FRICTION MATERIALS WITH LOW STORAGE TIME FOR BRAKE PADS BASED ON BINDER COMPOSITIONS AND RELATED BRAKE PADS

Abstract

A friction material with reduced storage time is described, comprising a binder composition based on a hydraulic binder and its use in brake pads and industrial applications.

Claims

1. A friction material for brake pads comprising: i) a multicomponent brake-pad compound; and ii) a binder composition or matrix based on a hydraulic binder, comprising: a) a hydraulic binder consisting of common cement clinker, composed of at least two thirds by mass of calcium silicates [3CaO.SiO2] and [2CaO.SiO2], the remaining part consisting of Al2O3, Fe2O3 and/or other minor oxides; b) an activator selected from one or more salts and/or hydroxides and/or oxides of alkaline and/or alkaline earth metals and/or silicon; c) one or more materials having a pozzolanic activity, one or more materials having a latent hydraulic activity and/or mixtures thereof, said binder composition or matrix being hardened by means of hydration reaction with water, characterized in that the hydraulic binder a) has a fineness, measured according to the standard UNI EN 196-6:2010, air permeability method (Blaine), ranging from 10,000 to 13,000 cm2/g, and component c) has a fineness, measured according to the standard UNI EN 196-6:2010, air permeability method (Blaine), ranging from 6,000 to 9,000 cm2/g.

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

3. The friction material according to claim 1, wherein component b) of the binder composition ii) is selected from silicon oxide, potassium oxide, sodium oxide, potassium hydroxide, sodium hydroxide and/or silicates.

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

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

6. The friction material according to claim 1, 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 having a pozzolanic and/or latent hydraulic activity c), when present, are present in a quantity ranging from 0.5 to 95% by weight with respect to the total weight of the binder composition ii), possible aggregates are present in a quantity ranging from 0 to 20% by weight with respect to the total weight of the binder composition ii), possible additives of various types 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, wherein the total water added is within a quantity ranging from 25 to 150% by weight with respect to the total weight of the binder composition based on hydraulic binder ii).

8. The friction material according to claim 1, wherein the multicomponent brake-pad compound i) is present in a quantity ranging from 30 to 97% by weight, preferably from 50 to 95% with respect to the total weight of the mixture constituting the friction material.

9. The friction material according to claim 1, wherein the multicomponent brake-pad compound 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 brake-pad compound i).

10. The friction material according to claim 1, wherein the friction material consists of: i) a multicomponent brake-pad compound comprising components selected from metal oxides, steel fibers, aramid fibers, chromite, metal sulfides, graphite, coke, metal powders and barite; and ii) a binder composition based on: a) type I Portland cement 52.5, with a fineness of 11,840 cm2/g, b) potassium silicate and potassium hydroxide alone or in a mixture or sodium hydroxide, c) slag with a fineness of 6,760 cm2/g, and water.

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

12. Use of a friction material comprising a binder composition based on a hydraulic binder and a multicomponent brake-pad compound according to claim 1, for brake pads and other industrial applications.

13. The friction material according to claim 1, wherein the hydraulic binder a) has a fineness, measured according to the standard UNI EN 196-6:2010, air permeability method (Blaine), ranging from 10,500 to 12,500 cm2/g.

14. The friction material according to claim 1, wherein the hydraulic binder a) has a fineness, measured according to the standard UNI EN 196-6:2010, air permeability method (Blaine), ranging from 10,700 to 12,000 cm2/g.

15. The friction material according to claim 1, wherein component c) has a fineness, measured according to the standard UNI EN 196-6:2010, air permeability method (Blaine), ranging from 6,700 to 8,000 cm2/g.

16. The friction material according to claim 2, wherein the hydraulic binder a) is type I Portland cement clinker.

17. The friction material according to claim 3, wherein component b) of the binder composition ii) is selected from silicon oxide, potassium oxide, potassium hydroxide and/or silicates.

18. The friction material according to claim 4, wherein component c) of the binder composition ii) is selected from one or more materials comprising microsilica, fly ashes, pozzolan, silica fume, metakaolin, blast furnace slag, hydrated limes, natural limestones.

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

20. The friction material according to claim 6, wherein the hydraulic binder a) is present in a quantity ranging from 10 to 93%, by weight with respect to the total weight of the binder composition ii), and the materials having a pozzolanic and/or latent hydraulic activity c), when present, are present in a quantity ranging from 10 to 93%, by weight with respect to the total weight of the binder composition ii).

