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 specially adapted for furnaces of these types
  • F27B9/36—Arrangements of heating devices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B11/00—Apparatus or processes for treating or working the shaped or preshaped articles
  • B28B11/24—Apparatus or processes for treating or working the shaped or preshaped articles for curing, setting or hardening
  • B28B11/243—Setting, e.g. drying, dehydrating or firing ceramic articles
• • 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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D99/00—Subject matter not provided for in other groups of this subclass
  • F27D99/0001—Heating elements or systems
  • F27D99/0033—Heating elements or systems using burners

Definitions

• This invention relates to a kiln and method for firing substantially flat basic ceramic articles.
• this invention finds advantageous but not exclusive application in the firing of substantially flat basic ceramic articles to obtain tiles or ceramic slabs.
• the ceramic article firing cycle is designed with great precision and involves heating the ceramic articles from the kiln inlet, holding them inside a firing chamber at a predefined temperature for sufficient time to fire them, and a subsequent controlled cooling before reaching the kiln outlet.
• the kiln is normally divided into a pre-heating zone, a firing zone proper, downstream of the pre-heating zone, and a cooling zone, located downstream of the firing zone, to reduce the temperature of the ceramic articles coming from the firing zone.
• the known kilns are typically heated by a series of gas burners, typically using methane gas, organised into groups of burners and arranged above and below the advancement plane of the ceramic articles to heat, respectively, the pre-firing zone and the proper firing zone, up to the firing temperature so as to fire the ceramic articles in transit through the various zones of the kiln and obtain finished ceramic products, such as finished ceramic slabs or tiles.
• gas burners typically using methane gas
• the environmental conditions inside the kiln very precisely, especially in terms of temperature and pressure.
• the purpose of this invention is to provide a kiln and method for firing substantially flat basic ceramic articles, which allow the drawbacks of the prior art to be overcome, at least in part, and which are, at the same time, both easy and cheap to make.
• a kiln and method for firing substantially flat ceramic articles are provided according to what is claimed in the independent claims that follow and, preferably, in any one of the claims depending directly or indirectly on the independent claims.
• reference number 1 denotes, as a whole, a kiln for firing substantially flat ceramic articles 2.
• this discussion will refer to the firing of substantially (but not necessarily) flat basic ceramic articles 2 (henceforth, for brevity, only “ceramic articles 2”) to obtain final ceramic products T, more precisely ceramic slabs, more precisely tiles.
• the ceramic articles 2 are generally obtained by pressing a ceramic powder (a semi-dry mixture, especially having a moisture content of between 5% and 7%) mainly based on silica.
• the ceramic articles 2 comprise additional inorganic oxides such as, for example, the oxides of Magnesium, Sodium Zirconium and Potassium.
• second component does not imply the presence of a “first” component. These terms are in fact used as tags to improve clarity and should not be understood in a limiting way.
• the kiln 1 for firing ceramic articles 2 (which advantageously is a roller kiln, as will be further explained below) comprises: a firing chamber 3, which, in turn, has an opening 4A at the input station 4, through which, in use, the ceramic articles 2 enter the firing chamber 3; another opening 5A at the output station 5 through which, in use, the final ceramic products T exit the firing chamber 3; a conveyor device 6 for conveying a plurality of ceramic articles 2 along a given path P extending through the firing chamber 3 in a forward direction A from the input station 4 to the output station 5; and a heating system 7 configured to provide heat to at least part of the firing chamber 3 so as to fire the ceramic articles 2 passing through it and obtain the final ceramic products T.
• the kiln 1 is a tunnel kiln and comprises: two side walls 8 facing each other to delimit the firing chamber 3 on the side, and a vault wall 9 and a back wall 10 facing each other to delimit the firing chamber 3 at the top and bottom.
• these walls 8, 9 and 10 are made of insulating and refractory material, for example, masonry in the cases illustrated.
• the firing chamber 3 comprises: at least one pre-heating zone PZ, downstream of the input station 4, wherein the ceramic articles 2 are gradually pre-heated from an input temperature (which is variable from the room temperature up to at most about 300°C) C up to a temperature of about 1100°C; and a firing zone FZ proper, arranged immediately (i.e., with no gap) downstream of the pre-heating zone PZ along the given path P, wherein the ceramic articles 2 are fired at a firing temperature, which varies from about 1100°C to about 1400°C; in particular, from about 1200°C to about 1300°C.
• a cooling zone RZ located downstream of the firing zone FZ, and designed to allow a controlled reduction in temperature of the ceramic articles 2 passing through it .
