January 28, 2022

Arc and electron beam melting of zirconium

Zirconium arc melting parameters and process conditions are shown in Tables 1 to 3.

Table 1 Zirconium vacuum consumable melting parameters

坩埚 diameter / cm

twenty two

twenty two

Electrode diameter / cm

15

16

Smelting times

1

2

Arcing current / kA

3.5

3.5

Smelting current / kA

4.5

7.0 to 7.5

Current density / A · cm - 2

(by 坩埚 section)

11.8

18.2 to 19.7

Melting voltage / V

33~35

34~38

Stable arc magnetic field / A · 匝

1.5×1800

1.5×1800

Vacuum degree / kPa

(1.3 to 6.7) × 10 - 4

(1.3 to 6.7) × 10 - 4

Air leak rate / kPa · min - 1

≤6.7×10 - 5

≤6.7×10 - 5

Table 2 Relationship between melting voltage, current and electrode diameter during arc melting of zirconium consumable electrode

Electrode diameter / cm

5.08

7.62

10.16

12.70

15.24

17.78

20.39

22.86

25.4

Melting voltage / V

25

28

30

40

40

40

40

40

40

Smelting current / kA

0.8

1

0.8

2.5

3.5

4

4.5

5

5.5

Table 3 Zirconium arc melting process conditions

project

Non-consumable method

Self-consumption

Consumable remelting

Electrode size / cm

Diameter 1.27 ~ 1.90

Length 1.9 to 3.8

(tungsten or tungsten coated with 1% to 2% ThO 2 )

5.08×5.08×50.8

Diameter 15.2

坩埚 size / cm

Inner diameter 10.2

Inner diameter 15.2

Wall thickness 0.635~1.587

Inner diameter 25.4

Cooling water flow rate of cooling copper crucible / L · min - 1

302

atmosphere/%

80He+20Ar

80He+20Ar

80He+20Ar

Pressure / kPa

101.3

101.3

0.067~0.4

Melting voltage / V

50

45

35

Smelting current / kA

1.1

3

6

Zirconium melting speed / kg · h - 1

5.4

108

270

1kg zirconium electricity consumption / kW · h

10.2

1.23

0.77

The main equipment for arc melting is shown in Figures 1 to 3.

Figure 1 Multi-furnace non-consumable electrode arc furnace

1-negative joint; 2-vacuum pressure gauge; 3-observation port; 4-insulating ring; 5-water-cooled six-inch; 6- mica support; 7-rotary handle; 8-inch cooling water pipe; Positive electrode joint; 10- vacuum pump valve; 11-clam pot mixed gas valve; 12-tungsten electrode head; 13-vacuum pipe; 14-cooling water pipe; 15-electrode; 16-water-cooled electrode

Figure 2 Schematic diagram of consumable electrode arc furnace

1-backup electrode; 2-welding box; 3-welding rail; 4-plate glass; 5-rubber glove; 6-welding wire; 7-gearbox; 8-steel roll; 9-hand crank; 10-arc Power supply wire (cathode); 11-copper contact roll; 12-insulation; 13-water jacket; 14-zirconium ingot; 15-water inlet; 16-water outlet; 17-arc power supply wire (anode); Window; 19-zirconium ingot transport trolley

Figure 3 consumable electrode remelting electric arc furnace

1-electrode cooling water; 2-electrode joint (cathode); 3-observation window; 4-assembly inlet and outlet; 5-vacuum pipe joint; 6-power joint; 7-water jacket; 8-zirconium ingot; Insulating ring; 10--operating car

The electron beam is a very pure source of high-energy, electron beam melting in a high vacuum (less than 1.3 × 10 - 5 kPa) for the lower, so the melting metals to achieve highly efficient purification. By adjusting the electron beam orientation, any part of the material to be smelted can be heated. Electron beam melting has no mechanical action on the molten pool, does not blow the molten pool, and can melt materials of various shapes.

Purification mechanism of electron beam melting: first, evaporation by alloy components, and second, evaporation and deoxidation of base metal suboxides.

The various parameters for electron beam melting are shown in Figure 4 and Table 4.

Figure 4 Relationship between power required for electron beam melting and metal melting point and ingot diameter

1-960kW; 2-480kW; 3-240kW; 4-120kW; 5-60kW; 6-30kW

Table 4 Trend of deoxidation of metals (represented by the vapor pressure ratio of metal to its oxide)

Deoxygenated

Not deoxidizing

The electron beam melting furnace is shown in Fig. 5. The comparison between the melting method and the vacuum sintering method is shown in Table 5.

