Furnace Charging I:

        
The first step in the production of any heat is to select the grade of
steel to be made. Usually a schedule is developed prior to each
production shift. Thus the melter will know in advance the schedule for
his shift. The scrap yard operator will prepare buckets of scrap
according to the needs of the melter. Preparation of the charge bucket
is an important operation, not only to ensure proper melt-in chemistry
but also to ensure good melting conditions. The scrap must be layered in
the bucket according to size and density to promote the rapid formation
of a liquid pool of steel in the hearth while providing protection for
the sidewalls and roof from electric arc radiation. Other considerations
include minimization of scrap cave-ins which can break electrodes and
ensuring that large heavy pieces of scrap.do not lie directly in front
of burner ports which would result in blow-back of the flame onto the
water cooled panels. The charge can include lime and carbon or these can
be injected into the furnace during the heat. Many operations add
some lime and carbon in the scrap bucket and supplement this with
injection.

        Furnace Charging II:

        The
first step in any tap-to-tap cycle is "charging" into the scrap. The
roof and electrodes are raised and are swung to the side of the furnace
to allow the scrap charging crane to move a full bucket of scrap into
place over the furnace. The bucket bottom is usually a clam shell design
. i.e. the bucket opens up by retracting two segments on the bottom of
the bucket. The scrap falls into the furnace and the scrap crane removes
the scrap bucket. The roof and electrodes swing back into place over
the furnace. The roof is lowered and then the electrodes are lowered to
strike an arc on the scrap. This commences the melting portion of the
cycle. The number of charge buckets of scrap required to produce a heat
of steel is dependent primarily on the volume of the furnace and the
scrap density. Most modern furnaces are designed to operate with a
minimum of back-charges. This is advantageous because charging is a
dead-time where the furnace does not have power on and therefore is not
melting. Minimizing these dead-times helps to maximize the productivity
of the furnace. In addition, energy is lost every time the furnace roof
is opened. This can amount to 1020 kWh/ton for each occurrence. Most
operations aim for 2 to 3 buckets of scrap per heat and will attempt to
blend their scrap to meet this requirement. Some operations achieve
a single bucket charge. Continuous charging operations eliminate the
charging cycle.

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