Abstract:
In the field of continuous mixer apparatus for commingling particulate thermoplastic materials, employing at least one main rotor with a helical profile body configuration, an improved profile for the peripheral threads is provided. It presents a first upstream feed flight having a plurality of Lowenherz profile outer threads and second downstream feed flight having a plurality of screw-type outer threads, both being adjacent and integral with the periphery of the main rotor.

Description:
CROSS-REFERENCE TO OTHER APPLICATIONS  
       [0001]     None.  
       FIELD OF THE INVENTION  
       [0002]     This is an examinable patent application under Code Section 111(a) submitted for a formal filing receipt and examination. The present invention lies in the field of plastic materials mixing in continuous mixer assemblies.  
       BACKGROUND OF THE INVENTION  
       [0003]     Materials mixing rotors with standard threads, configured as depicted in prior art  FIG. 1  and  2 , were seen to be breaking down, and would not run for more than a few weeks, causing down time and requiring major rotor construction, if salvageable. Such prior art rotors were wrapping molten materials about their periphery, creating pinch points, that caused the elongate rotor pairs to deflect. Such repetitive deflection eventually caused rotor cracking, and operational breakdown. Thus, the standard threaded rotor was structurally weakened and gave only limited and costly operational longevity when using standard threads on flights throughout the mixing length.  
         [0004]     According to the present invention, an alternative configuration for the peripheral threads was devised, whereby a second and distinct set (flight) of threads were provided by adding to the threads span, and by abutting the opposite helixes, so as to help the flow of material to the helix segments of the rotors. The second flight comprises a set of Lowenherz threads, adapted to make the rotors stronger, by adding a sloped radius to the threads of the added second flight. Such will also serve to cut and churn the multi-materials being fed to the materials mixer.  
         [0005]     The dual flight rotors of the present invention have typically operated for extended periods, without rotor flexing and associated cracking, calling only for infrequent shutdowns to change the composition of the polymer materials being processed.  
         [0006]     Accordingly, it is a principal object of the present invention to provide a rotor assembly that avoids jamming up from fluidized partial bottom feeds so as to extend the operational range for a given sealing means and paired rotor assembly.  
         [0007]     Another object of the invention is to modify the standard flight configuration to include a separate flight of threads, each having a linear bevel on the upstream stage for one of the flights, whereby more uniform cutting and churning of the particulate feed materials is accomplished.  
         [0008]     It is another object of the present invention to increase the root diameter of the mixing rotor significantly, which serves to increase its structural strength and obviates its flexing from materials binding with it during processing.  
         [0009]     A still further object of the invention is to provide improved means for the interconnection of the drive shaft and mixing rotor by adding to the drive surface provided at each longitudinal end of the rotor itself with a special keying means.  
         [0010]     Yet another of the invention is to preclude operational failures of the mixing assembly caused by deflection of the rotor under materials compression during the vigorous mixing phase. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0011]      FIG. 1  is a side elevational view of a conventional compact processor for plastic particulate materials comprising a unitized particulate mixing and extrusion system, wherein particulate plastics are mixed, liquified, and the resultant molten materials are pelletized for later molding into useful articles;  
         [0012]      FIG. 2  is a side elevational view of a prior art, single flight rotor, seen in isolation that is employable in the prior art compact processor of  FIG. 1 ;  
         [0013]      FIG. 3  is a side elevational view of one rotor of a preferred embodiment of the dual flight, rotor set of the present invention, having a representative number of the more effective flight profiles shown in each configuration;  
         [0014]      FIG. 4  is an enlarged top plan view, like that of the processor of  FIG. 1 , but now depicting a parallel set of material mixing, paired rotors, which rotors embody the dual flight features of the present invention first depicted in  FIGS. 3 ;  
         [0015]      FIG. 5  is a perspective view of one paired set of the dual flight rotors of  FIG. 3 , as seen in isolation from its assembly mode, depicted for clarity of viewing;  
         [0016]      FIG. 6  is an enlarged cameo (semi-encircled) of an adjacent set of a Lowenherz modified, and a standard thread flights, better depicting the outward bevel on the set of upstream flight.  
