JP2001214220A - Induction heating apparatus of cam shaft, and heat treatment method using the apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cast iron member excellent in pitching resistance by changing the ferritic phase of the cast iron member into a phase of high strength by the heat treatment, and a manufacturing method thereof. SOLUTION: A cam shaft is heated and kept at 830-1,030 deg.C for 7-90 seconds by the induction-heating normalizing, and then, naturally cooled to transform the ferritic phase as cast into the pearlitic phase 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating apparatus for a camshaft which improves the pitching resistance by heat-treating a cam portion, and a heat-treating method using the apparatus.

[0002]

2. Description of the Related Art In recent years, with the increase in the output of an engine, valve train parts such as a camshaft and a tappet of the engine have been required to have further improved durability. It has become. Pitching is a kind of fatigue failure that occurs when a large load is repeatedly applied to the surface of a member, in which a part of the surface is missing and fine holes are formed in spots.

Conventionally, chill cast iron, quenched steel, sintered alloy, and the like have been used for camshafts, and are subjected to annealing and quenching to improve pitting resistance (Japanese Patent Publication No. 61-47208). Official Gazette) and a double material formed of a high alloy cast iron for the outer shell and a tough cast iron for the inner shell are subjected to austenitizing treatment, followed by rapid cooling and 200-45.
Those subjected to a constant temperature transformation treatment at 0 ° C (Japanese Patent Publication No. 57-1564)
No. 8) has been proposed.

[0004]

Chill cast iron is low in cost and excellent in wear resistance, but is inferior in pitting resistance to other members, and is not suitable for high surface pressure applied to a cam. For camshafts and the like, materials more expensive than chill cast iron are used.

As shown in FIG. 1, the metal structure of chill cast iron is mainly composed of cementite (carbide) 1, pearlite phase 2, and ferrite phase 3 existing around cementite 1. Ferrite phase 3 is cementite 1
There is a problem that the ferrite phase 3 becomes a starting point of crack generation due to pitting fatigue or a crack develops along the ferrite phase 3 due to pitting fatigue.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a cast iron member excellent in pitting resistance by changing a ferrite phase of a cast iron member to a high-strength phase by heat treatment, and a method of manufacturing the same. It is.

[0007]

In order to solve the above-mentioned problems and achieve the object, a high-frequency heating apparatus for a camshaft according to the present invention is a high-frequency heating apparatus for a camshaft for heating a cam portion at a high frequency. Rotating means for rotating the camshaft about its axis, an outer cylindrical member arranged concentrically with the camshaft so as to surround the camshaft and capable of supplying a high-frequency current; ,
A heating unit that is supported at a portion facing the cam unit and that heats the cam unit by magnetic flux generated when a high-frequency current is applied to the outer cylinder member.

[0008] Preferably, the heating section has a core section, and the outer cylinder member is formed with an opening through which the camshaft faces to the outside.

Further, the heat treatment method using the high-frequency heating apparatus for a camshaft according to the present invention is characterized in that a rotating means for rotating the cast camshaft around the axis thereof, An outer cylinder member arranged in a shape and capable of supplying a high-frequency current, and a cam supported by a portion of the outer cylinder member opposed to the cam portion, and the magnetic flux generated when the high-frequency current is supplied to the outer cylinder member to generate the cam. A heating unit that heats the camshaft at a temperature equal to or higher than an austenitizing temperature by using the heating unit. Cool the shaft until it passes the austenitizing temperature by 5
A cooling step of cooling at 0 ° C./min or more.

Preferably, in the heating step, the camshaft is heated at 830 to 1030 ° C. for 7 to 90 seconds.

[0011]

As described above, according to the first aspect of the present invention, there is provided a high-frequency heating apparatus for a camshaft for heating a cam portion at a high frequency, comprising a rotating means for rotating the camshaft about an axial center. An outer cylindrical member which is arranged concentrically with the camshaft so as to surround the camshaft and which is capable of supplying a high-frequency current, and which is supported by a portion of the outer cylindrical member facing the cam portion, and the outer cylindrical member receives the high-frequency current. By providing a heating section for heating the cam section by the magnetic flux generated when energized, heat treatment can be efficiently performed without heating the camshaft other than the cam section.

According to the second aspect of the present invention, the heating portion has the core portion, and the outer cylinder member has the opening portion where the camshaft faces to the outside, so that the camshaft is mounted on the heating device. , Which facilitates removal and improves productivity.

