Abstract:
A method of making a mixing element for a static mixer, comprising: providing a split die set having a first die and a second die in axial alignment, each of the dies having an opening forming an extrusion pattern, each of the extrusion pattern mating with the other; rotating the first and second dies so that the extrusion patterns are aligned and mated with each other to allow axial flow of extrusion material through aligned portions of the extrusion patterns; extruding extrusion material through the aligned portions of the extrusion patterns of the first and second dies to form an extruded shape; rotating the aligned first and second dies simultaneously while maintaining alignment during said extrusion to provide an angular variation to the extruded shape; and rotating at least one of the first-and said second dies independently so that the extrusion patterns are misaligned to prevent the flow of extrusion material except through the center of the extrusion patterns.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to mixing devices. More particularly, this invention relates to a new and improved apparatus and method for making a multi-portion mixing element for a static mixer, a multi-portion mixing element for a static mixer, and a static mixer including a multi-portion mixing element. 
     2. Prior Art 
     Many polymerizable resins are used in multi-component dispensers where final mixing of the resin takes place in the disposable tip called a static mixer. One of the more common static mixer designs utilized today is the twisted ribbon or the two-paddle mixer. These stationary mixers rotate the fluid resin components 180°, then split each component in half. The fluid components go through a series of splits and blends until the desired mixing is achieved. The dual component, single fluid resin then exits the static mixer and is deposited as required. When use of the resin applicator is complete, the static mixer tip is disposed of and the multi-component dispenser can be used another day with a new mixing tip. Examples of such devices are found in U.S. Pat. No. 4,538,920 and U.S. Pat. No. 4,753,536. 
     Although the twisted ribbon mixer is quite reliable and inexpensive, it does have drawbacks. Resin components with large viscosity differences are difficult to blend. Since many of the multi-component dispensers are hand operated, highly viscous fluids cannot be blended by hand because of the back pressure developed during the circuitous route the resin blend must take in the two-paddle design. Also, when many blends are required, the length of the static mixer becomes cumbersome (up to twenty centimeters long, one-quarter of an inch or three eighths of an inch in diameter). This causes a considerable amount of wasted material and also reduces work efficiency. 
     Thus, there is a need in the industry for a mixing element for a static mixer which can provide better blending of all types of fluids, including highly viscous fluids, so that the length of the static mixer becomes less cumbersome and less material is wasted. 
     SUMMARY OF THE INVENTION 
     The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the method for making a multi-paddle mixing element for a static mixer of the present invention. 
     The method of making the multi-portion static mixer includes providing a split die set having a first die and a second die in axial alignment. Each of the dies has an opening forming an extrusion pattern that mates with the other die. The first and second dies are rotated so that the extrusion patterns are aligned. Extrusion material is extruded through the first and second dies. The first and second dies are rotated simultaneously during the extrusion. The first and second dies are rotated to a misaligned position. The method may also include varying the rate of extrusion during the rotation of the first and second dies to a misaligned position. Alternatively, the extruded material may be rotated as the dies are aligned in a stationary position with one of the dies rotating to a misaligned position to create a space along the shank between mixing portions. 
     The above description and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings wherein like elements are numbered alike in the several FIGURES: 
     FIG. 1 is a perspective view of an apparatus for making a mixing element for a static mixer from an extrudable material in accordance with the present invention; 
     FIG. 2 is a side view of a static mixing element in accordance with the present invention; 
     FIG. 3 is a cross-sectional view of the static mixer of FIG. 2 taken along line  3 — 3 ; 
     FIG. 4 is a cross-sectional view of the static mixer of FIG. 2 taken along line  4 — 4 ; 
     FIG. 5 is a perspective view of the static mixer of FIG. 2; 
     FIG. 6 is a front view of an extrusion pattern in accordance with the present invention; 
     FIG. 7 is a front view of another embodiment of an extrusion pattern in accordance with the present invention; 
     FIG. 8 is a front view of another extrusion pattern in accordance with the present invention; 
     FIG. 9 is a front view of another extrusion pattern in accordance with the present invention; 
