METHODS FOR THE PREPARATION OF A FRICTION MATERIAL AND FOR THE MANUFACTURING OF A BRAKE PAD USING SUCH FRICTION MATERIAL AND ASSOCIATED BRAKE PAD

Abstract

A friction element having a friction layer or block made at least in part of a compounded friction material having a homogenous fibrous microstructure, in which the fibrous aspect of the homogenous microstructure appears to be lost up to a magnification of 100. The friction material is obtained with a mixing step including a first step of hot blending of at least part of the organic binder with at least part of the other components of the friction material by a rolling mill blender that is open to atmospheric pressure at a temperature lower than the polymerization temperature of the organic binder but greater than or equal to its softening temperature, in order to obtain a semifinished solid product. A second step of grinding the semifinished solid product reduces the product to a powder.

Claims

1. A friction element having a friction layer or block made in at least in part of a compounded friction material in which a homogenous microstructure of fibrous material is contained therein, wherein the homogenous microstructure of fibrous material appears to be maintained up to a magnification of 100 or greater before the fibrous aspect of the compounded friction material can actually be discerned.

2. The friction element according to claim 1, wherein the compounded friction material appears fully homogenous without any fibrous aspect until viewed with a magnification of 1000.

3. The friction element according to claim 1, wherein the compounded friction material is mixed with non-compounded friction material wherein the fibrous material contained therein still maintains a fibrous aspect, the compounded friction material forming in the friction layer or block agglomerates having a size lower than 5 mm.

4. The friction element according to claim 3, wherein the total amount of the block agglomerates in the friction layer is lower than 40 percent by volume.

5. The friction element according to claim 1, wherein the friction element is a brake pad or brake shoe.

6. A braking system comprising an element to be braked consisting of a disc or brake drum made of a cast iron or steel and at least one braking element comprising a brake drum or a brake shoe, suitable to cooperate by means of friction with the element to be braked, wherein the at least one braking element is a friction element according to claim 1.

7. A friction material for a braking element, the friction material comprising as raw component materials inorganic and/or organic and/or metallic fibers, at least one organic binder, at least one friction modifier or lubricant and at least a filler or abrasive, in which the friction material does not include asbestos and in which the friction material is made by a method comprising: a mixing step involving the raw component materials of the friction material in order to obtain a raw mixture; and a molding step in which the raw mixture is molded under pressure in order to obtain a block or layer of friction material; wherein the mixing step comprises the steps of: a) a first hot blending step carried out by feeding at least part of the at least one organic binder and at least part of at least one other raw component material of the friction material in a first mixer provided with at least two hot rotating rollers and open to atmospheric pressure in order to have the at least part of the organic binder and said at least part of said other raw component material of the friction material passing through the rollers in a gap delimited therebetween at a temperature which is lower than the polymerization temperature of the organic binder, in order to obtain at atmospheric pressure and after the rollers a semifinished solid product in the shape of chips or ribbon or sheet; and b) a grinding step of the semifinished solid product, in order to completely reduce the semifinished solid product to a powder; and c) a second blending step performed in a second mixer, the second blending step being performed prior to or after the first hot blending step and including at least the remaining raw components of the friction material.

8. The friction material according to claim 7, wherein the friction material appears homogenous until viewed under a magnification of greater than 100.

9. The friction material according to claim 7, wherein the friction material appears to be homogenous until viewed under a magnification of at least 1000.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] The present invention will now be described in more detail with reference to the following practical non-limiting embodiment examples and with reference to FIGS. 1 to 3 of the appended drawings, wherein:

[0066] FIG. 1 illustrates schematically by means of blocks the method for manufacturing a friction material according to the invention highlighting schematically one of the steps that characterizes the method of the invention;

[0067] FIG. 2 illustrates the results of a diffraction analysis and a SEM analysis performed at two different magnifications on one of the raw components of the friction material that can be made using the method of the invention before and after a step of the method of the invention; and

[0068] FIG. 3 illustrates the results in graphical form of braking efficiency tests on the same friction material made using traditional methods and the method of the invention;

[0069] FIG. 4 illustrates a brake pad obtained in accordance with an embodiment of the invention; and

[0070] FIG. 5 illustrates a comparison of wear between brake pads which have made in accordance with aspects of the invention and brake pads having a similar composition that are made in a known manner.

DETAILED DESCRIPTION

[0071] The examples and comparative examples are reported here by way of illustration and are not intended to limit the invention.

[0072] With reference to FIG. 1, a non-limiting implementation is illustrated schematically in blocks of a method for obtaining a friction material according to the invention.

