Device for producing glass tubes by vello or down-draw method, method for producing glass tubes by vello or down-draw method and glass tubes

Abstract

To provide a device for producing glass tubes by a vello or down-draw method with minimal fluctuations in an outer diameter, a method therefor, and a glass tube.SOLUTION: A device comprises a melt feeder 3 with an outlet opening 5 for discharging a glass melt, and a shaping mandrel 9 having a shaft 11 and a shaping body 13, wherein the shaft extends through the outlet opening forming an outlet ring 15 between the shaft and a circumferential edge of the outlet opening, so that the glass melt can flow from the melt feeder through the outlet ring and over the shaping body, thereby forming a hollow glass drawing strand 19, wherein the shaping body has a first part 21 extending from a lower end of the shaft in an axial direction along a length X and having a conical outer surface, and a second part extending from a lower end of the first part in the axial direction along a length Y and having a cylindrical outer surface with an outer diameter Z, wherein a ratio X / Z is between 0.1 and 0.5 and a ratio Y / Z is between 0.02 and 0.35.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an apparatus for producing glass tubes by the Vello or downdraw process, a method for producing glass tubes by the Vello or downdraw process, and glass tubes.

[0002] Background of the Invention Large diameter glass tubes are typically drawn using the Vello or downdraw process. In this process, molten glass flows over a forming body contained within a forming mandrel. During the process, a drawn glass strand formed at the separated edge of the forming body is drawn downward through a drawing machine and cooled. When the drawn glass strand reaches a predetermined length, a predetermined length of tubing section may be separated from the drawn glass strand and sent for horizontal final processing. In addition to the force exerted by the drawing rollers of the drawing machine, the vertical orientation of the drawing process also affects the strand and the tube-forming process, and the weight of the drawn glass strand itself varies continuously due to the shearing of individual sections at the ends of the drawn glass strand.

[0003] Such variations in the weight of the drawn glass strand continuously affect the outer diameter and wall thickness of the drawn glass strand when it is formed in the region of the separating edge of the forming body. In the case of the Bellow or downdraw process, this leads to a runout path of the outer diameter along the tube axis. The length of the "runout" may correspond to the length of the tube section. The amplitude of the "runout" is a measure of the geometric quality of the produced glass tube. Therefore, it is generally desirable to further reduce the amplitude of the "runout" and thus the overall outer diameter variation.

[0004] It is therefore an object of the present invention to overcome the above-mentioned drawbacks of the state of the art by providing means which make it possible to produce glass tubes with a very uniform and large outer diameter. Furthermore, it is an object of the present invention to provide glass tubes of high quality.

[0005] Description of the Invention The object is achieved by a first aspect of the present invention, which provides an apparatus for producing a glass tube by the Vello or downdraw process, the apparatus comprising: a melt supply device having an outlet opening for discharging molten glass; and a forming mandrel having a shaft and a forming body; the shaft extends through the outlet opening forming an outlet annulus between the shaft and a periphery of the outlet opening so that molten glass can flow from the melt supply device through the outlet annulus and over the forming body, thereby forming a hollow drawn glass strand; The molded body is a first portion extending axially from the lower end of the shaft along a length X and having a conical outer surface; and a second portion extending axially along a length Y from a lower end of the first portion and having a cylindrical outer surface with an outer diameter Z; The X / Z ratio is 0.1 to 0.5, and the Y / Z ratio is 0.02 to 0.35. An apparatus is proposed.

[0006] Therefore, the present invention is based on the surprising discovery that by providing a forming body in which the dimensions of the conical and cylindrical portions are optimized, the glass flow can be "smoothed," resulting in the formation of a more uniform glass layer on the cylindrical portion. This results in a more uniform distribution of the glass mass in the drawn glass strand, significantly reducing the deviation in the outer diameter of the drawn glass strand in the axial direction. This makes it possible to obtain glass tubes with a larger outer diameter, for example, a glass tube with an outer diameter exceeding 90 mm, with a more uniform outer diameter.

[0007] Without being bound by any theory, the inventors believe that the proposed dimensions result in a more uniform temperature distribution in the flowing glass on the forming body, which in turn improves the uniform formation of the glass layer on the cylindrical portion.

[0008] This theory is supported by the observation that if the ratio of height to diameter of the conical portion is too large (i.e., if the outer surface of the conical portion along which the molten glass flows is too steep), it is no longer possible to achieve the required cooling capacity or glass layer thickness on the surface of the forming body, and the specific outer diameter and / or wall thickness of the glass tube produced cannot be achieved.

[0009] However, if the ratio of the height to the diameter of the conical portion is too low (i.e., if the outer surface of the conical portion along which the molten glass flows is too flat), the heat radiation from the glass layer increases, thus further reducing its temperature and increasing the associated viscosity. This slows the flow of the glass material over the subsequent cylindrical surface, resulting in uneven distribution of the glass gob on the now very flat, plate-like region of the forming body. Thus, in this case, the glass gob flows unevenly over the cylindrical portion of the forming body, resulting in uneven distribution of the glass gob on the cylindrical surface.

[0010] The cylindrical portion is recognized to have an important role in stabilizing the glass flow, as this is where the tube is "guided" before being drawn, and therefore together with the conical portion.

