Brake shoe and tread brake device for railway vehicle

Abstract

To provide a brake shoe including a synthetic resin-based friction material which improves a coefficient of static friction while maintaining a moderately low coefficient of dynamic friction, and a tread brake device for a railway vehicle including the brake shoe including the synthetic resin-based friction material.SOLUTION: A brake shoe includes a synthetic resin-based friction material containing a friction adjustment material, a binding material and a fiber base material, wherein the synthetic resin-based friction material contains natural graphite, artificial graphite and aluminum powder as the friction adjustment material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a brake shoe, and more particularly to a brake shoe that is suitable for use in a tread brake device of a railway vehicle. [Background technology]

[0002] A known braking device for railway vehicles is a tread brake device that generates friction by pressing a friction material against the wheel tread, and uses the friction force as braking force. This tread brake device has a brake shoe with an arc-shaped base metal and a friction material attached to the wheel-side main surface of the base metal, and generates braking force by pressing the friction material against the wheel tread.

[0003] The characteristics required of friction materials include a high coefficient of friction (effectiveness), heat resistance, wear resistance (long life), low aggressiveness to mating materials, low squeal, etc. Various technologies have been proposed to satisfy these required characteristics. For example, brake shoes equipped with synthetic resin-based friction materials have been proposed as a replacement for cast iron-based brake shoes in brake equipment, and it has been shown that sufficient braking performance can be ensured under both dry and wet conditions (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-31316 Summary of the Invention [Problem to be solved by the invention]

[0005] The synthetic resin-based friction material described in Patent Document 1 has a low dynamic friction coefficient (also referred to as "dynamic μ" in this specification), and its use can be used as a substitute for cast iron-based brake shoes. On the other hand, when a synthetic resin-based friction material is used, not only the dynamic friction coefficient but also the static friction coefficient (also referred to as "static μ" in this specification) decreases. Also, if the dynamic friction coefficient is too low, there is a problem in that it is difficult to control braking, in that the vehicle will not stop even when the brakes are applied. In recent years, there has been a demand for even higher performance brake shoes in order to further improve controllability during braking and further suppress rolling when the vehicle is stopped. Specifically, there is a demand for improving the static friction coefficient while maintaining a moderately low dynamic friction coefficient.

[0006] The present invention aims to provide a brake shoe with a synthetic resin-based friction material that improves the static friction coefficient while maintaining a moderately low dynamic friction coefficient. Another object of the present invention is to provide a railway vehicle tread brake device equipped with a brake shoe with the synthetic resin-based friction material. [Means for solving the problem]

[0007] As a result of extensive research, the inventors discovered that the above-mentioned problems can be solved in brake shoes equipped with synthetic resin-based friction materials (also referred to as "synthetic resin brake shoes" in this specification) by including natural graphite, artificial graphite, and aluminum powder as friction modifiers in the synthetic resin-based friction materials, and thus completed the present invention.

[0008] That is, the present invention relates to the following contents. [1] A brake shoe comprising a synthetic resin-based friction material containing a friction modifier, a binder, and a fiber base material, The synthetic resin-based friction material contains natural graphite, artificial graphite, and aluminum powder as the friction modifier. [2] The brake shoe according to [1], wherein the total content of the natural graphite and the artificial graphite in the synthetic resin-based friction material is 15 to 35 mass %. [3] The brake shoe according to [1] or [2], wherein the content of the aluminum powder in the synthetic resin-based friction material is 0.5 to 10 mass %. [4] The brake shoe according to any one of [1] to [3], wherein the friction modifier contains calcium carbonate. [5] The brake shoe according to any one of [1] to [4], wherein the friction modifier contains cast iron powder. [6] The brake shoe according to any one of [1] to [5], which is for use in a railway vehicle. [7] [6] A tread brake device for a railway vehicle, comprising the brake shoe described in [6]. [Effects of the Invention]

