Method for redrawing of glass

Abstract

A drawing method for glass is described. The method provides glass components that have a strongly increased ratio of width to thickness when compared to the preform, which makes the manufacturing of flat glass components more economical. The method purposefully controls the temperature distribution within the preform.

Claims

1. An apparatus for redrawing of glass, comprising: a glass blank having a deformation zone; a deformation region for heating the glass blank when the glass blank is in the deformation region; a temperature adjuster in the deformation region, wherein the temperature adjuster adjusts a temperature distribution within the deformation zone of the glass blank so that a center region of the glass blank reaches a first temperature (T.sub.1) and edge regions of the glass blank reach a second temperature (T.sub.2), wherein the first temperature (T.sub.1) is higher than the second temperature (T.sub.2), and wherein the temperature adjuster maintains the first and second temperatures (T.sub.1, T.sub.2) over a height of at least 75% of the deformation zone of the glass blank; and at least one cooling facility to cool the edge regions to the second temperature (T.sub.2), wherein the at least one cooling facility is at a distance from a center of the glass blank, and wherein the distance decreases with a decreasing width of the glass blank, wherein the glass blank has a width B and a thickness D on a first side of the deformation region, and a width b and a thickness d on a second side of the deformation region, wherein the ratio b/d is higher than the ratio B/D by a factor of at least 17.5, and wherein the deformation zone is the part of the blank which has a thickness of 1.05*d to 0.95*D.

2. The apparatus according to claim 1, wherein the at least one cooling facility comprises one or more baffles arranged between the glass blank and a source of heat.

3. The apparatus according to claim 1, wherein the at least one cooling facility guides a fluid through the at least one cooling facility.

4. The apparatus according to claim 1, wherein the at least one cooling facility is in the deformation region.

5. The apparatus according to claim 1, wherein the at least one cooling facility is a cooling finger.

6. The apparatus according to claim 1, wherein the at least one cooling facility comprises a first tube and a second tube, the first tube having one open side, the second tube having two open sides, the second tube having a smaller cross-section than the first tube such that a first opening of the second tube is inside the one open side of the first tube.

7. The apparatus according to claim 1, further comprising a horizontal distance between the center of the glass blank and at least one cooling facility that is less than half of a width of the glass blank at a site of the horizontal distance.

8. The apparatus according to claim 1, wherein the at least one cooling facility shields at least one of the edge regions from influence of a source of heat and/or actively cools at least one of the edge regions.

9. The apparatus according to claim 1, further comprising a cooling zone directly below the deformation region.

10. The apparatus according to claim 1, further comprising a feeding facility for moving the glass blank into the deformation region.

11. The apparatus according to claim 1, further comprising a preheating zone in which the glass blank is heated to a third temperature (T.sub.w) to provide the blank with a viscosity (.sub.w) of 10.sup.10 to 10.sup.14 dPas.

12. The apparatus according to claim 1, further comprising at least one source of heat in a center region of the redrawing apparatus.

13. The apparatus of claim 1, wherein the temperature adjuster maintains the first and second temperatures (T.sub.1, T.sub.2) over the entire height of the deformation zone.

14. The apparatus of claim 1, wherein the apparatus further comprises one or more heat shields for shadowing parts of the glass blank that are beyond the deformation region and thereby achieving a temperature in these parts of the glass blank which is lower than the temperature of the glass blank in the deformation region.

Description

DESCRIPTION OF THE DRAWINGS

(1) The figures and examples exemplify the features and advantages of the present invention. The invention is not limited to the shown embodiments.

(2) FIG. 1 shows a black according to the present disclosure;

(3) FIG. 2 shows another black according to the present disclosure;

(4) FIG. 3 shows in a schematic manner an apparatus for redrawing of flat glass components according to the present disclosure;

(5) FIGS. 4a and 4b show the apparatus of FIG. 3, but here in the direction of view towards plane B of the blank; and

(6) FIGS. 5a and 5b show a cooling facility according to the present disclosure.

