JP2004204762A - Sliding part and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sliding part capable of obtaining high wear resistance equivalent to a case of adopting high speed tool steel or alloy tool steel to the sliding part provided with a sliding surface contacting to a counterpart and sliding and increasing degree of freedom in structure material selection, and a method for manufacturing the same. <P>SOLUTION: A cam sliding surface of a tappet which is a sliding part is composed of chill cast iron, hard coating composed of CrN or TiN formed on the chill cast iron by PVD treatment at relatively low temperature. Consequently, high wear resistance equivalent to a conventional case of forming hard coating is obtained on high speed tool steel or alloy tool steel by PVD method and CVD method while using cast iron for structure material of the tappet. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sliding component typified by a tappet or the like, which is a component of an engine valve train, and a method for manufacturing the sliding component. In particular, the present invention relates to measures for improving the wear resistance of the sliding surface.
[0002]
[Prior art]
Conventionally, as a valve train of a diesel engine, a tappet and a push rod are disposed between a camshaft and a rocker arm. That is, the rotation of the camshaft is converted into the reciprocation of the tappet and the push rod, whereby the rocker arm is swung to open and close the valve.
[0003]
The tappet provided in this type of valve train receives the inertia force of the valve train and the load caused by the valve spring, and also receives the cylinder internal pressure. Therefore, particularly at the time of the valve-opening lift, a high surface pressure is generated between the sliding surfaces of the tappet and the camshaft, and the sliding surface of the tappet may be slid and worn.
[0004]
Heretofore, the tappet has been made of chill cast iron having high wear resistance in order to suppress sliding wear. In other words, when casting a tappet, a metal called a chiller is provided on a sliding surface forming portion in a mold, and a portion (a sliding surface portion of the tappet) in contact with the chiller is rapidly cooled, so that sliding is performed. A manufacturing method has been performed in which only the surface and its peripheral portion are chilled to partially increase the hardness.
[0005]
In addition, it has been proposed to provide a hard coating on the sliding surface to further improve the wear resistance of the sliding surface and improve the durability of the tappet. For example, it has been proposed that a tappet substrate be used as a tool rope and a material such as CrN (chromium nitride) or TiN (titanium nitride) be coated by a PVD (Physical Vapor Deposition) method or a CVD (Chemical Vapor Deposition) method. . Further, as a technique related to this, Patent Document 1 below discloses that a hard film (carbon film) is applied to a sliding surface of a tappet by a PVD method.
[0006]
The PVD method referred to herein is a surface treatment technique for forming a strong film on the surface of a substrate at a temperature of about 500 ° C. This is a method for forming a film. This PVD method is also called physical vapor deposition, and includes a vacuum vapor deposition method, a sputtering method, an ion plating method, and the like.
[0007]
On the other hand, the CVD method is called a vapor phase plating method, a chemical vapor deposition method, or a chemical vapor deposition method, in which a vapor in which a substance to be plated is heated and vaporized is sent to a periphery of a substrate together with a carrier gas and heated (at 1000 ° C.). This is a technique in which a vapor and a carrier gas are subjected to a high-temperature chemical reaction on the surface of the substrate that has been heated to a certain degree) to deposit a plating substance on the substrate surface.
[0008]
Further, as another method for improving the wear resistance of the sliding surface, as shown in FIG. 4A, a plate material b made of a tool steel, which is manufactured separately from the tappet a, is used. The surface is coated with the hard film c, and the plate material b is brazed to the sliding portion of the tappet a. As shown in FIG. It has also been proposed to silver braze the parts.
[0009]
[Patent Document 1]
JP 2000-327484 A
[Problems to be solved by the invention]
By the way, in recent years, demands for low pollution, low fuel consumption, high output, and the like of diesel engines have been increasing, and in order to meet such demands, adoption of a multi-valve system, a valve high-lift system, and the like are being promoted. As a result, the severity of the sliding surface of the tappet has been increasing, and it has been difficult to obtain sufficient wear resistance with the above-described measures, and there has been a limit in improving the durability of the tappet. .
[0011]
In particular, in the case of high-power engines for ships, conventional measures to improve wear resistance will result in insufficient wear resistance of the sliding surface of the tappet, leading to an increase in the frequency of tappet adjustment and an increase in valve opening / closing timing. There was a possibility that it would cause a gap.
