JPH0133658B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a piston ring for an internal combustion engine coated with a film having excellent wear resistance and seizure resistance. Prior Art Conventionally, hard chrome plating has been mainly used as a surface treatment for piston rings. Piston rings coated with hard chrome plating have long been the mainstream surface treatment for piston rings because they have excellent wear resistance and cause less wear on the mating cylinder. However, in recent years, as engines have increased in output and performance, the conditions to which piston rings are exposed have become increasingly severe, and stronger wear and seizure resistance has become required. . These demands can no longer be met by conventional hard chrome plating alone. In order to deal with such a situation, the applicant of the present application previously covered the sliding outer peripheral surface of the piston ring with a titanium nitride film of a predetermined hardness and a predetermined thickness by ion plating in JP-A-57-65837. A technique for reducing the surface roughness of the sliding outer peripheral surface to a predetermined value or less has been disclosed. According to this method, the wear resistance and seizure resistance were much improved compared to the prior art, but the following disadvantages were subsequently discovered. In other words, titanium nitride produced by ion plating has excellent wear resistance and seizure resistance, and is very useful as a surface treatment for piston rings. When the base material is exposed, wear progresses rapidly and the seizure resistance deteriorates, so the durability is not necessarily satisfactory. OBJECT OF THE INVENTION An object of the present invention is to make it possible to improve durability while maintaining the excellent frictional properties of titanium nitride by ion plating, in order to eliminate the above-mentioned drawbacks. Structure of the Invention In order to achieve the above object, according to the present invention, as a base treatment of titanium nitride with a thickness of 2 to 10 μm and a surface roughness of 1.5 μm or less by ion plating, the surface roughness is 10 to 100 μm and hardness is In addition to hard chrome plating with Hv600 or higher, it is characterized by the formation of one or more scratches on the outer circumferential surface of the sliding surface, so that even if some of the titanium nitride is worn away Even if the piston ring has a hard chrome plating layer as its base layer, the piston ring as a whole can maintain sufficient wear resistance and seizure resistance. Specific Structure of the Invention First, the constituent features specified in the claims will be described. The reason why titanium nitride is coated by ion plating on hard chromium plating as a base layer is as follows. In other words, the results of the wear test using the reciprocating friction tester shown schematically in Figure 1 (Figure 3)
As shown in Figure 2, when the piston ring base material is directly coated with titanium nitride (Japanese Patent Application Laid-open No. 57-65837), when the base material is exposed, micro-scutching of the base material is noticeable, accelerating wear. However, in contrast, when titanium nitride is coated on a hard chromium plating base layer (sample 3 in Figure 3), even if part of the titanium nitride is worn away, Such a tendency is not observed at all, and a good friction surface is exhibited, as well as cases where only hard chromium plating is used and no titanium nitride is coated (sample 1), or when the ring base material is directly nitrided without applying a hard chrome plating base layer. This is because the amount of wear is much smaller than when coated with titanium (Sample 2). This is because even if a part of the titanium nitride wears out, there is a hard chrome plating on the base that has excellent wear and seizure resistance, so no micro-scattering occurs and the wear itself is highly wear-resistant. Because it was covered with titanium nitride, it is thought that there was very little wear even though the base was partially exposed. In FIG. 1, an upper specimen 11 corresponding to a piston ring is held by an upper specimen fixing block 17, and a downward load is applied from above by a hydraulic cylinder 19. On the other hand, a lower test piece 13, which is a mating member corresponding to a cylinder, is held by a movable block 21, and a crank mechanism 2, for example, as shown in the figure.
3, it is caused to reciprocate in the direction of the arrow. Also 1
5 is a load cell. The friction tester shown in FIG. 1 is well known, and its configuration itself is not directly related to the present invention, so a detailed explanation will be omitted. The wear amount was evaluated using each sample 1 as shown in Figure 2.
The wear scar diameters a and b left on samples 2 and 3 (upper specimen) were averaged over three measurements each. The test conditions are as follows. Test sample ● Cylinder equivalent (lower specimen 13): Cast iron for cylinder liner (FC25 equivalent material) 70 ^L × 17 ^W × 7 ^t (mm)
Flat plate test surface buffed finish hardness HRB95, surface roughness 0.5μ Piston ring equivalent (upper specimen 11): Piston ring steel 8〓× ^23L (mm) end face finished with ^18R spherical surface Sample 1 (Conventional technology) - Hard chrome plating 8〓×
Add a 60μ thick layer to the end face of the 23 ^L (mm) and adjust the sample surface roughness to 0.8μ. Plating hardness Hv1020, base material hardness Hv440 Sample 2 (prior technology) - 5μ thick titanium nitride was applied directly onto the piston ring steel material by ion plating, and the sample surface roughness was adjusted to 0.8μ.
