GB2252524A - Distribution boxes, tundishes and like articles for casting molten metals - Google Patents

Abstract

Distribution boxes, tundishes, or like articles for casting molten metal are disclosed comprising a chamber (1) for receiving molten metal, the chamber (1) having one or more holes (2) to release molten metal to a mould or other like article in the path of casting of the metal, the or each hole (2) is formed in one or more nozzle preforms (3) embedded in one or more of the chamber walls by casting of the chamber walls about the preforms (3). <IMAGE>

Description

DISTRIBUTION BOXES FOR METALLURGY. TUNDISHES.AND OTHER LIKE ARTICLES FOR CASTING MOLTEN METALS This invention relates to distribution boxes for metallurgy, tundishes, and other like articles for casting molten metals. The invention is particularly applicable to the vacuum casting of superalloys, specialist steels and specialist alloys where high cleanliness is required.

Distribution boxes are used to spread molten metals during casting to ensure a predetermined distribution of molten metal entering a mould. Distribution boxes comprise one or more channels for accommodating the molten metal, the channels having holes in their bases to allow molten metal to pass through into a mould. The moulds may be of complicated shape or of simple shape and the actual form of the mould is not material to the present invention.

Such distribution boxes tend to be used only once and so costs have to be kept to a minimum.

Distribution boxes are ordinarily made of a fired refractory material comprising particles of a range of sizes.

The reason for using a range of particle sizes is to improve the packing density of the refractory material.

Problems have been encountered, particularly where casting superalloys, where material from the distribution boxes has been swept into the flow of molten material and resulted in inclusions in the moulded metal product.

Ordinarily these inclusions are at a low level and can be dressed out of the moulded material by machining but this necessarily adds to expense. The present applicants have found that a major source of inclusions is from the areas surrounding the holes in the distribution box which feed the metal into the mould.

The holes are conventionally provided in one of two ways.

In a first method the distribution box is cast in a mould having mandrels situated where holes are required so that in effect the holes are cast in place. This method has several disadvantages; in the casting process fine grain particles from the refractory material can form flashings which have to be subsequently removed; the edges of the holes tend to be friable; and there can appear voids in the casting, particularly at the edges of the holes, formed by gaps between the coarser grain particles. All of these problems can contribute to spalling of the hole edges during metal casting and consequent contamination of the cast metal.

In a second method pre-formed nozzles are cemented into place in holes in the distribution box. This has the advantage that the pre-formed nozzles are of higher finish than the cast refractory of the body of the distribution box.

However there are two main disadvantages to this method.

Firstly the cement may contribute to contamination of the metal. Secondly, and more importantly, the nozzles have to be cemented in place vertically; it is easy to cement the nozzles in place at an angle to the vertical and by misdirecting the stream of molten metal in casting this can lead to damage to distribution boxes further down the path of casting of the metal, or to moulds, and to subsequent contamination of the metal.

The present applicants have found that a way of reducing the number of inclusions is to pre-form nozzles to comprise the holes of the distribution box and then cast the distribution box about the nozzles.

Accordingly the present invention provides a distribution box, tundish, or like article for casting molten metal comprising a chamber for receiving molten metal, the chamber having one or more holes to release molten metal to a mould, characterised in that the or each hole is formed in one or more nozzle preforms embedded in one or more of the chamber walls by casting of the chamber walls about the preforms.

Advantageously the preforms are of a material less prone to spalling than the surrounding material of the chamber walls.

In a preferred embodiment the material of the nozzles is of similar chemical composition to the chamber walls.

The present invention is illustrated 'by way of the drawings in which: Fig. 1 is a schematic plan view of a distribution box, and Fig. 2 is a section of said distribution box on line A-A.

Fig. 3 is a schematic drawing, in plan, side elevation and enlarged part-section, of a tundish with cast in nozzle accordingly to the invention.

