Patent Application
20250206653
This application claims priority to European patent application no. 23219626.1, filed Dec. 22, 2023, which is incorporated herein by reference.
The present invention relates to a drawing head for producing a glass tube.
The Vello process is known for the production of glass tubes. It is a vertical drawing process in which the viscous glass melt is drawn off downward through a ring die. The glass melt is fed from a melting tank via a feeder channel or duct. At the end of the feeder channel, there is a cylindrical opening at the bottom with a nozzle through which the melt can flow out via a vertical cone, also called a drawing needle, which is adjustable in height and laterally and widens downward in the shape of a funnel. The cone is hollow and is connected to blowing air via an extension tube. As a result, the glass mass flowing around the valve body is kept open and can be drawn off as a glass tube downwards into a temperature-controlled shaft before it is deflected in freely suspended fashion or with the aid of a guide into a horizontal direction and drawn off by a drawing machine.
The down-draw process, which is also commonly used, is similar, with the difference that the formed glass tube is not deflected horizontally but is drawn off directly vertically downwards.
The end section of the feeder channel with the opening through which the glass melt is drawn off as a glass tube is often called the feeder head or drawing head. The above-mentioned vertical cone, i.e., the drawing needle, can be used to close the glass outlet of a drawing head which is intended for drawing glass tubes. The drawing needle is held and moved by a cylindrical extension, i.e., the needle shaft. The needle shaft protrudes from the drawing head at the upper open end. Before the glass melt leaves the drawing head via the glass outlet, it flows around the shank of the drawing needle, forming a so-called looping streak in the glass melt. A streak which may form in the glass is a chemical inhomogeneity that has a slightly different refractive index which differs from the base glass. A strongly pronounced streak can be seen with the naked eye, especially if the streak is located on the glass surface. It is also possible to make streaks visible in micrographs taken from cut cross sections of the glass tube.
DE 10 2008 009 811 A1 discloses a method for controlling and monitoring the temperature in the manufacture of glass tubes using the Vello or down-draw process. In this method a glass melt is introduced into a glass tube needle cell and metered through a nozzle ring onto a metering-drawing needle, wherein the metering-drawing needle is heated with its conical glass tube forming body. The wall of the metering-drawing needle with the connected glass tubular forming body consists of an electrically conductive material, wherein the heating is effected by current flow in the electrically conductive wall material. DE 10 2008 009 811 A1 also discloses a related device for controlling and monitoring the temperature in the manufacture of glass tubes using the Vello or down-draw process. Both the method and the device allow preventing devitrification which would manifest itself in the form of streaks on the glass tubes.
US 2017/0320766 A1 discloses bell assembly apparatuses with enhanced thermal dimensional stability that provide reduced siding loss during the production of glass tubing, and glass tubing forming apparatuses which incorporate bell assembly apparatuses with enhanced thermal dimensional stability such that undesired movement of bells within delivery orifices of glass delivery tanks due to thermal variation across the bell assembly apparatuses during glass tubing production is reduced.
US 2017/0341966 A1 discloses heating apparatuses and methods for glass tubing manufacturing. The heating apparatus includes a bowl configured to receive molten glass and a plurality of heating elements thermally coupled to the bowl, wherein the bowl includes a tub portion configured to hold the molten glass, a bowl well extending beneath the tub portion, and an orifice at a distal end of the bowl well. The plurality of heating elements include a first heating element disposed at a first vertical location along the bowl height, a second heating element disposed at a second vertical location along the bowl height, wherein the first vertical location is vertically spaced apart from the second vertical location. The heating apparatus is used to heat the molten glass as the molten glass flows from the tub portion through the bowl well and out of the orifice. The heating apparatus is configured to maintain thermal homogeneity of the molten glass exiting the orifice which mitigates variation in tube dimensions and instability in the glass tube manufacturing process.
A streak propensity of the glass undergoes a particular orientation as a result of the glass melt flowing around the needle shaft and is therefore visible as a looping streak. In the prior art it has been assumed that the looping streak is formed within the drawing head due to rejoining glass melt portions after passing the needle shaft in a stationary area and manifests itself as a streak in the manufactured glass tubes at a relatively stationary position with respect to their position relative to the forming components. If a glass tube is marked in such a way that its position can be traced as it flows out of the drawing head, the streak is found on a side of the glass tube surface which is opposite to the side of the glass inlet flow as it leaves the head. It was previously speculated that streaks forming on the surface of a drawn glass tube may be prevented by using a laterally positioned head overflow to draw off the affected portion of glass melt. This approach was however insufficient to sufficiently avoid the formation of streaks on the glass tube surface.
Drawing glass tubes with the known drawing heads, a so-called head overflow is used to suppress the formation of a looping streak in the glass melt and to thus prevent or at least mitigate the formation of streaks on the surface of the manufactured glass tubes. The glass melt drawn off via the head overflow is thereby no longer available for product manufacture, which reduces the overall yield and increases production costs.
What is needed in the art is an apparatus and a method for increased prevention of the formation of visible streaks during the manufacture of a glass tube.
The present invention relates to a drawing head for producing a glass tube and an apparatus including the drawing head. The present invention further relates to a process for producing a glass tube via a drawing process. The geometry and dimensions of the drawing head are designed in such a way that no streaks impairing the quality of the glass tubes are formed in a process according to the present invention. The the present invention meets this need.
In one aspect, the present invention provides a drawing head (1) for producing a glass tube, wherein the drawing head (1) includes a glass inlet (2) for receiving a glass melt and a glass outlet (4) for discharging the glass melt, the drawing head (1) having a total height h and an inner diameter d, characterized by one or more of the following features:
In a first aspect, the present invention provides a drawing head (1) for producing a glass tube, wherein the drawing head (1) includes a glass inlet (2) for receiving a glass melt and a glass outlet (4) for discharging the glass melt, the drawing head (1) having a total height h and an inner diameter d, the drawing head (1) further including a head overflow (5), wherein a central axis of the head overflow (5) is arranged vertically above a central axis of the glass inlet (2) by a vertical distance v, characterized in that a ratio v/h is at least 0.05/1, or at least 0.1/1.