         [0017]      FIG. 7  is an enlarged broken out view of a flight rotor with the drive shaft engagement (and alignment) at the upstream (and similarly so at the downstream) ends of the flight rotor; and,  
         [0018]      FIGS. 8 and 9 , are elevational views of the keyed driving means for each of the elongate flight rotor of  FIG. 3 , positioned at the upstream and downstream longitudinal ends thereof, respectively, of each of the modified flight rotor component of the present invention.  
     
    
     SUMMARY OF THE INVENTION  
       [0019]     Fluid materials mixing rotors can be provided with a variety of vertical cross sectional configurations on the rotors, such as the American standard thread (depicted schematically in the prior art assembly of  FIG. 2 ). We have concluded that the publicly described, Lowenherz thread can now be usefully adapted to concurrent and advantageous with the standard thread. This is done by providing a second thread flight having the Lowenherz profile, located upstream of the standard thread flight and being integral therewith, and also somewhat extending the linear span of the dual set of peripheral threads. The Lowenherz thread has flats at the top and bottom, the same as the U.S. standard form, but the depicted angle is 53 degrees 8 minutes. The depth equals 0.75×the pitch, and the width of the flats at the top and bottom is equal to 0.125×the pitch. This screw type thread is based on the metric system and is used for measuring instruments, especially in Germany.  
         [0020]     According to the invention, there is provided a continuous mixer apparatus adapted for commingling particulate thermoplastic material of varying polymeric compositions, and having a mixer barrel, at least one main rotor with a helical profile body section at one longitudinal end thereof, a driven journal located at an opposite end, a drive end rotor plate, a drive end packing seal retainer, and a packing gland seal means at the drive end, the improvement in the main rotor external configuration which comprises: (a) a first upstream (leading) feed flight having a plurality of Lowenherz profile threads integral with the outer periphery of the main rotor; and, (b) a second downstream (trailing) feed flight, abutting the first flight, and having a plurality of screw-type, outer standard threads, also being integral with the periphery of the main rotor, which standard threads terminate at an abutting trailing helix flight. In a preferred embodiment, a complemental pair of modified thread rotors operate in concert, as will be shown.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     With reference to  FIG. 1 , there is shown a prior art, compact processor  20  for plastic materials and comprising a unitized mixing and extrusion system that allows a user to customize mixing and extrusion of the plastic materials being processed. This unitized processor system comprises a two-rotor, continuous mixer  22  mounted on an upper level  23  of a framework  24 . Plastic materials, fillers, additives, colorants, and the like, namely various ingredients desired to be mixed with plastic materials, as desired by the user, are introduced into a feed entrance (sometimes called a “feed throat”) of the continuous mixer  22 , as indicated by an arrow  26 . The resulting molten plastic materials flow by gravity downward from the continuous mixer  22 , like a molten “rope”, descending within a vertical chute  28 , into a hot-feed extruder  30 . Standard screw type threads  29  ( FIG. 2 ) are used on rotor  31 . The molten output from the extruder  30  ( FIG. 1 ) issues through an extruder head  32 , which is adapted to have various types of configurations for an extrusion device  33  mounted thereon, as may be desired by the user.  
         [0022]     For driving the two rotors of  FIG. 2  ( 22 L/R) in the mixer  22  ( FIG. 1 ), there is shown a suitable drive system  34 , such as a d.c. drive motor  35 , arranged with suitable feedback speed and torque controls, as known in the art, for turning the mixer rotors preferably at predetermined constant speed. This motor  35  is coupled to a suitable speed-reducer  36 , for example, such as an all helical gear, speed-reducer with two output shafts coupled to two three-piece rotors for rotating the two rotors in opposite directions about their respective longitudinal axes. In this illustrative example, the two rotors are turned in opposite directions at the even/or ratio rates.  
         [0023]     The mixer  22  includes a drive end frame  38  (also called a “drive bearing housing assembly”) for rotatably supporting a drive end journal (not seen in  FIG. 1 ). This drive end frame  38  and its journal will be described in detail later. The mixer includes a driven end frame  39  “which may be called the “water end frame” and also may be called “driven bearing housing assembly”) for rotatably supporting a driven end journal (not seen in  FIG. 1 ). Mounted between drive and driven end frames  38 ,  39  is a mixer chamber barrel, or housing  40 , including an upper half (chamber)  41  and a lower half (chamber)  42 .  
