EP4153883A1

EP4153883A1 - Brake pad with a friction material having a geopolymer binder

Info

Publication number: EP4153883A1
Application number: EP21809662.6A
Authority: EP
Inventors: Agustin Sin Xicola; Valentina IODICE; Pavlo IVANCHENKO; Gianmario Martra
Original assignee: ITT Italia SRL
Current assignee: ITT Italia SRL
Priority date: 2020-05-20
Filing date: 2021-05-19
Publication date: 2023-03-29
Also published as: IT202000011716A1; WO2021236758A1; EP4153883A4

Abstract

Technologies are generally described for a method for synthesizing a geopolymer. The method includes mixing silica and metakaolin to form a pre-mixture. A silicate solution is prepared. The silicate solution and the pre-mixture are mixed to form a wet mixture. The method is carried out in absence of an alkali and in presence of water

Description

BRAKE PAD WITH A FRICTION MATERIAL HAVING A GEOPOLYMER BINDER

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Italian Patent Application No. 102020000011716 filed on May 20, 2020 by the same inventors. The entirety of the disclosures of the priority application are incorporated by reference herein.

BACKGROUND

[0002] Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted as prior art by inclusion in this section.

[0003] Brake pads are part of a brake disc system used in vehicles. Conventionally, there are two brake pads for each brake disc rotor. The brake pads are held in place and actuated by a caliper that is affixed to a wheel hub. The brake pads often have steel back plates, where a surface of the steel back plates have a friction material that faces the surface of the brake disc rotor. When the brakes are applied, the caliper squeezes the two brake pads together onto the brake disc rotor to slow and/or stop the vehicle. Brake pads convert the kinetic energy of the vehicle to thermal energy through friction. Thus, friction materials play an important role in a brake system since brakes use friction to decelerate/stop the vehicle.

[0004] The friction materials typically include reinforcements, friction modifiers, and binders. Asbestos was widely used as a reinforcement for friction materials because of its thermal stability. However, asbestos is highly toxic to human health. Asbestos has been often replaced by a number of materials, including both inorganic and organic materials, as well as metal fibers. Metal sulfides such as molybdenum disulfide, iron sulfides, copper, tin, graphite, and/or coke are example materials that may be used as friction modifiers. The binders may be thermosetting polymers, such as phenolic resins. However, during repeated braking, organic binders may release volatile gaseous compounds or fine dust into the atmosphere, which may be harmful to human health.

[0005] The present disclosure appreciates that geopolymers are a class of material that are synthesized from the reaction of an alumina-silicate powder with an alkaline siliceous solution under ambient temperature and pressure. Geopolymers have reasonable mechanical properties, and good thermal stability at temperatures above 1000 °C, and thus may be suitable as an alternative binder. SUMMARY

[0006] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings, the detailed description, and the claims.

[0007] According to some examples, a method for synthesizing a geopolymer is described.

The method may include mixing silica and metakaolin to form a pre-mixture; preparing a silicate solution; and mixing the silicate solution and the pre-mixture to form a wet mixture, where the method is carried out in absence of an alkali and in presence of water.

[0008] According to other examples, mixing silica and metakaolin may include mixing about 10 wt% of silica and about 90 wt% of metakaolin. Mixing silica and metakaolin may include mixing for about 5 minutes to about 10 minutes in an Eirich mixer or a Loedige mixer. Preparing the silicate solution may include adding sodium silicate or potassium silicate to water. Preparing the silicate solution may include adding about 38 wt% of sodium silicate to about 42 wt% of water. Preparing the silicate solution may include adding sodium silicate to the water; heating to a temperature up to 50°C; and stirring for about 2 to about 4 hours. Preparing the silicate solution may include preparing the silicate solution having a pH in a range from about 12 to about 14.

Mixing the silicate solution and the pre-mixture may include mixing for about 5 minutes to about 10 minutes in an Eirich mixer or a Loedige mixer to form the wet mixture. Synthesizing the geopolymer may include synthesizing the geopolymer without a phenolic resin.

[0009] According to further examples, a method for making a friction material is described. The method may include mixing silica and metakaolin to form a pre-mixture; blending the premixture and a raw mixture to form a dry mixture, where the raw mixture comprises one or more of inorganic, organic or metallic fibers, at least one friction modifier or lubricant, and at least one filler or abrasive; preparing a silicate solution; and mixing the silicate solution and the dry mixture to form the friction material, where the method is carried out in absence of an alkali and in presence of water, and wherein a reaction between the pre-mixture and the silicate solution forms a geopolymer.

