JPH05157134A - Disk brake rotor - Google Patents

Abstract

PURPOSE:To provide a disk brake which is excellent in wear resistance and ensures a given friction factor. CONSTITUTION:A disk brake rotor comprises a rotor body 1 having a slide surface 10 formed of a base material being cast iron having flake graphite and narrow cured layers 3 formed in a radiation pattern and molten through irradiation with laser beams and cooled and exposed to the slide surface 10, and a ratio of the areas of the cured layers to that of the whole of the slide surfaces 10 is 10-40%. The cured layer 3 comprises a chilled layer 3a formed of cementite being main texture and formed through solidification of molten liquid and an annealed layer 3b formed below the chilled layer 3a and of martensite being main texture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc brake rotor having a sliding surface having a cast iron with graphite as a base material.
This disc brake rotor can be applied to, for example, an automobile.

[0002]

2. Description of the Related Art Conventionally, as a disc brake rotor, there has been known a rotor body made of cast iron (gray cast iron) having a sprayed coating formed on the surface thereof to form a sliding surface (Japanese Patent Laid-Open No. 62-62). -88828). In this case, the thermal spray coating adheres due to the anchoring effect, and peeling of the thermal spray coating occurs when it is subjected to rapid heating and rapid cooling (such as going down a mountain path and entering a pool of water). Further, cracks are generated in the thermal spray coating even if the peeling does not occur. When such a phenomenon occurs, uneven wear of the brake,
Breaking vibration etc. occurs and normal braking action is not achieved. In some cases, different materials such as copper-based materials and hard particles are compounded in the thermal spray coating. In this case, a local battery may form between the materials in a corrosive environment, and corrosion may occur. There is. When this occurs, cracking and peeling of the thermal spray coating will occur as described above.

The reason why cracks are likely to occur in the sprayed coating is considered to be as follows. That is,
Since the thermal spraying is generally performed in the atmosphere, the surface of the molten particles is oxidized during the flight until they collide with the material. for that reason,
Oxides are present in the formed spray coating (eg,
Fe ₃ O ₄ ) When heating or cooling is repeated on such a thermal spray coating, tensile and compressive stress is generated in the thermal spray coating.
Here, the above-mentioned oxide generally has extremely small elongation,
Since it is hard and brittle, stress concentrates on this portion, and cracks originate from this oxide layer. When such a crack is generated, rust is likely to infiltrate through the crack, leading to peeling of the thermal spray coating.

Further, as a disk braker, there is known a disk braker in which a hardened layer is formed by electron beam irradiation or laser beam irradiation (Japanese Patent Laid-Open No. 63-31).
No. 2527). The base material of the disc braker according to this publication is carbon steel containing no graphite.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and an object of the present invention is to provide a disc brake rotor having excellent wear resistance and capable of ensuring a required friction coefficient.

[0006]

DISCLOSURE OF THE INVENTION The present inventor has conducted extensive studies on a disc brake rotor, and the rotor body is made of cast iron, and the area ratio of the hardened layer on the sliding surface is 1
If 0-40% and the remaining surface of the sliding surface is formed of a cast iron surface containing graphite, the ratio between the hardened layer and the cast iron surface becomes appropriate, and the wear resistance is excellent and the required friction coefficient can be secured. That is, the present invention has been completed.

That is, the disc brake rotor according to the present invention has a rotor body having a sliding surface which is made of cast iron with graphite as a base material, and is rapidly heated by irradiation with a high-density energy beam.
It is characterized in that it is composed of a narrow hardened layer that is rapidly cooled and has a predetermined pattern exposed on the sliding surface, and the area ratio of the hardened layer on the sliding surface is 10 to 40%. ..

The cast iron forming the rotor body is typically flake graphite cast iron or spheroidal graphite cast iron. The composition of cast iron can be set as appropriate, but for example, the amounts of C and Si are C: 3.1.
˜3.6%, Si: 1.9-2.4%. The hardened layer is exposed to the sliding surface by being rapidly heated and cooled by the irradiation of the high-density energy beam. The hardened layer can be composed of a chill layer formed by solidification of a molten liquid generated by irradiation with a high-density energy beam, and a quenching layer of a non-melted portion located below the chill layer and thermally affected by the beam. The main structure of the chill layer is generally cementite. The main structure of the hardened layer is generally martensite. If the beam does not melt by simply heating and cooling the metal part of the sliding surface of the rotor,
The hardened layer is generally composed of a hardened layer without a chill layer. The grain size of the structure of the chill layer and the quenching layer becomes fine due to rapid heating and rapid cooling as compared with other heating / cooling means.

