WO2005087477A1

WO2005087477A1 - Extrusion machine for processing of thermoplastic polymeric materials

Info

Publication number: WO2005087477A1
Application number: PCT/UA2005/000010
Authority: WO
Inventors: Evgeniy Petrovich Barmashyn
Original assignee: Evgeniy Petrovich Barmashyn
Priority date: 2004-03-16
Filing date: 2005-03-15
Publication date: 2005-09-22
Also published as: RU2006131486A; RU2329895C2; UA74926C2

Abstract

Extrusion machine for processing of thermoplastic polymeric materials comprises of: housing that includes feeding unit (3), plastication unit (5), degassing unit (6) equipped with ventilating duct (8), and pressing,-out unit (9); screw (2); perforated cylinder (12) that is fixed onto screw (2) within degassing unit (6) and divides space between the screw (2) core and housing (1) wall into internal “c” and external “d” annular channels communicating through holes (13, 14) in cylinder (12); and scraper unit (19). In order to provide for uninterrupted refinement of a polymeric material melt from mechanical impurities, a transverse annular partition (17) is fixed onto the housing (1) wall within the external annular channel “d” of said perforated cylinder (12). Said partition (17) divides channel “d” into a filtration zone communicating directly with plastication unit (5), and a degassing zone communicating with pressing-out unit (9).

Description

EXTRUSION MACHINE FOR PROCESSING OF THERMOPLASTIC POLYMERIC MATERIALS Field of the Invention The invention relates to the structure of one-screw extrusion machines, which are meant for processing such thermoplastic polymeric materials that contain mechanical (including gaseous and, especially, gas-forming) impurities. Prior Art The problem of effective refinement of said materials melts from above-mentioned impurities is emerged a long time ago. In fact, each (even makeup) thermoplastic polymeric material has property to absorb a moisture from air and air as such at the time of their storing in bulk or loading into an extrusion machine. Further, granular or powder thermoplastic polymeric materials collect impurities all the more than sorptive power and specific surface area of whatever granules or powders have being larger. Interest to this problem grows as application of secondary polymeric raw obtained by crushing or agglomeration of waste thermoplastic polymeric materials increases. Naturally, these wastes contain such polymers that are partially degraded as a result of antecedent processing and/or injurious effect of environment. Therefore, repeated melting of said wastes and their thermal and mechanochemical treatment using extrusion machines results in additional destruction of polymers and gasification frequently. In order to eliminate deterioration of extruded articles with ingrained inappropriate hard particles and/or gaseous bubbles, extrusion machines are equipped with means for filtering and degassing of melt usually. It is well known that inappropriate hard particles may be removed by means of simple filters, while gaseous bubbles' removing requires abrupt decompression of high-viscous melt and continuous renovation of "fluid melt - gaseous substances" phase interface. Strainers, which divide melt flows onto small streams, and vacuum-suction of gases are used for said purposes. A simplest strainer is shaped usually as an annular perforated screen that is placed within spiral screw channel at the input into degassing zone of an extrusion machine. Naturally, these strainers may be using for processing easy-flowing melts of such pure polymers as polyethylene, polystyrene and the like preferably. Viscous melts may be degassed using strainer, which is formed as perforated cylinder connected with screw, and scrapers. These scrapers are formed usually as practically flat plates coated by teflon and fixed within extrusion machine housing (L-JeHκeπb I^". LilHeκoBbie πpeccbi

