IMPROVED FRICTION MATERIALS FOR BRAKE PADS BASED ON BINDING COMPOSITIONS AND RELATED BRAKE PADS

Abstract

An improved friction material is described, comprising a binding composition based on a hydraulic binder, and its use in brake pads and industrial applications.

Claims

1. A friction material for brake pads which comprises: i) a multicomponent braking blend and ii) a composition or binder matrix based on a hydraulic binder, comprising a) a hydraulic binder consisting of a cement clinker, composed of at least two thirds in mass of calcium silicates [3CaO.SiO.sub.2] and [2CaO.SiO.sub.2], the remaining part consisting of Al.sub.2O.sub.3, Fe.sub.2O.sub.3 and/or other minor oxides; b) an activator selected from the group consisting of one or more salts, hydroxides, oxides of alkaline, alkaline earth metals, silicon, and combinations thereof; c) one or more materials having a pozzolanic activity, one or more materials having a latent hydraulic activity, and/or mixtures of the same; said composition or binder matrix adapted to be hardened by a hydration reaction with water.

2. The friction material according to claim 1, wherein the hydraulic binder a) is a Portland cement clinker of type I, a blast-furnace cement of type III, a pozzolana cement of type IV and/or mixtures thereof.

3. The friction material according to claim 1, wherein component b) is selected from the group consisting of silicon oxide, potassium oxide, sodium oxide, potassium hydroxide, sodium hydroxide, silicates, and combinations thereof.

4. The friction material according to claim 1, wherein component c) of the binder composition ii) is selected from the group consisting of one or more materials having a pozzolanic activity, one or more materials having a latent hydraulic activity, and combinations thereof.

5. The friction material according to claim 1, wherein the binder composition ii) based on a hydraulic binder is present in a quantity ranging from 3 to 60% by weight with respect to the total weight of the mixture forming the friction material.

6. The friction material according to claim 4, wherein the hydraulic binder a) is present in a quantity ranging from 0.5 to 95% by weight, with respect to the total weight of the binder composition ii), the activator b) is present in a quantity ranging from 0.5 to 50% by weight with respect to the total weight of the binder composition ii), the materials with a pozzolanic activity and/or latent hydraulic activity c) are present in a quantity ranging from 0.5 to 95% by weight, with respect to the total weight of the binder composition ii), optional aggregates are present in a quantity ranging from 0 to 20% by weight with respect to the total weight of the binder composition ii), and further optional additives of a different nature are present in a quantity ranging from 0 to 5% by weight with respect to the total weight of the binder composition ii).

7. The friction material according to claim 1, further comprising water in a quantity ranging from 25 to 150% by weight with respect to the total weight of the binder composition based on the hydraulic binder ii).

8. The friction material according to claim 1, wherein the multicomponent braking blend i) is present in a quantity ranging from 30 to 97% by weight with respect to the total weight of the mixture forming the friction material.

9. The friction material according to claim 1, wherein the multicomponent braking blend i) comprises at least one lubricant in a quantity ranging from 5 to 15% by weight, at least one abrasive in a quantity ranging from 8 to 25% by weight, at least one component containing carbon in a quantity ranging from 8 to 25% by weight, at least one modifier in a quantity ranging from 15 to 30% by weight, all the quantities being calculated with respect to the total weight of the multicomponent braking blend i).

10. The friction material according to claim 1, wherein the friction material consists of ii) a binder composition based on a) Portland cement of type I 52.5, with a fineness of 6,500 cm.sup.2/g, b) potassium silicate and potassium hydroxide, c) slag with a fineness of 6,500 cm.sup.2/g and metakaolin, and water, and the multicomponent braking blend i) comprises one or more components selected from the group consisting of aluminium oxides, steel fibres, chromite, tin and molybdenum sulfides, graphite, coke, metal powders, barite, and combinations thereof.

11. Brake pads consisting of a friction material according to claim 1 and a metallic support base.

12. A method comprising using a friction material comprising a binder composition comprising a hydraulic binder and a multicomponent braking blend according to claim 1, for braking pads and other industrial applications.

13. The friction material according to claim 3, wherein component b) of the binder composition ii) is selected from the group consisting of silicon oxide, potassium oxide, potassium hydroxide, silicates, and combinations thereof.

