DE20319832U1 - Sieve changing unit, comprises a housing with at least two sieve bolt receiving bores, melt inlet and outlet regions and branch channels which are connected to the bores - Google Patents

Abstract

A sieve changing unit for continuously filtering a plastic melt stream, comprises a housing (10) with at least two sieve bolt receiving bores, a melt inlet region (14) which splits into branch channels (11) leading to the bores and a melt outlet region (15). A sieve changing unit for continuously filtering a plastic melt stream, comprises: (1) a housing (10) with at least two sieve bolt receiving bores; (2) a melt inlet region (14) which splits into branch channels (11) leading to the bores; and (3) a melt outlet region (15). Outlet channels (12) from the bores flow into the outlet region. The unit also has a return flow channel (13) and at least two sieve bolts (20,30) which can slide in the bores. Sieve elements are located in sieve chambers and each chamber splits into two bolt flow channels behind the sieve element. The sieve chamber is opposite the return flow channel when in the back flushing position. The bolt flow channels are connected to the outer circumference of the bolt via a groove. The bolt flow channels have the same cross section.

Description

Such screen changing devices are known. Two sieve bolts are provided, which are flowed across and with its sieve elements agglomerations and impurities hold back the plastic melt. One sieve pin always remains in a production position, in which melt can flow through it, so that subsequent ones Processing processes, for example on extruders, continuously can be operated. The each other sieve pin can be moved for changing or for backwashing become. When backwashing occurs the melt filtered on the other sieve bolt from behind the sieve element to be rinsed through and wash away any dirt lying on the front continued. The problem is, however, that so-called dead water zones, also known as dead space zones, i.e. areas in which no flow with melt during of backwashing. The unmoved portion of melt in the dead zone is caused by the long residence time in the heated screen changing device thermally damaged and arrives after pushing back of the sieve pin into the production position unfiltered in the further plastic processing process.

From the EP 452 539 B1 is known a screen changing device of the type mentioned, which is provided with additional auxiliary rinsing channels, which - seen in the direction of the melt flow during production - are located behind the screen element. In the production position, the main channel and the auxiliary rinsing channel are flowed through at the same time, so that no melt portions remain in the auxiliary rinsing channel and are thus exposed to the risk of thermal damage. In the rinsing position, on the other hand, only the auxiliary rinsing channel is flowed backwards, whereas the main rinsing channel has no function and thus represents a dead water zone. There, the melt can degrade and get into the processing process when the sieve pin is pushed back into the production position.

The object of the invention is therefore to improve a screen changing device of the type mentioned at the outset, that so-called dead space zones in which the melt is standing still could stay avoided become. This applies in particular to the backwash phase of the Siebelements as for the entire production process in which the screen changing device is involved.

According to the invention, this object is achieved by a Screen changing device with the features of claim 1 solved.

The branch in at least two separate bolt flow channels on the The clean side of the sieve element causes directed flows in the production position without Dead zones.

It is essential to the invention that through the connection of the bolt flow channels via a Groove on the outer circumference of the sieve pin also during the backwash both Bolt flow channels are flowed through. The most prevalent Part of the backwash flow directly through one of the bolt flow channels on the Sieve. A partial stream passes through the groove and the other Bolt flow channel to Siebelement and causes a weaker, but continuous Flow. So it will be during the Always backwash fresh melt passed through both pin flow channels. At the push back of the sieve pin in the production position when the flow direction reverses again, only fresh melt is added to the production process forwarded so that there is no risk of decomposing Material is processed.

Another advantage arises in the case of refilling the flowable Cavities of the Sieve pin with melt after changing the sieve element. Here will by the provided according to the invention Nut a full one vent and refilling the bolt flow channels as well the rear screen chamber causes.

The groove is preferably designed so that it at their ends with different cross sections in the respective Bolt flow channel opens around a positive flow direction, resulting from the over the flute length narrowing cross section, ensure. Especially in the production position there is therefore a slight melt movement continuously, the degradation, burning or cracking of plastic melt prevented.

It is advantageous if the bolt flow channels approximately have the same cross-section, which means they are in the production position equally flows through become. The bolt flow channels should then in particular mirror-symmetrical to a diameter of the sieve element be arranged so that a symmetrical loading of the screen element he follows.

It is also advantageous if the Backwash channel one changeable Cross-section, which can be positioned, for example, in the backwash channel Screw tip can be effected. About the cross-sectional change the back pressure during backwashing is adjustable. It prevents more when backwashing Melt as for cleaning of the sieve element necessary outward managed and thus withdrawn from the plastics processing process.

The invention is described below With reference to the drawing explained. The figures each show the screen changing device according to the invention in a longitudinal section through a sieve bolt and in a cross section through a plane a main melt flow, in the:

1 . 2 in production position,

3 . 4 in backwash position, and

5 . 6 in screen change position.

The 1 and 2 show a backwash screen changing device according to the invention. These be essentially consists of a housing 10 and two sieve bolts that can be moved hydraulically across the melt flow 20 . 30 , each in a sieve pin receiving bore of the housing 10 are arranged.

In a melt inlet area 14 is the housing 10 designed so that an incoming melt flow in two subchannels 11 is divided by which a sieve element 21 . 31 of the upper and lower sieve bolts 20 . 30 is flowed through with melt. The flow directions are in 1 indicated by arrows.

Seen in the main flow direction behind the screen element 21 are in the sieve bolts 20 at least two bolt flow channels 22 . 23 introduced in the production position in a melt outlet area 15 in the housing 10 pass. For the sieve pin 30 the same applies. One on a sieve 21 . 31 impinging melt flow is thus in each sieve pin 20 . 30 each branched into at least two substreams.

