Patent Publication Number: US-2012034417-A1

Title: Fiber product, molded fiber part and method for producing the same

Description:
The invention relates to a fiber product and a molded fiber part as well as a method for producing the same. In particular, such a part can be used as a molded part for thermal and/or acoustic decoupling and/or fixation between components, and in particular as a thermally insulating wall duct, preferably in fluid-conducting systems such as, for example, components of exhaust units such as e.g. catalysts and mufflers with plastic external housings. 
     Novel mufflers for internal combustion engines are known from the prior art, in which the external housing consists of plastic. The muffler can thus be designed smaller and in any form for space-saving installation. What is critical in this case is the necessary thermal insulation of the wall duct in the plastic external housing through which the hot metal pipe conducting the exhaust gas is led. Because of the known properties, glass-fiber products are in this case also used as insulators. During insertion, they are frequently brought into shape by hand, optionally using several glass-fiber products. In order to facilitate assembly, these glass-fiber products can, for example, roughly kept in shape by sewing or similar aids beforehand. In another process step, sealing means are to be introduced into the area of transition between the hot metal pipe and the external housing, which ensure that the exhaust gases cannot escape between the external housing and the inner pipe. 
     It is therefore the object of the present invention to provide an improved fiber product and molded fiber part as well as a method for producing the same. 
     This object is accomplished with a fiber product, a molded fiber part as well as a method for producing the same having the features of the independent claims, as well as the wall duct or the muffler, respectively, having the features of claims  18  or  19 , respectively. 
     For better comprehensibility, the invention is explained below with reference to “glass fibers” as an example for the fibers used. The term glass fiber is not supposed to limit the invention to products containing the material glass. Rather, the invention relates to all fibers suitable for the respective purpose of use, in particular: all organic Fibers, preferably high-temperature resistant over 100° C., preferably 120° C., particularly preferably 220°, or non-organic fibers, preferably high-temperature resistant over 300° C., preferably 350° C., e.g. mineral fibers, man-made mineral fibers, thermoplastic fibers, glass fibers, PEEK. Furthermore, it is immaterial for the invention whether the threads consist of endless filaments or short fibers. Fibers of limited length are staple fibers; fibers with basically unlimited length are filaments or endless fibers. According to the invention, a fiber product or molded part can be formed from short fibers or long filaments. Textile fabrics within the meaning of the invention also include non-woven fabrics, such as for example a needle-punched non-woven or wadding. A wadding is basically a loose structure of fibers or threads which add up to a fabric or flat structure only due to the adhesion amongst one another. 
     According to the invention, it was first recognized that the fiber products suitable for thermal insulation—hereinafter referred to as glass-fiber products by way of example—can temporarily obtain an inherently stable shape due to activatable fixing agents. This enables an easier or fully automatic insertion of the molded fiber parts produced from the glass-fiber products according to the invention—hereinafter referred to as molded glass-fiber parts by way of example. 
     Processing the glass-fiber products into a molded part becomes particularly simple if these products themselves carry the fixing agents. Therefore, a fixing agent does not have to be added in a separate production step during the bringing-into-shape process. The glass-fiber products, i.e. the substantially flexible textile fabrics, are therefore themselves carriers of the fixing agent. They may be adhesives, e.g. reactive adhesives, hot-melt adhesives, inorganic adhesives, water glass or suitable substances that were applied by spraying or immersion. What is crucial is that the fixing agent can be activated when the glass-fiber products have been brought into the appropriate shape and that, after activation, they harden in such a way that the glass-fiber products can maintain the shape it has been given at least until installation or first use. 
     Thermoplastics, e.g. PE, which can be activated by heat within the meaning of the invention, are another suitable fixing agent. Once the temperature has dropped below the melting temperature, the thermoplastic solidifies. 
     The glass-fiber products can be produced, for example, from glass-fiber threads which themselves carry the above-mentioned fixing agent. This is particularly easily carried out with the machines commonly used in the textile industry, if each glass-fiber thread is assigned one fixing thread, for example by twisting, turning, carrying along, it etc. The fixing thread preferably consists of a thermoplastic. In another embodiment the glass-fiber threads or fixing threads can also comprise a plurality of fibers which are, for example, twisted. A single thread can be composed of numerous glass-fibers and fixing fibers, whereby any mass ratios suitable for the respective purpose of use can be produced. 
     Woven fabrics, knits, circular-knits, knitted fabrics, scrims or braided fabrics from glass fibers are particularly suitable for producing the molded glass-fiber parts according to the invention. They are easy to handle and to bring into shape. 
     In experiments, the proportions of fixing agent in the glass-fiber product specified in the claims proved to be optimal with regard to handling, strength and costs. 
     The molded glass-fiber part according to the invention is characterized by being temporarily held in shape by the activated fixing agents. This enables a simple or fully automatic provision, handling and insertion of the corresponding molded part into other products. In particular, passing other components through the opening in the molded glass-fiber part is facilitated because jamming or the pulling-out of threads is avoided due to the smoother inner wall. According to the invention it is only important that the molded glass-fiber part is sufficiently solid during assembly. In the installed state, the molded glass-fiber part is kept in shape by the surroundings, so that the fixing agents are allowed to lose their function, e.g. by thermal decomposition of the same, without the component&#39;s thermal insulation function being impaired. Therefore, the molded glass-fiber part is to be designed in such a way that, by the activated fixing agents, it is kept in a shape that is smaller than the shape that the molded glass-fiber part would assume in the absence of the fixing agents, prior to their activation and subsequent to their thermal decomposition. Therefore, the molded glass-fiber paths is to be designed and the materials are to be selected in such a way that it would be resilient without the fixing agents, and would assume a larger shape than the desired shape of the molded glass-fiber part with activated fixing agents. Even after the thermal composition of the fixing agent, the molded part, which may basically also consist of non-glass-fibers, remains so large that it can substantially maintain its position and shape in the installed state. In that case, the molded part most frequently still has the residual resilience which, however, is substantially smaller in practice than the original resilience of the molded part prior to activation. Fiber structures which are formed as knit, knitted fabric or the like have this resilience and can be correspondingly compressed for activating the fixing agents, so that they can be brought into shape. Therefore, when producing the molded part, it must be resiliently compressible so that it can be inserted into the mold prior to the activation of the fixing agents. 
     Thus, the molded part is suitable for insertion as a molded part for thermal and/or acoustic decoupling and/or fixation between components. It serves as a thermally insulating insulator, in particular in the form of a wall duct, and preferably in fluid-conducting systems such as, for example, components of exhaust units such as e.g. catalysts and mufflers with plastic external housings. The damaging influences, such as e.g. temperature and vibrations, are kept away from the plastic. The molded part is particularly suitable for components of the exhaust unit of internal combustion engines, but also in the field of industry, e.g. in power stations. 
     Preferably, the molded glass-fiber part is configured as a so-called wall duct. It serves for insulating and optionally holding a hot component through an opening in a component to be protected from heat. Expediently, such a component comprises an inner opening for passing through the hot component, as well as an outer contour that rests on the opening in the second component to be protected. In this case, the glass-fiber component may also have a supporting function, but this is not obligatory. 
     According to the invention, it was found that a—most frequently rotationally symmetric—wall duct is particularly easy to produce if a circular-knit or a tube is used. For example, the latter that can be rolled inwards from both sides so that, with regard to the shape, the approximate result is a “double sealing ring”. If, in the process, more turns are made on one side, the result is already a flange-like appearance, i.e. a substantially rotationally symmetric component with a duct, a thinner flange end and a thickened flange shoulder/flange base. The external diameter of the flange shoulder can be further enlarged if the molded glass-fiber part is composed of several glass-fiber products, namely the above described circular-knits rolled up inwards or outwards, as well as for example a flat-knit wound around it in a spiral shape. During production, the prepared circular-knit can for this purpose be inserted into a corresponding flange-like negative mold, for example, and inside the mold, the part of the flange shoulder that is not filled by the circular-knit is then filled with the flat-knit. The result after the activation of the fixing agent is a flange with a broader flange shoulder. 
     Preferably, at least a part of the flange shoulder is provided with a pressure-tight material, e.g. an elastomer. This ensures that the inserted molded part can be pressure-tight in the installed state. 
     The method according to the invention - in particular for producing the aforementioned molded parts - in particular makes a cost-effective production possible that is as accurate with regard to shape, as well as, optionally, even the application of the frequently necessary seal in a single method step during the activation. 
     Further advantages become apparent from the following description and the attached drawing. Also, the above-mentioned features, which are explained in detail, can each be used individually or in any combinations according to the invention. The embodiments mentioned shall not be understood to be final and have the character of examples. 
       FIG. 1  shows a molded glass-fiber part  1  produced according to the invention in the installed state in a plastic muffler  2  for internal combustion engines. Of the muffler, only the area of the wall duct  21  is shown in a schematic diagram. The hot inner pipe  3  is guided through the opening  21  of the plastic housing  2  of the muffler, with the glass-fiber component  1  according to the invention being disposed in the opening  21 . It thermally separates the pipe  3  from the housing  2  and at the same time serves as a pressure seal for preventing the escape of gases in the interior  22  of the muffler. 
    