14. The friction material according to claim 4, wherein the one or more materials having a pozzolanic activity comprises one or more of microsilica, fly ash, pozzolan, silica fume, and metakaolin.

15. The friction material according to claim 4, wherein the one or more materials having a latent hydraulic activity comprises one or more of blast furnace slag, hydrated calcium, and natural limestone.

16. The friction material according to claim 5, wherein the binder composition ii) based on a hydraulic binder is present in a quantity ranging from 5 to 52% by weight with respect to the total weight of the mixture forming the friction material.

17. The friction material according to claim 6, wherein the hydraulic binder a) is present in a quantity ranging from 10 to 93% by weight.

18. The friction material according to claim 6, wherein the materials with a pozzolanic activity and/or latent hydraulic activity c) are present in a quantity ranging from to 93% by weight with respect to the total weight of the binder composition.

19. The friction material according to claim 7, comprising water in a quantity ranging from 50 to 150% by weight with respect to the total weight of the binder composition based on the hydraulic binder ii).

20. The friction material according to claim 8, wherein the multicomponent braking blend i) is present in a quantity ranging from 50 to 95% by weight with respect to the total weight of the mixture forming the friction material.

Description

EXAMPLE 1

[0092] A friction material was prepared, having the composition indicated in Table 1 below.

TABLE-US-00002 TABLE 1 Hydraulic binder based on 11.56% TERMOCEM A 32.5 N LH Calusco with a fineness of 6500 cm.sup.2/g (blaine) Potassium silicate 0.74% Multicomponent braking blend 82.31% Hydrophobic agent 0.28% Water 5.10%

[0093] More specifically, the friction material was prepared using a binding composition containing a TERMOCEM A 32.5 N LH Calusco cement, over-ground until a fineness equal to 6,500 cm.sup.2/g, approximately, was obtained.

[0094] TERMOCEM A 32.5 N LH cement is a blast-furnace cement of type III. In accordance with the composition required by the standard UNI EN 197-1 (i.e. referring to the mass of cement excluding calcium sulfate and additives), it contains 35%-64% of clinker, whereas the remaining part consists of granulated blast-furnace slag and possible secondary constituents.

[0095] Said binding composition comprises the hydraulic binder TERMOCEM A 32.5 N LH Calusco in a quantity equal to 11.56% by total weight with respect to the total weight of the mixture forming the friction material and also contains potassium silicate in a quantity equal to 0.74% by weight and the waterproofing additive Seal 200 (a mixture of polyvinylalcohol and silane, i.e. an alkylsiloxane) in a quantity equal to 0.28% by weight, both with respect to the total weight of the mixture of the friction material.

[0096] The multicomponent braking blend used in the present example is composed of:

TABLE-US-00003 Aluminium oxides 6.0 Steel fibers 29.8 Chromite 4.8 Tin and molybdenum sulfides 8.4 Graphite 7.2 Coke 12.9 Metal powders 19.0 Barite 9.5 Rubber 2.4

[0097] The percentage quantities of the components of the multicomponent braking blend indicated in the previous table are fractions by weight with respect to the total weight of the multicomponent braking blend alone.

[0098] The friction material thus obtained was compression moulded using appropriate moulds, under temperature and pressure conditions of 50? C. and 4.5 kN/cm.sup.2, leading to the production of a pad having a surface of 77 cm.sup.2, and a thickness equal to 1.5 cm.

[0099] More specifically, the moulds used in the tests indicated in the present example are moulds that provide for the production of a pad with a surface of 77 cm.sup.2, and a thickness equal to 1.5 cm.

[0100] After a week of curing in air, the pads were ground.

[0101] After approximately 21 days of curing subsequent to moulding, the pads were subjected to a cycle of thermal treatment in a nitrogen atmosphere according to the thermal cycle indicated hereunder: [0102] Heating profile from 25 to 450? C. in 3 hours; [0103] Isotherm at 450? C. for 1 hour; [0104] Cooling from 450 to 25? C. by natural cooling in a closed oven in a nitrogen atmosphere.

[0105] The pads were then varnished according to the normal method.

[0106] Approximately 28 days after moulding (curing time), the pads were characterized and tested as indicated hereunder.

[0107] The pads obtained from the formulation indicated in table 1 were visually observed and do not show either surface oxidations or abnormal bulges.

