GB2096912A

GB2096912A - Filtering apparatus

Info

Publication number: GB2096912A
Application number: GB8112204A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-04-16
Filing date: 1981-04-16
Publication date: 1982-10-27
Also published as: FR2504820A3

Abstract

The apparatus comprises a series of filtering elements moved in succession across a channel along which molten plastics is flowing, each filtering element consisting of two superimposed plates (11, 12) which enclose a filtering net (13). The upstream plate (11) presents wide apertures (14) for the passage of the plastics, whereas the downstream plate (12) presents narrower slots 16). The filtering net (13) housed in a lengthwise passageway (18) open at both ends and deeper than the thickness of the net (13), which enables the plastic material to flow along the passageway (18) to expel air from various apertures and slots (14, 16) before these come into communication with the channel downstream of the element. The openings through which the elements enter and leave the channel (Fig. 1 not shown) have cooling units which maintain sealing plugs of partly solid plastics therein. <IMAGE>

Description

SPECIFICATION Filtering apparatus This invention concerns a filtering apparatus for plastic material in the melted state, of the type comprising filtering plates which are moved in succession crosswise to the flow of plastic material to be filtered in order to achieve a substantially continuous type of filter.

It is usually necessary, in the field of extrusion of thermoplastic materials, to carry out a preliminary filtering of the melted polymer in order to eliminate the solid impurities which are normally present in the mass of the material. A number of filtering apparatuses have been created for this purpose which use a filtering net held by sliding plates which are made to advance in a crosswise direction to the flow of melted plastic, from an inlet towards a lateral outlet.

The use of plate-mounted filtering elements has up till now given rise to a number of problems, amongst which in particular: substituting the soiled filtering net with a new one in each filtering element is a difficult and somewhat awkward operation to carry out, furthermore the platemounted filtering elements are designed in such a way as to unavoidably allow a certain amount of air to enter into the apparatus, resulting in the formation of defects in the film of extruded material.

The aim of this invention is to provide a slidingplate filtering apparatus as mentioned above, in which the entry of air into the mass of melted material through the filtering elements is completely eliminated, insofar as the melted plastic material itself is used to form a seal.

A further aim of this invention is to provide an apparatus of the aforementioned type, in which the plates of the filtering elements are designed with ample passages for the melted material which substantially decrease losses due to friction and pressure through the filtering elements themselves. A still further aim of this invention is to provide plate-mounted filtering elements for the aforementioned apparatuses which are of extremely simple construction and which permit quick and easy replacement of the filtering net in each of the elements itself.

According to this invention, a filtering apparatus is thus provided, of the type comprising flat filtering elements, moved in succession, crosswise to a flow of melted plastic material, means being provided, in correspondence with passages for the insertion and removal of the filtering elements, for forming an airtight seal, characterized by the fact that each filtering element comprises a front plate with large apertures for passage of the plastic material, and a rear plate supporting a filtering net, said rear plate having transversal slots for the passage of the material which are smaller in width than the apertures in the front plate, said plates defining a lengthwise channel for housing the net, which opens at both ends and, measured in the sense of the flow of material, is greater in width than the thickness of the filtering net itself.

This invention will be more fully explained hereunder with reference to the figures in the annexed drawings, in which: Fig. 1 shows a cross-section of a filtering element embodying the improvements of this invention.

Fig. 2 shows a lengthwise cross-section of a filtering element.

Fig. 3 shows a cross-section along the line 3-3 of Fig. 2.

Fig. 4 shows a view of the front plate.

Fig. 5 shows a view of the rear plate, from the inner side of the plate itself.

Referring to Fig. 1 , the latter shows a generic filtering apparatus 1 defining a path 2 for a flow of plastic material in the melted state, between an inlet 3 and an outlet 4 for the material. In correspondence with the intermediate filtering area, the apparatus comprises a lateral inlet opening 5 for the introduction of the filtering elements 6 and respectively, an outlet opening 7 for removal of the latter on the opposite side of the apparatus. The various filtering elements 6 are pushed along guides 8, for example, by means of an oleodynamic, mechanical or other type of pushing mechanism 9, which acts upon the end of the last filtering element 6 to be inserted into the guides.Moreover, 10 indicates lateral cooling elements situated in correspondence with the openings 5 and 7 for the introduction and the removal of the filtering elements, which enable the melted plastic material to form a seal.

The cooling units 10 are secured to the body 1 of the apparatus in such a way as to be removed, for example, by means of bolts or similar, in order to facilitate and speed up the cleaning of the cooling-water circuit channels 10'. Each filtering element assembly 6, as shown in the other figures, comprises a front plate 11 and a rear plate 12 between which is inserted a filtering net 13.