Referring first to Figs. 1 & 2 a distribution box comprises a body 1 formed of a fired refractory material such as a 66% alumina manufactured and sold by Morganite Thermal Ceramics Limited under the trade mark TRIANGLE 66V (a vibrocast sillimanite grade). This grade of material has a typical chemical composition: A12O3 66% SiO2 31% Foe203 1%.

and is formed from materials having a size distribution of less than 5mm.

This grade may be used in the manufacture of ordinary distribution boxes and the usual method of manufacture is to cast the material using plaster moulds. This technique enables a piece of excellent integrity to be manufactured but the area around the pouring holes (2) is the most critical in the terms of risk of contamination of the molten metal by erosion or break up of the refractory. There is a tendency for the fines in the refractory mix to form a skin on the mandrels which can lead to the formation of flashings and to insufficient consolidation of the material at the hole edge.

Further, the coarse grain material can form voids by bridging against the wall of the mould or mandrel, which voids are not filled by the fine grain material, and so lead to voids in the finished product. These faults can be corrected to some extent by subsequent fettling (dressing off the flashings and filling the voids).

In the distribution box of the invention nozzles (3) are pre-formed by pressing, extruding, or otherwise forming a fine grain material, for example the material sol'd by Morganite Thermal Ceramics Limited under the trade mark TRIANGLE 63P (a pressed sillimanite grade) which has the following typical composition: A12O3 68% SiO2 28% Fe203 0.78.

and is formed from materials having a size distribution of less than lmm.

The nozzles are fired to a temperature which ensures stability at the service temperature and are then placed in the mould, the coarser grained surrounding material then being vibro-cast into place. In this technique the mould is clamped to a vibrating table which assists flow and settlement of the refractory.

The whole mould and distribution box is then heated in a microwave oven to assist drying prior to demoulding. After demoulding the distribution box is fully dried prior to firing.

The distribution box is then fired to a temperature which is adequate to ensure that the distribution box is stable in service.

The slight difference in chemical composition between the nozzles and surrounding cast refractory is not important but of significance is the fine grain structure and manufacture by pressing, extruding or the like, which results in the fired nozzles having a more coherent, thermal shock resistant and erosion resistant character than the surrounding refractory.

Manufacturing distribution boxes by this method also has advantages in that the amount of machining and cleaning of the fired distribution box is reduced as pressing produces relatively clean finished bodies.

The above description has related primarily to distribution boxes formed of alumino-silicate based materials.

The invention is not limited thereto but also extends to distribution boxes, tundishes, or other like articles for casting molten metals, formed of other materials in which the holes are formed in one or more embedded nozzle preforms. For example high alumina materials can be used for the body of the box if desired. Further other setting systems can be considered such as cement-containing castable refractories which require impervious tooling rather than plaster moulds.

The nozzles can be made of other refractories such as high alumina or zirconia to suit metallurgical requirements.

Claims (6)

1. A distribution box, tundish, or like article for casting molten metal comprising a chamber for receiving molten metal, the chamber having one or more holes to release molten metal to a mould or other like article in the path of casting of the metal, characterised in that the or each hole is formed in one or more nozzle preforms embedded in one or more of the chamber walls by casting of the chamber walls about the preforms.

2. A distribution box, tundish, or like article for casting molten metal as claimed in claim 1, the preforms being of a material less prone to spalling than the surrounding material of the chamber walls.

3. A distribution box, tundish, or like article for casting molten metal as claimed in claim 1 or claim 2 in which the metal to be cast is a superalloy and the distribution box is for one-time use.

4. A distribution box, tundish, or like article for casting molten metal as claimed in any preceding claim 1 in which the material of the chamber is a cast alumino-silicate refractory and the material of the nozzle is a pressed alumino-silicate refractory having a finer grain size than the cast aluminosilicate refractory.

5. A distribution box, tundish, or like article for casting molten metal as claimed in any preceding claim and substantially as described with reference to the drawings.

6. A method of making a distribution box, tundish, or like article for casting molten metal as claimed in any preceding claim and substantially as described.