JPH02248355A - Firing method of earthenware - Google Patents

Abstract

PURPOSE:To obtain earthenware which has clear color tone like a fumigated roofing tile and also is colored in unexistent color heretofore by molding the raw material of earthenware into a required shape and housing the molded article to be fired into a furnace and thereafter performing firing, fumigation and oxidation in a specified state. CONSTITUTION:The raw material of earthenware is molded into a required shape and the molded article to be fired is housed in a furnace and thereafter the stages described hereunder are successively performed. (a) A firing stage for heating the inside of the furnace at the firing temp. (b) A fumigating stage wherein heating in the furnace is stopped and the temp. in the furnace has been lowered and thereafter gaseous fuel is introduced to the inside in such a state that the furnace is closed and reduced carbon is produced on the article to be fired and then this article is cooled while maintaining the closed state in the furnace. (c) An oxidizing stage for making the inside of the furnace to the oxidative atmosphere and also reheating the inside is the furnace to remove one part of the reduced carbon. In the above-mentioned fumigating stage (b), the inside of the furnace is made a state insufficient in oxygen by introducing the gaseous fuel to the inside in the closed state of the furnace. Earthenware is produced in such a state that the inside of the article to be fired has been penetrated with the reduced carbon. At this time, the temp. in the furnace is preferably regulated to 850-950 deg.C.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention returns to the method of firing ceramics such as roof tiles and decorative items.

(Prior Art) There are various types of ceramic roof tiles, such as colored glazed tiles and smoked tiles. Among these, smoked tiles have a unique dull silver color called oxidized silver, so they suit the tastes of 11 people and are widely available.

The firing of such smoked roof tiles is carried out as follows.

That is, first, a product to be fired, which is made by molding raw clay into the shape of a roof tile, is placed in a gas kiln, and a burner is ignited to heat the inside of the kiln to, for example, 1100°C.

Next, the burner is turned off to allow the inside of the kiln to cool naturally. When the temperature inside the kiln reaches, for example, 920"C as the cooling progresses, the burner and flue of the kiln are closed to seal the kiln, and at the same time, a fuel gas such as propane or butane is introduced into the kiln from the gas inlet. throw into.

After this, carbon dioxide is gradually introduced from the gas inlet while the burner and flue are closed, and this state is maintained. After the inside of the kiln is cooled to, for example, 300° C., the door of the kiln is opened to cool the inside of the kiln to room temperature, and then the kiln is taken out.

When such a firing method is used, reduced carbon is generated in a state where the fuel gas is introduced in an oxygen-deficient state and penetrates into the interior of the sintered product to be fired. As a result, roof tiles colored in oxidized silver are fired.

(Problems to be Solved by the Invention) Incidentally, although such smoked roof tiles have some color shading, they have a single color.

For this reason, if you wanted roof tiles with a variety of colors, you had no choice but to choose colored glaze tiles.

However, since colored glazed tiles generally have a glossy glass surface, their flashy tones may not be visually appealing.

The present invention has been made in view of the above circumstances, and its purpose is to provide a method for firing pottery that can be colored in an unprecedented color even though it has a dull color tone similar to that of smoked roof tiles.

[Structure of the Invention] (Means for Solving the Problems) The method for firing pottery of the present invention includes placing a product to be fired in which a pottery raw material is molded into a desired shape in a kiln, and then sequentially performing the following steps. It has some characteristics.

(a) A firing process in which the inside of the kiln is heated to the firing temperature. (b) After the heating in the kiln is stopped and the temperature inside the kiln has decreased, fuel is heated inside the kiln in a substantially sealed state. (c) Smoking step of injecting gas to produce reduced carbon in the article to be fired, and then cooling it while maintaining a substantially sealed state in the kiln; (c) creating an oxidizing atmosphere in the kiln and heating it again; Oxidation step (action) for removing a portion of the reduced carbon First, during firing, the inside of the kiln is heated to the firing temperature, thereby sintering the raw material particles constituting the product to be fired.

In the next smoking process, by injecting fuel gas into the kiln in a substantially sealed state, the inside of the kiln becomes an oxygen-deficient state (reducing atmosphere), and the reduced carbon reaches the inside of the product to be fired. Produces in a permeated state. The temperature inside the kiln at this time is preferably 850 to 950°C.

Thereafter, by cooling the kiln while maintaining a substantially sealed state, the reduced carbon is fixed to the fired product in a deposited state not only on the surface but also inside the product. Here, the product to be fired is colored oxidized silver. In this case, in order to sufficiently fix the reduced carbon to the fired product, it is desirable to cool the inside of the kiln to at least about 400°C.

Next, in the oxidation process, when the inside of the kiln is returned to an oxidizing atmosphere and heated, a part of the reduced carbon that has settled on the fired product is oxidized and becomes carbon dioxide, which is removed from the fired product. become. Removal of the reduced carbon is performed sequentially starting from the surface portion of the product to be fired. As a result, the original color of the fabric (the color when the item is unglazed, for example, the red envelope caused by iron oxide) is gradually exposed on the surface of the item to be fired, and it has a dull color tone similar to that of smoked roof tiles. The color is a mixture of the oxidized silver color of carbon and the color of the fabric.

