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Induction Furnace Refractory

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lining material importance to induction furnace

The induction furnace is an industrial equipment that converts electrical energy into heat to melt metals by using electromagnetic induction. There are mainly two types of induction furnaces, core-type (channel) and coreless-type.

Refractory lining materials are essential to the productivity, casting quality, and safe operation of induction furnaces. It is vital to choose the right refractory products that exhibit high performance and can prolong the life cycle of the induction furnaces.

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Induction furnace lining materials for sale

Refractory materials for induction furnace linings are divided into three types according to their properties: acidic, neutral, and alkaline. According to the construction method, they are divided into dry ramming materials, wet ramming materials, castable materials, coating materials, etc. In most occasions, unshaped refractory materials are used, and sometimes some shaped refractory products are used. The material of the furnace lining is selected according to the type of molten metal, the nature of the slag, the furnace capacity, and operating conditions.

Acidic lining for induction furnace

Silica-alumina-based refractories are commonly used for the coreless induction furnace for steelmaking. Because silica and alumina are extremely resistant to both high temperatures and acidic slag, they are used to make acid lining. Refractories made of silica are utilized in the furnace’s top section, and those made of alumina are employed in its lower section.

Basic lining for induction furnace

Magnesite lining, which has alkaline qualities, is used for steel materials. It assists in preserving the stability of the furnace lining and is resistant to common slags.

Neutral lining for induction furnace

Ramming mass consists of Al2O3 is mostly used as the neutral lining for induction furnaces in melting steel. The lining has a very high melting temperature, high strength, high hardness, and relatively high resistance to slag attack. In real applications, pre-reacted spinel(MgAl2O4) or fine MgO are added to help the Al2O3-based neutral lining gain more chemical durability, thermal shock resistance, and mechanical strength.

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Lining materials for core-type induction furnace

The cored or channel induction furnace lining should be made of refractory castables that are resistant to corrosion, and erosion resistance and have high chemical stability. Usually, low-cement refractory castables are made from fused corundum aggregate, added with an appropriate amount of sintered alumina fine powder, and high alumina cement as the binding agent. To improve the thermal shock resistance of the lining and take into account that the furnace is mostly a reducing atmosphere, a portion of SIC can be added to the castables in proportion to obtain aluminum silicon carbide refractory castables containing SIC material. This refractory castable can have a long service life as a refractory lining for cored induction furnaces.

channel induction furnace lining materials

Lining materials for coreless-type induction furnace

A coreless induction furnace is also called a crucible induction furnace. Lining materials are selected based on the properties of slag, furnace capacity, and operating conditions. Coreless induction furnace generally uses ramming mass as the lining materials.

  • Furnace lining materials for cast steel and special steel

Dry ramming materials such as quartz, magnesium oxide, and magnesia spinel are generally used, and the service life is generally 50-150 heats. Alumina spinel ramming materials significantly reduced the micro-cracks cracks on the hot surface of the furnace lining. It is gradually replacing other materials and being promoted in steelmaking induction furnaces.

  • Furnace lining materials for melting and insulating cast iron

The lining refractories of cast iron induction furnaces are generally acidic quartz ramming materials. It has stable long-term service life but low thermal shock resistance. Fused quartz is more commonly used in cast iron induction furnaces abroad. Compared with natural quartz ramming materials, fused quartz ramming materials have the characteristics of a small thermal expansion coefficient and excellent thermal shock resistance. At the same time, they overcome the phenomenon that natural quartz has a thicker or even burned-out sintered layer during long-term use, and retains the sufficiently thick green layer. It avoids crack penetration and ensures the safe and stable operation of the furnace.

coreless induction furnace lining material

How to choose lining materials for induction furnace

Whether it is used for a coreless induction furnace or a cored induction furnace, the common characteristics of their working conditions are:

  • The thickness of the furnace lining is thin, and the temperature gradient of the furnace lining material is large.
  • The electromagnetic stirring ability of the molten metal in the furnace is strong, which will cause mechanical corrosion to the furnace lining refractory material.
  • The furnace lining refractory material is repeatedly subjected to rapid cooling and rapid heating.
castables for induction furnace
castables for induction furnace
top cap spout lining material
capping and spout materials
coil cement
coil cement
induction furnace ramming mass
ramming mass
mica based material for induction furnace slip plane
mica-based materials

Based on the above working conditions, it can be seen that the furnace lining refractory material is an important factor in determining the output of the induction furnace, the quality of the castings, and the safety and reliability of the operation. To obtain a good quality, long-life induction furnace lining, the furnace lining refractory material must have the following characteristics:

  1. It has a sufficiently high refractoriness and load-softening temperature compared to molten metal, has good chemical stability, and does not react chemically with metal slag and its components when melted.
  2. It has good thermal shock stability. This is particularly important for coreless induction furnaces, because the coreless furnace operation mode is a continuous cycle of a “heating-melting-discharging” process, and the furnace lining material is repeatedly subjected to thermal shock. If the thermal shock stability of the lining material is poor, cracks and crack propagation will easily occur, and molten metal will penetrate the coil in a short period, causing the entire furnace lining to be scrapped.
  3. It has high mechanical strength at high temperatures. To make the furnace have higher electrical efficiency, the furnace wall materials are generally designed to be very thin. However, during the operation of the furnace, due to the action of electromagnetic force, the molten metal in the furnace keeps churning. and agitation, causing continuous erosion and wear of the furnace lining. For cored induction furnaces, due to the use of jet-type melting trenches, the erosion and wear of the molten trench refractory materials are more serious. Therefore, the refractory materials must have high high-temperature mechanical strength.
  4. It has good thermal insulation and insulation properties.
  5. The material has good construction performance, high filling density, good sintering properties, is not easily wetted and penetrated by molten metal, is not prone to the formation of knots, and is easy to maintain.

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