KR20140012306A - Oxy-nitriding brake disk for noise reduction and manufacturing method thereof - Google Patents

Abstract

The present invention relates to an oxy-nitrided brake disk for noise reduction and a manufacturing method thereof, wherein the oxy-nitrided brake disk comprises: a diffusion layer formed inside the base material of the brake disk by nitro-carburizing the base material; a nitrided layer formed on the diffusion layer; and an oxidized layer formed on the nitrided layer by oxidizing the base material of the brake disk. The oxy-nitrided brake disk includes a ground oxy-nitrided layer formed by grinding the entire oxidized layer and a part of the nitrided layer, which are formed by an oxy-nitriding process, thereby reducing noise such as grinding noise generated when a brake pad rubs on a braking surface at the time of braking.

Description

Oxy-nitriding brake disk for noise reduction and manufacturing method

The present invention relates to an oxynitride brake disc with reduced noise and a method of manufacturing the same, and more particularly to grinding the entire oxide layer and a part of the nitride layer of an oxynitrided brake disc in order to improve physical properties such as corrosion resistance. The present invention relates to an oxynitride brake disc in which noise is reduced by processing and a method of manufacturing the same.

The brake disc mounted on the vehicle is a device for decelerating, stopping or maintaining the vehicle while driving.The brake disc is composed of a braking surface that generates a braking force when the brake pad is in close contact, a wheel contact portion that contacts and fixes the wheel, a side portion, and a bent portion. do.

The material of the brake disc is generally gray cast iron. Gray cast iron is gray cast iron when cast iron is injected into the mold and carbon is precipitated in the form of graphite when the cooling rate is slow due to the difference in wall thickness. Gray cast iron is also corroded when exposed to moisture and oxygen in the atmosphere. As a result, the brake disc is usually subjected to a surface treatment in order to prevent the deterioration of durability and aesthetics.

FIG. 1 is a graph showing an oxy-nitriding treatment in the surface treatment method. In particular, the gas oxynitriding treatment is performed on the braking surface of the brake disc to prevent corrosion from being generated even in a long standing condition.

Specifically, the brake disc is first preheated to about 610 ° C. and then nitrocarburizing in ammonia (NH ₃ ), nitrogen (N ₂ ) and carbon dioxide (CO ₂ ) gases for about 250 minutes at this temperature. Perform the process. Through the soft nitriding treatment, a nitrogen diffusion layer is formed inside the brake disc, and a nitride layer is formed on the surface.

Thereafter, the mixture is cooled to about 555 ° C., and then subjected to an oxidation treatment to maintain the temperature by introducing a stream for about 20 minutes. The oxidation layer (Fe ₃ O) is applied to the nitride layer through the oxidation treatment. ₄ ) is formed. Finally, the oxynitride process is completed by the air cooling process, and the diffusion layer, the nitride layer, and the oxide layer form an oxynitride layer.

FIG. 2 is a view showing a brake disc in which an oxynitride layer is formed by an oxynitride process, and FIG. 3 is a cross-sectional view of a portion in which the brake disc of FIG. 2 is cut along a line A-A '.

As shown, a nitrogen diffusion layer 100 is formed on the base material through the soft nitridation treatment. The diffusion layer 100 is similar to the carburized layer and increases the surface hardness of the material and the toughness of the material therein. It serves to improve fatigue resistance, high temperature strength and corrosion resistance.

In addition, there is a softening process nitride layer (Layer Compound) (150) is formed above the diffusion layer 100, by which _{Fe 3 O 4 + Fe 2 -4} N mixed porosity layer and that the co-nitrogen compound layer As the porous layer absorbs the coating solution, the wear resistance and slidability are excellent. In particular, the Fe _{2 -4} N layer has a high hardness of 500 to 1000 Hv, thereby improving corrosion resistance and wear resistance.

In addition, an oxidation layer 160 of Fe ₃ O ₄ , in which oxidation does not proceed any further, is formed by the oxidation treatment, thereby further improving the surface corrosion resistance of the material.