According to the third aspect of the present invention, the heating unit heats and holds the camshaft at a temperature equal to or higher than the austenitizing temperature, and the cooling rate until the heated camshaft passes the austenitizing temperature is 50 ° C./min. By cooling as described above, the ferrite phase of the cast iron member is changed to a high-strength phase by heat treatment, and the pitting resistance can be improved.

According to the fourth aspect of the present invention, in the heating step,
By heating the camshaft at 830 to 1030 ° C for 7 to 90 seconds, the ferrite phase of the cast iron member can be changed to a high-strength phase by heat treatment while suppressing the decomposition of carbides, and the pitting resistance can be improved.

[0015]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

The cast iron member according to the embodiment of the present invention has a carbon (C) content of 3.0 to 3.8% by weight and a silicon (Si) content of 1.3 to 3.8%.
2.3% by weight, manganese (Mn) 1.0% by weight or less, phosphorus (P) 0.1% by weight or less, sulfur (S) 0.1% by weight or less, a kind of chromium (Cr) 1.0% by weight or less Or 2
Seed chromium (Cr) 1.0% by weight or less + molybdenum (M
o) 0.1 to 0.5% by weight, the balance being made of an alloy material with iron (Fe), which is cast so that 20 to 50% of cementite crystallizes in a portion corresponding to the sliding surface. .

If the content of carbon (C) is less than 3.0% by weight, castability is poor, and if it exceeds 3.8% by weight, a large amount of free graphite is crystallized. If silicon (Si) is less than 1.3% by weight, castability is deteriorated, and if it exceeds 2.3% by weight, a ferrite phase is easily formed, so that the above range is set. If manganese (Mn) exceeds 1.0% by weight, the material shrinks greatly, so it was set to 1.0% by weight or less. Phosphorus (P) and sulfur (S) were set to 0.1% by weight or less as the upper limit of impurities. Chromium (Cr) is used in an amount exceeding 1.0% by weight for stabilizing carbides and improving abrasion resistance. Molybdenum (Mo)
Is a component that is selectively added for strengthening the base structure. If the content is less than 0.1% by weight, there is no effect, and if it exceeds 0.5% by weight, the effect is saturated.

The use of the cast iron member of the present embodiment is mainly for a camshaft used for an engine, but can also be applied to other sliding elements.

FIG. 1 is a schematic view showing a metal structure of an as-cast cast iron member. FIG. 2 is a schematic diagram showing a metal structure during heat treatment of an as-cast iron member. FIG. 3 is a schematic diagram showing the structure of the as-cast cast iron member after the heat treatment.

The cast iron member in an as-cast state (before heat treatment)
As shown in FIG. 1, it is mainly composed of cementite (carbide) 1, pearlite phase 2, and ferrite phase 3. The pearlite phase 2 contains more carbon (C) than the ferrite phase 3. In order to uniformly dissolve the carbon (C) in the matrix and transform the ferrite phase 3 into the pearlite phase 2,
As shown in FIG. 2, the pearlite phase 2 and the ferrite phase 3 of the matrix structure are once austenitized to suppress the decomposition of carbides by performing a heat treatment so that carbon (C) is uniformly dissolved in the matrix structure. As shown in FIG. 3, the austenite 4 is rapidly cooled to crystallize the pearlite phase 2.

The as-cast cast iron member is subjected to a heat treatment under the following heat treatment conditions. [Heat treatment conditions] After the cast iron member is heated and held at the austenitizing temperature (A1 transformation point) or higher, the cooling rate until passing through the A1 transformation point is cooled at 50 ° C / min or more. By this heat treatment, carbon (C) existing in the base structure is uniformly dissolved as a whole, and the ferrite phase is transformed into a pearlite phase or a martensite phase to improve the strength.

From the region above the austenitizing temperature, A1
If the average cooling rate before passing through the transformation point is 50 ° C./min or less, ferrite is reprecipitated, so the cooling rate was set to 50 ° C./min or more.

Under the above heat treatment conditions, air or nitrogen gas is used as a cooling medium for cooling. As a result, defects such as bending and cracking of the cast iron member are less likely to occur. [Embodiment] As a preferred embodiment of a cast iron member, an alloy material having the chemical components shown in FIG. 4 is cast to manufacture a camshaft. did. The chill structure is composed of cementite, pearlite, ferrite, and graphite.

When molybdenum (Mo) is added, the amount of carbide is increased as compared with the case where molybdenum (Mo) is not added, but the cost is increased. Chromium (Cr) also affects the cost reduction effect.