The hardened layer has a predetermined pattern shape. The pattern shape may be a radial pattern in which the hardened layer 3 is radially extended from the center as shown in FIG. 1, or may be a spiral pattern in which the hardened layer 3 is swirled as shown in FIG. Alternatively, as shown in FIG. 6, the hardened layers 3 having different radii may be formed in multiple concentric circles, or, as shown in FIG. 7, the hardened layers 3 may be formed in multiple radial patterns and concentric circles. The hardened layer 3 may be formed by a pattern, or the hardened layer 3 may have a geometric pattern as shown in FIG. 8, or the hardened layer 3 may be scattered as shown in FIG. Although it is not shown, it may be a dot pattern in which the hardened layer is formed in a net shape, a grid pattern in which the hardened layer is formed in a grid pattern, or another pattern, which is not shown.

Incidentally, the advantage of discharging the abrasion powder generated at the boundary surface between the sliding surface of the rotor and the pad as the mating material is that
It is considered to be a radial pattern, a spiral pattern, or a dot-like pattern. The high-density energy beam is typically a laser beam or an electron beam. A CO ₂ laser or a YAG laser can be used as the laser beam. In the case of a CO ₂ laser, the laser processing conditions can be set as follows, for example.
Output: 1-5KW, power density: 5-25KW / c
m ² , beam diameter: 0.5 to 4 mm, moving speed: 10 to 4
It can be set to 00 mm / min.

The width and depth of the hardened layer can be appropriately selected depending on the sliding conditions, the material of the mating material and the like. For example, the width is 0.5.
The depth can be about 4 mm and the depth is about 0.3 to 1.5 mm. The hardened layer may be formed by moving either the rotor or the laser oscillator. The cured surface may be used as it is, or may be used after polishing.

[0012]

In the disc brake rotor according to the present invention,
Since the area ratio of the hardened layer on the sliding surface is 10 to 40% and the remaining surface of the sliding surface is formed by the cast iron surface containing graphite, the ratio of the hardened layer and the cast iron surface becomes appropriate, and the disk Both the wear resistance and the friction coefficient required for the brake rotor are secured.

[0013]

【Example】

(Embodiment 1) Embodiment 1 of the present invention will be described with reference to FIG. A cast iron (FC20) rotor body 1 having an outer diameter D1 of 240 mm and an inner diameter D2 of 140 mm (a sliding surface of the pad of about 50 mm) was used. The rotor body 1 has a central depression 1a, a central hole 1b, and a small hole 1c. Sliding surface 1 of the rotor body 1
0 is irradiated with the laser beam L through the condenser lens system 5,
The surface layer of the sliding surface 10 was partially rapidly heated and melted. When the laser beam L is moved, the melt is rapidly cooled by heat transfer to the rotor body 1. As a result, a large number of hardened layers 3 were formed on the sliding surface 10 of the rotor body 1 in a radial pattern as shown in FIG. In this example, the laser irradiation conditions are as follows. That is, laser type: CO ₂ laser,
Output: 2 kW, power density: 10 W / cm ² , beam diameter: 2 mm, laser beam moving speed: 200 mm / m
is in.

As shown in FIG. 3 (a cross section taken along the line AA in FIG. 1), which is a schematic cross-sectional view, the hardened layer 3 is mainly a chill layer 3a formed by solidification of a melt produced by irradiation with a laser beam.
And a quenching layer 3b located below the chill layer 3a and unheated by the laser beam. The hardened layer 3 had a width of about 3 mm and a depth of about 0.7 mm. The width and depth of the hardened layer 3 can be easily adjusted by the irradiation conditions of the laser beam.

The cross-sectional structure near the hardened layer 3 (A in FIG. 1)
A photograph of (A cross section) is shown in FIG. In FIG. 4, the magnification is 50 times and the etching is performed with a 3% nital solution. In FIG. 4, the center is a chill layer, a quenching layer is formed below the chill layer, and the lower part has a base material structure having flake graphite. The boundaries between the chill layer, the quenching layer, and the base metal are relatively clear. The chill layer is white pig iron and consists of cementite. There are black dots inside the chill layer, which are considered to be gasified pores of graphite. The quenched layer consists of martensite and retained austenite. Flake graphite is deposited on the quenched layer. The base material contains pearlite, ferrite, and flake graphite. The hardness of the chill layer is HV.
850, the hardened layer was HV700, and the base material was HV200.

