Apparatus and method for thermally treating an annular region of an inner surface of a glass container produced from a borosilicate glass tube

Abstract

A method for thermally treating an annular region of an inner surface of a glass container produced from a borosilicate glass tube is provided. The annular region is disposed at a tubular portion of the glass container and is disposed adjacent to a glass container bottom. The method includes: forming the glass container bottom from the glass tube; heating the annular region of the inner surface of the tubular portion to a treatment temperature T.sub.Beh above the transformation temperature T.sub.G, wherein the annular region is adjacent to the glass container bottom; maintaining the treatment temperature T.sub.Beh for a certain time period; and cooling the glass container to room temperature.

Claims

1. A method for thermally treating an annular region of an inner surface of a borosilicate glass container, wherein the annular region is at a tubular portion of the glass container, the method comprising the steps of: forming a glass container bottom from a glass tube and thermally processing the glass container bottom to obtain a shape of the glass container bottom, wherein during the thermally processing of the glass container bottom a diffusion zone is formed that extends at least partially over the annular region, wherein during the thermally processing of the glass container bottom, boron accumulates in the diffusion zone, while boron simultaneously depletes in the glass container bottom; heating only the annular region of the inner surface to a treatment temperature between 700 and 1000° C.; maintaining the treatment temperature for a period of time so that boron diffuses out of the diffusion zone; and cooling the glass container to room temperature; wherein the annular region has an end facing to the glass container bottom and an end facing away from the glass container bottom, wherein the end facing to the glass container bottom has a distance L.sub.B from the inside of the glass container bottom along an axis of the glass container of 0 and 20 mm and a distance L.sub.A between the end facing to the bottom and the end facing away from the bottom is between 1 and 10 mm.

2. The method according to claim 1, wherein the period of time is between 1 and 20 seconds.

3. The method according to claim 1, wherein the heating step comprises heating with a laser from inside the glass container.

4. The method according to claim 1, wherein the heating step comprises heating by a gas burner or a laser from outside the glass container.

5. The method according to claim 1, further comprising preheating the glass container, prior to the heating step, to a preheating temperature of 400 to 660° C.

6. The method according to claim 1, further comprising preheating the glass container, prior to the heating step, so that the glass container has a viscosity of 10.sup.12.4 dPa sec or less.

7. The method according to claim 1, further comprising the step of relieving stress from the glass container in a stress relief furnace at a stress relief temperature at which a viscosity of the glass container is 10.sup.13.3 dPa sec or less.

8. The method according to claim 1, further comprising the step of blowing out vaporous boron from the glass container with a gas stream, after the forming step and before the heating step.

9. A method for thermally treating an annular region of an inner surface of a borosilicate glass container, wherein the glass container comprises a glass tube having a longitudinal axis, a first end of the glass tube, and a second end of the glass tube, the method comprising the steps of: forming a bottom of the glass container on the glass tube at the first end, wherein the bottom is a closed container bottom, wherein the container further comprises an annular region; heating only the annular region of the glass container to a treatment temperature between 700 and 1000° C., wherein the heating is done from inside the glass tube; maintaining the treatment temperature for a period of time; and cooling the glass container to room temperature after the period of time has elapsed; wherein the annular region has an end facing to the glass container bottom and an end facing away from the glass container bottom, the end facing to the glass container bottom has a distance L.sub.B from the inside of the glass container bottom along a container axis of 0 and 20 mm and the distance L.sub.A between the end facing to the bottom and the end facing away from the bottom is between 1 and 10 mm.

10. The method of claim 9, wherein the heating only the annular region of the glass container step is conducted with a laser.

