Device for mixing flowable materials

A device for mixing flowable materials, especially relatively viscous liquids and flowable solids, comprises a pipe or tube section, preferably of circular cross section, provided internally with at least one mixing element helically twisted in a uniform manner about the axis of the pipe and formed with only two groups of surface regions which are folded relative to one another and which alternate along the mixing element. Each of these surface regions is of flat triangular outline with a base of the triangle formed along one of the helically twisted longitudinal edges of the mixing element and converging toward the other. The flat surface regions may be truncated, i.e. of generally trapezoidal outline with their narrow triangle side lying along the opposite edge of the mixing element from that occupied by the base, or of a pointed configuration where the triangle apex lies along this opposite side of the mixing element.

FIELD OF THE INVENTION 
The present invention relates to a device for mixing flowable materials 
and, more particularly, to a device which is capable of mixing viscous 
liquids and flowable solids as they pass through a pipe section, this 
device comprising a pipe section preferably of circular cross section 
formed internally with at least one mixing element. 
BACKGROUND OF THE INVENTION 
A device for mixing liquids and flowable solids while they tranverse a pipe 
section of, for example, circular cross section, can comprise a mixing 
element received within the pipe section and subdividing the flow of 
material into at least two streams while guiding them around and along a 
common axis. 
Such a device can be formed from a flat sheet-metal blank which can be 
provided with generally flat surface regions of triangular outline. 
The term "mixing element" as used herein is intended to refer to a static 
structure across which the stream to be mixed is passed, such element 
generally being provided in a fixed condition within a pipe through which 
the material is displaced, e.g. by a pump or other means. 
The term "flowable material" is used herein in its most general sense to 
mean any fluid or flowable solid, although it is particularly intended to 
refer to materials which are difficult to mix and are relatively viscous. 
The nature of materials which may be treated with the system of the 
present invention will be detailed below, but it should be understood that 
the treatment may involve any conventional treatment which utilizes the 
movement of such flowable materials. 
Thus the term may refer to homogenization, material exchange, heat exchange 
or a combination thereof whereby, for example, a flowable solid may be 
treated by a liquid, a liquid may be treated with a gas, a solid can be 
treated with a gas, or various heat exchange and material exchange or 
chemical reaction processes can occur with or within the flowable 
materials. 
Thus in the instant description, the liquids and flowable solids to be 
mixed can be subjected to a process in which each particle or portion of 
the liquid or of the solid in the medium comes into contact with a surface 
of the device which guides the flow and which induces a rotary movement 
therein. The particles are also brought into contact with other particles 
of the liquid or the solids. 
The mixing process of the present invention may thus also involve a heat 
exchange or an interchange of matter of interaction between the particles 
themselves or between the particles and fixed walls of the device, or 
between particles of the flowable material or layers arranged on or formed 
as part of the mixing device. For example, when the interchange is a 
catalytically induced chemical reaction, portions of the device may be 
constituted as a catalyst support. 
The "mixing" can thus include kneading, emulsifying, dispersing, 
plasticizing or homogenizing a flowable mass thereby retaining or altering 
physical or chemical properties. The production of a uniform molecular 
weight in a flowable synthetic resin of liquid or particulate form is thus 
a mixing process in the sense of the present invention. 
Furthermore, if the reaction involves a catalyst on a wall or pipe surface 
a mixing process nevertheless takes place in order to bring all of the 
particles of the flowable material into as uniform contact as possible 
with the catalyst as the streams traverse the pipe section. 
The mixing can occur during polymerization, condensation, neutralization or 
reduction, during oxidation or hydration, during fermentation or like 
processes. 
Layers of an adsorption agent, a grinding or polishing agent, or any other 
material-treatment agent may be provided on the surfaces of the device. A 
case in point is the dehusking of grain in which the flowable mass of 
grain, with husks or hulls thereon, is cause to traverse a device of the 
present invention in a uniform flow so that the grains of corn or rice, 
etc. are brought into uniform contact over their entire surfaces with 
solid grinding or abrading surfaces within the pipe section to carry out 
the treatment. 
