[0001] This invention relates to a method and relative plant for manufacturing bulk-coloured
multi-coloured porcellainized ceramic stone tiles by extrusion.
[0002] Said tiles result from irregular but controlled mixing of various types of different-coloured
pastes, which are fed to the forming mould partly mixed, to give rise to adjacent
co-penetrating masses of different colours and geometrical shapes in the extruded
tile.
[0003] Various systems and plants exist for forming such tiles, the intention of which is
generally to reproduce marble veining.
[0004] In all known systems, the porcellainized ceramic stone tile is formed dry, by pressing
powders in a mould followed by firing.
[0005] With these known systems, mutually copenetrating irregular veins can be reproduced,
interspaced within coloured masses to imitate many types of marble.
[0006] Plants are also known for forming terracotta or ceramic stone tiles by extrusion.
These plants enable tiles to be formed which are of a single colour or at the most
have a decoration imitating natural wood, consisting only of undulated dark veining
in a lighter matrix, or vice versa.
[0007] Up to now it has not been possible to manufacture tiles with those types of decoration
in which veining extends as volutes wrapping about themselves or as striated stains
comprising different coloured curls.
[0008] These latter types of decoration are typical of many varieties of marble.
[0009] The object of the invention is to provide a method and plant able to form porcellainized
ceramic stone tiles provided with these types of decoration.
[0010] This object is attained according to the invention by wet-forming the powders by
extrusion and operating on the interior of the extruder to compel the extruding material
to undergo a more or less tortuous path before reaching the die.
[0011] According to the invention, the material to be extruded is a powder paste of water
content sufficient to provide it with the necessary flowability for its advancement
through the extruder and its passage through the die, and to ensure sufficient consistency
after extrusion.
[0012] According to the invention, a convenient water content is between 15% and 27%.
[0013] The extrusion screw is fed with at least two masses of different colour, each consisting
of a porcellainized ceramic stone paste coloured by the known method.
[0014] These masses are firstly mixed so that they copenetrate but do not mix completely,
and are then fed to the screw of a usual extruder where they assume the shape of elongate
irregular bodies or streams, the at least two masses being generally parallel to each
other.
[0015] To obtain the desired appearance, according to the invention the material is subjected
in the converging portion of the extruder downstream of the screw to the action of
deflector or barrier means for deviating the flow, in order to introduce irregularities
in the mutual distribution of said elongate masses, so giving them the desired appearance.
[0016] The material leaves the die in the form of a consistent web, which is then separated
into sections each of which constitutes a tile.
[0017] The wet tiles obtained in this manner are subjected to a drying process with a thermal
cycle depending on their degree of wetness and the thickness of the extruded tiles,
after which the tiles are fired by the usual methods for porcellainized ceramic stone.
[0018] The partial mixing of the various pastes is done both upstream of the extruder within
a screw mixing device, in which the water content is also adjusted to the required
value, and in the extruder chamber.
[0019] Material compacting is facilitated between the screw mixer and the extruder by the
provision of a vacuum chamber.
[0020] In certain embodiments of the invention the pastes can be mixed directly in the vacuum
chamber, suitable means being provided for injecting the coloured pastes directly
into said chamber.
[0021] The deflector means of the invention consist of at least one barrier movable about
a diametrical axis of the extruder, so that it can be set parallel to this axis or
inclined to it.
[0022] Said means of the invention also preferably comprise at least one barrier, which
is inserted to a desired extent into the extruder in a plane perpendicular to the
axis.
[0023] According to a further embodiment, the invention comprises two adjustable coplanar
barriers, perpendicular to the extruder axis, to define a cutting screen for the material
flow, or a material passage port positioned outside the screw axis.
[0024] Said various deviator means or movable barriers can be used either individually or
in combination within the same extruder.
[0025] The merits and the operational and constructional characteristics of the invention
will be more apparent from the ensuing detailed description of a preferred embodiment
thereof, with reference to the accompanying drawings.
