DEJ0007670MA - - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

Registration date: September 4th, 1953 Official date of registration on July 26th, 1956

GERMAN PATENT OFFICE

When using rotating magnetic fields in connection with metal casting molds, either a layer of insulating material between the iron poles used to generate the rotating field provided, or it was the field-generating parts of the liquid metal through a wall non-magnetic steel and possibly also separated by a brick lining.

Such arrangements are for the application of rotating magnetic fields in the water-cooled Molds, especially in the case of tubular molds such as those used in continuous casting, are unsuitable, because the desired increase in performance is only achieved with these molds if there is good heat conduction is guaranteed between the cast material and the cooling liquid, that is, the shaping mold part consists of a material with thermal conduction properties, as they are usually peculiar to metals. A A large part of the continuous casting molds in practical use therefore consists of pure copper,

From the point of view of the lowest possible thermal resistance, it would also be low Aim for wall thickness; practical demands stand in the way of their degradation, for the Chill molds must not warp under the effect of the relatively high temperature differences and

609 576/438

J 7670 Yl 131c

must therefore be built to be sufficiently stable. In addition, continuous casting molds are considerably mechanical Exposed to loads when retracting and extending the approach bolt. After all, they have to Chill molds have a sufficient wall thickness to withstand the wear and tear of theirs during use To be able to eliminate shaping surfaces by reworking, whereby the wall thickness does not increase may be low.

ίο In experiments with tubular molds made of electrolytic copper, which material was chosen in view of its high conductivity, it was found that the Achieving a suitably strong rotating field inside the mold was not possible. Apparently this is on the shielding of the rotating magnetic field due to the induced eddy currents. the Measurements with the help of a rotating field measuring device (see Kohlrausch, ed. 1951, vol. 2, p. 163) showed this in Table I, column 2, the result of the shielding effect of a copper pipe of 112 mm shown Inside diameter.

Table I.

Wall thickness Torque in the pipe Torque undisturbed mm Cu pipe 10.0 0.01 9.0 0.02 8.0 0.027 7.0 0.04 6.0 O, o6 5, o 0.11 4, o 0, l8 3.5 0.23 3, o 0.28 Ms-63 pipe 0.30 0.33 0.40 0.436 0.516 O, 6o 0.634 0.70 0.714

The table shows that even with a wall thickness of only 3 mm, the torque set inside the copper pipe (referred to in the table as "torque in the pipe") - it was used to generate an alternating current of 50 Hertz - was only about 28 ° / _{0 of} the torque resulting without the use of the copper cylinder (referred to in the table as “torque undisturbed”). The shielding effect of the copper pipe was thus 72%. The wall thickness of 3 mm is already undesirably low for practical foundry operations. .. '.

In order to achieve less shielding of the rotating field in the mold wall, it arises therefore the task of using metals of lower electrical conductivity, but with the thermal conductivity at the same time must not drop too much.

According to Wiedemann-Frant's law, there is theoretically a certain constant ratio between thermal conductivity λ and specific electrical resistance ρ at a given absolute temperature T for all conductors. In fact, however, the relationship between thermal conductivity and electrical conductivity differs not insignificantly for different conductors (cf.Table II, in which, for different metals, thermal conductivity λ in cal / ° C cm see, specific electrical resistance ρ in μ Ω cm and the Product of both is given by absolute temperature T = 293 ⁰ K). Theoretically is

λ ρ -ψ- = k = 2 -44-ίο-

volt

= 0.588 x lo

cal μΩ

⁰ C ² -sec

Table II

ρ μ Ω ■ cm Acal / ° C-cm-sec ¹⁰ γ
cal-jitß / 'O'-sec Cu .... 1.673
6.6
5.5
, 13.0
1375.0
5.9
■ - 5.17
20000.0 0.94
0.28
0.48
0, l6
0.057
0.38
ο, 35
0.20 0.520
0.62
0.88 ■
0.69
26.0
0.75
Ο, 6θ
6666.0 MS 63 ....
W. Cr Graphite ..
Be ....... Mon Si

For Drehfeldkokillen, in particular those for Stranggießzwecke, materials appear used which is of copper with a thermal conductivity not those under io ° / _0, which is not under 0.094 cal / ° C · cm · lake, a so much higher resistivity than copper, that there is a product of thermal conductivity and specific resistance which is higher than that associated with copper. ■

Measurements on continuous casting molds with the rotating field measuring device resulted in the shielding of the rotating field in a tube made of brass of the alloy MS 63, which has the same inner diameter and the same length as the above-mentioned Cu tube possessed the values also listed in Table I. You can see that with a wall thickness of 6 mm, a shielding related to the torque achieved of less than 50% results, whereby it should be noted that this wall thickness is based on casting technology considerations is quite satisfactory. Table II also indicates that of the materials listed therein besides brass also chromium, tungsten and silicon appear very suitable.

Especially in the case of semiconductors, for which silicon is a typical representative, one finds that a proportion high thermal conductivity is associated with very low electrical conductivity.

Certain metal oxides, sintered oxides and sintered metals appear in the same way as semiconductors particularly promising.

Claims (7)

Patent claims: i. Rotary field mold, in particular for performing the continuous casting process, characterized in that, that its shaping, cooled part consists of a material whose thermal conductivity is not 609.576 / 438 J 7670 VI / 31c is below 10 ° / ₀ that of copper, which, however, compared to copper, has a considerably higher constant of the Wiedemann-Frant law. 2. rotating field mold according to claim i, characterized in that the wall thickness of its shaping Part is at least 6 mm. 3. rotating field mold according to claim 1 or 2, characterized in that its shaping part made of brass, preferably MS 63. 4. rotating field mold according to claim 1 or 2, characterized in that its shaping part consists of W, Cr., Be, Mo. 5. rotating field mold according to claim 1 or 2, characterized in that its shaping part consists of graphite. 6. rotating field mold according to claim 1 or 2, characterized in that its shaping part is a semiconductor such as silicon. 7. rotating field mold according to claim 1 or 2, characterized in that its shaping part consists of a metal oxide or a sintered metal. Considered publications: German patent specification No. 307 225. © 6095T6 / 43 & 7.9S