Recycled material for the production of friction linings

Abstract

Recycled material from friction lining material comprising production residues and / or old lining material, characterized in that the recyclate is in granulated form in the form of grains, and wherein the recyclate has a grain size distribution such that at least 40% to 85% of the grains have a diameter of 0.50 mm to 1.00 mm.

Description

The invention relates to a recyclate for the production of friction linings, a starting material for the production of friction linings and a friction lining thereof.DE 197 27 920 A1 and EP 0 889 081 A1 disclose processes for re-using dusts formed in the production of friction linings. For this purpose, it is proposed to collect the filter dusts separately at a preselected ratio after production stages, to mix the different filter dusts, to compact the mixed filter dusts to form filter dust granules and to carry out a heat treatment.First, it is proposed to collect the filter dusts separately after production stages. This is intended to ensure that the composition of the filter dusts and in particular their proportion of active and inactive binders is known and can therefore be fed in metered amounts to the mixture of filter dusts at a reproducible proportion. The filter dusts are to be mixed with one another in a ratio which is preselected at the dosage and is defined by the later end use, as a result of which the composition of the filter dusts and the proportions of inactive and active binders thereof is to be able to be adjusted reproducibly. This is intended to enable dusts containing active binders and modified fibre constituents to come together with dusts which no longer contain active constituents and have a very fine structure by the finishing process, such as milling, grinding, drilling etc. The mixing process is intended to compensate for production-related fluctuations in the dust composition, in particular in the binder content. Since the filter dusts from the preproduction of phenolic resin compositions contain disproportionately high active binder contents, it should be possible to press the mixed filter dusts during compacting to form a solid filter dust granulate. The heat treatment is intended to cure the filter dust granulate by heating the granulate to such an extent that the phenolic resins / novolacs react out.The heat-treated and compacted filter dust granules or the heat-treated filter dust agglomerates should be able to be fed to a friction material recycling plant for reuse, as described in the earlier European patent application EP 0 826 896 A1. Alternatively, the heat-treated filter dust granulate or filter dust agglomerate should be usable as an additive for friction material mixtures.In contrast, EP 0 553 404 A1 and DE 42 01 892 A1 teach the reuse of finely divided residual materials from friction lining production, such as filter dusts from the extraction of the mixers for the friction lining composition, together with compacted burr, grinding dust and cuttings, with addition of a binder, for the production of friction linings, and the pressing of a mixture of these residual materials to form an organically bound friction lining. Unlike in the teaching of DE 197 27 920 A1, all filter dusts are to be brought together by means of collecting filter systems and, for example, pressed together with grinding dust and binder to give friction linings. A disadvantage here is that the filter dusts and friction lining fragments mixed from different production stages contain an unequal proportion of binders, namely active and inactive binders. Since, in particular, the binder content of the filter dusts varies greatly depending on the production stage, the re-useability of the filter dusts is very limited.It is proposed to mix a mixture of 15 to 25 wt. % filter dust from the production of friction masses, 0 to 20 wt. % pressed burr, 50 to 85 wt. % grinding dust and 0 to 20 wt. % cuttings, optionally with the addition of a maximum of 15 wt. % heat-resistant polymers, in the usual manner and to press them to give organically bound friction linings. For a friction lining consisting of 18 wt % filter dust and 82 wt % grinding dust, a drop in the coefficient of friction from 100° C. to 400° C. from 0.43 to 0.38 is indicated. For a friction lining made of the following substances, 1.5 wt % organic fibers, 7 wt % mineral fibers, 20 wt % metal chips and fibers, 25 wt % metal powder, 11 wt % binder, 21 wt % friction support and solid lubricant, 14.5 wt % fillers, which are dry-processed in a double shaft trough mixer to form a friction lining mixture, a drop in the coefficient of friction from 100° C. to 400° C. from 0.48 to 0.40 is given as a comparison. In order to avoid dust leakage, the mixer should be operated under slight reduced pressure.It is concluded therefrom that friction linings for disc brakes with good friction coefficients and sufficient strength and acceptable abrasion can be produced from the proposed friction lining mixture if the residues originate from the production of correspondingly high-quality friction linings and the residues of approximately the same composition are stored and used separately.Furthermore, a mixture of 15 wt. % filter dust, 15 wt. % press burr, 10 wt. % drill cuttings, 50 wt. % grinding dust and 10 wt. % nitrile rubber is proposed, from which a friction lining mixture is to be produced and processed under the same conditions to form friction linings for drum brakes. Compared with a conventionally produced friction lining mixture of 13 wt % mineral fibers, 34 wt % metal chips and fibers, 25 wt % binders, 2.5 wt % friction promoters and solid lubricant, and 25.5 wt % filler, a drop in the coefficient of friction from 100° C. to 400° C. from 0.45 to 0.36 for the proposed composition, and from 0.45 to 0.39 for the comparative mixture without residues is stated.DE 42 04 776 A1 and EP 0 518 004 A2 disclose a recycling method for fiber-reinforced thermoplastic materials. It is proposed that the fiber-reinforced thermoplastic materials are comminuted and mixed with a novolak in a ratio of 10:90 to 90:10, this mixture is treated under high shear forces at a temperature in the range from 150° C. to 230° C. and the resulting product is granulated. It is further proposed, inter alia, that the products obtained be used as binders for friction linings. For this purpose, the product as binder should be mixed intensively with a mixture of steel wool, brass shavings, coke, graphite, polyaramid fiber (2 mm), barium sulfate and magnesium oxide and pressed at 170° C. for 30 s per mm layer thickness and postcured at 200° C. for 10 hours.US 2014 / 190777 A1 describes a method for producing brake linings for drum brakes for heavy commercial vehicles. Used drum brake linings are to be used. The proposed method comprises the use of recycled friction material from used friction pads, recycled unused friction material from production and friction pad material from fresh raw materials.For this purpose, a recycle mixture of used and unused friction lining material is first to be produced to form a granulate. In