[0011] Therefore, providing a forming body according to the proposed design will result in a beneficial effect on the overall stability of the glass flow, as fewer "waves" will be introduced into the glass layer, thereby reducing the amplitude of runout in the outer diameter of the drawn glass strand and the produced glass tube.

[0012] In one embodiment, the X / Z ratio is 0.1 to 0.3, or 0.2 to 0.5.

[0013] In one embodiment, the X / Z ratio is 0.15 or greater, preferably 0.2 or greater, preferably 0.25 or greater, preferably 0.3 or greater, preferably 0.35 or greater.

[0014] In one embodiment, the X / Z ratio is less than or equal to 0.45, preferably less than or equal to 0.4, preferably less than or equal to 0.35, preferably less than or equal to 0.3, preferably less than or equal to 0.25, preferably less than or equal to 0.2, preferably less than or equal to 0.15.

[0015] In one embodiment, the Y / Z ratio is 0.02 to 0.2, or 0.15 to 0.35.

[0016] In one embodiment, the Y / Z ratio is 0.03 or greater, preferably 0.05 or greater, preferably 0.1 or greater, preferably 0.15 or greater, preferably 0.2 or greater, preferably 0.25 or greater, preferably 0.3 or greater.

[0017] In one embodiment, the Y / Z ratio is less than or equal to 0.3, preferably less than or equal to 0.25, preferably less than or equal to 0.2, preferably less than or equal to 0.15, preferably less than or equal to 0.1, preferably less than or equal to 0.05.

[0018] The outer diameter Z may be 90 mm or more, preferably 100 mm or more, preferably 120 mm or more, preferably 150 mm or more, preferably 200 mm or more, preferably 220 mm or more, preferably 250 mm or more, preferably 300 mm or more, preferably 320 mm or more, preferably 350 mm or more, preferably 400 mm or more, preferably 420 mm or more, preferably 450 mm or more, and / or 1000 mm or less, preferably 700 mm or less, preferably 500 mm or less, preferably 400 mm or less, preferably 300 mm or less, preferably 200 mm or less, preferably 100 mm or less.

[0019] Preferably, the apparatus is designed to allow molten glass to flow from the melt supply device through the outlet annulus and over the forming body along a main drawing direction. The main drawing direction may be the direction in which the glass strand is drawn from the forming body by the drawing machine. During use of the apparatus, the main drawing direction may be vertical and / or parallel to gravity, respectively.

[0020] Preferably, the conical outer surface extends conically in the direction of extension.

[0021] The general principles of the Bellow and downdraw processes are known in the art and need not be described in further detail here. It is particularly known that, in such manufacturing processes, the proposed apparatus is used, whereby molten glass flowing from a melt supply device exits through an outlet opening. The forming mandrel extends into the outlet opening and forms an outlet annular passage. Advantageously, the forming mandrel has multiple sections: an upper section, a shaft, a central conical section, a first section, a lower cylindrical section, and a second section. The diameter of the lower edge of the conical section of the forming mandrel is preferably larger than the inner diameter of the outlet opening, so that the surface of the conical section of the first section and the cylindrical section of the second section are located below the outlet annular passage. The molten glass can then flow vertically (and / or along the main elongation direction) from the melt supply device through the outlet annular passage between the edge of the outlet opening and the shaft, and continue to flow radially outward as a glass layer over the surface of the conical region of the first part and around the periphery of the cylindrical region of the second part to its lower end (the "separation edge").

[0022] In one embodiment, a first aspect may be that the first and second parts are directly axially continuous, have a common central axis, are hollow, and / or are integrally formed, the maximum outer diameter of the first part is equal to the outer diameter of the second part, the outer diameter Z is 80 mm or greater, and / or the forming mandrel is axially adjustable and / or non-rotatable relative to one another.

[0023] If the first and second sections are hollow, the processing air can be blown through the forming mandrel or a portion thereof and exit the forming mandrel at the end of the cylindrical portion of the second section, further stabilizing the glass strand as it is drawn from the forming body. Of course, the shaft of the forming mandrel can also be hollow.

[0024] If the first and second parts are integrally formed, a robust molded body can be provided, the transition between the conical and cylindrical parts can be designed smoothly, and manufacturing costs can be reduced.

[0025] Preferably, the forming mandrel, in particular the forming body, is in a fixed position relative to the melt supply device and / or cannot rotate relative to it.

[0026] The problem is solved by a second aspect of the present invention, which is a method for producing a glass tube by the Vello or downdraw process, comprising: flowing molten glass from a melt supply device, through an outlet opening of the melt supply device, and over a forming body, thereby forming a hollow drawn glass strand; The molded body is a first portion extending axially from the lower end of the shaft along a length X and having a conical outer surface; and a second portion extending axially along a length Y from a lower end of the first portion and having a cylindrical outer surface with an outer diameter Z; The X / Z ratio is 0.1 to 0.5, and the Y / Z ratio is 0.02 to 0.35. A method is proposed.

[0027] The above description of the device of the first aspect of the invention applies here as is, unless the context dictates otherwise, and therefore there is no need to repeat that description here, but reference may be made to that description.

[0028] The forming body may be included in a forming mandrel. The forming mandrel may have a shaft. Preferably, the forming mandrel is in a fixed position and / or is non-rotatable relative to the melt supply device.

