the compound plating coat originally high in seizure resisance so as to improve lubricating oil retainability in the cracks.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston ring, particularly a piston ring for an internal combustion engine having excellent seizure resistance.

[0002]

2. Description of the Related Art A piston ring in which a hard particle-dispersed composite plating film in which hard particles are dispersed is formed on an outer peripheral sliding surface is known. For example, JP-A-59-96295 discloses a coating in which silicon nitride particles having an average particle size of 0.5 to 5 μm are dispersed in a nickel-phosphorus alloy matrix, and a coating having a coating hardness of Hv 800 or more in Vickers hardness is obtained by a thermosetting treatment. 2 shows a piston ring having the same. Japanese Patent Application Laid-Open No. 61-149498 discloses an alloy matrix containing 50 to 88% by weight of nickel, 10 to 40% by weight of cobalt, and 2 to 15% by weight of phosphorus.
1 shows a piston ring for an internal combustion engine having a composite plating film on a sliding surface in which 5 to 30% by volume of 10 μm silicon nitride particles are dispersed. In engines such as automobiles that use high-lead gasoline as fuel, the hard-chromium plating film used conventionally has insufficient abrasion resistance and corrosion resistance. A piston ring formed on a surface has been frequently used. A composite plating film in which silicon nitride particles are dispersed in a nickel-phosphorous or nickel-cobalt-phosphorous alloy matrix originally has higher seizure resistance than a hard chromium plating film.

[0003]

However, when a hard particle-dispersed coating is used on the outer peripheral sliding surface of a piston ring used for a diesel engine, particularly a high-load engine including a direct injection diesel engine, the outer peripheral surface of the piston ring is reduced. High surface pressure is applied to the sliding surface, and the wettability of the lubricating oil on the coating is low. For this reason, it was found that micro seizure occurred, the coating was brittle and the adhesion was insufficient, and due to the strong tensile stress, the coating was chipped or peeled off, resulting in abnormal wear of the cylinder liner. . In particular, the tendency is remarkable in a high-load direct injection diesel engine, and the seizure resistance is still insufficient. SUMMARY OF THE INVENTION An object of the present invention is to provide a piston ring having improved lubricating oil retention by a composite plating film and having improved seizure resistance.

[0004]

SUMMARY OF THE INVENTION A piston ring according to the present invention comprises 5 to 30 parts by volume of silicon nitride particles having an average particle size of 0.5 to 10 .mu.m in an alloy matrix consisting of 1 to 15% by weight of phosphorus and the balance being nickel. % Is formed on at least the outer peripheral sliding surface, and a network-like crack is formed on the surface of the composite plating film. Since a network-like crack was formed on the surface of a composite plating film having inherently high seizure resistance in which silicon nitride particles were dispersed in a nickel-phosphorus or nickel-cobalt-phosphorus alloy matrix, lubricating oil in the crack was formed. Oil retention, seizure resistance,
Initial conformability and scuff resistance can be further improved. In an embodiment of the present invention, the alloy matrix may contain up to 50% by weight of cobalt.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION A piston ring according to the present invention is characterized in that silicon nitride particles having an average particle size of 0.5 to 10 μm are contained in an alloy matrix consisting of 1 to 15% by weight of phosphorus and the balance being nickel.
A composite plating film dispersed at 30% by volume is formed on at least the outer peripheral sliding surface, and a network-like crack 2 is formed on the surface of the composite plating film 1. As shown in FIG. 1, the cracks 2 formed in the form of cracks are uniformly distributed over the entire surface of the composite plating film 1, and the cracks 2 form the composite plating film 1 in a number of polygonal islands. Further, as shown in FIG. 2, the crack 2 is formed deep in the thickness direction of the composite plating film 1.

[0006] If the content of phosphorus is less than 1% by weight, the effect of improving the wear resistance is insufficient, and if the content of phosphorus exceeds 15% by weight, the film becomes brittle, and the heat resistance and the adhesion are also deteriorated. The average particle size of the silicon nitride particles is preferably 0.5 to 10 μm, and if it is less than 0.5 μm, the effect of improving the wear resistance is insufficient, and if it is coarser than 10 μm, the plating layer becomes brittle and chipping occurs during operation. Occurs. On the other hand, if the amount of silicon nitride particles is less than 5% by volume, the effect of improving the wear resistance is insufficient, and if it exceeds 30%, the sliding partner material is often worn, and the phosphorus-containing nickel plating layer The strength also decreases.

