DE102021114190A1 - Process for the production of vacuum molded parts based on rice hull ash - Google Patents

Abstract

The present invention relates to a method for producing a vacuum molded part based on rice hull ash. Furthermore, the present invention relates to a vacuum formed part based on rice hull ash and the use of the vacuum formed part according to the invention as thermal insulation elements for high-temperature systems.

Description

The present invention relates to a method for producing a vacuum molded part based on rice hull ash. Furthermore, the present invention relates to a vacuum molded part based on rice husk ash and the use of the vacuum molded part according to the invention as thermal insulation elements for high-temperature systems.

State of the art

High-temperature systems, which are used in particular in laboratory furnace construction, special furnace construction and industrial furnace construction, place high demands on the thermal insulation elements used, as they are constantly exposed to high temperatures and chemical influences. Accordingly, such thermal insulation elements should have, among other things, high chemical resistance, high temperature resistance and good long-term stability at elevated temperatures. Furthermore, it is advantageous if the thermal insulation elements have good thermal insulation and thus good insulating properties, in order to enable low energy consumption of the system. In addition, it is important that the thermal insulation elements also have a certain mechanical strength so that they can be precisely machined or reworked and individually adapted to the corresponding systems.

Thermal insulation elements for high-temperature systems usually consist mainly of high-temperature wool or high-temperature fibers that are synthetically produced from mineral raw materials. The group of these high-temperature wools includes, for example, alkaline earth silicate (AES), aluminum silicate (ASW) and polycrystalline (PCW) fibers or wool. With these materials, however, it can be perceived as a disadvantage that thermal insulation elements based on alkaline earth silicate fibers have a rather low resistance to chemical influences such as acidic condensates and very high temperatures, which can be associated with poor long-term stability at elevated temperatures, so that these fibers are rather unsuitable for use in high-temperature systems with very high temperatures of > 1300 °C. Although aluminum silicate fibers are more resistant and stable than alkaline earth silicate fibers with regard to the aforementioned properties, these are classified as carcinogenic substances (category 2) according to the Ordinance on Hazardous Substances. Polycrystalline fibers are disadvantageous because of their high costs, which are due in particular to their complex production processes.

There is therefore a need for thermal insulation elements that have high chemical resistance, high temperature resistance and long-term stability at elevated temperatures, while at the same time being as inexpensive as possible and not harmful to health in terms of the raw materials used.

object of the invention

The object of the present invention was therefore to provide a molded part that can be used in particular as a thermal insulation element, in the production of which conventional high-temperature wool or high-temperature fibers are partially or almost completely replaced by raw materials that also have good thermal insulation properties - such as chemical resistance, temperature resistance and Long-term stability at elevated temperatures - and at the same time are as cost-effective as possible and not harmful to health. In addition, the molded parts should have good mechanical strength and be able to be individually adapted and precisely machined.

solution of the task

1. a) Einfüllen einer Suspension, umfassend oder bestehend aus den Komponenten A) bis F), in ein Formungswerkzeug, welches eine Suspensions-Einlassseite, einen Vakuum-Separator und eine an der Suspensions-Einlassseite gegenüberliegenden Seite des Vakuum-Separators ansetzende Unterdruckeinrichtung zum Anlegen eines Unterdrucks und Abführen der über den Vakuum-Separator abgetrennten Flüssigkeit aus der Suspension aufweist;
2. b) Anlegen eines Unterdrucks an die Unterdruckeinrichtung, wodurch die Flüssigkeit der Suspension den Vakuum-Separator passiert und auf dem Vakuum-Separator ein Grünteil erhalten wird;
3. c) Trocknen des Grünteils in einer Trockenanlage zu dem Vakuumformteil;
4. d) optional thermische Behandlung des Vakuumformteils;

wobei die Suspension die Komponenten

1. A) anorganische Fasern, bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Aluminiumsilikatwolle, Erdalkalisilikatwolle, Polykristalline Wolle, Mineralfasern, Silica-Fasern, Glasfasern, Basaltfasern, Keramikfasern oder Mischungen davon;
2. B) Reisschalenasche;
3. C) gegebenenfalls mindestens ein Füllstoff, bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Tonerde, Quarzsand, Silica, Mullit, Sillimanit, Andalusit, Siliciumcarbid, Spinell, Bariumsulfat, Borcarbid oder Mischungen davon;
4. D) mindestens ein anorganisches und/oder organisches Bindemittel;
5. E) gegebenenfalls Hilfs- und/oder Zusatzstoffe;
6. F) Flüssigkeit, bevorzugt protische Flüssigkeit, besonders bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Wasser, Methanol, Ethanol, Propanol oder Mischungen davon, ganz besonders bevorzugt Wasser;

umfasst oder daraus besteht.The object was achieved by a method for producing a vacuum molded part, in particular a vacuum molded part as a thermal insulation element, the method comprising or having at least the following method steps:

1. a) Filling a suspension comprising or consisting of components A) to F) into a molding tool which has a suspension inlet side, a vacuum separator and a vacuum device on the opposite side of the suspension inlet side of the vacuum separator for applying a negative pressure and discharging the liquid separated via the vacuum separator from the suspension;
2. b) applying a vacuum to the vacuum device, as a result of which the liquid in the suspension passes through the vacuum separator and a green part is obtained on the vacuum separator;
3. c) drying of the green part in a drying plant to form the vacuum molded part;
4. d) optional thermal treatment of the vacuum molded part;

the suspension containing the components

1. A) inorganic fibers, preferably selected from the group comprising or consisting of aluminum silicate wool, alkaline earth silicate wool, polycrystalline wool, mineral fibers, silica fibers, glass fibers, basalt fibers, ceramic fibers or mixtures thereof;
2. B) rice hull ash;
3. C) optionally at least one filler, preferably selected from the group comprising or consisting of alumina, quartz sand, silica, mullite, sillimanite, andalusite, silicon carbide, spinel, barium sulfate, boron carbide or mixtures thereof;
4. D) at least one inorganic and/or organic binder;
5. E) optionally auxiliaries and/or additives;
6. F) liquid, preferably protic liquid, particularly preferably selected from the group comprising or consisting of water, methanol, ethanol, propanol or mixtures thereof, very particularly preferably water;

includes or consists of.

Furthermore, the object was achieved by a vacuum molded part, obtained or obtainable by the method according to the invention.

1. A) anorganische Fasern, bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Aluminiumsilikatwolle, Erdalkalisilikatwolle, Polykristalline Wolle, Mineralfasern, Silica-Fasern, Glasfasern, Basaltfasern, Keramikfasern oder Mischungen davon;
2. B) Reisschalenasche, wobei diese bevorzugt aus ≥ 10,0 Gew.-%, weiter bevorzugt ≥ 50,0 Gew.-%, besonders bevorzugt ≥ 75,0 Gew.-% länglichen Partikeln besteht, die einen Längen zu Durchmesserverhältnis von ≥ 3:1 aufweisen;
3. C) gegebenenfalls mindestens ein Füllstoff, bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Tonerde, Quarzsand, Silica, Mullit, Sillimanit, Andalusit, Siliciumcarbid, Spinell, Bariumsulfat, Borcarbid oder Mischungen davon;
4. D) mindestens ein anorganisches und/oder organisches Bindemittel;
5. E) gegebenenfalls Hilfs- und/oder Zusatzstoffe.

In addition, the object is achieved by a vacuum molded part, comprising or consisting of the components

1. A) inorganic fibers, preferably selected from the group comprising or consisting of aluminum silicate wool, alkaline earth silicate wool, polycrystalline wool, mineral fibers, silica fibers, glass fibers, basalt fibers, ceramic fibers or mixtures thereof;
2. B) Rice hull ash, which preferably consists of ≥ 10.0% by weight, more preferably ≥ 50.0% by weight, particularly preferably ≥ 75.0% by weight of elongated particles which have a length-to-diameter ratio of ≥ 3 :1 have;
3. C) optionally at least one filler, preferably selected from the group comprising or consisting of alumina, quartz sand, silica, mullite, sillimanite, andalusite, silicon carbide, spinel, barium sulfate, boron carbide or mixtures thereof;
4. D) at least one inorganic and/or organic binder;
5. E) optionally auxiliaries and/or additives.

