Friction material

Abstract

A friction material, such as those belonging to the NAO or LS classes. The friction material is substantially free from copper and includes non-spherical particles in the form of powders and/or fibres each constituted by a preferably ferrous metallic core and by an at least partial coating of core formed at least partially or totally by tin and/or tin compounds, such as intermetallic Fe—Sn compounds.

Claims

1. A method of manufacturing a friction material for use in braking components, the method comprising: providing a plurality of non-spherical asymmetrical particles, each of the non-spherical asymmetrical particles having a metallic ferrous core that is asymmetrical and defined by a spongy configuration; at least partially coating the metallic ferrous core of the non-spherical asymmetrical particles with a coating layer of at least one of tin or tin compounds; mixing at least one fibrous base including at least one of inorganic, organic or metallic fibers, at least one filler, and at least one binder, with the plurality of said at least partially coated non-spherical asymmetrical particles, the plurality of at least partially coated non-spherical asymmetrical particles having a specific surface area between 0.1 and 0.3 m.sup.2/gm, and a granulometry comprised between 0.2 and 600 microns, wherein the non-spherical particles comprise between 3 and 20 percent of the total mixture by volume and the content of tin or tin compounds comprises between 20 and 30 percent by weight of the plurality of non-spherical particles; and heat pressing the mixture as a friction layer for the braking element.

2. The method according to claim 1, wherein the metallic ferrous core of each non-spherical asymmetrical particle comprises one of iron or steel.

3. The method according to claim 1, further comprising the addition of intermetallic compounds of tin and the metal constituting the core in the coating layer of at least one of tin or tin compounds.

4. The method according to claim 1, further comprising constituting the metallic ferrous core by one of iron or steel and presenting tin in the coating layer of at least one of tin or tin compounds in the form of intermetallic iron-tin compounds of the type Fe.sub.xSn.sub.y (where 1≤x≤5, 1≤y≤3).

5. The method according to claim 1, in which the coating layer of at least one of tin and tin compounds further comprises intermetallic compounds of Fe—Sn.

6. The method according to claim 5, in which the coating layer of at least one of tin and tin compounds further comprises FeMeSn ternary intermetallic compounds, where Me is a metal different from Fe.

7. The method according to claim 1, in which the granulometry of the plurality of non-symmetrical asymmetric particles is between 0.2 and 250 microns, wherein the average surface area of the particles is 0.15 m.sup.2/g and in which the average surface area of the particles is about 0.20 m.sup.2/g for those particles with a granulometry of less than 63 microns.

8. A method of manufacturing a friction material for use in a friction element, the method comprising: providing a plurality of non-spherical asymmetrical particles, each of the non-spherical asymmetrical particles comprising a metallic ferrous core defined by a spongy configuration; melting a coating layer of at least one of tin and tin compounds at least partially onto the metallic ferrous core of the plurality of non-spherical asymmetrical particles; cooling the plurality of at least partially coated non-spherical asymmetrical particles; and mixing at least one fibrous base including at least one of inorganic, organic or metallic fibers, at least one filler, and at least one binder, with the plurality of said at least partially coated non-spherical asymmetrical particles, in which the plurality of at least partially coated non-spherical asymmetrical particles have a specific surface area between 0.1 and 0.3 m.sup.2/g and a granulometry comprised between 0.2 and 600 microns, wherein the non-spherical particles comprise between 3 and 20 percent of the total mixture by volume, and the content of tin comprises between 20 and 30 percent by weight of the plurality of non-spherical particles.

9. The method according to claim 8, wherein the coating layer includes intermetallic compounds of tin and the metal constituting the core.

10. The method according to claim 8, in which the friction material is heat pressed and then configured for arrangement on the friction element, wherein the friction element is at least one of a braking element or a clutch disc.

11. The method according to claim 8, further comprising constituting the metallic ferrous core by one of iron or steel and presenting tin in the coating layer of at least one of tin or tin compounds in the form of intermetallic iron-tin compounds of the type Fe.sub.xSn.sub.y (where 1≤x≤5, 1≤y≤3).

12. The method according to claim 8, in which the coating layer of at least one of tin and tin compounds further comprises intermetallic compounds of Fe—Sn.

13. The method according to claim 12, in which the coating layer of at least one of tin and tin compounds further comprises FeMeSn ternary intermetallic compounds, where Me is a metal different from Fe.

14. The method according to claim 8, in which the granulometry of the plurality of non-symmetrical asymmetric particles is between 0.2 and 250 microns, wherein the average surface area of the particles is 0.15 m.sup.2/g and in which the average surface area of the particles is about 0.20 m.sup.2/g for those particles with a granulometry of less than 63 microns.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be described in more detail with reference to the following practical implementation examples and with reference to FIGS. 1 to 4 of the appended drawings, which illustrate:

(2) FIGS. 1 and 3 illustrate the results of a diffraction and SEM (Scanning Rlectron Microscope) analysis of the metallic particles coated in tin and its compounds as used according to one version;

(3) FIG. 2 shows an SEM image of particles used, which highlights their spongy appearance; and

(4) FIGS. 4 and 5 give the results in graphical form of a braking efficiency test.

DETAILED DESCRIPTION

(5) Examples and comparative examples are reported here by way of illustration and are not intended to limit the invention.

EXAMPLES

(6) Three formulations were prepared marked with the letters O, A and B, according to the following table.

