EP0900854A1

EP0900854A1 - Condensate retention arrangement for cold hearth refining

Info

Publication number: EP0900854A1
Application number: EP98202473A
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: 1999-03-10
Anticipated expiration: 2018-07-23
Also published as: JP3076306B2; DE69800856D1; DE69800856T2; EP0900854B1; JPH11132664A

Abstract

In the condensate retention arrangement for cold hearth refining described in the specification, a member (26, 40) having a concave water-cooled surface (22, 34) is disposed above a hearth (12) to collect condensate (25) of vaporized constituents of an alloy being processed in the hearth. The condensate (25) collected on the water-cooled surface is less brittle and less likely to break away and fall into the hearth (12) which could change the composition of the refined material. The member (26, 40) having the concave surface may be the lid of an enclosure (10) containing the hearth or a separate member disposed above the hearth. Dovetail retention grooves (36) may be formed in the surface (34) facing the hearth to enhance retention of the condensate.

Description

Technical Field

This invention relates to arrangements for collecting and retaining condensates of metal vapors generated during cold hearth refining of metal alloys.

Background Art

In election 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 vapor 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 vapor 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.

Disclosure of Invention

Accordingly it is an object of the present invention to provide a condensate retention arrangement for cold hearth refining which overcomes the disadvantages of the prior art.
Another object of the invention is to provide a condensate retention arrangement for cold hearth refining by which metal alloy constituents vaporized during refining can be effectively retained without causing contamination of the refined alloy.
These and other objects of the invention are attained by providing a water-cooled condensate retention surface above the hearth in a cold hearth refining furnace to collect condensate in a form which is less brittle and less likely to break away and fall into the metal being refined. Preferably, the ceiling of the furnace is water-cooled and has a domed structure so that condensate collected on the ceiling has a "hoop strength" tending to hold the condensate against the dome-shaped surface. In an alternative embodiment, a separate water-cooled member spaced from the ceiling of the furnace is provided. In addition, the water-cooled member may have a surface which is formed with dovetail retention grooves to enhance retention of condensate.

Brief Description of the Drawings

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.

Best Mode for Carrying Out the Invention

In the typical embodiment of the invention illustrated in 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 mold 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 vaporized 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. By thus providing a cold surface on which the vaporized 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.
In another embodiment of invention, shown in the fragmentary illustration of 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. The dome-shaped insert 32 may be used with or without dovetail grooves depending on the duration of the refining operation and the specific alloy being refined.
If desired, the dome-shaped cover 26 and the side walls of the enclosures 24 of the embodiment shown in Fig. 1 may be provided with the dovetail retention grooves in the same manner.
Although the invention has been described herein with reference to specific embodiments, many modifications and variations therein will readily occur to those skilled in the art. Accordingly, all such variations and modifications are included within the intended scope of the invention.

Claims

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.
A condensate retention arrangement according to Claim 1, wherein the member has a domed configuration and the surface facing the hearth has a concave curvature toward the hearth.
A condensate retention arrangement according to Claim 1 or 2, wherein the surface facing the hearth contains a plurality of dovetail retention grooves.
A condensate retention arrangement according to Claim 1, 2 or 3, wherein the member comprises a lid for an enclosure containing the hearth.
A condensate retention arrangement according to Claim 1, 2 or 3, including an enclosure containing the hearth and wherein the member having coolant passages 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 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.
A method according to Claim 6, including disposing a member having a concave surface above the hearth with the concave surface facing the hearth.
A method according to Claim 6 or 7, including providing dovetail retention grooves in the surface of the member facing the hearth to facilitate retention of the condensate.
A method according to Claim 6, 7 or 8, including disposing the member as a lid of an enclosure containing the hearth.
A method according to Claim 6, 7 or 8, including disposing the member between the hearth and the top of an enclosure containing the hearth.