CN-116324209-B - Friction material block for equipping brake pad, brake pad and method for producing brake pad

Abstract

Friction block or layer made of an asbestos-free friction material comprising inorganic and/or organic and/or metal fibers, at least a binder, at least a friction modifier or lubricant and at least a filler or abrasive as its constituent materials, wherein the asbestos-free friction material further comprises as a further constituent material or additive a hydrophobic wax, preferably present in an amount of 0.5 to 5% by volume, the asbestos-free friction material block or layer having a hydrophobicity defined as the absorption time of droplets formed by 20+/-5pL of distilled water in the friction material being greater than 60 minutes such that the friction block or layer has a force of separation from the metal surface to which it has been electrochemically pressed of less than 15Nw.

Inventors

• Agustin Sinchkola
• Andrea Aesop Ardi
• Laura Rinaldi
• Daniele Zhenta
• TROMBOTTO FLAVIO

Assignees

• 意大利ITT有限责任公司

Dates

Publication Date

20260505

Application Date

20210917

Priority Date

20200917

Claims (20)

1. 1. A friction block or layer made of an asbestos-free friction material designed to be provided as an integral part of a vehicle brake pad, the asbestos-free friction material comprising inorganic and/or organic fibers, a binder, a friction modifier, and a filler as its constituent materials, wherein the asbestos-free friction material further comprises a hydrophobic wax as a further constituent material or additive, characterized in that the relative amount of the hydrophobic wax is selected in accordance with the chemical nature and amount of the other constituent materials of the asbestos-free friction material such that the asbestos-free friction material block or layer has a hydrophobicity defined as an absorption time of droplets formed of 20+/-5 μl of distilled water within the friction material of greater than 60 minutes, such that the asbestos-free friction material block or layer has no tendency to press on the surface of its friction pair or has a low tendency to press on the surface of its friction pair, after having been chemically pressed on the metal surface by pushing the friction material block or layer against the metal surface of steel or iron and causing a corrosion phenomenon thereon, the friction block or layer exhibits a small electrical separation force of newtonian from the metal surface of 15.
2. 2. A friction block or layer made of asbestos-free friction material according to claim 1, wherein the friction modifier is a lubricant and the filler is an abrasive.
3. 3. A friction block or layer made of asbestos-free friction material according to claim 1, wherein the metal surface is a metal surface of cast iron.
4. 4. A friction block or layer made of asbestos-free friction material according to claim 1, wherein the hydrophobic wax is in the form of a solid powder, has a melting point higher than 110 ℃, and is chemically stable at high temperatures and pressures.
5. 5. A friction block or layer made of asbestos-free friction material according to any one of claims 1 to 3, wherein the hydrophobic wax is selected from the group consisting of polyethylene wax, modified PE wax, micronized amide wax, polypropylene wax, PTFE texture powder.
6. 6. A friction block or layer made of asbestos-free friction material according to claim 5, wherein the hydrophobic wax is selected from the group consisting of PTFE modified polyethylene wax, HDPE wax, micronized PE wax, oxidized PE wax, micronized polypropylene wax.
7. 7. A friction block or layer made of asbestos-free friction material according to claim 5, wherein the hydrophobic wax is selected from self-adhesive waxes.
8. 8. A friction block or layer made of an asbestos-free friction material according to any one of the preceding claims 1 to 3, wherein the hydrophobic wax is present in the asbestos-free friction material in an amount of 0.5 to 5% by volume calculated on the total amount of friction material.
9. 9. Friction block or layer made of asbestos-free friction material according to the preceding claim 8, characterized in that the hydrophobic wax is present in the asbestos-free friction material in an amount of 1.0 to 2.0% by volume.
10. 10. A vehicle brake pad designed to cooperate in use with a vehicle brake disc made of iron or steel, the vehicle brake pad comprising an asbestos-free friction material block or layer operatively associated in use with the vehicle brake disc, wherein the asbestos-free friction material block or layer contains as one of its component materials from 0.5 to 5% by volume of a hydrophobic wax having a melting point higher than 110 ℃, characterized in that the hydrophobic wax is capable of rendering the asbestos-free friction material block or layer free of a tendency to press against the surface of the vehicle brake disc or having a low tendency to press against the surface of the vehicle brake disc, the friction material block or layer exhibiting a separation force from the metal surface of less than 15 newtons after having been electrochemically pressed against the metal surface of steel or iron by pushing the friction material block or layer against the metal surface and causing corrosion phenomena thereon, such that the brake disc has a reduced or zero tendency to static friction even under wet weather.
11. 11. The vehicle brake pad of claim 10, wherein the hydrophobic wax is selected from the group consisting of polyethylene wax, modified PE wax, polypropylene wax, micronized amide wax, PTFE textured powder.
12. 12. The vehicle brake pad of claim 10, wherein said vehicle brake disc is made of cast iron and said metal surface is a metal surface of cast iron.
13. 13. The vehicle brake pad of claim 11, wherein the hydrophobic wax is selected from the group consisting of PTFE modified polyethylene wax, HDPE wax, micronized PE wax, oxidized PE wax, micronized polypropylene wax.
14. 14. The vehicle brake pad of claim 11, wherein said hydrophobic wax is selected from self-adhesive waxes.
15. 15. Use of a hydrophobic wax in an asbestos-free friction material comprising inorganic and/or organic fibers, a binder, a friction modifier, and a filler as its further constituent materials, the hydrophobic wax being contained in the asbestos-free friction material in an amount of 0.5 to 5% by volume calculated on the total volume of the friction material, the hydrophobic wax being selected such that the asbestos-free friction material exhibits a reduced tendency or no tendency to static friction even in wet weather, the hydrophobic wax being selected such that the asbestos-free friction material exhibits a separation force from the metal surface of less than 15 newtons after the asbestos-free friction material has been pushed against and caused to corrode on the metal surface causing electrochemical pressing thereon.
16. 16. The use according to claim 15, wherein the friction modifier is a lubricant and the filler is an abrasive.
17. 17. The use according to claim 15, wherein the metal surface is a metal surface of cast iron.
18. 18. A method of manufacturing a brake pad for a vehicle having a reduced tendency to ride on or not to ride on a friction surface of an associated brake disc, i.e. having a reduced tendency to stiction or not to stiction even in wet weather, the method comprising the steps of: i) -preparing an asbestos-free friction material of the organic non-asbestos type by mixing together the individual component materials comprising inorganic and/or organic fibers, a binder, a friction modifier and a filler; ii) -adding in step i) as a further component material an amount of a hydrophobic wax selected from the group consisting of polyethylene wax, modified PE wax, polypropylene wax, micronized amide wax, PTFE textured powder, and said hydrophobic wax being added in said asbestos-free friction material in an amount of 0.5 to 5% by volume calculated on the total amount of the friction material, to mix together with said component material of step i); iii) -forming a solid block or layer of the asbestos-free friction material comprising the hydrophobic wax by pressing and heating the mixed together component materials in a mold to form a backing block, wherein the solid block or layer exhibits a separation force from the metal surface of less than 15 newtons after having been electrochemically pressed onto the metal surface by pushing the solid block or layer of asbestos-free friction material against the metal surface of steel or iron and causing corrosion phenomena thereon.
19. 19. The method of claim 18, wherein the metal surface is a metal surface of cast iron.
20. 20. The method of claim 18, wherein the hydrophobic wax is selected from the group consisting of polytetrafluoroethylene modified polyethylene wax, HDPE wax, micronized PE wax, oxidized PE wax, micronized polypropylene wax.

