JPH05215239A - Piston ring - Google Patents

Abstract

PURPOSE:To provide a piston ring having efficient initial adaptability even in the condition of high temperature and high load, having no formation of scuffing, having almost no necessity of running-in, and having excellent wear and abrasion resistance. CONSTITUTION:A piston ring comprises a double layer at least on the peripheral sliding face of which are formed in order a hard chromium plating layer 2 as the first layer and a tin-nickel alloy plating layer 3 as the second layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston ring having good initial conformability with a cylinder and excellent wear resistance.

[0002]

2. Description of the Related Art In recent years, as engine performance has become smaller and lighter and higher output has been achieved, the requirements for piston rings have become more and more severe, and not only wear resistance but also seizure resistance. , Various improvements such as breakage resistance have been added.

Generally, in an engine immediately after assembly, it is inevitable that the piston ring and the cylinder are in contact with each other uncertainly due to restrictions in accuracy of parts production, and a gap is created between them. If the engine is operated with this gap still present, the airtightness of the combustion chamber becomes insufficient and gas blows out (compresses and leaks) into the crank chamber. The blow-through of the gas breaks the lubricating oil film that uniformly covers the inner surface of the cylinder, which causes abnormal wear between the piston ring and the cylinder, which causes scuffing. At the same time, the lubricating oil enters the combustion chamber through this gap and the oil consumption increases.

Therefore, in the initial operation, which is called a familiar operation, immediately after the engine is assembled, it is necessary to eliminate the gap between the piston ring and the cylinder in a short period of time by sliding the piston ring and the cylinder together to quickly adjust the two.

Generally, since a piston ring having excellent wear resistance has a sliding surface of high hardness, the familiar running period tends to be long. For this reason, as a method of fitting the piston ring and the cylinder in a short period of time, a method of providing a soft coating layer such as tin plating on the outer peripheral sliding surface of the piston ring or a method of processing the ring cross section into a taper shape is adopted. Has been.

[0006]

However, in the method of applying the tin plating, the tin plating layer is too soft under the condition of high temperature and high load, so that the tin plating layer is easily worn away at the initial stage of starting, and the familiar effect is not obtained. It almost disappears. The method of tapering the outer peripheral sliding surface of the ring has a problem that the taper angle affects the airtightness of the combustion chamber and the oil retaining property of the inner peripheral surface of the cylinder.

Therefore, recently, a method has been adopted in which a chromium plating layer is provided, and copper plating or copper-tin alloy plating, which is harder than tin plating, is applied thereon. However, in order to improve the adhesion with the surface of the chromium plating layer covered with a stable oxide, a cyanide bath is often used for these copper plating and copper-tin alloy plating, which causes environmental pollution. There is a problem. Therefore, alloy plating containing an alternative metal that does not cause environmental pollution is desired.

Therefore, an object of the present invention is to provide a piston ring which has good initial conformability even under conditions of high temperature and high load, does not cause scuffing, requires almost no familiar operation, and has excellent wear resistance. Is to provide.

[0009]

As a result of intensive studies to achieve the above object, the present inventor forms an alloy plating layer having an appropriate hardness on a hard chromium plating layer having excellent wear resistance. As a result, it was discovered that a piston ring having good initial conformability and excellent wear resistance can be provided, and the present invention has been completed.

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

[0011]

In the piston ring dual structure coating of the present invention, the upper layer (second layer) of the tin-nickel alloy plating layer is a material somewhat softer than the lower layer (first layer) of the hard chrome plating layer. Therefore, at the initial stage of starting the engine, it is well fitted to the cylinder, and at the same time, is not rapidly worn. Further, since the hard chromium plating layer of the lower layer (first layer) has a high hardness, it is possible to maintain good wear resistance for a long time (even after the wear of the upper layer).

[0012]

The present invention will be described in detail with reference to the accompanying drawings by the following embodiments. FIG. 1 is a partial sectional view of a piston ring for an internal combustion engine according to an embodiment of the present invention. In this embodiment, on the outer peripheral sliding surface of the piston ring 1,
The hard chromium plating layer 2 and the tin-nickel alloy plating layer 3 are formed to have a double structure.

The first hard chrome plating layer can be obtained by electroplating using a plating bath mainly containing chromic acid. As such a plating bath, a Sargent bath or a silicofluoride bath, which is a kind of a fluoride bath, can be used. The hard chrome plating layer has high hardness and excellent wear resistance. Therefore, the thickness of the hard chrome plating layer is 80 ~ 20
It may be 0 μm.

