Journal – Bulletin of Engineering
Author - Erika Monica, Imre Kiss
Abstract
The
development of continuous casting to produce semi-finished products is now so far advanced that almost any grade of steel can be
continuously cast, and in the most
appropriate cross section for further
shaping. High quality finished products can only be produced by using defect free slabs, blooms or billet.
The removal of defects is either performed selectively by removing the specific
defect. This paper, based on industrial research, refers to the possibility of
defining and cataloging the surface defects specific to the semi-finished
products continuously cast, in order to discover the generating source and to
take the proper measures to prevent and remedy them where appropriate. The
industrial experiments were
carried out over several
months in a steel company, period
when we searched the number and type of defects detected at
the reception of the studied metallic material. In conclusion, temperature
control and adjustment is required in the mould. The main method to reduce the
overheating consists of the introduction of consumable coolers.
Introduction
The continuous casting process,
both in the technological aspect as
well as on the plant parameters, was and
remained a basic concern of all the specialists in the major steel-making
companies. Concerns in the development of continuous casting technology, either
theoretically or through industrial experiments, refers to the possibility of
defining and cataloguing the surface defects specific to the continuously cast
semi-finished products, in order to discover the generating source and to take
the proper measures to prevent and remedy them where appropriate.
Experimental Study
The industrial experiments were
carried out over several months in a steel company, period when we searched the
steel quality level in continuously cast semi-finished products, determined by
the number and type of defects detected at the reception of the metallic
material we had studied. The steel is cast from the ladle into a tundish, which
ensures a controlled flow in moulds, of appropriate form, water cooled. To
prevent the sticking of the solidified crust, the mould oscillates in the
casting direction with a higher speed than the casting speed, and into the
mould is added a powdery lubricant. The mould is the essential technological
component of the caster, which determines
the shape of
the profile cross section, realizing the liquid-solid phase transformation, by a sudden and directed
cooling, at the vertical casting into a water cooled double walled metallic
cavity.
Result
The share of the bloom, continuously cast in the company,
represents approx 45-60%, the balance being billets for another company. The
material defects at the steel continuous casting appear during the
solidification and cooling
of the continuously
cast semi-finished products, often leading to important material losses.
To prevent these losses, the purpose of metallurgical technologies and constructive
solutions is to detect the causes of occurrence, prevention and removal.
According to
the literature, we can define
the “defect” as any deviation from the appearance, form, size, macro structure and chemical properties provided in standards
or other legal technical documents in force.
The defects are
found at the
reception of billets, through
visual inspection of their surface (on the inspection beds), or by checking the macro structure of the test samples. A
defect is not always the consequence
of a unique
cause. Many times, the defect is
the result of the interaction of many causes that depend on a variable number
of parameters.
Conclusion
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