Finally, the object is achieved by using a vacuum molded part according to the invention as thermal insulation elements for high-temperature systems, preferably for laboratory furnace construction, special furnace construction and/or industrial furnace construction, in particular for high-temperature systems with operating temperatures of 400° C. to 1650° C., particularly preferably from 1000° C. to 1500° C

As part of the development work that led to the present invention, it was surprisingly found that rice hull ash (RSA for short) is suitable as a partial or almost complete replacement for conventional high-temperature wool or high-temperature fibers (AES, ASW, PCW) for the production of molded parts, if the shaping process takes place via vacuum moulds. Because of their chemical resistance, temperature resistance (which is expressed, for example, in a high classification temperature and/or low shrinkage) and long-term stability at elevated temperatures, such vacuum molded parts are suitable as thermal insulation elements for high-temperature systems. Without being bound by theory, it is believed that due to the vacuum forming process of the present invention and the geometry of the elongated particles of the rice hull ash, a truss-like three-dimensional structure is created in the vacuum mold parts. On the other hand, others seem to Shaping processes in which the components used are mixed by stirring, the geometry of the rice hull ash is negatively affected by the resulting friction and the elongated particles are partially crushed, so that the aforementioned framework-like structure is not achieved or is not achieved to the same extent. Furthermore, the vacuum molded parts produced using the method according to the invention are characterized by reduced thermal conductivity and/or IR radiation, which leads to improved thermal insulation. Such an optimization of the thermal insulation in turn helps to save energy in the high-temperature systems.

In addition, the use of rice hull ash (BSA) improves the environmental and cost balance of the process. Conventional high-temperature fibers for the production of thermal insulation elements are also disadvantageous in this context, since they are energy-intensive and pollute both with regard to the production processes and with regard to the extraction of raw materials required for their production. In contrast, rice hull ash is both a highly sustainable and environmentally friendly raw material that is available in large quantities at low cost. Rice plants are among the most commonly grown and consumed grains in the world. The so-called rice husks, in particular, are a by-product of obtaining the actual food. These rice hulls are mainly burned to generate energy, with the rice hull ash being obtained as a waste product. Rice husk ash is therefore sustainable in two respects, since both the rice husks and ultimately the rice husk ash are waste products. In addition, rice hull ash is a CO ₂ -neutral raw material, since only the amount of CO ₂ that the rice plant absorbed during the growth phase is released. Furthermore, the use of rice hull ash leads to a reduction in current landfill volumes.

• • Verbesserte Wärmeleitfähigkeit und damit verbesserte Wärmedämmung;
• • Verbesserte Druckfestigkeit;
• • Verringerte Schwindung und damit höhere sowie langfristigere Temperaturbeständigkeit bei erhöhten Temperaturen bis zu 1650 °C;
• • hohe chemische Beständigkeit, insbesondere gegenüber Wasser bzw. Wasserdampf und dessen sauren Kondensaten;
• • Verringerung des Einsatzes von Gefahrstoffen;
• • Es sind geringe Rohdichten bis zu 150 kg/m³ erzielbar;
• • Individuelle Formgebung und damit komplexe Geometrie des herzustellenden Formteils durch das erfindungsgemäße Verfahren.

The combination of vacuum forming processes and rice hull ash according to the invention can also achieve one or more of the following advantages, without being limited to these:

• • Improved thermal conductivity and thus improved thermal insulation;
• • Improved compressive strength;
• • Reduced shrinkage and thus higher and longer-term temperature resistance at elevated temperatures of up to 1650 °C;
• • high chemical resistance, especially to water or water vapor and its acidic condensates;
• • reducing the use of hazardous substances;
• • Low bulk densities of up to 150 kg/m ³ can be achieved;
• • Individual shaping and thus complex geometry of the molded part to be produced by the method according to the invention.

Detailed description of the invention

In the context of this invention, a vacuum molded part is understood to mean a molded part that is obtained by the vacuum molding process according to the invention and can then be used, for example, as a thermal insulation element. The vacuum formed part is not limited to any geometry and can therefore be individually adapted to a wide variety of circumstances. The vacuum molded part is preferably obtained as a three-dimensional vacuum molded part that is close to the final shape.

In the process according to the invention, the suspension comprising or consisting of components A) to F) is first prepared. The suspension is preferably prepared in one or more mixing tanks, which are preferably each equipped with one or more stirring tools. These mixing tanks can be adapted to the production capacity. The tank size is preferably 1000 to 10000 liters. These tanks are preferably first filled with the liquid F) and then the components are added, although the individual components can also be added at different times. At this time, it is preferable that the suspension is stirred for a certain period of time, particularly for 5 minutes to 90 minutes.

The ready-to-use suspension can then be filled into a forming tool. The shaping tool preferably has a suspension inlet side, a vacuum separator and a vacuum device attached to the side of the vacuum separator opposite the suspension inlet side device for applying a negative pressure and removing the liquid F) separated via the vacuum separator from the suspension. The shaping tool is not restricted to any specific geometry and can accordingly be adapted to the respective circumstances, as a result of which individual shaping with a wide variety of dimensions is possible. The liquid F) of the transferred suspension can be removed by applying a vacuum to the vacuum device, with the liquid F) passing through the vacuum separator. A so-called green part (also called green product or filter cake) is then obtained on the vacuum separator.

The green part can be produced in two variants, namely discontinuously or continuously. In the discontinuous variant, the suspension is transferred directly into the molding tool and the water is removed by applying a vacuum and the solids are compacted into a green part. The molding tool can then be supplied with suspension again and the green part can be built up again by applying a vacuum. In the continuous variant, the shaping tool is located in a mold trough filled with suspension and is positioned in such a way that the liquid level of the suspension is above the suspension inlet side of the shaping tool until the end of the application of a vacuum to the vacuum device. A green part is also formed on the vacuum separator. The mold trough can be continuously or discontinuously supplied with further suspension via a tank or storage container. After the application of a vacuum to the vacuum device has been completed, the molding tool with the green part located on the vacuum separator is removed from the mold pan. Both the discontinuous and the continuous variant make it possible to obtain a green part of almost any thickness, with the thickness of the green part generally not exceeding the height of the forming tool for technical reasons. The continuous variant offers the advantage that it enables a more efficient process flow, since there is always sufficient suspension available to achieve the desired thickness of the green part.

If necessary, the content of the liquid F) in the green part can be further reduced by further applying a vacuum to the vacuum device of the forming tool. The green part can either remain in the forming tool for the following steps or be removed beforehand.

The green part obtained, which is preferably still moist, can then be mechanically reworked, depending on the requirement. The mechanical post-processing is preferably carried out by sawing, grinding, turning, drilling, milling, punching, cutting and/or other mechanical post-processing steps.

After drying the green part in a drying plant, the vacuum formed part can be obtained. The remaining content of liquid F) is removed as far as possible. Drying in the drying plant preferably takes place in a temperature range from 50 to 250.degree. C., particularly preferably from 95 to 180.degree.

Optionally, a thermal treatment of the vacuum formed part can then be carried out. The thermal treatment preferably takes place at 400 to 1650° C., particularly preferably at 600 to 1200° C., in an oven.

After the green part has dried or after the thermal treatment, the vacuum formed part can be post-processed mechanically, preferably by sawing, grinding, turning, drilling, milling, punching, cutting and/or other mechanical post-processing steps.

Optionally, the vacuum formed part can be treated further after the green part has dried or after the thermal treatment. The vacuum molded part is preferably treated by applying hardeners and/or coatings. Suitable hardeners are, for example, colloidal silicic acid, colloidal boehmite, sodium and potassium water glass (eg products from the Rath ^Kerathin® H group). In particular, coatings based on silicon aluminum oxide (eg products from the Rath ^Kerathin® C group) can be used as coatings.

In a preferred embodiment, the vacuum molding obtained by the process according to the invention has a bulk density of 150 to 2000 kg/m ³ , preferably 150 to 1000 kg/m ³ , determined according to ÖNORM EN 1094-4. In a further preferred embodiment, the vacuum molded part obtained by the method according to the invention has a wall thickness or thickness of 2 to 300 mm. The vacuum molding obtained by the method according to the invention preferably has a classification temperature in the range from 600 to 1650° C., determined according to ÖNORM EN 1094-1.

