Title:
PROCESS FOR MAKING FLUID FILTERS HAVING IMPROVED PROPERTIES
United States Patent 3648846


Abstract:
1. A process for making a filter cartridge comprising winding strand material in a crisscross pattern on a pervious core in a plurality of superposed layers with the strands in axially spaced relation and in substantially superposed position thereby forming circumferential series of diamond-shaped radial passages extending from the inner surface to the outer surface of said cartridge, the passages being progressively larger from said inner surface to said outer surface each of said series of diamond-shaped passages having substantially eight such passages per inch of internal diameter of the cartridge regardless of the degree of filtration expected from said cartridge and while winding applying a quantity of fibrous material on said strands and between the layers thereof to cause the fibrous material to lie on and be axially spaced by said strands and form within the passages filtering media, said fibrous material being determined by the desired degree of filtration expected from said cartridge.



Inventors:
SICARD MARCEL CLARENCE
Application Number:
04/825964
Publication Date:
03/14/1972
Filing Date:
05/19/1969
Assignee:
AMF INC.
Primary Class:
International Classes:
B01D29/11; B01D39/14; (IPC1-7): B01D27/00
Field of Search:
210/484,496,505,497,497.1 55
View Patent Images:
US Patent References:



Foreign References:
IT610747A
Primary Examiner:
Friedman, Reuben
Assistant Examiner:
Calvetti, Frederick F.
Claims:
What is claimed is

1. A process for making a filter cartridge comprising winding strand material in a crisscross pattern on a pervious core in a plurality of superposed layers with the strands in axially spaced relation and in substantially superposed position thereby forming circumferential series of diamond-shaped radial passages extending from the inner surface to the outer surface of said cartridge, the passages being progressively larger from said inner surface to said outer surface, each of said series of diamond-shaped passages having substantially eight such passages per inch of internal diameter of the cartridge regardless of the degree of filtration expected from said cartridge and while winding applying a quantity of fibrous material on said strands and between the layers thereof to cause the fibrous material to lie on and be axially spaced by said strands and form within the passages filtering media, said fibrous material being determined by the desired degree of filtration expected from said cartridge.

2. The process as defined in claim 1 wherein the fibrous material is attenuated before being applied on and between the layers of strand material.

3. The process as defined in claim 1 wherein the strand material is napped prior to winding.

4. The process as defined in claim 1 wherein the fibrous material is napped before being applied on and between the layers of strand material.

5. The process as defined in claim 1 wherein support fibers are applied on and between the layers of strand material along with the fibrous material.

6. The process as defined in claim 1 wherein the outside diameter of the strand material winding is wound for at least several revolutions before the fibrous material is applied on and between the layers of strand material.

Description:
This invention relates to fluid filters and more particularly to filters which comprise a winding of a yarn or roving in a diamond shape and having incorporated therein a septum, mat or sheet of filtering material or napped roving and intermediate support filaments and to a process for making the same.

Filters of two general types related to the above are known. Generally, they are made by winding upon a pervious, that is, perforated or foraminous core or tube of metal or other suitable material, a roving or strand of textile material to make diamond-shaped apertures extending from the outside to the inside of the resulting cylindrical filter. These apertures are pyramidal in shape, that is, they have decreasing length as they progress toward the core from the outside circumference of the body of the filter. Consequently, the diamond-shaped apertures are smaller in length near the center of the completed filter.

In one method for producing such filters, the roving or strand of textile material is napped, before winding, thereby producing fibers extending across the diamond-shaped openings. Generally, the napped fibers are supported only at one end, even where the diamond-shaped apertures are of small size and especially where they are largest. Moreover, the density of the napped fibers depends upon the amount of material which can be napped or combed. It is the napped fibers which provide the filtering media and accordingly its density is also limited. Furthermore, the napped fibers must be of the same material as the roving employed. Since the amount of material which can be napped from the roving or strand is limited, the density of the filtering mechanism, as mentioned before, is limited as well as the material which is employed as a roving. These particular limitations are distinctly disadvantageous although such filters are commercially used.

The disadvantages of the napped type of filter have been overcome, at least partially, by providing a filter in which the filtering media is applied separately, but simultaneously, with the roving while the roving is being wound on the supporting core. This permits the choice of a wider range of materials since the roving and filtering media need not be the same. Furthermore, the lengths of the inserted media can be varied at will, thereby providing lengths which can span one or more of the diamond-shaped apertures, if desirable. Such types of filters are also commercially employed in a wide variety of industrial applications. In both the napped type of filter and the filled or inserted media type of filter, none of the known products are suited to be useful over widely varying degrees of filtration without varying to a great extent the size and number of the diamond-shaped passages spread circumferentially around the core.

