Tungsten containing forming mandrel for glass forming

Abstract

A molding tool, a method, and an apparatus for hot forming of glass are provided that provide glass products used for pharmaceutical packaging. The molding tool includes a forming mandrel for reshaping at least a portion of a heated region of a glass precursor. The mandrel has a temperature-stable core material and an alloying element. The core material is made of precious metals, in particular of platinum group elements, and the further alloying element is made of one of tungsten, zirconium, rhodium, molybdenum, and rhenium.

Claims

1. A molding tool for reshaping hollow-body glass precursors, comprising a forming mandrel for reshaping at least a portion of a heated region of the glass precursor, the forming mandrel comprising a temperature-stable core material and an alloying element, the core material comprises a precious metal selected from the group consisting of iridium, palladium, rhenium, ruthenium, and any combinations or alloys based thereon, and the alloying element comprises tungsten in an amount of at least 0.01 wt % wherein the forming mandrel is configured to be introduced into an interior of each hollow-body glass precursor and configured to prevent introduction of impurities into an interior of the hollow-body glass precursors.

2. The molding tool as claimed in claim 1, wherein the alloying element further comprises a material selected from the group consisting of zirconium, rhodium, molybdenum, ruthenium, and rhenium.

3. The molding tool as claimed in claim 1, wherein the core material further comprises a material selected from the group consisting of platinum, rhodium, and any combinations or alloys based thereon.

4. The molding tool as claimed in claim 1, wherein the core material further comprises at least 20 wt % of platinum.

5. The molding tool as claimed in claim 1, wherein the core material further comprises at least 5 wt % of rhodium.

6. The molding tool as claimed in claim 1, wherein the core material is a platinum-rhodium alloy including at least 20 wt % of platinum and at least 5 wt % of rhodium.

7. The molding tool as claimed in claim 1, wherein the core material is a platinum-rhodium alloy including at least 25 wt % of platinum and at least 7 wt % of rhodium.

8. The molding tool as claimed in claim 1, wherein the core material is a platinum-rhodium alloy including at least 30 wt % of platinum and at least 10 wt % of rhodium.

9. The molding tool as claimed in claim 1, wherein the core material is a platinum-nickel alloy including at least 5 wt % of nickel.

10. The molding tool as claimed in claim 1, wherein the core material is a platinum-iridium alloy including at least 5 wt % of iridium.

11. The molding tool as claimed in claim 1, wherein the core material is a platinum-iridium alloy including at least 20 wt % of iridium.

12. The molding tool as claimed in claim 1, wherein the core material comprises at least 20 wt % of iridium.

13. The molding tool as claimed in claim 1, wherein the core material comprises at least 90 wt % of iridium.

14. The molding tool as claimed in claim 1, wherein the amount of the tungsten is at least 0.9 wt %.

15. The molding tool as claimed in claim 1, wherein the amount of the tungsten is at most 5 wt %.

16. The molding tool as claimed in claim 1, wherein the core material is an iridium-tungsten alloy with at least 0.1 wt % of tungsten.

17. The molding tool as claimed in claim 16, wherein the iridium-tungsten alloy comprises 0.96 wt % of tungsten, or 1.92 wt % of tungsten, or 3.84 wt % of tungsten.

18. An apparatus for reshaping hollow-body glass precursors, comprising: a heater configured to locally heat a region of the glass precursor to above a softening point; and a molding tool having a forming mandrel for reshaping at least a portion of the region of the glass precursor, the forming mandrel comprising a temperature-stable core material and an alloying element, the core material comprises a precious metal selected from the group consisting of iridium, palladium, rhenium, ruthenium, and any combinations or alloys based thereon, and the alloying element comprises tungsten in an amount of at least 0.01 wt %, wherein the forming mandrel is configured to be introduced into an interior of each hollow-body glass precursor and configured to prevent introduction of impurities into an interior of the hollow-body glass precursors.

19. The apparatus as claimed in claim 18, wherein the heater is a laser and the apparatus further comprises a rotation device configured to rotate the molding tool and the glass precursor relative to each other, wherein the molding tool is configured so that a surface area of the portion is not covered by the molding tool so that, during reshaping, light from the laser is irradiated onto the portion.

20. A molding tool for reshaping hollow-body glass precursors, comprising: a forming mandrel comprising a temperature-stable core material and an alloying element, wherein the core material comprises a precious metal selected from the group consisting of iridium, palladium, rhenium, ruthenium, and any combinations or alloys based thereon, and wherein the alloying element comprises tungsten in an amount of at least 0.01 wt % and a material selected from the group consisting of zirconium, rhodium, molybdenum, ruthenium, and rhenium, wherein the forming mandrel is configured to be introduced into an interior of each hollow-body glass precursor and configured to prevent introduction of impurities into an interior of the hollow-body glass precursors.

