Brake shoe and tread brake device for rail vehicles

Abstract

The present invention relates to a brake shoe comprising a synthetic resin-based friction material containing a friction modifier, a binder and a fiber material, wherein the synthetic resin-based friction material contains a natural graphite, an artificial graphite and calcium silicate as a friction modifier.

Description

TECHNICAL FIELD

[0001] The present invention relates to a brake shoe and, more particularly, to a brake shoe suitable for use in a tread brake device of a rail vehicle. STATE OF THE ART

[0002] As a braking device in a railway vehicle, a tread brake device is known that generates a frictional force by pressing a friction material against a wheel tread and uses the frictional force as the braking force. This tread brake device comprises a brake shoe with an arcuate base metal and a friction material attached to a main surface on a wheel side of the base metal. It generates the braking force by pressing the friction material against the wheel tread.

[0003] The required properties of the friction material include a high friction coefficient (efficiency), heat resistance, wear resistance (long service life), low aggressiveness toward a mating material, and low noise. To meet these required properties, various techniques have been proposed. For example, a brake shoe with a resin-based friction material was proposed as an alternative to a cast iron-based brake shoe as the friction material in the brake shoe of the braking device, and it was demonstrated that sufficient braking performance can be ensured under both dry and wet conditions (Patent Literature 1). CITATION LISTPATENT LITERATURE

[0004] Patent Literature 1: JP2017-31316A SUMMARY OF THE INVENTION

[0005] The resin-based friction material described in Patent Literature 1 has a small dynamic friction coefficient (also referred to as "dynamic μ" in this specification), and this can be used as an alternative to the cast iron-based brake shoe. On the other hand, when a 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. Furthermore, if the dynamic friction coefficient is too low, there is a problem that a vehicle does not stop even when the brake is applied, making it difficult to control the vehicle during braking.

[0006] In recent years, even higher performance has been demanded from the brake shoe to further improve controllability during braking and further prevent the vehicle from rolling away when stopping. In particular, it is necessary to increase the static friction coefficient while maintaining a correspondingly low sliding friction coefficient.

[0007] An object of the present invention is to provide a brake shoe comprising a resin-based friction material having an increased static friction coefficient while maintaining a correspondingly low dynamic friction coefficient. Another object of the present invention is to provide a tread brake device for a rail vehicle comprising the above-mentioned brake shoe with a resin-based friction material.

[0008] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by using a brake shoe containing a synthetic resin-based friction material (also referred to as a "synthetic resin brake shoe" in this specification), in which the synthetic resin-based friction material contains natural graphite, artificial graphite, and calcium silicate as friction modifiers. Thus, the present invention is completed.

[0009] That is, the present invention relates to the following content. [1] The brake shoe with a synthetic resin-based friction material containing a friction modifier, a binder and a fiber material, wherein the synthetic resin-based friction material contains natural graphite, artificial graphite and calcium silicate as a friction modifier. [2] The brake shoe according to [1], in which the total content of natural graphite and artificial graphite in the synthetic resin-based friction material is 15 mass% to 35 mass%. [3] The brake shoe according to [1] or [2], in which the content of calcium silicate in the synthetic resin-based friction material is 0.5 mass% to 12 mass%. [4] The brake shoe according to any one of [1] to [3], wherein the synthetic resin-based friction material further contains calcium carbonate as a friction modifier. [5] The brake shoe according to any one of [1] to [4], wherein the resin-based friction material further contains a cast iron powder as a friction modifier. [6] The brake shoe according to any one of [1] to [5], intended for use in a rail vehicle. [7] Tread brake device for a rail vehicle, including the brake shoe according to [6].

