Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR CASTING CONCRETE PRODUCTS
The present invention relates to casting of concrete products by means of a
substantially
horizontal slipforming process, wherein the concrete mass is pressurized at
least by
means of one feeding screw. More precisely, the invention relates to the
motion of the
feed screw and/or the element forming the hollow core during the casting
process.
When casting with traditional extruder and slipformnr casting machines, the
casting mold
is formed by a casting bed and side walls and upper surface moving along with
the
casting machine and forming the cross section of the product to be cast to the
desired
shape and size. When the casting machine proceeds, the side walls and the
upper surface,
and if necessary, the elements forming one or a plurality of hollow cores to
the product to
be cast, perform motion compacting the concrete mass. The ready-cast product
remains
on the casting bed to harden. Because the cast fresh slab remains lying on the
casting bed
in its final form, a high stiffness is required from the'concrete mass to be
used in the
solutions of prior art.
The stiff concrete mass used in the solutions of prior art causes strong wear
of the wear
parts of the slipforming machine, like the feed screws and the hollow-core
forming
elements, whereby these wear parts must be changed relatively often. In
connection with
the chance of the wear parts, also the casting process of the production plant
must be
interrupted for the duration of the change. The stiff concrete mass also
causes mechanical
burden on the processing devices, like the trowelling devices of the upper
surface, side
walls and the hollow-core mandrels, and the rotating devices of the screws,
and
degradation of the compacting efficiency caused by the fast wear.
The slipforming technique for manufacturing hollow-core slabs and massive
slabs is well
known in the art. For example Patent publication FI 80845 discloses a method
and an
apparatus for casting a hollow-core slab. The compacting method described
therein is
based on reciprocal swinging of the hollow-core mandrel simultaneously with
the
reciprocal longitudinal motion. Nowadays, the heights of the slabs are
increasing,
whereby also the heights of the hollow cores are increased. In case of high
hollow cores,
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with the described swinging of the hollow-core mandrel the adequate compacting
of the
hollow core is not achieved.
Patent publication FI 85350 discloses a compacting method, wherein wedge
surfaces
are moved in the casting direction in opposite directions with respect to each
other in a
reciprocal, opposite phase. The effect of the wedge surfaces, however, remains
quite
small, because the wedge surfaces must be quite low from the point of view of
the flow
of the concrete mix, which decreases their properties decreasing or increasing
the
compacting area. With deep wedge surfaces the flow of the concrete mix is
prevented.
With slipforming machines of extruder type known in the art, the length of the
reciprocal motion of the feed screw and the hollow-core mandrels ranges from 5
to 50
mm with a frequency from 1 to 10 Hz.
By means of the present invention, a slipforming machine having a simple
construction
is provided for the slipforming process, comprising a dual-frequency
compacting
arrangement, whereby a better compacting result with less wear of the
components can
be provided than with prior art machines.
Dual-frequency compacting method in this connection refers to a compacting
method,
wherein the mass is simultaneously with two different frequencies.
In accordance with an embodiment of the present invention there is provided in
an
improved method for casting concrete products with a substantially horizontal
slipforming process, where a concrete mass is fed by at least one feed element
through
a limited cross section forming a concrete product, the improvement wherein
the at
least one feed element is subjected to a dual-frequency longitudinal
reciprocal motion
for compacting the concrete mass.
In accordance with another embodiment of the present invention, there is
provided an
apparatus for casting concrete products with a substantially horizontal
slipforming
process, the apparatus comprising at least one feed element for feeding a
concrete mass
through a limited cross section for forming a concrete product, wherein the
apparatus
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comprises means for bringing the at least one feed element to a dual-frequency
longitudinal reciprocal motion for compacting the concrete mass.
The invention will be described in more detail in the following, with
reference to the
enclosed drawing, wherein
Figure 1 shows a schematic view of one slipforming machine in accordance
with the present invention.
