Centrifugal mixer

Apparatus for mixing liquid or fluent material in which the material is confined within a carrier which is revolved about a remote axis to generate centrifugal forces directed radially outward from the remote axis. The carrier is also rotated about an axis perpendicular to the direction of the radial centrifugal force so that the force on any differential part of the material is cyclically reversed at a frequency determined by the frequency of the rotation about the perpendicular axis. The rate of rotation about the remote axis may be varied to vary the amplitude of the centrifugal force and the rate of rotation about the perpendicular axis may be varied to vary the frequency of the cyclic forces generated by this combination. The specific apparatus disclosed has a pair of elongated tubular rotary carriers which may be connected to receive liquid material from a supply. The carriers have their rotational axes parallel to one another and to the remote axis about which they revolve.

The present invention relates to apparatus for generating 
cyclically-reversing forces in fluid material and is particularly 
applicable to a mechanism which combines predetermined rotary motions to 
produce controlled acceleration forces for the purpose of mixing the 
material. 
The invention is useful for mixing liquids and fluid materials having a 
density at least as high as liquids and utilizes a carrier which is 
designed relative to the physical properties of the material to insure a 
mixing action when operating in a prescribed manner. 
The invention operates by causing reversing flow within the body of 
material through the application of centrifugal forces first in one 
direction and then in the opposite direction, the reverse flows generating 
shear forces which cause the material to mix homogeneously. 
Specifically, the invention provides a centrifugal mixer in which the fluid 
material is contained within a carrier and in which there need be no parts 
relatively movable during its operation. 
The mixer of the present invention may effect both continuous-flow mixing 
and batch mixing, as required.

The generation of force components in the material is illustrated in FIG. 
1. In FIG. 1, a body of fluid material is indicated by the reference 
character S. The body S is rotated about a remote central axis A, in the 
present instance, an axis spaced from the specimen by a radial length R. 
As the body S rotates about the axis at the distance R, a centrifugal 
force is generated resulting from the acceleration of the body as it 
travels in a circular path, for example the path indicated at P in FIG. 1. 
When the body rotates at a constant speed, for example an angular velocity 
of .omega., the acceleration forces generated in a radial direction are 
directly proportional to the square of the angular velocity 
(.omega..sup.2) times the radius R, or, stated differently, the square of 
the tangential velocity (v.sup.2) divided by R. The primary radial force 
component generated by the rotation of the body S about the axis A is 
directed outwardly. 
The force applied at any point within the body is a differential force 
proportional to .omega..sub.1.sup.2 R in an outward direction where 
.omega..sub.1 is the angular velocity around the axis A and R is the 
distance of the part from the axis A. Since it is desired to mix the 
liquid, the body of liquid is rotated about an axis perpendicular to the 
radial force along the radius R. As shown in FIG. 1, the body may be 
rotated about an axis x tangential to the path P, about an axis y 
perpendicular to the path P or at any angle within the plane defined by 
the axes x and y. Rotating the body S about a perpendicular axis, for 
example the y axis, at an angular rate of .omega..sub.2 revolutions per 
second causes the direction of the force applied to a differential mass of 
fluid to be reversed twice for each revolution, so that the speed of 
revolution of the body S about the secondary axis y determines the 
frequency of the mixing force generated in the mass. 
The force generated by rotation about the secondary axis y is added to or 
subtracted from the primary force, depending upon the position of the 
differential mass of fluid in body S. In other words, as the body S 
rotates about the secondary axis, the centrifugal force generated on each 
differential mass of the body S by the rotation about the primary axis A 
varies cyclically between a maximum force directed away from the secondary 
axis to a maximum force directed toward the y axis as each part within the 
body rotates about the y axis. This primary acceleration force is 
modulated by the secondary acceleration force about the y axis. 
The same cyclic variation of the direction of application of the primary 
centrifugal force occurs regardless of the orientation of the secondary 
axis within the plane defined by the x and y axes, and regardless of the 
position of the secondary axis relative to the center of gravity of the 
body. 
The force generated by the rotation of the part about the axis A is a 
constant centrifugal force which results from driving the body S about the 
circular path P. However, by reason of the body being rotated about a 
secondary axis y during the rotation about the axis A, the constant 
centrifugal force is cyclically varied in direction to produce a mixing 
force upon each differential part of the liquid body S. The liquid must be 
contained within a chamber which insures rotation of the liquid body about 
the respective axes. 
