[0001] This invention relates to a method for producing cement slurry, and a device for
mixing cement slurry usable in that method, as well as an apparatus for producing
cement slurry which incorporates the device.
[0002] As is known, cement slurry is a viscous liquid product which comprises a mixture
of water and powdered cement, if necessary with the addition of specific additives
(for example pigments).
[0003] It may be used either as the base for producing concrete by adding aggregate, or
on its own for making various types of construction products (such as paving, plaster,
etc.).
[0004] Cement slurry is commonly made by simply mixing water and powdered cement. However,
it is known that, the composition being the same, cement slurry obtainable with different
mixing actions may have considerably different characteristics. In particular, the
composition being the same, the mixing method and its duration may have a major impact
both on the workability and cohesion of the cement slurry, and on the mechanical properties
of the product after drying. Indeed, cement slurry is not a simple dispersion of solid
cement particles in water, but also involves the development of chemical reactions
between water and cement, which are rendered evident by the development of heat inside
the mass being processed.
[0005] In particular, what the Applicant has observed, is also that, depending on the mixing
method adopted (and consequently its duration), it is possible to obtain the same
results in terms of both workability (or consistency) and cohesion of the cement slurry,
and of mechanical properties of the product after drying.
[0006] Since the main operating cost linked to producing cement slurry is that of the powdered
cement used, it immediately appears evident that managing to mix water and cement
powder in the optimum way could allow savings in cement powder, and considerably reduce
the operating cost of producing the cement slurry.
[0007] However, so far, in most real applications the poor quality of mixing is such that
it always requires the use of a quantity of powdered cement much greater than that
strictly necessary.
[0008] In this context the technical purpose which forms the basis of this invention is
to provide a method for producing cement slurry and to make a device for mixing cement
slurry, which overcome the above-mentioned disadvantages. In particular, the technical
purpose of this invention is to provide a method for producing cement slurry, and
to make a device for mixing cement slurry, which allow the obtainment of cement slurries
with optimum characteristics in terms of both workability (or consistency) and cohesion
of the cement slurry, and of mechanical strength properties of the product obtainable
after drying, using quantities of cement powder significantly lower than in the methods
and devices currently commonly used in the sector.
[0009] A further technical purpose of this invention is to provide a method for producing
cement slurry, and to make a device for mixing cement slurry, which allow the production
of cement slurry of optimum quality in shorter times than in the plants commonly used.
[0010] The technical purpose and the aims indicated are substantially achieved by a method
for producing cement slurry and by a device for mixing cement slurry as described
in appended claims.
[0011] Further characteristics and the advantages of this invention will be more apparent
from the detailed description of several preferred, non-limiting embodiments of this
invention, with reference to the accompanying drawings, in which:
- Figure 1 shows, in vertical axial section (except for some details such as the driving
shaft), a device for mixing cement slurry made in accordance with this invention;
- Figure 2 shows an enlarged detail of Figure 1;
- Figure 3 is a front view (from the right compared with Figure 1) of an impeller which
is part of the device of Figure 1;
- Figure 4 shows the impeller of Figure 3 in cross-section according to the line IV
- IV;
- Figure 5 shows, in an axonometric view, a fixed pierced wall which is part of the
device of Figure 1;
- Figure 6 shows the pierced wall of Figure 5 in side view;
- Figure 7 shows, in schematic side view, with some parts transparent, an apparatus
for producing cement slurry comprising the device of Figure 1;
- Figure 8 shows, in front view with some parts transparent, the apparatus of Figure
7;
- Figure 9 shows, enlarged, the detail IX of the apparatus of Figure 7;
- Figure 10 shows in schematic side view a part of the apparatus of Figure 7, illustrating
several tubes for introducing slurry into the tank; and
- Figure 11 shows, in horizontal section view, perpendicular to the generatrix of the
tank and at one of the tubes of Figure 10, a possible distribution of tubes for introducing
slurry around the tank.
[0012] Hereinafter there is initially a description of the innovative mixing device which
is the subject matter of this invention, followed by the apparatus which comprises
it, and finally the method for producing the cement slurry disclosed by this invention.