Description

EXAMPLE 1

[0087] A friction material s prepared, having the composition indicated in Table 1 hereunder.

TABLE-US-00002 TABLE 1 Constituents wt. % Hydraulic binder based on Portland Cement type I 52.5R 6.3% Calusco with a fineness of 11,840 cm.sup.2/g (blaine) and slag 3.5% Alkaline solution (KOH 11.5M and H.sub.2O in a ratio of 1:3) 11.5%  Multicomponent brake-pad compound: Abrasives: Aluminium oxides and Chromite 8.6% Carbonaceous components: Coke and Graphites 16.3%  Lubricants: Tin and molybdenum sulfides 6.7% Metal Fibers: Steel Fibers  24% Modifiers and fillers: metal powders and barite 23.1% 

[0088] More specifically, the friction material was prepared using a binder composition in a percentage equal to 10.1% by weight with respect to the total weight of the friction material, containing a Portland cement type I 52.5R Calusco, superground to a fineness equal to about 11,840 cm.sup.2/g (blaine) and blast furnace slag with a fineness equal to approximately 6,760 cm.sup.2/g.

[0089] The cement constitutes 65% by weight of the binder composition, whereas the slag constitutes about 35% by weight of the binder composition.

[0090] The resulting mixture therefore has a fineness equal to 9,500 cm.sup.2/g.

[0091] The particle-size distribution of the binder composition is shown in FIG. 1, whereas the granulometric data with Laser grinding are shown in Table 2, including the inclinations and position parameters x′ and n according to the Rosin-Rammler-Sperling-Bennet (RRSB) function. Table 3 shows the physical-mechanical properties of the binder composition according to the standard EN13892-2: 2005.

TABLE-US-00003 TABLE 2 D10 D50 D90 Blaine (μm) (μm) (μm) (cm.sup.2/g) x′ n Binder composition 0.42 2.79 7.67 9740 3.76 1.08 Example 1

TABLE-US-00004 TABLE 3 Binder compo- sition Consistency of the cement paste EN 196-3: 2010 % 36 Initial setting time EN 196-3: 2010 min 80 Final setting time min 170 Consistency of the mortar UNI 7044: 1972 42 Mechanical resistance to EN 13892-2: 2005 32.9 compression Rck 2 days Mechanical resistance to EN 13892-2: 2005 52.6 compression Rck 7 days Mechanical resistance to EN 13892-2: 2005 70.2 compression Rck 28 days Mechanical flexural strength EN 13892-2: 2005 MPa 5.4 (2 days) Mechanical flexural strength EN 13892-2: 2005 MPa 7.5 (7 days) Mechanical flexural strength EN 13892-2: 2005 MPa 7.6 (28 days) Specific surface area (Blaine EN 196-6: 2010 9740 Fineness)

[0092] The friction material thus produced was moulded by means of suitable compression moulds, under room-temperature conditions (20-25° C.) and a pressure at 4.5 kN/cm.sup.2, leading to the production of a pad having a surface of 77 cm.sup.2, and a thickness of 1.5 cm.

[0093] More specifically, the moulds used in the tests indicated in the present example are moulds which provide for the production of a pad having a surface of 77 cm.sup.2, and a thickness of 1.5 cm.

[0094] Approximately 7 days after moulding (curing time), the pads were varnished according to the usual methods and then characterized and tested as described hereunder.

[0095] The pads obtained from the formulation indicated in table 1 were observed visually and do not show either surface oxidations or abnormal bulges.

[0096] 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 80, also indicating a good homogeneity of the mechanical properties between peripheral and central surface areas of the pad.

[0097] This aspect of homogeneity is extremely important for producing a friction material that does not have potential detachment points and is characterized by a high wear resistance.

[0098] 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.

[0099] The “Compressibility” tests according to ISO-6310:2009 showed an average value equal to 35.6 microns.

[0100] The pads, tested according to the AK Master test, showed wear values of 0.30 mm (this value refers to the average of the measurements effected on the pair of pads), an average friction coefficient equal to 0.37, whereas the appearance of the pads and discs proved to be visually acceptable with respect to the standard represented by traditional pads obtained with thermosetting resins.

