A CO-ROTATING SELF-CLEANING TWO SCREW EXTRUDER WITH AN INTERNAL BAFFLE

Abstract

A self-cleaning extruding apparatus with two co-rotating screws and the method thereof are provided here. Said apparatus is comprised of a screw mechanism, a barrel (1), a feeding port (10), a venting port (11), and a discharge port (12). Said screw mechanism is comprised of the first screw with one tip (3) and the second screw with two tips (4). There is a baffle in the channel of the first screw and the baffle's height is lower than that of the screw flight. The baffle will cause hyperbolic perturbation in the shape of a ‘figure 8’ flow pattern above the top of the baffle. The first and second screws rotate at the same speed and touch each other at all times, thereby achieving a self-cleaning function.

The baffle will generate chaotic mixing in the screw channel caused by the hyperbolic perturbation. Topological chaos is also introduced into the screw channel by the mechanism ‘one part divided into two parts, then two parts converging into one part, and then one part divided into two parts once more’. Each of the screws in the present invention uses an asymmetrical flow channel geometrical shape, such that a periodic action like ‘compression—expansion—further compression—expansion further’ works. The above three enhancement mechanisms work together to efficiently accelerate melting and mixing.

Claims

1. A co-rotating, self-cleaning extruder with two screws and an internal baffle is comprised of a screw mechanism and a barrel; Said screw mechanism is provided inside of the inner section of the barrel, and placed horizontally; Said screw mechanism is comprised of the first screw and the second screw, where the axes of the first and second screws are coincidental with that of the barrel, the first screw has a one-tip configuration, the second screw has a two-tip configuration, and the first screw has an internal baffle, which is lower than the screw flight and can cause a hyperbolic perturbation in the shape of a ‘figure 8’ flow manifold; The first and second screws co-rotate at the same speed and keep in touch with each other at all times; The first screw and the baffle achieve the self-cleaning function with the channel of the second screw, and the second screw achieves the self-cleaning function with the channel of the first screw.

2. A co-rotating, self-cleaning extruder with two screws and an internal baffle in accordance with claim 1, characterized by the outer sides of the first screw and the second screw being tangential to the inner side of the barrel cavity, and the flow channel formed between the first screw, the second screw, and the inner side of the barrel.

3. A co-rotating self-cleaning extruder with two screws and an internal baffle in accordance with claim 1, characterized in that the cross-sections of the first and second screws are comprised of several circle arcs of different radii, and the number of circle arcs of the first and second screws are the same.

4. A co-rotating self-cleaning extruder with two screws and an internal baffle in accordance with claim 3, characterized in that the cross-section of the first and second screws are comprised of eight circle arcs of different radii, where the arcs of the first screw are M.sub.1M.sub.2, M.sub.2M.sub.3, M.sub.3M.sub.4, M.sub.4M.sub.5, M.sub.5M.sub.6, M.sub.6M.sub.7, M.sub.7M.sub.8, and M.sub.8M.sub.1; and the arcs of the second screw are N.sub.1N.sub.2, N.sub.2N.sub.3, N.sub.3N.sub.4, N.sub.4N.sub.5, N.sub.5N.sub.6, N.sub.6N.sub.7, N.sub.7N.sub.8, and N.sub.8N.sub.1; The arc M.sub.1M.sub.2 is engaged with the arc N.sub.1N.sub.2; Correspondingly, M.sub.2M.sub.3 is engaged with N.sub.2N.sub.3, M.sub.3M.sub.4 with N.sub.3N.sub.4, M.sub.4M.sub.5 with N.sub.4N.sub.5, M.sub.6M.sub.7 with N.sub.6N.sub.7, M.sub.7M.sub.8 with N.sub.7N.sub.8, and M.sub.8M.sub.1 with N.sub.8N.sub.1.

5. A co-rotating self-cleaning extruder with two screws and an internal baffle in accordance with claim 4, characterized in that the rotation center of the first screw is O.sub.1, arc M.sub.5M.sub.6 corresponds to the baffle, the polar angle of the baffle experiences cyclic changes or non-cyclic changes, and the polar angle is the angle between the centerline of the baffle and axis O.sub.1M.sub.3.

