EFFECTS OF PARTICLE SIZE ON MIXTURES DURING NONELECTROSTATIC AND ELECTROSTATIC POWDER COATING

Two mixtures, 44 and 256 mu m NaCl and 64 and 191 mu m starch, were nonelectrostatically or electrostatically coated onto an aluminum target. The coating processes cause the proportion of each powder in the mixture to be different on the target than in the initial mixture. First, some loss of powder occurs during the targeting step; thus, not all of the powder land on the target. This targeting loss is caused by the individual powder characteristics and interactions that occur between powders in the mixture. Also, an uneven distribution is produced on the target due to the way the powder is dispersed. Finally, adhesion loss occurs on the target, also due to individual and mixture characteristics. During nonelectrostatic coating, the largest cause of the change in proportion was targeting losses. During electrostatic coating, the largest cause was adhesion loss. Interactions in the mixture decreased the change in proportion, except for nonelectrostatically coated NaCl.