Constant-power grinding

Internal circular grinding machines are usually equipped with high frequency grinding spindles (three-phase asynchronous motors) and frequency converters for continuously variable speed control. As a measure of the mechanical power emitted by the grinding spindle, one can use the electrical output power delivered by the converter, which can easily be acquired by conventional measurement techniques. The required control variable - one speaks in this case of constant-power grinding - is therefore almost free of charge. 

Grinding operations may be sorted into four main categories fixed feed, fixed force, constant power, and cutting off. The choice of bond type and wheel specification for a given operation is determined by the specifics of the operation, the available power, speed, wet or dry environment, and work material and by re-... 

The actual grinding was carried out on a laboratory ball mill, using ceramic jars with dimensions of 5-13/16 internal diameter and 5-3/8" internal height. The overall volume is 1829cc. Initial experiments employed steel balls (seventeen of 3/4" diameter, eleven of 5/8" diameter and fifty of 1" diameter). The rate of jar rotation of the mill is nominally 80 rpm. The voltage and current feeding of the ball mill are measurable and constant therefore, the grinding time is used as a measure of power input. Experiments employed 100 g of coal. 

The Work Index is claimed to be capable of predicting the power for a ball mill of 8 ft (2.43 m) in diameter in closed circuit wet grinding. In dry grinding applications, the value of WI has to be multiplied by an empirical constant of 1.3. The Work Index is also supposed to represent the energy in kWh required to reduce one short ton (907 kg) of mineral from a theoretical infinite size to a size distribution at which 80% is smaller than 100 microns. 

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