Ana ππacT acc. - MocKβa: rocyflapcrBβHHoe HayMHo-τexHHMecκoe M3flaτeπbcτB0 xi/iMimecKow jιnτepaτypbi, 1962, c. 247-248; In English: Shenkel G. Worm screw Machines for Plastics. - Moscow: State science-technical Publishing House of Chemical Literature, 1962, pp. 247-248). Unfortunately, said flat scrapers decelerate melt flow all the more so melt viscosity is higher. Therefore, spiral screw channel may be filling with melt totally and degassing the melt may be stopping practically if die heads, which have high flow resistance, will be used. Extrusion machine for processing thermoplastic polymeric materials according to UA Patent 14796 A, that is the nearest to proposed further machine constructively, allows to abate said inappropriate phenomenon substantially. Known machine comprises of: (a) a housing which includes assembled in series and communicating with a common extrusion channel a feeding unit, a plastication unit, a degassing unit equipped with ventilating duct for volatile matter suction from melt, and a pressing-out unit whose the extrusion channel part exceeds to diameter the extrusion channel parts belonged at least to the feeding and plastication units; (b) a placed within the extrusion channel screw whose variable diameter corresponds to diameters of the extrusion channel parts within said units; (c) a strainer, that is formed as perforated cylinder fixed onto screw within said degassing unit and divides annular space between the screw core and said housing wall into internal and external annular channels communicating through holes in the wall of said cylinder; and (d) a scraper unit having at least one spiral band that is fixed onto the internal housing surface and surrounded external surface of said perforated cylinder with clearance that is sufficient for free rotation of said screw. Increase of the extrusion channel and screw diameters in pressing-out unit and use of spiral scraper elements exclude the blockage of decompression space with compact melt flow practically. This allows increasing output of extrusion machines equipped with degassing units and effective refinement of arbitrary polymeric materials from gaseous bubbles. However, proceeded (especially waste) polymeric materials contain quite often such mechanical impurities that may stop up the holes and the internal annular channel of the strainer. Therefore, extrusion machines must be stopping and dismantling for cleaning the strainers (and the degassing units as a whole) fairly often. Unfortunately, this cleaning don't exclude decrease of extruded goods quality because impurity particles may pass through strainer freely into pressing-out unit and decompose and evolve gaseous substances there under the action of high temperature within this unit (in comparison with temperatures within antecedent units). Summary of the Invention The invention is based on the problem of creation of such extrusion machine which would provide for uninterrupted refinement of polymeric material melt from mechanical impurities before their degassing and, thus, for effective remaking thermoplastic wastes into high-end goods. This problem is solved in that in an extrusion machine comprising: (a) a housing which includes assembled in series and communicating with a common extrusion channel a feeding unit, a plastication unit, a degassing unit equipped with ventilating duct for volatile matter suction from melt, and a pressing-out unit whose the extrusion channel part exceeds to diameter the extrusion channel parts belonged at least to the feeding and plastication units; (b) a placed within the extrusion channel screw whose variable diameter corresponds to diameters of the extrusion channel parts within said units; (c) a strainer, that is formed as perforated cylinder fixed onto screw within said degassing unit and divides annular space between the screw core and said housing wall into internal and external annular channels communicating through holes in the wall of said cylinder; and (d) a scraper unit having at least one spiral band that is fixed onto the internal housing surface and surrounded external surface of said perforated cylinder with clearance that is sufficient for free rotation of said screw; according to the invention a transverse annular partition is fixed onto the housing wall within the external annular channel of said perforated cylinder, said partition divides said channel into a filtration zone communicating directly with said plastication unit, and a degassing zone communicating with said pressing-out unit, said filtration and degassing zones are communicated through holes in the wall of said cylinder and confined by said cylinder internal annular channel only, a part of filtration zone space, which is confined by said partition, the internal side of said housing wall and said scraper spiral band, serves as receptacle for operational collection of strained sediment of hard impurities and is connected to an external receiver of said sediment through radial outlet in the wall of the extrusion machine housing, and the holes in the wall of said perforated cylinder lying in filtration zone are smaller to diameter in comparison with the holes lying in said degassing zone. Said partition forces polymeric melt, which flows out of the plastication unit into the degassing unit uninterruptedly, to overflow out of the inlet part of strainer's external annular channel into its internal annular channel and then into the degassing zone through the holes in perforated cylinder only. In this time, particles of mechanical impurities, which is larger than the holes in the perforated cylinder at filtration zone, settle on the surface of said cylinder. Then they, under the action of scraper spiral band, remove from filtration zone through the radial outlet in the wall of the extrusion machine housing. Thus, necessities of stopping and dismantling of the extrusion machine for cleaning degassing unit decrease, and quality of extruded goods increases. First additional feature consists in that said partition or said perforated cylinder is equipped with a baffle groove placed in the coupling area of theirs. This groove prevents from overflow of melt out of the filtration zone into the degassing zone between the said partition and said perforated cylinder if pressure difference between the opposite partition faces will be intensive. It provides for stable and effective functioning of the degassing unit. Second additional feature consists in that the input into ventilating duct out of degassing zone is abutted on said partition, and said perforated cylinder is hole-free within the bounds of said baffle groove and said input into ventilating duct. It decreases probability of said duct blockage with melt and frequency of extrusion process stopping for its