Filter media

#This invention relates generally to the art of filtering, and is concerned in particular with the filtering of pressurized material in flowable form.

#There are numerous commercial operations dealing with pressurized materials in flowable form where filter elements are employed to remove contaminants, impurities, etc. When the filter elements become clogged, they must be replaced, cleaned or renewed, and with certain operations this can present serious problems. An example of one such operation is the filtering of molten plastic being fed from an extruder, melt pump or the like to a die producing any one of a wide range of products, such as for example blow-molded bottles, thin-film plastic bags, etc. In operations of this type, the molten plastic is passed at elevated temperatures in excess of 200.degree.-300.degree. F. and high pressures typically on the order of 1000 to 5000 p.s.i. through a filter apparatus located between the extruder or melt pump and the molding machine. In addition to effectively removing contaminants from the melt stream, the filter apparatus must also operate safely and continuously over extended periods of time, with a minimum substantially constant pressure drop across the filter element. By minimizing the pressure drop across the filter element, the volume of plastic flow to the molding machine is maximized, thereby permitting higher production rates. Maintaining the pressure drop substantially constant simplifies the task of controlling the operation of equipment on both the upstream and downstream sides of the filter.

#The prior art filter devices which have heretofore been developed have failed to meet the criteria of successful operation outlined above. More particularly, in earlier devices of the type described in U.S. Pat. No. 642,814, separate filter screen elements are located in two laterally spaced positions on a shuttle plate which can be reciprocated in opposite directions transverse to the flow axis of the material being filtered. Such devices are characterized by numerous drawbacks, including pronounced fluctuations in feed pressures to downstream equipment due to infrequent changes of clogged filter screen elements, difficulties in cleaning and/or replacing clogged filter screen elements, and dangerous leakage of hot high pressure molten material when the shuttle plate is shifted.

#FIG. 1 is a horizontal cross-sectional view taken through a filter employing the filter element of the present invention;

#FIGS. 2 and 3 are sectional views on an enlarged scale taken along lines 2--2 and 3--3 of FIG. 1;

#FIG. 4 is a view in perspective of a filter element in accordance with the present invention, with portions of the filter strip and carrier strip broken away;

#Referring initially to FIGS. 1 to 3 there is shown at 10 a filter apparatus of the type disclosed and claimed in copending application Ser. No. 537,780. The filter apparatus includes a housing 12 defining an internal filter zone or chamber 14. Inlet and discharge pressure conduits 16 and 18 are connected to the housing 12 in communication with the filter zone. The conduits 16 and 18 establish a flow axis 20 for the material being filtered, the direction of material flow being indicated by arrows 22.

#An elongated guide 24 extends through the housing 12 in a direction transverse to the flow axis 20. The guide is comprised of mating walls 26, 28 which define a guide channel 30. The guide 24 has an entry section 24a leading into one side of the filter zone, an intermediate section 24b extending across the filter zone, and an exit section 24c leading out from the opposite side of the filter zone. The walls forming the entry and exit sections 24a, 24c are imperforate, whereas at the intermediate section 24b, wall 28 forms a "backer plate" 31 which is perforated as at 32, and wall 26 has an enlarged opening 33 therein opposite to the backer plate. Optionally, the backer plate can comprise a piece which is separate from wall 28.

#A filter element 34 in accordance with the present invention is adapted to move longitudinally through the entry section 24a, across the filter zone 14 along the upstream face of the backer plate 31 and through exit section 24c. Any conventional means (not shown) may be employed to move the filter element, either continuously or intermittently, along the above-described path. The pressurized material in flowable form enters the filter zone 14 through inlet conduit 16, and after being filtered by passing through the filter element 34, leaves the filter zone through discharge conduit 18.