JPH04252844A - Cylinder liner and manufacture thereof - Google Patents

Abstract

PURPOSE:To apply coating of a chromeplating layer on to an outer circumferential surface efficiently without using machining operation as well as to form a nitriding layer on an inner circumferential surface alone by using the chromeplating layer as a dummy layer for nitriding, in a cylinder liner and its manufacture. CONSTITUTION:A nitriding process for forming a nitriding layer 4 on an inner circumferential surface 3 is made after coating a substratal chromeplating layer 8a on an outer circumferential surface 5 of a cylinder liner 1. With this process the nitriding layer is also formed on a surface of this substratal chromeplating layer 8a as well. This nitriding layer is removed by means of anodization in a plating bath and, after the substratal chromeplating layer 8a is exposed, an upper-stratal chromeplating layer 8b is coated on this surface, whereby a chromeplating layer 8 consisting of both these substratal and upper- stratal chromeplating layers 8a and 8b is formed on the outer circumferential surface 5 and, the nitriding layer 4 is formed on the inner circumferential surface 3 alone.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder liner used in internal combustion engines and a method for manufacturing the same, and more particularly to a cylinder liner having a nitrided layer on the inner circumferential surface and a chromium plating layer on the outer circumferential surface, and a method for manufacturing the same. .

0002

[Prior Art] Generally, cast iron or the like is used for cylinder liners used in internal combustion engines, and the outer peripheral surface of the cylinder liner that comes into contact with cooling water is chromium plated to improve corrosion resistance and cavitation resistance. A layer is applied. Furthermore, in response to the recent demands for higher output, lower pollution, and longer life of internal combustion engines, we have created cylinders with a nitrided layer formed on the inner circumferential surface to improve the wear and corrosion resistance of the inner circumferential surface. Raina is requested.

A conventional method for manufacturing a cylinder liner having a nitrided layer on the inner circumferential surface and a chromium plating layer on the outer circumferential surface will be explained with reference to FIGS. 7 to 9.

In FIG. 7, reference numeral 11 denotes a cylinder liner, which has a cylindrical shape and includes a flange portion 12. As shown in FIG. The inner circumferential surface 13 is polished and has a nitride layer 14 formed thereon. On the other hand, the outer circumferential surface 15 is formed with a jacket part 16 serving as a passage for cooling water and ring grooves 17a and 17b into which O-rings for maintaining watertightness are installed. is covered.

In the method for manufacturing the cylinder liner 11 having the above structure, first, a cylindrical casting made of cast iron is machined into a predetermined shape, and then the cylinder liner 11 is machined to form a nitrided layer 14 on the inner peripheral surface 13. is immersed in a salt bath containing sodium cyanate as the main ingredient to perform nitriding treatment (tuftride treatment). As a result, nitrided layers 14 and 14' are formed on the entire surface of the cylinder liner 11, as shown in FIG. Here, the nitride layer 14' becomes a hindrance to the adhesion of the chromium plating layer 18 and causes cracks, etc.
As shown in FIG. 9, the nitride layer 14 around the jacket portion 16
' is completely removed by machining to expose the outer peripheral surface 15. Thereafter, the cylinder liner 11 is immersed in a chromium plating bath and subjected to anodic treatment (reverse electric treatment) as a pretreatment to activate the outer circumferential surface 15, and then a chromium plating layer 18 is deposited.

[0006]

[Problems to be Solved by the Invention] As described above, in the conventional manufacturing method, the cylinder liner 1 after precision machining is
1 is machined to remove the nitride layer 14' formed on the outer peripheral surface 15. If such machining is performed, there is a high risk that fatal mechanical damage such as eccentricity of the cylinder liner 11 or scratches on the inner circumferential surface 13 will occur.

Furthermore, if the nitride layer 14' remains due to insufficient machining allowance during this machining, cracks or the like will occur in the chromium plating layer 18 during the chromium plating process.

In order to solve these problems, a method has been proposed in which a nickel plating layer or a copper plating layer is previously deposited on the outer peripheral surface as a nitriding prevention layer. However, when these metal layers are used as a nitriding prevention layer, it is necessary to completely remove these metal layers in a separate process before applying the chromium plating layer, and then apply the chrome plating layer again. be. Therefore, it requires management to completely remove the metal layer and has problems such as adding the number of steps, so it has not been put into practical use.

