Liquid purification or separation – With alarm – indicator – register – recorder – signal or... – Fluid pressure responsive
Reexamination Certificate
2000-05-09
2001-12-04
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
With alarm, indicator, register, recorder, signal or...
Fluid pressure responsive
C210S107000, C210S333100, C210S412000, C425S197000, C425S199000
Reexamination Certificate
active
06325922
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a filter device for cleaning plastics (polymer) melts having a filter wheel for pivoting screening elements in and out of a melt channel through which the plastics melt flows in the filter device. The screening elements cover cavities arranged in the filter wheel and are exchangeable for fresh or cleaned screening elements at a removal/fitting opening of the filter device.
2. Description of the Related Art
German Patent Publication No. 42 12 928 A1 discloses a filter device where the individual screening elements include a number of filter cells arranged one above the other and which are operated parallel to one another. The filter cells are formed by two annular filter disks. The inner zones of the filter disks are connected to an interposed ring, which has radial passages, and the outer zones of the filter disks are connected to each other. The filter disks are formed by a multi-layer construction and have at least one filter layer and a supporting layer carrying the filter layer.
German Patent Publication No. 41 13 501 A1 relates to screening elements present in the openings of a rocker arm or a disk which, by pivoting or turning of the arm or disk, can be brought both into an operable position and into a removal position. Used elements can be replaced in the removal position by screening elements having new or cleaned filter areas.
A continuously operating filter system described in German Patent Publication No. 42 12 928 A1 employs a filter wheel through which a monomer melt flows eccentrically in a filter housing. The filter housing is fitted with screening elements or filter inserts which are arranged along a circle. The small pore widths of the filter inserts have a high cleaning effect, where the quality of the end product is improved. The filter wheel is equipped on the outer circumference with a toothed rim, which is engaged by a pinion. The pinion is connected via a lever to a drive piston, the movement of which is controlled by a hydraulic control system. The hydraulic device simultaneously serves for driving a backflushing piston (accelerator) for back-thrust cleaning of the filter cells with the screening elements and for driving a discharge piston. In the case of backflushing, the discharge piston channels the monomer to the outside and, in the case of normal operation, the discharge piston returns the monomer to the main melt line. The accelerator produces the required melt flow, briefly at a high rate, to backflush with the necessary pressure.
However, due to the high temperatures during operation, oxidation of the monomer or polymer of the plastics melt can easily occur during a filter change. Furthermore, it is not possible to blow a gas into the filter housing to reduce the risk of oxidation during the filter change, because cooling the filter wheel and screening elements could cause the plastics melt to solidify. This would inevitably lead to leaking or destruction of the filters. The high temperatures of the filter housing also have the effect of heating all the built-on parts so that their serviceability is no longer ensured. In this case, overloading of the drive elements, such as, for example, the drive piston, may also occur. The low mechanical support of the overall filter system is also problematical in the thrust-like backflow cleaning of the screening elements.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to overcome the drawbacks of the prior art and to provide an improved filter device.
It is further an object of the invention to provide a filter device in which the risk of oxidation during the change of a screening element is diminished.
It is furthermore an object of the invention to provide a filter device in which damage to the filter device caused by excessive pressure fluctuations as well as impairments in the quality of the filtered product caused by high operating temperatures are largely avoided.
In accomplishing the foregoing objects, there has been provided according to the present invention a filter device for filtering plastics melts, comprising: a melt channel through which a plastics melt flows; an exchanging area; a filter wheel having a plurality of cavities therein, wherein the filter wheel pivots the plurality of cavities between the melt channel and the exchanging area; a plurality of screening elements covering the cavities in the filter wheel; a melt inflow line upstream of the filter wheel and a melt outflow line downstream of the filter wheel in fluid communication with the melt channel; a first pressure sensor arranged in the melt inflow line; a second pressure sensor arranged in the melt outflow line; a removal/fitting opening formed in the exchanging area of the filter device for exchanging fresh or cleaned screening elements for soiled screening elements; a melt return line which branches off from the melt outflow line and includes a pump and a first melt discharge line for transporting filtered plastics melt into a backflushing slot of the filter device to backflush the screening elements; an accelerator connected to the first melt discharge line for increasing pressure in the first melt discharge line for backflushing the screening elements; and a second melt return/discharge line, leading away from the filter device on the opposite side of the filter wheel from the backflushing slot, and a valve for selectively directing backflushed plastics to the melt inflow line or a disposal line.
Further objects, features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments of the invention, when considered together with the accompanying figures of drawing.
REFERENCES:
patent: 5090887 (1992-02-01), Gneuss
patent: 5141631 (1992-08-01), Whitman
patent: 5449458 (1995-09-01), Gneuss
patent: 5536399 (1996-07-01), Kaneshige
patent: 5922194 (1999-07-01), Bruckman et al.
patent: 41 13 501 (1992-10-01), None
patent: 08 156 072 (1996-06-01), None
DE 42 12 928: Oct. 28, 1993; Abstract.
“Problem solutions for all fields of application”; PV International Plastic Magazine, vol. 3 No. 2, (1992).
Gneuss Detlef
Henke Ralf
Lindner Eduard
Schaller Rainer
Arteva Technologies S.A.R.L.
Drodge Joseph W.
Foley & Lardner
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