DEVICE AND METHOD FOR THE PRODUCTION OF A METALLIC STRIP

Abstract

A device for the production of a metallic strip using a rapid solidification technology is provided. The device includes a movable heat sink with an external surface onto which a melt is poured and on which the melt solidifies to produce the strip, and which device includes a rolling device which can be pressed against the external surface of the movable heat sink while the heat sink is in motion.

Claims

1. A metallic strip having a nickel-based composition and having a length of at least 20 km and at least one surface with a surface roughness R.sub.a, measured as center-line average heights, of less than 0.6 μm at a point at least 10 km before an end of the strip.

2. The metallic strip according to claim 1, wherein the surface with a surface roughness R.sub.a of less than 0.6 μm at a point at least 10 km before an end of the strip is a surface solidified at an external surface of a movable heat sink.

3. The metallic strip according to claim 1, wherein the metallic strip is amorphous.

4. The metallic strip according to claim 1, wherein the metallic strip is nanocrystalline.

5. The metallic strip according to claim 1, wherein the metallic strip consists of T.sub.aM.sub.b, wherein 70 atomic %≤a≤85 atomic % and 15 atomic %≤b≤30 atomic %, T being Ni and one or more of the elements Fe, Co, Mn, Cu, Nb, Mo, Cr, Zn, Sn and Zr, and M being one or more of the elements B, Si, C and P.

6. The metallic strip according to claim 1, wherein the surface roughness R.sub.a has a value between 0.2 μm and 0.6 μm.

7. The metallic strip according to claim 1, wherein the surface roughness R.sub.a varies by less than +/−0.2 μm over a length of at least 10 km.

8. The metallic strip according to claim 1, wherein the strip is produced by a process comprising: providing a melt, providing a movable heat sink with an external surface, pouring the melt onto the moving external surface of the moving heat sink, the melt solidifying on the external surface to form a strip, pressing a rolling device against the external surface of the heat sink while the heat sink is in motion, wherein the pressing of the rolling device against the external surface of the heat sink smooths the external surface of the heat sink.

9. A metallic strip having a nickel-based composition and having at least one surface with a surface roughness R.sub.a, measured as center-line average heights, of greater than 0.2 and less than 0.6 μm at a point which lies at least 20 km away from the beginning of the strip, wherein the surface with a surface roughness R.sub.a of less than 0.6 μm is a surface solidified at an external surface of a movable heat sink.

10. The metallic strip according to claim 9, wherein the metallic strip is amorphous.

11. The metallic strip according to claim 9, wherein the metallic strip is nanocrystalline.

12. The metallic strip according to claim 9, wherein the metallic strip consists of T.sub.aM.sub.b, wherein 70 atomic %≤a≤85 atomic % and 15 atomic %≤b≤30 atomic %, T being Ni and one or more of the elements Fe, Co, Mn, Cu, Nb, Mo, Cr, Zn, Sn and Zr, and M being one or more of the elements B, Si, C and P.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Embodiments are explained in greater detail below with reference to the drawings.

[0048] FIG. 1 is a first diagrammatic view of an embodiment of a device with a rolling device for the production of a metallic strip using a rapid solidification technology;

[0049] FIG. 2 is a second diagrammatic view of the device from FIG. 1;

[0050] FIG. 3 is a third diagrammatic view of the device from FIG. 1;

[0051] FIG. 4 is a detailed view of the rolling device from FIG. 1;

[0052] FIG. 5a shows the surface roughness of a strip underside facing the heat sink, as produced by means of the device from FIG. 1;

[0053] FIG. 5b shows the surface roughness of an underside of a comparative strip;

[0054] FIG. 6 is a graph showing the strip thicknesses as determined by weighing as a function of track length;

[0055] FIG. 7 is a graph showing a comparison of the surface parameter (centre-line average heights R.sub.a) of the strip undersides for a strip produced on a casting track which has not been roller-burnished and for a strip produced on a casting track which has been roller-burnished as a function of track length;