Further, in Example 1, the interval angle θ of the hardened layer 3 formed in the radial pattern was changed to 4 to 40 ° to change the number of hardened layers 3, and thereby the area ratio of the hardened layer 3 was changed. Then, a friction test was conducted by applying a pad to the sliding surface 10 of each rotor, and the relationship between the amount of wear of the sliding surface 10 and the friction coefficient was investigated. The test conditions are: pad: low carbon steel, vehicle speed: 130 km / h → 0, hydraulic pressure: 60 kgf / c
m ² , braking frequency: 500 times. The relationship between the area ratio of the hardened layer 3, the amount of wear of the sliding surface 10 and the coefficient of friction μ is shown in FIG. In FIG. 2, the ∘ mark indicates the amount of wear in Example 1, and the ● mark indicates the friction coefficient in Example 1. In Fig. 2, connecting the ○ marks gives a characteristic line A indicating the amount of wear.
When the marks are connected, a characteristic line B indicating the coefficient of friction is obtained. As can be understood from the characteristic line A of FIG. 2, the area ratio of the hardened layer 3 is 10
If it is more than 0.1%, the amount of wear of the rotor itself reaches almost equilibrium, and the wear resistance of the rotor is good. Further, as can be understood from the characteristic line B, it was found that the friction coefficient μ drastically decreases when the area ratio of the hardened layer 3 exceeds 40%. That is, as shown in FIG. 2, the optimum range of the area ratio of the hardened layer 3 is the range indicated by H where the area ratio of the hardened layer 3 is 10 to 40%. Further, since the chill layer of the hardened layer 3 has good corrosion resistance, it is advantageous for improving the durability of the brake rotor.

(Embodiment 2) A rotor body 1 having the same shape and material as in Embodiment 1 is used, and as shown in FIG. 6, a hardened layer 3 is formed on a sliding surface 10 of a rotor body 1 in a concentric pattern. Formed. In this case as well, the number of hardened layers 3, that is, the area ratio was changed in the same manner, and the relationship with the frictional characteristics was examined. In FIG. 2, Δ indicates the amount of wear in Example 2, and ▲ indicates the coefficient of friction in Example 2. The triangle marks are plotted along the characteristic line A, and the triangle marks are also plotted along the characteristic line B, and the optimum range H in Example 2 is effective. That is, also in the pattern according to Example 2 shown in FIG. 6, the area ratio of the hardened layer 3 is 1
It was confirmed that both the wear amount and the friction coefficient μ were good in the range of 0 to 40%.

(Embodiment 3) Using the rotor body 1 having the same shape and the same material as those of Embodiment 1, as shown in FIG. 7, the radial pattern according to Embodiment 1 and the concentric pattern according to Embodiment 2 are used. A cured layer 3 was formed by combining and. In this case as well, the area ratio of the hardened layer 3 was changed in the same manner and the relationship with the frictional characteristics was investigated. In FIG. 2, the symbol ⋄ indicates the amount of wear in Example 3, and the symbol ◆ indicates the coefficient of friction in Example 3. Example 2
In the case of, the ◇ mark is plotted along the characteristic line A, and
The mark is also plotted along the characteristic line B, and the optimum range H in Example 3 is effective. That is, even in the pattern according to Example 3 shown in FIG. 7, the area ratio of the hardened layer 3 is 10 to 4
At 0%, it was confirmed that both the wear amount and the friction coefficient μ were good.

(Comparative Example 1) Using the rotor body 1 having the same shape and the same material as in Example 1, the same friction test was performed without laser hardening treatment, that is, without forming the pattern of the hardened layer 3. In FIG. 2, the star marks show the amount of wear in Comparative Example 1, and the star marks show the friction coefficient in Comparative Example 1. In this example, the friction coefficient μ is relatively good, but it can be seen that the wear amount is very large as shown by the star.

(Comparative Example 2) A rotor body 1 having the same shape and material as in Example 1 was used, and a sprayed coating (Fe-Cr alloy + Cu alloy + hard particles) was formed by plasma spraying by a conventional method. Formed and finish the sprayed coating to a thickness of 300 μm,
Was tested under the same conditions. In FIG. 2, □ indicates Comparative Example 2
Shows the amount of wear, and the mark ■ shows the friction coefficient in Comparative Example 2.

