Note: Descriptions are shown in the official language in which they were submitted.
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"Method and apparatus for the manufacture of slabs of ceramic material"
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The present invention relates to the manufacture of slabs of ceramic material
and, more specifically, to an
improvement in apparatus for the manufacture of such products.
The following description will relate specifically to the manufacture of stabs
of ceramic material of the
type known commercially by the name of "Iapitech", that is, technological
porcelain or porcelainised
stoneware, upon the understanding that this reference is not intended to be
limiting but is purely an
example of the preferred embodiment of the invention.
European patent 378,275 describes a slab of ceramic material and a method for
its manufacture which
provides for the preparation of a ceramic mixture constituted by granulated
material and by an inorganic
binding phase having particular characteristics of composition; the granulated
material also has spocific
particle-size parameters.
The mixture is formed into slabs by being spread on a forming support and a
pressure, combined with a
simultaneous vibratory motion, is applied to the mixture thus spread, which is
kept under vacuum.
After the forming stage, the raw slab is subjected to a first, drying step at
a temperature below that at
which ceramics are fired but nevertheless greater than 100°C and to a
second, firing step in which the
dried slab is brought to a temperature of the order of 1000-1300°C.
In the practical implementation of the above-meirtioned method and for the
reasons which will be
explained below, before the metered quantity of mixture is deposited on the
fomuag support, it is
protect (for example, from possible soiling and from the fom~ation of
deposits) by means of a sheet or
strip of paper.
The layer of mixture deposited is then covered by a layer or shaet of paper
permeable to water vapour
and the whole thing is then transferred to the step for pressing under vacuum
and simultaneous
application of vibratory motion.
The raw slab thus formed is picked up by devices with suction cups and is
transferred, whilst being kept
in the same position and the same orientation, onto a support surface,
preferably in the form of a metal
mesh, after which the sleet of permeable paper is removed.
'Ihe raw slab is then transferred to the drying step after which a layer of
refiacKOry material (which is
known in the art as a "refractory slip"), the composition of which generally
consists of magnesium
carbonaxe and a plastic clay which are mixed with water, is applied to its
upper surface.
After the application of the protective refi~ctory layer, the raw slab is
turned over in order to be
introduced into the firing kiln where the protective paper, which at this
stage constitutes the upper
covering of the dried slab, is removed (by burning) whilst the lower surface
of the slab which is in
contact with the support on which the slab is transported or rests in the kiln
(according to the type of
kiln) is protected by the aforementioned layer of refractory material (the
slip).
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This layer may be removed by conventional techniques upon completion of the
firing step, after which the
slab goes on to conventional finishing operations (sizing, smoothing,
polishing) if desired.
It is clear from the short description given above that the processing
requires many precautions by the
operators to prevent damage particularly to the raw slabs before both drying
and firing, with problems
and disadvantages which are not due to the main characteristics of the process
for the manufacture of
these slabs but which have a considerable effect on industrial production
costs.
T'he main object of the present invention is to prevent these problems and
disadvantages by improvements
to be introduced in the apparatus and in the method of manufactlue of the
slabs defined above, without
detriment to the properties, quality, or appearance of the resulting slabs.
This object is achieved by the present invention which provides for a method
for the manufacture of slabs
of ceramic material of the type identified above which is characterized in
that the starting mixture is
deposited on the forming support after a layer of mechanically resistant
fabric, particularly felt, has been
arranged on this support, a layer of release material, permeable to water
vapour preferably paper, being
placed on the felt and the layer of mixture disposed on the support thus
prepared being covered with a
sheet of a release material, such as rubber or another substantially
elastomeric material, after which the
step of pressing under vacuum with the simultaneous application of a vibratory
motion of predetermined
frequency and duration is carried out and, before the drying step aad the
subsequent firing step, the
aforementioned rubber sheet is removed and the raw slab is transferred to the
subsequent drying step by
the gripping of the front portion (with reference to the direction of movement
of the support along the
production line) of the felt carrying the raw slab by pincer means so as to
transfer the assembly onto a
grid-like support to be introduced into the drying oven and, after the layer
of re5~actory slip has been
applied to the raw slab coming from the drying stage and the slab has been
turned over, it is then
introduced into the Bering kiln after the aforementioned layer of fabric or
felt has been removed so that the
raw slab bears on the grid-like support with the interposition of the
aforerneationed refractory slip whilst
the sheet or layer of permeable paper which, at this point, covers the upper
surface of the slab, is
removed by burning.
