Note: Descriptions are shown in the official language in which they were submitted.
~ ~8~S8
The presPnt invention relates to shaped articles prepared from a
plastically deformable composite material, to a composite material
per se, to a method for rolling a plastically deformable material,
and to an apparatus for rolling a plastically deformable material.
Canadian Patent Application No. 339,002 discloses a particular
type of material comprising a matrix, the matrix comprising
densely packed particles having a size of the order of 0.5 - 100
um, in particular densely packed cement particles, and inorganic
solid particles having a size of from about 50 A to about 0.5 um
and being at least one order of magnitude smaller than the
respectlve above-mentioned particles, in particular ultrafine
silica particles, the smaller particles being homogeneously
arranged and preferably densely packed in the volds between the
larger particles.
Such materials, in the following designated DSP materials
(Densified Systems containing ultrafine Particles), specifically
cement-based DSP materials (that is, DSP materials in which the
particles having a size of the order of 0.5 - 100 um are cement
particles), show a number of highly interesting properties,
including high density, high tensile, bending and compressive
strength, good durability, and extraordinarily good ability to
anchor reinforcing bodies, including fibers, embedded in the
matrix.
Due to their improved properties, cement-based DSP materials are
highly desirable materials for building products, including thin-
walled panels and components of the types which are nowadays often
made of asbestos-reinforced cement. Due to the excellent plastic
properties of the uncured DSP composite material, an attractive
method for shaping such articles of DSP is a plastic deformation
or compression process.
The present invention relates to important new developments
connected to the preparation of shaped articles from DSP
materials, in particular by plastic deformation such as extrusion,
rolling, or compression.
. . .
lZ :~5S~3
In connection with the development of practical methods and
apparatuses for the plastic deformation of the DSP materials,
various new aspects of the composition and working of DSP
materials have been investigated and have given rise to new
developments.
One aspect of the present invention relates to compositions of
cement-based DSP materials which are especially suitable for
plastic deformation processes, and to shaped articles made from
such compositions. Another aspect of the present invention
relates to a method for rolling a DSP material or other
plastically deformable material.
In the present context, the term "plastically deformable material"
designates a material which, as a single phase, is deformed
plastically when sub~ected to deformation forces such as
hydrostatic pressure and displacement compulsion, including shear,
as contrasted to materials which are shaped from a two-phase
system such as a cement-water slurry from which liquid phase is
removed during the shaping process ("slip casting"). One
characteristic of cement-based DSP materials is that although they
comprise cement particles and water, they show such a water
retention and such an internal coherence that substantially no
water will be removed from them during processing, including
deformation, so that the plastic DSP past behaves as a one phase
plastically deformable material.
As disclosed in the above-mentioned Canadian Patent Application
No. 339,002 the particular properties of the cement-based DSP
materials are ascribable to the dense packing of the cement
particles with homogeneously distributed and preferable densely
packed ultrafine particles in the voids between the cement
particles, the dense packing of the cement particles and the
simultaneous homogeneous arrangement of the ultrafine particles,
in particular ultrafine silica, being obtained by a unique
combination of a critical amount of
5~3
J 3
water in the paste and an unconventionally high dosage of a surface-
active dispersing agent, in particular a concrete superplasticizer. As
surface forces which would otherwise iead to "particle locking" be-
tween the cement particles and between the ultrafine particles have
5 been overcome by means of the high dosage of the surface-active
dispersing agent, a system has been obtained in which the resistance
to particle packing is solely due to particle geometry.
In the practical exploitation of cement-based DSP materials for the
rnass-production of shaped articles by plastic deformation, it has been
10 found that certain problems may arise which have been solved through
the principles of the present invention.
Thus, it has been found that when processing cement-based DSP
materials consisting of, e. g ., cement, ultrafine silica, water, concrete
superplastici~er, and fibers, the processing-relevant properties of the
15 fresh paste such as the resistance to shear deformation may vary to
an undesirable high degree dependent on the time elapsed after
mixing of the material. Thus, the period of time during which the
material has plastic deformation properties within desirable limits may
become too small for production on an industrial scale. This is the
20 case when such a formulation is intended for extrusion. In order to
possess a consistency suitable for extrusion, the formulation should
have an extremely low water/dry matter ratio within narrow limits.
However this extremely low water/dry matter ratio leads to serious
problems in controlling the consistency of the material, and the ma-
25 terial when shaped by plastic deformation appears with a cracky,crusty surface. Even small changes in the water/dry matter ratio of
the above-mentioned basic material may give rise to serious problems:
Even a minor reduction in the water content to below a critical mini-
mum, e.g., caused by surface evaporation, will lead to an unsatura-
30 ted densely packed particle structure The unsaturation will verysoon result in solidification of the material, whereupon the material is
no longer suitable for plastic deformation shaping such as low pres-
sure extrusion, calendering or compression shaping. Throughout the
present specification, "low pressure" in connection with plastic defor-
P~V F:2 '59A int. vers . OP~P 1982
lZ~ 58
mation shaping is intended to designate hydrostatic shaping pressuresbelow 10 MPa.
On the other hand, even a slight excess of water compared to the
critical amount results in a material which becomes sticky and is
5 unsuitable for plastic deformation extrusion as water will separate
from the material into slip zones during the plastic deformation and
the coherent nature of the material will be lost.
Hence, one major object of the present invention is to decrease the
sensitivity of the cement-based DSP materials to small changes in the
10 water content and to expand the period during which the DSP ma-
terial is suitable for processing by plastic deformation.
According to one main aspect of the present invention, this has been
obtained by incorporating, in the DSP paste, particles of a solid
plasticizing agent.
15 In the present context, the term "solid plasticizing agent" designates
a plasticizing agent which is in the form of particles which are typi-
cally at least one order of magnitude smaller than the cement particles
and which show surface-active or dispersing properties in the ce-
ment-based DSP system, typically particles which are known plastici-
20 zers in pastes or slurries for inorganic matrix-based materials, such
as ball clay (china clay), the particles of which typically have a
flaky-hexagonal shape. While the exact function of the solid plastici-
zer in the DSP system is not known with certainty, it is assumed that
the particles of the solid plastizicer such as ball clay will obtain a
25 negative charge all over their surface (both at the edges and the
surfaces thereof) in the highly alkaline environment (pH above 10)
and will adhere to cement particles due to electrostatic forces. Due to
their negative surface charge, ball clay particles on adjacent cement
particles will repulse each other, thus preventing the cement particles
30 from flocculating.
