EP0099599B1

EP0099599B1 - Method of forming continuous strip of amorphous metal

Info

Publication number: EP0099599B1
Application number: EP83200882A
Authority: EP
Inventors: Johannes Bernardus Antonius Bosman
Original assignee: Akzo NV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1982-07-15
Filing date: 1983-06-16
Publication date: 1986-03-26
Also published as: JPH0478391B2; JPS5924556A; ATE18726T1; EP0099599A1; DE3362675D1

Abstract

Continuous strips of amorphous metal are formed by forcing a row of jets of molten metal through a corresponding row of orifices in the nozzle of a reservoir for molten metal onto a chill surface moving transverse to said row and within a distance of 2,5 mm from said nozzle, on which surface the jets join together to form a melt puddle for solidication by very rapid cooling of the metal into an amorphous strip which is carried off by the chill surface. In order to obtain thicker strips than has been possible heretofore, the metal is forced onto the chill surface by at least two parallel rows of jets emerging from parallel rows of orifices in the same nozzle and the melt puddle is formed by the jets of all rows in combination.

Description

The invention relates to a method of forming a continuous strip of amorphous metal, comprising forcing a row of jets of molten metal through a corresponding row of orifices in the nozzle of a reservoir for the molten metal onto a chill surface moving transverse to said row and within a distance of 2,5 mm from said nozzle, on which surface the jets join together to form a melt puddle for solidification of the metal into an amorphous strip which is carried off by the chill surface.
A method of the type indicated above is known from U.S. Patent Specification 4 221 257. Said patent specification relates to the problem of the manufacture by the melt spin process of amorphous metal strips wider than 6 mm and having a uniform thickness. In the melt spinning process used to that end a short jet of liquid metal is directed against a rapidly moving chill surface, such as that of a rotating chill roll, on which the jet forms a puddle which cools to solidify into a strip. In that process it is possible to have the metal solidify in the amorphous state by applying very rapid cooling. In said patent specification it is mentioned that using a single jet of liquid metal results in obtaining a strip having a maximum width of about 6 mm, but that it has not been found possible to make wider strip that yet have a uniform cross-section. This difficulty is attributed to the fact that the molten metal puddle tends to assume the equilibrium shape of a droplet, i.e. thick at the centre and thin at the edges. As a result, it is difficult, if not impossible, to make uniformly chilled strips having a width greater than about 6 mm and a uniform thickness in cross-section.
Said patent specification also mentions that using a row of jets of liquid metal does not lead to a wider strip having uniform properties. In fact, the principal difficulty which is considered to be attached to the use of a plurality of jets is that either the jets do not join together to form a common puddle on the chill surface, or the jets do run together to form a ridge on the strip. These factors result in such irregularities that the amorphous strip formed does not have a uniform thickness or isotropic properties.
As a solution to these problems in the manufacture of strip wider than 6 mm said patent specification proposes the use of a slotted nozzle for the jet of liquid metal, which nozzle is to satisfy particular requirements, for instance as far as the dimensions of the nozzle lips are concerned.
It should be added that U.S. Patent Specification 4 154380 shows a nozzle for making amorphous metal strip using 2 coaxial slit-shaped orifices and a nozzle provided with a row of 3 round openings for the jets of liquid metal.
German Patent application 29 38 709 discloses a process and apparatus for making amorphous metal strip using relatively large orifices to avoid clogging. These orifices have a dimension in the range of 1.5―6.0 mm in the direction of the movement of the chill surface.
European Patent application 50 397 discloses a process and apparatus for making a rapidly quenched, cast metallic strip comprising a plurality of dissimilar longitudinal portions. Each individual portion of the strip is metallurgically alloy-bonded to the edges of adjacent portions.,along the longitudinal extent of the strip during casting. To that end separate streams of molten metal from separate crucibles are delivered onto the casting surface. The crucibles and their nozzles are arranged such that on the casting surface the peripheral edge portion of one stream contacts the peripheral edge portion of the adjacent stream.
In making metal strip with the metal being in the amorphous state there is still another problem. For the metal to solidify in the amorphous state the use is required of cooling rates of at least 10⁴ K/s, but mostly higher than 10⁶ K/s. These high cooling rates must, of course, be realized throughout the thickness of the strip, which sets a limit to the strip thickness that can be obtained. Thus it is known that the use in the melt spinning process of some Fe-alloys permits obtaining a strip thickness of 30-40 µm. In attempts to obtain a greater thickness it appears that especially on the side of the formed strip which is not directly cooled by the chill surface the cooling rate is insufficiently high for the metal to solidify in the amorphous state.
But the use of a slotted nozzle which does promote making wider strip is not found to also contribute to making thicker strip which is yet amorphous. For various uses, however, amorphous metal strip having a maximum thickness of about 30-40 11m is too thin. Because of this extremely small thickness the strip is very vulnerable mechanically and as a rule it does not quite satisfy the set standards of rigidity and strength and hence stability of shape.
