METHOD AND APPARATUS FOR CONTROLLING THERMAL ENVIRONMENT IN A GLASS FIBER PROCESS

Abstract: A fin cooler (10) having a plurality of hollow cooling fins (14), each provided with a coolant liquid flow passage and further having a header block (12) provided with separate coolant liquid inflow and outflow channels (30, 34), is placed in a closed loop coolant liquid circulation network. By regulating fluid flow, fin temperature can be manipulated to improve process control and product uniformity. The cooling fins (14) operate at a temperature high enough to prevent glass volatiles form condensing on the fin surfaces and to prevent the formation of fin corroding acids. The closed loop cooling path prevents fin coolant passage occlusion or clogging.

Description: The present invention is directed generally to a method and apparatus for controlling a glass fiber forming process. More particularly, the present invention is directed to a method and apparatus for controlling the thermal environment in a forming process by utilization of fin coolers having heat transfer liquid flow channels therein. Still more particularly, the present invention is directed to a method and apparatus for cooling glass fibers utilizing a heat exchange fluid which is passed in a closed loop system through heat transfer fins and heat exchange equipment. Glass fibers are typically formed by flowing molten glass through a large number of closely spaced orifices located in a container which holds the molten glass. Such containers or bushings often have 2000, 4000, or even up to 6000 of such glass fiber forming tips or orifices. The molten glass which flows out through these arrays of bushing tips must be cooled in a controlled manner so that the glass fibers or filaments which are formed from the molten glass will be substantially uniform in diameter. A plurality of generally planar, solid, elongated cooling fins are placed beneath the bushing tip plate and extend generally perpendicularly to the elongated rectangular bushing with the glass fibers or filaments passing between adjacent cooling fins and giving up heat to the fins. This heat transferred to the usually solid flat metal cooling fins is then transferred along the fins by conduction to a header block in which one end of the fin is embedded and which header block typically is provided with flow passages through which a relatively cold cooling fluid such as the plant cooling water passes. Heat is removed from the header blocks by the transfer of heat to the cooling water passing through them and the cooling fins are then kept at a relatively low temperature at their junction with the header. The free ends of the fins on the other hand are substantially warmer than the ends in the header block thereby giving rise to large temperature variations across the fin surfaces. With the advent of longer and wider bushing assemblies having 4000 to as many as 6000 glass forming orifices, heat removal has become more difficult necessitating the use of cooling fins that have been made longer so that they extend across the width of the bushing assembly. This increased cooling fin length has given rise to even higher free end fin temperatures in presently used commercial solid fins. These high free end fin temperatures that are caused by inadequate heat transfer rates from the free end of the fin to the fin cooler header block have caused excessive free fin end oxidation and distortion that leads to a short fin cooler life. The cooler portion of the fin surfaces also accumulate solids which corrode surfaces and require cleaning. Frequent fin cooler cleaning or replacement is expensive and disruptive of bushing operation with its concomitant loss of productivity. In addition, textile fiber glass strand products typically require higher levels of product uniformity than strand products used to provide rovings for resin reinforcement, for example. Textile glass fiber strands are used to manufacture cloth used for reinforcing high pressure laminates typically employed in circuit boards or for manufacturing decorative fabrics. These glass fiber strands have to be produced at a high level of product uniformity, consistent yardage per pound of glass fiber being one criteria. Consistent yardage is one indicator of uniform fiber diameters in a given strand. The use of the current commercial solid cooling fins has not provided the desired properties to textile fibers in many instances on a reproducible basis. Further, since the cooling capabilities of the current solid fins are somewhat limited, forming tensions for textile fibers tend to be high and the glass throughput from the bushings making these fibers is low. Attempts have been made to provide fin cooler assemblies in which the individual fins are hollow so that plant cooling water can be passed through the fins. Exemplary of prior art patents which disclose such