ITRE20060094A1 - TUNNEL OVEN FOR CERAMIC ARTICLES - Google Patents

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 control 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

28433-PPG

DESCRIPTION

of the Italian Patent for Industrial Invention entitled: "Tunnel kiln for ceramic products" in the name of SACMI FORNI S.P.A. based in 40122 BOLOGNA 5 * * * * *

The present invention refers to a tunnel kiln for ceramic products.

More particularly, the present invention relates to a tunnel kiln provided with a roller conveyor 10 on which the ceramic articles, such as for example tiles, are placed.

As is known, tunnel ovens are heated with two series of burners, one on each side of the tunnel, generally operating with methane gas, which 15 are placed on the side walls of the tunnel and facing the opposite walls.

Preferably, on each side of the tunnel, two burner alignments are provided, one above and one below the roller conveyor.

20 The burners are supplied in groups, placed in derivation, from a single gas pipe, and each group of burners is fed through a tap served by the temperature control systems.

25 The firing cycle of the tiles is 28433-PPG

determined with great precision through a firing diagram that provides for the progressive heating of the tiles starting from the entrance into the kiln, their permanence for a predetermined time at a predetermined temperature, and controlled cooling before reaching the kiln exit.

Different types of burners are known, as well as different characteristic arrangements of the same in order to obtain a perfect control of the operation of the oven, however the increasing size of the cross section of the ovens, and the adoption of increasingly rapid cooking cycles in order to increase their hourly productivity, highlighted certain 15 deficiencies in the functioning of traditional plants that compromise their efficiency.

In particular, the limits of traditional systems occur when the cross section of the tunnel kiln exceeds certain values. 20 In fact, in very large tunnel ovens there is an inconvenient distribution of the temperature in the cross sections, where temperatures are generally higher in the center than in the vicinity of the walls.

25 This inevitably leads to defects in 28433-PPG

firing in the tiles that travel near the tunnel walls, defects that result in dimensional and shape defects, such as a lack of flatness, with a consequent increase in waste. 5 In order to reduce this phenomenon, particular types of burners have been studied by the same applicant to conveniently heat the inside of the tunnel even near the side walls.

10 In particular, IT1287626 by the same applicant describes a tunnel kiln with two series of burners of different characteristics, where a first series of burners are suitable for heating mainly the central area and a second series 15 of burners are suitable for heating mainly the area proximal to the walls of the tunnel.

In said furnace, the gas flow to the burners designed to heat mainly the proximal area to the tunnel walls is controlled by a valve 20 enslaved by a control system which modulates the gas flow according to the temperature measured by special thermocouples placed at the inside the tunnel, near the side walls.

Unfortunately, the measurements of the thermocouples, 25 placed on the side walls, are often affected by 28433-PPG

from the turbulence present along the walls and from the proximity to the burners themselves. This involves the measurement of temperature values which, although it is correct as regards the point where the measurement is carried out, however, it is significantly different from the temperature measurement obtainable in the immediate vicinity of the tiles placed on the roller. In practice, in the same area, along the side wall, while operating 10 at a substantially homogeneous temperature, significantly different measurements are obtained at different points.

Therefore, the use of thermocouples placed along the side walls of the tunnel does not allow effective regulation of the system.

15 The need is therefore strongly felt to have available a tunnel kiln for ceramic products that allows effective regulation, without the drawbacks of the prior art, so as to obtain ceramic products having dimensional characteristics as close as possible to those of the project, in the context of a simple and rational constructive solution.

The purpose of the present invention is to provide a tunnel kiln for ceramic articles 25 having structural and functional characteristics such as 28433-PPG

to satisfy the aforesaid requirements and at the same time to obviate the drawbacks mentioned with reference to the known art.

This object is achieved by means of a 5-tunnel kiln for ceramic products according to claim 1.

The dependent claims outline preferred and particularly advantageous embodiments of the tunnel kiln for ceramic products according to the invention.

Further features and advantages of the invention will become evident from reading the following description provided by way of non-limiting example, with the aid of the 15 figures illustrated in the attached tables, in which:

Figure 1 shows a side view of a tunnel oven according to the present invention;

Figure 2 shows the partial enlarged section II-II of Fig.1;

20 - figure 3 shows the enlarged partial section III-III of Fig.2.

With reference to the aforementioned figures, the number 1 globally indicates a tunnel kiln for ceramic products in accordance with the present invention.