[0009] We also propose a method in which the cylinder liner is fitted into a cylindrical sleeve and the nitriding treatment is performed with the outer circumferential surface isolated from the nitriding atmosphere, thereby selectively forming a nitrided layer only on the inner circumferential surface. However, it is difficult to reliably prevent the formation of a nitride layer on the outer peripheral surface.

In view of the above problems, an object of the present invention is to adopt a method in which a lower chromium plating layer is formed in advance as a dummy layer for nitriding treatment, and to efficiently achieve the same without using machining. An object of the present invention is to provide a cylinder liner in which a chromium plating layer is deposited on the outer peripheral surface and a nitride layer is formed only on the inner peripheral surface, and a method for manufacturing the cylinder liner.

[0011]

[Means for Solving the Problems] In order to solve the above problems, an internal combustion engine is provided in which a nitrided layer is formed on the inner circumferential surface and a chromium plating layer is deposited on at least the portion of the outer circumferential surface that comes into contact with cooling water. The measure taken by the present invention in the cylinder liner for this invention is that the chromium plating layer has a two-layer structure consisting of a lower chrome plating layer and an upper chrome plating layer.

[0012] The method for manufacturing a cylinder liner having such a structure is to pre-coat the outer peripheral portion on which the chromium plating layer is to be applied.
A lower chromium plating process for depositing a lower chrome plating layer, a nitriding process for forming a nitride layer on at least the inner circumferential surface, and then a removal of the nitride layer on the surface of the lower chrome plating layer formed by the nitriding process. The present invention is characterized in that it includes at least an upper layer chromium plating step of depositing an upper chrome plating layer on the surface of the lower chrome plating layer after exposing the surface of the chromium plating layer.

[0013] Here, in order to remove the nitrided layer on the surface of the lower chromium plating layer, it is desirable to utilize anodization, which is performed as a plating pretreatment in the upper layer chromium plating process.

Furthermore, in order to improve cavitation resistance, the thickness of the upper chromium plating layer is preferably 0.05 mm or more, and the hardness thereof is preferably Hv800 (Vickers hardness) or more. It is effective that the thickness is 0.02 mm or more.

[0015]

[Operation] In the cylinder liner and the manufacturing method thereof according to the present invention, before forming a nitrided layer on the surface of the cylinder liner, a lower chromium plating layer is applied in advance to at least the portion of the outer peripheral surface that is to be in contact with cooling water. I'll keep it. Therefore, even if the surface of the lower chromium plating layer is nitrided by nitriding the inner peripheral surface, the lower chromium plating layer is exposed by removing the outermost layer of the lower chromium plating layer.
The upper chrome plating layer can be deposited reliably. Here, the remaining lower chromium plating layer, together with the upper chromium plating layer deposited on its surface, can be used as a cavitation-resistant protective film on the outer peripheral surface. In other words, the surface layer of the lower chromium plating layer can be used as a dummy layer for the nitriding process, and the remaining layer can be used as part of the cavitation-resistant protective film, so the chromium plating layer can be formed efficiently. .

Furthermore, since the outermost layer of the lower chromium plating layer is used as a dummy layer for nitriding, the portion to be removed is the nitrided layer. Therefore, anodization (reverse electric treatment), which is a common chemical pretreatment for chromium plating, can be used to remove this nitride layer. That is, the pretreatment for the upper layer chromium plating process can be used to remove the nitrided layer. In this case, there is no need to use mechanical processing to remove the nitride layer, and there is no need to perform it as a separate process.

Furthermore, the thickness of the upper chromium plating layer is 0.
05 mm or more and the hardness is Hv800 or more, excellent cavitation resistance can be ensured even if cracks and hardness reduction occur in the lower chromium plating layer due to the heat received in the nitriding process.

[0018] The thickness of the lower chromium plating layer is 0.
When the thickness is 0.2 mm or more, the thickness is sufficient as a dummy layer for nitriding treatment, and the cavitation resistance of the lower chromium plating layer can also contribute to improving the cavitation resistance of the outer peripheral surface.

[0019]

EXAMPLES Example 1 Next, a cylinder liner and a manufacturing method thereof according to Example 1 of the present invention will be described with reference to FIGS. 1 to 5.

FIG. 1 is a cross-sectional view showing the structure of a cylinder liner, and FIGS. 2 to 5 are enlarged process cross-sectional views of the peripheral wall of the cylinder liner, showing a part of the manufacturing method thereof.

