GB2264507A

GB2264507A - Electron beam overflow melting arrangement

Info

Publication number: GB2264507A
Application number: GB9223489A
Authority: GB
Inventors: Alok Choudhury; Matthias Blum; Harald Scholz; Volker Bauer; Josef Heimerl; Gerhard Reber
Original assignee: Leybold Durferrit GmbH
Current assignee: Leybold Durferrit GmbH
Priority date: 1992-02-26
Filing date: 1992-11-10
Publication date: 1993-09-01
Anticipated expiration: 2012-11-10
Also published as: FR2687691A1; DE4205797A1; FR2687691B1; GB2264507B; JPH0688146A; GB9223489D0

Description

2 422- 6 4 5 0 7 1 1 Electron Beam Overflow Melting Arrangement

Specification

The invention relates to an electron beam. overflow melting arrangement according to the preamble of Patent Claim 1 as well as a process for the production of a high purity metal or a metal allay.

In electron bean overflow melting a block of a given material.. for example a super allay or a titanium alloy, is progressively melted off by means of an elect= bean or by means of several electron beams. Miematerial which has been melted off falls hereupon into a trough having an overflow. When the level of the melted material reaches the overflow of the trough, it flows into a chill mould or into another device for further treatment.

Since the c=Wnents of an allay often have different vaporization temperatures, it can occur that same corponents vaporize from the melt of the trough. Hereby the properties of an alloy can be changed considerably. For example, in a nickel-ahramium alloy with a chromium content of 30% at a mean bath temperature of 17000 C approximately 30% of the chromium content can be lost.

In order to prevent this negative effect of unintentional vaporization, it is already known to provide a protective layer of slag above the melt disposed in the trouah (DE-A-3 827 074). The slag represents herein not only a blockage for the escape of allay components but also serves for the purpose of freeing the liquid metal or the metal alloy of oxides, sulfides, and other impurities. So that the slag does not flow off together with the melt into a chill mould, a water-cooled barrier is provided which retains the slag in the trough.

Two factors have been found to be of disadvantage in the known 2 arrangement: for one,, a layer of slag applied once does not suffice to carry out a refining process aver a relatively long period of time, for another, a rigidly disposed ingot is not suitable for adaption to different melt goods, slags, and melting rates.

The invention is therefore based on the task of creating an arrangement with which it is possible to carry out an electron beam melting process over a relatively long period of tim and with variable parameters.

Claims

This task is solved according to the features of Patent Claim 1.

The advantage achieved with the invention rises in particular that the melted material remains covered with a continuous covering of slag over the entire period of the process so that no allay elements can escape. The slag loss which occurs with the vaporization due to the electron beam inpinging m the slag or due to the slag portions iupinging on the edge of the trough are continuously replaced. Therein the feeding of new slag takes place in such a way that a given thickness of the slag layer is maintained. So that the slag does not flow off with the. overflowing melted material, a barrier known per se is provided which is vertically displaceable so that it can be adapted to the particular materials and their rate of flow.

An embodiment mmirple of the invention is depicted in the drawing and will be described in the following in greater detail.

The Figure shows a vac= melt chmrber 1 onto which an elect= beam gun 2 is flanged with whose electron pencil beam 3 the end of an ingot of metal or a metal alloy is melted off. The malted-off material falls into a watercooled ccpper trough 5 and form there a melt 6 whose level rises increasingly higher until it reaches an overflow 7 of the trough 5 from where it arrives in a cooled chill mould 8. There the melt solidifies to form an ingot 9. On the melt 6 is provided a layer 10 of liquid slag which is hindered by a vertical barrier 11 E flowing with the melt 6 into the chill mould 8. In addition to this upper barrier 11 a lower barrier 12 is also provided at the bottcm of the ccpper trough 5.

The upper barrier 11 is vertically displaceable by means of a drive 13 disposed on a carrier 14. This can be realized for exairple thereby that the drive 13 runs on rails (nat shown) of the carrier 14.

Above the trough 5 is disposed the end of a pipe 15 frcmn which slag granulate 16 is placed onto the surface of the melt 6. This pipe can be 1 3 swivelled vertically about an axle 17. Uhis axle 17, in turn, rests in a shaft (not shown) which is supported rotatably in a carrier IS so that the pipe 15 is also horizontally rotatable. Into the pipe 15 projects the end 19 of a vibrating spiral conveyor device 20 which is made to vibrate by a drive (not sham) in such a way that bulk material which is placed below on the conveyor device 20 arrives at the upper end of the conveyor device 20 through pulse impacts. By 21 is denoted a feed funnel for slag granulate containing as much granulate as is required for a relatively long refining process.

rihe copper trough 5 rests on a scale 22 which determines the total weight of trough 5, ne-lt 6, and slag 10 and supplies it to a regulator 23. In the regulator the determined total weight is caTpared with a ncminal weight and the conveyor device 20 is driven so that the actual weight corresponds to the rcminal weight. The nominal weight is therein defined so that a closed slag covering of given thickness is always formed on the melt. Since the specific weight of nvelt and slag as well as the volume of the trough 5 up to the overflow edge are known,, the particular thickness present of the slag layer can be calculated.

It is also possible to cbserve with the aid of a thermo-camera or a videocamera the surface of the trough content and to resupply slag granulate whenever the closed slag covering tears open. As soon as it arrives on the surface of the melt 6,, the granulate is melted through electron beans which come either from the gun 2 shown or from a second electron beam gun which is not shown.

with the aid of a wavelength-dispersive measuring method it is, in addition, possible to monitor the vaporization of the elements in the melt and to determine the vaporization rate. Hereby an optimum protective coating setting can be achieved, in conjunction with the determined vaporization rates, in order to hold the vaporizations of the remelting material at a minimum.

