Refractory material for casting a rare-earth alloy and its production method as well as method for casting the rare-earth alloys

Abstract

Rare-earth alloy is cast into a sheet (6) or the like by using a tundish (3, 13). The refractory material of the tundish used for casting does not necessitate preheating for improving the flowability of the melt (2). The refractory material used essentially consists of 70 wt % or more of Al2O3 and 30 wt % or less of SiO2, or 70 wt % or more of ZrO2 and 30 wt % or less of one or more of Y2O3, Ce2O3, CaO, MgO, Al2O3, TiO2 and SiO2. The refractory material has 1 g / cm3 or less of bulk density, has 0.5 kcal / (mh° C.) or less of thermal conductivity in the temperature range of from 1200 to 1400° C., and has 0.5 wt % or less of ratio of ignition weight-loss under the heating condition of 1400° C. for 1 hour.

Description

TECHNICAL FIELD [0001] The present invention relates to refractory material for casting a rare-earth alloy, which contains a rare-earth element (R) as one of the main components, such as an alloy for an R—Fe—B based magnet, an R—Ni based hydrogen-absorbing alloy and an alloy for an Sm—Co based magnet. The present invention also relates to a production method of the refractory material and a method for casting the rare earth-alloys. BACKGROUND TECHNIQUE [0002] Recently, attention has been paid to the rare-earth sintered magnet or rare-earth bond magnet, in which the excellent magnetic properties of the rare-earth alloys are utilized. Particularly, with regard to R—Fe—B based magnets, development for further enhancement of the magnetic properties has been conducted. There is in the R—Fe—B based magnets a ferromagnetic R2Fe14B phase, which is the basis of the magnetism, and an R-rich phase (a non-magnetic phase having high concentration of the rare-earth elements, such as Nd) which is ...

AI Technical Summary

Benefits of technology

The present invention relates to a refractory material for casting rare-earth alloys. The refractory material should have a specific content of Al2O3 and SiO2, as well as a specific bulk density and thermal conductivity. The refractory material should also have a low ignition weight loss and should not contain any impurities in a large amount. By using this refractory material, the melt flowability is improved, and the melt solidification process is prevented. The refractory material should also have a low thermal conductivity to prevent excessive heat loss during casting. The present invention also provides a method for preparing the refractory material by shaping it with an organic binder and then removing it as much as possible. The refractory material should also contain specific amounts of ZrO2, Y2O3, Ce2O3, CaO, MgO, Al2O3, TiO2, or SiO2 to achieve desired properties. The refractory material should also have a low ignition weight loss and should not contain any impurities in a large amount.

Problems solved by technology

This necessarily results in decrease of the volume fraction of the R-rich phase.

Therefore, when the casting is carried out by a conventional method, the R-rich phase is so poorly dispersed that the R-rich phase is locally deficient, resulting in unsatisfactory properties in many cases.

This α-Fe seriously impairs the crushability of the alloy for the magnet, and hence causes composition variation at the crushing process.

The formation of a -Fe is difficult in such alloy.

In the production by a conventional book-mold casting method, additive elements are liable to micro-segregate.

An alloy obtained by the book-mold casting method is difficult to pulverize, is of large particle diameter and contains a phase with rich additive elements.

The post-pulverizing distribution of the powder size is, therefore, non-uniform and exerts detrimental influence upon the hydrogen-absorbing property.

The final resultant powder of the hydrogen-absorbing alloy exhibits disadvantageously insufficient hydrogen-absorbing property.

However, such thin tundish is not only difficult to produce but also would be difficult to handle as it may be liable to crack.

However, the following problems are involved in the tundish heating.

A heater capable of heating at this temperature is expensive.

② An apparatus for heating the entire tundish is complicated.

③ Since the heat capacity of a tundish is large, heating takes long time and hence decreases the production efficiency.

There incurs, thus, a safety problem.

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