[0009] The brake shoe of the present invention has an improved static friction coefficient while maintaining a moderately low dynamic friction coefficient, and therefore, when used as a tread brake device for railway vehicles equipped with the brake shoe, it is possible to achieve further improvement in controllability during braking and further suppression of rolling when the vehicle is stopped. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a front view of an embodiment of the brake shoe of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a front view of one embodiment of the brake shoe of the present invention. Brake shoe 1 is basically composed of a base metal 2, friction material 3, and mounting plate 4. Base metal 2 is a generally rectangular flat plate that forms an arc that follows the arc of the wheel of a railway vehicle, and friction material 3 is affixed to its wheel-side main surface. Mounting plate 4 is loosely fitted into the brake shoe head on the vehicle side (not shown), and serves as a torque receiving part that receives torque generated during braking. Such brake shoe 1 constitutes a tread brake device in the braking system of a railway vehicle, and during braking, friction material 3 is pressed against the wheel tread to generate frictional force, which is used as braking force to stop or slow down the vehicle.

[0012] A brake shoe according to an embodiment of the present invention comprises a synthetic resin-based friction material containing a friction modifier, a binder, and a fibrous base material, and the synthetic resin-based friction material contains natural graphite, artificial graphite, and aluminum powder as the friction modifiers.

[0013] Examples of graphite include natural graphite and artificial graphite. In the brake shoe according to the embodiment of the present invention, a mixture of natural graphite and artificial graphite is used to obtain a desired friction coefficient from the viewpoint of realizing a low friction coefficient and ensuring braking performance in a synthetic resin-based friction material.

[0014] The natural graphite used preferably has an average particle size of 1 to 200 μm, more preferably 20 to 60 μm. By using natural graphite with an average particle size within this range, it is possible to improve the lubricity of the natural graphite with respect to the sliding surface of a mating material, such as the wheel tread of a railway vehicle, and reduce the coefficient of dynamic friction. Examples of natural graphite that can be used include scaly graphite, flake graphite, and amorphous graphite.

[0015] The artificial graphite used preferably has an average particle size of 100 to 1100 μm, more preferably 400 to 800 μm. By using artificial graphite with an average particle size within the above range, moldability and crack resistance can be improved. Artificial graphite is sometimes called granular graphite.

[0016] The average particle size in this specification can be determined as the particle size (D50) corresponding to a cumulative percentage of 50% on a volume basis from the particle size distribution measured using a laser diffraction particle size analyzer (e.g., "LS 13 320" manufactured by Beckman Coulter, Inc.).

[0017] The total content of natural graphite and artificial graphite in the synthetic resin-based friction material is preferably 15 to 35 mass%, more preferably 18 to 32 mass%, and even more preferably 21 to 29 mass%. A total content of natural graphite and artificial graphite of 15 mass% or more is preferable because it can reduce the dynamic friction coefficient to a level equivalent to that of a cast iron-based friction material. Furthermore, a total content of natural graphite and artificial graphite of 35 mass% or less is preferable because it can sufficiently maintain crack resistance and cleanliness of the sliding surface of the mating material.

[0018] The mass ratio of natural graphite to artificial graphite (natural graphite:artificial graphite) is preferably 1:1 to 5:1. Within this mass ratio range, the dynamic friction coefficient can be reduced to a level equivalent to that of cast iron-based friction materials. Furthermore, the effect of maintaining the cleanliness of the sliding surface of the mating material can be further improved. The mass ratio of natural graphite to artificial graphite (natural graphite:artificial graphite) is more preferably 2:1 to 5:1, and even more preferably 2:1 to 4:1. A mass ratio within this preferred range can further improve crack resistance.

[0019] Aluminum is thought to have the effect of generating adhesive friction with the forged steel mating member and improving the friction coefficient. Aluminum is used as a particulate material (aluminum powder) in view of its dispersibility in the friction material composition.

[0020] The aluminum powder used preferably has an average particle size of 30 to 300 μm, more preferably 50 to 200 μm, and even more preferably 70 to 150 μm. The aluminum powder has the function of improving the static friction coefficient while maintaining an appropriately low dynamic friction coefficient under high load with respect to the brake shoe. It is preferable that the average particle size of the aluminum powder is 30 μm or more because the static friction coefficient can be improved, and it is preferable that the average particle size is 300 μm or less because a sufficient static friction coefficient can be ensured.