         [0024]     For driving an extruder molten feed screw  45  ( FIG. 6 ) in the hot-fed extruder  30 , there is shown an electric motor  46  mounted on a base  48  of vertical framework  24 . This motor  46  is coupled through a suitable speed-reducer transmission  50  linked to the extruder screw  44 .  
         [0025]     The prior art rotor  31  of  FIG. 1  is shown in isolation, in  FIG. 2 , depicting that all peripheral threads flights are of like configuration, namely they are standard, screw-type threads for kneading and admixing the feeds in the type housing  40  of  FIG. 1 .  
         [0026]     In  FIG. 3 , is depicted one of the rotor pair of  FIG. 4 , which embraces the dual flight, set of threads of the present invention. Each of the modified rotors, like  50 R, has a first upstream (proximal the driven end feed flight,  54 L/R, have a plurality of Lowenherz vertical profiles  52 , (see  FIG. 6 ), disposed on rotor shaft  53 , and being integral with the periphery  55  of the rotor  50 R ( FIG. 4 ).  
         [0027]     A second downstream (distal the driven end) abuts the first flight of threads, but now presenting a standard set  54  ( FIG. 6 ) of screw-type threads, also being integral with rotor  50 R ( FIG. 4 ).  
         [0028]     The first and second flights are continuous in the zone of transition, varying only from the older to the newer profile. As to fabricating, the main rotor, such as  50 R, is first machined with standard thread profiles, which are spaced substantially more closely, as depicted in  FIGS. 3 and 5 . Certain of them are then subjected to follow-on machining to provide the novel flight periphery seen in  FIG. 3 . It is well within the skill of the rotor shaping art to produce the depicted dual flight rotor configuration of  FIG. 6 .  
         [0029]     Looking to top plan view of  FIG. 4 , with upper barrel half  41  ( FIG. 1 ) removed, there is shown a pair of parallel rotors ( 50 L/R), both positioned horizontally within housing  40  ( FIG. 1 ), and which are denominated the left and right side mixing rotors, respectively. The left-hand, longitudinal ends of the mixing rotors are mounted conventionally in journals at the drive end, frame  38  ( FIG. 4 ), while the drive ends each have a packing seal assembly, generally  56 L/R, respectively, to be described, in connection with  FIGS. 4 , et seq. The other longitudinal ends of the paired rotors are mounted in driven ends of the housing frame,  39  1). It will be apparent that first flight of screws present the Lowenherz threads, while the abutting second flight of standard screw present the standard (squared) profile.  
         [0030]     In the top plan view of the mixer  22 , cover removed, of  FIG. 4  are seen the side-by-side pair of complemental rotors,  50 L/R. The feed materials (not seen) are introduced into the open section of the mixing assembly (see prior art  FIG. 1 ), and are intimately mixed as they move rightwardly, until they reach vertical chute  28 , dropping therethrough into the conduit  30  containing extruder molten feed screw  44 .  
         [0031]     In the perspective of  FIG. 5 , are depicted dual flight rotor  50 R, each having a set of Loweriherz threads,  52 L/R, (three are exemplified), and an abutting downstream set,  54 L/R, of standard threads (four are exemplified). The connected helix segments  56  adjoins and functionally transitioning blends with the second set of screws  54 . The thoroughly mixed plastic component drops down to the extrusion stage just as depicted in  FIGS. 1 , and the description related thereto. The flanged, longitudinal ends  58 L and  58 R, are mounted as described in connection with  FIG. 4 .  
         [0032]     In the broken out, enlarged view of  FIG. 6  there is depicted a configuration of a standard thread with the abutting Lowenherz thread of the present invention. Standard thread  54  is on the right, and the Lowenherz thread  52  is on the left. As indicated earlier, a standard thread  54  is machined, by well-known machining methods, so as to provide the thread profile of the Lowenherz thread  52 .  
         [0033]     In Table 1, there is provided the agreed specifications for the integral relationship of Lowenherz thread diameter, pitch of thread, and appropriate number of threads per linear inch. The presently preferred embodiment has the following dimensions: total flight length, 24½ inches; linear distance between adjacent thread crests, 3 inches; depths of flights relative to the root diameter of the rotor; 7¾ inches; width of crest on the standard threads, 0.75 inches; and, pitch (width of slow surface of the linear threads of 3 inches.  
