Mixer for viscous liquids and masses

A mixer for viscous liquids and masses has a stationary first housing of circular cross section preferably disposed horizontally with inlet and outlet means for the material to be processed and surrounding a driven inner coaxial rotatably mounted second housing. The annular space jointly limited by the two housings with closing portions disposed on the faces contains a number of axially parallel mixer shafts driven in the same direction and disposed in a ring which perform a common revolving motion about the longitudinal axis of the housing. The mixer shafts extend with their envelopes as far as the inner and outer walls of the two housings leaving small gaps free. The mixer shafts formed as screw conveyors at least in portions are combined into meshing groups.

FIELD OF THE INVENTION 
The present invention relates to a mixer for viscous liquids and masses 
having a housing of circular cross section with feeding and removing means 
for the material to be processed and a number of axially parallel mixer 
shafts driven in the same direction which are disposed in a ring within 
the housing and perform a common revolving motion about the longitudinal 
axis of the housing. 
BACKGROUND OF THE INVENTION 
Mixers for viscous liquids and masses are known in manifold embodiments. 
They usually work with stirring or kneading tools which rotate within a 
housing and might perform a planetary motion in addition to the rotary 
motion about their own axis. For example DE-C 439 990, from which the 
invention departs, describes an apparatus for refining chocolate or 
similar plastic masses wherein mixer shafts in the form of rolls are 
disposed within a cylindrical housing so as to revolve about a center roll 
and simultaneously rotate about their own axes in the same direction, all 
or individual rolls--possibly including the center roll--having openings 
such that the material to be processed is able to penetrate them 
perpendicular to their longitudinal axis. The roll openings can be twisted 
helically, the result being that the material to be processed undergoes 
not only a motion perpendicular to the roll axis but also one in the 
longitudinal direction of the rolls. This device requires comparatively 
complicated mixing tools and is not readily suitable for processing 
viscous liquids for example. Furthermore it is difficult to clean, and 
mainly limited to its special purpose, namely the refining of chocolate 
masses. 
In addition there are so-called thin-layer reactors (compare for example 
DE-C 30 30 541) which likewise work with shafts disposed in a ring within 
a cylindrical housing. The shafts bear meshing, in particular disk-shaped 
treating members for the material to be processed which limit thin gaps 
with each other through which the material is conveyed while being 
simultaneously spread in a thin layer. The material to be,processed is 
brought from a thick-layer side onto a thin-layer side where a vacuum may 
be effective to cause degassing of the material spread in a thin layer. 
With such thin-layer reactors one strives for a comparatively long sojourn 
time of the material to be processed in the reactor. Although they permit 
viscous media, for example molten polymer masses or the like, to be mixed 
with additives they are neither intended nor suitable for use strictly as 
mixers for viscous liquids or masses. 
SUMMARY OF THE INVENTION 
The invention is directed to the problem of providing a mixer characterized 
by a very good mixing effect and more versatile possibilities of 
application while having a simple structure, whereby the mixing tools are 
simultaneously forced to clean one another on their entire surfaces 
perfused by the material to be processed due to their differential speeds 
relative to one other. 
This mixer can be constructed alternatively as a continuous or 
discontinuous mixer, in the first case having material to be mixed flowing 
through it in continuous operation and in the second case processing a 
certain amount of material batchwise. Typical applications for such 
continuous mixers are for example the production of pharmaceuticals, 
lubricating greases, paints, lacquers, adhesives, etc., while 
discontinuous mixers are used in many ways in pharmacy, chemistry and the 
like when continuous operation would be inexpedient for economic reasons 
due to the small batch amounts. 
