JP2000001704A - Build-up welded valve and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a build-up welded valve excellent in mechanical strengths, wear resistance and heat resistance without generating underfill and overfill in a build-up welded part and its manufacturing method. SOLUTION: In a die 31 having electric conductivity, a metal-made valve main body 22 is fitted and metallic powder 23a for build-up is filled into a cavity 35 formed with a notched part 22a of the valve main body 22 and an upper punch 36 of a die. Electric current is conducted to this metallic powder 23a and the metal-made valve main body 22 while pressurizing the metallic powder to heat these metals and also, generate discharge between the both metals. Diffusion-joining thereof and the build-up welding with the metallic powder are executed to make the ratio of a build-up welded part to the absolute specific gravity 0.95-1.00.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cladding valve suitable for use as an intake valve or an exhaust valve of an internal combustion engine and a method for manufacturing the same.

[0002]

2. Description of the Related Art FIG. 3 shows a cross section near an intake valve and an exhaust valve of a gasoline engine. A valve 1 is provided at each opening of an intake passage 3 and an exhaust passage 4 of a cylinder head 2. When the air-fuel mixture reciprocates and comes into contact with the valve seat 5, the air-fuel mixture explodes and has a role of maintaining the airtightness of the combustion chamber 6 which becomes high in pressure. In the figure, reference numeral 7 denotes a piston that is reciprocated in a cylinder 8, and reference numeral 9 denotes a spark plug.

A valve 1 for an intake valve or an exhaust valve as described above.
Is required to have high wear resistance and heat resistance because it is repeatedly brought into and out of contact with the valve seat at high speed. Therefore, conventionally, for example, as shown in FIG.
A metal material having excellent wear resistance, for example, a Co-based alloy made of Co-Cr-WC is formed along the entire outer periphery of the valve body 11 by heat-resistant steel such as UH11. What is welded into the overlay portion 12 is used. The overlay 12 thus formed is subjected to machining such as grinding to finish it to a desired shape.

As a method of performing the overlay welding, for example, an end face 11a on the valve body 11 side is erected on an installation surface 13a of a turntable 13 and a welding torch 14 is turned while the turntable 13 is rotated 360 °. Is carried out over the entire circumference while operating the welding.

[0005]

In the above-mentioned welded valve 1, since welding is performed from one point on the circumference in the circumferential direction, the joint between the welding start point and the welding end point, that is, Irregularities such as bulges and underfills due to overlapping welding are easily formed at the joints in the circumferential direction of the bulges 12, and advanced skill is required to avoid this. In order to solve this technical problem, a green compact formed by pressure molding is fired to form a ring-shaped sintered body, and this sintered body is brazed to the outer edge of the valve body to form a build-up portion. It is also considered to do.

However, since the built-up portion is made of a sintered body, there is no underfill or raised portion.
It tends to be slightly inferior in mechanical strength and abrasion resistance as compared with overlay welding. When the Co-based heat-resistant material described above is manufactured by powder metallurgy, the Co alloy powder as a raw material is hard, the powder hardly hardens during press molding, and hardly sinters under normal conditions. There is a problem that a high strength product cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has no built-up portion or raised portion in a built-up portion, and has an excellent mechanical strength, abrasion resistance and heat resistance. It is intended to provide a manufacturing method thereof.

[0008]

In order to solve the above-mentioned problems, a method of manufacturing a cladding valve according to the present invention comprises: loading a metal valve body in a conductive mold; The space formed by the mold and the abutting portion to the valve seat is filled with the metal powder for overlaying, and the metal powder is pressurized while the metal powder and the metal valve body are energized to heat these metals. In addition, a discharge is generated between the two metals, and diffusion bonding of these metals and overlaying with metal powder are performed. The valve thus obtained has a build-up portion made of a sintered metal diffusion bonded to a contact portion with the valve seat, and the ratio of the build-up portion to the true density is 0.95 to 1.00. High density.

That is, in this manufacturing method, the metal oxide film present on the surface of the metal powder is destroyed by the discharge, and the surface is activated, so that dense sintering at a relatively low temperature becomes possible. In addition, since the discharge is generated while applying pressure, the metal powder is deformed and compressed and has a high density as the sintering progresses, so that a sintered alloy having a high dimensional accuracy and a high density ratio can be obtained.

[0010] In a normal sintering method, 5 pores are present in the sintered body.
２０20%, the density is much smaller than the theoretical density, true density, and the ratio is 0.80
However, according to the manufacturing method of the present invention, the ratio of the sintered density to the true density is 0.95 to 1.00.
The mechanical strength, abrasion resistance and heat resistance can be improved. In addition, since the spark sintering causes diffusion bonding between the valve body and the build-up portion, the bonding strength thereof is also improved. Therefore, it is possible to use a Co-based heat-resistant material as the material of the cladding portion, and it is possible to exhibit high wear resistance and heat resistance.

