Patent Publication Number: US-2013227993-A1

Title: Apparatus For Use In The Glass Industry And Method For Processing Molten Glass

Description:
The invention relates to an apparatus which is suitable for being surrounded by molten glass and which may be designed, for example, in the form of an agitator, a needle, a plunger or rotary plunger or a Vello or down-draw needle, in order to be used in the glass industry, for example, for homogenizing molten glass. The invention relates, furthermore, to a method for processing molten glass, in which the apparatus is used. 
     Structural parts consisting of high-grade metal or high-grade metal alloys, such as preferably PGM materials, are employed in the glass industry, particularly in plants for the melting and hot forming of special glass. These plant components used in fusion technology, also called PGM (Platinum Group Metals) products, serve for melting, refining, transporting, homogenizing and portioning liquid glass. 
     Such structural parts, are essentially either structures consisting of solid PGM material or of materials resistant to high temperature, such as ceramic refractory materials or metallic special materials, with a thin-walled PGM cladding, for example, in the form of thin sheet metal or of a PGM surface coating which is applied, for example, by plasma spraying or flame spraying. 
     Plant parts carrying glass melt are often noble metal sheet structures which are designed as thin-walled pipe systems. The molten glass flows through these at temperatures of between 1000° C. and 1700° C. The pipe systems, as a rule, are surrounded on the outside by an insulating and, if appropriate, supporting ceramic, this, in turn, often being held by supporting metal structures, such as, for example, metal boxes. 
     Structural parts consisting of solid PGM material have molten glass flowing over or around them and are partly moved in the glass melt. 
     PGM (Platinum Group Metals) materials, because of their high melting point, are distinguished by high temperature resistance and, furthermore, by high mechanical strength and resistance to abrasion and are therefore especially suitable for the production of structural parts in plants or plant parts which come into contact with the glass melt. Suitable materials are platinum and alloys of platinum and/or of other PGM metals. 
     The prior art, as described in DE 43 26 143 A1, discloses a plunger which consists of a core consisting of molybdenum, tungsten or of an alloy of these. Furthermore, the plunger has a ceramic body which is provided with a covering consisting of platinum or of a platinum-rich alloy. The ceramic body serves for preventing intermetallic diffusion, specifically between the metal core and the platinum covering. 
     The plunger has the disadvantage, however, that the layer build-up with the molybdenum or tungsten core is relatively complicated. A further disadvantage is that, if the covering is damaged, oxidation of the molybdenum or tungsten core occurs, with the result that the plunger becomes useless. 
     Moreover, a plunger needle is known from U.S. Pat. No. 3,332,766, such a plunger needle in this case consisting of an outer cylinder with a hemispherical cap. Furthermore, reinforcing ribs are arranged inside the cylinder. Both the cylinder and the hemispherical cap and also the reinforcing ribs in this case consist of platinum or of a platinum alloy. 
     The object of the invention is to provide an improved apparatus which is suitable for being surrounded by molten glass, in order to be used in the glass industry. A further object of the invention is to provide an improved method for processing molten glass. 
     These objects are achieved by means of an apparatus and a method according to Claims  1 ,  2 ,  3  and  41  of the present invention. 
     An especially preferred advantage of the invention is the long and predictable service lives of the apparatus and its relatively low production costs. 
     In this case, in one embodiment, the apparatus has a shank which consists of at least one at least partially, preferably completely seamless tube consisting of an oxide dispersion-strengthened PGM material, the shank having at least one thickened portion on which an actuating device is fastened, for example, by means of welding. The thickened portion may, in this case, be designed in such a way that the shank has a larger diameter and/or a greater wall thickness. In this case, depending on the intended use or load, the shank may, for example, be stepped downwards and/or have a flowing transition. The stepping or the flowing transition may run from a greater wall thickness to a smaller wall thickness and/or from a larger diameter to a smaller diameter, and vice versa. Also as explained later with reference to  FIG. 12   a , one or more tubes may in this case be additionally introduced coaxially into the shank. The tubes may in this case have a continuous diameter and a continuous wall thickness or likewise be designed so as to be stepped or with flowing transitions. Furthermore, depending on the intended use, one or more portions of the shank may be reinforced additionally or alternatively from outside by at least one sleeve being pushed on or being shrunk on. 
     The provision of an at least partially seamless shank composed of oxide dispersion-strengthened PGM material has the advantage that this ODS material considerably increases the resistance to high temperature or the long-time rupture strength at high temperatures of the shank. This is achieved by means of the combination of hard, nonmetallic small particles finely distributed in the PGM material and of a very high mixing density. 
     A further advantage is that the shank exhibits only a low creep behaviour. The tendency to plastic deformation, that is to say a low creep behaviour, is in this case influenced positively by the admixture of finely distributed dispersoids. For this reason, such oxide dispersion-strengthened materials (referred to in brief as ODS materials) are especially suitable for self-supporting solid PGM structural parts. 
     A further advantage is that the thickened portion of the shank to which the actuating device is fastened can more effectively absorb forces or mechanical loads, such as, for example, tension, pressure, bending and/or shearing, which act on the shank via the actuating device. Furthermore, longer service lives and, consequently, a higher efficiency of the apparatus can be achieved. 
     In the further embodiment of the invention the apparatus has a shank which consists of at least one at least partially, preferably completely seamless tube, an actuating device being arranged on the shank, and the shank and the actuating device consisting of an oxide dispersion-strengthened PGM material. 
     The provision of the shank and of the actuating device consisting of an oxide dispersion-strengthened PGM material has the advantage that, preferably, the service lives can be further prolonged, since due to the ODS material, the actuating device, too, has a higher long-time rupture strength at high temperatures, and also improved corrosion resistance, on account of the textural structure and a lower tendency to creeping. 