• the cooling zone RZ is divided into a first cooling section immediately (i.e . without a gap) downstream of the firing zone FZ for the so-called rapid cooling of the ceramic articles from the above-mentioned firing temperature up to a temperature of at least approximately 600°C; a second cooling zone for cooling the ceramic articles 2 from a temperature of approximately 600° to a temperature of approximately 450°C, and a third cooling zone, at the end of which the finished ceramic products T will be at a temperature that is essentially equal to the room temperature.
• the kiln 1 (more specifically, the firing chamber 3) also comprises a pair of insulating separating bulkheads 12, essentially vertical, which extend within the firing chamber 3 transversely to the forward direction A at the ends 13a and 13b of the firing zone FZ to limit (or at least obstruct) the flow of air from the outside to the inside of the firing zone FZ (see, for example, Figure 1 ).
• a pair of insulating separating bulkheads 12 extend within the firing chamber 3 transversely to the forward direction A at the ends 13a and 13b of the firing zone FZ to limit (or at least obstruct) the flow of air from the outside to the inside of the firing zone FZ (see, for example, Figure 1 ).
• the insulating separating bulkheads 12 are made of an insulating and refractory material, for example, in the case illustrated in Figure 1 , in masonry. Even more advantageously but without imposing limits, these bulkheads 12 are provided with relative openings 14a and 14b, aligned with each other along the given path P, and configured to allow ceramic articles 2, passing along the given path P, to pass through them. In particular, these openings 14a and 14b are sized so as to allow the passage of the ceramic articles 2 while compromising as little as possible the insulation of the firing zone FR with respect to the rest of the firing chamber 3.
• the above-mentioned heating system 7 is configured to heat by convection the pre-heating zone PZ so as to impose in said zone PZ a temperature increasing from the above-mentioned input temperature of the ceramic articles 2 (in particular, from a temperature varying from the room temperature that is about 20°C, up to about 300°C) up to about 1110°C (in particular, up to a firing temperature varying from about 1100°C to about 1400°C) and to heat the firing zone FZ by radiation so as to impose in said firing zone FZ a substantially constant firing temperature.
• this firing temperature ranges from about 1100°C to about 1400°C; in particular, from about 1200°C to about 1300°C.
• the heating, by radiation, in the firing zone FZ ensures a more uniform distribution of heat, favouring the maintenance of substantially constant ambient conditions in terms of temperature and pressure, with obvious advantages in terms of the aesthetic appearance of the final ceramic product T. It should be added that the use of an electric heater 18a, 18b in this zone FZ of the firing chamber 3 allows a considerable reduction in the consumption of non-renewable substances and in the production of CO 2 and other combustion waste products compared to the known kilns 1, with consequent environmental and economic advantages.
• the second radiant heating module 17 comprises (in particular, consists of) at least one upper electric heater 18a (in particular, a plurality of upper electric heaters 18a, each) arranged above the conveyor device 6; at least one second lower electric heater 18b (in particular, a plurality of upper electric heaters 18b, each) arranged below the conveyor device 6; and a first electric power supply (not visible in the attached figures and known) for supplying power to the various electric heaters 18a, 18b.
• each electric heater 18a, 18b is a radiant panel comprising: an insulating support 19, advantageously but without imposing limits made of refractory material; a plurality of electrically conductive elements 20, which are supported by the support 19, have electric terminals 21 at their ends configured to receive electric current from the aforementioned first electric power supply and are configured to transfer heat by Joule effect to the firing zone FZ (see Figure 2 and Figures 4A and 4B ).
• the above-mentioned first electric power supply is configured to transfer an alternating electric current having an intensity ranging from approximately 10A to approximately 200A to each electrically conductive element 20 so as to heat these electrically conductive elements 20 and transfer heat by Joule effect to the firing zone FZ.
• each electric heater 18a, 18b is configured to receive a voltage varying between about 55V and about 220V; more advantageously but without imposing limits, the above-mentioned first electric power supply is configured to transfer a voltage varying between about 55V and about 220V to each electrically conductive element 20; in particular, at the above-mentioned electrical terminals 21 of each electrically conductive element 20.
• these electrically conductive elements 20 are wire-like elements arranged on the support 19 forming a resistive coil (see Figures 4A and 4B ).
• these electrically conductive elements 20 comprise (in particular, consist of) a material chosen from iron-chromium-aluminium alloy (FeCrAI alloy), nickel-based alloy, tungsten-based alloy or molybdenum-based alloy; even more advantageously but without imposing limits, these electrically conductive elements 20 are made of Kanthal TM .
