Material for friction components of disc brakes

Abstract

The invention illustrates a material for friction components of disc brakes comprising between 1% and 8% by weight of at least one preceramic resin and between 2% and 10% by weight of at least one organic resin. It also illustrates a friction component for a disc brake, a disc brake, and a process for producing such a material.

Claims

1. A material for friction components of disc brakes consisting of: a mixture between 1% and 8% by weight of a preceramic silicone resin and between 2% and 10% by weight of an organic resin selected from a phenolic resin, an acrylic resin, and an epoxy resin; and at least one catalyst, at least one abrasive agent, at least one lubricant, at least one metal, and at least one damping agent.

2. The material for friction components according to claim 1, wherein a total amount of preceramic silicone resin and organic resin is less than or equal to 12% by weight.

3. The material for friction components according to claim 1, comprising between 2% and 6% by weight of preceramic silicone resin and between 4% and 8% by weight of organic resin.

4. The material for friction components according to claim 1, comprising 2% by weight of preceramic silicone resin and 7% by weight of organic resin.

5. The material for friction components according to claim 1, wherein said preceramic silicone resin comprises at least one silicone resin.

6. The material for friction components according to claim 5, wherein said silicone resin is a siloxane resin.

7. The material for friction components according to claim 6, wherein said siloxane resin is a polysilsesquioxane resin.

8. The material for friction components according to claim 1, wherein said organic resin is a phenolic resin.

9. A friction component for disc brakes comprising a material consisting of: a mixture between 1% and 8% by weight of a preceramic silicone resin and between 2% and 10% by weight of an organic resin selected from a phenolic resin, an acrylic resin, and an epoxy resin; and at least one catalyst, at least one abrasive agent, at least one lubricant, at least one metal, and at least one damping agent.

10. The friction component according to claim 9, comprising at least one pad for a disc brakes.

11. A disc brake comprising at least two pads according to claim 10 and a caliper for a disc brake comprising thrusting means suitable for clamping said at least two pads against a braking face of a brake disc.

12. A process for producing a material for friction components of disc brakes comprising the following steps: providing between 1% and 8% by weight of a preceramic silicone resin; providing between 2% and 10% by weight of an organic resin selected from a phenolic resin, an acrylic resin, and an epoxy resin; mixing the preceramic silicone resin and the organic resin; forming a mixture consisting of: the preceramic silicone resin, the organic resin, at least one catalyst, at least one abrasive agent, at least one lubricant, at least one metal, and at least one damping agent; moulding and polymerising the mixture so as to obtain a semifinished product; and firing the semifinished product.

13. The process for producing a material for friction components of disc brakes according to claim 12, wherein a total amount of preceramic silicone resin and organic resin is less than or equal to 12% by weight.

14. The process for producing a material for friction components of disc brakes according to claim 12, wherein the preceramic silicone resin is between 2% and 6% by weight, and the organic resin is between 4% and 8% by weight.

15. The process for producing a material for friction components of disc brakes according to claim 12, wherein the preceramic silicone resin is 2% by weight and the organic resin is 7% by weight.

16. The process for producing a material for friction components of disc brakes according to claim 12, wherein the preceramic silicone resin comprises at least one silicone resin.

17. The process for producing a material for friction components of disc brakes according to claim 12, wherein the preceramic silicone resin comprises a siloxane resin.

18. The process for producing a material for friction components of disc brakes of claim 12, wherein the preceramic silicone resin comprises a polysilsesquioxane resin.

19. The process for producing a material for friction components of disc brakes of claim 12, wherein the organic resin is a phenolic resin.

Description

(1) In order to better understand the invention and appreciate the advantages thereof, it will be hereafter provided a description of some non-limiting example embodiments of the material for friction components of disc brakes, of friction components for disc brakes, of disc brakes and of processes for producing the material for friction components for disc brakes, with reference to the attached figures, in which:

(2) FIG. 1 represents a diagram showing two functions: the top part shows the progression of the average friction coefficient of a friction component in a material according to a first embodiment of the present invention, in a known organic material and in a known ceramic material, as far as the number of braking episodes increases, in normal operation; the bottom part shows the progression of the temperature of the disc, associated with the friction component during braking, as far as the number of braking episodes increases for the same three materials;

(3) FIG. 2 is a diagram showing the progression of the average friction coefficient of a friction component made from a material according to a second embodiment of the present invention, a known organic material and a known ceramic material, as the number of braking episodes increases, in the running in step;

(4) FIG. 3 is a diagram showing the progression of the instantaneous friction coefficient of a friction component of a material according to a third embodiment of the present invention, of a known ceramic material and of a known organic material, during braking.

(5) The material for friction components of disc brakes, according to the present invention, comprises between 1% and 8% by weight (wt %) of at least one preceramic resin.

(6) Such a percentage is preferably between 2% and 6%. Optimal results, with the materials given as examples, are obtained with an amount of preceramic resin of about 2% by weight.

(7) Some example of preceramic resins able to be used in the present invention are: polysilanes, polycarbosilanes, polysilazanes and polysiloxanes.

