US 3554723 A
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' Jan. 1971 R. w. WILSON 3,554,723 U METHOD AND APPARATUS FOR AIR cooLImGLAss TUBE Filed Aug. 1967 V l' I I. l f\ I I 3 Q co Q gq t l I ,3'\ Q x J\ i O\ I n A INVENTOR.
RICHMOND w. WILSON BY M WJZJLM ATTORNEY States PatentfO METHOD AND APPARATUS FOR AIR. COOLING GLASS TUBE Richmond W. Wilson, Corning, N.Y., assignor to Corning Glass Works, Corning, N.Y., a corporation of New York Filed Aug. 4, 1967, Ser. No. 658,572
lntLCl. C03b /14 us. (:1. 65-86 6 Claims ABSTRACT OF THE DISCLOSURE High velocity air is supplied to a confined space along an extended length of newly formed glass rod or tubing to provide improved controlled cooling rates and thereby permit higher production rates, and improved thermal stress control.
BACKGROUND OF THE INVENTION In form-ing glass tubing by either an updraw or downdraw process, including both hollow and solid tubing, a continuous length of such tubing is drawn from a suitable orifice and usually pulled horizontally along a plurality of support rollers or diabolos. However, due to its high heat of formation, extremely long cooling lines have been required in order to sufiilciently reduce the temperature of the tubing to a temperature where it could be cut without imparting deformation. Production speeds for drawing tubing have, therefore, been limited by the space available for the cooling lines, since the tubing must be cooled to a predetermined temperature before it can be cut to size.
United States Pat. No. 3,260,586 to Prohaszka et al. indicates that forced air cooling of hollow tubing has been tried in the past, but was found to be quite slow. In addition, the patent states that water cooling, although much faster, normally introduces uneven cooling effects. In order to avoid these problems, the Prohaszka et al. patent suggests the utilization of a cooling cone which directs an air-water spray in a conical form about the tubing. However, this approach is not entirely satisfactory since the tubing must cool sufiiciently before being subjected to such a water spray, or it could be deformed out of round. Over cooling can result in checks and crazing. In addition, since the conical spray appears to merely make a circular line contact with the tubing, the cooling application is not particularly eflicient.
SUMMARY OF THE INVENTION The present invention obviates the problems encountered in cooling tubing by theprior art devices, and actually improves cooling rates to an extent that production can be increased by more than 60% When cooling a continuous cylindrical length of glass tubing with air, whether it be hollow or solid, the cooling rate is proportional to the diameter of the tubing, the temperature difference between the glass tubing and the air, and the relative velocity of the air to the tubing. Therefore, for a given size tubing being formed at a predetermined temperature and speed, I have determined that the one practical controllable variable for cooling the tubing with air at room temperature is the velocity of the air. In embodying such concept, my invention employs the utilization of high velocity air, or other gas if desired, within a confined region along an extended length of the hot tubing as it is drawn horizontally along the supporting rollers.
In practice, a tunnel cooler of generally restricted cross section encloses that section of the draw which is to be cooled, including the tubing and the supporting rollers; and high velocity air is forced through the restricted area between the tunnel cooler and the tubing. The most efficient method of obtaining the maximum relative velocity 3,554,723 Patented Jan. 12, 1971 between the glass tubing and the gas is to create an air flow within the tunnel counter current to the direction of pull of the tubing. The exit end of the tunnel cooler is preferably open to the atmosphere with the inlet end closed except for a small opening to receive the tubing, and a high capacity vacuum source is applied adjacent the inlet end to draw air in the exit end, through the tunnel cooler, and out the hotter inlet end. An equal cooling efficiency could be achieved by operating the tunnel at above atmospheric pressure; however, such positive pressure would cause the tubing, while still in a relatively low viscous state, to deform and become out-of-round. The sub-atmospheric pressure, on the other hand, tends to cause the tubing to become more nearly round and provide for dimensional uniformity.
BRIEF DESCRIPTION OF THE DRAWING The figure is a schematic illustration, partially in section, of apparatus embodying my invention for carrying out the improved cooling process.
DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawing, glass tubing 10 is formed by a suitable downdraw process, such as from a Vello orifice 11. The tubing 10 may be pulled through a catenary 12 and along a horizontal path 13 by means of suitable rollers 14. A plurality of support rollers or diabolos 15 support the tubing 10 as it is being pulled along the horizontal path.
A suitable cooling tunnel housing 16 of generally restricted cross section is positioned along an extended length of the horizontal path so as to encompass both the tubing 10 and support rollers 15 along such length. The tunnel housing 16 is provided with a substantially closed hot inlet end 17, having a relatively small opening 18 to facilitate the induction of the newly formed tubing 10. The opposite cooler end 19 of the tunnel housing is unrestricted and open to the atmosphere. The tunnel housing 16 provides an elongated chamber or cooling zone 20 of limited cross-sectional area adjacent the longitudinal length of tubing 10. A conduit 21 is shown communicating with the chamber 20 adjacent the hotter substantially closed end 17 of the cooling tunnel housing 16. The conduit 21 is connected to a suitable high capacity vacuum source, such as a fan or vacuum pump 22.
