Tham khảo tài liệu 'handbook of lubrication episode 2 part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 630 CRC Handbook of Lubrication FIGURE 5. Effect of impact angle on erosion of ductile metal and brittle solid. From Wolfe G. F. Lubr Eng. 19 28 1963. With permission. IMPACT ANGLE-DEGREES FIGURE 6. Erosion as a function of impact angle. From Eyre T. S. Tribol. Int. 11 2 91 1978. With permission. Erosion Erosive wear can be caused by either solid participates or liquid droplets striking the surface at high velocities. 16 17 In this chapter emphasis is placed on erosive wear by solid particle impact. Typical problem areas include compressor and turbine blading helicopter rotor blades impeller-type pumps pressure letdown valves etc. Since the contact stress results from kinetic energy of the particles in the fluid stream size and density of the particles their velocity and angle of impact must all be considered. Erosive weight loss is roughly proportional to the square or cube of velocity. Relative hardness and shape of the particle its fracture characteristics and the ductility of the solid surface also influence the resulting damage. As illustrated in Figure 5 cutting wear predominates at low angles of impingement for ductile metals unless the particles are smooth spheres. The harder the surface the lower the rate of material removal. At higher angles of impact hard brittle materials show more erosive wear as elastic properties of the surface become much more important. Annealed materials often erode less than the same alloy in the hardened state. An elastomeric coating may be a very viable solution to erosion at high angles of impingement. Figure 6 compares the relative effect of impact angle on wear rates for a metal and a rubber material. While surface hardness becomes relatively less significant at high angles of impact coatings of very hard materials are being used to prevent erosion damage at both high and low angles of impact. For example Hansen et evaluated a large variety of metals alloys carbides and ceramics in a sandblast type of test at 20 and .