[0073] The block indicated with 100 represents the set or complex of raw component materials of the required friction material: this block is composed of, indicated with hatching, an organic binder 1, fillers 2, lubricants or friction modifiers 3, abrasives 4, fibers 5 and metallic powders 6.

[0074] The block indicated with 50 represents a mixing step, for example performed in a Henschel, Loedige or Eirich type blender, of all or only part of the raw component materials of the block 1.

[0075] The block indicated with 60 represents a characteristic step of the method of the invention consisting of a hot blending step of some or all of the raw components of the block 100, possibly pre-mixed or not, in correspondence to the block 50. If only some of the raw components of the block 100 are blended in the blending phase according to the block 60, these must be in accordance with a preferred embodiment of the invention, selected from at least part and, preferably, all of the organic binder 2, which should preferably be solid and in the form of a powder or granules and at least part of the other components. According to the prospective expansion of the block 60 shown schematically in FIG. 1, during this step the raw components, at least consisting of part or all of the organic binder 2 and of part or all of the remaining components of the friction material, possibly but not necessarily pre-mixed in the block 50, are fed into a hopper 7 and made to fall from said hopper, under atmospheric pressure conditions, between two (or more) heated and motorized counter-rotating rollers 8. The rollers 8 are heated to a higher temperature than the softening temperature and, preferably, higher than the complete melting temperature of the organic binder but below the polymerization or curing temperature of the organic binder, which is a resin or mixture of thermosetting resins, in such a way as to bring the organic binder up to a temperature that is greater than or equal to the softening temperature but lower than its polymerization temperature in order to maintain the ability of the organic binder to soften or liquefy again.

[0076] The rollers 8 and the hopper 7 form part of a roll blender 9 which is open to the atmosphere, therefore not pressurized. Within this blender 9 the raw component materials of the desired friction material are subjected to a high shear stress in the presence of the organic binder in the fluid state. At the output of the roll blender 9 a semifinished solid product 11 in the form of chips or ribbon or sheet is produced.

[0077] The rollers 8 are made to rotate at a speed between 10 and 30 revolutions/minute and are maintained at a temperature between 40 and 150 C. The gap between the rollers 8, which determines the magnitude of the applied shear stress and the thickness of the semifinished product 11 at the output, is between 0.01 and 5 mm.

[0078] The block indicated with 12 represents a grinding step, preferably performed in a ball or hammer mill, of the semifinished product 11, which is reduced to the form of a powder.

[0079] The block indicated with 13 represents a sieving or screening step of the powder obtained from the grinding of the semifinished product 11, which is made to have a controlled particle size distribution between 5 and 500 microns.

[0080] The block indicated with 14 and illustrated with hatching represents an optional further mixing step using a Henschel, Loedige or Eirich blender, of the predefined particle size powder obtained from the grinding of the semifinished product 11 with any other raw component materials of the desired friction material, for example consisting of all or part of the friction modifiers and/or fillers, that did not participate in the blending step in the block 60.

[0081] Finally, the block indicated with 16 represents a traditional molding step of a block or layer of friction material on a metallic support in order to obtain a braking element, typically a brake pad, obtained by feeding at block 16 a raw mixture of component materials of the friction material to be obtained at the output of block 14 or, directly, from the block 13. The block indicated with 17 represents an optional known step of thermal treatment of a braking element obtained using the method described.

Example-1

[0082] Five formulations were prepared, marked with the initials AMFN/194, prepared using the traditional method, and MFN/329, MFN/330, MFN/331 and MFN/328, respectively, with a composition that is similar/identical to that of the formulation AMFN/194 and obtained using the method of the invention, changing the raw component materials subjected to hot blending with rollers.

[0083] The compositions of the five formulations described above are shown in Table 1 below.

TABLE-US-00001 TABLE 1 FORMULA AMFN/ MFN/ MFN/ MFN/ MFN/ 194 328 329 330 331 Aramid fiber 6 6 6 6 6 friction powder 8 8 8 8 8 Graphite 10 10 10 10 10 phenolic resin 23 23 23 23 23 Silicates 9 9 9 9 9 Mild abrasive 6 6 6 6 6 Filler 5 5 5 5 5 Sulfides 3 3 3 3 3 Strong abrasive 13 13 13 13 13 Medium abrasive 17 17 17 17 17 TOTALS 100 100

[0084] The components shown in Table 1, which indicates values of % by volume compared to the total volume of the blend/mixture were uniformly blended within a Loedige blender in the case of the AMFN/194 mixture.