[0012]
Further, since the PVD method and the CVD method are performed at a very high processing temperature of 500 ° C. or higher, there are restrictions on the materials that can be used as tappets. Specifically, high-speed tooling ropes (for example, SKH51) ) And alloy tool steels (for example, SKD11), the tempering temperature of which is relatively high, and the degree of freedom in material selection is extremely low.
[0013]
For example, it is effective to use cast iron in order to reduce material costs.However, in the conventional method, a hard coating is formed under a high-temperature environment. This leads to softening, resulting in problems such as insufficient adhesion of the film due to plastic deformation and a change in the shape of the tappet.
[0014]
In the above description, the tappet, which is a component of the engine valve system, has been described as an example, but other sliding components, such as the camshaft and the vane of the compressor, have similar problems. I have.
[0015]
The present invention has been made in view of such a point, and an object thereof is to provide a high-speed tool rope or an alloy for a sliding component having a sliding surface that slides in contact with a mating component. An object of the present invention is to provide a sliding component capable of obtaining the same high wear resistance as when a tool rope is employed and increasing the degree of freedom in selecting a constituent material, and a method of manufacturing the sliding component.
[0016]
[Means for Solving the Problems]
-Summary of the invention-
In order to achieve the above-mentioned object, the present invention provides a sliding surface of a sliding component made of chill cast iron, and applies a hard coating made of CrN or TiN to the chill cast iron by PVD treatment at a relatively low temperature. Molding. As a result, it is possible to obtain the same high abrasion resistance as in the case of forming a hard coating on a conventional high-speed tool steel or alloy tool steel by a PVD method or a CVD method, while using a cast iron as a constituent material of a sliding part. I can do it.
[0017]
-Solution-
Specifically, it is assumed that the sliding component has a sliding surface that slides with respect to the mating component. For this sliding part, at least the sliding surface is made of chill cast iron. Then, a hard coating is formed on the sliding surface by PVD processing at a processing temperature in the range of 100 ° C to 200 ° C.
[0018]
Specifically, CrN or TiN is employed as a material for forming the hard coating.
[0019]
According to these specific items, a hard coating having high hardness can be formed on the sliding surface of the sliding component while using an inexpensive cast iron material (chill cast iron) as the base material of the sliding component. Moreover, since the forming process of this hard coating is performed by PVD processing at a relatively low processing temperature of 100 ° C. to 200 ° C. (the conventional PVD processing was a high processing temperature of about 500 ° C.), Softening can be prevented. Since the tempering temperature of chill cast iron is generally 180 ° C. to 200 ° C., it does not soften if the PVD processing temperature is 100 ° C. to 200 ° C. For this reason, it is possible to avoid deterioration of the adhesion of the coating due to plastic deformation accompanying softening. In addition, a change in the shape of the sliding component can be prevented. The reason for setting the above-mentioned processing temperature range is that if the processing temperature exceeds 200 ° C., the softening of the cast iron material is promoted, and if the processing temperature falls below 100 ° C., the hard coating formed on the sliding surface This is because the adhesiveness of the material rapidly deteriorates. Further, the temperature of the PVD treatment is preferably from 150 ° C to 200 ° C.
[0020]
Further, according to this solution, a hard coating can be directly formed on the sliding surface of the sliding component. For this reason, it is possible to reduce the material cost and simplify the manufacturing process as compared with the conventional method of brazing a plate material subjected to a hard film treatment, which was manufactured separately from the sliding component, to the sliding component. And the production cost can be reduced.
[0021]
In particular, when the above-described material is employed as a molding material for a hard coating, a very high hardness of about 1800 to 2000 HV can be obtained as a sliding surface of a sliding component. Has good slipperiness, so that the opponent aggressiveness (the aggressiveness of the opposing component in sliding contact) can be kept low, and the durability of not only the sliding component but also the opponent component can be improved.
[0022]
In addition to the above solution, the thickness of the hard coating is set to 1 to 30 μm. This is because if the film thickness exceeds 30 μm, the internal stress in the hard film rapidly increases and a stable hard film cannot be formed. If the film thickness is less than 1 μm, the film thickness of the hard film is insufficient. This is because sufficient abrasion resistance cannot be obtained. The hard coating preferably has a thickness of 1 to 10 μm.