Item sample After finishing (mm) After oxynitride (mm) Amount of change (mm) disk
thickness
Measure
(Thickness: 28mm) One 28.020 28.040 0.020 2 28.020 28.050 0.030 3 28.020 28.040 0.020 4 28.020 28.050 0.020 5 28.020 28.050 0.030

Table 1 shows the changes in the thickness of the brake discs of the five samples according to the oxynitride treatment, and the thickness of the brake disc is increased in the range of 0.020 to 0.030 mm by forming the oxynitride layer.

4 is a view showing a surface of a brake disc braking surface not subjected to oxynitride treatment, and FIG. 5 is a view showing a surface of a brake disc braking surface on which an oxynitride layer is formed by oxynitride treatment.

As shown, the surface of the brake disc braking surface that has not been subjected to oxynitride has a smooth surface without fine projections observed, while the brake disc braking surface that has been subjected to oxynitride treatment has a fine protrusion generated by the oxynitride treatment. It is understood that the branch has a rough surface by the oxynitride layer.

As described above, when the oxynitride is applied to the brake disc, the oxynitride layer having a rough surface is formed due to the fine protrusion, thereby improving physical properties such as corrosion resistance and abrasion resistance, but grinding noise when evaluating actual vehicle braking noise of the oxynitride disc. There was a problem that the noise of the back is increased.

In addition, the surface roughness, disk thickness variation (DTV) and R / O (Run / Out) are deteriorated by the fine protrusion of the oxynitride layer.

In addition, a stick-slip phenomenon occurs between the friction material and the brake disc during braking, so that the friction vibration is introduced into the room through the transmission system.

In particular, there was a problem in that the initial quality index (IQS) and the market evaluation of the vehicle were deteriorated because noise and vibration occurred in the brake operation not only in a long-term inventory vehicle but also in a vehicle used for less than three months.

An object of the present invention for solving the above problems is to include an oxynitride layer that is ground while maintaining the corrosion resistance by grinding the entire oxidation layer and a part of the nitride layer formed by the oxynitride treatment after the oxynitride treatment It is an object of the present invention to provide an oxynitride brake disc with reduced noise and a method of manufacturing the same.

In order to achieve the above object, the oxynitride brake disc of the present invention has reduced noise oxidizes the diffusion layer formed inside the base material and the nitride layer formed on the diffusion layer, the base material of the brake disc by soft-nitriding the base material of the brake disc. An oxynitride-treated brake disc comprising an oxide layer formed on top of the nitridation layer, the oxynitriding brake disc comprising: a ground oxynitride layer formed by grinding the entire oxidized layer and a portion of the nitridation layer formed by oxynitride. It features.

In addition, in one embodiment of the present invention, the ground oxynitride layer is preferably a honed oxynitride layer.

In addition, in one embodiment of the present invention, the honed oxynitride layer is more preferably a honed oxynitride layer for 10 seconds.

In order to achieve another object, in the manufacturing method of the brake disc, roughing the brake disc castings, finishing the roughing brake disc castings, oxynitriding the finished brake disc castings Processing, honing the oxynitride brake disc casting and brushing the honing brake disc casting.

In addition, the oxynitriding may be performed by soft-nitrating the finished brake disc casting product to form a diffusion layer therein and a nitride layer on the diffusion layer, and then oxidizing the nitride layer. It is preferable to form an oxide layer on top.

In addition, the honing may be performed by honing the entire oxide layer and a part of the nitride layer formed by the oxynitride treatment.

In addition, the honing step of the embodiment of the present invention is more preferably honing for 10 seconds.

The oxynitride brake disc according to the present invention includes a ground oxynitride layer, such as honing, to reduce grinding noise and the like caused by the close contact between the brake pad and the braking surface during braking, and a portion of the oxynitride layer remains. Corrosion resistance is maintained.

In addition, there is an advantage of minimizing the abnormal vibration in which friction vibration is transmitted to the room by preventing the stick slip generated during braking.