cooled fin coolers are U.S -A-(s) 3,251,665; 3,695,858; and 3,746,525. Nearest prior art document US-A-3,695,858 refers to a method and apparatus for the production of glass fibers wherein the temperature in the zone of attenuation of the fibers is controlled by a plurality of heat removing and gas emitting members in the form of shield units before the gas is released in the zone. From US-A-4,059,145 a method and apparatus for controlling the surface temperature is known by removing heat from the body with a first heat exchange liquid circulating between a heat exchanger in contact with the body and a second heat exchanger in which heat is transferred from the first heat exchanger liquid to a second, more volatile heat exchange liquid in boiling equilibrium with its vapor. The temperature of the second heat exchange liquid is controlled by regulating the pressure in the second heat exchanger in inverse proportion to the temperature of the body being cooled. GB-A-1 079 099 refers to a method and apparatus for the production of glass fibers wherein the extrusion nipples are cooled by cooling fluid. Past attempts at operating cooled fin coolers have met with only marginal success and these fin coolers have not been widely used by the glass fiber forming industry. Several general problems appear to be typical of prior art water cooled fin coolers. The flow of plant process or cooling water through the fins has produced fin temperatures which are unacceptably low, i.e., temperatures in the range of 21°C-38°C (70°F to 100°F) on portions of the fins. These low temperatures on fin surfaces cause glass volatiles to condense out on the surfaces of the cooling fins causing unacceptably high corrosion rates and short fin life. Contaminant build up on the surfaces of the cooling fins also alters their heat transfer characteristics and creates nonuniformity in the glass fibers produced since the glass cooling is not uniform or consistent. The low temperature of the cooling fins caused by flow of coolant water through passages in the fins also allows the glass volatiles to mix with water in the environment normally present around a bushing to form corrosive acids that shorten fin life. Further, ordinary plant cooling water may not be completely free of entrained solid particles and contaminants. As this water flows through the relatively small passages in the fins of the prior art water cooled fin coolers, the flow passages may also become plugged or occluded. Such passage plugging in a fin renders the cooling fin inoperative and causes rapid failure of such a fin. In a large bushing assembly having a correspondingly large number of water cooled fins, the inoperativeness of random cooling fins caused by cooling water flow passage fouling will cause the heat transfer rates to vary from cooling fin to cooling fin. Strand sizes will thus vary, the product formed will have non-uniform filament diameters as a consequence and will therefore be unacceptable. Water coolant flow passage clogging in individual cooling fins is difficult to correct and requires the entire fin cooler be removed from the bushing assembly and repaired. These shutdowns are, of course, disruptive of production schedules and interfere with plant productivity. As can thus be appreciated, there is a need in the glass fiber forming industry for a fin cooler which will be operable in a controlled, dependable manner so that fin surface temperature can be maintained high enough to reduce corrosion effects to acceptable levels and insure that temperatures be more uniform across the entire surface of the fin. Further, the cooled fin cooler must be able to operate free from distortions caused by inadequate cooling and must not be susceptible to failure due to flow passage clogging. It is an object of the present invention to provide a method and apparatus for controlling a glass fiber forming process. This object is attained by a method of cooling glass fibers formed from molten glass, wherein heat is extracted from the glass fibers as they are formed through a fin cooler assembly by indirect heat exchange through the fin surfaces, characterized by circulating in a closed loop, through each fin, a heat transfer fluid having a specific heat of at least 2,09 Joule (0,5 cal)/°C/g and a vapor pressure not over 1,01 bar (1 atmosphere) at operating temperature, at a rate sufficient to maintain the fin surfaces above about 66°C (150°F) which extracts heat from the filament forming environment into said heat transfer fluid. The object of the invention is also attained by using a cooled fin assembly suitable for use in cooling glass fibers formed from molten glass in a glass fiber forming bushing having a plurality of glass forming tips, and said cooled fin cooler assembly comprising: a fin cooler header positionable generally beneath said glass forming bushing, said header including separate