WO2005114081A1

WO2005114081A1 - System for detecting roller breakage in a tunnel kiln

Info

Publication number: WO2005114081A1
Application number: PCT/EP2005/004958
Authority: WO
Inventors: Giuseppe Pifferi
Original assignee: Sacmi Forni S.P.A.
Priority date: 2004-05-21
Filing date: 2005-05-04
Publication date: 2005-12-01
Also published as: DE602005003466D1; ES2296185T3; EP1747416B1; PL1747416T3; CN1961190A; EP1747416A1; BRPI0511020A; ITRE20040060A1; PT1747416E; CN100516745C

Abstract

Method for detecting roller breakage in a tunnel kiln comprising a roller conveyor for advancing articles to be fired inside the tunnel, the ends of said rollers being supported outside the tunnel of said kiln, one of said ends being associated with drive means and the opposite end being free and supported by suitable idle wheels, there being associated with said free end a circuit for warning of roller breakage and means for exerting on the free end of the roller a force, the modulus of which is such as to cause a displacement of the end portion of the roller on breakage, to activate said warning circuit.

Description

DESCRIPTION

SYSTEM FOR DETECTING ROLLER BREAKAGE IN A TUNNEL KILN

TECHNICAL FIELD

The present invention relates in general to a system for monitoring correct operation of a tunnel kiln, used for example to fire ceramic articles, and in particular to a system for checking the integrity of the conveyor which advances the articles within the kiln.

PRIOR ART

The kilns used to fire ceramic articles comprise a tunnel within which a motorized roller conveyor is arranged to advance the articles to be fired within the kiln. The ends of the conveyor rollers project from the tunnel and are supported at one end by idle wheels and at the opposite end by a drive system which rotates the rollers.

During use of the kiln the conveyor rollers can undergo breakage, in which case they must be replaced in good time to prevent serious mechanical problems arising, with consequent prolonged production interruption. Systems must therefore be provided to detect breakage of the conveyor rollers.

A first known system consists of positioning, between the tunnel entry and exit, laser beams, typically three equidistant laser beams, lying just below the plane in which the roller conveyor lies. In this manner when a roller breaks, the two roller portions, which incline to the conveyor plane, intercept at least one of the laser beams. This interception of the laser beam by at least one of the portions activates a warning system which warns the user of roller breakage.

This system has proved inefficient as it gives rise to false warnings due to laser beam deviation imputable mainly to the heat which develops within the kiln and to the gases which form within the tunnel during firing of the articles. A second known system consists of combining with the conveyor a circuit for sensing and indicating roller breakage, comprising a conductor cable which rests tautly above the free end of the conveyor rollers and is maintained at a determined voltage by usual means. A plurality of earthing elements are positioned equidistantly above the plane in which the rollers lie, along the line of the kiln. When a roller breaks, the two portions incline because of the moment generated about the support point. Hence the end of the roller lifts the conductor cable to bring it into contact with the earthing elements. In this manner the electrical characteristics of the sensing circuit change to trigger a roller breakage alarm signal.

This system also presents drawbacks. In this respect, if the roller breaks close to the side wall of the tunnel kiln, the moment acting on that roller portion having its end associated with the sensing system is very small and the displacement of the end is insufficient to activate the warning circuit, hence the roller breakage is not indicated to the operator.

DISCLOSURE OF THE INVENTION

The object of the present invention is therefore to overcome the stated drawbacks within the context of a simple, rational and reliable solution. The invention attains said object in accordance with claim 1. The dependent claims illustrate particular advantageous embodiments of the invention.

Specifically, the invention provides a system for detecting roller breakage comprising a warning circuit with which means are associated for exerting on the free end of each roller a force of predetermined sense and direction, to activate said warning circuit if one of the conveyor rollers breaks.

Preferably said force is directed upwards, its modulus having a value such as not to cause roller lifting during normal kiln operation, but sufficient to cause substantial displacement of the roller portion in case of roller breakage.

According to a first embodiment of the invention, said force is a mechanical force and said means comprise a compressed elastic spring which acts on the free end of the roller via a wheel. In a second embodiment, said force is electromagnetic. In this case each roller presents at its end a metal portion, said means comprising a magnet arranged to interact with said metal portion to exert on the end of each roller an attraction force such as to cause substantial displacement of the end of the roller in case of roller breakage. The extent of the force exerted by said magnet must not however be sufficient to cause roller displacement during normal operation, but sufficient to cause displacement of a portion thereof in case of breakage.

