GB1569195A

GB1569195A - Filter for polymer melts and solutions

Info

Publication number: GB1569195A
Application number: GB4748/77A
Authority: GB
Original assignee: Postavnichev V K Klochtov V I
Current assignee: Postavnichev V K Klochtov V I
Priority date: 1977-02-04
Filing date: 1977-02-04
Publication date: 1980-06-11

Description

(54) IMPROVEMENT RELATING TO A FILTER FOR -- POLYMER MELTS AND SOLUTIONS (71) We, VLADIMIR KONSTANTINOVICH PO6TAVNICHEV, of ulitsa Chernyakhovskogo, 12, kv.85, Moscow USSR., Vladimir Ivanovich Klochkov, of ulitsa Narodnogo Opolchenia 5, kv.57., Moscow, USSR., Semen llich Gdalin, of Oktyabrskaya ulitsa 19,kv.79, Moscow USSR., and Vyacheslav Vasilievich Sharonov, of Sumskayaulitsa, 12/17, kv.209 Moscow USSR., All citizens of the USSR, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to filters for polymer melts and solutions and may be most advantageously used for cleaning polymer melts.

For the manufacture of various products of polymeric materials using extruders, such as substratum for photographic materials, insulating films for electric insulation purposes and capacitors, transparent sheets and yarn, clean resin is required. During preparation of polymer and its subsequent pelletizing as well as during packaging and shipment thereof to processing plants, it is impossible to avoid contamination by solid inclusions in the material which should, therefore, be filtered. Fillers are added to some polymer to improve their properties and the quality of the finished products. Most of the ers are finely ground substances, such as titanium dioxide which may be added to polyethyleneterephthalate.

Despite appropriate classification of the filler powder, particles of a size exceeding an admissible limit enter the polymer.

For films and yarn made of polymeric materials filtered during the manufacture this limit is I to 30,u. Filtered particle diameter should not exceed the thickness of finished product and in majority ofapplications their size should be smaller than that of the product thickness.

Coarse inclusions in the films and yam result in breakage during continuous manufacture of products, increased quantity of discarded products and higher manufacturing cost.

In addition, films and yarn with coarse inclusions exhibit lower technical parameters as regards electric strength, transparence and other properties.

Filtering of polymer melts and solutions substantially differs from filtering of other contaminated liquids. Polymer melts feature high viscosity (500-50000 Pu), relatively high filtering temperature (up to 400 C), low concentration of solids, and low thermal stability.

Throughout capacity of extruder plants equipped with filters reaches from 500 to 1000 kg/h, and the fineness of filtering should be up to l-3Op, as mentioned above.

Combination of properties of processed material and requirements imposed on finished products calls for application of high pressure during filtering (up to 200-300 kp/cm ). It is to be noted that duration of continuous operation of plants is 15 - 30 days, and during this period thermal stability is required. Inoperative time of equipment and polymer losses associated with starting periods during which stable performance parameters are achieved should be minimised. Even at the processing temperature, continuous thermal exposure of the melt for 5-10 hours results in its destruction and impaired properties of manufactured products.

For this reason there should be no dead zones in filters for polymer melts, and filter construction should provide for directional flow of melt.

Widely known filters and filtering plants for separation of suspensions and purification of oils are unsuitable for filtering polymer melts because of different pressure and temperature parameters involved and dead zone formation.

Special filters are employed for polymer melts.

Filters for polymer melts are divided into three fundamentally different groups: - filters having replaceable filter elements; - filters with intermittent washing of filter elements; - filters with continuous washing of filter elements.

It is common knowledge that the filters of the first group having replaceable filter elements comprise a casing with heaters, an inlet opening and an outlet opening, a movable partition in the form of a cylinder or plate, two replaceable filter elements located therein which are made in the form of discs, and a pneumatic or hydr raulic drive system for displacement of the partition. The partition is arranged at right angle to the melt flow. With one of the filter elements being clogged, the partition is displaced and the other filter element is put in operation. The used filter element is removed to be replaced by a new one.

