WO1985001467A1

WO1985001467A1 - Polymer processors

Info

Publication number: WO1985001467A1
Application number: PCT/US1984/001527
Authority: WO
Inventors: Arthur Dwight Siegel
Original assignee: USM Corp
Current assignee: USM Corp
Priority date: 1983-09-26
Filing date: 1984-09-25
Publication date: 1985-04-11
Anticipated expiration: 1986-03-26
Also published as: IT1180231B; EP0155964A1; IT8422832A0

Abstract

Polymer processing apparatus (10) having a section for processing polymer at a relatively low pressure sufficient only for processing; and having a section for pumping the polymer in liquid form for increasing the pressure in the polymer using a shaft having radial blades rotating (18) in one or more annular chambers closed by a body (12) and seals formed by the shaft (16) in bearings (14) in the body thereby reducing the power needs of the processing apparatus.

Description

Polymer Processors

Field of the Invention

This invention relates to apparatus for processing polymers for melting, mixing, devolatilizing, pumping and the like.

Description of the Prior Art

It is well known in the polymer processing field to provide a screw rotating in a rather close fitting bore with the channels of the screw being deep enough so as to generate only sufficient pressure on the polymer to perform the required operation. In a melting operation the channels between the screw flights are relatively deep and the polymer melting on the bore of the heated barrel is scraped from the bore into the channels. However, as shown in U.S. Patent 3023456 the molten polymer must be pressurized for certain operations such as mixing and devolatilizing as well as pumping generally by alternately decreasing and increasing the screw channel depths. The operations requiring increased pressure also increase the power requirements needed to drive the screw.

As shown in U.S. Patent 4227816 a relatively new apparatus known as a DISK PACK Processor manufactured by Farrel Division of USM Corporation is available for processing polymer by a rotor which includes a plurality of disks which rotate in a bore so that moving channels carry the material from an inlet to an outlet with a fixed dam like member downstream blocking passage of the material and raising its pressure for diversion through the outlet. Certain relatively wide channels are adapted for melting, mixing, devolatilizing and the like while certain narrower channels are

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_O PI , 1?0 adapted to raise the pressure of the viscous polymer and pump the material through an extruding nozzle or to the other devices. As is expected the considerable pressure generated by the narrow channels requires expenditure of considerable energy and also tends to force the material over the peripheries of the disks into adjacent channels and/or to cause leakage outwardly from the unit. For this reason the channels designed to create pumping pressure on the material are generally located in central portions of the unit adjacent the outlet of the unit to minimize undesirable leakage from the unit. As discussed in U.S. Patent 4300842 special seals between the periphery of the disks and the bore have been used to minimize leakage of the material between adjacent channels. Such seals also require great expenditure of energy when enough pressure is generated for extruding or merely to feed the melt to other devices. Accordingly, it is an object of the invention to provide polymer processing apparatus particularly adapted to perform the processing operations using considerably less energy with greater efficiencies. To this end the processing portions of the device for the most part are performed at relatively low pressures with resultant reduced sealing requirements to minimize leakage. The pumping functions of the apparatus are performed by a highly efficient unit requiring less energy and minimizing leakage.

Summary of the Invention

The present invention provides novel polymer processing apparatus in which the pressurizing and pumping operations are performed by a novel pump section comprising blades extending radially from a shaft into annular channels which are closed except for inlet and outlet grooves in the shaft extending axially through close fitting bearings. The pressure required to pump is generated by the movable blades rotating in the channels. The processing portions of the apparatus are adapted to generate only sufficient pressure to perform specific processing operations on the polymer such as melting, mixing, devolatilizing and the like. With reduced pressure in the processing portions the energy required to perform the processing operations and is reduced. With the efficient pumping portion the sealing requirements and the energy required to generate pumping pressure also are greatly reduced.

Description of the Drawings

Fig. 1 is a schematic perspective view of a polymer processing device embodying the pump of the present invention; Fig. 2 is a section on line II-II of Fig. 1; Fig. 3 is a section on line III-III of Fig. 1; Fig. 4 is a longitudinal section through an alternate form of polymer processing device embodying the invention; Fig. 5 is a section on line V-V of Fig. 4; Fig. 6 is an exploded perspective view of parts of the pump unit of Fig. 4;

Fig. 7 is a longitudinal section through an alternate form of pumping unit;

Fig. 8 is a section on line VIII-VIII of Fig. 7; Fig. 9 is a longitudinal section through a further alternate form of polymer processing device embodying the invention; and

Fig. 10 is a cross section of a pumping unit diagrammatically illustrating the balancing effect caused by diametrically opposite blades.