In a second aspect, the present invention provides a drawing head (1) for producing a glass tube, wherein the drawing head (1) includes a glass inlet (2) for receiving a glass melt and a glass outlet (4) for discharging the glass melt, the drawing head (1) having a total height h and an inner diameter d, the drawing head (1) having a vertical distance c between the glass outlet (4) and a central axis of the glass inlet (2), characterized in that a ratio c/h is from 0.2/1 to 0.8/1, optionally the ratio c/h is from 0.4/1 to 0.6/1 or alternatively from 0.2/1 to 0.4/1.
In a third aspect, the present invention provides a drawing head (1) for producing a glass tube, wherein the drawing head (1) includes a glass inlet (2) for receiving a glass melt and a glass outlet (4) for discharging the glass melt, the drawing head (1) having a total height h and an inner diameter d, the drawing head (1) having a filling height of the glass melt hmelt between a glass melt level (6) and a central axis of the glass inlet (2), when in operation, characterized in that a ratio hmelt/h is at least 0.1/1, or at least 0.2/1.
In a fourth aspect, the present invention provides an apparatus for producing a glass tube including a drawing head (1) according to the present invention and a drawing needle (3).
In a related aspect, the present invention provides a process for producing a glass tube via a drawing process, including the step of passing a glass melt through an apparatus according to the present invention, wherein the process optionally includes a subsequent hot forming step.
Surprisingly, it was found that adaptations in the geometrical design of the drawing head can influence the convectional flow within the glass melt, with the result that the looping streak is no longer visible as a streak on the product. This result was also found at a greatly reduced glass discharge at the head overflow or without operating the head overflow. In the drawing heads according to the present invention, the flow of the glass melt in the drawing head is changed in such a way that the streak is displaced into the manufactured product, which is thus no longer present on the surface and is no longer visible on the product.
In a fifth aspect, the present invention provides a glass tube, wherein for any rotational position of a 3 mm thick glass tube sample in a chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum 2D slope angle of less than 20,000 arcsec and/or a maximum total wavefront error of less than 25 μm based on measuring cursors having a width of 360 μm shifted along the entire length of the outer surface line profile and of the inner surface line profile in increments of 180 μm, wherein both the outer surface line profile and the inner surface line profile have a length of 4500 μm.
In a first aspect, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, the drawing head further including a head overflow, wherein a central axis of the head overflow is arranged vertically above a central axis of the glass inlet by a vertical distance v, characterized in that a ratio v/h is at least 0.05/1, or at least 0.1/1.
In a second aspect, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, the drawing head having a vertical distance c between the glass outlet and a central axis of the glass inlet, characterized in that a ratio c/h is from 0.2/1 to 0.8/1, optionally the ratio c/h is from 0.4/1 to 0.6/1 or alternatively from 0.2/1 to 0.4/1.
In a third aspect, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, the drawing head having a filling height of the glass melt hmelt between a glass melt level and a central axis of the glass inlet, when in operation, characterized in that a ratio hmelt/h is at least 0.1/1, or at least 0.2/1.
Without being bound by theory, by way of simulations (cf.
Without being bound by theory, by way of simulations (cf.
Without being bound by theory, by way of simulations (cf.
The described features relating the ratio v/h of at least 0.05/1, the ratio c/h from 0.2/1 to 0.8/1, and the ratio hmelt/h of at least 0.1/1 may each be realised alone or in any combination with each other to reduce and/or avoid the formation of visible streaks during the manufacture of a glass tube. It shall be understood that the lower limit of the ratio v/h, the range for the ratio c/h, and the lower limit of the ratio hmelt/h shall not be interpreted in a way that leads to physically non-sensible geometric constraints on the drawing head.
In one embodiment, the ratio v/h is at least 0.05/1, or at least 0.075/1, or at least 0.1/1, or at least 0.125/1, or at least 0.15/1. In one embodiment, the ratio v/h is 0.3/1 or less, or 0.275/1 or less, or 0.25/1 or less, or 0.225/1 or less, or 0.2/1 or less. In one embodiment, the ratio v/h is from 0.05/1 to 0.3/1, or from 0.075/1 to 0.275/1, or from 0.1/1 to 0.25/1, or from 0.125/1 to 0.225/1, or from 0.15/1 to 0.2/1.
In one embodiment, the ratio c/h is from 0.2/1 to 0.8/1, optionally the ratio c/h is from 0.4/1 to 0.6/1, or alternatively from 0.2/1 to 0.4/1. In one embodiment, the ratio c/h is from 0.4/1 to 0.6/1, or from 0.425/1 to 0.575/1, or from 0.45/1 to 0.55/1, or from 0.475/1 to 0.525/1. In one embodiment, the ratio c/h is from 0.2/1 to 0.4/1, or from 0.225/1 to 0.375/1, or from 0.25/1 to 0.35/1, or from 0.275/1 to 0.325/1. In one embodiment, the ratio c/h is 0.2/1 or more, or 0.225/1 or more, or 0.25/1 or more, or 0.275/1 or more, or 0.3/1 or more, or 0.325/1 or more, or 0.35/1 or more, or 0.375/1 or more, or 0.4/1 or more, or 0.425/1 or more, or 0.45/1 or more, or 0.475/1 or more. In one embodiment, the ratio c/h is 0.8/1 or less, or 0.7/1 or less, or 0.6/1 or less, or 0.575/1 or less, or 0.55/1 or less, or 0.525/1 or less, or 0.5/1 or less, or 0.475/1 or less, or 0.45/1 or less, or 0.425/1 or less, or 0.4/1 or less, or 0.375/1 or less, or 0.35/1 or less, or 0.325/1 or less.
In one embodiment, the ratio hmelt/h is at least 0.1/1, or at least 0.15/1, or at least 0.2/1, or at least 0.25/1, or at least 0.3/1, or at least 0.35/1, or at least 0.4/1. In one embodiment, the ratio hmelt/h is 0.7/1 or less, or 0.65/1 or less, or 0.6/1 or less, or 0.55/1 or less, or 0.5/1 or less, or 0.45/1 or less, or 0.4/1 or less. In one embodiment, the ratio hmelt/h is from 0.1/1 to 0.7/1, or 0.15/1 to 0.65/1, or from 0.2/1 to 0.6/1, or 0.25/1 to 0.55/1, or from 0.3/1 to 0.5/1, or 0.35/1 to 0.45/1. In an alternative embodiment, the ratio hmelt/h is from 0.1/1 to 0.5/1, or from 0.15/1 to 0.45/1, or from 0.2/1 to 0.4/1, or from 0.25/1 to 0.35/1.
