Chapter 4-Abrasive Wear Testing

ABRASION TAKES PLACE ON CRUSHER JAWS WHEN rocks are crushed to make pea-size stones for pavement. This type of abrasion is termed gouging abrasion because handling big rocks gouges truck bodies and all of the equipment that is used to mine and process the rock to a finished product. However, once big rocks are converted to neat pea-size stones, they produce low-stress abrasion when they are conveyed or slide down chutes. If the same stone were milled to a one-micrometer powder, it might produce polishing wear on the comminution equipment. The mechanism of gouging abrasion is macroscopic plastic deformation of surfaces coupled with high-stress scratching abrasion. The pushing of the rock against and across the working surfaces is sufficient to cause the rock to crush; thus, it is high-stress abrasion. When the pea stone is sliding on a metal or plastic chute, it produces low-stress or scratching abrasion because the stone's sharp edges produce scratches on the contacting surfaces. Finally, the scratches are no longer macroscopic when one-millimeter stone particles rub on surfaces. It removes material probably by a mechanism of microscopic scratches and adhesive transfer of material from the rubbed surface to the harder rock. For these reasons, there are basically four categories of abrasion tests, and one should be selected to simulate a particular application. The purpose of this chapter is to describe ASTM tests and others that are commonly reported in tribology literature. Some opinions on applicability and precautions in use also will be presented. The objective of this chapter is an understanding of the differences between the tests and how to apply them to problems. This chapter will cover the major categories of abrasive wear: gouging, low stress, high stress, and polishing. The ASTM G 81 gouging abrasion test was developed by a task group with strong earth-moving/mining interests. They wanted a test that would enable them to screen materials for applications such as power shovel buckets, off-road dump truck bodies, and rock comminution equipment. The test rig is a commercially available laboratory jaw crusher. The crushers are not large, maybe two feet by two feet by four feet, but each test requires crushing two tons of mineral rock from football size to pea size with plates covered with test samples (Figure 4-1).