Consequently, the material either does not qualify for various uses or resort is had to the costly and complicated method of assembling several layers of the amorphous strip in order to meet rigidity and strength requirements. There is therefore a great need for amorphous metal strip, including that of Fe-alloys, having a thickness greater than that of the known range of 30-40 11m and having uniform properties.
The invention now has for its object to make metal strip by the melt spinning process in which use is made of a chill surface and the metal is solidified substantially in the amorphous state and the resulting metal strip has a greater thickness than realized with the previously known method and has a uniform thickness and width.
By amorphous metal is to be understood here a metal in which no crystalline phase can be detected by X-ray diffractometry.
The method according to the invention is characterized in that the metal is forced against the chill surface using at least two parallel rows of jets emerging from parallel rows of orifices in the same nozzle and the jets of all rows together form the melt puddle. The unexpected result of this method is that the thickness of the amorphous strip obtained is considerably greater and far more regular than can be realized by using 1 row of jets of liquid metal and, moreover, a considerably wider strip can be obtained than with said use of a single row of jets. This is the more surprising in that in prior art disclosures it was considered that the use of a plurality of jets could not possibly lead to wider strip having uniform properties.
Moreover, it has been found unaccountably that the use of 2 or more parallel rows of jets of liquid metal also results in greatly reduced instability in the melt puddle and hence in suppression of variation in strip thickness and width. The favourable result obtained in making amorphous strip is particularly manifest in that with the amorphous phase being retained, the metal strip can be made at least 1,5 times as thick as by spinning from a slotted nozzle under identical conditions, It is preferred that the jets of a liquid metal should be arranged in 3―4 rows. The rows need not be spaced at equal distances and the jets of the successive rows need not be staggered. Also the number of jets per row may differ. It is preferred that the rows should each be perfectly straight, but there is no absolute need for that. One or more of the rows may be arranged slightly curved or be interrupted for influencing the cross-sectional shape of the strip. For simplicity, the nozzle orifices in which the jets are formed may best be circular, but other forms, such as short slots, also may be used.
In order to prevent clogging by solidifying metal of the last row of orifices viewed in the direction of movement of the chill surface, it is preferred that the distance from the centres of the jets of the first row to those of the last row should not be greater than 10 mm. Depending on the nature of the alloy and the velocity range in which the metal still solidifies in the amorphous state it may be preferred to choose a distance not greater than 5 mm. The diameter of jets having a circular cross section may with advantage be chosen in the range of from 0,5 to 1,0 mm and the centre-to-centre distance between 2 jets of a row in the range of 1,1-2 times the diameter. The jets of a row may be of different thicknesses for influencing the cross-sectional shape of the strip.
Comparative melt spinning experiments in which use is made of a single jet formed in the slotted nozzle as described in the aforementioned US Patent Specification 4 221 257 and several rows of jets according to the invention demonstrate that the absolute uniformity of the thickness and the width obtained in the process of the present invention is hardly or not smaller than that of strip obtained using a single slot, but that the relative uniformity bf the thickness is generally somewhat more favourable.
Another advantage obtained with the method of the present invention consists in that the so-called flank angle, i.e. the angle between a side face of the strip and the base, is larger than that obtained with a slotted nozzle.
A large flank angle and a high relative uniformity of thickness are especially desired when making amorphous strip which is assembled into laminates. It is desirable then that the strips should fit together as closely as possible when placed side by side or one upon the other. This is of great importance in processing amorphous strip into a laminate for making electromagnetic cores as described in Netherlands Patent Application 8 201 427. The stacking fraction of the metal in the cores should be as high as possible.
The above particularly applies to amorphous strip of alloys of the MmZz type, wherein M is Fe, Ni, Co or blends thereof and Z is a metalloid, such as C, P, B, Si, AI or blends thereof and m is 70-90 at.% and z is 30-10 at.%. Part of the Fe, Ni and/or CO content may be replaced with other metals, such as Mn, Mo, Cr and the like. Such compositions of alloys rendered amorphous by very rapid cooling are mentioned in, among other publications, Acta Metallurgica Vo. 20, April 1972, pp. 485-491, and U.S. Patent Specification 3856513.
Metal strips of these alloys are very ductile and have excellent magnetic properties such as low hysteresis losses and are excellently suitable to be used for electromagnetic cores. These cores may then be built up of stack of amorphous metal strips. Since the stacking of these strips can be realized more readily as they are thicker, the aim will be to make the thickest possible metal strips while retaining the amorphous structure of the metal.
The invention will be illustrated with reference to the following figures.