     FIG. 10 is a cross-sectional view of the split die set in accordance with the present invention; and 
     FIG. 11 is a perspective view of a static mixer in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, an apparatus for making a mixing element for a static mixer from an extrudable material in accordance with a preferred embodiment of the invention is generally shown at  20 . Apparatus  20  includes an extruding head  22  to which a split die set,  32  and  34 , is rotatably mounted. The split die set  32  and  34  is axially aligned and receives extrusion material from extrusion head  22 . Extruder  44  provides the extruding material as is well known in the art. As shown in FIG. 8, each die  32  and  34  includes an extrusion pattern, such as the extrusion pattern generally shown at  58 . Dies  32  and  34  are capable of being rotated with the extrusion patterns aligned during extrusion so that mixing portions  110  of mixing element  100  vary in rotational position along the axis of mixing element  100 . Dies  32  and  34  are also capable of rotating to a misaligned position to prevent extruding material except for the very center of the extrusion pattern from exiting the die set to cause a break in the mixing portions  110  of mixing element  100 . Timing control  24  activates first and second motors  26  and  30  to rotate respective dies  32  and  34  and constitutes a controller for the apparatus  20 . Alignment marks  36  are provided on the split die sets  32  and  34  to indicate an aligned position and misaligned position of the die sets  32  and  34 . In a preferred embodiment, a microprocessor  28  is coupled via line  38  to timing control  24  and to motors  26  and  30  via respective lines  40  and  42 . A feed control  45  is coupled via line  49  to extruder  44  and regulates the flow of the extruded material from extruder  44 . As will be appreciated by those skilled in the art, as the rotational position of dies  32  and  34  enters into the misaligned position, the fluid forces vary significantly and feed control  45  regulates the flow of extrusion material to accommodate the reduction in need of extrusion material. Additionally, microprocessor  28  can be interfaced with feed control  45  via line  47 . Microprocessor  28  allows an operator to easily adjust the manufacturing parameters of feed and rotation to produce a variety of mixing elements  100  as set forth in more detail below. 
     In operation, extruder  44  forces the extrudable material into extrusion head  22 . Inward die  34 , as shown in greater detail in FIG. 10, includes an inner restriction  86  which communicates with extrusion pattern portion  88  of die  34 . Extrusion pattern portion  88  of die  34  is proportionally narrower than extrusion pattern portion  88  of outward die  32 . As the extrudable material enters die  34  it is confined by restriction  86  and forced into extrusion pattern portion  88 . During extrusion, timing control  24  rotates dies  32  and  34  simultaneously while the mixing element  100  remains stationary as it is drawn out of the extruding head  22 . The simultaneous rotation of dies  32  and  34  provides a spiral or angular variation in the extensions or paddles, as shown in FIGS. 2,  3 ,  4  and  5  (which depict a four paddle static mixer having paddles  102 ,  104 ,  106  and  108 ) at each mixing portion  110 . Timing control  24  activates first and second drive motors  26  and  30 . Drive motor  26  is coupled to die  32 , and drive motor  30  is coupled to die  34 . The connection of the motors to the dies is not critical and any conventional means of coupling motors  26  and  30  to dies  32  and  34  may be used (e.g., gear sets, pulleys, belts, cams, and the like). It will be appreciated to those skilled in the art that, alternatively, the mixing element  100  could be rotated as dies  32  and  34  remain stationary to provide an angular variation or spiraling effect for mixing portions  110  as mixing element  100  is extruded from extruding head  22 . After the desired length of the mixing portion  110  of mixing element  100  has been extruded, timing control  24  activates drive motors  26  and  30  to rotate respective dies  32  and  34  to a misaligned position so that alignment marks  36  are misaligned. In the misaligned position, only the very center  67  of the respective extrusion patterns (as shown in FIG. 8) are aligned so that only the shank  109  is extruded. It will be appreciated by those skilled in the art that the amount of time during which extrusions dies  32  and  34  are misaligned determines the length of shank  109 . Timing control  24 , after a predetermined amount of time, activates motors  26  and  34  to rotate dies  32  and  34  back into an aligned position for continued extruding of another mixing portion  110 . Extensions  102 ,  104 ,  106  and  108  of each mixing portion  110  can vary in angular position so that there is not a constant spiral along mixing portions  110 . It will also be appreciated to those skilled in the art that one of the drive motors  26  and  30  may be eliminated if the mixing element is rotated during extrusion and the dies  32  and  34  remain aligned and stationary during extrusion. 
