Vacuum Melting and Remelting Processes - ASM International

ASM Handbook Volume 15: Casting (#05115G) 

408 / Foundry Equipment and Processing 

Remelting Variations 

Under Vacuum 

Apart from the remelting of a consumable 

electrode in a water-cooled copper crucible, 

there is a recent development of the vacuum 

arc remelting process, namely vacuum arc 

double electrode remelting (VADER). Fig- 

ure 5 shows the basic design of the VADER 

process with a static crucible. The arc is 

struck between the two horizontal elec- 

trodes that are to be melted. 

As in vacuum arc remelting, the metal 

drops fall into a water-cooled copper mold. 

Bath temperature, and therefore pool 

depth, can be very closely controlled. Re- 

melting can be done with minimal super- 

heating; segregation is thus minimized. The 

advantages of the VADER process over 

vacuum arc remelting are as follows (Ref 

10): 

• Very low or no superheating of the pool 

and high rate of nucleation, producing a 

fine grain structure 

• The lowest possible influence of magnetic 

fields on melting bath movement 

• No condensation formation due to evap- 

oration of liquid elements on the crucible 

walls 

• Lower specific energy consumption 

• Good ultrasonic testability due to the fine 

macrostructure of the ingot 

REFERENCES 

l. W.A. Tiller and J.W. Rutter, Can. J. 

Phys., Vol 311, 1956, p 96 

2. W.H. Sutton, in Proceedings of the 

Seventh International Vacuum Metal- 

lurgy Conference (Tokyo), The Iron 

and Steel Institute of Japan, 1982, p 

904-915 

3. J. Preston, in Transactions of the Vac- 

uum Metallurgy Conference, American 

Vacuum Society, 1965, p 366-379 

4. A.S. Ballentyne and A. Mitchell, Iron- 

making Steelmaking, Vol 4, 1977, p 

222-238 

5. S. Sawa et al., in Proceedings of the 

Fourth International Vacuum Metal- 

lurgy Conference (Tokyo), The Iron 

and Steel Institute of Japan, 1974, p 

129-134 

6. J.W. Troutman, in Transactions of the 

Vacuum Metallurgy Conference, Amer- 

ican Vacuum Society, 1968, p 599-613 

7. R. Schlatter, Giesserei, Vol 61, 1970, p 

75-85 

8. A. Mitchell, in Proceedings of the Vac- 

uum Metallurgy Conference, Pitts- 

burgh, PA, 1986, p 55-61 

9. F.J. Wadier, in Proceedings of the Vac- 

Motor 

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control 

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lace 

Fig, 4 Schematic of automatic melt control system 

Fig, 5 Schematic of the VADER process 

Process 

line control 

1 

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graphics 

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Electrode 

CPU 

Man ~-"] Auto 

. Analog in/out 

I-- 

uum Metallurgy Conference, Pitts- 

burgh, PA, 1984, p 119-128 

10. J.W. Pridgeon, F.M. Darmava, J.S. 

Process 

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All rights reserved. 

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~1 Printer 

1 Alarms 

Uninterruptable 

power supply 

+ 

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Printer 

Crucible 

-- ~Static mold 

Plotter [ 

(option) 

Winchester 

Huntington, and W.H. Sutton, in Super- 

alloys Source Book, American Society 

for Metals, 1984


Vacuum Arc Skull Melting and Casting 

F. MOiler and E. Weing~rtner, Leybold AG, West Germany 

Titanium investment casting has recently 

gained the same importance as the precision 

casting of superalloys (see the article "Ti- 

tanium and Titanium Alloys" in this Vol- 

ume). Titanium skull melting originated at 

the Bureau of Mines in Albany, Oregon. 

The first castings were made in 1953, al- 

though possibilities had been announced as 

early as 1948 and 1949. In the late 1950s, 

this technology was applied by research 

institutes, which were looking for a practi- 

cal means of liquefying and pouring urani- 

um into graphite molds, for example, to 

produce uranium carbide. 

An early industrial vacuum arc skull 

melter was built in 1963 for the continuous 

production of uranium carbide. This fur- 

nace had a crucible volume of approximate- 

ly 0.01 m 3 (0.35 ft s) and used a nonconsum- 

able graphite electrode to liquefy the 

uranium pellets fed into the crucible. The 

crucible tilting system was hydraulically 

driven. The molds were stationary. It was 

not until 1973 that one of the first skull 

melters for titanium went into operation; 

this furnace started production in 1974 in 

West Germany. 

State-of-the-art titanium vacuum arc skull 

melting furnaces are often equipped with 

turntable systems for centrifugal casting (up 

to 350 rpm). Casting weights of more than 

1000 kg (2200 lb) are possible. Vacuum arc 

skull melting and casting is used for many 

titanium investment castings for aircraft, 

aerospace, medical, and chemical applica- 

tions. Electron beam skull melting is also 

used for titanium alloys (see the section 

"Electron Beam Melting and Casting" in 

this article). 

Furnaces 

Fig. ! Schematic of a modern 50 kg (110 Ib) vacuum arc skull melting and casting 

furnace. 1, fast retraction system; 2, power cables; 3, electrode feeder 

ram; 4, power supplies; 5, consumable electrode; 6, skull crucible; 7, tundish shield; 8, 

mold arrangement; 9, centrifugal casting system; 10, chamber lid carriage 

Vacuum arc skull casting furnaces basi- 

cally consist of a vacuum-tight chamber in 

which a titanium or titanium alloy electrode 

is driven down into a water-cooled copper 

crucible. The dc power supply provides the 

fusing current needed to strike an electric 

arc between the consumable electrode and 

the crucible. Because the crucible is water 

cooled, a solidified titanium skull forms at 

the crucible surface, thus avoiding direct 

contact between melt and crucible. 




