KR20040033825A - Coating method of piston ring for engine - Google Patents

Abstract

PURPOSE: A coating method of piston ring for engines is provided to obtain piston ring coating layer satisfying sufficient wear resistance and high temperature oxidation resistance and having superior cohesiveness, residual stress and corrosion resistance by alternately and repeatedly coating α-Cr and CrN on the surface of piston ring matrix. CONSTITUTION: In a method for coating the surface of a matrix of piston ring to improve wear resistance, scarfing resistance and high temperature oxidation resistance required in the piston ring, the coating method of piston ring for engines comprises the process of alternately and repeatedly coating α-Cr and CrN on the surface of piston ring matrix in such a way that α-Cr is coated on the surface of the piston ring matrix(10), and CrN is coated on the α-Cr coating layer(12), thereby constructing a structure in which a plurality of layers are laid up, and thickness ratio of finally formed α-Cr coating layer to CrN coating layer(14) is 1:3.

Description

Coating method of piston ring for engine {Coating method of piston ring for engine}

The present invention relates to a piston ring coating method for an engine, and more particularly, in the method of coating the base material surface of a piston ring, repeatedly coating α-Cr and CrN alternately so as to have a thickness ratio of 1: 3 on the base material surface of the piston ring. By coating a structure in which a plurality of layers are laminated, the piston ring coating method for the engine is improved to obtain a piston ring coating layer excellent in adhesion, residual stress and corrosion resistance while satisfying sufficient abrasion resistance and high temperature oxidation resistance required in the piston ring. It is about.

In general, an automotive engine is a representative internal combustion engine that obtains power by injecting air and fuel into a combustion chamber and burning it.

A piston that reciprocates at a high speed is installed in a cylinder of such an engine of an automobile, and the piston receives a high temperature and high pressure combustion gas pressure generated in a combustion chamber to rotate a crank shaft through a connecting rod.

That is, the piston is driven under severe conditions such that the piston head is exposed to high-temperature combustion gas, receives a high pressure shock, and a large friction is generated by a high-speed reciprocating motion in the cylinder.

Therefore, the piston should be provided so as to fully exhibit its function even under the above harsh conditions, and should be made of a material that is light and durable, and has good thermal conductivity and heat resistance.

On the other hand, a plurality of piston rings are provided on the upper outer circumferential surface of the piston, the piston ring is divided into a compression ring, which is usually provided two upwards, and one oil ring provided to the lower side.

Here, the upper compression ring in order to maintain the air tightness of the combustion chamber, the lower oil ring scrapes the oil sprayed on the cylinder wall to create a minimum oil film, thereby preventing the wear between the cylinder inner wall and the piston to smooth the reciprocating motion of the piston It is installed to induce.

Stainless steel (eg, SUS430) is mainly used as the material of the piston ring, and a coating layer containing chromium is laminated on the base material surface of the piston ring for wear resistance, scuffing resistance, and high temperature oxidation resistance.

As a coating method of the piston ring, conventionally, a method of sequentially stacking an α-Cr single coating layer and a CrN single coating layer on the surface of the base material of the piston ring using a physical vapor deposition (PVD) magnetron sputtering device This was used.

That is, in the related art, as shown in the accompanying FIG. 7, a double layer coating structure in which the coating layer of the piston ring is composed of a soft α-Cr single coating layer 12 and a hard CrN single coating layer 14 on the surface of the base material 10. It is supposed to be.

However, in the double layer coating structure of the piston ring consisting of the α-Cr coating layer 12 and the CrN coating layer 14 as described above, if an abnormal force is applied in the sliding portion between the piston ring and the cylinder bore, cracks are easily generated throughout the coating layer. It was difficult to exhibit the original coating layer properties, there was a disadvantage that the durability is reduced, such as poor adhesion and corrosion resistance when peeling the coating layer due to cracks.

Therefore, the present invention has been invented to solve the above problems, in the method for coating the base material surface of the piston ring by repeatedly coating α-Cr and CrN alternately so that the thickness ratio 1: 3 to the base material surface of the piston ring By coating a structure in which a plurality of layers are laminated, the piston ring coating method for the engine is improved to obtain a piston ring coating layer having excellent adhesion, residual stress and corrosion resistance while satisfying sufficient abrasion resistance and high temperature oxidation resistance required in the piston ring. The purpose is to provide.

