Method for producing a friction material, friction material produced thereby and its use

Abstract

A method for producing a friction material for use on synchronizer rings, clutches, friction clutches or transmission components, comprising the steps: • Obtaining a carrier material, • Tempering the components of the matrix materials to be applied before application to the carrier layer to more than 80°C but less than 200°C, preferably more than 80°C-120°C, • direct or indirect application of a friction layer to the carrier material, wherein the friction layer is applied by means of a printing technique of matrix material, wherein the friction layer is applied with a defined open-cell or closed-cell porosity during application, wherein the degree of porosity is between 1% - 30% and wherein the porous structures have less than 0.1 mm.

Description

[0001] The invention relates generally to methods for producing a friction material, friction material produced thereby and its use, but in particular to friction linings and friction layers, in particular on synchronizer rings, clutches, friction clutches or transmission components with defined porosity and a 3D printing method for their production. background

[0002] Friction linings are a component of many mechanical components. They are used in transmissions, brakes, etc. for vehicles or permanently installed systems, such as in manufacturing facilities and robotics.

[0003] It is known, in devices for generating or transmitting friction, to provide at least one of these friction surfaces with a friction lining in order to increase the frictional force between the two surfaces. State of the art

[0004] Conventional tribological systems consist of brake pads, which mainly contain friction agents bonded with phenolic resins or sintered metals, and a counter material, such as a disc made of cast iron, steel or C / SiC (carbon fiber reinforced ceramic).

[0005] The pads are pressed against the mating material, which moves relative to it. This transfers torque through friction between the pressed surfaces.

[0006] A distinction is made between dry-running and wet-running friction pairs.

[0007] Dry-running friction pairs are used when the friction surfaces only slide against each other for a short time during each actuation, or when high wear can be accepted.

[0008] The wet-running friction pairs, on the other hand, are cooled by liquid or lubricant, so that they wear much less.

[0009] Currently, three different friction lining systems are used: • Friction linings consisting of organic, resin-bonded powders mixed with abrasives, lubricants, fibers and mineral fibers. • Friction linings, preferably made of metal. German Offenlegungsschrift DE 29 28 853 A1 describes the manufacture of synchronizer rings from an abrasion- and wear-resistant metal, such as brass or bronze, as investment castings. Generally, the friction linings are applied to these surfaces; they are pressed and sintered as powder or sprayed on at elevated temperatures, as described, for example, in German Auslegeschrift DE 16 30 912 A and English patent GB 530 904 A. DE 42 39 441 A1 also discloses the production of reduced-density friction materials for dry clutches using a pressing process and thermal post-treatment steps. • Friction linings made of paper, fibers, carbon fiber fabrics or scrims and are preferably used in the area of synchronizer rings and clutches in accordance with European patent application EP 1 6491 83 A1.

[0010] In a few cases, friction linings made of C / SiC (see e.g. DE 102 33 729 A1) or graphite are used for thermal reasons.

[0011] Another new class of friction linings are printed linings, where mainly a resin or a mixture of organic polymers with abrasives, lubricants and fibers is printed onto a carrier.

[0012] Brake pads with organic resin bonding are subject to thermal decomposition, sintered metal brake pads melt at the surface.

[0013] These disadvantages can be reduced by using brake pads that meet the increased thermal demands of the systems. For prolonged or rapidly repetitive braking, clutching, or damping processes, the transferable surface-specific friction power of paper pads is limited to approximately 2.5 W / mm due to the tolerable pad temperatures. 2 Friction power limited.

[0014] Adding hard friction materials and lubricants to the friction materials leads to an improved service life and more comfortable shifting. The material, material structure, and density, in principle, allow for a wide range of design options. The material composition of the friction linings is largely homogeneous. A low level of porosity is observed on the surface.

[0015] DE 12 07 708 A describes a sintered iron-based friction lining that, in addition to small amounts of graphite, silicon dioxide, lead, and tin, may also contain 12-25% copper. According to US 22 14 104 A, the friction lining is a porous, sintered metal element consisting of 78 parts iron, 20 parts lead, and 2 parts graphite.

[0016] In the case of sintered metallic friction materials - especially with non-metallic additives and lubricants - it is not possible to set a defined porosity, i.e. either difficulties arise in producing a friction material of such strength that it can withstand the high pressures and temperature loads that occur during frictional engagement between the synchronizer ring and the friction partner, or the compression is so high that too little porosity is created.

