DE10137462C1 - Production and drying of thick walled components used in the concrete, ceramic and refractory material industries comprises using micro-fine flexible hot conductors made from thin metal foils as energy source - Google Patents

Abstract

Production and drying of thick walled components comprises using micro-fine flexible hot conductors made from thin metal foils of less than 0.6 mm thickness as energy source. The components molded from a wet molding composition are heated to 500 deg C or more and dried. Preferred Features: The metal foils have a thickness of 0.04-0.5 mm and are made from sheet metal, steel or high grade steel having an ohmic resistance of 0.1-1.5 ohm/m. The energy source is operated with a voltage of 2-70 V.

Description

The invention relates to a method for producing and drying thick-walled Components of the concrete, ceramic and refractory industries that come from wet Molding compounds are produced in a mold or layered construction in which the molding compound is compressed and dried and optionally sintered and before, during and / or after molding the molding compound, one as an electrical one Resistance heating is an effective energy source for drying the component is stored from the inside out using thermal energy, and Components manufactured using the process.

From the German patent DE 887 171, the production of large formatted components made of lightweight materials with cavities are known, these cavities are formed with the help of metal packing elements and in These metal packing elements contain heating resistors. The metal packing including the heating resistors are cast after molding removed from the cavities. In the manufacture of these cavity moldings the problem arises of a compact solid body that is in its entirety must be dried, taking moisture from the inside to the outside must hike, not.  

Drying large format compact components in the concrete and Refractory industry is usually done either in a dryer, whereby on all sides from the outside in or on site from one side, d. H. component is dried continuously from one side to the other, causing a temperature gradient during drying in both cases arises within the component. The temperature moves from the outside inside. This will make the water corresponding to the progressive Temperature front heated from the outside to the evaporation temperature. The already dried parts in the outer area of the component already have much of their pores and capillaries are closed. This results in a Increase in the vapor pressure in the core of the component. Only now does that happen Drying up and the emigration of water vapor from the inside out outside instead. The narrowing of the pores in the outer area will Diffusion of water vapor hindered from the inside out. Dependent The drying speed in the component is so high Vapor pressure that there is a risk of the component exploding and this can also be done. This drying process and the gluing of the Capillaries and pores are still added by chemical binders influenced, which crystallize on the surface of the component and the pores close. Another danger is that the Drying process from the outside to the inside of the outer skin Shrinkage process begins and the capillaries clog, causing the Drying process is additionally hindered. Cracks, flaking and Explosions are the result.

Furthermore, the drying of large-format components by means of Microwaves have been tested for some time, which is only an example of the WO 92/08084 is referred to. For large components, this type of Drying did not lead to a breakthrough, since the entire component is simultaneously and thus all water molecules are heated. The warmed Water molecules are directional, i.e. H. they have no flow direction in which can evaporate the heated water. With wall thicknesses of 200 mm thick, a drying time of 5 to 6 days is common. On  Another problem is the uniformity of the drying and the Heat transfer that is not achievable.

From DE 198 16 086 A1 a method for drying is now large format monolithic components known in the concrete and refractory industries become where drying from the inside out of the center of the component to the outside. Here, in the center of the component during this Shaping an energy source, which is due to its structure enables thermal energy to be generated in the center of the component. This energy source is made using carbon fiber structures such as Carbon fiber fabrics, carbon fiber felts or carbon fiber rods that go against each other if necessary, have it flexibly adapted to the component. The coal fiber structures are used to work on the principle of large surface as an electrical resistance heater a controllable high energy density and Generate heat in the component. However, since the carbon fibers at approx. 350 ° C on the fiber surface start to oxidize and burn, has the consequence that with thicker wall thicknesses and larger Temperature gradients within a component or masonry either the Drying or annealing time is very long or depending on the thermal conductivity (at Insulating materials) on the heating conductors are too high to be able to dry and heat them sufficiently.

It is therefore particularly important for thick-walled or large-format compact components drying and tempering at higher temperatures is desirable to achieve the Shorten drying time. At the same time, they should be wet or damp Molding cast components, such as porous concrete parts or microporous high density concrete parts, refractory concrete parts etc. fast, effective and can be dried inexpensively without the need for thick-walled compact Components are damaged.

According to the invention, this object is achieved by the method according to claim 1 solved.  

Advantageous developments of the method according to the invention are the characteristic features of the subclaims. A Formation of a component of the concrete, ceramic and Refractory industry made from wet molding compounds is marked through built-in heating conductors made of metal foils made of stainless steel, steel, sheet metal of thin strips with a thickness of 0.04 to 0.5 mm and a width of 5 up to 50 mm and a connection for a voltage source for permanent heating.