Description of Preferred Embodiments

Referring to Fig. 1, there is shown a polymer processing unit 10 embodying the present invention. The unit includes a body 12 having a central bearing 14 which receives a shaft 16. The shaft has fixed thereto one or more radially extending blades 18 which are received in an annular channel 20 in the body 12. At one end, the body is provided with an inlet 21 which leads to the surface of a drum 22 on one end of the shaft 16. As best seen in Fig. 2, solid thermoplastic pellets or liquid polymer may be fed into inlet 21 and as the drum 22 is rotated by a source of rotary power (not shown) the liquid polymer or pellets are fed along a space 19 between the surface of the drum and a cylindrical surface 23 of the body. To melt the thermoplastic pellets, the drum and/or the body 12 may be heated in any suitable manner not shown but which may for example be by circulation of fluid and/or electrical band heaters both of which are well known in the art. The pelletized polymer is progressively melted and fed toward a collection recess 24 leading to a channel 25. As is well known in the art a partial dam 26 may extend into the space 19 to spread the melted liquid or polymer on the surface of the drum forming a void 27 downstream of the dam. A port 28 extends through the body 12 into the void 27 so that volatile gasses may be drawn therefrom or additives may be introduced thereto. The melted polymer collects in the recess 24 and sufficient pressure is generated to cause the polymer to flow along the channel 25 (Fig. 1) in the body 12 and into an annular groove 30 in shaft 16. An axially extending groove 32 in the shaft leads the liquid polymer into a recess 34 behind and at the base of the blade 18 (see also Fig. 3). As the shaft rotates and blade 18 sweeps along the annular channel 20 the polymer continues to be fed into and fill the channel 20. The stationary walls of the channel apply a drag on the polymer and the advancing blade causes the pressure in the polymer to rise and force the polymer into a recess 36 ahead of the blade and along a groove 38 in the shaft.

As shown in Fig. 1, the pressurized polymer flows along the groove 38 into a recess 40 at the base of a second blade 41 also fixed to the shaft 16 and extending radially into an annular channel 42 similar to channel 20. The already pressurized polymer fills channel 42 and the advancing blade 41 further pressurizes the material which is forced into a recess 43 at the base of the leading side of the blade and along a groove 44 in the shaft and into-an annular groove 45. The pressurized polymer is led from the groove and the unit through a port 46 into any suitable apparatus (not shown) for further processing such as extrusion or molding into shapes or for pelletizing. Such further apparatus could include devices for injection molding without departing from the scope of the invention.

As shown in Fig. 3, the base of the blade 18 may be received in a recess 50 in the shaft 16 and secured by a bolt 51 which extends through the shaft. So that the forces acting on the shaft 16 can be balanced to minimize undesirable deflection forces on the shaft, the blades 18 and 41 can be arranged on opposite sides of the shaft or could be constructed as seen in Figs. 5 and 8 to balance forces in each annular channel as shown graphically in Fig. 10. As illustrated in Fig. 10, the forces which build up progressively from the inlet grooves 47 to the outlet grooves 49 are balanced by equal and opposite forces.

