TESTING OF BURDEN MATERIAL


Some laboratory tests have been devised to investigate, identify and quantify on a relative basis, an increasing number of burden properties to assess the extent of suitability of burden materials. These tests are empirical in nature and hence the results of two different investigation do not readily agree unless extensive standardisation is sought.

● The properties of burden material of interest are those properties which have bearing on its performance during handlings, until it is charge I'm the furnace, and subsequently on its behaviour inside the furnace. These properties are :

1. Room temperature physical properties
2. Reducibility
3. Physical behaviour during reduction at high temperature.

Room Temperature Physical Properties


It includes the physical properties such as the cold strength, resistance to impact and abrasion and porosity of the burden materials. The shatter and tumbler tests have mainly been devised for this purpose beside direct compression strength measurements.

Shatter Tests :

It essentially consists of dropping a certain amount of material from a standard height for certain number of drops. The amount of the material, retained on or passed through certain sieves expressed as percentage of the original weight which indicated as the shatter index.

Tumbling and Abrasion Test :

The tumbling test essentially consists of tumbling a standard weight of material of certain size in a standard drum. Tumbling carried out at a standard speed for a fixed number of revolutions. The % material passing through or retained on a certain seive is the index.

● This tests have shown that the pellets are a high quality product and sinter a poor quality with natural ore, in general falling intermediate between the two in respected of physics strength.

Compression Test :

The direct mesurment of compression strength of iron bearing material is difficult because of the uncertain geometry of the specimens. The compression strength of pellets, being more regular in shape, can be measured with better accuracy than those of ores and sinters. A large number of tests should be carried out and the maximum minimum and mean strength along with the standard deviation should be indicated.

Porosity :

It is the most difficult property to measure and expressed as the volume of the material tested. Two types of porosities, open and closed are recognized. Open porosity is accessible to fluids where the closed porosity is not. It is usually measured by simple method based on archimeds principle.

Reducibility


● The reducibility test essentially aims at measuring the rate of reduction of iron bearing material under blast furnace condition. Since the condition in a blast furnace vary from top to the bottom of the stack, a standardized condition.

● The use of reduction temperature in the range of 900 to 1000℃ and a reducing gas of CO or CO + N2 of constant composition is increasingly being used. Several tests have been devised that are.

1. Gakushin test
2. Verein Deutscher Eisenhuttenleute method
3. Centre National de recherches Metallurgists method
4. Non isothermal test.
5. Chiba test.








References :

1. Heat treatment principle and techniques  by : T.V. Rajan,  C.P. Sharma,  Ashok Sharma.
2. Physical Metallurgy Principle and Practice by : Raghavan V.,
3. Lectures of IITs & BPUT (ODISHA).

4. Iron making by : Dr. R. H Tupkary & V. R Tupkary

Author :
Subir Kumar Sahu.
Metallurgist.

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