Patent Publication Number: US-2017349474-A1

Title: Methods and apparatuses for forming glass tubing from glass preforms

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Application No. 62/346,832 filed Jun. 7, 2016, entitled, “Methods and Apparatuses for Forming Glass Tubing From Glass Preforms,” the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND 
     Field 
     The present specification generally relates to the manufacture of glass tubing and, more particularly, to methods and apparatuses for forming glass tubing from glass preforms. 
     Technical Background 
     Various methods of manufacturing tubes and/or rods of glass are known. Such methods may include drawing molten glass over a bell, which can generate flaws along the interior surface of the glass tube. Additionally, conventional methods may include contacting the exterior surface of the glass with equipment, such as to change the direction of flow of the glass and/or to continue drawing the glass. This contact with the glass can generate flaws along the exterior surface of the glass tube. For example, in these conventional processes, the glass viscosity may allow the forming tooling to impart longitudinal lines (also referred to as “longitudinal paneling lines”) onto the surface of the resulting tubing as the glass flows over the tooling. These longitudinal paneling lines are a series of peaks and valleys on the tube surface from the glass contact with the metal tooling. Other defects, such as seeds, blister, bubbles or inclusions, may result from melting the glass before it is drawn. 
     Accordingly, alternative methods and apparatuses for forming glass tubing are needed that reduce flaws in the final glass product. 
     SUMMARY 
     According to one embodiment, a method of forming a glass tube includes heating a glass boule to a temperature above a glass transition temperature of the glass boule, drawing the glass tube from the glass boule in a vertically downward direction, and flowing a pressurized gas through a channel of the glass boule as the glass tube is drawn in the vertically downward direction. The glass boule includes an outer surface defining an outer diameter of the glass boule and a channel extending through the glass boule. The channel defines an inner diameter of the glass boule. Drawing the glass tube decreases the outer diameter of the glass boule to an outer diameter of the glass tube and flowing the pressurized gas through the channel increases the inner diameter of the glass boule to an inner diameter of the glass tube. 
     According to another embodiment, an apparatus for forming a glass tube includes a furnace, a pressurized gas source, at least one pair of pulling rolls, an inner diameter gauge, an outer diameter gauge, and an electronic control unit. The furnace extends in a substantially vertical direction. The pressurized gas source is fluidly coupled to a channel of a glass boule positioned within the furnace with a supply conduit and provides a flow of pressurized gas to the channel. The at least one pair of pulling rolls is positioned downstream of the heating chamber and is configured to engage with the glass tube drawn from the glass boule. The electronic control unit is communicatively coupled to the inner diameter gauge, the outer diameter gauge, the pressurized gas source, and the at least one pair of pulling rolls. The electronic control unit includes a processor and a non-transitory memory storing computer readable and executable instructions which, when executed by the processor, adjust at least one of a speed and a torque of the at least one pair of pulling rolls based on a signal received from the outer diameter gauge and adjusts a flow rate of the pressurized gas provided by the pressurized gas source based on a signal received from the inner diameter gauge. 
     Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description describe various embodiments of methods and apparatuses for forming glass tubes and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a glass boule manufacturing system in accordance with one or more embodiments described herein; 
         FIG. 2  illustrates a glass boule accordance with one or more embodiments described herein; 
         FIG. 3  illustrates a glass tube manufacturing device for use in forming a glass tube from a glass boule in accordance with one or more embodiments described herein; and 
         FIG. 4  illustrates a process for forming a glass tube from a glass boule using the glass tube manufacturing device of  FIG. 3  in accordance with one or more embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to various embodiments of methods and apparatuses for forming glass boules and for forming glass tubes from the glass boules, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. 
     One embodiment of a glass tube manufacturing device is shown in  FIG. 3 , and is designated generally throughout by the reference numeral  300 . The glass tube manufacturing device  300  may generally include a pressurized gas source providing a flow of a pressurized gas to an inner channel of a glass boule positioned within a furnace, a downfeed unit for positioning the glass boule within the furnace and lowering the glass boule into the furnace at a controlled feed rate, at least one pair of pulling rolls positioned downstream of the furnace, an inner diameter gauge, an outer diameter gauge, and an electronic control unit. The glass boule is heated in the furnace to allow the lower portion of the glass boule to decrease in viscosity enabling the glass boule to attenuate down in size. The attenuated portion of the glass boule forms the glass tube which is engaged by at least one pair of pulling rolls below the furnace to draw the glass tube. The electronic control unit is configured to adjust a downfeed rate of the glass boule within the furnace, adjust at least one of a speed and a torque of the at least one pair of pulling rolls based on a signal received from the outer diameter gauge, and adjust a flow rate of the control gas based on a signal received from the inner diameter gauge in order to control the formation of the glass tube. Various embodiments of methods and apparatuses for forming glass tubing from a glass boule will be described herein with specific reference to the appended drawings. 