Titanium nitride hardness Hv1770, base metal hardness Hv440 Sample 3 (product of the present invention) - Hard chrome plating with thickness
On top of the 60μ coating, a 5μ thick layer of titanium nitride was applied by ion plating to reduce the sample surface roughness to 0.8μ.
Adjusted to, plating hardness Hv850, titanium nitride hardness
Hv1780, base material hardness Hv440 ●Ion plating conditions Equipment used: An electron beam is used as the evaporation source,
High-vacuum ion plating equipment with an ionization electrode near the evaporation source Processing conditions: Nitrogen partial pressure 6 x 10 ^-4 Torr, substrate temperature 400°C, processing time 45 minutes Wear test conditions Testing machine: Reciprocating friction tester ( (Schematically shown in Figure 1) Test conditions: Stroke 50mm, break-in 2Kg×
100cpm x 5 minutes, main test 20Kg x 600cpm x 30 minutes,
Lubricating oil SAE #10 engine oil (sprayed in a mist) Next, the reason why we limited the base treatment to hard chrome plating is that it has the necessary wear resistance even under the temperature history exposed during ion plating treatment. This is because there is no other inexpensive coating that can maintain a high level of hardness and has excellent seizure resistance. Incidentally, FIG. 4 is a characteristic diagram showing a general decrease in hardness due to the thermal history of chromium plating. The reason why we chose titanium nitride using ion plating for the coating on the hard chrome plating is that ion plating can form a coating with good adhesion at a relatively low temperature without damaging the mechanical properties of the piston ring base material. Titanium nitride is a ceramic material that meets the requirements of high hardness and high melting point, which are necessary conditions for wear resistance and seizure resistance. This is because the film does not peel off or cause large cracks even when used under certain conditions. Next, the reason why we limited the thickness of the hard chrome plating that is the base to preferably 10 to 100 μm is that if it is less than 10 μm, it will not have sufficient durability, and if it exceeds 100 μm, it will be subject to heat load during the ion plating process. This is because the occurrence of coarse cracks becomes noticeable at times, and coarse cracks are also induced in the titanium nitride film. This coarse crack causes edge loading due to the edge of the crack.
It also has a fatal adverse effect on the engine, such as inducing chipping of the film. Note that the most preferable thickness is 30 to 70 μm. The hardness of hard chrome plating decreases as shown in FIG. 4 by applying a heat load. Therefore, when subjected to heat load during ion plating treatment, hardness decreases. Therefore, samples were prepared with various hardnesses of the base chrome plating, and wear tests were conducted using a reciprocating friction tester. The results are shown in FIG. The test conditions in Figure 5 are as follows: ● Cylinder equivalent (lower specimen): Cast iron 70 ^L × 17 ^W × 7 ^t (mm) flat plate for cylinder liner, test surface buffed finish ● Piston ring equivalent ( Upper specimen): The end face ^of a cast iron ^8〓 After applying titanium nitride to a thickness of 4μ by ion plating, the surface roughness was adjusted to 0.8μ.

[Table] ●Ion plating conditions Equipment used: Same as Figure 3 Processing conditions: Nitrogen partial pressure 7×10 ^-4 Torr, substrate temperature 300°C, processing time 35 minutes As is clear from the results in Figure 5 When the hardness of the base chrome plating becomes less than Hv600, the amount of wear increases rapidly. Therefore, it is preferable to limit the hardness of the base chrome plating to Hv600 or higher. In order to ensure the hardness of the base chrome plating to Hv600 or higher, it is necessary to keep the substrate temperature at 600℃ or less during the ion plating process, which will cause deformation and softening of the piston ring base material, as well as the occurrence of large cracks in the Cr plating. It is also important from a prevention perspective. In addition, in order to ensure the adhesion of the titanium nitride film by ion plating, it is desirable that the substrate temperature is 300°C or higher, and the piston ring temperature during ion plating is preferably between 300 and 600°C.