In the melt outlet area 15 will be in the housing 10 introduced two pairs of flow channels, namely two flow channels 22 . 23 per sieve bolt 20 . 30 , merged again.

Around both pin flow channels 22 . 23 According to the invention, a connection of the two pin flow channels is equally to be filled with melt, vented and continuously flushed through with melt 22 . 23 in the sieve pin 20 via a back into the outer circumference of the sieve pin 20 inserted groove 24 intended.

In the in the 1 and 2 Production position shown are both sieve bolts 20 . 30 positioned so that their sieve elements 21 . 31 be applied to the entire surface of the melt. In this position there is an edge-free, dead space-free transition between the outlet-side flow channels 22 . 23 the sieve pin 20 . 30 and the housing 10 given.

To initiate a flushing process, one of the sieve bolts is used 20 hydraulically moved so far within the housing bore that the sieve element 21 on the front of the inlet flow channel 11 in the housing 10 is separated and a bolt flow channel 22 of the sieve pin 20 still engaged with an outlet flow channel 12 located in the housing. This backwash position is in the 3 and 4 shown, where 4 a section along the line IV-IV in 3 represents.

While with the sieve pin 30 melt still unhindered by the sieve element 31 can pass through and thus continuous operation of the screen changing device is possible, the screen pin 20 pushed out of the main melt stream. It is via the outlet flow channel 12 flows through from its rear side with a partial quantity of melt originating from the main stream in a flow direction reverse to the production operation, so that the sieve element 21 filtered melt is applied from the rear. The one before the sieve pack 21 Accumulated impurities are pushed away from the screen element and over one in the screen changer housing 10 introduced backwash channel 13 dissipated to the outside. The cross section of the backwash channel 13 is in the preferred embodiment shown by an adjusting screw 16 with its tip more or less far into the backwash channel 13 protrudes, adjustable.

After the cleaning process is complete, the sieve pin is removed 20 move back to the production position. The backwash process on the other sieve pin 30 can now be done in the same way.

Are the sieve elements 21 . 31 Finally contaminated to such an extent that after the backwashing process using a differential melt pressure is no longer able to detect a sufficient cleaning effect, they must be replaced.

A sieve pin is used for this 20 proceed so far that its sieve element 21 outside the case 10 lies and is accessible from the outside. This position is in the 5 and 6 shown, where 6 a representation of a section along the line VI-VI in 5 is.

By moving a sieve pin 20 the corresponding branch of the flow channel is in the screen change position 11 through the extended bolt 20 blocked itself, so that no unfiltered melt can get through the screen changing device into a downstream process.

Also the one for removing the backwashing melt into the housing 10 introduced backwash channel 13 is in the screen change position due to the extended screen pin 20 blocked itself, so that the melt cannot flow out while changing the sieve element.

The other sieve bolt 30 preferably remains unchanged in the production position during the change of the screen element.

The flooding of the sieve element 21 as well as the bolt flow channels 22 . 23 with melt and the venting of the sieve element 21 after changing the screen element, it is carried out in a venting position which corresponds to that in the 3 and 4 shown backwash position can match.

The sieve pin is used for ventilation 20 , starting from the screen change position, move hydraulically to the extent that its pin flow channels 22 . 23 and its sieve element 21 be flooded from the rear with a partial amount of melt originating from the main stream.

At the same time they are in the sieve bolt 20 existing bolt flow channels 22 . 23 as well as the sieve element 21 even through the backwash channel 13 vented until the melt is bubble-free on the backwash channel 13 exit.

After completion of the venting process the corresponding sieve pin 20 move back to the production position. The other sieve bolt 30 remains unchanged in the production process. The venting process is part of the screen change process and is after the screen pin has returned to the production position 20 completed.

Claims (5)

Screen changing device for the continuous filtering of a plastic melt stream, with a housing ( 10 ) with at least: - two sieve pin receiving bores, - a melt inlet area ( 14 ), which is divided into subchannels ( 11 ) branches, which each run to a sieve pin receiving bore, - a melt outlet area ( 15 ), in the at least two outlet flow channels running from each sieve pin receiving bore ( 12 ) open, and - a backwash channel ( 13 ), and with at least two sieve bolts ( 20 . 30 ), - each in the sieve pin receiving bore of the housing ( 10 ) are arranged to be displaceable and - through which at least one sieve chamber can flow, transverse to their direction of movement, in which at least one sieve element ( 21 . 31 ) is arranged, - with each screen chamber behind the screen element in the production flow direction ( 21 . 31 ) in at least two bolt flow channels ( 22 . 23 ) which each have an outlet flow channel in a production position ( 12 ) of the housing ( 10 ) are opposite each other, and - the sieve chamber being in a backwash position to the backwash channel ( 13 ) in the housing ( 10 ) opposite, characterized in that the bolt flow channels ( 22 . 23 ) via a groove ( 24 ) on the outer circumference of the sieve pin ( 20 ) are connected. Screen changing device according to claim 1, characterized in that the groove ( 24 ) at their ends with different cross sections in the respective bolt flow channel ( 22 . 23 ) flows out. Screen changing device according to claim 1 or 2, characterized in that the bolt flow channels ( 22 . 23 ) have the same cross-section. Screen changing device according to one of claims 1 to 3, characterized in that the backwashing channel ( 13 ) has a variable cross-section. Screen changing device according to claim 4, characterized in that the cross section of the backwashing channel ( 13 ) via a set screw ( 16 ) is changeable.