space fin coolant liquid inflow channel and fin coolant liquid outflow channel; a plurality of spaced cooling fins secured at first ends to said header block and extending outwardly therefrom beneath the plurality of glass forming tips to remove heat from glass fiber filaments which pass between said space cooling fins; a coolant liquid flow passage in each of said cooling fins, each of said flow passages including an inlet port in fluid communication with said coolant liquid inflow channel, and an outlet port, in fluid communication with said coolant fluid outflow channel, wherein said fin cooler header and coolant liquid flow channels and said cooling fins from a closed loop fluid flow path; a heat exchanger remote from said fin cooler header block and in fluid communication therewith; means to flow exchanger cooling fluid through said heat exchanger; means to control the flow of said exchanger cooling fluid to control the temperature of said fin coolant fluid. In one embodiment of the invention, the heat transfer fluid employed is one that has a boiling point above that of water although water can be employed if its operating temperatures are controlled within certain limits. The preferred heat transfer fluid is also one having a specific heat of at least 2,09 Joule (0,5 calories) per degree Centigrade per g ( J ( cal )/ °C / gm ) and a vapor pressure below 1.01 bar (1 atmosphere) at temperatures of 204 °C (400 °F ) and below. Each heat transfer fin has an elongated flow passage formed within it so that the heat exchange fluid can flow through the full length of each fin in the fin cooler assembly. When high fin temperatures are established and maintained in accordance with the methods and apparatus of the present invention i.e., temperatures above 66 °C (150 °F ), fin cooler life is prolonged and heat transfer fin fouling from corrosion products is substantially reduced. Uniform and controlled fin temperatures at and above 66 °C (150 °F ) which are obtained in accordance with the method and apparatus of the present invention further result in improved product uniformity, i.e., consisting fiber diameters, improved running efficiency, improved yardage uniformity and higher productivity. The fin cooler having heat transfer liquid flow passages therein and a heat transfer fluid system connected thereto and flowing through the passages to thereby maintain fin temperatures sufficiently high to minimize fin corrosion due to the condensation of volatiles adjacent to the fins. The method of controlling glass fiber forming utilizing a high specific heat fluid at controlled temperatures and rates of flow to provide a uniform environment around the fiber glass forming orifices or tips and uniform fin temperatures in the fin coolers used therein. The apparatus for controlling a glass fiber forming environment has a closed loop heat exchange fluid flow path at preselected operating temperatures, flow rates and heat removal rates. The method of controlling a glass fiber forming process preferably uses a heat transfer fluid having a higher boiling point than water and a heat exchanger to remove heat from the system. As will be presented in greater detail in the description of the preferred embodiment which is set forth subsequently, the present invention is directed to a method and apparatus for controlling glass fiber forming by attenuating molten glass fibers formed by a multiple orifice bushing assembly. A plurality of generally flat cooling fins, which are attached at first ends to header blocks to form fin coolers, are placed beneath the bushing tip plate. As the glass fibers pass between the spaced fins, the thermal environment area around the fins is controlled by transferring heat from the glass to the cooling fins while stabilizing the surface temperature of the fins. Each of these fins includes an interior, generally elongated U-shaped flow passage with an inlet port of this fin flow passage being in communication with a heat transfer fluid inflow channel in the fin cooler header block and with an outlet port from each fin heat transfer fluid flow passage being in communication with a separate outflow channel in the header block. A heat transfer fluid having a high specific heat and which has a boiling point substantially higher than that of water and a vapor pressure at its operating temperature of less than 1 atmosphere is preferably used and is caused to flow in a closed loop through the fins and out. The outgoing fluid is then passed through a heat exchanger. Thus, heat is extracted from the glass fiber filaments by the fins adjacent thereto, transferred from the fin surface to a heat transfer fluid and the heat is then transferred to a secondary heat exchange fluid such as plant process water in a separate heat exchanger connected to the fin cooler. "High specific heat" as used herein means a specific heat of at