DETAILED DESCRIPTION

(7) In a schematic manner FIGS. 1 and 2 show a blank 10 respectively a glass component 20 having a cross-section area 12 respectively 22. Blank 10 is defined by length l.sub.v and width B. Similarly, glass component 20 is defined by length l.sub.K in the drawing direction 18 and width b.sub.K perpendicular to the drawing direction 18. The width of the edge regions 14 respectively 24 is defined as b.sub.R. In the case of the thickness of the glass component 20 it is distinguished between the edge regions 24 with an edge thickness and/or sheet edge thickness d.sub.R and a center thickness d.sub.M of the center region 26. Due to the temperature in the edge region which is lower during the method according to the present invention and the higher viscosity which is a result thereof normally the following is true: d.sub.R/d.sub.M>1.

(8) Glass component 20 is preferably featured in that in the center region 26 one or both surfaces have a smoothness of lower than 500 m, preferably lower than 100 m and particularly preferably lower than 10 m, wherein smoothness according to DIN ISO 1101 means the distance between two parallel planes including the surface in the center region 26. Furthermore, the surface roughness Ra in the center region of the component is preferably at most 20 nm. Preferably, the glass component has a thickness of at most 5 mm. However, with the method according to the present invention also substantially thinner components with for example a thickness of 1 to 2 mm or also a thickness of at most 1.0 mm, preferably at most 0.5 mm, more preferable at most 0.1 mm, such as for example 0.05 mm or even 0.01 mm can be prepared.

(9) FIG. 3 shows in a schematic manner an apparatus for redrawing of flat glass components in the direction of view towards the small side of the glass ribbon (in the figures area A). A blank 10 is inserted into a deformation region 40. The blank is heated in region 42a and is drawn to a component with a lower thickness. The blank is fixed at its upper end in a mounting facility (not shown) and by means of rollers and/or rolls 44a and 44b a drawing force can be applied on the lower end of the glass ribbon. The drawn component can be separated into sections with suitable lengths by means of a cutting device and/or separation facility 49. In an alternative embodiment the drawn glass ribbon can be coiled onto a roll. Cooling facilities are not shown in this figure.

(10) FIGS. 4a and 4b show the same apparatus for redrawing of glass components as in FIG. 3, but here in the direction of view towards plane B of the blank. Preferably, during the drawing operation the blank is continually fed into the deformation region. In this case the blank may for example be fixed at its upper end by rollers or rolls. The speed of feeding of the blank into the deformation region is preferably adjusted to the conditions in such a manner that in the direction of the thickness a uniform heat penetration of the center region and/or the edge regions of the blank is achieved. Uniform in this case means that the difference between the core and the surface temperatures in the center axis of the blank is smaller than 20 K. For guaranteeing sufficient viscosity for drawing the glass and for preventing breakage of the glass in the case of a viscosity which is too high and deformation which is too strong in the case of a viscosity which is too low during the drawing step, in the deformation region the center region of the blank is heated to a temperature T.sub.1. The temperature of the edge regions is adjusted to temperature T.sub.2. The deformation region can be heated by one or more sources of heat, such as preferably by electric heaters, flames, inductive sources of heat, short-wave infrared radiation (KIR), medium-wave infrared radiation (MIR), long-wave infrared radiation (UR) and/or laser beam.

(11) According to the present invention the blank being inserted into the deformation region is adjusted to a lower temperature T.sub.2 and thus to a higher viscosity .sub.2 in the edge regions and to a higher temperature T.sub.1 and thus to a lower viscosity .sub.1 in the center region. To adjust such a temperature difference T=T.sub.1T.sub.2 in the deformation region here it is distinguished between the sources of heat 48a and 48b which heat the edge regions and the center region of the blank, respectively. Alternatively, the edge regions may also be cooled by means of one or more cooling facilities.

(12) According to one embodiment of the invention heat is applied onto the blank in such a manner that automatically the desired temperature difference is reached in the deformation zone of the blank. For example, this is possible with a kiln as shown in FIGS. 4a and 4b. In FIG. 4b three different heating zones can be seen. The temperature may be adjusted such that the edge zones are cooler than the middle zone. Furthermore, the temperature difference between the heating regions 48a and 48b can be adjusted by intensified heating with sources of heat in heating region 48b. Preferably, the deformation region 40 in the regions 48a and 48b is equipped with separately controllable, such as for example electric sources of heat. Furthermore, optionally in addition the middle region may be heated with a laser beam, a flame and/or inductively. For example, in the middle region an optional further heat supply may be realized by means of a laser beam by guiding a laser beam with high frequency over the width of the blank in region 48b. Here it is obvious that basically heating by means of a laser beam from one side of the blank is sufficient. However also, heating by means of a laser from both sides may be conducted. The temperature difference between the heating regions 48a and 48b may also or in addition be adjusted by cooling with cooling facilities in the heating regions 48a.