For example, in the napped type of filter when a fine degree of filtration is desired, the diamond-shaped passages are made smaller so that the napped fibers are more numerous and give greater or more dense coverage of the diamond-shaped openings. On the other hand, as the size of the openings increase this coverage is lost due to the inability of the napped fibers to efficiently cover a greater area. When roving yarn which is more coarse is employed, it is difficult to wind into a diamond-shaped structure in which the diamonds are small enough to give a fine degree of filtration. In addition, the inability of the napped fibers to cover efficiently a good portion of the area in a diamond-shaped passage severely limits the size of a filter which can be so made. In order to make an efficient filter of this type, therefore, a relatively large number of diamond-shaped openings around the core are necessary in order to achieve fine filtering. This necessitates the use of more material which is wound more tightly and consequently, considerable increase in costs and a reduction in flow capacity result. In those filters where a septum or mat is employed the same problems exist and in presently known diamond wound cartridges which contain an inserted media or septum attempts to control the degree of filtration simply include varying the number and size of diamonds, generally by increasing the number and decreasing the size, wound into a cartridge as with the napped type. More specifically, in present day diamond wound cartridges, whether they be made with napped support yarn or with inserted media, a typical one micron designated filter is wound with 39 diamonds spread circumferentially around an approximately 1 inch diameter center core. A typical 3-micron filter has 27 diamonds so distributed, while a 10-micron filter uses 19 diamonds and a 20-micron filter uses 15 diamonds and so on, all using fewer diamonds as the degree of filtration becomes more coarse.

In addition, to the stated disadvantages mentioned above, the present practice also includes the use of interleaved winds where fine degrees of filtration are desired, rather than use of an ordinary open diamond. Consequently, this reduces area open to flow, resulting in a corresponding penalty on flow capacity, as well as limited filter life.

This is aptly illustrated in the example mentioned heretofore where thirty-nine diamonds are wound around a one inch diameter core, that is, a total circumference of 3.14 inches, thereby giving a center to center distance between diamonds of only 0.80 inch between winding strands. Obviously, flow will have to pass through the filaments or strands which are the winding, since there will be little or no openings between winding strands.

There is some feeling among manufacturers in the filter field that in view of the fact that each layer of filter media is composed of a random layer of fibers across a diamond-shaped opening between strands, with wide random variations in the density of each layer from point to point around the circumference and along the length and depth of each layer, a large number of diamonds will provide an averaging effect to help control the degree of filtration and at the same time increase the useful life of such filters by providing a bypass effect. Accordingly, as an individual diamond becomes plugged with dirt at varying depths in the cartridge, lateral flow will occur. Such lateral flow will then permit the fluid to pass through the yarn walls of the plugged diamond and into an adjacent diamond not yet filled with dirt. However, with small diamonds of large number, as well as with interleaved winds, this provides only relatively small open area and consequently, a limited filtering capacity and limited life. Another disadvantage of presently known diamond would filters which contain inserted filter media is the strength of the web of filter media fibers which span the openings across the diamonds. Many of the media type filter cartridges available today, especially those which are designed for the coarser degrees of variation exhibit breakdown or collapse of the filter web at pressures as low as 17 pounds per square inch and less, thereby allowing passage of unfiltered fluid through the cartridge. For the same reason, most wound filters presently available, whether they be the napped or the inserted media type, are restricted to relatively small wall thicknesses, such as, for example approximately one inch inside diameter and around 2 1/2 inch outside diameter, thus providing a filter annulus of only about 3/4 inch because of the increasing size of the diamonds with increase in diameter. Consequently, thicker wall filter cartridges can be made only by compound winding or winding the cartridge in layers with progressively more circumferential diamonds in each layer as the critical span is exceeded. As a result of this graded density in the depth of the filter from extremely coarse on the outside to extremely tight on the inside is essentially impossible to maintain without expensive changes in either the character of the yarn or the extent of napping of the yarn in each successive layer or by changing the number of diamonds in different layers. Such a construction, however, results in a series of flow restrictions at each point where the number of circumferential diamonds is changed.