6. A co-rotating self-cleaning extruder with two screws and an internal baffle in accordance with claim 4, characterized in that the rotation center of the first screw is O.sub.1, arc M.sub.5M.sub.6 corresponds to the baffle, the polar angle of the baffle is constant, and the polar angle is the angle between the centerline of the baffle and axis O.sub.1M.sub.3.

7. A co-rotating self-cleaning extruder with two screws and an internal baffle in accordance with claim 4, characterized by the first screw, where the height of the baffle is constant, or experiences cyclic changes with the increase of the corresponding axial position.

8. A co-rotating self-cleaning extruder with two screws and an internal baffle in accordance with claim 1, characterized in that the inner cavity of the barrel consists of two cylindrical grooves which are communicated, whose cross-section appears as a hole in the shape of a ‘figure 8’.

9. A co-rotating self-cleaning extruder with two screws and an internal baffle in accordance with claim 1, characterized in that according to the motion direction of the materials to be processed, the inner section of barrel 1 is divided into a solid transporting zone, a melting zone, a venting zone, and a mixing and extruding zone; said feeding port is located above the barrel of the solid transporting zone, said venting port is located above the barrel of the venting zone, both the feeding port and the venting port are communicated with the barrel, and said discharge port is located at the end of the barrel.

10. A co-rotating self-cleaning extruder with two screws and an internal baffle in accordance with claim 1, characterized by the following steps: (Step 1) After the materials enter the barrel from the feeding port, the first screw and second screw co-rotate along their own axes; When the materials enter the solid conveying zone, the feed materials are pushed forward, partially under the positive displacement of the first and second screws and partially by the friction forces from the first and second screws, so that the materials are forced to move toward the melting zone; At the same time, the mixing of components from the first and second screws is achieved due to the action of the baffle in the first screw; (Step 2) When the materials move to the melting zone, heat transfer is enhanced because of the stir action of the baffle in the first screw channel; Compression action is exerted on the materials and pre-melting is achieved due to the action of compression energy of the second screw; Meanwhile, friction heat is generated by the high speed rotation of each of the screws and, at the same time, external heat is conducted through the barrel; Topological chaos is also introduced into the screw channel by the mechanism ‘one part divided into two parts, then two parts converging into one part, and then one part divided into two parts once more’; In addition, the cross-section of the flow channel will undergo the ‘expansion—compression—expansion’ action, and the separation of melt from solids will be accelerated; At the same time, the baffle in the first screw will cause hyperbolic flow perturbation in the shape of a ‘figure 8’ to generate chaotic mixing; All of these actions work together to accelerate the melting process, so that the materials become a cohesive melt; (Step 3) When the melt enters the venting zone, the single one-flow channel in the first screw is communicated with the two independent channels, which are separated by the screw flight in the second screw, so that the surface area of venting is increased; Furthermore, the stir action of the first screw, and the compression and expansion action of the second screw, will accelerate gas to discharge from the venting port, causing the melt to move further toward the discharge port; (Step 4) When the melt enters the mixing and extruding zone, the melt is subjected to the topological chaos from the flow channel, which consists of two screws and the barrel, where the action of “one part divided into two parts, then two parts converging into one part, and then one part divided into two parts once more” is effective; The baffle in the first screw channel will introduce hyperbolic perturbation in the shape of a ‘figure 8’ to generate global chaotic mixing throughout the whole screw channel; In addition, the periodic compression action will lead to elongational flow; These three effects will improve the mixing and plasticating of materials so that the melt can be stably extruded from the discharge port; At the same time, a self-cleaning effect is achieved by the inter-wiping effect between each of the screws.

Description

DESCRIPTION OF ACCOMPANYING DRAWINGS

[0025] FIG. 1 is a structural schematic diagram of embodiment 1 in the present invention.

[0026] FIG. 2 is an enlarged structural schematic diagram of embodiment 1 cut along E-E in FIG. 1.

[0027] FIG. 3 is an enlarged structural schematic diagram of embodiment 1 cut along F-F in FIG. 1.

