EP1083397B1 - Method for reducing defects in ceramic tile production - Google Patents

Method for reducing defects in ceramic tile production Download PDF

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Publication number
EP1083397B1
EP1083397B1 EP20000500199 EP00500199A EP1083397B1 EP 1083397 B1 EP1083397 B1 EP 1083397B1 EP 20000500199 EP20000500199 EP 20000500199 EP 00500199 A EP00500199 A EP 00500199A EP 1083397 B1 EP1083397 B1 EP 1083397B1
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EP
European Patent Office
Prior art keywords
oxygen
furnace
kiln
oxidizing atmosphere
ceramic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP20000500199
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German (de)
English (en)
French (fr)
Other versions
EP1083397A1 (en
Inventor
Carlos Alberto Paskocimas
Sergio Da Silva Cava
Clovis Germany Herter
Tulio Mendonca Sobrinho
Abilio Tasca
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Praxair Technology Inc
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Praxair Technology Inc
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Publication date
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Publication of EP1083397A1 publication Critical patent/EP1083397A1/en
Application granted granted Critical
Publication of EP1083397B1 publication Critical patent/EP1083397B1/en
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/30—Details, accessories, or equipment peculiar to furnaces of these types
    • F27B9/36—Arrangements of heating devices
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/14—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment
    • F27B9/20—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment the charge moving in a substantially straight path tunnel furnace
    • F27B9/24—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment the charge moving in a substantially straight path tunnel furnace being carried by a conveyor
    • F27B9/2407—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment the charge moving in a substantially straight path tunnel furnace being carried by a conveyor the conveyor being constituted by rollers (roller hearth furnace)