[0023]
Further, in addition to the above solution, the surface roughness of the sliding surface before the hard film is formed is set to 1 μmRy or less, and the hard film is formed on the sliding surface by the PVD process. This is in view of the aggressiveness of the sliding component. In other words, if the surface roughness of the sliding surface before the hard coating is formed is large, the surface of the hard coating reflects the surface roughness of the sliding surface as it is, and the surface roughness of the surface of the hard coating is large. It gets bigger. In this case, the opponent aggressiveness is significantly increased due to the so-called “rasp effect”, and the durability of the opponent component is greatly reduced. For this reason, the surface roughness of the sliding surface before the hard coating is formed is reduced, and the surface roughness of the hard coating is reduced to reduce the opponent aggressiveness. Further, if the surface roughness of the sliding surface exceeds 1 μmRy, the aggressiveness of the partner increases sharply, and the durability of the partner component is greatly reduced. It is set to 1 μmRy or less. The surface roughness is preferably as low as possible, but the lower limit is, for example, 0.1 μmRy.
[0024]
The following components are specifically adopted as mating components on which the sliding components slide. In other words, as the mating component with which the sliding surface of the sliding component comes into contact, a component made of carbon steel and having a surface induction hardened is employed (in this case, the hardness is about 600 HV). The sliding parts are arranged so that the sliding surface (the hardness is 1800 to 2000 HV) slides.
[0025]
This solution is particularly intended to minimize the wear of the sliding surface of the sliding component. For example, when the area of the sliding surface of the sliding component is equal to the area of the sliding surface of the mating component, in a situation where the surface pressure between the sliding surfaces becomes extremely high and wear occurs, the mating component has The sliding surface is worn, and the sliding surface of the sliding component is hardly worn. That is, the present solution can be adopted as a configuration for protecting the sliding component. On the other hand, when the area of the sliding surface of the mating component is larger than the area of the sliding surface of the sliding component, in a situation where the surface pressure between the sliding surfaces becomes extremely high and wear occurs, the The amount of wear between the sliding surface and the sliding surface of the mating component can be made substantially equal. According to this, it is possible to avoid a situation in which only one member is unilaterally worn and the replacement frequency is increased, so that the present solution is adopted as a configuration for reducing the maintenance frequency. can do.
[0026]
Note that the manufacturing method for manufacturing the sliding component according to each of the above-described solving means is also included in the technical idea of the present invention. That is, when the molten metal is cast and formed into a predetermined component shape, the sliding surface portion of the sliding component is rapidly cooled to chill the sliding surface portion, and the chilled sliding operation is performed. And a film forming operation of forming a hard film by PVD processing at a processing temperature in the range of 100 ° C. to 200 ° C. on the moving surface.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described. In this embodiment, a case will be described in which the present invention is applied to a tappet (sliding component) which is a valve train component of a diesel engine.
[0028]
First, the configuration of the tappet will be described. As shown in FIG. 1, the tappet 1 has a cam sliding portion 2 having one end slidingly (sliding) on a cam portion of a camshaft, and a push rod sliding contact portion having the other end sliding on a push rod. It is 3.
[0029]
The cam sliding portion 2 is formed to have a larger diameter than other portions. The distal end surface (lower end surface in FIG. 1) of the cam sliding portion 2 is a sliding surface 21 on which a hard coating 22 characteristic of the present invention is formed. The hard coating 22 will be described later.
[0030]
On the other hand, a concave portion 31 into which the push rod fits is formed on the distal end surface (the upper end surface in FIG. 1) of the push rod sliding contact portion 3. A hardening process such as induction hardening is performed on a peripheral portion of the concave portion 31.
[0031]
Next, the sliding surface 21 and the hard coating 22 formed on the sliding surface 21 as features of the present embodiment will be described.
[0032]
The peripheral portion of the sliding surface 21 is subjected to a chilling process. As a specific processing method, when casting the tappet 1, a metal called a chiller is provided on a sliding surface forming portion in the mold, and a portion that comes into contact with the chiller (a sliding surface portion of the tappet 1). Is rapidly cooled to chill only the sliding surface 21 and its peripheral portion (chilling operation) to partially increase the hardness to produce a tappet. Note that the shape of the sliding surface 21 may be a flat surface or a crown shape.
