MIXING AND FILTERING DEVICE FOR AN EXTRUDER

The invention relates to a device for an extruder. In particular the device could be embodied as a mixing device or as a filter device.

Plastics can be processed into products by heating the plastic in an extruder and injecting the plasticized plastic into a mould in which the heated plastic is cooled down and forms a desired product.

The plastic is supplied to the extruder as a granulated material. If the granules are of the same composition, the extruder will produce a plasticized plastic of a homogenous quality. However, it is common practice to mix different kind of granulated material to arrive at a desired composition of the plastic or in order to recycle used plastic. If granulated material of different composition is fed to an extruder, the resulting plasticized plastic is often not of a homogenous quality. It is therefor necessary to provide a mixing device, which ensures a homogenous plasticized plastic resulting from a heterogeneous granulated material.

A known mixing device consists out of a body in which a plurality of small holes are provided. The heterogeneous plasticized plastic is pressed through the small holes and after the mixing device the plurality of streams of plasticized plastic coming from the small holes are joined to a main stream. Such a mixing device provides a more or less homogenous plasticized plastic stream.

A disadvantage of such a known mixing device is the pressure with which the plasticized plastic can be pressed through the mixing device. Due to the small holes the internal pressure in the plasticized plastic increases substantially, which could result in a degradation of the plastic. This degradation of the plastic is the result of shear forces generated by the high pressures used.

When using recycled plastic granular material it is also necessary to have a filter in the extruder. The recycled granular material always consists of a small amount of alien particles such as metal particles. If these metal particles are injected into a mould, they could damage this mould and therefore a filter device should be used. A known filter device consists out of a plate provided with a plurality of small holes, which plate is placed in the stream of plasticized plastic. Again due to the small holes the internal pressure in the plasticized plastic is substantially increased, which could result in degradation of the plastic. It is an object of the invention to provide a device for an extruder, which does not have the disadvantage of small holes by which the internal pressure is substantially increased and which device also provides for a good mixture of the plasticized plastic.

This object is achieved by the invention with a device, which comprises a body with at least a first and a second helical channel for guiding the material to be extruded, wherein the first helical channel has a clockwise direction and the second helical channel has a counterclockwise direction, and wherein the first and second channel intersect at regular intervals.

The plasticized plastic is fed through the helical channels. As one helical channel is in clockwise direction while the other is in a counterclockwise direction, two

streams of plasticized plastic result, turning in opposite directions. By feeding the plastic through a helical channel, a first mixture is already achieved because the plastic stream will rotate in the channel as a result of the shape of the channel. By letting the two opposite rotating streams intersect a further mixture is achieved. At the intersection the two streams will collide causing a compression of the plastic material and the material expands back when the two streams leave the intersection. This kneading of the plastic results in a good mixture and provides a homogenous plasticized plastic stream.

Due to the use of channels, instead of small holes, the plastic streams are not subjected to high internal pressures. As a result, the overall pressure, in order to push the plastic stream through the device, is kept low while still a good mixture is provided.

A further advantage of the helical channels is the smooth passage for the plastic, while still a good mixture is provided. Sharp corners should be avoided as much as possible, as they will have an adverse effect on the properties of the plastic.

In a preferred embodiment the device comprises a pair of first helical channels and a pair of second helical channels, wherein both pairs of helical channels have a common centerline and wherein both pairs of channels intersect at least at a common intersection. Now four streams are formed by the channels and these four streams will join at an intersection and will provide a further mixture of the plasticized material. In another embodiment of the device according to the invention, the device comprises a plurality of sets of pairs of first and second channels, each set having a centerline,

wherein the centerline of the plurality of sets are substantially parallel.

In a further embodiment, the channels of a first set of pairs intersect with channels of a second set of pairs. This results in a device in which the plasticized plastic stream enters a number of helical channels and each stream in a channel encounters a number of other streams of adjacent channels providing a further increased kneading of the plasticized plastic. In yet another embodiment of the device according to the invention, the body comprises a plurality of holes extending from the outer surface of the body into the channels. With such an embodiment a filtering device is provided, in which the plasticized material can gradually flow from the channel to the outside of the device through the plurality of holes. As the plasticized material is not directly forced through a number of holes, but as the possibility exists to exit the channel at a position somewhere along the length of the channel, the increased pressure is substantially decreased, while still a filtering function is provided for.

In another preferred embodiment, the body is a tubular body and the diameter of the helical shape of the channel is substantially equal to the diameter of the tubular body. With such an embodiment the plasticized plastic will flow through the wall of the tubular body, while leaving a central passage open, which could be used for other purposes.

Preferably the channels discharge at one end of the tubular body and are closed off at the other end, and the central passage of the body is closed off at the one end of the tubular body and discharges at the other end. With the helical channels, the plasticized plastic is mixed, while by providing the openings also a filtering function is provided.

With the tubular body the filtered and mixed material can flow both the outside and to the central passage of the device. Downstream of the device the both streams originating from the central passage and from the outer surface are joined, which even provides a further mixture of the material .

In a further preferred embodiment of the device, the tubular body comprises a tubular inner body part and a tubular outer body part, which are coaxially arranged. This enables a simple disassembly of the device, such that the device can be cleaned. The channel extends through the section surface such that part of a channel is arranged in the outer body part while the other part of the channel is arranged in the inner body part. These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

Figure 1 shows a schematic view of an extruder device .

Figure 2 shows a perspective view of a device according to the invention.

Figure 3 shows a perspective view of the channels arranged in the device of figure 2.

Figure 4 shows a perspective, partially cross- sectional view of a second embodiment of a device according to the invention.

Figure 5 shows a different perspective view of the embodiment according to figure 4.

Figures 6 and 7 show perspective views of a third embodiment according to the invention. Figure 8 shows a perspective view of a fourth embodiment of a device according to the invention.

