Melting Furnace

What Is a Melting Furnace?

A melting furnace is a furnace that heats and melts a workpiece using heat supplied by some type of high-temperature heat source. Based on the type of heat source, Tanabe offers melting furnaces such as electric resistance, plasma, and burner types. While plasma-type and burner-type furnaces are limited in their applications and processing capacities, Tanabe has a proven track record of providing resistance-heated furnaces for a wide range of applications and processing capacities (please contact us individually for details on the applications and processing capacities Tanabe can accommodate).

Features of the Melting Furnace

The characteristics of melting furnaces vary depending on the type of heat source; here, we will explain the characteristics of electric resistance melting furnaces.

• This method involves passing an electric current directly through the raw materials or molten slag—rather than through electrodes embedded in them—to generate Joule heat, thereby heating and melting the materials; this results in high thermal efficiency.
• Because the electrodes are submerged in the raw materials or molten slag during operation, no open arc is generated, resulting in quieter operation compared to (open) arc furnaces.
• The raw materials charged into the furnace form a covering layer on the surface of the molten slag, which reduces wear on the furnace cover refractories caused by radiant heat from the molten slag’s bright flame and also reduces the energy lost through flue gas.
• Since the slag and metal separate into upper and lower layers inside the furnace due to their difference in specific gravity, recovery is made easier.
• Since there are no energy-related exhaust emissions, exhaust treatment equipment can be made more compact.
• Thanks to the technology and track record we have cultivated over many years, we are able to build highly reliable systems. We are also able to provide equipment that efficiently supplies electricity to melting furnaces.

Principles, Structure, and Operation of Melting Furnaces

Principles and Methods of Melting Furnaces

Melting furnaces are classified into [resistance-heated], [plasma-heated], and [burner-heated] types based on the type of heat source used.

Electrical Resistance Type

As a manufacturer of electric resistance melting furnaces, Tanabe has been supplying furnaces classified as Submerged Arc Furnaces (SAF) and Direct Resistance Furnaces for a wide range of applications for many years. It is called an SAF because it operates with electrodes submerged in the raw materials or molten slag. Furthermore, since electricity is passed directly through the raw materials or molten slag inserted into the furnace, and the materials are heated by the Joule heat generated therein, it is a melting furnace in which the material being heated serves as the heat source.

Plasma-type

As a plasma-type melting furnace, Tanabe offers furnaces classified as direct-current arc plasma furnaces for the melting of municipal waste incineration ash. A high-temperature plasma jet (20,000–30,000°C at its center) is emitted from a plasma torch inserted into the furnace toward the feedstock, heating and melting it. Since the furnace operates at a pressure close to atmospheric pressure, it is a melting furnace that uses atmospheric pressure discharge plasma (thermal plasma)—a state in which ions and electrons are combined—as its heat source.

Burner-type

As a burner-type melting furnace, Tanabe offers furnaces that utilize a burner-type surface reflection melting method for the melting of municipal waste incineration ash. This method heats and melts the feedstock starting from its surface using the combustion heat from the burners and the radiant heat from the furnace walls; it is a melting furnace that uses burners (which can be fueled by either liquid or gaseous fuel) as the heat source. We enhance the surface melting efficiency of the raw material by using special burners with a trumpet-shaped flame and by arranging an appropriate number of burners according to the processing capacity.

Structure and Operation of a Melting Furnace

The structure and operation of a melting furnace vary depending on the type of heat source; however, this section explains the structure and operation of an electric resistance melting furnace. Electricity is transformed by the furnace transformer into a high-current, low-voltage current, which is then supplied to the melting furnace via the power supply system and electrode system. The electrode system is equipped with a mechanism to raise and lower the electrodes, allowing for control of the electrical power (current) applied to the melting furnace. Raw materials are loaded into the furnace chamber, which is lined with refractory material, and melted inside the chamber. Additionally, a refractory-lined furnace lid is placed over the top of the furnace chamber. Various processing operations can be performed inside the melting furnace.

