EP0900854B1

EP0900854B1 - Condensate retention arrangement for cold hearth refining

Info

Publication number: EP0900854B1
Application number: EP19980202473
Authority: EP
Inventors: Stephen Martin Tilmont; William Frane Brinton; Leonard Earl Mcmullen
Original assignee: Titanium Hearth Technologies Inc
Current assignee: Titanium Hearth Technologies Inc
Priority date: 1997-09-04
Filing date: 1998-07-23
Publication date: 2001-05-30
Anticipated expiration: 2018-07-23
Also published as: JP3076306B2; DE69800856D1; JPH11132664A; DE69800856T2; EP0900854A1

Description

The present invention relates to a condensate retention arrangement for cold hearth refining and to a method of condensate retention in cold hearth refining.
In electron beam cold hearth refining of metal alloys an energy source, such as an electron beam gun, directs energy toward an alloy to be refined which is contained in a water cooled hearth. Typical refining arrangements for such alloys are described, for example, in United States Patents Nos. 5,171,357 and 5,222,547. In many cases, the alloys being refined such as, for example, various titanium alloys, contain elements with higher vapour pressures and/or lower melting points than other elements in the alloy and therefore evaporate preferentially to the other elements. The metals evaporated during the refining process are typically collected on a condensate screen as described, for example in United States Patent No. 3,690,635. Because of the difference in vapour pressures and melting points of the constituents of alloy, the condensate normally has a different composition than the alloy being refined and, to provide the desired alloy composition after refining allowance is usually made in the feed material for the loss of constituents to the condensate.
The condensate deposited on the screen or on the interior surfaces of the cold hearth furnace, however, often does not adhere adequately to assure retention until the refining process has been completed and an indeterminate proportion of the condensate may fall back into the material in the hearth, thereby affecting the composition of the refined product in an unpredictable way. In some cases, as for example in Patent No. 5,222,547, a condensate screen on which condensate is collected is vibrated in an attempt to return all of the collected condensate to the material in the hearth during the refining process. Such vibrating screen arrangements are complex and require vibration isolation systems. The variability in the composition of the refined alloy often requires a vacuum arc-remelting step resulting from loss of constituents to a condensate in order to meet chemical uniformity requirements. If the condensate variations during the original refining are of sufficient severity, the alloy may not meet the specification even after vacuum arc remelting, which can result in significant yield losses, additional processing costs and late deliveries.
WO-A-97/21965 discloses a panel for a high temperature furnace. The panel comprises an outer portion and an inner portion. The outer portion comprises a series of cooling pipes throughout which, in use, cooling fluid flows. The inner portion comprises a layer of fireproof material throughout which a number of bar-like means are dispersed. The bar-like means are in close contact with the cooling pipes to assist removal of heat from the fireproof material.
FR-A-2 254 247 discloses a high temperature electrical furnace comprising two hemispheres. Each hemisphere further comprises tubes throughout which, in use, cooling fluid can be circulated.
One aim of the present invention is to provide a condensate retention arrangement for cold hearth refining by which metal alloy constituents vaporised during refining can be effectively retained to inhibit contamination of the refined alloy.
According to the present invention there is provided a condensate retention arrangement for cold hearth refining comprising:
a member disposed above a refining hearth having coolant passages and having a surface facing the hearth to receive vaporized alloy constituents from the hearth and wherein the surface facing the hearth contains a plurality of dovetail retention grooves to, in use, facilitate retention of condensate.
Further features are set out in Claims 2 to 4.
According to another aspect of the present invention there is provided a method for condensate retention in cold hearth refining comprising disposing a member above a hearth in which an alloy is heated by energy beam impingement and constituents of the alloy are vaporized, and cooling the member by circulation of a coolant to cause the vaporized alloy constituents to condense and solidify on a surface of the member facing the hearth and providing dovetail retention grooves in the surface of the member facing the hearth to facilitate retention of condensate.
Further steps of such a method are set out in Claims 6 to 9.
Further objects and advantages of the invention will be apparent from a reading of the following description in conjunction with the accompanying drawings in which:
Fig.1 is a vertical sectional view schematically illustrating a representative embodiment of a condensate retention arrangement for cold hearth refining in accordance with the invention; and
Fig. 2 is a fragmentary view illustrating another condensate retention arrangement in accordance with the invention.
Referring to Fig. 1, a cold hearth refining furnace 10 includes a conventional cold hearth 12 which contains metal alloys to be refined and which is cooled in the usual manner by internal circulation of a coolant such as water. Energy is applied to the metal alloy to be refined from one or more energy sources such as electron beam guns 14 by which beams 15 of energy can be selectively directed toward the alloy material in the hearth. After refining the molten alloy is conveyed through a trough 16 from the hearth to a conventional water-cooled vertical mould 18 in which it is solidified to form an ingot or electrode for subsequent remelting 20.
During the refining process, various constituents 21 of the alloy being refined are vaporised and diffuse upwardly toward the inner surfaces 22 of an evacuated enclosure 24 having a lid 26 where they are condensed into a solid coating 25 on the surfaces 22. In order to effectively retain the solidified condensate 25 on the surfaces 22 in accordance with the invention, the lid 26 is provided with internal passage 28 such as conduits or jackets through which a coolant such as water is circulated and the dome-shaped cover 26 and the side walls of the enclosures 24 are provided with the dovetail retention grooves (similar to those shown in detail in Fig. 2). By thus providing a cold surface on which the vaporised alloy constituents condense and solidify, the condensate coating 25 has a different morphology than that of condensates deposited on surfaces which have not been cooled, the difference in morphology being somewhat analogous to that between snow (corresponding to condensate on conventional condensate screens and uncooled surfaces) and ice (corresponding to the condensate 25 on the water-cooled surfaces 22). As a result of this difference in morphology, the condensate coating 25 is less frangible and less likely to break away and fall into the liquid metal in the hearth.
In the embodiment illustrated in Fig. 1, the lid 26 for the furnace has a domed shape providing a concave interior surface facing the hearth. This produces a 'hoop' effect, which makes the condensate coating self-supporting and decreases any tendency of portions of the condensate on that surface to separate and fall into the hearth.
In addition, the relatively constant temperature of the surfaces 22 maintained by the coolant circulated through the conduits 28 eliminates thermal cycling of the surfaces, further reducing the likelihood that any of the condensate will separate from those surfaces.
Referring to Fig. 2, a dome shaped insert 32 mounted beneath the dome shaped cover 26 has interior surfaces 34 formed with dovetail-shaped grooves 36 to enhance retention of a layer of condensate 37 on the surfaces 34. Water cooling passages 38 are provided in the insert in the same manner as in the lid 26 of Fig. 1. The insert 32 is preferably positioned between the lid 26 and the hearth 12 and has openings 40 for passage of energy beams 15 from the energy sources 14 to the hearth.