Figure 1 is a side view in partial section of an apparatus for carrying out the method according to the invention.
Figure 2 is a detailed view of a nozzle provided with 16 orifices in 2 rows.
Figure 3 provides a view of the nozzle of Figure 2.
Figure 4 is a view of a nozzle provided with a slot-shaped orifice as known from the method according to the state of the art.
Figure 5 is a view of a nozzle provided with 44 orifices arranged in 3 rows as used according to the method of the present invention.

In Figure 1 the numeral 1 refers to a quartz crucible for a metal 2. The metal can be melted with the aid of an MF induction coil 3. At its bottom the crucible changes into a nozzle 4 which is provided with orifices 9. The nozzle 4 can be closed with a valve 5 which is actuated from a unit 6, from which also a particular gas pressure may be applied in the crucible.
Positioned at some adjustable distance from the under side. of the nozzle 4 is the internally water-cooled surface of a chill roll 7 which is driven by some device (not shown) such that it has a spinning speed in the range of 0 to 50 m/s.
In the operation of the apparatus the liquid metal flows through the orifices onto the cooled surface to 0 099 599 form on it a melt puddle 11 which is entrained and practically instantaneously solidifies into a strip 8. By spinning speed is to be understood the circumferential speed of the chill surface.

Figures 2 and 3 are views in more detail of the nozzle 4, which is provided with 16 orifices 9 arranged in two rows of 8 each. The underside has the same curvature as that of the surface of the chill roll.
Figure 4 shows a nozzle provided with a slot-shaped orifice 10 as is known from the state of the art.
Figure 5 is a view of a nozzle provided with 44 orifices 9 arranged in 3 rows.

The invention will be further described in the following examples.

Example 1

Use is made of the apparatus according to Figure 1, which is provided with a chill roll 224 mm in diameter, a quartz crucible having an internal diameter of 29 mm and equipped at its underside with an exchangeable nozzle, for processing the alloy Fe₆₂,₅, Ni_15,4, B_14,1, Si_8,0 (at.%) into amorphous strip under the following conditions:
The values found for the strip thickness are given in Table 1.
Spinning through a slot wider than 1,1 mm was not possible because of clogging. The strip obtained by using the nozzle 4 has a uniform thickness and width.
The comparative experiment demonstrates that the use of 3 rows of jets results in obtaining strip which is considerably thicker than that obtained with a single jet from a slot-shaped orifice. This experiment also shows that with the use of a slotted nozzle said alloy may be formed into amorphous strip having a maximum thickness of about 30 µm.

