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 fibers 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 FeSn compounds.

Claims

1. An asbestos-free friction material, comprising at least one fibrous base including inorganic and/or organic and/or metallic fibers, at least one filler and at least one binder, the friction material being substantially free from copper and including non-spherical particles that are constituted by a metallic core of asymmetric shape at least partially coated with a layer of at least one of tine or tin compounds, wherein the coating layer comprises intermetallic compounds of tin and of the metal constituting the core.

2. The friction material according to claim 1, wherein the material belongs to the classes known as NAO or LS.

3. An asbestos-free friction material according to claim 1, further comprising a granulometry comprised between 0.2 and 600 microns.

4. The friction material according to claim 1, wherein the metallic core is made from iron or steel.

5. The friction material according to claim 1, wherein the metallic core is constituted by one of iron or steel and in that tin is present in the partial or total coating layer of the core in form of intermetallic iron-tin compounds of the type Fe.sub.xSn.sub.y (where 1x5, 1y3).

6. The friction material according to claim 1, wherein the non-spherical particles have a ferrous metallic core either partially or totally coated by the layer of at least one of tin or tin compounds and are present in the friction material in a percentage by volume comprised between 0.5% and 50%, an Sn content of said particles being comprised between 20% and 30% by weight of the amount of present particles.

7. The friction material according to claim 6, wherein the layer of at least one of tin or tin compounds contains FeSn intermetallic compounds.

8. The friction material according to claim 7, wherein the FeSn intermetallic compounds are present in the friction material in a percentage by volume between 3% and 20%.

9. The friction material according to claim 6, wherein the coating of the ferrous metallic cores forming the non-spherical particles also includes FeMeSn ternary intermetallic compounds, where Me is a metal different from Fe.

10. The friction material according to claim 1, further including: lubricants/friction modifiers; abrasives; and metallic powders.

11. A braking system comprising a member to be braked, constituted by a brake disc or brake drum made of cast iron or steel and at least one braking member constituted by a brake pad or brake shoe, adapted to cooperate by friction with the member to be braked, wherein the braking member has a friction layer intended to cooperate with the member to be braked made of a friction material according to claim 1.

12. A friction element, having a friction layer made with the friction material in accordance with claim 1.

13. The friction material according to claim 1, wherein the material contains FeSn intermetallic compounds in the coating layer.

14. The friction material according to claim 1, wherein the non-spherical particles have a surface area between 0.1 and 0.3 m.sup.2/g.

15. The friction material according to claim 1, wherein the at least partial coating of the core is formed totally by FeSn intermetallic compounds.

16. An asbestos-free friction material, comprising at least one fibrous base including at least one of inorganic, organic or metallic fibers, at least one filler and at least one binder, wherein the material is substantially free from copper and includes non-spherical particles each constituted by a ferrous core and at least partial coating of the core formed either at least partially or totally by FeSn intermetallic compounds, and wherein the non-spherical particles have a surface area between 0.1 and 0.3 m.sup.2/g.

17. The friction material according to claim 16, in which the material belongs to the classes known as NAO or LS.

18. The friction material according to claim 16, wherein the non-spherical particles are constituted by a ferrous core of asymmetric shape.

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 TYPE COMPONENTS 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 with Sn 3.2 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:

(10) 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.
1000 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.

(11) 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.

(12) TABLE-US-00002 TABLE 2 Mix O - State of the art Friction layer wear - pad [mm] Brake Inboard Pad Outboard Pad Average pads Temper- Wear per Wear per wear per ature (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

(13) TABLE-US-00003 TABLE 3 Mix B - Invention Friction layer wear - pad [mm] Brake Inboard Pad Outboard Pad Average pads Temper- Wear per Wear per wear per ature (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

(14) 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).

(15) 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.

(16) 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:

(17) 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

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

(19) 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.

(20) 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. 3the 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).

(21) 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.

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