[0010] Since the brake shoe according to the present invention has an increased static friction coefficient while maintaining a reasonably small sliding friction coefficient, particularly when the brake shoe is provided in a tread brake device for a railway vehicle, it is possible to further improve controllability during braking and further prevent rolling when the vehicle is stopped. BRIEF DESCRIPTION OF THE DRAWINGS The figure shows the front view of a brake shoe according to an embodiment of the present invention. DESCRIPTION OF THE EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0012] The figure shows a front view of a brake shoe according to an embodiment of the present invention. A brake shoe 1 is essentially composed of a base metal 2, a friction material 3, and a mounting plate 4. The base metal 2 is a generally rectangular flat plate formed in an arc along an arc of a wheel of a railway vehicle, and the friction material 3 is attached to a main surface on a wheel side of the base metal 2. The mounting plate 4 is loosely attached to a brake shoe head on a vehicle side (not shown) and serves as a torque receiving portion that receives torque generated during braking.Such a brake shoe 1 constitutes a tread braking device in a braking device for a rail vehicle, and during braking, the friction material 3 is pressed against a tread of the wheel to generate a frictional force, and the frictional force is used as a braking force to stop or decelerate the vehicle.

[0013] The brake shoe according to the embodiment of the present invention includes a resin-based friction material containing a friction modifier, a binder, and a fiber material, wherein the resin-based friction material includes natural graphite, artificial graphite, and calcium silicate as a friction modifier.

[0014] 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, with the aim of achieving a low friction coefficient and ensuring braking performance in the resin-based friction material.

[0015] As the natural graphite, graphite with an average particle diameter of 1 μm to 200 μm is preferably used, and graphite with an average particle diameter of 20 μm to 60 μm is more preferably used. When natural graphite with an average particle diameter within the above range is used, lubricity with respect to a sliding surface of a mating material, such as the tread of a railway wheel, is improved, and the dynamic friction coefficient can be reduced.

[0016] Natural graphite can include, for example, vein graphite, flake graphite and amorphous graphite.

[0017] As the artificial graphite, graphite with an average particle diameter of 100 μm to 1100 μm is preferably used, and graphite with an average particle diameter of 400 μm to 800 μm is more preferably used. When artificial graphite with an average particle diameter within the above range is used, formability and crack resistance can be improved.

[0018] Artificial graphite is sometimes also called granular graphite.

[0019] The average particle diameter in the description of the present application can be determined as a particle diameter corresponding to a cumulative percentage of 50% (D50) on a volume basis from a particle size distribution measured using a laser diffraction particle sizer (for example, "LS 13 320" from Beckman Coulter, Inc.).

[0020] The total content of natural and artificial graphite in the resin-based friction material is preferably 15 mass% to 35 mass%, more preferably 18 mass% to 32 mass%, and even more preferably 21 mass% to 29 mass%. The total content of natural graphite and artificial graphite is preferably 15 mass% or more because the dynamic friction coefficient can be reduced to the same level as that of a cast iron-based friction material. Furthermore, the total content of natural graphite and artificial graphite is preferably 35 mass% or less because the crack resistance and cleanliness of the sliding surface of the mating material can be sufficiently maintained.

[0021] A mass ratio of natural graphite to artificial graphite (natural graphite: artificial graphite) is preferably 1:1 to 5:1. When the mass ratio is within this range, the dynamic friction coefficient can be reduced to the same level as that of a cast iron-based friction material. Furthermore, the effect on 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 preferably 2:1 to 5:1, and more preferably 2:1 to 4:1. When the mass ratio is within this preferred range, crack resistance can be further improved.

[0022] Examples of calcium silicate are a xonotlite type and a tobermorite type. The xonotlite type has the formula Ca6Si6O 17(OH)2 and is a porous particle with needle-shaped crystals within. The tobermorite type has the formula Ca5(Si6O 18 H2)·8H2O or Ca5(Si6O 18 H2)-4H2O and is a porous particle with a plate-like crystal structure called a house of cards.

[0023] As calcium silicate, a xonotlite-type product, “Promaxon” (product name), manufactured by Promat, can be used.

[0024] The calcium silicate is calcium silicate with an average particle diameter of preferably 1 µm to 120 µm, more preferably 5 µm to 110 µm, and even more preferably 10 µm to 100 µm. The calcium silicate acts to increase the static friction coefficient while maintaining a reasonably low dynamic friction coefficient for the brake shoe.

[0025] The average particle diameter of the calcium silicate is preferably 1 µm or more because the static friction coefficient can be increased, and preferably 120 µm or less because sufficient mechanical strength can be ensured.