[0056] FIG. 8 is a graph showing a comparison of the surface parameter (peak-to-valley heights R.sub.z) of the strip undersides for a strip produced on a casting track which has not been roller-burnished and for a strip produced on a casting track which has been roller-burnished as a function of track length;

[0057] FIG. 9 is a graph comparing the fill factors of measuring cores wound from a strip produced on a casting track which has not been roller-burnished and from a strip produced on a casting track which has been roller-burnished as a function of track length;

[0058] FIG. 10 is a graph that shows the development of the permeability of a strip produced on a continuously worked casting track as a function of track length;

[0059] FIG. 11 is a graph that shows the development of the permeability of a strip produced on a casting track which is not continuously worked as a function of track length;

[0060] FIG. 12 is a graph that compares the μ.sub.dyn/μ.sub.sin ratios at H=15 mA for a strip cast on a roller-burnished casting track and a casting track which has not been roller-burnished as a function of track length; and

[0061] FIG. 13 is a graph that compares the normalised permeability μ.sub.80 for these strips.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0062] FIGS. 1 to 3 are various diagrammatic representations of a device 1 for the production of a metallic strip 2 using a rapid solidification technology.

[0063] The device 1 comprises a heat sink 3 in the form of a wheel 4 which rotates clockwise about an axis of rotation 5 as indicated by arrow 19. The wheel 4 has a rim 6 with an external surface 7 onto which a melt 8 is poured. The melt 8 consists of a metal or an alloy which is stored in a container 9. The embodiment of device 1 further comprises a heater (such as, e.g., an induction heater) for producing the melt 8 from the metal or alloy.

[0064] The device 1 further comprises a rolling device 11 with a roller 12. The roller 12 rotates on an axis of rotation 13 and is arranged such that it can be pressed against the external surface 7 of the rim 6 of the heat sink 3 under pressure as indicated by arrow 21. The roller 12 rotates anticlockwise and therefore in a direction opposed to the direction of rotation of the wheel 4 (i.e., where the roller 12 contacts external surface 7 of rotating wheel 4, the surfaces move in a parallel direction). Together with the rotating wheel 4, the roller 12 forms a rolling mill which is used to roller-burnish and thus smooth the external surface 7 of the rim during the casting process.

[0065] The roller 12 is so arranged on the wheel 4 that it works the external surface 7 at a point 14 which is upstream (with respect to the direction of rotation of wheel 4) of the point 15 where the melt 8 first contacts the external surface 7. The melt 8 is therefore poured onto a smooth external surface 7 and solidifies on this roller-burnished and smoothed surface. Owing to the rotating wheel 4 and the stream of melt 8, a long strip 2 is produced as the melt 8 solidifies. As a result of the volume shrinkage of the solidifying melt 8 and the rotating wheel 4, the strip 2 separates from the external surface 7 and can be wound onto a reel (not shown in the drawing).

[0066] The underside 16 of the strip 2 approximately adopts the contour of the external surface 7. The surface of the underside 16 of the strip 2 can be kept uniform if the roller 12 continuously works the external surface 7 during the casting process. This permits the production of a long strip 2 with a surface roughness which worsens only slightly from the beginning to the end. The top side 17 of the strip 2 solidifies freely and therefore does not reflect the contour of the external surface 7. In addition, cleaning brushes for removal of debris from the surface of heat sink 3 may also be included, or these may be absent.

[0067] As FIGS. 2 and 3 show, the roller 12 of the rolling device 11 may be moved in directions parallel to the axis of rotation 5 of the heat sink 3 as indicated by the arrow 18.

[0068] The roller 12 may be arranged such that it works different tracks on the rim. The roller 12 may be moved parallel to the axis of rotation of the heat sink while being in contact with the rotating heat sink 3. In this embodiment, the rim 6 or the external surface 7 can be worked and smoothed spirally.

[0069] FIG. 4 is a diagrammatic representation of the working effect of the rolling device 11 with the roller 12 in contact with the external surface 7 of the heat sink 3.

