MXPA98007392A - Module forming part of a static mixer arrangement for a plastically flowable material to be mixed having a critical dwell time - Google Patents

Abstract

The invention concerns a module (3) forming part of a static mixer arrangement (2) which is provided for a plastically flowable material to be mixed (15, 16) having a critical dwell time. The arrangement (2) comprises a tubular housing (12) in which bars (31a, 31b, 32a, 32b) are disposed. The bars are inclined towards the longitudinal axis (20) of the housing and intersect substantially on a straight line (40), perpendicular to the longitudinal axis. The module comprises a sleeve (30) which can be inserted into the housing. The inner wall of the arrangement which deflects the material to be mixed is formed by sleeve interiors. The bars take the form of mandrels, each having a vertex (36) pointing towards the direction of movement (5) of the material to be mixed and a base (35) secured to the sleeve interior. Each vertex forms an intermediate space (6) relative to the inner wall of the arrangement.

Description

MODULE FOR A STATIC MIXER FOR A COMPOSITION -ri-UIBI-E, OF PLASTIC THAT GOES TO MIXING, WHICH IS CRITICAL WITH RESPECT TO THE MIXING TIME DESCRIPTION OF THE INVENTION The invention relates to a module for a static mixer according to the preamble of claim 1 for a flowable, plastic composition to be mixed, which is critical with respect to the drying time. The invention also relates to a corresponding mixer and to the uses of the mixer. In the manufacture of molded parts of Hard PVC, PVC in granulated and / or powder form is mixed with lubricants, stabilizers and other additives and the mixture is then treated in extruders to form a manageable composition. During this, the mixture is heated and pumped up to an adequate working pressure. Double screw extruders are advantageously employed. The intermediate product, thus produced, is, however, in a state that is not sufficiently homogeneous for the production of molded parts. Therefore, in static mixers of plants, the extruders and molding dies or tools are placed. In these mixed is, the mixture is homogenized and in fact - for the protection of PVC polymers - at low shear rates. PVC is a thermoplastic that can be worked at approximately 160 ° C. However, it is not thermally stable, since hydrogen chloride easily separates at 1 < 30 ° C. In the manufacture of sections of window of hard PVC the plastic is processed at temperatures between 190 and 200 ° C. At these temperatures the drying time in the static mixer is more critical. The drying time may turn out to be so long in special locations within the static mixer that discolorations and quality losses arise. As soon as the unfavorable phenomena are established, they increase very rapidly so that the manufacturing process must be inter- preted. Static mixers must be cleaned before the process is continued. The object of the invention is to further develop known static mixers of such more favorable conditions regarding the drying time are present and that a static mixer cleaning can be executed in a simple manner. This object is satisfied by a static mixer having a modular mixer structure and whose modules are defined by the features of claim 1. The module is a part of a static mixer that is provided with a flowable, plastic composition that is will mix that is critical with respect to drying time. The apparatus comprises a tubular housing in which bars are placed. The arms are inclined with respect to the longitudinal axis of the housing; they cross each other s'u s t an a lme n t e in a straight line pe pendicular to the longitudinal axis. The module comprises a sleeve that can be pushed into the housing. The inner wall of the device driving the mixing mass is fused by the internal sides of the sleeve. The briazos are formed in the form of rods each having a pointed tip or apex opposite the direction of movement of the composition to be mixed and a base attached to the inner side of the sleeve in each case. Each point forms a space intermediate coir with respect to the internal wall of the device. The module according to the invention or a mixer assembled from such modules can also be used for the processing of latex / rubber or other flowable plastic mass of a polymer that is critical with respect to the time of disposal. The dependent claims 2 to 6 relate to the advantageous embodiments of the module according to the invention. The object of the independent claims 7, 9 and 10 are the mixer, a plant with this mixer and the use of the mixer. The dependent claim 8 refers to an apparatus having modules that are particularly easy to clean. The invention will be explained below with reference to the drawings. Shown is: Figure 1 a schematic illustration of a plant for the manufacture of molded parts of hard PVC, Figure 2 is a section of a mixer with modules according to the invention.