In tum, the apparatus according to the present invention, which is of the type
comprising means for
preparing the starting mixture of granulated material and binding phase, means
for supplying and
spreading a metered quantity of the mixture onto a support movable along the
production line, means for
the pressing under vacuum of the metered quantit,~ of mixture spread on the
support and the simultaneous
application of a vibratory motion thereto, a drying zone, means situated
downstream of the drying zone
for applying a Iaver of refractory material for protecting the raw slab, and a
zone for the firing of the raw
slabs supported on the side covered by the layer of refractory material, is
characterized in that it
comprises means for supplying a layer of mechanically resistant fabric,
preferably a felt, and placing it in
position on the movable support upstream of the position in which the starting
mixture is supplied and
spread, means for supplying a layer of release material permeable to water
vapour , preferably paper,
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and placing it in position on the layer of felt. means for supplying a layer
or sheet or rubber and placing it
in position downstream of the means for supplying and spreading the mixture
and upstream of the means
for pressing under vacuum means for removing the layer or sheet of rubber
downstream of the means for
pressing under vacuum, pincer means for gripping the front portion of the
layer of fabric or felt in order
to transfer the felt, on top of which the layer of permeable paper and the
slab of raw mixture is carried.
onto a grid-like support movable in a controlled manner along the production
line for introduction into the
dning zone. means for picking up and removing the layer of felt prior to
introduction into the firing zone
when the raw slab, which has come out of the dning -zone, is turned over after
the refractow fyer of slip
has been applied. the contact between the slab and the means supporting it in
the kiln being constituted
solely by the layer of refractow material, whilst the sheet or layer of
permeable paper covers the upper
surface of the raw slab.
In the follow ng description of a preferred embodiment of the present
invention, given with reference to
the appended drawings, reference is made to apparatus and devices which are
know per se in the art and
do not therefore require more detailed description.
In the appended drawings:
Figure 1 is a general plan view of the apparatus according to the invention,
Figures 2A and 2B arc schematic side elevational views of a portion of the
apparatus of the present
invention,
Figures 3A and 3B are plan views of the portion of the apparaius of Figures 2A
and 2B,
Figures 4, 5, 6, 7, 8, 9, and 10 are partial views showing in section the raw
slabs in the successive stages
of their formation and movement through the various stations of the apparatus,
the sections relating to the
positions indicated S4, S5, S6, S7, S8, S9, and S 10 in Figures 2A and 2B, and
Figure 1 l shows the detail of the apparatus identified by the oval in Figure
2B.
It should be pointed out that, for clarity of illustration, both Figure 2 and
Figure 3 have been divided into
two halves so that Figures 2B and 3B should be understood as continuations of
Figures 2A and 3A.
respectively, showing an integral set of apparatus.
Moreover, Figures 4 to 10 show a support structure comprising a framework 18
which supports for
movement a convenor belt 2U which may~ differ in the various portions of the
apparatus. For example, in
the dn~ing and firing zones. the conveyor is replaced by a support surface
made of heat-resistant material.
With reference first of ail to Figure 1. the section of the apparatus for
preparing the starting mixture is
indicated l0, the mixture passing through the duct 12 and being transferred to
the mixture-supply and
spreading stations.