(8) Such a preceramic resin is preferably a silicone resin, even more preferably a siloxane resin. In the preferred embodiment it is a polysilsesquioxane resin.

(9) The material for friction components according to the present invention also comprises between 2% and 10% by weight of at least one organic resin.

(10) Such a percentage is preferably between 4% and 8%. Optimal results are obtained with 7% by weight of organic resin.

(11) As will be seen from the examples, the total amount of preceramic resin and organic resin is preferably less than or equal to 12% by weight.

(12) The organic resin may be selected from: phenolic resins, acrylic resins, epoxy resins.

(13) In accordance with the preferred embodiment of the invention, it is preferably a phenolic resin.

(14) The material for friction components also comprises, in a known way, catalysts, abrasives, metals, damping agents and/or lubricants.

(15) In particular, the catalyst is comprised in the mixture in an amount less than or equal to 2% by weight; the abrasive is between 10% and 30% by weight; the metals are in an amount less than or equal to 60%; the damping agents are in an amount less than or equal to 10%; and the lubricants are in an amount less than or equal to 50%.

(16) The damping agent is used to improve comfort and it preferably comprises planar silicates.

(17) The friction material according to the present invention may be used to produce friction components intended to cooperate tribologically both with brake discs made from composite ceramic material (CCM), and with brake discs made from grey cast iron.

(18) A friction component according to the present invention is preferably a pad.

(19) It has a known geometry, i.e. it is not necessary to make particular structural modifications to the geometry of the pad according to the invention.

(20) A disc brake according to the present invention comprises at least two pads and a caliper for a disc brake of the known type. Such a caliper comprises thrusting means to clamp the pads against a brake band of a brake disc.

(21) The geometries of the pads and of the caliper, being of the known type, will not be described any further.

(22) Preferred examples of processes for producing a material of components of disc brakes, according to the present invention, will now be described.

(23) A preferred process of the invention comprises to provide between 1% and 8% by weight of at least one preceramic resin and between 2% and 10% by weight of at least one organic resin.

(24) They are preferably in powder form.

(25) In a subsequent step, it is provided to mix at least one of the two resins, preferably the preceramic one, with a catalyst. Such a catalyst comprises Zincacetylacetonatehydrate Zn(C5H7O2)2 xH2O.

(26) Thereafter the preceramic resin and the organic resin are mixed together.

(27) The mixture thus obtained is added with the abrasive agent, the lubricant, the metal and/or the damping agent.

(28) The latter has a damping function, is used to improve comfort, and preferably comprises planar silicates.

(29) Then follows a step of moulding and polymerising the mixture so as to obtain a semifinished product.

(30) The moulding takes place through pressure moulding with a pressure of about 150-600 kg/cm.sup.2.

(31) Thereafter it is possible to carry out a firing step at temperatures that are not high, for example at about 300 C.

(32) In accordance with a first variant of the process of the invention, the preceramic resin, in powder form, is granulated, preferably together with abrasives, lubricants, metals, dampers and a liquid adjuvant, preferably water. The particles that form following such a step are left to dry, preferably at room temperature, and then pyrolysed.

(33) The pyrolysis preferably takes place in an inert atmosphere, for example in nitrogen, at about 500 C. in a pyrolysis furnace.

(34) The product thus obtained is mixed with the organic resin:

(35) Preferably, thereafter it is added to again with one or more from: abrasives, lubricants, metals, dampers.

(36) The mixture is then hot moulded and polymerised. Thereafter it is possible to carry out a firing step at a relatively low temperature, for example about 300 C.

(37) In this way, a structure is obtained made up of an organic matrix in which particles of ceramic material are incorporated.

(38) In accordance with a second variant, the process of the invention comprises providing the preceramic resin in liquid form and the organic resin in powder. Such a variant provides moulding and polymerising the organic resin so as to obtain an organic semifinished product.

(39) Thereafter, the organic semifinished product is heat treated at about 300 C. Such heat treatment preferably comprises a firing step in ambient atmosphere.

(40) Alternatively, the treatment takes place in modified atmosphere, in particular in nitrogen at about 500 C.

(41) Thereafter, the preceramic resin in liquid form, combined with optional additives, is allowed to penetrate in the organic semifinished product so as to obtain a hybrid semifinished product that is then pyrolysed.

(42) Said step is preferably carried out in a vacuum to promote the penetration of the preceramic resin in the porosities of the semifinished product.

EXAMPLES

Example 1

(43) 6% by weight of polysilsesquioxane resin, added with catalyst, is mixed with 4% by weight of phenolic resin.

(44) Such a mixture is added to with 24% by weight of abrasive agent, 40% by weight of metal, 21% by weight of lubricant and 5% by weight of damping agent.

Example 2

(45) 2% by weight of polysilsesquioxane resin, added with catalyst, is mixed with 7% by weight of phenolic resin.

(46) Such a mixture is added to with 24% by weight of abrasive agent, 41% by weight of metal, 21% by weight of lubricant and 5% by weight of damping agent.

