Thermal insulation.

p0001The invention is a thermal insulation for use in a non-oxidizing atmosphere containing at least one insulating layer formed of carbon fibers and a firmly connected with the insulating layer of graphite foil.

p0002As thermal insulation of furnaces, for insulating pipes, containers and the like., Which are in contact with hot gases or melt, are insulating layers of carbon felt, for example in the form of felts made famous. Carbon felts are obtained for example by carbonizing felting of cellulose, pitch or polyacrylonitrile. Because of the relatively poor oxidation resistance of the carbon felts their use is limited to furnaces and devices which operate in a non-oxidizing atmosphere or under reduced pressure or be operated. At very high temperatures, the thermal resistance of porous felt layers decreases considerably, since the proportion of the transmitted radiation energy grows. It has therefore been proposed, thermal insulation formed from layers of felt with heat or radiation shields to provide graphite foil (German Patent 1,814,052). The flexible sheets are suitably bonded with an adhesive with the insulating layer, which is present as temperature-resistant at the operating temperature coke. Such fiber from a porous layer and a connected to the layer substantially impermeable to gases film existing thermal insulation can be used with advantage at temperatures up to about 3000 ° C. DE-PS 28 53 397 a heat insulating material is finally known, consisting of a layer of carbon felt with a bulk density from 0.13 to 0.20 g / cc and a connected to the felt layer impermeable graphite foil. The graphite sheet has in this thermal insulation task is to protect the felt layer mechanically and sealed, mainly to losses by abrasion and the like., Which also can contaminate the furnace chamber, where appropriate, to avoid.

p0003A disadvantage of the known, an insulating layer of carbon felt and the felt layer protective and at the same time the radiation reflection enhancing graphite sheet containing thermal insulation is the frequent loosening the connection between the graphite foil and felt layer, starting to go from local bubble-like swellings of the film leading to its replacement. Cause of this effect is substantially the liberation of gaseous compounds from the foil. Graphite foils to manufactures of expanded graphite which is obtained by thermal decomposition of graphite intercalation compounds, for example graphite hydrogen sulfate. In graphite remaining remnants of the intercalation compounds are emitted at higher temperatures and affect even in small quantities, the strength of the joint insulation layer / film. A smaller portion also contribute gaseous pyrolysis products, which form in the adhesive layer between the film and felt at high temperatures, the detachment of the film from the felt layer or sheet. In principle, one can avoid the harmful gas evolution by prolonged heating of the various components of the thermal insulation to elevated temperatures. The components are glued to each other after the heat treatment, and completely removed by prolonged heating, the volatile pyrolysis products of the adhesive. Despite the high cost but you can not prevent the separation of the film with certainty, since the adhesion of the film to the felt layer is not very large, especially because of their poor wettability and even small gas radicals and induced by temperature changes shear stresses often lead to the detachment of the graphite foil ,

p0004The invention is therefore based on the object to provide a made of carbon felt and graphite foil thermal insulation whose components form a solid compound, which do not dissolve under thermal stress of isolation from each other.

p0005The object is achieved with a thermal insulation of the aforementioned type whose graphite foil is provided with perforations.

p0006The invention is based on the finding that the released during operation of the thermal insulation in the film and the adhesive layer harmful to the liability component gases are discharged through the openings, so that no more, a detachment of the film causing Direction gas pressure can build up. The comparatively rough edges of the perforations are also a good adhesive base for the adhesive, and mainly cause an increase in the shear strength of the connection. Shape and size of the perforations are of less importance than their number, so that you used to make the perforations suitably simple stamping tools, such as needles with a circular cross section. The number of openings should increase with the stress of the bonding surfaces, that is, with the amount of released gases on heating and the size of the mechanical stresses. Particularly advantageous are 5 to 70 hole-shaped perforations per square centimeter with a hole diameter of 0.05 to 0.5 mm. Openings with a smaller diameter, particularly below about 0.03 mm often become clogged by the coke formed during pyrolysis of the adhesive and thus do not contribute to degradation of the gas at excess pressure. Larger perforations weaken the film mechanically, complicate their use and facilitate the penetration of the furnace atmosphere in the Kohlenstoffilzschicht of thermal insulation. Damage to the carbon felt and jeopardizing their life in connection with the gas-permeable film through the furnace atmosphere, molten splashes and the like. Have not been observed.