11. A method for thermally treating an annular region of an inner surface of a borosilicate glass container, wherein the glass container comprises a glass tube having a longitudinal axis, a first end of the glass tube, and a second end of the glass tube, the method comprising the steps of: forming a bottom of the glass container on the glass tube at the first end, wherein the bottom is a closed container bottom, wherein the container further comprises an annular region; heating only the annular region of the glass container to a treatment temperature between 700 and 1000° C., wherein the heating is done from outside the glass tube; maintaining the treatment temperature for a period of time; and cooling the glass container to room temperature after the period of time has elapsed; wherein the annular region has an end facing to the glass container bottom and an end facing away from the glass container bottom, the end facing to the glass container bottom has a distance L.sub.B from the inside of the glass container bottom along a container axis of 0 and 20 mm and the distance L.sub.A between the end facing to the bottom and the end facing away from the bottom is between 1 and 10 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Hereinafter the invention is explained in detail based on preferred exemplary embodiments with reference to the accompanying drawings. In the drawings:

(2) FIG. 1 shows a glass container in which the evaporation, diffusion and precipitation processes taking place during the processing are shown in simplified form;

(3) FIG. 2 shows a first embodiment of a glass processing apparatus according to the invention based on a principal illustration;

(4) FIG. 3 shows a second embodiment of a glass processing apparatus according to the invention, also based on a principal illustration;

(5) FIG. 4 shows a third embodiment of a glass processing apparatus according to the invention, also based on a principal illustration;

(6) FIG. 5 shows a glass container, the annular region of which is thermally treated from the inside by means of a laser in a heat treatment station;

(7) FIG. 6 shows a glass container, the annular region of which is thermally treated from outside by means of a gas burner in a heat treatment station; and

(8) FIG. 7 shows a glass container produced by means of the method according to the invention.

DETAILED DESCRIPTION

(9) FIG. 1 shows a glass container 10 based on which the processings during the production process essential for the invention will be explained in more detail. The glass container 10 has a container axis C and is shown such as it is aligned during and immediately after the bottom formation. As mentioned above, the glass container 10 is produced from a glass tube. Consequently, the glass container 10 comprises a tubular portion 12 having an inner surface 14. In addition, a glass container bottom 16 is disposed upwardly adjacent to the tubular portion 12. Furthermore, the glass container 10 in the orientation shown comprises an open end 18 extending downwardly with a rolled rim 20, onto which, for example, a closure can be applied.

(10) As already mentioned several times, the glass container 10 is separated from the rest of the glass tube by a thermal separation process so that the glass container 10 has the highest temperature at the glass container bottom 16 during the separation process. The temperature T decreases towards the open end 18 as is indicated by the arrow. As also mentioned, the glass container bottom 16 has to be subjected to further thermal processings after the separation process in order to bring it into the desired shape. Consequently, the glass container bottom 16 is repeatedly heated, so that it has the highest temperature within the glass container 10 over several processing steps. The temperatures are above the vaporization temperatures of some components of the borosilicate glass used, so that in particular sodium evaporates from the bottom area, wherein sodium additionally entrains boron in the form of borates, so that boron is evaporated from the glass, too. At the same time a certain amount of sodium and boron diffuses back into the glass container bottom 16 and the tubular portion 12, wherein the degree of diffusion has a different temperature dependence than the degree of evaporation. The length and the direction of the arrows in FIG. 1 indicate which one of the two processes dominates. Near the bottom the evaporation dominates, whereas with decreasing temperature the diffusion is getting stronger and reaches a maximum in a diffusion zone 22. If the temperature of the glass container 10 decreases further, the diffusion process, too, is becoming increasingly weaker because it becomes increasingly difficult for sodium and boron to penetrate into the glass matrix. Below a certain temperature, neither sodium nor boron can penetrate into the glass matrix so that they form a precipitate 24 on the inner surface 14.

(11) The diffusion zone 22 is located on an annular region 23 on the inner surface 14 of the tubular portion 12 of the glass container 10. The annular region 23 has an end 26 facing to the bottom and an end 28 facing away from bottom. The end 26 facing to the bottom has a distance L.sub.B from the glass container bottom 16 in a range between approximately 0 and 20 mm. In addition, the end 28 facing away from the bottom and the end 28 facing to the bottom are spaced apart at a distance L.sub.A in a range between approximately 1 and 10 mm. Here, the annular region 23 is not necessarily congruent with the diffusion zone 22. The diffusion zone 22 is disposed on the annular region 23, but need not extend completely thereon.

