MIXING DEVICE

Abstract: Apparatus for mixing viscous fluids such as natural and synthetic polymers and their additives under thermally controlled conditions. Accordingly, the mixing device comprises a multitude of coradially nestled bell shaped cylinders (4, 8) with alternating stationary and rotating cylinders blades. The rotating body of cylinders is attached to an external power source such as a motor driven screw (3) of a plasticating extruder. The stationary body of cylinders is attached to the container walls of the plasticating apparatus, i.e., extruder barrel, either as an integral part of the die or sandwiched between the die and extruder barrel. The stationary block is cored to provide a passage (7) for a heating or cooling fluid thus providing efficient heat exchange capabilities to the apparatus. The coaxially positioned cylindrical blades may be provided with any number of pins, blocks, blades, channels (13), etc., designed to enhance the mixing capabilities of the device by slicing, shearing and mixing the viscous fluid. The mixed fluid is allowed to exit from the mixing device through a circular channel (9) in the center of the stationary component of the mixer. Throughout the device, the direction of flow is reversed 180 degrees at the end of each blade while the fluid is subjected to transverse shearing actions and each side of the main stream is alternately exposed to the temperature controlled stationary cylindrical blades. The combined and simultaneous application of shear, mixing, and cooling results in a highly efficient melt mixer and heat exchanger.

Description: MIXING DEVICE Background of the Invention The present invention relates to a melt mixing device. The most common use is in the area of polymers where mixing of dissimilar materials and additives such as fillers, pigments, and plasticizers is a frequent procedure. Other applications may be in the ceramics and food processing industries. Specific mixing requirements are as varied as the materials to be mixed in terms of specific dispersion and distribution needs. While many effective mixing devices are known in the trade, none provide effective heat exchange capabilities so important in most processes of polymers. The combined application of mixing action and cooling synergistically enhances the efficiency of both. Good, efficient mixing was shown analytically by R.S. Spender and R.M. Wiley, and more recently by L. Erwin to be dependent on frequent interruption and reorientation of melt flow between points of high shear. Intrinsic to the present invention is a 180 degree reversal in flow direction at the end of each cylindrical blade, and the application of shear perpendicular to the main flow direction not available in any of the devices known in the art. Shear and mixing in general is accompanied by the generation of heat which leads to difficulties with heat sensitive materials and processes. This problem is readily controllable in subject invention apparatus while none of the prior art devices provide this feature. Summary of the Invention The present invention maximizes mixing capabilities by virtue of the fact that melt flow is reversed 180 degrees at the end of each cylindrical blade while simultaneously subjecting the melt of shearing forces transverse to the direction of the main stream. This in itself meets the condition for efficient mixing as defined by earlier cited theoreticians on the subject of mixing. Mixing capabilities of the present invention may be further enhanced by varying the clearance in the annular space between cylindrical blades, by interrupted flow channels or ridges, intermeshing pins, blades and similar obstructions variously employed in the art for the explicit purpose of mixing. A most effective mixer configuration is described in U.S. 4,447,156 which combined with the present invention results in a highly effective and efficient mixing and cooling apparatus. The most significant feature of the present invention is in the synergistic enhancement of mixing and thermal control which arises from the fact that virtually every particle within the melt is exposed to the temperature controlled surfaces of the stationary cylinders of subject mixer. This is particularly important with heat sensitive materials and processes. The mixing apparatus of this invention may be connected to the exit end of the plasticating extruder with the rotating element attached to the extruder tip and the stationary component to the barrel or die or both. Alternatively, the mixer may be operated as a separate unit having its own motor drive. Description of the Preferred Embodiment Fig. 1 illustrates an embodiment of subject invention apparatus 1 constructed in accordance to subject disclosure. It is connected to the end of an extruder 2 in which the screw performs the essential function of melting, plasticating and pumping the melt to the mixer. The revolving component of the mixer, comprised of a multitude of concentrically positioned cylindrical, i.e., bell shaped, blades, is connected to the tip 5 of screw 3. This rotor revolves within a tapered cylinder 6 cored to allow circulating a cooling fluid -through it for precise temperature control of the mixing process 7. The stationary body of concentric cylinders 8 intermeshes with the cylindrical blades 4 of the rotor to form a nestled assembly of cylindrical blades with alternating stationary and revolving elements. The melt is thus forced to flow from the outer cylinder toward the center of the stationary body through the annular space formed by the intermeshing blades being, thereby, subjected to radial shear and axial flow shear simultaneously. Interrupted ridges 10, pins 11, blocks, grooves etc. provide enhanced mixing action as required. Points of high shear may also be incorporated by reducing the clearance in short segments of the annular space formed by the cylindrical blades. Cutting blades 13 revolving within radial channels with small clearance further enhance the mixing action. Melt conveying, i.e., pumping, flights may alternate with mixing elements to provide the desired balance of mixing and pumping. The stationary mixing element 8 is cored 12 to provide close temperature control at the points of high shear, i.e., at points of heat generation. What is claimed is:

Claims: CLAIMS 1. A mixing device comprised of a stationary and rotating body of concentric cylinders. 2. A mixing device as claimed in Claim 1 wherein both rotating and stationary components comprise a multitude of concentric cylinders. 3. A mixing device as claimed in Claim 1 wherein the rotating and stationary body comprise a nestled assembly of intermeshing cylindrical blades. 4. A mixing device as claimed in Claim 1 wherein rotating component is driven by an external power source or by a screw of a plasticating ext uder. 5. A mixing device as claimed in Claim 1 the stationary body is attached to the die, extruder barrel, or both of a plasticating extruder. 6. A mixing device as claimed in Claim 1 wherein a nestled assembly of cylinders in which rotating and stationary cylindrical blades alternate. 7. A mixing device as claimed in Claim 1 wherein an assembly of concentric, bell shaped cylinders in which the melt is caused to reverse 180 degrees in its flow direction at the end of each cylinder blade as it flows toward the exit 9 channel at the center of the mixer. 8. A mixing device as claimed in Claim 1 wherein the melt is thoroughly mixed and cooled simultaneously. 9. A mixing device as claimed in Claim 1 wherein the mixer barrel as well as the stationary mixer body is cored to provide passage for a cooling media. 10. A mixing device as claimed in Claim 1 wherein mixing elements are embedded deep in the mixed fluid and provided with cooling means for close temperature control of the mixing process. 11. A mixing device as claimed in Claim 1 wherein a melt mixer heat exchanger is operated coaxially with a plasticating extruder. 12. A mixing device as claimed in Claim 1 wherein a melt mixer heat exchanger is operated coaxially with a plasticating extruder. 13. A mixing device as claimed iii Claim 1 wherein a melt mixer heat exchanger is independently driven in tandem with a melt extruder.

Inventors: ALZNER BERNARD, CSONGOR DESIDER G, ALZNER, BERNARD, CSONGOR, DESIDER, G.
Applicants: ALZNER BERNARD, CSONGOR DESIDER G, ALZNER, BERNARD, CSONGOR, DESIDER, G.
Application year: 1987
Main classification: B01F5
IPC codes: B01F5, B01F7