This invention relates to plasticating using a screw. rotatable within a barrel to extrude or inject molten resinous material. More particularly, this invention is concerned with improvements in melting and mixing the resinous material using a screw having a material reorientation section between a barrier melt section and an undulating metering section.
A plasticating apparatus commonly used today receives polymer or thermoplastic resin pellets, granules or powders, from an inlet port, then heats and works the resin to convert it into a melted or molten state. The melt or molten material is delivered under pressure through a restricted outlet or discharge port to make the finished article. It is desirable that the molten material leaving the apparatus be completely melted and homogeneously mixed, resulting in uniform temperature, viscosity, color and composition.
Typically, the basic plasticating apparatus has an elongated cylindrical barrel which is heated at various locations along its length. An axially supported and rotating screw extends longitudinally through the barrel. The screw is responsible for forwarding, melting, pressurizing and homogenizing the material as it passes from the inlet port to the outlet port. Typically, the screw has a core with a helical flight thereon and the flight cooperates with the cylindrical inner surface of the barrel to define a helical valley for forward passage of the resin to the outlet port.
There are several different types of thermoplastic resins or polymers, and each has different physical properties and characteristics. Therefore, there are several different screw configurations. In general, however, the typical plasticating screw has a plurality of sections along its extended axis with each section being designed for a particular function. Ordinarily, there is a feed section, a melting section and a metering section in series. In the art, the melting section has been referred to interchangeably as the intermediate, compression or transition section.
The feed section extends forward from the inlet port of feed opening where solid thermoplastic resins, in pellet, granular or powder form, are introduced into the apparatus and pushed forward by the screw along the inside of the barrel. The resin is then worked and heated in the melting section. After approximately 40 to 80 percent of the resin has been melted, solid bed breakup occurs, and solids become randomly dispersed within the melt. It is important to note that most melting initially occurring in the melting section takes place at or near the heat source of the inner wall of the barrel.
To assure a homogeneous melt, therefore, it is often important that solid material be separated from the molten material in the melting section using a barrier to create two adjacent helical channels, a solids channel and melt channel with a barrier flight therebetween, so that the thin melt film which develops at the outer periphery of the solids channel at the inner wall of the barrel is conveyed over the barrier flight and upstream into the adjacent melt channel. As described in more detail by Chung, in U.S. Pat. No. 4,000,884, and further developed by Medici, et al. in U.S. Pat. No. 6,056,430, the typical barrier melting section maximizes the amount of contact between the solid material and the heated inner surface of the barrel wall. As further explained by Medici, et al. in U.S. Pat. No. 6,056,430, conventional barrier melting sections provide for the solid material to be located on the “trail side” of the main flight, whereas the melt material is located at the “push” side of the main flight.
Therefore, it is important to move solids to the push side of the main flight in the metering section of the plasticating screw to provide higher pressure and shear which mixes and melts solids more effectively. Medici, Jr. et al. accomplishes the interchange as described in U.S. Pat. No. 6,056,430, by reversing the diameter and width of the primary and secondary flights at the terminal end of the mixing section. As an alternative, Medici, Jr., et al., uses a barrier flight having a short section of increased pitch at the terminal end of the barrier melt section which abruptly narrows the solids channel and thereby forces solid material over the barrier flight into the melt channel and on the pushing side of the primary flight before the metering section.
Although the configuration made by Medici, Jr., et al., in U.S. Pat. No. 6,056,430 may satisfy many general needs, thermal and composite mixing can be improved even more for various thermoplastic resin and polymer materials by including a more novel reorientation section between a multi-channel barrier melting section and the undulating metering section to better allow reorientation of solid and molten materials. Additional melting can take place via heat convection from the molten material. At the same time this invention permits greater temperature control to avoid the overheating or degradation of the resin. Further, the cost and time needed to manufacture the screw of the instant invention is reduced since intricate structure described by the Medici, Jr., et al., patent is eliminated in the instant invention and unique functional elements and parameters added and described.