[0070] The rotation of the heat sink 3 is in FIG. 4 illustrated graphically by the arrow 19, while the counter-rotation of the roller 12 is illustrated by the arrow 20. In the Figure, both arrows can be illustrated as rotating toward the viewer, out of the plane of the paper, or both rotating away from the viewer toward the plane of the paper. The pressure applied by the roller 12 on the external surface 7 is graphically illustrated by the arrow 21. In this embodiment, the roller is moved across the external surface parallel to the axis of rotation of heat sink 3. This is illustrated in FIG. 4 by the arrow 22.

[0071] On the left-hand side of the roller 12, the figure shows the external surface 7 of the heat sink after the strip has been formed on this external surface 7. On the right-hand side of the roller, we see the external surface after roller-burnishing with the roller 12, the roughness of the external surface 7 having been reduced by roller-burnishing. This method can also be used continuously during the casting and production of the strip. As a result, the melt 8 always meets a smooth external surface 7, so that the underside 16 of the solidified strip 2 has a smooth surface along its entire length.

[0072] To explain the effect of working a heat sink surface 7 during a casting process, an experiment is carried out which permits a direct comparison between a worked surface and a surface which has not been worked.

[0073] For these experiments, the alloy Fe.sub.RCu.sub.1Nb.sub.3Si.sub.15.5B.sub.7, which is generally used for inductive cores, is chosen. In addition to a comparison of geometrical data, this permits the evaluation of magnetic properties using measuring cores. The chosen strip width is 25 mm, so that the strip did not have to be slit, for example by cutting, in order to produce the measuring cores.

[0074] To avoid the effects of unintentional parameter variations on the results, the whole experiment is carried out in one casting, i.e. all results are based on the same melt, the same heat sink including preparation and the same casting parameters. The only aspect which is changed is the position of the casting track.

[0075] To work the surface of the heat sink, a specific further development of “roller-burnishing” or “planishing” is chosen, which is adapted to the parameters of the casting process for rapidly solidified strip. The equipment comprises a resiliently mounted rolling head with a special roller, which moves parallel to the axis of the heat sink at a low feed rate. The working is carried out by the roller 12 which is pressed against the surface 7 of the heat sink 3 with a defined force as shown in FIG. 4.

[0076] In the first phase of the experiment, approximately 50 000 m of a 25 mm wide strip were poured onto a casting track which was worked continuously as described above.

[0077] In the next phase, another 50 000 m were to be poured onto a parallel track which had not been worked, in order to produce a strip for comparison. This process was, however, aborted after about 30 000 m for reasons of quality, as the state of the surface had deteriorated excessively.

[0078] The strips produced in this way were then evaluated and compared using geometrical and magnetic criteria. For the geometrical evaluation, the samples were left in the “as cast” state. For the evaluation of the magnetic properties, the wound cores were subjected to a heat treatment in order to obtain the magnetically relevant nanocrystalline material state.

[0079] The surface parameters R.sub.a and R.sub.z and the fill factor of the measuring cores were chosen as comparative variables, R.sub.a being the centre-line average height and R.sub.z being the averaged peak-to-valley height.

[0080] The surface parameters were determined on the side of the strip which faces the heat sink and largely reflect wear-related changes on the heat sink surface, while the fill factor is an essential quality criterion in magnetic cores.

[0081] FIG. 5a illustrates the roughness values of the underside of the strip, i.e. the side facing the heat sink, of a casting track which has been worked after ca. 39 800 m.

[0082] FIG. 5b illustrates the roughness values of the underside of the strip (facing the heat sink) of a comparison strip of a casting track which has not been worked after ca. 23 000 m.

[0083] The comparability of the investigated variables is at its best if, in addition to the casting parameters, the strip thickness is similar as well. This is because the fill factor change of the tested cores is greatly influenced by the relationship between roughness and strip thickness.

[0084] The strip thickness was determined by weighing in order to avoid errors caused by roughness in feeler measurements. Strip thickness values obtained by weighing are illustrated in the diagram of FIG. 6. FIG. 6 shows that the strip thickness values agree in both cases very well along the entire cast.

