[0001] The present invention relates to a method and apparatus for continuously mixing liquid
and powder to a substantially homogenous mixture. The apparatus comprises a mixture
having a mixer housing and individual lines for supplying liquid and powder respectively
to said apparatus.
[0002] In known methods of mixing a liquid with a powder, the liquid and powder are often
kneaded together. Such methods, however, often result in the formation of lumps and
agglomerates which is highly undesirable. it is often necessary to wet-grind the mixture
in order to obtain the desired structure. When producing readily flowable mixtures,
a further problem arises, namely that the internal friction in the mixture is so low
that it is often impossible to avoid the formation of agglomerates, meaning that the
lumps thus formed must be filtered off at a later stage.
[0003] The object of the present invention is to avoid the aforementioned problems when
preparing mixtures of liquid and powder. Accordingly, the method according to the
present invention is mainly characterized in that the liquid and the powder are charged
respectively, by separate lines, to a cavity arranged in a rotatable wheel and to
powder spaces also arranged in said wheel, so as to be thrown by centrifugal force
outwardly towards the periphery of said wheel, whereat the liquid is urged from said
cavity, via a gap in said wheel, towards the upper side of said wheel and forms a
mist curtain at the exit cf said gap, at which location the powder grains or particles
thrown from said cavity by said centrifugal force are captured in said mist curtain
and mixed therewith. The apparatus according to The invention is characterized in
that the mixer housing includes a wheel arranged for rotation about a shaft in the
mixer housing, whereat the line through which the liquid passes discharges into a
cavity in the wheel, while The line through which the powder passes discharges into
spaces in the upper part of said wheel, and the cavity communicates with said upper
side of said wheel via a circumferentially extending gap having a configuration substantially
corresponding to the configuration of the outer surface of a truncated cone, with
the apex of said cone directed downwardly.
[0004] One advantage afforded by means of the invention is that the amount of powder and
the amount of liquid fed to The apparatus can be held constant during the whole of
the mixing operation, which is extremely important, for example, when preparing mixtures
within the medical industry. The ratio of powder to liquid can be set to any desired
value for each particular mixture. Moreover, the apparatus according to the invention
operates continuously, as opposed to known apparatus where one "lump of dough" is
mixed at a time, for example, in a so-called "batching".
[0005] The invention will now be described in more detail with reference to the accompanying
drawing, which illustrates schematically an embodiment of an apparatus according to
the invention
[0006] Thus, Figure 1 is a vertical sectional view of an apparatus according to the invention.
Figure 2 is a sectional view taken on the line II-II of Figure 1. Figure 3 is a part
of the vertical sectional view of Figure 1 shown in larger scale. Similar elements
in the various views of the drawing have been identified by the same references.
[0007] The apparatus illustrated in the drawing comprises a mixer housing 1 having a lid
or cover 2. Arranged within the housing 1 is a wheel arrangement comprising an upper
wheel 3 and a lower wheel 4 which is rotatably mounted on a shaft 5 by means of bearings
6. Located beneath the upper and the lower wheels 3 and 4 respectively is a cavity
7 which communicates with the upper side of the upper wheel 3 via a circumferentially
extending gap defined by the outer surfaces 8 and 9 respectively of frusto-conical
elements, with the apexes of said elements directed downwardly. Milled on the upper
surface of the upper wheel 3 are blades 10, while blades 11 are milled on the lower
surface of said upper wheel 3. Arranged between the blades 10 are spaces 13 which
are intended to receive the powder to be mixed with said liquid, while the cavity
7, which is divided into compartments by means of the blades 11, is intended to receive
the liquid to be mixed with said powder. The lower wheel 4 has a circumferentially
extending edge 14 located adjacent the mouth of the gap 9. The lower wheel 4 is provided
around its periphery with blades 15 for throwing out the powder and liquid mixture
via a diffusor 16 and an outlet 17. The outlet may optionally be supplemented with
a nozzle 18 which is used when the finished mixture is more flowable. The lid or cover
2 has a compartment 19 located above the centre of the wheel arrangement for receiving
the powder phase, for further transport of said powder phase to the spaces 13. The
lid is also provided on the undersurface thereof with pins 2C which lie adjacent the
edge 14. The powder phase is fed to said compartment or space 19 with the aid of a
transporter 21, for example a feed screw. The liquid phase is passed to the cavity
7 through a pipe 22.
