Note: Descriptions are shown in the official language in which they were submitted.
1~29183
The present invention relates to an improvement in
brick making.
More specifically, the present invention relates to the
addition of specified amounts of a synthetic prefired flux
material, namely powdered glass, to a clay-based body prior
to forming and kiln burning to maturity to yield a brick of
increased compressive strength, decreased water absorption
and lowered apparent specific gravity, relative to a kiln
burned brick lacking powdered glass in the clay-based body
from which it is produced.
The present invention is particularly useful in the
production of the lightweight GIANT~ through-the-wall
bricks disclosed and claimed in Canadian Patent No. 986,288,
issued March 30, 1976, and in the water passage resistant
DRILINE~ bricks disclosed and claimed in Canadian Patent No.
962,852, issued February 18, 1975.
While the lightweight GIANT~ through-the-wall bricks
are conventionally produced by the dry press process, the
present invention is generally applicable to all burned clay
products, including those produced by the stiff mud process.
Market acceptance of burned clay bricks depends largely
upon two factors. First, the burned clay colour of the
bricks must be aesthetically pleasing. Second, the bricks
must satis~y all technical specification requirements of
appllcable regulatory bodies, the most important requirement
typically being a given minimum compressive strength.
~nlike the stiff mud process, the dry press process of
manufacture requires constant and diligent quality control
l~Z'g~83
surveillance to ensure ~hat every brick manufactured has
adequate end-product strength to satisfy the minimum applicable
technical specifications. By way of explanation, in the dry
press process compressive strength is proportional to density
and density is directly related to applied pressure. It is
thus common practice to operate dry press machines at near
- maximum pressing capacity to ensure that every brick produced
has the required density value to develop adequate end-
- product strength when kiln burned to maturity. Despite
this, normal variances in composition of the naturally
occurring clay and shale components employed in the clay-
based body make it impossible to absolutely predict the
physical properties of each individual brick manufactured.
The prior art provides two methods of increasing compressive
strength of burned clay bricks. First, the addition of a
natural fluxing mineral, for example nepheline syenite or
feldspar, to the clay-based body. Second, the addition of
a ballmilled fraction of the clay itself back into the clay-
based body. Both of these methods are well known in the brick
industry and both have the same shortcomings, namely that in
the dry press process at least a 15% by weight addition is
requisite to absolutely guarantee the minimum physical
properties of every brick. This is expensive to the point
of being uneconomical on a mass production basis. More
i~portantly from a market standpoint, such a level of addition
drastically alters the burned clay colour of the brick.
The present invention, by the addition of the powdered
glass, inexpensively provides sufficient low viscosity
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:, " ~::
13 29183
highly reactive flux within the clay matrix during kiln
burning to afford a significant increase in compressive
strength, a lowering of water absorption and a lowering of
apparent specific gravity, without a recognizable, or at
least unnacceptable, change in colour of the burned clay
brick. Thus, while maintaining colour characteristics
prerequisite to market acceptance, elaborate and expensive
quality control during the manufacturing process can be
minimized with assurance that all bricks produced will
possess at least a given minimum compressive strength.
Supplementary, but attractive, advantages which can
accrue from the present invention include an ability to
potentially employ reduced forming pressures in the dry
press machines, thereby lowering machine maintenance costs,
and an ability to potentially reduce kiln burning temperatures,
with attendant energy savings, dependent upon the particular
clay-based body employed and the requisite end-product
characteristics.
The use of powdered glass in the manufacture of ceramic
articles is taught in Canadian Patent No. 968,813, issued
June 3, 1975. The patent however teaches the use of from
about 25% to 45% by weight of powdered glass, an amount
significantly beyond that contemplated or acceptable for use
in the present invention, in the manufacture of dense ceramic
artlcles such as lamp bases. The patent further teaches, on
lines 12/13 of Disclosure Page 9, that the ceramic bodies
display a shrinkage of from about 8% to 12% between the
pressed and fired states, a shrinkage factor totally unacceptable
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in the brick industry due to a resultant cull rate estimated
to run as high as 40% of total production.
Thus, in a broad aspect the present invention
pr~vides in a method of making brick wherein a clay-based body
is formed to a desired shape and subsequently kiln burned to
maturity, the improvement comprising intimately admixing
powdered glass in an amount in the range of about 0.25 to
about 12.5% by weight with said clay-based body prior to
said step of forming.
