ITMI20061798A1 - EQUIPMENT AND EXTRUSION METHOD OF PLASTIC MATERIAL - Google Patents

Description

DESCRIPTION

0 CO of the patent for industrial invention co of FERIOLI FILIPPO S.P.A., -Q OS

of Italian nationality, [D

u .3⁄4 u based in Gorla Minore 21055 - Via Vallazza, 30 UJss Designated inventor: ROSSI Albino

M12006 A00 t $ 7.9 .t

*** **** ***

The present invention relates to a plastic material extrusion apparatus.

In particular, the present invention is relative

to an extrusion equipment for recycled plastic material with a high residual moisture content for

the production of pellets.

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A known type plastic material extrusion apparatus comprises a plastic material feeding hopper; an extrusion head;

a first conveyor for fluidizing, compressing, heating, and advancing the plastic material in a direction of advancement from the feed hopper

to the extrusion head.

The type of extrusion equipment identified above has proven to be particularly efficient in carrying out the extrusion of recycled plastic material containing a low level of humidity. On the contrary, the type of extrusion equipment identified above has proved ineffective to produce

the extrusion of recycled plastic material containing

a moisture content higher than 0.5% by weight because

the high level of residual humidity generates steam which

it affects the correct formation of the pellets.

Generally, the conventional recycling of plastic material, in particular of material packaging

plastic, provides the steps to select the packaging for

eliminate any extraneous fractions; subdivide the

packaging according to the type of polymer they are made of; crush and grind the packaging into flakes of

homogeneous even if irregular size; wash the flakes to eliminate any contaminants or other elements that could be harmful in subsequent processing; if necessary, grind the plastic flakes more finely to obtain flakes of

smaller size; centrifuge the plastic flakes in a centrifuge to reduce the rate of

humidity from 20-25% to 5-8% by weight; thicken the flakes of plastic material in a densifier to reduce the moisture content to a value below

0.5% by weight and make the humidity compatible

of the plastic material with known extrusion equipment.

At present, the centrifuge and the densification 0c rC xxQ o

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large plastic material. Also, the densifier

requires very high energy consumption. Consequently, the recycling of plastic material is a

expensive process and a large part of the cost is

determined by the necessary reduction in the moisture content of the plastic material.

The object of the present invention is that of realizing an extrusion apparatus capable of realizing an effective extrusion of plastic material

containing a relatively high moisture content e

higher than the humidity rate compatible with known extrusion equipment.

According to the present invention it is realized

a plastic material extrusion equipment,

in particular containing recycled plastic material

a high level of residual moisture, the equipment

extrusion comprising a feeding hopper for the plastic material; an extrusion head; a

first conveyor for fluidizing, compressing, heating, and advancing the plastic material in a direction of advancement from the feed hopper

to the extrusion head; the extrusion apparatus being characterized by the fact of comprising auxiliary channels which put the first conveyor in communication with the feed hopper so that with U1 = J uU want the steam generated during the heating of the plastic material from the first conveyor to the feed hopper .

The auxiliary channels that connect the first conveyor to the feed hopper allow the steam that develops into the atmosphere thanks to the heating and compression carried out during the advancement of the plastic material along the first conveyor to be released into the atmosphere. In other words, the extrusion apparatus carries out the extrusion of the plastic material and at the same time the drying of the plastic material before it reaches the extrusion head.

The present invention also relates to a method of extrusion of plastic material.

According to the present invention, a method of extrusion of plastic material is provided, in particular recycled plastic material containing a high level of residual humidity, the method comprising the steps of fluidizing, compressing, heating, and advancing the plastic material in a direction of advancement in a first conveyor from a feed hopper to an extrusion head; the method being characterized by conveying the steam developed during the heating phase of the plastic material from the first conveyor to the feed hopper through auxiliary channels.

For a better understanding of the present invention, a preferred embodiment will now be described, purely by way of non-limiting example, with reference to the attached figures, in which:

Figure 1 is a side elevation view, partially in section and with parts removed for clarity, of the extrusion apparatus object of the present invention;

Figure 2 is a side elevation view on an enlarged scale, with parts in section, parts removed for clarity, and exploded parts, of the extrusion apparatus of Figure 1;

- Figures 3, 4 and 5 are sectional views, with parts removed for clarity and on a further enlarged scale, of components of the extrusion apparatus of Figure 2 according to the respective section lines III-III, IV-IV, and V-V.

In Figure 1, 1 indicates as a whole a plastic material extrusion apparatus.

The extrusion apparatus 1 extends prevalently

in a direction of advancement D and comprises a feeding hopper 2 of plastic material preferably in flakes; an extrusion head 3; a screw conveyor 4 extending between the hopper of

infeed 2 and the extrusion head 3 in the feed direction D; and a recirculation screw conveyor 5, which connects an intermediate part of the screw conveyor 4 and the feed hopper 2.

