DE1061527B - Process for zone-wise remelting of rods and other elongated workpieces - Google Patents

Description

.MBL

The known method for gradually melting and solidifying one zone by zone in the form of a Elongated body located material is mainly used to remove the material from undesired Clean additives. It is based on the fact that as a result of the jump in concentration of the impurity between the solid and liquid phase an accumulation of the impurity - depending on the sign the jump in concentration for the respective contamination - either on the liquid or the solid side of this jump point is created. As a result, the melting zone gradually moves from one to the other The end of the elongated body (hereinafter referred to as "rod" for short) is displaced, can transport the contamination to one or the other end of the rod. It is known the process to repeat several times to increase the degree of purity achieved; it is also known to accelerate the process several melting zones at certain constant distances from each other at the same time to use. Here, either the rod relative to the heat source arrangement or this relative to be moved to that. In the practical implementation of the process, a number of Difficulties arise. It has z. B. found that in the previously used horizontal Arrangement of the rod in a corresponding carrier, for example .Schiffchen, the melting zones in were inhomogeneous; on the one hand, this was a consequence of the sedimentation effect or segregation different specific gravity and, on the other hand, resulted from the fact that the rotationally symmetrical around the rod arranged heat source, which for example consisted of a radiating glow ring, partially through the boat was shaded so that the heating within the melting zone was non-uniform. This resulted in a concentration inhomogeneity of the impurity along the melting zone in a vertical direction Direction.

The method, in particular the cleaning process, can be improved by avoiding these inhomogeneities accelerate or drive up to even higher degrees of purity. Another beneficial one The effect that is achieved by avoiding the inhomogeneities is that an improved Zone melting process leads to particularly uniform single crystals because of the relative displacement the melting zone along the rod becomes a crystal on the solidifying side of the melting zone formed if a seed crystal is formed at the first melting zone location before or at the beginning of the melting process is arranged in a known orientation.

Thus, in order to achieve the advantages described, the elongated, zone-by-zone successively becomes the melting process
for zone-wise remelting

of rods and others
elongated workpieces

Applicant:
Siemens & Halske Aktiengesellschaft,

Berlin and Munich,
Munich 2, Witteisbacherplatz 2

Dr. Karl Siebertz and Dr. Heinz Henker, Munich, have been named as the inventor

zende and again to be brought to solidification body so arranged in the room and / or heated that within the melting zone or the melting zones perpendicular to their direction of advance relative to the elongated body a minimum of temperature and / or concentration or mechanical Stress inhomogeneities occurs. This is z. B. achieved in that the longitudinal extension of the to melting and re-solidifying body and thus the direction of progress of the melting zone or zones is oriented vertically. The temperature homogeneity can also be achieved with a horizontal Achieve arrangement in that either the body to be melted and not to be solidified again arranged in a shuttle, but in an expediently cylindrical tube, which is closed on all sides is, which compared to the per se uniform radial heating, for example by means of a radiant glow ring, exerts the same shielding effect in all directions; or there is one Another possibility is the heating when using a boat on the one shaded by it Page to be dimensioned accordingly stronger. It has already been suggested that the one to be melted and again to be solidified elongated body practically upright and only to the to hold both ends, whereby the melting zone is dimensioned so thin in the axial direction of the rod, that the surface tension of the molten material is sufficient to hold it between the rigid parts to hold both sides of the melting zone together. This ensures that the melting zone does not have any

Has contact with a vessel wall and consequently does not absorb any new impurities from it.

In this so-called crucible-free zone melting with a vertical rod, there is also complete rotational symmetry preserved, which is advantageous for the formation of egg crystal rods. When pulling through the melting zone through the rod becomes, so to speak, the solidifying part of the cantilevered melt drawn.

To initiate the process, there are two bars, one of which is already an orientated germ Single crystal is held in moderate contact with one another, so when melting occurs in the contact zone initiated and the melting zone is continued from there in the direction of the polycrystalline part; the crystallization begins in the orientation determined by the nucleus and spreads over the entire rod monocrystalline fort; a single crystal is pulled from the freely floating melt. The melt has no contact with the walls of the vessel, so remains as pure as desired, and a crystallization germination effect is prevented by the wall.

The invention relates to a method for zone-wise remelting of rods and others elongated workpieces, in which by a heat source in which only in places, preferably a molten zone is created on the workpiece held at its ends and solid parts of the workpiece separated from one another by the molten zone are freely supported, while as a result of a relative displacement of the workpiece taking place parallel to the axis of the workpiece to the heat source, the melted zone gradually traverses and melts the workpiece. According to the invention, the cross section of the material crystallizing out of the molten zone by a relative displacement of the two fixed, Parts of the workpiece separated by the melted zone are regulated or balanced. By such an axial displacement of the rod parts delimiting the melted zone, which are either pulled apart or closer together, becomes a reduction or an enlargement of the cross section of the melted zone. The material crystallizes accordingly the melted zone with a smaller or a larger cross-section. This can initially a jump in volume occurring during solidification can be compensated for. Furthermore, by an analogous Acting on these measures a thick stick: to a thin and a thin stick to a thick one Rod to be remelted. The cross section of the crystallizing from the molten zone can be Material through which due to a rapid and unidirectional rotation of the entire Turn the workpiece adjusting centrifugal force further increased.