Definitions

  • This invention is generally related to a method for reducing the defects associated with heating of ceramic materials. More specifically, this invention relates to the use of oxygen to reduce or eliminate the black core defects during the production of enameled ceramic tiles in the roller hearth kiln.
  • the argillaceous minerals used in the formulation of the primary compounds in enameled tiles contain frequently a high quantity of substances that are susceptible to chemical reactions with oxygen at high temperatures.
  • the argillaceous minerals contain substantial quantities of carbon and organic materials, sulfur and its compounds, and some oxides of transition metals (particularly iron) which can generate defects in the sintered ceramic products in their lower valence state. Accordingly, it is necessary to use an oxygen rich atmosphere to have these materials oxidized, in a stage prior to the firing process.
  • a dark core known as "black core” will likely develop during the firing, which is formed by carbon residues from the thermal decomposition of the organic material contained in the clays. Particularly, the dark color in the center is believed to be caused by iron, which is present in a reduced condition.
  • the main source of reduction of the ferric oxide (Fe 2 O 3 ) to ferrous oxide (FeO), and/or metallic iron (Fe) is the presence of a carbonaceous residue which results from the carbonization of organic impurities.
  • This reduction is dependent on the oxidation rate of these transition metals contained in the clay and the oxidation velocity is dependent on various factors including: 1) the nature and quantity of oxidizible and reducible substances; 2) the particle size of these substances; 3) the heating rate; 4) the atmosphere concentration surrounding the oxidizible and reducible substances on oxygen, carbon monoxide and sulfur dioxide; 5) the composition and textural variation of the pieces during each step of the burning cycle; and 6) the enamel fusibility deposited in the "green body".
  • the black core defect occurs with greater frequency in the single firing process.
  • a slow firing cycle is preferred over a faster firing cycle in order to obtain a better quality product, although such a slow firing cycle may not be practical in the industry.
  • oxygen significantly benefits the ceramic production process including 1) reducing or eliminating the defects formed from the firing process; 2) maintaining or increasing the production rate; and 3) allowing the use of lower quality raw materials (i.e., rich in transition metals and/or organic compounds). Oxygen enrichment also allows the process, at a constant or higher production rate, to produce a final product having superior quality compared with the traditional method which does not use additional oxygen.
  • additives/flux agents enable the liberation of oxygen when heated, thus improving the oxidation of the organic compounds.
  • these materials have low melting temperatures during the enameled tiles pre-heating, promotes a rapid reduction of the opened porosity. This will avoid the interactions with the furnace atmosphere at a defined temperature. Additionally, the additive/flux agents promote further darkening of burned products.
  • the lower moisture content of the enamel tiles provides a lower volume of gases to be extracted from the green compact.
  • Lower content of moisture represents fewer opened channels for gases to exit, thus, greater difficulty of the oxidant atmosphere to penetrate into the green body.
  • Processing the enameled ceramic tiles with a thin enamel layer may compromise the abrasion resistance of the final product. Reducing the thickness of the green-compact enables a reduction in the mechanic stress.
  • the higher content of moisture provides a higher quantity of open channels, thus enhancing the green body oxidation but requiring an increase in green body residence time into the kiln for moisture extraction.
  • U.S. patent No. 4,329,142 relates to the reduction of defects caused by the incomplete oxidation of the carbonaceous materials and sulfur compounds present in the raw material.
  • US-A-4 391 585 discloses a method for reducing defects in the production of ceramic products during the firing process comprising one injection nozzle for spraying additional oxygen to the decarbonization zone.
  • the injection nozzle is mounted in the roof of a kiln.
  • a computer adjusts the oxygen concentration to try and maintain the average oxygen concentration at the kiln via the injection nuzzle.
  • D2 US-A-4 329 142 teaches also a method for reducing defects in the production of ceramic products during the firing process comprising one o more jets or streams of oxygen-rich gas extending into the spaces between the stacks of the ceramic products, but retractable thereform to allow kiln cars to be advanced through the kiln.
  • One aspect of this invention is directed to a method for reducing product defects in the production of ceramic products during the firing process and for increasing the production rate of the ceramic products, the method comprising the steps of providing an enriched oxidizing atmosphere in a furnace at the vicinity of the ceramic products to maintain a heated oxidizing atmosphere; passing the ceramic products for firing in the vicinity of the oxidizing atmosphere; and firing the ceramic products in the presence of the oxidizing atmosphere.
  • This invention provides a method for maintaining the characteristic of the raw material such as grain sizes, moisture content, compacting pressure, porosity, dimensions, thickness, enamel type and enameling process during the manufacturing of the ceramic material.
  • An enameled tile product using this process may be obtained with little or no defects, such as black core. Better mechanical resistance and high production rate are maintained.
  • this invention is directed to optimizing other process parameters such as higher compacting pressure, the use of lower quality raw material, higher moisture contents, larger raw materials, greater green compact thickness, enamel with lower temperature of fusibility, capacity for using low BTU gas fuel, such as gasogene, and reducing the specific consumption while increasing production.
  • This process is adaptable to any roller kiln, thus minimizing initial investments.
  • the quality of the ceramic products processed in roller kilns depends mainly on the furnace conditions.
  • the kiln atmosphere composition is one of the most important factors that characterizes the burning conditions.
  • the kiln furnace atmosphere must provide an-oxidizing condition to eliminate or reduce the occurrence of defects in the tile, such as black core.
  • the process of this invention is to locally control the kiln atmosphere composition by adding oxygen.
  • Oxygen may be preheated outside of the kiln to provide a higher oxidant atmosphere, mainly in the temperature where the defects can occur.
  • the material must be characterized in a ceramic specialized laboratory to determine these temperatures, as well as the composition of oxidizable substances.