[0026] The content of calcium silicate in the resin-based friction material is preferably 0.5 mass% to 12 mass%, more preferably 1 mass% to 10 mass%, and even more preferably 2 mass% to 8 mass%.

[0027] The content of calcium silicate in the resin-based friction material is preferably 0.5 mass% or more because the static friction coefficient can be increased, and is preferably 12 mass% or less because sufficient mechanical strength can be ensured.

[0028] The resin-based friction material preferably contains at least one organic filler selected from cashew and rubber dust (also referred to as "cashew and / or rubber dust" in this specification) as a friction modifier. By including at least one of the cashew and rubber dust, the friction coefficient can be ensured under light load under dry conditions.

[0029] Examples of cashew dust include those formed by carbonizing and hardening an oil extracted from the shell of a cashew nut. The cashew dust has an average particle diameter of preferably 10 µm to 500 µm, and more preferably 100 µm to 300 µm.

[0030] Examples of rubber dust include those produced by pulverizing tire rubber (e.g., tread rubber). The rubber dust has an average particle diameter of preferably 10 µm to 1500 µm, and more preferably 300 µm to 600 µm.

[0031] The total content of cashew and / or rubber dust in the resin-based friction material is preferably 1 mass% to 15 mass%, more preferably 2 mass% to 12 mass%, and even more preferably 3 mass% to 10 mass%. Note that in the case where the resin-based friction material contains only one of cashew and rubber dust, the "total content of cashew and / or rubber dust" indicates the content of cashew or rubber dust.

[0032] The total content of cashew and / or rubber dust in the resin-based friction material is preferably 1 mass% or more because the flexibility is improved, and preferably 15 mass% or less because the friction coefficient can be ensured.

[0033] Examples of other friction modifiers include: inorganic fillers such as barium sulfate, calcium pyrophosphate, calcium carbonate, calcium hydroxide, vermiculite, mica (phlogopite, muscovite, synthetic mica, and natural mica), potassium titanate, lithium potassium titanate, and magnesium potassium titanate; abrasives such as silicon carbide, aluminum oxide, silicon dioxide, magnesium oxide, chromite, ferric oxide, zirconium oxide, and zirconium silicate; lubricants such as molybdenum disulfide, tin sulfide, zinc sulfide, and iron sulfide; metal powders such as zinc, tin, copper, iron, and aluminum; and solid lubricants such as graphite, excluding natural and artificial graphite. These can be used individually or in combination of two or more types. The total content of the other friction modifiers can be appropriately adjusted depending on the desired friction properties.The content of the other friction modifiers in the resin-based friction material is preferably 30 mass% to 85 mass%, and more preferably 40 mass% to 80 mass%, depending on the desired friction coefficient.

[0034] From the point of view of formability in the production of the brake shoe, calcium carbonate is preferable as a friction modifier.

[0035] When calcium carbonate is present, its content in the resin-based friction material is preferably 8 mass% to 45 mass%, more preferably 10 mass% to 40 mass%, and even more preferably 13 mass% to 35 mass%. Its content in the resin-based friction material is preferably 8 mass% or more because wear resistance is improved, and is preferably 45 mass% or less because the friction coefficient is ensured.

[0036] To ensure the dynamic friction coefficient, a cast iron powder is preferably included as a friction modifier.

[0037] If cast iron powder is present, its content in the resin-based friction material is preferably 1 mass% to 30 mass%, more preferably 5 mass% to 25 mass%, and even more preferably 10 mass% to 20 mass%. The content of cast iron powder in the resin-based friction material is preferably 1 mass% or more because the dynamic friction coefficient can be increased, and is preferably 30 mass% or less because an appropriate friction coefficient can be ensured.

[0038] As the cast iron powder, it is preferable to use one having an average particle diameter of 10 µm to 200 µm, more preferably one having an average particle diameter of 30 µm to 150 µm, and even more preferably one having an average particle diameter of 50 µm to 100 µm.

[0039] The average particle diameter of the cast iron powder is preferably 10 µm or more because the dynamic friction coefficient can be increased, and preferably 200 µm or less because a suitable friction coefficient can be ensured.