In FIG. 1, reference numeral 1 denotes a cylinder liner, and a flange portion 2, which is a connection portion with the cylinder head, is provided above.
It is made of cylindrical cast iron with a The inner circumferential surface 3 is polished to be as smooth as possible as a sliding surface, and
A nitride layer 4 is formed on its surface. On the other hand, the outer circumferential surface 5 is formed with a jacket part 6 to serve as a passage for cooling water and ring grooves 7a and 7b in which an O-ring is to be installed. , a chrome plating layer 8 is deposited. Here, the chromium plating layer 8 is the lower chromium plating layer 8a.
It has a double structure consisting of an upper chrome plating layer 8b and an upper chromium plating layer 8b.

[0022] Here, a method of manufacturing the cylinder liner 1 having the above structure will be explained.

First, the cylinder liner 1, which has been processed into the above shape, degreased, washed with acid, is immersed in a chromium plating bath (Sargent bath) containing chromic anhydride and sulfuric acid. In this state, as a pretreatment, electrolysis is performed using the cylinder liner 1 as an anode to perform anodic treatment (reverse electric treatment) to slightly dissolve and activate the jacket portion 6 and the surface layer around it. After this pretreatment, as is,
Chromium plating is performed using the cylinder liner 1 as a cathode in a chromium plating bath at a temperature of 60° C. As shown in FIG.
A lower chromium plating layer 8a having a hardness of Hv300 is deposited (lower chrome plating step).

Next, in order to form a nitride layer 4 on the inner peripheral surface 3,
Cylinder liner 1 is made of sodium cyanate (NaCNO).
) in a salt bath for nitriding treatment, and the temperature was 580°C.
Nitriding treatment (tuftride treatment) is performed for 120 minutes. As a result, as shown in FIG. 3, a nitrided layer 4 is formed on the inner circumferential surface 3, and the surface layer of the lower chromium plating layer 8a on the outer circumferential surface 5 also becomes a nitrided layer 9 (nitriding step).

Next, in order to deposit the upper chromium plating layer 8b, the nitride layer 9 formed on the outermost layer of the lower chromium plating layer 8a is removed. To remove this nitrided layer 9, anodization, which is a pretreatment for activating the plating base surface in the chromium plating process, is used. That is, the cylinder liner 1 is immersed in a chromium plating bath at a temperature of 60° C., and the jacket portion 6 and its surroundings are partially coated so that electrolytic current flows only, and a counter electrode is placed at a predetermined position. Perform anodization using the material as an anode.

By this anodizing, the outermost nitride layer 9 of the lower chromium plating layer 8a is dissolved and removed, exposing the lower chromium plating layer 8a as shown in FIG. At the same time, this treatment brings the surface of the lower chromium plating layer 8a into an activated state.

Thereafter, in this state, chromium plating is performed using the cylinder liner 1 as a cathode, and an upper chromium plating layer 8b having a thickness of 0.05 mm and a hardness of Hv800 is applied to the surface of the lower chromium plating layer 8a. (upper layer chrome plating process).

After that, a final polishing process is performed, and the outer peripheral surface 5 is provided with a chromium plating layer 8 having a double structure of a lower chromium plating layer 8a and an upper chromium plating layer 8b, and the inner peripheral surface 3 is
A cylinder liner 1 with a nitrided layer 4 is manufactured.

As described above, in the manufacturing method according to this example, the lower chromium plating layer 8a is deposited in advance before forming the nitrided layers 4 and 9, so the lower chromium plating layer 8a is deposited after the nitriding step. By removing only the outermost layer of the layer 8a, the nitride layer 9 can be removed, and the lower chromium plating layer 8a can be left intact as the lower layer of the cavitation-resistant protective film. That is, the remaining lower chrome plating layer 8
The double-structured chromium plating layer 8 consisting of the upper chromium plating layer 8b and the upper chromium plating layer 8b deposited on the surface thereof can be used as a cavitation-resistant protective film. Moreover, it is not necessary to completely remove these metal layers before depositing the upper chromium plating layer, as is the case when a nickel plating layer or a copper plating layer is used as an anti-nitriding film.

Furthermore, since the outermost layer of the lower chromium plating layer 8a is used as a dummy layer for nitriding, the portion to be removed is the nitrided layer. Therefore, to remove this nitride layer 9,
Since anodization, which is a chemical pretreatment for the chromium plating process, is used, there is no need to remove the nitride layer 9 as a separate process. Therefore, the process is simplified and productivity is high. Moreover, since removal by machining is not required, mechanical damage to the cylinder liner 1 does not occur.