This color can be subtly changed because the degree to which reduced carbon is removed can be changed by changing the heating temperature and time. Incidentally, it is preferable that the heating temperature at this time does not exceed 700°C. This is because if the temperature exceeds 700°C, the reduced carbon will be removed to a large extent (so much so that the color of the fired product will be the original color of the fabric).

(Example) An example in which the present invention is applied to a method for firing roof tiles will be described below with reference to the drawings.

First, the configuration of the kiln 1 used for firing roof tiles will be briefly explained based on FIG. 2. In this case, the kiln 1 is a stand-alone gas kiln, and a heating chamber 2 lined with a refractory material is formed inside.

Further, although not shown, a door for opening and closing the heating chamber 2 is provided on the front surface of the furnace 1, and a door for opening and closing the heating chamber 2 is provided on the front surface of the furnace 1.
A fixed device is also provided. A plurality of burners 3 are provided in the lower part of the side wall of the furnace 1 so as to communicate with the heating chamber 2.

Moreover, this burner rotor 3 can be closed by attaching a lid (not shown) from the outside. 4 is a gas burner provided in the burner 13 portion, and this burner 4 supplies high-temperature combustion gas into the heating chamber 2.

On the other hand, a flue 5 is provided in the upper part of the kiln 1,
This flue 5 can be opened and closed by a damper 6.

Reference numeral 7 denotes a gas injection pipe, the tip of which serves as a gas injection lower a opening in the heating chamber 2, and the base end connected to a gas cylinder (not shown) outside the furnace 1. . Thereby, the gas in the gas cylinder can be introduced into the heating chamber 2 from the gas injection lower a. In this case, two gas cylinders for fuel gas (propane, butane, etc.) and carbon dioxide are connected, and either one can be selected.

Next, the firing procedure for roof tiles will be explained with reference to FIG. 1 as well.

First, a raw material (clay containing iron in this case) is pressure-molded into a desired roof tile shape to form a fired product (not shown). After drying, a large number of the products to be fired are housed in the kiln 1 (heating chamber 2).

After this, the following steps are performed in order.

(a) Firing process: This is a process in which the raw material particles constituting the product to be fired are sintered to fire the roof tiles based on the internal temperature of the kiln.

In this step, the burner 4 is first ignited. Then, the inside of the kiln 1 is heated and the temperature gradually rises.

This heating is performed until the inside of the kiln 1 reaches 1100°C. As is well known, during this period, depending on the temperature inside the kiln 1, there are two stages: the broiling firing period (the period from room temperature to approximately 300°C until the residual moisture in the product to be fired is completely removed, approximately 11 hours), and the medium firing period. (duration of approximately 9 hours until the firing temperature rises from 300℃ to approximately 1000℃), wood-fired firing period (1000 to 1
Period for sintering raw material particles at 100°C, approximately 6 hours)
The raw material particles that make up the product to be fired are sintered through these processes. In total, this took about 26 hours. In this step, the burner 3 and flue 5 are open, so the inside of the kiln 1 is in an oxidizing atmosphere, and both cylinders are closed.

When the temperature inside the kiln 1 reaches 1100° C., the burner 4 is stopped and this process is completed.

(b) Smoking process This is a process in which reduced carbon is generated and fixed on the product to be fired. This process can be divided into the following three steps, and these steps are performed in order based on the internal tolerance of the kiln 1 and the time.

b) Cooling period: Following the firing process, the inside of the kiln 1 is allowed to cool naturally in an oxidizing atmosphere. This means that the temperature inside the kiln is
This is the period until the temperature drops to, for example, 920°C, which is suitable for smoking. In this case, it took about 4 hours.

Gas input period: When the temperature inside the furnace 1 drops to 920°C, the burner 3 is closed with the lid, the flue 5 is closed with the damper 6, and the fuel gas is supplied from the fuel gas cylinder to the heating chamber 2. Insert.

This injection of fuel gas is carried out for 45 minutes. Panaro 3
Due to the blockage of the flue 5, the inside of the kiln 1 becomes substantially sealed, and by introducing fuel gas under this condition, the inside of the kiln 1 becomes an oxygen-deficient state, that is, a reducing atmosphere. In this state, the fuel gas in the furnace 1 is oxidized to produce reduced carbon, and this reduced carbon penetrates into the interior of the product to be fired.

C) Regular period: After 45 minutes of fuel gas injection, carbon dioxide is gradually introduced into the heating chamber 2 from the carbon dioxide cylinder while keeping the burner 3 and flue 5 closed. As a result, natural cooling of the kiln 1 progresses, and air is prevented from flowing in through minute gaps, thereby maintaining a substantially sealed state.

