Grinding equipment

Silicate. Once important, siUcate-bonded wheels have faded almost to obhvion increasing wheel speeds have made this inherently weak bond obsolete. Some wheels are produced, however, for old grinding equipment still in existence. 

Two classes of grinding equipment are used to prepare dispersions. The first, the coUoid mill, does not effect a particle size reduction but does break down aggregates of fine particles. CoUoid mills are used for such powders as clays, precipitated whiting, etc. Sometimes these mills are used to process zinc oxide but for dipped mbber products that is not satisfactory. 

The second class of grinding equipment is used to prepare dispersions. Typical of this class are baU and pebble mills, ultrasonic mills, and attrition mills. SoHds, eg, sulfur, antioxidants, accelerators, and zinc oxide, are generaUy ground on this equipment (see Size reduction). BaU mill action is assisted in some mills by a combination of dispersion circulation by an external pump and mechanical osciUation of an otherwise fixed nonrotary mill chamber. Where baU mill chambers are rotated it is necessary to experimentally estabHsh an optimum speed of rotation, the size and weight of the baU charge, and ensure the mills do not overheat during the grinding period. 

Exponential cost correlations have been developed for individual items of equipment. Care must be taken in determining whether the cost of the eqmpment has been expressed as free on Board (FOB), delivered (DEL), or installed (INST), as this is not always clearly stated. In many cases the cost must be correlated in terms of parameters related to capacity such as surface area for heat exchangers or power for grinding equipment. There are four main sources of error in such cost correlations ... 

The grain size distribution can also be changed by the use of different grinding equipment, e. g. by a series of different mills. 

Solids can be separated on the basis of their particle size. When crushing and grinding equipment is used, a determination of the distribution of the various particle sizes is important in evaluating the performance of the equipment. The size of particles in soil gives an indication of the porosity and the ability for the soil to hold moisture and nutrients. It affects manufacturing processes and the formulation of products. The size of particles in dry feed for farm animals, such as swine, is related to its nutritional value. Many times the size of particles in a process may be specified in a standard method, such as the USP or FDA. 

Objective 1. Validate the ability of the grinding equipment to safely reduce M28 propellant grains to V,-. V2-, and V -inch pieces. 

Results The grinding equipment could grind M28 propellant grains to pass the /4-inch screen. 

Objective 4. Demonstrate the ability of grinding equipment to safely process foreign objects such as detached antiresonance rods and igniter cables. 

Stickiness. A sticky material will tend to clog the grinding equipment and it should therefore be ground in a plant that can be cleaned easily. 

Crushing and Grinding. Some raw materials, such as hard clay and quartzite, must first be crushed to grains small enough for the grinding equipment. In general, a jaw, gyrotory, or roll cmsher is employed (see SIZE REDUCTION). 

Carstensen J. Advanced Pharmaceutical Solids. New York Marcel Dekker, 2000. Austin LG. Size reduction of solids crushing and grinding equipment. In Fayed ME, Otten L, eds. Handbook of Powder Science and Technology. New York Van Nostrand Reinhold, 1984 562-606. 

---