JPH0539559A - Treatment for wear resistance on surface of stem part of titanium alloy valve - Google Patents

Abstract

PURPOSE:To provide a treating method for the wear resistance on the surface of the axial part of a titanium allay valve having good adhesion and excellent durability as well as good dimensional accuracy. CONSTITUTION:In the treating method for the wear resistance on the surface of the stem part of a titanium alloy valve, the titanium allay valve is rotated round the rotary symmetry axis of the titanium alloy valve, furthermore, while stress more than that by which plastic deformation occurs by a prescribed heating temp. is continuously applied to the stem part in a direction perpendicular to the stem, the stem part is heated in an oxygen or nitrogen atmosphere, and the titanium allay is oxidized or nitrided and is cooled. By this invention, the oxidizing or nitriding method by which shape dimensional accuracy has not been secured heretofore in spite of its convenience and excellent capacity can be executed only to the part requiring wear resistance with sufficient shape dimensional accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating the wear resistance of the surface of a shaft of a titanium alloy valve used for engines of automobiles and other vehicles, and further, titanium having a rod-shaped portion which receives sliding. It can be widely applied as a wear-resistant treatment method for the rod-shaped surface of alloy parts.

[0002]

2. Description of the Related Art Up to now, as a method for treating the wear resistance of the shaft surface of a titanium alloy valve, oxidation (Japanese Unexamined Patent Publication No. Sho.
956), nitriding (see JP-A-61-81505), ion nitriding (see JP-A-61-234210), hard Cr plating, Ni-P plating (see JP-A-1-96407). ) And molybdenum spraying (see Japanese Patent Laid-Open No. 62-41908).

[0003]

Molybdenum thermal spraying has a proven track record as a method for anti-wearing the surface of the shaft of titanium alloy valves of automobile engines for competition, but the cost is high. Hard Cr plating and Ni-P plating are oxide films that inevitably exist on the surface of titanium alloys, so it is essentially difficult to secure plating adhesion, but surface roughening by shot blasting is essential. Efforts have been made to improve the plating adhesion by removing the oxide film by fluoric acid pickling and by heat diffusion after plating.

On the other hand, for oxidation and nitriding, a simple method is required in which the titanium alloy is heated in the atmosphere.
Although it has been attracting attention since it has excellent adhesion due to diffusion treatment, there is a problem in that it is not possible to secure the shape and dimension accuracy required for titanium alloy valves due to the need for heating at a high temperature, which causes thermal deformation. It was It is said that ion nitriding can lower the nitriding temperature,
The shape is still insufficient, and there are similar problems.

An object of the present invention is to provide a method for treating the surface of the shaft of a titanium alloy valve with wear resistance by solving the above problems.

[0006]

Means for Solving the Problems As a method for anti-wearing the surface of a shaft portion of a titanium alloy valve, the present inventor locally heats only the shaft portion of the titanium alloy valve to oxidize or nitride,
The inventor has invented a method of correcting the thermal strain generated at this time in the cooling process.

That is, according to the present invention, the titanium alloy valve is rotated about the rotational symmetry axis of the titanium alloy valve, and the shaft portion is subjected to a stress that causes plastic deformation at a predetermined heating temperature in a direction perpendicular to the rotational symmetry axis. In addition, the method is a wear-resistant treatment method for the surface of a shaft portion of a titanium alloy valve, characterized in that the shaft portion is heated in the atmosphere or in an atmosphere of oxygen or nitrogen to oxidize or nitride the titanium alloy and then cooled.

[0008]

1 is a side view of a valve to which the present invention is applied. In the figure, a is a tip surface, b is a shaft portion, c is a neck portion,
d is an umbrella portion and e is a shaft end portion.

Here, the titanium alloy valve is rotated about the rotational symmetry axis of the titanium alloy valve because oxidation or nitridation due to heating is completely axisymmetric, and the titanium alloy valve is slid on the mating valve guide. This is because the abrasion of the shaft is unlikely to occur and it is indispensable to correct the thermal deformation due to heating during the cooling process and to secure the straightness. The rotation speed may be, for example, 500 rpm to 5000 rpm.

The fact that the stress, which is more than the plastic deformation at the predetermined heating temperature in the direction perpendicular to the shaft, is continuously applied to the shaft portion, which is the biggest problem in the titanium alloy valve among the thermal deformation caused by heating. This is because it is necessary to correct the bend. The method of applying such bending stress is, for example,
This is a method in which the shaft end e side in FIG. 1 is attached to a rotating body and the blade is pressed against the shaft portion b near the neck portion c. It is preferable to use a blade having a solid lubricating action such as graphite, MoS ₂ or WS ₂ that has a small friction coefficient with a titanium alloy and does not vibrate even when a bending stress is applied.

The reason why the shaft portion is heated in the atmosphere or in the atmosphere of oxygen or nitrogen to oxidize or nitride the titanium alloy is to secure the wear resistance required for the shaft portion of the titanium alloy valve. 1 to 30 seconds for heating at 950 ° C. for oxidation, and 10 for heating at 950 ° C. for nitriding.
Seconds to 1000 seconds are sufficient. Here, if the heating time is long,
The method of the present invention may be carried out mainly for the purpose of straightening the bend after previously oxidizing or nitriding the shaft portion.

