Note: Descriptions are shown in the official language in which they were submitted.
s
FIELD OF THE INVENTION
The invention relates to a ceramic veneer which is manufactured
from a thin-fluid slip by a drying and firing of the slip.
BA~KGROUND OF THE INVENTION
Such veneers are manufactured in many ways but one such way is to
apply the slip on an endlessly rotating belt and at a thickness which is as
uniform as possible, dried while on the belt and is baked or fired subse-
quently in a kiln. A disadvantage of this method is tha~ a large percentage
portion of the manufactured veneers are nonusable because the veneers are
uneven and/or are curved at the edges. The purpose of the invention is to
manufacture a veneer made of a slip, which remains uniform in its thickness
during baking and during the subsequent cooling.
The present invention provides a ceramic veneer, manufactured from
a thinly fluid slip by the drying and firing of the slip~ and comprising at
least two different layers of slip, having different coefficients of shrinkage
during firing, and/or different coefficients of thermal expansion in the
fired state, said coefficients of shrinkage and/or thermal expansion of the
individual layers being selected so that differences in coefficients of
shrinkage and coefficients of expansion caused by segregation of the compon-
ents of the slip are compensated for~the veneer remains flat during drying,
firing and cooling.
A veneer which is manufactured of an even or uniformly thick slip
has no reason to shrink unevenly during baking or to expand unevenly during
cooling. However, as has been discovered, the combination of components
making up the wet slip layer does not remain even during drying. Slip con-
sists of fine clay particles and of coarser hard particles, as for example
finely crushed fireclay and others. During drying, the coarser particles
settle in the lower part of
. ~ - 2 -
- ~
~ '
the slip layer~ the fine particles remain on top. The shrinkage rates and
the coefficient of expansion along the height of thickness of the layer
become then uneven and the veneer is deformed during baking and during
cooling.
The uneven distribution of the slip particles, which occurs during
drying, can also not be avoided in the two layers of the inventive veneer,
however, one can choose the additives to the two different slips so that the
center values of the shrinkage rates and of the coefficients of thermal
expansion assume values which prevent a deformation of the veneer in the
kiln and during the subsequent cooling process. Differences in the skrinkage
rates can be achieved for example in the case of an otherwise equal com-
position of two slips in such a manner that one slip has added thereto finely
ground clay fired at 800 - 900C and the other one finely ground baked
fireclay. Further examples are mentioned at a later point in the description.
The present invention provides a ceramic veneer manufactured from
a thin-fluid slip by drying and baking of the slip, comprising the improve-
ment wherein said slip consists of at least two different layers which
have either different shrinkage rates during baking and/or different co-
efficients of thermal expansion in the baked condition, and whorein said
shrinkage rates and sAid coefficionts of thormal oxpansion of the individual
layers are determined such that the veneer is of a uniform thickness.
The present invention also provides a continuous method for pre-
paring a ceramic veneer of uniform thickness, which comprises the steps of:
depositing a first thin layer of a first thin-fluid slip onto a moving
surface; then applying a first glass fleece layer on top of said first slip
layer and pressing said first glass fleece layer into said first slip
layer so that said first slip layer is impregnated in said first glass
fleece layer; then depositing a second thin layer of a second thin-fluid
slip on top of said first glass fleece layer, said second thin-fluid slip
having a different composition than said first thin-fluid slip and having
,~` ~
.
-~ , . . . .
-- --
s
;. a different ~hrinkage rate during baking, a differ&nt coefficient of thermal
expansion after baking or both a different shrinkage rate and a different
coefficient of thermal expansion; then applying a second glass fleece layer
on top of said second slip layer and pressing said second glass fleece layer
' into said second slip layer so that said second slip layer is impregnated
in said second glass fleece layer whereby to form an assembly of said layers;
then heating said assembly to dry said slips whereby to form a dry assembly;
then firing said dry assembly to form a unitary first ceramic veneer product
of uniform thickness consisting essentially of two different layers and then
cooling said ceramic veneer product, wherein the compositions of said slip
layers are effective to cause said ceramic veneer product to remain flat and
of uniform thickness during firing and cooling.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and an arrangement or device for carrying out the
invention are described hereinafter with reference to the drawings, in which:
Figure 1 schematically illustrates a partial side view, partly in
a cross section of a device for applying the slip on an endless carrier
and conveyor belt;
Figure 2 is a cross-sectiona.l viow o tho ond of tho aorenlcntioned
conveyor belt and the front part of a dryin.g oven; and
Figure 3 is also a cross~sectional view of the rear part of the
drying oven, a kiln and a cooling oven following thereafter for receiving
the baked veneer.