[0010] According to yet other examples, mixing silica and metakaolin may include mixing about 10 wt% of silica and about 90 wt% of metakaolin. Mixing silica and metakaolin may include mixing for about 5 minutes to 10 minutes in an Eirich mixer or a Loedige mixer. Preparing the silicate solution may include adding sodium silicate or potassium silicate to water. Preparing the silicate solution may include adding about 38 wt% of sodium silicate to about 42 wt% of water. Preparing the silicate solution may include adding sodium silicate to the water; heating to a temperature up to about 50°C; and stirring for about 2 to about 4 hours. Preparing the silicate solution may include preparing the silicate solution having a pH in a range from about 12 to about 14. Mixing the silicate solution and the dry mixture may include mixing for about 5-10 minutes in an Eirich mixer or a Loedige mixer to form the wet mixture. Blending the pre-mixture and the raw mixture to form the dry mixture may include blending 40 wt% of the pre-mixture and about 60 wt% of the raw mixture. Blending the pre-mixture and the raw mixture may include blending the premixture and the raw mixture for about 5 minutes to about 10 minutes in an Eirich mixer or a Loedige mixer. Adding the silicate solution to the dry mixture may include adding about 32 wt% of silicate solution to about 68 wt% of the dry mixture. Adding the silicate solution to the dry mixture to form the wet mixture may include forming the wet mixture to have a final moisture content of about 20 wt%.

[0011] According to yet further examples, a method for making a brake pad is described. The method may include synthesizing a friction material; placing the friction material, an under-layer and a backplate in a molding press; molding at a temperature in a range of about 20°C to about 80 °C to form a soft brake pad; applying a load to the soft brake pad, wherein the load is in a range of about 100 to about 200 kg; and curing in an oven to form the brake pad, where synthesizing the friction material includes mixing silica and metakaolin to form a pre-mixture; blending the premixture and a raw mixture to form a dry mixture, where the raw mixture includes one or more of inorganic, organic or metallic fibers, at least one friction modifier or lubricant, and at least one filler or abrasive; preparing a silicate solution; and mixing the silicate solution and the dry mixture to form the friction material, where the method is carried out in absence of an alkali and in presence of water, and where a reaction between the pre-mixture and the silicate solution forms a geopolymer.

[0012] According to other examples, molding may include molding for about 1 min and at a pressure in a range of about 100 kg/cm² to about 300 kg/cm². Curing may include curing at a temperature in a range of about 150 °C to about 160 °C for at least about 30 min. Molding may be performed at a temperature in a range of about 20°C to about 80 °C to form a soft brake pad with a Rockwell hardness of substantially zero. Applying the load may include placing the soft brake pad in between two metal plates fixed on four vertical rails and applying load by a hydraulic press. Applying the load and curing in the oven forms the brake pad with a hardness of about 60 HRS, a compressibility of about 0.1 mm, and a detach of about 12.35 KN.

[0013] According to some examples, a braking system may include a brake disc rotor made of a metal; and a brake pad positioned on the brake disc rotor, where the brake pad comprises a friction material, the friction material comprises a geopolymer, and the geopolymer is free of alkali and phenolic resin. The geopolymer may include about 42 wt% of metakaolin, about 20 wt% of sodium silicate, about 5 wt% of silica and about 33 wt% of water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The foregoing and other features of this disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings, in which:

FIG. 1 illustrates an example brake pad including a friction material;

FIG. 2 is a flow chart illustrating a method for synthesizing a geopolymer;

FIG. 3 is a flow chart illustrating a method for synthesizing a friction material;

FIG. 4 is a flow chart illustrating a method for making a brake pad;

FIG. 5 is a schematic representation of a system for making a brake pad;

FIG. 6 is a schematic representation of a Spannrahmen device for applying a load on a soft brake pad;

FIG. 7 is a graph illustrating a measurement of hardness of a brake pad; and

FIG. 8 is a graph illustrating a measurement of a coefficient of friction of a brake pad that includes the disclosed friction material and that of a brake pad that includes low steel friction material, all arranged in accordance with at least some embodiments described herein. DETAILED DESCRIPTION

[0015] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. The aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.

[0016] This disclosure is generally drawn, inter alia, to a geopolymer, a friction material, a brake pad, and brake pads that utilize a geopolymer based friction material.

[0017] Briefly stated, technologies are generally described for a device, system, and method to synthesize a geopolymer. The method includes mixing silica and metakaolin to form a premixture, preparing a silicate solution and adding the silicate solution to the pre-mixture to form a wet mixture. The method is carried out in absence of an alkali and in presence of water.

[0018] The present disclosure recognizes that the geopolymers can replace the conventional organic binders used for making the friction materials, which in turn are used for making the brake pad. Some example benefits of the presently disclosed geopolymers are that they contain no harmful phenolic resins. The geopolymers of the present disclosure are comparatively less expensive than the organic binders. Further, the presently disclosed geopolymers enable using mild post curing conditions ((low pressures and ambient temperatures) for making the brake pads. As the geopolymers are made in absence of an alkali, they possess low alkalinity.