According to the invention, the particles B are suitably particles of
ultrafine silica having a specific surface area of about 50,000 -
P~V F2259A int. vers. OP/P 19~2
iZ48S5~
2,000,000 cm2/g, in particular about 250,000 cm2/g, and the particles
C are suitably ball clay particles.
According to another aspect of the present invention, an improved
processability in plastic deformation processes, e.g., lower extrusion
pressure necessary to obtain a good result, improved internal cohe-
rence), a prolonged pot life in processable condition, a smoother
surface of the plastically deformed material, and an increased bending
strength of the matrix, is obtained by incorporating bodies (D)
having an aspect ratio of about 3:1 - 100:1 and a diameter of the
order of 0.5 - 10 llm, such as smooth, rod-like or acicular bodies,
e.g., fine mineral wool or wollastonite, in particular such bodies
having an aspect ratio of about 3:1 - 20:1. Thus, the presence of
bodies D is generally preferred in the articles of the invention com-
prising bodies C, but the presence of bodies D, without the simul-
taneous presence of bodies C, also results in the above-mentioneci
improvements ascribable to bodies D. The bodies D are believed to
decrease the tendency of the material to form internal flaws which
otherwise may take place in slip pianes generated during the plastic
deformation, and are also believed to decrease, through a micro
reinforcing effect in the uncured paste, notch effects arising around
fibers or angular particles in the matrix, thus providing improved
internal coherence. Hence, another aspect of the invention comprises
a shaped article comprising a matrix, the matrix comprising
A) a coherent structure comprising substantially densely packed
inorganic solid particles of a size of 0.5-100 llm,
B) substantially densely packed inorganic solid particles having a
size of from about 50 ~ to about 0.5 ~m and being at least one
order of magnitude smaller than the particles A, or a coherent
structure formed from such homogeneously arranged particles,
the particles B being homogeneously arranged in the voids be-
tween the particles A,
P~V F2259A int. vers. OP/P 1982
855~3
the dense packing being substantially a packing corresponding to
the one obtainable by gentle mechanical influence on a system of
geometrically equally shaped large particles in which locking
surface forces do not have any significant effect,
D) additional bodies having an aspect ratio of about 3:1 - 100:1
and a diameter of the order of 0.5 - 10 llm,
and optionally
C) particles of a solid plasticizing agent,
a nd/or
E) reinforcing fibres having an aspect ratio of at least 100:1.
According to the invention, the particles B are suitably particles of
ultrafine silica having a specific surface area of about S0,000 -
2,000,000 cm2/g, in particular about 250,000 cm2/g, and the particles
C are suitably ball clay particles.
15 The reinforcing fibers E may typically include synthetic organic fibers
(polymer fibers) which have been found suitable for incorporation in
cement-based materials, such as plastic fibers, including polypropy-
lene fibers, polyvinyl alcohol fibers, or aromatic nylon fibers, and/or
they may include inorganic fibers, including glass fibers, mineral wool
fibers, asbestos fibers, metal fibers, and aluminum silicate fibers,
and/or thet may include cellulose fibers, including cotton fibers. The
selection of reinforcing fibers or combinations of reinforcing fibers
will depend upon the desired characteristics of the articles to be
p roduced .
25 Norrnally, the particles A constitute about 40 - 70 per cent by weight
of the matrix and comprise hydraulic cement in an amount of about
25-70 per cent by weight of the matrix and optionally fly ash in an
amount of about 15-40 per cent by weight of the matrix, particularly
at the most about 25 per cent by weight of fly ash and about 45 per
P~V F??59A int. vel s. OP~P 198?
~Z~185S~
cent by weight of cement. The maximum amount of fly ash relative to
cement is normally 1:1. The particles B preferably constitute about
5-30 per cent by weight of the matrix, preferably about 10-25 per
cent by weight.
S Preferably, the particles C, in particular ball clay particles, consti- tute 2 - 10 per cent by weight of the matrix, preferably 3 - 7 per
cent by weight, more preferably 4 - 6 per cent by weight.
The bodies D preferably constitute about 5 - 30 per cent by weight
of the matrix, preferably about 10 - 25 per cent by weight, although
the ranges of about 5-20, in particular 8-15, per cent by weight are
also interesting.
According to a particular aspect of the invention, sand may be incor-
porated in an amount of up to about 40 per cent by weight. When the
material is to be prepared in thin panels, the sand will normaliy be of
15 a size of between o.1 mm and 1 mm; otherwise, it may be of a size of
up to about 5 mm. The sand will contribute to increase the dimension
stability of the final product. Any loss of strength incurred due to
the incorporation of sand may be counteracted by autoclaving. When
reinforcing fibers E are present, they preferably constitute 0.5 - 10
20 per cent by weight of the matrix.
In accordance with the explanation given above, the matrices defined
above are particularly suitable for plastic deformation, and hence, the
shaped articles showing the above characteristics are typically made
by plastic deformation such as extrusion, rolling, and/or compression.
25 One typical kind of shaped article according to the invention is an
article which has been shaped by rolling of the DSP material into a
sheet and subsequent subdivision of the sheet, such as, e. g ., a
sheet, slate, or shingle for application as a cover or coating on other
structures, typically a slate or shingle for use as a roofing material.
30 According to another aspect of the present invention, an improved
processability in plastic deformation processes and a prolonged pot
P~V F2259A int. vers. OP~P 198
~Z~85~i8
life in processable condition, with extended useful range of
water/dry matter ratios, is obtained by using a dispersing agent
of the thickener type, preferably in combination with one or more
of the above-mentioned processability-improving measures and/or in
combination with other dispersing systems such as will be
explained below.
Examples of dispersing agents of the thickener type are water
dispersible polymers such as non-ionic cellulose derivatives,
e.g., hydroxyethylcellulose ethers.
Thus, e.g., it has been found that combination of
dispersing agents of the concrete superplasticizer type,
typically of the type represented by alkali or alkaline earth
metal salts of highly condensed naphtahlene sulphonic
acid/formaldehyde condensates, typically of the type of the
"Mighty"f(described below) and "Lomar D"~ (a highly
polymerized naphthalene sulphonate condensate),
with
compatible dispersing agents of the thickener type, such as
non-ionic cellulose derivatives, typically medium viscosity
non-ionic cellulose derivatives which are readily soluble in
water at pH above 10 and which have a uniform substitution of
the hydroxy groups on the cellulose molecules, typically
medium vlscosity hydroxyethylcellulose ethers such as
NATROSOLf 250 H4BR, NATROSO~ 250 HBR, NATROSOLf 250 MHBR,
and NATROSOLf 250 MBR
result in cement-based DSP materials having a prolonged pot life
and expanded range of water/dry matter ratios over which they
retain suitable properties for plastic deformation, including
suitable viscosity, without any stickiness or liquid separation
during the plastic deformation, and shaped articles made from such
materials by processes including plastic deformation will have
matrix properties which are as good as or even better than the
* Trade Mark
~2~855~3
matrix properties of articles made from similar DSP materials, but
without the dispersing agent of the thickener type.