Claims

A condensate retention arrangement for cold hearth refining comprising:
a member (26;32) disposed above a refining hearth (12) having coolant passages (28;38) and having a surface (22;34) facing the hearth to receive vaporized alloy constituents from the hearth and wherein the surface (22;34) facing the hearth contains a plurality of dovetail retention grooves (36) to, in use, facilitate retention of condensate.
A condensate retention arrangement according to Claim 1, wherein the member (26;32) has a domed configuration and the surface (22;34) facing the hearth has a concave curvature toward the hearth.
A condensate retention arrangement according to Claim 1 or 2, wherein the member comprises a lid (26) for an enclosure containing the hearth.
A condensate retention arrangement according to Claim 1 or 2, including an enclosure containing the hearth and wherein the member (32) having coolant passages (38) is interposed within the housing between the hearth and the top of the enclosure.
A method for condensate retention in cold hearth refining comprising disposing a member (26;32) above a hearth (12) in which an alloy is heated by energy beam impingement and constituents of the alloy are vaporized, and cooling the member (26;32) by circulation of a coolant to cause the vaporized alloy constituents to condense and solidify on a surface (22;34) of the member (26;32) facing the hearth (12) and providing dovetail retention grooves (36) in the surface (22;34) of the member (26;32) facing the hearth (12) to facilitate retention of condensate.
A method according to Claim 5, wherein said member (26;32) has a concave surface.
A method according to Claim 5 or 6, including disposing the member as a lid (26) of an enclosure containing the hearth.
A method according to Claim 5 or 6, including disposing the member (32) between the hearth and the top of an enclosure containing the hearth.