CA1047744A - Fast firing for ceramic tiles - Google Patents
Fast firing for ceramic tilesInfo
- Publication number
- CA1047744A CA1047744A CA225,861A CA225861A CA1047744A CA 1047744 A CA1047744 A CA 1047744A CA 225861 A CA225861 A CA 225861A CA 1047744 A CA1047744 A CA 1047744A
- Authority
- CA
- Canada
- Prior art keywords
- tile
- tiles
- treatment chamber
- firing
- raw
- 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
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B33/00—Clay-wares
- C04B33/32—Burning methods
- C04B33/34—Burning methods combined with glazing
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Ceramic Engineering (AREA)
- Dispersion Chemistry (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Finishing Walls (AREA)
- Compositions Of Oxide Ceramics (AREA)
- Devices For Post-Treatments, Processing, Supply, Discharge, And Other Processes (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE:
A process for the production of tiles made of ceramic material, comprising the steps of advancing in a heat treatment chamber a raw tile based on a clay material, dried and covered on one face with a glaze, also dried, the both faces of said raw tile being at least substantially exposed to direct trans-mission of heat by convection, treating the tile in the heat treatment chamber, said tile going through a first fast heating phase until it reaches a temperature slightly lower than maximum firing temperature, and through a successive firing phase during which it is kept at a range of temperatures comprised between the final heating temperature and the maximum firing temperature, and finally cooling said tile. This process enables the pro-duction of tiles of the highest quality, of regular geometric shape and free of flaws, which tiles can particularly be used for wall lining or flooring.
A process for the production of tiles made of ceramic material, comprising the steps of advancing in a heat treatment chamber a raw tile based on a clay material, dried and covered on one face with a glaze, also dried, the both faces of said raw tile being at least substantially exposed to direct trans-mission of heat by convection, treating the tile in the heat treatment chamber, said tile going through a first fast heating phase until it reaches a temperature slightly lower than maximum firing temperature, and through a successive firing phase during which it is kept at a range of temperatures comprised between the final heating temperature and the maximum firing temperature, and finally cooling said tile. This process enables the pro-duction of tiles of the highest quality, of regular geometric shape and free of flaws, which tiles can particularly be used for wall lining or flooring.
Description
`" 1047744 The present invention relates to a process for the production of ceramic products and particularly of wall-tiles or floor-tiles.
The conventional process used for the production of tiles is a double-firing process wherein the body of the tile, after having been formed by pressing the raw material, or in any other suitable way, is fired as such is subsequently glazed on ~--one of its faces, the obtained glaze then being fired.
This conventional process, which is used for a wide range of ceramic products, provides finished products of the desired quality but is obviously time consumming and expensive.
Attempts have been made to replace it with faster and cheaper processes, particularly by so-called single-firing processes in ---which the ceramic body is coated with glaze, thereafter eventually dried, and the glazed body is subsequently fired in a single-phase. -This single-phase firing processes are more critical and difficult than the conventional process and have been carried out more or less successfully according to the raw materials used and the shape and nature of the requested finished product.
However, these do not always afford the desired savings, for instance in cases in which the single-firing requires a considera-ble length of time and produces a poor quality product or a high rate of rejects.
A relative fast single-firing is feasible, as well known in the art, by using certain raw materials, especially batches with a high content, for example 70%, of talcum and ~ -wollastonite.
However, such a fast single-firing is economically advantageous only in some specific areas, like the United States, but not is most areas like Europe, South America and Asia, where, for economic reasons and according to the availability of .
.. , ~
1~47744 materials, there is required the use of natural clay bodies or -depending on the areas - of bodies firing with clay, kaolin, cal-cium or magnesium carbonates, silica and feldspathic materials and other natural components as well as pre-treated or synthetic materials.
The present invention relates to the production of ti-les made from materials or bodies which will be referred to in the following specification with the term "clay materials" it being understood that materials containing high percentages (50%
or more) of talcum and wollastonite, as well as materials contain-ing addition of clay as binder, are excluded from the above term.
The "clay materials" may contain raw clays and/or pre-fired clays, a certain percentage, at least about 40% by weigth of raw clay, being necessary to confer to the material the desired mechanical properties, and they must not contain, as mentioned above, substantial amounts of talcum and wollastonite.
As far as the rest is concerned, they may contain various mate-rials, such as siliceous or feldspathic sand and alkaline-earth metals, iron compounds and others.
The composition should be preferably such that the sum of magnesium and calcium oxides does not exceed much more than 20% by weight (a percentage of 30%, no doubt, should be excessi-ve) and such that the percentage of aluminium oxide contained be within the same percentage. Even more preferably the composi-tion may contain an amount of iron oxide of a few units per cent by weight.
The present invention proposes single-firing process for the production of perfect tiles in an exception short time, as was never achieved heretofore and consequently with substantial savings. The tiles are made of "clay materials", as specified before, thus resulting in a final 1(~47744 product of quality, of regular geometric shape and free of defects.