[0013] It should be noticed that hereinafter in the description of this patent application
"cement slurry" and "mixture of water and cement powder" will often be used interchangeably
with reference to all of the intermediate production steps. Indeed, whilst it is proper
to refer only to "mixture of water and cement powder" before its processing in accordance
with this invention beings, and only to refer to "cement slurry" after the end of
the processing, in all of the intermediate processing steps it is possible to consider
the product as a mixture being converted into an actual slurry.
[0014] With reference to the figures indicated, the device for mixing cement slurry according
to this invention has been labelled with the reference number 1 as a whole.
[0015] As shown in Figure 1 and 2, the device 1 comprises first a containment structure
2 which forms a mixing chamber 3 inside it.
[0016] A driving shaft 4 is mounted with a liquid-tight seal through the containment structure
2, and has a first end 5 positioned in the mixing chamber 3, and a second end 6 which
is outside the containment structure 2. The second end 6 is connectable in use to
a driving motor suitable for driving the rotation of the driving shaft 4 about its
axis of rotation 41.
[0017] In the preferred embodiment, illustrated in the accompanying figures, there is also
a supporting structure 7 which is fixed to the containment structure 2 and is suitable
for supporting, centring, and keeping in position axially, the driving shaft 4 at
an intermediate portion thereof between the first end 5 and the second end 6.
[0018] The containment structure 2 comprises an inlet 8 and an outlet 9, which allow fluid
communication between the mixing chamber 3 and the outside. The inlet 8 is aligned
with the axis of rotation 41 and is centred on it. Mounted in the mixing chamber 3
there is a pierced wall 10, which is centred on the axis of rotation 41, and which
divides the mixing chamber 3 into an inner part 11 and an outer part 12 which are
coaxial. The outer part 12 advantageously extends in an annular fashion and surrounds
the inner part 11, being positioned in a position radially further out relative to
the axis of rotation 41.
[0019] The inlet 8 is directly facing the inner part 11 of the mixing chamber 3, whilst
the outlet 9 is facing the outer part 12 of the mixing chamber 3. Therefore, the pierced
wall 10 intercepts the fluid paths which extend from the inlet 8 to the outlet 9.
[0020] In the preferred embodiment (Figures 4 and 5), the pierced wall 10 has frustoconical
extension coaxial with the axis of rotation 41, and with the larger base of the truncated
cone towards the inlet 8 of the mixing chamber 3.
[0021] Advantageously, the pierced wall 10 has a plurality of through holes 13 evenly distributed
along the entire extent of the self-same pierced wall 10. In particular, in the embodiment
illustrated, the through holes 13 are organised along four circular rows each of sixty
equally spaced holes, centred on the axis of rotation 41 and spaced from each other,
parallel to the axis of rotation 41, with a constant pitch. Moreover, preferably,
the pierced wall 10 has a plurality of through holes 13 each with a passage area of
between 40 and 200 mm
2, advantageously of between 60 and 130 mm
2. Moreover, in the preferred embodiments, the pierced wall 10 is made in such a way
as to have a ratio of pierced surface area to total surface area facing the mixing
chamber 3, of between 1 to 5 and 1 to 3.
[0022] The first end 5 of the driving shaft 4 is positioned at the inner part 11 of the
mixing chamber 3, and fixed to it there is a centrifugal impeller 14 also positioned
in the inner part 11 of the mixing chamber 3. In use, as described in more detail
below, the centrifugal impeller 14, driven to rotate by means of the driving shaft
4, forces the water-based mixture (slurry) to pass from the inner part 11 to the outer
part 12 of the mixing chamber 3, through the through holes 13 of the pierced wall
10.
[0023] In general, the centrifugal impeller 14 comprises a plurality of blades 15, but advantageously
their number is between 3 and 9. As shown in the accompanying figures, each blade
15 preferably extends cantilever-style, towards the inlet 8, starting from a circular
supporting plate 16 located near a wall of the mixing chamber 3. Each blade 15 also
has an external edge 17 (that is to say, the edge radially furthest from the axis
of rotation 41) which is substantially shaped to match the pierced wall 10 and near
it (advantageously the distance between the external edge 17 and the pierced wall
10 is less than 2 mm, preferably less than 1 mm). The profile of the blade 15 is also
such that the blade 15 has a height decreasing from its internal edge 18 towards the
external edge 17.
