Erosive wear particle size

Figure 8.12 illustrates a solid particle impinging on a surface. It has been found that the erosive wear rate depends upon the impingement angle, a, the particle velocity, vq, and the size and density of the particle, as well as the properties of the surface material. It has also been found that there is a difference in erosive wear properties of brittle and ductile materials. The maximum erosive wear of ductile materials occurs at a = 20°, whereas the maximum erosive wear for brittle materials occurs near a = 90°. Since the impingement angle is probably lower than 90° for these type of flow situations, we might consider only brittle materials, such as ceramics for this application. Let us examine brittle erosive wear in a little more detail first. 

Detailed studies have shown some further dependence of the wear rate on the attack angle, temperature of erosion, particle size, particle concentration, and particle hardness ... 

D. Mills, J.S. Mason, Particle size effects in bend erosion, Wear 44 (1977) 311-328. 

For smaller particle sizes ( 1,000 microns), polyurethanes provide a superior erosive wear resistance to metals at most normal velocities of up to 20m/s. Outside these limits, the materials need to be evaluated in a manner that is as close to real conditions as possible. 

Walker and Bodkin (1993) discuss the advantages and limitations of a number of the commonly used erosive wear testers. The influence of particle size and shape are very important as well as the impingement angle and concentration of the slurry. They found that the wear rate increases with the jet velocity to the power of 2.2 (Mens and de Gee (1986) gives 2.8-3.2.). Wear rate is at a maximum at 30° impingement angle. The mechanism is mainly cutting. The rate increases with the size of the particle. 

The effect of ultra-high molecular weight poly-(ethylene) (UHMWPE) the on mechanical and solid particle erosive wear behavior of aramid fabric reinforced-epoxy composites has been investigated [64]. A siUca sand of a size of 150-280 fim was used as an erodent. The erosive wear rate of UHMWPE in aramid-epoxy composite exhibits a lower value in comparison to neat composites. A maximum erosion rate was observed at an impingement angle 60 , and the material behaves in a semiductile manner. 

Friction and wear properties Both friction and wear belong to the discipline of tribology. Friction is the force of two surfaces in contact or the force of a medium acting on a moving object, and wear is the erosion of material from a solid surface by the action of another solid. Factors that exert influence on friction and wear characteristics of polymer composites are the particle size, morphology, and concentration of the filler [38]. 

Erosion resistance of materials is very dependent on the erosion conditions, the effects of which are dominated by a number of variables including particle size, shape, composition, and velocity angle of incidence and temperature. Unlike wear properties, the erosion rate of weld-overlay coatings generally increases with increasing hardness (Fig. 8). However, the erosion resistance of weld-overlay alloys depends on whether the... 

Lin and He (2005) have compared the role of eleetroless (EL) NiP composite coatings incorporated with micron- and nanosized SiC partieles on the cavitation erosion of AISI1045 steel. The EL Ni-P-nano SiC and Ni-P-micro SiC composite coatings were prepared by dispersing nano (25-50 mn) and micron- (5 pm) sized particles in an acidic hypophosphite-reduced EL nickel plating bath maintained at 90 1°C. The deposition time was 3 h and the coating thickness was 60 pm. All the coatings were subjected to post heat-treatment to achieve abetter hardness and wear... 

Obviously, if pressure drops on the order of 6 to 8 kPa are acceptable from a process point of view, an 8 or 13-unit multicyclone (or some number in between) could prove to be a viable option for the task at hand. If not, other types of separation equipment may have to be considered such as a baghouse, an electrostatic precipitator, or a wet scrubber. Nevertheless, even if the pressure drop across the cyclones were acceptable, one would still need to consider the long-term wear implications associated with operating the cyclones at velocities in the range of 35 to 40 m/s. If the solids being processed are not especially abrasive and/or if they are sufficiently flne in size, it may be possible to operate at these velocities. If not, erosion-protective liners may need to be installed. Some bare-metal multicyclone systems have been observed to operate for many years at velocities of 70 to 85 m/s while processing several tons per day of rather abrasive sand-like particles that were under about 25 fim in size. 

---