Since the hard chrome plating layer has high hardness and poor initial conformability, a tin-nickel alloy plating film is formed as the second layer on the first layer in order to compensate for this drawback. Nickel contained in the tin-nickel alloy coating is effective in enhancing the corrosion resistance of the coating and also enhancing the hardness of the coating. Although tin alone is too soft and disappears in the initial sliding, the tin-nickel alloy coating has a hardness of about HM _MV of 500, which is suitable for obtaining good initial conformability. The amount of nickel in this tin-nickel alloy is 20% by weight.
If the amount is less than 40% by weight, the above-mentioned effect cannot be obtained remarkably, and if the amount exceeds 40% by weight, the effect is not significantly changed. A more preferable nickel content is 25 to 40% by weight.

Further, tin, which is the matrix of the alloy, does not cause adhesion because it has low wettability with the metal and has a small coefficient of friction, which contributes to the improvement of seizure resistance and scuff resistance. The preferable tin content is 60 to 80% by weight.

The thickness of the tin-nickel alloy plating film is preferably 3 to 30 μm, more preferably 5 μm.
-25 μm.

To form the alloy plating film, a plating bath in which a nickel compound and a tin compound are dissolved so as to have the desired composition is used.

The obtained tin-nickel alloy film is washed with water, dried, and then heat-treated if necessary. Heat treatment temperature is 100 ~
At about 200 ° C, the time is 30 to 60 minutes. The matrix of the alloy coating is hardened by the heat treatment, and a composite coating having a hardness suitable for obtaining good initial conformability is obtained.

The present invention will be described in more 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, and a second step of forming a tin-nickel alloy plating layer on the first layer as a second layer. Then, a film was formed by the third step of subjecting the obtained double-structured layer to heat treatment.

First, in the first step, the nominal diameter × width × thickness is
A plurality of 100 mm × 3 mm × 4.5 mm SKD-61 piston rings were collectively used as a base metal, and a plating bath having a bath composition shown in Table 1 was used to perform hard chromium plating under the conditions shown in Table 2.

Table 1 Chromic anhydride 250 g / liter Sulfuric acid 2.5 g / liter

[0022]

The thickness of the hard chromium plating layer obtained by this first step was 100 μm. In the second step, the piston ring having the hard chrome plating layer obtained on the first step on the surface is dipped in a plating bath having the composition shown in Table 3 to obtain a plating bath temperature of 75 ° C. and a pH of 2.5.
Electroplating was performed by applying a current at a current density of 3 A / dm ² for 10 minutes.

Table 3 Bath composition Stannous chloride 100 g / l Nickel chloride 200 g / l Hooker Ammonium hydrogen 60 g / l Ammonia water Adjusted to pH 2.5

The second layer of tin-obtained by this second step
The thickness of the nickel alloy plating film was 10 μm, and the composition thereof was 65 wt% tin-35 wt% nickel. Then, in a third step, the obtained double-layered film was heat-treated at 150 ° C. for 1 hour to cure the film. The hardness of this time, the hard chromium plating layer as the first layer is a micro Vickers hardness (HM _MV) is 980, the tin of the second layer - nickel alloy plating film layer is micro-Vickers (HM _MV) 500
Met.

Actual machine test 4-cycle water-cooled 6-cylinder 2500cc engine cast iron (FC-25)
Incorporate the above piston ring into a manufactured engine cylinder, perform a bench test for 100 hours at a full load of 5000 rpm,
Oil consumption was measured. The test results are shown in FIG.

Comparative Example 1 An actual machine test was conducted in the same manner as in Example 1 using a piston ring in which only the 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 FIG.

Comparative Example 2 For further comparison, a hard chromium plating layer was formed on the outer peripheral sliding surface of the piston ring in the same manner as in Example 1,
Further, a tin plating film was formed with a thickness of 10 μm. Using the piston ring thus formed, an actual machine test was conducted in the same manner as in Example 1 to measure the oil consumption amount. The test results are shown in FIG.

As is apparent from FIG. 2, the piston ring of the present invention consumes more oil from the initial point in comparison with the piston ring having only the hard chromium plating layer on the sliding surface and the piston ring having the tin plating film. You can see that 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 Example 1, scuffing was not recognized at all.

[0030]

As described above in detail, the piston ring of the present invention having the hard chrome plating layer and the tin-nickel alloy plating layer on the outer peripheral sliding surface has an initial familiarity and scuff resistance due to the alloy plating film. Excellent and long-term wear resistance due to the hard chrome plating layer.

[Brief description of drawings]

FIG. 1 is a sectional view of a piston ring according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between test time and oil consumption in an actual machine test using the piston rings of Example 1 and Comparative Examples 1 and 2.

[Explanation of symbols]

 1 Piston ring base material 2 Hard chrome plating layer 3 Tin-nickel alloy plating film

Claims (1)

[Claims] 1. A layer having a double structure comprising a hard chrome plating layer and a tin-nickel alloy plating layer formed on the hard chrome plating layer, at least on its outer peripheral sliding surface. Piston ring for internal combustion engine.