Ultimately, the primary objective of the instant invention is to homogeneously mix select resins using an optimum combined barrier melting section and multi-channel undulating metering section, resulting in a completely molten material having uniform temperature, viscosity, color and composition at the terminal end of the metering section.
Medici, Jr. et al., confirms in U.S. Pat. No. 6,056,430 that multi-channel wave metering screws and barrier melting screws are well known. The present invention, like Medici, Jr., et al., modifies and combines the two technologies. Unlike Medici, Jr., et al., however, the instant invention eliminates the “interchange” at the terminal end of the barrier melting section, and describes and claims, instead, a unique reorientation section between the barrier melting section and undulating metering section.
Throughout a plasticating screw, higher pressure and shear rates are obtained on the push side of the main flight since the main flight, as opposed to the barrier or secondary flights, provide reduced clearance with the inner barrel wall and an increased thread width, which in turn produces greater shear rates for the material being conveyed. Often, however, in conventional plasticating screws, the solids are located primarily on the trail side of the main flight instead of the push side of the main flight throughout. The present invention overcomes this disadvantage by providing a screw having a multi-channel barrier melting section and a reorientation section for transferring a major portion of the solids to the push side of the main flight before entering a undulating metering section.
The present invention is a plasticating apparatus comprising a barrel having an inlet and an outlet. A rotatable screw having a longitudinal axis is disposed within and cooperates with an inner wall of said barrel. The screw comprises a feed section, a barrier melting section, a reorientation section and a multi-channel undulating metering section located subsequently downstream along said screw axis. The feed section includes a main helical flight having a push side facing downstream and a trailing side facing upstream. A barrier flight is disposed in said barrier melting section, intermediate said main flight, and said barrier flight with the main flight divides the barrier melting section into a melt channel and solids channel extending helically side by side. The barrier flight includes helical threads with a diameter less than the diameter of the helical threads of said main flight, so that melt material flows over said barrier flight and into said melt channel. This allows melt material conveyed along the barrier melting section to be positioned adjacent the push side of said main flight.
To switch solids to the push side of the main flight in the present invention to take advantage of the higher shear thereof, the barrier flight terminates near the terminal end of the barrier melting section. Following the terminal end of the barrier melting section, the pitch of the main helical flight decreases and then traverses continuously through the reorientation section at least one turn or 360° degrees along the longitudinal axis of the screw. Further, the solids channel and the melt channel in the barrier melting section merge into a substantially uniform reorientation channel at a location substantially coinciding with the decreased pitch of the main flight, thereby forcing solid plastic material conveyed into the reorientation section to move toward the push side of the main flight. After the reorientation section, the main flight traverses into the metering section with a secondary flight being introduced and disposed in said metering section intermediate the main flight whereby solid material conveyed along the metering section is positioned primarily adjacent the push side of the main flight.
In the metering section, the main flight is arranged in a helical direction extending radially from the core and is formed with cut-through recesses located on the main flight periphery and extending axially through the thickness of the main flight. The secondary flight is arranged in a helical direction extending radially from the core and is formed with cut-through recesses located on the secondary flight periphery and extending axially through its thickness. The cut-through recesses provide a passageway through which material being plasticated can cross through the main flight and secondary flight to recirculate with downstream material, in addition to passing over the periphery of the secondary flight, whose diameter is less than that of the main flight. Thus, this improves turbulence of the material in the metering section and improves thoroughness of the mixing that occurs therein.
Another advantage of the present invention is that the melt material conveyed along the metering section is positioned primarily adjacent to the trail side of the main flight, allowing higher pressure and shear to be applied to the remaining solids. Since the secondary flight is undercut and thinner than the main flight, the secondary flight does not provide the shear and pressure of the main flight. By placing solids on the push side of the main flight in the metering section, the present invention applies higher pressure and shear rates to the solids.
Still another advantage of the present invention is that the length of the reorientation section and depth of the reorientation channel may be easily changed to accommodate the various lengths and diameters of plasticating screws.
Many other objectives and features of the present invention will be obvious to those of skill in the art upon contemplation of the entire disclosure herein in connection with the accompanying drawings.