The process according to this invention comprises the steps of preparing a raw tile consisting of a dry, unfired tile body with a dried glaze coating on one face of the body, and with the body consisting predominantly of clay comprising at least 40% by weight of raw clay, an aggregate calcium oxide and magnesium oxide content of less than 30% by weight and alu-minum oxide content of less than 30% by weight, and an iron oxide content of less than 10% by weight; advancing the raw tile at a speed of the order of 1.5 - 2 meters per minute through a treat-ment chamber; in a heating step having a duration of 4 - 8 minu-tes, contacting both faces of the tile body concurrently with flowing hot gases as the tile body advances through the treat-ment chamber to raise both faces concurrently and, by substan-tially only direct convection heating, substantially to firing surface temperature; in subsequent firing step having a duration -of 11 - 20 minutes, contacting both faces of the tile body concurrently with the flowing hot gases as the tile body continues -to be advances through the treatment chamber to maintain both surfaces substantially at the firing surface temperature concur-rently, by substantially only direct convection heating, to fire the tile body and the glaze of the raw tile; and, following completion of the firing step, finally cooling the fired tile in a cooling step having a duration of less than 12 minutes; whereby the sum of the durations of the heating and firing steps is not in excess of about 28 minutes and the overall heating, firing and cooling time is not in excess of 40 minutes.
By the term "direct convection heating" it is meant that the tile is heated by the moving hot gases, with exclusion or wit~out determining presence of other types of heat transmis-sion (such as the conduction from the supporting means on which the tile rests and/or radiation from the walls of the treatment ~ , ~n , , .~
chamber. Obviously, this is accomplished when the hot gases forms the only source of heat within the chamber and therefore heat the tiles as well as the supporting means and the walls (eventually other high temperature bodies being placed into such a position as not to be able to directly contribute to the heating of the tiles).
Usually, the advancing of the tiles with both faces (which means the front glazed face and the rear face without tak-ing into account the edges which are of relatively negligible surface) substantially exposed to the direct transmission of heat contact with underlying transporting supports, preferably having - - 3 a -~)47744 a rotating surface and fixed axis, with each of which they come into contact ideally along a generatrix The feeding takes place at high speed, considerably higher than the ~peeds adopted heretofore for materials of this type, at the rate of 1.5 - 2 meters/minute (these figures not being considered binding), such speeds being optimum for wall-tiles and therefore 4 - 5 mm. thick, but may be slightly reduced for thicker tiles.
The heat treatment chamber is temperature-controlled a~d usually comprises a tunnel-kiln where in successive areas of the same the tile~ go through the successive steps of heatiDg a~d keeping at the firing temperature (or briefly firing, although proper firing actually starts during the heating step) and subse-quently cooled outside or eventually partially cooled iD the treatment chamber.
The drying of the ceramic body is a common operation iD
the manufacturing of ceramic products and may be usually carried out at a speed differing from that of the above mentioned opera-tion or at the same speed when the dryer i~ an integral part of the kiln. The same applies to drying of the glazing. In the following description reference is made to a process wherein ~ -dryi~g of the tile body i9 performed previously and separately whilst drying of the glazing is carried out immediately prior to heating and at the same speed; in this case it lasts a few minutes, for example from 5 to i minutes, at suitable temperatures, for example up to 200C, a~d under a~ adequate and intense gas circulation.
When drying of the glazing is completed and the actual heat treatme~t starts, the temperature of the tiles, according 3 to the present invention, is quickly raised up to the firing temperature. The firing temperature, measured rear the tiles - as .
1~47744 all the temperatures stated in this specification - may vary quite substantially according to the compositions, but it is generally comprised around 1000C, as for example between 800C
and 1200C, but more commonl~, between 1000C and 1100C, for example around 1050C and 1060C.
~ he heating of the tiles is carried out, as referred to above, in an environment where heat tranSmiSSioD takes place by CoDVeCtion with gas flowing in counter-current to the tiles, and besides heating the tiles, it heats also the walls of the heat treatment chamber which are normally made of refractory material and at times may become incaDdescent turning into a light-red colour. I~ these conditions the temperature differeDce between walls and tiles is always ~ept to such an amount that heat exchanges by radiation do Dot have a determining effect.
It is important to dose heating in the heating zone, so as to produce a quick rising of the temperature of the tile, the o.nly upper limitatlon regarding the rapidity of heating, since the material may be damaged by a too quick evolution of volatile products by uDcontrolled thermal co~traction and expansion iD the still raw tile and such a limit being set case by case. General-ly, a heating.time of 4 - 6 minutes is considered adequate and at this point it may be assumed that the tile has reached - at least OD the surface - a temperature a few degrees lower than chamber temperature.
During the actual firing step, the tile remains at a practically constant surface temperature (even if not exactly constant due to the fact that heat-exchanges st~1l continue an~
the temperature of the chamber is Dot exactly co~stant) and conti.nues to advaDce in the firing zone which is at an almost e~eD temperature tending to be lower at the start and at the end due to closeness of to the heating and cooli~g Z0De 1~47744 respectively, and in gas counter-current. ~his step lasting slightly over 10 minutes, for example between 11 and 15 minutes.
