Abrasive particles

One advantage of sintering is the close control of si2e and shape of the abrasive particle. Extmded, cylindricaHy shaped, sintered abrasives of circular cross section were produced from bauxite (24) and from calcined alumina (25). The Uelt2 sintered bauxite was also later produced in extmded cylinder form and designated as 76A. Extmded sintered abrasives of a wide variety of cross-sectional configurations, eg, square and triangular, were later patented (26). 

The highest G-ratios are obtained when grinding with straight oil coolants. Such oils reduce power, increase maximum depth of cut, and produce smoother finishes. Disadvantages include inabiUty to remove heat from the work, oil mist in the work area, fire hazard, and tendency to hold grinding swarf (fine metal chips and abrasive particles produced in the grinding process) in suspension. Reference 51 is an excellent survey article for grinding fluids. 

Metering Pumps. For small flow rates, such as dosing chemical additives where precise control is requited, progressive cavity self-contained pumping units are used. These can often handle shear-sensitive fluids or Hquids containing abrasive particles. These pumps are not as widely pubHci2ed or generally as well known in the Hterature as other pump types. 

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. 

The dust has a broad size distribution, including particles under 10 to 15 [Lm as well as larger and possibly abrasive particles. A large low-velocity cyclone may be used to remove the coarse particles ahead of a unit vrim small-diameter multiple tubes. 

Current designs for venturi scrubbers generally use the vertical downflow of gas through the venturi contactor and incorporate three features (I) a wet-approach or flooded-waU entry sec tion, to avoid dust buildup at a wet-dry pmction (2) an adjustable throat for the venturi (or orifice), to provide for adjustment of the pressure drop and (3) a flooded elbow located below the venturi and ahead of the entrainment separator, to reduce wear by abrasive particles. The venturi throat is sometimes fitted with a refractoiy fining to resist abrasion by dust particles. The entrainment separator is commonly, but not invariably, of the cyclone type. An example of the standard form of venturi scrubber is shown in Fig. 17-48. The wet-approach entiy section has made practical the recirculation of slurries. Various forms of adjustable throats, which may be under manual or automatic control. 

Abrasive pumps are made of hardened metal or even rubber-lined to handle abrasive particles in high quantities with minimal erosion. 

Blast Peening—a treatment for relieving tensile stress via inducing beneficial compressive stress in the surface by kinetic energy of rounded abrasive particles. 

Another hazard of compressed air is that it contains dust (organic and inorganic), water, and traces of hydrocarbons, which if they are not removed can cause excessive wear of tools or contamination of products. Morris writes, Those who use air for pneumatic tools or even paint spray seem to have an inbuilt resistance to any idea that the quality of their compressed air is of any serious consequence. The fact that it transmits concentrated quantities of abrasive particles and water into the finely machined orifices and cylinders of their tools seems to pass them by [12]. 

Coarse abrasive particles readily removed in primary collector types. 

The installation of mixers on long shafts in tall tanks may become a problem if whip of the shaft develops. To reduce this possibility, a bearing support in the bottom of the tank will hold the shaft steady. Lubrication is by the tank fluid. Therefore this has limited application if abrasive particles are present. Normally the manufacturers designs avoid this extra bearing. Sometimes a guide bearing is installed about midway in the tanks to steady the shaft at this point. Again it is preferable to avoid this, if possible, and the manufacturer should make recommendations for the installation. 

Lubricants must be protected from dirt and moisture. A filtration system should be utilized to remove such abrasive particles and minimize wear on the drive chain. 

Erosion due to sand or other abrasive, particles, suspended in the... 

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... 

Conditioning, an important technology in the CMP process, is to maintain the asperity structures on the pad surface, which force the abrasive particles against the wafer. A... 

The hrst mechanism specihcally for tungsten CMP was proposed by Kaufman et al. [67]. They thought, first, chemical action dissolves W and forms a very thin passivating him which stops growth as soon as it reaches a thickness of one or a few moleculars later. Second, the him is removed locally by the mechanical action of abrasive particles, which contact with the protrude parts of the wafer surface, and then cause material loss. In recent years, most of the analysis and models for metal CMP are built based on the Kaufman model [68,69]. However, the model is not involved in microscopic structure analysis for the polished surface, but focuses on interpreting macroscopic phenomena happening during CMP [18]. 

At first, the plated NiP layer of aluminum alloy substrate is oxidized to form an oxide film on the surface, which may be softer [ 122,123] or more friable, and hence is easier to be removed than the NiP layer. Then the oxide Him is worn away by Si02 abrasive particles and is dissolved in the acidic slurry, or both. The protruding region is removed faster than the recessed region [ 124], resulting in global planarization of the substrate surface. The role of the lubricant is to improve the mobility of the slurry and reduce the excessive friction... 

Zhang and Busnaina [128] proposed an equation taking into account the normal stress and shear stress acting on the contact area between abrasive particles and wafer surfaces. 

In 1996, Liu et al. [129] analyzed the wear mechanism based on the rolling kinematics of abrasive particles between the pad and wafer. They summarized that the kinetics of polishing are (1) material removal rate is dependent on the real contact area between the slurry particle and the wafer surface. The real contact area is related to the applied pressure, the curvature, and Young s modulus of the slurry... 

Sundararajan et al. [131] in 1999 calculated the slurry film thickness and hydrodynamic pressure in CMP by solving the Re5molds equation. The abrasive particles undergo rotational and linear motion in the shear flow. This motion of the abrasive particles enhances the dissolution rate of the surface by facilitating the liquid phase convective mass transfer of the dissolved copper species away from the wafer surface. It is proposed that the enhancement in the polish rate is directly proportional to the product of abrasive concentration and the shear stress on the wafer surface. Hence, the ratio of the polish rate with abrasive to the polish rate without abrasive can be written as... 

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