FORMING MANDREL WITH DIFFUSION LAYER FOR GLASS FORMING

Abstract

A glass molding tool is provided that includes a forming mandrel, a method for forming glass, and to an apparatus for hot forming of glass. The glass products obtained in this way may be used as pharmaceutical packaging. The forming mandrel reshapes at least a portion of a heated region of a glass precursor. The mandrel includes a heat-resistant core material and a diffusion layer that is in contact with the glass precursor during reshaping.

Claims

1. A molding tool for reshaping a hollow-body glass precursor, comprising a forming mandrel for reshaping at least a portion of a heated region of the glass precursor, the forming mandrel having a heat-resistant core material and a diffusion layer, wherein the diffusion layer is provided at least at a surface of the forming mandrel that is in contact with the glass precursor during reshaping.

2. The molding tool as claimed in claim 1, wherein the core material comprises a noble metal and/or a transition element.

3. The molding tool as claimed in claim 1, wherein the core material comprises tungsten or a tungsten-containing alloy.

4. The molding tool as claimed in claim 3, wherein the core material has a tungsten content of at least 90 wt %.

5. The molding tool as claimed in claim 1, wherein the core material comprises tungsten-zirconium dioxide (WZrO.sub.2) with a proportion of added ZrO.sub.2 from 0.01 wt % to 2.5 wt %.

6. The molding tool as claimed in claim 5, wherein the proportion of added ZrO.sub.2 is from 0.7 wt % to 0.9 wt %.

7. The molding tool as claimed in claim 1, wherein the core material comprises tungsten-cerium oxide (WCeO.sub.2) with a proportion of added CeO.sub.2 from 0.01 wt % to 2.5 wt %.

8. The molding tool as claimed in claim 7, wherein the proportion of added CeO.sub.2 is from 1.8 wt % to 2.2 wt %.

9. The molding tool as claimed in claim 1, wherein the core material comprises tungsten-lanthanum oxide (WLa.sub.2O.sub.3) with a proportion of added La.sub.2O.sub.3 from 0.01 wt % to 2.5 wt %.

10. The molding tool as claimed in claim 9, wherein the proportion of added La.sub.2O.sub.3 is from 1.8 wt % to 2.2 wt %.

11. The molding tool as claimed in claim 1, wherein the core material comprises a proportion of potassium between 5 and 100 ppm.

12. The molding tool as claimed in claim 11, wherein the proportion of potassium is between 50 and 70 ppm.

13. The molding tool as claimed in claim 1, wherein the diffusion layer comprises silicon (Si) and/or aluminum (Al).

14. The molding tool as claimed in claim 13, wherein the diffusion layer has a minimum content as measured at the surface of the forming mandrel that is at least 30 atomic percent.

15. The molding tool as claimed in claim 1, wherein the diffusion layer comprises silicon having a thickness from 1 to 200 m.

16. The molding tool as claimed in claim 15, wherein the thickness is from 1 to 20 m.

17. The molding tool as claimed in claim 1, wherein the diffusion layer comprises aluminum having a thickness 1 to 300 m.

18. An apparatus for reshaping a hollow-body glass precursor, comprising: a heating device configured to locally heat a region of the glass precursor to above a softening point; and a molding tool for reshaping the region of the glass precursor heated by the heating device, wherein the molding tool comprises a forming mandrel having a heat-resistant core material and a diffusion layer, wherein the diffusion layer is provided at least at a surface of the forming mandrel that is in contact with the glass precursor during reshaping.

19. A method for producing a pharmaceutical packaging made of glass, comprising the steps of: locally heating a region of a hollow-body glass precursor to above a softening point; and contacting the region of the glass precursor with a surface of a forming mandrel to reshape the region, the surface being defined by a diffusion layer on a heat-resistant core.