In the meantime the heat penetrates more deeply in the tile body firing the inner layers of the tile. Finally, the cooliDg step takes place in a shorter time slightly shorter than the firing time for example slightly shorter than 12 minutes, say 8 - 10 minutes and may be determined by a partly direct and partly indirect cooli~g and occurs partially inside and partially or entirely outside the chamber.
The times specified above by way of example are close to optimum for wall-tiles, 4 - 5 mm. thick, and may be increased with a variatio~ ratio generally not linear, for thicker tiles, such as those used for flooring, which may even be 10 mm thick and for which the length of time for heating may be for example up to 6 - 8 minutes and for firing 17-20 minutes.
It has been found, according to the present inventioD
that the best compromise between the necessity of suitably supporting the tile OD the generatrices of the fixed-axis rota-ting supports for feeding, and the necessity of not introducing an excessive difference in the thermal conditions of the two faces of the tile, is obtained when the tile is kept in constant ~ contact with two or three of that geDeratrices.
i, This is obtained in the more common case of the support rotating rollers, when the distance between the centers of the roller is e~ual to half thelength of the tile itself. In such a caæe it is ensured that the product obtalned is of regular geometric shape and free from defects. However, it is possible to modify to a reasonable extent this condition when in practice it i8 necessary to produce with the same equipment, tiles of ~ varying dimensions.
1~4774~ -According to the present invention, the tile body is formed of one of the bodies termed as "clay materials", as speci-fied above. ~ypical materials form~ng said bodies are for example: plastic t~pe clays; no fat or semi-fat clays; kaolins;
feldspars; dolomite and calcium carbonate; siliceous sand. The' formulation of the glazing materials varies according to the required product and to the type of support used and may be raw, semi-raw or with fritted glazes.
I~ the carrying out of the present invention it must be considered some physical properties of the material'as speoified in the following. A temperature/weight diagram of the material indicates a loss of weight with temperature increase according to the development of volatile substances.
With the increase in temperature and with the tile body kept at that temperature for some time, there appears first an increase and next, iD the phase of specific interest, a loss oi permeability of the tile body itself, which logically starts on the outer surface exposed to a quicker increase of temperature.
~he ceramic material used must have a total weight'loss during the eDtire process, which, although not ~ery low when the above materials are dealt with, is however not excessive, for example, not more than 15%. 'In addition, it must be able to keep substan-tially its surface permeability at least up to a temperature of 700 - 800~ and until there is no substantial weight loss, as shown i~ the temperature/weight diagram, obviously under the conditions of the process according to this invention, particu-larly with the thermo-gravimetry gradients contemplated by the invention. ~urther, the thermo-dilatometric behaviour of the material, i.e. variation of linear dimensio~s with increase in temperature, must be such as not to produce excessive diffe-rence in dimensions between the two faces of the tile, which due 1')47744 to the unavoidable unevenness in heating, may not in fact be at the same temperature at least during part of the process. Such behaviour of the material may be illustrated by plotting a thermo-dilatometric diagram.
By operating according to the invention, particularly under the preferred and optimum conditions, much better results are obtained, on an industrial scale with respect to those obtained heretofore and actually beyond expectations. In the ceramic art the attempts made heretofore to introduce single-firing of tiles made of common materials which required a firing time of a few hours and resulted in the production of mostly defective tiles, led to believe that such results were impossible. The speed increase, the lack of supports for the tile and the drastic reduction of operating times are all factors which, based on past technical experience, were supposed to be negative, so that it was assumed tihat manufacturing of excellent products from materials of the above mentioned type required operation un-der gentler, more gradual and mechanically easier conditions than those previously adopted and not the contrary. ~-The fact that by making all operating conditions simultaneously more severe, i.e. both speed and rapidity and mechanical feeding conditions of the tile, the result obtained was never achieved before even in conditions remotely approaching those of the invention, represents in fact a remarkable techni-cal achievement.
In the accompanying drawings:
Fig. 1 represents a tunnel-type furnace adapted for carrying out the process according to the invention and Fig. 2 represents an example of supporting and feeding means for the tiles.
For actuation of the invention a tunnel-type furnace running longitudinally on a single plane, as schematically ~ .
'' '. ': - - : :
1~47744 illustrated in fig. 1, is best suited.
The detailed structure is not shown, as it is not within the scope of the present invention, but generally comprises, assuming that drying of the tile body is carried e~e~ t~ly~
. ` ~r ~ 8a -. .~ j .
)47744 a section 1 for drying of the glaze, a section 2 for the heating step, a ~ection 3 for the firing step and a section 4 for the cooling step.
The furnace is coDveniently heated by gas burners5 fitted in the walls so as not to radiate on the tiles, as shown schematically in fig. l, or by other suitable means, for example electric heating, the furnace walls being adequately insulated.
In the case where gas burners are used, these will produce volumes of combustio~ by-products which will be conviently moved iD
counter-current with respect to the tile, by means of suitable suction devices (not shown) or other means so that gas masses increase from the outlet to the i~let of the treatment chamber and generally forthe ma~or portion of the chamber, usually in a linear manner; and in the case of electric heating, air will have to be introduced to provide such volumes.