It is to be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the instant invention, for which reference should be made to the claims appended hereto. Other features, objects and advantages of this invention will become clear from the following more detailed description made with reference to the drawings in which:
Referring to
Within the barrel 2 is an axially supported screw 10 which is rotated and which extends from the inlet port 4 to the outlet port 6. In the preferred embodiment the screw 10 includes a main helical flight 13 radially extending from and winding around a core or shaft 12, typically in a right hand threaded direction.
The main helical flight 13 includes a flight land 14 which moves in close cooperative association with the inner wall 3 of the barrel 2 with a clearance therebetween of about 0.005 to 0.007 inches. The main helical flight 13 defines a helical valley 21 forming a main helical channel 18 bounded by flight 13, inner wall 3 of the barrel 2 and the surface of the core 12. The depth of the helical valley 21 is measured radially from the core surface to the inner surface 3 of the barrel 2 and is referred to as the root depth. With the rotation of the screw 10, the helical channel 18 forces a forward flow of resinous materials.
The screw 10 includes a plurality of sections along its axial length, with each section intended to achieve a particular function. There is typically a relatively deep root feed section B for the admission, heating and working of solid resin, a transition or melting section C of reducing root depth to adapt to the reduced volume of resin due to melting and the elimination of air spaces between the solid particles, and a relatively shallow root metering section D wherein the majority of the resin is predominantly in a molten state. The inlet port 4 is typically at the rear-most part of the upstream feed section B and the outlet port 6 is located at the forward-most part of the downstream metering section D.
In the instant invention, the melting section C is a barrier melting section, and the metering section D is a multi-channel undulating metering section, as described below in more detail. In addition to these sections, the instant invention includes a reorientation section A, also referred to herein as a reorientation section, disposed between the barrier melting section C and undulating metering section D.
With reference to
As shown in
As further shown in
Further, the merging of the solids channel 40 and the melt channel 42 ends and the reorientation channel 43 begins at a location substantially coinciding with a decreased pitch of said main flight 13 to force solid plastic material conveyed along said reorientation section A toward said push side 44 of the main flight 13. In the illustrated embodiment, the merging of the solids channel 40 with the melt channel 42 of the present invention is complete within one turn or 360° about the longitudinal axis of the screw 10.
The depth of the reorientation channel 43 is preferably constant throughout the reorientation section A, although it may decrease from start to end by 10% without significantly affecting the performance of the present invention. Preferably, the compression ratio with reference to the last channel 43 of the reorientation section A is between 2.3 to 2.5. As used herein, the term “compression ratio” shall mean the ratio of the volume of material held in the first channel at the feed section to the volume of material held in the referenced channel.
As shown in
The main flight 13 then passes into the undulating metering section D. A secondary flight 56 emerges in the undulating metering section D, being disposed intermediate said main flight 13, thereby forming a new solids channel 50 located on the push side 44 of the main flight 13 and a new melt channel 52 located on trailing side 46 of main flight 13. The secondary flight 56 has a diameter which is 0.09 to 0.10 inches less than the diameter of the main flight 13.
Referring now to
The core 12 in the metering section D is formed with helically directed crests and valleys in channels 50 and 52 located between the main flight 13 and secondary flight 56. As
The core 12 in the metering section D is formed with helically directed crests and valleys in channels 50 and 52 located between the main flight 13 and secondary flight 56. As
With further reference to
The operation of the screw 10 in accordance with the present invention can be explained with reference to the figures. With reference to
Toward the end of barrier melting section C, solids in channel 40 are located adjacent the trailing side 46 of main flight 13 and melt in channel 42 is located adjacent the push side 44 of main flight 13. However, as noted, solids are more quickly transformed to a melt by placing them on the push side 44 of main flight 13 due to the increased pressure and shear force provided by the main flight 13. Accordingly, the above described reorientation section A of the present invention reorients a primary portion of the remaining solids to the push side of main flight 13 which then continues into and through the metering section D. Thus, as shown in
The cut-through recesses 62, 64 shown in
It will thus be seen that a new and useful plasticating apparatus, method and improved longitudinal portion have been illustrated and described. It will be apparent to those skilled in the art that various changes or modifications may be made to the invention without departing from the spirit thereof.
