EP3034666A1 - Insulating and filter material and its use as inert sound-absorbing material - Google Patents

Abstract

The invention relates to a fluid-permeable insulating and filtering fabric in the form of a consolidated nonwoven fabric, in which the fibers of the nonwoven fabric are formed at least predominantly of carbon fibers which consist entirely of carbon or at least in the region of its fiber surface, and in that the fibers at least a part of their contact points by binder droplets or solidified binder fibers, and its use as a sound absorbing material for mufflers.

Description

The invention relates to a fluid-permeable insulation and filter material in the form of a consolidated non-woven fabric, which is intended in particular for use as an inert sound-absorbing material that can come into contact with corrosive and aggressive fluids even at elevated temperatures.

In various fields of domestic engineering and in industry, for example in power engineering, automotive engineering and in numerous industrial processes, e.g. In the chemical and material processing industries, high-energy fluids are required which require treatment to extract at least some of their energy before they can be discharged, e.g. to the environment or the ambient air.

In the context of the present application, the term "fluids" refers to free-flowing gaseous, vaporous or liquid substances and substance mixtures to which liquid or solid particulate constituents which can have a corrosive and aggressive action, especially at high temperatures, can also be added as separate phases , High-energy fluids of the type mentioned may contain some of their energy in the form of sound energy or pressure waves or pressure. Since sound, which is perceived by the environment as noise or noise nuisance, in everyday life or at work is perceived as disturbing and proven to be harmful to health, have long been made considerable efforts to suppress sound emissions as far as possible by absorbing the sound energy.

Sound energy is removed from currently flowing fluids by various methods, which are often used in combination, and the devices used for this purpose are referred to as silencers. In addition to methods of active noise reduction with counter-noise, which leads to a sound suppression, come in many sound attenuation methods insulation materials used, in which the high-energy fluid can penetrate and in which it loses as much of the sound energy contained in it by interaction with the insulating material , typically in that the sound energy in the insulating material is converted into heat or that fine structures such as fine fibers and membranes of the insulating material are destroyed by the sound, wherein the fluid is deprived of the energy contained in it as sound or pressure waves.

In numerous mufflers, resonance phenomena are also used for sound cancellation, whereby the principle of the "Helmholtz resonator" is frequently used. In this case, openings of suitable sizes are used, which are arranged in the walls of the fluid lines through which the sound absorption occurs by excitation of natural frequencies in the opening cross-section and their deletion in an adjacent sound-absorbing material.

According to the present invention, a new fluid-permeable insulating material is to be provided which can in principle be used in a multiplicity of different silencer devices, in particular in those in which porous materials, such as rockwool, glass wool or glass fibers, which are currently used for sound absorption, are used At least partially convert sound energy into heat. An insulating material according to the invention should be able to replace the usual porous materials in mufflers of various constructions, but should in particular offer advantages over the currently used materials if the fluid to be extracted from the sound energy, as such or due to the gases contained or entrained liquid or Solid particles are also highly corrosive, especially at higher temperatures.

For the explanation of basic types of silencers in which an inventive insulating material can be used, reference is made only by way of example to the prior art according to FIG DE 10 2004 046 553 A1 , where a muffler is disclosed as an insert for a chimney, which has the form of a double-walled tube in which a sound-absorbing and heat-resistant absorber material, in particular rock wool, is arranged between a cylindrical outer tube and a perforated cylindrical inner jacket. In the related ones U.S. Patents 5,926,954 and 6,148,955 are described insofar similar muffler, as well as there a fluid is passed through a perforated inner tube that is surrounded by a sound-absorbing material. This is either a fiberglass material or a mineral wool. In mufflers of the type described so far, the sound-absorbing material is not arranged in the flow path of the fluid to which the sound energy is to be removed, but surrounds its flow path.

For related mufflers, eg according to DE 29 04 529 A , are used similar to the previously described mufflers perforated pipes, which are surrounded by noise-damping fillers, being proposed as fillers plastic foams, mineral fibers, felt, steel wool or a bed of plastic granules.

A muffler of a different kind and for a slightly different use is described in the European patent EP 2 152 556 B1 or the corresponding published US patent application US 2010/0140015 A1 in which a cup-shaped silencer filled with a sound-absorbing material in the form of a cartridge of a knitted fiber material surrounded by a felt layer is used to dampen the exit sound of compressed air from a compressed air system. In this case, flows through the fluid to be extracted from the sound energy, the sound-absorbing material. As the material polyamide fibers are provided in particular.