[0029] In one embodiment, the method of the present invention may comprise providing an apparatus according to the first aspect of the present invention and / or cutting a predetermined length of tubing section from the drawn glass strand, particularly when the drawn glass strand has reached a predetermined length. According to other aspects of the present invention, the tubing section may be further cooled and / or formed into a glass tube.

[0030] The general principles of the Bellow or downdraw process are known in the art and need not be described in further detail. In particular, it is known that the residence time of the glass material in the forming body can be adjusted, preferably by changing the surface area of ​​the conical section (of the first part). This can also lead to variations in the radiation loss of the glass material on the forming body, thereby increasing / decreasing the temperature of the glass material and / or decreasing / increasing its viscosity. This allows for the adjustment of the thickness of the glass material on the forming body, and consequently the outer diameter and / or wall thickness of the drawn glass strand, and therefore the outer diameter and / or wall thickness of the glass tube produced. Preferably, increasing the cooling capacity of the forming body allows for the production of glass tubes with larger outer diameters and / or wall thicknesses and / or increases the drawing capacity.

[0031] Preferably, the molten glass flows from the melt supply device through an outlet opening of the melt supply device and over the forming body along a main drawing direction, which may be the direction in which the glass strand is drawn from the forming body by the drawing machine. During the production of the glass tube, the main drawing direction may be vertical and / or parallel to gravity, respectively.

[0032] In one embodiment, a second aspect may be that the first and second parts are directly axially continuous, have a common central axis, are hollow, and / or are integrally formed, and the maximum outer diameter of the first part is equal to the outer diameter of the second part, and / or the outer diameter Z is 80 mm or greater.

[0033] If the first and second sections are hollow, the processing air can be blown through the forming mandrel or a portion thereof and exit the forming mandrel at the end of the cylindrical portion of the second section, further stabilizing the glass strand as it is drawn from the forming body. Of course, the shaft of the forming mandrel can also be hollow.

[0034] If the first and second parts are integrally formed, a robust molded body can be provided, the transition between the conical and cylindrical parts can be designed smoothly, and manufacturing costs can be reduced.

[0035] The outer diameter Z may be 90 mm or more, preferably 100 mm or more, preferably 120 mm or more, preferably 150 mm or more, preferably 200 mm or more, preferably 220 mm or more, preferably 250 mm or more, preferably 300 mm or more, preferably 320 mm or more, preferably 350 mm or more, preferably 400 mm or more, preferably 420 mm or more, preferably 450 mm or more, and / or 1000 mm or less, preferably 700 mm or less, preferably 500 mm or less, preferably 400 mm or less, preferably 300 mm or less, preferably 200 mm or less, preferably 100 mm or less.

[0036] The problem is solved by a third aspect of the present invention. The third aspect of the present invention is a glass tube having a central axis, A specific cross section of the glass tube can be defined that includes the central axis and is parallel to the central axis. Within the specific cross section, for each pair of outer diameters d1 and d2 of the glass tube at two arbitrarily selected first and second axial positions x1 and x2 along the central axis, |(d2-d1) / (x2-x1)|×(10 6 mm) / d1 The relationship is 60 or less. A glass tube is proposed.

[0037] The present invention is therefore based on the surprising discovery that, for the first time, it is possible to produce glass tubes having geometric qualities that meet the strength requirements dictated by the relationships proposed above, using the device proposed in the first aspect of the invention and / or the method proposed in the second aspect of the invention.

[0038] In other words, the outer diameter of the glass tube proposed in the present invention is very uniform, that is, the amplitude of the outer diameter fluctuation is preferably very reduced.

[0039] In one embodiment, the relationship is 0.1 or greater, preferably 0.5 or greater, preferably 1 or greater, preferably 5 or greater, preferably 10 or greater, preferably 15 or greater, preferably 20 or greater, preferably 25 or greater, preferably 30 or greater, preferably 35 or greater, preferably 40 or greater, preferably 45 or greater, preferably 50 or greater, preferably 55 or greater.

[0040] For example, the above relationship is 0.1 to 60, preferably 0.1 to 40, for example, 0.1 to 30, or 20 to 40, or 20 to 60, for example, 20 to 40, or 30 to 60.

[0041] The values ​​of d1, d2, x1 and x2 are preferably all in millimeters.

[0042] Preferably, the term "glass tube" as used herein refers to a hollow glass body. A glass tube typically has a wall surrounding a lumen and two open ends.

[0043] Preferably, the term "outer diameter" as used herein refers to the maximum distance between two points on the outer surface within a particular cross section of the glass tube, the two points being connected by a line that is perpendicular to and intersects the central axis of the glass tube. A glass tube may have two or more outer diameters.

[0044] Preferably, the term "inner diameter" as used herein refers to the maximum distance between two points on the inner surface of a particular cross-section of the glass tube, the two points being connected by a line that is perpendicular to and intersects the central axis of the glass tube. A glass tube may have two or more inner diameters.

[0045] Preferably, the term "wall thickness" as used herein refers to the shortest distance between the inner and outer surfaces of the glass tube. The glass tube may have two or more wall thicknesses.

