Sliding abrasion

Urethanes are processed as mbber-like elastomers, cast systems, or thermoplastic elastomers. The elastomer form is mixed and processed on conventional mbber mills and internal mixers, and can be compression, transfer, or injection molded. The Hquid prepolymers are cast using automatic metered casting machines, and the thermoplastic peUets are processed like aU thermoplastic materials on traditional plastic equipment. The unique property of the urethanes is ultrahigh abrasion resistance in moderately high Shore A (75—95) durometers. In addition, tear, tensUe, and resistance to many oUs is very high. The main deficiencies of the urethanes are their resistance to heat over 100°C and that shear and sliding abrasion tend to make the polymers soft and gummy. 

FIGURE 26.52 Sliding abrasion of three different tread compounds as function of temperature at a sliding speed of 0.01 m/s (a) styrene-butadiene rubber (SBR), (b) ANR, (c) NR,-tread compound, —gum compound. 

FIGURE 26.55 Abrasion surface appearance of a natural rubber (NR) black-fiUed tire tread compound for sliding abrasion at different temperatures. 

UHMWPE exhibits an outstanding sliding abrasion resistance, the highest notched impact resistance of any known plastic material and a low coefficient of friction (13). 

For sliding abrasive resistance, the tough polyesters are the best suited. This also must be balanced against the hardness of the material. The older style PPG materials do not have the physical properties to provide outstanding resistance to abrasive wear. 

Figure 4.1 Impact abrasion, sliding abrasion and abrasive angle. Reproduced with permission from Trelleborg AB, Sweden...

Natural rubbers, such as pure gum with a durometer hardness of 40 on the Shore A scale, display surprising long life in sliding abrasion. Such linings are used in sand and slurry handling pumps and pipings where particles are in fine size and no grit is present. 

Since the flow causes sliding abrasion at a low angle of incidence in the piping, the rubber which can be suggested for this application is a low durometer hardness (40 on the Shore A scale) natural rubber. For lower flow rates at ranges of 1,200 litres per minute up to 4,000 litres per minute, a hard rubber or a semi-ebonite rubber can be used since the abrasive wear of the finely meshed particles will be negligible. 

First, consider the tungsten carbide types. Notice that they are composed of very hard particles in a softer and less abrasion-resistant matrix. Although such material is the best for resisting sliding abrasion on hard material, in sand the matrix is apt to scour out slightly, and then the britde particles are exposed. These particles are rated poor in impact resistance, and they may break and spall off when they encounter the rocks. 

If the bulk solid s characteristics are such that a mass flow pattern is not required, a funnel flow bin should be designed. Not only will this save on headroom and maximise storage volume for a given headroom, it will also minimise the effects of sliding abrasion on the bin walls. 

Sliding Abrasive wear, 2Ax)dy Flat pin-on-rotating abrasive drum (spiral path), reciprocating pin-on-abrasive flat, flat pin-on-moving abrasive belt, traversing pin-on-abrasive disk (spiral path), twin rotating abrasive wheels... 

---