Devices utilizing the principles described above are known from various 
applications and mention may be made, for example, of German No. 3,861, 
No. 86,622 and No. 1,557,118. In these systems, for the purpose of heat 
exchange or to mix flowable materials it is known to provide several 
successive and oppositely twisted mixing elements in the form of short 
helically bent strips into a pipe or duct to internally subdivide the flow 
of fluid into two flow cross sections of uniform area. 
The adjacent end edges of the successive elements are arranged at an angle 
with one another to repeatedly subdivide the streams and combine them. 
Each flow cross section or stream thus can contain parts of the divided 
flows from the preceding mixing element. 
It is also known (see German open application, Offenlegungsschrift, Nos. 
2,205,371 and 2,320,741) to mix elements in the form of layers in contact 
with one another to form a multitude of flow channels. In this case, the 
longitudinal axes of the individual flow channels within each layer are 
parallel, at least in groups. The longitudinal axes of the flow channels 
of adjacent layers can be inclined to one another. Between the individual 
layers, exchange may occur between the respective streams of the flowable 
material through openings. 
German Pat. No. 2,058,071 and U.S. patent No. 3,804,376 describe systems 
for locking mixing elements in a pipe more firmly into position and 
provide a configuration which enables these elements to be manufactured 
more easily. In these systems twisted strip elements are provided and have 
a slit for engagement with adjacent or successive strip elements. 
Mention should also be made of French Pat. No. 2,209,601 which provides a 
pipe section with bent sheet-metal mixing elements. In these mixing 
elements, triangular flat sections are provided and the triangular 
surfaces or zones are of different shape and size with all of the triangle 
vertices terminating at a common point. Fold lines are provided between 
these triangular sections. 
Experience has shown that the mixing elements of this French patent do not 
bring about a uniform splitting and rotation of the flow material over a 
significant axial length, especially because the hydraulic diameter of the 
flow cross sections traversed by the streams into which the mixing element 
splits the flow are not constant over the length of the mixing element. 
Disadvantages also have been found with systems of the type described in 
the German printed application (Auslegeschrift) 1,557,118 mentioned 
briefly above. 
In all mixing processes, the shearing action of the respective mixing 
element has been found to determine the success or efficiency of mixing as 
well as the effectiveness of the subdivision of the incoming stream of 
flowable material into flow parts or streamlets. 
According to the type of loading, a change of shape and position of the 
folded layers of material which slide on one another can be achieved. The 
type and intensity of the loading is dependent on the respective 
constructions of the flow channel which is formed by the mixing elements 
built into the portion of the pipe through which the flowable material 
passes. 
In known devices in which the individual flow cross sections are of 
semicircular configurations and constitute the partial flow channels, an 
unchanging ratio between separating and shearing action is obtained. This 
ratio remains substantially constant even with the change in the pitch of 
the mixing element. In such systems, if it is desired to increase the 
shearing action to provide a certain degree of shearing within a 
particular material, i.e. to match the desired properties of the material 
to the mixing device, it is necessary to increase or otherwise alter the 
number of mixing elements. 
In practice, therefore, the devices of the prior art must be provided with 
numerous mixing elements and relatively long mixing paths. This is 
especially the case when the element can have the length of 1.25 to 1.5 
times its diameter, such a length having been found to be convenient from 
the point of view of manufacture. 
Difficulties have also been encountered in deforming the elements to form 
helically curved strips. These difficulties increase significantly as a 
result of extreme transfers and longitudinal distortions of the strip with 
increasing diameter. There is, therefore, a dependence between the 
thickness of the material and the diameter of the elements which can be 
fabricated therefrom. In twisting a conventional steel such as the V to A 
steel the thickness of the element must be about 0.075 times the diameter 
in order to avoid tearing or undesired deformation of the element upon 
helical twisting. This has been found to rule out largely the manufacture 
of such elements in large diameters from strip material. In practice one 
finds that it is necessary in manufacturing large diameter mixing 
elements, to apply casting techniques which are far more expensive and 
complex. 