The method according to the invention can be implemented in a variety of ways. For example is it possible, instead of premelted material, e.g. B. a premelted rod, of presintered Material, e.g. B. sintered powder to go out and the melting of the sintered material in the Execute arrangement according to the invention. You can-also just pre-pressed and with a fleeting one Use binder-bound powder.

In order to only support the rod in places, the small axial extension of the To be able to create a melting zone, it is necessary to concentrate the heating on a well-defined point. According to a special embodiment of the inventive concept, this is done by irradiation the heat of fusion using optical aids; a semi-toroidal one is expediently used for this purpose Concave mirror, which surrounds, for example, a glowing ring radiating the heat of fusion, which is heated, for example, by high frequency or direct current passage.

ίο In the drawing are some embodiments the device according to the invention shown for example.

In Fig. 1, 1 denotes a bismuth rod which is held at both ends by two brackets 2 and 3 in a vertical orientation. 4 is an annular heat source, e.g. B. a glow ring which heats the zone 5 of the rod 1 by radiation and melts it. The arrow 6 indicates the direction of advance of the glow ring 4 relative to the rod 1. That is, the glow ring is gradually shifted vertically from top to bottom or the holding arrangement 2, 3 with the rod 1 gradually shifted from bottom to top, the melting zone 5 gradually moving through the rod from top to bottom. The melting zone 5 is shown bulbous, which is intended to indicate that it experiences a certain deformation of the surface due to the surface tension. The device according to FIG. 1 is preferably used for cleaning the bismuth of impurities by the method known per se. The diameter of the rod which crystallizes out is then regulated in the desired manner by a corresponding axial displacement of the two solid rod parts separated from one another by the melted zone.

In Fig. 2 is an embodiment of the heating device for generating the melting temperature for example shown. 10 denotes a glow ring which is surrounded by a concave mirror 11 is.

The beam path generated by the semi-torus-shaped concave mirror 11 can be seen from FIG. 3 will. As you can see, there is no precisely defined focus of the radiation, but a long, disk-shaped one Coma, which on the surface of the rod is a narrow and well-defined ring zone of the Generates radiation.

The facility for carrying out the zone melting process, as shown in the figures, for example, is in accordance with what is known per se Melting process arranged in an inert protective gas atmosphere. It is even cheaper in many Cases to carry out the procedure under vacuum.

Claims (13)

Patent claims: 1. Process for the zone-wise remelting of stalls and other elongated workpieces, in the one held by a heat source in the only in places, preferably at its ends Workpiece creates a melted zone and from the adjacent, through the melted Zone separate solid parts of the workpiece is freely carried while as a result of a relative displacement of the parallel to the axis of the workpiece Workpiece to the heat source the melted zone gradually migrates through the workpiece and remelted, characterized in that the cross section of the crystallizing from the melted zone Material through an in-axis direction of the workpiece, relative displacement of the two fixed, through the melted Zone separate parts of the workpiece is regulated or compensated. 2. The method according to claim 1, characterized in that the cross section of the melted Zone of crystallizing material through which due to a rapid and co-rotating rotation of the entire workpiece adjusting centrifugal force is influenced. 3. The method according to claim 1 or 2, characterized in that the molten zone through a heat source surrounding the workpiece in a ring shape is generated. 4. The method according to any one of claims 1 to 3, characterized in that it is in a vacuum or is carried out in an inert protective gas atmosphere. 5. The method according to any one of claims 1 to.4, characterized in that it is on a sintered and / or pressed rod-shaped body made with a volatile binder is made. 6. The method according to any one of claims 1 to 5, characterized in that a single crystal is produced will. 7. The method according to claim 6, characterized in that that to establish the crystallization in a certain orientation seed crystals in the bodies to be remelted are stored. 8. The method according to any one of claims 1 to 7, characterized in that the to be treated Body is arranged vertically or almost vertically. 9. The method according to any one of claims 1 to 8, characterized in that the body is kept rotating. 10. The method according to any one of claims 1 to 9, characterized by one within the Melting zone a maximum of temperature symmetry and / or concentration or mechanical Arrangement or configuration of the melting zone causing tension homogeneity Heat source. 11. The method according to any one of claims 1 to 10, characterized in that the creation of the melting zone by optical means, for example one that concentrates the radiation on a narrow area of the body to be treated Concave mirror arrangement, is made. 12. The method according to claim 11, characterized in that an annular radiation source, For example, a directly or indirectly heated glow ring is used, the so is arranged within a semi-torus-shaped reflector that a disc-shaped coma of the Radiation is created. 13. The method according to any one of claims 1 to 12, characterized in that when held vertically Rod the melted zone is moved through the rod from top to bottom. Considered publications:
German patent specification No. 1 014 332. 1 sheet of drawings