[0028] FIG. 4 is a three-dimensional structural schematic diagram of the screw mechanism and partial barrel in embodiment 1.

[0029] FIG. 5 is the first principle schematic diagram of achieving chaotic mixing, topological chaos, and elongation action in embodiment 1.

[0030] FIG. 6 is the second principle schematic diagram of achieving chaotic mixing, topological chaos, and elongation action in embodiment 1.

[0031] FIG. 7 is the third principle schematic diagram of achieving chaotic mixing, topological chaos, and elongation action in embodiment 1.

[0032] FIG. 8 is a structural schematic diagram of the cross-section of the screw mechanism and partial barrel in embodiment 2.

[0033] FIG. 9 is a three-dimensional structural schematic diagram of the screw mechanism and partial barrel in FIG. 8 of embodiment 2.

[0034] FIG. 10 is a three-dimensional structural schematic diagram of the screw mechanism and partial barrel in embodiment 6.

PARTICULAR EMBODIMENTS

[0035] The present invention is further described in detail below by incorporating the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

Embodiment 1

[0036] As shown in FIGS. 1 through 7, the co-rotating, self-cleaning two-screw extruder with internal baffle is comprised of a screw mechanism and a barrel (1). Said screw mechanism is contained inside the inner section (2) of the barrel (1), and placed horizontally. Said screw mechanism is comprised of the first screw (3) and the second screw (4); the axis of the first screw (3) and the second screw (4) are coincidental with that of the barrel (1). The first screw (3) is a one-tip configuration, while the second screw (4) is a two-tip configuration. The first screw has an internal baffle (5), which is lower than the screw flight and causes the hyperbolic perturbation of the ‘figure 8’ shaped flow manifold as shown in FIGS. 5-7. The first screw (3) and the second screw (4) co-rotate at the same speed and touch each other. The first screw and the baffle achieve the self-cleaning function with the channel of the second screw, and the second screw achieves the self-cleaning function with the channel of the first screw. The contour lines of the threads of the first screw (3) and the second screw (4) are tangent to the inner wall of the barrel (1). The flow channel is formed between the outer sides of the first and second screws and the inner side of the barrel. The cross-section counters of the first and second screws are comprised of several circle arcs of different radii, and the number of circle arcs of the first screw and the second screw are the same. As shown in FIG. 4, the inner cavity of the barrel consists of two cylindrical grooves that are communicated, whose cross-sections appear as the hole with the ‘figure 8’ shape.

[0037] According to the motion direction of the materials to be processed, the inner section of the barrel (1) is divided into a solid transporting zone (6), a melting zone (7), a venting zone (8), and a mixing and extruding zone (9). The feeding port (10) is located above the barrel (1) of the solid transporting zone (9). The venting port (11) is located above the barrel (1) of the venting zone (11). Both the feeding port (10) and the venting port (11) are communicated with the barrel (1). The discharging port (12) is located at the end of the barrel (1).

[0038] The structure described above is shown in FIGS. 2 and 3. The cross-sections of the first and second screws are comprised of 8 circle arcs; the 8 arcs of the first screw are M.sub.1M.sub.2, M.sub.2M.sub.3, M.sub.3M.sub.4, M.sub.4M.sub.5, M.sub.5M.sub.6, M.sub.6M.sub.7, M.sub.7M.sub.8, and M.sub.8M.sub.1, and those of the second screw are N.sub.1N.sub.2, N.sub.2N.sub.3, N.sub.3N.sub.4, N.sub.4N.sub.5, N.sub.5N.sub.6, N.sub.6N.sub.7, N.sub.7N.sub.8, and N.sub.8N.sub.1. M.sub.1M.sub.2 is engaged with N.sub.1N.sub.2, M.sub.2M.sub.3 with N.sub.2N.sub.3, and so on.