21. A molding tool for reshaping hollow-body glass precursors, comprising: a forming mandrel for reshaping at least a portion of a heated region of the glass precursor, the forming mandrel comprising a temperature-stable core material and an alloying element, wherein the temperature-stable core material comprises a material selected from the platinum group elements, wherein the alloying element comprises tungsten in an amount of at least 0.01 wt % and a material selected from the group consisting of zirconium, rhodium, molybdenum, ruthenium, and rhenium, wherein the forming mandrel is configured to be introduced into an interior of each hollow-body glass precursor and configured to prevent introduction of impurities into an interior of the hollow-body glass precursors.

22. The molding tool as claimed in claim 21, wherein the amount of the tungsten is at least 0.9 wt %.

23. The molding tool as claimed in claim 21, wherein the amount of the tungsten is at most 5 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in more detail by way of preferred embodiments and with reference to the accompanying figures. Further details of the invention will be apparent from the description of the illustrated exemplary embodiments and the appended claims.

(2) FIG. 1 illustrates components of an apparatus for reshaping tubular glass;

(3) FIG. 2 shows a transmission spectrum of a glass of a glass precursor;

(4) FIGS. 3A-3F are sectional views through a tubular glass during the reshaping process;

(5) FIG. 4 is a plan view of a portion of a forming mandrel; and

(6) FIG. 5 is an overview of mass loss of different iridium-tungsten alloys at 1000 C.

DETAILED DESCRIPTION

(7) In the following detailed description of preferred embodiments, similar components in or on these embodiments are designated by the same reference numerals, for the sake of clarity. However, in order to better illustrate the invention, the preferred embodiments shown in the figures are not always drawn to scale.

(8) FIG. 1 illustrates an exemplary embodiment of an apparatus 1 for performing the method of the invention.

(9) The apparatus designated by reference numeral 1 as a whole of the exemplary embodiment shown in FIG. 1 is configured for reshaping glass precursors in the form of tubular glass 3. Specifically, the apparatus is used for producing glass syringe bodies, and the elements of apparatus 1 shown in FIG. 1 serve to form the cone of the syringe body from the tubular glass.

(10) The generation of the cone from the tubular glass by means of apparatus 1 basically comprises local heating of a region of a tubular glass 3 to above the softening point thereof, here the end 30 thereof, and reshaping of at least a portion of the heated end using at least one molding tool. In the illustrated example, the means for locally heating comprise a laser 5 which emits light of a wavelength to which the glass material of glass tube 3 is at most partially, i.e. not fully transparent, so that the light is at least partially absorbed in the glass.

(11) Instead of the laser 5 for locally heating a hollow-body glass precursor as illustrated in FIG. 1, it is of course also possible to use other means for local heating which are typically employed for glass hot forming processes. This may be a burner, for example, such as a gas burner. Since the use of such devices is well known, a detailed description thereof is omitted here.

(12) The laser beam 50 of FIG. 1 is directed onto the tubular glass 3 by means of an optical system 6. During the reshaping process, the molding tool 7 and the glass precursor 3 are rotated relative to each other, by rotation means 9. As in the illustrated example, it will usually be favorable to rotate the tubular glass 3 with the axis of rotation along the axial extension of the tubular glass 3. For this purpose, rotation means 9 comprise a drive 90 with chuck 91 which holds the tubular glass 3. Another possibility would be an inverted configuration in which the tubular glass is fixed and the molding tool 7 rotates around the tubular glass.

(13) In the exemplary embodiment shown in FIG. 1, molding tool 7 comprises two rollers 70, 71 which roll on the surface of the tubular glass 3 while the latter is rotated. The end 30 of tubular glass 30 is compressed by driving the rollers to approach each other in the radial direction of tubular glass 3. The radial movement is illustrated in FIG. 1 by arrows on the axes of rotation of rollers 70, 71.

(14) Furthermore, a forming mandrel 75 is provided as a component of molding tool 7. This forming mandrel 75 is introduced into the opening of tubular glass 3 at the end 30 to be reshaped. Using forming mandrel 75, the cone channel of the syringe body is formed. Forming mandrel 75 may be rotatably mounted so as to rotate together with tubular glass 3. It is also possible to have the rotating glass sliding on and around the stationary forming mandrel.

(15) To avoid adhesion, a releasing agent or lubricant which reduces friction in the sliding movement can be used for this purpose, as is usual with molding tools sliding over a glass surface. Furthermore, it is possible to use a lubricant which evaporates at the temperatures employed during reshaping. If such a lubricant is used, lubricant or releasing agent residues on the finished glass product can advantageously be avoided.