In the new mixer adjacent screw conveyors are combined into groups, each 
group containing at least two screw conveyors meshing with their spirals 
of like pitch while the contiguous screw conveyors of adjacent groups are 
disengaged from each other. The material to be processed is conveyed in a 
certain axial direction by the screw conveyors of each group generally 
comprising one pair of screw conveyors meshing with their spirals, while 
there is no axial conveyance in the areas between adjacent groups, the 
so-called "mixing wedges". In these areas a backflow can form; 
simultaneously a level compensation takes place. With continuous mixers 
the screw conveyors of the mixer shafts of all groups have the same 
conveying direction, while with discontinuous mixers the assembly is such 
that the screw conveyors of the mixer shafts of adjacent groups have an 
opposite conveying direction. In particular with discontinuous mixers it 
is expedient if the contiguous screw conveyors of adjacent groups are 
directly adjoining with the envelopes of their spirals, except for the 
necessary narrow working gap. Chiefly with continuous mixers, however, it 
can be advantageous if contiguous screw conveyors of adjacent groups limit 
a space therebetween which is selected in accordance with the viscosity of 
the material to be processed. In general, the higher the viscosity the 
greater the spacing between adjacent groups. 
Apart from exceptional cases, the two interconnected housings of the new 
mixer are disposed horizontally, i.e. with horizontal alignment of the 
mixer shafts in the working position. The working level for the material 
to be processed is then advantageously located in the annular space 
approximately in the area of the upper boundary of the inner housing. It 
should be noted that the annular space must never be completely filled 
with material to be processed. 
The outer housing can be provided with connecting means for an overpressure 
or vacuum source, making it possible for example to vent released gaseous 
components during the mixing operation, or to have a mixing operation take 
place under gas overpressure, for example in a protective atmosphere, 
depending on the type of material to be processed. 
Because the inner housing is of rotating design with the outer housing 
stationary, the drive of the mixer shafts can be derived from the rotating 
inner housing, the inner housing being fitted to be coupled with a power 
source. This can be solved constructionally by connecting the inner 
housing with at least one coaxial gearwheel associated with an internal 
geared wheel disposed in rotationally firm fashion on the outer housing, 
the mixer shafts bearing rotationally firm pinions engaging the gearwheel 
and the internal geared wheel. 
If the gearwheel, internal geared wheel and pinions are spur toothed, axial 
bearings fixed on the housing should be provided in the area of the 
closing portions on the faces of the annular space to take up the axial 
forces acting on the mixer shafts during operation of the mixer shafts. 
Such separate axial bearings can be dispensed with if the mixer shafts are 
supported on the end only via their pinions on an associated internal 
geared wheel and a gearwheel associated with the inner housing, whereby 
the inner housing is also supported on the end only via a gearwheel, the 
pinions of the mixer shafts and an internal geared wheel on the outer 
housing. The axial forces are thereby taken up by the gearing portions 
present for driving the mixer shafts themselves. 
For this purpose the particular gearwheel, the corresponding internal 
geared wheel and the pinions are helical toothed. On at least one end of 
the mixer shafts the helical toothed gearwheel of the inner housing has 
associated therewith on the outer housing an internal geared wheel with 
opposing helical toothing, each mixer shaft bearing on the end an 
accordingly toothed pair of pinions, one pinion of which engages the 
gearwheel and the other of which the internal geared wheel. 
Depending on the purpose of the desired sojourn time of the material to be 
processed in the mixer and the mixer's mode of operation (continuous or 
discontinuous) one can use single-, double-, triple- or multi-start worm 
shafts. In general, worm shafts with a higher number of starts (in 
particular triple-start worms) obtain a better mixing effect with a short 
sojourn time. For reasons of economy it is expedient to construct the 
mixer so that the worm shafts can be readily replaced without requiring 
any great reconstruction measures. To make this possible the pinions are 
advantageously connected positively with the particular mixer shaft by 
means of a serration whose number of teeth is divisible integrally by the 
number of mixer shafts. As precise tests have shown, this permits the 
correct mutual angular association to be obtained for all cooperating 
pairs of screw conveyors by simply slipping the pinions onto the mixer 
shafts in the corresponding angular position. 
The mixer shafts are preferably supported axially and radially on the end 
only via their pinions on an internal geared wheel and a gearwheel. 
Similarly it is advantageous to support the inner housing on the end only 
via its gearwheel, the pinions of the mixer shafts and the associated 
internal geared wheel on the outer housing. Also, the internal geared 
wheel and/or the gearwheel are braced preferably elastically against the 
associated mixer shafts in the axial direction on at least one side of the 
housing.