[0032] , it is recommended to aim for the largest possible surface area of the particles in order to promote a stronger resin embedding. The recycle mixture is to be preformed in a pre-forming step in a mold into a first layer of varying thickness having a non-uniform top surface. On this first layer, a second layer is preformed of friction lining material from virgin raw materials, the second layer assuming a non-uniform underside which is complementary to and engages the top of the first layer. The friction lining preformed in this way is already curved and adapted to the shape of the brake shoe as a brake lining carrier. The preformed friction lining is hot pressed and cures according to the non-uniform layer thicknesses, so that regions of different density form in the friction lining.It should be essential that the individual layers of the drum brake lining material should be interlocked with one another by uneven surfaces during the pressing process, and that the moisture content of the recycled fraction of used material is not more than 10% by weight.A method for recycling grinding dust from friction lining material is also known from CN 102321260 A. In the method described, the grit is mixed with phenolic resin for granulation and reuse. For this purpose, a method is proposed in which, in a first step, the moisture content of the friction lining grinding dust is determined. If the moisture content is above 3%, the grinding dust is first dried to a moisture content of below 3%. In a second step, the grinding powder and phenol resin in powder form are to be mixed in a mixing chamber of a granulator, with injection of industrial alcohol or ethyl acetate into the mixing chamber. The proportion of the phenolic resin should be 5 to 7% of the grinding dust and that of the injected industrial alcohol or ethyl acetate 3 to 4% of that of the total mass of grinding dust and phenolic resin. In a third step, the powder obtained is to be dried at about 80°C - 100°C and then usable for use in the production of friction material.Powder produced and cured from this by hot compression molding should have a stable coefficient of friction and low wear. Less different components are required than conventional material and after repolymerization with resin the friction performance is better than with conventional material.CN 113201309 A discloses a method in which grinding dust, phenolic resin and glass fibers are mixed to produce a friction material. The rotational viscosity of the phenolic resin should be between 16800 and 17200 mPa·s at 25° C., the solids content 75-85% by weight and the free phenol content 5-10% by weight.CN 105546001 A discloses a composite friction material which is to consist of pyrolized brake pads, recycled friction material, a matrix binder, reinforcing fibers and fillers, the fillers being iron powder, graphite and barium sulfate. For this purpose, it is proposed to pyrolyze a brake pad, then to break down the steel lining carrier, to break up the friction material and to sieve it for later use, to mix the raw materials in an optimized ratio, to add the mixture into a mold, to hot-press and to mold and finally to cool and form the mixture. The proposed method is intended to provide a composite friction material having low thermal precipitations, good thermal regeneration properties and high flexural strength.From the multiplicity of documents of the prior art it is apparent that intensive efforts have been made for decades to reuse production residues in particular in the production of friction linings.The object of the invention is therefore to provide an improved recyclate for the production of friction linings.This object is achieved by a recyclate of friction lining material comprising production residues and / or used lining material, characterized in that the recyclate is present in granulated form in the form of granules, and wherein the recyclate has a particle size distribution such that at least 40% to 85% of the granules have a diameter of 0.50 mm to 1.00 mm.Preferably, no more than 23% of the grains have a diameter of 2.00 mm. In order to prevent the grains from becoming too soft and from disintegrating during handling, it is expedient if grains having a diameter of 0.25 mm and less make up not more than 50%, preferably not more than 15%.The object is furthermore achieved by a recyclate having a content of uncured organic constituents of less than 0.6% by weight, preferably if the recyclate is substantially free of such constituents. As a result, outgassing of organic constituents is reduced and thus the tendency of a friction lining produced therefrom to fade.In order to improve the homogeneity of a friction lining produced from a recyclate according to the invention, it is expedient for the grains to be surface-modified in order to reduce the porosity. As a result, outgassing during the pressing process during the production of the friction lining is reduced and the breaking strength of the friction lining is improved.Production residues preferably contain one or more components selected from grinding dusts, drill cuttings, friction lining breakage, production waste, misproduction of friction linings, unused inventory or overproduction of friction linings.It is particularly advantageous from an economic and ecological point of view if, in the case of a starting material for the production of friction linings, in particular disc brake linings, without taking into account added binder, the recycle fraction is at least 95% by weight, preferably 100% by weight, and in the case of a friction lining, in particular disc brake lining, comprising such a starting material. The practically exclusive use of recyclate not only makes more than half the energy consumption during the production of a friction lining, but also reduces the environmental burden of disposing of the used lining material and of the production residues. In addition, there