(16) Between rollers 70, 71 the laser beam 50 can be directed onto the tubular glass without having the laser beam 50 interrupted by the molding tool. Accordingly, the molding tool is configured so that a surface region of the portion to be reshaped of the tubular glass is not covered by the molding tool, so that by means of optical system 6 arranged downstream of the laser the laser light is irradiated onto the region not covered by the molding tool during the reshaping process. Specifically, an area 33 between rollers 70, 71 on the circumferential surface of the tubular glass 3 is illuminated by the laser light.

(17) The reshaping process is controlled by a control device 13. In particular, control device 13 drives the laser 5 so that during the reshaping process the tubular glass 3 is at least temporarily heated by the laser light.

(18) Optical system 6 of the apparatus shown in FIG. 1 comprises a deflection mirror 61 and a cylindrical lens 63.

(19) Cylindrical lens 63 is provided for expanding the laser beam 50 into a fan beam 51 along the axial direction of the tubular glass 3 so that the area 33 illuminated by the laser light is expanded accordingly in the axial direction of tubular glass 3. Since tubular glass 3 is rotated while the laser light is irradiated, the irradiated power is distributed circumferentially on the tubular glass, so that a cylindrical portion is heated, or more generally, regardless of the shape of the glass precursor, a region in the axial direction along the rotation axis. This region has a length which is preferably at least as long as the portion to be reshaped. The latter has a length which is substantially determined by the width of the rollers. To achieve special laser power distributions in the axial direction of the tubular glass, it is also possible, alternatively or in addition to the cylindrical lens 63, to advantageously use a diffractive optical element.

(20) The forming process is controlled by control device 13. Among other things, control device 13 controls the laser power. Furthermore, the movement of molding tools 70, 71, 75 is controlled. Also, rotation means 9 can be controlled, in particular the rotational speed of drive 90, optionally also the opening and closing of chuck 91.

(21) When forming glass syringe bodies, a radiation power of less than 1 kilowatt will generally be sufficient for the laser 5 to ensure rapid heating to the softening temperature. Once the intended temperature for hot forming has been reached, the laser power may then be reduced by control device 13 so that the incident laser power only compensates for cooling. When producing syringe bodies, between 30 and 100 watts will generally be sufficient for this purpose.

(22) Controlling of the laser power may in particular be accomplished based on the temperature of the tubular glass 3. For this purpose, a control process may be implemented in control device 13, which controls the laser power based on the temperature as measured by a temperature measuring device so as to adjust a predetermined temperature or a predetermined temperature/time profile on the glass precursor. In the example shown in FIG. 1, a pyrometer 11 is provided as the temperature measuring device, which measures the thermal radiation of the tubular glass at the end 30 heated by laser 5. The measured values are supplied to control device 13 and used in the control process for adjusting the desired temperature.

(23) A particular advantage of the setup as exemplified in FIG. 1 is that the laser light is not directly heating the molding tools. As a result thereof, although the glass precursor is heated during the reshaping process, the molding tools will usually not be heated more than in a process with preceding heating using a burner. Overall, less thermal energy is produced in this way, and moreover this thermal energy is introduced into the glass precursor more selectively. Thus, heating of the entire apparatus is reduced, and therefore also running-in phenomena caused by thermal expansions, inter alia.

(24) A preferred glass for the production of syringe bodies is borosilicate glass. Particularly preferred is low-alkali borosilicate glass, in particular with an alkali content of less than 10 percent by weight. Borosilicate glass is generally well suited due to its typically high thermal shock resistance which is favorable to realize rapid heating ramps at the fast processing times that can be achieved with the invention.

(25) A suitable low-alkali borosilicate glass comprises the following constituents, in percent by weight:

(26) TABLE-US-00001 SiO.sub.2 75 wt % B.sub.2O.sub.3 10.5 wt % Al.sub.2O.sub.3 5 wt % Na.sub.2O 7 wt % CaO 1.5 wt %

(27) FIG. 2 shows a transmission spectrum of the glass. The transmittance values given refer to a glass thickness of one millimeter. As can be seen from FIG. 2, transmittance of the glass decreases at wavelengths above 2.5 micrometers. Above 5 micrometers the glass is substantially opaque, even in case of very thin glass thicknesses.

