Mechanical Strength Grade of Lump Coal According to Coal Quality Index
Introduction
Lump coal, also known as caking coal, is a type of coal produced by combustion of coal and is a solid combustible substance. It is mainly used for fuel production and is mainly used for domestic, commercial and industrial heating fuel. In terms of the mechanical strength level of lump coal, according to the recent criteria proposed by experts from the China National Coal Quality Supervision and Inspection Center, the American ASTM standard, the German DIN standard, the French NF standard and the British BS standard, the mechanical strength grade of lump coal can be divided into three categories: strong, medium and weak. The classification criteria of each classification are very different, and the related calculation methods and calculation relationships are different. Specifically, the main calculation methods used for the mechanical strength level of lump coal are the Yield Strength Factor, the Hardness Test, and the Impact Strength Test.
The Yield Strength Factor Test
This test is mainly carried out on the sample of coal particles obtained from a coal mine after sample preparation. It is mainly used to calculate the mechanical strength grade of large lump coal, which is generally in the form of small cube or cube blocks. The calculation method of this test is mainly through establishing the relationship between coal particle stress and displacement. According to the principle of force balance, it can calculate the force required for deformation and fracture, that is, the material yield strength. Generally, when the average yield strength value of all tested coal blocks is greater than 150 MPa, it can be determined that the mechanical strength of the lump coal is strong; when the average yield strength value of all tested coal blocks is between 120 and 150 MPa, it can be determined that the mechanical strength of the lump coal is medium; when the average yield strength value of all tested coal blocks is less than 120 MPa, it can be determined that the mechanical strength of the lump coal is weak.
Hardness Test
This test is mainly used to evaluate the brittleness of lump coal, determine the degree of coal strength, and estimate its resistance to crushing, grinding and abrasion. The hardness test of lump coal usually uses the Mohs hardness test as the basis. The hardness of lump coal is mainly divided into three levels according to the International Hardness Index (SGS), that is, soft, medium hard and hard. Generally, when the Mohs Hardness Index of lump coal is 7 or higher, it can be determined that the mechanical strength of the lump coal is strong; when the Mohs Hardness Index of lump coal is 5 or 6, it can be determined that the mechanical strength of the lump coal is medium; when the Mohs Hardness Index of lump coal is 4 or lower, it can be determined that the mechanical strength of the lump coal is weak.
Impact Strength Test
This test is mainly used to determine the impact mechanical strength level of the sample coal obtained from the coal mine, mainly using the coal sample in the form of crushed particles. Its main calculation method is to measure the impact toughness of the tested sample coal by using a rebound hammer to throw the test sample at the surface of the coal. Then, according to the rebound value and calculation formula, calculate the mechanical strength grade of the sample coal. Generally, when the rebound value of the test sample is greater than 50mm, it can be determined that the mechanical strength of the lump coal is strong; when the rebound value of the test sample is between 40 and 50mm, it can be determined that the mechanical strength of the lump coal is medium; when the rebound value of the test sample is less than 40mm, it can be determined that the mechanical strength of the lump coal is weak.
Conclusion
Through the explanation and analysis of the three main testing methods for determining the mechanical strength grade of lump coal according to the coal quality index, we can see that different calculation methods are adopted to obtain different mechanical strength grades. Therefore, the tests used to determine the mechanical strength grade of lump coal should be comprehensive and comprehensive, and comprehensive tests should be carried out on the tested sample to obtain an accurate mechanical strength grade of lump coal.