Vacuum Melting and Remelting Processes / 409 

Once the predetermined amount of liquid 

titanium is contained in the crucible, the 

electrode is retracted, and the crucible is 

tilted to pour the melt into the investment 

casting mold positioned below. For opti- 

mum mold filling, the mold can be preheat- 

ed and/or rotated on a centrifugal turntable. 

Figure 1 shows the operating principle of a 

modern 50 kg (110 lb) vacuum arc skull melt- 

ing furnace. At an operating pressure of ap- 

proximately 1 Pa (10 -2 mbar, or 0.075 torr), 

the specific working current ranges from ap- 

proximately 1 kA/kg for small furnaces to 

about 0.2 kA/kg for large pouring weights. 

This batch-type skull melting furnace allows 

for cycle times of approximately 1 h for a full 

50 kg (110 lb) pumping/melting/casting cycle, 

and in principle three consecutive pours can 

be obtained from one electrode. This furnace 

basically consists of a vacuum chamber, an 

arc voltage-controlled electrode drive sys- 

tem, a skull crucible, a centrifugal casting 

system with stepless adjustable turntable 

speed, an automatically sequenced vacuum 

pump system, a power supply, and an elec- 

trical control system with control desk. 

The cylindrical vacuum chamber is 

equipped with two large dished doors that 

support the crucible with the tilting mecha- 

nism, the mold platform with the centrifugal 

casting system, and the casting tundish with 

its cover. The crucible support system with 

an additional detachable device is also used 

for electrode loading. The chamber is jack- 

Fie. 2 Schematic of a modern semicontinuously operating vacuum arc skull melter 

for charge weights of up to 1000 kg (2200 Ib). 1, fast retraction system; 

2, power cables; 3, power supplies; 4, electrode feeder ram; 5, consumable electrode; 

6, skull crucible; 7, crucible carriage; 8, tundish shield; 9, mold arrangement; 10, 

vacuum pumping system; 11, centrifugal casting system 

- 9 

- 10 

11



eted for water cooling in regions that are 

subject to heat radiation. 

A top flange with a throat carries the 

electrode chamber and the electrode feed- 

ing system. Viewing ports allow for video 

monitoring of the melting and pouring. A 

vacuum pumping port is located in the cy- 

lindrical portion of the chamber. 

Figure 2 shows a semicontinuously oper- 

ated vacuum arc skull melter for charge 

weights of up to 1000 kg (2200 lb). The 

principal difference between this furnace 

and the smaller model (Fig. l)---apart from 

capacity-related layout features--is the 

rectangular vacuum chamber. Again, the 

crucible and the tilting mechanism are car- 

ried by a dished door. 

In this furnace design, the centrifugal cast- 

ing system is introduced from the bottom of 

the chamber to allow the horizontal connec- 

tion of a separate cooling chamber, if desired. 

Molds are loaded from the back side into the 

chamber and can be discharged through a 

front door, which also allows the use of a 

cooling and charging chamber with lock 

valves for continuous mold transport flow. 

Modern vacuum arc skull melting furnac- 

es are usually equipped with: 

• Coaxial power feed directly to the skull 

crucible to avoid electromagnetic fields 

that can disturb the melt bath 

• Programmable control systems for cruci- 

ble tilting to allow repeatable pouring 

profiles for consistent parameters 

• Highly accurate electrode weighing sys- 

tem for precise determination of pouring 

weights 

• XYadjustment system for coaxial position- 

ing of the electrode in the skull crucible 

• Compact air-cooled power-supply mod- 

ules of high capacity for achieving high 

melt rates, thinner skulls, and corre- 

spondingly increased yields above 80% 

• Proven vacuum pumping and measuring 

systems 

• Forced argon cooling systems for faster 

mold cooling 

Electron Beam Melting and Casting 

W. Dietrich and H. Stephan, Leybold AG, West Germany 

Electron beam melting and casting tech- 

nology is accepted worldwide for the pro- 

duction of niobium and tantalum ingots 

weighing up to 2500 kg (5500 Ib) in furnaces 

with electron beams of 200 to 1500 kW. 

Another application in East Germany and 

other Soviet bloc countries is the produc- 

tion of steel ingots weighing 3.3 to 18 Mg 

(3.6 to 20 tons) using electron beams of up 

to 1200 kW. Furnaces of up to 2400 kW in 

electron beam power have been used since 

1982 for recycling titanium scrap to produce 

4.8 Mg (5.3 ton) slabs 1140 mm (45 in.) 

wide. Furnaces of 200 to 1200 kW are used 

to refine nickel-base superalloys. Other 

metals, such as vanadium and hafnium, are 

melted and refined in furnaces between 60 

and 260 kW. Approximately 150 furnaces 

with melting powers ranging from 20 to 300 

kW are in operation in research facilities. 

These furnaces are used in the development 

of new grades and purities of conventional 

Table 1 Comparison of characteristics of electron beam melting and competing processes 

Siotering ] I Vacuum arc melting I [ 

Metal I Advantages Limitations Advantages Limitations 

Tungsten, 

molybdenum ....... Small grain size; 

most often used 

Tantalum, niobium... Small grain size; 

good workability 

Hafnium, vanadium ......... . - • 

Zirconium, titanium ......... • • • 

Refining limited; 

small batches; 

high energy 

consumption 

Same as above; 

rarely applied 

Same as above 

Not used 

Moderate grain size; 

acceptable workability; 

large ingots; low energy 

consumption 

Alloying; moderate grain 

size; large ingots; low 

energy consumption 

Alloying during remelting 

Very low contamination; 

wide range of alloying 

possible; large ingots; 

low energy consumption; 

economical melting 


costly electrode 

preparation; melting 

dangerous 


expensive electrode; 

melting dangerous 

Almost no refining; 

costly electrode 

preparation; melting 

dangerous 

Limited refining; 

expensive feedstock 

preparation; only 

round ingots 

and exotic metals and alloys, for example, 

uranium, copper, precious metals, rare- 

earth alloys, intermetallic materials, and 

ceramics. The total power of installed elec- 

tron beam melting and casting furnaces 

worldwide was approximately 25 000 kW at 

the end of 1987. 