25 Oven 1 is formed, in a totally 28433-PPG manner

general, by two opposite side walls 2, a base 3 and a vault 4.

Inside the kiln 1 there is a roller conveyor 5 of the type known per se, for the advancement 5 of the ceramic products, in the example tiles 100.

On each side wall 2 of the tunnel there are two alignments 31 and 32 of gas burners, respectively above and below the conveyor 5.

10 The burners of each alignment are placed inside holes 6 made in the side wall 2 of the oven.

In each alignment there are two series of different burners, 51 and 52 respectively, the 15 burners of each series being interspersed with the burners of the other series.

There are thus four alignments 31.32 of burners, two on one wall and two on the other. Each array 31,32 is made up of two sets of 20 burners. The burners of the two series of each alignment are interspersed with each other and with the burners of the other alignment placed on the same wall, and with the burners of the same series forming part of the coplanar alignment placed on the opposite wall 25.

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In particular, the burners 51, which we will call axial burners, are provided exclusively with an axial flame nozzle so as to mainly heat the central area of the tunnel, while the 5 burners 52, which we will call radial burners, are equipped with a plurality of nozzles. radial flame so as to mainly heat the proximal area of the side wall of the tunnel.

Alternatively, the radial burners 52, in addition to 10 having radial flame nozzles, can be further provided with an axial flame nozzle.

All the burners, axial and radial, are connected to a common duct 60 for feeding the fuel gas 15, as occurs in traditional ovens.

Each series of burners 51 or 52 can be conveniently divided into sectors involving different thermal zones of the furnace, each of which is equipped 20 with its own adjustment and control means, not illustrated for simplicity, leading to the gas supply duct 60.

In each of said thermal zones there are 70 thermoelements for temperature control, 25 as thermocouples or thermal probes, placed 28433-PPG

conveniently centrally, in the example at the vault 4 and the base 3, the signals of which are sent to the regulation and control devices of the thermal power, not shown here.

5 In accordance with the present invention and as can be seen in Figure 2, the axial burners 51 are connected to a common air supply duct 510 on which the usual adjustment and control means, not shown, are placed, while the 10 radial burners 52 they lead to a different air supply duct 520.

In particular, further ducts, indicated with 524, branch off from the duct 520, each leading to a single burner 52 of the second series. 15 In the example, the air duct 520 is intercepted by a motorized valve 521 located upstream of the ducts 524 and enslaved to a control unit 522 programmed to regulate the pressure of the air stream and therefore the flow rate 20 to be fed to the respective radial burners 52.

In particular, the control unit 522 regulates the pressure of the air to be sent to the radial burners 52, and therefore the air flow rate, as a function of signals received by suitable means 523, of which 25 will be better described in the following, which detect the 28433-PPG

dimensional deviation from the design value of the tiles 100 leaving the kiln 1.

Basically, in the presence of defects detected in the tiles 100, placed on the sides, at the exit from the kiln 5, the control unit 522, received the signals from the detection means 523, intervenes immediately by changing the quantity of air to be introduced into the burners 52 radial and thus changing the temperature. This is achieved by keeping the gas flow rate 10 constant to the radial burners 52, which is the same as that to the axial burners 51, thus keeping the thermal power delivered constant.

Naturally, the necessary variations in the air flow rate 15 will be modest and therefore they will not cause imbalances in the overall operation of the furnace.

In order to obtain an optimal regulation, the control unit 522 constantly receives the 20 pressure values through pressure transducers 81, 82 placed respectively on the line 510 for supplying the 51 axial burners and on the line 520 for supplying the 52 radial burners.

For the purposes of the present invention, the detections 25 of the "defects" of the tiles 100 can be 28433-PPG

carried out either by an employee who intervenes on a keyboard derived from the control unit 522 or through an automatic detection system of the size and flatness of the 5th tile of the type described in application RE2006A000007, by the same applicant, who here omits to report in detail.

Of course, any other means suitable for detecting tile defects and for sending a corresponding signal 10 to the control system 522 can be used.

Conveniently, the signal sent to the control system 522 is converted into pressure difference values to be maintained between the two 15 streams of air fed respectively to the axial burners 51 and to the radial burners 52.

Operationally, the oven is started maintaining the same pressure of the air fed to the axial and radial burners. Subsequently and only in the presence 20 of defects in the tiles coming out of the kiln, detected by the detection means 523, the control unit sends a signal to the valve 521 with greater opening or closing according to the pressure variation required, which variation of pressure 25 is conveniently calculated by unit 522 in 28433-PPG

function of the signal, representative of the defect in the tiles, received by the detection means 523.