Next, the sample piece of cylinder liner 1 manufactured by the above method was evaluated by a cavitation test. Furthermore, in addition to the cylinder liner 1 according to Example 1 above, as shown in Table 1, cylinder liners according to other examples in which the thickness and hardness of the lower chrome plating layer and the upper chrome plating layer were changed were also evaluated. I did it. Note that sample number 4 uses an amorphous chromium plating layer as the lower chromium plating layer. Here, the cavitation test uses a magnetostrictive ultrasonic cavitation tester,
The acceleration test was conducted at a frequency of 20 kHz and an amplitude of 86 μm, and distilled water at a temperature of 55±2° C. was used as the medium. The test time was 90 minutes, and the degree of damage was investigated by observing the cross section.

The results are shown in Table 1.

[0033]

[Table 1]

As shown in Table 1, both sample number 1 manufactured by the manufacturing method according to example 1 and sample numbers 2 to 4 in which the thickness and hardness of the chromium plating layer were changed,
The degree of damage was small or less, and good results were obtained. In particular, it was confirmed that no damage occurred in the sample No. 1 according to Example 1.

Furthermore, as a result of evaluating the thickness and hardness of the lower and upper chromium plating layers, it was found that the thickness of the upper chromium plating layer was 0.05 mm or more and the hardness was Hv.
If it is 800 or more, even if the lower chromium plating layer has cracks and a decrease in hardness due to the heat received in the nitriding process, excellent cavitation resistance can be ensured, and the thickness of the lower chromium plating layer can be reduced. When the thickness is 0.02 mm or more, the thickness is sufficient as a dummy layer for nitriding treatment, and the cavitation resistance of the lower chromium plating layer can also contribute to improving the cavitation resistance of the outer peripheral surface. This was confirmed. Therefore, a chromium plating layer in which the thickness of the lower chromium plating layer is 0.02 mm or more, the thickness of the upper chrome plating layer is 0.05 mm or more, and the hardness is Hv800 or more has excellent cavitation resistance and Most effective against corrosives.

Example 2 Next, as a cylinder liner and its manufacturing method according to Example 2, a diesel engine cylinder liner material equivalent to FC25 was machined into a cylinder liner with an inner diameter of 370 mm, and then the manufacturing method according to Example 1 was carried out. A nitrided layer was formed on the inner circumferential surface and a chromium plating layer was formed on the outer circumferential surface using the same process order. Here, the deposited lower chrome plating layer has a thickness of 0.03 mm and an initial hardness of Hv930, and the thickness of the upper chrome plating layer is 0.08 mm.

FIG. 6 shows the results of investigating the hardness distribution in the depth direction of the outer peripheral surface.

As shown in FIG. 6, 0.1 mm from the surface layer
At the depth of , the hardness of the chromium plating layer decreases to Hv400 or less. In other words, the lower chrome plating layer is
The hardness is reduced by the heat received during the nitriding process.

Even in such a chromium plating layer, the surface layer has a hardness of Hv930 due to the upper chromium plating layer.
After installing this cylinder liner in an actual machine and conducting an operational test using the actual machine for 3,000 hours, it was confirmed that no damage due to cavitation had occurred at all.

As described above, according to the manufacturing method of this example, a cylinder liner having a nitrided layer on the inner circumferential surface and a chromium plating layer on the outer circumferential surface can be manufactured efficiently without performing machining after precision processing. Can be manufactured well. Furthermore, the inner peripheral surface has excellent wear resistance and corrosion resistance, and the outer peripheral surface has sufficiently high cavitation resistance and corrosion resistance.

[0041] Here, the conditions for chromium plating are not limited to the plating bath used in the above examples, and the composition, temperature, immersion time, etc. of the nitriding salt bath in the nitriding process are also not limited. In addition to the nitriding treatment using a salt bath, nitriding treatment using ammonia gas or the like may also be employed.

Further, in this example, the anodization performed in the chromium plating process was used to remove the nitrided layer, but acid cleaning, which is a chemical pretreatment for the chromium plating process, may also be used. good. Furthermore, other treatment methods may be adopted, and there are no limitations as long as a chromium plating layer is previously formed as a dummy layer for the nitriding treatment.

Furthermore, a cleaning process such as water washing, a drying process, etc. may be added as necessary between each process, and in order to suppress the formation of a nitride layer on the surface of the lower chromium plating layer, for example, the cylinder liner The nitriding treatment may be performed while the material is covered with a covering member such as a cylindrical sleeve.

[0044]

Effects of the Invention The cylinder liner and the manufacturing method thereof according to the present invention are characterized in that a lower chromium plating layer is previously deposited before forming a nitride layer on the surface of the cylinder liner. It has the following effects.

