Wear surfaces

High wear type is also a general-purpose HPDL with increased surface wear resistance. 

PPS resins are chiefly used for injection mol ding. The melt flow of the glass-fiUed resins is very stiff, and high injection pressures are required. Mold surface wear is heavier than for most other engineering plastics. Mol ding melt temperatures are near 330°C for optimum surface gloss and impact strength, mold temperatures of 130°C should be used. The resins are brown to brown-black. 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

Surface wear is defined as the deformation and loss of surface material as the result of a mechanical, thermal, or chemical action. These three mechanisms can act singly but are more often found in combination, which may make the wear process very difficult to analyze. Materials for wear protection have different responses to each of these wear mechanisms and, consequently, no universal wear material exists. To select the optimum material or combination of materials, it is essential to determine the cause and the mechanism of the wear as accurately as possible. The selection can then be made of the best and most cost-effective material. 

There are, however, other components where the process of degradation is clearer and the rate of change easier to deduce, particularly when that process is mechanical rather than chemical. This would be so in a simple case where surface wear proceeded at a linear rate. Discussion of these problems will explain why there is still a shortage of reliable data and also why much durability testing falls short of the breadth and quality necessary to make reliable predictions. 

The mechanical erosion of a solid surface such as a pipe wall in a gas—solid flow is characterized by the loss of solid material from the solid surface due to particle impacts. The collisions of the particles either with other particles or with a solid wall may lead to particle breakup, known as particle attrition. Pipe erosion and particle attrition are major concerns in the design of a gas-solid system and during the operation of such a system. The wear of turbine blades or pipe elbows due to the directional impact of dust or granular materials, the wear of mechanical sieves by the random impact of solids, and the wear of immersed pipes in a fluidized bed by both directional and random impacts are examples of the erosion phenomenon in industrial systems. The surface wear associated with the erosion phenomenon of a gas-solid flow has been exploited to provide beneficial industrial applications such as abrasive guns, as well. 

Consider the surface wear by random motion of particles in a fluidized bed. The random motion is assumed to have the intensity of (ua). Determine the relationship between ED and Kd for overall ductile wear and the relationship between EB and KB for overall brittle wear. 

Cavitation is a form of corrosion that is caused by the repeated nucleation, growth, and violent collapse of vapor bubbles in a liquid against a metal surface. Cavitation erosion arises when a solid and fluid are in relative motion, and bubbles formed in the fluid become unstable and implode against the surface of the solid. Cavitation erosion is similar to surface wear fatigue.75 A metal having undergone a cavitation erosion has an appearance similar to a pitted metal.31... 

FIGURE 1.5 Refractory surface wear dominated by chemical corrosive (dissolution). 

Lower mating surface wear (Silica-free formulation reduces abrasion.)... 

Note. Patterned tile such as the diamond pattern will harbor grease and organic residue. It is not acceptable under some local sanitary laws. Labor safety laws often require a non-skid surface. Emery grit embedded in the surface of the quarry tile will meet the non-skid criteria. However, the employees may complain that the emery surface wears out their shoes too quickly and is difficult to clean. Warn the owner. 

Wear Debris Analysis When machine surfaces wear, they generate metallic particles that enter the lubricant. Monitoring and analyzing the generated debris enables analysts to detect and evaluate abnormal conditions to assist in directing needed maintenance activities. 

Boundary lubricants work by forming a thin solid film at the interface of the die and the tablet. Metallic stearates are the most widely used boundary lubricants, and their activity has been attributed to adherence of polar molecular portions on their surface to the surfaces of one particle species and of non-polar surface components to the other species surface. Such lubricants should have a low shear strength of their own and form interparticulate films that resist wear and reduce surface wear. A list of lubricants with typical ranges for their usage is given in Table 11.9. 

Conventionally, adhesive wear occurs when two interacting surfaces are not sufficiently lubricated, which results in the adhesive transfer or removal of near-surface material. Surface adhesion is dependent on the nature of the contacting surface. Wear material transfer in this region has been called "solid-phase welding," which occurs at asperity contacts.1 A schematic of adhesive wear is shown in Figure 5.1.2 Adhesive wear is related to the materials and slurries used. The amount of slurry can shift contact from the boundary lubrication regime to the EHD/micro-EHD regime where surfaces are more separated. 

In abrasive wear by hard particles we often find either two-body abrasive wear or three-body abrasive wear, as shown in Figure 5.3. Two-body wear is caused by hard protuberances on the counterface, while in three-body wear hard particles are free to roll and slide between two sliding surfaces. Wear rates due to three-body abrasion are generally lower than those due to two-body abrasion. Various mechanisms of material removal in these two cases differ only in relative importance. Slurry erosion belongs to the abrasive wear category. Erosion is caused by hard particles sticking to the surface entrained in a flowing liquid. 

Sand-asphalt-sulfur surface-wearing courses prepared with coarse sands have a sharp, sandpaper-like surface texture. Skid resistance tests carried out up to speeds of 50 mph have given favorable results. The road surface is not susceptible to polishing because as soon as a sand grain is worn away or dislodged, another sharp sand grain is exposed. Fine sands, such as dune sands, are not suitable for riding surfaces because they yield surfaces which are too smooth. 

In comparison with metals, most conventional polymers are low in wear resistance. For wear control, we need to understand various wear mechanisms for each polymer system (V). As discussed in a previous paper, for adhesive wear, surface energetics can determine the extent of surface wear. Thus, a low surface energy is preferred to minimize the surface attrition. In addition, a harder polymer is desired to lower the wear rate. For abrasive wear, fracture energetics become important a harder and tougher material should be more wear resistant. 

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