1 is a laminated state diagram of the piston ring coating layer according to the coating method of the present invention,

2 to 6 are graphs showing the measurement results of adhesion, residual stress, abrasion resistance, corrosion resistance and high temperature oxidative resistance with respect to the coating layer of the Example according to the present invention and the coating layer of the Comparative Example according to the conventional method.

7 is a laminated state diagram of a piston ring coating layer according to a conventional coating method.

<Explanation of symbols for the main parts of the drawings>

10: piston ring base material 12: α-Cr coating layer

14: CrN coating layer

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The present invention provides a method for coating the surface of the base material 10 of the piston ring in order to improve the wear resistance, scuffing resistance and high temperature oxidation resistance required in the piston ring,

Α-Cr is first coated on the surface of the base material of the piston ring, and the α-Cr and CrN are alternately repeatedly coated in such a manner as to coat CrN on the α-Cr coating layer, thereby forming a structure in which a plurality of layers are laminated. Characterized by coating so that the thickness ratio of the α-Cr coating layer and the CrN coating layer is 1: 3.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a laminated state diagram of the piston ring coating layer according to the coating method of the present invention.

As shown in the drawing, in the present invention, in order to improve the wear resistance, scuffing resistance and high temperature oxidation resistance required in the piston ring, the base material surface of the piston ring is coated with α-Cr and CrN, but α-Cr and CrN are coated. Coat alternately.

In other words, α-Cr is first coated on the surface of the base material 10 of the piston ring, and the α-Cr and CrN are repeatedly coated alternately by coating CrN on the α-Cr coating layer 12 formed thereby.

When the surface of the base ring 10 of the piston ring is coated as described above, the thickness ratio of the α-Cr coating layer 12 and the CrN coating layer 14 is 1: 3, and the top layer serving as the outer surface of the completed piston ring is coated. As in the prior art, it is preferable to finish with CrN coating so as to be a hard CrN coating layer 14.

As a result, the coating structure of the piston ring according to the present invention has a multilayer structure in which the soft α-Cr coating layer 12 and the hard CrN coating layer 14 are repeatedly alternately stacked as shown in FIG. 1.

In the multi-layer coating structure of the piston ring composed of the soft α-Cr coating layer 12 and the hard CrN coating layer 14 as described above, a plurality of α-Cr soft particles are applied when abnormal force is applied in the sliding portion between the piston ring and the cylinder bore. Since the layer 12 is buffered, crack generation is reduced, and even if cracks are generated, only cracks at the uppermost layer are generated, not cracks of the entire coating layer as in the double layer coating structure according to the conventional method.

That is, in the multilayer coating structure according to the present invention, even if the top layer is peeled off by the crack, the coating layer directly underneath has the advantage of improving adhesion.

In addition, the corrosion resistance is correlated with the adhesion of the coating layer, the multilayer coating structure according to the present invention has the advantage that the corrosion resistance can be improved compared to the conventional double layer coating structure.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

Example

According to the present invention, α-Cr and CrN were alternately coated on the surface of the SUS430 specimen used as the material of the engine piston ring, and the total thickness was increased by setting the thickness ratio of α-Cr coating layer and CrN coating layer to 1: 3. A multilayer coating layer of 30 μm was formed (see FIG. 1).

Comparative example

On the surface of the SUS430 specimen used as the material of the engine piston ring, α-Cr and CrN were coated in a single layer, respectively, according to the conventional method, and a total thickness of the same double layer as in the above example was formed (see FIG. 7). .

Test Example

Two specimens obtained in Comparative Examples and Examples were used to measure adhesion, residual stress, abrasion resistance, corrosion resistance, and high temperature oxidation resistance of the coating layer, respectively, and the results are shown in FIGS. 2 to 6, respectively.

First, the adhesion test results for the two specimens are shown in the graph of FIG.

As a result of the adhesion test, the critical load of 70N in the specimen of the embodiment having a multi-layer coating structure, the critical load of 56N in the specimen of the comparative example having a double-layer coating structure, the adhesion in the coating layer according to the present invention compared to the coating layer according to the conventional method This increased about 25%.

Next, the coating layer residual stress test results for the two specimens are shown in the graph of FIG. 3.