(7) TABLE-US-00001 TABLE 1 COMPONENTS/TYPE 0 B A Organic fiber 2.3 3.6 3.6 Binder 16.2 19.3 19.3 Rubber 2.3 2.3 2.3 Graphite 6.5 7.6 7.6 Fluorine compounds 3.1 3.1 3.1 Baryta 4.4 Strong abrasives 8.4 6.7 6.7 Sn sulfides 7.6 Metallic sulfides 5 5 Magnesium oxide 5.1 5.1 5.1 Chromite 4.1 4.1 4.1 Coke 20.5 20.5 20.5 Mild abrasives 4.5 4.5 4.5 Vermiculite 3.2 3.2 3.2 Steel fiber 10.9 10.9 10.9 SN powder 3.2 Metallic powder 0.9 0.9 0.9 Non-spherical metallic particles coated 3.2 with Sn Total 100 100 100

(8) The components shown in Table 1, indicating percentage values by volume of the total volume of the mixture/blend, were evenly mixed in a Loedige mixer and pressed in a die under a pressure of 20 tonnes for 3 minutes at a temperature of 160° C., thereby being cured by means of 10 minutes of heat treatment at 400° C., thus producing a friction material according to the invention indicated under the letter “B”, and materials according to the known art, indicted under the letter“O”, and a comparative, containing Sn in the form of powders only, indicated under the letter “A”.

(9) Brake pads produced as described were subjected to the following tests: Efficiency tests comprising: running in brakings, brakings at different fluid pressures, “cold” evaluation braking (<50° C.) cold, freeway simulation brakings, two series of high energy brakings (FADE test) interspersed by a series of regenerative brakings. Wear test comprising various series of brakings with initial braking temperatures (of the brake disk) comprised between 100 and 400° C. and precisely: 1000 brakings with an initial disk temperature of 100° C. 1000 brakings with an initial disk temperature of 150° C. 1000 brakings with an initial disk temperature of 200° C. 1.000 brakings with an initial disk temperature of 250° C. 1000 brakings with an initial disk temperature of 300° C. 500 brakings with an initial disk temperature of 350° C.

(10) The test results are shown in FIGS. 4 and 5 of the attached drawings and in the following tables. FIG. 4 refers to the comparison mixture/formulation “A” containing free tin within the mixture, while FIG. 5 refers to the mixture/formulation of the invention, containing ferrous particles covered with tin compounds.

(11) TABLE-US-00002 TABLE 2 Mix “O” - State of the art Friction layer wear - pad [mm] Brake Inboard Pad Outboard Pad Average pads Temperature Wear per Wear per wear per (° C.) 1000 Stop (mm) 1000 Stop (mm) 1000 Stop (mm) 100 0.33 0.25 0.29 200 0.42 0.36 0.39 250 0.26 0.15 0.21 300 0.17 0.14 0.15 350 0.21 0.18 0.19 Disk Wear [mm]: 0.136 Disk Wear [g]: 41

(12) TABLE-US-00003 TABLE 3 Mix “B” - Invention Friction layer wear - pad [mm] Brake Inboard Pad Outboard Pad Average pads Temperature Wear per Wear per wear per (° C.) 1000 Stop (mm) 1000 Stop (mm) 1000 Stop (mm) 100 0.27 0.23 0.25 200 0.40 0.32 0.36 250 0.14 0.14 0.14 300 0.17 0.12 0.14 350 0.10 0.10 0.10 Disk Wear [mm]: 0.078 Disk Wear [g]: 22.9

(13) Comparing the disk wear for both test sets it can be seen that it is lower in the formulation B (the one containing metallic particles covered with Sn).

(14) From the comparison between the formulation O and the formulation B, it can be seen in particular that the disk wear is much improved (it is significantly lower for formula B) from the formula B compared to the formula 0; also there is less pad wear.

(15) From the graphs of FIGS. 4 and 5 it can instead be seen that the braking efficiency of the formulation according to the invention is quite comparable to formulations known in the art but containing tin. Comparison measurements were also made between the formulations A and B with regard to wear, confirming the results of the previous test between the formulations O and B. In particular, the most evident results were obtained regarding the level of disk wear, which is greatly reduced, according to the following comparison:

(16) TABLE-US-00004 Start of Test g End of Test g Disk wear formulation A - Comparison 8814.2 8807.3 Disk Wear formulation B - Invention 8799.7 8794.9

(17) As can be seen the disc wear was less than 30% in the case of the formulation of the invention.

(18) Finally an investigation was made into the nature of the metallic particles containing tin which when added to a formulation of the type substantially known in the art allow surprising results to be obtained as revealed by the tests.

(19) With reference to FIGS. 1, 2 and 3, it became clear that the material used (ferrous particles obtained by mixing with tin, melting and cooling) presents itself in the form of powder particles or fibrous particles having a ferrous core asymmetrically shaped and sponge-like appearance (FIG. 2) which are at least partially coated with a layer of FeSn intermetallic compounds which are clearly identifiable by means of both the diffraction analysis (FIG. 1) and the SEM (FIG. 3—the particles have been cut). The surface area of the particles used, measured using the BET method, resulted surprisingly small (an average of 0.15 m.sup.2/g and equal to 0.2087 m.sup.2/g for those particles with a granulometry of less than 63 microns).

(20) It is assumed that the beneficial experimental results obtained are due to the fact that the tin present in the form of intermetallic compounds, which are weaker, or at least deposited upon ferrous particles with a reduced surface area, “spreads” (during braking) over the friction partner (disc brake in the tests) better during use than with the formulation containing tin, thus obtaining the resulting significant reduction in disk wear. With respect to traditional tin-free formulations the benefits are even more evident.

(21) The objectives of the invention are then fully achieved.