The vacuum molded part according to the invention can be used in particular as a thermal insulation element. The vacuum molded part according to the invention can preferably be used as a thermal insulation element for high-temperature systems, preferably for laboratory furnace construction, special furnace construction and/or industrial furnace construction, in particular for high-temperature systems with operating temperatures of 400° C. to 1650° C., particularly preferably from 1000° C. to 1500° C.

1. A) anorganische Fasern, bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Aluminiumsilikatwolle, Erdalkalisilikatwolle, Polykristalline Wolle, Mineralfasern, Silica-Fasern, Glasfasern, Basaltfasern, Keramikfasern oder Mischungen davon;
2. B) Reisschalenasche, wobei diese bevorzugt aus ≥ 10 Gew.-%, weiter bevorzugt ≥ 50 Gew.-%, besonders bevorzugt ≥ 75 Gew.-% länglichen Partikeln besteht, die einen Längen zu Durchmesserverhältnis von ≥ 3:1 aufweisen;
3. C) gegebenenfalls mindestens ein Füllstoff, bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Tonerde, Quarzsand, Silica, Mullit, Sillimanit, Andalusit, Siliciumcarbid, Spinell, Bariumsulfat, Borcarbid oder Mischungen davon;
4. D) mindestens ein anorganisches und/oder organisches Bindemittel;
5. E) gegebenenfalls Hilfs- und/oder Zusatzstoffe.

The vacuum molded part according to the invention comprises or consists of the components

1. A) inorganic fibers, preferably selected from the group comprising or consisting of aluminum silicate wool, alkaline earth silicate wool, polycrystalline wool, mineral fibers, silica fibers, glass fibers, basalt fibers, ceramic fibers or mixtures thereof;
2. B) rice hull ash, which preferably consists of ≧10% by weight, more preferably ≧50% by weight, particularly preferably ≧75% by weight, of elongated particles which have a length to diameter ratio of ≧3:1;
3. C) optionally at least one filler, preferably selected from the group comprising or consisting of alumina, quartz sand, silica, mullite, sillimanite, andalusite, silicon carbide, spinel, barium sulfate, boron carbide or mixtures thereof;
4. D) at least one inorganic and/or organic binder;
5. E) optionally auxiliaries and/or additives.

In the course of the optional thermal post-treatment, the vacuum molded part can also contain decomposition, degradation and reaction products of the components used. In these cases, the corresponding components are to be understood as precursor compounds. For example, corn starch as the organic binder of component D) can be partially or completely decomposed during a thermal treatment, so that decomposition products of corn starch—if they are not gaseous—can be present in the vacuum molded part and corn starch is a precursor compound in this respect.

The suspension comprises or consists of components A) to F), which are to be described in more detail below:

component A)

Component A) includes inorganic fibers. In the context of this invention, inorganic fibers are also understood to mean inorganic wools. The inorganic fibers are preferably selected from the group comprising or consisting of aluminum silicate wool, alkaline earth silicate wool, polycrystalline wool, mineral fibers, silica fibers, glass fibers, basalt fibers, ceramic fibers or mixtures thereof. According to the WHO definition, the fibers preferably have a length of >5 μm and a length-to-diameter ratio of >3:1. The silica fibers used preferably have an SiO ₂ content of more than 90% by weight.

component B)

Component B) includes rice hull ash. The rice hull ash of component B) preferably consists of ≥ 10.0% by weight, more preferably ≥ 50.0% by weight, particularly preferably ≥ 75.0% by weight of elongated particles which have a length-to-diameter ratio of ≥ 3 :1, determined using a scanning electron microscope, if necessary with the aid of a stereomicroscope if particles are present which cannot be measured using a scanning electron microscope because of their size. The elongated particles of the rice hull ash are preferably fibrous, amorphous structures which have both a platelet-shaped and a tubular particle geometry and appear predominantly crescent-shaped in their cross-sectional shape.

component C)

Optionally, component C) is used, which fillers, preferably selected from the group comprising or consisting of alumina, quartz sand, silica, mullite, sillimanite, andalusite, silicon carbide, spinel, barium sulfate, boron carbide or mixtures thereof. The particles of the fillers preferably have an average particle size (d ₅₀ ) of at least 1 μm, preferably from 1 μm to 200 μm, measured by laser granulometric measurement (laser diffraction analysis) or dynamic light scattering (dynamic light scattering, DLS). By adding or omitting component C), a series of properties of the vacuum molded part can also be adjusted, such as density, porosity, compressive strength, shrinkage and/or temperature resistance.

component D)

At least one inorganic and/or organic binder is used as component D). The inorganic binder is preferably selected from the group comprising or consisting of colloidal silica, alumina, boehmite, mullite, wollastonite, or mixtures thereof. In the context of the present invention, colloidal silica (also called silica sol) is understood as meaning an aqueous colloidal suspension of a liquid, preferably water, and amorphous silicon dioxide with a silicon dioxide content of 5 to 60% by weight, preferably between 30 and 55%. The organic binder is preferably selected from the group comprising or consisting of potato starch, corn starch, latex dispersions or mixtures thereof. All common polymer dispersions such as natural and synthetic latices can be used as latex dispersions. Furthermore, all suitable flocculants and precipitants can be used as component D). The particles of the binders, in particular the inorganic binders, preferably have an average particle size (d ₅₀ ) of 9 to 150 nm, preferably 10 to 100 nm, measured by dynamic light scattering (DLS). The components, in particular components A) and B), can be connected and/or flaked together by the binders of component D), for example by gelation.

component E)

Component E) is optional auxiliaries and/or additives. All common compounds such as pH regulators, acids, bases, fungicides, bactericides and mixtures of these can be used as auxiliaries and/or additives.

component F)

Component F) is a liquid, preferably a protic liquid. The liquid F) is preferably selected from the group comprising or consisting of water, methanol, ethanol, propanol or mixtures thereof. Water is particularly preferably used as liquid F).

1. A) 1,0 bis 90,0 Gew.-%, bevorzugt 1,5 bis 85,0 Gew.-%;
2. B) 1 bis 85,0 Gew.-%, bevorzugt 1,5 bis 80,0 Gew.-%, besonders bevorzugt 2,0 bis 75,0 Gew.-%;
3. C) 0,0 bis 50,0 Gew.-%, bevorzugt 1,0 bis 45,0 Gew.-%, besonders bevorzugt 5,0 bis 40,0 Gew.-%;
4. D) 5,0 bis 70,0 Gew.-%, bevorzugt 7,5 bis 70,0 Gew.-%, besonders bevorzugt 9,0 bis 60,0 Gew.-%;
5. E) 0,0 bis 5,0 Gew.-%, bevorzugt 0,1 bis 2,0 Gew.-%,

wobei die Angaben jeweils bezogen sind auf die Summe der Komponenten A) bis E) und sich zu 100 Gew.-% addieren. Mit anderen Worten ist bei den vorgenannten Einsatzmengen das Suspendierungsmittel, also die Komponente F), nicht mit eingerechnet.The suspension preferably contains components A) to E) in the following amounts:

1. A) 1.0 to 90.0% by weight, preferably 1.5 to 85.0% by weight;
2. B) 1 to 85.0% by weight, preferably 1.5 to 80.0% by weight, particularly preferably 2.0 to 75.0% by weight;
3. C) 0.0 to 50.0% by weight, preferably 1.0 to 45.0% by weight, particularly preferably 5.0 to 40.0% by weight;
4. D) 5.0 to 70.0% by weight, preferably 7.5 to 70.0% by weight, particularly preferably 9.0 to 60.0% by weight;
5. E) 0.0 to 5.0% by weight, preferably 0.1 to 2.0% by weight,

the figures are in each case based on the sum of components A) to E) and add up to 100% by weight. In other words, the suspension agent, ie component F), is not included in the amounts used above.

The ratio of the total amount of components A) to E) to component F) in the suspension is preferably 1:10 to 1:80, preferably 1:25 to 1:65. Accordingly, if water is used as component F), for example, 10 to 80 liters, preferably 25 to 65 liters, of water are used per 1 kg of components A) to E).

