Abstract:
“Tinkles” (also known as “gotchas”) (see reference number  20  in FIGS.  1  and  2 ) are portions of knitted metal loops produced when a tube of knitted wire mesh is cut into individual pieces. In the prior art, tinkles have been considered a fact of life and the approach has been to try to shake them out of the mesh or immobilize them on or in the mesh. By producing a knitted tube ( 11 ) having alternating segments ( 12,13 ) of knitted rows of yarn and knitted rows of wire, completely tinkle-free knitted socks are produced which are used to produce completely tinkle-free knitted wire mesh filters. Knitted wire mesh filters that cannot release tinkles because they do not have any tinkles can be used in such applications as fuel filters and airbag filters.

Description:
FIELD 
     This disclosure relates to knitted wire mesh filters and methods of making such filters where the filters are completely free of “tinkles.” 
     BACKGROUND 
     U.S. Pat. No. 5,217,515, which issued to Geno Guglielmi on Jun. 8, 1993 and is entitled “Abatement of Tinkles in Wire Mesh” (hereinafter the Guglielmi patent, the contents of which are incorporated herein in their entirety by reference), sets forth a long-standing problem in the field of filters made from knitted wire mesh, namely, the presence of “tinkles” (also known as “gotchas”) in knitted wire mesh and thus in filters made from such mesh. The Guglielmi patent at column 1, lines 48-56, describes the source of tinkles as follows:
         When knitted wire mesh is cut, it results in the production of loose pieces of scrap commonly known in the wire knitting industry as tinkles. The material making up the tinkles had formally been a portion of the knit. In other words, a tinkle is a knitted loop, or a portion of a knitted loop, which has been cut. Tinkles are of irregular shape and distribution and have no predetermined location, size or shape. However, they do tend to remain near the cut line where they were formed.       

       FIGS. 1 and 2  hereto are copies of the corresponding figures of the Guglielmi patent which show a knitted wire mesh sock  10  and its associated tinkles  20  formed when the sock was cut from a continuous length of wire mesh (a continuous tube of wire mesh) produced by a circular knitting machine. As described in the Guglielmi patent at column 3, lines 36-39: “Tinkles are portions of cut knit loops. They do not have a characteristic size or shape. Indeed, the act of cutting the mesh can distort the wire to produce shapes not found in the original knit.” Having come from the knitted wire mesh, tinkles are composed of metal and are thus undesirable for most filter applications and impermissible for applications where the introduction of small pieces of metal into the gas or liquid stream being filtered cannot be tolerated, e.g., the filtering of the gases produced by an airbag inflator or the filtering of a fuel stream being provided to an internal combustion engine. 
     As described in the Guglielmi patent, efforts have been made to solve the tinkle problem by shaking the knitted wire mesh sock or picking the tinkles off by hand (Guglielmi patent at column 1, lines 59-61). These are highly labor-intensive processes and do not guarantee that filters made from the socks will be free of tinkles. As an alternative to trying to remove the tinkles, efforts have also been made to try to immobilize the tinkles. The Guglielmi patent represents one such effort in which electric resistance welding is used to bond tinkles to the wire mesh. 
     U.S. Pat. No. 5,849,054, which issued on Dec. 15, 1998 to Katsuhide Fujisawa and is entitled “Filter for an Inflator” (hereinafter the Fujisawa patent, the contents of which are incorporated herein in their entirety by reference), shows another immobilization approach in which, in making a filter, the sock is folded upon itself so that the cut ends of the sock end up buried inside the filter.  FIG. 3  hereto is a copy of Fujisawa&#39;s  FIG. 6 ( b ′) which shows a folded sock in which knitted wire mesh  15  covers cut ends  14  of the mesh. 
     As the Guglielmi and Fujisawa patents illustrate, the mindset of inventors working on knitted wire mesh filters has been to accept tinkles as a fact of life and then look for ways of dealing with the tinkles. Unfortunately, no matter how sophisticated a tinkle control technique may be, at the end of the day, there can be no guarantee that every last tinkle has been dealt with. As indicated above, for a variety of applications, e.g., in-line fuel filters, airbag inflators, and the like, such uncertainty can be unacceptable. As discussed fully below, in accordance with the present disclosure, a completely new approach has been taken to the tinkle problem, namely, to make knitted wire mesh filters without generating a single tinkle. In this way, for the first time, knitted wire mesh filters that are guaranteed to be tinkle-free can be made. 