[0021] The content of aluminum powder in the synthetic resin-based friction material is preferably 0.5 to 10 mass %, more preferably 1 to 8 mass %, and even more preferably 2 to 7 mass %. The content of aluminum powder in the synthetic resin friction material is preferably 0.5% by mass or more because it can improve the static friction coefficient, and is preferably 10% by mass or less because it ensures a sufficient friction coefficient.

[0022] The synthetic resin-based friction material preferably contains at least one organic filler of cashew dust and rubber dust (also referred to as "cashew dust and / or rubber dust" in this specification) as a friction modifier. By including at least one of cashew dust and rubber dust, it is possible to ensure a friction coefficient under light loads under dry conditions.

[0023] Cashew dust is obtained by carbonizing and hardening oil extracted from the shells of cashew nuts. The average particle size of the cashew dust is preferably 10 to 500 μm, more preferably 100 to 300 μm. The rubber dust may be obtained by pulverizing rubber for tires (for example, rubber for treads).The average particle size of the rubber dust is preferably 10 to 1500 μm, more preferably 300 to 600 μm.

[0024] The total content of cashew dust and / or rubber dust in the synthetic resin friction material is preferably 1 to 15 mass%, more preferably 2 to 12 mass%, and even more preferably 3 to 10 mass%. When the synthetic resin friction material contains only cashew dust or rubber dust, the "total content of cashew dust and / or rubber dust" refers to the content of cashew dust or rubber dust. If the total content of cashew dust and / or rubber dust in the synthetic resin friction material is 1% by mass or more, flexibility is improved, and if it is 15% by mass or less, the coefficient of friction can be ensured, which is preferable.

[0025] Examples of other friction modifiers include inorganic fillers such as barium sulfate, calcium pyrophosphate, calcium carbonate, calcium hydroxide, calcium silicate, vermiculite, mica (phlogopite, muscovite, synthetic mica, natural mica), potassium titanate, lithium potassium titanate, and magnesium potassium titanate; abrasives such as silicon carbide, alumina, silica, magnesia, chromite, triiron tetroxide, zirconium oxide, and zirconium silicate; lubricants such as molybdenum disulfide, tin sulfide, zinc sulfide, and iron sulfide; metal powders such as zinc, tin, copper, and iron; and solid lubricants such as graphite other than natural and artificial graphite. These may be used alone or in combination of two or more. The total content of other friction modifiers can be adjusted appropriately depending on the desired friction characteristics. The content of other friction modifiers in the synthetic resin-based friction material is preferably 30 to 85% by mass, more preferably 40 to 80% by mass, depending on the desired friction coefficient.

[0026] From the viewpoint of formability when manufacturing brake shoes, it is preferable that calcium carbonate is contained as a friction modifier. When calcium carbonate is contained, the content in the synthetic resin-based friction material is preferably 8 to 45 mass%, more preferably 10 to 40 mass%, and even more preferably 13 to 35 mass%. A content of 8 mass% or more in the synthetic resin-based friction material is preferable for improving wear resistance, and a content of 45 mass% or less is preferable for ensuring a friction coefficient.

[0027] In order to ensure a sufficient dynamic friction coefficient, it is preferable to contain cast iron powder as a friction modifier. When cast iron powder is contained, the content in the synthetic resin-based friction material is preferably 1 to 30 mass %, more preferably 5 to 25 mass %, and even more preferably 10 to 20 mass %. A content of 1 mass % or more in the synthetic resin-based friction material is preferable because it can improve the dynamic friction coefficient, and a content of 30 mass % or less is preferable because it can ensure an appropriate friction coefficient.

[0028] The cast iron powder used preferably has an average particle size of 10 to 200 μm, more preferably 30 to 150 μm, and even more preferably 50 to 100 μm. It is preferable that the average particle size of the cast iron powder is 10 μm or more because the coefficient of dynamic friction can be improved, and it is preferable that the average particle size is 200 μm or less because an appropriate coefficient of friction can be ensured.

[0029] In order to improve the static friction coefficient and ensure mechanical strength, it is preferable to contain calcium silicate as a friction modifier. When calcium silicate is contained, the content in the synthetic resin-based friction material is preferably 0.5 to 12 mass%, more preferably 1 to 10 mass%, and even more preferably 2 to 8 mass%. A content of 0.5 mass% or more in the synthetic resin-based friction material is preferable because the static friction coefficient is improved, and a content of 12 mass% or less is preferable because sufficient mechanical strength can be ensured.