Figure 3 is an illustration of the geometry of the bars of the module according to the invention, Figure 4 is a longitudinal section through a module according to the invention, and Figure 5 are the flow conditions of the composition around a bar molded in a special way. The plant 1 in Figure 1 comprises a screw extruder 11 (impeller) and a molding tool 13 which is located downstream thereof, with a mixer 2 which is provided after the extruder 11. A part of the plant 10, in which the initially mentioned mixture 14 of PVC particles, lubricants, stabilizers and other additives is produced, is placed in front of the extruder 11. In the extruder 11, the mixture 14 is converted by heating and compression to a mass 15 or composition which is homogeneous afterwards in the mixer 2 with the modules 3 according to the invention which are placed in a housing 12. The homogenized mixed composition 16 is molded into products such as, for example, window sections , in the die or molding tool 13.

Figure 2 shows a delivery of the longitudinally sectioned housing 12 of the mixer 2 with correspondingly sectioned sleeves 30, 30 'of the modules 3 according to the invention. The arms 31a, 31b, 32a and 32b are completely drawn; they are located partially in front of the section plane. The arm-s are formed in the form of bars, and in fact each has a tip 36 directed opposite to the direction of movement 5 of the composition being mixed and a base 35 attached to the inner side of the sleeve. Each tip forms an intermediate space 6 with respect to the internal wall of the device 2. The central module 3 shows its construction completely; in the adjacent modules only the lower part or the upper part respectively, are illustrated. The sleeve part 30 'located upwards which may be the lower part of a module or also a sleeve which does not contain arms having a mixing function. The geometry of the central module 3 will be explained in more detail with reference to the Figure 3: The arms 31a, 31b, 32a and 32b are located in two ellipses 41 and 42 intersecting each other. The intersection line 40 is perpendicular to the longitudinal axis 20 of the housing 12 (see Figure 2). The center lines of the arms (not shown) intersect the ellipses at points 46. Intermediate spaces 6 each with a minimum width 60 are located according to the invention between these points 46 and the bar tips 36. The arms are fastened to the base 35 to a cylindrical periphery of the sleeve 30 - between the circles 43 and 44. The height h of this periphery is less than about half the internal diameter D of the sleeve 30. Thanks to the intermediate spaces 6 at the tips of bar 36, no stagnation accumulations or mixing mass are formed in those locations. A substantial improvement in the quality of the product results from this. The minimum width of the intermediate spaces 6 as measured in the radial direction should be greater than about 2 mm in each case. This width should not be selected greater than approximately 6 mm since otherwise the mixing action would be deteriorated too severely.