cleaning. Third additional feature consists in that said partition is made from such antifriction material as, for example, bronze or cast iron. It excluded emergency stop of extrusion machine as a result of said perforated cylinder jamming in said partition practically. Brief Description of the Drawings The invention will now be explained by detailed description of the structure and the operation of extrusion machine with reference to the accompanying drawings, in which: Fig .1 shows general view of extrusion machine (a small-scale longitudinal section); Fig.2 shows structure of the degassing unit (longitudinal section in a large scale); Figures 3, 4, and 5 show such a large scale cross-sections of the degassing unit that are signed as III- III, IV-IV and V-V on Fig.2 respectively; Fig.6 shows fragment of the degassing unit in the gas suction zone (longitudinal section in a large scale). Best Mode Carrying out of the Invention Proposed extrusion machine (see Fig.1) comprises of housing 1 and screw 2 that is placed within axisymmetric extrusion channel of this housing 1 and connected to not shown here a rotation drive. The housing 1 includes assembled in series and communicating with mentioned above common extrusion channel - feeding unit 3 that is connected to loading tray 4 and equipped with not signed especially exchangeable riffled on the inside cylinder sleeve and water cooling jacket, plastication unit 5 equipped with not signed especially controllable electric heating units and air cooling jacket, degassing unit 6 equipped with choker and radial outlet 7 that are meant for removing strained sediment out of extrusion machine, and with ventilating duct 8 that is meant for volatile matter suction, and pressing-out unit 9. Diameter of the extrusion channel increases in the line of transition from feeding unit 3 and plastication unit 5 to degassing unit 6 and pressing-out unit 9. This unit 9 communicates through passageway 10 with not shown here an arbitrary die head, when extrusion machine operates. Total length of the screw 2 is commensurate with length of the housing 1. The screw 2 consists of two portions. First portion 11 is placed within said units 3, 5, and 6 (see Figs 1 , 2) and includes - spiral channel «a», depth of which decreases in the line of transition from feeding unit 3 to plastication unit 5 (see Fig.1), and not shown especially smooth along the full length annular recess in such part of the screw 2 core that is located within the degassing unit 6 and surrounded by strainer (i.e. perforated cylinder) 12 having holes 13 and 14. Second portion 15 of the screw 2 has spiral channel «b». This portion 15 is - located within said pressing-out unit 9, assembled with said first portion 11 (see Figs 1) by spline coupling 16, and secured against axial displacement. Perforated cylinder 12 is fixed (e.g., screwed) between the end surfaces of said first and second portions 11 and 15 of the screw 2 (i.e. on the interval between said spiral channels «a» and «-b», as it is shown on Fig.2). Inside of the cylinder 12 and the surface of above-mentioned annular recess on the screw 2 core confine the internal annular channel «c». External diameter of spiral channel «ft» within the second portion 15 of the screw 2 and diameter of respective part of the extrusion channel exceed external diameter of spiral channel «a» within the first portion 11 of the screw 2. External diameter of the extrusion channel within the degassing unit 6 exceeds external diameter of perforated cylinder 12. Accordingly, inside of the housing 1 wall within said unit 6 and outside of said cylinder 12 confine the external annular channel « » that is coaxial with said internal annular channel «c». These channels «c» and « » are communicated through said holes 13 and 14 in the wall of said cylinder 12 only because a transverse annular partition 17 is fixed onto the housing 1 wall within the external annular channel «cf». This partition 17 - is slide assembled with perforated cylinder 12 (so as to it would being rotate freely), and divides the degassing unit 6 space (or, more particularly, said external annular channel «t ») into a filtration zone communicating directly with spiral channel «a» of said plastication unit 5, and a degassing zone communicating directly with spiral channel «b» of said pressing-out unit 9 and the ventilating duct 8 (see Fig.2 and, additionally, Figs 3, 4 and 5). In other words, the partition 17 forces polymeric melt to overflow out of the filtration zone into the degassing zone through the holes 13, internal annular channel «c» and holes 14 only, and allows to separate the filtration zone from the ventilating duct 8 surely, when extrusion machine operates. Clear dimension of holes 13 within the filtration zone is smaller than clear dimension of holes 14 within the degassing zone. At the same time, these holes 14 may be having clear dimensions increasing in the line of pressing-out unit 9. It is desirable in order to equalise velocities of inflowing any polymeric melt into the degassing zone along the full length of it. Said partition 17 or, preferably, said perforated cylinder 12 may be equipped with a baffle groove "e" placed in the coupling area of theirs (see Fig.6). It is desirable in order to suppression of overflow of the melt through the coupling area of said component parts. Said partition 17 is made usually from such antifriction material as, for example, bronze or cast iron. It is desirable in order to prevent the perforated cylinder 12 jamming. The input into ventilating duct 8 out of degassing zone is abutted on said partition 17, and said perforated cylinder 12 is hole-free within the bounds of said baffle groove "e" and said input into ventilating duct 8 (see Fig.6). The housing 1, within the bounds of degassing unit 6, is equipped with a scraper unit having at least one muff 18 and one scraper formed as spiral band 19 that are placed within filtration zone. However (see Fig.2), it is preferable if scraper unit is composed of two muffs 18 and two spiral bands 19 and 20 that are fixed onto the housing 1 wall within said external channel "d" on each side of the partition 17, i.e. within filtration zone and degassing zone separately. These bands 19 and 20 surrounds said cylinder's 12 external surface with clearance that is sufficient for free rotation of its together with said screw 2. The spiral bands' 19 and 20 turns (and their spiral channels "f and "A") are spread in the opposite direction with respect to the screw's 2 turns (and their spiral channels «a» and «f)» within plastication unit 5 and pressing-out unit 9). The coupling area of the perforated cylinder 12 and the spiral band's 19 turns may be decreased if these turns would be having cants up to 30° from the plastication unit 5 output (see