p0007For the production of heat insulation commercial about 0.2 to 1.0 mm thick graphite foils or formed of a plurality of mutually bonded films laminates with a density of about 0.8 to 1.5 g / cc are for example perforated by means of needle rollers. The film tears to the break-in points and it will be more or less lobed, formed from the surface of the sheets extending away protuberances an excellent primer for the adhesive layer. Consisting of carbon insulation contains fabric or scrim, of carbon fibers, especially carbon felt. The term carbon and graphite fibers are to be understood and containing graphite fiber structure. The thermal resistance of the fiber layers is adjusted by changing the layer thickness and / or their density the particular conditions of use. Larger layer thicknesses are produced suitably by gluing several thin felts. Particularly suitable carbon felts in thicknesses of 5 to 40 mm and bulk densities are from 0.1 to 0.3 g / cm³. Optionally, the structural stability of the felt web can be increased in a known manner by impregnation of the felt with pitch or a thermoset and subsequent pyrolysis of the impregnating agent. To join the graphite sheet with the carbon fiber-insulating respectively the contacting surfaces of both components of the thermal insulation with an adhesive, suitably from the group pitch or thermosets be coated, which are optionally mixed with solvents or diluents. Examples of suitable thermosetting resins are phenol formaldehyde resins, furan resins and mixtures of these substances with a viscosity of about 1 Pa · s Advantageously, the adhesive is applied with a spray gun or by brushing. its amount is to be dimensioned such that the graphite sheet is covered with a closed layer of adhesive. Graphite foil and kohlenstoffaserhaltige layer are then superimposed and optionally heated under pressure of a few kPa, initially when using thermosets to their curing temperature of about 120 to 200 ° C and subsequently to carbonization of the adhesive to about 800 ° C, but at least at the temperature of use the thermal insulation. The heat treatment is carried out in an inert or reducing atmosphere, the heating rate is not critical because of the small thickness of the adhesive layer.

p0008Does the thermal insulation several graphite sheets, each of the graphite foil can be provided with perforations. Consisting of insulation layer and graphite foil thermal insulation can be adapted within wide limits to the shape of insulating spaces. Especially with smaller dimensions is a one-piece design of Wärmeiso lation of benefit that follows the contours of such a furnace wall and is supported on this.

p0009Compared with known, formed from graphite foil and carbon felt for heat insulation assemblies, the embodiment according to the invention a number of advantages. The adhesion between the graphite foil and carbon felt is much better, so that delamination does not occur by blistering or delamination in the typical load of thermal insulation. The openings of the graphite foil promote the degassing of the felt layer so that the necessary vacuum furnaces in order to set a particular vacuum pumping time is smaller than with the use of known heat insulating material. On the other hand, the protective effect of the graphite foil is not impaired for the insulating layer of felt through the openings, there is no Verstaubungen the felt by scuffing or molten splash.

p0010The invention is explained below with reference to a drawing and to examples.

p0011In the Fig., A heat insulation is shown, which consists of an insulating layer 3 made of carbon felt and the graphite sheet 1, which are connected to each other through the adhesive layer 4 carbonized. The graphite foil is provided for the disposal of gaseous products with a plurality of perforations second

example 1

p0012Felts of carbon felt with dimensions of 1000 × 500 × 40 mm and a bulk density of 0.16 g / cc of flexible graphite sheets, thickness - 0.35 mm, Roch density - 1.0 g / cc, glued. The films had previously been perforated with a needle roller, the number of openings was about 50 per square centimeter, its diameter 0.2 to 0.3 mm. As the adhesive, a commercially available phenol formaldehyde resin having a viscosity at room temperature of about 1 Pa · s was applied to the contact surfaces; Felt web and graphite foil are compressed and heated to cure the resin under a pressure of about 0.1 MPa at 180 ° C. The residence time was 3 h. The assembly was then heated to 2500 ° C under a protective gas having an average temperature gradient of 50 K / h to 1000 ° C and at an average rate of about 200 K / h.

p0013The insulation capability of the thermal insulation generated is no different from thermal insulation materials containing Kohlenstoffilzschichten same thickness and density, and are equipped with gas-tight graphite foils. In comparative tests in sintering furnaces at temperatures up to 1500 ° C, there were in the thermal insulation for example prepared according to any failure by complete or partial detachment of the graphite foil of the insulating layer of carbon felt, due to erosion of the felt or its destruction by oxidation.

example 2

p0014Felts made of carbon felt having a thickness of 20 mm and a bulk density of 0.11 g / cm³ which have a relatively low stiffness, have been bonded to a laminate layer for shielding and reinforcement, which consists of two mutually bonded graphite foils with a thickness of 1 mm consist. The laminate layers contained per square centimeter of 25 perforations having a diameter 0.3 to 0.4 mm. For bonding of the two components a 2.1-mm-thick polyethylene film was placed between the contact surfaces loaded and the stack under a pressure of 0.12 MPa in a nitrogen atmosphere with a gradient of 50 K / h to 260 ° C and from 150 K / heated at 1600 ° C. The thermal insulation obtained is self-supporting, in comparative experiments, there was no separation of laminate and felt layer.