WO2007048759A1 - Single-screw extruder - Google Patents

Abstract

Single-screw extruder with a conical screw (2), which is held in a rotatable and driveable manner in a barrel (1), which has in the region of the largest screw diameter a feed opening (6) for a material to be melted, wherein the extruder has a feed section (I), which adjoins the feed opening (6), a homogenizing section (II), which adjoins the said feed section and in which the screw volume is reduced, and a metering section (IV), in which the screw volume is likewise reduced and which ends at an outlet die. To allow the polymer to be mixed with a relatively high proportion of fillers, it is provided that a substantially pressureless section (III), in which a supply opening (8) is provided in the barrel (1), is provided between the homogenizing section (II) and the metering section (IV).

Description

 description

SCREW EXTRUDERS Technical area

The invention relates to a single-screw extruder according to the preamble of claim 1.

State of the art

Extruder of the type mentioned are used for extrusion of plastic. The plastic is plasticized in the extruder and pressed under pressure through the nozzle.

In known extruders of this type directly connects to the plasticizing zone, the discharge zone, wherein the pressure of the plasticized plastic does not decrease in the transition region.

In the manufacture of plastics today, the prices are almost exclusively determined by the cost of the starting material. The machine costs are only a very minor part of the total cost. Therefore, there are efforts to stretch the relatively expensive plastic with the cheapest possible filling material.

In conventional single-screw extruders only one intake opening is provided, via which a mixture of plastic granules and filler can be introduced. However, there is the disadvantage that the plastic granules only relatively little filler can be mixed. With too much filler, the mixing is no longer homogeneous. This also results in the disadvantage that the filler contributes significantly to the wear of the screw and mixes poorly with the not yet melted plastic. This also applies to conical single-screw extruders, i. for single-screw extruder, where the auger bore in the housing is conical and of course the envelope of the screw is correspondingly conical.

For the sake of economical use of plastic granules, however, it would be desirable to mix about 30% filler material to the plastic.

Extruders have therefore already become known (see, for example, US Pat.

), where two intake openings are provided. The plastic is abandoned in the first intake opening and melted in the melting zone. After the melting zone, a substantially pressureless zone (III) is provided, where filler is added via the second intake opening. Here, the filler is so mixed in the already molten plastic, whereby a better mixing takes place, allowing a higher proportion of filler. These extruders However, all are cylindrical, ie with them the screw hole in the housing is cylindrical, as well as the envelope of the screw. These extruders have the disadvantage that not too much plastic can be fed. There are attempts to cool the catchment area, thereby changing the intake behavior and thus increase the amount of retracted plastic. However, this is associated with additional technical effort and limited effectiveness. If, however, not a constant amount of plastic is drawn in, higher filler proportions are again problematic.

Presentation of the invention

The aim of the invention is to propose an extruder of the type mentioned, which makes it possible to at least 30% filler material to mix the plastic material and - based on the size - has relatively high throughput.

This is achieved in an extruder of the type mentioned by the characterizing features of claim 1 according to the invention.

The proposed measures ensures in a simple manner that the molten plastic filling material can be added in a relatively large amount. Because of the conical design a very high collection volume can be realized, whereby relatively much plastic can be drawn in a constant amount and then melted. In this case, due to the fact that in the region of the feed opening of the plastic is substantially unpressurized, the filler material can be easily in large quantities, e.g. in the amount of 30% of the plastic to be added. The filler in the discharge zone is intimately mixed with the already molten plastic.

Due to the features of claim 2, there is the advantage of a structurally very simple solution. The reduction of the core diameter not only results in a reduction of the pressure, but also a corresponding increase in the volume of the screw accommodated in the region of the reduced diameter of the core of the screw.

In order to keep the degree of mixing of the plastic-filler mixture as high as possible, it is advantageous to provide the features of claim 3. Thereby, the backflow of the material over the gap between the outer edges of the screw flights and the inner wall of the housing counter to the conveying direction of the screw can be adjusted accordingly, this return significantly contributes to the intimate mixing of the material. The screw gap is thus adjustable and can be optimized for any combination of plastic / filler.

Brief description of the drawings

The invention will now be explained in more detail with reference to the drawing, which schematically shows an extruder according to the invention.

Best way to carry out the invention

The extruder has a conical housing 1, in which a substantially conical screw 2 rotates. In this case, the screw 2 relative to the housing 1 in the direction of the arrow 3 is held displaceable and lockable. By slidable in the axial direction support of the screw 2, the gap width between the outer edges of the flights 4 and the inner wall of the housing 1 can be adjusted, whereby the extent of the backflow opposite to the conveying direction of the goods between the individual flights 4 can be adjusted. This backflow occurs because of the increasing pressure in the conveying direction in the region of a melting zone II and the discharge zone IV (because of the reduction of the gap 5 between the core 7 of the screw 2 and the inner wall of the housing 1) to which the material is exposed.

The core 7 of the screw 2 also has a conicity; Nevertheless, the volume between the core 4 and the inner wall of the housing 1 decreases towards the outlet nozzle 9.

The screw 2 has a catchment area I in the region of an intake opening 6 of the housing 1, in which the gap 5 between the core 7 and the inner wall of the housing 1 remains approximately constant. Due to the relatively high peripheral speed of the screw in this area, the plastic granules are efficiently drawn. In the subsequent melting zone II, the gap 5 continuously narrows between the core 7 and the inner wall of the housing 1, whereby the pressure between the individual screw flights 4 increases and the granules melt.

Subsequent to the melting zone II, a substantially pressureless zone II is provided, at the beginning of the diameter of the core 7 of the screw 2 decreases rapidly. In this substantially pressureless zone III, a feed opening 8 of the housing 1 is arranged, via which a filler is introduced. In this area, the surface of the core 7 of the screw 2 runs partly parallel to the inner wall of the housing 1.

In the subsequent discharge zone IV of the molten plastic is intimately mixed with the filler and the pressure of the mixture due to the narrowing gap 5 between the core 7 and the inner wall of the housing 1 increases. The molten mixture exits through the nozzle 9.

Claims

 claims Single-screw extruder with a screw (2), which can be rotated and driven in one Housing (1) is held, which has a feed opening (6) for a material to be melted, wherein the extruder to the feed opening (6) subsequent feed zone (I), a subsequent to this melting zone (II), in which the screw volume reduced, and a discharge zone (IV), in which the screw volume is also reduced, which ends at an outlet nozzle, wherein between the melting zone (II) and the discharge zone (IV) a substantially pressureless zone (III) is provided a feed opening (8) is provided in the housing (1), characterized in that the screw hole in the housing (1) and the screw (2) are conical, wherein the feed opening (6) is in the region of the largest screw diameter. Single-screw extruder according to claim 1, characterized in that in Area of the non-pressure zone (III) of the core diameter of the screw (2) is reduced. Single-screw extruder according to claim 1 or 2, characterized in that the screw (2) is displaceable in the axial direction and held lockable.