Wear can be evaluated by calculating the abrasion index. This index is a measure of the abrasivity of the rock during crushing. The abrasion index (Ai) is then used to empirically predict wear rates of crusher liners.The single paddle impactor requires about 4 lbs of rock, mineral or ore for each test. The amount of material will vary depending on its bulk density.
The relatively high velocity of the single paddle tester seems to be the most practical answer to the problem of obtaining quick and fairly accurate indices of abrasion. It can be argued that the wear on this type of equipment is quite different from that on heavy jaw crushers; however, it seems more practical to design a single unit for abrasive testing rather than several, each specializing in a particular method of crushing or reduction.
During operation the single paddle strikes a column of falling rock or ore particles at a fairly high velocity. The particles are falling away from the outer, slowly revolving drum. The sampling size is 400 grams of broken rock, mineral or ore, (assuming that the solid density is 160 pounds per cubic foot), sized to pass Tyler screen 0.742 and to be held upon screen 0.371. Such a change constitutes only one quarter of a complete test, the total being 1,600 grams run as four batches of 400 grams each. Each 400 gram portion is run exactly 15 minutes by stop watch; then the drum is opened and cleaned out, a fresh lot of material is added and the test is continued.
The paddle is a piece of steel 1-inch wide, 3-inch long and ¼ inch thick, machined and ground to size. Before this test this paddle is demagnetized, and is accurately weighed on a sensitive balance, to a tenth of a milligram. After the completed run of 1,600 grams the paddle is removed and washed clean of all rock particles, dried, demagnetized and reweigh. The loss of weight recorded in tenths of a milligram represents the abrasive action for the particular rock, mineral or ore.