[0017] DE 37 08 866 A1 discloses a method for producing an abrasive using a casting process. DE 696 37 418 T2 discloses the production of an abrasive article with bonded abrasive on a film or fibers using a pressing process. International patent application WO 2017 / 127 221 A1 also discloses a method for producing polishing agents.

[0018] The porosity of friction linings or friction layers cannot be controlled with the known methods, or only to a very limited extent, by compaction through pressure and temperature. The problem of introducing additional pores into an otherwise dense material using pore-forming agents was already described in EP 202145 B1. In this case, organic fibers are incorporated into the lining, which are subsequently decomposed in a thermal process step.

[0019] EP 0251301 B1 describes the adjustment of porosity in a graphite coating by chemical vapor deposition. The importance of porosity for friction comfort is also evident in the attempt to provide friction coatings with different porosities (EP 1614926 A1). This is achieved here using materials that require different densification, with different resin flow properties, and with different fiber content. However, the process is limited to graphite coatings and is relatively complex.

[0020] In EP 3 133 134 A1, porosity is adjusted by using a porous compound component. Friction modifiers with a microporous structure are particularly used here.

[0021] US Pat. No. 6,135,258 A describes the use of different porosities in a friction lining. The porosity is determined by different materials and the flowability of the resins.

[0022] This is particularly critical in the case of printed friction linings, as porosity is necessary for optimal friction and / or shifting. In the currently common pressing process for friction linings, porosity is generally created by the pressing pressure, temperature, or porous formulation components. This is naturally not necessary in the production of printed linings, as there is no pressing process involved.

[0023] Porosity in the friction lining creates the following technical advantages: - Adaptation of the friction lining to the mating material through elastic deformation, even in partial areas of the lining - Reduction of wear through uniform pressure and compensation of shock loads and compression - Increased comfort by stabilizing the coefficient of friction - Increased comfort by reducing vibrations - Absorption and release of oil in wet operation and thus much less wear - Mass reduction - Reduction in the size of the article (with a higher friction surface)

[0024] When producing printed coverings, it is possible to use channel structures according to the printing program or by introducing channel structures using volatile polymers.

[0025] The introduction of porous structures below 0.1 mm, or microporosity, is not feasible in 3D printing due to technological constraints. Wet-running pads, in particular, are subject to significant technical limitations due to their low oil absorption and increased wear.

[0026] It is known that the production of friction linings using 3D printing processes allows for rapid and cost-effective production. However, these friction linings contain little or almost no porosity.

[0027] By using appropriate printing programs, friction linings with internal structures can be produced. The adjustment of oil absorption and release can be ensured by channel structures within the lining. These structures can be created either through the printing process itself or by printing materials that decompose or are removed in a subsequent process step, thus forming the channel structures.

[0028] This process is not suitable for the formation of porosity, especially micro-porosity, since the size of the pores is above 0.1 mm due to the process.

[0029] The use of decomposable organic fibers in a printing process with a 3D printer is also currently technically difficult to achieve. Task

[0030] It would be desirable to provide a cost-effective process that makes it possible to provide porosity of a defined type, in particular micro-porosity. Brief description of the invention

[0031] The object is achieved by a method for producing a friction material for use on synchronizer rings, clutches, friction clutches or transmission components according to claim 1. The object is also achieved by a friction material obtained by one of the methods according to the invention and by the use of such friction materials. Solution to the problem

[0032] It is therefore the object of the present invention to provide an improved structure of friction layers, particularly for corresponding clutch or synchronization devices, drives, and other industrial applications as friction-relevant devices, and to provide suitable manufacturing processes. These must have a defined porosity, which leads to a defined compressibility and oil absorption in order to improve friction comfort and wear.

[0033] The present invention enables the defined formation of porosity, especially micro-porosity, in a friction lining and thus a defined absorption of oil and formation of defined compressibility by introducing gas-forming substances and / or gases and / or decomposing formulation components which leave a cavity in the matrix after a thermal post-treatment.

[0034] The compression modulus of the friction layer can be adjusted according to the requirements, as well as the size and number of pores (porosity) of the friction layer can be determined.

[0035] The gas-forming substances can be both volatile liquids, for example from the group of hydrocarbons such as alkanes or alcohols, as well as the combination of isocyanate and water or alcohols which release carbon dioxide in 2-component systems or propellants which release gases when heated, such as azodicarbonamides.

[0036] The gases used can be compressed air or (mainly inert) gases such as nitrogen or carbon dioxide. The (controlled) addition of gas to the matrix material preferably occurs after evacuation to achieve a defined porosity setting.