OBJECTS OF THE INVENTION 
It is the principal object of the present invention to provide a device for 
mixing flowable material which avoids the difficulties, which is of 
simplified manufacture and which can be of relatively large diameter and 
inexpensive construction, 
Another object of the invention is to provide a device for the purposes 
described whose mixing elements can be fabricated with a relatively small 
length by comparison to the diameter without difficulty and without 
excessive cost. 
Yet another object of the invention is to provide a mixing device with an 
improved mixing efficiency and effect and which facilitates matching of 
the material and the treatment desired to the dimensions of the mixing 
device and especially the shape of the mixing elements. 
SUMMARY OF THE INVENTION 
These objects and others which will become apparent hereinafter are 
attained, in accordance with the present invention, in a device for mixing 
flowable materials, namely fluids and flowable solids, which comprises a 
pipe section or duct preferably of circular cross section having at least 
one mixing element which subdivides the flow of material into two streams 
and rotates them about a common axis while inducing a mixing movement in 
each of the streams. The mixing element is fixed in the pipe section and 
is formed from a flat sheet-metal blank with successive substantially flat 
surface regions having fold lines betwen them and of triangular outline. 
Each of these surface regions has a convergence in the direction of one of 
the walls of the pipe and in the direction of one of the longitudinal 
edges of the helically twisted sheet-metal member. 
According to the invention, the mixing element is curved helically in a 
uniform manner about the pipe axis and comprises only two groups of 
different surface regions which alternate with their convergences in 
opposite directions transverse to the pipe axis so that the vertex or 
narrow end of the generally triangular configuration of one surface region 
terminates along the longitudinal edge of the element opposite the 
longitudinal edge at which the base of the triangle terminates and at 
which the bases of two adjacent surface regions of the other group 
terminate. 
According to a feature of the invention, the successive surface regions of 
opposite orientation are folded from a flat sheet-metal blank of 
rectangular outlint and the surface regions belonging to the same group 
each have the same inclination with respect to a plane containing the axis 
of the pipe and passing through a fold edge of the surface region and an 
adjacent surface region. Every second or other surface region can be 
provided in a plane containing the pipe axis, i.e. an axial plane, while 
the surface regions adjacent thereto are inclined with respect to the 
latter plane. 
According to another feature of the invention, the surface regions lying in 
an axial plane extend from pipe wall to pipe wall while remaining in this 
plane whereas the surface regions therebetween and adjacent these 
axial-plane surface regions are inclined thereto and extend only between 
the axis of the pipe and the wall thereof. 
Each mixing element can comprise at least two identical portions joined 
together along a straight-line edge in the pipe axis according to yet 
another feature of the invention with the joint edge forming the 
terminuses of the narrow triangle side of the intermediate surface regions 
mentioned previously. 
In the latter case, narrow sides of the surface regions of one group, lying 
in the joint edge, can be smaller than the narrow sides of the surface 
regions of the other group pointing to the walls of the pipe. In this same 
embodiment, each portion of the mixing element can be folded out of a 
portion of an annular or circular flat sheet-metal disk. 
Extensions of the two fold lines of the developed portion of the mixing 
element, limiting the surface region, can pass through the center of the 
sheet-metal disk with different spacings. In this device, moreover, the 
extensions of two fold lines limiting each surface region can pass through 
the center of the sheet-metal disk when the latter is unfolded so as to be 
flat but with the same spacing and on opposite sides. 