[0019] The described technologies further provide a method for making a friction material that in turn is used for making a brake pad. The friction material includes the presently disclosed geopolymers. The disclosed friction material has minimum fluctuation in its effectiveness under varying conditions, such as vehicle speed, laden weight, or temperature change from brake usage. The disclosed friction material is also stable when exposed to different environmental conditions including humidity, water, and mud. The disclosed friction material has strength to withstand the thermal and mechanical disturbances and is durable. The disclosed friction material has low thermal conductivity to prevent temperature build-up of the brake pad or brake oil. [0020] Because of the presence of the disclosed geopolymers in the friction materials, no substantially amount of harmful gaseous compounds or fine dust will be released into the atmosphere during repeated braking of a vehicle. Various tests have been performed on some brake pads made in accordance with the present disclosure. The brake pads may perform better than the conventional brake pads when subjected to several physical tests such as compressibility, hardness and detachment. The brake pads were also subjected to efficiency tests according to the AKM standards and exhibited improved efficiency. AKM (Arbeit Kreis Master) standard refers to the European counterpart of a working group standard for dynamometer testing standards. The U.S. counterpart is referred to as SAE (Society of Automotive Engineers) J2522. [0021] FIG.1 is an example brake pad 100 including a friction material 108 that is arranged according to aspects of the present disclosure. The example brake pad 100 includes a shim 102, a back plate 104, an under layer 106, a friction material 108, and a friction surface 110. In some examples, the brake pad has a sandwiched structure. An example sandwiched structure may include friction material 108, which generates friction when pushed towards a brake disc rotor (not shown), followed by under layer 106 and back plate 104. [0022] In various examples, the shim 102 may be a thin layer of rubber (or some other elastomeric material) that is configured to fit between the brake pad 100 and the brake disc rotor. The shim 102 may be utilized to correct any imperfections in the surfaces of the brake disc rotor and/or the brake pad 102, which may otherwise result in noise. In some examples, the brake shim 102 may function as an anti-rattle pad. [0023] In some examples, the back plate 104 may be made of a substantially rigid materials such as metals, ceramics, or combinations thereof. Example rigid metals include steel, tungsten carbide, cast iron, and titanium. Example rigid ceramics include zirconium oxide, aluminum oxide, and silicon nitride. [0024] In various examples, the friction material 108 may be bound to the friction surface 110 that faces the brake disc rotor. Some examples, of the friction materials108 may include a geopolymer. The geopolymer in the friction material may act as an inorganic binder. The geopolymer is substantially free of phenolic resins. In some examples, even under adverse conditions such as repeated braking or high temperatures, the friction material having geopolymer may not release harmful gaseous products and fine dust into the atmosphere. [0025] FIG. 2 is a flow chart illustrating a method for synthesizing a geopolymer that is arranged according to aspects of the present disclosure. The described method 200, may include blocks 202, “MIX SILICA AND METAKAOLIN TO FORM A PRE-MIXTURE”, block 204, “PREPARE A SILICATE SOLUTION”, and block 206, “ADD THE SILICATE SOLUTION TO THE PRE-MIXTURE”.

[0026] At block 202, silica and metakaolin are mixed to form a pre-mixture. In one example, at block 202, about 10 wt% of silica may be mixed with about 90 wt% of metakaolin to form a premixture. The metakaolin may correspond to Argical™ Ml 000, in some examples. In one example, silica and metakaolin may be provided as dry powders and may be mixed in a dry condition in a mixer. The choice of the mixer may depend on the quantities of the powders to be mixed. In one example an Eirich mixer having a capacity in a range of about 8 lit to about 50 lit may be used. In some examples, silica and metakaolin may be mixed in a Loedige mixer having a capacity of about 25 lit. In one example, the mixing time may be in a range of about 5 min to about 10 min.

[0027] The weight percentages of silica and metakaolin may be varied from the above example. In other examples, 6 wt% of silica may be mixed with about 94 wt% of metakaolin to form the pre-mixture. In still further examples, 12 wt% of silica may be mixed with about 88 wt% of metakaolin to form the pre-mixture. The wt% of silica may be in a range from about 2% to about 10%, or alternatively in a range from about 5% to about 15%, etc. Also, in some examples, the wt% of metakaolin may be in a range from about 80% to about 90%, or alternatively in a range from about 85% to about 95%, etc.

[0028] Block 202 may be followed by block 204, where a silicate solution may be prepared by dissolving an alkaline silicate in water. In some examples the alkaline silicate may be sodium silicate. In some other examples, the alkaline silicate may be potassium silicate. The water used may be milliQ water, deionized water and even tap water. About 38 wt% of sodium silicate (or some other silicate) may be dissolved in about 62 wt% of water. The silicate solution may be prepared on a hot plate with a continuous stirring. In some examples, the stirring may be for about 2 hours. In some other examples, the stirring may be for about 4 hours. The temperature of the silicate solution may be increased up to about 50°C to enhance the solubility of sodium silicate in the milliQ water, deionized water and even tap water. The sodium silicate solution may have a pH in a range from about 12 to about 14. [0029] The weight percentages of alkaline silicate and water may be varied from the above example. In other examples, 32 wt% of silicate may be mixed with about 68 wt% of water to form the silicate solution. In still further examples, 40 wt% of silicate may be mixed with about 60 wt% of water to form the silicate solution. The wt% of silicate may be in a range from about 30% to about 50%, or alternatively in a range from about 32% to about 47%, etc. Also, in some examples, the wt% of water may be in a range from about 50% to about 70%, or alternatively in a range from about 55% to about 65%, etc.

