JPH0367006A - Ceramic link - Google Patents

Abstract

PURPOSE:To reduce the cost and improve abrasion resistance by providing a cylindrical axis part of a ceramic member and spherical surface parts to be sliding-contacting parts formed with the axis part in one body on both edge parts and making pores existing on the axis part surface and spherical surfaces less than specific values in their maximum diameters respectively. CONSTITUTION:A ceramic link 1 consists of a cylindrical axis part 2 and spheri cal surface parts 4 having convex semi-spherical surfaces 3 formed on its both end parts, and the axis part 2 and the spherical surface parts 4 are formed in one body of a solid ceramic sintered body. And the pores existing on the semi-spherical parts 3 are specified as less than 40 mum in their maximum diame ter, and the pores existing on the surface 2a of the axis part 2 are specified as less than 150 mum in their maximum diameter. Additionally, linear flaws are actually all eliminated from each of their spots. Consequently, a long life can be saved with less abrasion loss and a ceramic link which is superior in reliability and less costly can be acquired.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a link that is a power transmission member in a valve drive mechanism, etc. Regarding links.

(Prior Art) Rod-like parts for power transmission (hereinafter referred to as links) used in valve drive mechanisms and fuel injection drive mechanisms of diesel engines, such as bush rods and injection links, transmit power while in contact with a mating member. Conventionally, in order to improve the mechanical strength of the entire link, the entire link, including the hemispherical end that serves as the sliding part, was integrally formed from a metal member such as high-speed steel. It has been used extensively.

Incidentally, in recent years, there has been a strong desire to improve the lifespan of link parts by increasing the wear resistance of sliding parts. Ceramic members with excellent wear resistance, such as silicon nitride sintered bodies, have attracted attention as members constituting the hemispherical ends that serve as sliding contact parts, and are being put into practical use.

A link that uses a ceramic member for its sliding part is one in which a hemispherical tip made of silicon nitride sintered body or the like is made and attached to the end of a metal shaft by shrink fitting or brazing. Common.

(Problem to be Solved by the Invention) However, with a link in which a ceramic chip is attached to the end of a metal member, for example, the shape of the part is complicated to attach, and the labor required for assembly only increases costs. First, the reliability of the joints between the parts is low, so the improvement in wear resistance provided by ceramic members cannot be fully utilized.

Therefore, it is conceivable to form the entire link including the shaft part with a ceramic member, but when forming the entire link with a ceramic member, which is a brittle material unlike a metal member, the shaft part has to be It is necessary to ensure the mechanical strength of the parts.

However, even if ceramic links made of integrally molded materials such as silicon nitride sintered viscous materials are manufactured under certain manufacturing conditions, there is a real possibility that the mechanical strength of the shaft portion and the durability of the 1tJ contact portion will vary. This was revealed through experiments conducted by the inventors. Therefore, improving the reproducibility of these is the most important issue in providing highly reliable ceramic links.

The present invention has been made to address these problems, and it is possible to reduce the cost by improving the mechanical strength of an integrally molded ceramic link having spherical parts at both ends and the reproducibility of the durability of the spherical part. The purpose of the present invention is to provide a highly reliable ceramic link that can fully take advantage of the characteristics of ceramic members that have excellent wear resistance.

[Configuration of the Invention (Means for Solving the Problems) In other words, the ceramic link of the present invention includes a cylindrical shaft portion made of a ceramic member, and the ceramic member integrally attached to the shaft portion at both ends of the shaft portion. and a spherical surface portion having a spherical surface serving as a sliding surface formed by the shaft portion, the maximum diameter of the bore existing on the surface of the shaft portion is 150 μm or less, and the maximum diameter of the bore existing on the spherical surface is 40 μm or less It is characterized in that there are substantially no linear scratches on the surface of the shaft portion and the spherical surface.

(Function) The mechanical strength of the ceramic link integrally formed from ceramic members is greatly influenced by the bores existing on the surface in addition to linear flaws such as minute cracks.

Not only linear scratches such as minute clutter existing on the surface become stress concentration areas due to external force, but also bores existing on the surface of the ceramic link become stress concentration areas when external force is applied. Furthermore, the larger the bore diameter, the more likely it is that a small external force will cause cracks, resulting in a decrease in mechanical strength and even destruction.

The strength of the shaft is related to the mechanical strength of the entire link, and if there is a bore with a diameter exceeding 150 μm on the surface of the shaft, the mechanical strength of the link in various drive mechanisms of diesel engines, for example, cannot be satisfied. become unable to do so. In addition, the spherical surface that serves as the sliding contact surface is forced to operate under harsher conditions, and the presence of bores with diameters exceeding 40 μm7 reduces the reliability of sliding contact with the mating member and reduces wear resistance. The characteristics of the ceramic member, which has excellent properties, will be significantly reduced.