The feed hopper 2 is substantially defined by a cylindrical wall 6, which is joined to the screw conveyor 4 to directly introduce the plastic flake material into the screw conveyor 4 in a free, ie not forced manner. Consequently, the feed hopper 2 communicates directly with the surrounding environment.

The extrusion head 3 is arranged at the opposite end of the screw conveyor 4 with respect to the feed hopper 2 and is shown schematically in Figure 1. The extrusion head 3 is made according to known constructive characteristics which are not illustrated in the attached drawings, nor are they described in the present description.

The screw conveyor 4 extends between the feed hopper 2 and the extrusion head 3 along

an axis Al parallel to the direction of advance D. 0 The screw conveyor 4 comprises a conduit 7, and <a screw 8 rotatable inside the conduit 7 around the axis A1; an electric motor 9 and a gearmotor uLU 10 to rotate the screw 8 around the axis A1.

The duct 7 is heated and comprises a tube 11 having a maximum diameter D, and a tube 12, which has a diameter D2 smaller than the diameter D1 and a length significantly greater than the length of the tube 11 in the direction of advance D. The tubes 11 and 12 are aligned along the axis A1 and are connected to each other by a flange fixed with screws.

The tube 11 has in succession in the direction of advancement D a cylindrical seat 13 with a diameter D1, and a frusto-conical seat 14 converging towards the diameter D2 in the direction of advancement D. The tube 12 has a cylindrical seat 15 with a diameter D2.

With reference to figure 2, the frusto-conical seat 14 connects the cylindrical seat 13 of diameter D1 to the cylindrical seat 15 of diameter D2 and has three longitudinal straight ribs 16 (only two ribs 16 are shown in figure 2) uniformly distributed around the axis A1 and converging from the diameter DI towards the diameter D2. The screw 8 has a frusto-conical shape in correspondence with the frusto-conical seat 14 so as to couple with a small play at the ribs 16. 0 u With reference to figures 3, 4 and 5, the frusto-conical seat 14 has between each pair of ribs 16 0 adjacent to an expansion chamber 17 delimited by a vaulted surface 18 and by the ribs 16. In Figures 3, 4 and 5, circles C1, C2 and C3 are indicated respectively in dashed lines, which define the dimensions of the screw 8 in rotation around the axis Al. The height (measured in the radial direction with reference to the axis Al) of the surfaces 18 and of the ribs 16 with respect to the circles Cl, C2 and C3 progressively reduces as the truncated cone seat 14 converges towards the tube 12. Each expansion chamber 17 allows the steam generated by the heating of the screw conveyor 4 to reach the feed hopper 2 and to be released into the atmosphere. In other words, the expansion chambers 17 define auxiliary channels for conveying the steam in a direction substantially opposite to the direction of advance D of the plastic material. Evacuation of the steam is facilitated by the fact that the steam is able to pass through the plastic material, which in the frusto-conical seat 14 has started the fluidification phase, but still has free spaces between the flakes. The ribs 16 and the expansion chambers 17 are obtained by mechanical processing in the duct 7 itself, in particular 0 in the pipe 11. <

2. With reference to Figure 1, the screw 8 comprises a shaft 19; and a helix 20 which extends u VUJ

from the shaft 19. The shaft 19 extends along the axis A1 and has a cylindrical portion 21 in succession in the direction of advancement D; a truncated cone section 22 converging; a truncated cone section 23 diverging; a truncated cone section 24 converging; a cylindrical portion 25; and a truncated cone section 26 diverging.

The cylindrical portion 21 is arranged in the cylindrical seat 13; the converging truncated cone section 22 is arranged in the truncated conical seat 14; while the frusto-conical portions 23, 24, and 26, and the cylindrical portion 25 are arranged inside the cylindrical seat 15. The frusto-conical portion 22 has a taper lower than the conicity of the seat 14 and, consequently, the radial dimension of the helix 20 is progressively reduced in the direction of advance D. In this way, the plastic material is compressed along the converging truncated-cone portion 22.

Inside the cylindrical seat 15 the variations in diameter of the shaft 19 determine a reduction of the effective passage section or an enlargement of the effective passage section. In this way, the 0 CQ rv OC

plastic material is compressed along the diverging truncated cone sections 23 and 26 and is expanded along the converging truncated cone section 24.

U 3⁄4 U

The duct 7 comprises electrical resistances LU

27 schematically illustrated in Figure 1 to heat the plastic material during the advancement of the plastic material in the screw conveyor 4 according to

known modes.