[0030] Block 204 may be followed by block 206, where the silicate solution may be added to the pre-mixture prepared at block 202 to form a wet mixture. The wet mixture may have a final moisture content of about 20% (or alternatively in a range from about 15% to about 25%). The choice of the mixer may depend on the quantities of the powders to be mixed. In one example an Eirich mixer having a capacity in a range of about 8 lit to about 50 lit may be used. In some examples, silica and metakaolin may be mixed in a Loedige mixer having a capacity of about 25 lit. The geopolymer may be formed by a reaction between the pre-mixture and the silicate solution.

[0031] FIG. 3 is a flow chart illustrating a method for synthesizing a friction material that is arranged in accordance with at least some embodiments described herein. The described method 300, may include blocks 302, “MIX SILICA AND METAKAOLIN TO FORM A PREMIXTURE”, block 304, “PREPARE A RAW MIXTURE”, block 306, “BLEND PRE-MIXTURE AND RAW MIXTURE TO FORM A DRY MIXTURE”, block 308, “PREPARE A SILICATE SOLUTION”, and block 310, “ADD THE SILICATE SOLUTION TO THE DRY MIXTURE TO FORM A WET MIXTURE”.

[0032] At block 302, silica and metakaolin may be mixed to form a pre- mixture. In one example, about 10 wt% of silica may be mixed with about 90 wt% of metakaolin to form a premixture. The metakaolin is Argical M-1000™. In one example, silica and metakaolin may be provided as dry powders and may be mixed in a dry condition in a mixer. The choice of the mixer may depend on the quantities of the powders to be mixed. In one example an Eirich mixer having a capacity in a range of about 8 lit to about 50 lit may be used. In some examples, silica and metakaolin may be mixed in a Loedige mixer having a capacity of about 25 lit. In one example, the mixing time may be in a range of about 5 min to about 10 min.

[0033] Block 302 may be followed by block 304, where a raw mixture may be prepared. Preparing the raw mixture may comprise delivering and inspecting the ingredients, weighing the ingredients, and mixing the ingredients. In various examples, the ingredients of the raw mixture may be inorganic, organic, and/or metallic fiber materials, at least one friction modifier or a lubricant, and at least one filler material or an abrasive material.

[0034] In various examples the inorganic fiber materials may be comprised of rock wool, fiber wool, wollastonite, or fiberglass. In some examples, the organic fibers may be comprised of aramid fibers or carbon fibers. In additional examples, metallic fiber materials that are used may be comprised of copper fibers, tin fibers, iron fibers, and/or aluminum fibers. In some other examples, steel, bronze, or brass may be used in either powder or fiber forms. In some examples, a combination of inorganic, organic and metal fibers may be used. In various examples the friction modifiers may be comprised of metal sulfides such as molybdenum disulfide, iron sulfides, copper, tin, graphite, and/or coke, or a combination thereof. In other examples, the filler material may be comprised of barite (barium sulfate), calcium carbonate, talc, magnesium oxide, vermiculite, or a combination thereof. In additional examples the abrasive may be comprised of zirconium silicate, zirconium oxide, alumina, silicon carbide, mica, or a combination thereof.

[0035] Block 304 may be followed by block 306, where the raw mixture and the pre-mixture may be blended to form a dry mixture. The pre-mixture and the raw mixture may be provided as dry powders. The raw mixture and the pre-mixture may be blended in a mixer for about 5 min to about 10 min to form a dry mixture. The choice of the mixer may depend on the quantities of the powders to be mixed. In one example an Eirich mixer having a capacity in a range of about 8 lit to about 50 lit may be used. In some examples, the pre-mixture and the raw mixture may be blended in a Loedige mixer having a capacity of about 25 lit. In some examples, the ratio of the raw mixture to the pre-mixture may correspond to about 60 wt% of raw mixture to about 40 wt% of pre-mixture. In additional examples, the raw mixture portion may comprise about 50 wt% to about 75 wt%; while the pre-mixture portion may comprise about 50% to about 25% of the overall mixture.

[0036] Block 306 may be followed by block 308, where a silicate solution may be prepared.

In some examples, the silicate solution may be prepared by dissolving an alkaline silicate in water. The alkaline silicate may be sodium silicate, potassium silicate, or some other silicate. The water used may be milliQ water, deionized water and even tap water. The silicate solution may be prepared on a hot plate with a continuous stirring. In some examples, the stirring may be for about 2 hours. In some other examples, the stirring may be for about 4 hours. The temperature of the silicate solution may be increased up to about 50°C to enhance the solubility of sodium silicate in the milliQ water, deionized water and even tap water. The sodium silicate solution may have a pH in a range from about 12 to about 14. In some examples, the ratio of the alkaline silicate to water may correspond to about 38 wt% of alkaline silicate (e.g., sodium silicate) to about 62 wt% of water. In additional examples, the alkaline silicate portion may comprise about 30 wt% to about 40 wt%; while the water portion may comprise about 60% to about 70% of the overall mixture.