In one embodiment, the ratio h/d is from 2/1 to 7/1, or from 2.5/1 to 6.5/1, or from 3/1 to 6/1, or from 3.5/1 to 5.5/1. In one embodiment, the ratio h/d is from 3/1 to 4.5/1. In one embodiment, the ratio h/d is 2/1 or more, or 2.5/1 or more, or 3/1 or more, or 3.5/1 or more. In one embodiment, the ratio h/d is 7/1 or less, or 6.5/1 or less, or 6/1 or less, or 5.5/1 or less, or 5/1 or less, or 4.5/1 or less.
In one embodiment, the ratio di,inlet/di,overflow is between 5/1 and 1.5/1, or between 4/1 and 1.75/1, or between 3/1 and 2/1. In one embodiment, the ratio di,inlet/di,overfow is from 5/1 to 1.5/1, or from 4/1 to 1.75/1, or from 3/1 to 2/1. In one embodiment, the ratio di,inlet/di,overflow is 1.5/1 or more, or 1.75/1 or more, or 2.0/1 or more. In one embodiment, the ratio di,inlet/di,overflow is 5/1 or less, or 4/1 or less, or 3/1 or less.
In one embodiment, the inner diameter of the glass inlet di,inlet is from 100 mm to 250 mm, or from 110 mm to 240 mm, or from 120 mm to 230 mm. In one embodiment, the inner diameter of the glass inlet di,inlet is 100 mm or more, or 110 mm or more, or 120 mm or more. In one embodiment, the inner diameter of the glass inlet di,inlet is 250 mm or less, or 240 mm or less, or 230 mm or less.
In one embodiment, the inner diameter of the head overflow di,overflow is from 30 mm to 100 mm, or from 40 mm to 90 mm, or from 50 mm to 80 mm, or from 60 mm to 80 mm, or from 70 mm to 80 mm. In one embodiment, the inner diameter of the head overflow di,overflow is 30 mm or more, or 40 mm or more, or 50 mm or more, or 60 mm or more, or 70 mm or more. In one embodiment, the inner diameter of the head overflow di,overflow is 100 mm or less, or 90 mm or less, or 80 mm or less.
In one embodiment, the inner diameter d is between 120 and 400 mm, or between 135 and 350 mm, or between 150 and 300 mm. In one embodiment, the inner diameter d is from 120 to 400 mm, or from 135 to 350 mm, or from 150 to 300 mm. In one embodiment, the inner diameter d is 120 mm or more, or 135 mm or more, or 150 mm or more. In one embodiment, the inner diameter d is 400 mm or less, or 350 mm or less, or 300 mm or less.
In one embodiment, the total height h of the drawing head is from 600 mm to 1100, or from 700 mm to 1000, or from 800 mm to 950. In alternative embodiments, the total height h of the drawing head is from 600 mm to 900 mm, or from 700 mm to 1100 mm. In one embodiment, the total height h of the drawing head is 600 mm or more, or 700 mm or more, or 800 mm or more. In one embodiment, the total height h of the drawing head is 1100 mm or less, or 1000 mm or less, or 950 mm or less.
In one embodiment, the vertical distance c is from 150 mm to 700 mm, or from 200 mm to 600 mm, or from 300 mm to 550 mm. In alternative embodiments, the vertical distance c is from 150 mm to 300 mm, or from 350 mm to 550 mm. In one embodiment, the vertical distance c is 150 mm or more, or 200 mm or more, or 250 mm or more, or 300 mm or more, or 350 mm or more. In one embodiment, the vertical distance c is 700 mm or less, or 600 mm or less, or 550 mm or less, or 300 mm or less.
In one embodiment, the vertical distance v is at least 35 mm, or at least 50 mm, or at least 75 mm, or at least 100 mm, or at least 125 mm, or at least 150 mm. In one embodiment, the vertical distance v is 300 mm or less, or 275 mm or less, 250 mm or less, or 225 mm or less, or 200 mm or less. In one embodiment, the vertical distance v is from 35 mm to 300 mm, or from 50 mm to 275 mm, or from 75 mm to 250 mm, or from 100 mm to 225 mm, or from 125 mm to 200 mm, or from 150 mm to 200 mm.
In one embodiment, the drawing head further includes an inner wall. In one embodiment, the inner wall of the drawing head, which during use contacts a glass melt, may at least partially include a noble metal lining. In one embodiment, the noble metal lining can include platinum or a platinum alloy, e.g., a platinum-iridium alloy or a platinum-rhodium alloy. In one embodiment, the inner wall of the drawing head, can be provided completely or at least partially with a noble metal lining at the surface areas which come into contact with the glass melt. Platinum sheets or sheets made of platinum alloys are suitable as a noble metal lining for this purpose. On the one hand this way prevents contact between the glass melt and the material of the inner wall of the drawing head, which is commonly made of refractory materials. On the other hand contamination of the glass melt is thereby avoided. Additionally, the lifespan of the drawing head including a noble metal lining is increased.
In one embodiment, the noble metal lining has a thickness of 0.5 mm to 2 mm, or 0.8 mm to 1.2 mm. In one embodiment, the noble metal lining includes or consist of platinum or a platinum alloy, wherein the platinum or platinum alloy has a thickness of 0.8 mm to 1.2 mm.
In one embodiment, the noble metal lining can include connections for electrical heating and may be directly heated using an electrical current flowing through the noble metal lining. In one embodiment, the noble metal lining may be divided into segments which may be heated and controlled separately, resulting in the following advantages:
The drawing head according to the present invention can be optional for processing aluminosilicate glasses and borosilicate glasses, which are melted at very high temperatures and thus require high effort and high costs. The drawing head according to the present invention can achieve an increase in the directly usable glass melt quantity by approximately one fifth to one quarter which makes a process for producing a glass tube via a drawing process using the apparatus according to the present invention very economical.
The drawing head according to the present invention may be embedded in a steel construction which is further mounted in and surrounded by insulating brick. Mounting the drawing head in insulating brick is advantageous and avoids short circuits during electrical heating.