     In a further embodiment of the invention, the shank additionally has a sleeve which is arranged on the shank, at least in a region in which an evaporation or sublimation of the carrying shank occurs during operation. The sleeve may in this case consist, for example, of a PGM material. 
     The inventor found that the evaporation of the carrying shank during operation can be reduced considerably by the provision of such a sleeve. As a result the material loss on the shank can be reduced and, moreover, higher service lives can be achieved. Owing to the use of a sleeve manufactured from oxide dispersion-strengthened PGM material, the PGM material loss of the sleeve can be reduced, as compared with PGM cast alloys. 
     The above-described oxide dispersion-strengthened PGM materials, which may be used in the embodiments and exemplary embodiments described in even more detail below, may have, if appropriate, subordinate quantities of base metals as further alloying components or oxidic additives. Typical materials are fine platinum, platinum/rhodium alloys and platinum/iridium alloys. To increase the strength and high-temperature creep resistance, oxide dispersion-strengthened PGM materials may be provided, in which case a small quantity of finely distributed refractory metal oxide, such as, for example, zirconium oxide or yttrium oxide, is added to the PGM material, for example. 
     The strengthening of platinum materials by means of dispersion strengthening is preferred. The combination of hard, non-metallic small particles finely distributed in the PGM material and of very high mixing density allows a considerable increase in high-temperature resistance. The tendency to plastic deformation, that is to say a low creep behaviour, is also influenced positively by the admixture of finely distributed dispersoids. For this reason, such oxide dispersion-strengthened materials (referred to in brief as ODS materials) are especially suitable as self-supporting solid PGM structural parts. These oxide dispersion-strengthened materials are likewise used in the embodiments and exemplary embodiments described below. 
     The abovementioned PGM structural parts may, in turn, be built up from individual components, for example, bands, metal sheets, cups and profiles, as a welded structure. In this case, a suitable forming and joining technique is important. Any weld seam leads to a weakening of the mechanical strength of the basic material due to variations in textural structure. Precisely where ODS materials are concerned, it has to be remembered that, in the molten state, the dispersoids coagulate and are partially flushed out, thus adversely influencing the lifetime of the structural part. The avoidance of weld seams, that is to say the use of at least partially or completely seamless individual components, such as, for example, in the case of the claimed shank, is the basis for the efficient implementation of self-supporting solid PGM structural parts. 
     These seamless individual components then also have to be joined together, for example, welded, into a functioning structural part. It is appropriate, here, to place the weld seams as far as possible in low-stress or stress-free zones. In order to compensate weakening due to the weld seams, there is also the possibility, furthermore, depending on the type and size of the mechanical load—tension, pressure, bending and/or shearing, etc.—to adapt the seamless individual components in their geometry, according to requirements, within the limits of the forming technique, that is to say the use of profiles of stepped diameter and wall thickness or profiles with flowing transitions and seamless spun parts. 
     The external forces acting on the PGM structural parts are generated, inter alia, by the different primary types of movement of the PGM structural parts in the liquid glass:
         Agitators execute a rotational movement.   Needles execute a lifting movement and sometimes, at the same time, a rotational movement.   Plungers or rotary plungers execute a rotational movement, at the same time with a superposed lifting movement.   Vello and down-draw needles (used in the production of glass tubes) do not execute any movements in the operating state. These structural parts are merely rotated at certain time intervals, about their longitudinal axis into a new position in order to avoid permanent deformations of the PGM structural part. External forces are generated mainly by the viscous glass being drawn off, either horizontally to the side or vertically downwards.       

     By the provision of an apparatus according to Claims  1 ,  2  and  3  with a shank and an actuating device and with a sleeve, the external forces and mechanical loads, such as permanent loads, acting on the apparatus can be absorbed more effectively and, as a result, higher service lives can be achieved. 
    
    
     
       Some preferred embodiments and exemplary embodiments of the invention are explained in more detail below with reference to the present drawings in which: 
         FIG. 1   a  shows a longitudinal section through a first embodiment of the apparatus according to the invention, 
         FIG. 1   b  shows a detail of a view A of the apparatus according to  FIG. 1   a,    
         FIG. 2   a  shows a perspective view of a detail of a tubular device of the apparatus according to  FIG. 1   a  from below, a disc element and plate elements being fastened to the tubular device by means of welding, and the tubular device in this case lying on a holder, which is not part of the invention, 
         FIG. 2   b  shows a perspective view of a detail of the tubular device according to  FIG. 2   a , from above, the tubular device being shown before welding, 
         FIG. 3   a - f  show a side view of an actuating device according to the first embodiment, the actuating device in each case being composed of different actuating elements, 
         FIG. 4  shows a perspective view of a second embodiment of the apparatus according to the invention, 
         FIG. 5   a  shows a perspective view of a third embodiment of the apparatus according to the invention, a hollow profile being used as a blade element, 
         FIG. 5   b  shows a perspective view of the third embodiment of the invention, a sheet-like element (obliquely arranged plate) being used as a blade element, 
         FIG. 6   a  shows an apparatus according to the first embodiment of the invention in the form of an agitator, 
         FIG. 6   b  shows an apparatus according to the first embodiment of the invention in the form of a needle, 
         FIG. 6   c  shows an apparatus according to the second embodiment of the invention in the form of a plunger or rotary plunger, 
         FIG. 6   d  shows a further embodiment according to the invention of the apparatus in the form of a Vello or down-draw needle, 