The preferred powdered glass employed in the pres~nt
invention is of the readily available soda-lime silicate
type i.e. reclaimed ~aste glass, bottles, plate etc., of the
following typical chemical composition, in ~ by weight:
sio260.00 - 80.00
A1203 0.10 - 5.00
Na2O5.00 - 18.00
K 2 ; - : 5-00
Fe203 0 .01 - ; 1.00
MgO0.01 - 5.00
20 CaO3.00 - 15.00
As 23 Optional Trace Amount
cr23Optional Trace Amount
B203Optional Trace Amount
Co304 Optional Trace Amount
Sb 2 3 Optional Trace Amount
TiO 2 Optional Trace Amount
Other low melting point glasses can also be employed,
fox example lime and lead glasses.
The glass characterist~cally becomes pyroplastic at
about 130QF and begins to form a li~uid melt abo~e about 1400F,
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bm: ~.
1129~8:~
the ~iscosity of which decreases with increased temperature.
The powdered glass is added to the clay-based body
prior to forming and intimately admixed to ensure even
- dissemination. Powdered glass of a particle size of about -65
mesh has been found satisfactory.
Since clay-based bodies are typically kiln burned to
maturity, subsequent to forming to desired shape, at a
temperature in the range of about 1750 to 2400F, that is
about 450 to about 1100F above the softening point of the
powdered glass, the addition of the powdered glass, even in
relatively small amounts, provides increased intermediate
strength, due to reaction wi~h the clay matrix, at temperatures
where the clay is at its weakest because of break-down of
the clay molecule and lack of ceramic bond formation. The
use of the powdered glass thus tends to decrease production
lc~ssess inithe form of culls during the kiln burning.
The amount of powdered glass intimately admixed with
thé clay-based body can range from about 0.25 to about 12.5
% by weight. The upper limit is primarily dictated by the
extent of colour degradation acceptable, and will vary
somewhat according to thé particular composition of the
c~ay-based body. A preferred amount of powdered glass is in
the range of from about 0.5 to about 5.0 % by weight.
The clay-based bodies can additionally include an
~au~t of about 5.0 to a~out 80.0% by weight of a particulate
shrinkage control agent to reduce green to fired shrinkage
to an acceptab~e magnitude, ty-pically to a shrinkage of
ab-out a maximum of 3~. The particulate shrinkage control
agent is generally one or more members selec-ted from the
3~ yroup consisting of calcined refractory clay, naturally
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occurring aggregate or sand, calcined non-refrac~ory clay or
shale and grog.
In the stiff mud process, an amount of about 5.0 to
65.0% by weight of the shrinkage control agent is typically
employed, prefèrably ground to ~4 mesh or finer.
In the dry press process, an amount of about 5.0 to
about ~0.0% byweight of the shrinkage control agent is
typically employed, preferably ground to -4 mesh or finer.
The advantages of the present invention will become
apparent from the following Tables, the tests of which were
all conducted in accordance with CSA and ASTM Standard Test
Methods.
Table I compares the properties of dry press bricks
produced from a control clay-based body, Mix IA, against
those of bricks produced from the clay-based body having
2.5% by weight powdered glass added, ~ix IB, and bricks
produced from the clay-based body having 5.0% by weight
powdered glass added, Mix TC.
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TABLE I
Mix, % by weightIA (Control) IB IC
Buff Fireclay 56 56 56
Fireclay 14 14 14
Calcined Fireclay25 25 25
Grog (Buff) 5 5 5
Powdered Glass % by
weight Over ~ Above 0.0 2.5 5
Moisture Content as
Pressed, % 6.0 6.0 6.0
Forming Pressure, psi 2415 2415 2415
Burning Temperature, F 2290 2290 2290
Modulus of Rupture, psi 1645 2044 2180
Net Area Compressive
Strength, psi 8259 10690 13960
Apparent Porosity, % 20.7 18 12.5
Water Absorption, % 10.0 8.6 6.0
Bulk Dengity, pc~142.7 142.0 130.6
Apparent Specific Gravity 2.62 2.55 2.39
Colour Standard Standard Slight Darkening
Golden Golden of Golden Buff
Buff BuffColour
Colour Colour
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It may be noted from Table I that the bricks produced
from Mix IB display a significant increase in compressive
strength over bricks produced from the Control, and that the
bricks produced from Mix IC display an even more marked
increase in compressive strength.