Fig.6). It is desirable in case said cylinder 12 possesses any additional roughness (i.e. riffled surface, counterbored holes etc.) that is meant for better adherence of the melt with said cylinder 12 and transporting capacity of the spiral band's 19 turns. Said partition 17, cylinder 12 and scraper unit's muff 18 confine (within the filtration zone of the degassing unit 6) such annular receptacle «/» for operational collection of strained sediment of hard impurities that is connected to said radial outlet 7 in the wall of the housing 1. The described extrusion machine operates as follows. A raw polymeric material in the form of granules and/or crushed thermoplastic wastes runs out (usually by gravity) into the spiral channel «a» of the screw 2 through the tray 4. Rotating screw 2 presses this material within the feeding unit 3 and brings of it into the plastication unit 5. Viscous-flow melt, which results within said unit 5 under joint action of heat supplied from the above-mentioned heating elements and rotating screw 2, passes into enhanced as described above degassing unit 6 for cleaning from hard impurities and any volatile matter (see Fig.1). In fact, this "raw" melt flows, at first, into confined by said band 19 spiral channel «f» that is a part of located within filtration zone said external annular channel «c.» (Figs 6 and 3). Then polymeric component of this melt (in particular, together with fine filler particles, if they are present) flows, under counteraction of transverse annular partition 17, through small holes 13 in the perforated cylinder 12 wall into internal annular channel «c». At the same time, coarse particles of mechanical impurities settle onto said cylinder 12 surface and, under pressure of "raw" melt, remove into said annular receptacle «/^"» for operational collection of strained sediment. Said baffle groove "e", which is cut on hole-free surface of said cylinder 12, prevent from overflow of mechanically purified melt along the coupling area of said cylinder 12 and said partition 17 (see Fig.6). Above-mentioned strained sediment together with adsorbed liquid polymer removes from extrusion machine through said radial outlet 7 at least periodically, but always without stopping of the extrusion process (Fig.2). Purified from coarse mechanical impurities melt overflows through holes 14 from internal annular channel «c» into such part of the external annular channel «t/» that is located within degassing zone of said unit 6. This overflow takes place practically evenly and freely because said holes 14 are broader than holes 13 and expanded in the line of pressing-out unit 9. Abrupt decompression of melt stimulates impetuous separation of such volatile matter as air, products of thermal destruction of polymers, residual monomers etc. These volatile matter enter into spiral channel «ft» that is confined by scraper spiral band 20, and then remove from extrusion machine through said ventilating duct 8 by means of suitable vacuum pump (Figs 5 and 6). Arrangement of said duct 8 beside the partition 17 and lack of any holes in such part of perforated cylinder 12, that is placed under the input into said duct 8, prevent from blockage of exhaust zone by melt. Hence, stable processing of polluted polymers is secured. Purified and degassed melt of polymeric material flows into spiral channel «ϋ>» of the screw 2 within pressing-out unit 9. Rotating screw 2 compresses this melt and extrudes it through passageway 10 for production of desirable goods. Industrial Applicability Proposed extrusion machine may be manufactured easy. It is able - to separate of hard impurities from melts of thermoplastic (especially, waste) polymeric materials and remove sediment of these impurities out of any extrusion machine according to the invention when it operates, to degas even high-viscosity polymeric melts efficiently, and to generate high pressure in pressing-out unit. These advantages guarantee stable functioning of the degassing unit and the extrusion machine as a whole in wide-ranging viscosity of melts, and, by perforce, allow using an additional final fine filter before a die head.

