DE4018310C1 - Filtering plastic melts - includes using an arrangement which incorporates melt channel in housing and rotatable sieve plate inside sieve chamber - Google Patents

Abstract

A process for filtering plastic melts, includes using an arrangement which incorporates a melt channel in a housing, as well as a rotable sieve plate inside a sieve chamber filter zone. Plastic melt material which remains in the sieve chambers and the fillers, is forced out before the cleansing or filter change over processes occur, using a pressurised gas. The material is fed into the outlet end of the melt channel. ADVANTAGE - The process ensures that filters to be changed only contain minimal amt. of plastic material.

Description

The invention relates to a method for filtering Plastic melting by means of a device with a melt channel having housing and a rotationally drivable, inner Filters arranged in a ring zone in sieve chambers having and this cyclically in the melt channel bringing as well as leading into a cleaning position Screen disc and a device for carrying out the Procedure.

Filtering devices corresponding to the genus of plastic melts are, for example, from DE-OS 33 02 343 known. It has been shown to be essential that even with heavier pollution of the Recycling plastic melt a quasi-continuous Nuclear filtering is possible because of constant or gradual drive of the screen disc preferably depending on the degree of contamination of the filter Filters are placed in the flow channel and out this leading replaceable or cleanable. However, it was found to be disadvantageous here that, for example. When replacing filters, there are always parts of art melt in or stick to these filters, so that the required disposal not only the fil term material concerns, but also undesirably high  Proportions of the plastic melt to be cleaned. Especially this unwanted discharge of the Plastic noticeable when achieving larger Passage cross-sections and thus smaller, the Melt offered resistance large-area pot filter be used.

The invention is therefore based on the task, Filtra tion devices for plastic melts so on form that approved filters only as possible to keep small amounts of plastic melt ver to like.

This task is solved by the features of the patent claims 1 and 2, respectively zekanal extended filter containing filter chambers the sieve disc one in between Emptying station supplied, in which in the filters remaining plastic melt driven out by gas pressure will. From the opposite side of the Entlee Discharge and discharge channels go out, which the squeezed out Absorb plastic melt and the outlet side Feed end of the melt channel, with a return plastic melt after pressure relief is advisably avoided by a check valve. This will bind those in the filter or in the sieve chamber remaining plastic melt residues pressed out of these sieve chambers and filtered processed plastic melt in the circuit introduced so that removing filters in the Cleaning station is made easier and the plastic load of the removed filters is pleasingly low or goes to zero.

Advantageous and expedient further training of the Erfin are characterized in the subclaims 3 to 8.

In detail, the features of the invention are based on the Description of an embodiment in connection explained with this illustrative drawings. It show:

Fig. 1 is a view of a device for filtering of plastic melts,

Fig. 2 is a horizontal section CA through the Einrich device according to FIG. 1, and

Fig. 3 shows a bent section along the lines CB in FIG. 1.

In Fig. 1, a housing 1 is shown, which, as Fig. 2 shows, consists essentially of plates 2 , 3 , which are braced against each other by means of bolts 4 via a spacer 5 and an axle piece 6 . The axis piece 6 also serves as the axis of a screen disc 7 , which centers it and about which it can be rotated. In an annular zone of the sieve disk 7 are substantially cylindrical sieve chambers 8 incorporated into this, which are provided for receiving sieve inserts. In the exemplary embodiment, these sieve inserts are designed as pot filters 9 : they have a perforated support basket made of metal, which is worked in a ring shape, has an essentially trapezoidal cross section and in which the filter inserts covering the perforated wall areas are inserted. The ring area of the sieve disk 7 occupied by sieve chambers 8 is selected so that the sieve inserts are able to pass through the melt channel 10 which normally penetrates the housing. In order to keep the pressure drop that occurs low, the melt channel 10 penetrated by the melt to be filtered is expanded in the area of the sieve disk 7 via subsequent conical sections.

To drive the screen disc 7 , this is equipped with a toothed ring 11 , in which a pinion engages, which is provided on the output shaft of a locking mechanism 12 , which can be driven by means of a lever 13 , on the free lever arm of which a hydraulic cylinder 14 engages. Not illustrated is a control device influencing this drive, which responds to the pressure difference in front and behind the sieve disk 7 lying sections of the melt channel 10 and accelerates the drive of the sieve disk as the resistance of the filter inserts and thus the pressure difference increases and thus fresh, vented Inserting sieve inserts into the flow channel and swiveling out already inserted sieve inserts. The swung out, still filled with melt sieve chambers 8 and pot filter 9 achieve in the course of their further swiveling path an emptying station 15 in which the remaining melt is pressed out of the sieve chamber by supplying gas under higher pressure, for example nitrogen, under gas pressure and as far as it is still in front of the filter insert, is pressed through the pot filter 9 . For this purpose, a nitrogen feed line 16 is guided to a solenoid valve 17 , from which a connecting bore 18 leads to the emptying station 15 . On the opposite side a discharge channel 19, which brings the melt pressed out via a return check valve 20 in an introduction passage 21 which opens directly into the output-side melt channel 10 begins.

