Abstract:
The mixing nozzle of the present invention generally includes a casing and mixer. The mixer fits within the casing and includes alternating elongated helical flow directing lands and notched barrier lands. The flow directing lands extend from the body and seal against the inside wall of the casing. The barrier lands also extend from the body but are offset from said inside wall of the casing. The flow directing lands and the barrier lands have differing helix angles and thus define alternating converging inlet channels and diverging outlet channels. Mixing of molten plastic is accomplished when the molten plastic is received from the inlet end of the mixing portion primarily by the inlet channels, passes over the barrier lands and through the notches in the barrier lands and passes primarily via the outlet channels through the outlet end of the mixer.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Patent Application No. 60/465,083 filed Apr. 24, 2003. 

   FIELD OF THE INVENTION 
   This invention relates to a mixing nozzle that receives extrudate from an extruder or an injection screw and mixes the extrudate prior to further processing. 
   BACKGROUND OF THE INVENTION 
   Injection nozzles are used to inject extrudate from an extruder screw or an injection screw prior to further processing. Such further processing might include extrusion through a die to produce a continuos extruded shape or injection into an injection mold to produce a molded part. 
   In order to reduce inventory costs, operators often feed standard, uncolored thermoplastic pellets and colored pigments into an extrusion or an injection machine to produce colored plastic products. Other additives may be added to thermoplastic for a variety of purposes. Such additives might include glass fibers, glass beads, steel powder, calcium and even animal fat. It is usually important to the quality of the resulting product that these additives are evenly mixed with the thermoplastic. It is also important that resulting mixture be uniform, isothermal and relatively free of material degradation. 
   Operators who produce a wide variety of products often employ machines having standard injection or extrusion barrels and screws capable of processing a wide variety of thermoplastic materials. Such standard equipment is often not well adapted for optimally mixing a particular thermoplastic material and a pigment to produce an evenly colored product. Inadequate mixing causes streaks in the product due to contrasting areas have heavy and light pigment. Often excess amounts of costly pigment are used to compensate for inadequate mixing. Consequently, there is often a need for a mixing nozzle which can be mounted to an extrusion or injection machine that will receive molten thermoplastic material and pigment from the extrusion or injection machine and mix the thermoplastic and the pigment more completely prior to further processing. Still further, since excessive shear and compression of an extrudate can elevate the temperature of the extrudate and degrade its material properties, there is a need for a mixing nozzle that mixes extrudate thoroughly while subjecting it to minimum amounts of heat producing shear and compression. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In an embodiment of the present invention the aforementioned problem is addressed by providing a mixing nozzle for mounting to a thermoplastic processing machine such as an extruder barrel screw arrangement or an injection barrel screw arrangement. The mixing nozzle is designed to receive a flow of extrudate from an extruder screw or an injection screw and mix the extrudate prior to further process steps such as extrusion through a die or injection into a mold. The primary objective of the mixing nozzle is to mix the flow of extrudate while subjecting it to minimal amounts of shear and compression. The term extrudate used here should be understood as including molten thermoplastic and any additives which may have been added to the molten thermoplastic. 
   The mixing nozzle includes a mixer mounted inside a casing. The casing generally includes an inlet portion at the upstream end, a mixing portion and an outlet portion at the downstream end. The inlet and outlet portions of the casing have relatively narrow passages while the mixing portion has a larger diameter passage for accommodating the mixer. A diverging passage extends between the inlet passage and the mixing passage of the casing and a converging portion extends between the mixing portion and the outlet portion of the casing. The mixer is mounted within the casing in a stationary manner and includes a diverging nose portion for placement within the diverging passage of the casing, a generally cylindrical body portion for placement within the mixing portion of the casing and a converging tail portion for placement within the converging portion of the casing. Extending longitudinally from the upstream end to the downstream end of the body of the mixer and also extending radially from the surface of the mixer are alternating pairs of flow directing lands and barrier lands. The flow directing lands seal against the inside wall of the casing while the barrier lands are offset from the inside wall of the casing. The barrier lands also have transverse notches for promoting mixing and throughput. The flow directing lands and the barrier lands describe helixes as they wrap around the body of the mixer. The helix angles of the barrier lands are greater than the helix angles of the flow directing lands. Accordingly, adjacent pairs of flow directing lands and barrier lands that diverge at the upstream end of the mixer and converge at the downstream end of the mixer define converging inlet channels which communicates primarily with the inlet end of the housing. Adjacent pairs of flow directing lands and barrier lands that converge at the upstream end of the mixer and diverge at the downstream end of the mixer define diverging outlet channels which communicates primarily with the outlet end of the housing. 
