Gas Support Gathering Shoe for Forming Glass Fibers and Method for Using Same

Glass fibers are commonly attenuated from molten glass through orifices in a bushing. The number of these orifices can range from about 200 to 1200 or even more. These individual filaments are coated with a lubricant binder and/or size and are gathered into unified strands by gathering shoes. Such shoes are conventionally formed of materials such as graphite, tetrafluoroethylene and the like as can be seen in U.S. Pat. Nos. 2,782,563, 3,560,178, or 3,718,448.

As the strands are drawn across the gathering shoe, abrasion between the fibers and the shoe results in wearing of the shoe surface. The shoes are commonly rotated slightly about once every hour due to the wear and must usually be replaced at the end of each working shift, i.e., about every 8 hours. Further, due to the unevenness of this wear, breakouts often occur due to the glass fibers catching on the grooves formed on the shoe. This interrupts the formation of the glass filaments and adversely affects production.

By means of the present invention, wear of the gathering shoe can be reduced, thus lengthening the life of the shoe and improving production from the shoe. Further, due to the construction of the gathering shoe of the present invention, the glass fiber strands are subjected to a gaseous fluid stream which aids in drying the strands.

Briefly, the present invention comprises a gathering shoe which is formed of a material such as porous graphite, or a material such as stainless steel which has holes drilled in the area in which the glass fiber strand is gathered. Central within the gathering shoe is a hollow cavity having located therein fluid jets connected to a gaseous fluid supply source. The preferred gaseous fluid is air, however other gaseous fluids such as nitrogen may be employed. This fluid jet forces gas through the porous material or the holes in the material forming an air cushion on which the glass strands may ride across the gathering shoe. This decreases the abrasion between the glass fibers and the shoe thus improving the wear of the shoe. Further, since the glass strand is riding on gaseous fluid, the fluid aids in drying of the binder and/or size on the strand.

It is known from U.S. Pat. No. 3,285,721 to ride a graphite roller on a stream of air between the roller and the support. However, the graphite employed in this patent is not porous graphite and the only purpose of the air is to decrease friction between the support and the roller. Nowhere in this reference is there any mention of air passing through graphite so that glass strand can ride on an air stream as disclosed herein.

FIG. 1 is a diagrammatic illustration of a typical glass fiber strand forming operation of the present invention.

FIG. 2 is a side view partially in section of the gathering shoe mechanism of the instant invention.

FIG. 3 is a side cross sectional view of an alternative embodiment of the gathering shoe of the instant invention.

Turning now to FIG. 1 molten glass 11 is attenuated through bushing tips 12 in a bushing 10 into a number of glass filaments 14. These filaments are drawn across an applicator 32 which may be, for example, a belt applicator, a roller applicator, or the like where a coating of a lubricant binder and/or size is placed on the filaments. The filaments are then gathered by a gathering shoe mechanism generally illustrated in FIG. 1 as 16 into a unitary glass fiber strand 18. The glass strands may be drawn at speeds of from about 2500 to 18000 feet per minute or more (762 to 5486.4 meters per minute or more). The strand passes across spindle 28 and is wound on a winder mechanism 24 into a forming package 20 on mandrel 22.

The gathering shoe mechanism 16 of the present invention is illustrated in FIG. 2. The mechanism 16 comprises a shoe 40 which can be formed of such material as porous graphite or the like. This shoe preferably has a coating 42 thereon other than in the slot 41 in which the glass fiber strand rides. This coating renders the surface of the shoe 40 non-porous in those areas other than the slot 41 thus directing all air through the slot. The coating can be formed of numerous resins such as polycarbonate, polyester, etc. The preferred coating material is epoxy resin. Centrally located within the shoe is chamber or cavity 46 with air jet 48 having nozzles 50 located within. The nozzles 50 supply air under pressure to the chamber 46. The air pressure may range from about 20 to about 80 psig (240,000 to 650,000 pascals). This air is forced through the porous graphite, and, due to the resin coating of the bulk of the shoe 40, finds its way out of the porous graphite at the slot 41. An air connection 52 is used to seal the air line 48 and a mounting stud 54 is employed to connect the gathering shoe in its location along the fiber forming mechanism. As the glass filaments are drawn across the shoe 40 they are combined into a unitary strand within the slot 41. Due to the air pressure within the slot 44 the glass fibers ride over the air thus reducing the friction between the filaments 18 and the shoe 40. While the air supplied does reduce friction the glass filaments do still touch the grapite surfaces, but due to the air impinging on them erosion of the graphite is lessened by reduction of friction. In addition, the air at least partially drives the binder and/or size on the glass strand. This leads to a longer wear life of the shoe 40 and fewer breakouts of the glass strand 18 due to fewer catches of the strand in grooves formed by wear of the shoe 40.

While in the preferred embodiment the shoe of the present invention is formed of such material as porous graphite, it is within the scope of the invention to employ other porous materials or to form the shoe of such materials as stainless steel or the like as can be seen in FIG. 3, drilling holes 64 in the shoe 62 from the slots 41 to the air chamber. Such a shoe would operate in the same manner as a porous shoe.

Two G37 bushings were set up for comparison. The first employed a standard graphite gathering shoe of the prior art. The second employed a porous graphite shoe of the present invention. A stainless steel shoe was also attempted. However, due to the shape of the slot formed in this shoe, the glass strand would not stay in the slot and this shoe could not be compared. Both bushings were operated to draw glass strands across the gathering shoes at a rate of 12,420 feet per minute (3.785.6 meters per minute). The porous graphite shoe was supplied air at a pressure of 55 psig (480,000 pascals). The two shoes were run for 8 hours. During the 8 hour trial very little wear could be noted in the porous graphite shoe. The standard shoe was changed during the trial as part of a regular shoe change during the shift, it is not clear whether the change was necessary.

Samples from both shoes were evaluated. The cmparisons are shown in Table I.

As can be seen from Table I, the quality of the glass strands produced with the porous graphite shoe compares favorably with the strands prepared using the standard shoe. The fuzziness was somewhat higher and the quilling grade somewhat lower for the strand produced from the porous shoe, however the fuzzballs/MEY was lower. Very little wear was noted in the porous shoe, thus the shoe could have exceeded the normal life expectancy of a standard shoe.

While the invention has been disclosed with reference to certain specific embodiments, the various details set forth in the above description of the invention are not to be considered as limitations upon the scope of the invention except insofar as set forth in the accompanying claims.