[0046] In one embodiment, as a third aspect, it may be preferred that the above relationship is 50 or less, preferably 40 or less, more preferably 30 or less, and most preferably 20 or less, that the above relationship multiplied by the length of the tube is 90,000 or less, preferably 750,000 or less, more preferably 500,000 or less, and most preferably 300,000 or less, and / or that the above relationship multiplied by the length and diameter d1 of the tube, respectively, is 40,000,000 or less, preferably 30,000,000 or less, more preferably 20,000,000 or less, and most preferably 10,000,000 or less.

[0047] In one embodiment, the relationship is 35 or less, preferably 30 or less, preferably 25 or less, preferably 20 or less, preferably 15 or less, preferably 10 or less, preferably 5 or less, preferably 3 or less, preferably 1 or less.

[0048] The problem is solved by a fourth aspect of the present invention. The fourth aspect of the present invention is a glass tube having a central axis, A specific cross section of the glass tube can be defined that includes a central axis and is parallel to the central axis, Within a particular cross section, for each pair of outer diameters d1 and d2 of the glass tube at two axial positions x1 and x2 arbitrarily selected along the central axis, (i) the relative change in outer diameter, |(d2-d1) / d2|, is less than or equal to 0.035, preferably less than or equal to 0.03, preferably less than or equal to 0.025, more preferably less than or equal to 0.02, more preferably less than or equal to 0.015, and most preferably less than or equal to 0.01, particularly when d2>d1; and / or (ii) The d1 / d2 ratio is d2 > In the case of d1, a glass tube is proposed in which d1 is 0.95 or more, preferably 0.96 or more, preferably 0.97 or more, more preferably 0.98 or more, and most preferably 0.99 or more.

[0049] The present invention is therefore based on the surprising discovery that, for the first time, it is possible to produce glass tubes having geometric qualities that meet the strength requirements dictated by the relationships proposed above, using the device proposed in the first aspect of the invention and / or the method proposed in the second aspect of the invention.

[0050] In other words, the outer diameter of the glass tube proposed in the present invention is very uniform, that is, the amplitude of the outer diameter fluctuation is preferably very reduced.

[0051] In one embodiment, the relative change in outer diameter is less than or equal to 0.027, preferably less than or equal to 0.025, preferably less than or equal to 0.023, preferably less than or equal to 0.02, preferably less than or equal to 0.017, preferably less than or equal to 0.015, preferably less than or equal to 0.013, preferably less than or equal to 0.01, preferably less than or equal to 0.007, preferably less than or equal to 0.005, preferably less than or equal to 0.003.

[0052] In one embodiment, the relative change in outer diameter is 0.001 or more, preferably 0.005 or more, preferably 0.01 or more, preferably 0.015 or more, preferably 0.02 or more, preferably 0.025 or more, preferably 0.03 or more.

[0053] In one embodiment, the ratio d1 / d2 is 0.967 or more, preferably 0.97 or more, preferably 0.973 or more, preferably 0.975 or more, preferably 0.977 or more, preferably 0.98 or more, preferably 0.983 or more, preferably 0.985 or more, preferably 0.987 or more, preferably 0.99 or more, preferably 0.993 or more, preferably 0.995 or more, preferably 0.977 or more.

[0054] In one embodiment, the ratio d1 / d2 is less than or equal to 0.9999, preferably less than or equal to 0.999, preferably less than or equal to 0.99, preferably less than or equal to 0.985, preferably less than or equal to 0.98, preferably less than or equal to 0.975, preferably less than or equal to 0.97.

[0055] The values ​​of d1 and d2 are preferably all in millimeters.

[0056] In one embodiment, as a third and / or fourth aspect, preferably (i) the relative change in outer diameter multiplied by the length of the tube is 50 or less, preferably 40 or less, more preferably 30 or less, most preferably 20 or less, most preferably 10 or less, and most preferably 5 or less; (ii) the ratio d1 / d2 multiplied by the length of the tube is 1400 or greater, preferably 1450 or greater, more preferably 1500 or greater, and most preferably 1550 or greater; (iii) the relative change in outer diameter, multiplied by the length and diameter d1 of the tube, is 14,000 or less, preferably 11,000 or less, more preferably 8,000 or less, most preferably 6,000 or less, and most preferably 4,000 or less; and / or (iv) The ratio d1 / d2, which is the product of the length and diameter d1 of the tube, is 800,000 or more, preferably 700,000 or more, more preferably 650,000 or more, and most preferably 600,000 or more.

[0057] The above relationship has been found to be particularly advantageous for glass tubes with very uniform outer diameters.

[0058] In one embodiment, as a third and / or fourth aspect, it may be preferable that the distance between x1 and x2 along the central axis is (i) half or less of the total length of the glass tube, or (ii) 400 mm or more, preferably 500 mm or more, preferably 600 mm or more, preferably 700 mm or more, preferably 800 mm or more, preferably 1000 mm or more, preferably 1200 mm or more.

[0059] The distance may be 1500 mm or more, preferably 2000 mm or more, preferably 3000 mm or more, preferably 4000 mm or more.

[0060] The distance may be 5000mm or less, preferably 3000mm or less, preferably 2000mm or less, preferably 1500mm or less, preferably 1000mm or less, preferably 800mm or less, preferably 500mm or less.