     SUMMARY 
     In accordance with a first aspect, a method is disclosed for making a plurality of knitted wire mesh filters ( 19 ) each of which is free of tinkles ( 20 ) which comprises:
         (I) producing a knitted tube ( 11 ) that comprises (i) a plurality of segments ( 13 ) of knitted rows of wire and (ii) a plurality of segments ( 12 ) of knitted rows of yarn, the segments ( 13 ) of wire alternating with segments ( 12 ) of yarn;   (II) producing a plurality of separated segments ( 13 ) of knitted rows of wire without cutting any loops of knitted wire and thus without producing any tinkles ( 20 ); and   (III) producing the plurality of knitted wire mesh filters ( 19 ) from the plurality of separated segments ( 13 ) of wire; wherein step (II) comprises treating the knitted tube ( 11 ) or a separated portion thereof (i.e., a portion comprising at least one and, typically, multiple wire segments ( 13 )) to remove yarn.       

     In accordance with a second aspect, a method is disclosed of making a plurality of knitted wire mesh filters ( 19 ) each of which is free of tinkles ( 20 ) comprising:
         (I) producing a knitted tube ( 11 ) that comprises (i) a plurality of segments ( 13 ) comprising knitted rows of wire and (ii) a plurality of segments ( 12 ) comprising knitted rows of yarn, the segments ( 13 ) comprising knitted rows of wire alternating with segments ( 12 ) comprising knitted rows of yarn;   (II) producing a plurality of separated segments ( 13 ) comprising knitted rows of wire without cutting any loops of knitted wire and thus without producing any tinkles ( 20 ); and   (III) producing the plurality of knitted wire mesh filters ( 19 ) from the plurality of separated segments ( 13 ) comprising knitted rows of wire;
 
wherein the segments ( 13 ) comprising knitted rows of wire are connected to one another by non-knitted sections of wire ( 16 ) that span the intervening segments ( 12 ) comprising knitted rows of yarn and step (II) comprises:
   (A) cutting segments ( 12 ) comprising knitted rows of yarn and non-knitted sections of wire ( 16 ) to free segments ( 13 ) comprising knitted rows of wire from the knitted tube ( 11 ); and   (B) treating the freed segments ( 13 ) comprising knitted rows of wire to remove the yarn.       

     In accordance with a third aspect, a method is disclosed of making a plurality of knitted wire mesh filters ( 19 ) each of which is free of tinkles ( 20 ) comprising:
         (I) producing a knitted tube ( 11 ) that comprises (i) a plurality of segments ( 13 ) comprising knitted rows of wire and (ii) a plurality of segments ( 12 ) comprising knitted rows of yarn, the segments ( 13 ) comprising knitted rows of wire alternating with segments ( 12 ) comprising knitted rows of yarn;   (II) producing a plurality of separated segments ( 13 ) comprising knitted rows of wire without cutting any loops of knitted wire and thus without producing any tinkles ( 20 ); and   (III) producing the plurality of knitted wire mesh filters ( 19 ) from the plurality of separated segments ( 13 ) comprising knitted rows of wire;
 
wherein step (II) comprises unweaving ( 18 ) of knitted yarn.
       

     Tinkle-free wire mesh socks and tinkle-free wire mesh filters made from such socks are further aspects of the present disclosure. 
     The reference numbers used in the above summaries of the various aspects of the invention are only for the convenience of the reader and are not intended to and should not be interpreted as limiting the scope of the invention. More generally, it is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention. 
     Additional features and advantages of the invention are set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as exemplified by the description herein. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. It is to be understood that the various features of the invention disclosed in this specification and in the drawings can be used in any and all combinations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing illustrating a prior art knitted wire mesh sock and its associated tinkles. 
         FIG. 2  is a schematic drawing illustrating some of the shapes exhibited by tinkles. 
         FIG. 3  is a schematic drawing illustrating a prior art attempt to deal with tinkles by locating them internally within a folded knitted wire mesh sock. 
