JPH05279770A - Brake disk for rolling stock - Google Patents

Abstract

PURPOSE:To obtain a brake disk applicable to rolling stock of higher speed than heretofore. CONSTITUTION:This brake disk can be produced by casting a material where an Al-Si alloy containing 6-13% silicon is used as base phase and dispersion strengthening is done by uniformly blending silicon carbide of 3-50mum grain size with the base-phase metal by 5-30wt.%. Because silicon is contained in the molten metal, the added silicon carbide can be prevented from decomposing and forming into aluminum carbide. As a result, the deterioration in the flowability of molten metal during the pouring of molten metal can be prevented. By this method, the nondefective brake disk of complicated shape can be obtained without deteriorating castability. Even if the initial speed of braking of rolling stock is increased, friction characteristics at a level practically equal to that of the conventional brake disk can be maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brake disc for railway vehicles, and more particularly to a brake disc for high speed vehicles.

[0002]

2. Description of the Related Art For example, J. For the brake discs used for R Shinkansen vehicles, low alloy cast iron has been adopted exclusively for a long time through research and development at the time of its founding. This special cast iron is commonly called NCM cast iron, and the cast iron component contains nickel: 1.0 to 2.0, chrome: 0.3
.About.0.6%, molybdenum: 0.3 to 0.5% of an additive metal is mixed, and the matrix is a pearlite phase strengthened by solid solution of these mixed metals. It consists of a structure in which short graphite is deposited like a caterpillar. What is particularly required as a brake disc for a railroad vehicle is that it has friction characteristics that do not change substantially during normal stop or emergency stop, that is, when the vehicle speed at the moment of braking is high speed or low speed, It has the strength and abrasion resistance to withstand a large pressing force applied by braking at high speed, and withstands this even when the temperature of the sliding surface rises momentarily, and the progress of thermal cracks is extremely slow. There is an important requirement.

In this respect, in cast iron having a pearlite phase strengthened by the solid solution of the additive alloy as a parent phase, graphite precipitated on the sliding surface of the brake acts as a kind of lubricant and has high wear resistance. Since it also plays a role of a kind of cushioning material that absorbs deformation due to heat, it is widely adopted as a brake disc material having excellent characteristics that cannot be obtained by other metal materials. Among these, the friction characteristics mentioned above,
That is, the initial speed at the moment of braking is high (for example, 2
Even at 40 km / h, low speed (for example, 30 km / h)
Even in the case of h), since the material has the characteristic that the coefficient of friction is almost unchanged, it is the main reason why it is given a high evaluation by being distinguished from other materials.

However, recently, the speedup of the Shinkansen is J. It became the technical main goal of each R company, and the vehicle that was operating at a maximum of about 240 km / h was 300 km /
Development races for h have become more intense, and along with this, it has become difficult for conventional NCM cast iron to withstand the harsh conditions of use for brake discs attached to vehicles, and the development of new materials for brake discs has become difficult. The situation is urgent. There are two major trends in the direction of development, one of which is closely related to two or more materials, such as composite materials, such as a material made by laminating special cast iron with wear resistance based on steel. It is designed to be able to withstand harsh conditions by stacking and utilizing the advantages of each other. However, the biggest problem is that composite materials are generally troublesome to manufacture, have low production efficiency, and are expensive and bulky.

Another development direction is to convert the material itself from low alloy cast iron to another type. It is known that forged steel is used for the purpose of improving the mechanical strength, but it is easy to see from the essence of the material that wear resistance does not reach that of conventional cast iron. I can imagine. Contrary to this, the idea of using light metal mainly composed of aluminum has emerged as the most effective means for reducing the weight of a vehicle, and some proposals have already been published.

Japanese Unexamined Patent Publication Nos. 25-25538 and 3
Japanese Patent Publication No. 47945 is an example of this, and looking at the latter, it is an aluminum composite in which ceramics are dispersed and strengthened in an aluminum-based mother phase, and specifically, an Al-Mg alloy is used as an aluminum metal mother phase. Also, as ceramics, alumina (Al
₂ O ₃ ) or silicon carbide (SiC), respectively, are disclosed as embodiments. The reason why the Al-Mg alloy is selected as the matrix phase is that the strength reduction due to frictional heat is small. In addition to the improvement of wear resistance, it is explained that the effect of the addition of ceramics is to counteract the phenomenon that the aluminum of the base metal is heated to the point of being melted and seized due to the rapid rise of the surface temperature.

[0007]

Among the aluminum-based alloys, the Al-Mg alloy is a material that is relatively frequently used in many fields. However,
Considering the case of mixing and dispersing ceramics in an Al-Mg alloy as a mother phase, when silicon carbide powder is applied, silicon in silicon carbide reacts with molten aluminum to form aluminum carbide. However, this aluminum carbide has the property of significantly impairing the fluidity of the molten metal, which is a major obstacle to castability. On the other hand, there are various shapes of brake discs, but the common point is that the heat generated during braking is quickly dissipated to reduce the thermal shock on the sliding surface. Basically, a large number of ribs are provided radially in the circumferential direction, and the abutment portion of the center hole that is externally fitted to the axle often has a large number of projections for adjustment. It can be said that one of the products with a complicated shape and difficult to cast is that the basic shape of the whole is composed of a relatively thin plate thickness over a large surface area. There is a problem that it is difficult to obtain a non-defective product even if a molten metal having poor fluidity is cast into a place where such a difficult condition exists.
Aluminum alloy casting is susceptible to oxidation during casting of molten metal, and oxides tend to be caught in the molten metal and cause defects.However, if the flow of molten metal during casting is poor, this tendency is spurred and conditions are met. It gets worse. The die-casting method is widely used for casting aluminum alloys, but regardless of the casting method, if the temperature of the molten metal is raised to improve the flow of the molten metal, the reaction of the aluminum carbide described above is further promoted and the molten metal flow is increased. Inviting a vicious circle to make it worse.