Taken alone or in combination with each other, the disadvantages set forth hereinabove make it extremely difficult to develop a product line of such filters without long and tedious trial and error methods in determining the most effective diamond pattern and extent of napping or amount or media which must be inserted to produce the desired degree of filtration, especially where different materials or constructions with different filtering capabilities and different textile characteristics are employed. Among these varying factors are yarn composition, fiber staple length and denier, static charge, handling and winding characteristics and the like. Consequently, all such filters are extremely difficult to reproduce with precision and most filters being made today have wide tolerances on the nominal and absolute degree of filtration, on flow capability and filter life.

The present invention obviates the above listed disadvantages and provides improved diamond wound inserted media filter cartridges or napped matrix yarn with support filaments and a process for making the same and which have a flow capability increased by a factor of as much as eight or more and increased life as determined in a standard dust tester by a factor of two or more while at the same time the same degree of filtration is maintained and the cost of producing the filter is greatly reduced and wherein the number of diamonds spread circumferentially around the core is not more than eight per inch of internal diameter of the cartridges regardless of the degree of filtration which is expected from the cartridges, this last factor being controlled by insertion of media of sufficient web strength for the particular degree of filtration or rating desirable or sufficient support fibers inserted where a napped matrix and no inserted media is used.

Consequently, this allows wide latitude in the choice of support yarns which are used for the diamond-shaped winding. It can be natural or synthetic material or glass or metal. For example, it may be a single, large diameter monofilament yarn or it can be made of many crimped staple monofilaments formed into a yarn. Moreover, it may be tubular or of any cross-sectional design. Furthermore, depending on the frictional characteristics of the material, it may have ridge or other surface characteristics to improve its ability to clamp or hold the inserted media fibers. Its only necessary physical characteristics are sufficient flexibility and tensile strength to permit winding and sufficient cross-sectional area to effect separation of the various layers of filter media inserted in the winding. When it is a natural yarn or a synthetic yarn capable of being napped, it may also be so processed. In this context, however, the napped fibers do not function as filter media but rather as reinforcements for the filter media or act to mechanically entangle the filter media. On the other hand, where a napped yarn is used as the structural fiber and reinforced with support fiber, the napped yarn acts as the filter media as well, where no inserted media web is employed. It is to be noted, however, that regardless of what particular type of material is used or what its particular physical construction is like, the yarn or roving which forms the body of the filter is only a structural skeleton which does not contribute to the filtering characteristics of the final cartridge.

Accordingly, since the yarn or roving is used to form the diamond-shaped support structure, it should be wound in the largest diamond shape possible and the number of diamonds should never exceed eight per inch of internal diameter of the cartridge and can be as small as two and even one so long as it is possible to form one diamond per inch of internal diameter of the cartridge.

The inserted media may also vary widely in choice of material and properties, it being only necessary that it have sufficient strength to withstand the required use. Web strength is a function of radial location, filament strength and fiber length as well as the amount of media used and the manner in which it is deposited and in which it is supported. Consequently, the media itself may be chosen from the wide variety of materials mentioned above for use as the support yarn, except it will only be metal or glass in very special cases where particular requirements may specifically call for it. Moreover, it may be the same material or the support yarn or it may be different. It also can be a napped yarn. Furthermore, although it is essentially and preferably inserted or fed as a continuous web, it may also be fed in staple lengths. When staple fibers are employed, they should be of sufficient length to span the center to center distance of two adjacent diamonds at the point of maximum diamond length at a diameter 0.25 inch greater than that diameter at which the first insertion of media was made. However, staple lengths of media equivalent to one diamond length plus 0.2 inch are also satisfactory from a strength standpoint although wider tolerances on maintaining the degree of filtration result.

The filter cartridges of this invention also have a graduated decreasing density exhibited by the filter media as the diameter of the cartridge increases. This is brought about by attenuation of inserted media as explained more fully hereinafter. Moreover, as the diamond size of the structural matrix increases and the staple length of inserted media is no longer sufficient to span the diamond-shaped openings. Some of the fibers in the inserted media become cantilevered out from the structural matrix providing a cartridge which exhibits true depth filtration.