The elimination of moisture in area 1 may re~uire a separate circulation of hot gas, as showm schematically at 6 (gas inlet) and 7 (outlet) the burDers ~ot being provided iD this area. Suitable means will be provided to convey hot gases in counter-curreDt flow with respect to the tiles and suitable means will thus be provided for loading and unloading of the tiles, as showD schematically at 8, driving the rollers at the required speeds and eventually for speed control, and so on.
Fig. 2 shows aD e~ample of a supporting and feeding means for the tiles, two rollers 10 carried by shafts 11 supporting a moving tile 12; the roller shafts being controlled by any suita-ble means outside the furnace.
An example of carrying out the invention, illustrating the production of a particul æ tile, will now be give~ by way of example only, since the possibility of varying the composi-tions based OD product~ available in nature for the industry is .~ ., practically unlimited and those skilled in the art will be able to actuate the inventior based on what has hereiDbefore been described in the specification without departing from the true scope of the invention, even with compositio.ns very differeDt indeed.
The initial material is a mixture of "red beds" clays having the following formulation: Ignit. lo~s O - 15%
The conventional process used for the production of tiles is a double-firing process wherein the body of the tile, after having been formed by pressing the raw material, or in any other suitable way, is fired as such is subsequently glazed on ~--one of its faces, the obtained glaze then being fired.
This conventional process, which is used for a wide range of ceramic products, provides finished products of the desired quality but is obviously time consumming and expensive.
Attempts have been made to replace it with faster and cheaper processes, particularly by so-called single-firing processes in ---which the ceramic body is coated with glaze, thereafter eventually dried, and the glazed body is subsequently fired in a single-phase. -This single-phase firing processes are more critical and difficult than the conventional process and have been carried out more or less successfully according to the raw materials used and the shape and nature of the requested finished product.
However, these do not always afford the desired savings, for instance in cases in which the single-firing requires a considera-ble length of time and produces a poor quality product or a high rate of rejects.
A relative fast single-firing is feasible, as well known in the art, by using certain raw materials, especially batches with a high content, for example 70%, of talcum and ~ -wollastonite.
However, such a fast single-firing is economically advantageous only in some specific areas, like the United States, but not is most areas like Europe, South America and Asia, where, for economic reasons and according to the availability of .
.. , ~
1~47744 materials, there is required the use of natural clay bodies or -depending on the areas - of bodies firing with clay, kaolin, cal-cium or magnesium carbonates, silica and feldspathic materials and other natural components as well as pre-treated or synthetic materials.
The present invention relates to the production of ti-les made from materials or bodies which will be referred to in the following specification with the term "clay materials" it being understood that materials containing high percentages (50%
or more) of talcum and wollastonite, as well as materials contain-ing addition of clay as binder, are excluded from the above term.
The "clay materials" may contain raw clays and/or pre-fired clays, a certain percentage, at least about 40% by weigth of raw clay, being necessary to confer to the material the desired mechanical properties, and they must not contain, as mentioned above, substantial amounts of talcum and wollastonite.
As far as the rest is concerned, they may contain various mate-rials, such as siliceous or feldspathic sand and alkaline-earth metals, iron compounds and others.
The composition should be preferably such that the sum of magnesium and calcium oxides does not exceed much more than 20% by weight (a percentage of 30%, no doubt, should be excessi-ve) and such that the percentage of aluminium oxide contained be within the same percentage. Even more preferably the composi-tion may contain an amount of iron oxide of a few units per cent by weight.
The present invention proposes single-firing process for the production of perfect tiles in an exception short time, as was never achieved heretofore and consequently with substantial savings. The tiles are made of "clay materials", as specified before, thus resulting in a final 1(~47744 product of quality, of regular geometric shape and free of defects.
The process according to this invention comprises the steps of preparing a raw tile consisting of a dry, unfired tile body with a dried glaze coating on one face of the body, and with the body consisting predominantly of clay comprising at least 40% by weight of raw clay, an aggregate calcium oxide and magnesium oxide content of less than 30% by weight and alu-minum oxide content of less than 30% by weight, and an iron oxide content of less than 10% by weight; advancing the raw tile at a speed of the order of 1.5 - 2 meters per minute through a treat-ment chamber; in a heating step having a duration of 4 - 8 minu-tes, contacting both faces of the tile body concurrently with flowing hot gases as the tile body advances through the treat-ment chamber to raise both faces concurrently and, by substan-tially only direct convection heating, substantially to firing surface temperature; in subsequent firing step having a duration -of 11 - 20 minutes, contacting both faces of the tile body concurrently with the flowing hot gases as the tile body continues -to be advances through the treatment chamber to maintain both surfaces substantially at the firing surface temperature concur-rently, by substantially only direct convection heating, to fire the tile body and the glaze of the raw tile; and, following completion of the firing step, finally cooling the fired tile in a cooling step having a duration of less than 12 minutes; whereby the sum of the durations of the heating and firing steps is not in excess of about 28 minutes and the overall heating, firing and cooling time is not in excess of 40 minutes.