In one embodiment, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, the drawing head further including a head overflow, wherein a central axis of the head overflow is arranged vertically above a central axis of the glass inlet by a vertical distance v, characterized in that a ratio v/h is from 0.05/1 to 0.3/1, or from 0.1/1 to 0.25/1.
In one embodiment, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, wherein the drawing head has a vertical distance c between the glass outlet and a central axis of the glass inlet, with a ratio c/h from 0.4/1 to 0.6/1.
In one embodiment, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, wherein the drawing head has a vertical distance c between the glass outlet and a central axis of the glass inlet, with a ratio c/h from 0.2/1 to 0.4/1.
In one embodiment, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, wherein the drawing head has a filling height of the glass melt hmelt between a glass melt level and a central axis of the glass inlet, when in operation, characterized in that a ratio hmelt/h is from 0.1/1 to 0.7/1, or from 0.1/1 to 0.5/1.
In one embodiment, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, the drawing head further including a head overflow, wherein a central axis of the head overflow is arranged vertically above a central axis of the glass inlet by a vertical distance v, characterized in that a ratio v/h is from 0.05/1 to 0.3/1, wherein the drawing head has a vertical distance c between the glass outlet and a central axis of the glass inlet, with a ratio c/h from 0.4/1 to 0.6/1, or alternatively a ratio c/h from 0.2/1 to 0.4/1.
In one embodiment, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, wherein the drawing head has a vertical distance c between the glass outlet and a central axis of the glass inlet, wherein the total height h is from 600 mm to 1100, wherein the inner diameter d is between 120 and 400 mm, and wherein the vertical distance c is from 150 mm to 700 mm, wherein the drawing head optionally includes a head overflow with a ratio v/h from 0.05/1 to 0.3/1.
In one embodiment, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, wherein the drawing head has a vertical distance c between the glass outlet and a central axis of the glass inlet, wherein the total height h is from 700 mm to 1000, wherein the inner diameter d is between 120 and 400 mm, and wherein the vertical distance c is from 150 mm to 700 mm, wherein the drawing head optionally includes a head overflow with a ratio v/h from 0.05/1 to 0.3/1.
In one embodiment, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, wherein the drawing head has a vertical distance c between the glass outlet and a central axis of the glass inlet, wherein the total height h is from 600 mm to 1100, wherein the inner diameter d is between 150 and 300 mm, and wherein the vertical distance c is from 150 mm to 700 mm, wherein the drawing head optionally includes a head overflow with a ratio v/h from 0.05/1 to 0.3/1.
In one embodiment, the present invention provides a drawing head for producing a glass tube, wherein the drawing head includes a glass inlet for receiving a glass melt and a glass outlet for discharging the glass melt, the drawing head having a total height h and an inner diameter d, wherein the drawing head has a vertical distance c between the glass outlet and a central axis of the glass inlet, wherein the total height h is from 600 mm to 1100, wherein the inner diameter d is between 120 and 400 mm, and wherein the vertical distance c is from 150 mm to 300 mm, or the vertical distance c is from 350 mm to 550 mm, wherein the drawing head optionally includes a head overflow with a ratio v/h from 0.05/1 to 0.3/1.
In a fourth aspect, the present invention provides an apparatus for producing a glass tube including a drawing head according to the present invention and a drawing needle.
In one embodiment of the apparatus, a distance a between the drawing needle and an inner wall of the drawing head is in the range from 40 to 300 mm, optionally the distance a is in the range from 50 to 150 mm. In one embodiment, the distance a is 40 mm or more, or 50 mm or more, or 60 mm or more, or 70 mm or more, or 80 mm or more. In one embodiment, the distance a is 300 mm or less, or 150 mm or less, or 140 mm or less, or 130 mm or less, or 100 mm or less.
In the present invention, the distance a between the drawing needle and an inner wall can be understood as a position-dependent distance between any point on the surface of the needle shaft and the inner wall, which distance is measured within a horizontal plane and in a radial direction emanating from the horizontal axis of rotation of the needle shaft. The needle shaft may be oriented such that its axis of rotation is shifted with respect to the rotational axis of the drawing head which provides that the position-dependent distance a between the drawing needle and an inner wall may result in a sinusoidal functional behavior along the outer circumference of the drawing needle. It may be advantageous to position the needle shaft such that its axis of rotation is shifted with respect to the rotational axis of the drawing head in order to account for and/or mitigate viscosity differences within the glass melt. In one embodiment, the needle shaft can be oriented such that its axis of rotation is congruent to the rotational axis of the drawing head.
In one embodiment, the drawing needle has a shaft diameter s from 30 mm to 70 mm, or from 40 mm to 60 mm, or from 45 mm to 55 mm.
In a related aspect, the present invention provides a process for producing a glass tube via a drawing process, including the step of passing a glass melt through an apparatus according to the present invention, wherein the process optionally includes a subsequent hot forming step.
In one embodiment of the process, the drawing head includes a head overflow, characterized in that an amount of glass melt drawn off via the head overflow is less than 10%, optionally less than 5%, of the amount of glass melt fed into the drawing head via the glass inlet. In one embodiment, the amount of glass melt drawn off via the head overflow is 0% or more, or 0.5% or more, or 1.0% or more, or 2.0% or more. In one embodiment, the amount of glass melt drawn off via the head overflow is from 0% to 10%, or from 0.5% to 10%, or from 1.0% to 5%, or from 2.0% to 5%. The process according to the present invention may be controlled in such a way to draw off glass melt via the head overflow, if present, which may contribute to reducing and/or avoiding the formation of visible streaks during the manufacture of a glass tube. The amount of glass melt drawn off via the head overflow may be advantageously adjusted in combination with the geometric parameters of the apparatus according to the present invention.
In one embodiment of the process, the amount of glass melt discharged via the glass outlet for drawing glass tubes is substantially equal to an amount of glass melt received via the glass inlet. It is of advantage to control the process in such a way to strongly reduce or even avoid the loss of glass melt. In certain embodiments, the presence of a head overflow is either not necessary, or the amount of glass melt drawn off via the head overflow is near 0%.