[0024] Moreover, in accordance with the preferred embodiments, in use the centrifugal impeller
14 is activated with a speed of rotation of between 500 and 5000 revolutions per minute,
and/or a maximum tangential speed of between 10 and 80 m/s.
[0025] Joined to the inlet 8 there is a feed duct 19 and, in accordance with a further innovative
aspect of this invention, the feed duct 19 and/or the inlet 8 (the inlet 8 in Figure
1, but in general the one of the two which effectively guides the flow of cement slurry
entering the mixing chamber 3) are shaped in such a way as to form at least one introducing
duct 20. That introducing duct 20 has a cross-section increasing towards the centrifugal
impeller 14, and is directly facing the inner part 11 of the mixing chamber 3 and
the centrifugal impeller 14. The aim of the introducing duct 20 is to cause a sudden
increase in the pressure of the mixture, faced with a sudden reduction in speed compared
with the speed which, the mixture itself, has upstream of the introducing duct 20
(in the accompanying figures the feed duct 19 has a stretch 21 with constant cross-section
immediately upstream of the introducing duct 20 with increasing cross-section).
[0026] In particular, in the preferred embodiments, the introducing duct 20 is sized in
such a way as to cause, in use, an increase in the pressure of between 0.1 and 1 bar,
in the fluid to be mixed which passes through it (that is to say, between entering
and exiting the self-same introducing duct 20).
[0027] The mixing device 1 described so far may be inserted in various types of apparatuses
22 for producing cement slurry, and in particular in apparatuses 22 both of the continuous
type (solution not illustrated), and of the batch type (solution illustrated in the
accompanying figures).
[0028] In general, all of the apparatuses 22 comprise at least one first mixing device 1,
and a feeder 23 of a fluid mixture connected to the feed duct 19. Depending on requirements,
the apparatus 22 may also comprise, connected in series to the outlet 9 of the first
mixing device 1, one or more further mixing devices 1 which are also mounted in series
relative to one another. The use of multiple mixing devices 1 in series is preferably
always applied in the case of continuous type apparatuses 22, whilst in the case of
batch type apparatuses 22 the use of a single mixing device 1 combined with a system
for recirculating the mixture is the preferred solution for limiting the costs of
the apparatus 22.
[0029] In the case of continuous type apparatuses 22, the apparatus 22 will comprise a number
of mixing devices 1 equal to the number of mixing actions which, at the design stage,
has been considered optimal. In contrast, in the case of batch type plants, the slurry
will advantageously be made to pass in the mixing device or devices 1 a number of
times equal to the number of mixing actions which, at the design stage, has been considered
optimal, divided by the number of mixing devices 1 positioned in series which are
present.
[0030] In the case of a batch type apparatus 22, the feeder 23 comprises at least one tank
24 connected to the feed duct 19, and at least one return duct 25 (visible only in
Figure 10) connected between the outlet 9 of the mixing device 1 (or of the last mixing
device 1) and the tank 24. Moreover, advantageously, a stirrer 26 is mounted in the
tank 24 for mixing the mixture contained therein, before the mixture is sent to the
mixing device 1.
[0031] In the preferred embodiment, illustrated in the accompanying figures, the tank 24
is equipped with one or more delivery openings 27 positioned at its bottom portion,
and the stirrer 26 is positioned near the one or more delivery openings 27, in particular
just above them. In the case of the embodiment illustrated in the accompanying figures,
the stirrer 26 consists of a plurality of angled vanes 28, which are fixed to a vertical
shaft 29 which passes through the entire tank 24 and which is driven at the top by
an auxiliary electric motor 30 of the apparatus 22. The vanes 28 extend downward from
a lower end of the vertical shaft 29, and each of them is adjacent to an underlying
conical wall 31 of the tank 24, whose axis coincides with the axis of the vertical
shaft 29. The one or more delivery openings 27 which put the tank 24 in fluid communication
with the feed duct 19 are made along the perimeter of the lower part of the conical
wall 31. It should be noticed that, advantageously, at the stirrer 26, the lateral
wall of the tank 24 is near the conical wall 31 (in the embodiment illustrated this
stretch of lateral wall is a cylindrical wall with internal diameter equal to the
external diameter of the base of the conical wall 31).