Although the filter media bed can be inserted from the beginning of the wind, it is preferred that the bed extend from the first complete layer of diamonds and most preferred that it extend at least from a point smaller in diameter than the diameter of the seals normally used to close up the ends of a filter when it is in service. As an example, the smallest diameter seals generally used on a standard industrial cartridge with a one inch inside diameter core is 1.5 inches in diameter. Since a minimum depth of about 1/8 is needed to build an adequate filter bed ahead of the minimum diameter seal plate used, media is inserted starting at about 1.25 inches in diameter. This diameter should, however, be maximized since it provides a hydraulic cushion between the actual filtering layer and the perforated core, thereby minimizing the velocity effects of flow as the flow velocity increases to exit through the perforations in the core. At this point, the span across any diamond is still relatively small even in filters having eight diamonds or less and media fibers are available which in a minimum 1/8 inch thick bed will support flow and remain intact while allowing some flow at differential pressures up to 55 pounds per square inch.

In accordance with the structural requirements set forth above, a series of filter cartridges were wound using an eight diamond wind and having nominal ratings of one micron to 350 microns filtering capacity with no evidence of breakthrough. In contrast to this, present cartridges require a spread of from 8 to 39 diamonds to produce the same result and breakthrough occurred at differential pressures as low as 17 pounds per square inch and 5.7 pounds per square inch. The major costs of these diamond wound cartridges is the yarn cost and the manufacturing cost. Generally, the winding cost and the amount of yarn varies nearly directly with the number of diamonds. Consequently, the cost of a 39 diamond wind is reduced by about 80 percent and the 13 diamond wind about 40 percent, the filters of this invention containing not more than eight diamonds.

Furthermore, since the volume of the cartridge which is blocked off from flow varies in approximately the same manner, the flow capability at the same pressure differential should be expected to increase inversely in the same manner. Consequently, the 39 diamond wind cartridge flow should increase by a factor of 5 except where limited by flow capacity of the center tube. However, such is not the case as seen from the data presented below in regard to even the 27 diamond wind. It is also clear from the data that service life increases in proportion to change in open area where a large diamond structural matrix is employed. Moreover, even larger increases in service life occur where media feed or napping is programmed to decrease as by attenuating with increase in cartridge diameter during winding to produce an exaggerated graded density media.

Where the large diamond construction is employed with napped yarn used as a structural yarn which also acts as the filter media intermediate support fibers are employed and the napped fibers should span at least slightly more than one-half of a large diamond opening. Such support fibers may also be used when employing short staple media fibers where staple length is not materially changed by attenuation or with some natural staple fibers or when the diamond openings increase in size as the diameter increases where making thick wall cartridges. In such cases, a wide variety of small diameters, generally less than 10 percent of the diameter of the winding yarn, of high strength monofilament of long staple, hard lay yarns can be would along with the winding strand simply to act as supports for the filter media fibers which would otherwise be cantilevered out from the structural yarn and unsupported near the center of the diamond span. These support yarns provide a support structure on centers varying from approximately 0.05 inch to 0.5 inch, prevent media sag and media displacement as well as interlocking the media, thus providing more precise and reproducible degrees of filtration. Being of relatively small diameter, they present very little, if any, impediment to flow and in to to reduce the open area of the large diamond by only an insignificant amount.

In addition, bonding adhesives where compatible with intended use can be sprayed or roller coated on the filter media web to further strengthen and fix the filter bed. Where thermoplastic materials are used, heated rolls either plain or patterned can be employed to fuse together the filter media fibers, as well as the structural strand reinforcing strands where they are employed.

The process for making the filters of this invention is relatively simple in nature. The desired winding pattern of not more than eight diamonds per inch of internal diameter of the filter can be carried out on any standard winding machine. The inserted media and/or media and support yarns is fed through a standard textile draw frame and to the winding being formed by the structural yarns after passing between a pair of power driven rolls conveniently located adjacent the winding machine. As the outside diameter of the cartridge grows larger, attenuation of the media being inserted takes place until the cartridge is completed. One of more cartridges may be wound at the same time. Different densities can be attained simply by changing the speed of the media feed.

Even though some attenuation takes place as the winding and insertion of media progresses and the cartridge becomes larger, it is preferred that the material being inserted be positively drawn before insertion unless already in a drawn state. Generally, attenuation varies widely and is at least sufficient so that the resulting attenuated fibrous material forms a thin web of high porosity fibrous media. For example, using a corded lap of 600 grains per linear yard of a 1/2 inch width attenuation by a factor of approximately 8 to 1 is accomplished to provide a satisfactory web before the media is inserted. Any particular draw ratio is simply accomplished by changing the speed of the rolls on the draw frame.

A complete line of filters can be made by employing a constant winding speed while varying the media or fibrous material feed rate over a range of 15 to 1.