is a considerable cost saving, since the handling of untreated grinding dusts is extremely difficult. Owing to the extremely fine particles, untreated abrasive dusts dust massively and have a high flow velocity-they flow like water and are therefore considered a problem substance.The object is furthermore achieved by a method for producing a starting material for producing friction linings, comprising the mixture of production residues and / or used lining material, wherein the production residues contain one or more constituents selected from: grinding dust, drill cuttings, friction lining breakage, production waste, misproduction of friction linings, unused supernatants or overproduction of friction linings, and wherein used lining material comprises friction lining material of already used and worn friction linings which have been freed from foreign substances, such as lining carrier plates, rivets, spring clamps or the like, if required crushing and grinding the production residues and the used lining material, granulating the recyclate to a grain size distribution in such a way, at least 40% to 85% of the grains have a diameter of 0.50 mm to 1.00 mm, and modify the surface of the grains to reduce the porosity. The process according to the invention substantially improves the handling of production residues, in particular grinding dusts. The material no longer generates dust clouds, which can also be harmful to health in addition to dirt and problems in meterability. Thus, the process greatly facilitates production with such materials.The invention will be explained in more detail below with reference to the figures. The following are shown: FIG. 1 is a scanning electron micrograph of an abrasive powder granulate, and FIG. 2 shows a scanning electron micrograph of an abrasive dust granulate after surface modification according to the invention.According to the invention, a recycle of friction lining material is provided, comprising production residues and / or used lining material. The handling and environmentally appropriate disposal of production residues, such as grinding dusts, cuttings, friction lining breakage, production waste, misproduction of friction linings, unused inventory or overproduction of friction linings, requires considerable outlay and costs. Processing to give recyclate as starting material for the production of friction linings not only minimizes this outlay and the costs, but also saves the costs for obtaining new starting material in a corresponding amount. The lower consumption of resources also results in less environmental pollution, especially since many of the raw materials are obtained in a very environmentally friendly manner and, in addition, long transport paths have to be overcome.This is achieved, for example, by the method according to the invention for producing a starting material for the production of friction linings, comprising the mixture of production residues and / or used lining material. When replacing brake linings, approximately one third of the lining mass is still present when the wear limit is reached. This residual coating must be separated from the coating carrier during disposal in order to be able to be treated as prescribed. According to the invention, such used lining material, i.e. friction lining material of already used and worn friction linings which have been freed from foreign substances, such as lining carrier plates, rivets, spring clamps or the like, can be returned to the production process for new brake linings instead of complicated and expensive disposal.For this purpose, depending on the size of the starting material, grinding and grinding of the production residues and of the used coating material are carried out as required, granulating the recycle to a particle size distribution in such a way that at least 40% to 85% of the particles have a diameter of 0.50 mm to 1.00 mm, and modifying the surface of the particles in order to reduce the porosity. Preferably, no more than 23% of the grains have a diameter of 2.00 mm. In order to prevent the grains from becoming too soft and from disintegrating during handling, it is expedient if grains having a diameter of 0.25 mm and less make up not more than 50%, preferably not more than 15%.The recycled product in granulated form in the form of granules is not in a geometrically exact spherical form, but is irregularly shaped. The diameter data are therefore to be regarded as approximate and refer in doubt to the geometric average value of the spatial contour enveloping a grain.The method according to the invention and the recycle reduce the porosity of the grains, thereby reducing outgassing during the pressing process during production and thus improving the breaking strength of the friction lining. Due to the lower surface area of the grains compared to many primary materials, less resin is required for the production of a brake lining. The reduced use of this organic binder also reduces the tendency to degassed.By using cured production residues and / or used coating material, a recyclate having a content of uncured organic constituents of less than 0.6 wt %, preferably substantially free of such constituents, can be provided.Surprisingly, it has been found that brake pads produced with recyclate of this type, in particular if, in the case of a starting material for the production of friction pads, in particular disc brake pads, without taking into account added binder, the proportion of recyclate according to the invention is at least 95% by weight, preferably 100% by weight, the tendency of the brake pad to fade is reduced compared to conventionally produced ones. Particularly the feared high-temperature fading can be significantly reduced, since such a friction lining already contains fewer outgassing constituents than a conventionally produced friction lining.Fading or brake shrinkage refers to an undesired lowering of the braking