It is essential that the compressed gas is supplied when a sieve chamber 8 of the sieve 7 has reached the Entleerungssta tion 15 , and it is also important that the pressure is applied for a time which ensures that the melt is pressed out. In the exemplary embodiment, this is achieved by incorporating a groove 22 in the jacket of the screen disk 7 for each screen chamber 8 , into which a limit switch 23 can intervene when the screen chamber enters the emptying station and triggers a switching process. The solenoid valve 17 is thus opened via the control device 24 , so that the pressurized gas is able to act on the relevant sieve chamber and its pot filter 9 . When you continue to run the pin of the limit switch is pushed up by the groove, the solenoid valve 17 drops and blocks the compressed gas line. A relief opening is expediently released at the same time, so that the pressure built up in the sieve chamber is reduced even during the further run. The check valve 20 prevents the melt under pressure in the flow channel 10 from receding.

With further circulation of the sieve 7 occurs the traditional sieve chamber, as shown in FIGS . 1 and 2, out into the open and out of the housing, so that now the filter insert of the pot filter 9 , possibly together with the support basket, can be exchanged for a new filter insert can.

The embodiment of the invention can be largely modified. For example, as shown in FIGS . 2 and 3, it is possible to provide only a number of large-area pot filters; In the ring region led through the flow channel 10 , however, several ring-like rows of sieve chambers can also be provided, the sieve chambers also being able to have different diameters. It has proven useful to equip the sieve chambers with the sieve inserts through their flank-supporting grooves. Pot filters can be secured with over-screwed tabs or even screwed against flanks of grooves, whereby plug-in threads have proven their worth.

The duration of the pressurization can be determined by actuating proximity or limit switches; It has proven useful, however, to maintain the pressurization for predetermined time intervals by the control device 24 , which can be influenced by temperature sensors, pressure sensors or the like. It is also possible to determine the emptying by pressure monitoring and to determine the duration of the exposure using pressure criteria.

The drive can also be varied in many ways direction, the pneumatic, hydraulic or electric is effectively executable. It is useful in each of these Decrease the speed of rotation of the sieve disc in dependence the degree of contamination of the melt and / or Degree of clogging of the filter controls so that the desired constant pressure is ensured.

In all of these cases, the squeeze the melt residues from the sieve chambers, in particular from the filters, achieve that when periodically required Chen filter exchange essentially the disposal limited to the material of the filter itself and both unpleasant losses of the plastic melt ver be avoided as well as disposal limited to the actual filter to be changed remains.

Claims (8)

1.Method for filtering plastic melts by means of a device with a housing having a melt channel and a rotatably drivable filter within a ring zone in filter chambers and which bring them cyclically into the melt channel and into a cleaning position, characterized in that in filters ( 9 ) or sieve chambers ( 8 ) remaining plastic melt is pressed out by means of compressed gas before reaching the cleaning or filter change position and fed to the outlet end of the melt channel ( 10 ). 2. Device for filtering plastic melts according to the method of claim 1 with a housing having a melt channel and a rotatably drivable filter arranged within a ring zone in filter chambers and having these cyclically bringing into the melt channel and into a cleaning position leading sieve disk, characterized that the cleaning position is preceded by an emptying station ( 15 ) in which the sieve chambers ( 8 ) with filters ( 9 ) are pressurized on the inlet side and the outlet side of which via discharge and inlet ducts ( 19 , 21 ) with the filters in the forward direction End of the melt channel ( 10 ) is connected. 3. Device according to claim 2, characterized in that the discharge channel ( 19 ) of the emptying station ( 15 ) is assigned a check valve ( 20 ). 4. Device according to at least one of claims 2 or 3, characterized in that the compressed gas supply has a solenoid valve ( 17 ) which can be actuated after a sieve chamber ( 8 ) has entered the emptying station ( 15 ). 5. Device according to claim 4, characterized in that the sieve disc ( 7 ) with the positions of the sieve chambers ( 8 ) characterizing grooves ( 22 ) is provided, which a solenoid valve ( 17 ) influencing proximity switch or limit switch ( 23 ) is assigned. 6. Device according to at least one of claims 2 to 5, characterized by a control device ( 24 ) which, when the proximity or limit switch ( 23 ) responds, opens the solenoid valve ( 17 ) and, depending on the expiry of a predetermined time interval, from running through predetermined angle of rotation or on occurrence of a pressure change or the like closes the solenoid valve ( 17 ) and relieves the pressurized sieve chamber ( 8 ). 7. The device according to at least one of claims 2 to 6, characterized in that the screen chambers ( 8 ) of the screen disc ( 7 ) are equipped with pot filters ( 9 ). 8. Device according to at least one of claims 2 to 7, characterized, that nitrogen is provided as the pressurized gas.