CN111396482A

CN111396482A - Copper-free friction material and brake pad

Info

Publication number: CN111396482A
Application number: CN202010108339.9A
Authority: CN
Inventors: 陈小刚; 旷文敏; 陈耀
Original assignee: TMD Friction Holdings GmbH
Current assignee: TMD Friction Holdings GmbH
Priority date: 2020-02-21
Filing date: 2020-02-21
Publication date: 2020-07-10

Abstract

The invention discloses a copper-free friction material and a brake pad prepared based on the copper-free friction material. The scheme of the copper-free friction material is an environment-friendly friction material. The brake block made of the friction material has special heat conduction characteristics: the heat conductivity along the friction surface direction is very good, the heat conductivity along the thickness direction of the brake pad is relatively low, and the brake pad can timely release heat generated by braking in the braking process, so that local hot spots formed on the brake pad or a brake disc are avoided, and the brake pad has very good characteristics of recession resistance, wear resistance, shake resistance and the like.

Description

Copper-free friction material and brake pad

Technical Field

The invention relates to the technical field of friction materials, in particular to a copper-free friction material and a brake pad prepared based on the copper-free friction material.

Background

Friction materials can be classified into several types, depending on the materials used in the formulation, such as "semi-metals", "low metals" and "organic non-asbestos (NAO)". The semimetal formula is gradually eliminated due to large metal consumption and poor noise performance. The low-metal formula has better high-temperature resistance, so that the low-metal formula is more used in the field of high-performance automobiles with higher requirements on limit characteristics, and the use occasions generally have higher requirements on harsh braking conditions but are not very sensitive to noise and comfort. However, in the field of common household vehicles, driving conditions are not complicated and driving environments are relatively good, so that requirements on driving comfort and noise sensitivity are higher and higher, and under the conditions, the NAO formula without non-ferrous metals is produced and widely used.

Copper is one of the most critical components in most low metal and NAO friction material formulations, and is typically present in a mass proportion of about 5% to 25%. Relevant research shows that dust containing copper or other heavy metals generated in the automobile braking process is polluted by the ecological environment caused by rainwater rushing into rivers.

For the purpose of ecological protection, the states of california and washington, etc. in the united states have passed through related laws in an attempt to reduce the use of copper in brake pads. The related regulations stipulate that the copper content in the brake pad is reduced to below 5% in 2021, and is reduced to below 0.5% in 2025. The development and use of copper-free friction materials has become an inevitable trend.

The braking process of the automobile, in short, converts the kinetic energy of the vehicle into heat energy through the mutual friction between the friction plate and the friction disc, so as to stop the vehicle. The friction plates and discs will therefore experience higher temperatures during braking, especially in more aggressive driving conditions. As generally recognized in this field, excessive temperatures cause problems such as high wear, heat fading (reduction in friction coefficient), and deformation of the brake disc. From the perspective of the driver, greater wear can result in reduced service life of the brake pad; the heat fading causes the reduction of the braking efficiency and generates serious potential safety hazard; if the temperature of the friction pair is too high and the heat dissipation is poor, the brake disc can be deformed, so that the vehicle body shakes in the braking process, and potential safety hazards and poor driving experience can be caused.

The copper is widely applied to the field of friction materials, and the key point is that the copper has excellent heat-conducting property, so that heat generated by braking can be dissipated in time, the working temperature of a friction surface is prevented from being too high, and the problems of high abrasion, heat fading, deformation of a brake pad and the like can be avoided.

In order to achieve the same thermal conductivity, suitable copper alternatives must be found. As metal fibers such as steel fibers and the like with good heat-conducting property, the copper-based friction material can partially replace the copper in the formula of the friction material. However, it is unsatisfactory due to the noise problem caused by the steel fibers. Therefore, development of a copper-free friction material of NAO type which does not contain nonferrous metals is clearly more desirable.

Patent publication No. CN 103797085a uses "a titanate compound having a plurality of projections" in combination with "a biosoluble inorganic fiber" from the viewpoint of environmental protection, and the resulting friction material has good material strength even in a high temperature region of 400 ℃ or higher, and therefore has good wear resistance. In addition, because the titanate has the special feature of 'a plurality of convex parts', the rust removing capability of the titanate is stronger than that of plate-shaped or scaly titanate. However, this also creates a certain risk: the friction plate is too aggressive, which may cause uneven wear of the brake disc or form local friction high temperature heat accumulation, thereby possibly causing uneven deformation of the brake disc, and therefore, after the friction plate is actually used, the vibration and noise performance of the friction plate need to be further verified.