Where all of the triangular surface regions are of the same shape and size, 
the surface regions have small angles of between 5.degree. and 30.degree. 
which are inclined toward the walls of the pipe and the planes of adjacent 
surface regions are inclined with respect to one another at an angle 
between 30.degree. and 120.degree. . Where the surface regions are of 
different size, the smaller surface regions can have small angles between 
5.degree. and 15.degree. converging toward the walls of the pipe while the 
larger surface regions can have small angles between 15.degree. and 
45.degree. converging toward the pipe axis. The surface regions of the two 
groups lie in planes which include angles between approximately 
100.degree. and 160.degree. with one another. The thickness of the 
material or of the sheet metal can be significantly less than 0.075 times 
the diameter of the mixing element and advantageously the joint between 
portions of the mixing element can have a length which is smaller than the 
dimensions of the mixing element transverse to the joint edge. 
In the new device of the present invention the shearing action is markedly 
improved because of the cascade-shaped and stepped configuration of the 
flow channel brought about by the particular alternate arrangement of the 
relatively inclined successive triangular regions with convergences in 
opposite directions, especially in relation to the subdivision into 
streams of the material. 
This means that with the same length of a mixing element, the loading on 
the material flowing through the system is substantially greater in the 
system of the present invention so that a substantially more intense 
mixing action is achieved. 
This enables the length of the mixing path to be kept small relative to the 
diameter of the mixing element and hence the overall length of the device 
to be relatively small. The device of the present invention permits 
fabrication of the mixing element without particular concern for the 
thickness of the material (see the disadvantages mentioned earlier) and, 
more particularly, permits the mixing elements to be fabricated from sheet 
metal even when large diameter mixing elements are used. It is an 
important advantage of the present invention that the thickness of the 
sheet metal can be significantly less than 0.075 times the diameter of the 
mixing element. 
The pressure drop in the device and the losses due to congestion at the 
ends of the elements can be substantially reduced because of the increase 
in size of the flow cross sections into which the mixing elements 
subdivide the stream. In addition, a material can be used which is 
relatively more difficult to bend and is somewhat more rigid or less 
viscous. The result is a device whose rigidity is increased because of the 
configuration of the mixing element even with smaller thickness of the 
sheet-metal material. 
In the device, a plurality of identical or similar mixing elements can be 
disposed one after the other in the direction of flow of the material and 
the elements can have their end edges in mutual contact. However, some 
mutual spacing may be provided between the ends of the successive elements 
and locking and orientation of the elements can be achieved by means of 
slits in the end portions which interfit. Such interconnection is known in 
the art as noted previously. 
Usually the mixing element is closely encircled by the inner wall of a pipe 
or sleeve. Tolerances play no special role in the region of the peripheral 
edge of the mixing element and the inner wall of the pipe since clearances 
in this region do not not restrict the mixing action or the function of 
the new device. However, the mixing element can fit snugly and be entered 
in the pipe by any conventional means. 
Since clearances are not a factor, the fabrication of the device can be 
facilitated and made less expensive and, indeed, manufacture of the mixing 
elements by casting is no longer required. 
While it is preferred to fabricate the mixing elements by bending and 
folding from sheet metal in the manner described, of course, the mixing 
element can be produced from different materials and by other methods of 
manufacture. The fabrication from metal sheet has the significant 
advantage that the element can be folded, twisted and bent from flat 
sheet-metal blanks. 
The mixing device of the present invention can also be used as a condenser 
or vaporizer for producing fuel mixtures and is particularly inportant as 
a device (aerator) for introducing oxygen from the air into waste water 
for its biological water treatment. 
The cascaded flow channels of the system of the present invention can be 
constructed so that the cascaded steps or folds can extend transversely to 
the axis of the pipe from one side of the pipe wall to the opposite side 
thereof, i.e. diametrically across the pipe. Each mixing element can, 
however, comprise two elements running longitudinally parallel to the axis 
of the pipe so that the steps in each case run transversely from the axis 
of the pipe to the pipe wall. In either case, distortion-free fabrication 
is possible by by folding the unit form a flat metal sheet. The size of 
the triangular surface regions can be the same or different. In particular 
it is possible to vary the fold angle over the length of the given mixing 
element or from mixing element to mixing element so as to match a change 
in consistency of the flowable material which is processed. 