In a further preferred embodiment, the mass ratio of inorganic to organic binder is from 5:1 to 15:1, preferably from 6:1 to 13:1, more preferably from 7.5:1 to 12:1, particularly preferably from 9:1 to 11:1, most preferably about 10:1.

• Nach einer ersten Ausführungsform betrifft die Erfindung ein Verfahren zur Herstellung eines Vakuumformteils, insbesondere eines Vakuumformteils als Wärmedämmelement, wobei das Verfahren wenigstens die folgenden Verfahrensschritte umfasst oder aufweist:
  1. a) Einfüllen einer Suspension 6, umfassend oder bestehend aus den Komponenten A) bis F), in ein Formungswerkzeug 1, welches eine Suspensions-Einlassseite 3, einen Vakuum-Separator 5 und eine an der Suspensions-Einlassseite 3 gegenüberliegenden Seite des Vakuum-Separators 5 ansetzende Unterdruckeinrichtung zum Anlegen eines Unterdrucks und Abführen der über den Vakuum-Separator 5 abgetrennten Flüssigkeit aus der Suspension 6 aufweist;
  2. b) Anlegen eines Unterdrucks an die Unterdruckeinrichtung, wodurch die Flüssigkeit der Suspension 6 den Vakuum-Separator 5 passiert und auf dem Vakuum-Separator 5 ein Grünteil 7 erhalten wird;
  3. c) Trocknen des Grünteils 7 in einer Trockenanlage zu dem Vakuumformteil;
  4. d) optional thermische Behandlung des Vakuumformteils;
• wobei die Suspension 6 die Komponenten
  1. A) anorganische Fasern, bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Aluminiumsilikatwolle, Erdalkalisilikatwolle, Polykristalline Wolle, Mineralfasern, Silica-Fasern, Glasfasern, Basaltfasern, Keramikfasern oder Mischungen davon;
  2. B) Reisschalenasche;
  3. C) gegebenenfalls mindestens ein Füllstoff, bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Tonerde, Quarzsand, Silica, Mullit, Sillimanit, Andalusit, Siliciumcarbid, Spinell, Bariumsulfat, Borcarbid oder Mischungen davon;
  4. D) mindestens ein anorganisches und/oder organisches Bindemittel;
  5. E) gegebenenfalls Hilfs- und/oder Zusatzstoffe;
  6. F) Flüssigkeit, bevorzugt protische Flüssigkeit, besonders bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Wasser, Methanol, Ethanol, Propanol oder Mischungen davon, ganz besonders bevorzugt Wasser;

umfasst oder daraus besteht.The invention relates in particular to the following embodiments:

• According to a first embodiment, the invention relates to a method for producing a vacuum molded part, in particular a vacuum molded part as a thermal insulation element, the method comprising or having at least the following method steps:
  1. a) Filling a suspension 6 comprising or consisting of components A) to F) into a molding tool 1 which has a suspension inlet side 3, a vacuum separator 5 and a side of the vacuum separator opposite the suspension inlet side 3 5 attaching vacuum device for applying a vacuum and removing the liquid separated by the vacuum separator 5 from the suspension 6;
  2. b) applying a vacuum to the vacuum device, as a result of which the liquid in the suspension 6 passes through the vacuum separator 5 and a green part 7 is obtained on the vacuum separator 5;
  3. c) drying of the green part 7 in a drying plant to form the vacuum molded part;
  4. d) optional thermal treatment of the vacuum molded part;
• where the suspension 6 the components
  1. A) inorganic fibers, preferably selected from the group comprising or consisting of aluminum silicate wool, alkaline earth silicate wool, polycrystalline wool, mineral fibers, silica fibers, glass fibers, basalt fibers, ceramic fibers or mixtures thereof;
  2. B) rice hull ash;
  3. C) optionally at least one filler, preferably selected from the group comprising or consisting of alumina, quartz sand, silica, mullite, sillimanite, andalusite, silicon carbide, spinel, barium sulfate, boron carbide or mixtures thereof;
  4. D) at least one inorganic and/or organic binder;
  5. E) optionally auxiliaries and/or additives;
  6. F) liquid, preferably protic liquid, particularly preferably selected from the group comprising or consisting of water, methanol, ethanol, propanol or mixtures thereof, very particularly preferably water;

includes or consists of.

According to a second embodiment, the invention relates to a method for producing a vacuum molded part according to embodiment 1, characterized in that the molding tool 1 is positioned in steps a) and b) in a mold trough 10 filled with the suspension 6 in such a way that the liquid level 11 of the Suspension 6 is above the suspension inlet side 3 of the molding tool 1 until the end of step b) and then the molding tool 1 is removed from the mold trough 10 with the green part 7 located on the vacuum separator 5 .

According to a third embodiment, the invention relates to a method for producing a vacuum molded part according to embodiment 2, characterized in that the mold pan 10 is continuously or discontinuously supplied with further suspension 6 via a storage container.

According to a fourth embodiment, the invention relates to a method for producing a vacuum molded part according to one of the above embodiments, characterized in that after method step b) the liquid content of the green part 7 is further reduced by further applying a vacuum to the vacuum device.

According to a fifth embodiment, the invention relates to a method for producing a vacuum molded part according to one of the above embodiments, characterized in that the green part 7 is mechanically post-processed after step b), preferably by pressing, rolling, sawing, punching and / or cutting, where appropriate the green part 7 is removed from the molding tool for this purpose.

According to a sixth embodiment, the invention relates to a method for producing a vacuum formed part according to one of the above embodiments, characterized in that the vacuum formed part is mechanically reworked after step c) and/or d), preferably by sawing, grinding, turning, drilling, milling, punching and/or cutting.

According to a seventh embodiment, the invention relates to a method for producing a vacuum molded part according to one of the above embodiments, characterized in that the vacuum molded part is treated after step c) and/or d) by applying hardeners and/or coatings.

1. A) 1,0 bis 90,0 Gew.-%, bevorzugt 1,5 bis 85,0 Gew.-%;
2. B) 1 bis 85,0 Gew.-%, bevorzugt 1,5 bis 80,0 Gew.-%, besonders bevorzugt 2,0 bis 75,0 Gew.-%;
3. C) 0,0 bis 50,0 Gew.-%, bevorzugt 1,0 bis 45,0 Gew.-%, besonders bevorzugt 5,0 bis 40,0 Gew.-%;
4. D) 5,0 bis 70,0 Gew.-%, bevorzugt 7,5 bis 70,0 Gew.-%, besonders bevorzugt 9,0 bis 60,0 Gew.-%;
5. E) 0,0 bis 5,0 Gew.-%, bevorzugt 0,1 bis 2,0 Gew.-%,

wobei die Angaben jeweils bezogen sind auf die Summe der Komponenten A) bis E) und sich zu 100 Gew.-% addieren.According to an eighth embodiment, the invention relates to a method for producing a vacuum molded part according to one of the above embodiments, characterized in that suspension 6 contains components A) to E) in the following amounts:

1. A) 1.0 to 90.0% by weight, preferably 1.5 to 85.0% by weight;
2. B) 1 to 85.0% by weight, preferably 1.5 to 80.0% by weight, particularly preferably 2.0 to 75.0% by weight;
3. C) 0.0 to 50.0% by weight, preferably 1.0 to 45.0% by weight, particularly preferably 5.0 to 40.0% by weight;
4. D) 5.0 to 70.0% by weight, preferably 7.5 to 70.0% by weight, particularly preferably 9.0 to 60.0% by weight;
5. E) 0.0 to 5.0% by weight, preferably 0.1 to 2.0% by weight,

the figures are in each case based on the sum of components A) to E) and add up to 100% by weight.

According to a ninth embodiment, the invention relates to a method for producing a vacuum molded part according to one of the above embodiments, characterized in that the ratio of the total amount of components A) to E) to component F) in the suspension is 1: 10 to 1: 80, preferably 1:25 to 1:65.

According to a tenth embodiment, the invention relates to a method for producing a vacuum molded part according to one of the above embodiments, characterized in that the rice hull ash of component B) consists of ≥ 10.0% by weight, preferably ≥ 50.0% by weight, in particular preferably ≥ 75.0% by weight of elongate particles which have a length to diameter ratio of ≥ 3:1.