Description

Friction material block for equipping brake pad, brake pad and method for producing brake pad Cross Reference to Related Applications This patent application claims priority from italian patent application number 102020000021919 filed on 9/17 in 2020, the entire disclosure of which is incorporated herein by reference. Technical Field The present disclosure relates generally to friction blocks made of friction material designed to equip brake pads, wherein the friction material may have a formulation that allows reducing or eliminating the tendency of the friction block to ride on the surface of a friction pair (friction partner) with which it cooperates (a phenomenon known as "stiction"). The present disclosure relates generally to friction blocks for brake pads, and to related brake pads designed to cooperate with a surface of a vehicle disc brake to brake a vehicle. The present disclosure also relates generally to related methods. Background It is well known that especially under severe operating and/or environmental conditions, such as frequent off-road driving and/or driving on muddy roads or routes exposed to salty air or acid rain, this may result in one or more brake pads of the vehicle "sticking" to the associated brake disc made of cast iron or steel in use. This is generally due to corrosion phenomena that affect the brake disc and cause corrosion products to bond with the friction material of the brake pads during braking, resulting in inadvertent adherence of the brake pads to the brake disc (adherence that remains temporarily even when the vehicle brake is deactivated). Such sticking phenomenon is known by the english technical term "static" i.e. from the abbreviations and combined terms of the terms "static" and "friction" (i.e. the term "static friction"). Clearly, the occurrence of stiction or sticking phenomena in use of the vehicle involves various drawbacks, such as jolt/pull during braking and subsequent release of the brake, increased energy consumption and, in extreme cases, breakage of the friction material of the friction pads, which leads to malfunction of the vehicle and/or to the need for premature replacement of the brake pads. Thus, the phenomenon of stiction is well known in the art of brake pads and also affects vehicles that are always traveling on paved roads when exposed to wet weather conditions. Disclosure of Invention It is an object of the present disclosure to provide embodiments of friction blocks or layers made of friction materials having a formulation that allows reducing or eliminating the tendency of the friction blocks to ride on the surface of the friction pair with which they cooperate. In particular, it is an object of the present disclosure to provide embodiments of such friction blocks as an integral part of, or integrated in, a brake pad designed to cooperate in use with a brake disc made of steel or cast iron. Accordingly, the present disclosure relates to embodiments of friction blocks or layers made of friction materials formulated in a manner that reduces or eliminates the tendency of the friction block to ride on the surface of its friction pair, as defined in the appended claims. In general, the friction pad or layer may be an integral part of a brake pad for a vehicle and designed to cooperate in use with a brake disc made of steel or cast iron, or an integral part of a clutch disc for a vehicle or for any other application. The present disclosure also relates to embodiments of brake pads equipped with or having such friction blocks or layers as an integrated component thereof. The present disclosure also relates to a method for manufacturing a brake pad for a vehicle having a reduced tendency to press on or not to press on a friction surface of an associated brake disc, i.e. having a reduced tendency to stiction or not to stiction, especially in wet weather. EP3507587 (incorporated herein by reference in its entirety) discloses a method for studying and determining the physico-chemical conditions of adhesion between a first mechanical element and a second mechanical element comprising a vehicle braking element and an element to be braked, respectively, said method comprising the steps of: -coupling the first mechanical element to a first support and the second mechanical element to a second support, the first support and the second support being positioned opposite each other and being axially movable relative to each other, the second support being oriented towards the first support such that the second mechanical element is fully embedded within the second support except for a first face thereof, said first face being uncovered by the second support and being arranged flush with a front end of the second support facing the first support and the first mechanical element coupled thereto; -electrically connecting the second mechanical element to an insulated wire protruding from the second support in a fluid-tight manner; -adhering and then pressing