The first embodiment shown in FIG.
, The ferrite existing in the chill structure is decomposed and transformed into a high-strength phase.

FIG. 6 is a diagram showing the metal structure of the as-cast cast iron member. FIG. 7 is a view showing a structure of an as-cast iron member after normalization using an atmospheric furnace. FIG. 8 is a view showing a structure of an as-cast cast iron member after normalization using induction heating. [Example 1] The heat treatment conditions are varied as follows, but the structure in FIG. 8 is air-cooled (compressed air) after heating at 978 ° C. for 19 seconds.
It was done.

Example 1 is a heat treatment by induction heating normalization, in which the camshaft is heated and held at 830 to 1030 ° C. for 15 to 90 seconds, and then cooled by air cooling (compressed air).
By this heat treatment, the as-cast ferrite phase 3 shown in FIG. 6 can be transformed into the pearlite phase 2 shown in FIG. 8 to improve the strength. [Comparative Example] Although the heat treatment conditions vary as follows, FIG.
The structure No. was air-cooled (compressed air) after heating at 890 ° C. for 60 minutes.

The comparative example is a heat treatment using a heating furnace normalization.
Using a general atmospheric furnace, the camshaft is set to 830 to 91.
After heating and holding at 0 ° C. for 30 to 150 minutes, it is cooled by air cooling (compressed air). By this heat treatment, the ferrite phase 3 shown in FIG. 6 can be transformed into the pearlite phase 2 shown in FIG. 7 to improve the strength. [Effects of Heating Temperature, Heating Time, and Cooling Temperature] The heat treatment by the heating furnace normalization (Comparative Example) has a longer heating time, and therefore, the amount of carbides decomposed is larger than that of the heat treatment by induction heating (Example 1). Therefore, the comparative example is not suitable for a cam that requires not only pitting resistance but also wear resistance to slippage.

FIGS. 9 and 10 show the results of an experiment in which heat treatment was performed by induction heating.

FIG. 9 is a diagram showing the relationship between the austenitizing temperature and the amount of carbide. FIG. 10 is a diagram showing the relationship between the holding time at the austenitizing temperature and the amount of ferrite. As can be seen from FIG. 9, the influence of the heating temperature on the carbide is small, and in the heat treatment by the induction heating normalization (Example 1),
Since the treatment can be performed in a short time, the amount of carbide of the material can be maintained even at a high temperature of 1000 ° C. or more.

As can be seen from FIG. 10, in the induction heating normalization, if the heating time for austenitization is too short, diffusion of carbon (C) existing in the base structure is insufficient, and ferrite is partially contained in the material. Remains. Therefore, the heating time required for uniformly dissolving the ferrite uniformly in the whole body is required to be 7 seconds or more.

FIG. 11 is a diagram showing the relationship between the cooling rate and the amount of ferrite.

Even if the camshaft is heated to a temperature higher than the austenitizing temperature, if the cooling rate is low, austenite is transformed into ferrite and a desired matrix structure cannot be obtained.

Therefore, an experiment was carried out using an atmospheric furnace in order to obtain a required cooling rate. FIG. 11 shows the amount of ferrite in the metal structure obtained by heating and holding the camshaft at 890 ° C. for 60 minutes and then cooling at different cooling rates. The cooling rate is changed by adjusting the pressure of the compressed air blown during cooling.

As can be seen from FIG. 11, when the camshaft is heated and held at the A1 transformation point or higher, and then cooled at a cooling rate of 50 ° C./min or more until passing through the A1 transformation point, ferrite is greatly reduced. On the other hand, when the pressure of the compressed air is reduced at a cooling rate of 25 ° C./min, the ferrite is reprecipitated. Therefore, it can be said that the cooling rate is desirably 50 ° C./min or more. [Test Result of Camshaft] FIG. 12 shows the result of a test performed on the camshaft manufactured as described above under the conditions shown in FIG.

As can be seen from FIG. 13, the conventional product (without heat treatment) produced pitting in both the motoring test and the actual machine evaluation, whereas the product of this embodiment (heat treatment of Example 1) produced pitting in both tests. It can be confirmed that the pitting resistance was significantly improved. [High Frequency Heating Apparatus] In the induction heating normalization of the first embodiment, an induction heating oscillator as a high frequency heating apparatus shown in FIGS. 14 and 15 is used.

The induction heating oscillator is provided with a rotating jig 12 for holding the camshaft 10 as a cast iron member and rotating the camshaft 10 around an axis center, and a camshaft 10 surrounding the outer periphery of the camshaft 10. An outer cylinder member 14 formed in a semi-annular shape concentric with the axis 10, and magnetic cores 15 and 16 as heating units supported on portions of the outer cylinder member 14 that face each cam 11. .