Claims

CLAIMS 1. An extrusion machine for processing of thermoplastic polymeric materials comprises of: (a) a housing (1) which includes assembled in series and communicating with a common extrusion channel a feeding unit (3), a plastication unit (5), a degassing unit (6) equipped with ventilating duct for volatile matter suction from melt, and a pressing-out unit (9) whose the extrusion channel part exceeds to diameter the extrusion channel parts belonged at least to the feeding and plastication units; (b) a placed within the extrusion channel screw (2) whose variable diameter corresponds to the diameters of the extrusion channel parts within said units; (c) a strainer, that is formed as perforated cylinder (12) fixed onto screw (2) within said degassing unit (6) and divides annular space between the screw (2) core and said housing (1) wall into internal "c" and external "of annular channels communicating through holes (13, 14) in the wall of said perforated cylinder (12); and (d) a scraper unit having at least one spiral band (19) that is fixed onto the internal housing (1) surface and surrounded external surface of said perforated cylinder (12) with clearance that is sufficient for free rotation of said screw (2); characterised in that a transverse annular partition (17) is fixed onto the housing (1) wall within the external annular channel "of of said perforated cylinder (12), said partition (17) divides said channel "of into a filtration zone communicating directly with said plastication unit (5), and a degassing zone communicating with said pressing-out unit (9), said filtration zone and said degassing zone are communicated through holes (13, 14) in the wall of said cylinder (12) and confined by said cylinder (12) internal annular channel "c" only, a part of filtration zone space, which is confined by said partition (17), the internal side of the housing (1) wall and said scraper spiral band (19), serves as receptacle for operational collection of strained sediment of hard impurities and is connected to an external receiver of said sediment through radial outlet (7) in the wall of the extrusion machine housing (1), and the holes in the wall of said perforated cylinder (12) lying in filtration zone are smaller to diameter in comparison with the holes lying in said degassing zone. 2. The extrusion machine of claim 1 characterised in that said partition (17) or said perforated cylinder (12) is equipped with a baffle groove "e" placed in the coupling area of theirs. 3. The extrusion machine of claim 2 characterised in that the input into ventilating duct (8) out of degassing zone is abutted on said partition (17), and said perforated cylinder (12) is hole- free within the bounds of said baffle groove "e" and said input into ventilating duct (8). 4. The extrusion machine of claim 1 characterised in that said partition (17) is made from such antifriction material as, for example, bronze or cast iron.