GB1566980A

GB1566980A - Furnace for vacuum arc melting of highly reactive metals

Info

Publication number: GB1566980A
Application number: GB104178A
Authority: GB
Original assignee: BLOSHENKO V; DERJUGIN A
Current assignee: BLOSHENKO V; DERJUGIN A
Priority date: 1978-01-11
Filing date: 1978-01-11
Publication date: 1980-05-08

Description

(54) FURNACE FOR VACUUM ARC MELTING OF HIGHLY REACTIVE METALS (71) We, VLADIMIR VIKTOR OVICH BLOSHENKO of Kvartira 6. ulitsa Severnaya,36, Odintsovo Moskovskoi oblasti, SEMEN MOISEEVICH BEIZER OV, of Kvartira.72, Korpus 2, ulitsa B.Akademicheskaya, Moscow, ALEX ANDR NIKOLAEVICH DERJUGIN, of Kvartira 121, ulitsa Severnaya, 54, Odintsovo Moskovskoi oblasti, VLADIMIR ALEXEEVICH ILIN, of Kvartira.32, Mosfilmovsky pereulok. 16, Moscow, 1; all Union of Soviet Socialists Republics, all citizens of the Union of Soviet Socialist Republics, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: The present invention relates to furnaces for vacuum arc melting of highly reactive metals such as titanium and zirconium, and can be used for melting refractory metals such as tunsten and molybdenum.

It is an object of some embodiments of the present invention to provide a furnace for vacuum arc melting of highly reactive metals, which is explosion-proof and safer in operation than the known furnaces used for similar purpose.

Another important object is to provide a furnace which is more reliable in operation.

Still another object is to provide a furnace which is simple in operation.

The present invention provides a furnace for vacuum arc melting of highly reactive metals, which comprises a cooled mould having its bottom closed by a detachable cooled bottom plate, a cooled vacuum chamber being sealingly disposed above and communicating with the mould and fitted with a cover having an electrode holder movably mounted therein; cooling spaces of the mould, bottom plate and electrode holder being adapted to be filled with a liquid-metal heat transfer agent, and an expansion chamber communicating with the cooling spaces of said furnace units; each cooling space accommodating a tubular heat exchanger and the heat exchanger being connected to a closed circulation circuit adapted to be filled with a cooling agent chemically inert to the liquid-metal heat transfer agent and inert to water; a water heat exchanger for containing water and arranged for cooling the inert cooling agent; intermediate the inner wall of the cooled mould and its tubular heat exchanger there being disposed a shield in the form of a hollow cylindrical wall; fixedly mounted intermediate the shield and the outer wall of the cooled mould at lower and upper sections thereof metal strips being arranged along multiple-thread helicoidal paths to form channels; and electromagnetic pump means being disposed opposite said channels externally of the cooled mould for circulating liquid-metal heat transfer agent in the channels.

The disposition of tubular heat exchangers in the cooling space of the mould, of the vacuum chamber and in that of the electrode holder makes it possible to simplify the heat-transfer circuit design by reducing the number of fittings, pipes and pumps required for the transfer of liquid NaK alloy. In the event of destruction of the heat exchanger wall, the danger of explosion is nonexistent since NaK alloy is neutral with respect to diphenyl mixture which is preferably contained in said tubuler heat exchangers.

The provision of a hollow shield, whose interior is preferably filled with argon, enables an alarm signal to be produced in the event of the electric arc burning through the shield wall.

The shield disposed in the cooling space of the mould form. together with the mould outer and inner walls, a heat-transfer circuit which provides for excellent conditions of cooling the working (inner) wall of the mould with NaK alloy.

The provision of multi-thread channels at the upper and lower sections of the mould cooling space, as well as the provision of electromagnetic pump means arranged opposite thereto, enables the flow of NaK alloy to pass in a desired direction, i.e. along the mould wall, with the cooling thereof being effected at an appreciably high rate.

Carrying out the mould cooling by means of an agent chemically neutral to the liquidmetal cooling agent and to water ensures explosion-proof operation of the furnace and, consequently, improves operating reliability of the cooling circulation circuit.

Such furnace construction precludes the penetration of water to the furnace melting chamber or its coming into contact with NaK alloy, thereby rendering the circulation circuit simple in construction and reliable in operation.

It is advisable to secure an electrocontact means serving as a leak indicator on the lower portion of the hollow shield.

This being the case, any damage in the shield resulting in the metal penetration into its interior will actuate the leak indicator to produce an alarm signal.

It is preferable that a pressure pick-up means electrically connected with an alarm means be connected to the hollow shield.

The provision of the pressure pick-up means mounted on the hollow shield and electrically connected to the alarm means enables an alarm signal to be quickly obtained in the event of damage of the hollow shield wall.

