High-Temperature Flexural-Strength Tester for Refractory Materials

A high-temperature flexural-strength tester, also called a high-temperature bending-strength tester, applies a bending load to a bar-shaped refractory specimen in a heated furnace and measures its modulus of rupture at temperature. The result is used to assess structural stability under high-temperature service conditions.

The instrument uses three-point bending. A rectangular specimen, commonly 150 mm × 25 mm × 25 mm, rests horizontally on two parallel rollers as a simply supported beam. A third roller applies a vertical load at the midpoint at a controlled rate. The lower surface is subjected to tensile stress and the upper surface to compressive stress. When the tensile stress exceeds the material's tensile strength, cracking begins at the lower surface and the specimen fractures.

A force sensor records load and the system monitors displacement or deformation. The maximum load at fracture, span, and cross-sectional dimensions are used with the applicable mechanics equation to calculate flexural strength at the test temperature.

The furnace commonly uses silicon-molybdenum or silicon-carbide heating elements and high-purity alumina or corundum–mullite refractory lining. Stated furnace ranges extend from room temperature to 1,400 °C or, for some configurations, 1,700 °C. The loading system may use a servo motor or hydraulic drive. Loading noses and supports are made from heat-resistant, high-strength alumina ceramic or silicon carbide. A multi-segment temperature controller and acquisition software record load–time or load–displacement curves, calculate flexural strength, and generate reports.

Applications include comparing aggregates, binders, and additives during refractory formulation; checking refractory bricks and precast castables during production; and supplying strength data for furnace lining design and maintenance. Heating rate, hold time, and loading rate must follow the applicable test standard so that thermal gradients and excessive loading speed do not bias the result.