In addition to the electric resistances 27, the screw conveyor 4 is equipped with an exchanger

of heat 28 arranged around the tube 11 at the feed hopper 2 for cooling

the plastic material contained in the cylindrical seat f-13; and with a drain pipe 29 for evacuating the water which may possibly be accumulated and condensed in the

cylindrical seat 13.

The recirculation screw conveyor 5 extends

between an opening 30 made along the tube 12 and an opening 31 made in the wall 6 of the hopper

supply 2 and comprises a conduit 32 extending along an axis A2; a screw 33 rotatable around

to axis A2; an electric motor 34 and a gearmotor

35 connected to the electric motor 34 and to the screw 33. Il

duct 32 has a seat 36 with a constant diameter D3

and the screw 33 comprises a shaft 37 of constant diameter

and a constant pitch propeller 38. The conduit 32 has an end flange 39 fixed to the feed hopper 0 2 and is fixed to the pipe 12 by means of 1 =

u a manifold 40 arranged around the tube 12 and provided with a housing seat for the screw conveyor 5 so as to put the cylindrical seat 15 in direct communication with the cylindrical seat 36.

The opening 30 is arranged in correspondence with the cylindrical portion 25 of the shaft 19. In this area, the previously compressed plastic material expands thanks to the widening of the effective passage section and penetrates into the seat 36 and is fed by the screw conveyor 5 to the feed hopper 2 in which it is mixed with the flakes of plastic material fed through the feed hopper 2 itself.

The screw conveyor 5 is equipped with electrical resistances 27 to prevent the solidification of the plastic material and the condensation of the steam, and essentially defines an auxiliary channel through which the steam developed thanks to the heating of the screw conveyor 4 is led back to the feed hopper 2 and released into the atmosphere.

In use, the extrusion apparatus 1 operates in the following way. The flakes of recycled plastic material not subjected to centrifugation and thickening and, or Cu OC therefore, containing a percentage of water by weight on J8

<more than 0.5 per cent, are fed to the LLI hopper or already feed 2. The screw conveyor 4 advances H 3⁄4 in = ≥ the plastic flakes in the direction of advancement D towards the extrusion head 3 During the advancement the plastic material is heated thanks to the electric resistances 27 and compressed by the screw 8 so as to progressively transform the plastic material flakes into a pasty fluid and feed a flow rate Q1 of plastic material to the extrusion head.

The first phase of compression and heating of the plastic material is carried out in the truncated cone seat

14. In this first phase, heating and compression determine the production of water vapor which is able to rise up the screw conveyor 4 in a direction substantially opposite to that of the forward direction D thanks to the expansion chambers 17 which define some auxiliary evacuation channels obtained directly in the screw conveyor 4. In this way, the steam reaches the cylindrical seat 13 and, in part, is released into the atmosphere through the feed hopper 2 and, in part, condenses into the water which is evacuated through the drain pipe 29.

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In the cylindrical seat 15 the plastic material is D <Q> Ù

-Q heated and further compressed along the portion 23 o; truncated cone of shaft 19 and is expanded along the converging truncated cone section 24 and along the cylindrical section ci in -3⁄4 25. The plastic material from the structure is progressively transformed from the solid structure into flakes into a pasty fluid. In the expansion phase, the plastic material releases further steam. As the plastic material expands, it partially penetrates into the seat 36 of the screw conveyor 5 and is fed by the screw conveyor 5 to the feed hopper 2 in which part of the steam is released into the atmosphere and part of it is condensed by the heat exchanger. 28.

The mixing of the recirculated plastic material with the flakes fed to the feed hopper 2 accelerates the heating of the flakes and favors the release of the steam trapped in the plastic material itself.

In the cylindrical seat 15 the material is further compressed and conveyed through the extrusion head 3. The screw conveyor 5 has a capacity

Q2 of plastic material between 5% and 20% of the flow rate Ql. Consequently, along the portion of the first screw conveyor 4 comprised between the feed hopper 2 and the opening 30 a door is advanced

o0c £

3 CO ta of plastic material equal to the sum of the flow rates

Q1 and Q2.

u E The function of the heat exchanger 28 is to avoid excessive heating of the flakes in the feeding phase and to avoid any seizure.

Furthermore, the heat exchanger 28 allows any steam trapped by the plastic material to be condensed. The condensed vapor is evacuated through the drain 29.

