US 3644866 A
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5197A XR United States Patent Deardurff I Q l [451 Feb. 22, 1972  TIGHTLY BOUND BUNDLE OF FILAMENTS AND METHOD OF PRODUCING SAME  Inventor: Lawrence R. Deardurfl', Newark, Ohio  Assignee: Owens-Coming Fiberglas Corporation  Filed: Jan. 11,1971
21] Appl. No.: 105,175
 US. Cl. ..338/214, 57/140 G, 57/144, 161/170,161/176,156/166,174/130, 338/66  Int. Cl ..H0lc 3/00  Field of Search...
 7 References Cited UNITED STATES PATENTS 2,087,303 7/1937 Rosch ..l61/176 2,293,918 8/1942 Planiol ..l61/47 X Primary Examiner-E. A. Goldberg Attorney-Staelin & Overman [571 ABSTRACT This invention relates to a tightly bound textile strand productw suitable for use as a core element in a jacketed composite product in which coated filaments are held together by helically wrapping two separate strands of filaments around the bundle in opposite directions. More particularly, it relates to an improved high-resistance automotive ignition conductor and a method of producing the conductor wherein the overwrapping strands are glass filaments and the ignition conductor is a bundle of glass filaments coated with electrically conductive material.
- 10 Claims, 3 Drawing Figures Pmmmm ma 6 IN VENTOR. ZAWREA/CE A? 0154mm .4 TTORIV E YS 1 'i-ricnrrsv Bouun BUNDLE or FILAMENTS AND METHOD or PRODUCING SAME BACKGROUND OF THE INVENTION This invention relates to an improved textile strand product incorporating a core element of a bundle of continuous elements and adaptable to such use as high resistance electrical cable. In the method of manufacturing the cable, bundles of filaments, particularly glass filaments, are coated with electrically conductive material and are physically unified by this invention into a tight integral body. In this use, the invention provides greater bundle integrity than that given by the adhesion of individual conductive coatings on the filaments and facilitates the further processing step of enveloping the bundle with ajacket ofinsulating material.
High resistance electrically conductive elements incorporating glass fibers have been described in US. Pat. No. 3,247,020 and U.S. Pat. No. 3,269,883. Conductive elements of this type have found particular commercial usefulness as high voltage conductors in the ignition system of automobile engines. In this use, as in others, it is important that the filaments of the bundle are held tightly together. If the filaments separate from the compact bundle, the continuity of the conductive coating material is impaired. And a break in the conductive material of the conductor creates excessive electrical resistance at that location. Uniform electrical resistance through the bundle is no longer possible when these breaks occur. Lack of uniformity results in a poor quality product. Because of such breaks in the coating, it has been difficult to manufacture conductive elements of this type within good tolerances. For example, conductors to be used in automobile engine ignition systems have been manufactured to a desired resistance of 7,000 ohms per linear foot of conductor. Insuffcient integrity of the bundle has caused resistance variations up to 3.000 ohms per foot of conductor. Such wide variations are undesirable in most applications.
The conductive coating material on the bundle of filaments creates a matrix for the bundle and effects some interbonding of the filaments. But under certain rugged conditions matrix strength alone may be irisufficient to maintain the matrix intact. Such rugged conditions could occur when passing the bundle through an extrusion orifice to jacket the bundle. Additional binder material may be added to the conductive coating material to improve bonding. Preferably, the binder material, if used, is a carbonaceous material which will decompose to form carbon when heated. For example, sugar, starch, glucose, sorbitol, glycerol and the like may be used. It is preferable, however, to avoid or minimize the use of a binder material because the resultant electrical properties when a binder is used are not as good as when the binder is not used, due to the resulting heterogeneity of the coating. In order to allow flexibility in selecting the coating material, additional, external binding must be added to the bundle.
In the past, additional binding has been accomplished by braiding a nonconductive material such as rayon or nonconductive glass yarn over the bundle prior to jacketing it with the insulating material. However, this was not entirely satisfactory because the interlacing of the braided covering resulted in voids where the yarns crossed over and under each other. It has been difficult to jacket the bundle so that the jacketing completely filled these voids or air pockets. Air and moisture present in these voids caused corona discharge in the finished product. To cure this, the conductive bundle after being covered with the braid was run through a suspension of graphite in neoprene and then through a tower to set and cure the neoprene. This additional step was costly, time consuming, and not always entirely successful in eliminating the voids. In addition, this braided overwrap did nothing toward remedying damage caused to the bundle by bending which might occur because of unusually rough handling prior to applying the overwrap.