Vbether or not the barrier 11 mast project more or less deeply into the melt in order to prevent the slag 10 from. falling into the chill mould also is a function of the coaposition of the slag 10 and of the melt material 6 as well as of the melting rate. If melting takes place very rapidly, the flow under the barrier 11 which is symbolized by section 24 is very large so that portions of the liquid slag 10 can be entrained. in this case, the barrier 4 must therefore be imTe into the melt 6 relatively deeply. In the case of viscous slag materials, a lesser i=mrsion depth is required than in the case of less viscous slags. The same applies to the melt. The barrier 12 at the bottom of the trough serves the function of retaining, if necessary, heavy metals coaprised in the melt.

The iTaw=ion depth of the barrier 11 is preset at the regulator 23 since the data required for this purpose are knom. It is badever also possible to sense autcmatically particular data during the melting process, for exanple the rate of flow. This is characterized by the weight increase of the chill mould 8. Thereby that the weight of the chill mould 8 with the content is weighed and differentiated, a signal can be supplied via a line 26 to the regulator 23 which permits it to raise or lajer the barrier 11.

The slag for the covering of the melt camprises preferably a mixture of several oxides, for e-le of Cao, A1203.. M90.. Ti02, and Zr02. Its thickness should be at least 2 m.

1 Patent claims Electron beam overflow melting arrangement wj_th a trough for the reception of a metal or matal allay mit, which is nelted frem a solid netal or metal alloy body by ni--= of an electron beam, as well as with a prote-ve layer covering for the surf ace of the, melt, charactezed in that a sup-ply device (20) is provided which places material (16) for the protective layer covering (10) onto the surface of the mit (6).

2. Electron bean overflow malting arrangement as stated in Clain ll characterized in that a device (13) for the vertical displacement of a barrier (11) in the malt is provided.

Electron beam overflow melting arrangement as stated in Claim 1, characterized in that a regulating device (23) is provided which drives the conveyor device (20) in such a way that a given quantity of a 4- layer covering is disposed at all times an the surface of the itelt (6).

Electron be-am overflow melting arrangement as stated in claim 3 r characterized in that the t=ugh (5) is disposed on a weighing arrangement (22) which determines the total weight of the t=ti (5) wIth its part,:icular content (6, 10) and that a c=i:)c=tor device is provided which on the basis of a ccq=ison of the neasured total weight with a given total weight acts upon the regulating device (23) in such. a way that the measured tott-al weight corrnds to the given total weight.

5. Elect= bean over-flow melting as stated in Claim 3 j chazucterized in that a the=--are.-a J --- provided which de-tects the surf ace. of the trough content (6, 10), that f urther a device is provided which clue to the thennally recorded surface recognizes whether or not a closed Drott-tive layer is p-rezent or whetther it is broken, and that a device is pr-ovided which in the case of a broken pratective layer 6 lies material for the protective layer covering with the aid of the conveyor device (20).

6. Electron beam overflow melting arrangement as stated in Claim 3,, characterized in that by me= of a wavelength-dispersive measuring method which detects the vaporization rates of chemical elements the protective layer covering (10) is irplemented so that the least possible vaporization of the monitored chemical eleanent takes place.

Electron bean overflow melting arrangement as stated in Claim 5, characterized in that the thenno-camera also monitors the free melting zone in front of the barrier (11) and the'introductim of energy via the elect= bean (3) is controlled so that a low overheating of the material is achieved.

Electron beam overflow melting arrangement as stated in Claim 1, characterized in that the conveyor device (20) is a vibrating spiral conveyor device which transports material for the protective layer covering from a first site (21) to a second site (19) wherein this second site is located above the surface of the melt (6).

1 9. Elect= bean overflow melting arrangement as stated in Claim 8, characterized in that at the second site the one- end of a swivellable pipe (15) is provided whose other end is located in close vicinity above the surface of the melt (6).

0. Elect=n beam overflow melting arrangement as stated in Claim 1, zed in that as the material for the protective layer covering is provided slag.

11. Electron beam overflow melting arrangement as stated in Claim 9, zed in that the slag is applied in the form of granulate onto the surface of the melt.

7 12. Elec=n beam, overflow melting arrangement as stated in claim 2, characterized in that the barrier (I!) is intrcx:hmed into the protective layer covering (10) from above in the direction toward the trough (5).

13. Elect= be= overflow mlt-:Ln w=angenent as stated in claim 2, characterized in that the barrier (11) is introduced into the protective layer covering (10) and into the melt (6) perpendicularly F above in the direction toward the tzn4i (5).

14. 7,1 ectron beam overflow melting arrangement as stated in claim 1, characterized in that a barrier (12) is disposed at the bottom of the trox fti (5) and projects into the melt (6) in the direction toward the protective layer covering (10).

15. Process for the production of a high purity metal or metal alloy characterized by the follcwing steps: a) material is melted in an evacuated ch=ber with the aid of an electron beam which falls into a trough; b) the melting process is carried out until the melted material runs E' - an overflow of the trough; the barrier is moved into the melt of the trough whereby the surface of the melt is divided into two regions; d) material for the protective layer covering is applied on that area of the surface which is remote from the overflow.

16. Process as stated in Claim 15, cha icterized in that the protective layer coverinc j is kept constant through regulation.

17. Process as stated in Claim 15, cbaracterized in that through melting of the supplied metals an overflcw melt is set.

18. Electron beam overflow melting arrangement substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

19. Process for the production of a high purity metal or metal alloy substantially as hereinbefore described,with reference to and as illustrated in the accompanying drawings.