According to an eleventh embodiment, the invention relates to a method for producing a vacuum molded part according to one of the above embodiments, characterized in that the inorganic binder is selected from the group comprising or consisting of colloidal silica, alumina, boehmite, mullite, wollastonite or mixtures thereof.

According to a twelfth embodiment, the invention relates to a method for producing a vacuum molded part according to one of the above embodiments, characterized in that the organic binder is selected from the group comprising or consisting of potato starch, corn starch, latex dispersions or mixtures thereof.

According to a thirteenth embodiment, the invention relates to a method for producing a vacuum molded part according to one of the above embodiments, characterized in that the mass ratio of inorganic to organic binder is 5: 1 to 15: 1, preferably from 6: 1 to 13: 1, further preferably from 7.5:1 to 12:1, more preferably from 9:1 to 11:1, most preferably about 10:1.

According to a fourteenth embodiment, the invention relates to a method for producing a vacuum molded part according to one of the above embodiments, characterized in that the vacuum molded part obtained has a bulk density of 150 to 2000 kg/m ³ , preferably 150 to 1000 kg/m ³ , determined according to ÖNORM EN 1094-4.

According to a fifteenth embodiment, the invention relates to a vacuum formed part obtained or obtainable by a method according to any one of embodiments 1 to 14.

1. A) anorganische Fasern, bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Aluminiumsilikatwolle, Erdalkalisilikatwolle, Polykristalline Wolle, Mineralfasern, Silica-Fasern, Glasfasern, Basaltfasern, Keramikfasern oder Mischungen davon;
2. B) Reisschalenasche, wobei diese bevorzugt aus ≥ 10,0 Gew.-%, weiter bevorzugt ≥ 50,0 Gew.-%, besonders bevorzugt ≥ 75,0 Gew.-% länglichen Partikeln besteht, die einen Längen zu Durchmesserverhältnis von ≥ 3:1 aufweisen;
3. C) gegebenenfalls mindestens ein Füllstoff, bevorzugt ausgewählt aus der Gruppe, umfassend oder bestehend aus Tonerde, Quarzsand, Silica, Mullit, Sillimanit, Andalusit, Siliciumcarbid, Spinell, Bariumsulfat, Borcarbid oder Mischungen davon;
4. D) mindestens ein anorganisches und/oder organisches Bindemittel;
5. E) gegebenenfalls Hilfs- und/oder Zusatzstoffe.

According to a sixteenth embodiment, the invention relates to a vacuum molded part, comprising or consisting of the components

1. A) inorganic fibers, preferably selected from the group comprising or consisting of aluminum silicate wool, alkaline earth silicate wool, polycrystalline wool, mineral fibers, silica fibers, glass fibers, basalt fibers, ceramic fibers or mixtures thereof;
2. B) Rice hull ash, which preferably consists of ≥ 10.0% by weight, more preferably ≥ 50.0% by weight, particularly preferably ≥ 75.0% by weight of elongated particles which have a length-to-diameter ratio of ≥ 3 :1 have;
3. C) optionally at least one filler, preferably selected from the group comprising or consisting of alumina, quartz sand, silica, mullite, sillimanite, andalusite, silicon carbide, spinel, barium sulfate, boron carbide or mixtures thereof;
4. D) at least one inorganic and/or organic binder;
5. E) optionally auxiliaries and/or additives.

According to a seventeenth embodiment, the invention relates to a vacuum molded part according to embodiment 15 or 16, characterized in that the vacuum molded part is a thermal insulation element.

According to an eighteenth embodiment, the invention relates to the use of a vacuum molded part according to one of embodiments 15 to 17 as thermal insulation elements for high-temperature systems, preferably for laboratory furnace construction, special furnace construction and/or industrial furnace construction, in particular for high-temperature systems with operating temperatures of 400° C. to 1650° C., particularly preferred from 1000°C to 1500°C.

• 1: eine schematische Darstellung eines Formungswerkzeugs zur Herstellung eines Vakuumformteils in seitlicher Schnittdarstellung;
• 2: eine schematische Darstellung des Pressens eines Grünteils im Formungswerkzeug in seitlicher Schnittdarstellung;
• 3: eine schematische Darstellung eines Formungswerkzeugs in einer Formwanne zur Herstellung eines Vakuumformteils in seitlicher Schnittdarstellung und
• 4: fotografische Aufnahmen des Vergleichsbeispiels 3: A) Trockenmischung; B) Mischung nach Zugabe von Wasser; C) Formteil nach Zugabe der Mischung in eine Form.

The present invention is hereinafter based on the 1 until 4 and explained in more detail in the following examples. Show it

• 1 : a schematic representation of a forming tool for the production of a vacuum molded part in a lateral sectional representation;
• 2 1: a schematic representation of the pressing of a green part in the forming tool in a lateral sectional representation;
• 3 : a schematic representation of a forming tool in a mold trough for the production of a vacuum formed part in a lateral sectional representation and
• 4 : Photographs of Comparative Example 3: A) dry mixture; B) Mixture after addition of water; C) Molded part after addition of the mixture in a mould.

1 shows a schematic representation of a forming tool 1 for the production of a vacuum molded part in a lateral sectional representation. The shaping tool 1 is designed as a cylindrical hollow body 2 with an end face 3 open at the top, which forms a suspension inlet side 3 . The lower face 4 of the cylindrical hollow body 2 is closed. Inside the cylindrical hollow body 2 there is a vacuum separator 5 which is positioned substantially parallel to the end faces 3 , 4 of the cylindrical hollow body 2 . The vacuum separator 5 is designed in such a way that the liquid of a suspension 6 (indicated by the top three rows of further spaced dashed lines) can pass through and the solid components of this suspension 6 are deposited on the vacuum separator 5 as a green part 7 (indicated by the three rows of narrower dashed lines) remain. Below the vacuum separator 5, a vacuum line 8 leads from the lower end face 4 of the cylindrical hollow body 2, which opens into a vacuum unit, not shown here, which is used to generate a negative pressure in the through the vacuum separator 5, the lower end face 4 and the intermediate wall section of the cylindrical hollow body 2 defined space and for discharging the liquid of the suspension 6 is used.

When operating the in 1 In the molding tool 1 shown for producing the vacuum molded part according to a first embodiment of the method according to the invention, the suspension 6 is added via the suspension inlet side 3 directly to the vacuum separator of the molding tool 1. By applying a vacuum with the aid of the vacuum device, the liquid in the suspension 6 passes - Such as water - the vacuum separator 5 and is discharged via the vacuum line 8. The solid components of the suspension 6 are compressed into the green part 7 on the vacuum separator 5 . As soon as the supernatant of the suspension 6 has dropped to the level of the upper side of the green part 7, the shaping tool 1 is again supplied with suspension 6 and the green part 7 is further built up. This process is repeated until the green part 7 has reached the desired strength. The liquid content of the green part 7 is then further reduced by continuously applying the negative pressure. The green part 7 in the forming tool 1 can then be subjected to further processing.

In 2 is shown as the after in 1 The green part 7 obtained by the method shown is formed in the forming tool 1 by means of a ram 9 . The ram 9 is designed in such a way that it terminates without gaps on the inside of the cylindrical hollow body 2 . The ram 9 is controlled by a pressing device, not shown. The pressing pressure with which the pressing ram 9 acts on the green part 7 is also set via the pressing device. After completion of the press pre Initially, the ram 9 is removed from the forming tool. The green part 7 in the molding tool 1 is then dried at 110° C. in a drying system (not shown), the vacuum molded part being obtained. The vacuum formed part can then be subjected to further processing steps.