         [0034]     In a preferred embodiment, the Lowenherz threads has a diameter of 225.425 millimeters and a pitch of 76.2 millimeters while resulting threads per inch number 3.  
         [0035]     In the enlarged, broken out view of  FIG. 7 , such depicts the alignment configuration of the driving shaft  53  of  FIG. 3  to each of the modified rotor pair  52 L/R ( FIG. 5 ) of the present invention. Note drive shaft  53  ( FIG. 7 ) seats along recess  60 , of the rotor end which is provided in the longitudinal end flange,  58 R. This is reflected in the left side view of the present rotor assembly of  FIG. 4 .  
         [0036]     At each end of the rotor ends there are provided, specially configured recesses, or slots. In the upstream end of rotor  50 R ( FIG. 4 ) is seen a right angle, cross-type key  62 R ( FIG. 8 ), surrounded by a plurity of tapped bore holes  64 A-J, for receiving the mounting bolts (not seen) on the upstream end of rotors of rotors  FIG. 4 .  
         [0037]     At the downstream end of the paired rotors thereof, is provided a like right angle to cross-type key slot  66 R for receiving and driving the D/S bearing shaft of  70  of  FIG. 4 . A similar plurality  68 A-J of bore holes are provided. These keying components have been developed to provide higher torque carrying capability in the operation of the modified flight threads, rotors of the present invention. In a preferred embodiment, the total square inches of the drive key is greater than 4.5 inches.  
         [0038]     As to a suitable packing of gland seal assembly, which is not part of the present invention, see U.S. Pat. No. 6,399,666 (May 21, 2002), which discloses such an assembly, in  FIGS. 4-8  thereof, and in the associated description, being a suitable means. As to rotor dimensions, those set out below are typical of the present rotor assembly. It is well within the skill of the rotor parts machining art to modify such physical dimensions appropriately, so to adapt the approved rotor assembly to other particulate materials with various viscosities being blended in the inventive assembly here disclosed.  
         [0039]     With regard to the described rotor of the present invention ( FIGS. 3, 4 , and  5 ), a representative set of physical dimensions are now set forth: total body length of 56.12 inches; rotor diameter proximal the downstream end, 6.12 inches; span of the dual flight, set of threads from end flange to inception of connected helix 24.5 inches; span between apexes of adjacent lower horizontal threads, 3 inches (six inches overall)l; span between apexes of standard threads, 3 inches (nine inches overall); diameter of trough between threads, 7.37 inches; height of threads outward of rotor body, 0.75 inches; and, width of crown of standard threads, 0.75 inches. Such dimensions may be varied to accommodate the variety of plastic materials being blended and/or the volumes per unit times be effected.  
                                                                                                                               TABLE 1                           Lowenherz Thread Dimensions and Ratios                Approximate       Approximate           No. of       No. of            Diameter   Pitch,   Threads   Diameter   Pitch,   Threads            Millimeter   Inches   Millimeter   Per Inch   Millimeter   Inches   Millimeters   Per Inch                    1.0   0:0394   0.25   101.6   9.0   0.3543   1.30   19.5       1.2   0.0472   0.25   101.6   10.0   0.3937   1.40   18.1       1.4   0.0551   0.30   84.7   12.0   0.4724   1.60   15.9       1.7   0.0669   0.35   72.6   14.0   0.5512   1.80   14.1       2.0   0.0787   0.40   63.5   16.0   0.6299   2.00   12.7       2.3   0.0995   0.40   63.5   18.0   0.7087   2.20   11.5       2.6   0.1024   0.45   56.4   20.0   0.7874   2.40   10.6       3.0   0.1181   0.50   50.8   22.0   0.8661   2.80   9.1       3.5   0.1378   0.60   42.3   24.0   0.9450   2.80   9.1       4.0   0.1575   0.70   36.3   26.0   1.0236   3.20   7.9       4.5   0.1772   0.75   33.9   28.0   1.1024   3.20   7.9       5.0   0.1968   0.80   31.7   30.0   1.1811   3.60   7.1       5.5   0.2165   0.90   28.2   32.0   1.2599   3.60   7.1       6.0   0.2362   1.00   25.4   36.0   1.4173   4.00   6.4       7.0   0.2756   1.10   23.1   40.0   1.5748   4.40   5.7       8.0   0.3150   1.20   21.1   . . .   . . .   . . .   . . .