     Directional terms as used herein—for example up, down, right, left, front, back, top, bottom, vertical, horizontal—are made only with reference to the figures as drawn and are not intended to imply absolute orientation unless otherwise expressly stated. 
     Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification. 
     As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise. 
     Referring to  FIG. 1 , an exemplary glass boule manufacturing system  100  for forming a glass boule is schematically depicted. The glass boule manufacturing system  100  generally includes molten glass delivery system  102 , a delivery vessel  104  for receiving molten glass, and a mandrel  106 . 
     The molten glass delivery system  102  generally includes a melting vessel  108 , a fining vessel  110 , and a mixing vessel  112  coupled to the delivery vessel  104  of the glass boule manufacturing system  100 . 
     The delivery vessel  104  may include heating elements (not shown) for heating and/or maintaining the glass in a molten state. The delivery vessel  104  may also contain mixing components (not shown) for further homogenizing the molten glass in the delivery vessel  104 . In some embodiments, the delivery vessel  104  may cool and condition the molten glass in order to increase the viscosity of the glass prior to providing the glass to the mandrel  106 . 
     The delivery vessel  104  may include an opening  118  in the bottom thereof. In various embodiments, the opening  118  is circular, but may be oval, elliptical or polygonal, and is sized to permit molten glass  120  to flow through the opening  118  in the delivery vessel  104 . The molten glass  120  may flow over the mandrel  106  directly from the opening  118  in the delivery vessel  104  to form a glass boule  122 . 
     Still referring to  FIG. 1 , in various embodiments, the glass boule manufacturing system  100  further includes an outer mold  124  positioned around the mandrel  106  such that molten glass  120  flows from the delivery vessel  104  between the mandrel  106  and the outer mold  124 . The outer mold  124  can have an inner geometry being a non-circular shape corresponding to the opening  118  in the delivery vessel  104 . The outside shape of the outer mold  124  can be any shape conducive to the supporting infrastructure. 
     In operation, the glass batch materials are introduced into the melting vessel  108  as indicated by arrow  2 . The glass batch materials are melted in the melting vessel  108  to form molten glass  120 . The molten glass  120  flows into the fining vessel  110  which has a high temperature processing area that receives the molten glass  120  from the melting vessel  108 . The fining vessel  110  removes bubbles from the molten glass  120 . The fining vessel  110  is fluidly coupled to the mixing vessel  112  by a connecting tube  111 . That is, molten glass  120  flowing from the fining vessel  110  to the mixing vessel  112  flows through the connecting tube  111 . The molten glass  120  is homogenized in the mixing vessel  112 , such as by stirring. The mixing vessel  112  is, in turn, fluidly coupled to the delivery vessel  104  through the feed pipe  113 . 
     The molten glass then flows through the opening  118  in the delivery vessel  104  and over the mandrel  106 , which forms a channel  126  in the glass boule  122 . In embodiments including an outer mold  124 , the outer mold  124  shapes an outer surface  128  of the glass boule  122 . Together, the mandrel  106  and the outer mold  124  quench the glass, forming a glass boule  122  having an inner channel. Once formed, the glass boule  122  is annealed, which heats the glass boule  122  to a temperature at which residual stresses are relieved before the glass boule  122  is reheated so that it can be drawn into a glass tube  400 . 
     The molten glass  120  may be formed according to known methods of forming molten glass mixtures. Additionally, the particular glass composition components provided to form the molten glass  120  may vary depending on the particular embodiment. In particular, the glass composition components may include, by way of example and not limitation, silica (SiO 2 ), alumina (Al 2 O 3 ), boron oxide (B 2 O 3 ), alkaline earth oxides (such as MgO, CaO, SrO, or BaO), alkali oxides (including, but not limited to, Na 2 O and/or K 2 O), and one or more additional oxides or fining agents, such as for example, SnO 2 , ZrO 2 , ZnO, TiO 2 , Cl −  or the like. In one specific embodiment, the molten glass mixture may be formed from a glass composition as disclosed in, for example, U.S. Pat. No. 8,551,898. However, it should be understood that other glass compositions for use with the methods and apparatuses described herein are contemplated and possible. 
     In general, the temperature of the molten glass  120  in the delivery vessel  104  is controlled such that a viscosity of the molten glass  120  at the opening  118  of the delivery vessel  104  is suitable for providing a stable flow of glass from the opening  118 . For example, in some embodiments the temperature of the molten glass  120  in the delivery vessel  104  is such that the molten glass mixture has a viscosity of between about 1 kP (kiloPoise) and about 250 kP, between about 25 kP and about 225 kP, or between about 50 kP and about 150 kP to provide a stabilized flow from the delivery vessel  104 . The glass compositions used in conjunction with the methods and apparatuses described herein may be limited to glass compositions that yield both an appropriate working viscosity that allows for forming the glass without devitrification and the physical attributes required for the article to be produced. Working viscosity, as used herein, refers to the temperature over which the glass exhibits a viscosity of greater than about 25 kP. However, in certain instances, attributes of the finished article may be desired that cannot be met by glass compositions that are considered drawable. In other words, the desired glass composition may have a liquidus temperature that is sufficiently high that the temperature to prevent devitrification of the molten glass at the opening  118  of the delivery vessel  104  may result in a viscosity of the molten glass at the opening  118  that is below the lower limit of viscosities suitable for drawing. In such embodiments, the mandrel  106  and outer mold  124  may employ active cooling features to remove heat from the molten glass coming out of the opening  118  to increase the viscosity rapidly to overcome crystallization and enable boule formation. 
