JP2008069806A - Brake disk for rolling stock - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance durability by suppressing influences of a white layer produced due to rapid cooling after austenitization of a sliding surface and of residual stress generated by partial plastic deformation of a brake disk during braking. <P>SOLUTION: A steel brake disk 1 for a rolling stock includes a slide part 1b circumferentially keeping fins 1c at established intervals on the back of a plate part taking the surface as a slide surface 1ba and a fastening part 1a with a wheel 2 on the inner peripheral side of the slide part 1b. In this case, the thickness t2 of the radial center part 1baa of the slide surface 1ba between fins 1c of the slide part 1b is made larger than the thickness t3 of the inner peripheral edge and outer peripheral edge of the slide surface 1ba. As a result, the influences of a white layer and of residual stress generated on the slide surface can be suppressed, so that the durability to a slide surface crack is enhanced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a brake disk for a railway vehicle having an inner periphery fastening structure mainly for the purpose of suppressing cracks generated on a sliding surface of the brake disk for a railway vehicle.

  Block brakes, drum brakes, disk brakes, and the like are used as braking devices for land transportation machines such as railway vehicles, automobiles, and motorcycles. In recent years, disk brakes have come to be used with increasing speed and size of vehicles.

  A disc brake is a device that obtains a braking force by friction between a brake disc and a brake lining. Usually, a braking force is obtained by pressing a brake lining against a sliding surface of a donut-shaped disc-like disk attached to an axle or a wheel by a bolt, and the speed of the vehicle is controlled by braking the rotation of the axle or the wheel. The disk-shaped disc having this sliding surface is called a brake disc.

  Among these brake discs, railcar brake discs include a side disc and a shaft mount disc. Among these, the side disc is a brake disc fastened to the side surface of the wheel, and the shaft mount disc is a brake disc fastened to the axle. Hereinafter, in this specification, the term “brake disk” refers to both the side disk and the shaft mount disk.

  FIG. 10 shows the shape of a conventional rail car side disk, (a) is a radial-circumferential plan view showing 1/4 of a brake disk, and (b), (c) are fin cross sections and fins, respectively. It is radial direction-axial direction sectional drawing which shows the cross section of an intermediate part.

  As shown in FIG. 10, the brake disc 1 is generally composed of a sliding portion 1b having a sliding surface 1ba on the surface side and a fastening portion 1a having a fastening hole 1aa for fastening to a wheel. Further, fins 1 c are provided on the back side of the sliding surface 1 ba of the brake disc 1.

  FIG. 11 is a radial-axial cross-sectional view schematically showing a state in which a conventional railway vehicle brake disc is attached to a wheel. As shown in FIG. 11, the brake disc 1 is fastened to both side surfaces of the wheel 2 by bolts 3 and nuts 4 that are fastening members, and is attached to rotate integrally.

  A brake lining 5 that is movable in the direction of the sliding surface is attached to a position facing the sliding surface 1ba of the brake disc 1, and at the time of braking, the brake lining 5 moves to the brake disc 1 side and the wheel 2 The vehicle is stopped by braking the rotation of the axle through the wheels 2 by this frictional force.

  By the way, in a high-speed railway vehicle such as the Shinkansen, the rotational speed and inertial force of the brake disk are very large, so that the temperature increase of the brake disk during braking is significantly increased. For this reason, a great thermal stress is generated in the brake disc, and the occurrence and propagation of a crack on the sliding surface (hereinafter also referred to as a sliding surface crack) is a problem.

Conventionally, in order to improve durability against a sliding surface crack caused by a great thermal stress generated in a brake disk, conventionally, the thermal stress generated during braking is simply made uniform (Patent Document 1) and suppressed. The disk shape has been improved for the purpose of (Patent Document 2).
JP 2000-130481 A JP 2004-316829 A

  In other words, the technique disclosed in Patent Document 1 aims to prevent thermal fatigue and cracks generated on the sliding plate of the brake disk during braking. Specifically, as shown in FIG. 12, the temperature distribution is constant as a whole by gradually increasing the thickness of the plate portion of the sliding portion 1b from the outer peripheral portion 1bc side to the inner peripheral portion 1bb side. Thus, the thermal stress generated in the sliding portion 1b is made uniform, and the occurrence of thermal fatigue and cracks is suppressed.

