Agitating – Stirrer within stationary mixing chamber – Rotatable stirrer
Reexamination Certificate
1998-08-14
2001-05-08
Cooley, Charles E. (Department: 1723)
Agitating
Stirrer within stationary mixing chamber
Rotatable stirrer
C366S149000, C366S286000, C366S294000, C366S295000, C366S296000, C366S305000, C366S313000, C366S314000
Reexamination Certificate
active
06227698
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to an apparatus for processing dispersions of solids in a fatty phase.
Such an apparatus has been disclosed, for example, in EP-A-279255 and is used for reducing the viscosity of chocolate materials by means of shear forces between the two parts rotatable relative to one another, the outer of which usually being a stator forming a container, and the inner of which being the rotor exerting the shear forces. However, as is known in the case of other apparatuses acting with shear force, such as, for example, in the case of stirred ball mills, the function of the two parts can also be interchanged, the outer part being rotated and the inner part being stationary, or both parts can be driven and caused to rotate. Usually, both parts have shearing tools on the inner surfaces facing one another, which tools form shear gaps on the one hand between their radial end and the opposite circumferential wall and on the other hand also between one another.
SUMMARY OF THE INVENTION
If the object is to reduce the viscosity of chocolate, it is necessary to rely on the knowledge available to a person skilled in the art, according to which, in the course of liquefaction from a dry state, the chocolate is converted into a doughy, pasty state before it then finally reaches a liquid state. Depending on these different states, the energy consumption per time unit for processing such a material (and this applies in a similar manner to all materials containing solids in a fatty phase) differs very greatly, namely generally decreases.
In a first conceptual step, the invention is based on the following knowledge: if chocolate were actually to be allowed to pass through the known apparatus, the maximum power consumption would occur in the region of the feed orifice, whereas the chocolate would have become less viscous towards the outflow side and it would therefore be necessary to consume less power through shearing. This means nonuniform loading of the apparatus on the one hand and, on the other hand, that the efficiency of the apparatus decreases towards the outflow.
If the invention then examines the cause of this property of the apparatus in a further conceptual step, it is found that this phenomenon is primarily due to the cylindrical design of the two parts which are rotated relative to one another and whose uniform diameter permits only a uniform processing speed (with decreasing viscosity). This is because the shear stress &tgr; is obtained from the relationship &tgr;=D·eta, where D is the shear velocity (velocity of the moving surface divided by the gap width) and eta is the viscosity of the material.
In a further conceptual step, the invention is based on the consideration that it must be possible to increase the shear velocity. However, since the shear effect occurs chiefly at the shearing tools, this is achieved, according to the invention, by conical arrangement of the processing container with smaller end on the side of the feed orifice.
When the term cone is used in this context, it must be remembered that, according to Lueger “Lexikon der Technik” [Dictionary of Technology], Rowohlt Taschenbuch Verlag, 1972, page 704, a cone can be bounded not only by straight generators, as is the case with a proper cone, but also by curved generators, in which case the term improper cone is used. This is important in the present case because a relationship deviating from a straight line arises per se from the above-mentioned mathematical relationship. However, it can be very well approximated with a straight line, so that the cone may also readily be a “proper cone”.
Increasing the diameter of the processing container towards the outflow results, in the shear gap between the particular shearing tool and the radially opposite circumferential wall on the one hand and axially between the intermeshing shearing tools on the other hand, in a higher velocity which leads to an increase in the shear velocity and hence to at least partial compensation of the shear stress caused by the reduction in the viscosity.
Although under these conditions the inner of the two parts may be formed in any desired manner, for example it may also be cylindrical, another formation is preferred, wherein the increase in the volume due to a conical widening of the processing container is at least partly compensated, so that the residence time of the material in the individual zones is evened out over the axial length of the apparatus.
The fact that, according to the invention, the processing container is conical and widens in the direction of flow of the dispersion also focuses attention on the arrangement of the shearing tools from new points of view. On the one hand, particularly in the case of a conical shape of the second, inner part, this will give rise to additional surfaces on which such shearing tools can be mounted; on the other hand, it is in fact intended to increase the shear effect towards the outflow.
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Cooley Charles E.
Farber Martin A.
Richard Frisse GmbH
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