In such filters, small filtering surface results in cyclic changes in the melt pressure upstream the filter, i.e., from minimum value upon installation of a new filter element up to maximum value when the filter element is regarded as completely clogged. Such pressure changes result in increased difference in thickness of manufactured products. Filtering surface in such filters is within the limits of the extruder screw diameter, hence frequent replacements of filter elements. In addition, known filters are difficult to operate because of the necessity to replace filter elements at the polymer melting point (above 200 C); it is likewise difficult to avoid melt leakages along the travelling area of the movable partition wherethrough polymer may enter heaters to cause their failure and contamination of manufacturing environment.

Filters of the third group with continuous washing of filter elements are based on the principle of rotation of the filtering surface relative to the inlet chamber and washing device.

According to the present invention there is provided a filter for polymer melts and solutions comprising a casing having an inlet and an outlet, and a filter unit accommodated in the casing for filtering fluid passing through the casing from the inlet to the outlet, the filter unit including a hollow mandrel and a plurality of annular filter elements mounted on the mandrel between two flanges, each element comprising a pair of filter members separated by a spacer plate, by a sleeve having openings communicating the interior of the filter element with the interior of the mandrel and by a seal located at the outer periphery of the spacer plate, the filter elements being separated from each other and the flanges by additional spacer plates arranged to support the filter members over substantially the entire filtering surfaces thereof, by spacer sleeves located around the periphery of the additional spacer plates and having openings communicating the spaces between the filter elements with the exterior of the filter unit, and by auxiliary seals positioned on the mandrel, and at least one of the flanges being axially adjustable on the mandrel for clamping together the filter elements to tighten the seals, whereby the filter members of the filter elements can be washed free of deposits by reversed fluid flow through the filter unit.

Service life of the filter can be prolonged due to washing of the filtering elements direct ly in the filter, the filter elements being sup ported by the spacer plates.

Supporting contact is ensured due to the fact that the spacer plates located between the filter elements are not rigidly connected to the seals mounted on the periphery of the mandrel and at the periphery of the spacer plates.

The spacer plates mounted in such a manner make the filter construction less sensitive to variations in thickness of the plates, filter mem bers and seals, thereby improving the strength of the filter elements during washing, which results in higher admissible pressure difference at the filter elements, in more complete recov ery of the filtering baffles, hence in prolonged service life of the filter.

This filter construction considerably reduce manufacturing cost of products.

The provision of the end spacer plates be tween the flanges and the filter elements, as well as at least one axially adjustable flange enable more complete recovery of the filtering members with reversed flow of polymer melt or solution in the filter under high pressure.

This makes it possible to obtain more filtrate with the same area of filtering surface.

Means may be mounted for axial movement on at least one of the flanges for adjusting the compression and tightness of the seals of the filter elements and said means may take the form of a sleeve in screw threaded connection with a flange.

With this arrangement a cartridge of filter elements may be reliably compressed at the periphery of the filter elements. The sleeve compensates for the manufacturing tolerances of filtering members, sealing rings and spacer plates as regards their difference in thickness both for different pieces and within each piece, such tolerances being inevitable in the manu facturing process. The sleeve permits of obtain ing along with more complete recovery of filter elements, prolonging the service life of the fil ter, filtrate of better quality due to elimination of gaps and apertures.

In a preferred embodiment an outer sleeve surrounds the flanges, filter elements, and addi tional spacer plates to prevent radial displace ment of the filter elements, and additional spacer plates, which is important for reliable filtering and washing.

Displacement of the filtering members, and especially of the seals of filter element, along with the spacer plates, may result in unreliable construction due to the formation of gaps be tween mating surfaces.

The displacement particularly affects wash ing conditions of filter elements where melt or solution pressure is applied from within the filter element, and the peripheral part of the filter elements undergoes tensioning. It is noted that the strength of the filter element under tension is lower than the compression strength during filtering.

The other sleeve mounted on the flanges on the periphery of the filter elements and spacer plates prevents these components from radially displacing and makes the construction more reliable in filtering and washing.

The outer sleeve is preferably apertured, and provided with helical grooves on its inner surface. This form of sleeve, in addition to improvement of the cartridge strength during washing, helps lower the resistance offered to the melt flow during filtering and washing, thereby reducing size of dead zones at the points of contact between the filter elements, spacer plates and inner surface of the sleeve, and enabling the production of filtrate with lower contamination due to the polymer destruction and reduced clogging of filtering members.

The presently preferred embodiment of the invention will now be described in more detail by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of the filter for polymer melts and solutions according to the invention, shown partially in section; Figure 2 is an enlarged longitudinal axial section of part the filter; Figure 3 shows an outer sleeve of the filter; Figure 4 shows a spacer sleeve; Figure 5 is a cross-section along line V-V of Figure 4.