(12) FIG. 2 shows a glass processing apparatus 30.sub.1 according to the invention comprising a bottom side machine 32.sub.1 and a parent machine 34 according to a first exemplary embodiment. The bottom side machine 32.sub.1 comprises a number of holding units 36, each of which comprising a chuck (not shown in detail) into which a glass tube (not shown) can be chucked. The holding units 36 or chucks on the one hand are rotatable about their own axis H and on the other hand about the axis R. In the example shown the bottom side machine 32 comprises eight holding units 36 that can be carried to a total of eight processing stations 38, which in the example shown are divided into seven primary processing stations 40.sub.1-40.sub.7 and a further processing position 42. Furthermore, the bottom side machine 32 comprises a duct system 44 by means of which a gas, such as air, can be supplied from a pressure source 46 to the holding units 36.

(13) For the production of glass container 10 of FIG. 1, a glass tube (not shown) is first chucked in a chuck 34 of the parent machine 34. An open end of the glass tube (that will eventually become open end 18) protrudes downwardly from the chuck over a predetermined amount with respect to the direction of action of the gravitational force and is subjected to various processing steps, for example, such as to form the rolled rim 20 (see FIG. 1) or a thread. If the open end is completely formed the glass tube is carried into a first primary processing station 40.sub.1, in which the chuck of the parent machine 34 and the chuck of the bottom side machine 32 are in axial alignment. The chucks of the parent machine 34 are typically located above the chucks of the bottom side machine 32, that's where the bottom side machine 32 has got its name. In the original condition the glass tube has a length of about 1.5 m so that the downwardly protruding part of the glass tube has to be separated from the remaining part for forming the glass container 10. For this purpose, the glass tube is heated at the corresponding point by a separating means 48 which comprises one or more gas burners 50.sub.1. If the required temperature is reached the holding unit 36 is axially moved upwards with the chuck of the bottom side machine 32 towards the chuck of the parent machine 34, so that it can engage the glass tube. Thereafter, the chuck is again moved downwards axially, wherein the glass tube is separated at the point at which it has been heated while forming two closed bottoms. Already in the first primary processing station 40.sub.1 a gas stream is introduced into the glass tube through the duct system 44.

(14) The glass container 10, now disposed within the chuck of the bottom side machine 32, comprises the already completely formed open end 18 as well as the closed glass container bottom 16, wherein the glass container bottom 16 has not yet the desired shape. In order to shape the glass container bottom 16 as desired it is treated in a targeted manner with additional gas burners 50.sub.2 to 50.sub.4, to which purpose the bottom side machine 32 is carried into the further primary processing stations 40.sub.2, 40.sub.3, and 40.sub.4. The gas burners 50.sub.2, 50.sub.3, and 50.sub.4 are typically adapted to the particular processing step. During the processing by the gas burners 50.sub.2 to 50.sub.4 in addition a gas stream is introduced into the now closed glass container 10. If the glass container 10 has passed through the primary fourth processing station 40.sub.4 the glass container bottom 16 is finished to such an extent that the glass container 10 now can be brought to the desired length. To this end, the glass container 10 is pressed in the primary fifth processing station 40.sub.5 against a bottom side die (not shown).

(15) Subsequently, the glass container 10 is moved to the further processing station 42 in which the annular region 23 of the inner surface 14 of the tubular portion 12 is heated to a treatment temperature T.sub.Beh which is above the transformation temperature. This thermal treatment is carried out with a gas burner 50.sub.X which heats the glass container 10 from the outside by means of a flame provided by it and maintains the glass container for the desired time period at the treatment temperature T.sub.Beh. In order to achieve a uniform thermal treatment of the annular region 23 the holding unit 36 is rotated together with the glass container 10 about the axis H. The reference symbol 50.sub.X is to clarify that the gas burner 50.sub.X is not present in conventional glass processing apparatuses and comprises certain modifications that are tailored to the specific requirements of the thermal treatment of the annular region 23. A thermal treatment by means of other heat sources, for example by means of a laser or by use of short-wave infrared radiation, is also conceivable.

(16) Depending on the embodiment of the method the glass container 10 may be blown out prior to the thermal treatment of the annular region 23, which can be implemented with the same gas which is introduced into the glass container 10 during the formation of the glass container bottom 16.