[0039] Therein, arc M.sub.1M.sub.2 is tangent to the inner cavity (i.e., arc M.sub.1M.sub.2 is the outer curve of the first screw) and its corresponding central angle is α, which is symmetrical about the polar axis O.sub.1y. For the convenience of expression, the first screw (3) and the second screw (4) are simultaneously rotated at an equal angle so that the axis O.sub.1y is always points north. It follows that for different axial positions z, the arc M.sub.8M.sub.1, M.sub.1M.sub.2, and M.sub.2M.sub.3 in the first screw will remain fixed so the arcs N.sub.8N.sub.1, N.sub.1N.sub.2, and N.sub.2N.sub.3, in contrast, the rest of arcs will rotate about their own rotation axis of screws, i.e., O.sub.1 or O.sub.2, as shown in FIG. 2.

[0040] More exactly, the central angle of arcs M.sub.2M.sub.3 and M.sub.8M.sub.1 are all β, the central angle of arc M.sub.4M.sub.5 and M.sub.6M.sub.7 are all γ, and the central angle of arc M.sub.3M.sub.4 and M.sub.7M.sub.8 are φ1 and φ2. The arc M.sub.5M.sub.6 corresponds to the baffle, which has radius h, where d/2≦h<D/2 . The central angle of M.sub.5M.sub.6 is ε, which is symmetrical about O.sub.1A, and the angle between axis O.sub.1A and axis O.sub.1M.sub.3 equals the polar angle θ, where θ varies with an increase of axial position z, wherein 0≦z≦L, where L denotes the pitch of the first and the second screws. θ.sub.min≦θ≦θ.sub.max, where

[00001]${\theta }_{\min }=\frac{\alpha }{2}+\frac{\mathrm{.Math.}}{2}+\beta +\gamma .Math.$$.Math.\mathrm{and}$$.Math.{\theta }_{\max }=2.Math.\pi -\left(\alpha +2.Math.\beta +\gamma +\frac{\mathrm{.Math.}}{2}\right).$

The angle θ shows cyclic variation with an increase of axial position z, as shown below,

[00002]$\begin{array}{cc}\theta ={\theta }_{\min }+\frac{{\theta }_{\max }-{\theta }_{\min }}{z_{*}}.Math..Math.z,z\le z_{*},& \\ \mathrm{Or},& \\ \theta ={\theta }_{\min }+\frac{{\theta }_{\max }-{\theta }_{\min }}{z_{*}-L}.Math.\left(x-L\right),z\ge z_{*}& \\ \theta ={\theta }_{\min }+\frac{{\theta }_{\max }-{\theta }_{\min }}{z_{*}}.Math..Math.z,z\le z_{*},& \end{array}$

where z* corresponds to the axial position of θ.sub.max, where 0<z*<L, and z*/L=0.5˜0.62 is preferred. The height of the baffle remains constant with an increase of its axial position.

[0041] The arc M.sub.1M.sub.2 in the first screw is engaged with the N.sub.1N.sub.2 arc in the second screw, as is M.sub.2M.sub.3 with N.sub.2N.sub.3, M.sub.3M.sub.4 with N.sub.3N.sub.4, and so on. Therein, the arc N.sub.5N.sub.6 is symmetrical about the axis O.sub.2B, and the phase difference between the axis O.sub.2B and O.sub.1A is π, where the arc N.sub.3N.sub.4 and N.sub.7N.sub.8 are engaged with the inner cavity of the barrel.

[0042] The centerline distance between O.sub.1, the rotation center of the first screw (3), and O.sub.2, the rotation center of the second screw (4), is C, and the maximum diameters of the first and second screws is D. At the same time, the minimum diameter of the first and second screws is d, the angle degree for the arc M.sub.2M.sub.3 and M.sub.8M.sub.1 in the first screw is equal to β, where

[00003]$\beta =2.Math..Math.\arccos .Math..Math.\left(\frac{C}{D}\right);$

thus, the angle for the arc N.sub.2N.sub.3 and N.sub.8N.sub.1 in the second screw is also equal to β. The angle for the arc M.sub.4M.sub.5 and M.sub.6M.sub.7 in the first screw is equal to γ, where

[00004]$\gamma =\pi -\mathrm{arc}.Math..Math.\cos .Math..Math.\left(\frac{d^2+4.Math.h^2-4.Math.\mathrm{Cd}}{4.Math.\left(2.Math.C-d\right).Math.h}\right),$

such that the angle for the arc N.sub.4N.sub.5 and N.sub.6N.sub.7 in the second screw is also equal to γ.

