MX2007008526A

MX2007008526A - A tunnel kiln for ceramic products.

Info

Publication number: MX2007008526A
Application number: MX2007008526A
Authority: MX
Inventors: Giuseppe Pifferi
Original assignee: Sacmi Forni Spa
Priority date: 2006-07-28
Filing date: 2007-07-13
Publication date: 2008-10-29
Also published as: EP1884730A2; ES2377240T3; CN101113873A; ATE535768T1; PL1884730T3; CN101113873B; EP1884730A3; RU2007125862A; BRPI0703052A; ITRE20060094A1; RU2441187C2; PT1884730E; EP1884730B1

Abstract

A tunnel kiln (1) for ceramic products comprising two opposite lateral walls (2), a horizontal roller conveyor (5) destined to support and advance a layer of tiles (100) internally of the kiln (1), a first series of burners (51) and a second series of burners (52) arranged aligned along the two lateral walls and facing towards the opposite wall, each burner (51) of the first series (51) being provided exclusively with an axial flame such as to heat a central zone of the tunnel while each burner (52) of the second series is provided with at least a radial-flame nozzle such as to beat a zone which is proximal to the lateral wall of the tunnel, each burner (51, 52) of the first and the second series being connected to a common conduit (60) of combustible gas and respectively to a first (510) and a second (520) conduit of a comburent, comprising:; means (523) for detecting a dimensional out-of-size with respect to a design project specification for the products exiting the kiln (1); a con trol unit (522) for receiving data coming from the means (523) for detecting; means for regulating (521) a flow rate of the comburent to the burners (52) of the second series on the second conduit (520) of the comburent, the means for regulating (521) of the comburent flow rate being controlled by the control unit (522) which is programmed to command the means for regulating (521) according to the data received from the means for detecting (523).

Description

TUNNEL OVEN FOR CERAMIC PRODUCTS The present invention relates to a tunnel kiln for ceramic products. In more detail, the present invention relates to a tunnel kiln provided with a roller conveyor on which the ceramic products are located, the products are for example, tiles. As is known, the tunnel kilns are heated using two series of burners, one on each side of the tunnel, which usually operate with methane gas, which are located on the side walls of the tunnel and face the opposite walls. On each side of the tunnel there are preferably two lines of burners, one above and one below the roller conveyor. The burners are supplied in groups, arranged in a bypass, by a single gas conduit, and each burner group is provided via a tap that is controlled by temperature control systems. The firing cycle of the tiles is determined with great precision using a cooking diagram that establishes a progressive heating of the tiles starting from the furnace inlet, and the tiles remain for a predetermined time at a predetermined temperature, and controlled cooling of the shingles before they reach the exit of the furnace.

Various types of ovens are known, as well as various characteristic assemblies of the burners in order to obtain perfect control of the operation of the furnace; however, the progressively increasing sizes of the cross sections of the ovens and the use of even faster cooking times to increase production rates per hour have brought to light some functional defects of traditional ovens that compromise their efficiency. In particular, the limitations of traditional ovens emerge when the cross section of the tunnel kiln exceeds certain dimensions. In very large tunnel kilns, there is an inconvenient distribution of the temperature in the cross section, where there are usually higher temperatures in the center than in the vicinity of the walls. This inevitably results in cooking defects in the tiles that advance close to the walls of the tunnel, the defects emerge as dimensional and shape defects, such as the lack of planarity; which results in an increase in waste products. To reduce this phenomenon, research has been done by the Applicant on special types of burners that are directed to advantageously heat the interior of the tunnel including the areas in proximity of the side walls of the tunnel.

In particular, in IT1287626, by the same Applicant, a tunnel furnace having two series of burners exhibiting different characteristics is described, wherein a first series of burners is predominantly intended to heat the central zone and a second series of burners. Burners are predominantly used to heat the area near the walls of the tunnel. In the furnace described above, the gas flow rate to the burners to prevalently heat the area near the walls of the tunnel is controlled by a valve controlled by a control system that modulates the gas flow rate in accordance with the temperature measured by special thermocouples located internally in the tunnel, in the vicinity of the side walls. Unfortunately, measurements of the thermocouples located on the side walls are often influenced by the turbulence present along the walls and by the proximity of the burners themselves. This means that the measurement of the temperature values, which in fact are correct in relation to the exact point where the measurement is made, is considerably outside in relation to the temperatures found in the immediate vicinity of the tiles on the rollers. Actually, in the same zone along the side wall, although operating at a substantially homogeneous temperature, at different points there are considerably different temperature measurements.