(2) By removing only the surface layer of the lower chromium plating layer, the nitrided layer formed by the nitriding process can be removed. Furthermore, the remaining lower chromium plating layer can be used as a cavitation-resistant protective film for the outer peripheral surface, together with the upper chromium plating layer. Therefore, unlike when using other metal layers as an anti-nitriding film, there is no need to completely remove the metal layer and re-apply the chrome plating layer, improving production efficiency. .

[0046] The portion to be removed from the lower chromium plating layer is the nitride layer. Therefore, anodization, which is a pretreatment for the upper layer chromium plating step, can be used to remove this nitrided layer. In this case, since there is no need to perform the above-mentioned removal as a separate process, the process can be simplified and production efficiency can be improved. Further, since removal by machining is not required, no mechanical damage occurs to the cylinder liner. Therefore, reliability and yield can also be improved.

■ The thickness of the upper chrome plating layer is 0.0
When the hardness is 5 mm or more and the hardness is Hv800 or more, the cavitation resistance of the outer peripheral surface of the cylinder liner can be ensured even if the cavitation resistance of the lower chromium plating layer is reduced.

■ The thickness of the lower chrome plating layer is 0.0
When it is 2 mm or more, the cavitation resistance of the lower chromium plating layer can further contribute to improving the cavitation resistance of the outer peripheral surface of the cylinder liner.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a cylinder liner according to a first embodiment of the present invention.

FIG. 2 is an enlarged process sectional view of a peripheral wall of a cylinder liner showing a part of the manufacturing method according to Example 1 of the present invention.

FIG. 3 is a process sectional view showing a part of this manufacturing method.

FIG. 4 is a process sectional view showing a part of this manufacturing method.

FIG. 5 is a process sectional view showing a part of this manufacturing method.

FIG. 6 is a graph showing the hardness distribution in the depth direction of the cylinder liner manufactured by this manufacturing method.

FIG. 7 is a sectional view showing the structure of a cylinder liner manufactured by a conventional manufacturing method.

FIG. 8 is an enlarged process sectional view of a peripheral wall of a cylinder liner, showing a part of a conventional manufacturing method.

FIG. 9 is a process sectional view showing a part of this manufacturing method.

[Explanation of symbols]

1, 11...Cylinder liner 3, 13...Inner peripheral surface 5, 15...Outer peripheral surface 4,14...Nitrided layer 8a...Lower chrome plating layer 8b... Upper chrome plating layer 8...Chrome plating layer

Claims (7)

[Claims] 1. A cylinder liner for an internal combustion engine, in which a nitrided layer is formed on the inner circumferential surface, and a chromium plating layer is deposited on at least a portion of the outer circumferential surface in contact with cooling water, wherein the chromium plating layer is a lower layer. A cylinder liner characterized by a two-layer structure consisting of a chrome plating layer and an upper chrome plating layer. 2. In claim 1, the upper chromium plating layer has a thickness of 0.05 mm or more and a hardness of Hv.
A cylinder liner characterized by having a diameter of 800 or more. 3. The cylinder liner according to claim 1, wherein the lower chromium plating layer has a thickness of 0.02 mm or more. 4. A method for manufacturing a cylinder liner for an internal combustion engine, wherein a nitrided layer is formed on the inner circumferential surface, and a chromium plating layer is deposited on at least a portion of the outer circumferential surface in contact with cooling water, wherein the chromium plating layer a lower chrome plating step of depositing a lower chrome plating layer on the outer peripheral portion to which the chromium is to be deposited;
Next, a nitriding step of forming a nitrided layer on at least the inner peripheral surface, and then removing the nitrided layer on the surface of the lower chromium plating layer formed by the nitriding step to expose the surface of the lower chromium plating layer. A method for manufacturing a cylinder liner, comprising at least an upper layer chromium plating step of subsequently depositing an upper layer chromium plating layer on the surface of the lower layer chromium plating layer. 5. A method for manufacturing a cylinder liner according to claim 4, wherein an anodizing treatment, which is a plating pretreatment in the upper layer chromium plating step, is used to remove the nitride layer on the surface of the lower chrome plating layer. . 6. According to claim 4 or 5, the thickness of the upper chromium plating layer is 0.05 mm or more,
A method for manufacturing a cylinder liner, characterized in that its hardness is Hv800 or higher. 7. The method of manufacturing a cylinder liner according to claim 4, wherein the lower chromium plating layer has a thickness of 0.02 mm or more.