       FIG. 2  illustrates an exemplary glass boule  122  that may be formed with the glass boule manufacturing system  100  depicted in  FIG. 1 . As shown in  FIG. 2 , the channel  126  of the glass boule  122  defines an inner diameter ID 1  of the glass boule  122  while the outer surface  128  of the glass boule  122  defines an outer diameter OD 1  of the glass boule  122 . The inner diameter ID 1  and the outer diameter OD 1  of the glass boule  122  may vary depending on the particular embodiment. For example, in some embodiments, the inner diameter ID 1  of the glass boule  122  is from about 3 mm to about 50 mm and the outer diameter OD 1  of the glass boule  122  is from about 140 mm to about 250 mm. The inner diameter ID 1  of the glass boule  122  may vary depending on the outer diameter OD 1  of the glass boule  122  and may generally range from about 3 mm to about 50 mm, from about 3 mm to about 25 mm, or from about 3 mm to about 5 mm. For example, a glass boule  122  having an outer diameter OD 1  of about 150 mm may have an inner diameter ID 1  of from about 5 mm to about 20 mm. As another example, a glass boule  122  having an outer diameter OD 1  of about 250 mm may have an inner diameter ID 1  of from about 10 mm to about 50 mm. In one particular example, the glass boule  122  has an outer diameter of from about 140 mm to about 160 mm and an inner diameter of from about 6 mm to about 40 mm. In various embodiments, the glass boule  122  may be from about 1 m to about 3 m long or even from about 1.5 m to about 2.5 m long. 
     In some embodiments, the glass boule  122  can be formed according to alternative methods. For example, in one embodiment, a glass boule  122  is formed without a channel and the channel  126  is then drilled into or otherwise introduced to the glass boule  122 , such as by gun drilling or core drilling with a diamond-impregnated metal tip. In some embodiments, shorter lengths of glass (e.g., 12 inches or less) may be drilled and spliced together via flame working to form the glass boule  122 . 
     In other embodiments, a cylinder of glass may be pressed through an extrusion die including a piston to make the glass boule  122 . The extrusion die may include a mandrel to form the channel  126  of the glass boule  122 . In some embodiments in which the glass is extruded, the temperature of the glass is such that the glass mixture has a viscosity of about 1×10 5  P (Poise) to about 1×10 7  P. Alternatively, other methods of forming a glass boule  122  including a channel  126  may be used. 
     In embodiments, the process of forming the glass boule  122  may result in defects in the glass. Specifically, the channel  126  and/or outer surface  128  may include various defects, such as cracks or scratches. As used herein “defects” refer to bubbles, inclusions, glass particulates, scratches, cracks, airlines, surface impurities, paneling, or any other flaws on the surface of or internal to the glass which reduce the quality of the glass. Such defects may be the result of, for example, irregularities or defects present on the mandrel  106  that interrupt or alter the flow of the molten glass  120 . Internal defects such as bubbles and inclusions may result from glass quality coming out of the melting vessel  108 . Some bubbles may be drawn down making airlines internal to the wall thickness of the resulting tubing. External defects, such as paneling and blemishes, may result from the molten glass flowing against tooling and being embossed on the surfaces. Defects may also be found in qualities pertaining to geometry, such as areas that deviate from the desired surface shape, such as being out of round, bowing, and the like. 
     According to various embodiments, the defects on the channel  126  and the defects on the outer surface  128  of the glass boule  122  may be reduced by heating and drawing the inner and outer surfaces to form a glass tube  400  that has fewer defects. Without being bound by theory, when a boule is attenuated to a tube, there is a reduction ratio. The geometry plus any defects that are part of the glass make up are reduced in size by this reduction ratio. Therefore, if the glass boule includes a defect that is 10 mm in size and the reduction ratio is 100, the glass tube  400  includes a defect that is 0.1 mm in size. Accordingly, small defects can be reduced in size such that they become invisible to the human eye. Moreover, the drawing process employed to draw the glass boule  122  into a glass tube  400  may have a flame polishing effect on the surface. For example, if a scratch occurred on the glass boule  122  due to post-processing or handling, it could be “healed” when the glass boule  122  is drawn because the drawing process includes reheating the glass to allow it to flow, thus removing the defect. In particular, the inner diameter ID 1  of the glass boule  122  is increased while the outer diameter OD 1  of the glass boule  122  is decreased to form a glass tube  400  having an inner diameter ID 2  and an outer diameter OD 2 . 
