JPH02150574A - Piston ring - Google Patents

Abstract

PURPOSE:To make the extent of initial fittability better by forming a double plating layer, consisting of a hard chrome plating layer and a silicon nitride molecular dispersion nickel-cobalt-phosphorus alloyed composite plating layer, on a periphery sliding surface of the piston ring. CONSTITUTION:A hard chrome plating layer 2 and a silicon nitride molecular dispersion nockel-cobalt-phosphrus composite plating layer 3 are formed on the peripheral sliding surface of a piston ring 1 so as to make them form a double structural layer. Since this hard chrome plating layer 2 is poor in the extent of initial fittability because of being too hard, it is formed on the plating layer 3 to make up for the weak point. Phosphorus being contained in a film of the silicon nitride molecular dispersion nickel-cobalt-phosphate alloy composite plating layer enhances hardness of this film, and it is excellent in abrasion resistance and seizure resistance and, what is more, anticorrosion of the base is also improved. Accordingly, when heat treatment temperature is properly selected, it can be made into such hardness (HMV 600 - 800 or so) excellent in the initial fittability.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a piston ring for an internal combustion engine that has a dual structure of a hard chromium plating layer and a composite dispersion plating layer on its sliding surface, and particularly relates to a piston ring for an internal combustion engine that has a double structure of a hard chrome plating layer and a composite dispersion plating layer. This invention relates to a piston ring that has good initial conformability and excellent wear resistance.

[Conventional technology]

In recent years, as engines have become smaller and lighter and have higher performance such as higher output, the conditions required for piston rings have become increasingly severe, and the conditions that are required of piston rings are not only wear resistance but also seizure resistance, breakage resistance, etc. Improvements have been made from various perspectives.

By the way, in general, in an engine immediately after assembly,
Due to precision constraints in manufacturing parts, it is inevitable that errors will occur in the sizes of the piston ring and cylinder, and a gap will be created between them. If the engine is operated with this gap still present, the airtightness of the combustion chamber will be broken and gas will blow through (compression leak) into the crank chamber. This gas blow-through breaks the lubricating oil film that uniformly covers the inner surface of the cylinder, causing abnormal wear between the piston ring and the cylinder, resulting in scuffing. At the same time, lubricating oil enters the combustion chamber through this gap, increasing oil consumption.

Therefore, during the initial operation immediately after engine assembly, which is called break-in operation, it is necessary to eliminate the gap between the piston ring and the cylinder in a short period of time by rubbing together the piston ring and the cylinder, and to quickly get used to the two.

In general, piston rings with excellent wear resistance have a sliding surface with high hardness, so the break-in period tends to be long. For this reason, methods have been adopted to make the piston ring and cylinder fit together in a short period of time, such as providing a soft film layer such as tin plating on the outer sliding surface of the piston ring, or processing the cross section of the ring into a tapered shape. ing.

[Problem to be solved by the invention]

However, in this method of applying tin plating, the tin plating layer is too soft under conditions of high temperature and high load, so it is easily worn away at the initial stage of startup, and the breaking-in effect is almost lost. Further, the method of tapering the outer circumferential sliding surface of the ring has a problem in that the angle of the taper affects the airtightness of the combustion chamber and the oil retention of the inner circumferential surface of the cylinder.

Therefore, an object of the present invention is to provide a piston ring that has good initial break-in properties even under high temperature and high load conditions, does not cause scuffing, finishes break-in operation in a relatively short period of time, and has excellent wear resistance. That's true.

[Means to solve the problem]

As a result of extensive studies to achieve the above object, the inventors of the present invention have found that by forming a composite dispersion plating layer with appropriate hardness on a hard chromium plating layer with excellent wear resistance, good initial conformability can be achieved. The present invention was completed based on the discovery that it is possible to provide a piston ring that has the following characteristics and also has excellent wear resistance.

That is, the piston ring for an internal combustion engine of the present invention has a hard chromium plating layer as a first layer and a nickel-cobalt-phosphorus alloy composite plating layer in which silicon nitride particles are dispersed as a second layer formed in this order on at least its outer peripheral sliding surface. It is characterized by having a double structure layer.

[For production]

In the dual structure piston ring coating of the present invention, the upper layer (second layer) of the silicon nitride particle dispersed composite plating layer is made of a somewhat softer material than the lower layer (first layer) of the hard chromium plating layer. It fits well with the cylinder at the initial stage of startup, and at the same time does not wear out rapidly. Moreover, since the hard chromium plating layer of the lower layer (first layer) has high hardness, good wear resistance can be maintained for a long period of time (even after the upper layer is worn).

〔Example〕

The invention will be explained in detail by means of the following examples and with reference to the accompanying drawings.

FIG. 1 is a sectional view of a piston ring for an internal combustion engine according to an embodiment of the present invention. In this embodiment, a hard chromium plating layer 2 and a nickel-cobalt-phosphorus alloy composite plating layer 3 in which silicon nitride particles are dispersed are formed on the outer peripheral sliding surface of the piston ring 1 so as to have a double structure.

The first hard chromium plating layer can be obtained by electroplating using a plating bath mainly containing chromic acid. As such a plating bath, a Sargent bath, a silica fluoride bath, which is a type of fluoride bath, or the like can be used.

The hard chrome plating layer has high hardness and excellent wear resistance. Therefore, the thickness of the hard chromium plating layer should be 80 to 200 μm.

Since the hard chromium plating layer has too high hardness and poor initial conformability, in order to compensate for this drawback, a nickel-cobalt-phosphorus alloy composite plating film with silicon nitride particles dispersed therein is formed as a second layer on the first layer. .