         FIG. 7   a  shows a further embodiment according to the invention of the apparatus in the form of a plunger or rotary plunger in a perspective view, 
         FIG. 7   b  shows a side view of the apparatus according to  FIG. 7   a,    
         FIG. 7   c  shows a top view of the apparatus according to  FIG. 7   a  in the direction of the arrow A, 
         FIG. 8   a  shows an apparatus according to the second embodiment of the invention in the form of an agitator in a perspective view, 
         FIG. 8   b  shows the apparatus according to  FIG. 8   a  in a side view, with an enlarged detail Z, 
         FIG. 8   c  shows a top view of the apparatus according to  FIG. 8   a  in the direction of the arrow A, 
         FIG. 9   a  shows an apparatus according to the first embodiment of the invention in the form of an agitator in a side view, 
         FIG. 9   b  shows the apparatus according to  FIG. 9   a  in a perspective view, 
         FIG. 9   c  shows a longitudinal section through the apparatus according to  FIG. 9   a , with sectional views B-B and C-C and with an enlarged detail Z, 
         FIG. 10   a  shows a further embodiment according to the invention of the apparatus in the form of a Vello or down-draw needle in a perspective view, 
         FIG. 10   b  shows a longitudinal section through the apparatus according to  FIG. 10   a  with an enlarged detail C, 
         FIG. 10   c  shows a longitudinal section through the apparatus according to  FIG. 10   a , the longitudinal section being rotated through 90° about the longitudinal axis in relation to  FIG. 10   b,    
         FIG. 11   a  shows a further embodiment according to the invention of the apparatus in the form of a helical plunger in a side view, and also an accompanying sectional view C-D, 
         FIG. 11   b  shows a longitudinal section A-B through the apparatus according to  FIG. 11   a,    
         FIG. 11   c  shows a top view of the apparatus according to  FIG. 10   b  in the direction of the arrow X, 
         FIG. 12   a  shows various embodiments of a blade element in cross section, the blade element being a sheet-like element, 
         FIG. 12   b  shows further embodiments of the blade element in cross section, the blade element having a closed profile or rather a hollow profile, 
         FIG. 13   a - f  shows various embodiments of the shank of the apparatus according to the invention, the shank being illustrated in longitudinal section, 
         FIG. 14  shows various embodiments of the shank, the shank being illustrated in cross section. 
     
    
    
       FIG. 1   a  shows a longitudinal section through a first embodiment of the apparatus  2  according to the invention. The apparatus  2  is in this case designed, for example, as an agitator and has a shank  20  and an actuating device  4  which are moved via a drive (not illustrated). For this purpose, a drive or holding flange  5  is provided on the shank  20 . This drive or holding flange  5  is in this case received in the shank  20  and is provided with a protective cap  7  which preferably consists of a PGM material including, for example, oxide dispersion-strengthened PGM material. 
     The shank  20  of the apparatus  2  according to the invention has at least one at least partially or completely seamless tube which preferably consists of an oxide dispersion-strengthened PGM material or at least comprises this material. The shank  20  has a first thickened portion  9 , on which the actuating device  4  is fastened, preferably by means of welding. Welding in this case constitutes a possibility of stable and glass-tight fastening. 
     As shown in  FIG. 1   a , the first thickened portion  9  may in this case be formed, for example, by virtue of the preferred provision of a sleeve  28 . The sleeve  28  preferably consists of a PGM material, more preferably of an oxide dispersion-strengthened PGM material or of another suitable material. This sleeve  28  is fastened, at least glass-tight, to the shank  20  and may, for example, be pushed or shrunk on to the shank  20 . In addition to the sleeve  28  or instead of the sleeve  28 , the shank  20  may preferably have a larger diameter and/or a greater wall thickness. The shank may in this case be designed on the outside and/or on the inside with a flowing transition and/or so as to be stepped in terms of diameter and/or wall thickness. 
     As shown in  FIG. 1   a , the actuation device  4  is fastened to the sleeve  28  by means of a continuous weld seam  25 , the sleeve  28  forming the first thickened portion  9  of the shank  20 . Alternatively, however, the first thickened portion  9  may also be formed, for example, by a greater wall thickness of the shank  20 . In this instance, the actuating device  4  is welded directly to the shank  20  in the region of the first thickened portion  9 . 
     The thickened portion  9  has in this case the advantage that it can compensate the weakening caused by the weld seam  25  and at the same time can absorb the forces which act on the connection to the actuating device  4 , for example tensile, compressive, shearing and/or bending forces, etc. Higher service lives can be achieved therefore by means of which the efficiency of the apparatus  2  can be improved considerably. This also applies particularly to the second thickened portion  15 , to which the actuating device may likewise be fastened, as shown in  FIG. 1   a , with the result that the second thickened portion  15  has to absorb a higher load than the first thickened portion  9 . The second thickened portion  15  is dealt with in more detail below. 
     Furthermore, at one end of the shank  20 , a tubular device  8  is provided which corresponds here, in the first embodiment, to a prolongation of the shank  20 . This tubular device  8  is pushed into the actuating device  4 . As may be gathered from  FIGS. 1   a ,  1   b  and  3   a - 3   f , the actuating device  4  is composed of one, two or more actuating elements  16  which are preferably seamless spun parts. 
     The actuating device  4  is in this case composed of actuating elements  16 , for example, in the form of a cylinder, of a cone, of a cone frustum and/or of a spherical segment, this list not being conclusive. For the radial support and/or fastening of the actuating elements  16  at least one disc element  12  is provided on the tubular device  8  or the prolongation of the shank  20 . The disc element  12  in this case consists preferably of a PGM material, especially preferably of an oxide dispersion-strengthened PGM material, or alternatively of another suitable material. For weight reduction, the disc element  12  may have orifices or bores  11 . The actuating elements  16  and the disc element  12  may in this case be welded to one another in order to form the actuating device  4 . 