In 3 a second embodiment of the method according to the invention is shown schematically, in which the production of the vacuum molded part takes place with continuous addition of the suspension. This is below 1 described molding tool 1 in a mold trough 10. The mold trough 10 also contains the suspension 6 and thus has a liquid level 11. The shaping tool 1 is positioned in the mold trough 10 in such a way that the suspension inlet side 3 is permanently below the liquid level 11 and the shaping tool 1 is oriented essentially parallel to the surface of the bottom of the mold trough 12 . The mold trough 10 can be supplied with further suspension continuously or discontinuously via a further inlet, not shown. By applying a vacuum to the vacuum device, the suspension 6 is sucked through the vacuum separator 5 via the suspension inlet side 3, whereby, as in the case of FIG 1 explained mode of operation, the liquid of the suspension 6 passes the vacuum separator 5 and is discharged via the vacuum line 8 and the solid components of the suspension 6 are retained on the vacuum separator 5 and compressed to form the green part 7 . After completion of the green part 7 , the forming tool 1 with the green part 7 located on the vacuum separator 5 is removed from the mold trough 10 . Analogous to the in 1 described mode of operation, the content of liquid in the green part 7 is further reduced by further application of a vacuum with the aid of the vacuum device. The green part 7 in the shaping tool 1 can then undergo further processing - for example as in 2 explained way - are supplied.

examples

Measurement methods:

• • Rohdichte: Gemäß ÖNORM EN 1094-4;
• • Klassifikationstemperatur: Gemäß ÖNORM EN 1094-1. Diese ist als Maß für die Temperaturbeständigkeit anzusehen;
• • Schwindung: Gemäß ÖNORM EN 1094-1 (bei 1400 °C);
• • Chemische Beständigkeit: indirekte Prüfung über die Schwindung, dabei wurde eine Schwindung bei 1100°C unter überhitzter Wasserdampfatmosphäre (100 % Sättigung mit Wasser) durchgeführt;
• • Langzeitstabilität: Es wurden dafür fünf Schwindungen nach ÖNORM EN 1094-1 (bei 1400 °C) hintereinander an ein und derselben Probe durchgeführt;
• • Wärmeleitfähigkeit: Gemäß DIN EN ISO 8894-1 (bei 1200 °C);
• • Offene Porosität: In Anlehnung an DIN EN 993-1 gemessen. Dabei wurde ein 100 × 100 × 40 mm Probekörper verwendet und bei 110 °C bis zur Massenkonstanz getrocknet (jedoch mindestens für 2 Stunden). Anschließend wurde die Masse (m_T in [g]) sowie das Volumen der getrockneten Probe (V in [cm³]) bestimmt. Anschließend wurde der Probenkörper in einem Exsikkator bei 20 °C und einem Druck von 6500 Pa für 15 Minuten in destilliertem Wasser getränkt, wobei der Probenkörper vertikal ausgerichtet wurde und der Wasserspiegel mindestens 20 mm über dem Probenkörper lag. Die Probe wurde anschließend entnommen und es wurde die Masse der mit Wasser infiltrierten Probe (m_G in [g]) bestimmt. Die Dichte ρ des Infiltrationsmediums Wasser wurde mit 1 g/cm³ angenommen. Die Porosität wurde schließlich über die folgende Formel berechnet: $$\mathrm{\varphi }=\left[\left({\text{m}}_{\text{G}}-{\text{m}}_{\text{T}}\right)/\left(\text{V}\cdot \mathrm{\rho }\right)\right]\cdot 100$$
  
• • Druckfestigkeit: Bei 10% Kompression gemäß Norm DIN EN ISO 8895;
• • Das Längen zu Durchmesserverhältnis der Partikel der Reisschalenasche wurde mittels einem Nikon Stereomikroskop SMZ745T sowie einem REM Tescan Vega IV bestimmt, wobei alle Partikel, welche für das REM Tescan Vega IV zu groß waren, mit dem Nikon Stereomikroskop SMZ745T untersucht wurden. Dabei wurden die Partikel auf einem Probeträger aufgebracht und in das Messgerät gegeben. Dabei wurde besondere Sorgfalt darauf gelegt, die Proben nicht mechanisch zu zerstören. Probenstücke, welche offensichtlich beim Aufbringen zerstört wurden, wurden nicht berücksichtigt. Anschließend wurde ein optisches Image der Probe erstellt und mit der Auswertesoftware des jeweiligen Geräts ausgewertet. Dabei wurden die äußeren Kanten des Durchmessers an der dicksten Stelle automatisch bzw. mittels Mausklick ausgewählt. Dasselbe wurde auch bei den Längen durchgeführt. Aufgrund dieser Messungen wurden jene Partikel ermittelt, welche ein Längen zu Durchmesserverhältnis von ≥ 3:1 besitzen und der Massenanteil in Gew.-% dieser Partikel an der Reisschalenasche bestimmt.

The properties for the respective examples and comparative examples were determined on the finished vacuum molded parts. The following measurement methods were used:

• • Raw density: According to ÖNORM EN 1094-4;
• • Classification temperature: According to ÖNORM EN 1094-1. This is to be regarded as a measure of the temperature resistance;
• • Shrinkage: According to ÖNORM EN 1094-1 (at 1400 °C);
• • Chemical resistance: indirect test via the shrinkage, shrinkage was carried out at 1100°C under a superheated steam atmosphere (100% saturation with water);
• • Long-term stability: Five shrinkage tests according to ÖNORM EN 1094-1 (at 1400 °C) were carried out in succession on one and the same sample;
• • Thermal conductivity: According to DIN EN ISO 8894-1 (at 1200 °C);
• • Open porosity: Measured based on DIN EN 993-1. A 100 × 100 × 40 mm test piece was used and dried at 110 °C to constant mass (but at least for 2 hours). The mass (m _T in [g]) and the volume of the dried sample (V in [cm ³ ]) were then determined. The specimen was then soaked in distilled water in a desiccator at 20° C. and a pressure of 6500 Pa for 15 minutes, with the specimen being aligned vertically and the water level being at least 20 mm above the specimen. The sample was then removed and the mass of the sample infiltrated with water (m _G in [g]) was determined. The density ρ of the infiltration medium water was assumed to be 1 g/cm ³ . Finally, the porosity was calculated using the following formula: $$\mathrm{\varphi }=\left[\left({\text{m}}_{\text{G}}-{\text{m}}_{\text{T}}\right)/\left(\text{V}\cdot \mathrm{\rho }\right)\right]\cdot 100$$
  
• • Compressive strength: At 10% compression according to the DIN EN ISO 8895 standard;
• • The length to diameter ratio of the rice hull ash particles was determined using a Nikon SMZ745T stereomicroscope and a Tescan Vega IV SEM. All particles that were too large for the Tescan Vega IV SEM were examined using the Nikon SMZ745T stereomicroscope. The particles were applied to a sample carrier and placed in the measuring device. Particular care was taken not to mechanically destroy the samples. Specimen pieces, wel which were obviously destroyed during application were not taken into account. An optical image of the sample was then created and evaluated with the evaluation software of the respective device. The outer edges of the diameter at the thickest point were selected automatically or with a mouse click. The same was also done with the lengths. On the basis of these measurements, those particles were determined which have a length to diameter ratio of ≧3:1 and the proportion by weight of these particles in the rice hull ash was determined.

Examples 1 to 5 and Comparative Examples 1 to 2:

The vacuum molded parts of Examples 1 to 5 and Comparative Examples 1 to 2 in Table 1 were based on that in 1 described manufacturing process, the green part obtained being dried in a drying system at 110° C. to give the vacuum molded part. The amounts shown in Table 1 for components A) to F) were used for this.