In one embodiment of the process, a process temperature of the glass melt in the drawing head is substantially set, optionally controlled, by electrical heating of the noble metal lining of the drawing head. Because the noble metal lining of the drawing head is based on an electrically conductive material, whereas the mounting of the drawing head in insulating brick avoids short circuits, electrical heating becomes possible. Because the glass melt is essentially entirely surrounded by the drawing head, effective and homogenous electrical heating may be provided.
In one embodiment of the process, a filling height of the glass melt hmelt between a glass melt level and a central axis of the glass inlet has a ratio hmelt/h of at least 0.1/1, or at least 0.2/1, with the proviso that the glass melt level is between h-100 mm and h, with respect to the total height h of the drawing head.
In one embodiment of the process, the ratio hmelt/h is at least 0.1/1, or at least 0.15/1, or at least 0.2/1, or at least 0.25/1, or at least 0.3/1, or at least 0.35/1, or at least 0.4/1. In one embodiment of the process, the ratio hmelt/h is 0.7/1 or less, or 0.65/1 or less, or 0.6/1 or less, or 0.55/1 or less, or 0.5/1 or less, or 0.45/1 or less, or 0.4/1 or less. In one embodiment of the process, the ratio hmelt/h is from 0.1/1 to 0.7/1, or 0.15/1 to 0.65/1, or from 0.2/1 to 0.6/1, or 0.25/1 to 0.55/1, or from 0.3/1 to 0.5/1, or 0.35/1 to 0.45/1. In an alternative embodiment of the process, the ratio hmelt/h is from 0.1/1 to 0.5/1, or from 0.15/1 to 0.45/1, or from 0.2/1 to 0.4/1, or from 0.25/1 to 0.35/1.
If any streaks are present at all in the glass tubes of the present disclosure, the streaks are only found inside the tube and do not appear on the outer surface (11) or the inner surface (12) of the glass tubes. This can be determined in a quantitative manner by a chromatic confocal thickness measurement on tube segments of the glass tube.
In chromatic confocal thickness measurements, a white light source is used to guide the light to the measuring head with an optical fiber. The measuring head contains a lens system with a pronounced longitudinal defect, thus creating a chromatic aberration. The light, with its wavelength-dependent foci, then hits the test specimen. A wavelength is precisely focused and produces a sharp image. The reflected light is transported via the fiber to a calibrated spectrometer. A spectrometer is a device for the wavelength-dependent determination of intensities. A sharp peak with maximum intensity is generated at the discrete wavelength currently in focus. Calibration allows each discrete wavelength to be assigned a discrete distance value.
The thickness measurement corresponds to two distance measurements, since there are two interfaces in the measuring range. The prerequisite for this is that the sample is transparent to the light used. The front side of the sample is the first interface, and the back side of the sample is the second interface. At each of the two interfaces, a reflection is generated and thus an intensity peak in the spectrum. If the optical properties of the sample, refractive index and Abbe number, are known and homogeneous over the measured area, the thickness (z-value) can be calculated from the difference between the two distance measurements.
Assuming that the absolute thickness is also constant, the z-value determined is a measure of the wavefront deformation. This assumption can be made for example if the sample is polished on both sides to a predetermined thickness, in particular to a thickness of 3 mm. To verify that there is no wedge shape, the topography of both sides of the sample is measured.
This technique can be used for visualizing streaks in a glass tube in a quantitative manner. Streaks are optical disturbances that result in quantifiable wavefront deformations that can be detected by chromatic confocal thickness measurements. Glass tubes are rather specific in terms of their geometry so that special measures are required for the measurement. The measurement is done on tube segments having a thickness of 3 mm. Wavefront deviations are visible as apparent thickness variations in the measurement. For the measurement, the sample (tube segment) is clamped in a three-jaw holder, the front face of the sample facing the sensor. The sample is measured by scanning it in a meandering pattern (meander scan with (10×10) μm step size and (4500×2900) μm travel distance) resulting in measuring points defined by their position (x, y) on the tube segment and by the apparent thickness (z-value) corresponding to that position.
Due to the sample geometry and the geometry of the instrument, such a measurement generally provides measuring points only for a minor part of the sample, namely for a ring section covering only a fraction of the entire 360° sample depending on the geometry. Therefore, the sample is repeatedly rotated, for example in steps of 10° counterclockwise, and measured again and again to eventually cover the entire 360° sample after 35 rotations. Such a rotation scheme results in varying rotational positions of the sample. The initial rotational position of the sample may be referred to as the “12 o'clock position” or the “0° position”. After the first rotation, the rotational position of the sample may be referred to as the “10° position”. After the second rotation, the rotational position of the sample may be referred to as the “20° position” and so on until the “350° position” is reached after the 35th rotation. In such a manner, the wavefront deformation is measured for the entire sample based on 36 rotational positions thereof. Thus, based on measurements on the 36 rotational positions of the sample, the entire 360° sample is covered so that a z-value (wavefront deformation measured as apparent sample thickness) is provided for x-y-positions throughout the entire sample.
The step size of the rotation of the sample is chosen according to the size of the ring section covered by one measurement. In particular, the step size of the rotation is chosen to be smaller than the ring section covered by one measurement. For example, if one measurement covers 15° of the entire 360° sample, the step size of rotation may be chosen to be 10°. This ensures that no part of the sample remains unmeasured. That parts of the sample are measured twice in neighboring rotational positions is irrelevant to the outcome of the experiment because in the end the measurement aims at determining whether there are streaks at the outer surface or inner surface of the glass tube or not. If a streak is detected twice in neighboring rotational positions, this is not a problem. Rather, it is important that no streak is missed in the measurement.
The chromatic confocal thickness measurement results for each rotational position of the sample in measuring points representing the position of the measuring point on the sample as x- and y-coordinates and the corresponding wavefront deformation measured as apparent sample thickness as z-value. Thus, the data are 3-dimensional. 2D plots can be obtained by plotting the z-values against the x-coordinates for a fixed y-position. Respective 2D plots can also be referred to as “line profiles”. In general, one line profile can be plotted for each y-position based on the experimental data obtained by the chromatic confocal thickness measurement. In such line profiles, the x-position is plotted on the x-axis and the wavefront deformation measured as apparent sample thickness is plotted on the y-axis. Line profiles having a length of 4500 μm are reasonable representations of the experimental data obtained for any given rotational sample position.
