Media Balls Research Articles

Wear of Media Balls during the Ball Milling of Si<sub>3</sub>N<sub>4</sub> Powder

Wear of six kinds of media balls during the ball milling of Si3N4 raw powder with additives was tested. The materials of the ball were α′/β′-SiAlON, β-Si3N4, high purity Al2O3, Al2O3 (HD-11), SiC and tetragonal ZrO2. The material of the least wear was α′/β′-SiAlON. The Si3N4 powder milled with SiC ball resulted in the mixture of Si3N4 with 13vol% of SiC. The powder consolidated to almost full density by the conventional gas pressure sintering.

Cost Factors in Fine Grinding of Coal

A 5-horsepower Pitt Mill prototype has been used to develop information on the effects of coal characteristics and of mill design and operation on the cost of grinding coal to the 10 microns size range. Grinding media wear is the largest cost factor in fine grinding of coal using stirred bed technology. The specific media loss rate, pounds of media per kW-hour energy input to the grinding bed, more than doubles and the cost per pound of replacement media increases by a factor of four as the chrome steel grinding media ball size is reduced from 3/8 inch to 3/16 inch diameter. The specific media loss rate has been found to be directly related to the ash level of the coal. Estimates of the cost to grind 50 HGI coal to sizes between 10 and 20 µm in the Pitt Mill range from $29 to $10 per ton respectively.

Changes in the characteristics of potting media with time

Abstract Growing media for container plants composed of pine bark, peat and sand were evaluated before, during and after five months with ryegrass as the test plant in the greenhouse. Hydraulic conductivity of these materials is very rapid resulting in rapid loss of nutrients, even for the controlled‐release type fertilizers. Channels developed on the perimeter of the growing medium ball adjacent to the container wall resulting in a concentration of plant roots in this zone. Considerable shrinkage or compaction of the media occurred during the five months growth period, especially for peat. Movement of sand was observed for the very porous materials and found to accumulate as a layer lower in the container. All nutrients added were exhausted after 3 months, even for the controlled‐release types of fertilizers.

Empirical correlations for the effects of particulate mass and ball size on the selection parameters in the discretized batch grinding equation

Simple graphical procedures for determination of empirical correlations for the variations in selection parameters of the discretized batch grinding equation with the particulate mass and the size of the grinding media balls are described. The influence of the particulate mass is given by a single correlation function which is valid for all particle size intervals, as well as both starved and saturated mill loadings. The search for the correlation for the effect of ball size can be considerably simplified by plotting the data in a particular fashion which results in a self-preserving curve, independent of the particle size.