[0033]
Further, the sliding surface 21 of the tappet 1 formed by such a casting operation is polished prior to the forming process of the hard film 22, and the surface roughness is set to 1 μmRy or less. Specifically, in this embodiment, the surface roughness is set to 0.1 μmRy.
[0034]
The hard coating 22 is formed on the sliding surface 21 of the tappet 1 thus formed and surface-treated by PVD processing at a processing temperature in the range of 100 ° C to 200 ° C.
[0035]
The operation of forming the hard coating 22 will be described below. In this embodiment, the processing temperature is set to 180 ° C., and CrN is used as the material of the hard coating 22. That is, with the sliding surface and its surrounding environment kept at 180 ° C., Cr is evaporated, and the evaporated substance reacts with nitrogen gas to form a CrN thin film on the sliding surface (film forming operation). The thickness of the CrN hard film 22 formed here is set to 1 to 30 μm. Specifically, in this embodiment, it is set to 5 μm. In this embodiment, an arc ion plating method is employed as the PVD process (for example, arc current 160 A, nitrogen gas flow rate 1000 sccm, bias voltage 20 V, processing time 30 min × 4 times). However, the invention is not limited thereto, and a magnetron sputtering method, an unbalanced magnetron sputtering method, or the like can be employed. Since these methods are well known, description thereof is omitted here. The material of the hard coating 22 is not limited to CrN, but may be TiN.
[0036]
In the tappet 1 manufactured as described above, a hard coating 22 having high hardness is formed on the sliding surface 21 of the tappet 1 while using an inexpensive cast iron material (chill cast iron) as a base material. . For this reason, it is possible to avoid problems such as an increase in the frequency of tappet adjustment and a shift in valve opening / closing timing. In addition, since the forming process of the hard coating 22 is performed by the PVD process at a relatively low processing temperature such as 100 ° C. to 200 ° C., the softening of the cast iron material can be prevented. As a result, it is possible to avoid deterioration of the adhesion of the hard film 22 due to plastic deformation accompanying softening. Further, a change in the shape of the tappet 1 can also be prevented.
[0037]
In addition, since the hard coating 22 can be formed directly on the sliding surface 21, the material cost is lower than the conventional method of brazing a separately prepared plate material to the sliding surface. Reduction and simplification of the manufacturing process can be achieved, and manufacturing cost can be reduced.
[0038]
Further, in this embodiment, the surface roughness of the hard coating 22 can be reduced by reducing the surface roughness of the sliding surface 21 before the hard coating 22 is formed, and the opponent aggressiveness is suppressed low. It is possible. Thereby, the durability of the mating component can be improved.
[0039]
Further, by adopting CrN or TiN as the material of the hard coating 22, the sliding property of the hard coating 22 can be satisfactorily obtained, and not only can the opposing aggressiveness be reduced, but also the mechanical loss of the sliding portion can be reduced. Can also be reduced.
[0040]
-Experimental example-
Next, an experimental example performed for confirming the mechanical performance of the tappet according to the present invention will be described. Here, a scratch test and a sliding friction wear test described below were performed.
[0041]
In the scratch test, a tappet according to the embodiment described above as a product of the present invention and a conventional product having a CrN film formed by PVD processing on a high-speed tool rope (SKH51) as a comparative product were produced, and each of them was peeled off. The strength was measured. The result is shown in FIG.
[0042]
As is clear from the results shown in FIG. 2, the product of the present invention can secure the same peel strength (80 N or more) as the comparative product, and it can be seen that a stable hard film with high adhesion is obtained. . That is, it is understood that softening did not occur in the chill cast iron, and deterioration of the adhesion of the film due to plastic deformation accompanying the softening did not occur.
[0043]
In the sliding friction and wear test (one-way sliding friction and wear test), the following three types of tappets were prepared, each of which was slid against the camshaft, and the sliding surface of the tappet and the sliding surface of the camshaft, respectively. The wear ratio for was measured. The camshaft used in this test was obtained by induction hardening carbon steel.
[0044]
The first type of tappet is made of chill cast iron and has no hard film formed on the sliding surface (a conventional product when a tappet is made of chill cast iron).