In some embodiments, the line profiles are straight lines, for example as exemplarily shown in
In the present case, two line profiles are of particular interest, namely the outer surface line profile and the inner surface line profile. The reason is that streaks are particularly disadvantageous if they appear on the outer surface (11) or the inner surface (12) of the glass tubes. Thus, such streaks are desired to be identified. Streaks that are only found inside the tube are less relevant. Therefore, the outer surface line profile and the inner surface line profile are particularly relevant. If streaks are identified in one or both of these line profiles, the corresponding glass tube is disadvantageous. In contrast, if streaks are not identified in any of these two line profiles, there are at most streaks inside the glass tube which is generally not an issue.
Line profiles positioned directly at y-positions corresponding to the outer or inner surface of the glass tube are not suitable for determining presence or absence of streaks because the measurements are prone to produce artefacts in the vicinity of the interface of the sample with the surrounding. Therefore, the outer surface line profile and the inner surface line profile are determined based on the y-position of the center line profile.
The center line profile is positioned into the measured section of the glass tube sample, in particular as schematically shown in
The outer surface line profile is the line profile which is parallel to the center line profile and shifted towards the outer surface of the glass tube by 65% of the distance of the center of the center line profile from the outer surface of the glass tube measured along the radius. Likewise, the inner surface line profile is the line profile which is parallel to the center line profile and shifted towards the inner surface of the glass tube by 65% of the distance of the center of the center line profile from the inner surface of the glass tube measured along the radius. This ensures that the outer surface line profile and the inner surface line profile are close enough to the respective surfaces for giving meaningful results while at the same time they are sufficiently spaced apart from the direct interfaces of the glass tube with the surrounding to ensure absence of artefacts and thus sufficient data quality.
In order to decide based on a given line profile whether it includes a streak or not, it is necessary to analyze two parameters, namely the 2D slope angle and the total wavefront error. As streaks are local phenomena generally with extensions in x-direction of a few hundred micrometers, a global analysis of an entire line profile having a length of 4500 μm is not suitable for identification of streaks. Rather, shorter sections of the line profiles must be analyzed. For this purpose, measuring cursors having a width of 360 μm are shifted along the entire length of the line profiles in increments of 180 μm. The measuring cursors have a width of 360 μm. They are shifted along the entire length of the outer surface line profile and of the inner surface line profile in increments of 180 μm. Each of the respective line profiles has a length of 4500 μm. Thus, for each of the two line profiles there are 24 positions of the measuring cursor to cover the entire length, the first position covering the distance from 0 to 360 μm of the line profile, the second position covering the distance from 180 to 540 μm and so on until the last position covering the distance from 4140 μm to 4500 μm.
For each of the positions of the measuring cursor, the 2D slope angle and the total wavefront error (TWE) are determined. Thus, for each rotational position of the glass tube sample in the chromatic confocal thickness measurement, there are 24 values of the 2D slope angle and 24 values of the TWE. The maximum absolute value of the 2D slope angle and the maximum absolute value of the TWE can easily be determined among the respective values for each rotational position of the sample.
The outer surface line profile and the inner surface line profile of the present disclosure have a maximum absolute value of a 2D slope angle of less than 20,000 arcsec and/or a maximum absolute value of a total wavefront error of less than 25 μm. This ensures that there are no streaks on any of the outer and inner surfaces of the glass tube. Notably, a streak is only determined if both parameters exceed the indicated values. If only one of the parameters is higher, this is attributable to the presence of artefacts. For example, a very steep change from lowest to highest apparent thickness within an interval determined by the measuring cursor is irrelevant if the maximum absolute value of the TWE at the respective rotational position of the glass tube sample is small.
For a given rotational position of the glass tube sample, the maximum absolute value of the 2D slope angle and the maximum absolute value of the TWE are generally found at the same position of the measuring cursor. Even where this is not the case, data analysis is not compromised. Streaks are reliably identified based on both the maximum absolute value of the 2D slope angle and the maximum absolute value of the TWE exceeding certain thresholds at a given rotational position of the glass tube sample, independent of both maximum values being based on the same position of the measuring cursor or not.
The TWE is the difference between the highest apparent thickness and the lowest apparent thickness determined by a given position of the measuring cursor. For example, a measuring cursor covering the x-positions from 720 μm to 1080 μm of the outer surface line profile at a rotational sample position of 60° may have a readout of apparent sample thickness in a range of from 2860.1 μm to 2862.2 μm depending on the x-position. The corresponding TWE would be the difference of 2862.2 μm and 2860.1 μm, i.e. TWE=2.1 μm. For determining the TWE, the difference of maximum apparent thickness and minimum apparent thickness is calculated in the range of x-positions determined by the position of the measuring cursor on the line profile. As a smaller number is subtracted from a larger number, the TWE is always a positive number.
For a given rotational position of the glass tube sample, the maximum TWE of the outer surface line profile is the highest TWE among all 24 TWE values determined for the 24 different positions of the measuring cursor for this line profile. Likewise, the maximum TWE of the inner surface line profile is the highest TWE among all 24 TWE values determined for the 24 different positions of the measuring cursor for this line profile.
The 2D slope angle takes into account the steepness of the change from lowest to highest apparent thickness or vice versa within the interval determined by the position of the measuring cursor. The 2D slope angle is determined based on the TWE and the absolute value of the distance in x-direction of the x-positions of the corresponding maximum and minimum apparent thickness values. The 2D slope angle is a measure of the absolute value of the slope of a straight line connecting the corresponding minima and maxima.
TWE may also be written as Δy=ymax−ymin. The absolute value of the slope of a straight line connecting the corresponding minima and maxima is Δy/Δx=(ymax−ymin)/(xmax−xmin), with xmax being the x-position corresponding to ymax, and xmin being the x-position corresponding to ymin, respectively.
For example, in the above discussed example of TWE being 2.1 μm, let us assume that ymax of 2862.2 μm is at xmax=950 μm, and ymin of 2860.1 μm is at xmin=980 μm. The absolute value of the slope is 2.1 μm divided by 30 μm which is 0.07. An absolute slope of 0.07 approximately corresponds to a 2D slope angle of 4° because tan(4°) is about 0.07. Notably, a 2D slope angle of 4° is equal to 14,400 arcsec. As the absolute value of the slope is used for determining the 2D slope angle, the 2D slope angle is always a positive number.