least 2.09 J (.5 cal)/°C/gm, preferably in the range of 2.51 J (.6 cal)/°C/gm to 2.93 J (0.7 cal)/°C/gm. "Low vapor pressure" as used herein, means a vapor pressure at operating temperatures of less than 1.01 bar (1 atmosphere). Selection of the heat exchange fluid and its rate of circulation through the cooling fins and the rate at which heat is removed from it in the heat exchanger are parameters that are adjusted to insure that the surface portions of the cooling fins are maintained at a temperature of 66° to 204°C (150 to 400°F), preferably in the range of 66° to 93°C (150 to 200°F). Surface temperatures in the preferred range are high enough to prevent the formation of glass volatile contaminants on the surface of the cooling fins by condensation from the adjacent environment. In contrast to prior water cooled fins, the use of heat transfer fluid in a closed loop system in accordance with the present invention will maintain the fin surfaces at a temperature higher than possible with water passing in the prior art non-closed loop system because of the ability to precisely control the temperature of the heat transfer fluid in the fins. Acid formation due to the mixing of glass volatile components with water condensate on the fin surfaces should thereby he minimized due to the elevated fin surface operating temperatures that are provided by the use of a high specific heat, high boiling temperature heat exchange fluid and the closed loop system of the invention while adequate heat removal from the glass filaments adjacent the fins is still accomplished. The heat exchange fluid flows in a closed loop in accordance with the present invention. This flow path is continuous and extends between the flow path in the individual cooling fins, through the header block, to a heat exchanger unit that removes the heat from the heat transfer fluid, passes the heat transfer fluid through a filter and back through the cooling fins for further thermal treatment. This closed flow path prevents the clogging or plugging of flow passages in the cooling fins as was apt to be the situation with prior art open loop water cooled fins that generally utilized plant process water for cooling. Since the individual coolant flow paths in the various cooling fins are no longer apt to become plugged by inorganic oxide deposits, the frequency of fin cooler failure and failure related production interruptions are substantially reduced. When water is employed as the cooling fluid, utilization of distilled water is preferred. The fin cooler in accordance with the preferred embodiment of the present invention and its method of usage with a high specific heat, high boiling temperature heat transfer fluid flowing in a closed loop provides a fin cooler which has a reduced tendency to accumulate glass volatile contaminants thereon or to be subjected to attack by corrosive acids because of its ability to maintain elevated surface temperatures, while still acting as a cooling surface for the glass fibers. Similarly, where water is employed, the same benefits accrue so long as temperatures of the circulating water are maintained above 93°C (150°F). Uniform fin temperature is provided by circulation of the heat transfer fluid through the fin so that fin distortion and oxidation is not a concern. The closed loop fluid circulation system of the invention allows the heat transfer fluid to remain clean and provides a means for controlling fin surface temperatures by controlling the heat transfer fluid temperature through controlled heat removal at the heat exchanger to provide a given fin surface temperature. A controlled fin temperature is achieved by accurately controlling the secondary or plant water coolant flow through the heat exchanger. Thus the method and apparatus of glass fiber cooling in accordance with the present invention overcomes the disadvantages of the prior art while providing a system that is effective yet remains uncomplicated and reliable. Brief Description of the Drawings While the novel features of the method and apparatus of cooling glass fibers in accordance with the present invention are set forth with particularity in the appended claims, a full and complete understanding of the invention may be had with reference to the detailed description of the preferred embodiment as set forth hereinafter and as may be seen in the accompanying drawings in which: Fig. 1 is a perspective view of one embodiment of a fin cooler constructed generally in accordance with the present invention; Fig. 2 is a cross-sectional view of the header block of the fin cooler of Fig. 1 taken along line II-II thereof; Fig. 3 is a side elevation view of the fin cooler of Fig. 1, partly in section and taken along line III-III thereof; Fig. 4 is a cross-sectional view of one cooling fin taken along line IV-IV of Fig. 3; and Fig. 5 is a schematic side elevation view of one embodiment