By the term "direct convection heating" it is meant that the tile is heated by the moving hot gases, with exclusion or wit~out determining presence of other types of heat transmis-sion (such as the conduction from the supporting means on which the tile rests and/or radiation from the walls of the treatment ~ , ~n , , .~
chamber. Obviously, this is accomplished when the hot gases forms the only source of heat within the chamber and therefore heat the tiles as well as the supporting means and the walls (eventually other high temperature bodies being placed into such a position as not to be able to directly contribute to the heating of the tiles).
Usually, the advancing of the tiles with both faces (which means the front glazed face and the rear face without tak-ing into account the edges which are of relatively negligible surface) substantially exposed to the direct transmission of heat contact with underlying transporting supports, preferably having - - 3 a -~)47744 a rotating surface and fixed axis, with each of which they come into contact ideally along a generatrix The feeding takes place at high speed, considerably higher than the ~peeds adopted heretofore for materials of this type, at the rate of 1.5 - 2 meters/minute (these figures not being considered binding), such speeds being optimum for wall-tiles and therefore 4 - 5 mm. thick, but may be slightly reduced for thicker tiles.
The heat treatment chamber is temperature-controlled a~d usually comprises a tunnel-kiln where in successive areas of the same the tile~ go through the successive steps of heatiDg a~d keeping at the firing temperature (or briefly firing, although proper firing actually starts during the heating step) and subse-quently cooled outside or eventually partially cooled iD the treatment chamber.
The drying of the ceramic body is a common operation iD
the manufacturing of ceramic products and may be usually carried out at a speed differing from that of the above mentioned opera-tion or at the same speed when the dryer i~ an integral part of the kiln. The same applies to drying of the glazing. In the following description reference is made to a process wherein ~ -dryi~g of the tile body i9 performed previously and separately whilst drying of the glazing is carried out immediately prior to heating and at the same speed; in this case it lasts a few minutes, for example from 5 to i minutes, at suitable temperatures, for example up to 200C, a~d under a~ adequate and intense gas circulation.
When drying of the glazing is completed and the actual heat treatme~t starts, the temperature of the tiles, according 3 to the present invention, is quickly raised up to the firing temperature. The firing temperature, measured rear the tiles - as .
1~47744 all the temperatures stated in this specification - may vary quite substantially according to the compositions, but it is generally comprised around 1000C, as for example between 800C
and 1200C, but more commonl~, between 1000C and 1100C, for example around 1050C and 1060C.
~ he heating of the tiles is carried out, as referred to above, in an environment where heat tranSmiSSioD takes place by CoDVeCtion with gas flowing in counter-current to the tiles, and besides heating the tiles, it heats also the walls of the heat treatment chamber which are normally made of refractory material and at times may become incaDdescent turning into a light-red colour. I~ these conditions the temperature differeDce between walls and tiles is always ~ept to such an amount that heat exchanges by radiation do Dot have a determining effect.
It is important to dose heating in the heating zone, so as to produce a quick rising of the temperature of the tile, the o.nly upper limitatlon regarding the rapidity of heating, since the material may be damaged by a too quick evolution of volatile products by uDcontrolled thermal co~traction and expansion iD the still raw tile and such a limit being set case by case. General-ly, a heating.time of 4 - 6 minutes is considered adequate and at this point it may be assumed that the tile has reached - at least OD the surface - a temperature a few degrees lower than chamber temperature.
During the actual firing step, the tile remains at a practically constant surface temperature (even if not exactly constant due to the fact that heat-exchanges st~1l continue an~
the temperature of the chamber is Dot exactly co~stant) and conti.nues to advaDce in the firing zone which is at an almost e~eD temperature tending to be lower at the start and at the end due to closeness of to the heating and cooli~g Z0De 1~47744 respectively, and in gas counter-current. ~his step lasting slightly over 10 minutes, for example between 11 and 15 minutes.
In the meantime the heat penetrates more deeply in the tile body firing the inner layers of the tile. Finally, the cooliDg step takes place in a shorter time slightly shorter than the firing time for example slightly shorter than 12 minutes, say 8 - 10 minutes and may be determined by a partly direct and partly indirect cooli~g and occurs partially inside and partially or entirely outside the chamber.
The times specified above by way of example are close to optimum for wall-tiles, 4 - 5 mm. thick, and may be increased with a variatio~ ratio generally not linear, for thicker tiles, such as those used for flooring, which may even be 10 mm thick and for which the length of time for heating may be for example up to 6 - 8 minutes and for firing 17-20 minutes.
It has been found, according to the present inventioD
that the best compromise between the necessity of suitably supporting the tile OD the generatrices of the fixed-axis rota-ting supports for feeding, and the necessity of not introducing an excessive difference in the thermal conditions of the two faces of the tile, is obtained when the tile is kept in constant ~ contact with two or three of that geDeratrices.
i, This is obtained in the more common case of the support rotating rollers, when the distance between the centers of the roller is e~ual to half thelength of the tile itself. In such a caæe it is ensured that the product obtalned is of regular geometric shape and free from defects. However, it is possible to modify to a reasonable extent this condition when in practice it i8 necessary to produce with the same equipment, tiles of ~ varying dimensions.