Reduction Reaction Treatment

By melting raw materials containing oxides and reducing agents and maintaining a temperature above the reduction reaction temperature, a reduction reaction can be initiated (Examples of applications: melting furnaces for calcium carbide production, melting furnaces for ferroalloy production, and melting furnaces for the reduction and recycling of valuable metals).

Volume Reduction Treatment

Melting the raw materials makes it possible to reduce their volume (e.g., melting furnaces for municipal waste incineration ash).

Decontamination

This process can neutralize hazards by immobilizing some of the heavy metals in the raw materials within the slag, thereby reducing the leaching of harmful substances from the slag to levels below regulatory limits (e.g., melting furnaces used for melting municipal waste incineration ash).

Melting Process

Raw materials can be discharged in a molten state to downstream equipment (e.g., melting furnaces in general, particularly those used in rock wool production).

Density Separation Process

It is possible to melt raw materials, separate the slag and metal by specific gravity within the furnace, and discharge them separately (Applications: All types of melting furnaces, particularly copper smelting furnaces and melting furnaces for the reduction and recycling of valuable metals).

The processed metal and slag are discharged through tap holes in the furnace sidewall via a tap opening and closing mechanism, and are then cooled and solidified separately. The exhaust gases generated in the melting furnace are treated by the exhaust gas treatment system, rendered harmless, and released into the atmosphere.

Melting Furnace Product Lineup

Melting Furnace for Calcium Carbide Production

Calcium carbide (CaC₂) is produced by heating a mixture of quicklime and coke to approximately 2,000°C in a melting furnace, and is used in the industrial production of acetylene, among other applications. It is also used as a deoxidizer and desulfurizer in steelmaking and smelting. View Product Details

Melting Furnace for Ferroalloy Production

Ferroalloys are a general term for various alloys of iron and other elements used in the steelmaking process for deoxidation or as additives in special steels (including non-ferrous steels). We supply melting furnaces for the production of various ferroalloys, such as ferromanganese and ferrochrome. These furnaces are broadly classified into two types: sealed and semi-covered.View Product Details

Melting Furnace for the Recycling of Valuable Metals (Valuable Metal Recovery)

This is a smelting furnace for the carbon-reduction recycling of valuable metals, designed to process copper and precious metals contained in incineration residues from discarded circuit boards, as well as metal oxides and neutralization sludge found in byproducts of stainless steel manufacturing processes. Metal oxides are converted into metal through carbon reduction, and the molten metal can be easily separated from the slag via density separation. View Product Details

Melting Furnace for Municipal Waste Incineration Ash

These are melting furnaces designed to reduce the volume and render municipal incineration ash harmless. Depending on the heat source, we offer resistance-heated, plasma-heated, and burner-heated melting furnaces. The burner-heated type is suitable for small- to medium-sized incineration facilities that do not have waste-to-energy systems. View Product Details

Melting Furnace for Rock Wool Production

This furnace is used to manufacture insulation materials (rock wool) for various applications. It is broadly categorized into two types: the hot-charge method, which uses molten slag from blast furnaces as raw material, and the cold-charge method, which uses rock as raw material. The hot-charge method enables low energy consumption per unit of output. Using Tanabe’s proprietary slag metered discharge system, slag can be stably supplied to the downstream fiber production line, ensuring excellent product quality. View Product Details

Copper Smelting Furnace

This furnace recovers copper metal by using density separation to cause the minute particles of copper metal contained in the slag generated during copper smelting to settle to the bottom of the melting furnace, thereby separating them from the slag. Since the slag is fed into the melting furnace in a molten state, the electrical power supplied to the furnace is primarily consumed to maintain the slag in a molten state.View Product Details

Lineup of Auxiliary Equipment for Melting Furnaces

Tanabe is capable of providing engineering proposals that encompass not only the melting furnace itself but also ancillary equipment, and we will create the optimal design to meet your specific needs. We can also design and manufacture ancillary equipment on its own, so please feel free to contact us if you have any specific ancillary equipment in mind.

