Silicone resin-based friction lining mixture with metal fibers and friction lining

Abstract

To improve the wear resistance of friction linings. The present invention provides a friction lining mixture for the production of friction linings with reduced wear, the friction lining mixture comprising at least one silicone resin, a filler, friction particles and metal fibers, the metal fibers consisting of more than 50% by mass of soft iron and / or soft steel compounds.

Description

[Technical Field]

[0001] The present invention relates to a silicone resin-based friction lining mixture and friction linings, in particular for disc brake linings, to a method for their production and to their use. [Background technology]

[0002] Silicone resin-based binder systems and friction linings are known in the art.

[0003] EP 2 310 714 B1 describes a brake lining for a disc brake having a friction part made of a ceramic matrix material, which is produced from a silicon-ceramic starting material, particles of a hard material acting as an abrasive, particles of a substance suitable as a lubricant, and particles of a metallic material.

[0004] DE 11 2009 000 893 T5 describes a composition for brake linings based on silicone resin and NBR rubber.

[0005] US 5,984,055 relates to a friction lining comprising a fiber-reinforced ceramic matrix material containing ceramizable resin and fibers.

[0006] US 8,960,384 B2 describes a method for producing a ceramic matrix material for friction linings, in which a silicon-containing ceramic precursor, an abrasive, a lubricant and metal particles are used as starting materials (raw materials).

[0007] DE 101 30 395 A1 describes a friction material in which the framework components are formed from fibrous materials such as copper or brass. Additional impregnated components can consist of, for example, phenolic resins, soft metals or glass.

[0008] DE 697 18 346 T2 relates to a friction material comprising sintered masses of iron in which graphite particles are dispersed, the masses containing iron as fibers and as particles.

[0009] Finally, WO 2013 / 076744 A1 describes a friction material for disc brakes containing 1 to 8% ceramizable resin and 2 to 10% organic resin. Silicone resin can be used as the ceramizable resin. [Prior art documents] [Patent documents]

[0010] Summary of the Invention [Problem to be solved by the invention]

[0011] These silicone resin-based binder systems or friction linings generally represent some advances over the conventional friction linings already described in the prior art, but there is still room for improvement in these linings with regard to their performance characteristics in so-called high-performance applications, i.e., especially at high pressures and temperatures.

[0012] It is therefore an object of the present invention to provide friction linings and friction lining mixtures which are improved over the prior art, inter alia with regard to wear, coefficient of friction, pressure and temperature resistance. [Means for solving the problem]

[0013] [Brief explanation of the drawings]

[0014] DETAILED DESCRIPTION OF THE INVENTION

[0015]

[0016] It has been found that special silicone resin-based friction lining mixtures and friction linings produced from such mixtures are able to meet these increased demands, while at the same time their production does not involve additional requirements or modifications to the production methods known from the prior art.

[0017] To achieve the above objectives, the friction lining must be physically densified and at the same time have a high chemical density in the chemical bonds and polar interactions between its components. In this regard, the formation of a high chemical density in the chemical bonds between the various components of the friction lining is of particular importance and therefore requires special measures to ensure this.

[0018] The highly wear-resistant and friction-optimized silicone resin-based friction lining mixture or friction lining of the present invention preferably has the following composition: All the following data, here and below, unless otherwise stated, are in mass percent relative to the finished (finished) friction lining mixture:

[0019] Metals (e.g., fibers, mostly containing iron) 5-90% Friction particles (Reibkoerner) / friction agent 25~45% Filler (especially coke) 5-40% Lubricant 0~20% Crosslinking chemicals / catalysts (organic zinc compounds, etc.) 0.1-4% Silicone resin 6~16%

[0020] Metals, metal mixtures, alloys, or sintered metals, such as iron (Fe) or copper (Cu), ensure a high coefficient of friction even at elevated or high temperatures and simultaneously provide good wear behavior. A preferred component is metal fibers, whose content in the friction lining mixture of the present invention is preferably 5 to 90%, especially 5 to 30%. Iron or steel fibers are preferred in this regard, as they increase the strength of the friction lining mixture and prevent individual components from escaping from within the friction lining. Copper or copper fibers are less preferred due to their unfavorable environmental properties. Therefore, copper-free friction lining mixtures and friction linings are also considered by the present invention.

[0021] Advantageously, the undesired premature wear of the friction material can be reduced (suppressed) by using special iron or steel fibers in the silicone resin-based mixture (use of M2 or M3 in FIG. 1). These are rather soft iron or steel fibers. In this regard, it has been found that special iron fibers (M2) made with reduced amounts of alloying elements (components) have particularly good properties with respect to wear. In this regard, mention can be made, inter alia, of the carbon, manganese and silicon content (components: -gehalt) (see Table 1). They are therefore also referred to as pure iron fibers or, according to the invention, as soft iron compounds or soft iron fibers (in this case, preferably type M2 compounds in Table 1).