(Example) Hereinafter, an example of the ceramic link of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the ceramic link of the present invention. This ceramic link 1 is composed of a cylindrical shaft part 2 and a spherical part 4 having convex hemispherical surfaces 3 formed at both ends of the shaft part 2. The shaft part 2 and the spherical part 4 are solid. It is integrally formed from a ceramic sintered body.

This ceramic link 1 is used, for example, as a bushing rod in a valve drive mechanism of a diesel engine or an inject link in a fuel injection mechanism. For example, when used as a bushing rod in a valve drive mechanism, the ceramic link 1 is placed between a tappet having a concave spherical surface that is linked to the movement of the cam and serving as the mating sliding surface, and a rocker arm also having a concave spherical surface. JP? While in contact, the ceramic link 1 acts as an intermediate member for transmitting the m-movement of the cam to the valve arranged on the other side of the rocker arm.

The ceramic sintered body that is the material of the ceramic link 1 is preferably a silicon nitride sintered body, a sialon sintered body, a silicon carbide sintered body, a zirconium oxide sintered viscous body, etc., which have excellent wear resistance and high mechanical strength. In particular, the fracture toughness value (K lc) is 5 MPa ll! A silicon nitride sintered body of M or more is suitable.

As shown in FIG. 2, in the spherical part 4, the radius of curvature rl of the hemispherical surface 3 is set slightly larger than the cross-sectional radius rl of the shaft part 2, and there is a step 5 between the shaft part 2 and the spherical part 4. is configured so that it occurs. As a result, when the spherical part 4 comes into sliding contact with the mating member, interference caused by the shaft part 2 can be prevented, and the JF
The degree of freedom in I-contact operation is improved.

Further, a flat surface 3a having a diameter of about 115 to 1/lo of the radius of curvature of the hemispherical surface 3 is formed at the tip of the hemispherical surface 3 which becomes the sliding surface of the spherical surface portion 4. This flat surface 3a acts as a ridge during sliding contact, thereby enlarging the surface that actually makes sliding contact with the mating member, thereby preventing partial wear due to uneven contact or the like. Furthermore, by enlarging the surface that actually makes sliding contact, the hemispherical surface 3 that becomes the sliding surface is formed to substantially extend to about 70 degrees (θ in the figure) from the center of the shaft portion 2.

The spherical profile of this hemispherical surface 3 is preferably 20 μm or less. This is because if there are large irregularities partially on the sliding contact surface, wear during sliding contact with the mating member becomes significant and durability decreases. By defining with high precision, it becomes possible to make highly accurate sliding contact with the mating member, and it becomes possible to suppress the amount of wear of the ceramic link 1 and the mating member to a lower level.

The maximum diameter of the bore existing in the hemispherical surface 3 is specified to be 40 μm or less, and the surface 2a of the shaft portion 2
7J: The maximum diameter of the existing bore is specified to be 150 μm or less. In addition, substantially all linear scratches are eliminated from each.

Here, to distinguish between a linear flaw and the above-mentioned bore, a flaw in which the major axis of the flaw is 5 times or more as long as the short axis is defined as a linear flaw, and includes minute cracks and the like.

A fluorescent flaw detection test is effective as a method for determining the presence and size of these flaws (including the above-mentioned bores), and by performing a fluorescent flaw detection test on the ceramic link 1 of this example, It is determined whether the bore existing on the surface 2a is within the specified range.

The above-mentioned linear flaws including minute cracks become stress concentration areas when force is applied to the ceramic link 1, and are likely to cause breakage and develop into racks, so they are substantially eliminated. In addition, other bores (those whose major axis is less than 5 times the minor axis) also become stress concentration areas, and the larger the diameter (the major axis above), the more likely it is that a small force will cause cracks to form, resulting in a decrease in strength. It becomes a factor.

The strength of the shaft portion 2 is related to the mechanical strength of the ceramic link 1 as a whole, and if there is a bore with a major diameter exceeding 150 μm, the strength of the shaft portion 2 is related to the mechanical strength of the ceramic link 1 as a whole. mechanical strength cannot be obtained. In addition, since the hemispherical surface 3 serving as the sliding contact surface is subjected to direct force as the ceramic link 1 moves and is exposed to harsher conditions, it is necessary to further improve the reliability of mechanical strength.