Power Supply Equipment

This equipment supplies power to the electrodes of a melting furnace. Drawing on our extensive track record and expertise, we provide optimized equipment that minimizes power loss. Designing power supply and electrode systems requires a thorough understanding of production volume and the electrical characteristics of the molten material (temperature and specific resistance). Tanabe designs its systems based on data accumulated through many years of extensive experience and provides the optimal equipment. View Product Details

Electrode Equipment

This equipment is used to raise and lower the electrodes in a melting furnace and control the power supply. When designing power supply and electrode systems, it is essential to have a thorough understanding of production volume and the electrical properties of the molten material (temperature and specific resistance). Tanabe designs its systems based on data accumulated through many years of extensive experience and provides optimal equipment.View Product Details

Electrode Replenishment Device

This is a device that automatically extends synthetic graphite electrodes (for 10- and 12-inch electrodes). By installing this electrode extension device, the manual process of extending electrodes can be automated.View Product Details

Furnace Tilting Device

This is a device used to tilt the furnace body of a melting furnace in order to tap the molten material inside the furnace. It is an auxiliary piece of equipment used in cases where tapping through the tap hole is not suitable.View Product Details

Furnace Body Weighing System

The weight of the melting furnace is measured to control the amount of raw materials loaded and the output of slag and metal. Please note that, as a general rule, this system cannot be installed simultaneously with the furnace tilting mechanism.View Product Details

Slag Quantitative Tapping System

This device controls the flow rate of molten slag. It is installed in the melting furnace when it is necessary to control the slag intake volume in the downstream equipment following slag discharge.View Product Details

Tap Inlet Opening/Closing Device (Drilling Machine, Mud Gun)

This is an automatic tap opening and closing device used during the tapping of metal and slag. A drilling machine is used to drill a hole in the tap opening on the furnace sidewall to allow tapping. To stop tapping, mud is packed into the tap opening on the furnace sidewall using a mud gun.View Product Details

Melt Cooling and Solidification Equipment

This equipment cools and solidifies metal and slag as they are discharged from the melting furnace. We offer various configurations, including straight endless-type, trolley-type, and circular-type systems. In the endless-type system, the cooled product is released and drops by inverting the mold at the head section. In the circular-type system, release is performed via a mold inversion device.View Product Details

Slag Conveyor

This is a casting device for slag discharged from a melting furnace.View Product Details

Duct Cleaning Equipment

This device is designed to remove exhaust gas dust adhering to the flue (duct) of a melting furnace. A metal tip inside the duct automatically rotates while moving back and forth to scrape away the adhering and accumulated dust.View Product Details

Furnace Lid Equipment

From large furnaces to small ones, we provide furnace lids optimized for the operation of various types of melting furnaces to meet our customers’ needs. While the inner surface of the furnace lid is lined with refractory material, we can also supply the furnace lid shell alone.View Product Details

Implementation Process

• Based on the customer’s request, we will review the specifications and prepare a quote (if the raw material is one that Tanabe has not handled before, we will conduct verification tests to proceed with the specification review).
• We will provide you with a proposal outlining the equipment specifications and costs.
• Once we receive an order from a customer, we will begin the design and manufacturing process.
• If there are any changes to your order, please repeat steps 1 through 3 above in accordance with the changes.
• After manufacturing is complete, the equipment will be delivered to the site, where installation and commissioning will be carried out, completing the equipment implementation process.

Validation Test

Verification tests allow us to confirm whether a target material can be melted, assess its melting characteristics (such as melting point and fluidity), evaluate the progress of any reduction reactions if present, and determine the specific resistance of the slag—a parameter required for the design of the actual melting furnace. Tanabe possesses a demonstration test unit intended to support the introduction of the actual melting furnace, but it is currently undergoing renovation.

Specifications Before the Redesign

Transformer capacity: 100 kVA; three-phase AC power supply
Internal dimensions: φ660 x H400 mm
Electrode diameter: 4 inches (synthetic graphite)
Melting temperature: 1200°C to 1500°C (Please consult us regarding specific materials.)