    
     The molded part  1  is composed of two glass-fiber products  11 ,  12 , namely a circular-knit  11  rolled up inwards and a flat-knit  12  laid around it in a spiral shape. The circular-knit  11  comprises an upper rolled-in portion  111  and a lower rolled-in portion  112 , with the upper rolled-in portion  111  comprising more windings and thus requiring more volume. A flange-like external contour already results during the introduction into a corresponding—in this case flange-like—mold, so that the upper rolled-in portion  111  already forms parts of the flange shoulder. The further windings of the flat-knit  112  serve for enlarging the flange shoulder. 
     This widening of the flange shoulder is necessary for thermal reasons connected with the necessary diameter of the metallic pressure plate  31  which is firmly connected to the inner pipe  3 . This plate  31  is necessary in order to produce the pressure-sealing effect. The larger the plate, the colder the outer end of the plate. This reduces the thermal load on the necessary pressure seal  13  in this area, which is located at the outer part of the flange shoulder  12 . The seal  13  was molded onto the outer flange end by injection of sealing material during production, and has the task of providing a pressure-tight seal between the plate  31  and the inner contour of the opening  21  of the external housing  2 . 
     Two bowl-like half-shells are provided as an external housing  2  for assembling the muffler. The molded glass-fiber parts  1  produced according to the invention are inserted into the opening of the external housing  2 . Then, both half-shells  2  are pulled over the opposing free ends of the inner pipe  3  and connected to each other. The necessary pressure between the plate  31 , the inner opening  21  and the seal  13  of the molded glass-fiber part is produced thereby. 
     A single-part construction with an integrated seal  13  is preferred according to the invention. However, the seal can also be provided separately as a sealing ring. In view of the high demands with regard to the heat-resistance of the sealing material, however, the integral construction according to the invention offers the advantage that only comparatively little sealing material is used since it largely rests against the glass-fiber product all around it. 
     Preferably, the top surface of the sealing material  13  protrudes over the top side of the glass-fiber material so that an optimum and uninterrupted contact of the sealing material with the plate  31  is ensured. During production, this is advantageously accomplished by corresponding recesses for the sealing material in the negative mold. They accommodate the material, provide it with a defined and suitable surface in the hardened state, and ensure that the glass-fiber material is well-hidden in the sealing material.