Abrasive materials

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. 

A new form of coated abrasive has been developed that consists of tiny aggregates of abrasive material in the form of hoUow spheres. As these spheres break down in use, fresh cutting grains are exposed this maintains cut-rate and keeps power low (44). 

Except for siUca and natural abrasives containing free siUca, the abrasive materials used today are classified by NIOSH as nuisance dust materials and have relatively high permissable dust levels (55). The OSHA TWA allowable total dust level for aluminum oxide, siUcon carbide, boron carbide, ceria, and other nuisance dusts is 10 mg/m. SiUca, in contrast, is quite toxic as a respkable dust for cristobaUte [14464-46-1] and tridymite [15468-32-3] the allowable TWA level drops to 0.05 mg/m and the TWA for quartz [14808-60-7] is set at 0.1 mg/m. Any abrasive that contains free siUca in excess of 1% should be treated as a potential health hazard if it is in the form of respkable dust. Dust masks are requked for those exposed to such materials (see Industrial hygene). 

Abrasives. Abrasive materials are either bonded or coated. Bonded phenoHc abrasives have superior strength and shock resistance compared to sintered ceramic compositions. The higher stabiUty permits higher rotational speeds for resin-binder wheels however, temperatures are lower than with ceramic wheels. 

Mech nic l Impact Mills. The mechanical types include cmshers, hammer mills, pin disk mills, turbine mills, and mills with air classifiers. Impact Crusher. Feed material is introduced through a feed opening onto a rotor moving at between 25 and 50 m/s (Fig. 11). The initial impact by the rotor causes some size reduction, and the material is accelerated up to the speed of the rotor and flung against the impact plates, where further size reduction occurs. It is possible to wear-protect these units quite well, so that abrasive materials can be handled. The final end particle size can be varied by the inclusion of an outlet grid to vary the residence time in the machine. 

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. 

Sand and other forms of quartz are used as a powder in sandblasting. If a gender abrasive material is wanted, powdered walnut shells are often used. 

The screen is typically constructed of a vv edge-bar with an aperture betvv een adjacent bars, which opens up to a larger radius. This prevents solids from blinding the screen as vv ell as reduces conveyance torque. For abrasive materials such as coal, the screens are made of vv ear-resistant materials such as tungsten carbide,... 

Chromium Oxide is present in just about every maintenance shop in the world. We call it the GRINDING WHEEL The abrasive material in your electric grinding wheel Is Chromium Oxide. Cheap wheels may tend to use aluminum oxide. 

Suitable for corrosive and abrasive material if correctly designed... 

When glove boxes are used for abrasive blasting, their design must take into account that the ejector of the abrasive material is driven by compressed air. This influences the chosen flow rate, which should be large enough to generate an air velocity of at least 3 m s" in the openings. The necessary exhaust airflow rate recommended by INRS is then... 

Abrasive blasting The process of product cleaning by the use of an abrasive material. 

In one series of laboratory tests carried out to find the optimum wear resistance of heavy-duty epoxy resin flooring compositions, a number of different abrasion resistant materials were evaluated using BS 416, employing three different epoxy resin binders which themselves had significantly differing chemical compositions and mechanical properties. The results of this work, which was carried out under dry conditions, are given in Table 9.1. As can be seen from the table, the selection of the abrasion-resistant material and the resin matrix both influence the abrasion resistance of the system, although the abrasive material incorporated appears to play a more cmcial role. 

An air intake for a compressor should have a high capacity to remove abrasive materials, including those of small particle size, and good accumulating ability, that is, to collect large quantities of impurities without any significant decrease in filtering efficiency and air flow. 

To combat this problem, soft materials such as Babbitt are used when it is known that a bearing will be exposed to abrasive materials. Babbitt metal embeds hard particles, which protects the shaft against abrasion. When harder materials are used in the presence of abrasives, scoring and galling occurs as a result of abrasives caught between the journal and bearing. 

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