   Mixing of molten plastic occurs when the molten plastic is divided as it is received from the inlet portion primarily by the inlet channels, passes over the barrier lands and is further divided as it passes through the notches in the barrier lands into the outlet channels and then is recombined as it passes primarily via the outlet channels to the outlet end of the casing. As the flow of extrudate passes into the inlet channels, between the inlet channels and the outlet channels and out through the outlet channels, the flow is successively separated and later recombined to accomplished a relatively gentle mixing action with minimized shear and compression. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross section view of the mixing nozzle shown attached to a thermoplastic processing machine. 
       FIG. 2  is a cross section view of the mixing nozzle. 
       FIG. 3  is an exploded cross section view of the mixing nozzle. 
       FIG. 4A  is a side view of the mixer. 
       FIG. 4B  is a end view of the mixer. 
       FIG. 4C  is cross sectional view of the tail portion of the mixer taken from plane C—C of  FIG. 4B . 
       FIG. 4D  is cross sectional view of the tail portion of the mixer taken from plane D—D of  FIG. 4B   
       FIG. 5  is a cross section view of the mixing nozzle with arrows indicating the flow of extrudate through the mixing nozzle. 
       FIG. 6  is a planar projection of the surface of the mixer shown in  FIG. 4A . 
       FIG. 7  is a planar projection of the surface of a mixer similar to the mixer shown in  FIG. 4A  but having a different configuration of notches. 
       FIG. 7A  is a cross section of a barrier land taken from plane A—A of  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the drawings,  FIGS. 1–7A  show a mixing nozzle  10  in accordance with an embodiment of the present invention. As can be seen in  FIG. 1 , mixing nozzle  10  is shown mounted to a thermoplastic processing machine  5 . Thermoplastic processing machine  5  generally represents either an injection machine or an extrusion machine. Processing machine  5  includes a hopper  5 A for receiving thermoplastic pellets and additives such as colorants, a barrel  5 B having an axial bore extending from the inlet end of the barrel to the outlet end of barrel  5 B, heating elements  5 C and a screw  5 D which forces the melting thermoplastic material toward the outlet end of the barrel as screw  5 D rotates within barrel  5 B. The drive means for rotating screw  5 D is not shown. In an injection machine, the drive machine would not only rotate screw  5 D to push thermoplastic toward the outlet end of barrel  5 B but also periodically reciprocate screw  5 D to inject extrudate into an injection mold. As can be seen in  FIG. 1 , mixing nozzle  10  includes a casing  11  a mixer  20  mounted within casing  11 . 
   Mixing nozzle  10  is shown in greater detail in  FIGS. 2 and 3 . As can be seen in  FIGS. 2 and 3 , casing  11  and mixer  20  are generally radially symmetric about a nozzle axis  10 A. The components of mixing nozzle  10  are preferably fashioned from a hard steel capable of withstanding the temperature, abrasion and high pressure (often as high as 35,000 psi) of hot extrudate. 
   Casing  11  further includes an inlet portion  12 , a mixing portion  14  and an outlet portion  50 . Inlet portion  12 , mixing portion  14  and outlet portion  50  are assembled by engaging corresponding threaded surfaces  12 A and  14 A and threaded surfaces  14 B and  50 A. The disassembly of inlet portion  12  from mixing portion  14  provides access to mixer  20  so that mixer  20  may be easily removed after use. A standard nozzle tip  100  is shown threaded to the downstream end of outlet portion  50 . Nozzle tip  100  is representative of the type of tip for engaging an injection mold. Mixing portion  14  may be partially surrounded by a thermal element  15  which would most generally be used to maintain mixing portion  14  within a desired elevated temperature range suitable for maintaining thermoplastic material in a melted condition. 
   Inlet portion  12 , mixing portion  14  and outlet portion  50  of casing  11  present an axial passage for the passage of extrudate. This axial passages widens in mixing passage  16 C to accommodate mixer  20 . As can be best seen in  FIG. 3 , the axial passage presented by inlet portion  12  and mixing portion  14  can be further divided into an inlet passage  16 A, a diverging passage  16 B, a mixing passage  16 C and a shoulder portion  16 D. Inlet passage  16 A receives extrudate from the outlet end of barrel  5 B shown in  FIG. 1 . Mixing passage  16 C has a larger diameter than inlet passage  16 A. Diverging passage  16 B is a bounded by diverging surface communicating between inlet passage  16 A and mixing passage  16 C. A seal face  16 E extends between mixing passage  16 C and the wider shoulder portion  16 D. Shoulder portion  16 D has a threaded inside surface  14 B for receiving a threaded outside surface  50 A of outlet portion  50 . 