(17) Subsequently to the thermal treatment the glass container 10 is carried into the sixth primary processing station 40.sub.6 and removed from the chuck. In the seventh primary processing position 40.sub.7 usually no processing is carried out. From the sixth primary processing station 40.sub.6 the glass container 10 is then carried into a stress relief furnace 52 in which the glass container 10 is relieved by heating to a stress relief temperature. After completion of the stress relief process the glass container 10 is removed from the stress relief furnace 52 and cooled, which can be done passively by storage at room temperature or by active cooling in a cooling unit (not shown) in a targeted manner. The cooled glass container 10 can now be used.

(18) FIG. 3 shows a second exemplary embodiment of the glass processing apparatus 30.sub.2 according to the invention which also comprises a bottom side machine 32.sub.2 and a parent machine 34. Unlike the first exemplary embodiment the glass processing apparatus 30.sub.2 according to the second example comprises a commercial bottom side machine 32.sub.2 with a total of eight processing stations, namely 38.sub.1, 38.sub.2, 38.sub.3, 38.sub.4, 38.sub.5, 38.sub.6, 38.sub.7, and 38.sub.8. Here, no distinction between primary and further processing stations can be made since the thermal treatment of the annular region 23 is not carried out at the bottom side machine 32.sub.2 but in a separate heat treatment station 54. In place of the further processing station 40 of the bottom side machine 32.sub.2 in the second exemplary embodiment a processing station 38.sub.6 is provided at which the glass container 10 may be cooled.

(19) The glass container 10 is removed from the bottom side machine 32 at the seventh processing station 38.sub.7 and supplied to the heat treatment station 54, which is arranged in the processing direction of the glass container 10 between the bottom side machine 32 and the stress relief furnace 52. In the heat treatment station 54 the annular region 23 of the glass container 10 is thermally treated as described above, then stress relieved in the stress relief furnace 52 and subsequently cooled.

(20) FIG. 4 shows a third exemplary embodiment of the glass processing station 30.sub.3 according to the invention which includes only the heat treatment station 54 and the stress relief furnace 52. The heat processing station 54 and the stress relief furnace 52 are arranged spatially separated from the bottom side machine 32 and the parent machine 34. This embodiment is suitable for glass containers 10 which have been produced in a conventional manner and are now post-processed according to the invention. In this case there is a long time period between the formation of the glass container bottom 16 and the thermal treatment of the annular region 23. By means of an appropriate process control the stress relief of the glass container 10 after the thermal treatment of the annular region 23 can be omitted.

(21) FIGS. 5 and 6 show two different ways in which the annular region 23 can be thermally treated in the heat treatment station 54. In FIG. 5 the heat treatment station 54 includes a laser 56 which provides a laser beam 58. As a laser 56 in this context an apparatus should be understood by which the laser beam 58 is generated. The laser 56 has a substantially tubular guide portion 60 by means of which the laser beam 58 is guided and protected against external influences. At the same time the guide portion 60 also serves to protect persons who are staying in the immediate vicinity of the laser 56 or the laser beam 58. At the distal end of the guide portion 60 a deflection means 62 is disposed which ensures that the laser beam 58 is deflected by approximately 90° and exits radially from the guide portion 60. The guide portion 60 may comprise an opening or a window at the place where the laser beam 58 exits and is otherwise closed. Moreover, the deflection means 62 is configured so that it effects a widening of the laser beam 58. Assuming an approximately circular cross section of the laser beam 58 after exiting the laser 56 the laser beam 58 is modified upon impinging on the deflection means 62 such that it exhibits an approximately elliptical, oval or rectangular cross section.

(22) In addition, the laser 56 comprises a shifting means 64 by means of which the laser 56 may be moved forward and backward at least along the axis X of the laser beam 58 after exiting the laser 56.

(23) In the heat treatment station 54 the glass container 10 is held and transported by means of a support means 66. The support means 66 may be configured so that the glass container 10 may perform a two or three dimensional movement.