DETAILED DESCRIPTION 
The continuous vacuum mixer shown in a first embodiment in FIGS. 1 to 3 has 
cylindrical outer housing 1 bearing on each face sealingly welded ring 
flange 2 and provided on its outer circumferential surface over most of 
its axial length with circumferential spiral grooves 3 closed off from the 
outside by jacket 4. During operation a tempering medium, for example oil, 
water or the like, can flow through spiral grooves 3, if required, in 
order to remove heat from or supply heat to the material to be processed 
during the mixing process. A pair of connecting pieces 5 communicating 
with spiral grooves 3 serve to connect a corresponding tempering medium 
source. 
Outer housing 1 surrounds coaxial cylindrical inner housing 6 of smaller 
diameter which bears on each face tightly welded, inwardly protruding ring 
flange 7 and radially limits annular space 8 together with outer housing 
1. 
Housings 1, 6 are disposed horizontally, i.e. with horizontal longitudinal 
axis 9, whereby outer housing 1 is stationary and inner housing 6 is 
mounted to rotate about longitudinal axis 9 relative to outer housing 1. 
In the center between ring flanges 2 vacuum or overpressure connecting 
chamber 10 is joined sealingly to the top of outer housing 1. Chamber 10 
is sealed from the outside by viewing glass 11 and has connecting piece 
120 for a vacuum or overpressure source (not shown) leading thereinto. 
In annular space 8 a number of axially parallel mixer shafts 12 are 
disposed in a ring which are formed in the shown embodiment example as 
screw conveyors with spirals 13 of like pitch over their total length. The 
diameter of mixer shafts 12 is selected so that envelope 160 of each mixer 
shaft 12 formed by an imaginary cylindrical rotational body extends as far 
as the inner wall of outer housing 1 and the outer wall of inner housing 6 
leaving a small working gap free. All mixer shafts 12 are driven in the 
same direction, as indicated in FIG. 1 by arrows 14. Simultaneously mixer 
shafts 12 disposed in a ring perform a common revolving motion about 
longitudinal axis 9 during operation which, like the rotary motion of 
mixer shafts 12 about their particular longitudinal axis 15, is derived 
from the rotating motion of inner housing 6 indicated by arrow 16 (FIG. 
1). 
Instead of or in addition to spirals 13, mixer shafts 12 could also bear 
(perhaps in certain portions) other mixing tools, e.g. in the form of 
paddles, toothings or the like if this appears expedient in view of the 
type of material to be processed. For the same reasons it would also be 
conceivable to give spirals 13 openings at least in certain portions. 
As in particular the developed view of mixer shafts 12 in FIG. 7 indicates, 
two mixer shafts 12 formed as screw conveyors are combined in each case 
into groups 17 whose spirals 13 have the same pitch and mesh with narrow 
working clearance. The embodiment example shown in FIG. 1 has eight such 
groups 17 each containing one pair of mixer shafts 12, as mentioned. It is 
basically also possible to combine more than two mixer shafts 12, e.g. 
three or four mixer shafts, in group 17 in which mixer shafts 12 mesh with 
spirals 13. 
Outer mixer shafts 12 of adjacent groups 17 do not mesh with spirals 13 of 
their screw conveyors. In the embodiment of FIG. 1 the assembly is such 
that envelopes 160 of contiguous mixer shafts 12 of adjacent groups 17 
extend directly up to each other and touch, with consideration of the 
necessary working clearance. 
Depending on the type and viscosity of the material to be processed, 
however, a greater distance can also be provided between end mixer shafts 
12 of adjacent groups 17, as shown clearly by the embodiment example in 
FIG. 4. Here there are only six groups 17 of mixer shafts 12 with a 
comparatively great distance referred to as 19 present therebetween, which 
corresponds to about one half the diameter of envelope 160. The embodiment 
of FIG. 4 is suitable in particular for high-viscosity media. 
