US-12617122-B2 - Method for making a friction material, in particular for making brake pads and relative brake pads

US12617122B2US 12617122 B2US12617122 B2US 12617122B2US-12617122-B2

Abstract

Method for producing a friction material, including the following steps in sequence: mixing an aluminosilicate source with an alkaline silicate solution to form a geopolymer, adding a friction mix to the geopolymer solution of the previous step to obtain a slurry, casting the slurry in a mold at temperature between room temperature and 120° C. and for between 5 min and 2 h and demolding to obtain a pad, attaching a backplate to the pad, curing for a time between X and Y hours at a temperature of between X and Y. The friction material obtained with the method is for the manufacture of friction layers/blocks for friction elements such as braking elements, including vehicle brake pads or blocks, and/or friction discs.

Inventors

Agustin Sin Xicola
Francesco VANNUCCI
Paolo Colombo
Alberto Conte
Luca Martinotto

Assignees

ITT ITALIA S.R.L.

Dates

Publication Date: 20260505
Application Date: 20210120
Priority Date: 20200120

Claims (8)

1 . A method for making a braking element, including the following steps: a) forming a geopolymeric solution by mixing an aluminosilicate source with an alkaline silicate solution; b) obtaining a slurry by adding a friction mix to the formed geopolymeric solution from the previous mixing step, wherein the geopolymeric solution is a binder for the friction mix; c) casting the slurry in a mold without pressure at a temperature between room temperature and 120° C., and maintaining the slurry inside the hot mold for a time comprised between 5 minutes and 2 hours until the slurry is substantially solidified; d) demolding the solidified slurry to obtain a pad or block of solid friction material; e) attaching a backplate to the pad or block of solid friction material, wherein the step of attaching is carried out: i) either as a consequence of the casting step, having been provided the backplate within the mold, or ii) after the pad or block of solid friction material is demolded; f) curing for a time between 1 and 24 hours and at a temperature of between 60° C. and 120° C. the pad or block of solid friction material having the backplate attached to it; and wherein g) the aluminosilicate source and the alkaline silicate in step a) are chosen so that a SiO 2 /Al 2 O 3 molar ratio in the solid friction material is between 3 and 5; h) the alkaline silicate solution in step a) is chosen so that a SiO 2 /R 2 O molar ratio in the solid friction material is between 0.7 and 1.5, and wherein R is chosen among Na, K, and Li; and i) the binder formed by the geopolymeric solution is present in the slurry in a quantity equal to or greater than 30% by volume based on the total volume of the slurry.
2 . The method according to claim 1 , wherein the aluminosilicate source is chosen from the group consisting of metakaolin, kaolin, fly ash, bottom ash, and mixtures thereof.
3 . The method according to claim 1 , wherein the aluminosilicate source comprises metakaolin.
4 . The method according to claim 1 , wherein the alkaline silicate solution is chosen from the group consisting of sodium silicate and sodium hydroxide system, potassium hydroxide and potassium silicate system, lithium hydroxide and lithium silicate system, cesium hydroxide and cesium silicate system, and rubidium hydroxide and rubidium silicate system and mixtures thereof.
5 . The method according to claim 1 , wherein the friction mix comprises: fibers chosen from the group consisting of organic fibers, inorganic fibers, metallic fibers, and mixtures thereof and added in a quantity comprised between 2% in volume and 30% in volume out of a total volume of friction material; organic or inorganic fillers added in a quantity comprised between 2% to 40% in volume based on the total composition of the friction material; and friction modifier added in a quantity between 4% and 30% of the total volume of friction material.
6 . The method according to claim 5 , wherein the fillers are chosen from at least one of calcium carbonate, barium sulphate, magnesium oxide, calcium hydroxide, calcium fluoride, talc, mica, and mixtures thereof.
7 . The method according to claim 1 , wherein the geopolymeric solution in step a) is chosen so that the H 2 O/A 1 2 O 3 molar ratio is between 10 and 25.
