GENERAL INFORMATION Electrodes application and requirements.

Carbon and graphite electrodes are widely used in electric smelting, metallurgical and electrotechnical factories.

The range of electrodes application

is extremely wide. Almost all thermal-electric processes require electrodes usage. Carbon and graphite electrodes are used in electrochemical industry, acting as insoluble anods.

Electrodes used in electrothermy and metallurgy are divided into three types according to design characteristics:

- changeable block-electrodes (rectangular or square);

- cylinder electrodes, continuously lengthened with nipples;

- continuous self-baking electrodes, made from anode mass.

High quality electrodes should correspond the indicated below specifications, have no cracks and holes.

Difference in specifications of carbon and graphite electrodes is shown below:

	Carbon	Graphite
1. Apparent density	1,5-1,7	1,6-1,8
2.True density	1,7-2,0	1,6-1,8
3.(Moos) hardness	4-5	1
4.Specific heat at 100 Ñ	0,18-0,22	0,21
5.Ash content, %	6	0,2
6.Thermal conductivity, êàë/ì ÷àñ	24	120-240
7.Air oxidation temperature	425 Ñ	650 Ñ
8.Specific electric resistance, ìµÎhm•m	42-80	8-20
9.Allowable current density g/cm3	5-10	15-25
10.Allowable tensile strength kg/sì2	70-100	60-75
11.Allowable bending strength in cold state kg/sm2	50-70	15-30

Comparative analysis of carbon and graphite electrodes

Change of electric resistance of graphite and carbon electrodes is shown on pic.1.

This picture shows that resistance of carbon electrodes is indicated as ascending line. Corresponding graphite data is shown as more complex function, reaching its minimum in the range 400-500° Ñ and has at first negative, then positive temperature coefficient.

Ash content is especially not advisable in some technological processes (in aluminum production, electric steel etc.), and is allowable within the limits in the other technological processes (for example, calcium carbide). Nevertheless, large ash content in electrodes is not advisable, as ash reduces mechanical strength, worsens compressing, increases electric resistance and electric loss, causes dirtying of smelted product, etc., and increases product porosity in the process of graphitization.

It is necessary to consider all the above-stated factors when selecting electrode type.

Graphite electrodes

High-quality graphite electrodes for AC and DC electric arc furnaces of different capacities are manufactured from petroleum coke, petroleum or pitch needle coke and coal tar pitch (binding and impregnating pitch). They are intended for arc steel melting, refining, ferroalloy, ore furnaces and other electrical thermal equipment, operating at current density up to 25 A/sm2.

Electrodes are manufactured of RP, HP and UHP grades ranging from 200(8) to 700(28) mm (inch) in diameter compliant with globally accepted quality standards. Special technology of nipples manufacturing for electrodes ensures good physical and mechanical characteristics and operational properties.

Supplied electrodes and nipples are manufactured according to TU 1911-109-052-2003 , 75-400 mm in diameter and up to 2400 mm in length

Electrode grades: UHP-1, UHP-2, HP, RP-1, RP-2

TU standardizes electrodes bending strength and specific electric resistance. These parameters determine electrodes grade.

Dimensions of graphite electrodes, mm Nipples

Each electrode is supplied with nipple. By customer’s request, nipples can be supplied separately or additionally. Nipples for electrodes up to 200 mm in diameter have cylinder thread, nipples for electrodes 250 mm in diameter and more have taper thread.