SVEDA ALOIS (CZ)
SVEDA ALOIS (CZ)
| WO2006049444A1 | 2006-05-11 |
| DE19805889A1 | 1999-08-19 | |||
| FR2305407A1 | 1976-10-22 |
CLAIMS
1. Method of production of insulating ceramic porous article, characterized in that a squeezable elastic porous form which has the pores in shape of closed cells interconnected via voids in walls, is sunk into a liquid ceramic mixture that is absorbed into the pores of the elastic form after pressure on the squeezed form is released, the filled form is heated in order to release the liquid part of the mixture, the absorbed ceramic mixture is getting dried on the walls of the pores creating shape of interconnected cells, subsequently it is fired and the elastic material making up the walls of the form is burned.
2. Method of production of insulating ceramic article according to claim 1, w h e r e i n characterized in that a liquid ceramic mixture that is absorbed into the pores of the elastic form contains water in an amount at least 40 % by the weight of the mixture.
3. Method of production of insulating ceramic article according to claim 2, characterized in that a liquid ceramic mixture which contains water in an amount of 60 - 90 % by weight of the mixture is sucked into the pores of the elastic form.
4. Insulating ceramic article, particularly for acoustic and thermal insulating products produced according to claim 1, characterized in that it has a porous structure with the pores in the shape of closed cells, 5 to 18 pores per linear centimeter, the cells being interconnected through voids in ceramic walls, which are made by fired ceramic material stuck on walls of elastic porous form during drying.
5. Insulating ceramic article according to claim 4, characterized in that the amount of the pores is 9 to 12 per linear centimeter.
6. Insulating ceramic porous article according to claim 4, characterized in that the thickness of the ceramic walls of the pores is between 0.035 and 0.65 millimeters.
7. Insulating ceramic porous article according to claim 6, characterized in that the thickness of the ceramic walls of the pores is between 0.1 and 0.4 millimeters. |
Insulating Ceramic Porous Article and Method of its Production
Field of Invention
This invention relates to insulating, ceramic, porous articles and their method of production. In particular, the invention relates to fire insulations, acoustic insulations and thermal insulations.
Description of the Prior Art
The advantages of porous insulating articles are their low density, low thermal conductivity and ability to absorb sound.
The production of insulating ceramic articles usually has several phases, specifically: preparing a ceramic mixture, forming the desired shape from the mixture, then drying, firing and eventually adjusting the size and shape.
One typical method of producing insulating porous ceramic articles is foaming. With this method, a foaming substance that creates small bubbles is added to a ceramic mixture. The bubbles (pores) remain in the article even after its firing when the material hardens and strengthens.
Another well-known way to produce insulating ceramic articles involves adding small organic particulates to the mixture. During firing, the particulates burn away and the spots become pores.
Among currently known methods is production of ceramic filters. Production of the ceramic filters involves a fiber form, which allows the liquid ceramic mixture to flow through freely. When the form is poured over or dipped into the liquid ceramic mixture, the fibers are coated by the ceramic mixture and any excess liquid flows out of the form or is removed. After the excessive mixture is drained away, the form is- dried and fired. The flow ceramic filter does not accomplish needs of insulating materials.
Using these current methods of production, it is not feasible to reduce the density or enhance the insulating properties of the porous insulating articles. If more foaming substance or organic particulars are added to ceramic mixture, the product's strength decreases, as does its pressure resistance.
The purpose of this invention is to overcome the disadvantages of the current methods described above, thereby producing insulating, ceramic articles with lower density, better insulating properties, more strength and higher pressure resistance. The purpose of the invention is to maintain a production method of insulating ceramic articles with all of the above-mentioned properties.
Background of the invention
The insulating ceramic articles this invention creates will have a porous structure. The walls of the pores are made of fired ceramic material filling up the space originally formed by an elastic, porous form.
This production method is advantageous when the walls of the pores are made of ceramic material which is produced by firing a dried, water-based ceramic mixture originally containing water in an amount of at least 40 % by weight of the mixture.
It is also advantageous when the ceramic material is produced by firing a dried water-based ceramic mixture originally containing water in an amount of 60 - 90 % by weight of the mixture .
This invention's unique production method is accomplished as follows. When the liquid ceramic mixture is prepared, it is absorbed into the pores of an elastic porous form, after pressure on the squeezed form is released. Then the absorbed ceramic mixture is dried on the walls of elastic form pores. Finally, during the firing process, the elastic material making up the walls of the form is burned away.