According to one aspect of the present invention, dispersing
agents of the above-mentioned thickener type are used as the only
dispersing system in the DSP material. In such case the material
is subjected to a high shear mixing in the plastic state, such as
by intense kneading or roll milling, and the thickener may be a
thickener of the medium viscosity type, or even a thickener of the
high viscosity type such as hydroxypropylmethyl cellulose such as
Methocell~15MS from Dow.
According to a further aspect of the present invention, it has
been found that a combination of a soluble salt of a polymeric
sulphonate plasticizer and a melamine concrete superplasticizer is
effective in a smaller amount, on a weight basis, than either of
these superplasticizers alone. Therefore, an aspect of the
present invention comprises cement-based DSP materials containing
such a combination, in particular cement-based DSP materials which
also, in accordance with the above-discussed aspects of the
invention, comprise a solid plasticizer such as ball clay.
In the composite materials of the invention, the water will
normally constitute 7 - 20 per cent by weight. The dispersing
system will normally constitute about 1 - 4 per cent by weight.
When the dispersing system comprises a concrete superplasticizer
in combination with a thickener type dispersing agent such as a
water soluble polymer, the system will normally comprise 1 - 2 per
cent by weight of the concrete superplasticizer and 0.01 - 0.08
per cent by weight of the water soluble polymer, calculated on the
composite material.
The above-mentioned aspects of the invention involving the use of
special dispersing systems in cement-based DSP materials may be
summarized as a composite material for producing a shaped article,
comprising
* Trade Mark
i~8558
A) inorganic solid particles of a size of 0.5-100 llm, in particular
hydraulic cement particles and optionally fly ash particles,
B) inorganic solid particles having a size of from about 50 A to
about 0. 5 llm and being at least one order of magnitude smaller
S than the cement particles A,
and optionally,
C) particles of a solid plasticizing agent,
D) additional bodies having an aspect ratio of about 3:1 - 100:1
and a diameter of the order of 0.5 - 10 llm,
and/or
E) reinforcing fibres having an aspect ratio of at least 100:1.
water,
and a surface-active dispersing system which comprises,
i) a combination of a soluble salt of a polymeric sulphonate plasti-
cizer and a melamine concrete superplasticizer, or
ii) a dispersing agent of the thickener type (water dispersible
polymer), or
iii) a combination of a concrete superplasticizer and a dispersing
agent of the thickener type, or
20 iv) a combination of any of the systems ;,), ii), and iii),
the amount of the particles A substantially corresponding to dense
packing thereof in the composite material with homogeneously arranged
particles B in the voids between the cement particles, the amount of
water substantially corresponding to the amount necessary to fill the
P~V F2259A int. vers. OP/P 1982
lZ48S58
11
voids between the particles A, B and C, and the amount of disper-
sing system being sufficient to impart to the composite material a
plastic consistency in a stress field of at the most 200 kg/cm2, pre-
ferably at the most 100 kg/cm2.
5 A further aspect of the invention comprises improvements in connec-
tion with rolling of plastically deformable materials, in particular
cement-based DSP materials.
Rolling of a plastically deformable material comprises subjecting the
material to a hydrostatic pressure which will reduce the thickness of
10 the layer of the material subjected to the rolling. In principle, the
rolling is performed by moving the material through a wedge-like
space defined between oppositely arranged surface parts. Usually, the
wedge-like space is constituted by the space between a roller surface
and a plane surface adjacent to the nip between the roller and the
15 plane surface, or by the space between two roller surfaces adjacent
to the nip between the rollers.
In connection with the rolling of plastically deformable materials,
including DSP materials, it has been found that flaws may occur in
the rolled material, including scars and other flaws due to parts of
20 the plastically deformable material torn out from the mass to be rolled
(because of adherence to the roller) or due to air bubbles entrapped
in the surface. Thus, the rolled product may not always show the
superior properties aimed at.
It has now been found that this problem may be overcome, and that
25 plastically deformable materials, including DSP materials, may be
subjected to rolling or equivalent treatment with excellent results and
in an easily controllable and reproducible manner, by a special method
which constitutes an aspect of the present invention, and which
comprises
introducing the material into a wedge-like space defined between
oppositely arranged surface parts, of which at least one is gas-
permeable, preferably not liquid absorbing, and substantially
impervious to said material, and
P~V F ) )59A int vers. OP/P 198-)
1248558
moving said surface parts so as to draw said materiai towards and
through the throat or gorge of said space between said surface
pa rts .
The said one surface part may be the peripheral surface of a roller,
the surface having the above-mentioned characteristics, but usually,
said surface parts are defined by opposite surface parts of a pair of
spaced bands or belts which are, e. g ., passed around and backed up
by moving rollers and/or stationary guide members.
Preferably, the said one surface part is constituted by a textile web
or non-woven tissue made from man-made or natural fibers, such as a
web or non-woven tissue made from nylon or aromatic polyamide.
Although the present invention is not to be limited by any theory, it
is assumed that the surprising improvement with respect to the per-
formance of the rolling process and the surface properties and cha-
racteristics of the resulting rolled product is due to the following
combination of effects exerted by the gas-permeable, not liquid ab-
sorbing surface layer which is substantially impermeable to the plasti-
cally deformable material:
1 ) The fact that the surface is gas-permeable will contribute to
allow any air bubbles at the surface of the rolled material to
escape through the surface and, hence, not become entrapped in
the surface.
2) The surface acts as an intermediate layer which prevents the
plastically deformable material from adhering to any solid roller
surface such as a metal surface in connection with the plastic
deformation. On the other hand, the surface itself, due to its
gas-permeability, is relatively easily removed from the rolled
material, in particular when the surface is constituted by a band
or belt which, after the rolling action, is peeled off the rolled
material by being bent away from the material at preferably a
sharp angle,
P~V F2259A int. vers. OP/P 1982
1248558
3). Surface defects which are normally encountered in rolling
processes due to uncontrolled displacement and shear in the
material subjected to the rolling are obviated beçause a controlted
- and uniform high shear takes place between the layers of the
plastically deformable material immediately adjacent to the surface
(which, due to its gas permeability and tissue or web structure,
pulls along the surface layers while central portions of the pla-
stically deformed material between the surface layers are not
moved forward at the same high rate).