For a given rotational position of the glass tube sample, the maximum 2D slope angle of the outer surface line profile is the highest 2D slope angle among all 24 values determined for the 24 different positions of the measuring cursor for this line profile. Likewise, the maximum 2D slope angle of the inner surface line profile is the highest 2D slope angle among all 24 values determined for the 24 different positions of the measuring cursor for this line profile.
The glass tubes of the present disclosure are characterized by low values of the TWE and/or the 2D slope angle at any rotational position of the glass tube sample.
In a fifth aspect, the present invention provides a glass tube, wherein for any rotational position of a 3 mm thick glass tube sample in a chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum 2D slope angle of less than 20,000 arcsec and/or a maximum total wavefront error of less than 25 μm based on measuring cursors having a width of 360 μm shifted along the entire length of the outer surface line profile and of the inner surface line profile in increments of 180 μm, wherein both the outer surface line profile and the inner surface line profile have a length of 4500 μm. In some embodiments, the glass tube is produced or producible by the process of the invention.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum 2D slope angle in a range of from 10 to <20,000 arcsec, for example from 20 to 15,000 arcsec, from 50 to 10,000 arcsec, from 100 to 7,500 arcsec, or from 125 to 5,000 arcsec, and/or a maximum TWE in a range of from 0.1 to <25 μm, for example from 0.2 to 20 μm, from 0.3 to 15 μm, from 0.4 to 10 μm, or from 0.5 to 7.5 μm.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum 2D slope angle of less than 20,000 arcsec, for example at most 15,000 arcsec, at most 10,000 arcsec, at most 7,500 arcsec, or at most 5,000 arcsec, and/or a maximum TWE of less than 25 μm, for example at most 20 μm, from at most 15 μm, at most 10 μm, or at most 7.5 μm.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum 2D slope angle of at least 10 arcsec, for example at least 20 arcsec, at least 50 arcsec, at least 100 arcsec, or at least 125 arcsec, and/or a maximum TWE of at least 0.1 μm, for example at least 0.2 μm, at least 0.3 μm, at least 0.4 μm, or at least 0.5 μm.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum 2D slope angle in a range of from 10 to <20,000 arcsec, for example from 20 to 15,000 arcsec, from 50 to 10,000 arcsec, from 100 to 7,500 arcsec, or from 125 to 5,000 arcsec.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum 2D slope angle of less than 20,000 arcsec, for example at most 15,000 arcsec, at most 10,000 arcsec, at most 7,500 arcsec, or at most 5,000 arcsec.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum 2D slope angle of at least 10 arcsec, for example at least 20 arcsec, at least 50 arcsec, at least 100 arcsec, or at least 125 arcsec.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum TWE in a range of from 0.1 to <25 μm, for example from 0.2 to 20 μm, from 0.3 to 15 μm, from 0.4 to 10 μm, or from 0.5 to 7.5 μm.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum TWE of less than 25 μm, for example at most 20 μm, from at most 15 μm, at most 10 μm, or at most 7.5 μm.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum TWE of at least 0.1 μm, for example at least 0.2 μm, at least 0.3 μm, at least 0.4 μm, or at least 0.5 μm.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum 2D slope angle in a range of from 10 to <20,000 arcsec, for example from 20 to 15,000 arcsec, from 50 to 10,000 arcsec, from 100 to 7,500 arcsec, or from 125 to 5,000 arcsec, and a maximum TWE in a range of from 0.1 to <25 μm, for example from 0.2 to 20 μm, from 0.3 to 15 μm, from 0.4 to 10 μm, or from 0.5 to 7.5 μm.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum 2D slope angle of less than 20,000 arcsec, for example at most 15,000 arcsec, at most 10,000 arcsec, at most 7,500 arcsec, or at most 5,000 arcsec, and a maximum TWE of less than 25 μm, for example at most 20 μm, from at most 15 μm, at most 10 μm, or at most 7.5 μm.
In some embodiments, for any rotational position of a 3 mm thick glass tube sample in the chromatic confocal thickness measurement both the outer surface line profile and the inner surface line profile have a maximum 2D slope angle of at least 10 arcsec, for example at least 20 arcsec, at least 50 arcsec, at least 100 arcsec, or at least 125 arcsec, and a maximum TWE of at least 0.1 μm, for example at least 0.2 μm, at least 0.3 μm, at least 0.4 μm, or at least 0.5 μm.
In some embodiments, the glass tube has an inner diameter in a range of from 3.0 to 300 mm, for example from 6.0 to 150 mm, from 12.5 to 75.0 mm, from 25.0 to 37.5 mm, or from 27.5 to 35.0 mm. In some embodiments, the inner diameter of the glass tube is at least 3.0 mm, for example at least 6.0 mm, at least 12.5 mm, at least 25.0 mm, or at least 27.5 mm. In some embodiments, the inner diameter of the glass tube is at most 300 mm, for example at most 150 mm, at most 75.0 mm, at most 37.5 mm, or at most 35.0 mm.
In some embodiments, the glass tube has an outer diameter in a range of from 3.5 to 350 mm, for example from 7.5 to 175 mm, from 15.0 to 85.0 mm, from 30.0 to 45.0 mm, or from 35.0 to 40.0 mm. In some embodiments, the outer diameter of the glass tube is at least 3.5 mm, for example at least 7.5 mm, at least 15.0 mm, at least 30.0 mm, or at least 35.0 mm. In some embodiments, the outer diameter of the glass tube is at most 350 mm, for example at most 175 mm, at most 85.0 mm, at most 45.0 mm, or at most 40.0 mm.
In some embodiments, the ratio of outer diameter and inner diameter of the glass tube is in a range of from 1.02 to 2.00, for example from 1.05 to 1.75, from 1.10 to 1.40, or from 1.15 to 1.25. In some embodiments, the ratio of outer diameter and inner diameter of the glass tube is at least 1.02, for example at least 1.05, at least 1.10, or at least 1.15. In some embodiments, the ratio of outer diameter and inner diameter of the glass tube is at most 2.00, for example at most 1.75, at most 1.40, or at most 1.25.