• each electric heater 18a, 18b is a radiant panel having a power output ranging from about 1 to about 20kW.
• the upper electric heater 18a (in particular, each of the upper electric heaters 18a) is installed on the vault wall 9 of the kiln 1 with the electrically conductive element 20 facing the inside of the firing zone FZ.
• the vault wall 9 is mounted movable on the side walls 8 so that it can be moved away from the side walls 8 in order to open the kiln 1 (in particular, to access the firing chamber 3) and intervene for maintenance and replacement of the upper electric heaters 18a. While the lower electric heater 18b (more specifically, each of the lower electric heaters 18a) is installed (more specifically, rests) on the base wall 10.
• the use of this type of electric, so-called radiant panel, heaters 18a, 18b, essentially planar is suitable for the firing of substantially flat ceramic articles 2 as it allows for a better, in particular more homogeneous, heat distribution in the firing zone FZ.
• the kiln 1 also comprises a substantially horizontal protection layer 22 arranged between the conveyor device 6 (in particular, between the conveyor plane 15) and the lower electric heater 18b (in particular, and the plurality of lower electric heaters 18b) to protect the (that is, each) lower electric heater 18b in the event of unintentional damage to the ceramic articles 2 or the rollers of the conveyor device 6, which could unintentionally cause the ceramic material to fall onto the lower electric heaters 18b damaging them.
• damage to one (or more than one) electric heater 18b could jeopardise the firing step, but its replacement requires machine downtime, with all the productivity disadvantages this entails.
• the protection layer 22 comprises (in particular, consists of) one or more plates of conductive material, so as to physically protect the lower heaters 18b without unduly compromising their energy efficiency.
• the second heating module 17 comprises: a first plurality of radiating tubular elements 23a made of silicon carbide that are mounted between the side walls 8, above the conveyor device 6 (in particular, the conveyor plane 15); a second plurality of radiating tubular elements 23b made of silicon carbide that extend between the walls 8 below the conveyor device 6 (in particular, the conveyor plane 15); and a second electric power supply (not visible in the attached figures and known) in connection with the radiating tubular elements 23a, 23b, by means of electrical terminals 24 delimited by protection sleeves 25 made of ceramic material and/or alumina (see Figure 5 ), and configured to supply power to these tubular elements 23a, 23b so as to heat them up to a temperature of at least about 600°C; in particular between 600°C and 2000°C (more specifically, between 1100°C and 1650°C), thereby rendering them incandescent.
• the radiating tubular elements 23a, 23b are configured to transfer heat by radiation to the firing zone FZ.
• each plurality of radiating tubular elements 23a ,23b has a power output ranging from about 1 to about 20kW.
• the variant of the heating module 17 equipped with radiating tubular elements 23a, 23b is easier to produce than the solution with electric, so-called radiant panel, heaters 18a, 18b, since the radiating tubular elements 23a, 23b are installed by inserting them directly into special housings made in the side walls 8 of the kiln 1 and are also easier to replace in the event of damage, for example in the event of the unintentional breakage of some ceramic articles 2.
• the radiating tubular elements 23a, 23b have a diameter of approximately 12mm to approximately 75mm and a length of approximately 775mm to approximately 2150mm, depending on the dimensions of the kiln 1 in which they are to be installed.
• the above-mentioned second electric power supply is configured to transfer an alternating electric current having an intensity ranging from approximately 10A to approximately 200A to each radiating tubular element 23a, 23b so as to heat them to the above temperatures and transfer heat by radiation to the firing zone FZ.
• each radiating tubular element 23a, 23b is configured to receive a voltage varying between about 55V and about 220V; more advantageously but without imposing limits, the above-mentioned second electric power supply is configured to transfer a voltage varying between about 55V and about 220V to each radiating tubular element 23a, 23b; in particular, at the above-mentioned electrical terminals 24 of each radiating tubular element 23a, 23b.
• the kiln 1 in this case (that is, when the second heating module 17 comprises radiating tubular elements 23a, 23b), also comprises an upper conductive layer (not illustrated in the attached figures) arranged between the plurality of upper radiating tubular elements 23a and the conveyor device 6 and a lower conductive layer arranged between the plurality of lower radiating tubular elements 23a and the conveyor device 6.
• These conductive layers when provided, are configured to receive heat by radiation from the radiating tubular elements 23a, 23b and transmit it to the conveyor device 6, then to the conveyor plane 15. The presence of these conductive layers allows for a more homogeneous diffusion of heat, reducing the concentrated heat zones that could arise in the firing zone FZ by using discrete heating elements such as the radiating tubular elements 23a, 23b described above.
