Backflush attachment for a filtering device

Details Backflush attachment for a filtering device Backflush attachment for a filtering device

2000-11-14

2001-12-04

Lithgow, Thomas M. (Department: 1724)

Liquid purification or separation

Filter

With residue removing means or agitation of liquid

C210S341000, C210S425000, C425S197000, C425S199000

Reexamination Certificate

active

06325217

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a backflush attachment for a filtering device, in particular for a plastics melt filter, the backflush attachment comprising a housing having guide channels following an entry bore, as well as backflushing channels, and at least one rotary piston which clears a passage in the respective guide channel when in its passing position and which interrupts the passage in the guide channel from the entry bore to the filtering device when in its closing positon while providing a connection of a portion of the respective guide channel with an associated backflushing channel leading outside of said housing.
BRIEF DESCRIPTION OF THE BACKGROUND ART
Since filtering devices become clogged by the particles which they retain from the flows to be filtered, in particular plastics melt flows, and thus the passage of the fluid to be filtered would be disturbed in the long run, it is necessary to clean the filtering devices. Often filtering devices are used in which the passing medium is subdivided by the assistance of two guide channels into two partial flows, each partial flow is filtered separately, and subsequently the two partial flows are united again. In such filtering devices, the filtering elements therefore can be cleaned in that a control device, with injection molding devices and the like also termed backflush attachment, is provided by means of which it is possible to control the passage of the fluid to be filtered. In doing so, in the backflush position, the fluid enters a guide channel in a flow direction which is equal to the usual flow direction, flows through the associated filter and subsequently flows through the second filter and returns in the second guide channel, i.e. contrary to its flow direction in the normal state of operation. In doing so, the fluid flow entrains the particles adhering to the second filter. Thereafter, the fluid polluted with these particles is led out of the backflush attachment via control elements. Thus, the filtering device can be cleaned in a simple way. As a rule, the control elements of known backflush attachments include reductions or steps as compared to the remaining flow channels in the housing of the backflush attachment, which are necessary so as to maintain a certain pressure within the filtering device. Pollutants adhere to these reductions, or steps, respectively, which may block the control elements and thus greatly reduce the useful life of such backflush attachments. Moreover, the control elements of the backflush attachments frequently get into contact with the atmosphere resulting in a coking of the fluids, in particular in case of plastics melts. By this, hard layers are formed on the control elements which will have to be removed at regular intervals since otherwise the control elements may also become blocked thereby.
From DE 195 09 059 C1, a control device is known in which the supply to and discharge from two guide channels is controlled by means of rotary pistons. The flow channels in the rotary pistons have, however, a substantially smaller cross-section than the guide channels so as to provide for a pressure build-up, resulting in shoulders, or steps, respectively, at the channel transitions, primarily at the entry into the rotary piston, with deposits forming thereat which reduce the operability of the control device. In addition, the fluid is highly deflected in the rotary piston, and this deflection also contributes to the formation of deposits in the channels of the rotary piston in a detrimental manner. The pronounced deflections of the channels in the rotary piston do not only have the disadvantage of forming deposits, but are also complex to produce and thus involve high production costs.
It is an object of the present invention to prevent these deposits in the channels of the rotary piston, so that the useful life of such a backflush attachment is substantially increased and, moreover, the maintenance time and costs are reduced.
Moreover, it is another object of the invention to reduce the deflections of the fluid by providing an appropriate path of the channels in the rotary piston so as to avoid further deposits and to simplify the requirements of manufacture and thus lower the production costs.
SUMMARY OF THE INVENTION
In a backflush attachment according to the invention, the rotary piston has an eccentrically arranged passage channel of constant cross-section substantially corresponding to the cross-section of the guide channel, the axis of rotation of the rotary piston extending eccentrically in corresponding manner relative to the axis of the guide channel, and the passage channel forming a part of the guide channel when the rotary piston is in its passing position, whereas it provides for the connection to the backflushing channel when the rotary piston is in its closing position. By the eccentrical arrangement of the passage channel it is possible in an advantageous manner to ensure an unimpeded flow through the rotary piston and the guide channel (in the passage position of the rotary piston) by means of a single passage bore, and to form a connection with the backflushing channel in the closing position of the filtering device. Furthermore, the formation of deposits is prevented by the step-free transition between guide channel, or backflush channel, respectively, and passage channel and by the constant cross-section of the passage channel.
Cleaning of the filtering device can be performed with a particularly easy construction if two guide channels are provided and one rotary piston is provided for each guide channel.
In order to keep manufacturing requirements as low as possible and thus to keep production costs advantageously low it is suitable if the passage channel is formed by a straight-line eccentrical bore in the rotary piston.
For the step-free transition between the passage channel and the guide channel, it is advantageous if in its passing position the passage channel follows on the guide channel portions in the housing in coaxial alignment.
For the step-free transition between passage channel and backflushing channel, it is further advantageous if the cross-section of the backflushing channel substantially corresponds to the cross-sections of the passage channel and the guide channel.
Likewise, it is suitable for a step-free transition between the passage channel and the backflushing channel if the passage channel merges with the backflushing channel in coaxial alignment in its closing position.
In order to largely avoid greater deflections of the fluid passing the filtering device, and thus to avoid deposits, it is also advantageous if the passage channel and the entering guide channel portion of the housing enclose an obtuse angle when the rotary piston is in its closing position.
In order to prevent falling of the pressure in the filtering device below a certain value, it is advantageous if a throttle, e.g., a screwed-in nozzle of adjustable cross-section, is located in the backflushing channel so as to provide for a pressure build-up.
For a compact assembly as well as simple handling from the outside, finally, it is advantageous if a pivoting means is directly coaxially installed on the or each rotary piston so as to rotate the rotary piston from its passing position into its closing position, and vice-versa. Of course, it is also possible to employ other pivot drives, such as, e.g., a hydraulic cylinder with a linearly moved toothed rack that drives a pinion non-rotationally mounted on the rotary piston, or to use a pressure-cylinder driven pivot lever attached on the rotary piston.


REFERENCES:
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patent: 3896029 (1975-07-01), Beuselinck
patent: 3940222 (1976-02-01), Zink
patent: 5779898 (1998-07-01), Schwanekamp et al.
patent: 684976 (1964-04-01), None
patent: 4218756 (1993-04-01), None
patent: 4408803 (1995-09-01), None
patent: 1950959 (1996-03-01), None
patent: 554237 (1993-08-01), None
patent: 50-003346 (1975-02-01), None

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