DE10306910A1 - Firing ceramic molded parts comprises heating molded parts in first phase to maximum temperature in furnace, cooling in second phase, and coating with coating material in cooling phase - Google Patents

Abstract

Firing ceramic molded parts comprises heating the molded parts in a first phase to a maximum temperature in a furnace, cooling in a second phase, and coating with a coating material in the cooling phase. An independent claim is also included for a furnace for firing ceramic molded parts.

Description

The invention relates to a method for firing ceramic molded parts and an associated furnace.

Ceramic molded parts can be in continuous or discontinuous ovens in one or more stages Procedures are burned.

An example of a continuous oven is a tunnel furnace, these subforms such as roller furnaces, pusher plate furnaces or the like includes. An example for a batch furnace is a bogie hearth furnace.

In any case, the molded parts in a first phase heated to a maximum temperature in the oven and subsequently cooled in the oven again.

In the continuous oven the temperature profile in the longitudinal direction the furnace (according to the transport direction of the molded parts to be fired) represent. The temperature curve is in a discontinuous oven exclusively time-dependent, there the firing material is not moved.

Ceramic moldings based on this Way of firing are, for example, tiles, porcelain, Sanitary ware, but also special products such as ferrites.

Products like porcelain or sanitary ware are common glazed. The glaze forms a closed, smooth coating for the ceramic shards underneath (shards = fired ceramic Body).

Despite the formation of a closed, glass-like surface contaminate the ceramic products mentioned relatively quickly. It has therefore been considered in the past how pollution can at least be reduced.

In the DE 101 12 170 A1 a method is presented to make the surface of a silicate ceramic product hydrophobic or ultraphobic. A thin intermediate layer of at least one organometallic compound of silicon is applied to the surface; the product coated in this way is then heated. In a third step, an outer cover layer with the desired ultraphobic or hydrophobic properties is applied. The organometallic intermediate layer forms a kind of adhesion promoter between the ceramic base body and the outer, dirt-repellent cover layer, which can consist of a permanently elastic and / or thermoplastic polymer.

This is a multi-stage process relatively complex. In any case, those with the organometallic Connection coated objects first passed through an oven again be before the final Cover layer can be applied.

• – feinstteilige Oxide (Nanopartikel)
• – Oberflächenmodifikator
• – gegebenenfalls Hilfsstoffe, zum Beispiel amphiphile Stoffe.

In the DE 101 16 200 A1 different coating materials for ceramic products are presented. The coating materials essentially consist of the following components:

• - very fine oxides (nanoparticles)
• - surface modifier
• - optionally auxiliary substances, for example amphiphilic substances.

Suitable very finely divided oxides (with a grain size in the nanometer range) are, for example, silica sols, but also nanoparticles based of titanium oxide, zirconium oxide, aluminum oxide or other metal oxides.

As surface modifiers for the used Oxide nanopowder are called various alkali and alkaline earth ions that the Stabilization of the oxide fine particles in aqueous Serve dispersion. You can also inorganic or organic salts of aluminum, zirconium, zinc or Titanium compounds come into question which are suitable for the oxides stabilize in a suitable pH environment.

The auxiliaries mentioned include in addition Surfactants hygroscopic substances such as salts or organic compounds, which reinforce the hydrophilic effect of the inorganic network. Specifically named become hydrophilic polymers.

For further details, reference is made to the disclosure of the DE 101 16 200 A1 Referred.

The material is processed in liquid form the surface applied and then dried. A subsequent one Temperature treatment can increase the durability of the hydrophilic coating increase. The maximum temperature is the decomposition / melting temperature of the Coating material determined. The separate temperature treatment delayed the completion more salable Products and significantly increases the cost of production.

In the DE 201 05 361 U1 Finally, it is proposed to wipe ceramic molded parts with a cloth that is soaked in a specific coating fluid. It is readily apparent that such a method cannot be implemented on an industrial scale.

The invention lies in that The task is to offer ceramic molded parts that are less sensitive to dirt and are inexpensive to manufacture in a simple process to let.

The basic idea of the invention is to integrate the coating processes mentioned in a furnace for firing ceramic molded parts. In extensive preliminary tests de found that it is not necessary to subsequently coat a fired, possibly glazed product and then subject it to a thermal aftertreatment; rather, the thermal treatment of the coating material can take place directly in the furnace during the firing process of the ceramic molded parts.

The basic idea of the invention is first to be explained generally using the example of firing sanitary ware:
The ceramic parts are placed on kiln furniture and placed in a furnace via a lock. There they are heated in a first phase from ambient temperature to maximum temperature (e.g. 1,350 ° C) (to carry out the ceramic sintering process). On their way through the furnace, they are then cooled again until the furnace exit to approximately 100 ° C. During this second phase (in which there is a temperature interval between 1,300 and 100 ° C.), the products fired immediately before are coated according to the invention on the ceramic body or a corresponding glaze.