Referring now to the drawings, there is illustrated therein a filter which comprises a casing Figure 1) having an inlet opening 2 and an outlet opening 3 and inner spaces 4 and 5 accommodating filter units or cartridges 6 and 7, respectively. Each cartridge 6 or 7 consists of a hollow mandrel 8 supporting filter elements 9. A fixed flange 10 (Figure 2) and a movable flange 11 are mounted on the hollow mandrel 8, and the filter elements 9 are located between the flanges. Each filter element 9 comprises two filtering members 12, a spacer plate 13, a seal 14 mounted on the periphery of the spacer plate 13, and a sleeve 15 with through radial passages 16 communicating the inner spacer of the filter element 9 with the inner space of the mandrel 8.

The sleeve 15 is mounted on the periphery of the mandrel 8. The spacer plate 13 is made of a screen. Additional seals 17 are provided between the filter elements 9 on the periphery of the hollow mandrel 8. In addition, a sleeve 18 having through radial passages 19 communicawing the inner space of the filter element 9 with the filter space 4 or 5 and an additional, auxiliary spacer plate 20 corresponding to the surface of the filtering member 12 are mounted between the filter elements 9. An auxiliary seal 21s and an end spacer plate 20a are mounted between the flange 10 and the end filter element 9, a spacer sleeve 1 8a being located on the periphery of the spacer plate 20a. A device for tightening the seals 14 located on the movable flange 11 comprises a threaded sleeve 22. In addition, this sleeve presses the spacer sleeves 18 and 1 8a against the filtering members 12 and flange 10. The filter cartridge is provided with an auxiliary sleeve 23 mounted on the flanges 10, 11, on the periphery of the filter elements 9, auxiliary spacer plates 20 and two end spacer plates 20a, and on the periphery of the spacer sleeves 18a. The sleeve 23 prevents radial displacing of the filter elements, auxiliary and two end spacer plates and spacer sleeves; in addition, this sleeve is made perforated with through radial apertures 24. The flanges 10 and 11 are pressed together by mean of a nut 25 mounted on the mandrel 8. The mandrel 8 is formed with grooves 26 communicating with the radial passages 16 of the sleeves 15 and with the inner space 27 of the mandrel 8 via a through hole 28. The sleeve 23 is inter nail provided with multiple helical grooves 29 (Figure 3) for eliminating dead zones and lowering hydraulic resistance. The grooves 29 communicate with the through radial passages 24.

The filter casing 1 has a tap 30 (Figure 1) operable to connect the inlet opening 2 either with both the inner spaces 4 and 5, or with one of the inner spaces 4 and 5 while connectin the other space 4,5 to a drain outlet, and a tap 31 adjustable to connect the filter outlet 3 with inner space 27 (Figure 2) of the mandrel 8 of either filter cartridge or with the inner spaces of both mandrells 8 at the same time.

To simplify the construction of the filter cartridge, the spacer sleeves 15, 18 and 18a (Figure 2) have radial grooves 32 (Figure 4,5) communicating the periphery of each sleeve with the inner space thereof.

Along with the production of filtrate in the filter according to the invention, a part of the filtrate is used for washing contaminated cartridge elements.

The filter for polymer melts and solutions functions in the following manner in the operating mode of filtering, provided with one cartridge 6 with concurrent washing of filter elements of the other cartridge 7.

Contaminated polymer melt or solution is fed under pressure to the inlet opening 2 of the filter. By manipulating the tap 30, the melt is fed to the outlet space 4 of the filter cartridg 6 while the outer space 5 of the cartridge 7 is connected to the drain outlet. Then the melt flows through the passages 24 (Figure 2) of the auxiliary sleeve 23 and radial passages 19 of the spacer sleeves 18 moving along the spacer plates 20 on the surface of the filtering members 12. Filtrate passing through the filtering members 12 flows along the spacer plates 13 of the filter elements 9, through the passages 16 of the sleeves 15 into the groove 26 and thence via the hole 28 and inner space 27 to the outlet opening 3 (Figure 1) of the filter.