     As shown in  FIGS. 2   a  and  2   b , the disc element  12  may selectively have on its outer circumference a projection  13  which is at least partially or completely peripheral. The actuating elements  16  are in this case pushed on to the disc element  12  and at the same time come to bear against the projection  13 . The two actuating elements  16  and the disc element  12  can thus be positioned with respect to one another and subsequently welded to one another. The projection  13  may in this case project somewhat beyond the actuating elements  16  on the outside and be used to form a weld seam. 
     Furthermore, at least one plate element  24  for absorbing axial forces may selectively be provided on one or on both sides of the disc element  12 . As shown in the detail of the view A in  FIG. 1   b , the respective actuating element  16  has a clearance or slot  30 , into which the upper end  27  of the corresponding plate element  24  is received. The actuating elements  16 , the disc element  12  arranged between them and the two plate elements  24  may be welded to one another at a later stage. 
     Basically, the two actuating elements  16  may also be welded directly to one another, in which case no disc element  12  is arranged between them and/or no plate element  24  is received in a slot  30  of the respective actuating element  16 . Instead, the disc element  12  may bear against the inner circumference of at least one of the actuating elements  16  and selectively be welded to this from inside. This also applies to the plate elements  24 . These may likewise bear against the inner circumference of the actuating elements  16  and selectively be welded to the actuating elements  16  from the inside. The actuating element  16  correspondingly has no slot  30  in this case. 
     Preferably, on the tubular device  8  or the prolonged shank  20 , a second thickened portion  15  may be provided, on which the disc element  12  and the plate elements  24  are arranged. As illustrated in  FIG. 1   a , the second thickened portion  15  may in this case be formed on the tubular device  8  by virtue of the provision of a sleeve  28 . The sleeve  28  in this case likewise consists preferably of a PGM material, especially preferably of an oxide dispersion-strengthened PGM material or of another suitable material. The sleeve  28  may, for example, be pushed or shrunk onto the tubular device  8 . In this case the two sleeves  28  which are used on the first and the second thickened portion  9 ,  15 , may also be designed (not illustrated) as a continuous sleeve. In addition to the sleeve  28  or instead of the sleeve  28 , the tubular device  8  itself may be of thickened design. As in the case of the first thickened portion  9 , the tubular device  8  may in this case have a larger diameter and/or a greater wall thickness. For this purpose the tubular device  8  may correspondingly be designed on the inside and/or on the outside with a flowing transition and/or so as to be stepped. 
     Furthermore, the tubular device  8  and the sleeve  28  may in each case be provided with a corresponding break-out  26 , through which the respective plate element  24  is pushed, as shown in  FIGS. 2   a  and  2   b . In  FIG. 2   a , which shows the tubular device  8  from below, the plate elements  24  are welded continuously to the disc element  12  and the sleeve  28 . The disc element  12  in this case is likewise welded all round to the sleeve  28 .  FIG. 2   b , in which the tubular device  8  is shown from above, shows, in turn, the sides of the disc element  12  and of the respective plate elements  24  before welding. 
     In principal, the number and position of the weld seams  25  may also be provided differently, insofar as a sufficient fastening of the disc element  12 , of the plate elements  24  and of the sleeve  28  is ensured. As indicated in  FIG. 1   a  by a broken line and as is shown in  FIG. 2   a , the sleeve  28  may be prolonged as far as the end of the tubular device  8  and be optionally welded to the lower end of the tubular device  8 . However, as shown in  FIGS. 1   a  and  2   b , the sleeve  28  is preferably not welded at its upper end to the tubular device  8 , since here, for example, forces act by the actuating device  4  and a weld seam would lead to weakening. 
     For the additional support of the inner circumference of the actuating device  4  or of its actuating elements  16  or to increase the dimensional rigidity of these, at least one supporting ring  32  may be provided, which bears against the inner circumference of the corresponding actuating element  16  and which is selectively welded to the latter. 
     Furthermore, blade elements  18  may be fastened to the actuating device  4 , preferably by means of welding. These blade elements  18  may in this case be formed from solid parts or hollow parts, as shown by way of example in  FIG. 12   a, b . The blade elements  18  are in this case preferably made from PGM material, especially preferably from oxide dispersion-strengthened PGM material or from another suitable material. The blade elements  18  may in this case also have a set-up, such as is described below with reference to the second and the third embodiment of the apparatus according to the invention. 
     Overall, the shank  20  and at least parts of the actuating device  4 , that is to say preferably the parts of the actuating device  4  which come into contact with the glass, consist of a PGM material, preferably of oxide dispersion-strengthened PGM material or of another suitable material. Alternatively, however, all the parts of the actuating device  4 , including the disc element  12 , the plate elements  24 , the sleeve  28 , the supporting ring  32 , and the blade elements  18 , may also be made from a PGM material, preferably from oxide dispersion-strengthened PGM material or of another suitable material. By contrast, the drive or holding flange  5  may be made, for example, from a heat-resistant steel, since the temperature outside the molten glass is correspondingly lower. The actuation device  4  and the shank  20  or the tubular device  8  are preferably vented (not illustrated) inside the apparatus  2 . 
