CPT International 4/2019

MELTING SHOP
Figure 8: General view of the furnaces of the 6-t tandem.
rately. The boxes under the green bar
contain the charge number, the material
number and an ID number for the
operator. The vertical, orange bar is an
indicator of the current power.
By unmistakably relating the charge
and the corresponding melt via the
charge make-up number and the melt
number, Prodapt Enterprise complies
with the requirement of making the
melting process traceable. Additionally,
all treatment activities performed on the
furnace are logged. The log protocol stores
the general data of the melt and all
treatment-related activities minute-wise.
The treatment-related activities include
the heating process and activities such as
the taring of the scale, temperature
measurement and the tappings. For each
activity, related data such as time, duration,
furnace content and melt temperature,
are stored. The parameters of the
selected steel grade and the measured
analysis values are archived in the process
database.
In addition to the process data, Prodapt
Enterprise visualizes the current status
of the cooling, hydraulics and energy
supply systems. In case any limits are
exceeded or abnormal incidents occur,
this is indicated by changing the colour
of the respective value boxes or the corresponding
icons. Let’s describe the furnace
cooling system as an example of
these detailed process views (Figure 9).
The acquired data is displayed in a
schematic illustration of the plant. The
measured value boxes indicate not only
the current value but also any exceeding
of limits by a color change. By clicking
on a box, the evolution of the
value over the past eight hours can be
viewed. The icons are animated, i.e. different
colours indicate different statuses.
Additionally, the system captures
the water temperatures and quantities
for each individual cooling circuit. Any
deviations from trends generate warnings
that are automatically transmitted
to the maintenance staff.
Swift and targeted reaction to incidents
is essential for a high availability
level of the meltshop. Any incident is
firstly indicated in clear text in the head
line of the process diagrams. The messages
are displayed in different colours
depending on how they are classified.
This information is complemented by
the “switch off” sub-view, which lists all
incidents that may lead to the switchoff
of the plant or the respective furnace.
The explicit notes in the sub-view
make it easy for the operator to assess
the severity of an incident. Additionally,
the responsible operator will be notified
about the incident by text message.
This has proved very useful especially
during the times outside the shifts, e.g.
during the nights, when the cold furnaces
are being restarted automatically.
Monitoring of the crucible wear
In order for the meltshop to operate
smoothly, monitoring of the crucible is
of paramount importance. After tapping,
when the wall surface is still dark
red, the crucible is visually inspected. In
addition to the visual inspection,
> the resistance between a contact
established to the moltenmetal and
a coil is checked (earth-fault indicator),
> the active power and frequency are
measured and the results evaluated
by means of Prodapt Enterprise.
While the method based on earth-fault
indication is extensively described in the
literature [3], we here describe in greater
detail the second method, which is
based on the use of Prodapt data. Information
about the crucible wear is derived
from the change in coil inductance
as a result of a change in the distance
from the molten metal. Both the active
power and the frequency increase when
the wall thickness decreases. During
every melting of a charge, the frequency
is measured. The measurements
take place under uniform conditions,
i.e. with the furnace completely filled
and at a defined temperature. Based on
the result of the measurement, a wear
index is calculated from the given
power in each individual case and from
the ratio between the actual voltage
and the nominal voltage.
The measured frequency values and
the wear index are plotted as curves
over time for the duration of a lining
life. Figure 10 shows, as an example, the
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