[0108] HRR surface hardness tests of the end-product thus obtained were then carried out according to the standard JIS D4421, obtaining an average value of 44, also indicating a good homogeneity of the mechanical properties between peripheral and central surface areas of the pad.

[0109] This aspect of homogeneity is extremely important for producing a friction material that does not have potential detachment points and is consequently characterized by a high wear resistance.

[0110] Uniformity and regularity of the profile of the edges and homogeneity of the central part of the pad with respect to the peripheral areas are essential elements for having an analogous or improved wear of the pad with respect to the values typical of pads that use phenolic resins as binders.

[0111] The Compressibility tests according to ISO-6310 showed an average value equal to 72 microns. The pads, tested according to the AK Master test, showed surprising wear values ranging from 0.45 to 0.49 mm (this value refers to the average of the measurements effected on the pair of pads), an average friction coefficient equal to 0.41, whereas the appearance of the pads and discs proved to be visually acceptable according to the standards generally obtained with traditional pads with a binder based on thermosetting resin.

[0112] The pads tested according to the high-temperature internal test previously described, are shown in FIG. 1. It is evident on a visual level that the pads tested do not have any detachment of material from delaminating and/or extensive and significant cracks at the end of the test.

EXAMPLE 2

[0113] A friction material was prepared, with the composition indicated in table 2 below.

TABLE-US-00004 TABLE 2 Hydraulic binder based on 7.33% Cement type I 52.5 R (6500 cm.sup.2/g) and metakaolin Potassium hydroxide 4.73% Multicomponent braking blend 75.90% Water 12.04%

[0114] More specifically, the friction material was prepared using a binding composition containing a cement type I 52.5R produced in the Calusco cement plant, over-ground until a fineness of about 6,500 cm.sup.2/g was obtained, added to metakaolin, in a quantity equal to 7.33% by weight with respect to the total weight of the composition forming the friction material. The ratio between cement and metakaolin was 1:9 parts by weight respectively.

TABLE-US-00005 Aluminium oxides 6.1 Steel fibers 30.5 Chromite 4.8 Tin and molybdenum sulfides 8.5 Graphite 7.3 Coke 13.4 Metal powders 19.5 Barite 9.9

[0115] The percentage quantities of the components of the multicomponent braking blend indicated in the previous table should be considered as being quantities by weight with respect to the total weight of the multicomponent braking blend alone.

[0116] The friction material thus obtained was compression moulded using appropriate moulds, under temperature and pressure conditions of 50? C. and 4.5 kN/cm.sup.2, leading to the production of a pad having a surface of 77 cm.sup.2, and a thickness equal to 1.5 cm.

[0117] After a week of curing in air, the pads were ground.

[0118] Approximately 28 days after moulding (curing time), the pads were then varnished according to the usual method, characterized and tested as indicated hereunder.

[0119] The pads obtained from the formulation indicated in table 2 were visually observed and do not show either surface oxidations or abnormal bulges.

[0120] HRR surface hardness tests of the end-product thus obtained were then carried out according to the standard JIS D4421, obtaining an average value of 76 and also indicating a good homogeneity of the mechanical properties between peripheral and central surface areas of the pad.

[0121] This aspect of homogeneity is extremely important for producing a friction material that does not have potential detachment points and is consequently characterized by a high wear resistance.

[0122] Uniformity and regularity of the profile of the edges and homogeneity of the central part of the pad with respect to the peripheral areas are essential elements for having an analogous or improved wear of the pad with respect to the values typical of pads that use phenolic resins as binders.

[0123] The Compressibility tests according to ISO-6310 showed an average value equal to 36 microns. The pads, tested according to the AK Master test, showed surprising wear values ranging from 0.28 to 0.32 mm (this value refers to the average of the measurements effected on the pair of pads), an average friction coefficient equal to 0.39, whereas the appearance of the pads and discs proved to be visually acceptable according to the standards generally obtained with traditional pads with a binder based on thermosetting resin.

[0124] The pads tested according to the high-temperature internal test previously described, on a visual level do not have any detachment of material from delaminating and/or extensive and significant cracks at the end of the test.

EXAMPLE 3 (COMPARATIVE)

[0125] A friction material was prepared, with the composition indicated in table 3 below.