[0045]
The tappet of the second type is a tappet manufactured by the manufacturing method according to the present invention, and has a sliding surface having a surface roughness of 3 μmRy.
[0046]
The tappet of the third type is also a tappet manufactured by the manufacturing method according to the present invention, and has a sliding surface having a surface roughness of 0.6 μmRy.
[0047]
As is clear from the results shown in FIG. 3, the wear ratio of the second type tappet is lower in each of the sliding surface of the tappet and the sliding surface of the cam shaft than in the first type tappet. . In particular, the wear ratio of the sliding surface of the tappet is greatly reduced, and it can be seen that the wear resistance of the sliding surface is significantly improved by the stable hard film having high hardness. Further, the reason why the wear ratio of the sliding surface of the camshaft is lowered is that the hard film has good slipperiness and the opponent aggressiveness is suppressed low.
[0048]
Further, in the third type tappet, the wear ratio of each of the sliding surface of the tappet and the sliding surface of the cam shaft is lower than that of the second type tappet. In particular, the wear ratio of the sliding surface of the camshaft has been significantly reduced, and by reducing the surface roughness of the sliding surface of the tappet, the aggressiveness of the opponent has been significantly reduced. It can be seen that wear is suppressed.
[0049]
-Other embodiments-
In the above-described embodiment, a case has been described in which the present invention is applied to a tappet which is a valve train part of a diesel engine. The present invention is not limited to this, and can be similarly applied to other sliding parts, such as the camshaft and the vane of the compressor.
[0050]
Further, the camshaft, which is a mating part, is not limited to induction hardened one, but may be carburized hardened one.
[0051]
【The invention's effect】
As described above, in the present invention, the sliding surface of the sliding component is made of chill cast iron, and a hard coating made of CrN or TiN is formed on the chill cast iron by low-temperature PVD processing. This makes it possible to use a relatively inexpensive cast iron as the component material of the sliding parts, but also has a high abrasion resistance equivalent to the case of forming a hard coating on a conventional high speed tooling alloy or alloy tooling steel by the PVD method or the CVD method. Sex can be obtained.
[0052]
In addition, since the forming process of the hard coating is performed at a relatively low temperature, the softening of the cast iron material can be prevented, and deterioration of the adhesion of the coating due to plastic deformation accompanying the softening can be avoided. In addition, a change in the shape of the sliding component can be prevented.
[Brief description of the drawings]
FIG. 1 is a side view showing a tappet according to an embodiment.
FIG. 2 is a diagram showing the results of a scratch test.
FIG. 3 is a diagram showing the results of a sliding friction and wear test.
FIG. 4 is a diagram corresponding to FIG. 1 showing a conventional example.
[Explanation of symbols]
1 Tappet (sliding parts)
21 sliding surface 22 hard coating

Claims (6)

A sliding component having a sliding surface that slides with respect to a mating component,
At least the sliding surface is made of chill cast iron, and a hard film is formed on the sliding surface by PVD (Physical Vapor Deposition) processing at a processing temperature within a range of 100 ° C to 200 ° C. Sliding parts characterized by the following. The sliding component according to claim 1,
A sliding component, wherein the hard coating is CrN or TiN. The sliding component according to claim 1 or 2,
A sliding component, wherein the thickness of the hard coating is set to 1 to 30 μm. The sliding component according to claim 1, 2 or 3,
A sliding component wherein the surface roughness of the sliding surface before the hard film is formed is set to 1 μmRy or less, and the hard film is formed on the sliding surface by the PVD process. . The sliding component according to any one of claims 1 to 4,
The mating part with which the sliding surface contacts is made of carbon steel and the surface is induction hardened, and the sliding surface is arranged to slide with respect to this mating part. Features sliding parts. A manufacturing method for manufacturing the sliding component according to any one of claims 1 to 5,
A chilling operation for chilling the sliding surface portion by rapidly cooling the sliding surface portion of the sliding component when casting the molten metal to form a predetermined component shape,
Producing a sliding part characterized by comprising a coating forming operation of forming a hard coating on the chilled sliding surface by PVD processing at a processing temperature in the range of 100 ° C to 200 ° C. Method.

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