In patent publication No. CN 106634832A, the inventor adopts a composite fiber with zinc fiber as the main part and aluminum fiber as the auxiliary part to replace the copper fiber in the traditional NAO friction material, so as to solve the problem of environmental pollution caused by heavy metals such as copper in the traditional NAO friction material. The researchers found that: the zinc fibers can form an anchoring effect on the friction surface, and zinc oxide is formed after zinc is oxidized, so that the high-temperature friction surface is effectively stabilized; the aluminum fiber is oxidized to produce aluminum oxide with high hardness, and the high-temperature friction coefficient can be stabilized. The two fibers act synergistically to realize the substitution effect on the copper fiber. Meanwhile, the zinc has higher activity, and can also play a role in weakening the corrosion of the friction disc. Because of the low melting point of zinc, there is a possibility that large-particle metallic zinc will melt and adhere to the friction disk when the friction temperature is high due to heavy driving.

Therefore, the problem to be solved in the field is to provide a friction material which does not contain copper, can meet the requirements of high abrasion resistance, small heat fading, difficult deformation and good anti-shaking performance of a brake pad.

Disclosure of Invention

In response to the problems associated with the prior brake pad friction materials, a new copper-free friction material solution is needed.

Therefore, the invention aims to provide a copper-free friction material and a brake pad prepared on the basis of the copper-free friction material, wherein the copper-free friction material does not contain copper and can meet the requirements of high wear resistance, small heat fading, difficult deformation and good jitter resistance of the brake pad.

In order to achieve the purpose, the copper-free friction material provided by the invention adopts a heat conduction system formed by combining the anisotropic heat conduction material and the isotropic heat conduction material, wherein the isotropic heat conduction material is uniformly and randomly distributed and is filled among particles of the anisotropic heat conduction material to connect the anisotropic heat conduction material.

Further, the mass percentage of the anisotropic heat conduction material is 5-15%; the mass percentage of the isotropic heat conduction material is 1-6%.

Further, the copper-free friction material also comprises the following components in parts by weight:

further, the anisotropic heat conduction material is one or a combination of more of flake graphite, expanded graphite, flake artificial graphite, acicular petroleum coke and artificial graphite with a certain length-diameter ratio.

Further, the isotropic heat conduction material can be one or more of carbon black, microcrystalline graphite, coke powder and non-nonferrous metal powder.

Further, the binder can be one or more of straight-chain phenolic resin, modified phenolic resin for enhancing flexibility, modified phenolic resin for enhancing heat resistance, silicon modified phenolic resin for hydrophobicity and rapid curing resin for improving curing speed.

Further, the fiber material is organic fiber or inorganic fiber, and the organic fiber can be one or more of aramid fiber, cellulose fiber and polyacrylonitrile fiber pre-oxidized silk fiber; the inorganic mineral fiber is non-asbestos bio-soluble mineral fiber.

Further, the friction filler is a material with the Mohs hardness of 4-9.

Further, the lubricating filler may be one or more combinations of a sulfide, a compound lubricant, or a polymeric lubricant.

Further, the elastomer material may be one or more of vulcanized rubber powder particles, cashew nut shell oil friction powder particles, recycled tire powder rubber particles, heat-treated expanded vermiculite, coke particles with porous structure.

Further, the other functional filler includes one or more of a basic material for adjusting the PH, a low-hardness and low-cost filler, and a material for facilitating the formation of the transfer film.

In order to achieve the above object, the present invention provides a brake pad comprising a steel backing and a friction material layer provided on the steel backing, the friction material layer being composed of the above copper-free friction material.

The friction material provided by the invention does not contain copper element, and meets the requirements of environmental protection laws and regulations. The brake block formed by the friction material provided by the invention has special heat conduction characteristics: the heat conductivity along the friction surface direction is very good, the heat conductivity along the thickness direction of the brake pad is relatively low, and in the braking process, the friction plate can timely release heat generated by braking, so that local hot spots formed on the brake pad or a brake disc are avoided, and the brake pad has the characteristics of very good recession resistance, wear resistance, shake resistance and the like.

Drawings

The invention is further described below in conjunction with the appended drawings and the detailed description.

FIG. 1 is a process flow diagram for preparing a brake pad based on the friction material provided in the present example;

FIG. 2 is a schematic structural view of a brake pad prepared based on the friction material provided in the present example;

table 1 is a table of formulations of friction materials provided in this example and comparative examples;

table 2 is a table comparing the performance of brake pads made based on the friction materials provided in the examples with brake pads made with the copper-containing friction materials provided in the comparative examples.