[0022] Structurally, the fibers (according to the invention) are preferably characterized by having only a ferrite phase. Steel fibers containing alloying elements (components) have, in addition to the ferrite phase, a pronounced pearlite structure (structure). This pearlite structure (structure) makes the steel particularly hard (strong). This iron-carbon alloy is also called hard steel (hard steel).

[0023] In accordance with the present invention, type M3 steel fibers of Table 1 are preferred, which are also referred to herein as soft steel fibers or soft steel compounds.

[0024] In addition to the proportion of alloying elements, the strength of steel is also enhanced by its elongation. This elongation is realized in longitudinally aligned crystal structures. When the fibers are hot-hardened (strengthened), the resulting strength is lost. Therefore, the use of special hot-hardened steels is particularly advantageous in accordance with the present invention, since excessively high strength is actually detrimental to reduced wear. The difference can also be seen in the hardness (see M1 and M3 in Figure 1).

[0025] FIG. 1 shows photographs at different magnifications that allow one to appreciate the structure of materials M1, M2 and M3 shown in Table 1.

[0026] Table 1: Composition and dimensions of iron or steel fibers M1, M2, M3 TIFF2026507963000001.tif65156

[0027] Figure 1. Images of steel fibers M1 (left), M2 (center) and M3 (right) to approximate scale.

[0028] M1: STAX steel fiber (non-alloyed) Manufacturer: DEUTSCHES METALLFASERWERK Dr. Schwabbauer GmbH & Co. KG M2: STAX Pure Iron Fiber Manufacturer: DEUTSCHES METALLFASERWERK Dr. Schwabbauer GmbH & Co. KG M3: Heat-treated steel fiber; American Metal Fibers, Inc.

[0029] Table 2: Abrasion / Wear of linings with different metal fiber compositions TIFF2026507963000002.tif99156

[0030] Abrasion is determined by measuring the thickness of the lining at several locations before and after measurement.

[0031] For linings containing only M1 fibres, the abrasion values ​​are comparable to those of the reference (Ref) i.e. conventional lining. Linings containing M2 and M3 fibres as additional components (Anteil) have lower abrasion; see Table 2.

[0032] Advantageously, the metal fibers are made primarily, i.e., more than 50%, of soft iron and / or steel compounds. These may in particular be pure iron fibers or hot-hardened steel fibers. It is also conceivable to mix pure iron fibers or hot-hardened steel fibers. Particularly preferably, the metal fibers used according to the invention are made of more than 60% soft iron and / or steel compounds.

[0033] The friction lining mixture / friction lining according to the present invention contains a high proportion of friction agent, preferably in the form of friction particles, also referred to collectively as abrasives. Preferred representatives are, to name the most important, SiC (6.4 μm), ZnO (2.5 μm), MgO (12.7 μm), Al2O3 (5 μm), and various silicates. The preferred d50 value of the particle size is given in parentheses. The d50 value means that 50% of the particles have a smaller size (particle size) than the value in parentheses. This value is determined by light scattering. The particle size is determined by dynamic light scattering of a suspension of particles in suspension.

[0034] The cokes mentioned in the specification are called active fillers. An active filler is understood to be a material whose surface has as good an affinity as possible for the crosslinking chemicals used, in particular for silicone resins, so that a higher degree of crosslinking between the friction lining components and the final, more dense finished friction lining is achieved. Examples of active fillers preferred in accordance with the present invention include (calcined) petroleum coke or carbon black.

[0035] Here, the classification of active fillers is based on their ability to form chemical bonds with the silicone resin. Active fillers are distinguished by the fact that, firstly, they are able to react with the resin on their surface due to their functional groups, and (secondly) due to their relatively high specific surface area (the coke used is preferably 0.9 m). 2 / g) has many possibilities for forming bonds with the resin. The specific surface area of ​​the particles is determined by the BET measurement method.

[0036] The other materials of the friction lining mixture need to be surrounded by a highly crosslinked matrix, because active or intrinsic chemical bonding of these other materials to the matrix is ​​only poorly possible due to the chemically less active surfaces of these materials.

[0037] The lubricants used are in particular so-called high-temperature lubricants, examples of which include antimony sulfide, molybdenum sulfide and zinc sulfide, as well as graphite.

[0038] The cross-linking chemical (cross-linking agent) or catalyst is preferably an organozinc compound (catalyst).

[0039] As is known in the prior art, silicone resin-based friction linings require a curing reaction (condensation polymerization reaction) that can be carried out without a catalyst or, preferably, with a suitable catalyst. For this purpose, in accordance with the present invention, organic zinc compounds are used, such as zinc acetylacetonate, zinc pentadionate, zinc acetate, or their derivatives.