[0008] When the apparatus is in operation, the wheels 3,4 of the wheel arrangement located
within the housing 1,2 rotate about the shaft 5 at a speed which may lie between 1000
and 5000 rpm. The wet phase, or the liquid, is passed to the mixer via the pipe 22,
to the cavity 7. As a result of the centrifugal force, and with the aid of the blades
11, the liquid is thrown outwardly through the gap 8 and further through the gap 9.
The liquid thus obtains the form of a skin which extends constantly outwardly while
becoming thinner and thinner. When the liquid skin leaves the gap 9 it strikes the
edge 14 and is broken up into microscopic droplets so as to form a curtain. At the
same time as liquid is supplied through the pipe 22, powder is supplied by the conveyor
21 to the compartment 19 and further to the spaces 13. The powder is thrown from the
spaces 13, with the aid of centrifugal force and the blades 10, outwardly towards
the periphery of the upper wheel 3, at the same time as said powder is whipped up
and impinges on the curtain of liquid at the edge 14. The two phases, liquid and powder,
are now thrown outwardly together and collide with pins 20, where the instantaneous
mixture of powder and liquid takes place. The finished mixture is caught immediately
by the blades 15 and is thrown outwardly via the diffusor 16 to the outlet 17. Granulates
and stiff mixtures leave the mixer at the outlet 17, while the readily flowable mixture
is taken out via the nozzle 18.
[0009] The invention is not restricted to the described embodiment, but can be modified
within the scope of the accompanying claims. Particular note should be taken to the
expressions "cavity" and "powder spaces", since "a cavity" can in principle be said
to comprise "a plurality of cavities" while "powder spaces" can be well said to be
"a powder space".
1. A method of continuously mixing liquid and powder together to form a substantially
homogenous mixture, characterized by feeding the liquid and the powder via separate
lines to a cavity in a rotatable mixing wheel and to powder-accommodating spaces arranged
in said wheel, so as to be thrown out towards the periphery of the wheel by centrifugal
force, whereat the liquid is pressed from said cavity via a gap in said wheel in a
direction towards the upper side of said wheel and, as it exits from the wheel, is
thrown out towards a peripherally extending edge on the peripheral side of the gap
to form a mist curtain, which captures the powder particles thrown out by the centrifugal
force, whereat the mixture of liquid and powder particles are then thrown outwardly
towards the periphery of the wheel and are caught by mixer pins in the housing of
the mixer wheel, to form a homogenous mixture which is fed towards the outlet of the
mixer housing.
2. An apparatus for carrying out the method according to claim 1, comprising a mixer
and a mixer housing (1, 2) and having separate lines (21,22) for supplying liquid
and powder, characterized in that the mixer housing comprises a wheel arrangement
(3,4) arranged for rotation on a shaft (5) in the mixer housing (1,2), whereat the
liquid line (22) discharges into a cavity (7) in the wheel while the powder line discharges
into powder-accommodating spaces (13) in the upper part of the wheel, and the cavity
(7) communicates with the upper side of said wheel via a circumferentially extending
gap (8,9) which opens out adjacent a circumferentially extending edge (14) located
on the peripheral side of the gap, whereat the shape of the gap corresponds substantially
to the shape of the outer surface of a truncated cone with the apex of said cone facing
downwardly, and whereat the mixer housing (1,2) includes mixer pins (20) arranged
to capture liquid from the mist curtain and the powder thrown out by centrifugal force
from the powder spaces, to provide said mixture.
3. An apparatus according to claim 2, characterized in that the powder spaces (13)
in the upper part of the wheel arrangement are separated from one another by means
of blades (10) which are directed outwardly from the centre of the wheel.
4. An apparatus according to claim 2 or claim 3, characterized in that the cavity
(7), which is located around the centre of the wheel arrangement, is divided into
different compartments by means of blades (11) directed outwardly from the centre
of said wheel.
5. An apparatus according to any one of claims 2-4, characterized in that the conical
gap has a lower (8) and an upper (9) conical part, of which conical parts the apex
angle of the lower part is more obtuse than the apex angle of the upper part.