     Moreover, without being bound by theory, formation of a glass tube by drawing the glass tube from a glass boule may result in improved surface quality over glass tubes formed using conventional conversion processes. For example, conventional conversion processes can introduce surface defects due to the various changes in direction and contact points with the surfaces of the glass. By contrast, various methods described herein contact the inner surface of the glass boule with a mandrel during formation and contact the outer surface of the drawn glass tube with pulling rolls, but may not otherwise provide surface contact during manufacturing. 
     As shown in  FIG. 2 , in various embodiments, the glass boule  122  includes a handle  200 . The handle  200  may be integrally formed with the glass boule  122 , such as during extrusion or as the molten glass  120  is let down from the opening  118  in the delivery vessel  104 . For example, the molten glass  120  may be drawn faster to form the handle  200 , commonly referred to as “necking” the boule. The handle may be, for example, about one meter, about two meters, or even greater in length. Alternatively, the handle  200  may be attached to the glass boule  122  after the glass boule  122  is formed. For example, the handle  200  may be attached using flame work or another suitable technique after the glass boule  122  is annealed or at another point before the glass boule  122  is formed into a glass tube  400 . In various embodiments, the handle  200  provides a surface for handling or manipulating the glass boule  122  without contacting the surface of the glass boule  122  itself. Additionally, the handle  200  may act as a conduit for connecting the glass boule  122  to a pressurized gas source to provide pressurized gas to the channel  126  of the glass boule  122 , as will be described in greater detail below. For example, the handle  200  may be partly formed at the glass boule  122  with a pre-ground mating joint flame-worked to the handle  200 . Without being bound by theory, embodiments in which the glass boule  122  includes a handle may minimize waste and enable all of the glass of the glass boule  122  to be used to form the glass tube  400  without needing to dispose of the end of the glass boule  122 . 
     Referring now to  FIGS. 3 and 4 , after the glass boule  122  has been formed, the glass boule  122  may be inserted in a glass tube manufacturing device  300  to draw a glass tube  400  from the glass boule  122 . In embodiments, the glass tube manufacturing device  300  generally includes a furnace  302 , a pressurized gas source  304  for supplying a pressurized gas  306 , and at least one pair of pulling rolls  308 . As used herein, the term “pulling rolls” includes pulling devices including but not limited to tractor belts, pinch wheels, capstan, dual rolls, and the like. The glass tube manufacturing device  300  may further comprise an inner diameter gauge  310 , an outer diameter gauge  312 , a downfeed unit  320 , and an electronic control unit (ECU)  314  for controlling the process of drawing the glass tube  400  from the glass boule  122 . 
     In the embodiments described herein, the furnace  302  may be a tube furnace extending vertically (i.e., in the +/−Z directions of the coordinate axes depicted in  FIG. 3 ). The glass boule  122  (not shown in  FIG. 3 ) may be positioned in the furnace  302 . The pressurized gas source  304  may be a pump or other source of pressurized gas, such as a compressed gas cylinder, compressor of the like, that is coupled to the channel  126  of the glass boule  122  with a supply conduit  316 . In embodiments, the supply conduit  316  may further include a seal  318  which may be used to seal the supply conduit  316  to the channel  126  of the glass boule  122  when the glass boule  122  is coupled to the pressurized gas source  304 . For example, the handle  200  of the glass boule  122  may be coupled to the seal  318  to form a joint. The supply conduit  316 , coupled to the channel  126  through the seal  318  and handle  200 , provides the pressurized gas  306  from the pressurized gas source  304  to the channel  126 . The supply conduit  316  may be in the form of a flexible hose or include at least a portion capable of moving vertically. For example, the supply conduit  316  may include a chuck connected to a screw feed that can be controlled to move in the vertical direction. 
     The glass tube manufacturing device  300  also includes a handle engagement mechanism  303  to support the handle  200  of the glass boule  122  while it is coupled to the seal  318 . In various embodiments, the handle engagement mechanism  303  is open on at least one side to facilitate positioning of the handle  200  within the handle engagement mechanism  303 . For example, in various embodiments, the handle  200  of the glass boule  122  may be inserted in the +/−X directions of the coordinate axes depicted in  FIGS. 3 and 4  for coupling to the seal  318  and the supply conduit  316 . 
     In embodiments, the pressurized gas source  304  is communicatively coupled to the ECU  314 . The ECU  314  may include a processor and a non-transitory memory storing computer readable and executable instructions which, when executed by the processor, regulate the flow rate of the pressurized gas  306  emitted from the pressurized gas source  304 . The pressurized gas  306  may be, by way of example and not limitation, air, nitrogen, argon, helium, or another, similar process gas. In some embodiments, the pressurized gas  306  may be an inert gas, while in other embodiments, a forming gas may be employed to influence the chemistry of the surface of the channel  126  while increasing the inner diameter ID 1  of the glass boule  122 . 