[0043] The arc M.sub.1M.sub.2 has a radius value of D/2 and is centered at O.sub.1, the rotation center of the first screw. The arcs M.sub.3M.sub.4 and M.sub.7M.sub.8 have the same radius values, d/2, and their centers are all O.sub.1, the rotation center of the first screw. The arc M.sub.2M.sub.3 has the radius value C and is tangential to the circle, which is centered at O.sub.1 and has the radius value d/2 at the point M.sub.3. Thus, the arc M.sub.8M.sub.1 has the radius value C and is tangential to the circle, which is centered at O.sub.1 and has the radius value d/2 at the point M.sub.8. The arc M.sub.4M.sub.5 has the radius value C and is tangential to the circle, which is centered at O.sub.1and has the radius value d/2 at the point M.sub.4. Thus the arc M.sub.6M.sub.7 has the radius value C and is tangential to the circle, which is centered at O.sub.1and has the radius value d/2 at the point M.sub.7. The arcs N.sub.3N.sub.4 and N.sub.7N.sub.8 have the radius value D/2 and their center are all at O.sub.2, the rotation center of the second screw. The arc N.sub.1N.sub.2 has the radius value d/2 and is centered at O.sub.2, the rotation center of the second screw. The arcs N.sub.2N.sub.3 and N.sub.8N.sub.1 have the same radius value C and are tangential to the circle, which is centered at O.sub.1 and has the radius value d/2 at the points N.sub.1 and N.sub.2. The arcs N.sub.4N.sub.5 and N.sub.6N.sub.7 have the same radius value C and are tangential to the circle, which is centered at O.sub.2 and has the radius value d/2 at the points N.sub.5 and N.sub.6. The arc N.sub.5N.sub.6 has the radius value C-h and is centered at O.sub.2, the rotation center of the second screw.

[0044] Meanwhile, D/d=1.1˜5.5; and L, the first and the second screws, is equal to 0.01D 100000D.

[0045] The self-cleaning and extruding method by co-rotating two screws with an internal baffle carried out by the above-mentioned apparatus is comprised of the following steps.

[0046] (1) After the materials enter the barrel from the feeding port, the first screw and second screw co-rotate along their own axes. When the materials enter the solid conveying zone, the feed material is pushed forward, partially under the positive displacement of the first and the second screw and partially by friction forces from the first and second screw, so that the materials are forced to move toward the melting zone. At the same time, the mixing of components from the first and second screw is achieved due to the action of the baffle in the first screw.

[0047] (2) When the materials move to the melting zone, heat transfer is enhanced because of the stir action of the baffle in the first screw channel. Compression action is exerted on the materials and pre-melting is achieved due to the action of the compression energy of the second screw. Meanwhile, friction heat is generated by the high speed rotation of each of the screws. At the same time, external heat is conducted through the barrel.

[0048] Topological chaos is also introduced into the screw channel by the mechanism ‘one part divided into two parts (as indicated by the arrow in FIG. 5), then two parts converging into one part (as indicated by the arrow in FIG. 6), and then one part divided into two parts once more’ (as indicated by the arrow in FIG. 7). In addition, the cross-section of the flow channel will undergo the ‘expansion (as indicated by the label 14-1 in FIGS. 5 to 7)—compression (as indicated by the label 14-2 in FIGS. 5 to 7)—expansion’ action, and the separation of the melt from the solids is accelerated. At the same time, the baffle in the first screw will cause hyperbolic flow perturbation in the shape of a ‘figure 8’ (as indicated by the label 13 in FIGS. 5 to 7) to generate chaotic mixing. All of these actions work together to accelerate the melting process such that the materials become a cohesive melt.

[0049] When the melt enters the venting zone, the single one-flow channel in the first screw is communicated with the two independent channels separated by the screw flight in the second screw, such that the surface area of venting is increased. Furthermore, the stir action of the first screw, and the compression and expansion action of the second screw, will accelerate gas to discharge from the venting port, and the melt to move further toward the discharge port.