[0026] Figure 1 is an axial section through the extrusion plant of the invention.
[0027] Figure 2 is an axial section through one embodiment of the terminal part of the extruder.
[0028] Figure 3 is an axial section through the terminal part of the extruder taken perpendicular
to the preceding.
[0029] Figure 1 shows the plant 1 for forming tiles by the method of the invention. The
plant 1 comprises a first chamber 2 into which there open a pipe 20 for feeding the
basic tile paste, and a pipe 21 for feeding the coloured pastes which are to form
a part of the required decoration.
[0030] The basic paste used is a usual mixture of clear baking clay, feldspar and quartz.
The coloured pastes are prepared by adding coloured ceramic pigments to the basic
paste.
[0031] The two pastes have a water content of between 15% and 17% and are fed into the chamber
2 by a conveyor belt system, not shown.
[0032] Inside the chamber 2 there is a screw mixer 3 of usual type operated by an electric
motor 4, both to partly mix the two or more pastes so that they copenetrate to form
a single stream of paste having at least one coloured vein, and to feed said paste
stream to a second chamber 5 positioned downstream of the chamber 2.
[0033] A certain degree of vacuum is formed in the chamber 5 by a pump 50, to create a negative
pressure which facilitates paste compaction.
[0034] The extruder 6 comprises a screw 7 arranged to transfer the paste from the chamber
5 to the compression cone 8, two movable barriers 9 and 10 being provided between
the screw 7 and the compression cone 8.
[0035] The extruder 6 comprises a pipe 60 through which coloured paste is fed using a screw
pump injection system, not shown, to achieve further types of decoration.
[0036] The barriers 9 and 10 are positioned horizontally and vertically respectively, and
are oscillated about their axes by two motors 90 and 100, to deviate the central axis
of the paste stream.
[0037] The extent and frequency of the oscillations of the barriers 9 and 10 varies according
to the type of decoration to be achieved.
[0038] Within the extruder cone 8 there are provided a further two coplanar adjustable barriers
of guillotine type, inserted into the interior of the extruder cone in a plane perpendicular
to the axis, to define a cutting screen for the material flow, or a flow passage port
offset from the extruder axis.
[0039] The die 13 is positioned downstream of the extruder cone and comprises, for adjusting
the extrusion geometry, the traditional upper and lower braking system 200 through
which a paste web emerges to be then cut into sections, each of which constitutes
a tile.
[0040] The described plant 1, controlled by a microprocessor, not shown, is used to implement
the method of the invention.
[0041] Said method comprises preparing separately a basic tile paste of porcellainized ceramic
stone and at least one coloured mix, then feeding them to the mixer 3 and/or to the
screw 7, through the pipes 20, 21 and 60 respectively.
[0042] The water content of the paste is preferably between 15% and 27%.
[0043] The purpose of the screw mixer 3 is to partially mix the two pastes so that they
copenetrate each other to form a single paste stream having at least one coloured
vein, to then feed said stream to the extruder 6, which receives a second feed of
coloured paste, and within which the movable barriers 9 and 10 deviate the central
axis of said stream. The material is then passed through the barriers 11 and 12, which
define for the paste a cutting port by which the coloured vein present within the
stream is displayed.
[0044] The die 13 and relative braking system 200 are provided downstream of said barriers
11 and 12, to produce an exit web of paste which is divided into tiles by usual means.
[0045] The tiles obtained in this manner are then dried using a predetermined thermal cycle
depending on the characteristics and thicknesses of the pastes used.
[0046] According to a variant of the invention, the coloured paste can also be injected
directly into the chamber 5 by suitable material transfer means, such as usual screw
pumps. In this manner the vacuum present in the chamber 5 facilitates the feed of
the paste into the chamber, and its mixing with the pastes already fed into said chamber
through the pipes 20 and 21.