of a fin cooler in accordance with the present invention showing the closed loop circulation path of the heat transfer fluid through the fin cooler and a heat exchanger. Fig. 6 is a front elevation of a preferred embodiment of the instant invention showing the cooling fins, the header and their relationship to the bushing tips. Fig. 7 is a plan view of two fin coolers of the preferred embodiment showing their positioning in the headers. Fig. 8 is a side elevation in cross-section of header, fin and header fluid inlet and outlet. Description of the Preferred Embodiment Referring initially to Fig. 1, there may be seen generally at 10 a cooled fin cooler in accordance with the present invention. Cooled fin cooler 10 includes a header block generally at 12 to which are attached a plurality of outwardly extending cooling fins 14. As is known generally in the art, fin coolers of this general type are typically placed beneath the tip plate of a glass fiber filament forming bushing assembly (not shown). Individual glass fibers, which are pulled from molten glass cones formed at the bushing tip plate, are attenuated by a suitable winder or the like. Groups of these individual fibers pass generally downwardly between the spaced cooling fins 14 which take heat away from the glass so that the glass will be properly cooled. In the cooled fin cooler of the present invention, the header block 12 is generally in the shape of an elongated rectangular bar having a top surface 16, an opposed bottom surface 18, a front face 20 and an opposed rear face 22. Each of the plurality of cooling fins 14 is attached at a first end 24 to front face 20 of header block 12 in any generally conventional manner, such as by welding or brazing, and extends outwardly therefrom in a cantilever fashion to a second, free end 26. As may be seen in Figs. 2 and 3, header block 12 includes a pair of spaced, separate, elongated coolant flow channels. A coolant liquid inflow channel 28 is formed in the interior of header block 12 generally closer to bottom surface 18 and extends the length of header block 12. A coolant liquid inflow line 30 is secured to header block 12 and supplies coolant liquid to inflow channel 28. A separate coolant liquid outflow channel 32 is formed in header block 12 and extends the length of header block 12 adjacent the top surface 16 thereof. Inflow channel 28 and outflow channel 32 are generally parallel to each other but are completely separate from each other. A coolant liquid outlet line 34 is in fluid communication with outflow channel 32 and provides a means for coolant liquid egress from header block 12. Referring again to Fig. 3, and as may also be seen in Fig. 4, each cooling fin 14 is provided with a generally elongated U-shaped coolant liquid flow passage 36. Flow passage 36 in each cooling fin 14 has an inlet port 38 which is placed in coolant liquid inflow channel 28 in header block 12. An outlet port 40 of each coolant liquid flow passage 36 is disposed in coolant liquid outflow channel 32 of header block 12. Each coolant liquid flow passage 36 in each cooling fin 14 extends from the first end 24 of fin 14 along a lower leg portion 42 adjacent bottom portion 44 of fin 14, to the free end 26 of fin 14 and then back through a top leg portion 46 of fin 14, adjacent upper edge 48 of fin 14 and back to the first end 24 of the fin 14. Coolant liquid flows into header block coolant liquid inflow channel 28 and into the lower leg 42 of coolant liquid flow passage 36 through inlet port 38. The coolant liquid flows out to the free end 26 of fin 14 and then back through top leg 48 of flow passage 36, back through outlet port 40 and into coolant liquid outflow channel 32 in header block 12. While coolant liquid inflow channel 28 and coolant liquid outflow channel 32 in header block 12 are not in direct fluid communication, they are in fact in contact with each other through the plurality of coolant liquid flow passages 36 in cooling fins 14. A preferred structure of a cooling fin 14 is shown in Fig. 4 as being comprised of two similar, but opposed stamped metal panels 50 and 52, each of which is formed as one side of the cooling fin 14. Each stamped panel 50 and 52 includes a generally elongated U-shaped recess. When the two panels 50 and 52 are placed together and joined to each other by securement of peripheral and intermediate flange sections 54 and 56, respectively, by welding or the like there is formed cooling fin 14 having cooling liquid flow passage 36 therewithin. Each cooling fin 14 could be formed in one of several alternative ways to provide a generally rectangular hollow fin having a coolant liquid flow passage 36. For example, two planar metal panels could be secured together with peripheral and intermediate spacers to again define a generally U-shaped flow passage 36 in each cooling fin 14. Turning now to Fig. 5 there