   Outlet portion  50  has an axial bore  52  extending from upstream end to its downstream end. Axial bore  52  is further divided into a first cylindrical portion  52 A, a second converging portion  52 B and a third cylindrical portion  52 C. Mounted at the outlet end of outlet portion  50  is an optional nozzle tip  100 . Nozzle tip  100  shown in  FIGS. 1–3  and  5  is intended for engaging an injection molding device and is merely an example of a component that would be mounted at the outlet end of outlet portion  50 . A different type of tip such as an extrusion die might be mounted to the outlet end in lieu of nozzle tip  100  to support an extrusion process. As will be described in greater detail below, a tail flange  26  extending from the outlet end of mixer  20  is interposed between seal face  50 B of outlet portion  50  and seal face  16 E of mixing portion  14 . 
   Mixer  20  is primarily mounted within mixing portion  14  and also extends into outlet portion  50 . Mixer  20  includes a nose portion  22 , a body portion  24 , a tail flange  26  and a tail portion  28 . Nose portion  22  has a blunt cone shape which generally corresponds with diverging passage  16 B of axial passage  16 . Tail portion  28  includes a cylindrical section  28 A and a blunt cone portion  28 B which is generally similar in shape to nose portion  22 . The surfaces of cylindrical section  28 A and blunt cone portion  28 B are generally shaped for a constant offset relationship with first cylindrical portion  52 A and second converging portion  52 B of bore  52 . Extending from tail flange  26 , on opposite sides of cylindrical section  28 A are converging lands  28 C. Converging lands  28 C extend from the surface of cylindrical portion  28 A and seal with the inside surface of first cylindrical portion  52 A of bore  52 . The function of converging lands  28 C will be described in greater detail below. 
   Body portion  24  of mixer  20  includes flow directing lands  30  and barrier lands  32 . Flow directing lands  30  are spaced around body portion  24  and extend longitudinally in a helical fashion between the upstream end and downstream end of body portion  24 . Flow directing lands  30  also extend radially from body portion  24  and seal with the inside wall of mixing portion  14  thus presenting impassable walls for directing the flow of extrudate. Barrier lands  32  extend a portion of the distance from body portion  24  to the inside wall of mixing portion  14  and are thus offset from the inside wall of mixing portion  14 . 
     FIG. 6  is a planar projection of the portion of the surface of mixer  20  indicated in  FIG. 4A .  FIG. 6  illustrates the surface features of mixer  20 . As can be best seen in  FIG. 6 , the helix angles of barrier lands  32  are greater than the helix angles of the flow directing lands  30  such that barrier lands  32  and flow directing lands  30  form pairs of alternating inlet channels  34  and outlet channels  36 . As shown in  FIG. 6 , barrier lands  32  are set at a helix angle of approximately 50° while flow directing lands  34  are set at a helix angle of approximately 40°. An inlet channel  34  formed between a flow directing land  30  and an adjacent barrier land  32  becomes wider toward the upstream end of mixer  20  and narrows toward the downstream end of mixer  20  as barrier land  32  widens into a downstream offset surface  33  adjacent to flow directing land  30 . An outlet channel  36  formed between a barrier land  32  and an adjacent flow directing land  30  narrows toward the inlet end of mixer  20  and widens toward the outlet end of the mixer  20 . An upstream offset surface  31  is formed where barrier land  32  widens as it meets flow directing land  30 . A flat surface  31 A facets between offset surface  31  and the conical surface of nose portion  22 . Barrier lands  32  include transverse notches  32 A which facilitate the flow of extrudate material from inlet channels  34  to outlet channels  36 . 
   Tail flange  26  provides a means for mounting mixer  20  within casing  11 . As can be seen in  FIGS. 4A and 4B , tail flange  26  extends radially from the tail end of the mixer  20 .  FIGS. 4B and 4D  show that tail flange  26  includes radial channels  26 A as well as a forward seal face  26 B and a rear seal face  26 C. Radial channels  26 A provide passageways for the flow of extrudate from mixing portion  14  into rear outlet portion  50 . Tail flange  26  is shaped to seal between outlet portion  50  and mixing portion  14 . As outlet portion  50  is threaded into mixing portion  14 , forward seal face  26 B of tail flange  26  seals with seal face  16 E of mixing portion  14  and as rear seal face  26 C of tail flange  26  seals with seal face  50 B of outlet portion  50 . As mixer  20  is secured between outlet portion  50  and mixing portion  14  in the position shown in  FIG. 2 , the seal between tail flange  26 , mixing portion  14  and outlet portion  50  must be capable of withstanding the significant pressure of the extrudate. 