One embodiment of the present invention is illustrated by way of example in the accompanying drawings, in which: Figure 1 is a schematic longitudinal crosssection view of a furnace according to the invention; Figure 2 is an elevation view of the shield lower part which carries a leak indicator and an alarm signal means; Figure 3 is a perspective view, partially broken away, of the upper section of a mould, which carries a shield and metal strips arranged along multi-thread helicoidal paths and forming channels.

Referring now to the drawings, and to Figure 1 in particular, there is shown therein a furnace for vacuum arc melting of highly reactive metals, which comprises a cooled mould 1 whose bottom is closed by a detachable cooled bottom plate 2 and whose top is closed by a cooled vacuum chamber 3 fitted with a cover 4 having movably mounted therein a cooled electrode holder 5 with a consumable electrode 6.

The cooled mould 1 has a metal melting space 7 and a space 8 for the passage of a cooling agent, the latter being defined by the mould inner wall 9 and an outer wall 10.

Arranged in the space 8 is a tubular heat exchanger 11, and arranged intermediate the latter and the mould inner wall 9 is a shield 12 (Figures 2 and 3) made in the form of a hollow cylindrical wall. Fixedly mounted intermediate the shield 12 and the outer wall 10 of the cooled mould 1 at its upper and lower sections are metal strips 13 arranged along multi-thread helicoidal paths and forming channels 14. Arranged opposite said channels externally of the cooled mould 1 are electromagnetic pumps 15 (Figure 1) for example, d-c stators which function to create a rotating electromagnetic field, for inducing NaK alloy to travel along the helicodial channels 14 (Figure 3) and consequently over the entire circuit.

Mounted at the lower section of the shield 12 (Figure 2) is a leak indicator 16 which is an electrocontact means (e.g. a spark plug) electrically connected to a signal lamp 17 and to a power source 18. Should liquid metal get onto the contacts of the leak indicator 16, in the event of leakage of the liquid-metal coolant, the electric circuit is closed to result in a signal produced by the lamp 17.

In addition, the shield 12 (Figure 1) carries a pressure pick-up means 19 electrically connected to an alarm means (not shown). The shield 12 forms a closed heattransfer circuit filled with argon (Ar) under a pressure of upto 1.1 atm. and protects the tubular heat exchanger 11 from the destructive action of the electric arc in the event of damage to the inner wall 9 of the cooled mould 1. A flow of argon is passed to the shield 12 through a tube 20, the pressure pick-up means 19 (manometer) being responsive to pressure below 1.05 atm.

Provided in the middle part of the outer wall 10 of the cooled mould 1 is a compensator means 21 adapted to remove axial deformation load due to occur during thermal expansion of the cooled mould 1 in the process of melting.

The cooling space 8 of the mould 1 is filled with a liquid-metal heat carrier, such as eutectic NaK alloy having a sub-zero melting temperature (-120C). The tubular heat exchanger 11 located or arranged in the cooling space 8 of the mould 1 is filled with a coolant chemically neutral to NaK alloy and to water. This coolant may be selected from ionic and organosilicon heat-transfer agents such as diphenyl mixture composed of 26.5 wt.% of diphenyl and 73.5 wt.% of diphenyl ether, and having a melting temperature of +12.3"C. The detachable cooled bottom plate 2 has an interior space 22 for the passage of a coolant, wherein is arranged a tubular heat exchanger 23.The cooling space 22 of the bottom plate 2 is brought in communication with the cooling space 8 of the mould 1 by means of a flexible hose 24.

In turn, the upper section of the space 8 of the cooled mould 1 communicates through another flexible hose 25 with an expansion chamber 26 provided with a manometer 27.

The manometer 27 is responsive to a drop in pressure below 1.05 atm. in the event of damage of the wall 9 of the cooled mould 1, of the wall of the bottom plate 2 or that of the vacuum chamber 3; said manometer being likewise responsive to a pressure of from 1.6 to 1.7 atm., in case of any leakage occurring in the otherwise leak-proof tubular heat exchangers thereof.

The vacuum chamber 3 is connected to the expansion chamber 26 by means of a branch pipe 28.

A cooling space 29 of the vacuum chamber 3 is filled with NaK alloy and accommodates therein a tubular heat exchanger 30.

A cooling space 31 of the electrode holder 5 is filled in two thirds of its volume with a liquid-metal cooling agent, wherein is interposed a tubular heat exchanger 32. To control the gas (argon) cushion, there is arranged in the gas-filled space 31 of the electrode holder 5 a contact manometer 33 responsive to a drop in pressure below 1.05 atm.

The tubular heat exchangers 11, 23, 30 and 32 intercommunicate with one another by means of pipes 34 which are introduced into a heat exchanger 35 to provide for water-cooling of the diphenyl mixture circulating in the circuit under the action of a pump 36.