The drive of mixer shafts 12 and their support are apparent in particular 
from FIGS. 2, 3 which correspond to FIGS. 5, 6 of the second embodiment 
example of FIG. 4 and to FIGS. 9, 10 of the third embodiment example of 
FIG. 8. It therefore suffices to explain these parts only once with 
reference to FIGS. 2, 4; in FIGS. 5, 6 and 9, 10 the same parts are 
referred to by the same reference numbers as in FIGS. 2, 3. 
Fitted sealingly on ring flanges 2 of outer housing 1 are two internal 
geared wheels 21, 22 which are pinned, i.e. connected in rotationally firm 
fashion, with particular ring flange 2 by means of alignment pin 23. 
Internal geared wheel 21 is followed by thrust ring 24 which is axially 
braced with corresponding ring flange 2 via internal geared wheel 21 
located therebetween. Seal rings 26 located therebetween ensure proper 
sealing conditions between internal geared wheel 21 and thrust ring 24 as 
well as ring flange 2. 
Fitted sealingly on ring flange 7 of inner housing 6 coaxially to internal 
geared wheel 21 is gearwheel 27 which is pinned to ring flange 7 at 28 in 
rotationally firm fashion and followed on the outside by housing ring 29 
which is axially braced via gearwheel 27 by screw bolts 30. Seal rings 26 
are again disposed in the area of the cylindrical parting lines of the 
parts belonging together. 
Provided in the annular gap limited between thrust ring 24 and housing ring 
29 is seal unit 32 whose structure is seen in particular from FIG. 12. 
Seal unit 32 has locking ring 31 and fastening ring 33 which is fitted on 
the outside of thrust ring 24 and screwed to thrust ring 24 in 
rotationally firm fashion by means of screw bolts 34 (FIG. 2). Seal rings 
26 are provided between locking ring 31 and fastening ring 33 as well as 
housing ring 29. Disposed on the outer lateral surface of locking ring 31 
between the two seal rings 26 is annular groove 310 where a plurality of 
radial bores 35 originate, leading inwardly and crossing locking ring 31. 
Also, bore 36 present in thrust ring 24 opens into annular groove 310 so 
as to form a radial channel. Between inside opposing faces of locking ring 
31 and of fastening ring 33 two lip seal rings 324 with opposing sealing 
lips are mutually braced in pressure sealed fashion via two elastomer 
rings 323 with spacer ring 320 located therebetween. Disposed on the outer 
periphery of spacer ring 320 in the longitudinal center is likewise 
annular groove 321 into which radial bores 35 open from the outside and 
from which further radial bores 325 are guided inwardly to end in inside 
sealing lip space 322. In this way sealing lip space 322 can be subjected 
from the outside via connecting fitting 37 on bore 36 to a sealing medium, 
for example oil, gas, water vapor, etc., the type of which depends on the 
material to be processed. 
The working pressure in sealing lip space 322 is selected so as to be no 
more than one bar above the working pressure present in working space 8 so 
that the life of the sealing lips of lip seal rings 324 is not 
unnecessarily shortened. To ensure particularly good frictional conditions 
between the sealing lips and the lateral surface of housing ring 29 the 
lateral surface is provided with oxide ceramic layer 290 whose surface 
quality is under 0.4 microns. It is also particularly advantageous for the 
life of these sealing lips that the kind of drive provided permits no 
radial clearance of housing ring 29. 
If required, a cooling ring can be provided at this place instead of 
locking ring 31, a measure to be considered in particular when the 
material to be processed is thermoplastic and held at an elevated 
temperature during the mixing operation. In this case the free-flowing 
material can pass into the bearing gap in which it is cooled by contact 
with the cooling ring so that the solidified material produces the 
vacuum-tight seal from the outside in this area itself. 
Connected with gearwheel 27 in rotationally firm fashion via splines is 
coaxial shaft end 40 which is used for coupling with a power source (not 
shown) and for setting inner housing 6 rotating. 
Engaging internal geared wheel 21 and gearwheel 27 for each mixer shaft 12 
are the pinions of pair of pinions 41 which are fitted on coaxial journal 
42 and connected therewith via a serration in rotationally firm fashion. 
Pressure screw 43 is used for axial fixation in each case. 