     Timing control  24 , and optionally microprocessor  28 , allow for variations in the degree of spiral for each mixing portion  110  as well as the length of mixing portion  110  and the space  112  between mixing portions  110 . For example, for a two paddle mixer, the rotation from start to finish for a single spiral is 180°. For a four paddle mixer, the spiral from start to finish is rotated 90°. This is beneficial because the pressure drop or loss through the static mixer is reduced due to the fluid not having to travel as far before being subdivided each time. The pressure drop of the fluid being rotated through 90° per spiral will be less than the pressure loss of the fluid having to rotate 180° per spiral, as in the two-paddle mixer. However, the amount of rotation in the spiral can be different if the manufacturer so desires. For example, the four paddle mixture can be rotated 135° or 180° from start to finish of the spiral, if so required. This technique adds great flexibility to the manufacture of the static mixing element  100 . The mixing element  100  as manufactured comprises a plurality of mixing portions  110  which can be wound on a large spool, adding to the convenience of handling. Microprocessor  28  allows quick changes in manufacturing parameters to vary the rate of rotation, alignment and feed. 
     Referring now simultaneously to FIGS. 6,  7 ,  8  and  9 , a discussion of extrusion patterns for first and second die sets  32  and  34  follows. FIG. 6 depicts a double paddle extrusion pattern  46  having a single slot  48 . It will be appreciated to those skilled in the art that a center portion of slot  48  produces shank  109  when respective dies  32  and  34  are misaligned. FIG. 7 depicts a three paddle extrusion pattern  50 . Extrusion pattern  50  has three slots  52 ,  54  and  56  extending outward from a center of pattern  50 . It will be appreciated to those skilled in the art that the angular variation between slots  52 ,  54  and  56  may be symmetrical or asymmetrical to vary mixing ratios. FIG. 8 depicts a four paddle mixer  58  having four slots  60 ,  62 ,  64  and  66  extending outward from a center  67  of pattern  58 . As with the three paddle mixing extrusion pattern  50 , the angular variation between paddles  60 ,  62 ,  64  and  66  may be symmetrically positioned from center  67  or asymmetrical. FIG. 9 depicts an eight paddle extrusion pattern  68  having eight slots  70 ,  72 ,  74 ,  76 ,  78 ,  80  and  82  extending from a center of extrusion pattern  68 . In similar fashion, slots  70 ,  72 ,  74 ,  76 ,  78 ,  80  and  82  may be symmetrically positioned or asymmetrically positioned. 
     Referring now to FIG. 2, a discussion of the static mixing element  100  follows. Mixing element  100  has a plurality of mixing portions  110 . Each mixing portion  110  spirals independently of the other mixing portions  110 . Mixing portions have, in this embodiment, four extensions or paddles  102 ,  104 ,  106  and  108 . Each mixing portion  110  is separated by a space  112 . A shank  109  provides a central axis for mixing portions  110 . As shown in FIGS. 3 and 4, the angular position of the paddles varies along the length of mixing portions  110 . In this manner, the fluid is continually subdivided at each mixing portion for improved mixing. 
     Referring now to FIG. 11, a static mixer is generally shown at  200 . Static mixer  200  comprises two separate containers  202  and  204  for containing two fluid components to be mixed. Each container  202  and  204  has a respective opening  210  where the fluid components exit. Discharge elements  206  and  208  in the form of syringes force the fluid components out of respective openings  210 . Static mixing device  200  further includes a nozzle assembly  214  having an inlet portion  212  and a discharge portion  216  having a discharge orifice  218 . Mixing element  100  is positioned within mixing chamber  220  of nozzle assembly  214  and preferably positioned between respective openings  210 . When assembled, inlet portion  212  is in fluid communication with openings  210  so that fluid components enter nozzle assembly  214  with mixing element  100  symmetrically positioned between openings  210 . As fluid components are pushed through nozzle assembly  214 , the components are spiraled and subdivided along mixer  100  and eventually discharged through orifice  218 . As will be appreciated to those skilled in the art, such a static mixer using mixing element  100  can be in the form of a hand operated gun or automated mixing machine utilizing a mixing element  100  without departing from the spirit and scope of the present invention. 
     Thus, in use, an operator places two different fluid components to be mixed in respective containers  202  and  204 . At the desired time for applying the mixture of the two fluid components, syringes  206  and  208  are depressed forcing fluids out of openings  210  and into inlet  212  where the fluids travel along mixing chamber  220  and through mixing element  100  for discharge through orifice  218  for application. After use, the nozzle assembly and mixing element can be discarded. 
     Although the figures shown relate to two part fluid mixing, it is understood that one skilled in the art would recognized that the present invention is advantageously adapted to providing for the mixing of a plurality of fluids. For example, the three paddle mixer illustrated in FIG.  7  and the four paddle mixer illustrated in FIG. 8 are suitable for statically mixing three and four part fluid mixtures, respectfully, as described herein before for two part fluids. 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.