As shown by □ marks and ■ marks, the wear resistance and the friction coefficient μ were almost the same level as in Examples 1 to 3, but the surface after the test according to Comparative Example 2 was Hair cracks that did not occur in Nos. 1 to 3 were generated. The origin of the hair crack was the oxide layer. The cross section of the thermal spray coating at the hair crack generation portion is shown in FIG. (Evaluation) Steel fibers, hard particles, etc. are dispersed in the pad, which is the mating member of the rotor. Due to the presence of these, in Comparative Examples 1 and 2, the cast iron (about HV200) forming the sliding surface of the rotor body 1 is worn. When the material is softened by the high temperature caused by the frictional heat, the wear is further increased. On the other hand, in Examples 1 to 3, since the hardened layer 3 of HV700 to 800 is formed on the sliding surface 10 by laser beam irradiation, the wear resistance of the rotor is increased, and the attack from the mating material is increased. It is less likely to be worn.

Further, the friction coefficient μ of the sliding surface 10 having the hardened layer 3 is considered as follows. That is, a great feature of cast iron is that graphite is dispersed. In the case of cast iron, since such graphite is originally present, the friction coefficient μ as the disc brake rotor is sufficiently secured. The reason why the friction coefficient μ of the disc brake rotor is sufficiently secured is considered to be that the graphite of cast iron is carved into a concave shape when sliding, and the friction coefficient μ is increased due to the edge effect caused by the concave shape. ing.
By the way, as described above, in order to improve the wear resistance of the rotor, the hard layer 3 is required by laser beam irradiation.
The area directly hit by the laser beam is chilled by the laser beam irradiation, and the graphite disappears. Therefore, from the viewpoint of ensuring the friction coefficient μ, it is disadvantageous that the hardened layer 3 exists too much and the graphite disappears too much. Therefore, in Examples 1 to 3 according to the present invention, the wear resistance is shared by the hard layer 3 and the required friction coefficient μ is secured by other cast iron materials. The area ratio of the hardened layer 3 is 10-40% in the just appropriate ratio.

In the disc brake rotor, the main cause of cracks on the surface of the sliding surface is that tensile stress acts on the surface due to thermal stress. In this regard, in this embodiment, the hardened layer 3b of the hardened layer 3 formed by laser beam irradiation expands in volume due to martensite transformation, although the expansion amount is somewhat absorbed by the graphite contained in the hardened layer 3b. Therefore, the quenching layer 3b has an appropriate compressive residual stress. Therefore, it is effective in suppressing cracks because it becomes resistant to the tensile stress that is the main cause of cracks. Therefore, in Examples 1 to 3 according to the present invention,
It is possible to avoid and reduce cracking at the boundary between the base material of the rotor body 1 and the hardened layer 3.

[0024]

The disc brake rotor according to the present invention is excellent in wear resistance and can secure a required friction coefficient. Further, according to the disc brake rotor of the present invention, an appropriate compressive residual stress remains in the hardened layer forming the hardened layer, which is advantageous in preventing cracks from occurring.

[Brief description of drawings]

FIG. 1 is a perspective view showing a state in which a laser beam is applied to a sliding surface of a disc brake rotor.

FIG. 2 is a graph showing the relationship between the area ratio of the curing rate, the amount of wear, and the coefficient of friction.

FIG. 3 is a cross-sectional view schematically showing a cross section near a cured layer.

FIG. 4 is a micrograph showing a metal structure in the vicinity of a hardened layer.

FIG. 5 is a perspective view of another example showing a state in which a laser beam is applied to the sliding surface of the disc brake rotor.

FIG. 6 is a plan view showing another pattern of the cured layer.

FIG. 7 is a plan view showing another pattern of the cured layer.

FIG. 8 is a plan view showing another pattern of the cured layer.

FIG. 9 is a plan view showing another pattern of the cured layer.

FIG. 10 is a micrograph showing a metal structure in the vicinity of a sprayed coating according to a comparative example.

[Explanation of symbols]

 Reference numeral 1 is a rotor body, 10 is a sliding surface, and 3 is a hardened layer.

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[Procedure amendment]

[Submission date] December 2, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

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Claims (1)

[Claims] 1. A rotor body having a sliding surface made of cast iron with graphite as a base material, and a thin pattern having a predetermined pattern exposed on the sliding surface by being rapidly heated and quenched by irradiation of a high-density energy beam. A disc brake rotor comprising a hardened layer having a width, and the area ratio of the hardened layer on the sliding surface is 10 to 40%.