Machine Wear

Chromium carbide is important in powder preparations designed for thermal spray apphcations of corrosion and wear-resistant coatings on tool and machine parts. Lower carbon carbides of chromium are important in hardfacing tods and electrodes for weld-apphed ovedays on machine wear surfaces. However, these carbides are usually formed in situ from Cr and C in the rod and not added as preformed carbides. The properties of Ci2C2 are hsted in Table 2. 

Alloyed Iron. Tin-alloyed flake and nodular cast irons are widely used throughout the world. Estimated 1980 consumption was ca 1,200 t. As little as 0.1% tin when added to flake and spheroidal graphite cast irons in the pouring ladle gives the iron a structure that is completely pearlitic. Tin-inoculated iron has a uniformity of hardness, improved machinability, wear resistance, and better retention of shape on heating. Where pearlitic and heat-resistant cast irons are required, such as for engine blocks, transmissions, and automotive parts, tin additions may provide a suitable material. 

The previous errors addressed heterogeneity on a small scale. Now we examine heterogeneity on a large scale the scale of the lot over time or space. The long-range nonperiodic heterogeneity fluctuation error is nonrandom and results in trends or shifts in the measured characteristic of interest as we track it over time or over the extent of the lot in space. For example, measured characteristics of a chemical product may decrea.se due to catalyst deterioration. Particle size distribution may be altered due to machine wear. Samples from different parts of the lot may show trends due to lack of mixing. 

While the benefits of detecting abnormal machine wear or an aging lubricant condition are important and frequently achieved with oil analysis programs, they are of low importance when compared to the more rewarding objective of failure avoidance. This is achieved by treating the causes of failure, not just the symptoms. Also, it is the foundation of the popular practice known as proactive maintenance. 

A j-i.- Contaminated or LU>rlcat)on Condition Degraded Oil Failure Increasing Machine Wear Faiiure... 

Textile Amylases, cellulases, catalases Acids, alkali, oxidizing agents, reducing agents Energy, reduced machine wear... 

Oil in machines carries the products of deterioration resulting from wear and mechanical failure. Analyzing the oil resident in a machine or the debris the oil carries allows predictions to be made about the state of health of the machine. The critical measurement reflecting the condition of machine wear is the number of microscopic metal wear particles that are suspended in the oil system of the machine. The spectrometric oil analysis process is a laboratory technique that uses various instruments to analyze a used oil sample from a machine. The spectrometric result is compared to a baseline level of metal found to be typically suspended in the oil under normal operating conditions. When the wear is meaningful, the sample will show high levels (in parts per million) of wear metals compared to the baseline oil sample. 

Lasri L, Nouari M, El Mansori M. Wear resistance and induced cutting damage of aeronautical FRP components obtained by machining. Wear 2011 271 2542—8. http // dx.doi.org/10.1016/j.wear.2010.11.056. 

BuU SJ, Zhou Q. A simulation test for wear in injection moulding machines. Wear 2001 249 (5-6) 372-378. 

Internal lubricants are rather more miscible with the polymer. They alter its flow characteristics, lowering the melt viscosity, reducing shear forces, and allowing lower processing temperatures. Internal lubricants increase output rates, reduce machine wear, and lower the energy consumption used in the process. They also reduce the risk of thermal degradation and discoloration, improve the appearance of the finished product (especially its surface gloss) and... 

Welding electrodes for hard facing (Cr7C3 Cr3C2C eutectic) and weld-applied overlays on machine wear sur tces... 

Rheology and Processability. The presence of fillers affects the flow characteristics of the filled polymers. The immediate effect of a filler is to increase viscosity, interfere with the polymer flow pattern in a given process, produce thixotropy, and give rise to machine wear. The relevant properties of the filler are concentration, size, aspect ratio, stiffness, strength, and specific interaction between filler and the polymer matrix. Within these are the special cases of easily deformable fillers that could easily be broken down or shaped during flow. 

The extrusion step is not particularly costly in comparison with the price of the raw materials, but the cost is still significant and impacts on the overall economics of the final material. It is therefore worthwhile to devote effort to optimisation of the extrusion process in terms of increased thronghpnt (productivity) and decreasing energy consumption and machine wear. In the author s opinion, the subject of throughput does not receive the attention it deserves. There are conntless reports of the mechanical properties of thermoplastic composites hut no mention of the extension characteristics of the materials. For a meaningful comparison of different composites, one mnst consider not only their mechanical and aesthetic properties, bnt also the relative economics of extrusion. 

Machine wear is a concern, partly because it costs money to replace a worn barrel or screw. The main problem though, is the loss of productivity when the machines must be shut down for maintenance. Potentially, wear may lead to significant metal contamination levels with accompanying polymer stability problems. Although machine wear is an issue, it is not a subject that has received much attention. 

Machine wear in injection molding and extrusion is more significant in GRTP s due to the abrasiveness of the glass fibers and corrosiveness of fiber sizing materials. 

Many factors contribute to machine wear such as the corrosiveness of coupling agents, additives, and resin systems the improper choice of materials for screws, barrels, and shutoff valves and poor component design. Glass fibers in the normal processing of precompounded material are suspended in a melt of resin and do not cause excessive wear. However, improperly handled, they can multiply wear problems. ... 

Walter Lachowecki, Molding RTP s Here s How to Prevent Machine Wear , Plastics Technology, April 1972. 

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