400-500°C is preferred. Next, regarding the thickness of the titanium nitride, if it is less than 2μ, it will not be sufficient in terms of durability, and if it exceeds 10μ, cracks will easily occur during use, resulting in chipping, etc., which may damage the mating cylinder. It is desirable that the thickness be in the range of 2 to 10 μm, as this may have an adverse effect. The finished surface roughness of the titanium nitride film is compared to the mating cylinder equivalent material (FC25 equivalent material, hardness HRB94, surface roughness
Figure 6 shows the relationship between wear and tear of 0.5μ). As is clear from FIG. 6, when the finished surface roughness of the titanium nitride film exceeds 1.5μ, the wear of the mating cylinder material increases rapidly. This is thought to be because the titanium nitride film is very hard, so when the surface roughness becomes rough, it acts to scrape off the mating material. Therefore, it is preferable to limit the surface roughness to 1.5μ or less so as not to damage the mating cylinder. Note that the most preferable surface roughness is 1.0μ or less. As mentioned above, the thickness of the titanium nitride film is very thin at 2 to 10μ, so when manufacturing piston rings, it should be almost completed before applying the titanium nitride film, and after applying the titanium nitride film, It is necessary to only apply relapsing. Therefore, it is difficult to adjust the final finished surface roughness in post-processing. Furthermore, since the titanium nitride film formed by ion plating is thin, the surface roughness after coating almost follows the roughness of the underlying surface. Therefore, the final surface roughness is almost determined by the surface roughness of the base chrome plating, and the processing condition of the base is important. With a single-layer hard coating such as hard chrome plating, it is relatively easy to fine-tune the surface roughness, and there is an advantage to using hard chrome plating as a base in this respect as well. The test conditions in FIG. 6 are as follows. ●Cylinder equivalent (lower sample): Cast iron 70 ^L x 17 ^W x 7 ^t (mm) flat plate for cylinder liner, test surface buffed ●Piston ring equivalent (upper sample): Steel material for piston ring 8〓× 23 ^L (mm) end face 18 ^R spherical processing,
This end face was plated with hard chrome to a thickness of 60 μm and polished with the surface roughness varied as shown in Table 2. After that, titanium nitride was applied to the end face by ion plating to a thickness of 4 μm and the end face was supplied for testing.

[Table] ●Ion plating conditions Equipment used: Same as Figure 3 Processing conditions: Nitrogen partial pressure 6×10 ^-4 Torr, substrate temperature 400°C, processing time 35 minutes Also, the wear amount evaluation in Figure 6 is 7 As shown in the figure, the wear marks on the lower specimen (corresponding to the liner) were measured at three locations using a roughness meter, and the average wear depth was taken. FIG. 8 shows various cross-sectional shapes of piston rings according to the present invention. A and B are the states before use,
C and D are the states after use. 1 is a piston ring base material, 3 is a chromium-plated base layer, and 5 is a titanium nitride coating. By adopting such a cross-sectional shape, even if wear progresses and the base chrome plating 3 appears, the titanium nitride film 5 on the entire sliding surface will not be worn away all at once, and a titanium nitride film will always remain on a portion. , and the progress of wear is suppressed. In other words, even if a part of the titanium nitride film is worn away and the underlying chrome plating appears, if the titanium nitride film remains partially, the hard titanium nitride will take most of the wear and tear, so the entire surface should be nitrided. The wear rate will be the same as when titanium remains. If a hard chrome plating base layer is not applied, if the base metal 1 is exposed, micro-scissions will occur in the base metal 1, damaging the mating cylinder and further accelerating piston ring wear. Since the piston ring according to the present invention has a hard chrome plating treatment on the base that has a certain degree of wear resistance and scuff resistance, the above-mentioned problems do not occur, and even a relatively thin titanium nitride film has sufficient durability. It has the characteristic of being able to maintain sex. In addition, the piston ring shape in which one or several grooves are provided in the circumferential direction as shown in FIG. 8B in contrast to the barrel face shape shown in FIG. 8A is particularly effective when the width of the piston ring is large. It is. This is because these streaks become oil pools and improve scuffing resistance. Examples Examples of the present invention will be described below. Example 1 Hard chrome plating is applied to the outer periphery of the side rail of the steel top ring and steel combination oil ring.
Polished into a barrel shape, thickness 50μ, surface roughness 0.5μ
An electron beam was used as an evaporation source, and an electron beam was used as an evaporation source, and the outer periphery of the steel top ring and side rail base material was directly polished into a barrel shape to have a surface roughness of 0.5μ. Using a high-vacuum ion plating device equipped with an ionization electrode, the nitrogen partial pressure was 6×10 ^-4 Torr, the substrate temperature was 450℃, and the processing time was 35 minutes.
A titanium nitride film with a thickness of 5 μm was deposited under conditions of 10 minutes.