In other words, in one Process, the ceramic parts are fired, if necessary glazed and in any case additionally coated.

• – die Formteile werden in einer ersten Phase in einem Ofen auf eine Maximaltemperatur erwärmt,
• – die Formteile werden in einer anschließenden zweiten Phase im Ofen wieder abgekühlt,
• – während der Abkühlungsphase werden die Formteile mit mindestens einem Beschichtungsmaterial im Ofen beschichtet.

According to this, the invention in its most general embodiment relates to a method for firing ceramic molded parts with the following features:

• The molded parts are heated to a maximum temperature in an oven in a first phase,
• The molded parts are cooled again in a subsequent second phase in the oven,
• - During the cooling phase, the molded parts are coated with at least one coating material in the oven.

The coating material can be selected from the known coating materials, as described, for example, in the publications mentioned DE 101 16 200 A1 and DE 101 12 170 A1 are described.

The decisive difference to State of the art is that the coating with in-situ the burning process of the articles takes place.

A possible coating material is based on very finely divided metal oxides. The term "finely divided" includes powder or flour-shaped Treatments with particle sizes in the nanometer range. This Lead very fine powder to a microstructure that is beneficial for subsequent pollution counteracts (so-called lotus effect).

The coating material can be used as Suspension, dispersion or aerosol can be applied. It is sprayed on, for example or sprayed on. You can do this especially in the walls and nozzles corresponding to the ceiling of the furnace are provided. The Nozzles can be relative protrude far into the furnace (furnace duct). That way it can Coating material more targeted to the products to be coated be directed. At the same time, the coating material is prevented for example on the furnace walls reflected.

For this purpose, the air duct in the Furnace or furnace channel can be adjusted. For example a furnace channel can be parallel to the direction of transport of the fired material an air flow be generated. Particles of the coating material that are uncontrolled flying around are carried away and carried away before they undesirably open can knock down the inside of the furnace wall or ceiling.

Alternatively, or in addition, corresponding ones Suction devices are provided to remove excess coating material lead away.

Advantageously, the in the so-called cooling phase residual heat of the exploited ceramic goods to apply the coating and to stabilize. This is an essential procedural one Advantage. At the same time leads this process also drastically reduces the Cost because of a separate, additional thermal treatment process can be dispensed with.

Depending on the coating material and suitable / necessary temperature for curing it can be described Feeder device of the coating material in different zones of the furnace or provided at different times of the burning process or to be activated.

An associated oven points accordingly at least a device for feeding a coating material in the furnace and distribution of the coating material on surfaces of the fired molded parts.

With a discontinuous oven the device is activated after the maximum oven temperature is reached. In the case of a continuous furnace, the device in the so-called cooling zone educated.

According to the invention, “cooling zone” is understood to mean the entire furnace area, which connects to the furnace zone in which the maximum temperature is reached becomes.

Similar like burners in furnace walls or the furnace ceiling are arranged, the facilities to distribute the coating material in the wall and / or ceiling of the furnace.

The products coated with a method according to the invention or in an associated oven are distinguished by a significantly reduced risk of contamination. The SI OH groups of the ceramic base body or the glaze together with the molecules of the coating material lead to a firm connection between the coating and the base body. The coating itself (with its microstructure) makes it difficult for water and foreign particles to adhere ("lotus effect"). Any contaminants that build up a dust-like deposit on the coated surface can be easily rinsed off with water. This is particularly useful for Articles of sanitary ceramics of great importance. The parts are in fact "self-cleaning".

Claims (12)

Process for firing ceramic molded parts with the following features: a) the molded parts are in a first Phase heated in a furnace to a maximum temperature, b) The molded parts are then in the oven in a second phase cooled down again, c) while the cooling phase the molded parts with at least one coating material coated in the oven. The method of claim 1, wherein the molded parts coated with a material based on very finely divided metal oxides become. The method of claim 1, wherein the molded parts be coated with a material that is next to at least one finely divided metal oxide at least one surface modifier having. The method of claim 1, wherein the molded parts with a material based on an organometallic compound be coated. A method according to claim 1, in which a first Coating based on an organometallic compound then a second coating of a polymer applied to the molded parts becomes. The method of claim 1, wherein the coating then occurs when the temperature in the furnace is <1,000 ° C. The method of claim 1, wherein the coating done on a glazed molding. The method of claim 1, wherein the coating in a cooling zone a continuously working tunnel kiln. The method of claim 1, wherein the coating material deposited as a dispersion, suspension or aerosol on the molded parts becomes. Furnace for firing ceramic molded parts with at least one device for feeding a coating material in the furnace and distribution of the coating material on surfaces of the fired moldings. The furnace of claim 10, wherein the device is made of at least one nozzle unit consists, which is arranged in a wall of the furnace. The furnace of claim 10, wherein the device in a cooling zone a tunnel kiln is arranged.