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MATERIALS USED IN ELEGTROSLAG CASTING

To run the ESC process provision is to be made for consumable electrodes, flux or its components to prepare liquid slag; electric power to generate heat in slag pool; water to cool casting mould, in some cases dry air, inert or other gas suitable for blasting slag and metal pool; compressed air or working fluid to control the operation of pneumatic or hydraulic equipment.

The methods of manufacturing consumable electrodes include continuous and, centrifugal casting, casting into graphite or iron moulds and also making them of metallurgical rolled steel. The cast electrodes, even though affected by porosity and blisters, are usually not discarded since such defects never exert appreciable influence on the remelted metal quality. Neither is a failure of some melts to fall within the acceptable range of chemical composition values the reason for the electrodes to be discarded. By an adequate set-combination of electrodes of different melts, it is possible not only to obtain the castings whose chemical composition meets the technical requirements, but also to make closer the range of chemical composition values for a given grade of steel in its basic constituents and to ensure the highest possible and most stable properties of the casting metal. The surface of electrodes may be subjected to special pre-treatment like shot-blasting or machining in order to remove scale, rust, burning-on etc.

The ESC method is suitable for producing castings practically of all kinds and categories of material (steel, alloys, non-ferrous metals, nodular cast iron, high-strength cast iron etc.). Therefore, in each particular case of producing castings from a certain material, use should be made of proper chemically composed billets as consumable electrodes.

In the ESC process flux serves as a medium to generate the heat required for melting consumable electrodes and also as a basic means to maintain and control chemical composition of the remelted metal. The degree of refining, removal of impurities from the metal while preserving the alloying constituents therein, depend on the molten slag activity.

The melting temperature of flux should be slightly lower than that of the metal itself. Furthermore, the molten flux should have a low viscosity. In the ESC process these two factors create favourable conditions for a thin slag crust formation thus improving the cooling of castings and making their surface better. In the electroslag process oxyfluoride slag systems have the most multipurpose application.

The minimum oxidation capacity is inherent in the slags which contain no oxides. The higher the basicity of a slag (basic-to-acid oxide ratio), the higher its desulphurization ability is. A low or moderate content of alumina in a flux lowers the rate of metal melting thus reducing the possibility of axial porosity and shrinkage cavities to be formed in the casting. Reduction of lime content in the flux weakens its hydration susceptibility thus reducing its chance to cause porosity and shrinkage cavities in the casting. Hydrogen percentage in the metal largely depends on the flux composition. A flux with low lime content is less sensitive to hydrogen embrittlement than a flux rich in lime. In this respect the aluminous flux AHO-6 is considered to have high protective properties.

Prior to be used, the flux is prefused in a graphite crucible by a graphite electrode, due to which a proper refining of slag from moisture, silica, iron oxides, sulphur and lead is achieved. To start the ESC process the liquid slag is poured into the casting mould by a syphon method (through the bottom) or through its top. The consumption of cooling water depends in each particular case on the size of the casting to be produced and the cooling water temperature at the mould inlet.

Task 1. Find in the text English equivalents to the following words and word combinations:

витратний електрод, флюс, шлакова ванна, охолоджувати, інертний газ, продувка, управляти дією пневматичного чи гідравлічного обладнання, методи виробництва, центробіжне лиття, сталепрокат, впливати, міхур (здуття), помітний вплив, якість металу, розплав, відбраковуватись, відповідати вимогам, сорт сталі, основні складові, поверхня, шрото-струменевий, зчищати накип, утворення пригару, чавун з кулькоподібним графітом, високоміцний, заготівка, середовище, основні засоби, ступінь очищення, видалення домішок, низька в’язкість, утворення кірки, відношення, помірний вміст, усадка, вміст вапна, залежати від, склад флюсу, крихкість, захисні властивості, тигель, вологість, кремнезем, оксид заліза, свинець, споживання, вхідний отвір ливарної форми.

Task 2. Translate into English the following word combinations. Use the words given below. (N+N constructions)

ванна шлаку	ванна металу
металева ливарна форма (кокіль)	якість металу
активність шлаку	утворення кірки
здатність до окислення	здатність десульфуризації
усадочні порожнини	вміст вапна
відсотковий вміст водню	склад флюсу
графітовий тигель	рідкий шлак
температура води	вхідний отвір ливарної форми.

capacity crust slag metal iron temperature cavities lime mould metal quality mould slag composition inlet formation oxidation desulphurization pool shrinkage activity content percentage flux graphite ability pool crucible liquid water hydrogen

Task 3. Give Ukrainian equivalents to the following words and word combinations:

to run the process, liquid slag, to generate heat, casting mould, dry air, suitable, compressed air, fluid, casting into graphite or iron moulds, porosity, failure, chemical composition, value, to obtain the castings, to ensure, the highest possible and most stable properties, be subjected to, special pre-treatment, machining, rust, non-ferrous metals, high-strength cast iron, to generate, to maintain and control chemical composition, to preserve, melting temperature, favourable conditions, multipurpose application, oxidation capacity, to contain, ability, to lower, rate, cavities, to weaken, susceptibility, to cause porosity, percentage, less sensitive, high protective properties, prior to, prefuse, graphite electrode, due to, proper, iron oxides, sulphur, to achieve, to pour, bottom, top.

Task 4. Fill in the correct word from the list below and translate the word combinations. Some words may be used more than once.

a) melting, b) flux, c) equipment, d) electrodes, e) manufacturing, f) slag, g) casting, h) axial porosity, i) steel, j) castings, k) impurities, l) refining

1. refining of …, 2. possibility of …, 3. the cooling of …, 4. size of the …, 5. melting temperature of …, 6. the operation of …, 7. surface of …, 8. degree of …, 9. methods of …, 10. rate of …, 11. removal of …, 12. grade of …

Task 5. Match the following words Some words may be used more than once. Translate the word combinations into Ukrainian.

low moderate casting consumable main stable special protective favourable chemical appreciable melting technical proper

mould means conditions influence viscosity refining temperature pre-treatment electrode metal composition content requirements properties

Task 6. Try to explain the following notions:

multipurpose application, consumable electrode, shrinkage, porosity, component

Task 7. Answer the following questions:

1. What provision is to be made to run the ESC?

2. Name the methods of manufacturing consumable electrodes.

3. What castings can be produced by ESC?

4. Is the molten slag activity important for the refining, removal of impurities from the metal?

5. What slag has the most multipurpose application in electroslag process?

6. In what way does the content of alumina influence the quality of casting?

7. What does the hydrogen percentage of the metal depend on?

8. How can the refining of slag from moisture and silica be achieved?

9. How is the ESC process started?

10. What does the consumption of cooling water depend on?

Task 8. Translate the following sentences into Ukrainian, paying attention to the modal words.

1. To run the ESC process provision is to be made for consumable electrodes, flux or its components to prepare liquid slag; electric power to generate heat in slag pool; water to cool casting mould, etc

2. The surface of electrodes may be subjected to special pre-treatment like shot-blasting or machining in order to remove scale, rust, burning-on etc.

3. In each particular case of producing castings from a certain material, use should be made of proper chemically composed billets as consumable electrodes.

4. Practically all kinds and categories of material: steel, alloys, non-ferrous metals, nodular cast iron, high-strength cast iron etc can be produced by the ESC method.

5. The melting temperature of flux should be slightly lower than that of the metal itself. The molten flux should have a low viscosity.