[0040] Silicone resins suitable according to the invention are generally crosslinked polymethylsiloxanes or polymethylphenylsiloxanes or polyphenylsiloxanes commonly used in the (prior) art and having the constituent elements of formula I: TIFF2026507963000003.tif4159(I) where A and B can be various organic residues (same or different), such as methyl, ethyl, or phenyl. Such silicone resins are generally sold in pre-condensed form. Some of them are also combined with phenolic and polyester resins, for example, to further improve surface hardness and heat and chemical resistance. All of these silicone resins mentioned above can in principle be used for the purposes of the present invention.

[0041] Silicone resins with a high inorganic content (content of inorganic components) are particularly preferred. The inorganic content can reach approximately 82% by weight. The inorganic content is expressed as the amount remaining after calcination of a pure resin sample. An organic content in the resin is necessary because the resin must be melted during pressing. This is ensured by a certain amount of organic residues in the resin. The organic residues in the resin consist of phenyl and / or alkyl groups. Similarly, alkoxy groups can be constituents of the organic content of the resin. Preferably, ethoxy and methoxy groups are used as organic side groups in the resin.

[0042] The resin content (silicone resin content) in the mixture is preferably 6% to 16% by weight (based on the finished friction lining mixture). Suitable resins are sold, for example, by Wacker Chemie AG (Germany) under the trade name Silres®. Here, resins with the name Silres MK are preferred.

[0043] Due to the relatively low organic content (content of organic components) preferred in accordance with the present invention, the matrix of the friction lining (i.e., binder system and filler) is largely retained even during decomposition of the organic components. Silicone resins with a significantly higher organic content exhibit significantly greater mass loss (reduction) when the temperature is increased, which means that the matrix is ​​significantly decomposed, thereby simultaneously increasing the wear value (amount). The decomposition of the organic matrix can be easily and reliably monitored and determined using a thermogravimetric analyzer (TGA).

[0044] A further advantage of the silicone resins suitable according to the invention is their low softening temperature, preferably between 35 and 55° C. This low softening temperature is advantageous, for example, when pressing the friction lining mixture to form a pre-crosslinked friction lining press, since a lower molding temperature can be selected. A lower temperature results in a lower gas pressure inside the lining during molding.

[0045] However, the use of the above catalysts, preferably in amounts of 0.25 to 4%, is preferred according to the invention.

[0046] The use of silicone resin-based systems for high-temperature applications is known in principle. To do so, the system must still undergo a curing reaction, which can be achieved without a catalyst or with a suitable catalyst. During the curing reaction, the condensation polymerization reaction that begins when the friction lining mixture is pressed continues to occur. At the same time, organic residues are split off. However, due to the low curing temperature of less than 300°C preferred in accordance with the present invention, the methyl groups of the resin remain in the resin, and perhaps, the hydrolysis reaction will also not be 100% complete. This means that residual ethoxy groups still remain in the system.

[0047] The condensation polymerization reaction of silicone resins for use in brake linings is preferably catalyzed by an organozinc compound. During this condensation polymerization reaction, low-molecular-weight substances are split, which can lead to the formation of bubbles and cracks in the resulting friction lining during the pressing process of the friction lining mixture. Due to the gas generated in the material to be pressed, the lining can only be compressed insufficiently. As a result of all this, the wear and friction coefficient of such friction linings are negatively affected. Therefore, it is desirable to minimize the generation of gas during the pressing process as much as possible.

[0048] According to the invention, the following measures, alone or in combination, contribute to a further improvement of the friction lining obtained:

[0049] Due to the lower curing temperature of the lining, some of the reactive components remain on the surface of the filler, which improves the adhesion of the filler to the resin system. Upon curing, further covalent bonds are formed between the active filler and the resin system.

[0050] On the one hand, this increases the crosslink density of the material due to the resulting lower porosity, and on the other hand, the strengthened (increased) crosslinks reduce the tendency of the friction lining to relax again after pressing and therefore expand due to the increased number of active groups remaining on the surface. As a result, the overall network density within the system also increases. Therefore, in this case, a curing temperature of less than 361°C is preferred. Above this temperature, for example, oxygen-containing groups / residues present on the surface of calcined (calcined) petroleum coke decompose. For this reason, in accordance with the present invention, a curing temperature of less than 300°C is particularly preferably selected. This curing temperature has been found (by the present invention) to be sufficient for crosslinking of the silicone resin.

[0051] It is desirable to achieve maximum compaction of the mixture during pressing, which can be achieved by eliminating the venting step during pressing.

[0052] Likewise, a pressing time of the friction lining, preferably greater than 8 minutes, has proven advantageous, as a longer pressing time results in additional compression of the lining material.