[0032] Indeed, advantageously, the tank 24 has a funnel-shaped lateral wall 32 with a cylindrical-shaped
upper containment part 33 and a lower part 34 which is also cylindrical which houses
the stirrer 26.
[0033] Moreover, preferably, the stirrer 26 is activated with a speed of rotation of between
150 and 500 revolutions per minute, and/or with a maximum tangential speed (at the
lower tip of the vanes 28) of between 3 and 50 m/s. As regards operation of the centrifugal
impeller 14 of the mixing device 1, a belt drive 35 connects the driving shaft 4 to
a main electric motor 36.
[0034] As is schematically illustrated in Figure 10 and 11, in a preferred embodiment of
this invention, the return duct 25 comprises a main duct 37 connected to the outlet
9 of the mixing device 1, from which main duct a plurality of tubes 38 branches in
parallel, those tubes reaching the tank 24 at different heights (heights measured
vertically relative to a common reference).
[0035] Moreover, each tube 38 opens into the tank 24 at the cylindrical lateral wall 32
and according to an introducing line at a tangent to the cylindrical lateral wall
32 (Figure 11).
[0036] Depending on requirements, at a predetermined height there may be a single tube 38
which enters the tank 24, just as it may be the case that the tubes 38 are grouped
in groups, with the tubes 38 of each group opening into the tank 24 at the same height,
and the tubes 38 of different groups in contrast opening into the tank 24 at different
heights. Figure 11 schematically illustrates a group comprising three tubes 38 which
enter the tank 24 at the same height.
[0037] Moreover, preferably, the tubes 38 are not all the same as each other; the tubes
38 which open into the tank at a predetermined height have larger cross-sections than
the tubes 38 which open into the tank at lower heights. Moreover, in the preferred
embodiment, the return duct 25 is as a whole suitable for dividing the flow rate of
fluid which passes through it, in such a way that the speed of the mixture which enters
the tank 24 through the tubes 38 located at a predetermined height, is greater than
the speed of the mixture which enters the tank 24 through the tubes 38 located at
higher heights.
[0038] Operation of the apparatus 22 and of the mixing device 1 described above correspond
to specific embodiments respectively of the entire method for producing cement slurry
according to this invention and of several steps thereof.
[0039] In its most general embodiment, the method comprises first the operating step of
incorporating a predetermined quantity of powdered cement, and additives if necessary,
in a predetermined volume of water, creating a mixture. During implementation of this
step it is appropriate to pay attention to the fact that the cement powder (and additives
if necessary) mix with the water, avoiding, or in any case minimising, the formation
of lumps or the powder floating on the water. Since the step of incorporating the
cement powder in the water while avoiding lumps and floating is in itself part of
the normal know-how of the cement slurry production sector, it will not be described
in further detail herein.
[0040] Once the cement powder has been incorporated in the water and the mixture has been
formed, the mixture is subjected to a mixing step (carried out with the stirrer 26
in the apparatus 22 described above) and, then, to a step during which the mixture
is fed along a duct (the feed duct 19 in the apparatus 22 described above) and is
fed to a centrifugal impeller 14 (that of the mixing device 1 described above).
[0041] However, in accordance with this invention, at mixture entry into the centrifugal
impeller 14, there is a step of varying the pressure and the average feed speed of
the mixture, during which the average feed speed of the mixture is reduced, with simultaneous
generation of an increase in the pressure of the mixture which will strike the centrifugal
impeller 14. Preferably, the pressure increase which is generated during this step
is between 0.1 and 1 bar.