This braided overwrap was also not satisfactory for another reason; it interfered with the subsequent process step of LII jacketing the bundle. The jacketing process consists of enveloping the bundle in an elastomeric insulating material such as neoprene, silicone, or Hypalon-a synthetic rubber manufactured by DuPont. This process has been carried out by pulling the bundle through an extrusion die where theinsulating material is extruded over the bundle. In this step, the bulkiness and irregular shape of the braided coverings interfered with the smooth passage ofthe bundle through the die.
In the foregoing discussion it has been stressed that conductive elements of the type discussed must have good bundle integrity. In the past, bundle integrity has been accomplished with a braided overwrap or by the less desirable method of adding binder to the coating material. The braided overwrap has not been entirely satisfactory as indicated above. With these problems in view, it is an object of the present invention to provide a method for manufacture of novel electrically conductive bundles with sufficient bundle integrity to avoid filament separation or breaks in the conductive coating even under highly rugged operating conditions.
Another object of this invention is to provide a method of manufacture of electrically conductive bundles which will impart good bundle integrity and allow completely contiguous coverage of the bundle with a later applied insulating jacketmg.
A further object of this invention is to manufacture electrically conductive bundles with good bundle integrity and which will facilitate snag-free passage of the assemblage through an extrusion die without interference in the extrusion step process in which the insulating jacket is applied.
A feature of the inventionis its provision ofa product incorporating electrically conductive bundles with good bundle integrity and with a minimum or no tendency toward coronav discharge problems in use of the final product.
Still a further feature of this invention is provision of an electrically conductive product of filament bundles having good bundle integrity imparted by a step incorporated into the manufacturing process at a point before damage could occur to the bundle by unusually rough handling.
BRIEF SUMMARY OF THE INVENTION These objects are accomplished according to the present invention by helically wrapping two separate small strands or yarns of glass filaments over the bundle in opposite directions to each other. The strands are small and in the form of relatively flat, substantially untwisted bundles of fibers. Therefore, the overwrap causes substantially no air spaces or voids where the strands cross each other. This type of overwrap exposes a large percentage of the bundle surface to easy access by the jacketing material. The result is that the jacketing material can be placed in completely contiguous relationship with the overwrapped bundle, and the neoprene graphite treatment is not required. Thus, allowing the bundle with the glass yarns served thereon to be fed directly to the extrusion die rather than first being treated with graphite suspended in neoprene. The overwrap of the bundle is not bulky and irregular and therefore, passes easily through the extrusion die. Overwrapping in this manner results in exceptionally good bundle integrity. This method of binding the bundle also has the feature of being easily incorporated into the manufacturing process at a point before the bundle can be subjected to injurious bending and flexing by unusually rough handling. With overwrapping in this manner ignition conductors for automobile engines having a resistance of 7,000 ohms per linear foot of conductor have been manufactured within tolerances of plus or minus l,OOO ohms per foot. This is compared to a tolerance of plus or minus 3,000 ohms per foot without the overwrap of this invention. I
Other objects, advantages and features of this invention will become apparent when the following description is taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS conductive glass filaments including the overwrap of this invention; and
FIG. 3 illustrates an enlarged view of an illustration of the overwrapping step of this invention.
An embodiment of this invention is shown in FIG. 1 as a bundle of filaments 4 bound tightly together by clockwise wrapped yarn 5 and counterclockwise wrapped yarn 6.
The major steps in a method of manufacturing a bundle of conductive glass filaments are shown in FIG. 2. Strands of uncoated glass filaments are supplied from a creel 11. The strands are coated with the electrically conductive material at the applicator 19. The coated strands are subjected to a source of heat 29 to cure the coating. The overwrap is applied at the overwrap servers 34 and 44. And the coated, cured, and bound bundle of strands is collected on the spool 61.
DETAILED DESCRIPTION OF INVENTION The bundle of filaments as shown in FIG. 1 may be coated or uncoated, but when used as an electrical conductor, the glass filaments will be coated with a carbonaceous electrically conducting material. The size and number of filaments in the bundle can be varied, depending upon conductor size and flexibility desired. An example ofa satisfactory product is one having approximately 12,000 filaments of a 0.00036 inch diameter.