(28) The decrease in transmittance in the wavelength range above 2.5 micrometers as shown in FIG. 2 does not significantly depend on the exact composition of the glass. Thus, in preferred borosilicate glasses the contents of the constituents given above may even deviate by 25% from the respective given value, with similar transmission properties. Furthermore, glasses other than borosilicate glass may of course be used as well. As long as these glasses are at most partially transparent, i.e. not fully transparent at the wavelength of the laser, a laser source can be used for heating.

(29) FIGS. 3A to 3F are sectional views schematically illustrating a simulation of a reshaping process according to the invention for forming a syringe cone from a tubular glass 3 in order to produce a syringe body. The sections of the drawings are taken along the center axis of the tubular glass 3 around which the tubular glass is rotated. Rollers 70, 71 and forming mandrel 75 can also be seen.

(30) Lines 20 as indicated in the sectional views of the tubular glass and initially extending perpendicularly to the center axis of the tubular glass are imaginary boundary lines of axial sections of the tubular glass 3. These lines are intended to illustrate the material flow during reshaping.

(31) Forming mandrel 75 protrudes from a foot 76 which serves to shape the distal cone surface of the syringe. Foot 76 is a flat component perpendicular to the viewing direction of FIGS. 3A to 3F. Other than illustrated, the foot is rotated by 90 about the longitudinal axis of forming mandrel 75 in the actual apparatus, so that foot 76 fits between rollers 70, 71. That is to say, the overlapping of rollers 70, 71 and foot 76 as seen in FIG. 3C et seq. actually does not occur.

(32) Engagement by rollers 70, 71 and initial deformation takes place starting with the position shown in FIG. 3C. Then, the tubular glass 3 is compressed by rollers 70, 71 which are moved radially inwards toward the center axis of the tubular glass. In the stage shown in FIG. 3E, forming mandrel 75 contacts the inner surface of the tubular glass and forms the channel of the syringe cone. In the stage shown in FIG. 3F, finally, the shaping of the syringe cone has already been completed. Subsequently, the molding tools are retracted from the molded syringe cone 35. Thus, all forming steps for forming the syringe cone 35 were performed with the same molding tools 70, 71, 75 and foot 76. Such a forming station therefore performs all hot forming steps on a portion of the glass precursor. Subsequently, the syringe flange or finger rest on the other end of the tubular glass can be formed.

(33) Starting from the shaping stage as illustrated in FIG. 3E it can clearly be seen that radial compression on the syringe cone 35 results in a thickening of the wall thickness. Now there is an option to cause some material flow away from end 30 by setting an appropriate temperature distribution as described above. Also, a reduced wall thickness may be caused at the peripheral edges of the reshaped tubular glass in the transition area between syringe barrel 37 and syringe cone 35. This effect may be counteracted as well, by adjusting an axially inhomogeneous power input by controlling axial distribution of the laser power.

(34) FIG. 4 illustrates a portion of a forming mandrel 75 in a plan view. Starting from the tip 80 of forming mandrel 75, a region of the forming mandrel 75 adjacent to the tip is marked, in which the forming mandrel 75 will or may contact the glass precursor during the reshaping process. A portion 82 is intended for retaining the forming mandrel 75.

(35) According to the invention, forming mandrel 75 is made from an alloy which comprises at least a first temperature-stable core material. So the core material is the basic or base material of the forming mandrel 75 and is selected from the group of precious metals, in particular of platinum group elements. Accordingly, the forming mandrel is a solid forming mandrel, at least in the region 81 which serves for reshaping. Preferably, forming mandrel 75 is of monolithic configuration.

(36) In the present example the core material is a precious metal, preferably platinum or iridium, or an appropriate platinum or iridium alloy. In addition to iridium and/or platinum, the core material of forming mandrel 75 may include palladium, rhodium, rhenium and/or ruthenium, or a corresponding alloy.

(37) In addition to the core material, the forming mandrel 75 includes another alloying element which is selected from the group consisting of tungsten, zirconium, rhodium, molybdenum, and rhenium. The amount of these alloying elements is advantageously in a range of at least 0.1 wt %, preferably at least 0.3 wt %, more preferably 0.5 wt % and most preferably at least 0.9 wt %, and not more than 10 wt %, preferably at most 6 wt %, and more preferably at most 5 wt %.

(38) In a first embodiment, the core material of the forming mandrel 75 comprises at least 20 wt % of platinum or an alloy including at least 20 wt % of platinum.

(39) In another embodiment, the core material comprises at least 5 wt % of rhodium or an alloy including at least 5 wt % of rhodium.

(40) In a further preferred embodiment, the core material comprises a platinum-rhodium alloy with at least 20 wt % of platinum and at least 5 wt % of rhodium.

(41) In yet another embodiment, the core material comprises a platinum-nickel alloy including at least 5 wt % of nickel.

