A method of producing a low cost impregnated and coated fiber useful in forming pump, valve, expansion joint, hydraulic cylinder and similar packings capable of resisting high caustic concentrations is provided. In accordance with this method a relatively low cost yarn, such as rayon, is simultaneously subjected to a spreading operation and passed through a highly alkaline colloidal tetrafluoroethylene (TFE) solution. As the yarn fibers are spread from a fiber bundle to a flat ribbon-like array of spaced parallel fibers, the fibers swell or "balloon," thus allowing the TFE to completely penetrate the interior of each fiber. A subsequent coating step insures that the exterior of each fiber is completely coated with the TFE solution. Fibers produced according to the present process are characterized by substantially lower cost than available materials, are completely caustic resistant at a pH approaching or exceeding 14, and have a long, useful service life in a variety of different environments.
A process for producing a preform (44) includes pretreating roving by submerging it in a tank (18) and cooling the binder (20) on the glass fibers before the glass fibers are chopped. The fibers and solidified binder are then chopped and deposited onto a preform screen (32). Heat is applied to soften the binder that is on the chopped glass fibers and cooled to set the binder and form the preform on the screen.
An apparatus for continuously coating individual fibers of a fiber bundle with resin, which comprises a first concave support surface for grouping the fibers of the bundle substantially at a single grouping point and a second, convex, support surface at least partially described by an arc rotated about its horizontal axis, having a maximum radius R, which at least approximately satisfies the relationship expressed in the following formula: wherein r designates the radius of the arc at distance x from the plane of symmetry, passing through fiber grouping point (P): ##EQU1## and wherein L designates the length of a tangent to the second support surface which passes through grouping point (P), in the plane of symmetry, and .phi. designates the radian angle formed between the tangent and the vertical line.
A method for continuously coating individual fibers of a fiber bundle with resin. The individual fibers are grouped at a single grouping pint defined by a first concave supporting surface. The fibers are directed through a resin bath while spreading the fibers apart on a convex surface in a regularly spaced arrangement to form a continuous coating of resin along at least a portion of the fibers. The convex surface is at least partially described by an arc rotated about a horizontal axis, and comprises at least a portion of a surface of maximum radius R which is symmetrical relative to a vertical plane of symmetry passing through the fiber grouping point. The convex surface is substantially defined by the equation ##EQU1## wherein: r=the radius of the arc at a distance x from the plane of symmetry passing through the grouping point; L=the length of a tangent to the symmetrical surface passing through the grouping point, in the plane of symmetry, between the grouping point and a point tangent to the symmetrical surface; and .phi.=the radian angle formed between the tangent and a vertical line passing through the center of the second surface. The coated fibers are cooled to harden the resin thereupon, and are collected thereafter.
A system for spreading a multi-filament bundle of fibers such that most of the individual fibers are exposed for various treatment and coating processes is described. The system is particularly suited to, but not limited to, carbon fiber applications. In such applications it is desired to spread carbon fiber tows consisting of anywhere from less than 1,000 to in excess of 144,000 individual filaments such that a significant portion of the filaments are exposed for processing. A spreading system can consist of one or more individual spreaders placed in series to achieve a desired spread. Each spreader consists of expandable bands, an expandable tube, or a compressible and expandable piece of foam placed between two angled support discs. The discs are angled away from each other such that the bands, tube, or foam between the closest points of the angled discs will stretch or expand as the support discs rotate about their respective axes. The fiber bundle enters the spreader at the point where the discs are closest together and exits at the point where the discs are furthest apart. The bands, tube, or foam therefore support the incoming fiber bundle and stretch or expand to an established width, thereby separating a portion of the individual filaments. Changing the angle of the support discs can control the amount of stretch. As the angle is increased, the overall stretch or expansion that the bands, tube, or foam are subjected to will increase, thereby increasing the filament separation of the fiber bundle. One or more spreaders can be placed in series to obtain a desired spread beyond the capabilities of a single spreader. The spreaders can be free spinning or motor driven depending upon the application.
An article of manufacture which comprises a material for sealing threaded pipe joints comprising a multifilament yarn ready-coated with a joint sealing composition and packaged in a dispenser from which the coated yarn may be supplied for direct application to a threaded area of a pipe.
