Swelling Index Furnace (FSI / Crucible Swelling Number)

The Swelling Index Furnace, also known as the Free Swelling Index (FSI) furnace or Crucible Swelling Number (CSN) furnace, is designed to measure the swelling behavior of coals and other carbon-based materials. The FSI test evaluates the coking properties of coal, determining its ability to form a coherent mass, or “coke,” when heated in the absence of air—a critical parameter for the steel and metallurgical industries.

The Free Swelling Index is assessed by comparing the coke button size and shape to a standard chart, providing a numerical value from 0 to 9 in 0.5 increments. This measurement is essential for selecting coking coal used in blast furnace operations and other high-temperature industrial processes.

Standard Features

  • Maximum temperature: 900°C, continuous operation up to 850°C

  • Top-opening furnace compliant with ASTM D720, BS ISO 501, & ISO 501

  • Fitted with RCD (Residual Current Device) for enhanced operator safety

  • High-power resistance heating element with excellent temperature stability

  • Quick temperature ramping and energy-efficient low thermal mass insulation

  • Temperature measured with ‘N’ type thermocouple

  • High-end microprocessor PID temperature controller for precise thermal control

  • Includes a set of silica crucible, lid, and wire crucible holder as standard

Standard Supply

  • Free Swelling Index Furnace (FSI)

  • Silica Crucible – 1 No.

  • Silica Crucible Lid – 1 No.

  • Crucible Holding Wire – 1 No.

  • Instruction Manual – 1 No.

Optional Features

  • Over-temperature controller

  • Ceramic cooling block for crucibles

  • Analytical balance

This FSI furnace delivers reliable, repeatable results for evaluating coal coking ability, making it a vital tool in coal analysis laboratories and metallurgical research.

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