20. The method as claimed in claim 19, wherein the region is an inner cone of a glass syringe, the inner cone having a content of tungsten of more than 0.1 ng and at most 500 ng.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] 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. In the drawings:

[0075] FIG. 1 illustrates components of an apparatus for reshaping tubular glass;

[0076] FIG. 2 shows a transmission spectrum of a glass of a glass precursor;

[0077] FIGS. 3A-3F are sectional views through a tubular glass during the reshaping process;

[0078] FIG. 4 is a plan view of a portion of a forming mandrel with a diffusion layer;

[0079] FIG. 5 is an overview of material properties of tungsten;

[0080] FIG. 6 shows a transverse microsection through a silicided forming mandrel in a detail enlargement;

[0081] FIG. 7 shows a transverse microsection through an aluminized forming mandrel in a detail enlargement;

[0082] FIG. 8 shows a longitudinal microsection through a silicided forming mandrel in a detail enlargement after use;

[0083] FIG. 9 shows a further longitudinal microsection through a silicided forming mandrel in a detail enlargement after use;

[0084] FIG. 10 shows a non-treated tungsten mandrel after use; and

[0085] FIG. 11 shows a metallographic longitudinal microsection through a non-treated tungsten mandrel after use.

DETAILED DESCRIPTION

[0086] 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.

[0087] FIG. 1 illustrates an exemplary embodiment of an apparatus 1 for performing the method of the invention.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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 tube glass 3. Another possibility would be an inverted configuration in which the tube glass is fixed and the molding tool 7 rotates around the tubular glass.

[0092] 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. 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 deformed. By means of 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] Optical system 6 of the apparatus shown in FIG. 1 comprises a deflection mirror 61 and a cylindrical lens 63.

[0097] 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 additionally to the cylindrical lens 63, to advantageously use a diffractive optical element.

[0098] 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.

[0099] 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.

[0100] 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 in 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.

[0101] 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 by a burner. Overall, less thermal energy is produced in this way, and moreover this thermal energy is introduced into the glass precursor more selectively.

[0102] Thus, heating of the entire apparatus is reduced, and therefore also running-up phenomena caused by thermal expansions, inter alia.

[0103] A preferred glass for the production of syringe bodies is borosilicate glass.

[0104] 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.

[0105] A suitable low-alkali borosilicate glass comprises the following constituents, in percent by weight:

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 %, and CaO 1.5 wt %.

[0106] 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.

[0107] The decrease in transmittance in the wavelength range above 2.5 micrometers as shown in FIG. 2 is not significantly dependent 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.

[0108] FIGS. 3A to 3F are sectional views 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 mandrel 75 can also be seen.

[0109] 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. By way of these lines the material flow during reshaping is illustrated.

[0110] 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.

[0111] Engagement by rollers 70, 71 and initial deformation takes place starting with the position shown in FIG. 3C. Then, the tube 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.

[0112] 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.

[0113] FIG. 4 is a plan view illustrating a portion of a forming mandrel 75. Starting from the top 80 of forming mandrel 75 a region adjacent to the tip of the forming mandrel 75 is marked by A, in which the lateral surface 81 of forming mandrel 75 will or may contact the glass precursor during reshaping. Therefore, it is at least this area which is or will be provided with the diffusion layer 81 of the invention. The lateral surface of forming mandrel 75 may further comprise an area 82 without diffusion layer. This portion may be used for mounting the forming mandrel, for example.

[0114] FIG. 5 is an overview (Source: Wolfram-Werkstoffeigenschaften and Anwendungen (Tungsten material properties and applications), Plansee AG, Reutte, 2000) representing the modulus of elasticity of tungsten compared to that of other alloys. Clearly visible is the comparatively high modulus of elasticity of tungsten and the high heat resistance thereof.

[0115] FIG. 6 shows a transverse microsection through a silicided forming mandrel in a detail enlargement. The forming mandrel comprises tungsten as a core material. The diffusion of silicon into the mandrel was performed at a temperature above 650 C. over a period of more than 8 hours by pack cementation.

[0116] The core material 85 of the forming mandrel can be seen in the transverse section. Also, a diffusion zone 86 can be seen, which is located at the surface of the forming mandrel and protrudes into the interior of the forming mandrel. The thickness of silicided diffusion zone 86 indicated by B is about 4 to 6 m, preferably about 5 m. Thus, the silicided diffusion zone 86 extends into the core material by about 5 m as measured from the surface of the forming mandrel.