[0085] In the case of the MFN/329 mixture at least 40% of the envisaged phenolic resin and mild abrasive content was treated according to the invention in a hot roll blender at a temperature of 75 C., with the rollers rotating at a speed of 20 g/min. and with a gap between the rollers of 1 mm, obtaining a semifinished product in sheet form with a thickness of 1.3 mm, which was subsequently ground and sieved to obtain a powder having a particle size between 5 and 500 microns and preferably between 5 and 250 microns. The powder was mixed with the remaining components in a Loedige blender.

[0086] In the case of the MFN/330 mixture the same procedure was followed as with the MFN/329 mixture, though mixing together, using the roll blender, a phenolic resin and a medium abrasive; in the case of the MFN/328 mixture, a phenolic resin, a medium and strong abrasive were mixed together; in the case of the MFN/331 blend a phenolic resin and a strong abrasive were mixed together.

[0087] Subsequently, all of the mixtures/compositions were subjected to an identical molding and thermal treatment process, subjecting them to molding within a die under a pressure of 20 tons for 3 minutes at a temperature of 160 C., then cured with 240 minutes of thermal treatment at 210 C., thus producing brake pads with a friction material of a substantially identical composition but obtained using different processes.

[0088] The brake pads produced as described were subjected to the following tests:

[0089] Efficiency tests comprising: bedding in braking events, braking events at different fluid pressures, cold evaluation braking events (<50 C.), freeway simulation braking events, two series of high energy braking events (first FADE test) interspersed by a series of regenerative braking events. From this test it is also possible to extrapolate, in a manner known to a person skilled in the art, the wear to which the pad is subjected.

[0090] Some comparative test results are reported in FIG. 3 of the annexed drawings and in table 2 below.

[0091] From an examination of FIG. 3 it is evident that the braking coefficient remains more constant under equal conditions in the case of mixtures MFN/329, MFN/328, MFN/330, whilst there are great variations in the case of the MFN/331 mixture.

TABLE-US-00002 TABLE 2 FORMULA AMFN/ MFN/ MFN/ MFN/ MFN/ 194 328 329 330 331 Outboard Pad 26.8 20.1 21.7 23.7 25.4 Wear [gr] Inboard Pad 25.5 19.8 21.7 22.1 25.3 Wear [gr]

[0092] Comparing the wear of the brake pads on the outboard side (towards the outside of the vehicle) and the inboard-side (towards the inside of the vehicle) there is an obvious reduction in the wear of the pads for the formulations/mixtures MFN/329, MFN/328 and MFN/330 manufactured according to the invention compared to the comparison (reference) formulation AMFN/194 and to the MFN/331 formulation wherein only a non-fibrous material as the strong abrasive was treated together with the phenolic resin for blending using the rolling mill blender.

[0093] Finally, from FIG. 2, it is clear that the treatment according to the method of the invention provides a much finer and homogeneous microstructure of the fiber material with loss of the overall fibrous structure. In particular and according to FIG. 2, any fibrous aspect is lost when viewed with the naked eye and up to a magnification of 100 or greater (for example, 1000), with the material appearing to be fully homogenous. That is and only at a magnification of 100 or greater is it possible to discern that the shown matrix is in fact not homogenous, but instead a composition that is defined by mixed particles. The greater homogeneous nature of the friction material obtained by means of the method of the invention is particularly advantageous, both in terms of performance and robustness of the friction material.

[0094] Further tests were carried out, having care of mixing in the same brake pads, friction material obtained with the corresponding method as described herein (using the material mixtures MFN/328 and MFN/329) and obtained in the manner previously described. Brake pads were therefore obtained having the aspect shown in FIG. 4, in which the compounded friction material form agglomerates shown as darker spots having, according to one aspect of the invention, a size smaller than 5 mm. According to the invention, the total quantity of these agglomerates in the entire friction material of the brake pad is to be lower than 40% by volume.

[0095] Wear results obtained by comparing brake pads made in accordance with the herein described method with brake pads obtained entirely with the reference material AMFN/194 are reported in the following Table 3.

TABLE-US-00003 TABLE 3 Pad Wear Disc Lot Mixture Test Pad Wear (g) (mm) Wear (g) 343236 AMFN/194 Wear Test 40.5 2.02 52.9 343235 MFN/328 Wear Test 31 1.48 35.1 343234 MFN/329 Wear Test 30.1 1.56 34.9

[0096] It is evident from Table 3 that brake pads as shown in FIG. 4 provide not only reduced pad wear, but also significantly reduced disc wear. This latter aspect is also highlighted in the illustrations provided in FIG. 5, each evidencing the reduced wear of the discs between those (AMFN/194) made per the conventional mixture as contrasted with those (MFN/328 and MFN/329) with friction material prepared under the described method.

[0097] The objectives of the invention are therefore fully achieved.