Apparatus for filtering and extruding synthetic plastic scrap ma

Details Apparatus for filtering and extruding synthetic plastic scrap ma Apparatus for filtering and extruding synthetic plastic scrap ma

1994-02-25

1995-05-30

Cooley, Charles E.

Agitating

Rubber or heavy plastic working

With specified vent means

366 87, 366 88, 366 89, 425203, B29C 4776

Patent

active

054196345

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an apparatus for extruding thermoplastic synthetic plastics material, comprising an extruder housing in which an extruder worm driven by a drive means is bearingly supported for rotation around its axis, said housing being provided with an intake opening for the material to be plasticized, which opening, for example, is connected to a funnel, and with an exit opening for the melt disposed in axial distance from the intake opening and with at least one degasing opening for the escape of gases, and with at least one melt filter through which the melt passes, wherein the extruder housing is divided into two chambers by return screw threads disposed on the circumference of the worm, one of which chambers being provided with the intake opening and the other being provided with the exit opening, which chambers being interconnected by at least one channel in which the melt filter is disposed, and wherein each degasing opening is connected to the chamber provided with the exit opening and is disposed in axial distance from this exit opening, in which chamber the extruder worm has a geometry of its threads that causes a no-pressure-zone.
Apparatus of this kind are known (U.S. Pat. No. A 3,380,824). The melt discharged through the exit opening is supplied to a tool, for example to a mold, by which articles of thermoplastic synthetic plastics material are produced.
It is also known to subject synthetic plastics material scrap to a recycling process by supplying the synthetic plastics material scrap through an intake opening into the extruder housing and to melt it therein and to separate the impurities from the melt by means of the filter. Within this, there occurs the problem that on the one hand, the impurities contained in the synthetic plastics material scrap must be removed, but on the other hand the gases released during plasticizing must be removed, which gases, for example, are created by the fact that printing colours adhering on the scrap synthetic plastics material release gaseous components at a certain temperature or are even entirely transformed into the gaseous condition. For the removal of such gaseous components, a degasing opening is provided within the known construction, which opening--when seen in flow direction of the synthetic plastics material--is disposed immediately behind the screen constituting the filter. The purified and degased synthetic plastics material is then introduced into the second chamber and is conveyed through this towards the exit opening. Investigations have shown that such an apparatus does not meet the requirements. The investigations have shown that degasing of the treated synthetic plastics material is not sufficient, since the synthetic plastics material is subjected to turbulences when passing through the filter, whereby gaseous components which optionally have already been released from the synthetic plastics material or are ready for such a release, are worked in again into the synthetic plastics material mass.
In a one-part-worm, which, therefore, is disposed in one single chamber, it is also known to dispose a filter purifying the synthetic plastics material immediately before the exit opening. Within this, the degasing openings are disposed before the filter, so that the melt contains impurities also after degasing. In front of the filter or, respectively, of the exit opening, the extruder worm must have such a lead that the required conveying pressure is created in order to overcome the resistances caused by the filter and by the tool connected to the exit opening. Therefore, it depends from the geometry of the extruder worm in this section, which maximum resistance can be overcome. If this maximum resistance is exceeded, for example due to soiled filter screens, the output of the melt through the exit opening is decreased and there results a back pressure of the melt that causes an undesired exit of the melt through the degasing openings.
Other known apparatus show still further disadvantages. Th

REFERENCES:
patent: 3193877 (1965-07-01), Edwards
patent: 3360824 (1968-01-01), Schippers
patent: 4902455 (1990-02-01), Wobbe

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