       FIG. 3  further depicts a downfeed unit  320  electrically coupled to the ECU  314 . The downfeed unit  320  is further coupled to the handle engagement mechanism  303  and the supply conduit  316  and is used to move the glass boule  122  vertically (i.e., in the +/−Z directions of the coordinate axes depicted in  FIG. 3 ) within the furnace  302 . Vertical movement of the glass boule  122  within the furnace  302  enables a steady state reduction in size to be maintained in the glass as it is drawn. Accordingly, the handle engagement mechanism  303 , the supply conduit  316 , the seal  318 , the handle  200 , and the glass boule  122  are lowered into the furnace  302  until a lower portion of the glass boule  122  reaches the hot zone (not shown) of the furnace  302 . For example, the downfeed unit  320  may cause a screw feed associated with the supply conduit  316  and the handle engagement mechanism  303  to turn, lowering the handle engagement mechanism  303  and the supply conduit  316  into the furnace  302 , along with the seal  318 , the handle  200 , and the glass boule  122 . The portion of the glass boule  122  in the hot zone of the furnace decreases in viscosity, enabling that portion of the glass boule  122  to attenuate down in size, forming a glass tube  400 . As the glass tube  400  is pulled by the pulling rolls  308 , the downfeed unit  320  continues to lower the glass boule  122  into the furnace  302 . Once the glass boule  122  has been attenuated, the downfeed unit  320  may raise the handle engagement mechanism  303 , the handle  200 , the seal  318 , and the supply conduit  316  vertically out of the furnace  302 , enabling the handle  200  to be disconnected from the seal  318  and removed from the handle engagement mechanism  303 . In embodiments, the ECU  314  may include a processor and a non-transitory memory storing computer readable and executable instructions which, when executed by the processor, controls a rate at which the downfeed unit  320  adjusts the vertical position of the glass boule  122 , the supply conduit  316 , the handle engagement mechanism  303 , and the seal  318  within the furnace  302 . 
     In embodiments, the at least one pair of pulling rolls  308  are positioned downstream of the furnace  302  and engage with a portion of the outer surface glass tube  400 . The pulling rolls  308  may be actively driven, such as by a motor (not shown) electrically coupled to the ECU  314 . In embodiments, the ECU  314  may include a processor and a non-transitory memory storing computer readable and executable instructions which, when executed by the processor, control the rotation of the pulling rolls  308  (i.e., the torque and/or speed of the pulling rolls), and thus, the linear draw speed. 
     In some embodiments, a cooling fluid is provided to cool the glass tube  400 . For example, in embodiments in which the glass tube  400  has a large outer diameter OD 2  and thick wall, it may be desirable to cool the glass tube  400  before contacting the glass tube  400  with the pulling rolls  308 . The cooling may, for example, decrease the temperature of the glass tube  400  to reduce or eliminate damage to the pulling rolls  308  that can result from a glass tube that is too hot. The cooling fluid may be, for example, an inert gas or a fluid with a temperature sufficient to decrease the temperature of the glass tube  400 . The cooling fluid may reduce the temperature of the glass tube  400  to below about 300° C., below about 200° C., or below about 100° C. 
     Still referring to  FIG. 3 , the inner diameter gauge  310  and the outer diameter gauge  312  may be positioned downstream of the furnace  302  and are used to measure the inner diameter and outer diameter, respectively, of the glass tube  400  drawn from the glass boule  122  with the glass tube manufacturing device  300 . In various embodiments, the inner diameter gauge  310  and the outer diameter gauge  312  may be laser-based or visual-based measurement systems such that the inner diameter may be measured through the wall of the glass boule  122 . For example a visual-based inspection system may be employed to measure the inner diameter and outer diameter of the glass tube  400 . In particular embodiments, the refractive index of the glass may be employed to reduce or even eliminate lensing effects from the radius of curvature of the glass which may otherwise distort the measurement. In embodiments, the inner diameter gauge  310  may be positioned external to the glass tube  400  and is configured to measure an inner diameter of the glass tube  400  when the supply conduit  316  is coupled to the glass boule  122 , as will be described in further detail herein. The inner diameter gauge  310  and the outer diameter gauge  312  are communicatively coupled to the ECU  314  and provide the ECU  314  with electrical signals indicative of the inner diameter and outer diameter, respectively, of the glass tube  400  drawn from the glass boule  122  with the glass tube manufacturing device  300 . 
     In embodiments, the computer readable and executable instructions stored in the memory of the ECU  314  may be configured such that, when executed by the processor, the ECU  314  receives signals from the inner diameter gauge  310  and the outer diameter gauge  312  indicative of the inner diameter and outer diameter, respectively, of the glass tube  400  drawn from the glass boule  122  with the glass tube manufacturing device  300 . Based on these signals, the ECU  314  adjusts at least one of the flow of pressurized gas  306  emitted from the pressurized gas source  304 , the rate at which the glass boule  122  is lowered into the furnace, and the rotation (e.g., the torque and/or speed) of the at least one pair of pulling rolls  308  in order to control the dimensions (e.g., the inner diameter, outer diameter and, hence, the wall thickness) of the glass tube  400  drawn from the glass boule  122 , as will be described in further detail herein. 