• Komponente A):
  • • Rath ULTI^®-Wolle (PCW-Fasern)
• Komponente B):
  • • Biotherm B der Firma HAMAG (Reisschalenasche; Schüttdichte: 0,22 kg/dm³ (gemessen in Anlehnung an ÖNORM EN 1097-3); Glühverlust 4,17%; SiO2-Gehalt 89%; 79,4 Gew.-% der Reisschalenasche besteht aus länglichen Partikeln mit einem Längen zu Durchmesserverhältnis von ≥ 3:1)
• Komponente C1):
  • • Calcined Alumina AC34 der Firma ALTEO (Tonerde; Al₂O₃-Gehalt mindestens 99,5%; Glühverlust maximal 0,3%; Mittlere Partikelgröße d₅₀ (mittels lasergranulometrischer Messung (Cilas)): 75 µm)
• Komponente C2):
  • • Millisil^® W12 der Firma HPF The Mineral Engineers (Quarzsand; Schüttdichte nach DIN EN ISO 60 : 0,9 g/cm³; Spezifische Oberfläche nach BET (DIN ISO 9277) 0,9 m²/g; obere Korngröße d₉₅ 50µm; Mittlere Partikelgröße d₅₀: 16 µm)
• Komponente D1):
  • • Köstrosol^® 1540 der Firma CWK Chemiewerk Bad Köstritz GmbH (opalisierende, wässrige kolloidale Nanopartikel-Dispersion aus amorphen Siliziumdioxid (Kieselsol); spezifische Oberfläche: 194 m²/g; Festoffgehalt: 40 Gew.-%; Siliziumdioxidgehalt (als SiO₂): 38,8 Gew.-%; Dichte (bei 20 °C): 1,292 g/cm³; pH-Wert (bei 25 °C): 9,7)
• Komponente D2):
  • • Solvitose™ PLV der Firma Avebe U.A. (Kartoffelstärke)
• Komponente F):
  • • Wasser

Komponente Vergleichsbeispiel 1 Beispiel 1 Beispiel 2 Bespiel 3 Vergleichsbeispiel 2 Beispiel 4 Beispiel 5 A) [kg] / ([Gew.-%]*) 6,97 (30,49) 6,27 (28,35) 0,70 (3,06) 0,0070 (2,74) 6,97 (38,25) 6,27 (34,41) 0,70 (3,84) B) [kg] / ([Gew.-%]*) 0 0,70 (3,16) 6,27 (27,43) 0,0630 (24,70) 0 0,7 (3,84) 6,27 (34,41) C1) [kg] / ([Gew.-%]*) 2,32 (10,15) 4,65 (21,02) 2,32 (10,15) 0,0467 (18,31) 0 0 0 C2) [kg] / ([Gew.-%]*) 2,32 (10,15) 4,65 (21,02) 2,32 (10,15) 0,0234 (9,17) 0 0 0 D1) [kg] / ([Gew.-%]*) 9,76 (42,69) 5,11 (23,1 0) 9,76 (42,69) 0,1000 (39,20) 9,76 (53,57) 9,76 (53,57) 9,76 (53,57) D2) [kg] / ([Gew.-%]*) 1,49 (6,52) 0,74 (3,35) 1,49 (6,52) 0,0150 (5,88) 1,49 (8,18) 1,49 (8,18) 1,49 (8,18) F) [L] 250 250 250 3 250 250 250 Rohdichte [kg/m ³ ] 190 220 420 445 165 165 320 Klassifikationstemperatur [°C] 1450 1450 1450 1450 1450 1450 1450 Schwindung bei 1400°C [%] -0,54 -0,76 -0,39 -0,42 -0,63 -0,59 -0,45 Chemische Beständigkeit bei 1100°C [%] -0,18 -0,25 -0,30 -0,29 -0,21 -0,24 -0,27 Langzeitstabilität bei 1400 °C [%] -1<x<1** -1<x<1** -1<x<1** -1<x<1** -1<x<1** -1<x<1** -1<x<1** Wärmeleitfähigkeit [W/(mK)] bei 1200 °C 0,424 0,422 0,370 n.b. 0,512 0,499 0,455 Offene Porosität [%] 90 89 80 88 91 91 86 Druckfestigkeit [MPa] 0,4 0,4 0,4 0,4 0,3 0,3 0,2 n.b. = nicht bestimmt; * Bezogen auf die Summe der Komponenten A) bis E);** = Negative Werte bedeuten eine Verkleinerung und positive Werte eine Vergrößerung des Bauteils. The following materials were used for components A) to F):

• Component A):
  • • Rath ULTI ^® wool (PCW fibers)
• Component B):
  • • Biotherm B from HAMAG (rice hull ash; bulk density: 0.22 kg/dm ³ (measured based on ÖNORM EN 1097-3); ignition loss 4.17%; SiO2 content 89%; 79.4% by weight of Rice hull ash consists of elongated particles with a length to diameter ratio of ≥ 3:1)
• Component C1):
  • • Calcined Alumina AC34 from ALTEO (alumina; Al ₂ O ₃ content at least 99.5%; maximum loss on ignition 0.3%; mean particle size d ₅₀ (by means of laser granulometric measurement (Cilas)): 75 µm)
• Component C2):
  • • ^Millisil® W12 from HPF The Mineral Engineers (quartz sand; bulk density according to DIN EN ISO 60: 0.9 g/cm ³ ; specific surface area according to BET (DIN ISO 9277) 0.9 m ² /g; upper particle size d ₉₅ 50 μm ; Mean particle size d ₅₀ : 16 µm)
• Component D1):
  • • Köstrosol ^® 1540 from CWK Chemiewerk Bad Köstritz GmbH (opalescent, aqueous colloidal nanoparticle dispersion of amorphous silicon dioxide (silica sol); specific surface area: 194 m ² /g; solids content: 40% by weight; silicon dioxide content (as SiO ₂ ): 38.8% by weight; density (at 20 °C): 1.292 g/cm ³ ; pH value (at 25 °C): 9.7)
• Component D2):
  • • Solvitose™ PLV from Avebe UA (potato starch)
• Component F):
  • • Water

component Comparative example 1 example 1 example 2 example 3 Comparative example 2 example 4 Example 5 A) [kg] / ([% by weight]*) 6.97 (30.49) 6.27 (28.35) 0.70 (3.06) 0.0070 (2.74) 6.97 (38.25) 6.27 (34.41) 0.70 (3.84) B) [kg] / ([% by weight]*) 0 0.70 (3.16) 6.27 (27.43) 0.0630 (24.70) 0 0.7 (3.84) 6.27 (34.41) C1) [kg] / ([% by weight]*) 2.32 (10.15) 4.65 (21.02) 2.32 (10.15) 0.0467 (18.31) 0 0 0 C2) [kg] / ([% by weight]*) 2.32 (10.15) 4.65 (21.02) 2.32 (10.15) 0.0234 (9.17) 0 0 0 D1) [kg] / ([% by weight]*) 9.76 (42.69) 5.11 (23.1 0) 9.76 (42.69) 0.1000 (39.20) 9.76 (53.57) 9.76 (53.57) 9.76 (53.57) D2) [kg] / ([% by weight]*) 1.49 (6.52) 0.74 (3.35) 1.49 (6.52) 0.0150 (5.88) 1.49 (8.18) 1.49 (8.18) 1.49 (8.18) F) [L] 250 250 250 3 250 250 250 Density [kg/m ³ ] 190 220 420 445 165 165 320 Classification temperature [°C] 1450 1450 1450 1450 1450 1450 1450 Shrinkage at 1400°C [%] -0.54 -0.76 -0.39 -0.42 -0.63 -0.59 -0.45 Chemical resistance at 1100°C [%] -0.18 -0.25 -0.30 -0.29 -0.21 -0.24 -0.27 Long-term stability at 1400 °C [%] -1<x<1** -1<x<1** -1<x<1** -1<x<1** -1<x<1** -1<x<1** -1<x<1** Thermal conductivity [W/(mK)] at 1200 °C 0.424 0.422 0.370 nb 0.512 0.499 0.455 Open porosity [%] 90 89 80 88 91 91 86 Compressive strength [MPa] 0.4 0.4 0.4 0.4 0.3 0.3 0.2 na = not determined; * In relation to the sum of components A) to E);** = Negative values mean a reduction in size and positive values mean an increase in the size of the component.

Examples 1 to 5 and Comparative Examples 1 to 2 show that conventional high-temperature wool can be partially or almost completely replaced by rice hull ash, with the molded parts showing comparable properties in terms of classification temperature, chemical resistance and long-term stability at elevated temperatures. However, due to the use of sustainable and inexpensive rice hull ash, the method according to the invention also improves both the cost and the environmental balance.

Furthermore, the results from Table 1 show that it is possible with the method according to the invention to obtain vacuum molded parts with very good thermal insulation properties. This is reflected, for example, in the low thermal conductivity, which improves with higher rice hull ash content (see Examples 2 and 5). When using conventional fibers, open porosity occurs due to their structure, which is usually elongated, flexible and thin. As a result, thermal insulation can only be adjusted slightly via the raw density and the respective filler and is ultimately limited due to the fibers used or their porosity. In contrast, the platelet-shaped and tubular geometry of the elongated rice hull ash particles together with the vacuum forming process according to the invention presumably produces a truss-like three-dimensional structure in the vacuum formed part, which ultimately leads to a partially closed porosity in the vacuum formed parts according to the invention. Within the scope of this invention, cavities that are connected to one another and to the environment are referred to as open pores and cavities that are not connected to one another and to the environment are referred to as closed pores and the resulting porosity. This partially closed porosity achieves improved thermal insulation and consequently better energy efficiency for the vacuum molded part produced using the method according to the invention. Example 4 according to the invention shows improved thermal conductivity compared to comparative example 2, even with small amounts of rice hull ash, although they have the same bulk density and open porosity.