Electron beam melting and casting in- 

cludes melting, refining, and conversion 

processes for metals and alloys. In electron 

beam melting, the feedstock is melted by 

impinging high-energy electrons. Electron 

beam refining takes place in vacuum in the 

pool of a water-cooled copper crucible, 

ladle, trough, or hearth. In electron beam 

refining, the material solidifies in a wa- 

ter-cooled continuous casting copper cruci- 

ble or in an investment ceramic or graphite 

mold. This technology can be used for all 

materials that do not sublimate in vacuum. 

Competing processes include sintering 

(for example, for refractory metals), vacu- 

um arc melting and remelting (for reactive 

metals and superalloys), and electroslag 

melting and vacuum induction melting (for 

superaUoys, specialty steels, and nonfer- 

rous metals). Some advantages and limita- 

tions of the competing vacuum processes 

are given in Table 1. Additional information 

on some of these processes is available in 

the sections "Vacuum Arc Remelting 

(VAR)," "Electroslag Remelting (ESR)," 

and "Vacuum Induction Melting (VIM)" in 

this article. 

Electron Beam Melting and 

Casting Characteristics 

The characteristics of electron beam 

melting and casting technology are: 

• The flexibility and controllability of the 

process temperature, speed, and reaction 

• The use of a wide variety of feedstock 

Electron beam melting I 

Advantages Limitations 

Highest possible purity; Large grain size; 

economical feedstock brittle product; 

preparation; large very rarely applied 

ingots; low energy 

consumption 

Same as above; most Alloying limited 

frequently used 

Good refining; 

economical feedstock 

preparation and ingot 

production; most 

often used 

Economical feedstock 

preparation; refining 

of high-density 

inclusions; melting of 

slabs, ingots, and 

rods; high production 

rate; low energy 

consumption 




High melting costs 

Alloying limited; 

material losses 

from splatter; high 

furnace investment


materials in terms of material quality, 

size, and shape 

• The different methods of material pro- 

cessing available 

• Product quality, size, and quantity 

Contamination-free 

environment and 

crucible 

Material evaporation.-- , 

and splattering 

Reflected \..~__.~, 

electron beam 

X-ray emission 

Flexible melting rate 

and refining 

dwell time 

Feedstock 

Fig. 1 Schematic of the electron beam melting process 

(a) 

li' i 

~! (f) 

Contamination of the product is avoided by 

melting in a controlled vacuum and in wa- 

ter-cooled copper crucibles (Fig. 1). 

The energy efficiency of electron beam 

processing exceeds that of competing pro- 

Electron beam gun 

Flexible power and 

power distribution 


Scanning electron beam 

Drip melt area 

Refining in the 

pool zone 

i ( , ' ) ~ (g) (h) 

Water-cooled copper crucible 

Continuous casting and 

solidifying ingot 

Fig. 2 Examples of electron beam melting and casting processes. (a) Button melting with controlled solidification 

for quantitative determination of low-density inclusions. (b) Consolidation of raw material, chips, and solid 

scrap to consumable electrodes for vacuum arc or electron beam remelting. (c) Drip melting of horizontally or vertically 

fed feedstocks. (d) Continuous flow refining/melting. (e) Floating zone melting. (f) Investment casting. (g) Pelletizing 

(manufacture of pellets from scrap and other materials for scrap recycling). (h) Atomization and granulation of 

refractory and reactive metals 

(e) (b) /~ 




cesses because of the control of the beam 

spot dwell time and distribution at the areas 

to be melted or maintained as liquid. In 

addition, unnecessary heating of the ingot 

pool, as occurs in vacuum arc remelting, for 

example, is avoided. Power losses of the 

electron beam inside the gun and between 

the gun nozzle and the target are very small, 

but approximately 20% of the beam power 

is lost because of beam reflection, radiation 

of the liquid metal, and heat conductivity of 

the water-cooled trough and crucible walls. 

Electron Beam Melting 

and Casting Processes 

From the large variety of electron beam 

melting and casting processes shown in Fig. 

2 only the processes illustrated in (a), (c), 

(d), and (f) are related to processes used in 

foundry technology: 

• Button melting processes for the quality 

control of steel and superalloy cast parts 

to control the content of low-density in- 

clusions 

• Drip melting process for the preparation 

of refractory and reactive metal feedstock 

material for electron beam and VAR skull 

melting and casting 

• Continuous flow melting process for the 

feedstock refining of superalloys for VIM 

and electron beam casting 

• Electron beam investment casting process 

Electron Beam Heat 

Source Specifmcat,ons 

For all electron beam melting and casting 

processes, except for the crucible-free float- 

ing zone melting process, Pierce-type elec- 

tron beam guns with separately evacuated 

beam generating and prefocusing rooms are 

the key components of the furnaces used. 