The meaning of the reference numerals in the figures:

the brake pad comprises a brake pad back plate 1, a brake pad friction material part 2 and a brake pad, wherein the brake pad is transverse, the tangential direction X of a brake pad friction working surface, the brake pad is longitudinal, the radial direction Y of the brake pad friction working surface, the thickness direction of the brake pad and the normal phase direction Z of the brake pad friction working surface.

Detailed Description

In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further explained below by combining the specific drawings.

In order to achieve the above object, the present solution uses an optimized combination of anisotropic and isotropic heat conducting materials, the combined heat conducting system providing the brake pad with excellent heat conductivity along the friction surface and relatively weak heat conductivity in the vertical direction. In the braking process, the brake pad can timely release heat generated by braking, and local hot spots formed on the brake pad or a brake disc are avoided, so that the brake pad has the characteristics of very good recession resistance, wear resistance, shake resistance and the like, and simultaneously meets the requirements of environmental protection regulations.

Specifically, the anisotropic thermal conductive material includes: flake graphite, expanded graphite, flake artificial graphite, acicular petroleum coke, artificial graphite with a certain length-diameter ratio, and the like. These materials are characterized by a relatively large dimension in one or two dimensions (100-. The component is used as a main structural material of a heat conduction system of the friction plate, and has relatively high content in a formula, wherein the mass percent is 5-15%, and the preferable proportion is 7-12%.

In cooperation with this, the isotropic heat conduction material in this scheme includes: granular materials such as carbon black, microcrystalline graphite, coke powder, non-ferrous metal powder and the like. The isotropic heat conducting material formed by the material has small particle size (20-100 μm, preferably 30-50 μm) and is relatively uniform in three-dimensional size. When the isotropic heat conduction material is matched with the anisotropic heat conduction material to form a corresponding brake pad, the isotropic heat conduction material is uniformly and randomly distributed in the brake pad, is filled among particles of the anisotropic heat conduction material, and connects mutually independent anisotropic heat conduction materials; the distribution mode of the heat conduction materials formed by the method enables the brake pad to have excellent heat conduction along the friction surface direction and relatively weak heat conduction in the vertical direction. The brake pad with the characteristics is beneficial to heat emission in the braking process, and avoids local hot spots formed on the brake pad or a brake disc, so the brake pad has the characteristics of very good recession resistance, wear resistance, shake resistance and the like.

In order to be efficiently matched with the anisotropic heat conduction material and ensure that the performance of the formed brake pad is optimal, the content of the adopted isotropic heat conduction material in the formula needs to be accurately controlled, the anisotropic heat conduction material cannot be connected into a whole when the content is too small, and the oriented heat conduction characteristic of the friction plate can be lost when the content is too large. The inventor of the scheme determines that the mass percentage of the isotropic heat conduction material in the formula is 1-6%, and the optimal proportion is 2-5% through a great deal of creative work, so that the performance of the formed brake pad can be optimal.

In addition, as an important component forming the friction material, the friction material also comprises the following other components in parts by weight so as to form a friction material composition formula with mutual synergistic action:

in this example, the binder may be one or more of a straight-chain type phenol resin, a modified phenol resin for enhancing flexibility, a modified phenol resin for enhancing heat resistance, a silicon modified phenol resin for hydrophobic modification, and a fast curing resin for increasing curing speed.

Among them, as the straight-chain phenol resin, thermosetting phenol resin and thermoplastic phenol resin mixed with a curing agent can be used.

The modified phenolic resin for enhancing flexibility can be cashew nut shell oil modified phenolic resin or propylene rubber modified phenolic resin.

The modified phenolic resin with enhanced heat resistance can adopt boron modified phenolic resin and aralkyl modified phenolic resin.

In order to improve the heat fading resistance and the wear resistance of the friction material, one or more combinations of straight-chain type or reinforced heat-resistant modified phenolic resin with better heat resistance are preferably selected, so that the formed friction material has good stability at high temperature.

The fiber material in this example can be organic fiber or inorganic mineral fiber, which can increase the mechanical strength of the friction material. The organic fiber can be one or more of aramid fiber, cellulose fiber and polyacrylonitrile fiber and pre-oxidized silk fiber. The fiber has the characteristics of large specific surface area and can play roles in enhancing and reducing dust.

The inorganic mineral fibers herein are non-asbestos bio-soluble mineral fibers, preferably surface-treated, or surface-modified, or surface-coated inorganic mineral fibers. Such fibers serve to both reinforce and stabilize the coefficient of friction.