If a bore with a major diameter exceeding 40 μm exists, the durability against sliding contact will be insufficient.

The diameter of these bores has the strongest influence on the force applied, but the mechanical strength is also affected by the number of bores, so the number of bores on the shaft surface 2a is reduced to 1.
It is preferable to set it to 0 pieces/ld or less, especially 4 pieces/x
It is desirable that the diameter be less than i (long diameter of 10 μm or more). Further, in the hemispherical surface 3, the number of pores is preferably 3/- or less, and particularly preferably 1/rid or less (long diameter 10 μn or more).

Next, a method for manufacturing the ceramic link 1 having the above structure will be explained.

In this embodiment, the ceramic link 1 in which the spherical parts 4 are integrally formed with the shaft part 2 at both ends is made into a cylindrical molded body by press molding or the like, and after sintering, it is machine-processed to the final shape. Although it is possible to adopt a manufacturing method such as applying injection molding, it is possible to create a molded body with a shape that approximates the finished product by applying the injection molding method, and then sintering this to make the sintered surface the final surface. Since it is possible to omit machining, manufacturing is possible at low cost, and it is desirable to employ the injection molding method.

The conditions for applying injection molding to the production of the molded body of the ceramic link 1 are based on the known ceramic injection molding method, for example, using an injection mold as shown in Fig. 3. A molded body having a shape approximating the finished product is produced.

The injection mold 10 shown in the same figure has both open ends of the cavity llH, which will become the shaft part 2, and a spherical part 4, on both sides of a mold 11 for a ridge part, in which a cavity lla, which will become the shaft part 2, is provided.
The spherical part mold 12.13 is arranged and configured such that the cavities 12a and 113a form one cavity.

Note that a slight step is provided between the cavity lla, which is the shaft portion 2, and the cavities 12a, 13a, which are the spherical surface portions 4, so that the outer diameter of the shaft portion 2 is smaller than that of the spherical surface portion 4.

The shaft mold 11 is divided into two parts, and a gate 14 is provided on the -blade side. In addition, the mold for the spherical part 12.1
Through holes 12b and 13b are provided in the center of the cavities 12a and 13a, respectively, and an air vent bin 15.16 is inserted into these, and the air vent bin 15.16 and the through holes 12b and 13b are connected to each other. A slight gap (for example, about 0.01-0.02III) is formed between them. Further, the cavity side tips 15a, 16a of the air vent bins 15, 16 are each made into a flat surface so as to form a flat surface 3a at the tip of the hemispherical surface 3. Furthermore, an air vent (not shown) is also provided between the shaft part mold 11 and the spherical part mold 12,13.

These gaps serve as air vents, and the molding material injected into the cavities lla, 12a, 13a can rapidly flow without being hindered by the air in the cavities lla, 12a, 13a or by the gas generated by itself. (before it cools down), the surface of the molded body is smoothed, and defects such as air bubbles are prevented from forming inside.

Next, after removing the gate portion of the obtained molded body, the ceramic link 1 is produced by degreasing and sintering.

The ceramic link 1 obtained in this way easily satisfies the various regulations mentioned above even if it has a sintered surface, and can be used directly, but it can also be used directly by applying a surface treatment such as barrel processing. It is preferable to use it in a smoother state.

Next, a specific manufacturing example of the ceramic link 1 using the injection mold 10 described above and the results of evaluating the characteristics using the obtained ceramic link 1 will be described.

First, 25 parts by weight of additional components having the composition shown below were added to 100 parts by weight of silicon nitride powder having an average particle size of 0.8 μm.

Paraffin wax 50-65% heavy toxicity Plasticizers and lubricants (D, 0.P) 20-35% heavy
Ethylene-vinyl acetate copolymer lO~20LIf amount%
The composition thus prepared was kneaded at a temperature of 100° C. to obtain a homogeneous mixture, and then this mixture was pulverized to produce a ceramic molding material.

Next, this molding material was injected and filled into a molding die, the construction of which is shown in FIG. 3, to produce a molded body.

The molding conditions are injection molding machine cylinder temperature 100℃,
The injection pressure (ap+ constant with mold internal pressure) was 40 MPa, and the molding cycle was 60 seconds.

After the gate part of the obtained molded body was desized, the temperature was gradually raised from room temperature to 500°C to degrease it, and then 1
The temperature was raised to 750° C. and held at that temperature for about 4 hours to sinter, thereby obtaining ceramic link 1.