[0101] The pads tested according to the “internal high-temperature test” described above do not show any detachment of material by delaminations and/or extensive and significant cracks at the end of the test.

EXAMPLE 2 (COMPARISON)

[0102] A friction material was prepared with the same composition indicated in Table 1 of Example 1.

[0103] More specifically, the friction material was prepared using a binder composition in a percentage equal to 10.1% by weight with respect to the total weight of the friction material, containing a Portland cement type I 52.5R Calusco, superground to a fineness equal to about 6,100 cm.sup.2/g (blaine) and blast furnace slag with a fineness equal to about 3,900 cm.sup.2/g.

[0104] The cement constitutes 65% by weight of the binder composition, whereas the slag constitutes about 35% by weight of the binder composition.

[0105] The resulting mixture therefore has a fineness equal to 5,430 cm.sup.2/g.

[0106] The granulometric data with Laser grinding are indicated in Table 4, including the inclinations and position parameters x′ and n according to the Rosin-Rammler-Sperling-Bennet (RRSB) function. Table 5 shows the physical-mechanical properties of the binder composition according to the standard EN13892-2: 2005.

TABLE-US-00005 TABLE 4 D10 D50 D90 Blaine (μm) (μm) (μm) (cm.sup.2/g) x′ n Binder composition 0.88 7.34 25.2 5430 10.64 0.93 Example 2

TABLE-US-00006 TABLE 5 Binder compo- sition Consistency of the cement paste EN 196-3: 2010 % 30 Initial setting time EN 196-3: 2010 min 175 Final setting time min 240 Consistency of the mortar UNI 7044: 1972 83 Mechanical resistance to EN 13892-2: 2005 29.6 compression Rck 2 days Mechanical resistance to EN 13892-2: 2005 41.8 compression Rck 7 days Mechanical resistance to EN 13892-2: 2005 58.1 compression Rck 28 days Mechanical flexural strength EN 13892-2: 2005 MPa 5.3 (2 days) Mechanical flexural strength EN 13892-2: 2005 MPa 6.2 (7 days) Mechanical flexural strength EN 13892-2: 2005 MPa 7.4 (28 days) Initial setting time EN 196-6: 2010 5430

[0107] The remaining part of the friction material consists of the Multicomponent brake-pad compound.

[0108] The percentage quantities of each component of the friction material are fractions by weight with respect to the total weight of the mixture which constitutes the friction material alone.

[0109] The friction material thus produced was moulded by means of suitable compression moulds, under room-temperature conditions (20-25° C.) and a pressure at 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.

[0110] More specifically, the moulds used in the tests indicated in the present example are moulds which provide for the production of a pad having a surface of 77 cm.sup.2, and a thickness equal to 1.5 cm

[0111] Approximately 28 days after moulding (curing time), the pads were varnished according to the usual methods and then characterized and tested as described hereunder. It was impossible to carry out the characterization of the pads before 28 days

[0112] The pads obtained from the formulation indicated in table 1 were observed visually and do not show either surface oxidations or abnormal bulges.

[0113] 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 90, also indicating a good homogeneity of the mechanical properties between peripheral and central surface areas of the pad.

[0114] This aspect of homogeneity is extremely important for producing a friction material that does not have potential detachment points and is characterized by a high wear resistance.

[0115] 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.

[0116] The “Compressibility” tests according to ISO-6310:2009 showed an average value equal to 30 microns.

[0117] The pads, tested according to the AK Master test, showed wear values of 0.30 mm (this value refers to the average of the measurements effected on the pair of pads), an average friction coefficient equal to 0.36, whereas the appearance of the pads and discs proved to be visually acceptable with respect to the standard represented by traditional pads obtained with thermosetting resins.

[0118] On analyzing the results of Examples 1 and 2, it can be noted that the pads of Example 1, i.e. obtained starting from a binder composition with a fineness equal to 9,740 cm.sup.2/g, showed a slight improvement in the physical-mechanical performances with respect to the pads of Example 2, i.e. obtained starting from a binder composition with a fineness equal to 5,430 cm.sup.2/g, but, very surprisingly, the result of the AK master test after only 7 days of storage or curing (friction coefficient and wear of the pads) is completely analogous to that obtained for the pads of Example 2 which require a curing or storage time of 28 days.