The term "triangular surface region" is here used to refer to a surface 
region which is a perfect triangle, i.e. is made up of three sides joining 
at respective vertices and each of which lies along a straight line. 
However, it also is intended to refer to surface regions in which the base, 
lying along one longitudinal edge of the mixing element is somewhat curved 
to conform to the helical curvature of the longitudinal edges of the 
mixing element while the opposite end of the triangle terminates not in 
the vertex but in the narrow side so that the surface region has the 
configuration generally of a slender trapezoid. 
The mixing element of the present invention can be effected form a flat 
strip-shaped blank or from a sheet-metal disk. 
When a strip-shaped blank is used, the longitudinal edges of the folded and 
twisting mixing element lie substantially along helices of a constant 
pitch and are constituted substantially from the triangle bases of the 
surfaces and narrow sides of trapezoidal surfaces. 
Each substantially traingular surface can then extend over the entire width 
of the metal strip transverse to the axis. In each case, two adjoining 
triangular surfaces, oriented oppositely in the manner described, define 
an angle between them and constitute one of the cascade stages, the depths 
of which are determined by the triangular surfaces which are flatter 
relative to the longitudinal axis and the height of which is determined by 
the steeper triangular surfaces. 
By selection of the size of the acute angle of the triangular surfaces, the 
step height and depth can be changed without changing the diameter of the 
helix and hence of the mixing element. This allows the mixing element to 
be adapted to the particular mixing requirements. In the transition 
between laboratory testing and practical application, the elements can 
easily be obtained by three-dimensional scale enlargement without changing 
the angle and without changing the outline shape of the triangular 
surfaces. 
When the mixing element is fabricated from a disk, the longitudinal axis of 
the mixing element is simultaneously the joint edge for two identical 
sheet-metal portions which may be welded or otherwise bonded together. 
Helical longitudinal edges have a uniform pitch and are formed by narrow 
sides of the triangle. In each case, two oppositely oriented triangular 
surfaces of each portion of sheet metal which adjoin in a longitudinal 
direction form a step together. Each step constitutes one stage of the 
cascade. 
By changing the size of the small angle, a finer or coarser step is 
obtained for matching to the particular mixing task. The larger the 
difference in area between the two triangular surfaces, the longer the 
element will be and vice versa. Here too a three-dimensional scale 
enlargement is possible when proceeding from laboratory testing to 
practical production. In both embodiments the height of the steps changes 
transversely to the axis of the mixing element. Thus an additional 
improvement in the transfer of heat is made possible by the additional 
turbulence induced at the steps. The turbulence thus arising combines with 
other turbulent or vortex swirls to form larger pairs of resistances which 
are again subdivided into smaller pairs of induced resistances. The system 
has been found to be particularly effective when matching to specific 
mixing requirements is required. 
In contrast with known helical semi-circular channels using mixing elements 
from helically twisted strips, the elements of the present invention where 
the oppositely oriented triangular folds not only locate the flow about 
the hydraulic center of the flow channel, whereby the flow layers are 
curved concentrically about a center point, but induce multiple loading of 
the layers of flow which slide on one another in the region of the 
cascaded steps. The latter can have a different step height transverse to 
the axis of the pipe and step widths which also vary. The step heights and 
step widths change both radially and axially as seen by the advancing flow 
of the material. The shape and position of the layers and the layering is 
thus continually changing as a result of the differences in pair which are 
seen by the advancing stream. This facilitates optimum matching to the 
ratios required for a particular mixing process. 
It is also possible, within the framework of the present invention to vary 
the parameters of construction of the device empirically and without 
particular difficulty for each particular job. 
For example, the elements can vary in step number for a given incoming flow 
angle and, with a constant flow angle, one can change the step width and 
step depth. If the element has triangular surface regions of equal size 
then the incoming flow angle is 90.degree.+ half the angle of inclination. 