The essential features of these guns are: 

• Large power range of 0 to 1200 kW 

• Long free beam path of 250 to 1500 mm 

(10 to 60 in.) and the adjustable beam 

power distribution 

• Beam deflection angle of ---45 ° and spot 

frequency up to 500 Hz 

Schematics of electron beam consolidation and drip melting processes. (a) Consolidation of coarse and solid scrap. (b) Continuous consolidation of raw material, chips, 

Fig. 3 and solid scrap by direct feeding into a continuous casting crucible. (c) Drip melting of horizontally fed compacts, sintered bars, or consolidates for initial melting of 

reactive and refractory metals. (d) Drip melting of vertically fed vacuum induction melted or conventionally melted electrodes. (e) Drip melting of horizontally and vertically fed 

materials for the production of alloys from feedstocks with very different melting points



Table 2 Melting and refining data of refractory and reactive metals and alloy steels gained in laboratory and 

pilot production furnaces 

Electron beam Total specific Interstitial elements 

Ingot Ingot Integral power of Operating vacuum melting in feedstock 

Feedstock size, diameter, weight, melting rate, second melt, pressure of last melt, energy, Material and final ingot, ppm Hardness, 

Metal mm (in.) mm (in.) kg (Ih) kg/h (Ib/h) kW Pa (tort) kW • h/kg yield, % C O N H HB 

Tungsten .......... 40 (1.6) diam 

55 (2.2) diam, 

100 (4) long 

Tantalum ......... 60 (2.4) diam 

60 (2.4) square, 

160 (6.3) long 

Molybdenum ...... 100 (4) diam 

100 (4) diam 

120 (4.7) square, 

180 (7.1) long 

Niobium ......... 80 (3.2) square, 

150 (6) long 

120 (4.7) square, 

180 (7. I) long 

Hafnium ......... 60 (2.4) square 

80 (3.2) diam 

100 (4) diam 

100 (4) diam 

Zirconium ....... 60 (2.4) square, 

100 (4) long 

60 (2.4) square, 

150 (6) long 

Vanadium ....... 60 (2.4) diam, 

80 (3.2) long 

Titanium ........ 100 (4) diam 

Ti-6AI-4V ....... • • • 

Ti-8Al-lMo-IV .... 100 (4) diam 

4340 steel ......... 80 (3.2) diam 

60 (2.4) 

115 (4.5) 

80 (3.2) 

160 (6.3) 

100 (4) 

180 (7.1) 

150 (6) 

180 (7.1) 

80 (3.2) 

130 (5.1) 173 (380) 

100 (4) 19.5 (43) 

150 (6) 179 (395) 

80 (3.2) 7.7 (17) 

100 (4) 28.2 (62) 

100 (4) 28.2 (62) 

150 (6) 31 (70) 

150 (6) 31 (70) 

(a) The reproducibility of the refining data could not be confirmed. 

• Usable vacuum pressure range between I 

and 0.0001 Pa (10 -2 and 10 -6 mbar, or 7.5 

× 10 -3 and 7.5 x 10 -7 torr) 

• Reliability of the gun and cathode system 

The power control and distribution system 

allows a very accurate distribution of beam 

power and energy for achieving the required 

heating for material melting, superheating, 

refining, and electrothermal effects. 

Button Melting for 

Quality Control 

The button melting process (Fig. 2a) serves 

to control the quality of feedstock materials 

for investment casting and to produce casting 

samples• In contrast to the conventional elec- 

tron beam melting process, this process is not 

used for refining, but only for flotation and 

concentration of low-density inclusions• Dur- 

ing the eight-step process, the sample is heat- 

ed and drip melted. Low-density inclusions 

are floated to the surface and concentrated in 

the center of the pool of molten metal during 

controlled solidification by computer-con- 

trolled reduction of beam power and circular 

electrothermal stirring. The concentrated im- 

purities can be identified and evaluated by 

conventional metallographic methods, but the 

size of the raft gives the first indication of the 

quantity of impurities in the metal. 

37 (80) 10.5 (23) 

200 (440) 20 (44) 

65 (145) 16.7 (37) 

523 (1150) 38.4 (85) 

64 (140) 12.5 (27.5) 

408 (900) 50.2 (111) 

227 (500) 17.6 (39) 

326 (720) 13.2 (29) 

40 (90) 1.7 (3.7) 

7.5 (16.5) 

14.3 (31.5) 

73 (161) 

2.8 (6.2) 

45.2 (100) 

22.5 (50) 

10 (22) 

80 (176) 

119 

3O0 

130 

371 

130 

290 

240 

218 

80 

110 

80 

250 

80 

87 

6O 

52 

80 

8 x 10 -3 (6x 10 -s) 

2 x 10 -2 (1.5 × 10 -4 ) 

8 X 10 -3 (6 × 10 -5) 

3 × 10 -3 (2 × 10 -s) 

8 × 10 -4 (6 X 10 -6) 

10 -3 (7.5 x 10 -6) 

10 -2 (7.5 x 10 -5) 

5 x 10 -3 (3.8 X 10 -s) 

5 x 10 -3 (3.8 X 10 -s) 

4 X 10 -3 (3 x 10 -s) 

8 x 10 -3 (6 x 10 -5 ) 

2 x 10 -2 (1.5 x 10 -4 ) 

8 x 10 -3 (6 x 10 -5 ) 

0.8 (6 x 10 -3) 

0.4 (3 x 10 -3 ) 

4 x 10 -3 (3 × 10 -5 ) 

2.0 (0.015) 

Most button melting furnaces are com- 

pletely automated and microprocessor con- 

trolled to guarantee process reproducibility• 

Melting is usually carried out in the pres- 

sure range of l to 0.001 Pa (10 -2 to l0 -5 

mbar, or 7.6 × 10 -3 to 7.6 × 10 -6 torr). 