(13) A preferable cooling facility is for example a cooling finger 50 as shown in FIGS. 5a and 5b. The cooling finger 50 reduces the temperature in the edge regions of the blank by shadowing the source of heat and/or active cooling. In addition, the cooling fingers may actively be cooled by a fluid such as for example air, an aerosol or a liquid so that the cooling fingers have a controlled temperature during the time of the drawing process to exactly adjust the blank temperature in the edge regions. Such a fluid may be fed into the cooling finger with ambient temperature, cooled or heated.

(14) As shown in FIGS. 5a and 5b, for such a cooling finger 50 an one-sidedly opened tube 51 may be provided in which via the opening a second two-sidedly opened tube 52 with lower cross-section, in particular coaxial, is arranged such that a first opening of the second tube is located inside the first tube. Via the second opening of the second tube a fluid can flow with a defined flow into the second tube, out of the first opening thereof, then into the first tube and via its opening out of the first tube. In addition, also baffles 53 can be used as further elements of the cooling facility which are located in the region between the edge region of the blank and the source of heat. So in a suitable manner the temperature distribution in the glass cannot only be adjusted in circumferential direction (angle segment), but at the same time also in axial direction for example of a muffle as a source of heat. According to a preferable embodiment such a cooling facility does not contact the glass ribbon at any site. This in particular prevents the occurrence of disturbing impurities and tensions as well as defects with respect to the smoothness and/or surface roughness in the glass component created. Tensions may result in breakage of the glass ribbon during cooling. Preferably, the cooling facilities are positioned in a distance from the surface of the blank of 0 to 50 cm, preferably 0.1 to 10 cm and particularly preferably 0.1 to 5 cm. With the cooling and/or heating facilities a temperature profile is created, wherein the temperature difference between edge regions and center region of the glass ribbon is preferably >0 to 100 C., preferably 10 to 60 C.

(15) In FIGS. 5a and 5b also the center M of the blank can be seen. The width of the blank decreases in a top down manner. Also the horizontal distance of center M to cooling facility 50 decreases in FIG. 5a with decreasing width (B.fwdarw.b) of the blank. Numerous other possibilities are conceivable for achieving the temperature distribution in the deformation zone according to the present invention. Besides the possibility shown in FIG. 5a, wherein a cooling facility is provided with baffles 53 of increasing width, also a cooling facility may be designed as in FIG. 5b and may for example be aligned into the direction of the center of the blank.

EXAMPLES

(16) The following table shows the results of the measures of this invention with respect to the ratio of width to thickness of the glass components prepared.

(17) TABLE-US-00001 According to the present Prior art, Prior art, invention, without with According to with low edge edge the present deformation cooler* cooler* invention zone** Width of mm 508.0 508.0 120.0 120.0 blank B Thickness of mm 6.4 6.4 14.0 14.0 blank D Ratio B/D 80.0 80.0 8.6 8.6 Width of mm 19.1 61.4 45.0 100.0 product b Thickness of mm 0.1 0.1 0.3 0.3 product d Ratio b/d 250.0 853.3 150.0 333.3 Ratio (b/d)/ 3.1 10.7 17.5 38.9 (B/D) *method according to U.S. Pat. No. 3,635,687 **in addition to the temperature distribution according to the present invention a very low heating zone (30 mm) has been chosen.

(18) It can be seen that the cooling of the edge regions may result in an increase of the ratio of width to thickness by a factor of 10.7. When the temperature distribution according to the present invention is applied in at least 75% of the deformation zone, then this may result in an additional increase of this ratio of nearly 70%. The combined use of a low deformation zone in addition results in an increase of higher than 100%. So flat glass components in substantially more efficient methods can be prepared.

LIST OF REFERENCE SIGNS

(19) 10 blank 12 cross-section area 14 edge region 16 center region 18 drawing direction 20 glass component 22 cross-section area 24 edge regions 26 center region 40 deformation region 42 deformation zone 44a, b mounting facility 46 heating facility 48a, b heating regions 49 separation facility 50 cooling finger 51 tube 52 second tube 53 baffles