In addition, it is possible to improve the evaluation of the initial quality index and the like by preventing the noise and tremors generated during the brake operation, and to improve the marketability by preventing the deterioration of market claims related to the brake operation.

1 is a graph showing an oxy-nitriding treatment in the surface treatment method.
2 is a view showing a brake disc in which an oxynitride layer is formed by an oxynitride process.
3 is a cross-sectional view of a portion of the brake disc of FIG. 2 taken along line AA ′.
4 is a view showing the surface of a brake disc braking surface not subjected to oxynitridation treatment.
5 is a view showing the surface of a brake disc braking surface on which an oxynitride layer is formed by oxynitride.
6 is a table showing the composition ratio of a typical gray cast iron brake disc.
7 is a view showing a cross section before etching of a general gray cast iron disk.
8 is a view showing a cross section after etching of a general gray cast iron disk.
9 is a view showing a cross section after etching of an oxynitride treated brake disc.
10 is a table showing surface roughness, disk thickness variation (DTV) and run-out (R / O) according to each process.
11 is a view showing a brake disk after finishing.
12 illustrates a brake disc including an oxynitride layer.
It is a figure which shows the brake disc containing the oxynitride layer processed by honing etc.
14 is a table showing the disk thickness for each processing step of five samples.
15 is a cross-sectional view of a brake disc maximum outer diameter portion including an oxynitride layer.
It is a figure which shows the cross section of the brake disc maximum outer diameter part containing the oxynitride layer processed by honing process.
17 is a cross-sectional view of a brake disc center including an oxynitride layer.
It is a figure which shows the cross section of the brake disc center containing the oxynitride layer processed by honing etc.
19 is a cross-sectional view of a brake disc undercut portion including an oxynitride layer.
It is a figure which shows the cross section of the brake disc undercut part containing the oxynitride layer processed, such as a honing process.
Fig. 21 is a view showing a general disk being mass produced.
FIG. 22 is a view illustrating a brake disc including an oxynitride layer subjected to oxynitridation under outdoor standing conditions for 4 months.
FIG. 23 shows an oxynitride brake disc comprising an oxynitride layer honed in an environmental chamber for four days.
24 is a schematic diagram comparing the manufacturing process of the conventional brake disk and the manufacturing process of the oxynitride brake disk with reduced noise.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

According to an aspect of the present invention, a noise including a ground oxynitride layer formed by performing a grinding process such as a honing process to remove the entire oxide layer and a portion of the nitride layer including the fine protrusions formed by the oxynitride treatment is reduced. It relates to a reduced oxynitride brake disc.

6 is a table showing the composition ratio of a typical gray cast iron brake disc, carbon (C) 3.65% by weight, silicon (Si) 2.1% by weight, manganese (Mn) 0.6% by weight, phosphorus (P) 0.072% by weight, sulfur (S) 0.1 weight percent, chromium (Cr) 0.15 weight percent, molybdenum (Mo) 0.01 weight percent, 0.25 weight percent copper and 0.008 weight percent tin (Sn) and the balance iron.

7 is a view showing a cross section before etching of the ordinary gray cast iron disk, Figure 8 is a view showing a cross section after etching.

As illustrated, the boundary between the brake disc base material 300 and the mounting 310 is smooth before etching, and a protective aluminum foil 320 is formed on the brake disc base material 300 after etching.

On the other hand, Figure 9 is a view showing a cross-section after the etching of the oxynitride brake disk, the nitrogen diffusion layer 100 is generated in the base material by the oxynitride treatment, the nitride layer 150 and the upper portion of the diffusion layer 100 The oxide layer 160 is formed.

In addition, in contrast to the cross section of the general gray cast iron disk, the boundary with the mounting 310 is not smooth and rough as the oxynitride layer is formed by the oxynitride treatment.