  • any atmosphere having more available oxygen than the existing oxygen concentration in the furnace atmosphere will prevent black core defects.
  • the lowest measured concentration in the furnace atmosphere without oxygen added was about 1%.
  • pure oxygen and/or oxygen mixture capable of enriching the furnace atmosphere at an oxygen concentration of greater than about 1% will prevent the core defects and increase the production rate of the ceramic products.
  • the addition of oxygen in the process uses this available source of heat to promote the heating of the oxygen added to the furnace, thus improving the oxidation process reaction.
  • Increasing the oxygen concentration or increasing the oxidizing atmosphere temperature increases the oxidation process efficiency.
  • the oxygen may be preheated outside of the kiln furnace.
  • a typical method of injecting oxygen is by removing the rotating rolls to install static roll without the rotating movement for oxygen injection.
  • a variation of such oxygen injecting is by using small static rolls (or tubes) installed among the existing rolls for oxygen addition.
  • a control system is needed to feed oxygen only when the holes drilled in the rotating rolls have a good approximation of gas flow with the ceramic materials. Further, the oxygen rolls may be added above the tiles, below the tiles, or both above and below the tiles. In all cases, lower black core defect results when oxygen is fed close to the tiles undergoing treatment.
  • the oxidizing atmosphere is added into the furnace in the pre-heating zone (or the oxidizing zone).
  • the temperature of the furnace for the oxidizing atmosphere may range from about 200°C to about 1000°C, preferably from about 400°C to about 900°C.
  • a roller kiln for a single firing process was provided in which the acceleration of the burning cycle and the nominal production was increased from about 4300 m 2 /day to about 4900 m 2 /day for ceramic tiles with low softening enamel temperature, and from about 4500 m 2 /day to about 5000 m 2 /day for ceramic tiles with refractory enamel. This was accomplished due to the oxygen utilization to accelerate the reactions of the oxidation of the ceramic materials. The addition of oxygen was done by the substitution of one roll with spin movement by one static roll (without spin movement) in each of the three existing rolls, in a defined kiln section. These rolls (without spin movement) were built with the same sillimanite materials as the existing rolls, where several holes were drilled on its length and directed to the inferior piece-surfaces to enable the added oxygen to distribute uniformly in the kiln transversal section.
  • Ceramic material samples were ignited in a laboratory scale furnace, simulating the industrial burning cycle. Additions of oxygen and oxygen/nitrogen mixture were made by furnace atmosphere enrichment and addition of oxygen directly in the ceramic material samples. A scanning electron microscope was used to examine the structures of the oxidized layers and the non-oxidized layers (black core).
  • roller kilns are the most technologically advanced and widely used for enameled tile production and are very versatile as compared to conventional methods for introducing ceramic materials for firing. Some advantages for the use of roller kiln are its ability for good burning uniformity, bigger production with reduced burning cycles, lower production losses and lower fuel consumption.
  • Another type of furnace is the tunnel kiln. The roller kiln furnace is preferred because it uses a single stage burning cycle, while the tunnel kiln furnaces uses a two stage burning cycle.
  • the tile mass in the kiln inlet was about 16.6 ⁇ 0.4 kg/m 2
  • the mass tile in the kiln outlet was about 16.2 ⁇ 0.4 kg/m 2
  • the tile density in the furnace inlet was about 1.85 ⁇ 0.02 g/cm 3 .
  • the moisture content in the tile at the furnace was about 2.00 ⁇ 0.50% by mass.
  • the water absorption of the tiles at the kiln outlet was about 4.5 ⁇ 1.5% by volume.
  • the tiles size at the furnace inlet was 360.2 mm x 360.2 mm and the tiles size at the furnace outlet was about 335.8 mm x 335.8 mm.
  • Thermogravimetric analysis and differential-thermal analysis of the raw ceramic tile material showed mass loss and endothermic reaction in the temperature showed a range of from about 400°C to about 900°C.
  • Oxygen was directed to the pre-heating zone in the temperature range of from about 400°C to about 900°C.
  • Oxygen distributors were used to control the flow of oxygen to feed the four rolls in each module of the furnace. Each oxygen distributor was equipped with critical orifice system to measure the oxygen flow. Thirty oxygen distributors were installed in the kiln furnace. An oxygen rotameter was installed in to measure the total oxygen flow fed to the kiln furnace.
  • Fig. 1 provides a transverse view of the kiln furnace 100. Ceramic tiles 110 were passed through the furnace 100, preferably roller kiln furnace, at a position between the kiln roof 102 and kiln bottom 104. The static roll 132 used-for oxygen addition was placed transversally across the kiln furnace. Monitor probes were placed at various positions 120, 122, 124 and 126 to measure the atmospheric measurements in the kiln.
  • the production rate was 4500 m 2 /day of high softening temperature enamel; and where oxygen was added, the production rate was 4850 m 2 /day of the same high softening temperature enamel.
  • the total oxygen added by the rotameter was 138 Nm 3 /h @ fce.
  • Example C A trial to determine the formation of black core defect was performed using the procedure in Example C.
  • the baseline conditions, as determined without oxygen, for high temperature softening enamel tiles was 4500 m 2 /day without black core defects, with the compacting pressure of 280 bar. Results of this trial-show that a production of 5020 m 2 /day was achieved without formation of black core defects even when oxygen was provided at 2.25 Nm 3 /h of oxygen for each roll. The total oxygen flow rate was 81 Nm 3 /h.
  • the furnace temperature was from about 400°C to about 900°C, and the optimal temperature was from about 700°C to about 900°C. It was determined that at a furnace temperature of 700°C, the tile surface temperature was about 45°C lower than the furnace temperature. At a furnace temperature of about 900°C, the tile temperature was about 15°C lower than the furnace temperature.
  • the production rate was about 4540 m 2 /day without the addition of oxygen, and at a compacting pressure of 343 bar. Very high black core defect results in the absence of oxygen, other than ambient oxygen. Comparatively, the addition of oxygen to the kiln furnace of about 185 Nm 3 /h showed the increased production to about 5200 m 2 /day, and decreased in black core defects to near trace amounts.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Compositions Of Oxide Ceramics (AREA)
EP20000500199 1999-09-08 2000-09-07 Method for reducing defects in ceramic tile production Expired - Lifetime EP1083397B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US39229299A 1999-09-08 1999-09-08
US392292 1999-09-08