Drip Melting 

The drip melting processes (Fig. 3c and d) 

are primarily used for the production of 

clean, mostly ductile ingots of refractory 

and reactive metals or of specialty steels• 

The feedstock for the first melt (Fig. 3c) can 

be compacted sponge, granular, powder, or 

scrap, which might be presintered in a vac- 

uum heating furnace• In some cases, loose 

raw materials can be consolidated in a wa- 

ter-cooled copper trough (Fig. 3a). The con- 

solidated ingot can then be fed horizontally 

for drip melting• Raw material that is con- 

tinuously consolidated in a water-cooled 

copper crucible with a retractable bottom 

plate (Fig. 3b) can be fed horizontally or 

vertically for drip melting. In both consoli- 

dation processes, only 20 to 80% of the 

material is melted• Refining and losses of 

material by splattering are negligible• 

Drip melting of horizontally fed compacts 

is the most frequently used process for the 

production of ingots from refractory or re- 

active metals• The resulting ingot is of suf- 

10.3 

9.9 

6.0 

8.30 

10.4 

5.2 

12.3 

15.9 

38 

14.7 

4.6 

2.6 

3.1 

1.91 

2.66 

1.67 

1.0 




• .. 70 4100 30 10 

93.1 10 8 5 1 

• .. 200 5000 50 20 

90 10 8 7 1 

• .. 100 1200 140 10 

92 10 75 30 1 

...... 650 13 10 

91.8 6 15 13 2 

- • • 170 810 50 10 

95 12 10 10 2 

• • • 200 750 60 10 

96.8 10 12 11 2 

... 160 5220 554 35 

87 12 106 60 5 

• .. 80 4500 330 40 

96.8 6 111 52 8 

...... 1870 95 2 

93.1 • • • 170 25 I 

• • • 500 900 100 2 

93.5 100 200 50 1 

...... 950 95 30 

88.2 • • • 545 30 3 

...... 950 95 30 

...... 735 48 9 

...... 1045(a) 210(a) 16(a) 

91 ... 235(a) 95(a) 13(a) 

...... 2180 100 30 

99 • • - 1850 80 16 

...... 890 70 ' • • 

98 • • • 730 50 • • • 

• • • 3900 63 100 0.3 

93 4300 2.4 26 0.08 

99 3622 10 78 0.10 

200 

210 

65 

69 

140 

140 

77 

66 

160 

170 

120 

125 

30-100 

ficient purity, but has an area of inhomoge- 

neity caused by the shadow of the 

horizontally fed bar. Two or more electron 

guns are used in drip melting to make use of 

reflected electron beams and to reduce 

evaporation and splattering• The end of a 

compact is welded to the front of the fol- 

lowing one to avoid dropping semisolid ma- 

terial into the pool. Table 2 lists processing 

parameters that have been successfully 

used to electron beam melt various reactive 

and refractory metals and 4340 alloy steel. 

Vertical Feeding of Ingots. Refractory 

and reactive metal ingots of high purity, 

homogeneity, and smooth surface are re- 

melted by vertical feeding (Fig. 3d). The 

molten metal droplets run down the conical, 

rotating electrode tip, are refined, and then 

drop into the pool center• The crucible pool 

is normally of the same diameter as the 

electrode but is sometimes smaller or larg- 

er. It is kept in the liquid state to allow final 

refining and to guarantee ingot homogene- 

ity. Because two or more electron guns are 

used, the entire pool can be equally bom- 

barded; thus, shadow effects of the elec- 

trode can be eliminated• 

Simultaneous melting of horizontally and 

vertically fed electrodes (Fig. 3e) can be 

used for the production of critical alloys. In 

this case, the feedstock should be of the 

desired purity•


Drip melting of 330 mm (13 in.) square steel billet in a 1100 kW single-gun furnace. Melt rate: 1000 kg/ 

Fig. 4 h (2200 Ib/h). Courtesy of VEB-I:delstahlwerk, East Germany 

Horizontally Fed Ingots. Drip melting of 

horizontally fed material with a single elec- 

tron gun (Fig. 4) is used for refining some 

steel alloys in East Germany and other 

Soviet bloc countries. In this process, the 

feedstock size is smaller than the pool di- 

ameter to minimize the shadow effect of the 

horizontally fed bar. In production units, 

feeding can be carried out from two oppo- 

site sides. 

Other Process Considerations. To en- 

sure the production of clean, homogeneous 

metals and alloys in electron beam drip 

melting furnaces, various aspects of mate- 

rial processing and handling must be con- 

trolled. Key considerations include: 

• Dimensions and quality of the feedstock, 

and the feeding system used 

• Ingot cooling and unloading during melt- 

ing of another ingot 

• Passivation and removal of condensates 

from the melt chamber 

• Planning of melt sequences to minimize 

the number of furnace cleanings required 

• Routine preventive furnace maintenance 

to ensure reliability 

• Operator skill in operation of the furnace 

• Material yield and energy consumption 

Equipment for Drip Melting 

The essential equipment groups required 

for drip melting--melting furnaces, control 

systems, and power supply units---are all im- 

portant for achieving optimum productivity. 

The melting furnace (Fig. 5) includes the 

electron beam gun as the heat source, ma- 

terial feeding and ingot withdrawal systems, 

a crucible for material solidification, and a 

vacuum system to maintain the low pres- 

sure. Process observation, both visually 

and with video systems, is possible through 

viewports. The melt chamber flanges are 

equipped with x-ray absorbing steel boards, 




Vacuum Melting and Remelting Processes/413 

and interlocking systems prevent operation 

failures and accidents. 

The control system allows the adjustment 

and control of such operating process pa- 

rameters as electron beam power, operating 

vacuum level, material feed rate, and ingot 

withdraw speed. The control system also 

records and logs the process data. 

Power Supply Units. One or more high- 

voltage power supply units are needed to 

supply the electron beam guns with the 

required continuous voltage (30 to 40 kV). 

The beam power of each gun can be adjust- 

ed between zero and maximum power with 

an accuracy of -+2%. 