Also in the U.S. Patent 5,036,585 described exhaust silencer is proposed as a material for a sound-absorbing clad mineral wool.

For the sake of completeness, it is also intended to mention mufflers, in particular for low frequencies, in which no porous insulating materials are used in the usual sense, but in which one achieves a sound attenuation for low frequencies by exploiting resonance phenomena. As examples of this prior art may be mentioned the European patent EP 0 316 640 B1 or the silencer according to the European patent EP 1 382 031 B1 in which soundproofed pipes are used, possibly in conjunction with perforated foils. Although such silencers can do without porous sound-absorbing materials, they can be combined with insulating materials according to the present invention for additional sound attenuation, especially with regard to higher frequencies.

Insofar as sound-absorbing inorganic materials such as glass wool or mineral wool are currently used for soundproofing, it has been found that these are also hot and corrosive for certain periods of time Fluids such as combustion exhaust gases can withstand, however, it has been observed that such materials rotting over time. In particular, it has been observed that this rotting has to do with the fact that during the startup of a plant often comes to the condensation of chemically aggressive exhaust components in the sound absorber material, which attacks the entire muffler construction and makes monitoring and replacement of sound-absorbing insulation material necessary.

It is an object of the present invention to improve the treatment of high-energy fluids by providing a novel chemical and heat-resistant insulating material, wherein the new insulating material is particularly advantageous when it is used for soundproofing corrosive and aggressive fluids, e.g. of hot exhaust gases from power plants, serves.

Further objects emerge from the advantages mentioned in the following description of an insulating material according to the invention.

The above objects are achieved in the broadest sense by a fluid-permeable insulating and filter fabric in the form of a consolidated nonwoven fabric, in which the fibers of the nonwoven fabric are formed at least predominantly of carbon fibers, which consist entirely or at least in the region of their fiber surface made of carbon, and that the fibers are bonded to at least a portion of their contact points by binders, wherein the binders are preferably solidified binder droplets or solidified binder fibers formed from a molten or solvent-containing precursor.

Although various carbon fiber webs (carbon webs) are already known from the prior art. These are However, not for use as a fluid-permeable insulation and filter materials, which are suitable as sound-absorbing material in silencers, designed and therefore not suitable for such use.

Carbon fiber nonwovens have hitherto been mainly produced and used for uses in which the electrical conductivity properties of the carbon fibers are important or in which the electrical conductivity of the carbon fibers is used, for example their conductivity or their heatability in an electrical heating mat. According to DE 103 53 070 A1 For example, a carbon fiber preform for a carbon fiber reinforced plastic molding with a binder such as a bisphenol A based epoxy resin is solidified by induction induction heating. Unlike a use for sound absorption, in which the insulation material is claimed for very long periods of time and must retain its sound-quenching properties for a long time, preforms for carbon fiber reinforced plastic molded parts are primarily a only temporarily, during a production process required solidification EP 0 864 183 B1 For example, a carbon fiber nonwoven fabric of carbonized fibers is disclosed as a raw material for a gas diffusion electrode.

In a heater according to DE 195 09 153 A1 serves a stiffened with an electrically conductive binder carbon fiber fleece with power connections as a heating mat for a heater, in particular for outside mirrors of motor vehicles. A similar application as a heating element in a plastic composite is described in the WO 2006/131108 A1 ,

In the EP 0 612 221 B1 There is a suggestion to use a carbon fiber non-woven fabric solidified with a carbohydrate-based binder to heat the tobacco flavor component in an electric cigarette. The invention will be explained in more detail with reference to preferred embodiments.

Two figures also serve to illustrate this, which vividly describes the solidification of a carbon fiber fleece with a binder.

• Figur 1 eine Mikrophotographie eines Faser-Kontaktpunkts eines mittels eines organischen Bindemittels verfestigten Kohlenstofffaservlieses; und
• Figur 2 eine Mikrophotographie eines Faser-Kontaktpunkts eines mittels eines anorganischen Bindemittels verfestigten Kohlenstofffaservlieses.

Show it:

• FIG. 1 a photomicrograph of a fiber contact point of an organic binder solidified carbon fiber nonwoven fabric; and
• FIG. 2 a photomicrograph of a fiber contact point of an inorganic binder solidified carbon fiber nonwoven fabric.

The nonwoven fabric forming the body of the insulating and filtering fabric of the present invention is preferably a nonwoven fabric in the form of a tangled fabric of carbon fibers selected from carbon fiber composites (CFRP) of recycled carbon fibers or carbon fibers obtained by at least surface carbonization (pyrolysis) of plastics or carbon fibers Natural fibers, in particular cellulose and lignin fibers were produced.