Internal geared wheel 21 and gearwheel 27 are each helical toothed, the two 
helical toothings being of opposite inclination. One pinion 44 of pair of 
pinions 41 meshes with internal geared wheel 21 while other pinion 45 
meshes with gearwheel 27. Regarded together the pair of pinions therefore 
has a double helical gearing. 
On the opposite side mixer shafts 12 likewise bear coaxial journal 42 on 
which pinions 46, 47 of pair of pinions 48 are fitted via a corresponding 
serration in rotationally firm fashion, being again fixed axially by 
pressure screw 43. One of pinions 46, 47 of each pair of pinions meshes 
with internal geared wheel 22 connected with outer housing 1 in 
rotationally firm fashion, while other pinion 46 engages gearwheel 49 
which is sealingly fitted on corresponding ring flange 7 and pinned 
thereto via alignment pin 28 in rotationally firm fashion. As on the 
driving side, internal geared wheel 22 is followed outwardly by thrust 
ring 24a connected via fastening ring 33a with locking ring 31a. The 
sealing of housing ring 29a from working space 8 was explained above with 
reference to FIG. 12, the corresponding reference numbers applying to 
FIGS. 3, 6, 10 with the addition "a" so that no repeated explanation is 
necessary. 
Pinions 46, 47 of pair of pinions 48 are helical toothed as on the driving 
side, the toothings being of opposing inclination. The helical toothings 
of internal geared wheel 22 and gearwheel 49 are also designed 
accordingly. To ensure that mixer shafts 12 are supported substantially 
free from play axially and radially and any unavoidable differences in 
length of mixer shafts 12 taken up, internal geared wheel 22 and gearwheel 
49 are springily prestressed axially relative to internal geared wheel 21 
at the driving side and gearwheel 27 at the driving side. For this purpose 
spring assemblies 50 are fitted on screw bolts 25a connecting thrust ring 
24a with ring flange 2 as well as on screw bolts 30a connecting housing 
ring 29a with ring flange 7 for springily prestressing in the longitudinal 
direction internal geared wheel 22 guided in longitudinally displaceable 
fashion in outer housing 1, or gearwheel 49 guided in longitudinally 
displaceable fashion on inner housing 6. Simultaneously internal geared 
wheel 22 and gearwheel 49 can perform a small wobbling motion against the 
effect of Belleville spring assemblies 50 to compensate the abovementioned 
length tolerances of mixer shafts 12. 
It is fundamentally also possible to design the pinions of only one of 
pairs of pinions 41, 48 with the explained helical toothing and form the 
other pair of pinions with a spur toothing, the corresponding internal 
geared wheel or gearwheel then being toothed accordingly. In this case the 
springy support of the internal geared wheel and gearwheel on one side of 
the housing can be dispensed with, i.e. spring assemblies 50 omitted. 
With the described gear formation of the drive for mixer shafts 12 no 
separate axial or radial bearings are evidently necessary in the closing 
portions on the faces of stationary housing 1, which applies equally to 
the support of inner housing 6. Mixer shafts 12 and inner housing 6 are 
supported both radially and axially only via their pinions 44, 45 and 46, 
47 or gearwheels 27, 49 on stationary internal geared wheels 21, 22. 
The splines positively connecting pinions 44, 45 and 46, 47 with mixer 
shaft journals 42 are formed such that their number of teeth is divisible 
integrally by the number of mixer shafts 12. Due to the possible use of 
double-start screw conveyors they should additionally be divisible by 
four. This makes it possible to replace mixer shafts 12 for different 
modes of operation without changing the pinions. The serration always 
ensures that the mixer shafts are driven with the correct mutual angular 
position to ensure proper engagement of spirals 13 of the screw conveyors 
of adjacent mixer shafts 12. 