Therefore, after finishing and oxynitriding in the manufacturing process of the brake disc, the surface roughness and the disc are removed by removing the entire oxide layer 160 and the part of the nitride layer 150 including the fine protrusions formed by the oxynitride treatment. By improving the thickness variation (DTV) and the run-out (R / O), etc., the noise generated as the brake pad comes in close contact with the brake may be reduced.

At this time, the grinding work (Grinding work) is a kind of cutting process to finish the surface to the desired shape and dimensions, and includes a honing (Honing work) and super finishing (super finishing). In particular, the honing process is a kind of oil stone finishing processing means a precision grinding method using a tool equipped with an oil grindstone called horn, if insufficiently performed, the fine projection of the oxynitride layer is sufficient. Since it is not removed and the effect which this invention expects is not acquired, when it carries out excessively, since the whole nitride layer is removed and the corrosion resistance of a disk falls, it is preferable to carry out about 10 second.

That is, typically, the thickness of the oxide layer 160 formed by the oxynitride treatment is 1 to 2 μm, and the thickness of the nitride layer 150 is 10 to 25 μm, which is removed when the honing treatment is performed for about 10 seconds. The thickness is about 10 μm, and the entire oxide layer 160 and a part of the nitride layer 150 are ground.

10 is a table showing surface roughness, disk thickness variation (DTV) and run-out (R / O) according to each process.

Wherein the surface roughness (Surface Roughness) means the degree of minute unevenness occurs on the surface when the metal surface is finished, the disk thickness fluctuation (DTV) is because the brake surface is worn by the brake pad, the thickness of the disk is changed The run-out is a measure of the inclination of the brake disc with respect to the drive rotation axis, and the difference between the maximum and minimum values of the waveform generated when the brake disc rotates about an arbitrary point. Means.

As shown, the surface roughness increases from the 20s level after finishing to the 30s level by the oxynitride treatment, which means that the surface is rougher by the oxynitride layer having fine protrusions produced by the oxynitride treatment. However, when the honing process was performed for about 10 seconds, both the outer and inner portions of the circumferential and radial directions were lowered to about 8 to 10 s, which is the whole oxide layer including the fine protrusions by the honing process. And part of the nitride layer is removed to make the surface smoother.

In addition, the disk thickness variation increases to 6-7 um by the oxynitride treatment at the 5 μm level after finishing, because the thickness deviation is further increased by the oxynitride layer produced by the oxynitride treatment. However, after the honing process, the thickness was lowered to 3 μm, which means that the thickness of the brake disc became more constant by the honing process.

In addition, the run-out is increased to 13 to 26 μm by the oxynitride treatment at the level of 15 μm after finishing, because the deviation of the waveform is further increased by the oxynitride layer produced by the oxynitride treatment. However, when the honing process was performed for about 10 seconds, the outside and the inside were lowered to 10 μm, which means that the variation of the waveform was reduced.

That is, noise and vibration increase during braking by deterioration of factors such as surface roughness, disk thickness variation, and run-out by the oxynitride layer having fine protrusions by oxynitride treatment. The above factors are improved in the case of including the ground oxynitride layer.

Item Oxynitride layer Honed oxynitride layer Regular disc Grinding noise
(Grinding Noise) 39.6 to 41.0 dB 37.5 to 38.2 dB 37.5 to 38.2 dB Gron noise
(Groan Noise) No occurrence No occurrence No occurrence High speed judder
(Judder) No occurrence No occurrence No occurrence Squill noise
(Squeal Noise) No occurrence No occurrence No occurrence

Table 2 is a table comparing the actual vehicle noise evaluation of the disk including the oxynitride layer, the disk including the oxynitride layer, the honed process and the grinding oxynitride layer.

As shown in Table 2 above, no gron noise, high speed judder and squeal noise occurred in all disks, but in the case of a disk including an oxynitride layer in grinding noise, a noise of 39.6 to 41.0 dB was measured. In the case of including the ground oxynitride layer of 37.5 ~ 38.2 dB noise is measured can be seen that the noise generated from the disk is improved.