Carbon fibers of the type mentioned have due to the preceding recycling process or carbonization usually no smooth surfaces, but are rough and / or have superficially protruding fiber fragments, which is advantageous for the absorption of sound energy and sound attenuation.

Preferably, the binder contained in the insulation and filter material according to the invention is a binder which is at elevated temperatures against corrosive and aggressive chemicals that occur in an exhaust gas stream from combustion gases of a heating system or an internal combustion engine or in a process gas stream of an industrial plant has a resistance at least comparable to the durability of the carbon fibers. This contributes to the insulating material retaining its sound-absorbing properties over long periods of use.

Suitable binders can be found, for example, in the classes of epoxy resins, phenolic resins, organosilanes, inorganic silicates, lignin materials and / or lignin sulfonates.

According to a preferred embodiment, in particular for use with corrosive polar fluids, hydrocarbon polymers or perfluorinated or partially fluorinated hydrocarbon polymers are used as binders.

The invention also relates to the use of an insulating and filter material according to the invention as an inert sound-absorbing material for contact with corrosive and aggressive fluids at elevated temperatures, in particular in a muffler for an exhaust gas stream of combustion gases from a heating system or an internal combustion engine, for a compressed gas stream or for a Process gas flow of an industrial plant, eg in containers, pipelines and process plants.

In such use, the sound attenuating means may be a muffler formed by an inner tube sheathed with sound absorbing apertures and enclosed by a sound insulating fluid permeable material disposed in a closed outer tube for an exhaust gas flow or in a gas flow a fluid flowed insulation filled, eg cup-shaped, muffler or a muffler of another type known per se for fluids in the form of gases or vapors, in which porous sound-absorbing materials are used.

The carbon fiber fleece, which forms the body of the insulating and filter cloth, is made of carbon fibers (Carbon fibers), which are characterized by a high resistance to corrosive and aggressive hot fluids. In addition, carbon fibers show only a very low thermal expansion, so that in their use, the thermal stresses remain low due to strong temperature differences in the muffler.

For economic reasons, and because the mechanical characteristics of the carbon fibers are of minor importance when used in mufflers, recycled carbon fibers (carbon fibers) are primarily used, which can be recovered from carbon fiber composites (CFRP), or carbon fibers obtained by at least superficial carbonation of natural renewable raw materials, in particular lignin fibers, can be obtained. For an insulation and filter material according to the invention, it is not necessary for the carbon fibers to have a uniform, narrowly defined fiber length.

Carbon fiber waste in long fiber form has already been proposed as a material for certain nonwovens. However, these are, above all, fleece stitchbonded fabrics which are not intended and suitable for soundproofing purposes.

However, it is also within the scope of the present invention to use high quality "fresh" carbon fibers, which could be of particular interest if it turns out that such carbon fibers show a resonance behavior in the sound attenuation due to their elastic properties, which has a sound attenuation in the range of special and particularly problematic sound frequencies possible.

On the other hand, softer, more flexible fiber systems can be obtained from only externally or superficially pyrolyzed (carbonized) lignin fibers, which can have particular advantages for certain other applications.

The performance characteristics of an insulating and filter material according to the invention for sound insulation are also influenced by the binder used, its amount and the manner in which it is used to solidify the nonwoven fabric.

Basically, the binder is one for the intended use, i. on contact with the respective fluid at its typical temperatures, sufficient resistance, so that the solidification points do not become weak points for the resistance and strength of the entire insulation and filter material according to the invention.

For many uses there are suitable binders in the classes of epoxy resins, phenolic resins, organosilanes, inorganic silicates, lignin materials and / or lignosulfonates. The binders can be used to solidify the carbon fiber fabric in a manner known per se as binder solutions to be sprayed on (for example epoxy resins in a solvent such as butyl acetate, phenolic resins in aqueous carriers, organosilanes in an alcohol, lignin or lignin sulfonates in water or water / alcohol mixtures) , With a suitable wetting behavior they migrate along the fiber surfaces and accumulate at the crossing points of the carbon fibers, where they dry or solidify to solid droplets.

If special demands are placed on the corrosion resistance in view of the special soundproofing, and / or a hydrophobic character of the insulating material is desired, can be used as binders hydrophobic binders based on hydrocarbon polymers, in particular temperature-resistant perfluorinated or partially fluorinated plastics. These are advantageously scattered in the production of the nonwoven fabric as fine granules between the carbon fibers. The Granules can be obtained inexpensively using fluoropolymer waste.