In order to avoid centrifugal separation of the components of the liquid 
and obtain mixing of the liquid, the primary centrifugal force must exceed 
the secondary centrifugal force. The secondary force generated by rotation 
about the secondary axis y is adjusted relative to the primary force to 
provide optimum mixing. The maximum secondary force generated upon any 
differential part of the body is proportional to .omega..sub.2.sup.2 r; 
where .omega..sub.2 is the angular velocity around the axis y, and r is 
the distance of the differential part from the y axis. To obtain the 
desired shear forces, .omega..sub.1.sup.2 R must be greater than 
.omega..sub.2.sup.2 r. By controlling the secondary centrifugal force to 
be less than the primary force, the orientation of the net centrifugal 
force is determined by the orientation of the primary force. The 
orientation is outward from the primary axis A, but cyclically reverses 
relative to the secondary axis y. The cyclic reversal of the forces in the 
body S as it rotates about the y axis generates shear forces which effect 
a thorough mixing of the liquid which follows the rotation of the body 
about the y axis. The rotational speeds .omega..sub.1 and .omega..sub.2 
may be adjustable where it is desired to accommodate the operation to 
materials having different physical properties. When the apparatus of the 
invention is designed to operate on a single given fluid material, the 
rotational speeds and the chamber sizes may be selected to conform to the 
physical properties of that material. The physical properties to be 
considered in selecting the proper rotational speeds and chamber sizes 
include the surface tension property, the viscosity, the density, and the 
frictional relationship between the elements of the carrier and the fluid 
material. 
FIGS. 2 and 3 illustrate a suitable apparatus for imparting 
cyclically-reversing mixing shear forces to a fluid. In the present 
instance, the apparatus is designed to accommodate a fluid which is 
flowing through the apparatus as indicated by the arrows in FIG. 2, but it 
is also applicable to a batch process in which fluid is introduced into 
the apparatus as indicated by the first arrow and subjected to the mixing 
forces and then after mixing is withdrawn from the apparatus as indicated 
by the second arrow. While permitting axial flow of the liquid, the 
apparatus confines the liquid against radial flow arising from the 
centrifugal forces generated in operation of the mixing apparatus. 
FIG. 2 illustrates apparatus comprising a hollow main shaft 51 which, in 
the present instance, is connected to a liquid supply at its lefthand end, 
as indicated at 52 and to a liquid discharge at 53. Between the supply and 
discharge ends 52 and 53, the shaft is plugged, as indicated at 54, so as 
to divert the liquid into branch conduits 55 and 56, extending outwardly 
respectively from opposite sides of the shaft 51. The branch conduits 55 
and 56 lead into multiple elongated carriers or treatment chambers 57 and 
58 which are disposed parallel to the main shaft 51 and are spaced 
radially therefrom, for example by mounting structures 59 and 60. In the 
present instance, the chambers have imperforate cylindrical walls 
confining the liquid therein against radial flow while permitting axial 
flow therethrough. 
Each of the chambers 57 and 58 is rotatable within the structures 59 and 60 
and has a planet gear 61 or 62, respectively, fixed thereon to drive the 
chambers about their individual axes. The planet gears 61 and 62 mesh with 
a ring sun gear 63 so that as the shaft 51 is rotated about its axis A', 
for example on bearings 64 adjacent the ends 52 and 53, the individual 
chambers 57 and 58 may be rotated about their axes B'. In the present 
instance, the ring gear 63 has external drive teeth 66 thereon which mesh 
with an external drive pinion 67 having a drive shaft 68 therefor. Thus, 
the rotation of the ring gear 63 may be controlled by the drive shaft 68 
to either maintain the gear stationary or to drive it for concurrent or 
countercurrent rotation with the shaft 51. The rotation of the ring gear 
63 controls the rotation of the chambers 57 and 58 about their respective 
axes B'. The shaft 51 is driven by a suitable gear 69 to cause the 
chambers 57 and 58 to rotate about the central axis A'. Thus, the 
apparatus of FIG. 2 operates to apply cyclically varying forces to the 
liquid within the chambers 57 and 58 in a manner as described with 
reference to the differential part of the liquid body S in FIG. 1, the 
axis A' in FIG. 2 corresponding to the axis A in FIG. 1, and the axis B' 
in FIG. 2 corresponding to the axis y in FIG. 1. In this way, the liquid, 
and any particle entrained therein, within either of the chambers 57 and 
58 is subjected to cyclic forces determined by the angular rotation of the 
shaft 51 about its axis and at a frequency determined by the rotation of 
the chambers 57 and 58 about their respective axes B'. 