With elements formed from surface regions of different size, the incoming 
flow angle is the angle of inclination between the small and large surface 
regions. A change in step number for a constant incoming flow angle can be 
achieved by changing the size of the surface regions, or by changing the 
acute angle of the triangular outline, i.e. the angle of convergence 
toward a longitudinal edge of the mixing element. A change in the angle of 
fold between the adjacent surface regions also results in a change in the 
incoming flow angle. Moreover, with constant pitch twist of the element, 
the ratio of the length of the element to its diameter changes, for 
example, by 180.degree.. 
With elements made from differently sized triangular surface regions, the 
number of steps in the length of the elements determines the incoming flow 
angle and surface ratio between the large and small triangular surface 
regions determines the step depths and step widths. With very large 
differences small step numbers are provided with an incoming flow angle of 
almost 90.degree. there is a very small element length. This can be less 
than half the diameter. The height of the steps is very low as a result 
and the step area or width is very large. 
Because of the variation in the construction of the flow channel, the 
loading of the layers we slid on each other can be varied. This is 
particularly the case because of the zig-zag or cascade path over the 
longitudinal axis of the pipe resulting from the particular flow 
construction of the steps. This construction has been found to be 
particularly advantageous in the case of extreme differences in the 
viscosity of the fluids to be treated or to be mixed. The channel 
formation or straight through flow which has been feared in the case of 
large-diameter helical mixing elements in the past is simply absent. In 
folding the mixing elements, the stripped-form blanks or disks can be 
provided with left- and right-hand twists and folds as desired. 
In order to vary the construction of the steps for modifying shearing 
action, certain steps can be filled with appropriate material. The filler 
can be anything which bonds to the sheet metal of the mixing elements. 
This filler also tends to increase the stability of the mixing element. 
The surface of the mixing element can be coated with catalytically 
effective, absorbent, absorbent, grinding or polishing substances. In some 
cases the elements can themselves be formed unitarily from such 
substances. With laminated elements, the parts may be fixed to one another 
by welding, soldering or gluing, although preferably a formed or 
overlapping construction is provided with interlock seams.

SPECIFIC DESCRIPTION 
Referring first to FIG. 1A which illustrates the principles of the present 
invention, it can be seen that a pipe section P which can be used in a 
system of the type shown in German printed application (Auslegeschrift) 
No. 2,058,071 has an inner wall P.sub.w with an internal diameter D which 
is traversed in the direction of the axis C by a flow of viscous material 
to be mixed. 
Within this pipe section there are provided a plurality of successive 
mixing elements 1 shown to be axially spaced upon although they can be 
connected by a slot construction as described in the German printed 
application referred to last above. Each of the mixing elements can have 
the configuration shown in greater detail in FIG. 1 and illustrated only 
in the most diagrammatical form in FIG. 1A. 
Each of the mixing elements can be folded from sheet metal of a thickness t 
which is less than 0.075 times the diameter D. 
The mixing element 1 shown in FIG. 1 can be produced by simple bending and 
folding of a flat strip-shaped sheet-metal blank 20, the bending being 
effected along fold lines 3. 
The element thus has triangular surface regions 4 and 5 which are of equal 
size here and are connected to each other at the fold lines 3, but which 
are inclined with respect to one another in different planes. 
The flat triangular surface regions 4 and 5 are oriented in opposite 
directions, transverse to the longitudinal direction of the mixing element 
1. Thus the two longitudinal edges 7 and 8 of the mixing element are 
formed alternately with narrow sides 9 of triangular surface regions 4 and 
5, forming the bases of the respective triangular regions, and vertices or 
truncated apices 10 of these surface elements. 
The bases 9 can be formed on the straight longitudinal edges of the 
sheet-metal blank 20. However, in producing the sheet-metal blank, the 
narrow sides or bases 9 can also be outwardly convex as indicated by 
broken lines in FIG. 2 at 9a. 