The production line starts with a station 14 which provides for the loading of
a felt or cloth 16 in the
portion l4A and provides for a sheet or layer of paper 22 permeable to water
vapour to be placed on the
felt l6 in the portion 14B: the conveyor belt 20 then enters the station 24 in
which a mixture-supply and
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spreading mechanism spreads on top of the sheet of permeable paper 22 a layer
26 of mixture of
predetermined thickness, taken from the supply duct or channel 12.
The embodiment shown, provides for a reinforcing mesh to be inserted and
incorporated in the thickness
of the final layer of mixture and the station 24 is therefore followed by a
station 28 for loading a mesh 30
of a material compatible with the final slab and placing it in position on top
of the layer of mixture 26.
Bv compatibility is meant, in particular, that the shrinkage of the material
constituting the reinforcing
mesh should be substantially of the same order of magnitude as that of the
mixture when it is subjected to
the drying and firing steps.
A second !aver 32 of the same mi~~ture is placed on top of the reinforcing
mesh 30. forming the layer 26.
in the station 34.
Before being subjected to the action of the vacuum forniing and compaction
press and the simultaneous
application of a vibratory motion of predetermined frequency and duration, the
upper surface of the
mixture and thus of the layer 32, is covered and protected by a sheet of
elastomeric release material such
as, for example rubber, this sheet, identified by the reference numeral 36,
being applied in the station 38.
As can be seen from Figure 8, the rubber sheet 36 has dimensions such that its
periphery overlaps the
peripheries of the permeable paper sheet 22 and of the felt 16 which also
project, so that the mixture
which, in this case, is constituted by tvvo layers 26 and 32 with the
reinforcing mesh 30 interposcxt
beriveen them, is completely enclosed by a protective envelope which, however,
is porous on the lower
side (by virtue of the presence of both the felt and the permeable paper)
allowing moisture also to come
out of the lower side during the subsequent drying step.
The mixture is then transferred to the pressing station 40 where it is
subjected, under a pre-established
vacuum, to a predetermined pressure and to the simultaneous effect of a
vibratory motion, forming a raw
slab which does not, however, yet have sufficient mechanical solidity to be
handled without special
measures.
At the output of the pressing station 40. first of all. the rubber sheet is
removed (station 42) and is
returned to the application station 38 after suitable cleaning of residues of
mixture. The raw slab, which
is now in the condition of Figure 10, is advanced to the station 44 where it
is transferred onto a different
conveyor support, preferably constituted by a metal grid.
For this purpose, and to avoid the above-mentioned handling difficulties, in
the station 44 there are pincer
means which can grip the projecting front edge (in the direction of advance of
the conveyor belt) of the
felt 16 and of the permeable paper 22, so that the raw slab is slid forvvards.
together with the felt and the
permeable paper; until it engages the new conveyor support constituted, in
fact, by a metal grid.
The above-mentioned pincer means are shown in greater detail in Figure 1 I .
With reference to this drawing and to Figures 2B and 3B, it can be stated that
these means are constituted
substantially by a rectangular frame 70 which is formed by a series of side
members and cross members
arranged side by side and parallel to one another (see Figure 3B) and which is
movable forwrards and
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backwards relative to the fixed load-bearing structure on which it is mounted
between a position for
depositing a slab on the grid and a position for gripping the felt where the
slab is lying; Figure 3B shows
in broken outline the shape of the portion of the fi-ame arranged for gripping
a slab arriving in this latter
position.
In this embodiment, the frame is moved by an electric motor 71 acting on a
shaft 72 at the ends of which
there are respective pinions (not shown in the drawings;l coupled with
corresponding racks (also not
shown graphically) mounted on the fixed load-bearing structure.
The gripping action of the pincer means is ensured by a lower lip 75 and an
upper lip 76, of which the
former is fixed to the frame 70 and the latter is movable relative thereto
since it is fitted on the translating
element 77 of an articulated- quadrilateral kinematic mechanism of which hvo
rocker arms 78 articulated
to the frame 70 also form part; in particular, the movement of the upper (ip
76 is brought about by a
series of hydraulic cylinders 80 mounted on the frame and acting on the
translating element 77.