It is advantageous if the pores of the elastic form are filled by a water-based ceramic mixture containing water in an amount of at least 40 % by weight of the mixture.
It is advantageous if the pores of the elastic form are filled by a water-based ceramic mixture containing water in an amount of 60 - 90 % by weight of the mixture.
The elastic body used as a form for the production of the porous, insulating ceramic article needs to be initially squeezed in order to get out any air or other gaseous substance in its pores. After releasing the pressure, the form returns to its original shape as it absorbs the ceramic mixture into its pores.
After the pores are completely filled, and the form is removed from the solution, the elastic form must be able to hold the ceramic mixture effectively as it dries. Therefore, it is important to select an elastic form of the right material with pores of the right size, structure and shape.
The elasticity of polyurethane foam is advantageous, as it is able to absorb a large volume of ceramic mixture.
The elasticity of polyester foam is also advantageous, as it is able to absorb a large volume of ceramic mixture.
As described above, the liquid ceramic mixture will fill up the pores of elastic form. In order to hold the mixture in the pores of the elastic form, a ceramic mixture with the proper density and viscosity must be prepared.
Ceramic mixtures can have various bases, but for use in this process it is best to use a water-based solution.
To significantly reduce the weight of the ceramic product, it is advantageous using a solution with water in the ratio of 1 weight element of ceramic material and two or more weight elements of water. The amount of the water can be up to 60 - 90 % by weight of the mixture. The implication of a higher proportion of water in water-based ceramic mixture is a large decrease in the weight of the ceramic mixture as it dries.
The liquid ceramic mixture inside the pores of the elastic form starts to create a new porous structure as it dries. The new pores are bounded by the ceramic material which becomes
stuck on the walls of the form' s pores during the dehydration process.
Because the initial liquid ceramic mixture contained a large percentage of liquid, there is a large change in weight and volume during the drying process. Therefore, it is feasible to produce insulating porous ceramic articles with very low density.
The primary decrease in weight occurs during the drying of the ceramic mixture inside the elastic form. In addition, there is a small decrease of weight (as a single digit percentage) during the firing.
There is also a significant effect on the product's volume during drying and firing.
During firing, the rest of the liquid is released, the porous structure finalizes, the elastic form burns away, and the ceramic article hardens and strengthens. The thickness of the pore walls is small compared to the size of the pores, approximately 1% - 10%. After the elastic form burns away, the ceramic material essentially fills up the space of the burned elastic form. In this way the insulating porous ceramic article with high strength is created.
Another advantage of using the elastic form, apart from its ability to absorb and retain the liquid ceramic mixture, is its change in size during drying and firing. The elasticity of the form and its large changes of volume are beneficial because the insulating porous material does not break (rupture) during drying and firing and therefore the created
porous structure remains free of local damage.
The insulating, porous, ceramic articles produced by this method have very low density, lower than 1000 kg/m3 and it is easy to reach density lower than 500 kg/m3. Their insulating properties and crushing strength are better than comparable articles produced using current technologies.
If the liquid mixture consists of refractory material, the articles from the insulating porous ceramic material can be used as insulating firebricks.
The described production method is different from the production of ceramic filters, during which it is desirable that liquid ceramic mixture coats the fibers therefore the mixture does not fill up the pores. The mixture flows out of the porous body in order to create open mutually connected pores. Whereas, with this invention, the liquid ceramic mixture is retained in the pores of the form and after the firing the maximum number of closed pores are created.
Description of Drawings
The phases of the transformation of the liquid, ceramic mixture filling the pores of the elastic form, into new solid porous structure are depicted on the pictures where:
Picture Ia is the profile of the elastic form after the liquid mixture fills up the form - two pores of the elastic form are filled with liquid ceramic mixture.
Picture Ib shows the situation after drying - the ceramic material sticks to the walls of the elastic form and new pores are created.
Picture Ic shows the situation after firing - the elastic form is completely burned away and a new porous structure is created. Sequence Ia-Ic also symbolically shows the volume changes .