Phosphorus contained in the composite film increases the hardness of the film, exhibits excellent effects on wear resistance and seizure resistance, and also improves the corrosion resistance of the base. The hardness of the plating film containing phosphorus is improved by heat treatment, so by appropriately selecting the heat treatment temperature, the hardness (IIM) suitable for obtaining good initial conformability can be achieved.
V600-800). However, if the amount of phosphorus is less than 1% by weight, the hardness will be IIMV5 even after heat treatment.
It does not exceed QQ and has little effect on wear resistance and scuff resistance. Moreover, if it exceeds 10% by weight, the hardness will increase, but it will become brittle and the impact strength will also decrease. Therefore, the amount of phosphorus is 1 to 10% by weight.
It is better to A more preferable phosphorus content is 4 to 7% by weight.

Cobalt improves the heat resistance and corrosion resistance of the plating alloy base, and also improves the crush fatigue strength of the coating. If the amount of cobalt in the alloy matrix is less than 10% by weight, the above effects cannot be obtained significantly, and even if it exceeds 40% by weight, there is no significant change in the effect, so it is preferable to set the amount of cobalt to 10 to 40% by weight. .

A more preferable cobalt content is 20 to 30% by weight.

Silicon nitride particles, together with phosphorus, have an excellent effect on improving the wear resistance of the coating. Furthermore, since silicon nitride has low wettability with metal, it also contributes to improving seizure resistance and scuffing resistance. The amount of silicon nitride is 5-30% by volume, and its average particle size is 0.5-30% by volume.
5 μm is good. Volume less than 5% or particle size 0.5
If it is less than μm, the area occupied by silicon nitride on the base surface is small, and the effect of improving wear resistance and scuff resistance is small. Moreover, if the capacity exceeds 30% or the particle size exceeds 5 μm, the wear of the mating material will increase, and the strength of the composite film will also decrease. More preferably, the average particle size of the silicon nitride particles is 0.8 to 1.2 μm, and the content is 15 to 25% by volume.

For forming a composite plating film, silicon nitride particles are dispersed in a plating bath in which a nickel compound, a cobalt compound, and a phosphorus compound are dissolved so as to have the desired composition. As the nickel compound and cobalt compound, sulfate, sulfamate, etc. are used, and as the phosphorus compound, phosphoric acid, phosphorous acid, etc. are used.

The obtained composite plating film is washed with water, dried, and then heat treated if necessary. The heat treatment temperature is about 200-300℃,
The time is 30-60 minutes. The base of the composite film is hardened by the heat treatment, and a composite film having a hardness suitable for obtaining good initial conformability is obtained.

The present invention will be explained in further detail by the following examples.

Example 1 A first step of forming a hard chromium plating layer as a first layer on the outer peripheral sliding surface of a piston ring, a second step of forming a composite dispersion plating layer on the first layer as a second layer, A film was formed by a third step of heat-treating the resulting double-structured layer.

First, in the first step, the nominal diameter x width x thickness is 77mmxl.
A plurality of 5KD-61 piston rings measuring 5 mm x 3.1 mm were used as a base material, and hard chromium plating was performed under the conditions shown in Table 2 using a plating bath having the bath composition shown in Table 1.

Table 1 Immersion, plating bath temperature 60°C, pH 4, current density 10A
Electroplating was performed by applying a current of /dm2 for 5 minutes.

Table 3 Table 2 The thickness of the hard chromium plating layer obtained by this first step was 100 μm.

As a second step, a piston ring having a hard chromium plating layer on the surface obtained in the first step is prepared as shown in Table 3.
The thickness of the second layer composite plating film obtained in this second step in a plating bath having the composition shown in is 7 μm,
Its composition was 30% by weight of cobalt, 6.5% by weight of phosphorus, and 20% by volume of silicon nitride.

Next, as the third step, the obtained double-structured film is coated with 250
The film was cured by heat treatment at ℃ for 1 hour. At this time, the hardness of the first hard chromium plating layer was 980 micro Vickers, and the hardness of the second composite plating layer was 750 micro Vickers.

Actual machine test Cast iron for 4-cycle water-cooled 4-cylinder 1300cc engine (
The above piston ring was assembled into an engine cylinder manufactured by FC-25), and a bench test was conducted for 100 hours at 7500 rpm and full load, and the oil consumption was measured.

Comparative Example 1 For comparison, an actual machine test was conducted in the same manner as in Example 1 using a piston ring in which only a hard chromium plating layer was formed on the outer peripheral sliding surface of the piston ring, and the oil consumption was measured.

The test results are shown in Figure 2.

As is clear from FIG. 2, the piston ring of the present invention is
It can be seen that oil consumption is lower from the initial stage compared to piston rings that have only a hard chrome plating layer on the sliding surface. This is because the gap between the piston ring and the cylinder disappears in a short time, that is, the initial conformability is good.

Further, in the examples, no scuffing was observed at all.

〔Effect of the invention〕

As described in detail above, the piston ring of the present invention, which has a hard chromium plating layer and a nickel-cobalt-phosphorus alloy composite plating layer in which silicon nitride particles are dispersed, on the outer peripheral sliding surface, has excellent initial conformability and scuff resistance due to the composite dispersion plating film. It also has excellent long-term wear resistance due to the hard chrome plating layer.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a piston ring according to an example of the present invention, and FIG. 2 is a graph showing the relationship between test time and oil consumption in piston rings of Example 1 and Comparative Example 1. 1... Piston ring base material 2... Hard chromium plating layer 3... Silicon nitride particle dispersed nickel-cobalt-phosphorus alloy composite plating film

Claims (1)

[Claims] At least on the outer peripheral sliding surface, a hard chrome plating layer,
A piston ring for an internal combustion engine, characterized in that it has a double-layered layer consisting of a silicon nitride particle-dispersed nickel-cobalt-phosphorus alloy composite plating layer formed on the hard chromium plating layer.