     FIG. 5  illustrates the flow of extrudate through mixing nozzle  10 .  FIG. 6  presents a flat projection of body portion  24  as well as tail flange  26  and tail portion  28 .  FIG. 6  illustrates the flow of extrudate between body portion  24  of mixer  20  and mixing portion  14  of casing  11 . As is shown in  FIG. 5 , extrudate initially flows into inlet portion  12  and into mixing portion  14  where it encounters nose portion  22  of mixer  20 . As is shown in  FIG. 6 , the extrudate flows around nose portion  22  and is mostly divided into inlet channels  34  as it begins to flow between body portion  24  of mixer  20  and mixing portion  14 . Also, as can be seen in  FIGS. 5 and 6 , a relatively small portion of the extrudate enters outlet channels  36  at the upstream end of mixer  20  via upstream offset surface  31 . The extrudate flows from an inlet channel  34  to an outlet channel  36  via the offset spaces between barrier land  32  and the inside surface of mixing portion  14  and via the transverse notches  32 A in barrier lands  32 . When extrudate flows from an inlet channel  34  to outlet channel  36 , the flow is divided into separate streams as separate portions of the flow pass through each notch  32 A. At the same time, extrudate is also flowing over barrier land  32 . These various separate portions of the flow are then recombined in outlet channel  36  to accomplish a relatively gentle mixing action. After most of the flow of extrudate mixes and gathers in outlet channels  36 , it flows past the outlet end of mixer  20  through channels  26 A in tail flange  26 . In addition to the extrudate exiting via outlet channels  36  a small portion of the extrudate flow exits from inlet channels  34  at the outlet end of mixer  20  via downstream offset surfaces  33  and combines with the flow leaving outlet channels  36 . This combined flow, consisting primarily of extrudate from outlet channels  36 , is further mixed as it passes through channels  26 A of tail flange  26 , converges around converging lands  28 C and flows around tail portion  28  and finally flows into third cylindrical portion  52 C of outlet portion  50 . 
     FIG. 7  presents a second flat projection of body portion  24 . The configuration of body portion  24  shown in  FIG. 7  is identical to that shown in  FIG. 6  except that in  FIG. 7 , notches  32 A have been replaced by notches  32 A 1 ,  32 A 2  and  32 A 3 . Generally, notches  32 A 1 ,  32 A 2  and  32 A 3  increase in width in the downstream direction while increasing in depth in the upstream direction. Notches  32 A 1 ,  32 A 2  and  32 A 3  are also configured to have generally equivalent cross sectional areas. The extrudate flows from an inlet channel  34  to an outlet channel  36  via the offset spaces between barrier land  32  and the inside surface of mixing portion  14  and via the transverse notches  32 A 1 ,  32 A 2  and  32 A 3 . Concurrent with the flow of extrudate passing over barrier land  32  in to outlet channel  36 , a first stream of extrudate passes into outlet channel  36  through notch  32 A 1 . The stream from notch  32 A 1  is then combined with a second wider yet shallower stream from notch  32 A 2 . The combined stream from flow over barrier land  32 , notch  32 A 1  and notch  32 A 2  is then combined with an even shallower and wider stream from notch  32 A 3 . When extrudate flows from an inlet channel  34  to outlet channel  36 , the flow is divided into separate streams as separate portions of the flow pass through notches  32 A 1 ,  32 A 2  and  32 A 3 . At the same time, extrudate is also flowing over barrier land  32 . These various separate portions of the flow are then recombined in outlet channel  36  to accomplish a relatively gentle mixing action. 
   It is preferable that the flow area available between the various surfaces of mixer  20  and mixing portion  14  as well as outlet portion  50  remain generally constant. Accordingly the flow area between nose portion  22  of mixer  20  and forward mixing portion  14  should preferably be approximately the same as the flow area available through the inlet portion  12 . Similarly, the flow area available to the extrudate as it flows through the inlet and outlet channels of mixer  20  and between the inlet and outlet channels of mixer  20  should also remain generally constant. The availability of a generally constant flow area down most of the length of mixing nozzle  10  allows mixing to occur in an efficient stirring fashion and in a fashion that minimizes compression and shear in the material. It is well known in the art that compression and shear in a thermoplastic extrusion or injection process increases the energy requirements of the process and can degrade the extrudate. 
   Accordingly, the present mixing nozzle provides an efficient device for mixing extrudate that can be easily integrated within a plastic extrusion or molding process. Mixing nozzle  10  receives a flow of extrudate and mixes it in a low shear, low compression stirring fashion such that the extrudate experiences a sufficient amount of disruption to accomplish mixing with a minimal amount of degradation. This low shear, low compression mixing also reduces the amount of back pressure added to the system while maintaining a high degree of mixing. 
   It is to be understood that while certain forms of this invention have been illustrated and described, it is not limited thereto, except in so far as such limitations are included in the following claims and allowable equivalents thereof: