GB2082466A - High performance fibrillated film wound filter cartridge - Google Patents

Abstract

The invention relates to filters of the precision wound type in which the strands are of a yarn formed from highly fibrillated film. In one form of the invention a conventional filter cartridge of about 2-7/16 inch overall diameter on a core of about 1-1/8 inch diameter is prepared by winding a highly fibrillated film yarn of 10,000 total bundle denier, a fibril denier of less than 50 and greater than three percent broken fibrils onto a cartridge of any desired length.

Description

SPECIFICATION High performance fibrillated film wound filter cartridge This invention relates to improvements in the construction of filtering devices. It particularly relates to precision wound filter tubes comprising helically wound layers of yarn or roving.

It has been long known that filters may be formed by constructing a tubular element comprising a foraminous core precision wound with a multiplicity of layers of spaced convolutions of strand applied in criss-cross fashion to form a plurality of diamond shaped filtering passages through the sidewall of the element through which the fluid to be filtered is caused to pass. The fluid passing through the filter is clarified as particles in liquid adhere to the fibrous strands. The cartridge may be napped during winding to create additional loosely held fibres which occupy the passages and capture dirt particles. U.S. Reissue Patent No. 22,651 to Hastings et al is an example of such a filter.Such filters suffer from the disadvantage that when being used the filter suffers failure by excessive pressure drop prior to the fibers being totally or predominatly coated with the particles being filtered from the fluid. The loading of the filter generally occurs by large particles which coat and block the outer portion of the filter. Ordinarily the filtering direction is from the outside to the inner portion of the filter.

It has also been known to wind filter cartridges using yarns made from fibrillated films ordinarily of polypropylene. While these cartridges of propylene are advantageous in that they do not have a finish on the fiber and therefore are very suitable for filtering food materials, they suffer from the disadvantage that they do not have the ability to trap as large an amount of dirt in the cartridge as a cartridge wound with textile roving and further they do not have as high an efficiency which means that they do not filter as much dirt, expecially fine particles, from the material fed to the cartridge as would be desirable.

In addition to the wound cartridges utilizing fibrillated film yarn, there also has been proposed such as shown in United States Patent No. 3,904,798 to Vogt et al that filters of variable density be formed by extrusion of fibers directly onto a rotating collection device. However, such process is expensive to control for uniformity, the process is limited to extruded fibers rather than roving or napped fibres and the process involves expensive capital equipment for extrusion rather than the presently available winding equipment used to form precision wound cartridges.

Therefore, there remains a need for an improved wound fibrillated film cartridge of greater efficiency, extended life and improved dirt holding capacity.

It is an improved object of this invention to obviate or mitigate the above mentioned disadvantages. According to present invention there is provided a precision wound filter comprising a highly fibrillated polymer film yarn.

Preferably the highly fibrillated film yarn is one in which at least about 3% of the auxiliary fibrils are broken on one end from the main fibril strands. Preferably also the auxiliary fibrils are at least about 311 (1.25 cm) in length and are preferably of a denier of about 70 or less.

By way of example only the following table provides a comparison of the properties of typical highly fibrillated yarns as compared to typical normally fibrillated yarns.

PROPERTY HIGHLY FIBRILLATED NORMALLY FIBRILLATED Yarn denier 10,000 average 10,000 average Total fibrils in cross section 200-600 50-75 total main fibrils 8-25 per cent 30-50 per cent total aux. fibrils 75-92 per cent 50-70 percent aux. fibril length 1 /2in. to 3/4in. 1 /8in. to 3/8 in.

Aux. fibrils per inch of main fibril 6-10 1-4 Percentage of broken aux. fibrils 3-50 percent 0-1 percent Film thickness 1.0 to 1.75 mil 2.0 to 2.4 mil avg. 38 micrometers avg. 57 micrometers avg. 1.5 mil avg. 2.25 mil In a particularly preferred form of the invention a conventional filter cartridge of about 2-7/16 inch overall diameter on a core of about 1-1/8 inch diameter was prepared by winding a highly fibrillated film yarn of 10,000 total bundle denier, a fibril denier of less than 50 and greater than three percent broken fibrils on to a cartridge of any desired length. This cartridge exhibits much higher life and efficiency than previously available fibrillated film filter cartridges.

The filter cartridge and filtering process of the invention has a decided advantage over prior art fibrillated film cartridges. The cartridges have up to about 3 times longer life while exhibiting greater efficiency than previous cartridges. The cartridges have greater dirt holding capacity and are able to trap more fine particles of matter from the fluid passing through it than prior cartridges. Further the instant cartridges have the advantage that the technique of forming the cartridge remains the same as for prior wound cartridges, therefore making the increase in performance possible with no outlay for capital equipment.

In the instant specification the following terms of art are utilized in accordance with the definitions below which are considered to be in accordance with their accepted meaning in the cartridge filtering art: efficiency - ratio of number of or weight of particles of a particular size removed by a filter to the number or weight of that particular size particle in the feedstream fluid.

wind number - number of circumferential diamonds on the surface of a cartridge taken at the locus of points creating a circle in a plane perpendicular to the axis of the filter.

wind ration - equals spindle rpm divided by traverse frequency (complete cycles of the traversing mechanism up and back to the starting point).

life - the amount of dirt-containing fluid which may be passed through a cartridge.

dirt holding capacity (DHC) - the amount of dirt in fluid fed to a cartridge (corresponds directly to the life of the cartridge).

dirt capacity - dirt actually in the filter; (dirt capacity is considered difficult or impossible to measure directly.) pressure drop - the change in pressure between input fluid and fluid exiting a cartridge during filtering.

diamond - a diamond is the open area, measured strand center to strand center between adjacent strands of a diamond pattern precision wound on a filter cartridge.

diamond pattern - is the complete winding to form one layer of circumferential diamonds, i.e., 13 cycles of the traverse are required to form a complete diamond pattern for a 13 "wind number" car tridge.

fibrillated film yarn a yarn made by orienting a polymeric film sufficiently to cause it to separate into a fibrous structure (fibrils). The geometry and degree of separating into fibrils can be controlled and/or enhanced by several techniques known to those in the art, such as embossing or perforating.

It will be apparent from the above definitions that if efficiency remains the same, then an increase in dirt holding capacity equals the increase in dirt fed. It is known that in a precision wound filter, increasing the number of circumferential diamonds (finer winding) provides higher efficiency, but that it shortens the cartridge life. Conversely decreasing the number of circumferenced diamonds (coarser winding) provides greater cartridge life but with lower efficiency.

It is well known that reducing the average cross-sectional area (denier) of a fibrous assemblage reduces its bending modulus (stiffness). Ordinary fibrillated film yarns are usually produced such that the bending modulus is reduced while maintaining tensile properties of the strands. The highly fibrilated film yarns used to make the cartridges of the present invention are produced with stretching of the film to an extent such that only tensile properties sufficient to permit winding are retained while significantly reducing the average cross-sectional area (denier) of the individual fibrils. Thus the preferred highly fibrillated film yarns have an average fibril denier less than about 50 and more than 3 percent of the fibrils are broken. The total bundle denier may be any denier that gives good filter performance. A total bundle of denier of about 10,000 has been found to be satisfactory.

Filter cartridges made from highly fibrillated yarns have been found to be much more efficient in removing particles than cartridges of the same wind number made with ordinary fibrillated film yarn. Additionally, the life of the highly fibrillated film yarn cartridge usually increases relative to those made with ordinary fibrillated film yarns. It has been found that a significant increase in life without loss in efficiency is achieved with highly fibrillated film yarns when the wind number is reduced (coarser winding). Improvements in life of up to threefold that of those made from ordinary fibrillated film yarn are possible This amount of improvement in both life and efficiency generally can be achieved by forming the highly fibrillated cartridges at one or two wind numbers lower (coarser) than those made with ordinary fibrillated film yarn.

The preferred highly fibrillated film yarns of the invention may be formed of any film forming polymer. Typical are polyesters, polyethylenes, polyacrylics, polyvinyl chlorides, polypropylenes, polyesters, rubberized styrenes and polyamides. A preferred material has been found to be the polyolefins as they are low in cost, are easily fibrillated and are suitable for use in food products.

The optimum material has been found to be propylene as it is lowest in cost and easily worked to form fibrillated films and is safe for food products.

It has been found that for the conventional, about 2-7/16" diameter, cartridges a wind number of between about 10 and 13 is preferred, for A.C. coarse test dust, as the highest performance is in this range with greatly increased life and higher efficiency. As is apparent from the above set forth definitions a specific wind number cartridge has that specific number of circumferential diamonds at any circumferential circle, i.e. a 13 wind number cartridge has 13 circumferential diamonds. The ratio of axial diamonds to circumferal diamonds per 10 inch length of the cartridge is typically kept between about 2 and about 5. The preferred ratio is between about 2.5 and about 4 for good filtering performance. The optimum ratio is between about 3 and about 3.5 as this ratio gives the best filtering performance and ease of winding.

While not wishing to be bound by any particular theory to explain the dramatically increased performance of cartridges of the invention, it is theorized that the use of the highly fibrillated polypropylene in the relatively coarse winds results in a larger number of fibrils being available for trapping the dirt passing through the cartridge, than is possible with ordinary fibrillated film yarn. It is theorized that the highly fibrillated tight wind cartridges do not perform as well because the tight packing of the fibrils decreases the fluid passing openings resulting in early blockage and short life. However, it is believed that highly fibrillated yarns of lower denier could be utilized at higher wind numbers as the packing of the finer yarns would not be as tight.

The following examples illustrate the dramatic improvement in performance obtained by the instant invention. Parts and percentages are by weight and temperatures are in Farenheit unless otherwise noted.

EXAMPLES 1-13 A series of cartridges were formed in Examples 1-1 3 utilizing a cartridge rore of perforated tinned steel of a diameter of about 1-1/8 inch. Filters were wound in 10 inch lengths to an overall diameter of about 2-7/16 inches. In each of the test cartridges, polypropylene fibrillated material was used in the windings. Examples 1-7 are cartridges of the invention utilizing highly fibrillated polypropylene yarns. Example 8-13 are control Examples of ordinary fibrillated yarns that serve by comparison to show the superiority of the invention in Examples 1-7. Examples 8-1 3 were formed utilizing a ordinary fibrillated material defined as a polypropylene fibrillated yarn used in prior filter cartridges.The ordinary fibrillated film yarn had an average fibril denier of 62.5 and essentially no broken fibrils and a bundle denier of about 10,000. The highly fibrillated polypropylene yarns of Examples 1, 5 and 6 have an average fibril denier of about 12, between about 40 and 50 percent broken fibrils, a total bundle denier of about 10,000, a fibril length of about 5/8" and, a fibril frequency of about 8 per inch of yarn. The highly fibrillated polypropylene yarn of Examples 2, 3, 4 and 7 have an average fibril denier of about 22.4, a total denier of about 10,000, a fibril frequency of about 8 per inch of yarn length and between about 5 and about 10 percent broken fibrils. Broken fibrils are connected to the yarn by only one end of the fibril. The ordinary yarn has fibrils of about 3/8" in length, and a fibril frequency of about 4 per inch of yarn.Less than about 1 percent of the auxiliary fibrils are broken in ordinary fibrillated yarns.

All the cartridges were formed at a spindle speed of about 650 rpm. The cartridges were formed with a ratio of total diamonds of between 3 and 3.5 axial diamonds to circumferential diamonds on the 10 inch cartridge. The roving tension was between about 400 and 800 grams for winding of all cartridges. The winder was a Leesona winder which utilized a back plate which pressed against the turning cartridge after about the formation of the first 8th inch of windings.

The cartridges average about 220 gms of yarn. Back plate pressure was adjusted to give finished cartridges with air density as shown in the table below. Air density is the pressure drop measured in inches of water at 3.9 scfm airflow.

After formation, each cartridge was tested in flowing water containing A.C. Coarse Test Dust from the A.C. Spark Plug Company. A.C. Coarse Test Dust as available from A.C. Spark Plug Company contains particle size distribution as follows: weight percent at micrometer: 12% at 0-5; 12% at 5-10; 14% at 10-20; 23% at 20-40; 30% at 40-80; 9% at 80-200. The water was flowing at a rate of about 3.5 gallons per minute during testing and the test was stopped at a pressure drop across the cartridge of about 30 pounds or when no increase in the pressure drop was occurring. The test results from each cartridge are displayed in the listing below. This listing illustrates that highly fibrillated film yarn filter cartridges exhibit greater efficiency and generally greater dirt holding capacity than those made with ordinary fibrillated film.Additionally, when the wind number of the highly fibrillated film yarn filter cartridges is reduced as much as two values both the efficiency and dirt holding capacity are still higher relative to the finer wound ordinary fibrillated film cartridges. Compare Examples 1 with 11, 4 with 10, 7 with 9 and 6 with 8. Cartridges of Examples 6 and 7 would be expected to provide better filter performance filtering particles more coarse than those in the test dust. Note that one of the best of the ordinary fibrillated yarn cartridges, Example 11, holds only 19 gm at low efficiency. Whereas the Example 2 highly fibrillated film yarn cartridge holds 79 gms at efficiencies of above 50%. The cartridge of the invention has significantly better performance of about up to 3 times the life and much higher efficiency than the control cartridges of Examples 8-13.The cartridges of the invention have much higher efficiency and dirt holding ability at the low wind numbers than would be expected.