effect during operation of a mechanical brake system by heating the brake. The coefficient of friction at the brake between brake pad and, for example, a brake disk decreases with increasing temperature because of the material properties of brake pad and brake disk. In vehicles, the braking path can be extended sensitively after repeated or longer braking and can lead to a risk to persons in and outside a vehicle. The same applies, for example, also to an aircraft after landing. It occurs in practice especially in the case of long and steep downhill ramps. A reduced coefficient of friction due to temperature can be compensated by increased actuating forces which in turn contribute to a further temperature increase.Conventional gray cast brake disks are designed for surface temperatures up to 600° C. From around 700° C., the wafers begin to anneal. In addition, the material structure of a friction lining is subjected to such high stress at very high temperatures that outgassing of binders can occur. As a result, a hot gas cushion is formed between the friction lining and, for example, the brake disc, so that the braking action suddenly decreases. If this high-temperature fading occurs, it is only possible to try to penetrate the hot gas cushion by applying very high braking forces. If the brake cannot then be thermally released for a short time, the braking action falls dangerously.Fading also occurs after the mounting of new brake pads. Since these have not yet been adapted to the grooves of the brake drum or of the brake disk and, as a result, the brake lining does not bear over its entire surface, local overheating at the points of contact can occur during full braking. Fading occurs at these sites. In this case, temperatures which are so high can arise at these points that the coating material is exposed there to a structure transformation which leads to a hard vitreous surface. At these points, the coefficient of friction is substantially reduced permanently. The formation of grooves, lining chatter and vibration loading will result in premature wear of the brake system. In order to counteract this, some manufacturers attempt to shorten the required braking phase by applying special run-in layersOverall, drum brakes are more sensitive to fading, since in the case of these brakes, due to their design, the heat is dissipated less than in the case of disc brakes.The decrease or loss of the braking power due to the formation of vapor bubbles in the brake fluid as a result of the temperature rise in a brake system under continuous load is not a fading of the brake system in the actual sense. This is because this effect occurs independently of the design of the friction partners and is also not a consequence, for example, of the friction lining composition. In this case, the braking action does not gradually decrease, but the pedal travel suddenly becomes longer when the brake is actuated again until the brake system fails completely. This problem only occurs due to the system in brake systems in which the force transmission is effected by brake fluid, i.e. hydraulically. The cause here is typically poor maintenance in connection with user errors. Typical brake fluids are hygroscopic, that is to say they absorb water from the environment over time. If the water content now reaches the vicinity of the brake components, the water in the brake fluid can evaporate as a result of the high temperatures and form a compressible vapor bubble. However, this physical effect typically only occurs when the braking is interrupted, because only then can the water in the brake fluid evaporate due to the pressure relief and, due to the volume increase occurring in this case, push a part of the brake fluid back into the brake fluid container. Upon renewed braking, the displaced brake fluid volume is then missing in the system; upon actuation of the brake pedal, only vapor bubbles still present are compressed and no appreciable actuating force is transmitted to the brake pads. The brake pedal travel becomes longer and finally the brake completely fails. This can be counteracted at least partially by a hearted user only by rapidly delivering brake fluid by "pumping". This can be prevented preventively by periodic exchange of the brake fluid and by avoiding sustained braking, for example during downhill travel, and by timely reducing the speed, because the kinetic energy of the vehicle to be converted into heat by the brake during braking increases quadratically with the speed.The practically exclusive use of recyclate according to the invention not only makes more than half the energy consumption during the production of a friction lining, but also reduces the environmental burden of disposing of the used lining material and of the production residues. In addition, there is a considerable cost saving, since the handling of untreated grinding dusts is extremely difficult. Due to the extremely fine particles, the material dustes massive and has a high flow velocity-it flows like water and is therefore considered a problem substance.It has already been proposed in the prior art to allow grinding dust to flow back into the production process directly at the friction material manufacturer without any treatment. However, the grinding dust is often too fine and is partially removed from the mixture again by the necessary suction, whereby no controlled initial weighing into the press nest is ensured. Too fine constituents likewise lead to the coating being less able to degas effectively, which in turn may lead to fading and wear problems. Therefore, a recyclate according to the invention, a starting material produced therefrom for the production of friction linings and a friction lining produced therewith have the advantages described above compared with the proposals known from the prior art.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 197 27 920 A1 [0002, 0005]EP 0 889 081 A1