The apex angle of the vertex lying along the longitudinal edge 7 or 8 is 
designated at 6. The width of the narrow side of each triangular surface 
is designated 14 and the width of the truncated apex (forming the small 
base of a trapezoid) is designated at 13 in FIG. 1. 
The front and rear end edges are shwon at 11 and 12. 
Depending upon the size of the angle 6, the triangular regions are of large 
or small area. The triangular surface regions are curved by forming 
cascade-shaped steps in a zig-zag configuration at the fold lines, the 
folding taking place so that the element is twisted at the same time about 
its longitudinal center line or its longitudinal axis which corresponds to 
the longitudinal axis of the pipe. The twist may either be in the 
left-hand sense or in the right-hand sense depending upon the direction of 
folding. 
As has previously been described in connection with FIG. 1A, the mixing 
element is usually received in a pipe section so that the clear inside 
diameter D of the pipe corresponds substantially to the width of the 
sheet-metal element. 
As seen from the twist axis of the element, the height of the steps changes 
according to the longitudinal edges 7 and 8. A zig-zag path of the 
longitudinal edges is formed by cutoff apices 10. If the apices are not 
cut off or truncated, then a smooth helical path of the longitudinal edges 
is assured, these edges being formed only by the bases of the triangular 
regions. 
The twisting of the element is represented at 15 in FIG. 1 schematically 
and is shown to be helical about the longitudinal axis 15a of the element, 
this longitudinal axis coinciding with the axis of the pipe. 
In the embodiment illustrated in FIG. 1, the end edges 11 are inclined to 
the pipe axis. If one would have cut the triangular regions 4 and 5 which 
enjoin the end edges along the respective angle 6 so as to bisect the 
latter, the end edges would run perpendicular to the pipe axis as is 
possible in accordance with another embodiment of the invention. 
Even where relatively thin materials are used for making the sheet-metal 
elements of FIG. 1, there is a high degree of rigidity and stability of 
shape because of the zig-zag configuration and cascade formation of the 
steps. Coatings thus can be anchored effectively to the surfaces which are 
inclined to one another. 
The blank 20 of FIG. 2 has an end element forming the edge 21, as shown at 
23, so that the edge, upon twisting, will run perpendicular to the pipe 
axis. 
The mixing element shown in FIG. 3 at 30 is constituted of two halves A and 
B joined together along the axis 31 of the mixing element, e.g. by 
welding, overlap joints or interlocking seams. 
Each of the mixing element halves or portions have triangular surface 
regions 34 and 35 which are folded and converge in opposite directions in 
the manner previously described and alternating with one another. 
The triangular surface regions 34 abut in the region of the element axis 31 
at their triangular bases while the surface regions 35 terminate at this 
axis with their apices 54. 
The surface regions 34 each lie in pairs in a common plane while surface 
regions 35 of the two halves A and B lie in different planes. The apex 
angles 50, 51 of surface regions 34 are of the same size while the apex 
angles 52, 53 of the surface regions 35 are also of the same size. 
The halves A and B are in each case formed from a flat annular sheet-metal 
disk portion 36 and assembled in mirror image along their longitudinal 
axis 31. 
The end edges of the elements can be of different construction. The lower 
end edge 60 is here shown to be arranged at right angles to the element 
axis 31. If a cut were made at the lower region of the element along the 
triangular edges then at the lower end an obtuse angle would be seen. At 
the upper end of the embodiment of FIG. 3, this obtuse angle is shown to 
be formed by the edges 41a. If a cut were taken along the edges 41b, 
therefore, it would be a reflex angle of the two end edge regions. 
The sheet-metal disk shown in FIG. 4 has fold lines 37 and 38 so oriented 
that fold lines 37 on the disk are tangential to a small diameter circle, 
i.e. run past, at a small spacing, one side of the center of the disk 39. 