     Turning now to  FIGS. 3 and 4 , in the embodiments described herein, the ECU  314  of the glass tube manufacturing device  300  controls the pressurized gas source  304  in conjunction with the at least one pair of pulling rolls  308  to draw a glass tube  400  from the glass boule  122  in the downstream direction and thereby increase the length of the glass boule  122  while increasing the inner diameter ID 1  of the glass boule  122  and decreasing the outer diameter OD 1  of the glass boule  122 , thereby converting the glass boule  122  to a glass tube  400 . To start this process, the glass boule  122  is coupled to the supply conduit  316  through the handle  200  and seal  318 . The handle  200  and seal  318  are mated such that pressurized gas  306  is emitted into the channel  126 . The inner diameter gauge  310  is positioned external to the glass tube  400  below the furnace  302 . Thereafter, the glass boule  122  is lowered into the furnace  302  and heated to a temperature above its glass transition temperature T g  at which point the glass of the glass boule  122  behaves as a viscous liquid and begins to flow. This temperature generally coincides with the glass having a viscosity from about 100 kP to about 200 kP such that the glass tube may be drawn from the glass boule  122 . As the glass begins to flow from the glass boule  122  in the downstream direction, thereby forming a glass tube  400 , the glass tube  400  is directed by the outer diameter gauge  312  and between the at least one pair of pulling rolls  308  such that the pulling rolls  308  contact and engage the outer surface of the glass tube  400  and draw the glass in the downstream direction. 
     It should be understood that the at least one pair of pulling rolls  308  are located downstream of the furnace  302  a sufficient distance to allow the glass to cool below the glass transition temperature and solidify prior to engaging with the pulling rolls  308  so as to avoid damage to the pulling rolls  308 . More specifically, the at least one pair of pulling rolls  308  is positioned to contact the outer surface of the glass tube  400  at a point at which the temperature of the glass tube  400  is below a glass transition temperature T g  of the glass tube  400  and the glass boule  122 . At temperatures below the glass transition temperature T g , the glass tube  400  behaves like an elastic solid which may be mechanically manipulated, such as with the pulling rolls  308 , without damaging the pulling rolls  308 . 
     Although the glass transition temperature T g  varies with the particular glass composition forming the glass boule  122 , and thus the glass tube  400 , the glass transition temperature T g  typically ranges from about 1200° C. to about 450° C. Accordingly, in various embodiments, the pulling rolls  308  are positioned to contact the outer surface of the glass tube  400  at a point at which the temperature of the glass tube  400  is about 50° C. below the glass transition temperature T g , about 100° C. below the glass transition temperature T g , about 200° C. below the glass transition temperature T g , about 300° C. below the glass transition temperature T g , or about 400° C. below the glass transition temperature T g . In some embodiments, the pulling rolls  308  contact the glass tube  400  at a point at which the glass tube has a temperature of between about 50° C. and about 250° C. Without being bound by theory, when the pulling rolls  308  are positioned to contact the glass tube  400  when the glass tube  400  is at a temperature below the glass transition temperature T g , the pulling rolls  308  may draw the glass tube  400  (including the defects already present in the outer surface  128  of the glass boule  122 ) and heal at least some of the surface defects and/or geometry non-uniformities through heating without introducing additional defects in the outer surface of the glass tube  400 , thereby forming a glass tube  400  having fewer defects than the glass boule  122  from which it was formed. 
     As the glass tube  400  is drawn in the downstream direction, the pressurized gas source  304  directs the pressurized gas  306  through the supply conduit  316  and into the channel  126  of the glass boule  122 . The pressurized gas  306  pressurizes the channel  126  of the glass boule  122  (which is now plastically deformable due to the heating in the furnace  302 ) and increases the inner diameter ID 1  of the glass boule  122  to an inner diameter ID 2  of the glass tube  400  by virtue of the applied pressure and the increased plasticity of the glass due to heating. 