[0042] Finally, the method comprises a step during which the mixture exiting the centrifugal
impeller 14 is forced through a fixed pierced wall 10 which radially surrounds the
centrifugal impeller 14, partly reducing its tangential motion components and increasing
the counter-pressure downstream of the self-same centrifugal impeller 14.
[0043] In most embodiments, the steps described above of feeding the mixture, reducing the
speed, increasing the pressure and pushing the mixture, are repeated a plurality of
times. Advantageously, the repetition may be performed either by making the mixture
circulate a plurality of times through the same mixing device 1, or making it pass
in sequence through various mixing devices 1 in series.
[0044] Particularly in the case of use of multiple passes in a single mixing device 1, it
is advantageously the case that the step of mixing the mixture is also repeated before
each repetition of the step of feeding the mixture. Moreover, in the preferred embodiment,
the (or each) step of mixing the mixture is advantageously carried out using a stirrer
26 located in a lower part of a cylindrical tank 24 having a predetermined internal
diameter, and keeping a height of the mixture above the stirrer 26 which is in a ratio
relative to the internal diameter, of between 3 to 1 and 5 to 1.
[0045] This invention brings important advantages.
[0046] First, thanks to this invention it has been possible to provide a method for producing
cement slurry, and to make a device for mixing cement slurry, which according to the
results of experimental tests carried out by the Applicant, allow the obtainment of
cement slurries with optimum characteristics in terms of both workability (consistency)
and cohesion, and of mechanical properties of the product after drying, using quantities
of cement powder significantly lower than in the methods and devices currently commonly
used in the sector.
[0047] Second, thanks to this invention it is possible to produce cement slurries of optimum
quality in shorter times than in the plants commonly used. Therefore, thanks to this
invention, it has been possible to provide a method for producing cement slurry, and
to make a device for mixing cement slurry, which allow the obtainment of greater economies
in the production of cement slurry and if necessary of concrete than has been possible
until now, as well as allowing a more favourable water/cement ratio (understood to
be the quantity by weight) than the prior art methods and devices, by virtue of the
improved homogenisation which can be achieved between cement and water.
[0048] Finally, it should be noticed that this invention is relatively easy to produce and
that even the cost linked to implementing the invention is not very high. The invention
described above may be modified and adapted in several ways without thereby departing
from the scope of the inventive concept.
[0049] All details of the invention may be substituted with other technically equivalent
elements and the materials used, as well as the shapes and dimensions of the various
components, may vary according to requirements.
1. A device for mixing cement slurry, comprising:
a containment structure (2) which forms a mixing chamber (3) inside it;
a driving shaft (4) mounted through the containment structure (2), and which has a
first end (5) positioned in the mixing chamber (3), and a second end (6) outside the
containment structure (2) and in use connectable to a driving motor, the driving shaft
(4) having an axis of rotation (41);
a pierced wall (10) mounted in the mixing chamber (3), the pierced wall (10) being
centred on the axis of rotation (41) and dividing the mixing chamber (3) into an inner
part (11) and an annular outer part (12) which are coaxial; and
a centrifugal impeller (14), fixed to the first end (5) of the driving shaft (4) and
positioned in the inner part (11) of the mixing chamber (3), in use the centrifugal
impeller (14) forcing a water-based mixture to pass through the pierced wall (10);
wherein moreover:
the containment structure (2) comprises an inlet (8), centred relative to the axis
of rotation (41) and facing the inner part (11) of the mixing chamber (3), and an
outlet (9) facing the outer part (12) of the mixing chamber (3), the pierced wall
(10) intercepting a fluid path which extends from the inlet (8) to the outlet (9);
a feed duct (19) is joined to the inlet (8); and
the feed duct (19) and/or the inlet (8) are shaped in such a way as to form at least
one introducing duct (20) with cross-section increasing towards the centrifugal impeller
(14), directly facing the inner part (11) of the mixing chamber (3).
2. The device according to claim 1, wherein the pierced wall (10) has frustoconical extension
coaxial with the axis of rotation (41), with a larger base of the truncated cone towards
the inlet (8).
