Agitating – Rubber or heavy plastic working – Stirrer is through-pass screw conveyor
Reexamination Certificate
1998-11-12
2001-07-03
Cooley, Charles E. (Department: 1723)
Agitating
Rubber or heavy plastic working
Stirrer is through-pass screw conveyor
C366S078000
Reexamination Certificate
active
06254266
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is in the field of polymer extruders and mixers for use in connection with providing high pressure polymer melts for injection moulding and extrusion and the like.
It is well known in the art to provide a polymer melt mixer in a heated extruder barrel, sometimes referred to as a stator, including a bore defining a cylindrical internal chamber in which a screw rotor is axially positioned for a rotation within and with respect to the cylindrical chamber. It is also conventional to have the upstream portion of the rotor comprise a driven rotary screw member for feeding the polymer components along the length of the rotor or barrel to a downstream portion which provides mixing of the melted components prior to injection of the polymer melt into a die or the like. The polymer melt injection is effected by moving the rotor in a downstream direction to force the viscous polymer melt constituents from the barrel out through an opening communicating with the interior of a die or the like. A device of the foregoing type is exemplified in prior U.S. Pat. No. 5,013,233.
It is extremely desirable that the polymer melt be thoroughly mixed following melting so as to achieve optimum uniformity of structure in the finished product produced by the injection molding operation. A number of different approaches have been suggested for achieving improved polymer melt mixing as evidenced by the following discussed prior art.
The Semmekrot U.S. Pat. Nos. 5,013,233 and 5,158,784 disclose a dimpled downstream rotor portion having cavities 22, 23 surrounded by a mixing ring or sleeve 9 having radial openings through which the polymer melt moves to and from the rotor dimples as it works its way from the upstream to the downstream end of the apparatus. Mixing occurs between cavities 22, 23 of the rotor and mixing ring 9 which is arranged for free rotation about the rotor of the Semmekorot device. The mixing ring or sleeve 9 is provided with an annular valve body 17 that coacts with a valve seat 18 on the rotor to prevent reverse flow of polymer melt in an upstream direction beyond a valve seat 18 during the injection process.
Another approach is revealed in Upmeier U.S. Pat. No. 4,541,982 which discloses a polymer melt extruder employing multiple fixedly positioned distributing disks positioned one behind the other in alignment with each other to effect a plurality of flow dividing mixing operations. The disks are arranged as stationary structures through which melt flow occurs in serial manner.
Sato U.S. Pat. No. 4,057,379 discloses an extruder having a driven screw type extruder screw 6 which forces melt material to be extruded through a driven rotating disk 12 having holes 14 into a stationary disk 16 having holes 26 and which is spaced from contact with the driven rotating disk.
West German DL 0155, 504 of Elektroger discloses a static mixing device for injection molding having plurality of discs 3 having flow through apertures 4 for producing turbulence and effecting mixing of polymer melt. Each of the discs is separated from the next adjacent disc by spacers to provide chambers between the discs. The discs and spacers are firmly clamped together so as to prevent them from rotating relative to each other.
British Patent No. 1,475,216 discloses a driven cylindrical rotor cooperating with a plurality of inner and outer profile rings for cooperation with the rotor for effecting mixing of polymer melt.
Applicant's earlier U.S. Pat. No. 4,779,989 discloses a transfer mixer assembly for use with an extruder screw employing a stator in which a rotor body 36 having grooves 37 and 42 is positioned for cooperation in effecting mixing.
While some of the known prior art devices have provided fairly satisfactory mixing results, there have remained a number of problems including inadequate mixing performance and the high cost of fabrication and maintenance due to the complexity of some of the devices.
Therefore, it is a primary object of the present invention to provide a new and improved mixer and/or mixer-intruder that provides enhanced mixing results, is economical to fabricate and maintain and is reliable and easy to use.
SUMMARY OF THE INVENTION
Achievement of the foregoing objects is enabled by the preferred embodiment of the invention by the provision of a plurality of rotor rings provided on the downstream end of an extruder shaft mounted for rotation in a conventional heated barrel or stator. The upstream portion of the extruder comprises a conventional screw construction of spiral shape provided on the extruder shaft which is rotated by motor means so as to drive the polymer melt in a downstream direction toward the rotor rings.
The rings are of two different types, namely, a plurality of spaced driven rotor rings spaced apart from each other along the length of an extension of the shaft and a plurality of non-driven floating rings interleaved between each pair of rotor rings. The rotor driven rings are mounted on a rotor sleeve keyed to the shaft so as to be rotated by the shaft. Both the driven rotor rings and the floating rings have parallel upstream and downstream faces between which polymer flow passageways extend so that the polymer melt moves first through one type of ring followed by movement through the other type of ring toward the downstream end of the barrel.
The polymer flow passageways are arranged in their respective rings in concentric circles with respect to the axes of the shaft and the rings which are coaxial. The polymer passageways of both the driven rotor rings and the floating rings are alignable with each other, however, such alignment is only momentary since the floating rings and driven rings rotate at different speeds relative to each other. The speed differential is achieved because the floating rings have an outer periphery in the form of a cylindrical surface which contacts the inner cylindrical surface of the extrusion chamber so that there is some, but not absolute, frictional resistance to rotation of the floating rings.
In operation, the rotation of the extruder shaft results in rotation of the extruder screw and the driven rotor rings through which viscous polymer melt is forced by rotational operation of the extruder screw to move polymer melt through the polymer flow passageways of the first or upstream driven ring to enter the polymer flow passageways of a next adjacent downstream floating ring. The polymer melt passes through the polymer flow apertures of the next adjacent floating ring and into the polymer melt passageways of the second driven rotor ring which is rotating at the same speed as the first driven rotor ring which relationship adds to the rotational force applied to the floating ring. However, since the polymer melt is viscous, the rotation of the driven lings causes the viscous polymer melt to create a driving rotational force on the floating rings which is partially resisted by the frictional contact of the outer periphery of the floating ring with the cylindrical surface of the barrel in which the entire assembly is positioned. Consequently, there is relative rotary motion between the upstream driven rotor ring and the next adjacent floating rotor ring which creates a shearing force on the polymer melt to provide a substantial and effective mixing of the polymer melt so that by the time it reaches the downstream end of the mixing chamber, the polymer melt has been thoroughly mixed.
The upstream driven rotor ring is provided with a conical valve surface which during the initial portion of each cycle of operation is spaced from an identical conical valve surface on the downstream end of the screw shaft so that the space between the two conical valve surfaces comprises an annular polymer infeed aperture through which the polymer melt moves from the screw into the mixing chamber to pass through the driven rotor rings and the floating rings. However, when the shaft and the driven extruder screw begin to move toward the downstream end of the chamber to initiate an extrusion operation, the conical valv
Barr Robert A.
Myers Jeffrey A.
Barr Robert A.
Cooley Charles E.
Jacobson Price Holman & Stern PLLC
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