Basically, the 5 initial operating parameters are changed, albeit slightly.

As an alternative to the use of a valve 521 which regulates several radial burners 52, for example the burners of a specific thermal zone, as described above, it is possible to provide for the use of a valve 10 for each radial burner 52 placed on the ducts 524. In this case, a corresponding pressure transducer is provided for each regulating valve, located downstream of the valves, which sends the signal to the control system 522.

15 Since the control system 522 uses the pressure transducers to control the pressure difference between the air stream respectively to the axial burners 51 and to the radial burners 52, it is possible to replace said pressure transducers 20 with suitable systems for detecting the difference pressure "∆P" which send the ∆P value directly to the 522 control system.

Of course, the oven is managed as a whole by a central electronic unit to which the control unit 522 is also enslaved.

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As can be appreciated from what has been described, the tunnel kiln for ceramic articles according to the present invention allows to satisfy the needs and to overcome the drawbacks mentioned 5 in the introductory part of the present description with reference to the known art.

In fact, the kiln, according to the present invention, thanks to the modulation of the air flow to the radial burners controlled by a single 10 control unit, allows to obtain all the exit tiles with the required dimensions and flatness, without distinction between those coming from central areas or side areas of the kiln, with a consequent significant reduction in waste.

15 Furthermore, the oven according to the present invention can be easily made starting from traditional ovens with small structural modifications.

Obviously, a person skilled in the art, in order to satisfy contingent and specific needs, may make numerous modifications and variations to the tunnel kiln for ceramic articles described above, all of which are however contained within the scope of protection of the invention, as defined by the following claims.

Claims (11)

28433-PPG CLAIMS 1. Tunnel kiln (1) for ceramic products comprising two opposite side walls (2), a horizontal roller conveyor (5) capable of supporting and advancing a layer of tiles (100) inside the kiln, a first series and a second series of burners (51,52) arranged aligned along the two side walls and facing the opposite wall, each burner (51) 10 of the first series being provided exclusively with an axial flame nozzle so as to heat the area central tunnel while each burner (52) of the second series being provided with at least one radial flame nozzle so as to heat the proximal area of the side wall of the tunnel, each burner (51,52) of the first and second series referring to a common fuel pipe (60) and respectively to a first (510) and a second (520) comburent pipe, 20 characterized in that it comprises, - means (523) for detecting the dimensional deviation with respect to the design value of the manufactured articles leaving the kiln, - a control unit (522) adapted to receive the data 25 coming from the detection means (523), 28433-PPG - means (521) for adjusting the flow rate of the comburent to the burners (52) of the second series placed on said second duct (520) of the comburent, said means (521) for adjusting the flow rate being enslaved to said control unit (522) programmed so as to control said adjustment means (521) as a function of the data received from the detection means (523). Furnace (1) according to claim 1, wherein 10 said second comburent duct (520) comprises a manifold from which a plurality of comburent ducts (524) branch off, each duct (524) leading to a single burner (52) of the second series. 15 3. Furnace (1) according to claim 2, in which said adjustment means (521) are placed on each of said ducts (524) which lead to the burners (52) of the second series. 4. Furnace (1) according to claim 2, wherein 20 said adjustment means (521) are placed on said comburent manifold. 5. Oven (1) according to claim 1, wherein said second series of burners (52) is formed by a plurality of burners placed in an alternating manner 25 with the burners (51) of the first series. 28433-PPG Furnace (1) according to claim 1, wherein the burners (52) of the second series further comprise an axial flame nozzle. Furnace (1) according to claim 1, wherein 5 each side wall (2) comprises two alignments (31,32) of the burners, one above (31) and one below (32) the roller conveyor (5). 8. Furnace (1) according to claim 7, in which, along each alignment (31,32), the burners 10 of the first and second series are arranged alternately with each other. Furnace (1) according to claim 1, wherein said detection means (523) comprise an automatic detection system of the gauge and / or 15 of the planarity of the ceramic product exiting the tunnel. 10. Furnace (1) according to claim 1, wherein said means for regulating the flow rate comprise a motorized valve (521). 20 Furnace (1) according to claim 1, further comprising pressure sensing means (81,82) placed respectively on said first and second comburent duct, said pressure sensing means 25 being connected to said control unit ( 522).