Test Procedure Flow

• Meeting: We will discuss the purpose of the test and your requirements during the meeting.
• Test Plan Development: Based on the results of our meeting, we will develop a test plan that meets the client's needs.
• Test Administration: We will conduct the test in the presence of the customer. The test will be conducted in batches (8 hours of operation per day).
• Summary of Results Evaluation Data: We will organize the data—such as temperature conditions and processing times—and evaluate how the results compared to the plan.
• Incorporation into the actual equipment specifications: We will incorporate the test results into the equipment specifications and submit a proposal for those specifications.

List of Validation Tests

After-Sales Service

We will enhance our post-delivery support services for melting furnaces to help our customers create optimal operating environments.

Main After-Sales Services

Scheduled Maintenance
We propose the best maintenance plan tailored to your plant's shutdown period.
・Cleaning and replacing seals
・Replacement of spare parts and consumables
Spare Parts Sales
We carry a full range of consumables and spare parts necessary for stable, continuous operations. We provide recommendations based on equipment diagnostics conducted during routine maintenance.
Support for Renovation Projects
We are currently carrying out renovation work to enhance production capacity and modify the furnace mechanisms in conjunction with a product line changeover, among other measures, in order to achieve further functional improvements.

Frequently Asked Questions

How do the ingredients dissolve?

As the raw material is heated by the heat source, its temperature gradually rises, and once it reaches the material’s melting point, it begins to melt gradually from the surface.

What kinds of raw materials can be dissolved?

In an electric resistance melting furnace, since the main heating medium is molten slag, the raw materials must contain components that form the basis of molten slag, or the furnace must constantly contain molten slag; otherwise, melting cannot occur. Furthermore, depending on its composition, molten slag may not be suitable for use in a melting furnace. Therefore, please contact Tanabe with information about the raw materials you wish to melt to inquire about feasibility (plasma-type and burner-type melting furnaces have limited applications and processing capacities).

What is the maximum size of the melting furnace? Also, what is its maximum temperature?

Our track record includes a melting furnace (for ferroalloy production) with a maximum size of 12.6 m in inner diameter and 5.6 m in depth. Additionally, the highest temperature achieved in our melting furnaces is approximately 2,000°C (for calcium carbide production).

Even though the raw materials are being melted at high temperatures, how does the melting furnace maintain its shape?

Refractory material is installed on the inside of the melting furnace’s chamber; since this material is selected for its ability to withstand high temperatures, it enables the furnace to function properly. In addition, the furnace shell (known as the “iron shell”) is water-cooled to ensure that the refractory material can be used for as long as possible.

How much does it cost to install a melting furnace?

Prices vary depending on the application and size of the melting furnace, as well as whether ancillary equipment is included. Additionally, given the ongoing rise in raw material costs, please contact us for a specific quote.

I'd like to know your delivery track record. Could you tell me about it?

We have a track record of supplying products to industries such as steel (alloy steel), non-ferrous metal smelting, metal recycling, and waste treatment. Please contact us for details regarding our track record; we will be happy to provide them on a case-by-case basis.

What are melting furnaces used for?

We offer reduction treatment, volume reduction treatment, detoxification treatment, melting treatment, and density separation treatment. For specific applications, Structure and Mechanism of the Melting Furnace Described AbovePlease refer to the following.

How do you remove the melted mixture?

The material melted in the furnace is extracted by drilling a hole through the tap opening in the side wall of the furnace using a drilling machine. By adjusting the height of the tap opening, it is possible to extract only the metal or only the slag.

The raw material contains moisture. Is it okay to feed it into the melting furnace as is?

If the raw materials contain moisture, the evaporated water will accelerate wear on the electrodes and refractory materials; therefore, it is preferable to feed raw materials that have been dried as much as possible into the melting furnace.

Do you carry (open) arc furnaces as products?

Tanabe does not handle (open) electrode arc furnaces (EAF).

What are the advantages of your company's melting furnace?

Thanks to the technology and track record we have cultivated over many years, we are able to build highly reliable systems and provide equipment that efficiently supplies electricity to melting furnaces.