In the obtained ceramic link 1, the regeneration radius of the spherical part 4 is 3.95 no+, and the spherical contour of the hemispherical surface 3 is 15 μm.
Within this range, the surface roughness was Rmax 3μ, and the spherical portion 4 had no similar defects and was very good. The flat part 3a of the hemispherical surface 3 has a diameter of 1aIls, and the step difference between the spherical part 4 and the shaft part 2 is 0.02 mm (shaft part 2 has a smaller diameter).
Met.

In addition, a large number of ceramic links 1 produced in the same manner were individually subjected to fluorescent flaw detection tests, and ceramic links 1
All scratches (including bores) on the surface were confirmed. Then, a three-point bending strength test was conducted on ceramic links 1 having bores of various diameters, excluding those with linear scratches.

The test method was to perform a destructive test by arranging the ceramic link 1 so that the selected bore was located below the load point, and to evaluate the mechanical strength based on the load that led to failure. The results are shown in Figure 4 as the relationship between the selected bore diameter and three-point bending strength. Note that the measurement results are displayed separately for those that were destroyed due to the selected bore and those that were destroyed from other locations.

In addition, since the bore defined by the fluorescent flaw detection test is larger than the actual bore diameter, the actual bore diameter was measured by enlarging that part again using a microscope. Note that the marks that appeared in the fluorescent flaw detection test were approximately proportional to the actual bore diameter.

As is clear from the results shown in FIG. 4, it can be seen that the three-point bending strength decreases as the bore diameter increases. If the bore diameter is 150μm or less, the bending strength is 60kg/-
is achieved and the desired mechanical strength of the link is obtained.

In addition, if the bore diameter is 40μm or less, the bending strength is 80k.
g/mj is achieved, the desired mechanical strength of the sliding contact surface is obtained, and sufficient durability as a sliding contact member is obtained.

In addition, among the ceramic links 1 that have been folded, the ceramic links that meet the specifications of the present invention (bore diameter, number of bores, spherical contour) and those that meet the specifications except for the presence of bores exceeding 150 μm on the shaft surface 2a are selected. Inside (Comparative Example 1), Hemisphere 11
Diesel engine fuels are those that are within the specifications except for the presence of a bore exceeding 40 μm in j3 (Comparative Example 2) and those that are within the regulations except that the profile of the hemispherical surface 3 exceeds 20 μm (Comparative Example 3). It was mounted on a tower as an injector link in an injection drive mechanism, and was tested for the equivalent of approximately 1.8 million km of actual driving.

As a result, in the diesel engine using the ceramic link 1 of the example, no major wear was observed in either the ceramic link 1 or the mating member, and almost no decrease in strength was observed in the three-point bending strength test conducted after the test. Ta.

On the other hand, in the diesel engine using the ceramic link 1 of Comparative Example 1, no major wear was observed in either the ceramic link 1 or the mating member.
A three-point bending strength test conducted after the test showed a significant decrease in strength. Furthermore, in the diesel engine using the ceramic link 1 of Comparative Example 2, the spherical surface of the ceramic link 1 was partially abraded significantly, and a portion of the mating member was also abraded. Furthermore, in the diesel engine using the ceramic link 1 of Comparative Example 3, a portion of the mating member was significantly worn and required repair.

[Effects of the Invention] As explained above, according to the present invention, the reliability and reproducibility of links using ceramic members are greatly improved, and the excellent wear resistance properties of ceramic members can be fully utilized. becomes possible. Therefore, it is possible to provide a highly reliable and inexpensive ceramic link that has a long service life with little wear.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing a ceramic link according to an embodiment of the present invention, Fig. 2 is an enlarged view of its main parts, and Fig. 3 is an injection molded body of the ceramic link used in an embodiment of the present invention. FIG. 4 is a diagram showing the configuration of the molding die, and is a diagram showing the relationship between the bore diameter existing on the surface of the ceramic link and the three-point bending strength. DESCRIPTION OF SYMBOLS 1... Ceramic link, 2... Shaft, 2 a-- Shaft surface, 3... Hemispherical surface, 4
・・・・・・Spherical part.

Claims (3)

[Claims] (1) A cylindrical shaft portion made of a ceramic member, and a spherical surface portion having a spherical surface serving as a sliding surface integrally formed with the shaft portion and formed of the ceramic member at both ends of the shaft portion, The maximum diameter of the bore existing on the surface of the shaft portion is 150 μm or less, and the maximum diameter of the bore existing on the spherical surface is 40 μm or less.
A ceramic link characterized by a diameter of less than μm. (2) The ceramic link according to claim 1, wherein both the shaft surface and the spherical surface are substantially free of linear flaws. (3) The ceramic link according to claim 1, wherein the contour of the spherical surface is 20 μm or less.