The DSP material which is rolled in accordance with the aspect of the
invention described above is preferably a DSP material to which
improved processability in plastic deformation has been imparted
according to any of the measures of the present invention discussed
above .
According to an interesting aspect of the rolling method of the inven-
tion, a layer or layers of a fibrous material is incorporated in the
plastically deformable material during the rolling process by being
supplied to the plastically deformable material prior to the introduc-
tion of the plastically deformable material into the wedge-like space.
In this embodiment, the fibrous material may comprise one or several
layers of loose fibers which are optionally arranged in a desired
orientation and/or one or several layers of web, net, or non-woven
tissue. By this controlled incorporation of a fibrous material in a
desired orientation, an optimum reinforcing effect may be obtained.
Thus, one or several layers of web, nets and/or non-woven tissues
which are pervious to the plastically deformable material may be
introduced into the wedge-like space together with the plastically
deformable material in a controlled manner and at a controlled longi-
tudinal introduction velocity so that the web, net, or tissue is ar-
ranged substantially unbuckled in longitudinal direction in the resul-
ting rolled sheet.
According to another especially interesting embodiment of the in-
vention, the cross sectional geometry of the feed stream of the pla-
stically deformable material is controlled before introduction of the
P~V F2259A int. vers. OP/P 1982
lZ48558
14
plastically deformable material into the wedge-like space. In this
manner, a very high degree of control of the degree of deformation to
which the material is subjected is obtained. The control of the cross
sectional geometry of the feed stream of the plastically deformable
5 material may be performed by means of guide members arranged in
front of the wedge-like space and limiting the width of the feed
stream of the plastically deformable material introduced into the wed-
ge-like space, or the control of the cross sectional geometry of the
feed stream of the plastically deformable material introduced into the
10 wedge-like space may be performed by means of guide members de-
fining a desired cross sectional geometry of the feed stream of the
plastically deformable rmass.
A special embodiment of the control of the cross sectional geometry of
the feed stream of the plastically deformable material is performed by
15 subjecting the plastically deformable material to extrusion prior to the
rolling. In this case, the extruded plastically deformable material may
be rolled in a direction parallel to the extrusion direction, or it may
be rolled in a direction transverse to the extrusion direction, depen-
ding on the particular effect to be obtained, the orientation of fibers
20 incorporated in the material, etc.
According to a particular aspect of the invention, the sheet resulting
from the plastic deformation, in particular the rolling, is subjected to
a controlled hydrostatic pressure for a period subsequent to the
deformation . The controlled pressure may, e. g ., be between 2 and 10
25 MPa, preferably between 2 and 5 MPa, and may be maintained for a
period between 10 minutes to 24 hours, preferably for 2 - 10 hours.
This controlled pressure treatment subsequent to the plastic defor-
mation may reduce the formation of larger pores in the material,
thereby improving the strength properties, in particular the bending
30 strength, in the cured matrix.
The thickness of the sheet rolled in accordance with the present
invention is typically in the range of 1 - 40 mm, in particular 2 - 20
mm, especially 4 - 10 mm.
P~V F22~9A int. vers. OP/P 1982
lZ~8558
After the plastic deformation, the sheet may also be subjected to
subdivision and shaping, e.g. by compression shaping, in any de-
sired shape. According to a particular embodiment of the invention,
the rolled sheet used for the preparation of tubular articles, e.g. by
5 being wound in coiled configuration onto a cylindrical member with
contact between the edges of consecutive coils, or, according to a
particular aspect of the invention, the rolled sheet may, in connection
with the rolling treatment, be wound onto a cylindrical core in super-
imposing layers to build up a greater thickness of the tube; this
10 latter embodiment is particularly interesting when the sheet is rein-
forced with fiber material in accordance with the embodiment discus-
sed above.
The invention also relates to an apparatus for rolling a plastically
deformable material and comprising rolling members having oppositely
15 arranged surface parts defining a wedge-like space therebetween, at
least one of said surface parts being gas permeable, preferably non-
liquid absorbing, and substandially impervious to said plastically
deformable material.
The invention will now be described in greater detail with reference
20 to the Examples and to the drawing, in which
Fig. 1 is a schematic representation of an apparatus according to the
invention for rolling a plastically deformable material by the method
according to the invention,
Fig. 2 is a schematic representation of another embodiment of a sec-
25 tion of the aparatus shown in Fig. 1, and
Figs. 3 and 4 are enlarged views illustrating the material flow of the
nip between two rollers in the apparatus shown in Fig. 1.
In Fig. 1 fresh paste 10, for example of a DSP material of a compo-
sition corresponding to the composition given in the Examples, such
30 as Examples 5, 6 and 7, is fed to a roller assembly, in this case
consisting of two roller sets 13 and 13', by means of a feeding device
such as a belt conveyor 11. From the belt conveyor, the paste enters
into the nip between a first set of rollers 14 and 16 mounted in a
P~V F2259A int. vers. OP~P 1982
85513
frame 12 and adjustable in relation to each other by means of adjust-
able support members 18 and 20. In the embodiment illustrated in Fig.
1, a second set of rollers 14' and 16' is arranged at a distance from
the first set of rollers and is otherwise operated and supported in
S similar manner as the first set of rollers. Round the upper two rollers
and the lower two rollers, respectively, two endless sheets 22, 26
move with the same speed as the peripheral speed of the rollers.
These endless sheets or bands 22, 26 are supported by auxiliary
rollers 24, 24', 28, 28', and in the path between the two sets of
10 rollers, are supported by small supporting rollers 32. If necessary,
the sheets 22 are, furthermore, supported by supporting bands 23,
27, the tension of which is adjusted by means of tensioning rollers
25, 29. The sheets 22, 26 are made of a textile web or non-woven
tissue, such as nylon web, and is of a type which is gas permeable,
15 non-liquid absorbing, and substantially impervious to the constituents
of the paste treated, that is, the mesh or interstices in the sheets
are substantially not larger than the particle size of the cement
particles in the paste.
The supporting band 23, 27 may, for example, be of the same type of
material which is used for driving belts, and must not necessarily
show gas permeable characteristics. According to one embodiment,
however, only one pair of rollers is employed, whereby the suppor-
ting band is avoided. The sheets 22, 26 pass through cleaning sta-
tions 31, 33 where any paste entrained is removed, for example by
25 means of brushing devices, obtionally assisted by washing with water.