[0040] The fiber material is used to reinforce the resin-based friction material. Examples of fiber materials 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 (biosoluble fibers are preferred), glass fibers, carbon fibers, and rock wool. Examples of metal fibers include steel fibers. These can be used singly or in combination with two or more types. The content of the fiber base material in the resin-based friction material is preferably 1 to 50 mass%, and more preferably 3 to 45 mass%, to ensure sufficient mechanical strength.

[0041] The binder contains a thermosetting resin. Examples of thermosetting resins include a phenolic resin, an epoxy resin, and a resin obtained by modifying these thermosetting resins with cashew oil, silicone oil, and various elastomers, as well as a resin obtained by dispersing various elastomers, a fluoropolymer, and the like in these thermosetting resins. These can be used singly or in combination of two or more types. The binder content in the resin-based friction material is preferably 5 to 25 mass%, and more preferably 10 to 20 mass%, to ensure sufficient mechanical strength and wear resistance as a brake shoe.

[0042] The brake shoe according to the embodiment of the present invention can be manufactured using a known manufacturing method. For example, the brake shoe can be manufactured by a manufacturing method including a preforming step of a friction material composition constituting the friction material and a hot press molding step of a preformed body obtained in the preforming step. Each step will be described in detail below.

[0043] First, in the preforming step, the raw materials for forming the friction material are uniformly mixed, and the resulting friction material composition is pressed to obtain a preformed body. The friction material composition contains natural graphite, artificial graphite, and calcium silicate, and may further contain the above organic filler, other friction modifiers, fiber base material, binder, and the like.

[0044] The friction material composition is filled into a mold and press-molded, preferably under conditions of 6 MPa to 14 MPa, to improve mixability and processability in the hot press-molding step. If the pressure is less than 6 MPa, the preformed body may be difficult to form, and if the pressure is more than 14 MPa, the preformed body may crack, which is undesirable.

[0045] In hot pressing, the preformed body obtained in the preforming step is filled into a hot press mold, a base metal is placed on it, and hot pressing is carried out to obtain a brake shoe with the desired shape.

[0046] The conditions for hot pressing are preferably a temperature of 140 °C to 155 °C, a pressure of 10 MPa to 20 MPa and a time of about 20 minutes to 60 minutes.

[0047] The brake shoe according to the embodiment of the present invention includes a friction material having an increased static friction coefficient while maintaining a reasonably small dynamic friction coefficient at the same level as a cast iron-based friction material, and is therefore particularly useful as a brake shoe for a railway vehicle.

[0048] Therefore, the brake shoe according to the embodiment of the present invention can be provided in a tread brake device for a railway vehicle. Examples

[0049] Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0050] The tests performed on each example are as follows. (1) Dynamic friction coefficient (low load conditions)

[0051] Counter material wheel: forged steel (Q3S) Initial braking speed: 30 km / h, 60 km / h, 100 km / h, 120 km / h Contact force: 12 kN, 16 kN, 20 kN Mass of counter material: 1.8 tons

[0052] Using a dynamometer tester, tests were conducted under the above-mentioned conditions at the above-mentioned initial braking speeds and with the above-mentioned downforces, and the dynamic friction coefficient (dynamic μ) against the mating material wheel under a low-load condition was measured. Note that the μ used in the evaluation of the dynamic friction coefficient is the dynamic μ value at an initial braking speed of 30 km / h and a downforce of 20 kN.

[0053] The dynamic friction coefficient µ under a low load condition was evaluated (determined) as follows. A: 0.22 ≤ µ ≤ 0.29, B: 0.18 ≤ µ < 0.22 and 0.29 < µ ≤ 0.33, C: µ < 0.18 and 0.33 < µ (2) Coefficient of static friction

[0054] Counter material wheel: forged steel (Q3S)

[0055] Contact force: 5 kN, 14 kN, 30 kN, 40 kN

[0056] Using a dynamometer tester under the above conditions, tests were conducted at the above-mentioned pressing forces, and the coefficient of static friction (static µ) against the mating material wheel was measured. Note that the µ value used in the evaluation of the coefficient of static friction is the static µ value at a pressing force of 30 kN and 40 kN.