[0053] The densification of the material is achieved by crosslinking of the silicone resin. For this, a catalyst is preferably required. In order to achieve the highest possible densification even during pressing, all components that limit (inhibit) the activity of the catalyst are excluded.

[0054] The preparation of the mixture, pressing of the mixture, grinding and grooving of the lining and hardening of the lining are carried out in principle according to the methods known in the prior art, where, according to the invention, the temperature during pressing is preferably 100-170°C, in particular 140°C, and the temperature during hardening of the friction lining is preferably not more than 300°C.

[0055] All components of the friction lining mixture are first mixed in the composition described above in an internal mixer, followed by further mixing with a trough and swirler at medium speed for approximately 5 minutes.

[0056] The mixture is then filled into the cavity of a high-pressure press. The cavity then has the desired lining profile. The height of the lining is determined by the amount of mixture to be filled. A lining support plate is placed above the cavity. A rising piston compresses the mixture in the cavity and presses it against the lining support plate. A hold-down device holds the lining support plate in place above the cavity.

[0057] In this case, the surface pressure is preferably 15 N / cm 2 ~200N / cm 2 Typical pressing times are 2 to 14 minutes. To achieve maximum compression, the pressure is maintained constant throughout the entire pressing cycle.

[0058] The lining is then ground to the desired thickness.

[0059] Curing is then carried out at a temperature preferably below 300° C. In this case, the temperature is first increased from room temperature to below 300° C. at a constant rate of 1° C. / min. The temperature is then maintained at below 300° C. for 180 minutes. The furnace is then switched off and the lining is allowed to cool slowly in the furnace.

[0060] The brake linings obtained were subjected to a flywheel dynamometer test to determine their wear resistance. The compositions of the friction linings tested and the test results obtained are listed in Table 2. Reference (Ref) represents a control brake / friction lining, while Examples 1 to 3 represent brake / friction linings according to the invention.

[0061] The above-described method for manufacturing the friction lining of the present invention can be generally used and is not limited to only Examples 1 to 3 (compositions in mass %).

[0062] Thus, the present invention includes the above-described friction lining mixture, friction and brake linings produced from said mixture, methods for producing the friction lining mixture and the friction / brake lining, and the use of the friction lining mixture for the production of friction / brake linings and the use of friction / brake linings in high performance applications, such as 24-hour automobile races, under increased pressure and elevated temperatures.

[0063]

Claims

1. Friction lining mixture for the manufacture of friction linings with reduced wear, comprising: the friction lining mixture comprises at least one silicone resin, a filler, friction particles and metal fibers, The metal fibers consist of more than 50% by weight of soft iron and / or soft steel compounds. Friction lining compound characterized by:

2. 2. The friction lining mixture of claim 1, The metal fibers contain more than 50% by mass of pure iron fibers. Friction lining compound characterized by:

3. 3. The friction lining mixture according to claim 2, The pure iron fibers have reduced proportions of alloying elements, with the carbon content being less than 0.01% by weight, the manganese content being less than 0.5% by weight, and the silicon content being less than 0.05% by weight. Friction lining compound characterized by:

4. Friction lining mixture according to any one or more of claims 2 and 3, The pure iron fibers contain substantially only ferrite phase. Friction lining compound characterized by:

5. 2. The friction lining mixture of claim 1, the metal fibers contain more than 50% by weight of hot-hardened steel fibers; Friction lining compound characterized by:

6. Friction lining mixture according to any one or more of claims 1 to 5, the mixture contains one or more silicone resins having an inorganic component of 60 to 88% by weight, in particular approximately 82% by weight; Friction lining compound characterized by:

7. Friction lining mixture according to any one or more of claims 1 to 6, The mixture contains 6 to 16% by weight of one or more silicone resins overall based on the total mixture. Friction lining compound characterized by:

8. Friction lining mixture according to any one or more of claims 1 to 7, The mixture contains 10 to 20% by mass of petroleum coke based on the total mixture. Friction lining compound characterized by:

9. Friction linings that can be made from the friction lining mixture according to any one or more of claims 1 to 8.

10. A brake lining comprising the friction lining according to claim 9.

11. Use of silicone resin and metal fibers in combination with fillers and friction particles for the manufacture of friction lining mixtures and friction linings according to any of claims 1 to 9.

12. A method for producing a friction lining from the friction lining mixture according to any one of claims 1 to 8, comprising: The method comprises the steps of: a) providing a finished friction lining mixture; b) pouring the friction lining mixture into a press; c) the friction lining mixture at increased pressure, in particular 15 to 200 N / cm ２ and pressing at elevated temperature, preferably 100-170°C, for 8-14 minutes. d) removing the friction lining from the press; and e) Hardening the friction lining at a temperature below 300°C Including A method characterized by:

Images