[0061] In one embodiment, as the third and / or fourth aspect, it may be preferred that d1 and d2 are each 80 mm or more, preferably 90 mm or more, preferably 100 mm or more, preferably 120 mm or more, preferably 150 mm or more, preferably 200 mm or more, preferably 220 mm or more, preferably 250 mm or more, preferably 300 mm or more, preferably 320 mm or more, preferably 350 mm or more, preferably 400 mm or more, preferably 420 mm or more, preferably 450 mm or more, and / or 1000 mm or less, preferably 700 mm or less, preferably 500 mm or less, preferably 300 mm or less, preferably 200 mm or less, preferably 100 mm or less.

[0062] Glass tubes of varying diameters have proven particularly advantageous for very uniform outer diameters.

[0063] In one embodiment, as a third and / or fourth aspect, it may be preferred that the first axial position and the second axial position are each at a distance of at least 5%, preferably at least 10%, preferably at least 20%, preferably at least 30% of the length of the glass tube from the two ends of the glass tube.

[0064] In one embodiment, as the third and / or fourth aspect, it may be preferred that the glass tube has a length of at least 0.50 m, at least 1.00 m, at least 1.5 m, at least 2.00 m, at least 2.5 m, at least 3.00 m, at least 3.5 m, or about 1.5 m.

[0065] The glass tube may also have a length of at least 0.1 m, preferably at least 0.3 m, preferably at least 0.7 m, preferably at least 1.3 m, preferably at least 1.7 m, preferably at least 2.3 m, preferably at least 2.7 m, preferably at least 3.3 m, preferably at least 3.7 m.

[0066] The glass tube may also have a length of 7 m or less, preferably 5 m or less, preferably 3 m or less.

[0067] Preferably, the length of the glass tube is measured along the central axis of the glass tube, for example, from one end of the glass tube to the other.

[0068] In one embodiment, as the third and / or fourth aspect, it may be preferred that the glass tube has a wall thickness of 0.3 mm to 20 mm at any position, preferably 1 mm to 15 mm, preferably 2 mm to 15 mm, preferably 2 mm to 10 mm.

[0069] The glass tube may have different wall thicknesses at different locations, however each wall thickness is preferably within the ranges suggested herein.

[0070] In one embodiment, as the third and / or fourth aspect, it may be preferable that the glass has a VFT constant of A in the range of -5.0 to 0.0; B in the range of 4000 to 12000; and T0 in the range of 1°C to 250°C.

[0071] Generally, the Vogel-Fulcher-Tammann (VFT) equation is used to calculate the temperature required to achieve a specific viscosity of a glass (see DIN ISO 7884-2:1998-2): lgη=A+B / T-T0

[0072] In the VFT equation, η is viscosity, A and B are temperature-independent material parameters, T is temperature, and T is the Vogel temperature. A, B, and T are constants for any particular glass.

[0073] For example, A is in the range of -3.0 to -1.0; B is in the range of 4000 to 9000, and / or T0 is in the range of 200°C to 250°C.

[0074] In one embodiment, the glass of the glass tube may have a value of B of at least 4000, at least 4500, or at least 5000. Optionally, B may be up to 12000, up to 10000, or up to 9000. T0 may be at least 1°C, at least 10°C, at least 70°C, or at least 200°C. In an embodiment, T0 is in the range of up to 250°C, or up to 230°C. A may be less than 0, for example, less than -0.5 or less than -1.0. In one embodiment, A is at least -5.0, at least -4.0, or at least -3.5. Preferably, A may reach -5.0 to 0.0 or -4.0 to 0.0.

[0075] Regarding the glass of the glass tube of the present invention, T g The temperature may be in the range of 525°C to 600°C.

[0076] In one embodiment, as the third and / or fourth aspect, it may be preferable that the glass of the glass tube is borosilicate glass.

[0077] In one embodiment, as a third and / or fourth aspect, the glass of the glass tube is [Table 1] It may be preferable to include the following components in weight percent (wt%):

[0078] The selection of glass components affects the temperature dependence of glass viscosity. For example, adding a certain amount of SiO2 decreases the value of A in the VFT equation, while increasing the value of B and T0. The table below summarizes the effects of glass components on the VFT constants. In the table, with an increase in each glass component, "+" indicates an increasing effect, "++" means a significant increase in each constant, "-" indicates a decreasing effect, and "--" means a significant decrease in each constant.

[0079] [Table 2]

[0080] The glass may contain SiO2 in a proportion of at least 50 wt%, preferably at least 55 wt%, more preferably at least 60 wt%, and most preferably at least 65 wt%, based on the total weight of the glass. SiO2 is an important network-forming component in the glass matrix and affects the glass properties. In particular, SiO2 is particularly important for the chemical resistance of the glass. The SiO2 content in the glass may be up to 90 wt%, preferably up to 85 wt%, and more preferably up to 80 wt%, based on the total weight of the glass. An excessively high SiO2 content may result in a significant increase in the softening point of the glass.

[0081] In addition to SiO2, the glass may contain at least one second network former. The glass may contain B2O3 as a further network former in a proportion of at least 3 wt. %, preferably at least 4 wt. %, and more preferably at least 6 wt. %, based on the total weight of the glass. Due to its network-forming properties, B2O3 substantially contributes to the stability of the glass. If the B2O3 content is too low, the stability required for borosilicate glass systems cannot be guaranteed. Nevertheless, the B2O3 content in the glass is at most 20 wt. %, preferably at most 15 wt. %, and more preferably at most 12 wt. % based on the total weight of the glass. If the B2O3 content in the glass is too high, the viscosity may decrease significantly, and therefore a decrease in crystallization stability must be accepted.