This application is a continuation-in-part of prior and application Ser. No. 10/083,427, filed Feb. 25, 2002, issuing as U.S. Pat. No. 6,672,753 on Jan. 6, 2004.
Number | Name | Date | Kind |
---|---|---|---|
2753595 | Dulmage | Jul 1956 | A |
3006029 | Saxton | Oct 1961 | A |
3486192 | Le Roy | Dec 1969 | A |
3524222 | Gregory et al. | Aug 1970 | A |
3652064 | Lehnen et al. | Mar 1972 | A |
3698541 | Barr | Oct 1972 | A |
3941535 | Street | Mar 1976 | A |
4000884 | Chung | Jan 1977 | A |
4015832 | Kruder | Apr 1977 | A |
4085481 | Maillefer | Apr 1978 | A |
4128341 | Hsu | Dec 1978 | A |
4201481 | Iddon et al. | May 1980 | A |
4215978 | Takayama et al. | Aug 1980 | A |
4227870 | Kim | Oct 1980 | A |
4277182 | Kruder | Jul 1981 | A |
4330214 | Willert | May 1982 | A |
4341474 | Wheeler, Jr. et al. | Jul 1982 | A |
4405239 | Chung et al. | Sep 1983 | A |
4639143 | Frankland, Jr. | Jan 1987 | A |
4729662 | O'Brien | Mar 1988 | A |
4733970 | Yokana | Mar 1988 | A |
4752136 | Colby | Jun 1988 | A |
4770539 | Heathe | Sep 1988 | A |
4786181 | O'Brien | Nov 1988 | A |
4798472 | Chan et al. | Jan 1989 | A |
4896969 | Dray | Jan 1990 | A |
4944906 | Colby et al. | Jul 1990 | A |
5004352 | Tamura et al. | Apr 1991 | A |
5071256 | Smith et al. | Dec 1991 | A |
5088914 | Brambilla | Feb 1992 | A |
5141326 | Eshima | Aug 1992 | A |
5215764 | Davis et al. | Jun 1993 | A |
5599097 | Christie | Feb 1997 | A |
5599098 | Christie | Feb 1997 | A |
5816698 | Durina et al. | Oct 1998 | A |
5961209 | Kovacevic | Oct 1999 | A |
6056430 | Medici, Jr. et al. | May 2000 | A |
6132075 | Medici et al. | Oct 2000 | A |
6132076 | Jana et al. | Oct 2000 | A |
6139179 | Christiano et al. | Oct 2000 | A |
6176606 | Thompson et al. | Jan 2001 | B1 |
6488399 | Womer et al. | Dec 2002 | B1 |
6497508 | Womer et al. | Dec 2002 | B1 |
6547431 | Womer | Apr 2003 | B1 |
6599004 | Barr | Jul 2003 | B1 |
6672753 | Womer et al. | Jan 2004 | B1 |
20040126453 | Dray, Sr. | Jul 2004 | A1 |
20040141406 | Womer et al. | Jul 2004 | A1 |
20040253335 | Anderson et al. | Dec 2004 | A1 |
Number | Date | Country |
---|---|---|
0 046 631 | Mar 1982 | EP |
2137893 | Oct 1984 | GB |
55-132229 | Oct 1980 | JP |
56-92039 | Jul 1981 | JP |
59-188418 | Oct 1984 | JP |
59-202835 | Nov 1984 | JP |
61-222706 | Oct 1986 | JP |
61-222707 | Oct 1986 | JP |
63-291632 | Nov 1988 | JP |
Number | Date | Country | |
---|---|---|---|
20040141406 A1 | Jul 2004 | US |
Number | Date | Country | |
---|---|---|---|
Parent | 10083427 | Feb 2002 | US |
Child | 10746677 | US |