This state is maintained until the inside of the kiln 1 is cooled to, for example, 400° C., and the reduced carbon that has penetrated into the interior of the product to be fired is deposited and fixed on the dough. in this case,
It took about 24 hours.

When the temperature inside the kiln 1 reaches 400° C., the introduction of carbon dioxide is stopped and this process is completed, and by going through the above three steps, the product to be fired is colored in a so-called oxidized silver color.

(C) Oxidation step This is a step in which a portion of the reduced carbon deposited on the fired product is removed.

In this second step, first, the lid of the burner rotor 3 is removed to open the burner rotor 3, and at the same time, the damper 6 is operated to open the flue 5. As a result, the inside of the kiln 1 is returned to an oxidizing atmosphere. Then, the burner 4 is ignited to heat the inside of the kiln 1 to 700°C. In this case, about 4 hours were required for heating. After this, stop burner 4, and then turn on furnace 1.
Let the inside cool naturally to room temperature. During this cooling, the door of the furnace 1 is fully opened when the temperature reaches 300°C. In this case, it took about 24 hours to reach room temperature.

During this process, the reduced carbon that was fixed on the fired product is
At high temperatures of 400°C or higher, it is oxidized to carbon dioxide, which is gradually removed from the fired product. Removal of this reduced carbon is carried out in order from the surface of the dough, so that the original red color of the dough (color due to iron oxide) is gradually exposed on the surface of the product to be fired, and the oxidized silver color due to the residual carbon and this red color are gradually exposed. It will be colored in an intermediate color that is a mixture of.

Of course, the color tone is dull, similar to smoked roof tiles. Also, depending on the position of the product to be fired in the kiln 1,
It may also be colored in a mottled manner, with areas with a strong oxidized silver color and areas with a reddish tinge.

After that, the kiln is removed and the firing of the roof tiles is completed.

According to this embodiment, unlike the conventional firing method for smoked roof tiles, which can only be colored in a single color, the method uses an intermediate color that is a mixture of oxidized silver and red, or a strong part of oxidized silver. It can be colored in a variety of colors, such as mottled areas with reddish areas. Further, since the degree of removal of reduced carbon can be changed by changing the heating temperature or heating time in the oxidation step, the degree of mixing of these two colors can also be varied. Moreover, unlike colored glazed roof tiles, which have a glassy and flashy color tone, the roof tiles have a dull, subdued color tone, similar to smoked roof tiles.

Therefore, it is possible to fire roof tiles with high commercial value that have unique colors and tones never seen before.

By the way, if half-hearted smoking is carried out without sufficiently generating reduced carbon, it is conceivable that a roof tile of a neutral color mixed with oxidized silver and red similar to this example will be fired. For example, in the smoking process of the conventional method of firing smoked roof tiles, it is possible to reduce the amount of fuel gas input, lower the input temperature to 850°C or lower, or reduce the chemical time (reducing atmosphere in the kiln). This method involves shortening the maintenance time (maintenance time).

However, with half-baked products like this, the reduced carbon does not penetrate into the interior of the product to be fired, and -
Moreover, since it is not sufficiently deposited on the fabric, the reduced carbon is likely to separate from the fabric, causing the oxidized silver color on the surface to fade.

On the other hand, in this example, after the reduced carbon has sufficiently penetrated into the inside of the article to be fired and is sufficiently fixed in a state where it has been deposited inside the dough, a part of it is removed. Therefore, it is possible to apply the above-mentioned unique coloring while guaranteeing the durability of the color.

In the above embodiment, a method for firing roof tiles was described, but the present invention can be applied to firing various ceramic products such as decorative items. Moreover, it goes without saying that the temperature for one hour in each step may be changed as appropriate depending on the raw materials, the type of product, the size of the kiln, and the like.

[Effects of the Invention] As is clear from the above explanation, the pottery firing J of the present invention
According to the J method, it is possible to fire a ceramic product colored in an unprecedented color, which is similar to the dull color of smoked roof tiles, while guaranteeing the durability of the color.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG.
Fig. 2 shows the temperature fluctuation over time during the process.
The figure is a vertical cross-sectional view showing the general overall configuration of the kiln. In the drawing, 1 is a kiln, 3 is a burner, 4 is a burner 5
is a flue, 6 is a damper, and 78 is a gas inlet.

Claims (1)

[Scope of Claims] 1. A method for firing pottery, which comprises placing a product to be fired made of pottery raw material into a desired shape in a kiln, and then sequentially carrying out the following steps. (a) A firing process in which the inside of the kiln is heated to the firing temperature. (b) After the heating in the kiln is stopped and the temperature inside the kiln has decreased, fuel is heated inside the kiln in a substantially sealed state. (c) Smoking step of injecting gas to produce reduced carbon in the article to be fired, and then cooling it while maintaining a substantially sealed state in the kiln; (c) creating an oxidizing atmosphere in the kiln and heating it again; an oxidation step in which a portion of the reduced carbon is removed by