• the kiln 1 (in particular, the second heating module 17) also comprises a power modulator that can be operated to vary the magnitude, that is the voltage of the power supplied from the power source to the radiant panel electric heaters 18a, 18b and/or to the radiating tubular elements 23a, 23b.
• the kiln 1 also comprises at least one control unit CU configured to control the operation of the second heating module 17, for example by acting on the aforementioned power modulator, to ensure that substantially constant temperature and pressure conditions are maintained within the firing zone FZ.
• the kiln 1 comprises at least one temperature detector (not visible in the attached figures and known, which advantageously comprises at least one thermocouple) arranged within the firing zone FZ to detect the temperature within the firing chamber 3, and the control unit CU is configured to control the actuation of the second heating module 17, for example by acting on the aforementioned power modulator, at least according to what is detected by this temperature detector.
• the first convective heating module 16 comprises (in particular, consists of) at least one (known) burner 26 configured to burn a combustion mixture in order to heat the pre-heating zone PZ; at least one feeding device (not illustrated and known) for feeding a fuel mixture to (that is, at least part of) the burners 26; and a second feeding device (also known and not described in detail) for feeding an oxidizer, which advantageously but without imposing limits (comprises) is substantially ambient air (with about 21% oxygen), to the (that is, at least part of the) burners 26 so as to form the combustion mixture together with the fuel.
• oxidizer which advantageously but without imposing limits (comprises) is substantially ambient air (with about 21% oxygen), to the (that is, at least part of the) burners 26 so as to form the combustion mixture together with the fuel.
• the (or each) fuel feeding device comprises a motorised, e.g., electrically operated, control valve (not visible in the attached figures and known) arranged along the (or each) fuel mixture feeding duct or downstream of the (or the various) feeding ducts that can be operated (suitably opened) to regulate the quantity (flow rate - that is, the quantity by weight in the unit of time) of the fuel mixture to be fed to the burner 26 (or to each group of burners 26), and thus the quantity (flow rate) of the fuel mixture comprised in the combustion mixture.
• a motorised, e.g., electrically operated, control valve not visible in the attached figures and known
• the kiln 1 further comprises at least one temperature detection device 27, advantageously comprising at least one thermocouple, for detecting the temperature within the firing chamber 3, in particular in the pre-heating zone PZ, and a control unit CU (which may be the same as the one described above) that is configured to control the actuation of the control valve of the fuel mixture feeding device and/or the mounted control valve of the oxidizer feeding device so as to vary the quantity of fuel mixture and/or the quantity of oxidizer mixture according to the temperature detected by the temperature detection device 27, so as to ensure controlled temperature conditions, in particular, always between 300°C and 1100°C, within the pre-heating zone PZ.
• a control unit CU which may be the same as the one described above
• the first heating module 16 comprises (in particular, consists of) at least one electric heater 28 comprising, in turn: a tubular casing 29 having, at one end, an inlet duct 30 for introducing a gas comprising (in particular, consisting of) ambient air within the tubular casing 29; at least one electric heating element (not visible in the attached figures) extending within the tubular casing 29 and able to be operated to heat the gas fed via the duct 30; and a tubular outflow element 31 extending from the tubular casing 29, on the opposite side from the inlet duct 30, is configured to be traversed by the gas leaving the electric heater.
• a method for firing ceramic articles 2 is presented, which advantageously but without imposing limits, is implemented with a kiln 1 for firing ceramic articles 2 produced in accordance with any of the embodiments described above.
• the second heating module 17 comprises at least one plurality of radiating tubular elements 23a, 23b made of silicon carbide and mounted between the side walls 8 of the kiln 1, and a second electric power supply
• the second electric power supply supplies power through the radiating tubular elements 23a, 23b so as to heat them up to a temperature of at least about 600°C (in particular, between about 600°C and about 2000°C) and these tubular elements 23a, 23b, once heated, transfer heat by Joule effect to the firing zone FZ to impose the above-mentioned firing temperature.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Ceramic Engineering (AREA)
• Structural Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Furnace Details (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=91022875

Family Applications (1)

Country Status (2)

Citations (5)

Family Cites Families (1)

• 2024
  • 2024-02-19 IT IT102024000003460A patent/IT202400003460A1/it unknown
• 2025
  • 2025-02-18 EP EP25158545.1A patent/EP4603779A1/de active Pending

Patent Citations (5)

Also Published As

Similar Documents

Legal Events