     Some examples of the configuration of the actuating device  4  are explained below in more detail with reference to  FIG. 3   a - 3   f . In  FIG. 3   a  the actuating device  4  is composed of two cylindrical actuating elements  16 . Further, the actuating device  4  in  FIG. 3   b  is composed of a partially conical actuating element  16  and in each case a cylindrical and a hemispherical actuating element  16 . In  FIGS. 3   c  and  3   e , the actuating device  4  is composed in each case of two conical actuating elements  16 . Furthermore, in  FIG. 3   d  the actuating device  4  is composed of a conical and of a hemispherical actuating element  16 . In  FIG. 3   f  the actuating device  4  is formed from a conical actuating element  16  having a cylindrical portion. 
     The second embodiment of the apparatus  2  according to the invention is explained in more detail below according to  FIG. 4 . 
     The apparatus  2  is in this case designed, for example, as an agitator which has a shank  20  and an actuating device  6  which are moved via a drive (not illustrated). For this purpose, as shown in  FIG. 1   a  of the first embodiment, a drive or holding flange may be provided on the shank  20 . This drive or holding flange (not illustrated) is in this case received, for example, in the shank  20  and is provided with a protective cap. 
       FIG. 4  shows a detail of the shank  20  of the apparatus according to the invention which is provided with an actuating device  6  which has two blade elements  18 . As has already been described in detail above with reference to the first embodiment, the shank  20  in this case has at least one at least partially or completely seamless tube which preferably consists of an oxide dispersion-strengthened PGM material or at least comprises this material. The shank  20  in this case has a portion  19  to which the actuating device  6  is fastened. 
     The portion  19  may in this case selectively be designed as a thickened portion (not illustrated) to which the actuating device  6  or its blade elements  18  are fastened. The thickened portion serves for compensating the weakening of the shank  20  due to the welding-on of the blade element  18 . In this case, correspondingly to the first embodiment, the thickened portion may be achieved by a sleeve being pushed or shrunk on to the shank  20 . The sleeve in this case may preferably be made from a PGM material, especially preferably from an oxide dispersion-strengthened PGM material or from another suitable material. In addition to the sleeve or instead of the latter, the shank  20  may have a larger diameter and/or a greater wall thickness. The shank  20  can in this case be designed to be stepped inwards and/or outwards and/or with a flowing transition. 
     Provided on the shank  20  is an actuating device  6  which, as shown in  FIG. 4 , has, for example, two or more blade elements  18 . A tube of smaller diameter or a tubular device  10  is introduced at least partially into the blade elements  18  through an orifice  22  in the shank  20  or the sleeve. 
     In contrast to the first embodiment, the tubular device  10  is designed as a separate part and, for example, is not welded to the shank  20 , in order to avoid an additional weakening (transformation of the textural structure of the ODS material) of the shank. The tubular device  10  may be dimensioned in its dimensions, in particular in its length, such that the blade element  18  has to absorb as low a tilting moment as possible during operation. A tilting moment leads to bending stresses which have to be absorbed by the leak-tight weld seam between the blade element  18  and shank  20 . The occurrence of a tilting moment can be reduced or essentially avoided by virtue of the provision of the tubular device  10 . 
     Furthermore, on the tubular device  10 , at least one disc element  14  is provided, which serves for the radial support of the blade element  18  and which bears with its outer circumference, preferably continuously or at least partially continuously, against the inner circumference of the blade element  18 . The disc element  14  may be connected to the tubular device  10  by means of welding. The number and dimensions, in particular width, of the disc element  14  may be selected as a function of the length of the blade element  18  and as a function of which portions of the blade element  18  are additionally to be supported radially. The same applies correspondingly to the disc element  12  of the first embodiment and to the disc element  36  which is dealt with in more detail below. 
     The blade elements  18 , as shown in  FIG. 4 , are placed on to the portion  19  of the shank  20 . In this case, only two blade elements  18  are illustrated in  FIG. 4 . However, even only one blade element  18  or more than two blade elements  18  may be provided, as shown, for example, by means of the following  FIG. 6   c . In addition, at least one supporting ring (not illustrated) may also be provided in the blade element  18  correspondingly to the supporting ring  32  of the first embodiment. 
     As shown in  FIG. 4  and the detail A, the tubular device  10  has at least one orifice  23  for venting. The tubular device  10 , which is illustrated partially as a section in  FIG. 4 , is in this case vented inwards by way of the shank  20  via the orifice  23 . 
     Overall, the shank  20  and at least parts of the actuating device  6 , that is to say preferably the parts of the actuating device  6  which come into contact with the glass, consist of a PGM material, preferably of oxide dispersion-strengthened PGM material. Alternatively, however, all the parts of the actuating device  6 , including the blade elements  18 , the disc element  12 , the sleeve and the supporting ring, may also be made from a PGM material, preferably from oxide dispersion-strengthened PGM material or from another suitable material. By contrast, the drive or holding flange does not have to be made from a PGM material, since the temperature outside the molten glass is correspondingly lower. It may be produced, for example, from a “base” material, for example, a heat-resistant steel. 
       FIGS. 5   a  and  5   b  illustrate a third embodiment of the apparatus  2  according to the invention. In this case, the shank  20  of the apparatus  2  likewise preferably has a thickened portion  21  which may be designed in the same way as the thickened shanks  9 , described above, that is to say with a larger diameter and/or a greater wall thickness and/or a sleeve. In the illustration in  FIG. 5   a , a sleeve  28  is welded to the shank  20  in order to form the thickened portion  21 . Alternatively, however, the sleeve  28  may also be pushed or shrunk on to the shank  20 . In this case, the shank  20  and the sleeve  28  have a corresponding orifice  22  through which the blade element  18  in the form of a closed tube is led. The blade element  18  is in this case welded continuously to the thickened portion  21 . The thickened portion  21  in this case compensates the weakening due to the weld seam  25 . For venting, the blade element  18  may have at least one orifice  23 , as shown in  FIG. 5   a  and the detail A. The blade element  18  is in this case vented inwards, and the air is discharged outwards later via a further orifice in the shank  20  above the glass level. This principle may be applied to all the embodiments. 