(24) The support means 66 moves the glass container 10 into a position in which the container axis C and the axis X of the laser beam 58 after exiting the laser 56 approximately lie on each another. Depending on the design of the shifting means and the support means 66 the glass container 10 is moved toward the laser 56 so that the guide portion 60 is inserted through the open end 18 into the glass container 10 to such an extent that the deflected laser beam 58 impinges onto the inner surface 14 and can cover the annular region 23 from the inside of the glass container 10. Alternatively, the laser 56 can be moved toward the glass container 10 or both components may be moved toward each other. It is also conceivable to configure the guide portion 60 telescopically, for example, so that only the guide portion 60 is moved. Then, either the glass container 10 is rotated by means of the support means 66 or the laser 56 or the guide portion 60 is rotated by means of the shifting means so that the annular region 23 is completely covered by the laser beam 58 and hence heated. The glass container 10 therefore has to be rotated by at least 360° relative to the laser 56 or the laser beam 58, wherein also a rotation about an integer multiple of 360° is conceivable, in order to maintain the annular region 23 at the treatment temperature T.sub.Beh for the entire time required.

(25) After the thermal treatment the glass container 10 is moved away from laser 56 so that the guide portion 60 no longer protrudes beyond the open end into the glass container 10. The glass container 10 can now be transported by means of the support means 66 to the stress relief furnace 52 and be further treated in the manner already explained above.

(26) FIG. 6 shows a second way how the annular region 23 of the glass container 10 may be thermally treated in the heat treatment station 54. In this case, the heat treatment station 54 comprises a gas burner 50 which is arranged stationary in the heat treatment station 54. The glass container 10 is positioned by means of the support means 66 relative to the gas burner 50 such that the annular region 23 can be thermally treated from the outside by means of the gas burner 50. Since the gas burner 50 can be rotated about the glass container 10 only with considerable mechanical effort in this case the glass container 10 is rotated about the own container axis C by means of the support means 66 so that the annular region 23 is uniformly heated to the treatment temperature T.sub.Beh.

(27) After the thermal treatment of the annular region 23 the glass container 10 can now be transported to the stress relief furnace 52 by means of the support means 66 and be further treated in the manner already described above.

(28) Instead by means of the gas burner 50 the annular region can be treated in the same manner from the outside by means of a laser 56.

(29) FIG. 7 shows a glass container 10 which has been treated by the method according to the invention. The glass container 10 comprises a plastic deformation 68 at the tubular portion 12. The plastic deformation 68 is a result of the thermal treatment of the annular region 23 from outside of the glass container 10. In the treatment from the outside the entire wall has to be heated so that the treatment temperature T.sub.Beh is achieved on the inner surface 14. Due to the low viscosities of the entire wall achieved thereby a local flow of the glass container 10 cannot be prevented. This effect can be increasingly occur when a gas burner is used for the thermal treatment since the emitted gas exerts a back pressure onto the outer surface of the glass container 10 and thus promotes the local flow. The plastic deformation 68 is typically located in the annular region 23 or between the annular region 23 and the glass container bottom 16 (see FIG. 1). The plastic deformation 68 can be used in appropriate quality checks as an evidence if a glass container 10 has been thermally treated according to the invention or not.

(30) TABLE-US-00001 LIST OF REFERENCE SYMBOLS 10 glass container 12 tubular portion 14 inner surface 16 glass container bottom 18 open end 20 rolled rim 22 diffusion zone 23 annular region 24 precipitate 26 end facing to the bottom 28 end facing away from the bottom 30, 30.sub.1-30.sub.3 glass processing apparatus 32, 32.sub.1, 32.sub.2 bottom side machine 34 parent machine 36 holding unit 38, 38.sub.1-38.sub.8 processing station 40, 40.sub.1-40.sub.7 primary processing station 42 further processing station 44 duct system 46 pressure source 48 separating means 50, 50.sub.1-50.sub.X gas burner 51 flame 52 stress relief furnace 54 heat treatment station 56 laser 58 laser beam 60 guide portion 62 deflection means 64 shifting means 66 support means 68 plastic deformation C container axis H axis of holding unit L.sub.A distance L.sub.B distance R axis of bottom side machine T.sub.Beh treatment temperature T.sub.E stress relief temperature T.sub.G transformation temperature X axis