This was accomplished by making several cartridges. The high speed end of the media feed drive to determine the tightest degree of filtration which could be made selecting one of these cartridges as being satisfactory, a series of filters were produced at the low speed end of the media feed drive to determine the point at which the media web became so thin so that it produced widely varying thickness of filtration. Thereafter, increasing the media feed rate beyond this point it is possible to determine the coarsest degree of filtration which can be obtained with the particular fibrous media being utilized.

By plotting the degree of filtration of the two original cartridges so selected, their flow capacity at a fixed differential pressure and their standard text dust life against the media feed rate and connecting the two points for each characteristic a series of straight line graphs are obtained which accurately predict the media feed rate needed to produce all other cartridges having specific degrees of filtration, increasing flow and life capacity that fall within the parameters established by the graphs of the original cartridges.

Expressed more generally in terms of its accomplishment the process of this invention broadly comprises winding strand material in a crisscross pattern on a pervious core on a plurality of superposed layers, the strands being in axially spaced relation and forming a series of progressively larger diamond shaped radial passages extending from the inner surface to the outer surface of the cartridge, the number of diamonds so wound per inch of internal diameter being not more than eight. While such winding is taking place the fibrous media material is applied in desirable quantity on said strands and between layers thereof so that it lies thereon and forms a filtering surface. As pointed out hereinbefore, the fibrous material can be attenuated before being inserted into the strand material as it is wound. Moreover, where desirable the strand material can be napped prior to winding or likewise the fibrous material can be napped before being inserted.

In those cases where it is desirable or beneficial support fibers can be applied simply by winding simultaneously with the strand material.

Generally in carrying out the process of this invention introduction of the inserted fibrous media is not commenced until the strand material is wound for at least several revolutions. The purpose of this is to supply a hydraulic cushion between the actual filtering layer and the perforated core to minimize the velocity effects of flow as the flow velocity increases to exit through the perforations in the center core.

The improved filter cartridges of this invention and the process of their manufacture present numerous advantages. For example, the cartridges have more open area thereby permitting more flow and longer useful life. The flexibility of the process permits the utilization of a wide variety of materials which allows the insertion of strongly filter media, thereby supplying strongly filter beds in an open type cartridge. Numerous other advantages of the cartridges and the process for their manufacture according to the invention will be apparent. In addition, the process of this invention permits the manufacture of a complete line of filter cartridges from those which have the ability to filter fine materials to those which have the ability to filter relatively coarse material with relatively no change in the process except by merely increasing or decreasing the said rate at which the fibrous media is inserted.

In order to illustrate the improvements attained by the cartridges of this invention the following comparative data is set forth. In obtaining this data three types of cartridges were employed. All of the cartridges were made from rayon windings and rayon media, the cartridge designated by numeral one in the following table was a 27 diamond wind having inserted discrete fibrous media inserted therein. The cartridge designated by numeral two is a 27 diamond wind cartridge made from napped rayon winding and the cartridge designated by numeral 3 is the new and improved 8 diamond wind cartridge of this invention wherein fibrous rayon media was inserted to provide a filtering bed. These cartridges were manufactured to provide varying degrees of filtration as noted in the Table with the exception of the fact that the number of diamonds in the cartridges designated by numerals one and two was varied to achieve the desired degree of filtration as in accordance with the presently known methods in the filter field. ##SPC1##

In the above table the diameter of all cartridges were 2 7/16 inches plus or minus 1/16 inch by approximately 10 inches in length.

All test filters were made of rayon yarns. Rayon media was also used in all test filters except cotton media was introduced in the 3 to 25 Micron range for type 3 filters only to illustrate the flexibility of the inserted type media. Where rayon media was employed in the type 3 test cartridges a 5.5 denier crimp staple 1 9/16 of an inch in length was used to provide the best combination of filtering capability and high strength filter web for the more open cartridge.

Test results as shown in the accompanying table were run on the basis of measured flow in gallons per minute at 2 p.s.i. differential pressure for cartridges of the same degree of filtration. Life test consisted of flowing 3 gallons per minute of water contaminated with a fixed amount of Arizona coarse test dust. In all cases this flow was maintained until a differential pressure of 20 p.s.i. was reached. The figures shown in the table are the total weight of the test dust needed to reach the differential pressure. In the case of the 100 Micron type 2 filters, no life test data is shown because units were not able to support the standard 20 pounds differential pressure.

Numerous modifications of the invention may be made without varying the spirit and scope of this invention. Accordingly, this invention is not to be limited except as set forth in the appended claims.