Mixing tool

A mixing tool for installation in a mixing container and method of making same. The mixing tool has a disc-shaped member with a semi-circular section connected in radially spaced relationship to a rotatable shaft so as to be coaxial therewith and has plane top and bottom surfaces perpendicular to the axis of rotation of the rotatable shaft. The disc-shaped member also has a twisted section merging with each other the top and bottom surfaces of the semi-circular section and likewise arranged and connected to the shaft in spaced relationship thereto. The mixing tool is preferably made from a circular disc with plane top and bottom surfaces, which is cut open by a single radial cut. One of the cut end portions is then twisted and reunited to the other cut end portions whereupon the thus obtained member is arranged in spaced relationship to a rotatable shaft and connected thereto.

The present invention relates to a mixer with tool surfaces connected to a 
hub, for installation at the bottom side in mixers for a pulverous, 
granular or liquid substance to be mixed, said mixer having an upright 
cylindrical container in which a conical circulation of the substance to 
be mixed occurs at circumferential tool speeds up to 50 meters per second 
of the tool ends extending nearly up to the inner wall of the container. 
Heretofore known mixing tools for mixers of the above mentioned general 
type comprise wing-like arms which extend from the hub up to near the 
container inner wall. These arms are arranged close to the container 
bottom and substantially independently of the cross section of the arms 
cause the substance to be mixed to circulate in a funnel-shaped form at 
circumferential speeds up to 50 meters per second. The material to be 
mixed is by the tool arranged close to the container bottom centrifuged 
outwardly toward the inner wall where it rises in a spiral movement 
upwardly and drops or flows subsequently back to the center of the 
container, whereupon it is again by the tool at the bottom side of the 
container accelerated for a new circulation. Within the ring formed by the 
material to be mixed and sliding along the container inner wall, the 
adjacent particles to be mixed respectively have different velocities 
while, however, there exists the danger that in the annular core region of 
the ring formed by the material to be mixed, the different speed over the 
adjacent particles to be mixed becomes very small so that a portion of the 
particles of the material to be mixed stays there for a longer period of 
time. In order to avoid such zone of slower movement which has a 
disadvantageous effect on the quality of material to be mixed, frequently 
a plurality of tools are employed which are arranged in spaced 
relationship one above the other and rotate at the same speed. The 
installation of additional tools, however, greatly increases the costs for 
the mixer because the cost of material for the stainless tool steels to be 
employed, as well as the cost for the polishing of the tool surface, are 
relatively high. 
It is, therefore, an object of the present invention to provide a mixing 
tool for the installation in mixers of the above mentioned general type, 
by means of which the formation of a slow-moving zone in the annular core 
region of the ring of material to be mixed with a funnel-shaped 
circulation of the material to be mixed will be avoided while the costs 
for the tool will be considerably reduced over tools arranged at a 
plurality of levels.

The mixing tool according to the invention is characterized primarily in 
that the tool surface is formed of an originally plane circular annulus of 
a relatively thin wall thickness, the original outer diameter of which is 
to a slight extent less than the inner diameter of the container, while 
the original inner diameter of said circular annulus amounts to about from 
50 to 70% of the original outer diameter. The circular annulus is 
separated in radial direction at one area and while arching, said circular 
annulus is with the separating edges offset by 180.degree., again put 
together and by a plurality of arms is connected to the hub located in the 
center of the originally plane circular annulus while the seam between the 
separating edges butt together but offset by 180.degree., extend nearly 
parallel to the axis of rotation of the tool. 
Referring now to the drawings in detail, the plane annulus 1 comprises an 
outer diameter D.sub.1 which is slightly less than the inner diameter 10 
of the mixing container 9 for which the mixing tool is intended that is to 
be prepared from said circular annulus. The inner diameter has a length of 
about from 50 to 70% of the outer diameter D.sub.1. Arranged on said 
annulus 1 and spaced by 10.degree. over an angle of 360.degree. are 
graduations the zero and 360.degree. graduations of which are located on 
the horizontal axis a. The graduation is from the 0.degree. location 
marked by radially extending lines in counterclockwise direction. These 
graduation lines are not components of the finished mixing tool but are 
merely intended to explain and clarify the following remarks. 
According to the embodiment of the invention as illustrated in FIG. 2, the 
annulus or ring 3 which consists of stainless steel is cut open in radial 
direction at the 180.degree. area (on the left hand side of FIG. 2) of the 
360.degree. graduation. The separating edges located opposite each other 
are respectively designated with the characters A and B. While 
simultaneously arching the now open ring 1, the separating edge A which in 
FIG. 2 is located at the top is turned by 180.degree. and is brought in 
position so as to cover the separating edge B and is connected thereto for 
instance by welding. The seam 2 located on the original graduation line at 
180.degree. of the 360.degree. graduation between the now offset and again 
connected separating edges A and B extends substantially parallel to the 
axis of rotation 3 of the mixing tool 1a. 
The hub 4 is arranged by means of three arms 5, 6 and 7 respectively offset 
to each other by 120.degree. and connected to the tool surface arched in 
itself. The length of the arms 5, 6 arranged in the angular positions of 
the 360.degree. graduation 5a and 6a corresponds to the length of the arms 
which as indicated in FIG. 2 would extend from the original ring 1 to a 
central hub 4a. 
FIG. 1 illustrates a top view of the finished arched mixing tool. FIG. 3 
illustrates in perspective the mixing tool in its mounted position on the 
bottom side in the indicated mixing container 9. 
The preferred direction of rotation is indicated by the arrows C pointing 
in clockwise direction. 
The above described separation or cutting open of the ring 1 and the 
described connection of the separating edges A and B in a position offset 
by 180.degree. results in a single tool surface which is closed in itself 
and which, depending on the position within the indicated 360.degree. 
graduation exerts different effects upon the material to be mixed. The 
major horizontally extending portion within the region of from 270.degree. 
above 360.degree./0.degree. to 90.degree. in the manner of any tool or 
member having a first disc-shaped section throws the material to be mixed 
radially outwardly. The tool surface portion which is visible from above 
and which arches upwardly within the region of from 90.degree. to 
180.degree. from the horizontal plane into the vertical position 
intersects with its outer edge 1a in the material to be mixed, which means 
in the bottom side of the circulating ring of material to be mixed and 
draws said material downwardly and inwardly. The material to be mixed is 
conveyed primarily upwardly by means of the tool surface portion which is 
visible from above within the region of 180.degree. to about 270.degree.. 
By means of the said tool surface portion which from its vertical position 
again turns into a horizontal position and at the same time has in the 
area of from 180.degree. to 270.degree. increasing distances b.sub.1, 
b.sub.2, b.sub.3 from hub 4, the material to be mixed is conveyed 
primarily in upward direction. The non-symmetric configuration with regard 
to the vertical axis of rotation 3 of the mixing tool will at 
circumferential velocities of the tool up to 50 meters per second bring 
about a very pronounced funnel-shaped circulation of the material to be 
mixed. In this connection, by means of the arched portions of the tool 
surfaces, additional upwardly and downwardly directed pulses are in fast 
sequence imparted upon the particles of the mixture. These pulses bring 
about an additional intermixing of the circulating ring of mixing material 
in vertical direction. 
The advantage obtained by the mixer according to the present invention 
consists in that a formation of a dead center zone in the annular core 
region of the ring of mixing material circulating in the mixing container 
is avoided by the specific design of the one-surface mixing tool. 
It is, of course, to be understood that the present invention is, by no 
means, limited to the specific showing in the drawings, but also comprises 
any modifications within the scope of the appended claims.