Figure 9 shows an "inverted" view showing the spaces in the device according to figure 8.

Figures 10 and 11 show cross sectional views of the device according to figure 8.

Figure 12 shows a perspective view of a fifth embodiment of a device according to the invention. Figure 13 shows a cross sectional view of the device of figure 12.

Figure 14 shows an "inverted" view of part of the device according to figure 12.

Figure 15 shows another perspective view of the device according to figure 12.

Figure 1 shows a schematic view of an extruder 1. This extruder 1 is coupled to a mould 2. Extruder 1 has a housing 3 in which a screw is arranged which is driven by a motor 4. The housing 3 is heated, such that granulate material, which is fed through the hopper 5, is plasticized. The screw in the housing 3 provides pressure, such that the plasticized plastic is injected into the mould 2. This mould

2 comprises a first mould half 6 and a second mould half 7 which can be pressed together by cylinders 8. The device according to the invention can be arranged at the exit 9 of the extruder 1.

Figure 2 shows a perspective view of a device 10 according to the invention. A flow F of plasticized material is transported through this device 10. At the entrance 11 of the device 10 a number of channels 12 are arranged. In figure

3 these channels 12 are shown in more detail.

The channels 12 consists out of clockwise directed helical channels 13 and counterclockwise directed channels 14. The channels 13 and 14 intersect at an intersection 15. At such an intersection 15 the streams in the channels 13, 14 collide with each other as a result of which the two streams are kneaded providing a good mixture of both streams. Also in this embodiment, the intersection 15 is embodied as an

expansion chamber, in which the internal pressure in the plastic is temporarily relieved, improving the mixing and kneading action. In the middle of the device four channels arrive at an intersection 15 and four channels depart from such an intersection. At the boundaries of the device only two channels intersect at an intersection 16.

Plasticized plastic F flowing through the channels 13 and 14 encounter a plurality of intersections 15, 16 which provides again and again a mixing action. The flow of plastic resulting from the device 10 has a better homogeneity than prior art mixing devices.

In figure 4 a perspective, partially cross-sectional view of a filter device 20 is shown. This filter device comprises a tubular body with a tubular inner body part 21 and a tubular outer body part 22. At the sectional surface 23 helical channels 24, 25 are arranged. Plasticized plastic enters these channels 24, 25 through openings 26, 27. In the walls of the channels 24, 25 holes 28 are arranged through which the plasticized plastic can flow through the outside of the device 20 or to the inner central passage 29.

By the helical channels 24, 25 a mixing action is provided, while the holes 28 provide for a filtering action.

If debris is filtered out it will remain in the channels 24, 25. In order to clean these channels the tubular inner part 21 can be shifted out of the tubular outer part 22.

Figure 6 shows a third embodiment 30, which is in fact a combination of the embodiments shown in figures 1 through 5. This embodiment 30 has a body 31 in which helical channels 32 are arranged. The structure of these channels 32 is identical to the channels 13, 14 shown in figure 3. The body 31 has a central passage 33, which is shown in figure 7. The helical channels 32 are provided with holes, which extend

from the channels 32 towards the outer surface of the body 31 or towards the central passage 33. These holes 34 enable a filtering action of the device 30. To ensure that all the plastic fed through the channels 32 is filtered, the channels 32 are blind, i.e. only the holes 34 provide an exit for the plastic fed through the channels 32.

The device 30 is inserted in the tube of an extruder and the outer surface of the body 31 is in direct contact with the tube of an extruder. Plastic coming through the holes 34 is then guided through the channels 35. These channels 35 are shown in figures 6 and 7 as open channels, but in combination with the extruder tube are shaped as closed channels. The filtered plastic running through the channel 35 flows to exit openings 36, where the plastic is joined with the plastic exiting the central passage 33.

Figure 8 shows a perspective view of a fourth embodiment of a device 40 according to the invention. This device 40 has a body 41 in which a number of helical channels 42 are arranged. Figure 9 shows an "inverted" view of the device 40 of figure 8. Figure 9 shows the spaces in the body 41 of the device. From figure 9 it shows that a number of helical channels are present in the body 41, wherein part of the helical channels 42 are clockwise and others are counterclockwise. The channels meet at intersection points 43, where two or more plasticized plastic streams of the channels 42 meet and intersect and provide a kneading action increasing the homogeneity of the material .

Figure 10 shows a cross sectional side view of the device 40, while figure 11 shows a cross sectional top view of the device 40. The plasticized plastic stream F enters a channel 42 and makes a clockwise spiral through the body 41 towards the exit opening 44. From figure 11 is clear that the

intersections 43 of channels 42 are small chambers which the plasticized streams from the channels 42 enter and where the kneading action is performed. The kneaded plasticized stream then leaves the chamber 43 and continues its way through a further part of the channel 42.

Figure 12 shows a fifth embodiment 50 of the device according to the invention. This device 50 consists out of two sections 51, 52 having different functions. The section 51 provides for a mixing action while the section 52 is embodied as a filter. Both sections are maintained that a distance by spacers 53.

The flow F flows into the internal space of the filter section 52 and gradually is pushed through the openings 57 to the outside of the outer surface of the filter section, thereby filtering the plasticezed material. This outer surface is provided with helical grooves 56 which are provided at the bottom of the groove 56 with the holes 57. The plasticized material F flows through these channels 56 towards the mixing section 51. The mixing section 51 comprises, as is shown in figure 14, helical channels, in which the kneading action is performed as explained in the earlier embodiment. The plasticized plastic enters the channels 55 and due to the clockwise helical channels and counterclockwise channels the kneading action is performed. After the mixing action, the plasticized flow F exits the mixing section 51 through openings 54 (see figure 15) .