[0057] The static friction coefficient µ was evaluated (determined) as follows. A: 0.20 ≤ µ B: outside the range of A

[0058] In addition, based on the evaluation of the static friction coefficient µ, a comprehensive evaluation (determination) was carried out as follows. A: under the conditions of compressive force of 30 kN and 40 kN, both were determined as “A” B: under the conditions of a compressive force of 30 kN and 40 kN, determined as “A” and “B” C: under the conditions of compressive force of 30 kN and 40 kN, both were determined as “B” <Mischmaterialien von Reibmaterialien auf Kunstharzbasis>

[0059] The materials used in the manufacture of the resin-based friction materials in each example are as follows. Binding resin: phenolic resin Rubber dust: 500 µm average particle diameter Barium sulfate: 10 µm average particle diameter Calcium carbonate: 3.5 µm average particle diameter Calcium silicate: 20 µm average particle diameter Natural graphite: 40 µm average particle diameter Artificial graphite: 600 µm average particle diameter Cast iron powder: 80 µm average particle diameter (Example 1)

[0060] The resin-based friction material blends were charged into a mixer according to the blending recipe (mass %) shown in Table 1 and mixed in the mixer for 210 seconds. The blended resin-based friction material composition was preformed at a pressure of 7 MPa for 15 seconds to produce a preformed body. Next, the preformed body was placed in a hot mold at 145°C, a base metal was placed on top, and hot press molding was performed at a pressure of 15.0 MPa for 27 minutes to obtain a hot-pressed molded body. Grooves were then formed into the hot-pressed molded body to produce a brake shoe.

[0061] The above tests (1) and (2) were performed on the obtained brake shoe. The results are shown in Table 1. (Examples 2 to 6 and comparative examples 1 to 4)

[0062] Brake shoes were manufactured in the same manner as in Example 1, except that the blending material and amounts of resin-based friction materials were changed to those shown in Table 1.

[0063] The above-mentioned tests (1) and (2) were performed on the brake shoes obtained. The results are shown in Table 1.

[0064] As can be seen from the results in Table 1, the friction materials in Examples 1 to 6 exhibit an increased static friction coefficient while maintaining a reasonably small dynamic friction coefficient. Accordingly, the friction materials in Examples 1 to 6 exhibit higher performance of a brake shoe, which has been required in recent years from the viewpoint of further improving controllability during braking and further preventing rolling when the vehicle is stationary, and are particularly useful for a tread brake device for a railway vehicle.

[0065] In contrast, the friction materials in Comparative Examples 1 to 4 have small values ​​for both the dynamic friction coefficient and the static friction coefficient. [Industrial applicability]

[0066] The brake shoe according to the present invention can be used in particular in a tread brake device for a rail vehicle.

[0067] The present invention has been described in detail with reference to a specific mode, but it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

[0068] This application is based on Japanese Patent Application No. 2024-049539, filed on March 26, 2024, the entirety of which is incorporated by reference into this application. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2017-31316A

[0004] JP 2024-049539

[0068]

Claims

[1] A brake shoe comprising a synthetic resin-based friction material containing a friction modifier, a binder and a fiber material, wherein the synthetic resin-based friction material contains a natural graphite, an artificial graphite and calcium silicate as a friction modifier. [2] The brake shoe according to claim 1, wherein the total content of natural graphite and artificial graphite in the synthetic resin-based friction material is 15 mass% to 35 mass%. [3] The brake shoe according to claim 1 or 2, wherein the content of calcium silicate in the resin-based friction material is 0.5 to 12 mass%. [4] The brake shoe according to claim 1 or 2, wherein the resin-based friction material further contains calcium carbonate as a friction modifier. [5] The brake shoe according to claim 1 or 2, wherein the resin-based friction material further contains a cast iron powder as a friction modifier. [6] The brake shoe according to claim 1 or 2, which is intended for use in a rail vehicle. [7] A tread brake device for a rail vehicle, comprising the brake shoe according to claim 6.

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