Crushing and shrinking, storageCrushing should be carried out with equipment that does not generate obvious heat and little air movement in the machine to avoid moisture loss during the crushing process. Unless the test proves that crushing does not produce substantial bias of moisture, the sample cannot be crushed before air drying.
Shrinkage should generally be carried out after air drying. If shrinking before air drying, a shrinking machine with small air flow should be used and operated quickly to minimize the degree of moisture change. If the coal sample is too wet and cannot pass the shrinking machine smoothly, then the sample is first air-dried before shrinking, or the checkerboard method, strip method, or nine-point method is used for shrinking.
Store coal samples before preparation, after preparation, and at any intermediate stage in the preparation process. Store in a tight, non-absorbent, air-tight container in a cool place.
When the sampling process is very long and the sample is left for too long, the number of sampling units should be increased to shorten the sample time.
After the sample is prepared, it should be accurately weighed to determine the moisture change during storage and transportation.