Other Equipment. Large production fur- 

naces are equipped with lock-valve systems 

to allow simultaneous melting and unload- 

ing of ingots without breaking the vacuum 

in the melt chamber. Production is thus 

limited only when the condensate remaining 

in the melt chamber requires cleaning or 

when a different alloy is to be melted. 

Characteristics of Electron 

Beam Drip Melted Metals 

Electron beam melted and refined material 

is of the highest quality. The amount of inter- 

stitials present is very low, and trace elements 

of specific high vapor pressure can also be 

reduced to very low values (Ref 1, 2). 

Reactive and Refractory Metals 

Tantalum and niobium ingots have 

smooth surfaces and are of sufficient ductil- 

ity that they can be cold worked, and sheets 

and wires can be produced. 

Tungsten and molybdenum ingots are 

also of the highest possible purity, but the 

ingots are brittle because of the very large 

grain size and the concentration of impuri- 

ties at grain boundaries. 

Hafnium. Electron beam melted hafnium 

is of higher ductility than the vacuum arc 

remelted metal (Ref 3). The main application 

of electron beam melted hafnium is as control 

elements for submarine nuclear reactors. 

Vanadium is refined by electron beam 

drip melting. The aluminothermically pro- 

duced feedstock is drip melted in several 

steps. During this procedure, the ingot diam- 

eter is reduced at each step by approximately 

30 to 40 mm (1.2 to 1.6 in.) to obtain an ingot 

30 to 40 mm (1.2 to 1.6 in.) in diameter, 

regardless of the initial ingot diameter. The 

clean vanadium ingots are primarily used in 

nuclear reactor applications (Ref 4). 

Applications for electron beam melted 

refractory and reactive metals are listed in 

Table 3. 

Steels 

The purity and properties of electron beam 

melted steels are in some respects better than 

those of vacuum arc and electroslag remelted 

steels, but the processing costs are higher. 

The electron beam melting of steel is primar-



Melting chamber 

Feeding systems 

Oil diffusion pump 

Water-cooled 

copper crucible 

Device for ingot 

withdrawal 

U I 

/ 

M 

Electron beam 

Deflected 

electron beam 

Charging valves 

Remelting rod 

Ingot 

Single-gun 1200 kW furnace for horizontal drip melting of steels. Melting rates of up to 1100 kg/h (2425 

Fig. 5 Ib/hl are possible. 

Table 3 Principal applications for vacuum arc remelted (VAR), electron 

beam melted (EB), and powder metallurgy (P/M) reactive and refractory 

metal ingots 

Metal Applications 

Reactive metals, VAR and EB melting 

Hafnium .................................. 

Vanadium ................................. 

Zirconium ................................. 

Titanium .................................. 

Refractory metals, EB melting and P/M 

Tungsten .................................. 

Tantalum ................................. 

Molybdenum .............................. 

Niobium .................................. 

Flash bulbs and glow discharge tubes for the electronics 

industry; control rods and breakoff elements in submarine 

nuclear reactors 

Targets for high deposition rate sputtering processes in the 

electronics industry; breakoff elements, fixtures, and fasteners 

in nuclear reactors; standards for basic research; alloying 

element for certain high-purity alloys 

Getter material in tubes in the electronics industry; stripes for 

flash bulbs; fuel claddings, fasteners, and fixtures for nuclear 

reactors 

Components for bleaching equipment and desalination plants in 

the chemical industry; superconductive wires; turbine engine 

disks, blades and housings, rain erosion boards, landing legs, 

wing frames, missile cladding, and fuel containers in the 

aircraft and aerospace industries; shape memory alloys; 

biomedical fixtures and implants; corrosion resistant claddings 

Heating elements, punches and dies, and nonconsummable 

electrodes for arc melting and gas tungsten arc welding for 

metal processing equipment; targets for x-ray equipment and 

high sputtering rate devices such as very large-scale integrated 

circuits, cathodes and anodes for electronic vacuum tubes in 

the electronics industry; radiation shields in the nuclear 

industry; cladding and fasteners for missile and reentry 

vehicles 

Condensers, autoclaves, heat exchangers, armatures, and fittings 

for the chemical industry; electrolytic capacitors for the 

electronics industry; surgical implants; fasteners for aerospace 

applications 

Dies for conventional and isothermal forging equipment; 

electrodes for glass melting; targets for x-ray equipment; 

cladding and fasteners for missile and reentry vehicles 

Superconductive wire for energy transmission and large magnets 

for the electrical and electronics industries; heavy ion 

accelerators and radio frequency cavities for nuclear 

applications; components for aircraft and aerospace 

applications 




ily used in East Germany and other Soviet 

bloc countries. The resulting ingots are up to 

1000 mm (40 in.) in diameter and weigh up to 

18 Mg (20 tons). The furnaces used have been 

in operation since 1965, and have beam pow- 

ers of up to 1200 kW. Larger furnaces for the 

production of ingots weighing up to 30 to 100 

Mg (33 to 110 tons) are under construction 

(Ref 5). 

The essential advantage of the electron 

beam melting of steel is the drastic reduction 

of metallic and nonmetallic impurities and 

interstitial elements (Ref 6, 7). The principal 

applications for electron beam melted steels 

are in the machinery industry for parts for 

which high wear resistance and long service 

life are required. The extended service lives 

of the parts and the reduced manufacturing 

time (for example, less surface polishing is 

required for electron beam melted steel) can 

justify the higher material costs. 

The electron beam melting of steel and 

superalloys can become much more eco- 

nomical when melting and refining are done 

by continuous flow melting or cold hearth 

refining. These melting and refining meth- 

ods reduce energy costs and minimize ma- 

terial losses. 

