Abrasion accelerated tests

Wear related or abrasion related problems can only be determined by actually testing hardware in hill scale service. Accelerated tests have not proven successful in reflecting most service and performance. 

The exposure site is selected according to the service for which the data are to be applicable. For atmospheric service, such factors as marine and industrial contaminants, sunlight, dew and sand abrasion, must be considered. Atmospheric specimens are normally mounted at 45°, facing south. This has been shown to provide about a 2 1 acceleration of failure compared with a vertical exposure. Whether this or other standardised positions are used, the details of the exposure are an important part of the test record. 

It follows that there cannot be a universal standard abrasion test method for plastics and the test method and test conditions have to be chosen to suit the end application. Also, great care has to be taken if the test is intended to provide a significant degree of acceleration. 

The choice of abradant should be made primarily to give the best correlation with service, but in practice is often chosen largely for reasons of convenience. In laboratory tests the most common are abrasive wheels (vitreous or resilient), abrasive papers or cloth and metal knives . The usual abrasive wheels and papers really only relate to situations where cutting abrasion predominates. Where plastics are used in some form of bearing the conditions will involve much smoother surfaces and materials such as smooth metal plates would be more appropriate. A problem with smooth materials is that they abrade relatively slowly and, if conditions are accelerated, give rise to excessive heat build up. 

It is now well established that wear of rubber is not a purely mechanical failure process in that it contains a contribution due to thermal-oxidative breakdown of the polymer (226—228). Still, under severe conditions, which apply to all accelerated laboratory tests as well as to many situations encountered in tire wear, abrasion is dominated by tearing processes. 

AATCC Test Method 61-75 "Colorfastness to Washing, Domestic and Laundering, Commercial Accelerated," and International Standard Method C06 were modified to establish the laundry procedure to simulate one home laundering cycle. An Atlas Launder-Ometer equipped with stainless steel canisters was used. Teflon liners were used In the lids to prevent retention of pesticides by the rubber gaskets. Abrasive action was provided by the placement of 25 steel balls In each canister. 

The prime factor in choosing an abradant is its relevance to service, but it also has to be available in a convenient form and, for anything but ad hoc tests, it is essential that it be reproducible. In consequence of these considerations, abrasive wheels and papers or cloths predominate where cutting by sharp asperities is to be simulated. The abrasive wheel is probably the most convenient, because of its low cost, its mechanical stability, and the ease with which it can be refaced to maintain a consistent surface. Abrasive papers and cloths are cheap and easy to use but are not so readily refaced and will deteriorate in cutting power more quickly. Although basically low in cost, both wheels and papers are a considerable c.xpense when bought as standard reference materials. Materials such as textiles or smooth metal plates are more relevant for some applications, but they abrade relatively slowly, and if conditions are accelerated they give rise to excessive heat buildup. 

Wear is important in applications as diverse as tires, conveyor belting, footwear, and windscreen wiper blades, yet most of us would accept that the rubber industry still awaits a laboratory test or series of tests that can predict service performance with any confidence. Over the years, there certainly has been no shortage of small-scale tests for abrasion resistance and indeed no shortage of claims or reports of satisfactory correlation with the behavior of various products, but strong doubts remain, and some sectors, not least the tire industry, conclude that there is no substitute for a service trial or a simulated product test, for example, a road trial on tires held at a small slip angle to accelerate wear. 

Chou, P. and M. Lamers (2005). Quantitative study of magnetic tape abrasivity using accelerated wear testing. Microsyst technol 11,901-906. 

In electronics, these kinds of tests have been used to evaluate the effects of coarse particles on the insulation resistance of connectors. When the tests are done with the connectors mated, the connectors are sometimes vibrated in an attempt to drive particles into the interface. In other cases the connectors are exposed unmated. After exposure they are mated and the resistance is measured. Sometimes these tests are carried out iteratively, or multiple insertion cycles are undertaken to evaluate the ability of the contact metal (typically a gold or other noble metal finish) to withstand the abrasion from coarse particles. Acceleration factors either are not determined or, if they are, the confidence level is low because they are based on tests as simple as the weight gain of metal coupons. Under fortunate circumstances, these tests may point out opportunities for design changes that extend life, at least in a qualitative way. 

Since the slider coating film may be in contact with disk lubricant, it is possible that the lubricant may dissolve in and soften the film. This could potentially lead to some flow of the slider coating at the elevated temperatures inside the disk drive. To assess the possibility of film shear flow from the slider, or development of tackiness, the rheological properties of the fluorosurfactant and various concentrations of lubricant were measured. The fluorosurfactant coating is also compared with several other types of alternative coatings in an accelerated tribological test for the ability of the coating to inhibit lubricant transfer and abrasion of the disk by the slider. 

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