8 . The method according to claim 1 , wherein the braking element is a brake pad.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a national stage application under 35 U.S.C. § 371 of International Application No. PCT/IB2021/050418, filed Jan. 20, 2021, which claims priority of Italian Patent Application No. 102020000001012, filed Jan. 20, 2020, the entire contents of each application being herein incorporated by reference. TECHNICAL FIELD The present disclosure generally relates to methods for producing a friction material, in particular for making friction blocks and associated brake pads. SUMMARY Embodiments of the disclosure illustrate more efficient methods for the production of friction material for friction elements, such as braking elements, e.g., vehicle brake pads or blocks, and preparation of the associated friction material and a respective inorganic binder, which facilitate the obtaining of friction materials and associated brake pads resistant to the heat generated during braking, simultaneously providing optimal braking performance and optimal tribological characteristics. EP3128201 discloses a method for obtaining a binder for brake pads. The use of a geopolymer substitutes the traditional process using a phenolic resin. However, there can be certain disadvantages associated with the dry grinding process described in EP3128201. GB2357517 discloses a friction material comprising a continuous phase which is a reaction product obtained by reacting an alkali metal hydroxide, the metal being from Group 1 of the periodic table, and/or an alkali silicate, and reactive finely-divided material comprising silica, silicates, and/or aluminates. For example, during grinding (performed in air) and during opening of the grinder and unloading of product, soda powders can absorb a significant quantity of moisture from the environment. Some of this residual moisture is retained by the soda in subsequent mixes with kaolin and with other fillers added to the friction material compound, and is released in the form of a vapor during the hot molding of brake pads, which can some flaking and cracking in the finished friction material. However, embodiments of the friction material in this disclosure can be used for the manufacture of friction layers/blocks for friction elements, such as braking elements, i.e. vehicle brake pads or blocks, and/or friction discs, asbestos free, with performance similar to or better than those belonging to the NAO (“Non-Asbestos Organic friction material”), “Low Steel” and “Semi-met” classes of friction materials, while avoiding certain disadvantages disclosed above. The disclosure therefore can generally relate to a method for producing a friction material for friction elements such as braking elements, e.g. vehicle brake pads or blocks, as defined in the attached claims. The disclosure also generally relates to associated binders and friction elements, particularly brake pads or blocks, presenting a friction layer or block produced with the method of the disclosure. According to the present disclosure, such aim is obtained by the method for producing a friction material and by the method for producing a brake pad according to the claims. According to the present disclosure the method for producing a friction material, includes the steps of, preferably carried out in sequence: a) mixing an aluminosilicate source with an alkaline silicate solution to form a geopolymeric solution, wherein any geopolymer is not yet completely formed;b) adding a friction mix to the geopolymeric solution of the previous mixing step to obtain a slurry;c) casting the slurry in a mold at a temperature between room temperature and 120° C. and maintaining the slurry inside the mold for a time comprised between 5 minutes and 2 hours, anyway until the slurry is substantially solidified; andd) demolding the solidified slurry to obtain a pad or block of solid friction material. In some embodiments of the method disclosed herein, the mixing step can be carried out so as to have at the end thereof a slurry having a pseudoplastic behavior consisting of the aforementioned geopolymeric solution. For a pseudoplastic solution, a shear-thinning fluid, such as where the viscosity of these fluids will decrease with increasing shear rate. In some embodiments, the addition of a friction mix to the geopolymeric solution is carried out to obtain a slurry (e.g., a mixture including particulate solids suspended in water and/or another liquid) with pseudoplastic properties. In some embodiments, the SiO2/Al2O3 molar ratio in the slurry is preferably between 3 and 5. The SiO2/R2O ratio is preferably between 0.7 and 1.5 and R can be selected among Na, K, Li, Ce, Ru. Preferably, the H2O/Al2O3 molar ratio is between 10 and 25. The disclosure also generally relates to embodiments of methods for making a braking element, in particular a brake pad, comprising carrying out the method for producing a friction material as above and the further step of: e) attaching a backplate to the pad or block of solid frict