Abrade, abrasion

An abrasive is a substance used to abrade, smooth, or polish an object. If the object is soft, such as wood, then relatively soft abrasive materials may be used. Usually, however, abrasive coimotes very hard substances ranging from naturally occuring sands to the hardest material known, diamond. 

The abihty of organically modified ceramics based on alumina, zkconia, titania, or siUca (and mixtures of each) to function as abrasion-resistant coatings has also been studied (62). Eor example, polycarbonate, when coated with an epoxy—aluminosihcate system, experiences a significant reduction in the degree of hazing induced by an abrader, as compared to uncoated polycarbonate. 

In industiial metal finishing, pohshing is an abrading operation involving the use of coarse abrasives, which remove significant amounts of metal from a... 

Inflated Diaphragm Method (ASTM D3886). This method is appHcable both to woven and knitted fabrics. The specimen is abraded by mbbing either unidirectionally or multidirectionally against an abradant having specified surface characteristics. The specimen is supported by an inflated mbber diaphragm under a constant pressure. Evaluation of abrasion resistance can be either by determination of the number of cycles required to wear through the center of the fabric completely or by visual examination of the specimens after a specified number of cycles. 

The 3M Abrasion Test (51) is used to assess the durabUity of a protective fluorochemical finish by evaluating its resistance to abrasion and wear. The surface is abraded with an AATCC crockmeter fitted with sandpaper. 

Abrasive wear is encountered when hard particles, or hard projections on a counter-face, are forced against and moved relative to a surface. In aUoys such as the cobalt-base wear aUoys which contain a hard phase, the abrasion resistance generaUy increases as the volume fraction of the hard phase increases. Abrasion resistance is, however, strongly influenced by the size and shape of the hard-phase precipitates within the microstmcture, and the size and shape of the abrading species (see Abrasives). 

Dental abrasives range in fineness from those that do not damage tooth stmcture to those that cut tooth enamel. Abrasive particles should be irregular and jagged so that they always present a sharp edge, and should be harder than the material abraded. Another property of an abrasive is its impact strength, ie, if the particle shatters on impact it is ineffective if it never fractures, the edge becomes dull. Other desirable characteristics include the abiUty to resist wear and solvation. 

Dental abrasives can be classified either according to their use or according to the degree of their abiUty to abrade (see Dentifrices). The use classification, adopted for the ADA specification no. 37 for powdered dental abrasive materials, is based on removal of stain from natural teeth or on restorations of all types. Several abrasives are used in dentistry in a variety of grit sizes and shapes. 

After a few revolutions, the rubber lip of the oil seal beeomes an abrasive lip, w hieh eats a groove into the stainless steel pump shaft. The rubbing aetion abrades the pump shaft, removing metal, and depleting the ehromium eontent of the stainless steel, wdiieh further aeeelerates its erosion. 

There is usually more than one test method to determine a performance because each test has its own behavior and meaning. As an example there are different tests used to determine the abrasion resistance of materials. There is the popular Taber abrasion test. It determines the weight loss of a plastic or other material after it is subjected to abrasion for a prescribed number of the abrader disk rotations (usually 1000). The abrader consists of an idling abrasive speed controlled rotating wheel with the load applied to the wheel. The abrasive action on the circular specimen is subjected to a rotary motion. 

In this test for transparent plastics, the loss of optical effects is measured when a specimen is exposed to the action of a special abrading wheel. In one type of test the amount of material lost by a specimen is determined when the specimen is exposed to falling abrasive particles or to the action of an abrasive belt. In another test, the loss of gloss due to the dropping of loose abrasive on the specimen is measured. The results produced by the different tests may be of value for research and development work when it is desired to improve a material with respect to one of the test methods. The variables that enter into tests of this type are... 

An abrasion experiment is carried out by sliding a rubber sample over a given distance and determining the volume loss by some suitable method, usually by determining the difference in weight before and after. It is always assumed that the abraded volume is proportional to the distance covered between measurements, which is reasonable if the sharpness of the track remains constant. Hence, the abraded volume is always referred to unit distance covered. This basic quantity depends on the pressure between the sliding surfaces, the temperamre, speed, and the topography of the track, such as sharpness and coarseness of the asperities. 

This is about 2000 indicating that the energy required to remove unit volume of mbber even by the very sharp abrasive track is an inefficient process. A surprising result is that the tread compounds have a much higher abrasion loss than the gum mbbers, as shown in Figure 26.52. This shows the abrasion as function of temperature for three mbbers (A) SBR, (B) ABR, and (C) NR, the sohd fines are for the gum mbbers, the dotted one for the same polymer, filled with 50 HAF black. The reason will become apparent when examining the appearance of the abraded surfaces. 

FIGURE 26.53 Abrasion pattern (a) appearance for different rubbers under different testing conditions and (b) cross section through abraded samples. 

Champ et al. [47] devised a simple abrasion experiment by measuring the abrasion loss caused by a razor blade scraping under load across a mbber surface. For this an Akron abrader sample wheel was used. They used soft unfilled noncrystallizing mbber compounds based on different polymers. Under these conditions strong abrasion pattern develop. 

In Figure 26.60, the difference between abrasion in air and nitrogen is plotted as function of the abrasion in air for different compounds abraded on several surfaces of different sharpness using MgO and a mixture of Fuller s earth and alumina powder, respectively, as agents to counteract... 

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