11 is a view showing a brake disk after finishing, FIG. 12 is a view showing a brake disk including an oxynitride layer, and FIG. 13 is a view showing a brake disk including a ground oxynitride layer such as honing. .

As shown, the thickness of the brake disk after finishing is 28.020 mm, and an oxynitride layer including a diffusion layer or the like is formed by oxynitriding, so that the thickness of the entire disk is 28.050 mm. After that, a part of the oxynitride layer including the microprojections is removed by honing for about 10 seconds, and the thickness of the entire disc is 28.020 mm again, but since the oxynitride layer of about 15 μm remains, the corrosion resistance of the brake disc maintain.

14 is a table showing the disk thickness for each processing step of the five samples, as shown in the thickness change of about 0.020 ~ 0.030 mm from 28.020 mm to 28.040 ~ 28.050 mm by oxynitride treatment after finishing, about 10 As the thickness of 0.030 mm is reduced by the honing process for a second, a thickness of 28.010 to 28.020 mm is finally formed.

FIG. 15 is a view showing a cross section of a brake disc maximum outer diameter portion including an oxynitride layer, and FIG. 16 is a view showing a cross section of a brake disc maximum outer diameter portion including a ground oxynitride layer such as a honing process. An oxynitride layer having a thickness of 13 to 36 μm is formed by nitriding, but a part of the oxynitride layer is removed by honing for about 10 seconds, and finally includes a honed oxynitride layer having a thickness of 5 to 25 μm. .

17 is a view showing a cross section of a brake disc center including an oxynitride layer, and FIG. 18 is a view showing a cross section of a brake disc center including a ground oxynitride layer such as a honing process. 14 to 40 μm thick oxynitride layer is formed, but a portion of the oxynitride layer is removed by honing for about 10 seconds to finally include a 8 to 23 μm thick honed oxynitride layer.

19 is a view showing a cross section of a brake disc undercut section including an oxynitride layer, and FIG. 20 is a view showing a cross section of a brake disc undercut section including a ground oxynitride layer such as a honing process. 13 to 36 μm thick oxynitride layer is formed, but as a part of the oxynitride layer is removed by honing for about 10 seconds, and finally includes a honed oxynitride layer of 12 to 17 μm thickness.

That is, although the entire oxide layer 160 and a part of the nitride layer 150 are removed by the grinding process such as honing for 10 seconds, particularly around the maximum outer diameter part and the center part, the nitride layer 150 is still present in the entire braking surface. A part of the cavities and the diffusion layer 100 remain to maintain corrosion resistance.

FIG. 21 is a view showing a general disc in mass production, FIG. 22 is a view showing a brake disc including an oxynitride layer subjected to oxynitridation under outdoor standing conditions for 4 months, and FIG. 23 is a honing in an environmental chamber for 4 days. A diagram illustrating an oxynitride brake disc including a machined oxynitride layer (two specimens left and right).

As shown, it can be seen that a similar level of white blue is observed on the braking surface of both the brake disc including the oxynitride layer and the oxynitride brake disc including the honed oxynitride layer. It means that the moisture resistance level of the brake disc is maintained even if the entire oxidation layer and part of the nitride layer are removed by the processing.

In another aspect, the present invention is directed to a method of manufacturing the oxynitride brake disc with reduced noise.

24 is a schematic diagram comparing the manufacturing process of the conventional brake disk and the manufacturing process of the oxynitride brake disk with reduced noise.

In general, the machining of brake discs is carried out to satisfy the dimensions and tolerances for the flatness and mutual parallelism of the discs mounted on the brake system, which can affect the friction characteristics of the friction material with the counterpart material during braking depending on the accuracy of the dimensions. It is really a field that requires processing.