  On the other hand, the technique disclosed in Patent Document 2 aims to relieve thermal stress applied to each part when the temperature of a brake disk during braking rises, thereby making it difficult to cause crack damage. Specifically, as shown in FIG. 13, a plurality of notches 1d are formed in the circumferential direction of the inner peripheral edge of the brake disc 1, and fastening holes 1aa for inserting fastening bolts are formed between the adjacent notches 1d. By providing, the big thermal stress which arises by the temperature difference of the inner-outer diameter of the brake disk 1 is suppressed. In particular, by restricting the shape and forming position of the notch 1d, it is intended to suppress the thermal stress acting on each fastening hole 1aa that was a weak portion.

  By the way, when the brake disk is made of a steel material, the sliding surface is austenitized during braking (temperature rise) and then rapidly cooled to form a white layer, and a crack generated from this white layer develops. Therefore, the influence of this white layer must be considered. Further, since residual stress generated by partial plastic deformation of the brake disk during braking (at the time of temperature rise) also affects crack growth, this point needs to be considered. In addition, it is necessary to improve the total life until cracks are generated and propagated on the sliding surface to reach rapid fracture.

  However, in the conventional technique, the above two points are not considered at all, and the expected durability may not be obtained.

  For example, in Patent Document 1, it is assumed that many crack occurrence positions are found on the inner peripheral side of the brake disc. However, since the crack generation position differs depending on the contact state between the brake lining and the sliding surface during braking and the structure of the disc brake device, the crack does not always occur on the inner peripheral side. In particular, in a brake disc with a fastening structure attached to a wheel, the temperature of the sliding surface rises and heat expands at the time of braking, but the temperature does not increase so much at other portions, so the heat expansion is relatively small. From this, as shown in FIG. 14, the center of the sliding portion 1b of the brake disk 1 rises and frictional heat is concentrated at the center of the sliding surface 1ba, so that cracks often occur.

  Further, the technique of Patent Document 2 is intended for a fastening hole portion which is a weak portion of the inner peripheral edge portion of the brake disc, and considers a crack on the sliding surface of the brake disc which the present invention is to solve. Has not been made.

  The problems to be solved by the present invention are caused by the influence of the white layer that occurs when the brake surface is austenitized and then rapidly cooled during braking, or when the brake disc is partially plastically deformed. The effect of the residual stress is not taken into consideration, and the expected durability may not be obtained.

  The inventors, regarding the brake disk for railway vehicles, conduct a numerical analysis assuming a thermal stress when repeatedly performing braking, and investigating cracks actually generated on the sliding surface when braking is repeated. As a result of repeated research, the following knowledge was obtained.

(A) With brake discs that are currently used in railway cars and have a sliding surface on the front side of the plate part and fins on the back side, the origin of cracks generated on the sliding surface is on the sliding surface. Is a hair crack generated in the surface layer near the center in the radial direction.
(B) The depth of the hair crack that is the starting point of the crack generated on the sliding surface corresponds to that of the white layer generated by the brake heat or the heat-affected layer tempered by this.
(C) If tensile residual stress occurs around the hair crack due to brake heat, and further fluctuations in stress occur due to repeated brake heat, fatigue cracks start from the hair crack, and the sliding surface does not grow significantly. Form a fissure.

Therefore, in order to improve durability against cracks generated on the sliding surface, the following three points may be realized.
(1) Shallow hair cracks that are the starting point of sliding surface cracks. That is, the thickness of the white layer generated by the brake heat is reduced.
(2) Reduce the tensile residual stress caused by brake heat.
(3) Reduce stress fluctuation caused by brake heat. However, since the stress fluctuation that affects the crack growth is only in the positive range, when compressive stress occurs due to temperature rise like brake heat, the effective stress fluctuation is the fluctuation amount from zero to the tensile residual stress. Become. For this reason, if the tensile residual stress is reduced, the stress fluctuation is naturally reduced.

The brake disk for railway vehicles of the present invention is made based on the above knowledge obtained by the inventors' investigation and numerical analysis,
In order to improve durability by suppressing the influence of the white layer that is caused by rapid cooling after the sliding surface becomes austenite during braking and the influence of residual stress caused by partial plastic deformation of the brake disc,
A sliding part in which fins are formed at a predetermined interval in the circumferential direction on the back surface of the plate part whose surface is a sliding surface, and a fastening part with a wheel on the inner peripheral surface side of the sliding part A steel railcar brake disc provided with
The main feature is that the thickness of the central portion in the radial direction of the sliding surface between the fins of the sliding portion is thicker than the thickness of the inner peripheral end and the outer peripheral end of the sliding surface.

  In the brake disc for a railway vehicle according to the present invention, the thickness of the plate portion near the radial center of the sliding surface between the fins of the sliding portion is made thicker than the inner peripheral end and the outer peripheral end of the sliding surface. The effects of the white layer and residual stress generated on the sliding surface can be suppressed, and the durability against the sliding surface crack is improved.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to FIGS. 1 and 2 along with the progress from the idea of the present invention to the solution of the problem.

