Agitating – Stationary deflector in flow-through mixing chamber – Angularly related flat surfaces
Reexamination Certificate
2001-12-12
2003-10-28
Soohoo, Tony G. (Department: 1723)
Agitating
Stationary deflector in flow-through mixing chamber
Angularly related flat surfaces
Reexamination Certificate
active
06637928
ABSTRACT:
This invention relates to a static mixer, comprising at least a hollow housing with a multiplicity of mixer elements, which are arranged such that they are stacked in the housing. The hollow housing is defining an internal longitudinal passageway within which mixer elements are arranged. The mixer elements are planar elements having projecting longitudinal components.
For the mixing of liquids, static mixers are often used, whereby a pump forces the liquids through a tube provided with static mixer internals.
The following two devices are mentioned as examples of known static mixers:
In the case of the so-called Kenics mixers (see “Mischen beim Herstellen und Verarbeiten von Kunststoffen” [mixing in the preparation and processing of plastics], published by VDI Ges. Kunststofftechnik, VDI-Verlag 1986, pages 238-241), the liquid flow of the product to be mixed is divided into several individual streams by a separating plate fitted into the tube. This separating plate is twisted about the tube axis. In each of the individual streams, an eddy flow is produced, which leads to the liquid being redistributed in the cross section of the tube. In practice, a plurality of such mixing elements are arranged one behind the other in order to keep re-dividing the liquid and to achieve an adequate mixing result. Satisfactory mixing is typically achieved only after passing the liquids through 10 to 12 of such mixing elements.
The so-called SMX mixers (cf. U.S. Pat. No. 4,062,524) comprise two or more mutually perpendicular grids of parallel sheet-metal strips, which are welded to one another at their crossing points and are set at an angle with respect to the main direction of flow of the product to be mixed, in order to divide the liquid into several individual streams and mix it. The manufacturing effort for these mixers is very high because of the many weld connections required. A single mixing element alone is unsuitable as a mixer, since thorough mixing only takes place along a preferential direction transverse to the main direction of flow. Therefore, a plurality of mixing elements which are turned through 90° with respect to one another must be arranged one behind the other. Thorough mixing typically requires at least 5 or 6 elements.
This can be explained as follows: an SMX mixer has only two grids of parallel bars turned through 180° with respect to each other. These grids comprise layers of equi-distant bars. Neighboring layers are arranged in line with one another. Each layer represents a plane of symmetry which is not crossed during mixing.
The object of the present invention is to provide a static mixer which achieves the good mixing effect of the SMX mixer and combines this with minimal production requirements.
The object is achieved according to the present invention by a static mixer comprising a hollow housing defining an internal longitudinal passageway, having a longitudinal axis, within which a plurality of planar mixer elements are arranged, one after the other such that they are stacked in the housing to form an assembly of mixer elements, said planar mixer elements are comb- or star shaped planar elements with a central bar on which at least two teeth are provided on each of both sides of the bar and wherein adjacent mixer elements within the static mixer are rotated about the longitudinal axis of the longitudinal passageway of the housing by an angle &agr; with respect to each other so that one tooth of a mixer element in each case reaches into the intermediate space between two teeth of a respectively adjacent mixer elements.
Preferably, the turning angle &agr; is from 35° to 160° with particular preference for a turning angle of from 45° to 135°.
When so turned with respect to each other, one of the longitudinal components of a mixer element may project into the space between the longitudinal components of a neighboring mixer element.
The comb shaped elements preferably can be described as having
a) first and second longitudinal components, each having two transverse edges and two longitudinal edges; said two longitudinal components being spaced apart from each other and connected to each other by a third longitudinal component having two transverse edges and two longitudinal edges, one transverse edge of said third longitudinal component being connected to one longitudinal edge of one of said first and second longitudinal components, and the other transverse edge of said third longitudinal component being connected to one longitudinal edge of the other of said first and second longitudinal components, and optionally having one or more further longitudinal components between and spaced apart from said first and second longitudinal components and from each other, and joined to each other and to said first and second longitudinal components by said third longitudinal component, or
The star shaped elements preferably can be described as having
b) first and second longitudinal components which intersect each other to form a figure
wherein &ggr; represents an angle &agr; of from 10° to 170° , preferably 45° or 90°.
Preferably, the shape of the planar mixer elements define an H, or X.
In further embodiments, the mixer elements which comprise two spaced apart longitudinal components which are connected by a third longitudinal component may further comprise at least one further longitudinal component between and spaced apart from the two spaced apart longitudinal components, and also connected to the two longitudinal components by the third longitudinal component.
The X-shaped mixer element may, of course, also comprise one or more further longitudinal components (teeth) which cross at least one of the two longitudinal components defining the X-shape.
Preferably, each mixer element contacts at least one adjacent mixer element.
In a particularly preferred embodiment, the longitudinal components (teeth) of the mixer elements have at least one end which is shaped to provide for line or surface contact with the internal surface of the hollow housing defining the internal passageway. This increases the stability of, for example, a loose stack of mixer elements in the housing. Preferably, said at least one end of the longitudinal components has a transverse edge which has a width and a length, and is rounded across the length of its transverse edge.
Particular stability of the assembly of mixer elements is achieved if, in a preferred design, two neighboring mixer elements contact one another at at least three different points. As a result, the mixer elements are stabilized against displacement in relation to one another.
The stability is further increased in an embodiment of the mixer in which mixer elements which are one removed from each other, i.e., having a third mixer element between them, contact each other, in addition to contacting a mixer element between them.
This produces a particularly high mechanical load-bearing capacity and stability. The mixer elements thereby hold one another in their respective positions.
A particularly preferred variant of the static mixer comprises H-shaped mixer elements, wherein the planes of neighboring H-shaped mixer elements are turned with respect to one another by an angle &agr; of 100°-110°.
This is because, although an angle close to 90° would lead to a good mixing effect, the stated angular range of 100°-110° enables the ends of the longitudinal components mixing elements that are one-removed from each other to extend past one another without colliding. To clarify the meaning of the expression “the ends of the longitudinal components”, such “ends” of H, X shaped mixer elements are shown as a, b, c and d in the following representations of such mixer elements:
Likewise preferred is a static mixer wherein the mixer has H-shaped mixer elements, and the diameter of the housing is 3.5 to 5 times the (teeth) width of the space between adjacent ends of the longitudinal components. Examples of this distance, referring to the H configuration shown above, are the distance from a to b and c to d.
In this embodiment, the mixing effect
Bayer Aktiengesellschaft
Norris & McLaughlin & Marcus
Soohoo Tony G.
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