The friction filler in this example means a filler capable of increasing the friction coefficient.

The friction filler is preferably a material having a mohs hardness of 4 to 9, and may be a plurality of oxide materials such as zirconia, alumina, magnesia, titania, iron oxide, or a partially high-hardness silicate material. These high hardness materials may scratch the mating surface after being pressed, resulting in a large frictional force.

The lubricating filler in this example means a filler capable of reducing the friction coefficient.

The lubricating filler herein may be a sulfide, a compound lubricating material, or a polymer lubricating material.

The sulfide can be tin sulfide, copper sulfide, iron sulfide, molybdenum sulfide and the like; as the compound lubricating material, zirconium phosphate, boron nitride, or the like can be used; polytetrafluoroethylene powder can be used for the polymer lubricating material. The lubricating fillers have lower hardness, do not damage the dual surface and can reduce the wear rate of the friction plate product.

The elastomer material in the embodiment is a material with certain elasticity, so that the rigidity of the friction plate product can be reduced, and the effect of reducing noise is achieved.

The elastomer material can be one or more of vulcanized rubber powder particles after vulcanization, cashew nut shell oil friction powder particles, recycled tire powder rubber particles, heat-treated expanded vermiculite and coke particles with porous structures. The elastomer materials provide proper hardness and rigidity for the friction plate product, and can reduce or even eliminate the brake noise of the friction plate product in the use process.

The other functional fillers in the embodiment play roles in reducing cost and stabilizing friction coefficient.

Other functional fillers herein include basic materials such as calcium hydroxide and calcium oxide for PH adjustment, low-hardness and low-cost fillers such as inorganic materials including calcium carbonate, barium sulfate and mica, and titanates to facilitate the formation of transfer films.

The basic scheme for preparing the corresponding brake pad based on the friction material is also given in the example aiming at the composition scheme of the friction material.

Referring to fig. 1, a process flow for manufacturing a brake pad based on the friction material is shown in this example.

As can be seen, the process for preparing the brake pad based on the friction material of the present example is as follows:

(1) the preparation work needs to comprise the following three parts:

(1.1) based on the formulation given in this example, the components forming the friction material were first weighed, and then the weighed components were put together into a mixer and sufficiently mixed to form the friction material mixture of the present invention.

(1.2) weighing the components for forming the bottom cushion material, mixing the weighed components, and finally forming the bottom cushion material mixture.

And (1.3) carrying out sand blasting on the steel back of the brake pad, then carrying out phosphating and finally gluing.

(2) The mixed friction material and base material were mechanically pressed onto the steel backing.

(3) And solidifying the friction material and the base material pressed on the steel backing, machining and ablating, and then performing post-treatment to obtain the brake pad.

Referring to fig. 2, a diagram of an exemplary brake pad structure formed based on the preparation scheme of the present example is shown. In the figure, an XY surface is parallel to the friction surfaces of a brake pad back plate 1 and a brake pad friction material part 2, anisotropic materials are distributed along the direction, and the heat conductivity of the brake pad in the direction is better; the Z-axis direction is perpendicular to the friction surfaces of the pad backing plate 1 and pad friction material portion 2, and the pad has relatively poor thermal conductivity in this direction.

The brake pad with the structure has special heat conduction characteristic, the heat conductivity along the friction surface direction is very good, the heat conductivity along the thickness direction of the brake pad is relatively low, and in the braking process, the brake pad can timely release heat generated by braking, so that a local hot spot formed on the brake pad or a brake disc is avoided, and the brake pad has very good characteristics of recession resistance, wear resistance, shake resistance and the like.

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental methods of the following examples, which are not specified under specific conditions, are generally determined according to national standards. If there is no corresponding national standard, it is carried out according to the usual international standards, to the conventional conditions or to the conditions recommended by the manufacturer. Unless otherwise indicated, all parts are parts by weight, all percentages are percentages by weight, and the polymer molecular weight is the number average molecular weight.

Unless defined or stated otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention.

The examples herein were carried out based on the specific formulation ratios given in table 1, while corresponding comparative examples are given in table 1 for comparison of the performance of the inventive material and the copper-containing friction material.

In addition, it should be noted that the examples shown in table 1 are only used for explaining the scheme of the present invention, and do not set any limit to the technical scheme of the present invention.

Specifically, the copper-free friction material provided in the example and the copper-containing friction material of the comparative example were prepared by thoroughly mixing the materials for 10 to 20 minutes using an L odige or Eirich mixer according to the formulation given in Table 1.