The front plate 1 1 presents large apertures 14 for the passage of the melted plastic material, arranged along a lengthwise area of the plate itself; each aperture 14 is rectangular in shape.

approximately double in height as compared to the width, and separated from the adjacent aperture by a thin diaphragm 15 which extends over the entire thickness of the plate itself. A large area of flow of material is thus achieved which reduces pressure losses without excessively weakening the plate itself.

The dimensions and depth of the aperture 14 must be such as to retain solid matters even of a considerable size.

The rear plate 12, unlike the front one, presents on its internal face, that is to say, the side facing the plate 1 1, a series of transversal slots 16 substantially equal in height to the apertures 14 in the plate 11 and considerably smaller in width for example approximately one third smaller than the aforementioned apertures; thus each aperture 14 in the front plate 11 overlaps several consecutive slots in the rear plate, for the reasons which will be explained hereunder.

In fact, from the cross-section in Fig. 2, it can be seen that each transversal slot 16, measured in the sense of the flow of material to be filtered, is smaller in depth or length and equal to approximately half the thickness of the rear plate 12; therefore it occurs that pairs of adjacent slots 16 open out into a rear outlet aperture or cell 1 7 for the melted material, the width of which is more than double the width of each slot.It was found, from tests carried out, that the construction of the rear plate as shown, is important for the correct functioning of the filter; in fact the series of slots 16 placed close together which extend upwards and across the plate 12, make it possible to simultaneously obtain a satisfactory sectional area of flow for the melted plastic material and an excellent rear support for the filtering net when the latter is forced to adhere to the plate 12 by the strong pressure exerted by the melted material.

Moreover, due to the fact that the slots 16 in the second plate open out into wider apertures, it is possible to substantially reduce losses due to friction through the filter.

Figures 2, 3, 4 and 5 show a further feature of the filter of this invention, which makes it possible to improve its use. It can be seen in fact from said figures that the filtering net 13 is housed in a longitudinal channel 18 defined between the two opposing plates 1 1 and 12; said channel opens at both ends of the plates and therefore continues along the channel formed by the subsequent plates. In detail, in the example in Fig. 3 and Fig. 4, the channel 18 is formed on the inner face of the rear plate 12 and is greater in height than that of the net 13. Furthermore, it can be seen from the cross-section in Fig. 3, that the width or depth of the channel 1 8, measured in the sense of the flow of material to be filtered, is greater for example by two or three times the thickness of the net 13.

This fact, together with the opening of the channel at the ends of the plates is important for two different reasons: firstly, the use of a channel open at both ends permits easy removal of the filtering net in order to replace it with a new one; this can be done by simply sliding out the old net from one end and then inserting the new net; removal of the net may be made easier by chamfering the edges 1 8' of the channel 18 on at least one of its ends.

Moreover, depending upon the characteristics of the material to be filtered, it is possible to insert two or more overlapping nets of different types into one filtering element.

Secondly, the particular structure of the filtering element itself prevents the entry of air through the filter. In fact, because of the construction of known plate-mounted filters, the various apertures for the passage of the material through the plates have the tendency to allow a certain amount of air to be carried along with the mass of melted material which disperses and becomes incorporated into the material itself with the imaginable consequences; this is due mainly to the fact that the various apertures for the passage of the material through the plates are not in communication with each other. Therefore, the melted plastic material only fills each single aperture when the latter enters into the path of the flow of material, expelling the air held in it.

With the filter of this invention, this problem is overcome for the following reason: as it can be seen on the left hand side of Fig. 2, each aperture 14 in the front plate 11 is simultaneously in communication, by means of the longitudinal channel 18, with several slots 16.Therefore, due to the continuity of channel 18 even when passing from one filtering element to the next, a small lateral flow of plastic material occurs in correspondence with the lateral wall of the apparatus 1 through which the filtering elements 6 are introduced, which, flowing through the channel 1 8 in the opposite direction to that of the filtering elements themselves (as shown by the arrows), tends to completely fill each cell of the filter defined by the apertures 14 on one plate and by the corresponding slots 1 6 and the apertures 17 on the other plate, which is about to enter, or which has not yet entered the path 2 of the flow of material.

Thus, when each cell, as defined above, enters the filtering section of the apparatus, it is completely full of melted plastic and therefore does not contain air. The plastic is moreover prevented from flowing out of the filter by the cooling elements 10 which locally increase its density, thus forming a seal.

Fig. 5 shows a final feature of the rear plate; it can be seen, from the said figure, that at the end of the plate, in order to avoid weakening its structure excessively and, in place of one slot 16, a series of holes 19 has been used which still ensure the continuity of the flow of plastic material.