If the temperature load to be expected is not too high, the binders which can be used are also meltable thermoplastics, in particular in the form of solid hydrocarbon polymers without hydrolyzable or hydrophilic groups, e.g. made of polyethylene or polypropylene.

In addition to use as a binder granules most binders can also be used as fibers, which are mixed in the production with the carbon fibers of the nonwoven fabric and melt or soften when heated and connect the carbon fibers together.

It is also within the scope of the invention to chemically modify the carbon fibers, e.g. by doping with metals, by superficial oxidation, by etching or by treatment with a plasma, e.g. an atmospheric or low pressure plasma to cause the carbon fibers to be better absorbed by the binders used, e.g. strongly hydrophobic binders such as fluoropolymer binder are wetted and a favorable ratio of fiber wetting and surface tension of the liquid or molten binder is obtained.

A particularly preferred embodiment of an insulating and filter fabric according to the invention is obtained by solidifying a carbon fiber random mat with a fluoropolymer binder introduced as granules or in fiber form, in particular in quantities between 1 and 20% by weight of the finished consolidated nonwoven can be. For this purpose, carbon fibers and binder can be scattered substantially together on a conveyor belt, compacted by pressing and / or subsequently thermally treated, for example with IR lamps, by induction heating or in a microwave tunnel. The fluoropolymer bonds the fibers their points of contact and thus ensures when cooling for a stabilization of the structure of the fiber mat or the press cake. At higher binder to carbon fiber ratios, direct sintering of individual binder particles may also occur, and the carbon fibers then act to stabilize the binder presscake (fluoropolymer granules presscake), for example, during bending or tensile loading.

The insulating and filtering materials according to the invention can be produced as fiber mats or press cakes of various design and shape (thickness, density, running area) and subsequently for the intended use, e.g. in a form suitable for the particular type of silencer in which they are to be used.

Claims (9)

Silencer for an exhaust gas stream with a fluid-permeable insulation and filter material in the form of a consolidated nonwoven fabric, characterized in that the fibers of the nonwoven fabric are formed at least predominantly of carbon fibers which consist entirely of carbon or at least in the region of its fiber surface, and in that the fibers a portion of their contact points are formed by solidified binder droplets formed from a molten or solvent-containing precursor or by solidified binder fibers. Silencer according to claim 1, characterized in that in the insulating and filter material, a binder is contained, which against corrosive and aggressive chemicals that occur in an exhaust gas stream from combustion gases of a heating system or an internal combustion engine or in a Prozesgasstrom an industrial plant, at elevated temperatures, a resistance which is at least comparable to the durability of the carbon fibers. Silencer according to claim 1 or 2, characterized in that as binders epoxy resins, phenolic resins, organosilanes, inorganic silicates, lignin and / or lignin sulfonates are present. Silencer according to claim 1 or 2, characterized in that hydrocarbon polymers or perfluorinated or partially fluorinated hydrocarbon polymers are present as binders. Silencer according to one of claims 1 to 4, characterized in that the nonwoven fabric is a tangled scrim of carbon fibers, which are selected from Carbon fiber composites (CFRP) of recycled carbon fibers or carbon fibers made by least superficial carbonization of plastic and / or natural fibers, in particular cellulose and lignin fibers. A method of sound insulation in which a gas stream is passed through an insulating and filtering material made of inert sound-absorbing material,
characterized in that
the insulating and filtering material is in the form of a consolidated nonwoven fabric, wherein the fibers of the nonwoven fabric are formed at least predominantly of carbon fibers which consist entirely or at least in the region of their fiber surface made of carbon, and in that the fibers at least a part of their contact points by from a molten or solvent-containing precursor formed solidified binder droplets or bonded together by solidified binder fibers. The method of claim 6 wherein the gas stream contains or consists of combustion gases from a heating system or an internal combustion engine or the gas stream contains or consists of a compressed gas stream or a process gas stream of an industrial plant. The method of claim 6 or 7, wherein the insulating and filter material is introduced into a muffler which is constructed in the form of a sound absorbing openings provided with an open, enclosed by a sound-absorbing fluid-permeable material inner tube, which is arranged in a closed outer tube for an exhaust gas flow , or is a cup-shaped silencer arranged in a gas flow, filled with a fluid flowing through insulation material. Method according to one of claims 6 to 8, characterized in that the insulating and filter material is in contact with a corrosive and / or aggressive fluid.

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