The hardness of titanium nitride at this time was Hv1790, the roughness of the outer surface was 0.5μ, and the hardness of the base chrome plating was
It was Hv790. Top ring and side rail with titanium nitride applied on top of the chrome plating (the present invention) and top ring with titanium nitride applied directly to the steel base material (SWOSC-V material, outer periphery cross section barrel shape, surface roughness 0.5μ) , hardness Hv430) and side rail (SK-5 material, arcuate outer cross section, surface roughness
0.5μ) (comparison material) and a conventional top ring with hard chrome plating (SWOSC-V material, outer peripheral cross section barrel formation, chrome plating thickness 130μ, surface roughness
0.5μ) and side rail (SK-5 material, arcuate cross section, chrome plating thickness 120μ, surface roughness 0.5μ)
was installed in a 1300c.c. 4-stroke, water-cooled, 4-cylinder gasoline engine, and a 200-hour full-load durability test was conducted using high-lead gasoline (Pb3.2/US gallon). Figure 9 shows the measurement results of the amount of wear on the top spring and side rail after the test, and the amount of wear near the top dead center of the mating cylinder (FC25 equivalent material, surface roughness 3.0μ, hardness HRB93). The piston ring according to the present invention exhibits significantly less wear than conventional piston rings with only hard chrome plating, and is far more wear-resistant than piston rings with titanium nitride directly applied to the base material. It showed a small amount of wear. The hard chrome-plated sliding outer surface has many sliding scratches due to aggressive wear, and piston rings with titanium nitride applied directly to the base material expose the base material and cause microscuffs on the base material. However, the piston ring according to the present invention had few scratches and no scuffing occurred at all. Example 2 Two striations were made on the outer periphery of a top spring made of spheroidal graphite cast iron as shown in Fig. 8b), hard chrome plating was applied, and the ring was polished into a barrel shape with a thickness of 60 μm.
One has a surface roughness of 0.8μ, the outer periphery is plain, hard chrome plated, and polished to a plain shape, thickness 60μ, surface roughness 0.8μ.
The same ion plating equipment as in Example 1 was used on the same base material with two striations made and polished into a barrel shape with a surface roughness of 0.8μ under the same conditions. A cylinder with a titanium nitride coating of 5 μm thickness, i.e., a cylinder according to the present invention.
No. 2 and No. 3, cylinder No. 4 of comparative material, and a top ring (cylinder No. 1) was prepared. The hardness of the titanium nitride film was Hv1770, the hardness of the underlying chrome plating was Hv780, and the roughness of the outer peripheral surface was 0.9μ. These test top springs were installed in a 2956c.c., 4-cycle, water-cooled, 4-cylinder diesel engine and a 400-hour durability test was conducted under full load. Figure 10 shows the results of measuring the wear on the outer circumference of the top spring after the test and the amount of wear near the top dead center of the mating cylinder (FC25 equivalent material, surface roughness 3μ, hardness HRB97). The piston rings (Cylinder No. 2 and Cylinder No. 3) according to the present invention exhibit extremely small amounts of wear and at the same time reduce the wear of the mating cylinder. Cylinder No. 4, the comparative material, had no titanium nitride film left, and it is thought that the wear increased after the titanium nitride film was worn away. It can also be seen that the cross-sectional shape of the piston ring is preferably barrel-shaped rather than plain. However, although not particularly shown in the drawings, in the present invention, a piston ring with a plain cross section may be provided with grooves. Effects of the Invention As described above, the piston ring of the present invention eliminates the disadvantages of conventional piston rings with only a titanium nitride film by specifying the surface treatment of the titanium nitride film by ion plating to hard chrome plating. In addition to greatly improving the lack of durability,
It can also improve seizure resistance and maintain stable performance as a piston ring for high-load engines, so its industrial value is great.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a known reciprocating friction tester used in the wear test of the present invention, Fig. 2 is a diagram showing the dimensions of the wear scar diameter showing a method for evaluating the amount of wear, and Fig. 3 is a diagram showing the dimensions of the wear scar diameter and the conventional technology. For comparison, a graph showing the friction test results for the piston ring of the present invention, Figure 4 is a graph showing the decrease in hardness due to thermal history of hard chrome plating, and Figure 5 is the relationship between the hardness of the base hard chrome plating and the amount of wear. Figure 6 is a graph showing the friction test results for the relationship between the surface roughness of titanium nitride and the wear depth of the mating material by ion plating, and Figure 7 is shown in Figure 6. Figures 8A and 8B are schematic cross-sectional views of two types of piston rings of the present invention; 8C and D are cross-sectional schematic diagrams showing the respective states after use; FIG. 9 is a graph showing the durability test results of the top spring and side rail of the present invention in comparison with the conventional technology;
Figure 0 is a graph showing a durability test of the piston ring of the present invention conducted under different conditions in comparison with the prior art. 1... Base material, 3... Chrome plating, 5... Titanium nitride.

Claims (1)

[Scope of Claims] 1. A piston ring for an internal combustion engine, in which at least the sliding outer peripheral surface of the piston ring is coated with a hard chrome plating base layer, and the hard chrome plating layer is coated with a titanium nitride film by ion plating. The hard chrome plating base layer has a thickness of 10~
The hardness is Hv600 or more at 100 μm, the thickness of the titanium nitride film is 2 to 10 μm, and the surface roughness of the sliding outer peripheral surface is 1.5 μ or less, and the sliding outer peripheral surface has a A piston ring characterized in that one or more striations are formed. 2. The piston ring according to claim 1, wherein the sliding outer peripheral surface has a barrel shape.