High temperature structural strength refers to the resistance of refractory products to withstand pressure at high temperatures without deformation. It is often evaluated by the softening temperature of the load. The so-called load softening temperature refers to the temperature at which the refractory material is heated at a certain heating rate under 0.2 pressure, and the temperature at which the sample begins to deform and the temperature at which the compression deformation reaches 4% or 40%. The temperature of the former is called the starting humidity of load softening, and the latter is called the softening point of load softening 4% or 40%.
Refractory materials have high compressive strength at room temperature. Ordinary clay bricks can withstand a pressure of 12.5Mpa, and other refractory bricks have higher compressive strength. However, it is not possible at high temperatures. This is because the refractory brick internal fusible components melt prematurely to generate a liquid phase, which greatly reduces its compressive strength at high temperatures.
Refractory materials in the kiln masonry in addition to withstand high temperature, but also bear the load, so the high temperature structural strength of refractory materials is the main index to judge the quality of refractory materials. For example, the refractoriness of corundum brick is 2000 ℃, and the furnace tube of molybdenum wire furnace has to withstand a high temperature of 1700~1800 ℃, so corundum material should be selected. Because the molybdenum wire electric heating body of sintered cermet is usually wound outside the corundum furnace tube, it is required that the refractory material of furnace lining does not soften and deform at high temperature, otherwise the electric heating body will be damaged or even broken.