In the piston ring of the present invention, the composite plating film is formed of a nickel-phosphorous or nickel-cobalt-phosphorous alloy, and silicon nitride particles are dispersed in the alloy matrix. Network-like cracks are formed on the surface of the plating film. The cracks are formed uniformly on the entire surface and act as oil pools of lubricating oil deep in the thickness direction, which can increase the lubricating oil's oil retention in the cracks, seizure resistance, initial break-in, and scuff resistance. Can be further improved. To increase heat resistance and corrosion resistance, the alloy matrix may contain 50% by weight or less of cobalt. However, if it exceeds 50% by weight, stickiness is reduced and the cost becomes high. Therefore, the content of cobalt is preferably 10 to 40% by weight.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described specifically with reference to FIG. First, nominal size x width x thickness is 96mm x 2.5m
A plurality of piston rings formed of 3.5 mm SKD-61 (JIS-G4404) high alloy tool steel are collectively immersed in a plating bath to perform composite plating, and a composite dispersion plating with a layer thickness of 100 μm. The coating was formed on the outer peripheral sliding surface of the piston ring. The composition of the plating bath was as follows: nickel sulfate: 200 g / l, cobalt sulfate: 30 g / l, nickel chloride: 80 g / l, sodium hypophosphite: 3 g / l (average particle size: 1.5 μm), silicon nitride particles: 60 g / l l (Maximum particle size 10μ
m), thiourea: 3 g / l. The conditions for performing the composite plating were as follows: bath temperature: 55 ° C., cathode current density: 10 A / dm ² , electric field time: 2 hours, and pH 2.0. The composition of the composite dispersed plating layer was 30% by weight of cobalt and 6.5% by weight of phosphorus. Since silicon nitride particles were mixed in the plating bath, 20% by volume of silicon nitride was uniformly dispersed in the composite plating film. The groove width of the crack was 1.5 to 3.0 μm. When an organic compound such as thiourea is added to the plating bath, the electrodeposition stress and the tensile stress of the coating increase, and a groove-shaped crack occurs. Next, the obtained composite plating film having groove-shaped cracks is subjected to a heat treatment at 400 ° C. for 1 hour to harden the film to a micro-Vickers hardness HMV950, and at the same time, to reduce the groove-shaped crack width to 2.5 to 2.5. Enlarged to 4.0 μm. A 4-cycle water-cooled 6-cylinder 4100cc direct-injection diesel engine, FC-250 (JIS G5501) cast iron engine cylinder incorporating a piston ring with a composite plating film, 200 rpm at 3,200 rpm full load
A time bench test was performed to measure the amount of wear at the top dead center of the mating cylinder liner, the amount of wear on the sliding surface of the piston ring, the occurrence of scuffing of the mating cylinder liner and piston ring, and the amount of oil consumption.

[0009]

Comparative Example For comparison, 30% by weight of cobalt and 6.5 of phosphorus.
A composite plating film consisting of 20% by weight of silicon nitride was formed on the outer peripheral sliding surface of the piston ring. No crack grooves are formed on the surface of this composite plating film. Next, the composite plating film was subjected to a heat treatment at 400 ° C. for 1 hour to cure the composite plating film having a layer thickness of 100 μm to a hardness of micro Vickers hardness HMV980. An actual machine test was performed using the piston ring of the comparative example in the same manner as in the example, and the wear amount of the cylinder liner of the mating machine, the wear amount of the piston ring sliding surface, the presence or absence of scuffing, and the oil consumption were measured. The test results are shown in FIG. As is evident from FIG. 3, the piston ring according to the present invention consumes less oil from the initial stage than the piston ring having a sliding surface formed of a composite plating film having no groove crack. This is because the gap between the piston ring and the cylinder disappears in a short time, and the initial conformability is good. Also, no scuffing was observed in the examples.

[0010]

[Table 1]

[0011]

As described above, in the piston ring of the present invention, the lubricating oil has an improved oil retaining property due to the network cracks, and the initial break-in and scuff resistance can be improved. This not only makes the operation of the engine smooth,
Life can be extended.

[Brief description of the drawings]

FIG. 1 is a plan view of a composite plating film according to the present invention formed on an outer peripheral surface of a piston ring.

FIG. 2 is a cross-sectional view of a composite plating film according to the present invention formed on an outer peripheral surface of a piston ring.

FIG. 3 is a graph showing oil consumption.

[Explanation of symbols]

 1 .. Composite plating film 2. Crack

Claims (2)

[Claims] 1. A composite plating film in which silicon nitride particles having an average particle size of 0.5 to 10 μm are dispersed at 5 to 30% by volume in an alloy matrix composed of 1 to 15% by weight of phosphorus and the balance of nickel. A piston ring formed on a sliding surface and having a network-like crack formed on a surface of a composite plating film. 2. The piston ring according to claim 1, wherein the alloy matrix contains up to 50% by weight of cobalt.