In some embodiments, the glass tube has a wall thickness in a range of from 0.3 to 30 mm, for example from 0.5 to 15 mm, from 1.0 to 10 mm, from 1.5 to 7.5 mm, from 2.0 to 5.0 mm, or from 2.5 to 3.5 mm. In some embodiments, the wall thickness of the glass tube is at least 0.3 mm, for example at least 0.5 mm, at least 1.0 mm, at least 1.5 mm, at least 2.0 mm, or at least 2.5 mm. In some embodiments, the wall thickness of the glass tube is at most 30 mm, for example at most 15 mm, at most 10 mm, at most 7.5 mm, at most 5.0 mm, or at most 3.5 mm.
In some embodiments, the ratio of the inner diameter of the glass tube to the wall thickness of the glass tube is in a range of from 1.0 to 100, for example from 2.0 to 50, from 5.0 to 25, from 7.5 to 15, or from 8.5 to 12. In some embodiments, the ratio of the inner diameter of the glass tube to the wall thickness of the glass tube is at least 1.0, for example at least 2.0 at least 5.0, at least 7.5, or at least 8.5. In some embodiments, the ratio of the inner diameter of the glass tube to the wall thickness of the glass tube is at most 100, for example at most 50, at most 25, at most 15, or at most 12.
In some embodiments, the ratio of the outer diameter of the glass tube to the wall thickness of the glass tube is in a range of from 1.2 to 125, for example from 2.5 to 65, from 5.0 to 30, from 7.5 to 20, or from 10 to 15. In some embodiments, the ratio of the outer diameter of the glass tube to the wall thickness of the glass tube is at least 1.2, for example at least 2.5, at least 5.0, at least 7.5, or at least 10. In some embodiments, the ratio of the outer diameter of the glass tube to the wall thickness of the glass tube is at most 125, for example at most 65, at most 30, at most 25, or at most 15.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
The formation of the looping streak was assessed by a simulation of the glass melt flow in the drawing head for varying geometries using the CFD-software package FLUENT. The underlying mathematical model assumes an isothermal Stokes flow of the glass melt. The mass flow of the glass melt at the inlet into the drawing head and the portion x of the mass flow which is drained via the head overflow are prescribed. The free surface of the glass melt in the drawing head is idealized as a fixed wall with zero shear stresses. Its position is prescribed according to the theoretical glass level of the furnace. No slip condition applies to the inner walls of the drawing head.
The assumptions of this mathematical model are justified by typical parameter ranges of the Vello process. The model predicts similar velocity fields for geometrically similar drawing heads. The actual velocity magnitude scales with
where {dot over (m)} is the total glass flow rate, ρ is the glass density and L is a characteristic length scale of the head geometry, e.g. the inlet diameter. A single model result is thus representative for the whole range of similar drawing head dimensions, mass flow rates and material properties of the glass.
The transport of two marker species was simulated in the model system: The first species qualitatively models a contamination of the glass resulting from the contact with the drawing needle by imposing a constant species source jn on the needle surface. The temperature of the drawing needle is lower than the temperature of the glass melt. The second species qualitatively models a contamination of the glass at the free surface, for example by evaporation effects, by imposing a constant species source js on the free surface. The diffusion coefficients Dn and Ds of the marker species were chosen sufficiently small to assess convection-dominated species transport. Consequently, the species concentrations scale with
for similar drawing head sizes. The identities
were applied, using the boundary conditions cN=cS=0 for the inlet,
for the needle, and
for the surface.
The model system thus allows comparing different drawing head geometries with respect to their propensity of looping streak formation. For this relative comparison, the actual values of the sources jn and js are not relevant. The scaled species sources (shown in
The drain flow portion, i.e., the portion which leaves the drawing head via the head overflow, was set as x=0.042.
The following conditions were established in the simulations: {dot over (m)}=580 kg h−1, ρ=2290 kg m3, η=5000 Pa·s, L=0.115 m for the inlet diameter, and Re=2.8 10−4<<1. The Stokes approximation was thus sufficient, i.e., 0=−∇*{tilde over (p)}*+Δ{right arrow over (u)}*. The provided similarity solution holds for scaled geometries, in which the mass flow and/or the viscosity can be changed, provided that Re<<1 and provided that x=const.
A segment of a glass tube having a thickness of 3 mm was tested for streaks using chromatic confocal thickness measurements.
The glass tube had an inner diameter of 31 mm and an outer diameter of 37 mm. Thus, the wall thickness was 3 mm.
The tube segment to be measured by chromatic confocal thickness measurement was cut from the glass tube with a diamond saw. The tube segment was bonded to a glass carrier at 100° C. using C-putty. Subsequently, the tube segment was coarsely ground (SiC-free grain 250). The tube segment was then further ground on a pellet disk (45 μm). Subsequently, the sample was re-bonded to the second side and the grinding steps were repeated. Therein the sample was ground to a final thickness of 3 mm and polished. The sample was de-bonded and cleaned with ethanol in an ultrasonic bath.
The sample was clamped in a polymer ring in the “Spindler & Hoyer” sample holder (three-jaw holder). The polymer ring is designed to prevent distortion of the tube section. The notch marked as the start position was aligned at “12 o'clock” or 0°. The front face was facing the sensor. The specimen was measured by scanning it in a meandering pattern. The specimen was then step-by-step rotated 10° counterclockwise and repeatedly measured again until all positions from “0° position” to “350° position” were measured.
A center line profile was placed in the center of the measuring range, as shown in
The 2D slope angles measured within the line profiles were documented. The maximum 2D slope angle of the two measuring cursors was used for the evaluation. The angle is given in the unit arcsec.
As a further measurement parameter, the total wavefront error was evaluated in the same way. The evaluated TWE was the peak-to-valley value.
Due to the manual positioning of the measuring cursors, the determined absolute values of the 2D slope angles are not necessarily exactly the absolute maximum 2D slope angles of the entire evaluation range. The same applies to the TWE. However, as exemplarily shown in
The determination of the maximum value of the 2D slope angle (see
Exemplary representations of the measurement series 1 (M1) for the rotational positions 240° and 320° are shown in
The results of all rotational positions are shown in the following Tables 1 to 3 and summarized in
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of the present invention. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23219626.1 | Dec 2023 | EP | regional |
