ELECTROSLAG PROCESS WITH LIQUID METAL

Electroslag technologies with liquid metal is a way to form of an ingot (a billet, a surfacing layer) that provides the preparation in the separate unit of a liquid metal and its pouring from special pouring-holding tundish by small portions or thin stream into a water cooled sectional copper current supplying mould (CSMÒ). The power source is connected to top section of the mould. The slag pool is constantly heated by electric current passing from current supplying section of the CSM through a slag to a bottom plate. Actually the current supplying section is a non-consumable electrode of a ring shape. A liquid metal passes through the slag and forms a cylindrical or ring shape metal pool, which solidifies and forms a body of a solid ingot in the first case, and a surfaced layer or a hollow ingot in the second case, depending on type of the central inserts installed in CSMÒ. Being formed ingot is withdrawn from CSMÒ by certain speed that is 3‑10 times higher than at conventional ESR.

The base of electroslag technologies with liquid metal is current supplying mould (CSM). CSM performs a function of non-consumable electrode and, simultaneously, provides an ingot formation. Use of CSM provides a heat input into slag bath that gives us possibility to exclude consumable electrodes and to work directly with liquid metal.

In this case instead of a consumable electrode a core (for bimetallic roll production, ingot enlargement etc.) for surfacing or an inner mould for hollow ingot manufacture can be located in mould center. Thus ESR with liquid metal is very flexible processes with wide technological possibilities:

Elementary diagrams of electroslag technologies with liquid metal (from left to right) are following (from left to right): mill roll billet surfacing or ingots enlargement (ESS LM); direct producing of solid and hollow ingots from liquid metal (ESR LM):

1 – liquid metal pouring device;
2 ‑ metal pool;
3 ‑ surfaced layer;
4 ‑ surfaced billet;
5 ‑ slag pool;
6 ‑ water cooled current supplying mould;
7 ‑ water cooled insert;
8 ‑ hollow ingot;
9 ‑  solid ingot.

The use of liquid metal instead consumable electrodes sufficiently (up to 40%) reduces primary cost of ready product. The experience of industrial realization of the technology of electroslag surfacing with liquid metal of mill rolls billets prove that the process occurred to be more economical than the centrifugal casting of similar billets of mill rolls.

The highest quality of metal for the most critical application can be achieved by ESR LM because:

  • liquid metal temperature is lower that at standard ESR and it chemistry can be strictly adjusted in order to minimize mushy zone and to avoid segregation into solidified ingot;
  • all advantages caused by known peculiarities of physical-chemical processes in standard ESR are applied to technological processes of ESS/ESR LM;
  • ESS/ESR LM processes productivity can be controlled in wide interval of allowable efficiency.

The absence of consumable electrodes (neither manufacture and delivery, nor preparation and fastening) is an absolute undoubted advantage of electroslag technologies with liquid metal (to ESR specialists it is the most clear). It is known that from 40 to 60% of ESR cost is the cost of electrodes. Exception of consumable electrodes not just cut the operational costs on the ESR ingot manufacture, but significantly reduces the furnace height, because, in fact, the upper part of furnace (under a working platform) consists of a pouring-holding tundish only.

Besides, the ESR LM furnace is the most versatile unit, which allows producing the traditional solid ingots, hollow ingots, and also the multi-layered billets with a coaxial and horizontal layers (including the rolling mill rolls with the surfaced layer from high-strength steels and a composite rotors for power generating turbines).