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EP1083397A1 EP1083397A1 (en) 2001-03-14
EP1083397B1 true EP1083397B1 (en) 2004-03-24

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EP (1) EP1083397B1 (pt)
BR (1) BR0004049A (pt)
ES (1) ES2215596T3 (pt)
PT (1) PT1083397E (pt)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111322863A (zh) * 2020-03-10 2020-06-23 湖南新天力科技有限公司 一种辊道窑工艺气氛调整方法及调整系统

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116635684A (zh) * 2020-11-13 2023-08-22 康宁股份有限公司 用于在具有氧气气氛控制的窑中烧制陶瓷生坯器皿的系统和方法

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4329142A (en) * 1979-06-18 1982-05-11 Boc Limited Method for heat treatment of clay and refractory ware
GB2073384B (en) * 1980-03-26 1984-01-11 Air Prod & Chem Method of operating a continuous brick kiln
DE3444542A1 (de) * 1984-12-06 1986-06-19 Linde Ag, 6200 Wiesbaden Verfahren zum brennen von oxidierbare bestandteile enthaltenden materialien
DE3444536A1 (de) * 1984-12-06 1986-06-12 Linde Ag, 6200 Wiesbaden Verfahren und vorrichtung zum brennen von grob- und feinkeramischen materialien
JPH063070A (ja) * 1992-06-18 1994-01-11 Murata Mfg Co Ltd 焼成炉

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111322863A (zh) * 2020-03-10 2020-06-23 湖南新天力科技有限公司 一种辊道窑工艺气氛调整方法及调整系统

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BR0004049A (pt) 2001-06-19
EP1083397A1 (en) 2001-03-14
PT1083397E (pt) 2004-08-31
ES2215596T3 (es) 2004-10-16

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