Referring to Fig. 4, there is shown an alternate form of polymer processor embodying the invention. The unit includes an alternate preferred form of pump 60 which could be attached to and be fed fluid polymer by any one of a number of processors including a melting screw unit 61 as seen in Fig. 4, or the drum type shown in Figs. 1 and 2, or a DISK PACK processor 139 as seen in Fig. 9 or may be fed from a separate device as contemplated by the pump shown in Fig. 7. As seen in Fig. 4, polymer already in liquid form or in pellet form is fed through an inlet 62 to the single or multiple flights of a screw 63 which is rotated by a source of rotary power (not shown). The body 64 and/or the screw 63 may be heated by suitable means (not shown) to melt or otherwise process the polymer which is fed by the screw toward the pump unit 60. The liquid polymer is fed from the end of the screw to a passage 100 formed between a conical recess in an end frame 65 and a conical flange 67 on a shaft 68 fixed to the end of screw 63. The end frame 65 of the pump 60 is secured by bolts 66 to a flange on the end of unit 61 and in turn is secured by through bolts 70 to a stepped body 72 and a header 74. A recess between mating surfaces of the frame 65 and body 72 forms an annular channel 76 which receives blades 78 extending radially from a hub 80 mounted on shaft 68. and fixed for rotation with the shaft by keys 81. Two sealing collars 82, 84 and spacer 85 locate the hub 80 and blades 78 along the shaft 68 so the blades 78 are received in the channel 76. The collars 82, 84 are received with a close sealing but running fit in aligned bores 86 and 88 in the frame 65 and body 72 respectively. An impeller block 93 is mounted on each blade for relative movement in axial directions via key slots 91, 92 and closely fits the cross sectional area of the channel 76. This arrangement permits differential axial expansion between the pump body parts and the rotor parts on the shaft 68 without interference. The upstream collar 82 is provided with diametrically opposite helical grooves 94 (see also Fig. 6) which lead to the channel 76 through recesses 95 at the base of the trailing sides of the blades 78. The helix angle of the grooves is adapted to facilitate the flow of the liquid to be pumped.

During the operation of the processor the screw 63 is rotated by means, not shown, and feeds liquified polymer along the screw, through the passage 100 and in divided streams through grooves 94 and recesses 95 into the annular channel 76 behind the blades 78. It should be apparent that liquid polymer could be fed to the passage 100 from any suitable source other than the screw 63 Without departing from the scope of the invention. The hub 80 and blades 78 are rotated wi h the screw 63 and, when the channel 76 fills, the advancing impeller blocks 93 pressurize the material in the channel forcing the material through recesses 97 at the base of the leading side of each blade and through helical grooves 99 in the sealing collar 84. The liquid polymer then is forced through an annular passage between the aligned bores 88 and 90 and a collar 102 and through a passage 104 between a conical nose 105 and a recess in the header 74 to an outlet 106. The outlet can be used for die extrusion or may lead to other processing devices. it should be apparent that one or a series of impeller blades and annular channels could be provided in serial fashion axially along the shaft 68 to provide additional pumping facilities without departing from the scope of the invention.

Referring to Figs. 7 and 8, a further embodiment of the pump is shown. As seen a shaft 110 is mounted for rotation in bearings 111 formed in a pair of mating body members 112, 14 which are secured by bolts 113. An annular channel 116 is formed between the members by an appropriate spacer 118. Blades 120 extend from a hub 122 secured to the shaft 110 by a shear pin 115 are rotatable in the channel. Liquid polymer is fed into the channel through a central bore 123, a passage 124, an annular groove 125, grooves 126 and recesses 127 at the base of the trailing side of each blade 120. The pressurized polymer is lead through recesses 130 at the base of the leading side of each blade 120 and through grooves 131 to an annular groove 132 in a collar 135 on the shaft and then through an outlet 134 to a nozzle 136 or other suitable processing devices. The assembly on the shaft is secured by a nut 137 threaded on the shaft.

Another embodiment is shown in Fig. 9 as a combination of a DISK PACK processor 139 without pressurizing pumping channels and a modified pump unit embodying the invention. As shown schematically, polymer is fed through a hopper 140 into a plurality of channels 142 in which the polymer is melted or otherwise processed. Further channels 144 are connected in series by passages 146 as controlled by fixed channel blocks (not shown). Reference may be had to U.S. Patent 4227816 for a more detailed description of the general operation of a typical DISK PACK processor. At the end of a series of processing operations a final channel block (not shown) directs the liquid polymer through a passage 148, an annular passage 150 and grooves 152 in a central shaft 154 to an annular channel 156 having a wedge shape cross section as seen in Fig. 9. Obviously, the channel could have any of a variety of cross sectional shapes without departing from the scope of the invention. Complementary shaped blades 158 extend radially into the channel from the center shaft. Rotation of the shaft cause the blades to pressurize the polymer and pump the material to a second stage channel 160 where appropriate blades increase the pressure on the material which as an example may be forced along a conical passage 161 to an outlet 162.