The washing stations comprise conditioning means controlling the
moisture of the washed sheet to a preselected range.
The paste 10 is plastically deformed to a reduced thickness sheet 30
between the two sheets 22 and 26 in the nip between the rollers 14
and 16 and is thereafter further reduced in thickness between the
sheets 22 and 26 as these move increasingly closer to each other,
supported by roller sets 32. As will be seen from the drawing, the
plastically deformable material first passes through a wedge-like space
defined by the nip between the rollers 14 and 16 and the space
35 between the rollers to the left of the nip. A second wedge-like space
P~V F2259A int. vers. OP/P 1982
~Z'~8~58
17
comprises the nip between the rollers 14', 16' and includes the nar-
rowing space between the roller sets 32 extending to the left of the
nip between rollers 14 and 16, or the complete passageway from the
start to the left of the nip between rollers 14 and 16 to and including
the nip between rollers 14', 16' could be taken as the wedge-like
space defined above. As the paste passes through the wedge-like
space in Fig. 1, a hydrostatic pressure with resulting plastic defor-
mation is applied on the paste, first by the rollers 14, 16, whereupon
the hydrostatic pressure is maintained and further increased by
means of the roller sets 32 which, in the embodiment shown in the
drawing, exert a slightly increased hydrostatic pressure with resul-
ting plastic deformation of the sheet 34 to a smaller thickness. A final
plastic deformation results from the passage of the sheet between the
rollers 14' and 16'.
It will be understood that it is within the scope of the invention to
perform the complete plastic deformation by means of a single set of
rollers 14, 16 with appropriate transporting means. After the final
plastic deformation at 36, the finished sheet 38 is transported to a
curing treatment or to a further plastic deformation process by means
of a conveyor 40. (For example, the plane sheet 38 may be rolled or
compressed into a corrugated shape such as is used for roof panels,
or it may be compression shaped into any desired three-dimens;onal
shape, for example a roof tile, etc., and/or the sheet may be sub-
divided into smaller units such as bricks, shingle, slates, etc. When
roof panes in the shape of plane sheets are prepared, they are suit-
ably produced with a somewhat rough or irregular back to avoid that
capillary forces will cause that water will be entrained into the inter-
stices between the panels. -rO avoid efflorescence, the final panels
may be painted on one or both sides with a suitable paint in a de-
sired colour, e.g. an aqueous acryl polymer dispersion.
In Fig. 2, the supporting roller sets 32 of Fig. 1 are replaced by
supporting plates 42, 43 which support the sheets ~ 7 and 26 with a
pressure which is adjustable by adjusting the pressure of compression
springs 44, 45. In the embodiment shown in Fig. 2, the conveyors 11
and 40 are replaced by support plates 11 and 40 having smooth sur-
faces giving little friction.
P~V F2259A int vers. OP/P 19S2
~2~855~
Figs. 3 and 4 illustrate in deta;l the character of the plastic defor-
mation in the wedge-like space, the left limitation of which is the
position at which the paste comes in contact with the sheet 22, and
right limitation of which is the domain at the nip between rollers 14
5 and 16. (It will be understood that, having passed the wedge like
shape in the same manner as illustrated in Fig. 1, the paste may pass
through a further wedge-like space or part of a wedge-like space.)
Although the present invention is not to be limited by any theory,
the process which takes place in the wedge-like space is believed to
10 lead to the following improvements:
Due to the hydrostatic pressure established in the wedge-like space
and increasing from left to right, a pressure gradient is generated
throughout the paste, with maximum pressure in the nip and de-
creasing pressure towards the beginning of the wedge-like space to
15 the left. This pressure gradient will, in itself, tend to generate a
backward flow of the material, the most pronounced effect of this
being in the middle of the nip between the two rollers such as illu-
strated at 30. At the same time, due to the friction between the sheet
22 and the paste, an externally forced displacement of the layers in
20 immediate contact with the sheet 22 takes place, and these layers will
substantially move at the same speed as the speed of the rollers. Due
to the viscosity and coherence of the paste, the displacement is
transferred to the interior of the paste, superseding the backward
flow tendency cause by the hydrostatic pressure gradient, thus
25 resulting in a forward flow of the total paste with considerably higher
flow speed at the layers adjacent to the sheet than in the interior of
the paste. It is believed that one of the main reasons for the advan-
tages and quality improvements associated with the feature of the
invention comprising the use of the gas permeable, not liquid absor-
30 bing sheet 22 is that because of the much higher friction between thesheet and the paste than between a smooth roller surface and the
paste, not only a much faster displacement takes place in the layers
of the paste adjacent to the sheet, but also a much more uniform
displacement, which means that there will be a substantially uniform
35 shear gradient throughout the paste, ccntributing to a uniform sur-
P~V F2259A int. vers. OP/P 1982
~2~8S58
19
.
face quality after the rolling. Any gas bubbles or domains whichwouid tend to be entrapped between the sheet 22 and the paste will
pass through the gas permeable sheet 22, whereby defects ascribable
to entrapped air at the surface of the rolled sheet are avoided.
5 It is of importance that the sheets 22, 26 have a sufficient strength
for the purpose. As a guideline, the minimum strength of the sheets
should be 100 kp/cm of width. Also, the sheets should be sufficiently
resistant to being bent over a "knife edge", that is, they should be
capable of being bent minimum 90 over an edge having a radius of
10 curvature of 1 mm.
The materials used in the Examples are as follows:
Ordinary Portland Cement: Specific surface (Blaine): 3300
cm2/g Density 3.12 g/cm3.
Low alkali, sulphate resistant
15 cement: Specific surface (Blaine): 3000
cm2/g, C3A content approx . 1 . 5~.
Fly ash from power plant: Fine, spherical particles, parts of
which are hollow. Specific surface
(Blaine): 2800 cm2/g. Density
approximately 2.4 g/cm3.
Elkem Silica: Fine spherical SiO2-rich dust,
produced as a by-product in the
production of silicon metal or
ferrosilicium in electrical furnaces.
Specific surface (determined by
BET technique) about 250,000
cm2/g, corresponding to an ave-
rage particle diameter of 0.1 ~Im.
Density 2.22 g/cm3. From Elkem,
Norway.
P~V F2''59A int. vers. OP/P 1982
12 ~558
Quartz sand: Fractioned, natural quartz sand
0 - 2 mm . Density 2 . 63 g/cm3 .