The inventive method is characterized in that Energy source microfine flexible heating conductor made of thin metal foils of a thickness less than 0.6 mm are used and the heating conductors at temperatures up to 1200 ° C are heated, the molded from the wet molding compound Components are heated to temperatures of 500 ° C or more while doing so dry. This makes it possible to also build thicker walls in components to dry for a reasonably short period of time without the heating conductor as in Carbon fibers suffer damage.

A major problem when installing heat conductors in the wet Molding compound is the avoidance of tension and stress cracks in the component to be dried due to the heat conductor. This danger is caused by the Installation of microfine heating conductors in the form of a film is achieved, causing tension in refractory or ceramic structure of the components during drying is avoided. Heating conductors have proven to be particularly advantageous Metal foils with a thickness of 0.04 to 0.5 mm, preferably 0.04 to 0.1 mm proved. This makes it possible to insert very flexible heating conductors in tape form Introduce molding compound. The bands have a width of 5 to in particular 50 mm. The belts can be connected to each other like a kind of rust be equipped with a connection for a voltage source be, the connection of the molding compound and the component is brought out. The individual metal foil strips are preferred here arranged parallel to each other with the same distance a and are electrically connected to each other to form the entire heating conductor. The distance a  the metal foil strips from each other is preferably 20 to 30 cm. With Using the metal foils as heat conductors, the components can both be dried and be annealed afterwards. Using the metal foils as a heating conductor temperatures of over 1000 to about 1200 ° C can be reached. in this connection the wet molding compound - concrete - can be heated to around 600 ° C.

By using metal foils in tape form with widths from 5 to 50 mm, preferably from 20 to 40 mm, a higher heat transfer is possible than this is possible with conventional heating wires. Preferred as the heating foil heat-resistant steel foils, especially stainless steel foils are used. The ohmic Resistance should be 0.1 ohm / m to 1.5 ohm / m. The source of energy is for heating conductors in tape form with a length up to about 10 m with a Operate voltage from 2 to 70 V, depending on the temperature to be reached. at Heating conductors with a length over 10 m up to 50 m must be higher Voltages up to 250 V can be worked. The desired temperature The process for drying and tempering the component is controlled by the Tension reached. Advantageous training to control the Drying process are the characteristic features of claims 9 and 10 removable.

By using the thin metal foils as heating conductors, they have a high Flexibility and destruction, d. H. Tension build-up within the Component does not take place.

Heating with heating wires is a technically known fact, though the use of heating wire in ceramic to remain in this is not enforced has insufficient energy when inserting thin wires can be transferred to heat the mass and partially the wires Brittle and break easily when used multiple times. When using thicker heating wires that have a sufficiently large energy transfer enable, there is a risk of destruction of the refractory structure higher temperatures in contact with the heating wires.  

The metal foils used according to the invention do not have these disadvantages on. They have a large surface for heat transfer and only form very small - microfine - gaps in the component. Still, they can high temperatures are heated, causing the drying process is accelerated. By reaching higher temperatures during the the subsequent drying process of the refractory parts or Furthermore, all crystal water can be removed from concrete components, which means a further increase in quality for ceramic material.

The method according to the invention also works with a drying process, that goes from the inside out and an in-situ drying and tempering includes. In this way, the method according to the invention is used even when using metal foils as heat conductors and very high temperatures no vapor tension inside the structure of the component to be dried, therefore no pre-damage caused by cracks and flaking. The setting of the cement can be regulated by controlling the temperature and thus the quality of the product to be manufactured. Depending on the structure of one The heating conductors become part of the center or in the area of the middle level of a component inserted and remain in the component after drying and Annealing.

In addition, there is the further advantage that if the heating conductor is left on within the component these can be used as permanent heating Keep vessels at temperature. For example, it is possible in the Light metal industry, for example aluminum industry, channels for the Cast aluminum from refractory components produced according to the invention to use built-in heating conductors made of metal foils, these channels with With the help of the built-in heating foils can be kept at temperature. Such heating foils / metal foils built into a component can also be used during operation or after downtimes to heat up Refractory components, masonry or the like can be used.  

If a component or a wall is built up in layers, it is possible to arrange the heating conductor between two layers of a component, wherein a layer adjacent to the heating conductor consists of a wet one Drying molding compound is molded while the other layer for example is an insulating material. The drying of inside out through the wet molding compound, while on the on the other hand, the insulating material stops the heat transfer.

By combining the heating foils according to the invention with external ones Insulation layers can the energy required to warm up be significantly reduced to 1/5. By the invention used and embedded in the components as a heat conductor in the component to be dried, tempered, burned, it is possible to use these To house insulation materials, whereby the energy loss down to 1/5 in Compared to a drying process without insulation is minimized and corresponding energies can be saved during drying and tempering.