The structure shown in FIGS. 2 and 3 has utility for subjecting liquids to 
forces which will mix homogeneously. The cyclically-varying forces applied 
to the liquid are effective to provide a thorough mixing of the liquid 
passing through the chambers 57 and 58. The magnitude of the force applied 
is proportional to the angular rotation of the device around the axis A' 
and the radial distance between the axes A' and B', and the cyclic 
frequency of the force is determined by the rotational speed of the 
chambers 57 and 58 about their respective axes. 
Thus, in the illustrated embodiment, a body of liquid is subjected to 
cyclically-varying forces while in a carrier. The carrier is rotated about 
a first axis at a speed to generate a centrifugal force of a specified 
magnitude on each part of the body, and the carrier is rotated about a 
second axis perpendicular to the direction of the centrifugal force to 
effect cyclic variation of the orientation of the centrifugal force 
generated on each part. 
The cyclically-varying forces on the different parts of the liquid body 
provide homogeneous mixture by a laminar shearing action. The walls of the 
carriers are smooth and the rotational speeds are high. Protrusions, 
deflector vanes, and paddles or other agitators inside the mixing chambers 
can be added to increase the turbulence and mixing action and reduce the 
rotational speeds necessary. Such agitators may be desired when mixing 
low-viscosity fluids to insure rotation of the body of fluid with the 
mixing chambers. While turbulent mixing may be faster, it could be less 
thorough. 
Closed containers for the liquid may be used. Measured amounts of products 
are put into a container, and the container is closed with a lid, and then 
the container is rotated about two axes to mix the ingredients. The 
container may be devoid of interior protrusions or may have vanes mounted 
on its interior walls, or the lid can have vanes on it, whereby the 
product can be stirred after removal of the lid without the vanes being in 
the way. 
In many cases, where the mixing was done by the batch, the process might 
easily be converted into a continuous mixing operation. There are other 
cases that seemed to inherently require batch operation. With careful 
design, some of these might be converted to continuous operation. In a 
reaction that first requires heat to get it going, and then cooling to 
keep the temperature under control, consideration should be given to the 
possibility of having the heating and cooling concurrent in controlled 
zones of a cylindrical mixer. The product would flow continuously through 
the zones, being mixed all the while. 
In some cases, continuous operation simplifies the recycling of the output 
product. 
In cases where the product may cake in the mixing carriers, the elements 
should be so constructed that all parts of it can be reamed clean, either 
by elimination of agitators or by mounting any agitators for easy removal 
for cleaning of the carriers. 
If heating or cooling is required, the rotating parts considerably 
complicate connections to jackets on the mixing cylinders. The simplicity 
of the structure and the absence of relatively movable parts permits the 
entire apparatus to be put in a water shower, or a steam bath. 
Alternatively, the mixing may be done in stages, with two or more mixers, 
or recycling back into the same mixer. The heating or cooling would then 
be done between stages. 
It is expected that control over the two spinning actions will give a 
greater range of mixing conditions so that a single mixer can be used to 
produce a larger variety of products than present equipment can. 
The rate of mixing is believed proportional to the power input to the 
machine. A dynamometer may be attached to the driving means to show the 
power input. The machine operator can then control the operating 
conditions by watching a plot of the power absorbed by the mixer. The plot 
is relatively linear while laminar shearing is taking place. A sharp 
increase in power absorbed indicates the onset of turbulence. Conceivably, 
as the mixer speed is further increased, the power could drop, indicating 
loss of effectiveness due to improper mixing conditions. 
While particular embodiments of the present invention have been herein 
illustrated and described, it is not intended to limit the invention to 
such disclosures, but changes and modifications may be made therein and 
thereto within the scope of the following claims.