[0085] FIG. 7 shows a comparison of the centre-line average heights R.sub.a of the strip undersides, approximately in the middle of the width of the strip, for a strip produced on a casting track which has not been roller-burnished and for a strip produced on a casting track which has been roller-burnished.

[0086] FIG. 8 shows a comparison of the peak-to-valley height R.sub.z of the strip undersides, approximately in the middle of the width of the strip, for a strip produced on a casting track which has not been roller-burnished and for a strip produced on a casting track which has been roller-burnished.

[0087] In the diagrams of FIGS. 7 and 8, the development of the surface parameters R.sub.a and R.sub.z is plotted along the lengths of the worked and the non-worked casting track.

[0088] The comparison shows that the working of the heat sink surface can maintain and sometimes even improve the quality of the initial preparation over a very long casting process. In contrast, the surface of casting tracks which have not been worked deteriorates very rapidly.

[0089] Such differences are also found if we consider the fill factor of the measuring cores as a comparative variable. The diagram of FIG. 9 compares the fill factors of measuring cores (diameter 24.3/13×25 mm) wound from a strip produced on a casting track which has not been roller-burnished and from a strip produced on a casting track which has been roller-burnished.

[0090] The fill factors of the two groups noticeably drift away from each other after a relatively short run, illustrating that even small changes in the surface quality of the heat sink result in significant quality differences in the finished product.

[0091] The surface formation of the strips can affect their magnetic properties. It for example significantly affects the shape of the hysteresis loop and the remagnetisation processes in alternating fields.

[0092] The three characteristics μ.sub.sin at H=15 mA/cm, μ.sub.dyn at H=15 mA/cm and the μ.sub.dyn/μ.sub.sin ratio are measured and evaluated. These values are mainly related to the requirements of current transformer cores for earth leakage circuit breakers at 50 Hz.

[0093] The aim is high permeability accompanied by a high ratio. Empirical data permit comparisons between different permeability values and ratios. The normalised value is μ.sub.80 (=μ.sub.dyn at H=15 mA/cm and μ.sub.dyn/μ.sub.sin=0.8).

[0094] In the diagrams of FIGS. 10 and 11, the permeability developments are initially shown separately for worked and non-worked casting tracks. The permeability μ.sub.sin should remain largely constant, because it is theoretically determined only by the alloy and the heat treatment.

[0095] FIG. 10 shows the development of the permeability of a strip produced on a continuously worked casting track. The permeability changes only slightly over a length of 50 000 m.

[0096] FIG. 11 shows the development of the permeability of a comparative strip produced on a casting track which has not been worked. In contrast to FIG. 10, μ.sub.sin can be seen to have decreased considerably. This indicates significant disturbing influences after a relatively short track length.

[0097] As the permeability μ.sub.dyn reacts even more strongly to changes than μ.sub.sin, the μ.sub.dyn/μ.sub.sin ratio and the normalised μ.sub.80 decrease particularly strongly, which indicates a significant deterioration of linearity.

[0098] FIG. 12 compares the μ.sub.dyn/μ.sub.sin ratios at H=15 mA/cm for a strip cast on a roller-burnished casting track and a casting track which has not been roller-burnished, and FIG. 13 compares the normalised permeability μ.sub.80 for these strips. Both values are reduced more for a strip cast on a casting track which has not been roller-burnished than for a strip cast on a roller-burnished casting track.

[0099] On the basis of the results of the first experiments, it seems possible to achieve with this method and this alloy reliably and repeatably, at permeability values of μ.sub.sin >200 000, a μ.sub.dyn/μ.sub.sin ratio >0.80, possibly even >0.85.

[0100] On the basis of various geometrical variables (R.sub.a, R.sub.z and fill factor) and magnetic variables (μ.sub.sin, μ.sub.dyn and the μ.sub.dyn/μ.sub.sin ratio), it can be shown that the uniformity of product quality and the efficiency of the production method can be improved by the continuous working of the heat sink surface during the casting process.

[0101] The invention having been described herein with respect to certain of its specific embodiments and examples, it will be understood that these do not limit the scope of the appended claims.