According to the invention said warning circuit can be of electrical type or of optical type depending on the actual embodiment. BRIEF DESCRIPTION OF THE DRAWINGS

The constructional characteristics and merits of the invention will be apparent from the ensuing detailed description given with reference to the figures of the accompanying drawings, which illustrate some preferred embodiments thereof by way of non-limiting example, and in which:

Figure 1 is a schematic cross-section through the tunnel kiln on which the invention is installed.

Figure 2 is an enlarged portion of the view in the direction II of Figure 1.

Figure 3 shows the section Ill-Ill of Figure 2. Figure 4 shows the view in the direction IV of Figure 3.

Figure 5 is a schematic view of the section V-V of Figure 4.

Figure 6 is a schematic side view of a portion of the kiln of a variant of the first embodiment of the invention.

Figure 7 is the section VII-VII of Figure 6. Figure 8 is a schematic side view of a portion of the kiln of a different embodiment of the invention.

Figure 9 is an enlarged view of a portion of Figure 8.

Figure 10 is the section X-X of Figure 9.

Figure 11 is a schematic view in the direction XI of Figure 10.

BEST MODE FOR CARRYING OUT THE INVENTION Figure 1 shows a tunnel kiln 1 , the interior of which carries a conveyor 2 for advancing the articles to be fired through the kiln. The conveyor 2 comprises a plurality of rollers 3, which in the illustrated embodiment are made of amagnetic material and are internally hollow. However in other embodiments the invention can be used with rollers of different technical and constructional characteristics, for example be neither of amagnetic material nor hollow.

With reference to Figures 1 and 3, the ends 30 and 31 of each roller emerge from the side walls 200 of the kiln through holes 6. The holes 6 open into the outer side of the wall 200 and are aligned with cavities 66, coaxial thereto and of greater diameter, provided in an outer infill layer 77. The cavities 66 are partly filled with loose ceramic fibres 7 the purpose of which is to thermally insulate the kiln interior from the external environment and to provide a pneumatic seal. The end 31 if each roller is associated with drive means 8, of known type, which rotate the rollers, whereas the end 30 of each roller is supported by idle wheels 5. Said idle wheels are in contact with a spiral 28 mounted on the end 30 of each roller 3. With the free end 30 of each roller there is associated a system for detecting breakage of rollers of the conveyor 2, comprising a warning circuit 9 and means 10 for exerting on the end of each roller a force sufficient, in case of roller breakage, to cause substantial displacement of that roller portion comprising said free end 30. In the embodiment shown in the figures, the system for detecting breakage of the rollers 3 comprises (Figure 3) a warning circuit 9, of electrical type, consisting of a metal bar 90 positioned below the plane in which the roller table 2 lies and electrically connected to earth. A disc 11 of electrically conductive material is positioned below the bar 90 in correspondence with each roller 3, and is maintained at a determined electrical voltage by a usual voltage generator 12.

The disc 11 is associated with said means 10 for exerting a force on the free end 30 of the roller.

According to a first embodiment of the invention (Figure 3), said means 10 comprise an idle wheel 13 maintained resting against the lower surface of each roller by a spring 14. The spring 14 is inserted into a support 15 rigid with the side infill 77 of the kiln. The upper end of the spring 14 carries the disc 11 , from the upper surface of which there branches a vertical rod

16 which passes through said bar 90 and supports at its upper end a fork

17 with which the wheel is associated.

By virtue of this configuration, when a roller 3 breaks, the underlying spring 14 exerts on the free end of the broken portion of roller 3 a force sufficient to cause it to lift. This causes the disc 11 to contact the bar 90, with resultant current passage through the bar. This current passage is sensed by an ammeter, not shown, and indicated to the operator via suitable usual acoustic and/or light emitting warning devices. Figures 6 and 7 show a variant of the invention in which the warning circuit is not of electrical but of optical type. In the description of this variant of the invention, those components identical to those already described in the first embodiment of the invention are indicated by the same reference numerals. In this variant the wheel 13 is associated with the spring 14 via a prismatic part 18 presenting an elongate through hole 19 (Figure 7). Positioned at opposite ends of the kiln, or of that kiln part to be monitored, there are a transmitter 21 and receiver 22 for a laser beam 210 which passes though all the mutually aligned holes 19. In this manner, if one of the rollers 3 breaks, the part 18 is pulled upwards by the force exerted by the spring 14, to intercept the laser beam 210a and interrupt signal reception by the receiver. This latter is connected to usual acoustic and/or light emitting warning devices, not shown, which warn the operator of the need to intervene.