3. The device according to claim 1 or 2, wherein the pierced wall (10) has a plurality
of evenly distributed through holes (13), and/or has a plurality of through holes
(13) each with a passage area of between 40 and 200 mm2, preferably between 60 and 130 mm2, and/or has a ratio of pierced surface area to total surface area of between 1 to
5 and 1 to 3.
4. The device according to any of claims 1 to 3, wherein the centrifugal impeller (14)
comprises a plurality of blades (15), each having a radially external edge which is
substantially shaped to match the pierced wall (10) and near it.
5. The device according to any of claims 1 to 4, wherein the centrifugal impeller (14)
comprises between 3 and 9 blades (15), and/or has a speed of rotation of between 500
and 5000 revolutions per minute, and/or has a maximum tangential speed of between
10 and 80 m/s.
6. The device according to any of claims 1 to 5, wherein the introducing duct (20) is
sized in such a way as to cause, in use, an increase in the pressure in the fluid
to be mixed which passes through it, of between 0.1 and 1 bar.
7. An apparatus for producing cement slurry comprising:
at least one first mixing device (1) according to any of the preceding claims; and
a feeder (23) of a fluid mixture connected to said feed duct (19).
8. The apparatus for producing cement slurry according to claim 7, also comprising, connected
to the outlet (9) of the first mixing device (1), one or more further mixing devices
(1) mounted in series relative to one another.
9. The apparatus for producing cement slurry according to claim 7, wherein the apparatus
(22) is of the batch type, wherein the feeder (23) comprises at least one tank (24),
at least one return duct (25) connected between the outlet (9) of the mixing device
(1) and the tank (24), and a stirrer (26) mounted in the tank (24), and wherein the
tank (24) is connected to the feed duct (19).
10. The apparatus for producing cement slurry according to claim 9, wherein the tank (24)
is equipped with one or more delivery openings (27) positioned at its bottom portion,
and wherein the stirrer (26) is positioned near the delivery opening.
11. The apparatus for producing cement slurry according to claim 9 or 10, wherein the
tank (24) has a cylindrical lateral wall (32), wherein the return duct (25) comprises
a main duct (37) connected to the outlet (9) from which main duct a plurality of tubes
(38) branches in parallel, and wherein each tube (38) opens into the tank (24), at
the cylindrical lateral wall (32) and according to an introducing line at a tangent
to the cylindrical lateral wall (32).
12. The apparatus for producing cement slurry according to claim 11, wherein said tubes
(38) are grouped in groups, wherein the tubes (38) of each group open into the tank
(24) at the same height, wherein the tubes (38) of different groups open into the
tank (24) at different heights, and wherein the tubes (38) which open into the tank
at greater heights, have larger cross-sections than the tubes (38) which open into
the tank at lower heights.
13. A method for producing cement slurry comprising the operating steps of:
incorporating a predetermined quantity of powdered cement, and additives if necessary,
in a predetermined volume of water, creating a mixture;
mixing the mixture;
then feeding the mixture along a duct for feeding it to a centrifugal impeller (14);
at mixture entry into the centrifugal impeller (14), reducing the average feed speed
of the mixture and generating an increase in the pressure of the mixture; and
by means of the centrifugal impeller (14), pushing the mixture through a fixed pierced
wall (10) which radially surrounds the centrifugal impeller (14).
14. The method according to claim 13, wherein the steps of feeding the mixture, reducing
the speed, increasing the pressure and pushing the mixture, are repeated a plurality
of times.
15. The method according to claim 14, wherein the step of mixing the mixture is also repeated
before each repetition of the step of feeding the mixture.
16. The method according to claim 15, wherein the step of mixing the mixture is carried
out using a stirrer (26) located in a lower part of a cylindrical tank (24) having
an internal diameter, and keeping a height of the mixture above the stirrer (26) which
is in a ratio relative to the internal diameter, of between 3 to 1 and 5 to 1.
17. The method according to any of claims 13 to 16, wherein during the step of generating
an increase in the pressure of the mixture the pressure is increased by a value of
between 0.1 and 1 bar.