Liquid purification or separation – With alarm – indicator – register – recorder – signal or... – Fluid pressure responsive
Patent
1997-11-25
1999-07-13
Woo, Jay H.
Liquid purification or separation
With alarm, indicator, register, recorder, signal or...
Fluid pressure responsive
210232, 210236, 21033301, 210445, 210108, 425197, 425199, B01D 2996
Patent
active
059221941
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a screen-changing device according to the precharacterizing clause of claim 1.
Practical use of such a device is known from DE 39 05 963 A1. While in the following text reference is made generally to "screen", this is intended to mean the most varied types of screens, filters or other retaining devices for contaminants.
The screen-changing device of the generic type does not permit back flushing of the screen, but only venting. Owing to the fact that both the channel division and the channel convergence are performed within the housing, while the screen support just has the screens arranged in it, the flow channels are difficult to access for cleaning purposes.
AT 395 825 discloses a screen-changing device of a different generic type, which does not have channel division or channel convergence with two inlet channels, and in which a back flushing of the single screen is possible from a collecting chamber, in which polymer taken from the actual melt stream is collected during the operation of the device. Such a device is not advantageous for injection-molding installations in particular, since variations in the pressure and volume of the polymer material occur and may result in malfunctions or irregular degrees of filling of the downstream injection-molding device.
The invention is based on the object of improving a device of the generic type to the extent that the back flushing and changing of a screen is possible, while at the same time avoiding entrapped air in the products of a downstream injection-molding installation.
This object on which the invention is based is achieved by a screen-changing device having the features of claim 1.
In the normal operating position, in which the plastics processing installation is ready for use, a polymer stream thus runs through one or both inlet openings of the screen support and accordingly through one or through two screens to the common outlet channel of the screen support, which is in connection with the third section of the flow channel, on the housing side.
With respect to this operating position (first position of the screen support), according to the invention the screen support is arranged such that it can be moved into a second (back-flushing) position, in which there continues to be a connection between an inlet channel of the screen support and the first section of the flow channel and polymer can flow into the screen support.
However, the outlet channel of the screen support is no longer in connection with the third section of the flow channel, but is closed off and bears, for example, against a wall of the housing, with the result that here a flow reversal of the polymer is enforced and the latter flows back through the other inlet channel, respectively, of the screen support and consequently effects a back flushing of the screen arranged in this second inlet channel. The polymer thereby flowing back can be directed by a back-flushing line in the housing to a collecting reservoir or the like.
The screen support can be moved into a third (screen-changing) position with respect to its operating position such that free access to an inlet opening, and consequently to a screen, is possible, with the result that a screen change can be performed in this position.
According to the invention, entrapped air in the plastic products produced can be avoided by initially moving the arrangement into the back-flushing position after a screen change, in which air necessarily forces its way into the flow path of the polymer, and by conveying polymer through the first inlet channel and through the second inlet channel into the back-flushing line, with the result that in this conveyance of polymer the entrapped air is also conveyed to the outside through the back-flushing line, until the entire screen-changing device no longer has any entrapped air.
In this state, the screen support can be moved out of the back-flushing position into the normal operating position, with the result that the plastics processing installation can subsequently be operate
REFERENCES:
patent: 4814186 (1989-03-01), Trott
patent: 4849113 (1989-07-01), Hills
patent: 5032267 (1991-07-01), Petschner
patent: 5362223 (1994-11-01), Gneuss
patent: 5417866 (1995-05-01), Trott
patent: 5449465 (1995-09-01), Degan
patent: 5498334 (1996-03-01), Gneuss
Bruckmann Theodor
Simon Ralf
Firma Kreyenborg Verwaltungen und Beteilgungen GmbH & Co. KG
Prince Fred
Woo Jay H.
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