[0050] When the melt enters the mixing and extruding zone, the melt is subjected to the topological chaos that is a result of the flow channel, which consists of two screws and a barrel, where the action of “one part divided into two parts, then two parts converging into one part, and then one part divided into two parts once more” is effective. The baffle in the first screw channel will induce hyperbolic perturbation in the shape of a ‘figure 8’ to generate global chaotic mixing throughout the whole screw channel. In addition, the periodic compression action will lead to elongational flow. These three effects will improve the mixing and plasticating of materials so that the melt is stably extruded from the discharge port. At the same time, a self-cleaning effect will be achieved by the inter-wiping effect between each of the screws.

Embodiment 2

[0051] The present embodiment has the same structure as that of embodiment 1, except that the polar angle of the baffle remains constant with the variation of its axial position. The structural schematic diagram of the screw mechanism and partial barrel is shown in FIGS. 8 and 9.

Embodiment 3

[0052] The present embodiment has the same structure as that of embodiment 1, except for the following features: the polar angle of the baffle experiences non-linear cyclic changes with the variation of its axial position and meets the terms of the following function:

[00005]$\theta ={\theta }_{\min }+\left({\theta }_{\max }-{\theta }_{\min }\right).Math..Math.\sin .Math..Math.\frac{z.Math..Math.\pi }{L},0\le z\le L.$

Embodiment 4

[0053] The present embodiment has the same structure as that of embodiment 1, except for the following features: the polar angle of the baffle experiences non-linear cyclic changes with the variation of its axial position and meets the terms of the following function:

[00006]$\theta ={\theta }_{\min }+\frac{4.Math.\left({\theta }_{\max }-{\theta }_{\min }\right)}{L^2}.Math.\left(\mathrm{zL}-L^2\right),0\le z\le L.$

Embodiment 5

[0054] The present embodiment has the same structure as that of embodiment 1, except for the following features: the polar angle of the baffle experiences non-linear cyclic changes with the variation of its axial position, and meets the terms of the following function:

[00007]$\begin{array}{cc}\theta ={\theta }_{\min }+\frac{3125.Math.\left({\theta }_{\max }-{\theta }_{\min }\right).Math.{z\left(L-z\right)}^4}{256.Math..Math.L^5},0\le z\le L,& \\ \mathrm{or}& \\ \theta ={\theta }_{\min }+\frac{3125.Math.\left({\theta }_{\max }-{\theta }_{\min }\right).Math.z^4\left(L-z\right)}{256.Math..Math.L^2},0\le z\le L.& \end{array}$

Embodiment 6

[0055] The present embodiment has the same structure as that of embodiment 1, except for the following features: the height of the baffle experiences non-linear cyclic changes with the variation of its axial position, and meets the terms of the following function:

[00008]$\begin{array}{cc}h\left(z\right)=\frac{d}{2}+\frac{\left(\sqrt{5}-1\right).Math.\left(D-d\right)}{2.Math.L}.Math.\left(\frac{L}{2}-z\right).Math..Math.0\le z\le \frac{L}{2},& \\ \mathrm{or}& \\ h\left(z\right)=\frac{d}{2}+\frac{\left(\sqrt{5}-1\right).Math.\left(D-d\right)}{2.Math.L}.Math.\left(z-\frac{L}{2}\right).Math..Math.z\ge \frac{L}{2}.& \end{array}$

The screw mechanism is shown in FIG. 10.

Embodiment 7

[0056] The present embodiment has the same structure as that of embodiment 1, except for the following features: the height of the baffle experiences non-linear cyclic changes with the variation of its axial position, and meets the terms of the following function:

[00009]$h\left(z\right)=\frac{d}{2}+\frac{2.Math.\left(D-d\right)}{5}.Math..Math.{\cos }^2.Math.\frac{z.Math..Math.\pi }{L}.Math..Math.0\le z\le \frac{L}{2}.$

[0057] Each of the embodiments described above is the preferred embodiment of the present invention. However, the embodiments of the present invention are not limited to the above-mentioned embodiments; any other changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention are all equivalent replacement modes and should be encompassed within the protection scope of the present invention.