After the pincer means have released the felt and the permeable paper, the raw
slab thus reaches the
station 46 where it is advanced. together with the grid-like support on which
it is deposited; towards a
drying oven 48 of conventional type well-known per se, in which it is
subjected to the effect of heat,
preferably in the form of a forced circulation of hot air, the time spent in
the oven being such as to
achieve a first mechanical solidification of the mixture which forms the raw
slab so that it can withstand
gentle mechanical handling.
At the output of the drying oven, the slab, still on the grid-like support, is
sent to the station 49 in which
it is lifted up by a suction-cup system and transferred to a starring station
51 of the next portion of the
conveyor 20; after this lifting, the grid-like support and the felt disposed
thereon can then be taken finm
the station 49 for re-use in the production cycle as described above.
From the station 51, the slab then reaches the station 53 where a thin layer
of refractory material (the
aforementioned slip) is applied to it and is then dried in the next station
54; after this, the slab is turned
over in the station 55; that is to say, as a result of this turning over, the
layer of slip, solidified by drying,
is disposed underneath the slab and in contact with the conveyor which moves
it forwards.
At this point, it remains only to introduce the raw and dried slab resting on
its face which is covered with
and protected by the refractory slip, into the firing kiln 52, which is
preferably of the tunnel type well-
known per se, in which the firing of the mixture and its transformation into
ceramic material is also
combined with burning of the permeable paper which covers the upper surface of
the raw slab.
After firing, the slab may be transferred to normal finishing operations such
as smoothing, polishing, etc.
It is clear form the foregoing description that, with the present invention,
the problems and disadvantages
connected with pre-existing production technology are substantially eliminated
in an industrially
advantageous manner.
Although this should not be understood in any limiting sense, it can
reasonably be considered that the
advantages and results achieved by the present invention are due mainly to the
use of the primary
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supporting felt for the deposition of the starting mixture and to its coupling
with the paper permeable to
water vapour.
In fact, it thus becomes possible to achieve, on the one hand, a firm support
for the deposition and
spreading of the starting mixture and, on the other hand, a capability to
transfer the raw slab to the
drying stage without handling (with suction cups and the like) which might
irreparably damage the raw
slab just formed and compacted, as well as, in particular, changing of the
support of the raw slab (for
example, from a continuous conveyor belt to a metal mesh) simply by sliding of
the formed and
compacted raw slab by the gripping of the projecting edge of the felt by
simple pincer means.
It is appropriate to point out that the results set out above are achieved
without any change in the level of
quality of the production cycle . since the felt constitutes a layer which is
permeable to water vapour.
ensuring uniform diving on the two faces of the slab wzthoui warping or
cracking.
Of course the felt or fabric must be mechanically resistant and particularly
resisting to tensile stress.
Moreover, components such as the rubber sheets. can be re-used as they are
(after merely being cleaned
of debris and residues of mixture) so that industrial production costs are
also controlled and, in
particular. limited, whilst the number of slabs to be rejected owing to damage
resulting from handling
before the firing step is drastically reduced.
Finally, it should be understood that conceptually and mechanically equivalent
modifications and
variations are possible and foreseeable within the scope ofthe presert
invention.
For example, and in the first place, the two stations 24 and 34 may be reduced
to a single station for the
deposition and spreading of the mixture when the slab does not have to contain
a reinforcing mesh 30.
Moreover, the present invention may be applied in a similar manner with
suitable adjustments to
processes and apparatus in which slabs are formed from mixtures which are
subsequently subjected to
drying and setting steps in which, up to now, the mixture generally hard to be
incorporated between two
paper sheets for the pressing and subsequent operations, since it enables the
raw slab to be handled
without the hitherto unsolved problem of susceptibility to damage.