Example 3

(47) 4% by weight of polysilsesquioxane resin, added with catalyst; is mixed with 6% by weight of phenolic resin.

(48) Such a mixture is added to with 24% by weight of abrasive agent, 40% by weight of metal, 21% by weight of lubricant and 5% by weight of damping agent.

Example 4 (Comparative)

(49) 9% by weight of phenolic resin was added to with 24% by weight of abrasive agent, 41% by weight of metal, 21% by weight of lubricant and 5% by weight of damping agent.

Example 5 (Comparative)

(50) 9% by weight of polysilsesquioxane resin, added with catalyst, is mixed with 35% by weight of abrasive agent, 34% by weight of metal and 22% by weight of lubricant.

(51) With each of the five materials obtained, pads of known geometry were made.

(52) The pads obtained in the aforementioned examples 2u were tested through simulation of real braking on a chassis dynamometer reproducing the same inertia of a road vehicle.

(53) The top part of the graph of FIG. 1 shows the progression of the average friction coefficients of the pads according to the first embodiment of the invention (example 1) and according to the two materials of the prior art given, respectively, in example 4 and in example 5, as the number of braking episodes increases, in normal operation.

(54) As it can be seen from such a graph, the material according to the invention maintains a substantially constant average friction coefficient as the number of braking episodes increases. This demonstrates that is maintains good mechanical characteristics. Moreover, the material of the invention does not have the negative peaks of the organic material and therefore there are no sudden decreases in braking efficiency.

(55) In the bottom part of the graph of FIG. 1, it can be seen how the temperature of the disc associated with the pads themselves varies, as the number of braking episodes increases. The temperature of the disc with pads made from material of the invention is lower than the temperature of the disc with pads of organic material (example 4), with obvious mechanical advantages.

(56) From such a FIG. 1 it can thus be seen how the friction coefficient of the pads made with the material according to the invention remains high even at high temperatures.

(57) The graph of FIG. 2 shows the progressions of the average friction coefficients of the pads according to the second embodiment of the invention (example 2), i.e. the particularly preferred embodiment, and according to the two materials of the prior art given, respectively, in example 4 and in example 5, as the number of braking episodes increases, during a running in step. As it is well known, the running in step is a delicate step in which it is more difficult to ensure a constantly high friction coefficient.

(58) As it can be seen from such a graph, the material according to the invention maintains a substantially constant and high average friction coefficient as the number of braking episodes increases, even during running in. Such an average friction coefficient is also on average greater than the friction coefficient of organic material. Therefore, the braking efficiency of pads made with the material of the invention is greater than the braking efficiency of pads made from known organic material (example 4).

(59) The graph of FIG. 3 gives the progression of the instantaneous friction coefficients of the pads according to the third embodiment of the invention (example 3) and according to the two materials of the prior art given, respectively, in example 4 and in example 5, during braking.

(60) As it can be seen from such a graph, the material according to the invention maintains a substantially constant instantaneous friction coefficient during braking, and in any case greater than known organic material (example 4).

(61) The pads obtained with the aforementioned five materials were also subjected to comfort tests, i.e. noisiness tests.

(62) Whereas the pads of example 5, i.e. the ceramic ones, proved to be noisy, the remaining four pads gave good results, i.e. they proved to be sufficiently noiseless and comfortable.

(63) From the results of the tests it can be seen that the material of friction components for disc brakes according to the present invention has a substantially constant average friction coefficient, similarly to the case of ceramic material.

(64) In other words, the performance of the material of the invention, in terms of braking efficiency, is as good as the performance of ceramic materials.

(65) On the other hand, organic material is subject to rapid degradation of the friction coefficient, i.e. it does not withstand high temperatures, quickly losing braking efficiency.

(66) Comfort tests have shown that the performance of the materials according to the invention is as good as that of organic materials, i.e. better than ceramic materials.

(67) In conclusion, the materials for friction components according to the invention, and therefore the friction components obtained therewith, have good mechanical characteristics and excellent comfort.

(68) Of course, it is possible to vary the composition of the material of the invention, within the indicated ranges, according to the specific requirements. In other words, if particularly high mechanical characteristics were required, a percentage of preceramic resin close to 8% could be used. Similarly, if the particular application were to require good characteristics in terms of comfort, a percentage of organic resin close to 10% could be used.

(69) In the above description and in the following claims, all of the numerical magnitudes indicating amounts, parameters, percentages, and so on should be taken to be preceded in all circumstances by the term about unless indicated otherwise. Moreover, all of the ranges of numerical magnitudes include all of the possible combinations of maximum and minimum numerical values and all of the possible intermediate ranges, as well as those specifically indicated in the text.

(70) Of course, the man skilled in the art, in order to satisfy contingent and specific requirements, can bring further modifications and variants, all of which are in any case covered by the scope of protection of the present invention, to the material for friction components, to the friction components, to the disc brakes and to the process for producing the material for friction components according to the present invention.