Example 2

In the manner described in Example 1, use being made of the alloy mentioned in it, strip is made at different spinning speeds. Starting from a value of 30 m/s the spinning speed of the chill surface is decreased in each successive experimental run.
Strips obtained using a slotted nozzle, slot dimensions 8x0,6 mm, are-compared with strips obtained using a 7,1 mm wide nozzle having 14 orifices 0,7 mm in diameter arranged in 3 rows of 5,4 and 5 orifices, respectively, which are spaced at a centre-to-centre distance of 1,6 mm. The distance from the centre of the first to that of the third row is 2,6 mm. The orifices of the second row are staggered half a centre-to-centre orifice distance with respect to those of the 1st and 3rd rows. The values found are given in Table 2.
The width of the strip obtained using the slotted nozzle was 8,2 mm and that obtained using the multiple-row nozzle 6,3 mm. This experiment also shows that use of a multiple-row nozzle leads to a considerably greater strip thickness than that obtained using a slotted nozzle, irrespective of the spinning speed. The experiment moreover demonstrates that for the alloy used in it the spinning speed must be higher than 20 m/sec in order that the strip may solidify in the amorphous state.

Example 3

Use being made of the equipment and the alloy mentioned in Example 1, strip is made successively with the aid of:

nozzle 1 having a slot dimensioned 8x0,7 mm;
nozzle 2 1 row of 8 orifices 0,7 mm in diameter, width 6,3 mm;
nozzle 3 2 rows of 8 orifices 0,7 mm in diameter, width 6,3 mm; distance between centres of rows 2,1 mm; the orifices are not staggered.

Measured are average strip thickness, strip width and maximum variation in strip thickness, referred to as amplitude. The values found are given in Table 3.
This experiment confirms that the use of a single row of jets does not result in obtaining coherent strip, but a 2-row nozzle does, and moreover the thickness obtained in the latter case is considerably greater than that produced with a slotted nozzle.

Example 4

The equipment and the alloy used for Experiment 1 are employed for making a wider amorphous strip at different spinning speeds. The nozzle used has 44 orifices of 0,7 mm arranged in 3 rows of 15, 14 and 15 orifices. The distance between the centres of the first and the third rows is 1,6 mm and the width 12 mm. The centre-to-centre distance of the orifices of a row is 0,8 mm. Measured are the strip thickness, strip width and the amplitude of the strip thickness. The values found are given in Table 4.
This experiment demonstrates that use of a 3-row nozzle readily leads to amorphous strip wider than 6 mm without loss of uniformity.

Example 5

Use being made of the same equipment as employed in Example 1, amorphous strip is made from the alloy ^Fe ₇₂,₅ Mn_2,0 B_9,0 Si_16,2 CO,3 (at.%).
Use is made of a 3-row nozzle provided with 14 orifices of 0,7 mm as described in Example 2.
The values found are given in Table 5.
When use is made of a slotted nozzle of 6x0,7 mm with the process being carried out under otherwise identical conditions, no amorphous strip can be obtained at a speed of 26,6 m/s. For the strip to solidify in the amorphous state the spinning speed should be higher than 33 m/s; and the strip thickness obtained will be smaller than 30 µm.

Claims

1. A method of forming a continuous strip of amorphous metal, comprising forces a row of jets of molten metal through a corresponding row of orifices in the nozzle of a reservoir for the molten metal onto a chill surface moving transverse to said row and within a distance of 2,5 mm from said nozzle, on which surface the jets join together to form a melt puddle for solidification by very rapid cooling of the metal into an amorphous strip which is carried off by the chill surface, characterized in that the metal is forced against the chill surface using at least 2 parallel rows of jets emerging from parallel rows of orifices in the same nozzle and the jets of all rows together form the melt puddle.

2. A method according to claim 1, characterized in that the jets are arranged in 3-4 rows.

3. A method according to claims 1-2, characterized in that viewed in the direction of movement of the chill surface the distance from the centres of the jets of the first row to those of the last row is not greater than 10 mm.

4. A method according to claims 1-3, characterized in that viewed in the direction of movement of the chill surface the distance from the centres of the jets of the first row to those of the last row is not greater than 5 mm.

5. A method according to claims 1-4, characterized in that of jets having a circular cross-section the diameter is in the range of 0,5 to 1,0 mm and the centre-to-centre distance of the jets of a row is 1,1 to 2 times the diameter.