Figure 5 Schematic diagram of NRC electron beam furnace melting furnace

1-cathode; 2-accelerated anode; 3-electron gun chamber; 4-focus coil; 5- spacer; 6-4in gate valve; 7-melting chamber; 8-ion vacuum gauge; 9-vibration feeder ; 10 - water-cooled copper crystallizer; 11 - puller; 12 - pull down; 13 - zirconium ingot; 14 - 10in oil diffusion pump; 15 - peep window; 16 - electron beam; 17 - 4in oil diffusion pump; 18-water cooling coil

Table 5 Electron beam melting on a productive scale, vacuum arc

Comparison of smelting (self-consumption electrode) and vacuum sintering

Comparison project

Electron beam melting

Vacuum arc melting

Vacuum sintering

Remarks

Starting material (material to be melted)

When the drop method is used, the material to be smelted must be made into a consumable electrode type. When using the molten pool smelting method, the feeding form is arbitrary: sponge, powder, granule, and the like. In the case of smelting for casting, even large pieces of waste can be added to the charge. Materials with high gas content should be pre-vacuum degassed

The material to be smelted must be made into a consumable electrode. Limited possibilities for smelting waste

Only powder can be applied. When using waste, the waste must be powdered first.

Electron beam melting method is the most superior

Ingot size

It is easy to smelt long and medium-section long ingots. For large-section ingots, the melting equipment is expensive (the vacuum pump needs to have a large exhaust speed)

Can easily smelt ingots of any reasonable size

Sintering of small ingots (10 to 20 kg) is easy. For medium-sized ingots, (1) large presses, sometimes hydraulic presses are available; (2) high energy must be supplied to keep the entire ingot at the sintering temperature.

Vacuum arc melting is the most superior

Insulation power consumption

Varying with smelting speed

Minimal power required

Because the sintering efficiency (similar to the smelting speed) is extremely low, the energy required is extremely high. The reason is that the diffusion of impurities to the surface is extremely slow and takes a long time; the entire ingot must reach the sintering temperature; sometimes secondary sintering is required.

Vacuum arc melting is the most superior

Pressure in the melting chamber

Any small pressure can be achieved. Usually around 4 × 10 - 5 ~ 10 - 6 kPa (related to metal gas content, pump capacity and melting method)

It is best to use a pressure of 6.7 × 10 - 3 to 10 - 4 kPa, and the pressure is low and useless.

Any small pressure can be achieved. Normal sintered 1.3 × 10 - 7 kPa pressure at - 5 ~ 6.7 × 10

Electron beam melting is as beneficial as vacuum sintering

Processing time

medium

least

most

Vacuum arc melting is most beneficial

Annual production

medium

maximum

Minimum

Vacuum furnace smelting is most beneficial

Degree of metal purification

Best (reason: high vacuum, highest temperature reached, long metal in molten state)

Worst (lower vacuum, lower temperature than electron beam melting, shorter time in molten state)

The purity obtained by electron beam melting is poor, but it is still good (high vacuum, long sintering time, lowest temperature)

E-beam smelting is superior

Grain size

Very coarse (since the melting rate is small, the metal purity is high)

Thick, but still much thinner than electron beam melting

Very fine (because of the powder as the starting material)

Sintered grain is the finest

Recent research results on smelting and refining methods of zirconium include: rotating electrode smelting high-purity metal zirconium (non-consumable rotating water-cooled copper electrode, water-cooled copper crucible, vacuum); electroslag smelting of zirconium; recrystallization of zirconium in vacuum region; electrode Zirconium is transported and purified (Principle: When direct current is applied at high temperature, the solute atoms migrate under the action of an external electric field, and the migration of oxygen, nitrogen and carbon is the same as the direction of electron flow. The raw material used is zirconium smelted in the electron beam region, and the degree of vacuum (1) ~2)×10 - 8 Pa, temperature 1402~1627°C); BB Suming (Cy MNH ) measures the transfer coefficient of titanium and iron when zirconium is smelted in the electron beam region, the transfer coefficient of iron is 0.29±0.06, and the transfer of titanium The coefficient is 0.48±0.15. The literature studies the absorption of gas phase impurities in the regional refined zirconium process. It is found that the rate of oxygen absorption is extremely fast. The absorption depends on the partial pressure, the moving speed of the melting zone and the number of melting times. It has been found that oxygen is in the zirconium solution ( Solubility in oxygen: metal <0.1) follows Henry's law.

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