In addition, instead of filling the space between the valve body and the mold with the above-mentioned metal powder for overlay, a molded body for overlay formed by press-molding the metal powder is loaded. You may make it generate | occur | produce an electric discharge, and sinter while pressing a compact.
In this case, it is also possible to preliminarily fire the molded body. By using this build-up molding, since it has been press-molded in advance, the shrinkage during discharge sintering can be reduced, the dimensional design of the member can be facilitated, and the dimensional accuracy can be improved.

The discharge sintering is performed in any one of the atmosphere, an endothermic metamorphic atmosphere, a reducing atmosphere, an inert atmosphere, or a vacuum.

[0013]

FIG. 1 shows a valve head of a cladding valve according to an embodiment of the present invention.
No. 1 has a configuration in which a built-up portion 23 made of a sintered alloy is formed on the outer periphery of the valve body 22 along the entire circumference, and the ratio of the build-up portion 23 to the true density is 0.95 to 1. 00 range.

The valve body 22 is made of, for example, heat-resistant steel such as SUH11.

On the other hand, as a material of the overlay portion 23, for example, 26 to 33 wt% of Cr, 3 to 14 wt% of W,
0.9 wt% to 3 wt%, Ni 3 wt% or less, Fe 3 w
t% or less, the balance being Co-based alloy consisting of Co and unavoidable impurities, for example, No. 5 of Mitsubishi Stellite (registered trademark of Mitsubishi Materials Corporation). 1, No. 6, no. 12 and the like are preferably used. For use in a special corrosive environment, as a Co-based alloy containing a large amount of Ni, for example, Mitsubishi No. 32 is also suitable.

In this case, in a gasoline engine, the temperature of the valve on the intake side is, for example, about 200 to 500 ° C., whereas the temperature on the exhaust side is about 400 to 800 ° C., and the exhaust side is more than the intake side. Also, since the influence of heat is large, on the exhaust side, those having more excellent properties such as physical properties such as hardness, mechanical strength, abrasion resistance, heat resistance, and heat conductivity (for example, No. 1, Mitsubishi Stellite, No. 12).

Next, a method for overlaying the valve 21 will be described with reference to FIG. First, the mold 31 used for this overlay will be described.
A lower punch 3 for supporting the valve body 22 from below.
3, a first upper punch 34 for pressing the periphery of the stem portion 22b from above except for the cutout portion 22a of the valve body 22 placed on the lower punch 33, and are arranged coaxially with the upper punch 34. Notch 22a of the valve body 22
And a second upper punch 36 which forms a build-up cavity 35 is provided between them. Also, at least the lower punch 3
The third and second upper punches 36 are made of conductive metal, carbon, or the like, and are connected to a power supply 37.

In the mold 31, the valve body 22 is inserted.
Is disposed between the lower punch 33 and the first upper punch 34, and a lubricant such as boron nitride (BN) is provided on the surface of the valve body 22 opposite to the notch 22 a and the second upper punch 36. Is applied, and the metal powder 2 for overlaying is placed on the notch 22a of the valve body 22 with the second upper punch 36 raised.
Fill 3a. Next, a voltage of, for example, about 10 volts is applied between the second upper punch 36 and the lower punch 33 and a pulse current of several hundred amperes is applied between the punches 33 and 36 while pressurizing the metal powder 23a. The mold is heated to heat the metal powder 23a, and at the same time, a discharge is generated between the mold and the metal powder particles, so that the alloy powder 23a is fired. In this series of operations, the mold 31 is left in the atmosphere as it is,
Alternatively, the heat treatment is performed in any of an endothermic metamorphic atmosphere, a reducing atmosphere, an inert atmosphere, and a vacuum.

By the above-described method, if necessary, machining such as straightening and finish grinding is performed to obtain the sintered overlay valve 21 as shown in FIG. In addition, mold 3
When the interior of the mold 1 is any of an endothermic metamorphic atmosphere other than the atmosphere, a reducing atmosphere, an inert atmosphere, or a vacuum, the entire mold 31 is housed in a chamber (not shown).

By using the above-described manufacturing method, valves were manufactured by using various alloy powders and by varying the firing temperature, time, atmosphere, and pressing force depending on the mold, and their performance was evaluated. Table 1 shows the results. The valve body is SU
H-11 was used. The following materials were used as the sintered alloys A to C used for the overlay.

A: Co-30wt% Cr-12wt% W-
2.5 wt% C-3 wt% Ni-3 wt% Fe B: Co-28 wt% Cr-4 wt% W-1 wt% C-3 wt%
Ni-3 wt% Fe C: Co-29 wt% Cr-8 wt% W-1.4 wt% C-3
wt% Ni-3wt% Fe

No. Nos. 1 to 8 are manufactured by the method of the present embodiment. 9 is a conventional example.
The above-mentioned alloy powder of B is vacuum-applied to
What was sintered separately was used. In addition, "IN"
“EX” indicates that it was used on the intake side, and “EX” indicates that it was used on the discharge side.