- 3a -
s
DETAILED DESCRIPTION
Two rollers are identified by the reference numerals
1 and 2 in Figures 1 and 2, respectively, of the drawinys
and are rotatably supported in a frame consisting of two
posts 3 and 4 and a bridging member 5. A carrier belt 6
is looped around these rollers and is used to receive and
transport the slip. ~eference numerals 7, 8, 9 and 10
identify schematically illustrated application devices.
The first application device 7 is used to apply form
oil to prevent the adhesion of the sl~p to the belt. The
second application device 8 applies a first slip layer onto
the belt, so that it forms a thin lay~r 13. A glass fleece
14 is introduced into this layer. The fleece is rolled off
from a roll lS, the axis 16 of which is supported in an arm
17 of a frame 12 mounted on and extends upwardly from the
bridging member S. The fleece 1~ is pressed into engagement
with the slip layer 13 by a roller 19 which is rotatably
; supported on the arm 17 so that it becomes soaked with the
slip. A second slip layer 20 is applied with the third ap-
plication device 9 onto the now soaked fleece 14 and a glass
fleece 21 is applied onto said second slip layer. The
fleece 21 comes from a roll 22 and is pressed into the slip
A ~ 20 by a roller 23 to soak the fleece 21 with the slip
of li ~er
Reference numeral 24 identifies a~ arrangement of radiant
heating members which are used to dry the slip layers 13 and
20. Finally the fourth application de~ice 10, if desired,
applies a glaze mixture 25.
From the belt 6 the predried veneer, as shown in Figure
2, travels into a drying oven which is identified as a whole
--4--
l~Z,~l~S
by the reference numeral 27. The oven forms a channel 28.
Transport roll'ers 29 and heat resistors 30 are arranged in
said channel. The channel is closed off on top and below
and on the sides by fireproof walls 31. The rollers 29 are
used to transport the predried veneer, the solidity of which,
which has been reached in the meantime, permits further
transport on rollers. The veneer is thereby pulled through
the dr~ing oven.
The drying oven 27 may form a part of a kiln 32, the
baking zone of which is formed (see Figure 3) by a channel
33 which is closed off to all sides i9 divided preferably
by a ceramic plate 34. Below, this horizontally lying plate
34 there are arranged heat resistors 35 in individual
chambers and in the upper part of the channel 33 equally
arranged resistors identified by the reference numeral 36.
A cooling-off oven 37 follows the baking zone. It too forms
a channel 38 having heat resistors 39, 40. Rollers ~1, 26
are mounted at the start of the channel 38, over which rollers
a continuous belt 11 is looped. The cooperating counter
rollers which cooperate with the belt to effect a return
thereof are not illustrated in the drawings. One of the
rollers is driven and the belt 11 is ~sed to transport the
finished baked veneer. The belt is made of a high temperature-
resistant material. A weight-loaded roller 12 is arranged
above the roller 41 and applies a force to the finish baked
veneer to assure the veneer to be frictionally grab,bed by
and taken along by the belt 11.
The two slip layers 13 and 20 differ according to the
invention in their composition. Several suitable layers are
listed hereinafter:
-5-
/` :
First Example: Layer 13 Layer 20 : :
Clay 40% 30%
Hard burned fireclay 20% 30%
Feldspar 40% 40%
3t~,s
l~lL Both layers have different shrinkage lu~es. Different
shrinkage ~ of both layers can also be obtained by replacing
: the common hard burned fireclay partly with clay fired at 800 - ::
900C, for example with the following composition:
Second Example: Layer 13 Layer 20
Clay 30% 30%
Hard burned fireclay 15% 30%
Clay fired at 800 - 900C 15%
Fledspar 40% 40%
In the given composition, the layers 13 and 20 have
r~e r
: different shrinkage ~x~h~s. If one desires at the same time also
different coefficients of thermal expansion, then this can be
achieved for example with the following composition:
Third Example: Layer 13 Layer 20
; Clay 30% 30%
Fireclay having a
: high coefficient of ~5%
thermal expansion
Fireclay having a
low coefficient of - 30%
thermal expansion
Clay fir0d at 800 - 900C
having a high coefficient 15%
of thermal expansion
Feldspar 40% 40%
In the composition of the layers, it is also possible
to take into consideration the influence of the glaze in as far
as it contributes to the deformation of the evenness of the slip
layers.
- . - . . . -, , , .:
s :~
:
The given percentages are approxlmate~ values, they can
be higher an,d,lower.
Although a particular preferrëd embodiment of the inven--
tion has been disclosed in detail for illustrative purposes,
it will be recognized that variations or modifications of
the disclosed apparatus, including the rearrangement of
parts, lie within the scope of the present invention.
.
