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.
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.
The above mentioned system is disclosed in the document
discloses a roller breakage detector for roller kiln wherein a roller
breakage accident is detected by an electric detecting circuit associated to an
end of each roller.
In detail each roller, which comprises a metallic support
shaft and a metallic collar, has a wire connected through a lead wire to the positive
side of a DC power supply, while the collar is grounded. A detecting circuit is
thus constructed in which both electrodes of the power supply are connected to each
other through a normally open switch constituted of the wire and the collar. When
the roller is broken, the support shaft is pushed out axially by the recoil strength
of a compression spring to the side of the kiln wall while pushing the broken roller,
and the collar at the rear end of the shaft comes into contact with the wire stretched
on the front side of the collar.
As a result, the switch of the detecting circuit relevant
to the unit containing the broken roller is closed, and an electric current flows
In the circuit, operating an alarm indicating the breakage of the roller.
discloses a roller breakage detector for roller kiln wherein a roller
breakage accident is detected by an electric optical circuit associated to an end
of each roller.
In detail the ends of the rollers are provided with shielding
plates, established orthogonally to the axial lines of the rollers, so as to be
arrayed and positioned respectively on one line among a multitude of pieces of arrayed
rollers. A light beam is provided near the light shielding plates, and it is projected
from a projector against a photo detector in parallel to respective light shielding
plates toward the lengthwise direction of the kiln.
The shielding of the light beam, which is caused by the
light shielding plate of a broken roller deviated from the normal position of the
roller, is detected as the break of the roller.
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
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
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:
BEST MODE FOR CARRYING OUT THE INVENTION
- Figure 1 is a schematic cross-section through the tunnel kiln on which the invention
- Figure 2 is an enlarged portion of the view in the direction II of Figure 1.
- Figure 3 shows the section III-III 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.
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
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
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.