The overwrap material 5 and 6 is preferably a low twist yarn. Although the terms yarn and strand are not always considered synonymous, they are used interchangeably in this discussionand are intended to mean both a twisted yarn of continuous filaments as well as an untwisted strand of continuous filaments. As one of the features of this invention is to avoid air spaces where the overwrap yarns cross, it is important that the yarn size is small. By way of example, it has been found that a plurality of uncoated glass filaments having approximately 204 filaments of 0.00036 inch diameter has worked successfully for each overwrap yarn. The number of wraps per inch of bundle can be varied from 4 wraps per inch to wraps per inch and give satisfactory results. It has been found that 2 wraps per inch is particularly satisfactory.
- Glass in filament form is not the only material which can be used for overwrap. Filaments of other materials, such as rayon, nylon, polyester, as well as carbon and boron can be used. Yarns of natural staple fiber, such as cotton, sisal, and the like, can also be used. It is preferable that nonconductive or semiconductive material be used because it would not be desirable to have the overwrap conduct any substantial amount of the electricity. If the overwrap were too conductive, it might have an undesirable effect upon producing the desired resistance of the bundle. Glass filaments are particularly desirable as the overwrap material because of their low electrical conductivity in addition to other quaiities such as high strength and low elasticity. Glass filaments are especially desirable where the bundle is to be used as automobile engine ignition conductor because glass maintains its strength in the presence of high temperatures. This feature will become even more desirable as more pollution control devices are added to automobiles. The addition of these devices may increase the temperature under the hood of the cars to the 350 to 400 F.
The use of two overwraps wrapped in opposite directions is critical to this invention. Single overwraps have been tried in the past to bind the bundle together with unsatisfactory results. The single overwrap creates unbalanced forces on the bundle which tends to distort the bundle into catenaries. The bundledistortion impedes smooth passage of the bundle through the jacketing extrusion die. The single overwrap is skinned back by the extrusion die and causes jams and breakouts. In contrast, the double overwrap of this invention establishes a more balanced relation of forces on the bundle because the forces created by one overwrap are counterbalanced by the opposite forces of the other overwrap. The result is a more uniform cross section which passes smoothly and easily through the orifice ofthe extrusion die.
A detailed description ofa method of manufacturing a bundle of conductive glass filaments with the double overwrap binding follows. Referring to FIG. 2, there are mounted a mately 204 filaments of a 0.00036 inch diameter. The strands are pulled from the creel I1 and through a guide eye 15, where they are gathered into a bundle and then to the coating applicator 19.
To describe the operation more specifically at'the coating applicator 19, the bundle of uncoated glass filaments passes through a reservoir of coating media 23 held in a container 21 and then through a die 25. The bundle is routed through the container by passing over roller bar 17 and under other roller bars (not shown) submerged in the reservoir of coating media. The die 25 wipes off the excess coating to maintain a uniform coating thickness and also forces the individual filaments together to achievesome degree of mechanical bond between them. The coating media 23 consists of small particles of carbonaceous electrically conducting material in liquid suspension. A number of different electrically conductive particles may be used to coat the glass fibers. For example, one suitable commercially available material which has been used with success is sold under the trade name Aquadag." This materi al is a concentrated colloid dispersion of pure elcctric-fu rnace graphite in water. The material is preferably diluted with water, for example, three parts water to one part Aquadag, to obtain a fluid which will give the desired surface coating thickness. The amount of coating desired is that amount which will give carbonaceous particles between l.5 and 8.5 percent by weight of the composite of glass and cured coating.
After passing through the die 25, the coated bundle 27 is advanced to the source of heat 29. The heating step cures the coating by drying the coated bundle, adhering the conductive particles to the filaments and interbonding the filaments to each other. The heating can be carried out in a number of different ways such as by passing the bundle through an oven. However, a particularly satisfactory arrangement is that of helically wrapping the coated bundle of glass filaments about a heated drum. The rotation of the drum pulls the bundle of glass from the creel and through the coating applicator. As will be appreciated, the drum diameter, temperature and the number of times the bundle is wrapped around the drum may be varied to obtain the desired curing. It has been found that with the bundle travelling at 35 feet per minute through l0 wraps about the drum, drum temperatures in the range of from 550 to 650 F. are satisfactory.
