AMRITA SCHOOL OF ENGINEERING, COIMBATORE

PRESENTED BY:SABIQ (CB.EN.P2MFG15017)SANDEEP NAIR (CB.EN.P2MFG15018)M.TECH (MANUFACTURING )

ELECTROSLAG MELTING AND REFINING

INTRODUCTION This process was developed originally in the erstwhile USSR in

1930. Electro-slag melting is also known as Electro-flux melting is a

process of melting and refining steel and super alloys for mission critical application.

It principle is based on the electro-slag welding process. It dispenses completely with the rising and gating system and

also with the need for separate melting unit ,pouring ladle and transportation arrangements.

Graphite and ceramic mould has been used in place of metallic ones.

Consumable steel electrodes are used.

ELECTROSLAG MELTING FURNACES

WORKING OF ESM FURNACE The electro-slag melting process is used to melt and refine

steels and various super-alloys, resulting in high quality ingots.

Electric current (generally AC) is passed between the electrode and new ingots ,which is formed in the bottom of a water-cooled copper mold.

The new ingot is covered in a engineering slag that is superheated by the electric current.

These metal droplets travels through the slag to the bottom of the water cooled mold and slowly freeze as the ingot is directionally solidified upwards from the bottom of mold.

Solidification takes place without any contact with the atmosphere.

The slag pool floats above the refined alloys, continuously floating upward as the alloy solidifies.

The molten metal is cleaned of impurities that chemically react with slag or otherwise float to the top of the molten pool as the molten droplets pass through the slag's.

Electro-slag melting uses highly reactive slags to reduce the amount of sulfide present in bio-metal alloys.

ESM furnaces can be designed for melting of round, square and rectangular (slab) ingots.

WORKING OF ESM FURNACE

SLAG USED AND ITS PROPERTIES

Slag for electro-slag melting are usually based on calcium fluoride (caf2), lime (Cao) and alumina (al2o3). magnesia (mgo), titania (tio2) and silica (sio2) may also be added, depending on the alloy to be melted.

To perform its intended functions, the slag must have some well-defined properties, such as:-

1). Its melting point must be lower than that of the metal to be melted.

2). It must be electrically efficient.3). Its composition should be selected to ensure the desired

chemical reactions.4). It must have suitable viscosity at melting temperature.

ESM PROCESS INVOLVES FEWER STEPS THAN SAND CASTINGFABRICATE PATTERN

SPLIT MOLD FLASK

SPLIT FLASK REMOVE PATTERN

INERT COREASSEMBLE

MOLDBAKE

CENTRIFUGAL OR GRAVITYSHAKE OUTTRIM GATE AND RISERSURFACE CLEANHEAT

SAND CASTING

FABRICATE MOLD

ADD SLAG

ELECTROSLAG CAST

REMOVE FROM MOLD

SURFACE CLEAN

GRIT BLAST

MACHINE TOP

HEAT TREAT

ELECTROSLAG

MELTING

PROCESS No removal of hydrogen and nitrogen. Minimum sulphur content due to slag reaction. Smooth surface due to slag skin on surface. Less material defect due to melting of dendrite

clumps Electrode can be used in cast condition due to

cleaning by slag. Melt rate choose to slag skin equal to dendrite arm

spacing. No manganese losses in alloys.

KEY FEATURES Ingot weights from 100 kg to 165 metric tons. Alternating current as re-melting energy with melting currents

from 3 ka to 92 ka. Ingot diameters from 170 mm to 2,300 mm, depending on

material being melted. Circular, square and rectangular ingot shapes are possible. Surface electrode preparation normally not ground. Melting effect on gas content - constant nitrogen and hydrogen. Melting rate-13kg/min No modification ; maximal homogeneity. Casting yield is almost 100%.

NEW DEVELOPMENT IN ESM PROCESS

Electro-slag melting under Vacuum (VAC-ESM): Melting is carried out under vacuum as in VAR, however, using a slag. Problems of oxidation of the melt do not arise. In addition, dissolved gases such as hydrogen and nitrogen, can be removed .The danger of white spots, as encountered during VAR, is reduced to a minimum. That is of interest for super-alloys or titanium melting.Low gas content in final material ,then VAR process is chosen.

MELTING UNDER INERT GAS ATMOSPHERE (IESM):

MELTING UNDER INERT GAS ATMOSPHERE (IESM): This is a great step forward in freeing the ESM

process from hydrogen pick-up problem and the influence of seasonal atmospheric changes. In addition it allows melting under oxygen-free inert gas.

The following results have been obtained:- Oxidation of electrode and slag is completely

avoided; Oxidizing loss of elements such as Ti, Zr, Al, Si,

etc. is almost completely avoided.

MELTING UNDER INERT GAS ATMOSPHERE (IESM): This is especially important when melting high Al

and Ti-containing alloys, like super- alloys with very narrow analytical ranges:-

1). Better cleanliness in the ingot is achieved. 2). When using argon as the inert gas, pick-up of

nitrogen and hydrogen is avoided. Due to the absence of oxygen in the furnace

atmosphere, desulfurization via the gas phase is no longer optimal.

PROCESS CHARACTERISTICS IN MELTING

CHEMICAL ELEMENT CHANGE IN MELTING

ADVANTAGES1) Uniform mechanical properties in the longitudinal and

sectional direction.2) Very large ingots such as 3000mm diameter and more than

200ton weight can be produced.3) Homogeneous, sound and directionally solidified structure.4) High degree of cleanliness.5) Free of internal flaws (e.g. hydrogen flakes).6) Free of macro-segregation.7) Smooth ingot surface resulting in a high ingot yield.

LIMITATIONS1) Slag treatment to achieve lowest hydrogen in

Ingot.2) Closed melting to avoid hydrogen pick-up from

atmosphere.3) Melt rate adjusted according to slag system, alloy

composition and furnace size.4) Gases (like nitrogen & hydrogen) need to be

adjusted to lowest level in the electrode.5) Adjustment of slag chemistry and composition of

the electrode.

APPLICATIONS

AIRCRAFT

MILITARY TECHNOLOGY

1. Plug lid2. Cardboard lid3. Primer lid4. Axis of firing pin5. Spring6. Firing pin7. Leather circlet8. Screw thread9. Body of plug10.Wick11. Primer 212.Detonator13.Primer 114.Bolt15.Pin16.Lever17.overview

THERMAL POWER STATIONS

NUCLEAR POWER PLANTS

CONNECTING ROD

HIGH PRESSURE VESSELS

CRANKSHAFTS

MILLING CUTTERS

REFERENCES New Technology of Electro slag Casting of Solid Horn-

Shaped CoresE.N. Eremin,Omsk State Technical University, Omsk, Russia.

Materials Research and Engineering Edited by B. Ilschner and N.J. Grant.

Commercialization effort in support of electroslac-casting technology ,V. K. Sikka.

Principle of foundary technology, P.L. Jain