At the upper end 14a of the arc portion of the outer cylinder member 14, two electrodes 13 through which a high-frequency current can be supplied are provided.
The current frequency is appropriately set according to the area and the structure of the cam portion. The core 15 is provided as a coil at both ends 14 b of the arc portion of the outer cylinder member 14 so as to sandwich the cam portion 11, and a magnetic flux generated when a high-frequency current is applied to the outer cylinder member 14 is concentrated on the cam portion 11 to heat the core member 11. I do. Arc part 1 of outer cylinder member 14
4c is formed with an opening 17 in which the camshaft 11 faces the outside. The outer cylinder member 14 is formed in a half-split shape,
The camshaft 11 can be easily set on the rotary jig 12.

It should be noted that the present invention can be applied to a modification or modification of the above embodiment without departing from the spirit thereof.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a metal structure of a cast iron member in an as-cast state.

FIG. 2 is a schematic view showing a metal structure during a heat treatment of an as-cast cast iron member.

FIG. 3 is a schematic view showing a structure after heat treatment of an as-cast cast iron member.

FIG. 4 is a view showing chemical components of a cast iron member of an example.

FIG. 5 is a diagram illustrating heat treatments of Example 1 and a comparative example.

FIG. 6 is a view showing a metal structure of an as-cast cast iron member.

FIG. 7 is a view showing a structure of an as-cast cast iron member after heat treatment by induction heating normalization.

FIG. 8 is a view showing a structure after heat treatment of an as-cast cast iron member by heating furnace normalization.

FIG. 9 is a graph showing a relationship between an austenitizing temperature and a carbide amount.

FIG. 10 is a graph showing the relationship between the heating time for austenitization and the amount of ferrite.

FIG. 11 is a diagram showing the relationship between the cooling rate and the amount of ferrite.

FIG. 12 is a view showing test conditions for pitting resistance of an example product and a conventional product.

13 is a diagram showing test results of an example product and a conventional product based on the test results of FIG.

FIG. 14 is a diagram showing a shape of an outer cylindrical member of the high-frequency heating device of the present embodiment.

FIG. 15 is a diagram showing a state where the camshaft of the high-frequency heating device of the present embodiment is attached.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cementite (carbide) 2 Perlite phase 3 Ferrite phase 4 Austenite 10 Camshaft 11 Cam part 12 Rotating jig 13 Electrode 14 Outer cylinder member 15, 16 Magnetic core

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Norio Sakate 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Masahiko Shibahara 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Tamio Tanaka 3-6-24 Oshu, Minami-ku, Hiroshima City, Hiroshima Prefecture Inside Nagato Co., Ltd. F-term in the company Nagato (reference) 4K042 AA17 BA01 DA01 DB01 DC02 DC03 DE05 DF02 EA01

Claims (4)

[Claims] 1. A high-frequency heating apparatus for a camshaft for heating a cam portion at a high frequency, comprising: a rotating means for rotating the camshaft around an axis; and a concentric axis with the camshaft so as to surround the camshaft. An outer cylinder member arranged in a shape and capable of supplying a high-frequency current; and a cam supported by a portion of the outer cylinder member opposed to the cam portion, the magnetic flux being generated when the high-frequency current is supplied to the outer cylinder member. A high-frequency heating device for a camshaft, comprising: a heating section for heating the section. 2. The high-frequency camshaft according to claim 1, wherein the heating portion has a core portion, and the outer cylinder member has an opening formed so that the camshaft faces the outside. Heating equipment. 3. A rotating means for rotating the cast camshaft about its axis, an outer cylindrical member arranged concentrically with the camshaft so as to surround the camshaft and capable of conducting a high-frequency current; A high-frequency heating device for a camshaft, comprising: a heating unit that is supported by a portion of the outer cylinder member that faces the cam portion and that heats the cam portion by a magnetic flux generated when a high-frequency current is applied to the outer cylinder member. A heating step of heating and holding the camshaft at a temperature equal to or higher than the austenitizing temperature by the heating unit; and a cooling rate of 50 ° C./sec until the heated camshaft passes the austenitizing temperature. A heat treatment method using a high-frequency heating device for a camshaft, comprising: 4. The heat treatment method according to claim 1, wherein in the heating step, the camshaft is heated at 830 to 1030 ° C. for 7 to 90 seconds.