The fold lines 38 on the opposite side run past at a larger spacing. 
The sheet-metal disk is cut through at 40 and 41 along fold lines 40a and 
40b or along fold lines 41a or 41b, respectively, according to the desired 
orientation of the end edges of the element in FIG. 3. 
The inner edge 31a of the annular sheet-metal disk is then stretched out 
during folding of the sheet-metal disk portion along the fold lines 37, 38 
into a straight line which coincides with the element axis 31. The two 
element halves A and B are connected along this inner edge by means of 
soldering, welding, gluing or, preferably, by means of the overlapping 
connection previously described. Thus inside the disk, triangular 
extensions can be attached to the edges 31a which are pushed over the 
smaller of the triangle portions 34 to the other half and in the same 
plane therewith. A particularly firm connection of the two halves of the 
element can be effected by means of these overlapping portions. 
However, separate overlapping portions may be provided as shown in 79 and 
80 in FIGS. 6 and 7, these being matched to the triangular surface 
portions lying in the same plane and overlapping two related triangular 
portions of the element halves A and B. The overlapping portion in FIG. 6 
serves to connect the element halves as shown in FIG. 3 while in FIG. 7 an 
overlapping part is shown which can be used with mixing elements 
fabricated from the modifying disk illustrated in FIG. 1. 
In the embodiment of FIG. 4 the central circle which is produced by the 
tangential orientation of extensions of the fold lines 37, has its 
diameter so selected that it is equal in length to the narrow side 31a of 
the smaller triangular surface regions 34. 
Folding along the fold lines is effected so that the element halves are 
twisted about the common axis 31 and thus define cascade-shaped stepped 
and coiled flow paths. 
The larger the ratio between the angles 50, 51 on the one hand and 52, 53 
on the other hand, the shorter will be the entire element. The surface 
elements of different size thus form steps with step depths corresponding 
to the expanse of the smaller triangular surface regions. 
The step depth decreases from the element axis 31 to the longitudinal edge 
36. The step area is determined by the element of the large triangles. 
This area increases from the element area axis 31 to the longitudinal 
edges 36. Large surface regions that lie adjacent to each other and belong 
to the two series A and B, lie in different planes and therefore are 
rotated with respect to one another. 
The disk of FIG. 5 provides an extreme surface ratio between a smaller 
triangle and large triangle as can readily be seen. 
The fold lines 71 and 72 run past the center of the disk on both sides of 
it at equal spacings so that the angle bisectors 74 of the small triangle 
pass through the center of the disk. 
The inner opening of the annular disk is here polygonal with an edge length 
75 corresponding to the base of the smaller triangle. The separation 
through the annular disk is effected at 76 and at 78. The central opening 
has been shown at 77. 
From the small length of the narrow sides 75 it can be seen that an element 
of very small length can be obtained relative to the diameter. Here too, 
after separation, zig-zag folding is effected with twisting and two 
identical elements are assembled in mirror-symmetrical relationship along 
the element axis, e.g. where the overlapping elements are shown at 80 in 
FIG. 7. The resulting mixing element thus has an incoming flow angle which 
is approximately 180.degree. and is equal to the fold angle. The element 
length corresponds to 0.39 times its diameter. The angle of increase of 
the element amounts to 72.degree. with the element having four stages 
containing five large and five small surface regions. 
Because of the different inclinations of the end regions and a different 
edge path of the two edges of each element, different loads may arise on 
the material, different loadings resulting also depending upon the 
direction of flow of the material across the mixing element. Another 
element may be provided which is rotated through 180.degree. about the 
axis of the device from the first. This has been found to be desirable for 
the element fabricated from the disk of FIG. 4. 
In the element fabricated from the disk of FIG. 5, there are identical 
incoming flow ratios from either side of the device. By joining the inner 
edges of several element parts in a star configuration, more than two flow 
channels extending over the length of the elements can be obtained and the 
element parts can be mutually offset along the element axis.