  FIG. 1 is an explanatory view of a brake disc for a railway vehicle according to the present invention, showing a 1/24 model of the entire circumference of element division used in the finite element method (FEM) analysis, and (a) is the back side of the sliding surface. (B) is the perspective view seen from the sliding surface side, (c) is the side view of the cross section between fins. In FIG. 1, the same reference numerals as those in FIGS. 10 to 14 denote the same or corresponding parts, and a detailed description thereof will be omitted.

1) Thickness of the white layer generated on the sliding surface 1ba of the brake disc 1 The white layer is formed by quenching after the sliding surface 1ba of the brake disc 1 is austenitized. It is determined by the area of the brake disc 1 that is austenitized at the time (temperature rise).

  Therefore, in order to reduce the thickness of the white layer, it is necessary to increase the heat capacity of the brake disk 1. The only way to increase the heat capacity is to increase the thickness of the plate portion between the fins 1c adjacent to each other in the circumferential direction (inter-fin portion).

2) Tensile residual stress Tensile residual stress is generated in the brake disc 1 by brake heat due to the following mechanism. During braking, the surface layer portion of the sliding surface 1ba tends to thermally expand due to a temperature rise. However, it is constrained by other parts where the temperature rise is slow (parts deeper than the surface layer part of the sliding surface 1ba, fins 1c, fastening parts 1a on the inner peripheral surface side of the sliding part 1b), and compressive stress is generated, which is the yield point. Yielding in the compression direction occurs.

  After that, when cooled, the region that does not yield tends to return to its original shape, so that a tensile residual stress is generated on the surface layer of the yielded sliding surface 1ba. In order to reduce the tensile residual stress, two methods are conceivable: a temperature difference in the brake disc 1 is reduced or a maximum temperature is reduced.

  Fig. 2 shows the analysis of residual stress generated by brake heat using FEM for two brake disc shapes with a plate thickness between the fins of 18mm (conventional product: ◯) and 21mm (comparative product: △). It is the result.

  From FIG. 2, it can be seen that the larger the thickness of the plate portion between the fins, the smaller the residual stress in the circumferential direction becomes deeper from the sliding surface 1ba. From this, it has been found that in the railway vehicle brake disc 1 which is the subject of the present invention, it is effective to increase the thickness of the plate portion between the fins in order to reduce the tensile residual stress.

  Note that the thickness of the plate portion between the fins at this time is determined in consideration of the strength and durability required for the brake disc 1 to be applied, the limitation on the total weight of the brake disc 1, and the like. For this, it is desirable that the thickness be about 20% to 60% with respect to the thickness (axial width) t1 of the fin 1c.

  This is because when the thickness of the plate portion between the fins is less than 20% with respect to the thickness t1 of the fin 1c, the effect of increasing the thickness as described above cannot be obtained. On the other hand, if it exceeds 60%, the entire heat dissipation area of the brake disc 1 is lowered and the total weight is increased.

3) Crack Propagation The crack generated on the sliding surface 1ba of the brake disk 1 is the initial crack (6 in Fig. 3) of the white layer phase etc. of 1) above. It is thought that this is caused as a result of stress fluctuations such as the tensile residual stress phase and progressing as a fatigue crack, and its life can be predicted in terms of fracture mechanics.

4) Increase in thickness at the center of the sliding surface 1ba As described in 2) and 3) above, in order to reduce the thickness of the white layer and the residual tensile stress, the thickness of the plate between the fins However, if the thickness of the plate portion between the fins of the entire brake disc 1 is increased, there is a problem that the total weight of the brake disc 1 is increased.

  Therefore, as shown in FIG. 1 (c), the inventors have determined the thickness of the plate portion at the radial center 1baa of the sliding surface 1ba of the brake disk 1, which is the starting point of the sliding surface crack. It was considered to reduce the total weight of the brake disc 1 by increasing only t2 beyond the thickness t3 of the outer peripheral side or inner peripheral side plate portion.

  The radial center 1baa of the sliding surface 1ba at this time includes the radial center of the sliding surface 1ba, and the radial length of the center of the sliding surface 1ba is the radial length of the entire sliding surface 1ba. On the other hand, it indicates a range from 10% to 50%.