20
30
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Essential parts of the slipforming machine shown in Figure 1 are the mass
container 1,
feed screw 2, driving devices 3, 4, 5 of the feed screw, hollow-core mandrel
6, side walls
7, trowelling beam 8, driving devices 9 of the trowelling beam, surface
leveling plate 10,
casting bed 11, drive motor 12 and the chute 13 of the feed screw. The
apparatus shown
in the figure is meant for casting hollow-core slabs or beams.
When using the casting machine shown in Figure 1, stiff concrete mass is fed
from the
mass container 1 to one or a plurality of feed screws 2. Each of the feed
screws 2 is
located in a chute 13 guiding the concrete mass to the feed screw at the
forward end of
the feed screw. The feed screws 2 extrude the concrete mass under pressure to
the cross
section defined by the casting bed 11, side walls 7 and trowelling beam 8
defining the
outer dimensions of the product to be cast. The rotating motion caused by the
extrusion
of the concrete mass by the feed screws 2 is effected by means of the driving
device 3 of
the rotating motion. When casting products with hollow cores, there are hollow
core
mandrels 6 mounted after the feed screw, forming the hollow cores to the
product to be
cast.
The casting machine moves supported by wheels along the casting bed driven by
the
reaction force of the feed screws 2, said force moving the casting machine
forward being
accelerated or decelerated by means of a drive motor 12 connected to the
casting
machine.
The product to be cast is compacted by means of the reciprocal motion of the
feed screws
2 and the hollow-core mandrels 6, as well as by the compacting trowelling
motion of the
side walls 7 and the trowelling beam 8, which in case of the trowelling beam
is effected
by the driving devices 9 of the trowelling beam. The surface leveling plate 10
following
the trowelling beam 8 levels the upper surface of the final product.
The reciprocal motion of the feed screws 2 and the hollow-core mandrels 6 is a
dual-
frequency motion effected by means of a long-motion driving means 5 and a
short-
motion driving means 4. Thereby the driving means 4 performs several
reciprocal
motions during one long reciprocal motion of the driving means 5. Thus, the
compacting
assembly formed by the feed screws 2 and the hollow-core mandrels 6 performs
several
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short reciprocal motions at the same time when said compacting assembly
performs one
long reciprocal motion.
In the solution in accordance with the invention, the length of the short
reciprocal motion
preferably ranges from 0,2 to 4 mm having preferably a frequency from 15 to 50
Hz. The
length and frequency of the long reciprocal motion of the solution in
accordance with the
invention essentially corresponds to the corresponding motion of the solutions
known in
the art, in other words the length ranging from 5 to 40 mm with a frequency
from 1 to 10
Hz.
This kind of a dual-frequency compacting motion in accordance with the
invention
provides for the part of the short motion:
= efficient working of the concrete mass, whereby the concrete mass will be
partly compacted already over the length of the feed screw,
= pumping of the cement paste against the surface of the moving components,
which decreases the friction and the wear of the components,
= loosening the hollow-core mandrel from the compacted concrete, whereby the
separate loosening movement can be omitted,
and for the part of the long motion:
= provides the compacting effect over the total length of the hollow-core
mandrel,
and
= intensifies the feed of the concrete mass to the area of the limited cross
section
having the biggest pressure.
By connecting the long and short motion, in addition, a more coarse thread of
the feed
screw can be used, due to the intensified feed and compacting of the concrete
mass,
which provides bigger casting speed of the casting machine, and at the same
time less
relative wear of the feed screw.
The solution in accordance with the invention is not limited to the method and
apparatus
for casting concrete products with hollow cores, only, like shown in the
example of the
figure, but it is also applicable to casting of for example massive slabs
without hollow
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cores. Thereby the hollow-core forming elements are removed from the casting
apparatus, and only the feed screw/screws is/are moved reciprocally with the
dual-
frequency compacting motion.
5 The solution in accordance with the invention can also be implemented with a
fixed
casting station, whereby the casting apparatus is located in the fixed casting
station, but
the casting bed moves with respect to the casting station. Thereby the movable
casting
bed moves the finished product out of the fixed casting station, and the ready-
cast
product remains on the casting bed.