During operation the material to be processed flows through the continuous 
vacuum mixer described with reference to two different embodiments in 
FIGS. 1, 4 via inlet and outlet connections 101,102, filling annular space 
8 up to level 51 which is just below the upper boundary of the inner 
housing, as indicated in FIGS. 1, 4. After the power source for shaft end 
40 is turned on, inner housing 6 and mixer shafts 12 disposed in a ring 
rotate in the direction indicated by arrows 16, 20, i.e. in the same, 
counterclockwise direction. Since the pinions of pairs of pinions 41, 48 
roll on the particular stationary internal geared wheel 21 or 22, mixer 
shafts 12 simultaneously perform a rotary motion about particular 
longitudinal axis 15 in the same direction, as indicated in FIGS. 1, 4 by 
arrows 14. Since the screw conveyors of mixer shafts 12 combined into 
individual groups 17 mesh with spirals 13, local forced transport of the 
material to be processed takes place in the area of groups 17 within 
annular space 8, directed toward the driving side with the formation of 
the screw conveyors selected for the embodiment example. This conveying 
direction is indicated by arrows 52 in FIGS. 2, 5 and 7 and opposes the 
direction of flow of the material through annular space 8. 
Since no forced transport of the material to be processed takes place in 
"mixing wedges" 53 (FIG. 7) or in large free spaces 19 in the embodiment 
of FIG. 4, a level compensation can take place in these areas so that a 
backflow comes about as indicated by arrows 53 in FIG. 7. 
The material to be processed is thus mixed not only between meshing spirals 
13 of mixer shafts 12 of groups 17 but also because axial flow conditions 
opposing the axial direction of flow of the material are produced in 
certain areas within annular space 8, and because the mixer shafts 
additionally perform their revolving motion about longitudinal axis 9 
thereby successively dipping into and emerging from the material contained 
within annular space 8. 
These necessarily interacting measures produce an excellent mixing effect 
in the material to be processed. 
FIGS. 8 to 11 illustrate a modified embodiment of the novel mixer in the 
form of a discontinuous vacuum mixer. The basic structure of this mixer is 
the same as in the described embodiments of the continuous vacuum mixer 
according to FIGS. 1 to 7. The same parts are therefore provided with the 
same reference numbers and not explained again. 
The discontinuous vacuum mixer differs from the above-described embodiments 
in that inlet and outlet connections 101,102 for the material to be 
processed on outer housing 1 are replaced by processed material outlet 103 
disposed sealingly on the outer housing in the longitudinal center and 
provided with stopper 104. Also, the screw conveyors of mixer shafts 12 
are formed and combined with each other into groups 17 in such a way, as 
apparent from FIG. 11, that meshing spirals 13 of the screw conveyors of 
adjacent groups 17 result in opposing conveying directions 520 for the 
local forced transport of the material to be processed. In mixing wedges 
530 between individual groups 17 a certain flow also comes about here for 
level compensation, but the material to be processed is conveyed on 
substantially closed flow paths within the annular space between adjacent 
groups 17 because the forced conveying direction of adjacent groups 17 is 
axially opposed. 
During operation a proportioned amount of material to be processed, 
dimensioned so that maximum level 51 is not exceeded, is introduced into 
the annular space via connecting chamber 10 with the stopper in place, for 
example with viewing cover 11 removed. After the mixing time necessary for 
the particular material to be processed the thoroughly mixed material is 
let out of annular space 8 again with stopper 104 removed, whereupon 
annular space 8 may be thoroughly rinsed to prepare the mixer for the next 
batch. Such rinsing of annular space 8 can also be provided in the 
continuous vacuum mixer of FIGS. 1, 4 if the material to be processed is 
to be changed. 
Finally it should be mentioned that if mixer shafts 12 are very long they 
can be supported in at least one place between their end bearings to 
prevent sagging of mixer shafts 12. This can be achieved in a simple way 
if a gearwheel disposed on inner housing 6 meshes at the supporting place 
with pinions of pairs of pinions fitted on mixer shafts 12, the other 
pinion of each pair meshing with an internal geared wheel on outer housing 
1. The same gearing conditions therefore fundamentally exist at the 
particular supporting place as were explained with reference to gearwheels 
27, 49 and associated pairs of pinions 41, 48 and corresponding internal 
geared wheels 21, 22 on the end. It suffices to provide these elements 
with spur toothings in each case.