     Alternatively or additionally, instead of a blade element  18  with a hollow profile in  FIG. 5   a , at least one blade element  18  with a sheet-like profile may also be welded to the thickened portion  21 , preferably by means of a continuous weld seam  25 . As already described above, the thickened portion  21  is in this case formed by the sleeve  28  which is welded to the shank  20  in each case by means of a preferably continuous weld seam. In  FIG. 5   b , for example, two blade elements  18  in the form of sheet-like elements are welded on. Basically, these two blade elements  18  may also be designed as one continuous blade element  18  (not illustrated) which is led through corresponding orifices in the thickened portion  21  and is fastened to the latter by means of welding. 
     The venting of the weld seams  25  of the blade elements  18  is illustrated in  FIG. 5   b  and the detail A. The venting serves for discharging air, which is formed during welding between the weld seams  25 , inwards into the shank  20 , where it is subsequently discharged outwards via an orifice in the shank  20  above the glass level. The shank  20  in this case has at least one orifice  29  for venting which is arranged opposite the blade element  18  with its weld seams  25 . The sleeve  28  in this case preferably has a clearance  31  which lies with the orifice  29  opposite the blade element  18  and its weld seams  25 . As shown in  FIG. 5   b , the clearance  31  may in this case be designed, for example, as a continuous depression, since this is easy to produce in manufacturing terms. 
     Various embodiments of the apparatus  2  according to the invention are shown in  FIG. 6   a - 6   d.    
       FIG. 6   a  shows the apparatus  2  according to the invention as an agitator. The agitator executes, for example, a rotational movement in an operating state. Furthermore, as illustrated in  FIG. 6   a , the agitator has as an actuating device  4  an essentially cylindrical basic body on which various blade elements  18  are arranged. However, the agitator may basically assume any other shape, for example shapes such as are shown in  FIG. 3   a - 3   f  and  6   b - 6   d  and combinations of these. This also applies correspondingly to the needles described below in  FIGS. 6   b  and  6   d , and to the plunger in  FIG. 6   c.    
     In  FIG. 6   b  the apparatus  2  according to the invention is designed as a needle. In an operating state the needle executes, for example, a lifting movement and/or, at least intermittently, a rotational movement. The needle has, furthermore, an actuating device  4  which is composed of a conical, of a cylindrical and of a hemispherical actuating element  16 . 
     Moreover, in  FIG. 6   c , the apparatus  2  according to the invention is designed as a plunger or rotary plunger. In this case in an operating state, the plunger executes a rotational movement and/or a lifting movement. The plunger is in this case composed of a spherical and of a conical actuating element  16 , blade elements  18  being additionally fastened as further actuating elements to the shank  20 . 
     Further, in  FIG. 6   d , the apparatus  2  according to the invention is designed as a Vello or down-draw needle. The needle may in this case be rotated about its axis at predetermined time intervals, while it otherwise executes essentially no movement. The needle in this case has a conical actuating device  4  with a cylindrical portion. 
     In  FIG. 7   a - c , an exemplary embodiment of the third embodiment of the invention is shown which in this case is designed as a plunger. The plunger has a seamless shank  20 , at the upper end of which is provided a drive or holding flange  5  which has a protective cap  7 . The shank  20  has at its lower end an actuating device  4  in the form of a thickening or bell. The actuating device  4  in this case may be composed, for example, of three actuating elements  16 , a conical, a cylindrical and a hemispherical actuating element  16 . The actuating device  4  may additionally be stiffened further from inside by at least one supporting ring  32 , in which case the supporting ring  32  may selectively be welded to the actuating device  4  on the inside. 
     Furthermore, the shank  20  has a continuous sleeve  28 , to which three closed tubular blade elements  18  are fastened as a further actuating device, for example, by means of welding. The three tubular blade elements  18  are in this case led through corresponding orifices in the shank  20  and in the sleeve  28 . As shown in  FIG. 7   a , the arrangement of the blade elements  18  may form, for example a type of spiral. 
     The apparatus can be vented outwards via at least one orifice  33  at the upper end of the shank  20 , above the glass level. The blade elements  18  themselves may be vented, for example, according to what is shown in  FIG. 5   a, b . This principle may be applied to all the embodiments. 
     Moreover, an exemplary embodiment of the second embodiment of the invention is illustrated in  FIG. 8   a - c . The apparatus  2  is in this case designed, for example, as an agitator and has a multiplicity of blade elements  18  which are reinforced in each case via a tubular device  10  and corresponding disc elements  14 . The blade elements  18  are in this case fastened to a portion  19  of the shank  20  preferably by means of welding. As has already been described in detail with reference to  FIG. 4 , the portion  19  may in this case be designed as a thickened portion (not illustrated). A tubular device  10  is introduced through corresponding orifices  22  through the shank  20  into the blade elements  18 , the tubular device  10  preferably not being welded to the shank  20 . A disc element  14  is fastened to the tubular device  10  at each of the two ends in order to support the blade elements  18  additionally radially. For venting, an orifice  23  is provided in the tubular device  10 , in order to vent the latter and the blade elements  18 . 
     The blade elements  18  are arranged, for example, spirally on the shank  20  of the apparatus  2 . At the upper end of the shank  20 , a drive or holding pin  5  is provided, which has a protective cap  7  at its lower end. 