It may further be noted from Table I that the bricks
produced from Mix IB display a decrease, and the bricks
produced from Mix IC a greater decrease, in water absorption
over bricks produced from the Control, indicative of increased
resistance to penetration and passage of moisture, liquid
and vapour through the bricks.
It may additionally be noted from Table I that the
bricks produced from Mix IB display a decrease, and the
bricks produced from Mix IC a greater decrease, in apparent
specific gravity over bricks produced from the Control.
Decrease of apparent specific gravity is indicative of an
increase in the percentage of sealed pores within the brick
and, in addition to leading to the reduced water absorption,
tends to lower thermal conductivity values.
Table II is similar to Table I, and compares the properties
of dry press bricks produced from another control clay-based
body, Mix IIA, against those of bricks produced from the clay-
based body having 2.5% by weight powdered glass added, Mix IIB,
and bricks produced from the clay-based body having 5.0% by
weight powdered glass added, Mix IIC.
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TABLE II
Mix, % by weightIIA (Control)IIB IIC
Buff Fireclay 25 25 25
Red Shale 42 42 42
Calcined Fireclay28 28 28
Grog 5 5 5
Powdered Glass % by
Weight Over ~ Above 0.0 2.5 5.0
-
Moisture Content as
Pressed, % 6.0 6.0 6.0
Forming Pressure, psi 2415 2415 2415
Burning Temperature, F 2090 2090 2090
Modulus of Rupture, psi 1446 1924 2379
Net Area Compressive
Strength, psi 7183 10030 13790
Apparent Porosity, % 17.3 14.0 10.4
Water Absorption, % 8.2 6.5 4.8
Bulk Density, pcf143.1 143.0 139.9
Apparent Specific Gravity 2.572.50 2.39
Colour .Standard Standard Slight Darkening
Autumn Leaf Autumn of Autumn Leaf
Colour Leaf
Colour
As in the case of Table I, the bricks produced from the
powdered glass-containing mixes, Mixes IIB and IIC, display
increased compressive strength, decreased water absorption
and decreased apparent specific gravity over bricks produced
from the Control.
Table III compares the properties of dry press bricks
produced from a further clay-based body having gradiated amounts
ranging from 0.25% to 1.00% by weight of powdered glass
added, Mixes IIIA through IIID, against bricks produced from a
control clay-based body, Mix IIIE. Since the powdered glass
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is most reactive with low refractoriness dry press clay
matrices, an impure red burning shale based mix was employed
to illustrate the effectiveness of even small amounts of the
powdered glass.
TABLE III
Mix, % by weight IIIA IIIB IIIC IIID IIIE
~Control)
Red Shale 51 51 51 51 51
Buff Fireclay 8 8 8 8 8
Calcined Fireclay 27 27 27 27 27
Grog (Red) 14 14 14 14 14
Powdered Glass Z by
Weight Gver & Above1.000.75 0.50 0.25 0.00
Modulus of Rupture, psi 806 761 686 635 600
Net Area Compressive
Strength, psi 3535 3272 2770 2785 2440
Water Absorption, %11.4 11.7 11.6 11.6 12.1
Bulk Density, pcf125.0 124.9 125.3 125.5 125.9
Green-Fired Shrinkage, % 1.85 1.83 1.76 1.72 1.76
Colour Standard Standard Standard Standard Standard
Colour Coloor Colour Colour Colour
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1~29~3
It may be noted from Table III that the bricks produced
from Mixes IIIA through IIID all display improvement, albeit
modest in the bricks produced from Mix IIID, of all properties
re~ative to the bricks produced from the Control.
Table IV compares the properties of dry press bricks
produced from another Control clay-based body, Mix IVA,
against those of bricks produced from the clay-based body
- having gradiated amounts ranging from 5.0% to 15% by weight
of powdered glass added, Mixes IVB through IVD. Since the .-
powdered glass is least reactive with high refract~riness
dry press clay matrices, a high purity buff burning Cone 34
kaolinitic clay was employed to illustrate the effects
. of relatively large additions of powdered glass.
TABLE IV
.