[0117] In order to protect the near-surface region during metallographic preparation, in particular during grinding and polishing of the mandrels, the mandrels are surrounded by a nickel coating. This layer 87 can be seen on forming mandrel 75. This layer 87 is not employed during the use of the mandrels in the hot forming of pharmaceutical packaging.

[0118] FIG. 7 shows a transverse microsection through an aluminized, or alitized, forming mandrel in a detail enlargement. The core material 85 of the illustrated forming mandrel 75 is made of tungsten. Furthermore, a diffusion zone 88 can be seen, which is marked by C. The alitized diffusion zone extends into the core material by about 50 to 70 m, preferably by about 300 m, as measured from the surface of the forming mandrel.

[0119] FIG. 8 shows a longitudinal microsection through a silicided forming mandrel in a detail enlargement after use. The presence of a diffusion layer 86 is clearly visible. In this example, a silicon diffusion layer was generated on the forming mandrel 75, and the forming mandrel was in use over an extended period of time. It has run through a number of about 10,000 cycles, i.e. reshaping processes, for hot forming syringes.

[0120] FIG. 9 shows a further longitudinal microsection through a silicided forming mandrel 91 in a detail enlargement after use. The presence of a diffusion layer 92 is clearly visible. The diffusion layer was generated on the basis of silicon and comprises a diffusion zone D with a thickness of about 10 m. In this example, the forming mandrel 91 was in use over an extended period of time. It has run through a number of about 10,000 cycles, i.e. reshaping processes, for hot forming syringes.

[0121] The original outer edge of forming mandrel 91 is indicated by dashed line 93. It can be seen that the outer edge is still in very good condition. Moreover, the outer dimension is hardly changed after use. In particular, the outer edge still exhibits high straightness. Thus, the forming mandrel 91 having the surface provided with the silicided diffusion layer can therefore be regarded as exhibiting very low wear.

[0122] At the positions marked by X, Y, and Z, the silicon and tungsten contents were determined. In the region marked by Z, which defines a position in the core material of the forming mandrel, the tungsten content is 100 wt %. In the region marked by X, which is in the region of the diffusion zone D, a silicon content of about 22 wt % and a tungsten content of about 78 wt % were determined. In the region marked by Y, which is in a transition region in which the content of the diffused material decreases significantly, a silicon content of about 18 wt % and a tungsten content of about 82 wt % were found.

[0123] Starting from a relatively high value in the outer region of the diffusion zone near the surface of forming mandrel 91, which may be about 22 wt % or even higher in the example, the silicon content in the diffusion zone decreases inwardly.

[0124] As a comparative example, FIG. 10 shows a non-treated tungsten mandrel 101 after use. The illustrated forming mandrel without the inventive diffusion layer has run through about 3,000 shaping steps. The coloring indicates a formation of surface oxides on the mandrel, clearly recognizable is a waisting 102 on the left side of the illustrated forming mandrel 101.

[0125] Finally, as a further comparative example, FIG. 11 shows a metallographic longitudinal microsection through a non-treated tungsten mandrel 111 after use. The illustrated forming mandrel without the inventive diffusion layer has run through about 3,000 shaping steps. In the marked oval 113, formation of an oxide layer is observable, which layer has a thickness of about 3 to 5 m and which can be removed and reproduces itself.

[0126] A molding tool according to the invention, in particular a forming mandrel, has a number of advantages. It is possible in this way to continue to use the material tungsten which is very well suited for the hot forming of hollow-body glass precursors without however thereby causing any undesirable contamination, especially in the interior of the reshaped glass product.

[0127] This brings many advantages, in particular with regard to the manufacturing of pharmaceutical packaging, such as syringes, cartridges, ampoules, or vials. The invention is therefore particularly suitable for tungsten-free or low-tungsten pharmaceutical packaging, such as especially syringes.