Introduction to Determination Methods of Slag Resistance and Thermal Shock Resistance of Refractories

The methods used to determine the slag resistance of refractories include static and dynamic methods. The static method includes the melting cone method, the crucible method and the dipping method; the dynamic method includes the rotating dipping method, the slag scattering method, the dripping slag method and the rotary slag etching method. my country's international standard GB8931-88 stipulates that the slag resistance is determined by the rotary slag corrosion method. Its expression method can be expressed in mm or % of slag erosion.

(1) Melting cone method: also known as the triangular cone method, the refractory material and the slag are separately ground into fine powder, mixed in different proportions to make a truncated triangular cone, the shape and size of which are the same as the standard temperature measuring cone, and then press The refractoriness test method is used to test, which is the simple method in the slag resistance test.

(2) Immersion method: Cut the refractory product into a round bar shape, soak it at a specified temperature for a certain period of time, take it out to observe the erosion, measure its volume change, and calculate the erosion percentage.

(3) Rotary slag corrosion method:
One is that when measuring the slag resistance by the forming masonry method, attention should be paid to the atmosphere in the furnace, and it should be carried out in an oxidizing atmosphere. After the test, the experimental bricks built on the lining are removed, and the thickness of the sample is measured after the slag bonded on the surface is clear to avoid errors. The other is to divide the tested refractory products into 6 or 9 pieces. Built in a rotary furnace, the furnace body can be tilted freely, and the speed is: -10r/min. Heat it to the experimental temperature with gas, add a certain amount of slag within a certain period of time, observe the slag corrosion, continue for a period of time, and then blow it out. After cooling, disassemble the test blocks that are built together, cut along the length of the test block perpendicular to the slag corrosion surface, measure the thickness change of the test block before and after the experiment, and calculate the amount of slag corrosion. This is a relatively good dynamic determination of fire resistance. Test method for slag resistance of materials.

Of course each method has its own advantages and disadvantages.

Advantages of the melting cone method: it is simple and easy to operate. Disadvantage: It can only reflect the influence of chemical mineral composition on slag resistance, and other influencing factors cannot be shown. Compared with the dipping method, it is a better experimental method for dynamically determining the slag resistance of refractory materials. The advantages are: intuitive, strong contrast and good repeatability. However, there are also shortcomings: the atmosphere in the furnace is difficult to control, and the thickness measurement of the test block after the experiment is not easy to master.

How to test the thermal shock resistance of refractory materials? Thermal peeling resistance test example

When the refractory is used in an environment with temperature fluctuations, especially under the conditions of rapid cooling and rapid heating, stress is generated due to the temperature difference between the surface and the interior of the refractory material, which deteriorates or destroys the structure of the refractory material, thereby causing spalling damage. It can be seen that compared with the loss of refractory materials caused by slag erosion, the spalling damage caused by the deterioration or destruction of the structure is non-progressive, that is, sudden. Therefore, the thermal spalling damage resistance of refractories, that is, the thermal shock resistance of refractories, not only directly affects refractories

The evaluation of the thermal shock resistance of a refractory generally consists of two experimental parts. The first is to heat and cool the refractory sample, that is, to conduct a thermal shock test, to deteriorate or destroy the internal structure of the refractory. This is followed by the measurement and evaluation of the refractory samples after the thermal shock test. For a refractory sample, different methods can be used for heating and cooling, and different methods can be used to evaluate its thermal shock resistance. Due to the limited space, this paper only analyzes the thermal shock resistance performance of the electric furnace heating experimental method.

The refractory samples are made by pressing high-purity magnesia and chrome ore as the main raw materials. The formed refractory bricks (230mm*114mm*65mm) were fired at 1800°C for thermal shock test. The experiment is mainly to investigate the effect of special additives on the thermal shock resistance of magnesia-chromia refractories.
The experimental temperature was 1200 °C, and air cooling was adopted. The experiment was repeated until the heating surface of the refractory sample peeled off, and the number of heating and cooling when the refractory sample peeled off was used as an index to evaluate the thermal shock resistance of the refractory material. The experimental results are shown in Figure 12-1-4. When the addition amount of the special additive is 3%, the thermal shock resistance of the refractory material is good, which is about 1 times higher than that of the standard refractory sample (the addition amount of the special additive is 0).

Test method for thermal shock resistance of refractory materials

The ability of a refractory to resist abrupt changes in temperature without bursting or peeling off pieces is called thermal shock resistance. Refractory materials used in high temperature equipment are almost all subject to different degrees of thermal shock. The temperature change in the kiln will inevitably lead to a temperature difference between different parts of the product, resulting in a difference in deformation between different parts of the refractory material. If the temperature difference between adjacent parts of the product is excessive, that is, the deformation difference is too large, considerable internal stress must be generated in the material. When the internal stress value exceeds the structural strength of the material itself, the material will crack. During the use of cement kilns, there are often changes in process conditions and sudden equipment failures, sudden kiln shutdown for cooling and re-opening of the kiln for heating. When the rotary kiln rotates, the shear stress of the ovality has a periodic effect on the lining brick, the change of the flame combustion state, the shedding of the kiln skin, the detachment and coverage of the clinker, and the lining brick is subjected to thermal stress, mechanical stress and their increase. The co-action will eventually lead to cracks in the lining bricks, so as to peel off. In this case, whether the refractory material can maintain a long service life should be confirmed through the inspection and assessment of its thermal shock resistance.

In the test method of thermal shock resistance, the conditions that cause temperature difference (such as heating method, high temperature of heating, cooling method) and measurement methods (such as the weight loss of damage, the product of damage loss, the mechanical strength The standards of national regulations and history are inconsistent, and the inspection conditions stipulated in the national standards may not all meet the real conditions of use of refractory products in high-temperature equipment, but in order to obtain the results of this inspection in a short time , the rapid change of heat and cold is often used to accelerate the rupture of the product, and the test results obtained from this can still be considered to have a relatively meaningful evaluation value.

Current standards for thermal shock resistance of refractories:

"GBT 30873-2014 Refractories
"Thermal shock resistance test method": This standard specifies the terms and definitions, principles, equipment, samples, test procedures, result presentation and processing and test report of the test method for thermal shock resistance of refractory materials. This standard applies to the determination of thermal shock resistance of refractory materials.

"YBT 376.3-2004 Refractory products-Test method for thermal shock resistance
Part 3: Water quenching-crack determination method": This part of YB/T376 specifies the principle, equipment, samples, test procedures, result calculation, etc. of the test method for thermal shock resistance of refractory products (water cooling-crack determination method). . This part applies to the determination of thermal shock resistance of refractory materials such as long nozzles, submerged nozzles, stoppers and sizing nozzles.