The Expert's Corner
A Better Way to Dry Powders
December 18, 2019
A major adhesives company was looking for a better way to dry a pigment formulation used for a particular urethane-based product. They had tried using different types of horizontal blenders to bring the moisture level down to 0.5% or less. However, they experienced problems including leaking at the seals and batch times of at least 8 hours.
This company came to test their formulation on a 1 cubic foot vacuum-rated Ross Vertical Blender/Dryer in an effort to improve the process. First, we loaded talc, fumed silica, carbon black, titanium dioxide and zinc oxide powders into the machine and blended these for 15 minutes to create a homogeneous mixture. We then stopped the blender, took a sample of the batch and measured moisture level, which came out to 15.8%.
After this step, vacuum was pulled to 28.5"Hg in the blender while the heating system was set to 230Â°F and allowed to recirculate hot water through the blender`s stainless steel jacket. The slow-turning auger screw of the Vertical Blender lifts powders upward as it orbits around the conical vessel, constantly exchanging materials between the heated sidewalls and center of the blender. After just an hour of mixing under these conditions, another sample was measured and met the desired moisture level. This was an impressive improvement on their current manufacturing practices. The combination of deep vacuum, gentle heat, and agitation achieved significantly shortly drying time.