[0037] Block 308 may be followed by block 310, where the silicate solution may be added to the dry mixture prepared at block 306 to form a wet mixture. The wet mixture may have a final moisture content of about 20%; although other acceptable moisture contents may be in a range of about 15% to about 30%. The choice of the mixer may depend on the quantities of the silicate solution and the dry mixture to be mixed. In one example an Eirich mixer having a capacity in a range of about 8 lit to about 50 lit may be used. In some examples, a Loedige mixer having a capacity of about 25 lit may be used. The wet mixture may be the friction material having the geopolymeric binder. The geopolymer may be formed upon a reaction between the pre-mixture and the silicate solution. The geopolymer binder may harden the raw mixture and may form the friction material the required intensity.

[0038] FIG. 4 is a flow chart illustrating a method 400 for making a brake pad that is arranged in accordance with at least some embodiments described herein. The described method 400, may include blocks 402, “SYNTHESIZE A FRICTION MATERIAL”, block 404, “PLACE THE FRICTION MATERIAL, AN UNDER-LAYER AND A BACK PLATE IN A MOLDING PRESS”, block 406, “MOLD AT A TEMPERATURE IN A RANGE OF ABOUT 20°C TO ABOUT 80 °C TO FORM A SOFT BRAKE PAD”, block 408, “APPLY A LOAD TO THE SOFT BRAKE PAD”, and block 410, “CURE THE BRAKE PAD IN AN OVEN”.

[0039] At block 402, the friction material may be synthesized according to a method such as described in FIG. 3. Block 402 may be followed by block 404, where the pre- weighed friction material along with an under-layer and a back plate may be placed in a molding press. In one example, the under-layer may have viscous polymers that may be able to transform the mechanical energy into thermal energy when the brakes are applied in the vehicle. In various examples, the under-layer may be placed between the friction material and the back plate. The under-layer may bond the friction material with the back plate. The under-layer may also provide a moisture barrier and may adjust the compressibility of the brake pad. [0040] Block 404 may be followed by block 406, where the friction material, the under-layer and the back plate may be molded at a temperature in a range of about 20°C to about 80°C. The molding press may be closed and may compress the friction material, the under-layer and the back plate together at any appropriate temperature, such as room temperature, by operating a punch provided in the molding press. Since the molding press can be operated at room temperature, in some examples, the operation may be termed as “cold molding”. In various examples, the pressure applied in the molding press may be on the order of about 250 kg/cm². In some examples, the pressure may be applied for about one minute. Molding/compressing in the molding press may be necessary to form the soft brake pad. The soft brake pad thus produced may have a Rockwell hardness of about zero.

[0041] Block 406 may be followed by block 408, where a load may be applied to the soft brake pad. The soft brake pad may need a period of maturation under pressure to achieve the required hardness. Further, the soft brake pad may need time under pressure to allow the ingredients of the friction material to react and to improve compacting of the materials. In some examples, the soft brake pad may be left at room temperature for a few days. In some other examples the soft brake pad may be left at room temperature for more than five days.

[0042] Pressure may be applied on the soft brake pad using a Spannrahmen device, a handmade device. In a Spannrahmen device, two metal plates and springs may be used to apply the load. The load applied may be in a range of 100- 200 kg. The Spannrahmen device may be formed by two metal plates fixed on four vertical walls. Four springs may be loaded by a hydraulic press which may press on a third plate to distribute the load homogeneously on the springs. The springs may press the plates which in turn press the soft brake pad to form a pre-cured brake pad with required hardness and compressibility.

[0043] Block 408 may be followed by block 410, where the pre-cured brake pad may be cured in an oven. In some examples, the curing temperature may be in a range of about 150°C to about 160°C, although other temperatures are contemplated and may be adjusted based on the specific materials of the brake pad. The brake pad may be cured for an appropriate curing time, such as about 30 min, or another curing time in a range from about 20 min to about 45 min. The heat applied to the brake pad during the curing time may activate and solidify the fibres, the geopolymer and other ingredients of the friction material. The pressure applied in the Spannrahmen device and the specific curing temperature may be necessary for adhesive activation and detachment improvement. During curing, the under-layer may thoroughly be adhered to the back plate without any substantially detachment.

[0044] FIG. 5 is a schematic representation of an example system 500 for making a brake pad that is arranged in accordance with at least some embodiments described herein. The described system 500 may include multiple devices such as a mixer 502, a molding press 504, a Spannrahmen device 506 and an oven 508.

[0045] A controller (not shown), may be utilized to coordinate the operation of system 500, such as via software instructions that when executed by a processor in the controller coordinate the operation of each of the devices for specified times, temperatures, and other process-based parameters for the devices. Thus, each of the described devices in system 500 may be configured and operated in response to signals (e.g., analog or digital signals) from the controller.

Additionally, conveyance systems (not shown) such as conveyor belts and other robot operated conveyors may be utilized, configured, and operated by the controller, to transfer between the various devices.

[0046] In one example configuration, the mixer 502 may be configured to mix a pre-mixture, a raw mixture and a silicate solution to form a wet mixture 512. The choice of the mixer 502 may depend on the quantities to be mixed. In one example an Eirich mixer having a capacity in a range of 8 lit to 50 lit may be used. In some examples, a Loedige mixer having a capacity of 25 lit may be used.