Uniformly molded rounded features, which effect a favorable flow composition of the mixing composition, are provided on the base 35 of the rods for the connection area towards the inner surface of the sleeve 30. Contrary to the illustration of the Figure 2, the adjacent bars can touch each other. In this case, welds can be advantageously connected together along the crossover line 40. The structure formed by the bars is reinforced by the connection in a manner that better resists the pressure forces of the mixing mass. The crossing lines 40 in the bars of the adjacent modules 3 are oriented transversally one with respect to another; in particular they are - as shown in Figure 2 - rotated relative to each other through 90 °. This placement of the bars produces a good mixing action. So that the drying time of the mixing mass is of equal dimension at all points in the mixing region, the cross sections are provided for the bars that they are substantially circular or elliptical. In an elliptical cross section its larger diameter must be perpendicular to the longitudinal axis 20 of the housing 12, and must be substantially greater than the smaller diameter. Figure 4 shows a longitudinal section through a module 3 whose bars 31b and 32a - only those that are located behind the plane of the section are shown here - are completely placed inside the sleeve 30. In the modules 3 of Figure 2 , the bars of a module project from its sleeve 30 and protrude into a free space of an adjacent sleeve 30 or 30 'respectively. The design of Fig. 2 is particularly advantageous with respect to a cleaning of the mixing apparatus 2, which as a rule must be carried out in the e e t-t e e. The surfaces intended for contact with the mixing mass are advantageously coated. Cleaning is facilitated in this way and also the flow behavior and therefore the mixing process is improved. These advantages are particularly pronounced if nitrite- titanium (TN) is used as the material of coating .-- Ceramic materials, in particular organically modified ceramic materials ('' Ormocer1 ': organically modified ceramics), are also suitable for coating. The downstream sides and / or the upstream sides of the bars may each have a longitudinal strip that is made at least approximately planar. With longitudinal strips of this type, an initially circular profile can, for example, be modified in such a way that it acts in a manner similar to an elliptical cross section. Figure 5 shows a bar 32 with a flat longitudinal strip 34 on the downstream side. An improvement of the mixing action is cured with this special formation, mainly with respect to the following phenomenon, in which the mixing process, in static mixers is partially based: The composition being mixed is separated in bar 32 in two partial flow 51 and 52 that are close to each other - the partial flows 51 'and 52' - on the downstream side. In this arrangement, a third partial f1-ujo 53, which flows "along the bar 32, is embedded between the flows partial 51 'and 52'. As a result of the strip 34, the edges 39 are present on the bar surface which protrudes to release the partial flows 51 and 52. An improvement of the transverse flow 53 results from them and therefore an improved mixing action. The following points must be observed with respect to the design of the mixing apparatus 2 according to the invention: Up to a diameter D = 15 cm, 4 bars per module, 3 are advantageous (see Figures 2 and 3). For diameters -more - of up to 25 cm - 6 bars are more suitable. The angle of inclination of the bars must be an amount of approximately 45 °. In this case, the longitudinal of the module 3 is selected to be the same size as the diameter D. Four modules are advantageously provided as the number of modules 3 in the mixing apparatus 2.

Claims (10)

1. A module for a static mixer for a flowable plastic composition to be mixed, which is critical with respect to the drying time, the apparatus comprising a tubular housing in which the arms are placed which are inclined with respect to the longitudinal axis of the housing and substantially crossing in a straight line perpendicular to the longitudinal axis, with the module including a sleeve which can be pushed into the interior, characterized in that the internal wall of the apparatus driving the composition which is to be mixed is formed by the internal sides of the sleeves; wherein the arms are formed in the form of bars - each having a pointed tip opposite the direction of movement of the composition to be mixed and a base attached to the internal sides of the sleeve -; and in that each tip forms an intermediate space with respect to the internal wall of the mixer.

2. The module according to claim 1, characterized in that in each case the minimum width of the intermediate spaces at the tips of the bars is greater than about 2 mm when measured in the radial direction.

3. The module according to claim 1 or claim 2, wherein the bar cross-section is substantially circular or elliptical, with the larger diameter of the ellipse being perpendicular to the longitudinal axis of the housing and not substantially greater than the ellipse. smaller diameter of the ellipse.

4. The module according to claim 3, characterized in that the downstream sides and / or the upstream sides of the bars each have a longitudinal strip that is made at least approximately planar.

5. The module according to one of claims 1 to 4, characterized in that the adjacent bars are connected, in particular welded, one with another along the crossing line.

6. The module according to one of claims 1 to 5, characterized in that the surfaces intended to make contact with the composition to be mixed are coated, with titanium nitrite or a particular ceramic material that are provided as a coating material .

7. The mixer with modules according to claims 1 to 6, characterized in that the crossing lines of the bars of two nearby modules are transverse to each other and are particularly pitted with respect to each other by 90 °. .

8. The mixer according to claim 7, characterized in that the bars of the module project from its sleeve and protrude into a free space of an adjacent sleeve.

9. The plant for the processing of hard PVC, flowable plastic, or other material that is critical with respect to the drying time, the plant is characterized in that it comprises a screw extruder and a molding tool which is located downstream with a mixer according to claim 7 or claim 8 which is provided between the screw extruder and the molding tool.

10. The use of a mixer according to claim 7 or claim 8 for the processing of a flowable plastic composition of a polymer that is critical with respect to the drying time, in particular, of hard PVC or rubber.