Continuous Flow Molting 

The continuous flow melting process (cold 

hearth refining process) (Fig. 6) was devel- 

oped approximately 10 years after drip melt- 

ing (Ref 8). Continuous flow melting is mainly 

used for refining specialty steels and superal- 

loys and for refining and recycling reactive 

metal scrap, especially Ti-6AI-4V from high- 

density tungsten carbide tool tips (Ref 9). 

Principles of 

Continuous Flow Melting 

Continuous flow melting (Fig. 7) is the 

most flexible vacuum metallurgical melting 

process. It is a two-stage process in which 

the first step (material feeding, melting, and 

refining) takes place in a water-cooled cop- 

per trough, ladle, or hearth. In the second 

step, solidification occurs in one of several 

round, rectangular, or specially shaped wa- 

ter-cooled continuous copper crucibles. 

Both process steps are nearly independent 

from each other; they are linked only by the 

continuous flow of the liquid metal stream. 

The major refining actions are carried out in 

the hearth, but some postrefining takes 

place in the pool of the continuous casting 

crucible, similar to the drip melting of hor- 

izontally fed billets. Refinement in continu- 

ous flow melting occurs by vacuum distilla- 

tion in the hearth pool, superheating, and 

stirring of the molten metal pool. 

Removal of Impurities. Most impurities 

with densities lower than that of the melt (for 

example, metalloids in steels and superalloys) 

can be segregated by flotation and formed 

into a slag raft. The raft is then held in place 

by either mechanical or electrothermal


Beam rot 

on the pc 

Programmed electron beams 

for refining low-density 

inclusions and maintaining a 

flat. shallow inaot oool 

Fig. 6 Schematic of the continuous flow melting process 

means. Impurities denser than the melt, such 

as tungsten carbide tool tips in titanium, are 

removed by sedimentation. Inclusions with 

densities such that efficient flotation or sedi- 

mentation does not occur can be partially 

removed by adhesion to the slag raft. 

Hearth dimensions are based on the type 

and amount of refining required. For exam- 

ple, hearths for vacuum distillation should 

be nearly square and relatively deep to 

allow sufficient melt stirring. For flotation 

refining, the hearth should be long and 

narrow (for superalloys, approximately 10 

mm, or 0.4 in., of hearth length for each 100 


3n beam 

feedstock 

lat 

9ntal bar feeding 

per 

anical 

val of 

~ions 

kg/h, or 220 lb/h, of melt rate is recommend- 

ed). Hearths for titanium alloy scrap recy- 

cling can be relatively short if all the mate- 

rials can be transported to the pool of the 

hearth rather than to the ingot pool. 

Feeding. Material feeding criteria include 

100% homogenous material transportation 

to avoid uncontrolled evaporation of alloy- 

ing elements and correct feeding into or 

above the hearth pool. Horizontal feeding of 

compacted, premelted, or cast material is 

most often used. Loose scrap and raw mate- 

rial are used only when compaction is too 

expensive. Feeding of liquid metal was used 

Table 4 Comparison of the characteristics of drip melting and continuous 

flow melting 

Characteristic Refractory metals Reactive metals, superalloys, and specialty steels 

Power density ............................. High Soft; smoothly distributed 

Inclusions ............................. Irrelevant Must be removed 

Ingot shape and structure ............... Round; coarse grain Round or flat; fine grain, segregation-free 

Mass production ....................... Low High 

Competitive economical processes ....... Vacuum arc remelting Vacuum arc remelting; electroslag remelting 

Preferred method ...................... Drip melting Continuous flow melting 




in one of the first continuous flow melting 

furnaces to produce a ferritic steel in a vacu- 

um induction furnace (Ref 10). Postrefining 

was carried out in a cascade of five hearths 

1.5 m (60 in.) long and 1 m (40 in.) wide. 

Casting and Solidification. The criteria 

for material casting and solidification include 

the shape of the final product and the solidi- 

fication rate required to avoid ingot tears or 

other defects and to ensure a homogeneous 

ingot structure. The multiple casting of small 

ingots is sometimes used, especially when 

forging is impossible because of the brittle- 

ness of the solidified material (for example 

MCrAly wear-resistant coating alloys). The 

casting of round and rectangular ingots and 

slabs is common practice, and the continuous 

casting of hollow ingots is also being used 

(Ref I 1). The casting of segregation-free in- 

gots and ingots with a fine grain size is under 

development to improve the workability of 

superalloys (Ref 12, 13). 

Continuous Flow 

Versus Drip Melting 

Table 4 compares the essential features of 

drip melting and continuous flow melting. 

Generally, continuous flow melting is used 

for all refractory metals, superalloys, and 

specialty steels, especially when flotation or 

sedimentation of inclusions is required. 

Drip melting is used for refractory metals 

because of their high melting points and the 

resulting high heat losses to the water- 

cooled copper crucible. Depending on pro- 

duction quantity, double or triple drip melt- 

ing may require less energy than a single 

continuous flow melt of some materials, 

such as niobium. 

Refining and Production Data 

Data on continuous flow electron beam 

melting and refining in laboratory and pilot 

production furnaces are given in Table 5. The 

data demonstrate the effectiveness of the pro- 

cess in reducing impurities and interstitial 

elements. It can also be seen that the selective 

evaporation of chromium from superalloys 

can be controlled by the distribution of beam 

power at the trough pool and by controlling 

trough pool area and melt rate. The selective 

evaporation of aluminum from Ti-6A1-4V al- 

loy is much more difficult to control; addition- 

al aluminum must be used to compensate for 

the aluminum evaporated. 

Equipment for Continuous 

Flow Electron Beam Melting 

The equipment required for continuous 

flow melting is different from that used in 

drip melting mainly because of the trough 

and the somewhat larger melting chamber. 

In addition, because of the materials often 

melted in the continuous flow process (su- 

peralloys and titanium alloys), additional 

instrumentation is often provided. This may 

include an ingot pool level control system,



/ 

/-//~// ......... 