[0047] A pre- weighed wet mixture 512 along with an under-layer and a back plate may be placed in a molding press 504 and may be molded at a temperature in a range of about 20°C to about 80°C. The molding press 504 may be closed and may be configured to compress the friction material, the under-layer and the back plate together at room temperature by operating a punch provided in the molding press 504. In various examples, the pressure applied in the molding press may be on the order of about 250 kg/cm². In some examples, the pressure may be applied for about one minute. The brake pad at this stage may have a Rockwell hardness of about zero and may be termed as a soft brake pad 514.

[0048] A Spannrahmen device 506 may be configured to apply a load to the soft brake pad 514. The soft brake pad 514 may need a period of maturation under a pressure (load) to achieve the required hardness. The soft brake pad 514 may need further time under pressure to allow the ingredients of the friction material to react and to improve the compacting of the materials. In some examples, the soft brake pad 514 may be left at room temperature for few days. In some examples the soft brake pad 514 may be left at room temperature for more than five days.

[0049] Pressure may be applied on the soft brake pad 514 using the Spannrahmen device 506, a hand-made device. In Spannrahmen device 506, two metal plates and springs may be used to apply the load. The load applied may be in a range of 100- 200 kg. The Spannrahmen device 506 may be formed by two metal plates fixed on four vertical walls. Four springs may be loaded by a hydraulic press which may press on a third plate to distribute the load homogeneously on the springs. The springs may press the plates which in turn press the soft brake pad resulting in a precured brake pad 516 of required hardness and compressibility.

[0050] The pre-cured brake pad 516 may be cured in an oven 508 at a curing temperature in a range of about 150°C to about 160°C for a time period (curing time) of about 30 min. to form a brake pad 518. The brake pad 518 may have a hardness rating of about 55.9 HRS, a compressibility rating of about 0.1 mm and a detachment rating of about 12.35 kN (a force required to detach layers of the pad).

[0051] FIG. 6 is a schematic representation of a Spannrahmen device for applying load on a soft brake pad. Spannrahmen device 600 is a hand-made device and is configured to apply a load on the soft brake pad 610. Spannrahmen device 600 includes two metal plates 602 and four springs 604 that may be used to apply the load. The load applied may be in a range of about 100 kg to about 200 kg. The Spannrahmen device 600 may be formed by two metal plates 602 fixed on four vertical walls 606. Four springs 604 may be loaded by a hydraulic press (not shown) which may press on a third plate 608 to distribute the load homogeneously on the springs 604. The springs may be configured to press the two metal plates 602 which in turn press the soft brake pad 610 resulting in a pre-cured brake pad 610 of required hardness and compressibility.

[0052] FIG. 7 is a graph 700 illustrating a measurement of hardness of a brake pad that includes the disclosed friction material. In graph 700, vertical axis 702 represents hardness and horizontal axis 704 represents time spent in the Spannrahmen device (in hours). In graph 700, the hardness value increases linearly from zero to a value of about 60 in about 50 hours elapsed time, and then the hardness rate decreases from about 50 hours to about 120 hours of elapsed time, slowly stabilizing at a hardness value of about 75 at about 150 hours. The hardness value remains substantially constant thereafter, as illustrated by the elapsed from about 125 hrs to about 250 hr. [0053] The hardness test is performed according to Rockwell test protocol, which measures a depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). Rockwell scale is a hardness scale based on indentation hardness of a material. The classification used as HRS indicating the indenter is a steel ball.

[0054] FIG. 8 is a graph 800 illustrating a measurement of a coefficient of friction of a brake pad that includes the disclosed friction material compared to a conventional brake pad that includes standard low steel friction material.

[0055] The vertical axis 802 represents a coefficient of friction and the horizontal axis 804 represents various standard tests. The graph 806 indicates the variation of the coefficient of friction over the various tests for a brake pad that includes the disclosed friction material. The graph 808 indicates the variation of the coefficient of friction over the various tests for a brake pad that includes LS material according to the AKM standard. Both brake pads exhibited similar average coefficient of friction.

[0056] Brake materials can be tested in on-vehicle stopping tests or in a full-scale dynamometer. In dynamometer tests, real pad or rotor can be tested under protocols simulating the conditions required to stop a vehicle. Different standards may be used such as the SAE J2522 developed by the AK Working Group (AKM), which represents European manufacturers of passenger car brakes. The tests assess the effectiveness of the brake pad and the rotor system under different conditions of speeds, temperatures, pressures, and deceleration.

[0057] Some of the physical parameters used by dynamometers (e.g., according to SAE J2522) include contact pressure between the pad and rotor, deceleration, sliding speed, and initial temperature. The tests are focused on deceleration, where the vehicle is simulated during stopping or speed-reduction conditions (e.g., in many of the test steps according to SAE J2522 snubs from 80 km/hour to 30 km/hour are used applying 3,000 kPa in the fluid line that applies the force to the caliper).