KRENIT7M fibers: Polypropylene fibers made from
polypropylene film stretched in a
ratio of about 1:17 and fibrillated
on a needle roller in analogy with
Example 4 in International Patent
Application No. PCT/DK79/00047.
Mighty~: A concrete superplasticizer, so-
dium salt of a highly condensed
naphthalene sulphonic acid/form-
aldehyde condensate, of which
typically more than 70~O consist of
molecules containing 7 or more
naphthalene nuclei. Density about
1.6 g/cm3. Available either as a
solid powder or as an aqueous
solution (42~ by weight of Mighty,
58% by weight of water).
Water: Common tap water.
Wollastonite: Nyad G. A naturally occuring
calcium methasilicate CaSiO3 of
which 80~o has a size equivalent to
a sphere diameter of less than
4 llm, and 20`3o has a size equi-
valent to a sphere diameter of less
than 1 llm.
Melment: An anionic melamine resin powder.
Available from SKW Trostberg.
P~V F2259A int. vers. OP/P 1982
1~485~8
Natrosol 250 H4BR A non-ionic medium visçosity water
soluble polymer derived from cel-
lulose (hydroxy ethyl cellulose
ether). The characteristic 2~
Brookfield viscosity at 25C is
50,000 mPa . s . Other preferred
Natrosol 2S0 types in the medium
viscosity range are H4BR, HBR,
MHBR and MBR. (The letter B
designates improved biological
stability obtained by regular sub-
stitution of the hydroxy groups,
and the letter R designates that
the product is readily soluble in
water). Available from Hercules.
Cormix* SP2 A concrete superplasticizer based
on a soluble salt of polymeric sul-
phonate. Available from Cormix.
8all Clay* 895 Ball Clay, comprising about
56~ of clay and 243 of micaceous
matter, chemical composition pre-
dominantly SiO2 and A12O3, the
main clay mineral being kaolinite,
particle size distribution: 50~ of
the particles being finer than 0.3
ym, from English China Clays Sales
Co., Ltd.
Carbon black: Colour pigment, Kenotor)e 2 AL.
* Trade Mark
lZ'~ 5$~3
Example 1 (reference example).
Formulation:
Component ~ by weight of dry matter
. _ . .
Cement,
ordinary Portland cement 70.9
Elkem Silica 23.9
6 mm polypropylene fibers
(KRENITTM) ~ g
Mighty (dry matter) 3.3
Water/dry matter 0.1198
,.,
P repa ration:
Mixer: "Maren *, supplied by Effort, Kold;ng, Denmark, 16 liters of
15 dough mixer w;th planetary movement.
Paste preparat;on:
1) The dry mater;al was m;xed for 3 m;nutes.
2) Water and dispersing agent were added and mixed for 10 minutes
whereby the material was formed into a dough. When the dough
consistency was reached, the fibers were added and further
mixing took place for about 3 minutes.
Shaping:
Mernbers were produced by pressing in a laboratory single screw
extruder (type "Handle", Strengpresse) . The dough was extrudt d
25 twice and the hydrostatic pressure in the die was about 0. 6 MPa. The
dirnension of the die was 40 x 10 mm.
:~Z48558
Test specimens of dimensions 10 mm x 40 mm x 210 mm were prepared.
Curing:
The specimens were cured for 24 hours under a plastic film.
Thereafter,
5 the specimens were cured in water until testing took place.
Testi ng:
The testing was performed as a four point bending test in a Zwick
universal testing machine.
Test results:
10 Properties (after 7 days of curing)
Density (dry), kg/dm3 2.06
Bending strength of matrix, MPa 12.1
Modulus of rupture, MPa 20.1
15 Elongation at break, o/oo 14.2
Other properties:
Frost resistance .
By means of microcalorimetry it was found .hat the amount of freezable
20 water at temperatures above -30C was ~ero.
P~V F2259A int. vers. OP~P 1982
lZ48558
24
Pore structure analysis:
By means of quantitative microscopy, the pore si~e distribution was
obtained according to ASTM C 457 modified for automatic quantitative
microscopy. The theoretical pore size distribution by volume was
5 calculated according to Lord and Willis.
Total volume of pores larger than 7.5 ~m in percentage of total volume:
1,93O .
Percentage of pores by volume greater than:
2000 ~Im: 0.0%
10350 um: 1.08%
97 llm: 1.38%
52.2 llm: 1.70%
22.4 llm: 1.79%
E x ample 1 a ) .
15 Specimens were prepared as described in Example 1 using the fol-
lowing formulation:
Component -O by weight of dry matter
Ordinary Portland Cement 67.8
20 Elkem Silica 22.9
6 mm E-glass fibers 6.0
Mighty (dry matter) 3.3
Water/dry matter ~ 0.12
25 The pore size distribution of the cured material was obtained accor-
ding to the method mentioned above with the following result:
P~V F->259A int. vers. OP/P 198~
~'~48558
Total volume of pores larger than 7.5 lJm in percentage of total:
l .37%.
Percentage by volume of pores greater than:
2000 ~Im: 0 0~,
5350 IJm: 0.0%
97 IJm: 0 . 65%
52.2 ~Im: o 95%
22 . 4 llm: 1 . 18%
Example 2.
lO Formulation:
Component -O of dry matter
.
Cement, ordinary Portland cement 67.2
Elkem silica 22.4
15 6 mm polypropylene fibers,
(KRENITTM) 1.8
Wollastonite, Nyad G 5.5
Mighty 3.3
Wate r/d ry matte r ratio 0 .1 337
The preparation was performed as described in Example 1. However,
wollastonite + dry powder were mixed for 3 minutes, and the extru-
sion pressure was l.0 - 1.2 MPa.
P~V F2259A int. vers. OP/P 1982
1~8558
26
Test resuits:
Property After 7 28 90 180 days
Dry density, kg/dm 2.08 2.13 2.122.11
8ending strength of
matrix, MPa 20.6 22.0 22.020.5
Modulus of rupture, MPa 23.1 23.824.0 23.3
Elongation at break, o/oo 8.5 7.7 5.5 6.2
10 ) The figure does not differ significantly from the 90 day strengths.
Eval uation:
Compared to Example 1, the experiments indicated
1 ) Improved processability in extr usion (lower necessary extrusion
pressure, improved internal coherence) . This is believed to be
due to the presence of wollastonite.
2) A smoother surface with a less amount of surface defects.
3) A prolonged pot life, which means that the paste remains plastic
to the extent necessary for low pressure extrusion. In comparison
with the paste prepared according to Example 1, the pot life of
the paste prepared in this example was prolonged by a factor of
4 - 5.