In addition to the various aspects of the present invention which have been set out hereinbefore there is provided in accordance with one, main, broad aspect of the invention, a filtering apparatus comprising a main housing, flat filtering elements arranged to be moved in succession crosswise to a flow of material through the housing, and means, associated with passages in the housing for the insertion and removal of the filtering elements, for forming an airtight seal at said passages, in which each filtering element comprises a front plate with apertures for passage of the material, and a rear plate for supporting a filtering member, said rear plate also having apertures for passage of the material, said plates defining a channel for housing the filtering member, the said channel extending lengthwise along the intended direction of movement of the filtering elements across the flow of material, the channel being open at both ends, and the channel being deeper, measures in the sense of the flow of material, than the thickness of the filtering member itself.

Claims

1. A filtering apparatus comprising a main housing, flat filtering elements arranged to be moved in succession crosswise to a flow of material through the housing, and means, associated with passages in the housing for the insertion and removal of the filtering elements, for forming an airtight seal at said passages, in which each filtering element comprises a front plate with apertures for passage of the material, and a rear plate for supporting a filtering member, said rear plate also having apertures for passage of the material, said plates defining a channel for housing the filtering member, the said channel extending lengthwise along the intended direction of movement of the filtering elements across the flow of material, the channel being open at both ends, and the channel being deeper, measured in the sense of the flow of material, than the thickness of the filtering member itself.

2. A filtering apparatus according to Claim 1 in which the front plate is provided with relatively large apertures for passage of material and the rear plate is provided with slots, transverse to the intended direction of movement of the filter elements, for passage of the material, said slots being smaller in width than the apertures in the front plate.

3. A filtering apparatus as claimed in Claim 1 or 2, in which the apertures in the rear plate open out into apertures of greater width.

4. A filtering apparatus as claimed in Claim 1, 2 or 3 in which the lengthwise channel is equal in width to at least twice the thickness of the filtering member.

5. A fiitering apparatus as claimed in any preceding Claim in which said channel is formed on the inner face of the rear plate.

6. A filtering apparatus as claimed in any preceding Claim in which the channel is greater in height than that of the apertures in the plates for the passage of the material.

7. A filtering apparatus as claimed in any preceding Claim in which the rear plate presents, at each end, a series of holes for the passage of the material.

8. A filtering apparatus as claimed in any preceding Claim in which the channel housing the filtering member in one filtering element continues with the channel of the adjacent filtering element.

9. A filtering apparatus as claimed in any preceding Claim in which the channel housing the filtering member presents chamfered edges on at least one of its ends.

10. A filtering apparatus as claimed in any preceding Claim for filtering melted plastic material in which the means for forming an airtight seal in association with the openings for the insertion and removal of the filtering elements, comprise cooling units provided with water circulation ducts, said cooling units being interchangeably secured to the apparatus itself.

1 1. A filtering apparatus according to any preceding Claim in which the filtering member comprises a filtering net.

12. A filtering element suitable for use in a filtering apparatus according to any preceding Claim, when having the filtering element features as set out in any preceding Claim.

13. A filtering apparatus as hereinbefore described with reference to the figures of the accompanying drawings.

14. A filtering element, suitable for use in a filtering apparatus substantially as hereinbefore described with reference to the accompanying drawings.

1 5. A filtering apparatus of the type comprising flat filtering elements moved in succession crosswise to a flow of melted plastic material, means being provided in correspondence with passages for the insertion and removal of the filtering elements, for forming an airtight seal, in which each filtering element comprises a front plate with large apertures for passage of the material, and a rear plate for supporting a filtering net, said rear plate having transversal slots for passage of the material which are smaller in width than the apertures in the front plate, said plates defining a lengthwise channel for housing the net, which opens at both ends and, measured in the sense of the flow of material, is wider than the thickness of the filtering net itself.

16. A filtering apparatus as claimed in Claim 15, in which the slots in the rear plate open out into apertures of greater width.

1 7. A filtering apparatus as claimed in Claim 15 in which the lengthwise channel is equal in width to at least twice the thickness of the filtering net.

18. A filtering apparatus as claimed in Claim 15, in which said channel is formed on the inner face of the rear plate.

19. A filtering apparatus as claimed in Claim 15, in which the channel is greater in height than that of the apertures and slots in the plates, for the passage of the melted material.

20. A filtering apparatus as claimed in Claim 15, in which the rear plate presents, at each end, a series of holes for the passage of the melted material.

21. A filtering apparatus as claimed in Claim 15, in which the channel housing the net in one filtering element, continues with the channel of the adjacent filtering element.

22. A filtering apparatus as claimed in Claim 15, in which the channel housing the net, presents chamfered edges on at least one of its ends.

23. A filtering apparatus as claimed in Claim 15, in which the means for forming an airtight seal in correspondence with the openings for the insertion and removal of the filtering elements, comprise cooling units provided with water circulating ducts, said cooling units being interchangeably secured to the apparatus itself.

24. A filtering apparatus as hereinbefore described with reference to the figures of the accompanying drawings.