As a heating method, a method of locally heating with a width of, for example, 10 to 15 mm by a high frequency heating or a burner is convenient for correction. For example, starting from a place near the end e,
Move the heating band to the neck c side. At this time, the shaft end e
The bending stress applied at a position close to is small and needs to be increased toward the neck c side. When the method of heating the entire shaft portion is adopted, the maximum bending moment occurs near the shaft end portion e side, and only that portion is corrected, so during cooling, from the shaft end portion e side to the neck portion c. If it cools down, the whole is corrected and there is no problem. The bending stress changes depending on the yield strength, thickness, heating position, and heating temperature of the shaft portion b, and the rotation speed is high and the strain rate dependence may be a problem. Further, at the cooling end temperature, no bending stress exceeding plastic deformation should be applied.

Any of water cooling, oil cooling and air cooling may be used as the cooling method, but oil cooling is suitable in view of shortening the processing time, improving the material strength and easiness of handling.

Here, the titanium alloy is α-type Ti-5Al-
2.5Sn, near α type Ti-8Al-1Mo-1V, T
i-6Al-2Sn-4Zr-2Mo, α + β type Ti−
3Al-2.5V, Ti-6Al-4V, Ti-8Al
-6V-2Sn, β type Ti-13V-11Cr-3A
l, Ti-15V-3Cr-3Sn-3Al, etc., each form an oxide film or a nitride film by oxidation or nitridation, under which oxygen or nitrogen diffuses, forms a solid solution hardened layer, and wear resistance It was confirmed that there was no problem in processing.

Finally, in the present invention, even if the rotor and the portion near the blade are thermally deformed, the heating temperature cannot be sufficient, and therefore the bending stress cannot be corrected by a predetermined bending stress. Since it is smaller than the shape accuracy, there is no problem.

[0016]

【Example】

[Example 1] Finished titanium alloy valve (material:
Ti-6Al-4V, shape: shaft portion 90 mm, shaft diameter 7 mm), the tip portion a to 12 mm was fixed to a drilling machine chuck and rotated at 3000 rpm. In order to apply a bending stress to the shaft portion b, a blade of a plate having a thickness of 5 mm and containing graphite as a main component was pressed against the shaft portion b side from the neck portion c by a force of about 10 kg. At this time, the shaft part b is slightly curved,
It was confirmed that the shaft portion b and the face f smoothly rotated without causing blurring. In this state, near the shaft end e in the atmosphere with a burner, a part with a width of about 15 mm is 950 ° C,
After heating for 3 seconds, the heating part at 950 ° C. was moved to the neck c side at a speed of 5 mm / sec. At this time, the initial load applied to the blade was pushed with 0.5 kg weight, and increased in 0.05 kg weight / sec in synchronism with the movement of the heating zone. Further, in synchronization with the movement of the heating body, the heating end portion was cooled by water cooling.
The bending of the shaft portion b of the titanium alloy valve in which both ends except about 15 mm were oxidized by such a method and the deflection of the face f when the shaft portion was rotated were measured and found to be 2 μm.
The following were only minor variations.

The same process as above is carried out using Ti-6Al-4V.
When a test was carried out at 6028 RPM for 150 hours using a 4-cylinder engine that was applied to the shaft of the alloy valve and used a valve guide equivalent to FC25, no problems such as seizure occurred.

[Example 2] Table 1 shows the results including Example 1 together with Comparative Examples. A titanium alloy valve after finishing was used as a test material. The bending of the shaft and the deflection of the face were 0 μm and 0 to 2 μm, respectively. The shaft thickness is
6.60 mm, length 90 mm, treated part 60 mm, heating was carried out by high frequency heating in the atmosphere or in oxygen or nitrogen, and cooling was carried out by an oil mist. From Table 1, it is clear that according to the present invention, a shaft portion of a titanium alloy valve having excellent bending, deflection and wear resistance can be obtained.

[0019]

[Table 1]

[0020]

EFFECTS OF THE INVENTION According to the present invention, the oxidation and nitriding methods for which the shape and dimensional accuracy could not be ensured for the shaft surface of the titanium alloy valve, which has been excellent in processing simplicity and performance so far, can be obtained. It can be performed with sufficient shape and dimension accuracy only in the portion where abrasion resistance is required.

[Brief description of drawings]

FIG. 1 is a side view of a valve.

[Explanation of symbols]

 a: Tip surface b: Shaft portion c: Neck portion d: Umbrella portion e: Shaft end portion f: Face

Claims (1)

[Claims] 1. A method for anti-wearing a surface of a shaft portion of a titanium alloy valve, wherein the titanium alloy valve is rotated about a rotational symmetry axis of the titanium alloy valve, and the shaft portion is predetermined in a direction perpendicular to the rotational symmetry axis. Continue to apply more stress than plastic deformation at the heating temperature of the titanium alloy valve, which is characterized by heating the shaft in the atmosphere or in an atmosphere of oxygen or nitrogen, oxidizing or nitriding the titanium alloy, and cooling. Abrasion resistant surface treatment method.