4) The bending strength of the matrix was increased by some 50~O.
P~V F2259A int. vers. OP/P 1982
1~8~58
27
Example 3.
Formulations 1 and 2:
Component ~ by weight of dry matter
Cement, ordinary Portland cement 68 6 63.3
Elkem Silica 29.4 27.2
6 mm polypropylene fibers, (KRENITTM) 2.0 1.8
Wollastonite, Nyad G - 7. 7
10 Mighty 4.15 3.8
Water/dry matter ratio 0.140 ().136
Prepa ration: .
Mixer: LAEIS, PZM 1000, with a 1000 liter vessel, and water spray.
15 Batch size:
Formulat;on 1 Formulation 2
Dry matter 802 kg 869 kg
20 Mixing procedure:
The dry matter was mixed for 5 minutes whereafter water and Mighty
were added, and mixing was continued for a further 2 minutes.
Thereupon, the fibers were added to the mix, and further mixing was
P~V F2259A int. vers. OPiP 19S2
129~8558
28
performed for 8 minutes to obtain a stiff nodule-like appearance of
the mix. Thereupon, the mixture was passed twice through a twin
screw continuous kneader of the type "Handle" MDZ25A.
Extrusion:
5 Extrusion was performed in a ' Handle Strengpresse' PZM45B, 350 mm
barrel, under vacuum. The die pressure was 3.4 MPa when extruding
formulation 1, while 1.3 MPa was sufficient when extruding formu
lation 2.
Eval uation:
10 As appears from the above, the use of wollastonite permitted the use
of a lower die pressure to obtain a material of an equally good quality.
Example 4.
Formu lation:
Component Weight, g
Cement 7350
Elkem Silica 2450
Melment 10 (powder) 171
Dispersing agent
Cormix SP2 (liquid) 40B
KREN ITTM 6 mm 200
Water 1300
PIV F2259A int. vers. OP/P 1982
,, . , ,, " ~
lZ4~i58
Prepa ration:
The preparation was performed as described in Example 1.
Test res u Its:
Property After (days)
7 28
Dry density, kg/dm32.01 2.00
Bending strength
of matrix, MPa 13.9 15.7
lO Modulus of rupture, MPa 21.4 22.0
Elongation at break, o/oo 9.4 8.3
Eval uation:
As compared to Example l, the combination of the two particular
15 dispersing agents at a lower dosage than Mighty results in the same
strength characteristic as when using Mighty.
P~V F2 59A int. vers. OP/P 1982
8558
Example 5.
Components ~ by weight
Portla nd cement 12 . 3
Low alkali, sulfate-resistant
cement 49 . 4
Elkem silica 18.5
Wollastonite, Nyad G 13.0
Ball clay 5.0
Mighty l.0
Polypropylene fibers, 6 mm 1.8
" N at rosol " 250 H4 B R0 . 04
Water/dry matter ratio 0.162
15 Preparation:
The preparation was performed as described in Example 1.
Production of sheets.
About 6 mm thick sheets were prepared from the dough by means of a
laboratory two roll calendering apparatus. The fresh dough was
20 placed on a flat metal sheet. The sheet was provided with frames so
that an appropriate hydrostatic pressure could be achieved in the
material during the shaping process.
Experiments were performed by calendering the material without or
with an intermediate gas-permeable, non liquid absorbing layer
25 substantially impervious to the DSP material (fine mesh nylon fiber
web), between the material and the calender, the intermediate layer
being placed on top of the fresh material before performing the ca-
Iendering process.
P~V F2259A int. vers. OP/P 1982
~2~8558
31
The sheets prepared without using the intermediate layer had scarred
and defective surfaces owing to torn out parts and to inadequate
filling of the surface (entrapped air).
The sheets prepared using the intermediate layer had no defects.
5 Specimens were cut out of the sheets for mechanical testing The size
of the specimens was about 76.5 x 6 x 210 mm.
Results Without intermediate With intermediate
layer layer
___ ____ ~__ ___
10 Orientation of the test
body in relation to the Paral- Trans- Paral- Trans-
direction of production lel verse lel verse
Density, kg/dm3 2.00- 2.09 2.00 - 2.09
Modulus of rupture, MPa 17 - 25 9 - 14 20 - 31 12 - 27
Elongation at break, o/oo 0.4 - 0.8 0.4 - 0.fi 0.7 - 4.8 0.6 - 4.3
From the above results, it appears that not only an improvement of
20 the surface quality of the sheets, but also an improvement of the
mechanical properties is obtained when using the intermediate layer
between the material and the calender roll in accordance with the
principles of the present invention.
Example 6.
25 Sheets of the dimensions 300x600x4 mm were produced by rolling a
pre-extruded string of material (dimensions 15x150 mm). The direc-
tions of extrusion and rolling were identical
P~V F2259A int. vers. OP/P 1982
~Z~8~
32
Formulation:
~ by weight of dry matter
Component Sample 1 Sample 2 Sample 3
Low alkali, sulphate
resistant cement37.8 33.9 46.8
Fly ash 24.9 15.9 10.0
Quartz sand 0.4-1 mm - 19.9
Elkem Silica 21.0 15 9 20.9
10 Wollastonite, Nyad G 13.9 12.0 19.9
TM 1.O 1.O
Mighty, (dry matter) 1.0 1.0 1.0
Carbon black 0.4 0.4 0 4
Water/dry matter ratio 0.098 0.087 0.097
P repa ration:
Mixer:
Samson, supplied by Hans Jensen, Hadsund, Denmark. A 27 liter
dough mixer with planetary movemerit.
20 Mix prepa ration:
Cement, fly ash, quartz sand, Elkem Silica, Mighty, carbon black and
water were mixed for 12 minutes. Wollastonite was then added and
mixing continued for 7 minutes. Finally Krenit-fibres were added and
mixing continued for another 7 minutes.
25 Kneading:
The dough was kneaded for approx. 10 minutes in a kneading mixer,
type K l l l 100 A, supplied by Hermann Linden Maschinenfabrik GmbH,
BRD.
P~V F2259A int. vers. OP/P 1982
124855~
33
Processing:
The dough was extruded by low pressure in a continuous string.
This string was fed into a rolling machine like the one described in
connection with Fig. 1 and rolled into a continuous sheet of cross
5 sectional dimensions 340 x 4 mm. Roliing speed approx. 6 m/minute.
Finally the continuous sheet was cut into sheets of 300 x 600 mm by
means of smooth, fast rotating cutting d;scs. These sheets were cured
as described below.
