You can witness the use of refractory materials in multiple fields like iron and steel, ceramics, petrochemical, electric power, etc. Refractory bricks are also a kind of refractory material.
These are necessary as basic materials to ensure the functioning of several industries. Refractory materials are inorganic, nonmetallic materials that have a high refractory degree. They include products made by specific processes for specific purposes and natural ores.
These materials come with various thermal insulating properties. The bulk density of refractory materials is an important physical property expressed using the units – kilograms per cubic meter or pounds per cubic foot.
Thermos Insulating Properties of Insulating Refractory Materials
The efficiency of insulating refractory materials is dependent on the thermal insulating properties of these materials. Some of the thermos physical properties of refractory materials are as follows:
1) Thermal Shock Resistance
A refractory material suffers from frequent temperature changes. These changes lead to thermal stresses in the refractory materials, which, in turn, cause the expansion and also contraction of the material. Two commonly used tests that measure thermal shock resistance include the prism spalling test and the test that checks loss of strength.
The prism spalling test is about cycling samples of refractory materials from 2200 degrees Fahrenheit for around 10 minutes, then put to water for around 2 minutes, followed by air for 7 to 8 minutes. This cycle continues till the specimens break, or there have been 40 cycles. The more the number of these cycles, the higher the thermal shock resistance of the refractory insulation materials will be.
In the test that checks the loss of strength, a sample of the insulating refractory material is brought from room temperature to 2200 degrees Fahrenheit five times. After that, the Modulus Of Rupture ( MOR) is done on cycled, and uncycled samples, and then the strength loss is calculated in percentage using the MOR values of the cycled and uncycled specimens. It is done 5 times with different samples of the refractory material, and also the corresponding loss of strength percentage is calculated. The thermal shock resistance is good if the strength loss is minimal.
2) Reversible Thermal Expansion
A refractory material usually expands when it is heat and suffers from contraction when cooled. Data sheets show a thermal expansion curve graph, which represents the expansion rates of the refractory material at different temperatures. The expansion rates are different for various refractory materials. Some refractory materials may also become larger than their usual size when they are cooled. The reheat tests will demonstrate the linear and also volume change.
3) Thermal Conductivity
Thermal conductivity measures the amount of heat flowing from the hotter side to the colder face of any refractory lining. This flow of heat depends on the wall thickness and the refractory material’s conductivity value. The thicker the wall, the less the heat flow will be. The thermal conductivity is also directly related to the drop in temperature from the hot side to the cold side, the time and the wall’s area.
There may be various ways to measure thermal conductivity; you must compare the results of the same tests to check for the thermal insulating properties such as rockwool insulation.
The thermal insulating properties play a key role with respect to the refractory materials. Moreover, we have discussed three such properties.