Therefore the use of thermocouples located along the side walls of the tunnel does not result in an efficient regulation of the system. There is, for the reasons set forth above, a strongly felt need to provide a tunnel kiln for ceramic products that provide efficient regulation, without the disadvantages found in the prior art, to obtain ceramic products having dimensional characteristics that are as close as possible to design specifications, within the scope of a simple and rational construction solution. The object of the present invention is to provide a tunnel kiln for ceramic products having structural and functional characteristics which satisfy the requirements and which at the same time obviate the disadvantages mentioned with reference to the prior art. The object is achieved by the tunnel kiln for ceramic products described in claim 1 of the present application. The dependent claims delineate preferred and particularly advantageous embodiments of the tunnel kiln for ceramic products of the invention. The additional features and advantages of the invention will emerge better from a reading of the following description, provided by way of non-limiting example with the help of the appended Figures, in which: - Figure 1 is a side view of a tunnel kiln of the present invention; - Figure 2 is a partial section enlarged along ll-l of Figure 1; - Figure 3 is a partial section enlarged along ll-l l of Figure 2. With reference to the figures mentioned above of the drawings, 1 denotes in its entirety a tunnel kiln for ceramic products as in the present invention. The furnace 1 is formed, in a very general description, by two opposite side walls 2, a base 3 and a dome 4. A roller conveyor 5 of known type is located internally of the furnace 1, the roller conveyor 5 makes advancing the ceramic products, which in the example are tiles 100. Two lines of gas burners 31 and 32 are disposed on each side wall 2 of the tunnel, respectively above and below the roller conveyor 5. The burners of each line are located internally of holes 6 provided in the side wall 2 of the furnace 1. Each line of burners comprises two series of different burners, respectively 51 and 52, the burners of each series are interspersed with the burners of the other series. There are thus four lines 31, 32 of burners, two on one wall and two on the other wall. Each line 31, 32 is composed of two series of burners. The burners of the two series of each line are interspersed between them and with the burners of the other line located on the same wall, and with the burners of the same series that are part of the coplanar line arranged on the opposite wall. . In particular, the burners 51, which we will call axial burners, are provided exclusively with a nozzle that produces an axially directed flame such as prevalently to heat the central zone of the tunnel, while the burners 52, which we will call burners Radial, are provided with a plurality of radial flame nozzles such as prevalently to heat the area near the side wall of the tunnel. Alternatively, radial burners 52, in addition to having radial flame nozzles, may also be provided with an axial flame nozzle. All the burners, axial and radial, are supplied from a common conduit 60 for the supply of combustible gas, as is the case with traditional ovens. Each series of burners 51 0 52 can conveniently be divided into sectors that interest different thermal zones of the kiln, each of which is provided with its own means to regulate and control, which for the sake of simplicity are not illustrated herein, and all the supply from the gas supply conduit 60. The heat control elements 70 are located in each of the thermal zones, which may be thermocouples or thermal probes. The elements 70 advantageously are located centrally, in the example in the vault 4 and the base 3, and the signals they emit are sent to the devices for regulation and control of thermal energy, not illustrated here. In the present invention, and as is visible in Figure 2, the axial burners 51 are supplied from a common duct 510 for the supply of air on which usual means for regulation and control are placed (not shown), while the radial burners 52 are supplied from a different conduit 520 of air supply. In particular, the additional conduits 524 branch off from the conduit 520, each additional conduit 524 gives rise to a single burner 52 of the second series. In the illustrated embodiment, the air supply conduit 520 is intercepted by a motorized valve 521 positioned upstream of the conduits 524 and connected to a control unit 522 that is programmed to regulate the pressure of the air flow and thus the flow rate in supply to the respective radial burners 52. In particular, the control unit 522 regulates the air pressure to be sent to the radial burners, and therefore the air flow, according to signals received from special means 523, of which more is present in the present below, which detect the out-of-size dimensions of the products leaving the furnace 1 with respect to the design specifications of the 100 tile. In essence, in the presence of defects detected in the tiles 1 00, located on the sides and come out of the furnace 1, the control unit 522, which has received the signals from the detection means 523, intervenes immediately, changing the amount of air supplied to the radial burners 52 and thus modifying the temperature thereof. This is obtained by keeping the gas flow constant to the radial burners 52, which is the same as the supply to the axial burners 51, thus keeping the thermal energy supplied constant. Naturally, the necessary changes in the air flow will be of small size and therefore there will be no negative alteration to the general operation of the furnace 1. To obtain optimum regulation, the control unit 522 constantly receives the pressure values via pressure transducers 81, 82 located respectively on the The supply to the axial burners 51 and to the supply line 520 to the radial burners 52 are provided. For the objects of the present invention, the detection of "defects" in the tiles 100 can be done by a staff member operating on a board connected to the control unit 522, or via an automatic detection system of the caliber and planarity of the tiles, of the type described in the Italian Application RE2006A000007, by the same Applicant, which is not reiterated in detail herein. Obviously any other suitable means can be used to detect defects of the tiles and send a corresponding signal to the control system 522. The signal sent to the control system 522 is advantageously converted to pressure difference values to be achieved between the two air streams respectively supplied to the axial burners 51 and the radial burners 52. In operation, the furnace 1 is put into operation, maintaining the same air pressure in supply to the axial and radial burners. After this, and only in the presence of defects in the shingles leaving the furnace 1, detected by the means 523 for detecting, the control unit sends a signal to the valve 521 to open or close much more in accordance with the change of requested pressure, the pressure change is advantageously calculated by the control unit 522 of agreement with the signal, representing the defect in the tiles, received from the means for detection 523. In essence, the initial operating parameters change, in a small amount. Alternatively to the use of a valve 521 which regulates several radial burners 52, for example the burners in a given heating zone, as described above, a valve can be used for each radial burner 52, the valves can be located on the ducts 524 In this case, a corresponding pressure transducer, located downstream of the valves, which sends the signal to the control system 522, is provided for each regulating valve. As the control system 522 uses pressure transducers to control the pressure difference between the air stream respectively to the axial burners 51 and the radial burners 52, the pressure transducers can be replaced by special systems for detecting the pressure difference? ? which directly sends the value of ?? to the control system 522. Naturally the furnace 1 is generally operated by a central electronic unit, and the control unit 522 is also operated by it. As can be seen from the above description, the tunnel kiln for ceramic products of the present invention satisfies the requirements and obviates the disadvantages described in the introductory part of the present description with reference to the prior art. Thanks to the modulation of the air flow rate to the radial burners commanded by a single control unit, the furnace 1 of the present invention confers on all the tiles that leave the required dimensions and planarity, without distinction between the tiles that come of the central zones or the lateral zones of the furnace, and with a consequent considerable reduction in the waste. In addition, the oven of the present invention can be easily manufactured using traditional ovens with small structural modifications. Obviously an expert in the field, in order to meet special and specific contingent requirements, can make numerous modifications and changes to the tunnel kiln for ceramic products described above, and all fall within the scope of protection of the invention as defined in following claims.