Claims (17)

ZJ <Q> O R IV EN D ICA Z ION I o u 1. Equipment for extrusion (1} of material Iu .3⁄4 THERE plastic, in particular recycled plastic material containing a high level of residual humidity, the extrusion apparatus (1) comprising a feeding hopper (2) for the plastic material; an extrusion head (3); a first conveyor (4) for fluidizing, compressing, heating, and advancing the plastic material in a direction of advance (D) from the feed hopper (2) to the extrusion head (3); the extrusion apparatus (1) being characterized in that it comprises auxiliary channels {5; 17) which put the first conveyor (4) in communication with the feed hopper (2) to convey the steam generated during the heating of the plastic material from the first conveyor (4) to the feed hopper (2). 2. Extrusion apparatus according to claim 1, characterized in that the first conveyor is a first screw conveyor {4} comprising a first duct (7) extending along a first axis (A1); and a first feed screw (8) rotatably mounted inside the first duct (7) around the first axis (A1), 3. Extrusion apparatus according to claim 2, characterized in that the first screw conveyor (4) has a cross section of variable passage along the first axis (A1) so as to compress and expand the plastic material during the advancement of the plastic material. 4. Extrusion apparatus according to claim 3, characterized in that said first screw {8) comprises a first shaft {19} and a first helix (20) which extends radially from said shaft (19); said first shaft (19) having a variable diameter along the first axis (A1) so as to vary the cross section of passage along the first axis {To the) . 5. Extrusion apparatus according to any one of claims 1 to 4, characterized in that said auxiliary channels {5; 17) include OURO MACC <E> TT <E> a second conveyor {5} extending between the first <lbll} B87> A <d '(iittrh> a <r> or a <sc> conveyor {4) and the feed hopper {2 ) to feed part of the partially fluidized plastic material from the first screw conveyor (4) to the feed hopper (2) together with the steam, 6. Extrusion apparatus according to claim 5, characterized in that the second conveyor (5) is arranged outside the first convo developer {4}; the first conveyor (4) comprising an opening {30} arranged between said feed hopper (2) and the extrusion head {3} to put P u in communication between the first and second conveyors uEU i4, 5). 7. Extrusion apparatus according to claims 5 or 6, characterized in that the second conveyor {5} is a second screw conveyor (5) comprising a second conduit {32} and a second feed screw {33} mounted in a manner rotatable inside the second duct (32} around a second axis (A2). 8. Extrusion apparatus according to any one of claims 2 to 7, characterized in that said auxiliary channels (5; 17} comprise expansion chambers formed in the first duct (7); said expansion chambers being in communication with said feed hopper (2). 9. Extrusion apparatus according to claim 8, characterized in that the first duct (7} has a frusto-conical seat {14} arranged downstream of the feed hopper (2); said first screw (8) comprising a conical shape in the coupling area with the frusto-conical seat (14); said frusto-conical seat (14) comprising ribs (16); each expansion chamber {17} extending between two adjacent ribs (16). 10. Extrusion equipment according to a qual any of the preceding claims, characterized in that it comprises a heat exchanger (28) for cooling the first conveyor (4) in proximity to the feed hopper (2). 11. Extrusion apparatus according to any one of the preceding claims, characterized in that it comprises a drain pipe (29) arranged along the first conveyor (4) in correspondence with said feed hopper (2). 12. Apparatus according to any one of the preceding claims, characterized in that said feed hopper (2) is non-forced feed. 13. Method of extrusion (1) of plastic material, in particular recycled plastic material containing a high level of residual moisture, the method comprising the steps of fluidizing, compressing, heating, and advancing the plastic material in a direction of advance (D) in a first conveyor from a feed hopper (2) to an extrusion head (3); the method being characterized in that it conveys the steam developed in the heating phase of the or plastic material from the first conveyor (4) to the feed trough (2) through auxiliary channels £ (5; 17). r0 "u U 14. Method according to claim 13, characterized in that it comprises the step of conveying from the first conveyor (4) to the feed hopper (2) part of the plastic material partially fluidized together with the steam; the auxiliary channels (5; 17} comprising a second conveyor {5) disposed outside the first conveyor (4). 15. Method according to claim 14, characterized in that the first conveyor (4) feeds a first flow rate (Ql) of plastic material to the extrusion head (2), while the second conveyor (5) feeds a second flow rate (Q2) of plastic material from the first conveyor to the feed hopper (2) through said second conveyor (5). 16. Method according to claim 15, characterized in that the second flow rate (Q2) of plastic material is comprised between 5% and 20% of the first flow rate (Ql). Method according to any one of claims 13 to 16, characterized in that the steam is conveyed from the first conveyor (4) to the feed hopper {2} through auxiliary channels (17) formed in the first conveyor (4) -18. Method according to any one of the claims 13 to 17, characterized by cooling the first conveyor (4) near the hopper of power supply (2). p.i FERIOLI FILIPPO S.P.A. EXCEPT MAURO (Enrolled O <E> CC <ET> T U <R> O