[0082] Furthermore, borosilicate glass can contain aluminum oxide. The addition of aluminum oxide helps improve glass formation and generally supports chemical resistance. The proportion of aluminum oxide in the glass can be up to 12% by weight, preferably up to 9% by weight, and more preferably up to 7% by weight, based on the total amount of glass. However, if the aluminum oxide content is too high, the tendency to crystallize increases. Preferably, the amount of aluminum oxide in the glass is at least 1% by weight, more preferably at least 2.5% by weight, and most preferably at least 4% by weight, based on the total amount of glass.

[0083] The glass may contain alkali metal oxides in a proportion of at least 3% by weight, preferably at least 5% by weight, and more preferably at least 6% by weight, based on the total weight of the glass. Both Na2O and KO may be present in the glass.

[0084] Alkali metal oxides improve the meltability of glass, allowing for economical production. When producing glass, alkali metal oxides act as fluxes. The total amount of alkali metal oxides in glass should not exceed 20% by weight, preferably 13% by weight, and more preferably 10% by weight. If the alkali metal oxide content is too high, the weather resistance of the glass may be weakened, which may significantly limit the range of its applications.

[0085] Optionally, the R0 / R0 ratio, which is the ratio of the total weight of alkaline earth metal oxides (e.g., CaO, BaO, SrO, and MgO) to the total weight of alkali metal oxides (e.g., NaO, KO, LiO), is at least 0.10, at least 0.15, or at least 0.20. A minimum value for this ratio helps to obtain good hydrolysis resistance without compromising the viscosity profile of the glass.

[0086] The proportion of Na2O in the glass may be at least 3 wt. %, preferably at least 5 wt. %, and more preferably at least 6 wt. %, based on the total amount of glass, although the proportion of Na2O in the glass may be limited to a maximum of 15 wt. %, preferably at most 10 wt. %, and more preferably at most 8 wt. %, based on the total amount of glass.

[0087] The proportion of K2O in the glass may be at most 5% by weight, preferably at most 3% by weight, and more preferably at most 2% by weight, relative to the total amount of glass.

[0088] In addition to the above components, borosilicate glass can also contain additives. These additives can be, for example, alkaline earth metal oxides (e.g., BaO, CaO), which can be added to the glass to manipulate the flow and melting properties or chemical resistance of the glass. Additionally or alternatively, the glass can contain oxides of d-group metals, such as iron oxide (FeO, Fe2O3, or Fe3O4). Iron oxide is a common impurity in the main components of glass, especially sand.

[0089] The proportion of BaO in the glass may be up to 6% by weight, preferably up to 4% by weight, and more preferably 3% by weight, respectively, relative to the total amount of glass.

[0090] The proportion of CaO in the glass may be up to 5% by weight, preferably up to 3% by weight, and more preferably 2% by weight, respectively, relative to the total amount of glass.

[0091] The proportion of Fe2O3 in the glass may be up to 3% by weight, preferably up to 2% by weight respectively, and more preferably 1.5% by weight relative to the total amount of glass.

[0092] The glass composition may contain titanium dioxide. The TiO content in the glass is at most 10 wt. %, preferably at most 8 wt. %, and more preferably at most 6 wt. %, based on the total weight of the glass. A very high TiO content may lead to undesirable crystallization of the glass.

[0093] In one embodiment, the glass comprises, in weight percent: [Table 3] may include: [Brief explanation of the drawings]

[0094] Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying schematic drawings. [Figure 1] 1 shows a schematic cross-sectional view of an apparatus according to a first embodiment of the present invention; [Figure 2] FIG. 3 shows a flowchart of a method according to a second aspect of the present invention. [Figure 3a] FIG. 2 shows a schematic glass tube according to a third embodiment of the present invention. [Figure 3b] 3b shows a cutaway view of the glass tube of FIG. 3a in a particular cross section. [Figure 4a]FIG. 10 shows a schematic glass tube according to a fourth embodiment of the present invention. [Figure 4b] 4b shows a cutaway view of the glass tube of FIG. 4a in a particular cross section.

[0095] Detailed Description of the Drawings FIG. 1 shows a schematic cross-sectional view of an apparatus 1 according to a first embodiment of the present invention.

[0096] The apparatus 1 comprises a melt feeder 3 having an outlet opening 5 for discharging molten glass 7 held in the melt feeder 3 , and a forming mandrel 9 having a shaft 11 and a forming body 13 .

[0097] The shaft 11 extends through the exit opening 5, thereby forming an exit annulus 15 between the shaft 11 and a periphery 17 of the exit opening 5. Molten glass 7 can therefore flow from the melt supply 3 through the exit annulus 15 and over the forming body 13, thereby forming a hollow drawn glass strand 19.

[0098] Forming body 13 has a first portion 21 extending from the lower end of shaft 11 in axial direction R along a length X and having a conical outer surface. Forming body 13 also has a second portion 23 extending from the lower end of first portion 21 in axial direction R along a length Y and having a cylindrical outer surface with an outer diameter Z.

[0099] The X / Z ratio is 0.1 to 0.5, and the Y / Z ratio is 0.02 to 0.35.