For washing the filter elements, a part of the filtrate flow is fed, by manipulating the tap 31 (Figure 1), to the inner space 27 of the mandrel 8 of the other filter cartridge 7, concurrently with feeding to the outlet opening 3.

This clean flow of filtrate, moving in the reversed order as compared to the abovedescribed filtering flow, washes the filter elements of the cartridge 7 and is discharged with the deposits through the drain outlet associated with tap 30.

Alternate switching of the filtrate flow by manipulating the taps 30 and 31 provides for washing of both cartridges 6 and 7 during continuous filtrate feeding to the outlet opening 3 of the filter.

Helical grooves 29 provided on the inner surface of the auxiliary sleeve 23 (Figure 3) eliminate the formation of dead zones in the path of flow between the passages 24 and the filtering members 12 in the filtering mode, as well as in the recovery mode with reversed filtrate flow.

During assembly of the filter elements 9 on the mandrel 8 (Figure 2) the threaded sleeve 22 enables elimination of loose contact of the seals 14 and the filtering members 12 along their periphery which would be otherwise inevitable due to manufacturing tolerances.

In addition, the sleeve 22 prevents the formation of a gap between the filtering members 12 and the seal 14 located on the periphery of the member when melt or solution is fed under pressure to the inner space of the filter elements 9 during washing. The auxiliary sleeve 23, along with fixing of the filter elements 9, spacer sleeves 18 and spacer plates 20, 20a providing for reliable assembly, prevents radial displacement of the seals 14 during washing of the filter elements 9, thus enabling the washing of the filtering members under high pressure. The latter facility provides for more complete recovery and prolongs service life of the filter.

The filter constructed in accordance with the invention enables continuous filtering at high throughput capacity and at high pressure difference (on the order of 400 kp(cm2). The filter enables fine and superfine cleaning of highly viscous polymer melts and solutions (up to 500-50000 Pu).

With the filter featuring the washing of the filter elements directly in the filter during continuous operation of the filter, as well as comparatively simple accommodation of a large filtering surface (10 - 20 m2) in one cartridge, continuous filtering of heavily contaminated and highly viscous liquids is ensured.

The construction of the device for tightening seals provides the conditions for reliable operation of the filter both during the removal of contaminants from the liquid and clearing the filtering members.

Compact arrangement of the filter elements and spacer plates with their reliable fixing in the cartridge in both axial and radial directions enabled the provision of the compact filter having a large filtering surface within a smallvolume chamber. Alongside with high strength parameters of the construction, streamlined configurations of both the cartridges as a whole, and filter elements are provided, thus allowing the filtering of polymer melts and solutions without impairing quality of liquid.

WHAT WE CLAIM IS: 1. A filter for polymer melts and solutions comprising a casing having an inlet and an outlet, and a filter unit accommodated in the casing for filtering fluid passing through the casing from the inlet to the outlet, the filter unit including a hollow mandrel and a plurality of annular filter elements mounted on the mandrel between two flanges, each element comprising a pair of filter members separated by a spacer plate, by a sleeve having openings communicating the interior of the filter element with the interior of the mandrel and by a seal located at the outer periphery of the spacer plate, the filter elements being separated from each other and the flanges by additional spacer plates arranged to support the filter members over substantially the entire filtering surfaces thereof, by spacer sleeves located around the periphery of the additional spacer plates and having openings communicating the spaces between the filter elements with the exterior of the filter unit, and by auxiliary seals positioned on the mandrel, and at least one of the flanges being axially adjustable on the mandrel for clamping together the filter elements to tighten the seals, whereby the filter members of the filter elements can be washed free of deposits by reversed fluid flow through the filter unit.

2. A filter as claimed in Claim 1, wherein means is mounted for axial movement on at least one of the flanges for adjusting the compression and tightness of the seals of the filter elements.

3. A filter as claimed in Claim 2, wherein said means mounted for axial adjustment on at least one flange comprises a sleeve in screw threaded connection with a flange.

4. A filter as claimed in Claims 1, 2 or 3 wherein the filter unit includes an outer sleeve surrounding the flanges, filter elements and additional spacer plates.

5. A filter as claimed in Claim 4, wherein the outer sleeve is apertured and is provided with helical grooves on the inner surface thereof.