Claims

CLAIMING IS 1. Tunnel kiln for ceramic products comprising two opposite side walls, a horizontal roller conveyor intended to support and advance a layer of tiles internally of the furnace, a first series of burners and a second series of burners arranged aligned along the two side walls and facing the opposite wall, each burner of the first series is provided exclusively with a nozzle that produces an axial flame such as to heat a central zone of the tunnel while each burner of the second series is provided with at least one radial flame nozzle such as to heat an area that is close to the side wall of the tunnel, each burner of the first and second series is connected with a common fuel gas conduit and respectively with a first and a second conduit of an oxidizer , characterized in that it comprises: -means for detecting an out of dimensional size with respect to a cification of design project for the products that come out of the oven; - a control unit for receiving data arriving from the means to detect, - means for regulating a flow rate of the oxidizer to the burners of the second series located on the second conduit of the oxidizer, the means for regulating the speed of The comburent flow are controlled by the control unit that is programmed to command the means to regulate according to the data received from the means to detect.
2. Oven according to claim 1, wherein the second combustor conduit comprises a manifold, from which a plurality of combustion conduits are branched, each conduit giving rise to a single burner of the second burner series.
3. Oven according to claim 2, wherein the means for regulating are located on each of the conduits that supply the burners of the second series.
4. Oven according to claim 2, wherein the means for regulating are located on the oxidizer distributor.
5. Oven according to claim 1, wherein the second series of burners is formed by a plurality of burners located alternately with the burners of the first series.
6. Oven according to claim 1, wherein the burners of the second series further comprise a nozzle having an axial flame.
7. Oven according to claim 1, wherein each side wall comprises two lines of the burners, one of which is above the roller conveyor and one of which is below the roller conveyor.
8. Oven according to claim 7, wherein, along each line, the burners of the first series and the second series are arranged alternately with each other.
9. Oven according to claim 1, wherein the means for detecting comprises an automatic system for detecting a lime and / or a planarity of the ceramic product leaving the tunnel. 1 Oven according to claim 1, wherein the means for regulating the flow rate comprises a motorized valve. eleven . Furnace according to claim 1, wherein further comprises means for detecting the pressure respectively located on the first conduit and the second conduit of the oxidizer, the means for detecting the pressure are connected to the control unit. SUMMARY The present invention discloses a tunnel furnace (1) for ceramic products comprising two opposite side walls (2), a horizontal roller conveyor (5) designed to support and advance a layer of tiles (1 00) internally from the furnace (1), a first series of burners (51) and a second series of burners (52) arranged aligned along the two side walls and facing the opposite wall, each burner (51) of the first series (51) it is provided exclusively with an axial flame such as to heat a central zone of the tunnel while each burner (52) of the second series is provided with at least one radial flame nozzle such as to heat an area which is close to the side wall of the tunnel, each burner (51, 52) of the first and second series is connected to a common conduit (60) of combustible gas and respectively to a first (51 0) and a second (520) conduit of an oxidizer, comprising means (523) to detect an out of dimensional size with respect to a design project specification for products leaving the oven (1); a control unit (522) for receiving data coming from the means (523) for detecting, means (521) for regulating a flow rate of the combustor to the burners (52) of the second series located on the second conduit (520) ) of the comburent, the means (521) for the regulation of the The flow rate of the oxidizer are controlled by the control unit (522) which is programmed to command the means (521) to regulate according to the data received from the means (523) to detect.