1~4774~ -According to the present invention, the tile body is formed of one of the bodies termed as "clay materials", as speci-fied above. ~ypical materials form~ng said bodies are for example: plastic t~pe clays; no fat or semi-fat clays; kaolins;
feldspars; dolomite and calcium carbonate; siliceous sand. The' formulation of the glazing materials varies according to the required product and to the type of support used and may be raw, semi-raw or with fritted glazes.
I~ the carrying out of the present invention it must be considered some physical properties of the material'as speoified in the following. A temperature/weight diagram of the material indicates a loss of weight with temperature increase according to the development of volatile substances.
With the increase in temperature and with the tile body kept at that temperature for some time, there appears first an increase and next, iD the phase of specific interest, a loss oi permeability of the tile body itself, which logically starts on the outer surface exposed to a quicker increase of temperature.
~he ceramic material used must have a total weight'loss during the eDtire process, which, although not ~ery low when the above materials are dealt with, is however not excessive, for example, not more than 15%. 'In addition, it must be able to keep substan-tially its surface permeability at least up to a temperature of 700 - 800~ and until there is no substantial weight loss, as shown i~ the temperature/weight diagram, obviously under the conditions of the process according to this invention, particu-larly with the thermo-gravimetry gradients contemplated by the invention. ~urther, the thermo-dilatometric behaviour of the material, i.e. variation of linear dimensio~s with increase in temperature, must be such as not to produce excessive diffe-rence in dimensions between the two faces of the tile, which due 1')47744 to the unavoidable unevenness in heating, may not in fact be at the same temperature at least during part of the process. Such behaviour of the material may be illustrated by plotting a thermo-dilatometric diagram.
By operating according to the invention, particularly under the preferred and optimum conditions, much better results are obtained, on an industrial scale with respect to those obtained heretofore and actually beyond expectations. In the ceramic art the attempts made heretofore to introduce single-firing of tiles made of common materials which required a firing time of a few hours and resulted in the production of mostly defective tiles, led to believe that such results were impossible. The speed increase, the lack of supports for the tile and the drastic reduction of operating times are all factors which, based on past technical experience, were supposed to be negative, so that it was assumed tihat manufacturing of excellent products from materials of the above mentioned type required operation un-der gentler, more gradual and mechanically easier conditions than those previously adopted and not the contrary. ~-The fact that by making all operating conditions simultaneously more severe, i.e. both speed and rapidity and mechanical feeding conditions of the tile, the result obtained was never achieved before even in conditions remotely approaching those of the invention, represents in fact a remarkable techni-cal achievement.
In the accompanying drawings:
Fig. 1 represents a tunnel-type furnace adapted for carrying out the process according to the invention and Fig. 2 represents an example of supporting and feeding means for the tiles.
For actuation of the invention a tunnel-type furnace running longitudinally on a single plane, as schematically ~ .
'' '. ': - - : :
1~47744 illustrated in fig. 1, is best suited.
The detailed structure is not shown, as it is not within the scope of the present invention, but generally comprises, assuming that drying of the tile body is carried e~e~ t~ly~
. ` ~r ~ 8a -. .~ j .
)47744 a section 1 for drying of the glaze, a section 2 for the heating step, a ~ection 3 for the firing step and a section 4 for the cooling step.
The furnace is coDveniently heated by gas burners5 fitted in the walls so as not to radiate on the tiles, as shown schematically in fig. l, or by other suitable means, for example electric heating, the furnace walls being adequately insulated.
In the case where gas burners are used, these will produce volumes of combustio~ by-products which will be conviently moved iD
counter-current with respect to the tile, by means of suitable suction devices (not shown) or other means so that gas masses increase from the outlet to the i~let of the treatment chamber and generally forthe ma~or portion of the chamber, usually in a linear manner; and in the case of electric heating, air will have to be introduced to provide such volumes.
The elimination of moisture in area 1 may re~uire a separate circulation of hot gas, as showm schematically at 6 (gas inlet) and 7 (outlet) the burDers ~ot being provided iD this area. Suitable means will be provided to convey hot gases in counter-curreDt flow with respect to the tiles and suitable means will thus be provided for loading and unloading of the tiles, as showD schematically at 8, driving the rollers at the required speeds and eventually for speed control, and so on.
Fig. 2 shows aD e~ample of a supporting and feeding means for the tiles, two rollers 10 carried by shafts 11 supporting a moving tile 12; the roller shafts being controlled by any suita-ble means outside the furnace.
An example of carrying out the invention, illustrating the production of a particul æ tile, will now be give~ by way of example only, since the possibility of varying the composi-tions based OD product~ available in nature for the industry is .~ ., practically unlimited and those skilled in the art will be able to actuate the inventior based on what has hereiDbefore been described in the specification without departing from the true scope of the invention, even with compositio.ns very differeDt indeed.