  When the radial direction length of the central portion 1baa in the radial direction of the sliding surface 1ba is less than 10% with respect to the radial direction length of the entire sliding surface 1ba, the thickness t2 of the plate portion of the central portion 1baa in the radial direction This is because there is a possibility that the effective range by increasing the value becomes very narrow and a sufficient effect cannot be obtained. On the other hand, when it exceeds 50%, the total weight increases when the thickness t2 of the plate portion of the central portion 1baa in the radial direction is increased.

  From the above, in the brake disc 1 having the sliding surface 1ba on the front surface side of the plate portion and the fins 2c provided on the back surface side, the sliding surface 1ba has a cross section perpendicular to the circumferential direction between the fins. The thickness t2 of the plate portion of the central portion 1baa in the radial direction is made thicker than the thickness t3 of the plate portion at the inner and outer peripheral ends of the sliding surface 1ba, thereby reducing the thickness of the white layer and pulling it. It was possible to reduce the residual stress and improve the durability against the sliding surface crack. This is the brake disk for railway vehicles of the present invention.

Hereinafter, in order to confirm the effect of this invention, the result of having performed FEM analysis for the brake disk of this invention is demonstrated.
In the FEM analysis, material constants of forged steel materials used in railway vehicles (see Japanese Patent Laid-Open No. 56-44756) were used. In the finite element division, 1/24 (15 °) of the entire circumference was modeled in consideration of symmetry. The radial width of the sliding surface of the modeled brake disc is 127.5 mm.

  The details of the analysis model are shown in Table 1 below, and the FEM analysis model is shown in FIGS. As shown in Table 1, in the product 1 of the present invention shown in FIG. 4, the thickness of the plate portion at the center of the sliding surface is different from the conventional product in which the thickness of the plate portion of the sliding portion is constant at 18 mm. The distance was gradually increased linearly from the outer peripheral portion to the center of the sliding surface so as to be 23 mm. In the product 2 of the present invention shown in FIG. 5, the thickness of the plate portion at the center of the sliding surface is 24 mm in order to further increase the thickness of the plate portion at the outer peripheral portion and the center of the sliding surface. The thickness of the outer peripheral plate portion was 15 mm. Moreover, in order to compare what increased the thickness of the board part of the whole sliding part, the thing which increased the thickness of the board part of the sliding part in a conventional product to 21 mm is shown as a comparative product.

  FEM analysis conditions were a short-time brake load from 275 km / hr. The brake was repeatedly loaded four times, the first time assuming a stop brake, the brake time was 45 seconds, and the second to fourth times, the brake time was assumed to be 31 seconds.

  FIG. 8 shows the relationship between the depth direction distance from the center surface of the brake disk sliding surface and the circumferential residual stress after the fourth brake cooling as the FEM analysis result. From the results shown in FIG. 8, it can be seen that the product 1 of the present invention and the product 2 of the present invention have reduced tensile residual stress in a region having a depth of 3 mm or more as compared with the conventional product.

  In addition, the residual stress shows the same value compared with the comparative product in which the entire thickness of the plate portion is increased. It turns out that an equivalent effect is acquired.

  Table 2 below shows a comparison of the white layer depth under the three brake conditions in which the white layer depth is 1.0 mm, 2.0 mm, and 3.0 mm in the conventional product. The brake conditions at this time were such that heat input assuming a stop brake of 275 km / hr was applied to the sliding surface, and the brake times were 49.2 seconds, 57.2 seconds, and 65.2 seconds, respectively. The depth of the white layer was a depth from the disk sliding surface at which the austenite ratio during phase transformation obtained by FEM analysis was approximately 50%.

  From Table 2 above, it can be seen that the comparison product, the product 1 of the present invention, and the product 2 of the present invention have a smaller depth of the white layer, and the depth of the white layer is particularly small in the product 2 of the present invention. You can see that

  FIG. 9 shows the expected crack growth life for the conventional product derived from the initial crack conditions shown in Table 3 below based on the conventional product and the residual stress distribution in the circumferential direction obtained in FIG. Indicates the ratio.

In addition, this crack growth prediction lifetime was calculated | required in the following procedures.
First, the variation range ΔK of the stress intensity factor of the initial crack is obtained from the stress amplitude until the residual stress in the circumferential direction of the sliding surface is reduced to zero by repeated braking and returns to the original value. Then, the crack growth rate (crack propagation amount per brake) is obtained from the crack propagation characteristics of the brake disc material measured according to ΔK and ASTM (American Society for testing Materials) E647. Next, the obtained crack growth amount is added to the initial crack depth, and the crack growth rate is recalculated when ΔK.