TABLE-US-00006 TABLE 3 Hydraulic binder based on 11.79% Cement type I 52.5 R (6,500 cm.sup.2/g) and metakaolin Multicomponent braking blend 78.05% Water 10.16%

[0126] More specifically, the friction material was prepared using a binding composition containing a cement type I 52.5R produced in the Calusco cement plant, over-ground until a fineness of about 6,500 cm.sup.2/g was obtained. Said binding composition was added, in a quantity equal to 11.79% by weight with respect to the total weight of the composition forming the friction material. The multicomponent braking blend used in the present example was composed of:

TABLE-US-00007 Aluminium oxides 5.4 Steel fibers 27.2 Chromite 4.3 Tin and molybdenum sulfides 7.6 Graphite 6.5 Coke 12.0 Metal powders 17.4 Barite 8.7 Magnesium oxide 6.5 Aramidic fiber 2.2 Rubber 2.2

[0127] The percentage quantities of the components of the multicomponent braking blend are expressed as quantities by weight with respect to the total weight of the multicomponent braking blend alone. The friction material thus obtained was compression moulded using appropriate moulds, under temperature and pressure conditions of 50? C. and 4.5 kN/cm.sup.2, leading to the production of a pad having a surface of 77 cm.sup.2, and a thickness equal to 1.5 cm.

[0128] After a week of curing in air, the pads were ground.

[0129] Approximately 28 days after moulding (curing time), the pads were then varnished according to the usual method, characterized and tested as indicated hereunder. The pads obtained from the formulation indicated in table 3 were visually evaluated and do not show either surface oxidations or abnormal bulges.

[0130] HRR surface hardness tests of the end-product thus obtained were then carried out according to the standard JIS D4421, obtaining an average value of 70 and also indicating a good homogeneity of the mechanical properties between peripheral and central surface areas of the pad.

[0131] This aspect of homogeneity is extremely important for producing a friction material that does not have potential detachment points and is consequently characterized by a high wear resistance.

[0132] Uniformity and regularity of the profile of the edges and homogeneity of the central part of the pad with respect to the peripheral areas are essential elements for having an analogous or improved wear of the pad with respect to the values typical of pads that use phenolic resins as binders.

[0133] The Compressibility tests according to ISO-6310 showed an average value equal to 63 microns. The pads, tested according to the AK Master test, showed surprising wear values of about 0.33 (this value refers to the average of the measurements effected on the pair of pads), an average friction coefficient equal to 0.42, whereas the appearance of the pads and discs proved to be visually acceptable according to the standards generally obtained with traditional pads with a binder based on thermosetting resin.

[0134] The pads tested according to the high-temperature internal test previously described, on a visual level, have significant surface delaminations at the end of the test with detachment of the material and/or deep cracks, as shown in FIG. 2.

[0135] It is therefore evident that under more severe conditions such as those characteristic of the high-temperature internal test, the brake pad produced with the friction material according to the present invention (table 1 or table 2) has a better overall general behaviour with respect to the brake pad obtained starting from the friction material described in table 3.

EXAMPLE 4 (COMPARATIVE)

[0136] A friction material was prepared, with the composition indicated in table 4 below, by mixing in a planetary mixer.

TABLE-US-00008 TABLE 4 Potassium silicate 3.85% Potassium hydroxide 4.92% Metakaolin 9.62% Alumina 11.15% Graphite 23.08% Iron powder 15.38% Resin 3.85% Water 28.15%

[0137] More specifically, the friction material was prepared using the composition described in Table 4, by mixing in a planetary mixer, until a homogeneous blend was obtained; the blend was then poured into a mould for the production of brake pads and then subjected to thermal treatment at 80? C. for 90 minutes and subsequently at 120? C. for 2 hours.

[0138] More specifically, the moulds used in the tests indicated in the present example are moulds for the production of a pad with a surface of 77 cm.sup.2, and a thickness equal to 1.5 cm.

[0139] Approximately 28 days after moulding (curing time), the pads were then characterized and tested as indicated hereunder.

[0140] The pads obtained from the formulation indicated in table 4 were visually observed: they show visibly irregular and relatively non-compact surfaces, the surface proves to be fragile and easily friable to touch, as shown in FIGS. 3-5.

[0141] For these pads, it was therefore not possible to carry out the tests effected for the friction material according to the present invention.