Provided on the circuit means is an expansion vessel 37 filled with nitrogen or argon; gas pressure within said vessel being checked by means of an electrocontact manometer 38 which is responsive to a drop in pressure of 0.2 to 0.3 atm. below a predetermined working pressure. The manometer 38 also functions to produce a signal in the event of failure in the leak-proof circuit through which circulates diphenyl mixture, inclusive of the heat exchangers of the furnace units. The diphenyl mixture is discharged into a receptacle 39 specially provided for this purpose.

Water is delivered to the water heat exchanger 35 by means of a pump 40 from a vessel 41.

The furnace according to the invention for vacuum arc melting of highly reactive metals operates in the following manner.

When the consumable electrode 6 (Figure 1) is fixed in the electrode holder 5 and vacuum within the furnace is brought to a preset value, the furnace is then energized to commence the process of melting. As the electrode 6 is consumed, the arc burning zone is gradually shifting from the bottom upwards. As this happens, the inner wall 9 of the cooled mould 1, the walls of the bottom plate 2, of the vacuum chamber 3 and those of electrode holder 5 absorb the heat radiated by the electric arc and then transfer it to the liquid-metal heat carrier.

Thereafter, the heat is transferred through the heat exchangers of the furnace units to the diphenyl mixture circulating in the closed heat-transfer circuit. The diphenyl mixture cooled in the water heat exchanger 35 is then recycled by means of the pump 36 through the pipes 34 to the heat exchangers of the furnace units.

Heat transfer in the electrode holder 5, vacuum chamber 3 and in the bottom plate 2 is effected by virtue of natural convection of NaK alloy in their cooling spaces.

In the mould 1, wherein calorific intensity is maximum and natural convection is insufficient to maintain a prescribed temperature of from 250 to 3000C at the inner wall 9, the liquid-metal heat carrier is caused to move by means of the electromagnetic pumps 15.

Caused to move by means of said pumps 15 along the multi-thread helicoidal channels 14, the liquid-metal heat carrier is thus forced to circulate in the circuit.

By this means the heat-transfer process is intensified in the mould cooling space. The electromagnetic pumps 15. arranged at the ends of the cooled mould 1. prevent electromagnetic field from affecting the electric-arc process, as well as the ingot crystallization process. During initial stage of the melting process, when the arc is burning in the lower section of the cooled mould 1, the upper electromagnetic pump 15 is in operation.

When the melting process passes above the middle section of the cooled mould 1, the upper pump 15 is automatically switched off to actuate the lower one. At the end of the melting process the furnace is deenergized while the cooling system continues to operate. In the event of burning through in the inner wall 9 of the cooled mould 1 or in the wall of the bottom plate 2, the contact manometer 27 arranged on the expansion chamber 26 is actuated.

The furnace is thus automatically shut down.

In case of damage in the shield 12, the electrocontact leak indicator 16 is actuated to produce a signal for automatic shut-down of the furnace, and the manometer 19 gives corresponding readings in units of pressure.

The electrocontact manometer 33 produces a signal responsive to leakage in, or damage to, the electrode holder 5.

The furnace according to the invention for vacuum arc melting of highly reactive metals when used in combination with electrocontact alarm means eliminates the possibility of explosion in the event of burning through in the wall of the cooled mould 1, thereby providing for safer and more reliable operation.

Claims

WHAT WE CLAIM IS:

1. A furnace for vacuum arc melting of highly reactive metals, which comprises a cooled mould having its bottom closed by a detachable cooled bottom plate, a cooled vacuum chamber being sealingly disposed above and communicating with the mould and fitted with a cover having an electrode holder movably mounted therein; cooling spaces of the mould, bottom plate and electrode holder being adapted to be filled with a liquid-metal heat transfer agent, and an expansion chamber communicating with the cooling spaces of said furnace units; each cooling space accommodating a tubular heat exchanger and the heat exchangers being connected to a closed circulation circuit adapted to be filled with a cooling agent chemically inert to the liquid-metal heat transfer agent and inert to water; a water heat exchanger for containing water and arranged for cooling the inert cooling agent; intermediate the inner wall of the cooled mould and its tubular heat exchanger there being disposed a shield in the form of a hollow cylindrical wall; fixedly mounted intermediate the shield and the outer wall of the cooled mould at lower and upper sections thereof metal strips being arranged along multiple-thread helicoidal paths to form channels; and electromagnetic pump means being disposed opposite said channels externally of the cooled mould for circulating liquid-metal heat transfer agent in the channels.

2. A furnace as claimed in claim 1, wherein electrical contact means serving as a leak indicator is secured inside a lower portion of the hollow shield; any liquid metal leaking into the shield establishing electrical continuity across the contact means.

3. A furnace as claimed in Claim 1 or 2, wherein a pressure pick-up means is connected to the hollow shield and is electrically connected to an alarm means; the pick-up means being responsive to variations in pressure within the shield.

4. A furnace for vacuum arc melting of highly reactive metals, substantially as herein described with reference to, and as shown in the accompanying drawings.