As a result of the residual stress test, it was found that the residual stress was reduced by about 60% in the specimen of the example having the multilayer coating structure compared to the specimen of the comparative example having the double layer coating structure, which is a coating layer according to the present invention with respect to the external environment. This shows that the coating layer is more stable than the conventional method.

Next, the coating layer wear resistance test for the two specimens was carried out by a ball crater method.

Here, the counterpart was a steel ball having a diameter of 15 mm, and the ball rotation speed was carried out at 300 rpm for 90 minutes, in which a diamond paste having a size of 1 μm was used as an abrasive.

After the test, the wear amount was calculated by measuring the diameter of the wear trace, and the result is shown in the graph of FIG. 4.

As a result of the coating layer abrasion resistance test, a wear volume of 0.006 mm 3 was shown in a specimen of an example having a multilayer coating structure, and a wear volume of 0.003 mm 3 was shown in a specimen of a comparative example having a double layer coating structure. The wear volume was rather large in the coating layer, but this was a very slight increase, indicating that the abrasion resistance of the two specimens was nearly equal.

Next, a potentiodynamic polarization test was conducted to test the corrosion resistance of the two specimens. At this time, a 3.5 wt% NaCl aqueous solution was used as the solution, a high-purity carbon rod as the counter electrode, and a saturation-based electrode as the measurement electrode. (Saturated calomel electrode) was used, and the polarization potential was measured at room temperature by applying a scan rate of 0.166㎷ / s from -250㎷ to 1000mV from the corrosion potential.

Coin polarization test results are shown in the graph of FIG.

As a result of the corrosion resistance test, comparing the two result curves, it can be seen that the current density value of the example specimen having the multilayer coating structure is smaller than the current density value having the double-layer coating structure, which is an example specimen of the present invention. It exhibits greater corrosion resistance than this conventional comparative specimen.

Next, the high temperature oxidative test measured the amount of oxidation by weight change after maintaining for 20 hours in an air atmosphere of 700 ℃ using TGA, the results are shown in the graph of FIG.

As shown in Figure 6, the high temperature oxidative properties of the coating layer according to the present invention and the coating layer according to the conventional method was found to be almost the same level so as not to know the difference.

In conclusion, the results of measuring adhesion, residual stress, abrasion resistance, corrosion resistance, and high temperature oxidation resistance of the coating layer using the two specimens obtained in Comparative Examples and Examples are summarized as compared with those of the conventional Comparative Example specimens having a double layer coating structure. In the example specimens of the present invention having a coating structure, the adhesion, residual stress, and corrosion resistance were more excellent while showing the same level of wear resistance and high temperature oxidation resistance.

In this way, in the piston ring coating method according to the present invention by repeatedly coating alternately coating α-Cr and CrN on the surface of the base material of the piston ring to have a thickness ratio of 1: 3, by coating a structure in which a plurality of layers are laminated, required in the piston ring It is possible to obtain a piston ring coating layer excellent in adhesion, residual stress and corrosion resistance while satisfying sufficient abrasion resistance and high temperature oxidation resistance.

As described above, according to the piston coating method for the engine according to the present invention, in the method of coating the base material surface of the piston ring, repeated coating alternately α-Cr and CrN on the base material surface of the piston ring so that the thickness ratio is 1: 3. By coating a structure in which a plurality of layers are laminated, a piston ring coating layer having excellent adhesion, residual stress, and corrosion resistance while satisfying sufficient abrasion resistance and high temperature oxidation resistance required in a piston ring is obtained.

In addition, since the durability of the piston ring can be improved by applying the coating method of the present invention, when the piston ring to which the coating method of the present invention is applied is mounted on the piston of a passenger diesel vehicle or a commercial vehicle engine having a large engine combustion explosion pressure, the overall durability of the engine is increased. The effect of improving this is expected.

Claims (1)

In the method of coating the base material surface of the piston ring in order to improve the wear resistance, scuffing resistance and high temperature oxidation resistance required in the piston ring, Α-Cr is first coated on the surface of the base material of the piston ring, and the α-Cr and CrN are alternately repeatedly coated in such a manner as to coat CrN on the α-Cr coating layer, thereby forming a structure in which a plurality of layers are laminated. Piston ring coating method characterized in that the coating so that the thickness ratio of the α-Cr coating layer and the CrN coating layer is 1: 3.