     The increase in the inner diameter ID can be controlled by, for example, controlling the pressure of the pressurized gas  306  supplied to the channel  126  of the glass boule  122 . In embodiments, the pressure of the pressurized gas  306  emitted by the pressurized gas source  304  is regulated by the ECU  314  based on signals received from the inner diameter gauge  310 . For example, the ECU  314  may receive signals from the inner diameter gauge  310  indicative of the inner diameter ID 2  of the glass tube  400  being formed. The processor of the ECU  314  may compare the measured inner diameter ID 2  of the glass tube with a target ID value stored in the memory of the ECU  314 . When the processor determines that the target ID value is greater than the measured value of the inner diameter ID 2 , the processor of the ECU  314  sends a control signal to the pressurized gas source  304  which increases the flow rate of pressurized gas  306  emitted from the pressurized gas source  304  thereby increasing the inner diameter ID 2  of the glass tube  400 . Alternatively, when the processor determines that the target ID value is less than the measured value of the inner diameter ID 2 , the processor of the ECU  314  sends a control signal to the pressurized gas source  304  which decreases the flow rate of pressurized gas  306  emitted from the pressurized gas source  304  thereby decreasing the inner diameter ID 2  of the glass tube  400 . Thus, the inner diameter gauge  310  and the ECU  314  form a feedback loop with the pressurized gas source  304  to control the inner diameter ID 2  of the glass tube  400  by measuring the inner diameter ID 2  of the glass tube  400  and adjusting the pressure of the pressurized gas  306  based on the inner diameter ID 2  of the glass tube  400 . In various embodiments, the pressurized gas  306  is directed through the inner diameter ID 1  of the glass boule  122  at a pressure of between about 5 kPa and about 50 kPa, between about 7.5 kPa and about 25 kPa, or between about 10 kPa and about 15 kPa. 
     As the pressurized gas  306  is directed into the channel  126  of the glass boule  122 , the pulling rolls  308  pull the glass tube  400  in the downward vertical direction (i.e., in the −Z direction of the coordinate axes depicted in  FIGS. 3 and 4 ) by contacting the outer surface of the glass tube  400 . In embodiments, the ECU  314  may be employed to control the thickness of the glass tube  400  drawn from the furnace. The thickness of the glass tube  400  may be controlled by controlling the inner diameter ID 2  of the glass tube  400 , as described above, and/or controlling the outer diameter OD 2  of the glass tube  400 . For example, the decreased viscosity of the glass of the glass boule  122  combined with the drawing force exerted on the glass by the pulling rolls  308  decreases the outer diameter OD 1  of the glass boule  122  to an outer diameter OD 2  of the glass tube  400 . The change in the outer diameter OD can be controlled by, for example, controlling the speed and/or torque of the pulling rolls  308 . In embodiments, the rotation of the at least one pair of pulling rolls  308  is regulated by the ECU  314  based on signals received from the outer diameter gauge  312 . For example, the ECU  314  may receive signals from the outer diameter gauge  312  indicative of the outer diameter OD 2  of the glass tube  400  being formed. The processor of the ECU  314  may compare the measured outer diameter OD 2  of the glass tube  400  with a target OD value stored in the memory of the ECU  314 . When the processor determines that the target OD value is greater than the measured value of the outer diameter OD 2 , the processor of the ECU  314  sends a control signal to the pulling rolls  308  to decrease the speed and/or torque of the pulling rolls  308  thereby increasing the outer diameter OD 2  of the glass tube  400 . Alternatively, when the processor determines that the target OD value is less than the measured value of the outer diameter OD 2 , the processor of the ECU  314  sends a control signal to the pulling rolls  308  to increase the speed and/or torque of the pulling rolls  308  thereby increasing the outer diameter OD 2  of the glass tube  400 . Thus, the outer diameter gauge  312  and the ECU  314  can form a feedback loop with the pulling rolls  308  to control the outer diameter OD 2  of the glass tube  400  by measuring the outer diameter OD 2  of the glass tube  400  and adjusting the speed and/or torque of the pulling rolls  308  based on the outer diameter OD 2  of the glass tube  400 . In various embodiments, the pulling rolls  308  are turned at a rate that corresponds to a linear draw speed of between about 0.1 m/minute and about 60 m/minute, between about 1 m/minute and about 30 m/minute, or between about 10 m/minute and about 20 m/minute. In particular embodiments, the pulling rolls  308  contact the glass at a point at which the glass temperature is below about 200° C. 
     In one example, a glass tube was drawn from a glass boule having a 90 mm outer diameter OD 1  and having a 10 mm inner diameter ID 1  at a viscosity of about 50 kP and no pressure. The glass boule was fed into the furnace at a downfeed rate of 25 mm/min and the temperature of the furnace was about 930° C. The resultant glass tube had a 3:1 reduction ratio and resulted in a tube having a 30 mm outer diameter OD 2  with a 3.33 mm inner diameter ID 2 . However, when pressurized gas was applied to the channel of the glass boule at a pressure of about 1.5 psi, the inner diameter ID 2  increased to about 25 mm. Along with the increase in the inner diameter, the outer diameter OD 2  of the tube also increased. Accordingly, to reduce the outer diameter OD 2  of the tube back to 30 mm, the speed of the pulling rolls was increased to produce a linear draw speed of 1 m/min to yield a glass tube having a 30 mm outer diameter OD 2  and having a 25 mm inner diameter ID 2 . 