[0023]

[Table 1]

The radial compression load in the column of characteristic evaluation is an outer diameter of 35 m.
The test piece was manufactured under the same conditions as the valve using a test piece having a diameter of 27 mm, an inner diameter of 27 mm, and a thickness of 8 mm, and the radial crushing strength was determined according to JIS Z2507. The amount of wear is defined as
The shape of the intake-side or exhaust-side valve of a 000 cc gasoline engine was incorporated into the cylinder head, and a so-called bench durability test was performed while applying a load, and the amount of wear was measured. The engine speed was 6500 rpm.
m, and the test time was 450 hours. The density ratio was determined by measuring the density of the build-up portion after sintering by the Archimedes method, and calculating the ratio with the true density (theoretical density).

As is clear from Table 1, in the valves (Nos. 1 to 8) of this embodiment, the density ratio is 0.98 or more, the radial crushing load is 140 kgf / mm ² or more, and the wear amount is 5 μm on the intake side. Below, it can be seen that the mechanical strength and the wear resistance are 18 μm or less on the exhaust side, which is better than that of the conventional example (No. 9). On the exhaust side of the bench durability test performed for measuring the amount of wear, the valve temperature was about 750.
The temperature of the valve was raised to about 400 ° C., but no abnormality was found in the valve of this example, and it was proved that the valve was excellent in heat resistance. In this case, if the density ratio is 0.95 or more in practical use, mechanical strength, wear resistance and the like can be sufficiently improved as compared with a general sintered member.

When the cross section of the valve of this embodiment was observed with a metallurgical microscope, the valve body and the cladding were diffused and bonded to each other. Structure. Therefore, according to the valve of the present embodiment, mechanical strength, wear resistance and heat resistance, and the joining strength of these joints can be improved, and the life of the member is prolonged, and the reliability thereof is improved. be able to.

On the other hand, according to the manufacturing method, since the built-up portion is formed by the mold, the built-up portion has no underfilled portion or raised portion, and the built-up portion can be formed uniformly over the entire circumference. In addition, workability is improved because skill is not required as compared with welding.

The structure and manufacturing conditions of the valve according to the above embodiment are merely examples, and can be appropriately changed according to the required valve shape. Further, the metal powder for overlaying may be formed into a molded body by pressure-molding in an annular shape so as to fit with the notch, and the molded body may be fitted into the notch, and the molded body may be subjected to discharge sintering. By firing the compact formed by pressing the metal powder, the shrinkage of the obtained sintered body is small, and the dimensional accuracy of the entire member is further improved.

[0029]

As described above, according to the method of manufacturing the cladding valve of the present invention, the surface of the powder is activated by the electric discharge sintering under pressure, and the dense sintering is performed at a relatively low temperature. In addition, since current is applied while pressurizing the mold, the filled powder can be deformed and shrunk along the mold to achieve high density. In this case, since the build-up portion is formed by the mold, the build-up portion has no underfilled portion or raised portion, and the build-up portion can be formed uniformly over the entire circumference. Therefore, it is possible to increase the dimensional accuracy and density ratio of the built-up portion, reduce the burden of post-processing, and obtain a valve having excellent mechanical strength, wear resistance, heat resistance, etc. The durability is improved. In addition, workability is improved because skill is not required as compared with welding.

Furthermore, if the metal powder for overlaying is press-molded in advance and the compact is subjected to electric discharge sintering, the dimensional accuracy of the overlay can be further improved.

[Brief description of the drawings]

FIG. 1 is a partially cutaway sectional view showing one embodiment of a cladding valve of the present invention.

FIG. 2 is a cross-sectional view showing a state in which the mold is filled with a valve body and a cladding alloy powder in one embodiment of the method for manufacturing a cladding valve of the present invention.

FIG. 3 is a sectional view showing the vicinity of a valve of a gasoline engine.

FIG. 4 is a cross-sectional view showing a conventional valve and a method for overlaying the same.

[Explanation of symbols]

 21 Overlay Valve 22 Valve Body 22a Notch 22b Stem 23 Overlay 23a Overlay Metal Powder 31 Type 32 Die 33 Lower Punch 34 First Upper Punch 35 Overlay Cavity 36 Second Upper Punch 37 Power Supply

Claims (3)

[Claims] 1. A metal valve body is loaded into a mold having conductivity, and at least a space defined by a mold and a contact portion of the valve body with a valve seat is filled with metal powder for overlaying. By energizing the metal powder and the metal valve body while pressurizing the metal powder, the metal is heated and a discharge is generated between the two metals, so that the diffusion bonding and the cladding of the metal powder are performed. A method for manufacturing a build-up valve, comprising: 2. A method for producing a cladding valve according to claim 2, wherein a molding for molding is formed by pressing said metal powder in place of said cladding metal powder. 3. A build-up portion made of sintered metal is diffusion-bonded to at least a contact portion of the metal valve body with the valve seat, and a ratio of the build-up portion to the true density is 0.95 to 1.
00. A cladding valve characterized by being set to 00.