         FIG. 4  is a photograph of a knitted tube prepared in accordance with an exemplary embodiment of the present disclosure. 
         FIG. 5  is a close-up photograph showing a wire segment/yarn segment/wire segment portion of  FIG. 4 . 
         FIG. 6  is a photograph showing the structure of  FIG. 5  with the yarn segment unwoven. 
         FIG. 7  is a photograph of a knitted tube prepared in accordance with another exemplary embodiment of the present disclosure. For purposes of illustration, the rightmost yarn segment in  FIG. 7  has been unwoven. 
         FIG. 8  is a photograph of an exemplary knitted wire mesh filter having a configuration suitable for use as a filter for an airbag inflator. 
         FIG. 9  is a schematic diagram illustrating an exemplary configuration for a circular knitting machine for use in preparing the knitted tubes of the present disclosure. 
     
    
    
     The reference numbers used in the figures refer to the following: 
       10  knitted wire mesh sock with associated metal tinkles—prior art 
       11  knitted tube 
       12  segment of knitted tube comprising knitted rows of yarn 
       13  segment of knitted tube comprising knitted rows of wire (when separated from its knitted tube, such a segment is referred to herein as a “sock”) 
       14  cut end of knitted wire mesh—prior art 
       15  knitted wire mesh—prior art 
       16  non-knitted section of wire 
       17  non-knitted section of yarn 
       18  unwoven yarn 
       19  filter 
       20  metal tinkles—prior art 
       21  circular knitting machine 
       22  wire 
       23  spool for wire 
       24  knitting needles of circular knitting machine 
       25  yarn 
       26  spool for yarn 
       27  plate 
       28  apex for wire 
       29  apex for yarn 
       30  eyelet in plate for wire 
       31  eyelet in plate for yarn 
       32  feed eyelet for feeding wire to needles 
       33  feed eyelet for feeding yarn to needles 
       34  positioning cylinder for wire 
       35  positioning cylinder for yarn 
       36  plate 
       37  cam hub 
       38  timing stub 
     DETAILED DESCRIPTION 
     As discussed above, the present disclosure relates to the production of knitted wire mesh filters that are free of tinkles. In overview, the filters are made by: (1) producing a knitted tube having segments composed of wire and segments composed of yarn, (2) using the segments composed of yarn as the means for separating the segments composed of wire into individual (i.e., separated) wire mesh socks without the generation of tinkles, and (3) then using the tinkle-free wire mesh socks to make the filters. 
       FIG. 4  shows a representative knitted tube  11  composed of alternating wire segments  13  and yarn segments  12 , while  FIG. 5  shows a close-up of the transition from one of the wire segments  13  to a yarn segment  12  and then to a another wire segment  13 . As can be seen in this figure, as well as in  FIG. 7  discussed below, yarn segments  12  are considerably shorter than wire segments  13 . This will typically be the case in order to minimize the amount of yarn needed to make knitted tube  11 , although longer yarn segments, including yarn segments longer than their abutting wire segments, can be used if desired. Typically, on the order of 3-5 rows of yarn per yarn segment has been found to work successfully. 
       FIG. 6  shows the structure that results when yarn segment  12  of  FIG. 5  is removed. As can be seen in this figure, wire segments  13  are connected to one another by a section of wire  16  that is not knitted. As discussed below in connection with  FIG. 9 , this non-knitted section of wire is produced as the circular knitting machine is knitting yarn. Similarly, when the circular knitting machine is knitting wire, a non-knitted section of yarn is created which can be seen at  17  in  FIGS. 6 and 7 . 
     As discussed more fully below, yarn segment  12  can be removed in various ways, in some of which the non-knitted section of wire  16  is cut before (or simultaneously with) the removal of the yarn segment. As shown in  FIG. 6 , the yarn segment has been removed by being unwoven leaving the non-knitted section of wire intact. In this figure, the unwoven yarn is shown at  18 . 