The initial material is a mixture of "red beds" clays having the following formulation: Ignit. lo~s O - 15%
2 ~0%~A1203 15 - 20%J Fe203 2- 8% CaO 1 - 10%
MgO 1 - 10%, ~2 1 - 6~o~ Na20 1 - 5%~ The percentages are by weight.
The glaze used has the following composition: frits or glazes made of alkaline-boro-silicates containiDg Pb, ~i, Ti, Ba, Ca, Mg, Sr, Sn, Va, Zr; ceramic stains made of oxides or/
silicates or silico-aluminates of metals such as Fe, Co, Ni, Cr III, Ti, Mn, Cu, Zn, Ba, 2r, Sn, etc.; various additives for grinding such as kaolins aDd clays, Zr silicates; sodium-silicate, -chloride and -carbonate.
The tiles are of two main types having dimensions of 150 ~ 150 x 4.5 ancl 200 x 200 x 9, respectively.
After pressing, drying and glazing the tiles are fed by means of rollers, as shown in fig. 2, into an apparatus as illustrated in fig. 1.
The feeding speed in the first case is 1.9 meters/
minute and in the second case 1.4 meters/minute. Drying of the glaze lasts 5 and 6 minutes respectively, at a maximum temperature of 200C. HeatiDg lasts 5 and 6 minute3 respectively. The time required for firing is 13 and 17 minutes respectively and the temperature measured in the chamber rear the tiles is 1060C
Cooling lasts 9 and 12 minutes respectively.
The tiles thus obtained are perfectly regular and meet the required technical speclfications.
..
- ~ ` .
MgO 1 - 10%, ~2 1 - 6~o~ Na20 1 - 5%~ The percentages are by weight.
The glaze used has the following composition: frits or glazes made of alkaline-boro-silicates containiDg Pb, ~i, Ti, Ba, Ca, Mg, Sr, Sn, Va, Zr; ceramic stains made of oxides or/
silicates or silico-aluminates of metals such as Fe, Co, Ni, Cr III, Ti, Mn, Cu, Zn, Ba, 2r, Sn, etc.; various additives for grinding such as kaolins aDd clays, Zr silicates; sodium-silicate, -chloride and -carbonate.
The tiles are of two main types having dimensions of 150 ~ 150 x 4.5 ancl 200 x 200 x 9, respectively.
After pressing, drying and glazing the tiles are fed by means of rollers, as shown in fig. 2, into an apparatus as illustrated in fig. 1.
The feeding speed in the first case is 1.9 meters/
minute and in the second case 1.4 meters/minute. Drying of the glaze lasts 5 and 6 minutes respectively, at a maximum temperature of 200C. HeatiDg lasts 5 and 6 minute3 respectively. The time required for firing is 13 and 17 minutes respectively and the temperature measured in the chamber rear the tiles is 1060C
Cooling lasts 9 and 12 minutes respectively.
The tiles thus obtained are perfectly regular and meet the required technical speclfications.
..
- ~ ` .
Claims (16)
1. A process for the production of ceramic tiles, each having a front face and a rear face, comprising the steps of preparing a raw tile consisting of a dry, unfired tile body with a dried glaze coating on one face of the body, and with the body consisting predominantly of clay comprising at least 40% by weight of raw clay, an aggregate calcium oxide and magnesium oxide con-tent of less than 30% by weight and aluminum oxide content of less than 30% by weight, and an iron oxide content of less than 10% by weight; advancing the raw tile at a speed of the order of 1.5 - 2 meters per minute through a treatment chamber; in a heating step having a duration of 4 - 8 minutes, contacting both faces of the tile body concurrently with flowing hot gases as the tile body advances through the treatment chamber to raise both faces concurrently and, by substantially only direct convec-tion heating, substantially to firing surface temperature; in a subsequent firing step having a duration of 11 - 20 minutes, contacting both faces of the tile body concurrently with the flowing hot gases as the tile body continues to be advanced through the treatment chamber to maintain both surfaces substan-tially at the firing surface temperature concurrently, by substantially only direct convection heating, to fire the tile body and the glaze of the raw tile; and, following completion of the firing step, finally cooling the fired tile in a cooling step having a duration of less than 12 minutes; whereby the sum of the durations of the heating and firing steps is not in excess of about 28 minutes and the overall heating, firing, and cooling time is not in excess of 40 minutes.
2. A process as claimed in claim 1, in which, for tiles 4-5 mm thick, the time during which the tiles are contacted by hot gases having a duration of 15-21 minutes, with the duration being increased proportionately for tiles thicker than 4-5 mm.
3. A process as claimed in claim 1, wherein, for tiles 4-5 mm thick, the speed of the tiles through the treatment chamber is 1.5-2 meters per minute, and the speed is proportiona-tely reduced for tiles thicker than 4-5 mm.
4. A process as claimed in claim 1, in which the iron oxide in the dry, unfired tile body is not in excess of 8%.
5. A process as claimed in claim 1, including the step of supporting and advancing each raw tile through the treatment chamber by spaced rotating cylindrical supporting surfaces having a spacing such that each raw tile is continuously supported -on at least two, and no more than three, successive cylindrical supporting surfaces while traveling through the treatment chamber.