[0058] The J2522 protocol includes 15 different main steps and many other sub-steps aimed at evaluating the friction performance of the brake materials under various conditions. A non- exhaustive, example list of test steps may include green m characteristic (30 cycles): snub 80-30 km/hour, 380 N; burnish (192 cycles): snub 80 to 30 km/hour, varying the applied load; characteristic value 1: (6 cycles): snub 80-30 km/hour, 380 N; speed/pressure sensitivity 40 km/hour (8 cycles): snub 40-5 km/hour, varying the load; speed/pressure sensitivity 80 km/hour (8 cycles): snub 80-40 km/hour, varying the load; speed/pressure sensitivity 120 km/hour (8 cycles): snub 120-80 km/hour, varying the load; cold application: 1 stop 40-5 km/hour, 380 N; Fade 1: 15 stops 100-5 km/hour, 500 N; and recovery 1 (18 cycles): snub 80-30 km/hour, 380 N.

EXAMPLES

[0059] The following examples are intended as illustrative and non-limiting and represent specific embodiments of the present disclosure. The examples show that the disclosed geopolymers are substantially free of phenolic resins. In addition, the examples demonstrate that the friction materials are synthesized using the disclosed geopolymers. Further, the examples demonstrate that the brake pads including the disclosed friction materials have a high hardness, compressibility and detach.

Example 1

Synthesis of a geopolymer

[0060] Table 1 presents an example recipe for geopolymer synthesis. The metakaolin used was comprised of Argical™M1000. 98% Sodium silicate was obtained from Sigma. The water used was milliQ water and the other type of water. 10.3 wt% of silica was mixed with 89.7 wt% of metakaolin in an Eirich mixer having a capacity of 50 lit. The mixing time was 5 to 10 min.

[0061] Sodium silicate solution was prepared by dissolving 37.5 wt% of sodium silicate in 62.5 wt% of water by continuously stirring for about 2 to about 4 hours on a hot plate. The temperature was increased up to 50°C to ensure that sodium silicate was completely soluble in the water. The sodium silicate solution has a pH in a range from about 12 to about 14. The sodium silicate solution was then added to the mixture of silica and metakaolin and mixed in the Eirich mixer to form a geopolymer.

TABLE 1

Example 2

Synthesis of a friction material

[0062] 10.3 wt% of silica was mixed with 89.7 wt% of metakaolin in a 50 lit Eirich mixer to form a pre-mixture. The mixing time was 5 to 10 min. 58.5 wt% of a raw mixture was mixed with

41.5 wt% of pre-mixture to form a dry mixture. The raw mixture had pre-selected components that include fibers, fillers, friction modifiers and abrasives.

[0063] Sodium silicate solution was prepared by dissolving 37.5 wt% of sodium silicate in

62.5 wt% of water by continuously stirring for about 2 to about 4 hours on a hot plate. The temperature was increased up to about 50°C to ensure that sodium silicate was completely soluble in the water. The sodium silicate solution has a pH in a range of about 12 to about 14.

[0064] 31.7 wt% of sodium silicate solution was mixed with 68.3 wt% of the dry mixture in an Eirich mixer for about 5 to about 10 min to form a wet mixture. The wet mixture has a final moisture content of about 20%.

Example 3 Brake pads

[0065] Pre-weighed friction material along with an under-layer and a back plate were placed in a molding press and molded at room temperature. The friction material was prepared as described in Example 2. A pressure of about 250 kg/cm² was applied for about one minute in the molding press. The soft brake pad thus produced had a Rockwell hardness of zero. A load of about 100 kg to about 200 kg was applied using Spannrahmen device. The soft brake pad was left in Spannrahmen device at room temperature for more than five days. The pre-cured brake pad was cured in an oven. The temperature of curing was in a range of about 150°C to 160°C. The pre-cured brake pad was cured for about 30 min at that temperature. The brake pad after curing had a hardness of 55.9 HRS, a compressibility of 0.1 mm, and a detach of 12.35 kN.

[0066] The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, are possible from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0067] The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. Such depicted architectures are merely examples, and in fact, many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermediate components. Likewise, any two components so associated may also be viewed as being "operably connected", or "operably coupled", to each other to achieve the desired functionality, and any two components capable of being so associated may also be viewed as being "operably couplable", to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically connectable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

[0068] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

[0069] In general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation, no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations).

[0070] Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general, such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

[0071] For any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non- limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, a range includes each individual member. Thus, for example, a group having 1 -3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth. [0072] While various aspects and embodiments have been disclosed herein, other aspects and embodiments are possible. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

CLAIMS WHAT IS CLAIMED IS:

1. A method for synthesizing a geopolymer, the method comprising: mixing silica and metakaolin to form a pre-mixture; preparing a silicate solution; and mixing the silicate solution and the pre-mixture to form a wet mixture, wherein the method is carried out in absence of an alkali and in presence of water.

2. The method of claim 1 , wherein mixing silica and metakaolin comprises mixing about 10 wt% of silica and about 90 wt% of metakaolin.

3. The method of claim 1, wherein mixing silica and metakaolin comprises mixing for about 5 minutes to about 10 minutes in an Eirich mixer or a Loedige mixer.

4. The method of claim 1 , wherein preparing the silicate solution comprises adding sodium silicate or potassium silicate to water.