Cu ri ng:
Samples 1 and 3 at 60C, 100o RH for 16 hours, then for 7 days at
20C, wrapped into plastics. Sample 2 was autoclaved for 16 hours at
120C, then for 3 day at 20C, 60~ RH.
Test res u Its:
Sample 1 Sample 2 Sample 3
1 5
O rientation
of the testbody
in relation
to the direction
20 of production:
par./transv. par./transv. par./transv.
Modulus of rupture,
MPa 26 18 2518 3120
Density kg/dm32.03 2.12 2.14
P~V F2259A int. vers. OP/P 1982
~L2~8558
34
Example 7.
Formulation:
Amounts in % by weight of dry matter
Material Testno.812-1812-2 812-3 ôl2-3-1 812-3-2
Low alkali, sulphate
resistant cement 63.7 61.5 61.5 63.6 61.5
Elkem Silica 21.3 18.5 18.5 21.3 18.5
Ball clay - 5.0 5.0 - 5.0
10 Wollastonite Nyad G 15.0 15.0 15.0 15.0 15.0
Mighty 1.0 l.0 1.0 1.0 1.0
Natrosol 250 H4BR - 0.02 0.06 0.06
Water/dry matter 0.0930.127 0.1470.118 0.123
15 Test results:
Heat curing 16 hours at 60C wrapped in plastic
Curing
method Test No. Density kg/dm3 Modulus of Rupture, MPa
1 812-l 2.26 29.2
812-2 2.16 26.9
812-3 ').08 26.6
812-3-l 2.1g 31.6
812-3-2 2.10 29.6
P~V F2259A int. vers. OP/P 1982
'i~L?~f~558
Autoclaving 60 hours at 125C:
Curing
method Test No. Density kg/dm3 Modulus of Rupture, MPa
2 ôl2-1 2.31 39.2
2 ôl2-2 2.27 35.4
2 812-3 2.27 36.4
2 812-3-1 2.28 48.0
2 812-3-2 2.19 33.3
1 0
Reference, 7 days in water:
C u ri n g
method Test No. Specific weight kg/dm3 Modulus of Rupture, MPa
3 812-1 2.32 26.6
P repa ration:
The preparation was performed as described in Example 1.
Preparation of Test Specimens:
20 Extrusion was performed as described in Example 1. The test speci-
mens had the following dimensions: 10 mm x 40 mm x 210 mm.
P~V F2259A int. vers. OP~P 1982
~4855~3
36
Curing:
Method 1.
The test specimens were wrapped in plastic immediately after the
extrusion. About 2 hours later, they were placed in an oven for 16
5 hours at 60C for heat curing. The specimens were then stored at
ambient temperature and normal pressure and tested after 7 days.
Method 2.
The test specimens were stored under plastic for 24 hours subsequent
to the extrusion. They were then autoclaved for 60 hours at 125C
10 and a pressure of 2 atmospheres. The test specimens were stored at
ambient temperature and normal pressure and tested after 7 days.
Method 3,
The test specimens were stored under plastic for 24 hours after the
extrusion. They were then stored in water and tested after 7 days.
15 Testing:
The testing was performed in a Zwick universal testing machine, and
a 4 point bending test was performed. The following results were
obtai ned:
1. The reference sample 812-1 shows the strength level which can be
obtained using the formulation of the present invention and a
suitable curing method, the level being 26 - 30 hlPa (modulus of
rupture). It appears from all of the formulations that the amount
of dispersing agent (Mighty) has been minimized compared to the
general level for DSP, cf. Example 1. The use of this low content
of Mighty is rendered possible by the use of appropriate combi-
nations of cement type, dispersing agent, wollastonite, and/or
ball clay, in accordance with the principles of the present inven-
tion .
P~V F2259A int. vers. OP~P 1~82
~Z4~355~
37
2. As appears from formulation 812-1, the water/dry matter ratio is
very small. This exact water/dry matter ratio is necessary in this
formulation in order to achieve an adequate consistency for extru-
sion using the said formulation. However, this extremely low
water/dry matter ratio leads to serious problems in controlling the
consistency of the material, and the material when shaped by
plastic deformation appears with a cracky, crusty surface.
3. As appears from the table, use of NATROSOL 250 H4BR and/or
ball clay or combinations thereof makes it possible to increase the
water content without destroying the processing characteristics of
the material. Furthermore, it appears from the table that the
mechanical properties of the material are substantially unaffected.
By using these measures, a prolonged pot life of the material in
relation to low pressure extrusion is obtained. For example,
formulation 812-3 retains its extrusion consistency 3 - 5 times
longer than does 812-1.
4. Also, it appears from the above test results (formulation 812-3-1)
that it is possible to combine the obtainment of such a material
composition which is optimal for plastic deformation with the
obtainment of good strength properties in the cured state.
Example 8.
Formulation:
The same as 812-1 in Example 7 was used. Preparation of the dough:
2 methods were used:
1 ) Silica was intensively disper sed in water (about 60% dispersion)
for 25 min. in a dissolver of the type DIAF. The temperature of
the water was 80C . This slu rry was then added to the dough
mixer as mentioned in Example 1 and the further mixing proce-
dure was the same as in Example 1.
P~V F2259A int. vers. OP/P 1982
lZ4855l5
2) Same procedure as 1), but the temperature of the water was
20C. Furthermore, Mighty was added from the start of of the
dispersing process. After 25 minutes of dispersing, about 50~O of
the cement was added and mixing was continued for further 5
minutes . Thereafter the same method as described in 1 ) and
Example l was performed.
Lengths of the materiai were extruded as described in Example 1 and
specimens were cut for curing as described in Example 7, curing
method no. 2.
Specimens were tested after 3 days in a 3 point bending test tenso-
mete r .
Results:
The specimens prepared according to method 1 ) had a dry density of
2.27 kg/dm3 and a modulus of rupture of 30.5 MPa.
The specimen prepared according to method 2) had a dry density of
2.32 kg/dm3 and a modulus of rupture of 36.7 MPa.
This example shows that denser packing and an increased modulus of
rupture can be achieved by improved dispersing techniques. As
compared to the level of the moduli of rupture obtained for the basic
formulation 812-1 of Example 6, the strength was increased by some
40 to 50 % when the special dispersion technique of the present
Example was applied. This is presumably due to the breaking up of
particle agglomerates during the intensive dispersing, resulting in
more densely packed particles and less incidence of macro-defects in
the material and shaped articles made therefrom.
P~V F2259A int. vers. OP/P 1982