     In this exemplary embodiment, an additional sleeve  37  is arranged on the shank  20 , for example, in the region of the glass level. The sleeve  37  in this case projects above a glass level by a predetermined length L 1 , for example, of 10 mm-100 mm or preferably of 80-100 mm, and/or extends with a predetermined length L 2 , for example, of 10-20 mm, below the glass level. In principle, the length L 1  may even be markedly greater than 100 mm. The length L 1  should be selected such that the sleeve  37  covers a part of or the entire region of the shank  20  where evaporation occurs. This applies correspondingly to the length L 2 . The selected length L 2  may likewise be greater than 20 mm or lower than 10 mm, insofar as evaporation of the shank  20  can be suitably reduced or prevented. 
     The inventor found that the evaporation of the shank  20 , which occurs, for example, during the agitation of molten glass, can be prevented by virtue of the provision of the sleeve  37  described above. Hitherto, during the evaporation process, an appreciable part of the shank has evaporated, and therefore the shank or the agitator loses weight with progressive use, with the result that the service life of the agitator is reduced. This is prevented by the sleeve  37  according to the invention. The sleeve  37  may in this case be produced from an alloy similar to the protective cap  7 , for example from a PGM material or another suitable material. Basically, an oxide dispersion-strengthened PGM material may also be used. 
     The sleeve  37  may be fastened to the shank  20  by being pushed on or shrunk on. Basically, however, it may also be fastened to the shank  20  by means of welding, insofar as it has no carrying function, as is the case in  FIG. 8   b.    
     Alternatively, the sleeve  37  may also be arranged (not illustrated) at a distance from the glass level, the distance being selected such that an evaporation of the shank  20  can be suitably prevented or reduced. 
     The sleeve  37  may be employed in all the embodiments and exemplary embodiments described. It is also conceivable in this case to combine the two sleeves  28 ,  37  into one continuous sleeve, instead of designing each of the sleeves  28  and  37  as an individual part, as described above. 
       FIG. 9   a - c  illustrate a further exemplary embodiment of the apparatus  2  according to the invention in the first embodiment. In this case, the agitator first has a shank  20 , at the upper end of which is provided a drive or holding flange  5  which has a protective cap  7 . Furthermore, the shank  20  has at its lower end a tubular device  8  (prolongation of the shank  20 ) which is introduced into an actuating device  4 . The actuating device  4  consists, for example, of three actuating elements  16 . Moreover, a sleeve  28  is provided on the tubular device  8 , in order to form a thickened portion to which the actuating element  16  is fastened by means of welding. A plurality of plate elements  24  are inserted through the sleeve  28  and the tubular device  8 . In addition, at least one supporting ring  32  may also be provided, in order to increase the dimensional rigidity of the actuating device  4 . Furthermore, a disc element  36  is provided for centring the tubular device  8 . The disc element  36  in this case has an orifice through which the tubular device  8  is led. The disc element  36  is in this case fastened to the actuating element  16  on the inside, for example by means of welding. Further, a disc element  12  is provided, which may have, for example, a projection  13  as shown in the enlarged detail Z. The two actuating elements  16  are in this case pushed on to the disc element  12  and bear against the projection  13 . The actuating elements  16  and the disc element  12  are in this case connected by means of welding. Alternatively, the two actuating elements  16  may also be welded directly to one another, and the disc element  12  may be welded to an actuating element  16  from the inside, as already stated in detail in the description relating to  FIGS. 1 ,  2   a  and  2   b.    
     Blade elements  18  in the form of sheet-like elements are fastened to the outside of the actuating device  4 , for example, by means of welding. Additionally, or alternatively, the blade elements  18  may also have a closed profile, as shown, for example, in  FIG. 11   b.    
       FIG. 10   a - c  show a fourth embodiment according to the invention which is similar to the first embodiment. In this case the apparatus is designed, for example, as a Vello needle or down-draw needle and has a bell-shaped actuating device. The shank  20  is in this case provided at one end with a drive or holding flange  5 , a detail of this being shown in  FIG. 10   a - c . The drive or holding flange  5  has a protective cap  7  at its lower end. The shank  20  is provided at its other end with a thickened portion. The thickened portion may in this case be formed by a larger diameter and/or a greater wall thickness and/or a sleeve  28 , comparably to the thickened portions  9 ,  15  and  21 . In the illustration in  FIG. 10   a - c , the shank  20  is provided outwardly, for example, with a stepped wall thickness. The shank  20  in this case becomes thinner downwards, since the transverse forces and the bending moment profile increase upwards and the shank  20  therefore has to have a thicker design at the top, whereas it may have a thinner design at the bottom. This, however, is only one example of a load situation. In the reverse load situation, the selected wall thickness of the shank  20  would, for example, have a thicker profile downwards. So as not to weaken the shank  20  by a weld seam, a sleeve  28  is provided, which forms the thickened portion. In this case, an actuating element  16  is fastened to the sleeve  28  by means of welding, as illustrated in the detail C of  FIG. 10   b . To absorb the axial forces, plate elements  24  may additionally be provided, which are inserted through the shank  20  and are welded to the actuating element  16  from inside. The actuating element  16  is closed at the lower end by means of a cover  34  having an orifice  35 . The venting of the apparatus  2  has not been illustrated in  FIG. 10   a - c.    
     Furthermore, a fifth embodiment of the apparatus  2  according to the invention is shown in  FIG. 11   a - c . The apparatus  2  is in this case designed, for example, as a plunger. The shank  20  is in this case provided at one end with a drive or a holding flange  5  which has a protective cap  7  at its lower end. The shank  20  is widened in diameter at its other end in order to form an actuating device. The shank  20  is in this case closed at its end by means of a hemispherical actuating element  16 . A spiral blade element  18  is fastened to the outside of the widened portion, preferably by means of welding. For venting, the shank  20  has an orifice  33  above the glass level (not illustrated) in order to discharge the air inside the shank  20  outwards. 