The foregoing description illustrates a method of producing an electrically conductive bundle of glass filaments up to the improvement step of this invention. While this description alone is sufficient to enable one to produce a satisfactory product, additional description may be found in U.S. Pat. No. 3,247,020 and U.S. Pat. No. 3,269,883, and the disclosures in these patents are intended to be a part of this specification.
After completing the heating step, the bundle is advanced to the overwrap servers 34 and 44 where the improvement step of this invention takes place. In this step the coated bundle of glass filaments 31 is passed through server 34 where one overwrap is wound over the bundle in one direction and then through server 44 where the other overwrap is wound over the bundle in the opposite direction. The bundle 33, held tightly together by the two overwraps, is then wound on the collectferred to the place where the insulatingjacket will be applied.
To more specifically describe the overwrapping step, reference is made to FIG. 3 which shows an enlarged view of the overwrapping process. counterclockwise rotating overwrap server 34 consists of a bobbin of glass yarn 35 mounted on a rotatable spindle 37. The coated bundle 31 passes through a hole in the spindle 37. The spindle 37 and bobbin of yarn 35 rotate about the bundle 31 and wind the overwrap yarn 41 counterclockwise about the bundle 31. After passing through the clockwise server 34. the bundle 32, with one overwrap, advances through clockwise server 44 where the second overwrap is applied. Clockwise rotating overwrap server 44 consists of a bobbin of glass yarn 45 mounted on a rotatable spindle 47. The spindle 47 and bobbin of yarn 45 rotate about the bundle 32 and wind the overwrap yarn 51 about the bundle 32 as it passes through the bobbin. The number of wraps of the overwrap material per linear inch of the bundle is dependent upon the speed of the bundle passing through the overwrap server and the rotational speed of the servers. For example, if the bundle is travelling at 35 feet per minute and it is desired to have one wrap per inch, then the rotational speed of the overwrap server must be 420 r.p.m.
The illustration of FIG. 2 shows the overwrapping step being carried out after the heating step. It should be noted, however, that the overwrapping step can be carried out before the heating step. ln fact, there may be a desired advantage in overwrapping before heating, because the cured coating will adhere somewhat to the overwrap yarns and give even greater integrity to the bundle. This invention contemplates carrying out the overwrapping step either before or after the heating step. It should also be noted the designation herein of the first overwrap as being counterclockwise is only for illustrative purposes and the process will also work successfully if the directions of both overwraps were reversed.
The specific description of this process was given for an example only. lt will be obvious to one skilled in the art that many variations can be made within the spirit of this invention. For example, the manner in which the overwrap material is served can be varied. The server shown is only one of many workable methods. Thesize and configuration of the overwrap material can be varied and still obtain satisfactory results. And, as already stated, the overwrap material is not limited to glass. This invention is not intended to be limited to electrically conductive bundles of glass filaments. lt also inv eludes binding of bundles of filaments coated with functional particles other than electrically conductive material where that material does not sufficiently adhere the filaments together. For example, glass or other filaments, coated with a magnetic material could be advantageously bound by the overwrap of this invention. And the coating of magnetic material, as well as the electrically conductive material, can be of either metallic or nonmetallic material. This invention also includes binding of uncoated filaments. Other variations are obvious in view of the present disclosure and it is to be understood that variations and modifications are contemplated within the spirit and scope of the appended claims.
1. A core element for processing through ajacketing orifice in forming a jacketed composite product, comprising a bundle of coated filaments interbonded by said coating, a first and second plurality of filaments helically wrapped about said bundle of coated filaments, said first plurality of filaments being wrapped in a direction opposite to the direction of wrap of said second plurality of filaments, said first and second plurality of filaments securing said bundle of coated filaments together in more tight intimate association than said coating alone binds said bundle, said first and second plurality of filaments being wrapped about said bundle a sufficient number of turns along the length of said bundle to present a uniform outer dimension for smooth snag-free passage through a jacketing orifice.
2. A core element for processing through ajacketing orifice in forming ajacketed composite product, comprising a bundle of filaments, a coating of functional particles secured to said bundle of filaments. a double overwrap comprising two strands of filaments helically wrapped about said bundle of filaments in opposite directions to each other, said functional particles of said coating being held in a stable functional relation by said double overwrap and said double overwrap imparting a uniformity of outer dimension for smooth passage through ajacketing orifice.