[0100] The first and second portions 21, 23 are integrally formed. The shaft 11 and forming body 13 are all hollow, allowing process air to flow through the forming mandrel 9 from top to bottom in FIG. 1. The glass draw strand 19 is drawn from the forming body 13 by a drawing device (not shown in FIG. 1) along a main drawing direction parallel to direction R. In practice, direction R is also parallel to gravity while the device 1 is in use. The glass draw strand 19 separates from the second portion at a separation edge 25.

[0101] FIG. 2 shows a flow chart of a method 100 according to a second aspect of the present invention.

[0102] In carrying out the method, an apparatus according to the first aspect of the invention may be used, such as the apparatus 1 described above with reference to FIG.

[0103] Thus, at 101, a respective apparatus 1 is provided. At 103, molten glass 7 flows from the melt supply device 3, through the outlet opening 5 of the melt supply device 3, and over the forming body 13 along the main drawing direction R, thereby forming a hollow drawn glass strand 19. At 105, when the drawn glass strand reaches a predetermined length, a tubular section of a predetermined length is cut from the drawn glass strand 19.

[0104] The tube portion is preferably a glass tube according to the third and / or fourth aspect of the invention, in particular as described below.

[0105] Figure 3a shows a glass tube 201 according to a third embodiment of the present invention, having a central axis C. Figure 3b shows a cutaway view of the glass tube 201 in a particular cross section that includes and is parallel to the central axis C. That is, the drawing plane of Figure 3b is the particular cross section.

[0106] Within a particular cross section (see FIG. 3b), for each pair of outer diameters d1 and d2 of the glass tube 201 at two arbitrarily selected first and second axial positions x1 and x2 along the central axis C, the distance between x1 and x2 along the central axis C is 400 mm or more, and the following relationship is satisfied: |(d2-d1) / (x2-x1)|×(10 6 mm) / d1 is less than 60.

[0107] Of course, Figure 3b shows only one pair of outer diameters d1 and d2. However, the above relationship holds for all pairs of outer diameters d1 and d2 selected accordingly. In Figure 3b, positions x1 and x2 are shown on coordinate axes parallel to the central axis C for illustrative purposes only.

[0108] Figure 4a is a diagram showing a glass tube 301 according to a fourth embodiment of the present invention, having a central axis C. Figure 4b is a diagram showing a cross section of the glass tube 301 in a specific cross section that includes and is parallel to the central axis C. That is, the drawing plane of Figure 4b is the specific cross section.

[0109] Within a particular cross section (see FIG. 4b), for each pair of outer diameters d1 and d2 of the glass tube 301 at two arbitrarily chosen axial positions x1 and x2 along the central axis C, when the distance between x1 and x2 along the central axis C is 400 mm or more, the relative change in outer diameter, |(d2-d1) / d2|, is less than or equal to 0.035, particularly when d2>d1.

[0110] Of course, Figure 4b shows only one pair of outer diameters d1 and d2. However, the relative changes in outer diameters described hold for all pairs of outer diameters d1 and d2 selected accordingly. In Figure 4b, positions x1 and x2 are shown on coordinate axes parallel to the central axis C for illustrative purposes only.

[0111] The features disclosed in the specification, the drawings and the claims may be essential, either alone or in any combination, for the realization of different embodiments of the invention. [Explanation of symbols]

[0112] 1 device 3 Melt supply device 5 Outlet opening 7 Molten Glass 9 forming mandrel 11 Shaft 13 Molded body 15 Exit Loop 17 Edge 19. Glass Stretched Strands 21 First Part 23 Second Part 25 Separation edge 100 Flowchart 101 Provide equipment 103 Molten glass is poured from the melt supply device over the forming body, thereby forming an elongated glass strand. 105 Separating the tube section from the drawn glass strand 201 Glass tube 301 Glass tube C center axis d1,d2 Outer diameter R direction X length x1,x2 Axial position Y length Z outer diameter

Claims

1. An apparatus for producing glass tubes by the Vello process or the downdraw process, a melt supply device having an outlet opening for discharging molten glass; Forming mandrel having a shaft and a forming body and the shaft extends through the outlet opening forming an outlet annulus between the shaft and a periphery of the outlet opening so that the molten glass can flow from the melt supply device through the outlet annulus and over the forming body, thereby forming a hollow drawn glass strand; The molded body is a first portion extending axially from a lower end of the shaft along a length X and having a conical outer surface; and a second portion extending axially along a length Y from the lower end of the first portion and having a cylindrical outer surface with an outer diameter Z; and The X / Z ratio is 0.1 to 0.5, and the Y / Z ratio is 0.02 to 0.35; Device.

2. the first and second portions are directly axially continuous, have a common central axis, are hollow, and / or are integrally formed, the maximum outer diameter of the first portion is equal to the outer diameter of the second portion, and the outer diameter Z is 80 mm or greater; and / or The apparatus of claim 1 , wherein the forming mandrel is axially adjustable and / or non-rotatable relative to the mandrel.

3. 1. A method for producing glass tube by the Vello or downdraw process, comprising: flowing molten glass from a melt supply device, through an exit opening of the melt supply device, and over a forming body, thereby forming a hollow drawn glass strand; The molded body is a first portion extending axially from a lower end of the shaft along a length X and having a conical outer surface; and a second portion extending axially along a length Y from the lower end of the first portion and having a cylindrical outer surface with an outer diameter Z; and The X / Z ratio is 0.1 to 0.5, and the Y / Z ratio is 0.02 to 0.35; method.