In the prior art shown here, Al--Mg
When an Al-Mg alloy is selected from the alloys having the alloy as the matrix phase, the obstacles when the ceramics dispersed therein are silicon carbide are as described above. No problem occurs. However, alumina generally has poor wettability with the molten metal, and it is considered quite difficult to produce a cast product in which the alumina is uniformly dispersed in the matrix. That is, in this conventional technique, even if the suitability of a brake disc made of a material is recognized, it is currently difficult to mass-produce it industrially, which is a major factor that hinders its practical use.

In order to solve the above-mentioned problems, the present invention has excellent castability even when silicon carbide is selected as the ceramic, and easily obtains a good product. Moreover, the friction characteristics required for a vehicle brake disc are better than those at present. It is an object of the present invention to provide a material capable of maintaining at least a level substantially equal to that of conventional NCM cast iron even under a high-speed braking condition.

[0010]

A vehicle brake disc according to the present invention is an Al-Si containing 6 to 13% silicon.
The above problem was solved by uniformly blending silicon carbide having a grain size of 3 to 50 μm in an amount of 5 to 30% by weight with respect to the metal of the parent phase by using an alloy as a parent phase and strengthening the dispersion.

[0011]

[Function] Aluminum containing silicon is also applied to various applications as a light metal product.
When silicon carbide is added in the molten state of the alloy, the decisive difference from the case where the molten metal is an Al-Mg alloy is that since the molten metal contains silicon, silicon carbide decomposes to form free silicon. It is to prevent it from becoming aluminum carbide. This is a difference that can be inferred even considering the equilibrium relationship between the metallurgical reaction energies of silicon and aluminum in the molten state.Since silicon carbide maintains its molecular structure as it is and forms one independent phase, And the silicon in the molten metal crystallizes a binary eutectic with the aluminum during the solidification process to form a mother phase. That is, since the generation of aluminum carbide that hinders the fluidity of the molten metal is significantly suppressed, it is possible to obtain a good product having no defects even when cast into a mold of a brake disc having a complicated shape with less loss of castability.

Since this brake disc is mainly intended for high-speed railways among railroad vehicles, the content of silicon carbide must be at least 5%, and if it is less than this, the friction and wear characteristics will be deteriorated. It is not suitable for sudden sliding action from high speed such as braking. In addition, the problem of seizure due to rapid temperature rise has not been solved, which is unsuitable. However, there is a restriction on the mechanical strength as a product in the proportion of addition as an independent powder that is uniformly dispersed in aluminum. If the content of silicon carbide exceeds 30%, the castability deteriorates and the workability of the brake disc deteriorates. Or, a remarkable increase in brittleness is observed, resulting in loss of suitability as a brake disc. On the other hand, as the particle size of silicon carbide, a powder in a relatively wide range can be applied.
It is practical to appropriately select from the particle size of ˜50 μm in consideration of the size of the brake disc and the usage conditions. It has been confirmed in the examples described below that the particle size range of 10 to 30 μm is most preferable.

[0013]

EXAMPLE A brake disc for a vehicle, in which AC4CH (Al-Si alloy) defined in JIS was used as a matrix and dispersion-reinforced with silicon carbide powder having a particle size of 3 to 50 μm, was manufactured. That is, the shape and size are the same as those of the brake discs currently operating as actual vehicles on the Tokaido Shinkansen, and 10% silicon carbide is added to the above-mentioned mother alloy.
And 20% were compounded and cast. In order to confirm the characteristics as a brake disc, the brake evaluation tester applied to the conventional brake disc was used, and the non-asbestos fiber-containing resin type was used as the friction partner. The test conditions are the initial braking speed of 30, 120,
170, 240, 270 km / h, the pressing force on the sliding surface is 1400 kgf × 2, and the moment of inertia is wheel diameter 9
168.6kgf in consideration of the mechanical loss of the tester in the value obtained with 10mm and wheel weight of 8000kgf
・ Sm and the average coefficient of friction was used as the measurement item. The results are shown in Table 1.

[0014]

[Table 1]

As is clear from the results of this embodiment, even if the initial braking speed is varied from a low speed to a planned ultra-high speed over a wide range, the average friction coefficient remains within a certain numerical range. , Suggests that it responds stably to changes in braking force. In the accuracy test for the current Shinkansen brake disc (NCM cast iron), the design parameters are calculated based on this average friction coefficient of 0.25 to 0.30, so it is faster than the actual vehicle. Staying within the bounds clearly illustrates that it can be applied to future high-speed vehicles.

[0016]

As described above, the brake disc for a vehicle according to the present invention maintains the friction characteristics which do not substantially change over a wide range of the initial braking speed of the vehicle from high speed to low speed.
It is extremely lightweight and has excellent compatibility as a brake disc for ultra-high-speed vehicles currently under development. Moreover, since it is composed of a metallurgically stable component, it is endowed with good castability, and has an advantageous characteristic that a good product can be mass-produced regardless of a brake disc having a complicated shape.

Claims (1)

[Claims] 1. An Al—Si alloy containing 6 to 13% of silicon as a mother phase, and silicon carbide having a grain size of 3 to 50 μm is uniformly blended within a range of 5 to 30% by weight with respect to the mother phase metal to strengthen dispersion. Brake discs for railway vehicles characterized by the above.