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The Hardgrove Grindability Index Standard Reference Sample (HGI-SRS) is a sample of coal used to calibrate instruments that are designed to determine the ease with which coal can be pulverized. The HGI value provides information for determining grinding power consumption and pulverizer capacities.
The HGI-SRS is prepared in a series of steps over several days. All procedures conform to American Society for Testing and Materials (ASTM) standard methods (Appendix A). Coal is purchased according to specifications. The Hardgrove Grindability Index is calculated on four splits (or portions), two each taken from the two reserved cans. The results are averaged to give the index for the entire lot. Cans of standard reference sample are shipped to customers upon request, along with a questionnaire designed by ASTM to obtain data on the quality of the sample. The data obtained on the questionnaire is used by ASTM to perform detailed statistical analysis of HGI-SRS production.
The National Energy Technology Laboratory has a Contributing Funds Agreement with ASTM to produce HGI-SRS, which are the Primary Standards for the D409 Analysis.
The HGI-SRS come in sets of four, containing 4 standards of approximate HGI values 40, 60, 80, and 110. Each set costs $1,400 for domestic orders and $1,470 for foreign orders to help cover the manufacturing and shipping costs.*
For more information: HGI-SRS Order Form and Data Sheet 
* There is a temporary increase in the cost for an HGI-SRS set. Penn State was down to one working calibrated screen used in the production of HGI-SRSs and has recently calibrated two backup screens. The cost for an HGI-SRS set, which has not been increased for more than 11 years, has been increased to recoup the screen calibration costs since these costs are not included in the standard fee. This fee will remain in effect until the recalibration costs are recouped, which is anticipated to be approximately 2 years (based on historical data on the number of sets sold per year) at which time the cost per set will be reduced. This time period will be adjusted based on the number of sets sold so the length of time the increased fee is in effect may be shortened or lengthened.