Mix, % by weight IVA (Control) IVB IVC IVD
Kaolinitic Clay 100 95 90 85
Powdered Glass % by
Weight Over & Above - 5 10 15
Modulus of Rupture, psi 165721602460 1585
Net Area Compressive
Strength, psi 6115 9942 15062 6005
Water Absorption, % 6.3 4.5 5.0 8.2
Bulk Derlsity, pcf 140.7 138.0 133.5 124.6
Wet--Fired Shrinkage, % 11.2310.068.63 6.82
Colour Clean Clean Slightly Dark
Buff Buff Greying Grey &
Colour Colour of Clean Bloated
BufE
Colour
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The bricks produced from both Mixes IVB and IVC
display significant improvements in properties relative to
the bricks produced from the Control, although a slight, but
acceptable, greying in tonal colour was evident in the
bricks produced from Mix IVC. Interpolation of the results
of Table IV suggests a maximum addition of powdered glass of
about 12.5% by weight, although as stated earlier the maximum
amount is in practice dictated by the extent of colour
degradation acceptable, and will vary according to the
particular composition of the clay-based body.
Table V compares the significance of grog content
to the reactivity of powdered glass in dry press clay-based
body mixes. Comparat;ve experiments were conducted to
determine whether the powdered glass was preferentially
reacting with high grog content clay-based body mixes.
TABLE V
Mix, % by weight Y~ (Control? VB VC (control) VD
Red Shale 51 51 51 51
Buff Fireclay 8 8 44 44
Calcines & Grog41 41 5 5
Pcwdered Glass ~ by
Weight Over & Akove 0,0 2 5 o~o ~ ~ 2 5
.. .
~bdulus of Rupture~ psi 600 908 1169 1372
Net Area Compressive
Strength, psi 2440 3592 5257 6469
Water Absorption~ % 12.1 11 3 9 7 9 4
Bulk Density, pcf 125 9 126 2 131 3 131 4
Wet-Fired Shrinka~e~ % lt76 2 02 1 96 2 12
Colour Standard Standard Standard Standard
Colour Colour ColourColour
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~129183
Table V indicates that the addition of the powdered
glass leads to property improvement of the bricks regardless
of grog content. The grog content does however influence
the degree of improvement since high grog content mixes
always tend to be more open textured and have lower compressive
strength than low grog content mixes, and thus display a
~more pronounced improvement upon addition of the powdered
glass.
Table VI compares the properties of bricks, all produced
by the stiff mud process, from a Control clay-based body,
- Mix VIA, agains~ those of bricks produced from the clay-
based body having 2.5% by weight powdered glass added, Mix
:~ VIB, and bricks produced from the clay-based body having
5.0% by weight powdered glass added, Mix VIC.
TABLE VI
Mix, % by weightVIA (Control)VIB VIC
Red Shale 51 51 51
Buff Shale 44 44 44
Grog 5 5 5
Powdered GlasR % by
Weight Over & Above 0.0 2.5 5.0
ModuluR of Rupture, psi 3197 - 3840 3119
Net Area Compressive
Strength, psi12505 20032 15069
Water Absorption, % 4.7 4.4 4.2
Bulk Density, pcf 141.6 140.0 138.6
Wet-Fired Shrinkage, % 8.7 8.8 8.S
Colour Standard Standard Slight
Colour ColourDarkening of
Standard Colour
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As in the case of Tables I and II, the bricks produced
from the powdered glass-containing mixes, Mixes VIB and VIC,
display recogni~able improvements in properties over those
of bricks produced from the Control. However, since brick
manufacture by the stiff mud process generally produces
products of lower porosity and higher compressive streng~h
than those manufactured by the dry press process, the degree
of improvement is relatively lower.
In summary, the inclusion of powdered glass in an
amount in the range of about 0.25 to about 12.5% by weight
intimately admixed in the clay-based body from which a kiln
burned brick is produced, whether by the dry press process
or the stiff mud process, results in a brick of increased
compressive strength, decreased water absorption and lower
apparent specific gravity, relative to a kiln burned brick
lacking powdered glass intimately admixed with the clay-
based body from which it is produced.
Of significance, the inexpensively obtained, marked
increase in compressive strength in bricks produced by the
power press process, while maintaining the prerequisite
colour characteristics, permits minimi~ation of elaborate
and expensive quality control with assurance that all bricks
produced will possess a predictable minimum compressive
strength.
Modifications falling within the true broad spirit and
scope of the invention will be readily apparent to those
skilled in the art.