3. An electrically conductive element suitable for applying an insulating jacket while passing the element through a die, comprising a bundle of continuous glass filaments coated with a coating material including an electrically conductive material, a first overwrap ofa plurality of continuous glass filaments helically wrapped around said bundle of coated filaments in one direction, a second overwrap ofa plurality of continuous glass filaments helically wrapped around said bundle of coated filaments in a direction opposite to said direction of said first overwrap, said first and second overwrap being wrapped about said.bundle a sufficient number ofturns along its length to hold said bundle together tightly enough to maintain substantially unimpaired the electrical conductivity of said coating and to impart a uniformity of outer dimension for smooth passage through said die.
4. A high resistance electrical conductor such as for use in the ignition system ofinternal combustion engines comprising a bundle of glass filaments coated with a coating material including carbonaceous electrically conductive material distributed throughout the coating and imparting electrical conductivity to the bundle, a first overwrap of glass filament yarn helically wound over said bundle of coated filaments in one direction, a second overwrap of glass filament yarn helically wound in close engaging relation over said bundle of coated filaments in a direction opposite to said direction of said first overwrap in snug engaging relation thereover, and an insulating jacket surrounding said bundle of coated filaments and said first and second overwrap contiguous with said bundle and overwraps to exclude air pockets between said jacket and said bundle, said first and second overwraps holding said bundle of coated filaments together in stable uniform electrically conductive relation.
5. A high resistance electrical conductor as defined in claim 4 wherein said insulating jacket is of elastomeric material.
6. A high resistance electrical conductor as defined in claim 4 wherein said insulating jacket is of neoprene material.
7. The method of manufacturing a core element for processing through a jacketing orifice in forming a jacketed composite product, comprising the steps of:
coating a bundle of substantially aligned filaments with a liquid coating material, the coating on said filaments being sufficient in quantity to provide a matrix for said bundle;
heating said bundle of coated filaments to secure the coating material thereto;
helically wrapping first and second pluralities of filaments about said bundle of coated filaments in opposite directions to each other, each said plurality being wrapped a sufficient number of turns along the length of said bundle to maintain said matrix material intact upon passage through a jacketing orifice and assure uniform smooth passage therethrough. v
8. The method of manufacturing a core element for processing through a jacketing orifice in forming a jacketed composite product, comprising the steps of:
coating a bundle of substantially aligned filaments with a liquid coating, the coating on said filaments being sufficient in quantity to provide a matrix for said bundle upon drying;
helically wrapping first and second pluralities of filaments about said bundle of coated filaments in opposite directions 'to each other, each said plurality being wrapped a sufficient number of turns along the length of said bundle to maintain said matrix material intact upon passage through a jacketing orifice and assure uniform smooth passage through the jacketing orifice;
heating said bundle of coated filaments to secure the coating 'material to the filaments of said bundle and to said first and second pluralities of overwrapped filaments.
9. The method of manufacturing an electrically conductive element suitable for applying an insulating jacket while passing the element through a'jacketing die, comprising the steps of passing a bundle of substantially aligned glass filaments through a liquid containing carbonaceous electrically conductive particles therein whereby the bundle of glass filaments is coated therewith, heating the bundle of coated filaments to dry the coating and to adhere the conductive particles to the filaments, and helically wrapping first and second pluralities of glass filaments about said bundle of coated filaments in opposite directions to each other to present a uniform outer dimension for smooth snag-free passage of said element through said jacketing die and to maintain said conductive particles in stable uniform electrically conductive relation.
10. The method of making a high resistance electrical conductor such as for use in the ignition system of internal-combustion engines, comprising the steps of:
coating a plurality of glass filaments with a coating material' including electrically conductive material;
heating said plurality of coated filaments to dry said coating material and adhere said electrically conductive material to said filaments;
overwrapping first and second yarns of glass filaments helically around said plurality of coated glass filaments in opposite directions to each other to present a uniform outer dimension for smooth snag-free passage of the overwrapped bundle through ajacketing extrusion die and to maintain stable uniform electrical conductivity of the conductor;
passing said overwrapped bundle through ajacketing extrusion die to apply a covering jacket of electrical insulating material thereto.