may be seen a schematic representation of a fin cooler and heat exchanger closed circuit for a cooled fin cooler in accordance with the present invention. A coolant liquid, which flows through flow passage 36 in cooling fin 14, enters header block 12 through coolant liquid inflow line 30 and exits through coolant liquid outflow line 34 as has previously been discussed. During its passage through cooling fin 14, the coolant liquid takes on heat through indirect heat transfer from the glass fiber filaments which pass between the cooling fins 14. This heat must be removed from the coolant liquid and this is accomplished by passing the hot liquid through a heat exchanger generally at 60. The hot liquid from the fin cooler 10 flows through a heat exchange core 62 around which continually circulates a secondary heat exchange fluid such as plant process water by means of a water inlet 66 and a water outlet 68 or by forced air cooling. The hot coolant liquid is cooled, and upon exiting from heat exchanger 60, is reused. The coolant liquid can thus be seen to be flowing in a closed loop in which it takes on heat in the cooling fins and gives off heat in the exchanger. Turning to Figs. 6, 7 and 8, there is shown the preferred embodiment of the fin cooler system of the instant invention. In Fig. 6, a fin cooler header 71 and 72 are shown positioned behind and below a bushing, 80 which has a multiplicity of fiber forming tips 81 on the bottom thereof. The tips 81 are arranged in rows and as shown, two rows of tips, 81 are positioned between the fins 74 of header 71 and fins 75 of header 72. Fluid is introduced into headers 71 and 72 through inlets 82 and 83 respectively. Fluid exits the header 71 and 72 through outlets 84 and 85 respectively. Fins 74 and 75 are formed of two sheets of metal which are pinched toward each other along their center line and welded together to form the U-shaped channel 86 shown in Fig. 8. The solid metal center 87 divides the fin to provide that channel 86. In the header 71 shown in Fig. 8, a rectangular configuration is provided with a dividing wall 88 therein to provide an upper chamber 89 and a lower chamber 90. As will be readily understood, the inlets 82 and 83 and outlets 84 and 85 are connected to a heat exchanger 60 such as shown in Fig. 5 so that fluid circulating in the fins 74 and 75 can be treated to extract heat and supply cooled fluid during operation. As has been alluded to previously, in the preferred embodiment, the heat exchange liquid or coolant liquid which flows in the closed loop and which thus passes through the cooling fins 14 is selected from one of a number of heat exchange fluids that have a boiling point higher than water, a vapor pressure of below 1.01 bar (1 atmosphere) and a high specific heat value at operating temperature, i.e., at least 2.09 Joule/°C/g . Exemplary of heat exchange fluids which would be suitable for such use are Hydrotherm® 700-160 and Hydrotherm® 750-200, manufactured by American Hydrotherm Corporation, or Dowtherm® A or Dowtherm® E which are made by Dow Chemical Company. Alternatively, various mineral oils or other heat exchange fluids may be used in the closed loop, cooled fin cooler in accordance with the present invention so long as they conform to the specific heat and vapor pressure requirements. Thus, high boiling alcohols such as glycerol, ethylene glycol, propylene glycol, 1,3-propanol may be used alone or diluted slightly with water, i.e., up to 15 to 20 percent so long as the boiling point of any such diluted alcohol is higher than water and the specific heat remains at a value of at least 2.09 J (0.5 cal)/°C/gm with a vapor pressure below 1.01 bar (1 atmosphere) at an operating fin temperature of 66°C (150°F) or above, preferably 66°C - 93°C (150°F to 200°F). These heat exchange fluids have boiling points substantially higher than water and allow the cooling fins to operate at a temperature of 66°C - 204°C (150-400°F) or higher, preferably (150°F to 200°F) 66°C - 93°C. In instances where water alone is employed, it should be free of contaminants, maintained at or above 66°C (150°F) and below its boiling point as it circulates through the fins. This temperature is controlled by the heat removal in the heat exchanger and the rate of flow of water through the closed loop in which the water flows. The upper limit of temperatures used with material liquids other than water alone is determined by the failure point of the materials used in the fin and the boiling point of that liquid. Operation in temperature ranges of this magnitude reduces the deposition amounts of glass volatiles on the fin surfaces and also reduces the tendency to form corrosive acids on the cooling fin surfaces. Although the fins operate at a higher temperature than would be the case if they were operating in accordance with the teachings of the prior art with water used in an