[0030] The calcium silicate to be used preferably has an average particle size of 1 to 120 μm, more preferably 5 to 110 μm, and even more preferably 10 to 100 μm. It is preferable that the average particle size of calcium silicate is 1 μm or more since the static friction coefficient is improved, and it is preferable that the average particle size is 120 μm or less since sufficient mechanical strength can be ensured.

[0031] The fibrous base material is used to reinforce the synthetic resin-based friction material, and examples of the fibrous base material include heat-resistant organic fibers, inorganic fibers, and metal fibers. Examples of heat-resistant organic fibers include aromatic polyamide fibers (aramid fibers) and flame-resistant acrylic fibers. Examples of inorganic fibers include potassium titanate fibers, ceramic fibers (biodegradable fibers are preferably used), glass fibers, carbon fibers, and rock wool. Examples of metal fibers include steel fibers. These can be used alone or in combination of two or more. To ensure sufficient mechanical strength, the content of the fibrous base material in the synthetic resin-based friction material is preferably 1 to 50 mass %, more preferably 3 to 45 mass %.

[0032] The binder is made of a thermosetting resin, and examples of the thermosetting resin include phenolic resin, epoxy resin, resins obtained by modifying these thermosetting resins with cashew oil, silicone oil, various elastomers, etc., and resins obtained by dispersing various elastomers, fluoropolymers, etc. in these thermosetting resins, and these can be used alone or in combination of two or more. The content of the binder in the synthetic resin-based friction material is preferably 5 to 25 mass %, more preferably 10 to 20 mass %, in order to ensure sufficient mechanical strength and wear resistance as a brake shoe.

[0033] The brake shoe according to the embodiment of the present invention can be manufactured by a known manufacturing method. For example, it can be manufactured by a manufacturing method including a preforming step of a friction material composition that forms a friction material, and a heat-pressure molding step of the preform obtained in the preforming step. Each step will be specifically described below.

[0034] First, in the preforming step, the raw materials for forming the friction material are uniformly mixed, and the resulting friction material composition is pressure-molded to obtain a preform. The friction material composition may contain natural graphite, artificial graphite, and aluminum powder, as well as the above-mentioned organic fillers, other friction modifiers, fibrous base materials, binders, etc. The friction material composition is poured into a mold and is preferably pressure-molded under conditions of 6 to 14 MPa to improve mixing properties and workability in the heat-pressure molding process. If the pressure is less than 6 MPa, it may be difficult to form a preform, and if it exceeds 14 MPa, cracks may occur in the preform, which is not preferable.

[0035] In the heat and pressure molding step, the preform obtained in the preforming step is placed in a heat forming mold, and a base metal is placed on top of it, followed by heat and pressure molding to obtain a brake shoe having a desired shape. The conditions for heating and pressing are preferably a temperature of 140 to 155° C., a pressure of 10 to 20 MPa, and a time of about 20 to 60 minutes.

[0036] The brake shoes according to the embodiment of the present invention are particularly useful as brake shoes for railway vehicles, since they are provided with a friction material that has an improved static friction coefficient while maintaining a moderately low dynamic friction coefficient at the same level as cast iron-based friction materials. For this reason, the brake shoe according to the embodiment of the present invention can be used as a tread brake device for a railway vehicle. [Example]

[0037] The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0038] The tests carried out on each example are as follows:

[0039] (1) Dynamic friction coefficient (high load conditions) Mating wheel: forged steel (Q3S) ·Initial braking speed: 30, 60, 100, 120km / h Pressing force: 20, 60, 100kN Counterpart material weight: 11.25 tons Using a dynamometer tester under the above conditions, tests were conducted at the above initial braking speeds and with the above pressing forces, and the dynamic friction coefficient (dynamic μ) against the mating wheel under high load conditions was measured. Note that the μ used to evaluate the dynamic friction coefficient was the value of dynamic μ at an initial braking speed of 100 km / h and a pressing force of 100 kN. The dynamic friction coefficient μ under high load conditions was evaluated (determined) as follows. A: 0.08≦μ≦0.10 B:0.07≦μ<0.08, 0.10<μ≦0.12 C: μ<0.07, 0.12<μ