     Sundry variations of the blade elements  18 , such as are used in the embodiments and exemplary embodiments described above, are illustrated in  FIGS. 12   a  and  12   b .  FIG. 12   a  shows various shapes of blade elements  18  illustrated in cross section. The blade elements  18  are in this case designed in the form of sheet-like elements.  FIG. 12   b  illustrates, furthermore, blade elements  18  in the form of closed profiles or rather hollow profiles in cross section. Both the sheet-like elements in  FIG. 12   a  and the hollow profiles in  FIG. 12   b  may be arranged, for example, as single-flight or multi-flight spirals. It is obvious to an average person skilled in the art, however, that the sheet-like elements or hollow profiles may be arranged on the shank  20  or the actuating device and combined with one another in any desired way, depending on their function. 
       FIG. 13   a - f  and  14  illustrate various shapes for the shanks  20 , such as may be used in the embodiments and exemplary embodiments described above, the shanks  20  preferably being of seamless or at least partially seamless design. The shanks  20  may in this case have a continuous wall thickness ( FIG. 13   a ) or a stepped wall thickness ( FIG. 13   b ). 
     Furthermore, the shank  20  may also have a continuously identical wall thickness, but a stepped diameter ( FIG. 13   c ). Moreover, the shank  20  may also have a stepped wall thickness and a stepped diameter ( FIG. 13   d ). Furthermore, according to  FIGS. 13   e  and  13   f , the shank  20  may also have a plurality of shanks inserted coaxially one in the other, in which case these shanks  20  may be shanks according to  FIG. 13   a, b, c  and/or  FIG. 13   d . Instead of a stepping, flowing transitions may also be formed.  FIG. 14  shows possible radial cross sections of the shanks suitable for the invention. 
     The elements, described above with reference to the figures, of the various embodiments of the apparatus according to the invention, including, inter alia, the shanks  20 , tubular devices  8 ,  10 , actuating devices  4 ,  6  with actuating elements  16 , disc elements  12 ,  14 ,  36 , supporting rings  32 , sleeves  28 ,  37 , plate elements  24 , protective caps  7  and blade elements  18 , are preferably all or at least parts of them made from a PGM material, preferably from oxide dispersion-strengthened PGM material or from another suitable ODS material. However, the drive or holding flange, basically, does not necessarily also have to be produced from a PGM material or oxide dispersion-strengthened PGM material. Alternatively, as described above, it may however also be produced from a “base” material, such as, for example, a heat-resistant steel. The shank  20 , as described above in the embodiments, is preferably seamless, but at least partially seamless. The same also applies to the actuating elements  16 , these, too, being seamless or at least partially seamless. 
     The disc elements, plate elements and/or supporting rings may be provided with orifices  11  for weight reduction. 
     Furthermore the various embodiments and exemplary embodiments, as described above with reference to the drawings, may be combined with one another, in particular individual features of these. 
     In particular, the configuration of the actuating device in the first embodiment may also be combined with the reinforced blade elements of the second embodiment. Thus, an apparatus is possible which has an actuating device according to the first embodiment and, in addition, at least one blade element according to the second embodiment. This applies likewise to the other embodiments illustrated in the figures. 
     Moreover, the actuating elements  16 , blade elements  18  and disc elements  12 ,  14 ,  36 , as illustrated, for example, in  FIGS. 4 ,  5   a ,  6   c ,  7   a - c ,  8   a - c  and  9   a - c , do not necessarily have to have a round cross section. The blade elements  18  may also have cross sections, as illustrated in  FIG. 12   b . This also applies correspondingly to the actuating elements  16  and the disc elements  12 ,  14 ,  36 , connected to them, and also the tubular device  8 ,  10 . 
     The embodiments described above are used in a temperature range with a mean operating temperature of 1000° C.-1500° C. In this temperature range, torques of, for example, up to 100 N·m may be achieved, or torques in ranges of, for example, 10 N·m to 30 N·m or 30 N·m to 80 N·m or up to 100 N·m, with service lives of several years. Furthermore, the length of the agitators or plungers, etc. according to the invention may lie, for example, between 1 m and 2.5 m. The blade elements may have an overhang of up to 500 mm in diameter. As regards the material, quantities of, for example, up to 50 kg of PGM material or oxide dispersion-strengthened PGM material can be processed. 
     LIST OF REFERENCE SYMBOLS 
     
         
           2  Apparatus 
           4  Actuating device 
           5  Drive or holding flange 
           6  Actuating device 
           7  Protective cap 
           8  Tubular device 
           9  First thickened portion 
           10  Tubular device 
           11  Orifice (disc element) 
           12  Disc element 
           13  Projection 
           14  Disc element 
           15  Second thickened portion 
           16  Actuating element 
           18  Blade/blade element 
           19  Portion (on the shank) 
           20  Shank 
           21  Thickened portion 
           22  Orifice (shank) 
           23  Orifice (venting) 
           24  Plate element 
           25  Weld seam 
           26  Break-out 
           27  Upper end (of the plate element) 
           28  Sleeve 
           29  Orifice (shank) 
           30  Slot (in the actuating element for receiving the upper end of the plate element) 
           31  Clearance (sleeve) 
           32  Supporting ring 
           33  Orifice 
           34  Cover 
           35  Orifice 
           36  Disc element 
           37  Sleeve