open system as a heat transfer fluid, the difference between the fin temperature of 66° - 204°C (150-400°F) and the typical 1204°C (2200°F) bushing tip exit temperature of the glass affords good heat transfer to the fins. It has been found further that by maintaining a margin of generally 14° - 56°C (25 to 100°F), preferably 28° - 56°C (50 to 100°F) or more between the operating temperature of the system in the fins and the boiling point of the heat transfer fluid used therein insures that the fluids employed will remain in liquid form at all times in all parts of the closed system. The specific operating temperature of the fin cooler can be controlled by proper selection of the desired heat transfer fluid and by control of the flow rate of the heat transfer fluid through the heat exchanger. The method and apparatus for glass fiber cooling in accordance with the preferred embodiment of the present invention makes use of a heat transfer liquid having a boiling point higher than water and a high specific heat to allow the cooling fins to operate at a temperature of generally about 66°C - 204°C (150 to 400°F ), preferably 66° - 93°C (150 to 200°F). Operating in this temperature range helps prevent glass contaminant deposition on the cooling fins, provides even fin temperature distribution, and prolongs fin life by impeding the formation of fin corroding acids. The closed loop path of the heat transfer fluid through the cooling fins and the heat exchanger allows the use of a contaminant free heat transfer medium which will remain contaminant free during use and will not occlude or plug the coolant liquid flow passages in the cooling fins. Thus the method and apparatus for cooling glass fibers in accordance with the present invention provides a substantial advance in the art. Further, benefits are provided in that, by adjustment of the fluid employed and the circulation rates through the fins and its consequent effect on fin temperature, the forming process itself can be adjusted to alter glass viscosities in the area of glass forming cones to adjust fiber diameters. In a preferred mode operation a fin cooler of the instant invention was used on an 800 tip fiber glass forming bushing in a laboratory furnace forehearth with a 90 percent ethylene glycol - 10 percent water mixture used as the heat transfer media. The media was pumped through the fins of the fin cooler at a rate of about 500 milliliters per minute per fin. The fin surface temperatures were maintained at 71°C (160°F) by removing heat from the heat transfer fluid in the fluid heat exchanger which was operated with water as the heat exchange fluid at inlet temperatures of 26.7°C (80°F) and outlet temperatures of about 66°C (150°F). In another preferred mode of operating the instant invention ten 800-tip fiber glass forming bushings were operated off a fiber glass furnace forehearth in a manufacturing plant utilizing the fin cooler system of the instant invention, each fin cooler having 38 fins per position. The ethylene glycol, the primary heat transfer media, circulating through the fins was a 70 percent ethylene glycol - 30 percent water mixture. This ethylene glycol-water mixture was pumped through the fins of the fin coolers on all bushings at a rate of between 0.38 and 0.57 liter (0.1 and 0.15 gallons) per minute per individual fin. The fin surface temperature of the fins on the 10 bushing positions was maintained at 71°C (160°F) by removing heat from the primary heat transfer media, i.e., the 70/30 ethylene glycol water mixture in a heat exchanger in a closed loop system with water operating as the heat exchange fluid in the heat exchanger. Plant process water at approximately 26.7°C (80°F) was fed to the heat exchanger, and the outlet temperature of the water from the heat exchanger unit was about 66°C (150°F). Operating in this manner the fins were maintained at the approximate 71°C (160°F) surface temperature during the operation. The fins, except for a minor leak problem on three fins associated with the fin coolers, which were leaks at the braizing jointure of the fin with the fin cooler header, the operation of the fin system has been satisfactory and no system failures have occurred. During the course of this run which was conducted on a production furnace, two bushings and associated fins were utilized at the beginning, and as the trial progressed, further bushings and fins were added until the total number of 10 bushings and associated fins was achieved. One of the fin cooler positions employed during the course of the trial has achieved a service of 34 weeks without any failure. It has also been observed when the system was utilized on these positions that a lower broken filament levels were experienced during the operation of the bushings than was experienced with the normal solid fins previously employed for production from bushings of this design.

