Browsing by Subject "Mechanical wear"

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    The sliding wear of polymers against steel
    (1988) Clarke, C G; Allen, Colin
    A laboratory wear testing facility has been developed to generate wear rate data for polymeric materials sliding at constant velocity against a hardened stainless steel base. The polymers investigated were ultra high molecular weight polyethylene (UHMWPE), ultra high molecular weight polyethylene-with a friction reducing additive (UHMWPE/FILL), polyoxymethylene (POM), poly(ethylene terephthalate) (PETP), molybdenum disulphide filled polyamide 6 (PA6/MoS₂) and graphite filled poly(amide-imide) (P(A-I)/GR). Testing was carried out as a function of sliding velocity between 0.13 to 2.27 ms⁻¹, loads of 1, 3 and 5 MP a and counterface roughnesses which varied from 1 micrometre to 0.25 micrometres. An increase in the counterface roughness resulted in a variable increase in the wear rate of the individual polymers except for the filled UHMWPE. These changes in the wear rate have been explained in terms of the mechanism of material removal. A progressive increase in sliding velocity has been shown to result in an initial increase in the wear rate followed by a decrease and finally a rapid increase for all materials under the majority of applied conditions. Explanations for such behaviour have been advanced in terms of the viscoelastic response of the polymers to strain rate and temperature. Low modulus materials however showed a significant drop in wear rate under low loads above a critical velocity which is believed to be due to a transition from boundary to partial el astohydrodynamic lubrication. Generally an increase in load gave an increase in wear rate for all polymers except for UHMWPE and filled UHMWPE at a counterface roughness of 1 micrometre. These conditions have been discussed with reference to the materials response to thermal effects and counterface interactions.
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    The wear of materials in an ash conditioner
    (1989) Cuddon, Alan; Allen, Colin
    The abrasive nature of fly ash handled in large coal-fired power stations results in unacceptable material and maintenance costs in ash-water mixing plant. Wear testing has been carried out in situ using a variety of generic materials. A ranking order of wear performance has been established both as a function of material and operating costs, and it has been demonstrated that impressive cost savings can be effected by the use of ceramic-coated steel mixing blades. The performance of such composites has been found to be sensitive to the design and method of application. To optimise materials selection, a family of tungsten carbide-cobalt cermets together with a number of structural ceramics were tested in situ. The modes of wear can be related to material constitution. By ranking the performance of these candidate materials, value based materials selection and design for use can be applied.