6. A process as claimed in claim 1, including drying the clay by flowing hot gases immediately prior to heating the raw tile and the glaze in the treatment chamber while advancing the raw tile and the glaze at the same speed as the raw tile and the glaze is advanced through the treatment chamber.
7. A process as claimed in claim 6, wherein the drying of the glazing lasts about 5 - 7 minutes.
8. A process as claimed in claim 1, in which firing of the tile is effected at a temperature of 800-1200°C as measu-red in the treatment chamber near the tile.
9. A process as claimed in claim 1, wherein firing of the tile is effected at a temperature of 1,000°C-1,100°C.
10. A process as claimed in claim 1, wherein the clay used contains at least 40% of raw clay free from substantial amounts of talcum and wollastonite.
11. A process as claimed in claim 1, wherein the clay includes calcium and magnesium oxides in a total amount substantially not exceeding 20% by weight.
12. A process as claimed in claim 10, wherein the clay comprises aluminium oxide in an amount substantially not exceeding 20% by weight.
13. A process as claimed in claim 10, wherein the clay includes the following components:
SiO2 55-70%, Al2O3 15-20%, Fe2O3 2-8%, CaO 1-10%, MgO 1-10%, K2O 1-6%, and Na2O 1-5%.
SiO2 55-70%, Al2O3 15-20%, Fe2O3 2-8%, CaO 1-10%, MgO 1-10%, K2O 1-6%, and Na2O 1-5%.
14. A process as claimed in claim 10, wherein the clay has a total weight loss not exceeding 15%, under process conditions.
15. A process as claimed in claim 1, in which the heat-ing step has a duration time of about 4 - 6 minutes and the firing step has a duration time of about 11 - 15 minutes, for tiles 4-5 mm thick, and, for tiles thicker than 4 - 5 mm, the heating step and firing step duration times are increased, but to a value less than that proportional to the increased thickness of such tiles thicker than 4 - 5 mm.
16. A process as claimed in claim 1, wherein the speed of movement of the tiles through the treatment chamber is maint-ained at 1.5 - 2 meters/minute, for tiles 4 - 5 mm thick, and, for tiles thicker than 4-5 mm, the speed of the tiles through the treatment chamber is reduced, but to a magnitude greater than that proportional to the increased thickness of such tiles thicker than 4 - 5 mm.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT2204074A IT1010205B (en) | 1974-04-29 | 1974-04-29 | PROCEDURE FOR COOKING STEPS OF CERAMIC PRODUCTS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1047744A true CA1047744A (en) | 1979-02-06 |
Family
ID=11190576
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA225,861A Expired CA1047744A (en) | 1974-04-29 | 1975-04-28 | Fast firing for ceramic tiles |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS6127346B2 (en) |
| BR (1) | BR7502580A (en) |
| CA (1) | CA1047744A (en) |
| DE (1) | DE2519311A1 (en) |
| ES (1) | ES436956A1 (en) |
| FR (1) | FR2268767B1 (en) |
| GB (1) | GB1489012A (en) |
| IT (1) | IT1010205B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1096751B (en) * | 1978-06-21 | 1985-08-26 | Marazzi Ceramica | PROCESS AND APPARATUS FOR COOKING CERAMIC MATERIALS |
| DE4210501C1 (en) * | 1992-03-31 | 1993-08-19 | Bayer Ag, 5090 Leverkusen, De | |
| US6520928B1 (en) | 1999-08-19 | 2003-02-18 | Alceu Meibach Rosa Junior | Medical liquid injection system and method |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2001340A1 (en) * | 1970-01-13 | 1971-07-22 | Nii Str Keramiki | Firing ceramic tiles |
-
1974
- 1974-04-29 IT IT2204074A patent/IT1010205B/en active
-
1975
- 1975-04-23 GB GB1687875A patent/GB1489012A/en not_active Expired
- 1975-04-24 FR FR7512838A patent/FR2268767B1/fr not_active Expired
- 1975-04-25 ES ES436956A patent/ES436956A1/en not_active Expired
- 1975-04-28 DE DE19752519311 patent/DE2519311A1/en active Granted
- 1975-04-28 BR BR7503277A patent/BR7502580A/en unknown
- 1975-04-28 CA CA225,861A patent/CA1047744A/en not_active Expired
- 1975-04-30 JP JP50051576A patent/JPS6127346B2/ja not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| ES436956A1 (en) | 1977-04-01 |
| JPS5116315A (en) | 1976-02-09 |
| DE2519311C2 (en) | 1987-05-27 |
| BR7502580A (en) | 1976-03-09 |
| JPS6127346B2 (en) | 1986-06-25 |
| GB1489012A (en) | 1977-10-19 |
| DE2519311A1 (en) | 1975-11-06 |
| FR2268767B1 (en) | 1978-06-30 |
| IT1010205B (en) | 1977-01-10 |
| FR2268767A1 (en) | 1975-11-21 |
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