Claims: A method of cooling glass fibers formed from molten glass, wherein heat is extracted from the glass fibers as they are formed through a fin cooler assembly (10) by indirect heat exchange through the fin surfaces, characterized by circulating in a closed loop, through each fin (14, 74, 75), a heat transfer fluid having a specific heat of at least 2,09 Joule (0,5 cal)/°C/g and a vapor pressure not over 1,01 bar (1 atmosphere) at operating temperature, at a rate sufficient to maintain the fin surfaces above about 66°C (150°F) which extracts heat from the filament forming environment into said heat transfer fluid. The method of claim 1, wherein the heat transfer fluid has a boiling point higher than water and a specific heat of at least 2,09 Joule (0,5 cal)/°C/g and a vapor pressure below 1,01 bar (1 atmosphere) when the heat transfer fluid is at a temperature of between 66°C and 204°C (150°F and 400°F). The method of claim 1, wherein the fin surfaces are maintained at temperatures between 66°C and 93°C (150°F and 200°F). The method of claim 1, wherein the fin surfaces are maintained at temperatures above 93°C (200°F). The method of claim 1, wherein there is a temperature differential of 28°C - 56°C (50°F - 100°F) between the fin surfaces and the boiling point of the heat transfer fluid. The method of claims 1 to 5, wherein the heat transfer fluid is passed to a heat exchanger (60) remote from the fins (14, 74, 75) and extracting heat from the heat transfer fluid in the heat exchanger (60) and balancing the heat removal in the heat exchanger (60) and the flow rate of the heat transfer fluid to maintain the temperature of the heat transfer fluid in the fins (14, 74, 75) at 66°C (150°F) or greater but below the boiling point of the heat transfer fluid. The method of claim 3, wherein the heat transfer fluid is water. The method of claims 1 to 7, wherein said heat exchanger (60) utilizes plant process water as a secondary heat transfer fluid. A cooled fin assembly (10) suitable for use in cooling glass fibers formed from molten glass in a fiber glass forming bushing (80) having a plurality of glass forming tips (81), said cooled fin cooler assembly (10) comprising: a fin cooler header (12, 71, 72) positionable generally beneath said glass forming bushing (80), said header including separate space fin coolant liquid inflow channel (28, 90) and fin coolant liquid outflow channel (32, 89); a plurality of spaced cooling fins (14) secured at first ends (24) to said header block (12, 71, 72) and extending outwardly therefrom beneath the plurality of glass forming tips (81) to remove heat from glass fiber filaments which pass between said space cooling fins (14, 74, 75); a coolant liquid flow passage (36, 86) in each of said cooling fins (14, 74, 75), each of said flow passages including an inlet port (38) in fluid communication with said coolant liquid inflow channel (28, 90), and an outlet port (40), in fluid communication with said coolant fluid outflow channel (32, 89) wherein said fin cooler header (12, 71, 72) and coolant liquid flow channels (28, 32, 89, 90) and said cooling fins (14, 74, 75) form a closed loop fluid flow path; a heat exchanger (60) remote from said fin cooler header block (12, 71, 72) and in fluid communication therewith; means to flow exchanger cooling fluid through said heat exchanger (60); means to control the flow of said exchanger cooling fluid to control the temperature of said fin coolant fluid. The cooled fin cooler assembly (10) of claim 9, wherein said coolant liquid flow passage (36, 86), in each of said cooling fins (14) is generally an elongated U-shaped passage.

Inventors: JENSEN, THOMAS HULEGAARD
Applicants: PPG INDUSTRIES, INC.
Application year: 1989
Main classification: C03B37
IPC codes: C03B37, F28F27, F28F3