       FIG. 7  shows another representative knitted tube  11  having a different aspect ratio for the knitted wire mesh segments  13 , i.e., in  FIG. 4 , the wire segments  13  are longer than they are wide, while in  FIG. 7 , they are wider than they are long. For example, the wire mesh segments in  FIG. 4  can be on the order of 8 inches long by 2½ inches wide when flattened, while in  FIG. 7 , the segments can be on the order of 2 inches long by 3½ inches wide when flattened. In general terms, subject to the capabilities of the available circular knitting machines and the availability of yarn having the requisite breaking strength (see below), tinkle-free wire mesh socks of essentially any desired size, aspect ratio, density, and wire composition, configuration, and dimensions can be produced using the techniques disclosed herein. The ability to make wire mesh socks having a wide variety of properties, in turn, means that knitted wire mesh filters having a wide variety of properties can be made using the technology disclosed herein. 
     In particular, knitted wire mesh filters of the types now known or which may be developed in the future can be made using tinkle-free, knitted wire mesh socks produced in accordance with the present disclosure. As just one non-limiting example,  FIG. 8  shows a knitted wire mesh filter  19  having a configuration suitable for use as the filter of, for example, an airbag inflator, which could be made from a tinkle-free, knitted wire mesh sock of the type disclosed herein. Commonly-assigned U.S. Pat. Nos. 7,025,797 and 7,559,146, the contents of which are incorporated herein by reference in their entireties, illustrate other filter configurations that can benefit from the technology disclosed herein. It should be noted that the tinkle-free, knitted wire mesh socks disclosed herein will primarily be used in making filters for applications where freedom from tinkles is important, but can also be used in other situations, if desired. 
     As noted above, there are a number of ways to remove yarn segments  12  from knitted tube  11 . A preferred approach is to treat the knitted tube to remove the yarn. For example, the knitted tube can be treated with a solvent in which (i) the wire is insoluble and (ii) the yarn is soluble. The entire composition of the yarn need not be soluble in the solvent. For example, the yarn can comprise fibers that are bonded to one another by an adhesive (binder), with the adhesive, but not the fibers, being soluble in the solvent. By restricting the length of the fibers, the yarn will fall apart when the adhesive (binder) is removed. 
     A particularly preferred yarn comprises fibers, e.g., polyester fibers, which are bonded to one another by polyvinyl alcohol, the polyvinyl alcohol (but not the fibers) being soluble in water, which is a preferred solvent. Yarns composed of fibers, e.g., polyester fibers, bonded to one another by polyvinyl alcohol are commercially available for use in the manufacture of various consumer products, e.g., high loft towels, and thus in addition to the physical and chemical properties that make such yarns well-suited for use in the present technology, these yarns have the additional advantage that they are already being produced in large quantities and thus are relatively inexpensive. 
     When water is the solvent used in the treatment, it typically will be employed at an elevated temperature and indeed, the water may be entirely or partially in the form of steam at the time of use. The water (steam) can be applied to the yarn at various points in the process, e.g., it can be applied to an intact knitted tube produced by a run of a knitting machine, or it can be applied to a portion of a knitted tube which contains multiple yarn segments and has been separated from the main body of the tube by cutting at least one non-knitted section of wire, or it can be applied to an individual wire segment or a group of segments each having yarn on either or both of its ends, the wire segment(s) having been freed from the knitted tube by cutting at least one non-knitted section of wire. Other variations will be evident to those skilled in the art from the present disclosure. 
     The cutting of non-knitted sections of wire can be performed, for example, using a guillotine cutter located below a circular knitting machine or it can be performed offline. The cutting of the non-knitted sections of wire prior to the removal of the yarn produces cut knitted loops and cut portions of knitted loops, but these loops and portions of loops are not the troublesome tinkles of the prior art because rather being composed of metal, which cannot be removed, they are composed of yarn, which can be removed. 
     The yarn removal treatment can be performed online as the knitted tube is being formed or, more typically, will be performed offline in a separate processing operation. For a water (steam) treatment, equipment of the general type used to wash/sanitize kitchen utensils can be used to perform the yarn removal, with the water/steam being renewed at a sufficient rate so as not to compromise the rate of dissolution of the adhesive and to avoid the creation of a water/adhesive solution of high viscosity. 
