The recent ILS 047 has shown the precision estimates to be wider than thought previously. Data tends to show that laboratories not using primary HGI reference materials (first introduced in 1971)obtain the same level of precision (r and R) as laboratories using primary HGI reference materials. Additionally, data shows that using the original 1951 Hardgrove equation (HGI = 6.93 * W + 13) provides results equally precise. The accurancy / trueness is difficult to assess given the empirical nature of this test. This task group and its ILS will provide additional data that may convince D05 members to return to 1970, discontinue the use of primary reference materials, and use the 1951 equation to calculate the results of this empirical test.
Keywordsgrindability; Hardgrove Grindability Index; HGI; pulverization;
Draft Under Development