YARN FIBRILLA- EFFICIENCY TION WIND AIR DHC" (Percent at Micrometers) EXAMPLE DEGREE NO. DENSITY (grams) 5mm lOmm 20mm 30mm 50mm 1 High 13 5.1 57 68 94 99.8 100 100 2 High 12 2.0 79 54 65 76 79 89 3 High 10 1.0 227 20 40 55 62 75 4 High 11 1.5 35 89 96 99 99.4 99.9 5 High 15 17.1 8 50 74 84 90 97 6 High 8 .4 2 psid rise 10 14 20 25 30 7 High 9 .6 5 psid rise 20 25 30 38 56 8 Ordinary 10 .4 0.2 psid rise - 9 12 15 18 9 Ordinary 11 .6 .3 psid rise 20 23 28 32 35 10 Ordinary 13 3.3 13 37 44 54 58 64 11 Ordinary 15 5.1 19 38 44 51 54 60 12 Ordinary 19 - 5 66 66 65 66 -66 13 Ordinary 8 0.3 No rise To Low to Measure "Dirt Holding Capacity (DHC) is expressed in grams fed to achieve 30 psid (pounds per square inch drop). Some cartridges are inefficient and to not achieve 30 psid.In such cases cartridges achieving higher pressure drop are considered to have higher dirt holding capacity. Those not achieving 30 psid substantially cease to provide filtering and merely pass dust fed after trapping an initial amount.

Numerous modifications of this invention may be made without departing from the spirit and scope of the invention. For instance, the cartridges may be formed in irregular shapes rather than onto tubes. Further, while the invention is set forth primarily with the conventional 2-7/16 nominal diameter filter tube, the invention is viable for any diameter tube. Further, the invention is viable for any length tubular filter and the invention may be utilized with highly fibrillated yarns of materials other than the demonstrated polypropylenes such as polyethylenes or polyesters. Further highly fibrillated yarns may be utilized of higher or lower total bundle denier which would result in a shift of wind number values to account for the change in dimensions of the diamond opening caused by yarn size difference. For instance lower bundle denier highly fibrillated yarns would be expected to reach best filter performance at higher wind numbers. The important factors of high fibrillated yarns which are low average fibril denier and the presence of broken fibrils are present at other total bundle deniers.

These and other modifications will be apparent to the person with skill in the filter art. For instance, the core material also could be modified to be other than tin material such as plastic or stainless steel, both of which are particularly desirable in the food industry. Such modifications are within the scope of the invention. Accordingly, the invention is not to be limited except as set forth in the appended claims.

Claims (23)

1. A precision wound filter comprising a highly fibrillated polymer film yarn.

2. A filter as claimed in Claim 1 wherein said highly fibrillated film yarn is formed of a material selected from polyolefins, polyesters, polyamides, polyacrylics and mixtures thereof.

3. A filter as claimed in Claim 1 or 2 wherein said yarn has greater than about 3 percent broken fibrils.

4. A filter as claimed in Claim 3 wherein said yarn comprises between about 5 and'about 50 percent broken fibrils.

5. A filter as claimed in any of Claims 1 to 4 wherein said yarn has an average fibril denier less than about 50.

6. A filter as claimed in any of claims 1 to 5 wherein said filter has a wind number between about 8 and about 15.

7. A wound filter as claimed in Claim 5 wherein said filter has a wind number between about 10 and about 13.

8. A filter as claimed in Claim 1 wherein said yarn comprises a material selected from the group consisting essentially of polyproplene, polyethylene, polyester and mixtures thereof.

9. A method of filtering comprising passing a contaminant containing fluid through a precision wound filter comprising a highly fibrillated film yarn.

10. A method as claimed in Claim 9 wherein said highly fibrillated film yarn comprises a polyolefin.

11. A method as claimed in Claim 9 or 10 wherein said yarn has greater than about 3 percent broken fibrils.

12. A method as claimed in Claim 11 wherein said yarn comprises between about 5 and about 50 percent broken fibrils.

13. A method as claimed in any one of Claims 9 to 12 wherein said yarn has an average fibril denier of less than about 50.

14. A method as claimed in any one of Claims 9 to 13 wherein said filter has a wind number between about 8 and about 15.

15. A method as claimed in Claim 14 wherein said filter has a wind number between about 10 and about 13.

16. A method as claimed in Claim 9 wherein said yarn comprises a material selected from the group consisting essentially of polypropylene, polyethylene, polyester and mixtures thereof.

17. A precision wound filter comprising a core member about 1 -1 /8" (about 2.85 cm) in diameter and a highly fibrillated film yarn precision wound onto said core so as to give an overall diameter of about 2-7/16" (about 6.20 cm).

18. A filter as claimed in Claim 17 wherein said yarn is wound at a wind number between about 8 and about 15.

19. A filter as claimed in Claim 18 wherein said yarn is wound at a wind number between about 10 and about 13.

20. A filter as claimed in any one of Claims 17 to 19 wherein said yarn material comprises polypropylene and said yarn has greater than about three percent broken fibrils and an average fiber denier of less than about 50.

21. A filter as claimed in any one of claims 17 to 19 wherein the yarn fibrils are of less than about 50 denier and greater than 3 percent of the fibrils are broken.

22. A filter substantially as hereinbefore described.

23. A method filtering substantially as hereinbefore described.