4. 4. The method of claim 3, wherein the first and second parts are directly axially continuous, have a common central axis, are hollow, and / or are integrally formed, and the maximum outer diameter of the first part is equal to the outer diameter of the second part, and / or the outer diameter Z is 80 mm or greater.

5. A glass tube having a central axis, A specific cross section of the glass tube can be defined that includes the central axis and is parallel to the central axis, Within the specific cross section, for each pair of outer diameters d1 and d2 of the glass tube at two first and second axial positions x1 and x2 arbitrarily selected along the central axis, |(d2-d1) / (x2-x1)|×(10 ６ mm) / d1 The relationship is 60 or less. Glass tube.

6. the relationship is 50 or less, preferably 40 or less, more preferably 30 or less, and most preferably 20 or less; said relationship multiplied by the length of said tube is equal to or less than 90,000, preferably equal to or less than 750,000, more preferably equal to or less than 500,000, and most preferably equal to or less than 300,000; and / or The relationship obtained by multiplying the length and the diameter d1 of the tube is 40,000,000 or less, preferably 30,000,000 or less, more preferably 20,000,000 or less, and most preferably 10,000,000 or less. The glass tube according to claim 5.

7. A glass tube having a central axis, A specific cross section of the glass tube can be defined that includes the central axis and is parallel to the central axis, For each pair of outer diameters d1 and d2 of the glass tube at two axial positions x1 and x2 arbitrarily selected along the central axis within the specific cross section, (i) the relative change in outer diameter, |(d2-d1) / d2|, is equal to or less than 0.035, preferably equal to or less than 0.03, preferably equal to or less than 0.025, more preferably equal to or less than 0.02, more preferably equal to or less than 0.015, and most preferably equal to or less than 0.01, particularly when d2>d1; and / or (ii) the d1 / d2 ratio, when d2>d1, is 0.95 or more, preferably 0.96 or more, preferably 0.97 or more, more preferably 0.98 or more, and most preferably 0.99 or more; Glass tube.

8. (i) the relative change in the outer diameter multiplied by the length of the tube is 50 or less, preferably 40 or less, more preferably 30 or less, most preferably 20 or less, most preferably 10 or less, and most preferably 5 or less; (ii) the ratio d1 / d2 multiplied by the length of the tube is 1400 or greater, preferably 1450 or greater, more preferably 1500 or greater, and most preferably 1550 or greater; (iii) the relative change in the outer diameter, multiplied by the length and diameter d1 of the tube, respectively, is 14,000 or less, preferably 11,000 or less, more preferably 8,000 or less, most preferably 6,000 or less, and most preferably 4,000 or less; and / or (iv) the ratio d1 / d2, calculated by multiplying the length and diameter d1 of the tube, is 800,000 or more, preferably 700,000 or more, more preferably 650,000 or more, and most preferably 600,000 or more; The glass tube according to claim 5 or 7.

9. 8. The glass tube according to claim 5 or 7, wherein the distance between x1 and x2 along the central axis is (i) half or less of the total length of the glass tube, or (ii) 400 mm or more, preferably 500 mm or more, preferably 600 mm or more, preferably 700 mm or more, preferably 800 mm or more, preferably 1000 mm or more, preferably 1200 mm or more.

10. 8. The glass tube according to claim 5 or 7, wherein d1 and d2 are each 80 mm or more, preferably 90 mm or more, preferably 100 mm or more, preferably 120 mm or more, preferably 150 mm or more, preferably 200 mm or more, preferably 220 mm or more, preferably 250 mm or more, preferably 300 mm or more, preferably 320 mm or more, preferably 350 mm or more, preferably 400 mm or more, preferably 420 mm or more, preferably 450 mm or more, and / or 1000 mm or less, preferably 700 mm or less, preferably 500 mm or less, preferably 300 mm or less, preferably 200 mm or less, preferably 100 mm or less.

11. 8. A glass tube according to claim 5 or 7, wherein the first axial position and the second axial position are respectively at a distance from the two ends of the glass tube of at least 5%, preferably at least 10%, preferably at least 20%, preferably at least 30% of the length of the glass tube.

12. 8. The glass tube of claim 5 or 7, wherein the glass tube has a length of at least 0.50 m, at least 1.00 m, at least 1.5 m, at least 2.00 m, at least 2.5 m, at least 3.00 m, at least 3.5 m, or about 1.5 m.

13. 8. Glass tube according to claim 5 or 7, wherein the glass tube has a wall thickness at any point between 0.3 mm and 20 mm, preferably between 1 mm and 15 mm, preferably between 2 mm and 15 mm, preferably between 2 mm and 10 mm.

14. The glass is A in the range of −5.0 to 0.0; B in the range of 4,000 to 12,000; and T in the range of 1°C to 250°C ０ 8. The glass tube according to claim 5 or 7, having a VFT constant of:

15. 8. The glass tube according to claim 5, wherein the glass of the glass tube is borosilicate glass.

16. The glass of the glass tube is Table 1 8. The glass tube according to claim 5 or 7, comprising the components in weight percent (wt%):

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