5. The method of claim 1, wherein preparing the silicate solution comprises adding about 38 wt% of sodium silicate to about 42 wt% of water.

6. The method of claim 1, wherein preparing the silicate solution comprises: adding sodium silicate to the water; heating to a temperature up to 50°C; and stirring for about 2 to about 4 hours.

7. The method of claim 6, wherein preparing the silicate solution comprises preparing the silicate solution having a pH in a range from about 12 to about 14.

8. The method of claim 1, wherein mixing the silicate solution and the pre-mixture comprises mixing for about 5 minutes to about 10 minutes in an Eirich mixer or a Loedige mixer to form the wet mixture.

9. The method of claim 1, wherein synthesizing the geopolymer comprises synthesizing the geopolymer without a phenolic resin.

10. A method for making a friction material, the method comprising: mixing silica and metakaolin to form a pre-mixture; blending the pre-mixture and a raw mixture to form a dry mixture, wherein the raw mixture comprises one or more of inorganic, organic or metallic fibers, at least one friction modifier or lubricant, and at least one filler or abrasive; preparing a silicate solution; and mixing the silicate solution and the dry mixture to form the friction material, wherein the method is carried out in absence of an alkali and in presence of water, and wherein a reaction between the pre-mixture and the silicate solution forms a geopolymer.

11. The method of claim 10, wherein mixing silica and metakaolin comprises mixing about 10 wt% of silica and about 90 wt% of metakaolin.

12. The method of claim 10, wherein mixing silica and metakaolin comprises mixing for about 5 minutes to 10 minutes in an Eirich mixer or a Loedige mixer.

13. The method of claim 10, wherein preparing the silicate solution comprises adding sodium silicate or potassium silicate to water.

14. The method of claim 10, wherein preparing the silicate solution comprises adding about 38 wt% of sodium silicate to about 42 wt% of water.

15. The method of claim 10, wherein preparing the silicate solution comprises: adding sodium silicate to the water; heating to a temperature up to about 50°C; and stirring for about 2 to about 4 hours.

16. The method of claim 15, wherein preparing the silicate solution comprises preparing the silicate solution having a pH in a range from about 12 to about 14.

17. The method of claim 10, wherein mixing the silicate solution and the dry mixture comprises mixing for about 5-10 minutes in an Eirich mixer or a Loedige mixer to form the wet mixture.

18. The method of claim 10, wherein blending the pre-mixture and the raw mixture to form the dry mixture comprises blending 40 wt% of the pre-mixture and about 60 wt% of the raw mixture.

19. The method of claim 10, wherein blending the pre-mixture and the raw mixture comprises blending the pre-mixture and the raw mixture for about 5 minutes to about 10 minutes in an Eirich mixer or a Loedige mixer.

20. The method of claim 10, wherein adding the silicate solution to the dry mixture comprises adding about 32 wt% of silicate solution to about 68 wt% of the dry mixture.

21. The method of claim 10, wherein adding the silicate solution to the dry mixture to form the wet mixture comprises forming the wet mixture to have a final moisture content of about 20 wt%.

22. A method for making a brake pad, the method comprising: synthesizing a friction material; placing the friction material, an under-layer and a backplate in a molding press; molding at a temperature in a range of about 20°C to about 80 °C to form a soft brake applying a load to the soft brake pad, wherein the load is in a range of about 100 to about

200 kg; and curing in an oven to form the brake pad, wherein synthesizing the friction material comprises: mixing silica and metakaolin to form a pre-mixture; blending the pre-mixture and a raw mixture to form a dry mixture, wherein the raw mixture comprises one or more of inorganic, organic or metallic fibers, at least one friction modifier or lubricant, and at least one filler or abrasive; preparing a silicate solution; and mixing the silicate solution and the dry mixture to form the friction material, wherein the method is carried out in absence of an alkali and in presence of water, and wherein a reaction between the pre-mixture and the silicate solution forms a geopolymer.

23. The method of claim 22, wherein molding comprises molding for about 1 min and at a pressure in a range of about 100 kg/cm² to about 300 kg/cm².

24. The method of claim 22, wherein curing comprises curing at a temperature in a range of about 150 °C to about 160 °C for at least about 30 min.

25. The method of claim 22, wherein molding comprises molding at a temperature in a range of about 20°C to about 80 °C to form a soft brake pad with a Rockwell hardness of substantially zero.

26. The method of claim 22, wherein applying the load comprises placing the soft brake pad in between two metal plates fixed on four vertical rails and applying load by a hydraulic press.

27. The method of claim 22, wherein applying the load and curing in the oven forms the brake pad with a hardness of about 60 HRS, a compressibility of about 0.1 mm, and a detach of about 12.35 KN.

28. A braking system comprising: a brake disc rotor made of a metal; and a brake pad positioned on the brake disc rotor, wherein the brake pad comprises a friction material, the friction material comprises a geopolymer, and the geopolymer is free of alkali and phenolic resin.

29. The braking system of claim 28, wherein the geopolymer comprises about 42 wt% of metakaolin, about 20 wt% of sodium silicate, about 5 wt% of silica and about 33 wt% of water.