In operation, newly formed hot tubing 10 enters the cooling tunnel housing 16 through small opening 18 in the closed end 17, and exits from the housing through the opposite large opening 19. Pull rollers 14 maintain a desired pull rate on the tubing 10, which is supported by support rollers 15 along its horizontal path. Vacuum pump 22 creates a high velocity air flow through the restricted cross section of elongated chamber or cooling zone 20 by drawing air in through large opening 19 adjacent the cool end of the draw, and discharging such air through conduit 21 adjacent the hotter end of the draw. As shown by the -flow arrows, a counter current heat exchange is provided between the movement of the glass tubing and the air flow, so as to obtain maximum relative air -flow velocity with respect to the glass and thereby provide optimum cooling efliciency.
While the most efficient means of cooling is to have the point of withdrawal of the air at the hotter end of the draw for counter-current heat exchange, the point of withdrawal may be located at any point along the length of the tunnel so long as at least one of the ends of the tunnel is open to the atmosphere. The elongated tunnel provides an extended cylindrical surface contact between the glass and air, thus providing for increased cooling efficiency. Further, as previously pointed out, superatmospheric pressure may be utilized in place of subatmospheric pressure to achieve the same degree of cooling; however, I have found that uniformity of tube quality is enhanced by utilizing sub-atmospheric pressure. Additional efficiency can be achieved by blackening the inside surface of the tunnel so that more heat can be absorbed by radiation from the glass.
As a specific example, but by no means limiting in nature, hollow tubing having a .45" CD. was introduced into one end of a 30 blackened cooling tunnel housing at a temperature of about 550 C. and at a rate of about 10 feet per second. The tunnel housing had a cross-sectional area of about 40 sq. inches, and a counter current vacuum air flow of about 100 ft. per second was provided through the tunnel housing by a suitable fan, resulting in the tub ing being cooled about 100 C. as it passed through the elongated cooling chamber provided by the tunnel housing. This represents an increase in cooling rates of more than 3 times that obtained in an open 30' length with the usual ambient air-radiation cooling.
It can be well appreciated that various parameters may be varied to accommodate different production operations and facilities. For instance, depending upon the rate of draw and diameter of the tubing, the elongated cooling chamber may vary from 5 to 40. If desired, the air could be cooled to increase the temperature differential between the glass and air, and thus increase the cooling rate. Also, optimum efficiency of the tunnel cooler may be obtained by reducing the cross-sectional area, or increasing the length of the tunnel, or increasing the capacity of the fan, all of which will increase the velocity of the air with respect to the tubing, thus increasing the overall efficiency of the cooling operaiton. Although the preferred embodiment has been shown with respect to hollow tubing, it is understood that the invention is equally appliciable to solid tubing such as cane or rod, and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims,
1. An improved method of manufacturing hollow and solid glass tubing by a tube drawing process which comprises, pulling such newly formed glass tubing in one direction along a defined path at a predetermined rate, and passing a confined stream of high velocity air in an opposite direction over the surface of such tubing along an extended length of such path.
2. An improved method of forming glass tubing as defined in claim 1 wherein sub-atmospheric pressure is applied to such path adjacent to the point where the tubing enters such path.
3. Apparatus for cooling newly formed glass tubing which comprises, an elongated cooling tunnel housing, said housing having a closed end with a small opening for the introduction of the tubing therewithin, the opposite end of said housing being open to the atmosphere, said housing having a cross-sectional area sufficient to encompass both the tubing being drawn therethrough and supporting rollers for such tubing, and means communicating with said housing adjacent its closed end for producing a high velocity stream of air through said housing toward said closed end.
4. Apparatus as defined in claim 3 wherein said means for forming a high velocity stream of air through said housing is a vacuum producing means.
5. Apparatus as defined in claim 3 wherein means pull said newly formed glass tubing through said cooling tunnel housing in one direction, and said high velocity air stream producing means provides a high velocity stream of air in an opposite direction through said cooling tunnel housing.
6. Apparatus as defined in claim 3 wherein said cooling tunnel housing is provided with a blackened inside surface to increase the absorption of heat from the glass tubing by radiation.
References Cited UNITED STATES PATENTS 1,766,638 6/1930 Howard 87X 1,892,126 12/1932 Bailey 6587X 3,190,739 6/1965 Wilson 6586X 3,298,808 1/1967 Macks 6586X FOREIGN PATENTS 1,356,644 5/1963 France 65-187 FRANK W. MIGA, Primary Examiner US. Cl. X.R.