  The above was repeated, and the number of brakes until the maximum value of the stress intensity factor reached fatigue fracture toughness was taken as the predicted life (from the Fate Design Handbook, edited by the Japan Society of Materials Science). As the initial crack depth estimated at this time, the value shown in Table 2 was used as the depth of the white layer seen during cooling after the stop brake. For this white layer depth, brake conditions where the white layer depth is 1.0 mm, 2.0 mm, and 3.0 mm in comparison with the depth of the conventional product are CASE1, CASE2, and CASE3, respectively. The white layer depth is derived by applying a brake to the brake discs 1 and 2 and the comparative product.

From the results of FIG. 9, it is predicted that the product of the present invention will have an average life of approximately twice as long as that of the conventional product, and a maximum of three times the life.
In other words, from the comparison results of the weights of the brake discs shown in Table 1, the weights of the brake discs of the present invention products 1 and 2 in which the thickness of the plate portion at the center of the sliding surface is increased are slightly larger than the brake disc weight of the conventional product. Although it increases, it is less than the weight of the brake disc of the comparative product, and it can be seen that the product of the present invention is highly durable for its weight.

  From the above example, as shown in FIG. 1 (c), the shape of the brake disk is a fin relative to the thickness t3 of the inner peripheral edge and the outer peripheral edge of the sliding surface of the brake disk. It can be seen that it is better to increase only the thickness t2 of the plate portion at the center portion in the radial direction of the sliding surface.

  From the results shown in FIG. 8, the thickness of the plate portion on the entire sliding surface of the brake disc was increased in reducing the residual stress in the circumferential direction, reducing the depth of the white layer, and improving the total life of the brake disc. This is because there is a performance equivalent to the case. In addition, as shown in Table 1, the overall weight of the brake disk can be reduced and the unsprung weight of the vehicle can be reduced as compared with the case where the thickness of the plate portion of the entire brake disk sliding surface is increased. It also leads to improvement.

  FIG. 1 shows a railway vehicle brake disk obtained from the above examination results according to the technique of the present invention.

  It goes without saying that the present invention is not limited to the above-described example, and the embodiment may be appropriately changed within the scope of the technical idea described in claim 1.

  The present invention described above is not limited to a brake disk for a railway vehicle, but can be applied to a brake disk for an automobile, a motorcycle, or the like.

It is explanatory drawing of the brake disc of this invention, Comprising: The 1/24 model of the perimeter of the element division used for FEM analysis is shown, (a) is the perspective view seen from the back side of the sliding surface, (b) is a sliding The perspective view seen from the moving surface side, (c) is a side view of the cross section between fins. It is the figure which showed the relationship between the depth direction of a sliding surface, and the residual stress in the circumferential direction. (A) is a figure explaining the initial crack of a brake disk sliding surface, (b) is a figure explaining the surface length and depth of an initial crack. The product 1 of this invention which performed FEM analysis is shown, (a) is a side view, (b) is a side view of the part between fins. It is a side view of the fin part of this invention product 2 which performed FEM analysis. It is a side view of the fin part of the conventional product which implemented FEM analysis. It is a side view of the fin part of the comparative product which implemented FEM analysis. It is a figure showing the residual stress distribution after repeated brake cooling. It is a figure showing the crack growth prediction life ratio of an invention product vs. a conventional product. A conventional brake disc is shown, (a) is a radial-circumferential plan view showing 1/4 of the brake disc, (b) is a radial-axial sectional view showing a fin section, and (c) is between fins. It is radial direction-axial direction sectional drawing which shows a partial cross section. It is a schematic diagram of the state with which the conventional brake disc was mounted | worn with the wheel. BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the brake disk for rail vehicles disclosed by patent document 1, (a) is a front view which shows a part, (b) is AA sectional drawing of (a) figure. It is explanatory drawing of the brake disk for rail vehicles disclosed by patent document 2. FIG. It is a schematic diagram of a state in which the center of the brake disk sliding surface is warped.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Brake disc 1a Fastening part 1aa Fastening hole 1b Sliding part 1ba Sliding surface 1baa Radial center part 1bb Inner peripheral part 1bc Outer peripheral part 1c Fin 2 Wheel 3 Bolt 4 Nut 5 Brake lining 6 Initial crack

Claims (1)

A sliding part in which fins are formed at a predetermined interval in the circumferential direction on the back surface of the plate part whose surface is a sliding surface, and a fastening part with a wheel on the inner peripheral surface side of the sliding part A steel railcar brake disc provided with
A brake disc for a railway vehicle, wherein a thickness of a central portion in a radial direction of the sliding surface between fins of the sliding portion is made thicker than thicknesses of an inner peripheral end and an outer peripheral end of the sliding surface.