[0040] (2) Coefficient of static friction Mating wheel: forged steel (Q3S) Pressing force: 5, 14, 30, 40kN Using a dynamometer tester under the above conditions, tests were conducted for each of the above pressing forces, and the static friction coefficient (static μ) against the mating wheel was measured. Note that the μ used to evaluate the static friction coefficient was the static μ value at pressing forces of 30 and 40 kN. The static friction coefficient μ was evaluated (judged) as follows. A: 0.20≦μ B: 0.16≦μ<0.20 C: μ<0.16 If the static friction coefficient μ ratings at 30 and 40 kN differed, the lower rating was used as the overall rating. For example, if the static friction coefficient μ ratings at 30 and 40 kN were A and B, respectively, the overall rating would be B.

[0041] <Compound materials for synthetic resin friction materials> The materials used to prepare the synthetic resin friction materials of each example are as follows: Binder resin: phenolic resin Rubber dust: average particle size 500 μm Aluminum powder: average particle size 100 μm Calcium carbonate: average particle size 3.5 μm Calcium silicate: average particle size 20 μm Natural graphite: average particle size 40 μm Artificial graphite: average particle size 600 μm Cast iron powder: average particle size 80 μm

[0042] Example 1 The synthetic resin friction material ingredients were added to a mixer according to the formulation (mass%) shown in Table 1 and mixed for 210 seconds in a mixer. The mixed synthetic resin friction material composition was preformed at a pressure of 7 MPa for 15 seconds to produce a preformed body. The preformed body was then placed in a thermoforming mold at 145°C, and a base metal was placed on top of it, followed by hot-press molding at a pressure of 15.0 MPa for 27 minutes to obtain a hot-press molded body. Grooves were then machined into this hot-press molded body to produce a brake shoe. The obtained brake shoes were subjected to the above tests (1) and (2). The results are shown in Table 1.

[0043] (Examples 2 to 7, Comparative Examples 1 to 3) A synthetic resin-based friction material was prepared in the same manner as in Example 1, except that the ingredients and amounts of the synthetic resin-based friction material were changed to those shown in Table 1. The synthetic resin-based friction material thus obtained was subjected to the above tests (1) and (2). The results are shown in Table 1.

[0044] [Table 1]

[0045] As can be seen from the results in Table 1, the friction materials of Examples 1 to 7 had improved static friction coefficients while maintaining a moderately low dynamic friction coefficient. This demonstrates that the friction materials of Examples 1 to 7 have the higher performance of brake shoes that have been sought in recent years in terms of controllability during braking and suppression of rolling when the vehicle is stopped, and are particularly useful for railway vehicle tread brake devices. In contrast, the friction materials of Comparative Examples 1 to 3 exhibited low values ​​for both the dynamic friction coefficient and the static friction coefficient. [Industrial Applicability]

[0046] The brake shoe according to the present invention can be used particularly in a tread brake device for a railway vehicle. [Explanation of symbols]

[0047] 1 Bracelet 2 base money 3 Friction material 4 Mounting plate

Claims

1. A brake shoe comprising a synthetic resin-based friction material containing a friction modifier, a binder, and a fiber base material, The synthetic resin-based friction material contains natural graphite, artificial graphite, and aluminum powder as the friction modifier.

2. 2. The brake shoe according to claim 1, wherein the total content of the natural graphite and the artificial graphite in the synthetic resin-based friction material is 15 to 35 mass %.

3. The brake shoe according to claim 1 or 2, wherein the content of the aluminum powder in the synthetic resin-based friction material is 0.5 to 10 mass %.

4. The brake shoe according to claim 1 or 2, wherein the friction modifier contains calcium carbonate.

5. The brake shoe according to claim 1 or 2, wherein the friction modifier contains cast iron powder.

6. The brake shoe according to claim 1 or 2, which is for use in a railway vehicle.

7. A tread brake device for a railway vehicle, comprising the brake shoe according to claim 6.

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