[0047] Finally, further extrusion shapes such as steps, skirting, corner pieces and others
can be obtained by changing the die 13.
1. A process for forming tiles or tile accessories of extruded porcellainized ceramic
stone, characterised by comprising the following operations:
- preparing at least two pastes, typologically defined as porcellainized ceramic stone,
having different colours;
- feeding said at least two pastes directly into the chamber of a screw extruder (6);
- subjecting the mass advancing within the extruder (6), downstream of the screw (7)
and upstream of the die (13), to the action of at least one flow deviator means (9,
10, 11, 12);
- from the extruded web obtained in this manner, separating portions corresponding
to tiles or tile accessories such as steps or skirting;
- subjecting the tiles or tile accessories obtained in this manner to a drying cycle;
- subjecting the dried tiles or tile accessories to a firing cycle.
2. A process as claimed in claim 1, characterised in that said at least two pastes are
subjected to the action of a mixer (3) before being fed to the extruder (6).
3. A process as claimed in claim 1, characterised in that the flow deviator means (9,
10, 11, 12) is a barrier (9, 10) which can rotate about a diametrical axis of the
extruder (6) to lie in a plane containing said axis or in a plane cutting said axis.
4. A process as claimed in claim 1, characterised in that the flow deviator means is
a barrier (11, 12) which can be inserted into the extruder (6) by a desired amount
in a plane parallel to the axis of the extruder (6).
5. A process as claimed in claim 4, characterised by comprising at least two coplanar
barriers (11, 12) arranged to define a slot positioned outside the extruder axis.
6. A process as claimed in claim 1, characterised in that pastes of different colour
are injected between the mixer device (3) and the extruder (6) by pumps or equivalent
material transfer systems.
7. A process as claimed in claim 1, characterised by comprising, between the mixer device
and the extruder, a chamber (5) maintained under vacuum to degas the mixed material.
8. A process as claimed in claim 1, characterised in that at least one coloured paste
is fed into said chamber (5) by pumps or equivalent material transfer systems.
9. A process as claimed in claim 1, characterised in that the paste has a water content
of between 15% and 27%.
10. A plant for forming tiles or tile accessories by extrusion, comprising:
- an extruder (6) comprising a screw (7), a pressure cone (8) and a die (13),
- means for feeding said extruder (6) with at least two porcellainized ceramic stone
pastes of different colour,
- material flow deviator means (9, 10, 11, 12) positioned between said extruder (6)
and said screw (7).
11. A plant as claimed in claim 10, characterised by comprising, upstream of the extruder
(6), a mixer (3) which receives said at least two pastes from the feed means.
12. A process as claimed in claim 10, characterised in that said means for feeding at
least two porcellainized ceramic stone pastes of different colour are two conveyor
belts, two screw pumps or equivalent material transfer systems.
13. A process as claimed in claim 10, characterised in that said mixer (3) is a screw
mixer.
14. A process as claimed in claims 10 and 11, characterised in that between the mixer
device and the extruder there is provided a chamber (5) maintained under vacuum to
degas the paste.
15. A plant as claimed in claim 14, characterised by comprising means for feeding at least
one coloured paste into said chamber (5).
16. A process as claimed in claim 10, characterised in that said material flow deviator
means (9, 10, 11, 12) are at least one barrier (9, 10) which can be rotated by known
drive means about a diametrical axis of the extruder.
17. A process as claimed in claim 10, characterised in that said material flow deviator
means (9, 10, 11, 12) are at least two barriers (9, 10) of mutually perpendicular
axis, each of which can rotate about a diametrical axis of the extruder.
18. A process as claimed in claim 10, characterised in that said material flow deviator
means are a barrier (11. 12) which can be inserted into the extruder by a desired
amount in a plane parallel to the extruder axis.
19. A plant as claimed in claim 18, characterised by comprising at least two coplanar
barriers (11, 12) arranged to define a slot positioned outside the axis of the extruder
(6).