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: morita-arimichi@fujielectric.co.jp

[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.

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