[0037] The decomposing formulation components used can come from the group of synthetic polymers such as polyacrylamides or polyacetals, or can be added as wood components or cellulose. Examples 1. Introduction of gases or liquids

[0038] Highly volatile alkanes (e.g. propanes, butanes, pentanes) or alcohols, dimethyl ether, compressed air, water, oxygen (O2), nitrogen (N2), carbon dioxide (CO2), noble gases e.g. argon, nitrous oxide (N2O, “laughing gas”), chlorofluorocarbons (CFCs) and other compounds known as propellants or propellant gases. 2. Use of gas-forming formulation ingredients. Organic reactions that release gases:

[0039] The reaction of isocyanates with alcohols or water releases carbon dioxide (CO2). Furthermore, condensation reactions, for example, release water, which evaporates upon heating. Gas is also released when amines react with carboxylic acids to form amides or polyamides, as is the case during the production of phenolic resins. Hydrogen (H2) is also released when epoxy resins are crosslinked with polyesters or amines. b. Inorganic reactions that release gases:

[0040] When copper reacts with sulfur, gaseous sulfur is produced.

[0041] During the production of paints, hydrogen is produced in the presence of metal particles. Until now, the paint industry has placed great emphasis on preventing blistering by adding additives. In the application presented here, however, the formation of blistering and thus microporosity is desired. 3. Use of decomposing recipe ingredients

[0042] Furthermore, compounds can be used that release gases when decomposed, such as azodicarbonamides, which release nitrogen when decomposed, as well as carbonic acid. Sodium bicarbonate, sodium dihydrogen carbonate release carbon dioxide, and titanium hydride or zirconium hydride decompose to hydrogen and titanium or zirconium.

[0043] In a method according to the invention for producing a friction material, a plurality of steps can be carried out.

[0044] Typically, a carrier material is obtained in a first step. The carrier material usually already has the external shape of the final product (e.g., a round disc). Furthermore, retaining structures and / or edges can be provided. Optionally, a so-called adhesion promoter can be applied to bond an intermediate layer or the friction material to ensure a secure bond. This intermediate layer serves, for example, to approximate the different expansion coefficients of the carrier material and the friction material. Suitable adhesion promoters can also improve the durability of the friction material obtained at the end of the process.

[0045] In a further processing step, a friction layer is applied to the resulting substrate. This process is carried out using a printing technique.

[0046] In this process, matrix material is applied. The matrix material is not necessarily a single material, but usually consists of a mixture of materials. The composition is selected such that expanding regions (be it due to expanding gas (mixture) or liquid (mixture)) are created within the process parameters.

[0047] In one embodiment of the invention, it is provided that the matrix material of the friction lining comprises at least one organic or inorganic polymer.

[0048] In contrast to organic polymers, whose basic frameworks mostly consist of carbon chains, the basic framework of (in)organic polymers also contains inorganic elements such as phosphorus, boron and / or silicon.

[0049] In a further embodiment of the invention, the application process is a printing process, wherein gases or liquids are added in a defined amount to at least one of the matrix materials to be printed before or during printing. For example, highly volatile alkanes (e.g., propanes, butanes, pentanes) and / or alcohols, dimethyl ether, compressed air, water, oxygen (O2), nitrogen (N2), carbon dioxide (CO2), noble gases (e.g., argon, nitrous oxide (N2O, "laughing gas"), chlorofluorocarbons (CFCs), and other compounds known as propellants or propellant gases can be used.

[0050] According to yet another embodiment of the invention, the porosity is adjusted by blowing agents and / or gas-forming components.

[0051] In yet another embodiment of the invention, the porosity is adjusted by decomposing components of the applied friction layer.

[0052] It should be noted that the porosity of the friction material at the end of the process chain can be determined by different components. For example, printing technology may already provide a certain basic porosity, which is further influenced by propellants and / or gas-forming components and / or decomposing components. This makes it possible to provide a porosity spectrum of different sizes and shapes.

[0053] In a further embodiment of the invention, a gas-forming component is formed during the combination of a multi-component matrix material. For example, when printing a multi-component matrix material, individual components can only be combined during printing.

[0054] Without limiting the generality of the invention, the matrix material can already be obtained as a preliminary product. However, it can also be provided that the matrix material is created within a period of a few days, a few hours, or even a few minutes before application. For example, it may be necessary to mix the components of the matrix material of the friction layer to be applied with a surface speed of the particles of 1 m / sec to 50 m / sec, preferably of 10 m / sec to 20 m / sec. Suitable mixing devices can be used for this purpose, whereby the specified surface speeds refer, for example, to the outer edge of the mixing vessel.

