Grinding action

Heat resistance is an important characteristic of the bond. The strength of typical abrasive stmctures is tested at RT and at 300°C. Flexural strengths are between 24.1 and 34.4 MPa (3500—5000 psi). An unmodified phenoHc resin bond loses about one-third of its room temperature strength at 298°C. Novolak phenoHc resins are used almost exclusively because these offer heat resistance and because the moisture given off during the cure of resole resins results in undesirable porosity. Some novolaks modified with epoxy or poly(vinyl butyral) resin are used for softer grinding action. 

The technique of trituration is frequently useful. The organic product is stripped of solvent and the oily residue is placed in a mortar and covered with a layer of a solvent in which it is only slightly soluble. The mass is ground with a pestle mixing in the solvent as thoroughly as possible. In favorable cases, the solvent removes traces of impurities that may be inhibiting crystallization, and grinding action induces crystallization. 

It can be detonated on impact, but is normally considered a stable intermediate (m.p. 288° C), suitable for purification of pyridine [1]. Occasionally explosions have occurred when the salt was disturbed [2], which have been variously attributed to presence of ethyl perchlorate, ammonium perchlorate, or chlorates. A sample was being dried in a glass vacuum desiccator. Over-enthusiastic release of vacuum distributed some of the salt onto the lid. The grinding action as the lid was slid off initiated explosion of this, shattering the lid [6], A safer preparative modification is described [3], It explodes on heating to above 335°C, or at a lower temperature if ammonium perchlorate is present [4], A violent explosion which occurred during the final distillation according to the preferred method [3] was recorded [5],... 

Figure 8.4 shows the Trost Jet Mill from Colt Industries. In principle, it is an opposed jet mill and its grinding action is achieved by interparticle collisions in impinging streams. It has a centrifugal classifier, the grinding capacity can be 1 to 2300 kg per hour and the airflow rate varies from 0.2 to 28 m3minf. ... 

Alternatives to ball-mills include vessels with rotating paddles and rotating barrels that contain baffles that ensure that the powder is tossed about. These have no grinding action so that the particle size is unaltered. They also have little effect on aggregates. 

At this point, the raw material goes into either a batch or continuous cooking system. Within the cooking system, the heating and grinding action breaks down the fat cells in the animal tissue to release the fat. The rendering process consists essentially of two steps. First, the raw material is heated or cooked to evaporate the moisture. The second step is the removal of fat. 

The operating speed of ball mills is usually 55-75% of the critical speed. Operating close to drastically reduces the effectiveness of the grinding action. 

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