That is, as shown in the upper part of Fig. 24, in the prior art, the rough grinding (Rough Grinding) processing for rough machining of the brake disc castings, and then after the finishing (Finishing) processing for smooth processing, the surface is refined to fine powder Grinding is a finishing method, in which roughing is about 1 μmRa or more, finishing is about 0.5 to 0.2 μmRa, and grinding is precisely less than roughness. As such, the reason why the machining process is divided into several stages is to smoothly sequentially polish the surface roughness of the disk by adjusting tool conditions. Then, after oxynitriding, brushing is performed to remove foreign matters generated by processing.

Therefore, in the conventional processing method, as the oxynitride layer having the fine protrusions formed by the oxynitride treatment is present as it is, there is a problem that noise such as grinding noise occurs when evaluating braking noise.

In order to improve this, as shown in the lower part of FIG. 24, the machining method according to the present invention roughs the cast-iron product, and then finishes the finishing process, and then the acid rather than the conventional grinding process. Nitriding treatment is carried out first. Then, the entire oxide layer formed by the oxynitride treatment and a part of the nitride layer are subjected to a grinding process such as a honing process, and then brushed to remove contaminants such as powder and dust.

At this time, if the honing process is insufficiently performed, the microprojections of the oxynitride layer may not be sufficiently removed to obtain the effect expected by the present invention. It is preferable to carry out about 10 seconds.

That is, as described above, the thickness of the oxide layer 160 formed by the oxynitride process is typically 1 to 2 μm and the thickness of the nitride layer 150 is 10 to 25 μm, and the honing process is performed for about 10 seconds. In this case, the thickness removed is about 10 μm, and the entire oxide layer 160 and a part of the nitride layer 150 are ground.

Therefore, unlike the conventional processing method, after the oxynitriding treatment is performed by grinding processing such as honing processing, the brake pad is in close contact during braking by removing a part of the oxide layer 160 and the nitride layer 150 including fine protrusions. The noise and vibration, such as the grinding noise generated accordingly, are reduced.

As described above, the oxynitride brake disc according to the present invention is removed from the conventional oxynitride brake disc by removing a part of the oxide layer 160 and the nitride layer 150 including the fine protrusions essentially accompanied by the oxynitride treatment of the braking surface. Noise, such as grinding noise, is reduced, and part of the oxynitride layer remains, so that the corrosion resistance is better than that of a general disk, and thus the productability can be greatly improved.

100: diffusion layer 150: nitride layer
160: oxide layer
300: brake disc base material 310: mounting
320: aluminum foil

Claims (7)

A diffusion layer 100 formed inside the base material by soft-nitriding the base material of the brake disc and a nitride layer 150 formed on the diffusion layer 100;
An oxidation layer 160 formed on the nitride layer 150 by oxidizing a base material of the brake disc; In the oxynitrided brake disc comprising:
The noise reduction oxynitride brake disc including a grinding-processed oxynitride layer formed by grinding all the said oxide layer (160) formed by the oxynitride process, and a part of the nitride layer (150).
The oxynitride brake disc of claim 1, wherein the ground oxynitride layer is a honed oxynitride layer.
3. The noise oxynitride brake disc of claim 2, wherein the honed oxynitride layer is a honed oxynitride layer for 10 seconds.
In the manufacturing method of the brake disc,
Roughing the brake disc casting;
Finishing the roughed brake disc casting;
Oxynitrating the finished brake disc casting;
Honing the oxynitrided brake disc casting;
Brushing the honed brake disc casting; Method for producing a oxynitride brake disc with reduced noise comprising a.
The method of claim 4, wherein the oxynitride treatment,
The nitrided brake disc casting is soft nitrided to form a diffusion layer 100 therein and a nitride layer 150 on the diffusion layer 100, and then oxidizes an oxide layer on the nitride layer 150. 160) a method for producing a noise-oxygenated brake disc with reduced noise.
The method of claim 5 wherein the honing process,
Honing the entire oxide layer (160) formed by the oxynitride process and a portion of the nitride layer (150) characterized in that the manufacturing method of the oxynitride brake discs with reduced noise.
7. A method according to any one of claims 4 to 6, wherein the honing is honing for 10 seconds.

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