Figures 8, 9 and 10 show a second embodiment of the invention. In the description of the second embodiment of the invention those components described in the first embodiment are indicated by the same reference numerals.

Said figures show that with the free end 30 of each roller there is associated, for detecting breakage of the rollers of the conveyor 2, a system comprising a warning circuit 23 and means 24 for exerting on the end of each roller 3 a force sufficient, on roller breakage, to cause that roller portion comprising said free end 30 to undergo substantial displacement. Said means 24 for exerting a force on the free end of the roller comprise a horizontal bar 25 positioned above the plane in which the roller table lies. With particular reference to Figure 9, in correspondence with each roller 3 said bar 25 presents a cylindrical cavity 26, the base of which is perforated. In each cavity 26 there is a cylindrical permanent magnet 27 arranged to exert a magnetic attraction force on the underlying roller 3. The extent of this force is such as not to lift the roller 3 during normal kiln operation but to lift an end portion of the roller if it breaks. For this purpose, on the end 30 of the roller there is mounted a spiral 28 (Figure 10) of metal material able to interact with the permanent magnet 27. The warning circuit 23 for sensing any breakage of one of the rollers 3 is also associated with said means 23.

The warning circuit 23 comprises a plurality of electrically conductive plates 29 fixed above said bar 25 carrying the magnets 27, a layer of electrically insulating material 32 being interposed between said plates 29 and said bar 25. Each plate 29 has a length slightly less than the distance between the axes of the holes 26 of the bar 25. The ends of each plate are U-shaped and partly extend above said holes 27 in which the magnets 27 are inserted. As the plates 29 are of metal, the magnets 27 are normally rigid with the end portions of said plates 29, to ensure electrical connection between them. The two plates 29 at the end of the bar 25 are connected to a current generator 33 such that the plates 29 are traversed by electric current. If a roller breaks, the end of the roller approaches the magnet 27, the magnetic attraction between the spiral 28 mounted on the roller end 30 and the magnet being such as to detach the magnet from the overlying plates and draw it towards the bottom of the cavity 26, to hence interrupt current passage through the plates 29. The interruption in current passage is sensed by a suitable ammeter, not shown, connected to an acoustic and/or light emitting warning device provided to warn the operator of roller breakage, but not shown, being of known type.

Claims

1. A system for detecting roller breakage in a tunnel kiln comprising a roller conveyor for advancing articles to be fired inside the tunnel, the ends of said rollers being supported outside the tunnel of said kiln, one of said ends being associated with drive means and the opposite end being free and supported by suitable idle wheels, there being associated with said free end a circuit for warning of roller breakage, characterised in that with the free end of each roller there are also associated means for exerting on the free end of the roller a force, the modulus of which is such as to cause a displacement of the end portion of the roller on breakage, to activate said warning circuit.

2. A system as claimed in claim 1 , characterised in that said means for exerting said force comprise a compressed spring which maintains resting on the free end of said rollers an idle wheel which undergoes displacement on breakage of the respective roller.

3. A system as claimed in claims 1 and 2, characterised in that said warning circuit comprises an electrically conductive disc associated with said spring and maintained under voltage by a voltage generator, and an electrically conductive plate positioned at a predetermined distance from said disc such that, if one of the rollers breaks, said disc comes into contact with said plate.

4. A system as claimed in claim 2, characterised in that said wheel is supported by said spring via a prismatic part provided with a through hole of horizontal axis.

5. A system as claimed in claim 4, characterised in that said warning circuit comprises a laser beam transmitter and receiver positioned at the ends of the kiln portion to be monitored, such that said laser beam passes through the aligned holes of said prismatic parts.

6. A system as claimed in claim 1 , characterised in that said means for exerting said force comprise a bar comprising, in correspondence with each roller, a plurality of cavities, in each of which there is slackly inserted a permanent magnet interacting with a metal portion associated with the end of each roller.

7. A system as claimed in claim 6, characterised in that said warning circuit is also associated with said bar.

8. A system as claimed in claim 7, characterised in that said warning circuit comprises a plurality of plates fixed above said bar and electrically connected together via said magnets, said plates being connected to a current generator.

9. A system as claimed in claim 8, characterised in that a layer of electrically insulating material is interposed between said plates and said bar.

10. A system as claimed in claim 1 , characterised in that said warning circuit is connected to warning devices of acoustic and/or light emitting type.