6. A filter according to any one of Claims 1 to 5, wherein two filter units of the same construction are accommodated in respective chambers in the casing, a tap is provided and is adjustable to connect the inlet to either one of said chambers and the other of said chambers to a drain outlet, the casing outlet being adapted to communicate with both chambers at the same time, whereby said tap is selectively adjustable to direct liquid entering through the inlet to either one of the chambers to be filtered by the unit therein, a portion of the filtrate from

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. (Figure 1), to the inner space 27 of the mandrel 8 of the other filter cartridge 7, concurrently with feeding to the outlet opening 3. This clean flow of filtrate, moving in the reversed order as compared to the abovedescribed filtering flow, washes the filter elements of the cartridge 7 and is discharged with the deposits through the drain outlet associated with tap 30. Alternate switching of the filtrate flow by manipulating the taps 30 and 31 provides for washing of both cartridges 6 and 7 during continuous filtrate feeding to the outlet opening 3 of the filter. Helical grooves 29 provided on the inner surface of the auxiliary sleeve 23 (Figure 3) eliminate the formation of dead zones in the path of flow between the passages 24 and the filtering members 12 in the filtering mode, as well as in the recovery mode with reversed filtrate flow. During assembly of the filter elements 9 on the mandrel 8 (Figure 2) the threaded sleeve 22 enables elimination of loose contact of the seals 14 and the filtering members 12 along their periphery which would be otherwise inevitable due to manufacturing tolerances. In addition, the sleeve 22 prevents the formation of a gap between the filtering members 12 and the seal 14 located on the periphery of the member when melt or solution is fed under pressure to the inner space of the filter elements 9 during washing. The auxiliary sleeve 23, along with fixing of the filter elements 9, spacer sleeves 18 and spacer plates 20, 20a providing for reliable assembly, prevents radial displacement of the seals 14 during washing of the filter elements 9, thus enabling the washing of the filtering members under high pressure. The latter facility provides for more complete recovery and prolongs service life of the filter. The filter constructed in accordance with the invention enables continuous filtering at high throughput capacity and at high pressure difference (on the order of 400 kp(cm2). The filter enables fine and superfine cleaning of highly viscous polymer melts and solutions (up to 500-50000 Pu). With the filter featuring the washing of the filter elements directly in the filter during continuous operation of the filter, as well as comparatively simple accommodation of a large filtering surface (10 - 20 m2) in one cartridge, continuous filtering of heavily contaminated and highly viscous liquids is ensured. The construction of the device for tightening seals provides the conditions for reliable operation of the filter both during the removal of contaminants from the liquid and clearing the filtering members. Compact arrangement of the filter elements and spacer plates with their reliable fixing in the cartridge in both axial and radial directions enabled the provision of the compact filter having a large filtering surface within a smallvolume chamber. Alongside with high strength parameters of the construction, streamlined configurations of both the cartridges as a whole, and filter elements are provided, thus allowing the filtering of polymer melts and solutions without impairing quality of liquid. WHAT WE CLAIM IS:

1. A filter for polymer melts and solutions comprising a casing having an inlet and an outlet, and a filter unit accommodated in the casing for filtering fluid passing through the casing from the inlet to the outlet, the filter unit including a hollow mandrel and a plurality of annular filter elements mounted on the mandrel between two flanges, each element comprising a pair of filter members separated by a spacer plate, by a sleeve having openings communicating the interior of the filter element with the interior of the mandrel and by a seal located at the outer periphery of the spacer plate, the filter elements being separated from each other and the flanges by additional spacer plates arranged to support the filter members over substantially the entire filtering surfaces thereof, by spacer sleeves located around the periphery of the additional spacer plates and having openings communicating the spaces between the filter elements with the exterior of the filter unit, and by auxiliary seals positioned on the mandrel, and at least one of the flanges being axially adjustable on the mandrel for clamping together the filter elements to tighten the seals, whereby the filter members of the filter elements can be washed free of deposits by reversed fluid flow through the filter unit.

said one chamber flowing through the filter unit in the other chamber in reverse direction to wash deposits from the filter members thereof and being directed to the drain outlet by the said tap.

7. A filter according to Claim 6, wherein a second tap is provided and is selectively adjustable to connect the casing outlet with either one of said chambers for directing all the filtrate from said chamber to said outlet, or with both chambers at the same time for a portion of the filtrate from one chamber to flow to the other chamber for washing the filter members of the filter unit therein.

8. A filter substantially as herein described with reference to the accompanying drawings.