[0002] EP 0 826 896 A1

[0004] EP 0 553 404 A1

[0005] DE 42 01 892 A1

[0005] DE 42 04 776 A1

[0009] EP 0 518 004 A2

[0009] US 2014 / 190777 A1

[0010] CN 102321260 A

[0013] CN 113201309 A

[0015] CN 105546001 A

[0016]

Claims

Recyclate of friction lining material comprising production residues and / or used lining material, characterized in that the recyclate is present in granulated form in the form of granules, and wherein the recyclate has a particle size distribution such that at least 40% to 85% of the granules have a diameter of 0.50 mm to 1.00 mm.Recyclate according to claim 1, characterized in that not more than 23% have a diameter of 2.00 mm.Recyclate according to any one of the preceding claims, characterized in that grains with a diameter of 0.25 mm and less make up not more than 50%, preferably not more than 15%.Recyclate according to the preamble of claim 1 or any of the preceding claims, wherein the recyclate has a content of uncured organic components of less than 0.6 wt.%, preferably substantially free of such components.Recyclate according to the preamble of claim 1 or one of the preceding claims, characterized in that the grains are surface modified to reduce the porosity.Recyclate according to one of the preceding claims, wherein the production residues contain one or more components selected from: grinding dusts, drill cuttings, friction lining breakage, production waste, misproduction of friction linings, unused inventory or overproduction of friction linings.Starting material for the production of friction linings, in particular disc brake linings, wherein without taking into account added binder the proportion of recyclate according to one of the preceding claims is at least 95% by weight, preferably 100% by weight.Friction lining, in particular disc brake lining, containing a starting material according to Claim 7.Recyclate of friction lining material obtainable by a method comprising the mixing of production residues and / or used lining material, wherein the production residues contain one or more constituents selected from: grinding dusts, drill cuttings, friction lining breakage, production waste, misproduction of friction linings, unused supernatants or overproduction of friction linings, and wherein used lining material comprises friction lining material of already used and worn friction linings which have been freed from foreign substances, such as lining carrier plates, rivets, spring clamps or the like, optionally crushing and grinding the production residues and the used lining material, granulating the recyclate to a grain size distribution such that at least 40% to 85% of the grains have a diameter of 0.50 mm to 1.00 mm, modifying the surface of the grains to reduce the porosity.

Images