Morita, A. and Kano, T.
Development Report:
Melting Automation Using a Medium-FrequencyInduction Furnace
Arimichi Morita and Toshiyuki KanoFuji Electric Thermo Systems
Co., Ltd.
5520 Minami Tamagaki, Suzuka, Mie 513-8633, JapanE-mail:
[email protected]
[Received March 28, 2008; accepted May 30, 2008]
Automating the melting process is critical to theeconomical
production of metal castings with stablequality. We discuss
manufacturing process monitor-ing, safety devices, automatic
melting operation, andlabor-saving furnace refractory construction
and dis-mantling.
Keywords: induction furnace, monitoring, automation,relining of
refractory materials
1. ForewordConventional metal melting involved largely
manual
execution of required processes that made operating
pro-ductivity dependent on the skills of individual craftsper-sons
compelled to work under adverse conditions charac-terized by high
temperature and dirty air.
Automating metal melting operations is indispensableto a market
supply of economic products with stable qual-ity. Improving the
working environment and introducinglabor-saving features are also
expected to help solve laborshortages plaguing the industry.
We review topics related to energy-saving and labor-saving
automation involving medium-frequency induc-tion furnaces.
2. Characteristics of Medium-Frequency In-duction Furnaces
Medium-frequency induction furnace operations are akey casting
industry process used for melting metals,maintaining molten metals
at prescribed temperatures,and warming and adjustment of components
(Fig. 1).
Induction furnaces feature the following;1 High thermal
efficiency in which substances being
processed generates heat through electromagnetic in-duction
leading to energy saving.
2 Improved working environments because the heat
source is electricity, which reduces heat, noise, dust,and
carbon dioxide emission.
3 Thanks to quick heating, mental surface oxidation is
reduced and the introduction of foreign matter lim-ited,
improving product quality and productivity.
4 Electrical heating control facilitates temperature
control, stabilizing product quality and saving en-ergy.
Fig. 1. Medium frequency induction furnace.
These features have caused induction furnaces to beused for
melting and melting cast iron and steel productsand products
involving nonferrous metals such as copperand aluminum.
3. Monitoring and Automation of Melting Pro-cesses
3.1. Induction Furnace Operation Monitoring Sys-tems
Simplified induction furnace operation monitoring
withtouch-panel features introduced for localized furnace con-trol
(Fig. 2). Are widely in localized control, but arealso capable of
tasks such as simplified control of induc-tion furnace operations
for melting or streamlining main-tenance.
Melting process control involves operation programscovering
multiple processes such as warming up of thefurnace and then the
working piece, and dissolution ofmolten metal residue and sintering
programming.
Using these systems has the advantages of:1 Reducing wasted
energy through improved opera-
tions guidance.2 Improving operation safety and product quality
by
preventing overheating.3 Improving overall work efficiency and
melting oper-
ations.4 Simplifying safety procedures.
276 Int. J. of Automation Technology Vol.2 No.4, 2008
Melting Automation Using a Medium-Frequency Induction
Furnace
Fig. 2. Monitoring system.
5 Reduction of the running cost which is due to de-
mand control.
Induction furnace operation monitoring with
improvedfunctionality enables control capabilities such as
opera-tion and/or maintenance logging to be added to the
sim-plified induction furnace operation monitoring. This inturn
enables trends in operation data to be displayed onoperations
panels.
Ongoing automated monitoring may be applied to elec-trical
furnace features, cooling water temperature, flowrate, and
electricity fluctuations due to molten metal leak-age. Warnings are
issued as abnormalities arise andguidance for required remedial
measures is displayed.Records on melting operations are
automatically andcomprehensively logged and information preserved
foruse in managing whole-plant production, streamlining,and
maintenance measures.
Moreover in such systems are structured for charg-ing the
furnace with raw materials and analyzing chemi-cal components of
molten metal indispensably associatedwith main operation
establishing links for improving co-ordination among them. Linking
different systems andinformation such as material mix, automatic
sub materialcalculation, automatic transfer status, and the storage
ofdata needed for simplifying production and security op-erations
enables optimizing furnace operation includingmolten metal
temperature control, melting and/or melt-ing operation automation,
and coordination with castingprocesses leading to total scheduling
of all production op-erations.
3.2. Temperature Control in the Melting ProcessAutomation
Melting processes involve the handling of high-temperature
molten metals, making precise temperaturemeasurement the most
effective factor in ensuring high-quality cast products, conserving
energy, preserving re-fractory material life, and improving
operation safety.
Immersed thermocouples are most widely used for tem-perature
measurement. Continuous temperature monitor-ing is particularly
needed in high-frequency induction fur-naces that raise temperature
quickly. This requires the fol-lowing:
1 Continuous temperature measurement via radiation
thermometer.2 Initial temperature measurement by immersed
ther-
mocouple when charged materials are completelymolten, followed
by predictive calculation for esti-mated temperatures.
3 Continuous temperature measurement using a sheath
thermocouple and control by predicted actual tem-perature.
Temperature accuracy measured by a radiation ther-mometer
deteriorates with increasing fumes and slag cov-ering molten
metals. The life of the sheath of thermocou-ples is less than 100
charges. Technical problems exist fordifferent methods, and
technological developments solv-ing these problems are eagerly
awaited.
Simpler methods more widely used include tempera-ture prediction
through measurement of electricity con-sumed, starting with the
preparation of estimates of ref-erence total power required by
multiplying the weight ofprocessed raw material by reference
melting power unitrequirements (ton/kWh). When reference total
power hasbeen consumed after furnace operation starts, operationis
switched to temperature retention mode to prevent ex-cessively high
temperatures from arising (Fig. 3). This isused in monitoring
introduced earlier and is currently themost widely used automatic
melting.
4. Automation and Adoption of Labor-SavingTechniques in the
Erection and Dismantlingof Refractory Linings
4.1. Automation of Refractory Lining DismantlingQuick lining
removal System (QLR) (Fig. 4) is being
introduced in which the furnace is tilted 90 and pusherrams
preset on the bottom of the furnace shell is presetwith hydraulic
cylinders. Conventionally, all refractorymaterials in a furnace
were removed by breaking up anddismantling them inside the furnace
manually using jackhammers, etc. QLR enables the refractory lining
to becompletely removed in one piece a process most effec-tive in
larger furnaces whose capacity exceeds 1 ton. QLRachieved the
following:
1 Frees personnel from heavy labor under hazardous
working conditions such as filthy air.
Int. J. of Automation Technology Vol.2 No.4, 2008 277