[0055] In the invention, the components of the matrix materials to be applied are tempered to more than 80°C but less than 200°C, preferably between 80°C and 120°C, before application to the carrier layer. This allows the appropriate flow properties for printing to be achieved. Furthermore, the tempering makes it possible to achieve a more uniform formation of porosity.

[0056] In a further embodiment of the invention, the application process is a printing process, wherein the applied friction layer is cured and / or tempered after the printing process at up to 300°C, preferably 95°C - 220°C. This makes it possible to achieve a more uniform porosity formation through tempering.

[0057] According to yet another embodiment of the invention, the application process is a printing process, wherein the components of the friction layer to be applied are heated during the printing process to up to 200°C, preferably 80 to 150°C, particularly preferably to 120°C. This allows the appropriate flow properties to be achieved. Furthermore, the temperature control makes it possible to achieve a more uniform formation of porosity.

[0058] By means of the presented methods it is possible to obtain friction material with a porosity level between 1% - 30%, particularly preferably between 4% - 8%.

[0059] It is also possible to achieve friction layer thicknesses from less than 1.5 mm down to 0.3 mm.

[0060] Friction layers can be tested, for example, by measuring the friction coefficient on material samples in a (conventional Mercedes Benz SS60) brake. For example, such a test can be used to assess the quality of the friction material. The test can be performed, for example, on a Krauss friction tester type RWS100B with appropriate performance data and the HRW-I option for measuring the static friction coefficient using the main drive.

[0061] These properties make it possible to produce cost-effective friction linings or friction layers even for high-performance applications. Nevertheless, it is possible to keep the thickness of the friction linings or friction layers low, thus minimizing material usage and allowing for compact dimensions and low mass. This allows the resulting friction materials to be used as friction linings or friction layers, particularly on synchronizer rings, clutches, overload clutches, friction clutches, or transmission components.

Claims

[1] A method for producing a friction material for use on synchronizer rings, clutches, friction clutches or transmission components, comprising the steps: • Obtaining a carrier material, • Tempering the components of the matrix materials to be applied before application to the carrier layer to more than 80°C but less than 200°C, preferably more than 80°C-120°C, • direct or indirect application of a friction layer to the carrier material, wherein the friction layer is applied by means of a printing technique of matrix material, wherein the friction layer is applied with a defined open-cell or closed-cell porosity during application, wherein the degree of porosity is between 1% - 30% and wherein the porous structures have less than 0.1 mm. [2] The method of claim 1, further comprising the step of applying an adhesion promoter to the resulting carrier material before applying a friction layer. [3] Method according to claim 1 or 2, characterized by that the matrix material of the friction lining comprises at least one organic or inorganic polymer. [4] Method according to one of the preceding claims, characterized by that gases are added in a defined quantity to at least one of the matrix materials to be printed before or during printing. [5] Method according to one of the preceding claims, characterized by that the porosity is adjusted by blowing agents and / or gas-forming components. [6] Method according to one of the preceding claims, characterized by that the porosity is adjusted by decomposing components of the applied friction layer. [7] Method according to one of the preceding claims, characterized bythat a gas-forming component is created when a multi-component matrix material is combined during printing. [8] Method according to one of the preceding claims, characterized by that the components of the matrix material of the friction layer to be applied are mixed at a surface speed of the particles of 1 m / sec to 50 m / sec, preferably of 10 m / sec to 20 m / sec. [9] Method according to one of the preceding claims, characterized by that the applied friction layer is cured and / or tempered after the printing process at up to 300°C, preferably 95°C - 220°C. [10] Method according to one of the preceding claims, characterized by that the components of the friction layer to be applied are heated to up to 200°C, preferably 80 to 150°C, particularly preferably to 120°C, during the printing process. [11] Friction material obtained by a process according to the preceding claims. [12] Friction material obtained by one of the preceding processes according to claims 1 to 10, wherein the degree of porosity is between 4% - 8%. [13] Use of friction material according to claim 11 or 12 as a friction lining or friction layer on synchronizer rings. [14] Use of friction material according to claim 11 or 12 as a friction lining or friction layer on clutches or friction clutches. [15] Use of friction material according to claim 11 or 12 as a friction lining or friction layer on transmission components.