Fig. 7 Four-gun 1200 kW combined electron beam drip melting and continuous flow melting furnace 

metal vapor and partial pressure analyzers, 

a two-color temperature control system, 

and a data logging system. 

Accurate beam power distribution is 

achieved in two- or three-gun furnaces by 

microprocessor control, which allows the 

splitting of a single beam to 64 locations and 

the adjustment of dwell time at each loca- 

tion between 0.01 and 1000 s. The beam 

spot at each of the 64 locations can be 

scanned over an elliptical or rectangular 

area. With such systems, the required refin- 

ing can be achieved without unnecessary 

power consumption and evaporation of al- 

loying elements (Ref 15). 

Process observation is accomplished with 

a video monitoring system. Samples can be 

obtained from both the trough pool and the 

ingot pool for nearly continuous control of 

material quality. 

Feeding systems for continuous flow fur- 

naces must maintain homogeneity along the 

length of the feed material. The trough and 

crucible should be easily accessible for con- 

venient maintenance, especially when dif- 

ferent alloys are to be melted in the same 

furnace. 

Characteristics of 

Continuous Flow 

Melted Materials 

Titanium ingots and slabs can be pro- 

duced from titanium scrap contaminated 

with tungsten carbide tool tips. The electron 

beam melted product contains tungsten car- 

Table 5 Refining and production data for the continuous flow melting of reactive and refractory metals and 

stainless steels in laboratory and pilot production furnaces 

Electron Specific 

beam Operating melting ] Composition of feedstock and product [ 

Feedstock size, Trough size, Ingot size, Ingot weight, Melt rate, power, pressure, energy, C, O, N, H, AI, V, Cr, 

Metal mm (in.) mm (in.) mm (in.) kg 0b) kg/h 0h/h) kW Pa (tort) kW • h/kg ppm ppm ppm ppm % % % 

Hafnium ........... 60 (2.4) square 120 × 250 100 (4) diam 

(5 x 10) 

Zirconium ........ I00 (4) square 120 x 300 150 (6) 

(5 x 12) 

Zirconium ........ 80 (3.2) square 120 x 300 100 (4) 

(5 x 12) 

Vanadium ........ 50 (2) square 120 x 300 100 (4) 

(5 x 12) 

Ti-6AI-4V ........ Swarf 120 x 300 150 (6) 

(5 x 12) 

Ti-6AI-4V ........ Solid scrap 120 x 300 150 (6) 

(5 × 12) 

Ti-6AI-4V ........ 125 (5) diam 150 × 400 2 x 75 (3) 

(6 × 16) diam 

Commercially pure 

titanium ........ 160 (6.3) 150 x 250 100 x 400 

(6 x 10) (4 x 16) 

Commercially pure 

titanium ...... Sponge 150 x 500 100 x 400 

(6 x 20) (4 x 16) 

Stainless steel .... 150 (6) diam 150 x 400 2 x 75 (3) 

(6 x 16) diam 

Alloy 718 ........ 133 (5.2) diam 150 x 400 2 x 75 (3) 

(6 x 16) diam 

AISI type 316 

stainless steel... 150 (6) diam 150 x 400 3 x 65 (2.6) 

(6 x 16) diam 

Source: Ref 14 

83.0 (183) 40 (88) 

90.5 (200) 42 (92.5) 

40.2 (89) 80 (176) 

. - - 20 (44) 

62.6 (138) 40 (88) 

62.6 (138) 70 (154) 

2 x 32 (70.5) 91 (200) 

96.4 (213) 86.3 (190) 

103.0 (227) 41.2 (91) 

2 × 55 (121) 136 (300) 

2 × 57 (126) 136 (300) 

3 x 41.5 136 (300) 

(91.5) 

180 4 x 10 -2 

(3 x 10 -4) 

185 3.5 X 10 -2 

(2.6 x 10 -4) 

140 3.5 X 10 -2 

(2.6 x l0 -4) 

130 1.5 x l0 2 

(1.1 x l0 4) 

122 2 X 10 -2 

(1.5 x 10 -4) 

140 7 × 10 2 

(5.3 x 10 4) 

147 6 X l0 2 

(4.5 x 10 -4) 

148 6 × 10 -2 

(4.5 × 10 -4) 

226 8 x 10 -2 

(6 x 10 -4) 

144 6 x 10 -2 

(4.5 x 10 4) 

156 6 × 10 -z 

(4.5 x 10 -4) 

156 6 X 10 -2 

(4.5 x 10 -4) 




4.5 

900 . . . . . . . . . . . . . . . 

600 . . . . . . . . . . . . . . . 

4.4 

950 95 30 ......... 

540 30 3 ......... 

1.75 

4000 800 10 ......... 

1520 210 3 ......... 

6.5 

1045 210 10 ... 99 '-" 

277 50 3 ... 99 .'' 

3.0 400 2600 110 84 6.0 4.0 '' 

200 2700 110 22 4.4 4.2 ' " 

2.0 1520 1520 75 15 6.0 4.0 ' ' 

• . . 1320 76 8 4.8 4.1 • ' 

1.61 . . . . . . . . . . . . 6.0 4.0 • • 

. . . . . . . . . . . . 3.6 4.3 • • 

1.71 . . . . . . . . . . . . . . . . . . . . . 

5.5 . . . . . . . . . . . . . . . . . . . . . 

1.06 701 97 155 ......... 18.25 

536 33 68 ......... 18.11 

1.15 417 14 52 ......... 19.11 

363 17 34 .'' 0.72 ''' 18.73 

1.15 . . . . . . . . . . . . . . . . . . . . .

Vacuum Melting and Remelting Processes - ASM International

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