     In various embodiments, as the glass tube  400  is drawn from the glass boule  122 , the ECU  314  provides feedback to the downfeed unit  320  which, in turn, causes the downfeed unit  320  to lower the handle  200 , and thus the glass boule  122 , further down into the furnace  302 . In some embodiments, the ECU  314  can cause the downfeed unit  320  to lower the handle  200  and the glass boule  122  into the hot zone of the furnace  302  at a particular feed rate. The feed rate may be selected based on the desired inner diameter and outer diameter of the glass tube  400  and the temperature of the furnace  302 . Without being bound by theory, a fast feed rate results in a shorter glass residency time in the hot zone of the furnace  302 , which may enable a higher viscosity of the glass. Therefore, in some embodiments, the downfeed rate may be adjusted in order to control the outer diameter OD 2  and/or inner diameter ID 2  of the glass tube  400 . 
     According to various embodiments, the glass tube  400  has an outer diameter OD 2  that is less than the outer diameter OD 1  of the glass boule  122  and an inner diameter ID 2  that is greater than the inner diameter ID 1  of the glass boule  122 . The inner diameter ID 2  and the outer diameter OD 2  of the glass tube  400  may vary depending on the particular embodiment. For example, in various embodiments, the inner diameter ID 2  of the glass tube  400  is from about 0.5 mm to about 70 mm and the outer diameter OD 2  of the glass tube  400  is from about 1 mm to about 80 mm. The inner diameter ID 2  may be from about 0.75 mm to about 50 mm, from about 0.8 mm to about 40 mm, or from about 1 mm to about 35 mm. The outer diameter OD 2  may be from about 1.25 mm to about 65 mm, from about 1.5 mm to about 45 mm or from about 2 mm to about 40 mm. In various embodiments, the resultant glass tube  400  has a wall that has a thickness t of from about 0.100 mm to about 10 mm or from about 0.2 mm to about 5 mm. In some embodiments, the glass tube may have an inner diameter ID 2  of from about 1.6 mm to about 7 mm, an outer diameter OD 2  of from about 2 mm to about 10 mm and a wall thickness of from about 0.2 mm to about 1.5 mm or an inner diameter ID 2  of from about 1.8 mm to about 4 mm, an outer diameter OD 2  of from about 2 mm to about 5 mm and a wall thickness of from about 0.100 mm to about 0.5 mm. In one particular embodiment, the glass tube  400  has an inner diameter ID 2  of about 2.4 mm, an outer diameter OD 2  of about 3 mm and a wall thickness of about 0.3 mm. 
     Larger glass tubes may also be made according to the methods provided herein. In one embodiment, the glass tube may have an inner diameter ID 2  of about 8 mm, an outer diameter OD 2  of 10 mm and a wall thickness of about 1 mm. In another embodiment, the glass tube may have an inner diameter ID 2  of about 14.35 mm, an outer diameter OD 2  of about 16.75 mm and a wall thickness of about 1.2 mm. In yet another embodiment, the glass tube may have an inner diameter ID 2  of about 20 mm, an outer diameter OD 2  of about 25 mm and a wall thickness of about 2.5 mm. In other embodiments, the glass tube may have an inner diameter ID 2  of about 36 mm, an outer diameter OD 2  of about 40 mm and a wall thickness of about 2 mm or an inner diameter ID 2  of about 54 mm, an outer diameter OD 2  of about 60 mm and a wall thickness of about 3 mm. In still another embodiment, the glass tube may have an inner diameter ID 2  of about 62 mm, an outer diameter OD 2  of about 70 mm and a wall thickness of about 4 mm. Accordingly, various embodiments may provide for glass tubes of various sizes and with various wall thicknesses. 
     In one embodiment a profiled glass tube  400  can be formed from a glass boule  122  having a non-circular outer geometry. The glass boule formed from an outer mold  124  having an inner geometry that is non-circular in shape, such as oval, elliptical or polygonal, and corresponds to the opening  118  in the delivery vessel  104 . The profiled glass tube  400  drawn from the glass boule  122  may maintain its outer shape when the viscosity of the drawn tube is kept high enough (e.g., &gt;50 kP or &gt;80 kP) to prevent surface tension of the glass to distort the outside shape of tube  400 . Active cooling can be applied to the outside of the glass boule  122  while the glass boule  122  is attenuated down and transitioned to the glass tube  400  just below the draw furnace  302  Tt maintain the outside shape of tube  400  while pressurizing the inside diameter  126  of boule  122 . 
     The glass tube  400  may be cut using a tube cutter and/or otherwise converted into another product. For example, the glass tube  400  may be converted into one or more syringes, cartridges, or vials. Depending on the particular embodiment and desired product, the glass tube  400  may be converted before being cooled using the cooling fluid. Coatings or other processing, such as ion exchange, polishing, or the like, may be performed on the resulting product depending on the particular embodiment. 
     Accordingly, various embodiments described herein may be employed to form glass tubes, glass syringes, glass cartridges, glass vials, and the like from glass boules. Various embodiments enable defects in the surface of the glass boule to be drawn during formation of the glass tube, thereby reducing the amount of defects in the glass tube (and thus in the glass syringes, cartridges, and vials formed therefrom). 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.