On the basis, the uniformly mixed copper-free friction material and the comparative copper-containing friction material are respectively prepared into brake pads with specific shapes according to the production process of FIG. 1.

TABLE 1

For 5 groups of brake pads and 1 group of comparative brake pads prepared based on the 5 groups of friction material proportioning schemes and 1 group of comparative proportioning schemes given in table 1, the following performance tests were respectively performed:

(1) coefficient of friction and resistance to thermal fade test: specifically, the SAE J2522 procedure was used to run the coefficient of friction and thermal decay tests on an inertia stand apparatus to account for the coefficient of friction level and the resistance to thermal decay level of the friction material in the present embodiment.

(2) And (3) wear resistance test: the wear test was run on an inertia stand apparatus using the SAE J2707 procedure in particular, taking into account the level of wear resistance of the friction material in the present embodiment.

(3) Anti-jitter property test: specifically, a brake disc Thickness difference tester is used to measure the brake disc Thickness difference after a wear procedure, i.e., dtv (disc Thickness variation), so as to consider the anti-vibration characteristic of the friction material in the present embodiment.

Referring to table 2, it can be seen that the friction material without copper provided in the embodiment completely meets the specification requirements in terms of friction coefficient level, friction coefficient heat fading resistance level, wear resistance level, anti-shudder level, etc., and some results are even better than those of the comparative example of the friction material with copper. Therefore, the friction material provided by the embodiment can meet the relevant requirements of the vehicle brake pad, and has strong market competitiveness.

TABLE 2

As can be seen from the above embodiment, the friction material provided by the invention does not contain copper element, and meets the requirements of environmental protection laws and regulations. Meanwhile, in the braking process of the brake pad prepared from the friction material provided by the invention, the brake pad can timely release heat generated by braking, and local hot spots formed on the brake pad or a brake disc are avoided, so that the brake pad has the characteristics of very good recession resistance, wear resistance, jitter resistance and the like.

The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. The copper-free friction material is characterized in that a heat conduction system is formed by combining an anisotropic heat conduction material and an isotropic heat conduction material, wherein the isotropic heat conduction material is uniformly and randomly distributed and filled among particles of the anisotropic heat conduction material to connect the anisotropic heat conduction material.

2. The copper-free friction material of claim 1, wherein the mass percent of the anisotropically thermally conductive material is 5-15%; the mass percentage of the isotropic heat conduction material is 1-6%.

3. The copper-free friction material as recited in claim 1 or 2 further comprising the following components in parts:

4. the copper-free friction material of claim 3, wherein the anisotropic thermal conductive material is one or more of a combination of flake graphite, expanded graphite, flake artificial graphite, acicular petroleum coke, and artificial graphite having a certain aspect ratio.

5. The copper-free friction material of claim 3, wherein the isotropic thermal conductive material may be one or more combinations of carbon black, microcrystalline graphite, coke powder, non-ferrous metal powder.

6. The copper-free friction material of claim 3, wherein the binder is selected from the group consisting of straight-chain phenolic resins, modified phenolic resins with enhanced flexibility, modified phenolic resins with enhanced heat resistance, silicon modified phenolic resins with hydrophobic modification, and fast curing resins with enhanced curing speed.

7. The copper-free friction material of claim 3, wherein the fiber material is an organic fiber or an inorganic fiber, and the organic fiber can be one or more of aramid fiber, cellulose fiber, polyacrylonitrile fiber and pre-oxidized silk fiber; the inorganic mineral fiber is non-asbestos bio-soluble mineral fiber.

8. The copper-free friction material of claim 3, wherein the friction filler is a material having a Mohs hardness of 4-9.

9. The copper-free friction material of claim 3, wherein the lubricating filler may be one or more combinations of a sulfide, a compound lubricant, or a polymeric lubricant.

10. The copper-free friction material of claim 3, wherein the elastomeric material is one or more of a combination of vulcanized crumb rubber particles after vulcanization, cashew nut shell oil friction powder particles, recycled tire crumb rubber particles, heat treated expanded vermiculite, coke particles having a porous structure.

11. The copper-free friction material of claim 3, wherein the other functional fillers include one or more of a basic material for pH adjustment, a low hardness, low cost filler, and a material that facilitates the formation of a transfer film.

12. A brake pad comprising a steel backing and a friction material layer disposed on the steel backing, wherein the friction material layer is comprised of the copper-free friction material of any of claims 1-11.