     Although water (steam) is a preferred solvent for removing the yarn, other solvents which will not adversely affect the knitted wire, e.g., organic solvents, can be employed in the treatment step if desired. For example, alcohol can be used to dissolve nylon yarn. As a further, non-limiting, alternative, caustic solutions can be employed as the solvent. As with a water treatment, these solvents can dissolve all of the yarn or just a portion thereof, e.g., just an adhesive portion of the yarn. As another alternative in the treatment category, the yarn can be burnt off of the knitted wire, which can be advantageous in cases where the wire is going to be heat treated for other reasons, e.g., to anneal the wire of the wire mesh. However, burning off the yarn can lead to hard-to-remove chemical residues on the wire that are unacceptable for some applications. 
     In addition to the treatment approach for removing the yarn, unweaving of the knitted yarn can also be used if desired. The unweaving can be performed on a knitted tube or a portion thereof prior to cutting the non-knitted sections of wire to produce the separated wire mesh segments or can be performed on the separated wire mesh segments, the former approach being preferred.  FIGS. 6 and 7  illustrate the unweaving approach applied to a portion of a knitted tube, where reference number  18  in these figures shows the unwoven yarn. The unweaving can be performed online as the knitted tube is being formed or offline, as desired. In should be noted that unlike trying to remove tinkles, unweaving can, in many cases, be performed by simply pulling a single thread to remove the entire knitted yarn. The treatment and unweaving approaches can be used in combination, if desired. 
     Knitted tube  11  can be produced by a variety of commercial or custom knitting machines, now known or subsequently developed.  FIG. 9  is a schematic diagram of a representative commercial circular knitting machine  21  sold by Karl Müller GmbH Maschinenfabrik, Weissenburg, Germany, adapted for use in making knitted tube  11 . So as not to obscure the discussion of the primary components of the machine, various conventional components, e.g., pulleys, tension monitors, drive mechanisms, electronic control equipment, etc., have been omitted from  FIG. 9 . Also, the rows of knitted yarn that make up yarn segment  12  of knitted tube  11  have not been explicitly shown in  FIG. 9 , again to facilitate the presentation. 
     In overview, circular knitting machine  21  feeds wire  22  from wire spool  23  to circular knitting needles  24  or feeds yarn  25  from yarn spool  26  to those needles. As is conventional, the wire or yarn travels upward to pulleys (not shown) located above plate  27  before turning downward at apices  28  and  29  and passing through eyelets  30  and  31  (e.g., ceramic eyelets) mounted in plate  27 . The wire and yarn then pass through feed eyelets  32  and  33  (e.g., tungsten carbide eyelets) whose positions relative to circular knitting needles  24  are controlled by positioning cylinders  34  and  35  (e.g., non-rotating positioning cylinders of the type sold by Festo Corporation, Hauppauge, N.Y.). Positioning cylinders  34  and  35  are, in turn, controlled by pneumatic and programmed electronic control equipment. 
     In operation, the positioning cylinders determine whether wire or yarn is being knitted by knitting needles  24 . Thus, when wire is to be knitted, positioning cylinder  34  moves feed eyelet  32  into position so that wire  22  is captured under the hooks of the knitting needles. Conversely, when yarn is to be knitted, positioning cylinder  35  moves feed eyelet  33  into position so that the needle&#39;s hook captures yarn  25 . The positioning cylinders also move the wire/yarn feed eyelets away from the needles when the other material is being knitted. During such non-knitting periods, the material that is not being knitted continues to be fed from its spool and forms the non-knitted sections  16  and  17  of wire and yarn discussed above and illustrated in  FIGS. 6 and 7 . 
     In practice, a distance on the order of, for example, 25 millimeters between the knitting and non-knitting positions of the feed eyelets has been found to work successfully. To avoid the problem of double stitches, a stripper (not shown in  FIG. 9 ) can be employed to hold the loops in position, i.e., to hold the loops down, as the needles move upwardly. 
     To produce a tube, either the circular array of knitting needles  24  needs to rotate past the positioning cylinders  34 , 35  or the positioning cylinders need to rotate around the array of knitting needles. In the former case, i.e., the rotating needles case, the knitted tube will rotate with the needles, which may be undesirable for some applications.  FIG. 9  illustrates the latter case, i.e., the case where the positioning cylinders rotate around the array of knitting needles. Specifically, positioning cylinders  34 , 35  are mounted on cam hub  37  which surrounds the circular array of knitting needles  24  and rotates with plate  36 . For this embodiment, plate  27 , which carries spools  23  and  26 , and is supported with standoffs (not shown) from plate  36 , also rotates. To count the rotations or partial rotations of the plate and the hub, plate  27  can, for example, include a series of timing stubs  38  spaced along its perimeter to trigger a fixed sensor (not shown) to control sock length. 