Example 1 of the Preferred Embodiments
A liquid ceramic mixture containing 2,2 kg of finegrained, plastic clay (SiO2 50%, A12O3 33%, Fe2O3 2,5%) mixed with 4,51 of water. The elastic porous form is Molitan®, a polyester foam with a density of 30 kg/m3, pressure resistance of 3,7 kPa (40% according to Czech State Norm 645441) medium- sized pores (14-16 per inch) . The form - the Molitan block with sizes of 300x150x90 mm - is squeezed in a way that air comes out of its pores. The form is sunk in liquid ceramic mixture, the pressure is released and the form absorbs the ceramic mixture into its pores. The immersed form can be compressed several times and the pressure released out or otherwise manipulated to absorb up the maximum amount of liquid mixture into its pores and to re-gain the initial shape of the form. After fully absorbing the mixture into the pores, the form is taken out of the mixture. Ceramic mixture remains inside the pores of the form. The elastic form recovers its original size and shape.
Picture Ia shows the profile of the elastic form after the mixture is absorbed: position 1 is the wall of the pore of the
elastic form; two interlinked pores of the form are filled by liquid ceramic mixture 2.
During drying, as the water is being released a new porous structure is being created and the volume of the form is decreasing. In order not to harm the article, the essential rules for drying of ceramics need to be followed.
Picture Ib shows the situation after drying, the ceramic material sticks to the walls of the elastic form 1 and new pores are created; position 3 is the dried ceramic material and position 4 shows the pores created by release of liquid from the ceramic mixture.
During firing the rest of the water is removed and the elastic form is burned; the porous structure finalizes and ceramic material hardens and strengthens. Firing can be at a temperature of 1450 0 C, with a pause at the highest temperature in order to balance the temperature across the whole profile of the form. Also, during firing the article gets smaller. Picture Ic shows the situation after the firing - the elastic form is gone and the new porous structure is created; position 5 indicates the pores after the firing and position 6 the fired ceramic material comprising the new walls of the pores.
After firing, the ceramic article is cut to obtain the desired size and shape. The result is a lightweight insulating firebrick of the desired shape and size, with a temperature classification of 1427 0 C (2600 0 F), density 520 kg/m3 and crushing strength 2,5 MPa.
Example 2 of the Preferred Embodiments
The content of the liquid ceramic mixture is the following (amount in percentage by weight of the liquid mixture) : 13% Sedlecky Kaolin Ia Czech State Norm 72-1310 (content SiO2 47%, A12O3 37%, K2O 0,95%, Fe2O3 0,85%), 20% Kyanite 100 producer Virginia Mining Corporation (content SiO2 40,3%, A12O3 57,5%, TiO2 1,2%, Fe2O3 0,6%), 67% water. The elastic porous form is Molitan®, a polyester foam with a density of 30 kg/m3, pressure resistance 3,7 kPa (40% according to Czech State Norm 645441) medium-sized pores (14-16 per inch), in a block sized 300x150x90 mm. The production method of this invention and firing at temperature 1550 0 C results in a lightweight insulating firebrick with a density of 450 kg/m3, temperature classification 1538 0 C (2800 0 F), crushing strength at 4 MPa and chemical content SiO2 45,1%, A12O3 51,7%, TiO2 1,1%, Fe2O3 0,7%.
Example 3 of the Preferred Embodiments
The same content as in example 2, the liquid ceramic mixture is made of (amount in percentage by weight of the liquid mixture): 13% Sedlecky Kaolin Ia C " SN 72-1310 (SiO2 47%, A12O3 37%, K2O 0,95%, Fe2O3 0,85%), 20% Kyanite 100 producer Virginia Mining Corporation (SiO2 40,3%, A12O3 57,5%, TiO2 1,2%, Fe2O3 0,6%), 67% of water. The elastic porous form is Molitan®, a polyester foam with a density of 30 kg/m3, pressure resistance 3,7 kPa (40% according to Czech State Norm 645441) medium-sized pores (14-16 per inch), in a block sized 300x150x90 mm. The production method of the invention and firing at temperature 1660 0 C results in lightweight insulating firebrick with a density of 600 kg/m3, temperature
classification 1649 0 C (3000 0 F), crushing strength 6MPa and chemical content SiO2 45,1%, A12O3 51,7%, TiO2 1,1%, Fe2O3 0,7%).
Industrial Application
Insulating, porous ceramic articles manufactured with this method are useful for the following products: insulating firebricks, lightweight ceramics, ceramic articles used for thermal insulation, ceramic articles for other insulating purposes (e.g. sound-insulation) and other construction materials.