(42) In yet another preferred embodiment, the core material comprises a platinum-iridium alloy including at least 5 wt %, preferably at least 10 wt %, and more preferably at least 20 wt % of iridium.

(43) In yet another preferred embodiment, the core material comprises at least 20 wt %, preferably at least 50 wt %, more preferably at least 70 wt %, and most preferably at least 90 wt % of iridium as an alloying element.

(44) In an especially preferred embodiment, iridium is chosen as the core material for the forming mandrel 75, and tungsten as the alloying element.

(45) Very suitable for reshaping a tubular glass made of borosilicate glass using a molding tool 1 as described above is a material for the forming mandrel 75 which comprises an iridium-tungsten alloy with at least 0.01 wt %, 0.05 wt %, 0.1 wt %, preferably at least 0.3 wt %, more preferably at least 0.5 wt %, and most preferably at least 1 wt % of tungsten. It is furthermore advantageous if the tungsten content is not more than 10 wt %, preferably at most 6 wt %, and more preferably at most 5 wt %. A particularly suitable forming mandrel 75 comprises an iridium-tungsten alloy with 0.96 wt %, 1.92 wt %, or 3.84 wt % of tungsten.

(46) The comparatively high hardness and high recrystallization temperature of iridium have a very positive effect on the service life of forming mandrel 75 during the reshaping of borosilicate glass. This even enables reshaping processes at temperatures above 800 C. or above 900 C. This is further promoted by the high acid resistance of tungsten.

(47) Even after a great many of processing cycles or reshaping operations, such as between 8,000 and 10,000 cycles, the forming mandrel 75 did not show any tendency to cracking on the surface or any other signs of wear.

(48) Due to the low wear, in particular due to the low material erosion of the forming mandrel 75 comprising an iridium-tungsten alloy, it was observed that the degree of contamination with tungsten was very low.

(49) It could be observed that the use of a forming mandrel 75 on the basis of an iridium-tungsten alloy with a tungsten content of about 1 wt % results in a particularly long service life of the forming mandrel 75. At the same time this low material erosion has the advantage that contamination with tungsten is particularly low.

(50) Glass syringes, preferably made of borosilicate glass, which were reshaped using the aforementioned molding tool had a very low tungsten content in the reshaped cavity.

(51) Syringes reshaped using forming mandrel 75 can be obtained which have a tungsten content within the cavity of the syringe of less than 50 ng, preferably less than 30 ng, more preferably less than 10 ng per syringe.

(52) In a particularly preferred embodiment, the tungsten content within the cavity of a syringe that has been reshaped using the forming mandrel 75 is between 1 and 10 ng per syringe, preferably between 1 and 5 ng per syringe, and more preferably between 1 and 3 ng.

(53) Thus, the manufacture of such syringes could be implemented with significant cost savings.

(54) FIG. 5 gives an overview of the mass loss of different iridium-tungsten alloys at 1000 C. (source: Liu, Inouye, December 1976 Oak Ridge National Laboratory, Tennessee). In the diagram the ordinate axis represents time in hours, and the abscissa axis represents weight change in 10.sup.2 g/cm.sup.2.

(55) Samples made of three different alloys were exposed to a temperature of 1000 C., and material erosion was measured. Besides pure iridium, two iridium-tungsten alloys with 1.92 wt % of tungsten and 3.84 wt % of tungsten (Ir-1.94W, Ir-3.84W) were compared with each other in terms of material erosion. The diagram shows that material loss depends on the content of tungsten and decreases with higher tungsten contents.

(56) The advantages of iridium-tungsten alloys are on the one hand the long service life, combined with a high dimensional tolerance. Mass loss due to a formation of volatile oxides is significantly reduced compared to pure iridium because of the tungsten content so that no measurable material erosion is detectable at the iridium mandrel. The low material erosion on the forming mandrel provides for a consistently high dimensional tolerance of the cone channel during manufacturing, with a very narrow tolerance.

(57) Furthermore, the forming mandrel based on an iridium-tungsten alloy is characterized by low reactivity to glass constituents. For example, iridium as a precious metal only exhibits minor reactivity to glass evaporation products such as alkali oxides or boron oxides, so that corrosion is substantially suppressed.

(58) Introduction of contamination into the reshaped glass product is very low and hardly measurable by chemical analysis.

(59) Moreover, there is no deposition formed in the cone channel, e.g. of oxide particles.

(60) Therefore, the molding tool of the invention, in particular the forming mandrel 75 according to the invention brings about several advantages which make the molding tool considered to be particularly suitable for the production of low-tungsten pharmaceutical packaging, such as in particular syringes.