     Once the tinkle-free wire mesh socks have been produced, they can be formed into tinkle-free wire mesh filters using a variety of techniques now known or subsequently developed. The filter can have a variety of configurations, including, without limitation, circular (disc-shaped), annular, elliptical (oval), triangular, square, octagonal, etc. Typically, the sock will be pressed into its desired shape using a compression mold, which in the case of an annular filter may include a mandrel and a plunger to produce a filter having an annulus with the desired physical dimensions, weight, and density. 
     The wire employed in producing the tinkle-free socks will be chosen based on the filtering requirements, the fluid (gas, liquid, or mixed phases) that is to be filtered, and the environment in which the filter will operate. Suitable materials for the wire include, without limitation, stainless steels, including austenitic and nickel alloys, such as,  304 ,  309 , and  310  grades of stainless steel, or combinations thereof. The diameter of the wire will depend on the particular application of the filter. For example, the wire used for fabricating airbag filters can range from about 0.011 inches in diameter to about 0.03 inches in diameter (from about 0.35 mm to about 0.75 mm in diameter), although larger or smaller wires can be used, if desired. In the case of filters designed to filter fuel for an internal combustion engine, the wire diameters can range from about 0.001 inches to about 0.006 inches, although again larger or smaller wires can be used if desired. The cross-sectional shape of the wire will also depend on the particular application, with round and flat cross-sections being most common. As a further alternative, the filters of the present disclosure can employ wire that has been subjected to various types of processing to alter its properties. For example, additional strength can be obtained by heat treating. 
     Although typically a single type of wire will be used throughout the tinkle-free sock, a combination of two or more wires of different types, e.g., wires having different diameters, compositions, and/or geometries, can be knit into a single mesh if desired. Rather than using different types of wires in a single sock, a composite filter can be produced by compressing tinkle-free socks made of different types of wires into a single filter. 
     Yarns having a variety of compositions and structures can be used to produce the knitted tubes of the present disclosure. In general terms, the yarns will be metal free, but otherwise essentially any yarn that can be removed by the treatment and/or unweaving approaches discussed above can be used. Importantly, however, because yarn segments  12  need to interface with wire segments  13 , the yarn needs to have sufficient strength properties to withstand the forces (takedown forces) applied to the yarn as the wire is being knitted. These forces increase as the diameter and strength of the wire increases and/or as the mesh becomes finer (tighter). 
     As a rule of thumb, to avoid damage to the wire while it is being knit, the maximum force applied to the wire is kept substantially below the yield strength of the wire, e.g., the knitting is performed at or below approximately 50-60% of the yield strength of the wire. Accordingly, the breaking strength of the yarn should be at least 50% of the product of the wire&#39;s yield strength times the wire&#39;s cross-sectional area. Quantitatively, for wire having a diameter in the range of 1 to 30 thousandths, the yield strength runs in the range of 20,000-150,000 psi, so that the yield strength times area product runs in the range from under 10 grams to over 100 pounds. Taking 50% of these values gives a representative range of breaking strengths for the yarn of from ˜5 grams to ˜50 pounds. A variety of yarns having breaking strengths in this range and above are commercially available. Also, individual strands of yarn can be wound together to achieve a net breaking strength value sufficiently high to withstand the forces associated with knitting the wire chosen for the filter. In particular, a variety of yarns composed of polyester fibers bonded to one another by a polyvinyl alcohol adhesive (PVA binder) and having a breaking strength for a single strand on the order of 20 pounds are commercially available at reasonable costs. By winding together ten or so strands of this yarn, breaking strengths in the above range or higher are easily achieved. 
     A variety of modifications that do not depart from the scope and spirit of the invention will be evident to persons of ordinary skill in the art from the foregoing disclosure. The following claims are intended to cover the specific embodiments set forth herein as well as modifications, variations, and equivalents of those embodiments.