Experimental tests were run using a pump having a blade diameter of nine (9) inches running at 100RPM in a channel having a .25 inch width. The experimental pump successfully pumped polystrene, HDPE, LDPE, polypropylene and ABS using a 3.5 inch diameter screw melter similar to that shown in Fig. 4 to feed liquid polymer to the pump. LDPE was pumped at the rate of 502 Ibs/hr at 1200 psi with specific energy use of .033 HP hr/lb. (The specific energy was based on motor amperage and includes motor and gear drive losses plus energy consumed by the feed screw which had a capacity of 500 Ibs/hr.) HDPE was pumped with the rotor speed lowered to reduce the melt temperature at a rate of 153 Ibs/hr. at a pressure of 2400 psi with specific energy use of .06 HP-hr/lb. In other tests two pumping stages were operated in series and it was found that the pressure generated nearly doubled with about the same specific energy use. Test analyses also indicate that use of the pump in combination with a screw type processor is more efficient with specific energy use of .032 HP-hr/lb than a comparable screw extruder generating pressure in the usual way at .044 HP-hr/lb.

Little energy savings are expected at such low flow rates. However, it is indicated that substantial energy savings can be realized using larger pumps at higher flow rates, and pressures in excess of 3000 psi can be reached with low density polyethylene. This means that there is a significant potential of replacing metering sections of conventional feed screws or other processing units such as shown in Figs. 1 and 9 with more efficient pumping sections as herein described that occupies less space and uses less energy.

The pumping/pressurizing units have been described with reference to specific types of polymer processing shown only schematically. It should be apparent that such description is by way of reference to typical processing units and not by way of limitation. Obviously, the features and advantages of the novel pump unit in a variety of forms could be used in combination with a variety of simple or sophisticated polymer processing units without departing from the scope of the appended claims.

Claims

1. Apparatus for processing polymer including a processing section and a pumping section; the processing section being adapted to operate on liquid polymer at pressures sufficient only to process the polymer; the pumping section comprising a body having central bearings and a shaft rotatable in the bearings, the shaft having one or more blades extending radially into an annular channel in the body, the channel being closed by the body and the shaft in the bearings, the shaft having at least one groove extending axially from the output of the processing section through the bearing and into the channel behind each blade, considered in the direction of rotation of the shaft, for progressively filling the channel with the processed liquid polymer as the shaft and blades rotate, the front side of the blade engaging and pressurizing the liquid polymer for forcing the polymer through at least a second groove in the shaft extending from the base of the front side of the blade, through the bearing toward an outlet.

2. Apparatus according to claim 1 in which the pumping section has at least a second annular channel receiving a second set of one or more blades extending radially from the shaft, the second groove conducting the pressurized polymer to the backside of each of the second set of blades to fill the second channel, the shaft having a third groove for conducting the further pressurized polymer from the base of the front side of each of the second set of blades axially through the bearing toward an outlet.

3. Apparatus according to claim 1 in which the processing section comprises a drum rotatable with the shaft in a cylindrical chamber extending from an inlet for the polymer to a recess at the end of the chamber and a passage for conducting the polymer in liquid form from the recess to the one groove in the shaft for pressurizing the polymer in the pumping section.

4. Apparatus according to claim 2 in which the processing section comprises a drum rotatable with the shaft in a cylindrical chamber extending from an inlet for the polymer to a recess at the end of the chamber and a passage for conducting the polymer in liquid form from the recess to the one groove in the shaft for pressurizing the polymer in the pumping section.

5. Apparatus according to claim 1 in which the processing section comprises a screw rotatable with the shaft in a barrel, the screw having channel depths sufficient only to generate pressure for performing the desired operation on the polymer and for feeding the polymer in liquid form to the one groove in the shaft.

6. Apparatus according to claim 5 in which the pumping section has at least a second annular channel receiving a second set of one or more blades extending radially from the shaft, the second groove conducting the pressurized polymer to the backside of each of the second set of blades to fill the second channel, the shaft having a third groove for conducting the further pressurized polymer from the base of the front side of each of the second set of blades axially through the bearing toward an outlet.

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7. Apparatus according to claim 1 in which the processing section comprises a rotor rotatable with the shaft in a bore, the rotor having a series of parallel annular grooves for processing polymer fed thereto through an inlet and for feeding the polymer in liquid form to the one groove in the shaft for pressurizing the polymer in the pumping section.

8. Apparatus according to claim 7 in which the pumping section has at least a second annular channel receiving a second set of one or more blades extending radially from the shaft, the second groove conducting the pressurized polymer to the backside of each of the second set of blades to fill the second channel, the shaft having a third groove for conducting the further pressurized polymer from the base of the front side of each of the second set of blades axially through the bearing toward an outlet.

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