According to the invention, all heat-resistant stainless steel foils can be used as heat conductors are preferably used, in particular with thicknesses between 40 to 500 µm and widths from 10 to 100 mm. When using stainless steel foils for Drying and tempering of wet molding compounds of concrete, ceramic and Refractory industry can easily reach higher temperatures above 1000 ° C be heated with a very good heat transfer. The used Metal foils can be made with existing known elements, electrical Connections can be easily contacted. The used as heating conductors Metal strips can have lengths of up to 50 m, depending on the size of the component.

Incidentally, with a gap of 100 microns in the component Surface tension of the steel too large to be in a possible gap penetrate.

In Fig. 1 a component 1 is shown schematically which is molded of a refractory material in a mold, with the center a power source made of stainless steel foil strips 2 in the manner of a grid is embedded in the component. The individual heating tapes made of stainless steel foil are electrically connected to each other and the connection 3 is led out to the side. The number and size of the heating tapes 2 made of stainless steel foil, for example, depends on the size of the component 1 , ie on the mass to be dried. This also applies to the distance a between the heating tapes 2 .

In Fig. 2, a layered structure of a component 1 is shown schematically in cross section, with an insulating material 11 being applied to a tank wall 12 , to which the energy source in the form of the heating conductor made of metal foil strips 2 is applied with the connection 3 led out and then the one forming the concrete component wet molding compound 10 is applied. When the heating conductor 2 is heated by applying a voltage, the heat also exits from the inside out in the direction of the arrow P and the drying process also takes place from the inside out, shielded on the opposite side by the insulating material 11 . Such an arrangement is also energy efficient in terms of drying.

In the example of Fig. 1, the drying of the component 1 takes place uniformly in all directions from the inside to the outside, and the heating conductor in the form of the metal foil strips 2 remains in the component 1 after the drying and tempering. Because of the small dimensions of the metal foil strips 2 , the component is not damaged by tension or the like.

Claims (12)

1. A method for producing and drying thick-walled components of the concrete, ceramic and refractory industry, which are made from wet molding compounds in a mold or layered construction, in which the molding compound is compressed and dried and optionally sintered and before, during and / or after Forming the molding compound is an energy source effective as electrical resistance heating for drying the component by means of thermal energy from the inside to the outside, characterized in that microfine flexible heating conductors made of thin metal foils with a thickness of less than 0.6 mm are used as the energy source and the heating conductors are heated up to temperatures are heated to 1200 ° C, the components molded from the wet molding material warming up to temperatures of 500 ° C or more and drying. 2. The method according to claim 1, characterized in that as a heating conductor Metal foils with a thickness of 0.04 to 0.5 mm are used. 3. The method according to claim 1 or 2, characterized in that the Heating conductor in the form of strips with a width of 5 to 50 mm become. 4. The method according to any one of claims 1 to 3, characterized in that as a heat conductor metal foils made of sheet metal, steel, stainless steel with a Ohmic resistance from 0.1 Ohm / m to 1.5 Ohm / m used become. 5. The method according to any one of claims 1 to 4, characterized in that the energy source with a voltage of 2 to 70 V with heating conductors up is operated to about 10 m, the desired temperature profile for drying the component is achieved by controlling the voltage.   6. The method according to any one of claims 1 to 5, characterized in that that the components on for removing crystal water from the wet Molding compound sufficient temperatures are heated. 7. The method according to any one of claims 1 to 6, characterized in that that the heating conductor in the center or in the area of the central plane of a Component are stored and in the component after drying remain. 8. The method according to any one of claims 1 to 6, characterized in that that the heating conductor is arranged between two layers of a component be, wherein a layer applied to the heating conductor from a wet is molded to dry molding compound. 9. The method according to any one of claims 1 to 8, characterized in that the temperature of the component during the drying process inside and measured outside and the measured values obtained for control and Monitoring the drying process, in particular by means of the Energy source generated temperature and temperature curve set become. 10. The method according to any one of claims 1 to 9, characterized in that for temperature measurement when the molding compound is introduced into the Form thermometer elements, such as thermometers, for measuring the Temperature and further sensors for the detection of moisture inserted into the component via a conductivity measurement and are poured and further thermometer elements and / or Sensors for the detection of moisture via a conductivity measurement be attached to the surface of the component. 11. The method according to any one of claims 1 to 10, characterized in that that the surfaces of the component during the drying process be isolated.   12. Components of the concrete, ceramic and refractory industries, made from wet molding compounds such as concrete, porous concrete, microporous high density Concrete, characterized by built-in heating conductors made of metal foils Stainless steel, steel, sheet metal in the form of thin strips with a thickness of 0.04 mm up to 0.5 mm and a width of 5 to 50 mm and a connection for a voltage source for permanent heating.