Comparative example 3:

In order to examine the influence of the method according to the invention on the vacuum formed parts, comparative example 3 was carried out based on example 3 from Table 1, in which the shaping was not carried out using the vacuum forming according to the invention but using a conventional method. Table 2 Comparative example 3 component Amount [g] a) 7.0 b) 63.0 C1) 46.7 C2) 23.4 D1) 100.0 D2) 15.0

In this comparative example 3, the raw materials were first mixed dry with a stirrer for 10 minutes in accordance with the quantities given in table 2. The resulting dry mix is in 4A) to see. The dry mixing seems to result in the inorganic fibers being torn and the ream shell ash being severely re-shredded. Accordingly, the fibers are not separated and there is therefore no flocculation. The same is observed when the inorganic fibers are added pre-chopped. The resulting dry mixture is powdery and, due to its lack of strength, does not have a malleable consistency, so that 100 ml of water were added in addition to the Kiesol sol ( 4 b) ). The water was sprayed into this dry mixture by means of a spray device in order to also get the silica sol into the fiber gussets of the anor to get ganic fibers. This mixture was then placed in a mold. The molded part was obtained as an inhomogeneous mass with a bulk density of 450 kg/m ³ ( 4c) ).

Comparative example 3 thus clearly shows that no molded parts with usable properties, let alone with good thermal insulation properties and at the same time low bulk densities of up to 150 kg/m ³ , could be produced from suspensions containing rice husk ash without vacuum forming.

Reference List

1

shaping tool

2

cylindrical hollow body

3

open end face, suspension inlet side

4

Lower face

5

vacuum separator

6

suspension

7

green part

8th

vacuum line

9

press stamp

10

mold tub

11

liquid level

12

bottom of the mold pan

Claims (18)

Method for producing a vacuum molded part, in particular a vacuum molded part as a thermal insulation element, the method comprising or having at least the following method steps: a) Filling a suspension (6) comprising or consisting of components A) to F) into a molding tool (1) which has a suspension inlet side (3), a vacuum separator (5) and a suspension inlet side (3) opposite side of the vacuum separator (5) attaching negative pressure device for applying a negative pressure and removing the via the vacuum separator (5) separated liquid from the suspension (6); b) applying a vacuum to the vacuum device, as a result of which the liquid in the suspension (6) passes through the vacuum separator (5) and a green part (7) is obtained on the vacuum separator (5); c) drying of the green part (7) in a drying plant to form the vacuum molded part; d) optional thermal treatment of the vacuum molded part; wherein the suspension (6) the components A) inorganic fibers, preferably selected from the group comprising or consisting of aluminum silicate wool, alkaline earth silicate wool, polycrystalline wool, mineral fibers, silica fibers, glass fibers, basalt fibers, ceramic fibers or mixtures thereof; B) rice hull ash; C) optionally at least one filler, preferably selected from the group comprising or consisting of alumina, quartz sand, silica, mullite, sillimanite, andalusite, silicon carbide, spinel, barium sulfate, boron carbide or mixtures thereof; D) at least one inorganic and/or organic binder; E) optionally auxiliaries and/or additives; F) liquid, preferably protic liquid, particularly preferably selected from the group comprising or consisting of water, methanol, ethanol, propanol or mixtures thereof, very particularly preferably water; includes or consists of. procedure after claim 1 , characterized in that the molding tool (1) is positioned in steps a) and b) in a mold trough (10) filled with the suspension (6) in such a way that the liquid level (11) of the suspension (6) reaches the end of the step b) above the suspension inlet side (3) of the molding tool (1) and then the molding tool (1) with the green part (7) located on the vacuum separator (5) is removed from the mold trough (10). procedure after claim 2 , characterized in that the mold pan (10) is continuously or discontinuously supplied with further suspension (6) via a storage tank. Method according to one of the preceding claims, characterized in that after method step b) the content of liquid in the green part (7) is further reduced by further application of a vacuum to the vacuum device. Method according to one of the preceding claims, characterized in that the green part (7) is post-processed mechanically after step b), preferably by pressing, rolling, sawing, stamping and/or cutting, with the green part (7) optionally being removed from the forming tool ( 1) is removed. Method according to one of the preceding claims, characterized in that the vacuum formed part is post-processed mechanically after step c) and/or d), preferably by sawing, grinding, turning, drilling, milling, punching and/or cutting. Method according to one of the preceding claims, characterized in that the vacuum molded part is treated after step c) and/or d) by applying hardeners and/or coatings. Process according to one of the preceding claims, characterized in that the suspension (6) contains the components A) to E) in the following amounts: A) 1.0 to 90.0% by weight, preferably 1.5 to 85.0% wt%; B) 1 to 85.0% by weight, preferably 1.5 to 80.0% by weight, particularly preferably 2.0 to 75.0% by weight; C) 0.0 to 50.0% by weight, preferably 1.0 to 45.0% by weight, particularly preferably 5.0 to 40.0% by weight; D) 5.0 to 70.0% by weight, preferably 7.5 to 70.0% by weight, particularly preferably 9.0 to 60.0% by weight; E) 0.0 to 5.0% by weight, preferably 0.1 to 2.0% by weight, the details being based in each case on the sum of components A) to E) and adding up to 100% by weight add %. Process according to one of the preceding claims, characterized in that the ratio of the total amount of components A) to E) to component F) in the suspension (6) is 1:10 to 1:80, preferably 1:25 to 1:65 . Process according to one of the preceding claims, characterized in that the rice hull ash of component B) consists of ≥ 10.0% by weight, preferably ≥ 50.0% by weight, particularly preferably ≥ 75.0% by weight, of elongated particles , which have a length to diameter ratio of ≥ 3:1. A method according to any one of the preceding claims characterized in that the inorganic binder is selected from the group comprising or consisting of colloidal silica, alumina, boehmite, mullite, wollastonite or mixtures thereof. Method according to one of the preceding claims, characterized in that the organic binder is selected from the group comprising or consisting of potato starch, corn starch, latex dispersions or mixtures thereof. Method according to one of the preceding claims, characterized in that the mass ratio of inorganic to organic binder is 5: 1 to 15: 1, preferably from 6: 1 to 13: 1, more preferably from 7.5: 1 to 12: 1, more preferably 9:1 to 11:1. Process according to one of the preceding claims, characterized in that the vacuum molding obtained has a bulk density of 150 to 2000 kg/m ³ , preferably 150 to 1000 kg/m ³ , determined according to ÖNORM EN 1094-4. Vacuum molding obtained or obtainable by a process according to any one of Claims 1 until 14 . Vacuum molded part, comprising or consisting of the components A) inorganic fibers, preferably selected from the group comprising or consisting of aluminum silicate wool, alkaline earth silicate wool, polycrystalline wool, mineral fibers, silica fibers, glass fibers, basalt fibers, ceramic fibers or mixtures thereof; B) Rice hull ash, this preferably consisting of ≧10.0% by weight, more preferably ≧50.0% by weight, particularly preferably ≧75.0% by weight, of elongated particles which have a length to diameter ratio of ≥ 3:1; C) optionally at least one filler, preferably selected from the group comprising or consisting of alumina, quartz sand, silica, mullite, sillimanite, andalusite, silicon carbide, spinel, barium sulfate, boron carbide or mixtures thereof; D) at least one inorganic and/or organic binder; E) optionally auxiliaries and/or additives. Vacuum molding according to claim 15 or 16 , characterized in that the vacuum molded part is a thermal insulation element. Use of a vacuum molding according to one of Claims 15 until 17 as thermal insulation elements for high-temperature systems, preferably for laboratory furnace construction, special furnace construction and/or industrial furnace construction, in particular for high-temperature systems with operating temperatures of 400°C to 1650°C.

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